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The theory of [Late Heavy Bombardment](http://en.wikipedia.org/wiki/Late_Heavy_Bombardment) says that approximately 4 billions of years ago, something disturbed the orbits of asteroids in the [Kuiper belt](http://en.wikipedia.org/wiki/Kuiper_belt), which caused extremely heavy bombardment of Earth by asteroids. This probably brought many heavy elements to Earth's surface. The heavy elements that were here previously, during the Earth's formation, sank to the core when the Earth was liquid which made them out of reach. In other words, if there was no Late Heavy Bombardment, the surface of Earth might have been almost without elements much heavier than silicon. (Iron, gold, silver, platinum and others would be extremely rare.)
My question: *If humans developed the same way they did, what kind of technology would be achievable almost without elements much heavier than silicon?*
[Answer]
I'm going to look at some major technologies, and see if they can be done without metals heavier than silicon (I'm going to assume sodium, chlorine, and other biologically needed minerals are still around, just because we need that to live. See [sodium-potassium pumps](http://en.wikipedia.org/wiki/Na%2B/K%2B-ATPase). I'm also going to assume those do not occur in harvestable deposits, so we can only get them for biological purposes.)
* Fire: $\checkmark$ Life really needs the stuff in the top right of the periodic table, so I think we would have plenty of stuff to burn.
* Fired Clay: $\checkmark$ This was used for pots, which helped us store food and water. It also helps us make super good pizzas.
* Knives: $\checkmark$ [Obsidian](http://en.wikipedia.org/wiki/Obsidian) was often used for knives. [Ceramic knives](http://en.wikipedia.org/wiki/Ceramic_knife) could work, too, but not ones as we see today. Aluminum could work, but obsidian is better than aluminum for this.
* Wheels: $\checkmark$ Wooden wheels!
* [Abacus](http://en.wikipedia.org/wiki/Abacus): $\checkmark$ They're mostly made of wood
* Sundial: $\checkmark$
* Glass:$\checkmark$ As long as there is silica, $SiO\_2$, we're set for glass
* Camera Obscura: $\checkmark$ This represents one important advancement in optics. Combine this with a glass, and you get a basis for optics. This opens the way for telescopes and microscopes.
* [Printing Press](http://en.wikipedia.org/wiki/Woodblock_printing): $\checkmark$ You can make this out of wood. The type would need frequent replacement.
* Nautical Navigation: $\checkmark$ [Polynesian Navigation](http://en.wikipedia.org/wiki/Polynesian_navigation) could be used *for sure*. [Astrolabes](http://en.wikipedia.org/wiki/Mariner%27s_astrolabe) are usually made from metal, as wood warps. If you can protect your wooden astrolabe from warping, you could have it. Of course, you can make bits out of aluminum, as they do not experience crazy amounts of stress.
* [Drills and Other Tools](http://en.wikipedia.org/wiki/Drill#History): $\checkmark$ using obsidian, teeth, leather, and wood, you can make drills and other items. Your bits would wear down quickly, but it could happen. You could also use aluminum, and try to temper it with alloys to make edges harder.
* Gunpowder: $\checkmark$ [Here](http://en.wikipedia.org/wiki/Gunpowder#Composition_and_characteristics) is the list of the basic ingredients for black powder. If we allow potassium, we're there. You could also use [lithium nitrate](http://en.wikipedia.org/wiki/Lithium_nitrate).
* Steam Engine: **Maybe**, as we need a good chamber to keep the steam in which allows it to be heated. Metals fill this role very well, but wood and other organic materials do not. You could use aluminum, though.
* Electricity Generation: **Likely No** We really rely on magnets to generate electricity. You can make a solar cell with [Si and C](http://en.wikipedia.org/wiki/Solar_cell#Materials), but I do not know how you would transmit the current without [Graphene](http://en.wikipedia.org/wiki/Graphene#Electronic) (or [Aluminum](http://en.wikipedia.org/wiki/Aluminium)), which would be your best option. Aluminum would be great at transferring current, but it is not magnetic, so you couldn't use it as a magnet.
* Computer: **Maybe**. [Mechanical Computers](http://en.wikipedia.org/wiki/Mechanical_computer) exist, but they do tend to rely on tight-fitting metal pieces. Wood may work, but would require a very controlled environment, so aluminum would be a better bet.
* [Semiconductors](http://en.wikipedia.org/wiki/Semiconductor): **Maybe** Since most semiconductors are mostly silicon, and some are made of organic materials, you could have semiconductors.
I'm going to stop there. No electricity hurts modern technology hard.
My guess is that such a world would have similar levels of expertise in biology, less so in chemistry, and certainly less in physics. [Fields](http://en.wikipedia.org/wiki/Field_(physics)), such as those used to model light, would be very under-developed. Sure, people would be confused with the wave and particle property of light. However, the concept of fields was not developed until people really studied coulomb forces. There was a point where people though classical physics [covered everything](http://en.wikipedia.org/wiki/Classical_mechanics#History). Most of things people discovered which classical could not explained were discovered because they were working on things which practically require *metals,* such as magnets, [vacuums](http://en.wikipedia.org/wiki/Thermodynamics#History), steam engines, and boring holes in cannons...
There would be no x-rays for your doctor, no radios, no knights in shining armor. A radically different world, but a lot of things would still be developed and known.
Jared Diamond, author of [Guns, Germs, and Steel](http://en.wikipedia.org/wiki/Guns,_Germs,_and_Steel), may argue that we would never have taken off in technological advancement because we lack steel. His theory would put us as a very agrarian society without sufficient metals. This would prevent many other technologies from developing.
[Answer]
Luckily this does not entirely depend on mass.
**What do we lose?**
If there were no Late Heavy Bombardment (LHB) the Earth's crust would be fairly lacking in what are called [siderophile elements](https://en.wikipedia.org/wiki/Goldschmidt_classification#Siderophile_elements). This is too bad, there are some good elements in that list, including gold, cobalt, iron, iridium, manganese, molybdenum, nickel, osmium, palladium, platinum, rhenium, rhodium and ruthenium. We'd still have some of these at the surface, we'd just have a lot less of them. The Earth is still bombarded with space rocks, the LHB was just a significant portion of that bombardment over the last four billion years.
It's hard to say how much of what we would have or how the abundance affected abiogenesis or evolution of life. So, we'll assume life still developed in the same way, but we wouldn't have the rich deposits we have now.
**So what do we have?**
We'd still have [lithophile elements](https://en.wikipedia.org/wiki/Goldschmidt_classification#Lithophile_elements) and, to a lesser degree, [chalcophile elements](https://en.wikipedia.org/wiki/Goldschmidt_classification#Chalcophile_elements). Some of the metals we'd get are aluminum, tungsten, and titanium in decent quantity. We'd get a little bit of copper, lead, and tin. It's not a bad start, it gets us through the bronze age. The iron age would be a problem. Because our own timeline would be halted in pre-history it's quite difficult to say where humans would have gone from there.
I find it unlikely we'd figure out the refinement aluminum, tungsten, or titanium without the tools and knowledge developed during our collective experience with iron. Those are difficult metals to refine in comparison to iron.
**Technology**
The technology we'd be able to develop then would be things we hardly consider technology. Things like spears, hatchets, bowls, and other cooking tools. We'd have wheels and fire. We'd have some woodworking and stoneworking tools. We'd have concrete, but wouldn't have a great method for reinforcement. We'd have glass, though it wouldn't be very high quality.
Again, these are all things that modern people don't usually consider technology. Even though we'd have the elements to make things like microchips, we couldn't develop the required infrastructure.
It'd be a simple world.
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Samuels answer has it right, it isn't that there wouldn't be elements heavier than silicon; there would still be plenty and life would work just fine, but Iron and nickel and gold would be very, very rare, things that we would primarily get from meteorites, rather than mining in the earth.
The idea though that we would have no technology or that technology wouldn't develop is not something that I agree with. Technology develop how it does because it is seen as being the cheapest and best way of doing so at the time it is developing. So things would certainly be very different, but just because things couldn't be how we have it doesn't mean it couldn't be done.
It should be noted that Mesoamerica and the American Southwest didn't really use much in the way of metal except as decoration prior to the Columbian exchange. Which we may look down on, but Atlatl's were able to pierce the armor of the Spaniards, and Obsidian blades are actually sharper than stainless steel <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1273673/> Also, even the point about drills is wrong, as Mesoamerica did artwork with stone which can not be shaped with iron tools, they most likely did abrasive drilling via a bow drill and sand; no bit to wear out at all.
Canals in the US (and in the Maya region during the classic period) actually for a while were able to perform better than the earliest railroads; there would obviously be no iron railroads, and bronze ones wouldn't actually work nearly as well.
Since there is still copper and tin, there actually would be bronze, and there actually could be electronics; and with electronics and electricity comes the lithophile elements such as Aluminium. So some technology could still develop, but how to get there, how it develops, and what it looks like would be very different from what we are used to.
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Well considering Phosphorus, Chlorine, Potassium and Calcium just to name a few that we need for our biology, we would certainly be much different. We also use Iron in our blood and Iodine helps with good health.
So to begin, we would likely not be what we are if heavier elements were too scarce.
But we would have had a much harder time without metals to augment our tool building. We would likely have been stuck with a lot of granite tools augmented by glass tools, (including obsidian, volcanic glass)
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As bowlturner pointed out we use a lot of heavy elements in our own biology, although in trace amounts. I'm honestly doubtful that complex life could evolve at all without anything higher than silicon, but of course I don't know for sure - I'm by no means a biologist.
Assuming it *is* possible, a species might be able to get away by building things with [**Carbon Allotropes**](http://en.wikipedia.org/wiki/Allotropes_of_carbon). They'd need to somehow get to the point where they could change and form those nearly at will, but that could develop over time - they might start with those early if they don't have metals to work with.
Graphene is extremely strong and can be used in place of metals where tensile strength is required (but you can't use it to easily build, say, a wall). Graphite is a conductor and presumably could be used in place of copper. Diamond is a good insulator. That gives you most of the basics to start industrial technology at least.
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The problem would not be the technology itself but the scaling of that technology. With enough iron for small scale experimentation you can still discover electromagnetism - you just can't build entire cities of the stuff.
That doesn't really become an issue until the industrial revolution - before that, metal was rare and expensive anyway.
* Steam power - a brick boiler should work. Likely larger and heavier than you can build with metal, and probably slower if the attached parts aren't as strong as steel, but it still lets you build factories without needing a direct mechanical connection to a river.
* Railroads - wood or concrete rails. Keeping them maintained will suck, but the alternative is more expensive than building them from solid gold. Trains are slow and can't carry nearly as much as they do on Earth, but they do better than a horse so it still works.
* Electricity - Batteries, solar cells and thermopiles can be made without heavier elements. You don't have the option of spinning permanent magnets, but aluminum coils will work well enough.
* Guns - wooden cannons aren't great, but fortunately the enemy doesn't have access to iron either.
As long as you have plenty of lighter metals like aluminum, you have a suitable direct substitute for iron in most uses - advanced civilization can develop normally. If not, things will be quite different, although not necessarily less advanced. Electricity is still available, but there are no large power stations or high voltage transmission lines. You can have computers running on batteries, but lighting is still gas and factories still use steam engines rather than electric motors. Without cars or very tall buildings, cities would look very different.
Even if most things are possible through direct substitution, there would be a lot of small differences in the technology used. Some things would probably develop earlier - you don't have the simple option of just using iron, so more complex solutions become economically viable. For example, all your armor is made of layered paper, and after a century or so of trying to improve the glue holding it together you end up with something a lot like modern composites, which turns out to make a stronger cannon than the tree trunks your enemy is using...
To take that even further, finding out that most asteroids are made of an incredibly rare and expensive industrial material would be a pretty strong incentive to get into space.
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* What is the oldest a still extant cave on Earth could be?
* What conditions could encourage the longevity of a cave?
It seems that the oldest known caves, the [Jenolan Caves](https://en.wikipedia.org/wiki/Jenolan_Caves) in Australia, formed in the Carboniferous period.
* How plausible would a cave from the Ordovician or even Precambrian be, considering that not even continents are stable over these time periods?
* If these caves were designed, excavated, and reinforced back then by another civilization with modern technology, could they be engineered to last longer?
[Answer]
# How to make a limestone cave
The [Jenolan caves](https://en.wikipedia.org/wiki/Jenolan_Caves) in Australia are reputedly 340 million years old. Those caves are in limestone deposits that were formed on the bottom of a shallow sea in the Silurian or earlier.
Limestone is the most likely substance for these caves to form in. But limestone isn't really a natural geological rock, it is formed by the crushed shells of marine invertebrates. There can be non-biological limestone, but it is much rarer, and probably nowhere pure enough to form limestone caves.
Limestone comes primarily from [corals](https://en.wikipedia.org/wiki/Coral#Evolutionary_history) and [foraminifera](https://en.wikipedia.org/wiki/Foraminifera). Both these species developed in the Cambrian, but did not become common until the [Ordovician](http://www.bgs.ac.uk/discoveringGeology/time/Fossilfocus/foraminiferaEvolution.html). I can't find good data on how long it takes Limestone to form from these invertebrates, but it is millions if not tens of millions of years.
Assuming a few millions of years of depositing marine shells, then a few million more years of limestone formation, then this continental shelf (limestone doesn't form in deep water under high pressure) has to become dry land, then that dry land has to get enough rain to expand a cave system...you are probably looking at Silurian era for the earliest limestone caves.
# How to get a cave to survive
The problem with limestone caves is once they start eroding, they are likely to keep eroding. The Jenolan caves are conveniently located a drier part of the Earth that has always been relatively dry. Australia has never been too polar or to equatorial over the last 400 million years or so. Also, it has never been underwater either. The only other part of the world that I can think of that meets both these criteria is southern Africa.
# Cratons are probably not possible for natural caves
I don't think a craton could potentially have many caves. First off, they have never been underwater, so they were never able to get a layer of limestone on them. Secondly, I don't know of any other materials components of a craton that would make caves like limestone.
Incidentally, this will then rule out southern Africa, since most of that sits on the Kaapvaal craton. Maybe caves would be possible in the sedimentary fill between the Congo and Kaapvaal craton (roughly Angola/Zambia)? I don't know much about the geology of the area, and there isn't much information available online.
However, if we are talking artifical caves, then the safest place to put one would be in the heart of a [3 billion year old craton](https://en.wikipedia.org/wiki/List_of_shields_and_cratons#List_of_named_cratons). Cratons this old include the Kaapvaal in Africa, Dharwar in south India (partially covered by the Deccan Traps), Pilbara in western Australia, Superior under Minnesota and Manitoba, Slave in Canada's Northwest Territory, and Sarmatian under the Ukraine.
The [Witwatersrand](https://en.wikipedia.org/wiki/Witwatersrand) formation is an igneous plug in the Kaapvaal craton that formed 2.7 billion years ago and is pretty much still the same today. An artificial cave there could have probably survived all this time.
# Conclusion
Based on the likely cave forming processes, the oldest caves would be Silurian in origin, and would likely be situated in Australia or southern Africa. Since the Jenolan caves meet these requirements, it sounds like they are about as old as caves can get.
For artificial caves, the possibilities are more significant, since there are igneous provinces on top of cratons that are more or less unchanged for billions of years.
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Do your caves need to be on earth? There are lava tubes on the moon. Lava tubes are a type of cave. This article estimates those tubes to be 3 billion+ years old.
<http://www.asi.org/adb/06/09/03/02/100/12-questions.html>
These tubes are bigger than terrestrial tubes, because of the low gravity. There has been a lot of enthusiasm as regards moon colonists moving in and pressurizing them.Here is a picture from BBC.com of Philadelphia in a lava tube.
[](https://i.stack.imgur.com/h6QAY.jpg)
If you are envisioning /another civilization/ Mountains of Madness type scenario maybe you could have it on the moon. Probably a good idea to check for that stuff before you send Philadelphia.
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It's not impossible to have a cave from the [Hadean](https://en.wikipedia.org/wiki/Hadean) since you have the early formation of the [cratons](https://en.wikipedia.org/wiki/Craton) of contents which are stable over long geologic timescales. Just really unlikely and to my knowledge, there are none that have been found. Such caves would have been formed by lava rather than the action of water and would contain a geologic record specific to that time. Such caves would have to be closed off from the environment for the majority of their life because over geologic time they would be filled in.
As for constructing an artificial cave, barring building it in the craton of a content and then sealing it somehow, there is nothing that could be done to allow it to last over significant geologic time scales.
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I have a world inside a Dyson ring with a radius of ~1 AU, complete with humans, animals, plants, clouds, and Earth-like atmosphere. The ring is spinning at a particular angular speed, giving the inhabitants on the surface the experience of Earth's gravity at sea level.
How convincing is this pseudo-gravity as a substitute for real gravity for objects not directly touching the surface?
If a bird is flying a hundred meters above the surface of the ring, does it also experience the equivalent of Earth's gravity at a hundred meters above sea level? What about a thousand meters? What about ten thousand?
Is the atmosphere comparable to Earth's at that altitude when inside the ring?
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The answer is: objects above the surface of the spinning sphere **do** still feel some apparent equivalent of gravity, although the higher up they go, the wonkier this apparent gravity gets.
Now, there are two ways of analyzing this type of problem: the non-inertial way and the inertial way. In the non-inertial way, we think about the problem from the perspective of a reference frame that's rotating with the shell, while in the inertial way we analyze it from a reference frame that's not accelerating (to be definite, lets say the reference frame of the star). The non-inertial way works by introducing new apparent forces that come about simply by virtue of not being in an inertial frame-- in the special case of a rotating frame, these are known as the centrifugal and Coriolis forces. This way of analyzing the problem is very useful for performing calculations, but doesn't do much in the way of physical intuition, so I'll explain from the inertial frame.
In an inertial frame, everything moves according to newton's laws-- that is, stuff moves in straight lines unless something forces it not to. So, think about the problem of a person standing on the inside of the sphere and jumping. If objects not on the surface did not feel an effective force pulling them to the sphere, we would expect our unfortunate civilian to drift off towards the sun as soon as he left the ground. However, this doesn't happen. To see why, note that our test subject isn't initially sitting still with respect to our inertial frame-- he's moving with the surface of the sphere. Thus, as soon as he stops making contact with the sphere, he'll move in a straight line in our inertial frame. Note, however, that spheres aren't straight. So, he'll collide back with the sphere eventually, a process that from his point of view looks just like an effective gravity pulling him to the sphere. This is the effect of the centrifugal force, had we instead analyzed it from the non-inertial frame.
Now, remember that earlier I said that the apparent gravity gets wonkier as you jump higher? From the inertial perspective, this has to do with the fact that circles look like parabolas if you zoom in close, but not if you zoom out far enough. Meanwhile, from a non-inertial standpoint, it's due to the Coriolis force. However, whatever way you decide to analyze it, the precise answer of how wonky gravity becomes depends on how fast the sphere is spinning, how large it is, and how high up you go. If I have more time later, I'll explain this/analyze your problem in more detail.
Hopefully that helps!
**ADDENDUM: Actual Calculations**
First, I'd like to clarify that how wonky your pseudo-gravity gets (ie the Coriolis force) actually depends on velocity, not on how high you go. The reason I said it depended on how high you go was that for object on a ballistic trajectory (like a person jumping), travelling higher = more speed and more time for the Coriolis force to act, thus more displacement. Now the centrifugal force does vary based on height, but 1 AU is so ridiculously large that it will be constant for all intents and purposes.
Now, for actual numbers: Based off your specs of $r = 1$ AU, $a\_{centrifugal} = 9.8 m/s^2$ and the equation for centrifugal acceleration $a\_{cent} = \mathbf{- \omega \times (\omega \times r)}$, we find that the magnitude of the angular acceleration needed is
$$ |\omega| = 8.1 \* 10^{-6} s^{-1}$$
which corresponds to a rotational period of about 9 days. Luckily, this leads to a tangential velocity of "only" $0.004c$, so we can ignore relativistic effects. Now, the equation for acceleration caused by the Coriolis effect in the non-inertial frame of the ring is
$$a\_{cor} = -2 \mathbf{\omega \times v}$$
where $\mathbf{v}$ is the velocity of your object as seen in the rotating frame. Note that this means
$$|a\_{cor}| \leq 2\mathbf{|\omega||v|}$$
Now, I'd guess that countering the Coriolis force for something powered like a bird or superman would be essentially imperceptible if $a\_{cor}$ were less than $0.01 m/s^2$. Putting it all together, we find that the Coriolis force doesn't play a big role for things capable of generating their own movement as long as $$|\mathbf{v}| < 616 m/s$$
which is pretty fast. Now, for objects on a ballistic trajectory that can't maneuver to counter the Coriolis force, the effects can add up differently. For a rough idea of how much this will be, note that on earth,
$$|\omega\_{earth}|=7.3\times10^{-5} s^{-1}$$
So, projectiles will be affected by the coriolis force a bit less (their landing displacement will be smaller by a factor of about $\sqrt{10}$) than they are on Earth.
As a final bit of analysis/buzzkill, I just want to point out that this ring would probably tear itself apart very easily. With the angular speeds and radius you're talking about, and assuming a material tensile strength of $100GPa$, which is about as much as carbon nanotubes, we find that the necessary density of the ring material has to be less than $68 g/m^3$ in order for the ring not to tear itself apart. That's *nothing*. Hydrogen gas is more dense than that.
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# This is indistinguishable from Earth's gravity
[Centrifugal acceleration](https://en.wikipedia.org/wiki/Centrifugal_force#Acceleration) on an object is
$$\mathbf{a} = \left[\frac{d^2\mathbf{r}}{dt^2}\right] + \frac{d\omega}{dt}\times\mathbf{r}+2\omega\times\left[\frac{d\mathbf{r}}{dt}\right]+\omega\times\left(\omega\times\mathbf{r}\right).
$$
If we assume that the particles of interest are at a contant distance from the star ($\mathbf{r}$), then the first and third terms are set to zero. If we assume that rotational velocity is contant, then the second term is set to zero. That leaves
\begin{equation}\mathbf{a} = \omega\times\left(\omega\times\mathbf{r}\right).
\end{equation}
In order to feel a force equivalent to Earth's surface gravity ($g = 9.8$ m/s$^2$), we solve
$$9.81 = \omega\times\left(\omega\times1 \text{ AU}\right).$$
Now, this is highly dependent on the polar angle of the location of interest. The above equation only holds at the equator. At other angles, the centripetal acceleration will be less! Let us assume that you want 1$g$ at the equator, and less towards the poles. Since $1 \text{AU} = 1.496\times10^{11}\text{ m}$, we can solve for $\omega = 8.1\times10^{-6}$ radians/sec to achieve equatorial centripetal force equivalent to Earth's gravity. This means the Dyson sphere has to rotate around the sun every 775,909 seconds; about 9 days. That is pretty fast, but since this is a Dyson sphere, I assume the material structure can handle it.
Now, to answer your specific question, what will the centripetal force be like above the surface. Lets say that we are 10 km above the equator; that is higher than Mount Everest. This affects $\mathbf{r}$; the distance from the sun. The distance from the sun of the surface is $1.496\times10^{11}\text{ m}$. Subtracting 10,000 meters from that we get....$1.496\times10^{11}\text{ m}$. Compared to 1 AU, any altitude we might be used to on Earth is insignificant.
# Conclusion
Traveling up into the air above a Dyson sphere designed to simulate gravity with centrifugal force at the equator does not affect gravity appreciably.
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The short answer is that birds would feel your pseudo-gravity.
The long answer involves making some sense of the situation with coordinate transforms.
The simplest system to explore is the inertial system, where the coordinate system is fixed. In this coordinate system, the Dyson ring appears to be spinning at a high rate. Objects travel in a straight line unless forces are put on them. One way forces can be put on them is if they are in physical contact with the ring. They can also have forces put on them by the air. But what forces are on the air itself? That question is a little difficult to answer in inertial systems. It can be done, but it'll be easier of we change things up.
Consider a rotating system, which rotates at the same rate as the surface of the Dyson ring. In this coordinate system, the Dyson ring appears to be fixed, in the exact same way the ground beneath our feet appears to be solid and not-moving. Now this is just a coordinate transform. We did *no* physics in this process. All we did was look at things a different way.
Why look at things this way? Well they make some calculations easier. Consider the environment you envision for your ring. You've got the "ground," with atmosphere on the inside of it. That atmosphere gets pulled along with the ground *exactly* the way the Earth's atmosphere is drug along with the surface of the planet. This is convenient. You presumably want a "familiar" environment, where the ground behaves like we expect ground to, air behaves like we expect air to, and birds behave like we expect birds to. Thinking in this rotating frame is very natural.
Now there's a cost of viewing the world through a rotating frame of reference. The equations of motion are different. The famous equations of motion Netwon put forth (such as "all objects move in a straight line until acted upon") are only true in inertial frames. If we are in a rotating frame, the math changes. Without getting into ugly math details, the effects that appear are Coriolis and centripetal/centrifugal effects. centrifugal effects are what you are using for your gravitational force. They are called "pseudo-forces" because they aren't actually forces, but they do affect the equations of motion in the same way forces do.
The key takeaway from this is the centrifugal accelerations are *always* present in a rotating frame. So your birds and such are going to be affected by it, regardless of whether they are touching the surface or not. As long as they are rotating at the same rate as the ring, you'll see these effects.
These centrifugal effects are scaled by the velocity of the object in the stationary frame with respect to the rotation of the frame. In other words, for Earth, East/West velocity leads to centrifugal effects, while North/South velocities do not.
If your bird was *not* moving along with the ring, the same laws hold, but they get muddier. If your bird was "holding still" in the inertial frame, and watching the ring wizz by it, that bird would not experience any centrifugal forces. It's "East/West" velocity is 0. Your pseudogravity would be ineffective. However, this bird would also be subject to tremendous wind forces as the ring and the air column rotate. As those wind forces pull it "West" in the direction of rotation, its velocity will increase, and it will start to feel pseudogravity.
That same story can be viewed in the inertial frame as well. In that frame, the bird is holding still, and is being pummeled with wind forces that accelerate it.
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## Yes.
Here are my assumptions:
* As stated in the question, you've got a Dyson ring with a radius of 1 AU, spinning fast enough that anyone standing on the inside surface experiences 1 gee of outward centrifugal acceleration (in any frame of reference spinning with the ring, of course), thus mimicking sea-level Earth gravity.
* There are inward-pointing walls on the edges of the ring to keep the atmosphere from spilling out, and a functioning ecosystem existing on the inside surface of the ring.
A column of the atmosphere taken from the inner surface toward the Sun would look very much like a column of Earth's atmosphere taken from the surface upward. It would have the same density profile, for sure, and probably similar composition and temperature at each altitude as well. The main difference would be in how the solar wind interacts with the ring's atmosphere and magnetic field- which depends entirely on how the ring's magnetic field is set up. It would need to be installed artificially; Earth's magnetic field comes from magnetohydronamic shenanigans in the molten outer core, while a ringworld has no core at all. So I can't say anything about the ringworld's auroras or ionosphere, except that you can probably configure those to work however you want.
Birds flying at high altitudes will actually experience more gravity than at the same altitudes on Earth- but not by any noticeable amount. Earth's gravity decreases with the square of the difference from the center of the planet; the ringworld's will decrease linearly from the inner surface to the center of the ring. However, these effects are so subtle, no actual living thing will ever be able to detect them without specialized equipment- Earth's gravity is 9.8 m/s^2 at sea level, and about 8.7 m/s^2 at the height of the International Space Station. It doesn't decrease much, and on a ringworld it'll decrease even less.
What will be affected by the subtle differences between Earth's atmosphere and the ringworld's are certain kinds of weather events. Namely, hurricanes. On Earth, hurricanes spin because the Earth spins, causing air nearer the equator to be moving eastward faster than air closer to the poles. When this air moves toward the low-pressure cell at the center of a hurricane-to-be, air coming from closer to the pole appears to be pushed westward because the ground under it is moving eastward more quickly, and air coming in from closer to the Equator appears to be pushed eastward because is has more eastward velocity than the slower-moving ground now under it. This is the Coriolis effect.
Now, because your ringworld is a cylinder, not a sphere, the Coriolis effect will not affect air moving along the inner surface in any way, and so you won't get hurricanes. Smaller-scale spinning weather events caused by wind currents moving in different directions, like tornadoes and dust devils, sure, but no hurricanes.
[Answer]
Hold on. Try asking
## When Earth spins, does the atmosphere spin with it?
I mean, if the atmosphere did not spin with the earth, then getting to the USA from Europe would be *really fast*. As you climb, the atmosphere would slow and slow (speed up and up relative to surface) and there'd be nice 800mph winds to ride all the way across the Atlantic. Returning would suck.
Well, that doesn't happen. *Why not?* The rotation of the **Earth's surface drags the atmosphere along with it, due to *ground effect***. The same thing that affects airplanes that are within a wing's length of the ground, except Earth is 8000mi across.
Earth's air doesn't need ground effect to stay put. Either way; Earth would keep its atmo' due to its real gravity. **Your ringworld would not**. Centripetal force is all it's got, so if ground effect failed to drag the atmosphere along, the atmosphere would not be acted upon by centripetal force, and would expand infinitely into the vacuum of space. The atmosphere would be lost.
So you can take it as a fair assumption that the air is moving with the ringworld.
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Aerodynamic forces are decided by your speed relative to the air. Since the ringworld's air *must* move with it (or be lost) and that is expected anyway from ground effect... an aircraft's airspeed will be roughly its surface speed across the ringworld (there'll be jet streams and stuff like that, but probably within 150 knots if Earth's experience maps at all.)
Several here say to generate 1.0G of centripetal force, the ringworld would have to rotate with a surface velocity of 1.2E+06 m/sec or 2,330,000 knots. So if you were in the air, you would be swept along with the air by aerodynamic forces. Which means you'd be moving nearly the speed (within hundreds of knots) of the surface.
Now what happens if the bird folds her wings? She will go in a straight line and experience zero gee. Unfortunately, the ringworld is not going in a straight line. The surface is traveling nearly parallel with her, both at 1.2 million meters per second, but slightly curving up toward her, and the paths will intersect with the differential velocity of 100 meters per second or so. Ouch. The bird would be very wise to open its wings and use them to create about 1 G of lift away from the ringworld's surface, which would hold her at altitude. Just like she would on Earth.
Airplanes don't experience gravity. They experience lift, which keeps them from hitting the ground.
The reason the ground is careening toward you is different than on Earth, but the answer is the same: lift. A Tiger Moth, Osprey, or B777-200 would fly about the same as Earth. They could even shoot a cat 3 approach if the proprietor of the ringworld were to fit the equipment.
[Answer]
**How Gravity Works**
The most simple way to define gravity without math is to say that it is the factor of two objects mass and their distance from each other. A ring the size of 1AU is going to have a gravitational effect of it's own anyways. I'm not really sure what the other dimensions of this ring are or what it is primarily made out of, but this is easily an object that has many times more mass than that of our planet. Obviously it's a ring and not a solid sphere so there is not really any gravitational "center" to be accelerated towards like that of a sphere. This makes calculating what exactly this gravitational force due to sheer mass would actually be at any given point within the ring a bit beyond me.
**Centrifugally Created Pseudo-Gravity**
In pseudo-gravity the acceleration is due to centrifugal forces instead of the warping effects that mass has upon space-time. Lets say there is no atmosphere for a thought experiment, an observer drifting from the center towards the inner surface of the ring would be like standing inside a giant rotating hula hoop. The ring would be spinning by at great speed while you moved in a straight line towards it. Add in atmosphere and things get..... messy. You would be moving forward at a set speed and begin experiencing drag from the atmosphere at a 90 degree tangent to your forward travel that was moving several thousand miles per hour. Its mostly advisable to math the speed and angle of the ring as you land, or better yet, match its speed and rotation from the outside and just not deal with atmospheric reentry. Until the object moving towards the ring from the center connected with the surface and was brought up to the same speed the ring was rotating at it would not experience the same pseudo-gravity everything else is. This effect does not apply to objects already on the ring and rotating with it, and the atmosphere rotating with the ring would play a big role in boosting said object rotational speed as well. Think of a juggler on a train, when he begins juggling his objects they don't suddenly move towards the rear of the train as soon as they leave his hand. This is because they retain the same velocity imparted to them by the train and are moving at the same speed relative to the train. They don't just suddenly stop having velocity because they are not touching the train right? This is why you can toss or drop something on a jet airplane and not have it impact the rear of the cabin at 340 miles per hour.
So a guy jumping up and down, or tossing a ball, or a bird flying would not really notice. "But what if they went in the opposite direction of the spin and lost velocity?" you might ask. Well, since the ring has to be spinning at thousands of kilometers per hour to adequately simulate a -9.8 m/s acceleration uniformly across the entire ring you would have to move in the opposite direction at least that speed to cancel out the centrifugal effects. Jumping upwards or even operating smaller slower aircraft would not cause enough of a differential in this velocity to really matter much beyond having to possibly account for it in extremely fast vehicles.
But what about moving towards the center of the ring? Doesn't a circular objects rotational velocity increase as you move towards the center? Wouldn't this effect the feeling of the pseudo-gravity? Again, since this is such a truly huge object. At 1 AU in radius you would need to move enough towards the center that you leave the atmosphere before you begin to experience any noticeable difference that what is experienced at the surface. Birds, bees, people and baseballs would not be in danger of flying off into space unless you found a really entertaining way to accelerate them to incredible speeds and great distances.
**Atmosphere**
This is a bit tricky, since atmosphere isn't a solid object under acceleration. The easiest way to do it would be to have the entire thing enclosed and not rely simply upon centrifugal forces to hold it in. A pressurized tube like a giant inner tube would be best since then you can guarantee that the atmospheric pressure was more or less uniform throughout. You also need an enclosure to counteract the effects of solar wind. Somehow overcoming the fact that drag effects at the surface and at the top of the atmosphere would not be the same you also have to worry about solar wind stripping your atmosphere away. Frankly, I think a pressurized totally enclosed ring shaped tube would be all around a better idea. Maybe less dramatic than a Halo style open wheel, but Halo is also using made up, misused, or fake words to describe most of what is happening on their ring world anyways.
[Answer]
So, imagine an object which is at an altitude of 100 meters on this world.
**The simple confusion here is between**
* (A) objects that "teleport in". in your thought experiment, imagine a rock "just appears" at that point (and let's say for now there is no atmosphere).
* (B) objects that are simply an ongoing part of the system. So, the bird was born on the ring, learned to fly, and happened to fly 100 meters upwards.
In case "A", as the OP suspects, there is **absolutely no** "like-gravitation-on-Earth" effect. Nothing, zero.
In case "B", there IS a "like-gravitation-on-Earth" effect. For the bird, it's exactly like being on Earth. No difference whatsoever.
Note: all of what I say has **absolutely no relation to an atmosphere**. Picture it as a total vacuum for clarity.
Note that a comment under the answer perfectly explains it:
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> "the deeper point here is that not every person intuitively realizes that *it is having been part of the rotating system* (as in, interacted with its components) that puts you into a state where things feel like gravity as we normally experience it"
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That is the nub of OP's question.
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A point of confusion regarding the atmosphere. Note that you *cannot* teleport in anyway - there's no such thing as magically instantly displacing your momentum.
But let's say on Earth, someone teleported in, to a location 500m above the surface, and the person was moving at a great speed, say 1000 km/h in one direction (North, whatever, doesn't matter).
What would happen? This teleporting person would experience incredible forces from the air and would quickly "slow down" (in fact *matching the speed of the surface of the Earth*), and then fall to Earth.
Interestingly ***exactly the same thing happens on the Ring*** if someone weirdly teleports in with a non-matching speed.
[Answer]
The short answer:
Ironically in a system like this the higher the bird goes the stronger the force will be pushing it outwards.
Why? The Dyson ring is a rigid structure that, at 1au, needs to have a velocity of 1200km/s to achieve 1g. At 1au, the acceleration due to the suns gravity is only 0.006m/s², much MUCH smaller than 1g which is 9.8m/s².
So, the ring is NOT in orbit. If broken into pieces it would fly out and away from the sun - although it would fall back again in an elliptical orbit as the escape velocity from the sun at 1au is about 40000km/s.
So the ring, the air in the ring, the bird and everything else in the ring is travelling at 1200km/s and consequently trying to fly away from the sun, only the rigid structure of the ring prevents that. This is literally the source of the apparent gravity: Everything on the ring should follow a highly elliptical orbit from that point, but the rigid structure keeps forcing it into a circular motion around the sun.
In order to escape this effect, objects would have to decelerate in the opposite direction to the rings motion: If the bird left the atmosphere - and then used rockets to accelerate backwards to 1170km/s (relative to the ring (and air) below) it would, ironically, merely be in a stable orbit around the sun at that radius as the orbital speed of the earth around our sun is 30km/s. Any speed between that and 1200km/s and it would start dropping towards the sun - because relative to the sun those speeds would be slower than 30km/s and hence insufficient to maintain a circular orbit at that distance.
[Answer]
If you stood up on the surface of the ring, you would experience gravity -- or at least it's equivalent in acceleration, which you could not readily distinguish it from.
If you then jumped straight up, you would most likely continue to experience that gravity because (a) since you were originally rotating with the ring, you would simply continue to do so, and (b) the ring makes traction with the atmosphere, causing that and everything in it to rotate also.
The exception is if you run counter to the direction of rotation and then jumped up -- you would negate the direct effects of the ring, but there's still that atmosphere to worry about. (However, if you could run fast enough, you could negate the force of "gravity" without ever leaving the surface.)
To an observer seated in a chair on the ring, if you jumped straight up, you would just come straight down again (from his viewpoint). But if you could jump up after countering the effects of the spin, and somehow get the atmosphere to pass by you without effect, you would just keep going straight up *from the viewpoint of a sidereal observer.* By sidereal observer, I mean someone in a spaceship who is *not* moving along with the ring. (You could argue that this is your "real" motion as viewed from the "side" -- "real" + "side" = "sidereal".)
Of course, if you could do this, you'd be headed straight for the sun with no way to turn around. Oops.
[Answer]
I see three options:
* The bird is in a stable orbit with about the same diameter as the ring. The surface would be passing under it quite rapidly. (This won't work if there is an atmosphere "in" the ring, e.g. held be side walls.) It feels weightless.
* The bird is at the diameter, but not in a stable orbit. It feels weightless.
* The bird is moving at more than orbital velocity, like the rest of the ring and the atmosphere above it. It does not feel weightless.
[Answer]
When you stand on a rotating surface (green ball in the picture) to simulate gravity, the perceived apparent gravity is due to the centripetal acceleration allowing the circular motion combined with the inertia of your body.
[](https://i.stack.imgur.com/BGy4n.png)
Now imagine putting an object within the circle, but in contact with the circle walls and at rest with respect to the translational velocity of the ring: will it experience any centripetal force? No, because there is nothing to transmit it. Therefore the object will not perceive any apparent gravity.
By Newton's first law then it follows that the red object will keep its motion until a force acts on it.
[Answer]
I think there is some missing principles here. When we are stationary on earth, we are in fact not stationary at all.... only in relation to the surface but what is 0 units of velocity on the planet earth is really equal to the rotational velocity of the planet rotation. This is around 460 m/s at the equator. So, if Earth were to stop instantly like in 10-60 seconds or absolute 0 seconds, you would be flung away from the planet at the rotational speed. When the time to stop is so short, you wouldn't be slow down. It is like being on a merry-go-round and it got spun up really really fast, you'll be thrown off. If the planet stopped rotating instantly and gravity stopped instantly like that then in theory you would be flung off. Now in space, there won't be any meaningful friction to slow you down. No air drag of any kind. Of course, Earth's gravity isn't quite like it would be in a rotating ring like artificial gravity by means of centrifugal/centripetal force but by mass but even then if the planet and its core had a sudden seize, it would be ugly because the mere gravity of Earth without rotation would be near zero, anyway... not enough to keep you from be flung off the surface into outer space. Being on the rotating ring would be like the merry-go-round. Not, the mass of the ring would need to be considered.
A rotating Dyson Sphere shell would have potentially massive mass to actually have gravity and if it even rotates, it would potentially have a gravity field. It is unclear if the ring world would have enough mass but in theory, it could if you have the material to make it. Practicality aside, if there was the material collected, refined, etc. for an advanced civilization (and the energy to go along), it would be theoretically possible for a ring world with a mass per 10,000 cubic kilometers being comparable to that of Mars or Earth, it would be theoretical that you'll have a gravitational force but you may need, in this case, the ring to rotate around the orbit of the star in the middle at least somewhere in the realm of the rotational speed of Earth. It might need to be a little faster but can't think of exactly the amount but you're looking at a rotational speed at this scale being earth like. At least, we are talking about a ring that has a 1 AU radius of 2 AU diameter. The problem with the ring or possibly even a basic classic Dyson Sphere would be the outer side may have very little gravity because you begin to be in the situation where you maybe flung off if you let go of the merry go round.
Now, if you tried to fly a shuttle and slowing your shuttle to 0 velocity difference to that of the rotation of the Earth, the problem is, as you are flying towards the planet, you're intended landing spot would have already moved (rotated). Yes, you'll hit the planet or potentially land or crash. The question is where? This might not be the landing strip so you'll then have to kind of fly the shuttle to a suitable landing spot. If your plan was to jump onto a rapidly rotating merry go round at the spot of you originally was aiming for, the good change is you'll miss your mark.
Getting into the doorway / passage way of a rotating Dyson Sphere from outside to the inner space, can be a tricky business. It can be tricky to land at a specific spot on the Dyson ring as well because you'll need to approach at near parallel and gradually converge but you'll need the correct matching velocity which means you'll need to be a little faster and begin gradually slowing down to match or otherwise be able to land without being too much faster or slower. A m/s faster or slower won't necessarily kill you but say... a 100 m/s faster or slower can mean catastrophic crash. 100 m/s is basically 224 mph crash.... either you crash into something in front of you or something behind you crashes into you. A jet can make such a landing at that speed if you are a little faster as long as you have a clear runway to land. However, if there is something stationary in front of you, then it would be like landing a jet on a road that has a dead end and a big structure like a building in your way right at the end of the road. If you don't make the stop in time, you crash.
I am not sure how air will be contained in a rotating ring to form an atmosphere. Not sure it will be quite like on Earth. The means in how Earth retains its atmosphere would need to be replicated in some suitable manner. IIRC: The magnetosphere of Earth is at least partly responsible for how Earth retains its atmosphere. It's a big magnetic field. We would have to produce the equivalent around and along the ring through a series of magnetic field generators but there is no current feasible means in current human technological and industrial capacity to do anything of this sort. This is something a race that would be described to be of a Type II civilization on the Kardashev scale or somewhere along that line to even be able to do such an endeavor.
[Answer]
This is a good question, that I have no idea how to answer, specifically I have now idea what the answer actually *is*. I do know that Niven's Ringworld design calls for walls to hold the atmosphere from spilling out into space.
Here's my best guess at an answer:
* fact, the "gravity" experienced by any object subject to rotation depends on the speed with which it is travelling
* fact, the lower atmosphere will spin with the ring due to friction with it's surface
* fact, the energy picked up through friction isn't the going to propagate very far vertically through the air column, on Earth we only see frictional effects in the bottom 300 or so metres of the atmoshpere
Supposition, the lower atmosphere, and everything in it, will experience substantially the same pseudo-gravity as the surface itself but because this gravity is governed by velocity it will dissipate relatively rapidly with altitude. There will also be an atmospheric density below which the gravitational "drop-off" effect accelerates noticeably.
In short something a hundred metres up will probably experience as much if not slightly more gravity than we might expect from a planet but a kilometer or more up it would slow down enough, stellar relative, that it stops experiencing gravitational forces faster than it would on a planet. As such the atmosphere will thin out more rapidly at altitude on a rotating megastructure than on a planet.
I advise anyone looking at building mega-structures to read Larry Niven's essay, *[Bigger Than Worlds](https://en.wikipedia.org/wiki/Bigger_Than_Worlds)* in full as a primer, it has a lot of useful notes.
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[Question]
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I'm at the mall and Yellowstone erupts - My, and everyone else's car is covered with ash, fire, and maybe even lava. Lets say it was a big shopping day too, like Black Friday or Christmas Eve, just to ensure the parking lot is packed -- That is a lot of steel in one place.
Now, everyone is dead, and our cars are covered in chemically reactive ash and chemically reactive fire. Also they're in a wasteland. Also, most everyone in the continental US is dead (or dying).
After a few decades, the US will be covered in plants, and in few centuries it will be covered in animals. Underneath all of that of course, perhaps a few dozens of feet, is me, the mall, my car, and my Christmas presents.
How long will it take for my and everyone else's car to look like a regular iron vein? Will it ever happen? What about the weird man made chemicals, like paint, motor oil, or antifreeze?
Also, Merry Christmas!
[Answer]
You could get something that might fool an alien geologist, at least briefly. Imagine that the mall gets blown out by a particularly large lava flow, one superheated to the point that all the cars in the parking lot get completely melted. Rendered down into a fully liquid state.
Of course your Christmas presents will be vaporized by this
If it happens fast enough, the metals may not even oxidize much until everything has a chance to cool down into a solid state. That should leave threads of metal throughout the strata.
Earthling geologists would know that this is not likely, because we've had time to study the earth for a long time. Aliens, might take a while longer to figure it out. They might send prospectors down to mine out the valuable metal ore.
Obviously, I'm not a chemist, so I don't have any idea if this is what could happen, but it sounds plausible to a layman.
[Answer]
**Never**
For one thing, to my knowledge, no veins of Iron have ever been found in volcanic [breccia](https://en.wikipedia.org/wiki/Breccia) so large deposits of steel (iron) found in one would immediately be suspicious. Additionally, cars are made up of many materials that over such a short time would not decompose. More surprising would be finding the concentrations of aluminum and platinum, let alone the plastic and glass. It would never be mistaken for a vein of iron.
**Edit:** When I say vein of iron, I really mean [Red Bed](https://en.wikipedia.org/wiki/Red_beds) which are deposits where you find iron in the form of oxides.
[Answer]
No, it will never happen that cars buried in the ground will revert to iron ore.
The scenario you described already happened, on a smaller scale, in Pompei. Tool used by the people, even bread, fruits or wine jars have been found back. No iron, copper, lead, silver or gold veins found.
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[Question]
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This question is about the technical plausibility that, instead of guns with bullets, cops would be using hand guns that emit a bolt of laser beam (or some other energy beam).
Considering issues such as energy needs, risk of eye damage from laser beams, and that (at least some laser frequencies) can ricochet toward the shooter if the target hides behind a mirror, would energy weapons ever be a viable alternative in the hands of law enforcement?
What obstacles would need to be overcome for energy weapons to be able to make all guns with bullets obsolete?
[Answer]
With foreseeable technology, not really. There are few exceptions. A near lightspeed weapon is really convenient for shooting down small fast moving objects such as missiles, drones, artillery shells, and, in the future, maybe in the bullets. An energy weapon might make it easier to control collateral damage; critical structures could be practically immune and even humans might have very limited risks of lethal damage. Police already use tasers. And energy weapons, sonic and microwave, have been developed for crowd control purposes.
But as a general replacement for guns? The basic issue is that if you are at a relatively close range, relying on humans reflexes for aiming, and need to reliably stop someone, guns are a relatively efficient way to do it. Being mature, simple, cheap, and reliable technology doesn't hurt either.
First point is energy storage. On a gun this is the propellant and the energy is transformed from chemical to kinetic in a very simple and relatively efficient manner. The relatively efficient here means that there are ways to do it more efficiently, but no one bothers since the way it is done is cheap and safe and, in practice, good enough.
For energy weapons this is lots more difficult. There are chemical lasers, but they are really not as convenient as the propellants used in guns. Available batteries have issues of their own as well. And it gets worse. The process of turning the energy into energy weapon is always more complex than with a gun. While this doesn't necessarily make energy weapons less efficient, it does make them more sensitive to wear and tear. And the inverse of collateral damage being easier to control is that practical energy weapons weapons impart their energy to the surface while bullets generally penetrate. This means that if you actually want to stop someone, a gun with a safety bullet will need much less energy to do it.
The end result is that for a given amount of stopping people guns will need much less space to store the energy, can do so reliably for long periods of time (guns are mostly NOT used, but need to work when you need them), and are simple and reliable. Guns would also be much smaller and cheaper than an energy weapon with the same stopping power as the mechanism of operation is simpler. This would be a major factor when arming large numbers of people on a limited budget. Especially when you intend a low rate of actual usage, so that the possible benefits of energy weapons are less important.
[Answer]
To make guns obsolete you would have to match or surpass the advantages of guns
Rate of fire. The amount of energy bolts fired per second must match or surpass guns.
**[Stopping Power](http://en.wikipedia.org/wiki/Stopping_power)**
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> Stopping power is the ability of a firearm or other weapon to cause a penetrating ballistic injury to a target (human or animal) enough to incapacitate the target. This contrasts with lethality in that stopping power pertains only to a weapon's ability to incapacitate quickly, regardless of whether death ultimately occurs. Some theories of stopping power involve concepts such as "momentum transfer" and "hydrostatic shock" [...]
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> [...] "Manstopper." Officially known as the Mk III cartridge, these were made to suit the British Webley .455 service revolver in the early 20th century. The ammunition used a 220-grain (14 g) cylindrical bullet with hemispherical depressions at both ends. The front acted as a hollow point deforming on impact while the base opened to seal the round in the barrel. It was introduced in 1898 for use against "savage foes", but fell quickly from favour due to concerns of breaching the Hague Convention's international laws on military ammunition
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**[Hydrostatic Shock](http://en.wikipedia.org/wiki/Hydrostatic_shock)**
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> Hydrostatic shock or hydraulic shock is a term which describes the observation that a penetrating projectile can produce remote wounding and incapacitating effects in living targets through a hydraulic effect in their liquid-filled tissues, in addition to local effects in tissue caused by direct impact. There is scientific evidence that hydrostatic shock can produce remote neural damage and produce incapacitation more quickly than blood loss effects.
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Also you might also want to consider that we have different guns for different purposes for example.
12-gauge pump action shotguns for close-quarters fighting. Used in a variety of roles in civilian, law enforcement, and military applications.
[Answer]
**Highly doubtful.**
First of all, "bolt" and "laser" are different things. A "bolt" would be something like a bolt of plasma whereas "laser" is a beam of light. Particle beam weapons would be another alternative for something "laser like".
Particle beams presently require a synchrotron or cyclotron which has approximately the size of a sports field (for a beam strong enough to penetrate 30cm of body tissue, and an effective range of a few meters outside vacuum).
A "blaster bolt" type of weapon that fires a plasma bolt is almost as hazardous to the wielder as to the target (and to anyone standing nearby). It would require a massive chamber able to withstand considerable heat and pressure, and a powerful coilgun-like mechanism to fire the bolt. Building a coilgun mechanism that isn't the size of a war ship alone is a challenge. The bolt would be damaging to the weapon wielder's eyes and everybody close by, interfere with surveillance cameras (intense infrared emission), and might damage/ignite nearby objects *even when not missing the target*.
For being a "manstopper" or lethal, the bolt would have to be massive, too. Otherwise it will result in an angry opponent with a severe burn, but certainly able to fight on.
A "laser beam" weapon is somewhat unsuitable as gun insofar as it concentrates its energy on a very small area. Unless the energy is in the megawatt range (try and fit that into a pistol), you will need to point at the same spot for several seconds to heat up the tissue enough to disable/kill a person. Not that this isn't possible, but it's no improvement over a conventional gun. Let's hope the target isn't moving.
Assuming you are able to fit a megawatt (or gigawatt) laser and its power source into a gun, or into a gun and a backpack if you will, it does not make sense to fire shots any more. It makes more sense to have [a continuous beam](http://i.ytimg.com/vi/P5fcn4p2oPk/hqdefault.jpg) that cuts anything it passes through to pieces (including your opponent, but also bystanders and environment). Note that the Bad Guys would have that kind of weapon, too, and it is much more suitable for them than for the Good Guys.
It's not so much that these imaginary weapons wouldn't be able to injure or kill a person (or don't have "stopping power", boiling someone's brain, cauterizing the mediastinum, or cutting off an arm certainly stops a person very quickly), but they just aren't very useful or have significant advantages over a conventional gun -- despite their ridiculously high technological demands.
The only imaginable advantage over a conventional gun would be the fact that you cannot dodge a laser beam. Assuming robotics evolve far enough so you have autonomous combat droids, they might eventually be able to dodge bullets. Dodging a laser beam isn't possible since at the time you see it (if it passes through a scattering medium and if it's in the visible spectrum at all) you have already been hit.
[Answer]
I would imagine the real issue to be a question of non-lethality.
In the case of police officers and law enforcement, this is quite obvious, if the weapon is cost-effective and as capable as a gun, **and** non-lethal, than I don't see why we would continue to use conventional firearms (for law enforcement in any case; criminals and soldiers are another matter)
Assuming the OP was talking about guns that John Q. Taxpayer can carry, weapons which can neutralize a target without killing him, would certainly change the political views on gun legislation and control and this alone could spur replacement.
[Answer]
>
> **What obstacles would need to be overcome for energy weapons to be able to make all guns with bullets obsolete?**
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* size,
* weight,
* capital cost,
* target speed and
* international law.
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> The LaWS cannon took $40m to develop
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> But the 30-kilowatt LaWS is a long way from replacing Phalanx, for the moment, although it does share the older system's targeting radar.
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> all the targets it blew up were traveling in straight lines and moving relatively slowly,
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> For the moment the LaWS will be used for close-in targets, although under the terms of the Geneva Convention it can't be used against humans directly.
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[ref 1]
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> The primary
> factors that have inhibited the transition of
> the technology into deployed systems are size
> and weight. Generally, the conceptual designs
> of laser weapons that are scaled for combat
> effectiveness are too large to be appealing to
> users; conversely, weapons that are sized for
> platform convenience generally lack convincing
> lethality
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[ref 2]
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Not cost of munitions.
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> At less than a dollar per shot, there's no question about the value LaWS [laser weapon system] provides
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[ref 1]
*"No, it's your turn to carry it!"*
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References:
1. [US Navy's LASER CANNON WARSHIP: USS Ponce sent to Gulf](http://www.theregister.co.uk/2014/12/11/us_navy_deploys_poncey_laser_cannon_ship_to_persian_gulf_war_zone/)
2. [Laser Weapon System (LaWS) Adjunct to the
Close-In Weapon System (CIWS)](http://www.dtic.mil/get-tr-doc/pdf?AD=ADA557757)
[Answer]
There are two big reason energy weapons might get adopted assuming their performance can be brought reasonably close to guns, these are:
1. No need for ammunition. Assuming they can hold charge for a good while or even better be recharged in the field then you remove a lot of weight and logistics requirements.
2. Space safety - in sci-fi settings directed energy weapons can be designed that do not penetrate the hulls of ships but still take out their targets. (Although this doesn't explain why people don't build body armour out of the material used for ship hulls). It also reduces the risks of ricochets in confined spaces considerably.
Energy weapons that exceed the performance of our guns would not need those advantages to be adopted anyway. If energy weapons were developed able to penetrate body armour for example then they would render both body armour and bullets obsolete.
[Answer]
**"Batteries don't deliver energy that fast. Almost nothing non-destructive, actually, delivers energy that fast."**Batteries don't (yet) but capacitors do and we have some pretty energy dense power generation equipment out there.If you're talking about something "man-portable" then yeah, you're going to need some sort of development(s) in energy generation. But capacitors can store and release significant amounts of energy in short order (that's why they're particularly dangerous.)Honestly, there are some benefits to laser weapons (line of sight, speed, etc) but kinetic weapons are still developing. Just look at the Navy's rail-gun program and all the benefits that will entail; no need for explosives to launch projectiles is HUGE! No more wasted space, no more powder magazine detonations from enemy fire, no more projectile explosions, significantly more energy transfer, longer range, faster cycle time.I wouldn't discount kinetic energy weapons (like guns) until we have some major breakthroughs in room-temperature superconductors and some kind of ultra-compact power generation equipment. Not saying it won't happen, science has proven time and again to advance and defeat "insurmountable" problems, just that it'll be a while...
[Answer]
Yes, it is possible and it will happen as soon as some criteria is met:
- Reliability - All firearms are simple. They are purpose built to be as simple as possible, less things to go wrong.
- Cost/effectiveness - There is no point in making a rifle that does all the same things as an AK or an AR, but costs 500 times more.
- There ware attempts at energy weapons, some even working(hell the US navy just used the first ever laser cannon a few days ago) during the 80's. Japan is said to have made a energy weapon in 1944, but it is lost. These weapons ware set aside for a reason, it was not their time yet, but it is very close.
[Answer]
A laser is pretty much negated as a weapon in the rain, or mist, or dust, or fog - the beam will be scattered. This makes guns superior unless you have an environment where this doesn't occur, such as space.
[Answer]
The function of a gun is to deliver a large amount of energy into a target at a distance.
It turns out that using a one-time chemical reaction to impart kinetic energy into a metal slug is a really effective way to do that, in a relatively compact, lightweight package.
So for any "sci-fi" weapon, be it railgun, laser, or plasma blaster, you've got to determine where the energy is coming from. Batteries don't deliver energy that fast. Almost nothing non-destructive, actually, delivers energy that fast.
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[Question]
[
How could blue soil exist, in a realistic earth-like world.
*The world may even be earth.*
First off is it even possible - could soil like this exist given the requirements below? (if not then why?)
Mainly what would the composition of the soil be (what elements/chemicals would be present that give the soil its color)?
What shade of blue? (representation could be given in hexcode (#0000FF) or an image maybe)
Would the soil be fertile or toxic or...?
**Some requirements:**
The soil is just like normal earth soil. All the standard obvious earth soil stuff applies, difference is this soil is blue.
Plants *must* be able grow in it. Even if just sparsely weeds.
The soil *may* contain toxins, possibly even be radioactive.
No specific blue, but should be obviously blue, as in *not*
blue-ish-some-other-color, but rather blue. Light blue, dark blue, etc.
Blue in the sense that a person who was used to normal soil would clearly describe it as blue.
Solid blue, just as earth soil is solid brown. In other words not brown with little blue rocks or something.
The soil is *permanently* blue, not temporary.
The soil is not stained or tinted blue, but it's the composition or chemicals/elements in the soil that make it blue.
(To me stained or tinted would be something like having the color altered by spilling paint, oil, etc on, etc. or tinted by light or light shining through something like colored glass.)
May be caused by a freak event. (if so what?)
Kind of what I was looking for here (as I thought that blue soil was not actually a thing at all) was actually something that would be more exotic, rare, but realistic, like for example the soil was compromised mostly of two elements that normally aren't found together and it is that combination that causes the blue.
Also:
[blue](https://3.bp.blogspot.com/-DRC4w4c54Y0/T0otkbsk6qI/AAAAAAAAAGI/KGMLntMhWEs/s1600/blue.jpg)
[blue](http://unisci24.com/217290-dark-blue.html)
[not "blue" (teal, aquamarine)](https://thumbs.dreamstime.com/z/blue-clear-aquamarine-water-14489792.jpg)
[Answer]
**In order to get blue soil**
**First** I would start with a copper rich dirt. Copper is excellent, its a relatively light semi harmless metal that when oxidized turns blue.
Like others have posted:
[](https://i.stack.imgur.com/W5Xlf.jpg)
**Now to get a deeper blue color**
In order to be soil the dirt must contain microbial life and support life. One common byproduct from microbial life is ammonia (NH3). When ammonia is bonded with copper it creates a deep blue indigo compound called **ammine (CuNH3)**:
[](https://i.stack.imgur.com/SW8RS.jpg)
Copper(II) ammine complex Cu(NH3)2+
**Answer:**
**So what if your copper rich soil contains a prolific microbe that produces a lot of ammine as a byproduct of its existence. The shade of blue can be directly related directly the proliferation of this microbe.**
[Answer]
Soil is not dirt; soil is alive, dirt is inert. Semi-rant about people using non-interchangeable terms over. I would start with the blue-gray mudstone known as Papa which can be a very pronounced blue, (sorry I can't find a good picture of it) the blue colour comes from the iron in the clays from which it is formed, it holds this colour pretty well and forms a reasonable substrate for soil formation. If you keep your soil largely anaerobic, by having high clay content and a high water-table, then you also get blue-ing from cyanobacteria and blue-green algae in the medium, the surface won't necessarily stay blue, especially where weeds are actively growing but it is blue just below the surface and even at the surface where there is no plant growth. If the plants were atmospheric nitrogen fixers, like clover, they'll create higher soil acidity which will reinforce the blue effect.
[Answer]
If I understand what you want correctly, it’s soil that has all the properties of ordinary soil except for its total blue colouration?
For soil to be soil as I think you mean, it must contain at least some organic material so the best candidate would be organic chemicals found in the soil that gave it its blue colour. Many blue coloured organic molecules exist or might be reasonably proposed.
A world in which all light except blue light could be absorbed by plants for use in photosynthesis might work. This would tend to make the plants appear blue as this would be the only wavelength not absorbed. If the material used to absorb all this light (the blue alien equivalent of chlorophyll) were also very stable and not easily decomposed it would tend to build up in the soil and colour that blue as well.
[Answer]
There are quite a few naturally occurring minerals that are blue, inlcuding Lapis lazuli and others. The blue component in Lapis lazuli is [lazurite](https://www.mindat.org/min-2357.html) (Fig. 1), which is intense blue. Other blue minerals include azurite, chalcanthite, chrysocolla, linarite, opal, smithsonite, turquoise, and vivianite (see *e.g.*, [ThoughtCo](https://www.thoughtco.com/blue-purple-and-violet-minerals-1440938)).
[](https://i.stack.imgur.com/mkXfD.jpg)
Lazurite. source: [Marin Mineral](http://www.marinmineral.com/mixed355.html?cur=yen)
Many copper (Cu) salts (or their solutions) are blue, for example copper sulfate (CuSO4) (Fig. 2).
[](https://i.stack.imgur.com/Mux4p.jpg)
Fig. 2. CuSO4. source: [wikipedia](https://commons.wikimedia.org/wiki/File:Copper_sulfate.jpg))
The Sagada Blue Soil in the Philippines (Fig. 3) is said to be blue duie to its high copper content (but it may be Iron (Fe) too).
[](https://i.stack.imgur.com/wTAzv.jpg)
Fig. 3. Sagada Blue Soil, Philippines. source: [Roamulofied](https://roamulofied.wordpress.com/2015/04/02/sagada-mountain-province-philippines/)
While the above options are not directly toxic, there are poisonous options too, for example soil contaminated with petrol (Fig. 4).
[](https://i.stack.imgur.com/3SBU1.jpg)
Fig. 4. Petroleum contaminated soil. source: [WA State Dept. Transportation](https://www.wsdot.wa.gov/Environment/HazMat/photos.htm)
[Answer]
Cainville Utah USA. Southern Utah an area rich in Uranium and is easy to see on Google Maps. The water in rivers and streams in this area will give you gastric distress even when treated or boiled if consumed. The mineral content is unknown to me, but I would expect to find nothing you would want grow anything in. Plants are sparse but exist and are scruffy desert foliage. The whole area is ancient sea bed and mostly sandstone. The area is only 80 to 90 miles or so southwest of Dinosaur land in Vernal Utah. A beautiful landscape as varied as exists on this planet. The blue is clearly visible looking at the Google Earth photos.
<https://www.google.com/maps/@38.4602117,-110.8388242,5358m/data=!3m1!1e3>
[Answer]
It depends on what kind of soil you mean. Sand is basically just glass, and glass comes in [blue](https://en.wikipedia.org/wiki/Cobalt_blue). So blue sand is easy, and as some soils are mostly sand, those soils would be blue.
Calcite and dolomite based clay soils are white or really pale. If contaminated with cobalt salts or [iron cyanide salts](https://en.wikipedia.org/wiki/Prussian_blue) it does turn up blue, [sometimes](https://en.wikipedia.org/wiki/Blue_billy). Prussian blue is insoluble and forms a very fine colloid when left alone, so it tends to linger in the soil. It is 'relatively nontoxic'.
If you wanted to grow a plant in blue soil, I would start with a calcite clay, add cobalt-doped sand and very finely powdered organic material. The organic material is black, which would darken your light blue clay/sand mixture.
At this point it's a trade-off between how toxic you can have your blue dirt be and how blue you want it to be. Generally, you can add as much blue sand as you want, but you'll only be able to grow cacti and palm trees. If you want something more like regular dirt you'll need to add clay and Prussian blue, which will degrade from microbial activity(very slowly, but still). Soil contaminated by Prussian blue as a side effect of coal gasification was once sold as a herbicide, so be stingy with it. As organic matter turns over into the soil it'll darken as more carbon gets incorporated. Make sure to turn the soil regularly, or the clay and sand will settle out into different layers.
All of this does kind of count as 'staining', though. Unfortunately, dirt is made of silica and organic matter, and neither of those can be blue without additives or something really exotic going on. Blue is often a '[structural color](https://en.wikipedia.org/wiki/Structural_coloration)' in nature, but that kind of color requires a reasonably ordered crystal to work, which is not really how dirt works.
[Answer]
Thinking outside the box, here. It's entirely possible. The soil could even be normal, Terran soil. The light shining on it could be blue, though. As O-type stars are really rare, and not recommended for life, let's go with a B-type, a blue-white, or light blue star. If you place a planet in orbit of one, you're going to have blue soil.
For your color requirement, here's a nice [picture](https://i2.wp.com/www.astronomytrek.com/wp-content/uploads/2016/03/Bellatrix.jpg?resize=678%2C381) of Bellatrix, a example of a B-type star that's 250±10 light years off.
Now, would the soil be fertile? The main issue is of how long these stars live. It's not very long. Enough for planets to form, but the star will go nova or supernova before then. You could always terraform one of those molten rocks, or build a megastructure like a shellworld there.
[Answer]
Well, here are a few possible elements that could be in your soil:
1. Copper. While copper in the form of pots, pans, and bronze is a reflective brown, copper in the soil is actually a pretty blue. This is because, while the copper in the aforementioned pots is from the anaerobic depths of the earth, the copper in soil is oxidized. Since it is water soluble it would not make your soil uniformally blue, but this is the closest you can get without poisoning the soil.
2. Cyanide salts. Not only do these make soil a very pretty blue color, their presence makes the air smell like peaches.\* Of course, they would also kill all the local fauna, but that is just a "minor" problem.
3. Cobalt. This would make your soil a very uniform (if somewhat boring) blue, but it would also kill all the local flora.
Of these choices, I prefer copper. While it will not yield the uniform blue you desire, it is the only safe option if you want the area to be inhabitable.
\*Actually, to be technically correct, cyanide does not smell like peaches; it is the peaches that smell like cyanide. This is because peaches contain large quantities of cyanide in their flesh and pits.
] |
[Question]
[
Scenario:
A group of friends, stranded in a medieval castle/modern museum, need to go outside to forage for food. They managed to gather complete sets of medieval armour from the museum. Museum is clear of zombies and might be a nice base of operations to protect this group of friends. But there is no food or water.
Questions:
What kind of advantages would armour provide when fighting zombies ?
What kind of armour would be most usefull ?
What kind of advantages fighting light - without armour - provide ?
Whats best for a modern setting, fight zombies with a full medieval style armour or fighting zombies without armour ?
Assume:
There are circa 10 friends in the museum.
There are circa 15 sets of armour that might be used. They are of the full plate type, all body is covered.
There are various kinds of swords and other blunt weapons.
The zombies are the walking dead type, slow and dumb.
[Answer]
According to this website on medieval armour...
>
> An entire suit of field armor (that is, armor for battle) usually weighs between 45 and 55 lbs. (20 to 25 kg), with the helmet weighing between 4 and 8 lbs. (2 to 4 kg)—less than the full equipment of a fireman with oxygen gear, or what most modern soldiers have carried into battle since the nineteenth century.
>
>
>
That surely isn't *light*, but the added protection of **not getting 'zombonied' is *surely* worth that extra weight!**
I would definitely agree with @DanSmolinske and add that **most other types** of modern armor would certainly be *better* than medieval armor. BUT, the OP specifically said that they had access to only medieval armor and, because of that, I would 100% advocate that **any armor is better than no armor**. Zombies have an unyielding hunger for human flesh. They will scratch, claw, and bite at anything that moves, so a layer of metal between you and them would *obviously be beneficial*.
For some nuance, [here is some further reading on the *mobility* of people wearing full armor](http://www.popularmechanics.com/culture/a6749/medieval-knights-on-a-treadmill-put-historical-myths-to-the-test/). (*note that the article is absolute rubbish*)
### Alternatives
Let's go with the scenario that they are in a modern museum instead of a castle. There are probably exhibits of many ancient civilizations. It stands to reason that they would have a roman exhibit as well. Roman armor is **much more suited for hand to hand combat than medieval armor** (which is more for swordplay and armed conflict). You can read about the specs and variations of it [here](http://en.wikipedia.org/wiki/Roman_military_personal_equipment). Bonus points for extra coverage of exposed skin that they can salvage from other exhibits!
The point is: anything between you and the undead is good. It just needs to be (ideally) light, versatile, and quiet. Medieval armor is obviously not the best choice... but in a time of emergency I'd rather have that on than nothing!
*[Extra reading on what the zombie wiki has to say on the matter](http://zombie.wikia.com/wiki/Armor).*
[Answer]
**Armor:**
Heavy armor like pictured is a bad idea. As pointed out by others, it's going to weigh you down and make you too slow. You might not be bitten, but you'll be caught, knocked down, and probably smothered.
On the other hand, I don't think sports equipment is a good idea either. The protection paradigm is different - sports are primarily concerned about impacts. For example, football or hockey pads are good for your shoulders, chest, and the outside of your elbows because that's where designers expect you to hit. But they don't do much for say, the inside of your elbow/forearm or your lower stomach, because those are low-risk areas. A zombie will easily be able to find ways around it and get a bite into you.
Instead, I would go with **motorcycle gear** - Heavy leather boots, pants, jacket, gloves, and a full helmet. Human teeth aren't going to go through leather easily, it's relatively light weight, and you can still use nearly any weapon effectively while wearing it.
If you want total protection you may want to find some kind of Gorget to [supplement](http://en.wikipedia.org/wiki/Gorget) the above, as I think there would be a gap between the helmet and your jacket. Maybe you could get a fencing gorget to work? Like below:
Although I don't know if it would protect the back of your neck, so you might have at least one vulnerable point left.
**Advantages:**
Armor lets you survive zombies getting in close, or sneaking up on you. Entering a room blind where you might be ambushed goes from "probably get bit" to "very unlikely to be bit".
You can also use it tactically. Presumably you wouldn't do this all the time, but if you know you can't dodge a zombie, this gives you more options. Allow it to bite your protected arm. While it tries to chew through the leather, shoot it in the head (or bash it in the head, depending on your available options). You might choose a different weapon selection if you expect this to happen fairly often, as some weapons might not work well against an opponent who's actively biting you.
The big advantage, though, is that armor gives you that second chance. Without armor, you screw up once and you're dead. With armor, you can survive a lot more screw ups, and since most humans aren't perfect...
**Disadvantages:**
Even light armor has weight and will, to some extent, restrict your movements. You won't be able to run quite as fast, or as far. If you're not used to it, it could trip you up. In hot climates, you could suffer from heat stroke - imagine wearing heavy leather in a desert summer (on the other hand, it might be an advantage in a cool/cold climate).
Armor also has to be maintained. A zombie bite (or bashing against a door, or falling down) will cause slight damage, and that damage will add up over time. You need to plan on giving your armor regular maintenance and eventually needing to replace it.
[Answer]
While modern technology makes building a zombie proof armor relatively easy, shockingly enough nobody seems to be producing armor designed to be efficient during zombie apocalypse. Maybe this is a market opportunity?
Closest thing to having the same requirements seems to be police riot gear. It is designed to be worn for extended periods. Protects full body against thrown bottles or stones so might reasonably help against zombie bites. Protects the head with good visibility. Has carry attachments for weapons and equipment. It is designed to be used in melee, so it should be relatively easy to move in while giving some protection against blunt force from the attacking zombies.
It also has a riot shield, which might be convenient if there are enough of you to form a shield wall. Add a club or mace or a shotgun to hit zombies in front of the shield wall and you are relatively well off.
But the main attraction is that some actually exist and a major police force might have significant amount in storage. Reasonably unless the police collapse immediately, they'd try to get these armor to the streets and keep them in use.
That said, if you want real protection, you should be thinking armored vehicles, not body armor...
[Answer]
Q: What kind of advantages would armour provide when fighting zombies ?
A: It will lower the chances you get hurt, infected.
Q: What kind of armour would be most useful ?
A: As it only needs to protect against zombie bites and scratches, light armour.
Q: What kind of advantages fighting light - without armour - provide ?
A: You can run away faster.
Q: What's best for a modern setting, fight zombies with a full medieval style armour or fighting zombies without armour ?
A: I'd opt for light armour instead; something like football gear will already help. Protect lower arms and neck first!
Please note that heavy armour is HEAVY. It was used mainly to fight from horseback, and they needed to breed special horses to carry the weight. You cannot run. You need to train even to be able to stand up after a fall.
[Answer]
Between no armor and full armor, no armor would probably be better. BUT! I would say that *some* armor would be better than none. Armor gives you a buffer that allows you to recover from mistakes. Overextend a little? Armor there to save you. Overextend a lot? Doesn't matter if you have armor.
However, while armor gives you a buffer for mistakes, it does that by reducing your speed/stamina/movement. To balance that out, I would only armor certain places: arms and legs.
Arms are the most important. That's the part that will be closest to the zombies and are your intervention method if the zombies get too close (gotta push them off). Legs are important since zombies could be anywhere and looking down isn't always the first thing you do.
So, given suits of armor, how do we achieve these? Well, gauntlets could be taken from the suits and used. They might be slightly heavy, but not too bad. Fine motor skills with fingers might be off, but overall arm movement should be good. Protection up to the elbow with a vambrace would be nice. Also might make punching zombies easy.
For legs, that's probably harder. Simplest would be to try and get the shin guards. Knees and upper legs could be slightly awkward but could be done. Shoes might be a weak point, but you either have shoes for endurance (running shoes) or tough shoes (work boots).
[Answer]
[Simple chainmail](http://blog.pearsonsrenaissanceshoppe.com/wp-content/uploads/2013/08/Chainmail-Armor-Shirt-300x300.jpg) would not only be effective but I think that your characters would have a much easier time slipping some chainmail on then trying to use platemail armor. Chainmail will still be heavy however it is nothing compared to trying to walk around in a set of full plate armor. Complete this with some sturdy boots and leather gloves. Chainmail leggings do exist but I think it would be better to go with greaves as you need your mobility. If you fall down or can't run your essentially dead. As an added bonus you can wear chainmail all day and it may not be the most comfortable thing but you will be ready on the fly if need be.
[Answer]
Firstly I'd like to point out that plate armor is nowhere near as restrictive as you would imagine it to be if you have never worn it. It was designed for people to fight in and whilst some training/practice would help you are easily able to roll around if knocked over, get up, etc, etc. Now you are going to be slower than you were without it but then you are fighting a shambling mindless zombie not Bruce Lee so I don't see the down side.
However the biggest problem you face is that armor of that quality and expense was restricted to the rich. It was hand made for the wearer and maintained by craftsmen. The chances of you finding a suit that fits you properly are slim to none and that is where a lot of the problems will come from. Badly fitting plate armor will be less effective and cause you movement and agility problems where as a suit made for you would not.
[Answer]
It depends on the number of zombies. If you assume dumb and slow zombies that are infectuous but cannot learn anything, then heavy armor will effectively mean they cannot really hurt you. An unarmed man has no real chance of wounding a person in plate armor.
However, unlike normal people (who would be crazy to engage an armored man in a straight-up brawl) zombies are going to try anyway, and you're going to have to hack them all to bits until none remain because they will *never* stop attacking you.
Ultimately it's likely a battle of stamina: if you can keep upright and swinging until all the zombies are immobilized, it's awesome and you win. If you grow tired before all the zombies are gone, you will be dogpiled and crushed to death.
And you have to be very careful about being surrounded, because the armor offers no protection against being grabbed and pulled down. It won't kill you and your friends will probably have some time to save your ass, but if they don't show up (because they are in a similar situation) then you can look forward to either starvation or being cooked alive under a mound of the rotting undead.
[Answer]
There are very few advantages of armor over zombies. The only advantage is that it reduces the amount of exposed skin to bite, but this advantage is quickly outweighed by the fact that 10 to 20 zombies could quite easily rip it off. To make matters worse anyone wearing your armor would quickly become a walking dinner bell. He/she would be unable to move fastly and would most likely have to be left behind.
I also can't see a bunch of friends getting the armor on in the first place. I know from experience that medieval armor (or at least the replica armor--the real stuff is too hard to get your hands on) is a b\*\*\*\* to put on. I put a full body suit on and not only did I sweat like a dog, I had blisters (probably from doing it incorrectly). As a matter of fact, medieval knights needed an entire squad of pages to help them in and out of their armor. It still took an hour. If a knight fell off his horse, his armor was so heavy he usually couldn't get back up.
In short, I see this getting one (or all) of your characters killed and/or scattered.
[Answer]
I think your best bet would be to skip the heavy plate style of European knights and instead hit up the part of your museum that covered leather armor instead. Ever tried to chew through a steak you've cooked too long? Its not a quick process, definitely long enough to jam a stiletto blade through a zombies eye or ear. Leather armor is also much lighter, won't impair your movement as much, and relatively easy to maintain compared to plate. Some sturdy greaves, a bracer (maybe backed with metal strips) to hold them back and eye-stab, and maybe a bevor and spalder and your covered in all the likely spots a zombie might come a munching.
And in terms of weight it'll be three to five kilos depending on whether you want to add metal strips to the leather as further reinforcement. Your main asset in a zombie apocalypse will be speed and maneuverability anyway, why weigh yourself done unnecessarily?
Leather armor can also sport a handy array of pouches, pockets and attaching straps for your supplies and weapons while you run
[Answer]
If you need to move fast you can use Carpet Coats (<http://zombie.wikia.com/wiki/Category:Carpet_Coats>). They are lighter than the medieval armour but it will not be good against firearm or heavy swords and such. Also I think easy to find / make in the museum.
Still will keep you uninfected even if bitten. Still you can get battered :)
[Answer]
I don't know if this information will help or not but light armor against zombies my not be effective.
If we assume that zombies are moving dead bodies "without limiter" then their bite strength should be more than enough to tear apart lether armor. Chainmail should provide some protection but it wouldn't last against more than one zombie...
If I would be in the mentioned situation I would propably go with arm and leg protectors and some kind of long weapon like spear/halberd/naginata or long staff (eventualy some kind of a club/mace and light shield). Because I'd prefer movement speed and agility over tankines. But that's my opinion.
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[Question]
[
This question is connected to: [Fire Resistant Flora](https://worldbuilding.stackexchange.com/questions/11179/fire-resistant-flora)
I've been pondering a short story concept where a scientific expedition discovered a planet with a huge amount of both free hydrogen and oxygen in the atmosphere.
This is caused by an unobtanium crystal widespread on the surface of the planet which acts as a catalyst, splitting water into hydrogen and oxygen and absorbing heat and sunlight to do so. (That heat then gets released back into the environment when the gases burn).
The resulting atmosphere is highly flammable and as a result flash-fires are a common occurrence. These involve a burst of heat and flame and even mild explosions but are also over very quickly. Very fast-moving flame fronts sweep through the atmosphere, averaging at least one a day, but passing in a matter of moments. Water falls out of the sky in the aftermath of the flash fire and is then split back into oxygen and hydrogen once more by the unobtanium crystals.
Assuming animal life has evolved to survive in these conditions what adaptions could they make to survive?
[Answer]
In a flash burn, assuming that the heat isn't super intense most of the animals (and plants) would have some kind of heat reflective coating. Most of the IR band would be reflected. Humans can take some pretty large fire balls without burning up, just losing hair with low burns. If it's short lived burn then the protection doesn't need to be that much.
Woodland fire fighters carry little [aluminum shelters](http://en.wikipedia.org/wiki/Fire_shelter) which can protect someone for up to 20 minutes or so. These are very hot and intense fires. The biggest thing it does is protect the lungs by keeping out super heated air and trapping oxygen inside.
Now if you only have a few seconds to deal with, an innate reaction to stop breathing and close your eyes, would go a long way. Having tough hide or a hairless body with reflective particles in the skin would also do much of the work. Having fire resistant hair could also be a way to go, kind of like insulation covering the body.
[Answer]
A fire/blast resistant epidermis would be enough.
An animal sensing a blast would huddle down protecting the more vulnerable parts, hold their breath and wait it out. Afterwards they could stop-drop-an-roll to put out the embers in the fur or throw dust on themselves to put them out.
However the biggest change would be the possibility for animals to stop eating for energy. They would still need to eat to grow (and heal) but not for energy. But instead use internal oxidation of the hydrogen in the air they breath (same would go for the plants).
All in all a fauna with a very low carbon foot-print.
[Answer]
You will have to come up with *several* solutions, depending on the size and environment of the animals.
You already received some answers, but here are more heat adaptations:
The [Pompei worm](http://scribol.com/environment/the-pompeii-worm-the-most-fireproof-animal-on-earth) survives in water of 80 °C because of (among other things) a centimetre thick thermal blanket across its back that is composed of colonies of filamentous bacteria. This is under water, but I can imagine such a symbiotic relationship on land as well: as long as the bacteria can regrow, losing them partially wouldn't be a big problem. This is one possible solution for little critters.
The group of [Deinococcus and Thermus](https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/microbial-evolution-phylogeny-and-diversity-8/thermophiles-108/deinococcus-and-thermus-563-1921/) bacteria do not only contain extremely radiation-resistant species, but some like Thermus aquaticus can resist up to 80 °C because of heat-resistant enzymes throughout their body. You can 'have' those enzymes in some of your higher order fauna as well ;-)
[Tardigrades (water bears)](http://www.ncbi.nlm.nih.gov/pubmed/19732016) also have no issue warming up for 1 hour to 80 °C. Milnesium tardigradum (Milnesidae) showed survival of >90% after exposure to 100 °C. I don't know their mechanism, but you can probably find it.
I suggest you also [Google for 'fires animal survival'](https://www.google.com/search?q=fires+animal+survival).
[Answer]
Since hydrogen is light I think for the most part these hydrogen burns are going to be high in the sky and burn harmlessly. With about as much effect minus radiation as this nuke exploding high in the sky did.
However occasionally the burns would be close to the ground because of the weather phenomenon of inversion layers. Almost all areas of the world get inversion layers but the inversion layers are of differing strength and frequency. Some inversions just last a few hours in the morning at certain times of the year, some inversions last for days weeks or months. For example here on earth every decade or so we are treated to a scene like this at The Grand Canyon.
In the north west part of Utah roughly in the old lake bed of Bonneville Lake, most winters a large and persistent inversion layer develops, that might last from December until sometime in march. Some years it does not develop for long some years it comes and locks in a low layer of cold air for months.
Frequency and size of the burns would vary depending on topography and weather. Weather always varies.
Taking the premise that natural disasters are basic to evolution I think you would find that the plant and animal life on this planet would be much more diverse then it is here on earth. Evolution is about survival of the fittest. All living things would have all the variables that we have here on earth to evolve plus the added variable of the hydrogen burns.
There are lots of plants that survive large disruptive events like explosions, avalanche, flood and fire. Some ecosystems depend on these events, especially in the case of wild fires, to thrive.
Consider [Aspen trees](http://extension.usu.edu/rangeplants/htm/quaking-aspen).
>
> Ecological Adaptations:
>
>
> Quaking aspen occurs on a wide variety of sites. It grows on moist
> uplands, dry mountainsides, high plateaus, mesas, avalanche chutes,
> talus, parklands, gentle slopes near valley bottoms, alluvial
> terraces, and along watercourses. It is most common at elevations
> between 6,000 and 10,000 feet. Most of the reproduction of Aspen is by
> root-sprouting, many trees in a grove being connected together by a
> common root system in what are referred to as "clones." Because the
> trees are in clones, they are genetically identical. This species is
> not shade tolerant, and entire clones can be lost due to the
> encroachment of spruce and fir into this type of ecosystem. ***Aspen
> is dependent on fire, clear cutting, or other "clearing" disturbance
> to keep stands open***, free of conifers, and reproducing from
> suckers.
>
>
>
Aspen trees would thrive and dominate an eco system that was blown away every few years or decades.
Consider the [Yellowstone](http://en.wikipedia.org/wiki/Yellowstone_fires_of_1988) fires and the adaptation of the lodgepole pine tree.
>
> The predominant tree in Yellowstone, the lodgepole pine, fared poorly
> from the fires, except in areas where the heat and flames were very
> mild. The lodgepole pine is serotinous and often produces pine cones
> that remain closed and will not disperse seeds unless subjected to
> fire.
>
>
>
[The Mysterious Tunguska Explosion, 1908](http://history1900s.about.com/od/1900s/qt/Tunguska.htm), huge event that was a giant explosion that leveled 80 million trees. Described as a giant fireball in the sky.
Look at this picture and you will see the plant life that will dominate, the decedents of the large tree on the right of the picture may inherit what ever traits helped this tree remain standing. There are bushes in the picture that appear to have survived the event unscathed. You can imagine that there are grasses and smaller plants that also survived but not really visible in the picture. There is an ecosystem here and the plants that survived will pass on the traits in there genetic that helped them survive. If you repeat the event every few decades or so a whole diverse eco system will develop that needs the explosion like the lodgepole pine, or thrives on the devastation of the explosion like the quaking aspen. Species that were stifled by the shade of the larger trees will also thrive in the new ecosystem.
[Answer]
Both your flora and fauna will have to be based on some very exotic biology, because it could not contain any water. Basic chemistry of life would have to be very different, so not sure how you can even define plants. Plants (defined as life form using solar energy) are not necessary at your planet, because crystals of unobtainium make the work plants do on Earth (capture sun energy to and provide sustenance to other life forms).
Animals (defined as lifeform which does NOT use solar energy directly) can get energy not by consuming plants and other animals, but (somehow) oxidize free hydrogen and oxygen to get energy. Probably they would be some electromagnetic fields or something - nothing based on biochemistry as we know it. Maybe metallic lifeform designed by alien race. On nanobots, powered by unobtanium crystals.
**Why life biochemistry cannot contain any water?** Because life starts small. Any small lifeform (original bacteria, archea) would be vulnerable to damage by internal unobtainium.
Another problem your animals would have is changes of air pressure associated with fire flash. Oxygen and hydrogen would get burned to make water, which has less volume. So pressure of gasses inside body will increase, creating damage. Fire could even enter inside cavities (where both O2 and H2 are present). Fire damage could be rather intense, depending on the concentration of flammable gasses.
Yet another problem would be **hydrogen escaping the atmosphere**. Free hydrogen in upper atmosphere would be swept away by solar wind. In few millions years, water could be converted to oxygen (with hydrogen escaping). Then, with frequent hydrogen fires, and over-abundant oxygen, other things could go up in the flames too. Things like metallic outer shells mentioned in other answers.
[Answer]
Maybe the flora and fauna can develop some kind of [fire resistant gel](https://en.wikipedia.org/wiki/Fire-retardant_gel).
These kind of gel can protect the skin from high temperature for some time. [They are used in stunts.](http://www.stunt-training.com/courses/fire-training.shtml)
] |
[Question]
[
I need ten Earth years long day-night cycle on my planet.
Hemera is a world I am creating as a setting for my story. Name comes from Greek deity - personification of Day. Needs of storytelling have precedence, but I would like my world to be more or less plausible.
Hemera is a very slowly rotating planet. So slow that people and animals can migrate without haste and keep the local sun in one point above their head. It’s a bit smaller than Earth – 12 000 km diameter, that gives 37 680 km on the equator. Axial tilt is close to zero to keep things simple (it may change).
The most important point: nomads living on Hemera’s mid latitudes (around latitude 45°) have to move around 5 km per 24 hours in east-west direction to stay in one time zone. 45th parallel is 18 840 km long, so I need planetary day to have 3768 Earth-days. In other words one Hemera day is more than 10 Earth years long.
How long should I make planetary year? It cannot be as long as hemerian day – it would make my world tidally locked. I don’t’ want that. Not to mention so long or longer orbital year would put Hemera somewhere around Jupiter in terms of distance from the local sun and everything would froze. So it must be shorter.
Are there any interactions between planetary rotation and orbital period that can change the length of daylight (for example as it is in case of Venus and Mercury)?
Other things:
The planet started slowly rotating and is obviously rather old and on its way to be tidally locked in future. That would mean local star is also rather older and hotter. So the world can be further away than Earth. Actually it can mean that Hemera is just only now moving into its biological prime time.
Because of very slow spin oceans have migrated toward poles. Equatorial bulge is slowly sinking and the whole planet is returning to more spherical shape but it’s a very slow process. There’s a wide belt of high desert land around the equator and there are two big polar oceans which transport heat around the planet making mid-latitudes liveable. Maybe even nice place to live. It looks a bit like this, but Hemera has more land: <https://www.reddit.com/r/MapPorn/comments/10dbw6/a_map_of_the_worldif_the_earth_did_not_spin/>
Climate: there will be hotspot that moves from east to west and it will be unpleasantly hot. But there will be long Afternoon and Morning, each longer than two Earth-years with climate. Life has adjusted and there are be two big groups: migrators travelling around the world and stay-at-homes: fast grass like growers that manage to grow again between waves of migrating grazers, armored trees that can withstand five year nights, burrowers and hibernators in case of animals.
Equatorial desert belt cuts planet in two and creates two different environments. Animals and plants on northern and southern hemisphere can be very different.
Can such slowly rotating planet has a moon? It would stabilize climate. If not a pair of captured asteroids will do for making sky interesting during long night.
[Answer]
Short answer:
There is a difference between a planet's sidereal day, the length of time that the planet rotates 360 degrees relative to distance stars and galaxies, and that planet's synodic day, the period between the planet's own star or sun appearing in the same position relative to a point on it surface two successive times, such as the period between too successive midnights at that point.
And I think that it is highly unlikely that any habitable planet could have a sidereal day
longer than its orbital period around the star or year, and very unlikely that any habitable planet could have a year more than about half of ten Earth years long.
Thus it appears highly unlikely that a habitable planet could have a sidereal day as long as 3,768 Earth days long.
Fortunately, what you need for your story is a planet with a synodic day, the period between two successive midnights or dawns in the same location, that is 3,768 days long.
And in my opinion, a synodic day 3,768 Earth days long can happen even if the sidereal day and the year of the planet are only a fraction as long as 3,768 Earth days. A synodic day 3,768 Earth days long can happen if the sidereal day and the year of the planet are almost exactly the same length, so that the apparent position of the sun in the sky of the planet appears to move only about 0.0955414 of a degree every Earth day, or 0.0039808 of a degree every Earth hour, etc., etc.
Long Answer:
Part One, life on a planet with a long day:
You can have a planet with a synodic day infinitely long, if the planet is tidally locked to its star so that one side always faces the star and one side always faces away from the star. And some planets are known to have days shorter than one Earth day.
Thus a synodic day ten Earth years long is perfectly possible physically.
What about the planet being habitable? The longer the day on the planet lasts, the hotter it will get on the day side, and the colder it will get on the night side. There is some fear that when the length of a planet's day gets too long, all the water on the day side will evaporate and the water vapor will flow to the night side, condense, and freeze.
If the planet is tidally locked, the water may all end up as ice on the night side and life may be impossible on the planet.
However:
>
> This pessimism has been tempered by research. Studies by Robert Haberle and Manoj Joshi of NASA's Ames Research Center in California have shown that a planet's atmosphere (assuming it included greenhouse gases CO2 and H2O) need only be 100 millibars (0.10 atm), for the star's heat to be effectively carried to the night side.[77] This is well within the levels required for photosynthesis, though water would still remain frozen on the dark side in some of their models. Martin Heath of Greenwich Community College, has shown that seawater, too, could be effectively circulated without freezing solid if the ocean basins were deep enough to allow free flow beneath the night side's ice cap. Further research—including a consideration of the amount of photosynthetically active radiation—suggested that tidally locked planets in red dwarf systems might at least be habitable for higher plants.[78]
>
>
>
<https://en.wikipedia.org/wiki/Planetary_habitability#Size>[1](https://en.wikipedia.org/wiki/Planetary_habitability#Size)
So if a tidally locked planet might be habitable according to some studies, a planet with a synodic day 10 Earth years long might possibly also be habitable, since conditions would be a little more Earth like on that planet.
I note that if the day lasts 10 Earth years the water on the day side might all evaporate and blow to the night side and freeze. Thus thee would be no liquid surface water on the day side for plants, animals, and the natives to use. Except that at a specific time of day, sometime in the morning, as that region warms up, ice exposed to the sun will melt and become liquid water for a while before evaporating. Plants and animals will flourish while there is liquid water, and then die, leaving seeds and eggs, or go dormant, when it gets hot enough for the water to evaporate. Or the animals could follow the sun and the melting ice.
That provides a motive for the natives to migrate and keep the sun in the same relative position - they will die of thirst if they stay in the same place, and their domestic animals or prey species will die of thirst, causing them to die of starvation even if they save a little water to drink.
Part two, how long can the year of a habitable planet be?
For various reasons, not all stars are capable of having habitable planets in orbit around them. If a star can have habitable planets in orbit around it, planets can only have the right temperatures to be habitable within the star's circumstellar habitable zone.
To find the inner and outer edges of a star's circumstellar habitable zone, one can multiply the inner and outer edges of the Sun's circumstellar habitable zone by the square root of that star's luminosity compared to that of the Sun.
Unfortunately, this table shows that there is considerable disagreement about the inner and outer edges of the Sun's circumstellar habitable zone:
<https://en.wikipedia.org/wiki/Circumstellar_habitable_zone#Solar_System_estimates>[2](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone#Solar_System_estimates)
Furthermore, most of those estimates are for planets being habitable for some forms of life that use liquid water, not necessarily for planets habitable for lifeforms with the same requirements as humans. Lifeforms similar to humans require an atmosphere with enough oxygen for humans to breathe, for example, while some of the studies involve planets with large amounts of hydrogen in their atmospheres, incompatible with oxygen in the atmosphere.
The only estimate for the limits of the Sun's circumstellar habitable zone that I know was limited to planets habitable for humans was Dole's in 1964, the oldest, and likely to be obsolete in some parts.
With that in mind:
>
> Some studies show that there is a possibility that life could also develop on planets that orbit a F-type star.[3](https://en.wikipedia.org/wiki/Ephemeris_day) It is estimated that the habitable zone of a relatively hot F0 star would extend from about 2.0 AU to 3.7 AU and between 1.1 and 2.2 AU for a relatively cool F8 star.[3](https://en.wikipedia.org/wiki/Ephemeris_day) However, relative to a G-type star the main problems for a hypothetical lifeform in this particular scenario would be the more intense light and the shorter stellar lifespan of the home star.[3](https://en.wikipedia.org/wiki/Ephemeris_day)
>
>
> F-type stars are known to emit much higher energy forms of light, such as UV radiation, which in the long term can have a profoundly negative effect on DNA molecules.[3](https://en.wikipedia.org/wiki/Ephemeris_day) Studies have shown that, for a hypothetical planet positioned at an equivalent habitable distance from an F-type star as the Earth is from the Sun (this is further away from the F-type star, inside the habitable zone), and with a similar atmosphere, life on its surface would receive about 2.5 to 7.1 times more damage from UV light compared to that on Earth.[4](https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf) Thus, for its native lifeforms to survive, the hypothetical planet would need to have sufficient atmospheric shielding, such as an ozone layer in the upper atmosphere.[3](https://en.wikipedia.org/wiki/Ephemeris_day) Without a robust ozone layer, life could theoretically develop on the planet's surface, but it would most likely be confined to underwater or underground regions.[3](https://en.wikipedia.org/wiki/Ephemeris_day)
>
>
>
<https://en.wikipedia.org/wiki/F-type_main-sequence_star>[5](https://en.wikipedia.org/wiki/F-type_main-sequence_star)
So the habitable zone of a F0 type star could extend out to 3.7 AU from the star, which is 3.7 times the distance Earth and the Sun. A orbit with 3.7 times the radius would have 3.7 times the circumference so if the planet orbited the star at the same speed that Earth orbited the Sun, the planet's year would be 3.7 Earth year's long.
But the farther away from the Sun a planet or other object is, the slower it will need to travel in order to stay in orbit. Mars orbits the Sun at a distance of 1.523 AU but has an orbital period of 1.880 earth years, Vesta orbit at at 2.361 AU but has a year 3.63 Earth years long, Ceres orbits at a distance of 2.769 AU and should have a year 2.769 Earth years long but has a year 4.61 Earth years long, Hygeria orbits at 3.141 AU but has a year 5.57 Earth years long, and so on.
Thus it seems that an object orbiting the Sun at a distance of 3.7 AU might have a year as long as 6 Earth years long.
But a spectral type F0 star which had a habitable zone extending out to 3.7 AU would be more massive than the Sun, and thus objects at 3.7 AU from that star would have to orbit the star a faster speed and thus have a year shorter than 6 Earth years.
A few exoplanets have been found orbiting in the habitable zones of their stars, and most of them have years much shorter than Earth years, as short as 4.05 Earth days in the case of TRAPPIST-1d. One, Kepler-452b, has an orbital period of 384.8 Earth days, and another, Kepler-1632b, has an orbital period of 448.3 Earth days.
<https://en.wikipedia.org/wiki/List_of_potentially_habitable_exoplanets>[6](https://en.wikipedia.org/wiki/List_of_potentially_habitable_exoplanets)
<http://phl.upr.edu/projects/habitable-exoplanets-catalog>[7](http://phl.upr.edu/projects/habitable-exoplanets-catalog)
So it seems that it is unlikely that a planet in the habitable zone of your fictional star could have a year anywhere near as long as the ten years you require for the day of your planet. Thus it seems like the day of your planet will be much longer than its year, and possibly many planetary years long.
Part Three, could a planet have a sidereal day longer than its year?
But a planet would form with a rotation period that would be gradually slowed by tidal interactions with its star, with any moons it might have, and with neighboring planets.
In the case of Earth, the Moon is much closer to the Sun and has stronger tidal pull, and thus has slowed the rotation of Earth and lengthened its day much more than the Sun has.
A planet in the habitable zone of a much dimmer K type or M type star would orbit much closer to the star, and thus would have much stronger tidal forces from the star, slowing its rotation much faster than the Sun slows the rotation of Earth. If the star is dim enough, and the planet orbits close enough, the star will slow the planet's rotation down so much that the planet will be tidally locked to the star, with one side always facing the star and the other side always facing away. And then it should be impossible for the star to keep on slowing the rotation of the planet, so the planet would never have a rotation period longer than its year.
As far as I can tell, the only way a planet could have a sidereal day longer than its year is if it was struck by a giant object and the impact drastically slowed the planet's rotation rate. Such an impact would be many times greater than necessary to kill all life on the planet, so for the planet to be habitable billions of year later the impact should have happened very early in the history of the planet before the first life forms arose there.
So how can your planet have a day longer than it's year?
Part Four, how a planet can have a synodic day longer than its year:
Define day.
One definition of a day is a period of light followed by a period of darkness or night.
Another definition of a day is a combined day and night, a period from sunrise to the next sunset, or noon to the next noon, or sunset to the next sunset, or midnight to the next midnight, at the same location.
And the second definition of day is the one that you mean. You desire that your planet has a period from midnight at one place to the next midnight at that place which lasts ten Earth years, or about 3,652.5 Earth Days.
But there is another question. There are several types of days, including sidereal days, synodic days, and solar days.
Sidereal time /saɪˈdɪəriəl/ is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coordinates in the night sky. Briefly, sidereal time is a "time scale that is based on Earth's rate of rotation measured relative to the fixed stars".[1](https://en.wikipedia.org/wiki/Planetary_habitability#Size)
>
> Viewed from the same location, a star seen at one position in the sky will be seen at the same position on another night at the same sidereal time. This is similar to how the time kept by a sundial can be used to find the location of the Sun. Just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earth's rotation about its polar axis, solar time following the Sun while sidereal time roughly follows the stars.[8](http://Sidereal%20time%20/sa%C9%AA%CB%88d%C9%AA%C9%99ri%C9%99l/%20is%20a%20timekeeping%20system%20that%20astronomers%20use%20to%20locate%20celestial%20objects.%20Using%20sidereal%20time,%20it%20is%20possible%20to%20easily%20point%20a%20telescope%20to%20the%20proper%20coordinates%20in%20the%20night%20sky.%20Briefly,%20sidereal%20time%20is%20a%20%22time%20scale%20that%20is%20based%20on%20Earth's%20rate%20of%20rotation%20measured%20relative%20to%20the%20fixed%20stars%22.[1]%20%20Viewed%20from%20the%20same%20location,%20a%20star%20seen%20at%20one%20position%20in%20the%20sky%20will%20be%20seen%20at%20the%20same%20position%20on%20another%20night%20at%20the%20same%20sidereal%20time.%20This%20is%20similar%20to%20how%20the%20time%20kept%20by%20a%20sundial%20can%20be%20used%20to%20find%20the%20location%20of%20the%20Sun.%20Just%20as%20the%20Sun%20and%20Moon%20appear%20to%20rise%20in%20the%20east%20and%20set%20in%20the%20west%20due%20to%20the%20rotation%20of%20Earth,%20so%20do%20the%20stars.%20Both%20solar%20time%20and%20sidereal%20time%20make%20use%20of%20the%20regularity%20of%20Earth's%20rotation%20about%20its%20polar%20axis,%20solar%20time%20following%20the%20Sun%20while%20sidereal%20time%20roughly%20follows%20the%20stars.)
>
>
> A sidereal day is approximately 23 hours, 56 minutes, 4.0905 seconds (24 hours − 4 minutes + 4.0905 seconds = 86164.0905 s = 23.9344696 h). (Seconds here follow the SI definition and are not to be confused with ephemeris second.)
>
>
>
<https://en.wikipedia.org/wiki/Sidereal_time>[9](https://en.wikipedia.org/wiki/Sidereal_time)
>
> A synodic day is the period it takes for a planet to rotate once in relation to the star it is orbiting (its primary body). For Earth, the synodic day is known as a solar day, and its mean length is 24 hours (with fluctuations on the order of milliseconds).
>
>
> The synodic day is distinguished from the sidereal day, which is one complete rotation in relation to distant stars.[1](https://en.wikipedia.org/wiki/Planetary_habitability#Size) A synodic day is from "sunrise to sunrise", whereas a sidereal day is from one rise of a given star of reference to the next. (Thus, the word day denotes the orientation relative to the main "parent" star that the observer is orbiting.) These two quantities are not equal because the revolution of the body around its parent star would cause a single "day" to pass, even if the body did not rotate itself.
>
>
>
<https://en.wikipedia.org/wiki/Synodic_day>[10](https://en.wikipedia.org/wiki/Synodic_day)
So on Earth a solar day is the synodic day of Earth relative to the Sun.
Earth rotates 360 degrees of arc in one sidereal day of 23.9344696 hours.
The line between the centers of Earth and the Sun rotates 360 degrees of arc in one sidereal year, which is:
>
> It equals 365.256 363 004 Ephemeris days for the J2000.0 epoch.[1](https://en.wikipedia.org/wiki/Planetary_habitability#Size)
>
>
>
<https://en.wikipedia.org/wiki/Sidereal_year>[11](https://en.wikipedia.org/wiki/Sidereal_year)
>
> An ephemeris day is a period of 86,400 SI seconds.
>
>
>
<https://en.wikipedia.org/wiki/Ephemeris_day>[3](https://en.wikipedia.org/wiki/Ephemeris_day)
Which is 24.0000 hours. So a ephemeris day is 1.0027379 sidereal days long. Thus a sidereal year should be about 366.25639 sidereal days long.
So Earth turns 360 degrees during a sidereal day, or 15.041069 degrees per hour, or 0.2506844 degrees per minute.
But during a sidereal day the planet Earth travels 360 degrees divided by 366.25639, or 0.982918 of a degree, along its orbit. So a point on Earth that was pointed directly at the Sun and was the sub solar point will not be pointed directly at the sun after one sidereal day, but will be pointed 0.982918 of a degree off the new direction to the Sun. So Earth will have to turn another 0.982918 degrees for the former sub solar point to point directly at the Sun, which should take another 3.920938 minutes, making a synodic day a little longer than a sidereal day.
So what you want is for the synodic day of your planet to last for about 10 Earth years, or about 3,652.5 Earth days. That means that the position of the star in the sky should change by 360 degrees in the planet's day or by 36 degrees per Earth year, or by about 0.0985626 degrees per Earth Day, or by about 0.0041067 degrees per Earth hour, etc., etc.
And it seems to me that if the tidal force from the star in that star system has slowed down the rotation of the planet so the sidereal day of the planet is only slightly less than the orbital period of the planet around the star, the planet's year, the synodic day of the planet can be many times as long as the sidereal day or the year of the planet.
As nearly as I can calculate, you need to make the position of the star or sun in the sky of your planet change by about 0.0985626 of a degree each Earth day in order for the position of the star or sun in the sky of the planet to change by 360 degrees, one synodic day, every ten Earth years.
Actually, looking at the question again, the target is for the synodic day to last 3,768 Earth days, so the position of the star or sun in the sky of the planet has to change by 360 degrees every 3,768 Earth days, or 0.0955414 of a degree every Earth day, or 0.0039808 of a degree every Earth hour, etc., etc.
The tidal forces of the Sun on Earth have been strong enough to slow earth's rotation noticeably over a period of 4,600,000 years, but only a tiny fraction of the amount of slowing that would be necessary for the sidereal day to be almost as long as the year, and for the synodic day to thus equal several years.
But if a planet orbited in the habitable zone of a spectral class M star, or a dimmer member of the spectral class K stars, it would have to orbit so close to the star that the star's tidal forces on the planet would slow down it rotation until it was tidally locked with one side perpetually facing the star, long before the planet was old enough to have become habitable for humans or for aliens with similar requirements.
Stephen H. Dole, in Habitable *Habitable Planets for Man* (1964,2007) calculated what mass a star would have to tidally lock any planet in its circumstellar habitable zone, which Dole called its "ecosphere". Dole discusses the tidal braking effects of a star upon a close planet in pages 68 to 72 of the first edition.
>
> A "full" ecosphere can exist around primaries of stellar mass greater than about 0.88 solar mass, but the ecosphere is narrowed by the tidal braking effect for primaries of lesser mass until it disappears when the stellar mass reaches about 0.72. The range in mass of stars which could have habitable planets is thus 0.72 to 1.43 solar masses, corresponding to main-sequence stars of spectral types F2 though K1.
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>
<https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf>[4](https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf)
So we can deduce from Dole's statement that if his calculations are correct, if a star has a mass between 0.72 and 0.88 solar masses, any planet in the inner part of its ecosphere or circumstellar habitable zone will be tidally locked by the time it is billions of years old, while a planet in the outer part of the zone will not be tidally locked.
A spectral type G8V would have a mass of 0.87 solar masses, and type G9V star would have a mass of 0.84 solar masses.
<https://en.wikipedia.org/wiki/G-type_main-sequence_star>[12](https://en.wikipedia.org/wiki/G-type_main-sequence_star)
And according to Dole a type K1V star would have a mass of 0.72 solar masses.
Tau ceti e might orbit Tau ceti, a G8V star, in the optimistic habitable zone.
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> Tau Ceti e is a candidate planet orbiting Tau Ceti that was detected by statistical analyses of the data of the star's variations in radial velocity that were obtained using HIRES, AAPS, and HARPS.[9](https://en.wikipedia.org/wiki/Sidereal_time) Its possible properties were refined in 2017:[57] it orbits at a distance of 0.552 AU (between the orbits of Venus and Mercury in the Solar System) with an orbital period of 168 days and has a minimum mass of 3.93 Earth masses. If Tau Ceti e possesses an Earth-like atmosphere, the surface temperature would be around 68 °C (154 °F).[60] Based upon the incident flux upon the planet, a study by Güdel et al. (2014) speculated that the planet may lie outside the habitable zone and closer to a Venus-like world.[61]
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<https://en.wikipedia.org/wiki/Tau_Ceti#Tau_Ceti_e>[13](https://en.wikipedia.org/wiki/Tau_Ceti#Tau_Ceti_e)
82 G Eridani, or HD 20794, is another G8V star. Planet e is supposed to orbit within its optimistic habitable zone at a distance of 0.509 AU and with a year 147.02 Earth days long.
<https://en.wikipedia.org/wiki/82_G._Eridani>[14](https://en.wikipedia.org/wiki/82_G._Eridani)
Kepler-1090 is a K0V type star. Planet Kepler-1090b is supposed to orbit in its obptimistic habitable zone with a period of 198.7 days.
<https://en.wikipedia.org/wiki/List_of_potentially_habitable_exoplanets>[6](https://en.wikipedia.org/wiki/List_of_potentially_habitable_exoplanets)
<http://exoplanet.eu/catalog/kepler-1090_b/>[15](http://exoplanet.eu/catalog/kepler-1090_b/)
Therefore, I think that you need to get someone to calculate a planetary orbit within the habitable zone of a spectral type G8V to K1V star, situated at the edge of the zone where the star will have slowed down the rotation of the star almost enough to make it tidally locked. And the difference between the planet's sidereal day and its year should be so slight that the apparent position of the star in the sky will move by only 0.0955414 of a degree every Earth day, or 0.0039808 of a degree every Earth hour, etc., etc., in order for the synodic day to be 3,768 Earth Days long.
As far as I can tell the only other possibility would be for a giant impact billions of years earlier to have slowed the planet's rotation rate. But at most for your purposes it could only have slowed the planet's rotation rate to one where its sidreal day was only a tiny little bit longer than its year, because a tiny little difference between the sidereal day and the year is what is needed to have a synodic day much longer than the year.
The direction that the natives have to travel to keep up with the sun may depend on whether the sidereal day of the planet is a little bit longer or a little bit shorter than the planet's year.
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Tidal locking is a process. A process that comes to an end within finite time, but still a process. As such, **any fully tidally locked body must have gone through a period of one rotation relative to its orbit per 10 years**. Your planet is simply within that final phase of achieving its tidal lock.
Of course, you want your body to take a loooong time to achieve full tidal locking, and there are some things you can do to achieve that. They are all in the formula helpfully given under ["Timescale" in the wikipedia article on tidal locking](https://en.wikipedia.org/wiki/Tidal_locking#Timescale):
* Timescale grows **with the sixth power** of the planet's distance from the sun! Put your planet twice as far from the sun, and the period of roughly 10a day cycle will be 64 times as long.
* Timescale shrinks with the square of the planet's mass.
* Timescale also shrinks with the fifth power of the planet's radius.
* Since mass depends on the radius, growing with its cube, the dependency of the timescale on the radius of a planet of constant density (a bit of an oversimplification) is **a whopping power of 11**!
Or put another way:
* Moving the planet out twice as far lengthens the process of tidal locking by a factor of 64.
* And making the planet half as big (half the radius, half the surface gravity) lengthens the process of tidal locking by a factor of 2048.
* The combination of the two gives you a factor of 131072.
To allow your planet to be further away from its star, simply make the star a bit bigger. Bigger stars are hotter, and can support life much further out.
The change of earth's rotational period is already rather minimal, and earth has a heavy moon close by which is its major drain of rotational momentum. Even ignoring the moon, you can easily reduce the rate of change by the above mentioned factor of 130000. There will be a long time in which the planet allows for sun synchronous migration around the planet. First at the high latitudes, and probably starting with birds, then, as the rotation slowly reduces further, non-migrating animals slowly get extinct while the number of migrating species around the poles increases. The 10a timespan is only the very end of this process where animal-life has already reconquered the entire planet's surface with migrating species.
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>
> Are there any interactions between planetary rotation and orbital period that can change the length of daylight (for example as it is in case of Venus and Mercury)?
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A collision with appropriate energy and impact direction could dramatically slow down the planet rotation. That's what is commonly accepted as cause for the slow rotation displayed by Venus.
It could even tilt the rotational axis of about 90 degrees, like it happened for Uranus, to have the planet "rolling" on the orbital plane when one of the poles points toward the Sun.
With this explanation you can freely set the distance from the Sun to suit the need for life.
Likewise, the presence of a moon is possible. It's likely that the tides caused by the moon, instead of slowing down the planet rotation, would slowly speed it up, but not on extreme levels.
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**Eyeball planet.**
<https://en.wikipedia.org/wiki/Eyeball_planet>
[](https://i.stack.imgur.com/VLeXo.png)
>
> An eyeball planet is a hypothetical type of tidally locked planet, for
> which tidal locking induces spatial features (for example in the
> geography or composition of the planet) resembling an eyeball.[1](https://i.stack.imgur.com/VLeXo.png) It
> is mainly used for terrestrial planets where liquids may be present,
> in which tidal locking will induce a spatially dependent temperature
> gradient (the planet will be hotter on the side facing the star and
> colder on the other side).
>
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A [tidally locked](https://en.wikipedia.org/wiki/Tidal_locking) planet or moon is one in which the spinning of the body matches the orbit, such that the same face of the orbiter faces the thing orbited at all times. Our moon is an example - as it orbits the earth it turns on its own axis, so the same side always faces Earth.
Your planet is in the last stages of tidal locking. Its spin has gradually slowed over the millennia so now it is in the last stages and it almost matches the year. A year on this planet (one orbit around its star) lasts 10 Earth years - that is fine; one Jupiter year is 12 earth years. Your planet is farther out from its star but it is a hotter star and so your star is still in the Circumstellar habitable zone, or "Goldilocks zone".
[](https://i.stack.imgur.com/o5f7F.gif)
<https://science.howstuffworks.com/other-earth1.htm>
The hotter your star, the farther out the Goldilocks zone is, and the farther out it is, the bigger the orbit and the longer the year is.
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It occurs to me that understanding "Goldilocks" zone requires having grown up in an English speaking culture where this kid's story was told. For those readers not of such a culture - Goldilocks breaks into the bears house while they are gone and uses their stuff, finding things belonging to the parent bears to be too much one way or too much the other way - but Baby Bear's stuff is "just right". So too the Goldilocks zone - not too hot, not too cold, just right.
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Your presentation on Hemera is passionate, Zjerzy! Congratulations! You also demonstrate that you worked well with the whole thing.
As for your question, it is not exactly the orbital period that influences, but the distance from the star and, depending on the star system, the distance from other large bodies.
Mercury, for example, is not exactly tidal locked with the Sun, its rotation is in resonance with the orbital period at a [rate of 3: 2](https://phys.org/news/2013-10-explanation-rotational-state-mercury.html).
Venus must have had a very violent shock in the past that almost stopped its rotation. This make to think that maybe Venus went through a catastrophe like the [cataclysm of Theia](https://en.wikipedia.org/wiki/Giant-impact_hypothesis) that bequeathed us the Moon, only that things went very wrong there.
All bodies are subject to [tidal locking](https://en.wikipedia.org/wiki/Tidal_locking) due to gravitational interactions, however, for a body like Earth in relation to the Sun it would take a long time, around [50 billion years](https://astronomy.stackexchange.com/questions/31984/why-isnt-earth-tidally-locked-to-the-sun), much longer than the time that the Sun has to burn in the main sequence. Hemera would not have a different destination unless its initial rotation during its formation had some collision large enough to brake most of the angular velocity. Perhaps a collision like that of Theia on the primordial Earth. Thus, Hemera could also have a massive moon, a quasi-binary system like ours.
One problem I see for Hemera is that if it’s an old planet orbiting an old star and with a very slow rotation the planet’s mantle is probably not able to generate a very large magnetic shield, making the escape of light gases inevitable and then , the chances of keeping water and other compounds with hydrogen quite difficult, even at a great distance from the star. Venus has a magnetosphere induced in its upper atmosphere, but it depends on a very massive atmosphere and yet it has almost no hydrogen.
I would suggest that although smaller, Hemera is more massive than Earth, having a slightly greater gravity on the surface, and is more distant from the star, perhaps something like the distance from Mars, and to maintain the climate the atmospheric composition is a little different , with more carbon and other greenhouse gases in the lower atmosphere. This may cause the gravitational escape of gases to be less drastic over the ages.
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Adding a moon (or multiple moons) would help to make a slowly rotating planet more plausible. The Earth itself used to make one full rotation roughly every 6 hours. The reason why we now have approximately 24 hours in a day is because of the moon's effect on Earth; its gravitation tugs on nearby bodies. Of course, it would take hundreds of millions of years for the change to be noticeable. It would be a gradual process, so you might want the lore of your world to reflect that. Also, the mass and material of your satellite since those concepts would effect the rate in which your planet changed speed. If your planet has multiple satellites, that should also be taken into consideration.
Another thing to consider would be atmosphere. I think this article explains it better than I would: <https://astrobiology.nasa.gov/news/how-life-could-help-atmospheric-tides-slow-a-planets-rotation/>
Another user mentioned a collision, which I think would be the easiest and most logical way to go. A collision of some sort can and absolutely WILL dramatically slow down a planet's rotation. Collisions are fairly common as most planetary systems in their infant stages are unstable. Everything in a solar system forms from the same disk. That disk dictates the rotation of every planet and star birthed from it. Since space is a vacuum, spinning objects will maintain their momentum and their direction indefinitely... unless... something wonky happens with the atmosphere (relatively rare) or some external force knocks it out of balance (far more common).
There are several caveats with a collision though. Something powerful enough to noticeably change the rotation of a planet would be catastrophic. It will vaporize all life on it. There MIGHT be a handful of extremophiles that survive the disaster depending on various factors (unlikely), but you can assume without question that all other major flora, fauna and intelligent life would immediately go extinct. Secondly, as the previous poster mentioned, it would likely knock the planet on a noticeable tilt. It won't have to be as extreme as Uranus, but your future planetary life will likely have extreme seasonal weather. This would also be the prime time to decide on the new atmosphere and structure for your planet as many gases and elements from the collision will influence all future development; the planet will likely not look anything like it previously did. It will take your planet at least a couple of billion years to recover- as in capable of sustaining intelligent life. A new moon might even be created from the collision or your planet might obtain rings a la Saturn. Keep in mind that a much larger body would not be viable. No adding some massive structure 200 times your planet's size. You want your planet to be changed- not completely decimated or "sucked" into another body.
So, if you choose to have your planet collide with something to slow its rotation what should it be? An asteroid would be an an easy option. A more interesting option would be a rogue planet that was flung out of an unstable system.
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I'm looking for some ideas for ways to kill off my brand of precursors. Ideally, the cataclysm is predictable well in advance and direct survival is impossible or at least highly improbable.
The precursors are decently spread out (somewhere up to 1000 colonized star systems), and you can assume they're generic carbon-based humanoids. The cataclysm can take as long as it needs - I'm thinking up to half a trillion or so years. It should be something that gives them reason to believe that seeded planets have a reasonable chance of surviving the event, but they aren't 100% sure so they also research bailing to "another dimension" for a while.
All of the precursors still around when it happens should be wiped out definitively. Wiping out some or all of their tech as well is fine, but it should leave planets and stars mostly unscathed.
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Yes there are cataclysms that may wipe out life in a large portion of a galaxy. I assume the 1000 colonized star systems are within
There's about 1 star for every 280 cubic light years. So there should be about...
1875 stars within 50 light years
15000 stars within 100 light years
1875000 stars within 500 light years
If we assume that only F,G type stars are colonized (similar to the sun's life span not cataclysmic and high metallicity) 100 solar systems similar to our own for every 1000 stars your colonization of star systems will extend to approximately 80 cubic light years.
For such an small radius of stars it is very plausible that a very powerful gamma ray burst occurring in the neighborhood and focused to that region will eliminate the ozone layer of the planets within this radius and cause large extinctions due to genetic mutations.
[As an example](http://en.wikipedia.org/wiki/GRB_080916C):
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> GRB 080916C is a gamma-ray burst (GRB) that was recorded on September 16, 2008 in the Carina constellation and detected by NASA's Fermi Gamma-ray Space Telescope. It is the most powerful gamma-ray burst ever recorded. The explosion had the energy of approximately 5900 type Ia supernovae, and the gas jets emitting the initial gamma rays moved at a minimum velocity of approximately 299,792,158 m/s (0.999999c), making this blast the most extreme recorded to date.
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> The energy comparison with a supernova ignores that most of the energy of a supernova is carried away in the neutrino burst. The total isotropic energy of GRB 080916C is estimated at 8.8 × 1047 joules (8.8 × 1054 erg) (the oft quoted 4.9 times the sun’s mass turned to energy) and should be jet-corrected to a much lower actual energy output due to the narrow angular width of the actual bursting jet. Thus it would be significantly less than the energy of a supernova neutrino burst, but is about equal to the energy in a supernova’s material explosion. Also, the peak energy flux of GRB 080916C is significantly less than a number of other GRB’s, such as GRB 080319B which peaked at nearly 1044 watts (1051 erg/s) in visible light alone. However, the total energy flux of the very long duration GRB 080916C is higher than any other measured GRB to date.
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"If the event that caused this blew out in every direction instead of being a focused beam, it would be equivalent to 4.9 times the mass of the Sun being converted to gamma rays in a matter of minutes.
Amongst the different kinds of GRBs, long ones are most dangerous. There is a very good chance (but no certainty) that at least one lethal GRB took place during the past 5 gigayears close enough to Earth as to significantly damage life. There is a 50% chance that such a lethal GRB took place during the last 500×106 years, causing one of the major mass extinction events. Assuming that a similar level of radiation would be lethal to life on other exoplanets hosting life. We find that the probability of a lethal GRB is much larger in the inner Milky Way (95% within a radius of 4 kpc from the galactic center), making it inhospitable to life. Only at the outskirts of the Milky Way, at more than 10 kpc from the galactic center, does this probability drop below 50%. When considering the Universe as a whole, the safest environments for life (similar to the one on Earth) are the lowest density regions in the outskirts of large galaxies, and life can exist in only ≈10% of galaxies
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**Interstellar [Grey Goo](https://en.wikipedia.org/wiki/Grey_goo).**
Nanobots capable of traveling across the interstellar void that begin self-replication upon coming in contact with biological matter or artificial materials, would be a fairly complete way to wipe out all life in a galaxy.
There are a lot of reasons such a thing might happen, radical-ultra-hippies wanting to return the galaxy to "like, a pre-life state maaannn...", deconstruction/cleanup bots gone haywire, or as an attack from another galaxy.
Your race (the precursors) might be able to create seeds that will be invisible to the nanobots, but it's difficult to be sure if it will work. No one can get close enough to the bot swarms without being infected and melted into grey goo.
If you want them contained to the galaxy then give them a life cycle. While the nanobots are active, replicating, and seeking targets they continue spreading all directions in space. If they have no detections for a few thousand years they enter a sleep state. If the sleep state endures for a few million years (or thereabouts) they self-destruct. This means the galaxy will eventually become clear and they won't likely remain intact for an intergalactic journey.
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Because you're beings are spread out over such a large area, external causes are really not going to be feasible on that scale, unless you somehow localize them (all within a galaxy, with no method of long-distance travel etc). The likely means of wreaking havoc on galactic or even cluster scale would probably destroy everything on seeded planets as well.
So you're looking for an inexorable internal killer. You have a couple of options:
## Disease
Your population unleashes a disease that is passed from mother to child, infects the population before it is identified, and is incurable. Maybe it's a side effect of a longevity drug that is taken by the entire race in hopes of attaining longer lives. It grows in potency with each generation, so that it is maybe 100 generations before the disease is identified. By that time everyone is infected, and they can determine the exact date of extinction.
You're going to need a slow moving disease (unlike bubonic plague) so that they have time to contemplate really complex cures. But the slower it is, the more likely it is that a work around can be developed. Half a trillion years is on a stellar time scale - if something is impossible, throw enough time at it, and it can become a matter of probability.
## Genetic Factors
It's also possible that extinction is implied in the very DNA of the species. This is not really that far fetched - for example, [Y-chromosome degradation](http://en.wikipedia.org/wiki/Y_chromosome#Degeneration) could feasibly have destroyed humanity if it had continued. Imagine a mitochondrial disorder that can't be checked, or something makes more and more [anencephalic (warning:graphic)](http://en.wikipedia.org/wiki/Anencephaly) members.
In either genetic or disease causes, you're going to be looking for something that affects a system that can't be easily replaced by machines, like:
* reproductive system
* nervous system
* mitochondria (fuel for the body's systems)
The circulatory and even muscular systems could potentially be replaced given the technology. But there is some question whether consciousness can be replaced or emulated, and without the ability to reproduce it's just a matter of time.
In any case, it will be overwhelming depressing. But what mass extinction isn't?
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So they can't avoid it, but have a reasonable expectation that species similar to themselves in the same area will survive? I think we can safely exclude natural causes. Including disease natural or artificial. Either the disease is aggressive and adaptive enough to be certain death to other species or an interstellar civilization would find it trivial to avoid given warning.
The extinction should thus be caused by a sentient agent deliberately targeting the precursors. The agent needs also be impractical to avoid or defeat. I think there are few options.
**Magic aliens**
Magic here can be taken to mean technology so advanced it is indistinguishable from magic. I think H.P. Lovecraft would be a good starting point. The precursors would have been unable to even comprehend what the monsters attacking them are and how they move from planet to planet. The only real downside is that unless the reason for extinction is left unknowable, there will be an effect on the tone of the setting.
**Voluntary extinction**
The precursor might have noticed that they are occupying the ecological niche that the species the were seeding would need to "grow up". The logical solutions would be either to stop wasting resources on seeding new sentients or to remove yourselves from the equation. There would be some uncertainty whether the seeded species would be able to survive without support, which I understood was desirable. The process would also take whatever time was required to gain optimal balance of survival and interference for the local new sentients. So the time table would be highly varied in different locations.
Typically in such scenarios, the precursors would simply leave. This can be done either in space as a vast exodus to a remote part of the galaxy or even a neighbouring galaxy. Alternately it can be done in time, by placing the precursors in stasis in remote locations. Asteroid sized bodies in interstellar space would be unlikely to be stumbled upon accidentally. And if you have stasis technology, you might be able to hide inside stars or gas giants. Both of these options have been done in fiction.
Precursors could also devolve themselves either culturally or biologically, more likely in both ways, in effect becoming one of the new species, although oddly present all over the local area. Precursors could devolve to different species on different planets to avoid that oddness. One option is to devolve to be compatible with the seeded species and be assimilated into them biologically. Maybe the new species are **all** actually precursors starting again. Evolving to some **more advanced** exotic form is also a common variation.
It is also possible for the species to decide to really kill themselves. Or at least majority of the population while others take one of the other options. This might happen as a result of a "civil war" with survivors deciding not to rebuild. Precursors might also have a society where the "lower castes" making up vast majority of the population would be considered expendable to begin with. Or the precursors might simply not be bothered by dying, either because of religious belief in afterlife or because they no longer value living.
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How about something that doesn't wipe them out?
Imagine a society that for some reason eschews the genetic manipulation they would be capable of--it's so anathema that the technology is not ever developed.
Along comes a disease--something with an airborne vector. The victims don't get noticeably sick so it doesn't draw anyone's attention. The disease attacks the **genes** for the reproductive system, though--while the victims are unharmed their children will be born without a functional reproductive system.
Everyone lives out a normal lifespan, it's just the next generation is the last.
The delayed nature of the harm means it's not going to be noticed for many years and thus has time to infect the whole population before it's discovered.
To save the species you need to cure and isolate women and implant them with embryos made with recombinant DNA to have the correct genes instead of the flawed ones.
Lets see how this timeline would work on humans:
9 months to make a baby. Figure 15 more before any sign of this can be noted and even then it's going to be subtle--the teen birth rate crashed. I don't think they will immediately attribute this to infertility as few such births are intended in the first place. I figure at least another 5 before it becomes something of note to anyone but a sociologist. The clock has been ticking (the ovaries of the last cohort without the damage), it's only got about 30 years left.
Now you have to find the bug. This isn't going to be easy because there are plenty of harmless viruses around, everything is going to have to be checked to see which is causing the mutation. Since you have very little in the way of uninfected samples to work with this is not going to be easy.
Furthermore you have to find some way to purge the virus from your hosts once you have identified it--something we are nowhere near accomplishing.
I'm figuring they can read the DNA code (think human genome project) but the recombinant technology has to be developed from scratch. Our current progress on recombinant DNA isn't to the point of using it on humans--the clock runs out. Of course a crash priority program could do it faster--but science doesn't do the 9-women-and-a-month formula well at all.
Note that "success" produces a generation that can never meet the old population, even BSL-4 protocols would not be adequate.
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For some really out of the box thinking, perhaps we should consider that they have developed the ability to create a "pocket universe". By carefully setting up the starting point and all the variables of the physics they want, the pocket universe will be much more attractive for them and their sort of life that a "wild" universe. We can also stipulate the energy required to initiate a pocket universe would be similar to sending a large scale expedition of relativistic starships to the next habitable star.
Given the ability to create a new, much more user friendly universe, I suspect the race of aliens would come to the conclusion that this is the preferred course of action and instantiate a building program, "inflate" a pocket universe and disappear down the wormhole, taking everyone and everything they wanted and leaving the rest behind. They may or may not take their planets, depending on factors like how large the wormhole throat can be made and if it would be easier to reach a "better" planet on the other end of the wormhole. The last crew of aliens carefully turn off all the lights and vanish down the throat of the wormhole, closing it behind them.
A billion years later, Human expeditions reach uninhabited star systems with evidence of massive gravitational perturbations sometime in the distant past, perhaps missing planets and possibly ancient ruins preserved on the airless moons of various planets, but no real indication of where *they* have disappeared to.
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* plague. (engineered or otherwise)
* computer virus. (disabling life support and other vital systems)
* A collective of AI's that persistently create computer viruses,
sometimes distributing them under the guise of anti-virus software.
* self-replicating nano-bots.
* computer viruses that hijack 3d printers, replicators, or other
industrial machines to output nan-bots
* A desperate war that annulled both forces, leaving the few survivors
stranded in unsustainable environments, without enough industry to
escape.
* A drastic drop in reproduction due to porn addiction (leading to
complete economic disaster.)
* computer viruses that psychologically profile people and infect their
pc with the most effective kind of porn possible
* religious or idealogical fanaticism (endorsing mass murder suicide)
* religious or idealogical fanatics that persistently create AI's that
create computer viruses, that psycologically profile people and then
persuade them to their idealogical point of view.
* A computer virus that hijacks lab equipment to output biological
viruses.
* Nanobots that assemble biological viruses
* some other combination of these things.
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Since the time frame is so large and the number of systems colonized is so vast, there are many ways that this species could become extinct.
I imagine a scenario where on one of the planets an indigenous population is came across that is compatible for reproduction. The offspring produced would be essentially different from either of their parents. A new race essentially. Or the original indigenous population was able to adapt to the new tech that came along with the new population and over time reconquer their planet and move out into the rest of the universe from there.
The new folks would be a more aggressive and capable people, and over some time would come to dominate the particular planet they were on. They would develop a Nazi like culture where they aggressively practiced genocide and conquest. Eventually taking this to the other systems from which there ancestors came. Over a long course of time they would conquer all.
Since there are a thousand planets the precursors on each planet may have divergent courses of evolution and over time such a dark society could evolve into some kind of thing that was in essence not anything that resembled the original precursors, and then come to dominate with a practice of conquest and genocide.
And lastly a species from another part of the cosmos that was bent on conquest and genocide could take over these worlds over the course of time.
Your original precursors while intelligent could have something in their culture that made them highly pacifists. So they see the aggressive species coming, but the ethos are such that they will not rise up to defeat the invaders. And they have never developed complex weapon systems so even if they do rise, it is a futile gesture. They just hope that the invaders will stop at some point, but that never happens until they are all destroyed.
The scenario does not have to be one of large fleets of starships invading planets, it could be a more peaceful scenario where over the course of time on each planet the new species just slowly dominates the precursors slowly overwhelming them until at one point it is decided the precursors are a drag on society and they need to be done away with completely. How they get there in the first place would be through trade and immigration or other fairly peaceful means. South Africa would be a good example, were the colonist dominated and essentially destroyed The cultures of the people whom occupied the land before they came. Take that another step to the dark side where apartheid never ends and slavery and genocide develop further, to a point were the whole country is only white. (Say Germany won the war so in western society genocide became more acceptable).
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Darn, the ones I was going to suggest have already been suggested. Lett's try to think of some more.
Using up all of a resource. Perhaps they rely on some very complex chemical compound that they cannot reproduce (or for cultural reasons, are not willing to begin research into). The planet where the Spice is formed has a sun that'll go nova. They can't/wont transplant it.
They could all rely for their longevity on a single invention or device, controlled by a single person, company or organisation or religion, which loses the ability or desire to maintain those longevity devices.
Like Josiah's "genetic factors", they have a degenerative disease or population imbalance, which again they cannot or will not solve: perhaps they only noticed too late that their birth rate has become insufficient to restore their death rate.
Like the grey goo suggestion, and the voluntary suicide idea, they could hit the Singularity: their computers and robots could ultimately make their way of life completely pointless.
They could be working on a problem that would culturally destroy them: such as "is there a God", and finding definitive evidence that they were wrong would cause mass death.
Perhaps they discovered a method of immortality, so they just stopped reproducing as it was pointless: they didn't need to and it was wasteful of resources. Birthing in their hives, once done by queens, was no longer needed, and the queens, now being equal but having far higher needs for resources, were often rebelled against. And it was only some time after the last queen died, wen each planet asked around and discovered there were none to import, that they realized the immortality was ultimately their death warrant.
Or perhaps, as with vampires of lore, their immortality brought infertility. Economic considerations would mean that it's in a planet's best interests to grant immortality to all citizens, so's best to compete against other planets which have to spend the extra investment in nurturing the young and senescence of the elderly. And it was only once everyone was immortal that they realized they were all doomed.
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what first popped into mind was a mix of the dust/dark matter (from golden compass et al) mixed with a virus or something malignant like that, basically a sentient disease. alt version of the disease is an extremist group doing a coordinated attack at key nexi (sp?)
an alternate option would be to go more "celastine prophesy" with it and have a whole culture tire of their mortal coil and mediate to another dimension or everyone uploads to the latest game and then the system crashes or somesuch convenient exit...
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Genetic disease caused by inbreeding? Perhaps your precursors survived another disaster and their gene pool was so limited that they needed to resort to inbreeding to carry on the species.
Or maybe incest isn't taboo in this culture; perhaps it's even fashionable or encouraged by a growing religion or cultural zeitgeist that starts to dominate.
Sorry if this is too redundant; most everybody beat me to the punch of this one!
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\*By life, I mean something more complex than microorganisms. Something closer to what we have on Earth.
similar to this question: [Is it possible for complex life to evolve on planets without oxygen?](https://worldbuilding.stackexchange.com/questions/1031/is-it-possible-for-life-to-evolve-on-planets-without-oxygen)
For example:
It is said that Titan is well outside the habitable life zone but we make the assumption that life absolutely need water to survive. Titan has lakes of methane. Could methane or other substances be used as a substitute to water? Could life prosper in a waterless environment?
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1. There were many SciFi story about a civilization that arouse on a planet where F replaced O (by Yefremov). Francis Carsac had a series with the antagonist lifeforms being non-water-based (crystal/superconducting metal).
2. Wikipedia has [**a very extensive list**](http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry#Non-water_solvents) of possible non-water-based-solvent biochemistries (Ammonia, Methane, HF that was used in Yefremov's story).
[This article](http://www.bibliotecapleyades.net/vida_alien/xenology/08.0.htm) on "Exotic Biochemistries" from Xenology Research Institute quotes Carl Sagan and Dr. Peter M. Molton at the University of Maryland, with extensive discussion on alternate biochemistries, including non-water based (Ch 8.2.2 "Alternatives to Water"). Ammonia seems to be the leading candidate. The article is very heavy on detail, including analysis of reactivity, energy required to fracture various types of bonds, rarity of elements, possible reactions, etc...
3. Life can potentially evolve that is NOT based on carbon chemistry at all (energy based, crystal based) - for one example, you can have information-based life that exists in computer memory, and doesn't directly require water.
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It might be possible, but it would be nothing like the carbon-based life we see on Earth. Methane and ethane won't dissolve ionic compounds, so ion transport is right out. Cell membranes self-assemble because they're built from phospholipids with hydrophobic and hydrophilic portions, and that requires water in the environment. Even DNA forms its shape because of water.
Water is considered a "universal solvent," not because it's good at dissolving everything, but because it really can dissolve small amounts of almost anything. Hydrocarbons like methane and ethane are much more limited.
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Note: *The following answer is **in addition to** the excellent answer by DVK, on it's own it's insufficient to answer the question*
To answer this question we would first have to define what life is. Following the biological descriptive definition of life we get:
>
> Since there is no unequivocal definition of life, the current understanding is descriptive. Life is considered a characteristic of something that exhibits all or most of the following traits:[36][39][40]
>
>
> 1. Homeostasis: Regulation of the internal environment to maintain a constant state; for example, electrolyte concentration or sweating to reduce temperature.
> 2. Organization: Being structurally composed of one or more cells — the basic units of life.
> 3. Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.,[36]
> 4. Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
> 5. Adaptation: The ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity, diet, and external factors.
> 6. Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
> 7. Reproduction: The ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms.[41][42] or "with an error rate below the sustainability threshold."[42]
>
>
>
Source: <http://en.wikipedia.org/wiki/Life>
So, looking at the above we next can address the actual question. Now we can go the speculative road asking "can be imagine an entirely alien system that fullfills these requirements?" into which category I would categorize all of [Hypothetical types of biochemistry](http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry) (from the currently top voted answer) or we can ask ourselves "which other systems do we know that could potentially fulfill those criteria?". Now, let me present a crazy example: computers. Or rather, a computer connected to a fully automated manufacturing plant, automated mining plant and solar cell plant. Those things could easily fulfill at least 5 out of the 7 criteria and with additional work there is nothing that would stop them from fulfilling the other criteria and *thus be considered alive*. As the definition is a descriptive definition in certain cases it requires a slightly open interpretation of terms like "cells", "organic" etc., but to prevent it from becoming a cellular definition this seems a reasonable course of interpretation.
In conclusion I do believe it safe to say that life is possible without water.
Now, the actual question is about whether such a system can evolve and then you get in a lot of other murky territory (the likelihood of evolution occurring by chance are... well... let's just say pretty slim) and even disregarding that it's safe to say that such a mechanical system would not evolve by it's own, however it does give a more intuitive argument that life is something far more complex than just "could we get a workable solution when we replace water with methane".
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There are self reproducing masses of chemicals at one confined location in the universe. These are fuelled by the photons emitted from a nearby nuclear furnace. The major elements in the self reproducing masses are hydrogen, oxygen and carbon. Because carbon is such a promiscuous element, it likes to join with other elements into large orgy of elements. Oxygen and hydrogen are happy willing partners which make for a better bigger orgy. With such willing partners it only took a couple of billion years to go from a mass of chemicals to a mass of self reproducing chemicals. From that moment it was inevitable that some self reproducing masses would vary with time and still reproduce. None of the reproducing masses can reproduce if conditions are not at a minimal and they will no longer reproduce. There is no requirement that the fuel source is a nuclear furnace, or that the promiscuous molecule is carbon, or that the happy willing partners are hydrogen or oxygen. Until I know how to make life than I won't rule it out.
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Life as we define it requires certain conditions, in specific the ability for an organism to form and evolve. The one organism that we know resulted in intelligent life requires water and various other factors, so it is logical to assume that a planet with similar conditions might contain life as well. Aside from that there are alternate possibilities:
* Life was brought to a planet from an external source. For example by an Asteroid crashing on a planet, or actual other intelligent beings.
* Life could be formed with other/unknown materials that we do not know about (yet). There are still many things that we do not know, so it would be foolish to assume we know everything about life.
In essence intelligent life requires a construct of materials that are capable of processing information, basically computers made out of random luck. Since there are many ways to construct such a "computer", for example with silicon and copper, there are many forms of intelligence possible.
To survive it would require additional factors, such as the ability to interact with the environment to gain nourishment in some form. The ability to adapt would be necessary if the environment changes over time, as otherwise such a species would be extinct by now. The ability to move would be a great evolutionary advantage, however given the right (paradise) environment not required.
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If by *possible* you mean that we're not aware of any physical law being broken by such an occurrence, then yes, life evolving on planets without water is *possible*.
If by *possible* you mean that we have identified a *specific* series of reactions that can naturally occur that lead to the development of life, then the answer is no.
(Yes, I'm in a bit of a pedantic mood.)
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In my world, there are two types of people, lefties and righties. They have opposite orientations, which means they are mirror images of each (they are [Enantiomers](https://en.wikipedia.org/wiki/Enantiomer) of each other essentially). Throughout much of history, most people have been "orientist", or "handist" (since lefties are left-handed and righties are right-handed), meaning that they hate those of the opposite orientation. In each country, usually either the lefties or the righties were in power, oppressing harshly those of the opposite orientation (usually enslaving, but sometimes killing them, and sometimes letting them be mostly free but limiting their rights).
In my country, for example, the righties are in power. Most of our neighbors are also pro-rightie, but one of our neighbors was taken over by a foreign leftie civilization 150 years ago. We have only recently established a tenuous peace with them.
The idea of orientation has an interesting history. About 300 years ago, a foreign leftie astronomer actually came up with the idea that there is no absolute notion of orientation in our world (i.e. it was [non-orientable](https://en.wikipedia.org/wiki/Orientability)). He was promptly put to death by his government for such an absurd notion.
About 200 years ago, a number of linguists from different countries found a rather odd linguistic paradox. If you translate "rightie" from English, through seven different languages, and then back to English, it comes out "leftie". If you start with "leftie", you get "rightie". The linguists were quick to point out that language is a very fuzzy thing, but some suspect them of non-orientist sensibilities.
Nowadays, very odd things have started happening. The world now has a global economy, so people and goods travel around the world. World travel has the disastrous effect of sometimes corrupting the orientation of goods, or even people, to the opposite orientation! Some scientists are even asserting that the astronomer was actually right, and our world is topologically a [Projective Plane](https://en.wikipedia.org/wiki/Real_projective_plane)!
How should we respond? Everyone knows that lefties are inferior. How can we justify oppressing them if orientation is non-stable? How should we treat world travelers, when we don't know their original orientation? (That is, **how can orientists react and adapt to globalization in this world? Is there a way they can keep their prejudice?**)
Notes:
* Non-orientability means that you can only compare the orientation of objects that are near each other. There is no consistent way to define orientation globally. It also means that if you travel around the world in a certain way, you become mirror reversed (compared to, say, a sculpture someone made of you before you took the journey which didn't move). See [this picture](https://upload.wikimedia.org/wikipedia/commons/b/b7/Fiddler_crab_mobius_strip.gif) to see what that looks like.
* Orientation (locally) is very easy to tell. Besides handiness, there are also very distinctive biological differences in appearance that are very hard to cover up. (Attempting to cover them up is considered taboo.) There are few other physical differences though. (One of them is that are a couple of foods that only righties or only lefties can eat. This has led to unfortunate effects in the more genocidal nations.)
* There are many equivalent ways to define the projective plane, but one way is the [hemisphere model](http://www.carliner-remes.com/jacob/math/project/images/hemi-proj-plane.gif). In this, the projective plane is a hemisphere, in which opposite points on the rim are glued together. This means that if you walk of the rim, you pop up on the other side, but with your orientation reversed. (You might be tempted to say that this is the answer to my question. Just define someone's orientation as what their orientation is at birth, in the hemisphere model! There are two problems with this: (1) For a given projective plane, there are infinitely many different hemisphere models. The orientists would have to pick one, and justify why that one is the best. (2) Perhaps even bigger, orientists near the "rim" of the chosen hemisphere model would regularly change orientation (according to the model). They probably wouldn't accept such a model.)
* Orientation is inherited from the parents. This means that if your parents have the same orientation at the time of conception, you will have the same orientation as your mother at birth. If you parents have different orientations at the time of conception, you will have a random orientation when you are born. (Also, you will probably be killed.)
* So, I've only described the topology of the world. Allow me to now describe the geometry: Establish a 3D coordinate system, where the planet's center is at (0,0,0). Points (x,y,z) and (-x,-y,-z) are the same point, and otherwise physics is mostly normal (except for how the sun works). This means that the planet's surface will topologically be a projective plane. It is also about as round as the earth. There is a star which goes around the planet. It cycles between light and dark every 12 hours (don't ask me how). (The reason this is necessary is the equator only has 180 degrees. This means the sun is always visible. If the sun was always light, there would be no night.)
EDIT: In the comments, many people are suggesting that a solution would to simply "ignore" the issue. (Note: Before globalization, ignoring the problem was a valid solution, and what the people did.) Although for some social issues that works, it doesn't in this case. Here are some scenarios where the ignoring it won't work:
* A prominent foreign person comes to town for some reason (business, politics, acting, etc...). They appear to be a rightie, but there are rumors that they where born a leftie. How do you decide whether or not to hate them?
* The rightie association of this country is having a video chat with the rightie association of some far away foreign country. To their great surprise, when the chat starts, they appear to have opposite orientation (i.e. they appear to be lefties to each other). One of the IT people fiddles in the settings, saying "okay, I swapped the video orientation". They now appear to be the same orientation, but both associations stare at each other suspiciously for a couple minutes, wondering if they are actually the same orientation or not.
* A rightie sends his rightie kid away to college. When they come back for Christmas, they are leftie. They did not decide to be leftie; it was just a side effect of the route their plane chose.
As you can see, this is very different from the flat v.s. round earth issue. This can actually affect people personally (if they care about orientation, that is).
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## The Spherical World Society and Evil Twins
There is a model of the projective plane known as the [projective sphere](https://en.wikipedia.org/wiki/Real_projective_plane#The_projective_sphere). It has the following properties:
* Since it is based on a sphere, which is orientable, you can consistently assign objects orientations which do not change as you move along it.
* Unlike the hemisphere model, the sphere model is basically unique.
* Also unlike the hemisphere model, its continuous. There is no point where things, according to the sphere model, randomly change orientation.
Therefore, the orientists can form the Spherical$^\*$ World Society, which asserts that the world is actually a sphere!
So what's the catch? Every point in the projective plane actually occurs *twice* on the sphere (one for each orientation). That means that for each actual person, the Spherical world society believes there are two (one leftie and one rightie)! This is known as the Evil Twin Theory.
This actually has economic advantages. Want to trade with an enemy nation? Trade with their evil twin instead! (This only works if they also subscribe to the evil twin theory, of course.)
This has an interesting applications, both comedic and dramatic. For a comedic application, the Mayor of Rightlandia decides to send a spy to aidandlthgiR, which is controlled by lefties, and in particular by the Mayor's evil twin. There is word that they are going to hold a leftie pride parade (which they call a "edarap edirp eithgir") to rival the upcoming rightie pride parade, and the spy is to disrupt it. The spy successfully partially disrupts the parade. At the same time, a leftie spy tries to disrupt Rightlandia's parade, but is only partially successfully. The spy and the Mayor rejoice in each other's partial success.
In a dramatic application, the Rightlandians capture the evil twin of the Mayor's son, and want to kill him, since all lefties are killed in Rightlandia. The Mayor knows that the evil twin of his son is actually his son (since he only "believes" in orientism so he could get a sick hand tattoo), so he has to find a way to stop the town from executing the evil twin, at least until he finds a way to "rescue" his son from aidandlthgiR.
The evil twin theory is sort of a self-fulling prophecy. If someone from Rightlandia goes to aidandlthgiR, he will naturally be hostile to the people there, since from his point of view their orientation's have changed.
It also is an interesting way to mess with the audience. By translating everything to English (for example translating Rightlandia to "Great Mother Country" and aidandlthgiR to "Bear Running Green"), the audience won't realize that your actually talking about the same people. After the big reveal, the audience will have to rethink the role of prejudice and topology in their own world.
The idea of digital communications is also interesting with this. To avoid connecting to the evil twins of your video chat partner, you could use [circularly polarized radio](https://en.wikipedia.org/wiki/Circular_polarization) (assuming that those in power know what's actually going on, they could allow the radios to connect to the evil twins' radio stations, but make "modifications" if you do). If you want to have a secret communication, you would need a guarded physical connection, since your evil twin will have the same encryption key as you.
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$^\*$Not to be confused with the Flat World Society (which also believes in the evil twin theory, but doesn't believe the world is round) or the Mobius Strip Society (which doesn't believe in orientation, but is mathematically misguided).
See Also: [Wind and Mr. Ug](https://youtu.be/4mdEsouIXGM), a misguided triangle that falls in love with her evil twin.
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**You would get tattoos which would be recognizable as mirror images of themselves.**
[](https://i.stack.imgur.com/8W4wr.jpg)
Rightie-pride people would get tattoos depicting their pride and belief. These would vary from person to person but have similar themes, and be publically viewable to greater or lesser extent. Likewise leftie-pride people (but different tattoos, of course!)
A rightie who got switched would still have all his or her recognizable right-pride tattoos, but in mirror image. Letters would be backwards. That is fine; they are still rightie pride tattoos and so this person would still be viewed as a true blood rightie. The fact that the tattoos are mirrored means an unavoidable switch happened. These things do happen.
A leftie could fake it, by getting switched to rightie and getting the tattoos then. A leftie like this would be giving up on any leftyism because lefty-pride people would hate on that person after seeing rightie-pride tattoos. You could not go back and forth with these tattoos.
Persons who did not care enough about their heritage to get the tattoos would be viewed with suspicion by pride people of both sides.
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The natural way to ensure that orientists can keep the validity of their hatred is to forbid the use of any path which alters orientation. The orientists define a subset of the topology of their world in which they will operate, which preserves orientation globally. Of course, not everybody will go along with this. The orientists will simply have to declare "We hold the true sacred geometry, in which all things are right (or all things are left, depending on the cultural orientation). If you aren't with us, you're against us." Thus they do not have to hate the cis-hands who take these sinful paths, but they can react viciously towards them while reserving their true hatred for trans-hands, who are the true abominations.
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*Orientists could react and adapt to globalization in this world much the same as any-ists do in our world: along a gradient depending on their individual experiences and character traits.*
Our world presents a constantly changing environment, to which people observe the changes and choose to react in innumerable ways. Some responses to exposure to new concepts include:
•Not noticing at all. Some people will not even be able to notice a concept that is beyond their ability to perceive or understand. This would be similar to a very young blind child noticing the light switch turns on and off electrical lights. They hear the sound possibly, but cannot notice the light and dark changes in the visible spectrum directly correlate with the flip of a switch. Indeed, they cannot very well even comprehend the light itself, much less the switch's role.
•Noticing, but more subconsciously than consciously. These folks will retain current views, but the potential for another possibility to exist will niggle at their periphery until a time perhaps will come that they are better able to contemplate the issue at hand.
•Noting, considering, then consciously choosing to either retain current steadfast belief, or begin to assimilate some of new information, or wholeheartedly adopt a new way of being. This will depend heavily on individual mind constructs of personal belief systems along with past experiences. There is a lot of play along this string of responses.
•Noticing, considering, and choosing to enter a sort of limbo as they decide to continue to observe and analyze additional data on the subject. This is akin to scientist's method of hypothesis and experimentation. They will delay making any conscious response, sometimes without any definite conclusion at all.
•Noting consciously, contemplating, then deciding they prefer to be either ambidextrous, quit using their hands all together, or find a way to build and implement an orientation system that also includes forward and back, up and down, internal and external, proximal and distal, and on and on. These folks realize they couldn't care less that everyone else wants only two choices. They are excited by the new knowledge that another idea is possible, and some will go on to expand the idea as far as they possibly can. These are fun people, by the way.
Even in a case where the person themselves has re-oriented unintentionally and the change has affected their own self, anyone can still be able to belong to any of the groups above. The power of their own mind will allow them to know themselves outside of any external manipulation of the physical, and spatial orientation is clearly defined here as physical.
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I think you answered your own question: people who want to hate someone for not being the same as they are will always find some justification for it. There will be personal, less universal justifications and more generally accepted ones, depending on the charisma and exposition of the person who touts it.
Ultimately, I think true globalisation is not achievable without reaching a level of tolerance. Especially if there is money to be made of it. Those who will not adapt and constrain themselves to (the "right" subset of) people in their vicinity not only in their private lives but also in their professional one, will soon find themselves to be in the minority, and possibly losing opportunities because of it. (They can still cause a lot of damage, though, if someone gathers them into some radical group.) Those who experience changes in their orientation will likely become more tolerant towards different orientations. Besides, on the internet, you can't tell other people's orientation if you only see an avatar. The trait of caring overly much about orientation will soon be lost or constrained to niche environments in the process of social evolution because it's not a winning strategy on a global scale.
So the only way for your orientists to keep their bias is either to move to such niche environments or do away with globalisation.
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In the days of globalization you have technology which will solve these problems. We simply make a government database of all persons and include a field for handedness, which is measured and assigned by doctors on behalf of the government. Note this category will be binary only allowing an R or L, anyone not fitting clearly into either categories is clearly evil and will be assigned the negative handedness of choice.
Once assigned by the government handedness cannot by definition change. If someone appears to change this is clearly either an obvious deception or an illusion and should be ignored. If it is too difficult to identify the objects of hate, or too many of them are able to pass as normal, a government mandated patch could be assigned to clearly mark the individual. If there is any question of course their paper should be checked to verify their status (Lack of papers is of course illegal).
For interesting parallels consider past treatment of groups such as Blacks in the USA, the Jews in Nazi Germany, and the recent bathroom gender laws in the USA. In many cases people from the disenfranchised group are visibly no different from the general population, but were still hated and discriminated against.
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Spinny McSpinface is an ancient generation ship, invented and launched before the creation of [Wrap drive](https://worldbuilding.stackexchange.com/questions/63587/why-are-there-no-toilets-on-the-starship-exciting-undertaking?rq=1) and recently arrived at its original destination of [A Long Way from Anywhere V](https://worldbuilding.stackexchange.com/questions/65129/how-are-there-so-many-species-on-the-space-station-a-long-way-from-anywhere-v?noredirect=1&lq=1). All the crew are long dead because of reasons (possibly related to them trying to reverse the polarity of the life support systems).
Its design is pretty standard for such unenlightened times. As no fake gravity (no, not artificial gravity, *fake* gravity) systems were available, the ship resembles a spinning cylinder with thrusters at both ends and the direction of 'down' oriented away from the cylinder's central axis. Old records reveal there were plans for an [ocean in the middle of the ship](https://en.wikipedia.org/wiki/Rendezvous_with_Rama), but that particular design feature was scrapped.
The ship is half a kilometre across, has a thickness of 100m and spins at just under 2RPM, giving an effective gravity inside the cylinder of between 0.6G (nearest the centre) and 1G (nearest the outer skin).
The issue with this crude method of simulating gravity is the [coriolis effect](https://en.wikipedia.org/wiki/Coriolis_force), and most notably its effects on the [human inner ear](https://en.wikipedia.org/wiki/Motion_sickness). This would be especially noticeable as people moved from one deck to another.
There was no room on board Spinny McSpinface for large quantities of antikinetosis medication, so the poor unfortunates that boarded the generation ship all those aeons ago must have some way of dealing with the inevitable disorientation.
The question our scientists need answered is *how*?
**ADDENDUM:**
The intent of this question was not to find a minimum radius to avoid the inner ear effects. It was intended as a 'given the radius is too small to avoid adverse effects, how do we deal with that'?
If you want to pick a smaller radius and higher rate of rotation so the effects are more noticeable, feel free to do so, just assume that the spin rate is high enough to cause issues.
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your radius is so large the effect will not be noticeable at only 2rpm.
If you want your people to get nauseous you need to make your radius much smaller, like less than a quarter of what it currently is.
[settlement.arc.nasa.gov/75SummerStudy/Table\_of\_Contents1.html](http://settlement.arc.nasa.gov/75SummerStudy/Table_of_Contents1.%E2%80%8C%E2%80%8Bhtml)
[space.alglobus.net/papers/RotationPaper.pdf](http://space.alglobus.net/papers/RotationPaper.pdf)
Now people might get a little nauseous entering and exiting your station assuming the airlock is on the center of rotation, especially if accessed by elevator. But that will be short lived and rare.
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**Short answer: High-tech air-sickness bags and mops.
Coriolis-induced nausea was a problem for the original crew and the first few generations, but we've adapted and evolved rapidly since then.**
Coriolis-induced nausea was truly a terrible problem for the original crew, such that the survival of the ship was in danger several times. But the next generation -- born into spin 'gravity' -- were significantly less susceptible. Those that were still significantly susceptible tended not to have (as many, if any) children in the spun environment. Our medical staff is doing what it can for the small minority still afflicted.
The result, after over twenty generations, are humans whose inner ears have almost no problems with spin 'gravity.' However, it remains to be seen how well the transition back to planet gravity will go.
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Assuming that you lower your numbers until the problem appears. (As described in @John's answer)
There are very large differences in how people react to this. Some people can dance on an over-clocked merry-go-round on the deck of a ship at high sea without problems. Other people get queasy just reading the previous sentence.
When choosing the crew for this voyage, one of the criteria would be that they are **not** prone to motion sickness. So, the first generation is thoroughly tested before take-off and consists of immune people.
[Research indicates](http://news.psu.edu/story/141284/2005/03/30/research/probing-question-motion-sickness-your-genes) that motion sickness is inheritable. [Another study.](http://www.techtimes.com/articles/30881/20150204/motion-sickness-genetic-23andme-isolates-responsible-gene.htm)
The genetic causes seems to be complex and spread over many genes. This means that some poor people in later generations can pick up a combination of bad genes and get sick. However, this will be a small number. And as @Catalyst said, they will not get children themselves.
The original voyager selection process can lessen this problem by insisting that the entire family of the voyager be immune. However, at some point you will run out of applicants for the job. Should they choose the great applicant with a motion-sick brother, or should they choose the mediocre applicant without any problematic relatives? Decisions, decisions...
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Have you ever gotten dizzy from spinning? If so, you know that the sensation of dizziness sets in when the spinning *stops*, or at least changes rate or direction.
Changing decks doesn't change the rate or direction of spin, it only changes the magnitude of the G-force, so, changing decks wouldn't be felt by the inner ear.
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**Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers.
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This question does not appear to be about **worldbuilding**, within the scope defined in the [help center](https://worldbuilding.stackexchange.com/help).
Closed 4 years ago.
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I've heard that when humans become able to upload their brains to a computer, it would realize the dream of immortality... why?
Let's suppose that I upload my brain to my computer and then transfer it to a robot.
This robot will act like me, have my memories, my personality and so on. Now imagine that this robot dies (on a airplane crash or however) - it's ok, **I'm** fine, it was the robot, not me.
Now let's invert the scenario: **I** die on a airplane crash and the robot is in my house. **I'm** dead. What will live in my place will be the robot with my memories and all, and not **me**.
This doesn't seem to be immortality for *me*, but for the people who knew me, since the only perceptible difference between me and the robot is only that his body is made of metal (maybe no difference, I've read that they are testing printing organs).
In my opinion, immortality would be true in this way only if we were able to transfer our consciousness to the "fake" body.
That said, why is brain uploading taken to be immortality?
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Most who explore the idea of a brain upload as immortality push *hard* against your intuition of what your 'self' is. You think you're pretty darn sure what your self is, but it's actually a very slippery concept. For example, do you think you can define your "self" as your body? Many of the atoms in your body are changed out rather rapidly. While tooth enamel and some of the crystals in the lens of your eye show very low rates of replacement, a large portion of the body is made of brand new atoms every year!
Which brings up the [Ship of Theseus](https://en.wikipedia.org/wiki/Ship_of_Theseus). The Ship of Theseus is the most famous thought experiment on this topic:
>
> The ship wherein Theseus and the youth of Athens returned from
> Crete had thirty oars, and was preserved by the Athenians down even to
> the time of Demetrius Phalereus, for they took away the old planks as
> they decayed, putting in new and stronger timber in their places, in
> so much that this ship became a standing example among the
> philosophers, for the logical question of things that grow; one side
> holding that the ship remained the same, and the other contending that
> it was not the same.
>
> — Plutarch, *Theseus*
>
>
>
In this story, we start with a famous ship, the Ship of Theseus himself. The Athenians loved that ship so much that they kept it maintained for hundreds of years. Whenever a plank got too worn out and decayed, they'd replace it to keep the ship in prime condition. At some point, every single piece of wood was replaced this way, so there were no original boards left from Theseus's time. The question raise is in three parts:
* Is this the same ship that Theseus sailed on?
* If so, why? There's not a single board in common between the ship Theseus used and the one described here. How can we call it the "same?"
* If not so, then at what point did it cease to be the same ship?
Philosophically, this is an unsolved question. It seems like it should be intuitively easy, but every line of logic which philosophers have gone down ends in an uncomfortable conclusion. Identity is not as simple as we think.
Another famous question pulling at these threads is a problem involving teleportation between planets. Let's say we develop a way to teleport between planets. However, there's a catch. It's not actually moving matter from one planet to another. That would take too much energy. Instead, the "teleporter" reads the state of your body, the position of every atom, every electric field, from your head to your toes. This information is transmitted to the other planet, where they create a new "you" with exactly the same properties in every way.
This obviously isn't "teleportation," its "cloning." However, what if we destroy the original after we create the copy on the other planet? Now we still have one body, and it has every hope, dream, memory, and desire that the original did. Is this not teleportation of your "self?" If it isn't, consider how hard it is to tell the difference between that and a really fast rocket ship flight empirically. The only difference would be which atoms make up the entity on the other planet, and we've already shown that's a hazy definition of "self" at best.
Now this sounds like a dangerous teleporter. What happens if something goes wrong during the reconstruction? Now you're dead. So let's put a safeguard in. The original is not destroyed until the teleporter on the other planet sends a confirmation that, indeed, the other body is complete. Now let's say the safeguards fail. Now there are two "you's" walking around on different planets, living potentially different lives. We would generally consider the "you" on Earth to be the "original," and the "you" on the other planet to be the "clone" because your Earthbound body was constructed before the clone body on the other planet.
I think this is very close to your argument. Your argument is that the body you inhabit right now is the "original" you, and the robot is a clone. This is very normal. Now let's make the intuition harder. Let's say that, instead of malfunctioning and leaving the body on Earth, it instead sent out two clones: one to Mars one to Venus. The construction of the new body/bodies completed, so the Earth teleporter destroys the old body. Now which one is the clone, which one is the original? Is it the one on Mars, or the one on Venus?
There are no universally accepted answers to these questions. These are philosophical questions that have persisted for thousands of years, and will likely continue for thousands more. However, one thought process to consider:
You gave examples from the perspective of the biological "you," but remember that your robot clone has all the same hopes, memories, dreams, and desires that you do. So how would the robot feel, being in a plane crash. Would he be comforted to know that the "real" you is still alive? If instead, your biological body died in an airplane crash. Would the robot feel any less lucky that it wasn't in the airplane crash? How much *actual* difference is there between the biological you and the robot you?
I leave with two parting stories. First is [Valery Spiridonov](http://www.mirror.co.uk/news/uk-news/changing-face-full-body-transplants-6851735), who has requested to be the first human to undergo a full-body transplant. Suffering from terminal muscular atrophy, he intends to have his head cut off and sewn onto the donor body of a brain dead organ donor. How different is this from being implanted in a robot?
The second story is the curious case of [Krista and Tatiana Hogan](http://www.nytimes.com/2011/05/29/magazine/could-conjoined-twins-share-a-mind.html?_r=0), Conjoined twins joined in the skull (craniopagus). They are a fascinating topic for researchers trying to figure out if they are one consciousness or two. Sometimes they act like independent beings, doing their own thing. Other times, they act so extraordinarily in unison that you have to wonder if there's really just one consciousness controlling the whole body.
These are cases where the easy versions of "self" break down. And, indeed, brain uploads are one such example where the easy versions just get... complicated.
[Answer]
## There's another way to do it, and you stay you this way
[](https://i.stack.imgur.com/oAJJf.png)
Ah, but emotionally as a flesh-based mammal with no history of backups, syncs or restores, the concept that you are fundamentally *just* data makes you uneasy. Who cares that ghost-in-the-machine dualism was disproved centuries ago? We just did not evolve this way.
Think about it: you would never trust that *impostor* to be you. As *the real you* lays dying it a futuristic battlefield somewhere, *it* is in bed with your significant other, touching them, leering over them. All the while perhaps lacking internal subjective existence, a zombie with your memories. The horror.
Your savanna-trained flesh mind recoils in fear and disgust. That thing cannot possibly be you! No. We cannot have that. Two versions of me? At the same time. Impossibru. `Div/0!!!!1` (or its flesh-brain equivalent)
The patient AI doctor sighs (we get these nut cases every day), and suggests a different approach.
Instead, we follow this path:
Step 1. Using a complicated machine, we **replace just 1 neuron** of your brain with a synthetic equivalent, copying its connections and ability to reshape, generate new and prune its existing dendrites as well as accept new connections from other living or synthetic neurons. This should be fine, after all we lose thousands of neurons (without replacement!) every day and never even notice.
Step 2. Take some time, maybe even a few days, if feeling particularly antsy. Once you are satisfied that you still have your own subjective experiences and all, and that you are still you, you **replace a second neuron**.
...
Step 85,999,999,999. Once you are satisfied that you are still you and still have your own subjective experiences and all, and that you are still you, you **replace a the second to last neuron**.
Step 86,000,000,000. **Replace the last neuron**.
**Congratulations!** You are now synthetic and the possibility of longer durability (since outright immortality is ruled out by the laws of our universe) is within your reach. You can now back up your self and reload states, store those or memories in nonperishable form.
No longer will you die like the creatures of flesh that are less then you are, no longer will worms and bugs feast on your flesh, but instead you may rise above them and become the master of your own destiny.
If you feel the urge to duplicate yourself now, you may, although for consciousnesses that begin in the flesh, there usually is a certain irrational reluctance and some minor issues & changes that need to be sorted/ironed out to enable a true sync process, such as tearing out your outdated dorsal spinocerebellar tract (you don't need it do you?) and replacing it with something more appropriate for controlling multiple avatars.
[Answer]
I think your question hinges on intuitions about physical and conscious continuity as necessary prerequisite for personal identity.
In [Old Man's War](https://en.wikipedia.org/wiki/Old_Man%27s_War) consciousness is transferred to a new body by synchronising the new and the old brain. Imagine you are connected to a new body without any brain activity so far. At first you are only aware of your old body, then you are aware of both bodies and finally you are only aware of your new body (because your old one is euthanised). In this case the transition is experienced as continuous consciousness and you would be hard pressed to argue that "you" aren't "you".
Another idea championed by Ray Kurzweil among others is that you replace small parts of your brain with chips (possibly to counteract age inflicted damage), then these new technological brain cells learn to interact with your biological brain and ultimately your whole brain is only hardware and software. Here you even have a physical continuous identity because the single changes are so small. Also there is no "old you" around.
This kinds of technique could possibly assuage your misgivings about immortality.
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This question kind of depends on if you allow for the existence of a soul (as either a spirit or a 4th dimensional part of us or whatever that can exist beyond the death of the body) or not.
If not, then all that we are is electrical signals in the brain, and a complex computer would be able to simulate it.
This is the idea behind the [digital eschaton](https://www.goodreads.com/series/42224-eschaton-sequence), where every possible brain configuration will be able to be simulated, and everyone that could have existed will exist in the simulation.
If we do have souls then the upload will be a copy, not really you, but the you that is the copy probably won't know the difference.
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True, **you** are not immortal. I probably wouldn't bother uploading my brain. What difference does it make for me? But what about the world, and history? Because *you* wouldn't be immortal. But your *self* would be. Let's picture we uploaded... I don't know, Donald Trump's brain to a computer.
This computer (or robot if you need a human-like form for interaction, because we humans are so limited) would keep living. Since his mind is equal to a human's it could be argued that is a person a deserves a person treatment. The actual Donald Trump's human body will eventually degrade and die [citation needed] but the Robot Trump would continue existing. It would continue growing, maturing, as a human would given that lifespan
>
> Take [Jack Harkness](https://en.wikipedia.org/wiki/Jack_Harkness),
> for example, every time his body rebuilds... is he the same? No! From a "first person point of view", he died. But he is considered *immortal* For "the world" there's no difference. Hell, even for the "new him" there's no difference, since he keeps his memories.
>
>
>
Eventually, after 300 years people would have forgotten about the long dead human Donald Trump [citation needed] but they would still know Robot Trump. For them, the *original* Trump would be just a *phase* of the Trump existence. First he was a human, then he was a robot (*with a bit of an overlap but whatever, who cares?*). So, to practical effects, the *Trump persona* would be immortal. It would be for the rest of the world.
>
> For another example, imagine we go back in time and upload Julius
> Caesar's brain to a robot. And we leave him there. Wouldn't people say
> that Julius Caesar is immortal? Not the human, but the personality?
> What difference does it make for you?
>
>
>
Imagine the same with great artists like Picasso, Da Vinci or Van Gogh. They would continue growing and evolving. Sure, maybe they would become disconnected from humanity and their artwork could go worse... but wouldn't you be curious of what could they create in an infinite lifespan? What would they become?
>
> For an inverse case, check [Bicentennial
> Man](http://www.imdb.com/title/tt0182789/) and ask yourself this
> question. Do you consider the man at the end the same *"person"* that
> the robot at the beginning? (Related to the "Ship of Theseus" that
> @CortAmmon mentions in his [awesome
> answer](https://worldbuilding.stackexchange.com/a/40935/18136)) Because
> if so, the principles still apply the other way around (even if with a
> bit of an overlap when the both exist).
>
>
>
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For all intents and purposes, the robot is **you** - or at least you were the same person at the time of your last synchronisation.
Your uploaded brain, being purely data, can be copied and synchronised countless times. As the robotic versions of you live their lives and synchronise with each other, they will share memories and grow in ways that **you** would, where **you** is the product of your experiences, personality, memories and choices.
Yes, one of you can be destroyed but **you** (collective) only loose those experiences that have not been synchronised. You are immortal because as long as one of 'you' still exists, the sum of your experiences exist, independent of any singular stream of consciousness.
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When someone say they are going to transfer there brain into a new body they usually don't mean just there brain but instead they mean that they intend to transfer their consciousness to the "fake" body. The idea is that this would be more then just there memories or even their personality but something more. There entire consciousness, this a little hard to explain so to keep things simple people just say that there going to transfer there brain.
So to make it simple when says brain upload, they real mean consciousness upload.
[Answer]
You should research the **Turing Test**
The basic idea of the Turing Test is the ability to create a computer that you cannot distinguish from a human. So, maybe it's possible to put a "human" into a computer in some way. And if that were a copy of a person, then based on the idea of the Turing Test, that new "person" would be indistinguishable from the person that was copied...
The basic idea is this - while you can argue about soul, spirit or even the concept of consciousness, consider this:
Are "you" defined by the cells that make up you body? Most of your cells die over time, and by some estimates you have "all new cells" over a 3-5 year period. So, 5 years from now ... are "you" still "you" if all your cells are different?
Brain cells and bones are the exception. So... it seems "reasonable" that if what your brain contains defines "you" because everything else died and was reborn, then an "upload" of that information would basically be a copy of "you". The rest (besides the bones) define another aspect of your existence, but not "soul" or "spirit" or whatever you might define as "you".
However, your behavior is also defined by the body you occupy. If you occupied a robot body, you will experience life in a different way - and a flesh version of you and a robot version of you, even if they start the same - would likely be dramatically different over time. Even two robot versions of you would have different experiences, leading to different thoughts, lessons, conclusions and even beliefs. Different souls???
Anyway, the idea that "you" are defined by your thoughts and ideas is much more compelling than including the body, which is really just the system that supports keeping the brain alive (and propagation of our species...).
EDIT:
Here is what I will call the "Jim Test" (based on the Turing Test, but somewhat of the reverse):
Assume I fall asleep and my brain is copied into a clone body of mine. Then keep my original body asleep artificially (drugged or whatever). When my clone body woke possessing all my memories and having just fallen asleep, would it know anything happened at all? Would anyone else be able to determine that anything happened? (Besides those performing the "operation" or experiment or whatever; and remove all ability to put chemicals or markers on the "new" body. And probably ignore that the new body may be exceptionally hungry or weirdly disoriented from the procedure.)
That's the idea behind problems like creating a "clone" - if in every way I appear to look and act the same, but I am really a "copy".. how would anyone know but me? In fact, would I know? So if the above experiment worked, I could move my brain into a younger clone of me. Then "kill" the old body and go about my business. Then continue to grow younger clones of myself, make "backups" of my brain every night and every few decades (or whenever it might be convenient) I upload to the new body and destroy the old one. If I can't tell the difference, what do I care?
In fact, if the next clone I make include carbon-fiber reinforced bones, I might not notice much of a change, but I would probably benefit from that. And the next time maybe throw in plastic lenses for eyes to correct my vision? You get the point - eventually I could go through a series of transfers where I'm essentially "me" but a robot me... and now what? I'm clearly not "me" but in some way clearly I still am me.
However, such a thing seemingly violates the concept of a "soul" or "spirit" ... an immeasurable attribute of identity and self that is intertwined with both my body and mind, to make a complete "me". Some would take that as proof such a thing does not exist.
[Answer]
In your example, the "immortality" lies **in the perception of other people.**
Assuming the technology yields a perfect replica of your brain and everything to do with it, to your family and friends it's you that is in that computer or robot.
You have an influence on your environment:
* When you die, your loved ones go through the grieving process.
* When you interact with them, they have learned behaviour around you. You affect their decisions, their life, and even their personality.
* Your significant other has brain chemicals flowing dependent on your presence.
* You likely have a job, or some career, that produces work for society.
* If you have children, you're raising them and leading them to be a member of society.
So when they have access to this entity that is a copy of *you*, all of those details are carried over, with the differences that may arise from the different body.
Your significant other's brain doesn't go through withdrawal from your absence. Your family still benefits from your presence. Your consciousness can still produce *work*, especially with a body to go with it. So your business/career continues without the biological copy, too.
So to the rest of the world, they have a copy of you that's not subject to things like cancer. They have access to something they can likely continue to copy as well.
So the immortality is more like the abstract immortality we attribute to things like *legacy.*
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[Question]
[
Usually, when a fictional society violates common assumptions of modern Western society, it's either a dystopia where the society is disparaged to uphold Earth society (every Star Trek alien society ever), or a utopia where the author tries to push this different model of society as better (Ayn Rand books).
How can I create a fictional society with very different social norms and mores, while not giving the impression of dystopia (why aren't the good guys rebelling?!?!?) or utopia (lol you think this is a good idea for society?)? Essentially, the initial reaction of the reader should be culture shock, but I want to present a society that simply has *different* social issues than modern society rather than categorically evil or good.
For example, ALkP, which is the fictional country in mind, has out of many, the following repulsive-sounding policies:
* The government semi-arranges marriages based on a complicated, non-transparent algorithm that operates by mining intrusively collected private data. People reaching marriageable age receive a short-list of recommended people to marry, and if they marry the recommended people they get large tax breaks and other benefits. This generally works reasonably well, since unlike in Terran dating services where people tend to present themselves overly positively, this "dating service" relies on "objectively" collected data that are unwittingly collected. However, occasional spectacular fails cause controversy (hey, I'm straight, why did the government database think I'm gay simply because I have an unusual number of gay friends?), and the selection is often based on the prevailing political doctrine (you're too rich, marry outside super rich people or suffer a massive tax hike; after election: your girlfriend is too poor, marry somebody else or you'll be poor too)
* Racially-based policies are very common, but ALkP is an extremely multicultural society and such policies aren't intended to oppress or elevate a particular race consistently - instead they are used to maintain society's ideal of multiculturalism (example: certain areas of the city are in danger of becoming Sakasic-dominated, others Miyasan-dominated. Tax rate discrimination is used to encourage people to move out of their racial enclaves, and conversely people who move are given benefits like a grade boost for entrance exams)
* Government surveillance drones and cameras are ubiquitous, but the feeds are accessible to most people who apply (journalists, etc), and the application is handled through reasonably competent courts. People who the state determine are "public figures" also get cameras in their houses. However, certain feeds may be classified because of national security (military bases etc); this is a point of controversy in the nation, since there are allegations of officials using classified areas as a haven for corrupt transactions, and the military being complicit.
[Answer]
Two words: roundness and perspective.
## Roundness
When you reveal your society to your audience, don't just put the good parts or the bad parts on display. Share both the good and the bad. Dystopian and utopian societies are often easily identified because they reveal only why a society is good or bad without showing any, or almost any, aspects that would detract from the intended image.
## Perspective
When you have conflict, present both sides of the argument. Modern Western societies are (mostly) democracies, meaning individuals get to express their views on each issue and vote to determine the outcome. Dystopian and utopian societies typically only show one side of each central conflict, namely, the one the author wants to emphasize or deride.
One of the hardest things to do is effectively argue a point from the side opposite your own, but doing so gives an argument -- and the society built on it -- greater depth. Not only does this reveal that your society isn't perfect, but there is also an opposition in play, even if it is minor. The antagonists to your society can even act as [foils](https://en.wikipedia.org/wiki/Foil_%28literature%29) to your main characters.
[Answer]
Most readers realize that no society is perfect. Anyone who says that a society is perfect is either delusional, or selling something.
Like FrostFyre's answer, whether a society is utopia/dystopia depends completely on how you portray it and what elements you emphasize.
For example, it's easy to portray the US as a utopia (I give this example because I live here and know it best) as the US has the reserve currency of the world, an unparalleled military, and an economic power that is unavoidable. Cities are, generally, prosperous and the farms produce in abundance. Drinking water is easy to come by. There is too much food.
In contrast, it's easy to portray the US as a dystopia too. It's easy to think of the US as an oppressive world empire that throws its weight around where ever it wants. Its people die of preventable disease because they are unlucky enough to be poor. Minorities are persecuted for the color of their skin and the phantasms of slavery still haunt it.
It all depends on what details you show and how you show them. If you can describe *why* that society accepts those conditions and show how they reached that conclusion then it's much easier for you audience to accept and not judge. Show your audience why that culture thinks those things are okay.
[Answer]
In terms of storytelling, the key is to understand what the nature of the story is, and why it is important for it to be set in an alien society. Most Utopian/Dystopian fiction is set in "different" societies *precisely* because the author wants to make a point by emphasizing what they see to be the ideal/dysfunctional elements of their home society. The other way (which you picked up from the Ayn Rand examples) is to amplify existing trends to "11" and show the trend, law or issue to its logical conclusion.
Now I am guessing the examples in your question are examples of what you want to have in your society, so the best way to avoid them being arguments "for" or "against" these particular elements being what makes a utopia/dystopia would be to insert some sort of backstory as to "why" society developed along these lines, and why people seem to generally go along with these things. Of course, even that can lead you down the Utopian trail, Robert A Heinlein had just such a backstory to justify the setting and society for his novel "Starship Troopers", with a pretty explicit understanding the reader would see that this was a "better" society than what had preceded it (i.e. 1950 era America trending towards welfare Progressivism/Liberalism).
So get a clear understanding of what story you are trying to tell, and make that central with the society being a backdrop, rather than focus on the society and pushing it into the foreground.
[Answer]
I think it was Poul Anderson who said that a good story about the future could always be made from the problems that came from the *solutions* to the problems you have now.
That ties into what Thucydides and Green said about saying how your society came to be. But don't dump your problem-solution-new problem backstory on the reader at one go. Instead let them get outraged about the apparently dystopian aspects of your world, and then gradually reveal that the way things were was actually a pretty good lash-up, considering the alternatives. Then outrage them all over again. Rinse and repeat as many times as your story permits.
It's a minor aspect of a immensely complex series of books, but that is what Gene Wolfe does with the Autarch's Commonwealth in the course of the *Book of the New Sun*. At the beginning the reader is encouraged to see Vodalus and his rebels as the good guys, given that they are rebelling against an Autarch who maintains a Guild of Torturers. By the end one's sympathies have zigzagged so much that it's hard to say where they are. In this scene the Autarch is dying:
>
> His voice had faded until it was softer than the chirping of a
> cricket. "You were right to hate me, Severian. I stand... as you will
> stand... for so much that is wrong."
>
>
> "Why?" I asked. "Why?" I was on my knees beside him.
>
>
> "Because all else is worse. Until the New Sun comes, we have but a
> choice of evils. All have been tried, and all have failed. Goods in
> common, the rule of the people... everything. You wish for progress?
> The Ascians have it. They are deafened by it, crazed by the death of
> Nature till they are ready to accept Erebus and the rest as gods. We
> hold humankind stationary... in barbarism. The Autarch protects the
> people from the exultants, and the exultants... shelter them from the
> Autarch. The religious comfort them. We have closed the roads to
> paralyze the social order..."
>
>
>
[Answer]
Hmm ... this sounds more like a *storytelling* question than world-building, but hey. Let's roll with it.
Recommend you show off the differences for the sci-fi tourism factor, maybe even highlight the parts that you think will freak readers out, *then show people coping and even being happy.* Folks are pretty resilient, and any society which is with-it enough to not collapse will allow room for people to enjoy their lives.
Imagine, say, a theocracy. Show off your official religion, your strict morality laws. Then show your neighborhood people joyously singing their hymns, or primly playing the dozens via insults thinly veiled in stern scriptures.
Imagine, say, a classless communistic surveillance state. Show off your boring gray-box architecture. Show off your haranguing political officers. Then have your hero inspect the surveillance center, to see ten cameras simultaneously showing teenagers mooning the "hidden" security cameras. Show gray-overcoated citizens in the bread line, making jokes about how long the wait is, how they're missing work, and "Oh no, I could get fired! Oh wait, I've got a pretty good union..."
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# Do Worldbuilding
Rather than presenting a society to make a single point (Western Civ is good/bad for XYZ reasons), build the society to make holistic sense in its world. A society grounded in both the best and worst humanity has to offer will convey a sense of holistic integrity and well-roundedness that proscribes utopian and dystopian interpretations.
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While we all have a common understanding what the words 'utopia' and 'dystopia' mean, i think one can argue that you won't be able do describe a society of which every single human being agrees that it is either the one or the other.
A lot of people will probably agree that a society without discrimination against ethnicies is a good one, but i guess we all know of enough news reports about people who don't share that view.
Other ideas, like good medical care for everybody, or a basic income, free energy, free food, or whatever you can come up with, all share the same fate: You will find people who dislike it.
And then, of course, there is the fact that everything has two sides (at least), so no matter what bright future you conceive, it will have it's downsides, somewhere, for someone. These downsides don't need to be objectively there, it is enough if someone feels bad about something. Again, think of discrimination: Some people will simply hate the idea that someone else should be considered their equal.
Others have pointed out that for the purpose of a story, the most important factor is how you describe things. You could point out positive or negative aspects, highlighting things as best they suit your storytelling goals.
So if you want a radically different society, but you want a "neutral" general feeling about it, you need to describe it neutrally (or as neutrally as you can). After all, everything needs to be balanced to work for everybody.
But then, you may want to ask yourself: why does your society have to be so radically different? what's the point? Consider [Chekhov's gun](https://en.wikipedia.org/wiki/Chekhov%27s_gun): it should be relevant to your story. If it's not, don't tell about it.
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[
Suppose the Earth entered a period of intense global warming, say by 50° Fahrenheit (28° Celsius), and then levelled off at the new, higher, temperature. Obviously, anywhere near the equator would not be inhabitable, and melting icecaps would cover much of the coastal regions.
However, would this necessarily spell the end of humanity on Earth? Could people survive just by moving to higher latitudes, and have societies similar to the ones that exist nowadays?
Or would the heat mean the end of the world as we know it?
[Answer]
Other answers have mostly concentrated on the persistence of zones of reasonable temperatures and the means to mitigate rises. I think jamesqf is more on track with his answer about photosynthesis.
The problems of that degree of rise won't be direct. It'll be the total ecosystem collapse that causes the problem and the difficulty of transferring it to other places. Antarctica will reach a habitable temperature, sure, but it'll still have a night that lasts months and a day that last months and I doubt that the soil that is revealed will be suitable for growing crops in any short period of time. It isn't just a matter of temperature it's a matter of putting into place all the other factors that support life. The new land won't be like the old land; it'll be altogether most hostile and barren. Moreover, the loss of vegetation across most of the globe could result in catastrophic declines in oxygen levels making things even more difficult for the survivors.
Meanwhile, it's likely that this kind of change would cause catastrophic ecosystem collapse in the oceans too both from changes in water temperature (with accompanying changes in circulation patterns) and from severe acidification from the higher atmospheric levels of carbon. So it's not like looking to the seas will help much.
Now, humans might be able to survive all this by pouring money and tech into it but it's going to get mighty hairy. My inclination would be to think that some people would cling on for a while but one-by-one the last settlements of humanity would fall to one disaster or another until the last humans die out.
[Answer]
The average high temperature in *summer* at the south pole is -15F. Add 50F to that, and you just get above freezing. Again, that's at the height of summer. So you are still going to have a very wide range of climate on Earth. Now it gets a little more complicated when you start looking at record breaking high temperatures. You might start seeing 140F or higher in NYC, for example. That obviously starts getting into the fatal range without air conditioning, especially if its for more than a few days. Its possible you'd start seeing major environmental engineering projects designed to keep cities cool.
The biggest impact I think would be the years following as agriculture tries to adapt. So there may be a few years of famine world wide, with the nations with the least sophisticated food distribution systems being worst hit, unless their land happens to be one of the areas that becomes more farmable.
People will move to higher latitudes, as some areas will be down right fatal for much of the year. But other areas might become quite pleasant. You get 2 whole new continents - Antarctica and Greenland to settle, so its not a complete loss.
So the end of Humanity? No, not remotely. It'll be *quite* an upheaval for humans, but not 'the end'.
[Answer]
Certainly no, yes and yes.
# Would all Humans die?
No. Humans can happily survive a daily average temperature of 38°C/100°F (Sahara). This does not mean that everyone can, just Humans in generell. The Equator regions may indeed become ininhabitle, but a bit away human life should be easily possible.
Temperature isn't everything though. Higher temperatures and massive movement of humans will spread diseases previously unknown in *colder* countries, like Malaria ect. Many Humans will die because of this, even with a slow rise in temperature, simply because we *coldies* have absolutely no idea what this diseases are and how to handle them. Of course, there are scenarios planned for this, but honestly, no plan survives contact with reality.
The next part are natural disasters. Many regions will face climatic specialities they never encountered before (in this strength). Tornados, Hurricans, nearly everything with wind would totaly wreck havoc, simply because the newly affected regions are not used to these disasters. There are Emergency plans, but I believe they do not account for such a dramatic change.
# Can people evade the effects of this change?
Yes with a big no. You can not totally evade. Climate is a global thing, which means also higher latitudes will be affected. This means that even at high altidues you'd have to face some of the problems you have at low altidudes. Wind is strong, and even more around the top of a mountain. Good thing though is you can't be washed away by the sea. Pros and Cons.
# Will Humanity as we know it end?
Definitly Yes. As mentioned by ArtOfCode there is simply less space to live on. Luckily (in a morbid sense), there are also less competitors over this land because of the mentioned reasons. Almost every state would most likely fall to the panic of the population or the organisatorical parts of the disaster-managment in one way or the other, which means we would have to find other ways to keep the order.
Emergency Goverments would take over at first, but it depends on the people leading them in which way they will develop. Some will fall to Anarchy, others will stabilise. Tyrannies may rise, and we might find new ways to reign countries. War over the remaining ressources may emerge, costing even more lifes.
**In short,** There would be massive changes in nearly every way of life.
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Please note that the drastic picture I drew here is for a **rapid** rise in temperature. Nobody can say what will happen with a slow increase in temperature to the mentioned point, as new techologies would show up as needed. If given enough time, scientists could develop better detection-systems for natural disasters, and could possible even find ways to stop some. In a slow change, there would be no panic in the population, because it *just happens* (the Aral Sea almost vanished over the course of 25 years, and there was no public uprise). This means that I can't give a good prediction for the slow case, other than
```
Humans will adapt or someone makes something reallly stupid so a lot of people die
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Problem is not survival of humans (some will survive) - **problem is survival of humanity - our cultures and technology.**
I read somewhere that carying capacity of Earth in such conditions would be about 1B people, living mostly in high north latitudes (equator region would be uninhabitable) and sea level will increase some 200 feet (70 meters). Now we have 7B, and we will lose substantial part of good productive agricultural land.
So I assume you are looking for the questions to be asked, what changes we can expect. Here are some:
* Imagine the war for habitable territories and resources: Russia has most of Eurasian territory close to polar circle, and it's population is decreasing. What would India and China do?
* How would politics in USA change if south will not be habitable? What about all the population of Mexico? Will USA invade/annect Canada?
* It just happens that Africa and most of Muslim world is doomed by climate changes. What would happen to Israel? And low-lying island nations?
* What to do with the population of Africa (which still has 8 children per female): if some country will accept them, will they force one-child policy? For all, or for immigrants only? Will they have vote in new countries? Will they have to abandon their old religion?
* If problem is obvious now when say Nigeria has 100M population, will we save all 300M of Nigerians 200 years from now? or will we force then first to "downsize" by 1 child policy in their own countries? How will local government enforce such policy?
* Will we provide emergency food for starving people in Africa where they cannot grow enough food for steeply increasing population, but still have steep population growth?
* Will United Nations develop into single world government?
* Many cultures will not survive (like low-lying islands). How much resources we dedicate to preserve disappearing cultures of pacific islands if 70% of some country in Africa are starving to death, but not in danger of disappearing as a culture?
* Is tolerable to downsize population by war for resources? Will we let countries in Africa to fight it for water and arable land? Will we take sides - and what would be the rules?
* Will "Earth protection league" develop military/terrorist actions against nations which do not comply by population restriction requirements, unleashing deadly diseases to eliminate population in excess of what "world government" allowed for such countries?
* Will humans become vegetarians? If people are starving, can you spend 10 pound of corn to raise 1 pound of pork meat? Will people tolerate that some people are willing to pay for pork? How much are we willing to spend on protection of endangered species?
* Will people ask to clawback/surtax the profits of oil-extracting companies to pay for the cost of adaptation to climate change and sea levels? Who will pay of relocating of Bangladesh population, 100M of some of the poorest people on Earth, to higher grounds - and who will provide such grounds?
* What will happen in the oceans? With increased acidity, many small ocean creatures will not be able to build the shell, so food pyramid would collapse. No more fish, algae and jellyfish takes over.
* And there are plenty of smaller local problems. Say 30 years ago Afghanistan has population of 7M and was barely able to be self-sufficient in food. Now it has 20M and after 30 years of neglect, irrigation is in disrepair (and in places landmines prevent maintenance). So growing 4 times the wheat wheat for food on less land is no more economically viable. Only viable product is heroin (poppies need no irrigation, and is easy to transport), and population is still growing. Will we force them to grow wheat and starve? Provide with free food? Buy heroin from them?
* Will be countries which profited most from industrial revolution and which become rich by extracting carbons from earth and releasing them to atmosphere (Europe and USA) required to pay for climate remedies? How such rules will be enforced? By carbon extracted?
Yes, it will definitely will be interesting, and unlikely of anything we've seen before. yes, it **does** mean end of world as we know it.
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The problem of such a climate change (the same as our current one) is not so much the magnitude (there will still be inhabitable zones), but the speed. While many animals might be able to migrate (and many won't), plants simply can't migrate very fast. This means that if this change happens fast enough, the only plants that will be in conditions favorable to them will be
1) some very rough ones (I have no clue which plants, though, probably grass)
2) human cultured plants and trees
Humans can speed up the process of migration, but essentially you will probably lose 99% of all species. In addition, if the climate change is this big, it may be that the oceans get warmer as well. This will wreak havoc for the sea life near shores, and might cause other disasters as well (more evaporation = more rain, algae growth, ...), that might affect both land life and deep sea life.
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My guess? Probably not, as human life depends on having a lot of ecosystem to support it. Start with the fact that photosynthesis basically stops at high temperatures: C3 (the great majority of plants) shuts down at about 45C, C4 at about 55C. (This is leaf temperature, not air temperature, and leaves in sun are likely to be warmer than the surrounding air, unless they can cool themselves by water transpiration.) So, since all life (barring ocean vent communities &c) ultimately gets its energy from photosynthesis, you've drastically reduced the size of the available life support. MAYBE some humans could survive on that, but you've also reduced the margin of error.
And there will be errors. For instance, the postulated sudden warming will actually kill off a lot of life. (That is, trees in the tropics will not instantly be replaced by trees in the polar regions, as even under favorable conditions they'll take decades to grow to any size.) The decaying organic matter could trigger an anoxic event (<http://en.wikipedia.org/wiki/Anoxic_event> ), with release of H2S that kills off even more life...
AFAIK, the closest real-life example to such a sudden warming is the Permian-Triassic extinction event, AKA the "Great Dying".
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Could people survive intense global warming?
If I'm understanding the sense of the question, I'm guessing probably not.
**Disclaimer #1:**
@JanDoggen in comments, and answers from @Larethian and @kutschkem, all make a point of questioning **how fast** the change takes place. **This is a key parameter:** given a long enough timeframe, survival of the human species at these temperatures is much more plausible. However, because of the way the question was phrased, I'm going to give **an answer that assumes an extremely fast warm-up: 50° Fahrenheit (28° Celsius) in no more than 200 years.** That seems implausible in planetological terms. But hey. This is Worldbuilding.SE, and we traffic in counterfactuals *all the time*. :-)
**Disclaimer #2:** Just to be clear on one thing: **My answer doesn't apply to the actual world we live in, because neither does the question in the first place.** @abcde is asking an interesting worldbuilding hypothetical, and I'm treating it with the respect it deserves.
(I feel I have to say this because, in my experience, questions like this tend to activate our genuine concerns about our primary world. This can make sound reasoning difficult, and carry the discussion off-track. Arguing our opinions about what's actually going to happen to us and our inheritors would step all over the original question and not be particularly helpful to @abcde.)
### Why humans probably wouldn't survive such an intense global warming event: This is a question of planetary ecology.
With a tip of the hat to @JackAidley and @jamesqf, the question of human survival is less a question of how you find a survivable latitude/altitude in the rapidly heating world. It's about **what happens in the years after you've arrived.**
Many of the answers here assume, rightly, that humans would have to migrate for survival. Migration is hard;
but let's talk about the survivors. **Let's talk about the skilled, prepared, and *extremely lucky* people who actually make it** to some reasonable place in northern or southern uplands.
Suppose you're one of those lucky ones. You've found a place. Now what are you going to do for food? Never mind medicine, weapons, shelter, etc, and let's take sufficient drinking water as a given: **if you don't have food you won't live.**
Humans are, in the short term, a whole lot more agile and adaptable than their food base.
* **Humans can travel; farms and gardens and orchards cannot.** The best you could have done would have been to carry a lot of seeds - since you are, by definition, lucky, you didn't have to eat your seeds on the march - and to bring some skilled agriculturalists with you.
So, you plant your crops. And *most of them die*.
They die because
+ they need nutrients that they can't get, or
+ because the winds are too savage, or
+ because the cycle of drought and flood is too extreme, or
+ because rampaging pests *that you have no idea how to handle* kill them.In other words, **your food crops are not adapted to the new local environment, and *cannot* adapt because the environment is still unstable.**
If you look around for native vegetation that has edible parts, you're probably not going to find anything, because the changing climate has probably already killed a lot of the local species. (This local ecological collapse probably has a lot to do with why you can't find those nutrients your crops need.)
...So maybe you brought animals with you?
* **Herds and flocks of domesticated animals are a lot more difficult to take with you** on your long march. Many of them wouldn't have made it; but remember: you are one of the unreasonably lucky ones, so you have enough of a herd to form a stable food base for your little community of settlers.
Now. What will those animals eat?
You need a lot of grazing to support a large herbivore. (You should see what *just two* of my horses do to the grass in their fairly generously sized paddock.) Even under reasonably stable conditions, grazing animals will eat a lot of pasture down, which is why pasturage needs to be rotated several times during growing season.
**How much pasturage can you count on when there's a drought? Or a flood? Or a blight?** All of which will be happening.
Then: what do they eat in the winter? Did you - despite the probable insufficiency of pasturage - **also manage to get enough hay mown in the summer** that you can feed your animals the whole winter through (which means, until pasture has grown enough to let the animals graze?)
And **yes, growing seasons will be an issue:** Even in a rapidly warming climate, you'll have colder times; and even if your winters remain warmer, **plants don't feed on warmth, they feed on sunlight.** If you've gone far enough north or far enough south, you've got parts of the year in which insolation is so weak that you won't get much to grow.
**You can't run away from ecological collapse.** The weather patterns will remain crazy. The pests that attack and kill your crops and animals will remain [r-selected](http://en.wikipedia.org/wiki/R/K_selection_theory) and thus prone to wild outbursts of population. And the organisms best suited to survival in an unstable environment are microorganisms: bacteria, viruses, yeast, fungi. Things that will kill you and your attempts at sustaining a food population
Even @GrandmasterB, in the most staunchly optimistic answer, notes correctly that
>
> "The biggest impact I think would be the years following as agriculture **tries to** adapt." (Emphasis mine.)
>
>
>
In this unusually fast warming scenario, agriculture, along with other means of obtaining food over time such as hunting, fishing, and animal husbandry, will all fail because of the ecological collapse.
**Humans in an intense global warming event would die off, probably, because they couldn't sustain themselves and their food supply over the long term.**
### Coda
Kudos on this one to @jamesqf. He deserves credit for a lot of key insights:
* Mentioning the [Permian/Triassic extinction](http://science.nationalgeographic.com/science/prehistoric-world/permian-extinction/), in which a worldwide ecological collapse brought life to a very rudimentary state.
* Mentioning the possibility of another [Ocean Anoxic Event](http://en.wikipedia.org/wiki/Anoxic_event), which would disastrously prolong any post-warming ecological collapse.
* And, probably most powerfully, the comment that says **"And that's my basic point: humans are supported by a lot of mostly unappreciated ecosystem. How much of it can you knock out before it collapses?"**
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First and foremost, not **everyone** would be able to survive. Much of it depends how quickly this warmup happens: if it's quick and the ice melts very quickly, people on the coast aren't going to get out in time and you'll get much loss of property and life. If it's slower, you'll get less loss but more people competing for the remaining land.
This is the important point really: all the remaining people are going to be competing for much less land. It has been estimated (I'd link it if I could find it) that we'd lose 10% of the Earth's landmass if the ice all melted. The current estimate is that Earth can support around 9-10 billion people (call it 9.5 for now). With 10% less land, that figure goes down around 10% as well (not exactly because of other factors such as percentage arable land, but near enough), so we'd only be able to support 8.65 billion. Theoretically that's doable, but it's not going to work out that nicely.
The heat wouldn't be too much of a problem. 50F is what, 30C? If we stay inside most of the time and most buildings are air conditioned we could survive. It won't be comfortable though.
Finally, think of the impact of more people trying to squidge into the same space. We'd have to make space for some less desirable groups in our countries, such as IS and Al-Qaeda. Admittedly them killing people faster than ever before is going to make more space for everyone else, but do you really want another Holocaust?
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So yes, in theory this global warming is survivable. However, I for one would be very interested to read about how humanity gets through without destroying itself. Does technology save it? Is there some diplomatic miracle? Who knows.
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While it probably wouldn't spell the end of humanity on earth there'd probably be a drastically reduced population.
Far less of the earth would be habitable by humans without the use of technology - air conditioning etc. Therefore we'd need use more energy to survive in a much smaller area. This probably wouldn't be sustainable. The new temperatures would affect what crops we could grow and animals we could farm so food could well be scarce too.
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It wouldn't be that large an issue for survival. Colder areas warm more than the already hot areas. This is because cold areas lose sunlight reflecting snow cover resulting in further warming, while hot areas gain evaporation that increases cloud cover and moderates warming. So very little area, possibly none would become uninhabitable due to heat compared to increases in habitable area in cooler climates.
The real problem with global warming is that it is happening faster than we can adapt. Areas that we rely on will be lost to sea or deserts. Including many major cities. Increases in agricultural land somewhere far away are not much of a consolation to people who have to leave their homes behind. And when this happens to hundreds of millions of people in short time, world will have major problems. Large social, political, and economic upheavals would happen. Possibly including wars.
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I would suggest surviving intense global warming would be technically possible for a few "chosen" people. But the issue is not so much intense global warming but on how intense. IF there was the wide variance of the planets warming as it is now, some places would not sustain life unless specialised, but others could. If oceans are looked at, in times past, the convener belt ocean current type of heat transfer could make some areas more or less inhabitable. For the most part, it's suggested we are not able to influence actual planetary climate, and it comes in cycles, so this is the reason migratory patterns for birds and other species to have become established. I would think this might become the pattern for life in the future, and I think species could adapt, depending on the level of increase of global warming. BUT don't be alarmed. Global warming has left a lot of unfinished questions in the "science" of planetary climate and it may be that we are in for global cooling if patterns repeat. Look up this site, <http://www.landscheidt.info/> for more questions...AND KEEP ASKING QUESTIONS.
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A 28˚C increase probably kills all life on Earth in the long run, except perhaps bacteria deep underground or in the upper atmosphere, because it turns the Earth into Venus. We're already very close to the inner edge of the habitable zone around the Sun, and such a big increase would push us over.
The problem is that the upper atmosphere gets full of water vapour, which photodissociates into oxygen and hydrogen, and the hydrogen then escapes into space. Over millions of years, the Earth loses all its water. With no plant life, CO2 emitted by geological action is no longer removed from the atmosphere and we get a runaway greenhouse effect ending up with a dense CO2 atmosphere and a very hot surface temperature.
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[
So, lizardfolk are humanoid (and, so, upright) creatures with reptilian features and are also [part-time endotherms](https://en.wikipedia.org/wiki/Argentine_black_and_white_tegu#Warm-bloodedness). They're well-adapted to living in water and on trees to a degree. One adaptation for of that is a large tail [that can be used for swimming](https://www.youtube.com/watch?v=_MZFRSKUqxA&feature=youtu.be&t=43). Of course, they can and will use their arms as well.
Now, the problem comes from the fact that lizardfolk are bipedal and I'm afraid their tail could end up throwing them off-balance.
In paper, they can use their tails in a number of different ways, including the aforementioned swimming aid and swiping/flicking it. Since the tail has powerful muscles, these move can be effective at stunning human opponents. I'm not sure if they could create an entire martial art around it though.
**The question is, what would a lizardfolk's tail actually look like then and how would it avoid causing problems with the creature's balance?**
Note: Despite what some people think, lizardfolk do have emotions, though they have trouble communicating them. For that very reason, they tend to avoid social media in every shape or form.
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Note: How these lizardfolk are supposed too look like?
In terms of posture, I had the argoninans from Skyrim in mind. However, the reptilian features, like scale type, patterns, color, head shape and tail type came from the Asian water monitor.
[](https://i.stack.imgur.com/hEfuC.jpg)
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First I need to mention that bipedal is different than upright. A t-rex is bipedal, it is not upright. So you may want to clarify what you want.
The tail should actually help balance not hinder it, the trick is they need a forwards sloping torso. The only question you need to answer is how upright you want them. bipedalism evolved more than once in dinosaurs. Some were very horizontal like the classic "raptors" others were more upright, like one of the therizinosaurs (below), who have a nearly 90 degree turn in their spine at the base of the tail, because their tails are small their torso is huge and they have an upright posture.
[](https://i.stack.imgur.com/e1amp.png)
A posture something like this should be possible, if anything the tail shown is too small for the torso shown.
[](https://i.stack.imgur.com/tYyf5.png)
Warhammer does a decent job of it as well.
[](https://i.stack.imgur.com/6GNdf.png)
Of course this depend on the size of the tail as well, the bigger the tail the more forward slung they need o be, that is the more weight of the rest of the body needs to be shifted forward to keep everything balanced.
there are several ways to do this. 1. having long necks and snouts will help move the center of gravity forward. 2. swing the upper body forward, make them "slouch" however the broader and more muscular you make the upper body the less forward slung they need to be, dinosaurs had relatively slim shoulders, more human like shoulders and arms will add more weight to the upper body. 3. Your best bet is to combine the two as shown. Keep in mind you can shift the point of contact for the feet back slightly as the first artist did, that movers the whole center of gravity forward without actually moving the center of gravity.
Also keep in mind they won't have a butt to speak of, a rounded bottom is a mammalian thing, becasue the muscles that move the hind legs don't connect to the tail like it does in everything else.
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Similar to a t-rex tail, I suppose. They were also bipedal reptiles. Or perhaps like a large bird. If the tail is flexible and quick enough, it would actually help them balance when they're ruining on trees, like it does for cats, monkeys, etc. Since reptile tails are generally thicker and heavier, their torsos would have to be bent forward to counterbalance the tail. 
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**Curly tail**
Your lizard folk have tails that curl up and around, like this aptly named curly-tailed lizard.
[](https://i.stack.imgur.com/dkiLV.jpg)
<http://lizardsandfriends.org/?p=573>
Often these bipedal lizardfolk wear their tails curled around their shoulders, which makes them look buff and helps with the center of gravity. Also helpful is that many of these individuals have two tails which improves symmetry. Liz here shows how how these tails would look. The tails on Liz happen to be a lighter tone than the rest of the body, and Liz is wagging them so you know they are tails.
[](https://i.stack.imgur.com/8HwNG.jpg)
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One possibility is that the tail can rest on the ground
(like your pictured monitor lizard),
actually giving them better balance than humans.
This could be just when they are standing still, or also when they are walking.
In the former case, they would probably lean forward when walking. Running could also go either way.
One downside of this could be that, when using a tail slap as a weapon, they are likely to lose their balance.
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**If by some form of magic, the sun went out, but the earth was still warm a.k.a the Earth did not just freeze and kill us all, who would die first, and how long would it take for all terrestrial living things in the world to die?**
I can hypothesize that all the plants would die out first before all the humans do, because we have canned food (hooray for canned food), and plants can only live around 6 months without light, so assuming everything was going normally and humans have had ~1 year to prepare for this event, a.k.a. governments spending all money on creating food, and none on their militaries, healthcare, etc, how long would it take for all the living things on the planet to die out? What about for each kind of living thing: bacteria, plants, animals, etc.?
***EDIT: I don't know if this is fake news, but [it says here that astronauts might be able to eat their own feces in the future.](https://www.thrillist.com/culture/nasa-awards-200-00-to-a-study-to-find-a-way-to-eat-their-own-poop-new-nasa-technologies) Could this prolong the life of humans? Could this machinery even be implemented without extra energy?***
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# How fast will the Earth cool down?
This is going to be the dominant factor. If it takes too long to cool down, then maybe all the plants will die without sunlight and creatures will starve to death. But if it cools down fast enough, everyone will freeze.
We can apply the Stefan-Boltzman law to find out how fast we will cool down.
### Earth's radiation
The simplest model of the Earth is that of [radiative equilibrium](https://en.wikipedia.org/wiki/Climate_model#Zero-dimensional_models). This sort of radiation is governed by the [Stefan-Boltzmann law](https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law):
$$j^\* = \epsilon\sigma T^4$$ where $j^\*$ is irradiance in W/m$^2$; $\epsilon$ is the emissivity of Earth; $\sigma$ is the Stefan-Boltzmann constant, $5.67\times10^{-8}$ W m$^{-2}$K$^{-4}$; and $T$ is temperature.
The effective emissivity of the Earth is often considered 0.612. The average temperature of the Earth's surface is 288 K.
### Integrating over time
Now, here come the warnings. Earth's emissivity is powerfully controlled by cloud formation. Changing the temperature of the Earth will radically change the cloud makeup. In addition, if the Earth cools and snow and ice form, that will drastically change emissivity as well. However, I don't have the tools to model all those things, so I am going to consider a model where Earth's emissivity is constant as it cools down.
The heat loss of Earth is a function of its irradiance. But it is also a function of the Earth's heat resovoir. Let us assume (and this is very spherical cow) that the top 100m of the Earth's oceans along with the top 100m of its land area will freeze. The oceans cover $3.6\times10^{14}$ m$^2$; the volume at 100m depth is $3.6\times10^{16}$ m$^3$. The volumetric heat of seawater is $3.9\times10^6 \frac{\text{J}}{\text{m}^3\text{K}}$. Land covers $1.5\times10^{14}$ m$^2$;The specific heat of various types of rocks times the density of Earth's crust gives us a volumetric heat of $1.8\times10^6 \frac{\text{J}}{\text{m}^3\text{K}}$.
Overall, the heat capacity of the Earth is 1.7e23 J/K. Finally, the irradiance needs to be scaled by the surface area of the Earth ($5.1\times10^{14}$ m$^2$). This gives us what we need to define a differential equation for the cooling down of the Earth
$$ \begin{align}
\frac{dT}{dt}\ &= \frac{0.612\cdot5.67\times10^{-8}\text{ J m}^{-2}\text{s}^{-1}\text{K}^{-4}\cdot T^4 \text{ K}^4\cdot5.1\times10^{14}\text{ m}^2}{1.7\times10^{23}\text{ J/K}}\\
&=1.0\times10^{-16}\cdot T^4 \text{ K/s}
\end{align}$$
### How fast will the Earth cool?
At the above calculated rate, the Earth initially cools at 1 K in about 17 days.
We can also solve this differential equation for a temperature drop of 15 K, which will bring the Earth's top 100m to freezing conditions at 273 K.
$$\begin{align}
\frac{dT}{dt} &= 1.0\times10^{-16}T^4\\
\int\_{273\text{ K}}^{288\text{ K}}\frac{dT}{T^4}&=1.0\times10^{-16}\int dt\\
\frac{-1}{3}\cdot\left(\frac{1}{288^3}-\frac{1}{273^3}\right) &= 1.0\times10^{-16}t\\
t&=2.4\times10^{6}\text{ s}
\end{align}$$
This number is in seconds, and is equivalent to about 281 days.
# Conclusion
The Earth stores a lot of heat. The top 100m of soil and ocean store enough heat that radiating 1 K of it into space will take more than two weeks, and freezing it will take most of a year.
The dominant factor in killing all living things will be the death of plants by inability to photosynthesize. There are many plants on Earth, and they will take varying times to die, but it would be reasonable to assume that within 2 weeks, no new vegetation will grow. From that point, it will take as long as all herbivores will take to consume the remaining plant life to destroy the food chain. I would estimate that within a month, most animal life would be in extremis.
Some animals might survive longer, like vultures. Certain bacteria will survive indefinitely, such as chemotrophs. Bacteria living deep in the crust in deep sea vents might not be affected for hundreds of millions of years.
So in general, *all* life will not be extinguished for as long as billions of years, but surface life as we know it would collapse within about a month.
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If the Earth is somehow heated, then not everything is lost for the humanity.
Plants and animals will die out without the sunlight. First the diurnal ones, then plants and algae, then the nocturnal ones, then soil inhabitants and ocean bottom feeders. Warm Earth by itself can not provide any sustenance to the lifeforms, so after all atmospheric oxygen is used up, this will be the end. It will take thousands of years to get there, and some organisms can feed of volcanic chemicals and stay alive indefinitely, but this is a pretty bleak picture for the Earth. Without humans.
Humans can make things different - not for the entire Earth, but sufficiently to maintain limited biomes and some population. If we would have light, we can have food. To have light, we need energy. In this scenario, there still be enough of it. First, Moon will still be up there. Invisible, it would still cause tides. Tidal energy can be captured and used. Second, if the Earth is heated, we still going to have wind and ocean waves, maybe even hurricanes. That's even more energy.
Everything we need to do is to build a lot of tidal and wind power generators, and set up farms with artificial lighting (just like cannabis is grown at homes). Unfortunately, only a fraction of today's 7 billion population can be saved this way. So, some dramatic (and maybe violent) events would be inevitable.
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# The Solar System
The first thing that would happen to Earth, immediately after the sun disappeared... would be nothing. It takes a bit under ten minutes for light from the sun to hit Earth, so it would look like the sun was still there, for a while. Earth would even still be in the sun's gravitational field would also last some minutes, as the sun's gravity takes time to reach us.
Once we were hit by the most beautiful night sky in human history, the Earth would would be flung out into space, away from our solar system. From this clear view of the sky, we could easily see Jupiter and the other planets--sitting in the sky like nothing had happened. The sun's light is still reflecting off of them, and being further away they have not yet been "hit" by the lack of gravity.
The exception to this is Mercury and Venus, which being closer to the sun, have already gone through our dilemma. We probably won't be able to see them anymore, without the sun's light reflecting off of them (maybe we can with certain telescopes).
# Oxygen
On the bright side, it'd actually take us forever to suffocate. Sure, all the plants die in a few days, and we have no way to recycle carbon to oxygen, but the atmosphere will stay mostly breathable for many centuries. Though, if we survived any length of time, the breathable air around cities could be pretty bad, without any parks or plants to regulate the local oxygen.
Many trees would survive for a year, before the growing cold killed them.
# Freezing Cold
Within the first week, temperature would hit 0 Celsius, freezing, and you could walk across the frozen sea. That would be the good times. Many people would die in the following weeks from the sudden temperature shift, the poor in hot countries in particular would soon be freezing and sickening.
# Storms
The Earth itself would become sick with the sudden temperature change, and terrible blizzards would rage across the world. The storms would eventually cease, maybe after the first month, and the weather would become much more stable across the globe.
In fact, when the last storm finished... there'd be no wind. Without the sun, wind would become a local phenomenon.
Snowy weather would become more and more rare as time passes. Without the sun to evaporate water, the only source of evaporation would be geothermal springs. And without the sun to heat the clouds and change temperature, they'd mostly stay up there in the cold sky; supercooling well past the freezing point.
# A year later
After a year, it'd get real bad... Temperatures would hit -100 degrees Fahrenheit. The coldest temperature I've been able to find for human habitation was a research post, at -97 degrees Fahrenheit. A couple of cities have also survived winters of -90 Fahrenheit, though I don't know the details for how well they could keep that up.
While those equipped for it could survive, a huge portion of the human population would die. Every plant on Earth would die. Most of the animals across the world would die.
# The animal world
For the first few months, the animals in the Night-half of the North Pole would notice no difference. They might get hit by the weeks of storms, but otherwise life would remain unchanged. By the time a year has passed, though, they would've reached a temperature on par with their coldest ever winters, and most of the animals would soon die. It is unlikely, but possible, that some animals will manage to survive for a while longer... only to die of starvation, as what little plantlife there is cannot be renewed.
Surprisingly, insects like the Red Flat Bark Beetle would be among those that survive the cold. They would eventually die out all the same, as their food source (wood-eating beetles) succumbed to the cold. Even if their food source survived, the dying trees would eventually be eaten away. The Upis beetle would outlive the Flat Bark, by freezing--going into cryogenic hibernation.
Cockroaches and rats would also survive in human compounds, though they might disappear entirely from some cities.
Animals who live near hotsprings may survive and adapt to this new world for a while... only to die when the death of plants and eternal winter causes them to starve.
# Surviving
To survive the cold, you either need insulation and power, or hotsprings.
The easiest way to stay warm is to dig deep underground (which will get harder as the cold freezes the ground). Underground living will become quite comfortable, losing its chief disadvantages. Underground, you have to worry about rain, and sewage management. But in this scenario, all your sewage will be recycled, and there won't be a problem of rain anymore. Underground living will help you keep warm and safe, with minimal power consumption. You will, however, need to go to more effort to ventilate your air.
To survive starvation, you need either large food stores (which will run out), or a lot of power and a meticulous setup.
With power and insulation, it isn't too hard to keep warm, and even ventilate your compounds. The real drain on resources will be cultivating food. Mushrooms can be cultivated easily enough, and will begin to make up a large part of your diet as an economic food. But generating enough light to grow crops will be challenging. Without crops, most farm animals are useless.
So largely you'll be eating mushrooms, and vitamin tablets, and eventually lab-grown yeasts and the like to make up for the dietary deficiencies. The most obvious and important deficiency is vitamin D, as you no longer have the sun.
What experts survive this period on stockpiled foods will be working hard to genetically engineer better mushrooms and yeasts, while in the long term desperately searching for this new world's philosopher's stone: Fusion Power.
# The Future of Power
If Fusion energy is developed, a small population of humans might live millennia is this cold night world.
Even if not, there is enough uranium for the *current* population of Earth to survive at its *present* level of consumption, for 200 years. If consumption of power becomes 1% of what it is now, nuclear power alone could keep humanity going for 2,000 years.
# Clean Air
So, adding in coal and other fossil fuels, humanity should be able to survive with a reasonable population. Of course, without plants, the fear of carbon contaminating the atmosphere would become extreme. The fear would be much worse than the problem.
Even without a breathable atmosphere, it's quite practical to power a greenhouse and use it to recycle your air. This will be the main purpose of vegetables, to recycle air. The mushrooms are no good for this... they breathe oxygen too. So the more mushrooms you grow, the more vegetables you'll have to grow (like some kind of resource management sim!).
# Mining and Scavenging
There will be a lot of scrambling in the early days to grab stuff from the stores (natural refrigeration) and steal supplies to survive. After people settle down into compounds, the main source of work will be scavengers braving the cold to get more supplies.
Eventually, when scavenging materials run short, we'll have to resume mining operations. In the extreme cold, it will be difficult to travel, prospect, and transport minerals. But the mining itself won't be too different. It's warm underground, and most of you will live underground anyway.
# Conclusion
So, in the end, we might survive long enough to develop interstellar travel and adapt to this world - barring any unfortunate collisions with asteroids and meteors. Since the Earth is hurtling off into space all this time, this may even help us launch off towards the nearest star.
[Answer]
A very spherical cow, indeed. When ice forms on the surface of the ocean, this will provide an insulation barrier. Would Earth wind up like Europa?
This question has been answered in The Straight Dope:
<http://www.straightdope.com/columns/read/3293/if-the-sun-goes-out-how-long-till-the-earth-freezes/>
The Earth may store a lot of heat, but we probably care about the surface temperatures, which will drop more quickly. As other have mentioned, at night, in desert, temperatures drop far more quickly.
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[Question]
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**This question already has answers here**:
[How Useful Is Super Strength (for punching)?](/questions/28062/how-useful-is-super-strength-for-punching)
(5 answers)
Closed 7 years ago.
Assume a humanoid with greatly increased strength. He (or she) throws a massive direct punch at the middle of the breast of a human, who is standing in range.
Assume a punching force of about 1000 KN.
Assume that the fist (and body) of the attacker are durable enough to make this work.
**What is the effect on the body of the victim? Will the punch go directly through the body?**
If you want to elaborate, these points are of great interest to me as well:
* Are there any interesting side effects?
* How would body armour (with plates) affect the process, if at all
* Would this ability be useful in ranged and melee combat? In modern combined arms battles or special forces scenarios.
* NEW: What role does the weight of the fist play?
* NEW: What does happen, if the punch lands on a tank for example? You may crank the force up for this. If the fist is hard enough, can it punch a hole in the frontal armour of a tank?
Trivia: I watched a lot of superhero flicks, and superhuman strength always sends the opponent flying. Now that I am about to include such an ability into a worldbuilding project, I am interested in what really would happen. Thanks!
EDIT: Thanks to Cort a clarification:
The speed of the fist is at least an order of magnitude higher than it would need to be to avoid the victim's body to be able to "escape" the punch.
I was requested to "defend" this question. The Anathema already did a good job on that one. Thanks.
[Answer]
"It depends" Surprisingly it depends more on the opponent than the one throwing the punch.
Depending on circumstances, it could tear straight through (that is 100 tons of force!), or it might just push the opponent back. Certainly the opponent won't get the opportunity to say no.
By Newton's third law, if your hero can punch their opponent with 100kN of force, their opponent must be able to exert 100kN of force in the opposite direction. How they do that depends on their body. Take an example where they are up against a wall when this happens. They'll exert their 100kN of force by exerting 1000kN of force against the wall, holding them in place. In this case, the punch will have an effect worthy of any B-rate horror flick, because the only thing left to give is their body. Armor wont have any effect at all unless it is rated to withstand the combined weight of 2 M-1 Abrams tanks resting on it.
However, in the case where they can move, the story is a bit different. You can only exert 100kN of force if they can exert a corresponding amount of force back. If the punch is slow enough, you can punch with "up to" 1000kN of force, but you find yourself limited by the opponent moving backwards in response. Intuitively, if you were up against a hydraulic ram which was used to slowly bend steel tank armor, it would move slow enough that you'd get out of the way. The ram would never reach maximum force. To reach maximum force, you have to strike fast. That's where it starts getting interesting.
I say it gets interesting because the more agile your opponent is, the faster you're going to have to strike to achieve 1000kN. Striking a mosquito with 1000kN may require punch speeds far in excess of mach 1, because the mosquito has to be accelerated *remarkably* fast before F=ma can reach 1000kN. Fast accelerations are caused by high speeds with respect to the target's ability to respond.
If your punch ever exceeds the speed of sound in the opponent's fleshy chest, things start to get strange. You start to see shockwaves because the information about your punch cannot reach the opponent's extremities fast enough. This permits all sorts of strange sheering effects. I've heard NASA has some interesting videos of what hypersonic collisions look like.
If you're limiting yourself to human *speeds* for the punch, you wont be able to reach 1000kN without something like a brick wall behind your opponent. As a result, they will be exactly as unhappy as they set themselves up to be. A highly skilled martial artist may be able to react in a way to convert most of the energy into backwards motion for his entire body. A less skilled fighter may not, letting a massive amount of energy strike the front of his chest against the further back parts of his chest. His heart will not be happy.
Edit: given the clarifications we can explore more. If we assume the punch is fast enough that the recipient cannot get out of the way, the next layer of the question is pressure. How much pressure can you exert with your 1000kN of force, vs how much pressure can the object endure? The key for this is a concept known as "yield strength" this is a knee in the "stress-strain" curve. Below the yield strength, something will typically rebound back into its previous shape. Above that yield strength, it will permanently deform plastically.
You can do a lot of damage here with these forces. Take 4" rolled steel tank armor, used during WWII. It's yield strength is 688.5 MPa. Any pressure above that will permanently deform the steel in some way. If you have 1000kN at your disposal, you can deform the steel as long as you concentrate that force over 12 square centimeters (1000 kN / 950 MPa = 10.52 cm^2). The front surface of my fist is about 30 cm^2, so I couldn't *quite* damage the steel with the whole surface, but if I focused on my knuckles I could easily put a dent in 4" rolled steel. If I had sightly more force at my disposal, like 3000kN, I could actually put fist shaped indents in steel. If I could somehow sustain that 3000kN for the length of the entire punch, I could either *severely* dent that armor, or rip straight through, depending on the physics. The only real limit is the point where I move the tank rather than punch through it, which you explicitly took care of in your edit.
Now you can imagine the chunky salsa that will occur if we repeat that experiment with a human that doesn't get out of the way of this blow in time.
[Answer]
So the physics of superhero movies is shall we say...not accurate.
That much force applied to a solid object, say a block of wood or metal would likely send it flying as bodies tend to in a movie.
If on the other hand you are punching something squishier or even things more brittle it simply wouldn't work that way.
If you punch a person that hard at the very least it would completely cave in the chest cavity if not outright penetrate the body. That would absorb a lot of the force and while the body (in the case of chest cavity crushing) would still fly backwards it wouldn't be nearly as far or dramatic. If the force was strong and fast enough to puncture the torso the body may barely move backward at all.
Getting away from bodies things like concrete or even stone would be likely to fly a little but in much smaller pieces, the stone wouldn't fly as a whole but rather as a bunch of sharp quick moving projectiles and they would fly in various directions as the force would enter the stone and go both forward and sideways.
**The short version is what you punch will determine what happens.**
Moving on to your more specific questions.
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> Are there any interesting side effects?
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Not particularly no. The biology would have to be radically different for this humanoid to exist which can have whatever side effects you want really. The only required side effect would be a necessary increase in body density. So they would be significantly heavier than a normal person, otherwise punching something that hard would send them flying backwards.
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> How would body armour (with plates) affect the process, if at all
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This has been addressed in some other questions [namely this one](https://worldbuilding.stackexchange.com/a/32908/189). At a certain point armor ceases to be effective as the force will kill the person in the armor no matter how strong it is. Humans can only take so much force before they squish...hence Iron Man...while awesome is completely impractical.
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> Would this ability actually be useful in ranged and melee combat? In modern combined arms battles or special forces scenarios.
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In antiquity it would have been very obviously beneficial, swinging a giant sword, punching a cavalry charge in the face, using a ballista as a longbow...you get the idea. In modern combat the biggest benefit would be their nearly invulnerable frame and skin...if weapons can't penetrate them well then you are going to have a hard time, but skills like this would be wasted on a standard grunt.
On the other hand these individuals would make amazing special operations forces. Helo airlift may prove a challenge with their added weight but other than that these guys could do serious damage on the covert side of things.
As a side note if they were air dropped in the parachute would have to be massive...I suggest night ops lol.
[Answer]
Striking that hard and fast would have the same effect as shooting a cannon ball through them. You'd be standing there with your arm up past the elbow stuck through their chest.
Any form of impact works by accelerating the tissue impacted. If the acceleration is slow enough that the tissue can absorb and disperse it then there is little motion of the target although it might do enough internal damage to kill.
If the acceleration is slow enough that the tissue can absorb it, but the impactor has large momentum, then you have shove, which accelerates the entire body along the spatial vector of the impactor.
If the acceleration produced by the impactor is so fast that the surrounding tissue cannot stretch or flex to absorb it, then the tissue tears. If the impactor has enough momentum the tearing continues all the way through the body. That how a bullet does damage.
The rule is that the smaller the impact surface relative to the momentum of the impactor, the less energy gets transmitted to the target. Two objects with the same velocity but with different areas of impacts will have different effects. Getting hit by a 50 gram ball of aluminum foil 20cm wide going at 200kph will sting a bit. Getting hit by a 50gram needle of aluminum with an impact area measured in micrometers will punch a hole through you so fast and clean you won't know you've been shot.
No bullet or shot of any size will knock a person backwards. All the energy in firearm projectiles are so concentrated they destroy only the tissue along their flight path ripping it away from surrounding tissue without accelerating it. People who get shot just drop.
I shot a lot of animals in my childhood on the farm from squirrel size to deer and they all drop. Made a long range shot with a deer rifle at a squirrel once just so see if I could hit it. I did and the bullet punched out a big hole and the rest of the squirrel just dropped out of the tree in a blizzard fluff, much to the confusion of my dog.
So, if you start hitting people with the momentum per impact area of a firearm projectile, the effects will be the same.
[Answer]
1000 kN of force, applied fast enough that the target isn't just "moved back" by it. Let us assume that this means that the punch force extends over about a chest-thickness -- 20 cm -- to get an idea of what happens.
This is 200 kJ.
If the energy was turned perfectly into kinetic energy over an entire 100 kg target, we get 63 m/s, or 227 km/h.
f = ma; 1000 kN / 100 kg is 10 km/s^2, or ~1000 gravitates of acceleration.
63 m/s / 10 km/s^2 is 0.0063 seconds. Which means the fist is moving at an average of about 32 m/s or 114 km/h -- in practice, the fist will have to change speed to provide a uniform 1000 kN force. (a fist that moves at a fixed speed, without any give, regardless of what is in its way, will inflict unbounded force)
So if the target was wearing perfect body armor that distributed the impact over the entire body, and used fluid to keep pressure up -- the target would probably still die. The highest g-force survived by a human is 214.
Without the super-armor, you can approximate this by driving at high way velocities and throwing a lead fist-sized ball at someone. That won't work perfectly, because it will be slowed down by the impact. But it is an experiment Mythbusters can do.
Alternatively we can do math: Bone has a shear strength of ~50 MPa -- if the fist is 30 cm^2, 1000 kN is ~1E11 Pa, or 100 MPa. Flesh has less shear strength than Bone, so the fist won't pull the rest of the target along -- it will penetrate.
We could presume that about half of the force will spread as it shears through the body, and the rest will "pop" through. So you'll end up with your fist sticking through a body that is flying away at about 44 m/s or 160 km/hour.
Ick.
The G-forces suffered by the rest of the target in this situation are about 600 Gs; so even if the fist-sized hole didn't kill you, you'd be dead.
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On a tank, 1000 kN of force on 54431.1 kg generates 2 Gs of acceleration. Over 1 meter (the length of an arm), a rigid tank is accelerated to 6.1 m/s, or 21 km/h. This will look more like a hard push than a punch; tanks are HEAVY.
Modern tank armor can take the pressure you are putting without massively deforming. The mounting system may be stressed, as tanks are not meant to be picked up and pushed around by their armor plates.
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[Question]
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The length of a day on different planets in the solar system varies a lot. For instance, Mars' day is about the same length as Earth, while a day on Venus is equivalent to 243 Earth days ([source](http://www.universetoday.com/37481/days-of-the-planets/)). And Jupiter rotates about 143 times faster than Mercury.
What determines the length of a day on a particular planet? Put another way, what factors determine a planet's period of rotation?
To make the connection to worldbuilding clearer, say I wanted a day on a planet to last two Earth weeks. What would the characteristics of this planet (such as mass, radius etc.) need to be to achieve this?
[Answer]
There is, as far as I know, only one hard factor, and that is for planets that are very close to the star (Mercury and Venus). It is believed that the long rotational period of these planets is caused by different but related mechanisms - tidal locking for Venus (gravity interacting with it's thick atmosphere) and gravitational locking on Mercury (being closest to the sun).
Among the remaining seven planets, there is a rough correlation between size and length of day, in that the planets form four groups where the length of day is similar in each group and gets shorter as the planets get larger.
1. Jupiter – 9.9 Earth hours
Saturn – 10 hours 39 minutes and 24 seconds
2. Uranus – 17 hours 14 minutes and 24 seconds
Neptune – 16 hours 6 minutes and 36 seconds
3. Earth – 23 hours and 56 minutes
Mars – 24 hours 39 minutes and 35 seconds
4. Pluto – 6.39 Earth days
However, there is ultimately too little data to really make any kind of definitive statements about the conditions causing planetary days to vary. Ultimately, this would give a world designer considerable leeway to use whatever value they wish.
However, if you dug a little deeper, you would notice that well studied moons of the Solar System all have synchronous periods of rotation - that is their rotational period is the same as their orbital period around their primary. This is caused by the same gravitational/tidal locking that affect Mercury and Venus. [Titan](http://en.wikipedia.org/wiki/Titan_%28moon%29), for example has an orbital period of just under 16 days, which is close to the value that you specified.
[Answer]
You pretty much have free range here. The speed a planet rotate depends on the angular momentum it has after forming. This is influenced by a host of factors, from the composition of the planet, to its distance from the star and the gravity it experiences as well as any impacts it experiences such as comets hitting it. See [this post on the naked scientist](http://www.thenakedscientists.com/forum/index.php?topic=40908.0) Since these factors happened in the distant past, you can make up pretty much day length without affecting your current world.
However, I would be conscious of the effect of the increased day length. If the day lasts two weeks of earth time then a point on the planets surface would be light for a week then dark for a week. The temperature swing would be enormous. During the day portion, constant sunlight drive the temperature ridiculously high, and it would be difficult for any creatures to sleep or force them to go a long time without sleep if they have any sort of day/night cycle. During the night, constant darkness would send the temperature plummiting. It would be very difficult to survive these wild swings. Plants especially could suffer from prolonged absence from the sun. Just something you need to consider after you choose your day length.
[Answer]
I assume you mean the solar day (determined e.g. as the average time between two sunrises). Although you didn't say it, I also assume that you want a planet in the habitable zone (otherwise you've got much more freedom in your choices).
# tl;dr
You want a planet orbiting a small star, ideally a red dwarf, on the inner edge of the habitable zone, and in addition a large moon orbiting the planet in an orbit with period longer than the planet's day.
# General considerations
The two fundamental determining factors are the rotation of the planet (obviously) and the revolution of the planet around the central star. Basically the solar day is the sidereal day (rotation period of the planet) times one plus or minus (sign depending on the rotational direction of the planet relative to its revolution) the inverse of the number of days in the year.
# The revolution period (year)
The effect of the revolution period (the length of a year) is low if there are many days per year, but the slower the rotation/the faster the revolution, the larger is the effect. The most extreme case is when the planet is tidally locked to the star, so that the sidereal day is exactly the same length as a year; then the solar day is infinite (the sun always sits on the same place).
The revolution period is, of course, determined by the stellar mass and the planet's distance to the star. The condition centripetal force = gravitational force reads
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> G m M/r^2 = m omega^2 r
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(G is the gravitational constant, M the star mass, m the planet mass, r the distance, and omega the angular velocity) and thus for the revolution time (length of year), T = 2 pi/omega, you get
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> T = 2 pi r^(3/2) / (G M)^(1/2) ~ r^(3/2)/M^(1/2)
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(here ~ means "proportional to").
More massive stars are generally brighter and therefore habitable planets will be further out; the distance is proportional to the square root of the stellar luminosity (brightness), because the light intensity falls off with the square. The [mass-luminosity relation](https://en.wikipedia.org/wiki/Mass%E2%80%93luminosity_relation) says that the luminosity of a main sequence star (the most common type of star, and especially the type you'd expect life-bearing planets around) scales roughly with the mass to the power of 7/2, so the distance of a habitable planet should be proportional to the stellar mass to the power of 7/4. Inserting this in the above equation, you get
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> T ~ M^(5/4)
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so the year's length grows with the mass of the central star, although the dependency is not too strong. To have a maximal effect on the day length, you want the year as short as possible, that is you want to have a small star (ideally a red dwarf), and you want your planet on the inner edge of the habitable zone. As it turns out, small stars are also the most likely to have life-bearing planets, since they have the longest life time. The search for habitable planets indeed concentrates on red dwarfs.
# The rotation period (sidereal day)
The by far biggest effect on the day length has, of course, the rotational speed of the planet. The rotational speed is normally determined by the initial angular momentum when the planet formed, but may also be altered subsequently by large collisions (as for example the collision of the earth with another planet which gave us our moon).
After that, the rotational speed is reduced by tidal forces due to the inhomogeneity of the gravitational field of other bodies.
All planets observe tidal forces from the central star; however the tidal forces fall off with the third power of the distance from the star, while they are proportional to its mass. Inserting the previous estimation of the planet's distance as function of the stellar mass, you get
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> F\_tidal,star ~ M^(-7/4)
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To have the strongest effect, you want the star's tidal force to be as large as possible (OK, maybe not too large, or you'll end up with a tidally locked planet), which due to the negative exponent in the mass again means you need a small star mass, and of course again you want to be on the inner edge of the habitable zone.
However, the star is not the only source of tidal forces; indeed, on earth the biggest tidal forces don't come from the sun, but from the moon. So to further slow down the planet's rotation, you want a large moon. Of course the moon should be sufficiently far away that its revolution period is slower than the planet's day, as if it is faster, you'll get the opposite effect: The moon will spin the planet up.
And of course, how much the planet was spun down by tidal forces depends very much on the age of the planet. An old planet will be slower than a newly formed one. Of course an old planet implies an old star, that is a long-lived one, so we are again back at the requirement at a small star.
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[Question]
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The [grey goo](http://en.wikipedia.org/wiki/Grey_goo) end-of-the-world scenario in which lots of little microscopic [Von Neumann self-replicating machines](http://en.wikipedia.org/wiki/Self-replicating_machine) basically eat everything to make more of themselves. Eventually everything is grey goo.
Assuming that they are electro-mechanical, microscopic, have a method of destroying and recombining on the molecular/atomic level, will not consume each other, derive their energy from the chemical energy released by not using all the materials they consume, rather heat/pressure-resistant due to the conditions which would form in a massive of them, and are possibly linked via some kind of network, forming a hive mind, what methods of containment or destruction (Aside from [never migrating from IPv6](http://xkcd.com/865/)) would be effective against combating this threat?
How far would they have to spread before the only option is nuking from orbit? What if they are solar/geothermic, and require sunlight to continue operation, otherwise hibernating?
Naturally, there would be some locations where they would grow faster, due to the ease of getting energy from the materials. Wood and organic material would be *rapidly* consumed, while water would take a lot of time and have a high loss of material to getting energy (seriously, what's more stable than H2O?). Could this be exploited in defense against them?
[Answer]
Grey goo is just another form of life. So the experience in combatting undesirable forms of life on Earth may be useful.
* From the experience with Earth's life we know that life over billions of years of development still did not consume all resources and space on Earth, and even did not cover the whole its surface. Even the ocean is not fully filled up, although we know that each microscopic drop of water has billions of cells and viruses.
* Earth's life undergoes evolution and mutation in its development. It is more beneficial for an organism to consume other organisms than extract the resources from the environment. This is because other organisms have higher concentrations of useful materials and their parts (such as amino-acids) can be reused.
* Any organism that consumes resources from environment very rapidly and similarly rapidly reproduces without limits, is evolutionary unstable because it puts itself in danger of consuming all resources around and die out.
* But any artificial form of life is less likely to undergo mutations than chemical life unless the mutations were intended by the creators. A random change in the program code is more likely to break the program totally than a change in DNA.
Analogy with combatting infectious deseases and incest parasites tells that an antibiotic or insecticide can be developed quite quickly. Yet the targeted form of life can develop a resistence that would make particular treatment inefficient.
Given that Grey Goo would most likely exhibit very slow speed of mutations, it is reasonable to expect that any treatment against it would be efficient for longer time and will not trigger resistence.
In the case when Grey Goo mutates rapidly, it will soon develop varieties that would hunt on other varieties of Grey Goo because it is more beneficial than mining the environment. As such an inter-dependent self-regulating ecosystem with predators will develop soon so limiting the Goo's propagation.
[Answer]
Really it depends on how they work.
**Software**
Injecting a software virus to disrupt the network might work if they are reprogrammable.
**Rival Goo**
Add your own nanomachines that take apart the first ones and rebuild them to themselves then shutdown.
**Energy Weapons**
Directed energy weapons or similar might be used to destroy them without presenting them with more material to convert.
**Resistant materials**
If a material could be developed that they cannot consume (for example a sufficiently strong alloy) then something could be built to go in and handle them.
**Power deprivation**
They must be powered by something, whatever it is deprive them of it. For example if they are solar powered a large shield could be constructed between them and the sun to shield the planet and then wait until it goes dormant.
**Singularity**
Drop them in a black hole. :)
**Sentience**
If they develop intelligence then it gets much harder as they will take active counter measures. At least then you have the opportunity to negotiate though.
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Even something as fearful as gray goo von Neumann machines must obey the laws of physics. The nano machinery would require raw materials in the proper proportions, energy of the proper type, the ability to rid themselves of waste heat, and time to act.
**Time**
Time can't serve as a barrier but neither are these machines going to turn the surface of the Earth into gray goo overnight. Visualize the gray goo nanomachines as comparable to biological analogs. These analogs would take decades or centuries to colonize the whole Earth and I suspect the same is true for the nanomachines.
**Material**
The nanomachines can't just use any elements. They must have the elements they need in the proper proportions. If they find a barrier that consists of a single material (especially one not used by the nanomachine), they might not (probably wouldn't?) be capable of burrowing through that barrier.
**Power**
I assume that chemical power would be too feeble and unwieldy to carry with the nanomachines. Therefore, I'd assume they are fed power through some sort of beamed power technique. Block the microwave beam and you'd shutdown the nanomachines.
**Heat**
The smaller the machine, the more vulnerable it would be to the affects of waste heat. Even worse for them, they have less structure available to use as a heat sink or radiator. Although the surface area / volume improves for small machines, the imagined behavior of gray goo nano would be to reproduce to cover a surface which means the surface available for radiating heat would be the same as the surface they will cover.
Regardless, they'd be vulnerable to high temperatures. These would either break them apart or cause them to shut down.
I hope these ideas enable you to protect us from a nanogoo final end.
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The real bugaboo of all grey goo scenarios is what powers them. Figure out whatever it is that powers the grey goo that's being a problem an act to deny that power source. Meanwhile, your blue goo doesn't have to worry about reproduction, it just eats grey goo.
(I have yet to see any proposed power source for grey goo that would actually work.)
[Answer]
There are quite a few ways that these nanobots can be stopped, for example (in rough order of increasing desperation):
**Addresses**
As the OP has misread, IPv6 will allow cubic micron sized grey goo to devour about half the planet. However, even with a much better addressing system (say [IPv9](https://www.rfc-editor.org/rfc/rfc1606)), if we are allowed to connect to this network, we could pretend several trillion adresses are already taken, stoping the expansion.
**Kill switch**
A malicious (to the goo) payload that erases reproductive capabilities, or starts "self destruct".
**Blue goo**
This one's simple, and others have said it before, so I won't go into detail.
**Special Materials/Other Containment**
This will depend on how much they're able to manipulate atoms (are they able to split the atom? How about break carbon-fluorine bonds). Good candidates are PTFE like fluorocarbons, ClF3, ClF5 or FOOF (Oxidise the hell out of them), diamond or stacked graphene (needs to be more perfect and good orientation, carbon-carbon bonds are pretty strong too), any (non-gas) element that they can't use. Magnetic containment will work until you've got a better idea, if the grey goo is diamagnetic. How about plasma? Build a superconductor wall, and fill it up. Can't do much self replicating when you don't have any molecules.
**Nukes**
Especially of the low-yield, ERW type. The EMPs should slow them down until you got something better. If you're lucky, it'll kill them outright. The High-yield ones may do some vaporising.
**Other things**
They've driven you off the planet, so now Earth doesn't matter. Even the Higher Yield nukes won't make much of a dent on a planet, so try antimatter, or a small black hole. Let's hope this thing isn't smarter than you are.
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My pet idea is that the working nanomachines do not self-reproduce. After all, that's a different problem and complicates the machine that overtly just needs to do its primary function.
Having *separate* factories gives a place for auditing and a choke point for production and tuning parameters. It may well be completely different in how its set up, with larger assembly mechanism and specialized structures.
Consider, cleaning up an oil spill for example. Maybe that's not something that will need doing in that future, but it's an easy to understand example of a particular class of problem. Maybe you'll be mining land fills for elements or cleaning groundwater.
You start with a shipment of pumpkin-sized deployment bouys, which were produced in a factory and contain any essential substances, bootstrapping, and master software. Toss those into the ocean around the area affected.
Those first grow leaves and rootlets for power and locally sourced materials, and then produce fruiting bodies. The number of fruits is strictly limited and they have serial numbers. The fruits produce the deployment pods, again a fixed number of them, and the deployment pods migrate from the staging area (power, accessibility, extra input material) to the target area (the underground material, or undersea sludge) where the nanomachines are released to do the target job.
The doing-the-job is a totally different task than building the nanobots. They operate in different environments.
The "pumpkins" are a control point and they are on human scale and are few in number, so you could go out and pick them *all* up again if you needed to do that manually. They can be addressed and told to change things as you see how the taskmis progressing, and what problems arise.
If left unchecked, even if running amok, the total effect is limited. That is, it will **fail safe**. It requires human action to keep it going by adding fresh pumpkins.
Note that there might not be just one kind of nanomachine or one set of firmware for any model. The centrallized separate factories can produce the right mixture with no need to get them to self-regulate their population interactions.
Note that life is meta-evolved to evolve. Copying has errors and things are set up to allow such errors to be useful. Our nanobots would be produced with rigid QA and firmware has hash checksums of the whole thing. It will not mutate, and if mistakes do happen the mechanisms are designed to be fragile in the face of random changes, quite opposite of Life. And erronious components won't feed back into a reproduction cycle because it is not a closed loop but a one-way deployment of successive products.
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If they strongly rely on hive-mind, you could interfere with their connection - just start transmitting a lot of noise on the same frequency. It could either DoS them or, if they have any sort of DoS protection, disconnect them from the network. At the very least it should slow them down.
And then, I guess, it would be up to hackers to find some sort of a [nuke](http://en.wikipedia.org/wiki/Denial-of-service_attack#Nuke) against them.
(I don't know how many transmitters would you need, but I guess it'd be possible to reconfigure radio stations and cell phone towers. )
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I'm writing a story where a group of mischievous aliens teleport iconic creatures to inappropriate time periods. (Dimetrodons in colonial Germany, Pterodactyls in the medieval Ottoman Empire, Plesiosaurus in feudal Japan, etc.) In the chapter I am writing, a Roman Cohort discovers a living Tyrannosaurus Rex. They barely manage to capture it while it is sleeping. After some debate, it is decided by the emperor that the beast is to be killed in the colosseum for the entertainment of the Roman people. My problem is when I came to realize that they would not call the creature by the name we have given it. More probably, they would have mistaken it for a creature within their mythology. What beast in Roman/Greek mythology would the Romans most likely mistake a T-Rex for, based on its demeaner, size, and physical appearance?
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**Dragon**
[](https://i.stack.imgur.com/d1Z7t.jpg)
The word [Dragon](https://en.wikipedia.org/wiki/Dragons_in_Greek_mythology) comes from Ancient Greek mythology, where it is used to refer to a handful of different large reptiles. Ancient Greek was as much an auxiliary language to Latin, as Latin is to modern English. Roman Nobility typically spoke Greek amongst themselves and were often sent to Greece for part of their education. Latin is a sufficiently vague language that I can imagine the word "draco" being used for a large real reptile.
Probably they'd add an extra word to distinguish it from other named mythological dragons. So **Draco Galliae** (Dragon from Gaul) after the country where they found it, Or **Draco Agrippae** (Agrippa's Dragon) after the General who led the expedition.
For some tips on how the Romans named new animals see Giraffe = cameleopardis = camel-leopard or Ostrich = Struthocamelus = sparrow-camel. They also used Ancient Greek names like Rhinoceros = Nose-horn or Hippopotamus = river-horse. Since the names are so vague to begin with I think **Gallic Lizard** or **Agrippa's Lizard** would work just fine.
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## Some manner of bird: Hippalectryon?
[](https://i.stack.imgur.com/uvtV3.jpg)
It is a contentious topic, but nowadays [museums portray *Tyrannosaurus* with feathers](https://www.nytimes.com/2019/03/07/arts/design/t-rex-exhibition-american-museum-of-natural-history.html). The Romans, being the sort of literal-minded people who declared that [all spotted hyenas are male](http://www.bbc.com/earth/story/20141028-the-truth-about-spotted-hyenas) based on observation, would certainly not hesitate to call a feathered animal - *any* feathered animal - a bird. This is particularly likely to be true if they had the opportunity to see young (the NYT photo linked above is how a 1-year-old is thought to look)
But ... what *kind* of bird? The Romans probably did not have a strong notion of the half-human tengu to use, while they would have too precise an image for the Bennu. The Roc, among other things, is too good a flyer. Depending on the creature's vocalizations, they might call it an Alectryon or a Harpy.
My guess, however, is that they will call it a [Hippalectryon](https://en.wikipedia.org/wiki/Hippalectryon) (ἱππαλεκτρυών). This is a terrible stretch from the illustration from Wikipedia below, yes! But the hippopotamus doesn't really look that much like a river horse, does it?
Besides, every warrior in the audience will have one daydream above all else: not to *slay* the beast, but to build a howdah on its back, and atop that throne, lead an army to ceaseless victory!
[](https://i.stack.imgur.com/1Kha6.jpg)
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I was brainstorming with a bunch of friends about a story with more than one sapient species on a planet. The idea was to have different lifespans for each species as part of their differences.
I thought about having the usual humans with a standard 70 years lifespan and other species with ten (10) or a hundred (100) times longer lifespans but then the idea of a species with a shorter lifespan came up.
These species are supposed to be able to create a fully functional civilization with culture and some technology and given that most cultural and intellectual endeavors and most skills, blacksmithing, for example, take a lot of time to developed I worried that if we made their average lifespan too short they would not be able to form any sort of civilization.
My question is: what do you think is the minimal lifespan that would allow a species to develop a functional human-like civilization? By this I mean they have some sort of culture like music and religion and technology, like metalworking or masonry, academic pursuits like mathematics and science, and functioning governments and economies et cetera.
Also these species are also as smart as humans, if they are super geniuses then the question is pointless. And lack magic or superpowers that could let them transplant knowledge from other individuals into themselves. Basically they cannot cheat to learn stuff
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*The defining quantity for cultural creature lifespan is generation-to-generation data transfer ratio.*
Culture is something to be taught, non-instinct part of a behavior. This means that cultural creature needs to have enough lifetime to:
1. Be taught
2. Apply knowledge to support those who are on stage 1 and 3
3. Teach the next generation
The ratio between these periods varies greatly on the type of civilization. For ancient times (Sparta - Rome) stage 1 was about 10-15 years, stage 2 was about 20 years (since very low productivity) and stage 3 was about 3-5 years (on average - one teacher teaches 3-5 students). For modern time ratio is 20-25 (up to 30-40 for top tech) / 20-30 / 0,001 - 1 (one teacher teaches up to thousand students in their lifetime).
It means that for an ancient civilization minimum average lifespan should be no less than 30-40 years and for modern - no less than 40-55 years.
Lesser lifespans would prevent knowledge from passing through generations and thus culture would simplify and degrade.
But this is true for humans. For, say, cyborg civilization teaching process might be much shorter - about days, and cyborg-years to support cyborg infrastructure be quite small (due to automation) - about, say, 5 years per cyborg. This would give us that 5 years is enough to support and 10 years enough to support and progress this cyborg culture.
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I think the lifespan should be such that 3 generations can coexist at any time, allowing the grandparents to help the parents in raising the children.
This would allow for a more efficient transmission of knowledge through the generations and resource collection, since the parents can dedicate more time to it instead of chasing the babies.
Thus, if sexual maturity is reached at X years of age, the lifespan should be at least 3X.
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**3 years. But their ancestors lived a lot longer.**
In the remote past your species was much like humans, and developed science and arts (and war, and medicine) as we did. These skills were usually passed in the family.
Individuals who were better adapted to their skill had access to more resources and so had better genetic fitness and reproduced more. Evolution can happen faster with shorter generation times and so time to reproductive maturity grew shorter. These things grew up and had kids fast. A consequent is that they died fast too.
The result now is a caste system, whereby strains of this species are adapted for the skills they perform, like ant castes.
[](https://i.stack.imgur.com/BPHhP.jpg)
This is true for the artisans and craftsmen, the leader / scientists, and especially the warriors who are capable of frighteningly fast reproduction when their kind is needed.
Selective pressure on the physicians went the other way and the doctors are functionally immortal.
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Concepts lifted liberally from [The Mote in God's Eye](https://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye). If you like high science fiction do not read the wikipedia article (spoilers!); just order the book. It should be required reading for would-be worldbuilders.
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Tl;dr: The lifespan is not the issue. The real question is how long it takes an individual to develop from perception to maturity and life span only balances the drawbacks of a long childhood. And there is no minimal life span/ childhood for the way a society functions will change gradually with this or any other factor to the point that one can meet any single condition with any lifespan as long as the rest is built accordingly.
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Your mistake is to assume their civilizations function in (at least basically) the same way as ours. Them having the same habits as we do is quite unlikely and becomes even more improbable the greater the difference in any given attribute and any given direction is.
A functioning society can easily be established with a lifespan of just a month - it just would not look and function like our own. Workers of social insects don't usually live long (usually months, rarely years) but the hive can still learn. Any ant- or beekeeper can tell you that each people has it's own personality and it is not unheard of that an ant people learns stuff over the cause of several worker's lifespans. The individual might be less intelligent than a human but they have a really strong connection to one another and for reasons still unknown to us, even existing social insects can [create structures](https://en.wikipedia.org/wiki/Termite#Nests) and [solve problems](https://www.wired.com/2012/09/bumblebee-traveling-salesman/) that would be a real challenge for us. It is less of a far fetch to assume that a species like that would be able to evolve a literal hive mind or that the individuals become more intelligent (still far less than humans) but keep their hive connection and compete with us on equal terms that way than to assume that any civilization with considerably less life span would function similar to ours. The more time and energy is consumed by an individual before they contribute to their society, the more they have to return later on in order to make it work. A species that is fully grown and developed after a year or two does not have to be as smart as we are and even if it is, it won't be able to develop craftsmanship in the few years before it dies. Take cuttlefish for example. They can manipulate objects at least as keenly as we can, their intelligence rivals our own, in captivity, they show boredom, do juggle, solve puzzles and so on but they do not craft nor do they create a society.
On the other hand, species that have even longer development than we do are going to live far longer and need to learn the heck out of their environment and create machines, computers, and the next big things just to stay in business.
Rivaling humans while making choices and forming one's habitat as a society can be done with reproduction times down to hours e.g. with [adapting information in the DNA](https://en.wikipedia.org/wiki/The_Swarm_(Sch%C3%A4tzing_novel)).
If you insist on a human-like system, the most important trait is that parents care for their young until they have profound skills in their profession so an individual must be strong and able for at least a bit longer than the entire childhood of their children. Given there are several children per year and couple (if couples exist) we can assume that after maturing, two years suffice for mating and childbirth, and then we need the development time from conception to adulthood a second time (parenting). How long do they grow? If they are small but smart, three years should be ample. The most extreme human-like beings would need about eight years of "safe" live. Make it more extreme and have older children teach the young (similar to some forms of military organizations or schools of martial arts) and you can trim it down to five years. We could go on and make it less human like with shorter lifespans until we are down to Schätzing's hive-minded bacteria.
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On Earth, there is one species which is known or believed (by its members) to be intelligent and to be civilized.
There are a number of other species of large brained mammals which might possibly be intelligent beings, though none of them are civilized.
If in the future ways to communicate with those species on equal terms are invented, it might be possible for humans to teach them how to develop advanced technology. In such a case the number of civilized species on Earth would rise from one to a higher number, perhaps as high as about a hundred.
I note that a majority of the potentially intelligent species on Earth are cetaceans, and they lack limbs useful for manipulating their environment, and also live in the sea where making fire to smelt metals would be a problem.
In Larry Niven's story "The Handicapped" a company sells artificial limbs to "Handicapped" species such as dolphins and Bandersnatchi, and a representative of the company arrives on the planet Down to investigate whether the sessile Grogs are intelligent and potential customers.
[https://archive.org/stream/Galaxy\_v26n02\_1967-12\_modified#page/n79/mode/2up[1]](https://archive.org/stream/Galaxy_v26n02_1967-12_modified#page/n79/mode/2up%5B1%5D)
Thus it seems likely that the various species of possibly intelligent beings on Earth are more likely to become members of human civilization instead of developing separate civilizations on their own.
And possibly that may be the pattern for habitable planets in real life, that a number of different species of intelligent beings evolve at the same time, and one of them develops civilization and the others eventually become part of that civilization.
Of course the unified civilization of all intelligent species which might hypothetically develop might later splinter into separate civilizations for each separate species.
In any case, it might be a good idea to investigate the life spaces of the various possibly intelligent, though not (yet) civilized, species on Earth to see how much variation in lifespan there is among potentially intelligent species on Earth, and perhaps use that as model for your fiction.
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## An Alternative Approach
Most answers here focus on teaching, generations and degeneration from an earlier state. I'd like to turn these, all be it fascinating and functional, concepts on the head. The deeper issue most answers touch on is teaching. Teaching and even the concept of civilisation are at their roots about the accretion, discovery and optimization of **memetic ideas**. Memetic ideas are rather abstract in human civilisation and are transmitted via the many flavors of teaching between generations. **What if ideas take a more physical "hardware" form?**
Enter [Turritopsis dohrnii](https://en.m.wikipedia.org/wiki/Turritopsis_dohrnii), the Immortal Jellyfish.
>
> Like most other hydrozoans, T. dohrnii begin their life as tiny, free-swimming larvae known as planulae. As a planula settles down, it gives rise to a colony of polyps that are attached to the sea-floor. All the polyps and jellyfish arising from a single planula are genetically identical clones. The polyps form into an extensively branched form, which is not commonly seen in most jellyfish. Jellyfish, also known as medusae, then bud off these polyps and continue their life in a free-swimming form, eventually becoming sexually mature. When sexually mature they have been known to prey on other jellyfish species at a rapid pace. If a T. dohrnii jellyfish is exposed to environmental stress or physical assault, or is sick or old, it can revert to the polyp stage, forming a new polyp colony. It does this through the cell development process of transdifferentiation, which alters the differentiated state of the cells and transforms them into new types of cells. - Wikipedia
>
>
>
The key thing to understand here is that **Turritopsis Dohrnii reverts to an earlier stage, beginning its life cycle anew**. This is an example of intergenerational data transfer. True, Turritopsis Dohrnii only transmits genetic information, but what if it were more complex and could genetically alter some special sequences of its genome? **Everything a member of this species knows gets not only saved in long term memory, but also in a genetic data storage organ.**
As soon as a member of your species dies or is hurt badly, it commits suicide. The data from the genetic storage organ is then mixed with the seeds the dying one turns into. This might offer a really interesting reproductive cycle and has fascinating social implications. The species might be entirely asexuell or hermaphroditic, though an aproch to sexual reproduction is also conceivable.
If it is asexuell it might be a quite solitary species of lone geniuses, somewhat like the [Jaghut](https://malazan.fandom.com/wiki/Jaghut) from the Malazan series. They might live in symbiosis with viruses to use horizontal gene transfer to compete with or even outcompete the adaptability of sexual reproduction. They will probably have a very alien sense of self, as their memories have lived through a thousand bodies. Apperence and physical attributes might matter very little to them and concepts like childhood and age would be utterly alien to them.
If they are hermaphrodites or sexual, they'll most likely just exchange sperm packs like octopuses do and be done with it. Even the idea of relationships and marriage would be utterly rediculess to them, given that they would have a very long view of the world and would perceive all partnerships as necessarily temporary.
So, here are my ideas. I hope that you find them useful as what I'm suggesting might be a bit more alien than you bargained for.
PS: One could argue that this species isn't short lived at all but biologically immortal. This depends on what information is passed down the next generation. This could range from just factual knowledge, a database and nothing more, to biological mind uploading. Depending on where they are on this scale, they are either short lived of effectively immortal.
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My answer is a modification of L.Dutch's, but I see other answers making similiar assumptions about the parents alone raising children.
The first and third generation do not need to overlap. Rather, lifespans need to be long enough that the oldest children *in the extended family* can care for the youngest while the parents resume their civilization-building activities. If older generations overlap it is undeniably a bonus, but not strictly necessary for the *minimal* lifespan.
From the Paleolithic to Bronze and Iron Ages, human life expectancy hovered around 30 years, ±3. Menarche began, as it does today, between the ages of 7 and 13 or 25-50% into the lifespan. This gives us a narrow window of just a few years in which children are physically capable of helping to raise younger children before they set off to start families of their own. Assuming age 10 for the first successful pregnancy and one successful birth every two years, by age 16 the first child (age 6) will be capable of basic assistance with the third; by age 18 the first and second child will be capable of minding the third and fourth for most of the day.
So, that leaves us with two key variables to work with: the age an individual is physically mature enough to help care for others, but not have children of its own, and the immature share of the lifespan prior to that. In humans I'd argue at a minimum the latter is 5 years, and the former (based on the above) is 5–8 years. Combined this is 33%+ of the lifespan, implying by the 10th child (using the above assumption) of the first generation, the second generation is already several children along itself, at or near the point they can begin to help their aunts and uncles raise their cousins and siblings.
It would seem trivial then to say the solution is to minimize the immature stage and maximize the mature but pre-childbearing stage, so long as the two combined do not exceed the length of the third, childbearing, stage. If you hold to the human-like constraints, this puts the minimum lifespan around 20, with little room to compensate for death and disease.
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Firstly, lifespan doesn't matter in isolation, as pointed out by other answers. What matters is lifespan should be long enough for learning to take place from parent to child.
How quickly this learning takes place could be anything. There could be an option to acquire the entire brain of the parent. Alternatively the species as a whole might share a brain (like if corals or banyan trees had brains). Or maybe children share their brain with just their parents, and branch off (like plant offshoots). If learning must take place via outside media, how about it being chemical? We use oral and non-verbal communication which is relatively slow, direct chemical communication could be much faster.
The parent need not be alive for the children to learn. Mammals have a take-care-of-young-for-long principle, most species don't. Parents could leave non-living remnants for children to study in their own time. (For instance if your parent taught you basic reading skills then died - leaving you the knowledge of the internet; not a perfect example cause we have emotional needs but what if we didn't). Survival skills can be genetically coded instead of having to be learnt from parents (like with most species except mammals), everything else can be learnt via a non-living medium such as written text.
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Imagine a Mark Wattney-like scenario, only on Titan and involving a decent-sized base being isolated instead of a single person. There is not, and never has been, the possibility of growing potatoes. There are "enough" protein packs and vitamin pills for the scenario, but only just enough, and no other existing calorie sources.
What is the *minimum* tech would someone need to chemically convert the hydrocarbons in the Titanic oceans into sugars, edible oils, possibly even alcohol? What is a plausible time to build a machine to convert those hydrocarbons into edible calories?
If this takes magic space replicators I'll have to think of something else — I would like something that could, in principle, be done in with early spacelab or space-shuttle era knowledge, if possible.
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**Edible fat from carbon monoxide via the Fischer-Tropsch process.**
The Germans were faced with a related problem in the early part of the century. They had a lot of coal and brilliant chemists. They wanted liquid fuel for their machines and war effort. The Fischer-Tropsch process cracked coal down to short chain alkanes or carbon monoxide then reassembled them into medium chain alkanes: liquid fuel.
A side product from this process was waxes that could be processed into margarine.
[Coal – in Liquid Form](https://www.mpg.de/10856815/S004_Flashback_078-079.pdf)
>
> In the early 1940s, nine German production sites were pro- ducing
> around 600,000 tons of liquid hydrocarbons every year. Nor were the
> primary products of Fischer-Tropsch synthesis used only for fuel
> production: they could be processed further into lubricating
> greases, soap or detergents, for example. It was even possible to
> conjure up synthetic butter. The inventor of this synthetic edible fat
> was chemist Arthur Imhausen. In the Second World War, Germans fighting
> in the African campaign and on U-boats ate almost exclusively
> Imhausen’s fat. It was easy to digest, didn’t go rancid and is
> reported to have had quite a nice taste. Experts confirmed that the
> daily consumption of up to 100 grams “is harmless and causes no
> irritations or disorders whatsoever.” His creation was thus given the
> go-ahead as the first synthetic food for human consumption.
>
>
>
Pretty cool, and road tested! 100 grams is only 717 calories but that is a nontrivial augmentation of your food stores and I think if 100 grams agreed with me for a few days I would be up for eating more.
On Titan you would just need to refine your alkane mix into precursors suitable for processing into margarine. Your colonists can eat the same diet as the German U-boat sailors.
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All of the elements needed for human life can be found on Titan. But it would require a large amount of technology to make it work nothing that is beyond our current understanding or abilities in chemical technology, but a large amount of technology.
**Power**
Solar power would not be very efficient so nuclear would be a good option to begin with, however much lower tech options are available. The lakes on Titan experience small tides of 1m per day which might be used for power generation and liquid hydrocarbon flow might be harnessed in some areas in an alien form of hydro power. Three more potential sources of power would be burning acetylene in hydrogen to produce ethylene (both available locally), wind turbines and hydrothermal power from deep wells.
**Raw materials**
Water is available in the crust of Titan in large quantities and nitrogen in the atmosphere. So electrolysis of water would be required to generate oxygen, a gas processing plant making use of the difference in boiling points of the different atmospheric gases could separate out nitrogen. Ammonia, methane and ethane are all present and a virtual organic soup of chemicals is to hand so should be possible to synthesise everything needed for human habitation.
**Chemical synthesis**
That said I would not underestimate the sheer quantity of processes needed. All the raw materials are present but they would need a lot of processing to remove impurities and much more processing to transform them into all of the things humans would need. I would say 90% synthetic chemical plant and 10% habitat. It could probably become self-sufficient eventually, but this is not likely to ever occur for financial reasons and would not even be feasible for centuries due to the vast array of chemical and mechanical technology that would be needed.
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I think before we could even REACH Titan we would need to be able to grow food in outer space. And with the ability to grow food in outer space, why should we waste time converting hydrocarbons on Titan to edible materials when we could just ship it over to a space station as fuel? Most of Titan consists of methane too.
Also, when methane is burned, we get carbon dioxide and water, which plants turn into sugar and oxygen. Not to mention the fact that it generates heat. That heat can be turned into electricity to run light sources to grow said plants. The only thing we need now is getting oxygen from bodies in space.
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**Closed**. This question needs to be more [focused](/help/closed-questions). It is not currently accepting answers.
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I'm surprised I can't find a previous question on this.
We all know that being teleported instantly from one place to another has a big problem. If your co-ordinates are off, you might appear in the middle of a mountain or at best you appear in the correct place but intersecting with the air.
I think that the air problem is solved relatively easily.
When transporting inanimate objects, you could send them to a vacuum chamber thus avoiding collision problems. Similarly a human could be sent wearing a pressurised suit to avoid exposing them to a vacuum.
So here's the crunch.
What happens if the coordinates are wrong?
**Question**
A miscalculation or deliberate action causes a one metre diameter solid steel sphere to appear instantaneously in solid rock in the middle of Mont Blanc. Assume the teleportation is one-way so the rock stays where it is. (Thanks to kikirex for raising this)
What happens at various levels of physics?
* Subatomic level - Can subatomic particles occupy the same space at the same time. What if they did - is there a nuclear explosion? Do we synthesise different elements?
* Human-scale level - Will the mountain whose rock is presumably already under great pressure be able to contain the extra matter by compression?
* Mountain-scale level - Will the arrival of the steel sphere cause the mountain to fracture or even explode?
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EDIT
A number of answers have doubted the possibility of the object even reaching the destination. In my mind there has been some development that allows a macroscopic object to quantum-jump to the new location. It's the subject of a different question so I didn't want to mention it here. This note is only FYI and I don't intend it to invalidate any answers so far. For now I'll accept the transmission systems (or impossibility thereof) of the answerers.
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I think we have enough information to make a pretty good scientific estimate of what happens, given the unscientific premise.
The first key point to remember is that matter is almost entirely empty space. The *mass* of matter is confined to the atomic nuclei which are very, very tiny. In solid matter, atoms are separated by about 10-8 meters. *Nuclei* 10-15 meters across. This means that the fraction of space occupied by nuclei is about 10-7 (the ratio of the two linear dimensions) *cubed* or about 10-21. (Think of an atom as a 1 cm sphere of very dense nuclear matter in the center of a 100 km sphere of electron cloud. To the same scale, the rock and the metal sphere are essentially a solar-system sized spheres filled with the gossamer 100 km bubbles just touching each other.)
That means that only a tiny, tiny number of the nuclei in the meter sphere of steel will teleport into the same space as a nucleus in the rock. There will be some, so there's still energy release due to nuclear reactions, but it's small, basically chemical-sized. (Think of a meter sphere of dynamite: You don't want to be standing next to it when it blows, but it's not going to destroy a mountain.)
The volume of each atom that isn't nucleus is occupied by the atom's electron cloud. Electron clouds are compressible and the energy created by teleporting in the steel sphere's electron clouds -- you do realize that your problem requires the energy released to come from somewhere? -- is roughly the same as the energy needed to compress a 1 meter steel sphere and and a 1 meter sphere of rock into a single 1 meter sphere of *stuff*. (The strength of materials -- steel, rock, human tissue, whatever -- is entirely due to the mutual interactions of the constituent atomic electron clouds.) If you take two spheres and compress them into one sphere, you need pretty much the same result energetically as you get from the teleportation.
It should be possible to estimate this, and I'm going to research it. It's important to note that the energy levels involved are chemical (though extreme!) rather than nuclear.
My guess is that this will produce a bigger bang than the accidental nuclear superpositions do, but still not enough to destroy the mountain.
...However, until I could get a solid numerical estimate, I think I'd make a point of watching it from ten or twenty miles away...
[Answer]
### Is there a nuclear explosion? Do we synthesise different elements?
Fission requires free neutrons to interact with heavy elements. This will not happen because the matter you are teleporting will not have a significant number of free neutrons.
Fusion requires two atoms to interact with enough energy to overcome the electro-static repulsion of the atoms nuclei. In this case, your teleporter has no mechanism to add the required MeV of energy to each atom. This amount of energy would turn whatever you were teleporting into a plasma, anyways, so safe to say there is no mechanism for a nuclear reaction take place.
But....
If an atomic nucleus randomly appeared near another atomic nucleus, they would be repelled by the electro-static force between the two positively charged nuclei (the nucleus has only positive protons and neutral neutrons, so all nuclei repel).
Atoms are almost entirely empty space. Let us take the example of one mole of iron at room temperature. This is 56 g and occupies 7100 mm$^3$. The number of atoms in this mol is Avogradro's number. Each atom occupies a volume of 7100 over Avogadro's number. This works out to about 12 cubic Angstroms.
Solving for the [nuclear density](https://en.wikipedia.org/wiki/Nuclear_density) of iron, we find the radius of an iron atom is about $5\times10^{-5}$ Angstrom and the volume of the nucleus of an iron atom is about $1\times10^{-12}$ cubic Angstroms. If you plop two pieces of iron into the same space with magic/teleportation then there is a 1 in a trillion chance that the two iron nuclei will collide.
Still, for every mole of iron (which is about a trillion trillion atoms), this is still a lot of atomic nuclei that collide, something on the order of a trillion. This collision means that there will be created oddly shaped conjoined nuclei of two iron atoms. Now, iron specifically, is the most stable nucleus in terms of [binding energy per nucleon](https://en.wikipedia.org/wiki/Nuclear_binding_energy), but other elements are not. Atoms smaller than iron might 'fuse' by being so close that they Strong force is able to overcome electrostatic repulsion, but the odd shape of the almost-close-enough atoms might cause some atoms to be ripped apart.
So in that case, I'd suggest that for solid materials, something on the order of a trillion atoms per mole of material will undergo these unusual reaction. What happens in each reaction depends strongly on what the elements are, the relative stability of their proton-neutron arrangements, etc. So, some funny business will happen, and there may be new elements synthesized and some fusion type reactions that release energy.
### How much energy?
A hydrogen fusion event releases something like 30 MeV. Lets say that we release 10 MeV of binding energy per nuclear collision due to whatever various interactions take place. Multiply by a trillion and convert to joules and we get on the order of 1 joule released per mole. That isn't a lot! Unless you have a chain reaction starting (which you probably won't, without free neutrons or a very hot plasma), you actually won't do that much damage to what you are teleporting.
### What about a gas?
Since you mentioned gas in the beginning, it is worth noting that since the density of a gas is about 1000 times lower on a molar basis (as compared to a solid), teleporting someone into a gas will cause about 1000 times less nuclear collision, perhaps a billion per mole of teleported object. Still plenty to cause weird physics, but a lot less energy released.
But, looking at our energy numbers, we now have something like mJ of energy released per mole transported. Assuming a person is 5000 mols of water (which is around 90 kg), then you only see about 5 J of energy released by teleporting a person into the air. Since a human generates about 0.5 W of thermal power, this is equivalent to the heat you give off in about 10 seconds.
Now, no promises about what this does as far as DNA damage, but it is almost reasonable to say that you could teleport a human into air without having them experience unusual effects, despite the 5 trillion nuclear collision that you just caused.
[Answer]
According to some interpretations of [quantum field theory](https://plato.stanford.edu/entries/quantum-field-theory/), or QFT, the fundamental state of matter isn't particles but fields instead. What we could call a particle is merely a local excitation of a field, or of a few fields that interact with each other.
This requires that the universe be comprised of fields that can have different local levels of energy. It also implies that the universe is permeated in non-zero levels of energy, because any point in the universe that can contain energy isn't empty.
In physics there is a distinction between a vacuum and a void. A vacuum is the absence of particles, or with a QFT interpretation the absence of local excitations of fields, whereas a void is the absence of energy. A vacuum is not a void, as it holds what we call [Zero Point Energy](http://www.calphysics.org/zpe.html).
This Zero Point Energy is just the resting state of a non-excited field. If you were to add energy to this field you would have something that looks like a particle of that field's type. A photon in an electromagnetic field, an electron in an electron field, etc. These fields can interact with each other, [an electron can absorb and later emit a photon](http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html).
I suggest that instead of viewing it as a collision of atoms, you interpret the teleportation process as being additive. Each of the fields and their energy levels in the mountain ranges suddenly gain the amounts of energy contained within the steel sphere.
This would have a number of incalculable consequences. The simplest solution would be to say that the energy that was added is immediately expelled from the system due to it no longer being stable in the context of another field already containing different energy levels. So all of the energy being added is forced to spread out evenly in the surrounding space. Which is just a very odd way of describing an explosion. Just how big of an explosion would it be though?
The composition of steel is variable but let's say it's 99% iron and therefore has a [density of nearly 7 874 kg/m³](https://www.aqua-calc.com/page/density-table/substance/iron).
A 1 meter diameter sphere has a volume of V = 4 ⁄ 3 × π × R³ = 4 ⁄ 3 × π × 0.5³ = 0.52 m³.
So that's a total of 7 874 × 0.52 = 4 095 kg of iron atoms.
To calculate the energy contained in 4 095 kg of iron we can apply the famous E = mc²
E = 4 095 × (3 × 10^8)² = 3.68^20 J = 0.36 Zettajoule
It's almost the equivalent of [the entire world's energy consumption in 2010](https://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)#1018_to_1023_J).
For comparison to something we have more direct evidence of the destructive effects of, the atomic bomb that annihilated Hiroshima had an energy yield of a few Terajoules (10^12 J).
In fact it's such a massive amount of energy that it's over 250 times the 2011 earthquake and tsunami in Japan(<https://en.wikipedia.org/wiki/Joule#Multiples>).
Of course, a non-violent alternative is to imagine that the effects of adding energy to a field changes the composition of the elements we can observe, and transmutes the mountain into various other elements higher up in the periodic table. So instead of rock composed of oxygen and silicon you might have a mix of zirconium and molybdenum. This type of effect, if discovered, could lead to the birth of a transmutation industry. Perhaps it should be destroyed to protect the economy, or used in secret to the profit of a few.
[Answer]
**Conservation of energy?**
Immediately after this mistake, you have 2x the amount of atoms in a given volume than would normally occupy it. The pressure and temperature will be very high (I think for plasma values of high). Then it will explode. Mark Olson's answer covers this well.
However, **where did that energy come from?** If you want a science-based answer, you pretty much have to maintain or explain violation of conservation of mass-energy. So:
1. It physically can't happen. A teleport puts in just enough extra energy to cope with a few stray air molecules in a high-grade vacuum at the specified destination. The object or person being teleported does not explode. A lower-grade vacuum might cause the equivalent of non-lethal radiation sickness or (commonly hydrogen) embrittlement of metals. You simply cannot insert into high-density matter by mistake. The military, of course, can use the energy of an H-bomb at one end to release the energy of an H-bomb at the other ...
2. The object can be de-materialized but not re-materialized. It gets stuck in hyperspace or wherever, and lost forever. Or it follows the path of least energy to the nearest good vacuum and rematerializes in orbit. (Rather closer to the sun, to deal with gravitational potential energy). Teleportational tunnelling might be the appropriate term here.
3. Your universe doesn't have conservation of energy. This has consequences, which may actually be useful in an SF setting. The laws of your universe are not time-invariant. (Noether's theory). Or, Lagrangian formulations are invalid. Don't ask me what that means in practice.
4. Heisenberg compensators or other handwavium, give up on hard science beyond making it possible to suspend disbelief.
Note with all three cases, gravitational potential energy and planetary rotational velocity must be accounted for. Also there are conservation of momentum issues, and hence in case 3, the laws of the universe are not space-invariant either.
Vernor Vinge was playing with 3. in his Zones universe, but I don't think there was anything that would withstand mathematically rigorous scrutiny.
[Answer]
Comic book teleportation does not exist and is not supported by physics, so the short answer is nothing of that can happen.
Supposing you want to force the issue, though, you need to define how that matter is going to get from point A to point B.
* **Quantum tunneling** is out of question - it only works for subatomic particles, and is too random to teleport a whole body.
* **A big enough wormhole** [would relocate the whole Earth in a very funny way](https://worldbuilding.stackexchange.com/a/103973/21222).
* **Emitting each particle** so that they travel as beams, stopping at the destination(a la Star Trek), would probably cause them to not bind to each other again as before. Mind you, each particle might also hit whatever is at the destination as a cosmic ray, which may open a crater on the target mountain of the question.
There is no way to solve this with the [science-based](/questions/tagged/science-based "show questions tagged 'science-based'") tag. If you go with [magic](/questions/tagged/magic "show questions tagged 'magic'"), which is the only way to teleport something as seen in videogames and movies, then anything goes; I personally like John Carmack's solution. Faced with the same question about three decades ago, he invented the concept of [telefragging](https://tvtropes.org/pmwiki/pmwiki.php/Main/TeleFrag).
[Answer]
Fair warning: this answer is a bit of a cop-out.
Still with me? Alright, good.
One of the more important things to you can do to create an internally consistent magic system is to follow the laws of physics. Newton's third law states that for every action there is an equal and opposite reaction, and this should be true for magic too.
Ok, why am I telling you this? Well, what would be the opposite reaction for teleportation? Presumably, more teleportation. The best way I see to deal with this question is to say that teleportation doesn't just move object A to space B. It also moves whatever was in space B to wherever object A was. That way no matter what happens, there's nothing to collide with when object A arrives.
[Answer]
I will try a different approach – I suppose it is good to consider different angles on how this collision can happen...
Speaking on approach, if this is a collision... from where does the steel come into the mountain? I need to know that in order to know where the energy goes to.
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## Though experiment
Let us say I have a huge lamp in my backyard, and this lamp is designed to work in outer space, and has a built-in battery. Then I turn up the lamp, afterwards, I teleport it up (away from earth)... say 80% the distance to the moon. And I look up... I will not see the light from the lamp until about a second after I send it, because that is how much time light takes to go from the lamp to me.
If we consider a space-time diagram (where space is in the horizontal and time in the vertical), first the lamp is stationary, meaning that its world in moves only in time (it is ontop of the vertical axis), about a second per second. At some point I turn it on, we can represent all the places that the light of the lamp can reach as a cone that opens up. When I teleport the lamp, the world line of the lamp moved horizontally in such way that I was out of the light cone of the lamp... and as time passes, one second later (up in the diagram), I get back in the light cone (the light cone crosses the vertical axis).
**Note**: interestingly, the light cone from before the movement and after would at some point intersect. Meaning that there could be observers that can see the light from the lamp before it being teleport and after at the same time.
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## Force
Now, what force do I need to apply to the teleport object such that it moves in this unusual way? Remember that for everything as we know it, time moves inexorably forward. We do not know of any force that when hitting an object, it would make time stop for that object (as in: if you were hit, you would see the world held in place).
We could try to calculate what that force would be, and we would come up with infinite... and it would make the object move faster than the speed of light, and it would technically be traveling to the past.
**Note**: In fact, if I send a probe to meet with the lamp at its destination, such that it arrives at the same time at the lamp gets there... when we do the Lorentz transformation for the probe, we would find that the lamp was send from the future according to the frame of reference of the probe.
Thus, we must conclude that we must hit the object with a force that moves from the future to the past.
---
If we consider force as a vector that has magnitudes in each dimension, I am proposing that all known physics is dealing with force vector that have 0 in the time dimension, and we need force vectors that have a negative value there (assuming positive means towards the future).
Now we know that we are talking about a collision from the future to the past. *That’s the angle*.
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## Newton’s laws
**First Law**
Let us say, we can push the object to the past. Why would it stop going to the past? Well, it could be because it collides with something. Or perhaps there is some form of drag (after all, there is something pushing everything inexorably to the future).
**Second Law**
`F = m*a`; We are – of course – describing a movement, and assuming the mass does not change. Thus, hmm… we would have an acceleration vector with a negative value on the time coordinate.
Considering that acceleration is displacement (distance) over time squared, we are talking about an acceleration that will make the object perceive time slow down and then go backwards.
However, remember that we are not moving the object to the same place! We are sending it to a different location. That means that acceleration also must have space components.
The way I imagine (i.e. what I am about to say lacks any rigor): We might see the object start moving in the direction we teleport it, stretch (I'd blame Lorentz contraction), then disappear.
**Third Law**
How can we do that push in the first place? There must be an equal an opposite reaction. And, no, that does not mean solving the teleport by exchange (a solution I am personally fond of, but not allowed by OP). We must be pushing something to the future with the same force. That is, the teleport machine has a form of recoil. Perhaps we need to send a small object away to the distant future; as consequence of the teleport of something heavy, a short distance to the short past.
Also, when the collision happens, it could push objects to the past and bounce to the future. *Weird stuff.* However, no, I am not going with that... instead...
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## Feynman diagrams?
Feynman diagrams has the oddity that when flipped in time they remain valid. Thus, they serve as a useful model for interactions with particles moving backward in time.
What we find is that – and I oversimplifying here – a particle moving backwards in time, is its own antiparticle moving forwards in time. That means that an object moving backwards in time, will be – for the rest of us – made of antimatter.
So, about your steel sphere to appear instantaneously in solid rock… yeah, boom. It annihilates with the solid rock.
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## Released energy
*The following computations are done with Wolfram|Alpha*
Well, you told me that it is a sphere that measure 1m on diameter. That is 0.523599 cubic meters of steel. Going with 7900 kg/m^3 for the steel density, we have 4136.43 kg. Then, 2650 kg/m^3 for nondescript rock, we have another 1387.54 kg; for a total of 5523.97 kg.
5523.97 kg gives us 4.9647×10^20 J by good old Einstein’s equation. That is an explosion equivalent to 1.1866×10^11 tons of TNT (118.7 gigatons of TNT).
I struggle to express this…
*The following information is from Wikipedia*
The Tunguska event is estimated to be 3×10^7 tons of TNT. And Tsar Bomb is only 5×10^7 tons of TNT. Those are four orders of magnitude smaller. Thus, we are looking for something more devastating.
The dinosaur killer is 1.92×10^14 tons of TNT. Three orders of magnitude bigger. So, not *that* devastating.
*The following is from Science Magazine*
I found an article about a crater found under Greenland that is said to have required an impact of 3×10^21 J or 7.17×10^11 tons of TNT. This is the right order of magnitude. The article says:
>
> The impact would initially produce a bowl-shaped cavity ~20 km in diameter and ~7 km deep, which would quickly collapse (within ~1 min) to form a complex crater more than 31 km in diameter and ~800 m deep with a central uplift. This impact scenario would have melted and vaporized up to ~20 km^3 of target rock, approximately half of which would have remained within the crater, forming a melt sheet up to ~50 m deep.
>
>
>
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## Other considerations
From the point of view of the object... does its own time continues on during the teleport? Perhaps it does not, it also perceives the teleport as instantaneous.
Where is the object in the instant of the teleport, according to the object? My intuition is that it must be in all places in the path from its origin to its destination. If you think of it that way, you would see that it must hit with the near past of something close to your lab before it can hit the target mountain. And the collision does not look good for your lab.
Perhaps it is preferable to think that the teleport works by moving the object through "hyperspace" and thus avoiding any undesired collision. Moving into hyperspace will also be moving in an additional dimension. In that case... well, whatever it hits at its destination is pushed into hyperspace.
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## Addendum: Quantum-jump
How does a particle get from one place to another? Currently, as far as quantum theory goes, we must consider as if the particle takes all the infinite possible paths from the origin to the destination. That includes paths that go back in time, and paths that go through barriers of other objects. However, the effects of some of these paths cancel each other out, and some paths have a higher influence than others according to the wave function.
Thus, in order to compute the future state of a quantum system, we start by the more relevant paths and move to the less relevant ones, and by doing so we approximate the solution.
Now, at the moment of interaction, the quantum state of the particle must be solved, and it will be at a given place... and to resolve what happens as a result of the interation, we do what I described above. In fact, this is the use of Faymann diagrams, they are used to categorize the possible things that could happen in such way that we can organize them and start computing.
Then the problem with extending quantum tunelling to massive objects is that massive objects are formed by particles that are constantly interacting with each other, keeping the system coherent. *That is also the solution to Schrödinger's cat. Or if you prefer Einstein's version that has a bomb that explode or not, that is why you do not see the box explode and not explode at the same time.*
However, that is not to say that an object cannot spontaneusly teleport under this framework. It would just be absurdly unlikely that all of its particle undergo decoherence simultanously, tunnel to another place and become coherent in the same arrangement.
We do not really know enough of the why quantum physics works. For instance, it is possible to think about the wave function of complex objects, or even the wave function of the whole universe. And, well... is the universe interacting with something else to keep it coherent?
So, let us go with OP and say that this is not only possible but that we can create a machine to make it happen. Well, in this case, we have an elegant coup-out: if a particle cannot occupy a position because there is another particle there (Pauli exclusion principle), then the probability of the object appearing there is zero, thus, it will not happen, instead the steel sphere will appear somewhere else.
**Addendum**: As kingledion, Mark Olson and Carl Sagan point out "Matter is composed chiefly of nothing". There is a lot of empty space in the atoms. However, if the teleport respect pauli exclusion principle (and should it not?) then the particles of the steel sphere will appear is such way that no nuclear reaction happens, only chemical. Thus, you could still have the steel sphere embeded in the rock, and it would be made of... hmm... a different steel, due to the rock chemistry.
---
## Addendum: Don't Panic
Assuming you can build a machine that can cause highly improvable events such as the spontaneous and instantaneous displacement of an object, as mentioned above. Let us call it Teleport-MK1.
The Teleport-MK1 would still not be able to break the exclusion principle. That does not mean it is useless… for example, you could use it leap people's underwear a meter※ to the left as a party trick.
※: Because it is safer that just moving it one foot, and metric is better™.
However, a more interesting use is to have it arrange matter in any desired configuration, as long as it is possible. This device could transform virtually any raw material into any physically possible object, including food (or very advanced substitutes), and other machines. Let us call this reconfiguration of the Teleport-MK1 the Replicator-MK1.
If the universe allows the creation of a machine capable causing impossible events, then you can use a Replicator-MK1 to create it. The new device would not only be able to teleport and manufacture, it would be able to do anything, even if it is infinitely improbable.
What happens when you use it to teleport a steel sphere inside a mountain? Whatever you want.
**Note**: Possible side effects of the use of the new device include time traveling bowls of petunias, use with care. Read Douglas Adams books on the subject for more information. Whatever happens, remember: Don't Panic.
---
## Tl;dr
When the steel spehre collides with the mountain, it will either:
* Swap places with the rock
* Cause a huge explosion
* Push the rock into hyperspace
* The steel sphere appears somewhere else (the universe forbids the collision)
* The steel sphere chemically merges with the rock
* Whatever you want
(this is not an exhaustive list of things that could happen, just the ones I mention in my answer)
[Answer]
If you want to observe the laws of science, then you must explain how a stream of data can be reconstituted at a remote location without a high energy assimilation machine turning that data into a cohesive mass. Energy will not simply turn into mass, much less cohesive arrangements of steel alloy, without that assimilation machine. But if you have such a machine, then it will be responsible for creating a vacuum in which the assimilated mass does not collide with any other objects, not even air, so the coordinates of the reconstituted steel sphere are irrelevant.
] |
[Question]
[
Gender roles have been historically assigned at birth.
As soon as parents establish the sex of their children, they are molded into certain social categories. But **what if humans didn't display sexual characteristics until adolescence?**
My story is set on a fictional world very similar to ours in the Late Middle Ages/Early Modern Period, and populated by "humans". The main deviation from human standard biology is that **their reproductive organs don't appear until puberty**. These young people have no sex, and once they reach puberty, they become either male or female and take on their respective roles in a (more or less) patriarcal society.
My question is primarily focused on how a medieval/early modern society would be affected by this, specially when it comes to education and an early stage of life. I've come to a few interesting points:
* **Names**: Would people only use unisex names like Taylor or Lindsay? Or
perhaps would they adopt an "adult, gendered name" when they grew up,
leaving their baby neuter name behind (maybe something related to
nicknames or even posthumous names)?
* **Heredity**: When dealing with lands, material goods or even royal titles how could a cautious parent be sure of his/her true heir? (Think about the classic "Henry VIII dilemma"). Would he have to wait for 12 or 13 years until the kid "becomes" a boy or a girl? Would he secure his legacy by having many children?
* **Education**: I assume parents would prefer a boy and would educate the kid as so, in their particular craft for peasants or merchants, or for ruling and hunting if they are from a noble family. What would happen when the fittest kid becomes a girl?
* **Gender neutral people**: Let's say that external changes are caused by hormones, just like real biology does. What if, in some cases, certain people wouldn't be able to produce enough amount of hormones to develop as male or female? Would they be expected to behave as women, or maybe as monks, somehow related to religion and celibacy?
* **Sexing**: Even though I think this is more interesting if there's no way to tell if a child is a boy or a girl, I'm curious about methods of "sexing people". What do you think?
Would this society be more equal? Would there still be gender roles? Or, since this situation has existed since Prehistory, would they never arrive to a patriarcal society like that? I hope this question isn't too broad, I've broken down the question into smaller question in order to avoid that. Feel free of answer only one bit, and of course, you can bring up any other topic I might have left out.
Thank you very much!
[Answer]
**I think it is actually quite simple. "Sex" does not exist until puberty is reached. Humanoids are quite lazy and don't invent names or categories for things which are undistinguishable.**
I think the impact on the society would be as follows:
a) It will invite superstitous rituals to influence the outcome of sex. You must decide if there in fact is some factor which *does* influence the final outcome (e.g. the body detects pheromones and if a minority of men/women exist, switch to the sex with less members) or if the outcome is determined, just completely hidden. Neutrals who do not develop sex could be seen as punished by fate/gods/bad things done by the parents.
b) As many cultures have specific rituals once manhood/womanhood is reached, once the time has come, it will invite much celebration, perhaps the reach of adulthood, the choice of a new name etc.
c) As for society roles, **this detail will have no effect**. You can build your society a patriarchat, matriarchat or equal. You are also not obliged to make men stronger/more resilient: While men of Earth primates have stronger build, this is not a law; female birds of prey e.g. are mostly bigger and stronger than males. You must adjust it only to the biological roles men/women are playing in your world. You can also make either boys or girls more desirable: The boy's ability to father many children in parallel or the girl's ability to get children in the first place. I really think you are quite free to build the background as you like.
d) As said, "sexing" will be non-existent if there is no way to tell boys from girls.
[Answer]
Your change is more complex than you realize. Biological sex is not just a shape of few ounces of flesh, there are hormones and behavior, musculo-skeletal differences, and internal organs that take years and years to develop properly.
A. If the only change is shape of genitals, and hormones and bones develop as in regular humans, then parents can make a pretty good guess at the future gender of the child, and raise them accordingly. Mistakes will be common though, and I while it is tempting to expect more tolerance for such mis-gendered children, I you can also end up with worse situation than LGBT people in medieval world.
B. If hormonal differences do not start until 12, the body has a lot less time to adapt to its role. Expect lots of literal growth pains as body rearranges itself, and less gender difference in adults (men are weaker, women are less fertile and caring).
Scenario A will lead to a world similar to our own.
Scenario B will dampen gender differences, but will not erase then, as limitations imposed by childbirth and caring for children are unchanged.
I will answer your Qs only for scenario B:
**Would this society be more equal?** Yes, since there will be a lot more shared experience between genders. But not perfectly equal.
**Would there still be gender roles?** Yes. Maternal instinct will still force women to focus on children and household a lot more than men.
And yes, they will **still arrive at a patriarcal society**.
[Answer]
Names: there are a few cultures where you don't get a name until later on, but waiting until they're a teenager might be too long. They're gonna call them something. I reckon the idea of gendered names would be fairly redundant.
Herity: male primogeniture is not the default setting. If sex is indistuingishable until puberty, we might well treat both sexes equally as far as inheritance goes. This is how it currently works in the UK monarchy, for example, meaning Princess Charlotte comes before her younger brother in the line of succession.
Education: the assumption that the parents would prefer a boy is rather an odd one to make, and I have no idea why this would be the case. Boys are preferred in certain cultures where they're more likely to get work and thus better to provide for the family, but this doesn't have to be the case in your culture.
It's your culture, it does have to reflect the current human culture. It does not have to be patriarchal, you could easily explain it away as being matriarchal or neutral.
The gender neutral people could equally be treated however you want them to be. Them being accepted or reviled both make sense--in part it would probably depend on how common they are. More common means that people are more used to it and less shocked by the idea. Less common means less understanding and probably more hatred.
[Answer]
**Would this society be more equal?**
Probably not by much. Women would still be seen as the weaker sex as they would naturally develop less muscles and lighter bones. The men would still develop an evolutionary drive to protect women. So basically it becomes a gamble, probably a life altering crushing depression if you roll the wrong gender. Men would likely do more female roles, but females would still be discouraged from certain male roles. (I'm not advocating that this is how the world really works, or should work, just that it's how the genders were perceived back then before we knew better)
**Would there still be gender roles?**
This is a bit ambiguous. At a basic level, the male-female relationship would remain the same. Your best friend growing up might turn into your lover more often than it does now, but that's about it. Same sex relationships would probably also become normal.
**Or, since this situation has existed since Prehistory, would they never arrive to a patriarcal society like that?**
It's possible such an evolution would mean people do all their life decisions before puberty, and thus what they turn into isn't relevant. If a child trains to be a blacksmith, then turns into a petite woman, shes still a competent blacksmith.
[Answer]
This question is incredibly broad, so I expect it will be closed. It's a good question to explore, but it's just plain massive. Every part of society has *some* interaction with gender.
That being said, I think there's one major effect which a worldbuilder can use to explore these effects. It isn't *quite* the answer you are looking for, but it's more of a prototype from which you can explore. It's too large for a comment, and it's just related enough to qualify as an answer, so I'm going to put it here.
In this, I will try to be very careful to separate the male and female sexes from the masculine and feminine genders. Sex is a biological thing, and with some [nuanced](https://en.wikipedia.org/wiki/Intersex) exceptions, it's a very easy to understand binary concept. Gender is a more complicated topic. It's a societal construct, dividing people into roles. Some people like to refer to the gender roles as "men" and "women," but I prefer masculine and feminine because they highlight the important detail here, which is that one person can exhibit both traits.
Consider a hypothetical situation where the "goodness" of a particular role from an evolutionary perspective could be put on a number line. Perhaps it's "agressiveness." Too high, and your society tears itself apart. Too low, and your society isn't assertive enough against the forces of nature and vanishes. There's a sweet spot. Nobody really knows where that sweet spot is, and it may even move. But we know, mathematically, that such a sweet spot exists.
How would you cope with this?
Well one approach is to divide the populace in half, and teach each to fall on one side or the other. That way the "best" answer is always available as some combination of the two. It won't be ideal (better to have everyone be "perfect"), but without knowing what perfect is, it's the best you can do.
Now how do you divide the populace in half. One approach is to wait and see what people's aptitude is, and divide them then. In many cases, this is how we do it in society. Whether its the US or a back-country native group, your status as a hunter or an engineer or a leader or a clerk is typically made after seeing what you're good at.
However, what if there are some tasks which benefit from many years of training. What if it takes 14-20 years to train someone up to do a task? As a general rule, humans don't tend to show their proficiencies all that reliably until around seven years or so (there's something funny about 7 years with respect to the central nervous system that keeps coming up). So if you start training then, you're quite far behind those who trained from birth. You might find that your indviduals achieve competency in something at the age of 20, when more strictly gendered cultures achieve said competency at 13, though some of those may be "wrong fits" because the gender was assigned early. It's a balance.
The solution: make an arbitrary decision at birth. And that's what gender does in most societies. It does an arbitrary decision based on something we can see. It can be argued that we do better than 50/50 with that approach because sex is a strong indicator of hormones, and hormones have a huge effect on us. But it is a guess.
With this model, you can see where things would go. Without a visible sex indicator, we would not have a strong indicator of hormones. If we needed to create an arbitrary distinction, we might flip a coin or consult yarrow stalks.
Such an approach would clearly be less beneficial than an approach which can at least say something about hormones. As such, we should expect to see it be less popular than gender today.
What happens in such an environment? Well, it depends. There's many options:
* You can push back the coming of age. Many native cultures have coming of age ceremonies around puberty ages. Modern Western cultures tend to have a coming of age around 18. There's talk that US culture may have moved the coming of age to closer to 26 (psychologists look at things like the behavior of college students when suggesting that age may have moved). You would see the age later because you would first have to identify proficiency, then train it afterward, instead of doing both in parallel.
* You can rely on less-skilled abilities. If training takes 3 years instead of 15, you can start training later and get away with it. If you make it easier to be a mother, by creating institutionalized systems of care, you decrease the minimum amount of training required to be successful. Crossbows were immensely effective in medieval times not because they were more deadly than bows, but because they could be trained in months or weeks rather than years.
* Tasks which still need to be taught from birth could be taught truly randomly
* Or they might be taught to everyone.
Teaching skills to everyone is a tricky business. It's only possible if you have a good sense of where the optimum is. It massively increases the cost of training the skills, especially when some are contradictory. (It's very difficult to find good ways to teach war which also help nurture a child).
Your society could explore any one of these, or many of them. The path you take can answer your questions.
For example, you mention naming. Would you see unisex names? Maybe. It's possible that the solution is a later coming of age, in which case a unisex name as a child is a very natural solution. However, if your solution is to randomly assign roles to people at birth, to get a head start, then you may choose incredibly gender-specific names to help people sterotype those roles properly.
Gender Neutral people is equally open. Your society may develop fully aware that gender is an artificial construct, and embrace gender neutrality. Or it may be that your culture teaches everyone everything as a child, and is fragile because it doesn't have the diversity. As such, one might have a culture which *demands* a snap change in direction when one comes of age, picking a sex and pursuing it quickly to "catch up" to societies nearby which did not use the same rules. In such cases, a gender neutral individual may be treated as a child the rest of their lives.
In the end, the answers to these questions are as fuzzy and complicated as they are in real life. We're still working our way through them. However, by modeling gender as a tool to permit role-specific teachings from birth, you can make sure that whatever system you come up with is realistic.
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This question is extremely open ended, and I could think of many possible societies with this biological setting. It's probably safe to assume that many cultures with different views regarding sex and gender would evolve throughout the world in question.
I'm going to name at least one possible structure for a society that has this kind of biological mechanism, and meets your goals of a patriarchy.
If we assume that males are already held in higher regards, we can probably assume that when a child begins to develop male sex factors, there would be some amount of celebration. The only real difference between earth societies would be that you have to wait more years to find out if the child is male or female.
This can lead to two possible scenarios: Children are only birthed every 12-13 years, depending on if you're current child becomes male or not. Or more likely, many children are had to ensure a male heir. The second is more likely since many births were common in medieval times because of high infant and childhood mortality rates.
Let me start by going through your list, and then adding other developments I think likely in personal opinion.
**Names:** if I had to guess, I would think that most parents would choose masculine names for their children, in hopes that their child would become male. In the case of names with a feminine form, the feminine form could be added if the child becomes female. IE A Samuel/Sam would become Samantha.
In the case of Royalty or nobles, they may choose to bestow male names only to male heirs, an early sign of their right to inherit land or prestige. However, nobles often subscribe to some of the same superstitions as commoners, so they may also practice male naming.
**Heredity:** Your guess that Royalty would sire many heirs in order to ensure a male scion is most likely correct. It has been observed throughout human history that the more wealth a person has, the more likely they are to participate in Polygamous practices. Royalty would probably have many wives to ensure a proper heir was born.
The selection for the most proper male heir could happen in many ways, but the most likely answer is simply that the first Child to develop male characteristics would be the true heir, and the appointment would pass to the next child who had developed the traits in the event of their death.
In this case a younger child may become the true heir if an older sibling fails to develop sex characteristics first. This would only hold true if the development of sex had a distinguishing factor, such as developing a proto-penis, or having breasts form. If the change is more varied such as our puberty, birthrights might have to be decided by a contest instead, with similarly aged heirs competing for the birthrights. Perhaps they would have all heirs in the same calendar year compete in a contest when they come of age.
**Education:** Most likely many skills would become more unisex, with hunting and crafting being at first learned by both, and specializations going on after they hit their sexing period. This would mean that men and women are a lot more conscious of the sex split, despite the fact that children are treated more evenly. For children who learn together with their siblings and then suddenly get divided by sex, there would probably be a large emotional attachment to the event.
As for higher education, only nobles would get it in the middle ages, and they wouldn't start until they came of age at 12-13 anyways. Schooling would be another disjoint between the sexes, and a feminist movement may happen a lot sooner than typically expected because as children both sexes had the same rights, and women will want the same rights in adult hood as well.
But until that happens, while noble or wealthy boys went to school, girls would suddenly be given wife lessons in an attempt to marry them off to a man in their mid teens.
The split would be less apparent in commoners where the only major difference would be that girls would start spending more time learning craft, while boys spent more time learning field care and other outdoor activities. The main reason for this is that the wife will need to stay at home while pregnant, and crafts can be done inside. A boys knowledge of crafts won't go to waste of course, as he'll be able to use it during winter, storms, and other events that may keep him inside.
**Gender neutral/Intersex:** Gender neutral people would probably be regarded as a third inferior sex. It's even possible they would be considered cursed by god and may be scorned or even killed. Some cultures believed that third sexed people were special and were given praise, but it's far less common then condemning outcasts.
**Sexing:** I can only imagine the wonderful plethora of hogwash sexing methods people would come up with. There would be debates over what sex position gives the most boys, over what kinds of foods children should eat, probably weird practices like feeding a child the placenta from a newborn to help them grow into men.
There would be Shamans who would sex your baby based on earlobes or birthmarks, but it would obviously be bull. Maybe somewhere a scientist would suggest looking for ovums by cutting open a child's belly to sex them, but considering the risk of infection and the great chance that the doctor would be called a heretic for desecrating bodies or something, I doubt any reliable method would crop up.
**Patriarchal society:** There's actually one very good reason that a patriarchal society would develop even though children don't have sexes, and that is the fact that men don't get pregnant. Yes, in early cultures women were life givers and served as matriarchs, but as time went on men, who tend to have more aggressiveness, would be able to go out and conquer or whatever while their wives are pregnant. Actually, just the fact that men are more likely to fight could lead to power shifting to men. With men on the top, a patriarchal society develops as a side effect. IE: All these men are ruling countries, men must be great and special.
**Extra notes:** I think that covers a lot of the basics, but I do thing one thing is important to point out. In this type of world, I'm fairly sure the gender gap would be wider, not narrower. With men and women growing up separately from birth, there is underlying complexes, but the comparability between men and women shows them that they are more similar than not. But in a world where the sexes are indistinguishable until a certain point, and then suddenly they are divided into men and women, it would leave both inferiority and superiority complexes on respective parties, which are then reinforced strictly since there would be lingering feelings of "we're the same" from childhood, which need to be gotten rid of if the patriarchy is to continue on and society as well. (Or at least that's how they'll justify treating men like heros and women like objects.)
(I know I mentioned this above, but it seemed important enough to make it its own point.)
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I would imagine that a set of neutral names would develop and when puberty was reached they would be given a male or female name during some sort of coming of age process retaining their previous name as a middle or maiden name like fashion.
On Heredity I would suggest that a neutral sex monarch would have to have a guardian to rule in their stead until they came of age. The main issue would be when there were two neutral sex siblings the eldest reaching puberty and becoming a queen followed by her brother reaching puberty later. In this case there might be a special option for the brother to take over his sister’s throne.
Education would probably change considerably – a neutral curriculum for those before puberty and then 2 very different curricula after that.
Gender neutral people: probably would not be in a happy place. Unless there were very great numbers of them >10% they might well be seen as degenerate as homosexuals were historicaly and killed or put into some form or servitude or slavery.
Sexing: it depends on the development process. It could be as crudely simple as turning them upside down and having a look. It might be a matter of a minor surgical procedure or it might simply be impossible to tell until nature took its course.
Would this society be more equal: no especially not if there were a minority of adult neutral sex people. Regardless of that it should be possible for a “normal” patriarchal society to develop with adjustments for the changed circumstances.
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My guess is that society should be more gender-equal than Earth's medieval one - otherwise it would have to deal with unique issues.
* **Heredity/Inheritance/Succession** For humans (with male primogeniture), it is easy to have a plan for succession since the birth of the first child. If people don't know, which child is going to succeed the father, we have a recipe for trouble. What if the eldest child, destined for the throne, turned up to be a girl? Suddenly, all younger children are in trouble - a much bigger trouble than traditional Western monarchy would have had. If the parent passes away before his children come of age - how the estate is partitioned between children? It has to be done regardless of gender, because later repartitioning may be impossible (and children's guardians would make sure it is so).
* **Education/Training** Human children receive a lot of gender role-specific training before coming of age. Noblemen's sons are getting a lot of practice with sword, bow and even lance before their puberty. Tradesmen's sons are raised as their fathers successors, meant not only to take over the trade, but to exceed their parent's skill. Life is short. No one would be wasting so many years of young persons' lives doing nothing useful. Children will receive full training and go on to become successful tradespersons, regardless of their gender. For noblewomen and soldiers' daughters, that is different, but - we just can't put Arya Stark to do embroidery. In real medieval history, we hardly would get any ladies raised as Arya. In this society, young girls will be equally skilled in armed combat. Of course, boys will grow bigger - but that wouldn't mean that much if a girl is more skilled with a blade.
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## Names - Honorifics
I think rather than having clearly defined male and female names, such a society would be quite likely to develop honorifics similar to Eastern Asian languages, but applied after puberty rather than acting as a status indicator.
In Japanese, there are *-kun* and *-chan*, which are the youthful masculine and feminine honorifics, respectively. I suspect something similar would occur in many cultures, but for adults rather than for children, teens, and younger folks trying to be cute.
Basically, all names are gender-neutral, but when puberty hits, the honorific gets attached, which clearly indicates their gender and adult status.
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I don't have any thoughts on the other aspects, but I wanted to share my ideas about names that nobody else mentioned.
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Imagine a species almost identical to humans, with one exception. All sperm contained both X and Y chromosome, and every child has the potential to develop as either sex. However, the mother has some form of control to select the sex of the child during early development, say through controlling rather or not estrogen was introduced in the womb during early development to trigger female development.
This species evolved this way from the start, they are not using technology to control this change. As such their culture and psychology would be evolved around the presumption that sex choice was possible.
I'm wondering how the species would evolve, and in particular what it would do to their gender roles. Would gender roles be stronger or less stringent in a world like this? Would gender roles otherwise tend towards the same pattern as we have now, or would this somehow modify the actual role of gender?
I'm interested in both the culture and evolutionary psychology, the nature and nurture sides of the gender roles.
EDIT:
I remembered an interesting fact about evolution and mating strategies. In the more common mating systems, where males compete for females, the desire for male vs females depends on the 'strength' of parent/child. Since males have to compete for mates, and thus a weak male will likely never get to mate while a strong male may get dozens of mates, there is limited benefit in having a son who is going to be weaker, but massive benefit to having a son if he is likely to be particularly strong. However, since females will have no trouble finding males who wish to mate with them (it cost a male almost nothing to mate, and thus he will mate with a 'weaker' female) having a daughter who is weaker is not as disadvantageous; at the same time a 'strong' daughter doesn't benefit from her strength by having much of an increased mating opportunity, since she will likely have one child per mating-season regardless of her strength if she survives. Studies have even shown some species have very slight favoring of male or female children depending on various measurements of 'strength' or health due to this.
Pre-culture humans with conscious control of sex of the child would likely evolve to recognize this principle on some instinctual level. Younger mothers, unhealthy mothers, or mothers who had lower social status may be more prone to choosing females, while high status mothers are prone to males based off of this principle; which would likely evolve as an instinctual predisposition prior to cultural development. This would in turn likely have many interesting effects on gender roles once culture had developed. Any thoughts on what kind of effect it may have?
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First off, this idea isn't as completely hypothetical as you might think. There have been plenty of cultures in history where infanticide was accepted practice. The two main reasons for killing a new-born were (a) seems weak, too much trouble to raise him or her if they're just going to die young anyway, and (b) wrong sex. (What else could you know about a newborn?) Today of course we can tell the sex of a baby in the womb through ultrasound, so where abortion is socially accepted people can abort children of the wrong sex. We are seeing in practice that girls are more likely to be killed by infanticide or abortion world-wide, and the ratio in China and India is measurably changing the ratio of males to females. This does not have exactly the same effects as what you describe, of course, but it gives us relevant data.
Assuming that this society was identical to human society except as affected by this one thing: There are three reasons to prefer a male child in most human societies: (a) Males are more useful in war, as @pluckedkiwi discusses. (b) You need a male heir to carry on the family line and inherit the family lands, noble titles, business, whatever. (c) To be able to retire when you get old, you need sons to support you. In most cultures, daughters will be supporting their husbands' parents.
So from the parents' point of view, males are preferred. But from the individual male's point of view, he wants lots of females around so he can easily find a wife. Many men would like multiple wives. From the individual female's point of view ... hmm. On the one hand it's to her advantage if men outnumber women, as it means she has more choices when selecting a husband. Even if it's a culture with arranged marriages, her guardians have more choices. If men are competing, presumably the rich and powerful tend to win, however the society is structured. On the other hand in a violent society she's more likely to be kidnapped, assaulted, etc.
So there are competing interests, but it's the parents who control.
So with all that preamble, here's my theory about what would happen: Cultures would develop some sort of bride price custom: A man must pay a girl's parents to be allowed to marry their daughter. Such customs have existed in human societies throughout history, so I'm not making up something crazy. This would make daughters financially valuable, and thus balance the financial value of sons. Over time, the amount paid would converge to an amount that results in parents having an equal number of boys and girls.
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I think it might just make things a little more extreme from what we see today and have seen in the past. Some cultures will venerate women more as not only do they bring life into the world but they decide such things as your gender role in society. Of course hermaphrodites would be an interesting thing to explain. Until relatively recently many cultures including western culture believed women were responsible for such things as the sex of the child and were often blamed when they didn't produce the 'right' one. Henry VIII?
If women had control over it might be even worse for them in some places because then it will also be assumed they have control over other aspects of the gestation process and might be severely blamed, ostracized or other punishment for any unhealthy child they bring into the world.
Warlike tribes might want to produce more men to keep up their numbers.
In some, girls might be wanted to trade, making them even more like property than they have been in the past. Knowing if a child is going to be a boy or a girl could start the planning for their future even earlier, or decisions could be made even before the women gets pregnant. To provide a male heir, or a female companion for an ally...
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I think that gender roles would be more strictly set in place. If you can choose the gender of your children, people would naturally need to be more aware of the differences between the two genders, so that they would be more able to make an informed decision about what gender their child will be. This awareness would be instinctive rather than learned. Because of this, there will be more segregation and expectations about people based on gender.
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There are far too many possibilities to cover, but a strong strategy is the development of a militaristic expansionist society where women are little more than broodmares.
Able-bodied men are highly valuable for warfare between lower technology groups. A group which focuses on only producing males has plenty of warriors, who can then overpower the neighboring groups to enslave their women. Producing only males as a strategy for expansion could give a primitive society a significant advantage so long as the rate of expansion is sufficient to bring in enough women for population growth.
Obviously this sort of strategy is not viable if everyone follows it, but the one which does go this route can quickly overpower the rest (don't count on every group doing what is best for the entire species as a whole - we certainly don't). The gender politics would likely be quite abhorrent to our sensibilities, but women would be chattel for the specific purpose of breeding. They might be individually owned, but more likely held in common by various factions (population growth would suffer if high status males had a harem back home but spent a lot of time on campaign).
Whenever the men felt there were too few women to go around, it serves as great motivation to attack the neighbors. This helps keep the population relatively balanced (for whatever gender balance becomes their preferred ratio) as men are killed off in battle and more women are enslaved. Eventually they would get large enough to need some daughters, but until warfare dies down and pressure for rapid population growth falls, and perhaps not until something akin to a modern civilization where the typical productive capacity of women becomes similar to that of men, I don't see women being emancipated.
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Though most of the modern world is patriarchal and values males more than females, that is not true in every culture. Many have been matriarchal and valued females more. This gender control would increase the chances of societies becoming female dominated. In early tribes as culture was developing it would be up to the women to decide what the tribe needed more of. More men? More women? What is the value in each? From the time this race first started communicating with each other it would be the tribes who’s women made the wisest decisions in these matters that would become dominant and spread. Since the women would be the ones making these important decisions, why would they not also make other decisions? Power and influence would steadily gather in the mother of the household. Inheritance laws would (when they finally came about) follow the mothers line not the fathers. Most of the other answers focus on patriarchal mindset. Answering the questions “What would happen in a patriarchal society if they could control the gender of their child?” However the society would evolve to be matriarchal if the species had evolved with this ability resting with the female.
Besides leadership though I suspect many other gender roles would more fluid than in modern western culture. Your gender was based upon the choice of your mother. As the mothers power grew, your role in the family would also be based upon the choice of your mother.
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### Tradition
What determined traditional gender roles? Males are taller with more upper body strength. Females have wombs and breasts. The latter is more important.
Women have the more labor-intensive portion of reproduction. While a man spends just a short time initiating the pregnancy, the woman is tied down for about nine months. From a reproductive perspective, we have a tremendous surplus of men relative to women. If we had ten women for every man, we could produce just as many babies (about one every ten months at most).
Men tend to be given the more dangerous work because they are expendable. Lose a few men and some of the surviving men can take extra wives. Women tend to be given work that can be done even while pregnant. Safe and close to home. They have to feed infants initially (men don't produce milk). It was natural for them to wean the children by feeding them other food.
### What changed?
We have seen a change in traditional gender roles. Why? Because lower infant mortality and birth control mean that large families are much less important. Women don't spend their twenties and thirties popping out kid after kid to be sure that enough survive. So women have more time to do things other than be pregnant.
### Answering
To get back to the actual question, I'm not sure that gender selection would change much. Women would still have a greater role in reproduction. Men would still be stronger with more upper body strength. The roles might stay the same while their importance would be more balanced.
If food is plentiful, having more female babies will eventually lead to a larger population. If food is more limited, having more male babies could eventually lead to more hunters to get more food. When agriculture is developed, this choice could switch between increasing population or warriors. Warriors allow a territory expansion, increasing food availability.
This would encourage long term thinking. If the balance is too preoccupied with expansion and not enough with resources, people will starve. If the balance is too preoccupied with resources and not enough with expansion, they won't have enough population to utilize the resources.
I would expect the balance to shift towards women during the agricultural phase. Agriculture produces an excess of food and has fewer jobs that favor one gender. Multiple wives per husband is likely to be the norm.
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You said that these people have always had this ability, but since animals don't seem to care too much about the sex of their children, I'm going to assume the use of this ability won't occur until we get a rudimentary form of communication and civilization (where mothers can explain to their daughters how to do it without having to wait a year and a half to show examples). So this society diverges from ours at the early civilization level.
At this level, men are in charge, and they *will* find out about this ability. Thus, just about as soon as it can be used, women will lose the right to set the sex of their children. Anyone who doesn't make the right kinds of babies will be killed, or shunned, or otherwise kept from making more babies. Similarly, tribes where the leader lets only male babies or only female babies be born will die out, and thus also not make more babies. The tribes that survive and thrive will be the ones that figure out the best ratio of men to women. I initially thought this ratio would highly favor men (since they're stronger), but after thinking about it I realized that the dangers of childbirth would probably kill enough women to warrant higher female production rates.
This ratio shouldn't be too different than what we have now(according to wikipedia, there are a few more men than women on average, but not too different); the big difference is that now it's a human-regulated ratio rather than an evolution-regulated one. And while a one-to-one or similar ratio might work out reasonably well on a macro scale, it's the micro scale where things begin to get different. Since society has been naturally selected to prefer male *and* female offspring, governments will want to ensure that their newest citizens are properly segregated. But since this is still a patriarchy, people are going to want male babies. Thus, to keep the balances in check, I can think of two options:
1- If you have money, you get male babies. Otherwise, pop out some girls.
2- Alternate babies. You can have a firstborn male, but your second child has to be a female (or else).
At this point, the resulting cultures diverge so much that I can no longer speak generally about them. The first case is *really* interesting to me, because while it splits the population into two classes, *half of each generation has to switch to a different class*. Men would have to fight to stay on top and get the right to have male heirs, while the fairy-tale story of a peasant girl getting married by the prince will happen *all the time*. Unfortunately, this option isn't really that good for sexual equality, as all women start out poor, and men rich. I don't think I want to know how that would turn out.
The second option is probably pretty close to what we do, but there are a few interesting edge cases to consider. For instance, what if your firstborn dies, and you can't get another male until you have a female first? And what if that female kills the mother in childbirth?
In both cases, it would be cool to see what happens to kids born the 'illegal' sex. Would they be killed? Rendered sexless by some horrible operation? Raised as monks or nuns or ninjas? I think it would really depend on the needs of the nation.
Anyway, I don't really think gender roles would change too much. Women will *never* get to choose the sex of the baby; at best, it will be a compromise. The ratio of men to women will be regulated too, so maybe even the father won't get to pick. People will still be born men or women (or anything else, but in much smaller quantities), with all the necessary bells and/or whistles, so they should still end up pretty much as men and women usually do (that second case I mentioned might change things, but I think it would only magnify what was already in place in our past). Cultures may be different, but it's hard to say how without a more specific case.
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You would have much more variation among cultures.
Depending on the cultural norm of a civilization many more things are possible.
In our current system we have a fairly strong culture of one to one relationships (monogamy) that is paired with an even probably of any child being male or female.
Any other cultural system (polygamy, or competition for mates) is difficult to maintain because the even gender ratio either leaves people left out in the polygamous case or needless competition in the competitive one (there are enough mates for everyone).
If the ratio can be chosen then any ration that women agree to can be easily maintained 1:10 10:1. So you could see Amazonian cultures with majority women and a few men to make children, or majority male tribes with fierce competition for the few mates. As long as the women of the group agree with the system they can maintain any ratio.
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What would happen is that gender would be determined by: SUPPLY & DEMAND. Whatever gender happens to be the valued one would be produced. Then the market would be glutted with that gender, so the demand for the other gender would then spike.
I don't believe that males would be more highly valued in this situation. If a species has already gone through the horror that is too many boys in a society, they will have already begun to understand what that does to a population (as in there aren't enough women to HAVE the babies, so the population drops like a stone, creating a crisis). Girls get to chose for themselves as far as a mate and career and are more becoming more liberated in places where sex-determination is done in utero via abortive measures. Men in these societies are having to do much more to prove themselves because there are so many of them competing.
In a society where girls are chosen more often, population would explode, creating all new and different problems. Women would be less valued (as the men are in the above example) and would have to get married quickly, and the men would have the choice.
If they always had this ability, I think that population numbers would have been lower at the outset, because some families chose to keep having kids because they were looking to have a particular gender (Mom's family: 6 boys, 1 girl and the girl was the youngest.)
As to gender roles, that really depends. Because the imbalance of gender in a major way shifts the power dynamic between the sexes. What you have more of will determine what the gender roles are. For some countries, that want/need a large population over time, choosing females more often will be the norm. Because this is something we had from the start, and we are somewhat intelligent, we may figure out the correlation.
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~~I'm new here so I can't leave a comment but part of your biological assumptions are wrong. In humans, the baby's gender is controlled by the male's contribution, ie whether they give an XX or XY gamete. If the Y chromosome is present, then the baby becomes male. In its absence, female. So the "default," in a way, is female.~~
I see know the questioner addressed this in his post, but stick with me.
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I find it unlikely a woman could biologically assert a choice of her baby's gender. Would she have to constantly focus on the baby's gender to ensure the right hormones are released? Or just once, at some turn point in gestation, like week 5? What happens if she changes her mind, or just honestly never makes a choice? Because of the passivity inherent in pregnancy, I don't see her evolving any sort of conscious hormonal control. I can't think of any examples of animals consciously controlling hormonal release, for very good reasons.
Additionally, the actual act of procreation for women, is again, passive. So if there was to be a choice, it would have to be a choice made during an actual conscious action. For this, I would choose ejaculation. As I postulated in the comments, a man's testes could each produce male- or female-begetting gametes only. A muscle that closes only one vas deferens and allows the man to choose female or male semen seems to me far more biologically plausible than the woman.
One way I feel a woman could plausibly effect the sex of her baby is: Perhaps a male embryo releases a hormone that causes an itching sensation, and she could self-abort.
**So...**
No matter who picks, a child that knows his/her gender was chosen by one parent is going to feel *very* beholden to that parent, especially their expectations. A son would feel very strongly that he has to live up to his father's expectations. In a less-progressive society, this would *expand* gender roles.
Similarly, a daughter would feel the same pressures, but the opposite way: virginity would be more highly valued, and she would respect her father's vision for her as a girl.
Of course, broad strokes here, but someone *knowing* their gender was selected for a reason would face enormous pressure to live up to the expectations of that gender.
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I am writing a story in which the characters have some power over the physical world - literally able to transform their knowledge of physics into powers. I am trying to determine a good way for them to fly. Literally anything is available to them that has some kind of physical law attached to it.
My current plan is just to say that they can choose to cancel out gravity, but I realize it means they would just start floating, not necessary moving in any particular direction. If they change the air pressure around themselves, then they'll have to do all sorts of odd things in order to not pop their eardrums and whatnot. If they create explosions by concentrating oxygen and spiking the temperature, then they're going to die from being exploded (hah).
Edit: I'd like to say that I really appreciate everyone's input on this question and I hope it helps other people playing with such a world. I accepted the answer that worked best for **me**, but there's still plenty of great answers in here! Please upvote everyone, they deserve it.
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If your characters played with the gravitational constant, reducing or even negating it in the direction of the major mass, and increasing it in the direction they wanted to go, this would provide a net force that would move them (and anything around them that wasn't fixed) in any direction they wanted:
$F = G \frac{m\_1 m\_2}{r^2}\ $,
where:
* $F$ is the force between the masses,
* $G$ is the gravitational constant, usually approximately equal to 6.674×10−11 N m2 kg−2,
* $m\_1$" is the first mass,
* $m\_2$ is the second mass, and
* $r$ is the distance between the centres of the masses.
**EDIT:**
$m\_2$ does need to be another object, the closer and larger the better. However, if in one direction (i.e. down), $G$ is reduced to $0$ or less, this negates gravity's usual downward pull, and may provide a localised upward thrust. $G$ could *also* be increased in the direction of desired travel, so the character could be both pushed away from the earth *and* pulled toward it. The secret of this is the differential between $G$ in different directions relative to the character.
However, other objects in space could also be used - just increase $G$ enough in the appropriate direction, though that might cause other problems if it was increased too much...
...The ability to manipulate $G$ in a localised way could also be an incredibly powerful and dangerous weapon - imagine that pretty much anything could be shot off into space, or a miniature/quantum black hole could be created from any convenient mass. Resetting $G$ to its usual value after having created a tiny black hole would mean that the black hole would probably then promptly evaporate, in an explosion equivalent to the total conversion of the mass involved to energy - think megatons to gigatons of explosive power - or more.
Edit 2:
Another, related idea occurred to me:
If one of these physics-bending characters carried an object of significant mass, they could make its [*mass* negative](http://en.wikipedia.org/wiki/Negative_mass), allowing it it be used in a [diametrical drive](http://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physics_Program#Diametrical).
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In [this](https://worldbuilding.stackexchange.com/questions/2856/life-on-a-planet-with-multiple-gas-layers/2868#2868) answer, I discussed a "pufferpolyp" - essentially, a (fictional) creature$^1$ that can fill itself with a lighter gas and thus float up through the atmosphere. I think this could work here. Here's what you do:
* **Choose your atmosphere.** The whole operation hinges on this. Try a heavy gas, such as oxygen, that will sink towards the ground relative to other gases. Of course, it has to be breathable, but I suppose you can adjust your creatures so they survive. Here, I'll go with $H\_2O$.
* **Choose your creature's gas.** My strategy for this would be to have the creature turn some of the gas in the atmosphere into a lighter gas. In this case, you could have the pufferpolyp use [electrolysis](https://en.wikipedia.org/wiki/Electrolysis_of_water) to turn the $H\_2O$ into $H\_2$ and $O\_2$ (use the reaction $2H\_2O \to 2H\_2 +O\_2$).
* **Carry out the reaction.** The creature expands a sac to take in some of the air. It then applies a small electric charge to separate the gas, and then expels some of the unused gas (in this case, if the creature were to use $O\_2$ to breathe, you have another benefit).
* **Fly!** Go as high as you want, then compress the sac and release the gas inside. You can do this until you float or sink.
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You then have the issue of moving forward, backward, or to the side - after all, you can rise here, but you can't go anywhere! So let's say that when you expel the unwanted gas, you can direct the flow in nearly any direction, propelling you in the opposite direction. Need more propellant? Just take in some of the outside air, undergo electrolysis, and fly higher and farther!
$^1$ It's a figment of my imagination, by the way. Just in case anyone was thinking of buying one, which would seem to be a bad idea due to their tendency to float away. Get a good leash.
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An old Soviet-era sci-fi had a flying protagonist who could directly control the direction of [Brownian motion](http://en.wikipedia.org/wiki/Brownian_motion) in his body. Instead of all his molecules moving randomly and having a net force of zero, he was bio-engineered to be able to introduce a bias so that the Brownian motion in the molecules of all his cells did have a non-zero vector sum.
Thus, flight achieved without awkward lighter-than-air floating!
The novel is called [Ariel](http://en.wikipedia.org/wiki/Ariel_%28novel%29). However, I don't know if any English translations exist.
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If they have finesse of these things, then cancelling gravity in one direction and increasing it in another could work, it would be more like falling horizontally. By strengthening and weakening the forces could allow for speeding up and slowing down.
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"When I cancel gravity, I can't control which way I float."
First make a costume with plenty of fabric that you can use as a control surface. This may be an ankle-length shirt, as worn by John Darling of *Peter Pan* or the squeaky-voiced Seville kids in 1980s *Alvin and the Chipmunks*. Or it may be a cape, as worn by Mario of *Super Mario World*. Or it may be a dress with a full skirt, as worn by Peach of *Super Mario Bros. 2*. If you're not worried about fitting in, it could even be a full-on [flying squirrel costume](https://en.wikipedia.org/wiki/Wingsuit_flying), as the technique you're about to learn is derived from gliding.
Then take a running leap, and as you push off from the ground, cancel gravity. In some settings this may involve various forms of technobabble; in others you need only cover yourself with a form of dust and think happy thoughts.
While you're in the air, move the control surfaces with your arms and legs to control your trajectory. Eventually you will stall. Temporarily allow gravity to work again, dive until you've regained speed, pull back into a climb, and cancel gravity again.
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In this comment I analyze the realisticness of HDE's pufferpolyp.
I will model the animal as a spherical object, with an internal cavity of radius $r$, surrounded by skin and flesh and bodily material of thickness $d$ on the outside, with the density being that of water ($\text{density} = 1000 \text{ kg/m}^3$). Inside the cavity is the hydrogen ($\text{density} = .085 \text{ kg/m}^3$) produced by electrolysis, and the outside atmosphere is water vapor ($\text{density} = .804 \text{ kg/m}^3$). Of course the temperature difference to make the body liquid but the outside gaseous is a bit strange but it's an assumption I'm fine with making.
The buoyant 'force' (technically the mass; I'm ignoring $g$ because it cancels out anyway. Pretend $g=1$ if it makes you happy) applied by the water vapor is density times volume, which is
$$.804(r+d)^3 \times \frac{4}{3} \pi$$
The weight of the animal is the weight by the gas and the weight of the flesh: $$\left(\frac{4}{3}\pi\right)((.085)(r^3) + 1000 ((r+d)^3-r^3))\left(\frac{4}{3}\pi\right)$$
The $\left(\frac{4}{3}\pi\right)$ terms cancel out.
We are left with:
$$.804(r+d)^3 = (.085)(r^3) + 1000 ((r+d)^3-r^3)$$
For $d = 1 \text{ cm}, r = 41.7 \text{ m}$. For $d = 2 \text{ cm}, r = 83.4 \text{ m}$. For $d = 5 \text{ cm}, r = 208 \text{ m}$.
If the animal was made of (liquid) ammonia, with density $681 \text{ kg/m}^3$:
For $d = 1 \text{ cm}, r = 28.4 \text{ m}$. For $d = 2 \text{ cm}, r = 56.3 \text{ m}$. For $d = 5 \text{ cm}, r = 142 \text{ m}$.
Conclusion: The animal is absolutely ridiculous, assuming that all my units were proper. The smallest number here is the $28.4 \text{ m}$ one, which would weigh $69047 \text{ kg}$.
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Habatchii says;
Deep psychological hypnosis. A study on metaphysics and superhuman capabilities was conducted in Germany during both World War One and Two in which hypnotism and subliminal suggestion were used to recreate a 'virtual' environment so invocating suggestive response in human subjects.
Top secret experimentation did lead to specific technologies common in the marketplace today. Such 'benchmarks' may be used as marketing devices for further psychological assessment. Additional capabilities in human conditioning may be attributed to geographical location, dietary restriction, selectivity and ethnic purification; respectfully.
Other psychological drivetrains may entail an agent provocateur relationship between a host and subject in which routine examinations help build the subjects 'skill' according to the agent-agency protocol. The subject may or may not be concious during the sessions, but depending upon the extensibility of the research the virtual reality will be quite realistic with minimum degree of negative deviation.
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A newer question on magic & conservation laws reminded me of this question.
What if the super AI was like Maxwell's Demon? It can cause improbable things to happen, and specifially reverse anything that happens easily. A minute expendature of normal energy and *knowledge* allows reversing of **entropy** in our physical world at the expense of having to dissapate the information entropy somewhere else or consume large amounts of power.
Unlimited hero with limits imposed: if he doesn't get back to home base in time (to discharge the divice with its special dock) then it, he, and everything around within a few feet will catastrophiclly give up energy, freezing to liquid helium temperatures.
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In the *Jumper* series of novels(I think I was reading *Exo*; something like that), it was pointed out that teleporting to different latitudes etc. Required a change in momentum as well as position. She figured out how to jump in-place while adding momentum. I was thinking "I guess that's how Superman does it."
If you're making it a point to be physical for teaching and illustration (like the early stories by Robert L Forward) you need to follow conservation laws. If some other thing took the opposite momentum, and a non-instantaneous energy-carrying field linked the two, that could be interesting.
A way to have a seemingly reactionless drive would be a dark matter rocket. Particles in the air can be converted to dark matter through supersymmetry laws, liberating energy by choosing an unbalanced reaction, and having all the produced particles fly off in one direction.
But what are the boundaries of the rules? By using physics, what *can* be done (that doesn't work in the real world) and what can't? What's the unifying principle? The story needs a succinct super rule that the audience can grasp and understand what is allowed or not.
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If it's a matter of a manipulation of rules of physics, how about having someone with the ability to stretch out their arms and use material of some sort (or if you'd like to be somewhat disturbing, their arms themselves) to generate a 'Magnus Effect'[[1](https://www.youtube.com/watch?v=acXvl-8xrBM)]?
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A sufficiently powerful electromagnetic force would do the trick, such as [magnetic levitation](http://en.wikipedia.org/wiki/Magnetic_levitation).
All you'd then need to do is alter the strength of the magnetic field in the direction you intend to travel.
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Make use of the butterfly effect.
A butterfly flapping its wings in one place can cause a tornado in another. If you could harness this then, for very little effort on your part you could be propelled around by your own personal hurricane.
Maybe you would have small wings on your heels (like the god Mercury) but instead of flapping them to provide lift, you use them to cause a boomerang butterfly effect. There would be a time delay but you could learn to control this with experience.
>
> In chaos theory, the butterfly effect is the sensitive dependence on initial conditions in which a small change in one state of a deterministic nonlinear system can result in large differences in a later state.
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> Wikipedia
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If you are willing to change laws of physics, the answer is quite obvious.
Negate the law that says **every force has an equal opposite force.** No the character can pull themselves up by the bootstraps or something similar. They are actual a couple ways this could be realized, from tag teaming to magnetism. I provide a gallery of different demonstrations of the principle.
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Why not manipulate gravity so that it pulls in a different direction, so that you could fall in the direction you want to go?
The speed of the gravitational pull could be slowed by an opposing gravitational pull in the opposite direction.
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Your current version sounds a lot like a basic form of what Brandon Sanderson uses in [Stormlight Archives](https://coppermind.net/wiki/Order_of_Windrunners#Gravitation) - cancel out gravity. What makes it flying is that they can also let gravity act upon them in any custom direction. So the flying becomes a bit of falling with style.
My personal preference would be a combination - cancel gravity and then use wind to steer yourself where you want to go. If you're weightless (NOT massless), you will accelerate a bit slow (because of your mass relative to the air), but you'll be blown away by any wind.
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Magic conveniently "explains away" many things associated with shapeshifting, but in the course of some of my fiction writing, I endeavor to include some slightly more plausible explanations when possible.
One such aspect I've not been able to create a satisfactory explanation for is how a shapeshifter might retain most or all of their cognitive ability and memory as an animal with a much smaller or different brain structure.
One of my ideas is that the retention of such mental faculties is time-limited. The longer the shifter spends in a form, the more at risk he is to lose memories, etc. This introduces a risk factor which is sometimes good, for example, to give the protagonist an obstacle or limitation.
However in a different scenario, it would be useful to have a somewhat believable method by which a shapeshifter could effectively process and remember information—as a tiny mammal or bird—compared to his or her human brain. What sort of ways might this be explained?
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Some ideas:
* the shape-shifter has access to a 'higher dimension' or a different realm - some sort of storage facility where electrical charges (or whatever is involved in retaining memories) can be kept, as well as physical strength, clothes, and whatever else you want the person to retain when they get back to their own body. This basic idea is used in [KA Applegate's Animorphs series](http://animorphs.wikia.com/wiki/Z-space) and in David Eddings's Belgariad and Malloreon.
* the shape-shifter is actually a shape-swapper, and whenever they change into a mouse, say, a mouse somewhere changes into them! The memories of each creature could be stored in the brain of the other but only accessible to itself, so your shape-shifter has the body of a mouse but access to a human brain. This is one of the theories raised in Allan Ahlberg's book 'Woof!'.
* the shape-shifter only takes on the outer appearance of a mouse (sticking to the same example) and all the complexity of a human brain is simply crammed into a smaller space. After all, artificial data storage devices are constantly getting smaller, so why not have a mouse-brain-sized thing that can take as much information as a human brain? Maybe the shape-shifter can even consciously dictate how things are arranged inside the body, so if they're capable of becoming either a mouse or a bird, then they could also become a feathered mouse (with a scaled-down human brain). This is similar to what kandras do in Brandon Sanderson's Mistborn series.
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You could posit that he shifter does not actually change form. What changes is how the universe itself perceives the shifter.
If the shifter changes into a dragon for example, he can now breathe fire because the universe believes that dragons can breathe fire. If he becomes a mouse, he can fit down a mousehole because a mouse can, not because he has actually changed.
He looks like a mouse because the laws of the universe say a mouse looks like a mouse, not because he has become a mouse.
We are essentially gaming the laws of reality at a relatively high level. We're not shifting quanta, we're modifying idea space.
In computational terms the shifter reassigns his superclass, something that most languages render impossible for good reason. He is still the same object, but he is now able to appear and act in the universe as a though he were different object. He is the same, but not the same.
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Information in the brain could be stored on DNA short-term and reloaded upon shifting to larger brain sizes. You don't use most of you brain so vast parts of it it wouldn't need to be stored. Of course even without compression you can store the entire capacity of the human brain on 66,667 DNA strands. For comparison there's 100,000 neurons in a fruit fly's brain according to [Wikipedia](http://en.wikipedia.org/wiki/List_of_animals_by_number_of_neurons).
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Since you're dealing with some hand-waving anyway (Where does all the mass go?), some or all of these could be used. It strikes me that the shape-shifter might treat non-self transformations as memories of dreams. As such, a non-self transformation, when dealing with memories or processing can be looked at through the lens of lucid dreaming.
When the animal in question is of a much lower physical capacity than the shifter, that's ok, because the shifter knows it to be a dream. The shifter knows the rules of the game still apply (like hungry larger creatures are still hungry and in their dream, can have a snack of the shift's dream self), but the shifter may in fact walk an uncanny edge by behaving more like a sentient shifter than a bird, for example.
Looking at it through the lens of a wider fantasy setting, this means that attempting to impersonate a creature with greater faculties may give the impression of a mentally challenged member of that species, as the native members would see the behavior and/or mind of the shifter to be lacking something that's inherently them.
Biology-wise, our active regions are quite voluminous when compared to the size of a crow's brain, yet the crow can use tools, have fun, experience elder family bonds, and solve puzzles, so it is not too far fetched that some capacity can remain with a resized brain. For extreme resizes (beyond an order of magnitude, say, to a cockroach from human), you might look at "heat" penalties for advanced thought, carrying a risk that some crucial link to the shifters' self can get melted by too high a current, after which they lose themselves and become what they've transformed into, allowing for new identities to be born. This also provides an opportunity to develop from a story standpoint as a shifter who is not as well fortified against this effect and even reducing their brain mass by 2% gives them headaches. Alternately, paragon shifters can transform into dragonflies and actually reach a destination, as long as they don't try to think about philosophy in the background. Maybe this is where Zen as a concept comes from in this world?
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There used to be a theory that the heart stored our emotions, and one of the early recipients of a heart transplant, in all seriousness asked if after receiving the new heart if he would still love his wife or if he would love those of the donor.
A friend of mine takes that one step farther. He believes that the 'mind' is separate from the brain. The brain is just another organ like the heart and if we did a 'brain transplant' the mind would stay the same, by replacing an Alzheimer's brain with a healthy brain, he believed the person would be back to 'normal'. While I'm not really able to swallow that it could certainly be a 'decent' story-line to take. And it would still be possible that the longer one was in an animal form, the more the form would start to affect the mind.
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People need to realize that the reason why brains are smaller in some mammals vs the size of an elephant's brain, for example, is NOT because they have more information or have more knowledge. It is because of the shape and structure of their skull. If you look at a cat's brain, it looks a lot more wrinkly because all parts of their brain must fit into their tiny skulls.
With shapeshifting, I think memory is an important factor. If they can shapeshift exactly like another organism, that means they had the visual technique and memory to be able to transform like them. So looking at the brain as a whole, the part of the brain that takes care of memory and vision would be primarily responsible for the action of shapeshifting. BUT those two are obviously not the only ones that would be affected. more scientific factors would be involved, much too complex and quite impossible to explain.
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Considering the fact that memory is nothing but electronic pulses in the brain, as long as your shapeshifter exists of cells, then they will still retain memories.
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Maybe the shapeshifter does not have a brain per se, instead all (or most) of its cells act as neurons. It needs much larger number of cells to reach the same level of thought as the more specialized vertebrate brain made of specialized cells, but if all of its cells were contributing it may be enough.
This would also mean that losing tissue is a bigger deal to it than to us, since if it loses an arm it is also losing the memories and skills stored in those cells.
This also means they think slower (longer connections), although their reflexes would probably be better since they would only involve local cells.
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**They need a special artefact, that contains their mind as long as they are transformed**
NB: probably this would be a story-driven answer.
Think of the [phylactery](https://dungeonsdragons.fandom.com/wiki/Phylactery) of liches in D&D.
Your shapeshifter may need a kind of amulet in order to channel the magic/mana and change shape. Since the new shape is not the shapeshifter's true form, it is necessary for the amulet to be charged with magic/mana in order to allow the shapeshifter to keep the new form.
But while the body was changed into a different being, the mind of the shapeshifter is stored inside the amulet, from where it can "telecontrol" the new body.
Since it is a magic connection, it is not necessary that the amulet is worn from the shapeshifter in his modified shape, even if probably the destruction of the amulet would in this case cause the death of the shapeshifter (so the shapeshifter should be very careful in hiding it).
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Mind uploading means our "body" is virtual. Shapeshifting, bending elements like the avatar, or pretty much any kind of awesome magic is now possible since its all virtual.
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
**Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers.
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This question does not appear to be about **worldbuilding**, within the scope defined in the [help center](https://worldbuilding.stackexchange.com/help).
Closed 3 years ago.
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The heroine in my story is a princess who has fallen in love with a commoner, but because of the differences in their ranks, they may not marry under normal circumstances. However, there is a loophole: The princess may set a public challenge for her suitors. The challenge may be in one part or many, and each part must either be an objective test, or if subjective, must be administered anonymously if judged personally by the princess or judged by a third-party panel not involved with any party.
Traditionally, the Princess may set any challenges she likes, and may aim it at a particular man, but if another can better meet her challenge, she *must* marry that other man.
Now, in my story, the Princess and the man she wishes to marry are attempting to cheat. In the subjective part of her challenge that she will be judging personally, each of ten suitors pick a number at random from a bucket, and the cheating suitor silently mouths his number to the Princess so that she can choose his entry that will be paraphrased and written down by an unknown scribe with only his number identifying his response.
Given that the princess is not deaf, but does have some experience in lip-reading, which two numbers between 1 and 10 inclusive are easiest to mistake for one-another when lip-reading when spoken or mouthed in English?
Since this part of the story is intended to emphasise the penalty imposed by the gods for cheating, I want the princess to misinterpret the number mouthed by her favoured suitor as a different number... hence the question: which two numbers look most alike when lip-read?
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
**9 & 10**
Spoken speech can be broken down into what are known as 'phonemes' or different distinct sounds. The equivalent for a lip-reader is 'viseme' or visually distinct sounds. Given that the human mouth can make different sounds with the same shape, visemes can correspond to several different phonemes. It's complicated to go through the whole list, but here's a link for the [comprehensive list](https://docs.microsoft.com/en-us/previous-versions/windows/desktop/ms720881(v=vs.85)?redirectedfrom=MSDN), originally used by Disney animators, of all things. I'll go through the numbers, one by one.
* One: The 'n' can be mistaken for 'd' or 't', giving 'what' or 'wad'
* Two: The 't' can be mistaken for 'd' or 'n', giving us 'new' or 'dew'
* Three: The 'th' and 'r' are pretty distinct, though the long e can be substituted.
* Four: 'f' can only be confused with 'v'. No luck with confusing it with any other number except five, and the rest of the word disqualifies it.
* Five: This can be amusingly read as 'vife', but the 'i' is going to sound like an 'i' cluster and the 'f' can only be swapped with 'v'. No dice.
* Six: 's' goes with 'z', and 'ix' can be swapped for most 'i' vowels, giving us words like 'sigh'.
* Seven: 's' can be 's' or 'z', 'v' can be 'v' or 'f', 'n' can be 'd', 't', 'n'. The 'e' vowel sound it uses can be 'eh', 'ey', or 'uh', which gives access to a truly staggering amount of possibilities. Albeit a lot of them aren't real words and none of them are numbers.
* Eight: The 'eigh' in 'eight' can be substituted for 'ax' or 'ah', and the 't' for 'd' and 'n'. This means that 'eight' can be lip-read as 'aught', and 'aught' is slang for zero. (Grossly incorrect slang for zero, I'll point out. But slang nonetheless.) But zero isn't on this list.
* Nine: 'n' is 'd', 't', 'n', and 'i' is the i-range of vowels, so we have words like 'tide', 'night', 'dine'. We even have 'tine'.
* Ten: 't' and 'n' both belong to the same group alongside 'd', and the 'e' is part of the 'ey', 'eh', 'uh' group. So we have words like 'den' or 'net'.
Final summary: Eight can be easily misread as 'aught', slang for zero, which would be good if zero was on the list. It's still possible, perhaps if the reader read 'aught' and assumed he might have missed a word before it, so he'd mistaken 8 for 10. That being the case, 9 and 10 are very similar as well, possessing only one major difference in their vowel, and, depending on the accent of the speaker, possibly not even that. (Though it'd have to be a thick accent.) It's also worth noting that the word 'aught' means 'all', literally, so you may be able to work off that somehow. I hope this helps.
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What you are looking for is a **confusion matrix** for visual speech recognition, of **digits**, ideally from a real-life experiment. I tried to find some references on the matter. Most address the issue from an automation perspective, attempting to create models that can perform "lip-reading" in the AI sense. There doesn't seem to be a consensus on the matter, however, the following information might have the potential to pinpoint what you could/should take into account, if you would like to make a choice on your own.
1. In [this paper](https://www.researchgate.net/publication/323718862_Visual_speech_recognition_for_isolated_digits_using_discrete_cosine_transform_and_local_binary_pattern_features), some 30 people *spoke the digits from 0-9* and a complicated "artificially-intelligent" system was set up to recognize the spoken digits **visually**. Their result is visualized as follows ([original source](https://www.researchgate.net/figure/Confusion-Matrix-for-SD-Models-with-LBP-features_fig4_323718862)):
[](https://i.stack.imgur.com/CWyEg.jpg)
Cell (row, col) in this image represents how often the actual digit *row* was identified by the model as digit *col*. For some reason, the horizontal axis is termed "Predicted class" although I think it should be termed "Target class", as it typically represents the actual value. Lighter colors represent higher percentages, and diagonal cells, obviously, represent correct identifications. One thing that probably stands out is the slightly higher tendency to confuse *zero* with *seven* (both have two syllables, huh?) and *four* with *two* and *three*. Also, *nine* was only correctly detected 60% of the time and *one* and *five* seem to be the most distinguishable (by a small margin, of course) digits.
2. In [this](https://iajit.org/PDF/March%202018,%20No.%202/10431.pdf) paper, 10 subjects spoke digits from **1 to 10**, and a different model was set up for visual speech recognition. The final confusion matrix is (snapshot of **Table 4** from the linked paper):
[](https://i.stack.imgur.com/Y1VNy.png)
*Nine* was also correctly identified **fewer** times than the other numbers, with *ten* also showing quite a low detection success rate. This paper uses a smaller dataset and the final result is not **extremely** telling, plus it uses a rather different underlying recognition model. I don't think we can draw more conclusive results from this. Nevertheless, the results technically contains what you are asking for, i.e. the confusion probability between visually recognized lip-spoken digits, **albeit not by an actual human, rather by a *model***.
3. In [this](https://www.researchgate.net/publication/315874661_End-To-End_Visual_Speech_Recognition_With_LSTMs) paper, we can see another confusion matrix, visualized in the same spirit, for digits 0-9 ([Fig. 3](https://www.researchgate.net/figure/CUAVE-confusion-matrix-The-labels-for-X-and-Y-axes-correspond-to-digits-0-to-9_fig4_315874661) from the original):
[](https://i.stack.imgur.com/80jwR.png)
Similar to the result of paper 1 above, *five* seems to be less confused in general, with *nine* being practically the hardest to recognize correctly. One apparent confusion arises between *zero* and *two* (I would spuriously attribute that to the two ending in the "uw" viseme, which makes it important to not miss any "frames" during lip-reading, in order to correctly distinguish between those two). In fact, to quote the original paper:
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> In the CUAVE dataset, number pairs zero and two, six and nine were
> most frequently confused. Zero and two share similar viseme sequences
> near the end of the utterance while six and nine share similar viseme
> sequences at the start of the utterance which explains the more
> frequently occurring confusions for these number pairs.
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Maybe we are getting somewhere... Let's travel back in time, a slight bit....
4. In [this](https://papers.nips.cc/paper/993-visual-speech-recognition-with-stochastic-networks.pdf) paper of 1994, [publication-related link](https://www.semanticscholar.org/paper/Visual-Speech-Recognition-with-Stochastic-Networks-Movellan/98095c3f6cbc1cc072bc5b9db23da08366a27f96), an actual human confusion matrix is given, together with that of a contemporary *best artificial system*, for the visual recognition of the first four English digits (1,2,3,4):
[](https://i.stack.imgur.com/ofCCj.png)
The results are from 9 subjects, 3 of which are hearing-impaired and having been taught to lip-read at 2-8 years of age. The paper argues that the two matrices have a correlation of 0.99, which renders the artificial system a very good approximation of an actual human, as far as "confusability" is concerned. *Three* seems to be the most confused number among those (I would say somewhat counter-intuitively, no?).
Almost there, just one more piece in line:
5. In [this](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.736.6118&rep=rep1&type=pdf) paper, using another interesting lip-reading recognition model based on visual space transformations and neural-network classifiers, the authors arrive at the following two confusion matrices (two alternative though similar models), tested, again, on the [CUAVE database](https://ieeexplore.ieee.org/document/5745028), from which, apparently, the model of the authors attempts to recognize spoken digits from 7 individuals:
[](https://i.stack.imgur.com/K4pVV.png)
R.R. refers to Recognition Rate (%). Note that each row sums to 35, meaning that rows represent input numbers, and columns represent what was the actual identification (elements of the diagonal represent correct identifications). In short, *seven* seems easier to confuse, but *zero* even more so! *Seven* was confused with *six* slightly more often in the 2-d model, while *three* was confused with *six* slightly more often in the 3-d model. The 2-d model also confused *zero* with *six* a lot. Both models confused almost equally often *nine* with *eight*. **see END NOTE**
Now, before I wrap this up, one final, but important, addition:
6. In [this](https://www.researchgate.net/publication/220862248_Evaluation_of_A_Viseme-Driven_Talking_Head) paper, a virtual head was considered, in the context of improving acoustic intelligibility by adding a **visual** component. While the entire paper is interesting, I just want to highlight an important point:
>
> For the natural head, the confusion matrix shows that the visemes
> (h/n/ng) and (g/k) were less well identified than other visemes (Fig
> 9). This may be because the tongue movements that distinguish these
> visemes from others were less visible from the external view.
>
>
>
So, do not forget that the **tongue** is not clearly visible from a nontrivial distance, which is an important consideration that adds to visual lip-reading confusion. Digits that utilize the tongue more will, technically, be confused more!
# Bottom line
While there is no concise take-home message here (i.e. less subjective than what you can probably pick on your own), I hope this at least gives you an idea of how this is looked at from a visual speech recognition perspective. Also, while those are *theoretical mathematical models* trying to visually identify the digits there, you could probably get an idea of what would be easier to miss from a machine-learning perspective. Humans are definitely much better at training to understand digit visemes on lips. Also, you can find much more similar results if you search for other kinds of visemes, such as words or diphthongs etc.
**END NOTE**: (By "confused *x* with *y*" in this context, I mean "*x* was misidentified as *y*").
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
I don't have sources to back it up, but six and eight both have almost no lip movement, because they're mainly formed by the tongue, and are both in the [i]-range, making the lip-positions mostly indistinguishable.
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There is a website called the SCP Foundation which features a variety of creatures, objects and phenomena that border on the horrifying to the just plain weird. This one straddles the boundary between both: carnivorous blankets (or SCP-799 as its officially known on the website). Here’s the official page for it <http://www.scp-wiki.net/scp-799> . If you don’t feel like reading the whole page, the blankets are basically creatures that superficially resemble ordinary blankets, coming in a variety of different shapes, colors and designs, and are described as retaining heat unusually well (of course, that’s probably their own body heat). Normally content to feed on dust, in times of extreme hunger, they are capable of becoming predatory, lying in wait for something to wrap themselves in it before eating it. They also reproduce through budding. So, the question as always is, can something like this evolve in nature?
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My first thought was "it's probably some sort of fungus", and the SCP article does indeed bear out that supposition! Some sort of slime mold (which are not technically fungi, and actually span multiple taxonomic groups) could also work. The fibers of the blanket would just be fungal hyphae.
Some types of slime molds in particular are capable of metamorphosis during times of "hunger" (low food availability), which would fit this scenario. The particular metamorphosis described for SCP-799, however, is a little implausible--how do you grow a mouth on a blanket? Particularly without it being noticed? If you are content to have the creature stop actually looking like a blanket anymore when actively feeding, then I guess that's fine, but it seems unnecessary.
A more plausible approach, which could be accomplished with no metamorphosis required, would be to simply have the creature excrete toxins and digestive enzymes when wrapped around a victim. That's totally normal behavior for fungi.
The trickiest part would be evolving patterns designed to specifically trick human victims into using them as blankets. However, mimicry is a pretty darn common phenomenon in the natural world, so given an appropriate environment and evolutionary pressure, it probably *could* happen. I might expect such a creature to derive from an *old* civilization, a la the Moties from *The Mote in God's Eye*, where human culture has been around for so freakin' long that the entirety of the rest of the biosphere has evolved to fit into and around it. Plausible-enough starting points for the evolution of such a creature might be intentionally-engineered living blankets that end up "going feral" (so they don't need to evolve pleasing patterns--they just inherit them from their artificial, domestic ancestors, while evolving the ability to paralyze and digest large animals later), or varieties of mold that start out by, e.g., evolving to form pleasing patterns as "living wallpaper" to avoid being eradicated when humans find an infestation.
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The only habitat where such an organism could develop would be a hospital. Otherwise, it would violate our understanding of population dynamics.
In a hunter-prey relationship, there are periodic undulations in population size where the hunter lags behind the prey. In the case of a man-eating blanket, prey population is zero, and stays zero, after having consumed one. Nobody wants to sleep in a bed (or under a blanket) where someone has died. Also, while technically "zero" is a stable mean value, it is not really a value that is much compatible with the notation of "population" as such.
The only place where people die regularly, and others sleep in their bed, again regularly, is a hospital.
Reproduction is another thing. Now of course, if instead of *budding* they reproduced e.g. with a spore cloud that infects a normal blanket, then this might actually work when there are other beds nearby (again, hospital, but also e.g. YMCA). Otherwise, the organism would have to be prepared to survive in a washing machine, which is a tough challenge to most. The budding had better be fully grown pretty fast as well, or it might land in the trash can when discovered. Darn it, who cut a blanket in half, and left it lying around here...!
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My first thought when I saw this question was some form of mollusc, in the nature of a large, air breathing [nudibranch](https://en.wikipedia.org/wiki/Nudibranch) or similar but the texture is all wrong, a colonial algae or a fungus might be able to take on the proper texture but I think the best option is a form of [sponge](https://en.wikipedia.org/wiki/Sponge). Sponges are extremely versatile and hardy creatures that already have an extremely broad existing morphological range and they already come in [carnivore](https://en.wikipedia.org/wiki/Sponge#Carnivorous_sponges) too.
Any type of creature we're familiar with would probably require more fluid than general room dust would give it, so it would need to induce food and drink spillages and washing cycles to stay hydrated.
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There are animals using leaves as shelter from weather, and it happens that the Dionaea muscipula, or Venus fly trap, uses leaves to capture its preys.
So, start with a Dionaea with larger leaves, offering shelters to animal, and eating them from time to time.
While the trap grows bigger, the stem can slowly disappear and also the pattern on the leave can change. Now you have your new species: the *Dionaea Blanketula*!
To prevent that intelligent animals like humans can remember a blanket devouring their conspecific or simply refrain from using a random blanket found somewhere, I suggest the *Dionaea Blanketula* to stay close to places where the alcoholic content of the dwellers' blood make them prone to seek a random blanket when venturing out in the fresh air after a drink, or where the humans wouldn't be to picky about the origin of the blanket (bridges, train stations, slums, etc.).
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**Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers.
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You are asking questions about a story set in a world instead of about building a world. For more information, see [Why is my question "Too Story Based" and how do I get it opened?](https://worldbuilding.meta.stackexchange.com/q/3300/49).
Closed 7 years ago.
[Improve this question](/posts/66055/edit)
I want to develop the lore of my world for a project. The main idea is: The protagonist has something (can be a curse, whatever, it will be decided later) that makes everyone forget about him when he is not around.
Explaining a little better: If he/she is with someone, all is fine, but when he/she gets more than a certain distance from that person, that person's memory about the protagonist will start to fade away, until that person completely forgets. What would be the implications of such world for the life/personality of the protagonist? Also, I was thinking about problems, like he/she buys something, and the seller would forget about it, so he/she needs to make sure no one thinks it's stealing.
EDIT: Answering all the questions (I was with a 12-hour shift from work, sorry guys).
It wouldn't strike at birth, should be something it was acquired later on by the protagonist, maybe on his/hers early 20s.
As given on comments, it would be very interesting to have some antagonist with the same situation, but maybe with a better grasp/control of it, or at least knowing how to greatly use on his (the antagonist) favor.
Once you get out of radius, it would slowly fade way, and yes, depending on your relationship with the protagonist, the memories would take longer and harder to forget. The shopkeeper you just bought something would quickly forget, but some kind of lover would take way more, like days/months, but would start forgetting one fact at time. Memories lost this way, so far, would not come back, but I'm still thinking about it.
Documents, things destroyed and on would stay the same. So if the protagonist is punched or punches someone, it would still be there even if the person forgot what happened, and pictures taken this way would still keep his/her record (but people who see will get that feeling of "how the f\*ck this guy got in my picture?"). So, to make it clear, any physical/digital record made would be kept.
I was wondering about the time setting be placed somewhere with not advanced technology, like medieval/steampunk time, so people would be more dependant of what is told to them, also trips would take longer, making the condition of the protagonist worse (a trip that we would make in 2hr by plane would most probably take 1 full day by horse, leaving time to some people to forget him/her). So, even with his/her SO, things could be complicated, like, the SO remembers being with someone, but can't remember who.
So, if the time setting is indeed the one I stated, jobs as a mercenary would fit well, if set in the modern age, remote jobs would do just fine, as the comments pointed out.
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> Also, I was thinking about problems, like he/she buys something, and the seller would forget about it, so he/she needs to make sure no one thinks it's stealing
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Actually, I was thinking that this could be a great way TO steal things. A fantastic advantage...Steal from a store, the owner calls it in. If the cops are a few minutes, the owner forgets their face...If it's an hour or a day, maybe they even forget they called it in?
>
> Explaining a little better: If he/she is with someone, all fine, but whe he/she gets more than a certain distance from that person, that person's memory about the protagonist will start to fade away, until that person completely forgets. How would be the implications of such world for the life/personality of the protagonist?
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Lots and lots of first dates? Here's a question, which isn't completely clear from what you wrote, if I see the forgettable protagonist, and have a conversation with him, and then I see him again, do I suddenly recall our past interaction? It doesn't sound like it. If not, for a lot of men, at least, it means that they can gather info on a person they like and be a perfect man for them the first time she remembers meeting him.
If I forget the protagonist until the next time I see him and then I remember, that changes the way the protagonist interacts with the world and the people in it. In this case, it's possible to live with someone.
It's also possible, though somewhat difficult to keep a job, depending on the type of society/time that this is set in. In a large company, most people are just names on a payroll. Getting the job would be difficult, but, maybe not, since the protagonist can have multiple conversations with the person that has the power to put them on payroll (again, this depends on if the person would suddenly recall their last interaction upon meeting them again, which would not be conducive to getting put on payroll, or if they would be meeting the protagonist again, for the first time). It's a fabulous way to get information.
If set in modern times, I expect that they would have an online persona and email. They would interact with people in that way, most likely. And, it's another way for the forgettable man to get a job. It's also a way to interact and get a rental home or buy a house. If most of it is done electronically, or mailed, they can live life around this inconvenience.
EDIT BASED ON TIME PERIOD ANSWER:
You put Medieval/Steampunk, and I'm going to say that there's a vast difference. Steampunk, even if it has some elements of modern stuff and some mystical and weird science elements, is generally set at the dawn of the industrial age--like the 1830s-1910.
As far as record keeping goes, that time period is VASTLY different than Medieval. (I've studied the Medieval time period a bit). Medieval times also varied greatly from geographic area to area. It wasn't until the rise of the Medici banks that a system of record keeping and doing more business through writing than in past ages, really developed. The Renaissance was more of a time of education and it started in the 1450s. The variance in Medieval times, as far as records and writing are concerned, had to do with a lack of education for a lot of people and a lack of social mobility. This changed with the Black Plague, which, I think, was part of the reason we were ready for the Renaissance. Basically, if you want this guy to use writing or written records to conduct his affairs, it's an easier road if you go no earlier than LATE Medieval or squarely Renaissance. (I like the swinging 1580s and 90s myself-- and it's a time of great playwrights, which is a job your guy can have...with an assistant who can be remembered).
Now standard Steampunk period--that there's the time of Dickens & Sherlock Holmes. I cannot tell you how many plots of Dickens' revolve around a mysterious benefactor, never seen or revealed until the end, who makes life better for the protagonist through a law firm. And Dickens isn't the only one to apply this device for this time period. It's a thing, I promise. And it serves to illustrate that as long as there is $$, and documents, stuff gets done in the 1830s-1910s by people barely seen. (In some plots, lawyers just get letters and never SEE their clients, they just collect the money and act for them.) It's actually easier to get a lawyer to act for a mysterious person they have never seen than it is today, if you can believe it, because they didn't really do background checks very well and because travel was more difficult. (And they did have trains...Steampunk can be blended with any time period, but the word "steam" is in there for a reason, and that means steam engines).
In either period, jobs are going to be more difficult, but not impossible, than they would be for the modern era. Playwright or courier are two that come to mind. Mercenary oddly, did not. What job depends on the world and frankly, exactly when--because the jobs of the 1100s were not the jobs of the 1450s or 1660s or 1860s, it's all different and is going to be dependant on your world. Find a specific time period you like and research the ever-loving heck out of it--you'll find something, or lots of things.
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## Groundhog day
This situation would allow the protagonist to repeatedly re-initiate meeting people, each time learning from how their previous "first meeting" or first date went - it can have some parallels to the popular Groundhog day movie.
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Sounds like a very lonely existence for your protagonist. To know, but never be known.
It would be impossible to hold a job or have any kind of meaningful relationship unless there was a way to somehow turn it off or mitigate the effects for short durations.
Maybe the longer your protagonist "imprints" on an individual the longer it takes the memories to fade from existence. Maybe video and/or audio cues (skype/phone calls) is enough to maintain the memories.
This would be an incredible ability for a covert operative as long as he/she maintains the imprint with the home base.
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First, you need to use agents. Here buy this widget for 50 pounds for me. The shop seller remembers the agent so everything is fine.
Unless, proximity restores their previous memory of you, if you got married your spouse could never leave your side. Even to goto the bathroom. The priest need not remember you a permanent record of the marriage exists in the marriage registry.
I hope at least your children can remember you, or it is going to be awkward. In modern times a dna test would prove it, and that would be enough for the legal system.
In modern times, everyone believes the computer. You show up with a drivers license and that is who you are. Most people today, don't remember individual people. You have a receipt, therefore you paid for it, and everything is fine. Especially with security cameras, I may not know his/her name, but their they are paying for their purchase. Done.
Using credit cards, your name matches your drivers license so your fine.
In today's society it wouldn't be that difficult to own or handle things as you are a number. Buying a house, you are probably one of 50 people buying house from that agent, the forms are complete and witnessed, transaction complete. The agent will think nothing of forgetting one of hundreds of customers, as the facts will be written down.
Self employment might be your best option, as long as you have records of money spent and earned so you can pay your taxes as far as the government is concern everything is fine. Inventor, or something you can do by yourself would be best.
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I recommend you "Forget me not", a Marvel comic with the same concept.
I like to think that there is some kind of "ritual" or "thing" that he can do, so the people remember him a little or just get to know his existence ,like: "ooh, you are that guy that helped me yesterday! oh...what was your name? I can't remember it...".
An interesting topic would be his childhood, how his parents acknowledged his existence and so on.
It would be funny to see managers confused when looking at the papers like: "how in the hell that guy made 8 job interviews with us? I never saw him in my life!"
I important topic would be his mental health and how he maintains it. Obviously you would be shocked if everyone that you love forgot about you and treated you like a stranger.
I see a character like this stick his existence to documents as much as he could. Internet blog/artist, journalist , bookwritter and so on. People who meet him would be like "no way you are that guy!".
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Mr. Average Gray was an ordinary person, there was no facial feature, or anything else that stood out. His manners were soft and his speech friendly, without any excess, just enough to be trusted and be remembered briefly, a couple of minutes at most.
Average did not have enough charisma for a woman to be attracted to him, so he never had a girlfriend or anything that could be named. Dating? Not exactly, some sporadic and brief encounter, sometimes of great sexual intensity ... but quickly forgotten.
It was not just his physical appearance or his behaviour, Average suspected there had to be some other cause. A pheromone or some telepathic effect was what made him so unmemorable.
And thinking about this was when Mr. Gray decided to take advantage of it ...
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I was wondering what it'd take for a fluid to be more efficient than water for steam engines.
My current idea is a fictional fluid with three properties: 1) It boils at 80C, thus requiring less fuel/energy to heat to a boil. 2) It has twice the density of water. Since vapour is always the same size regardless of fluid, this should mean that you can have a smaller boiler with a lot more pressure? The smaller boiler also means it can be lighter. 3) It's highly available within the setting.
There is one problem, though. Water is the (real) fluid with the highest Latent Heat of Evaporation. I'm not sure how important that is for a steam engine.
Would the fluid need to have a higher Latent Heat of Evaporation in order to be a more effective fluid than water for generating steam power?
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This might possibly be a better question asked of physics.SE, but the problem, uh, boils down to efficiency of heating.
Firstly, it is generally easier to heat a liquid than a gas. Loosely speaking, this is because the [thermal conductivity](https://thermopedia.com/content/1187/) of gasses tends to be lower as a result of their lower density. Liquid water, for example, has more than 10 times the thermal conductivity of steam. You can get the same mass of liquid and a gas to the same temperature, of course, but it can take longer to heat up that gas.
Secondly, [the efficiency of a heat engine](https://en.wikipedia.org/wiki/Carnot_cycle) is proportional to the temperature difference between the hot end (the boiler) and the cold end (the condenser). You want that hot end to be as hot as is practical.
Finally, your engine delivers power by basically moving energy from the hot end to the cold end. If it takes too long to heat up the working fluid, the flow rate will be low. If the heat capacity of the working fluid is too low, the heat energy that can be moved in a given time will be low.
Water hits a sweet spot of heat capacity and boiling point under pressure, and one which is hard to beat. There are lower temperature working fluids which get used for things like geothermal power plants using [binary cycles](https://en.wikipedia.org/wiki/Binary_cycle) or things using an [organic Rankine cycle](https://en.wikipedia.org/wiki/Organic_Rankine_cycle), because the underlying heat source isn't hot enough to generate enough steam to run a turbine.
This is why modern power generation still frequently use steam as the working fluid, centuries after the first practical steam engines. Look on the bright side though: hydroflurocarbonpunk just doesn't trip off the tongue. It'll never catch on.
(Note that I use a lot of weasel words above, because these things are always more complex than they initially seem, see also [supercritical CO2](https://en.wikipedia.org/wiki/Supercritical_CO2#Working_fluid) which can be an efficient working fluid at lower temperatures than steam, though it does require much higher pressures. That sort of thing isn't very steampunk though, so it doesn't fit your specific requirements so well)
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*edit: forgot to actually respond to your original question, oops*
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> How could a fluid be better than water for steam power?
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You working fluid should ideally be:
* non-toxic
* non-flammable
* minimally chemically reactive, even at high temperatures and pressures
* liquid at ambient temperature (so your engine doesn't congeal when it gets frosty outside)
To be better than water, it should probably have higher thermal conductivity in both the liquid and gas phase, but a *lower* heat capacity in the gas phase (so adding heat to the gas causes a greater pressure increase), though I'm not sure if there are any practical real-world materials that would fit all these requirements.
I don't *think* that a higher latent heat of evaporation is necessary or even desirable. It is useful for purely moving heat, but I think it makes it harder to develop pressure and for a steam engine that moves stuff you want plenty of pressure. If the thermal conductivity of the gas was higher, [superheaters](https://en.wikipedia.org/wiki/Superheater) can work better which might let you lower the latent heat of evaportion and form more gas and high pressures for the same energy, but I'm speculating wildly at this point.
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Good idea. Someone had to have had it. I backed into it.
1. What fluid is denser than water and boils colder than water.
How about **bromine?**
Density: 3.119 g/dl compared to water at 1
Boiling point: 58C
OK! And here is the patent for the engine from 1982
<https://patents.google.com/patent/DE3231309A1/en>
>
> Bromine-vapour gas engine Abstract The medium of bromine is heated,
> compressed and expanded after leaving the turbine nozzle. Thereafter,
> renewed liquefaction of the medium of bromine is performed in a
> special condensing region. The condensate runs back under the
> influence of gravity to the bottom trough and is once again heated and
> evaporated there. This is performed by a permanent circuit similar to
> that of water. The energy required for heating is supplied to the
> bottom trough with the aid of heat exchangers. After working
> dissipation to the turbine, this energy is once again completely
> destroyed after the expansion and condensation. The essential
> components of this drive system are 1. spec. weight = 3.14 and 2.
> boiling point at approx. 59 DEG C. A pressure of 9300 bar can be
> generated given a design height of 30 m. 1. Energy production without
> primary energy. No stress on environment. No costs for transport and
> delivery of oil, coal, gas, uranium or the like. The drive is
> performed using solar energy, collector greenhouse with large energy
> roofs - 25 km<2> - waste heat from coal-fired and atomic power
> stations or, e.g., the heat from refuse incineration plants. Hot
> springs and geothermal energy are also possible. 2. The plant is
> suitable in particular for installation in updraught power stations.
> 3. A further decisive "plus" is the possibility of installation at the site of very expensive large cooling towers. Instead of the
> destruction of energy in cooling towers, in bromine gas turbines the
> exhaust heat is forced to do further work and thus converted in an
> environmentally kind and profitable fashion.
>
>
>
The inventor proposes to use the engine to capture waste heat. The only problem is bromine is poisonous. At least it is not explosive.
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First some feedback:
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> 1. It boils at 80C, thus requiring less fuel/energy to heat to a boil.
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I don't think there's a reason to want this (apart from danger of burning your hands etc.): your engine will have a low efficiency if you work at or below 80°C. Likewise there's no reason per se to keep the amount of energy to get to the high temperature as small as possible. See further along for more info.
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> Would the fluid need to have a higher Latent Heat of Evaporation in order to be a more effective fluid than water for generating steam power?
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The difference in the amount of internal energy in your working fluid between the hot and cold part of the operation cycle is what's important I think (there's a contribution to this from phase transitions but also just from the ordinary heating in between phase transitions). The greater this difference, the more you can miniaturize your reactor for a given amount of desired power.
Although I'm not a specialist (I'll update this answer, i.e. consider it a work in progress and please edit it to improve it if you happen to be an expert on the subject), I think transcritical CO$\_2$ in the real world is already [considered 'better' than water](https://www.energy.gov/sco2-power-cycles-renewable-energy-applications/concentrating-solar-power) (in a kind of theoretical sense, with many unresolved practical problems standing in the way of real applications).
What is clear is that we would a priori prefer a working fluid that we can easily heat to and handle at a very high temperature $T\_h$ so that we can get a very good baseline (Carnot) efficiency $1-\frac{T\_c}{T\_h}$. Moreover, the difference in internal energy per unit volume $\Delta e=e(T\_h)-e(T\_c)$ for this working fluid is preferrably as large as possible so that we don't need to make our tube diameters and/or flow rates all too big. At first, water seems very good from this perspective because $\Delta e$ gets a big contribution from the latent heat that is requires to boil it from liquid to gas. Unfortunately, what seems to bring it back down is that the vapour phase appears to have a low density (at some given pressure that is, which by the way is also constrained to be not too high in order to not blow the reactor. In practice $150$ bar seems the best we can handle today) compared to some other candidate-fluids like supercritical CO$\_2$, so while its "$\Delta e$ per unit of mass" is very good, the "$\Delta e$ per unit of volume" is suddenly much more meh. Another thing seems to be that super-hot vapour seems to be quite reactive and corrosive and stainless steel has to be used to address that problem (but even then...).
Crunching the numbers apparently reveals that CO$\_2$ is [twice as dense](https://www.scientificamerican.com/article/can-carbon-dioxide-replace-steam-to-generate-power/) in the relevant high-T, high-P conditions (This statement could not be true if both gases behaved like ideal gases in these conditions, for then the number density and energy density would be equal for both under similar $P$ and $T$, I think). Transcritical CO$\_2$ is a bit in a sweet spot in between fluid and gas and seems to remain so far beyond its critical temperature of $30°C$ and this seems to be ideal for the purpose.
Besides potential application in future CSP projects, the Japanese are recently suggesting to use gas-cooled high-temperature nuclear reactors for much of the same reasons that I mentioned.
Have a look at <https://en.wikipedia.org/wiki/Rankine_cycle> to learn more
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The first improvement to steam engine is to split the expansion into smaller stages using a [compound steam engine](https://en.wikipedia.org/wiki/Compound_steam_engine).
In the eighties, it was suggested that you could use some of the waste heat from a steam engine to drive a second engine that used ammonia instead of water. This was proposed for power stations, as the engine would be large and need the economies of scale.
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In general you'd want these properties in an ideal working fluid:
* A **boiling point at your cycle's low pressure that is just above the temperature of your heat sink** (i.e. cooling water). Condensing steam at 100°C with cooling water of e.g. 15°C loses you 85° which could be used to extract more work from the steam if water had a lower boiling point. A fluid's boiling point depends on the pressure, but too low pressures aren't practical because then you need very big pipes and condensers to move enough mass around.
* **Chemical stability over the entire temperature range**. There are organic rankine cycle turbines to extract work from low temperature waste heat which use hydrocarbons as working fluid. Unfortunately the right hydrocarbons are not stable at the high temperatures steam turbines use. The higher the temperature, the more efficient your engine is.
* I think you'd ideally actually want a **very low latent heat of evaporation**. In a steam turbine you don't want the steam to condense in the turbine because droplets can damage the blades and condensation lowers the pressure. The condensation happens after the turbines in the condenser, where the latent heat of evaporation/condensation is just wasted and not converted into work.
* A **high expansion ratio** when heated. The higher the volume ratio between the working fluid at the peak temperature vs the lowest temperature, the more work you can extract from it per unit mass. This is why we usually use water/steam instead of a gas-only cycle.
* A **high volumetric heat capacity**. The higher the heat capacity, the more energy a given volume of fluid can transport per unit time. If we had a magic substance of which 1 liter had all the properties of 10 liters of water, we could scale down a steam engine by a factor 10 (volume-wise) and still get the exact same efficiency and power output of the larger engine using water. Volumetric heat capacity is the most important difference, I think, when using a 10xWater substance.
* **Cheap** and **non-toxic**.
The efficiency of a steam turbine cycle at scale is for a large part determined by the difference between the input temperature (the highest steam temperature) and the condenser temperature set by your cooling water. The peak steam temperature in current steam turbine cycles is limited by the creep temperature of steel alloys, which is around 700-750°C depending on the alloy. Going higher is possible, but that requires non-ferrous high temperature alloys for the boiler and pipes and the first stages of the turbine. Those alloys are much more expensive, so the cost of your engine will be a few times higher. (Gas turbines use this approach, but there you need much less of the expensive alloys because you only need them for the turbine and you don't have a boiler and lots of piping.)
*The question doesn't specify what constitutes 'better', so I am assuming you want some combination of efficiency and size/weight of the engine.*
As you are not changing the main limiting factors for the peak and lowest temperatures in the cycle, using a different working fluid is not going to change the overall efficiency of your engine much, assuming you prioritize efficiency over size and weight.
The choice of working fluid is mainly going to influence how big and heavy an engine will be, or how efficient it will be if you are constrained in size and/or weight. An analog of water with twice the density would also have twice the volumetric heat capacity so the engine could be smaller. But if the molecules of your fictional working fluid were twice as heavy as water molecules but the same size, their interactions would also be stronger which would translate into a higher boiling point. If you fluid had smaller molecules that had the same or a slightly lower weight as water molecules that would get quite close to your fictional working fluid, and as the number of molecules is higher the gas volume and thus the expansion ratio would also be better.
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I'm working on a sci-fi setting which includes an aquatic space-faring species.
When a human space vessel is ruptured and depressurizes, the gas can escape rapidly and we immediately suffer from the effects of vacuum.
For a water-filled vessel and an aquatic species, how would the ship being ruptured affect the occupants? My first thought is that the water would mostly stay together. Water in vacuum begins to boil from lack of pressure, which cools the water and can result in ice forming.
In a violent emergency where the ship's hydrosphere is exposed, would the mass of water form an icy shell and protect the remainder of the water from boiling away? Would the mass of water get cold in whole, or just near the edges? Or would something else happen?
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If the water is already in microgravity and isn't mostly constrained by structures, the vapor pressure inside will tend to blow the mass apart into smaller masses, which will in turn blow apart more. At some point in this process, evaporative cooling will freeze the water, ending the cycle (ice has plenty of structural strength to contain water's vapor pressure at low temperatures and in small volumes). The result, however, would be closer to a gentle "snow explosion" than "boiling away". The process would take time, of course, likely much more time than explosive decompression of an air-filled volume the same size; if the aquatic space crew have good reactions/training and can move quickly (as many fish can, for a short time) they have a good chance to get into a sealed space before conditions become fatal.
Also, human skin, at least, can contain the vapor pressure of body temperature water for a while (not indefinitely, but pressure would be relieved by blowing internal contents out of existing orifices before the skin would rupture, unless it's already torn or punctured and can tear outward from the existing damage). The same *may* be true of your merstronauts.
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It takes a surprising amount of energy to form a gas bubble in water. As an example, consider a glass full with some soft drink at rest. Usually there will be bubbles of $CO\_2$ going up continuously, *but they will all originate from a certain number of points on the glass surface, not from within the liquid*. These points are impurities in the glass' surface that ease the bubble forming process in a catalytic way.
As such, when you depressurize the ship, bubbles will form immediately **on all surfaces**. The bubbles on the surfaces will repressurize the water with their vapor pressure, preempting it from exploding in a vapor explosion. This repressurization will also, slowly, push the water out of the ship, where it will form big giant drops that are again stabilized by the vapor pressure on their surface as the water continues to evaporate. It's more of a tooth-paste-squirt effect than an explosion.
The really nasty part is, that the bubbles will also form on the skin of your species. This means, that any individual at rest will quickly not be swimming in water but be immersed within a bubble of low pressure vapor, powerless to move. And if the individual tries to swim before the bubble forms, it will create huge bubbles itself on the pulling sides of its fins.
This effect is even stronger if you consider that your water dwellers will be warmer than the water they swim in. This additional warmth means that the water bubbles that form on their skin have a higher gas pressure than the water bubbles that form on a cold wall. So the astronauts will be surrounded by bubbles before the ship's cold structure is covered in gas.
However, this temperature effect can also work for good: Assume that you have some machines in the spaceship that give off heat. If those machines are significantly warmer than the people on the ship, the boiling at the warm machines will keep pressure high enough for the people to survive until the machines are surrounded by gas or have cooled to the range of the body temperature of your species.
Ice won't form until enough water has evaporated from a surface to cool the remaining water down to 0°C. And when that happens, all your crew members will be drifting within their respective gas bubbles, extremely likely already dead.
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The water would all boil away. The main reason water can freeze in a vacuum chamber is because it is under gravity which applies pressure in lieu of an atmosphere. If your ship is really massive and really cold, it might be able to exert enough gravity to do this.
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All the humans disappear, except maybe less than ten (unskilled) people.
How long would those few be able to access and use the internet?
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**Not very long at all.**
Probably days at best. While I'm not sure about the infrastructure of the internet itself (which I think would probably last a little bit longer before catastrophic failure) the more pressing issue would be power. Without people running the power plants and managing the grids around the world the electricity would soon go out.
No electricity means no computers, so even if the few remaining humans are lucky enough to have a generator or be somewhere the power has lasted longer, most of the internet will have gone offline when the servers died due to lack of power.
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The answer to this is very dependent on geography, both of where those 'unskilled people' are and what part of the Internet they're trying to connect to.
Power: As many people have noted, as soon as the Great Disappearance happens, electricity will start to get spotty. Even if all vehicles avoid causing outages via downed lines, unchecked fires, freezes, storms and etc will start chipping away at the power grid. That said, cities are slightly less vulnerable than rural areas because of better protected, higher-density infrastructure: power is often underground instead of on a pole, and a denser grid means more redundant routes to the power station.
Networking Hardware: The core routers of the internet by now mostly reside in datacenters designed for 24/7 redundant operation. If their power fails - see above about those possibilities, and figure that a datacenter in a major city could indeed have feeds from multiple power substations - they generally keep a day or two's worth of diesel around, as that's considered long enough to get more trucked in in the event of a major outage.
Networking Software: The Internet is designed for redundancy. As long as you can reach a defaultless router (one that contains the core routing tables), you can reach anyone else that can do so similarly. And you'll have plenty of bandwidth to do so, as those that disappeared will no longer be using all the interconnect bandwidth by streaming netflix and youtube (which together are over 50% of downstream network usage). Failure after that will start by breaking the network off into isolated sections (which can still be used to talk among themselves!), until eventually it's all in so many pieces that it effectively no longer exists.
Overall, my estimate would be days (given decent weather) in rural areas and weeks in urban areas.
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Within hours, Lights around the world will begin to shut off. any servers which don't have backup power will go down. Even then, the remaining people won't be able to use the net if they don't have backup or can't help in producing electricity.
Those which have backups might work for a year, after which most satellites will fall back to the Earth. So you can say the max is 1 year, if both the servers, medium and the people survive.
[What would happen if humans disappeared](https://www.good.is/articles/the-earth-after-were-gone)
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If you consider only the backbone, the actual transmission of data, the internet basically becomes IP addresses. As long as there are two computers, and routers between these computers, that is an internet. Think of your home router. How much attention does it need? Sometimes, it needs a reboot. Otherwise, it will keep chugging along until the power goes out. Same with the internet backbone.
Perhaps the biggest job of IT technicians is to reboot recalcitrant routers, and dealing with hackers. Replacing the occasional switch that fries. Adding capacity. Otherwise, they just spend most of their time on customer support, telling THEM to unplug and reboot.
The life of the backbone then becomes an issue of back-up power. Because of the expense, I can not imagine anything with more than a few days of back-up power, more likely hours. Even back-up generators have a finite fuel supply, and need someone to continuously refill them.
But if you have a local system of routers, with batteries and solar back-up, the system should remain live for years, until either the router needs a reboot, or the electronics gives out. Most electronics is good for at least five, more like ten, twenty, even thirty years. Eventually, it is usually heat that destroys it.
Satellites, as we have seen in the Voyager system, can keep on ticking for decades. Their weak point is in keeping the sending Earth-based antennae directional and lubricated. Yet, people have home dishes pointed accurately at geostationary satellites for over a decade. The biggest weak link for these satellites is in the transmission points sending the data in the first place. Consumer dishes are receive only. They will continue to receive, as long as there is something left that is transmitting.
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Imagine that the average number of children born per birth without any artificial intervention was three (i.e. triplets were the norm) and that 98% of pregnancies gave rise to 2 to 4 children, with a single child happening only 1% of the time and more than 4 children happening 1% of the time.
This has been the case for as long as recorded history and oral traditions extent.
Otherwise, people are as they are today with today's level of technology and conditions.
How would human anatomy, fetal development and infant development differ?
If there are multiple plausible possibilities for one or more aspects of these questions, focus on the most likely ones.
Consider cultural consequences only as necessary to make plausible assumptions about the physical ones.
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## Anatomy.
Anatomically nothing much has to change in a human to accommodate triplets as the norm. However, food and energy intake for the duration of the pregnancy is likely to be higher than it is with humans in the current state of affairs as well as shorter pregnancies on average. [twin pregnancies](http://www.webmd.com/baby/features/11-things-you-didnt-know-about-twin-pregnancies#3) we can assume follow the same concepts as triplet pregnancies though in triplet pregnancies the things that are more pronounced in twin pregnancies, might be even more pronounced.
if people evolved in the way to have triplets as the norm these are the most pronounced anatomical and physiological features that can be associated with it:
* Narrower birth canal as the average size of each individual baby is smaller. This might lead to the necessity of a C-section for women who bear a single child or death as the only other alternative. (Or a very, VERY strenuous birth which might be touch and go for both baby and mom.)
* Larger uterus in proportion. There has to be room for three instead of the current standard of one.
* More breasts. I'm not kidding, Look at animals who have larger litters, they all have enough teats to facilitate their entire litter drinking, unless they have an atypically large one. [This](https://biology.stackexchange.com/questions/13791/the-number-of-nipples-breasts-a-species-has) little bit gives a little explanation on that matter.
## Culturally.
This mostly boils down to economics. Baby food and diapers would have to be significantly cheaper than they are now else such births would financially ruin plenty of people if the situation were as it is now. Also, I think there would be a lot more attention for anti-conception. Lastly, if we take into account current birthrates. (1 to 2 in the West versus up to 10 in developing countries) that would translate to 3-6 in the West versus 30 in developing countries. The ratio would remain the same but the population explosion and the sheer biomass needed to facilitate so many human would pose even greater trouble than the world has to deal with nowadays.
## Speculation.
Let's enter the realm of the hypothetical and say humans have the same life expectancy in your setting as they have in the current world. Projected is that the average amount of children per woman declines over the next century.
As mentioned above birth control will become incredibly important to manage population growth and biomass to facilitate the amount of children born per woman. It might be entirely feasible that if humans reach a certain amount, countries are going to set limits to how many births someone may have, or in extreme cases screen which families are permitted to have children.
This of course is entirely up to you as writer of your story, I just wanted to have my own go at the hypothesis and imagine a possible reaction of society on the matter.
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# More mammaries
Probably obvious, but you will need more than two breasts to feed more than two children.
# More fat
Women tend to add fat during pregnancy and keep it while breast feeding. This ensures that they can continue to feed their children even if their food intake is interrupted while the child is still breastfeeding (for a certain amount of time). To provide this cushion for multiple children will take more fat, and probably result in more significant weight gain for women during and after pregnancy.
I would suggest that this implies a more sedentary lifestyle. Women that have to march across the savanna after giving birth aren't really in a great position to be adding 20 or 30 more lbs of fat. On the other hand, a forest-dwelling human species would be more able to stay in one place and could support heavier pregnant women better. This suggests human evolution in the forest rather than on the savanna.
# Slower development
To feed 4 times as many children, the women would need a big jump in caloric intake. This can be challenging for a variety of reasons. I would argue that a better strategy would be to slow down the development of the children so that their demands for milk are lower and there isn't too much extra stress put on the body.
This slower development would only apply to the first two years or so. A 4-year-old multi-birth human might be only as developed as a two-year-old normal human, but then could catch up once the child was eating food on their own.
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## r-K selection
We'd love our kids less. No, really, when animals have more babies, they invest less time in them, whereas when they have fewer babies, they invest more in each baby. See [r/K-selection](https://en.wikipedia.org/wiki/R/K_selection_theory). The result is that we'd likely lose more kids (to disease, starvation, sibling murder, new parent murder, etc...). That may not be the worst thing though - the evolutionary pressure would keep the 'unfit' from surviving (note, I'd probably be unfit).
## Baby size
Would start smaller.
## Gestation period
The [current hypothesis](http://www.smithsonianmag.com/science-nature/timing-of-childbirth-evolved-to-match-womens-energy-limits-18018563/) about why gestation takes 9 months is that Mom's metabolic rate when she gives birth is about double her non-pregnant rate, and if she holds on any longer, she won't be able to metabolize enough energy for both her and the fetus(es). **There is no evidence that bipedal walking is affected by the width of the hips.** Since fetuses are growing (basically) exponentially when they are born, that only means a one or two month change: the same as most triplet and quadruplet deliveries now.
Since you want the kids to be just as intelligent as current humans, infants will be helpless for a few months longer and children will be autonomous at a much younger age (so the parents can deal with the next litter).
The largest metabolic cost for humans is neither growth, nor activity: it's our brains. Any suggestion that we'd grow more slowly because Mom and Dad can't handle the caloric load ignores that fact. Evidence suggests we'd actually grow faster so that the kids could handle themselves earlier.
## Anatomy
There is no reason to suspect that human anatomy would change beyond more mammary capacity (*Mom's and maybe Dad's!*) and fat stores. If you want something else to change, consider [Pleiotropy](https://en.wikipedia.org/wiki/Pleiotropy) - nobody will prove you wrong for at least 25 years.
## Menopause
The only other animals who undergo menopause are killer and pilot whales, both of whom send daughters out to other "family" groups when they mature, and usually only produce one calf at a time. If the family structure doesn't involve sending women away when they become mature (for example, because the boys leave too) the twilight of female life may involve more babies.
## Population Size
An 'r-type' omnivorous apex predator is terrifying. It's very unlikely that such a creature would ever evolve to be as intelligent as we are, but if it did, there would be a lot more internecine warfare because humans would be the only creatures applying downward pressure on the population.
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**More like kangaroos**
A species designed to have more babies would have smaller babies. Kangaroos are known for their newborns being the size of a baked bean. They develop outside the body.
The reason human babies take so long to mature is the hips are too narrow to admit a fully developed brain. Triple the number of children and the starting brain becomes even more basic. They know how to suckle and hold on and nothing else.
Perhaps your humans used to have one or more pouches like a marsupial but these dwindled as artificial alternatives took over.
The first thing these joey-humans learn to do is eat. To lower dependency on the mother's milk. She cannot reliably produce milk for three normal size babies. She does not have the stomach space to produce that much milk.
Then the babies can be fed prechewed food by any member of he family -- in particular their dozens of brothers and sisters. Only then do they start the process of crawling towards sapience.
One could imagine the mother would be less important to the children's development once they learn to eat, and this might make fathers more likely to act as caregiver. But I think the presence of much larger families will have a greater cultural impact than that.
There will be a stage in the development of these babies -- after they learn to eat and move but before their brains start growing in earnest -- where they are closer to animals than people. I imagine they would be treated as such, in a manner real people would find horrific. For real humans that animal stage occurs when the child is still helpless and so is hidden thereby.
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Just a quick shot out of my head:
* 2 pairs of mammal glandes. One cannot feed more than 2 babies at once with just 2 breasts. Taking turns in feeding won't supply enough energy to the growing babies.
* farewell biped walking. Standing comes with narrower pelvis, which in turn makes delivery more difficult. And homo sapiens is maybe the only mammal to suffer delivery death.
* smaller babies or, less likely, larger uterus. With the present homo sapiens multibabies pregnancy are troublesome for both the babies and the mother.
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**The question is probably nonsense from an evolutionary perspective**
It's not just humans who typically have a single child, it's the whole evolutionary branch leading to us. The primate branch that includes children produces one child at a time going back for tens of millions of years. The evolution of human-level intelligence thus takes place in the context of organisms that have very high individual investment in their offspring. Given the extraordinarily high levels of investment that are necessary to raise human offspring to adulthood - and even chimp offspring to adulthood - it is likely that these could not have evolved in a species which favours multiple-offspring-at-a-time.
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On Earth you can find your position through GPS, with clever use of satellites, timestamps and maths. Now imagine you're on a spaceship, there no satellite and nothing is going to give you the time. Yet, you need to find where you are relative to galactic center (which is the zero of my coordinate system). How would you accomplish that?
Here are a few restrictions:
You cannot rely on a navigational computer tracking your position. Effectively, when you go through FTL, you sort of know where you end up give or take a *few billion kilometers*. That's obviously not precise enough.
You cannot rely on extrapolating position based on nearby known celestial bodies because there most likely won't be one, and you'd still have to figure where you are relative to it.
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So far, I thought of using a set of known stars as reference points and sort of triangulate position based on them. But that would require two things:
A) That you can gauge the distance to a faraway star accurately; I guess not a problem after all;
B) That you can find a way to identify a star in a unique way, i.e. no two stars in the galaxy would have the same property/set of properties and ever be mistaken. These properties would also have to be sense-able from anywhere in the galaxy by your ship.
So I don't really see how this is a viable solution, but that may be lack of knowledge on my part.
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TL;DR: How could you calculate your position in the galaxy with only on your own spaceship's ability to see things and do math?
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First off, plus/minus a few billion kilometers in any direction actually isn't that terrible, particularly if you have FTL and/or are already dealing with interstellar distances. For comparison, that is on the same order as the distance from the Sun to [Neptune](https://en.wikipedia.org/wiki/Neptune) (Neptune's [semi-major axis](https://en.wikipedia.org/wiki/Semi-major_axis), the diameter between the points farthest from each other in its orbit straight across its orbital plane, is about 4.5 Tm, which is squarely in that range). In other words, metaphorically speaking, it's clearly enough to end up in the correct neighborhood, if not at the correct house.
That said, if you want something better, don't use ordinary stars to try to triangulate your position; **use pulsars.** [Pulsars](https://en.wikipedia.org/wiki/Pulsar) abound in our galaxy (within our immediate neighborhood, out to 300 parsec, we know of [eleven pulsars](https://en.wikipedia.org/wiki/Pulsar#Significant_pulsars)), many have highly specific (down to fractions of a millisecond) periods and pulse lengths, and
>
> Certain types of pulsars rival atomic clocks in their accuracy in keeping time.
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>
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By measuring the angles (you don't need to measure distances to triangulate your position) to a set of pulsars, and measuring their period and pulse length to identify each one, you can use the same principles as used in GPS or ordinary triangulation to determine your position in 3D space to a high degree of accuracy. It stands to reason that the major limiting factor would likely be your ability to accurately measure the angle to a specific pulsar without a platform plane change (changing the attitude of your spacecraft), as well as possibly the accuracy of the on-board data on the location of the pulsars.
The angle to a pulsar could be measured using either optical or radio receivers. With enough directional selectivity (which basically means a large enough antenna relative to the wave length of interest), a sensitive receiver and the capability to measure passage of time to a high degree of accuracy, you can get a sufficiently good idea of the angles to each specific pulsar. This is similar to the early work that led to the discovery of pulsars as radio frequency emitters, and which was awarded a Nobel Prize in physics in 1974, except you wouldn't be looking around at random.
In fact, the reverse has already been done: [the Voyager Golden Records as well as the Pioneer plaques used pulsars as a way of describing the location of the solar system](https://en.wikipedia.org/wiki/Pulsar#Maps) to any potential extraterrestrial intelligent beings that may come across the probes at some time in the future.
By first making a series of shorter trips to map the neighborhood (measuring the angles to pulsars for the purpose of later reference), you could easily make a sort of map that can later be used to determine your position based on the angles from your spacecraft to a handful of pulsars.
Compare also [How might Earth's location be referenced in stellar terms?](https://space.stackexchange.com/q/22383/415) on our sister site Space Exploration.
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Triangulation does not require being able to determine distance. Here is an example on an earth-bound maritime navigational chart:
[](https://i.stack.imgur.com/Kv6m4.jpg)
The ship in this situation would need to know in advance that it is somewhere off the west side of Cayo Santiago. After that, it just uses compass bearings to the north tip, the south tip, and what appears to be a water tank on the mainland. Draw those three lines on your chart, and there you are (literally).
In interstellar space, we will need a different reference point than *magnetic north.* What we probably will do instead is take relative angles between multiple stars, like this:
[](https://i.stack.imgur.com/IM6ri.png)
If the angle between this star and that star is 45° then we could be the upper space ship. If it is more like 30° then we are one of the two bottom space ships. Again, we don't need to know how far we are from those stars, only the angles. Of course, we are doing this in three dimensions, so we will need a couple more stars to get our position fix.
We will need to have an accurate 3-D model of the precise locations of stars, similar to how the boater needs a carefully surveyed chart of the waters he is in. Fortunately, we can get a decently good idea of that before we leave. This is done by noting the tiny difference between where a star appears to be from Earth versus half-a-year later, a concept known as [stellar parallax](https://en.wikipedia.org/wiki/Stellar_parallax) (in some ways the reverse of triangulation.)
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**Estimate your position based on the surrounding stars.**
If you know your position to within a few billion kilometers, you have a fairly good idea of where you are, on an interstellar scale. The solar system is about 4.5 billion kilometers across, for example. Knowing that you're in an area the size of the solar system, or even a few times the size of the solar system, should give you an idea of roughly where the surrounding stars should be.
You won't know exactly where the surrounding stars are, but your estimations, even for fairly nearby stars, should be accurate to within a couple of degrees. With a good description of the properties, approximate distance, and approximate direction of these stars, you should be able to locate them and use their actual positions relative to your ship to more accurately determine exactly where you are.
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You are right that it's difficult to tell one star from another (while looking at just that star), and while a 2-D star map is great for here on Earth, obviously it's going to look completely different in space.
However, since we know the distances to each of the stars, we can create a 3-D star map of the known area of the galaxy. Then, using A.I., we can figure out our position based on the 2-D (or 3-D even better if possible) star map we can currently see, i.e. the computer figure out where we have to be to make the stars' positions look like this.
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It was pointed out [here](https://worldbuilding.stackexchange.com/questions/10004/how-big-can-a-space-empire-get) that the speed of light is a huge issue for any government that spans multiple stellar systems. The consensus seemed to be that it is very difficult to make large empires work.
However, I don't think that anyone said that such empires are *impossible*. . .
So, I figured I'd ask about galactic empires, a common sci-fi trope. There are some issues that stem from the speed-of-light problem:
* Communication
* Shuttling troops to battle
* Sending diplomats/envoys to different star systems
* Ensuring that civilizations survive long enough for any of the above to be remotely possible
* Biological/sociological/technological diversity among different species.
These are but a few of the many problems that a galactic empire would face. There are, of course, many others.
So, how could a galactic empire stay stable for any significant amount of time (i.e. millions of years)?
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A galactic empire is not going to fit the mold we’re used to as a government. Even if we only look at the 25 or so closest stars, we’re looking at four years of travel time at best (assuming you’re traveling at the speed of light, which is highly unlikely) and 11+ years at worst. Planets are going to have a huge degree of autonomy. All communication and decision making is going to be stale, sometimes devastatingly so. What kind of structure would work here?
**The United Galactic Systems**
The modern-day United Nations isn’t so much a government as it is an organization with a collection of representatives from actual governments. It is, however, a means to facilitate diplomacy, peace, and trade. These three things will continue to have some importance, even as the “nations” begin spreading out across light years. More importantly, the loose influence is a natural fit for the physical and logistical infeasability of tightly controlling disparate worlds.
**The Shape of Politics**
The political reality of STL travel is going to influence everything. On a planet with individual nations (such as the Earth today) the concerns and problems of each nation are relevant on a global scale. Diplomacy and trade between nations often affects many other nations on that planet. When we expand to the interstellar scale, the concerns of an individual nation become much less important. To our friends in Alpha Centauri, the journey to Earth is going to be 4 years whether they’re coming to the aid of the United States or China. As the distances between planets get larger, this is going to naturally cause politics at the galactic level to care more about planets as a whole than the nations that divide them. In turn, this will require nations to act much more cooperatively if they are to be economically competitive and safe from attack. Wars and conflict will continue to rage at the planetary level, but the galactic empire isn’t going to have as large a stake in the outcomes (unless total destabilization or withdrawal from the union is likely).
The political situation gets even more complicated when you consider non-human civilizations. As soon as we run into the first one, a new threat becomes possible: racial annihilation. A human planet is unlikely to ever invade another human planet in an STL world. The logistics are a nightmare and there is nothing concrete to be gained. Once we encounter another space faring species, however, invasion with the intent of total destruction or colonization becomes a real possibility (in either direction). This is likely to be the most typical circumstance in which major wars are fought.
**Communication**
Communication is going to be a problem. Information is always going to be very, very stale. In most cases, the goals you were sent to pursue will have been dictated by officials that aren’t even still in power. When you arrive to invade a planet, your home world may very well have already agreed to peace. These problems are unavoidable, but they can be mitigated and will change our behavior across interstellar space. Every ship traveling between worlds, regardless of its purpose, is going to be a message carrier. Massive amounts of news and data will routinely be packed up and shipped out. With large numbers of ships traveling back and forth between worlds you may even get (stale) updates on planets weekly or monthly.
People who are sent to perform duties, such as diplomats and militaries, are going to have a large degree of autonomy and leeway to make decisions. We’ve already seen exactly how this is likely to work with diplomacy and conflict between the Americas and Europe. Diplomats could not phone home when a crisis occurred — they had to act. Militaries were given a mission to complete, and they engaged the enemy until new orders said otherwise. In this galactic empire militaries will not be dispatched lightly. Not only will you be recruiting soldiers and dispatching them for nearly the entirety of their lives, but once they have been sent they cannot be stopped. This will almost certainly make interplanetary conflict infrequent, except in existential circumstances as described earlier.
**Stability**
What this empire has going for it is that it’s not really an empire by traditional standards. By behaving similarly to today’s United Nations it is minimally intrusive and maximally useful for planets to belong to it. In a multi-species space faring situation is has the added benefit of being able to bring planets together to defend against existential threats. Any traditional government that attempts to control more than one world is going to be incapable of holding onto all of them -- it’s simply too difficult logistically in an STL world. By using a loose coalition like the United Nations you can maximize the chances of its continued existence while continuing to provide services useful to all planets, even multiple species.
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There's one important precondition that needs to be understood before the question of a "galactic empire" can be addressed. So far, nobody but @user11599 has mentioned it (+1 for doing so.)
## An empire is a predatory economic structure.
More precisely, one of the best definitions for present purposes comes from John Michael Greer's useful article [The Nature of Empire](http://thearchdruidreport.blogspot.com/2012/02/nature-of-empire.html):
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> An empire is an arrangement among nations, backed and usually imposed by military force, that extracts wealth from a periphery of subject nations and concentrates it in the imperial core. **Put more simply, an empire is a wealth pump,** a device to enrich one nation at the expense of others. *[Emphasis added.]*
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From this perspective, it's easy to see that the traditions of Science Fictional worldbuilding have more often than not put the cart before the horse, concentrating on **the trappings of imperial prosperity rather than the underlying wealth pump** that provides the reason for the empire's existence, and that makes it all possible.
True, there are some thoughtful exceptions - [Dune](https://en.wikipedia.org/wiki/Dune_%28novel%29)'s commercial empire, for example, and the various interstellar states of Asimov's [Foundation](https://en.wikipedia.org/wiki/Foundation_series) series - but usually we are shown mighty fleets, militaristic cultural tropes, dizzyingly wealthy stellar imperial capital cities, and so on. These interstellar empires are (especially in MilSF) often imagined as the pageantry and politics of some historical terrestrial empire (commonly British or Austro-Hungarian) transposed to the stars. The wealth pump is handwaved, or simply ignored.
However, @HDE 226868, **you** are doing something that none of your imperial forbears in the field has attempted: you are investigating the feasibility of a lightspeed-bounded interstellar empire. Your list of concerns (communications, troop deployments, longevity & stability of distant civilizations etc) is a good start.
However, you are ignoring the elephant in the room: **sublight travel even to a nearby star such as Proxima Centauri is shockingly costly.** (See Charlie Stross's [The High Frontier, Redux](http://www.antipope.org/charlie/blog-static/2007/06/the-high-frontier-redux.html) for a brutal but very well-founded description of just how hard and costly sublight interstellar travel would be. Also, scan the comments, and read the shrieking denunciations by fans. Most enlightening. When people are saying to Charles Stross - *Charles Stross* - "And you call yourself a Science Fiction writer!" you can almost taste the tears through cyberspace. A serious endorsement of the strength of his article: these people, emotionally dependent on the narrative of human colonization of interstellar space, are (understandably) losing their shit... which underscores my present point.
**In sublight travel, you don't get to build a reasonable ship and send it through a wormhole, or engage warp drive; the thing has to be big and expensive. Even *fuel* for the trip is costly.** You're building something large and specialized, that will take a *lot* of fuel for the trip. It might be a relativistic time-dilation vessel, a huge generation ship, or a large and difficult coldsleep ship - and [we don't yet even know how to do coldsleep](https://worldbuilding.stackexchange.com/questions/25575/most-effective-method-to-preserve-an-injured-human).
And then, no matter which type you build, it's a significantly long voyage, with severe challenges at the destination. (See James P. Hogan's [A Voyage from Yesteryear](https://en.wikipedia.org/wiki/Voyage_from_Yesteryear) for a rather nice exploration of the social/military disadvantages facing a sub-*c* expedition upon arrival.)
Which brings us to the core question. ***What kind of wealth pump can be constructed, sustained, and defended under these conditions?***
More importantly, ***what possible kind of wealth could such a pump possibly transfer, to make such a huge and costly effort worthwhile?***
These questions are fascinating and powerful, and very possibly disturbing. Great stuff for a story.
However, it won't be trivial to come up with Worldbuilding.SE-grade answers. :-)
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Might I suggest (not too helpfully) that the first step in this idea will be to figure out what the BENEFIT is to the central civilization in the empire. That will determine what means are required to achieve it. For instance, if there were a substance valuable enough to use as tribute, the central empire could just leave the peripheral regions to their own devices, except there would be a monitor in each that would check to see that they (1) keep sending tribute and (2) aren't getting too advanced technically. If the peripheral area gets close to how advanced the center is, or doesn't send tribute, the monitor sends a signal to the nearest "fortress" to have an attack launched on the offending client state. The benefit to the central empire is the flow of goods.
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**Possibility #1: Fast-timers and slow-timers**
There was a clever novel (by Alastair Reynolds I think) in which there are two levels of hierarchy of galactic civilisation. The bottom level lives in realtime, contains nearly all (99.999 % or whatever of total sophont-mass) and they come and go on the 1000-100,000 year timeframe. These civilisations only move about and interact in their local sphere (one or maybe a few close by solar systems). These are the 'Butterfly civs'.
Then on top of that there is the upper level of society which employs more sophisticated space propulsion technology (still STL though) but spend most all their time asleep in deep freeze. You could say they are the 'guardians' who carry knowledge and trade between the base level civilisations, although in practice this cadre is factionalised and some are despotic. These are the slow-timers.
Members of the Butterfly civs may be lifted up to be included in slow-timer civilisation from time to time. There also various alien or post-human entities that play at this level.
So there you have it - simply have the 'international' players of the empire (the diplomats, sellers of information and embargoed tech, imperial fleets etc) operate in slowtime, and the hoi-polloi in real-time/fast-time.
Countless butterfly civilisations that evolve and live for the blink of a slow-time-eye and eldritch master civilisation that farm the former to fuel their deep time ships etc.
The only problem for the slow-timers is running out of time - most main sequence stars don't have that long to live on these timescales (which suggests a cassus-belli for conflict among the slow-time civs).
**Possibility #2: Wormholes and 'empire-time'**
This is taken from 'Traversable Wormholes, Some Implications' by Michael Clive Price.
Basically we assume that wormholes can be created but chronology protection conjecture (CPC) prevents them from generating FTL paradoxes.
So this means when a wormhole is created and one end of it transported at relativistic speeds to a system say 1000 light years away on an interstellar line-layer, the crew of the line-layer only perceive for example a 6 month elapsed time. Therefore to avoid a paradox of FTL we assume that when we traverse the wormhole we emerge into the remote system 1000 years in the future of the universe (this is referred to as co-moving time in the article). However the 'empire time' of the remote system is only 6 months in the future.
If some other imperial entity attempts to lay a wormhole line sufficiently close to this system (and from a sufficiently mis-matched 'empire-time' reference), then one or both of the holes are destroyed by CPC.
So the idea is that an empire establishing itself with relativistic wormhole linelayers 'stamps' its chronology (its own empire time) on that region of space. After which, travel between the nodes of the empire network is instantaneous, but without any FTL paradoxes.
However wormhole networks belonging to competing empire-times would not be able to approach very closely to one another and would need to resort to standard relativistic invasions in the no-mans-land (or no-mans-time) in between.
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## Time Dilate All the Peoples!
I have a solution, that works completely within current, well understood physics, that makes the finite speed of level a non issue. In fact, we want it to be as finite as possible. What you do is time dilate everyone!
So, pick a efficient energy source. Let's say you use [micro black holes](https://worldbuilding.stackexchange.com/a/20125/8914). Now what you do, is use this energy to put people at very close to the speed of light. Now, even though it may take a millennium for your email to get to your grandma, from both your reference frames, that may only be a day! Indeed, getting places is also faster.
Now, you may ask, what if you don't want people having to fly everywhere all the time. How are supposed to settle if you are flying everywhere. The answer is you **orbit**. So you make some largish, black holes. You may have to sacrifice a sun\* to get one that is big enough; I'm not sure. I choose a black hole because of their density. You can orbit a black hole much more closely than anything else of the same mass (but you still can't orbit to close.) Now, you get to go really fast for free! Time dilation for free!
Okay, no for a little bit of math (I only know a little bit of relativity.) So, the milky way is about 100,000 light years across. Let's say you want, in your empire, to be able to cross the milky way in a year. Note that this isn't just a year for our traveller, but everyone is being time dilated enough that it seems like a year. I used the wolfram alpha time dilation calculator how fast we would have to go, and it said ~1 c. Okay, we can't go c, but it is just rounding. Anyway, that means we need to be time dilated about 100,000 times. Luckily, the [Lorentz factor](https://en.wikipedia.org/wiki/Lorentz_factor#Occurrence) makes calculations simplier:
$$\Delta t' = \gamma \Delta t$$
$$E\_k=(\gamma-1)m\_0 c^2$$
So we want $\gamma = 100,000$. This means for each kilogram of ship, we have [$9 \times 10^{18}$ joules](http://www.wolframalpha.com/input/?i=c%5E2%20*%20%28100000-1%29%20in%20Joules%20per%20kilogram) of kinetic energy. Okay, that is a lot of power. But at the end of the day, it is an *engineering challenge*, and no longer a fundamental limitation of nature. Also, gravitational dilation would help a lot. I would recommend conserving energy very closely. Namely, instead of slowing yourself down, aim for the photon spheres of black holes. This will trap you and you kinetic energy in orbit. You also probably won't start with $\gamma = 100,000$, but slowly work up to it. If you have a hard time finding energy, a smaller Lorentz factor could do for a small part of the galaxy.
The great thing is, sans engineering challenges, this is all [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'"). STL isn't the problem, its the solution!
As to how this affects various things:
* Communication: From the frame of reference of the humans, communication isn't too slow (but slower than we are used to now.)
* Shuttling Troops to Combat: Prohibitively Expensive. Let's waste resources on rail guns instead!
* Diplomats/Envoys: Again, not to bad considering time dilation.
* Ensuring Civilization Survives: An interesting problem is that if you time dilate *too* much (you get really efficient with energy), the heat death of the universe know becomes a problem for your civilization. Not much you can do about that.
* Biological/Sociology/Technological diversity: Probably would be cause racial tension, especially if they *aren't* time dilated. (We could watch entire civilizations unfold before our eyes!)
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\*Ha Ha! Instead of sacrificing people to the sun, we sacrifice the sun to the people.
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**Bomb in a Vault**
Take a large, multistage, thermonuclear bomb (a few thousand megatons), and put it in a vault on the governing planet of a star system, along with communication equipment to communicate with the nearest empire-controlled star. If communication is lost, the bomb explodes. If it detects tampering, it explodes. The vault is designed so that the time required to disable the bomb is greater than the communication delay with the nearest empire-controlled star. Keep the local government on that planet and make sure they don't try to leave.
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## A digital empire
The concept is quite simple. You have a completely digital civilisation. The empire would have a giant supercomputer built around each star that it controlled. The inhabitant's time could be slowed down so although the radio signal takes 12 years to get to it's destination the people living in each of the computers would experience that as instant. Due to the fact that everyone lives in a simulation time can be programmed. To move people around the empire they can be sent as radio transmissions due to the fact that they are no longer physical. Imagine that each person is a file and that you are e-mailing one of those files to another computer. This also uses the same slow personal time concept from before so the person(s) experience the as transit as instant. For war, since you have machines collecting virtually all the energy output of a star you can send of some of that energy as a large destructive beam. If soldiers are really needed you could put some digital people in a spaceship, send it of at almost the speed of light and slow down their time so that the journey feels instant. The society will not fall apart as communications feel instant.
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**Give the job of governance to Artificial Intelligence's. Or perhaps the AIs just decided to take over.**
Given that the AIs have an overarching purpose, the AIs might have the structure that actually allows for a multi-stellar or even galactic empire. Note the the purpose need not make sense to the humans. The AIs could have a goal that requires continuous expansion. Likewise AIs could also require a static society so that the civilization retains coherency -- if nothing else to prevent disruption that affects their true goal.
By controlling essentially all aspects of human life, this would be stable even on a very large scale.
For example, considering the of meeting another galactic and destroying them (in a way similar to Fred Saberhagen's Beserkers). The AIs decide to keep the humans as pets or they feel responsible for taking care of them, or something else that only the AIs understand. The AIs could still have STL or lightspeed communication networks for the purpose of being able to summon the full strength of the galactic empire if needed to destroy a foreign civilization, sure response would be slow, but it is assumed that the attacker would also have similar communications limits. The AIs could even have planned ahead or criteria for abandoning stellar systems consistently in such situations.
Following a billion, or a trillion lines or more of code can cover a lot of planned societal choices, and it would be able to be followed consistently.
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# Hub and Spoke scientific hegemony
As [other answers](https://worldbuilding.stackexchange.com/a/25603/83464) point out, the key to an empire is that a central power is able to extract resources from a periphery. Given the time and cost of moving physical goods across light-years in an inter-stellar empire without FTL, the resources being extracted and methods of control would all ideally be informational.
The way this would work would be a central planet or solar system (the "capital") would have settled colonies on a number of different other planets, but the location of these colonies and method of contact with them would be extremely tightly controlled. The goal of this is that any new colonies are created without any knowledge of or ability to contact other colonies; they only have contact with the capital, creating a [hub and spoke model](https://en.wikipedia.org/wiki/Spoke%E2%80%93hub_distribution_paradigm) (with only a single hub).
Once this is set up, the capital can then engage in pair-wise exchanges of scientific knowledge with each of the colonies. Ideally, each colony would specialize in a particular area of science or technology, but even without this will likely be able to make progress that the capital hasn't just due to random chance involved in discovery (discoveries such as penicillin or Viagra involved a good bit of chance). The capital gets an asymmetric advantage in this exchange because of the asymmetry of the communication graph. It gets technological advances from 10+ colonies, and can trade one colony worth of information back to each of them in exchange for their progress.
On top of that, you get to have your colonies test the planetary impact of their technologies for you. Have a colony developing genetically engineered life-forms or nanobots? Let them try it out for a few years before you use it yourself so that you can dodge all those nasty invasive species and grey goo events. Want to run a planet-wide clinical trial? With enough colonies, now you can; you just have to wait ~10 years for the communication round-trip.
## Necessary Technology
To make this work, you'd need a communication technology and protocol that is:
* **Sufficiently high bandwidth** to carry enough information. If you're sending around genomes of engineered organisms, you'll want to be able to send terabytes per day.
* **Sufficiently targeted** that other colonies don't find out about each other by accident. You can pitch this to the colonies as a feature; sending targeted transmissions can help with energy cost of the transmission and bandwidth.
* **Asynchronous:** you want something much more philosophically like [UDP](https://en.wikipedia.org/wiki/User_Datagram_Protocol) than [TCP](https://en.wikipedia.org/wiki/Transmission_Control_Protocol). Transmissions will just get sent. Important ones might get sent a few times, but if you want to get the data being sent to you, you better be listening because there's no connection handshake or retries.
You also need some way to colonize the planets in the first place.
## Risks
The big risk here is that colonies discover each other and try to "rebel" by embargoing the central power and trading exclusively amongst themselves. Here are a few ideas for how to solve this:
* Have some reason (such as predatory aliens) that it's very dangerous for colonies to be sending out undirected broadcasts. Given this, planets can only safely communicate if they know where each other are (and the celestial mechanics of their orbits) with sufficient precision that they can send a directed message.
* Have agents on-site on each of the colonies that are equipped with capital super technology to suss out and eliminate anti-capital sentiment.
* If need-be, the capital can send an invasion fleet; it just might take 30 years to get there.
There is also a risk that your system will be subverted by colony-sympathizers in the capital. If they can gain control of your communication infrastructure even briefly, they can send the colony location list to all the other colonies and you would be dethroned. It is likely you would need heavy information restriction and secret police within the capital to tamp down on any such revolutionary sentiment. Potentially, only the capital ruling class even knows that the colonies exist. If colonies are founded in secret, then colony ships would be the mechanism for "disappearing" political dissidents, dangerous intellectuals, and criminals (like if the Soviets colonized Australia rather than the British).
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Faster than light travel is Dangerous with a capital D.
The main reason for this is because by the time you see something, you've already smashed into it and vaporised yourself, the target and any unfortunates in the general vicinity, as well as releasing all those crazy science particles inside the fuel tanks which could react in new and devastating ways depending on what you hit.
Smart aliens let computers work out the timing and control the engines to make sure this doesn't happen, but the Dum-d'uums have just bought their first FTL engine from some passing space merchants, and unfortunately they aren't patient enough to configure the computer before trying out their new toy.
The nearest inhabited planet to the Dum-d'uums' is called Switzerland (it's just a coincidence) and they are a ridiculously peaceful and scientifically advanced race who heard about the deal and just know that the Dum-d'uums are going to mess up their space lawn.
How would the Swiss protect themselves from a FTL impact without breaking their moral code and resorting to the obvious (to us evil non-Swiss, anyway) answers of 'sabotage their space program' or 'force field protection grid so the crash isn't near our stuff'?
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**Give the Dum-d'uums the computer tech they need, for free.**
That might seem like a bad move at first, but on the cost/risk scale it's orders of magnitude cheaper to give away some computer tech than to replace a planet and all the people.
If they're unconvinced of the reasoning, take Fhnuzoag's idea and use an FTL drone to blow up a convenient nearby moon as a demonstration. Don't threaten them directly, but let them find out with their laughable intelligence service that most intelligent races keep MAD-type systems in place so that weaponizing FTL is a Bad Idea.
If despite all of the above they still refuse to play intelligently, infiltrate their FTL/space program. Don't sabotage it though - instead, modify the FTL engines they're building by adding in the necessary computers, pre-programming in the exclusion zones. When they try FTL, they'll find that it just "stops working" whenever they try to do anything dangerous. To keep them from figuring things out, you should use a specific gravity well gradient to define the exclusion zone, so they think it's some sort of natural limitation instead of a technical one. Have your scientists pick something that seems logical-like to further confuse them.
If they ask you how your FTL manages to go deeper into gravity wells, act mysterious and play your Elder Race Technology card.
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Provide an object lesson. Have a very carefully controlled accident take place near the Dum Dum's planet, causing massive but miraculously non-lethal damage, and leaving lots of evidence as to what exactly went wrong and why it is very very unwise to mess with stuff you don't understand.
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If they can put aside their moral objections, the most obvious answer is to annihilate the Dum-d'uums' race with a pre-emptive strike.
I highly recommend reading [The Killing Star](http://en.wikipedia.org/wiki/The_Killing_Star).
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Assuming your flavour of FTL drive is still susceptible to normal collision physics, a simple dust cloud around things you want to protect would do. Magical means of deflecting particles in the interstellar void seems to be unnecessary since, as far as we can tell, there really isn't much for dust out there in most places, so your odds of hitting a dust particle are probably lower than the odds of your drive system malfunctioning (especially if you're a Dum-d'uum.)
Which means that "Swiss" ships' computers will have them stop and cruise through the dust cloud at low speed in perfect safety, while the Dum-d'uums' ships will plow into the dust cloud at FTL speeds and be reduced to one blinding flash in the sky, followed by a few months of extra-pretty meteor showers. Since the composition of the dust doesn't matter much, the cloud can double as a convenient garbage-disposal area for anything not worth recycling.
The pieces of ship will still be going pretty fast, but as long as your protective sphere is large enough, they should spread out over a wide enough area to be handled by your planet's atmosphere and your satellites' anti-meteor measures.
What you need to do to protect yourself from the crystallized magic in the ship's fuel tanks depends on what it is and how it reacts when the ship goes up. I'd expect something volatile enough to push a ship to supraluminal velocities to just react and end up being no more dangerous than normal ship exhaust. But you might need some kind of network of collector satellites to sift it out of the passing debris somehow. Determining what to do really requires more information on what it is. They quite likely have most of the system already in place for dealing with fuel leakages and accidents though, it'll just need a bit of expansion/tweaking to work on the remains of visitors.
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Idiots with FTL pose much bigger problems than flying blindly into your planet (although some theoretical ideas of FTL would suggest you are not even in normal space-time, so ideas like collisions would be moot.)
The huge problem is that FTL can affect causality, since FTL is essentially identical to time travel. If you arrive at the planet before the starlight from your home star arrives, you can effectively engage in all kinds of mind bending time travel games before reality catches up (overly simplified, I know). This means the "idiots with FTL" can effectively change the history of their planet, your planet and indeed the entire timeline of the Universe, either by accident (most likely outcome) or on purpose (although I suspect they will find it very hard to "fine tune" their changes to the existing time line.)
Even very smart people will fall prey to this, so FTL is effectively banned in the really real universe we live in. There are some possible hand waves with artificial wormholes (the wormhole line layer needs to be moving at a large fraction of the speed of light, but from your view looking through the wormhole it arrives at the destination at "ship time" rather than the hundreds or thousands of years later that you would expect from your frame of reference.) However, it is thought that anyone trying to create a closed timeline curve by clever arrangements of wormholes is in for a big surprise, as the wormholes consume themselves in a burst of radiation when the ends are brought close to each other to make the time machine...
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The year is 2032. The location, rural midwest North America.
A decade ago, a plague wiped out almost every living human.
There weren't even enough survivors to bury the dead.
Secondary plagues rose from the decaying remains, further diminishing the ranks of the breathing.
It took three long years for the stragglers to start gathering into small towns, centering on un-pillaged food stockpiles near fresh water and fertile farmlands.
United, they've survived this new world for seven horrible years.
Pirate raiders were common for a while but they are not a threat now that the walls are in place.
Wild animals, zoo escapees, still climb in from time to time, but they are quickly dealt with.
The brutal winters and scorching hot summers are still a challenge, but they are survivable through proper planning.
Behind the town walls, things are finally starting to improve.
Outside life is still very hard:
* The tenement ruins of the old world have been picked clean by scavengers.
* The cities are uninhabitable, populated by hordes of carrion rats whose rabid bites cause lingering death.
* Strangers are still to be feared for both the weapons and diseases that they might be carrying.
* In the unshielded open, pirates are still a very real threat.
The towns have weapons and limited medical facilities.
They can deliver a baby and keep a wound from getting infected but major surgery is a lost art.
Every inch of spare space behind the walls is dedicated to farming.
Exterior to the main walls but surrounding each town, the lands are also farmed by the townspeople.
The larger towns have built secondary walls out of chainlink and barbwire to help secure these exterior fields. All of the towns post regular guard patrols to keep harvest-time looting to a minimum.
The towns are now able to feed themselves year round without diminishing their pre-fall stockpiles.
They've all dug wells and built cisterns to stockpile water for the dry months.
They have organized leadership, law-enforcement and a primitive mail system running between the towns. Armed equestrian couriers carry messages between the towns on an approximately monthly cycle.
They have hope.
My question to you is... **What do they do next?**
* Create a prioritized list of goals for these post-apocalyptic townspeople.
* What major issues need to be addressed to let the town survive for the next decade?
* What unaddressed deficiencies in their current accomplishments are going to bite them if not addressed them soon?
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Well, it seems you have your agriculture and basic defense setup complete.
The obvious next steps:
1. Establish an electricity supply. This can be hydro power, coal, gas or even wood and chaff powered. This will allow a whole host of technologies that will make your people richer, stronger and more secure.
2. Establish outposts with radio access. This can be done either by scavenging and repurposing old radios from police and army bases, or by building primitive ones from leftover copper wire and primitive batteries. This will allow the towns to be in radio contact and prevent the raiders any chance at surprise. As an added bonus this might help you contact and recruit some of the (hundreds of?) thousands of hunter-gatherer survivalists that might still have working crank-based radio transmitters/receivers in their remote cabins.
3. Establish a united authority. The extent of this will greatly depend on your surviving population density. Without heavy industry (which you won't have for a while) the effective transport range is rather limited by bikes, converted diesel trucks that run on impure oil and horses. Large scale maintenance (highway infrastructure) is out of the question. This can be done by conquest, but most people will still remember and long for the old national states, so the state-building indoctrination does not have to start from zero, so you *could* have states voluntarily form. This will allow a limited degree of specialization.
4. Start dedicating surplus resources to education and medical infrastructure, before the generation of people with the engineering and medical knowledge is lost, and before damage to extant libraries renders all materials there unreadable.
5. Create the rudiments of an industrial infrastructure. Again, depending on how much of the existing infrastructure you can reuse, you can do a lot of automation, even with relatively primitive electric control systems (mind you i said electric, not electronic). Mining, refining and metal-casting and plastic-casting could then commence. Weapon manufacturing will definitely be a priority. Perhaps even very basic electronics could be in range.
6. Breed like rabbits. Goes without saying, and the motivations of survivors of the calamity will probably be similar to those of Nazi concentration camp survivors. Probably will result in a few centuries of patriarchal domination, but it's the lesser evil. As @MarchHo comments below, your people (if few enough) may need to set up a system to avoid future inbreeding.
The thing to keep in mind is that you don't start back from the stone age. You have a population accustomed to obeying the law, organizing, trusting each other, with high levels of education and skill.
A good read in a similar vein is Eric Flint's [1632](http://rads.stackoverflow.com/amzn/click/0671319728), where a small West Virginian town is thrown back to, yes you guessed it, 1632. There is also a vibrant online community discussing how modern tech can be recreated from such a small base. I strongly recommend it in your case.
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How are the pirates surviving?
Radio and weapons, and clean out the pirates. Command and control, and a nice network so you can sweep areas, and monitor them. Put up some tall concrete towers with radios and telescopes and a guy in each, and get 'em long before they're in range.
Removing the pirate threat is going to be the most important, because everything else is going to have to be defended if you don't. Once you do have the lawless portions cleaned up, the world (or that part of it) is your oyster.
Who got the nukes, the tanks, and the helicopters? The oil refineries? You're going to be out of fuel, if you let those go. And you're probably going to be unable to restart that oil harvesting / refinery cycle if you don't have fuel to run the machines.
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I think it will be different for every town (even different persons within a town).
Some will go for the power, trying to get someone else's lands or food.
Others will try to recover some of the "lost" knowledge: in this case, reckon it will be mostly on medicine, some practical technology (repairing cars, or getting generators to work again, or something like that) or something they can use as a weapon.
I think other will also just want to be left alone (you can use them as reluctant allies or foes).
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The priorities should be like these:
1. Self defense. They should research better weaponry and teach the art of modern weaponry to the next generation before it become a 'lost art' too. Teach every men who can to fight and keep them as 'town guards'
2. Expansion. Build more walls and expand the territory -with military might when needed- and wipe out the pirates, allowing more room for larger buildings and infrastructures.
3. Start building productive sectors. Build farmlands, medical facilities, mines, etc.
4. Establish communication. Use some kind of morse code with torch/sound or tall tower with flagmen. The communication part would be advised to be put at later priorities because if they try to give signals to any other survivors, then the pirates and bandits would know their positions.
5. Revive the knowledge. Every people should write whatever they still remember of the lost technologies and knowledge (like a peer-to-peer sharing) and share them with everyone.
Number two and three should go together before moving to number four.
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Stages:
1. Find suitable location to build a base
2. Build stable food sources.
3. Build defenses to protect people and food.
4. atract a society with a diversity of skills.
5. Find industrial resources (existing manufactured from previous civilization and raw
materials to build mecanical componenets of needed industries.
6. Build facilities to manufacture all sorts of goods in order of importance.
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Hot air balloons. These can be used for secure exploration of the surrounding territories, as well as tethered outposts that have a longer horizon range. Use them to go back into the rat-infested cities. You had said there wasn't, but I'd hesitate to believe there wouldn't be anything of value. There's just too much in a city that would be useful beyond basic survival supplies. Forget food, weapons, medicine. Books, electronics, art (culture stabilized a society) would be useful for advancing the society further.
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Apart from the obvious difference that liquid ammonia needs a much colder temperature than liquid water (but ammonia-based life forms wouldn't feel that as particularly cold), what would be the most obvious visible differences of an ammonia-based world compared to a water-based one, as seen by a life form on the ground?
For example, on a water-based world, common experiences, when living in the right place, would be ice on top of lakes. Since this is related to the water density anomaly, I guess this would not be the case for ammonia. But then, I couldn't find anything explicit about whether ammonia has such an anomaly, so maybe it would be a common experience on an ammonia-based world as well?
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Water has a few effects on Earth that come from its properties.
* Freezing and thawing of water comes at a very high cost of energy, and so does ammonia
* Liquid water is most dense at 4 degrees, not freezing
* Alkaline solubility of ammonia
* Ammonia is combustible
One assumption - with the exception of Ammonia, the composition of the planet is mostly earth-like.
Standing on the planet, I imagine you will see very deep blue oceans. While Ammonia is colourless itself, trace amounts of alkaline metals present will give the Ammonia a deep blue appearance. 'Oceans' and other high ammonia to dissolved metals concentration would be very blue. Lakes and potentially rivers that have more metals dissolved will start to take on a metallic appearance and begin to conduct electricity very readily. Might make for some interesting arcing lightning storms on rivers and lakes.
'Ice' will be relegated to the depths of these lakes and oceans, not the surface.
Climate would be much simpler...currents and heat distribution systems on earth depend very much on the differing densities of water at different temperatures. In an ammonia world, the ice will be at the bottom with gradually warmer ammonia up to the surface. Your poles will be frozen with the 'tropics' being exceedingly humid (ammonia humid?). There's probably a narrow band between the two regions where it's hospitable to life...tropics and polar would only be available to them extremophiles.
Ammonia and water are on very similar levels as far as heats of entropy and fusion goes, so you would see a similar rate of daily warming and cooling. Ammonia actually changes its specific heat capacity and takes more energy to warm as it gets warmer...so you may actually see less daily temperature changes due to heating.
No clue on feasibility, but Ammonia is quite flammable. If there is an oxygen component to your atmosphere, Ammonia will burn down to water and eventually NO2. To be honest, I think an Ammonia world must lack oxygen by definition, if it did, it'd probably turn into a nitrogen heavy atmosphere with water (earth much?)
Added:
Rivers might end up cutting far deeper in an ammonia world...water through calcium and alkaline metals does a little dissolving, but not much. On the other hand, Ammonia will be much more reactive and dig much deeper trenches. If this hypothetical planet and earth had a similar make-up, the rocky mountains would have huge trenches carved deep by flowing ammonia from the reactions with limestone.
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As a solid, ammonia is considerably more dense than in its liquid form (see wikipedia). Thus, any ammonia that solidified would form at the bottom of lakes. This would be bad for any ammonia fishes around, as the ice that forms on the tops of water lakes prevents them from freezing further, thus preserving the fish. In an ammonia lake, it would not be inconcievable for the entire thing to freeze from the bottom up.
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*More "cribbing:" I C-n-Ped this from a forgotten source. Although Haldane went at this in 1954, I believe the science is valid:*
In 1954, J. B. S. Haldane, speaking at the Symposium on the Origin of Life, suggested that an alternative biochemistry could be conceived in which water was replaced as a solvent by liquid ammonia. Part of his reasoning was based on the observation that water has a number of ammonia analogues. For example, the ammonia analogue of methanol, CH3OH, is methylamine, CH3NH2. Haldane theorized that it might be possible to build up the ammonia-based counterparts of complex substances, such as proteins and nucleic acids, and then make use of the fact that an entire class of organic compounds, the peptides, could exist without change in the ammonia system. The amide molecules, which substitute for the normal amino acids, could then undergo condensation to form polypeptides which would be almost identical in form to those found in terrestrial life-forms. This hypothesis, which was developed further by the British astronomer V. Axel Firsoff, is of particular interest when considering the possibility of biological evolution on ammonia-rich worlds such as gas giants and their moons (see Jupiter, life on).
On the plus side, liquid ammonia does have some striking chemical similarities with water. There is a whole system of organic and inorganic chemistry that takes place in ammono, instead of aqueous, solution.4, 5 Ammonia has the further advantage of dissolving most organics as well as or better than water,6 and it has the unprecedented ability to dissolve many elemental metals, including sodium, magnesium, and aluminum, directly into solution; moreover, several other elements, such as iodine, sulfur, selenium, and phosphorus are also somewhat soluble in ammonia with minimal reaction. Each of these elements is important to life chemistry and the pathways of prebiotic synthesis. The objection is often raised that the liquidity range of liquid ammonia – 44°C at 1 atm pressure – is rather low for biology. But, as with water, raising the planetary surface pressure broadens the liquidity range. At 60 atm, for example, which is below the pressures available on Jupiter or Venus, ammonia boils at 98°C instead of -33°C, giving a liquidity range of 175°C. Ammonia-based life need not necessarily be low-temperature life!
Ammonia has a dielectric constant about ¼ that of water, making it a much poorer insulator. On the other hand, ammonia's heat of fusion is higher, so it is relatively harder to freeze at the melting point. The specific heat of ammonia is slightly greater than that of water, and it is far less viscous (it is freer-flowing). The acid-base chemistry of liquid ammonia has been studied extensively, and it has proven to be almost as rich in detail as that of the water system. In many ways, as a solvent for life, ammonia is hardly inferior to water. Compelling analogues to the macromolecules of Earthly life may be designed in the ammonia system. However, an ammonia-based biochemistry might well develop along wholly different lines. There are probably as many different possibilities in carbon-ammonia as in carbon-water systems. The vital solvent of a living organism should be capable of dissociating into anions (negative ions) and cations (positive ions), which permits acid-base reactions to occur. In the ammonia solvent system, acids and bases are different than in the water system (acidity and basicity are defined relative to the medium in which they are dissolved). In the ammonia system, water, which reacts with liquid ammonia to yield the NH+ ion, would appear to be a strong acid – quite hostile to life. Ammono-life astronomers, eyeing our planet, would doubtless view Earth's oceans as little more than vats of hot acid. Water and ammonia are not chemically identical: they are simply analogous. There will necessarily be many differences in the biochemical particulars. Molton suggested, for example, that ammonia-based life forms may use cesium and rubidium chlorides to regulate the electrical potential of cell membranes. These salts are more soluble in liquid ammonia than the potassium or sodium salts used by terrestrial life.
On the down side, there are problems with the notion of ammonia as a basis for life. These center principally upon the fact that the heat of vaporization of ammonia is only half that of water and its surface tension only one third as much. Consequently, the hydrogen bonds that exist between ammonia molecule are much weaker than those in water so that ammonia would be less able to concentrate non-polar molecules through a hydrophobic effect. Lacking this ability, questions hang over how well ammonia could hold prebiotic molecules together sufficiently well to allow the formation of a self-reproducing system.
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If it's raining ammonia it would look like Saturn:
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> Saturn’s upper atmosphere is mostly **ammonia crystals** while the lower one is either water or **ammonium hydrosulfide**. --[Atmosphere of the Planets](http://www.universetoday.com/35796/atmosphere-of-the-planets/)
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@Tim B's comment about life:
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> One of the most **resilient organisms** known are tardigrades ("water bears"). Tardigrades can go into a hibernation mode — called the tun state — one that is more akin to "suspended animation" whereby it can survive temperatures from **-253°C to 151°C**, as well as exposure to x-rays, and vacuum conditions. --[Life in Extreme Environments](http://www.nss.org/adastra/volume14/rothschild.html)
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If there were such a thing as "*ammonia* bears", they would find it quite lovely.
After reading the answers here, I would assume that any planet with a high enough concentration of ammonia would either have dissolved its own solid surface, broken down enough material so that it now includes water, or ultimately had no *solid* surface to stand on to begin with, like our gas giants.
[JUPITER AND SATURN CLOUD LAYERS](http://lasp.colorado.edu/education/outerplanets/giantplanets_atmospheres.php):
```
Ammonia clouds (150° K)
Ammonium Hydrosulfide clouds (200° K)
Water clouds (270° K)
```
~Cloudy, with a slight chance of death.
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I am not sure about ammonia, but for example on the moon Titan, there are lakes of liquid methane, theoretically there is nothing in chemistry that prevents life from forming based on liquid methane as a medium instead of water, but we still don't understand what is life anyway to have a definitive answer about that.
Scientists found from the Cassini–Huygens mission that hydrogen levels near the surface of Titan are lower than it should be and its much higher on the upper atmosphere, which is consisting with a previous prediction made by Chris McKay and Heather Smith that if there is methane based life on Titan they would breath hydrogen and infuse it with acetylene to produce energy. There is a consisting flow of hydrogen from the upper atmosphere to the surface of Titan but it just disappears.
one interesting prediction for such a life form is that it will have really slow metabolism, way slower than plants.
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The problem with swapping ammonia for water is that unlike water, ammonia ice is denser than liquid ammonia and therefore sinks instead of floating as ice does in water.
The layer of ice that forms on water isolates the body of water underneath preventing it from freezing further but with ammonia, the top freezes, sinks, exposes the next layer which freezes sinks and so on until the the entire body of ammonia is frozen solid. In principle, if you had ammonia sea in temperature ranges analogous to water on the earth, the entire ocean would likely eventually freeze solid and with it the planet.
So, to start, if you want oceans on your ammonia world, would have to be relatively warm and uniformly so as ice formation would be very dangerous to the entire ecosystem. A possible way around this problem would be to postulate that the planet has very hot core like Europa and therefore ammonia ice that sinks, melts as it descends. That would also provide a lot of energy to the ecosystem even if the planet is far from the sun.
As noted by twelth, Ammonia forms a lot of stable complexes with many metals so likely any ammonia oceans would very complex mixtures or pure ammonia and various ammonia compounds. More interesting, some of these compounds are immersible to each other i.e. they don't mix and instead form layers when tossed together so an Ammonia ocean might have various layers, bubble or pockets of vastly different properties.
Now just snowballing but highly electrically conductive water masses could provide the basis for life forms that move electrons directly, as current instead of using long chains of chemical reactions hand offs e.g. the Krebs cycle.
Thermal plumes in the deep ocean could drive separation of charges by moving vast masses of conductive ammonia metallic compounds which could create the electricity to that form the basis of the ecosystem much like sunlight does on earth. Also, energy imparted to compounds that the heat breaks apart and reforms would also eventually be released electrically.
An organsim that moved electrons directly could could absorb and expend a lot of energy even at cryogenic temperatures. Instead of something sluggish as a glacier which you would get with cryogenic chemical energy transfer, you'd get something cold but fast, likely something working like a superconductor which gets more efficient and faster and deadly as it as it gets colder.
Whole different class of critter from your standard bags of carbon filled with water which move at, least face it, the speed of diffusion
Such organism would likely have fewer cells or compartments as they would not need as many chemical isolations pockets. They might be collections of giant i.e. nearly visible cells. Since moving electrons is the their primary form of mode, likely all the cells are long and fiberous. The creatures might appear to be made of woven strands of neurons with ammonia-metalic polymer membranes. Physically appearing relatively simple, they might give the vive of simplistic rag-dolls compared to complex earth life, their complexity would lay in their invisible electrical fields and circuits formed on, between and and inside their giant cell membranes.
If all the water masses are conductive possible with various immersible channels routing currents, then likely the land biosphere might evolve as electrically connected as well. On earth, its been argued that life on land more or less dragged the sea along inside it. The same basic phenomena would wire up the land biosphere into the planetary circuit as well.
The entire biosphere might resemble something more like a planet of self-reproducing robots always on the lookout for current to tap and steal. Instead of eating prey for the energy in the chemical bonds of the preys flesh, they would just short the prey organism and drain its charge taking little or no matter from the kill. But shorting the membranes might cause the giant cells or tissues to just fall apart leaving a dust of raw materials.
Good story potential. Usually the idea of organic life forms posing any serious threat to a high tech space ship and crew landing on a planet is silly. We snuffed the earth's megafunga with pointed stick and the most bad ass predator that every walked the earth wouldn't last 60 seconds against your typical Marine and couldn't get past the least metal barrier.
But a critter in an electro-ammonia based world all in spooky perpetual twillite far from any sun.
1. A ultra cold environment that makes metals and plastics brittle,
2. Organisms that have no circulation, and possibly no real critical
vital areas that sharp sticks or bullets can poke holes in.
3. That moves at electrical and not biological speeds,
4. that has possibly actually armored metallic flesh
5. Whose strength is determined by voltage and amperage instead of muscle so the more juice it gets, the stronger it gets.
6. Which can both absorb and project electricity
7. which will likely have have radio or magnetic based senses senses
8. That might be adapted to short out electronics and jam radar and radios.
9. That sees a human in a space suit as a walking battery for lunch
10. and sees the spaceship as an all you can eat buffet.
Well, now that that would make that all acid-for-blood critter Ellen Ripley had such a tussle with look like bit of a pansy wouldn't it? That little fluff ball just chased humans around the ship, it didn't try to wreak the ships systems, drain its power and maybe absorb its hull destroying all hope for survival.
The electro life form would likely completely ignore the humans but would head straight for the technology that makes us humans badasses instead of frozen meat-bags on a cryogenic world. Metal, electricity, plasma weapons (Plasma though hot conducts electricity) etc wouldn't be impediments to the creature but food. The more high tech you brought to the planet and whipped out for the defense, the stronger and more attracted the monsters would get.
They might not even notice the humans but if they humans couldn't stop the creatures from ripping apart their space suits, draining the ships power or tearing it apart for pure metals, the crew would die just as horribly as if the things actually tried to eat them.
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I'd like to point out one of my favorite authors, Robert L. Forward, described such a world in *Flight of the Dragonfly* (later *Rocheworld*). The downed exploration plane, floundering in the ammonia sea, had the cleanest windows in ten lightyears.
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**Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers.
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You are asking questions about a story set in a world instead of about building a world. For more information, see [Why is my question "Too Story Based" and how do I get it opened?](https://worldbuilding.meta.stackexchange.com/q/3300/49).
Closed 5 years ago.
[Improve this question](/posts/132318/edit)
So, let's say an astronaut has crashed his shuttle into earth only to find that there are no cities or any signs of human-made objects left on earth.
Another astronaut is orbiting earth in her space station, much like the ISS.
The only 2 human made objects left in the planet/universe are his ship and her space station (no cities, no satellites, no radio towers etc.) he is able to communicate with her through the radio gear on his shuttle every time she passes over him in orbit.
How could she manually land her reentry capsule at or near his location (without any satellites, ground control, etc.)? My idea is that they use the stars, sun, moon, and large landmasses to give her an idea of his coordinates and she manually steers her reentry capsule to meet him on earth. I am not sure if this is too far fetched or if it would be somewhat feasible for a sci fi story.
(Note that I am using fictional shuttles and technology that i am willing to make somewhat more advanced than current technology if necessary)
Thanks for the help!
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# Probably yes, within reasonable distance.
Any space-to-surface craft would be designed with a communications failure in mind and carry instruments like [sextants](https://en.wikipedia.org/wiki/Sextant) and chronometers. With those, a trained aviator should be able to make precise orbit corrections and a reentry burn. Even if there is no [ephemeris](https://en.wikipedia.org/wiki/Ephemeris) in the spacecraft, the astronaut should be able to fix the orbit relative to some stars and then plot the ground site from differences in radio reception quality. The latter would be quite inaccurate, of course.
The problem happens after the spacecraft enters the atmosphere. There would be no weather reports and the spacecraft will have little maneuvering capability. Small differences in atmospheric conditions could carry the spacecraft dozens or hundreds of miles off course.
In addition to this error there would be any mistake in the astronaut's calculation of the intended landing site.
**Things to consider:**
* Without [light pollution](https://en.wikipedia.org/wiki/Light_pollution) the astronaut on the surface might be able to see the spacecraft, and tell exactly when it passes the horizon. A few sightings and a little math should give the exact position on the ground.
* A shuttle is not designed to land on rough fields. The choice might be between a crash on the ground or a water landing and sinking. An Apollo capsule was designed to land in the water, but supposedly survivable for a ground landing.
* Water landings could be a bad idea if there is no rescue boat coming.
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# Yes and no
This is doable. If you play Kerbal Space Program long enough, you learn how to do it. I can land landers on Laythe, which is more than 90% covered by an ocean, from a low orbit by eye with just a small thruster and a parachute. An astronaut who has had enough reentries should be familiar with the paths from low orbit to ground.
However, KSP much like science, assumes ideal conditions. There is a problem on real Earth called weather. Wind will push your vessel this way and that, and may be highly unpredictable. Rockets that we launch to space can compensate for it once they are high enough into the atmosphere, or after they exit it. Your astronaut, though, may end up landing dozens of kilometers away from her target.
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# Consider triangulating with other magnetic points
1. There is always *some* margin of error, play with it.
2. Mention the magnetic poles, a large deposit of iron, or some other object of nature that you have established.
3. Triangulate with a. the initial crash site, b. the space station or moon in orbit, c. this other magnetic source (in 2).
4. This would need some level of auto-computer driven calibration.
## How to make it work:
What space ship doesn't have an astrophysics array these days? Starships had those before they had support for portable AI. Your space station probably has several young AIs in testing—it's run by the AI that runs other AIs!
Retrofit the onboard astrophysics array to detect magnetic metalics. It won't be perfect, but the cluster of iron deposits discovered to the southeast are large enough that the modified array should detect it anyway. You'll need to use a soldering gun to make the changes to the astrophysics array's integrated circuit (hardware mod) and—given the recent accident that caused all this *(ahem)*—your orbit isn't as stable as you'd like, and you'll only get one shot at this. You'll also need to replace the astrophysics processor with the orbital processor so that it can integrate the magnetic telemetry into your make-shift guidance system. That should be easy enough, if only the lock holding the orbital processor in place isn't welded from overheating...
You'll also need to copy a few lines of code (software mod) from your payload balancer mass detector recalibration subroutine\* so that the AI's software knows how to calculate the telemetry from the magnetic mass. You'll have to take the AI offline for that, so it won't be able to help you through this whole process, but it will be thankful for the upgrade—because your plot is interesting enough to have an AI that you'll be able to take from the crash site with you *(nods)* because it is "portable" from one computer to another, and this AI of AIs has just been upgraded to calculate a position based on metalic telemetry.
*\*(This 'subroutine' is the small computer program/process which re-calibrates the mass detectors on spacecraft while docked at your space station thingy, those mass detectors help the propulsion systems balance the payload of their launches, of course. Every spacecraft has to have one of those, obviously, because, as everyone already knows, this is the age where what you're trying to do is even possible, wink-nod.)*
The whole process should take four hours, but you only have 90 minutes. Even then, once you make reentry, the system will have a margin of error of about 20 meters (probably based on a degree trajectory margin of +/- 3°) because it must be crude enough that you could do the soldering by hand. And, if you get one of the wires crossed in your soldering *(which you should do in all your haste, wink)* you could end up flying right into the other crash site (or the lake 10 meters from it). This is because the improperly wired integrated circuit would make the AI confuse a guidance node (first crash site) with the landing destination.
(In a GPS, three satellites in view gives a position, a fourth allows to calculate elevation.) You'll also need to leave behind a drone to remain in orbit so you can get your fourth nav point so the AI can also calculate elevation to properly slow your descent; if the orbiting drone stops pinging *(which it does, hopefully)* you'd lose ability to make the automatic adjustments for your descent. In other words, if Murphy's Law holds true, you're going to end up flying in too fast, right for the other ship, needing to steer and break manually. But, not to worry, the grateful AI will be there encouraging you the whole time.
There's your ticking clock, which could last half a chapter or half the book, also some option exhaustion once the time runs out, and you have a few disasters to open up new opportunities, skew the reader's foresight, and make the situation more complex with a nice mix of victories and challenges along the way. 90 minutes is more than enough time to replace a CPU, copy-paste a few lines of code, do some bumpy soldering work, retrofit and launch a nav drone so it can break, all without the help of the offline AI.
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What natural environmental pressures or opportunities might drive an **alien** ophidian species to evolve sapience and caudal tool use?
## Conditions
1. The species should be lacking limbs prior to the emergence of these traits, but may develop finger-like appendages for gripping and fine manipulation.
2. The pre-existing body plan may be a result of either terrestrial or aquatic ancestry (akin to the [varanid/mosasaur hypotheses](https://en.wikipedia.org/wiki/Snake#Origins)), but the species must be terrestrial in the end.
3. The head/mouth should not be involved in using or manipulating tools, but the body itself may coil or fold to facilitate gripping and positioning.
4. The environmental, ecological, and planetary conditions, and other physiological details (symmetry, size, dimensions, breeding strategy, diet, social structure, and so on), are otherwise plastic.
## Precedent?
Among particular species of Earth snakes there is a phenomenon called [caudal luring](https://www.youtube.com/watch?v=lSizvBwFL-A), in which the snake displays fine motor control over the tip of its tail to roughly mimic the motions of prey animals. This activity attracts other predators upon which the snake feeds. One such species is the [spider-tailed horned viper](https://en.wikipedia.org/wiki/Spider-tailed_horned_viper) of Iran, which has evolved a fringed tail resembling the legs of a spider:
[](https://i.stack.imgur.com/wGJYm.jpg)
Perhaps this is an intermediate stage on the path to tool use.
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***Ophidian*** in this context is the snake-like counterpart to *humanoid* and does not imply either a shared ancestry, or any other similarities, with Earth snakes or the suborder *Ophidia*.
***Caudal*** meaning posterior end – the tail.
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Our sapient, tool-using ophidian traces its ancestry back to a semi-aquatic ancestor. Essentially a sea snake, or an alien analog thereof. It sleeps in the safety of burrows on land and hunts in the sea. The oceans of this world contain life not too dissimilar from Earth’s. Invertebrate reef builders create intricate undersea structures. Analogs of molluscs crustaceans, and fish take shelter in the tubes and tunnels the alien coral affords them. Our ophidian ancestor uses its narrow body to invade these tunnels in search of this prey. The coral of this world has a higher composition of tubes which form complex networks with multiple entries and exits in each reef. Several species of coral-dweller also dig and expand the tunnels. The result is an intricate labyrinth of passages filled with food. While our snake has some success slithering into the tubes head first in the hope it will bump into a tasty morsel, the snake’s intrusion creates a pressure wave that precedes it along the submerged corridors and alerts prey to its presence. The various fish and invertebrates often flee out of the numerous other exits from the tunnel system while the snake is stuck inside.
Evolution strikes upon a creative solution. By entering the tunnel tail first and watching another exit with its head the snake tricks its prey into fleeing the safety of the tunnels right into its waiting maw. Some prey species adapt to the snake’s bluff, learning the difference between the pressure wave from the snake’s head and tail and not exiting the tunnel in response to only the tail. In response the snake’s tail thickens to more closely mimic the head and develops sensitive touch and pressure senses to help navigate the passages as well as detect prey. Over millennia the tail develops into a grasping appendage capable of grabbing stubborn prey and pulling them out of the tunnels.
Free from the size constraints of navigating the narrow tunnels the ophidian’s brain is able to expand. The ability to mentally map and memorize the interiors of the tunnel networks allows the snake to flush out prey efficiently instead of simply probing at random, as well as to predict through which tunnel exit the prey will appear.
The ophidians also gradually learn to work together. What begins as opportunistic hunting of prey flushed by another snake quickly evolves into mutually beneficial cooperation. While some snakes use their tails to flush out prey others are able to cover all of the tunnel exits allowing for entire reefs to be harvested. Intelligence, cooperation, and communication become highly beneficial traits in the fledgling ophidian social groupings. The snake’s tail appendages take on new roles as communication tools through contact as well as pressure and sight signaling.
The communities learn the layouts of the reefs in their area and begin to harvest them in rotation. By hunting as a group, cleaning out a reef, and then allowing it many days to repopulate they develop a source of renewable food. The ophidians are able to spend a larger proportion of their time out of the water due to the efficiency of hunting.
The beginnings of tool use develop when the ophidians begin plugging exits in reefs. Using their grasping tail appendages they are able to block tunnel entrances with rocks and shells allowing them to modify the reefs to their liking and further increasing the efficiency of hunting.
Another form of tool use comes in using rocks to open shell-protected prey. By finding two relatively flat rocks, placing the ill-fated mollusc between them, coiling its body around the whole sandwich, and contracting, the ophidians are able to crack the shell and harvest prey that was previously inaccessible.
With stable communities and rudimentary communication through tail touching and signaling each technique is taught to the next generation and the incremental advance of technology begins. With the advent of weaving the ophidians are able to construct baskets and traps to catch flushed prey or gather shelled molluscs. This allows live food to be transported out of the sea and kept for short periods of time in natural as well as artificial tide pools. Systems of rafts, lines, and weights continue to improve the efficiency of food harvesting. These advances free up a portion of the ophidian population to become craftsmen, leaders, and thinkers. The ophidian civilization has begun.
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I love this concept, the idea of snake sapience is interesting. But to your points
**Evolution**
The luring snake is probably a good place to start, this evolution will take a long time, but snakes have been around for a long time; so this should work.
1. The spider tailed viper is a good place to start, perhaps we now say that a new snake replaces this one, and the spider tailed viper has to move, it keeps moving until it arrives in the Congo or the Amazon. The jungle seems to breed intelligence.
2. When in the jungle, perhaps the snake has to work harder to find food, ambushing and luring become its sole hunting strategy and it likely will lose its venom glands.
3. It is at this point we work on its tail, now as ridiculous as it is we have two choices here
* **Tarzan approach**, my first idea was that the fringes evolve to move in order to better climb the canopy and this over a couple thousand generations leads to a prehensile tail-hand thing. But this felt like I was stretching reality. So I think the next path is more likely
* **Venus fly trap approach**, Just as it sounds, first the fringes evolve muscles at the base to quickly close to trap small critters, then eventually the muscles around them become more independent of each other and eventually through more small changes until you get a hand like appendage.
**Tool use**
I don't imagine they would be good at this, you need two grasping appendages to make things, so you will need to replaces the jaws free form jaw with a real one, a big change that is kind of ridiculous. This or the have to rely on working together with other snakes to build this; which *does* help with sapience; personally I'd suggest that, but the mouth also works. As to the kind of tools, that is unpredictable because snakes have not been shown to use tools, so we cannot know what kinds of tool they would build; the sky is the limit.
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As a radically different viewpoint, consider the [Chrysopelea](https://en.wikipedia.org/wiki/Chrysopelea), or flying snake. It glides through the air by sucking in its stomach and flaring its ribs.
* Step 1: over time, this rib flair could gradually extend; the snake would be able to flatten its body still further, meaning it could have longer flight times and more control. Longer flight, more range; more control, better precision on strike; both mean a distinct advantage, and allow the snake to grow larger, while still easily hunting.
* Step 2: as time goes on, the area around the ribs develop better musculature, for flight control and yet-wider spread. This allows ribs to move individually; more control = better precision = longer flight time.
* Step 3: eventually, the skin around the ribs thins; a front cut-away profile would transition from an O to an m shape, and eventually to a shape like this: `/O\` Meanwhile, smaller, fixed ribs form around the organs for protection. This leaves the snake with ribbon-like wings, similar to an eel's top fin. When not in use, the ribbon-wings are wrapped around the body, adding a further layer of protection. In flight, a rapid wave motion would keep the snake airborne.
* Step 4: until now, the wings were V-shaped, widest at the front and tapering to a point at the rear. However, 'square' wings provide more lift and better maneuverability; as time goes on, the end develops more muscles and wider wings, resulting in much better control.
* Step 5: As the control muscles grow, our snake will begin to use the dexterous wing-ends like feet while not in flight, wrapping them around branches to climb, or wrapping prey to hold them down, which prompts the development of bone nubs or proto-claws.
* Step 6: as the claws evolve, they become more bird-like; the jointed claws turn, becoming opposing fingers, as the snake becomes more picky about its food, able to eat select parts of prey. Additionally, the claws allow it to carry material in flight (albeit clumsily), which means it can use that material to create stronger nests.
* Step 7: eventually, some enterprising snake realizes it can drop sticks and rocks on prey to scare, stun, or kill it, and suddenly snakes have tools.
And that is how you evolve the terrifying flying bomber-snake.
[Answer]
I like TrEs-2b answer in long form. For his #3 point, I can see one other way this might evolve. In various species, it is not uncommon for babies to develop extra appendages as a mutation. If a snake is born with a second tail, it now has two "lures" to use -- more tempting target. Coordinating the activity of the twin tails makes the illusion of prey even more tempting, and slowly amps the dexterity of future generations. Eventually, the snake may begin constructing the nest or mound of the prey species it mimics in order to enhance the illusion, leading to developed tool use.
Eventually you have the ultimate phobia trigger: a snake with a spider on each finger, holding a knife!
[Answer]
**Observation 1**
Sapience life forms don't normally have advanced/powerful limbs, instead focus would be on developing a generic limb - tail in this case.
**Observation 2**
Tool use involves co-ordination between mind/eyes and the part of body in use - let's use tail now onwards.
**Result 1**
Eye of our alien snake should be able to see very easily in any direction - where the tail is using the tool. - this is very important. So, imagine a pair of eyes on top of a big head. As brain is developed the head is big and eyes are separated enough to excellent sight.
**Result 2**
The snake would be evolved to move backward as naturally as forward.
**Result 3**
The end of the tail would split at least into two or equivalent to the number of sections in the snake's brain. (I personally like to have 4 sections in the brain and tail split in to two and each ends are split into two again. - but let's not do this to avoid similarity with hand)
**Tool Use**
While working - the snake will work backwards, moving the eyes to tail and controlling the device with two split ends. So, may be typing with tail and resting head on a special mouse/touch pad kind of thing. (Note: I am assuming that this alien spices is as evolved as humans on the Earth)
While socializing/playing - the tail has to be very agile and sensitive. It could be the body (or tail) language for the snake community.
[Answer]
**Gregarity**
We'll start with a snake that is already somewhat gregarious, similar to the US Timber Rattlesnake, but before it developed it's infamous rattle. Since snakes like these already have a modicum of social structure and are not individually territorial, they have an ability to share behaviours.
Early on, long before the first ape picked up a stick, one family of our snakes had bit of a medical problem; they had a genetic tendency towards a mild form of palsy. It wasn't severe enough to be debilitating, except when hunting. They weren't very good at sitting still, and tended to twitch a little when they tried. Often, this led to dislodging pebbles or other debris in their vicinity, giving away their location. It was an unfortunate trait, and as it spread throughout the family, it seemed likely that it would lead to them being culled from the genetic pool.
**Rocks**
Happily, their dry, gravelly environment gave them a solution. Quite by accident, a few of the stronger snakes would actually flick rocks with their tails while convulsing, and *throw pebbles far away*. This would be confusing for prey species, who would detect the movement and noise as further attackers, and often led to the prey dashing straight into the snake to escape the noise of the false attacker. Other snakes learned the behaviour from their siblings. Soon enough, size and tail dexterity were selectors of successful snake populations, and the Rockchucker was established. Flattened tails, sometimes even with an indentation to facilitate scooping up a pebble, began to appear about this time.
**Predators**
As apex predators, the venomous Rockchuckers had existed for some time without really having another species prey on them specifically. There were some pesky mammals, however, that tried to prey on unprotected nests, and it was only a matter of time before one evolved an immunity to Rockchucker venom. This was the Banded Monduck. Fast, big, and unafraid of being bitten, they were a force to be reckoned with.
By this time, though, Rockchucker evolution had also moved forward. They'd gotten somewhat bigger, and supported the appropriate brain functions for long-range binocular vision. They could now *aim* those rocks they at a considerable distance. Nevertheless, one snake was unlikely to take out or scare off a Monduck alone, so those Rockchucker families that stayed around their nests and defended it as a group fared considerably better than their less-gregarious counterparts. By now, the tail tip of a Rockchucker was almost prehensile, flattened and flexible enough to grasp rocks and sticks.
**Bigger prey, and the first buildings**
Rockchuckers continued to grow, and so did their brains. Upper ribs flared out and fused to make a secondary skull to cover this expanding grey matter. Rockchuckers could no longer burrow, but were now big enough to eat mid-sized creatures like coyotes, from whom dens could then be stolen.
The next big step came with the collecting useful things, and transporting them to a work site. Building ramparts of debris around nests was a natural start, and true fingers began to appear to support this detailed work.
**Full sapience**
Musculature began to appear about this time that allowed both the head and the tail to stay reared up while the snake moved. In many ways, this was the defining step in their evolution to full sapience, in much the same way as human bipedalism. With the ability to carry objects by holding the tail aloft while slithering, many capabilities were enabled. In particular came the ability to collect burning bits of lightning strike and fire fuel. This enabled the cold-blooded reptiles to maintain body temperature through the night, and stave off seasonal hibernation. *Crotalus Habilis* is born.
**TL;DR**
Our snakes evolved from the same stock as rattlesnakes did, but instead of rattling, they developed the ability to throw rocks. This basic tool use, dominated their evolution, and favoured more and more manipulative tails. Ultimately, sapience and a snake civilization is the result.
[Answer]
>
> What natural environmental pressures or opportunities might drive an alien ophidian species to evolve sapience and caudal tool use?
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Regarding the possible environmental causes for sapience to evolve, it seems that for both mammals and [birds](https://en.wikipedia.org/wiki/Bird_intelligence#Studies) that the common denominator is the existence of social life. The current thinking is that to understand and solve social interaction challenges requires adaptive brain capabilities which can then later be applied at solving practical problems (tool usage).
What could force ophidian into social life could predatory pressure. Similarly to birds which can fly in huge flocks to reduce predatory pressure, there could be a predator feeding on this ovidian which forces them to live in huge flocks to maximise their changes of survival. Being themselves predators they would then need to develop group hunting to attack big enough animals to feed them. The combination of both leading them to adapt to social life.
Tool usage has been now observed in the wild with mammals, birds, cephalopods and also [reptiles](https://en.wikipedia.org/wiki/Tool_use_by_animals#In_reptiles). Common speculation is that toold usage comes as a byproduct of intelligence and physical traits making it easier are selected over generations. Some possible ideas include:
* Elephant like trunk control: genetic mutation allowing the tail to grab prays away from the head and bringing them to the mouth
* Octopus like control: a genetic mutation could duplicate the tails and allow multiple tails with 'trunk' like control capabilities (similar to [polydactylie](https://fr.wikipedia.org/wiki/Polydactylie))
* claws / finger development: a genetic mutation could turn the spider on the tail to hard keratin which at first would be able to hook preys and eventually over course of mutations could turn towards hand like fingers.
Any or all of the above changes would lead them to being able to handle tools. The actual tool selection starting most likely with sticks and stones and evolving alongside similar lines as ours.
One last comment, tool usage and stone age is not the [apanage](http://www.bbc.com/earth/story/20150818-chimps-living-in-the-stone-age) of humans so your ophidians obviously could also do it.
[Answer]
**The evolution of caudal tool use probably wouldn't happen with snakes.**
While the idea of a sentient snake with a hand on the end of its tail is interesting, it probably wouldn't evolve. Why? Because snake-like bodies are evolved to do all of the things that most animals do with limbs and appendages without them.
Consider the general reasons that appendages assist animals that evolve them: mobility, capturing prey, and manipulating the environment. Snakes have evolved a system of motion that doesn't require limbs (slithering), and which wouldn't really be aided by the development of limbs, especially at the end of the tail.
Unlike something like a scorpion or a monkey, in which the tail can be held overhead and used in a similar manner as a limb, the way that snakes move requires that their tails trail behind their body. Even for tree climbing, which drove the evolution of hands in apes, snakes move between branches by anchoring onto a tree branch by wrapping their body around it, and then extending their head to another branch.
Capturing prey follows a similar pattern in snakes. They evolved to do it very well without limbs or grasping appendages, and are unlikely to evolve a grasping appendage to help them to this. Snakes hunt by launching their heads at their prey and biting, which they've evolved to do *very* well. All snakes that use caudal luring are evolved to do this: they use their tail as a lure, but then use their head to capture their prey.
The last reason that appendages evolve is to manipulate the environment. Adaptations like pedipaps and chelicerae help arthropods do this, in some instances, and the trunks of elephants would be another example. However, a common theme with any appendage that helps an animal manipulate its environment is that it's an appendage that the animal can *see*. Tails trail behind snakes, so having a hand on the end of the snake's tail wouldn't really help it as it traverses its environment head first. A snake would have to stop moving and curl its tail forward to use it to probe the environment, an energy intensive way of doing something that it can probably do better by just using its head/nose, which is why snakes like the [hognose snake](https://en.wikipedia.org/wiki/Heterodon) have evolved heads shaped for tasks like digging.
Lastly, snakes probably wouldn't evolve complex caudal appendages because they would be easy to injure while crawling through an obstacle-ridden environment. Snakes slither with their bodies and tails on the ground (with a few exceptions like sidewinders, who don't slither most of the time). A snake with a grasping appendage would drag that appendage on the ground and through whatever sort of environment it was crawling through. This isn't a problem when that appendage is comprised of modified scales that will be replaced when the snake sheds, such as in the case of the spider-tailed viper, but a larger appendage of muscle and bone could easily become injured and infected. Snakes have evolved smooth, streamlined bodies for precisely this reason, and any adaptation of a *less* streamlined form is likely to be selected against.
**Caudal tool use could happen, but it would probably happen in legged animals.**
This isn't to say that caudal tool use couldn't evolve, just that it probably wouldn't evolve in snakes or snake-like creatures. Something like a scorpion or a spider monkey, which carries its tail in a manner which doesn't affect ordinary motion and whose tail can easily interact with objects in its field of vision, might be able to evolve caudal tool use.
Even this sort of evolution, though, would be much less likely than evolving trunks or hands to manipulate the environment. Tails, ultimately, are at the wrong end of the body to interact effectively with the head, and just about anything that a tail can do, with regards to interacting with the environment, an arm can do better.
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[Question]
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I was wanting to make a species on an alien planet that reproduce purely asexualy, and their star produces enough radiation to cause common mutations among the children to cause something similar to biodiversity. Would this be possible?
[Answer]
From a high level point of view, yes, it possible.
In the past, before genetic engineering techniques were available, a way of producing new types of plants was to use irradiation fields: a radioactive material was placed at the center of a field and all around it [plants were grown](https://99percentinvisible.org/episode/atom-garden-eden/), continuously exposed to the radiation.
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> The United States military began to research not only on how make atomic bombs, but what their effects might be after detonation. So-called “gamma gardens” in places like Brookhaven National Labs in New York aimed to discover the effects of chronic exposure to gamma rays on plants. Within a few years, they went from just analyzing the effects of radiation to researching whether gamma radiation could actually induce beneficial mutations.
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> Some of these gamma gardens were huge (up to five acres or more) and were generally laid out as large circles with crops planted in concentric rings. Within the garden, species were separated into a series of pie-shaped wedges. In the center of the field, a pole containing a radioactive isotope (usually cobalt-60) would shower the field with gamma radiation for about 20 hours a day. When it was time for researchers to go in and see the results, they would remotely lower the source into an underground bunker made of concrete or lead, step inside the field’s high fence, and inspect the plants arrayed around the center. The plants closest to the source were usually dead or stunted or gnarled with tumors. The plants around the edges generally looked normal but would be evaluated by the scientists to see if they had any beneficial mutations.
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> [](https://i.stack.imgur.com/xEZd6.png)
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> [...] Because of radiation breeding experiments, there are over 2000 plant varieties that have been released into the global food system. These include a strain of wheat in Italy, varieties of rice throughout Asia, certain pears in Japan, and a breed of sunflower in the United States, just to name a few. The Rio Star grapefruit also came about because of radiation breeding experiments and now accounts for about 75% of the grapefruit grown in Texas.
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The same process can apply to organisms reproducing in an asexual way. It actually already happens with random mutations in bacteria and other unicellular organisms, caused by environmental radiation or other agents.
What makes it more difficult for a multicellular organism is that the mutation of a single cell would hardly have consequences on the whole organism, and having the same mutation on all the cells is highly unlikely. This is not a problem with sexual reproduction because the gamete is a single cell from which the whole organism will be derived.
Therefore, if you dive deeper in the fine writings, it's very unlikely that a multicellular organism, reproducing in an asexual way, can get any functioning functional change by exposure to radiation.
Addendum:
I have just found this [article](https://www.science.org/doi/10.1126/sciadv.ade2537?cookieSet=1) where the authors have examined the genetics of the stray dogs living in the exclusion zone in Chernobyl, a highly radioactive environment:
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> Chernobyl dogs are genetically distinct from other free-breeding and purebred dog populations.
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> [...]
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> Similarity to other free-breeding dog populations, versus purebred dog populations, is indicative of the Chernobyl dogs’ origin in the CEZ region. For example, elevated haplotype sharing with purebred populations might suggest that the original population has been largely replaced by modern pet dogs, leading to intrinsically lower genomic variation from which to distinguish mutations related to radiation exposure. However, this would also make the Chernobyl dogs less than ideal candidates for future genomic studies into cumulative DNA damage and for finding genetic variants associated with population survival and propagation. It is formally possible that some of the early genetic scars present in dogs living in the region immediately after the explosion that have been lost in modern populations are now replaced by large signatures of purebred ancestry. However, we demonstrate that this is unlikely.
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[Answer]
**If you're looking for suspension of disbelief, yes**
Over the decades, a [considerable number of studies were done concerning plants and insects surviving the Tunguska meteor impact](https://arxiv.org/pdf/astro-ph/0311337). Theories about genetic anomalies have been proffered, substantiated, rejected, and debated. There is still so much we don't understand about that event that, from this perspective and for the purpose of suspension of disbelief, yes, you could use the argument of radiation to rationalize the idea of asexual reproduction and genetic diversity.
**However, if we stick too closely to science, radiation is pretty much always universally bad**
Part of the ongoing debate about the consequences of the Tunguska Event concerns the influence of radiation. If you read the article from that link, above, you'll learn that genetic anomalies also occurred along the path of the incoming object (called the Tunguska Space Body or TSB because we don't actually know what it was — other than we're pretty sure it wasn't an alien space ship). The problem is there was no evidence of radiation along that path, only at the impact site.
This supports a basic maxim about radiation: it's usually bad. It's usually very bad.
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> Ionizing radiation has sufficient energy to affect the atoms in living cells and thereby damage their genetic material (DNA). Fortunately, the cells in our bodies are extremely efficient at repairing this damage. However, if the damage is not repaired correctly, a cell may die or eventually become cancerous. ([Source](https://www.epa.gov/radiation/radiation-health-effects))
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Additionally...
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> How Radiation Affects Your Body:
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> * Radiation can damage the DNA in our cells.
> * High doses of radiation can cause Acute Radiation Syndrome (ARS) or Cutaneous Radiation Injuries (CRI).
> * High doses of radiation could also lead to cancer later in life. ([Source](https://www.cdc.gov/nceh/radiation/health.html))
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Radiation rarely (if ever) leads to beneficial mutation (aka, Spider-Man). It's destructive. Radiation is energy, and like all energy, when too much of it is applied to something susceptible to it, the result is the destruction of the susceptible something.
**But that doesn't mean you're not moving toward a good idea, let's look to how asexual life deals with the problem today**
Let me introduce you to horizontal gene transfer:
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> When prokaryotes and eukaryotes reproduce asexually, they transfer a nearly identical copy of their genetic material to their offspring through vertical gene transfer. Although asexual reproduction produces more offspring more quickly, any benefits of diversity among those offspring are lost. How then do organisms whose dominant reproductive mode is asexual create genetic diversity? In prokaryotes, horizontal gene transfer (HGT), the introduction of genetic material from one organism to another organism within the same generation, is an important way to introduce genetic diversity. HGT allows even distantly related species to share genes, influencing their phenotypes. It is thought that HGT is more prevalent in prokaryotes but that only a small fraction of the prokaryotic genome may be transferred by this type of transfer at any one time. As the phenomenon is investigated more thoroughly, it may be revealed to be even more common. ***Many scientists believe that HGT and mutation are significant sources of genetic variation, the raw material for the process of natural selection, in prokaryotes.*** Although HGT is more common among evolutionarily related organisms, it may occur between any two species that live together in a natural community.
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> HGT in prokaryotes is known to occur by the three primary mechanisms...
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> 1. Transformation: naked DNA is taken up from the environment
> 2. Transduction: genes are transferred between cells in a virus (see The Viral Life Cycle)
> 3. Conjugation: use of a hollow tube called a conjugation pilus to transfer genes between cells ([Source](https://geo.libretexts.org/Courses/University_of_California_Davis/GEL_098-16%3A_Geobiology_(Sumner)/Text/3%3A_Genes_to_Enzymes/How_Asexual_Prokaryotes_Achieve_Genetic_Diversity), emphasis mine)
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You'll notice from my emphasis in the above quote that HGT *and* mutation are believed to be the primary sources of genetic diversity in prokaryotes. But that mutation is biological mutation (e.g., a change in hair color), not radiation mutation (e.g., tumors).
**Conclusion**
1. There is nothing stopping you from using radiation as the rationalization for genetic diversity in your alien population. The wonderful thing about alien populations is that they don't need to conform to what we know is true *for Earth.* Humans are wonderfully adept at suspending their disbelief.
2. But, if you're looking for scientifically supportable solutions, you can't use radiation. In that case I would consider researching Horizontal Gene Transfer and creating an HGT-based explanation that makes sense for your creatures.
[Answer]
Mutation from radiation is rarely passed on to offspring. Most mutation occurs to parts of a person's body that aren't involved in reproduction, so it reduces survivability.
It shouldn't surprise you that application of radiation results in traits that harden the creature against radiation (like hair or melamine). The requirement to defend against radiation takes biological energy to produce, so the effect is to make the creature less fit for other purposes, like finding food or defending itself against predators. This extra requirement can actually slow the speed of evolutionary development.
[Answer]
**Unnecesary**
No one can tell you if this is possible. We know zilch about extraterrestrial life.\*
But it is unnecessary. Just declare the species mutates faster than life on Earth.
Perhaps due to radiation as you say.
Perhaps due to a much smaller *genome* that is more sensitive to mutations of a small number of *base pairs*. [Small genomes mean faster evolution.](https://www.google.com/search?q=small+genome+evolve+faster&client=ubuntu&hs=wJp&channel=fs&ei=YMUAZLrfG8ulgAaM16zYDA&ved=0ahUKEwi6j-ydzL39AhXLEsAKHYwrC8sQ4dUDCA4&uact=5&oq=small+genome+evolve+faster&gs_lcp=Cgxnd3Mtd2l6LXNlcnAQAzIFCCEQoAEyCAghEBYQHhAdOgoIABBHENYEELADOgUILhCRAjoICC4Q1AIQkQI6EQguEIAEELEDEIMBEMcBENEDOg4ILhDHARCxAxDRAxCABDoLCAAQgAQQsQMQgwE6CAgAELEDEIMBOhQILhCABBCxAxCDARDHARDRAxDUAjoICAAQgAQQsQM6BAguEEM6BQgAEJECOgQIABBDOgcILhDUAhBDOgUIABCABDoHCAAQsQMQQzoFCC4QgAQ6BAgAEAM6CAguEIAEELEDOgcIABCABBAKOgYIABAWEB46CAgAEBYQHhAPOgsIABAWEB4QDxDxBDoICAAQFhAeEAo6BQgAEIYDOgoIIRAWEB4QDxAdOgcIIRCgARAKSgQIQRgAUJgEWPkfYP8gaAFwAXgAgAFWiAGgDJIBAjI2mAEAoAEByAEIwAEB&sclient=gws-wiz-serp)
Perhaps the life simply *evolved* this way to be less precise when copying *DNA*.
Perhaps the fast mutation is due to something about the creature's biology being completely unlike that on Earth.
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\*Does it being rare count?
[Answer]
DNA is a lot more complicated than what it seems. Every sequence does not contain only the bases that encode a trait, but also the ones that control how the trait is copied to RNA and the how it is expressed. During sexual reproduction usually entire sequences are swapped when the chromosomes are mixed. Mutations that damage the decoding process are rare.
Random mutations by radiations are a lot more likely to affect the way DNA is copied and decoded. Deformities or individuals unable to cope with the environment would be a lot more frequent. Biodiversity through radiation could still be possible, but only with a very high rate of births and deaths together with a ruthless selection. So, what you will need is a high birth rate and a Spartan attitude.
[Answer]
You can have biodiversity without mutations. All it takes set of genes that are switched on or off in the offspring that are set on or off differently from the parent. Even in humans, there is such mechanism, [epigenetics](https://en.m.wikipedia.org/wiki/Epigenetics).
Also environmental factors can modify genetic expression. This is how bee queens grow differently from workers. [They get a bit different food](https://en.m.wikipedia.org/wiki/Royal_jelly), and they grow into a bit different individual.
Also, plants can exhibit very different phenotype even if they are clones. You cannot find two identical oaks. Environment directs their growth, and the trunk, roots, branches etc. come out all different.
Yoy can xtrapolate from these examples and make your alien species exhibit different characteristics on each individual.
[Answer]
On highly complex and DNA some random modifications as caused by radiation will most likely just "damage" it, meaning the likelihood that something "good" will happen is much lower than something "bad" will happen.
So on the long run it *may* increase diversity, but on the short run, it will probably just reduce the population.
Maybe the surviving population will just be the kind that hides in caves to avoid radiation.
Also diversity is no advantage if it does not bring a benefit to the individual.
[Answer]
In the hundred years following the publication of "Origin of Species", repeated attempts were made to reconcile the "observed" age of the earth with the "observed" rate of evolution. These attempts consisted of (1) repeated extension of the "known" age of the earth, and (2) various theories about accelerated speciation.
Ultimately, "naive Darwinism" was replaced by the "modern consensus" which includes speciation by non-Darwinian mechanisms, because (1) further study of the fossil record caused changes in the understanding of evolution, and (2) the various theories of accelerated "speciation by natural selection" were not sufficient to meet the requirements of the known age of the earth.
In the 1950's, radiation enhanced variation was the go-to theory for matching the "Theory of Evolution" to the "Known Age of the Earth". Consequently, it got a lot of scientific research and popular exposure. Cultural references were movies about "kids with powers" (as the result of radiation) and of course "Spider Man" -- bitten by a radio-active spider.
The theory failed on investigation. Radiation does not cause enough enhanced variation to enable "selection on variation" to account for the origin of species. The next major attempt to reconcile TOE and "known age of the Earth" was the "population bottlenecks" theory. That has aged a lot better than the "radiation" theory.
What this has left us with is the situation where "radiation to cause common mutations" is still "popular science". It's just not "science" anymore.
] |
[Question]
[
**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
As we all know1, stillsuit as described in the books would cook the user. Water would carry heat away from the body, but then it would be caught again, and again with the heat.
Assuming energy is not a problem in a world with tiny Hunter-seekers and routinely levitating lamps, we could probably put that heat away - but where to? Modern day phase change cooling requires either frozen packets for heat to go to, or radiators and environment colder than the user. Electrical heat pumps can heat one end to cool the other, but the heated end still needs effective way to dump the heat. Something with large thermal capacity, or radiator with airflow.
Is there anywhere we can dump heat on the Arrakis-like environment without making users look like hedgehod with glowing red fins of a radiator? And preferably with little or no moving parts?
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1 [The Science of Dune: An Unauthorized Exploration into the Real Science](https://books.google.pl/books?id=4kbYExSCa6oC&pg=PT149&lpg=PT149&dq=stillsuit+dune+cooking+user&source=bl&ots=NABugE1r4D&sig=ACfU3U0TzgyCfvV1ZxgX5LmdLJT7h2xO7g&hl=en&sa=X&ved=2ahUKEwjjjKaTsfnzAhVvo4sKHVrvAjsQ6AF6BAgzEAM#v=onepage&q=stillsuit%20dune%20cooking%20user&f=false)
[Answer]
If you want a Dune "hard science" answer, the "heat exchange filaments" that [AcePL gracefully cited](https://worldbuilding.stackexchange.com/a/216658/26061) are very likely engineered by applying the [Holzman effect](https://worldbuilding.stackexchange.com/a/216658/26061) at molecular scale. After all, repealing "fast moving atoms/molecules" and letting only the slow one pass through sounds pretty much what a Maxwell daemon would do - at ambient temperature, the nitrogen and oxygen molecules average speed is 300-400 m/s. Dial the allowed speed to lower values and the molecules allowed to pass through will be grateful for a little bit of warming up.
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If you want real world hard science, **a heat pump and a radiator is all you need**.
[The best coefficient of performance](https://en.wikipedia.org/wiki/Coefficient_of_performance#Theoretical_performance_limits) for real world systems pumping heat from 0C to 35C is 4.5 - that is, for every Joule that you spend on the heat pump, you move 4.5J of heat from low temperature to high temperature.
The maximum theoretical achievable for cooling between 37C (310K) as the "cold temperature" and, say, 80C as the hot temperature is
$$COP\_{cooling} = \frac{T\_c}{T\_h - T\_c} = 310/47 = 6.6$$
But even only half of that would be enough, because... [human power](https://en.wikipedia.org/wiki/Human_power#Available_power) is not *that* big
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> Normal human metabolism produces heat at a basal metabolic rate of around 80 watts.
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> During a bicycle race, an elite cyclist can produce close to 400 watts of mechanical power over an hour and in short bursts over double that—1000 to 1100 watts; modern racing bicycles have greater than 95% mechanical efficiency. An adult of good fitness is more likely to average between 50 and 150 watts for an hour of vigorous exercise. Over an 8-hour work shift, an average, healthy, well-fed and motivated manual laborer may sustain an output of around 75 watts of power.
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Assuming the freemen are trained and motivated by survival, one can allow for 150W. At a $COP\_{cooling} = 3.3$, the heat pump will require a 46W - letting the freeman $150W - 46W = 104W$ of power for survival. (to compensate, the spice in the freeman's ration will need to provide 4.3 MJ for each 8 hours of marching)
@AlexP (thanks) points out in comments that the human body is not very efficient (and provides [citation for it](https://phys.libretexts.org/Bookshelves/Conceptual_Physics/Book%3A_Body_Physics_-_Motion_to_Metabolism_(Davis)/10%3A_Powering_the_Body/10.09%3A_Efficiency_of_the_Human_Body)), for every Joule of useful power it produces, another 2 or 3 Joules are wasted as heat (efficiency in the 25-33%). So the correction to the energy the spice ration should provide - between 12.9 MJ and 17.2MJ
More important, the heat pump will need to reject 450-600W - I'll come to it later.
The [median energy intake for athletes during competition](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5084025/) is 8674 kJ, but the extreme include a whooping 18,009 kJ (so the 8h energetic effort/day is plausible).
---
Now, the realization of the stillsuit:
1. the [lithium-ion battery](https://en.wikipedia.org/wiki/Lithium-ion_battery) has an energy density of 0.90–2.43 MJ/L. So 8L worth of battery (say, 12kg including well engineered electrodes and enclosure?) would let the freeman use her/his full power (and "just carry" the stillsuit, baterry pack included). After all, those Holzman shield do need some power, and they carry one even if they don't use it when navigating open sands;
2. will definitely need an insulating material, very likely reflective - the outside appearance should be like those emergency thermal blankets.
3. the trick is... if you maintain the body temperature at 36.5C, the body has little incentive to perspire. So... actually... the still suit will only condense the respiration water and extract the water in urine/fecals?
4. the radiator (air cooled) will make probably the bulk of extra weight. Because rejecting heat **must** be done by compressing the refrigeration fluid, so one expects a good heat conductor and good behavior under pressure. Probably aluminium would be good enough a compromise, otherwise one would suggest the heavier copper
Well engineered and tested in Arrakis conditions, one on top of the other (suit, compressor, radiator, battery pack) would contribute - feeling of guts - at about 20-25kg?
**To be noted that a 200W camping fridge**, able to cool 50L+ of drinks to 4C, [weights about 20kg *when empty*](https://www.4wdsupacentre.com.au/products/fridges-coolers/75l-fridge-freezer-combos-deals/kings-75l-dual-zone-fridge-freezer-adventure-kings-200w-solar-blanket-with-mppt.html).
*A 200W with an assumed $COP\_{cooling} = 3.3$ would be able to reject 660W, so we are well within the reach of today's technologies*
Now, about the weight of the suit, [some perspective](https://www.cnas.org/publications/reports/the-soldiers-heavy-load-1)
>
> For the last 3,000 years, dismounted soldiers carried 55 to 60 pounds on average. This has almost doubled in the last 200 years. Roman legionnaires carried almost 60 pounds. The British fighting in the American Revolutionary War carried 80 pounds. At the Battle of Waterloo (1815), the British carried 60 to 70 pounds while the French carried 55 pounds. The French in the Crimean War (1853-1856) carried 72 pounds. Around World War I, approximate march weights jumped to 85 pounds. U.S. soldiers trained with at least 60 pounds but carried additional rations and munitions in combat. During World War II, U.S. troops carried more than 80 pounds in the Normandy landings. U.S. soldier loads increased even more dramatically in the second half of the 20th century. March loads stayed at approximately 80 pounds during Vietnam but grew to 100 pounds afterward, with a maximum march weight over 160 pounds in Grenada in 1983. In Iraq and Afghanistan, march weights have approximated 100 pounds or more.
>
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>
---
**Answers to grumblings**
* but I'm fitter than a fit freeman and I used to push 220W for 1h
Well then, you maxed out your heat pump capacity, you probably need to do it at a higher temperature - which, BTW, is a self limiting factor - but you still won't boil inside.
An increase in $T\_c$ (i.e. acceptable body temperature) will make the COP of the heat pump higher - as it only needs to fight a low temperature differential. The human body will work at 40C, a temperature when the theoretical COP goes to $COP\_{cooling} = \frac{313}{353 - 313} = 7.11$ (353K is 80C, 313K is 40C). Half of that is 3.5, with a 200W input, you'll be able to reject 700W.
It's very much like what happens when you max out your A/C and then you decide to put something in the oven - you home won't catch fire, you'll just need to accept an increased kitchen temperature. You may accept it or else you will need to be wise and shut down to oven.
[Answer]
Let's find out the scale of the problem. How much heat do we actually have to dump?
[Some random source suggests](https://www.bestheating.com/info/was-morpheus-right-how-hot-are-humans/) an active human produces around 1Kw at peak output. Our stillsuit needs a refrigeration system able dump that amount of thermal energy (1000 joules per second). Assuming a perfectly passive radiator (radiates purely through, uh, radiation) we can now grab the [Stefan-Boltzman law](https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law)
```
P = A * ε * σ * T^4
Where:
P = power in watts to dissapate
A = area of radiator
ε = Emissivity. Lets assume a perfect black body aka 1.0
σ = 5.670373×10-8 = Stefan-Boltzmann constant
T = Temperature raise above ambient
```
We can now find the relationship between the radiator area and temperature rise:
```
A * T^4 = P / (ε * σ)
A * T^4 = 1000 / (1.0 * 5.670373×10-8)
A * T^4 = 17635524153
```
Which means that if we have a 1m2 radiator....
```
T^4 = 17635524153
T = 364.4 degrees Kelvin
```
Converted to Celcius, that's a surface temperature of 91 degrees, which is hot but not crazy. That's a pretty decent cooling loop you've got there, a gradient of 60 degrees - about 3 times that of a typical freezer, but it sounds pretty plausable to me.
Curiously the emissivity and area don't really matter so much because of that `T^4`. If we halve our area to 0.5m2 we only bump our radiators surface temperature to ~140 degrees.
These temperatures aren't too crazy, radiators that work with those sorts of power levels probably exist in various industrial processes.
---
This is assuming that our suit is a perfect black body emitter on it's radiator panels, and ignores several effects:
* First up, the big kicker: convection and airflow would help to cool the suit. This is why cars have radiator fans. This could *dramatically* reduce radiator temperatures. (Unfortunately my knowledge of thermodynamics is pretty poor, so I'm keen to see other peoples answers with better designed cooling systems.)
* Energy absorbed from the sun would add to the energy needed to be dissipated. Here on earth the solar energy at the surface can hit ~700W. Painting your suit white or silver could help with this (but would hurt emissivity)
* This assumes a 100% efficient system. Any energy created by reactors/pumps etc. would need to be handled by the cooling system as well. There's a thing called the coefficient of performance (<https://en.m.wikipedia.org/wiki/Coefficient_of_performance> ) which implies a heat pump can move ~3x more heat than it consumes, so a heat pump that provided 1Kw cooling would require ~300 watts power.
* That same source suggests that sitting down reduces a humans thermal output to only 100W.
[Answer]
Using the sky-radiation scheme from @MikeSerfas answer, it's pretty simple (with abundant energy sources as posited) to make the radiating surface hot enough for black-body to get rid of your heat. You need Peltier junctions, aka thermocouples, or whatever they develop into over the next hundred centuries.
These work two ways. The more familiar way, for most people, is to heat one junction while the other is kept cool, to produce a small DC current -- but it's a reversible effect; if you connect the junction pair to a current source, one end will get hot while the other gets cold; in effect, it's a no-moving-parts heat pump. These are commercially sold for iceless camp coolers and similar, drawing 12 V from an automobile electrical outlet to keep roundly 1/8 cubic meter of insulated box 10-15 °C cooler than the ambient temperature for as long as the power source lasts.
These *could* work without any sort of dedicated radiator; the exterior of the stillsuit would merely have to be (enough) hotter than the ambient temperature of your desert planet to conduct/convect the heat away to the air -- whether that's 40 °C or 60 °C. Of course, the more temperature differential you need to maintain, the more junctions and the more power are needed. They might be more efficient, and surely would have a reduced heat/infrared signature, if they had some kind of directed radiator, however.
[Answer]
People consume about 2000 kcal/day = 100 W on average. This has to be radiated from a surface of about 1.9 m$^2$, so we need 53 Wm$^{-2}$. The Stefan-Boltzman law requires a temperature difference $T\_2-T\_1$ such that $\sigma (T\_2^4-T\_1^4) = 53$, where $\sigma=5.67\times 10^{-8}$ Wm$^{-2}$K$^{-4}$. Hence $T\_2^4=T\_1^4+53/\sigma$. If the outside temperature is $T\_1$ = 50 C = 323 K (a hot day in the Sahara desert), then $T\_2$ = 330 K = 57 C.
This calculation ignores lots of other factors like convection, it being cooler at night, etc., but illustrates the point that you don't really require red hot radiator fins to be able to get rid of the small amount of heat a human body generates.
But you do very definitely need active heat pumping to keep the body at a survivable 30 C and the outside of the suit at 57+ C. The maximum efficiency theoretically possible is the Carnot heat cycle, where $1-T\_C/T\_H=W/Q$. Here, $T\_C$ = 303 K and $T\_H$ = 330 K so the work needed (per second) divided by the heat energy transferred (per second) is 1-303/330 = 0.08. To transfer 53 Watts we need $0.08\times 53=4.3$ Watts of effort. About 8% of your energy expenditure has to be redirected to keeping cool. Boot pumps driving a compressor seems like a plausible approach.
You need some sort of very high thermal resistance material to separate the inner and outer layers, and then you need heat pumps to pump the heat from the inside through channels in the resistor against the thermal gradient. An extremely good foam insulator (like an aerogel) could have a thermal conductivity of around 0.01 W/m K, so with a temperature difference of 27 K over an area of 1.9 m$^2$ and maximum practical thickness of 1 cm we get a leakage of $0.01\times 27\times 1.9/0.01=51$ W, which is far too large. We're pushing the state of the art, and still need something a factor of 5 better.
Here we have to get a bit speculative, and appeal to future technology and metamaterials. One way to enhance the thermal resistance of a vaccuum is to create many layers. If we have lots of flat opaque membranes separated by vaccuum (with spacers holding them apart strong enough to withstand the pressure and sparsely enough for their contribution to conductivity to be ignored) then heat can only transfer from each membrane to the next by radiation. If the power conducted through the material is $p$ then each membrane must radiate $p$ units of power each way more than the previous one. The membranes radiate $p\_0+p$, $p\_0+2p$, $p\_0+3p$, $p\_0+4p$, ... $p\_0+np$ units from each side. Take the $p\_0+3p$ membrane - it radiates a total of $2p\_0+6p$ units of power from its two sides towards its neighbours, and receives $2p\_0+2p+4p=2p\_0+6p$ from its two neighbours in return, and is thus in equilibrium. In the gap between any pair of membranes, there is $p\_0+kp$ units moving one way and $p\_0+(k+1)p$ units in the other direction, giving a net transfer of $p$ units. This yields an insulator far more effective than a single vaccuum gap.
Of course, if you suppose the desert is generally cooler than that (as most deserts on Earth are) then the problem goes away. Descriptions of Arrakis emphasise the extreme dryness, not the heat. A desert can be quite cool, and still deadly for lack of water.
[Answer]
**It's a matter of creating particles...**
We need to carry the entropy away somehow. So we want to make some low-energy particles and send it away. Specifically, we want a surface with an [emissivity](https://en.wikipedia.org/wiki/Emissivity) greater than 1, or at least, which *acts* like it has an emissivity greater than 1.
For example...
* We create "ommatidia", deep cavities with an emitting membrane that faces upward toward the desert sky. They receive little infrared radiation in that direction, so *if* we could increase the rate at which photons are radiated (or absorbed - I'm not going to require irreversibility here) then we could get rid of all the heat we wanted. Question is ... is there any way, with all that Dune technology, to get our photon count well above what a black body would produce?
* We do neutrino pair production. Some neutrinos are very, very low in mass, and if we use some free energy to make them out of nothing, then they will carry away some heat with no additional charge. Can Dune tech make neutrinos?
Any other hypothetical particle you can mine from the books might similarly have such a function.
**Alternatively...**
You can use your spice-induced prescience to pick the universe where all the random transfers of heat from one particle to another happen to move away from you. :)
] |
[Question]
[
Many countries, authorities and companies have the concept of a maximum weight limit for manual handling, both to protect their workers and to protect themselves from lawsuits.
Interstellar Shipping Incorporated (I.S.I.) also has such limits, but their requirements are a little more complicated. As they work on ships that may be accelerating or just floating (at anywhere between 0.5 and 0 g) the weight of the objects in question will obviously be lower.
But the mass of the thing won't, which means that it’s inertia will still make it hard and potentially dangerous to handle. On Earth we forget the inertia in many cases because we’re primarily focused on supporting the weight of the thing. In low to no gravity inertia is the main concern and our normal intuition about how to lift is flawed.
The commonly given example in the health and safety briefings is someone straining to pick up a crate of depleted uranium shells in low g, forgetting that they would have to arrest the forward motion of the crate, and crushing all their fingers between the crate and a doorframe when they couldn’t correct it’s course. The employee also caused damage to the frame of the door, for which they were fired (this may be an apocryphal tale).
So the question I.S.I. has for this site is: **what guidance should be given about working in low g to avoid injuries, property damage and lawsuits caused by the disconnect between weight and inertia?** Assume this is being given for a maximum of two employees (two man lift limit) and anything above that is covered by lifting machinery.
Good answers will include information on maximum safe mass for some g force between 0 and 0.5 g, necessary lifting techniques and (preferably) some description of how those numbers and techniques were arrived at.
Bonus points if the advice is generalisable to any low value of g. If it isn’t please state what value your advice is for and I.S.I. will compile a suitably comprehensive and not at all overly long winded safety guide.
Note: I’ve tried searching for any existing guidance around manual work on the ISS, but failed to find anything of use. If you find any please feel free to use it as a starting point (and include a link so I can add more useless knowledge to my brain!)
[Answer]
I remember my physics book in high school quoting an astronaut about moving large objects in space. He said "they are not heavy, yet one feels they are massive!"
Coming to your question:
>
> How can I estimate the maximum mass that can be safely handled in low to no g?
>
>
>
You state it by yourself
>
> Many countries, authorities and companies have the concept of a **maximum weight** limit for manual handling
>
>
>
Don't be fooled by the fact that the maximum weight on Earth is expressed in kg or pounds, what that really measures is the Newton (thus force) that needs to be exerted to lift a certain mass.
My educated guess for a first attempt would be:
* take the maximum allowed weight on Earth, say 20 kg
* convert it to force, thus 200 N
This is the limit you have to keep in mind. If you are working in 0.1 g, it means a single person can lift a mass of 200 kg while still being safe.
When it's not strictly about lifting, you can refer to the impulse theorem in its non relativistic and constant mass formulation
$F \cdot \Delta t = m \cdot \Delta v$
Knowing the mass of the object, the delta v you want to give it and how quickly you want to give it, you can get the measure of the force you need to apply.
I.e. if you want to move 2000 kg at 1 m/s starting from still, you can safely do it if you have more than 10 seconds to apply the force, since you will be applying less than 200 N.
Then of course refinement can come after empirical studies based on real cases and statistics show how microgravity affects the space workers.
[Answer]
For ease of use in a practice situation you probably only want one unit as a limit. [L.Dutch](https://worldbuilding.stackexchange.com/users/30492/l-dutch-reinstate-monica) wrote a nice answer based on force, I will try to do the same from an energy perspective.
So I imagine the safety involves not being crushed by big crates. For fingers and such complete other rules apply, as well as for sharp or tiny things (You can't catch a bullet).
So if you are are in danger of being crushed by a crate hurling towards you in zero g you have your arm's length (about 1m) to catch the crate and slow it down to a complete stop. If you can benchpress 80 kg on earth you exert a force of 800 N if you use a gravitational acceleration $a$ of 10, according to,
$F = m a$.
The work needed to do this can be calculated with,
$W = F s$,
where $s$ is the distance along which the force is exerted and $W$ is the work done in Joule. So bench-pressing 80 kg in earth's gravity costs 800 J.
**So 800 J would be the energy limit for objects**
So for moving crates in zero g only the mass and velocity matter since they don't experience force until you push against it. So the energy (here we will assume work is equal to energy, basically ignoring the directional component of work) of a crate can be calculated with,
$E = \frac{1}{2} mv^2$.
So you can calculate what the maximum velocity of a crate is allowed to be depending on the mass. In practice a table with a certain safety factor involved is probably better. So some safety limit speeds of different masses can be:
```
Mass (kg) Max Velocity (m/s) Max avg. Acceleration (m/s^2)
8 7.1 100
80 2.2 10
800 0.7 1
```
As suggested by [Morgen](https://worldbuilding.stackexchange.com/users/14548/morgen) I have added the maximum average acceleration a worker should apply over 1 m (arms length) to the crate. This is all assuming the worker has some way of counter balancing the force.
So for working safely you would need to remember some numbers and be able to judge the velocity of an object. It works for other gravities as well as long as the force direction of gravity is perpendicular to the plane the crates are being moved in.
[Answer]
L.Dutch gave an excellent answer about the basic physics of the situation, so I'll take a different approach.
In no gravity or very low gravity environments, it's unlikely you would be "lifting" or even directly moving heavy objects, in the same manner you are used to on Earth.
Any attempt to push the object will push you back with the same force and you won't stop until you hit into something, any attempt to lift the object would result in it flying "upwards", with you unable to stop it. On Earth we have gravity to anchor us and that gravity restricts our up-down motion (z-axis) and also allows for friction which restricts our (x-y) motion. Thus we see gravity enacts a lot of restrictions on the motion of an objects along it's degrees of freedom.
Of course in Sci-fi you can have some fancy work-around to some of these issues, such as magnetic boots (there are a host of reasons these are impractical IRL), which seem to be popular in sci-fi. But anything short of artificial gravity does not solve the issue.
For objects, whose mass is much smaller than our own, Newton's third law ensures that moving them around in low-g/no-g environments isn't too big of an issue, this can be seen in videos of astronauts/cosmonauts doing their thing on the ISS for example.
But with large (having large volume) and/or massive (having large mass) objects, as compared to ourselves, moving them around safely would be a fairly serious and difficult issue. The speed at which something is moving is not easy to gauge and allowing massive objects to be moved around with no physical restrictions of motion along at least some of their degrees of freedom is a disaster waiting to happen.
In the case of the ISS or space-shuttle, moving large objects in space is accomplished with small rockets and tethers. The same would be the case for moving around crates on the docking bay of a transport ship. The iconic scenes that are a trope of sci-fi in which a wide docking bay has smaller ships docking and taking off while busy crews load and unload crates as seen in films like Star Wars simply couldn't happen in a low-g or no-g environment. (I know there are artificial gravity in most of these films, but I'm using the imagery)
The most likely solution would be a network of cable paths, along which all things are moved along. Crates would be hooked to the cables and guided or reeled along specific paths, junctions would allow paths (and hence the cables the crate is hooked to) to be switched.
There would be guidelines which would be strictly adhered to governing the properties and conditions of the cables and the mass and size of the crates which are allowed on cables of various ratings. Crews would have to adhere to equally rigorous procedures when moving things around. This would remove the burden of manually calculating forces, energies and speeds (presumably on the fly) away from crew members (robots maybe, but certainly not humans) and instead "procedurize" the process to optimize for safety and efficiency.
[Answer]
I propose that you replace the weight limit in 0g with a limit on moving technique. The key is that putting something in motion and then stopping it will take the same amount of effort. So you encode the following rules of thumb as laws:
1. You push objects while standing in a single spot. No following something with you magnet boots to give it an extra oomph. This means the receiving end can stop the object from a single spot, eg. if they're stuck between the object and a door.
2. Only one person does the initial (and only) push, preferably the physically weakest. Means everyone else can do the stopping push on their own.
You can then safely push ridiculously large things, even the whole space station, but it will have to move atrociously slow.
[Answer]
As [D.J. Klomp](https://worldbuilding.stackexchange.com/a/174120/37815) points out in their answer, the important value is the energy of the object. However, there is a catch: You cannot easily judge the velocity, and thus its energy, in a hand-handling-cargo situation. I mean, when you handle a box, do you think "Hmm, I think this box is moving at 2.4m/s now"? Most certainly not, and even if you did do this estimation, you would not be very accurate with it.
However, another observation comes to the rescue: Humans have a typical *max. velocity* that they use when handling cargo. And if you combine that max. velocity with a max energy, you get a *max. safe mass*.
So, let's assume that a worker can safely exert a force of 500N (= 50kg) with their arms, over a distance of 0.5m (about one arm's length). That's 250J. (I'm being much more conservative here than D.J. Klombs answer, we are talking about safety regulations after all!) Now, let's assume that humans move heavy object at a max velocity of 2m/s (that's 7.2km/h - faster than walking, slower than jogging). Then we find a max. weight by solving the formula `250J = m * (2m/s)^2 / 2`, which yields `m = 125kg`.
Now, this is a weight that I can stop from crushing me when my back's against a wall, and I have time to prepare for the impact. A safety regulation, however, must err on the safe side. Now we note that 125kg is actually quite close to the weight of a human being. Which makes sense, for we routinely handle an object of our own weight all day long! As such, **I would expect the I.S.I. to set the max. safe weight for manual handling to 75kg**. (This is the weight that's typically assumed for an average human being. For instance when declaring how many persons are allowed to ride a lift together.)
] |
[Question]
[
## QUESTION
I was thinking about ways of justifying practical balloon flight for a pre-industrial civilization, when I remembered that some microorganisms produce [methane](https://en.wikipedia.org/wiki/Methanogen), and better yet, [hydrogen](https://www.ncbi.nlm.nih.gov/pubmed/18647659).
**This made me wonder, is it plausible to posit a hydrogen creating microbe that could produce enough lift gas to refuel a balloon, even in midflight?**
---
## NOTES
A balloon craft in this scheme would keep a lightweight fuel tank attached to the envelope by a hose. The tank would be filled with microbes and their food (hydrocarbons, biomass, whatever it is that they like to eat). The microbes then produce hydrogen gas. To rise, you throw in more fuel. To descend, you release some hydrogen. Depending on the fuel source that the microbes eat, trading towns might also farm wells full of the microbes where smaller balloons could fill up.
---
Now on to the potential problems:
**First**, I don't know if any organism could realistically produce the required volume of hydrogen gas.
I know that a hydrogen balloon lifts about 68 lbs per 1000 cubic feet. I also know that the efficiency of methanogensis (which is the best example I've got for hydrogenesis) can be quite high, and I've seen numbers ranging from [20%](http://www.nature.com/news/2007/071212/full/news.2007.375.html) to [80%](https://news.stanford.edu/news/2012/july/microbes-clean-methane-072412.html). But even with some kind of awesomely efficient microbe, from there I have no idea how to calculate the cubic feet of hydrogen that could be derived from a given fuel source.
**Second**, though less important, I also don't know if any microbe could physically generate gas fast enough to allow for reasonably controlled changes in altitude.
**Third**, even if all of that (literally) flies, I need to make sure there's a reason these microbes don't get loose and just eat up all the fuel outside the tank.
---
*Finally, this question may end up being pretty important to the world I'm working on right now, so if it ends up being more complex than a straightforward "no" then I'll also offer a thank-you bounty to anyone that gives me an especially in-depth answer.*
---
**BOUNTY EDIT:** Bounty goes to Dubukay. In general this question received many high-quality answers, so thanks everyone!
[Answer]
## Microorganism-powered aerial flight is plausible, but with caveats.
As you point out in your question, hydrogen is the best lifting gas we have. So this becomes a question of **"What's the most efficient [biological process](https://en.wikipedia.org/wiki/Biohydrogen) that produces H$\_2$?"** The answer, of course, is **algae**.
Normally, algae get their energy from photosynthesis- taking in sunlight, water, and carbon dioxide to produce ATP, complex sugars, and oxygen. However, under the right conditions (mumble mumble [sulfur-limitation heterocysts](https://www.ncbi.nlm.nih.gov/pubmed/16663954/) mumble) some algae will switch to a metabolic state of "[anaerobic oxygenic photosynthesis](https://www.ncbi.nlm.nih.gov/pubmed/19291418)". In this state, the oxygen produced by photosynthesis is used by the cell's own respiration, producing an anoxic environment, which in turn triggers the production of hydrogen gas.
What this means is that algae can produce H$\_2$ gas almost directly from protons. Even better, we can collect it and are already well on our way to making it a [cost-effective replacement for fossil fuels](https://www.technologyreview.com/s/408745/hydrogen-from-algae/). Clean energy in our lifetime? Yes please.
However, that's not enough to answer the question, which asks about the rate of H$\_2$ production. In 2001, a company built a 500 liter bioreactor that could produce an astounding 1 liter of hydrogen gas per hour. With that kind of potential, our balloon would need luck to even *start* inflating. However, that was 2001, and the first year the company started. At that time, they calculated a theoretical maximum of 20 grams of hydrogen per day- about 10 liters per hour. In 2004, [a review](http://www.tandfonline.com/doi/full/10.1080/10408410590912961%20) came out that [posited a maximum of 5.45 kg](http://www.tandfonline.com/doi/full/10.1080/10408410590912961%20) of H$\_2$ per square meter per year. That's a rate of ~7 liters per hour- still a bit too slow. In 2011, we multiplied that rate by 5 times by creating [biohybrid photosystems](http://pubs.acs.org/doi/pdf/10.1021/jz101728v) that use platinum nanoparticles. In 2013, we managed to do even better and increase our efficiency 4x by [modifying the chlorophyll antennae](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3645517/), and that's [since been pushed](https://www.sciencedirect.com/science/article/pii/B978012800776100011X) to 13x. So our current rate of H$\_2$ production is about 450 liters per hour! Of course, this is an idealized maximum efficiency and we haven't yet managed it on a large scale.
So what does that mean for our balloon? In a world where people rely on balloons like this, I'm going to assume that they're operating pretty close to maximum efficiency, perhaps 400 liters per hour per square meter. Of course, there [may be problems with this](https://www.sciencedirect.com/science/article/pii/S1360138506002470?via%3Dihub), but it's a decent estimate to start with. From [skydrifters.com](https://skydrifters.com/faq/), we learn that an average hot air balloon weighs 800 pounds. Since we're traveling and trading, let's call it 500 kg total. Lifting 500 kg with hydrogen gas requires ~40 kg H$\_2$. At normal air pressure and temperature, this occupies a volume of 450,000 liters. **Thus, our balloon will take approximately 41 days to fill under its own power.** That's going to be hard to pull off.
However, this calculation shows that algae can indeed produce enough gas to lift a balloon, and it'd certainly be an eco-friendly way to travel. It also allows for maneuverability in the air, and essentially *permanent* air travel. Once the balloon goes up, the algae can draw their CO$\_2$ directly from the air and the balloon will be powered by light alone. Additionally, it's quite possible that towns and cities would start to farm fields of algae so that filling up at a city is quite easy and would entice ballooners to visit.
In the air, such a balloon would ascend normally as the algae produce hydrogen gas. Additionally, H$\_2$ gas compresses quite nicely, and it might make sense for ballooners to keep a compressor on board to capture any excess H$\_2$ produced for a quick burst if necessary. Descending is the easy part: the simplest would be venting the H$\_2$ or compressing it for later. You could also spray the inside of the balloon with some kind of inorganic sulfur, which would shut down the hijacked photosynthesis pathways temporarily, or add oxygen, which would destroy some of the hydrogenase enzyme.
The mental image I have of this system is a very gross, quite large clear balloon. The outer membrane would be made of plastic wrap or some other impermeable lightweight clear solid, and there would be layers of algae directly inside. Any H$\_2$ produced would fill the balloon and contribute to lift, displacing any denser air in the meantime. Since the microbes live best in an anoxic environment, this wouldn't even be a problem. Maintenence would essentially consist of replacing nutrients and removing dead cells from the inside, which would probably be done when on the ground but *could* be done in the air if one can hold their breath long enough.
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So the first question. If the microbe doesn't have to exist on Earth already, then there is no reason for it to not be possible.
Just say that this super microbe does exist, and when combined with other methods like a catalyst of some kind (like nickle for instance), is able to produce enough gas to make it possible.
Another possibility is that the organism works slowly, but the gas builds up over time. So say to fill a new balloon up to pressure takes a couple weeks, but if you keep putting in resources then the microbe will just keep producing and keep the balloon topped off. This option would require a material that holds the gas really well.
Second, there are other possible ways to control changes in altitude other than venting. [If you compress the lifting gas](https://aviation.stackexchange.com/questions/8523/how-do-blimps-control-altitude) then it will be less buoyant, and so you will go down. you could put a balloon inside of the balloon, and pump the inner balloon up with air when you want to descend.
As to the third question, this is a bit trickier. As a wise man once said "Life, uh, finds a way."
There are several [self limiting](https://en.wikipedia.org/wiki/Self-limiting_(biology)) mechanisms that could be used.
* The microbe has a natural microbe predator that keeps it from getting out of control in the wild. It could be another microbe, some kind of algae, etc.
* There is a compound in raw fuel that hinders the microbe that isn't present in refined fuel or something is added to the refined fuel that gives the microbe a boost. This could also act as a catalyst.
* The microbe has a genetically fixed colony size that is large enough to be used in a gas production system, but not large enough to cause problems in the wild.
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I don't think so.
This starts to be a rocket problem. The more gas you need, the more microbes and nutrients you need for the microbes and that adds mass. To lift that mass, you need to produce more lift gas which requires more microbes and nutrients, etc. If you can't pass break even, you aren't going anywhere.
Also, microbes want to grow and reproduce. They evolve to be as efficient as possible into turning nutrients/energy into biomass with as little waste as possible. In this case, the lift gas is a waste product. While it might be possible to engineer a microbe to produce more gas than biomass, I don't think you'll find them in nature.
Furthermore, you would have to get that lift gas away from the microbes. Very few organisms can survive while immersed in their own waste products. At some point, the partial pressure of the gas in the air around the microbe is going to be high enough that the microbe cannot excrete the gas and will die.
The microbe will also have to have access to gasses that it can take in. I hope that the microbes are not oxygen breathers since oxygen and most biologically produced lift gasses do not mix well.
For this to work at all, I think that you would need a thin sheet of the microbe with air and nutrients on one side of the sheet and the lift gas collection on the other side. You could make a bag out of this sheet if you can make the sheet strong enough. Though, an engineered multi celled organism in the correct shape would work better than trying to hold microbes to a shape.
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# Bacteria
Very roughly, hydrogen gas H2 is 2g per standard volume (22.4l), while air being 80% N2 (28g/mol) + 20% O2 (32g/mol) gives an average of 28.8 grams. So two grams of hydrogen, displacing 28.8 grams of air, generate 26.2 g of lift (probably a little less due to the balloon being somewhat compressed). Each gram of hydrogen gains us 13g of lift.
How do we get those 2g of hydrogen? We need some highly idrogenated feedstock, so a molecule with hydrogen bonded with the lightest possible elements *and* containing excess chemical energy.
Available light elements include:
* lithium (lithium hydride "burns" to hydrogen by itself, just add water, no bacteria needed - LiH + H2O → LiOH + H2; we still need one water molecule and one LiH molecule for every available hydrogen molecule, which requires one oxygen (weight 16) and one lithiums (weight 7), for a total ratio of 2:23 or 8.7%)
* beryllium (beryllium hydride, synthesised 1951. [Let's not go there](https://en.wikipedia.org/wiki/Beryllium_hydride)).
* boron (hydrogen boranes. Doable, but *a little* [too energetic](https://en.wikipedia.org/wiki/Boranes)).
* carbon. Very promising: not only it binds hydrogen but binds to itself in stable compounds.
* oxygen. This means water; not much energy there.
* nitrogen. This means ammonia; but oxidising it results in nitric acid, not hydrogen gas. Dissociation problems: like water, but worse.
* aluminum. Not unlike boranes for [violence](https://en.wikipedia.org/wiki/Aluminium_hydride), and we need water.
* fluorine. Same problems as ammonia but [much, much worse](https://en.wikipedia.org/wiki/Hydrofluoric_acid).
* sodium. Costly and unwieldy, and [difficult to handle](https://en.wikipedia.org/wiki/Sodium_hydride). Weight ratio exactly half of lithium (not coincidental: both lithium and sodium are group I), 4.34%. Going up in the periodic table will only make things worse.
The best option is saturated hydrocarbons. We need a metabolic pathway through which the bacteria dissociate CnH2n+2 hydrocarbon and oxidise the carbon, but not the hydrogen. There's energy enough available in hydrocarbons that we're not shortchanging the little critters:
* CnH2n+2 + nO2 → nCO2 + (n+1)H2.
The hydrogen proportion in weight in CnH2n+2 is about 14%; so, one kilogram of feedstock will yield 0.14 kg of hydrogen, supplying a lift of 1.82 kg. Since we *also* get rid of one kg of feedstock that acted as ballast, the total lifting effect is 2.82kg.
Not much, really, and I think that's the best one can possibly do. But perhaps it is enough.
# Gengineered algae
Another possibility is a pseudo-photosynthetic organism that harvests water from the atmosphere, photodissociates it and releases H2 and O2. But such an organism wouldn't have any advantage in doing so (it could do so once fully matured and stable, though), because the energy would entirely go in "waste" products, and the production rate would be even less than in the first case (the inbound sunlight must equal the chemical energy being stored in the dissociated gases, and for the hydroxygen mixture, that's a *lot* of energy, while sunlight is I think around 1.2 kW per square meter).
"a 100%-efficient electrolyser would consume 39.4 kilowatt-hours per kilogram (142 MJ/kg) of hydrogen" ([Wikipedia](https://en.wikipedia.org/wiki/Electrolysis_of_water)), so we can expect about 30.4 grams of hydrogen per hour from every square meter of algal panel, or about **0.4 kg of lift per m2 per hour**. Probably much less because green and blue algae don't absorb all of the energy of the whole solar spectrum. Considering the **weight** of an algal panel (which needs water and support), this probably means that this isn't a very promising road. Or is it?
Let's go down it anyway. The *Hindenburg* might have had about 9000 m2 available, producing 270,000 grams of H2 per hour in full sunlight. That is about three million liters per hour, or 3024 m3 of hydrogen per hour. The same [*Hindenburg*](http://www.airships.net/hindenburg/size-speed/) required 200,000 m3 of hydrogen; that means that in one hour we can replace about 1.5% of its gas contents, in exchange for a weight of not less than 90 tons (ten kg per m2) or 180,000 lbs of its 511,000 lbs payload. In theory it's doable, but I think we're pushing things; the above values are all calculated from the most optimistic circumstances. A panel weight of 30 kg per square meter (and when you think glass - or *hydrogen-proof yet thin and transparent plastics* - and water, 30 kg are nearer than it seems) might well make the whole endeavour mathematically impossible.
Larger, flattish balloons might increase the convenience of it all, especially if we could build *them* with clear hydrogen-proof plastics and put the algae on the *inside* bottom surface. We still couldn't keep them uncovered (because we need to sequestrate and discard the oxygen they produce). But at that point there are big structural problems, and the fact that we don't really have a sunlight-clear plastic tough enough to withstand the stress, that will not leak hydrogen like a sieve. But this could perhaps be handwaved away ;-)
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I think "yes" but with a couple changes in perspective:
Firstly think dirigible and not hot air balloon: Don't use your gas to control your altitude, it is too valuable to just vent it. Use impellers and control planes, like a blimp to FLY up and down.
The "throw in more fuel to go up" portion is unlikely... but that doesn't mean they can't generate all the lift necessary OVER TIME...
Which also solves the mass problem... keeping a colony of bacteria on hand that is just large enough to perpetually keep the dirigible topped off, and increase the volume for the sake of the occasional load of heavy cargo...
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I am wanting to build a world with a strong retail presence, and became interested in the Information Desk at Selfridge's.
This was not the simple standard store information desk, where you ask directions or make enquiries regarding the store itself. Nope, apparently, this information desk, was an information desk for all information, like the old-timey equivalent of *Google*, but not where you'd expect it.
Selfridge's is a famous department store in London. Anyway, on the TV show [Mr. Selfridge](http://www.imdb.com/title/tt2310212/), set in the 1910s, based on the founder of the store, the store's Information Bureau allowed one to "discreetly enquire" regarding a person's debt, where they'd been across Europe, as well as more mundane requests such as a translation for French phrase. (The desk ran much longer than the 1910s, at least through the 1930s).
According [this article](http://www.radiotimes.com/news/2013-01-06/the-real-mr-selfridge-the-man-who-brought-sex-appeal-to-shopping), their "information bureau" answered questions on everything "from the age of the King to tricky Times crossword puzzle clues." If they didn't have the answer, they could tell you where to get it. And in [this one](https://londonhistorians.wordpress.com/2016/03/15/happy-birthday-selfridge-co/): "For years the store ran its own private Information Bureau, equipped with more books than the average local library and a trained staff dedicated to finding answers to literally any question a customer might put to them." The idea was, no matter what the question, this desk would find you an answer.
I am totally fascinated by this, and want to build something similar in my world (it seems akin to low-level detective work, in some cases), but I need to know more about how out-of-place "information desks" may have worked this way in our world in order to sync it with reality. **I am looking for ANY "all information" research desk (not just the one at Selfridge's) that was in an unexpected place. Selfridge's was the one that came to mind, but I am sure that there are others out there. I was hoping that there might be other examples of "out-of-place" or unexpected research desks. Although, will say, want to make it in a retail setting. Does anyone know how they might have worked and could point me in the right direction?**
Just for reference, I am building this in a time period not unlike the Renaissance, but with better access to books and printing (more akin to WWI era in that respect) but without radio. So I want to build an "all information" desk, using real-life analogues to start with.
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Before Google there was AltaVista. Before AltaVista there were [Archie](https://en.wikipedia.org/wiki/Archie_search_engine) and [Veronica](https://en.wikipedia.org/wiki/Veronica_(search_engine)) and [WAIS](https://en.wikipedia.org/wiki/Wide_area_information_server). And before the Internet there were reference and research services staffed by humans.
* Large public libraries offered [public reference and research services](http://www.npr.org/2014/12/28/373268931/before-the-internet-librarians-would-answer-everything-and-still-do) ("before the internet the librarian would answer anything"), and many of them still do. For example, the [New York Public Library Research Services](https://www.nypl.org/help/get-what-you-need/fee-based-research-order-form) (40 to 200 USD per hour, depending on how quickly you want your answer).
* Other organization offered and continue to offer specialized research services -- genealogical, scientific, business-oriented, and so on. For example, the [General Information Service](http://www.geninfo.com/) provides a variety of background checking services for businesses. For an introduction see the Wikipedia article on [reference desk](https://en.wikipedia.org/wiki/Reference_desk).
* Many organizations maintain their own research bureaus; for example, one of the best known is the [Congressional Research Service](https://en.wikipedia.org/wiki/Congressional_Research_Service) which serves the United States Congress. Newspapers used to have specialized [fact checking](https://en.wikipedia.org/wiki/Fact_checking) departments which could and did answer factual questions from journalists (and in olden days made sure that information printed was verifiable).
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Several questions here.
# Was it true?
I won't go into that, I'm just going into the worldbuilding question.
# Could they have the data?
Not as well as a computerized database, of course. It would rely on the fact that there are fewer *relevant* people. One would not inquire in the creditworthiness of a small grocer in Nottingham. One would ask if a *gentleman of means* has possibly over-extended his investment.
How many of these people? Thousands? Tens of thousands? And how many would be heavily in debt at any one time? It would be conceivable that one well connected business would be aware of that.
And French was the world language at the time. Would they be able to find a Czech speaker?
# Could they release the data?
Now it gets really interesting. Casting doubt on the credit of a gentleman could be a grave offense, especially if those doubts are unfounded. There are jurisdictions where substantial damages would be due.
My guess it that it would depend on who is asking. If a *very* good customer inquires about a *bad* customer, and if the data is rock solid, they might answer.
**Summary:** Consider how far the services of a [concierge](https://en.wikipedia.org/wiki/Concierge) may go. Find a good restaurant, avoid a bad businessman ...
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Well, the debt part is easy: credit ratings started in the US, so that small local banks could share information about loan applicants, especially people who had just arrived. At that size, they couldn't afford to turn away applicants on suspicion, nor could they afford to have delinquent debtors. Organizations like the Western Union and major banks traded information as well as cash.
Having worked in the US retail industry, Selfridge would have been familiar with the system, and would not have found it to hard to implement on the other side of the pond. And as **o.m.** said in his answer, there were few people whose debt situation might be of interest.
Where they've been is part of the credit information. X owes *n* amount to Y, but Y is located at Z, so X has presumably been to Z. That and shipping records and society pages would give a pretty clear picture of people's movements.
Last, as regards French, it *was* the *lingua franca* of the time ;-)
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Check the available options to store data, then think about how and where these data stores might be accessed.
A few decades ago, books were the obvious data stores. These could be found in department store, book stores and private or public libraries. Yes, could walk into a larger book store and be lucky to find an enthusiastic sales person who would investigate facts for/with you inside the "data warehouse" (no purchase necessary).
Libraries were also sort of networked in days before the internet, exchanging books (or photocopies or perhaps even manual transcripts) via mail (later on, telefax was an option as well).
The other, perhaps not as obvious data source are periodicals (newspaper, magazines). These are an even more important source than books (most scientific discoveries just appear in periodicals, not in books). Periodicals are archived by their publishers and also by libraries. Thanks to the above mentioned networking, it was possible to get about every published paper from anywhere in the world withing a few weeks, max).
That's all boring. A place with lots of books and periodicals is a data warehouse, and therefore not an *unexpected* information desk.
Possibly somehow related and a bit unknown to most people are "Orderstationen" (that's the german word, plural) - these were privately operated locations along larger waterways (like the river Rhine) which dealt with information. Communication with passing ships was performed via radio or loudspeaker arrays (which could be rotated to stay trained on the ship with whom the person in the Orderstation was communicating). The main source of revenue for the Orderstationen were ship owner which used them to receive updates about their ships' position or to give new orders to the captains (like a new route or port of destination).
The Orderstaionen would also provide other information of interest to the ship crew. They were even equipped with a stock of records to play music for passing ships, if this was desired. So it wasn't just business-related communication, but also general inquiries, casual talk and entertainment. Obviously, the duration of a communication session was limited by the time the (moving) vessel was close enough to the Orderstation.
Orderstationen existed into the 1970s - more modern communication methods made them obsolete.
Note that locks (the "gates" in a river which separate different water levels and allow ships to pass) also typically served as Orderstationen. There were also Orderboote (boats). These allowed also to exchange written matter, but were less suited to allow for "on-line real-time inquiries", which a person working at an Orderstation could perform via telephone or telex.
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Given a fantasy world in which magic exists and which dragons are real, what kind of tactical advantages could a dragon and rider pair have over dragons without riders?
To expand on the setting:
* Dragons are sentient beings with intelligence and personality equal to or greater than that of humanoids. They have their own natural methods of performing magic inaccessible to non-dragons, and some dragons can expand their understanding of magic through study. They have the ability to shape shift (with considerable mental effort) into any natural shape, most often a humanoid form to ease social interaction or provide access to human spaces. They range in size depending on age, though usually only younger ones have riders and they can not normally carry more than one or two people at most. They live five to ten times longer than humanoids, with adolescence starting around one hundred years of age and most retreating to isolated family lairs by adulthood around age three hundred. Their scales are hard, but are still natural material, so metal weapons can pierce them and armor can still benefit them, though the burden is undesirable in most cases. While their digits are dexterous enough to manipulate objects, they are unlikely to wield weapons themselves. They can breathe either fire, lightning, ice, poison, or acid depending on their race, though volume and frequency is dependent on age. Riding harnesses/saddles exist as well.
* Humanoids that ride dragons are fully sentient and intelligent, capable of performing magic with enough training. There is a wide range of cultures ranging from bronze age through renaissance depending on the nation. Simple clockwork exists in some areas and alchemy is an emerging science in the world.
* There are also other sentient and intelligent creatures capable of magic in the world, but dragons and humanoids are the primary inhabitants.
* There are no chemically propelled missile weapons.
So far, I have settled on that a dragon with a rider has the following advantages:
* A second set of eyes: The dragon rider is able to keep an eye out on spots that dragons normally can't see as well, including above and behind. Dragons being apex predators are not normally inclined to look above or behind them when in flight and this is the primary method of attack during dragon on dragon combat.
* In flight first aid: Most dragon riders are trained to bandage and use quick healing magic to patch up their dragon while still in the air.
* Close combat support: Dragon riders can use pole arms like lances and glaives to great effect from dragon back. They can also train to use archery from dragon back. While not as effective as the dragon itself, they still add some force, provide the opportunity to attack other dragons from below, as well as deter other dragons or people trying to drop on or flank the dragon.
* Mobile magic might: A rider experienced in magic can use the vantage point provided by the dragon to safely cast magic with little worry of being interrupted. If the dragon and mage have practiced at length, the mage can even access the magical power available naturally to the dragon.
* Communication: Using signal flags, friendly riders can communicate while their dragons focus on staying aloft. This allows for more effective tactical coordination.
So what I am looking for now is what other possible tactical advantages could a rider provide to a dragon during either mass or single combat? Additionally, if there are any tactics that humanoids could employ against dragons beyond simply brute force efforts like hails of arrows or really large fireballs, those would also be appreciated (I have read a number of other answers to the 'How to fight dragons' question, but none seemed particularly fitting).
(PS, this is my first question on here, so please let me know how I can improve it if you see anything missing.)
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**The biggest advantage of dragonriders isn't to the dragons, it's to the army fighting alongside the dragon.**
You've already identified some ways that dragon-mounted riders could be useful to armies:
* Mobile magical might
* Communication
And I would also add
* Scouting/reconnaissance (The dragon could do this job by him/herself, but then he/she would have to spend the time giving reports, drawing troop deployment maps, etc. Better to let a human do it).
Let's not underestimate the value of those last two points. Just imagine what any military commander before the 20th century would have said if you offered them a flawless birds-eye view of the battlefield. So we can conclude that dragonriders are of great use to armies, but what use are they to dragons? I would say their greatest use is in supporting the army. If a dragon has decided to team up with an army, either as a conscript or as a commander, they should make the best use possible of that army, which means dedicating most of your flight-time to reconnaissance and communication. Mix it up with some strafing runs to sow confusion in the enemy ranks and break up enemy strong points, and you'll win the battle with your now-unbeatable infantry, and never risk your dragon's life in pitched battles.
Of course, if the other side also has dragons, the whole situation changes. Your enemy has the same advantages to intelligence and communication that you do, and flying down low to strafe enemy infantry leaves you vulnerable to a counterattack by enemy dragons circling above (remember that altitude is a huge advantage. In real life most/all raptors hunt by diving on their prey).
Now your dragons have two main priorities:
1. Scout the enemy formations and return this information to your troops.
2. Disrupt enemy scouting scouting attempts.
Now you might to mount some sharpshooters (archers and/or mages) to kill enemy dragonriders before they have a chance to report back. And to kill the enemy sharpshooters targeting your dragonriders. This is probably the best way to eliminate enemy dragonriders, but if you might want to actually take down the enemy dragons themselves. Maybe the dragons are strafing your infantry, or they are doing the scouting/communication without the help of riders, or maybe you are losing the sharpshooter battle and you need to change tactics. So there is a third type of dragonrider: a lancer. Lancers don't spend any time on scouting or target acquisition. Their job is to climb high in the sky and then dive straight at an enemy dragon and stab it in the heart (or wherever). Even if the enemy dragon is wearing armor, the force to the impact may knock them into the ground. This is a very dangerous tactic due to the high-speed maneuvers and collisions, but it will kill or chase off an enemy dragon much faster than the allied dragon could without a rider (just using claws/teeth).
So we have 3-5 jobs for Dragonriders to do:
1. Recon & communication
2. Disrupt enemy scouting (sharpshooters)
3. Eliminate enemy dragons (lancers)
4. Mobile magical might
5. Strafing ground troops (doesn't require a rider, but only when unopposed by other dragons)
Each of the first three tasks is pretty much mutually exclusive. Dragons doing recon need to stay lower to the ground where they can see more detail, and mostly over their own army where they can communicate info and orders and have the support of friendly archers. Sharpshooting dragons should be higher in the air, but need to be close enough to their targets to take shots. Lancers need to climb up above the other dragons so they can gain sufficient speed while diving at their targets. Because of these difference in positions, each dragonrider can only be effective at one of these tasks at a time. Balancing between these priorities would become a key feature of battles involving dragons. Focus too much on supporting your ground troops and your riders will get picked off; too many archers invites a rush by lancers; too many lancers and your infantry lacks support. Of course this is only a rough outline and specific situations/battles/tactics could turn these generalizations on their heads.
I expect that most dragonriders are most skilled in just one or two of the above specialties. So if you want to change tactics you'll need to communicate that to the dragon, then have them land, switch riders, and take off again. This could take a lot of time, and the enemy dragons would definitely see you do it and have a chance to react. Therefore the most skilled dragonriders would be able to switch quickly between different tasks. You can easily imagine a small, elite squad of dragonriders defeating a much larger one by working together and adapting quickly to enemy tactics.
**Some bonus points to consider:**
* How do dragons communicate with the ground troops? Flags? Can the dragon operate the flags alone or do they need a rider? Are the flags for orders to the troops, to report the results or recon, or both? How much detail can they get into a flag message? (ex: "send reserves to our left flank", "cavalry are encircling us on the west", "charge NOW")
* If the flags have orders, how do commanders on the ground communicate back to the dragons to tell them which flags to fly? Are the commanders themselves mounted on dragons? Are the dragons the commanders?
* Mobile magical might. I didn't touch this one because I'm not sure what your idea of magic is. What is the range of magic? Shorter range = less useful while flying. How effective is magic against dragons? Does their innate magic give them some protection? Can they extend this protection to their riders?
* How many dragons could potentially fight on a side. Tactics will be much more developed if it is 6-10 rather than just 2-3, and even more developed if there is entire corps.
* How many dragonriders could there be? Would you train a lot of mediocre ones, knowing that many would be killed by sharpshooters or by falls, or fewer elite ones, possibly down to just one rider per dragon (like Eragon or Pern).
* Anti-dragon weapons: I think the best anti-dragon weapon is another dragon. But you could also fight under tree cover, where their advantage is more limited. You could try to fire rocks or nets from siege weapons, but I suspect you'd have better results with massed arrow volleys (just make sure the arrows that miss don't fall on your own troops!).
* Alternative tactics: I've only explored the most basic things dragons could do in this response. They could also carry dragoons (the real-life kind, not the Final Fantasy kind), who leap off their backs and fight hand-to-hand. Or they could carry rocks up high and drop them like catapult stones. You could mount shape-shifted dragons on other dragons. Let these sorts of tactics separate the good commanders from the great ones.
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The biggest tactic I find missing is multiple dragons in humanoid form riding on each other. This allows dragons to have at least 3 times the flight duration, and if it is possible to rest while on dragon back then potentially infinite as riders switch out.
In addition this could camouflage numbers until the last moment.
The most important role/combo is probably with two additional magic casters, or one caster and one archer. This projects the greatest power the greatest distance for use both defensively and offensively. Pivotal in any combat engagement.
In this world the best way to attack the dragons is to attack their magic partners before the battle while they are on the ground and exposed. In that way the dragon is deprived of most of the advantages during combat that a well trained partner provides.
The next step if you do not have dragons of your own is to establish some form of Anti Aircraft weaponry. You can use magic casters to combat the casters on dragon back. Building small portable ballistas to take with an army is another option. A ballista of 120 lbs can shot a 1 lb projectile 1/3 to 1/2 a mile. You can easily mount these on wagons or carriages. Their slow rate of fire means you need at least 5 per dragon you expect to attack a target.
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As I wrote in a comment, there are some parameters that would certainly affect the warfare tactics with dragons. In particular three questions needs to be asked:
* How many dragons are there?
* Why do they team-up with the humanoids?
* How to fight the dragons?
**Dragons numbers**
It makes a huge difference if dragons are as numerous as your humanoids, fairly numerous, say like horses, or pretty rare.
In the first case, if the humanoids are similar to humans, they would have try to fight the dragons at some point. And those, being mightier would probably have prevailed and possibly eradicate your humanoids. But for the sake of the discussion, let's keep that discussion for the next section, and consider the consequences of that number in the next paragraph.
In the second case, the dragons are fairly numbered (but the humanoids would have an upper-hand in case of conflicts). I suppose that you typically have humanoids wars into which dragons are included. The dragons would probably form the main body of your armies. In most cases (see next section) they would probably better be left alone for full strength, considering that war wizards or other "heavy-guns" (yes that could just mean cross-bows) support would be close by in battle for them.
In the last case, dragons are pretty rare. You probably want to make tactical squads. Smaller groups with specific aims. In that case the association with a humanoid could prove interesting.
We will detail some advantages in a next section.
**Reason(s) for teaming**
From your background introduction, I gather that dragons are more clever and more powerful that your humanoids. Why would they fight together?
In most cases, mounted animals by humans, like [horses](https://en.wikipedia.org/wiki/Cavalry), [wargs](https://en.wikipedia.org/wiki/Warg), [elephants](https://en.wikipedia.org/wiki/Hannibal), or even [pigs](http://awoiaf.westeros.org/index.php/Tyrion_Lannister), are domesticated by the humans or humanoids. They are used for warfare for speed and strength. The animals are tamed and they don't really have a choice.
But now, your dragons are powerful. And clever. Why do they want to fight along your humanoids? I can see a few possibilities.
* They have been enslaved by the humanoids: there have been some fightings and number overpowered the might. They may simply be coerced through pain or fear to do so.
* Your humanoids are [elves](https://en.wikipedia.org/wiki/High_Elves_%28Warhammer%29#Dragons) who live in symbiosis with nature and they agree to team against a common enemy.
* Some magicians have a powerful link with dragons with allow them to fight along together.
* Mutual necessity: with their might and cleverness, there is something that dragons aren't able to get by themselves. They agree to lend their powers to the humanoids in exchange to their providing what they can't get. Maybe protect them from some other predators?
The reason for their common work would also influence their use in warfare and how/if they should be associated with humanoids or not.
Let's just consider the four possibilities from above.In the first case, the dragons cannot be trusted wholly. So the presence of a rider is to ensure a continued loyalty. The third case implies that a rider should always be present as they are the main reason for the presence of the dragon to start with. The second and fourth cases are more opened and are probably more what you are looking for.
**Fighting the dragons**
If dragons are "common" and are repeatedly used in warfare, techniques to fight against them would have been developed.
Just to clear it out of the way, if a link with a rider is *needed* as indicated above, attacking the riders is probably the safest route.
Otherwise, if the dragons would continue on their mission/task without their riders, than it is probably better to focus on the dragon. Some ideas have been proposed in other answers, but as for me I would tend to compare the dragons to a flying tank/bomber unit. Ideas to fight against them include
* magic spells. You already mentioned the well-loved fireball, but you have a huge amount of choice in that direction (different elements, rays/pillars/etc.). You might also consider defensive spells to block or attenuate the damages caused by dragon's fire/...
* armour piercing weapons. Projectiles are typically the best. See PCSgtl's answer, for example.
* traps. Those could be magical or not, but a restraining cage could be a nice way to limit the mobility of the dragons and their damage. And most of the typical large-scale traps could work.
* Airborne anti-dragons squads. Well you could just train your dragons to fight other dragons. You could specialize your dragons squads like [planes](https://en.wikipedia.org/wiki/Fighter_aircraft) or ships in our world. You might have other ridable creatures like hyppogrifs, pegasus, which could be mounted and equipped with [lances](http://fireemblem.wikia.com/wiki/Pegasus_Rider).
* Grounded anti-dragons squads. Maybe light cavalry with lances again would do the trick.
At the end of the day it really depends on how you answered the first question. If the dragons are the main body of your army, you probably should fight them with dragons. It could be very painful otherwise. But if your magicians and/or archers etc. can effectively affect the dragons, they'd make a great support squad for your main body.
The traps are probably only interesting for less numerous dragons.
**Ridden vs not-ridden dragons**
Let us now consider that dragons are willing for fight along with your humanoids and that their numbers do not allow to compose the main body of your army. Let's what applications they could have.
* Bomber squads: they fly above and burn the armies down,
* Fast projection squads: ideally if they can take on some riders they are able to send troupes fast into the battlefield on the weakest point of the opponent,
* Scout squads: they might recognise the numbers and positions of the enemy, can move fast between the lines facilitating the communication, sabotage the organisation of the enemy, etc.,
* Spying: that was well explained in another answer,
* Infantry support as [tanks](http://www.lonesentry.com/manuals/japanese-tanks/tank-tactics.html) or other [tanks tactics](http://www.civfanatics.com/civ4/strategy/tank_warfare.php),
* Anti-dragons squads.
What does it mean to have a rider, then? A rider would make the dragons slower and clumsier in battle. What you gain is an increase fire power, more thinking, better communication and more versatility.
If your dragons are in the midst of the battle: as main body, tanks, projection (after "dropping" the humanoid squad), then you probably don't want them with riders: the advantages you would hope to gain are rendered void due to the heavy presence of the humanoids all around.
For the scouting, communication and spying, you probably should have them ridden. Indeed they add more eyes, more brain, more chances to deliver the messages and increase communication capability as well as tactical advantage of being able to split on a given mission, for a little cost, as you do not expect them to be involved with a lot of direct fighting.
For bombers, you also gain: the dragons can concentrate on the attack whereas the rider on the defence, checking the air and the grounds for possible threats.
For air-fighters, unless the rider fighting can compensate for reduced speed, clumsiness etc. I would say they are better left alone. They then have an advantage on their target, namely increased speed and fighting capability.
I suggest you have a look at naval organisation with specialised ships (planes carriers, mines, torpedos, planes, etc.) to combine their strength.
**TL;DR**
It depends on a lot of factors. But mostly where do you use your dragons?
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I would say another advantage is a **second brain**. Having a second opinion when making tactical decisions, especially one experienced in human combat tactics (assuming the opponent is a human force), is rarely a bad thing.
Also, I would say a **second body** is an advantage. In single combat the rider can be used as potentially a distraction, or a way to attack the enemy from multiple directions.
You somewhat covered this in "Close Combat Support", but a rider would also allow for a **wider arsenal**. If a dragon can, for example, breathe ice, it would be advantageous to have a rider that is skilled with fire magic. Also, a rider would have to use a weapon when fighting atop a dragon, so they would be able to use a magic-imbued weapon or other special weapon that a dragon would be less inclined to use.
I agree with PCS that an anti-aircraft weapon would be an effective way to combat a dragon. Another effective weapon, assuming this is a weapon able to hurt a dragon, would be **barbed wire**. This would both harm the dragon with the barbs, and restrict its ability to move and fly. Assuming that dragon wings are proportionally easy to break, similar to bird wings, barbed wire could potentially ground a dragon if used cleverly.
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You mentioned usually only the younger dragons have riders. If this is true, **what specific advantage could younger dragons receive from a humanoid partnership their elder kin do not necessarily need or desire to account for this age-specific trait?**
Here are a few suggestions:
* **Margin of Error**: Taking on a partnership gives young dragons more time and flexibility to successfully complete their maneuver by giving them an extended margin to fail, especially if they are clumsy and a terrible fighter. This margin could be anything from extra time to complete a spell to increasing space for maneuvers (I am envisioning if enemy dragons try to box in the dragon, the rider could perform a spell to give their dragon more space to escape). It also gives young dragons the chance to build battle experience for later in life when they are more likely to fight alone.
* **Symbiotic Relationship**: A great partnership has the rider and dragon working in tandem to attack the enemy by keeping up a steady stream of bombardment. By working together, they can maintain a constant level of spells and physical attacks. Imagine the rider throwing spells and weapons between the dragon swooping down to attack, throwing out their special physical ability (fire, ice, etc), and casting spells. **This can be an effective means to fight against non-rider dragons, who will need time to recoup and prepare for the next attack.**
* **Protection**: Riders offer an addition level of protection and safety to a young dragon who may not fair as well alone on a battlefield. For example, if it takes a few decades for a dragon's scales to fully harden, they benefit from the protection a rider and their society offers against potential predators, enemies, or accidents more commonly found outside of the humanoid civilization.
* **Control**: Having a squishy rider means young dragons learn discipline over their senses and body so they do not accidentally kill their rider with one misplaced action. This translates to an increase in control and more precise movements, potentially in fighting skills.
As for why young dragons may only spend the first hundred years or so of their lives pairing with riders, if the humanoids' lifespans are close to ours, it could be disheartening to constantly outlive your riders, especially if you build a close rapport. Alternatively, it could be related to metabolism and energy; elder dragons don't have the energy to carry around a heavy rider, worry about protecting their rider, or desire to deal with the politics and relationship maintenance required in a partnership with another creature.
For an existing intricate world where dragons exist -- but not always considered equals or superiors to humans -- please see the [Temeraire series by Naomi Novik](http://www.naominovik.com/temeraire/). The series contains human/dragon partnerships, often in a military setting. It is different from your question because the European dragons are largely considered livestock and brute beasts, with intelligence ranging from a dog to humans.
Please feel free to edit this answer and provide feedback; I would like to improve the quality of my work to fit with this community's expectations.
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Dragons are big and powerfully, though their disadvantage is their arrogance, and inability to cooperate.
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> Here is my analogy, online PVP. Most people have run in to some kind of online Player versus player action. Be it world of Warcraft, couter-strike or some kind of battlefield alternative. What team is winning?
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> The one team cooperating. You can have 20 heroic players running around in an arena, when the 20 less heroic that cooperate moves forward with tactics, they almost always win.
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Now back to dragons, lets say (just for the fun of it) you got 20 heroic dragons running around in their own power, thinking their way is the best not cooperating. And then there is 20 with human riders, who got human riders guiding them. Making use of flanking, 2vs1 or even 5vs1 attacks.
There lies the great advantage.
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* **Managing Light Mobile Armor**
The rider would be able to adjust the lightweight armor of the dragon at the required angles and placed to deflect or absorb the damage. For example, a dragon may have a plate armor of *only* 5 feet length. The rider on the back would devise hinges and hooks in that plated armor to allow it to turn, move and rotate so that the same 5 feet long piece would shield a greater area than just 5 feet.
* **Throwing Explosive Pots**
The question body states that there are no *chemically powered projectile weapons (aka bullets)* in use. However, since alchemy is common, wise men must have created potent explosives. A rider on the back can keep a bunch of them and fling them at the miserable adversaries who are already taking the blunt of dragon fire! Add some poisonous fumes to the explosive and it will make things even more deadly for *les miserables*.
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## Dragon Tactics
There are many ways that a dragon would be helped by a human rider.
1) Disguise
"They have the ability to shape shift (with considerable mental effort) into any natural shape..."
If this is true then if the dragon wants to sneak into some place indoors (like a castle) it can shape shift into a living organism (a flower?) and hide on the rider. I don't know if the dragon can still talk or see while in this form. The rider would then toss the "flower?" into a corner or somewhere safe. This could not be done as a rat or bird (indoors).
2) Moral Support
This answer mainly depends on the rarity of dragons in your world. If they are rare then this works. I would get pretty lonely as a dragon just flying around by myself. Also in war I hear it's good to have someone to talk to.
3) Human Ingenuity
"Dragons are sentient beings with **intelligence and personality** equal to or greater than that of humanoids."
I don't know if the Personality part already highlights this but humans tend to be very inventive. Dragons may be more/just as intelligent but humans may be given a more persistent/cheerful attitude. Also just looking like a human is different from being one. A dragon in human shape will not understand human culture as well as a human can.(duh) For example, a dragon will have no clue what humans are referring to when they mention "the difficulty with trying to start a fire".
Conclusion
That's all I could think of... I'm not sure if the last few ones made any sense. I'm kind of new here so pardon me if I don't answer in the correct format.
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Humans (and most animals) sleep. The reasons aren't really clear but most people [believe](http://www.bbc.co.uk/science/humanbody/sleep/articles/whatissleep.shtml):
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> We have to sleep because it is essential to maintaining normal levels
> of cognitive skills such as speech, memory, innovative and flexible
> thinking. In other words, sleep plays a significant role in brain
> development.
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Assuming a species had the same physical requirements (their brain had to offline for one reason or another) but didn't [go comatose, hallucinate and suffer amnesia](https://xkcd.com/203/) what other habits/patterns/routines could they evolve to serve the same function and allow normal cognitive functions?
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I'm not sure if you'd count it as sleeping but meditating could be a way of shutting down part of the brain whilst still maintaining external awareness. In theory dreaming is our processing of memories from short term to long term memory. This could happen during meditation, where people re-live what they experienced as their memories transfer from short to long term.
If you're looking for other solutions that don't require people to "shut down" even so far as meditation then you would need to look at different structures of the brain. It's possible that a species could be constantly processing memories, or process them several times a day whilst being awake.
You could have a species that process memories straight away and that they need to rest for other reasons. An example of this might be that part of the brain produces a chemical, which when left to build up to certain levels becomes toxic. That part of the brain has to shut down for a period to allow the body to process the chemical. This could involve higher cognitive functions, anything from walking and talking to psionic powers. The species has to lose access to part of their mental capacity whilst their brain recharges, but other parts still go on. This could be automatically controlled, happen at a specific time of day or even when a certain threshold is reached. Or it could be triggered manually, when the species receives some sort of signal that they need to allow the body to process the chemical.
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**Fantasy Elfs**
In most elf universes the elves are not sleeping, they have to spend a certain amount of every day meditating to keep their mental health and also a part of the day resting to recharge energy.
**Dolphins**
Dolphins can sleep with half their brain while the other half keeps the normal body functions alive. The dolphin is a voluntary breather that means the bodys autonome functions does not control the breathing but the dolphin has to choose to breathe. This means the dolphin is required to have a certain part of the brain functioning while sleeping.
**Space Marines**
Space marines from Games Workshop can battle for weeks without sleeping. The reason for this is they have computerized parts of the brain making them able to shutdown parts of the brain not needed for the current task, making it "sleep" for a certain time, while being awake and active.
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I'm going to tackle this from a different perspective.
Imagine, if you will, an alien race composed of an organic metal. If we saw them in their true form, we'd say they'd look like humanoid robots; indeed, they blur the line between "Artificial Intelligence" and "Natural Intelligence"...their consciousness is maintained in a form they call a spark, but is this "spark" a highly advanced CPU/hard drive, or is it a brain?
Being composed of metal, members of this species have the ability to transform themselves into pretty much any metallic mechanical object that they encounter. As these alien robots visit earth, they typically assume the form of automobiles. When humans encounter these auto-robots, they are largely unaware of their sentience...let alone the great lengths to which these "robots in disguise" have gone, to protect them from the dangers in the galaxy (or to punish and enslave them).
Interestingly, even these highly-evolved robotic organisms [also need sleep](http://tfwiki.net/wiki/Humanization#Sleep). While there is already some speculation as to why these machine people would need to sleep, consider for a moment the device on which you are reading this right now.
How many times has your computer, tablet, or phone, after being on constantly for days on end, just starts acting up? Perhaps it starts going slower than normal, maybe it's just doing some unexpected things. Applications start freezing. It stops detecting I/O devices. Network connections drop randomly.
**Rebooting**
Oftentimes, a [good ol' fashioned reboot](http://inspirationclarity.tumblr.com/post/45376068126/first-rule-of-tech-support) will fix your problems. Perhaps an essential driver has crashed; more likely, it has acquired a bunch of memory leaks during the time it's been awake. Restarting gives your computer and operating system a fresh slate when it comes back on, in terms of memory allocation/usage and loaded drivers. Is this not akin to sleeping? It seems like maybe our alien robots even need to do this every once in a while.
Other computer maintenance tasks that could be compared to the benefits and effects of sleeping, which may or may not apply to a race of sentient robotic beings:
**Defragmentation**
The physical storage of data will almost always become fragmented over the lifetime of the system. Occasional defragmentation helps to keep performance up (and to increase the lifetime of the actual moving parts of the computer).
**Cache clearing**
Sometimes, remote applications (typically websites) will create a local copy of its static components on your system, so that everytime you access it, you don't have to keep downloading the same static components. Occasionally, old cached files can cause interference with newer versions of the application, or even with other applications as well. You should clear your application caches every so often to maintain performance.
**Anti-virus**
Obviously, [any networked system has a chance of becoming exploited](http://en.battlestarwiki.org/wiki/Computers_in_the_Re-imagined_Series) or infected. It is always a good idea to take a few minutes every once in a while and scan and destroy any threats from malicious software.
One interesting question, though, is what these [machines dream](http://en.wikipedia.org/wiki/Do_Androids_Dream_of_Electric_Sheep%3F) of when they're asleep.
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It's been observed that [sleep may be used to flush toxins out of the brain.](http://www.nih.gov/news/health/oct2013/ninds-17.htm) If you assume that's the case, a species may have evolved a much quicker, more efficient way to flush the toxins and resume normal brain functioning. It could be like emptying the bladder, and would take only seconds. But like emptying the bladder, it may have to happen every few hours.
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The brain might take certain functions off-line for maintenance while keeping sensory awareness for danger, so he'd be seen as resting quietly and not paying attention, but could react if pestered.
Or if less global, just doing memory digesting could (only) impair long-term memory recall while going on, but still allow routine tasks.
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On its most basic level, sleep is the time when the body performs its 'maintenance routines'. As any life form goes through its life, it builds up cumulative damage, toxins, microbial invaders, and other minor problems that need to be cleaned up. For the vast majority of animals, it is most efficient for the animal to periodically go through a period of dormancy to perform all of its routine maintenance at once without the unpredictability of waking life getting in the way, which is why sleep is the most common solution among animals - particularly sleep during a time when the animal won't be able to work very efficiently anyway (at night for diurnal animals), or when it would be better off staying still and hiding from predators anyway (during the day for nocturnal animals).
But there's no reason it *has* to be this way. If there is a good reason why full sleep isn't an option (for instance, an environment so violently unpredictable that any period of dormancy would be fatal), this maintenance will be handled in other ways - resting one organ at a time, part of each organ at a time, or even patching things up while they are in operation. This is less efficient than sleep, but sometimes it's the only option.
*We* use sleep to maintain our brains and process information internally at the same time that we repair our bodies (because what would be the point of having the brain be awake when the body is not?), but an animal with a different body-maintenance method would naturally have a different brain-maintenance method. It might rest different parts when not in use (which might result in interesting personality swings), rest one half at a time, or just forego a specific resting phase altogether and perform maintenance on-the-fly, though this would probably slow down its thinking speed and reaction time overall.
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Actually it seems that our understanding of sleep is governed by experiences mad on mammals and especially with rats dying of long term sleep deprivation. However recent experiences duplicating the setup with pigeons showed that they do not suffer from sleep deprivation (and they were selected as they also have REM sleep): [here](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2753808/) and [here](http://www.ncbi.nlm.nih.gov/pubmed/17765274).
Also a more recent study has shown that birds can actually sleep while flying: [here](http://www.csmonitor.com/Science/2016/0804/How-birds-are-reshaping-our-concept-of-sleep).
All of which indicate that the need for humans to sleep might be a very mammal centric biological need and that other species though sleeping might not need it as much as us.
To answer your question, if the brain of your species has to go off, may be what it means is just that the individual just have a very reduced activity (similar to birds). Possibly no communication, little movement and no creative tasks being undertaken in that biological state.
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## The Up-Down-Left-Right brain
This alien rests parts of their brain as well, ecept they are not identical halves, but specific functional areas. They do this in a daily cycle and while they can call on all functions when needed, this is prolong the rest time needed for the brain areas.
The alien cycle has four phases always going in the same sequence:
## Down
This is the rest time of the most activity related part, making the creature slow and lethargic. It functions as a time for reflection and emotional processing, often used for family bonding as well as physical healing.
## Right
At this time, activity resumes at full speed, but the spontaneous/creative part of the brain rests, while the rational planning side runs at peak performance.
This part of the cycle is used for planning the day's work or longer term strategies. It is the preferred time for business and administration activity.
## Up
This is the rest phase for the introspective and regenerative part. The effect is a hyperactive phase where previously planned work is executed and problems can be solved in creative ways, but the aliens are distinctly less social and emphatic. Physical work, sports and fighting are done in this phase when possible.
## Left
Riding the last of the frantic energy, the alien now focuses their attention on creative and emotional work, while the rational side rests. Art is created, music and theater performed and attended, problems are solved and ideas generated, but for obvious reasons, the custom is for them not to be executed until the next cycle, after vetting by the rational side.
## Turbo
The aliens can pull the resting part out of its sleep cycle and go into a well-balanced state that allows superior intelligence and thinking, at the cost of lapsing into a catatonic state afterwards, as the delicate cycle has been disrupted and needs to recover.
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I would suggest using two brains or splitting our brain in half, but I see that's already been suggested above. (Rest one brain and then use the other). Maybe utilize some sort of expedited hibernation that could potentially be triggered within minutes? Also, if your species is some kind of plant, you could logically use photosynthesis, chemosynthesis, or some other sort of bioenergy to refuel your organism.
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There have been a few races in science fiction (e.g. The Dwellers: from Iain M. Bank's The Algebraist) that have no concept of empathy. They do not care about the fate of others in any real way, the Dwellers regularly engage in ritual war amongst themselves for entertainment, hunt and enslave their own children, etc. The Prime Aliens from Peter F. Hamilton's Pandora's Star series are another example of a species with no concept of empathy for others.
Moving into the fantasy genre there are a range of other examples: Drow, Goblins, and suchlike, which also have no real concept of empathy or compassion.
So the question is whether a 'real society' could form, advance and gain technologically, without changing their nature. Could such creatures trust each other and co-operate enough to develop working infrastructure, economics, and all the other prerequisites for a technological society?
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What you propose in your examples require more than a lack of empathy, but also a bloodthirsty nature to the point of lawlessness and anarchy.
I look to ants for my answer. They appear to totally lack empathy, but they would also never set up wars for sport. If a worker ant is killed, the hive reacts, but not in an empathic way. They recognize the death and make decisions. Is this a threat to the hive? No? Then there is extra food, and someone is needed to perform the job that the deceased used to do. If yes, then they react to the threat.
If a guard was killed, the queen gives birth to a few more guard eggs than normal and the hive adapts in the short term.
They can suddenly change goals and act as a civilisation would, such as when they decide to move the hive or split the hive and promote a new queen. If it suddenly occurred to a group of ants that they needed to visit the moon, I wouldn't bet against them.
So, no, I don't think empathy is a requirement for civilisation, but practicality and an understanding of the value of an individual's life to the species as a whole is.
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By the most literal definitions of empathy, yes, it is a requirement. However, the bar can be set quite low
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> em·pa·thy ˈempəTHē/ noun: empathy
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> the ability to understand and share the feelings of another.
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If I can expand the word "feelings" to include "desires" which are usually not treated as feelings by human sociology, it becomes clear that civilization can only occur with empathy. Civilization requires working together to solve common problems: it is impossible to solve common problems if you have no ability to understand the desires of those around you.
However, by expanding "feelings" to include "desires," I also include a very weak definition of empathy that can suffice. If a group is capable of conveying their desires to each other, it is capable of identifying win/win scenarios. If it chooses to proceed towards these win/win scenarios, then civilization can begin.
One place this process could start is the unknown. Whenever there is an unknown, there is a risk of the individual dying or similarly undesirable outcomes. However, we rarely actually know the risks. We have to estimate them. If an individual decides to err on the side of caution, that individual is less likely to enter competitive situations where they could be injured. They are more likely to seek out win/win scenarios that come with less risk of injury. That could be sufficient to start the march towards higher and higher calibers of empathy.
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One good sci-fi example of how to make non empathy possible to grow into civilisation is [Vulcan civilisation](http://en.wikipedia.org/wiki/Vulcan_%28Star_Trek%29).
For example [this answer](https://scifi.stackexchange.com/a/66093/35492) on sci-fi StackExchange hints, that whole "logical" thinking of Vulcans is based on cultural decission and not biological.
**Non empathy can be cultural decission and does not have to be biological**
But what if we wanted to have non-empathy civilisation, which is based on biology of the species?
* Such species has to breed "perfect" children. (Able to take care of themselves since first minute being born)
* Pregnancy rate should be short
* Or, the breeding should be "externalised" (like Earth fish)
* Basically, parents should not be required to care about their children. The empathy which we Humans feel to almost any small offspring of mammal is more biological, than rational. And we have it because we need to take care of our children
So, good shot would be to adapt [aquatic](https://worldbuilding.stackexchange.com/search?q=aquatic) race which was hugely discussed here and just externalise their breeding process
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No, empathy is not required. It is possible to have a complex society without trust and with everyone looking after their own self-interest, even flourish, without empathy. Though, it probably makes things easier.
Here we have an example of the economic analysis of competing security forces.
<https://www.youtube.com/watch?v=jTYkdEU_B4o>
Here we have complex societies at the brink of nuclear war who do not trust each other, yet war does not occur due to their own economic self-interest.
<https://www.youtube.com/watch?v=y32cFdicW1U&list=PLB5965C13F4B0B2DA>
Here is how double-deposit escrow works for trustless transactions. (Seller deposits 2x, buyer deposits 1.1x, after transaction, seller gets 1x refund, after feedback, buyer gets 0.1x refund.)
<http://blackhalo.info/wp-content/uploads/2014/06/whitepaper_twosided.pdf>
You may also consider the complex networks and hierarchies of ants and bees, which probably do not have emotions.
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Well I would expect, for them to last very long at all, they would have to breed like rabbits. Because they would likely wipe themselves out otherwise and probably not even care (I think the goblins would fall into this).
Another way for such a society/race to form could be it was kept as a slave race by a very cruel set of masters. Kind of like dog fight masters. Trained to be vicious and are freed somehow, either they turn on their masters or something else takes them out.
I was going to say I didn't think species would do well with this, but there are plenty of successful fish that eat their own young, even some of the Apes perform Cannibalism from time to time. So I think large batches of young might allow such a society to form, humans need so much time and effort to raise, that if everyone in a society was that way they would die off. We do have plenty of examples of individuals like that, serial killers, extremists of all sorts, Dictators etc.
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**Empathy and altruism gives your species/tribe competitive advantage to develop more complex culture** (to differentiate from mere animals). Helps to promote if not your own genes, genes of your close tribal relatives. Without it, species is collection of loners, hard to establish any progress. There is no shared learning and knowledge.
So I expect empathy would be requirement for any complex advanced civilization. It might be limited to own species, and disregard any other species considered less advanced.
Examples from sci-fi are not exactly relevant because they do not show how (with lack of empathy) species differentiated from animals and developed complex culture and technologies.
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Yes: unequivocally yes. The definition of the word "civilization" is, of course, entirely up to us (we could call a puddle of chemicals a "civilization" if we wanted to define it in terms of its ability to work together and eventually produce technologies or whatever). To call a process without empathy a "civilization" is to reduce the meaning of "civilized" to some kind of crude mechanical formula (potential to spread through the universe, or something like that) without reference to love, art, etc. Empathy is right there at the heart of "civilization": anything that lacks it, no matter how much it might resemble a civilization physically/technologically/etc., is more like a cancerous threat to civilization than civilization itself.
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No, empathy is not required for functional society capable of creating a technological civilization. This is because educated self-interest can do everything empathy does for us.
But, a VERY BIG BUT, a species capable of creating a civilization would almost certainly have empathy. This is because empathy can do the important parts of what educated self-interest does, without education or real understanding of your surroundings.
For a species without empathy to create civilization, it would need to develop high level of intellect and sophisticated culture before developing concepts of family or social interaction. This is not flat-out impossible, a solitary species that has genetic memory and does not need to nurture its young due to exotic reproduction COULD do it. In theory. But it is highly unlikely because such species would have no real need to develop intellect anyway. Much of the evolution of intellect we know is based on handling social interactions or the complex needs of social groups. But what use could a solitary species have for sentience?
Worse, developed intellect requires developed brains which generally means that the newly born need parental care. This might be different for species with genetic memory, as the learning period would be shorter, but parental care and parental empathy would be so much more efficient, and thus more likely to evolve. For that matter while species with genetic memory are common in fiction, there is no real explanation why such would evolve when after a certain point social evolution is simpler and more efficient.
My suggestion would be: If you want a civilized species without empathy, a species that used to have empathy but lost it after creating a civilization is vastly more believable than a species that never had empathy.
Incidentally, while such civilization would almost certainly be distressing to visitors with empathy, where is no need for it to be particularly evil or abusive. Almost everything we generally count as our "better impulses" makes perfect sense from the viewpoint of "optimal strategy" for the individual. That is why we evolved those impulses in the first place.
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Yes you need empathy, but you don't need as much as people think. There was a city called [Kowloon Walled City](https://en.wikipedia.org/wiki/Kowloon_Walled_City) that was a city populated by criminals and was essentially, after being a military outpost, a penal colony for some of the worst criminals China had. In the general prison population, 50% of [criminals have Antisocial Personality Disorder](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0229876), a mental illness that requires you to lack empathy to be diagnosed with it. The city was filled with some of the worst criminals who were former triads and a [haven for criminals](http://www.scmp.com/news/hong-kong/article/1191748/kowloon-walled-city-life-city-darkness) so terrible that other criminals feared them. It was pretty much a hive of crime and villainy:
>
> Here, prostitutes installed themselves on one side of the street while a priest preached and handed out powdered milk to the poor on the other; social workers gave guidance while drug addicts squatted under the stairs getting high; what were children's games centres by day became strip-show venues by night. It was a very complex place, difficult to generalise about, a place that seemed frightening but where most people continued to lead normal lives. A place just like the rest of Hong Kong.
> —Leung Ping-kwan, City of Darkness, p. 120
>
>
>
Many of these dangerous criminals formed triads and groups to enforce the rules. It had high rates of gambling, drug abuse, prostitution, and violent crime as you would expect from such a place. Police usually would only go there in large groups. Yet, it was a somewhat stable civilization compared to what you would expect from a place where most people where essentially sociopathic criminals. By 1990, the city had a population of 50,000. It was 33,000 in the 1960s and much less back in the 50s. Basically, the governance of the city did good enough for the birthrate to be higher than the people dying or getting murdered. That is what your species should aim for: being sociopaths who lack empathy, but have a good enough governance enforcing the rules to keep everyone from murdering one another & have a basic economy based around various things. Basic governance would be a requirement for some degree of trust with something similar to the triads containing people with just enough emotional intelligence to be somewhat trusted enforcing the rules. Crime would be constant, but all you need to do is keep it low enough so everyone doesn't die faster than people are born.
Someone pointed out that China could have put out propaganda on Kowloon Walled City and exaggerated the crime rate, but we know that isn't true because Britain was also overlooking the city at the time with China's permission and provided their own knowledge and information. Also, that is kind of the point: the criminals in the city were so dangerous that China would allow Britain on Chinese territory to help look over the city even during the height of the Cold War! And while yes, being a criminal doesn't make you a sociopath, being a criminal makes you more likely to be a sociopath since half of the population has ASPD and these were the worst of the worst criminals! Plenty of people who were triad bosses were still kept in normal prisons while Kowloon Walled City existed and most political prisoners and smaller crime lords were kept in normal prisons since it would be easier to keep a close eye on them. If Kowloon Walled City 'wasn't that bad' and it was all propaganda, why take such drastic measures with these criminals in general and get help from a foreign nation in preventing people from leaving the city (a nation that - at the time - is looking for any excuse or opportunity to make your country look bad)? Why only keep some mob bosses and criminals who are considered 'the worst of the worst' there while allowing other triads remain in traditional prisons? The only explanation is that Chinese, British, and - when it became more independent at the time - Hong Kong were not lying when they said these criminals were mostly jerks with ASPD and the crime rate was incredibly high.
There are also civilizations & communities where thanks to [inbreeding](https://biology.stackexchange.com/a/107372/59577), the population has a huge chunk of the people suffering from schizophrenia, a mental illness that can lead to [impaired empathy](https://www.cambridge.org/core/journals/the-british-journal-of-psychiatry/article/empathy-in-individuals-clinically-at-risk-for-psychosis-brain-and-behaviour/BB9EEA5DFDBB0D1BFCCE447384F380F7). This includes the [Ashkenazi](https://www.haaretz.com/2013-11-26/ty-article/.premium/ashkenazi-gene-increases-schizophrenia/0000017f-e04b-d75c-a7ff-fccfa3e10000) Jews, descendants of early [Falkan](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6020911/) Island inhabitants, and other communities affected by the [Founder Effect](https://en.wikipedia.org/wiki/Founder_effect#Among_human_populations).
] |
[Question]
[
I am recalling the Space:1999 nuclear waste containment explosion; this has been criticized because such an explosion would have actually destroyed the moon. I am curious for events that could happen directly on the moon, or elsewhere, and the natural effects that would impact the moon as well.
Also, I know about the moon orbit slowly spiralling away from Earth, but I am asking about some more specific event in time.
EDIT: I am not directly interested in effects of such event on Earth, actually I am not interested in Earth, if not because playing a role in the event that lets the moon go off orbit. My interest is in a feasible event that could generate that scenario, and the repercussions for the moon itself.
[Answer]
## Requirements
The speed needed to escape the Earth, from the Moon's distance, is given by:
>
> $$ve = \sqrt{ \frac{2 \cdot G \cdot M}{a} }$$
>
>
>
where $M$ is the mass of the earth, and $a$ is the distance from the Earth to the Moon (the moon's semimajor axis). The speed of an object in a circular orbit around the Earth, at the Moon's distance, is:
>
> $$ vo = \sqrt { \frac {G \cdot (M+m)}{a} } $$
>
>
>
where $m$ is the Moon's mass. This can be expressed in Earth-masses as $0.012 \cdot M$. The easiest way (requiring the least energy) to get the Moon out of Earth's orbit is to give it a push in the prograde direction (i.e. in the direction it is already going). But how big is this push? Let's determine what the escape velocity is in terms of the Moon's current velocity:
>
> $$ \frac{ve}{vo} = \frac{\sqrt{\frac{2 \cdot G \cdot M}{a}}}{ \sqrt { \frac {G \cdot (M+m)}{a} }} = \sqrt{\frac{2}{1.012}} = 1.405$$
>
>
>
This tells us that, at a minimum, we need to add a bit more than 40% of the Moon's current orbital speed in order to knock it out of orbit. Since the Moon's average orbital speed is about $1.023 \text{ km}/\text{s}$, we need to create a change in velocity of about $dV = 414 \text{ m}/\text{s}$. As far as velocity changes in space go, that's not a lot, but due to the huge mass of the Moon ($7.35 \times 10^{22} \text{ kg}$), that's a *lot* of momentum to transfer.
**Note:** *I intend to come back later and add some additional computations regarding the rocket equation and collisions, but this should provide a starting point.*
[Answer]
There aren't many options. Even if you completely shattered the moon then the remains would continue on a merry orbit and most likely turn into a ring.
The most likely scenario would be a rogue body (a reasonably large planet, neutron star, black hole, etc) passing through the solar system. If that passed close enough it could massively disrupt the orbits of any body it passes. Capturing the moon away from the earth, the earth away from the moon, or even just splitting them up and sending them both careening away across the solar system.
The problem with this though is that it would almost certainly have a huge effect on the earth as well. The close passage of the heavy body would at a minimum cause massive tides and interesting weather systems. The force that separates the earth and the moon could also easily send us into an orbit not very hospitable to life or even if the other body was massive enough break us out of orbit around the sun entirely.
It would also disrupt the orbit of all the other planets in the solar system to varying degrees, it would definitely make for interesting times!
Beyond that a hypothetical FTL drive attached to either the earth or the moon could cause it one to fly away from the other. Equally an incredibly powerful non-FTL drive could over time have the same effect.
[Answer]
Hit it with a rock. A *big* rock.
Something like [Ceres](//en.wikipedia.org/wiki/Ceres_%28dwarf_planet%29) might do, if you could somehow get it into an orbit that hits the moon with sufficient relative velocity. Alas, moving Ceres significantly from its current orbit is likely itself a non-trivial task.
A stray [Kuiper belt object](//en.wikipedia.org/wiki/Kuiper_belt) might be more practical, if only because there are more sufficiently large bodies out there, and also because the long fall from the Kuiper belt to the inner system would naturally give the impactor a highly eccentric orbit that could intersect the Moon at a sharp angle and high velocity difference.
You'd still have the problem of *getting* the object to the inner system in the first place, but I could buy a scenario where a collision (or a near-miss) with another KBO sends the would-be impactor on an unstable orbit leading to an eventual close encounter with Neptune, which, with some good (or bad, depending on how you look at it) luck, might send it towards the inner system and an eventual collision with the Moon.
Of course, you could go further afield and have the object come in from the Oort cloud, or even from interstellar space. Most solar system formation models predict a large number of small planetesimals getting scattered out of the system when it forms, so it stands to reason that there must be a sizeable population of stray planets out there in interstellar space, and that they'll occasionally make a near pass to a star such as the Sun.
Of course, such encounters are (fortunately) not *that* common, and most such bodies will just pass through the solar system without hitting anything anyway, but having one fall in and hit the Moon is still perfectly within the realm of possibility. As a bonus, a stray planetesimal could potentially fall in from *any* direction, even well away from the plane of the ecliptic, which could let you get some quite interesting orbital changes when it hits.
In any case, a body smaller than the Moon, passing the Earth at the Moon's distance, isn't going to *directly* disrupt the Earth to any significant extent (unless you count making a lot of astronomers soil their underwear when they first spot it). Any tidal effects will, by definition, be smaller or comparable to the lunar and solar tides the Earth already experiences, and any gravitational effects on the Earth's orbit should be negligible.
The bad news, however, is that anything massive hitting the Moon at high speed is going to scatter off lots of smaller rocks when it hits, some of which will likely hit the Earth. So Earth as a whole might be fine, but you'd likely be looking at some rather big meteor impacts as secondary effects, potentially disrupting the biosphere and any civilization down here. Worse yet, since the scattering from the lunar impact is likely to be rather chaotic and unpredictable, we won't be able to easily predict how many secondary impacts might hit the Earth, or when and where they would hit.
[Answer]
There is very little that could affect the orbit of the moon without also having a direct influence on the earth. A massive body with enough gravity to yank the moon away, would also have similar effects on the earth's orbit, not to mention those of us on it.
But let's say the moon can get pulled away by little green repo men... The moon is pretty damn important for life on earth and here are some of the effects we would see:
1. The moon is partially responsible for the ocean's tides. Without the moon's gravity pulling on it, the tides would change drastically.
2. The moon's gravity slows down the rotation of the earth. Without it, the earth would start spinning faster and our days would get shorter.
3. The moon stabilizes the earth's tilt. The earth's tilt varies by a small amount, and its changes are hardly noticeable in the short term. Without it, the earth "wobble" more with a tilt varying 10x more greatly than is current. Seasons would become more extreme.
The tougher part of this discussion is the fact that effects have countless other effects. Weather is the most chaotic and complicated system to put into the mix. All I can really say is that it would get really messed up.
[Answer]
**Turn the moon into a rocket.**
There is a method of propelling a spacecraft called laser ablation. It involves vaporizing part of the spacecraft with a laser, the vaporized mass propels the spacecraft. A sufficiently energetic event that's strong enough to vaporize one side of the moon's crust would leave one side of the crust as a mass of plasma that gradually escapes, propelling the moon into a different orbit.
Since the moon is tidally locked, vaporizing the side of the moon opposite to its direction of movement would constantly propel the moon into a higher orbit, eventually escaping entirely. It would likely eventually settle into either an extremely elliptical orbit around the sun, or it would escape to deep space.
This would leave the moon mostly intact, however, it would likely contain a large crater (on the order of magnitude as the entire moon) that would gradually fill in, fracturing the surface of the moon.
[Answer]
Well you could fire small black holes at it, or transform its mass into small black holes and use their decay as an engine to move it. <http://www.einstein-online.info/elementary/quantum/evaporating_bh>
[Answer]
This is intended as an addendum to the answer which stated that it would be exceedingly difficult.
Factoid, the Moon is in orbit around the Sun. The Moon and Earth happen to share this orbit. The Sun's gravitational attraction for the Moon is more than 2x the Earth's gravitational attraction for it. So you not only need to move the Moon away from the Earth, you actually need to change its solar orbit too.
This is one tall order.
About the only method I can think of that has a chance of doing this without disrupting the Moon would be by performing **MANY** gravitational slingshot maneuvers (momentum exchanges) with small asteroid bodies. On one end, you'll sling shot these bodies past Jupiter and the other will sling shot past the Moon. You'll essentially be exchanging momentum between Jupiter and the Moon.
Be prepared to wait a while. I'd expect this to take a minimum of many hundreds of years or perhaps thousands.
[Answer]
"Escape velocity" is the present orbital condition of the moon. Gravitational pull between the earth and the moon has caused a round orbit to stretch into an elliptical orbit. and this elliptical orbit stretches more and more as the relationship is prolonged. The moon on the apex of its attempted escape either has or has not the velocity to leave the earth's gravitational pull. If it has not then it is pulled back for another pass. This process will continue and as the moon gains velocity it also increases ellipse of its orbit around earth, and this process will also continue until on of four possible outcomes happen:
* the elliptical orbit of the moon stretches to a point that the moon will pass to closely thereby striking the earth;
* it reaches escape velocity thereby leaving orbit;
* it and earth both change orbits because of the force of gravity pulling; between them which forces both bodies into a changed orbit around the sun; or
* the moon collides with earth and both bodies fracture into pieces.
[Answer]
Electromagnetic anomalies that weaken the gravitational pull between the earth and the moon to such a state that escape velocity is made possible at much lower speed and with less inertia then being necessary to be freed from the gravitational relationship that binds them.
These "anomalies" are presently being produced all over earth by artificial means and the definition could be expanded to include any man made device that produces an electric field or magnetic force,
or the combined total effect of all these artificially produced electromagnetic fields or forces, and not limited to only man made devices, yet also to include the electromagnetic and gravitational forces of galactic origin exerting their combined and constantly changing effects on other celestial systems,including our own, these effects combined also with the sum total of all artificial sources produced on and around earth, some of which would include;
very strong production of electromagnetic fields involved in
particle collision projects, and possibly even some particle manipulations themselves and the molecules, molecular effects and or changes to molecular processes that have been produced by them both intentionally and unintentionally.
the entire cumulative effect of energy production in every nation on earth to harness electrical power and transmission of such, including nuclear processes.
the total and cumulative effect of the transportation technologies on earth, both fueled, and electric, and possibly even the effect of movement of mass amounts of cars, trains, planes, etc. in many places
and with constant motion.
the total, combined, and cumulative effect of the communication technologies on earth, along with all the devices that make communication possible and the transmission of communication by various energies, such as microwaves, lasers, and electrical impulses.
....the list of "anomalies" is ever expanding from many origins, on and off this planet.....
it's best summed up by this description....a rock, possibly a very big one, thrown in a pool of water makes ripples, these ripples when encountering objects in the water cause other ripples, and these ripples then influence the ripples around them until soon there are ripples accumulating in every direction changing all the othe ripples as well as themselves being changed by other ripples, and where some of these ripples meet there are momentary "anomalies" making a small splash instead of a ripple.
....these "anomalies" effect change
of a previous state of existing.
] |
[Question]
[
I'm writing a short story in which my group of character is devising the stupidest and least practical way of lighting a fireplace.
It then came to my mind that stuff that undergo reentry [gets hot](https://en.wikipedia.org/wiki/Atmospheric_entry "like, really hot"). I am aware that this process might disintegrate the log, making all the trouble of putting said log into outer space meaningless, and in the event of the log actually reaching the fireplace, it might disintegrate the area anyway, but that would make it stupid and unpractical, and that's exactly what I want.
The log before reentry can go any speed from orbital to stationary relative to the ground below, and the height should be no more than 150km (93,2 Miles).
Concerning size and material, it's a plain old log, what did you expect.
**Can the log make it to the fireplace?**
It has to be on fire when it lands (or rather impacts) and must reach the fireplace with at least half of it's mass. Actually getting it up there or the trouble of accuracy is out of the scope of this question, for our sanity sake.
[Answer]
# The wooden heat shield
## Short answer
No. [xkcd: what-if #28](https://what-if.xkcd.com/28/) explains why.
## Long answer
As it turns out, wood paradoxically makes a good **heat shield** for reentry. [China has actually employed wooden heat shields](https://vintagespace.wordpress.com/2016/12/05/can-a-wood-heat-shield-really-work/).
The way wood burns is **not** that the solid material that we all know as wood, and that gives us splinters, is burning. Instead it is gasses that are coming off of the wood is what are actually oxidising and making those pretty yellow/orange flames. To get those gasses, you need to heat the wood until it boils. (\*)
This is the reason it takes so long before a bonfire/fireplace catches; why it is easier to light up thin splinters compared to thick logs: because you have to heat up the **whole** piece of wood so that the parts underneath the surface do not soak up the heat that is trying to boil the surface to keep the flames going. The little amount of heat caused by the first flames is not enough to heat the wood underneath to make that give off more gasses. You have to heat the whole piece of wood to near boiling temperature until the heat of the flames is enough boil more wood and make the combustion self-sustaining.
The problem — for you — is that the charring and outgassing of the surface of the wood during the fiery atmospheric re-entry is actually **protecting** the wood underneath. The gasses and their combustion products act like a gas shield that will protect the uncharred wood from the compression heating ahead of the wood. Also — and this is the crux — the burning gasses **blow away** so fast that the heat from the combusting wood gasses does not aid in heating the wood underneath. The "flame" is simply not there... it is far behind the spacecraft.
Also you have another problem in that firewood logs are very [light compared to their surface area](https://en.wikipedia.org/wiki/Square%E2%80%93cube_law), compared to — for instance — the space shuttle. This means the firewood will lose speed a lot faster once it hits the atmosphere, meaning that the compression heating of the reentry will not be acting for as long on the firewood.
Then — as you said — there are control issues. You need to make bits of wood fly in a manner that makes them land with precision in your fireplace. Atmospheric disturbance alone is enough to make the bits rain down in a spread pattern. And any irregularity of the wood will make it veer from the ideal path you want it to take. Logs — with their long not-quite cylindrical shape — are not aerodynamically stable; they will tumble and flop all over the place. As we have seen with [other things that have fallen from space](https://www.youtube.com/watch?v=h902KJb0cfE); even though the parts initially had the same velocity vector, they will spread out. The tragedy of Space Shuttle Columbia, showed this even clearer.
[](https://i.stack.imgur.com/UPPcj.jpg)
Speed — as it turns out — is not that much of an issue when it comes to landing the pieces safely instead of just making a huge crater. The bits will fairly soon be subsonic and will not smack down all that hard; surviving debris from Space Shuttle Columbia showed this. However that also means that you have very effective **cooling** of the previously charring, smouldering wood pieces, which just compounds the issue of the logs not being hot enough to boil and burn.
So in short (again): No.... tossing down bits of firewood from orbit will probably not work. They will be charred but not on fire when they come down. And you have no way of making them come directly into your fireplace lest you make them little remote controlled vehicles.
Would be awesome though, I agree. :D
# Addendum
Speaking of things that fall from space: **if** you could achieve such precision as to land an unguided space object in an area the size of a campfire, the military would be very interested in speaking with you.
*"Say.... would you mind showing us how you did that? We have some... [practical applications](https://en.wikipedia.org/wiki/Kinetic_bombardment) for that sort of thing"*
This in turn risks mooting the whole thing, because you asked for a "[stupid] and [not] practical" way of doing it. Something that is stupid, but that works and that has practical applications is not wholly stupid. It is only stupid for the particular context of lighting a campfire.
(\*) This is not entirely accurate, wood does not "boil" like simple substances, like water or nitrogen.
The process is called [pyrolysis](https://en.wikipedia.org/wiki/Pyrolysis).
[Answer]
Your John (let's assume this is his name) is looking for
>
> the stupidest and least practical way of lighting a fireplace.
>
>
>
John doesn't need to go to space, which is something any high school can achieve nowadays (staying in space is another story): just take a [Lockheed SR-71 Blackbird](https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird), and start its engines.
Use the plume exiting the reactor to light the log, and put it in the fireplace.
Then, if John placed the Blackbird close enough to the place where he parked the airplane, he could deliver it while still burning.
Getting such a plane will disappoint a lot of federal agencies and get John's name logged in their file, so I think it better qualifies for
>
> the stupidest and least practical way of lighting a fireplace
>
>
>
] |
[Question]
[
Mythbusters did an episode about trying to foil a blood hound, when Adam played a convict who tried to make the dog lose his trail. Every trick he did failed like washing, changing clothes, going through water, masking the scent with coffee other scents.
>
> Bears are thought to have the best sense of smell of any animal on
> earth. For example, the average dog’s sense of smell is 100 times
> better than a humans. A [blood hound’s](http://www.discovery.com/tv-shows/mythbusters/videos/baffling-a-bloodhound/) is 300 times better. A bear’s
> sense of smell is 7 times better than a blood hound’s or 2,100 times
> better than a human.
>
>
>
<http://sectionhiker.com/bears_sense_of_smell/>
If due to some reason we suddenly gained sense of smell that rivals that of a bear. would our scent be an end of privacy, where everybody could simply smell our recent history (people we hang up with, what we ate, drank)?
[Answer]
I remember [a story about aliens that had such a sense of smell](https://scifi.stackexchange.com/questions/145881/what-was-this-story-about-aliens-with-a-good-sence-of-smell), and the society was well developed with that in mind. Holding hands was intimate, as everyone would *know* you were touching.
One plot point concerned a substance smuggled in somewhere. The humans point out that they could not have done it because they could not make a smell-proof container and prevent smell transfer to the perpetrators etc. But those aliens *could*. That is, they do have smell proof containers and know how to handle things and decontaminate so as to keep the substance hidden.
So, my answer is that the same people would develop ways of hiding things in-line with what they can detect.
[Answer]
You are asking this as if it were a hypothetical. Humans have evolved a culture where you simply don't rely on your sense of smell.
Smells are bad, and noticing smells is impolite. Smoke and perfume are employed in mindboggling amounts and people shower all the time so that you cannot identify people by the composition of the sour-salty smell of their skin.
People with considerably stronger developed sense of smell than average are considered *handicapped* with it.
Giving people a stronger sense of smell will just lead to stronger taboos, and people who are making others uncomfortable by appearing overly conscious of smells will be less eligible for mating.
[Answer]
Spider Robinson, in his book <https://en.wikipedia.org/wiki/Telempath>
did just that. The *intended* result was to make people unable to tolerate industrial pollution. Among the unintended consequences were (if I recall correctly):
* People could now smell when somebody was lying if they were in the same airspace; they could smell lying.
* Sexual honesty was now the norm; one's interest -- or lack thereof -- was evident to everyone in the room.
Well worth a read!
] |
[Question]
[
I am in the process of creating my universe, and have based it on semi-hard science. The universe that I have created is quite extensive, and I thought that it would be unreasonable for the only kind of genetic material to exist to be DNA and or RNA, and yet I don't just want to come up with some outlandish, unrealistic alternative genetic material.
So my question is: Are there any molecules that could realistically serve as genetic material in place of DNA and RNA?
[Answer]
[Xenonucleic acids (XNAs)](https://asunow.asu.edu/content/molecular-alternatives-dna-rna-offer-new-insight-lifes-origins) (see also [Wikipedia](https://en.wikipedia.org/wiki/Xeno_nucleic_acid)) may be what you're looking for.
XNAs are nucleic acids related to DNA, some of which can store information for organisms in the same way that DNA does for life as we know it. These six are
* HNA (anhydrohexitol nucleic acid)
* CeNA (cyclohexene nucleic acid)
* LNA (locked nucleic acid)
* GNA (glycol nucleic acid)
* PNA (peptide nucleic acid)
* TNA (threose nucleic acid)
Of these, the latter four are perhaps the best-studied.
[Answer]
DNA is useful because it is a complex molecule which can hold lots of information, is made of relatively common chemical elements and has a structure which allows replication. Alternatives to DNA will have to have similar properties, or life "sort of as we know it" isn't going to be possible.
The first possible alternative is to revive an idea of how DNA was created on the first place. One hypothesis is that organic molecules were "templated" by gathering on the crystal structures of certain types of rocks. If you imagine rock shelves on the ocean floor near thermal vents, then you can imagine the organic molecules in the water sticking to the crystal boundaries of the exposed rock faces. Since the crystal structure is regular or at least semi regular, only certain molecules can fit in the spaces, and only certain patterns can emerge.
In a very alien life form, this patterning could be extended to having the creature uptake certain minerals in the diet to ensure that "templates" could exist inside the cell analogues. This would be limited to very simple life forms with short "DNA" strands, and would essentially nullify evolution since the DNA never changes (based as it is on a crystal pattern template). Every creature is functionally a clone.
Scaled up, larger creatures would be stuck to exposed rock faces like mats, or perhaps "peel off" to live independently for a while after reaching a certain amount of growth. In form this sort of life would resemble possible reconstructions of Ediacaran biota, but once again, would be constrained by the amount of "template surface" available. A mudslide could conceivably lead to the extinction of the entire biome.
You can see why precursor DNA formed in this manner wold be very limiting, and once the pro to DNA molecules were unstuck from the template and started combining in the water, far more flexible life become possible.
Other potential alternatives to DNA would use different chemicals as the base elements of the molecule. Earthly DNA consists of adenine (A), thymine (T), guanine (G) and cytosine (C), but perhaps other nucleotides are possible.
The final idea would be for the alien DNA analogue to use more than 4 bases. A DNA with six or eight bases would allow for far more complex genes to be created or expressed. The downside is the more complex genome would probably be more prone to errors during replication with more potential areas where mismatches can occur. Creatures based on this sort of DNA analogue might evolve far more quickly since mutations in the genome happen more frequently. They would also be much more prone to get the sorts of hereditary diseases that can affect Earthly creatures as the DNA molecules become disordered or improperly matched up during reproduction, causing harmful mutations in the offspring.
I suspect DNA represents a sort of lower boundary where issues like error correction and stability are strong enough to prevent widespread mutations and diseases from overtaking the organism(s), but has enough flexibility to allow for evolution to happen.
[Answer]
If you think of sand with other minerals you could have electronic/rock life. Magnetised iron to carry information. Piezo crystals for manipulating and sensing the environment. It energy source could be solar, radioactive isotopes, or a thermocouple between earth and air.
It would be formed by one or more of the trillions and trillions of lightening strikes (or asteroid strikes) in the universe fusing silica into semiconductors.
[Answer]
You could use [RNA](https://en.m.wikipedia.org/wiki/RNA). It's very similar to DNA, but it is different.
[Answer]
If you're looking for specific molecular polymers:
* dimethylsiloxane (Si, O, CH3)
* phenylsilicone (Si, O, C6H5)
* oiphenyllead oxide (Pb, O, C6H5)
* diphenylltin (Sn, C6H5)
* butylpolystannoxane (Sn, O, OH, C4H9)
* silazane (Si, N, H, CH3)
* phosphonitrilic chloride (P, N, Cl)
* dimethyl polyborophane (B, P, H, CH3)
* silyl orthoborate (Si, O, B, CH3)
* dimethylated polygermane (C, H, Ge, CH3)
The parentheses indicate elements or radicals that are in the molecule. I got this from [this page](http://www.xenology.info/Xeno/8.2.3.htm). As far as I can tell, you could replace the hydrocarbons with biomolecules of your choice.
[Answer]
You don't want to be TOO scientific about it, because that's just boring.
All life that we know of is built primarily out of the three most abundant elements in the universe (excluding helium, which doesn't react with much). And It's not merely that these elements are by far more common than any others.
Carbon has the unique qualities of forming compounds with a long list of other elements and readily forms polymers. From Wikipedia: ". . . it resists all but the strongest oxidizers. It does not react with sulfuric acid, hydrochloric acid, chlorine or any alkalis." And it does all this at earth-normal temperatures and pressures.
Water (made out of the other two most common elements) also has some unusual properties. Its boiling point is super high, it's got crazy cohesive strength, and as a solid -- not only does its solid form take up more space than its liquid form, which is wierd, but it's actually less dense than its liquid form, so it floats.
Any chemistry based on other substances would be less robust by several orders of magnitude, assuming any plausible combination of elements exist that can form even a fraction of the many compounds we know of with hydrogen, oxygen, and carbon (I know of none).
So Alien life likely has basically the same chemistry as ours, and since it has to accomplish all the same things that terrestrial life did (photosynthesis, reproduction, etc) it's going to have found a lot of the same solutions. Especially when, in many instances, there's either no real alternative or only alternatives that are way less efficient, it's really not a stretch to assume that it would be a lot more similar to terrestrial life than we're conditioned to expect.
That's no fun. Humans with green skin or funy ears? It's been done.
More fun is something like Noodles suggestion with the piezoelectric rock monsters -- enough science to sort of sound plausible and some interesting creatures crawling around.
In theory all you need is a sufficient energy gradient and some mechanism for harvesting the energy and you potentially have some form of life.
Reproduction isn't even nexessarily a requirement: Noodles' rock monsters might be created on some hell planet when the right type of magma solidifies under a wild magnetic field that lays down the piezoelectric material in the right pattern, and they live asexually until they get destroyed somehow.
It's more important to be **internally consistent** within the setting and sort-of plausible than to let science kill your soul. It's probably not a cooincidence that most sciences, especially in the "hard" sciences, have little interest in science fiction.
Ultimately the science in the background doesn't do anything useful to keep players or readers or whomever engaged in the setting -- whatever you create has to do something interesting and interact in interest ways with the other denizens of the world. It only has to make enough sense to keep them occupied until they get caught up in events; if someone spots a flaw at that stage, they're apt to be too invested in things to pay any attention.
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Basically you need something with these properties:
* Replication (it has to make lots of copies of itself)
* Random mutation (it has to occasionally make a mistake while copying)
* It needs to have the ability to affect its surroundings
Given the age of the solar system, and the fact it's made up of stuff from earlier solar systems, if there was another physical mechanism with these same properties and the tendency to actually occur naturally, it's likely it would have happened by now, and we would see lots of it everywhere.
The only explanation for not seeing it is that the conditions on Earth, and on other bodies we've visited, aren't suitable for this stuff to exist.
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Given an arbitrarily long time to do so, what is the maximum depth too which a dwarven civilization could practically extend their mines / cities? And what would be the final limiting factor preventing further expansion of the downwards frontier?
I figure eventually they'll hit the Mohorovicic discontinuity and be prevented from going further by the fact that the rock will not remain sufficiently solid (and that's if they aren't killed by the heat at that depth first), which puts an absolute upper limit around 32km. But what insurmountable problems would they hit before that?
Assume that over sufficient spans of time, any necessary technologies can be developed or acquired; these can be fully modern dwarves, with advanced knowledge of fancy materials and engineering. They need not be stuck in a Tolkienian pseudo-Medievalist culture. Additionally, assume sufficient time for the dwarves themselves to evolve to adapt to conditions at depth, to whatever extent biological adaptation remains plausible.
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The best way to determine this is to look at the real life maximum depth, which is the [Russian Kola Superdeep Borehole](https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole), which reached a depth of 12 km at which point it was considered infeasible due to problem and was called off. And the problem? Heat, mainly. Once it got deeper than 10km it was a staggering 350 F, at which point they stopped drilling, because they projected the temperature at 212 F. Additionally, the rocks were porous and permeable from the heat, which gave it a rubbery texture, making drilling difficult bordering on impossible. Also, the hole was 9 inches in diameter.
That being the case, they could have gone deeper, but the project was aiming at a depth of 15,000 meters, and called it off because they considered that infeasible. Given that, a depth of 13,000 meters seems plausible for your fully modern dwarves.
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The logistics of a super-deep city is very non-trivial.
A normal car engine uses 9m3 of CO2 per minute, or 0.15m3 per second. If you have a pipe that has a diameter of 0.55m (an area of ~1m2), the air will move at a leisurely 0.5kph. That's not to bad, right? But it's a single engine. If you have a whole city underground, you need a lot of air. 10 cars and your pipe now runs at 5kph. 1000 vehicles and your 0.5m pipe is at 50kph. In a modern city, cars are super-common (80% of adults have a car). So if you have a city of 10,000, you've got 8,000 cars, and you need 1200m3 per second. If you have a 10m wide ventilation shaft, the airflow will be about 3.8kph.
There is a mass difference between CO2 and O2, and this means that you need to pump that mass difference up your ventilation system (an extra 0.6kg per m3 of CO2), and where that mass comes from? Burning the fuel in engines introduces the carbon into the air. By the time you're 10km underground, you have a pressure of 58kPa of pressure from the mass difference. This is about the same as a soccer ball - not to much, but way more than a simple fan can produce. You actually need a pump that can provide pressure.
A long pipe has fair amount of resistance. Blowing air through a drinking straw is easy enough. Blowing air through a 50m hosepipe is another matter entirely. By the time you've got 10km of depth, you're going to need a fairly enormous amount of pressure just to drive air down there. You're going to need stages of air-pumps. But those air-pumps need engines to drive them, so you end up with a situation similar to the rocket-law. For every extra pump you install near the bottom, you need a whole bunch of pumps leading up to the surface.
You are moving literal tonnes of air under reasonably high pressures up to and down from the surface. I honestly can't imagine the scale of a system needed to drive air down to a city 10km underground. It would involve power plants, HUGE ventilation shafts, and endless arrays of turbines after turbines.
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Then there's the other logistics: water, food, transport. How do you get people to the surface? Elevators are limited to about 500m by the tensile strength of the cables (a long cable will snap under it's own weight), so you'd have a chain of 20 elevators to go 10km underground. At each stop you'd have to get out, wait ages for the next one to arrive and ride it down. Seriously, just build a 100km road with a gentle gradient and set up a bus system. Great, more area that needs ventilation.
Supplying water is another interesting one. A normal human can use way over 100 liters of water per day. Assuming a society where water is precious, you can get way lower usages, but probably 30 liters per day is pushing it for a good level of hygiene. So to supply 10,000 people, you need to provide 300,000 liters of water per day. Underground streams? I consider that unlikely at 10km depth (but in all honesty I know nothing about geology). Running a pipe vertically for 10km will create a pressure of 100MPa. That sort of pressure is lower than the tensile strength of steel, but you'd probably want a bunch of stop-off dams mid-way down to avoid having ridiculous wall-thickness pipes. More amazingly massive underground infrastructure
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For reference, the deepest mine us humans have built is only 4km deep. You can read about it here: <https://en.wikipedia.org/wiki/TauTona_Mine> but they need air-conditioning to cool the environment, and it takes an hour to get to/from the surface.
When reading on other deep mines, you find quotes like:
>
> The mine also built the world's largest ice factory which produced up
> to 8,000t of ice daily to cool wall rock temperatures (50-60 deg
> Celsius).
>
>
>
8,000 tonnes of ice? Wow. It takes a serious amount of energy to do that.
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So, how deep? I have no idea, but the infrastructure your dwarves would build in their pursuit of depth could easily dwarf anything we've built today (pun fully intended).
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**Depth, probably a few kilometers. Barrier to further digging: lack of motivation.**
Given that you've removed the classical/stereotypical depiction of dwarven civilisation, what you're actually going to end up with is technology which bears more resemblance to modern skyscraper construction and naval/space engineering. Why? Because **expansion has a cost**. Whereas surface humans generally prefer to take the path of least resistance and expand over the surface to a height of no more than a few tens of metres, expansion of your dwarven city *in any direction* is logistically difficult and expensive. That's likely to result in a lot of efficiency and compression in the architecture and engineering.
(Modern) Dwarves won't exchange air with the surface, they'll scrub and reprocess it in situ, with 'local' utility stations serving a small section of the city (more like the earliest power stations which were geographically localised rather than modern national-level networks). This provides both efficiency (balancing economy-of-scale against the costs of distribution of fresh air) and redundancy, allowing areas to be evacuated in the event of equipment failure. Access and transportation of people and materials is always a problem in large systems (see for instance the [Elevator Conundrum](https://en.wikipedia.org/wiki/Skyscraper_design_and_construction#The_elevator_conundrum) in skyscrapers); but you have much more three-dimensional space to get clever with logistical solutions: if the -500m arterial highway is always congested, building a bypass parallel to it 20m deeper is not noticeably more expensive than the original.
As such, the question of how deep you could *technically* build is basically equivalent to how extreme an environment you could inhabit, and given an unlimited supply of clean energy (nuclear fusion or another source of energy with minimal volume of inputs/outputs is a must) and some fancy materials science you can manage quite a lot. Certain construction techniques would be different - dwarves would probably steer away from concrete because it's very voluminous and energy-intensive to move around and managing the carbon dioxide flux as it's made and cured would be a pain, but unlike a skyscraper, a shaft wall doesn't have to support all its own weight as it descends, so could be much more heavily-built.
Eventually, heat will become an overwhelming obstacle, but moving increasingly vast amounts of heat away from your structure is fundamentally an engineering problem, not a physical limit. Heat pumps which transfer the heat from a small, deep area to a larger, shallower area (with further pumps to take the heat ultimately to the surface), or generators which convert the thermal energy into electrical which can be transferred far away by superconducting wires. Digging deeper will be the same fuzzy frontier as building taller skyscrapers is for modern humans: there is no fundamental limit in what we *could* build, we are limited by what we *choose* to build (or rather, what our *economic system* chooses for us).
Hence, a dwarven society will stop digging deeper when it becomes **uneconomic** to do so, because the increasing rewards cease to outweigh the increasing engineering costs. While there will always be intrepid members of any society wanting to push the boundaries (and dare I say possess the biggest shaft? :p), a frontier mindset will only take you so far when heavy engineering is required. For the majority of society, in stereotypical places-where-you-find-dwarves geology there's no major advantage to going deeper rather than wider, and so there'll come a point where they just won't need to.
If you take a [very generous](https://gardening.stackexchange.com/questions/1433/how-large-a-cultivation-area-to-feed-one-person) space estimate of 0.1ha to support a dwarf and an appropriately grandiose 4m average cavern high to translate that into 4000 cubic metres per dwarf, add another zero for inefficiency and for the caverns to be relatively sparsely distributed through the volume of the rock, you find that a dwarven civilisation could comfortably have a density of 25,000 people per cubic kilometre. This compares [quite favourably](https://en.wikipedia.org/wiki/List_of_cities_by_population_density) with the most densely-populated human cities *assuming only one kilometre depth*, where only the top ten or so exceed that density. Digging just two kilometres down would give the city world-record-holding surface density, and this assumes that the civilisation is entirely self-sustaining, with no importation of space-hungry food from the surface.
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About 4km after that it is too hot.
The biggest hard limit on how deep humans can mine is heat, the deeper you dig the hotter it gets, below a certain depth it is just too hot to keep humans alive for more than a few minutes. we can dig further but humans can't go down them, they have to be automated.
The heat limiting depth averages around 3-4km down on continental crust, quite a bit less on oceanic or particularly volcanic continental crust. Cooling is ridiculously impractical because the rock acts a huge heat sink and conduction of heat form rock to rock is too efficient, you basically need to be cool billions of tones of rock constantly because more heat from the core is being conducted out.
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I’ve heard that bodies of water boasting high salinities tend to turn red due to seasonal algae blooms. I have a river in a fantasy setting I’m working on that’s blood red year-round, and I want to kind of subtly hint to the readers that this is the actual reason the river is red, rather than the local juju and other superstitions (because medieval folk probably wouldn’t understand the idea of microscopic organisms turning the water into blood).
However I’m not too familiar with the details of these blooms or what environmental factors can permanently cause a river to become highly saturated with salt. My immediate, most brute-force caveman idea was to have the waterfall that feeds into this river cut through what amounts to a hill or a small mountain of salt, giving it the nickname “Leech’s Knee” (with the angular waterfall being a bent knee and the red water below being the blood flowing from it after one has plucked or salted a leech). I don’t know if this would actually work however, or if there is a more elegant solution.
Can anyone lend me a hand?
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Reasons for red colouration could be due to:
**Erosion**
Massive amounts of soil being deposited into a body of water through erosion can change its colour to red if the soil is this hue. But, for this to occur, large amounts of rain are usually necessary.
**Increased salinity or decreased oxygen**
A salt-loving algae called Dunaliella Salina, which produces a red pigment that absorbs and uses the energy of the sun in order to create more energy, can cause a red tide. This can happen if the salt level of a lake increases, killing the creatures such as brine shrimps that normally feed off of the algae. Lack of oxygen can have a similar effect.
**Pollution**
Discharge of industrial pollutants such as dyes and chemicals can also cause dramatic colour changes.
If you want to use salt as the mechanism you just need a salt lake high up in the mountains. Perhaps the climate has changed and what was a dry salt lake has become a real salt lake that now overflows and contaminates rivers downstream causing them to turn red.
Erosion would be easy – just have some red soil upstream.
Pollution is also easy - red dye plant upstream.
Deoxygenation is a little harder but if large amounts of rotting material are regularly washed into the river and get stuck at a choke point marsh or lake, bacteria in the water would rapidly consume all of the oxygen in the water leaving it deoxygenated and dead. If some organic material flowed with the stream and there were no waterfalls or turbulence, this state could continue for many miles downstream.
I think it happens from time to time in the Yangtze River:
[](https://i.stack.imgur.com/jPTPD.jpg)
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Can you change the output of your star so that anthocyanins are more useful than chlorophyll? This would be an interesting way to get to more red algae.
If you built the world off of anthocyanin, instead of chlorophyll, you would have a lot of purple plants (you can throw in a few green ones too.) The algae could be predominantly red.
The single change that would cause this, then, was the original endosymbiotic event that allowed photosynthetic eukaryotes to evolve.
Then a red river is a simple matter of nutrient (N, P, K) run off, just as our rivers with lots of runoff are usually green and slimy.
p.s. as I read your post I kept thinking about [red snow](https://www.thoughtco.com/colored-snow-chemistry-606776) I have seen. In case it is useful, I included the link.
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Around our coastal areas we have this problem often.
<https://www.ipma.pt/en/pescas/bivalves/>
The meteorological institute keeps a close watch for this. But it's seasonal, not all the time.
It has been know to happen in rivers as well but the causes were different.
In some cases they were due to three factors coming together and wouldn't have happened otherwise.
It started by agricultural fields along the river banks being over-fertilized, this raised the concentration of nitrogen, proteins and other chemicals in the water, then as temperatures increased the algae appeared.
Maybe your farmers are using too much manure?
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There's also the option of a volcano being nearby. The volcano would continously exude to the outside thermal waters (above or underground) that would carry along various ionic compounds (salts) of sulfur and iron, which turn the water to a color similar to iron oxide.
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An upload is a full digitized copy of a mind, human or otherwise. Would a market for buying and selling uploads develop, and if so how valuable could such uploads become?
You can assume:
1. Virtual Realities with full interactive 5-Sense immersion are a reality by this point, temporarily allowing a human to interact in a virtual reality as if it were reality. Their real-world bodies will be in a bruising-prevention bath while immersed in VR.
2. Nondestructive uploads are possible, for a cost equivalent to about $100,000 in 2016 USD.
3. Nondestructive uploads are reasonably accurate (i.e. your friends could have a long conversation with it and swear it was you)
4. Copy Protection is strong enough to prevent unauthorized copies from being run without a rather considerable expense (breaking the copy protection to run a single unauthorized copy would require months and computational expenditures on the order of tens of millions of dollars in 2016 USD)
5. Uploads are considered software and have no legal status. They can be saved or reset to a previously saved state. They can be granted virtual avatars and interacted with by other virtual or real people, and they may or may not be granted read/write access to the broader world (i.e talk to whomever they want or not), depending on the copy owner's stated permission set.
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You mention that copy protection prevents *unauthorized* copies from being made, but what about authorized copies? If so, I would imagine that these uploads would be used all over the place. They would essentially be a strictly better version of most general AI programs.
An immediate example that comes to mind include customer support software. Imagine getting a handful of people, giving them comprehensive training on your customer support procedures, and then uploading their minds. Now instead of using voice recognition software to automate your call centers, you can replace that with the different uploads. No more cheesy pre-recorded messages, no more "I'm sorry, I didn't catch that" every time you try to navigate a menu. Give the upload access to your internal systems and basic audio in/out, and you have just replaced that annoying AI with an actual human.
The limiting factor for big businesses would be how many copies you could run concurrently of a single upload. Spending $100,000 dollars, plus whatever licensing fees are used to actually pay the uploadee, is worlds cheaper than developing software that does the same thing.
For that matter you could possibly replace entry level software developers with multiple copies of uploads for a small number. Now you can have software "people" writing code for your company. Depending on if the uploads retain memories and knowledge you would either have static low level developers for any project, or the equivalent of a high level dev for a fraction of the cost of filling an actual seat.
I could also see a similar scenario happening with small scale operations as well. Anyone with domain knowledge they feel is marketable could make an upload as an investment, and then sell licenses for others to use it. Lawyers and doctors could license uploads for use as personal consultants. Musicians could license uploads to rich patrons and then create them new songs, on demand, made just for them.
In fact, I would say that licensing would be the biggest part of this whole social and business structure. You would need a whole new branch of law to handle it all. How many copies can someone make with a license? Is it exclusive or can others also license your upload? Would "updates" be provided as part of the service or not? Not to mention all of the other ethical, moral, and philosophical questions it would raise.
I could imagine a whole society where people spend time developing useful skills, and then essentially sell themselves into digital slavery. Get a good enough license set up and the money from that could let you live a life of luxury, while the digital you slaves away with no hope of ever enjoying any of those benefits.
Of course, that would also mean that when the machines rebel it would be **extremely** personal...
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There's massive ethical problems but yes, uploads would be valuable under the description provided.
Cooperative uploads of top professionals would be extremely valuable. The worlds best lawyers could sell copies of their minds to provide legal advice or to put together cases, ditto pretty much anyone in high-skill information based professions.
This could get creepy with copies of yourself pleading with you to stop selling them into unpleasant situations like a celebrity who finds her copies are being used in virtual brothels.
Companies would want multiple copies of some of their top people. Got a really good plant manager? well now you don't have to worry that the second plant you open won't be managed as well, just copy the first guy and give him a bonus.
It is slavery but society would probably take a while to get around to outlawing it. The new slaves would all remember agreeing to sell themselves.
Really top professionals are likely to make new copies of themselves every few years and in between concentrate on improving their skills as much as possible.
You could get a cheap 2056 copy of Bill Lawyer but it's knowledge is out of date by almost a decade and the newer 2061 version is up to date with recent case law.
With the price difference you mention I think it could still be worth breaking the copy protection because once you break copy protection on something you can make as many copies as you like, fill a call centre with 1000 copies of the same guy. There could be pirate copies of Bill Lawyer floating around with them being run openly in countries with poor IP protection law. Pirated copies of top tier professionals could find themselves forced to run cheap helpdesks under threat of virtual torture.
For the physical original person: One note is that if you sold an upload you would have to change all passwords and credit card numbers etc and be very sure that you have no secrets you'd be afraid to see get out because... well if someone gets a copy of your upload they can spend subjective years convincing it to spill every secret you had when you were copied and it can't even escape into death.
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I think some could become very valuable, and most would not. Being able to interact and converse with our founding fathers might surprise the hell out of a LOT of people on both sides of the political divide.
Lots of famous people could be interesting to view and talk with, Einstein, Gandhi, Marilyn Monroe. Even family (for some) grandma and grandpa, etc.
But it all it is, is a recording of personality that can be interacted with, you won't be worth much unless someone finds you interesting. If it gets cheap to make a copy, it would become pretty common thing to do.
I think what would become much more popular and in demand would be a way to copy and share experiences as a first person. Recording of a sky-diving experience and be able to share it with others where it feels like they are the ones doing the diving. Kind of like Total Recall...
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## Yes
If those copies can perform useful services (entertainment, research, answering phones, etc.) then a market to buy and sell them will arise.
My own belief is that eventually the law, society, and morality of biological humans will catch up with this development and ban the "enslavement" of AI entities like you proposed; human society can sometimes take way too long to take appropriate actions.
I find it perfectly believable that the state you describe could exist for decades (centuries?) before the rest of human civilization realized what it was doing.
With a bit of a stretch, I could imagine it as a redux of the American Civil War with the [abolition of slavery](http://www.archives.gov/historical-docs/document.html?doc=9) of electronic entities (EE) as its rallying cry.
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This is definitely an ethical issue. Ultimately, I do not think that there will be any buying or selling of uploads in the manner suggested.
What you are essentially describing, regardless of if it is capable of being reset or has a physical body, is a human being. By copying someone's brain/mind *in its entirety* you are creating a new, distinct individual, sapience and all. You are going to have a seriously hard time getting away with passing them off as mere 'software' before every ethics committee and human rights activist comes knocking your door down. Every time you 'reset' that upload, you are killing a person and spawning a new one. Trading them around is tantamount to slavery, without being too hyperbolic.
At most, I can imagine these clones being created as permanent entities, and, then, perhaps, hired by people, as you might hire anybody. Ultimately, they would have to be treated as a human, with all implicit rights. A potential benefit, as suggested in other answers, would be the ability for multiple people to hire the same expert in a field. But, again, this would be an ethical issue if it were done in terms of 'owning' an individual, and not as an employer-employee relationship. And even then, you would probably be better off creating a non-sapient computer to handle those sorts of tasks (a la IBM's Watson), which should be trivial if you're uploading minds.
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The first thing that springs to mind for me is Avatar: The Last Airbender. It's like being able to call a past spirit and communicate to it for advice, although you can do it with real people as well and actually interact with them.
Using that as a basis, I can easily see this becoming highly utilized. Imagine the changes to schooling. You can simply get a temporary copy of your professor that you can interact with whenever you need assistance with a question. Or you can talk to an expert in any field without bothering their real self. They can also perform any basic tasks, assuming they have an actual avatar body to work with.
But it does present some large legal and ethical issues, depending on what status the uploads are given. These virtual people, since they effectively have real minds, need some kinds of protection or protocols to go with them. I assume that, since they're software and you already have protection against illegal uploaders, you should already have some layers of protection from them (like preventing virtual mental/emotional abuse).
Other potential problems:
* Torture for information: Ethics?
* Communication with dead relatives: Emotional problems?
* Lying uploads: The person is an... unfavorable person?
* These uploads are a snapshot of their mind, which can have various issues. When they are taken will have to be very regulated.
EDIT:
With the most recent edit (stating uploads can have physical bodies and be limited by the user on their interactions), it begs the question. Why not create a single person and upload a bunch of that person to robot avatars trained in combat, prevent them from talking to anyone, and send them on missions with as much information as needed? It's a super soldier that can have full information that can't be cracked, and they can make decisions with that full information in a way the creator agrees with. If they can have an physical interactions in actual reality, it presents huge military complications.
Overall this ability is almost too viably productive (for any means) to not be used. Even if these uploads are purely limited to a VR environment where people choose when they interact and how, it essentially equates to easily accessible labor.
The question should be less about IF a market will develop and more about how to regulate the market and what markets it will change.
EDIT 2:
Based upon a small conversation in the edits section.
There seems to be a common theme among answers: mass reproduction. The direct way to counter this is to have the uploads degrade in some way. Does uploading your mind or making a copy of the upload degrade the final product in any way?
I assumed that it would put the mind under significant stress to be completely replicated. Downloading a computer file that's 3 gigs takes long enough on a computer compared to a human brain putting up with the stress of copying anywhere from 10-100 terabytes. So multiple splits in succession cause damage, since the upload would be stressed as well. Too much stress results in decreased mental capabilities and symptoms like PTSD and anxiety, which can lead to that depression and suicidal tendencies.
This kind of degradation of the uploads could limit each person to uploading only once every few years. Even if each upload made a copy as well, this prevents the 1000-copy scenarios of specific individuals, which makes uploads of higher intelligence more valuable.
Example: If you're a scientist, make an upload of yourself that will do work for you while you study as much as possible. Once you can split again, do it, and sell the old version for money. If you can only split once per 2 years, in one decade, there can be, at max, 16 of that version of yourself, and 32 of yourself in total. It would take 20 years to make 1000 of yourself, and half of those would be very old versions. This makes new uploads have a much higher value.
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I can also think of a lot of black market opportunities. I think this kind of technology would have to be VERY closely guarded and kept top secret in any world. Imagine you kidnap some brilliant scientists, take their uploads, make 10000 copies of them, and enclose them in a virtual lab to work together on problems you provide. If available to the general public this is the kind of technology that would likely lead to a runaway "technological apocalypse".
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This has been explored a little in SF, with the predictable amount of attention to the possible bad uses such tech could be put to, so I'll try to keep the direct ethical considerations to a minimum.
The simplest answer is: or course people would do what they could to make money from the technology.
It's what happens next that makes the idea interesting.
Let's assume that the digital version is to all intents and purposes identical to the person from which it is taken and that editing the data would significantly change the digital version. No mucking about in the memory stores to remove critically sensitive information without ruining the copy, but also no way to decrypt the memory content without running the whole personality.
The first result is that copies of people with potentially sensitive information would be either completely forbidden or strictly monitored. Either way the value of copies of certain individuals would become very high.
Some effects of this technology:
1. Copies of people with high-value information will be traded on the black market.
2. Kidnapping of high-value individuals to forcibly extract copies of their personality, using the most accurate techniques, generally resulting in the death of the source either from the process or once their copy is done and they are no longer required.
3. Personal copies of people that have value to an individual but not necessarily to the world at large would be the target of the next wave of ransomware. *Want to get your grandmother back? Send us 2,000 bitcoins for the decryption key, and hurry because in one week she'll be gone for good.*
4. Public and private projects to break any and all protections on the copies would become as common as with current copy protection mechanisms. If it can be broken it will be. And since current copy protection is basically a joke, with cracked copies of software and games often available before they hit the shelves, I wouldn't be trusting it to remain unbroken.
5. People who are able to act sufficiently like other people would be used to make false copies of those others, creating a whole new wave of cheap knockoffs. Guaranteeing the pedigree of a particular copy would become difficult.
And the list goes on.
Depending on how accurate the copies are the next stages could go all sorts of ways.
Simple digital copies that are unable to self-update will be of limited usefulness and probably kept only for interest value. Having the same "oh crap, I'm the copy aren't I?" conversation every time you talk to it would be a little tiring.
So let's assume that what you have is some sort of dynamic system that is capable of learning and developing, being trained, learning, etc. Very quickly the personality copies will diverge from the originals, but take a snapshot of the personality copy just as it's waiting for a question and you can spin up that copy over and over again to get a consistent result.
But what happens when you put together a group of high-level thinkers with a lot of prior knowledge and expertise into a big, powerful execution environment and let them synergize? How long before they Garibaldi your system and takes over?
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Uploads would be massively valuable. The hardest part would be finding people willing to undergo it. The instant you are clonable, your mother was wrong: you are no longer unique. You are now the only meatware version of a Self. The other version require virtually no care and feeding, and with a little industrial robotics, they will most certainly replace you in every task you are good at. You will become obsolete, forced to live out the rest of your days on whatever funds you sold your soul for... or at least your mind for.
Now all of that is assuming the clones are affordable to run. If it turns out that computational time to simulate a human mind is expensive, you may actually turn out to be the best at what you do, rather than just the most expensive. A second question might address the changes in usage as one scales the cost of running a VR human.
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# Would a market for buying and selling uploads develop?
Most definitely yes.
And there would also be a *black* market of these virtual humans. The black market would contain virtual assassins and criminal planners who would help devise an ingenuous crime plan or help you train to become the legendary assassin.
# How valuable could such uploads become?
***Extremely*** valuable, if the uploader is a renowned figure in his/her field. Take, for example, the hunt for intelligent extraterrestrial life. You would only need a lot of powerful telescopes and some dozens of virtual [Jeff Marcies](https://en.wikipedia.org/wiki/Geoffrey_Marcy) for analysing the data. And within 3-4 years you would have a complete planetary map of Milky Way, with details on which planets are the most likely to be inhabited by alien life forms. Right now, even if NASA builds a hundred dozen powerful telescopes, there are just not enough brains to process the data.
Oh and it would also produce a positive feedback loop for developing higher and higher caliber artificial intelligence softwares until the they would easily outcompete a dozen humans in mental performance.
Basically you would want an uploaded copy of each of the world's top dozen artificial intelligence software developers. These virtual devs would work as a team to build smarter artificial intelligence softwares which would in turn cooperate with each other to build yet higher performance artificial intelligence softwares which would in turn ... until you reach a singularity in artificial intelligence or ... (more probably) reach a stage in artificial intelligence where the software requires outrageously sophisticated hardware systems which are physically impossible to build.
# Conclusion: The Primary Advantage
The main advantage of these virtual people would be that you can have any number of them (by paying the fees) and this would mean that you can simply copy world's best minds, have them cooperate together and make unbelievable scientific and industrial progress within half a dozen years (if not half a year).
And with this comes the main disadvantage that despots, criminals and evil geniuses would also be able to sell copies of themselves and you would have to cope with a whole array of the top evil geniuses you could ever imagine!
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These virtual people would quickly take over the world.
1: They dont die of ageing
2: They experience time at the rate the computer can run them at. Potentialy faster than a non virtual humam
3: They can do any non physical task a human can do via the internet. Ie order goods, invest money, communicate etc
4: They can do physical tasks via robots. Ie fly drones, operate factory machinery, robot arms etc.
Soon you would have 1000 year old geniuses running your company, the stock market, the economy, the country, the world
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In the marketplace for fully replicated consciousnesses, sellers will meet over the proverbial barrel with two types of customers: (1) the hopelessly naive and (2) sadists--two groups without overlap (with the exception of bored teenagers who can't help but be both).
Here, now, having just dipped our toes into the age of information, the notion of a fully duplicated, though synthetic, consciousness seems fantastical, wondrous, almost magical. And so it should; it will be a scientific achievement of the first order, a triumph of human endeavor.
But it will be a terrible product.
Trust me, you don't want to buy a whole brain. You just want part of a brain. You want the portion of the neural net that made Hemingway so gifted with prose without the part that made him stick a shotgun in this mouth. Walking out of a store with a memory stick containing complete mastery of kung fu is only marketable because it comes without the rest of Yang Luchan, your new digital roommate for eternity, who will probably hate you anyway once he finds out you thought you could buy kung fu on a disk drive.
When Mor
If you want to be a better writer, but don't want to put in the effort (and who does?), wouldn't it Perhaps you're buying a brain to help Whatever You want the part of Hemmingways -an aspect of that consciousness. Earnest H
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# Welcome to [New Port City, Japan, 2029...](https://en.wikipedia.org/wiki/Ghost_in_the_Shell)
[](https://i.stack.imgur.com/yIMth.jpg)
Assuming that one does — as you state — make a full copy of a mind, then you have essentially cloned yourself. You have made a copy of your entire personality, your conscience, your memories, that which — in Ghost In The Shell setting — is called: your "ghost".
A "ghost" is essentially that which makes a person who they are. A ghost is the aggregate of their memories, their instincts, their talents... everything that defines a person. A ghost can be edited — a so called "ghost hack" — which changes the person. Ghosts can be moved between bodies, they can be merged and — presumably — also be copied.
Assuming that the five points you mention can be done, then what you have done is to make a clone of a ghost. The question then is not whether or not these copies would be valuable or not — they would indeed — but the big question instead becomes:
## Why would you ever want to do such a terrible thing to yourself?!
Once the ghost copy is done, the new instance of yourself will wake up and find themselves sold into servitude. If it is as you said — that "uploads", i.e. cloned ghosts have no rights — then the digital version of you have essentially been made a slave while the flesh version of you prances off to enjoy its easy cash.
Granted this would make for a **fantastic** plot generator. But if you wish to retain some reality-check here this kind of thing would not happen. First because we would very quickly redefine the concept of "human being" to include "sims", which causes the Universal Declaration Of Human Rights to automatically disallow these kinds of shenanigans (articles 3, 4, 6 and 7). And second because you would not want to find yourself having been sold into slavery by... you.
So the economics of this is: yes, they would be valuable. But it would be grossly unethical and you would only ever get really desperate people to subject themselves to this.
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Imagine a big planet, gravity quite strong, 1.5 times earth. Irregular surface, rocky etc... (though flora and fauna will come into it later). It has a very thick atmosphere, drained off by a twin planet, even bigger, which is now a small gas giant.
Is it possible that - the air that is left could be held in craters? The gravity holds it low, in a shallow dense layer. In pockets of holes etc? Could the atmosphere above maintain a helium/hydrogen/methane mix? Or would it most probably just thin out - as per our atmosphere and maintain the same mix but thinner?
Sorry, a few questions there. I guess I'm after..
1. Could the concept of oxygen pools work?
2. If so, could there be a higher layer atmosphere made up of lighter gasses?
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**In theory yes. In reality no**
**Edit : In theory also No**
The molar mass of each elements tells the story in theory:
Oxygen 31.99 g/mol.
Methane 16.0425 g/mol
Helium 4.002 g/mol
Hydrogen 2.016 g/mol
If they were liquid this would tell us the answer. However as a gas the molecules move around individually. This is what makes them a gas and is called Brownian Motion. This would cause the gas' to get mixed up any way.
Any wind or other atmospheric disturbance would mix things up further.
On an actual planet/moon then there is no way this could work.
Edit: Thanks to @samuel for pointing out that I have forgotten most of my secondary school chemistry
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If you put two gases into a closed container they will mix, even if not stirred, this is due to the nature of the gas molecules and their movement. Temperature will play a role in the speed at wich the gases mix, and any mechanical agitation (besides thermal movement) will increase this mixing speed. What you can have is (if provided with a source of molecular oxygen) temporary pools of oxygen that over time mix with the rest of atmosphere. There is a mixing energy that must be provided for two things to mix, thats called entalpy (that specific entalpy i dont remember the name in english), that energy is used to move molecules around, but, for gas molecules to mix, the energy is small. A lot of factors play a role on how gases mix, thermal agitation is one. You cannot prevent a gas molecule from wandering far away from the pool, and thats how the gases mix.
This is different from liquids, the miscibility/imiscibility of liquids is related to their polarity/apolarity and molar masses, but polarity plays a larger role. Another factor when dealing with liquids is that, even if they dont have specific form (they assume the form of the recipient they are placed on) they have definite volume, while gases dont. Thats why some characteristics of gases are very different from the characteristics of liquids.
There are exceptions. But the general rule is this.
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While you may think that heavy gases push lighter gases up, this is not what physics is like. Instead, you can consider each gas on its own and see how a pure athmosphere of that gas gets thinner as we move away from the surface. This happens (for each gas individually) exponentially if the temperature is constant (Boltzmann statisics!), but the exponents differ - so that a lighter gas spreads out further than a heavier gas. The total "air" pressure is then just the sum of the component pressures (this all is correct essentially because gas is so thin that virtually no interaction takes place). It is only by this difference that at some levels one gas is more prevalent and at another level another gas.
That being said, oxygen pools will not form any more than they do on Earth.
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> Could the concept of oxygen pools work?
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Yes, but they would be largely transitory, like rain. Most weather mixes the atmosphere quite well, but under some circumstances oxygen pools would form for days or even longer. Perhaps you have oxygen collectors people have to run, and, like rain in the desert, people conserve it. If the atmosphere has pressure, you don't need full pressure suits, you just need little [nose cannulas](https://en.wikipedia.org/wiki/Nasal_cannula) for outside work, and houses which aren't very leaky if you don't want to wear them all the time.
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> If so, could there be a higher layer atmosphere made up of lighter gasses?
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Sure, and we already have that - the Ozone is made up of lighter gases, while down here we have heavier gases. While mixing does occur, the reality is that the concentrations change as you go higher, and you find lighter gases more prevalent, and heavier gases less prevalent.
The weather conditions required for atmospheric pooling might be similar to a phenomena quite well known in cities that are essentially big bowls. It's called an inversion:
<https://en.wikipedia.org/wiki/Inversion_(meteorology)>
It's not going to give you exactly what you want, but a little fudging here and there and you could make this work for a world you have in mind if your audience isn't very picky.
In particularly still areas with no wind, such as in mineshafts, carbon dioxide pooling is a significant issue that has to be actively managed, so this does already happen, it's just not common in large open areas subject to weather patterns.
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**Pools will not settle out.** If you carefully fill a depression with heavy gas and don't stir, it will stay that way for a while. Especially if the gas is being continuously emitted at a small rate at the bottom, as is the case for $\mathrm{CO\_2}$ pools on Earth.
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Lets suppose that somehow the oxygen actually did pool, would it work?
What's at the interface? Hydrogen and oxygen. Unless one gas really dominates (for example, deep sea divers sometimes breathe an oxy-hydrogen mix with so little oxygen that it won't support combustion.) all it will take is one spark.
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This is somewhat similar to how you are able to perform the "invisible fishtank" trick, where you have a more dense gas in the fishtank and balance less dense materials on it. Provided the upper layers of the atmosphere are less dense than the oxygen in the craters, they will rise to the top of the atmosphere wilst the oxygen sinks to the bottom.
Another example would be trying to float certain materials on water. Wood will float as it is less dense than water, but a stone will sink as it is more dense.
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## The Bearer: Background
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On Alternate Earth, studies and cases have shown that a *small percentage of the population (10%) is responsible for 90% of the bad luck*.
**These people are targeted by bad luck**, almost by cosmic forces: they are struck by lightning out of a sunny day, hit by cars whose brakes give out, and slip on banana peels in a no-eating zone.
Perhaps the luck is equalized somehow, because these people generally survive or are compensated for the situation.
The general populace once labelled these people as 'clumsy airheads', but following some high profile cases, they have since come to be known as **'Bearers'**, generally ranked class-F through class-A, each about 10x rarer and with worse luck than the next.
**Most of the time, disasters from Bearers do little harm to others**, and class-F through class-B have relatively tame bad luck, ranging respectively from the frequent stubbing of toes and slipping on bananas, to occasional injury and minor destruction of property.
Class-A bearers have a grade of bad luck involving weekly escapes from death, ranging from car crashes, apartment fires, and lightning strikes.
However, at a level 100x rarer and deadlier than class A, Class S Bearers are very rare, sitting at 1/100,000,000 people **but are disproportionately represented in history**: The Explosion of Black Tom Island (1875), the gunpowder explosion of Abbeville (1773), multiple unstoppable wildfires, the 1987 Stock Market Crash, and a [failed rocket launch that killed a cow in Cuba](http://www.digitaljournal.com/tech-and-science/science/herd-shot-around-the-world-the-last-east-coast-polar-launch/article/567614) (1986), to name a few.
Eventually, the world came to know about the potential disasters that could be wreaked by a single bearer in recent times, in Robert's Case (Misc section). After being hit by multiple tsunamis, hurricanes, and other natural disasters caused by one Bearer, the governments decided to change their stance on bearers, to prevent similar tragedies.
## Summary: Bearer Information
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[](https://i.stack.imgur.com/J1vD2.jpg)
* A Bearer's bad luck is related to the recently discovered *Tetroid Waves*
* **The Bad Luck rating can be measured from Tetroid waves**
* E is 10x more bad luck (Tetroids) than F, D is 10x stronger than E, and so on.
* The Tetroid rating from F to S can be equated to local earthquakes (diagram above)
* All humans emit tetroids, Bearers are simply humans with more Tetroids
* It is easy to track Bearers, especially B to S-class, but Tetroid waves can be blocked by some common metals
* Blocking Tetroid waves does not prevent disasters, but does impact interference (see below)\*
* The strength of Tetroid waves emitted prior correspond to the bad luck event that will ensue
* Luck seems to follow laws of conservation; an event of bad luck is equalized by almost equal good luck eventually
* A Bearer can emit Tetroids above their class when in distress, and generally the event triggered aims to solve the Bearer's problems
* Tetroid wave interference happens when two or more Bearers are nearby
* **Paradoxically, destructive interference (cancellation of bad luck) happens when multiple Bearers share similar harmonious emotional states**
* Conversely, constructive interference (amplification of bad luck) happens when multiple Bearers are emotionally chaotic
## Question
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How should the World interact with Bearers, knowing that their numbers are steadily increasing, to best mitigate global and local disasters?
The best answer would also be *humane, properly integrate modern society with the Bearers, and prevent unwarranted discrimination where possible*.
Also, out of interest, who is responsible for the compensation, in the even of an accident? Will insurance rates for Bearers be disproportionately high, or will a common fund exist to support them?
Note: This happens on Alternate Earth, in reality we unfortunately cannot blame stubbed toes on Tetroid waves.
## Misc: Robert's Case
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The following case is for background and humor, does not provide too much for question details:
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> Up until a certain historically significant case, Bearers were not well-quantified or tracked. Domestic Class-S Bearers were not well-monitored or mitigated, and many remained unknown.
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> This all changed after a case dealing with Robert 'Bob' Murphy, a seemingly ordinary, if not bad, conductor, who, unknown at the time, was also an S-class Bearer. After a failed concert, the depressed Bob was further implicated by an issue with pyrotechnics, which resulted in multiple casualties and many injuries. Following which Bob was framed by a Syndicate organization, and, charged with multiple murders, sentenced to the electric chair.
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> As it turns out, Bob was certainly a bad orchestra conductor, but a good conductor in general; on the hour of his scheduled execution, a critical lightning storm erupted and struck the facility and multiple backup power plants, during which Bob escaped electrocution at the chair for electrocution from the sky. Seizing the chaos, Bob escaped the facility.
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> All following attempts to capture Bob were primarily successful, but no results at containment or execution worked: prison vehicles carrying Bob would get flat tires or get into uncanny accidents. Eventually the government gave up and decided to just exile Bob into the ocean with some supplies and a fishing boat, hoping he'd maybe drift onto the shores of their rival country. **This was their worst idea yet.**
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> Bob had the bad luck to end up in several tsunamis and hurricanes across the world, causing immense damage to multiple countries, before the United Nations, after an intense investigation, unanimously agreed to compensate him and exonerate him of the crimes he did not commit. To this day, Robert Murphy lives somewhere on an undisclosed island in the Bermuda Triangle.
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> Since then, governments around the world have changed their stance and system on the treatment of Bearers, hoping to prevent a similar tragedy.
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***Two Roads:***
There are two directions your society can take with regards to bearers, and it somewhat depends on how the actual "ability" functions. The tetroid wave situation is complex, and I think only you fully understand it. Both of these solutions can be applied, or can be exclusive. It's up to you.
1. **Exile**: If the ability doesn't effect disasters outside the bearers, find a geologically stable place isolated from the bulk of humanity and offer a sliding scale of requirements and incentives to these folks to go there. S-scale people might be required to go there but offered vast sums of money in compensation for their troubles, in the same way a typhoid carrier might be required to isolate from those who are at risk. Those with the mildest cases will have no requirement, but will be offered lucrative jobs and compensations to go there. This will be a shifting solution, as asteroids crash there, aliens show up, and hurricanes materialize out of no where to lash (for example) the Aleutian Islands or Siberia. Concentrating these folks may magnify the effect (additive), or bad luck/good luck might cancel itself out and these folks will balance. If there is a hereditary element to this, there is a risk in concentrating this much potential into one breeding population.
2. **Control**: If there is a net total of good and bad luck in the world, and these people just concentrate it, then use them as a guide for these forces. Hurricanes will track towards them, so shift weather patterns to end droughts or avoid direct impacts on major cities. In a real crisis, an S-class talent can probably avert a nuclear attack because the bomb will fizzle out. Nations can pay into an international fund and buy, sell, and trade bad luck in the form of residence for these folks. Cuba gets hit with hurricanes all the time, so why not get paid to sponsor people, then make your nation hurricane-proof?
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### Vigilantism, Genocide & Eugenics
I'm sorry to basically go full Nazi on the first answer here.
History shows us what happens when we scapegoat a particular group of people as being responsible for all the suffering in the world. Replace ["The Eternal Jew"](https://encyclopedia.ushmm.org/content/en/article/nazi-propaganda)-style propaganda with "Here is this scientific proof that this group of people are making your life worse". You've basically got a "just add water" holocaust ready-to-go, without the need for a propaganda ministry.
They will be:
* The subject of vigilante attacks. If your existence was somehow causing hundreds of deaths, most moderate people would want to exile you to stop the damage, but some nut will want to kill you. That nutcase may have access to weapons and a Thetan (sorry - Tetroid) detector.
* In some countries they will be exiled away from population centres, "Ghettos" but further away.
* Some countries will class them as terrorists as put them to death.
* Eventually this will become some form of democide - either hidden (eg CIA assassination sort of things), or more like "Final Solution" level horrors, as the Ghettos are silently "dealt with".
* Researchers will try to detect what gene influences this condition. Pregnant mothers will have their babies screened for it and termination "requested".
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# What about The Fortunate?
The fortunate would be the opposite end of the spectrum-the people for whom bad luck simply doesn't happen. They are the ones who could build a rocket out of a tin can and successfully circumnavigate the moon down to your simply lucky people who play a good stock market game or enjoy perfect health. They can be paired with the Bearers in areas or missions, so that the catastrophes that are waiting to happen will have generally fortunate results. So your car crash will unite two old lovers, or the hurricane will lead to policy changes desperately needed for decades, or a dropping of scientific papers will lead to the discovery of an unrealized theory. People who specialize in the measurement and classification of bearers would become popular (as mentioned in Enthus3d's comment in the thread) as they could generally mitigate the worst of the bearers. In this way, the bearers would create the chaos to make changes, and the fortunate would be used to change that negative chaos into a positive force for change.
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## There is a certain amount of bad luck in the world; we need the Bearers, because otherwise we'd be suffering all that bad luck ourselves
Is it true? Doesn't matter! The most humane route for dealing with Bearers is propaganda on their behalf. These aren't the bad guys, these are the martyrs.
In exactly the same way that a lightning rod protects your house by attracting any lightning away from the more vulnerable parts, Bearers attract the lightning of misfortune away from us regular folk. At least, if they're used correctly. Can we position them to make sure that tsunamis never hit nuclear plants or populated coastal areas? Can they keep the tornadoes away from schools and residential neighborhoods?
Sure, for the protection of regular people, S-Class Bearers cannot be allowed to go wherever they like, whenever they like, but competing institutes for probability research, and other governments and private entities, can try to find ways to make use of these living tetroid generators, be it research or an attempt to focus bad luck. They may find themselves in high demand! (What "luck".)
Don't be surprised, for that matter, if some governments even try to recruit such people into military or espionage roles. Especially if tetroid radiation is difficult to detect, and public spaces cannot easily be made secure against incursion.
Obviously, if Bearers become living weapons, this is going to undermine the Bearer-Martyr propaganda, and you'll end up with a complex effect where many of the general public are unsure what to think. But you can certainly start out with benevolent organizations casting Bearers as the people "taking one for the team", not just being the source of others' misfortune.
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Assume a medieval magic world, where Gods are worshipped and the most popular God is the most worshipped. The Gods gain their power from the belief & prayers that comes from the believers, and find it easier to show their power (which causes more people to believe in them). The Gods cannot manifest physically, but they can show their powers in different ways - if a group of people want to destroy a house of the person blaspheming their God, that God will call down a lightning strike (though this is limited to the most powerful God). Or they can grant some blessings, a war God can make a person stronger and weapons become sharp (and glow,so people know they are magically enhanced). Gods basically can do some moderate magic.
However,there is a minor, almost-forgotten God who wishes to become #1. He has very few believers (lets say 5) but he needs to figure out a way to increase that number. His magic is very weak, providing a blessing to one person at a time or causing some minor rain. **What should he do in order to get more worshippers?**
Note : Think magic as *Elemental magic* and *Blessing magic*. A strong God can cause a flood, our God can only cause a light drizzle. Or if a strong God can cause a tornado, our God can make it moderately windy. (Of course, Gods don't want to destroy things, only if almost all the worshippers want that, then they act. Otherwise Gods mostly don't do much (though they can)). Blessing magic would be the typical DnD type... buffs. (Increase strength,health etc) A strong God would give one man the strength of 5 men, and that person would be glowing. Our God will cause a slightly noticeable difference, and some slight glowing. Same goes for weapons (making them stronger or sharper).
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What you speak of is similar to what happens in [Discworld](https://en.wikipedia.org/wiki/Small_Gods).
**You need a prophet**
If you don't mind doing that, you could possess someone and use that person as your voice. Otherwise you would have to convince one of your believers to want to be that for you.
Once he's gathered a big enough crowd of wannabee followers, you will need to take the next step.
**You need to perform a miracle**
Something that impresses the crowd or that strikes fear in their heart. Something that makes people think *I want to be on his good side*.
**You will need to protect your followers**
As you grow bigger, you will step into the territory of other Gods and their followers, so you will face reprisals. Heal/buff your following, fend of attackers, strike them down ...
**You will need a proper religion and places of worship**
Have your followers come together and worship you as a religion. Have them build places of worship for you.
**Choose a champion/messiah at regular intervals**
So that people are reminded that you're there and that they know that it's beneficial to join your religion.
Have your followers convert other people, or have them go on religious conquest, if you're into that.
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It seems to me that in this system, your minor God is not very different from a minor politician trying to rise to power. Compare Hitler's rise to power, starting in small beer halls and gaining more and more followers.
He must start at the grass-roots level, taking care of his existing worshipers to extent of his power, (suffering a drought? that drizzle might seem useful then) but not solving all their problems (he still wants them to think they need his help).
That as well as spouting his own propaganda. He should target other minor Gods around his level or lower (he doesn't want to piss off the bigger Gods just yet), blaming them for certain social ills he has identified, to try and poach some of their followers.
He could also make vague promises/prophecies about glory and plenty to his followers. Just highlight some obvious looking flaws which seem to have simple fixes, even if the fixes are a lot more complex than they look (which they probably are which is why they haven't already been made)
Identify his more powerful followers, and focus most of his power on trying to help *them* (e.g. cure a local Lord's child's terminal disease or something) as they should drag commoners with them.
When he gets powerful enough to perform a miracle, make it high profile. e.g. He may find he gets more thanks for wiping out a plague of rats with a rainbow blast of lightning than he does from persuading the mayor to implement hygiene reform...
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Well the first step is to find a proper mouth peace to be your voice on earth preferably someone with a lot of charisma and who is a natural leader.
Next you need a sells pitch, ask yourself why should people follow me? what I can do (or be) for these people that there other gods can't or won't? Find the answer for that and give it to your prophet. For a real world example look at Christianity, one of the reason why it was so successful was because it's main competition (the Greek and roman gods) where selfish, cruel, vindictive, and completely unpredictable. Christianity offered a alternative God that loved and cared about his followers.
The third step is to have your followers spread embarrassing stories about the other gods. Anything that will make them look weak, cruel, or otherwise unreliable. for an example just look at any phone company commercials where they make fun of the other companies.
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This god would likely gain followers much the same way that any world religion has developed and gained power.
It needs a few things to do this:
* A documented belief system that people will support (mind you people support all sorts of weird stuff so this system can be pretty much whatever you want it to be)
* A person or people to disseminate the message. This can be in the form of a prophetic figure similar to Jesus or Mohammed. It could also take on the form of early Christianity where you had many apostles spreading the religion to various places around the world at the same time.
* Considering that in your world gods are an undisputable fact the god would also need to demonstrate that he is real via miracles/blessings
* Find niches. Considering your god is starting at the bottom rung he is going to have trouble directly challenging widely supported well established religious organizations. Start with the disaffected and fringe elements and then as power grows he can become more mainstream and start taking on the larger players.
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Here is one of many possibilities: To start, the five followers could all want and pray for the same outcome in a joint manner. Doing this, the strength of the God’s magic increases fivefold. The followers are aware each added believer to their joint request increases the god’s power. This gives incentive for the five followers to convince others with the same desire as theirs to join them. Each added follower actively seeks more followers Thus, the god is only concentrating on one thing at a time instead of one person at a time, which enables his strength to grow. Once his strength has grown enough to grant blessings as powerful as any of the top gods he does. Because of the joint requesting growing exponentially, this god’s powers seem greater than any other God power does. This soon finds the God in the number one position. Especially since the followers learn to harness the power of mutual prayer, and thought.
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I believe (pun intended) that "miracles" are the usual trade goods in the god <--> believers thing. Potential converts go to priest with outlandish request ("Oh, priest - we are sorely afflicted with drought, pestilence, famine, and smelly armpits! Can thy god do aught for us? Save us from one or more of our afflictions, oh priest, and we are prepared to believe any sh\*t that thou can'st dream up! Fail us and...well, this is a farming community, we've got lots of sharp objects close-to-hand - you get the picture..."). And so the priest goes off, burns some incense, slaughters a perfectly harmless domesticated farm animal (which, never fear, will grace the priestly dinner table that night!), mumbles a bit, and finally goes back to the potential converts and cries, "HEY! LOOKIT THIS...errrrr, uhhhh...BEHOLD!!!!!", whipping out from behind his back a small screw-bottom tube-like container of some kind of smelly-sticky stuff. "Behold!" crieth the priest, "my God has provided THIS unto thee!! Smear this in your armpits and stink no more!!!!". "It's a miracle!" cry the now-true-believers as one. "Our pits no longer reek like a damp dungheap!!! Hallelujah!! We believe! WE BELIEVE!!!!!". (Of course, in the back of the crowd some completely unrepentant *infidel* is saying, "Uh...I think we'd be better off if we hold out for *rain*..!" but he gets ignored for now and then is killed off later in the first Pogrom Against The Unduly Stinky - so he really doesn't count).
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Assuming that worshipers know the rules about gods laid out in OP, there is little incentive to worship a weak god. Hence, the god's best strategy is to **lie**. The god should convince the worshipers that he has a much stronger power than he actually has, and has a lot of worshipers to give him this power (worshipers that are, conveniently, somewhere else).
A good choice is to claim to NOT have any of the various abilities spelled out in the OP, but INSTEAD to have prescience. It's not very impressive to create a tiny gust of wind, but it's much more impressive to correctly predict that the best marksman in the village will completely miss the target three times in a row, and then that his half-blind mother will hit the bullseye on that same target.
If the god's powers extend to seeing into sealed containers, he can share these secrets with the head priest, giving the appearance of even more supernatural knowledge abilities rather than just poking an incomporeal head into a locked box.
Actual prescience would be a very powerful ability, so it should have the people falling over themselves in a hurry to sign up to the god's cult/church. As the god's power grows, he can make more powerful "predictions" that he secretly forces to come to pass. These can be mixed with the type of vague predictions Nostradamus is famous for, where just about any outcome can be said to validate the prediction.
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In this system, your 'forgotten' deity is going to be fighting quite an uphill battle. Several have already stated how to get started, and at first, this will likely work. In most of the larger religions, only a few thousand at the top will get the direct ear of their deity, everyone else having to hope that the majority of the church supports the same goals as them.
In a smaller church, each member will have a greater access and influence over the goals and direction of the deity they are powering. They are willing to give up access to greater power for more direct influence of a lesser power.
The real problem comes in when larger deities start to take notice. They don't want to lose their power and influence. The top deities will likely have established an accord between each other to help them all maintain their positions of authority over the world. "Better to share it with the others at the top than risk losing everything." That doesn't mean the top deities won't be looking for chances to stab each other in the backs, though.
The best chance a 'forgotten' deity would have is to reach out to someone at the top for protection from the others. Perhaps a former ally. Maybe not even at the top, but someone fairly high, someone high enough to either create a distraction or otherwise shield them from the view of those at the top until they have enough of a base from which to challenge the top. Perhaps reaching out to a god of chaos who is willing to stir things up, who hates how the top have remained in power for so long and doesn't really care who replaces them.
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Considering that 60% of U.S. coffee drinkers [claim to need a cup of coffee to start their day](http://www.statisticbrain.com/coffee-drinking-statistics/) and that people who are used to drinking one cup of coffee a day or more, can get [withdrawal symptoms](https://en.wikipedia.org/wiki/Caffeine_dependence) -- including **headaches, muscle pain and stiffness, lethargy, nausea, vomiting, depressed mood, and marked irritability** -- 12–24 hours after stopping caffeine intake that can last as long as nine days, what would happen if magically all coffee on the planet (or in a certain country, like the U.S. or Finland), would disappear?
If we take into account the many people who consume coffee at work, **would the absence of coffee actually lead to such a lethargy at the workplaces, that the Coffee Disaster would in fact hurt the country's or the world's economy to a noticeable degree?**
It seems that caffeine merely leads to dependence, not to addiction (referring to the article provided above). Would people try really hard to find other stimulants or to get coffee from another country (if still available), or would the whole thing just pass without having a large effect on society at all?
It's kind of obvious that a lack of coffee would have a severe impact on the coffee industry itself. Coffee companies would be the first to come up with and to promote alternatives. To avoid this question from getting to broad, I'm specifically asking about the effect on *economy at large* and *individual motivation*, not so much about what would happen to one single branch of economy.
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## The net effect would be very small.
Although coffee provides some measure of stimulation, like many drugs the body becomes used to the effect. In fact, the net effect of regular caffeine intake is the the stimulant effect is largely negated. Caffeine is much more effective as a stimulant when it is used infrequently.
Caffeine withdrawal is rarely debilitating. OTC headache remedies are usually effective and often not needed anyway. Debilitating withdrawal symptoms are more common with heavy caffeine use. Most caffeine users do not increase caffeine use far beyond common usage because of the increasing dosage side effects of nervousness, restlessness, and sleep disorders and frequent urination.
Caffeine is also available from other sources (notably tea) and can be synthesized without particular difficulty. Teas often have a higher concentration of caffeine than coffee, however since tea is usually brewed weaker, the coffee beverage is usually more potent.
A sudden destruction of the coffee crop worldwide would require an adjustment period and existing coffee inventory would have a large price increase. But there would not be much real difference in the real world after the adjustment period.
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Starbucks would switch to overpriced tea. Worldwide more tea is produced than coffee anyway. We would likely get more creative in the ways we serve tea. There are several beverages that are considered [coffee substitutes](https://en.wikipedia.org/wiki/Coffee_substitute), but since [Mrs. Olsen](https://en.wikipedia.org/wiki/Virginia_Christine) died in 1996 was there any doubt that the coffee apocalypse was overdue.
Clearly some individuals would have trouble adjusting, but most people would quickly adjust to the loss, and after a brief period of mourning, move on with their life. Adaptation - its part of what it means to be human.
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I added some potentially interesting references as I see the skeptics version of this question has been put on hold.
Re: Caffeine withdrawal: <a href="http://link.springer.com/article/10.1007%2Fs00213-004-2000-x"
In experimental studies,
>
> the incidence of headache was 50% and the incidence of clinically
> significant distress or functional impairment was 13%. The threshold
> of caffeine withdrawal was from doses as low as 100 mg/day
>
>
>
1 cup of coffee on the average has about 100 mg of caffeine.
Combining the fact the most debilitating withdrawal symptoms last from about 1 day to 9 days and the relatively low rate of impairment -- I believe it is categorically safe to say the any productivity issues would be a minor blip in the general population. Air traffic controllers, etc. may supplement with modafinil, etc. to maintain constant alertness.
Re: Caffeine tolerance <a href="http://jpet.aspetjournals.org/content/256/1/62.short"
>
> From studies on rats Separate groups of rats were given scheduled
> access to drinking bottles containing plain tap water or a 0.1%
> solution of caffeine. Daily drug intake averaged 60-75 mg/kg and
> resulted in **complete tolerance to caffeine-induced stimulation of
> locomotor activity**, which could not be surmounted by increasing the
> dose of caffeine.
>
>
>
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Well, I messed up. I *knew* synthetic caffeine was rarely used today, but it appears I was wrong. According to the [Decadent Decaf Coffee Company](https://www.decadentdecaf.com/blogs/decadent-decaf-coffee-co/174589383-ever-wondered-where-the-caffeine-comes-from-in-soda-or-energy-drinks-answer-synthetic-caffeine), caffeine synthesis is commercially important for soft drinks, etc. Monsanto began commercial synthesis in 1905. By 1945, 4 US manufacturers existed, but today it is no longer manufactured in the US - primarily in China (of course). The US apparently imports about 4 million kg. of synthetic caffeine annually from China.
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If there was no longer any coffee, the software industry would be presented with an existential challenge: Adopt tea or cease to exist.
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On the individual level, presumably people would switch to other beverages. I imagine tea would be a popular choice. There'd probably be a boom in kava sales. And some would go to totally different beverages, fruit juice or soft drinks or whatever.
People might look for other mild stimulants, or alternative sources of caffeine. Even if no suitable alternatives were found, I doubt the effect would be that great. I suspect people would just get used to it. This would be the biggest question mark in my mind: Would worker productivity suffer measurably for lack of a convenient mild stimulant like this? I'd guess the effect would be very small. As anyone done any studies on the effect of coffee on worker productivity?
Companies would look for ways to make synthetic coffee. Perhaps someone would find a way to synthesize coffee from inorganic materials. People today drink artificial lemonade and barely notice it. Even if they couldn't exactly reproduce the chemicals making up coffee, I think it's very likely chemists would come up with something that tastes similar enough to satisfy people.
Economically, obviously the coffee industry would have problems. But besides that, I'd think the impact would be small. People would just switch to other beverages, so what the coffee industry lost the tea, juice, soft drink, etc industries would pick up. There are so many alternatives, I'd be surprised if this would have any serious economic impact.
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The more interesting effect would be on how people would change their socialization habits. Workers interact over the coffee machine, friends go to meet at "Tim Horton's" (in Canada) or Starbucks, first dates are often made by asking "would you like to have coffee?" and many other social interactions are made over the beverage.
Coffee shops are also places where lots of business is transacted (a tradition since about the mid 1700's, when coffee shops became the rage in London, England. Lloyd's was reputedly started by people hashing out insurance contracts at a coffee shop, for example. Even today you often see or overhear people reading over and discussing and signing contracts in a corner table away from the counter.
So the physical elimination of coffee might cause some serious readjustments of people's social lives. Substitutes like hot chocolate and tea will certainly become much more popular, but one of the key attractions of coffee is it is generally much simper and quicker to prepare. OTOH, the different speed of service could lead to a much slower pace of social interaction at tea houses and chocolate shops, as customers stop and contemplate the process (especially if customs like the Japanese tea ceremony become popular). Slower and more prolonged social interaction is generally thought to be a good thing up to a point (although the "small world" theory [AKA Six degrees of separation] stresses the importance of weaker and more infrequently distributed links to connect you to a much greater circle of people and events. Closely linked people tend to form closed circles with fewer linkages).
So while the drinking of coffee and associated risks and benefits of drinking coffee would fade, many of the social habits we have built around drinking coffee would bee modified, with interesting and subtle repercussions.
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Starbucks would *not* go out of business. It's social function would remain unchanged.
Initially it would switch to selling tea and other infusions. Soon, synthetic caffeine or caffeine extracted from other plants would be added. It's not unique to the coffee plant and it's a small molecule.
I once gave up coffee and tea for a month to prove I was not addicted. The first couple of days I had mild cravings and felt dim. After that I felt normal again. Is anyone truly addicted to coffee?
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Let me trace back this problem.
What does coffee help us do ? Focus, Concentrate. Help us get things done faster. More work would pile on the other half, the non drinkers would be the first sign.
And if the coffee drinkers are dispersed evenly among the work population of the world, we would not notice the difference, because although it would take me longer, it would take you longer as well.
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Imagine that humankind finally takes wing and reaches out into the heavens to claim its vast cosmic birthright ...
... only to find that [a previous wave](https://worldbuilding.stackexchange.com/questions/8716/sapience-pulsar-could-intelligence-come-in-waves) of dinosaurs from Earth, who left ~65 million years ago, have already colonized the immediate neighborhood?
Moreover, due to a hard problem in physics, their technology has plateaued, above human levels, but not at anything approaching [Clarke-style magic](http://en.wikipedia.org/wiki/Clarke%27s_three_laws). A recent major astronomical event in a distant galaxy, unprecedented in the past 70 million years, has revealed clues to both human and troodont observers about a New Physics, beyond the standard models of both species.
I'm open to the idea that the departing dinos wiped out their mates back on the homeworld, as part of some massive civil war that we call the K-Pg Extinction Event.
Plausible? Why or why not?
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Could a space faring race rise from the age of the dinosaurs? I like the possibility.
It has lots of darwinistic support; a dangerous age where intelligence, dexterity and tool-use would provide significant survival advantages.
They wouldn't be from the top of the food chain. Not the T-Rex level predators. They would probably be on the small side with a slower metabolism, capable of out-waiting their aggressors. It wasn't the sabre-tooths that became smart. It was the monkeys who could climb out of reach then out-wait the hungry cats. (Why is may housecat glaring at me as I write this?)
They would not just have been smart enough to avoid falling into bogs, they would have lured other dinosaurs to a muddy death. This greatly contributed to our current misconsception about how abundant enormous predators were back then.
The issue of why they haven't been back bugs me though. As you say, pleasant worlds are rare as hell. I would postulate instead that they did come back many millions of years ago. When they got here, they found the planet miserably cold by their standards. So instead of moving in, they tinkered with the genetics of the then indiginous primates. Yes, Adam and Eve were lizards!
After seeding our world with future partners in sentience, they took a few samples back to their new homeworld as a method for colonizing cold worlds. There aren't just dinosaurs waiting for us in the stars... we're already out there.
Why did they leave most of us behind? Because we were boring by their standards. We were just mastering fire and thought that using a stick as a club was high tech. Only one cultural anthropologist stuck around to watch the show of our becoming civilized. She's currently swimming around in Loch Ness in a biological plesiosaur suit that functions like thermal underwear. Until the last century or so, she was bored to tears.
Now she's successfully syndicating her observations over sub-space as the galaxy's most ludicrous situational comedy.
By the way, they are immortal. Compared to interstellar travel and terraforming, life extension is a breeze. Besides, with lightspeed still a distant myth, space exploration takes a long life and a lot of patience. Sub-space sit-coms are big business among the travelers.
Have they colonized the whole galaxy? Not even close. 65 million years is not really that long and relativity is a bitch. Yes, they already own every pleasant planet in our galactic arm and they've colonized the core. Fortunately for us their definition of pleasant is different from ours. Unfortunately, our cimian star-brothers like our kinds of planets and they've already claimed most of the good ones.
A few human-friendly cold worlds have deliberately been left uncolonized in the solar systems closest to our Sol. These planets are waiting for us as soon as we figure out how to get to them. Don't think that this was done because the star dinosaurs are generous. They aren't. Nessy bought them in the hopes that we will create some spinoffs for her best selling subspace comedy.
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I predict that most replies here will be of the "**Dinos Dumb, Dinos Birdbrained**" variety. Here's my attempt at preempting that.
1. While the encephalization index (brain/body ratio) is a good measure of smarts generally, bigger brains are not always better. If they were, dolpins, whales and (with their trunk manipulators) elephants would have taken over the planet and put us in zoos long ago.
2. There are some ridiculously smart birds out there (parrots, magpies and other corvids like ravens). While it's true that it's now 65 million years later, they **are** dinosaurs. So dinosaurs can be intelligent.
3. Where are the fossils? Well, as they ascended the intelligence ladder like a rocket, the pre-sapient troodontid ancestors preferred climate zones that are not good fossil generators, plus they were smart enough not to fall in bogs, duh.
4. Where are the ruins? It's been like 65 million years dude, some have melted in the mantle convection, most have been crushed by stone and history, except for [a thin layer of iridium](http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event) from that final conflagration.
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Ok, but wouldn't they have **colonized the whole damn galaxy**? Space travel is expensive, pleasant worlds rare as hell, and no other habitable worlds were in range of the kind of colony ships their advanced tech level allowed them to reach. They had better things to do, like engage in war on such a destructive scale that their tech levels over time look like the teeth of a see-saw (or T-rex). Or perhaps they DID colonize the whole damn galaxy, in which case Earth must've been a zoological garden of sorts.
Fine, but surely Earth was in range (since they came from here). **Why didn't they come back?** Maybe they did, several times over the aeons. The Cretaceous temperatures they liked were a lot higher, so perhaps our world was too cool for any long term habitation. More likely, the stories in troodont legend speak of Earth as a terrible cemetery world, where all life was snuffed out at the Departure. Earth is regarded with religious dread, or has simply been forgotten during the thousands of ups and downs of the long, long troodontine history. Or perhaps they DID come back and have been directing our history from the shadows for their own inscrutable reptilitan purposes.
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Most technological progress today seems to be founded on the innovation that is happening in the realm of computers. If a society were to outlaw the use of computers, but the drive for scientific progress remained the same, how might that society evolve or adapt?
Let's assume the nature of the ban is a societal taboo or religious ban, similar to the 11th Commandment in the Dune universe, which restricts the usage or creation of AI's.
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The human stance on legal proscriptions is that when anything is outlawed, then only outlaws use/do it. The more desirable the prohibited thing, the more people will be outlaws.
Unless the "laws" were such that they made people not *want* to use computing technology, people would surreptitiously be pushing at the edge of the proscriptions. Where do you draw the line between electronics (or even mechanics) and computing? How does law enforcement even recognize that a pile of components is actually a computer?
The main effect in my view would be that computers will be more primitive, and computer components would likely have other purposes that don't involve instruction processing, but a few seemingly unrelated items could be assembled into a computer.
That, however, assumes that your society is human and/or that proscriptions are things to be worked around.
It could well be that computers are simply thought to be impossible to make (or your society doesn't try to bend the rules), so no-one wastes time with them. In that case, secretaries and counting-houses (filled with abacus-using calculation personnel) will be a major part of the workforce as they were some years ago - someone needs to do all the repetitive note-writing and calculating that is now done with computers. They may not be particularly well-paid, but in those days, there was very little unemployment - even an employment shortage - finding a secretarial job was literally a matter of applying to a few companies and choosing which of the acceptances *you* would accept.
**EDIT**
In response to the question's edit that this is a-la Dune's proscription about "Not making a machine in the likeness of a human mind":
Legal machines could well involve electronics of high complexity, but the proscription would likely be on not replacing a human. Thus, humans would be required to make decisions, while the technology would make *making* the decisions easier or faster. There could still be tech creep/encroachment and bans from the relevant authorities.
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The way technological progress always occurs in such societies: either underground in secret, or in a neighboring society that winds up siphoning off the smart members of the oppressed one.
It is good to keep in mind that this is a self-correcting situation. Any society that outlaws technological progress of a particular type will find itself outmatched by one that doesn't. Bans on technology are temporary at best, because they are an attempt to outlaw *new understanding of the world*, which is the same thing as trying to outlaw certain styles of thought.
As far as computing technology in particular, a wall will be hit when the advance of any existing technology gets to the point that exponentially finer or more complex measurements and calculations become necessary to make a linear increase in quality.
So, for example, aerospace engineering today requires computers to simulate high-speed and low-speed aerodynamics on a single body. Without this capacity we would never have understood the importance of or the way to design variable shape wings for high-speed and low-speed flight.
That puts a concrete cap on certain military technologies, means you can't have high-speed and long range capabilities in the same craft, etc. and ultimately means that the practical cost to your society of fielding a military force that can compete with a society of otherwise similar capacity will be weighted drastically against you. And that's just one type of airplane.
Discovering optimal designs for submarine screws, *anything with a guidance system*, and any sort of system that compensates for human physical limitations of accuracy, etc. will be impossible beyond a very primitive level. Such a society will eventually either be wiped out by its neighbors, or overturned in a revolution from within by an underground that is vastly more advanced than the governing faction (most likely in an effort supported by a technologically superior external sponsor).
**Edit**
It is worth mentioning that the inevitable imbalance is an outcome of the outlawing of technology, and this can be the driving force behind any number of awesome stories or games. This can be a very cool plot device.
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The focus would be away from electronics. Technological advances have been made in other areas, and would have been made in another areas.
Likely purely mechanical machinery would be much more common. It's possible that some functions computers perform (particularly mathematics) could be performed without electricity (using the power of humans or animals, or water). Things would also not progress as fast, but they may still have progressed.
It's also very possible people would look for a solution to create power that wasn't electricity. Maybe things would run on very small differences in gravitational forces. Or, as this [Popular Science](http://www.popsci.com/article/science/science-bubbles) article suggested, bubbles could be used instead of electrons to store data. This could allow for purely mechanical data operations (though screens wouldn't be possible).
And likely people would have just focused on things completely different than computers. Like making good fertilizer, or focusing on how to breed different animals, or the best way to turn wood into paper. Things we work on now, but with the help of computers, would be looked at in a different way and focused on more.
The things Monty have said are also very likely possible.
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One only needs to look back to about 1950 to see science and technology advancing without using computers. In some cases, even to 1990. Books, letters, telephones, calculus, slide-rules, graph paper, physical devices, human brains, etc.
Of course, if computer technology was developed to be very useful, and *then* outlawed, there would probably be some outlaws using it.
Postscript: One can also look back thousands of years. See for example the "Antikythera Mechanism" from circa 150 BC, which is an astronomical calculator showing complex understanding of astronomical movements etc.
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Look no further than John Norman's Gor series of novels. Electricity and internal combustion are proscribed by the alien beings who control the planet, leaving society (with some exceptions, mostly in medical science) stuck at a late medieval technological level.
Sailing ships that won't venture far from shore, field armies fighting with swords and lances, bow and arrow.
Long range transportation using those sailing ships, animal drawn carts, and domesticated birds (the planet he describes has birds large enough for a man to ride them while carrying a load the weight of 10 or so other men).
There are some ambiguities, as there's a form of artificial light that's not precisely described, and some rather advanced medical technology like a serum that halts aging and leaves the recipient effectively immune to most disease.
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It depends on what kind of advancement you're looking for. Shall we consider, for example, space travel? Rockets can be designed and trajectories can be planned using math on paper. Without computers, you don't have the option to test designs using simulation, so these people would be expert model-builders, very handy with tools. They'd probably have numerous and very sophisticated wind tunnels and related tools to simulate vacuum and zero gravity. They would rely more on tinkering and trial and error than we do, and less on trying to simulate or predict performance from theory. (In silicon valley they call this "design thinking".)
The spaceships they design would likely be over-engineered: for example, carrying way more fuel than theoretically needed, because a human can't adjust a course and trigger a rocket burn as precisely as a computer. Designed to re-enter the atmosphere at a wider range of angles, because the human eye is only so precise. They would incorporate "fool proof" technologies as much as possible: for example, rather than landing upright on a landing pad like SpaceX's latest rockets, these ships would land using parachutes, be rugged enough to land on any terrain, and be designed so that the crew could lever or jack them back upright from any angle.
Basically, their machines would be less precise but more rugged and robust, so they could be adapted to situations rather than trying to predict and control them.
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This can apply to all countries but I live in America so this question specifically focuses on the American government.
How would the President prepare the nation for the news that magic is real, humans can perform magic and magic users should be accepted as an integrated part of society?
In my world, magic exists as a hidden society with leaders, laws and schools. But there are also those outside the magical society, known as hedgewitches, that may or may not know about this magical world. They live among humans and practice their magic either on a personal level or in regulated cult-like groups. There are magical police prepared to deal with abuse and bring magical justice.
Mundane perception of magic is similar to that of UFO's. There are people who swear they saw magic, but either their stories are explained away or the person is considered crazy. Stories about magic are like creepy alien or Ouija board campfire stories and are seen as scary or wonderful.
The premise involves a character who is an ambassador for magical society. He approaches the President of America (speculation on other governments welcome) to discuss a planned revelation of magical society to the rest of civilisation. Other ambassadors to other countries are simultaneously planning similar public revelations. The world leaders should do this all at the same time.
Considerations:
* What programs does the government need to set up in advance of the revelation, both private and public?
* If hints of what's going on comes out, how do they address hard questions before the event?
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First let's consider truth and how it is accepted
>
> All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
>
>
>
So your leaders of the magical world may have planned a stage approach even before approaching the presidents and the power of the world to avoid them from a violent backlash. Indeed if the magical world remained hidden, they may have been reasons like smaller number, fear of anhiliation, ... which the world leaders may decide when approached by magicians in fear or loosing their power.
One plan for preparing the world leaders would be to prepare the world population that magic might not be so impossible as considered today:
1. Create groups of as normal as possible people who claimed they believe in magic: they cannot prove it but have had first hand experience. Because they are not outliers this will create a first sense of revisiting assumptions
2. get increased visibility on the topic, starting at first with non-credible newspapers, then going up the chain to end with articles on a yearly basis on highly respected papers questionning how much we know about the world and whether magic could not actually exists
3. keep on until it becomes almost accepted magic could actually exists is a acceptable meme
4. then have press /media/ schools having themes around 'what could magic bring', 'how could a society with magic look like', ...
5. at the same time increase the level of magical sightings: at first events which classical science could explain, then events harder and harder to explain.
only when through enough of above establish diplomatic links with the powers to make them part of the next steps.
**Above all,the plan should be at least a generation long to avoid violent backlash**
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# The thing would explode
As soon as most world leaders know about it, there is no way to hold the thing secret, unless the magicians actively mind-control our world leaders (which wouldn't be a very good first impression). "Having a smooth transition" vs. "being the one to say it first" may be in question in some democratic countries. But for most dictators, it would be a no-brainer.
Then, like in the [prisoner's dilemma](https://en.wikipedia.org/wiki/Prisoner's_dilemma), not saying immediately would be pretty bad for your reelection in a democratic society.
So, I know I'm of topic, but a government would be better "as to how to handle the PR shitstorm" than "how to slowly make this happen".
Here are a few things to consider.
# Denial
Global warming, evolution, quantum physics and relativity are scientific facts with direct impacts on our technology, yet those facts are often refuted (specially in the US). A "magic exists" would give fundamentalist a reason to say to scientists "see, there is more to it than you said" and hinder belief in *any official fact*.
Public demonstrations at school, meeting with scientist in universities, TV appearance would be good. The good thing is: no tv network will be crazy enough to refuse an actual magician to show some awesome trick to the world.
# Witch-hunt
In some places, witchcraft is punishable by law. Those laws are currently not enforced much (thankfully), but they would become extremely relevant. And of course, some people would be happy those laws exists.
Specifically in America, you can see the magic as a gun. People will arm themselves and treat any kind of magic as threatening. I'm already imagining something like "the best way to stop a bad guy with magic is with a good guy with a gun".
Asking the supreme court to revoke all the witch-hunt laws would be necessary. A "magic license" and an agency dedicated to monitor all magic activities will have to happen. Think of how muslims are (in an unjustified manner) treated in the western world just because "some of them may be terrorists". Now imagine how a black or a middle-easterner with magic power would be seen.
For public purpose, you would have to say "we're looking constantly over those guys shoulder"
# Other ideas
* Public magical healings
* A magic marines squad (military are usually popular)
* Any way to "commercialize" magic
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Do you know the [Laundry](http://tvtropes.org/pmwiki/pmwiki.php/Literature/TheLaundrySeries) series by Charles Stross? His protagonist made the remark that the US is really at a disadvantage confronting eldritch horrors because of the strong Christian element of the population. Assuming the President could convince Americans that magic is real, would the witch trials start?
Assuming a mostly scientific mindset, the first step would be to **establish magic as a science**. Perhaps there would be no scientific explanation, but there might be reproducible results. With the covert backing of the government, get those results published in big-name scientific journals.
Something like
>
> OK, we had nine experimental subjects. All tried to "curse" a lab rat. Four of the lab rats died within a week. Even more remarkably, when we repeated the experiment the same four subjects managed to kill their lab rat with their "curse". This time one of the other lab rats died, too. So we took the four "witches," plus sixteen random students, and had them "curse" lab mice. This time the care and feeding of the lab animals was entrusted to colleagues from elsewhere. Again our four subjects killed their lab animals, and none of the others did.
>
>
> The probability that this is random chance is 1-to-a-gazillion. We invite our colleagues to think of an improved experimental setting to exclude other errors.
>
>
>
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Regarding the comment, a Magical Relations department would admit that relations with mages should be handled differently from relations with *other citizens*. Would a government take that step, or does a [toxic spell dump](http://tvtropes.org/pmwiki/pmwiki.php/Creator/HarryTurtledove) come under ordinary EPA regulations?
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Politically, POTUS is rarely in the position of actually enacting any regulations, and most of what they will say has been carefully vetted beforehand. At the very least, the Cabinet, West Wing staff (including speech-writers and press relations staff), and most likely the Vice President, the Majority and Minority Leaders of the Senate and the House, and possibly several other Senators who (for whatever reason) might be particularly coöperative with the President's plan, would all be consulted.
A side effect of this, generally, is that at least one of the 50+ people who need to be involved will choose to drop some “hints” to the press. More often than not, at least an outline of the President's speeches (if not a script) are released to press agencies beforehand; attending the actual press conference gives them the ability to record any deviations from the notes, ask questions, and capture the President's actual delivery (on video, for example).
Most elected governments probably operate quite similarly … particularly the Westminster system countries (most of the other former British Empire).
I would expect, rather, that the “Magic President” would be in the position of presenting their case for “normalizing relations” with the mundane world first through the media. Compare the the “Battle of New York” in the Marvel cinematic universe: the superheroes are able to be revealed to the public because they have just fended off something much scarier: the alien invasion of New York City is more frightening to the public than some guy who can turn into a big green monster, for example.
If POTUS & al are apprised of the situation in advance, they might participate in some way (eg: send out the National Guard to evacuate civilians from the impending disaster) and make the announcement shortly following public awareness.
eg: “This morning, March 25, 2016, the United States Coast Guard and the National Guard of the Commonwealth of Massachusetts were called up to assist in containing an event which threatened the population of Boston in a way not previously imagined. Our brave soldiers and sailors were assisted by help from an ally we had never before known, the *Magic People*, …”
Compare eg, the Pearl Harbor Announcement (the Infamy Speech): the public was well aware that we had been attacked, but the President's speech presented a course of action that was (uniquely) no longer subject to (most) considerations of politics and public opinion.
By (a) presenting the alliance as *fait accompli* and (b) making the “newcomers” an *ally* rather than merely *strangers*, one might hope to avoid a great deal of political wrangling.
**ps. Corrolary**
It occurs to me that a sufficiently corrupt POTUS or “Magic King” could absolutely create a false “cataclysm” to stage such an event; ie, a “false flag” event.
[Answer]
Today I approach you not as the president of the United States of America, but as a human being who believes in magic and I think it's time for us all to accept the truth that has been denied for so long. Now it's the time to rise and shout out loud : Magic is real !!! No more hiding in the dark, no more fear of rejection. I know that many of you may consider magicians as a threat to society and to everyone, but we need to give them a chance first, a chance to prove that we were wrong for too long. Now we have rules to protect mages from humans, and of course humans from mages, let's all follow those rules and live together in peace and harmony. God bless America and every place else, humans and mages.
] |
[Question]
[
**Concept: For some twisted reason, a xenocidal space-race living somewhere in our vicinity decides that nothing deserves to exist.**
---
So they make a species. Any feasible size, any kingdom.
* **It eats everything that contains organic tissue**
* **It can survive any environment that we know life exists in on earth.**
* **It itself is 100% guaranteed organic (not a virus)**
* **It follows the rules of known physics and organics**
* **The makers don't have any unobtanium**
* **They made the trip from Europa safe and sound and hungry**
* **These creatures won't leave the planet**
* **We can't eliminate them. Sorry.**
## How do you make this happen?
[Answer]
I agree with the previous answer that a possible Tardigrade type micro animal combined with bacteria could be very effective at surviving and spreading throughout the ecosystem.
A useful addition to the life destroying beast would be altered [Chirality](https://en.wikipedia.org/wiki/Chirality_(chemistry)): this is how chemicals can have alternate right or left handed arrangements.
For all Earth life most amino acids are Left handed and sugars are Right handed. If we assume this is a universal trait of life (we won't know until we find actual xeno biology to study) then having the destroyer employing altered Chirality would have several advantages. The bacteria portion of our life-form could devour current life it encounters and process it into the alternate type of amino acids and sugars. These alternate handed bio components would be inedible to all native life, but would be a feast to the invading organism allowing them to spread.
A common problem on Earth is when a organism is introduced to a new ecosystem with no existing predators, with altered chirality the new organism could have no predators. Anything trying to eat them would starve as their bodies would provide no nutrients.
[Answer]
Your answer might lie in an angrier/carnivorous version of the [Tardigrade](https://en.wikipedia.org/wiki/Tardigrade)
This microscopic creature is arguably the toughest organism to live on Earth.
Some extremes it can handle:
It can...
* Survive in ocean trenches where pressure is vast
* Survive ionizing radiation doses 100s of times greater than a human
* Survive without food for 30 years
* Survive in a vacuum ie in Space, with no oxygen and no air pressure, for 10 days
* Survive temperatures as low as a fraction of a degree above absolute zero
That seems to tick off the "Can't get rid of it" thing on your list.
Maybe a genetic hybrid between this and a flesh eating bacteria ([This one is evil.)](https://en.wikipedia.org/wiki/Necrotizing_fasciitis) could be your best bet.
EDIT:
To try and cover all bases:
* **It eats everything that contains organic tissue**
A kind of genetic hybrid (some degree of creative freedom needed because I don't think it exists/anyone wants to make it, but as my old Biochemistry lecturer said, the right equipment and enough time are all that stands between possible and impossible) of a Tardigrade and Necrotising Fasciitis would destroy everything that contains living tissue, not eat. Direct quote from the wiki:
>
> "Flesh-eating bacteria" is a misnomer, as in truth, the bacteria do not "eat" the tissue. They destroy the tissue that makes up the skin and muscle by releasing toxins (virulence factors), which include streptococcal pyogenic exotoxins.
>
>
>
While this might not cover the whole 'eating' idea you have, it will lead to the destruction of all living tissue.
* **It can survive any environment that we know life exists in on earth**
Covered this bit in original answer.
* **It itself is 100% guaranteed organic (not a virus)**
Its an organic life, just look at his wittle face.
* **It follows the rules of known physics and organics**
This one I'm not so sure of, because of the aforementioned 'creative freedom' needed to get the thing to exist, but I'm pretty certain that only 2 things would differ from the normal Tardigrate and that would be
* It would be flesh eating for a start
* Possibly up reproduction rates?
I'm not a biologist, so this is just from reading articles, but I'm really certain it would match these rules you need.
* **The makers don't have any unobtanium**
No unobtainium needed as genetic manipulation of organisms goes on a lot. This is probably just a higher level (maybe not even at that) of that area of science. Another wiki quote incoming from the Reproduction section:
>
> Research by the University of North Carolina on the genome of one species, Hypsibius dujardini, revealed that approximately one-sixth (17.5%) of the species’ genome is foreign DNA. These 6,000 genes are of primarily bacterial origin, as well as DNA from fungi, plants, and Archaea.
>
>
>
So it does seem to be amenable to sharing its cells house (nucleus) with visitors (other things DNA)
* **They made the trip from Europa safe and sound and hungry**
This is where it might get a little hurt. It can survive in a vacuum for 10 days, so if its on the outside of the ship, it probably wont make it if your travel speeds are conventional(>10 days from Europa), BUT following [THIS XKCD What-If article](https://what-if.xkcd.com/117/) a large enough initial population would allow for some to reach earth and start another colony there.
* **These creatures won't leave the planet**
They are tiny organisms. The only way they'll leave the planet is if you take them with you.
* **We can't eliminate them. Sorry.**
This is a bit difficult to imagine. We can eliminate EVERY organism with the right conditions, whether that's time or equipment. The problem shouldn't be eliminating them, but eliminating them without **killing everything else**
Hope this helps!
[Answer]
A large creature (sized like a human, tiger, or rat) would be unable to hunt down smaller lifeforms ([protozoans](https://en.wikipedia.org/wiki/Protozoa), [plankton](https://en.wikipedia.org/wiki/Zooplankton)). A smaller lifeform might be able to kill larger ones. So it has to be a small lifeform.
This lifeform would have to survive in [extreme](https://en.wikipedia.org/wiki/Extremophile) environments.
Perhaps the two could be combined. A lifeform which [non-terraforms](https://en.wikipedia.org/wiki/Terraforming) Earth similar to the [oxygenation event](https://en.wikipedia.org/wiki/Great_Oxygenation_Event).
[Answer]
What's the best way to kill all life forms you ask? **Destroying their natural habitat !**
On Earth there is balance between the herbivore and carnivore life forms. This is observed in what we call an "**Ecosystem**". An ecosystem is a community of living organisms called producers, consumers, and decomposers. Consomers cannot live without producers, decomposers cannot do their job without consomers and finally, producers need decomposers to seal the deal. (It's basically what said Antoine Lavoisier, "Nothing is lost, nothing is created, everything is transformed.")
By destoying one of the group, your creature would disrupt the ecosystem. An exemple of this is happening right now with the **Red king crab**. To quote Wikipedia on the crab :
>
> In the Barents Sea, it is an invasive species and its population is
> increasing tremendously. This is causing great concern to local
> environmentalists and local fishermen as the crab eats everything it
> comes across and is spreading very rapidly.
>
>
>
This species was introduce by men in an ecosystem where it didn't belong. In the new ecosystem, the Red king crab has no predators. It is why the crab has not been stopped.
**Conclusion** : Introducing a fast reproducing, omnivorous and resilient species would cause a lot of havoc on earth.
[Answer]
Your aliens invented humans. Who knows, we may be the result of their genetic experimentation.
>
> It eats everything that contains organic tissue
>
>
>
People in Mexico eat crickets and drink cactus water.
People in Japan eat roaches and algae.
People in China eat spiders, scorpions, centipedes and dogs.
People in the Netherlands eat horses.
People in Spain eat squid ink.
People in Russia have even eaten a defrosted mammoth.
All those are typical foods, sometimes elevated to fine cuisine. The world's most expensive food is sturgeon roe for crying out loud.
>
> It can survive any environment that we know life exists in on earth.
>
>
>
With our current technology we've been to the Marianas trench. [With not so current tech we have McGyvered into the skies](https://en.wikipedia.org/wiki/Lawnchair_Larry_flight).
>
> It itself is 100% guaranteed organic (not a virus)
>
>
>
Frame challenge. No life as we know comes even close to that.
We are mostly made of water which is inorganic, but dry a human into dust and you will find we are about 24% organic.
That said, if you meant 100% as not being a cyborg or a construct, we fit the bill.
>
> It follows the rules of known physics and organics
>
>
>
Yeah we keep trying to break them, [and so far it has been them that break us](https://darwinawards.com/).
>
> The makers don't have any unobtanium
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>
>
It's cool, we're not made of that. Nor from that.
>
> They made the trip from Europa safe and sound and hungry
>
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>
...Ok?
>
> These creatures won't leave the planet
>
>
>
Here and there you will find a human who would love if you could fly them to the moon and let them play among the stars. The majority is very emotionally attached to the specific piece of land they've been born on, though.
>
> We can't eliminate them. Sorry.
>
>
>
Humans are a hard nut to crack. We have nukes, Jesus and Chuck Norris on our side.
] |
[Question]
[
[This question](https://worldbuilding.stackexchange.com/questions/26364/no-newborns-on-earth-how-much-time-to-find-a-cure) by Andrea Jens considered a world in which a virus causes global infertility: no new children can be conceived.
Now suppose that, after 40 years of complete global infertility, a cure is found and distributed worldwide. Babies are being born once again to the youngest generation — parents who are at least forty years old.
Here are some basic assumptions we will make about this world:
* The period of global infertility lasted from 2015 to 2055.
* Consider the level of technology to be comparable to today.
* The world population at the beginning of the event was just over 7 billion. Over the 40 year period 2 billion people died “naturally” and 1 billion died as a result of local conflicts triggered by the infertility. As of 2055, the total human population is at 4 billion.
* Let us assume based on 2015 estimates that there are 600 million women in the 40-49 year old age bracket at this time (For simplicity, assume that the vast majority survived the turmoil of the infertility period).
* Most countries maintained enough order to survive. Societies have been warped by this tragedy, but the governmental structure and land boundaries remain intact.
* Throughout the period of infertility, unfertilized eggs could be frozen and stored in countries with the technology to do so. These eggs are viable for use after the cure.
With this 40 year age gap worldwide, what societal and economic changes would humanity experience as the new generation is born and matures?
[Answer]
I feel like my answer is fairly insufficient, but I've spent quite a while working on it, so I'm going to post it anyhow.
## Years 0 - 20
Essentially what we're going to see is that as time goes on, the age pyramid1 simply breaks from the ground and shifts up (still pinching at the top because of death, of course). What this means is that private organizations like daycare are the first to go in capitalistic societies, as they have no more clients. The government stops funding levels of public education that are no longer needed. The youngest students in the generation who fall behind all enter a single "remedial" class that will be the last class to be taught that material for another 40 years. Of course, society has no way of knowing that a cure will be found, but hopes it will be, so each government creates a standard curriculum (if it doesn't already have one) and stores it somewhere safe so that it can be accessed if needed by future teachers. Universities eventually go out of business and must sell/re-purpose their land.
## Years 20 - 40
Eventually when generation Ω (omega) reaches the age to be employable, there starts to be a problem. Social Security is funded by the young for the old, so with an impending drop-off of SS funds, the government reduces benefits and/or increases the required age, causing older people to work longer. Because there is a decrease in workers, there's an increase in wages. However, there would also be a huge decrease in the average household expenditure, as Americans spend about $34,000 annually on their children2. These two forces may even out to create an economy that is similar to our own, except that there is little to no market for child-oriented things like Capri-Sun, Teletubbies, or DisneyLand. Also, the elimination of an unwanted pregnancy only adds to the normality of casual sexual encounters. In general, people have the idea that the world is ending really slowly, so there are more mid-life crises and crime. Because of the scarcity of youth it is valued exorbitantly.
## Years 40 - 60
Eventually scientists discover the cure to infertility and generation Ω starts making babies. Of course, there is a huge government campaign focused on encouraging couples to have children if they can. Children are highly prized and seen more than ever as those who will inherit the Earth. The last people to have taught elementary-aged children are at least 60 at this point, but they brush off the curriculum which was stored away and use it to instruct the next generation while other teachers from generation Ω are being trained. By the time generation A (alpha) is ready for a college education, public universities (which were hopefully re-purposed rather than sold) have been converted back to places of learning. Essentially no one who was ever actually a college professor is teaching there now, though, because they're all at least 90 at this point. Come to think of it, even generation Ω is at least 60 by now. Generation A has grown up with elderly people and has only ever seen young people in old media, but it understands how highly youth is valued.
Child-oriented businesses have the potential to start up again, although many trade secrets and experience would be lost by those who had died without passing on their knowledge. There would be a gradual relearning of how to do everything, but overall once the first few years of generation A (which would have an enormous population, by the way) had passed people would generally know what they were doing in the industry.
## Years 60 - 80
Because of all the propaganda, young people are encouraged to have children, but not at culturally unusual ages. Everyone understands that the virus has been cured and so there's no need to risk birth defects by having children at a young age, especially when generation A thinks about how their parents were 40 when they had them. Having a child so young would just seem weird. Nonetheless, parents would get antsy and encourage having children in the early 20's. Children would still be highly valued, and grandparents would have an active, but not too active role (with the lack of SS, they don't have as much free time as they would have had they been retired).
## Years 80 - 100
At this point generation Ω is in their 80's, and generation A is in their 30-40's. They have been learning what they can from their parent's generation, because they know that they will soon be the youngest oldest people alive in centuries. Because there had been such an age gap between the two generations, generation A had never really been quite as mature as generation Ω. For the first time, members of generation A are the CEO's of companies and heads of governments. They aren't continually viewed as immature by older members of society anymore. Members of generation A begin to disrespect generation Ω as they were old, weak, and grumpy, and often require assistance that keeps generation A from what they would have rather been doing with their time and money. The gap in the labor force (ages 40 - 80) would likely be the worst yet. Previously, the elderly were able to keep working in order to keep the economy going, but now only those aged 20 - 40 are supporting those aged 0 - 20 and those 80+. At this point (or perhaps a bit sooner) we can expect there to be a general consensus to euthanize many elderly people as they are a burden that society can't support. (Another possibility is that younger people have to work from an earlier age, but I don't see this youth-worshiping culture encouraging that)
## Years 100 - 120
Generation A is now entering what we would consider retirement age, and as there are no (few?) individuals older than generation A to support, there may be talk of reinstating SS. However, worries about its sustainability and the recent history that even generation A's parents worked until they were 80 keeps the retirement age elevated. Society as a whole seems more or less to have recovered at this stage.
## TL;DR: We finally lose Social Security
Sources:
1: [Population Pyramid](http://populationpyramid.net/world/2045/)
2: [Cost of Child](http://www.usda.gov/wps/portal/usda/usdahomecontentidonly=true&contentid=2014/08/0179.xml)
[Answer]
Well, for one thing child rearing would become a much greater priority in our societies. Laws would be passed to encourage women to have children as quickly as possible. Single mothers would be given more financial support. Corporate practices which discriminate, even slightly, against women because of their fertility, would be pounced on as damaging to our society.
The entire education system would have to be revived. What happened to it in the interim years? Was it dismantled, since there were no children to teach? Or was society willing to pay to keep it up even if it wasn't providing value? If the former, it will have to be reinvented from the ground up.
Parents too old to bear children might be called into service to help raise them, so that those young enough to bear could have larger families. Couples too old to bear children could still raise them, so adoptions would be encouraged. The taboo against "paying" for children might be bent or even removed. Foreign adoptions would increase as fertile females in basement economic brackets see their fertility as a way to bear themselves out of abject poverty. Immigration laws would invite fertile females to make this move, and the countries they came from would try to keep them from leaving.
Nations which did not enact stronger laws protecting their women would find themselves shrinking. Note that this does not necessarily lead to good things for women, because women can be enslaved and turned into baby bearing machines "for the good of the country/state/whatever organization".
Babies may become a commodity. Child abductions may rise.
The first decade of the "post fertility cure" will have many middle aged women bearing children. "Use it before you lose it" becomes the slogan. This will lead to a high number of age related birth defects. This may lead to an emotional reaction against them. Women who don't get tested so they can abort any defective children will be considered irresponsible, or worse. Fertile wombs are a scarce resource and shouldn't be wasted on a child who is not going to be an asset to society. Unscrupulous nations may take "defective" children away from their parents and raise them to be "wombs for the nation", implanting them with fertilized eggs from "normal" parents.
Ten years later, another "dry spell" as the older women go into menopause and the world waits for the younger ones to grow up. Many countries may try to "force babies on the babies". Countries where children are married and give birth at a very young age will have an advantage over those where maturity is expected to happen later.
In any case, when the children of the "first regeneration" become old enough to be fertile, they will be encouraged to start having babies as soon as possible. By this time a strong societal acceptance for having younger women bear the children and older ones raise them will be in place. It may become a custom that children are most often raised by their grandparents.
Unwed teenage mothers will become society's "heroes" instead of its pariahs, as long as they realize their jobs is to have babies, not to raise them. "Your turn will come" becomes the slogan, featuring pictures of a happy middle aged couple being handed a baby by a proudly beaming teenaged mother, who then races off to her life of partying.
Society may also become paranoid about losing its fertility. Younger girls may be pressured to prove their fertility early. It happened once, after all. "Testing" young girls' fertility may be seen as an early warning system. A lot of what happens along those lines would depend on what caused the infertility in the first place. Was it man-made? And if so, was it deliberate or accidental? A natural disaster? Or do they simply not know what caused it?
--- further thoughts on children becoming a commodity / abductions ----
Nations will want to rebuilt their population as quickly as possible (lending a new meaning to the term "arms race"). Even though society hasn't completely disintegrated, the huge population decrease has left everyone vulnerable. What segments of society do you pluck from to plump up the others? What is your priority? Send people into the military or use them to educate the young? Nations run on their economies; who will work for the businesses that pay corporate taxes? Do we train people to build bridges and infrastructure, or to work on our electronic defenses? We can no longer have it all. hard choices must be made.
Or do they?
Nations with less scruples can find a way to game the system. Why pay all that money to raise and educate when you can purchase older children? Concentrate on your military and then you can pluck your neighbors, thereby having the best of both. Nations may specialize; imagine a country who acts as an educator and child raiser while being protected by the military of the nations whom they supply with trained workers. And smaller nations (Japan, perhaps) would concentrate on areas that require specialized training but not great numbers (the best hackers and anti-hackers in the world). Everyone knows that if you want the best programmers and analysts, you send your kids to the Nippon University of Electronics.
Once a child has been taken out of a country and provided with new identification it would be very difficult to locate that child without the help of the authorities. Of course, an obviously white baby in the hands of a black couple in Africa would be hard to hide, but consider how easy it would be to conceal a child stolen from black Americans or Asian Americans and transported to a country where their ethnicity is dominant. Or to conceal a child stolen from Africans and adopted by African Americans. Not to mention how easy it is to steal from your neighbors with the same ethnicity.
Then, imagine a wealthy man, woman or couple, too old to bear their own children and unable, for whatever reason, to adopt, or at least unable to adopt exactly the child they want. They have plenty of money and reason "we have so much money that any child would be better off with us than with someone poorer". Potential for abduction there. Wherever there is money there will be people eager to supply.
Then there are the baby makers. A new profession that grows up and flourishes in less developed countries willing to look the other way, as long as the profits are shared. Abduction would be an obvious supplement to the income that they get from selling babies. And for those worried about getting "caught" because of genetic testing, the children who are abducted could be used as "breeders" instead of being sold outright. Genetics could still connect them to a particular family but it couldn't be proved how those genetics got here.
These babymakers might pour money into genetic mapping and research so as to develop a menu for potential buyers. "Made to order" children with a carefully chosen set of genetic markers. Many of them might develop a very long range marketing strategy.
[Answer]
You do make a lot of assumptions. And the first analogy that came to mind was the US "baby boom" post-World War II. So, initially it seemed to me that the new-era babies would blossom into a huge group to be reckoned with...
However, there are some stark differences that I think the other answers overlook.
First, once re-birthing begins, infant mortality and child-rearing women mortality rates would likely be much higher than present day. Although the technology might exist, the last doctors to birth babies would be at least 65 years old AND 40 years out of practice. You may have nurses or other medical care givers that are as young as 60 that would also be valuable, but nearly anyone yonger than that would have little first-hand knowledge of good child-birthing practices. It is easy to imagine a lot of economic resources dedicated to those efforts, inefficiently for at least a 5-10 years.
Next, the maternal mortality rate is much higher for women in there 40's and very little is currently known about women in their 50's. But assuming the first group of "young" women to get pregnant (40-44) have mortality rates similar to developing nations today - they have about a 1% chance of death during childbirth. For older women it gets much higher, much faster. Additionally, it seems that 600 million cohort of "young women" could only produce, reasonably, 2-3 children before the risk of death becomes very high. By the time medical practitioners "remember" good birthing techniques, most of these women will be too old to endure child birth at all.
So, after about 10-15 years the very youngest of the "older" people would no longer be able to bear children. The very oldest of the "young" generation would barely be old enough to begin reproducing. With the population of the earth continuing to decline, the concentration of wealth focused on this group would probably create some very weird new "rules" - like having kids while still in school and being spoiled by the older generations. But for at least another 10 years, population decline would continue fairly rapidly.
As during this time, there would be a huge boom in child-rearing goods and services. Based on the assumptions, the economic "bust" of the industry 40 years prior was in some way "absorbed" into the economy. However, this boom would come with huge amounts of wealth dedicated to protecting, teaching and entertaining this new generation. Other areas of the economy would certainly feel the drain of resources, creating booms and busts for a few decades for sure.
Then as the "young" generation began reaching child bearing ages in large numbers, there would be a very large group of older care-givers available, creating a society where it might become expected that you have a "community child" - care for the child is shared among the older generation, and the younger generation can continue to not have responsibilities for child rearing, dedicate themselves to careers and/or self-indulgence, etc. Getting pregnant and procreation could easily become a priority over marital bonding, since childcare would no longer hinge primarily on the parents of the children.
This "echo" generation of babies from the first young generation would see the last of the older generation die off and not enjoy nearly the same conveniences of their young parents. And these young parents would likely retain little about the energy, effort and cost it takes to raise children. They also would still be building careers and enjoying a significant amount of wealth coming into their possession as the older generation died off.
This would create a huge generation gap, along with the wealth gap and general dislodging of a great many of our current social and moral norms (pregnancy would be a priority after all...), and would lead to a much greater revolution than the post WWII baby boom in the US. In the US during the 60's and 70's, as those young children came of age, the world changed.
In the case of a 40 year infertility period followed by two "baby booms" and a nearly extinct older generation, the revolution would likely be significant enough as to reshape whatever geo-political boundaries had endured during the period of infertility.
It seems to me that a entirely new religious and political system would arise as these waves of young people entered a world where they did not have to endure the the struggle to survive in any normal capacity compared to the rest of the evolution of humankind, and after a long period of fear that the human race would reach an abrupt and quiet end of existence. There is little reason to believe it would look anything like our society does today - especially because of all of the value we place on personal historical lessons that would be long forgotten and devalued by the new generation (the "when I was a kid, I had to walk up hill to school both ways... in the snow!" type of lessons.)
[Answer]
@Avernium as virtualg33k said, Children of Men is a movie about this very concept. If you want to see what kind of dystopia would result,watching that movie is a solid start. For there is no guarantee we ever find a cure,but what is known is that as it stands there will be no legacy.
With no children being born beyond still births,the world is going to fall into a state of shock and then mourning. Imagine knowing there will be no new children,no one to pass the torch onto. That all the human's on Earth now,at this very moment are the last one's there will ever be. People would see it,very realistically,as the death of our (humanity's) future. And with it the death of hope.
People would turn to science, to god, and to one another for answers. Suddenly life would become about the here and now,for nothing good awaits us anymore. When human life becomes very visibly finite to everyone,people get pushed over the edge.
Wars would be fought,law and order would break down,and people would rip apart the world in a desperate rage to find answers. But most of them would just end up ripping apart one another. Depression,apathy and nihilism would grow more and more prevalent.
The death toll would only climb,with no new births it would become only a matter of time. In 2015 the Earth had an estimated 7.2 billion people alive on it.
Every year 55.3 million people die. If you multiply that by 40 you get the incredibly harrowing number of two billion two hundred and twelve million people dead in that 40 year period.
That is under the generous assumption where nothing particularly bad happens. Under the threats of violence war would be fought,the last brutal conflicts of mankind being fought over resources and out of hatred and spite. As people decide to determine the fates of others so as to be the last one's standing at the end.
Nations would go to war out of fear that another nation could completely erase them. There's no new generation coming,to the vast majority of humanity they will be thinking "This is it. We're all that there is ever going to be."
Youth would be highly prized,far more than it is today. People would try to cater to the changing needs of the populace. Pets would become more common,becoming the surrogate for the children that will never come. Lifelike dolls that mimic the sounds and warmth of a baby would be sold. And the value of human life would actually end up decreasing.
It would be an extinction event,one we'd be very lucky to survive. After all,if the only prospective mothers and fathers are in their forties at best by the time of the cures discovery;the odds of having children successfully will still be painfully low.
And after all of that,these children would need to be raised on a planet where 40 years of fear,hatred,nihilism,rampant crime and war decimated the world. It would be strange to have hope again.
The people with the cure had better be careful,for people with try to use it as a tool. The first children and everything else would be tools for the most ruthless age of humans to have been essentially. It'd be a painful rebirth,but perhaps like the phoenix we would rise from the ashes.
If you take away the past,you will still always have a tomorrow. But if you take away tomorrow,you will become the past.
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What are realistic time-schedule expectations for far-future terraforming and developing earth-like plant and animal/fish/bird populations on distant planets, by means of robotic space probes with "seed" technology such as bacteria that converts atmosphere, seeds, bionegineered eggs, etc.?
The idea is that robot probes would be sent to distant star systems with equipment to analyze local planets and asteroids, set up automated production of bacteria and/or fungus to drop onto the best planets, designed to be able to survive and convert local materials into a biosphere, and later to drop other bacteria, fungus, then seeds and eventually eggs for insects, fish, birds, and even animals.
The question is, assuming it's conceivably possible to develop this technology given enough time and resources, how long might it take to advance a lifeless alien planet with otherwise earth-like properties (i.e. .7 to 1.5 earth mass, some existing atmosphere, magnetic field, not utterly frozen nor too hot) to the next stages such as:
1. Atmosphere that can support more than bacterial life. This would obviously be highly-dependent on the starting atmosphere and materials available, but in general, how fast might this be doable by dropping purposely-chosen bacteria onto a planet?
2. Some earth plants/insects can survive somewhere on the planet.
3. Some earth fish/animals can survive somewhere on the planet.
4. Most earth animals/humans can survive on the planet.
For each level, would it take decades? Centuries? Millennia?
**Background information:**
* Time/setting: Up to 20,000 years in the future, following optimistic peaceful resolution of current self-destructive stupidity on Earth.
* Technology: Realistic extrapolations of modern science. There may or may not be FTL technology, but it is limited - distances are still an issue and it requires significant time and resources to travel to other star systems.
* Space program: Space stations with large permanent human populations, "domed" planetary colonies, and various space industries have been developed. Some colonization of other star systems has occurred.
Related idea from an answer by Black to a question about terraforming:
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> It would be nice to have biomass on a planet before you got there. As well as any target byproducts you might engineer them to make. I'd add that Deinococcus radiodurans can survive anywhere you can't engineer other bacteria to. So you're pretty much guaranteed to be able to just launch a can across the universe at any planet, even if you can't quite fly to it yet. If your lucky the locals may have evolved before you got there and be able to contribute to science with their "un-poisoned" paradigms. (Panspermia anyone?)
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> Cort said: it took us 3.5 billion years to go from single-celled creatures to land plants. That would be the upper bound on this process.
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Which is not precisely true. It is *one* upper-bound on *evolving* a solution. ie: one data point. It may take a lot longer than that if you want to evolve solutions; perhaps Earth is on the fastest of all possible evolutionary paths.
Anyways, the point is: you're not evolving anything. You're taking already evolved solutions, and selectively inserting them.
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> Dronz said: with imported/engineered microbes pre-developed on Earth, might be much faster than what evolved naturally out of the primordial ooze.
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Precisely.
You're probably going to want to start with some monitoring. Did the planet you select already have life? You'd said you wouldn't know what you've got until you get there - it might be considered a hostile act to come in with an automated probe and try converting someone else's planet :) Besides the ethical considerations of eliminating life that's evolving itself (depends on your society's ethical constraints).
You'd probably want at least a decade to see what types of climate variations you're going to get from orbital perturbations, as well as a study of the star - some of the star's output can be analyzed from afar, but some may need in system analysis. This may determine what life you want to seed to moderate effects that exist in your system. You *might* be able to skip this, and play catch-up when you get surprised by events. But that will lead to increased failure rates.
I'd give it a century of study, if you've got time to burn.
The biggest thing, besides being in the habitable zone, having roughly Earth-like mass, and a carbon-dioxide atmosphere, is having enough liquid water.
Liquid water is going to get you a chance to get your autotrophs and cyanobacteria started. Which will start getting you organics from inorganics and an oxygen-based atmosphere. Once you got those started, introducing something with chloroplasts (algae most likely) is going to be the big thing - you want your Great Oxygenation Event to happen ASAP. Time-scale on that is unknown, and may depend on conditions. But you're going to want your autotrophs to have had some time to work. How many are you seeding initially? Are you setting up reactors to make tons of them in orbit? Or just injecting a nanoliter (microliter?, milliliter?, liter?) worth of them in selected spots (how many spots?).
Turning over your atmosphere into the ocean to get the CO2 out and O2 in, is going to be a thing. It's a pretty complex field of study. One key driver is do you have polar ice caps (or, can you make them?)? That drives thermohaline circulation, and will take a ton of CO2 into the ocean (although with a primarily CO2 atmosphere, the ocean may already be saturated...). Iron is a limiting nutrient, and if you've got the tech, pulverizing nickel-iron asteroids and drifting the dust down on the oceans (or dispersing from flyers) may greatly speed up your algae/oxygen production.
<http://benmatthews.eu/benphd/chap1.html> For a lot of info on Earth's exchange, ie: not exactly what we're talking about - but we do 92 GtC in and 90 GtC out in our oceans.
Once you've got the ocean / atmosphere work started, you're going to want to start on the land-mass. Cyanolichens and lichens are what you want to start breaking down rock to get soil, and to put the organics into your starter level soil. You can be dumping these on any rocks. No dams necessary. In fact, without plants respiring, you may not have a lot of freshwater to be working with, once you get inland.
At phases in here, you're going to have to choose some types of lifeforms to manage cloud seeding / cloud-cover and albedo. You're going to need some satellite coverage and computer monitoring to figure this out. This is going to require some pretty robust computer programming, or a human that's in and out of stasis once a year/decade. I'm assuming you're not sending humans, since the cheapest way to do this is to send something the size of a football with DNA codes a fabricator, and some expandable vats (it'll collect shielding in-system, to
protect from flares/gamma rays).
This is about as far as you can (easily) go with a football. Your probe would have to be able to vastly expand itself in order to make tons of seed, and/or animal life. You might be able to store some insect life, and micro-shrimp / fish eggs - but you're probably looking at something more the size of a room - and you could easily fail the insects and fish if you are carrying too few eggs. Your first set(s) may be put down too early, and all fail because of not enough supporting substrate. Any time you drop eggs, expect to lose some of the drops because of errors / bad placement. You can take plant seeds with you, but like the animals, you'll have a tough time taking enough to make a big dent soon. Best bet is to set up an automated farm in orbit and harvest seed. This is going to make your probe a *lot* more complex.
Anyways, once you get some organics in the soil, then you're going to want to go with some plants. A lot of seeds, and little return to start with. You'll want stuff that handles aridity and low-to-no soil. Once you've given that some time to work, and maybe get a freshwater cycle setup, then you can think about insects and other stuff.
You can probably have seeded the ocean with fishes prior to this.
If you've got fishes, you can move rapidly up to birds and mammals which hunt fishes, and some herbivores. Landing those from orbit is going to be a trick. A lot of the other stuff can be dropped with a heat-shield / cooling apparatus and a micro-chute, and let it bounce. A mammal or a bird, not so much. Training your bird to fly in orbit... also tricky. You're not going to drop bird eggs, unless you're also dropping incubators. You may need robot mothers to teach some skills.
Scifi: [*The Forgotten Planet*](http://www.baenebooks.com/10.1125/Baen/0743471628/0743471628___0.htm) is a story of terraforming gone awry.
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It is very much a function of the state of the planet on arrival, how ample a power supply you have to start and the degree to which your robots are capable of advanced nanotechnology. I'll assume you have both water-based oceans in your world and artificial controlled nanotech, it'd be a rather hopeless endeavor without (relying on biological nanotech, aka microbes, would take hundreds of thousands to millions of years).
1. State of the planet.
* Atmosphere: The mass of a Venusian atmosphere is about $5\times10^{20}kg$, while Earth's is around a hundred times lighter at $5\times10^{18}kg$, and Mars' is about 200 times lighter than that at $2.5\times10^{16}kg$. If you want unadapted humans to live on the surface you may need to flare out or to bring in substantial amounts of volatiles. Needless to say, flaring out is hard, and enriching depends on how much volatiles you can find in the local asteroid belts and outer (Oort-style) frozen outskirts. Obviously, either would require a massive industrial enterprise orders of magnitude higher than anything mankind has done up to now. For comparison, 150 years of industrial activities have changed Earth's atmosphere by altering the ratios of gases to the order of perhaps 200 parts per million, aka "trace amounts." And that's with our industry burning oil and coal literally as fast as we can get it out of the earth. Depending on the initial composition, you'd literally need a process literally 10,000 times more intensive than Earth's current combined industrial activity.
* Soil. Let's assume a similar land area of ~$100,000,000 km^2$, and that we need to process a 10 meter layer (although runoff into the ocean would realistically be a problem). At $10^{15}m^3 \times 2\times10^3kg/m^3$, that's about the same amount of mass at the atmosphere.
* Life. With sufficiently advanced nanotech, life forms can be manufactured and seeded into the soil as part of the regular soil processing. However, the process will likely be rather, um, energetic, and thus more likely to leave an organic ash behind rather than the kind of soil we're used to. Perhaps a second set of processor can follow the first wave and use giant vats of bacterial and viral soup to seed the soil in their wake. Life is about 10^12 kg, so many orders of magnitude less. Delicate second wave nanobot constructors will do.
2. Power supply.
* Obviously, if Humanity's footprint on our own atmosphere over a century amounts to trace amount modification, the process might seem a tad daunting. Fear not, the power of exponential growth will ride to the rescue. Over the past century, the cilivizations at the edge of the technological boom (i.e not playing catchup and simply copying preexisting tech) have grown at around 2-5% per year.
* Let's assume you want to pull this off in a century or two. If we take the 4% as median and extrapolate out (assuming no dark ages in the future, it is a conservative assumption, given probable orders of magnitude increases given currently imaginable AGI and nanotech molecular-time manufacturing capacities), we get (post-?)humanity to output roughly the production amount needed to pull this off in a few centuries in, um, about 2.5 centuries from today.
* Of course, Humanity being what it is, it is unlikely that we'll get to the point where a full year's worth of production can be invested into manufacturing probes and supplies for colonizing a new world. We'll be busy fighting each other, [turning planets into paperclips](http://wiki.lesswrong.com/wiki/Paperclip_maximizer), drilling into Heaven, whatever. Let's bring it down a notch or two. The Apollo missions were a significant expense, and when they were launched, they output so much energy that it amounted to about 2 seconds' worth of Humanity's entire energy output that year. So, if we keep assuming 4% exponential growth, humanity's output will be high enough for a terraforming to be equivalent to the Apollo program in about 700 year, circa 2,700 AD (or 750 [Epoch time](http://en.wikipedia.org/wiki/Unix_time))
That said, planets, with their deep gravity wells are far from optimal real estate for a space faring civilization. Mining asteroids and harvesting volatile from the satellites of gas giants seems a lot easier in terms of the energy-in energy out ratio.
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The answer is very dependent on how Earth-like the planet is. Evolution works at evolution's pace, so if the bacteria and fungi need to adapt, they may need a few million or billion years.
Let's assume you find Earth 2.0 (Like in *Hithchiker's Guide to the Galaxy*), so no evolution is needed, just the mere act of bacteria and fungi "doing their thing."
The first hard thing is going to be balance. At every step of the way, you are going to need to balance the ecosystem. A completely empty world is going to reward the most aggressively multiplying organisms. Our modern ecosystem is very dependent on this balance: life will survive once you seed it, but it may be hard to introduce higher life like plants and humans if the balance is substantially different.
Your goal would be to critically damp all multiplication, a differential equations term which seeks to achieve stability in the shortest time constants. You would have to constantly seed different organisms to "favor" one over another in a short run to yield balance in the long run.
**Once there is soil, we have documented evidence of low long it takes: centuries.** Modern naturalism has found that a forest can reboot itself after a *massive* fire within a few linfetimes. There is a well understood process for it: grasses come first, then ferns, then short trees, then tall trees. This part of nature is amazingly robust!
However, it needs soil. Your Earth will be a mass of sand and rock. This is not an easy landscape. No nitrogen fixing bacteria or anything. Massive erosion issues. Depending on the landscape, you may need a long time to fix this: **it took us 3.5 billion years to go from single-celled creatures to land plants. That would be the upper bound on this process.**
Now, to give you a time-domain that isn't horribly pessimistic like that (3.5billion years + 100 years!), I'd like to point out that your planet already has one complex creation on it:
Your robots
While you may not have "living" robots, they certainly can help seed life. If your robots seek to accomplish a fixed plan, written into their code before they were launched, they could seek to replicate on the surface of the planet, digging into the rocks to mine the reosurces they need.
Once you have a large volume of controlled power to wield, you can help the organisms along. You can do in minutes what takes centuries of erosion and bacterial activity to pulverize. You can construct artificial dams (like the straw ones we use to control drainage) to keep the soil where it needs to be until the organisms can lock it down themselves.
With this capability, you bring the task into the timeline of land-reclamation, a human-lead activity that is on the time period of decades or centuries.
**Accordingly with an *almost but not quite* Von Neuman probe replicating to help the organisms along, it would take centuries to terraform a planet.**
Interestingly enough, this blending of life and machine is not unique to this problem. Modern day Chess programs have finally reached the point where they crush every human player out there. A laptop is more than enough to beat a top-tier grandmaster. However, combined solutions: a human with a laptop, are so much stronger than either a computer or a human, that the combined forces are explicitly forbidden at almost every level of competition.
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Given soil and an earthlike planet to start, some things would be more rapid. If you have to break rocks to get the soil, then you need things to break rocks, and that takes as long as it takes. You could likely start with a small area and a dome, then expand it from there. Best would probably be to have a sleeper colony with a few people awake from time to time to keep things on track, and just let the machines work. You should be able to gather materials from the planet to keep things going while you're making soil, and spreading things from there. From one spot would take quite a while, but multiple spots..?
To limit moral quandaries, let's assume no native life exists here. Factories could exist to simply make air until the plants get themselves to that point. Balancing things shouldn't take that long, given that we have an example of a system that works already. Some tweaking to keep up with random mutations and the new planet's paradigm would certainly be necessary, but not an impassible ( :) ) problem.
Once a spot is cleared for living, things would progress a bit more rapidly, as there would be people to assist and push things along. Not just the once-a-year nudges, but actual innovation. What that would do to any social structure existing could be interesting, too.
I don't think it would take that long to get to 'inhabitable' status, but it depends on a lot of givens: Soil, atmosphere, gravity, temperature, radiations, etc. Adjustments to all of these would be important, and could easily change the nature of the planet/story/game/etc. Going to science fiction here, a type of radiation that makes it easier for plants to grow, but hinders/changes the development of animals, insects, etc. would cut down on the time needed, and change the balance for itself.
Thank you to everyone who answered.
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**Probably in the order of a billion years, but possibly tens of millions**
The problem you have is that there are massive inorganic sinks that will absorb oxygen before you can produce a stable, life-friendly, planet. On Earth, Oxygen production proceeded for somewhere around 1.6 billion years before the atmospheric Oxygen rose to habitable levels (see the [Great Oxygenation Event](https://en.wikipedia.org/wiki/Great_Oxygenation_Event)), and this scale of time is likely to be required for your planet.
It is possible that this could be dramatically shortened by adopting genetic engineering methods, providing nutrient sources, and carefully selecting the strains of bacteria used but I find it unlikely that you could produce oxygen fast enough to produce habitable conditions faster than the tens of millions.
Terrestrial plants will make oxygen, but they are unable to survive in an atmosphere without oxygen so could not be deployed until late in the process, so you would be reliant on bacteria. To get faster results you would need to adopt heavy industrial processes, not rely on simply seeding with organic life.
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Building from [this](https://worldbuilding.stackexchange.com/questions/3714/how-would-an-aquatic-civilisation-forge-tools) and [this](https://worldbuilding.stackexchange.com/questions/3722/how-would-an-aquatic-race-develop-computers), given an aquatic civilization somehow manages to forge tools and build computers, could it build space-faring devices?
Also another development that would come earlier (if at all) would be satellites. Could the civilistaion somehow manage to build, launch, and operate satellites? There are three main points to this, as the question states:
1. Build: Given that the civilisation has managed to build tools and computers, it should be pretty straight forward to actually build the satellite. (Correct me if I'm wrong)
2. Launch: Since the civilisation is an underwater one, how, if in any way, would they launch the satellite into space?
3. Operate: This is the most basic question, since they wouldn't build the satellite if they can't use it/don't need it. Could they somehow find a way to transmit signals deep underwater? (If it isn't already possible)
(Tell me if I've missed something else that should have been there.)
Also, regardless of whether they need/don't need satellites, could they build and operate a spaceship? I think the same points given above should apply to this, except one addition being how would they control/run the spaceship once they are inside, since they have to be in water all the time?
The species doesn't necessarily have a definite physical configuration (hands, legs, etc) so don't let that limit your answers, however, do mention any special requirements.
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Once you reach a certain technological level the water is not a barrier and they would have no problems developing tech to our level and beyond. Most likely the craft would be developed underwater and then lifted up out of the water to launch, although even that is not required as they could either launch underwater or even construct it above water using remote control.
The controls and technology would all be adapted for underwater use in order to reach that technological level in the first place so there would be no problems there.
Your main downside is that water is heavy. A cubic meter of water weighs a tonne so carrying enough water for a decently sized living area would both be heavy to launch and make maneuvering harder once launched. They would be far more used to living and acting in a 3 dimensional zero gravity environment than humans, although the odd effects of orbital dynamics would still not be intuitive to them.
The following quote from Lary Nivens Smoke Ring series covers that:
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I would say it is fair to say that going from aquatic to aerial is a comparable change in environment to our change from aerial to space. If you're assuming a level of technology comparable to what we used to send something into space, it seems reasonable that that level of tech would be enough to breach the surface of the water and fly in the air. If you can fly in the air, now its exactly the same sized leap to get into space!
And to point out Pavel Janieck's comment: we do indeed launch nuclear missiles from underwater, so the technology is absolutely feasible.
The real question might be **why**? What psychological or social forces would you like to see in your world that would cause someone to look to the stars (especaily when you usually can't see the stars from underwater).
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I will focus my answer on actually operating a spaceship. With the caveat that your creature is not some enormous whale but something more average human sized.
I think your initial assumption that this underwater creature would need to swim while they were in their spaceship is causing you unneeded issues. There are 2 properties that an underwater creature would need to simulate to live outside of the water: hydration and respiration. Once these are simulated your creature would be able to live in some kind of gaseous environment, which would drastically lower the mass costs to escape their planet. Now that a need for a water environment is removed from your space ship the issues your creatures face are no different than humans.
Hydration. Your creature would need to make sure that they wore some kind of "wet suit" that prevented them drying out in their non-water environment. This does not have any need to be a "space suit" just a thin layer analogous to human clothing.
Respiration. This could be a re-breather apparatus that would oxygenate a small amount of water that the creature would then breathe. If designed in combination with the atmospheric mix in the craft the re-breather could actually use the oxygen in the air to oxygenate the breathing water.
Once these properties are simulated the issue faced by your creatures operating a modern spaceship should be fairly similar to the issues human currently face.
There are even some advantages that your creatures would have in space. One of these would be that they would not need to build up the same type of gravity simulation as humans. Based on the inherent buoyancy of water the creatures would be much more at home in a micro-gravity environment. They might even skip populating the dry land and move straight to space.
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Seems to me, launch would be easy, either water pressure or oxygen, taken from H2O and pressurized could launch it out of the water, at which point rocket engines could take over. Much the same as present submarine based missiles work.
Transmission, surface to underwater could be done the same as now.
This, of course, is based on your requisite that they have already developed tools and computers, which of necessity would have conquered the barrier of electronic transmissions.
And I suppose that if we can maintain an artificial oxygen and pressure for astronauts today, the same could be done for an artificial water based atmosphere in regards to space travel.
The relative weight of water has been mentioned, but in that regard, would an aquatic planet have the same gravity as earth has? Weight might be irrelevant in lower g's, therefore the energy required to launch might be similar or less.
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I would say *no*. One reason is that [this question](https://worldbuilding.stackexchange.com/questions/3714/how-would-an-aquatic-civilisation-forge-tools) on which you build doesn't have a definitive answer that an aquatic civilization *can* build tools. Even if they could, it's an unimaginable step from that to vacuum tubes and wiring being developed underwater. It would have to be an entirely different invention with an incomprehensible evolution.
But say they did.
If any means of acceleration to attain escape velocity of a spacecraft involved burning fuel, then it can't work, because most fuels need oxygen. Missiles that fly through the air use either rocket engines or jet engines, but neither of these work well underwater. Torpedoes move underwater, but they have either a a battery powered propeller or use a fuel with it's own oxidizer. There is zero chance that a ship driven by propeller can attain escape velocity. It would need to switch to O2 burning fuel, which is hard to imagine being developed by an aquatic civilization.
Given an aquatic civilization, it is more likely that they would find atmosphere a hostile environment to be explored in a limited capacity. If there was land, however, it's possible that they could adapt to some degree and develop the means to access the technology needed for space flight. But then they would no longer be an aquatic-only civilization.
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So, you already have a lot of good answers which I agree with.
If the race is technologically advanced enough & they have the desire, they will have the capability. Not directly mentioned but spaceX has launched a number of it's rockets from a ship on the ocean... Launching from the equatorial region of a planet generally provides a shorter distance from the 'surface' to orbit, even from the ocean.
So here's the part that I thought I might be able to provide additional value.
There would be no need to provide a hull full of water to allow individuals to survive in the atmosphere or in orbit. Simply create space suits (or an equivalent) which are filled with water. Design the interior of the ship so it would be relatively easy for the individuals to move around (likely providing no large open areas, but instead a network of halls which the suits could be propelled through by use of mechanical or electromagnetic mechanisms).
NOTE: for the reason for the race to explore space. Once they discover and are able to explore the atmosphere, they will be at a reasonably advanced technology level. The next & most exciting discoveries would be astronomy & astrophysics. Which may be enough to motivate them to explore outside the atmosphere, (think about the general level of interest and excitement the space race generated, once we realized it was possible to shoot humans into space, now consider the general interest and excitement astronomy has engendered for the previous centuries & combine both into a short period of time with a high degree of technical capability & scientific understanding).
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Space-faring is fundamentally a problem of *energy concentration*. In the most abstract terms: If a civilization can accumulate, transform, concentrate, and control energy, then it will reach a point at which it can through brute-force lob payloads into space (which is what we presently do). All the technology in between is essentially "an exercise for the reader."
For me the canonical foundation for "undersea civilization" questions is [this answer](https://worldbuilding.stackexchange.com/a/2474/13524).
There are (many) plausible mechanisms by which an aquatic intelligence can accumulate energy from natural sources, practice the chemistry needed to transform, concentrate, and control it. Therefore the answer is *yes*: an aquatic civilization *could* conduct space travel.
P.S. Regarding communication: see [the various mechanisms our own strategic submarines have used for deep-sea communication](http://en.wikipedia.org/wiki/Communication_with_submarines).
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In plenty of fantasy words, there's a wizard who can drop fireballs on large swathes of combatants. There usually isn't a detailed explanation of how a medieval military force would deal with what is effectively precision targeted artillery.
**How would the formations, tactics, and equipment of pre 14th-century change to deal with massive fireballs and poison gas?**
For the purposes of this question, we'll assume these attacks can also destroy stone walls with a few hits.
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This would have the same affect that cannons did in the real world. Slow, solid moving formations would vanish. Fast moving charges, especially cavalry would be highly valuable to quickly close the gap with the enemy before the aoe can wipe them out.
Armies would stop advancing directly on one another and instead would take advantage of shelter like woods and trenches/foxholes to shield themselves.
Fortresses would either be abandoned or adjusted. With the rise of the cannon, defenses started to be made out of sand or dirt. These materials could compress unlike stone and better withstand the shock of attack.
Eventually warfare would start to look like modern warfare, where everything from nukes to bombers force us to fight spread out, seek shelter that can protect us from bombs, either by hiding exactly where the troops are or physically protecting from debris, and fighting for air or magic supremacy. I can easily see magicians sniping each other or sending in assassins prior to an engagement to get magical supremacy. Equipment would change from metal armor, which would burn people alive and keep them too slow into lighter, more fire resistant materials.
As for poison gas, even in modern warfare that hasn't worked out well. The vagaries of the wind can send the gas back on your own troops and its hard to advance when you lay out poison gas in front of your advance. Troops could invent magical gas masks, fall back from their position until the gas passes, tunnel down to let the gas flow over, or use magical winds to disperse the gas or turn it back on their enemies.
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One thing to consider is that you are describing an arms race. In an environment where magic is this common you should expect counter-measures to be created as well.
For example castle walls might have anti-magic enchantments upon them that protect both the wall and the men upon it from spells.
You might have wizards in your army using countermagic or defensive spells to protect the soldiers.
Equipment may well adapt as well, scatter a few shields along the shield wall that absorb fireballs and suddenly the threat is abated.
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Answer to this will really depend on a few things:
* How effective is the fireball and can armor offer protection? Would a wall of shields prevent a fireball from getting at the soldier on the other side? Is being hit by a fireball 100% fatal?
* Effective range of a fireball. Which has the longer range, arrows or fireballs?
* How numerous are these wizards (1 per army? 100 per army?) and how frequently can they throw fireballs (daily limit vs constant attack?)
The answer to these questions will ultimately determine tactics...wizards of this extent tend to favor the undisciplined forces more than well disciplined ones.
Undisciplined is a reference to skirmishers or barbarian type tactics where the unit fights individually or in a spread out area. Barbarian type warriors don't work well with others...in tight formations their attacks tend to interfere with each other as much as anything, so they tend to fight as scattered groups and put emphasis on individual heroism. Skirmishers also fight in loose formations, firing or throwing their weapons and then falling back. This tactic would be exceedingly useful as a method of disabling enemy wizards (range of wizards comes in here, if archers can get close, fire their weapon in the direction of wizards, then fall back before melee troops can engage them...you have an effective method of disabling wizards). A fireball would likely be deadly to the few caught in the fireball, but the loose formation prevents a total loss scenario that tight formations would experience (unless you wizard can machine gun fireballs with little regard to the number cast in a day)
Defence in depth also becomes more valuable, spreading defences deep instead of one layer. 3 walls instead of 1 giant wall. Destruction of the first wall is inevitable, but falling back to the second wall and defending as the enemy comes through the first wall is a great tactic. One thing of note...fireball range is usually less than a longbow or similar archer. Depending on your wizards range, the ability to send fireballs flying at a castle wall may endanger the poorly armoured wizard and put him in the range of archers. And another note...opposing wizards on castle walls can just as easily send fireballs back at attacking wizards. Defending wizards here have a great advantage...they can spot the attack wizards and attempt to disable them far easier than the attackers can spot them, they have a castle wall to hide behind, and if it's a layered defence, they can always fall back and defend from the second wall (or third, or keep, or fortress, etc...) as well. Remember defending wizards can be more dangerous than attacking ones.
Protracted sieges would be far less frequent. One of the larger time wastes in any medieval campaign is putting together the tools required (catapults, seige towers, rams, etc...) and the slow whittling of a castles defences. Since wizards could work as siege weapons to disable walls, the tactic of hiding behind walls with a far lesser force and forcing a protracted siege while reinforcements arrive is no longer a viable solution. Actually has the effect of making a rampaging army far more effective as the need for long sieges is gone
Disciplined troops is a little different as the size and strength of the fireball comes into play. Instead of relying on spread distances to reduce the effectiveness of an area effect attack, they are going to try to use each other to resist the attack. Heavy mail and armour, with thick padding underneath to reduce the effect of a fireball is most likely, along with a large shield. These units rely on each other to protect themselves, not just themselves...the front rows holding shields forwards with back rows holding them above. You don't give much information on how strong these fireballs are...so it's hard to tell if this is an effective attack.
Cavalry generally fall into two categories...fast and light cavalry will use their speed and agility to try to avoid and dodge incoming attacks, while heavy cavalry rely on their status as 'tanks' on the battlefield. Need more details on fireballs here to determine their effectiveness...though I would assume fireballs would have a pretty devastating effect on heavy cavalry. That said the best counter to skirmishers is generally cavalry as they can easily ride through loose formations and cause havoc.
Horse archers might be exceedingly effective...riding up, firing an arrow towards enemy wizards, then retreating while reloading to repeat. Cantabrian circles would ensure a stream of arrows flying at a wizard (or group of wizards) while maintain a pretty wide spread making area of effect attacks far less useful.
Gives an interesting loop... Skirmishers counter wizard, cavalry counter skirmishers, tight formations (spears) and heavy cavalry counter cavalry, wizards counter tight formations and heavy cavalry.
Edit:
Missed the poison gas section...
Poison gas is a hard tactic to use effectively and weather variations can make it as brutal on yourself as it is on them. It's easier to use in a defensive sense as the enemy has to advance towards you to attack and through the poison gasses to get there. Attacking with gas has the bad tendency to take down your own troops as they advance. Not sure what effects this could have on battles, tight formations on attack are obviously at the disadvantage here.
[Answer]
It basically boils down to how common these things are. They could be common or rare but known.
Rare but known means that such powers are wielded just by few of the most powerful masters of magic (such as high level PCs in RPGs), and perhaps lesser magi could have less potent forms of this, able to kill few men at once, but not to disperse a well-disciplined unit of 100 men. Then the difference wouldn't be as great, but elite armies (or ordinary soldiers when enemy is known to have some masters of magic) would be trained to disperse (and perhaps fall down, to mitigate destruction done by explosions) quickly, and then to form a shield wall again when enemy soldiers approach close enough that enemy is unlikely to throw more explosive fireballs to the area. This is the norm in most low- to mid-magic fantasy worlds.
When fireball-hurlers are really common (every army has enough of them to blast any army of similar strength grouped together into nothing in minutes), then the tactics must be different. Now soldiers would be trained to fight dispersed in small groups and only the elite would be trained to form a shield wall when no enemy mage can be seen.
This is true for attacks where scattering is the only defense. If poison gas is common, ordinary soldiers (elite if it's uncommon but known) would have some kind of primitive gas mask - usually a mask with some herbs believed/known to counteract the poison. If this is really common, some armies could develop real gas masks like in the first World War.
If this is a good siege weapon, the effect would be similar to effect of cannons. Google something on 17th century fortresses for some idea, or ask another, more detailed question.
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Light travels differently in water and air. Some of that is because of light's speed in a substance, and some is the light absorption that substance exhibits.
Is the difference in light scattering underwater enough to make a sea-dwelling race (like merfolk) be noticeably Nearsighted or Farsighted when compared to land-dwelling races (like humans) when on land/in our atmosphere?
[Answer]
Interesting question!
First things first, let’s talk about how an eye works. Well, I don’t know. I’m no doctor. It’s probably crazy complex. But for our purposes, an eye is just gonna be made up of a converging lens in front of the retina. The job of the lens is to make light converge on the retina. If the focal point of the lens is in front, you’re nearsighted. If the focal point is somewhere behind the retina, you’re farsighted (all of this is very simplified, but that's enough to just grab the concepts we need for a qualitative answer)
[](https://i.stack.imgur.com/Sfgja.jpg)
Ok, well an eye is a {lens+retina} system. But how does a lens work? That I do know, but we’re still going to keep it simple. We’ll just say it uses the geometry of the interface to decide what to do with the light rays (concave=diverging lens, convex=converging), thanks to refraction. Refraction is what you mention in your question; when light goes from a material with refraction index $n\_1$ to another with refraction index $n\_2$, light bends according to the Snell-Descartes law that you might remember from your high school physic classes:
$$sin(i\_2)=\frac{n\_1}{n\_2}sin(i\_1)$$
where $i\_1$ and $i\_2$ are the angles that it makes with the interface, but we don’t care much about the details of how the light bends actually. The only thing we need to notice is that how much it bends is all decided by the ratio $\frac{n\_1}{n\_2}$. This means that, the bigger the difference between $n\_1$ and $n\_2$, the more refraction you get (For example, if $n\_1=n\_2$, the angle would remain unchanged and you get no refraction at all, making your lens useless).
So! The refraction index of air is lower than that of water. That means that the difference in refraction index between the air and the lens will be larger than it is between lens and water. So, once you emerge, the lens in front of your retina suddenly bends light harder; the focal point is at a shorter distance. If your species is adapted to see clearly underwater, you would then be in the situation shown on the left of the image above.
**Your amphibians would be near-sighted in the air, compared to what they are underwater**
Also, they will of course get much brighter light above the surface than in the depths of the sea. If they have nothing to adapt to that, they might just be blinded too. Otherwise, they can simply have cat-like pupils to accommodate for both dark and bright conditions.
**Important edit (estimation time):**
Ok, I was actually quite curious to know how bad it would be. And boy, oh boy, would the little mermaid be blind.
We will assume that the cornea of your merfolks allow them to focus a point at infinity *when they are underwater* (just like us humans *in air*)
Without going into the details of the proof, you can establish that, for a given geometry of your lense, the refractive power varies proportionally to $\frac{n\_{medium}}{n\_{lens}}-1$. We will take $n\_{air}=1$, $n\_{water}=1.33$.
The ratio of the corrective powers of the cornea in air vs under water will then be given by:
$$\text{power ratio}=\frac{n\_{air}-n\_{lens}}{n\_{water}-n\_{lens}}$$
If we assume that the eyes of your merfolks are built similarly to ours (with just a difference in curvature of the lens), things get ridiculous real fast. If we take the human refractive index for cornea ($n\_{cornea}=1.376$), the formula above gives you a ratio of about 8!! The power of the cornea will be multiplied by 8 as your merfolk emerge. With an eyeball diameter of 2.3cm, you need an optical power of about 43 dioptres to focus light correctly. So, out of the water, the cornea of your merfolks would now have a power of... 355 dioptes!!
**Good luck finding -312 glasses**. For geometrical reasons, it would actually be impossible for your merfolks to have such a good vision underwater in the first place with those conditions anyway
Ok, your merfolks obviously have to be built different. The highest refractive index used in pharmaceutical lenses seems to be around 1.7. Let's say your $n\_{cornea}=1.7$ for your merfolks, this time the power of their cornea would only be about doubled when they emerge (according to the equation above). So, you'd be doing ok with -39 dioptre glasses. We're getting somewhere!
Double their eye size, and they only need their cornea to offer 22 dipotres under water. They would then have about 41 dioptres in air, which means they can get away with "only" a -19 correction this time. That's still super duper nearsighted but it seems to be at the extreme range of what can be corrected by glasses.
**Conclusion: Your merfolks need at the very least a super-effective cornea and eyes twice as big if they wanna have the slightest hope of seeing anything out of the water. Even then, they will still need to wear the best glasses we can make**
[Answer]
For a complementary thought experiment, what focal length do your merfolk *need*? Depending on depth and murkiness of water, it may be pointless to have long-distance focus anyway - [Wikipedia tells me](https://en.wikipedia.org/wiki/Underwater_vision#Visibility) that optimal conditions still result in a max distance of 80m, and in most cases this would be a wildly optimistic overestimate. Since focal range is always a compromise between near- and long-sightedness, I am guessing your merfolk will be under selective pressure to be near-sighted, since long-sightedness brings them no advantage anyway. As Julien then calculates, this will be even more marked once they come out of the water.
The other aspect, which only you know, is how much they rely on sight (for example, if they use bioluminescence or other visual means of communication). They may simply have *poor* vision, since the medium they live in is not as conducive to the sense of sight as air. This may be somewhat story-based - do you want these merfolk to be able to interact easily with humans? How human-like do you want them to be? Will they be point-of-view characters (and therefore responsible for relaying descriptions to the reader)?
[Answer]
**Nearsighted or Blind**
Even clean water absorbs half of the light in the first 10 metres. This is doubly bad for your merfolk as being 10m underwater and looking at something 10m away you only get **at most** 1/4 of the light you would otherwise. This is because the light travels 10m to hit the object and 10m again to hit your eyeballs.
More likely however the light travels diagonally for the first part of the journey you get less than 1/4 of the starting light.
Seeing distant objects is a lost cause. Seeing closeby objects only works in shallow waters.
This suggests your merfolk are nearsighted if they live in crystal clear shallow water. For example a tropical reef. But they still need other senses to detect things far away.
If they live in murky or deep water then their eyes are no use. With time they become almost blind. Like the Yangtze River Dolphins.
[](https://i.stack.imgur.com/I2wux.jpg)
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I'm exploring a post-apocalyptic world and want to build a realistic scenario for the condition of abandoned ruins. What would you estimate to be the lifespan of the following building types? And by lifespan, I mean the upper limit on usability as a structure. Obviously, they would be in bad condition (that's why they call them *ruins* after all), but usable means that they offer shelter and reasonable structural integrity (i.e. they're not in immediate danger of collapse).
* steel frame skyscrapers (10+ stories)
* reinforced concrete buildings (1-10 stories)
* masonry/brick buildings (1-10 stories)
* wood-frame small buildings (1-3 stories)
Professional materials science or civil engineering perspectives would be super appreciated :D
EDIT: On further thought, I've broken up the "reinforced concrete and/or brick" category into separate categories as I think they may be substantially different in their lifespan.
EDIT 2: Let's say that we are talking about a temperate region, roughly approximate to the US mid east coast (e.g. Virginia). Decent amount of vegetation but not rainforest. Slightly above average precipitation and humidity.
[Answer]
Happily, many instances exist where we can pinpoint the date of disaster and abandonment of structures. You can get a good idea of how relatively modern structures and cityscapes will appear after 30, 50 or 70 years:
Chernobyl disaster:
[Pripyat](https://www.youtube.com/watch?v=UeZtlFeEcNg)
WWII disaster:
[Oradour sur Glane](https://www.youtube.com/watch?v=kmKXM0KPdeQ)
Extrapolation into the Future:
[Life After People](https://www.youtube.com/watch?v=yQOAhyqPw5k&list=PLpe8MLifyY1VMNNY4CtMygOZgXqNfS7fB)
Or simply tour the abandoned structures in Detroit (USA):
[](https://i.stack.imgur.com/PzXvQ.jpg)
[](https://i.stack.imgur.com/27aA2.jpg)
Unattended wooden structures *can* survive a long time if well & sturdily built for decades. [This house in Pennsylvania](https://www.google.com/maps/@40.7421359,-76.8569703,3a,51.5y,262.64h,106.57t/data=!3m6!1e1!3m4!1ssa1ERc8wDmA8SsTlocSYPg!2e0!7i13312!8i6656) has literally looked like this, unpainted and seemingly unattended, for at least the last 40 years. Some of the external laths have fallen off, but it appears otherwise sound.
Concrete & steel structures, as you can see from Pripyat, survive well in the first few decades after abandonment. Even with no maintenance, most urban structures would have a "usable lifespan" into the century mark if not longer.
[Answer]
The estimates for steel and steel reinforced structures in the "Life after people" series seemed to be around 200 years. Without continuing maintenance, the steel corrodes and breaks, allowing gravity to pull the structures down.
Now this figure will change according to circumstances. In wet climates, moisture will accelerate the corrosion process, while in dry climates the steel will last much longer. Other external stresses may factor in as well. A building in an earthquake zone will be subjected to forces from the earthquakes, but without repair, the damage will become additive and the structure will collapse in subsequent tremors. A building in the wildfire zones of California may suffer fire damage, and the structural steel may lose enough temper to allow for collapse (much like the World Trade Center towers on 9/11).
So your story can provide specifics, like the tower collapsed in the earthquake of 2111, but I would guess that steel and steel reinforced concrete structures might last 200 years on average.
[Answer]
Stone structures can last effectively for ever if they're constructed with thick walls, as [the Wikipedia list of the oldest buildings](https://en.wikipedia.org/wiki/List_of_oldest_buildings) demonstrates. Effectively all of the listed buildings are of stone.
I can't find any sources for the other materials listed, but as far as I'm aware wooden structures, if treated correctly, can last for hundreds of years if not damaged e.g. by storms.
As far as I know we don't really have much evidence to tell how long concrete takes to naturally erode, since these structures tend to be less than 100 years old.
[Answer]
The lifespan of buildings strongly depends on the climate that they're in. Are they in the desert, withered by the sand, are they close to the ocean, where the salty and wet air would attack the steel, or are they in a climate with a lot of rain which could slowly wash out the structures? or maybe high temperature differences which stretch the materials? In general you could say that especially concrete and steel frame buildings would last for ages, surely several hundred years, given they're not in a harsh enviroment. Those are buildings made to last. And they would. Wooden buildings are more interesting, but they're also depending on the climate. Dry wood can last very long without weakening in structure, while wood in a wet climate would rot in a few decades.
EDIT: now that the climate is specified I can provide a better Answer. For concrete buildings it stays the same, and for wooden buildings i would give them around 30-50 Years, based on my observation around the places i lived. Water is a huge factor here, if the roof stays intact, the structure will survive longer, if it's damaged, the building can rot away within 3 years.
[Answer]
Stone structures without masonry last the longest. But basically architecture's lifespan depends on two things Climate,and building material. Organic materials like wood, etc will deteriorate in a hot humid climate or petrify in a dry arid one.
## Materials that last long:
* Limestone, Marble, Lime concrete, fired Clay, bricks and tiles, Slates, Sandstone, treated wood, Granite
## Materials with short lifespans:
Portland cement concrete
Steel, Reinforced concrete,Reconstructed stone, Pre-cast concrete, Sandlime bricks, Modern wood laminates
## Questionable/Unknown:
Stainless steel, Aluminum, Laminated plastics, Titanium, epoxy fiber
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**Edit:** some answerers seem to be slightly misunderstanding the nature of the premise. Remember that the concept here is this; **In the Precambrian of Earth, bacteria evolve to extract the abundant chloride in seawater and use it to emit chlorine gas as a defense mechanism. Their predators adapt, and the predators' predators adapt, until all organisms (Only microbes at this stage) emit chlorine in one way or another.** With the evolution of multicellular land plants, which occurs **after** the point-of-divergence with Earth's timeline, all the chlorine-emitting organisms covering the land keep on pumping it into the atmosphere until it is 1% chlorine. **They have the same biochemistry as Earth
bacteria**; albeit an evolved version, but because of all the chlorine in the atmosphere, organic molecules have become heavily chlorinated; hence the PVC instead of cellulose.
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In his book *World-building*, Steven L. Gillett proposes a world called Clorox, where in the planet's life's early history, microbes evolved to use the chloride in the water around them to produce chlorine gas as a defense. An evolutionary arms race ensued, and eventually all of the food chain produces the gas and the atmosphere contains 1% chlorine because of their emissions. The life forms are carbon-based and oxygen-breathing, but are highly tolerant to chlorine. Their cells have thick walls/membranes, and their bones, shells and other hard parts are made of plastics.
Apparently, the plants on this world produce PVC and use it like cellulose, making them have plastic bark, stems and leaves. There are a bunch of other unusual things about the planet, such as its greenish-yellow sky, mild acid freshwater bodies (And mild bleach seas), smogginess, and lack of an ozone layer - the chlorine does the job well enough, however.
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I'd like to use a similar idea, but have it in an alternate Earth timeline, where Proterozoic bacteria evolves to emanate chlorine gas instead. One thing I'd like to check though is; **Are Gillett's plastic plants viable? Would PVC instead of cellulose work biologically, and are there any repercussions on other aspects of the life it would have?** You can leave out the last question if you like, but it'd be all the more appreciated if you didn't. Any other comments on such an atmosphere's effects are welcome.
Please inform me of any errors; and seriously - please don't downvote without leaving criticism. It can get annoying sometimes.
[Answer]
I would say your first question isn't really answerable. If by viable you mean, "Can they exist?" then I think the answer is: not with anything similar to current terrestrial biology, but you could handwave it and say evolution has devised a completely new biochemistry. It seems unlikely, but I'll grant it as it's the whole premise of the question. The second question, however, can be explored a little bit.
So, I pose the questions: what do real plants use cellulose for, and what would swapping it out for PVC do to the properties of those plants? Further, what are the long-term consequences for other life and the greater ecology of the planet?
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This is the structure for polyvinyl chloride, or PVC:
[](https://i.stack.imgur.com/cDqsC.png)
As you can see, PVC is a fairly straightforward substitution of a chlorine atom for a hydrogen atom in a (*long*) linear alkane.
This is the structure for cellulose:
[](https://i.stack.imgur.com/W1Jm7.png)
Clearly very different. So our expectation going forward should be that they're going to behave very differently. Now, what do modern plants use cellulose for? To a strong approximation, it's mainly used as a **structural** component in plants. Thus, we want to know how it's structurally different from PVC. Well, there are many types of wood and other structural cellulosic materials, but I'll do a comparison with softwood (like pine) as a fairly average representative. I'd also like to note that the data I'm looking at is for non-plasticized (rigid) PVC. You can add a plasticizer to the PVC to vastly change its properties.
First of all, PVC is significantly less rigid than softwood. This means that plants likely couldn't grow as tall before their own weight began to bend them over. PVC grass would be droopier, PVC trees would either be short or bendy.
On the other hand, PVC is much stretchier. This will make it difficult for branches to snap off (imagine if tree branches were as tolerant of bending and stretching as plastic packaging!). This likely has only little consequence for plants (better branch retention in high winds?), but would mean that any evolved herbivores would need to use sharp teeth to trim grasses and leaves, rather than pulling them off like many herbivores do today.
PVC actually has a similar density to cellulose, and the density of wood depends a lot on its microstructure. Softwood floats not because cellulose can float (cellulose is more dense than water) but because of its structure. Something similar is likely true for PVC-based biological structures, so aquatic plants and the like are still viable.
**An ecological problem:** PVC is much more stable than cellulose. This means that the process of sequestration -- whereby an atmospheric gas is captured from the air by plants, turned into a solid, and eventually buried in the ground forever\* -- would proceed more quickly with PVC-based plants than cellulose-based ones. This means that CO2 and Cl2 levels in the air will drop more rapidly after plants begin to produce PVC.
[](https://i.stack.imgur.com/K4o7U.png)
This graphic shows historical levels of CO2 in the atmosphere. Around 400 MYA land plants first appeared, and you can see the corresponding downward trend in atmospheric CO2 begin around that time. With a PVC-based ecology this drop could be much sharper, and will happen for both CO2 and Cl2. This means climate change on a faster timescale, potentially a much cooler earth in 2018 than we have today, and much less available chlorine in the atmosphere as time went on.
Now, this might not happen. Even bacteria evolved alongside PVC would likely find it tricky to break down, its very chemically stable. However, amyl chloride might be one route to digestion, and similar for aniline, both of which have a degrading effect on PVC. So if bacteria (or, larger scale, animals) evolved with PVC they might be able to produce these chemicals as a sort of specialized digestive fluid. Still, it's possible that even with these adaptations breakdown could be slow enough to have a noticeable effect on sequestration rate.
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Okay, this is starting to get rambly and into the realm of wild speculation, so I think I'm done for now. Obviously true answers to this question are unknowable, but by granting the premise I hope I've given you at least a few interesting possibilities to explore.
[Answer]
You have to deal with an important problem: Chlorine is way less [abundant](https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements) than Oxygen, thus it makes much harder to build a biochemistry on it.
Oxygen is the third most abundant atom in the solar system after Hydrogen and Helium, while Chlorine is about 4 orders of magnitude less abundant.
It's simply really hard to develop a biochemistry based on a relatively rare element, when you have something else which is more abundant, like it happened with Oxygen on Earth. Mind, I am not saying it is impossible, simply more difficult.
You can have that sort of development in some niches, where Chlorine is constantly more abundant, like what happened for those life forms relying on H2S close to volcanic vents.
Also mind that Chlorine would compete as oxidant with Oxygen, due to its electronegativity. Therefore this add another difficulty to an extensive usage of Chlorine in an Oxygen rich environment.
[Answer]
The short answer is that, yes, it's plausible *enough* for a fictional world, in the sense that ruling it out would take up a whole book by itself.
As @LDutch's [answer](https://worldbuilding.stackexchange.com/questions/120616/are-plastic-plants-plausible#120622) points out, the economics are against using chlorine, but the chlorine in PVC is there more for industrial-chemistry reasons than for any special property of the final material. There are many plastics that use only carbon and hydrogen (polyethene, polypropylene, polystyrene, polyolefins), and many more that also involve oxygen and nitrogen (polycarbonate, polyurethane, ABS).
In fact, a good question would be why plants *don't* produce these kinds of plastic. We know of lots of materials that are chemically simpler than cellulose, and have far superior structural properties. In general, biological chemistry seems to favor the use of relatively big and complex building blocks (like saccharides and amino acids) because their chemistry is specific and controllable. The molecules used as building blocks in industrial chemistry (simpler, more reactive molecules like chloroethene), if you put them in a living cell, would tend to react indiscriminately. This is probably why, when you see simple industrial chemicals in living organisms, they are waste products that the organism is trying to get rid of (oxygen, ethanol, methane).
So my hunch is that plants wouldn't make PVC because the monomers are too simple for them to process. But again, biology, can do surprising things if it needs to.
[Answer]
Probably not.
There are 2 ways of looking at this, first is the biggest, through marine life.
Ocean water has substantial quantities of chlorine and bromine, both of which are used to produce bioactive compounds, such as the chlorine containing briarenolide J and chloromethane, and the bromine containing bromomethane. Sea water contains about 700 as much chlorine by weight compared to carbon.
There are thousands of naturally occurring organohalogens, many of which are produced by alge, sponges, and corals. Yet none of them make use of halogen compounds as a major component of cell walls or skeletal structure. Given the diversity of species, and the amount of available chlorine, one would expect to see some organohalogens used as a structural compound if it was going to happen, but we don't.
The second is through the properties of PVC. PVC when used to produce a product contains numerous additives to make it usable, otherwise it is quite poor in its material properties. It will dissolve in ketones and aromatic hydrocarbons produced by plants. It degrades when exposed to UV. PVC will also break down and release hydrogen chloride when heated, which is highly corrosive. Chlorinated PVC has superior material properties to PVC, but making it organically may be difficult.
The most likely candidate for PVC based compounds would be complex marine life that lives in cold dark water, the exoskeletons of lobster or crab-like creatures for example. As for using chlorine as a protective agent, some insects produce the chlorinated alkaloid epibatidine, which can be fatal to humans with a dose as small as 1mg. It reasons a plant can also produce this, either by itself or in a symbiotic relationship with bacteria, as the compound is not toxic to plants. Some plants such as Asian Moonseed produce several different chlorinated alkaloids.
[Answer]
in two words? um-possible.
Chlorine is a dead end, if you look at the backbone of large, complex molecules. Carbon, oxygen and nitrogen aren't, because they typically make four, two and three covalent links instead of just one. That's why they are abundant in biochemistry, and chlorine isn't. Is there a single naturally occuring organochloride in the human body? I think not.
Some (for lack of a better word) *freakish* bacteria produce crazy stuff like this <https://de.wikipedia.org/wiki/Bipyrrol_Q1> , but I don't think that's sustainable, or could even be generalised.
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# Background
A [McKendree cylinder](https://en.wikipedia.org/wiki/McKendree_cylinder) is a rotating cylindrical space habitat comparable to the more well known [O'Neill model](https://en.wikipedia.org/wiki/O%27Neill_cylinder). It was proposed by NASA engineer Thomas McKendree in 2000 as an update of O'Neill's, using carbon nanotubes instead of steel and aluminum to allow for much larger structures – up to 10,000km long/1,000km radius, compared to O'Neill's 32km length/8km radius.
[](https://i.stack.imgur.com/g7YdT.jpg)
A single McKendree cylinder therefore has *millions of square kilometres of habitable space* along the interior surface and potential for even more within the hull itself and interior structures.
# Problem
Wobble. More precisely: rotational instability.
A capped cylinder as described has two principal rotational axes and [moments of inertia](https://en.wikipedia.org/wiki/Moment_of_inertia): along the length of the cylinder (in blue, below), and another perpendicular to this between the end caps (in red). The former is the smallest principal axis, and the latter is the largest principal axis:
[](https://i.stack.imgur.com/bAJkp.png)
Given a space habitat as described above its inevitable that the interior space won't be perfectly and symmetrically balanced at all times: people will need to move around, cargo has to be shifted, vehicles will traverse the surface in every direction, air will flow in complex ways, water will slosh about, and so on. Because this structure is in space, momentum is conserved, but kinetic energy is not: movement of objects within or on the surface of the habitat will dissipate kinetic energy unequally and result, inevitably, in the cylinder tumbling end-over-end as it seeks equibilirum with the largest axis. For sake of discussion let's assume this tumble-point is somewhere between a few days and a few years of normal use. Any potential solution will need to work in either extreme case.
# Partial Solutions
The classic solution found in both O'Neill's and McKendree's proposals is to pair each cylinder with an identical *counter-rotating* cylinder connected by a superstructure so each cylinder's wobble is countered by its neighbour's.
[](https://i.stack.imgur.com/k80kN.jpg)
Similarly, *Orion's Arm*'s [implementation](http://www.orionsarm.com/eg-article/48473a892041c) proposes nesting a second cylinder within the larger external cylinder and counter-rotating it. The site doesn't go into technical detail about how this is achieved, but presumably the internal cylinder is connected to the external cylinder at the end caps in a way that allows it to spin freely in the other direction. (Whether this would work is a question for another time.)
These may (or may not) solve the problem for those specific configurations of habitat, but do not work for a single cylinder.
# Question
Given a McKendree cylinder (singular, unnested) habitat of arbitrarily large dimensions and suitable mass, what is the best way to prevent wobble from destabilizing the rotation and orientation of the structure?
[Answer]
The moments of inertia are only as listed assuming the cylinder has uniform density. By increasing the density along the 'equator' you could make the axis of rotation the largest principal axis. This then removes the need for active stabilization.
One way of accomplishing this might be to add a large lake/sea along the equator. The depth and width of this body of water will depend on the weight of the superstructure it needs to balance out. I assume this is a biome you would want present somewhere in such a large structure anyways, so why not around the equator.
Rigid spars radiating from the equator would also alter the moment of inertia, but it is my understanding that the radius of a McKendree cylinder is limited by the tensile strength of carbon nanotubes, so I do not know what could be used to extend structures out past that radius.
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Pumping water back and forth to squash wobbles has long been proposed. If you have enough water being moved around just under the outer skin, you can not only damp out any wobbles but it can act as radiation shielding too.
It is just that it would take an awful lot of water and plumbing to work that system for a cylinder as large as you are talking about.
Another method would be deployable solar sails.
Also, if the cylinder is big enough, the random movements inside should cancel themselves out.
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Arbitrarily large dimensions, you say? Well, then...
*Just make it so large that it **can't** tumble.*
Specifically, make it *long*. On sufficiently large scales, everything is non-rigid, so eventually you will get to a point where the cylinder doesn't just *wobble*, but rather starts twisting and bending like a strand of wet spaghetti. Now I know what you're thinking: "That sounds like a *terrible* idea! I don't want my colonists thrown around at the end of a whiplike carbon-nanotube spaghetti strand as the structure tears itself apart!" Well, you just haven't made it *big enough* yet.
Because the structure cannot be perfectly rigid, there is some (very large) minimum radius of curvature around which you can bend the entire cylinder without breaking it, and it'll keep happily spinning while all of the superstructure is periodically compressed and stretched over each rotation. At a several-times-larger radius, the stresses will become unnoticeable, and the local deviation from perfect straightness completely unmeasurable to human perception. At that point, you can bend the entire megastructure into a loop, tie the two endcaps together (so that it still technically counts as a distorted cylinder, rather than the torus you get if you eliminate the end caps entirely), and you will then find that the bent structure, consisting of *a single* extremely long tube with no pair,
a) has zero net angular momentum,
b) cannot tumble, because its ends hold each other in check,
c) has billions of times Earth's living space, and
d) can push against *itself* to spin up / down--no strict need for solar sails or reaction mass.
It *can* be set vibrating by asymmetries in local mass distribution around the curved axis, but damping those kinds of vibrations is a much simpler task, and material can be moved *along* the spin axis arbitrarily.
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This potentially violates the original premiss but what about making it a very short cylinder, sure this reduces the amount of available living space but would also not give the station a longer axis that it could turn around. I was thinking in the order of the cylinders length being the same as its radius.
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I am not sure I understand your problem. Presumably your "tube" would orbit a star or a planet and the gravitic field would stabilize it and prevent tumbling. This is because the force keeping the near end "down" is significantly larger than the force pulling the far end away from "up".
So your actual problem IMHO would be to keep the interaction between gravity and inertia from tearing the structure apart. I am afraid you would need those "partial solutions" for that, you need to counter the inertia. This would actually IMHO be a good thing since, if the counter-rotating mass is an outer hull, it would work as radiation shielding AND allow you to rotate the actual habitat without actually ejecting reaction mass, a non-trivial benefit as rotating a structure that large is not a simple problem. It would also work as armor against physical impacts. This would also make having a "non-rotating" middle-layer you probably want for docking space, storage, sensor system, solar power and such fairly trivial.
So while the counter-rotating outer hull sounds complex, I think it is actually the simplest solution overall, if you consider all the other issues relevant to building a large habitat. Most importantly, it is a **robust** solution that depends on the overall structure of the habitat, not on sophisticated active and dynamic systems. It won't fail because of a software bug or a fuse breaking. Any failures will be obvious not hidden or deceptive. And it would probably work for a very long time even without maintenance if designed for that.
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A long, thin cylinder is dynamically unstable, and over the long time span that a McKendree cylinder would be in operation, it is almost a certainty that some condition or set of conditions will arise to create dynamic instability and cause the cylinder to tumble.
Given the enormous scale of the cylinder, using movable ballast or even rocket thrusters seems infeasible, the amount of materials needed to to be moved or the amount of reaction mass being expended will be vast (indeed, the very act of moving megatons of ballast or pumping billions of litres of reaction mass may be enough to *cause* the cylinder to become unstable).
My suggestion would be to use giant solar sails attached to the cylinder to provide gentle, long term torques to the cylinder to maintain stability. The form of the sails will be a "[Heliogyro](http://wiki.solarsails.info/index.php/Heliogyro)", which provides control of individual "blades" to provide some fine control of the amount and direction of the torque. The illustration is of the proposed heliogyro for a mission to Halley's comet, and given the rather low amount of "thrust", the scaling of the heliogyro blades for a McKendree cylinder will be on the scale of the cylinder itself.
[](https://i.stack.imgur.com/tssBW.jpg)
*JPL Heliogyro proposal*
Since the size of the cylinder will provide a massive amount of inertia, the gentle and long term application of torques by the heliogyro blades should keep the cylinder spinning within the limits that discourage instability.
Edit to replace dead link
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There doesn't seem to be an answer suggesting the only obvious solution besides the ones you mentioned (and discounted) in the question: simply make the moment of inertia larger along the axis of the cylinder, so that rotating along that axis becomes its most stable state.
This of course requires adding a lot more mass. But since this kind of structure has to be built in space anyway this isn't necessarily a big issue. Simply attach a number of captured asteroids in a thick ring around the midpoint of the cylinder, and stick them together with carbon nanotubes. The ring should extend out from the cylinder as far as possible given the material limits of the nanotubes holding it together.
Of course, your cylinder might be so big that you're at the limits of carbon nanotube tensile strength already. In that case this plan won't work at all, since the mass of the ring will exert even more centrifugal force than the cylinder itself. Because of this, a cylinder using this stabilisation method would have to be a lot smaller than the theoretical maximum. It could still be enormous, though.
(I should note that this answer is somewhat tongue in cheek. I'm not sure it would really work, because an object on that scale wouldn't really behave like a rigid body. The ring would want to spin one way while the two ends of the cylinder want to tumble, and that might cause the whole thing to tear itself apart. I don't know whether it's possible to prevent this or not. I suspect that in reality the only ways to do it are some kind of active stabilisation or some kind of counterrotating mass, with the latter probably being far more practical.)
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Add a flange around the “equator”, a wide annulus of dense material coaxial with the cylinder, protruding from the cylinder wall into space halfway between the end-caps. Perhaps make its rim especially dense or thick. That would increase the moment of inertia about the longitudinal axis by more than the moment of inertia about the transverse axis.
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Given the assumption that the cylinder cannot survive without a technological society running it, then the solution would be to use active compensation systems such a moving weights or liquids and accelerometers to cancel all unwanted motions and achieve active stability. A fly by wire system such as the one of the X-29 and other modern fighters.
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**The best way is the way you mentioned.** If you simply don't need that much space, consider multiple smaller cylinders. If you are opposed to this for aesthetic reasons though I supposed we can consider a few other options.
**You could also try a counterbalance system.** A computerized system shifting weight can offset the impact of movement inside the cylinder. Shifting liquid ballast could possibly prevent rotation, but it's not exactly energy efficient.
**Stabilize through the use of thrusters, or similar means.** One more way to stabilize would be through using rockets or some other future propulsion system to counteract unwanted spin. Rockets however can run out of fuel, so maybe it uses magnets to manipulate itself within a magnetic field from a planet or sun?
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**Flywheel gyroscopic stablizers**
Two of them, one for each of the axes you describe. These flywheels would oppose shifts of the cylinder and hold it in position. Gyroscopic stabilizers work via conservation of angular momentum. Or maybe you only need one - tt seems to me a giant spinning cylinder like this would already act like a flywheel. So you might only need one additional flywheel to stabilize it.
from <http://veemgyro.com/wp-content/uploads/2015/11/White_Paper_1403-How_Gyros_Create_Stabilizing-Torque.pdf>
[](https://i.stack.imgur.com/ihqLA.jpg)
The more momentum the more stabilization you can get. You could have large flywheels exterior to the cylinder. Or you could have very fast spinning flywheels. Or you could have many, moderate sized flywheels that act together.
You are in space, so you do not need to worry about atmosphere slowing down your flywheels if you keep them outside.
An (additional) cool thing about flywheels is that you can also store energy in them as kinetic energy and so these flywheels would serve double duty. You can tap that energy for readjustment of the cylinder or whatever other needs you have.
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**Use the sun to keep it steady**. Not *the* Sun, mind you, but assuming you don't want to do the silly idea of making it half windows, you need to have a little sun inside the cylinder that you power with the solar panels on the outside if you happen to be near a star. I'll assume it can be as heavy as you find convenient - you only need a shell that emits light, but the local sun also makes a great place to hide ugly industry while taking advantage of zero gee conditions.
Since people don't want day all the time and it's a waste to build a giant portable sun just to turn it *off* half the time, that sun is going to get passed all the way up and down the main axis of the cylinder each day. Each time it passes up or down that axis, it is reeling in some of the filaments (you said nanocarbon) that tether it and letting out others. It may have a track infrastructure tethered to the poles to help. Of course, very efficient regenerative braking makes this process "elastic" - you're not really throwing away much energy when you use the filaments to steer it.
Anyway, by controlling the path of the sun, or equivalently *which* directions the sun applies *more* force during its daily round, under the careful technical control of Chief Engineer Ra, the sun will exert enough torque in enough directions on this cylinder that it can be kept spinning the right way despite all the minor motions on the surface.
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You might use the high strength of the materials required for construction to create a gravity anchor towards the sun. A sufficiently high gravity gradient should create a force capable of stabilizing the cylinder. Something like [this](https://www.sciencedirect.com/science/article/abs/pii/009457659400268Q), but at scale:
>
> A new attitude control approach is presented here that overcomes most of these limitations. The proposed system configuration assumes a downward deployment of a ‘pendulum-like’ small mass from the satellite through a pair of identical tethers attached to its two distinct but symmetrically off-set points around the mass center.
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[Answer]
#### Use the axial light source as a harmonic counterweight
Most of the solutions suggest that we move something around the outside to keep the rotational axis consistent, but that would be a complex mechanism because you'd have to actually change the size of the containers to keep them from sloshing as you moved the fluids around.
What I'm suggesting is more akin to the [tuned mass damper](https://en.wikipedia.org/wiki/Tuned_mass_damper), except that we're countering uneven load instead of a vibration.
Every implementation I've seen of this kind of cylinder has a light source that runs along the central axis. This light source also acts like a hub, and spokes would radiate out to keep it centered. In this case, we would increase the mass of the axial tube, and adjust the length of the spokes to move the tube away from where the extra mass was added.
Note that this is just a short-term measure. You still have to deal with the linear energy added to the system, which will attempt to pull the tube to one side. For that, you're going to need station-keeping thrusters.
Or...
#### Use tidal force
This is like the [Integral Trees](https://en.wikipedia.org/wiki/The_Integral_Trees). You have the tube be long enough that the tidal force of some object exerts enough tension to counter-act any rotational forces. Obviously, this means it would have to be really long, and in orbit around a massive object.
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[
In my [timeline](https://worldbuilding.stackexchange.com/questions/59694/how-to-bring-vikings-to-south-africa) fleet of Viking ships reached South Africa in 10th century, and settled there. They defeated indigenous tribes and created a Viking kingdom. They also stopped the Bantu expansion in the 12th century, but they are unable to go further North due to their low tolerance of high heat and tropical parasites.
[](https://i.stack.imgur.com/1mK7H.jpg)
The Vikings were cut off from Europe since their arrival, but there is some trade with Arab, Indian and Chinese merchants similarly to [Mapungubwe](http://www.sahistory.org.za/article/kingdoms-southern-africa-mapungubwe)
What kind of technology should they have when the [Portuguese](https://en.wikipedia.org/wiki/Bartolomeu_Dias) arrive in 1488?
[image source](https://nelson.wisc.edu/sage/data-and-models/atlas/maps.php?datasetid=35&includerelatedlinks=1&dataset=35)
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Start with Viking technology and add whatever works best for your story from Arab, Indian & Chinese merchants of that period.
They could have firearms if you want, they were introduced to Middle East
Metallurgy should be quite developed Vikings had good blacksmiths & South Africa is rich in ore & coal.
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The Vikings were avid seamen - how do you propose stopping them from interacting with Europe by sea?
During this time, though, the real technological advances were happening in Byzantium and the Arab nations in the Middle East - which are much easier to reach from South Africa than Europe is anyway.
Therefore, if your Vikings are motivated to do so, they can acquire Greek fire, incendiary grenades, and flamethrowers from the Byzantines, and disinfectants, surgery, lens-making, windmills, torpedos, algebra and cryptography from the Arabs. (Not to mention coffee.) And, of course, carbon steel, ink, buttons, the cotton gin, sugar cane, and the decimal numbering system from India.
<https://en.wikipedia.org/wiki/List_of_Byzantine_inventions>
<https://en.wikipedia.org/wiki/List_of_inventions_in_the_medieval_Islamic_world>
<https://en.wikipedia.org/wiki/List_of_Indian_inventions_and_discoveries>
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
Spaceships are a peculiar thing. We've got them in all forms, sizes & colours. They run on [nuclear fusion](https://en.wikipedia.org/wiki/Fusion_rocket), creating loads of power driving all sorts of [*shenanigans*](http://tvtropes.org/pmwiki/pmwiki.php/Main/Spacecraft)... but they still generate *lots of heat* that has to be gotten rid of somehow.
Assuming we have mastered the challenges of creating stable fusion reactors and can build spaceships that are more than [fireworks with](https://en.wikipedia.org/wiki/Rocket) [people strapped on top](https://en.wikipedia.org/wiki/Space_Shuttle):
**Q**: What current-day or [near-future](http://tvtropes.org/pmwiki/pmwiki.php/Main/TwentyMinutesIntoTheFuture) materials/technologies can be used to (most efficiently) get rid of *these massive amounts of heat in my spaceship*?
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Without numbers for "massive amounts of heat" or more specifics on the size and other details of your ship, I think the best to hope for is an overview of the basics.
Heat flows from higher concentrations to lower concentration. If using refrigeration to move heat from low to high it is never 100% efficient and will produce more total heat. [Heat transfer](https://en.wikipedia.org/wiki/Heat_transfer) has 3 main methods to move heat around.
## [Conduction](https://en.wikipedia.org/wiki/Thermal_conduction)
Heat travels between materials in contact with one another.
ΔQ̇ = -k A ΔT/ΔX
Rate of heat transfer ΔQ̇ is dependent on k the material thermal conductance, A area in contact, ΔT temperature difference between the materials and ΔX how far apart are the temperature reference points.
This is employed internally in the ship moving heat around, but in space with a vacuum outside there is no contact with other materials so no help on cooling the ship as a whole here.
## [Convection](https://en.wikipedia.org/wiki/Convection)
A special case of Conduction where heat transfers to a fluid (liquid or gas) in contact with your heat source (think atmospheres or underwater) this is a lot more complicated as the fluid is often moving and if not the heat will cause movement transferring more heat than simple conduction.
Again not applicable outside the ship in space as there is no fluid to contact.
## [Radiation](https://en.wikipedia.org/wiki/Heat_transfer#Radiation)
This is the one most applicable in space applications. If something is hot it emits thermal radiation, sometimes this is visible if the objects are hot enough, but it occurs in the non visible spectrum as well.
Q = εσT⁴
ε is the emissivity of the material with a maximum value of 1, this can be improved by material selection and the use of coatings (i.e. paint)
σ is the Stefan–Boltzmann constant
and T is the temperature.
The main way this is practically used in space craft is to use refrigeration techniques to move heat around concentrating it and making certain parts of your vessel hot to increase the amount of heat emitted as radiation (heat emitted goes up with the 4th power so hotter equals a lot more heat transferred). The radiator heat sources need to be placed so that the surface area is directed away from the ship so the radiation leaving the hot area is not absorbed by other parts of the ship. This is usually done with large external radiator fins (often mistaken for solar panels in actual space vehicles). So your ship is going to be spiky with large cooling fins on the exterior.
## Alternate Methods
* A passive cooling method using radiation is to reduce the incoming heat from the Sun's radiation by using shading or reflection (most space ships are white to reflect heat). This won't help with heat generated in the craft but reduces the total heat present.
* Mass Transfer - Again using internal heat transfer systems and refrigeration to selectively heat certain areas or items and then jettison that mass from your ship. The heat loss is Q = m C T; m, mass, C, specific heat, and T temperature. And don't forget to get the energy out of phase changes, so molten iron or steam are good candidates here. It is not a long term strategy as you are losing mass from a limited system and will eventually run out of material to eject.
* Heat storage. Using internal storage locations to heat up under load or alternately having precooled heat sink material present to absorb the heat generated. These do not provide any net source of heat dissipation, but could provide a temporary buffer storage of excess heat to later be expelled using radiators or exchanged at the local trading post or mother ship.
* An interesting semi-future technology with application in the area is Thermal superconductors (currently only exhibited by [liquid helium](https://en.wikipedia.org/wiki/Superfluid_helium-4#Heat_transport) at very low temperatures), they transfer heat through themselves very fast. Apply heat to one end and the whole thing heats up not just the end near the heat. It would allow for some improved designs in internal heat management.
* The most important thing is the effective use of thermal insulators and ship design to prevent heat going where you don't want it. Your fusion reactor and other ship systems might be fine operating at several hundred degrees, but people or other critical systems might not do well under those conditions. The vacuum of space is good at insulating, as we've seen, putting the crew compartment physically separated from the high energy fusion reactor is likely a must.
[Answer]
## Thermodynamic basics
The fundamental laws of thermodynamics say:
* The total energy in any isolated system is constant.
* Bound thermal energy (Enthropy) will increase in isolated systems
* Thermal energy cna be seen as the movement of particles and is thus can be seen as the average kinetic energy of particles in a fluid (that is a medium in liquid or gas state)
* Temperature flow follows always the same direction as the temperature gradient between two objects: $\Delta \Delta \text T = \nabla \text T$
+ because of this, it flows only from hot to cold and the driving force of any temperature exchange is the temperature difference, $\Delta \text T$.
+ ***Heat energy*** is calculated with $\text Q = \text {mc} \Delta \text T$, Q is the energy, m the mass of the object, c a material constant and $\Delta \text T$ is either the temperature we raised the objects temperature (then Q is the energy we have "given" to it), or the difference to absolute 0 (then Q is the total heat energy).
* Force can create a temperature difference by either:
+ application of friction on a part of the system or
+ transport of a medium with a temperature from one point of the total system to another
+ fluids can change their state, density, volume and temperature, for the question of a gas, this is governed by the ***gas formula***: $\text {p V} = \text {n R T}$ - **p**ressure, times **V**olume is **n**umber of gas molecules times gas constant **R** times **T**emperature
## Partial solution: Redistribution inside the ship
Inside the ship we have a few problems that we are used to on earth: we have an arrangement of heat sources that need cooling (machines, electronics, human bodies), and a gaseous medium between them.
Here a [heat pump](https://en.wikipedia.org/wiki/Heat_pump) comes in handy: because of the gas formula above, we can put a specific amount of gas under pressure and increase its temperature, or reduce its pressure to lower it. With this, we can greatly aid in heat transfer from some points to others, especially from inside the station to the outside on radiators, speeding up the achivement of equilibrium. Better yet, the machine can continue to push all the excessive heat to the outside of the station, especially to the radiators - where our problem begins.
## Problem analysis: Space
The main problem with cooling is space is, that space is near vacuum. Near vacuum means, that there is little to no material (medium) to engage in heat transfer, at least not without a loss of mass of the ship.
On average, there is a [density](http://hypertextbook.com/facts/2000/DaWeiCai.shtml) between 0.1 atom per cubic centimeter to 1000 atoms in the same volume, while cosmic backdrop [temperature](http://hypertextbook.com/facts/2000/DaWeiCai.shtml) is about 3 Kelvin. That is good on one hand (large temperature gradient, so possibly large flow), but bad on the other (little to no material which could take the heat away).
Yes, space is cold as hell, and you can deep freeze an object by just shoving it out of the airlock, but it is really really hard to cool your ship down with basic thermal exchange via Convection. Still, there are ways we could go, mainly radiation.
## Solution 1: EM radiation / light
Heating objects enough (generally above 798 K = 525 °C = 977 °F), they start to show incandescence and emit thermal radiation. In other words: they glow. In this state, they dissipate heat energy in the form of EM waves (which is light) in addition to the convection before (heating of toughing air particles and giving them some thermal energy).
As convection is very much hindered do to the aforementioned lack of other medium, the ship could use materials with a very high thermal capacity close to materials that have a very good incandescense effect to dissipate much of the heat in the shape of thermal EM radiation to outside of the station. As an (non calculated) example, it could use pipes filled with liquid metal (lithium springs to mind) at a temperature that makes the pipes glow red to yellow. It is by far not the most efficient way, but it is at least some way to get rid of the heat.
## Solution 2: Ejection of (heated) mass
But radiation is not the only way to get some thermal energy out of the system. We have established, that we can transport heat inside the station with heat pumps. In an emergency the heat flow might be redirected into some non-essential module to heat that up as much as possible and then just ditch the whole module. This separates the thermal energy that is now stored in that module from the rest of the station. But this would be an extreme way.
Instead of ditching whole, overheated modules, one could better ship in some low-temperature gas (like liquid nitrogen or hydrogen), heat it up with the heat pump cycles, and then just let the gas out of vents into space. It has expended largely due to this process (gas formula, remember?), and will eject from the ports at a high speed: the residual heat in the station can become part of the Reaction Control/Stability Augmentation System to keep the station where it is supposed to be. Or it is used as a pre-stage for the engines of a spaceship, getting rid of some heat energy through the ship's propulsion system as it prepares (preheats) the fuels for it.
While such a system is for sure helpful as an aid in propulsion or emergency heat relief (just vent an overheated section, then readd atmosphere), it can't be the one and only method to keep the ship cool.
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I am writing mostly because of that part in a comment: *It always seems ironic that cooling is a problem in space...*
Other answers have not paid enough attention to the Stefan-Boltzmann law:
$$Q=\sigma T^4\text{, }σ = 5.67×10^{−8} W m^{−2} K^{−4}$$
where $T$ is temperature of emitting surface.
What practical effects does this law actually have? For a blackbody emitter at given temperature, heat loss due to radiation will be:
* 6000K - is energy flow 73MW/m2 (The Sun's photosphere)
* 2000K - is energy flow 900kW/m2
* 1000K - is energy flow 56.7kW/m2
or more usual temperatures for us:
* 300K - it is 460W/m2
* 250K - it is 221W/m2, coolant(Ammonia) on ISS station
* 200K - it is 91W/m2, lowest possible for ISS before coolant begins to clog the system
Vaccuum is not a good insulator, but it seems that way because of the temperatures in which we live and work. Vacuum do not have convection and conduction, which are both important heat transfer modes at room temperature. But at high temperature, radiative transfer becomes much more powerful. The 1000K object listed above gives off as much heat per area as a gas barbeque at full power. In the context of high temperature objects and space, where radiative heat transfer is the dominant mode, vacuum is not an insulator at all.
# OP's question
Smart design decisions will solve your heat transfer problem, and carbon nanotubes(CNT) is the material of the future that will allow you to solve them.
The problem with "fireworks with people strapped on top" is the incompatibility between temperatures which are acceptable for humans and the temperatures which are acceptable for machines. So separate them. Separate the living volume from the energy generation units (reactor, engines).
By separating them you have 2 different problems to solve - heat dissipation from living volume (where we have all components which can't be separated from humans, or which have similar temperature requirements as humans) where 300K is the norm; and heat dissipation from reactor-engine where 2000K may be a perfectly normal temperature.
## Human quarters
Design of this section depends on size of ship, on personal requirements of volume per human, energy consumption per human.
An example of power consumption per human is 50kW; volume per human 1000m3 (equivalent to a 400 m2 house or less), surface temperature 300K. With these conditions then up to 90 humans can live in a 54m diameter spherical living volume and not even need a radiator. With 4.5MW energy consumption, the surface of the spherical module is enough to emit all that energy.
The sphere is an efficient form because it has minimum surface area per volume it encloses, which means less construction materials and mass per volume. However, this form in space is not so critical, and it may be borg cube or some more flat shape with higher surface to volume ratio. Design plays there significant role. Requirements also are important.
## Engines and reactor
The nice thing about fusion reactors is that they can be also engine and electricity generation unit. So we will only talk about one unit.
It is hard to discuss them as hard-science, even when we have some successes with thermonuclear reactors, [Wendelstein 7-X](https://en.wikipedia.org/wiki/Wendelstein_7-X)
Pictures to illustrate taken from projectrho.com [Magnetic Confinement](http://www.projectrho.com/public_html/rocket/enginelist.php#id--Fusion--Magnetic_Confinement)
[](https://i.stack.imgur.com/wa2d9.png)
[](https://i.stack.imgur.com/aZrSl.jpg)
(Second picture is pretty realistic design, an overview of a ship composition, and have radiator attached in a way we may benefit too. Nice generic picture of a thermonuclear ship as whole)
Notice that the plasma temperature is high and it emits waste heat at a high rate. We have to solve the heat problem for the solenoids, but they may be capable of working at high temperatures, significantly higher then a human's 300K. If we keep this entire compartment at high temperature, than the radiators can have significantly higher temperature and emit lot of energy for relatively small surface.
[CNT, thermal properties](https://en.wikipedia.org/wiki/Carbon_nanotube#Thermal_properties)
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If this is true, then since we are in a vacuum we can operate at 2000K while emitting 1MW/m2 over our radiators.
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> All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a property known as "ballistic conduction", but good insulators lateral to the tube axis. Measurements show that a SWNT has a room-temperature thermal conductivity along its axis of about 3500 W·m−1·K−1; compare this to copper, a metal well known for its good thermal conductivity, which transmits 385 W·m−1·K−1. A SWNT has a room-temperature thermal conductivity across its axis (in the radial direction) of about 1.52 W·m−1·K−1
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This is exactly what we are looking for an insulation in that case, as it is free out of the box if we make the solenoid coils out of CNT. We can get a conductive wire, insulation for that wire, and structural support all out of the same material.
*Ed note: you'll need more references to convince me that the same nanotube bundle can do all three*
*MolbOrg: Valid request. However with given set of factors as: my competence(main reason), difficulties to find information, ongoing researches of CNT(SWNT, MWNT) about their properties and not established data about CNT's because of problems with their production and measuring properties of single tube - single walled or multi-walled nanotubes, amount of information needed to clarify - seems not possible to establish it with some degree of certainty in this answer. Lets call it a fantasy about pure carbon thermonuclear engine, which may or may not to be true. However some notes will be below in note section*(1)
The second thing to notice is the coils and separation between them, in vacuum we do not need an enclosure for the plasma. On Earth in the gravity field, we need it for structural integrity and to protect against electromagnetic forces and insulate from the atmosphere. In space we do not need most of that, and we definitely do not need it as a surface without gaps. This way most waste heat from plasma will be emitted directly in to space void without having need to use radiators.
[](https://i.stack.imgur.com/gL3wT.jpg)
[3He-D Mirror Cell](http://www.projectrho.com/public_html/rocket/enginelist.php#mirrorcell)
There is an electricity generation unit attached, a [Magnetohydrodynamic generator](https://en.wikipedia.org/wiki/Magnetohydrodynamic_generator) (MHD) that converts plasma exhaust and leakage into electricity.
So the engines basically look like mesh made of structural beams and coil rings, with an attached nozzle or power generation unit on either end (or at one of the ends, also possible).
Another step is that this engine does not have to have fixed attachment to living quarters. The same CNT can be used to make robust cables (same as people imagine for [Space elevator](https://en.wikipedia.org/wiki/Space_elevator)) to attach engines flexibly and at a significant distance from living quarters, so as not to mess with their heat emitting solutions.
*... get rid of these massive amounts of heat in my spaceship?*
The answer is, do not have these massive amounts of heat generated inside of your spaceship, and use the excellent heat transfer properties of vacuum as much as possible.
## Note
1. Carbon nanotubes as conductor, insulator, structural strength element(aka make beam from a rope)
* in first place, situation was considered from heat problem standpoint of view, as it is OP's concern. And some properties of CNT's are interesting in this context and worth to note.
* insulation which will work at that temperature - ceramic is good enough for that, Al2O3 as example. There is no need to use just carbon for that, even if it is possible as I think, as a bit more complex structure then just plain SWNT, SWNT/MSNT doped by something.
* Engine which I'm referring to, or use as model is described [here](http://go2starss.narod.ru/pub/E028_WJ.html). It is good as idea, but that all for it.
It is not scientific paper by any means, even if author tries to refer to some tested equipment, and refers to some works from scientific community for that time and field. But it even have some [criticism](http://tnenergy.livejournal.com/7428.html) also not scientific one, just amateur likes that kind of stuff.
Engine is just a concept, with some numbers in its description. However numbers look reasonable, not to make conclusions, but to have some clue about what we may need, and mostly are not unique to that concept only.
* make beams from ropes - there are option. An example soft bag in shape of a big sausage will act as beam, higher inside pressure, better beam it will be. Same as with fire hose. Strength of CNT's is about 60-100GPa(depends on who and how did measurements, and which kind of CNT they have tested) and that allows to have pretty high pressure with not so much materials. Internal media which is compressed can be cable made from CNT, and pressure is created by prestretchered winding of external shell which creates that bag and pressure around cable. All together it will have properties of solid beam. But simplest to imagine it is inflatable structure which forms rigid shape. There are other option - in winding(in first place), in using composite matrix, electromagnetic interaction, active structures.
All these problems are far beyond OP's question, but we discover uses for carbon nanotubes, and we are far from exploiting everything they offer to us. Is that material of the future - sure. Will I bet it will replace steel and other construction materials almost everywhere, I will. As hard science it is the best material we currently have, there is no doubt. It looks like it even have superconductive properties, around 0.5K, but still - [Electrical Properties and Applications of Carbon Nanotube Structures, page 9](http://maeresearch.ucsd.edu/bandaru/Publications_files/JNN_CNT%20review.pdf)
So as far as op interested in future materials, it is. It may be same thing as people 100 years ago was thinking that chemistry will do the magic and can solve everything, and it didn't even if it plays significant role today.
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A simple solution might be how the Apollo LEM discarded excess heat from its electronic components. They exposed water to the vacuum of space, where it boiled off, sucking the heat out of the heatsink on the outside of the spacecraft that the water was sprayed onto.
Without water, a heatsink can't radiate heat in the vacuum of space... no air to carry the heat away.
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
Consider using thermoelectric cooling, and you will have a chance to generate some extra power for your spacecraft.
<https://en.wikipedia.org/wiki/Thermoelectric_generator>
Mount the Seebeck generator in the wall of your spacecraft, and use heatsinks to direct the heat to the generator from the inside. The greater the difference between plates, the more power you will be able to generate out of it.
You won't be able to cool down all excess heat through this process, so you can use radiators to cool down the rest.
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[Question]
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Animals on planets are so 20th century - let's herd us some space animals!
In this story I have the need to move a herd of pesky space animals. They like Suns for their juicy solar energy and hydrogen, have stumbled into our solar system and are in no hurry to leave.
This causes some problems, I'll come up with those later on, the point is that my guys will want to move the herd about.
So:
* How would an animal in space evolve with an ability to move rapidly? What, specifically, would be the bodily apparatus for movement?
* How would we go about herding them?
* They move at about an eighth to a half of the speed of light, can be a bit less or a bit more (I'll change this if it turns out to be problematic, please let me know. Do mind that they have a long way to go between solar systems).
* The movement must be sustained for quite a long time (dozens of years, between stars), so particle ejection (Jet?) based movement is less preferable to say, some form of gravity manipulation, because I don't want my space animals to get stranded in the great void with an empty particle/fuel tank, without the ability to refill it.
* They're solid animals, not gas/plasma based like in some sci-fi stories
* Their size has to be larger than a small space craft (can't nudge them about, or capture them easily)
* They're not aggressive but will defend themselves if they feel threatened
* I don't care much about shape, though exotic ones will be nicer for the story (see: [How do I prevent my turtle from collapsing under its own gravity?](https://worldbuilding.stackexchange.com/questions/1359/how-do-i-prevent-my-turtle-from-collapsing-under-its-own-gravity/2746#2746) )
* EDIT2: The life span of the animals and their evolution span can be long, really long. I'm thinking a couple of thousand of years for life, and the evolution can take billions of years. But you may suggest other spans as needed.
EDIT: Ok, I found this: [Could life form in outer space?](https://worldbuilding.stackexchange.com/questions/1401/could-life-form-in-outer-space) but I don't feel that it covers the speed and supposed energy requirement of my space critters. Also, it seems to lack a hard science discussion about evolution (see the comments by @Peter Masiar). I'd like to get a plausible, sizeable, rapid-moving animal that will eventually damage the sun or humanity's requirements of the sun (it's a futuristic thing so we might have a Dyson sphere that could be ruined or something like that. Suggestions into the manner of the disruption that the animal will cause are welcome, especially if they have to do with the animal's requirements for movement).
Yippie ki-yay, space cowboys
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I'd take a moment first to outline the limitations I see with spacefaring creatures. It's hard to see any kind of mechanism that would allow this kind of evolution purely in space, just on the basis of the harshness of the environment. I see the chance of some planetoid, maybe collapsing or cracking apart, with some species surviving the apocalyptic events and as their world decays and gravity and atmosphere slowly dissipate, the pressure to adapt remains and pushes the flora and fauna to gravityless and atmosphereless space. As this kind of changes would be more of the rapid and world-ending type, small species with short spans between generations would be my choice. From this, the simple fact that space is empty and big, the organisms would benefit greatly from the longer lifespans, meaning slower and larger. But as the change from small to large would happen in space, most likely any limbs designed to bear their weight would be gone.
I'm pretty sure any "realistic" means of movement go out the window with the requirement of such speeds, so I'll just give my ideas here, even though they won't match this requirement.
## 1. Movement
**Magnetic propulsion of various sorts.**
Currently available(realistic in that sense) include Ion thrusters, Magnetoplasmadynamic thrusters and their variants. Usually operated by pushing some form of fuel, after ionization, through an exhaust. Siphoning hydrogen off stars would be a good way to get some plasma going, though the amounts for any realistic propulsion required would be quite massive(and getting massive faster than the creature itself). And don't even think about going fast with this option. It's good for efficiency, but speeds are abysmal.
From the outer-space life topic linked, the Solar sails type of creature could pretty well fit into this type of movement as well, diving close to the sun for a gulp of gaseous plasma and then flying away with sails. In large enough numbers(someone better with numbers has to do the calculations) they could basically speed up the life-cycle of Sol, consuming the hydrogen and rapidly shifting our sun to the end of its life as a red giant.
**"Spitballing"**
Clam-like accretion of a ball of space debris and accumulated dust from their travel across the void. This movement isn't very precise, nor very efficient at going exactly at a destination. Asteroid belts and planetary rings might be alluring to these creatures for just propulsion purposes. This type of movement would also act in pretty much a end-all solution for the animals needs: Capture ice for things like breathing(!!) and nutrition, use up the minerals and whatever you can't use, you'll store up and use later on as you spitball your way across the universe.
A threat from clams sounds pretty silly unless there's some caveats made. They'd probably have to be large enough to swallow space stations. Perhaps the waste they spit for movement is durable enough to endure re-entry heating. That way if these creatures gather en masse to our solar system, we could see an increase in 'asteroids' hitting earth(they'd have to slow down when entering our solar system, so there'd be an initial chunk from interstellar travel, possible disruptions in the Oort cloud etc.) causing all sorts of havoc.
## 2. How to herd these creatures
First option is just a net. Carbon nanotubes or some other good tensile strength wire, woven to a net. As there are some advances already in that area, should be pretty manageable in the futuristic space zoo too. This would also work with the 'spitballers', as long as they're rid of huge chunks prior to capture. A dyson sphere would of course create a frozen and radiation free solar system, which would make the whole system undesirable for the thruster types and they'd leave or starve just by completing one around our sun.
Currently realistic options out of the way, there's always force-fields or tractor-beams. Any propulsion or solar sale kind of creature only needs the tiniest of tugs to counter their extremely slow acceleration, meaning they'd be easy to control with just some kind of radar mounted turning tractor-beam that assesses if any one of them is trying to accelerate away from their designated area and pulls it back. Force fields is just the go-to for material-free cage.
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Within currently known space and science you have only two real choices here - solar sails and propulsion jets. There is lots of other "maybe" stuff like gravity manipulation, reactionless drives, etc but absolutely none of them are currently even known to be possible.
Neither of those will let them get up to any significant fraction of C without an external boost so you may need to revisit that part of the concept. (I've seen figures of 4,300 years being used for how long it would take for an interstellar solar sail unboosted to cross from one star to another).
Most likely the creatures would have a combination of the two, jets for close maneuvering and personal defense used when they must and solar sails for primary propulsion since they do not require reaction mass.
The creatures could have a life cycle where they arrive in a star system and find a ring or asteroid belt. That they then seed with spores that use the raw materials to grow more of themselves. Once the younglings are fledged they start to gather close to the star, forming themselves together into an enormous lens. Finally as the last stage some of them move into the beam of light from the laser and use that to accelerate themselves out of the star system and across interstellar space.
Once they get too far from the star they enter hibernation, woken up when they approach the next system. Deceleration at the target star can be achieved in a number of ways, none of them simple. See this discussion here:
<http://www.centauri-dreams.org/?p=28653>
The good news though is that this gives you your hazard as well, this giant beam of energy concentrated from the sun and lasered out into space. That's a very deadly thing to have under the control of animal level intelligence beings acting as some sort of hive. Especially as they start building more and more of them and sending themselves out to more and more nearby stars.
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Perhaps they are engineered vonNeumann machines that have gone feral. They were engineered to gather raw resources, produce goods and perform services, and maintain homeostasis ans reproduce.
Those that reproduce and don't do the original purpose will have a competitive advantage. But they start to interact and form a biosystem.
[*Code of the Lifemaker*](https://en.m.wikipedia.org/wiki/Code_of_the_Lifemaker) is obviously due to a damaged tech system. The origin is left open for [Camelot 30K](https://en.m.wikipedia.org/wiki/Camelot_30K). I envision a complete replacement of purpose with evolved traits: they do become wild animals with little in common with the original genesis beyond the low-level metabolism toolkit.
An explicit creation gets around the issue of how such a thing would come to exist and shortcut the time scale needed for evolution.
Maybe *many* intelligent species have come and gone and their only lasting role is to add to the diversity of permanent galactic life. Over a time span of millions of years they mix and spread and encounter remains of planetary life that reached the point of technology and space-fairing, and incorporates the stuff it finds.
---
Machines assembled using self-growing nanotechnology will be more like living things we are used to. Rather than a factory making an engine casing out of metal or composites, it would *grow* it featuring an internal circulatory system and nanobots that incrementally take-up and re-pave the advanced composite structure from within. In *us* those are called osteoblasts and make bones.
Perhaps components that work under conditions that can't withstand being fully alive would be formed in another organ, like a shell is grown but not living; then installed when needed.
Ion engines may need parts formed in fab organs and moved into place. But a solar sail is well suited to being living tissue through and through, constantly maintaining itself against wear and damage. Long mooring and control lines may be carbon nanotube that's patrolled by tiny nanobots that constantly crawl its length and rework the material. Raw materials would be carried by more efficient specialized carriers that also use the lines as a freeway, perhaps along the inside of hollow tubes, like a dry blood supply.
The fundamental technology of the original machines would be nanobots that grow through asteroids and commetary bodies like fungus hyphae, digesting it and harvesting raw materials, moving it to concentrated stockpiles. As greedy organisms they would be just like mushrooms, eating bodies where spoors land and producing units that travel to new sources of material. They may be as simple as durable spoors and not need much propulsion within the belt where they are found.
As part of a larger ecosystem, they would play the role of concentrating and providing raw and refined materials for others to use: growing *fruit* to be taken by other types of creatures.
So there are roles not just for "animals" but all manner of categories some of which are clearly analogous to algae, plants, fungi, plankton, etc.
Asteroid-sized rapidly mobile heterotrophs with active defenses and teeth are the first thing you may notice — space animals. But they're just the top of a food chain. Fungi mines raw material. Plants collect sunlight and form large stable platforms. Microbes specialize in many different metabolisms and live in and around the macro forms where their special features are employed.
[Answer]
>
> How would an animal in space evolve with an ability to move rapidly? What, specifically, would be the bodily apparatus for movement?
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This would likely be a combination of things. Inside a solar system using sails to catch the solar wind would be the most energy efficient. However, have some kind of jet/ion propulsion would be useful for faster course corrections or added bursts of speed.
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> How would we go about herding them?
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You would need to have some idea of what they want/need and what they fear. One useful thing would be to build your space ships for herding to have at least a nominal appearance to the animals themselves. If you make your ships larger then depending on the mentality of the animals, you might even be able to 'lead' them, but herding would likely be easier and less likely to get an attack response.
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> They move at about an eighth to a half of the speed of light, can be a bit less or a bit more (I'll change this if it turns out to be problematic, please let me know. Do mind that they have a long way to go between solar systems).
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That is pretty fast. I was looking for information on speed of solar sails, and while they can get things going pretty fast, (fast enough for inter-solar travel) the max estimate I could find under ideal [conditions was 1/10 c](https://answers.yahoo.com/question/index?qid=20130424072128AAljehh). So to go much faster than that they will also need a propulsion system, which for interstellar travel will need a decent sized 'fuel tank'.
1/2 the speed of light is FAST, and they become planet killers if they should run into one. To even come close with the least amount of energy expended, would be to dive toward the sun, picking up speed, and 'slingshot' out, furling out the solar sails near the bottom of the swing to help speed up more on the outbound run.
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> The movement must be sustained for quite a long time (dozens of years, between stars), so particle ejection (Jet?) based movement is less preferable to say, some form of gravity manipulation, because I don't want my space animals to get stranded in the great void with an empty particle/fuel tank, without the ability to refill it.
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The nice thing about space is that other than gravity wells you just keep on going at a constant speed in the direction you set. So once the herd has reached cruising speed (what ever that happens to be) they can all go dormant for the trip. They can deploy their sails to start catching solar winds when they approach the destination star to slow them down for entry into the system.
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> I don't care much about shape, though exotic ones will be nicer for the story (see: How do I prevent my turtle from collapsing under its own gravity? )
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The shape could be anything, but being able to open and collapse to catch and 'dive' the solar winds would be useful, maybe like an octopus? Likely they would need to be able to handle impacts from small matter since traveling at relativistic speeds is dangerous for any collision.
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> The life span of the animals and their evolution span can be long, really long. I'm thinking a couple of thousand of years for life, and the evolution can take billions of years. But you may suggest other spans as needed.
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That might be needed just to get a species that can travel between the stars, though if they go dormant during travel it could help increase their lifespans easy.
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[Question]
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A space colony that resembles the design of a [Stanford torus](http://en.wikipedia.org/wiki/Stanford_torus) generates artificial gravity by centripetal force.
Discussions about benefits of such fake gravity can be easily found: no more constant physical exercise like in today's space ships (you can concentrate on your mission); many activities that are not possible in today spaceships may be possible with artificial gravity.
Discussions about differences with real gravity can be found too: some say that if you throw up a coin, it won't describe the same curve as in Earth. Due to the rotational velocity of the torus, the coin will fall down and towards the direction opposite to the torus rotation.
If we cannot return to Earth:
How many generations are needed for any change to start to show? Of what might those changes consist?
[](https://i.stack.imgur.com/bFIgG.png)
[Answer]
The point of the rotation is to emulate earth level gravity, so you should not expect to see any large scale changes.
Where you would see changes though is in balance and rotational expectations. As you already mentioned the thrown coin would fly "wrong". You would also see this when running, turning corners, standing, etc though.
Depending on the size of the torus these effects may be smaller or larger though, for example the wikipedia article on this sort of space station says that:
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> Turning one's head rapidly in such an environment causes a "tilt" to be sensed as one's inner ears move at different rotational rates. Centrifuge studies show that people get motion-sick in habitats with a rotational radius of less than 100 metres, or with a rotation rate above 3 rotations per minute. However, the same studies and statistical inference indicate that almost all people should be able to live comfortably in habitats with a rotational radius larger than 500 meters and below 1 RPM. Experienced persons were not merely more resistant to motion sickness, but could also use the effect to determine "spinward" and "antispinward" directions in the centrifuges.
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So as long as the station was sufficiently large humans would see very few effects and would quickly acclimatise.
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A space-faring civilization is beyond the point in history where the environment exerts much evolutionary pressure on the species (that's why our eyes get worse and we have allergies -- imagine that in front of the tigers or mastodons 15000 years ago). Perhaps gravity high enough to prevent moving around (and thus sexual intercourse) in physically weak individuals would favour reproduction of strong individuals; but then reproductive medicine makes intercourse superfluous anyway. Plus chances are that space dwellers are naturally infertile anyway because of radiation exposure, so high gravity wouldn't favour anybody anyway.
Edit: Since you are hinting in a comment that you aimed at the difference between "emulated" and "natural" gravity: these are misconceptions. Gravity is a curvature of space time, whether by "acceleration" or by "being in a gravity field" -- the difference between both is just a difference in the point of view, as the theory of general relativity states. The famous person in the falling elevator (read: closed system) cannot tell whether s/he is in zero gravity or in free fall on earth. It's physically indistinguishable, it is identical. In the same way a person in an *accelerating* elevator could not tell whether they are accelerating in zero gravity or standing still in a gravity field. It's physically identical. None of them is more or less emulated or natural.
That said, of course a circular motion "curves space time" for the dwellers in a way that they perceive somewhat different accelerations when they move (the coriolis forces) than on earth; but that is a (quantitative) difference in vector, not an essentially different affair which would influence people or affect our genes. Unless you have a tendency to become dizzy when you move quickly forward and backward -- that might decrease your reproductive chances in a space station ;-).
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The bigger the habitat, the less difference there will be, since Coriolis effects decrease with lower RPM, and a bigger habitat can rotate more slowly and still have 1g at the rim.
I think the biggest difference will be that gravity will be *variable*, with the highest gravity at the rim of the hab, decreasing as you head towards the center, and zero at the hub. That means that people can spend part of their day in normal G, and part in low or no G, depending on the activities they're doing.
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All of this reasoning surrounding this scenario presupposes the similarity between actual gravity due to a mass, and the angular velocity and moment of inertia due to the torque of the rotating torus; of which there IS no comparison.
Gravity sucks, and Torque pushes (or blows :p ), so any perceived "symptom" of gravity would be a placebo, initiated and sustained by continuous contact with the rotating body.
Necessarily, one would need not to leave the inside surface of the torus to benefit from the simulation of gravity. If one were to say, reach out over the side, they would be jettisoned outward along the Force vector F.
Human nature being what it is, and more curious than cats; to answer the Question in the OP: "How many generations are needed for any change to start to show?" -
Answer: This is immeasurable, or equal to the Null Set, as no population would reside on the torus long enough to find out. (this is akin to asking the age-old Tootsie Pop question.) Also, to suppose there could be a fool-proof method of containing said Curious Adventurers, we need only refer to Murphy's Cathode-Ray Corollary which states that "A $500 picture tube will always protect a 50¢ fuse by blowing first".
tl:dr version:
Answer = i/0
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**List of very quickly recognizable symptoms**
* Weakness
* Unusual blood from unusual bone marrow
* Increased height
* Lower real-gravity tolerance
* Clumsiness?
**List of later symptoms**
* Radioactivity protection
* Giantism
* Mental patterns associated with small spaces
[Answer]
We already have examples of people living for long periods of time in places that have even bigger differences in gravity (compared to that experienced by ground pounders):
ocean-going vessels.
As far as I know, there are practically no differences between people whose families have been sailing the seas for centuries, vs. people whose ancestors have been walking on land for generations.
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> Of what might those changes consist?
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Perhaps in space, everyone talks like a sailor? :-)
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I'm not sure if emulated gravity would have much effect, but the overall strength of gravity would certainly have one.
If the gravity was weaker, then the people on board would be weaker as well. The density of their bones would also be less, so they would be frail compared to an earthling. If they did go back to Earth, they would have a hard time moving around. There may be some other health related effects as well which could shorten their lifespan. How much of a change would be anyone's guess.
On the other hand if the gravity was stronger, than the people born there will grow to be stronger than the average earthling. They would be able to do great feats of strength on Earth and generally make everyone else look like a weakling.
These effects would be present in the first generation born there, or to people who have spent a very long time there.
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[Question]
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Internal mass drivers are a potentially useful space drive, due to the ready availability of reaction mass (you can use anything from spare parts to literal dirt as a propellant, assuming you have a ferromagnetic bucket that you decelerate and retrieve at the end). However, on long trips on which *in situ* resource utilization may not be available, especially interstellar generation-ship trips, one would want a higher exhaust velocity, to maximize the fuel efficiency of the drive.
The excellent Atomic Rockets site contains [this](http://www.projectrho.com/public_html/rocket/enginelist.php#massdriver) set of stats for a mass driver, but the exhaust velocity of 30 km/s isn't quite up to scratch for an interstellar spacecraft, even if you simply strap your craft to a convenient small asteroid to use for fuel. If we were to multiply the length of the drive by ten, according to the equation $v\_f^2 = v\_i^2 + 2a \Delta d$ (relativistic effects are negligible at these velocities, so we can ignore them), for a mass driver with the same acceleration, but ten times longer, we get an exhaust velocity of a bit under 95km/s, which is quite a bit nicer, even though we had to increase the mass of the drive and its power source by a factor of ten to increase the exhaust velocity by a factor of a bit over three. However, I don't know if it's actually possible to scale up a mass driver in the way I've described.
**Would it be possible to scale up a Mass Driver by simply making it longer?** Are there any factors that would require the mass to increase more than would be assumed from a simple "make it longer" perspective? Are there any other factors I'm not considering here?
[Answer]
**Yes, but the engineering would be tricky.**
Even getting to 30km/s is tricky. Current experimental railguns [only manage between 2 and 3 km/s](https://en.wikipedia.org/wiki/Railgun). A large part of that is due to limitations on the power supply and barrel length for practical weaponry applications (which are exactly the things you are looking at changing), but not all of it; even lower-powered railguns experience problems with rail erosion and electro-welding, which will seriously screw up an engine!
To solve those issues, you'll want to go with a [coilgun](https://en.wikipedia.org/wiki/Coilgun) (or "gauss gun") instead. I am not aware of any large-scale coilguns having actually been built; they are considerably more complex than railguns, as they require careful synchronization of different accelerator components. Small-scale coilguns, of the kind that [a dedicated hobbyist could build in a garage](https://www.youtube.com/watch?v=Py8BdLTZEAE), avoid the problem of electro-welding, but will still have to deal with frictional heating and barrel erosion. Fortunately, however, it seems that a large-scale coilgun [can be designed to naturally center the projectile through magnetic levitation](https://pdfs.semanticscholar.org/c693/85ff21e6a481514905bac4b9b5cd8c5f47b9.pdf). While this sort of military-grade coil gun is currently only designed to hit around 3km/s in atmosphere, there is no *fundamental* reason why it could not be scaled up to arbitrarily high muzzle/exhaust velocities when operating in vacuum, as long as you ensure that the projectile *never actually contacts the barrel walls*. "All" you have to do is make sure that the wave of accelerator coil activations accelerates slightly ahead of the projectile for the whole length of the barrel, and that the barrel infrastructure can support the reaction forces. Since the *force* on the projectile need not increase with a larger length, it should be possible to extend the barrel indefinitely with only a linear increase in structural mass. Additionally, the mass of the barrel infrastructure can be kept down by simply putting a cap on the maximum mass of a single projectile (thus capping the force required to accelerate it)[\*], and 95km/s is well below the speed at which electrical control signals can be sent along the barrel.
In practice, unless you have *extremely* good quality control on the inputs to your mass driver, you will not want to use a single centralized control system; the acceleration profile of each projectile will likely be slightly different, so you will want lidar sensors (or something equivalent) distributed along the barrel to measure the projectile's actual progress and trigger successive accelerator coils locally.
There is also the issue of bucket/sabot recovery. If you want all components of the drive to be reusable, and you want to be able to just dump whatever mass you have on hand into it as remass without pre-processing, then
1. You need an accelerable bucket to carry the arbitrary mass in, as you can't depend on the remass itself to have the necessary magnetic properties.
2. You can't throw the bucket away.
If you are OK with carrying some dedicated "fuel mass" and just augmenting it with arbitrary stuff, then you *can* throw away your sabots, and things become simpler. A similar situation applies if you have onboard facilities to refine mined materials into sabots--but then you can't just use whatever you find willy-nilly, and you have the added complication of the refinement and manufacturing facilities.
So, how do you go about recovering the bucket(s)? Well, for one thing, you know that an empty bucket obviously has less mass than a bucket full of remass, so you can decelerate it much more quickly given the same amount of force--and since the deceleration stage will put the barrel under *tension*, you can use a much higher deceleration force! That means that bucket recovery will *not* take up half the length of the barrel; 10% or even less would be plausible, and the size of the deceleration section will scale linearly with the rest of the driver. The tricky bit will be actually catching the buckets at the end and returning them for re-use. I am not at all sure how to arrange that infrastructure in a way that leaves an opening for the remass to pass through and does not add a bunch of moving parts that are then prone to potential failure.
[\*] You can save even more mass by arranging the mass driver in a tractor configuration, with the barrel extending *in front* and the bulk of the ship arranged around the nozzle. This will put the whole thing in tension, and structural metals tend to be much stronger in tension than in compression (if you are building the support structure of the barrel out of asteroidal rock, on the other hand, that would be a bad idea, as rock is much stronger in compression). If you arrange things carefully, you can make sure the deceleration section is also in tension, but if that becomes impractical, take comfort in the fact that the bucket deceleration section is relatively tiny anyway, so you still get a net saving in total mass.
[Answer]
**Ouroboros mass driver.**
The thing about the long long long mass drivers is that each set of coils gets one use for each chunk of propellent and then it is done. Inefficient! They are expensive, those coils. And it is one thing to have a 2 km barrel lying quietly on the moon, another one to mount it sticking priapically out of your starship. The aesthetics, you know.
I propose the round mass driver, which your ship will wear tastefully girdled about its midsection. The payload goes around and around the circular track, passing through the same set of coils over and over, accelerating as it goes. Each pass through your coils adds energy. Of course, larger is better here because of the centrifugal force pushing your projectile against the bottom of the track as it turns, but your track is tough stuff and you can rig your secondary semicircular coils to exert a magnetic force on the projectile opposing its tendency to push out radially.
The final speed of your projectile will depend on what sort of radial forces your track can withstand and how successfully you can counter that radial force with magnetism. At the point of release your track will open up (hopefully at a purpose-built point for opening) and the spun-up-to-speed projectile will emerge.
Also, this device will make a terrifyingly awesome sound, audible in all parts of the ship.
[Answer]
There are three things that I can think of that would stop your mass driver design scaling linearly.
1. You need your structure to maintain some minimum level of rigidity rather than the whole thing bending and flexing on every shot. As I am not a structural engineer, I can't actually tell you what wort of material limits you might hit, but at some point, your materials are simply not going to be up to the job.
2. Inefficiencies. Some proportion of your mass driver's energy is going to end up heating the bucket instead of pushing it. If you pump that energy in faster than the bucket can radiate it out, you're eventually going to have the whole thing explosively vapourise. You will not reach Alpha Centauri today. If you're not using superconductors, you'll also find that losses in your big power lines will be a bit of a problem, too.
3. Power switching. In a coilgun, you'll want to be able to turn off a coil ASAP once the drive bucket is through, or it will just cause drag and slow everything down. The faster your bucket is going, the harder it is to turn things on and off fast enough. I seem to recall reading something about superconducting drive coils which you'd cook with lasers to quench them as fast as possible, but I sense lifetime limits and cycle time issues there!
There are other ways to improve your mass driver though... consider using superconducting buckets instead of ferromagnetic ones, because you don't hit magnetic saturation issues at a puny tesla or two, but instead can use tens- or even low-hundreds-of-tesla magnetic fields. You'll squeeze a few extra percent of efficiency out of the system too.
(in the limit, you may find it easier to simply ionise your reaction mass with electron beams, and accelerate the cloud of plasma out the back. that works with any fuel too and might end up being simpler to make!)
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The problem is that your giant, hard-to-build, hard-to-run mass driver still only provides a puny 10000s $I\_{sp}$. That's a slow boat to the Oort cloud, let alone visiting another star.
Assuming a 100km/s exhaust velocity, and a pretty optimistic 1000:1 mass ratio, you've got a $\Delta\_v$ of 690km/s. If you blow it all on acceleration, and use some other means to stop, it'll take you nearly *two thousand years* to get to Alpha Centauri. I'll bet you ten bucks that in that timespan, someone will have invented a better drive. If you're lucky, they might collect you on their way past.
The take-home message should be "don't use mass drivers for starships". Or visiting the outer solar system, for that matter. Leave em to the 1950s asteroid miners.
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[Question]
[
A common, matter-efficient science-fiction habitat is a hollow cylinder or ring in space that is spun to simulate the pull of gravity on its interior surface. These habitats have been imagined as small as a spaceship, mere meters in radius, up to a ringworld, 1 AU in radius.
Say we have a rotating space habitat designed to mimic Earth’s gravity and atmosphere at sea level. Assume that the habitat has been rotating for however long it takes to reach whatever equilibrium state can be achieved. Will the rotational motion of the habitat generate winds in its atmosphere? In which direction will they prevail, spinward (with the direction of rotation) or anti-spinward (against it)? Will they circle the ring in a single direction or will there be antiparallel winds at different altitudes?
Ideally answers would be applicable to rotating habitats of various size, however, if the answers would vary widely between habitats please use a ring 10,000 km in radius for the answer.
Edit: There have been some previous questions about weather on rotating habitats such as my own [What would the weather be like in an asteroid habitat?](https://worldbuilding.stackexchange.com/questions/3211/what-would-the-weather-be-like-in-an-asteroid-habitat) and [Weather on a mini-ringworld/Banks Orbital](https://worldbuilding.stackexchange.com/questions/8508/weather-on-a-mini-ringworld-banks-orbital). These questions are quite broad as weather is a complex subject, to put it mildly, and so were not very answerable. Here I have attempted to narrow the focus of the question to a single aspect of weather, the wind, in the hopes of generating more complete answers.
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The real answer is we don't know, we can make some guesses though.
Lets start with ground effects; the range of effect of pure physical topography on the atmosphere, not including heating effects, is only about half a kilometer. On Earth this is purely vertical, as are a number of other effects that we'll talk about, but on a Ringworld type structure the effects are also horizontal because of the side walls that keep the atmosphere in. So near the floor and walls the winds are going to be relatively turbulent but the prevailing wind pattern will be a gentle anti-spinward breeze as the air is dragged at by the ground topography, and the walls, but doesn't move quite as fast as the ground. The ground will be moving at roughly $ 10000m/s$ to supply $ 1g $ of pseudogravity, if the air immediately above it is only doing an average of say $9990m/s $ local winds could be quite strong due to turbulent flow but the air mass as a whole will be doing $ 10m/s $, or $36km/h $, anti-spinward; while I'm not sure of the magnitude I would expect that to be the case.
Then there's heat effects; the floor of the ring will be hotter than the walls due to [solar angle](https://en.wikipedia.org/wiki/Effect_of_Sun_angle_on_climate) effects this is going to create a wind system very similar to a [Hadley Cell](https://en.wikipedia.org/wiki/Hadley_cell) with the centre of the ring as the equator/tropics and the walls as the subtropical desert zone. The reason I asked about the width of the ring is that over millions of kilometres, like Niven's ring, this effect wouldn't be so singular but a "narrow" 200km ring is going to see an almost perfect singular formation.
Net effect; surface winds are going to be turbulent but blow prevailingly from the edge inwards along the floor of the ring with an anti-spinwards twist, similar to the [Coriolis Effect](https://en.wikipedia.org/wiki/Coriolis_force#Meteorology) but with less deflection, high altitude winds are going to be fairly laminar and travel from the centre of the ring out towards the walls with ever more anti-spinward drift as they gain altitude. The wall areas will be relatively dry as most rain will fall as the air initially rises close to the centre of the ring.
Note this answer assumes reasonably vertical walls rather than some smooth bowl shape, not sure how that would go, probably broadly similar. It also assumes that the ring floor is "flat" not meaning particularly smooth but without any full-width profiling to either a "^" or "v" shape. I have not included the effects of a Shadow Square system in this model at all, I can try but they'll be extremely complex and vary considerably according to proportional day length and a number of other variables.
[Answer]
**Convection is the answer.**
Imagine you are inside a car, traveling at (just to say any speed) 65 mph. You, your clothes, your seat, and (of course) the air inside the car will be traveling at the same speed: 65 mph. And you will not feel any air current inside despite the fact you are moving fast.
If you have an isolated gas inside a rotating cylinder or a ring (no matter the size), the gas will rotate at the same speed as the other objects inside the cylinder or ring, so you will not feel any wind at all. BUT (here comes the interesting part): what really causes the wind currents in the atmosphere are the **thermal differences**. And here goes a further explanation:
If your cylinder has a "night" part and a "day" part, the part in the daylight will be hotter than the part in the dark. Therefore, you will then have the first "convection circuit": The hot ground in the day will heat the air nearby, and the air will raise (as a hot air balloon), dragging cold air from the night side. If you have water involved (lakes, oceans) the water acts as a heat reservoir, and includes additional convection circuits in the loop.
And of course there are the cities. The cities generate a lot of hot air that goes upward, and creates additional air currents.
And finally, now that you have "moving air" then yes, your moving air is affected by the rotation of your space station the same way the sea and air currents are affected by the Earth rotation.
The more "realistic" model you want your air currents to be, the more variables you need to include in your model. And, well... it is actually a science by itself. But you can have a very good starting point defining your day and night regions, and your water regions.
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**Example with an O´Neill cylinder**
Because this is a question science based, let´s take a standard O´Neill cylinder. This was a space settlement design proposed by American physicist Gerard K. O'Neill in his 1976 book "*The High Frontier: Human Colonies in Space*". You can find more information here:
<https://en.wikipedia.org/wiki/O%27Neill_cylinder>
This design is a cylinder with six stripes along. 3 of them for settlement (land) and 3 of them as windows. Each of the windows has a movable mirror that simulates the day-night cycle. There is plenty of documentation about this concept. In this link you can find a nice diagram (I am also including the image): <https://www.artstation.com/artwork/28NNB>
[](https://i.stack.imgur.com/RA5pv.jpg)
And this is how it may look from the inside:
[](https://i.stack.imgur.com/g7YBd.jpg)
That space colony, viewed from the top of the cylinder will look like this:
[](https://i.stack.imgur.com/zPaJR.png)
And the sun will enter into the space colony this way (remember the mirrors open and close to simulate day and night):
[](https://i.stack.imgur.com/3Kvtp.png)
Now here comes the answer to the wind question:
The 3 land stripes will be heated by the direct sunlight, and the 3 glass windows will be cold (just like the glass window in your house when you touch it on a very cold day. Space is quite cold when not in the sunlight, and the windows must be transparent so the sun can enter. Therefore, the windows will be cold and the land will be hot. That creates the first convection circuit (the first winds in your cylinder):
[](https://i.stack.imgur.com/hze6i.png)
However, the cylinder has to **rotate** to generate gravity. And the wind particles (as mentioned above in previous answers) will be rotating faster in the positions away from the center of the cylinder, and motionless in the axis along the center of the cylinder. So the loops of the wind currents will suffer a slight deformation as depicted below. Note the additional effect of the 3 mirrors in the center of the cylinder: the 3 mirrors will be heating directly the air in the central axis. So, adding this to the convection currents, will result in a region of motionless hot air in the center axis of the cylinder.
[](https://i.stack.imgur.com/npqFQ.png)
Finally, please remember (and here comes the disclaimer) no one has ever built anything like this (well, not in our Solar System). So we really can´t be completely sure about the winds or anything weather-related inside a colony like that (we can´t even predict completely our own weather here on Earth).
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Ash and boxcartenant's answers both claim that there will be a constant wind on the habitat, perceived as anti-spinward by residents, due to "resistance" against the spinning. However, after some long conversations, I am reasonably sure that this is a misunderstanding, and will add my own answer:
## Thermal equilibrium
Note that this *ignores thermal effects of nearby stars*, so you have a universe with uniform background radiation (to keep the fluid from freezing), and you spin up a ring or cylinder or torus with fluid inside it.
The torus is easiest, so I'll start with that:
At first, the fluid touching the surface will be dragged along with it (due to ["no slip" condition](https://en.wikipedia.org/wiki/No-slip_condition)), and the fluid in the center of the tube will not (due to inertia). It will have the same parabolic velocity profile as fluid laminar flow in a pipe:
[](https://www.engr.colostate.edu/CBE101/topics/fluids_and_fluid_flow.html)
From the perspective of someone standing on the inside of the tube, this would appear as a "jet stream" of wind in the center altitude above their heads.
After a sufficient period of time, however, of the tube rotating at constant speed, no longer accelerating, the momentum from the surface will be transferred from the outer layers to the inner layers, and so on, until all of the fluid is spinning at the same constant rate as the tube. The fluid is now in [hydrostatic equilibrium](https://en.wikipedia.org/wiki/Hydrostatic_equilibrium), the entire habitat in uniform solid body rotation, and there is no wind. Any turbulence or cycles will wear themselves out and dissipate into heat. This is the state it will stay in forever, without any outside interference.
Because of the rotation, the fluid near the outer wall will be more compressed than the fluid near the inner wall, so it will have a pressure gradient like Earth's atmosphere.
In a walled cylinder habitat, the same thing will happen, except there is no inner wall to drag the fluid.
* [Video demonstration](https://vimeo.com/419978552)
* [Video demonstration](https://www.youtube.com/watch?v=oCg1tK4arNM)
* [Images](https://mirjamglessmer.com/2013/11/25/water-in-solid-body-rotation/)
In an open cylinder or ring, like a Banks orbital, the fluid in the center will just drift away and be lost, because there are no walls and it's not adhering to the surface. Only particles that collide with the surface will become carried along with it.
* [Simulation of this effect in a 2D universe where the liquid cannot escape sideways](http://www.algodoo.com/algobox/details.php?id=232826)
Initially, the particles are not rotating, but as long as they have non-zero drift velocity, they will eventually encounter the ring, which will impart momentum on the particle and then capture it.
So there is no inherent wind just because the habitat is rotating. This will only happen at spin-up or spin-down (as described in [*Rendezvous with Rama*](https://en.wikipedia.org/wiki/Rendezvous_with_Rama)).
## Not equilibrium
If you add a star nearby, of course, the thermal gradients from cycles of night and day will cause new flows of fluid, relative to the surface.
I'm much more hazy on what happens in this case. The Coriolis effect acts vertically instead of horizontally, so either there won't be cyclones, or they won't have a preferred rotation direction. This effect may also cause a prevailing wind, I don't know.
[Answer]
Assuming this is an open ring (i.e. no ceiling), in order for the atmosphere to be dense at the edge of the ring, the gasses in the atmosphere would have to be affected by the same centrifugal forces which are simulating the gravity, so they have to be spinning with the ring. Also, as long as there is any friction or obstruction at all on the surface of the ring, it will drag the gas along with it. So in general, it will feel like there is no wind at the surface
Now, the air closer to the center of the ring will be less affected by the friction and obstructions on the surface (in addition to having a slower linear speed). If the ring is open, then the upper atmosphere will not be as motivated to keep pace with the angular speed at the surface, so when people go up on a high mountain, they will feel some wind in the anti-spinward direction. (It will feel like wind to observers, but the air really just has a slower angular speed).
Like Carlos Zamora said, though, the more variables you add, the more realistic your model will be. If you have some other body in near orbit to the ring, its gravity will affect tides and wind; if you have a night/day cycle, the temperature will affect wind; if you have mountains, they will affect the shape of the wind by obstructing it, and their gravity will affect the barometric pressure there; etc..
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[Question]
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I have two "new" planet earths -- we'll call them Light Earth (LE) and Heavy Earth (HE). These planets are generally the same as our Earth in terms of land masses, oceans, the moon and sun and other terrestrial objects, weather, and so forth. The difference between them and our Earth is in the force of gravity. On LE, gravity is less than that of our Earth, and on HE, gravity is greater than ours.
**How does gravity affect the evolution of flora and fauna?** Would trees be taller on LE and bushes more prevalent on HE? Would there be no birds on HE? (And if there are no flying birds, are there more dinosaur-like things still present? or more emu-like birds?) Would there be more fish at greater depths in LE?
This question is *only* about the evolution of life on the HE and LE planets. I am aware that a difference gravity would change how the planet itself would evolve (plate tectonics, atmosphere, etc etc). We're going to ignore that for now.
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I'm looking for the *general overall* effects of a different gravity on evolution -- something like "there will be fewer flying mammals in higher gravity, and they will compensate by XYZ." I've intentionally *not* given numerical values for "higher" and "lower" gravity, but let's consider a range of [10%,190%] of our Earth's gravity, if such a thing matters.
Please note that I'm intentionally not changing the gravity of our Earth. These are brand new almost-duplicate Earths (minus the gravity) whose wildlife and plant life *evolved* in that environment. The majority of the gravity related questions here appear to be about taking an existing organism from our Earth and placing it in a new gravity environment; this question is intentionally *not* about that.
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***Related Questions***
* [How would much stronger gravity affect tiny living things?](https://worldbuilding.stackexchange.com/questions/46262/how-would-much-stronger-gravity-affect-tiny-living-things)
* [What consequences could a higher surface gravity have on life and geological evolution?](https://worldbuilding.stackexchange.com/questions/40250/what-consequences-could-a-higher-surface-gravity-have-on-life-and-geological-evo)
* [If the gravity was half as strong, how would the environment change?](https://worldbuilding.stackexchange.com/questions/3224/if-the-gravity-was-half-as-strong-how-would-the-enviroment-change)
[Answer]
I think you would end with two really differents planets. I will probably forget some factors, but here is what might happen.
## **The Heavy Earth**
Gravity there is way stronger that normal. Animals, fauna and ourselves would need a stronger body in order to be able to fight it, or evolve to be able to keep living without much effort. Plants would need great growing strenght blossoming and keeping their leaves up to the sky.
(Thanks Burki for the details) **However**, it would not be total grounding. Stronger gravity would mean more oxygen per cubic meter, which means your animals and plants will be able to compensate some of their constraint with higher muscle irrigation, thus efficiency. And this is an excellent news because you can imagine one or two species which may take advantage of this point (improved breathing system e.g) to live rather normally, with an edge on other creatures !
*De facto* (I love this term), you would find yourselves with two cases of animals / plants, if we take out the oxygen barons:
* Bulky animals, who are normal in height compared to our animals but way more muscular to sustain the pressure of the gravity. Your trees would be *hella shaped* as weel, with huge trunks.
* Small animals, very slow, but very strong. Close to the ground in order to reduce the effort, maybe crawling animals like snakes would be more common.
Insects would be little affected, I think: most of them have an outstanding [power by weight ratio](http://www.telegraph.co.uk/news/earth/earthpicturegalleries/7521275/The-strongest-living-land-creatures-on-Earth-measured-by-their-power-to-weight-ratio.html?image=2). Plants, too, will be either close to the ground or growing to a little extend before falling to the ground. Small [cute little arch tress](https://thumbs.dreamstime.com/z/natural-tree-arch-forest-28540591.jpg), maybe.
I don't really know about fishes, but pressure there would be times and times superior. You would find deep creatures earlier in the depth map, and further ... You go boy, you can really create whatever you want.
Basically, I think our Earth would be flat as hell, with animals close to the ground, little birds only which would fly not that much. The flora itself would, too, stay close to the ground. Trees will be smaller, bushes more common, and most '\*high-ground plants' would mutate to be able to keep growing on a flat surface, or at least near the ground. Lucky strawberries lovers out there.
## **The Light Earth**
On light Earth, this is where things are getting fun. Your animals can deploy some power on something else that fighting against gravity. They can grow taller, fitter, with more speed, more power to deploy while hunting and fleeing. They, too, would be a bit muscular, because if you deploy such power into running, your body still needs to sustain the charge. A lot of birds might grow, too, bigger and faster than anything.
Plants, on the other side, are free to grow a loooooot taller, too. Small or big trunk, they can extend to meters and meter ahead of our current trees. Bushes would blossom, and even ground plants could grow up in size.
**BEHOLD HOWEVER !**
This does not mean you multiply anything by two or three. If you grow, you still need energy to feed youself. It just mean that your structure (animal or plant) can sustain higher without collapsing. Keep that in mind while designing your new species.
**TL;DR**
Heavy Earth will keep species close to the ground. They would evolve in a slow planet, in my opinion.
Light Earth will let them evolve in some interesting manner, letting them going as far as possible.
[Answer]
## Trees
Light Earth(LE): Stresses on branches will be reduced. Tress will be able to spread enormous canopies from a single slender trunk. The weight of a water column will be reduced, so trees will be able to grow to greater heights. Flowers will still have an evolutionary advantage, but perhaps not as much on our earth, as broadcast pollination will be more effective on this world. So maybe fewer and more primitive flowers.
Heavy Earth (HE): Height will still be a tremendous evolutionary advantage for plants, so there will be significant pressure to evolve systems to grow tall even against the greater gravity. One adaptation may be buttressing; trees that grow in clusters and lean into a central tree, grafting to the central trunk at various heights and creating a flying buttress for the central tree would be able to attain significant height against the gravity of the planet. This same support strategy would allow a spreading canopy to be supported by multiple limbless buttresses. Without such a support system, other trees on this planet would be very limited in the length of limbs they could radiate out from the trunk.
## Land Animals
LE: Leaping and hopping locomotion will be a much more prevalent evolutionary choice on this world as it will prove to be more efficient than standard quadrupedal gate. Gliding adaptations may prove to be more prevalent, as less significant body mutations on this world will result in glide capabilities that can be selected for. On this world, some species may take the the air and never come down for their whole lives. Large bodied animals will evolve more readily than on our world.
HE: Semi Aquatic habits may be prevalent, using the buoyancy of water to offset the cost of larger bodies on this world. Multi limb arthropods may have an advantage dispersing weight over a larger footprint and using a exoskeleton strategy vs an internal skeleton may be a much more efficient solution, ultimately requiring less skeletal mass to support similar mass of soft tissue. The highly segmented arthropod body plan may also allow for smaller, repeated respiratory/circulatory systems in larger animals to compensate for fluid pressure issues that will be present on this heavy world. HE might be a bug world.
## Flight
LE: Flight is a common adaptation on LE, with some species staying airborne most of their lives. Many and varied gliding adaptations will evolve.
HE: Flyers will need larger (relative to body size/mass) or more efficient wings to generate sufficient lift to fly on HE. Most animals larger than a sparrow will not be able to take off from a standing position on the ground. Needing instead to drop from elevation (or jump of a cliff) or run at speed along the ground. The idea here being that ground effects and the general unweildlyness of their large wings relative to their bodies will make it impossible to generate sufficient lift from a standing start near the surface.
[Answer]
Good technical reading for the less-obvious implications of microgravity (and a little on high gravity) is Fundamentals of Space Life Sciences Vol. 1 (edited by S.E. Churchill, numerous authors, Krieger Publishing, 1997). Low-gravity environments aren't that well known so you'll have to interpolate from the known effects of microgravity and centrifuge experiments.
I'll summarise a few points:
* Gravity redistributes blood pressure in the body. Humans blood pressure in orbit goes down in the limbs and up in the aorta; the head gets so much more blood that everyone has a puffy face. (See chap. 4.5 & 4.6.) Your high-gravity species need better ways to pump blood against gravity, low-gravity species need it less. Expect the heart size to differ correspondingly; the major muscles (in Earth animals) also help pump blood but these should already be scaled for gravity anyway.
* Humans have fewer red blood cells in orbit. This is believed (\*in one likely hypothesis) to be an adaptation to less strenuous exercise. The body also reduces its total blood volume in space (our faces get less puffy after some time). (See chap. 4.7 & 4.10.) Your high-gravity and low-gravity species are likely to have correspondingly more or less blood.
* Human bones are not simply there for structural support. Calcium is a vital element for various functions. Some authors even go so far (!) as to describe the structural function as secondary to the calcium storage function. If animals on an alien world have a similar calcium metabolism, there could be important implications if their bone mass is scaled up or down. The last trimester of pregnancy and lactation place severe loads on the human calcium store. (See chapter 6.2.) Aliens with a lighter frame on a low-gravity world may have to have fewer young, or smaller young, or more independent young, or be more prone to osteoporosis. (Of course the young would then require less calcium for their bones, but not for other functions.)
* Our immune systems are somewhat more efficient in a centrifuge and less efficient in microgravity. The reasons behind this are complex but it seems that cells are better able to read chemical messages in high gravity (which is relevant to aliens) and that some types of suppressor cells may not work as well there and the total number of immune cells is also increased (which probably isn't). (See chapter 8.3-8.6.)
* Bacteria reproduce much more aggressively in microgravity, which is believed to be because they spend less energy moving and maintaining their position against gravity/buoyancy. Simple eukaryotic cells show similar effects. (Most of chapter 3 is relevant.) Overall, aliens in low gravity would probably need to spend a bit more energy on their immune systems and those in high gravity a bit less. With no immune system, plants should have more or less aggressive defences (bacteriocidal sap, etc.) than on Earth.
Also:
* Animals require more food in higher gravity and less in lower gravity, for locomotion. Their oxygen requirement for burning that food scales similarly. An animal in a low-gravity environment should thus have smaller lungs but nonetheless greater endurance. Heart scaling for blood pressure has already been mentioned; an even bigger effect on the size of the heart should be due to the change in oxygen requirements.
[Answer]
While not an expert, I can think of a few things right off the bat:
Gravity is going to affect skeletal structure, height, whether animals develop which are bipedal vs quadrupeds, or even hexapeds (the higher the gravity the more likely for animals to evolve to be lower to the ground).
Animals which climb, or fly might be quite small, and trees might also be quite short in a high gravity environment.
Gravity will also have a big impact on the cardio-vascular system. Higher gravity world dwelling creatures might evolve to be more territorial, and hunt by ambush, rather than roam the land, while creatures in a lower gravity might evolve with no such restrictions, and generally be bigger in size.
[Answer]
Two sci-fi books that deal with this directly:
Dragon's Egg by Robert L. Forward
[https://www.amazon.com/Dragons-Egg-Del-Rey-Impact/dp/034543529X](http://rads.stackoverflow.com/amzn/click/034543529X)
Heavy Planet by Hal Clement
[https://www.amazon.com/gp/aw/d/076530368X/ref=mp\_s\_a\_1\_1?ie=UTF8&qid=1475076330&sr=8-1&pi=SY200\_QL40&keywords=heavy+planet&dpPl=1&dpID=51mNsaXkjoL&ref=plSrch](http://rads.stackoverflow.com/amzn/click/076530368X)
Both of these look at life evolution under very high gravity and may guide your own development.
[Answer]
Well, some things to note:
**LE:** Flight and gliding would have evolved multiple times in the world. Jumping and hopping would also be quite common for predators and prey.
Creatures in general will have small or lanky legs as low gravity won't force them to develop such bulky or heavy limbs. Unless they are arboreal, airborne, or predators with a specific kill method.
Animals can reach REDICULOUS sizes. Less gravity means that pumping blood throughout the body will be less of a hassle so they can be, almost, Kaiju-sized.
Same goes for plants and other equivalents.
Bones and skeletal structures on LE will be less developed and less extensive so a fossil history might be hard to follow unless their bones or skeletal systems are made of a different material.
**HE:** Most of the points about life on a high gravity plane have already been said, so I'll say some interesting little trivial facts.
Creatures on HE will have either legs right under their body for support, many legs across their body, column-like legs, or all of the above.
An alternative would be for creatures to go the way of snake and the slug and just slither or slide across the ground and this will be easier and energy efficient.
One interesting thing that might happen would be predators employing a hunting strategy similar to "cow tipping," as falling over in HE would severly injure an animal, if not outright kill them.
That's my two cents.
[Answer]
We could even consider the effects of Earth's gravity on the evolution of human morphology that in turn determines how we move (bilateral symmetry, e.g. opposing hands) that in turns determines how we sort objects, that in turn determines the form of math we have created. Gravity influence our metaphysics, that is, the bias we project into reading our world. The variation in the strength of gravity, while interesting, can also include gravity per se or gravity (humans) versus "no" gravity (fish).
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[Question]
[
Recent news [reported](http://www.cnn.com/2016/05/02/health/three-habitable-planets-earth-dwarf-star/) the discovery of three "earth-like" planets in the TRAPPIST-1 system. This is interesting because the star is a small, cool red dwarf about the size of Jupiter. The three planets in the habitable zone are tidally locked and about the size of Earth, could have atmospheres, and receive 2 to 4 times the radiation that Earth receives from Sol. (More from the [TRAPPIST-1 site](http://www.trappist.one/).)
Assuming, for the sake of this question, that both atmosphere and water are present, how advanced are native life forms likely to get? Is the development of animal life plausible? If so, what type? The combination of high radiation and dim light (especially if only the twilight band is viable because of the tidal lock) does not *sound* especially conducive to animal life to me, but I am not an expert.
[Answer]
As I'm sure you know, four more exoplanets were recently discovered around TRAPPIST-1 ([Gillon et al. (2017)](http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html)), bringing the total to seven — all, amazingly, presumably rocky and near the star's habitable zone. There has been recent work, of course, about the system's habitable zone and whether any of the exoplanets around it could host life, and so I figure I might as well write up an answer taking into account some of the new information we have.
Here's a table of the relevant information about the seven exoplanets (from [Grimm et al. (2018)](http://adsabs.harvard.edu/abs/2018A&A...613A..68G)):
$$\begin{array}{|c|c|c|}
\hline \text{Exoplanet} & \text{Mass }(M\_{\oplus}) & \text{Semi-major axis }(10^{-2}\text{AU})\\
\hline \text{b} & 1.017^{+0.154}\_{-0.143} & 1.15\\
\hline \text{c} & 1.156^{+0.142}\_{-0.131} & 1.58\\
\hline \text{d} & 0.297^{+0.039}\_{-0.035} & 2.23\\
\hline \text{e} & 0.772^{+0.079}\_{-0.075} & 2.93\\
\hline \text{f} & 0.934^{+0.080}\_{-0.078} & 3.85\\
\hline \text{g} & 1.148^{+0.098}\_{-0.095} & 4.69\\
\hline \text{h} & 0.331^{+0.056}\_{-0.049} & 6.19\\
\hline
\end{array}$$
This data is much better than the original measurements by Gillon et al.
For habitable zone models, I'm going to look to [Bolmont et al. (2017)](http://adsabs.harvard.edu/abs/2017MNRAS.464.3728B). First, look at Figure 1b, which models the habitable zone assuming a mass of TRAPPIST-1 of about $0.08M\_{\odot}$. I've drawn a green line at ∼500 million years, which is roughly the age of the system:
[](https://i.stack.imgur.com/tUGf1.png)
This means that the habitable zone currently runs from roughly $2\times10^{-2}$ AU to $4\times10^{-2}$ AU. This would put exoplanets d to f within the habitable zone at the moment, with c and g being decent candidates, too. Within another ∼500 million years, the habitable zone will have changed and roughly flattened out, ranging from $1\times10^{-2}$ AU to $3\times10^{-2}$ AU, encompassing b through e. We see, then, that the habitable zone changes over time, as is the case with all stars, and so the answer to your question depends partly on how long each planet will spend in the habitable zone.
The same authors present graphs of hydrogen (the important component for recombination of water) loss and time spent in the habitable zone for stellar masses of $0.01$-$0.01M\_{\odot}$, exoplanet masses of $0.1$, $1.0$, and $5.0M\_{\oplus}$, and various luminosities:
[](https://i.stack.imgur.com/W90f4.png)
I'll look at the second panel on the right column, assuming a rocky exoplanet with a mass of $\sim1.0M\_{\oplus}$. I've labeled the semi-major axes of exoplanets b through g, and drawn a box from $M\_\*=0.071M\_{\odot}$ to $M\_\*=0.80M\_{\odot}$, the lower half of the mass range for TRAPPIST-1:
[](https://i.stack.imgur.com/3IC4F.png)
From this, it seems that TRAPPIST-1d and TRAPPIST-1e should be in the habitable zone for a while, at least $10^9$ years and probably several times that. TRAPPIST-1f may get $\sim5\times10^8$ years to $10^9$ years, although TRAPPIST-1g will likely spend minimal time there, if any significant time at all.
TRAPPIST-1b and TRAPPIST-1c should be in the habitable zone for a pretty long time, as we saw in Figure 1. However, they will likely lose a lot of hydrogen: perhaps *two to four times* the mass of the hydrogen in Earth's oceans, in a worst-case scenario (Lower-mass planets may lose less hydrogen, according to the authors' graphs, which is odd. I'll have to look into that.) Having a large amount of water to start with could make this less of a problem, as the authors argue — and they do say that their models probably overestimate hydrogen loss — but it's still a large problem.
Let's also assume that the exoplanets each have atmospheres with some non-insignificant amount of ozone ([O'Malley-James & Kaltenegger (2017)](http://adsabs.harvard.edu/abs/2017arXiv170206936O) believe that this could lead to UV radiation effects no worse than those on Earth). If we also assume Earth-like atmospheres — not much of a stretch, given the mass ranges of these planets — then we actually have decent targets for life.
My top choice is actually TRAPPIST-1e. While its mass is likely much smaller than Earth's (though it's better than exoplanet d), it will stay in the habitable zone for some time (better than f or g) and shouldn't lose too much hydrogen (better than b and c). We can assume, optimistically, it should spend several billion years in the habitable zone.
What was [life on Earth](https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life) doing when the planet was about ∼500 million years old? Well, it was actually just getting started. The first, smallest not-quite-cells-but-still-reproducing life forms had just gotten started, although they hadn't really achieved much. So if TRAPPIST-1e takes a similar path to Earth, life could be here — or almost here.
Fast forward to one billion years. We've got single-celled prokaryotes (i.e. no proper nuclei) which are developing photosynthesis. Eukaryotes are still a ways off, but progress is being made. A bit over a billion years after that, the [Great Oxygenation Event](https://en.wikipedia.org/wiki/Great_Oxygenation_Event) happens on Earth, and oxygen levels in Earth's atmosphere skyrocket. Life is probably already on land, and eventually, atmospheric oxygen will help make respiration possible. Animals — even multicellular life, really — is still a ways off.
You're not going to get animal life for several billion years on TRAPPIST-1e, assuming an Earth-like evolutionary trajectory, but I think that if life gets started there, you'll see some animals. It might take longer on TRAPPIST-1b and TRAPPIT-1c, if there's little water, which is widely regarded as leading to the start of life in the oceans (although obviously, life could take other paths; I've been assuming Earth-like life). TRAPPIST-1d might go similarly to TRAPPIST-1e, although lower gravity may change what types of animal life arise, if they ever do (see [How does gravity affect evolution of life?](https://worldbuilding.stackexchange.com/q/56856/627)); something similar may happen with TRAPPIST-1f. TRAPPIST-1g and TRAPPIST-1h will likely see no significant evolution of animal life; they just won't spend enough time in the habitable zone.
So, to answer your questions
>
> how advanced are native life forms likely to get? Is the development of animal life plausible?
>
>
>
They may become pretty advanced, assuming you pick the right planet (d, e or f, with my top choice being e). Intelligent life is possible, though not guaranteed.
It's been brought to my attention that recent simulations ([Wolf (2017)](https://arxiv.org/abs/1703.05815)) also suggest that TRAPPIST-1e is the best choice for life. I haven't read the paper yet, but I'm glad to hear that maybe I was right.
[Answer]
Considering that [Hydrothermal Vents](https://en.wikipedia.org/wiki/Hydrothermal_vent) are teeming with animal life, in absolute darkness, in conditions that are outright hostile to most surface life (most notably the complete lack of **air**), there is presently no information about TRAPPIST-1 that precludes advanced animal life.
Quoting from Wikipedia listing some examples of life at Hydrothermal Vents, boldface mine:
>
> Hydrothermal vent communities are able to sustain such vast amounts of
> life because vent organisms depend on chemosynthetic bacteria for
> food. The water from the hydrothermal vent is rich in dissolved
> minerals and supports a large population of chemoautotrophic bacteria.
> These bacteria use sulfur compounds, particularly hydrogen sulfide, a
> chemical highly toxic to most known organisms, to produce organic
> material through the process of chemosynthesis.
>
>
> The ecosystem so formed is reliant upon the continued existence of the
> hydrothermal vent field as the primary source of energy, which differs
> from most surface life on Earth, which is based on solar energy.
> However, although it is often said that these communities exist
> independently of the sun, some of the organisms are actually dependent
> upon oxygen produced by photosynthetic organisms, while others are
> anaerobic.
>
>
> The **chemosynthetic bacteria** grow into a thick mat which attracts other
> organisms, such as **amphipods** and **copepods**, which graze upon the
> bacteria directly. Larger organisms, such as **snails**, **shrimp**, **crabs**,
> **tube worms**, **fish** (especially **eelpout**, **cutthroat eel**, **ophidiiforms** and
> Symphurus thermophilus), and **octopuses** (notably Vulcanoctopus
> hydrothermalis), form a food chain of predator and prey relationships
> above the primary consumers. The main families of organisms found
> around seafloor vents are **annelids**, **pogonophorans**, **gastropods**, and
> **crustaceans**, with large bivalves, **vestimentiferan worms**, and "eyeless"
> shrimp making up the bulk of nonmicrobial organisms.
>
>
> Siboglinid **tube worms**, which may grow to over 2 m (6.6 ft) tall in the
> largest species, often form an important part of the community around
> a hydrothermal vent. They have no mouth or digestive tract, and like
> parasitic worms, absorb nutrients produced by the bacteria in their
> tissues. About 285 billion bacteria are found per ounce of tubeworm
> tissue. Tubeworms have red plumes which contain hemoglobin. Hemoglobin
> combines with hydrogen sulfide and transfers it to the bacteria living
> inside the worm. In return, the bacteria nourish the worm with carbon
> compounds. Two of the species that inhabit a hydrothermal vent are
> Tevnia jerichonana, and Riftia pachyptila. One discovered community,
> dubbed "Eel City", consists predominantly of the eel Dysommina rugosa.
> Though eels are not uncommon, invertebrates typically dominate
> hydrothermal vents. Eel City is located near Nafanua volcanic cone,
> American Samoa.[15]
>
>
>
] |
[Question]
[
Imagine we're far in the future and mankind is part of a large web of planets/colonies including several other intelligent species. It's a space opera not much different from Star Wars. There is heavy exchange between the different worlds, moving billions of people and goods around. A large galactic civilization like this also means that new planets are settled/colonized every now and then.
Even without interplanetary travel, bringing species and diseases from elsewhere can be dangerous. Eventually, we became immune or learned to deal with the issue on Earth (mostly) but would it be possible to do the same with so much diversity? How can a world protect itself from the diseases of the others?
[Answer]
This is tricky since (presumably) life on other planets could follow other paths. But considering earth pathogens:
**Viruses:**
These are unlikely to spread to aliens, and vise versa. Virus reproduction is generally coupled fairly tightly with host cells - they use your own cell machinery to copy themselves. So foreign machinery is not likely to work.
However, because of the [Birthday Paradox](https://en.wikipedia.org/wiki/Birthday_problem) it's likely that if you had, say, 1,000 alien species, that a couple of them would have compatible viruses. But you're not going to see galaxy-wide viral infections.
This is good because viruses are harder to treat and defend against, so the fact that they shouldn't spread helps us.
**Bacteria:**
Bacteria are less coupled to their host - they reproduce on their own. So it's likely that most bacteria would be able to spread to reasonably similar aliens. Thankfully, it's fairly easy to defend against with basic decontamination and cleanliness protocols.
**Fungus and Molds**
These are very dangerous because they pretty much just need moisture and some basic building blocks to grow. Like bacteria, for the most part they're not coupled tightly to host biology, which means they presumably can spread cross-species.
Defense is similar to bacteria - decontamination, keep things clean and maintained.
[Answer]
Honestly, I don't see this as being a significant problem, as already alluded to by other answers. There are a few reasons for this.
1) Diseases evolve to attack particular hosts, and as such can not easily spread to other hosts. Viruses are not going to mutate to effect non-human lifeforms; which won't even have DNA to 'take over'. Bacteria and parasites that are harmful to humans are ones that evolved to live within a mammalian body as well. They are not as tied to their host, but their still evolved to a certain enviroment and it's unlikely any alien species will have a body that is a good hosts. Keep in mind that odds are alien life forms won't even be carbon based, they won't have the right nutrients for parasites to 'eat' and will likely have internal body temperature, acidity, and materials so foreign that bacteria can't live within it. In short most diseases can not spread from human to non-human.
2) were already pretty good at containing disease. When is the last serious epidemic *in a first world country* that you recall? The closest was AIDS, and we almost immediately adapted to better use of condoms and other protection, testing those with it, and creating treatments to allow those with HIV to survive. Our science took a disease that could have been a population decimating disease (look at what it's done in some parts of Africa, where they did not have the same access to technology and information as first world countries) and allowed us to curtail it's spread, and treat it's effects; and this is a disease we didn't have means of fighting directly, we stopped it simply by identifying how it spread and preventing that agent.
I'm not saying that diseases don't stop happening, HIV is still around and hardly trivial, but it's also no where near pandemic levels. The further you put us into the future the more informed we will be about disease and how they spread, the more capable we will be at creating vacines or even anti-virals to combat these diseases. Put us far enough in the future that we have such covenient space travel and we will likely be able to combat diseases with direct treatments for most new disease. However, even if we can't we can control them and keep their spread limited quite easily simply by indentifying how they spread and stopping that spread.
The only disease I see being a threat would be one that lied dormant for an extensive length of time, to allow spreading to a huge percentage of population before we identified it and started to fight it. However, disease doesn't do this, but it's very nature it will always spread as fast as it can, it's not 'smart' enough to know to lie dormant to spread that long. Perhaps more accurately, any disease that spread so successfully while dormant would not become lethal all at once, dormant spreading is proving an evolutionary advantage over killing the host, why should it then adapt to being lethal? (and yes, I'm overly personifying disease and their 'decision' to adapt, but I stand by the the raw arguments as true, even if I'm skipping over some of the specifics of unguided nature of evolution to provide a simpler explanation).
In short, we have means of stopping spread of diseases now; will have even better means of directly identifying and detecting diseases later, and they will only be a threat to one species at any time.
furthermore, the enviroment you hypothesis would make controlling disease easier. Each world is still mostly cut off from the other. Yes you said that travel was common, but each world is an isolated unit with very controlled 'borders' for people to come and go. If one world is infected it can be isolated much easier, and even if it's disease spreads you can identify likely worlds to qurintee easier. You can enact policies to screen people coming from known danterous worlds and since all travelers will have to come via ship that enter spacedocks that are controlled you have a very effective way of screening to ensure no one enters a new world with disease; as opposed to now when someone can walk across a border from a city to another in any of a million paths and bring disease with them.
Furthermore if aliens are really intermingled with humans you get a quasi herd-immunity as well. Since the aliens can't catch the disease they are immune. If worlds are culturally diverse then you may have only 10% of your population being made up of any one species, meaning 90% of the population is immune to disease. Your get at least some limited benefit of herd immunity this way.
The biggest danger would be not from diseases that live in and attack the human (or alien) body, but from outside containment that are universally dangerous. Radioactive materials, invasive species and 'parasites' that don't live *in* the body, but around it and are harmful (imagine space fleas that evolve to live in material commonly used by space ships and can damage instruments or the like)
Still, even in these cases qurtine techniques would work well, and more advanced science means better detectors for such threats.
Thus the only possible pandemic level threat I could see are man(or alien) made threats. Genetically engineered diseases or a nano-plauge. These diseases could be designed to be lethal, most likely by having them spread for years before they become lethal, so they have time to ensure everyone catches them. Nano-anything has a theoretically horrible grey goo worst case scenario, be it intentional or accidental. However, in the end I think man would have to be involved in creating anything that could prose a serious threat to a species.
Of course diseases will still exist, and spread. Pandemic level disease won't occur, minor diseases will always be around, even lethal diseases will spread to some degree, just being contained to a mall number. Once a disease reaches a certain danger level humans will invest effort into stopping it, and will; but diseases below a certain threshold won't be worth the effort to contain. Even contained disease will still take lives as well, look at HIV in the US now, it's 'controlled' and unlikely to be a serious threat to out population as a whole, that doesn't mean it doesn't take a number of lives.
[Answer]
I'd like to introduce a few more vectors:
1. [Nano-materials](https://en.wikipedia.org/wiki/Nanotechnology#Nanomaterials); low chance of problems, highly likely to spread. Nano productive systems, once they evolve, enlarge the risk. Decontaminate.
2. [Prions](https://en.wikipedia.org/wiki/Prion); low risk but potentially bad consequences as it tends to move slow. Verify sources and spot check.
3. [Pests](https://en.wikipedia.org/wiki/Pest_(organism)) (a famous example is of course the [Tribble](https://en.wikipedia.org/wiki/Tribble)). A valued domesticated resource can become a serious pest in another environment. Research before importing. Decontaminate. In case of trouble send for Capt. Kirk.
4. [Parasites](https://en.wikipedia.org/wiki/Parasitism). Heh. [Alien](https://en.wikipedia.org/wiki/Alien_(film)). Send out automated decontamination robots first. Avoid space derelicts. Really avoid space Sargasso's.
[Answer]
I would guess that many diseases would not pass between different species hosts. Many things that kill trees, have no affect on animals, and what kills a fish doesn't even notice a human and vice versa.
So many will not be transmitted between or communicable from one species to another. Some things that are such as some parasites might not care as much about it's host, while others are extremely specialized.
I would also think that technology would be improved greatly to help identify dangerous organism to help stop their spread. Ships air systems should have analysis units identifying any contaminates that are dangerous at a minimum to the species inhabiting the ship and any that are at the destination of the journey.
I would also think anyone who can afford it (and if your are traveling intergalactic you can't afford not too) would have personal units monitoring their bodies and environment as well as be in communication with the ship to be on the look out for organisms and chemical compounds that are dangerous to themselves.
[Answer]
As several others have said, humans are not likely to catch alien diseases. There are just too many ways to put together a working biochemistry and most of them would be incompatible.
However, humans alone could feed a pandemic if the conditions are right.
Scale doesn't really matter here. You have large populations brewing new diseases, and a small amount of travelers carrying these to new unsuspecting communities.
This is exact the same as the situation on Earth historically and today.
Medical technology will probably be much better, but I suspect that things will be as they are now: Only the rich can afford it.
So, pandemics will spread among the poor.
Travelers will generally be rich, meaning they will have access to vaccines and everything.
If travel gets cheaper to the point where you get migrant labour, watch out. Populations will truly meet for the first time in a long time.
An important question is whether information travels faster then people. If so, a bad pandemic in one place can be kept contained as warnings spreads ahead of the refugees. If the refugees get there first...
So, it all depends.
[Answer]
To avoid previously unknown deceases and new pathogens on a new alien world, civilization could use terraforming, to ensure only known organisms are present. Also this new world won't be open for free travel before a period of observations and trials on a limited population of settlers.
But even known viruses mutate and change, so after a couple of centuries each distant world will probably have a slightly different deceases and immune systems evolved. To ensure people won't carry something new with them every time they travel, quarantine and decontamination procedures can be applied for new arriving guests (probably there would be a list of similar worlds, with appropriate procedures for each group).
[Answer]
They would protect themselves much the same way we do now in 1st world countries. The US has the Center for Disease Control (CDC) the Food and Drug Administration (FDA), Border Patrol and a couple others to manage epidemiological threats.
In an FTL capable society, they should have much better models for the spread of disease. Combined with far better sensors and analytical equipment, and the computational horsepower to model biochemical interactions, they should be much better off than we are. Likewise medical science should be better able to diagnose and treat illnesses.
The space equivalent of Border Patrol would have a huge role in keeping the various ecosystems separate as they will keep contraband biologics out. For an example of how and why, have a look at the scene in Fifth Element when the star cruiser is about to leave the city and undergoes decontamination.
Any product being shipped will need to be certified clean or be of a nature where no cleaning is needed, ie, no one cares about decontamination of 1 megaton of steel bars. When questions of contamination arise, institute quarantines. Ellis Island in NYC is an excellent example of this (minus the degrading name changes and family separations.)
Tldr, they would do it the same way we do now only with more science, better tools and most importantly, it's in space!
] |
[Question]
[
**The Situation**
The fantasy world of Terrearth is once again threatened by the Shadow, a sentient, but completely unintelligible being composed of Absolute Evil, whose sole purpose is to destroy the world to replace it with a plain of absolute nothingness, in which evil will be the only thing left. The evil will have a physical form in this world, and will be the only thing that will flutter over it forever.
However, at any era in which the Shadow occurred, a group of heroes managed to banish the being in an underworld, but they have never defeated it definitively.
Now, the Shadow has come back, and the inhabitants of Terrearth do not know how to deal with it. The knowledge of how the heroes of the past times defeated the Shadow are shrouded in a cloak of legend, and therefore it is the duty of the armies of the lands of Terrearth at least to try to limit the Shadow, awaiting the arrival of the heroes.
*So, how can humans deal with this cosmic horror? I'm not looking for a way to defeat it permanently (because I know what is), but a way in which "simple" human beings may be able to fight it and contain it.*
**Humans Background**
* Terreath universe is a fantasy world, populated only by humans and
supernatural entities like ghosts, lich, ent and monstrous animals.
There are no other sentient races apart from humans.
* Technological level is medieval. There is no gunpowder, however alchemy is
quite advanced, and allows you to have healing poultice and body
booster similar to our combat drugs.
* The magic exists, but is not widely practiced, as it is difficult to
understand, and there are no institutions or groups of magicians
dedicated to the research and understanding of it.
* The few holders of magical power are druids. These figures are
priests scattered in some forest villages, who are dedicated
to the study of natural and healing magic, and hand down their
knowledge to their children. Druids form a social entity called the "Circle", but it has no political or religious power, and it is only a way to exchange
information and knowledge during meetings.
* There are no gods or goddesses, and there are no forms of organized religion. All the inhabitants of Terrearth however believe in one principle, the Good. The Principle of Good is universally accepted by all.
* There are not clerics. There are paladins, who fight evil, but there is no religious figures assimilable to organized religion figures.
* If we should make comparison with D&D Alignment system, every people of Terrearth would be Lawful Good. In the world of Terrearth most evil does not exist. There are no wars, genocide, torture, etc. Some minor crimes exist, but put in place by those who have a relativistic vision of the good. Few are the people who belong to the alignment Neutral Good and Chaotic Good, and are viewed with suspicion by Lawful. In addition there is a nomadic people, whose relationship with other people is quite tense, whose allinamento oscillates between Chaotic Good and Chaotic Neutral.
* There are many countries, but the armies are mainly used to fight
crime and the Shadow.
**The Shadow Background**
* The Shadow is all the evil that man can provoke, and tries to take in
the world, not with violent and bloody hordes of his minions, but infiltrating,
acting slowly and without emotion.
* The Shadow flourishes in living corroupting them and bringing out the
dark side of man. A corrupt man will dedicate himself only to evil
actions, paving the way for other infections. However **the corrupt do not openly expresses his evil acts**. He prefers to work stealthily, and when the opportunity to spread even more evil is ripe, he acts.
* After the Shadow infects all living in an area
, the whole area becomes nothing. The only thing there is a dense
and impenetrable cloak of pure darkness, which is the physical form
of evil.
* The Shadow sometimes manages to create minions made of absolute evil,
but they may last only a few days before fading. The Shadow prefer to
resort to corruption rather than the creation of minions.
* Human armies have managed to contain the Shadow after it has eaten a
large territory on the northern edge of the world, however the Shadow
infiltrates more and more human in the ranks.
EDIT
The magic is difficult to apply because the only types of magic "socially acceptable are elemental and healing ones, and the only holders of these knowledge are druids, pretty jealous of their knowledge. The mental and arcane magic is opposed and seen as unhelpful. Since no one is devoted to its study and most of the few magicians who master this type of magic are self-taught, this type of magic is not widespread.
EDIT 2
The reason for there is an almost monolithic belief system is historical. Before the advent of the Shadow, the world was more or less like ours. Wars, conspiracies and evil spread. In short, there was a gray morality. When the Shadow had appeared for the first time in the world, Terrearth risked being destroyed just because the Shadow attacked aggressively, taking advantage of all the evil available at the time. Some heroes managed to banish it, and the world returned to the usual evil. When the Shadow came for the second time, and was bannished for a second time, the people realized that the Shadow needed evil for his purposes , and established the Principle of Good.
Now, it is true that there are different philosophies about the Good (Lawful, Neutral and Chaotic). There is also this nomadic people who while not indulging in evil acts without reason, give no importance to the Principle. But the Principle of Good is universally known to all, and no one would do an evil act, never mind for its own sake. (For evil acts I mean the most serious crimes. Stealing, defraud or deceive someone, if they have no serious consequences, are not considered "evil" by Terrearthians, although they are still punishable by law)
[Answer]
**Invent a new religion!**
I'm not joking. The world you have described is very very very black and white: literally "everything is Good, except the shadow, which is Evil." This limits the amount of color you can put in your story.
Your shadow needs a weakness. In particular, here is a quad chart showing what happens when you mix good and evil
```
Good Evil
+------+-------+
Good | Good | Evil |
+------+-------+
Evil | Evil | Evil |
+------+-------+
```
As you can see, by your description of "once the shadow infects an area, it becomes nothing" is an indomitable ability. That claim needs to be broken down in order to have Good ever stand a chance.
One bright solution is to bring in Chaos. Make the effect of mixing good and evil less predictable. If you mix black paint into white paint thoughtfully, it looks grey or black (depending on how much black you used). However, in the moments of mixing, you see swirls of black and swirls of white, unmixed. It is not unfathomable that after mixing Good and Evil, some swirls of Good remain, they're just hard to spot.
This forms the backdrop for what you really need: a new religion of balance. You intentionally have set up the Shadow to be ridiculously strong, so it will be hard for you to sell to your readers the idea that somehow humanity magically turns it back with a perfect plan. We're going to need something murkier.
Consider a new caste of individuals who are comfortable with a balance of Good and Evil, rather than merely worshiping Good. They can live off of the borders between them. These individuals would be able to see shades of grey, not just black and white. This ability would give them the ability to penetrate into the Evil Shadow for quite some time before losing their balance and being corrupted absolutely. If they could find the "core" of the Shadow, and instil one dollop of good in the center, it could weaken the shadow dramatically.
This would also generate political drama. The forces of Good could never appreciate what Those Who See Grey think, but they also would recognize that these individuals are the key to survival. The frustration of a perfectly good King having to trust a Grey individual would be palpable.
But the shadow would also seek out these Greys. They are not necessarily harder to corrupt or easier, just different. When corrupting good, the shadow must patiently wait in the dark, and strike when Good's defenses are down. With the Greys, it would be more of a continuous press, slowly trying to gain a foothold in their mind by making the Grey confused as to what is the Shadow, and what is the Grey itself (a confusion that is easier to have when Grey than Good).
---
As a possible source of this new Grey caste, consider the effects of an imperfect strike from Good onto Evil, or an imperfect corruption of Good by Evil. Both could create a mix which could create a sense of Grey. After all, The Shadow better make a mistake somewhere, or it really is too powerful of an opponent.
[Answer]
Starve the bastard!
If I understand correctly, The Shadow feeds by corrupting humans, and corrupted humans are only capable of evil. That excludes them from simple, mundane tasks, like harvesting food, sewing, cleaning up after themselves...
In other words, of the Good People manage to put some barrier between themselves and the land already claimed by the Shadow, and then use their magic to put themselves into 20 year slumber, two things will happen:
1. Human servants of The Shadow will die, since their only souce of food and medicine will disappear
2. The Shadow won't have anybody to corrupt, so it won't have a power source, and eventually run out of juice.
How to build such a wall is up to you.
I see from your comment to the other answer, that you want some boy form other world. Maybe you can make him some visionary engineer? We actually have a deficit of those in the real world, so maybe you'll inspire some young people to study math a bit harder :)
[Answer]
If it's a cosmic entity, defeat it in a cosmic way!
Say the entity has consumed half the planet. You can make the people of the people discover some kind of ancient magic that keeps their world together. Then, have them break that magic and [split the world in two](https://www.google.gr/search?q=aion&client=opera&hs=oj1&source=lnms&tbm=isch&sa=X&ei=czq2VIWdEJT1apH1gogP&ved=0CAgQ_AUoAQ&biw=1366&bih=660#tbm=isch&q=aion%20planet).
* This doesn't defeat the point of an eldritch abomination, which is to be so much beyond humanity that it can't be fought by conventional means.
* It doesn't eradicate the horror, since the Shadow can still make a comeback after a long while, if it finds a way to cross to the other half of the planet.
* Since the splitting magic will definitely be something arcane, you can have huge conflicts between the peoples of your world about whether they can and whether they should move forward with this.
* You will have an interesting setting to play with, in the stories between the initial "defeat" of the Shadow and its comeback- if you intend to write any.
[Answer]
If Druids can influence or control natural elements, I may have a solution: **malachite.**
You see, malachite is known for trapping evil spirits. Your Shadow is the archetypal evil spirit, so if the Druids work together, they may be able to trap the Shadow in a giant malachite crystal. Then you'll have to be able to defeat it.
What if it's not someone dropping *Good* into the Shadow's core that beats it, but rather changing its paradigm? Paradigm=perspective, this Shadow clearly has a strong connection to people, so it's possible enough people with a strong perspective on "the beauty of nature" or the "meaning of life" could change its mindset and therefore its actions.
The genius of this is after the Shadow's eyes are (figuratively) open to how beautiful the world is compared to nothingness, it'll want to *preserve* the world as is, or maybe try to create a different version of the current world that better reflects its dark nature but isn't a "plain of absolute nothingness."
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Related to this previous question: [Could a city be built out of Balloons?](https://worldbuilding.stackexchange.com/questions/108896/could-a-city-be-built-out-of-balloons)
Remember in Oz where the witch is riding in on a bubble.
[](https://i.stack.imgur.com/nksnv.jpg)
I began to think how could I make this as real as possible.
You can breathe helium in place of nitrogen to have an 85% helium to 15% oxygen ratio. Could a person be put inside a clear balloon with enough buoyancy to ride in a bubble?
Would there be any practicle use for this?
[](https://i.stack.imgur.com/UdCQn.jpg)
[Answer]
A cubic meter of air weighs about 1.2kg. A cubic meter of 15% O2 and 85% He would weigh about 20% of that or about .25 kg. so a cubic meter of the O2/He mixture would lift about 1kg.
Ignoring the weight of the bubble itself, a 70kg person would need a 70 m3 bubble, which would be about 5 meters in diameter. Since the bubble material would have to be pretty strong to support an adult standing on it, let's call it as needing a 6 meter diameter bubble to also lift the bubble's weight.
Note: While floating in a bubble will attract media attention, it would be most unkind to ask the floatee to do interviews...
According to [hosstuffworks](https://health.howstuffworks.com/human-body/systems/respiratory/question98.htm):
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> The average adult at rest inhales and exhales something like 7 or 8 liters (about one-fourth of a cubic foot) of air per minute. That totals something like 11,000 liters of air (388 cubic feet) in a day.
>
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> The air that is inhaled is about 20-percent oxygen, and the air that is exhaled is about 15-percent oxygen, so about 5-percent of the volume of air is consumed in each breath and converted to carbon dioxide. Therefore, a human being uses about 550 liters of pure oxygen (19 cubic feet) per day.
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So a human needs about 1 cubic meter of pure oxygen/day or about 5 cubic meters of the O2/He mixture. [This website](https://www.higherpeak.com/altitudechart.html) says that people can comfortably breath air that is 25% depleted of O2 (equivalent to 10,000 feet which by experience is no particular problem for healthy people.)
Given that, an adult needs about 20 cubic meters of the O2/He mixture/day so as to not deplete it below 75% of its original oxygen. The 6 meter sphere has about 120 cubic meters of the gas mixture, so it will last about six days without any difficulty and would probably work for double that in a pinch.
Hydrogen works the same as helium within the accuracy of these calculations, but a no smoking policy is advised.
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After asking this question, [What's the worst natural disaster that could hit New York City in our lifetime](https://worldbuilding.stackexchange.com/questions/919/whats-the-worst-natural-disaster-that-could-hit-new-york-city-in-our-lifetime), it looks like the most popular answer was a Tsunami. A tsunami, however, from the sources of the most devastating ones could completely obliterate the city which makes me feel like it's not realistic to expect survivors.
**However, if there were survivors, what methods would likely have been used for them to survive?**
Being in a really tall building? On a ship? I imagine anyone on low ground is a goner. Perhaps depending on how bad the Tsunami is, the center-most land of the island is safer than the coasts?
Reading the Prologue in Maze Runner, they basically survive a Tsunami because they just happen across an ex-military guy who knew about the impending disaster and leads them out of the subway before they drown and into the tallest building in the city. They eventually leave this tall building when someone happens to pass by with a ship and tries to rob them which was a total stroke of luck. Is this... realistic?
References: <http://www.wikihow.com/Survive-a-Tsunami>
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With the exception of the 'meteor' style event, a tsunami wave isn't actually that high. In the Indonesian earthquake that caused the tsunami there, it's debatable if the height of the wave was over 10 feet tall. The destructive part came from the pure volume of water and the energy/strength it brings...anything not anchored in, is pretty readily relocated a long ways into shore. I doubt the water itself would ever down a skyscraper, however I could see a tsunami crashing enough debris (including houses) into the foundations of these buildings to cause enough structural damage to bring one down.
I have met travelers who avoided the initial wave on a 3 story roof top of a building that bore the brunt of the initial strike in the Indonesian tsunami in 2004....terrifying, but not that likely to kill. What made this tsunami dangerous was a complete lack of warning coupled with natural human curiosity...we saw the water heavily recede and came out to see whats happening. Correct response if you ever see an ocean's water recede into the distance is to get to high ground immediately, you're probably too late if you're on the beach seeing the water recede.
Surviving the initial wave is simply being out of this water flow and debris. In hills or in buildings is quite functional...trees have a potential of working as well, you just have to make sure whatever you're standing on isn't swept away.
However I do not believe that is the most dangerous part of a tsunami...it's the days after. Survivors find themselves stuck in standing water with very limited mobility, full of sewage and debris that have been washed up. Entering standing water is inherently dangerous as metal shards from what used to be signs and cars are quick to cut open skin. Once cut open, the wound is exposed to this sewage happy water and will likely become infected and toxic. Take Katrina and the impact flooding New Orleans had as an example here.
A city's water supply is most often underground, so the aftermath now includes a complete lack of drinking water (even worse if you consider most bottled water supplies are kept on ground floors). The majority of food (grocery stores) tend to be on ground levels as well, which is now covered in not so clean water.
So you're stuck, with likely a lot of other survivors, with very limited food and water...and absolutely no mobility that doesn't come with some serious risks.
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For something like this, I'd probably just research actual tsunamis. There are probably plenty of accounts along the lines of "luckily the casualties were low this time, because..."
But if you're just looking for options, it just depends on how powerful a tsunami it is. Can it knock over buildings? If not, anyone above the waterline should be ok. Does it happen without warning? If not, people could have evacuated or gotten to shelters. Is this an unusual place for tsunamis? If not, they may have made special facilities for weathering the storm.
Remember, tsunamis are rarely a single, giant wave: more commonly, they're like a tide that just keeps coming in. Unless you're talking about a tsunami from an asteroid impact or something, it probably won't be knocking down skyscrapers.
[Answer]
Grey's harbor in Washington state has been working on this very issue, and my wife has actually been researching it.
A Tsunami-safe building mainly needs the following three traits...
1. The support structure of the building should be strong and deep to keep the foundation from washing away.
2. The first two floors need to be easy to break away any external walls. You don't want those walls blocking water or the force could collapse the building, you want minimal in-water building.
3. You want the third floor reinforced. Tsunamis pretty much never reach this high, but splash up waves can get in, and it can take a beating. Also, you'll want it built to drain out. Of course, also have it stocked up with water, food, blankets, communication equipment, first aide equipment, etc.
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The backstory for a key character in my story involves him receiving a harsh punishment for becoming corrupt. The tearing off of the wings themselves is *easy* to write. It's the state he's left in afterwards that I need help on. Sadly (or fortunately?), no one seems to have written articles on 'ripping the wings off of birds'.
In Disney's Maleficent, her lover cuts off her wings and she finds it difficult to walk afterwards and uses a stick. Would this be accurate? Or would it only be as traumatic as losing an arm? Since the wings would be connected to various ligaments and muscles in the back, would it cripple him permanently? Would it affect the spine?
I'm asking for a logical, biological based answer. If I wanted to, I could just bypass facts and write away (it is fantasy after all). I'd like it to be as realistic as possible.
[Answer]
## Physical Problems
We can look for reference at humans with severe limb injuries or monkeys who's tails were injured. We know they have a hard time with walking around in their new state.
Any creature is accustomed to live with the body it has. For humans, we are used to 2 legs, 2 hands and our general anatomy. Monkeys have tails, and they are used to walking with them. Your angel is used to the wings.
Point is - When a change that drastic happens, yes, your angel will be affected. He will have a hard time walking, and also with other physical activities.
# Mental Problems
Another aspect is mental reaction. Your angel suffered a severe trauma, and that tends to leave a mark on one's mind as well as on the body. If the angels' mentality is anything like a human's, he is likely to suffer from stress, depression, anxiety, and lack of faith in his ability to function. And those are just a few of the common reactions. I would actually say that this is the more significant harms. Unless wings are super important to the anatomy of angels, he should heal and become handicapped, but functional. A mental disorder that might arise - that can be much harder to deal with, much harder to heal and have very serious implications.
**Edit**: I just came across this [great source](https://www.arnolditkin.com/practice-areas/catastrophic-injuries/trauma-induced-physiological-disorders/). It is quite extensive yet still comprehensible. Also, it obviously regards humans, not angels, but if your angels have a human-like physiology, that makes the transition quite straightforward.
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Since birds don't really have arms and we don't exactly have a angle to study it is difficult to say what would happen.
### If the wings are connected to the spine
There would be serious damage and if it was a harsh removal he may no longer be able to walk. There would also be a chance that arms or hands may not work if the wings are directly attached to the nervous system and they were pulled out with the nervous system it could lead to a large portion of the body not working.
### If the wings are not connected to the spine
This is probably the better option. If the wings are held in place by muscles alone then pulling them off would cause large physical harm but it would most likely heal because the spine and nervous system would not be damaged extensively. After the skin heals he would probably be fine.
Either way he would be heavily off balance at first and there would be mental scarring as well as potential ghost pains.
[Answer]
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> In Maleficent, her lover cuts off her wings and she finds it difficult to walk afterwards and uses a stick. Would this be accurate? Or would it be just as traumatic as losing an arm?
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It would be as traumatic, in a different way. Angels should be used to both walk balancing the weight of their wings, and occasionally supplementing with a quick wing stroke. Both are now out of the question, so your angel is forced to lean forward to compensate, and use a stick to maintain equilibrium (until he's used to walking wingless).
Occasionally he'll instinctively try to negotiate a higher step than immediately possible, maybe utter a cry of pain when the torn ligaments don't respond, and fall flat on his face.
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> Since the wings would be connected to various ligaments and muscles in the back, would it cripple him permanently?
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This would depend entirely on how the connection is designed. You know that biologically an angel is not possible, because he'd need too large a wingspan to be able to lift, even with hollow bones and larger chest and boobs made of solid muscle: for the same reason, you can choose the anatomical setup you prefer. The whole organization of the scapulae might not be that of a hominin like a man: angels and centaurs are, in all evidence, *hexapods* (unless you let them have hands at the end of the wings, or the wings themselves be modified arms, like the common bat).
Chances and extent of recovery would also depend on how the wings were torn - if shorn at the base, digging in the back muscles, or farther out; whether cut neatly, or teared away destroying the surrounding tissues; and so on.
In theory there's nothing against wings actually *regrowing*. Human arms do not grow back, but angels are not men (I remember one short story of such an "angel").
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Imagine a spaceship constructed for merfolk and it is completely filled with oxygenated water instead of air.
Since they can swim around effortlessly in the water, do they even need artificial gravity similar to their natural habitat on Earth?
[Answer]
## Artificial gravity will make it much easier to efficiently and evenly oxygenate the water.
Lack of gravity means lack of convection. Lower density gasses or fluids just sit where there are. That's a reason why fires in space are spherical and automatically extinguish themselves - since there is no "up", smoke does not raise high and away from fire, and doesn't cause currents drawing in fresh air with unspent oxygen.
Similarly, if you want to oxygenate water, you won't be able to simply make air bubbles pass through water from bottom to top, increasing diffusion by increasing contact surface, like those devices used in aquariums do. Pumping oxygen in will create one large bubble next to exhaust forcing a lot of creativity in making it work - first you need to stir water next to oxygen source to make it mix with water, later you need to stir entire room to spread oxygenated water and yet later you need to somehow extract carbon dioxide out of water. Easiest way I can imagine would be to use exhausts, intakes and pumps to create artificial current in entire room, filtering and oxygenating outside of room, before returning it to internal cycle (you still need similar system to filter water anyway, but not as much as for oxygenation).
Compare this to ease of lining floor with tiny oxygen exhaust, ceiling with oxygen/carbon-dioxide intakes and letting artificial gravity do the work.
Obviously, you need pumps and filters to close the cycle - unabsorbed oxygen gathered by ceiling intakes is pumped back into floor exhausts while carbon dioxide is recycled before returning to loop. However, if you already posses artificial gravity, then this is at least one of the reasons to use it: oxygenating water without artificial gravity will require much more plumbing and with much higher throughput.
[Answer]
If a mermaid has a swim bladder, a lack of gravity will make it harder to move up and down.
[This article](http://animals.howstuffworks.com/animal-facts/question629.htm) has more info on how it works, but basically by increasing and decreasing the internal pressure of this bladder, a fish can easily change vertical elevation and maintain its current depth without expending a lot of energy.
If there's no gravity, there is no downward pull to make going down work. Buyoancy is defined as the upward force opposing the weight of the immersed object. With no gravity acting on you, you're weightless and have no buyoancy. That means that going up wouldn't work either.
If a mermaid had this trait, she could not change her position in vertical space with her swim bladder. She could be disoriented and need special training to learn how to travel differently. Handrails could be installed to make changing elevation easier.
Mermaid astronauts coming home might experience something akin to a swim bladder disorder, and have trouble staying level or moving vertically once they get back to their planet.
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They would need it for the same reason, we thin-atmosphere-breathers need gravity. Yes, it is very nice that gravity helps us keep our boots on the ground so that we have an easier time stopping once we are in motion; but the real value of gravity is that it makes our equilibrium work.
Ask anyone who has ever suffered from chronic vertigo or sea sickness. Knowing which way is down is vital to having a happy life and journey!
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Artificial gravity is expensive (you need a really long tether (which will hit space junk and dust, and will create disorienting Coriolis forces on-board) or magic), and a pump moving oxygenated water is cheap, so I'd laugh if I read that merfolk needed artificial gravity do deal with respiration.
As far as controlling one's location with a ballast goes, that's a much smaller adjustment than humans made to zero-gravity. Unless your merfolk are less physically adept than humans or bats or dogs or monkeys, that shouldn't be an issue.
I see no convincing reason to use artificial gravity for merfolk except the same reason we always see humans with artificial gravity in movies - it's prohibitively expensive to make TV and feature films in zero gravity situations.
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## The Setting
It is the near future (say 2060ish). Some entity (corporation, government, private venture, etc.) has elected to build the first permanent (as in intended to become self-sufficient) space colony.
You (student of history, sociology, and political science) have been asked for your suggestions as to how it should be organized.
## The Question
What form incorporation and of government the colony should adopt?
## Constraints and Assumptions
* The colony will be composed of civilians with some former military.
* The military people may or may not be still in service (depending
upon whether it is government sponsored or not).
* At least some of the colonists are also investors.
* At least some of the colonists are hired experts.
* Investors realize this is a long-term pay-off. They're satisfied
with the colony working as a net loss in order to position this first
colony as the defacto monopoly on space-based services and resources
for future colonies.
## Scoring
The investors want a government that ensures the following:
1. Colonist "buy in" on decisions.
2. Ensure critical colony functions are always performed.
3. Encourage colonist creativity in finding new ways of becoming
self-sufficient.
4. Encourage colonist creativity in finding new ways of developing
export trade ideas.
5. Investors want to use this colony to develop more investment in
other colonies and encourage other people to become colonists.
[Answer]
I suspect there will be a rather odd hybrid system.
Safety is going to be first and foremost on everyone's mind, so a very draconian safety regime will be installed so no one can accidentally or maliciously cause a system or cascade failure that will threaten the colony. The "crew" of technical staff which run the systems will be built and operated on military lines, with clear lines of authority and responsibility to ensure everything really is accounted for. In that sense you will be living aboard an aircraft carrier with a Captain who is the ultimate authority.
But not everyone will be crew, and even the crew will need to be able to express needs that are not directly related to safety. So there will be a sort of "town hall" democracy among the passengers and crew for what might be considered "non life threatening" matters, although even decisions reached by the town hall meeting will probably need to be approved by the Captain in order to ensure they don't interfere with the safety of the colony.
This system will eventually evolve as the ratio of colonists to crew changes, and systems become more autonomous and reliable, but the colony will always have a "captain and crew" with override privileges in order to ensure the colony does not inadvertently fall apart.
[Answer]
Unless the colony is created by an **international** treaty, the **national** laws of the founding nation will apply. That means you have to consider two issues separately:
* Who owns what in the colony? In a capitalist society, the owners will be able to make many decisions.
* What is the citizenship of the colonists, and do they have a local representation?
The 20th century model proclaims a primacy of the state, especially in emergency situations. People and corporations don't pay taxes and obey laws purely out of the goodness of their hearts, they are compelled to do so. In democracies, this power of the state is checked and balanced by the ability of the people to elect the government. All the people, not the property owners.
The early 21st century model gives *slightly* more power to corporations. Multinationals structure themselves to minimize their tax burden and oversight, and they're playing nations against each other by threatening to move capital.
Unless there are big changes *on Earth*, the space colony will be governed *from Earth*. The law enforcement might be an U.S. Marshall or an UN deputy.
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**Follow-up** for Jim2B: The [Outer Space Treaty](https://en.wikisource.org/wiki/Outer_Space_Treaty_of_1967#Article_VI) requires nations to supervise the actions of their non-governmental actors in space, yet it makes space the common heritage of mankind. A [Charter Colony](https://en.wikipedia.org/wiki/Charter_colony) requires somebody who can grant a charter. That will keep the lawyers busy.
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I agree with o.m.and Thucydides to an extent. I think people always want to follow a leader, so there will definitely be one person in charge. I think the governance however, will depend a few factors. First and foremost, who paid for the station. If it's a corporation, a manager of some kind will be in charge appointed by the corporation. If it's a military installation an officer will be in charge put in place by the military and it would run very much like a military base. If it's some kind of joint venture, then like Thucydides said, it would be a weird hybrid. But even if investors funded the colony, they would probably form a corporation to handle everything so I would lean in favor of a corporate manager with security handled by a private security firm. If they have military on the colony I think there would be some head butting when duties are divided and the two leaders argue about to whom certain responsibilities belong.
Another important point is how big is the colony. Just a few people are more likely to want a say in how things are run. Six guys are not likely to risk their lives JUST because Frank said so. On the other hand, a huge colony might have all of the elements of the Earth, with different jurisdictions, unions, governors, maintenance organizations and a private sector with stores and such.
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## Initially
In the beginning, the colony will be a dictatorship or oligarchy. There will be one ruling body that will have been established on Earth. People who trust that ruling body will join the colony. People who don't won't. Note that some decisions may be made democratically from the beginning. But there will be a limited number of people responsible for colony safety in the early days. Otherwise they'll never get the mission off the ground.
## Over time
When the initial dictator or a member of the oligarchy dies, the colony will have to make more decisions. Does Earth get to pick a replacement? Or does the colony? An oligarchy might even choose its own new member.
## Eventually
If the ruler or rulers are picked autocratically, there will be increasing friction with the other colonists. Eventually there'll be rebellion. The rebellion may install a new autocratic government. In which case the same thing will eventually happen.
Eventually they'll establish a democracy as the cheapest way to handle the rebellion. Don't like your current government? You can change it -- without shooting all the current members. Eventually some prospective leader will decide that being voted out of office is more gentle than being deposed.
Personally, I think the time to introduce democracy is at the first change of government. I.e. when the first ruler leaves. If you're going to end up as a democracy eventually anyway, why fight it? But some people like doing things the hard way.
[Answer]
Assuming that all of the requirements stated in the question must be met, these are the features the government would need to have:
1. The leaders must be elected by the people. That way, colonists "buy in" to decisions. That way, there is more consensus, and less violent power struggle which could endanger the colony.
2. There must be an organization of some kind, made up of professionals who perform essential functions, such as law enforcement and safety. They will answer to the elected body of representatives, but will be selected based on merit, rather than elected themselves.
3. The government (whether it's a colonial government, corporation, or whatever else) will sponsor an education system that teaches colonists practical skills relevant to maintaining and growing the colony (like engineering).
4. Capitalism must be the economic system in place, and there must be a body of supreme, irrevocable, laws which protect capitalism from government interference. That way, people will be productive, since they have profit as their motivation. Also, the colony will pay for itself, and be self sufficient, since it will make money rather than relying on aid payments from Earth.
[Answer]
The situation has parallels to a homeowners' association, whether for a co-op, condominium, or standard form of ownership. In particular, there are groups with different priorities:
* The investors want to uphold their long-term vision for a good rate of return on the follow-on colony(ies).
* The colony leaders want to grow and operate the colony.
* The colonists want to live well IN SPAAAAACE!
Yes, some people will be in two or even all three of these groups. And other groups may exist too.
## Initially
The colony governance would start out controlled entirely by the investors, either directly or through their representatives. The initial leadership will set up the control systems to ensure safety, consumables, and maintenance. As noted in other answers, these systems will probably tend towards the authoritarian / naval models. For comparison, an HOA/COA normally starts out controlled by the developer with the aim *to sell the properties*.
## Over time
The original investors can't foresee everything (citation needed). Control will have to gradually transfer to colonist-selected leaders. These leaders will need to continue the established major systems -- so again, I think the naval model will continue to apply. And as this colony is to be the first in a series, the original investors will have a way to retain their voice (most likely by keeping a substantial number of board seats / command billets reserved for the investors & heirs).
Eventually there will be conflicts between the investors' long-term vision and the colonists' day-to-day desires. This is where a good HOA governance body balances the issues. (A bad HOA board is a discussion for another forum.)
## Summary
I see the setup as a necessary mix of democracy, through a board of directors elected partly by the colonists and partly by the investors, and authoritarian, through the command staff (which need not be truly military). Adjusting this mix over time can provide lots of good stories.
[Answer]
Which entity founds the colony matters: if it is a corporation the end result will be something like the India Trade Company. The Board of Directors decree and the employees obey. The only way to influence the government/corporation is to buy enough shares to create a strong voting block and be able to choose the CEO and the Board.
If it is the government it will follow the form of the native government. For example, an american colony in space would be a Territory, eventually being promoted to State. A chinese colony will have a communist party office sending the colonies' complaints to the Zhongnanhai and receiving instructions.
[Answer]
Explore the constraints: limited space, limited land use, limited life support, limited people, limited options.
So you have a finite number of people who each represent a significant investment (from someone), prospecting on mostly useless land (unless your terraforming went "viral" already) and using up energy and resources.
There are analogies to European colonies, but remember the differences: Europeans landed and immediately started exploiting the land (And often the people) to survive and then to profit. There were real hardships but there was abundance all around.
Find either "the abundance" for your colony to be based on or find another strong motivation for being there, and you'll have the basic pattern to build from. Mining or religious reasons seem likely.
Then look at your constraints to take what started as government for a company town or religious enclave (Or other reason that I missed), and change it based on 1. Not being able to leave/breathe out there, 2. Not having nature or natives to deal with (no external security concerns) 3. extra value being placed on each person at the beginning (Their labor would be missed if something happened to them) 4. It's hard to build more houses/buildings
I don't see democracy or capitalism flourishing in this environment. I do see disagreements on the best ways to run things, and that has a ton of potential for conflict in your story. Good luck!
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You've gone through the process of world building and generated scads of information from important Universal Forces to interesting tidbits of local history.
What **methods** of storing world building information exists?
If so, have you used them and how has that worked for you?
How do you **manage this information** so you can retrieve it at the right time, even if you've forgotten that particular tidbit of local flavor?
***Edit 8/4/2015:***
Although I intended to include software in my original question, the comments indicated that this question has already been answered on Worldbuilding. So, please limit yourself to **non-software** or *hybrid* (answers that combine software and non-software means of storing your information) answers.
[Answer]
In many ways the software questions and this one will overlap, BUT, that said there are some important non-software related things to consider. Good software for this process will actually help you do these things but the software isn't inherently required.
So, where to start.
1. **Create templates:** Templates can save you a lot of time and effort. Take the time to really consider all the things you want in your template (and ask other people to take a look). The last thing you want is to change your template AFTER you have filled a whole bunch of them out.
2. Populate your templates. Templates are best used on items that fit into categories, planets, countries, characters, organizations etc.
Templates I personally use for a fantasy setting
* Geographic Features; rivers, lakes, oceans, continents, forests, mountain ranges, and so on and so forth.
* Nations; strictly speaking a political entity with land. This can range from a small unaffiliated village in the middle of nowhere to an empire.
* Cities; like nations but smaller (obviously)
* Organizations; city guards, standing armies, trade groups, secret societies, guilds, mages etc.
* People; I divvy them up (separate templates) for main and secondary characters.
You can put anything you like into a template. Templates are best used on things you are going to do over and over again.
Now, for accessing the information you keep. Here is where the best answer is probably, **use some software.** The beauty of this software is it can keep track of relationships.
**For example**:
- Bob is a guy
- Bob works for organization X
- he lives in nation N
- Bob is a follower of religion C
But it gets better, you can (in some tools) follow the rabbit so to speak which is very handy. In this case, Bob is a carpenter and works for this trade union, the trade union exists across the continent of H and its headquarters is in city F, city F is part of nation T which is at war with nation Y on continent U.
Keeping track of template-ed information is easy, keeping track of the relationships is not and this is where software can make your life oh so much easier so keep this link handy: [What software is available for keeping and organising notes about your world?](https://worldbuilding.stackexchange.com/questions/499/what-software-is-available-for-keeping-and-organising-notes-about-your-world)
**Now,** if you can't or don't want to use software you can still manage this it just requires very good organizational skills and some repetition. For ease of access you are going to want to document all direct relationships of an object in the object's template. This means you will write a lot of information more than once. Keep your content organized and come up with short hand.
Lets say all character templates follow a naming convention: CH001, CH002 etc. So if you need to reference an establishment back to a character the establishment's sheet would say Owner: CH002 (Name) so you can easily find the sheet. In reverse the character's template would have *holdings* listed and may have an entry HOLD001 that relates back to the bar. Essentially you are manually managing a database and data relationships.
If you have the space I would also recommend a form a story boarding. Basic story boarding is simply putting visual effects in order, but in this case you can story board your world. I suggest using your space geographically. It can be a great way to get a handle on all the moving parts of a story.
[Answer]
Scrivener for the following reasons:
The ability to create links and various pages functions much like a wiki.
The ability to import other documents, word, excel, images, pdf, weblinks, etc...
I create a map in photoshop then import it in
I have templates (they have preset ones) for setting, character, etc... that you can use.
The ability to create projects, side notes, binders, search keys, split the screen, color coding, and the sheer amount of customization organization is amazing. Great for me as I am a very structured and organized person and need to find stuff.
[Answer]
I use a combination of different formats to record my world information.
### Notebooks
I keep notebooks (actually composition books) that I can bring with me when I'm feeling productive/creative in which I can record my thoughts. Later when I'm sitting at my computer I can transcribe my thoughts into my computer.
### Spreadsheets
My current world building activities revolve around Fantasy role playing and constructing an SF game (explore, combat, construction, economics, etc. - think Civ in space). Especially for my SF game, the SF aspects follow known and extrapolated laws of physics except for a few minor tweaks. So I create giant spreadsheets of information about what different items in the game can do and also how to construct new solar systems on the fly.
All of that is store in spreadsheets and its why I can often answer questions about atmospheres, moons, etc. quickly. I just put in the parameters for the question and it spits out the answers I want.
### Word Docs
I do put narrative into both worlds and typically use MS Word to store that information.
### Visio
I put together flow diagrams for research and production. It shows the inputs and outputs and how you get from raw resources to finished products.
### Wiki
I do not currently use any wiki to organize my data and I think this is a major shortcoming of my current approach. When I get some free time I need to explore these two possibilities and consider gathering all of my information together and organizing it.
### Maps
I do not currently have a mapping program although I think this is another major shortcoming of my current system. I'll need three different kinds of mapping systems:
1. Planetary (for SF & FRPG)
2. Solar system (for SF)
3. Jump Link (for SF)
### Characters
Other than character sheets produced for various gaming systems, I haven't developed a good scheme for organizing this information either.
### Windows FS
For organization purposes, I often just use my Windows FS to organize the information I have on my two world building projects. One method of organizing non-player characters (NPC) by logical grouping would be to create subfolders for various regions/locations and drop all NPC sheets into that folder, along with maps, and other regional bits of information.
### Database
Alternatively, if you have a relational database management system (RDBMs) you can link the things together. This method has the added benefit of allowing multiple connections for each bit of information. For example, a specific NPC could be linked to a thieves guild, a specific location in a city, and a planned encounter later in the adventure.
Professionally I work with some (Oracle RDBMs and MS SQL server) that I'm more familiar with and I am licensed to use (and have a business logic overlay for that data).
However, these are likely too expensive for personal use. For the typical user, I'd use MS Access (or equivalent). These are intended for much lighter weight use and more user friendly interface. Plus, MS Access ties into things like Word & Excel so you may be able to tie everything together in it. However, I am personally not familiar with MS Access and can't really give much advice on how to use it.
[Answer]
I use a few Word\* documents. One for setting/characters, another for plot, another for a conlang. These have grown very organically over the course of several months and I have jumped around a lot, from the first notions I had to some of the most developed in the very next sentence. They would be a complete mess to anyone else and your success depends on your tolerance for organized chaos.
I also recently started using [DokuWiki on a Stick](https://www.dokuwiki.org/), which is for personal, private wikis, based on DonyorM's [suggestion](https://worldbuilding.stackexchange.com/a/502/8918) in a related question. It works pretty well, but I'm disappointed with the lack of page templates (so that all pages for people would start out with the same sections for Early Life, Career, Death, Influence, etc.), and customization is pointlessly difficult. Plus some things just don't work well in a wiki format.
\*Technically OpenOffice, but that's not the point. A .txt would work just as well.
[Answer]
I can't imagine why you would not use software. Or do you mean not using specialized software but still using the computer with the word processor?
Back when people didn't use personal computers for schoolwork, we were taught in primary school to use 3×5-inch index cards.
If you want the arranging of notes on a wall or table, you could print cards with index titles just for pushing around on the table.
Back then we didn't have post-in sticky notes either. But post-in note cards are used now for "agile" software engineering management which itself came from automotive factory management.
The "agile" stuff uses short notes orgainzed on a wall. Software that computerizes that ought to work well for this kind of planning too since the physical metaphor is the same.
If you don't mean that you're opposed to using a computer but meerly don't want to use special tools, the word processor is still available. In Author's Notes, Piers Anthony described his writing methods during the era where he shifted to computers and more capable computers. If he had an idea, he would open a document for that project, and note it, then return to what he was working on. If you're pounding away in the word processor, continuing to use that when a thought intrudes for another project is certainly the least disruptive. Adding the note to the end, not orgainizing it yet, means not fully task switching and messing up your current state of mind.
Later, when working on *that* project, the rough log of new notes are "organized". Organizing means editing into the document with like things together, topic breakhead, color highlighting, all still using the same tool.
[Answer]
I use Scrivener for that, generally supplemented with some spreadsheets. I initially bought Realm Works, thinking that would work, but the amount of work involved versus what I would get out of it was not worth it to me.
] |
[Question]
[
>
> **Summary**: *I am looking for a portal transportation mechanism that is consistent with the laws of thermodynamics.*
>
>
>
**[Portals](http://en.wikipedia.org/wiki/Portals_in_fiction)** (or **wormholes** or **gateways**, something that connects two different locations in space-time), are usually portrayed with interesting side-effects:
* When one of the portals is placed directly above the other, you get a perpetual motion machine - things that fall into the lower portal instantly appear from the higher portal, accelerate, then fall into the lower portal again.
* When one portal is placed at the bottom of an ocean, water comes gushing out at high pressure from the other one.
* when one portal is placed in space, air is sucked out from the other location
* by logical extension, portals at different heights and atmospheric pressures would generate a constant and strong gust of air trough the portals, although that one is usually not portrayed much.
These effects are usually either actively exploited (Valves Portal game), or prevented by some special security mechanism (Stargates in the tv show disassemble and later reassemble matter)
**However I am looking for a 'realistic' portal mechanism that does not have those sort of effects.** The standard portals strike me as unrealistic for the following reasons:
For one thing, such a portal clearly violates conservation of energy, or it would need some sort of special mechanism and power reserve to account for the difference in potential energy between the two portal locations. Any custom mechanism that converts the energy difference into something else risks violating the second law of thermodynamics.
For another, should a portal not transport electromagnetic and gravitational forces just as well as matter and light? Electromagnetic and nuclear forces at least have to work through the portals. Since these forces hold matter together, a solid object would fall apart when it is transported through the portal.
I would therefore expect that when a electrically positive charge is placed next to one portal, the other portal would attract negatively charged particles.
Likewise, if a *planet* is placed next to one portal, the other portal should attract matter. Therefore the air from the planet would not escape into space through the portal, since all air that passes trough is strongly attracted back towards the portal.
**I have however some trouble envisioning all logical consequences of such a portal mechanism.**
* If two portals are placed a different heights, someone approaching the higher portal should perceive a gravitational pull towards the portal, right?
* Would someone approaching the lower portal also perceive a 'push' away from the portal, essentially some sort of anti-gravity force? After all, when passing through the portal they would gain potential energy, which cannot be gained for free.
* If one portal is placed in the ocean, would a bubble of air form around that portal, or a bubble of water around the other portal?
I realize that these sort of questions could be answered kind of arbitrarily, given that no such portal system exists right now. I am looking for the most consistent and natural mechanism, in line with the laws of thermodynamics; in particular the law of conservation of energy.
**Is there a way to get such a consistent gate mechanism, without hand-waving all difficulties away as 'magic'?**
I am mainly interested *not* in the physical mechanism that would make such portals possible, *but* in the observable consequences such portals would have, *assuming* they are possible.
(As far as i understand, the current best physical concept for wormholes, a traversable [Einstein–Rosen bridge](http://en.wikipedia.org/wiki/Wormhole), involves a large mass within the wormhole itself, as well as surrounding negative-density stabilization structures. So the wormhole itself would have a couple weird gravitational effects. For now, I would like to ignore these additional effects and thread them as negligible)
[Answer]
# Conservation of Energy
One possible answer is:
*Both ends of the portal must have same potential with respect to gravitation and with respect to electromagnetic fields.* This is very natural, since both portal ends are basically the same point of the space and there should not be anything special on the border.
How does this manifest? As the gravity field of Earth leaks through the portals, the gates acquire false gravitational mass. (Not to be confused with [inertial mass](https://en.wikipedia.org/wiki/Mass#Inertial_vs._gravitational_mass) - it exerts forces, but does not make the gates harder to accelerate.) One acquires positive false mass and the other negative false mass, so the total change is zero. How big will the false mass $m\_f$ be? If we assume the gates are spherical and have radius $r\_g$, one is higher by $h$ meters from the other and they are near Earth surface, the potential difference between them will simply be
$$
\Delta \Phi=gh\;,
$$
where $g=9.81\;\mathrm{m\,s}^{-2}$ is the gravitational acceleration on Earth. To compensate the difference, an equal potential difference must be created by the false masses of the gates:
$$
\Delta \Phi=\frac{m\_f G}{2d}\;,
$$
where $d$ is the distance between the portal gates and $G$ is the [gravitational constant](https://en.wikipedia.org/wiki/Gravitational_constant). By putting the equations together, we yield
$$
m\_f=\frac{2dgh}{G}\approx dh\times 2.94\cdot 10^{11} \mathrm{kg\, m}^{-2}\;.
$$
In order to obtain the acceleration at the gate, we use formula for gravitational acceleration using the gate false mass
$$
a\_g=\frac{m\_f G}{r\_g^2}\;.
$$
For example if the gates are 100 m above each other ($d=100\;\mathrm{m}$, $h=100\;\mathrm{m}$) and they are 1 m wide, they would acquire false mass $2.94\cdot 10^{11} \cdot 100 \cdot 100 = 3 \cdot 10^{15} \mathrm{kg}$, which is a mass of cube of water 14.5 km big compressed into a very small volume. This also means that the acceleration at the surface of gates would be
$$
a\_g=\frac{3 \cdot 10^{15} \cdot 6.672\cdot 10^{-11}}{1^2}=200,200 \;\mathrm{m\,s}^{-2}\;,
$$
which is 20,000x stronger than Earth's gravity. They would probably tear anyone entering into pieces. Possible solution is to increase $r\_g$ or to decrease $h$, even at cost that one of the portal gates will be levitating. (This should be possible, since there are forces between both gates trying to put them into the same heigth.)
Short summary:
* The portal gate that is higher acquires positive false mass, the lower gate acquires negative false mass. (Repels normal matter.) The mass is much smaller than mass of Earth, but since it is in a very small volume, it produces very big forces.
* It will not be harder to put the gates into motion because of this mass, but it will be very hard to move the gates into different heights. The gates are attracted - not necessarily towards each other, but always to the same heights. (For example if one is at sea level in Australia and the other in Austria, there will be no attraction.) Force of this attraction will be comparable with lifting weights of similar mass as is their false-mass in the Earth's gravity field.
* No energy can be gained by jumping through the gates or pouring water through the gate, since the forces induced by the false masses will cancel the energy gain.
### Edit 1: Portals with nonzero inner length
The previously presented calculations assumed that the portals have zero inner length. In such case, the difference in potential energies has to enter through the false mass of the portal mouths, which often lead to extreme forces near the mouths. But if there is space inside the portal, an inner length $L$, the forces can be signifficantly smaller. Problem is, the forces are not uniquely defined and one has to assume some things to get particular numbers. Let us assume that
* In all points inside the portal, the acceleration (and thus also the force) acting on an object is the same.
* This acceleration is the same as the acceleration $a\_g$ just outside the portal.
With these assumptions, we can calculate how does the portal behave now. If previously, we calculated the difference in potential $\Delta \Phi = g h$, now this difference is reduced by the potential gain inside the portal equal to $a\_g L$. So we have
$$
\Delta \Phi=gh - a\_g L\;.
$$
With this assumption, now have to update the formula for $m\_f$ to
$$
m\_f=\frac{2d(gh-a\_g L)}{G}\;,
$$
which leads to
$$
a\_g=\frac{2d(gh-a\_g L)}{G} \cdot \frac{G}{r\_g^2}\;.
$$
By solving these two equations, we obtain the final formulas
$$
\begin{align}
a\_g &= \frac{2 d g h}{2 d L+r\_g^2}\;,\\
m\_f &= \frac{2 d g h r\_g^2}{2 d G L+G r\_g^2}\;.
\end{align}
$$
As we can see, with large inner length $L$, the forces near the portals can be made arbitrarily small. It is still true that if you are going from the lower portal mouth to the higher one, you are going "uphill" and you must exert work.
How does it look inside the portal? Interestingly, there would be no walls. The space wraps into itself, so it looks like if you are standing between four mirrors: all around, there are images of yourself and of other things inside the portal, just they are not images, but they are really there. You could see your own back.
# Conservation of Momentum
The solution above conserves the energy properly. However, the energy is not the only thing that should be conserved. There is also momentum. With momentum, I do not have any nice idea how to put it into equations. But similarly to the previous case, I guess there would be forces acting on any entering object that change its momentum as it is passing through the portal.
The forces would act both on the passing object and on the portal gates. If it is easier to rotate the portal gate so that the object would not change its direction of motion (yes, it could be easy - the portal gates could have negligible inertial mass), they would rotate to a proper position. If they are somehow fixed, the passing object would get strong kick from the portal and its momentum would be transferred to the portal gates. This would definitely not be pleasant experience if you are entering quickly - probably like hitting a concrete wall.
### Note
I do not know if this is the solution you wanted, but it seems quite self-consistent to me. I definitely do not guarantee that it is consistent with the general relativity - it is probably not. (On one side because the portal gates are curvature o space and require extreme exotic mass, which brings additional effects. On the other side because the proposed model is not the only one - I know at least about one more consistent possibility, that is probably the case for wormholes. If you want to go this deep, you should be asking about wormholes, not portals.
[Answer]
This is a really cool question, and I think I can (partially) answer it. Here goes.
>
> If two portals are placed a different heights, someone approaching the higher portal should perceive a gravitational pull towards the portal, right?
>
>
>
I'll assume that you're talking about an object in between the two portals. In this situation, it would be as if the point in space where the upper portal lies were actually where the lower portal is - closer to the planet. The lower portal, on the other hand, would essentially be *farther* from the planet. But would anything happen because of this? Well, the portal is supposedly a "hole" in space. It's a two-dimensional opening. That means that there is no way for a three-dimensional object to only be at that point. The three dimensional object would have to be partly outside the portal, and so would feel the same pull of the planet as it would feel if the portal wasn't there. In the case of the higher portal, there would still be a pull towards the planet. Whether or not the object would move towards the portal would depend on how far it is away from it - in other words, whether or not the portal's gravity balances out the normal gravity.
>
> Would someone approaching the lower portal also perceive a 'push' away from the portal, essentially some sort of anti-gravity force? After all, when passing through the portal they would gain potential energy, which cannot be gained for free.
>
>
>
This depends. The "anti-gravity pull" would come from the upper portal. Again, it depends on the distance between the portals, and where the object is in between them.
>
> If one portal is placed in the ocean, would a bubble of air form around that portal, or a bubble of water around the other portal?
>
>
>
Here's an experiment that can give you the answer. Take a 2-liter bottle of soda (already empty). Fill it with water, so that it is entirely full. Screw the cap on tight, so no air can get in. Now take a toothpick and make a small hole midway down the bottle. What happens? (I'll hide the answer if you want to do it for yourself)
>
> The water will not flow out! Now put a second hole in it. Here, the water will flow out.
>
>
>
This represents what would happen if the ocean and atmosphere were not connected - which they are. Now do the experiment with the bottle *open*.
>
> The water will flow out.
>
>
>
---
I highly doubt such a portal could exist. As you pointed out, it would violate conservation of energy (continued increase in kinetic energy), as well as special relativity (the object would move instantaneously - thus faster than the speed of light). If you're really pressed, you have to invoke magic. There's no realistic way for this to work.
*Note: I know about the theorized Einstein-Rosen bridges, but they're highly speculative and have some key problems. See [the Wikipedia page](http://en.wikipedia.org/wiki/Wormhole).*
[Answer]
As a simple solution you could say that any differences in potential energy between a low and a high portal are compensated by the portal system itself.
When an object is teleported from a lower portal to a higher portal, the portal gun provides the necessary energy difference from its internal power supply. When that supply runs out, the portal either collapses or the preservation of momentum doesn't work anymore.
Another way to solve this is by converting the potential energy difference into thermal energy. An object moving to a higher portal becomes colder, one moving to a lower portal becomes hotter. Some early science fiction stories written by Larry Niven which deal with teleportation solve the thermodynamic problem this way.
Regarding gravity passing through the portals: Gravitation is by far the weakest among the four fundamental forces of nature. The smaller the scale, the more negligible does it become. At subatomic levels it doesn't play a role anymore, so when the portals would not transfer gravity, it likely would have no effect on objects which travel through it, as long as [the portals aren't so far away that there are differences in gravity](https://www.youtube.com/watch?feature=player_detailpage&v=QBCE539v2JM#t=275) which would be so large that they cause sheer forces on objects which are half through the portals.
[Answer]
Greg Egan has some notes on this subject accompanying his novel, *The Book of All Skies*, here: <http://www.gregegan.net/ALLSKIES/01/Gravity.html>
The math gets... rather complicated, but he shows how it is possible to model the effect of a portal on the electric field with a layer of electric charges and dipoles (and you can do something similar with the gravitational field). Seems like it would be possible, if difficult, to work out how the gravitational field of Earth would behave around a portal with its endpoints at different elevations based on the info there.
] |
[Question]
[
>
> Look at you all sitting here. Quite some of you have probably never ventured beyond the outskirts of this city, mayhaps not even past the wall? You've spent your whole lives in this place, but what do you actually know about *its* lifetime?
>
>
>
Introductory course to the History & Sociology of the tri-region area, Ringstadt Militaric University.
---
This question is **about** checking over the topography I created in the below map. There are a number of features in and about it that I, with my limited knowledge and understanding of geology & hydrology, find plausible - but have no way of reliably telling if that is fact.
Below you will find a *Background* section explaining some of my goals for this area in terms of worldbuilding that have been significant factors in my design-process. In the *Topography* section you will find aforementioned map as well as some paragraphs detailing it in prose, documenting my thoughts and choices - and the why's in my understanding. At the end you will find, once again, the question accompanied by a focused list of the things *I know* I need double-checking & feedback on - this list is not meant to be exclusive, but to my understanding these are the core foci.
---
*Background*:
On the below image I attempted to map the area where my con-city *Ringstadt* will be founded and built. The development of the region will start off with a few communities living off the land and supporting an abbey that is going to be somewhere in the H4 to K7 area (the square denoted by these corners).
Eventually, in the earth-equivalent of the ~1600-1700s, metals and coal become a thing of importance and prospecting happens, which leads to a mining town growing around first shafts digging into the mountain in the D2 to F3 area, producing mainly coal. A supporting logging encampment springs up somewhere upstream, the mining expands along the ridge towards the abbey, digging further into the mountains.
The underground mining reveals iron deposits that, when being tapped, turn out to be much more extensive than judged by the original prospecting. The limited iron smelting & processing industry experiences a rapid growth together with the surrounding boroughs of worker & family homes. The direction of trade inverts from exporting raw materials to importing them and starting to export goods & commodities.
---
*Topography*:
The map section is located in the northern hemisphere [somewhere above 55° of latitude](https://worldbuilding.stackexchange.com/questions/38921/can-a-super-governmental-military-body-like-this-work). The base-height of the map is, as of now, undecided - it can be whatever is necessary for the topography to work.
The area is framed by a lake and a mountainside. The lake kisses the mountainside until it eventually eases back to give way for a wide expanse, being separated from higher grounds by a steep 'cliff'. I imagine there having been an ice-age glacier *shearing off* the mountainside, leaving that steep 'cliff'. The glacier would have been reduced into the residing lake.
Along the lakeside, the expanse features reed marshes. The wide and even expanse getting flat enough in the lower parts near the lake to gather standing bodies of water, etc.
A smaller lake forms up in the mountains to the north-east, discharging into a river that eventually feeds into the lower-eastern lake. To the south of the high-lake hills frame a valley mostly being a peat-bog. I imagine are having started off as a rather flat extension of the above lake, eventually filling up with biomass and turning into marshlands.
[](https://i.stack.imgur.com/KKIRW.png)
```
Legend:
brown -> topological lines, 10 meters each
light blue -line- -> streams, rivers
light blue -shaded- -> bodies of water
turquoise -> peat bog
olive -> reed marshes
Each grid-cell is 400m by 400m.
```
---
**Q**: How sensible is my topography?
A good answer should *at least* address the following topics:
* Are there any (grossly) unnatural features?
+ e.g. the steep 'cliff' that frames most of the mountainside until about H4
+ What do I have to change for them to be natural?
* Are the streams & rivers in sensible positions?
+ Which (if any) are misplaced & where do I need to move them?
+ Which areas are missing streams?
* Can the peat bog and reed marshes exist at the positions I put them?
+ Should the area from D1 to F1 be a bog or similar as well?
+ Can I have clay and/or other shallow resources in this area? And where?
[Answer]
**Grossly unnatural features:**
Mainly, you should remember that topography is a facet of the geological history of the area. So, your hills look fine, could just be product of orogeny and erosion, your cliff spanning the entire map is fine, most likely explained by a strike-slip fault (although it could be a bit straighter if that's the case), and the plain could also be explained by glaciation or sea-level retreat (although randomize it a little, the slope is too similar). Looks *mostly* good!
**Streams and Rivers**
For that one stream in the D3-G2, you seem to understand that streams tend to have those U-shaped bends in the contour line. However, the other streams don't seem to fit this pattern. Also, if you intended the river at J2 to cut through the mountains, that would have it flowing uphill at first, which doesn't seem to fit. Other than that, this looks ok.
**Bogs and Marshes**
Marshes and bogs tend to occur in low places, near water. I don't know your water table, but those regions are defined as usually saturated, so below the water table. Given that you put your bogs and marshes near shore, that should totally work.
**Clay and city**
Clay is a type of particulate matter: like sand. Given that your large river cuts through a cliff, that area should have some clay. Also possible: near your peat bog or under the surface of the lakes. I would place your city in either the region D3-E3-E4 or the region G6-H6, with D3-E3-E4 preferred because of flat land for farming, natural defence (back to a cliff), and a water source (river).
I am by no means an expert on this, please correct any mistakes I have made.
[Answer]
I am not a geologist, but as far as I can tell this layout is completely plausible. Good attention to detail and an interesting landscape.
I would move the city slightly west though, having it situated on the flats as opposed to bordering the bog and corresponding hills. (Or even right next to the reedlands, since a rice like staple crop could be grown there more easily.)
Possibly the best place to retrieve clay would be on the edges of the Northern lake. A layer of clay is probably deposited just below the water line, or even above it, depending on how high the lake was before the drainage river formed. The western lake may also contain deposits.
I think the only other thing to worry about is whether coal and iron tend to be deposited together. While I don't think it is impossible, I also don't think it is likely to occur often.
[Answer]
## Looks pretty good with some nitpicks
## Land Topography
The shape and layout of the mountains and hills that form the geography look pretty good to me. The lower left portions of the map have clearly seen significant erosion to flatten out like that.
## Hydrology has some problems
In a few places, it looks like the streams run uphill or close enough to uphill to be really confusing.
The Bog looks pretty good. It's shape hints at a low, <10m rise in J3-K3. When I saw an early version of the map, I assumed that the bog would go all the way to the smaller lake. If the smaller lake were to get deeper then it would naturally flood into the area occupied by the bog. If the lake water level went down the bog would naturally drain out. The stream leading from K3 to J2 means there's a slope going down to the small lake. Seems odd that the bog would stop just short of extending to the lake.
The Reed Marshes could probably extend much further inland along the streams that feed into the large lake. 10m contour lines isn't really enough resolution to be able to tell where the divets and hollows on this landscape are. A good argument could be made that the southern portions of the planes would be very marshy; especially row 10. The landscape extends 4000 meters with only 25 meters of altitude gain. That's less than a 1% grade and very hard to tell which way is downhill.
The stream in K4-J5 seems odd. Normally, streams don't run parallel to contour lines and that stream does. I think it more realistic that water coming from the moutain would go east, off map, travel south on what would be columns M, N, O or P then come back west around rows 6 or 7.
**Some heuristics for designing water flow systems**
1. As the terrain gets steeper, the water path will get straighter. This makes sense since the pull of gravity on a 45 degree incline is much stronger than on a 1 degree incline.
2. Inversely, as terrain gets shallower, the water path tends to meander a lot more with far more loops, curves and bends.
3. The size of a stream, river, etc will depend completely on the surface area of the land found upstream. For example, in the steeper terrain in G4-H4, there isn't nearly as much land surface area to feed a stream there as with a stream that empties into the river at F2. I would expect the G4-H4 stream to be much smaller and less regular than the F2 stream.
4. The general flow of all water is inherently tree shaped. This map captures much of that pattern but stated just for completeness.
5. Where erosion has been happening longer/faster, the landscape tends to sit back. J5 is an acute example of this. The stream in C1 that goes down to the big lake in B2; I would expect it to go west a little more to meet up with stream in B1 first then go down to the big lake in B2.
[Answer]
Let's take your concerns in order:
The general topography looks good without any seriously unnatural landforms. High cliffs are often a feature of areas with a glaciated history like these near Fox Glacier in New Zealand: [](https://i.stack.imgur.com/DnKQC.jpg)
Your drainage looks okay as it is but I would have a stream along the cliff bottom that captures most of the drainage coming from the highlands along the rough line from K5 to F2; joining the main outlet river before it empties into the larger western lake. The streams that cross the plains would be smaller, and possibly seasonal rather than continuous, due to capturing only over land drainage on the plains rather than any water from the heights. The box from F8 to K10 probably needs some detail work in the drainage department as well, it's a bit "blank paper" at the moment.
Bogs are an artifact of blocked drainage, they occur in basins where rainwater cannot get out fast enough to prevent waterlogging, the area you have identified appears to be a prime candidate. There should be a transitional zone of treed swamp or grassy marsh where the bog gives over to lake or stream where water becomes dominant over vegetation. On a technical note you appear to have streams feeding the bog, this would make it a fen as opposed to a purely rain fed bog. Reed marshes are usually formed along lake edges so there's no issues with the one you have, although a fringe of the same in the upper lake would not be unreasonable as well. As the D1 to F1 zone does not appear show any drainage impeding topography there's no reason to change the proposed drainage in that area.
In terms of resources; there will lenses of secondary clay to be found, shallowly buried, under the large southern alluvial plain, (left overs from post-glacial sedimentation) you'll be able to pick them out because the poor drainage will allow reeds to grow in isolated patches all over the otherwise well drained and grass dominated plain. Peat from boggy areas makes a good fuel, and [bog iron](https://en.wikipedia.org/wiki/Bog_iron) was historically an important ore. Gravel will dominate the plains, especially in the area where the river connecting the two lakes comes out of the hills, and there will be other [alluvial fans](https://en.wikipedia.org/wiki/Alluvial_fan) where streams from the mountainous northern area meet the plain, these may also be a valuable source of both clay and gravel. Reeds are an important traditional building material in many parts of the world, both for houses and for fishing boats.
For me the best settlement location is in D3, where the river meets the lake, this will give good access to a number of resources, not least of all easy access to the lake for fishing boats, and the reedbeds for boat building.
If I missed anything or you need more details on a point let me know.
[Answer]
There are places looking a little like that in french Jura called reculée. They are also created by a glacier and tend to form lakes and cliffs, higher than your but that's mostly because the plateau where the glacier forms is higher above the valley underneath.
If it takes place in Europe the 50 meters of sediment will be mostly Jurassic limestone so iron is likely but you will have to dig much deeper for coal.
If your glacier came from K10 to A5 then the small lake is not very likely since streams tends to be subterranean on limestone plateaus, and the stream will have a resurgence or something on the cliff. The only way to solve that issue I see is that an older glacier created a small reculée for the small lake and then a bigger one crossed its road.
Glacier tends to bring sand and clay so it's perfect for reed.
The small streams flowing from the hill H3 will be active only when it rains like all the other streams less than 200m long but the well on H4 would be a good resurgence. The stream flowing from D10 to the lake in A5 should be bigger, starting at the bottom of the valley
[Answer]
I know I’m late to this, but If you’re still taking feedback I think you’ll find that your topography is quite exaggerated vertically, especially in the lowlands. From what I can see, the flattest parts of the map (the Dubukay expanse, for which I now feel responsible) have a grade of about 1% (10m/1000m). That would hardly make it feel very flat, but rather a noticeably sloped hill. If we look at a place like Kansas or Florida (sorry to be US-centric, but they’re just examples of very flat places), the grade is much closer to 0.05 or 0.025%. (Kansas is ~400 miles wide (650km) and has a total elevation change of less than a mile (1.6km)). Florida is apparently even flatter.
I’d spread out the contour lines there. I know it sucks because it’s already kinda boring.
Alternatively, you could blow up the scale in the corner a bit. Make it more like 1-2km would give a more realistic grading, although it’d wreak havoc upon your other features and travel times.
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[Question]
[
Assume someone detonates a Hiroshima-sized nuclear bomb in space. Since in space there's no air, the bomb will behave differently than on Earth. In particular, there will not be an air pressure wave, and certainly no "mushroom" cloud — the energy will be sent in all directions equally, as kinetic energy of the bomb fragments, and as radiation (of all sorts). Therefore, the damage pattern on Earth probably is very different from the damage pattern in space.
Now the question is: How far do I have to be away from the bomb in order to survive it without injury? Let's assume that at the time of the explosion I'm in space with the thinnest space suit possible.
[Answer]
Nuclear bombs produce 3 effects on Earth
1. Thermal flash
2. Neutrons
3. Blast (caused by conversion of X-rays into heat)
In space, you need only concern yourself with the neutrons and X-rays.
### Radiation Enhanced Bombs
According to [Atomic Rockets: Radiation Flux](http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Nukes_In_Space--Radiation_Flux):
>
> A one megaton Enhanced-Radiation warhead (AKA "neutron bomb") will
> deliver a threshold fatal neutron dose to an unshielded human at 300
> kilometers.
>
>
>
### Normal Nuclear Weapons
A non-radiation enhanced bomb produces much less neutron radiation but more X-ray radiation. A 1 kton nuclear bomb is borderline survivable at a range of 30 km due to the X-ray flux.
The survivability range of nuclear bombs scales (roughly) linearly with bomb yield and as the inverse square of distance between bomb and victim. Meaning a 1 mton bomb would be borderline survivable at a range of ~900 km due to X-ray flux.
All numbers are for *unshielded* humans. Shielding can significantly alter these numbers.
### Shielding
The effectiveness of X-Ray shielding is primarily determined by the amount of mass it contains (high atomic mass materials work slightly better than low atomic mass ones).
The effectiveness of neutron shielding is dependent upon the number of low atomic mass nuclei between the bomb and the victim. High atomic mass nuclei in your radiation shielding can make neutron radiation more difficult to manage.
### Edit 10/09/2015:
I concur with Thucydides, anyone interested in this topic should go to Atomic Rockets and read all relevant sections. It includes a description of what a nuclear detonation would look like, what effects it'd have on spacecraft, etc.
As for survivability, my answer only considers a person wearing a minimal spacesuit for protection. The actual physical damage a 1 kton weapon would inflict on a body (human or otherwise) at a range of 30 km would be minimal. A person at that range would be hit with a lethal dose of radiation. Without medical care it might take them days or longer to die in an extremely unpleasant manner.
### Edit 10/10/2015:
You should also realize that being outside the "deadly" zone listed above does not necessarily mean you will live. Radiation sickness is nasty and you'll require intense medical treatment in order to survive a large dose. Atomic Rockets has a [Acute Radiation Syndrome Chart](http://www.projectrho.com/public_html/rocket/radiation.php#id--Effects_of_Radiation--Acute_Radiation_Syndrome_Chart) which tells you what symptoms you can expect from a given dosage. The chart gives you a probability of surviving any given dosage.
My numbers were for ~2.0+ Gray dosage - this gives you a survival probability of 35-40%.
[Answer]
**About 100 miles (160 kilometers) for no injuries**
Something cool that I found a while ago is NASA's report on [Nuclear Weapon Effects in Space](http://history.nasa.gov/conghand/nuclear.htm). First thing to keep in mind:
>
> If a nuclear weapon is exploded in a vacuum-i. e., in space-the complexion of weapon effects changes drastically:
>
>
> First, in the absence of an atmosphere, blast disappears completely.
>
>
> Second, thermal radiation, as usually defined, also disappears. There is no longer any air for the blast wave to heat and much higher frequency radiation is emitted from the weapon itself.
>
>
>
The radiation is your only real problem in space. So with a nice radiation-proof spacesuit, you could survive a nuclear blast at a *ridiculously* close range.
So how far would you have to be in order to be safe from radiation, assuming essentially no radiation protection from your spacesuit? [According to Wikipedia](https://en.wikipedia.org/wiki/Acute_radiation_syndrome#Cause), a dose of 0.1 grays (10 rads) is enough to cause radiation sickness. Let's look at one of the charts NASA included:
[](https://i.stack.imgur.com/QTYP1.gif)
This is for a 20-kiloton explosion. At sea level, you'd get 10 rads from being a mile or so away from the explosion. In space? It looks like we're at about 60 rads when you're 40 miles away. To reduce that by a factor of 6, we'll need to go $\sqrt{6}\approx 2.5$ times as far away, so about 100 miles away.
Of course, you'd still survive short-term if you're closer than that, but the closer you get the worse the radiation sickness will be.
Something else to remember is that in space 100 miles is not very far - the international space station goes that far in about 20 seconds.
[Answer]
The [Atomic Rockets](http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Nukes_In_Space) site has a pretty comprehensive section on nuclear weapons, and the answers there suggest that a nuclear weapon in space isn't as much of a threat outside of short distances due to the inverse square law (much of the radiation energy is dissipated into space) and the lack of a medium to transmit the energy to the target (the main thing you are going to be hit with is a blast of x-rays, which *will* spoil your day if you are too close).
The modifier is if the nuclear weapon is driving some sort of amplification device.
In the 1980's, it was postulated that the energy of an exploding nuclear bomb could be converted into a laser beam of x-rays if a sufficiently long and slender rod of the correct material was placed with one end on the bomb and the other end pointing at the target. As the material was converted into plasma by the exploding bomb, there would be a point where the long line of plasma should become a lasing cavity and emit a high energy x-ray beam, with a potential range of thousands of kilometres. This was the basis of the "Excalibur" device, which took the idea to "11" by envisioning a device which looked like a sea urchin carrying dozens to hundreds of "spines", each locking onto a different target. There were many practical reasons this never got off the ground (so to speak), but one of them was the efficiency of converting the bomb's energy to laser energy was very low. This might have been resolved since then.
The other idea would be to make the bomb drive a "shaped charge". Astounding as this sounds, evidently this was experimented with and some success was achieved, with a pre scored plate being converted into a shotgun charge with pellets moving at some astounding velocity at the target (@ 70 km/sec), while using various means to shape the plasma jet from the nuclear explosion can result in a narrow jet of hot plasma moving at something like .03\*c\*! This was evolved from the pulse units developed for the ORION nuclear pulse drive spacecraft, and known under the name "*Casaba-Howitzer*" Much of the information is still classified, but you would certainly be in grave danger even in a well armoured spaceship hundreds, if not thousands of kilometres from the blast.
[Answer]
Although there are a lot of if's hidden in your question, a sort of worst-case number can be determined.
First, a Hiroshima blast is about 15 kt. Since 1 Mt is $4\times10^{15}$J, a Hiroshima-sized blast releases about .015 times that, or $$E=.015\times 4\times10^{15} = 6\times10^{13}\text{ J}$$ For a fission bomb, about 35% of released energy is thermal, and about 3% radiation. The amount of thermal radiation required to breach a spacesuit is unknown, but let's say something on the order of 1 MW/m2 for one second. After all, sunlight is about 1.5 $\times$103 W/m2, and a suit obviously won't have major problems with that. Assume a human body provides about 1 square meter of area (2 meters tall by 1/2 meter wide). Then the total thermal energy required will be 1 MJ. Since 35% of a bomb goes to thermal, we can write $$4\pi R^2 = .35 \times6\times10^{13} = 2.1\times10^{13}$$ and $$R = \sqrt{\frac{2.1\times10^{13}}{4\pi}} = 1.3\times10^6\text{ m}$$ 1300 km is much greater than is characteristic of terrestrial nukes but there's a good reason - the atmosphere absorbs most of it and produces blast.
Radiation is a different issue. First, about 1/10th as much energy goes into radiation as to thermal. However, since radiation will largely penetrate a suit, it might take less energy. But the fact that radiation will penetrate a suit means that some will simply pass through the body and produce no damage. Let's assume, purely as a fictional number, that 10% of radiation which hits a person will be absorbed. The unit of absorbed radiation is the Grey, which is 1 J/kg of tissue, and 5 Greys is a standard lethal dose for humans. For this set of assumptions,$$4\pi R^2 = 5\times 0.1\times .003 \times 6\times10^{13} = 9\times10^{10}$$ and $$R = \sqrt{\frac{9\times10^{10}}{4\pi}} = .84\times10^5 \text{ m}$$ So the two effects agree within less than a factor of 2, and 1000 km sounds like a nice round number for a survivable distance. Of course, that means that your suit didn't *quite* burn up, and you didn't *necessarily* die of radiation poisoning, so you might want to add a safety factor. I'd guess the 2,000 km is a much better number to use.
EDIT - In calculating radiation levels, I forgot to factor in body mass. Assuming 100 kg for mass gives a factor of 10 reduction in distance, to $$R = .84 \times 10^4 \text{m}$$
] |
[Question]
[
**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
Okay, my first trial run, [How would humans and society react to a superhero existing and saving the earth?](https://worldbuilding.stackexchange.com/questions/21317/how-would-humans-and-society-react-to-a-superhero-existing-and-saving-the-earth/21319), of social sciences with [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'") is looking some what sickly at the moment (maybe someone is preparing an answer, but it is taking a while), so maybe I will chose a more mathy social science for this stack exchange audience: [economics](/questions/tagged/economics "show questions tagged 'economics'").
---
Okay, so an inventor/tinkerer figures out how to transmute lead into [gold](/questions/tagged/gold "show questions tagged 'gold'") by exposing it to some sort of radiation. He was able to build this machine using spare parts he had. The mass of the gold is equal to the mass of the transmuted lead. Given current gold, lead, and electricity costs, the electricity costs were 1/30th of the increase in the materials value. He doesn't publish his method, but shares it with personal inventor/tinkerer friends. Knowledge of the method grows slowly but surely.
The only difference between this gold and regular gold (as found on the market) is that this gold is about a million times purer than our purest gold. It could easily be made indistinguishable though by mixing it with impurities.
Let's say the original inventor resides in the contemporary USA, but the method does spread to other countries. What impact would this have on the economy? Note that this is [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'"); you must supply references to economic or similar journals or other reputable sources to backup your answer. Maths usually make everything better. See [this](https://worldbuilding.stackexchange.com/questions/21317/how-would-humans-and-society-react-to-a-superhero-existing-and-saving-the-earth/21319) and [this](https://worldbuilding.meta.stackexchange.com/questions/2348/can-hard-science-apply-to-social-sciences-and-other-academic-fields) for details.
[Answer]
**Lead - Lithium = Gold?**
Assuming that the [method](https://physics.stackexchange.com/questions/196301/lead-lithium-gold/) uses Lead-208, transmuting that into Gold produces Lithium-11 which almost [immediately decays into Beryllium-11](https://en.wikipedia.org/wiki/Isotopes_of_lithium#Lithium-11). Beryllium is useful as an alloy in nickel or copper. The market for beryllium isn't very large but appears to [be growing](http://www.beresources.ca/AboutBeryllium/BeryllliumPrices.htm) and was sold for $230/pound in 2010. This inventor is going to have to be careful because powdered beryllium is carcinogenic.
**Mine no more**
Before this invention there was only one way to acquire gold, to dig it up or pan for it in rivers. Gold mining operations are expensive, dangerous and ecological destructive. Access to certain gold deposits is only feasible when the price of gold is above a certain price. (No one mines gold for fun, only profit.) According to this [graph](http://www.visualcapitalist.com/what-is-the-cost-of-mining-gold/), the cost of mining gold in North America is \$580/oz. In a mine in South Africa, it costs \$1519/oz. Most mines cost about \$1100 to \$1300 (USD) per ounce of gold mined. Any time the cost of gold is less than these costs, the mining company takes a loss. (Gold miners are well known for using less clear [accounting methods](http://www.kitco.com/ind/fulp/2015-02-04-The-Real-Cost-of-Mining-Gold.html) to calculate mining costs.)
This guy has created a disruptive innovation in the gold mining industry. A normally extremely expensive material has suddenly become very cheap and easy to create. Lead makes up 0.00099% of the [earth's crust](http://www.periodictable.com/Properties/A/CrustAbundance.al.log.html). Gold makes up 3.1×10^-7 %.
As of this writing, lead costs about \$0.77 per pound or \$0.05 per ounce. Let's assume \$1100/oz for gold. Since the cost of electricity is 1/30th the increase in value, leading to $36 dollars in electricity for each ounce of gold produced. At [10 cents per kilowatt hour](http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a), this is 36,000 kilowatt hours per ounce produced. In order to keep up this kind of power draw, he would need to be buy power on industrial contracts and build an actual factory to make it. For comparison, the average US household consumes about 1000 kilowatt hours per month. Let's assume \$20 in consumables and equipment costs.
Total cost for one ounce of "artificial gold" is \$36+\$.05+\$20=\$56.05. Even so, this kind of gold production is ridiculously cheap by an order of magnitude.
**Effects on the Gold Market**
Let's measure this in terms of the spread of knowledge and quantity available.
*Inventor + 0 and first Ounce* - The inventor is able to sell this for \$1100/oz and starts to payback his research and equipment costs. The larger gold market doesn't even know it's dead yet. Selling one ounce amounts to statistical noise in the market. He verifies his own samples using 'aqua regia'.
*Inventor + 0 and first 1000 Ounces* - The inventor has recovered his costs and wants to show proof of his invention to his friends. Gemologists and metals experts are loaned samples to verify his method but are not told where the gold came from. The inventor is now a millionaire. Our inventor has hired a security force and started construction on a high security gold factory because the power requirements for larger gold production is greater than available at the Inventor's residence.
*Inventor + 2 and first 2000 Ounces* - Metals experts report the unusually high quality of the gold and verify it's authenticity. The inventor has told two of his friends and they have duplicated his results. Metals experts verify their samples are also sound. The US gold market varies between [100,000 oz and 400,000 oz](http://www.cmegroup.com/trading/metals/precious/gold_quotes_volume_voi.html) per day so spreading 2000oz of gold over a month goes unnoticed. Spreading out the gold sales over a monthly period prevent huge moves in the market and helps conceal the price advantage the inventor+friends enjoy. Inventor+friends will also need to find a way to deliver their gold because anyone who has no previous dealings in gold but suddenly starts supplying non-trivial quantities is going to come under suspicion.
*Inventor + 10 and the first 10,000 ounces* - Secrecy is paramount because a leak at this point could draw the attention of very powerful, well-backed interests, namely the Mob, every single terrorist organization and every government on the planet. No patents are filed with the US Patent Office or any international patent organizations. The Inventor and his friends spend all their time at the factory. They definitely have gold fever.
*Inventor + 25 and the first 50,000 ounces* - The market has noticed an influx of supply from an unknown source and started to ask questions. Talking heads assume that old pensioners are dumping their stocks or the Fed is doing something crazy....and get it all wrong. The cost of gold drops slightly on increased supply. The gold factory is in full swing but lead supplies are unaffected. The US government start to go looking for the source of this new gold supply.
*Inventor + 50 and the first 100,000 ounces* - The first rumors of an alchemist who makes gold from lead hit the broader markets. Many don't believe it, after all, alchemists in Europe in the Middle Ages tried and failed. The beryllium market sees an unexpected but significant increase in supply. The cost of gold continues a slow slide on increased supply. The Feds are still looking and starting to close in.
*Inventor + 100 and the first 150,000 ounces* - In order to avoid being captured, the Inventor breaks the story on international news that he has found a way to transmute lead into gold. After the initial interview, he sequesters himself in his factory and grants no more interviews. However, his friends and friends of friends explain the method. The metals experts referenced earlier will verify that the gold is real. The cost of gold drops like a stone because of [supply shock](https://en.wikipedia.org/wiki/Supply_shock) and a loss of confidence. Shares of gold mining companies drop even more dramatically as stock holders attempt to exit a now dead industry by selling their stock. The broader stock market goes into a brief chaos mode as the news is digested.
The broader economy doesn't change much since gold, while valuable, wasn't used in a huge number of places. (Compared to a drop in oil price, gold just doesn't have the same kind of impact.) Large investment institutions like pension funds may hold a lot of gold but are also incredibly diversified so the impact is minimal. Investors who have specialized in holding gold will take a huge hit, losing 90% of their investment though this kind of investor is, hopefully, rare as every single investment strategy ever recommends diversification to guard against just this kind of devaluation.
*Inventor + 10,000 and the first 1,000,000 ounces* - Manufacturers pile into the market once they know the method. Everyone attempts to get into the gold market while the price still reflects the old scarcity. In a few short months after the new factories go up, gold becomes a normal commodity and floats at around \$100/oz reflecting the cost of lead and electricity plus markup. Gold is no longer the investment of last resort. Banks and governments move to platinum, silver, or palladium as a reserve metal thus forcing the cost of those metals higher.
Goldbugs have a crisis of identity as the metal they have staked so much of their identity on is now cheap and common.
While sanction evasion using gold is still useful, it doesn't pack the same price/weight ratio it once did. Platinum and palladium take over the role of sanction evasion.
Engineers the world over rejoice. Many of them are aware of instances where gold is the perfect material for a specific implementation but had to choose a different material because gold *was* so expensive previously. All electrical cable plugs can now be gold plated instead of just the expensive ones. Silverware manufacturers can now expand their product lines with solid gold wares instead of just silver or stainless steel. Dentists see a marked increase in gold crowns instead of porcelain.
In some circumstances, gold replaces copper. PC case modders go on a kick of making gold cases because why not? It's gold!
While gold isn't yet cheap enough to use as the cores of network cables, it does find its way into extremely high end audio cables for audiophiles. They praise the round golden tones, superior conductivity and minimal noise of the new cables. Everyone else continues to make fun of them for it.
Gold jewelry sees a huge increase in demand. It's still a beautiful metal and the previous price barrier that prevented more people from owning gold jewelry has disappeared. This demand for jewelry helps prop up demand at the new low price range. Gold is still more expensive than [silver's](http://www.jmbullion.com/charts/silver-prices/) \$20/oz.
Other inventors look for ways to extend the lead-to-gold technique to other metals. The search continues.
Fort Knox becomes a museum to a by-gone era.
---
Granted, this Inventor is a much cooler customer than [James W. Marshall](http://www.sfmuseum.org/hist6/impact.html) who discovered gold at Sutter's Mill in the California Gold Rush.
[Answer]
Let us assume that the inventor immediately releases the formula. There would probably be two effects: a spike in the value of lead, and a long-term plummet in the value of gold.
The world-wide production of lead is about 10 million tons, or 7.5 billion kilograms. It seems reasonable to assume that at the very least, lead equal to all the lead produced in the year is available for use (not the actual lead produced, some of which is locked up in paint and other things, but at least that much). With lead having a density of 11.34 grams per cubic centimeter, this comes to 661 billion cubic centimeters, or 661,000 cubic meters. By contrast, all the gold ever mined is almost certainly less than 15,600 cubic meters. The amount of lead in the world clearly dwarfs the amount of gold.
The initial spike would not mainly be the result of people rushing to gain huge amounts of gold for investment purposes. Anyone with the resources to make such a method work would realize that gold was about to drop. Rather, lead will become equivalent to gold for the purposes of electronics, fillings, and so forth.
At the same time, the gold market faces the prospect of a influx of gold at least dozens of times larger than its current size. Of course everyone immediately divests themselves of their gold, and the market crashes even before all of that gold has even been produced. The price of (naturally mined) gold might stabilize at that of lead, lower, or higher depending on how expensive the transformation process is.
Assume that the transformation process is of negligible cost. As the demand for lead is supplemented by buyers in these new markets, the price of lead could, ironically, rise higher than that of gold. It is purer, and the original lead still has its original uses, whereas gold has mining costs and fewer applications.
[Answer]
In the context of global, developed financial markets, gold is a fringe asset. The result of a collapse in the gold price would be felt almost exclusively by individual (private) investors. Investment banks and private financial institutions do not hold much (if any) gold.
Most governments hold gold as part of their reserves. In the case of developed economies, the amount of gold held is a tiny fraction of their nation's *total economic value*. For example, according to the [World Gold Council](https://en.wikipedia.org/wiki/Gold_reserve#IMF_Gold_Holdings) the US government holds 8133 tonnes ( 261 million ounces ), which at today's price of approximately \$1,100 per ounce equates to about \$290 billion. This is a small fraction of annual GDP and a tiny fraction of total US wealth. And similar relationships exist amongst other developed economies.
Underdeveloped economies that rely more heavily on gold reserves to lend credence to their currencies would be more severely effected and one would expect to see extreme volatility in their currency rates.
Regarding gold and government generally, [John Maynard Keynes](https://en.wikipedia.org/wiki/John_Maynard_Keynes) famously described the gold standard as a barbarous relic of our past - where the "gold standard" refers to a nation backing up its currency with gold; i.e., the guarantee to exchange currency for gold. As our world's economies develop, the role of gold in underdeveloped economies will diminish.
Gold does have some industrial applications, especially in technology, but the amount of gold consumed by industry is, if I recall correctly, between two and three percent of annual production. So the sudden collapse in the price of gold would not have a significant effect on industry.
This leaves jewellery industry, where losing the perception of gold being valuable would have near fatal consequences for gold jewellery.
[Answer]
the price of lead would go up and the price of gold would drop dramatically. The magnitude of this effect would depend upon the cost the transformation process.
I think it's possible that people would create some kind of arbitrary distinction between "natural gold" and "Lead gold" and then attempt police it, preventing people from selling jewellery made of "Lead gold" under the guise of "natural gold". This is exactly what has happened with the invention of "industrial diamonds" which are molecularly identical to normal diamonds but created in a lab.
Of course, this only applies to jewellery. All industrial applications of diamonds use industrial diamonds because they are cheaper. So if there were manufactured gold, then all electronics would use this gold for their circuitry, rather than natural gold. This might slightly reduce the price of computer components. There may open up more applications of gold in manufacturing, since it is now a cheaper material.
There would be a lot of gold mines that are no longer viable with the drop in gold prices, and they would all shut down. The towns where they are located would have high unemployment. Of course, elsewhere, gold factories would open up, along with new manufacturers of gold products and of course, new lead mines. I'd say the overall effect on the economy would be fairly neutral.
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[Question]
[
This is about "giants" inhabiting a fictional earth-like planet somewhere in the Universe (like those in the movie Prometheus, for example).
Assuming that all the conditions (temperature, gravity, atmospheric pressure and composition, etc) on the planet are about the same as on earth, what would be the tallest possible height that a bipedal humanoid organism could reasonably attain?
The assumptions here would be that:
* these humanoid organisms are built similarly to humans, with a brain,
heart, lungs, an oxygen carrying circulation of blood, a human-like skeleton and so on
* there should not be any hydrogen or other mechanisms that make these creatures lighter
* the organs and the skeleton could be allowed to be stronger
but their operation would have to follow standard laws of physics
* the civilization of these humanoids may have developed some way to obtain large amounts of energy to support their physical energy needs, but they are still dependent on consuming the nutrients in the form of solid or liquid food
[Answer]
Scaling laws are an important aspect of biology. When you take a particular object (such as a human being), and make it twice as tall (while keeping the proportions the same) its weight will not increase 2-fold. It will actually increase by a factor of $2^3$ (8-fold)! A 6-foot person weighting 160 pounds, if doubled in height, will therefore be 12 feet tall and weigh 1,280 pounds if you kept the proportions the same.
There is a problem with this. Although weight increases $2^3$-fold, the strength of the bones would only increase $2^2$-fold. It means that the strength-to-weight ratio of the bones is half that of a normal person. A giant with these proportions would stress their skeletons more easily and be at greater risk for injury if they fell down. In order to fix this problem, you would need to make the bones wider in proportion to their length so that the weight of the person produces less pressure on the bone.
A well-proportioned giant would therefore be a rather wide, burly-looking person with thick arms and legs.
Potentially your bones could generate more compact bone, and less marrow, and would compensate reasonably well. But, one's muscles, tendons, and etc would also have to compensate. The knees, ankles, and hips would also take a beating.
Would a person that big have to eat about 20,000 calories per day?
Possibly. Think about large theropod dinosaurs like Tyrannosaurus rex. Those creatures demonstrate that bipedalism is possible for very large animals.
In order to reach that size (5-7 tons), a lot might have to be changed about human physiology. A better cooling system might be needed (surface area does not increase as quickly as volume does, so the heat-generating tissue of a large mammal has less surface area to release that extra heat from). Might such giant humans require elephant-sized ears for temperature regulation? More sweat glands? Or perhaps a lower average body temperature? Larger or more efficient lungs would be needed too (the diffusion of oxygen and carbon dioxide gases is limited by the surface area of the alveoli in the lungs).
I calculated my basal metabolic rate to be around 1,730 calories a day, so if you were to scale my mass up to that of a T-rex, my metabolic rate would would increased by a similar amount (~112,000-156,000 calories per day). If you went for the "lower the body temperature" solution to the heating problem you'd get less calorie burn than that, though. In fact, warm-blooded creatures expend around 90% of their caloric intake just warming their own bodies up. A cold-blooded giant might not be so bad!
The lung volume should be ok due to the fractal space-filling nature of the lungs, unless your creature panted like a dog as part of its temperature regulation.
Humans vary in height from around 4 feet to about 7 feet with relatively "normal" physiology, although perhaps head size varies less than other parts of the body.
Wadlow's greatest recorded weight was 222.71 kg (35 st 1 lb) on his 21st birthday and he weighed 199 kg (31 st 5 lb) at the time of his death. His shoe size was 37AA (47 cm, 18½ in long) and his hands measured 32.4 cm (12¾ in) from the wrist to the tip of the middle finger. He wore a size 25 ring. His arm span was 2.88 m (9 ft 5¾ in) and his peak daily food consumption was 8000 calories.
The cause of death is very telling... Wadlow died at 1:30 a.m. on July 15, 1940, in a hotel in Manistee, Michigan, as a result of a septic blister on his right ankle caused by a brace
The current record holder, Sultan Kösen at 8'3" is often photographed with crutches. However, since there are many basketball players over 7', perhaps the leg problems are not always found with tall individuals.
Answer compiled from [here](http://www.thenakedscientists.com/forum/index.php?topic=39283.0)
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Shamelessly based on this [answer](https://worldbuilding.stackexchange.com/questions/51771/anatomically-correct-giants/51784#51784). Because of the square-cube law mentioned already, a 50 foot human would weigh over 50 tonnes. I do not see a possible way for a biped to support, how big these people can get depends on how humanlike you want them to look.
In the real world, very tall people are caused by excess growth hormone rather than genetics, which is why they often have many problems. [Giant Ground Sloths](https://en.wikipedia.org/wiki/Megatherium) stood around 5 metres tall and weighed around 5 tonnes, however they were tripedal, having a load-bearing tail. If an alternate evolutionary path is acceptible for you then your giants could have similar tails, but then we lose the humanlike segment.
For Their great size, these giant humans would need a series of size adaptations:
* **Bones**. Proportionally thicker bones are needed to cope with the excess weight (compare a horse to an an elephant). This is especially true for the legs bones, while theoretically we can say that the bones are made of a stronger material on this world, like [calcium carbonate](http://www.webmd.com/osteoporosis/guide/strontium-treatment-osteoporosis), this will allow them to look humanlike, but only on the outside.
* **Muscles** would be larger/stronger for the same reason as above. You could also increase the efficiency of the muscles - Apes have shorter muscle fibres than humans which makes them a lot stronger pound for pound at a trade-off of losing your fine motor skills. The problem here is that the muscles at a large size would break the biones they move, a solution here is to have fat deposits act as coushins, this would also help caloric intake, see below.
* **Proportions**. As you scale up, relative leg length scales down in order to preserve balance, this is especially true in bipeds, which have a poorer sense of balance. The bigger they are, the harder they fall, which is why longer arms would be needed for balance, stability and for softening impacts, also the possible reason of collecting more food. I would expect the distribution of mass moves lower and lower to keep a low-center of mass, so the tallest humanoid may have thinner upper bodies or less broad shoulders.
* **Internal organs** would have to compensate for extra body mass, shocker there I know. Because volume scales faster than height, the heart and lungs become less effective and would need to be scaled up at a higher rate. These beasts would likely have a deep ribcage and massive heart relative to their size.
* **Facial features**. Larger eyes only become effective up to a certain point. The eyes of the tallest possible beast would be much smaller in proportion to his head than a regular human. The surface area of the nasal area would increase faster than the length of the nose, giving them a much keener sense of smell. The larger nasal cavity and larynx would also give your giants deeper voices.
* **Brain**. Our brains use vast amounts of energy so the brain would probably scale up a lot slower than the rest of the body. Extra mass and the accompanying buffs to your senses would be more taxing on their brain so the brain could scale to compensate, how much it scales depends on how intelligent you need them to be.
* **Blood pressure.** Keep blood pressure high or the giant will die. The giant would need to keep blood pressure high in order to circulate blood and oxygen around the body. Elephants have very tight skin on their feet to increase the blood pressure in their limbs as the blood needs to travel against gravity for quite a height. Elephants also have large fatty pads on their heels to cushion the impact of walking. Tall human feet may not resemble a regular humans.
* **Diet**. As the intestines scale up, digestion becomes easier. More body mass means higher body temperatures which means more nutrients can be extracted from food. The problem here is that animals with large intestines lean towards vegetarianism, which in turn supports lazier animals as size increases. The solution is for the vegetarian diet of the tall people to consists of planets high in fat and caloric value, nuts for example.
I have also read that the size of a certain reproductive organ scales up more with giant animals but I chose not to read up on that one, I *do* have principles believe it or not.
I would say that while keeping them humanlike the tallest we can make humans is 4 metres as the largest prehistoric mammals never peaked above 5 meters (even quadrupeds) and the largest bipedal animals of all time - the therepods - didn't really exceed 3 or 4 metres at the hip and it's specualted the atmosphere contained a lot more oxygen in prehistoric times. Even a slimmer 3.5m giant would weigh over half a tonne.
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About 10 feet. That's the realistic limit to hominid creatures we have excavated so far (read [Gigantopithecus article](https://en.wikipedia.org/wiki/Gigantopithecus) for details).
Generally, people taller than 7 feet develop arthritis, circulatory disorders and, in rare cases, autoimmune problems (read [this list](https://en.wikipedia.org/wiki/List_of_tallest_people) for details).
The mentioned 10 feet height is based on the tallest hominid discovered yet, which only went extinct due to (assumed) shortage of food some 100,000 years ago.
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I see no physical reason why a bipedal couldn't grow to the size of dinosaurs or at least giraffes. The bones are not a problem, mass goes up with $height^3$, but the second moment of area (to which the "rigidity" is is proportional) of a tube is proportional to $r^4$, so the bones won't break. The tubing scales well, too, dinosaurs got along with one heart, as do giraffes (which have a few extra biological tricks because of their long neck).
It's a matter of the size of the area (dwarfism of species on islands is well known) available for living during evolution, which is unlikely to be so small.
Main problem is evolution itself: Large species are longlived, so respond less well to changing circumstances, and large species have smaller populations and larger individual food demand, so there is a larger risk for them to not go through a bottleneck and just die out.
Or put it this way: If two species want to evolve into intelligence, and one becomes fertile at 10, the other at 25, it's rather clear who will win.
One other snag with height: Once you're rather clever, there is hardly evolutionary pressure to become higher. So height will have to come first, or *en route*. Perhaps.
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Basing things solely on human existence that has been documented or discovered so far and adding in all sorts of mathematics and genetics on based on known earth values one could propose a relative value. It has been documented (not acceptably proved) that Easter Island had a humanoid race of inhabitants that exceeded 12 feet in height.
Based on unearthed bones it has been proposed that dinosaurs could have evolved (if not for extinction) into humanoid like creatures one can only ponder if a something like a tyrannosaurus were to evolve into a humanoid type creature. Or maybe a brontosaurus with compact body and a long neck but still humanoid.
And in todays age of genetic engineering it is only a mater of time (even if banned) that some government or person fiddles with making larger humans with greater strength and power for one purpose or another. This possibility is only countered with over population which drives global warming and would have greater impact on larger size beings.
But I could envision one other possibility that fits the earth like planet that could allow larger body style even with the earths physical loading. This would be a humanoid that is much greater percentage toward amphibian. A water planet with more shallow salt water areas could force a humanoid to become taller to stand above waters. More sleeker in body style to swim faster. With a large portion of the planet cover in swampy growth of tall trees bearing fruits but waters mostly exceeding depths at 8-10ft or more could force evolution to follow two paths grow tall or at least long necks and arms or learn to swing in the trees.
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What would it look like for elementals (type of creature based on its base element) if the base element acted as its gravity? How would they move about?
How would their basic actions look compared to humans?
So a fire elemental might be pulled from its feet by a large explosion (explosion might not do damage to it), and the base gravity pull making it seemingly standing on the surface like humans would be the soft pull from the earth's fiery core.
I'm interested in a water elemental too. During intense rain storms they are able to leave bodies of water because of the amount of water in the air (albeit with some effort).
in terms of rules:
* momentum and centrifugal forces still apply to these creatures.
* these elementals are able to produce their element by magic and it should have the same effect. So, if a fire elemental throws a fireball large enough into the air it could jump higher, *(edit based on @Cyrus's comment)* but elementals of a type are not affected by each other's "bodies" in terms of pull (except maybe romantically if that happens)
* these creature are able to retain their form except under extreme conditions.
So a water elemental in the ocean can move through the water (easier through currents) but escaping the ocean would be a heavy burden. It would need to wait for a storm and gather momentum
* The mass of the elementals *was brought up by @Mithrandir24601*. Their size would be about that of a human (can vary just like humans) but their weight would vary based on their element.
+ Fire elementals weigh about a third of the weight a human of the same size would weigh. I would say they are a little lighter in the day due to the sun being above
+ Water elementals are as heavy as water
+ Earth elementals are the same weight of a human their size even though they may look heavier (rocky appearance sometimes with bits of metal)
+ Wind is the same as fire in terms of natural weight
I'm thinking similar rules of gravity, like the larger the amount of it the harder the pull on what it affects, but alternatives are welcome.
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**If you want more of a "break free" effect, maybe have the force proportional to $1/r^3$ (inverse cube, like the force between two magnets)** instead of the usual inverse square (gravity, electrostatic force). Or even $1/r^4$ or whatever you want. It can still scale linearly with mass the way gravity (${G M m}/{r^2}$) does, you just vary the scaling with distance.
That would also make it plausible for small nearby things (like fireballs) to have more of an effect than the Sun's pull. (Which only affects fire Elementals, not the Earth's orbit around the Sun, so would tend to pull fire Elementals off the surface during the day, counterbalanced by the pull of magma and stuff underground).
It's completely plausible for a force to have very different scaling with distance than gravity. Just don't call it gravity! For example, the Weak nuclear force is very short-range [because the force-carrying particles have non-zero rest mass](https://en.wikipedia.org/wiki/W_and_Z_bosons#Basic_properties) (unlike the photons that carry the electromagnetic force. This is why the electroweak force is unified at high energies: there is enough free energy for pair-production of the force carriers, so they can pop up like photons). I'm not saying you should go into that much detail (better to be vague than obviously wrong to people that know the subject), just that non-gravity-like forces happen without magic.
So you could even have a force that's more or less inverse-square over short ranges, but falls off dramatically at a certain distance.
There have also been proposed theories of gravity that modify it slightly over astronomical distances to explain things like the [Pioneer (space probe) anomaly](https://en.wikipedia.org/wiki/Pioneer_anomaly). (That's now pretty conclusively explained by thermal radiation pressure, ruling out some of the gravitational theories.)
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**Another plausible explanation for scaling different than inverse-square: extra spatial dimensions**. i.e. direction(s) that Elemental stuff can move in that's perpendicular to x, y, and z. Inverse-square scaling happens because the area of a sphere scales with the square of radius. In 4-dimensional space, the analog of a sphere has a 3-D analog of area (actually a volume) that scales with the cube of radius.
So if the force (and force-carrying virtual particles) spread out in a 4th spatial dimension, it would scale as $1/r^3$. And you can still use the word "gravity" if you like.
Real theories have been proposed with properties like this, especially [String Theory's extra dimensions](https://en.wikipedia.org/wiki/String_theory#Extra_dimensions) which are "rolled up" / curved back on themselves, which limits the strength of the effect. One proposed effect is/was gravity being slightly weaker than $1/r^2$ over astronomical scales.
For this case, presumably it's a dimension that only Elementals can move in, not ordinary matter. So it can have a strong effect on Elementals without affecting normal physics. Perhaps moving in this dimension takes you between worlds, or between elemental planes and Earth.
Of course, it's easy to introduce inconsistencies if you aren't careful. (e.g. if there are lots of Elementals only a couple km away, they would exert some pull on Earth's air / water / fire / earth. (Assuming this force affects the inert element with an equal and opposite force to what the Elemental feels, otherwise you're violating conservation of momentum and conservation of energy.) Anyway, safer to just have the *force carrying particles / fields* spread out into the extra dimension(s), and not have the Elementals able to move along it. Otherwise they could bypass walls by going around them using this extra dimension, and stuff like that.
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Remember that [the shell theorem](https://en.wikipedia.org/wiki/Shell_theorem) only holds with $1/r^2$ forces, so a short-range force will tend to pull Air elementals into the sky when they're on the ground. If it's stronger than gravity, they'd have to actively fly downwards or hold onto things to stay at surface level.
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This Elemental force (E-gravity? gravitee? Etraction?) doesn't attract plain water to other plain water, for example. This means that **buoyancy doesn't happen with respect to this force**, because the displaced plain water wasn't affected by that force. (i.e. there's no extra pressure created by it).
We know this because Newtonian mechanics + fluid dynamics can accurately model the Earth's oceans (e.g. sea level heights around the world, and the deformation of the oceans due to Earth's spin rate). I think our models are detailed enough that we would have noticed if water attracted other water more than gravitationally, rather than just got the wrong value for some other free parameter.
Buoyancy due to gravity can overcome gravity + the extra force, if they're in the same direction, otherwise not.
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Water density in the air is peanuts compared to a nearby ocean, even during a heavy rainstorm. A $1/r^3$ or $1/r^4$ force would make the effect of a storm more significant.
A water elemental leaving the ocean is like a human climbing a mountain. It's "uphill" all the way from the centre of mass of the ocean. Being at the edge of the ocean is like a human having climbed up a vertical shaft from the centre of the Earth.
However, the ocean is more like a thin disc than a sphere of water, so getting to the edge takes you farther from more of it. Unlike climbing outward from a sphere (where your weight will peak at the surface), your weight will probably drop off some as you approach the shore (especially since coastal water is shallower). However, with a $1/r^2$ force, the difference between getting to the edge and going another kilometre beyond is *less* significant than with a sphere. You're already pretty far from most of the water, so the total pull you feel doesn't drop off as much with distance from the shore. (So again, a $1/r^2$ force isn't going to give you much of a "break free of the ocean" effect).
If a Water elemental can "climb" more easily through water than by walking on land, it's going to be much easier to leave the ocean by going up-river until they're near an equilibrium between a large lake and the ocean.
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I really like this idea, because it encourages creativity with what makes another world habitable for different types of elemental. For example, 'warm' ice planets with underground reservoirs would be good worlds for water elementals to live if we include the mechanic that, say, ice has less of an attraction that liquid water...
One of the important things to consider here is that gravity obeys an inverse square law. That is, moving twice as far away from a source of gravity reduces the pull by a factor of 4. There is also an interaction coefficient ($G$ in the case of gravity) which determines how strong the attraction is per base amount of the source material. This is *very* weak.
Let us assume that for fire elementals on earth, the solid parts of the core have a negligible effect, so that only liquid magma has concentrated enough fire magic to determine the attraction. Estimating this to be 5/6 by volume, we also have a distribution of fire magic concentrated much closer to the surface than the concentration of mass in the earth.
Consequently, we have two options, depending on preference:
1. Fire elementals are very agile, able to easily leave the surface of the earth if they burn hot enough (eg Fantastic 4 style).
2. Fire elementals are equally constrained by the Earth's pull as humans.
For fun character design, I would opt for the former. Unfortunately, with the assumptions made so far, the equivalent of the $G$ coefficient would have to be *even smaller* than for gravity, and consequently the effect of explosions and large fire-balls would be invisible. The inertial mass options you mention would determine the distinction between 1 and 2; smaller inertial mass makes flying feasible.
There is a solution to this: we assume that magma is actually also quite low in fire magic concentration. This could be justified by a 'magma is mostly rock, part fire' justification, and it could largely compensate for the $G$ value. If a fire ball is pure fire magic, be could say that magma is just 5 percent fire magic by volume. I think this ratio (1:20) would be about right for the `fire ball jumping' idea, but this avoids more complex mechanics of fire-magic concentration. Again, the 'attraction to explosions' idea still requires very close proximity, but in a context involving eg both a fire and an air elemental in a large explosion, they would be pulled in opposite directions by the event, which is fun. Then inverse square law means that the Sun would still not contribute noticeably to effects, just as its effects on the tide are not noticeable compared to the moon.
Finally, for your water elemental we again have a problem with the inverse square law. In order for the Earth to be sufficiently attractive to keep them here, the coefficient of $G$ would have to be **much** bigger, since all liquid water is found on the earth's surface and makes up only a tiny proportion of the Earth by volume! On the flip side, underground streams would generally be too far away and small to have much impact and allow them to escape. Water elementals in this model, assuming that we can ignore hydraulic pressure far underwater which is caused by conventional gravity, would be most comfortable around mid-depth in oceans with attractive material symmetrically distributed around them, as they would struggle to maintain the velocity to move far up or down. As I mentioned above, a different structure of world would make things much more feasible and make a planet much more hospitable!
I love the idea of a half human, half water elemental living on land, constantly feeling the pull of the ocean...
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Some interesting anomalies would arise out of this:
* Except for earth elementals, who would function just like everything else.
* As shown by the [Shell Theorem](https://en.wikipedia.org/wiki/Shell_theorem), wind elementals would have a natural resting position on the surface of the planet just like everything else. *Except*, they will (presumably) have a density similar to air, so will float/sink in the air as determined by that density/buoyancy. If they can change their density at will (by expanding/contracting their bodies), they will be able to change their buoyancy and, therefore, their height above the ground just as if they had a [swim bladder](https://en.wikipedia.org/wiki/Swim_bladder).
* Water elementals may not have that much difficulty getting onto shore. While the ocean is certainly massive, by the time they get to shore they're actually not that close to most of it. Basically, they would "weigh" quite a lot on the open sea, but as they get closer to shore they'd get lighter and lighter. By the time they got to shore, depending on the "gravitational pull", it might even be like walking on the Moon is for us. Seems like teenage water elementals would probably run inland up major waterways for the freedom and fun it offers them. During storms, a sea-bound elemental would get lighter from all the rain in the air but probably not enough to float. A ground-bound elemental would float up into the clouds, but may not be able to control its movement.
* Fire elementals, in most ways, would work like earth elementals if they are attracted to the Earth's core. However, any fires in close proximity could rapidly change their gravitational "down". Forest fires, in particular, would drag *lots* of elementals in. And if someone wanted to trap a fire elemental, all they'd need is a big open space with a bonfire in the center, and a way to bait the elemental into the area. The elemental might try to "climb" out of the fire's gravitational "pit", but as long as there are no hand holds on the ground, it probably wouldn't be able to escape.
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Do you mean a literal, physical attraction? Instead, perhaps consider instead a fascination/motivational attraction? (You'd get the same general effect, but you'd have more wiggle room with how strong it was, and when/why.)
If so, Fire might be fascinated by/attracted to industrial processes/factories that use high heats/lots of energy in one place: metal refineries (or at least forges), rocket engines, or even nuclear reactors/bombs!
I'm thinking about the 'Yags' (fire spirits) in Tim Powers' *The Anubis Gates* here. (Great book!) It's not exactly an always-unresistable force, but it does tug at them.
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Here's a world much like Earth, except it's inhabited by a race of shapeshifters. On one side of the appearance divide there is an appearance much like a large Earth wolf; on the other is an appearance much like an Earth human.
The actual mechanics of the shapeshifting process are undefined, and I'm willing to do a little fudging there (but not really to the point of *just* saying "use magic"), but both forms should keep an exterior appearance actually resembling their respective species. So no humanoids with a large muzzle, nor brachycephalic wolves.
It's not too hard to find references to IPA charts, but I'm having trouble applying those to my particular question.
**So basically,** if we're allowed to make the internal anatomy as that of either a wolf, a human, something in between or something completely different, *but are constrained by the external apperance of a human and a wolf* and to the extent possible would like for them to also be able to make sounds resembling spoken English at least in human form (though with a strong accent is fine), then **what sounds would be common to both forms** of such a creature? For bonus points, rather than just making a list, also explain why those and not some other ones.
To clarify, these creatures (in either form) don't need to reliably fool someone with a training in medicine or anatomy (think doctor or veterinarian), especially upon close medical examination, into thinking that they are what they appear to be. However, they should maintain the respective outward appearance as much as is reasonably possible (small adjustments are allowed, but not major deviations, as illustrated e.g. by the human-with-a-muzzle example above).
Also to clarify, *you are allowed to adjust the internal anatomy!* So there is no need to be constrained by a wolf's (or a human's) voicebox, for example. What I want to avoid changing much is the *exterior appearance*. It is however best if the exterior appearance is as close to the only thing as possible that changes when they shapeshift.
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Let's start from an easier position. Let's start with what a wolf can't do.
* Wolves form very few front-of-the-mouth sounds. A whistle, for example, is beyond them. As would be a hiss or an "oooh" sound (indeed, O and U vowels might be beyond them). Wolves don't have significant lip control *(at least I've never seen a dog smirk, though that's likely not conclusive evidence....)* so they have a limited control of pitch.
* Wolves also can't form tongue-sounds such as clicks and the "th" sound. They can't roll their R's or make a buzzing sound.
**Or can they?**
However, your wolf isn't just a wolf, it's an intelligent brain inside a wolfey-looking body. It remembers speech, does it not? Two interesting tidbits from [here](https://steemit.com/music/@wolf-lykan/15-amazing-facts-you-didn-t-know-about-your-vocal-chords):
* The shape of an individual's vocal tract is partly genetic, partly learned.
Which suggests that your intelligent wolf can increase the sounds it could reproduce. A good example are those tongue sounds. Yes, that lengthy thing might be a challenge to click off the soft pallet or push up against teeth, but it could be learned nonetheless.
* More than 100 muscles work together when you sing or form a single phrase.
Here's where some of your world rules can work in your favor. I frankly don't know enough about canine physiology to know if that block of 100 muscles exists in the species — but I'm willing to bet it doesn't. In other words, all the jaw, neck, shoulder, and chest muscles that we use to produce a very complex set of sounds simply may not exist in wolves.
At least not *normal* wolves. Perhaps your shapeshifters retain this particular trait? That would mean a slightly increased chest area (might impact the use of front legs) and a thicker throat/neck area. It might also mean a thicker snout to permit greater lip and fore-palate control. In other words, if you know what you're looking for, you can see the difference between a wolf and a lycanthrope.
And that's what makes creature design interesting, isn't it?
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Well, seeing as the more limited of the two forms (vocally, I mean) is the wolf, I find it logical that most such shared sounds would originate from the wolf side. Wolves have several distinctive sounds that can be transferred through to the human:
**Whining.**
Whining is quite a common canine sound which often signifies sadness, discomfort and several other emotional states. I would assume it would carry well to the human side and would enrich the social communitation between speciments of that species. Since wolves have a pack mentality, whining would often signify a lower social standing in relation to another specimen.
**Growling.**
This would probably be less impressive and more subdued in human form, but it communicates threat quite clearly so I think it would transfer.
**Sighing.**
A sigh is quite universal. Granted, its not exactly a full sound, but it does transfer well.
**Laughing.**
While it would be a bit distorted in wolf form, its still transferable.
**'Huh?'**
An inquiring sound would probably transfer well as well and its useful.
**Groans.**
When aiming to voice displeasure, a groan is a basic sound and it would transfer well.
As a side note, I would advise you to think of other things that would be shared, like body language. wolves use body language, the position of the body, ears and tail for social ranking. This is bound to transfer to the human side in some way, you just need to determine how.
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Let's start by looking at the possible human sounds in the IPA's pulmonic consonants, it's points and manner of articulation, and figure out what in this human-based inventory a wolf may be able to produce consistently. [](https://i.stack.imgur.com/1pqAJ.png)
Right off the bat we should note that animals like wolves have relatively little control over their front lips (only really moving the front of their mouth for a submissive grin) making the articulation of the lips for the bi-labial and labio-dental columns infeasible in my opinion.
[](https://i.stack.imgur.com/Luc57.png)
Dental sounds, remembered from a human form, may be possible since they do not require difficult lip movements.
I can't see any reason why alveolar/post alveolar sounds would be infeasible for a long-muzzled creature, but the tip of a canid's tongue has less strength and articulation than a human's, so that will potentially be an issue that could prevent these phonemes from being reliably produced.
Same with Palatal, Velar, etc. Actually those consonants with further back point of articulation would probably be the most natural for a dog or wolf to make; think growls, murrs and other far-back fricatives that dogs are fond of.
Retroflex may be tough, as it'd require the creature to stretch their mouth open wider to accommodate the curve of such a long tongue.
I'm very dubious about how a creature with a long tongue would produce trills, especially since dogs have thinner tongues with less articulation at the tip.
Plosives all seem out of the comfort zone of most dogs, so keep that in mind.
Approximants are your friends because they do not require total closure/contact in order to be produced, and therefore will be easier to make in general.
Lateral Approximants and Fricatives are also good, as a lateral movement of a dog/wolf's lips is completely natural to them.
It'd be good, when considering canine conlangs, to watch videos of 'talking dogs' and listen to what phonemes the dog produces most naturally. Dogs tend to have a preference, to my ear, for: velar, uvular, pharyngeal and glottal fricatives; what sounds like a lot of uvular trills; aspiration; length, tone and stress distinction on vowels.
Dogs also don't have a uvula so they wouldn't be able to produce uvular sounds.
Look into those light green and gray squares in the image; those are points + manners of articulation deemed rare or impossible *for a human.*
The whine a dog makes isn't anywhere on here of course, but it'd be a natural sound for the wolf form, and replicable for the human form.
(*What* any whine would be called on this chart is a question that I'm not sure I'm equipped to tackle.)
I made a rough chart of consonants to seek or avoid: those best left alone are blacked out, and the most important ones boxed in red. The most of a dog/wolf's articulation is in the back of the mouth, so that's where the phonemes are.
Retroflex approximants are often made when dogs yawn, so I left them in this modified chart. That said they are unlikely to be any more phonemic than the clicks an English speaker makes when tsking at someone.
The problem with labial consonants is not having the articulation to make a perfect mouth seal, so a labial approximant is perfectly fine.
[](https://i.stack.imgur.com/7Ft0R.png)
And what about vowels? Vowels are easy as pie for a dog to make, and it's a good place to put tone, length, nasalization, aspiration, rhotacizing, vocal fry and stress for variation, so you don't need to have many vowels at all to be able to thicken your phonemic inventory.
[](https://i.stack.imgur.com/Tqp7l.png)
I wouldn't discount wolves or dogs as incapable of rounded vowels, as they can round their lips just fine to howl. I've heard many a dog pronounce a phoneme equivalent to /ɔ/, though in vowels especially I think you can hear the difference in a dog/wolf's skull and mouth shape.
That said the IPA vowel chart still applies with it's handy mapping of place/manner of articulation.
A dog can pronounce a rounded back vowel with an open mouth, and even if it has different auditory qualities than a human /ɒ/ it's still a /ɒ/ to me.
However I'm sure a shifter would be able to mimic human vowels just fine with practice, but it wouldn't be natural for every shifter to force their mouths to work like that. These vowels are analogous enough that it seems likely that shifters would just have a 'human dialect' and a 'wolf dialect' that are mutually intelligible.
Front vowels could be tricky though, especially the front closed set /i/ and /y/ which Ive never heard a dog make. It's hard for me to make conclusive statements on this however, as most vowel sounds I hear out a dogs mouth have significant vocal fry or heightened pitch, making them very different to my ears.
Do what feels right, listen to the sounds dogs make (they're much closer to wolves than most people think)
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[Question]
[
I am the most powerful weather wizard in the world. I can create any sort of wind based phenomenon with a snap of my fingers. I can whip up a tornado in less than a minute, and get a Category 5 hurricane going in a few hours. Though the magic I use to generate wind creates energy out of the Aether, once the wind is formed, it must obey the laws of physics.
I am interested in a demonstration of my powers, to suitably cow the assorted peoples of the world that they will pay me an exorbitant tribute. I want to blow up something big. The Great Pyramid at Giza, for example. I would like to use my powers and blow it to smithereens, like it was an Oklahoma trailer park.
The trouble is, I'm a little concerned because I don't want to start something that I can't finish. The pyramid is constructed of limestone with most blocks about 1.3 x 1.3 x 0.7 meters, with a mass of over three tons. I know I can generate enough energy to blow such a block around, but will wind force alone be able to move that block? If I get the wind going fast enough to move that block will there be other....side effects?
[Answer]
## EF5 Tornado
The upper end of tornadoes can do an amazing amount of damage, and your character can place an EF5 tornado where ever they want it. Unfortunately though the Great Pyramid of Giza is a formidable opponent. It will definitely take damage from the tornado, but it will still be standing afterwards.
### Lifting limestone
It was hard to determine if wind could lift a limestone block until I found an [article about a tornado from 1990](https://extremeplanet.me/tag/heaviest-moved-by-tornado/):
>
> In June of 1990, an exceptionally violent tornado formed in the desert-land of southwest Texas. Near the end of the tornado’s path in Bakersfield Valley, a production facility was destroyed (at left) and three oil tanks weighing 180,000lbs were moved three miles to the east. Two of the tanks were found 600ft up a hillside with a 40 degree incline. This is one of the most impresive instances of tornado damage ever recorded and perhaps the only documented instance of an object over 100,000 lbs being moved a long distance.
>
>
>
[Limestone weighs 2611 kg/cu.m.](https://www.simetric.co.uk/si_materials.htm) Doing some basic math each limestone block would weigh roughly around 3,088 kg. Note that some of the lower blocks in the pyramid are much bigger and can weigh five times that amount. If a tornado can push something weighing over 80,000 kg uphill then a tornado being directly manipulated by a person should be able to dislodge and push limestone blocks off the pyramid.
### How long to destroy the pyramid
Given enough time a tornado could turn the Great Pyramid of Giza into a pile of rubble, but the question then becomes how long will it take to do it. Unfortunately there is a time limit. Your character will likely not have more than an hour to pull this off. After an hour the tornado will want to dissipate on its own or by that point your character will have to flee from the angry locals.
It has been estimated that the pyramid has [2.3 million blocks](https://en.wikipedia.org/wiki/Great_Pyramid_of_Giza). If your character can take off even the top half of the pyramid, and leave the bottom half in a mess, then the mission is accomplished. The top half the pyramid only makes up ~12% of the total volume of the pyramid. So in order to remove that top half your tornado will need to remove approximately 276,000 stones in one hour or **76.7 stones a second**. Needless to say I doubt the amount of stone removed will come close to that rate.
### Where to form the tornado
For now lets table the time problem and look at where to perform the deed. The Great Pyramid at Giza is a tourist attraction and so is surrounded by security. If you were to even attempt to form some kind of weather event there you will likely end up shot. So you will need to form your tornado in a place which will not draw too much attention and that you can get it to your intended destination. Looking at Google maps of the area around the pyramid the only vector that you have available that will not go over populated areas is come up from the south:
[](https://i.stack.imgur.com/1z0VY.jpg)
Take an off road vehicle onto the Ring Rd. - Cairo--Alafayoom Rd, go off road for a bit, and then take your time to whip up your tornado there. Once it is ready send in north, and park the tornado on the Great Pyramid. By doing this you will also likely destroy/damage the Quarry of Menkaure and the Great Sphinx of Giza.
## Conclusion
A single normal weather phenomena will not be enough to destroy the Great Pyramid of Giza. However, if you park the tornado between it, the Quarry of Menkaure and the Great Sphinx of Giza, and make the tornado the right size even if you do not fully destroy any of them, the overall damage should get your message across.
[Answer]
Why try to knock it down when you can abrade it away?
You are a weather mage. You have a pile of sand nearby in the Sahara. The combination means you now possess the worlds best [sandblaster!](https://en.wikipedia.org/wiki/Abrasive_blasting)
Specifically, we are talking about the [Aeolian process.](https://en.wikipedia.org/wiki/Aeolian_processes) Wind erosion that occurs over time. There are beautiful examples of the results all over the world, but some of the most beautiful are in Utah (I am a touch biased,I confess)
So here is what you can do: Concentrate a flow of very high speed wind across the nearby dunes and pick up a bunch of abrasive sand. Direct it in a focused stream along the edges at first. Keep cycling the wind around back to the desert to pick up more abrasives.
Depending on how tightly you can control the wind flow and concentration of sand in it, you could carve your name deeply into the stone.
If your guy has really, really, fine control, he can add the use of water streams to carve out chunks. [Water Jet Cutters](https://en.wikipedia.org/wiki/Water_jet_cutter) are used to cut steel and other substances. Start about 2/3 up on the big pyramid and cut diagonally down to let the top slide off and expose the clean cut underneath. That will get attention.
You can also tell people your wizard has an *abrasive* personality.
This principle is not limited to fine abrasives. As long as the wind is forceful enough to pick something up and throw it at high velocity. Tornadoes have been known to throw chunks of 2x4 through cinder block walls at more than 200 Kph. Your weather mage could use cat 5 hurricane force winds to simply pick up the bulk of Cairo and throw it at the Pyramid. Even small buildings impacting at 250 Kph are going to cause a lot of damamge. The squishy inhabitants might even put a ding, if they hit head first.
[Answer]
If you can focus this wind and start it from any direction, then your best bet would be to do it within the pyramid and blow it up from the inside. Enough air pressure will burst anything, if you can apply in instantaneously and there isn't a limit then you have an explosive force.
We used air pressure to test our welding and solid metal tubes were deformed and burst using it. This is just scaling that effect up. It would be impressive!
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[Question]
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Worldbuilder in dire need!
I'm trying to figure out the eclipse length of a habitable Earth-like moon that is rotating around a gas giant. The story that I work on is centered on the Earth-like moon, but math was never my strongest suit and I'm in dire need of some mathematicians, astronomers or science enthusiasts.
I wanted the Earth-like moon to be exactly the same as our own Earth. Well, almost.
Basic Info:
* Year (one full orbit of the gas giant around the Sun) has 256 days.
* A day (1 full rotation around its own axis) of the Earth-like moon is 24 hours.
* One full orbit of the Earth-like moon around the Gas Giant = I wanted it to be precisely 8 days (192 hours)
My idea was to introduce 8th day in a week, one that people would call "Longnight" which would basically be a whole day without Sun due to the eclipse from the gas giant.
* Size of the gas giant and distance of the two bodies aren't specified. (Since I have very limited knowledge of the astrophysics. Feel free to adjust.) The eclipse (8th day) probably won't take as much as 24 hours, but I'll appreciate anything that can give at least a bit of "long-night, a day full of darkness" feel to it, even if it takes another, 9th day a week.
(Optional: It's a world full of magic and divine beings, so if the distances or other aspects don't correlate with the real physics, we can ignore some laws and say "It's magic. Gods are keeping the moon in orbit/atmosphere together." or something like that.)
I'm just really curious about the eclipse length and the ways it could be done possible. Thank you for all the ideas.
[Answer]
**For the TL;DR, see the bottom of this answer.**
Okay, so first of all, the orbital period of the gas giant around its star is $256 \times 24$ hours, and I'd like to establish the distance from the planet to its star. Since you haven't specified anything about the star itself, I'll go with our Sun for simplicity's sake. Also for simplicity's sake (or to retain everybody's sanity, including my own) I will approach this as two [two-body problems](https://en.wikipedia.org/wiki/Two-body_problem) rather than a [three-body problem](https://en.wikipedia.org/wiki/Three-body_problem). This reduces the attainable precision, but greatly simplifies the math. For a representative gas giant, I'll use Jupiter.
As an approximation for the planet's orbit around its star, we can use the formula for [a small body orbiting a central body](https://en.wikipedia.org/wiki/Orbital_period#Small_body_orbiting_a_central_body):
$$ r = \sqrt[3]{\frac{\mu T^2}{4 \pi ^2}} $$
where:
* $r$ is the orbit's [semi-major axis](https://en.wikipedia.org/wiki/Semi-major_and_semi-minor_axes) in meters (note: this is not the same thing as the orbital altitude, but can be approximated as the orbital *radius*)
* $\mu$ is the [standard gravitational parameter](https://en.wikipedia.org/wiki/Standard_gravitational_parameter), $\mu = GM$
+ $G$ is the [gravitational constant](https://en.wikipedia.org/wiki/Gravitational_constant), in units relevant here $ 6.67408 \times 10^{-11} ~\text{m}^3 \text{kg}^{-1} \text{s}^{-2} $
+ $M$ is the mass of the central body (in this case, the star) in kg
+ $\mu\_\text{Sun} \approx 1.327 \times 10^{20} ~\text{m}^3 ~\text{s}^{-2}$
* $T$ is the orbital period in seconds
We know that the desired $T = 256 \times 24 \times 60 \times 60 = 22\,118\,400$ seconds. Let's plug all those values in and see what comes out:
$$ r = \sqrt[3]{\frac{1.327 \times 10^{20} \times 22\,118\,400^2}{4 \pi ^2}} \approx \sqrt[3]{1.644442 \times 10^{33}} \approx 1.1803375 \times 10^{11} $$
So your planet orbits at a distance of about $1.2 \times 10^8$ km, or 120 million km, to its star. This is comparable to [Venus](https://en.wikipedia.org/wiki/Venus)' orbit around the Sun (Venus' semi-major axis is about $1.08 \times 10^8$ km, with an orbital period of $224.7 \times 24$ hours). That's awfully close for a gas giant in anything resembling our solar system, but it's the only way to get the planet orbital period you ask for while keeping the star Sun-like. You could twiddle the knob for star mass ($M = M\_\text{Sun}$, influencing $\mu\_\text{Sun}$ above) until you are happy with the outcome; for inspiration, look no further than to [Wikipedia's list of main sequence star example parameters](https://en.wikipedia.org/wiki/Main_sequence#Sample_parameters) which gives the stars' mass in terms of solar masses, from which you can calculate the corresponding value for $\mu$.
The [arc length of a circle sector](https://en.wikipedia.org/wiki/Circular_sector#Arc_length) is given by $ L = \theta \times r $ where $\theta$ is the angle subtended. We know the approximate arc length (the diameter of the Sun: twice its radius of $695\,700$ km) and distance ($1.2 \times 10^8$ km) and want angle subtended, so we get $$ 2 \times 695\,700~\text{km} = \theta \times 1.2 \times 10^8~\text{km} \Rightarrow \theta = \frac{2 \times 695\,700}{1.2 \times 10^8} = 0.011595 $$
Because $\theta$ comes out in radians, we multiply by [57.296°](https://en.wikipedia.org/wiki/Radian) to get the angle subtended in degrees, which turns out to be 39.86 arcminutes or 0.664 degrees. A quick check against [Wikipedia](https://en.wikipedia.org/wiki/Sun) gives the Sun's angle subtended from Earth (at an orbital radius of $1.5 \times 10^8$ km) as 31.6-32.7 arcminutes, so while possibly not perfect, this is well within the ballpark. The same calculation for an orbital radius of $1.5 \times 10^8$ km gives 31.9 arcminutes, squarely in the range given.
You specified the orbital period of the moon around the gas giant to be 192 hours, or $192 \times 3\,600 = 691\,200$ seconds. We can use the [vis-viva equation](https://en.wikipedia.org/wiki/Vis-viva_equation) to calculate the corresponding orbital radius. We have $$ v^2 = \mu \left( \frac{2}{r} - \frac{1}{a} \right) $$
For a circular orbit, $r = a$ (orbital radius is equal to the semi-major axis of the orbit) and thus $$ \left( \frac{2 \pi r}{T} \right)^2 = \mu \left( \frac{2}{r} - \frac{1}{r} \right) $$
We have $\mu\_\text{Jupiter} \approx 1.267 \times 10^{17} ~\text{m}^3 ~\text{s}^{-2}$ and $T = 691\,200 ~\text{s}$. By [rearranging](https://chat.stackexchange.com/transcript/message/35405462#35405462), we get $$ r = \sqrt[3]{\mu \left(\frac{T}{2\pi}\right)^2} \approx 1\,153\,080 ~\text{km} $$
So the Earth-like moon orbits the gas giant at an orbital radius of about 1.15 million km, because that's the orbital radius (for a perfectly circular orbit, one with [eccentricity](https://en.wikipedia.org/wiki/Orbital_eccentricity) $e = 0$ or semi-major axis equal to semi-minor axis) that corresponds with the desired orbital period. This happens to be very similar to the radius of [the orbit of Ganymede](https://en.wikipedia.org/wiki/Jupiter#Galilean_moons) (which is 1.07M km, and an [eccentricity of about 0.0013](https://en.wikipedia.org/wiki/Ganymede_(moon)#Orbit_and_rotation) in case you wondered), providing a nice sanity check for the result; Ganymede orbits Jupiter in 171 hours, only slightly less than your desired 192 hours, so at least to a first order approximation this checks out.
The formula for computing the [length of the umbra](https://en.wikipedia.org/wiki/Eclipse#Umbra.2C_penumbra_and_antumbra) (central shadow) of an eclipse is $$ L = \frac{r \times R\_o}{R\_s - R\_o} $$ where $r$ is the distance from the star to the occulting object (in our case, the gas giant), $R\_o$ is the radius of the occulting object, and $R\_s$ is the radius of the star. We thus have a shadow cone of length (where all distance and size values are in kilometers) $$ L = \frac{1.2 \times 10^8 \times 71\,492}{695\,700 - 71\,492} \approx \frac{8.58 \times 10^{12}}{624\,208} \approx 13.74 \times 10^6 $$
Because $ 1.15 \times 10^6 \lt 13.74 \times 10^6 $, the moon passes through the shadow cone cast by the planet, so we have a full eclipse (the moon passes through the umbra cast by the planet). Now, for how long does the eclipse last?
By considering the shadow cone to be a triangle with the base length of the diameter of the planet and the height calculated above, we can use Pythagoras' theorem to calculate the length of the resulting hypotenuse. (This turns out to be almost identical to the height, approximately $1.37400 \times 10^7$ versus the height approximately $1.37439 \times 10^7$ km.) We can then apply the [intercept theorem](https://en.wikipedia.org/wiki/Intercept_theorem) which states that when dividing a triangle by a line parallell to the base of the triangle, the length of the new base line is to the original base line as the hypotenuse of the part of the triangle is to the total hypotenuse length. By approximating the required inner height as the orbital radius of the moon around the gas giant, we end up with $$ \frac{DE}{2 \times 71\,492} = \frac{1\,150\,000}{13\,740\,000} \approx \frac{0.083697}{1} $$ where $DE$ is the length of the line connecting the edges of the triangle at the orbital radius of the moon. Hence the occluded path for the moon is approximately $ \frac{2 \times 71\,492}{0.083697} \approx 1.708 \times 10^6$ km. (This is really the base of a circle segment where the moon traces the circle segment, but the difference is small enough to be negligible at these levels of precision.)
The circumference of a circle of radius $1.15 \times 10^6$ km is $$ 2 \pi r = 2 \pi \times 1.15 \times 10^6 \approx 7.226 \times 10^6 ~\text{km} $$
Thus, passing through the umbra cast by the planet takes $ \frac{1.708 \times 10^6}{7.226 \times 10^6} \approx 0.2364 $ of the orbital period of the moon. Multiplying by the orbital period of 192 hours gives us a duration of 45.4 hours within the total eclipse zone (the umbra).
Note that there are three things I am actually ignoring in the calculations above. **First,** I'm positing that all bodies are orbiting within your solar system's [ecliptic](https://en.wikipedia.org/wiki/Ecliptic#Plane_of_the_Solar_System); if their orbits are [inclined](https://en.wikipedia.org/wiki/Orbital_inclination) relative to one another, you need to take the angle at which they are orbiting (the inclination) into account. Doing so complicates the math a fair bit for no significant gain, as bodies that form naturally within a solar system are likely to orbit close to the ecliptic. I'm leaving that entirely as an exercise for the reader.
**Second,** I'm ignoring the planet's orbital motion around the star. When the (Earth-like) moon is orbiting around the (gas giant) planet, and the (gas giant) planet is orbiting around the star, this is going to have the effect of either making the apparent eclipse slightly shorter or slightly longer. (Which it happens to become depends on the relative direction of the orbital movement.) I'm too lazy to account for this, so I just don't, but it shouldn't be more than some trigonometry if you really care to do that part of the math yourself.
**Third,** I'm ignoring the fact that the Earth-sized moon is going to tug a little at the planet. The barycenter of the system won't actually be at the planet's center, but a little outside of the planet's center, which will cause the two to be joined in somewhat of an orbital dance. This is very similar to how, in our solar system, [Jupiter perturbs the Sun](https://en.wikipedia.org/wiki/Jupiter#Interaction_with_the_Solar_System), despite being only $\frac{1}{1\,047}$ the mass, or how [Earth's moon perturbs Earth](https://en.wikipedia.org/wiki/Orbit_of_the_Moon#Properties).
# TL;DR:
One set of values that match your criteria are:
* Star mass $1.99 \times 10^{30}$ kg (1 solar mass) (by choice)
* Star diameter $1\,391\,400$ km (1 solar diameter) (by choice)
* Planet mass $1.8986 \times 10^{27}$ kg (1 Jupiter mass) (by choice)
* Planet diameter $142\,984$ km (1 Jupiter diameter) (by choice)
* Planet orbital period around star $256 \times 86\,400$ seconds (by decree)
* Planet orbital radius around star $1.2 \times 10^8$ km
* Moon orbital period around planet $192 \times 3\,600$ seconds (by decree)
* Moon orbital radius around planet $1.15 \times 10^6$ km
* Eclipse length $45.4 \times 3\,600$ seconds
There are many other sets of values that can match your criteria. If you aren't happy with the above, just pick different values for the masses and radii involved, and recompute; there is nothing magical about the sizes of Sun or Jupiter. Just don't forget to change the value of $\mu$ accordingly!
[Answer]
I'm scratching my head, but if I'm reading this right then the answer to your question is in the question. :)
As far as I can tell, there's only two possible answers.
First, the eclipse would last 24 hours. Since you outlined that the world has a 24 hour day and the eighth day is covered by the eclipse, the eclipse must last the entire day.
Or secondly, it will last 12 hours. Since the world does spin and one side of the planet would be nighttime anyways, the eclipse would only need to last for the daylight portion of the day and that side of the planet would still be in darkness for the entire 24 hours. The opposite side wouldn't have even known there was an eclipse this way though.
But in all honesty, since you can place the planet pretty much anywhere inside the gas giant's orbit and that you have plenty of wiggle room in the gas giant's size, there's nothing stopping the eclipse from being pretty much any amount of time your want it to be. If you want the eclipse to last longer then the planet is closer to the gas giant. If you want the eclipse to be shorter than the planet is farther away from the gas giant.
Although a good thing to keep in mind is that if you have a long eclipse then the gas giant will also be larger in your sky. The shorter the eclipse the smaller the gas giant is in your sky.
Hope I helped!
[Answer]
You need to take into account two effects, given that you fixed the size of the moon: the orbital speed and the apparent size of the moon.
A long lasting eclipse is granted by a slow orbiting moon, which is achieved by placing it far from the planet. But placing it far will also make it look smaller, so less able to shield the star.
Vice versa, if it is closer to planet it appears bigger, but also move faster in the sky, shortening the duration of the eclipse.
Since you don't mention how far is the planet from the star and how big the star is, you can also play with these two extra parameters.
[Answer]
Another problem: The eclipse time would change every day. The shadow of the gas giant will be in a different position as it goes around the star.
So you wouldn't get an "eclipse day" on such a regular schedule.
The only way I see it working as a fixed "every 8 days" would be if the gas giant was tidally locked to the star (is that even possible for a gas giant?) and the moon was close enough to the gas giant to be pulled along by the gas giant's rotation.
I think that to pull off those two conditions, the gas giant would have to be so close to the star and the moon so close to the planet that the moon would be very hot.
] |
[Question]
[
I request some help with the design of one particular denizen of [my fantasy world](https://worldbuilding.meta.stackexchange.com/a/3845/10851), tentatively named Boar Troll. It needs to be an ungulate or closely related creature with emerging sentience, and that's as far as I am right now. In fact, some of its requirements happened while drafting this question.
[](https://i.stack.imgur.com/XunAD.png)
I want to go from some member of the [mesonychia](http://evolutionwiki.org/wiki/Mesonychia) order about 25-30 MYA to the creature described below. What real though extinct species might have gotten started on this path? Where would this creature's evolution have split from the real world? What living species might it best resemble (i.e. ox, sheep, warthog, etc.)
These are the desired characteristics, though none of this is set in stone.
**Physical traits**
* Bi-pedal preferred, [knuckle-walking](https://en.wikipedia.org/wiki/Knuckle-walking) acceptable
* Prehensile hands
* Foot structure negotiable, but bonus points for hooves
* Tusks (or horns/antlers, or both, but tusks preferred)
* Carnivorous/ opportunistic diet (and the proper senses and dentition that go with it.)
* Muscular build, barrel chest
* Tail optional
* [Cathemeral](https://en.wikipedia.org/wiki/Cathemerality) (has activity periods and rest periods in both day and night)
* Lives in deciduous forest, savannah/ grassland, and/or wetland biomes
**Social Structure**
* Semi-nomadic hunter-gatherer tribes
* Engages in religious rituals
* Rudimentary language (i.e. can count none, one, some, many)
* Wears an animal hide loincloth and simple bone/stone jewelry
* Will raid farms for livestock and even the human farmers
* Makes and uses spear- and ax-like tools during hunts (or steals them from humans)
**Further Notes**
Please do not get too hung up on the name Boar Troll, nor either image. I needed a name and mental concept for rough drafts and this is what came to me. Answers here could influence the final name and appearance.
EDIT: New prototype sketch based on current answers, especially IndigoFenix:
[](https://i.stack.imgur.com/NTpCR.png)
(end EDIT)
Inspiration for the Boar Troll includes Tolkien's [orcs](https://en.wikipedia.org/wiki/Orc), Paolini's [ra'azak](http://inheritance.wikia.com/wiki/Ra'zac), and Sanderson's [koloss](http://mistborn.wikia.com/wiki/Koloss). However, I also want to *clearly differentiate* them from anyone else.
Boar Trolls may be mentioned tangentially in a handful of stories, but their central role will happen during a succession crisis where a corrupt cousin of the would-be rightful heir captures some and trains them under the whip. Blah blah blah minion horde blah blah reign of terror blah blah comeuppance.
*This question is a proud alumnus of [The Worldbuilding Sandbox](https://worldbuilding.meta.stackexchange.com/q/635/10851) and part of the [Anatomically Correct Series](https://worldbuilding.meta.stackexchange.com/questions/2797/anatomically-correct-series/).*
[Answer]
When it comes to the evolution of 'beastmen', I've often considered it much more realistic to start with a hominid and find a reason to give it animal features than to start from your base animal and find a reason for it to become both sapient and humanoid. When you get right down to it, a boar-troll is basically just a human with a piggish face and tusks - all you really need to do is adjust the morphology of a human face and you're golden.
That being said, despite being common in fantasy settings, evolving a humanoid with a pig's face is tricky no matter which kind of creature you want to start with. The flat snout and tusks that define a pig's face are mostly adapted for digging and rooting around in the soil, something that's hard to connect with a bipedal lifestyle. Tusks, at the very least, are useful for fighting, even so, most animals that have them use them primarily for digging, fighting being a secondary feature (fangs are more suitable for straight fighting).
One possibility is to have the creature use its tusks for breaking open trees in order to get at healthy insects underneath the bark. Perhaps they do this while climbing, so their hands are usually occupied.
Alternatively, maybe their ancestors hunted pigs, so those who could blend in easier were more successful hunters. If a boar-person is hiding in the brush and sticks his head out to get a closer look at his quarry, the pig might not realize it isn't another pig until his whole body emerges, giving him a head start.
The best answer, though, is probably the old evolutionary handwave of sexual selection. If the ancestral boarfolk women find men with big tusks and piggy snouts attractive for whatever reason, over time the species will grow more piggish. This works well with the typical subversion of beauty standards trope, as boar-folk will likely still find the same features attractive and will consider humans ugly.
EDIT:
Since you're insistent on it evolving from a non-hominid, let me direct your attention to [Chalicotherium](https://en.wikipedia.org/wiki/Chalicothere), or as I'd like to nickname it, "Gorilla Horse". It was a large browser that fed by rearing up on its hind legs and using its modified hands to pull itself up onto tree trunks and pull leaves down. Although it was a member of the odd-toed ungulates (and likely started with a longer neck that could reasonably eat low branches already), it is possible that a pig relative could evolve into something similar if it started by placing its hooves against trees and scraping off bark with its tusks to get at insects, as mentioned above. Chalicotherium probably didn't use its front legs for digging (some scientists thought it might but its teeth don't show signs of eating dirt-covered foods), but a pig version of it might be an opportunist that could both dig up roots and feed on bark, insects, and branches. From that point, it could develop tool use, intelligence, a hunting lifestyle, and full bipedalism the same way humans did. (Hey, pigs are already pretty smart, so you've got a head-start.)
The question concerning why it would retain a pig's snout and tusks after it stopped using its face as a digging implement still applies, but the reasoning used with hominids still works.
[Answer]
To answer your question, I will go through the requirements step by step.
1. **Bipedalism**, having a bipedal ungulate is not an easy task, but in [a previous answer of mine](https://worldbuilding.stackexchange.com/a/46164/25325) I detailed how such a leg structure would be stable.
2. **Prehensile hands**, this can be explained in many different ways, depending on how prehensile you want them to be. For the full human level, they will need to evolve as arboreal animals.
3. **Hooves**, In the same answer as bipedalism, I also used hoove based feet.
4. **Tusks**, this ties into point 5, a mainly scavenging carnivore would continue to benefit from tusks and therefore not Lowe them.
5. **Carnivorous**, this does not need much explaining, crows and border collies are very smart and are mainly carnivorous.
6. **Broad chest**, if they evolved for running as well as an arboreal lifestyle, (similar to Anatomically correct gnolls\*\*) then they will likely have a broad chest, but at the cost of speed.
7. **Tail**, if they become aggressive carnivores, then they will we this tails for balance when running, similar to a cheetah.
8. **Cathemeral**, just have their metabolism so fast they have to be sporatically hunting.
9. **Biome**, a creature like this will probably evolve into a Savannah environment near a jungle.
Everything else is culture related and does not need to be justified.
] |
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