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[Question]
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I'm in the process of designing a creature loosely resembling a theropod dinosaur that sports a number of horns/tusks on its head and face, and I'm wondering if anyone can help me evaluate its feasibility. I'm not terribly concerned with the practicality/ functionality of the horns/ tusks themselves or their arrangement. They're strictly ornamental and probably stupid from an evolutionary perspective, but I'm pretty resigned to that fact.
[](https://i.stack.imgur.com/J6YMG.jpg)
What I am concerned with is whether or not they might compromise the creature's ability to lift/ hold up its own head (is the neck thick and muscular enough?) or balance. (Would a longer tail or a tail with a source of extra weight at the end help any?) Are there any compromises I might be able make if they do prove unfeasible in these regards? I've come up with tentative estimates of the horns'/ tusks' weights based on what info I've been able to garner about deer antlers and black rhino horns. I'm estimating the two large horns at 2-3 pounds each, the vertical horn jutting up between these two at 1.5-2 pounds, the snout and chin horns at 0.75 to 1 pounds each, and the tusks (which are made of the same material as the horns) at 1.5 to 2 pounds each.
Here is an updated version of the creature design featuring a thoracic hump as per one of the suggestions I've received.
[](https://i.stack.imgur.com/0ddNz.jpg)
[Answer]
**Your creature is fine**, there are theropods with crests and other crap on their head, and your theropod is short necked and stocky so ballance should be fine. Air sacs make the front of the animal a lot lighter than it looks. Also you should straighten that top line on the hips (it should not curve down much), otherwise you are cutting away about half the muscle mass of the hind legs.
**Your rider however is all wrong**.
If you look at ostrich riders they need to be seated directly over where the feet touch the ground in a standing position. More importantly the rider needs to stay upright not lean forward. If anything they may want to lean back and swing their legs forward. Posture wise it is more like sitting on a motorcycle than a horse, this is becasue a theropod is going to be a lot wider than a horse. So you should mover your rider back over the hips in a more seated position.
Alternatively they could sit behind the hips and lay forward, but they will have to stay in that position.
Now yes an ostrich is smaller than your theropod but the balance issue is the same.
[](https://i.stack.imgur.com/Yo1WE.jpg)
[](https://i.stack.imgur.com/AxUzg.jpg)
here is an allosaurus for body comparison. I also recommend <http://www.skeletaldrawing.com/>
[](https://i.stack.imgur.com/gzAwY.gif)
[Answer]
To be frank, I'm not so worried about the horns on your creature; the rider on the back is a far bigger problem.
The real issue you have with this creature is centre of gravity. The legs are too far back to balance the creature correctly, unless it has a very heavy tail. Most of the body (where the bulk of the weight will be) sits forward of the legs, as does the rider. This creature looks to me like he'll tip forward constantly.
The smaller front 'paws' are about right, as is the hip placement, but I'm thinking the best way to solve this is to give it a longer, stronger hamstring / quadriceps configuration in the first joint of the leg, that largely brings the leg forward, then have the calf go straight down from there so that the foot (which probably needs to be larger) is sitting close to the centre of the body (the head and tail would then counterbalance each other). This means that the calf of the leg could come down at (say) 40% distance between hips and shoulders, then the foot could be (say) 20% of the same length. That should make it far more likely that such a creature could support a rider, who'd be sitting on the back roughly above the foot.
That said, I'd strongly consider making your dinosaur stand more upright if supporting a rider, as the configuration I'm describing above would put a lot of stress on the leg and foot bones because there's a lot of off axis joints that would leave the animal's most powerful leg muscles working more as shock absorbers than power transfer conduits.
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I suggest the rider would be better placed directly over the animal’s hind legs or perhaps just slightly in front of them. When the animal is walking or stationary it would have its head and upper body raised and its tail lowered so the rider will be on a slope and much closer to the animal’s body (any saddle or stirrup’s used need to accommodate this).
When the animal runs it would lower its head and raise its tail as a counter balance. At this point the rider probably needs to be more upright and over the hind legs to avoid unbalancing the creature. Another option would be riding as a horse jockey does, with the legs well up to avoid getting in the way of the animal’s leg movement.
If you want the rider to be a little further forward, it would always be possible to counter balance that by adding a little weight behind the rear legs, sword, shield, extended saddle packs etc, but obviously don’t overdo it. A larger animal would make the whole thing easier, provided it was trained not to eat the rider ;o)
Another option on a bigger animal would be two riders - one forward and one aft of the rear legs.
[](https://i.stack.imgur.com/WdrxC.jpg)
(<https://phys.org/news/2017-07-tyrannosaurus-rex-couldnt.html>)
I think the rider needs to sit between where the animals feet are...
[Answer]
If the head is heavy, your creature would likely need big neck muscles and corresponding spinal processes on its backbone to support the weight. It isn't so much the actual carrying around of the head/horns which is the problem - it is the muscle power needed to raise and lower the head when the creature wants to eat something on the ground, or have a drink of water.
The hump of a bison is a good example of an animal with this muscle mass and enlarged spinal processes on the thoracic vertebrae.
Here is a modern bison, showing the skeleton inside the hump:
[](https://i.stack.imgur.com/adTuP.jpg)
And this is a prehistoric bison, with enormous horns:
[](https://i.stack.imgur.com/hqn2J.jpg)
All this weight at the front (head, neck muscles, thoracic hump) will indeed need some sort of counterweight. Probably in the hip region or the root of the tail, rather than by giving the creature an ankylosaurus-style tail club. Massive great leg bones and muscular legs would be a start - and would also make it a more powerful runner or kicker. If you don't mind it having a slightly waddling run - so it gallops like a crocodile, rather than like an ostrich - then the tail muscles would be providing energy for walking/running, and you could justify a thick heavy base to the tail.
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Assume that Amazon has set up a processing station on the Moon for whatever motive as a way to ship things out to space (Mars, etc.) faster and more efficiently.
How much time today and perhaps in the near future would it take for shipments to be delivered from Earth to the station on the Moon?
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Note - I'm excluding all processing time taken by the company, because that all depends.
According to [this somewhat reputable source](http://www.space.com/18145-how-far-is-the-moon.html), the Apollo missions took **three days** - including landing, which is relevant. However, New Horizons - which did not land - took about **eight hours.** Considering that the second option was headed out to Pluto - with extreme speed in mind - and that going too slow means the competition wins - a reasonable guess would be **between one and two days**, depending on the size of the package and the urgency with which it needed to be shipped.
# [That's fast enough for Amazon Prime.](https://rads.stackoverflow.com/amzn/click/com/B00DBYBNEE)
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**Alternatively,** you could use [a somewhat modern idea](http://news.nationalgeographic.com/2017/02/closest-earth-planet-proxima-b-centauri-solar-sail-space-science/) for a near-future delivery system. Designed to propel spacecraft out of the solar system to our neighbor [Proxima Centauri](https://en.wikipedia.org/wiki/Proxima_Centauri), a giant laser could push packages at around **20%** the speed of light.
Completely ignoring time required to load the "cannon", power it up, and unload - and completely ignoring cost or *general common sense*:
It takes **2** seconds for light to travel between the Earth and the moon.
Going **1/5** that speed takes **5/1** times as long.
You could potentially make the trip in **10 seconds**.
# [That's *also* fast enough for Amazon Prime.](https://rads.stackoverflow.com/amzn/click/com/B00DBYBNEE)
[Answer]
**In the near future, how often do flights depart to Luna?**
Right now we don't have an active Luna program. Back when there was one, the answer was "about once per year." I think it is a safe assumption that the parcel will travel on a regular scheduled flight.
If those depart once per week, there is a delay of 0-6 days from scheduling.
**How long to package the cargo?**
Right now things which go to space are checked in different ways for safety, designed for low weight, carefully stowed, etc. That takes weeks or months.
By the time we're talking about an Amazon delivery, obviously shipping stuff to space has become more routine. How much more routine? Can I order a can of beer? A lawnmover? Let's say packing the crate takes a day.
**Transfer in orbit?**
The Apollo missions launched the complete package from the Earth surface and discharged expensive vehicles at each step. A "mature" system would use a reusable shuttle to a transfer station in Earth orbit, a reusable vehicle from there to another transfer station in Luna orbit, and finally a reusable lander to the surface.
If the same flights carry cargo and passengers, the delays won't be too long. If only cargo is carried, it might sit in the transfer stations for a couple of days each.
**The pure flight time is the smallest problem.**
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The Apollo missions took a direct transit route which allows for short travel times (important with astronauts aboard), but is relatively expensive in terms of fuel requirements. Some Lunar probe missions take longer, more efficient routes, which can take months to complete.
For example, the [LADEE mission](https://en.wikipedia.org/wiki/Lunar_Atmosphere_and_Dust_Environment_Explorer) took a month to complete its trip, which involved three highly-elliptical Earth orbits before finally transiting into Lunar orbit. The [GRAIL probes](https://en.wikipedia.org/wiki/Gravity_Recovery_and_Interior_Laboratory#Transit_phase) took an even longer flight path. Their roundabout, low-energy route swung almost all the way out to the Earth-Sol L-1 point and took over three months to complete.
So, Space-Amazon could charge more for "Space Prime" two-day shipping, but its regular "when-it-gets-there" shipping option might take months!
Having said all that, if your end goal is to deliver from Earth out to further destinations (Mars, asteroids, etc.), you don't want to go all the way down to the Moon's surface if you can avoid it. You'd need to spend a lot of fuel getting down to the surface in one piece, and then a similar amount to get back up into orbit. Ideally, you'd want to have your transit hub in Earth's orbit, so that you only have to launch your package up out of a gravity well once. To borrow a line from Heinlein, "Once you get to Earth orbit, you're halfway to anywhere in the solar system."
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[Solar Sails](https://en.wikipedia.org/wiki/Solar_sail) are a great, low-impact way of driving your spacecraft. Whilst [wind turbines](https://en.wikipedia.org/wiki/Wind_turbine) are a low impact way of collecting power from the wind, however, they only work when the wind is blowing.
My thought is, the solar wind is always blowing in one way. Would it be feasible to use `Solar Sail Wind Turbines`,
* How big would they need to be?
* What speed would they spin at?
* How much power would they generate?
* Would they be blown out of their orbits?
[Answer]
# No, they are not feasible
There is one way you could possibly do it, and that is to have counter-rotating turbines that provide counter-torque to each other. You can then orbit this satellite at a speed that is slightly too slow for the orbit altitude, and the force of the solar wind will provide the "missing" part of the centrifugal force.
**However...**
[According to Wikipedia](https://en.wikipedia.org/wiki/Solar_sail), the radiation force on a solar sail that is...
1. 800 meters by 800 meters in size
2. in a co-orbit with the Earth around the Sun
...is approximately 5 Newton, which is about 1 lb of force. Even if you could convert this from a normal force to one that acts radially instead, it would be a next to infinitesimally small force compared to the photoelectric energy that is hitting the turbine.
That same solar sail of 800 meters by 800 meters would be receiving $800m \cdot 800m \cdot 1400 {W}/{m^2}$, which is approximately 900 MW... which is **the power of a decently sized nuclear reactor**.
In short: it is extremely doubtful that the radiation pressure of the solar wind could even overcome the friction forces of this counter-rotating turbine. And just making it into a static solar panel is many magnitudes more efficient.
But it would make for one heck of an impressive space novelty toy...
[](https://i.stack.imgur.com/go2sD.jpg)
*Picture two of these, stacked on top of each other, about 1 km wide, **in space***. :D
[Answer]
# Yes, it is possible
* But it is not what sane solution should be
## How big would they need to be?
* Depends on how much energy you wish to have, but bigger than solar panels.
## What speed would they spin at?
* Limit are defined by strength of material you have build it from and size of construction. To be efficient, fast. IDK more.
## How much power would they generate?
* Depends on how big they are, but less than solar cells and other solutions.
Also depends on mass of construction, how close to star they are, how deep they are in gravity well(deeper they are, better and more efficient per kg they work)
## Would they be blown out of their orbits?
* Whole point of such system is based on the fact that they do not have natural orbit, and they hover using force of solar wind near star, which counteracts attraction from star, which(attraction) allows to actually generate energy.
They are called [Statite](https://en.wikipedia.org/wiki/Statite), I'm not very familiar with them, but you may probably even find something similar to your idea. It is perfectly valid idea, it is just not mass efficient and have lots of other problems, and only positive thing I may say about it, is that it is perfectly capable to work.
## As note
That fact that solar wind blows in one direction(from star), does not mean Solar Sail Wind Turbines should rotate in one direction, and direction can be regulated by angle of blades. And system of 2 such Propellers is perfectly capable to keep momentum. Theoretically you even do not have to have 2 propellers for this system to work, just change rotation periodically, and use massive core (I fail to describe it in English, so just use 2 Propellers it is simpler to describe).
### As note2, efficiency
Efficiency depend on speed of rotating blades. Faster this thing rotates, more energy it will generate, more efficient it will be. Work is equal force multiplied by distance, Power is equal force multiplied by velocity.
If we take same sail 800x800m as in Michael Karnerfors answer and same force 5N, then to get 900MW with this "blade" it have to have velocity 180'000'000m/s it is almost 2/3 of speed of light. Centrifugal force in this situation will be a problem, would be construction bigger(light years big), this would be less a problem. But "blade" not necessary have to be thin foil, it can be a plasma, and with magnetic field this plasma can be contained at this velocity, in similar size construction(km sizes or less). Although with small size(km's) and not dense plasma we will have other issues(plasma will be to transparent, so we should have ticker layer of that plasma, or something like that)
It still can have exterior of big Solar Sail Fan, where blades used to change angle of light on which it hits the plasma rotor. Faster it(plasma fan) will rotate, bigger red shift of reflected light will be.
But eventually it will be just particle accelerator, which uses light to accelerate particles(plasma) inside it.
So as simple construction SolarSailTurbine may be not the most efficient solution, but more sophisticated design may improve situation.
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The answer is no.
The reason is that a turbine works by spinning something around a non-moving, anchored hub. The power is generated by the speed difference. The spinning causes a wire coil to break the magnetic lines of a magnet; which induces an electric current. The process of drawing power from the spin induces drag on the hub. The only reason the hub doesn't start spinning is because it is anchored.
In space, the hub has nothing to keep it from spinning. Even on a large ship, the ship would eventually start to spin with the solar turbine unless you used the power that you generate to keep the ship from spinning. That would be counter productive.
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There is a alien species known as the Titanians.
The Titanians are organic biologically, but of a alien biochemistry much more cryophilic and oily. They drink ethane, breathe oxygen (you can have oxygen in a environment like Titan- Oxygen doesn't condense too much at those temperatures) and eat other Titanian fauna. The Titanians bleed a reddish, oily substance, as they drink hydrocarbons and I figure the reddishness may come from tholins.
The Titanians generally enjoy a temperature of around 90-140 Kelvin.
Chemically they're made from Nitrogen, Carbon, Ethane, Sulfur, Hydrogen, Acetylene and have plastic bones. Much like with us they have bones that are harder to break than the 'meat'. Overall their biochemistry is very oily.
One of them is to exposed to the sun of a Cuban beach without protection.
This Titanian has no unique properties, it's human sized and has no special resistances. It's an average Titanian.
What happen to this poor Titanian if it was:
1. Splashed with water
2. Exposed to the heat
3. Touched by a human or stabbed by one (in the latter case- do they bleed or does their blood boil away?)
As a bonus question, would there be a difference if the Titanian was radiation resistant or would the results be the same?
I ask since I am not really certain how to predict any of this.
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Sadly, the answer is horribly. Assuming the Cuban beach is warm and not too hot, say, 30 degrees Celsius (C). The temperature difference is 209 C, between Earth and Titan. Titan has a temperature of minus 179 C. A splash of water will burn. If water is rock hard on Titan, liquid water may be more like a splash of lava.
The Titanian will collapse under Earth's gravity as it is roughly 5.4 times stronger than on Titan.
The Titanian will be suffering from decompression. The atmosphere of Titan is 1.6 bar (where Earth's atmosphere has a pressure of 1 bar at sea level). This isn't serious decompression, but it won't do your average Titanian any good.
Contact or being touched by human will burn. Stab wounds will be effectively like being stabbed with a red hot blade.
Will their blood boil? Quite likely due to a combination of high temperature and low pressure (in Titanian terms). Unpleasantly if Titanian blood is rich in hydrocarbons it might burn too.
Radiant sunlight would be a searing blast of energy. Titanian flesh would rapidly heat and undergo breakdown.
Considering Titanian visitors to Earth will be wearing environment suits and mechanized support structures to facilitate mobility, exposing one to the conditions of a Cuban beach would have to be a deliberate act.
Titanians be warned. The planet Earth is a Hell planet of high temperature, high gravity, low pressure, burning with high levels of deadly solar radiation, a surface too hot to stand upon without serious injury, and with oceans of molten lava. Its beaches are portals to sudden agonizing death and a quick trip to the afterlife.
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They are much like living (alt least for a few seconds) bio-fuels (probably bio-diesel) from outer space...
They can easly catch fire because of volatile flammable organic compounds.
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Well, the title is the question. I searched for a similar question but only found one asking about sand deserts and swamps together, so I think this is not duplicated.
I have a strange mind and almost all the time I'm living in alternate worlds and histories that I create myself in the moment. In one of them, my world has an ice desert and a sand desert next to each other... Is this possible?
**Edit: I need the sand desert to be hot, as requested in a comment.**
Assuming there is magic in my world but people in that continent are not aware of that, but trying to be as realistic as possible.
I will be probably posting more question of all my alternate worlds and histories for other opinions, and probably write them down. Thanks for your help
PS: I don't know at all which tags should I use for this, as is my first question here but I've been following some posts here for a while. Re-tag someone if need to.
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Assuming you want a hot desert and a cold desert, then they could be next to each other with an elevation change.
You have a high, cold desert where arctic winds blow constantly, a cliff with several thousand feet of sheer drop where some ancient cataclysm caused the land to shift, and at the bottom a hot desert where the cliff keeps the cold wind away.
Elevation and air pressure can make a lot of difference with temperature. I've been to the area around the Dead Sea, where it was around 60f in Jerusalem which has an elevation of 2,582 feet, and then traveling to the Dead Sea which has an elevation of -1,401 feet, and the temperature was over 100f.
Other geographic factors could exaggerate this effect.
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A sandy desert in a cold region actually [exists on earth](https://en.wikipedia.org/wiki/Chara_Sands). I'm no geologist, but given right landmass, mountain, and air currents configuration it looks like it can be moved to the north and/or made bigger.
Here are some [more pictures](http://lifeglobe.net/entry/2283), though the text is all in Russian.
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Dessert are actually related to the [total amount of precipitation](https://en.wikipedia.org/wiki/Desert#Classification) over the year. our polar regions have [polar deserts](https://en.wikipedia.org/wiki/Polar_desert) where actual precipitation is very small, it just doesn't melt away. So sand/ice deserts are going to be at an edge where a sandy area connects to a polar region. So the ice lasts from year to year and what little falls in the sand desert melts during the 'summer' months.
Now if you mean can there be a 'Hot' desert next to ice, that would be much more of an elevation situation. mountain glaciers near a desert
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This depends if they're 'right' next to each other. I would assume a day's walk is okay, which Wikipedia informs me is about 40 kilometers. On a tidally locked planet, there's a large ice side and desert side. But that's too large. Good thing we can lower the mass, while lowering diameter, to have the same gravity. Not sure about the exact measurements, and you could have a mountain range blocking light from getting to a specific area, which could just be cold enough for snow and ice to exist at all times.
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I think it could exist without too much of a handwave:
You need some really major mountains, stuff that towers way above Everest. (Which is either a low-g world or a handwave.) The air pressure above them is so low that it seriously limits winds going over them, the winds are channeled by them instead. You have multiple chains of mountains, they run east-west. (Cause: A major subduction event from plates meeting in a north-south direction.)
The layout of the mountains directs warm wind towards the poles, other mountains direct cold winds away from the poles. Your ice/sand desert exists where these two winds are once again moving east/west and parallel to each other. Eventually the temperatures equalize but you'll have a zone where you have substantially different temperatures right next to each other.
While you will find no place on Earth where air behaves like this you can find examples of it in water--places where water from a hot spring join an ordinary stream. Earlier this year I even saw a spot where water of two different colors was flowing down the same streambed. (Go farther downstream and it's all mixed.)
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**What would a medieval society without access to metal look like? How would things like wagons, weapons, coinage, and tools be different?**
"Medieval" in this sense would mean something like feudal Japan, medieval Europe, or the Muslim/Arab nations during the Crusades period. Technology is different without metal, but they understand the basics of medicine (like disease) but not concepts like bacteria or genetics, they have roads, the wheel, tamed animals, boats capable of at least limited ocean voyages, farming, semi-accurate cartography, books written by hand on paper or paper-like materials, some form of carpentry or stone work that enables fortifications like castles, etc.
Other Conditions:
* Metal still exists in the world (and in plants/animals/people). It just isn't used by this society for anything
* No fantasy creatures like dragons or dwarves. Only real animals and plants
* Topography, geography, and climate can be anything found on Earth
* Magic exists, but I'm looking at how things would be without magic. Explaining the magic system would be unnecessarily involved for this question. I can take your ideas and add magic to it
([Related: Warfare without Metal](https://worldbuilding.stackexchange.com/questions/11042/warfare-without-metal))
[Answer]
# Substitutes
You can make this work with substitutes. Armor can be made of items other than metal. For instance, [Cuir Bouilli](https://en.wikipedia.org/wiki/Boiled_leather), which is speculated to be the [origin of cuirasses](https://www.youtube.com/watch?v=lxkb-a0f9Wc), is boiled leather. It gives a "plastic-like" leather armor, which can be an effective defense. Padded armor was popular throughout the medieval period as well, especially for archers, as it retains mobility and is a cheaper alternative to other armors.
[Obsidian](https://en.wikipedia.org/wiki/Obsidian#Historical_use) have been used since time immemorial, at least before written records. This stone is used for knives, arrow heads, and other items. Obsidian is even used by modern surgeons, as the blade can be much more even (and therefore better at cutting) than metal blades. Durability is an issue with obsidian. [Stone tools](https://en.wikipedia.org/wiki/Stone_tool) of other types are well documented, and can be used for many things.
[Coinage and economy](https://en.wikipedia.org/wiki/Monetary_system) would be a little different. Metal coins were used because metal was valuable, and therefore the money had intrinsic value. In the absence of metal coins, other valuables could be traded. The natives of Aruba used round stones for their coinage. (I know this from their museum!) There are also other economies which do not rely on cash. They could use one of those systems. (My personal favorite are [gift-economies](https://www.youtube.com/watch?v=EaxjxICgahc)!)
Wagons can be made almost entirely of wood. In the place of nails, you can use wooden pegs. Old furniture (antiques) can often be found with wooden pegs instead of nails. Joints can be made with rope lashings, or slots in the wood. No metal can be worked around. The fact that wood warps when wet can cause lots of problems. Wagon wheels would need to be sealed or treated often in order to avoid cracking and warping.
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Well there are plenty of societies without metal out there, or at least traditionally had none. The Inuit, the Aborigine, many tribes in Borneo and South America.
One of the things about metal is that it is stronger than wood and is more shapable than stone, not as brittle as bone etc. So without metal you are left to make tools out of the other three options.
So bows are not going to change much, the metal arrow heads are more important to pierce heavy armor, but now they are limited to boiled leather, which while still tough doesn't need as much of a punch as steel, unless you have it in layers.
instead of swords, you will have clubs/maces. Lances/pikes can still have sharpened points or stone heads.
Bones make good weapons too.
Wood, Stone and bones all can make a multitude of tools, often one can be made that we normally see in metal, but will many times have a different weakness. It's hard to make wood sharp, but it can have great points and it works well as a frame. Bones are harder and stronger than wood, can be made sharp but don't hold an edge well and are difficult to sharpen. Stone is heavy, and easy to find. Practice can be used to make many different kinds of tools. Using sharp stones to shape the other materials.
So Many tools might never be made because the effort put into them might not be worth the value one gets out of them. A stone sword it fairly pointless, since one good swing at another stone sword, and both will shatter to nothing and weeks/months of effort gone. Why build a two story house when you will need to cut and shape much larger trees by hand, when you can just make another building nearby?
Economy? I suspect it will be primarily trade/barter. However, anything that is agreed upon can be used as currency. [Sea Shells](https://en.wikipedia.org/wiki/Shell_money) have been used in the past, and so have rocks. I also suspect precious gems could work well too.
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In reality the same but everything would take longer and cost more (in terms of absolute calorific cost, prices would be the same because it would all be relatively the same). For example a wagon is wagon shaped because it works, the tools are different but the products are going to be very similar, there are certain pieces of technology that are now "top end" that weren't, the double bow spring for suspension since leafsprings are out, bricks and mortar over steel frame, that kind of thing, but most of that only comes late in, or after the time period you're interested in emulating. In terms of weapons and armour I'd look to the Aztec and Maya as a guide to the science of the possible in that arena. Coinage isn't a necessity of the time period you want to emulate but it helps, shells, beads, letters of credit in a sufficiently sophisticated society all work, so does a grain standard for setting prices against.
But I'm not actually sure you can get to the population densities you need for a Medieval/Renaissance society and technological base without metal, one of the biggest things about the Iron Age was the fact that humans started to be able to cultivate land that was previously inaccessible. Not a little bit of land, tens of thousands of square miles of land previously under impenetrable old-growth forest went under the plow in Europe and Asia. It changed the coastlines of whole continents, without those farms producing a surplus urbanisation would never have gotten started, specialisation and division of labour couldn't have progressed to any great degree because everyone would still be scrambling to eek out a living on the little pockets of good plow land around the edges. Unless you can break ground on the same kind of land another way, or have some super abundance of good farm land that the trees don't like you're a bit stuck.
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Fairly common in sci-fi literature is the scenario where the Earth is destroyed by an all out nuclear war. Typically, the protagonist has survived by remaining in underground shelters for decades until finally emerging when the radiation is gone.
But given the nature of the world's nuclear arsenals (mostly H-bombs) and the fact that it makes the most sense to detonate the bombs in the air rather than at ground level, is the above even a semi-realistic scenario considering that Hiroshima and Nagasaki are inhabitable today?
In other words: If all major cities in the world were hit, how long would it take for the radiation to present little danger to human health?
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It depends on where you are and what you consider an acceptable level of risk.
If you're worried about an elevated risk of cancer, you'll need to stay in the shelter for about 300 years. The long-lived isotopes [Strontium-90](https://en.wikipedia.org/wiki/Strontium-90) and [Caesium-137](https://en.wikipedia.org/wiki/Caesium-137) (the two with half-lives long enough to stick around for a while, but short enough to produce high levels of radiation) have half-lives of around 30 years, and ten half-lives is a good rule of thumb for when an isotope has decayed far enough to no longer present a risk. You'll need to provide a 300-year stock of food if you plan to do this: both isotopes bioaccumulate, so food from outside your shelter will have a higher risk than the general environment.
If you're in an area with heavy fallout (50-100 km downwind of a target) and you're only worried about radiation poisoning, the Swiss civil defense organization estimates that [three weeks](https://en.wikipedia.org/wiki/Fallout_shelter#Use) will see enough of the radiation decay that you can safely leave the shelter for extended periods.
If you're in the middle of nowhere (say, the Canadian Arctic), you've got nothing to worry about. Almost all the fallout will leave the atmosphere before reaching you, so sit back and enjoy the fireworks.
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You might enjoy a free pdf of Nuclear War Survival Skills by Cresson H. Kearny at www.nuclearwarsurvivalskills.com among a dozen other sites. He anticipates a rapid return, rather than waiting decades.
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I hope this is more focused D:
**Setup**; Hela is a exoplanet in the fictional Eurydice system, about 4 Ly from Earth. The exoplanet is significantly younger than Earth, and life on her is in a late carboniferous stage of development. Due to the star being larger than the sun and the exoplanets atmospheric composition, the average temperature is at ~30 C, and sea level pressure 40% higher than on Earth. EDIT; The Atmospheric composition contains a lot of Co2 and volcanic gases (and what they react to with water vapor) making it so Humans cannot breath it. In some places, the co2 concentration gets high enough that "death pits" develop, where if you breathed the air you would be dead before hitting the ground. A full face respirator is really all it takes to walk outside though.
Leavenworth is the main base for Humans on Hela. The complex is designed to facilitate the export of a valuable resource. Its basically a refinery. Roughly 4000 people live and work there. They live in a small town, *Little Summer*, which is inside a "Dome" Habitat.
[](https://i.stack.imgur.com/VW56f.jpg)
Little Summer is where the big "You are Here" arrow points, the soft edged rectangles show the outline of the Hab Dome. The structure is nothing more than several *strong* and light transparent polymer sheets. This roof covers Little Summer and is held afloat by slight positive interior pressure. Anker cables hold it all in place. At least for now the roof is ~200 meters tall in the middle strip. The entire structure is roughly 3000x1800 meters.
The goal of the Hab Dome, and Little Summer, is to be as Earth like as possible. They got trees, normal Houses, wide open spaces, the whole 9 yards. The inside temperature is ~10 degrees colder than the outside.
**Question**; Given all of the above, a problem develops. This is a greenhouse. I might be overestimating this problem, but from what i see it seems this habitat would have serious heat problems as the interior air cant get out. The entire thing is isolated from the outside, as it has to be. This is made worse by the higher W/m² of solar energy on Hela and temperatures. I dont think using big fans on the inside would cut it either.
The question is, given this situation how could i realistically deal with the issue of the hab dome becoming a sauna ?
**Solution ?**; I gave this a solid think before asking here. My solution would look a bit like this;
[](https://i.stack.imgur.com/Dstpz.jpg)
There are already at least 2 layers to the roof, so i figure maybe they can move cold air quickly through this "interlayer" to pick up heat from the in- and outside. Thermodynamically, i think this works because the interlayer is much colder than both the outside and inside. It will absorb most heat which can then be dumped into water. This could potentially also be a sort of "active support" mechanism for the roof as a whole.
However, i am not sure this is a, let alone, the best solution to this problem. One issue i can see is the cold air having to be at a higher pressure than the outside, which given its high speed, might put to much weight on the roof, which is only held up by pressure.
**Conclusion**; Scale wise, i am aiming for "Hard" Sci Fi. I didnt put it in the tags because thats nerd stuff and this is a fairly minor element. I just want to make sure whatever solution i present is functional. For story purposes, or at least visuals, this might also be interesting. It rains a lot on Hela and depending on what the solution is there might be visible side effects. Which is always nice to write about.
I hope i explained the issue and, potential, solution in enough detail without making another question which needs a book to be answered.
Thanks for reading !
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>
> The structure is nothing more than several strong and light transparent polymer sheets.
>
>
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If you don't want a greenhouse, reduce the transparency. Cut down on the amount of light coming in, and the amount of in-dome heating will go down. If you had fancy future material tech, you could have variable opacity or reflectivity, to keep the sun out during the day, but keep things dark and enhance radiative cooling at night.
If you want the inside of the dome to be cooler than the outside, you're going to need some insulation in order to avoid your A/C bills becoming apocalyptic. Instead of having a plain dome shell, go for something a little more like bubblewrap. For a real world example, consider the [Eden Project](https://en.wikipedia.org/wiki/Eden_Project):
[](https://i.stack.imgur.com/dt8AI.jpg)
(image credit: [A1personage/wikimedia](https://commons.wikimedia.org/wiki/File:Eden_project.JPG))
The Eden domes are held up by a space frame underneath, rather than air pressure, but the basic principle is the same. One of the internal volumes is held at a higher temperature and humidity than the outside to let rainforest flora thrive, and the cells in the dome structure help reduce heat loss.
I would suggest *not* following the advice of Monty Wild when it comes to using water mist for cooling, however. It is quite an effective and economical approach, however on the scale of something as large as your domes the risk is that the humidity of the air inside the habitat rises to the point where it make cooling of people *more* difficult (due to a reduction in the efficiency of sweating) and increases problems like mold and fungus growth that represent sources of damage to infrastructure, reduction of output in agriculture and health risks for humans and other animals living in the dome.
The dome air should be kept clean and relatively dry. Cooling via water mists and [swamp coolers](https://en.wikipedia.org/wiki/Evaporative_cooler) and the like could be done inside buildings, but probably doesn't belong in the dome itself.
A potentially good source of cooling would be geothermal, depending on what the local [geothermal gradient](https://en.wikipedia.org/wiki/Geothermal_gradient) looks like. If the ground deep enough beneath the surface of your habitat is cool, you can use it as a heatsink... circulating cooling fluid from the hot parts of your dome and the buildings within to cooler underground heat-exchanging regions like a city-scale [ground-source heat pump](https://en.wikipedia.org/wiki/Ground_source_heat_pump). On Earth, a 20 m deep pit will reach far enough that you don't get sun and weather-induced seasonal variation. Your world might be different, of course, but even if the ground were weirdly hot a heatpump can cope with that, given sufficient power.
This might require significant excavation, but honestly: if you want to stay cool in a hot place, hiding in a deep hole isn't a terrible idea. You'll probably want to have some underground stuff anyway... emergency shelters to be used in the event of dome failure or compromise.
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The trouble with the double-walled dome setup is that air doesn't have a particularly high heat capacity, and in a dome, the interior air won't be moving all that quickly. The inner surface of the dome would be cooler, and would remove some of the heat from the air, but I can see solar radiative heating contributing more to the temperature inside the dome than this cooling.
Air cooling is always going to be a problem. Whenever heat needs to be managed, water cooling is more effective given the very much higher heat capacity of water.
I'm not saying that you'd get rid of the double-layered dome, that's probably a good safety backup to isolate the inside air from the outside air, as well as an insulator, especially if the outer layer was partially silvered, but you'd need a number of other cooling methods.
Firstly, I'd make the roofs of the buildings from white or silver surfaces, to reflect as much solar energy as possible and minimise solar heating. I'd also water-cool them. Secondly, I'd set up water sprayers and fans to circulate water mist through the domes. The evaporation of water will remove a lot of heat from the air, and will also help with growing any plants kept in the dome. With a flow of humid air through the dome, it can be passed over refrigeratively cooled condensers to recover the water so that it can be misted again.
The air could be circulated by placing vents near ground level, mostly along the centre-lines of the dome, and forcing water-misted air upwards toward the top of the dome, where the largest body of hot air would otherwise tend to accumulate. By drawing air from the edges of the dome and passing it underground through condensers to cool and dry it, the air would circulate throughout the dome, mixing with air warmed by hot surfaces within the dome. By forcing the misted air upwards at speed, friction within the body of air within the dome would cause movement of the whole body of air inside the dome.
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The main problem of your Little Summer is that the inside is designed to be *colder* than the outside, so the residents of your hab dome are living in a literal *fridge*. Therefore your proposed air cooling system would work with less effectivity than you expect, as the air flow would take off energy from the outer layer which has more to take than from the inner layer. Still it would be needed.
You should make the *outer layer of the dome* reflective and transparent, a thin reflective foil would do on top of the relatively thick but transparent structure layer; this way the energy income into the dome would be lessened, and you are able to control the amount of reflection at least at design time so that the interior insolation is comparable to earthly conditions when the local sun is in zenith, or at midday. Still, as earthly habitats are cooled by emitting radiation into open space, and your hab dome is closed, you would need a great air cooling system to instead cause this energy to be radiated from outside the hab dome; you would need a radiator field or a cooling tower that uses evaporating water as a means of energy sink that should be located somewhere uncovered.
Air cooling could be done the conventional way within the dome, however the entire A/C system should be pretty large. Develop several air tubes within the dome that would reach the top layers of air, above the levels where humans operate, place sucking pumps at their bases, provide a heat exchange with water and lead that water underground outside to the radiators to form the second heat exchange circle there, as well as produce a smaller water heating structure for the hab dome's internal use, because spending extra energy to heat it would be heating the dome and putting more load on the cooling systems.
Alternatively, check for water, if there's an above-ground or underground river somewhere close to the hab dome, you might position your heat exchangers in there, so your hab some would work like a modern power plant works with rivers in here, heating the waters of it with excess heat generated by the plant. If the river would overheat, and it's above-ground one, engineer a dam to increase the water volume available for heating and radiiating it away, as well as employ waterless radiators as either a backup or redundant heat sink.
PS: am I reading it so that you've put entire *manufacture plants*, including antimatter one, under the dome? Heavy industry is a serious heat source, so your industry is best to develop their own A/C systems each that would have heat sinks outside the dome, as the residential part would already be producing enough heat to justify a large scale air cooling of the dome's atmosphere.
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Gut feeling, solar radiation and air temperature **are not your *real* problems**.
Your dome interior is supposed to average 20°C and your planet has an average temperature of 30°C. So the ground, a couple of meters down, should have pretty constant temperature year-round which is close to that average.
* Put an insulating layer between the ground and the 'topsoil' of your habitat.
* Even so, you will need active cooling (a fridge), which means that by putting energy into the system you make it colder in some places (the dome interior) and even hotter elsewere (cooling towers? a river?).
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Large scale solar cooling system like [this one in Singapore](https://www.power-technology.com/projects/uwcsea-solar-thermal-energy-plant/?cf-view). You could manage it fairly cheaply. You could cover the entire dome in solar collectors.
Then use the power to run refrigeration using water as one of the coolants. As a byproduct you have plenty of hot water for daily use. Better still run a lot of your infrastructure on steam power and vent it outside.
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You have 3 approaches I see to cooling here:
1.) Reduce the energy input. A lot of your heat will actually be coming from the sun, not the hot air around your dome. Make your domes provide shade by making them only semi-transparent, or you can have a grid or checkerboard pattern of sun-shades (or even mirrors) interspersed with transparent sections, (the checkerboard pattern might be cheaper to produce as it could come from support struts and it would introduce a more alien feel, without making everything uniformly dim.) In real life this has been used in the Sahara dessert to make habitable areas through large sun-shades (Although they were not fully enclosed.) It has also been proposed as a way of terraforming Venus, (placing a lot of mirrors in orbit to reduce the heat reaching the surface.)
2.) Active cooling. You are creating a fridge or AC cooled-room on a huge scale. This is incredibly expensive. Look into real life heat pumps, AC systems, and refrigeration. I don't recommend this as the costs would be enormous and any power failure could result in cooking your residents.
3.) Passive cooling. Your atmosphere is hotter than your settlement so you can't passively transfer heat to the atmosphere, and the ground is probably too hot because it takes on the average temperature of the air... but space is incredibly cold and you CAN transfer heat to that if your atmosphere is transparent to the right light frequencies. On earth we have developed passive cooling white paint from BaSO4 that turns heat energy on the surface into infrared light that passes through our atmosphere. (Currently the paint works, but is extremely fragile and relies on a light spectrum that glass is NOT transparent to, so we can't protect it from the elements.) Your planet's atmosphere is different so it might have a different spectrum of light that works for this effect, (possibly one that can be made with a less fragile paint, or a spectrum that glass is transparent to.) It's also possible your dome will adequately protect the BaSO4 and is made from a material that is transparent to the relevant spectrum of light.
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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.
This is for a sci-fi universe depicting an interplanetary civilisation using fusion torch-ships. Think "1G for days".
For a run to Neptune at 1G the peak velocity at turnover works out to about 2.2%C or about 6,650 km/s, although plugging the more optimistic values from [this table of fusion exhaust velocities](http://www.projectrho.com/public_html/rocket/fusionfuel.php) into the [rocket equation](https://www.omnicalculator.com/physics/ideal-rocket-equation) suggests you could theoretically have a total delta-V in your tank much higher than that.
The interplanetary medium is pretty diffuse compared to air at sea level, but you would still have to contend with particles from the solar wind, gas molecules and the (hopefully) very occasional dust grain.
The question is, at what speed do these things start to become a practical problem? The issues I've seen suggested include heating of the leading edges of the ship, abrasion of the same and at very high speeds, actual nuclear fusion.
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## G-forces are the limiting factor.
Assuming your civilization attained the incredible energy densities necessary to go up to these ludicrous speeds, the fact is that any ship containing humans still can't accelerate faster than a few g's without killing everyone on board. And if you want to accelerate constantly for several days (which is what it would take to cross the solar system), you'll get major health risks above 1g - good ol' Earth gravity.
The Expanse (book/TV series) is notable for its vertical ships, oriented like multi-story buildings that accelerate at 1g, providing artificial gravity and fast transport in one fell swoop. I recommend it as a good example of hard sci-fi at the limits of plausible interplanetary travel (and great storytelling to boot).
The maximum speed in your setting will simply be the midpoint speed of the longest journey you can take through the solar system, accelerating at 1g for the first half and decelerating for the second half (nobody will ever go much faster than this since it would leave the solar system). Some simple math, plugging in Pluto's mean orbit for the rough size of the solar system, gives a maximum travel time of about 15 days, at which point the ship has reached **0.04 c**.
So hopefully that makes it clear that, for interplanetary travel with humans on board at least, nobody will be moving at especially high relativistic speeds.
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## Use dimensional analysis
Let's say that you are trying to travel through the solar wind at 0.2 times the speed of light. You said "interplanetary," so you're pushing through the solar wind. The solar wind has 4 hydrogen atoms per cubic centimeter. We wish to know the mass per second of hydrogen atoms that we are hitting.
Let's say that the spaceship has a frontal area of 100 m^2.
So the calculation is:
mass of hydrogen atoms hit per second = 4 (hydrogen atoms/cubic centimeter) \* 0.2 \* (speed of light) \* 100 m^2 \* (10^(-27) kg)/(hydrogen atom)
WolframAlpha will do unit conversions automatically, so you can just plug it in [here](https://www.wolframalpha.com/input?i=%284+atoms%2F%28cubic+centimeter%29%29+*+100m%5E2+*+0.2+*+%28speed+of+light%29+*+1.67+*+%2810%5E%28-27%29+kg%29%2F%28atom%29) and you get
= 4 \* 10^(-11) kg/s
Now, that's not a lot of mass, but we are hitting the atoms at 0.2c.
[This post](https://physics.stackexchange.com/questions/393947/minimum-speed-of-a-baseball-to-cause-nuclear-fusion-in-air) suggests the collision speed required for fusion is in the area of 0.05c, so the atoms will be fusing with the hull. Fusion releases around 0.7% of the mass of the hydrogen as energy. So that means in one second it releases [this much](https://www.wolframalpha.com/input?i=0.007+*+4+10%5E%28-11%29+kg+*+c%5E2) energy:
0.007 \* 4 \* 10^(-11) kg \* c^2
= 25,000 joules
The more significant factor is the kinetic energy of the hydrogen atoms. Relativistic kinetic energy is (1/sqrt(1 - v^2/c^2) - 1) \* mc^2. m is the amount of mass, which we'll take to be the mass in one second, 10^(-11) kg. So, the kinetic energy from collisions in one second is:
(1 / sqrt(1 - (0.2 c)^2 / c^2) - 1) \* 4 \* 10^(-11) kg \* c^2
which [WolframAlpha](https://www.wolframalpha.com/input?i=%281+%2F+sqrt%281+-+%280.2+c%29%5E2+%2F+c%5E2%29+-+1%29+4+10%5E%28-11%29+kg+*+c%5E2) tells us is:
= 74,000 Joules
(74,000 Joules + 25,000 Joules) per second is 99 kilowatts. It's as if you had a heating element on the front of your spaceship drawing 99 kilowatts. Your spaceship is going to have to get rid of 99 kilowatts of heat.
That's probably possible, with powerful refrigeration units to conduct the heat to radiators and get rid of it. Projecting a magnetic field ahead to push the atoms out of the way might be an alternative.
Of course, this assumes you do not hit a pebble. Hit a pebble at 0.2c and that's probably game over.
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# Practical speed limit for any ship is limited by energy
You will want to read up on the initiative called [Breakthrough Starshot](https://breakthroughinitiatives.org/challenges/3) which has several of he most wealthy people on earth trying to get us close-up pictures of Proxima Centauri within a generation.
Their goal is to send a “starChip” probe of only a couple grams mass at a speed of 0.2c on a trip to our nearest star by a 20-30 year trip through 45,000,000,000,000 miles of space, snap a selfie, and radio it home.
The practical limits of this adventure have been deeply explored, and the interstellar medium is incredibly hostile to small things. The shielding on this craft, by NASA calculations, can withstand several impacts with interstellar molecules of hydrogen or helium which they expect, but they calculated that impact with a grain of dust the diameter of a human hair would completely vaporize the probe at that velocity. NASA also calculated that the ship would only survive if the density of interstellar dust were below a certain fraction (it is among those many papers in the Breakthrough page, I could not find it), and unfortunately the calculated interstellar dust is significantly higher than wht is needed. If you want to consider interplanetary dust, even Star Trek admits you can’t go to warp inside the solar system. You WILL hit something big, and enough small things to burn you up.
But the energy to drive this can’t possibly fit onboard theprobe, so they are using sails. And a 100 Gigawatt laser system. Yes, 100 Gigawatts to get a raisin up to 0.2c, which it is hoped to reach within 6 months of acceleration.
So the solution is to obviously build a bigger ship with bigger shields. This means more mass, and that means more energy. How many raisins does your scifi ship weigh? Multiply 100GW times that, and decide if this is practical. But, you need energy to accelerate AND to decelerate. Twice, if you want to come home. So one round-trip excursion anywhere is the energy of acceleration x4.
But with unlimited energy (like every respectable sci-fi author invents), all you need to do is accelerate faster and trips between Earth and Neptune can be done in a day,right? As long as [you don’t have any squishy organisms](https://worldbuilding.stackexchange.com/questions/160164/can-a-human-crew-handle-cyclic-extended-high-relativistic-speed-operations) onboard, that is fine. But I think in the hard-science sorting machine’s calculations, G’s matter. Even *The Expanse* [gets this right](https://youtu.be/JS7x4Bq_gR8).
The hard science answer today is that it is simply not practical to produce the energy required to make a massive object accelerate and decelerate for an interstellar trip at high-fractional light speeds. Yes, fusion particles reach high-fractional light speed. The hard science sorting machine puts sub-atomic particles and spaceships into different boxes, however, because mass matters. A lot. And doing this inside the tiny space of a solar system is up against the hard science of inertial momentum.
Please determine what scientist you want to embarrass before attempting this story. It’s a necessary evil of the genre.
Your science fiction story needs to decide what part of hard science it wants to break, because you absolutely have to make some scientists do a face-palm to make your world work.
Don’t fret. Every sci-fi author has done this already. It was much easier back in Jules Verne’s day when we didn’t know what was out there.
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I'm not sure where, but you've definitely made an error with your math. Going by that table from atomic rockets, it gives the most optimistic figure of .117c. With a mass ration of 10 (90% fuel) then you're talking about an effective delta-v of around .26c. Even if we go by a less optimistic value like the space shuttle's mass ratio of 16 then we're talking about something around .32c. It's not called the tyranny of the rocket equation for nothing, as much of the extra fuel is wasted by the mass of carrying extra fuel, which is why you probably want staging for something at this scale. I will note that even this .26c value only includes the total delta-v, as your useful speed is half that unless you want to collide with the destination at full speed.
That is also proton-proton fusion, which has a pretty good chance of not even being possible outside of a sun. Considering how hard even dirtier De-T fusion is on Earth, sustaining that reaction in space is rather unlikely. Going by a more realistic figure of .087c for duterium-helium3, this gives you a delta-v of .2c instead.
Something else you're missing is that exhaust velocity and effective exhaust velocity are not the same. So while the fusion rocket might have an exhaust velocity of .3c, the effective exhaust velocity is even lower. Orion drives for example were only 25% efficient, while a modern rocket bell is somewhere in the 90%+ range. Fusion power could never be this efficient because a truly efficient rocket design would melt due to the extreme heat without any good way to dissipate it in space. You're left relying on magnetic nozzles which are less efficient. Somewhere in the 50-60% range is all you're likely going to get. At that level your .26c max velocity is now down to around .16c with an effective max velocity of .08c. If you want the kinds of speeds you're suggesting then you need some version of antimatter, which is almost certainly impossible to store at the scale required in a safe fashion.
As for mitigation, streamlining will help slightly, but it also makes your frontal armor less efficient, so that it requires more surface area to cover the same volume of ship. Most hypothetical design's I've seen use umbrella style shields. At the lower practical values, streamlining is almost entirely pointless.
Magnetic sails just plain won't work, because in order for it to push particles out of the way they will also slow the ship down due to conservation of momentum. There is some debate about whether a Bussard Ramjet would produce more drag than it does thrust. The upside is that you can use this conservation of momentum to slow down like an interstellar parachute. The best use for a magnetic sail is that you can use it to slow down and so can burn up nearly all of your fuel on the way there. A fairly plausible mission profile for an unmanned ship with such a design [can be found here](http://www.projectrho.com/public_html/rocket/slowerlight2.php#id--Go_Slow--Sublight_Starships--Project_Icarus--Ghost_Ship). I will note that it has a mass ratio of 35 because it is using D-D fusion.
EVAs are a bad idea any way you shake it. While an umbrella shield would help with physical impacts, the biggest problem is radiation that there is no practical way to shield against. The ISS is only relatively safe because it is in LEO and is still under Earth's magnetic field, while astronauts still have shortened lifespans. Space suits just can't do it without becoming extremely impractical unless you have something better than Iron Man level powered armor.
There is also another problem with fast ideas like this. Unless there is already infrastructure in the destination star system, then you'll need to bring along essentially a self contained society a la a generation ship. If you're doing this, then there is less reason not to just go slower in the first place and just use the greater payload to carry more stuff. If you're talking about these kinds of speeds within the solar system, see the discussion of The Expanse.
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Didn't want to answer this one under hard-science tag, but considering present answer and danger of the q being closed, I can't keep silence, so on the softish side.
Practical is defined by what you have and what you want and can achieve, so, in a sense if you can 0.9c it practical in some sense as it saves time for people onboard of the craft, and it not so much practical to fly at 0.1c even to proxima (maybe practical if there is such neccessity) and even less practical and more difficult to fly at that speed to more distant stars.
But torch ship won't be able to get close to 0.9c(it can but...), and more resonable balance is indeed so often used 0.1c, and it potencially (close so) what a torch ship can do. So it your practical speed, due limitations of rocket equation
As ISM it does not have such an impact on speed limits, as sure a dust particle colliding at anything with more than 1000km/s may be problematic, but it also worth noticing that even more so it is for a dust paticle to collide with another dust particle at such speeds.
So making shield in front of the ship, by "saturating" (1-10-100x of ISM density) a cloud in front of a ship(by torch exchaust as an example, which then moves at about the speed of the ship) may be an effective mean to destroy all small particles into a plasma before ship arrives and bring that plasma to speeds closer to speed of the ship. Project orion(if I remenber correctly, or someone in reference to that project at that time) or something were proposing use of foil shreds for that - may work as well, cloud of paticles - ice grains of somehing may work as well. It should provide protection from lobe collisions so as side collisions. And it can be done in more than few ways - but it all is the same sacrificial material vs ISM, which you can constantly recycle, in that sense water ice as shield, water ice and sand, gas cloud, etc whatever it is easy to fix/deploy in the flight)
So potencially there are ways to protect caft from particles, and create warning sytem to detect things by hours ahead for big chunks which can not be destroyed by this cloud. And speed does not matter here 0.1c-0.9c it is not of much difference.
So practical velocity is defined by spacecraft capacities, what a practical space craft can achieve as a max velocity. In a sense torch ship and fusion ships are not practical for intertellar travel, but good stuff for interplanetary one. So as technologies which do not have self healing self repair properties(aka nanobots of some kind 1-2-3D nano) are not that suitable for interstellar travel.
As EVA - depends on approach, if it is a cloud infont of the ship, then space next to the ship, is quite safe and protected as km's around it
## PS
* *Not downvoting because there have been scientific studies of spray, gas, and cloud shielding of spacecraft, but not upvoting because you haven't cited any of them.* – @Mark
True, true. For same reason I can't comment, old browser and pad to write an answer, for same reason I didn't want to write an answerto this one, because finding links is very inconvinient on this setup.
You can edit the q and add few links, I would like to read it myself as well, maybe. As the q and a discussion of dust particles problem is not new in public discourse, and I do not see those solutions to be mentions as often as they should. I have impression that at some point it was only me pushing that idea on WB at least. I mean - I first come up with the idea writing answer or something, and then some time later I found(while researching material for some answer) a short cite mentioning proposal/connection between shred of foil and orion(or something) it was not a research work but a mentioning, I remembered it, then I even lost a link to that mentioning(I do remember as I did try years ago to find it again but without a success). I mean those solution should be 101 of space travel discourse, not forcing ppl to reinvent weels as it happened to me, but clearly they aren't, still.
So I literally forced myself to write an answer to the q, considering how not well discussed the problem and its solutions are, to which current answers are another demonstration - at time of writing a guy started to talk about energy limitations, as if the fuel does not provide enough energy, and problems of project starshot, forcing OP to invent/handwave unlimited energy sources in a hard science answer, as it fusion alone is not enough.
Further answers didn't do much better and q is about to close, so there won't be a single answer which adresses OP's clearly stated worries. @cuasative answer is somewhat exception, but his crew dies from pebble and can resist only hydrogen of ISM. For reasons I can not comment(broken javascrip for my browser) I can not upvote or downvote, or all of them would get you understand what.
So, save the planet, edit the answer or write your own if you have a chance, and add links to solutions. I hope you do not wavered once The expanse was used as an example, source, lol.
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### Intro
I'm developing a real time game that have dynamically generated map and I'd like to add rivers going from mountains to the sea.
### Brief info about the map
In my game, when a player moves to the edge of currently generated map, new chunks (small, square piece of map) of map are being loaded on server. If there are no chunks found for the requested location, they are generated using the same seed which is used in other parts of map. Currenly, there is no limit in map size or total amount of generated chunks. I'm using Perlin noise to generate the map. I treat it as a hight map, with every field having a range of values it occupy e.g. shallow water starts from `-0.12` inclusive ending on `0` exclusive.
I already read about how to make the river look realistic:
* [Is my river map even remotely realistic?](https://worldbuilding.stackexchange.com/questions/167148/is-my-river-map-even-remotely-realistic)
* [How do I simulate the path of a river?](https://worldbuilding.stackexchange.com/questions/73977/how-do-i-simulate-the-path-of-a-river)
* [Creating a realistic world map - Waterways](https://worldbuilding.stackexchange.com/questions/21402/creating-a-realistic-world-map-waterways)
### Question
How do I add rivers to the map when I don't know how the whole maps look like? If I don't know where the mountains are I cannot place the river source. And if I have some part of the map already generated I cannot just add the river a little later when a player encounters a mountain chain.
### Similarities
Similar scenario (I think) is in Minecraft. There too, map generates as player moves using a seed and there are rivers which continue to swirl while the map generates on. Sadly, I don't know the technique used there.
### Screens from the game
[](https://i.stack.imgur.com/8s2Qi.png)
[](https://i.stack.imgur.com/ovpn6.png)
Chunk loading temporarily disabled, to show the boundaries:
[](https://i.stack.imgur.com/WRpvZ.png)
[Answer]
The problem is unsolvable as asked. You may end up generating a river which the player traces back to the top of a minor hill in the middle of a desert.
There are a few alternatives that can make this work:
### LOD and physics:
You can sub- and super- sample perlin noise in order to create multi-resolution maps. If your tiles there are 1 tile per 1meter, you can create the entire map at a more manageable level, say 1 tile per 1km, calculate realistic spring points and a rough river path, and then subdivide down, to say 1 tile per 100m - at that level you know where the river flows to an accuracy of within 10 tiles, work out where the river flows along that path, and then where the river flows through those smaller tiles recursively, etc, until you arrive at your full detail level.
It's better to precalcualte this and store it, if possible. You can still run this on-demand, but it's not trivial to code.
### LOD and 1D perlin
As above, on your low resolution map, find the high point where a spring would come from, find the closest sea level point, draw a straight line. Now use 1D perlin noise to make the river wind perpendicular to the line.
This is much easier to code - it can have some unrealistic artefacts, but for a 2D tile game like this you're unlikely to notice them.
### Fake it
Have 2 styles of rivers. One going "uphill", one going "downhill". Create tiles to show the river coming from a spring and forming in to a full river, and one showing a full river draining into a small below ground feature.
If the perlin noise value for a coastal area is a very precise value, then it spawns an "uphill" river. This travels to the highest edge point in the tile which doesn't border an explored tile, which then when the next tile loads, goes to the next highest point. If it detects it's gone to a local max (there's no higher point) or all neighbouring tiles were already explored, backtrack to about the middle, put a tile which shows the river coming out of a cave or spring or something else below ground, so the user doesn't see the river starting from the top of a small hill.
If the perlin noise value for a mountain is a very precise value, then it spawns a "downhill" river, follow to the lowest other border of an unexplored tile, and if it gets to a local minimum, or a chunk with no unexplored neighbours, put a tile in which shows the river disappearing below ground.
This is usually good enough for a tile based 2D game.
### 2 (or more) perlin channels
Currently you're running the perlin generator once per tile, to give a single value. I'd suggest run it multiple times per tile (with different seeds of course, and usually different scaling factors). The use those multiple values to populate the tiles, instead of just one;
This can help break the expectation that beech is next to plains, plains is usually next to forest, forest is usually next to mountains, etc.
If you run it twice - I'd suggest humidity and elevation. If you run it 3 times, I'd suggest feature size (sand / rock, ice / snow, or baren -> grassland -> scrub -> trees), humidity (desert -> fertile -> river -> swamp), and elevation (water -> plains -> hills -> mountains). 4 times maybe would include a temperature too.
Rather than focus on running your river "downhill", try to run it where the humidity is within a particular contour range. While the river wont "realistically" flow downhill, in a tile game like what you're showing elevation is obscured, you're better off ensuring that trees grow near rivers, rivers aren't bordered by desert, and the land near rivers is fertile farmland.
[Answer]
>
> How do I add rivers to the map when I don't know how the whole maps
> look like? If I don't know where the mountains are I cannot place the
> river source. And if I have some part of the map already generated I
> cannot just add the river a little later when a player encounters a
> mountain chain.
>
>
>
You cannot do it entirely within a chunk. If you are on the edge of a chunk and there appears to be a local minimum you have two choices.
1. Extend the terrain invisibly around the minimum until you find the perimeter of that minimum in the as yet unexplored chunk. You don't have to complete the whole of the new chunk because by then you know where the pool will drain to. This will either be back into the current chunk or to somewhere, as yet incomplete, in the not yet explored chunk. In other words you have to extend beyond what is visible/has been explored. You could call this *just-in-case* programming.
2. Have a deterministic algorithm that deals specifically with this eventuality. I.e. deliberately close off any possible outlets into the new chunk. Effectively you have built a dam. This will almost certainly lead to fake-looking artefacts.
Note that using local minima in this way (assuming non-permeable terrain) will allow the grain to be as fine as you wish. This could even allow you to show springs and other small sources of the river.
[Answer]
Some years ago I wrote an algorithm for an RPG game that worked in similar way.
Think in "Minesweeper". When you discover a mountain square there is a x% probability there will be water. But that square influence probability of chunk next to it being mountain. Which influence the appearance of water. For each map you might impose water sources. Map is started from a range 0-100 number is chosen. It's the amount of water sources. The more the map is un-shadowed the more probability of water showing up rise.
Now, to aid you nature came with this nifty thing that brooks appear and then it seep into crack and dissapear. Nowaday with modern technology we can trace where it come back but in "discovery" phase one source might show as 3 or 4 different brooks. SO they don't need to be one continous line from discovered source to "somewhere". It might end after 4 or 5 chunks.
So you might just end the water generated chunks when player meet already discovered "dry" chunk.
OR
Create a fun change in your map. With time (player move) dry chunk became wet ones when generator try to link biggest water "puddle" (if lower). Generator might also have probability of creating creek so it won't go in straighest line.
Remeber that your player act a typical human. So they might discover river source, it might flow into undicovered regions but just by divocery and their presence they change how the water flow.
[Answer]
The simplest algorithm is for rivers to "snap" to a mountain valley whenever an existing river is within some threshold distance (and perhaps angle) to a valley that meets the minimum requirements.
Let's say you have a river generated by whatever algo you happen to be using. There is no existing source yet, and it ends at the "fog of war" on your map. But the player moves to reveal that, and you use the algo to again generate the missing pieces.
Presuming that your algo occasionally generates mountains, if mountains/valleys are created withing n units from the "end" of the river and at any angle shallower than +/-45 degrees of the tangent of the river, then generate a river path from that point to the mountain valley and place a glacier there.
If the river endpoint is farther away than n units, start to generate its path and if that path comes within n units of the valley, do as above.
It would be necessary to generate mountains first, and then overlay the river on top of such a map.
You might even manage to allow it to connect to *several* mountain/valleys if there are multiple potential sites, and this would give you tributaries feeding into a main sea-bound river.
This of course relies on a two-part map generation scheme, where most map features are generated, and rivers are "painted" onto the top of that. It would work for Minecraft, for instance, which I believe does this. If your game were more sophisticated and used elevation to determine the paths of rivers, this would be unviable.
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[Question]
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Fairly straightforward question. Imagine a gas giant planet, like the size of Jupiter, in orbit around a massive star. The star goes supernova.
What happens to the planet? Is the energy of the supernova enough to strip away the atmosphere, leaving just the rocky core behind? Is there a way for the planet to remain in orbit around the resulting white dwarf?
[Answer]
Simulations of the dynamics of planets close to massive stars during a supernova ([Veras et al. 2011](https://arxiv.org/abs/1107.1239)) indicate that a planet in a reasonably tight orbit ($\sim2\text{ AU}$) around all but the lowest-mass supernova progenitors is almost certainly going to be ejected from the system. The cases where a planet *does* survive place it near periapsis, almost as far from the star as it can be. As many giant planets are hot Jupiters and thus reside only a fraction of an AU from their parent stars, the percentage of these planets that are not ejected from the system is extremely tiny. The survival rate for a planet in an orbit like Jupiter's are certainly better, but still quite slim.
Additionally, many supergiants undergo periods of extreme mass loss ("superwinds") in the stages of their lives immediately preceding a supernova. This mass loss plays a significant role in the evolution of the star and the evolution of the orbits of any planets bound to it. In fact, Veras et al. argue that it could lead to the ejection of small bodies orbiting the star even *before* the supernova itself occurs.
Of course, a large fraction (although not all!) of the planet's material will be stripped away by the ejecta. I haven't been able to find many good treatments modeling mass loss by the planet, but [Vila et al 1980](https://ui.adsabs.harvard.edu/abs/1980ApJ...236..645V/abstract) (not the clearest or most detailed paper, I know) put together a couple grids of models of various planet masses and semi-major axes. It looks like a 1-2 Jupiter-mass planet at a couple AU around a 4-8 solar mass star could lose about 30% of its material. In addition to being flung out of the system, your planet is going to get a lot of its mass ablated away and ejected.
As a side note: The remnant of a star that undergoes a supernova will be a neutron or a black hole, not a white dwarf. The planet will remain in orbit around it (assuming the scenario where it orbits far enough away to not be fully destroyed) but will actually [have its orbit expand](https://astronomy.stackexchange.com/a/21171/2153), as the remnant will be several times less massive than the original star and angular momentum must be conserved. This expansion could be on the order of several times the original orbit's semi-major axis.
[Answer]
Quoting [Randall Munroe](https://what-if.xkcd.com/73/):
>
> [the] rule of thumb for estimating supernova-related numbers: However big you think supernovae are, they're bigger than that.
>
>
> Here's a question to give you a sense of scale:
> Which of the following would be brighter, in terms of the amount of energy delivered to your retina:
>
>
> 1. A supernova, seen from as far away as the Sun is from the Earth, or
> 2. The detonation of a hydrogen bomb pressed against your eyeball?
>
>
> Applying the physicist rule of thumb suggests that the supernova is brighter. And indeed, it is ... by nine orders of magnitude.
>
>
>
Based on the above, my guess is that the gas giant will be stripped naked of all its gases and maybe even part if not all of its rocky core will sublimate under the astonishing large radiative flux which will shower it.
Then, whatever remains will be probably moving too fast to be gravitationally bound to the remaining dwarf, and would probably fly away into space, or at least on a different orbit.
[Answer]
From ["Rescue Party" by Arthur C. Clarke...](https://www.baen.com/Chapters/0743498747/0743498747___1.htm)
"He increased the magnification until only the center portion of the nova was visible. Close to its heart were two minute condensations, one on either side of the nucleus.
'Those are the two giant planets of the system. They have still managed to retain their existence—after a fashion. And they were several hundred million miles from the sun. The nova is still expanding—but it's already twice the size of the Solar System.'"
Yes, this is science fiction from 1946, but it actually seems to be pretty accurate.
**A more scientific analysis**
It has often been claimed that a supernova can radiate as much energy as the Sun will in its entire lifetime.
10 billion years \* 365 days \* 86400 seconds \* [3.8 \* 10^26 J/s](https://en.wikipedia.org/wiki/Sun) = roughly 10^43 Joules of energy.
Now, to find the binding energy of the gas giant(to see if it even survives the explosion)
E = 3GM^2/5R. Let's use Jupiter as an example.
(3 \* (6.67 \* 10^-11) \* (10^54 kg))/(5 \*(6.6854 \* 10^7 m)) = 10^35 J.
The gravitational binding energy of Jupiter is *eight orders of magnitude* less than the total amount released by the supernova.
"But Jupiter's orbit is 2.444 billion kilometers in circumference!" says the annoying man in the back row. "Surely all of that energy cannot be distributed in a cone *directly at* it!"
sqrt(6.6854 x 10^5 km Jupiter radius/7.606 \* 10^18 kilometers orbital "surface area") = ~8.7 \* 10^-13. Multiply by 10^43. Yep, Jupiter is toast. Within an order of magnitude of the necessary gravitational binding energy, but most of the upper atmosphere will boil off. The most you can probably hope for is a rapidly expanding plasma cloud. At that point, it doesn't really matter whether it still orbits the white dwarf or not, you at most will only have an Earth-mass barren rock anyway.
TL;DR: Your gas giant is toast unless it is *very* far from the host star. Hope you weren't using it for a [fusion candle](https://www.schlockmercenary.com/2003-08-03).
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[Question]
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I've seen many concept arts of aliens that have some sort of glowing bioluminescent pupil-less eyes. I'm inventing a creature that has yellow glowing eyes like that and can see in the dark. My questions are:
* How do the eyes work without pupils?
* Is yellow bioluminescence a thing?
* Doesn't the creature get blinded by the light of its own eyes?
* Why would it evolve glowing eyes in the first place?
[Answer]
# It can be an illusion
Many mammals have (the illusion of) glowing yellow eyes - deer, dogs, racoons, etc.
I say "illusion" because the eyes themselves are not *emitting* the light, but *reflecting* the light. You can think of this something like someone with bleach-white teeth in a dimly-lit room. If the light hits it right, the contrast between that much white and the darkness makes it *seem* like their teeth are glowing, even though they are not.
1. **How do the eyes work without pupils?** Like Ruby said, they don't. However, most creatures have pupils which dialate at night to allow more light in. A predominantly daytime animal will have smaller pupils in general (humans have smaller pupils than owls, for instance). It's not far-fetched that a creature mostly adapted to daytime may have tiny pupils, or never evolved dilating pupils at all, relying on other methods of engagement at night (such as sonar, like bats). As such a tiny pupil may be too small to see. Or perhaps their eyes rolled back (have you ever seen someone's eyes roll back in their head so only the whites are seen?)
2. **Is yellow bioluminescence a thing?** Yes, but in this answer I'm going more with the "reflection-as-illusion-of-luminescence" thing, so not as germane here.
3. **Doesn't the creature get blinded by the light of it's own eyes?** No, because again, the light is not coming forth from the eye; it's an illusion because the eye is reflecting a lot of the light.
4. **Why would it evolve glowing eyes in the first place?** @Ruby gave great options here - luring prey in, mating, identifying others, etc. I will add that perhaps it makes predators less likely to attack when glowing eyes are staring them down (when my dog's eyes are yellow-reflective at night it's definitely creepy).
[Answer]
**Is yellow bioluminescence a thing?**
Yeah, look at [Firefly](https://en.wikipedia.org/wiki/Firefly)
**How do the eyes work without pupils?**
It does not, without hole in iris no light would came to eye. In case you meant absence of iris, it can work, but you lose ability to accommodate to different light insensitivity, situation when someone don't have it is called [Anidrida](https://en.wikipedia.org/wiki/Aniridia), look it up.
**Doesn't the creature get blinded by the light of it's own eyes?**
It depends on how intensive light would be, but we can safely assume it would not, there would be no evolutionary point in having glow from eyes which makes you unable to see.
**Why would it evolve glowing eyes in the first place?**
Maybe to lure preys in darkens like abyssal fishes do? Or for some strange mating reasons? Or to find other companion from society in darkness more easily? Or simply to light when its to dark to see without it?
[Answer]
One possibility is has been answered already, for various reasons related to evolution in a low light environment.
Another possibility is similar to an astronaut's visor:
[](https://i.stack.imgur.com/YpEi3.jpg)
The eyes may have evolved a reflective sheen to reduce the incoming light. Ideally this would adjust for lighting conditions the same way the iris would contract or expand. In this scenario there may still be a pupil but it would not be visible from outside of the eye. Note the golden color of the visor's reflective coating. There are similarly all hues of metallic reflective coatings, including red, blue and green.
Edit:
Finally the eye could also have a layer of bioluminescent cells over the reflective coating. The effect of this would be that the light from the bioluminous cell would be blocked from entering the eye.
[Answer]
An option that others have not mentioned... Consider a creature whose vision works well down in the infrared (effectively 'seeing' heat), or well up into the ultraviolet (the way some insect eyes do). In that case, a yellow glow would not interfere with its vision, because yellow is out of its visual range, and pupils might not be recognizable as such because they would be made of material that is transparent in frequencies that we ourselves cannot see.
Such a creature would evolve, obviously, in an environment where the light bandwidth peaked in the infrared or ultraviolet range (not in the green range that our own sun provides). The glowing eyes might be entirely incidental (a function of the materials that make up the working parts of an infrared or ultraviolet eye) or may act as a kind of biological flashlight (sending out a beam that reflects back in frequencies the eye can see (the way ultraviolet light will cause phosphorescent materials to glow in human visual range). If the alien is a predator, the glow might also serve as a 'startle' mechanism, causing hunkered down prey to panic and run, making them easier to catch.
[Answer]
Cat's eyes glow [because](https://www.infoplease.com/askeds/why-do-cats-eyes-glow) they have a layer of reflective material at the back of the eye. This causes any light that gets to the back of the eye to reflect forward. This gives the retina a second chance at detecting any given light, and makes the retina effectively much more sensitive. You see light reflected back, and so light coming from the eyes like a mirror. It's not due to bio-luminescence.
Typical bio-luminescent species don't have bio-luminescence in their eyes. That would be quite inefficient for the reasons you mention. Typically, such glow is somewhere else, such as on their skin or in a special appendage. [Angler fish](https://en.wikipedia.org/wiki/Anglerfish) have a lure. [Fire flies](https://en.wikipedia.org/wiki/Firefly) glow from their abdomen. Unless it's a creature that does not have eyes as such. There are jellyfish that glow all over. And there are micro-organisms and fungi that glow. Such organisms don't usually have eyes to be dazzled.
Such reflective layers would develop in a species that operates in low light levels. This could be because the species is nocturnal. Or because the species is subterranean.
Operating in low light levels would tend to mean they need their eyes to have as wide iris as possible. Cat's have irises that can clamp down to very narrow openings in daylight, and open up to a very wide portion of the eye at night. A narrow iris when light levels are high blocks non-required light, and also increases the sharpness of focus.
So an alien with very wide pupils and glowing or reflective eyes tends to suggest a nocturnal or subterranean sort of critter. Either creepy or exotic, depending on the context and the presentation.
[Answer]
*Why would it evolve glowing eyes in the first place?*
These creatures are social animals like us. Things that set off the eye against the face are attractive.
[](https://i.stack.imgur.com/9juuM.jpg)
<https://www.marieclaire.com/beauty/makeup/a134/smoky-eyes/>
*How do the eyes work without pupils?*
They do have pupils. The pupils are big. The entire visible eye is the enormous pupil. The rest of the eye is within the orbit and not visible.
*Is yellow bioluminescence a thing?*
Sure. Lots of glowy things glow yellow.
*Doesn't the creature get blinded by the light of its own eyes?*
That light is meant to be seen by the conspecific that the creature is looking at. The light is channeled down short filaments such that it is not visible from an angle or by the emitter, only by the creature directly in the line of sight. . There are traffic lights that work that way. Just as in our species we have whites surrounding the pupil so others will know where we are looking, this species uses the glow to indicate gaze direction to others.
[Answer]
## They are not the real eyes
Eyes need a pupil to see, and that pupil must absorb light, meaning it will be black. But that doesn't mean you can't have a creature that *looks* like it has glowing eyes.
Exhibit A, the flashlightfish:
[](https://i.stack.imgur.com/acdln.png)
Looks an awful lot like pupil-less glowing eyes, doesn't it? But the glowing organs are not the real eyes. The real eyes are the dark circles above the glowy bits. In the dark, of course, you can hardly notice the real eyes.
They use the glowing organs to see, and also to signal each other (they can turn them on and off quickly). They have to be careful though, since the lights can make them visible to predators.
Fun fact about deep-sea bioluminescence: most bioluminescent sea creatures use the same few species of bacteria, which exist in the ecosystem. Animals that evolved a suitable pouch to breed these bacteria have the ability to use them as light sources, even though the animals are not related to each other. A similar bacterium might evolve on land and be utilized by land animals; evolutionary pressure just hasn't been strong enough for bioluminescence to become widespread among land-dwellers, though there are of course a few exceptions like fireflies (which are often yellow).
I'd expect a large bioluminescent land animal to be a social pack-hunter, like wolves - they can use their glowing organs not only to see in the dark, but also to signal each other silently and coordinate their attacks at night.
[Answer]
very few animals if any use bioluminescence to see, this is because it makes you visible to predators. Uses for bioluminescence are baiting prey, finding a mate or using a flash to distract predators.
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[Question]
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Things like Dyson spheres need a whole lot of raw material, which is rather difficult to come by, since the elements needed for good structural steel are scattered fairly thinly into the universe upon the death of the stars that produce them.
The obvious solution is to somehow get at the approximately one solar mass of iron while it's still cooking, or at least before it has time to fully disperse, which would be before the star turns into a neutron star which is [even harder to mine](https://worldbuilding.stackexchange.com/questions/91444/neutron-star-mining). Supposing you have the world-smelters and transport capacity to strip mine several solar systems' worth of planets, how would you go about shutting a star down so you can get at the layers of heavier elements of the inner layers of the star?
[Answer]
It is called star lifting, and is a known concept.
Basically, you generate a magnetic field which channels solar radiation through the poles. The magnetic field is created using orbiting electromagnets powered by the sun itself. There are three variations of this technique in Isaac Arthur's Youtube series.
<https://youtu.be/pzuHxL5FD5U>
[Answer]
**Kinetically.**
Let the star run. It is a pain in the butt to shut down and anyway it is still really hot once you do. Also it is liable to restart while you are poking around in the guts. Plus if you shut it down it stops making stuff for you. That is like cutting down an apple tree to get at the apples.
Instead, kick chunks out of the center. Here is the scheme.
1. Identify sizable chunk of strong stuff that you don't need. A planitesimal will do.
2. Accelerate sizable chunk to speed.
3. Allow fast moving chunk to plow into star. It will lose material to ablation on the way in, which is why it is sizable.
4. Solid stuff hit in the center will be ejected out, according to Newtonian physics.
5. Catch that stuff at some distance from the star. That is the good stuff you want.
If your chunk does not kick material out of your star, try a larger chunk and greater speed and maybe a different angle, hitting the core at the edge.
For a fiction this would be extra awesome because of the weaponization potential. The aliens would scoff at the futility of trying to hit them with a giant rock they can easily dodge. The rock is instead thrown at the star...
[Answer]
Mining a star when you want to build a Dyson sphere is the high tech version of the slapstick joke of the man sawing the branch on which he is seating.
If you mine the star you switch it off, and once the car it's off you have no power supply for your Dyson sphere.
As usual, you start mining out planets. Once you are in transhumanism you don't need barionic bodies any more.
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[Question]
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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.
What would it look like if a human (with the proper protection) walked across a lava stream?
Assume that 'proper protection' means
* some way of insulating against the heat so that they don't get cooked alive (insulation does not hold forever, but at least a couple of hours before the human loses consciousness due to overheating - should be enough time to cross a single lava stream),
* clean air supply so that they don't choke on the hot or toxic gases
* enough high-tech that the human's foot print isn't much larger than a normal human foot print (at most +5cm on all sides)
* weighs less than 20kg, so assume that the total weight of human + protection is around 100kg
* non-stick - none of the lava sticks to the protection
Since lava is rock, will the human just walk along the surface of the lava stream like across a slightly spongy surface? Or will they sink in to their ankles / knees and have to slog through something resembling jelly?
Will they get carried away by the lava flow? Will their weight make enough of a dent in the surface tension that they get something resembling a 'grip', or will it be more like trying to walk on moving ice with next to no friction (due to the non-stick property)? Or like walking across a water bed? Will they even break surface tension?
Does it matter which kind of lava it is (highly viscous lava vs. not very viscous)? Does the temperature of the lava matter as long as the stream does not have a solid cover?
Are there any other dangers to walking across a lava stream that I missed except the temperature and the gases? Assume that I have seen several nature documentaries of volcanic eruptions, but do not know anything else about how lava flows.
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# TL;DR
Assuming temperature and breathing issues are negated by proper protection, what would it look like if a human crossed a lava stream? Are there other hazards that 'proper protection' does not cover yet?
I am looking for an answer that has **as much hard science as possible** to support the results. (Except for the handwavey 'proper protection'.)
[Answer]
Density of lava varies a small amount, but you can more or less handwave it as an average 2800kg/m3, which is roughly the density of Earth's crust. This is the important figure for your needs, because it is substantially higher than the density of humans, who can float in water, which has a density of about 1000kg/m3.
The second most important figure is viscosity, which not only varies quite a lot but is also quite hard to measure. There's a handy diagram in [this paper](https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/jgrf.20111) on page 2 (labelled page 1517 in the document) which shows that some rhyolitic lavas can have a viscosity as high as 108Pa·s, whereas Komatiite lavas can be as fluid as 0.1Pa·s, equivalent to a [very low viscosity motor oil](http://www.vp-scientific.com/Viscosity_Tables.htm). The extremely viscous lava is probably one you can walk across if you don't hang around (you'll still sink if you wait long enough), but those runnier lavas are a different matter altogether.
[Here's a video](https://www.youtube.com/watch?v=bumUw0lNOz0) of a man running up a small, high-viscosity lava flow on Mount Etna (alternatively, an [article link](https://www.theverge.com/2018/5/30/17406774/lava-flow-hazards-hawaii-kilauea-volcano-eruption-human-body-burns) with the video embedded in case you don't want to sign in to youtube). Etna [mostly produces Andesite-type](http://volcano.oregonstate.edu/book/export/html/521) lavas, which are relatively viscous at 105Pa·s. Because the flow rate is low, an insulating crust forms on the top of the lava and he doesn't need a whole lot of protective gear. So lets assume that we only need to care about the less viscous lavas, as given your fancy protective gear you'd have no problem running around over the more viscous ones.
Now, Concrete has a viscosity of about [20-2000](https://www.researchgate.net/publication/326823896_Powder-scale_multi-physics_modeling_of_multi-layer_multi-track_selective_laser_melting_with_sharp_interface_capturing_method)Pa·s, which is at the low end for most lavas. [Concrete also has a density of about](http://www.newsteelconstruction.com/wp/theyve-changed-the-density-of-concrete-or-have-they/) 2500kg/m3. So, can you walk across wet concrete? Well, you'll certainly sink into it to some extent whilst standing (see example in [this video](https://youtu.be/OOkZvvk1Dh0?t=371) at 6m11) which does not bode well for your lava walking plans, at least as far as low viscosity lava goes. You won't be completely immersed of course, the density of the lava being what it is... your legs are about [a third of your bodyweight](https://exrx.net/Kinesiology/Segments) so you'll sink up to your groin. You may be able to haul yourself out, if a crust is forming on the lava, but otherwise you're toast.
I have a plan B, though. Mud, of the sort you find in tidal mudflats is of a similar viscosity to wet concrete, though it has a much lower density (as low as 1200kg/m3 [in some harbours](https://www.leovanrijn-sediment.com/papers/Fluidmudformation2016.pdf)). Wading through it in boots is an exhausting and often futile exercise, but this problem has been solved by various means including things called "splatchers" or, more boringly, [mud-pattens](https://smallboatsmonthly.com/article/mud-pattens/). These are foot-square (or about 0.1m2) wooden slabs attached to your feet, preventing you from sinking into the mud. A lava-friendly equivalent, made of whatever magical material you have that lava does not adhere to, should serve you just fine. You might do well to carry some walking poles made of suitable refractory materials to help you balance. Remember that lava flows do in fact flow (lava lakes don't, but beware of gas bubbles forming) and you'll have to be careful not to be swept off your feet. For the least viscous lavas, you can solve the issue with bouyancy. A 32l hollow float will be quite enough to keep an 80kg person above the surface of the lava, so two big 15l boots would do though [balancing may require quite a bit of practise](https://www.youtube.com/watch?v=SZMW6WvUz2s)... you might be better off with a paddleboard!
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Note that lava is [shear-thinning](https://en.wikipedia.org/wiki/Shear_thinning) and [thixotropic](https://en.wikipedia.org/wiki/Thixotropy), meaning that under the right circumstances its viscosity will *decrease*. This contrasts with stuff like quicksand or cornstarch-water mixtures which are [shear-thickening](https://en.wikipedia.org/wiki/Dilatant). Tricks that work on one may have quite the opposite effect on the other, so don't take those [custard-walking videos](https://youtu.be/Iz9KnPZWOgs?t=173) as helpful advice in this situation! The correct gait will depend very much on the specific lava flow and temperature. For low viscosity flows, I suspect that running will increase the chance of Bad Things Happening, though it won't matter for very high viscosity lavas.
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GrinningX's now deleted answer referenced surface tension; assuming they don't bring it back I'll briefly mention it here as it is passingly interesting and relevant (and feel free to ask me to delete this if the answer resurfaces).
[Lava has a surface tension](https://link.springer.com/article/10.1007/BF00371487) of 350mN/m to 370mN/m. Water has a surface tension of more like [72mN/M](https://en.wikipedia.org/wiki/Surface_tension#Data_table). That's only a 5-fold increase, so unless your lava-walker weighs no more than five times as much as big [pondskater](https://en.wikipedia.org/wiki/Gerridae) (the largest of which weighs a mighty 10 grams) they'll break the surface tension and they'll need to rely on bouyancy to save themselves.
[Answer]
## It depends on the lava
**First to answer the question about consistency.**
Most lava streams are very shallow, density wise it is like walking across something between **wet cement and hot taffy (or oobleck)**. Lava varies in consistency due to composition and temprature so I can't get more detailed than that. Lava varies widely in consistency, so you can pick what you want within that range.
Lava actually ranges from the consistency of wet cement to more or less rigid, but saying it is a stream narrows it down ot the lava that can flow. of course it is possible for the top to be hardened while it is flowing underneath, in which case you have to take the thickness of the hardened portion into account. If thick it can create an oobleck like effect where the surface disperses the load over a large area.
[Source 1](https://link.springer.com/chapter/10.1007/978-1-4612-3128-8_1)
[Source 2](https://www.annualreviews.org/doi/abs/10.1146/annurev.fluid.32.1.477)
[Source 3](https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/84/11/3563/186417)
[](https://i.stack.imgur.com/dlOTX.png)<https://www.esc.cam.ac.uk/research/research-groups/cambridge-volcano-seismology/images/viscosity-graph.png/image_preview>
[](https://i.stack.imgur.com/Mc6QW.png)
**Best case scenario**
you have a cool crusted rhyolitic lava and your character can run a few step across the soft yielding surface with only slight difficulty.
**Worst case scenario**
You have hot basaltic lava and you character sinks into it and the sheer kinetic energy of the flow pulls their feet out from under them and they fall into the lava. The density is so high they cannot swim effectively and just get carried along by the flow until the heat overwhelms their protection. You could survive this only with handwavium. We just don't have materials that will let you survive this kind of prolonged conductive heat, even aerogels will conduct enough heat to burn in this amount of time.
[Book including lava working procedures.](https://books.google.com/books?id=l_7KqCtujSYC&lpg=PA147&ots=KCnMDYm4g0&dq=lava%20sampling%20precautions&lr&pg=PP1#v=onepage&q=lava%20sampling%20precautions&f=false)
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As noted in another answer, magma is both several times as dense as a human, and (mostly) has a relatively high viscosity, more like freshly poured concrete than anything we'd normally think of as liquid.
Given the question allows for small foot extensions (a few centimeters), a human equipped with suitable protection (assuming the protective wear doesn't restrict movement significantly) might bear some resemblance to a Jesus Christ Lizard crossing a pool of water: running at a sprint, so that each footstep doesn't have a chance to sink enough to cause a problem.
Assuming the distance to be traveled isn't more than about a hundred meters, an unladen human with free movement (and in good training) can run close to 10 m/s (track stars can beat that by a significant margin). There would be a learned technique to running that fast wearing what amount to clown shoes, of course, but one could train safely on suitable mud pools.
Given a [referenced link](http://adsabs.harvard.edu/abs/2004AGUFM.V51D..04B) (from comments on another answer) that magma is a non-Newtonian liquid (where viscosity is higher at higher shear rates), running for all you're worth looks even better -- you aren't dependent solely on the inertia of the material you'd otherwise displace with each step, as the Jesus Christ lizard is -- rather you get a boost from the rigidifying effect of your foot's impact. It might even be that you don't need the "clown shoes" to get the job done (you try it first).
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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.
It would be not walking, but sort of swimming.
Since lava density is times more than that of humans, even quite a shallow stream (about 40-60 cm) foot would not touch the bottom. But lava is still a liquid - a human would not be able to stand or walk on it, unless hi/she is an acrobat with special training in liquidwalking. So the human would just float on top of it in a horizontal position.
And even if a human can stand on a bottom any lava, the flow would create enough pressure to drop him/her down.
Most dangers come with lava high viscosity:
1. A human would not be able to freely move in lava. He/she would get tired very soon. Any movements in lava would be greatly slowed down. Handfull of water weighs tens to hundred grams, while a handfull of lava would be about a kilogram in mass. Swinging in lava would be very exhausting.
2. A human would not be able to counter any lava movement. He/she would be easily pulled downstream and even under the surface if there is some vertical movement.
So even a small lava stream hlafmeter across and few centimeters deep, moving at a speed of tens of centimeters per second can drop human down and pull him/her over the rocks, preventing him/her to stand up.
Only small (few meters) shallow ( < 20-30 cm) still pools of lava would be comparebly safe to cross.
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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.
Given that sort of hand-wavey protection against heat and toxic fumes, it would certainly be possible to walk on lava, though you would have to keep walking or sink in.
[Lava is a non-newtonian fluid](http://adsabs.harvard.edu/abs/2004AGUFM.V51D..04B), and there are plenty of examples of people walking on non-newtonian fluids like [oobleck](https://www.youtube.com/watch?v=q-DZ0f0_NCA) (a mixture of cornstarch and water), [custard](https://www.youtube.com/watch?v=Iz9KnPZWOgs), and cold oatmeal porridge (no video, but I've seen it in a science quiz on Danish TV). Similar to these substances, lava has low viscosity, which is more important than density ([you can't walk on liquid mercury](https://www.cnet.com/news/mercury-stand-float-codys-lab-video-liquid/)).
I imagine it being rather tiresome, since you would have to constantly adjust your balance, as when walking on a mattress - and you would not want to fall.
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The setting I'm interested in would involve a cold planet (cold enough for most bodies of water to be frozen - I'm thinking of an average global temperature of -20C or below). The simplest way would have to have the planet far away from its star. However I'd rather not deal with the low-light aspect, so I was wondering if there's a way to avoid that. The luminosity level I aim for is above 'Sun as seen from Mars'.
Having no atmosphere would be easy, but not exactly what I'm aiming for. I'd prefer an atmosphere that allows human life. (I mean in the breathing sense. Separate shielding for cosmic rays can be provided, if necessary)I'd prefer weather (eg. ground covered in snow, whether water-based or something else, which would also increase the albedo). I realize that Earth had several Snowball eras, but I'm wondering if there could be a planet with the above characteristics whose main state is 'snowball'.
Also - could this be possible with a blue star?
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Just remove greenhouse gases from the atmosphere: CO2, H2O, CH4, for example.
This would lower the amount of infrared radiation trapped by atmosphere, lowering as a consequence the temperature.
Keep in mind that since the climate is a complex system with several feed-back and feed-forward, a snowball planet would reinforce its conditions: more water trapped as ice ==> less water in the atmosphere ==> lower temperatures ==> more water trapped as ice.
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Our planet is just a few thousand years out of an ice age. To get a habitable planet covered in ice (or mostly covered in ice):
* Make the sun slightly dimmer (less radiated heat)
* Make the planet slightly further from the sun (less intercepted heat)
* Make the planet have slightly less green house gas (less retained heat)
* Be at an extreme cold point in a planet's natural heat/cold cycle
The difference you'd need to have a planet in your required range would be surprisingly slight. Any of these listed tweaks could result in a planet colder than Earth for thousands or maybe millions of years.
As a note: to have native terrestrial life, the planet would have had to have open ocean and warm land at some point to encourage flora and fauna onto the land. Also keep in mind seasonal variation. With seasons due to axial tilt, that would mean open ocean near the equator and further toward one pole for half the year. For seasons caused by elliptical orbits, that would mean open ocean for part of the year and pack ice for the other part.
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The answers you've received are great! I'd like to piggy-back off of them - specifically L.Dutch's:
We can add to this answer by incorporating volcanic activity. A decent supervolcano will start a nuclear winter. An overactive, planet-wide 'ring of fire' with many small volcanoes could potentially prevent a forever-cold feedback loop. I could have mentioned something like ozone-creation-supporting environments to prevent the needless build-up of ice + providing a weak greenhouse gas, but volcanoes are cooler haha.
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If you are talking about low light problems in the sense of people not being able to see well, you should be fine. The human eye can adapt to massive changes in light level. For example, even though Pluto receives about 1/1000 of the light as does the Earth, if you were standing on Pluto at noon you could read a book by sunlight.
To get a -20c average temperature, the orbit of Mars or just a bit beyond would be fine for a sunlike star with the right planetary conditions. But even at Jupiter's distance (which would be VERY cold), you'd get about 3% of the light you get on Earth. That may not sound like a lot but your eyes can easily handle it, as the human eye can handle about 4-stops of brightness change - a range of about 1,000,000:1. For example, a bright day outside will be about 100,000 lumens, but even a bright room like a classroom or an office may be only about 2,000-3,000 lumens. And once your eyes adapt, you can see just as well inside.
So on a planet out where Jupiter is, it would seem pretty much as bright as it does on Earth, but people's eyes would be dilated more. The amount of light would be about what you get in a well lit room indoors.
But you don't really need to go out as far as Jupiter. The equilibrium temperature at Mars' orbit is -63 degrees C. So a planet at Mars' distance with a modest greenhouse could produce the temps you need. And Mars gets plenty of sunlight - about half of what the Earth gets. The human eye would scarcely notice the difference. People would have slightly more dilated pupils and then still perceive the same amount of light.
For a blue star, just scale out the distance to correct for the higher luminosity of the star. The habitable zone of a Blue star is larger than for a yellow star like our sun, so you'd have some more room to play with distance.
Solar power, on the other hand, would have to be scaled up to match the available light.
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Some nice answers already. If you don't mind doing some math, look up effective temperature of a planet. You can design the star size, the planet's albedo and calculate the effective temperature.
Earth's effective temperature isn't too far off from -20 degrees C, in fact it's -21 C.
<https://en.wikipedia.org/wiki/Effective_temperature#Earth_Effective_Temperature>
Some problems you'd run into is that with no CO2, your planet would have a hard time undergoing photosynthesis, but you could make the planet a light color so a lot of the heat is reflected off, not absorbed, and that would significantly increase the cooling. Covering a planet with ice is one way to make it reflective.
Somebody mentioned volcanoes, but volcanoes are tricky. Volcanic soot tends to be dark and it's thought one way Earth emerged from it's snowball phase is the dark volcanic soot darkening the ice. (hypothesis not certainty).
Cover your planet with white sand and it can be nice and cold. White sand could increase it's apparent brightness as well. Create sufficient sea ice on the North and South pole or if you prefer, a permanent glacier on either pole.
YOu mentioned no atmosphere, but no atmosphere actually makes planets hot under direct sunlight. The moon for example gets very hot under direct sunlight. The atmosphere spreads the heat around, so you probably want an atmosphere.
YOu can also play around with axial tilt and seasons and cold locally vs cold globally if you like. Lots of ways to go with this.
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Deep in a laboratory far under the megacity of Exampleville, a scientist is experimenting on a new compound found in an alternate, magical universe. He accidentally knocks over a vial of Handwavium, which falls into a sink. Suddenly, the magic spreads through the city's water, instantly thickening it to the viscosity of maple syrup.
This transformation spreads at about 100 feet/second, but I'd also be interested in how the effect would be different if it were instant. Assume that any water touching the sewer or fresh water systems would be converted. Lakes and rivers are out of the scope I'm looking for; I might make that a second question.
Anyway, **how would this affect our water/sewer infrastructure, and would the effects be permanent?** These buildings are skyscrapers, and there are at least 10 million people. Precipitation and dew are obviously not affected unless they contact contaminated water. Note that there is no magic aside from the Handwavium that affects the water, so no magical answers.
[Answer]
# Most pumping systems are damaged, possibly destroyed.
Low viscosity fluids (like water) are usually pumped using centrifugal pumps, which are very efficient but generate high shear. An increase in viscosity will reduce the flow, increase the head, and markedly increase power requirements and heat production. Maple syrup levels of viscosity will make most electric pumps overheat and burn.
Some pumps will have overheating protection; most will not.
# Most people die.
The human body is mostly composed of water. Consider that a comparatively small increase in blood viscosity due to high hematocrite is enough to increase the risk of a stroke. Should the water component assume the viscosity of maple syrup, absolutely 100% of people would immediately die of both cerebral ischemia and heart attack. Pulmonary embolia would also kill, but no one will survive long enough for that.
There is a novel by Kurt Vonnegut - Cat's Cradle - that I think deals with a special form of ice (Ice IX) that freezes way above 0 °C, so that when coming in contact with ordinary water, that too is frozen into ice IX (ice IX actually [exists](https://en.wikipedia.org/wiki/Ice_IX), but has no such property).
I also remember some French novel in which a scientist developed a catalyst capable of burning water. If dropped in the Seine, it would have set [the whole world on fire](https://www.poetryfoundation.org/poems/44263/fire-and-ice).
[Answer]
Blocked pipes and sewers.
[Fatbergs](http://www.bbc.co.uk/news/uk-england-london-41577219) are already issues in sewers. Causing running water to immediately become more viscous would only accelerate the issue immensely.
In fact, it may be that the problem doesn't even spread very far, if the flow of magic relies on the water (as you might expect, given that it took being spilt down the drain to have an effect) because of the slow flow of the water.
The end result would be that the sewers very quickly stop working, leading to huge sanitary problems for the city, like [sewage flowing down the streets](https://www.thesun.co.uk/news/1363818/residents-forced-to-endure-stream-of-raw-sewage-flowing-down-their-street-for-nearly-two-days/).
In addition to that, backed up viscous water could break free, leading to disasters on its own - even viscous liquids can, given enough of it flow [remarkably quickly](https://en.wikipedia.org/wiki/Great_Molasses_Flood).
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The Earth-like planet I'm working on is the culmination of years of labor by the galaxy's best scientists. It consists of fully artificial ecosystems, and is, for all intents and purposes, like Earth. The life-forms are carbon-based and have similar structures, metabolic processes, and habits as animals on Earth. Since the scientists and engineers set things in motion, they have been monitoring the planet from the equivalent of Low Earth Orbit, in a number of spacecraft equipped to monitor the atmosphere, oceans, weather patterns, etc.
A new instrument has been proposed: a satellite capable of monitoring the movements of large groups of animals. In an effort to interfere as little as possible with the current ecosystems, the scientists removed almost all equipment and temporary artificial structures from the planet. This means, for instance, no [tracking collars](https://en.wikipedia.org/wiki/Tracking_collar). Instead, the group wants to use what is essentially an [Earth observation satellite](https://en.wikipedia.org/wiki/Earth_observation_satellite), capable of taking pictures of herds of animals.
The test target would be the near-equatorial regions, including savannas, where there is little tree cover. The various species of quadrupeds there are roughly zebra-sized, and move in groups of about 50, give or take. They aren't migratory, but they do move around in search of new food sources, as well as to avoid predators.
What I'm currently thinking about is using optical imaging, as a reconnaissance satellite might do. The thing is, I have no idea if that's enough to observe herds this small. The satellite will have to be cobbled together using spare parts, so there's not a lot of flexibility when it comes to instrumentation. I'm therefore open to other methods besides optical imaging - although I can't see to come up with any. The technology is essentially that of present-day Earth (2018).
Using optical imaging or some other related technology, can my scientists correctly identify and track herds of these quadrupeds from Low Earth Orbit? Ideally, this would be done by directly taking pictures of the herds, but if another method is possible, I'm open to suggestions.
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This is the same world as mentioned in a number of previous questions ([1](https://worldbuilding.stackexchange.com/q/39059/627), [2](https://worldbuilding.stackexchange.com/q/39117/627), [3](https://worldbuilding.stackexchange.com/q/39183/627)).
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The [angular resolution](https://en.wikipedia.org/wiki/Angular_resolution) and the correspondent [Dawes' limit](https://en.wikipedia.org/wiki/Dawes%27_limit) put an absolute theoretical max resolution to any telescope. The bigger the lens and the closer the target, the better the resolution but remember that...
* The size of the lenses and mirrors is limited by the diameter of the rocket, since these lenses and mirrors are made of a single piece (composite mirrors can be made, but they have their own limitations). With today's rockets, that's a maximum of less than 3m of diameter.
* The closeness to the target is determined by the orbit altitude. The lower, the better, but if the satellite flies too low is going to be short-lived since the atmospheric drag will brake it below orbital speed fairly quickly.
So, for a typical mirror of 240 cm of diameter we have a Dawes' limit of 0.048 arcseconds. With a typical orbit of 550 km that means a best optical resolution of 13cm. So is, each pixel of the camera represents 13 centimeters on the ground. With perfect cameras and no aberration of atmospheric losses, which of course we are not going to have.
That means that an elephant is going to be some like 10x30 pixels, but a dog is probably a blurry 4 pixels line. And that's without accounting with problems such as exposure, moving targets (both the satellite and the animals), atmospherical aberrations and the problem that a satellite can only make a picture of something every time it passes over, which usually means several hours after or even days.
You can make use of highly elliptical or other weirder orbits, such as [Molniya orbits](https://en.wikipedia.org/wiki/Molniya_orbit) which can make your satellite approach to about 150 kms of the surface for a better resolution, but it comes with a cost in timetables - the satellite can only make good pictures at the perigee.
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Yes this is possible, but at this time only with large groups of animals.
Scientists already watch colonies of penguins in Antarctica from space,bizarrely by the fact that their poo stains the snow/ice, so they actually track them using poo... i wish i was making this up
<http://www.bbc.com/earth/story/20141210-surprising-use-of-penguin-poo>
They are also capable of observing Wildebeest migration from space, however as you can see below, it's not the clearest thing to know what you're looking at, and only really acceptable because Wildebeest stand out from the grass they stand in, or roads, when the ground gets really dry, then it is possible to see the dust they kick up while moving en masse as well. but at this time this is not capable of tracking, as the satelites orbit in LEO, not geostationary so they can only take snapshots as they pass overhead
[](https://i.stack.imgur.com/TFt41.jpg)
If i were to assume you have far better quality cameras on your satellites then yes this is doable, however... you have to remember that the cameras that can take these pictures have a very very small angle on their lenses, they can't take panoramic images because, to get the high quality and high zoomed images they reduce the angle drastically so they tend to increase the size of their images by taking multiple small images and then stitching them together in editing.
then there are the other generic design requirements none of these mean it won't work, but worth considering with the design of the satelite
The longer the focal length, the harder it is to maintain the stable image due to shift of the visible field. Your average mobile phone has a focal length of 3-16mm problably. Compare it to 57,6m (f=57600mm) in Hubble
Therefore, it is preferred to have larger single pixel size (and less resolution) to limit visible shake (as movement during exposure won't affect nearby pixels) while keeping sensor relatively small (easier to produce, operate, heat, less prone to failures), as the sensor size requires larger lens, which are heavier and harder to produce.
All this affects resolution. There also radiation issues - the semiconductors in space cameras must be resistant to radiation, which changes state of cells when collides with electronic circuits. This is just a noise that needs to be detected and suppressed.
You're getting close to a next hard enemy: outer space. This means hard vacuum, containing low density of particles, low baseline temperature (under 3 deg Kelvin), that's around -270C or -454F. its cold.
But energy is still carried by radiation, coming from the Sun- it causes heating on the spacecraft. Therefore the equipment (sensor, mechanics,lens elements) must be capable of surviving both low and high temperatures.
Another issue is amount of information. The further the distance from the light source, the less amount of light can be reflected and reach the sensor. This required amplification, denoising, degraining and so on.
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If you could stretch the timeline of satellite parts by just a couple decades, you would be capable of tracking individual animals quite well.
This is a piece of Vancouver, seen with today's satellites:
[](https://i.stack.imgur.com/ku0ow.png)
Remember that satellites will be moving around the planet - each satellite can only cover a piece of land for a limited time before it gets out of view. But if you have unlimited satellites, you can track bands of moving animals quite well at any time.
Now this is visible light. [In order to see through clouds and tree canopies, you can use microwave radar](https://earthobservatory.nasa.gov/IOTD/view.php?id=80982).
Since what you really are interested in are animal movements, you don't want look at regular pictures... You want a motion map. You can do it by taking many regular pictures, and them combine them into a new image by applying the following formula:
* Pixels that stay nearly the same in all pictures are painted black;
* Pixels that do not stay nearly the same in all pictures get painted in a tone of gray. The more recent the picture that has the variation for that pixel, the lighter that pixel is - all the way to white in the last picture.
You can, of course, introduce other colors and rules as you like. The point is that you will get the path that animals have walked in the last few hours, and the more recent places they have been on will be lighter in color. Superimpose this path over any regular image, or a map of the region, and you will actually see where the animals have been. You can also add time markers on specific points, so you may learn, for example, that they tend to go into a river by day, and by night they sleep under trees or something.
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I believe the largest development for satellites in the last couple decades has been on electronics, not lenses. After all, Hubble is still taking amazing shots with just regular maintenance. With 90's technology, you would probably be able to do all I mentioned above, just with less resolution.
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Mapping satellites will just snap whatever is under them, without tracking small objects. If a satellite is made to track a certain region, they can take long exposure pictures. Hubble is a kind of satellite that does this, though it only looks are objects away from Earth. With some tweaking to look at the planet, a satellite could take a picture of a region, and anything moving object would appear in the image as a line that covers its path. This is an example of a long exposure picture taken from Earth, a piece of Newcastle, in England - notice that the blue streaks are lights from the cars that passed as the picture was taken:
[](https://i.stack.imgur.com/bzlhr.jpg)
In order to give a satellite more time over a target, simple move its orbit up. The higher a satellite is, the slower its orbital speed at that point is, so it will stay longer over an area.
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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 have a story in which a King, knowing his kingdom will fall, would like to have a scorched earth policy. The King would order all residents to begin salting the earth to ensure nothing there can grow. The city would have plenty of salt nearby as it is situated near a salt mine (I'm personally imagining Salzburg). There's some historic accounts of "salting" cities to starve people so it was thought about in the classical/medieval eras but all accounts seem to be very vague and improbable.
Let's say you were to salt a 5km radius from a city. That comes out to nearly 20,000 acres. And for a larger area, say 10km radius from a city that's an insane 77,000 acres to have to salt. And initially I wanted it a 20km radius which is 310,000 acres.
I'm not entirely sure there was enough salt throughout the entirety of pre-industrial earth to be able to salt anywhere near that much, even if only half was farmable land.
But the problem is any smaller and I can't see it being that large of an impact.
The question actually becomes three fold:
1. How much land realistically would need to be salted around a city to starve residents?
2. How much salt would this require?†
3. Even with a literal salt mine would it be realistic for an average sized kingdom to already have/have to produce that much salt within a reasonable time frame (say in under 3 months before the invasion)?
†I know different soils and different plants react to salt differently, so for simplicity assume they only grew wheat (or any other grain) in whatever soil can support the grain.
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Wow, I like counting. Soooooo:
Sowing by hand usually takes one handful every two steps. The range would be approximately **1,5 metres** wide. Assuming two steps are 1 meter one handful would be enough for **1,5 square** metres. Handful of salt (the rock one, like Himalayan salt) is around **50 grams**.
So you have 310,000 acres which is **1254527427 square metres**. Divided by that 1.5 square metres give you **836351618** handfuls needed to cover the whole area.
$$836351618 \* 50 grams = 41817.58 tons$$
Now some history, medieval salt mine Wieliczka excavated around 7000-8000(modern) tons a year [source in polish](https://www.enumi.pl/pl/artykuly/306/Kopalnia_soli_w_Wieliczce). So 5 times less what would you need. But enough for that 5 km circle.
**BUT**
What you need to take into consideration is the place and reason for salting the earth. It actually make no sense in salting earth around city:
1. enemy is at the gates, he have whole country behind him to pull resources from.
2. Salting earth was a tactic during march of the army where resources were depleted, reserves were too far away and army couldn't pull food from earth. Imagine a game where your sorcerers use all his mana on spells, there is no mana potion around, he used everything he had stored and then he meet the boss.
3. Salting the earth was more of a cheap way to poison water reservoirs. With rain the salt was transferred to wells and creeks making them unusable for humans and animals. Usually war wagons were caring only food as armies relied on water sources on the way. Also it was cheaper to just scorch the earth. Just one torch and horse and in one day you could kill food resources on dozens of kilometres. Plus with good wind you could set fire trap against enemy.
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**Don't use salt, use seawater.** It's free, it's plentiful and it has 35g of salt (mainly sodium chloride) per litre. Only salt tolerant plants can live close to the sea, where the wind will blow a bit of spray now and then, so any crop which can't survive in a saltmarsh will die. Downside is you'll have to lug barrels and barrels of seawater around, so you'd better have lots of ox carts and horse drawn wagons on hand.
**Don't use salt, set the crops on fire.** Do an actual scorched earth. You don't have to spend months preparing for it - you just send your trusty soldiers galloping around with their flint and steel to set fire to fields and granaries. Of course it won't work if its been raining for the last fortnight, or if your crops grow in paddy fields.
**People don't like doing things which will cause their children to starve to death.** They'll be refusing to do it, holding a peasants revolt, pretending to obey but actually scattering sand instead of salt, etc. And having a secret tract of land which they didn't salt, in the hope of having enough food for their family to survive.
**People can spot a way to become rich.** Hey if all my neighbours' crops die and mine don't, my grain will be worth a fortune!
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Wheat is relatively salt-tolerant; this source appears to suggest that 150 mM of salt per meter (I assume that's square meter) will reduce wheat biomass production by 50% even for resistant wheat strains.
That's almost 9 grams per meter^2. 9 metric tons per square kilometer.
Other things equal, clay soils are more affected than sandy soils, and they would already have reduced yield. There will be other salts already present which partly count so you don't have to add that much salt.
By comparison, modern corn farmers typically add 5 tons of ammonium nitrate per square kilometer. It isn't a tremendous amount by modern standards. But then, a modern nation that wanted to destroy cropland could seed it with radioactivity. The land doesn't have to be very radioactive before it will be considered valueless for farming.
The paper makes it look complicated. Less water means it takes less salt, but without enough water, yield would already be low. Some places, too much water means that saline groundwater gets high enough to hurt roots. Ignoring the complications, it's a ballpark figure of 9 tons/km^2.
(Does that make sense for Carthage, doing it with oxcarts and hand tools? I'm not sure. Wikipedia says there are no ancient sources for the story, but it was a legend as early as 1299 AD. Sowing salt over the city itself would be a cheaper symbolic gesture.)
For a hi-tech society, this is no big deal. If it's time to add fertilizer, adding salt instead is no harder. If you expect to be genocided before harvest time, then there's no particular reason not to.
<http://plantstress.com/Articles/salinity_i/salinity_i.htm>
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That depends on a myriad of other factors, how much excess food does the city produce? how much food is already stored in the city? What type of Salt mining is going on in the Kingdom? Shaft or Solution Mining? how many people live in the city. how is this mined salt stored?
Plants get their water through osmosis, this means the ratio of salt to water is higher in the root than the ground soil, so just by adding maybe about $100\space\text{grams per m}^2$ would be more than enough to change the ratio for most crops (Yes these are ball park numbers and based off logic not actual tests, and this is for most crops but potentially not all), however this also requires the salt to be dissolved by rain water, but if this number is accurate, then an acre of land would be $$4046\space\text{m}^2.$$ Call it $4000$ to make maths easier. So you would need $$4000\text{m}\times 100\text{g} = 400,000\text{g}$$ So about $400\text{kg}$ per acre...
Roughly $7\text{ billion}$ people on just under $4$ *billion* acres of arable and permanent cropland. You can more than triple this figure if you include land for cattle to graze to then be slaughtered for meat. This is about $0.5$ acres of farmland per person, or over $1.5$ acres per person if we include cattle land, and this also doesn't include the sea based food the world eats so one could comfortably extend that to 2 acres per person per year...
This is aslo with some fairly advanced farming techniques that were definitely not available in the medieval times, but these days a lot of food is wasted and some of that cropland is used for growing crops specifically for cattle or other farm animals, so that number could possibly go even higher per person... but lets assume for a minute that it doesn't...
if an average medieval city housed, say, $50,000$ people before the war, that would go down to about $35,000$ after all the men were off fighting or dying for their mean old king... so... here we go again
$$35,000\text{ people} \times 2 \text{acres/person}\times 400\text{kg per acre} = 28,000,000\text{kg}$$ But thats so that *everyone* would starve... that sort of answer. Point 1
So the question remains... how many people does your Kingdom support therefore how many acres of land would be needed to support these people.
**Excess Food**
If the city normally has about $10\%$ excess of food, this excess is normally traded away, then by simply salting $20\%-30\%$ of the farmland is likely to cause starvation for much of the populace this lessens the amount needed albeit $20\%$ of $28,000$ tonnes is a meager $5,600$ tonnes still one hell of a lot to be stored unused... this sort of answer point 2
**The Farmers**
Remember very few kingdoms in the medieval times had permanent armies, most were men that had jobs and were conscripted in times of war. If the King is about to lose, then it suggest that many of the farmers would logically already be dead or encamped elsewhere fighting the war for their king, and therefore would not be home to tend to their crops, therefore the yield of those fields would be a lot less, before the salting even began
**Stored Food**
Most cities in medieval times couldn't last on their stored food for more than a year, so rather than salting the earth, simply burning the crops to the ground would cause starvation for the populace, as it would take another full season for those crops to be grow, providing there was even a stock of seeds to do so
**Stored Salt**
Salt is hydrophilic, this means it actively absorbs water and therefore is not stored correctly then it will absorb moisture from the air, and begin the process of dissolving away into a Salty Brine that would then leak away
**Type of Mining**
If Shaft mining is the type used, then no realistic amount from medieval times would be enough to salt all the land to the point where no crops can grow, this unfortunaetly answers point 3
If it is solution mining, then an alternative is fairly simple, have the pumps that bring the Salty Brine to the surface be pumped directly onto the farmland, or have the the king could organised basic pumps to flood the farmland with salt water, sea water wouldn't be as potent as raw salt, but the Brine would be, and both far easier to do, and dependent on the terrain of the kingdom, may be able to flood much larger areas then you are hoping for, however would it be enought? doubtful
Another option is to pump the brine solution or poor the salt mine stores into the "presumably Nearby???" freshwater lake or river, this would (again dependent upon how well it was performed) turn the kingdom's fresh drinking water into salt water. potentially far more damaging to the invading force then even salting the farmland. however it would not be a permanent thing, unless it was a truly massive amount into a lake, then the river would eventually clear the excess salt
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I’m not sure that actual salt was used to ‘salt’ the land. Certainly it’s unlikely to have been anywhere near pure, as for much of history, salt has been expensive - the Romans famously paid their soldiers with salt. So any ‘salting’ would likely use inedible rock salt at best.
More realistically, here’s a description of a ‘scorched earth’ policy from the Bible: “They destroyed the towns, and each man threw a stone on every good field until it was covered. They stopped up all the springs and cut down every good tree.”
(Woah, font size changed when I pasted and can’t undo it on mobile...)
The stones from the town walls were carried and thrown on the fields; I wouldn’t imagine them literally covered with no soil showing, rather that there’s enough stones to prevent ploughing. Clearing the land of stones would then be a large job, and rebuilding the walls also, as you’d need to wander the area to re-collect the stones. The springs would probably be filled with the stones also, and the ‘good’ trees - probably the fruit trees - cut down.
It’s entirely feasible to significantly damage the fields around the city to make Re-developing it very difficult, but doesn’t require salt.
] |
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[
Building on this question about space exploration on the slopes of a [50 mile high volcano](https://worldbuilding.stackexchange.com/questions/96872/exploration-of-a-50-mile-high-mountain), I'm curious what would happen when the volcano erupts.
The volcano is:
* 50 miles high, just on the edge of official space at 62 miles (100km)
* [Shield volcano](https://en.wikipedia.org/wiki/Shield_volcano). 2 or 3 degree slopes at the base. Max, 10 degree slope at the summit.
* As shield volcanos tend to do, this one is erupting more or less continuously, though because of how shield volcanos work, there are no explosions without water.
* Every thousand years or so, a bunch of water laded lava makes it to the summit providing delightful fireworks
* Set on an Earth analog. Gravity, atmospheric parameters, atmosphere structure, weather systems, climate, geology are all equivalent to Earth.
* The mountain is held up by magic. (Yes, I know that mountains/volcanos never get this high on Earth and the reasons for this. Why this is falls outside the scope of this question.)
* There is one main vent at the top of the volcano of interest to this question. While, there are other smaller vents further down the slopes of the volcano, I don't really care about them for this question.
**I'm interested in the immediate atmospheric effects of injecting large quantities volcanic gases at 50 miles up.**
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What we're concerned with here is the [eruption column](https://en.wikipedia.org/wiki/Eruption_column) and subsequent plume arising from the volcanic eruption. This is a shield volcano, so it's not going to erupt *a la* Mount St. Helens; rather, it will slowly spew out material. Granted, for a volcano this large that's still going to be quite the eruption. First, let's figure out some basic properties and quantities:
* **Height:** 50 miles, or about 80 kilometers, as you stated. Obviously, no mountain should be this tall, but that really doesn't matter.
* **Radius:** Given an average slope of about $5^{\circ}$, the volcano should have a radius of $\sim80\text{ km}\tan(5^{\circ})\simeq914\text{ km}$. This means that the volcano should be more than one half as wide as the United States, and about three times as wide as [Olympus Mons](https://en.wikipedia.org/wiki/Olympus_Mons).
* **Rate of mass ejection:** The [Volcano Explosivity Index](https://en.wikipedia.org/wiki/Volcanic_Explosivity_Index) (VEI) ranks how powerful a volcanic explosion is. The top level is VEI 8, ejecting over $1000\text{ km}^3$ of material. Let's assume that this volcano ejects $4000\text{ km}^3$ of material over a period of one week. Assuming typical ash densities of perhaps $1500\text{ kg m}^{-3}$, this gives us $Q\sim10^{10}\text{ kg s}^{-1}$. [Carazzo et al. (2008)](http://www.ldeo.columbia.edu/~ruprecht/Site/Classes_files/Week8_Carazzo.pdf) lists values for other eruptions (see Table 1 and Table 2). Our $Q$ is two orders of magnitude greater than most Plinian (think high, tall plumes) eruptions, and about the same as many explosive eruptions producing pyroclastic flows. Ours simply lasts a lot longer.
Let's start with a simplified model, namely, a [Gaussian plume](https://ansn.iaea.org/Common/Topics/OpenTopic.aspx?ID=13012). This means that the concentration of the material, $C$, is
$$C(x,y,z)=\frac{Q}{2\pi U\sigma\_y\sigma\_z}\exp\left(-\frac{y^2}{2\sigma\_y^2}\right)\left[\exp\left(-\frac{(z-H)^2}{2\sigma\_z^2}\right)+\exp\left(-\frac{(z+H)^2}{2\sigma\_z^2}\right)\right]$$
where
$$\sigma\_y=\sqrt{2Dy\frac{x}{U}},\quad\sigma\_z=\sqrt{2Dz\frac{x}{U}}$$
and
* The wind is blowing in the $x$-direction with speed $U$, which might be $25\text{ m/s}$, or $56\text{ mph}$.
* $y$ is the $y$-coordinate and $z$ is the $z$-coordinate.
* $H$ is the reference height - in our case, $80000\text{ m}$.
* $D$ is the diffusion coefficient, which is probably $\sim10^3\text{ m}^2\text{ s}^{-1}$.
There are some assumptions the model makes:
* The opening is roughly point-like.
* In our case, we assume that the diffusion coefficient is isotropic, i.e. it is *not* directionally dependent.
* This is a "steady state" solution, meaning that it is approximately constant. This works well for a week-long event.
* The atmosphere (and gravity) are homogeneous and don't affect the plume *too* much. On large scales, this assumption doesn't always work.
I wrote some Mathematica code to look at the concentration of the plume as a function of distance. This code currently outputs a contour graph in the plane $y=0\text{ m}$. It is cut off at $x=25\text{ m}$, because otherwise the densities near the opening are too large and make it hard to see the rest of the contours.
```
U = 25;
H = 80000;
Diff = 1000;
Q = 10000000000;
Sigmay[x_, y_] := Sqrt[2*Diff*Sqrt[y^2]*x/U];
Sigmaz[x_, z_] := Sqrt[2*Diff*Sqrt[z^2]*x/U];
Conc[x_, y_, z_] := Q/(2*Pi*U*Sigmay[x, y]*Sigmaz[x, z])*
Exp[-y^2/(2*(Sigmay[x,y)^2)]*(Exp[-(z - H)^2/(2*(Sigmaz[x, z])^2)] +
Exp[-(z + H)^2/(2*(Sigmaz[x, z])^2)]);
TopView[x_, y_] := Conc[x, y, H];
SideView[x_, z_] := Conc[x, 0.001, z];
ContourPlot[SideView[x, z], {x, 25, 10000}, {z, 78000, 88000},
PlotRange -> {{25, 10000}, {78000, 88000}, All}, Exclusions -> None,
PlotLegends -> Automatic, Contours -> 50, ContourLines -> False,
RegionFunction -> Function[{x, y, z}, y - 80000 + 0.0875*x > 0]]
```
This outputs the following plot:
[](https://i.stack.imgur.com/PXyU0.png)
Notice that even two kilometers away from the summit, the plume is still incredibly dense. Its density doesn't become negligible until it's hundreds and hundreds of kilometers away from the summit. If you were to raise the upper limit on $z$, you would see that the plume rises to a height of over $160\text{ km}$! That's way beyond the upper limit of the mesosphere. And to be honest, I think I've been conservative in my estimate for $Q$.
Is this realistic?
First, let's consider what kind of eruption we're dealing with. It's a shield volcano, so most of the material that comes out will *not* be in the plume. However, as I said before, I likely underestimated $Q$, and so such a plume isn't that unrealistic.
That final height of the plume - $\sim80\text{ km}$ - seems a bit much. However, it's really not that far-fetched. In general, the relationship between plume height $H$ and $Q$ is
$$Q\propto H^4$$
[Kaminski et al.](http://www.ipgp.fr/~kaminski/web_doudoud/eyjafjoll_JGR2011.pdf) use the equation
$$Q=aH^4+b$$
where, for $12\text{ km}\leq17\text{ km}$, $a=258\text{ kg s}^{-1}\text{ km}^{-4}$ and $b=-4.6\times10^6\text{ kg s}^{-1}$. We can assume that $H$ is going to be even greater than $17\text{ km}$, so we should expect the result to be close but not totally accurate. Rearranging, plugging in for $Q$ and then solving yields a total plume height of $79\text{ km}$ - which is *very* close to what Mathematica told us. Perhaps that result isn't too ridiculous after all.
One thing you'll need to consider is [column collapse](https://en.wikipedia.org/wiki/Eruption_column#Column_collapse). It might be the most important factor behind the eruption's evolution. An eruption column will collapse when the bulk density of the material (a combination of its density and the density of the air inside the column) becomes too dense compared with the air around it. Looking at [some standard atmospheric tables](https://www.engineeringtoolbox.com/standard-atmosphere-d_604.html), we can see that the mesosphere is not at all dense, meaning that collapse is highly likely. The plume will form, certainly, and material will travel hundreds of kilometers (during which the Gaussian plume model is a good fit), but it won't last for that long.
So, what happens then? Well, the material now coming out of the volcano will form [pyroclastic flows](https://en.wikipedia.org/wiki/Pyroclastic_flow), which scare the living daylights out of me. They are fast, dense and hot, and destroy anything in their path. And they will begin by rushing down the mountain at fairly high speeds, and probabaly will not stop quickly. Assuming these flows reach high speeds ($300$-$600\text{ mph}$), they'll reach the base of the volcano in a few hours, after ruining anything on its slopes. An area the size of a medium-sized country will be decimated.
It's unclear what will happen when the flow reaches an atmospheric layer with a density high enough to support an eruption column. I'll have to get back to you on that. It's possible that the gas will form clouds of ash and soot at that altitude, which would then spread out even more. That said, that's currently just a conjecture on my part.
Here's the bottom line:
* Ash, gas and dust will be spread for hundreds of kilometers away from the volcano - possibly up to $1000\text{ km}$ or more.
* A plume will rise into the mesosphere and possibly low thermosphere before collapsing; I don't know how high it will actually go.
* Pyroclastic flows will then descend from the mountain, destroying anything on it. Any further atmospheric affects will be from them.
[Answer]
At the mountain top the atmosphere would be so thin that it would not be able to hold any significant amount of suspended dust particles. Most dust and other ejecta from the volcano would quickly end up on the ground around the vent and spread out further downhill depending on how energetic the eruption was. If in sufficient quantities this could cause landslides of ash down to lower levels.
The gas from the eruption would spread out into the mesosphere where it would probably form a band of gas around the entire planet. The effects of injecting the gas would very much depend on how much was injected. If sufficient was injected it would likely have a strong greenhouse effect, especially as particulates such as sulphates would probably fall back to earth relatively quickly. The effects would be longer lasting than gases injected into lower levels of the atmosphere but might spread out more rapidly.
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**I applaud HDE's effort but I have to disagree with his fundamental approach**
* First, a 50mi volcanoe on Earth would be impossible but ill ignore that for now
* Earth's Atmosphere is roughly only 62 miles high so that leaves 12 miles between the summit and the edge.
* at that altitude air pressure and gravity is much smaller (easier to obtain escape velocity)
* the volcano itself is effectively a cannon barrel
* the amount of energy needed to travers the 50 mi mountain would likely cause the amount to explode rather than shoot up.
The amount of energy needed for this volcano to erupt would likely send debris into outer space as well as orbit. Dust and gas would likely permeate the entire atmosphere with planet wide impacts. This could even form a planetary ring that would cause impacts for centuries to come. In short this would be a super volcano greater than yellow stone, capable of causing multiple and subsequent extinction level events.
] |
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[
I’ve seen a lot of questions on here about the possibility of more than two sexes but I’ve found nothing on the possibility of only a single sex. The closest thing I’ve found is [isogamy,](https://en.wikipedia.org/wiki/Isogamy) is there any way to scale that up into complex sentient beings? Or is there another way?
Question: Is it possible for a species to have a single sex? - As in no male or females only one reproductive type.
*(As much more neatly put in the comments by Slarty: There is just one sex but two organisms of the same type are required to reproduce.)*
[Answer]
# Remove the Y chromosome
I'm going to use mammalian humanoids since that's easier for my brain to work with.
Regardless of whether there's a single sex or multiple sexes, the embryo always has to start from an egg. The egg must have plentiful resources for growing and must contain all the DNA required to mature into an adult organism. Lacking either of these characteristics, the egg won't fair as well as an egg that does have these characteristics.
If the author requires two parents, then it's not possible to choose "males" since male gametes lack the cellular infrastructure to grow into a fully-formed embryo. Thus, we have two egg donors that mate (somehow). Which or both of the parents gets to be pregnant is left as an exercise for the author.
# Fertilization
Somehow (handwaving) the two eggs find each other and fuse together. Some mechanism transfers DNA between the eggs and that DNA is recombined with the host egg's DNA. After DNA transfer is complete, the two eggs separate to find their own spot on the placenta. The process of becoming an embryo begins in earnest. As a result of this process, pregnancies are almost always twins. Although, depending on how the rest of the organism is designed, [resorption](https://en.wikipedia.org/wiki/Vanishing_twin) (WARNING: icky pictures) to produce only a single offspring may be possible.
# Conclusion
With two egg donors, it's entirely possible to have a species that only has a single sex.
There are some very interesting implications on nurturing juveniles with this system. Females with non-precocious young usually spend a lot of time caring for and protecting their young while males go off and do things (namely, get other females pregnant.) Since both parents are the same sex and are both liable to get pregnant, I suspect a more communal child rearing environment would work better.
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I think it would be very difficult, though you could create a world where it could occur.
If we may work backwards, the tremendous ubiquity of sexual reproduction should be a strong indicator suggesting that there's an advantage to it over other reproductive approaches. Indeed, we see sexual reproduction *later* in the evolutionary tree than other approaches such as isogamy, which suggests that it has a higher fitness for reproducing "advanced" organisms than other approaches.
Now I won't be able to bring up a full scientific argument for why this is so. Sexual reproduction is buried so deeply into the genetics of our ecosystem that it would be folly to try to claim to have "the one reason" why sexual reproduction works better. However, with a little hand waving, we can try to build enough of an argument to build a world which stymies these advantages, leaving readers to ponder whether it is indeed possible.
If I wanted to grab the biggest part of the advantages of sexual reproduction in one topic, to make it easy for a reader, I'd say the big advantage is differentiation. Sexual reproduction creates a very strong opportunity for differentiation into two different classes of individuals with common DNA between them. If there is value in differentiation, this provides a powerful place to do it.
I think we can generally say that any sufficiently hostile environment to make an interesting story (say, Australia) is going to select for differentiation. It's just too useful. However, perhaps your planet can cause differentiation to happen later.
For expository purposes, let's call the two differentiated sides of your species masculine and feminine. We H. sapiens are familiar with the meaning of those gendered terms, so it's convenient. Now what if your planet had a long chaotic cycle, on the order of 30-50 years. Perhaps its weather, or maybe it's some alignment of some god-awful trinary star system (the stability of which is a separate question). Regardless, it may be very effective to have a large number of non-sexed children, waiting to see what the planet does before adjusting the mixture of masculine and feminine to fit. Maybe 10 years into their life, we find that the planet has created an ecosystem where boisterous strong stubbornness is needed. Then an entire generation can take the path towards the masculine side right then and there.
If your species took this path, it would have to take care not to rely on sexual reproduction. If the phases of the planet demand a vastly masculine approach, there may not be enough females to sustain the population. Likewise, if the population needs to be mostly feminine to get through a subtle crisis, there may not be enough genetic diversity left in the few masculine individuals. This would create a strong incentive for the species to be able to mate regardless of such a gendered arrangement.
The price, of course, would be that the differentiation happens later. If there were value in differentiating early (such as teaching one half of the species child rearing from day 1, literally), then that would encourage sexual differentiation. Since you don't want that, you need to make sure that there's value in waiting until you have more information about the perils that your species faces. That'll ensure there's selective forces to make the differentiation happen late.
If the planet isn't enough of a force to compel your species to evolve for late differentiation, you can always borrow some [spiders](https://news.nationalgeographic.com/2015/05/150518-spiders-australia-silk-webs-animals-environment/) from Australia. I don't know if a swell of spiders will encourage masculinity or femininity, but if you'll excuse me, I'm going to go jump in my wife's arms now while shrieking like a little girl.
[](https://i.stack.imgur.com/aGkwQ.jpg)
(Credit: [National Geographic](https://news.nationalgeographic.com/news/2012/03/pictures/120307-spiderwebs-australia-floods-wagga-wagga-world-science/))
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Sexual reproduction between diploid beings (have double chromosomal endowment, have it and mix) is *one* way our specific evolutionary lineage found to "mix & match" genetic characteristics from one generation to the other.
This fact (mix useful mutation and spread them, not necessarily the way we do it) gives a huge boost to whatever being "invents" it.
It is arguable there are other mechanisms to achieve something similar (in truth we already know this is [possible](https://en.wikipedia.org/wiki/Bacterial_conjugation), at least for unicellular beings), but it's clear that, once the method has been discovered, all beings lacking it are at a serious disadvantage.
This for two reasons:
* diploid beings are much more resilient to "single damage" (this is more serious than it seems, because the "damage, if not immediately fatal, can be the stem of "further development).
* new developments can be "tested in the wild" with less negative impact.
Currently haploid beings are limited to:
* unicellular
* specific subsexes (male bees)
* some very strange [occurrences](http://onlinelibrary.wiley.com/doi/10.1002/bies.10044/abstract)
From there evolution of "sex" as we know it is a "natural consequence", but may well not be the *only possible* consequence.
So the answer is: Yes, it's conceivable to have beings exchanging genetic material in a "aequalitarian" basis, but what it could be is really pure speculation and I won't venture in it.
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[Sequential hermaphroditism](https://en.wikipedia.org/wiki/Sequential_hermaphroditism) is not exactly what you're asking for but may be of interest.
Some fish (and amphibians and invertebrates) spontaneously change sex either as a normal part of their life-cycle or in response to their social environment.
In a fictional world, it could potentially occur in intelligent species.
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A neonatologist (doctor who cares for newborns) I talked to recently pointed out that a larger percentage of babies need serious medical care after being born. This change came about about a generation after some serious improvement in the way we care for premature and sick babies in the 70s and 80s. He concludes that the genes that make it impossible to give birth without the help of advanced medical infrastructure are already spreading in our society.
If you take this doctor's assertions to the (possibly ridiculous) extreme, you might imagine a race of highly advanced being with no reproductive organs at all who are only capable of reproducing by combining genetic material in a lab. You and your partner both swab your cheeks, pay the fee, and in nine months the lab calls you in to make you parents.
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Male and female crocodiles have all the same chromosomes. Their sexual differentiation is determined by the ambient temperature when they develop in the egg.
There are flowering plants which produce flowers with both male and female structures, combining both sexes in one structure. So that means individuals are all the same sex.
So let's combine the two: what if instead of sexual differentiation in the egg, crocodiles just went the way of flowers and each individual just got both types of reproductive organs. They would still need two partners to reproduce but the roles would be interchangeable (or determined by some sort of mating fight, more likely).
I think such a thing would be evolutionarily possible if at the beginning there had been a lot of near-extinctions and communities where the sexual differentiation continued further to form only-male and only-female individuals did not manage to survive them.
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**Yes**.
While many reproduction strategies exist, they boil down to two basic methods. [Asexual reproduction](https://en.wikipedia.org/wiki/Asexual_reproduction), where a single organism reproduces using its genetic material in the offspring, and [sexual reproduction](https://en.wikipedia.org/wiki/Sexual_reproduction) which involves two organisms who exchange genetic material after it was shuffled by [meiosis](https://en.wikipedia.org/wiki/Meiosis).
There are over 65,000 species of [Hermaphroditic](https://en.wikipedia.org/wiki/Hermaphrodite) animals (not including plants), so there is no reason that I see why an organism could have a reproduction technique such that both partners give and receive gametes during mating.
[Answer]
Research at University of Oregon used *C. elegans* to study this. *C. elegans* are hermaphrodite and carry both male and female organs. They can be programmed to cross fertilize or self fertilize. So they took two batches, one batch they programmed them to cross fertilize and another to self fertilize.
They found the group that cross fertilize , would show more mutations , and so better able to adapt in the wild.
<https://www.youtube.com/watch?v=pEc0DI-n4Pk>
Hope that helps.
[Answer]
Sure. There are plenty of organisms that mate to reproduce but all have the same sex. However, unless you're going for an organism that can reproduce asexually, this creates a problem of self-fertilization. Gametes are generally produced *en masse*, and you don't want them to be combining with each other before they leave the body, so there needs to be some way to ensure that the gametes don't recombine. There are two main ways to prevent this.
### Isogamy and mating types
For some species, all gametes look basically the same, unlike organisms with two sexes where the egg cell is bigger and the sperm must seek out the egg. To avoid self-fertilization, such species have what is called "mating types" - an individual can only mate with another who has a different mating type. Now this might seem like a cheat (since mating types are basically sexes with a different name) but many species can have up to hundreds or even *thousands* of different "sexes", all of them physiologically identical, rendering the distinction moot. Any individual can mate with any other individual provided they don't have the same mating type, and the chance of another individual having the same type is very low. Many fungi use this system.
Imagining isogamy in an intelligent species would be interesting, but as long as there were enough mating types, they might not even know that mating types exist until their science develops to that point. Anyone could mate with anyone else, and one out of a few thousand couples would just be unable to have children and nobody would know why. Or maybe they would have pheromones that would simply cause them to not be attracted to another individual with the same mating type as themselves.
### Hermaphrodites
Hermaphrodites are organisms with two kinds of gametes, and each individual has both male and female parts. Technically, it would be possible for such an organism to self-fertilize, but they are usually constructed in a way to make this physically impossible (or at least unlikely). Such organisms usually exchange gametes during mating, causing both to produce children as is the case with snails and earthworms. Flatworms will fight for dominance; whoever gets stuck first must bear the children. Many plants are hermaphrodites as well and avoid self-fertilization by having the male and female parts develop at different times.
[Answer]
there are plenty of [**Asexual**](https://en.wikipedia.org/wiki/Asexual_reproduction) organisms.
I believe the majority of microbes are asexual.
Mitosis is an asexual process and genetic divergence happens with that all the time (cancer).
Even some trees can have an asexual reproduction cycle in the absence of a mate.
**Let me clarify Asexual Reproduction**
Asexual reproduction is when a single organism reproduces without a partner. Once you add a partner there becomes the ambiguous differentiation of sex. These gender distinctions don't boil down to sperm and egg exclusively but more the roles the different parties play in reproduction. So in effect its impossible to have genderless non asexual reproduction. Even in certain fish who trade off being the male or female are still at one point male, female, neutral.
] |
[Question]
[
There are a lot of acids in the world, many of them present in biological creatures. Humans, for instance, have hydrochloric acid in their stomachs. What I'm wondering here is just how nasty it could be if one such creature could use such an acid as a weapon. I suppose this is a two-part question: **just how nasty could that acid be**, and **what would the creature have to be like in order to use it effectively**?
I'm envisioning a creature (not necessarily intelligent) that spits acid at its prey, hopefully at a distance of more than a few feet, but feel free to poke holes in that assumption if you come up with something creative. Ideally, it should be able to use acid like what one might see in answers to [this question](https://worldbuilding.stackexchange.com/questions/82204/is-there-a-real-life-substance-like-movie-acid), but that might not be realistic. If it comes down to a choice between two (or more) acids that would be better against different targets (flesh versus metal, for instance), I'd like to see the choices outlined, but you can assume this creature would be using its acid for hunting, not destroying buildings.
You can include suicidal examples for the sake of a thorough answer, but I'm looking for something that can actually survive using its own acids without serious side effects. Surviving its own acids being used against it, like if it was fighting another of its kind, would be interesting but is not required (although it's obviously detrimental if it can't eat any prey it used its acid on, so it should at least be able to survive ingestion in small quantities).
For the purposes of this question, I'm focusing on how the creature could plausibly do this naturally, without magical or technological assistance. An answer with evolutionary reasoning behind the development of such a trait would be a bonus, but genetic engineering is allowed if necessary.
[Answer]
I think perhaps a more practical approach would be a creature that spits or projects two substances which are relatively unreactive apart, but which will combine spontaneously with each other in a violent or corrosive way.
A create doing this might store these liquids (or something in liquid suspension) in two separate areas of the body and the propel both out aimed at the same point. Both will combine on impact and burn or corrode.
This avoids the need for extremely corrosive acids to be stored or moved internally.
I'm afraid my knowledge of biochemistry is too limited to go beyond the concept, but I think it would be worth exploring for your creature.
I've made this a community wiki so that others can easily expand or contribute to this without comments getting out of hand.
[Answer]
Many naturally occurring acids such as formic acid used by ants or citric acid found in citrus fruits would be useful as temporary blinding agents although these are not strong acids concentrated solutions of them can still be dangerous to the eyes.
The problem with strong acids is their ability to damage the creature storing them. Making this difficult, but perhaps not impossible. Some nasty acids that might be worthy candidates:
Hydrofluoric acid: A colourless liquid. The fluoride ion is very small and is readily adsorbed through the skin causing severe burns.
Aqua Regia: a mixture of hydrochloric and nitric acid acids in the proportions of 3:1. It is a fuming orange liquid that is powerful enough to dissolve metals such as Platinum and Gold under the right conditions.
Sulphuric acid: a clear liquid which also has powerful oxidizing and dehydrating properties and also causing severe burns.
As a very rough rule of thumb the rate of chemical reaction doubles for every 10 degree C rise in temperature, so to be even more effective the acid should be as hot as possible.
One solution to prevent the acid burning the source is to create or activate a substance immediately before use. Such a method is used by the Bombardier beetle (although this is not an acid spray it is very unpleasant).
<https://en.wikipedia.org/wiki/Bombardier_beetle>
[](https://i.stack.imgur.com/jnFGJ.jpg)
[](https://i.stack.imgur.com/Iq9nG.png)
**Proposal**
If you wanted to make a more devastating acid attack version then perhaps use a large bombardier beetle type weapon but also carrying a third chamber containing [oleum](https://en.wikipedia.org/wiki/Oleum). The oleum on its own is nasty enough but if oleum is added to the spray as it is fired it would be very unpleasant indeed.
The bombardier beetle carries supplies of hydrogen peroxide and hydroquinone solution which react together to produce steam. Oleum is effectively dehydrated sulphuric acid (also known as pyrosulfuric acid H2S2O7) so what you would end up with is a spray containing hot concentrated sulphuric acid as the steam reacts with the oleum to produce sulphuric acid. Oleum and sulphuric acid also get hot when mixed with water (or steam) increasing the temperature further. I think pure oleum is a solid but it becomes liquid if a little water is added.
[Answer]
The [vinegaroon](http://what-when-how.com/insects/vinegaroons-insects/) does spray acid.
screenshot from <https://www.youtube.com/watch?v=snv3uoTZHBE>
[](https://i.stack.imgur.com/QdhqB.jpg)
Vinegaroons are arachnids; cousins of spiders and scorpions. The spray is defensive, hunting being done in the manner of solfugids, scorpions and the like (grab thing, hold on, eat it). The spray is a mix, being mostly acetic acid.
from <https://thetransientbiologist.wordpress.com/2014/01/10/the-biochemistry-of-defense-vinegaroons/>
>
> As the name implies, this creature has a tail from which she can quite
> accurately, aim and spray a chemical defense: acetic acid, aka
> vinegar, which is where it gets it’s more appropriate name, the
> vinegaroon. So normally, vinegar is a very low percentage of acetic
> acid. The vinegaroon actually has the highest concentration of acetic
> acid found in nature: 84%.
> This chemical is used defensively, primarily other things with
> exoskeletons. The vinegaroon has a slight problem though. Although
> acetic acid is quite a wonderful defense on soft fleshy parts, it is
> water soluble and will roll off of an exoskeleton of it’s attacker
> without harming it. So it needs to employ another tactic. Mixed with
> the acetic acid is another acid, caprylic acid, which is able to move
> through the waxy cuticle of the exoskeleton. This mixture with spread
> to cover more area as well as actually getting under that exoskeleton
> so it can do some damage. In the end, when the mixture is actually
> shot out of two storage compartments in the vinegaroon it is composed
> of 84% acetic acid, 5% caprylic acid, and 11% water.
>
>
>
from <http://what-when-how.com/insects/vinegaroons-insects/>
>
> Over years of experimentation in which M. giganteus has been
> challenged by numerous and varied vertebrate and invertebrate
> potential predators, no examples of successful predatory species that
> normally encounter adults or fourth instar immatures have emerged. A
> reason for this paucity of meaningful predation is rooted in the
> exceptional deterrence of the vinegary allomone discharged by
> threatened individuals. Rodents, lizards, toads, spiders, centipedes,
> large carabid beetles, and solifugids flee and rub affected body parts
> in the soil when struck with the chemical discharge. Even voracious
> and determined grasshopper mice (Onychomys spp.) are unlikely to be
> serious predators because when sprayed they flee and plow their mouths
> through the sand, giving the vinegaroon ample time to escape
>
>
>
So how strong is this? Strong enough to irritate predators and buy time to flee.
Here is the problem with acid as an offensive weapon: it does not have much knockdown power. Acid expends itself fast against body tissue, especially wet tissues. If I am doused with sulfuric acid it will hurt like crazy, but I can turn and run as fast as I could before. I might die of my infected burns after a while, and so a Komodo dragon type strategy might work (they bite then track the prey for days or week, waiting for it to die of infection). But compared to venoms, acids are poor tools for predators.
One cool thing about the vinegaroon is that it has evolved mechanisms to get more out of the acid punch - a second acid that enhances activity against exoskeletons, and a slew of chemicals in smaller proportions that (I think) make the stuff stink worse.
[Answer]
There are actually quite a number of creatures that prefer to digest (or partially digest) their food *before* eating it. Spiders inject digestive juices into their prey and suck out the organs, leaving the exoskeleton intact. Houseflies have a sponge-like mouth; they eat by spitting up acid onto their food and mopping up the liquefied result. An acid-spitting creature could easily evolve from a creature like this; starting by using its acid in self-defense (perhaps by spraying the eyes of a predator) and gradually moving toward making it their primary hunting tool.
In general, an acid can be made stronger by simply concentrating it. Plain old hydrochloric acid (found in the stomach) is extremely corrosive when concentrated and can cause serious damage to organic materials in *seconds* - the concentration in our stomachs are pretty low so you don't dissolve your mouth when you throw up, but it *could* be higher in a species that had use for it.
] |
[Question]
[
I would like to genetically modify a human being in one concrete case like I did in other parts of my little series of [How would it affect a human to suddenly...](https://worldbuilding.stackexchange.com/questions/91230/how-would-it-affect-a-human-to-suddenly-have-the-visual-senses-of-a-martial-eagl) This time I would like to add a pretty long foxtail and get a feeling for how much muscle mass would be needed to make the modified human able to move his new tail around.
The foxtail will be an appendage to his coccyx and I would like to ignore the question about *How* this transformation exactly happened. For this little experiment I want to use simple up-scaled data from the [Arctic Fox](https://en.wikipedia.org/wiki/Arctic_fox), which normally has around 55 cm head-and-body length plus 30 cm tail length. To make it easier I will assume that the length of the tail is roughly half the length of the head-and-body. Thinking about humans head-and-body length is quite different from what we normally perceive as height. Still, using the normal height seems convenient and postulating that the human in question is supposed to be around 1.80 metres tall we get a tail with a length of 0.9 metres. Let's pump that up to 1 metre for ease of calculating stuff.
The above shows that I am not really picky about numbers when genetically modifying humans, but I would like to get a feeling for the amount of muscles needed to have control over such a long tail. For example the arctic foxes can, according to the linked Wikpedia article, curl up into a little ball of fur when sleeping so that they won't lose as much body heat. And it would be quite bad if the tail was always dragging around the floor.
I couldn't find any numbers about muscles needed for tail control. Furthermore my knowledge of how tails work in animals is best called *rudimentary*. I would like the human to be able to control the foxtail in such a way that he can for example wrap it around himself like a little fluffy blanket.
If you need more information about what I have in mind I can refer you to a picture I linked in my first question on the site ([The role of anthropomorphic foxes in a medieval army](https://worldbuilding.stackexchange.com/questions/68131/the-role-of-anthropomorphic-foxes-in-a-medieval-army)) which is of the *League of Legends* character [Ahri](http://pre03.deviantart.net/a6f8/th/pre/i/2014/203/3/a/ahri_fox_fire_lol_wallpaper_by_77silentcrow-d7rrntx.png). The picture depicts multiple tails that are far longer than I am interested in for the scope of this question, but it might give you an idea of what I want the tail to look like and be able to do as you can see how the different tails twist in different ways.
If I simply scale a fox's tail to the above size how much muscle mass would I need to add to my human? It would be very nice if answers could compare this number to something else that might be easier to grasp, for example whether this would be more muscle mass than people normally have in their biceps.
[Answer]
**Back of the envelope ~ 0.4 - 0.9 kg for just the muscle and 1-2kg for the tail as a whole**
First, this image may help you get a feel for tail anatomy. It is a fox who has lost all of its hair, either due to a genetic disorder or mange, but you can see how much tissue there actually is to the tail. That is why holding them up all the time takes so little effort.
[](https://i.stack.imgur.com/37YrP.jpg)
You can have a look at the musculature in this image from this [site](https://www.joshuanava.biz/animal-anatomy/pectoralis-profundus-pectoralis-minor-dog-and-feline.html).
[](https://i.stack.imgur.com/E3qnd.jpg)
Now let's work on our estimation. The musculature of a cat and dog tail is identical, and you will have more luck finding information on cat tail masses in that range. Cat tails are proportionally longer, but that will not affect the musculature or weight estimate significantly since we are not going to use body mass of your people. Body mass based estimates would not work for such a different body anatomy, so instead let's find a tail close to what we want.
Cheetah tails are something we actually have a little [data](http://ajplegacy.physiology.org/content/227/4/848) on but it is all [estimation](http://ieeexplore.ieee.org/abstract/document/6386240/). No one has been willing to chop off tails of an endangered species to get mass estimates. A large cheetah's tail is around 80cm long and weighs about ~1-2kg. That's just about perfect since a fox's longer hair will add length getting us to at least the 1 meter you want. So your entire tail should weigh about 1-2kg. Now we have to do some back of the envelope calculations.
A tail is basically little more than skin, muscle/tendon, and bone.
Let's start with the upper estimate. We shave off ~20% to account for the skin and hair, so that gets us ~1.8kg.
Bone weighs half as much as muscle on average (3:2), but the muscle makes up about 3/5th the volume of the tail, so let's call it a wash for simplicity and say half the remaining mass is muscle. That leaves you with about ~0.9 kg of soft tissue. The majority will be muscle and/or tendon in the tail.
Now we repeat this for our lower estimate and we get 0.4 kg. So there you go, **muscle mass of approximately 0.4 - 0.9kg**.
For comparison in humans, the entire tail is about the mass of a single foot, from ankle down, while the muscle weighs about as much as a single hand from the wrist down. I don't know of any information about how much individual muscles weigh so I can't give you a comparison of a human muscle. There was even a StackExchange question about it that never got a detailed [answer](https://fitness.stackexchange.com/questions/22260/average-muscle-breakdown-by-percentage-by-weight-of-the-total).
Keeping the tail off the ground will not be an issue, it does not require much tension. No large mammals habitually drag their tail after all. If the tail is the same length as the torso and head it should barely reach the ground as it is. On an average human, the distance from the top of the head to the tailbone is the same as the distance from the tailbone to the ground. (Humans have really long hind limbs.) Even a partial curl will keep it off the ground.
[Answer]
The muscles required for movement of the tail are [rectococcygeal muscles](https://en.wikipedia.org/wiki/Rectococcygeal_muscle).
Its primary function in most animals is assisting with the bodily mechanisms for elimination.
>
> The rectococcygeal muscles form part of the complex arrangement of muscle surrounding the rectum, sometimes termed the anal-sphincter complex, which act to stabilise and support the anal canal during defecation. The rectococcygeal muscle acts to lift the sphincter, thereby effectively shortening the rectum and aiding evacuation.
>
>
>
However, in animals with tails
>
> In many animals with tails, such as horses and dogs, the rectococcygeal muscles are involved in the response to the raising of the tail during defecation.[6] In tailed animals the muscle attaches to vertebrae in a more caudal position than in humans due to the additional vertebrae in the tail, in dogs there are connections to the 5th and 6th caudal vertebrae and in horses to the 4th or 5th.
>
>
>
While this information about the rectococcygeal muscle gives some preliminary concept about the muscles needed for human fox's tail, it may be assumed that the necessary musculature may be similar to that of the dog.
>
> The canine tail usually consists of between six and 23 highly mobile
> vertebrae. These vertebrae are enclosed by a versatile musculature
> that make the various segments, especially the tip, capable of finely
> graded movements that lift the tail, move it from side to side, or
> draw it down toward the anus or between the hind legs. The caudal
> muscles lie on the lumbar vertebrae, sacrum (in the lower back region)
> and tail vertebrae. The muscles insert on the tail/caudal vertebrae
> exclusively. The muscles are attached to the tail vertebrae by
> tendons. The most posterior tendons attach to the last tail vertebrae.
>
>
> Part of the musculature is formed from muscles associated with the
> rectum, the anus and the pelvic diaphragm. Four to seven paired nerves
> serve the tail muscles. These muscles have many tendons that insert
> from the fifth or sixth caudal vertebra, then onto the next vertebra,
> and so on to the end of the tail.
>
>
>
Regrettably none of this information gives sufficient idea about how to determine, precisely, the muscle mass for the fox tail of a GM human. However, it may be able to provide an approximation of the necessary musculature.
[Answer]
It would seem that some humans do have tails, although it’s a very rare occurrence.
[](https://i.stack.imgur.com/kvYVj.jpg)
see
<http://evolutionbioc334.blogspot.dk/2012/03/vestigial-human-tail.html>
If you want to know about the musculature required the obvious example to use would be [new world monkeys](https://en.wikipedia.org/wiki/List_of_New_World_monkey_species) or other similar species such as the [Northern Tamandua](https://en.wikipedia.org/wiki/Northern_tamandua). It really depends on what you want them to do with the tail. Do they need to be [prehensile](https://en.wikipedia.org/wiki/Prehensile_tail)? If not, then I doubt they would need very much muscle.
[Answer]
Not much.
[This](https://sanctuarytraders.com/?product=sun-fox-tail) fox tail is 0.4 meters and weighs 100 grams.
A 1 meter tail would therefore weigh 250 grams. The muscle would be a small fraction of that; the bones would comprise the bulk of mass.
That the tail is on a human is beside the point. The answer is the same if your creature is a human or a large fox.
[Answer]
It depends on a number of factors. A tail that simply hangs from the rear would require less musculature than one that is held erect, or can sway from side to side. Additionally, muscle mass can be built up with exercise - if they exercise their tail by doing things like lifting weights with it, the tail will have more muscle than it would if they were just moving it normally.
] |
[Question]
[
The ground shakes as a colony of Triopticpelorovenatorius Baromassobrachiosaurus (T.B.) shamble across the forest floor. A glorious mix of blue, purple, and green colors shift under the treetops as our camera crew provides us with a perfect birds eye-view of the sparse alien canopy.
[](https://i.stack.imgur.com/9STS4.jpg)
In this episode of Strolling with Nightmares, we examine the realism behind the musculature and skeletal structure of a bipedal lower body plan and monobrachial (single arm) upper body plan.
## Generic Movement
On the two sides of T.B. there are planar joints which allow for the raising, and limited rotation, of both "shoulders" (as depicted in figure 1.0). In addition to the movement provided by the planar joint, there is a ball and socket joint which further increases the flexibility and mobility of the legs.
The leg itself is then further split into a front and back section; thus allowing for the stability of a wide stance quadruped whilst having a bone structure similar to that of a biped. The front section is controlled by a hinge joint, which allows for the front piece to move left and right separately compared to the larger, heavier back "heel" of the leg. Think of it as a single toe.
As the creature moves, the frontal arm provides support for the center of mass as one side of the creature raises, shifts forwards, and lowers; a slow shuffle, with each step requiring a different positioning of the arm for support.
## Arm Movement
Due to the relatively low speed of the T.B., the species is unable to chase its prey - instead, it hunts stealthily at range, as if it were a hunter with a rifle.
This creature uses its wide stance in order to stay stable whilst engaging in long range hunting; its incredible accuracy and strength provided to it by the single arm it has grown from the center of its body. The arm folds up, and launches sharp, spear-like projectiles in straight lines, as if it were a spring pushing outwards. (See Figures 1.1 & 1.2 for a depiction of the arm's movement ranges)
Alternative weaponry choices include bladed weapons, as the single arm has enough dexterity to wield the weapon to great effect; at least from the front. It is also able to lob rocks, although the accuracy there is significantly worse than if it were chucking spears.
[](https://i.stack.imgur.com/rI0gX.jpg)
Figure 1.0 - Bone & Joint Structure of Specimen
[](https://i.stack.imgur.com/6xVHx.jpg)
Figure 1.1 - Arm Movement Range (Side View)
[](https://i.stack.imgur.com/pP7Lc.jpg)
Figure 1.2 - Movement Ranges (Extended)
# Is the depicted musculature & skeletal structure realistic? If not, how should it be modified to better address the traits and movement written above?
Tip: If the pictures are too small, open them in a new window. They're actually huge, I promise.
---
For those interested in different views of the model, here are some additional photo links.
* Front View (<https://i.stack.imgur.com/28ix9.jpg>)
* Side View (<https://i.stack.imgur.com/uhMcF.jpg>)
[Answer]
I'm sorry to say that this shape seems very unrealistic to function as you describe. I can think of only one halfway plausible scenario.
Think about this from an evolutionary perspective, what and how has this creature evolved? Where is it well adapted to?
It's very wide, so it will be useless in trees or any other overgrown area.
It's very slow which vastly restricts its hunting options.
You've identified that and tried to solve it by saying that it's a ranged hunter, but how would that have come to be? What's the intermediate stage?
The only way I can think of this working is if it was an amphibious ambush predator. Basically think of it as being like a crocodile but it lurks in the river until something gets close by sinking under the water with the legs coiled under it. It then surges out with one long leap and grabs the target.
The wide stance and powerful body is used to launch out of the water and then drag the prey back in and drown it. An extension from this to then using ranged hunting tactics to surge out of the water and then throw a weapon becomes more plausible.
In other words it's a cross between a frog and a crocodile :)
[Answer]
Looking at the diagrams, the joints and musculature seem very unwieldy, and unlikely to arise from natural evolution.
A possible work around is to recast the creature as being "radially symmetrical", in other words, when you look at it from the top, the shape is a tripod, with the legs splayed at rest like a triangle. Since you have it evolving to live in a forest, the shape will be rather tall and narrow, similar to a giraffe if it lives by eating the leaves off trees (you speak of it as being large, so small tripodal animals evolved to live and forage on the forest floor should also exist).
Since the head isn't going to be able to successfully rotate 360 degrees, the "front" arm is going to become more specialized to be able to manipulate objects, bring food to the mouth etc. One can picture the creature either balancing on two legs while the "arm" brings food to the mouth, or it squats or kneels in order to engage the arm.
This would imply that the "hip" structure is quite flexible (perhaps a girdle of bones and cartilage rather than a unitary pelvis), and the elbow and "wrist" joints will also be very flexible. Evolving an elongated "ankle" like many running or jumping creatures have done on Earth would depend on things like the need for energy recovery (creatures like Rabbits often use the ligaments like giant rubber bands to store energy and release it on the step off portion of the movement). In any event, the articulation will be quite different from Earthly creatures.
If the creature is a apex predator (like T-Rex), many of the same considerations apply. It lurks in the forest waiting for the herbivores to come close, then springs into action. The front "arm" might be equipped with a raking or stabbing claw or set of claws, and perhaps the head might be outsized not only to mount a large set of teeth but also to use as a weapon (swinging the head and neck to knock down the prey, for example). If it exists on the plains, then the legs (for both predators and prey) are modified to allow for long, ground covering strides and bursts of speed to run down prey or evade predators).
Perhaps the easiest way to consider how to "design" creatures is to carefully examine the environment they are supposed to live in, and see how they would need to adapt to maximize their survivability in such an environment.
[Answer]
In figure 1.1, that throwing motion would probably not evolve. The creature would probably have a stronger throw if it started from the down position and rotated up, releasing when it is at the correct angle. If the arm uncurls as it is rising, it can get more force out of it since it will be easier to accelerate the arm in the curled position.
Also, from 1.0, I would assume that the creature is either relatively small or is from a low G world since those leg joints don't support the weight very well. As the creature gets larger, its weight will go up faster than the strength of the joints will.
[Answer]
So, the creature is effectively a living catapult. A slow moving distance hunter makes no sense under most circumstances. Wouldn't its kills always be stolen by scavengers before it even got to the kill?
The two legs and one arm configuration could be because of an unfavorable ancestry. Its stuck with modified versions of what its ancestors had.
A catapult for an arm might work well as a defensive weapon. This is especially true if there are a group of them using their catapults together. Groups of humans throwing rocks can fend off most large predators. Of course, they should be in more open territory than a forest for this to be effective.
Alternatively, trebuchets (similar to catapults) are a good way of smashing hard walls. Maybe the prey is small but hide in termite like mounds, which need to be smashed opened. It is a good strategy to find food. Gorillas and even humans eat termites.
<http://www.wikihow.com/Build-a-Trebuchet>
Gorillas breaking termite mounds. <https://www.youtube.com/watch?v=l-sd4FsfZQU>
Catapult like limbs have significant advantages over other limbs in that they use less muscle to exert a high force over a short amount of time. For instance, fleas and locusts have a version of a catapult in their legs.
Biological catapults work by having a locking mechanism. The flea leg is locked in a flexed position. For your catapult arm, you would need to study how levers work in catapults. After locking the limb, the muscles would contract slowly, storing energy in a block of protein similar to the Resilin in insects. Then, the leg (or arm) is unlocked. Elastic recoil makes the limb move very quickly back into the relaxed position.
<http://jeb.biologists.org/content/212/18/2881>
A wide stance where each leg acts as two legs would probably be because of stability. All four "feet" should be lightweight. Legs are Pendulums. The feet need to accelerate with every stride. Extra mass in the leg means that more energy is wasted moving the feet relative to the body. The mass that costs the most is the mass at the end of the limb. I say this because your alien is packing giant bone extensions on the back half of its legs that are without obvious function.
So, looking at the arrangement of the joints, the main body of the alien is like the upper part of a human torso if you cut off the human head and stuck a small alien arm in its place. The alien's head is sitting between the shoulder blades.
See the "top view." <http://www.pasttime.org/wp-content/uploads/2013/07/Shoulder-evolution.jpg>
What you should really have is less bone and give it a clavicle in shape and location. The poor thing doesn't have any space for organs!
Overall, if you give the creature a catapult in its arm and if it moves slowly, its musculature should be small and maximize efficiency over speed and strength. This is the strategy used by tortoises.
[Answer]
Some thoughts ...
First, I'm a little confused by the gigantic bone spurs on the back half of the rear legs. Not really sure how those help. If you got rid of them, you could have the creature be essentially a "reverse kangaroo", with the arm taking the place of the tail.
Generic movement would be either short hops (powered entirely by back legs) or a "knuckle-dragger" kind of walk, looking a lot like a guy on crutches. At rest, it will tend to lean *forward* a lot and rest on all 3 legs. Assuming that the big spurs are gone.
Hunting would be akin to male lion (when they bother to) hunting... Trioptic is big enough that it's neither faster than the prey nor has more endurance. What it has is terrific *acceleration* from jumps. If it can get with in 2-3 jumps of the prey it can catch it before Lunch manages to get up to a speed Trioptic can't match. It's big enough that this stealth part may be hard, so it'll have to hunt in (at least) pairs. The beater goes upwind and chases the prey toward the hidden catcher, who is downwind and breaking its outline with trees.
The second thing I'm worried about is the projectiles. It seems like a bit of a stretch to evolve those, as it's *expensive* to throw away body mass. Speaking of stretch, one approach might be to give the creature an extra joint (hence extra length) to it's front arm, which it usually keeps tucked up, but can extend out to a pretty good reach for an attack. Think chameleon or mantis or squid. It's strategy might be, using above info:
* Wait semi-concealed until beater chases prey toward catcher Trioptic.
* Trioptic then uses explosive leaps to get close to prey
* Uses long-reach arm to **trip** the Lunch. See cheetahs hunting for examples.
* Once Lunch is down, use big claws to cripple or slay it
Even with all this, it'll be hard to hunt enough provender to satisfy this beast. So some other thoughts:
* It'll help if there are other, smaller predators around. Prey "wants" to grow big enough to disqualify them as predators, which (ha ha!) makes them big and ungainly enough for Trioptic to target.
* Another great Trioptic tactic would be to sniff out these smaller predators' kills, and bully them away; Trioptic will steal their lunch.
* You could have Trioptic be omnivorous, kind of like bears. If it's too frustrated hunting, it can sulk away and go eat some grass and berries.
TL;DR -- I think you can make this guy work!
[Answer]
Unfortunately this creature cannot be changed to be realistic without massive changes. The design does not offer any evolutionary benefit, and it has quite a few disadvantages:
Wide body doesn't help it move faster or more efficiently, doesn't offer much to stability, and prevents the creature from fitting in between natural obstacles.
The legs are actually the largest impediment to its movement. With lighter legs it would weigh less, making massive bones no longer necessary. In this creature the legs are bigger in order to support bigger legs. This simply isn't helpful, and is counterproductive too its movement.
It almost certainly cannot swim.
It certainly cannot climb, or possibly even go up a steep incline.
Its arm is in a location that offers poor leverage for throwing things.
**So what should be changed?** For starters I assume the heavier build is linked to a defensive need? If this were the case the width should be decreased and almost certainly the height. Animals with more armored builds always tend to be tighter and more compact to maximize protection.
The arm should also probably be moved to the back like a scorpion tail and be long enough to reach all the way around in front of it. The extra length would help it work as a catapult.
And the legs, they basically are simply not evolutionarily justifiable.
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[Question]
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Underground societies have been a trope in fiction for a long time, but in the real world they don't seem to exist (at least not in the way they are often portrayed). Yeah, we sometimes see people living right near the surface in partially excavated [cave dwellings](https://en.wikipedia.org/wiki/Underground_living), but from what I can tell large scale underground facilities remain limited to [missile silos](http://www.titan2icbm.org/compx.jpg) and generally groups really big budgets.
At first glance, it would seem like living underground would solve an interesting set of problems:
* Heating and Cooling would no longer be necessary
* Land could be used more efficiently (You can expand downwards, and leave the surface open)
* Materials for construction could potentially be gathered during excavation
But it also creates a few new ones:
* Massive amounts of material needs to be moved
* Ventilation could become a potential problem
* Radon and other radioactive materials pose a higher risk deeper underground
In general, people seem to gravitate towards doing things the easiest (and by extension usually cheapest) way they can, so I can only assume that large scale underground structures are simply not cost effective. So here's my question, what technology would need to be developed to make it cheaper than building above ground? Is it even possible, or is underground construction inherently less efficient?
TLDR; What feasible inventions could mankind develop that would allow them to live as mole people?
[Answer]
### There are no wonders. If you want to move large cities underground, you have to dig. A lot.
Radon concentration and similar things do exist, but - except some very few areas on the world - they are negligible. Although the [highest purely natural radioactivity](https://en.wikipedia.org/wiki/Background_radiation#Areas_with_high_natural_background_radiation) of the world is far higher as any prescribed health standard (around 0.8 Gy/year, living there means a much higher risk as smoking).
People doesn't really like to move underground, but if they have enough motivation, they will do. You don't need some cataclysmic event for that, it is enough if they can find work only there.
A radioactive surface isn't enough motivation, because in this case, also the ground water will contain a lot of solved radioactive materials, mainly metal salts, which doesn't make the situation better underground (while the increased costs of the digging still exist).
The main problem with digging, that it requires a lot of people, working a lot of dirty work, with big and costly machines. Consider the costs of the underground train tunnels. The [Eurotunnel](https://en.wikipedia.org/wiki/Channel_Tunnel) (binding UK and France) costed around \$21billion. The cost of similar underground tunnels costs mainly between \$10million-\$30million for every km.
Building the big and costly machines requires also a big and costly machine industry.
The better usability of the free, now empty surface land isn't a big advantage, because most of it is already uninhabited, even in largely overpopulated countries. We, humans, tend to concentrate ourself into big cities.
About the actual costs and technologies of the digging there is a quite useful [SE site](http://engineering.stackexchange.com).
In any case, the opencast building (i.e. digging a big hole from the surface) is always *much* cheaper as digging essentially large mines.
Although heating won't be a high cost of these cave-cities, their cooling may be much bigger. And also their air ventillation. There are no wonders also in this case: you have to circulate water and air between the surface and (if it is irradiated, a closed water loop and air filters are adviced). You have to use pumps and ventilators for the task.
Note: there are radioactive gases, some of them won't be filtered by anything (noble gases). Although most of them decays very fast (thus they long decay as the caves will be built), or very slow (thus they aren't very radioactive). Fortunately, practically none of them is produced by normal fission processes (nuclear energy production + atomic bomb explosions), thus we have luck.
Fire, and any carbon dioxide producing objects (non-electronic cars) would mean much bigger risk and cost (air).
Energy production will still have a lot of contact with the surface, because there is no energy production without heat production, and you have to do something with the heat. Of course you can use surface solar panels and windmills to produce the energy on the land. In this case you will have a lot of cables.
The whole society will be much more strongly dependent from the technology, which will elevate its worth. The probable result will be that the law and the customs will follow the same. Smoking will be much more evil as now, destroying any technology, particularly if it has anything to do with the life-sustaining systems, will be much more hardily punished.
Working on technology (engineers, scientists, teachers of these) will be probably much more honored as today.
Sustaining the civilization will require much more work. It will have a negative effect to the life quality.
The civilization would require around 30-50 years to adapt (and, to reach the life quality of their old surface again).
If the move to underground is the result of a hard pressure, then the first years will be crucial and for the large masses, mainly catastrophic.
After such events - revolutions, downfall of a world system, world wars, etc - the society needs around 1-2 decades to stabilize.
I can advice two very interesting novels from societies in similar situations:
* [The Moon is a harsh mistress](https://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress) from Heinlein (it is a communist book, so don't believe its ideology, read it only as a sci-fi novel)
* [The Caves of Steel](https://en.wikipedia.org/wiki/The_Caves_of_Steel) from Isaac Asimov
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So we already have the technology to do this. Humans have been developing the technology to exist underground since we first started mining.
**The problem with your question is that, on an Earth-like world it will never be more efficient and therefore cheaper to build underground.** You just can't get there, building down requires more work and will generally require you to fight gravity more often in the maintenance of said dwellings.
So the problems:
* More expensive to build initially, moving material, digging, reinforcing etc.
* Plumbing gets weird and will require extensive use of pumps
* Air Quality, you'll have to have filters and you'll have to make sure air flow doesn't stop otherwise you end up with suffocation...you know dead people.
That being said there are reasons to build underground on a future earth or a planet only slightly different from Earth.
* Storms. If a planet has regular, very strong storms, building up is a bad idea.
* Lack of wood. Now its still probably cheaper to mine stone and build stone dwellings, or clay works...or sod. But its not unreasonable to think it'd be more common.
* Creatures. If you have a man hunting beast it is way easier to secure an underground dwelling.
* Post apocalypse...if the surface is a barren hellscape...
Inventions: Ironically we don't really need any *new* tech to make this feasible. As mentioned it is still going to be more difficult/expensive but with modern technology we can certainly create a stable effective underground dwelling.
* Water systems. You are going to need pumps to REMOVE waste as opposed to needing it to get water, which is the flipside of how we do it today, but doesn't require anything special.
* Ventilation. Special filters for radon and others stuff (as you mentioned) will be needed and the supply needs to be constant and need backups. This is particularly true with larger underground settlements. O2 is good for humans...
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Living and working underground is fine.
Huge expanses of empty limestone mines under Kansas City are used for all sorts of industrial and office space.
<https://www.usnews.com/news/us/articles/2015/09/14/ap-news-guide-kansas-citys-network-of-underground-caves>
But the coolest has to be the underground cities in Turkey.
<http://www.goreme.com/kaymakli-underground-city.php>
These are huge and very old. I am not sure how they addressed ventilation back before electricity. Especially if your only light was fire. One would think there would be giant piles of rubble on the surface nearby.
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First of all, I don't think that people, given the choice, would like to live underground. Our ancestors might have lived in caves, but they spent most of their time outdoors.
As far as technology goes, the most important thing that we missing is good burrowing technique. Building tunnels is bedrock is very slow and expensive today. Erecting a building of the same volume on surface costs just a small fraction of underground building's costs.
Second thing is reinforcing the structure. When we have relatively small caves in a large amount of rock, the structure is stable. But if we want to use the most of the volume, walls and floors are becoming too thin to support it. Right now humans need to excavate the whole cavern and then build the walls and floors out of manufactured materials. This only makes underground buildings more expensive. If there was a quick and reliable way to reinforce rock, that would help. Another concern is earthquakes. For a surface building, we can design it with a certain seismic resistance. For underground tunnels, there is just no way of saying when they can collapse.
Other concerns, like ventilation, heating and cooling (yes we will need those too, even underground) and energy generation are relatively minor, but would also benefit from a more effective solution. For things like radon, carbon monoxide, carbon dioxide, methane - we just have to constantly monitor them.
[Answer]
# It won't be about tech
As other answers already pointed out, we already have all the technology needed, and with any given tech level building and living on the surface will be cheaper. At least, technology-wise.
1. **Over population** — if you have so much people that all your surface is either farming or last remnants of wild nature, then underground is cheapest place for living.
2. **Prices on terrain** — rich people like to have land. There is not enough for everybody.
3. **Air pollution** — and it's easier to keep it at bay in a cave than in dozens buildings with windows.
Et cetera. **Just add factors that will make surface expensive**, and you'll have underground economically viable.
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**Summary**
In my world, I have created a species of anthropomorphic wolves, who are nomadic hunter-gatherers. They are like humans in some respects and like wolves in others, but with some minor physical differences unique to them, as they do not live on Earth. When they hunt, they rely upon their teeth and claws rather than the traditional spear or bow, and I am wondering if they would be able to accomplish this, considering their mixed physiology. Unfortunately, the research I have done has not proved helpful, so I now turn to the people here.
**Conditions**
* Animal mindset and instincts, with human intelligence and reasoning
* Large, paw-like hands capable of manipulating objects
* Claws are tough and non retractable, teeth are carnivorous
* Excellent jaw strength, comparable to a wolf's
* Pack hunters, place strong emphasis on teamwork and cooperation
* Long, human-like arms with flexible joints
* Strong muscles
* Digitigrade legs
* Move upright most of the time but assume an "all fours" position when stalking prey
* More speed and agility than a human
* High stamina, able to run at a steady pace for long periods of time
* Can run fast for short bursts when pursuing prey
* Chest larger and deeper than a human's, greater lung capacity
* Patterned fur that blends into surroundings, providing camouflage
* Tail for balance
* Good jumpers
* Prey includes large herbivores similar to elk and bison
* Typically hunt on flat, open plains
**Question**
Would these creatures have enough of an advantage to be able to hunt and take down their prey without weapons, or would their human qualities (moving upright, for example) only hinder their efforts?
[Answer]
No reason why they wouldn't be able to hunt effectively. In the wild, chimps will hunt monkeys and other small animals for meat as a supplement to their diet. They are structurally similar enough to humans to be used for comparison. Chimps would probably have smaller teeth than your anthropomorphic wolves and are likely slower on flat land. It really depends on what they are trying to hunt. The larger the prey, the more likely they would need tools to take it down. Of course, being wolves, they would probably be pretty good at working as a team against a single target.
One thing that wolves in the wild do is run down a lone herbivore they have cut off from a herd. They can continue to chase an animal until it is exhausted thanks to their incredibly efficient running physiology. Your guys will probably lose a lot of that open terrain running advantage in order to have arms that are good for tool use. That kind of begs the question: if they have developed tool-adapted arms that hinder their ability to run like conventional wolves, why accept the worst of both worlds by not using tools to hunt?
[Answer]
Humans use weapons to take down prey for two main reasons:
1. Because our apemen ancestors didn't have carnivore teeth and carnivore claws, they used sharp sticks and sharp stones as a substitute. (Also we are not as strong as chimps, so not quite as good at bodily ripping some hapless antelope fawn or colubus monkey in two).
2. To minimise risk.
The risk thing is an interesting one... human hunting weaponry (and warfare weaponry) has evolved to put a greater and greater distance between the hunter and the hunted. You start off up close and personal, jumping on something and bashing its head in with a rock. Then you put the sharp rock on the end of a spear, and slam the prey in the ribs. Then you invent spears for throwing. Then you improve those to the atlatl or the bow and arrow. Etc etc. (Or you set snares).
Getting bitten, gored or kicked by big, pissed off herbivores is a serious risk for a hunter - humans and wolves included. I've seen a wolf skull with a deer hoof sized indentation in it! Humans chose to minimize the risk by inventing better weaponry.
Studies of African wild dogs (Lycaon pictus) show that it is pretty much always the alpha male, alpha female or beta male which is the dog who makes the first grab at the prey - the point when a kick or gore is most likely. Those high ranking pack members are the risk-takers, willing to risk that injury. (Interestingly, the alpha female stops taking risks when she has small pups back at the den). I don't know enough about wolves to say if they are the same.
So your anthropomorphic wolves could either:
1. Be like humans at a more 'caveman' or 'apeman' stage of development. They are taking prey down by hand, then using tools to skin it or butcher it for cooking. They simply haven't got around to inventing spears or arrows yet.
2. They could use spears if they wanted to, but they have a cultural prohibition against it. Perhaps it is not 'honorable' to the prey. Perhaps only cowards or weaklings use distance weapons. Perhaps their deity told them not to.
[Answer]
Human hunters could literally run their prey to death. Wolves can also perform a similar feat in chasing their prey until exhaustion overtakes it.
This
* More speed and agility than a human
and this
* High stamina, able to run at a steady pace for long periods of time
make them ideally suited to run their prey to exhaustion, when they would rush in and "dog-pile" it, knocking it over and holding it down. Perhaps the packleader would be the one designated to go for the throat to end it.
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A species like the one you created would in fact be at an advantage in taking down prey without the use of tools.
That is until they run into a prey animal that you would need to use tools to take down. This is because all things never stop evolving and adapting. Let's take an example: raccoons and foxes.
Odd examples, of course, but let's take a look at them shall we?
Prior to the development of big cities, both raccoons and foxes mainly hunted. However, as land was cleared away and cities grew, raccoons and foxes had to adapt. They found new sources of food by keeping an eye on people. How else could they have figured out about us putting food in our trash cans?
Another example would be the jaguar. The jaguar is unique in how it makes its killing blow that it uses its fangs to bite through a prey's skull directly into the brain. Most predators go for the neck. Zoologists and other biologists believe that during the jaguar's evolution, its ancestors evolved in the need to penetrate certain animals' tough shells (jaguars actually prey on armadillos).
Your wolfoids (humanoid wolves) could adapt and evolve in order to use both their natural born weaponry (claws and fangs) and tools (spears, clubs, axes, etc) in order to both fight and hunt better.
Some experts believe that the key for a species's success in hunting is via problem-solving. This is what I interpreted from this article: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427591/>
And these next few parts are ones you could take into further consideration:
Some experts believe that war might have been a consequence to the creation of hunting tools, although there is some disagreement with the scientific community on this. The combination of using tools, fangs, and claws would almost guarantee your wolfoids into becoming extremely fierce and deadly warriors.
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I have a magic carpet, but the only thing magic about it is that it flies where and how its owner directs it. No bubble around it, no other magic; she has to hold onto it.
I'm wondering how fast and high it can go. It is large - 3m x 4m (and very stiff) - and ALL other factors are based on using 11th Century Arab Renaissance technology level to help the rider.
[Answer]
There are two important limits I can think of.
**Altitude**
For a human just hanging out on a carpet, the effects of altitude may be noticeable at 3500 meters and perilous at 8000 meters. At 3500m a low-altitude-lubber might experience altitude sickness with increased chances of an edema as altitude increases. 8000 meters is the mountain climber's "Death Zone" so you probably don't want to be up there that high for too long, even if you aren't exerting yourself. Unless you want to fly over Mt. Everest, there aren't a lot of reasons to need to go that high. There really aren't many reasons to go over 4000 meters. The highest settlements are up at 5000m, but very few people live above 4000m.
**Velocity**
From personal experience, waterskiing in the rain sucks, so going through a cloud at 30 mph would be less than fun. Motorcyclists on the highway pretty much have to wear eye protection to see. If you didn't it would be uncomfortable, you would need some sort of glasses or visor. Also, it gets really cold at high speeds. All in all, I would suspect that the discomfort caused by going 100 mph would probably be limiting.
If you really had to get somewhere in a hurry and would tough out being a squinting, shivering mass for the duration of your trip, the next limit would be your ability to hold on. Lets say you lie down flat on the carpet with your head facing forward, and heavy clothes as tight as possible (given medieval technology). Assume a surface area of 0.3m^2 (about 3 square feet). The force of wind is 1/2\*(density of air)\*(v^2) in N/m^2. For 100 mph we have 44m/s->1210 N/m^2 -> 37 lbs pressure on you. For 200 mph we have we have 89m/s -> 4951 N/m^2 -> 152 lbs pressure. Now its pretty hard to hold on. These calculations are not likely to be super accurate, since I'm counting your head as a flat wall, and discounting drag and such. But the numbers match what you'd guess from riding a motorcycle, I'd say that between 100-200mph is your hold on limit. At this point your gloved hands have a death grip on the rug's tassels to get any kind of hold, and the high winds and cool air at altitude is rapidly freezing them to numbness. Probably better to relax back to a leisurely flying pace. You'll get there sometime, inshallah.
[Answer]
**Height**
Altitude sickness begins at about 8,000 ft (2.4 km), with more minor symptoms typically found at 5,000 ft (1.5 km) on up. Assuming it's just her there, riding the carpet she'll likely want to stay at a lower altitude than these heights.
**Speed**
She could reasonably do as Henry Taylor said by rolling it up, but even if it can't be rolled up I imagine a saddle could be fashioned, as well as something to strap her legs down. The fastest a horse has ever reached was about 44 mph (70 km/h), while a normal gallop is about 20 - 30 mph. This should give you an idea of what is comfortable to fly.
If there's no limits on how tightly she straps down herself, and how fast it can go, it's more about the acceleration. Most people can survive up to about 5G (49 m/s2) for very short periods of time without blacking out. Your carpet probably shouldn't accelerate (including changing directions) faster than this.
[Answer]
I don't think it has a [service ceiling](https://en.wikipedia.org/wiki/Ceiling_(aeronautics)), specially since it is magic that keeps it afloat.
As for speed, there is only one way to find out. You'd have to fly so fast that [ablation](https://en.wikipedia.org/wiki/Ablation) due to air friction becomes an issue. The rider would be in danger way before you attained that speed anyway, so unless you are planning to do a sketch on Jackass, you shouldn't worry about that.
Here's what you should worry about:
Being stiff (probably due to all the cheicals you put on it to protect your property against ticks, fleas and silverfish, and to keep it impermeable), I surmise it will [bank](https://en.wikipedia.org/wiki/Banked_turn#Banked_turn_in_aeronautics) to turn. The traditional picture that comes to mind when we think about magical carpets allows for [VTOL](https://en.wikipedia.org/wiki/VTOL), but for some reason I am thinking it has to [pitch](https://en.wikipedia.org/wiki/Aircraft_principal_axes#Lateral_axis_.28pitch.29) to go up. Given these characteristics, even for slow, tranquil flight I would suggest you sew some security harness onto the thing. Lawnchair Larry knew that safety comes first when it comes to [flying on your furniture](http://www.darwinawards.com/stupid/stupid1998-11.html).
Also beware that the friction with air will charge the carpet and its passengers with static. This may have all sorts of effects and hazards, so be careful with electronics and discharge safely whenever you land.
Fire is also an important safety hazard, so the use of narguile's on the carpet should be strictly forbidden according to international aviation laws.
Some people may have carpet allergies ([seriously](http://home.howstuffworks.com/home-improvement/home-diy/flooring/carpet-allergy.htm)), so be sure to always have some [antihistamines](https://en.wikipedia.org/wiki/Antihistamine) on you for your passengers.
Last but not least, if you have to take a pet along with you, be sure it is in a box. [Not only because their claws might damage the carpet](http://pbfcomics.com/127/).
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Because the magic carpet flies how and where its owner directs, its maximum height and speed will be set by the perceptions and cultural mindset of its owner.
For someone who is a product of the 11th century Arab Renaissance this is likely to be a maximum altitude of around one hundred metres and a maximum speed of no more than ninety kilometres per hour. At an altitude of one hundred metres this is well above the height of most ground structures like buildings which would come nowhere near that, and it's well above the tallest trees. While still being enough to the ground to have a good view of what you are flying over.
A maximum speed of ninety kph is reasonably comfortable, especially in a warm climate where it would be very pleasant to have warm air blowing over you, and while it is much faster than those noble horses the justifiably famous Arab steeds it isn't terrifying fast like several hundred kph would be.
Those are owner friendly maxima for frequent magic carpet fliers. It is reasonable to expect that most trips will be below the maxima, but if an owner does a lot of flying they might gradually push the envelope. Most likely owners will stick with flight characteristic they feel most comfortable with, and magic carpets being good and obedient servants will comply with their wishes.
if the magic carpet is stiff and rigid during flight, the simplest way to ensure you won't fall off is to bind cords or ropes around the carpet. When the carpet becomes rigid and stiff the cords or ropes will tighten around the owner to hold them in place for the duration of their flight. The cords don't need to be too tight, just tight enough to hold someone securely.
Left to their own devices magic carpets can easily cruise at orbital velocities, at least, one thousand kilometres above the Earth's surface. Unfortunately, few 11th century Arab Renaissance magic carpet owners can survive flights of that nature. However, over the generations the makers of magic carpets have worked tirelessly to ensure their magic carpets have all the latest safety features and designed to be user friendly. Their motto: It is better to travel in comfort than speed.
[Answer]
For a real answer, if you don't want to rely on pure magic, we need more details about the means of lift. If lift is achieved through some sort of bernoulli effect, as in airplanes, the performance envelope is going to be completely different than if it's magnetic or some form of electrodynamics. The change in atmospheric viscosity at altitude is different than the change in electromagnetic field potential, and is therefore going to create totally different limits at which the lift and propulsion crap out. So, the only possible answer is, "no assertion", pending further clarification.
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The real physic answer is not much faster than 70MpH because over that you wont be able to stay on the carpet.
Now for not real physic:
king Salomon eat noon lunch in Damascus and supper at Media. 1734km in around let say 4 hours: 400-500 km/h
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[Question]
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Bob is a thirty year old atheist man from our modern times. One day, he is irreversibly thrown back into medieval France around 1300 C.E. His education consists of a Bachelor's degree in mathematics, and unfortunately he does not bring back any modern technology with him. By handwave, he becomes the king of France.
Bob's priorities (in no particular order) are:
1) Modern civil rights
2) Modern science and medicine
3) Widespread democracy
4) Limit peasant suffering and abuse
What sort of ruler should he be in order to help society move towards these goals? I understand that he will probably not be able to accomplish any of these developments in his lifetime, but can he do anything to at least accelerate them?
Some food for thought:
Should he try to give more rights to peasants at the risk of angering the nobles?
Should he attack and invade neighboring kingdoms in order to bring them under his kind rule, or should he set a peaceful example?
Should he invest a lot in education and science at the risk of being regarded weak by his nobility and neighboring kingdoms?
[Answer]
Oh average Bob with his time-travel powers. What can we do for you?
**Let's analyse Bob's problem.**
Bob is now in 14th century France, a time where people tends to be really religious, in that specific year it's not a good time to be the king of France in the eyes of the church, but this does not matter so let's move on.
You are right, too much investment in education and science will make Bob look like a wimp in the eyes of other rulers that will probably want a piece of France. Probably some cousin of the previous king that lives in England or some sort of pretender. Bob is from the future! **Bob uses his investment to develop gunpowder**!
Not modern gunpowder, like we have today, but a fair amount of black powder so when the invader army tries to invade, Bob's army will be ready. And there it goes. **They came, Bob conquered**. Now Bob is a war hero, but there is a catch, now a sect of the nobility thinks Bob is a heretic because of his advancements. So what does Bob do? What absolute monarchs of the 14th century do best. **He gathers a sect of loyalist nobles, and his morale enhanced army and wipes his enemies out, accusing them of treason**. He takes their land and spreads it through his supporters, making the rich, richer. Bob will not have to worry about any uprisings for the time being.
But now Bob has another problem. We're still in the Middle Ages, where we don't have any sort of basic sanitation. So, Bob's next priority should be **Improving the infrastructure of their forts and cities**. But to do that, Bob needs a labor force.
So, Bob gathers his loyalists again and explain his plan. He wants to create a thing called job. We will start to pay your peasants some money for their labor. He continues with that while everyone in the room is completely in shock. **By paying your peasants for their labor, we make them happy. They will start to think that they are being valued by their lords, and will be more willing to comply.**
At the same time, someone shouts that this is madness, asking what a peasant will do with money? Bob smiles and says that **in addition to the fact that we will be paying them for their job, we will be charging for our products**. And by that, everything will be back to where it was.
So it starts. Bob now is constructing all sorts of infrastructure. In mean time, He also introduces his next great idea, **a machine in which he puts a blank paper, some metal pieces in the form of letters, and ink and presses them against each other**. Bob is a simple man, so he calls that machine a press.
But now one of Bob's lords brings him a new problem. Since parents are working in Bob's infrastructure project, the children are alone because their parents aren't there to take care of them.
So Bob says, "I have the solution to this problem. **Let's take the children and put them in a place where we can teach them the principles of what we are doing, so that when they come of age, they will already know what to do. And I have a name for this place, 'School'**. We'll divide them by age, start teaching the most basic things to the youngest and the more complicated things to the oldest".
And so it goes. A good ten years pass, all of Bob's infrastructure work is done. The first kids that went to school very young finish their study and now are ready to work in all sorts of fields. The nobles also adopt that model of Bob, but with private schools, which focus on other kinds of fields of higher knowledge.
So other kingdoms see Bob's progress, some of them want to buy their products, others want to take what Bob has. Bob, not being a fool, was improving his war machinery at the same time their infrastructure was being built. **And now that Bob has access to a factory and specialized work force, the less developed kingdoms are no match for him** and his most brilliant war machine, the airplane. Bob's wrath rains down from sky in the stone forts from his opponents, and the marvelous products that Bob exports delight his allies.
But not everything is sunshine and daisies. Some of the Bobs peasants start to think that their Lords are tyrants, that they are being exploited and are threatening to stop working unless their demands are accepted.
So Bob proposes a council, a House of Lords, composed by the nobility and a house of representatives elected by the people from common men to represent them, Bob calls that House of Commons. And to ease the anger of the Nobles, **he announces that he will be giving way his powers as government leader, and maintaining only the powers of the state leader**. He will ensure that the in parliament (which is what he calls both houses together), the people and the lords elect someone to decide what should be done.
And so it goes. For the first time the people have the power to control their future. Factions in both houses of the parliament are created but **Bob doesn't see a problem with that. When asked by a member of a group that possesses one of Bob presses** (whom Bob also calls the press, he is a simple man after all), **he says that is a good thing that some call democracy.**
A few years pass by, some ups and downs. Bob makes another announcement, after all those years, due to his poor health, **he is stepping down of the throne in favor of his son, Bob II**. And so there it is. Bob goes to his summer castle in a South France beach to live with his queen for his final years.
And so there it is, the history about how Bob changes history.
[Answer]
Start with sanitation. Armies and cities have to build proper outhouses. This will make you stronger, as more of your armies' people will survive conflict.
The 1632 series developed [chloramphenicol and sulfa drugs](http://ericflint.wikia.com/wiki/Antibiotics) for further medical treatment.
Increase the size of your personal armies so as to avoid nobles killing you. This works because of your increased survival rates.
Trade medicines to your enemies for use by nobles. Charge lots so as to finance your armies.
If you run low on money, go steal some by plundering your richer neighbors. Similarly, if short on farms to support your armies, expand your land. Note that you can choose to prey on the worst of your neighbors.
When soldiers, particularly officers, retire, give them their own noble title and domain from your new lands. These will be your counter-nobility. Hold them to a higher standard in terms of human rights. Encourage them to recruit additional peasants from outside your country.
Find a reason why a big, rich noble is a traitor. Kill him and take his lands. Spread them out to your retiring veterans.
Invest in a food taster and a strong bodyguard force to avoid assassinations.
Loan armed forces with your soldiers and officers to your nobles when they ask. Make sure that your nobles' forces bear the brunt of the fighting. But ensure that they win in the end. This leaves them reliant on you, as their armies are diminished and they feel little pressure to replace them. Yes, I realize that this means that they will use your armies to do things of which you disapprove.
Tell your nobles that peasants are necessary for a strong economy and military, so they will be fined for any that die outside your armies. Note that you should probably wait to do this until after your armies are clearly bigger than theirs.
Draft serfs from your nobles' domains into your army. Both to deprive them of potential military personnel and to build your own army.
Recruit like-minded people into an organization dedicated to your ideals. Focus on idealistic youth. Raise them with better principles than their peers. Possibly take in orphans so as to start their education earlier.
Raise your kids in the organization. Make sure that the one who succeeds you is pro-democracy. Build a long term plan that you expect them and the organization to implement.
Send out colonists to the appropriate places to mine gold and other resources. The colonies can be more democratic. I would suggest that you also put your research and development there, where the natural resources are.
Over time, your goal should be to increase the power of newer, more democratic nobles at the expense of the existing nobles. Repeat until they can stop being nobles. Note that this may not happen in your lifetime.
Ratchet up civil and human right protections over time. Don't hurry. Whatever speed you manage is likely to be faster than what would happen without you.
Concentrate your medical and science research on your armies. Members of your armies should survive while your enemies' armies do not.
Encourage research centers to maintain especially high standards for education, rights, and democracy. Draw the aspirational to them.
[Answer]
The answer here is simple. **Colonies**. As a modern man in 1300 C.E. France, Bob, and Bob alone in mainland Europe, has access to the single most valuable piece of knowledge in geopolitical history—the existence of the American continents.
So what does Bob do? He invests in explorers and navigators, similar to what the rulers of Portugal did in the fifteenth century in Africa, except he instructs them to head westward, not southward. Some, to be sure, think this is suicide—after all, fourteenth century sailors don’t even know of the trade winds that would take them home, but there will always be *someone* in the country adventurous enough to take the risk. It won’t be easy for Bob to get off the ground, though, sailing technology was not as good in 1300 as it was in 1492. Bob’s noble rivals, like most educated Europeans at the time, [understand the world is round](https://en.wikipedia.org/wiki/Spherical_Earth), so they don’t think Bob is *batshit crazy*, but at the same time, they dismiss it as just another pet hobby of the king and privately gossip amongst themselves about how stupid the king is to send ships into empty water. They don’t anticipate any threat to their power.
# 1. Gold, Bob, and Glory
Then, one of Bob’s explorers comes back with news of a strange new land far across the ocean. Most likely, if they set out from France, his captain landed somewhere in Canada or New England and Bob is told that the land is cold, barren, uninteresting, and devoid of any precious metals worth mining. But Bob doesn’t give up. He sends more navigation parties out radially from France, knowing that the continent extends continuously for the entire length of Europe and Africa. Subsequent expeditions find the Caribbean, Mexico, Bolivia, Brazil, and all the accompanying treasures within. Colorful birds, Native American souvenirs, news of an entirely new land, all of this excites the populace. The serfs who previously knew of no greater life outside of their manor, are now clamoring for a taste of the great new world. Bob, who is now looking for loyal colonists, has no shortage of volunteers. Because they are mostly poor peasants with nothing to lose, most of his volunteers are loyal to Bob, and Bob alone.
# 2. Sorry, Pocahontas.
First, Bob needs to deal with the Native Americans. Despite any progressive quips he might have inherited from the 21st century, this choice is already made for him. Disease wipes out the Native Americans whether or not he wants to. The rest are reduced to bands of survivors, wandering what is, to them, a post apocalyptic world with an alien invasion thrown in—something of a mix between the Walking Dead and Falling Skies. Bob is now free to move in with his forces.
Millions of natives are still around, and more than a few attempt to mount a resistance, but Bob has knowledge of something called “gunpowder”, and he instructs his tinkerers and alchemists to start improving upon the [strange explosive dust coming over from the Middle East at the time](https://en.wikipedia.org/wiki/Gunpowder_artillery_in_the_Middle_Ages). His tinkerers, psychologically, are also benefiting from the expanded horizons resulting from the discovery of a new continent, and so they start experimenting and hacking. Soon, Bob has new explosives, new alloys, new weapons, etc. The Native Americans, never much of a match to begin with, are steamrolled by Bob’s armies, who, with their new military technologies, Bob also uses against the nobles in France. If he is smart, he swiftly takes them out before they have a chance to adopt and incorporate his new weapons into their own armies. If he is *really smart*, Bob the Atheist uses the existence of the New World to discredit the church & [expels the Catholic clergy](https://en.wikipedia.org/wiki/Cult_of_Reason) from the country as a “cult of liars and conspirators”.
# 3. Bob the Athiest
The Pope, never as powerful to begin with as we usually imagine him to be in this time period, is helpless to stop it, as Bob’s neighbors in Germany, Spain, and England start hatching their own plots to expel the church. Kings and nobles across Europe are [*very interested*](https://en.wikipedia.org/wiki/Thirty_Years%27_War) in this new “I don’t have to listen to the Pope anymore!” idea. The Protestant Reformation comes early.
Now, Bob’s power is vastly magnified. He has land. He has natural resources. He has weapons. He has exclusive divine right, from expelling the Catholic church. He has money, from the silver mines of Mexico and Bolivia. (The silver [messes with his economy](https://en.wikipedia.org/wiki/Price_revolution) for a little while, but that’s fine because all of Bob’s rivals in Europe are affected too.) Because he has land, he has the loyalty of the population, since he can gift peasants with their own land in the New World in exchange for service. Because he has the loyalty of the people, he has an army.
# 4. Liberté, Égalité, Roberté: How Bob protects his empire
Now, Bob puts his knowledge of 21st century civil rights and liberties to use. He teaches his people about natural rights, about freedom, about democracy. He promises that his colonies will become republican utopias for the poor. The people also begin to take an interest in education, since they now have a vision of becoming men and women into themselves. They begin valuing rights and freedoms, and the new education fad doesn’t hurt Bob’s ability to get new military or health technologies either. Bob’s people quickly become the most educated, healthy, and wealthy people in Europe (though at the time, this isn’t exactly a high bar to clear). But even more important than that, his people are transformed from subjects to **citizens**. And that gives Bob, and Bob alone, access to the most [terrifying force in world history](https://en.wikipedia.org/wiki/French_Revolutionary_Wars)—the **citizen army**.
The citizen soldier isn’t like the your typical mercenary in a king or noble’s army. The citizen soldier is motivated. He (not she; Bob’s technology and social cohesion is still not sufficient to launch a full blown women’s rights revolution) is willing to die for his country. And not just his country. Just as Bob invents the citizen in this timeline, Bob also invents the [**nation state**](https://en.wikipedia.org/wiki/Nation_state). The nation state is not like anything else in Europe, or many thousands of miles from Europe. (China was a nation state many times in its history, but China is China, and very far from Europe.) His people pledge allegiance to the flag of France, everything it represents, and by extension to Bob. To his citizens, France is no longer just the place they live, it’s an ideal, a cause worth dying for. It’s also transferable.
# 5. World Domination?
By now, the peasants in surrounding Europe have probably heard of the enlightenment Bob has set off, and a few demagogues amongst them may already be fomenting revolutions. If Bob is smart, he preempts them. Bob knows if the King of Castille (Spain isn’t one country yet even) gets overthrown by the local demagogues, his own French constitutional monarchy is probably next, since these revolutions have a habit of [spiraling out of control](https://en.wikipedia.org/wiki/Reign_of_Terror). Instead, Bob uses this to his advantage. He invites the people of Spain and Germany to “join France”. Remember, he now runs a nation state, not a country, and just because you speak Spanish or German doesn’t mean you aren’t allowed to be a part of his new state. Bob casts himself as a liberator. The locals cheer on Bob’s armies as they take out their old rulers.
Most of the locals don’t mind being ruled by France, because they no longer see themselves as Castilian or Aragonese or English. Remember, Bob’s rival monarchs never managed to convert their own countries into nation states. The King of Spain (Castille) never had a chance to imprint his own flag on his people. France is the first state they know. And instead of seeing themselves as Castilian or French or English, his people see themselves as “Free Europeans”, with “Slave Europeans” as the out-group.
There will be no [Treaty of Tordesillas](https://en.wikipedia.org/wiki/Treaty_of_Tordesillas). Bob is now head of a state that rules the entirety of Western Europe, and the Eastern and coastal portions of the Americas (it will take generations to settle the interior, but Bob has time). Bob is now at a crossroads. The enlightenment he has set off has not been lost on his colonists in the Americas. Bob himself probably has nothing to worry about. His colonists will be content to gorge on the plentiful land for perhaps a century if he is lucky. But, if no changes are made, they will eventually demand self-rule. If there is to be a central government, every citizen of Bob’s vast hemispherical nation must feel like they have a say in the composition of that government, and elections are very hard to hold when it still takes months to cross the Atlantic.
# 6. Who’s in charge?
Bob, a hero to his people, can probably get away with autocratic *federal* rule as “benevolent dictator for life” (with citizen legislatures in each province to provide democratic local rule), but his successor would certainly have to be democratically elected. The people would not automatically pledge allegiance to his son, although his son would probably have the best chance out of any candidate in a theoretical election. Quasi-hereditary rule is a bad precedent to set for the new democracy, but Bob would have to be of substantial character and republican virtue to instruct his people to not automatically “vote the bloodline”. Bob’s nation, having been built in a few decades, does not have the benefit of a long tradition of enlightenment and republican literature that the United States did in the 18th century, although the U.S. in the early 19th century does demonstrate it is possible for the populace to teach themselves a great deal of democratic ideology in a very short amount of time (~30–40 years).
# 7. “War against the brown people” vs. “The Federal Republic”
Bob’s successor would have two choices to preserve the unity of the nation. He could start a racial war against the “others”, further expanding the borders of “liberated” (and white) France across the world. Racism is a pretty recent invention, a product of the need to justify African slavery; for most of human history skin color was like any other physical trait—hair color, eye color, etc. What mattered was what was “inside”—religion, language, customs, etc. But even without the concept of racism, there would still be plenty of ways to stir up hatred against nonwhites in this timeline. Citizen armies would be fighting “savage” natives in the American interior, and “ignorant” Slavs and Arabs in Eurasia. A patriotic expansionary war would probably keep the secession genie in the bottle for a while, especially if it was portrayed as a war of liberation to spread democracy. But this would have to last until the communication technology caught up to make planetary democracy workable. Or the war could devolve into a [war of perpetuity](https://en.wikipedia.org/wiki/Perpetual_war) as the citizen armies come up against their limits in Africa and India.
Alternatively, Bob’s successor could devise a federal system capable of withstanding long communication times. This would be the more difficult, but also more sustainable solution. Each province of Greater France would elect four sets of representatives—two to form a local legislature, and two to represent the province in the central government in metropolitan France. Bob’s knowledge of bicameral legislatures proves very valuable in getting every citizen of Greater France to agree to this. Greater France becomes the **Federal Republic of Greater France**. The central government would initially be very weak, both by design and by circumstance, as the sheer distances involved make it unresponsive and remote. Most of the power would be vested in the regional legislatures. However, as communication and travel technology improves, the central government would become more and more powerful. You essentially have a [single nation of white people ruling half the planet](https://en.wikipedia.org/wiki/Nations_of_Nineteen_Eighty-Four)—unimaginable in our own timeline (though perfectly imaginable for anyone who has ever watched a sci-fi show with [single-culture aliens](https://scifi.stackexchange.com/questions/26425/why-do-alien-cultures-tend-to-have-one-language-one-religion-etc)).
# 8. What about everyone else?
It is interesting to think about what would happen to the rest of the world in the federal scenario. It is possible that an expansionary war would still be waged, although the leaders of the Federal Republic would probably be prudent to invest their resources in improving communication infrastructure rather than expanding the borders of an already overextended nation. More likely, the enlightenment ideals unleashed by Bob would travel beyond the French umbrella, but not across the entire globe. Arabs, Indians, and Chinese would all probably pose rough, though not impassable terrain for Bob’s democracy. You would probably see many small “vassal democracies” spring up along the borders of the Federal Republic in Russia and North Africa (Bob will be unable to colonize Sub-Saharan Africa for the same reasons that prevented European colonization in our timeline until the late 19th century).
The vassal democracies will be dwarfed by the vast Federal Republic and will be under its heavy influence, for economic reasons, if none other. They will mostly function as cultural and migratory buffers for the Federal Republic, and military buffers protecting the rest of the world. While small, the vassal democracies are nation states like the Federal Republic, and their populations will resist any attempt by the French to bring them under their direct military control. So they would hem in the enormous superstate on its northeastern border. Because smaller democracies would pop up as soon as Bob’s superstate stopped expanding, the Federal Republic would be unable to start expanding again if it ever stopped, something its leaders would be unlikely to foresee. Thus, it’s very possible that “[One World Government](https://en.wikipedia.org/wiki/World_government)” does not occur in this timeline.
[Answer]
Probably the only thing he could realistically do is create a solid education system. It would be funded by the government, as well as guided, but not controlled. The more educated people are, the faster they will move to a modern society. As access to education has increased in our lifetime, monarchies have fallen and democracy has grown. Science advances by leaps and bounds. Morals and civil rights have increased. Etc. Education gives people power.
[Answer]
OK, by handwave he becomes king of France. Now what? He doesn't speak the language, he has no ties of blood to provide a base for alliances, he's an atheist in a time when public piety was essential, and he can't even fight for himself.
He has no time to spare for widespread social reform - survival will take up all his energy. And in some respects all he has to do is wait. In less than 40 years the Hundred Years' War kicks off (in our time), and in less than 50 years time the Black Death comes a'knocking.
As for Bob's priorities,
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> 1) Modern civil rights
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What? Do you include suffrage? Any attempt to empower the 80 to 90% of the population which are peasants will be seen as a direct blow to the power of the nobility, and will ensure that the nobles join together to take him down. The Church (which was by modern standards wildly influential) will support the existing order, and any suggestion that women should be given power will only harden the Church's resolve to get this heretic off the throne.
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> 2) Modern science and medicine
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Without knowing any science or medicine? Please. Stop and think about this. Another answer suggested increasing his power base by pushing for public sanitation. Where? In the lives of the peasants? In the cities? Do you have any idea of the capital investment required to retrofit a country with water pipes? Or the technological advances needed to make those pipes on the scale required? Or the cultural changes needed to get people to actually use plumbing? Some diseases will potentially respond to sanitation (cholera, for instance, but that requires a heroic waste control effort). Others, such as the Black Death and typhus, won't. Even as late as the end of the 18th century, control of fleas was pretty much nonexistant. There exists a letter from George Washington
to a young woman who will move to the big city, warning her that a high-class woman does not scratch her flea bites in public.
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> 3) Widespread democracy
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Democracy in 1300 is, simply, treason. Treason was dealt with by death and torture. I suggest you read about the fall of the Knights Templar (1308 - 1312)
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> 4) Limit peasant suffering and abuse
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What abuse? Beyond the taxes they paid to support their rulers, there isn't a great deal of evidence of abuse, at least by local standards. In fact, France as a whole at that time had a markedly lower incidence of peasant revolts than England and Germany.
Unless you want to eliminate serfdom itself, so that the peasants are not legally tied to their land. In that case, you'll just make section 1 all the worse.
[Answer]
Politics of the time aside, there are 3 things he could do to accelerate development of the country
1) Schooling. Maybe institute something along the lines of the the Hitler Youth. Teach children how to read, regardless of class, with propaganda. Train them in basic drill and tactics with the peasant weaponry of the day. Make sure that they learn to revere the king fist, the local lord second. Reading is the most important thing in this, with the farthest reaching pass along effects. Propaganda and militarism are the bonus points here. As the youth come of age, you will have more effective military forces when the serfs have a clue. They will also be more loyal to you, personally. Also teach things like basic sanitation and agriculture. A huge thing to teach, though, would be the Scientific Method. Pound this into their heads.
2) The Printing Press. This kind of goes hand in hand with Education. Once the peasant knows how to read, you can give them something to read that is not insanely expensive to produce with the printing press. You can make sure they are reading what you want them to read at first. Include information on germ theory, sanitation, agriculture, and how to deal with the black death. Make a drumbeat of the Scientific Method. Appease the church by printing Bibles. They won't realize the dangerous part of that until it's too late.
3) Libraries and Universities. Give people a place to learn. The commons could go to the libraries, the Nobility to the university. Take the power of information control away from the Church by bypassing it.
You could probably get away with these and they will likely have the largest impact on civilization as a whole. Maybe you can bring about the Renaissance early.
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Well, here's one idea. Try to exploit the most influential social network in the country, the church. Get it to start teaching more children to read and write, and teaching mothers basic hygiene. If you can do that and get it established, you're laying the foundations for long-term development.
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Introduce basic industrialization (this doesn't mean machinery necessarily, just assembly lines, specialization) and advanced agricultural practices. Work on sanitation, especially any advancements that contribute to a lower child death rate and fewer casualties to birth.
These will work to accelerate the development of the middle class, and allow France to shift workers away from agriculture and towards innovation, education, and other advancement.
Use the freed headcount and wealth to introduce *basic* education as widespread as possible, thus further encouraging innovation and development after his lifetime.
I'd say these things, if successfully implemented without making enemies, would certainly speed up the development of the world, and push it faster towards the popularization of democracy.
[Answer]
Being King does not make you God, despite what Kings try to say. The King's word is not law because it's the King's word. It only becomes law because other people with power like it and/or are willing to go along with it.
So whatever the King does, it has to be something which will not upset the existing noble structure.
I'll group your priorities based on the ease with which a King could actually accomplish them:
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> Modern science and medicine
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This is something a King could actually help kickstart. Kings have money, so the King could fund various people. Indeed, a lot of the scientists/alchemists/etc of that era were wealthy noblemen. Find some of these people and fund them.
But the most important thing the King can do with regard to this is bring forth future *knowledge*. While most 30-year-olds probably aren't conversant enough with the history of science to know the best place to jump-start a scientific revolution, even a basic education can help them move certain things forward.
The medical profession would probably be a good place to start. The King could start training medical professionals in germ theory (firing those who don't want to give up their leeches). The King may not know much about antibiotics, but the concept of sterilization could work wonders for relatively primitive surgeries. If these techniques are effective, then those medical professionals trained in them will likely be hired by other nobles (who else can pay for a physician?), which can help the King build up support among them.
The King's ability to improve matters of science would be very contingent on how much the person knew. If he learned calculus, being able to teach the mathematicians about the Fundamental Theorem could work wonders long-term. Someone knowledgeable about the Theory of Evolution might be able to assemble a cabal of biologists to accept it and gather evidence to help sustain it.
But even so, there are many scientific fields that even a trained modern scientist couldn't help with, simply because they don't know how to use the tools that would exist in that day.
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> Limit peasant suffering and abuse
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The suffering due to general day-to-day life for most peasants is a consequence of having to do lots of back-breaking agricultural work day-in and day-out. One King cannot invent the time-saving machines and infrastructure that would allow such a society to alleviate that kind of suffering.
Nor can the King simply get more peasants so that they individually don't have to work as hard. Just as in modern capitalism, the number of people working the fields is essentially the fewest number they can get away with. More bodies means more cost for the same agricultural return, which now must be divided among more mouths to feed.
And that cost will be taken out of some noble's pockets, since the King doesn't actually own those nobles' land. Take it out of enough of them, and suddenly the King will no longer be King.
Abuse of peasants comes in two directions: bandits/lawlessness and the nobility.
While banditry certainly existed, it's not like it was an epidemic or something. Criminal acts against peasants generally were not tolerated. So there's not a whole lot the King could do to improve things. At least, not without costing a lot more money for relatively little gain. Plus, the nobles might start thinking that the King's trying to undercut their authority in their own lands.
As for noble abuse, curbing that would require serious politicking. Most 30-year-olds cannot politic at the level required to effect such change.
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> Modern civil rights
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What does that even mean? Free speech means very little to a populace where the literacy rate is a *rounding error* and most people live&die in the same village in which they were born. Free practice of religion is going to piss off the local church. Right to privacy is irrelevant to people who live in shacks and don't have very much stuff. And so forth.
Most civil rights just don't make sense for the kind of society that these people live in. The most you could do is just strengthen the existing justice system. But even that requires getting the permission of the nobility. And they would make sure that such judicial inquiry cannot be brought against them.
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> Widespread democracy
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Define "democracy". Leadership of local towns and really local issues were often handled "democratically" by some measures.
But if you're talking about *significant* self-governance, that's not going to happen. Not so long as there is a nobility in place who has all of the de-facto power.
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> Should he try to give more rights to peasants at the risk of angering the nobles?
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Not being King anymore will help nobody. So no.
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> Should he attack and invade neighboring kingdoms in order to bring them under his kind rule, or should he set a peaceful example?
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If this guy is trying to make significant reformations in his kingdom, that's going to be *expensive*. Whether it's funding research, large public-works projects, buying the loyalty of nobles so that he can set up independent tribunals to investigate matters, whatever. Doing all of that *as well as* funding a war is insanity.
It should also be noted that random 30-year-olds probably don't know the land well enough to know who would be a good idea to even attack, let alone the ramifications of declaring war.
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> Should he invest a lot in education and science at the risk of being regarded weak by his nobility and neighboring kingdoms?
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This is really coming closer to the biggest unasked part of your question: can a random 30-year-old actually function as King without being deposed or conquered?
I highly doubt it.
Imagine running a business. Can most 30-year-olds actually keep a business functioning? Drumming up new customers, keeping old ones, getting things done on time, dealing with competition and government regulations, etc? Lots of small businesses fail, after all.
Now, how many such people could run *Apple*, without cratering the company within 10 years.
The thing about running a kingdom is that you have to *run it.* And the fact is, most people wouldn't have the first damn clue what to do with a kingdom.
[Answer]
I would certainly want to encourage science with endowments for scientific research and so on.
What about democracy, human rights, and limiting peasant suffering?
IMHO War violates democracy (killing people who have not voted to be killed today)(drafting people into the army against their will), and human rights, and causes massive peasant suffering. So therefore I would want to eliminate the independent sovereign national governments of Europe that would kill a couple of hundred million people with their future wars, and caused vast poverty by their crushing military taxation, and strengthen the Holy Roman Empire and the eastern Roman or "Byzantine" Empire.
By chance this question makes the time traveler the evil rebel anti king of France, the leader of the forces of evil that will cause so much horror and suffering in the future, soon after the French kingdom turned evil and began increasing its evil power.
So it would be relatively easy for the time traveler who somehow made himself leader of the forces of evil to sabotage and reverse this evil process, and weaken France and strengthen the Holy Roman and Eastern Roman Empires. By weakening France and strengthening the Holy Roman Empire so that France can never destroy it, he can prevent the independent nations of Germany and Italy from ever arising to afflict an unhappy world, thus killing three evil birds with one stone.
[Answer]
I want to add to my answer that for many centuries the French governments believed that what was bad for the Holy Roman Empire and the kingdoms of Italy, Burgundy and Germany within it was good for France. But what was bad for the Holy Roman empire and the Kingdoms of Germany, Italy, and Burgundy was good for the future nation of Germany, and what was good for the future nation of Germany was bad for France.
So for many centuries the the actual result of French foreign policy was basically making 1914-18 and 1940-45 possible.
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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.
Okay, so now that we've established that the [badger folk](https://worldbuilding.stackexchange.com/questions/20335/how-to-justify-digging-claws-and-opposable-thumbs-in-the-same-being) (or *Melinae sapien*, if you want to be politically correct) are trading their ore to the humans for [cat food](https://worldbuilding.stackexchange.com/a/30054/8914). Now we need to determine what kind of culture exchange they'll have.
To look at one particular issue, what kind of human music would badger folk prefer? Of course, individual badger folk will have different preferences, but in a similar way that Americans liked British Rock best back in the day, badger folk will like a specific type of human music best.
We can assume that badger folk have similar [musical preferences](https://en.wikipedia.org/wiki/Zoomusicology) to that of real badgers.
(Note: If you are questioning the [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'") tag, see [Can hard-science apply to social sciences and other academic fields?](https://worldbuilding.meta.stackexchange.com/questions/2348/can-hard-science-apply-to-social-sciences-and-other-academic-fields) and [Is the use of the [Hard-Science] tag acceptable in questions with a non-hard premise?](https://worldbuilding.meta.stackexchange.com/questions/2761/is-the-use-of-the-hard-science-tag-acceptable-in-questions-with-a-non-hard-pre))
(Note: This isn't opinion based. I'm asking for [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'") answers based on zoomusicology (or other fields), not opinion based-answers.)
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Let's approach it the way we can (generalize) human music. I can find nothing on badger behavior towards music, so this is all just speculation. Also, badger humans don't exist (yet?).
**Dwellings**
Badgers live in underground dwelling units that are tightly knit. This could suggest a large interest in community and cooperation in tough times and good. This could also suggest a little bit less on the bass, because you'd be shaking dirt all over the place.
**Diet**
Diet of a badger is largely known to eat bugs to small mammals. This helps me in no way.
**Precedents**
[Mr. Badger](https://en.wikipedia.org/wiki/The_Wind_in_the_Willows#Main_characters) was a grumpy, but wise character who pointed out the realities of the world to an arguably naive character in the Wind in the Willows.
**Geography**
Badgers are primarily found in North America, Britain, and Ireland, but can be found in many other places.
**Society**
I am guessing that Badger-People might feel marginalized from both human and badger populations.
From those five generalizations, I would put their favorite to be **Alt-Country**.
Brit/US Indie [Geography] music with a realist, sometimes sad slant [Mr Badger]; a bit of alternative feel [Society], a hint of bluegrass [Diet], a social component [Dwelling], and not too much bass [underground Dwelling].
While it is not my favorite music, but I'd call it [Indie/Alt/Country/Bluegrass](https://www.youtube.com/watch?v=braQeLkJUvE). That is broad speculation.
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I will start by adding a link to the audio frequency ranges of some [animals](http://www.lsu.edu/deafness/HearingRange.html) . Although the badger is not present in the list provided at the bottom of the above link , a ferrets frequency range is provided. Since the badger is closely related to a [ferret](http://a-z-animals.com/animals/badger/) , we can assume that the badgers audio frequency lies between 16 and 44,000 Hz. A human beings range is 64-23,000 Hz.
So a badger can pick up on wider spectrum of frequencies than humans. Most music genres humans enjoy or recognise fall into the audio spectrum they can identify , so it is probable that badgers will enjoy the same , also you might invent a new genre that falls into the badgers spectrum.
As far as the question is concerned , with their level of sophistication it would be unfair to generalise a particular genre for the whole species. They might not be huge fans of music that may that may hamper their burrows which is completely logical.
My guess is they will invent new genres like humans did , I guess this too is a part of evolving.
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I would expect that any music with synthetically added room effects would be very bothersome for them. Living in tunnels, they would be quickly aware of what sounds carry through a tunnel and which ones do not. Our human tendency to "just add some reverb" to make it sound better would be appalling to them in the same way it hurts the eye to see a really garish green and red image, or the feeling of fingernails down a chalk board. Most modern pop would be impossible to listen to (for the badgers I mean...)
The real badger is a solitary creature, which would certainly have an effect on the kind of music they like. I think it could have any one of a number of effects, but I'd peg the most likely to be a preference for music with many instruments playing together, as such music might be a symbol differentiating them from their solitary lesser kin.
Between these, I would say classical orchestral music would be most preferable to them.
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I'm guessing the badgerfolk don't natively speak the human language? They probably don't get much out of lyrics, then.
They may not even be able to read human emotions. A human might think a song was "sad" or "melancholy", but a badger might not recognize that those intonations mean sadness.
Badgerfolk probably prefer instrumental music (or classical music, as AndreiROM said), because that music is designed to be interesting even without lyrics.
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I'm unsure if the music trade is possible, though. Checking your other questions, this is a fantasy world, and the technology level is "early 1800s". The phonograph wasn't invented until 1877, and even after that it would take several years for the technology to be widespread enough to make music for trade.
If badgerfolk like human music, the way they listen to it is the way everyone else does at that time: they go find a tavern, buy a drink, and listen to whatever the bard wants to sing.
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> what kind of human music would badger folk prefer
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They would like music that they could sing themselves and join in with. If you listen to these badger vocalisations - <https://youtu.be/b4lpFjHsGLo>
- you will realised they have high-pitched voices so songs by the Chipmunks would be suitable <https://youtu.be/-RP19fnff_c>
Or
They would be fascinated by human music that seemed at least superficially to be about badgers:
1. The White Stripes
<https://en.wikipedia.org/wiki/The_White_Stripes>
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2. Ebony and Ivory by Paul McCartney and Stevie Wonder
<https://www.youtube.com/results?search_query=ebony+and+ivory>
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3. Badger badger badger by Brian May
<https://youtu.be/EllYgcWmcAY>
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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.
This is what envision when I think "what music would play in the town square of a badger folk village?"
<https://www.youtube.com/watch?v=8bzziAv9o4w>
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So here's what I'm trying to do.
I've got a setting that at a medieval level of technology and is rather similar to Europe with knights, castles and all that jazz. However to give the setting some character, I thought I replace the horse with a suitable dog based alternative that been breed to a suitable size and form for being a knights mount.
What would be the major differences to consider, as well as adaptations needed to get similar results in practice to horses?
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Realistically, a well-trained backpacking dog can carry up to anywhere between 30% and 50% of its weight on its back. While the dog's spine is possibly going to be a problem, that can be worked around with a suitably designed mount, so isn't the showstopper. People regularly take dogs backpacking with large dogs carrying tens of kilograms with no real trouble. Well-conditioned sled dogs, especially in teams, can pull a lot more for each unit of weight of dog, but that isn't what you are asking about.
You mention knights mount, which makes me think of knights in armor and with weaponry. I imagine you'd be looking at *at least* 100 kg for something reasonably realistic there. Let's say these dogs are specifically bred for the purpose, and bred specifically for carrying ability; let's say they can carry something like 40% of their own weight on their backs, as an average.
Given that, the dog would need to weigh *at least* $ \frac{100}{0.4} = 250 $ kg to be able to carry the load.
**Note that this establishes *a lower bound.*** The 100 kg human is probably on the low end, and the 40% carrying ability is probably reasonably high (30% being a generally suggested target to aim for in backpacking with dogs), leading to the distinct possibility and indeed *probability* that the dogs would need to be yet larger. I'm going with 250 kg in this answer to have a single figure to work with, but realistically, you might be looking at the range 250 kg to 500 kg weight for these dogs, and would need to adjust everything below accordingly.
As a general rule of thumb, raw-fed dogs eat about 2% of their weight per day. Since high-energy dry dog food isn't available at a medieval level of technology, this is probably the closest readily comparable to what your dogs would need to eat. 2% of 250 kg is about 5 kg per day, but this could easily be anywhere from 3 kg to 10 kg, depending on the individual dog and the level of activity for the day.
Bowlturner mentioned hip dysplasia, and specifically how the incidence of hip dysplasia tends to go up with size, in the comments to [Francine DeGrood Taylor's answer](https://worldbuilding.stackexchange.com/a/28255/29). While this is a valid consideration, it is also important to keep in mind that if you are breeding these dogs for riding, anything that inhibits their motion in any way is going to be an extremely serious fault. Even more so in an environment where resources are scarce; if these people have any understanding of how breeding for specific traits works, which it sounds like based on your question, they would absolutely not allow any such dog to breed. Breeding out hip and elbow dysplasia to the point that it isn't a major problem probably wouldn't be very difficult even in breeds that currently have a significant percentage of dysplasia, if we didn't have the bad taste of also breeding for many other traits. Also keep in mind here that breeding for "pure breeds" generally speaking is a very new phenomenon, dating back only to the late 1800s or so. Before then, breeding was purely for function: you wanted a guardian dog, a sheepdog, a sled dog, or something else, and you didn't particularly care what it looked like as long as it did its job (and the value of a dog was in how well it did its job). In some breeds this preference of function over form remains even today, and you don't need to look much farther than to working-bred sled dogs to find it in abundance. You may want to compare [Why didn't Antarctic sled dogs have hip dysplasia?](http://www.instituteofcaninebiology.org/blog/why-didnt-antarctic-sled-dogs-have-hip-dysplasia) from the [Institute of Canine Biology blog](http://www.instituteofcaninebiology.org/blog).
You possibly wouldn't want just one animal. Having a single one puts you at risk if something ever happens to it. If nothing else, you might want one animal that you are riding on, and another for carrying supplies. That would instantly double the amount of food needed for the animals. Even more so since in the comments you talk about "packs".
Instead of horses, which are herbivores, you are now dealing with dogs, which are basically carnivores. Not only are you going to have to be able to procure that amount of meat on a regular basis (that's on the order of a pig per week for two of these), you will also have the issue of the dogs' instincts to contend with. (Instincts can be controlled to some extent through breeding and training, but they will still be there, and a potentially pack-living carnivore large and strong enough to actually carry a human on its back isn't the kind of animal you'd want to meet!) Horses can simply be allowed to graze during calm periods, and are unlikely to cause significant trouble; doing the same with dogs, especially dogs of this size, probably wouldn't be very appreciated by the locals.
It's instructive to look at the size of pack-hunting carnivores. Consider for example [hyenas](https://en.wikipedia.org/wiki/Hyena) (up to some 70-80 kg), [wolves](https://en.wikipedia.org/wiki/Gray_wolf) (30-80 kg), [lions](https://en.wikipedia.org/wiki/Lion) (females, being the primary hunters, at 120-130 kg) and so on. Even really big current-day dog breeds rarely top 100 kg (for examples, look to the [Caucasian Shepherd](https://en.wikipedia.org/wiki/Caucasian_Shepherd_Dog), [Anatolian Shepherds](https://en.wikipedia.org/wiki/Anatolian_Shepherd_Dog), or [St. Bernards](https://en.wikipedia.org/wiki/St._Bernard_%28dog%29) for some really big ones). Beyond the size needed for a group to take down the commonly available prey, growing larger comes at a significant cost for no real corresponding gain; it then becomes a better strategy to team up than to grow even larger.
You would have to come up with a situation where this cost on the people keeping these animals is less than the gain these animals would bring. In a medieval level of technology society, you are already looking at most people being at a subsistence level of existence. Knights might have it slightly easier for serving the King, but their resources are still going to be significantly limited.
Looking back to pigs, you would need something like 20 pigs per year per dog, just for feeding. Realistically, then, you need anywhere from 75 to 100 or so pigs per dog, just to ensure a consistent availability of food. And you need to bring these with you while you are travelling, because while dogs can go for some time without eating, they tend to get somewhat grumpy after a while -- which is a quality you absolutely would not want in abundance from the animal you are riding, and even more so from one that probably would be able to kill you right away with one bite if the thought crossed its mind that you are actually a big lump of meat, sitting conveniently nearby.
TL;DR: **Properly trained horses, possibly coupled with smaller groups of regular-sized dogs, sound much more practical.**
[Answer]
The reason horses can be used as mounts and not dogs is because the muscles of their back are not strong enough and their spines are not constructed to carry weight on top. It has nothing to do with size. There are Shetland ponies smaller than some dog breeds but if you tried to ride the dog the way you ride a pony, the dog will eventually suffer severe back damage.
An interesting link:
<http://www.dogster.com/the-scoop/dear-abby-child-rode-my-dog-now-my-dog-is-crippled-for-life>
Now, that being said, it doesn't seem unreasonable that people would be able to breed a dog with a spine capable of supporting more weight than a dog might normally be able to support. They might have to design a "saddle" that distributes the weight differently.
One other consideration; the larger a dog is, the shorter their lifespan. Dogs large enough to bear the weight of an armored knight might not live long enough to be trained to do so...
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*dog chariots*
Just look at that noble beast [](https://i.stack.imgur.com/edOH1.jpg)
You might also be able to run them as a team
[](https://i.stack.imgur.com/2dDxz.jpg)
Rather than using them as pure mounts though, I'd consider the traditional dragoon. Rather than fighting mounted, a knight and his team of utility dogs would allow a knight to reach where he's needed swiftly, and dismount. The dog team, with appropriate harnesses could act as a force multiplier, harassing an enemy knight.
I distinctly remember reading a story where an unhorsed knight was protected by his faithful dog, who'd knock over or otherwise attack enemies who tried to take him hostage. A *pack* of dogs might even be able to knock over and maybe even sit on an enemy knight in full armour.
They might also be useful for digging fortifications of protecting encampments.
Size is useful for all these things.
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Okay, I will make a little premise/context to give the question a decent background. I know that the scenario could look rather "handwavy", but take it as the framework on which the answer should be given (I will elaborate more on the causes, but this is *not necessary* inside this post).
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> Oceans and seas have become higly corrosive. This seems to affect almost every metal, plastic, organic and biological compounds but seems to arbitrarily spare some minerals and hydrocarbons to certain degrees (i.e. no dissolution of the oceanic floor), nothing - however - that could be shaped effectively for practical uses. As a result, 99% of the sea life died and boat travels are no more feasible due to the short duration of the hulls. For unknown reasons, fresh water is not affected, nor it is rain (lakes, rivers, glaciers "work" as usual).
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So, how would this affect our world? I have thought of several things:
* The complete lack of fish / sea food would cause problems for all those regions which consistently live on fish (see [list of most important fish-exporting countries](https://en.wikipedia.org/wiki/Fishing_industry_by_country) and [this page which pretty sums up a FAO report](https://www.msc.org/healthy-oceans/the-oceans-today/fish-as-food)).
* Travels between continents would only be feasible by airplane; also, all the goods which are usually transported by cargo ships would have to be moved by airplane - or not to be moved at all, since [if we consider only Europe and only short range transportations, we are talking about more than *1.5 billion tonnes* of stuff](http://ec.europa.eu/eurostat/statistics-explained/index.php/Maritime_transport_statistics_-_short_sea_shipping_of_goods).
* [Submarine cables](https://en.wikipedia.org/wiki/Submarine_communications_cable) would be destroyed, cutting most of communications (see [this map](http://www.submarinecablemap.com/) just to have an idea -> the only alternative would be satellite communications or radio waves.
* Oil extraction platforms would collapse and couldn't be used anymore, thus [reducing oil extraction by approximately 30%](http://oils.gpa.unep.org/facts/extraction.htm) and force the use of other resources or extraction sites.
* People from small islands without or with only one airport per several islands (e.g. [Fær Øer islands](https://it.wikipedia.org/wiki/F%C3%A6r_%C3%98er)) should be evacuated, since they would not be able to get by in any other way.
* Sea/oceanic water couldn't be used anymore as [a coolant for thermal power plants](http://www.world-nuclear.org/info/Current-and-Future-Generation/Cooling-Power-Plants/).
* Economic crisis for most sea/ocean turistic places.
* Seaside cities would be mostly abandoned or "moved back" to the inland.
* Sea birds would either die of starvation or massively change their diet / habitat.
* Last but not the least, oxygen production would drop due to the disappearance of almost all [phytoplankton](http://earthsky.org/earth/how-much-do-oceans-add-to-worlds-oxygen) (50 to 85% of the total oxygen produced by our own world). Since this would be pretty world-ending, either assume that the population of phytoplankton decreases enough to cause *"massive human casualties"* but not enough to completely wipe out the world population (yes, this is contrast with the opening, but a "everyone dies" answer is not exactly constructive - so let's handwave it a bit more :P) or that we have some other ways of supplying a decent quantity of oxygen to the atmosphere - which one you prefer.
Quite a bunch of stuff, huh? But I still feel like I am missing something. So, now the question:
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> **Aside from the points listed, what would be the major effects of the described scenario on a contemporary/[near-future-like](http://tvtropes.org/pmwiki/pmwiki.php/Main/TwentyMinutesIntoTheFuture) world?**
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If the question is too broad, I will try to stretch it to the bones :D
**N. B.** This is **not** a question on the feasibility of the scenario, this is a question on the consequences of such scenario ;)
**EDIT:** since it looks like my last bullet point would have killed everyone on the planet just by itself, I have edited it ^\_^
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Here are some more points. Note that some of them are consequences of the point given in the question.
From an economics point of view :
* Trans-Siberian railway got a second youth, since it suddenly become the most practical way to transport the many products from China to Europe.
* Europe become very dependant on Russia for food and petrol, since importation from Africa, South America and Arabia are drastically reduced.
* USA becomes isolated and lost access to the very important markets of China, India, Europe and Russia.
* The rise in the need for petrol (due to air planes being more used) speed up the use of the remaining petrol reserves.
* Economic crisis for most of the world, since most countries heavily relies on exportations and importations overseas.
From a military point of view :
* Military operations overseas (e.g. war in Afghanistan and in Middle East) from Western countries become very hard and their doctrine about sea supremacy becomes obsolete, forcing them to heavily reconsider their strategies.
* Ships and submarines carrying nuclear engine or warheads are destroyed with unknown consequences due to the nuclear material they were carrying.
* Corroding sea water is studied for its military applications.
Migration point of view :
* European union is happy, because migrants can no longer cross the Mediterranean sea.
Polar point of view :
* North pole either dissolve, giving birth (for a time) to giant iceberg deriving in the oceans, or do not dissolve and become seen as a possible way to rely the American continent to the rest of the world.
Disaster point of view :
* Country (e.g. United Arab Emirate and Israel to a certain extend) relying on sea water desalination to get water are doomed.
* Nobody wants to accept people who need to be evacuated from islands, and their are doomed.
[Answer]
**Planet Earth is going to smell really really bad.** Depending on where the corrosion stops in breaking down sea life, the oceans are going to get really stinky, really quickly. As those aromatic compounds "boil off", the winds will carry them over the land and the attendant stench will be fantastic. It will be very clear to any human survivors that the oceans have died.
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**Corrosive Atmosphere**
I'm adding this despite the question having an accepted answer as this would be an important addendum.
You can't have just one but not the other. If the oceans are massively corrosive, a good portion of that material is going to transfer to the air. If it's CO2, then that's going to raise the CO2 content of the atmosphere substantially higher than fossil fuel burning would. We're going to look like Venus in a hurry.
If it's something else like sulfur dioxide (sulfuric acid) or hydrogen chloride (hydrochloric acid) the that's going to leach into the atmosphere and soak into our very moist lung tissue and get busy burning the heck out of our lungs.
Think being downwind of a volcano that's belching gas like crazy. If you've ever visited the Big Island volcanos, you have the beginnings of an idea of just how nasty it can get. But there's no getting away from this issue. It's going to burn pretty much all breathing life forms to death in short order. Masks and breathing apparatus will save you for a bit. But eventually those air supplies will run out.
We'll also be down to primitive forms of life pretty quickly as vegetation won't be able to take massively lowered soil pH for very long either. Remember the pictures showing the effects of acid rain on forests? This will be much worse.
With the collapse of a good portion of the biosphere, the remaining parts won't last long either. The sunsets will be pretty though.
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Pretty much on track for happening now, but not quite as bad.
They're predicting the end of coral reefs, and most things that have shells. Massive re-organization of sea-life. Elimination of a lot of foodstuffs, even if we weren't already over-fishing.
Higher CO2 leads to ocean acidification.
Increased sea-levels and as the ocean heats up it expands - nevermind the melting of ice, decreasing salinization, destruction of oceanic conveyor belt, disruption of sea-currents, and general pollution. Ocean has kicked over, and we cannot stop it. This will result in more, and more violent, storms as warmer oceans put more water into the atmosphere.
<http://www.theguardian.com/environment/climate-consensus-97-per-cent/2015/jan/22/oceans-warming-so-fast-they-keep-breaking-scientists-charts>
<http://news.mit.edu/2015/ocean-acidification-phytoplankton-0720>
Etc, etc.
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In my world, for reasons that are unimportant for now, there can be no agriculture. Because of this, civilization can not depend upon agriculture, as we practice it, for a food supply.
A solution for this would be a food chain **similar** to the marine food chain on Earth. In this system 70% (give or take) of the ecosystem is algae and small creatures, eaten by fish, with fewer large predators.
The species required to fill this role would need to reproduce at a young age, grow quickly, and produce many offspring. If they reproduced fast enough, I think that harvesting these animals (and other life) could fill the role of traditional agriculture on Earth.
What sort of animal could fulfill this role in my ecosystem?
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Animals are *always* less efficient then plants for providing food. Think about it, you still need plants of some form (plankton counts as 'plants' since they use photosynthesis) to produce the energy, and then something to eat it. All the energy the animal spends eating, breathing, growing, mating, and having young is energy that is 'wasted', The animal is going to need substantially more energy in it's lifetime then you get out of eating it, and thus is going to eat substantially more plants.
There are two reasons we grow livestock despite this (well three if you include 'i just love the taste of sausage over corn').
1. Humans *need* a certain amount of proteins and other resources that, until very recently, could only reliably come from animals. We know know enough about nutrition to allow pure vegetarians to exist and be healthy, but they do have to be very careful about what they eat to ensure they replace those resources that our body evolved to get from animals.
2. Some animals can consume resources we can not able to consume ourselves, thus converting a source of energy that we could not utilize into one we can. Sure the animal may waste 80% of the energy consumed, but that still gives us 20% of the consumed energy rather then the 0 percent we would have gotten if we just left that inedible grass untouched.
Option 1 doesn't really apply if your looking to use animals as your staple food (except in reverse, you need to still make sure you get enough plant to avoid scurvy and other nutritional issues).
Thus option 2 is the important factor in making livestock a productive option. To make your animals useful they *must* consume something that humans just can't consume otherwise. If not they are an extravagant waste.
Keep in mind that most places where grass can grow plants can grow, so making a situation where there is plentiful food to feed animals but where you can not eat the food yourself, and you can not plant foods you could eat, takes some work. Generally this is going to be limited to areas where even grass has difficulty growing, and thus any other plants will struggle and die before bearing fruit. This would, however, limit your food supplies.
In your world there is plenty of life around you, and if not they can move to a place where there is more life easily. The best option for exploiting the existing life would be to catch animals and gather food directly, use of livestock that consumes anything humans can eat will be too wasteful.
If you wanted to make livestock viable the biggest thing you must consider is not how fast the grow or health, but what they eat. All livestock must consume resources that humans can not, none of it can be eating things humans *can* eat or it's a waste.
This makes grazing animals possible, however, not everywhere the humans travel will have large grazing lands to consume. That makes feeding the livestock while traveling through areas that don't have heavy grasses difficult; where there aren't grasses you have to feed your livestock from your own food reserves and thus they are a liability.
In this situation the best solution would be have lots of livestock while in areas with lots of grassland, and very little in areas without it. In other words your want to butcher and eat most of your livestock when leaving grassland areas, keeping only enough breeding stock to start up a good herd later.
This suggests your want livestock that is smaller then the traditional cows or even pigs we use. Your want comparatively small creatures that have short life cycles. Thus it costs you less resources to keep a breeding stock alive when there isn't grassland (they don't eat too much), and their quicker breeding cycle means they can quickly (and exponentially) to fill up large grasslands when you find them.
You would likely be breeding your own grazing creatures. They would grow to be potentially quite fat for their size (mostly meat not bone, like modern cows), but smaller (not as tall or big as a cow, despite having the same proportions as one). The creature would likely be one that is very good at adapting to available food as well. When it's starved it stays somewhat skinny, when it has lots of food it eats up and throws on lots of fat reserves, doubling or tripping in size. This allows them to not be too expensive to keep while traveling, and still be useful for harvesting when you have grazing lands.
I describe what the creature is like because humans will make it! You can do some amazing things with breeding, compare a Chihuahua to a wolf, or maize to modern corn. In a short period of time we have bred creatures to be substantially different from what they started, and to better meet our needs. Modern animals that are slaughtered for food could *not* survive in the wild, we have bred them to be so full of fat (that we can eat) that they are slow and unable to fend for themselves. We've even bred dogs that can not even reproduce without human intervention to meet our needs. Humans will decide what they want their livestock to look like, and breed those traits into whatever animal they started with.
As I said in your first question I imagine flying creatures would be some of the most common non-aquatic species, due to the ease of migration. Thus another common creature would be some sort of 'flying' livestock. This could come in two forms. The first is one that survives off of bugs (like bats), but is bread to put on more weight and produce lots of milk/nectar. They consume all the tiny bugs that are too small to be worth catching and eating for humans, but produce something humans can use. They wouldn't be your primary foodstuff, but it is a 'free' supplemental source of food, for a group that can't rely on growing their own finding ways to exploit all available food in an area will be important.
They will likely use hawks to hunt flying animals as well, though this will likely be more about training them to catch food and bring it back to humans then letting them hunt their own food to fatten them up.
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Your best bet is **Insects**. They fit all of your criteria - grow fast, tons of offspring, etc. Check out the wikipedia link below, they claim that insects take roughly 10x less plant nutrients to produce equivalent animal biomass. So that's well within your 70% target.
Many human cultures consume insects [deliberately](https://en.wikipedia.org/wiki/Entomophagy), and most of us consume at least some insects [unintentionally](https://en.wikipedia.org/wiki/The_Food_Defect_Action_Levels), so this seems quite possible.
Eat up!
[](https://i.stack.imgur.com/WDDIK.jpg)
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There isn't really an answer to this question. Whatever fish you like really :)
The faster they grow then the fewer of them you need but if there are enough of them compared to the population of people eating them then it doesn't matter.
You should look at the Inuit. They live on snow and eat basically diet very heavy in meat and fish. No agriculture and just a few berries and suchlike that they can gather occasionally.
<https://en.wikipedia.org/wiki/Inuit_diet>
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**Uh.. you can do this now if you want.**
Start with your [phytoplankton](https://en.wikipedia.org/wiki/Phytoplankton), which get their energy from the sun, and move up the food chain with the [kinds of plankton](https://en.wikipedia.org/wiki/Zooplankton) that eat them. Continue up the food chain.
For the types of fish we can eat, that reproduce quickly, I wouldn't go with just "one successful type," but rather a wide-variety in order to maintain a healthy ecosystem. The amount depends on the population you're sustaining.
You may want to (cringe) milk the mammals to add to the diet; dolphins, for example, [produce high fat milks](http://www.whalefacts.org/dolphin-milk/). Or you can have predatory land mammals who eat fish, and get your extra nutrients from them.
There are groups of people, particularly some [Brahmin](https://en.wikipedia.org/wiki/Pescetarianism#Hinduism), who stick to pescetarianism and milk.
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The answer are:
>
> silkworms
>
>
>
**They grow quick**, can be coocked and you can even obtain silk from them, actually they are part of the diet in several countries because they are [edible](https://en.wikipedia.org/wiki/Beondegi).
Of course I'm assuming your world has anyway a lot of vegetation ("no agriculture" is different from "no vegetation") growing natively. Silkworms can simply be placed on plants, you wait them to grow, and once they become crysalis you take them off the vegetation.
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If humans are not native to the environment and were unable to introduce terrestrial food crops, then it's possible that the autotrophs are toxic or otherwise inedible to humans. In that case we might find an animal that can eat the autotrophs but which we can eat in turn or which produces something we can eat (as in the case of Eric Flint's novel "The Mother of Demons" although the animals there are also sapient and so not really "farmed")
We might also genetically engineer such an animal, but if we could do that we could also probably engineer a plant we could grow and eat safely.
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From what I know about these music styles, the only problematic part may be the instruments - [sampling](http://en.wikipedia.org/wiki/Sampling_(music)) was impossible in medieval times.
Apart from that, is there anything, which would rap music impossible in the European Middle Ages?
Notes:
1. Some scientists [believe](http://www.telegraph.co.uk/culture/music/3998862/Rap-music-originated-in-medieval-Scottish-pubs-claims-American-professor.html) that something similar to rap existed in Scotland.
2. I assume that in its simplest form the only things you need to perform rap music are drums (which probably existed in the Middle ages) and lyrics.
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There is a line of "reasoning" I sometimes hear from people in the SCA: "well they had indigo dye, and they had french seams, and they had pants, so blue jeans are totally period!" Well, yes and no.
So too with modern music forms. Yes you can trace some elements back -- they had drums in the middle ages, and recited poetry with instrumental accompaniment, and certain musical forms like [isorhythmic motets](http://en.wikipedia.org/wiki/Isorhythm#The_isorhythmic_motet) were all *about* rhythmic presentation, and you can squint and tilt your head sideways and say "sounds like rap". But a musical style develops in a *context*, so you would need to find some reason in your world for these particular events to come together in this particular way to produce a given result. What problem is solved by blue jeans? What development is facilitated by rap? Can you find *that need* within your world?
One path you could take: not everybody is skilled with musical instruments, and not all of them can play drums either (trust me...), but rhythmic accompaniment is a lower bar to entry than the lyre or the lute. So you could imagine a setting in which a drum-accompanied alternative to the lyre-accompanied poems arises, because that's what people in that small village know how to do. From there, you might find the texts evolving, perhaps to emphasize simple rhythms better. Throw all that into the pot for a while and you can see how something kind of like rap could emerge. Or you could start from the aforementioned isorhythmic motets and start simplifying the melodies and reduce them from 2-3 parts down to one to accommodate the skill of the singers you have, and then go from there.
But it will only be believable if it *arises from within* your world, not if it is *retrojected into it*.
(By the way, medieval and renaissance music is one of my hobbies.)
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The answer to your question depends largely on your definition of rap. If you want something that sounds very similar to nowadays perception of rap, it would rarely be possible. Rap in its current form developed from a mix of many music styles not yet invented in the middle ages (obviously). You won't get Tupac instead of Luther ;-).
**BUT:** You answered your question already. There were many forms of "speech song" and similar things with techniques used in rap. In operas (not middle ages, I know) there was [recitative](http://en.wikipedia.org/wiki/Recitative) and in christian songs there was [reciting tone](http://en.wikipedia.org/wiki/Reciting_tone).I am pretty shure that bards in the middle ages also used a form of singing where they could get much text into a song (to get the plot moving).
So, it depends what you want to find. The harsh environment of poor townsmen in the middle ages may have brought some amateur musicians to life which would have much in common with "gangsta rappers" of our present.
But keep in mind, "free time" did not exist back then. You pretty much worked as much as you could to feed yourself. I doubt that these musicians would be very skilled. Some drums to beat on, and homebrewed texts without much refinement is everything you can expect.
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The answer, I think, is a resounding yes and no. It depends on what aspects of rap/hip hop you're talking about.
The yes part applies if you're talking purely about the musical structure of rap.
The no part applies if you're thinking about the "cultural edginess" of, especially, gangsta rap, although it applies across the board. Those were far less permissive times, and much of the critical tone of rap / hip hop would come under the heading of "treason" and "impiety", depending on whether it addressed politics or religion, respectively. And both were capital offenses. For instance, Elizabeth I, in 1603, responded to the activities of Irish harpers by a command to Lord Barrymore, “to hang the harpers, wherever found, and destroy their instruments.”
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[Check this out](http://rads.stackoverflow.com/amzn/click/B000002SKX). Also, what did minsterals and harp-carying sheapards do? People would relate stories and poems without writing a full melody line; rather, just speaking with an accompaniment.
The specific rythems used would be different from what you've used to, and reflect both the language and the instrument used.
Disclaimer: nobody really knows, as repeating songs automatically changed with prevailing style, and applied pailentologists are biased with what they already know of music.
In short, it is beleivable. You could write something using the ideas of what a travelling minstrel would sing about and the capabilities of the instrument, and be inspired by your knowlwdge of hip-hop, and make it plausable to the audience.
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One question that needs to be asked is who's supporting the... well, if it's rap, I can't exactly call them musicians, can I? Maybe performers is the appropriate word. If you look at history, bards/minstrels basically got supported by the nobility, who later on supported more musicians, so that well up to the 1700s, musicians (and other artists) were essentially supported by the aristocracy.
Another question that needs to be asked is why the musical sensibilities of contemporary popular culture seem to be so much different from the music that has come down to us since the Middle Ages. AFAIK, there really are no ancient (European) parallels to rap, hip-hop, rock, disco, or really anything popular since the 1950s. Now maybe it's just that while similiar types of things existed in popular culture, they didn't get written down (or about). But we do have some fairly old collections of folk songs &c, and they're nothing like what is popular today.
PS: Another question is whether rap, rock, and so on could actually exist if it had to be played on purely acoustic instruments, with words sung by unamplified human voices? Certainly it seems to me (and I do admit to a prejudice here) that much of its effect depends on it being played at volume ranges that cause discomfort to people with sensitive hearing.
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On earth most of our sealife is fishlike (excluding a few other species such as squid/octopus). As far as I'm aware there are no legged creatures which live solely in the sea.
In my world I'd like to have creatures like the [sando aqua monster](http://starwars.wikia.com/wiki/Sando_aqua_monster) from Star Wars, it clearly has four legs and uses it's tail to help with swimming.
Firstly could this creature evolve? Second, is it likely that a creature with a body shape such as this would live purely in the water or would they congregate on land too?
For a bonus point is it likely that a creature like this would breath with lungs or gills?
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A primarily aquatic creature with four legs can only really be a valid design if it uses those legs to walk, not to swim. Since legs can only get in the way when swimming. So it would need to dwell on the bottom of the sea (and thus be heavier than water). This is actually a useful feature, since having those legs additionally to a tail can give this creature superior manouverability along bottom of the sea as well as the ability to grab prey with these appendages. Being heavy enough to stay on the bottom shouldn't be a big problem, since there are many [aquatic animals that already achieve this](http://en.wikipedia.org/wiki/Deep_sea_creature).
I can think of two different evolutionary paths that could lead to this creature.
**It evolved from a fishlike creature.**
Consider a predatory fish that lurks the ocean floor, it is imaginable that more developed appendages would grant this fish an advantage. It is after all easier to accelerate (and slow down) when you can get traction on something more solid than water. From that point on, these appendages could grow stronger and stronger up to the point where they can be used to pin down prey. From then on, claws and "fingers" (which were likely already present for increased traction) could develop even further.
**It's a land dwelling creature that returned to the sea.**
It's not uncommon for [land animals to return to the water](http://en.wikipedia.org/wiki/Aquatic_mammal). And If this animal were heavy enough, it could conceivably use its legs to walk across the bottom of the ocean rather than develop fins to swim. It could also already have a powerful tail, which easily be adapted to aid it when swimming. For a land dwelling animal to be heavy enough to never start developing fins, it would likely need to be relatively large (since this would require it to have heavy bones to support itself). I assume that is what you wanted to go for in the first place.
**Can you tell me more about this creature??**
Well, As I said, it hunts at the bottom of the ocean. I would guess it's the apex predator down there and mainly feeds on middle sized fish. Larger predatory fish would likely stay clear of it since an encounter between the two doesn't really benefit either of them. Creatures like sharks stick to the area closer to the surface and this creature sticks to the floor.
Depending on which evolutionary path it took, the gills vs. lungs question is obvious. An important thing to keep in mind is that if this creature has lungs, it would need to stay *relatively* close to the shore or be light enough to swim to the surface, Doing this would likely leave it rather vulnerable since it's not developed for swimming. But since it's still the only creature in the sea with claws, I imagine no one would be overly keen on attacking it.
Whether this animal would have a [horizontal or vertical or horizontal tail](https://worldbuilding.stackexchange.com/questions/1339/is-it-more-likely-that-merfolk-would-evolve-with-horizontal-or-vertical-tails?rq=1) is also an interesting issue. Vertical tails are not extremely compatible with walking movements. But snakes did evolve from creatures with four legs, so it's not entirely unlikely. Horizontal tails however don't work well with being close to the ground. Keeping this information in mind, I'd expect this animal to have a vertical tail and walk more like a reptile than like a mammal, with legs coming out of its sides, rather than beneath it.
Since this creature could also move out of the water, it's not unlikely that it would occasionally dare to leave the water. I can't imagine that it would manage more than a short sprint out of the water though, much like crocodiles do.
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Actually, the first tetrapods where totally aquatic. They had four legs and grasping claws but the joints in the limbs were not load bearing. They used their legs to hold onto to solid objects, anchoring them and preventing them from giving away their location by the vibrations of moving fins to keep position. They had gills.
They could evolve in any place where vision was obscured (making vibration detection a primary sense) and which had complex underwater surfaces e.g. coral. Really, a nocturnal coral hunter would do. Real tetrapods evolved in fresh water swamps an developed the limbs to hold onto sunken logs.
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there are 4 legged sea creatures: sea mammals and reptile and aquatic birds have a 4 legged design (though most limbs are devolved into fins or vestigial).
They are air-breathers largely because gills that would support such a large creature would need to be immense (partly due to square-cube law: square surface area for the osmotic action, cube volume of tissue needing the oxigen). And because the evolution chain had them spending some time on land before migrating back the water.
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There are a number of benthic arthropods that you are forgetting.
But only four legs is a bad idea for an animal that lives on the bottom of the ocean. At the sea floor it would be subject to intense pressure and ocean currents, both of which could cause it to easily lose balance. The more legs the better.
What you're describing is a decent enough idea, but it wouldn't work for deep sea. It would work best if it dwells above the thermocline.
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Suppose a very large planet orbited a star or other spacial body in an oval shaped path, similar to Earth's but closer to induce a varying gravity during orbit.
The planet has a large gravity well and the star or other body has a stronger one when nearest to it on the planet's orbital path.
1. Is this possible?
2. Assuming it is possible and life has started and it has adapted to the shifts in gravity, would the organisms be pulled towards the star or other body when it is closest the the star or other body but still remain on the planet, creating a stretched effect?
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As an expansion to Mark's good answer: the increased tidal forces (which cause the stretching you want) aren't directly from increased gravity -- a planet in orbit is already in "freefall" and so doesn't directly feel this force. It's "weightless", the same way you would be in a freefalling elevator car.
Tidal forces are caused by the *difference* in gravity between the front and back of the planet. It is the planet's center of mass that is in orbit. Anything closer to the central mass than the center is slightly deeper in the gravitational well, and feels an additional tug toward the center. Anything on the far side of the planet (not facing the central mass) will be in a slightly weaker gravitational field, and will thus feel a slightly stronger centrifugal force (from the planet's orbital revolution) pushing away from the central mass. This difference of forces creates a stretching effect which, on Earth, causes the tides.
The strength of the stretching effect depends on how quickly the gravity drops off with distance. The closer you get to a central body, the more rapidly gravity's strength increases, so the strength of the tidal forces would increase. The stretching force would always be along an axis towards/away from the central body, so if that body was on the horizon, you'd have a horizontal stretching. As Mark suggests, I'd strongly recommend making the central body be a gas giant (and making the planet *actually* be its moon) so that you can get close enough to it to feel substantial forces without getting burned.
Such a planet would be "tidally locked" to the central gas giant, although in an eccentric ("oval-shaped") orbit, this would actually end up resulting in a wobbling motion (even the moon has a slight wobbling, called [libration](http://en.wikipedia.org/wiki/Libration#Lunar_libration)). This is because, although the rotational and orbital periods are identical, the orbital angular velocity will vary depending on distance, while the rotational rate will essentially be constant. The wikipedia article I linked to has a neat animation which shows this libration effect, and the moon's orbit is nearly circular. It would be more pronounced for a more eccentric orbit. From your planet's perspective, this would cause probably the large central body to appear to trace a sort of figure-8 pattern in the sky over the course of the orbital period (which would be essentially a month-long day if you're orbiting a gas giant).
As a side note: You wouldn't have to have an eccentric orbit for this stretching effect to exist. You could just orbit close to the central body in a nearly-circular orbit, and you'd feel the effect year round. In an eccentric orbit, though, you'd only feel the strongest effects for a fraction of the year.
But you have another problem (as Neil Slater points out in a comment). The strong tidal stretching forces, coupled with the libration from the eccentric orbit, is going to cause a lot of bending and flexing in the planet itself, which will cause a lot of friction and heat, a hot molten mantle, and a cracked crust. This will almost certainly lead to lots of volcanoes and earthquakes (and in fact, is exactly the reason why Jupiter's moon [Io](http://en.wikipedia.org/wiki/Io_%28moon%29) is covered in over 400 active volcanoes).
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Yes, it's possible.
The limiting case for approach distance is the [Roche limit](https://en.wikipedia.org/wiki/Roche_limit): the distance at which [tidal forces](https://en.wikipedia.org/wiki/Tidal_force) will pull a body apart. For two bodies of similar density, this distance is about 2.4 times the radius of the larger body (in the fluid-body case); at this distance, you would see a gravity reduction on the near and far sides almost all the way to zero.
Now, you can't do this with the Sun (the Roche limit is far inside the orbit of Mercury, so the planet's life would get cooked), but a habitable moon around a gas giant could experience varying gravity.
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My very fancy planet, has a green blotch approximately the size of Africa on its surface, which looks like a forest from space but is actually the planet's ocean. A sea, which, over millions of years, has been colonized by a free-floating species of halophyte. This plant was so prolific that nearly 100% of the planet's ocean is covered by it (with some holes here and there). This plant mat is about 3 to 5 inches thick and floats thanks to pockets of air. If you think about it, it's basically a continent-sized lawn bubble.
Other than that the planet is completely earth-like. Size, rotation, distance from the sun, atmosphere and so on. It's the kind of planet that humans would look for but it's also meant to be a desert planet. Or just generally speaking a very arid planet.
**With conditions like these, what would the weather look like? Do the plants make a difference?**
On hindsight I should have asked about this before making the flora and fauna, but I guess I'll have to make adjustments as I go. What I care about first and foremost is the amount and distribution of rain.
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**It would look startlingly like Arrakis**
*If I've understood your question correctly, your entire planet the size of Earth has a single ocean the size of Africa and that ocean is covered in plant life.*
So, rather than the surface being 71% water, it's only 6% water.
* 90%-98% of your planet (at a rough guess) is raging sandstorms and desert. An ocean that small can't supply enough water to allow a planet the size of Earth to flourish. In fact, if I took the time to do some ugly research, I bet an ocean that small on a world this big tips the planet's entire ecology into "dead in no time from a geological standpoint" territory. There's almost no water on your planet.
* Some water is locked away at the poles similar to Mars. The poles are cold so any water that does get around in the atmosphere condenses to ice at the poles, just making everything worse.
* Your ocean is the only place going where life can be abundant, so it's little wonder your world evolved a plant that would protect the ocean from evaporating, finally killing the planet.
**Consequence**
1. Those sandstorms seriously threaten your ocean. Not a little, a lot. Let's ignore that.
2. Water must recycle or it stagnates, becoming over saturated with stuff (usually the stuff of decay) that locks up free oxygen and promotes deadly bacteria. Let's ignore that.
3. You don't actually say where on your world (what latitude) your ocean is. That actually matters in this case. I suspect a tropical location (as in, "the Tropic of Capricorn") would promote more rain than the equator, which would cause the plants to lock everything down since heat expansion in the atmosphere would draw water too far away from the ocean to return. But let's ignore that.
Everywhere on the planet other than near the ocean (within 100 miles of the ocean at most) is devastatingly dry. Terrible sandstorms, terrible heat... what can I say? Terrible.
Near the ocean it will be somewhat muggy, condensing into small water sheds that drain back into the ocean. Almost no rain, just condensation. By definition your ocean must be (for all practical purposes) the lowest point on the planet or the ocean would be diversified into groups of small lakes planet-wide. So everything drains to this point. Death valley with fauna-locked water.
*The garden spot of Ceti Alpha VI.*
---
**Thoughts I've had over time...**
1. On Earth water is constantly evaporating. There's exposed water under sunlight 24/7. On your world, your ocean is exposed to daylight only 50% of the day. That's a *serious hit* on evaporation as the ocean must reheat from nighttime cooling every day. On Earth with sunlight constantly striking the oceans what develops are currents that carry the heat around, raising the average temperature to facilitate maximum evaporation. You won't have that effect — and with so much surrounding desert cooling so quickly at night, despite the "hot" nature of the desert during the day, I expect your ocean will be on average substantially cooler than Earth's even if it's located at the equator. To give you an idea of this impact: Your ocean is 8.5% the size of Earth's oceans with no better than half the direct sunlight time (4.25%) and the need to reheat every morning, which is a difficult to calculate effect. Let's be generous and say your planet will enjoy only 3% the evaporation of Earth. At best that's 3% the precipitation of Earth, some of which is lost at the poles, and anything that gets out of the ocean's watershed is forever lost for the value of rain (sinks into the sand or bound into fauna/flora and is proverbially never heard from again). Earth's average rainfall is [39 inches](https://www.britannica.com/science/climate-meteorology/Precipitation), so your planet annually will see 1.17 inches of rain—pretty much all of which must fall within the watershed of the ocean for the planet to survive. And that's not taking the insulative effect of the plant life into account. 3–5 inches of plant life and you might not see a drop of rain at all anywhere on the planet. (Which believably solves the problem of the ocean drying up from evaporative loss. There's still those sandstorms, though.)
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That depends a lot of specific properties of the plants.
On one hand, transpiration through the extended surface area of leaves can enhance evaporation. On the other hand, plants on average have higher albedos than open ocean, which means the plant cover will have a cooling effect which decreases evaporation. How the evaporation balances out comes down to specific details of the plants' structure.
Less heat means less intense storms. Less evaporation along with less heat means less water to produce rainfall downwind. More evaporation with less heat means more water to produce heavier rainfall whenever those air masses get to a place where they can form a storm.
The salinity and thus conductivity of ocean water makes lightning strikes over ocean less common but more individually powerful than over land. The plant cover might tip the balance to make oceanic lightning storms a little more terrestrial-like, but with only a few inches of insulating cover, the effect probably won't be very large.
Plant cover will also suppress waves, which has more significant effects. Since winds won't be able to dump energy into waves as efficiently, wind across the ocean will tend to get faster and stronger than it does over Earth's oceans. Lack of waves will also suppress sea spray at the shores, which is another fairly minor effect but would slightly suppress lightning strikes near shorelines compared to Earth.
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First, about the plants: evaporation could plausibly be in a range more, less than, or just the same as it would be in open water. Many real-world plants increase evaporation by exposing so much leaf area. In other words, whatever you want it to be.
The ocean should have some sort of top-to-bottom circulation or else whatever marine animal life there is will consume all the oxygen in deep waters and the lower levels of the ocean will become completely anoxic.
Next, assuming there's some sort of equilibrium in the water cycle, at least as much water has to fall as rain, somewhere, as evaporates from the ocean. That means that humidity levels have to reach 100% at least some of the time, over part of the planet. If the air is sucked dry of moisture by mountain ranges, etc. before it reaches the remoter regions, it's possible that it never rains on much of the planet.
If rain does fall everywhere, it's implausible that water in distant areas can find a path to drain all the way back to the ocean. The alternative is that there are inland salt seas, along the lines of Great Salt Lake in Utah, here and there. Your "ocean" might well be considered just the largest of these.
The Earth's weather is more or less divided into latitude bands--certain latitudes where it rains a lot, others where deserts occur. This is driven by long-term continental-scale convection patterns where rising air creates rain and falling air doesn't. Your planet might have the same thing, in which case all the clouds and rain only happen in certain horizontal bands around the planet.
Or maybe your planet's water cycle isn't driven by rain after all--isn't it kind of a cop-out to assume the planet is like Earth in every other way? There could also be a geological water cycle in which water circulates through the planetary mantle and crust by plate tectonics, trapped in rock layers, and your ocean is the only area where it reaches a liquid form. Mars is suspected of having enormous amounts of water trapped beneath the surface as ice. You could also plausibly create a system without a steady equilibrium if the planet is geologically young and its ocean is fated to last for "only" a few tens of millions of years.
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Marine plants provide 70% of the Earth's oxygen, so this green patch should be more than enough to provide enough oxygen for the planet. Transpiration would increase precipitation in regions close to the ocean, making them damper than regions on a similar planet with a blue ocean.
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I just found out how European colonisation of Africa was aided by the spread of diseases such as small pox and measles, which the the colonisers were relatively resistant to.
Of course, its goes both ways; Africa was called the whiteman's grave because of malaria and other tropical diseases.
More relevant to the topic, I also came across an article which denounces missionaries who spread the risk of diseases to isolated tribes.
<https://www.theguardian.com/global-development/2020/mar/23/the-isolated-tribes-at-risk-of-illness-from-amazon-missionaries>
Made me wonder the impact one person visiting a foreign land might bring (as contrasted with trade which brings more contract). I hope that will be answered here.
This will depend on were the person comes from: urban, rural; tropical, temperate; history, etc.
I'm more interested in what organisms might lie dormant in symptomless or immune carriers who might not even know they were carriers in the first place. And also how they even survive in an population resistant to them.
Incidentally, as a Malaysian and someone who rarely gets sick, I can't think of anything on me that might spead and wipe out an isolated tribe. Can you?
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There are a lot of viruses and bacterias we are immune to which we could transport without knowing. Eppstein-barr-virus is a good example. Roundabout 95% of adults have antibodies against it, so nearly everyone gets infected sooner or later in his live, most of them never showing symptoms. Especially by vaccination we made ourself nearly immune against a lot of very dangerous deseases we still could carry elsewhere. Another point is, as you mentioned a portal to a fantasy world: evolution there could have taken an absolutely different path, you don't know which bacteria living symbiotic in our body can be very dangerous to your fantasy lifeforms. Could be that bacteria like Escherichia coli, Staphylococcus aureus or Candida albicans are able to kill whole populations over there.
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Virtually every disease could be spread provided it was contagious. Very few have no cases where the disease can not be carried by a person who showed mild or no symptoms, because those diseases tend to have problems spreading. (Though this can be caused by the symptoms, even lethal ones, taking a long time to develop.)
The only condition would be that your fantasy world did not have it. However, if you have first contact through the portal, the only possible safety would be parallel evolution. For instance, rinderpest, a cattle disease, jumped to humans and became measles. (There is some evidence that it jumped more than once before becoming endemic.)
Edit: Malaria and yellow fever, being mosquito borne, could also be brought in if something brought mosquitoes. This would normally be something like a ship, though.
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Botulism comes to mind. It's a particularly terrible disease that almost no humans ever get (though there is a risk from spoiled food; this is why you shouldn't eat canned food from a bulging can), but dormant spores from it are common, especially in honey, where the extremely low-water conditions keep them dormant. (this is why you're told to never give honey to babies, by the way.) These spores are quickly killed by the human immune system in children and adults (but as mentioned before, not infants), but your fantasy people could very well have no immune response to it at all. As far as I know person-to-person transmission is uncommon if it exists at all; it's only really carried in foods, especially preserved foods like honey and canned goods (it's resistant to most sterilisation processes, and it's not enough of a problem in humans or any Earth animals to go to more extreme measures), but it's not too hard to imagine an explorer to another world brings a jar of honey or some tins of beans, one of which may contain botulinum spores.
An alternative is having some perfectly benign bacterium to humans turn out to be deadly to elves or whatever species your fantasy world is inhabited by. There are a ton of bacteria that live inside the human gastrointestinal tract, including in the mouth, where they could easily be spread by a human explorer kissing a particularly attractive orc that they fall for. (or by sharing a drink in a pub, but that's got less of a story behind it!).
Harmless microbes causing havoc when they jump to a different species is a well-known thing. Swine flu is a well-known recent case of this; it's harmless to pigs, but when a mutated strain of it made the jump to humans, it caused all sorts of problems. I believe it's generally thought that most diseases that run the risk of killing the person with the disease originated this way, as it doesn't make much sense evolutionarily for a parasite to actually kill its host if it can't survive outside of a host. But if a virus that evolved as a mild disease in pigs suddenly finds itself in a human, well, it doesn't know it's in a human now, so it still does the stuff that is mildly irritating but not harmful to pigs, which it turns out is very harmful to humans, and that's how you get swine flu.
I think COVID-19 is a case of this too, but I don't know what particular animal it made the jump from or even if that's actually true anyway.
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**Cancer?**
Having your protagonist give chlamydia to persons he enounters in fantasy worlds would be realistic enough but not that exciting. You could turn to other diseases to make your fantasy exciting.
There are people who hold that cancer did not exist in the ancient world and is a disease of modern times. For some cancers that is a stretch because some with obvious physical changes (e.g. breast cancer) were described by ancient writers. But there are persistent reports of cancers because caused by infectious agents and some of these might not have been described. These infectious agents could cause epidemic cancers in unexposed populations.
Some cases of Hodgkin disease (a blood cancer) are definitely associated with EBV infection. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2360469/>
There is controversial research associating glioblastoma with a different virus called CMV. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3922527/>
There is no question that [Kaposi's sarcoma](https://en.wikipedia.org/wiki/Kaposi%27s_sarcoma) is associated with a virus (KSHV; Kaposi sarcoma herpes virus) and also no question that the tendency to form cancers after virus infection has to do with a person's genetics. Africans and people of African stock can be immunologically normal and get "endemic" Kaposi's that is disfiguring and bad. For caucasians to get similar tumors they must be immunosuppressed.
If you want your character to be a plague dog with disease in his wake, these cancers and others could be the diseases. Cancer is dramatic and terrible and would work for a story. All the listed viruses are herpes viruses and many people are asymptomatic carriers of several. If cancers are driven or associated with viruses it is plausible that unexposed persons in a different land might have a higher rate of these cancers or reduced resistance to them.
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## Yeast
This could seriously update food activities, and produce poisons (alcohol) that their bodies can't handle.
## anything
Actually, almost ANY organism could have nasty effect. So called "flesh eating bacteria" is a common bacteria found on skin. Of course, their sensitivity to its toxins could be different, as could its ability to penetrate their skin.
Rabbits, in Australia, are another reasonable example.
## and worse
An interesting related point. Antibiotics are actually toxins selected for toxicity to microbes we don't like and not to us. A transmigrator taking antibiotics or antibiotic cultures might find the antibiotics toxic to the other world residents ... and maybe not their microbes.
## and even worse
The transmigrator himself might produce a toxin. For instance, suppose urea is unknown and a deadly toxin to them.
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# Retroviruses have infected the human genome
[Retroviruses](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC138943/) have a rather unusual life cycle. Normal viruses inject their genetic material inside a cell, where it hijacks the cell's transcription machinery so that the cell begins following the directions that the virus genes are giving it. Retroviruses get into the nucleus and modify the DNA of the host cell, creating in effect a new variant of the original host DNA plus the retroviral genes reverse transcribed into it.
The human genome turns out to be [littered with DNA of retroviral origin](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC138943/). I believe the working theories are the retrovirus successfully infected either sperm cells or egg cells and/or the testes tissue that makes sperm cells and/or an embryo in the early stages of gestation. The viral DNA would essentially be an integral part of the resulting child, and thus potentially all of that child's descendants.
It appears to be possible for these virus genes to [be reactivated](https://www.nature.com/articles/s41389-018-0114-y), meaning the human body will essentially infect itself with this ancient virus.
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My scifi settings armory is filling up with many interesting weapons. However, while energy weapons, Gyrojets, Tangler guns and the like outperform slugthrowers in special applications, concentional slugthrowers still reighn supreme as all-round guns. The wide array of special ammunitions make them even more versatile and useful. Sure, a Gyrojets fire rate and heat management in vacuum or an IR-laser-snipers stealthyness can't be achieved, but carrying 15 different kinds of special ammunitions allows the slugthrowers to keep up by being versitile.
I do want to mix up slugthrower design a bit to drive home that this is the future. While handheld rail- and gauss guns exist, they are more of a novelty like plasma guns, than actually useful weapons. What caught my attention however are [combustion light-gas guns](https://en.m.wikipedia.org/wiki/Combustion_light-gas_gun). These guns use oxygen-hydrogen or hydrocarbon mixtures to propell their projectiles. The wiki article says that muzzle velocities of 3 km/s are achivable, but that they have a poor accuracy at artillery ranges. This is bad for artillery applications, but doesn't really limit the use of these a vehicle mounted or handheld guns.
**Advantages and Disadvantages**
* the fuel, be it hydrogen, methane, ethanol or a higher order hydrocarbon, is readily available and cheap; especially spacecraft will have a pretty much infinite supply of "gun gas"
* the fuel is harder to handle; while hydrogen gas has an amazing gravimetric fuel density, the volumetric fuel density is atrocious; carbon containing fuel alternatives metigate the issue a bit, but are still hard to handle; however advanced material science could solve this, a fuel cartouche made of graphene will make handling high pressure hydrogen much more pleasant
* increased muzzle velocity allows one to either go for more damage or to reduce projectile mass while keeping the damage on a similar level, this in turn would increase magazine capacity significantly
**Are combustion light-gas guns capable of competing with conventional solid fuel ones, given the technology matures significantly? What would be other advantages and disadvantages? If they can't compete, what would have to happen so they can?**
Edit1: This is a conventional gun, except that the gunpowder has been replaced with explosive gas. It shoots normal bullets, not Gyrojet Rounds.
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There may be special applications in which a gas-fueled gun would compete with "conventional" types, but it'll never be more than a niche weapon at artillery scale, and never competitive at the small arms level.
Why?
First, gas has a very low energy density relative to the propellants now in use -- there's a lot more energy in redox combustion *per gram*, but it's very hard to get a gas anywhere near the grams per cubic centimeter density of ordinary single- or double-base smokeless propellant. By the time you manage it, your cartridge will be effectively a high pressure tank full of fuel and oxidizer, and will still be several times the size and weight of a ballistically comparable smokeless cartridge.
For a battleship gun, using external tankage and very long barrel with "pump gun" feeds, gas fuel might produce a small improvement in range over a conventional naval rifle -- but at the cost of hugely increased complexity (= failure rate) and the general fragility that goes with an extremely long barrel. It's been demonstrated a number of times that fixed, land-based pump guns are impractical (as is any other kind of fixed artillery, with the exception of shore defenses, even if you're limited to WWII tech).
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They're probably not very useful as small arms.
Firstly, they seem to need longer barrels than their conventional propellant equivalents in order to develop those high muzzle velocities. The artillery prototypes are 50-100% longer than the regular kind. That's a really awkward thing for infantry to have to tote around... even for snipers that's something of an inconvenience.
Secondly, it isn't obvious that lightweight, high-velocity projectiles are useful in small arms... the flechette rifle fad of the 80s fired long, fin-stabilised rounds at substantially higher velocities than conventional rifles (1400m/s 1.6x42mm dart vs more like 900m/s for a 5.56mm NATO round at ~23mm long) and were found to have issues with deflection in rain and penetrating light cover like vegetation. That was a long time ago of course and technology marches on, but those worries haven't gone away yet and may be insurmountable.
Thirdly, the big advantages of such a weapon, ability to synthesise propellant in-situ, variable muzzle velocity or constant muzzle velocity with different mass projectiles, is not particularly useful for infantry either. Great for naval artillery, and the potentially long range is very useful even for conventional land-based artillery. Increased range isn't useful for most infantry engagements, and given the possibile sensitivity of the round to environmental problems it may not be achievble.
For vehicle use the downsides are largely surmountable, but it requires that vehicle mounted railgun and coilgun technology does not march on appreciably. The CLGG would at least not require a large power plant to operate. The innaccuracies for artillery use are also readily surmountable. I'm not sure it has any relevance in space combat at all; its velocity is too low compared to rocket propelled projectiles, and there are too many competing alternatives for it to be plausible that *all* of them are worse than this one.
Seems to me like these will make for good artillery weapons in the short-to-medium term, depending on how electromagnetic guns pan out. Not much more than that, though.
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**Automated paintball shooting riot control robots.**
These large and imposing robots are armed with paintball cannons which are fired by an onboard tank of propane rather than compressed air. Rotating barrels like a Gatling gun each get a paintball and then the combustion chamber detonates, firing the ball with 2-3x the power of a standard paintball rifle (and a cloud of flame!). The paintballs are full of paint and capsicum; they are fairly solid and they hurt. Some contain poison ivy juice instead of capiscum. Some contain sodium butyrate.
A flame-spewing robot is more imposing than a small riot control cop with a rifle that shoots invisible things, if he shoots. Flying balls that leave giant irritating splotches can easily be appreciated for what they are, and they are many, every second, and leave many nasty burning, itching, stinking welts. The robots can carry a lot of paintballs and one big tank of propane is enough to propel tens of thousands of them.
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The problem is the amount of gas that can be generated in a given volume and the speed with which it can be generated.
Using a compressed gas as a starting point is better than an uncompressed gas but is far worse than using a solid to create the gas because gases are so much less dense than solids.
An explosive solid (or liquid) will generate a very large volume of ultra-compressed gas in micro seconds. In addition when most of the chemical bonds break and rearrange themselves in a more stable configuration a great deal of energy is released making this ultra-compressed gas very hot as well.
A gas is simply not going to be as good an explosive as a solid because it is so much less dense.
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While it is certainly *possible* to achieve extremely high velocities using exotic weapons and equipment like gas guns, gauss guns or rail guns, the *probability* of them being common or effective military weapons is actually rather small. This is because the primary issues for military weapons revolve around the reliabilty of the weapons system itself, and the associated logistics involved in using the weapon.
Consider a 155mm howitzer, a fairly common calibre among Western armies. The gun is essentially a steel tube with a movable cap on one end, a design first demonstrated in the 1400's. The sorts of weapons modern armies use simply take the tube capped at one end principle with about 600 years of refinement. Although it takes a great deal of industrial know how to make reliable and accurate artillery, the end result is pretty easy to use and soldier proof.
The ammunition is similar, highly refined over centuries of development, producable in mass quantities for a relatively low cost and compact and easy to transport, store and quick to utilize in the field once the transport or shipping containers are opened.
A simple gas gun, on the other hand, not only has more parts than a conventional cannon, but requires a very high degree of machining and ultra fine tolerances. If the bursting disc isn't inserted right, or was damaged in transit, then the crew will go through an elaborate setup, fill the tube with hydrogen, put the charge behind the piston and instead of a shot screaming out the barrel at 8km/sec, you have a high pressure detonation right in the gun crew's face. And in addition to ammunition, they need bursting discs, tanks of high pressure gasses (or cryogenic dewars of liquified hydrogen and oxygen), spare pistons or piston rings, and a host of other stuff, all which needs to be carried to the battlefield and delivered at the right time and place. The combustion light gas gun has similar issues, even if the detailed parts and supply lists are different.
Rail and Gauss guns fail as battlefield weapons because of their immense energy requirments, and may really only work well on ships, and to a lesser extent aircraft which have high energy power plants which can be tapped and a nice cold sink to dump the waste heat into (ocean water or air passing over heat exchangers build into the wings and fuselage). Spacecraft might be a good third choice because they can access high energy via rocket engine like generators (either turbogenerators spinning high speed generators or MHD generators), nuclear reactors or possibly beamed power from a solar array. Spacecraft can also carry or unfurl large radiator surfaces to deal with the waste heat.
Gas guns *could* work as space weapons, but since a spacecraft needs to carry all its supplies aboard, there will be a limit to the amount of propellant which can be carried. A ship the same size can use the space devoted to fuel and oxidizer tanks for the gas gun to house a larger generator and more slugs to fire through the rail or gauss gun. And since even a 1980 era design like "HAVE STING" has a muzzle velocity of 15 km/sec, it will outperform any gas gun.
So gas guns (either simple two stage weapons or combustion gas guns will likely be bypassed as being overly complex, not soldier proof and heavy logistical burdens.
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**Variable power.**
If you use gas on a munition and can adjust the amount, you can get the Judge Dread's gun.
Hard walls? More fuel.
Soft walls and want to avoid over penetration? Less.
Set your gun to hold the fuel and the ammo only the tip of the projectile on the magazine.
Lets you carry far more ammo per clip.
The magazine can be safer to carry around since it only holds inert tips.
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I think many of the problems other people mentioned could be avoided by using a mix of ordinary air and gasoline as the "gas" to be combusted.
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**Absolutly no**
You see, the "speed of explosion" and thus the theoretical maxumum of bullet speed (relative to gun) are
* for morden gunpowder 2 500 m/s
* for gas 160 m/s
Real bullet speed is about 250-700 m/s, about 10-25% of theoretical maximim. Things are non-lineer here (less gas speed - more %), so for gas 30-50% is achivable. But this will only give bullet speed 50-80 m/s. Its less than BB gun! It means that just compresed gus without explosion would be more effective. And you can't use "combined" effect. Speeds do not add up here.
I personaly experimented with natural gas and air mixture in pneumatic gun (do not repeat it - its dangerous!!!). It gave no mesarable effect (only louder sound).
So no - it better to use some form of modern [scorpio](https://en.wikipedia.org/wiki/Scorpio_(weapon)) (it is more energy efficient than crossbow), than gas-gun.
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Assuming you could "read" the memories of a once living person, how long after death could you read the memories stored in the human's head? How long does it take for the pathways (dendrite, axon, etc.) to break down?
Is there a difference in the literal decay times for areas & physical methods used by the brain to store short, long, and sensory memory?
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Few minutes (4 to 5) of anoxia (lack of oxygen supply) are sufficient to cause permanent damage to neurons, compromising a brain's functionality.
<https://www.spinalcord.com/anoxic-brain-injury>
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> On average, the brain can survive a mere four minutes without oxygen, so if you suspect a stroke or other injury that is cutting off oxygen to the brain, you need to act immediately.
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With the neuron gone, gone is also the capability of releasing neurotransmitters and electric signals, which is how the collective behaviour of the brain neurons emerges.
Since with death also the respiratory function ceases together with the blood stream and neurons are the first to be damaged, it's likely that your technique will read increasingly noisy signals the more minutes are passed from the moment of death, until the read out just becomes a white noise.
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Although L. Dutch's answer probably contains all the information you need, I think it would also be important to take into account the manner of the person's death.
If an elderly person passes away in their sleep, I would guess that their memories would be readable for longer than someone who fell down a cliff and died of concussion, especially if they damaged their memory centre. Some diseases and poisons could also harm the victim's brain before killing them.
An entity such as the army of the United States of Nowhere In Particular might want to use such a technology to harvest sensitive information from prisoners. They would therefore need to choose an appropriate manner of "putting down" their source. Of course the electric chair is out of the question, but even modern day [lethal injection](https://www.youtube.com/watch?v=0lTczPEG8iI) isn't as "peaceful" as one may think...
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i don't think you can, since memory isn't stored in the way you think it is (at least, base on my understanding of this subject).. to recall something, your neuron network need to be "connected" in a certain way - the fact that memory can be faulty or changed indicates that this is an active, ongoing process: and if this fail, then the memory is lost..
for simplicity, i'll compare our head with a computer.. if you download things from the internet and print them out, then you can always access these.. however, our "brain" computer only save things as a bunch of 1 and 0, that need to be arranged a certain way to access.. and as you may know, once the computer s down, everything will be unretrievable..
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Scenario: two states, (A) and (B). Both nations contain a very small percentage of supers, or rather, citizens with extended abilities (though low-level in nature, more circus acts than comic-book heroes).
(A) is reasonably small, moderately prosperous, and more-or-less democratic. It treats its supers as harmless eccentrics, and attaches no stigma to them. Think: 1940's Switzerland.
(B) is much larger, moderately poverty-stricken, and more-or-less authoritarian. It treats its supers as convenient scapegoats and second class citizens -- and often rounds them up and puts them in camps. Think: 1940's Germany.
The supers community in (A) would like to liberate/extract the supers community of (B), including their families. However, they need some form of leverage or incentive for the government of (B) to cooperate.
One model I looked at was the 1% of the French population (royals, aristocrats, priests, clergymen, and landowners) who fled overseas during the French Revolution of 1789. Most settled in Britain, since it was the only European nation to reach out to the émigrés with financial assistance. However, this method lacks support from the government of (B), whose cooperation would truly grease the wheels of the migration. Other angles I have considered:
* (A) informs the government of (B) that they have discovered a plague specific to supers, and they need all of the research subjects they can acquire. They beseech the government of (B) for assistance by turning over their supers to (A) -- and pray that (B) doesn't take the simpler solution of exterminating its supers.
* (A) offers to negotiate for the release of the supers from (B), offering some form of trade concessions...with hints of trade sanctions for their lack of cooperation.
* (A) considers armed intervention, by sending capture teams into (B) covertly, and hope that the element of surprise will dampen the effects of Murphy's Law.
My question is this: What is the most realistic form of "leverage or incentive" that (A) can apply to (B)?
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Would (B) object to the supers departing for (A) if (A) is willing to accept them?
I'm not an expert on holocaust history, but Wikipedia's page on [Jews escaping from German-occupied Europe](https://en.wikipedia.org/wiki/Jews_escaping_from_German-occupied_Europe) makes me think Jewish emigration was permitted in 1933; forced by Eichmann in 1938; and forbidden by Himmler in 1941. The same Himmler who in 1940 [declared that he hoped to see "the term 'Jew' [...] completely eliminated through the massive immigration of all Jews to Africa or some other colony"](https://en.wikipedia.org/wiki/Madagascar_Plan#In_Nazi_Germany). And in the meantime, emigration was taxed at increasing rates from 65% in 1934 to 96% in 1939 - which would seem like something of a deterrent.
My point being two things:
* If your supers are Jews and (B) is Nazi Germany, (B) might permit (or even force) them to emigrate, if your story calls for it. Especially if they leave their money behind on their way out.
* They weren't consistent though, so you can add *flip-flopping* to the list of Nazi crimes.
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Since (A) is smaller, and it seems only mildly interested in helping the supers, a military intervention is probably out. These rarely happen without an additional major economic incentive, vast military superiority, or both.
An economic trade is more likely, and has historical precedent: in the 80s, the United States gave grain and aid to the Soviet Union, and in return, the USSR would allow set numbers of Jewish people to leave the country. It’s a lot easier for (A) to swallow a humanitarian trade like that when their soldiers’ lives are not on the line, and (A)’s government also benefits from better relations with (B).
You could also have more informal methods, where the government of (A) is not directly involved but prominent private citizens of (A) use their influence to smuggle out small numbers of supers at a time. There was a Swedish diplomat iirc who gave out hundreds of Swedish passports to Jews in Nazi occupied Europe (Sweden was neutral like Switzerland). Commando teams might even be used for very high profile targets, like the Niels Bohr of supers.
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# Do it like it is done in the real world, with foreign aid
This was already suggested by TzeraFNX but he just stated that it works, not how it works. Selectocrate Theory ([Theory](https://en.wikipedia.org/wiki/Selectorate_theory), [Rules for Rulers](https://www.youtube.com/watch?v=rStL7niR7gs), [Dictators Handbook](http://www.burmalibrary.org/docs13/The_Dictators_Handbook.pdf)) offers a great explanation on why and how foreign aid works and will work in this situation.
**Theory**
Every state has three groups (there are several designations for these groups in literature). The residents, the selectorate, and the winning coalition.
[](https://upload.wikimedia.org/wikipedia/commons/thumb/6/6d/Selectorate_Theory_Euler_Diagram.png/703px-Selectorate_Theory_Euler_Diagram.png)
How the sizes of these groups are what determines how the state works. Let us take your democracy. Everyone is a resident, everyone with the right to vote is the selectorate (the disenfranchised: children, mentally disabled people, foreigners are not part of it), and the winning coalition is the part of the selectorate which must support you so you can rule (optimally 50%, but in any chase large).
The Autocracy, on the other hand, looks different. Everyone is still a resident, optimally with the option to become part of the selectorate (this is not good for the people, this give the leader the power to replace anyone who cause trouble in the selectorate). The selectorate, on the other hand, is the smallest possible amount of people you need to control the country (loyal head of the military, loyal head of the police, loyal religious leader, loyal family members, loyal clan-chiefs, ... (Whoever you need as long they are loyal.)). Optimally it is the same as the winning coalition if it isn't a purge is in order.
Ruling is nothing but controlling the flow of revenue and paying off your winning coalition so they continue to support you. This is the essence of success in politics. See chapter four, *Steal from the Poor, Give to the Rich*, and chapter five, *Getting and Spending* of the book for more details.
**Foreign Aid**
The following is based closely on chapter seven, *Foreign Aid*, of the *Dictators Handbook*, if you want to read more about it or check the proof for the examples I give you'll find them there.
Imagine you rule a democratic country of 100 people. The winning coalition is 50 people big. You got 1000 € to buy political support. Thus you give everyone in the coalition public goods worth 20 € to keep their support.
Now you rule an autocracy of 100 people. Your winning coalition only has 5 people in it. You again got 1000 € to buy political support. Thus you give everyone in the coalition private goods worth 200 € to keep their support.
The rewards for being in the winning coalition of an autocracy are bigger than those for being in the winning coalition of a democracy. This is in part due to the smaller size of the coalition and because being in the winning coalition of an autocracy is a messy job. How many people do you know who would beet up dissidents for 20 €? Way less than those who would do it for 200€ I guess.
If an outside power now seeks to change the policy of your country it will be much easier for them in the autocracy then in the democracy. I'll assume the policy is unpopular in your country, say it is the recognition of Israel as a nation. Every person in both nations has dislike for this policy, yet for 20 € they would be willing to change their minds. The foreign power would only have to pay the autocracy 100€ for this policy change, as this is how much the winning coalition needs to be paid to accept it. The democracy, on the other hand, would need 1000 € to change its stance on the subject.
It is thus very good that B is an autocracy. If it were a democracy buying the policy-concession of freeing the supers would be prohibitively expensive for A. Now *one does not simply send money*. One sends foreign aid because it sounds so much less like corruption. Ever wondered why so much foreign aid gets embezzled and the western democracies still keep paying it? Because it does not get embezzled, it was always meant to pay off the relevant people in the receiving country. The USA paid a lot of money to autocratic Egypt and Egypt recognized Israel as a state and made peace with them. They paid money to the autocratic, Muslim regime in Pakistan and they fought the Taliban. The book has a lot of these examples and analyses them as well. There even was a chase where Americans grew annoyed about the useless aid going to Pakistan. So they set up a catalog of rules on how the money had to be used. Pakistan refused to take the money until it was ensured that no one would actually check if these conditions were met.
Now if A is a transparent democracy and its people are opposed to paying fake foreign aid to an autocratic regime there are ways to remedy this. This situation is quite unlikely however as it is very likely that these kinds of deals happened before between these countries and as A is a democracy it is quite likely that they support the dictator of B as the democratization of B would make gaining policy concessions much harder. Assuming that B's leadership does not have the blessing of the [resource curse](https://en.wikipedia.org/wiki/Resource_curse), they need their people to be minimally cared for as they would be unproductive otherwise and no money could be made of them. This means that they need to invest in primary education, basic healthcare and supply money for people to start small business. If A were to pay foreign aid targeted at these sectors (the only ones where real-world foreign aid is truely successful) B's government would not need to embezzle the money. They could just cut their own spending in these sectors and use the money for more relevant things.
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**TzeraFNX:** As I envision the scenario (for the moment, anyway), travel is strictly limited and expensive at best. Otherwise, there would be a wide-spread migration out of (B) into (A) due to the potential for a better life (my intent was not to reflect current real-world issues, but sometimes these stories write themselves). However, I do like the suggestion for smuggling out the supers in small numbers, like the old Underground Railroad. Thanks!
**TheDyingOfLight:** Fascinating, but more likely to play into long-term, subsequent relations between (A) and (B) after the sudden transfer of supers. But I am definitely intrigued enough to follow the links you provided -- and since I live in Iowa, and this being a presidential election cycle, there is some definite relevance. Thanks!
**mjt:** I had not found those references before, but they come the closest to getting past my plot-point, or adding a layer of negotiations before the inevitable confrontations begin. Much obliged!
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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).
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I found that creating a wiki may be the best way to keep track of everything. It shouldn't be too complicated for me to get into. But most importantly I want to be able to edit it on my computer and on the go on my phone. But I don't want to host it somewhere. It would be amazing if it would be simple a file/folder that I could put on Google Drive and open it with a Desktop app from home and with an Android app on the go.
Is there something like this?
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Our [list of worldbuilding resources](https://worldbuilding.stackexchange.com/a/143607/40609) includes [World Anvil](https://worldanvil.com/), which sounds like it's what you're looking for.
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> Welcome, Worldbuilder! If you’re a writer or author, World Anvil is a game-changer in the best way possible! Our integrated worldbuilding system is the perfect World Bible for storing your setting information, images and research. Our mentions system makes it incredibly easy to navigate! You can map out and nest your plots, plan your character arcs, keep track of locations, side characters and languages, and add timelines to document the history behind your writing.
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> You can also publish your writing on World Anvil with the easy-read prose template, and give access to select groups - for example, your Beta Readers or your Patreon supporters. You can embed images and soundtracks into your work, and change the presentation of your world’s pages, for an even more immersive reading experience.
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It's a free service if you put up with advertising, or you can pay to be ad-free.
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As @JBH has already mentioned World Anvil (great software, used it for a few things myself); I'll list a few other options I've used over the years (one currently):
## Microsoft OneNote
I currently use Office 365 with [OneNote](https://products.office.com/en-us/onenote/digital-note-taking-app) for collaborating with others on research papers & know that several of them use it for writing and/or worldbuilding as well. It offers a lot of features (and offline capabilities), is usable on tablets & phones (draw diagrams regularly), and all the other basic note-taking & organizing capabilities. It is not focused on Worldbuilding but on generic note taking and is [not free](https://products.office.com/en-us/compare-all-microsoft-office-products?&activetab=tab%3aprimaryr2)
## [Notion](https://www.notion.so/)
Now Notion is free for the basic usage (which includes offline & private capabilities) but I would recommend at least the $4 a month version for the advance permissions if you really want to collaborate (control more than "all private" or "all public"). This one, I have not used much at all but know it includes full Android & iOS versions and allowed me to do all the things I did with OneNote but with a steeper learning curve.
## [Scabard](https://www.scabard.com/pbs/page/main/About)
Once again, Scabard is free but for the fully private mode you will need to buy the $40 yearly subscription (making it the cheapest private version I've found). The free version allows you to set certain items as "not viewable by players" but not everything and you cannot make secret pages. This is geared (heavily) towards RPG & TableTop campaigns but I've used it for general Worldbuilding too. It offers: Map creation, Timelines, Event handling, Character/Group/Item/Location creation options, and graph options for seeing connections. This is my absolute favorite tool for RPGs and is awesome for any world/story which you need to build as well.
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A straight up personal wiki: <http://wikidpad.sourceforge.net/>
It’s a downloaded program with files saved to your computer so no one but you can access it. I don’t think there’s a mobile version, though.
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You may want to look at [TiddlyWiki](https://tiddlywiki.com/). It's basically a single HTML page but with functionality to make it act like a wiki. I haven't looked at this in a long time, but always thought it was cool because it's browser based, which means you have to host it somewhere but then you can access it wherever a browser runs. I also believe it is free. As for privacy, I *think* you can set it up with a password.
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## I'd like to also suggest **TiddlyWiki** as a good alternative.
I started using it a few months ago and it's absolutely wonderful!
* As Terri stated, **the wiki itself is a simple compact HTML file**. I believe you can either host images directly on your hard drive or through an external source such as Imgur, but that shouldn't be much of a problem.
* There are a myriad of ways to edit it. You can't edit directly in your browser AFAIK but there exist browser extensions to enable editing, or even full-on dedicated clients for all platforms. I use TiddlyDesktop on my PC and AndTidWiki on my Android phone myself.
* Editing is not complicated at all. It boasts a rather simple WSIWYG editor and documentation isn't too difficult to understand.
* Since TiddlyWiki is just a single file, you could (hypothetically) have multiple wikis for multiple worlds all in the same folder.
* Best of all, **you don't need to host it online!** I use **Syncthing** to sync a TiddlyWiki folder between my PCs and my phone, all on my home network. No one that you have to pay to host your content :)
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What would the appearance and structure of trees be like if they used chitin, instead of lignin, for cell walls? This is assuming that all other properties are basically unchanged.
These trees would be in a tropical environment with nutrient rich soil and plenty of water and sunlight available. They utilize photosynthesis and have efficient vascular systems.
Would chitin effect how hard or soft they can get? Or how tall they can grow?
[Answer]
## Prototaxites
[](https://i.stack.imgur.com/jWl4i.jpg)
*Credit to Philip Newsom*
Whilst not plants as you specify in your answer, you may very well be able to draw inspiration from this. [From an answer i received on my own question](https://worldbuilding.stackexchange.com/questions/141173/plausibility-of-mushroom-buildings) i learned that prototaxites were large fungal structures that existed long before trees dominated the earth. [These structures could grow up to seven meters tall.](https://www.smithsonianmag.com/smart-news/long-before-trees-overtook-the-land-earth-was-covered-by-giant-mushrooms-13709647/)
[](https://i.stack.imgur.com/ICTH0.jpg)
<https://www.researchgate.net/figure/Transversely-sectioned-Prototaxites-fossil-This-overview-image-originating-from-a_fig1_51174561>
As you can see, these structures had rings similar to that of trees. However, unlike trees, they were composed of chitin. The image you see here has been edited to enhance the ability to distinguish the outlines of each ring. The pressence of rings shows that these prototaxites were able to withstand changing environments and endure for a long time, no small feat for a structure of that size.
Willk compares this to the modern bracket fungus which produces spores and is hard as wood, it is also called the shelf fungus as it is used to make actual shelving.
Applying this to your question, your trees would likely have a very similar internal structure to these prototaxites, still consisting of rings but their shape and colour may be different than those you find in wood.
[Answer]
Note: This answers refers to the original version of the question, which was about replacing cellulose with chitin.
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The structural material in tree mechanics is not cellulose, but [lignin](https://en.wikipedia.org/wiki/Lignin).
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> Lignin is a class of complex organic polymers that form key structural materials in the support tissues of vascular plants and some algae. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily. Chemically, lignins are cross-linked phenolic polymers.
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[](https://commons.wikimedia.org/wiki/File:Chitin.svg) [](https://commons.wikimedia.org/wiki/File:Cellulose_Sessel.svg)
*The chemical structures of chitin (left) and cellulose (right). See how similar they are. Pictures from Wikipedia.*
Chemically, cellulose and chitin are very similar; they are both simple polymers, derived from glucose. Lignin (from Latin *lignum*, "wood") is entirely different:
[](https://commons.wikimedia.org/wiki/File:Lignin_structure.svg)
*A possible chemical structure of lignin. Note the aromatic rings, utterly absent from chitin and cellulose, and the numerous and irregular cross-links between units. Picture by Karol Głąb, available on Wikimedia under multiple licenses including a public domain dedication.*
>
> As a biopolymer, lignin is unusual because of its heterogeneity and lack of a defined primary structure. Its most commonly noted function is the support through strengthening of wood (mainly composed of xylem cells and lignified sclerenchyma fibres) in vascular plants. (Wikipedia, *s.v.* [Lignin](https://en.wikipedia.org/wiki/Lignin))
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The conclusion is that replacing cellulose with chitin is immaterial; the strength of the mechanical structure is given by another material entirely.
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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.
[Improve this question](/posts/139045/edit)
Over 99% of the transcontinental internet traffic goes through a network of 280 sets of undersea cables.
How vulnerable are these to deliberate sabotage by the major powers?
I'd rather not focus much on why any nation would want to attempt such a thing or to what degree principles of MAD will apply, I'm just assuming that it's a war scenario and such intentional sabotage is desirable.
Such sabotage won't actually shut down the internet rather it would only slow it down. If the slow down is significant enough it could have serious impact on productivity, and it would cost more to send the same amount of data. Or certain kinds of internet traffic might get banned altogether by the governments in favour of maintaining higher bandwidth for more important traffic. Again this is another discussion that's out of the scope of this question, also it's not something that's easy to predict and will depend on the nature of the war/emergency.
I'm just asking how much would it cost to do it (sever say, 50% of the cables)? Is it possible at all? What technology would work best (I'm assuming some sort of robots but not 100% sure)?
Also take into account the fact that the sabotage operations will probably have to be geographically distributed and/or fast and/or discreet enough (with options for plausible deniability and blaming others nations for the sabotage) ... If you set up an entire city just to create the infrastructure required for the operation there's a good chance you could get bombed or nuked before the operation succeeds.
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The power who wants to cut the cables is China. The U.S.A. has no reason whatsoever to cut the cables, because they control the core internet routing tables and they can obtain the same effect by tapping a few keys; Russia doesn't have enough naval vessels; India will never want to cut the cables because *a lot* of their income depends on providing high-quality low-price services over the Internet; Pakistan / Iran / other wannabes don't even begin to have the resources to do it.
* *"I'm just asking how much would it cost to do it (sever say, 50% of the cables)?"*
1. There is no point in cutting 50% of the cables. Either you cut *all* (or at leat *almost* all) the cables reaching the enemy or adversary, or the entire exercise is pointless. There is a lot of overcapacity, cutting half the cables will cause only very minor inconvenience.
2. As an opening just before the shooting starts, it's not that hard for China to do. The cables themselves are not armored or guarded in any way, so all they have to do is send out a few hundred destroyers armed with long steel cables with hooks attached and drag them crosswise over the cable.
3. After the shooting starts, it's almost impossible to do. Any Chinese vessel trying to leave the protective arms of the mother country and reach open ocean will meet with a watery grave. The U.S.A. has satellites, and sonar networks, and submarines, and more naval vessels than everybody else combined.
(Of course the war is China against the U.S.A. In a war with Russia there is no point the cut the cables -- the Russian Supreme Internet Censorship Authority ([Roskomnadzor](https://en.wikipedia.org/wiki/Federal_Service_for_Supervision_of_Communications,_Information_Technology_and_Mass_Media) would actually thank you for such a service); the only other possible enemy of China is India, and the benevolent Chinese Communist Party knows very well that a war with India would be unprofitable.)
* *"Is it possible at all? What technology would work best (I'm assuming some sort of robots but not 100% sure)?"*
Surprinsingly primitive technology. Get a small-ish naval ship with a few thousand meters of steel cable aboard. Affix a bunch of hooks at the end of the cable. Throw the end of the cable with the hooks overboard. Drag the hooks across the cable. Bam, done.
Don't try to be smart. Submarines don't work -- nobody has enough submarines to do this, not even the U.S.A. Robots are useless -- there is no point in using a very expensive robot when a hook at the end of a dumb cable will do the job.
* *"Also take into account the fact that the sabotage operations will probably have to be geographically distributed and/or fast and/or discreet enough (with options for plausible deniability and blaming others nations for the sabotage)"*
Well, duh. As soon as the Americans notice that somebody is cutting Internet cables wholesale the mighty U. S. Navy will become very very interested in finding out who exactly is playing with the livelihood of Amazon, Google, AT&T, etc. etc. The entire exercise is worthwhile only if all the cables can be cut more or less at the same time, and then only as a first act before an actually shooting war. As for plausible deniability, forget it. Ships are big are hard to hide.
(P.S. That's why you need *naval* ships. The actions must be co-ordinated, and you really really don't want to tell civilians what you are up to.)
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Less vulnerable than they were 10 years ago and it's getting better.
In 2008 I lost my phone. You wouldn't think anything of it, but it just happened that the same day someone dropped anchor on an undersea cable near Egypt. That anchor cut off the connection from the UK to the Indian call centre my mobile operator used so I couldn't contact them about it.
The powers that be are very aware of the vulnerability of the undersea cables. They used to primarily only guard them at the landing points, but they're also building up redundancy in the system as the connections become ever more critical to day to day life.
Some countries or regions will be easier to cut off from the rest than others. The islands (UK, NZ, Aus), isolated continents (Americas), those behind closed firewalls necessitating limited external connections (many Arab countries, China, soon Russia).
As mentioned in the comments, satellite connections do exist but they're far harder to access. Also weapons to solve that do exist, though only available to certain states.
In terms of the easiest way to do it, underwater ROV is effective but expensive. Dragging a large ship anchor through where the cable lies is also effective, but probably surprisingly expensive, large ships cost a lot to run.
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Could a great power sabotage these cables? The answer is definitely yes. To do that, they would need submarines and/or ships that could drag a big anchor someplace on the ocean floor to cut the cable.
How hard would that be in a war scenario depends on the capabilities of who is going to war. If it is known that the cables are desirable to tap or cut, warships will be tasked with defending them. Then the effort required to cut them increases, because the force who wants to cut the cable will need to commit more resources to fight off the defenders and then cut the cables.
This is a problem that has been studied; the SOSUS warning system in the North Atlantic is essentially a series of cables with microphones attached to them, that were draped in several places in order to detect Soviet submarines. They would likely be targets for the Soviet Navy in the event of World War III. I do not know offhand how difficult it would be to cut those cables but I’m certain the Soviet Navy had a plan to do so and that the US Navy anticipated it. It might be a good case to research.
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Search for phrases like "maritime cable cut" and top of the list just now was a BBC article from 2017 discussing just such a scenario. Sites like The Register regularly carry stories of accidental cable cuts - there are maintenance ships located around the world built specifically to locate and repair cables. I'm sure I've read other articles on The Register about how the cables are laid, repaired as well as how they have in the past been tapped.
In regards to cutting, as has been proven several times a ship dropping anchor or even trawling in the wrong place can do it easily. This shouldn't happen as the cable locations are known and charted. It doesn't take a lot to imagine somebody could send a fleet of "fishing boats" out to launch a coordinated cable cutting attack.
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No great power or anything needed. Some storm, anchors and weights for nets of small fishing boats also do the trick, that even quite frequently as well as even thieves. One only careful can guess, but 30% are almost always more or less damaged.
This does not mean, there is no internet ... it just gonna be slower, especially during peak hours on international basis.
Internet uses some quite sophisticated protocols for it's traffic, 'scanning' and adjusting itself, similar to electricity or road traffic - following the ways of least resistance, managed by routers - 'Hey, have a long time not heard back, try another one'.
So in worse cases it even can be routed via power cables or electric fence, satellites and other media. Until routers have picked up new routes, delays/low speeds might happen, same as traffic jams occur and finally via side roads dissolve.
Can one really take a country take a country offline - ot really, as today's cables are just another medium for communication - today no bus, ok, take a car or even walk
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I'm developing an independent cartoon web series with talking dragons. The designs of the dragons in Spyro (especially the Legend of Spyro) is one of the main influences in how I want my dragons to look. But despite its cartoony nature, I want to take a realistic approach to what their voices would sound like based on the shape of their heads (assuming they have human-like vocal cords).
Here's an example of what they might look like. It's Spyro and Cynder from Dawn of the Dragon.
[](https://i.stack.imgur.com/mdeHi.png)
Notice the shape of the face. Wide mouth and medium length snout. What would a voice sound like coming out of that kind of face shape? Assuming the pitch stays the same and only the quality of the formants (resonance) change. Would it be deeper than a human's voice? The opposite? Would the basic vowel sounds (ah, eh, eeh, oh, ooh) sound different? If so, what would each vowel sound like? I'm fascinated by how the sound of the voice is affected by the shape of the throat, oral and nasal cavities, so I'm not sure I want to just give them human voices like all the other talking dragons. I'm also just genuinely curious.
**Edit:**
They're about human-sized. The shape of the throat, nasal cavity, and oral cavity would probably be similar to that of lizards or dinosaurs. They also have lips and teeth somewhat similar to that humans, but still clearly not human. I'm just wondering what their voice would sound like if their nasal and oral cavities were longer than those of humans. Also, it's "formants", not formats. If you don't know what formants are, they're the actual phonetic quality of the voice -- that is, the resonance. The formants of the voice would be different if the oral and nasal cavities and throat were bigger, but the pitch would stay the same if the vocal cords were the same size. Pitch is determined by the vocal cords, and the resonance (or formants) are determined by the shape and size of the oral cavity, nasal cavity, and throat.
[Answer]
**Dragon: Squeaky, flamey patois.**
In the movies, dragons are big and are given big low voices. That is fine. How could it be different? And especially how can it be different for a way that lends itself to a visual medium like a game.
I can think of 3 ways dragon speech can differ from a humans: pitch, visual effects with speaking and word choice.
1. **Pitch.** Anything that vibrates can be used to produce speech sounds. We use our vocal cords but persons who have had laryngectomies can learn esophageal speech - vibrating the epiglottis with air expelled from the stomach. No doubt you have heard people who can burp while talking - same thing.
A dragon is a large animal capable of fast movement and so would have endogenous capability to call out to members of its species.
But let us say this apparatus is not suitable for speaking to humans. **Instead the dragons use the biological structures they use to close off their flame production.** This would have the following consequences.
A: Flame is hot gas and so much less dense. The dragons, regardless of size, would have voices like they inhaled helium.
B: The vocal sounds are being made with flame. When the dragons speak, little flames will flicker around their mouths.
2. Word choice. @AlexP as usual puts fine answer material in the comments which I gleefully poach here. Dragons don't have lips. They would struggle with the same sounds that ventriloquists struggle with, because ventriloquists can't move their lips.
<https://www.brownielocks.com/ventriloquism.html>
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> 3. The troublesome letters are : B, F, M, P, Q, V and W right? (We won't go into the word extensions yet like "ing" and "able.")
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> I hate to disappoint you but there is absolutely no way you can say
> those above letter without moving your lips.
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> So how do the ventriloquists do it? By sound substitutions and fast
> rolling over of the troublesome letters so that your brain will fill
> in automatically the letter..
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Dragons are not going to try to do ventriloquism. It will not sound right. **They will choose words that do not use those letters.** They probably understand the other words depending on how much they talk with humans, but they will not try to say them.
Example: We must fly. A storm is coming.
Dragon: Us take to sky. The thunder is near.
Dragon English will need different words for "fire" and "fly". The fun of this is that phrases in dragon will be very characteristic of dragons and it is easy to follow the rules. Fans of your game will talk to each other in dragon speak and hopefully you can invent some catchy turns of phrase in dragon.
For proper names they will swap in letters as they see fit. - Cynder will be fine but Spyro might be called Skyro. They might decide to call Fabio Sassio. If he objects, they will be content to call him Tootio.
[Answer]
>
> What exactly would a talking dragon's voice sound like?
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Animal vocalisations evolved as a result of a number of behavioural factors interacting such as kin recognition, dominance/submission, mating displays and dances, differential alarm calls, aiding in coordinating hunting behaviour, play in younglings - perhaps even to lure prey and I'm sure many others.
* If there's one thing that observing social animals has taught us is a very common thing in the animal kingdom is that they mimic each other's vocalisations.
Many birds are good mimics, for an expert level demonstration see the [Lyrebird](https://www.youtube.com/watch?v=VjE0Kdfos4Y).
Human mimics are able, with practice to generate an astonishing variety of sounds, not just to satyrise politicians and celebrities as [Charlie Hopkinson](https://www.youtube.com/watch?v=1AUglmXa3b0), but mimicing [other animals and birds](https://www.youtube.com/watch?v=2Qa9YDgtcaM) or [this guy](https://www.youtube.com/watch?v=4EUobFfx-tU), trimphones, the Millenium Falcon, creaky staires when telling ghost stories and then comes the popular (and highly competitive) passtime of [beatboxing](https://www.youtube.com/watch?v=LeBiXBic3sE). There's an interesting paper [here](http://www.eyethink.org/resources/papers/Gueguen-et-al..pdf) on social mimicry in humans and it's effects.
* All of which goes to demonstrating huge versatility in the way we direct air over our vocal aparatus and focus and mix the resonances within the multiple sinuses, resonance cavities and tubes available. Our coordinated lips, jaw, larynx, throat, soft palate, tongue and the diaphragm and ribcage offer us a huge variety of possibilities.
* *This is to say - it aint what you got,* **it's how you use it.**
# Conclusion.
**I posit that your dragons would be no different.** They may in private have their own language which could be an ugly clucking and clacking, or a whispered susurration as of breeze through aspen, or booming and honking as appropriate. Among humans and other creatures they may adopt tones more familiar to their companions, up to you. Beware though, that during exertion control of the breath muscles may become sloppy because of the urgency of breathing itself. They could sound strained and strange.
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For a creature that has a similar sound-producing range to humans, but has a very different face/throat anatomy, you'll want to look at "talking" birds- parrots, mynas, and corvids. Lacking lips or vocal cords, they produce sounds using an organ at the base of their trachea known as the syrinx. It operates on similar mechanisms of airflow and vibration.
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In a world of magic, spells are songs. They aren't easy to sing and becoming truly proficient requires a similar amount of time and effort as it does to become an opera singer on Earth. Of course some people are just naturally talented singers and in fact this is how magic was originally discovered by someone singing away as they worked.
Simple songs can help people lift things. A more complicated song can light a fire. An operatic aria in co-operation with a swordsmith could help to forge a powerful magical weapon. (see note at bottom)
Spells are not permanent - they only occur whilst the singer is actually singing.
**The problem**
Anyone who is tone-deaf (4% of the population) simply can't do magic, and magic isn't fine grained enough to perform any kind of 'healing' on them. In any case, being tone deaf isn't an illness - it's just a lack of a particular musical ability. Remarkably, people who are simply deaf can learn to sing perfectly well given either healing or the right feedback unless they are also tone-deaf.
The benevolent chief wizard wants everyone to be able to practise magic but she and her advisers simply don't know how to go about it.
This is a medieval society in terms of technology so there is no recording equipment or anything like that. People have tried playing the tunes on musical instruments by rote but it simply doesn't work without the words.
**Question**
How can the tone-deaf people be allowed to perform magic in a world where the *only* magic available is through singing?
**Notes**
Many high wizards have tried to come up with a magical answer to this and failed so ideally I am looking for a non-magical solution.
There is a complex relationship between the words of a spell and the melody. It takes a lot of study and understanding to create new spells. Most people simply memorise existing songs that have been found to work by others or that have been especially created by gifted 'composers' (i.e. wizards). Of course only very talented people can sing some of these more difficult works.
It is important that the correct pitch is sung (different octaves are equivalent). Thus people who have perfect pitch have an extra advantage. Those who are musical but do not have perfect pitch must carry a tuned whistle around to get them started. Unfortunately tone-deaf people can not pick up the pitch or sustain it.
**Important** - To use a magical device such as the powerful sword, the user must sing whilst using it. The magical item simply acts as an **amplifier**.
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**Example**
At the risk of being somewhat controversial I present the final verse of the original British National Anthem. We don't often hear this being sung!
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> Lord grant that Marshal Wade
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> May by thy mighty aid
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> Victory bring.
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> May he sedition hush,
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> And like a torrent rush,
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> Rebellious Scots to crush.
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> God save the Queen!
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> <https://www.classicfm.com/discover-music/british-national-anthem-lyrics/>
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This anthem has a very simple tune and so leaves a lot to be desired in terms of effectiveness. However we can imagine the average soldier being able to sing it and march in time to it as they go into battle. The combined low-grade magic of all the troops could be backed up by an intricate descant from a trained opera singer equipped with a megaphone.
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The thing with being truly tone deaf is that there's no way past it. It can't be trained out, you can never learn to hear the correct pitch.
However what becomes interesting is that in studies of people with amusia who speak tonal languages it's perception that matters, tone production is unaffected.
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> Tone production was highly accurate in both groups, with 98.6 and 99.6% correct in amusic participants with tone agnosia and controls, respectively, and did not differ significantly from each other (all Mann–Whitney tests being non-significant.). In both groups, tone production scores did not differ between reading and repeating tasks or between meaningful and nonsense words (all Wilcoxon signed rank tests for two related samples being non-significant). Taken together, the amusic participants with tone agnosia seemed to be impaired mainly in lexical tone perception, not in tone production. - [Congenital amusia in speakers of a tone language: association with lexical tone agnosia](https://academic.oup.com/brain/article/133/9/2635/353638)
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So your tone deaf population *will* be able to do magic, they just won't be able to distinguish the tones of other people doing magic.
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There are orders of magnitude more kinds of music than the laysman can think of. Not all of them require you to be particularly good at tones to sing.
Below is a link to an Youtube video on *Danger Music*. The description of the video goes *"to study music at AIM is all about having a **fun, professional, academic experience**, that helps set you up for a diverse lifelong career in the music industry."* For added fun, open this link only between 1 and 4 AM. Don't use headphones, set your speakers to 11. It gets even better if your spouse is sound asleep.
[Danger Music #17 - Dick Higgins - Fluxus](https://www.youtube.com/watch?v=HS5ZkPXkto0)
If music goes as you say...
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> Simple songs can help people lift things. A more complicated song can light a fire. An operatic aria in co-operation with a swordsmith could help to forge a powerful magical weapon.
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... Then *Danger Music* is the kind of thing people sing after midnight in cemiteries as an equivalent to the [Raise Dead](http://www.d20srd.org/srd/spells/raiseDead.htm) spell. Also the dead must make a save against constitution to immediately flee at haul-ass pace upon being ressurrected this way, otherwise they just die again from heart attack.
Using *Danger Music* spellsongs can also charm people (one command only: *"run to the hills"*) and cause creatures guarding a place to leave their posts, though there is dispute among scholars about whether the last two effects are really magical. If used by a bard prior to battle it can diminish morale among enemy troops, at the cost of diminishing morale among friendly troops.
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There are several ways you can do this just by looking at our own musical industry.
Firstly, you can have special instruments. Simply blow into it, press a series of buttons and the spell activates since the instruments allows you to hit all the tones.
Secondly, not all songs need to have a proper tone. Music is more than just the tone. You could have spells that are simply based off of making noises at a certain time, or require words to create key noises which invoke the spell. Rap music comes to mind as a good example you could build off... or something like death metal where my ears literally bleed and everything is yelling.
Finally, if you can teach a person who literally can't hear your music to sing a spell, than someone who is tone deaf can also be taught to sing that same spell. Like... you can teach a person who might literally not understand the concept of sound to sing a song, then you can 100% teach someone who can hear but can't replicate the sound.
[Answer]
**Another solution would simply be not to have tone deaf people.**
It sounds like there would be some pretty strong selective pressures in your world against tone-deafness, so it would be eminently believable that it would have been selected out in your people's evolutionary past, depending on how early magic was discovered (considering that song is used by a fantastic array of animals, I doubt it would be humans who would be the first to practice magic).
There's evidence to suggest that tone-deafness is at least partially heritable:
* <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1950825/>
* <https://genetics.thetech.org/ask-a-geneticist/tone-deaf-genetics>
The history of vocalisation and song is at the very least millions of years old. The oldest found syrinx (the bird equivalent of a human voicebox) is a [66 million year old specimen found in Antarctica](http://mentalfloss.com/article/87422/oldest-evidence-birds-voice-box-found-antarctica). Considering the vocal capabilities of birds (and the suggestion that non-avian dinosaurs were unlikely to have been able to produce as sophisticated sounds), I'd argue that the first magic-wielding creatures would be avian dinosaurs (unless there's evidence of complex vocalisation earlier than I've found so far).
The ability to produce what amounts to free work simply through song is such a significant boon to a creature that I would expect it to be very strongly selected for. So much so that I'd expect vocalising creatures to rather quickly dominate the ecological landscape of the earth.
The history of human singing stretches back at least [1.8 million years](http://www.bbc.co.uk/earth/story/20140907-does-music-pre-date-modern-man), and the existence of four other singing primates (lemurs, tarsiers, titi monkeys and gibbons) indicate that even in a world without such a strong selective pressure, the ability to sing occurs frequently enough for our ancestors to have stumbled upon it.
Over the (at least) 1.8 million year history of human magic use in your world, I sincerely doubt that the hereditary causes of tone-deafness would endure. Developmental tone-deafness still might occur (say from brain injury), but I see no issue with that preventing magic use (nature is not nice after all).
**tl;dr**
Due to the (at least) 66-million-year history of complex vocalisation on planet earth, and the fantastic boon magic use would provide to a creature, I'd highly doubt tone-deafness would exist in any human-analogues that evolve.
You could probably even argue that tone-deafness would be non-existent in the majority of organisms populating your version of earth!
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It could be, a person who lacks adequate singing abilities have a less effective or less controlled spell. A person who cannot hold a note, trying to cast a fireball may result in the fireball exploding or flying about all wild.
A tone deaf person trying to conjure a beautiful rose may end up with a dull, grey colored pansy.
Its not that the person cannot cast spells, its that they have less than ideal results. Not everyone can be in the magic business, just like not everyone can be in the music business. But who knows, maybe there is a need for dull or crazy spell casting
[Answer]
What is music? What are words? What makes the combination singing?
While these questions are pretty philosophical you *have* to answer them (for your world) in order to find a way to have tone-deaf people perform magic.
Normally we use sound for words and making those sounds harmonic, which we then call singing and in your world that makes it magic. To make magic available to tone-deaf people, we need to figure out/decide which "parts" of the singing process actually produce the magic:
* Is it just the combination of words and music?
Just playing a magic song on an instrument may not work, but maybe speaking above the right kind of music works?
* Is it the harmonisation of words and sound/music?
While some people may argue that Rap isn't music, it is still similar. Even tone-deaf people can be rhythmic and speaking rhythmically while playing some drums might well be worth a try.
* Is it the harmonisation of language with is medium?
We use sounds as the main medium of our language, but there are other ways as well: an actually deaf person using sign language may be able to 'harmonise' his language with a special movements/dance into a magic sign-language song (look up deaf poetry videos - it's really interesting).
In reply to the OPs comment & to make the point of this answer clearer:
If singing (the harmonious combination of music and words) produces magic in this world, one can think if this comes just from the exactly these two components or an underlying principle. I have tried to formulate examples of such a principle that would still allow magic in the form the OP describes, but *also* allow tone-deaf people to perform magic with the same system.
If the requirements for magic are directly: singing with words and music the the answer to the OPs direct question (How can tone-deaf people perform magic) has to be: they can not.
[Answer]
Teach them the notes individually, in the presence of someone with either Absolute Pitch, or Relative Pitch and a Tuning Fork (to tell them "higher", "lower", or "that's correct").
Rather than the "tone", they are learning the position of the throat and larynx necessary to form a specific pitch through muscle-memory, and then associating this with a visual or linguistic cue such as a letter or note on a musical scale - in the same way that you might teach them hand positions for sign language. They may never sing a smooth and sweeping aria, but plodding one-note-at-a-time chants will be well within reach.
Descending into that most unreliable of examples, an anecdote: I have a relatively weak capability for Relative Pitch - I can *hear* a tune, and memorise it, but have great difficulty recreating it. Unfortunately, I was also roped into my school's chamber choir, because they needed a Bass - singing alongside a number people who had Absolute Pitch.
As the only Bass, there were a handful of songs that I had to start, instead of joining in at a pitch (roughly) relative to everyone else. Over time, I was able to train myself to "lock" the first note of those songs in the manner detailed above, and thus fake a reasonable level of near-competence.
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[Question]
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Working on a future history setting; the question arises, since the world cannot run on fossil fuels forever, one way or another, something must end up replacing them; what will that something be?
A co-author has suggested using nuclear energy to electrolyze water for hydrogen which is combined with carbon dioxide to produce methanol. The chemistry of this is sound but I'm not sure about the economics of getting hydrogen that way. As I understand it, hydrogen produced by electrolysis currently costs several times as much as that produced from natural gas, which suggests methanol produced by this method will always be at least a few times more expensive than current fossil fuels (assuming future nuclear energy will never be as cheap as current solar for applications like this that don't need external storage); it seems likely to me that the world will be very reluctant to accept a several-fold increase in the cost of fuel. (I'm not talking about what *should* happen, but what plausibly *will* happen.)
On the other hand, it turns out to my surprise that there already exists a facility making methanol by the above method except geothermal substituted for nuclear: <https://www.chemicals-technology.com/projects/george-olah-renewable-methanol-plant-iceland/>
On the third hand, that article does not discuss the economics of the hydrogen source; for all I know, maybe it's a pilot project built as proof of concept that is not, nor expected to be, economically competitive.
I can't find a clear answer as to how much hydrogen costs from various sources. Google finds estimates all over the map, ranging from a dollar per gram to a dollar per kilogram.
So my question is:
Assuming advanced nuclear reactors can provide a reasonably cheap (and clean and safe enough to satisfy political requirements) source of heat, and the technology is mature and acquires relevant economies of scale, how much would electrolytic hydrogen end up costing? Either in dollars per kilogram, dollars per joule, or relative to the price of oil or natural gas?
[Answer]
## Analyses by Real Experts
In 2009, [a study at the Idaho National Laboratory](https://inldigitallibrary.inl.gov/sites/sti/sti/4247218.pdf) came up with an estimate that this kind of nuclear reactor would be able to sell hydrogen for $3.23/kg. It also discussed the economics of producing syngas rather than hydrogen, and nuclear-assisted gasification.
[This study from MINES ParisTech in 2013](https://core.ac.uk/download/pdf/82142608.pdf) estimated the cost of syngas (hydrogen and carbon monoxide in the correct ratio to produce methanol) from a nuclear reactor at 1.30 €.
## My Estimates
**These estimates handwave a lot of technology that does not yet exist, but people are actively working to build.** I think I’m playing fair by the rules of hard science fiction. Don’t base any investment decisions on them!
If we could build the nuclear reactors as cheaply as South Korea manages to in the real world, and gave them no other subsidies, we could bring the cost of the hydrogen in a gallon of methanol down between 72 cents and a dollar. The total cost of all the raw materials, using captured carbon dioxide rather than fossil fuels, might be \$1.14–1.41. Since the process is not perfectly efficient, we might actually end up spending \$1.34–1.91.
Since one gallon of gasoline has twice the energy content of one gallon of methanol, we should double this: replacing a gallon of gasoline with methanol would consume gases that cost \$2.67–$3.83 to produce, unless a more-efficient process is found. But, the question specifies hydrogen production as a separate step.
An amount of hydrogen equivalent to a gallon of gasoline, if you used it directly in a fuel cell rather than making methanol from it, would cost \$1.88–2.66.
For comparison, the price of an energy-equivalent amount of methanol has fluctuated in recent years from \$1.08 to \$3.00.
I came up with a lower cost estimate than the US government-funded study mainly because they didn’t handwave cheap nuclear reactors, 70% of the cost was paying off the capital cost, and they assumed a 10% rate of return.
The bottom line here is that this process would not be commercially-viable without a subsidy, unless the price of natural gas rises. It’s not a several-fold increase in the cost of fuel, though, but a modest one. The most plausible way to change that would be to discover a better catalyst to produce either carbon monoxide or methanol from water and carbon dioxide.
## Building the Plants
The best-case scenario for nuclear power construction is South Korea, [the only country in the world where the cost of building nuclear plants is falling over time.](https://www.sciencedirect.com/science/article/pii/S0301421516300106) (However, even there, its current government plans to phase nuclear power out.) Recent plants there cost 2,000,000 KRW/kW. [This is equivalent to an “overnight” construction cost of \$2,000/kW. The World Nuclear Association, admittedly not a neutral source, estimates that, at a 3% discount rate, this equates to a levelized cost of electricity of \$29/MWh. If the discount rate increases to 7%—that is, the investors need the plant to be paid off faster—that increases to \$40/MWh.](http://www.world-nuclear.orgfof-nuclear-power.aspx) (Note that the high range of the estimate in @kingledion’s excellent answer was based on an electricity price of \$80/MWh and a cost to nuclear energy of double that, while the low end of both estimates is approximately the same.)
Could the South Korean cost be replicated? To some degree, maybe. A major reason for the savings is that they’ve built the same design over and over, and this scheme calls for a lot of standardized reactors. The reactors could also be built wherever the economics are best, and export the fuel to other countries.
## Generating Hydrogen
However, the point of using nuclear energy for this is that it can beat the alkaline water electrolysis technology that the US Department of Energy assumed, and reduce the cost by even more than the 50–62.5% that simply using the real-world cost of nuclear power in South Korea would suggest.
What this plan actually calls for is for a reactor like the [Very High Temperature Reactor](https://www.gen-4.org/gif/jcms/c_42153/very-high-temperature-reactor-vhtr) or the [Gas-cooled Fast Reactor](https://www.gen-4.org/gif/jcms/c_42153/very-high-temperature-reactor-vhtr), which both work on the same principle, except that the former uses the uranium fuel cycle and the latter a fast-breeder reactor. Both are sealed, integral reactors that use supercritical helium as both the coolant and the working fluid to drive the turbines. For this application, you would want to run the reactor at the supercritical temperature of helium, 850°C, and the high-temperature steam hydrolysis reaction around 800°C. The cost of construction could be further reduced if we ever figure out how to use carbon dioxide in place of helium.
The current state of the art in hydrogen production can achieve energy efficiency of up to 50% (by high-temperature steam electrolysis, or other methods such as the sulfur-iodine process). In other words, since the energy density of hydrogen is 33,300 Wh/kg, a thermal reactor using its process heat plus a voltage of about 1.2V could potentially achieve a yield of $0.5 × \left( \frac{3.330·10^{-2} \mathrm{MWh}}{\mathrm{kg}} \right)^{-1} = 15.02 \frac{\mathrm{kg}}{\mathrm{MWh}} $.
If we naïvely (excuse me, optimistically) handwave that you can get power from a GFR as cheap as South Korea gets it from third-generation reactors in the real world, that is, \$29–40 per MWh, that cost would fall to \$1.93–2.66 per kilogram of hydrogen. Most of this can be thermal energy used as process heat with no conversion or transmission losses. It’s probably not realistic to pull that off, but it definitely is possible to do better than \$80, the basis for the high-end estimate in the DoE report.
The DoE report assumed a cost of \$3.00/kg.
This does not include the cost of demineralized water.
## Synthesizing Methanol from Hydrogen and Carbon Dioxide
This technology does not require a high-temperature reactor and more likely runs off clean electricity from the grid. It is in use in the real world already, but with carbon dioxide captured from sources such as coal plants.
Each (US liquid) gallon of methanol contains
$$ \begin{align\*}
\frac{3.785·10^3 \mathrm{cm}^3}{\mathrm{gallon}} &× \frac{0.7920 \text{g CH₃OH}}{\mathrm{cm}^3} \\
&× \frac{1 \text{ mol CH₃OH}}{32.04 \text{g CH₃OH}} \\
= \frac{93.56 \text{ mol CH₃OH}}{\mathrm{gallon}}
\end{align\*}$$
Hydrogenating carbon dioxide to produce methanol needs two moles of H₂ and one mole of CO₂ per mole of CH₃OH. ([If you convert the carbon dioxide into carbon monoxide.](https://phys.org/news/2017-09-scientists-fine-tune-syngas-co2.html#nRlv))
In practice, the reaction would be more complicated: either it would consume 50% more hydrogen (the reaction 3H₂ + CO₂ → CH₃OH + H₂O turns the extra hydrogen back into water, which can at least be recycled back to hydrogen) or it would replace some of the hydrogen generation with a process generating hydrogen and carbon monoxide from water and carbon dioxide, whichever were more efficient.
Since the molar mass of H₂ is 2.014 g/mol, if we use 3 moles of hydrogen gas per gallon of methanol, each gallon of methanol requires 0.5654 kg of hydrogen as input. Using the numbers in the previous section, the hydrogen used to produce a gallon of methanol would cost between \$1.09 and \$1.50.
The molar mass of CO₂ is 44.0095 g/mol, times 93.56 moles, so we need 4.118 kg of CO₂ to produce one gallon of methanol. The idea is to use captured carbon dioxide, rather than fossil fuels, for example from incinerating biomass or direct air capture. The existing Climeworks AG plant in Zurich captures carbon dioxide from the air at a cost of \$600/tonne. If hypothetical technology could bring the cost down to \$60/tonne, which many sources believe is possible, the carbon and oxygen in a gallon of methanol would cost 24.7 cents. A more conservative estimate of \$100/tonne would cost 41.2 cents.
This gives us, using assumptions about cost that are optimistic but somewhat plausible, a cost of \$1.34–1.91 for the raw materials. Since one gallon of gasoline contains as much energy as two gallons of methanol, double this to get an estimate of \$2.67–$3.83 per equivalent of a gallon of gas. This is just to produce the raw materials; there would also be a cost to synthesize the methanol, blend it, and distribute it.
## Subsidies
However, this assumes that the governments of the world do nothing to subsidize green fuels or to tax carbon-dioxide emissions. If they start taking climate change—and energy independence—so seriously that they would be willing to totally reverse course on nuclear power, that seems unlikely. Someone has to make energy producers pay the external cost of the pollution they create, or else it will always be cheaper to use the same nuclear reactor to make methanol from fossil fuels.
If a government were willing to simply eat the cost of a hydrogen plant that could produce megatons of clean domestic energy, the way they’re willing to eat the cost of a war in the Middle East, or subsidize it like they subsidize oil and biofuels, the marginal cost to produce hydrogen would fall drastically. If the hydrogen did not have to pay back the capital cost of the reactor, just break even on operating cost, the marginal cost to produce hydrogen would be tiny.
Although you said in a comment that the methanol is meant for use as a transportation fuel, if it were turned into something that isn’t burned, such as [olefins](http://www.cchem.berkeley.edu/molsim/teaching/fall2009/mto/background.html) or formaldehyde, it would remove and sequester large amounts of carbon from the atmosphere.
The reactors would also produce other products that generate profit, such as electricity. Or, for example, since electrolysis of water produces half as many molecules of hot oxygen as hydrogen, it might react that with phosphorous to produce food-grade phosphoric acid.
## Alternatives
If you already have hydrogen and captured carbon dioxide (from an incinerator or any other source), you can make methanol at relatively low temperatures. One alternative would be to increase the amount of hydrogen by 50% and use a catalyst [such as Ni-Ga at 200°C](https://www.nature.com/articles/nchem.1873). Another is [co-electrolysis of hydrogen and carbon monoxide](https://etheses.whiterose.ac.uk/8497/1/Kayode%20Omojola%20E-%20thesis.pdf) from carbon dioxide and water. Another is [splitting carbon dioxide and water through a thermochemical cycle.](https://www.sciencedirect.com/science/article/pii/S1876610212015068?via%3Dihub)
Another possible pathway is to [turn carbon dioxide into methane using hydrogen](https://pubsdc3.acs.org/doi/10.1021/acscatal.7b03063). We could then use the oxygen we also got from electrolysis of water to [oxidize the methane to methanol](https://www.sciencedirect.com/science/article/pii/S1877705813000581)—if someone discovers a good process for that. (Although that would end up making methanol from natural gas even cheaper.)
Both [biomass gasification](https://digital.library.unt.edu/ark:/67531/metadc900831/m1/) and [pyrolysis of biomass](https://www.osti.gov/biblio/1056023) have been proposed as part of a system with a nuclear reactor generating electricity, hydrogen and oxygen.
The cost of the inputs might also be brought down if the captured carbon dioxide came from emissions that otherwise would have entered the atmosphere, as in the municipal trash incinerator in Oslo that captures its carbon dioxide for use by the oil industry.
[Answer]
# $3-6 per gallon of gasoline equivalent (gge)
In 2009 the National Renewable Energy Laboratory assembled a panel to generate 80% confidence intervals for the future costs of hydrogen production. The report is [here](https://www.hydrogen.energy.gov/pdfs/46676.pdf). This panel used technology available in 2005, but capitalized with a full industrial infrastructure, to make the best use of production scale (this is the 'central production model' discussed in the report). They panel focused on two technologies: [alkaline water electrolysis](https://en.wikipedia.org/wiki/Alkaline_water_electrolysis) and [polymer electrolyte membrane electrolysis](https://en.wikipedia.org/wiki/Polymer_electrolyte_membrane_electrolysis).
A kg of hydrogen is referred to as a gallon of gasoline equivalent, since it has roughly the same amount of energy as a gallon of gasoline.
The average cost was strongly dependent on the cost of electricity. The assumed 'high' price for electricity was \$80 per MWh, whereupon hydrogen costs are \$4.78 per gge. However, the [levelized cost](https://www.lazard.com/media/2390/lazards-levelized-cost-of-energy-analysis-90.pdf) of nuclear power is [currently around](https://www.lazard.com/media/2390/lazards-levelized-cost-of-energy-analysis-90.pdf) \$120 per MWh. If we introduce this increase in electricity power, we get an assumption of more like \$6 per gge in costs.
The low costs for electricity at $0.03 per kWh, and all other factors minimized would be about \$1.70 per gge.
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I'm creating a near future world where laboratories could create human gametes (sperm & ova) using chromosomes from different people. So theoretically we could take 1st chromosome from a 1st person, 2nd from the 2nd, 3rd from the 3rd and so on.
In the end sperm (ova) has 23 chromosomes same as natural one, but they are all from 23 different parents (chromosome donors).
Is that plausible in the near future?
My story is soft science based, but I don't want to be completely unrealistic.
[Answer]
It's certainly plausible.
However, there are lots of various technical difficulties that one would face in performing this operation, Nothing major enough to suggest it couldn't be done, but I'll describe some of them here.
The first obstacle is that most of the time chromosomes don't look like the classical pictures of rods or crosses in the nucleus. These structures only form when the chromosomes condense during mitosis or meiosis. Most of the time the chromosomes are actually loose and intermingled like a big bowl of spaghetti. What this means is that if you want to separate one chromosome from the rest you likely need to take them while they are in their portable, condensed form. Easy enough right?
But another issue is that the chromosomes of eggs and particularly sperm are heavily modified compared to normal chromosomes. Perhaps you've heard the term [epigenetics](https://en.wikipedia.org/wiki/Epigenetics) which in this case is referring to the modifications of the DNA and its associated proteins. These epigenetic features are essential for properly regulating the functions of the cell. If you think about it, a liver cell and an egg cell have exactly the same chromosomes, but must do completely different things. This is accomplished to a large extent by epigenetic regulation. What this means though, is that if you take a chromosome out of a liver cell and put it into an egg cell its epigenetic state comes with it and it's not going to behave exactly like an egg cell. Specifically, sperm chromosomes are very different from other cells in that the histones that the DNA is wrapped around are mostly replaced with a different protein called a [protamine](https://en.wikipedia.org/wiki/Protamine). Sperm chromosomes also have very different methylation patterns.
Another issue related to the epigenetics of the chromosomes is [genomic imprinting](https://en.wikipedia.org/wiki/Genomic_imprinting). It turns out that some genes are epigenetically programmed during the production of gametes so that they will be turned on in the sperm, but off in the egg or vice versa. Essentially, certain genes will only be expressed from your maternal genome and certain others will only be expressed from the paternal genome and this is caused by different epigenetic programs on the different chromosomes. This is critically important as dysregulation of these genes causes known disorders. So, you’ll also need to ensure that these imprinted genes are properly programmed.
So, to solve all these epigenetics problems why can't we just take chromosomes from sperm and eggs to make our chimeric sperm and eggs? Well, most of these epigenetic changes occur *after* the last division of that cell. This means we will never naturally encounter a separable, condensed chromosome with all of the epigenetic programming we need. There are multiple potential solutions to this problem but I think the most likely is to develop a process to reprogram chimeric cells into gametes, but this is not trivial as those processes are generally more complex than the differentiation of other cells.
[Answer]
It will be hard, but possible.
Now, we can extract arbitrary chromosome from human genome and add it to a baby. So far, it's only a mice baby ([Mice containing a human chromosome 21 model behavioral impairment and cardiac anomalies of Down's syndrome.](https://www.ncbi.nlm.nih.gov/pubmed/11371509)) but we can do it.
We can also create 3-parent babies, where mitochondrial DNA is from another person.
Humanity is starting to be good at mixing genes at chromosome level, so 4~5 parents looks really near-future. Making 46 parents is far-fetched, but it is mostly an issue of getting this process error-proof.
## TL;DR What we know we can, because it was done:
* Extract arbitrary chromosome from human,
* implant it into an mammal egg cell
* prepare chromosome-less human egg cell
[Answer]
During meiosis the DNA gets packed into what we observe as chromosomes.
Assuming that in that specific moment we can:
* open up the cellular nucleus
* extract the chromosomes without damaging them
* identify each of of them
* transfer the chosen ones into the empty nucleus of a new cell
* seal the newly filled nucleus
The answer is yes, it is possible.
And I think is also sufficient as explanation of the process, if any is supposed to be given within your world.
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In the sci-fi setting that I've had on the backburner for a while now, there is a species known as the Azmarans. They are a very socially adept species, between them having a rather communicative psychology to their unique ability to conform to whatever shape they might need in dealing with another species.
How they do this is through the use of artificial, inorganic exoskeletons, which are designed based on whatever bodily arrangement they so desire. They can also change their exoskeletons like a hermit crab would change their shell once they've grown too large for it. But for the Azmarans, this is more to achieve certain physical characteristics for social or practical benefit. For example, if they wanted to deal with a dog, they would make a dog-shaped exoskeleton, meanwhile if they wanted to deal with a human, then they would merely remove themselves from the dog exoskeleton and reinsert themselves into a human-shaped exoskeleton.
The way I'm imagining it is that their anatomy and the arrangements of their internal organs shifts and changes so that they can fit into whatever exoskeleton they want to. They have no mouths, as their diet consists of large amounts of bacteria and other microbial lifeforms, they are very sensitive to sound when naked, due to the atmosphere of their evolutionary homeworld having been rather thin, and they have a set of eyes developed for ultraviolet light, though they can perceive other wavelengths through the aid of their technology--which is often integrated into their exoskeleton's visors.
But something I can't quite wrap my head around is; how do they change their anatomy so that they can conform to the shape of their exoskeleton? They have no endoskeleton, that's for sure, and I'm wanting to make them a single organism rather than a symbiotic colony of smaller lifeforms like the Lekgolo from *Halo*, but beyond that I'm unable to figure it out. How might such a species develop their biology in such a way that their organs, veins, arteries, and so on would shift and reshape for the shape of their exoskeleton?
[EDIT] This is distinct from the other question because the Azmarans are supposed to be able to take on any selection of limb numbers and structures (10 limbs, 100, 1,000, etc.) and they are generally rather formless without an exoskeleton; resembling more of a mass of living flesh with eyes than a true animal when they don't have an exoskeleton. The idea of the Azmarans being many smaller intelligent lifeforms is tempting, but for your information, my brother had already introduced me to the *Portuguese Man O' War*, which is more of a colony of unicellular organisms functioning as one larger organism. This, however, is not what I'm looking for, as they are supposed to be distinct multicellular organisms. Not to menton that they are also supposed to be able to take the form of only what the exoskeleton is. That they use metamorphosis for this is out of the question, as they are expected to change their shape and physique depending on the shape of their exoskeleton.
I've also seen the comments regarding their size and whether I'm looking for that to change as well. I'm not. I'm wanting them to be stuck to their own regular mass and volume in what is possible, so if they were to take a mouse-type exoskeleton, then they would look like a massive mouse in their silhouette. Though the use of silhouettes that an organism would be comfortable with that are other than the organism's own is certainly a good idea, such as the dog issue; although simply being a large dog would typically suffice, they'd just as likely take a humanoid appearance, as dogs had been bred and raised to love humans and do what their human master says. In addition, I'm certain that humans wouldn't mind interacting with a humanoid of larger or smaller size, as the Azmarans would have different sizes depending on factours and variables similar to how size works for humans; age, nutrition, health, genetics, and the environment.
[Answer]
**Your aliens are amoeboid, without fixed shape.**
Amoebas move by exerting leverage against one area and pushing out another via fibers extending through their protoplasm.
<https://biology.stackexchange.com/questions/39883/how-does-an-amoeba-move>
>
> It has a cytoskeleton, a network of fibers stretched across the cell
> which it can shorten and expand (by adding or subtracting actin
> monomers which build them) in a coordinated manner to more-less
> arbitrary change shape.
>
>
>
Your aliens do likewise. They will move exoskeletal appendages via pushing protoplasm down into the appendage (or pulling it out) and increasing / decreasing pressure relative to the rest of the exoskeleton.
Sidenote - your adept aliens might know to avoid the "uncanny valley", in which something which is like a human but not close enough gives off super weird vibes. It would be cool if the shape they chose for a human was not humanlike at all - maybe even customized for individuals. One human would get a Shmoolike snowman. One would get something like a walking tree stump. One would get something like a hedgehog. Dogs would get fire hydrants. Each entity would feel comfortable with the manifestation the Azmaran chose, because they are that good.
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I tend to approach my fictional species from an evolutionary perspective, which isn't a necessity in science fiction due to uplifting, self-genetic modification, and artificial sapients. That being said, I'm still going to try an evolutionary approach for your Azmarans.
Okay, so the first thing about Azmarans is they are clearly not claustrophobic. They have no qualms about spending a good majority of their lives in these stiff suits, which is almost like humans being okay with wearing deep-sea-diving suits all the time. That makes me think that they evolved to appreciate tight spaces, likely to avoid predators or secure food.
With that in mind, I totally agree with Clay Deitas that these creatures would have a lot in common with an earth cephalopod, specifically the octopus and squid. In addition to very malleable anatomy (I'm imaging a long body with several tentacles with smaller branching tentacles on them, severing the same function as fingers, but that's just me), the Azmarans will have multiple hearts and a decentralized nervous system. This would not only allow for a unreal amount of flexibility, but gives them access to more far more brainpower than most animals.
With that kind of anatomy in mind, you have a species that is great at hiding and tool use, but has very few defensive options. For most of their prehistory, they would survive by planning out well defended settlements, making traps, and forming groups for hunting more dangerous animals. The beginning of some "suits" could be seen here, with some Azmarans making suits of wood, bone, or stiff hide to give them more leverage and protection in a fight. After a few technological revolutions (agricultural, metallurgy, mathematics, scientific method, warp drives, etc.), I can totally imagine this mindset leading to the diplomatic exoskeletons you're talking about.
Here's some miscellaneous brain-drizzling regarding this idea:
* This setup doesn't effect your idea for ultraviolet-sensitive eyes, as octopuses and cuttlefish already have eyes that can see in the ultraviolet. As a side bar, a problem octopuses have is that their decentralized nervous system makes it so their limbs have a great deal of autonomy, meaning they have to actually look at their tentacles to see what they are doing sometimes. That might be a fun detail to include if you go with this idea.
* This set up does have the Azmarans being omnivores. This is because I have a hard time imagining a herbivorous species (or, in this case, a bottom-feeding species) needed to develop a high level of intelligence. I mean, what is the incentive to invest in expensive neurons when all you need to do is outsmart bacteria? This a failing on my part, just wanted to be clear on that.
* In my opinion, the big evolutionary cheat-code that made the Azmarans become the top of their planet's food chain would have to be longevity. Maybe they are like lobsters in terms of not having a fixed lifespan, they just keep growing bigger and bigger till they can get enough oxygen to support their bodies? I'm imaging a process similar to molting for this, although I'll be damned if I know if Azmarans have more in common with reptiles, mammals, or cephalopods at this point.
* While the species I'm talking about has worn plate-mail for clothing for much of their history (in terms of rigidity, I mean), by the time your story takes place I think they would have upgrades those suits with all kinds of useful gadgets, such as the visors you were talking about.
Sooo, yeah. A before the Azmarans were talking to humans while wearing a human suit, they had a long history of being squid(-like organisms) kicking around in these:
[](https://i.stack.imgur.com/kVekL.jpg)
[Answer]
Multipurpose organs.
If your species has evolved in such a way that one organ or another can do any job that it needs to do, as well as a form of proprioception which allows the individual to know where its internal organs are and re-purpose them to different functions. This way the organs don't have to go very far at all, they just change what they are going to do.
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If they are just eating bacteria, they can be blobs. They don't need any large organs anyway, just nuclei, ribosomes, and some other organelles. The problem won't be shrinking, they can just dump a bunch of cells off of themselves (or exocytosize some of their cytoplasm if they are one big cell), the problem will be scaling back up in size, for which they will need some stored cells/cytoplasm they can use, which might be contained in canisters in the suits.
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It takes a lot of work, but it can be done. The Mongol [Yam](https://en.wikipedia.org/wiki/Yam_(route)), a horse-based mail system, is probably the best example that has been done before. But after visiting the local science museum recently, I saw [these](https://en.wikipedia.org/wiki/Acoustic_mirror).
Acoustic Mirrors, you speak in front of one, and a person at the other one, some distance off, can hear what you say. In between them, you cannot hear anything from them.
I was wondering if a system of these could be set up, to have rapid transportation of information from one point of a kingdom to another, especially when I don't have horses.
If possible, what's their max range? How would weather affect them?
[Answer]
**Bull's Eye Lighthouses**
[Lighthouses](https://en.wikipedia.org/wiki/Lighthouse) have been in use since Antiquity.
The idea is relatively simple:
* a stone tower, build at the top of a hill, guarantees that the light at the top is visible from afar,
* a fire, at the top, is fueled by whatever is handy: wood, turf, etc...
On top of that, we apply the [Bull's Eye Lantern](https://www.the-saleroom.com/en-gb/auction-catalogues/candt-auctioneers/catalogue-id-srct10014/lot-c1e0d33f-b83d-4172-a578-a47f01478725) principle: the light source is encased in an opaque (reflecting) material which only lets the light out in a particular direction, somewhat focusing the beam.
And then we put a movable panel in front of the light exit, allowing the operator to modulate the output.
---
That's it. Make a network of such lighthouses across the countryside, teach morse code to the operators, and you have messages propagating at the speed of light (minus delays incurred at each hop).
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Disadvantages:
* Requires good visibility conditions, heavy fog could be crippling.
* Requires a lot of fuel.
* Works best on moonless nights.
[Answer]
Your major problem is wind.
Sound travels through the air, when the air is moving the velocity of the sound and the velocity of the air sum to get a new net velocity relative to the ground. This is a problem if your just shouting across a large field but is much more of a problem in your system, especially in crosswind.
In order for your system to work sound from one dish must hit the other but wind will likely blow that sound off course. In order to ensure you have some sound hitting the other dish you may need a dish whose length in ratio to the length of the distance across which the message is being sent is greater than the ratio of the wind speed to the speed of sound.
Doing some back of the envelope maths and using 8m/s as a good wind speed then we find that your dish length needs to be 2.3% the length of your route AT least. The longer the better if you want a strong signal in high wind. This means for a five mile route you have a dish about two hundred metres across this is hard but not impossible. Even then however a strong breeze is all it takes to render your relay system useless.
You might be able to solve this by moving your sound source or acoustic mirror, but that requires the sort of quick, reliable precision you get with lasers that would make for much more reliable communications technology.
You could put everything in a tunnel, but those sorts of tunnel systems would be incredibly hard to maintain. A more reliable system might be using acoustic mirrors as telescopes to listen in on extremely loud sounds, such as gongs, bells, organs or large firecrackers, similar to acoustic aircraft detection.
[Answer]
I am aware that this question asks about acoustic mirrors, but there is a far better alternative. Normal mirrors! you can make aqueduct style stone tubes that are a few centimeters wide, bury them between points, using mirrors to turn, and then flashing a light from a lantern down the tube will cause the light to be reflected off of the mirrors all the way to the other end. Use a Morse code-like system, and you have a light based telegram system.
[Answer]
Such a system, assuming it was feasible (which isn't) would not be practical, let me explain you why.
First, the principle behind it is to have the speaker and the listener being positioned at the focal points of an ellipse, similar to the [whispering gallery](https://en.wikipedia.org/wiki/Whispering_gallery).
[](https://i.stack.imgur.com/MrJZH.png)
The properties of the ellipse make it that the acoustic waves emitted in one focal point will converge into the other. But this mean that, once you have built your elliptical mirrors, you are bound to a fixed distance. Not one meter more, not one meter less.
But first you need to be able to build two elliptical surfaces with narrow enough tolerances that the waves are properly focused, which is rather challenging.
You can bypass the problem by building two [parabolic](https://en.wikipedia.org/wiki/Parabola) surfaces (you just need to be able to spin a liquid fast enough while it becomes solid), but that would be less efficient, as you would lose part of your signal.
[](https://i.stack.imgur.com/sOrbY.png)
But at this point you would need an extremely precise alignment to be able to capture the acoustic waves. In practical this could be, at best, a though task, since you have to compensate for the motion of the air in between the two surfaces. Any shear in the wind flow will surely destroy the synchronization between the various paths, destroying the communication channel.
Late addendum: apparently the approach with parabolic surfaces was used in UK around 1920, to detect airplanes crossing the Channel. They could hear an airplane from 25 miles, giving 15 minutes of warning. More info [here](http://www.nationalgeographic.it/wallpaper/2018/08/10/foto/inghilterra_acoustic_mirror_specchi_acustici-4071591/1/) (page is in Italian). Mind that, being just a receiver, they were less annoyed by wind: they just needed the airplane to be at the suitable location.
[Answer]
Others already said why acoustic mirrors are hard to use. My suggestion is a system of flags, not unlike the maritime flags:
<https://en.wikipedia.org/wiki/Maritime_flag>
The communication system would be composed of many flag stations, each one with 4 to 6 flag sets (for communication with several stations at the same time) and an equal number of telescopes (to see other stations' flags).
There would be flags for specific meanings, for letters, numbers and symbols, for start/end character, start/end word, start/end message, and signal incoming message.
The system would be slow to transmit, from the taking out and putting on several flags at once, for each character/word; but the bigger distances traveled (several kilometers with almost no delay) would make up for it.
[Answer]
I think the idea is brilliant, but without using magic as a means of facilitating it, you'd be hard-pressed to truly explain it without some system of underground tubes or wires - even only if left behind by a previous civilization.
In my own story, I've borrowed from HTTYD's tv series and created messenger dragons that work like a little like messenger pigeons only a little more intelligent. They can be told to seek, much like a scent dog. Or told to go somewhere specific. I can't say they're the same level of intelligence as humans, but there are some dogs that can be trained to read or count, or differentiate colors, to a certain extent. And my mom is always telling me: "I'm sure you'll figure it out, with a little time and some patience, towards yourself if nothing else."
I certainly always expect too much of myself and get frustrated when I don't live up to my own expectations. Me thinks it is a weakness in all of us writers.
PS: Although I still think the idea is plausible, I looked at the link you provided. It was not the 'mirror' I expected it to be, I guess I was thinking of the mirror on the wall type. :-) silly me. Still a neat concept though. I will be following this conversation for future input.
[Answer]
As others have noted, this is not going to be a very practical system, in terms of cost or reliability.
But if you are willing to live with these issues, then maybe go for something mildly interesting such as the [whistle language of the Canary Islands](http://www.guinnessworldrecords.com%2Fworld-records%2Ffarthest-distance-travelled-by-a-human-voice) to either boost range (requiring less reflectors, and therefore cheaper) or reliability of the overall communications system.
[Answer]
A possible solution can be the African drum language [1](https://en.wikipedia.org/wiki/Drums_in_communication). It was probably the fastest means of communication before the invention of telegraph.
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[Question]
[
If someone from our Earth- from, say, NYC or some other big city- ended up on Planet "Qwerty" for some reason or the other and bit someone in a no holds barred fight, would diseases transfer between the combatants? If so, which direction is more likely and how quickly would effects show?
Assuming the planet in question has superstorms that isolate most communities and neither the Earthling nor the "Qwert" are actually ill when the fight occurs. And that this is not the Earthling's first contact with the native species (like they've run into several people since arriving on the planet) but the Qwert has no idea that the Earthling is alien and has never seen them before.
[Answer]
## Human disease will only affect humans.
You might think a disease would spread rampantly among an alien population considering the effects Smallpox had on the south american natives when they were exposed to it. And while this is a perfectly reasonable assumption, it's also incorrect.
**It is almost impossible for there to be any human diseases that can affect the alien at all.** The reason for this is that human diseases evolved to infect *humans.*
**Alien Cells would be too different from Human Cells for any disease to attempt to infect. For example, a Plant can't catch Smallpox from you.**
And while there is some precedent for cross-species infections as has been the case on Earth, these have been between animals that share a relatively recent common ancestor, like Cats and Humans, or Birds and Humans. This is why I said "almost" impossible, because there is a tiny, *tiny* chance it is compatible, but this is less likely (and less plausible) as winning the Lottery every time for about 100 years.
**But that doesn't mean that there's no way for you to make it plausible. Using something like the Panspermia theory, you could have the two species share a common ancestor, which would massively raise the odds of an infection.**
War of the Worlds can be considered incredibly inaccurate. Until, that is, you consider the theory that the Martians and the Humans are biologically connected from a common ancestor, which makes it just slightly more likely, and into the realm of plausibility.
[Answer]
What we call disease is a non normal interaction between (our) organism and another one.
If you consider that our skin and mouth host millions of bacteria, and likely will do your qwerties, it is easy to understand that chances of transmission are equal, and that the chance of getting a disease are also equally split.
But to get a disease you will need to have a bacteria or virus which can use the host organism to reproduce.
If you have read the War of the Worlds, you know how this can end..
[Answer]
When we speak about infection, we are either thinking about microbes, virii or prions.
Virii will only infect aliens if those aliens have something akin to our cells in their phisiology. The virii would also require the aliens to have the same receptors in their cells' membranes in order for virii to work. So this relies heavily on aliens' biology being based on DNA, or at least RNA, which might not always be the case.
Diseased prions do their nasty work by converting sane prions into a bent shape. If the aliens don't have prions, these are out of the question as well.
**When you get to bacteria and protozoa, though, it's a whole other story.** Unlike prions they are not zombie protheins, and unlike virii they don't get into your body to steal your ribossomes. They hang inside you because you are a good environment for them to live and reproduce.
In fact, most bacteria within us don't cause any harm, and some are even necessary for our good health.
Now, imagine that you have cavities. Those are caused by bacteria eating through your teeth enamel. For us humans, specially after the 20th century, these bacteria are just a nuisance at worst.
But imagine that the alien you bit has a carapace made of the same material as your tooth enamel (but you happened to bite an unprotected, soft body part). If that alien doesn't get treatment, they may end up with serious dermal injuries over the course of a few weeks.
There are many species of bacteria that live in our surroundings, but don't thrive within our bodies - mostly because they can't handle the competition with the ones we do carry inside. If aliens came in contact with humans, and the aliens' bodies turn out to be a fostering environment for those bacteria, then the aliens will suffer infections very often. If the aliens have any equivalent to our bacteria in their world, then we can add "and vice-versa" to it: what is harmless for them might be dangerous for us.
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[Question]
[
So Chlorine Trifluoride is a very dangerous chemical known to burn through things like concrete and asbestos. It's so bad that the Nazis, THE NAZIS, decided it was too dangerous to use. So I need an organic substance that takes forever for this compound to burn through (3 hours to a day) that is about as thick as your skin. I am willing to take softer science answers (like silicon or germanium bonded to carbon chemistry like some microorganisms have done) but I would prefer to stay as close to mammalian biochemistry as possible.
[Answer]
Almost exactly the same question was asked here. Linked is my answer.
[How can Bronze Age people make hazmat gear for chlorine trifluoride?](https://worldbuilding.stackexchange.com/questions/80155/how-can-bronze-age-people-make-hazmat-gear-for-chlorine-trifluoride/80190#80190)
The answer: make the gear out of calcium fluoride, or [fluorospar](https://en.wikipedia.org/wiki/Fluorite). Chlorine trifluoride is caustic because it fluorinates anything that can be fluorinated which is just about anything. But calcium fluoride already has all the fluoride it can have. It is full of fluoride and no more can be added. Also, it is a stable crystalline substance.
Make your vessels out of fluorspar. Bonus: it is pretty.
[Answer]
Unfortunately you ask the impossible. Chlorine trifluoride will eat through any organic material, fluorinating the carbons. Even *teflon* is not completely safe from it, because the reagent will attack the carbon-carbon bonds.
You need a substance that is both completely fluorinated and mechanically stable, which pretty much restricts you to solid metal fluorides, calcium fluoride, etc..
You might have your organism secrete calcium fluoride or copper fluoride, but then you wouldn't have a mechanism to produce *those* organically. Remember that the final product must be completely anhydrous, or chlorine trifluoride will burn through.
[Answer]
If you read this: <https://www.cdc.gov/niosh/ipcsneng/neng0656.html>
Practically nothing. Any biological substance with water in would make for a horrifying show. Maaaybe if you can biologically produce large amounts of Carbon like Graphene, which contains no water, you might be slightly safe from the burning (but not of the vapour as it is now boiling and getting everywhere). But after reading about this substance I'm willing to bet that pure Carbon is somehow also going to do something horrible when in contact with chlorine trifluoride. In fact, most of the time I see "fluoride" somewhere in a molecule name it's usually something naaaasty.
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[Question]
[
I've been conceptualizing a species of intelligent insects. They would have 6 limbs, they can fly, but they walk bipedally. I've been thinking of having them get down on all limbs of they need to go fast and can't fly away from something, but I do want them to be at least mostly bipedal.
Here's my problem though: I can't find anything relating to insects walking bipedally, and I don't know where I should look as far as anatomy I can adjust to work in this situation.
How can I make a bipedal insect?
[Answer]
**Cockroaches can run bipedally.**
[J. exp. Biol. 156, 215-231 (1991) MECHANICS OF A RAPID RUNNING INSECT: TWO-, FOUR- AND SEX-LEGGED LOCOMOTION BY ROBERT J. FULL AND MICHAEL S. TU](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.547.9445&rep=rep1&type=pdf)
[](https://i.stack.imgur.com/eQ9tj.jpg)
image from <http://www.berkeley.edu/news/media/releases/2002/09/rfull/locomotion.html>
>
> (Another wacky congruence between the bug world and ours: At top
> scuttling speeds, the roach actually rears up on its hind legs — which
> are longer than its front and middle pairs — and runs upright, like a
> human sprinter. The roach is also the world's fastest land insect,
> able to run the human equivalent of 200 miles per hour, as Full's
> students relished informing the Guinness Book of World Records.)
>
>
>
Interestingly it is when the roach is really running fast that it goes bipedal. Bipedal is its top gear. Look how far forward it is leaning.
I must say that I was disappointed I could find no videos of the cockroaches running bipedally. Dr Full, time to represent for your lab!
In any case - high speed 2 legged cockroaches. Maybe your bipedal bug goes everywhere fast. It occurs to me that an insect with wings could extend them to offer resistance against the top of the body falling forward (at the cost of some speed). Wings would be a good way to brake too.
[Answer]
**Short answer**
*Insecta* are not designed for bipedal locomotion.
**Background**
The trick of *insecta* is that six legs allow for locomotion while keeping 3 limbs on the ground at all times (Fig. 1). This tripod gait is the direct results from having six appendages [(Lanham, 1951)](http://www.sciencemag.org/content/113/2945/663.1.full.pdf). Importantly here, **locomotion of a small animal encased in a rigid exoskeleton is not effective with less than 3 pairs of legs**. Insects generally walk by lifting the two outer legs on one side and the middle on the other side, sweeping them forward and placing them down together. Hence, insects support their rigid structures with a tripod at all times. Tripods are among the most stable configurations, and they never wobble (why on earth do tables have 4 legs?) [(Lanham, 1951)](http://www.sciencemag.org/content/113/2945/663.1.full.pdf).
Note that the praying mantis is stationary when praying (hunting) while it uses all six extremities when moving around. The dung beetle is a fascinating exception; when rolling a ball of dung it indeed appears to use just two legs for walking and four to roll the dung (Fig. 2); however four legs are also in constant contact with the ball so the tripod is still in effect, albeit on two different planes in this exceptional insect. Moreover, they 'cheat' by using their head for balance to (Fig. 2).
Further, while acknowledging the fallacy inherent in thinking that an *[absence of evidence is not evidence of absence](https://en.wikipedia.org/wiki/Evidence_of_absence)*, I couldn't find evidence that insects have a vestibualr system, or an equivalent control system of balance.
In mammals for example, the inner ear houses the vestibular system that registers acceleration in any direction through the semi-circular canals and the otolith system.
In all, given their rigid exoskeleton and the absence of a balance system as far as I know, I would reckon that *insecta* are simply not designed for bipedal locomotion.
One of the answers mentions running cockroaches; indeed they do, as do some species of lizards when in danger. This, however, is a matter of short bursts of rapid locomotive activity and is not their regular way of moving. The bipedal gait is simply maintained through speed and cannot be sustained for a long time and cannot be used other than sprinting away in a more-or-less straight line.
[](https://i.stack.imgur.com/MktxS.png)
Fig. 1. Insects' locomotion resembles a double tripod. Insects have a cyclic gait which consists of two phases, the stance phase and the swing phase. The stance phase is the power stroke, it pushes the body forwards in the direction of travel while the leg remains on the ground. Three legs are used is this phase by forming a tripod with the front leg and the hind leg on one side of the body and the middle leg on the other side. This formation is why this gait is known as the tripod gait. Source: [Insect robotics](http://robotic-insects.weebly.com/).
[](https://i.stack.imgur.com/G8HRK.jpg)
Fig. 2. Dung-rolling beetle. source: [Phys.org](https://phys.org/news/2017-04-scientists-dung-beetles-milky.html)
**Reference**
- [Lanham, *Science* (1951); **113**(2946): 663](http://www.sciencemag.org/content/113/2945/663.1.full.pdf)
[Answer]
**Bipedal motion is semi rare in the animal kingdom**
few mammals can even do it, and even fewer are purely bipedal (humans and kangaroos). Few reptiles ever managed it and they mostly went extinct (except the Jesus lizard). One common pattern between all of them is specialization or minification(T-Rex) of upper legs into arms and specialization of lower legs into more robust and capable legs. With this in mind there are some examples in the insect world approaching this trend.
**Grasshopper**
[](https://i.stack.imgur.com/S2dUo.jpg)
These guys have specialize rear legs capable of propelling their whole body forward great lengths under their own power. If they were to walk bipedally these legs could provide the strength to do so.
**Praying Mantis**
[](https://i.stack.imgur.com/EvKFg.jpg)
Here you start to see the erect posture of bipeds and the specialization of forward legs into arms.
**So to answer your question one way. You could view the combination of the mantis and grasshoppers traits to come up with a structure capable of bipedal motion.** This isn't feasible for insects simply because jumping and flying are often more easily achieved and offer more range and capability, but it is physically possible.
[Answer]
Don't worry so much about what terrestrial insects look like. You're "evolving" something from those critters. So, let's look at the first problem: what do you need for bipedal locomotion?
**Balance**
You need something that provides the "gyroscope" that keeps the critter upright. [For humans](https://www.sharecare.com/health/bone-joint-muscle-health/body-keep-me-upright), that's a combination of...
* Our inner ears (air pressure),
* Sight (visual alignment with surroundings),
* Touch (heat and air motion),
and a host of other systems all "detecting" how "upright" we are (based on the brain's "I want to do this" control). The result is muscle changes that put us in the position we want (e.g., "upright").
So, first and foremost you need to think abut how your target insect would evolve those basic systems (don't worry to much about the details, you're looking for "good enough" so readers can suspend their disbelief... not so PhD's can nod their heads in agreement that you correctly predicted a million years of evolution).
*Goal:* how would the insect create it's internal "gyroscope?" If it still has its exoskeleton, then it will need to compensate for the loss of touch (but, for example, it may compensate by developing the ability to detect minute stress against joint muscles).
**Delicate Muscle Control**
Without electronic help, we really can't detect the bazillion of muscule corrections that occur moment-by-moment to keep us in the position we want (well, when you're standing on your toes trying to screw in a lightbulb with the tips of your fingers you can tell...). However, those adjustments are needed. The basic problem with insects is that most of those limbs have very little in the way of muscles (or whatever squishy goo they use to create basic contractions). They may evolve muscles/squishy-goo such that they can, but that means...
*Swiveling Joints*
Here's the next problem. Balance requires the bendy parts to adjust in a lot of different directions. If you think about it, your toes, ankles, knees, hips, spine, and shoulders must all make minute adjustments to keep you upright. Nearly everything on those darn bugs is ramrod ridged. Now, exoskeletons means no internal bones. That's OK (...ish) if we evolve really tough "skin" that can better articulate the joints and allow for greater range (and more subtle range) of movement.
Perhaps your biggest challenge here will be side-to-side corrections. Imagine (probably because I saw the picture in another post) a grasshopper standing up. The ability of its legs to "rotate" forward (and, with evolution, backward) covers half the problem, but the basic design means very limited side-to-side correction. If you pushed on his "shoulder," he might just fall over because he can't do anything about it. Without an internal bone structure for hips, our friend might need a short but tough "tube" that extends from the abdomen to the leg, giving it a bit more separation from the body and therefore greater side-to-side range of motion.
*The "Other Side" Muscles*
Another thing your bugs will need is muscles on the "other side" of the "bone." Humans have muscles, for example, on the front and back of the leg. Those muscles work together to keep you upright. They also allow you to move both backwards and frontwards.
Insects can kinda do this (beetles and spiders better than most, grasshoppers would suck at it) because the legs tend to be engineered for just one or two motions. However, if we think of the "squishy goo" as hydraulics, then everything you need is basically already there: you just need a better pumping system that can precisely forward and reverse the fluid, so to speak.
*Goals:* joints and "muscles" (aka, hydraulics, I kinda like that idea).
>
> Give your insect these abilities and, while the cute critter won't be the best dancer in the world, he/she would be capable of bipedal locomotion.
>
>
>
[Answer]
By going the other way conceptually and then back again in the detail work, so take an existing biped like a human, why and how would you put extra arms and wings on a human? The actual anatomical design is going to be fairly similar it's just the surface details that say "bug" or "mammal" or "bird" for that matter.
As to some notes on an actual design; for my money you want not four arms but two pairs of arms, a fine pair for detail work and a heavy pair for brute force projects. I would go with multiple pairs of wings arranged down the back of the torso also, think dragonfly rather than angel. A tail may or may not be useful for balancing large weights etc... that's an argument that can go both ways when you're talking about technological species versus evolutionary necessity.
Now there may be an issue with size, true insects have no lungs; they have something more akin to gills that use air instead of water as a working fluid. They are therefore very strictly limited in their maximum size by oxygen levels, modern insects max out at either 71 or 115 grams, depending on the definitions being used.
[Answer]
To start, there are few insects that don't have that long abdomen, and that's really what receives support on something like a mantis. I assume we want to keep this feature, as it really is the visual indicator of "insect". If we want that to be supported by two legs, they have to be bulky like on a cricket, but probably not made for jumping, as they'd need to be long, too.
Walking upright with that configuration seems to me as if it would require the mantis' thin upper body, as well. I have a little bit of an issue wrapping my head around the idea of specialized "arms" that double as "legs", though. It doesn't seem like the kind of thing that could happen. It really depends on the kind of arms/hands you want these creatures to have.
I think instead of running on all legs at a greater speed, I would suggest having the back legs be extremely good for running, and joint them in such a way that the insectoid can lean forward for maximum aerodynamics while running. The upper arms, in that case could be used to counterbalance the otherwise lightweight top.
[Answer]
Your species sort of reminded me of the [Mantid](https://wow.gamepedia.com/Mantid) from the Warcraft universe. They are an insect race that have 4+ limbs and they are bipedal. They can fly and their bodies can support them walking up right.
If the no-fly thing is important, you can talk about how their wings atrophied as their intelligence or civilization advanced.
The wiki page is limited so you can just google for more information and also search for videos from the related Mantid dungeons on youtube to see how their animations work to get some ideas.
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[Question]
[
A *normal* respiration is:
$${\displaystyle C\_{6}H\_{12}O\_{6}+6O\_{2}\to 6H\_{2}O+6CO\_{2}+38ATP}$$
A *normal* cellular respiration uses O2, so my question is if it's possible to have a respiration with **CO** instead of **O2**.
Something like this (an example of how can be done that):
$${\displaystyle C\_{6}H\_{12}O\_{6}+12CO\to 6H\_{2}O+6CO\_{2}+12C+38ATP}$$
**Is that possible?** If not, **is it possible with some changes like the chemical reaction or the whole mitochondrion (e.g: the animal must be able to eliminate graphite from cells)?**
[Answer]
CO is not going to give up that oxygen without a fight. It is happy as it is, but in a reaction it wants to become CO2. Its function in any metabolic pathway is as a [reducing agent](https://en.wikipedia.org/wiki/Reducing_agent). That is the role played by sugar in our metabolisms.
from Carbon Monoxide, National Academy of Sciences 1977
<https://www.nap.edu/read/20333/chapter/3#10> page 10
>
> Carbon monoxide is quite stable and chemically inert under normal
> conditions (25 C and 1 atm) despite a carbon valency of two. At
> higher temperatures it becomes reactive, behaves as though on
> saturated, and can act as a *powerful reducing agent*-a property used in
> many of metallurgical processes such as in blast furnaces.
>
>
>
emphasis mine.
From [Thermophilic carboxydotrophs and their applications in biotechnology.](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0ahUKEwib977ywpvVAhXGbD4KHezfDC8QFghPMAg&url=http%3A%2F%2Fwww.springer.com%2Fcda%2Fcontent%2Fdocument%2Fcda_downloaddocument%2F9783319118727-c2.pdf%3FSGWID%3D0-0-45-1482722-p177006568&usg=AFQjCNFech81U-y23iXku08sWBJhIDAWiA.)
>
> CO metabolism begins with a reaction that can be considered a
> thermodynamically favorable disproportionation, resulting in CO2 and a
> pair of reducing equivalents, or molecular hydrogen as products: CO +
> H2O -> CO2 + 2H+ + 2 e-
>
>
>
same source; this diagram showing various metabolic pathways which all start with CO acting as a reducing agent.
[](https://i.stack.imgur.com/bZK97.jpg)
These metabolic paths count as respiration, some aerobic some anaerobic. But in every metabolic path I found the CO was oxidized and donated electrons. I do not think there would be a metabolic path where CO was happy to become a reduced carbon of some sort.
[Answer]
Will's answer is excellent and very thorough.
However, if you'd like to take it a step further, the fact that carbon monoxide only acts as a reducing agent does not exclude its participation in a species' metabolism. The trouble is that the organism would have to have a wildly different metabolism, meaning that it would have to be evolved from a common ancestor *much* further down the evolutionary tree.
Most of the organisms we've found with strange metabolisms (called extremophiles) are in the archaea family. It would be conceivable (although of course unlikely) that a multicellular organism had evolved within the archaea rather than eukaryote domain.
One of the most consequential moments in the evolution of life on our planet were the mutual endosymbioses between chloroplasts and cyanobacteria, and between mitochondria and proteobacteria. In the world you're building, it would be possible that there was an endosymbiosis involving an archaea, such that the multicellular organism's metabolism evolved around the symbiosis of an archaea.
The idea of the mitochondria is that it generates ATP through pumps that exploit a chemiosmotic potential across its membrane. This potential can be established without having to start from the same reagents.
To borrow from Will's answer, you could for example have a metabolic pathway that starts from carbon monoxide using CODH
$CO+H\_2O \rightarrow CO\_2+2H^+$
You could thus have a buildup of $H^+$, establishing a gradient just like in a mitochondrion. The $CO\_2$ produced in this reaction could also be used to produce methane, which would establish [yet another gradient.](https://en.wikipedia.org/wiki/Methanogen)
$CO\_2+4H\_2 \rightarrow CH\_4+2H\_2O$
In summary, the existence of the organism you are describing is totally plausible, but you would have to tie it in with an alternative evolutionary branch. Do keep in mind that if you try to approach the problem in extreme detail, you may find yourself digging a deep hole. We don't yet fully understand *real* metabolism, so to try and invent a complete metabolic system would be a mammoth of a task, given the incredible complexity and interconnectedness of metabolic pathways.
Good luck with your little carbon monoxide breather!
[Answer]
I'm only in partial agreement with the two previous answers. I think there are two parts to this question. The first part is to explain where all of the CO is coming from to allow its concentration (in the atmosphere??) to be high enough for it to be a principle source of energy. Assuming an atmosphere with high amounts of CO, then there is no obvious reason why it couldn't be used. You may be aware that the human body produces CO and uses it as a signalling molecule. You may also be aware that certain bacteria metabolize it, so there's no reason why a multicellular animal couldn't, afaik. The issue, as I see it, is the question of whether a given atmospheric composition (say 60% nitrogen, 1% water and 39% CO) would be meta-stable. Oxygen is both the product of and the source for respiration reactions. CO would have to be the same. Even starting on a world where some life exhales (emitted) it, and some life metabolized it, it isn't obvious to me that such a world wouldn't evolve rapidly into one similar to ours (with say a 78% N2, 21% O2, 1%H2O atmosphere) leaving your CO breathers as fossils. Note that CO is 30 times less soluble in water than CO2, which would be another problem for a development by natural selection (if life evolved first in water)...
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[Question]
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I'm trying to plan a rotating wheel space station for a project. It should be noted that I have to stay as close to real physics as possible, although it takes place in far future. The space station is orbiting an Earth-like planet.
The deck 0 is one with reactor core. Besides it's practically a one long tunnel to transport stuff from the manufacturing center to various sectors or to the docking bay.
The manufacturing center can be used to produce almost anything from food to spaceships (can't be bigger than maintenance tunnels). There is a constant supply with resources by a fleet of autonomous spacecraft, which mine asteroids and planets.
*(additional notice): Power is not a problem here. Let's just assume there is a sufficient enough power source, which would be more than enough for most problems. Be it a nuclear reactor or thermonuclear one, doesn't matter.*
And for everything else it's easier to show sketches.
As I'm really bad at physics, I'm not sure if the station has some problems. Does it look feasible? Are there obvious and not-so-obvious problems? If so, what could be improved?
[](https://i.stack.imgur.com/uA28z.png)
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Welcome, Elza...! Your physics background is fine, you expressed the first key ingredient in true intelligence, you asked a question.
Your basic space station concept is sound, and has been the subject or central to fictional venues as diverse as *'2001: A Space Odyssey'* to ( think more what you're looking for) *'Star Trek Deep Space Nine'*.
The concerns most likely to affect your product are around construction techniques and materials, Secondary only to the concerns of what will likely be a self-supporting environment. Use the wrong metal, or design ( think of a shipyard), and your structure doesn't hold up. Use the wrong or insufficient air/water/environmental controls, and it becomes unlivable.
Good luck with you construction, your ideas, and with this place.
SE is one of the most entertaining and educational places I have ever known..
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Is the core nontrotating? It doesn't appear to be, so docking will be tricky!
Big issue is shielding. How does it handle normal radiation and solar events?
Power?
With all this coming and going—you focused on distrubtion of goods—you’ll have to keep it ballanced.
You ought to be able to find detailed design discussions on line, and popular essays written over the past 50 years. You don’t have to invent from scratch! [Wikipedia](https://en.wikipedia.org/wiki/Rotating_wheel_space_station) is a good place to start to find primary material referenced.
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One thing I saw that concerned me that no one else has brought up yet is the location of the manufacturing area. Manufacturing in zero-G would probably be more efficient, so I would guess that it would be moved towards the center, with people on the outside.
Same with the power core. It is being subjected to stresses which it doesn't need to be subjected to. Gravity is useful to people because we evolved with it, but it's a pain for a lot of machinery.
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As Nathaniel pointed out, you need to have weight distributed evenly. On larger scale, you can have manufacturing on 2 opposing segments and one backup core opposite the live one (or something else of similar weight, perhaps another (smaller/larger) manufacturing segment). You would probably also need some movable weights along entire structure to balance moving of heavy stuff through maintenance tunnels and to counter changes in layout and contents of rest of station. I hear water is pretty good radiation shield, and it can be pumped easily from one place to another, so parhaps you can use that as your weights. Have some layer of water at the outer edges of station (to keep some minimum shielding) and another layer of water that will be moved around as needed
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I'd get sick of watching the damn stars rotate and wobble all the time. It may seem silly but please put windows on the edge/floor so I can watch stars streak by in nice straight lines so I can imagine I'm going somewhere, even if I'm seeing the same stars every 34 seconds.
I'd hate to have to hang out in a maintenance tunnel to do this. Sure I can't sleep in 1g and work in .85g?
Windows are incredibly expensive to provide. Yet despite having camera and monitor technology for years we humans continue to install them on capsules, shuttles, and space stations. Before deciding they aren't needed because of technology x, be sure you understand why we keep installing them in the first place.
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I see only a few problems with this design. The first is: Deck 0, and possibly other decks, don't have the correct calculated g-forces. If Deck 0 is 300m away from the center of rotation, and the station is rotating at 1.75rpm, the gravity at a point 300m away will be 10.0752m^2/s or 1.02739g.
However, the main problem that is seen with rotation space stations is scale. I don't know the size or biology of the inhabitants of this station, but if they were human, they might have the following problem:
At a distance of 293m away from the center, the centripetal acceleration is only 1.00341g, which is 0.02398g less than at 300m. In fact, the entire structure has an acceleration gradient over it.
If a human was standing in Deck 0, he might exhibit some rather serious health problems after a few minutes of standing. Because there is less force acting on his head than his feet, his heart will have to work harder to pump blood to his brain. I don't exactly know what the lethal gravitation gradient is, but I think it is a long-term effect of living in an artificial gravity scenario rather than an immediately deadly problem. It would also have relatively no effect if the inhabitant was prone (sleeping).
Again, I'm not sure what scale would be necessary to diminish this effect, but then again, I'm not sure if your potential inhabitants will have the same biological systems as humans.
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This is a follow up question based on a previous question I had asked a while ago ([1 Light Year Diameter Planet](https://worldbuilding.stackexchange.com/questions/38027/1-light-year-diameter-planet?lq=1)). How many human civilizations could exist? How would society operate on a planet of this magnitude if we assume that the planet is habitable, has a gravity of 1g and the same land to water ratio as Earth?
What kind of methods of communication could exist and how would travel/transportation work?
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**Science**
Since the dimensions are so huge, it is pretty much impossible that their society will realize they are actually sitting on a planet (instead of a huge, endless flat plane) until they have a comparable tech-level as today. Also see this question, about [how a civilization would find out they are on a dyson sphere](https://worldbuilding.stackexchange.com/questions/39064/how-and-when-could-a-dyson-sphere-civilization-figure-out-the-shape-and-size-of), the accepted answer about a 3AU dyson sphere. Your 1LY planet is still about 20000 times greater than the dyson sphere, but the similarities apply.
Compared to that, we on the other hand have already discovered that the earth is round in ancient Greek times -- we've known it for more than 2000 years. And we have known that we (earth) are not the center of the universe for more than 400 years. Meaning: your 1LY civilizations will have very... planet-centered religions, since they can't really imagine they are just one object amongst many in a huge cosmos (until they have reached at least 1950 technology and really great telescopes and really great scientists that can actually make sense of what the telescopes are telling them). Also, another hardship is that the physics (where the heck does a sun/moon come from on such a huge planet) must follow such complicated rules that we today can't even imagine them -- meaning their astronomy and exploration of the cosmos will be very, very delayed. Following from that will be, that a lot of technologies that have been developed for such cosmos explorations (first thing: space travel and sattelites) will get delayed a LOT.
**Travel**
Travel, on the other hand, should develop completely normally up to planes and other travel by air. However, space travel won't make a lot of sense until they are capable of bridging interstellar distances within a reasonable time.
The important step (where we currently are, trying to jump from orbit distances to interplanetary distances) will be pretty much useless to them, since they could just bridge the distance a lot easier in an airplane (at least you can land in the airplane, don't have to worry about exposure to cosmic radiation, no zero-G problems, etc.). If you compare the **distance Earth-Mars** (50-100 million kilometers when they are closest, let's say 1e8 km) to your 1LY planetary radius (ca. 1e13 km), you get that the radius is about 100,000 times greater than the measly Earth-Mars distance. That **would be like traveling a couple hundred meters on earth**. So, no, they really do not have any incentive of developing interplanetary-distance space flight for travel purposes -- they'd need to go for full interstellar right away.
You might see a need for interplanetary space travel though if you've got some strange objects orbiting your planet (like suns to make it light, for example?)
**Communication**
Planet-wide communication has the same problem as planet-wide travel: you need to be able to bridge interstellar distances within a reasonable amount of time. Because waiting for an answer for an entire (earth) year is not reasonable. So you need FTL technology -- and until you develop that, you've got isolated states/empires/... that can't really talk with each other, just like it was on earth before the invention of the telegraph. Travelers bringing news, hear-say of far-off countries, etc.
If you've got, for example, a desert on your 1LY planet that takes the same procentual space as the Sahara does on earth, it will be a completely insurmountable obstacle for hear-say communication spread with travel. Same with oceans if you just blow Earth geographics up to 1LY -- even a comparatively small ocean like the Caspian Sea will span distances from here to Pluto, not to mention the Atlantic or, worse, the Pacific. Oceans cannot be bridged in those dimensions. So, you would need two civilizations on both sides of the ocean who develop radio communication at approximately similar times, so that they can receive the radio waves from the other and realize: oh, there must be something beyond the Great Waters.
**Ecology and Evolution**
When considering such huge distances, you might get life evolving sentience in several places at once -- and in various different forms. Same for plant-life -- it might be a lot more diverse than we have on earth. Just travel a couple of AU (=distance earth-Sun), and you've got dinosaurs roaming the ground. Another couple AU later, you might have huge mammals like Mammoths and Sabertooth Tigers. Another couple AU later, insects might be the top of the food pyramid. And once you've gone another couple AUs, let's say, 60 AUs in total, you have still only covered a distance that would be around 12km on earth. Not even the stars will look different from there.
Planet-wide extinction events will be absolutely impossible, only local-sized.
**Societies**
Despite a technology level that might surpass us, they will be isolated societies comparable to countries in Midieval times. Yes, there will be trade amongst neighboring empires/states, and there will be ones who trade with countries even further away. But knowledge of all civilizations that exist around the globe (heck, even a rough map of the globe) will be pretty much impossible until technology for interstellar travel has been found.
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The escape velocity of this world is 10% of lightspeed.
Space will be limited to sounding rockets until they develop technologies way beyond anything we can envision. Furthermore, putting something in orbit gains you very little because the craft rapidly departs, not to be seen again for many decades.
Astronomy will be pretty much limited to locating objects until the development of general relativity--until you know how (and that you even need to) to correct for the gravity well you're in no observations of the sky will match observations on the surface.
Beyond this, the inhabitants won't be very ecologically minded. Pollution that blows away from you due to the prevailing winds never comes back.
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**Number of Human Civilizations** : Many, many orders of magnitude more than on Earth. Emigration from existing civilizations would be quite common as there is, almost literally, limitless free space to spread out.
I will assume stockpiles of metals and other resources are available because technology would regress to stone-age level at locations not receiving imports from off-planet.
Given modern tech, you could have large countries, but these will be limited to relatively near-by land. Civilizations located at different points on this planet will likely not have any interaction.
**How would society operate?** By splitting into many, many, many different societies. The distance is too great for a single society to maintain any coherency.
**Communication** Communication will largely be by existing methods. Civilizations far enough apart will not have much communication. Unless there are radio stations set up inside the planet to facilitate communication, direct communication will be impossible for those over the horizon from each other. Even with communication, the time-delay would be horrible.
**Travel** Largely the same. Sub-orbital flights might become a thing, given a large enough incentive to need to travel far enough for the expense to be worth it. If internal "spacedocks" or "airports" are available, traveling through the interior will be a more direct line for far off locations. This travel will be quite lengthy however.
**Additionally** Most of these assumptions depend on the humans on the planet being seeded by the civilization that built the planet, rather than *being* the civilization that built the planet. If they are that civilization, or have access to its toys (FTL travel or communication, endless energy, etc) then basically the answers become "Whatever you want".
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Quite honestly it all depends on the speed of travel.
If they have only cars and planes then @Michael has the right answer. However it is only possible to expand great empires if you have great transportation. Take an example from history. "All roads lead to Rome" Rome literally built myriads of roads and pathways. This enabled them to travel safely and efficiently across their gigantic empire.
The Romans made transportation fast, and available to everyone. Do this and you will conquer the world.
The culture of the world conquering super country will be one that values roads and values conquest.
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First of all. Let me make some basic assumptions.
I will assume your world will consist of mostly ocean. I will also assume that there are many continents roughly the same size that we have on earth. That will mean an awefull lot of continents.
Furthermore I will assume that your humans evolved on this world.
**Evolution**
One light year means that on with a speed of 1km/h one would need 1 billion years to cross the planet. With this speed a species that reaches the other side of the world would have evolved into something completelly different by that time. This speed would also mean that even if we assume life starts at one place by one billion years life would be everywhere.
Probably live would move to each continent separately, but nearby continent would influence one another.
**Intelligence**
Intelligent life could evolve on many of these continent. But it would still be unlikely for two species to evolve to intelligence at exactly the same time on neighbouring continents.
Looking at human evolution it appears that we could not cross any oceans until quite late in our evolution. The americas where only settled 40000 years ago. That means that for most of its evolution sentient life will be bound to only a few continents.
Only after devoloping ships will people discover the other islands. Note that by that time the people will propably already have developed an advanced culture.
From there a culture can spread across the rest of the world at a relative slow speed. In our society it took only a few centuries from there to developing modern communication technology.
**Effects**
This would mean that each civilization has a mother continent from where it originates. Politically people further away will become independent from their mother continent. However it would be unlikelly for them to lose all communication with their mother continent.
Some information of general interest (scientific for instance) could well spread very wide, but a lot of information will probably be only of local interest and people on other continent would not be interested in them.
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# Background and Explanation
I recently asked [a question](https://worldbuilding.stackexchange.com/questions/23430/what-us-states-are-most-likely-to-rebel) inquiring which US states would be most likely to rebel in the event of a secession war. Now, it was pointed out in the comments on @Samuel's answer that it is unlikely that Americans would rebel over simple infringements of rights. It is done all the time and nobody raises hell over it because Americans have soft, comfy lives and are more than a little hesitant to give them up.
I would still, however, like to believe that one day Americans will reach a breaking point and will rebel. What is the most probable cause (statistically) of a rebellion occurring in the United States in the next ten years? Is there a single infringement on American rights that can cause the desired secession?
# Things to note
The only one that came to my mind was if guns were banned; however, I have known many people in the larger cities that dislike that people can own guns and would support this law, so I think this rules out the majority of public support for a rebellion caused by this.
# Desired states
I am sure that which states I want to secede influences the situation directly. The desired states are:
* California
* Texas
* Oregon
* Idaho
* Nevada
* Georgia
* the Carolinas
* Oklahoma
* Alaska (apologies HDE)
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# Nixing the [First Amendment](http://en.wikipedia.org/wiki/First_Amendment_to_the_United_States_Constitution)
There are five main freedoms guaranteed in the [First Amendment](http://www.law.cornell.edu/constitution/first_amendment):
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> Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.
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How could a government go about violating as many of those as possible? One way would be to have agents enter and break up a gathering of a public reading of the newspaper of a religious institution, then confiscate and burn all copies available and arrest anyone who protests. That's four out of five right there.
Without the First Amendment, the government could start violating the rights of citizens in different ways, including . . . well, doing whatever it wants and can legally do, silencing all dissenters (remember, freedom of speech is a thing of the past). At present, if Congress wants to declare war on a certain country, it can do so, but it generally won't if there is heavy opposition to it (a notable exception was, at some points, the Vietnam War).
*However*, if it controls the press and silences those who disagree with it - oh, and bans the practice of any religions practiced in the opposing country1 - then it can most likely keep the war going, to a slightly better extent. If the military machine works as necessary, then things should be fine.
The fury won't end in the states you name, though. I expect most of the country to be up in arms (quite literally, with or without the [Second Amendment](http://en.wikipedia.org/wiki/Second_Amendment_to_the_United_States_Constitution)).
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1 Good choices are ones that are popular in the United States.
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An abrupt federal ban on the possession and sale of firearms is your best bet.
The challenge here is that for a subset of the states to secede, you need the governments of these states to maintain control and you need the majority of the states to be willing to remain in the union. If you look at most major rights intrusions, such as sudden implementation of orwellian surveillance or dismissal of the first amendment, these are problems that everyone, regardless of state, are going to be up in arms about. This is also more likely to trigger a popular uprising in which governments would be forcefully dissolved by the people, not seceding.
What you’re left with are polarizing issues that are enshrined in the U.S. constitution. Gun rights are an absolutely perfect issue on multiple levels. For starters, many people, including many state governments, are in favor of gun control laws. This ensures that many people will agree with the federal ban, and ensures most states will not act so rashly that they secede. On the flip side, many conservative states would be in an absolute uproar. Government officials in many of these states are themselves proud gun owners, ensuring that the people’s desire to secede will extend up the governmental ladder (even resulting in further pressure for secession). The best part is that the people most incensed by this ban are very likely to be heavily armed and willing to use their weapons to defend their rights.
The bigger problem here is that you’re looking for nine out of fifty states to secede. That’s immediately a terrible idea, as was pointed out in the linked question. That’s an infrastructure disaster waiting to happen, not to mention the U.S. military that is about to be bearing down on them. Even worse, these states are not close together, so they are now in the worst possible strategic position for defense.
What’s much more likely than a genuine desire to secede permanently is a desire to take a brash action to negotiate a reversal of the ban. Secession sends a very serious message to the country and the world. It puts the union in a position to either slaughter its former citizens or reverse an arguably unnecessary ban. It seems quite likely to me that secession in this circumstance would achieve their goal, returning things to normal and simply generating some amazing headlines and news coverage.
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If there were to be a break, I suspect it would be along the so called "Red/Blue" divide. American rights are being violated all the time. Look at so called "free speech zones" at American universities, a blatant violation of the First Amendment; restrictive gun ownership laws in various cities and States, violating the Second Amendment; and the Star Chambers that have been set up in many US Universities to deal with allegations of sexual assault, the way they are set up violates the Fifth and Fourteenth Amendments.
The difference is the response of the American public in the various States, with the biggest pushback against these violations and the politicians who promote them coming from the so called "Red" States, while the most support comes from the so called "Blue" States. I suspect the reason that we have not seen open rebellion is due to a multitude of factors, including the fear of loss if there were armed rebellion, the "boiling frog" theory that these losses of freedom have been gradual and incremental so far so people have adjusted, and that other effective means of opposition are still available and viable (everything from using legal challenges, voting for the opposition parties, "Irish democracy" (i.e. non compliance with onerous rules and regulations) and simply "bypassing" gatekeepers with Internet enabled technologies (Uber, for example, breaks the comfy monopoly of the Cab industry and the financial support these monopolists give to politicians who restrict commercial freedoms).
The American Civil War was avoided for at least a decade as various analogous solutions were tried; the final break came when the "Slave States" were defeated in their attempts to extend slavery into the Territories, at which point they knew they would be outnumbered and economically and politically smothered. Should a similar point be reached where a large number of Americans were to believe their freedoms were to be extinguished with no possibility of compromise or eventual vindication, *then* you have the possibility of armed rebellion.
Based on American history, I suspect the true trigger would be economic, for example the US Blue States have amassed anywhere between $2 and 4 *trillion* dollars of unfunded liabilities in the form of pensions for State employees (figures vary due to the different ways States calculate their liabilities or take them "off the books"). Should Washington decide that every American should be subject to an extra tax to pay for the unfunded liabilities of a small favored group in a favored group of States, I think a breaking point will be reached (especially as it is becoming more and more clear that a lot of American taxpayers are being looted for the benefit of a few crony capitalists and favored groups).
Anyone want to go for a spot of tea?
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# Federally Mandated Removal of Agricultural Subsidy
I struggled to think what interests these states could possibly have in common. *They are all states either highly dependent on agricultural subsidy, or very strongly associated with a state that is.*
[In 2005, US farmers received $14 billion in agricultural subsidies](https://en.wikipedia.org/wiki/Subsidy#Agricultural_subsidies). This is peanuts to the American budget, but this is suddenly a dramatic loss of income to groups of individuals and corporations who are highly connected and clustered in areas.
The value percentage of agricultural revenue in each rebelling state is tiny compared to other sectors, but it is a direct economic sector (e.g. - almost directly from the producer). Manufacturing includes a whole range of economic activities, while agriculture is food, food production, and food distribution; often in one company. Here's why they rebelled.
* California, Texas, Idaho, Georgia\*, the Carolinas have received
tremendous pressure from farmers, corporations, and other
agricultural interests. As a sector that can mobilize very quickly,
they have struck fear in their fellow residents about food
insecurity. It spiraled out of control and the states knew it was
time to re-think citizenship in the United States. The Oregon
Willamette Valley, the Texas Hill Country, and the Napa Valley (for
sure) ensures a stranglehold on wine exports that can cripple the
American wine-drinkers. Suddenly, Tobacco prices in the Federal United States have gone up, too.
* Alaska does not have much on-land agriculture, but does have a lot of
off-shore fishing: a LOT. This industry and their dependence on
shipping ports on the West Coast states who are rebelling, has their
interests urging state government for secession.
* Oregon, Oklahoma, and Nevada have great economic interests in their
neighboring, rebelling states. While the people of Portland, Oregon
are reluctant to side with the people from Dallas, Texas, they
acknowledge they need to stick with Idaho and California (and urge
Washington to follow); for example.
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> What sort of violation of American rights would cause a civil war?
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At this point in history I suspect a draft would do it... (and yes I'm aware of the pun there)
Forced conscription with the current political climate, and with Vietnam in recent memory would probably inspire the sort of split you're looking for. Confidence in the federal government is pretty low right now, and even more right leaning states would likely be hesitant to send their young people to fight under the current commander in chief...
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> it is unlikely that Americans would rebel over simple infringements of
> rights. It is done all the time and nobody raises hell over it because
> Americans have soft, comfy lives
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Sending another generation to war against their will would certainly tip the scales away from soft and comfy. If enough people are touched personally by the conflict, as in they know people personally that have been drafted, the backlash will probably be considerable.
I could certainly see more than a few governors sending state police, or national guard troops to shut down unwanted draft offices. From that point all it would take is one frightened officer to pull a trigger and things could get really messy, really quickly.
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(I think that violation of first and second amendment are already taken)
Violation of third amendment:
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> No Soldier shall, in time of peace be quartered in any house, without the consent of the Owner, nor in time of war, but in a manner to be prescribed by law
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Imagine a guy afraid of gov that would violate the second amendment. He stockpiled a huge stack of guns and ammo in his house. He would forgive that two marines park armoured infrantry vehicle in his garage. He would accept them making mess in guest room and not wash up the dishes. He would tolerate that they hog the whole bandwidth of his WiFi. But the fact that they borrow without permission his beloved guns simply makes him vivid.
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It would be useful for a story I'm working on to color the world or various dominant parts of it red. I'm trying to look into the following alternatives, but am open to further suggestions. Essentially I'd like to know what gives some things their color and how this could be plausibly explained to be red on another planet.
1) grass and vegetation: as far as I understand, plants are green in order to absorb a particular wavelength of light, but it is unclear to me why that one color in particular. Is it feasible that a different type of sun would give rise to red plants?
2) water generally: both rivers and the ocean; to us it appears blue, but could it appear red and how/why?
3) the clouds. What makes them white and can they be red on another planet?
Finally, I'll probably settle on just one such element, but I'm curious as to whether all could be coherently part of the same world.
Following on the great answers provided I want to further clarify the following:
Would humans living there/having evolved there see things other than red, and humans coming from Earth perceive more of the red? Would the skin of indigenous people be/appear red to visitors? (And not vice versa). Could it be that foreign humans see things reddish, while indigenous humans see them... how? Normal?
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I am going to ignore many of the more philosophical point on color, and really just focus on what could make a human visitor see mostly red (light of wavelengths of about 620-750 nm).
# Making the Sky Red
The sky is blue, on earth, for many different reasons. The simplest thing to blame for the earth's blue sky is [Rayleigh scattering](http://en.wikipedia.org/wiki/Rayleigh_scattering). This is kind of complicated, so most children do not get this answer when they ask why the sky is blue. The short explanation is that the sun's light, which does not produce an [even amount light](http://en.wikipedia.org/wiki/Sunlight#Spectral_composition_of_surface_illumination) of all wavelengths, get scattered as it hits the atmosphere. The shorter wavelength light, blue light, get scattered more easily than the red. So, when the sun is overhead, you see the scattered blue more than the scattered red.
Rayleigh scattering is also responsible for the colors at sunset. More atmosphere means you see the other wavelengths getting scattered more than the already-gone blue. A simple way to produce this color on a planet would simply to have a thicker atmosphere, so the blue light gets scattered before it reaches the surface.
# Red Water
We actually have red water on earth. It is just very rare to see it. Check out the [Blood Falls](https://www.youtube.com/watch?v=pIaf9LDJR9c) of Antartica. The color of Blood Falls is due to a lot of iron in the water. If Mars had oceans, it would be likely be deep red due to the amount of iron found there.
Red clouds could, in theory, be done if the dust on that world was iron. It is also prudent to mention that, if the light a world receives is mostly red, things which would be white will appear mostly red. This is due to the fact that white things merely reflect most light at most wavelengths, so a white thing that only has one color to reflect will look like it's that color.
# Red Plants
There are already red plants. There are all sorts of red-leafed plants out there; just do a google image search for "[red leafed plants](https://www.google.com/search?safe=strict&espv=2&biw=1252&bih=778&tbm=isch&sa=1&q=red%20leafed%20plants&oq=red%20leafed&gs_l=img.3.0.0l7j0i10.14495.16092.0.17556.11.11.0.0.0.0.102.1014.10j1.11.0.msedr...0...1c.1.64.img..0.11.1009.MhfBuCPdcfY&safe=high)". To make the majority of plant life red is a tricky proposition. [Chlorophyll](https://www.youtube.com/watch?v=aAQYpra4aUs) are green because they absorb red and blue light. Scientists are unsure why green is reflected, so there is no reason to color hypothetical plants to be any color.
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A quick rundown of light...
The color spectrum of red through blue/violet is the wavelengths of light our eyes are sensitive to. If a red light enters our eye, it's actually a certain wavelength that enters our eye which is in turn detected and translated by our brain into the color we recognize. So for a item to appear 'red', that item must be sending red wavelengths at our eyes. Of course most items don't generate light, but instead absorb all other spectrums and reflect just the red we see. Hopefully that makes sense...a plant is not green because it absorbs green light, rather it's green because it absorbs the other spectrum's of light and only reflects the green light that we see.
The suns light is light across all spectrums (almost all anyway, a few are blocked which is actually how we determine the chemical make up of the sun) which we see as white/bright yellow. However it's not actually white, it's all spectrum's coming at us, including red and blue. Blue is a shorter wavelength, and as such it will reflect off of things that a longer wavelength of light will not.
So your questions answered in reverse order:
3) Clouds are white because they are formed of water vapour that reflects all light across the visible spectrum (in short, we are seeing all colors to get white). 2 potentials to get them red...if only red light is hitting them then only red light is reflected and we would see them as red. Alternatively, if your clouds absorbed the other colors wavelengths and reflected only red, then we would see them as red as well.
2) Water absorbs more light as it goes deeper and deeper, reflecting only a small amount of the light. Long wavelengths absorb more readily (red) and short waves reflect more readily (blue) which gives water a blue color as more blue light is being reflected back to our eyes than anything else. Sky is blue for the same reason.
1) We do sort of have red plants already and many plants will have their young leaves in a red hue (this is actually the origin of why we're the only creature with the ability to detect red while most others only see green/blue...red leaves are more nutritious and our ancestors living in the trees had an evolutionary pressure on them to see the more red nutritious leaves). So they can and do already exist and in the right environment can be the majority of trees.
Easiest way to get the effect you are going for here is to have the sun lighting the world giving off fewer shortwavelength lights (blues) and more red ones. Red sun?
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I've seen articles about what color photosynthetic life *might* be on other planets, and numerous were listed. Here on Earth we have [red](https://www.wikipedia.org/wiki/Phycoerythrin) and yellow algae as well as green and blue-green, and Venture's ocean genome survey is showing *many* different ways for photosynthesis to work.
Find a reason why red chloroplasts became the dominant form. Maybe lack of magnesium. The forest or plankton that shows the color of the planet might be pigmented for [other reasons](https://www.wikipedia.org/wiki/Chlorophyll#Complementary_light_absorbance_of_anthocyanins_with_chlorophylls).
A red variety of photosynthesis mechanism may be more suitable for becoming the endosymbiote used to make the original eucaryote-equivalent plant cells and that became the established standard very early.
The star might be red, with red light being the only choice: it would look black in that light, but red to our flashlights and as lab samples.
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Water looks like the stuff around it, such as the sky reflection.
So take care of the clouds and beach, and the water will follow.
I recall a place where water is extraordinary blue due to the mineral content. So you could have red water (looks ok in a glass, slightly pink in a barrel, and red in a large deep body) due to minerals, salts, or life. We have "red tide" algae blooms on Earth. As noted above, if plankton were red, the world would look red from space.
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Titan has red-orange clouds. Tholins are produced on many worlds and worldlets in our own system. Even Pluto/Charon has red (plains?). Mars sand is full of rust, and dust storms can reach global scale.
You'll have no trouble finding plausible reasons for red *stuff*, some of which could be airborne.
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Firstly I would consider the reason for a *red* world. What significance does red have? Considering that different colors (reflections of materials, prisms) should be possible, why did the inhabitants remove non-red natural and synthetic items? Is there a philosophical reason ingrained in said inhabitants?
For example, "suppose a man wanted a
particular kind of world; say, a blue world. He would have no cause to
complain of the slightness or swiftness of his task; he might toil for a
long time at the transformation; he could work away (in every sense)
until all was blue. He could have heroic adventures; the putting of the
last touches to a blue tiger. He could have fairy dreams; the dawn of a
blue moon. But if he worked hard, that high-minded reformer would
certainly (from his own point of view) leave the world better and bluer
than he found it. If he altered a blade of grass to his favourite colour
every day, he would get on slowly. But if he altered his favourite
colour every day, he would not get on at all. If, after reading a fresh
philosopher, he started to paint everything red or yellow, his work
would be thrown away: there would be nothing to show except a few blue
tigers walking about, specimens of his early bad manner. This is exactly
the position of the average modern thinker. It will be said that this is
avowedly a preposterous example. But it is literally the fact of recent
history." - [G.K Chesterton](http://archive.org/stream/orthodoxy16769gut/16769.txt)
In other words, possibility of single-colored planet may imply the constancy of the inhabitants more than (or in addition to) the natural causes of physical red.
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I'm currently doing some research for my first book which involves a planet with an empire that has had its roots in Antiquity. It's basically a country that formed about 2200 years ago and has started to take over the world 1500 years ago, forming a global empire around 200 years ago.
What would a global empire, grown from a country that was born during antiquity and took over every other nation by a combination of force and diplomacy look and feel like? I understand that the Romans kept their empire together against internal struggles by assimilating the different cultures. Would that work on a global scale? Or should it go the entirely opposite way, with an empire only in name and extreme independence for every conquered state?
I mainly would like to know 3 things:
1. how can such an empire stay in power without losing grip on the distant parts?
2. How do the logistics of such an empire work? Would their world economy be better or worse than ours, assuming similar tech level?
3. How would the empire keep the military at a functional level? there are no other countries to wage war against, so I think there would be a pretty high likelihood of the armed forces just not staying at a proper level.
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# How can the empire stay in power?
The way to stay in power is to have everyone in the empire being convinced that it is better to stay in the empire than to leave it (forcefully), and to convince everyone outside the empire (during the time when there is an outside) that it is a bad idea to attack it or support any separatist forces inside the empire.
For the people inside the empire, there are several strategies:
* Make the people happy. Happy people are unlikely to revolt. For the Romans, this strategy was known as *panem et circenses,* bread and games: You keep the people fed (so they don't revolt due to need), and you keep the people entertained (so they don't revolt out of boredom). In a more modern setting, TV would likely take the role of the games. Also, while the empire is not yet worldwide, it is important to have a better economy and more advanced technology than all the countries around, in order to avoid people finding that they could have a better life outside the empire.
* Propaganda. Tell people constantly how lucky they are to be in the empire. If you tell it to them often enough (and they don't have an objective reason for doubting it, see the first point), most people will believe in it. This also means that the empire should control education so that already the children learn about the greatness of the empire. Having mandatory schooling with strict controls on who can become and remain teachers would certainly be an advantage in that case.
* Control of resources. Make sure that no part of the empire (apart possibly of the core) has the necessary resources to build a self-sustainable economy, or, if they are near the border of the empire, can get the necessary resources from countries outside the empire. Also make sure that everyone knows how much they depend on resources from other parts of the empire (maybe make them believe it even more than actually the case; see the point about propaganda above).
* Participation. Have people from every part of the empire taking part in whatever official roles people can get in the empire. People have to feel that the empire is *their* empire, which means that people from everywhere should have the same rights all over the empire. Also, having a certain autonomy of parts of the empire may be helpful (but on the other hand, it might encourage separatism, so it is probably a delicate balance).
* A strong and effective police. On one hand, the police will keep crime low, adding to the point of making (non-criminal) people happy, but on the other hand, the police will also be able to stop any separatist movements.
* A good intelligence service. The better the government of the empire is informed about what happens in it, the better and earlier it can react. Note that earlier reactions may also mean less visible reactions, which is an advantage because any visible actions might feed "us against them" feelings.
* A good communication system: The faster and more reliable the information can flow between the central government and the outer parts of the empire, the more effective it can govern the empire. Also, fast communication may also help in making the people feel more connected to the empire (especially if communication to outside the empire works less well).
* A good transportation system (roads, later railways etc.). This is important to have a lot of internal trade (see the point about resources above, but a common trade system may also help people feeling connected with the empire), but also to have fast movement of police groups/military if required, and at least in pre-technical time for fast communication.
* A well-trained military, in case things get too much out of control. Coupled with mandatory military service, it may also be a way to further increase loyalty with the empire (that would, however, require that the experiences from the military are not too bad, except if the bad experiences come from external enemies).
* Control of local governments. A local government might act in its own interest opposite to the empire's interest, or even plan to separate their territory from the empire. Also, the local government may become lazy or corrupted and stop enforcing empire policies or managing its territory as it should. You want to always be informed about anything the local governments do or don't do, and you certainly want to make sure that you always have the power to throw out any local government that doesn't behave properly; ideally through a pre-defined process as to not produce unnecessary unrest.
As soon as the empire grows too large, the main problem it will face is the lack of equally powerful external enemies. Nothing helps to keep an empire together as well as a common external enemy. Probably to compensate for the lack of external enemies, internal enemies will be needed. Separatist movements can make a great internal enemy as long as they don't have a real chance to succeed. So maybe the key of a lasting empire would be to *not* completely avoid separatists, but let them happen, but keep them sufficiently under control that they are not an actual threat.
For the countries outside the empire (during the time they exist), the following points apply:
* A strong military. This is the most important part, especially in phases where a significant part of the world is not yet under control of the empire. You have to make sure that no one can reasonably expect to win a war against you. Ideally, you can also use it to further your control
* Military contracts with other countries. If the empire is strong, other countries may like to be under protection of the empire; by making contracts, you can bind them to you, making sure that they won't attack you, and at the same time make them dependent on you.
* Trade with other countries. The bigger the empire, the more likely it will have the monopoly on certain resources. Such a monopoly always comes with a certain amount of power, especially if coupled with military power.
# How does the logistics of such an empire work?
It either works very well, or the empire will break down sooner or later.
# How would the empire keep the military at a functional level?
See the controlled separatist movements above.
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**It Just needs to looks like it survived**
A large empire may lose cohesion or power for many reasons but if a subsequent ruler conquers much of the same territory and claims the same name then "the empire" has survived.
The best example of this is China it has had hundreds of emperors that have been overthrown dozens of times, but since the subsequent emperor reconquers much a china and has a similar political structure we speak of dynasties of China rather than the rise and falls of Kingdoms of Europe. Even in periods where the central government had no real power and provinces were basically autonomous, they all still claimed to serve the emperor.
Internally provinces would battle for control and power, dynasties and aristocratic families would rise and fall in power but the empire would survive. Every successive emperor claims to be part of the old empire to justify his right to rule.
The internal warring would lead each district to have a strong military.
**The economy would be both better and worse.**
There would be fewer barriers to trade in 1 large empire than many small countries. The single central government and single rule system would limit opportunities to innovate.
Many of the great innovations in finance like free market trade, fractional reserve banking, national fiat currency, insurance and others were invented and adopted in attempts by small countries to gain advantages over their foes (the Netherlands and England are the major examples). But a central government might severely limit these innovations
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**This question already has an answer here**:
[What would the Universe be like if gravity was slightly stronger?](/questions/2870/what-would-the-universe-be-like-if-gravity-was-slightly-stronger)
(1 answer)
Closed 6 years ago.
Almost the same as my [other question](https://worldbuilding.stackexchange.com/q/2870/24) but it isn't about how the universe would form.
What would happen if to the universe if someone changed the strength of gravity by say 2%?
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Everything would become slightly heavier. 2% isn't enough to make huge changes, although birds would find it harder to fly. Buildings would be slightly weaker and fall more easily. Trips and falls would become slightly more dangerous, etc. Most buildings, supports, etc we make have far more than 2% redundancy so they would not start collapsing as a result of this change.
This would have interesting effects on the orbit of planets though. Suddenly planets are not moving fast enough to maintain their current orbit, that will cause them to fall in towards the sun until they gain enough speed and settle into a new orbit. The new orbit would almost certainly be both more eccentric than the previous one and shorter, the length of the year would change.
Equally the moon would shift into an eccentric orbit, and tides would grow stronger. The faster orbit of the moon would also break the tidal lock, causing it to no longer always point one face towards the earth. Over time that would correct but the correction would not be instant.
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Things would be *extremely* bad, for large values of extreme.
Stars are a balancing act of external radiation pressure exactly counteracting the gravitational attractive force. By increasing gravity stars suddenly have 2% more gravitational potential energy they need to shed to regain equilibrium. How much energy is that? The gravitational potential energy of the Sun is 1041 Joules. Or roughly the same energy as would be released if the *entire Earth* were to be anhiliated with anti-matter. 2% of that is huge and it suddenly appears out of nowhere. So, very quickly the Sun has to shed about 10,000 times its yearly energy output. Life is certainly not going to survive that, but this happens for every star in the galaxy. Many, many will jumpstart to a higher order of fusion at the massive sudden increase in pressure and temperature, if they start iron-burning, you are in trouble.
Expect every supergiant to go supernova concurrently and many lesser stars to flare with the energy output comparable to a nova, any life that survives the semi-nova/flare of the Sun will be wiped out by the bombardment of gamma rays that will be bathing the Earth for the next few thousand years.
Every black hole will get a bit bigger all of a sudden as escape velocity increases, eating part of its accretion disk. Hard to say what effect this would have actually, but sounds like it may cause trouble.
Depending on exactly how the increase in gravity is carried out, even more esoteric things might happen. It is a well known unsolved problem in physics that the gravitational mass and inertial mass of matter are independent yet appear to always be exactly the same. As in, there are no laws that say they should be the same nor does it naturally arise from any currently accepted theories, but observationally it is always the case that they are identical to the limits of measurement. It is a good thing too as the exact correspondence between gravitational and inertial mass makes a lot of things like having stable orbits work. If you were to increase gravity by increasing gravitational mass and not inertial mass, suddenly things like angular momentum and stable orbits get all sorts of wonky. It is hard to say if solar systems are even possible in such a case.
All in all, it is a bad idea. Unless you are an energy being that really wants the universe to end in a Big Crunch instead of a Big Chill in which case crank up that constant, but expect biological life to take exception.
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[Here](https://worldbuilding.stackexchange.com/questions/2639/is-it-possible-to-terraform-a-hot-planet), I asked if it's possible to terraform a hot planet. But now, if we have a volcanic active planet, can we use the same techniques to cool it down?
1. Normally, the planet cool off slowly after its formation. Is there
any way to speed up the process?
2. Some planets like Venus have formed billions of years ago but are
still very active, with lot of volcanic eruptions. is it possible to lower this activity to make the planet more hospitable?
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Volcanic planets are actually in the process of cooling themselves down already (see bolded answer further down.) In addition, the heat is not from the volcanoes but rather the greenhouse effect. "Venus is hotter due to the greenhouse effect: Venus has an atmosphere about ninety times thicker than that of Earth, and made almost entirely of carbon dioxide, which is one of the gasses that causes the greenhouse effect on Earth." [(Source)](http://scienceline.ucsb.edu/getkey.php?key=3824). As such, most of the following keep that in mind.
**DRAIN ATMOSPHERE**
Draining the atmosphere from the planet by ejecting it would be one way of dealing with it. Since a hot volcanic planet probably has a very thick atmosphere, this might actually help terraform it towards livable conditions. The opposite problem that Mars has.
*Pros*: Can help terraform a planet towards our own tolerance.
*Cons*: Difficult to achieve and astronomically expensive.
**SPACE SHIELDS**
Steerable micrometers-thick refractive screens could divert a portion of the sun’s energy away from planet, thus cooling the atmosphere. The screens would orbit between the sun and the planet.
*Pros*: No pollution; can be turned on or off quickly.
*Cons*: Even using futuristic launching technology, the 20 million metric tons of mesh would cost $4 trillion to deploy
**SPACE DUST**
Reflective particles in low orbit reflect sunlight and cool the planet.
*Pros*: Closer orbit and low manufacturing costs could make dust cheaper to deploy than space shields.
*Cons*: Costly to deploy and would require frequent replenishment as solar radiation drives dust down to planet.
**PARTICLES IN THE STRATOSPHERE**
Sulfate or other reflective particles injected at the equator stay aloft in the stratosphere for one or two years, reflecting sunlight and cooling the planet.
*Pros*: **Principle proven by volcanic eruptions**; $130 billion price tag is relatively reasonable.
*Cons*: Increased acid rain, ozone layer damage.
**REFLECTIVE BALLOONS**
Reflective balloons would bounce a portion of the sun’s energy away from planet before it had a chance to warm the surface or the lower atmosphere.
*Pros*: Cheaper to launch than space shields or space dust.
*Cons*: Would require millions of balloons that would eventually fall to planet as trash.
**CLOUD COVER**
Ships spray salt-water droplets that make ocean clouds more long-lasting and reflective, cooling the planet.
*Pros*: Pollution free.
*Cons*: Would take some 5000 salt-water spraying ships, at \$2 million to \$5 million apiece, to counter a carbon dioxide doubling.
**IRON DUST**
Iron particles spread over unproductive parts of the ocean cause photosynthetic plankton blooms. The plankton absorb carbon dioxide. When they die, they carry some carbon to the ocean bottom.
*Pros*: Some experiments indicated that thousands of metric tons of carbon were absorbed per metric ton of iron.
*Cons*: Unclear how much carbon is permanently trapped; plankton blooms can poison other sea life.
**REFLECTIVE ROOFS**
Simply painting roofs and roads white could cool populated places by reflecting sunlight.
*Pros*: Paint is cheap.
*Cons*: A small effect because much of the sun’s energy is absorbed in the air before it reaches the ground; cooling is local and so could make the local weather worse.
**SEQUESTRATION**
Carbon in the atmosphere or in smokestacks is converted to a form that can be stored underground.
*Pros*: Already being intensely investigated.
*Cons*: Could be expensive to deploy the technology and store the carbon; carbon reservoirs could leak.
**REFORESTATION**
Trees pull carbon dioxide out of the air and use it to form wood.
*Pros*: Uncontroversial and already accepted under the Kyoto Protocol.
*Cons*: Most carbon uptake happens only in the early part of a forest’s growth; new forests could compete with agriculture for land and water.
[Original Source for the previous ideas](http://spectrum.ieee.org/images/may07/images/clim01.pdf) modified slightly by myself (added drain atmosphere).
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I think there is a confusion here, for the most part volcanoes are a symptom of the heat of the planet, not the cause of it.
When a planet forms it's a super-heated ball of lava. Gradually that Lava cools and the heat escapes, radiating out into space and carried off with escaping gasses.
Over time an equilibrium forms when the incoming heat from the sun and from nuclear reactions within the planet's core matches the outgoing heat lost into space. The position of that equilibrium is what determines the conditions on the surface.
If the crust is thin and the surface volcanic then that means either less of the heat has escaped or more is being generated. In the case of Venus it's a combination of being closer to the sun and having a thick and heavily insulating atmosphere. So far as I know we don't have any real detailed information on what lies below the surface so we cannot speculate as to any further heat sources there may be.
Cooling the planet will reduce the number of volcanoes as it causes the crust to thicken. The problem is that we are talking a huge amount of energy that would need to be lost. There is no known technology that would do the job in less than centuries, probably you would need thousands of years.
First you would need to change the atmosphere, possibly by seeding it with specially engineered bacteria assuming you can even engineer them that will survive those conditions. You would need to scatter reflective particles in the upper atmosphere, and then you would still need to construct heat shields in space to reduce the incoming heat from the sun, and that's just to get you started!
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Eventually the gasses caused by the volcanic activity would condense and create an atmosphere. As the atmosphere thickens it would condense. Depending how close the planet is to its parent star the atmosphere would condense its gasses causing rain-ice building oceans, or creating thick dense atmospheres of carbon dioxide and nitrogen raining sulfuric acid. Pick your planets wisely.
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I perceive multiple distinguishable and yet interdependent components of any world. Things like:
* individual creatures
* societal constructs / interaction
* geography
* history
* sources of strife
* etc.
However, it is daunting to design all of them completely simultaneously. **Is there a natural starting point?**
And if so... **Which of these is the most natural / easiest foundation to establish first when designing a world?**
I guess I'm asking if one of these really flows into and facilitates the others.
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In the real world at least, geography (and climate etc.) is definitely the base.
From there you can easily lead on to what creature varieties and sources of strife. Sources of strife are always about resources until you get "intelligent" enough to have dogma; geography/climate determines what food sources, water, minerals, shelter etc. are available; and hence may be desired by others.
Social constructs are basically a combination of sources of strife and history. History is a the evolution of social constructs, external events, internal events and sources of strife. So history is pretty complicated and so are social constructs. In some ways things like geography/climate are just as complicated but the complicated details aren't really as apparent to a casual observer nor do they have as much impact on society.
So I'm basically suggesting you go from simplest to most complex in terms of the amount of details you'll have to provide to have it seem real. To detail that a bit more: start by working out a *rough but serviceable geography/climate* and then building up with creature/sources of strife (which often will be geographical features - for example adding in an oasis at this point of the desert). Now the reason you only did a rough physical world is that for the social constructs/history you may say oh it'd be nice if there was this canal here so that there could be trade between the (for example) Alemorids and the Zydia; if your geography is really hard built adding that is going to involve a lot more editing than if you have the broad brush only up to that point. Then once you've built everything, go back and fill in any holes.
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If you were to take a large enough sample of writers, you would probably discover that every possible starting point has been tried, and worked, for someone. Every storyteller is inspired in an different way from every other storyteller, and differently for each story. Every story is discovered via a new path that has never been traveled before, and will never be traveled again.
When starting a new story, game, etc., hopefully you have some starting point - an idea, a theme, a character, etc. Take your starting point, and ask yourself what that starting point requires. A character who is wizard is going to need a magical system in which he practices and a history - parents, birthplace, etc. A theme implies an appropriate conflict, which in turn requires a set of combatants and a context.
As you start to fill in details, it will be like tracing the components of a tree. If you start with a leaf, you will trace it to its branch, which will trace back to a larger branch, and so on until you eventually find all of the other branches, the trunk, and the roots. If you start at a root, it will lead you to a larger root, and then a large one, until eventually you find all the roots, the trunk, then the branches and the leaves.
My ideas are usually something along the lines of "What would happen if there was a person X living a world Y?" Where the properties of character X and world Y are defined only in the very broadest terms. From there, I can usually figure out how the story is going to end. Everything else must follow logically from those starting conditions to make the story interesting, compelling, and inevitable.
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David Eddings claimed he always started with the map, but he wrote fantasy.
Sci-Fi I think would be different. I would think History and the current challenges would be more relevant. As in how did we arrive at where the story is taking place and why is it important to us.
Mysteries would center around the people(things) involved.
Is the story going have a large social commentary? Then societies and cultures would be the starting point. basically what kind of story are you trying to build, then identify what is important for that story and build out form there.
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From my experience in both three of fantasy, sci-fi and roleplaying games, the best start is always the history you want to tell (or play). From the history you get the events, the people, the terrain inside the zone you need, and you do not need to go further.
Think on Middle Earth. Do we know all of it? No, we only know the north-western part of it, because that is what Tolkien needed to tell his history. We known the languages on that zone, but do we know all the relations among them? No, because Tolkien only needed details for main characters' languages, and even there, mostly for naming details in Westron. Do we know about climates? really not, just some vague descriptions throughout the books, most of them not defining climate but the specific weather of the day the characters were somwhere.
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**Backstory**
There is a double planet system. Both planets are habitable. One planet has humans and the other one animals. So instead of seeing a grey Moon in the sky, the humans living on the first planet see another world with forests, oceans, rivers, etc. So it is widespread knowledge that the "Terra" is just another planet, that humans live on a sphere. I want these double planets to be closer to each other than our Moon is to our Earth, but I want to have a scientific facts whether that is possible or not. For long time, humans on planet 1 (the "Terra") have looked at the habitable planet 2 (the "Luna"), but they haven't been able to reach it yet, until now.
On the "Earth" there is a civilization with pre-modern technology. By that I mean that they haven't had the industrial revolution yet. But they are slowly going into an industrial evolution. I imagine this civilization being similar to medieval China. Medieval China was known for having a strong totalitarian government, and many advanced mechanical inventions. The Roman empire would also be a good example describing this one empire on the planet "Terra".
The most advanced civilization on "Terra" is an empire with a strong government, prosperous economy, and a current level of technology similar to Leonardo DaVinci, medieval China, or Hellenistic Egypt. This empire is starting to undergo an industrial evolution, with the steam engine being just invented. The government heavily finances science and technology, employing geniuses similar to Archimedes or Newton. So they have access to both mechanical engineering knowledge, and mathematics physics such as calculus. Although cars and trains have not been invented yet and all travel and work has to be done by beasts of burden. The empire is about the size of maybe 2/3 the United States, with lots of fertile land, natural and man made waterways, coal and metal deposits near the surface. It is ruled by an emperor as a supreme monarch with a centralized bureaucracy similar to medieval China. The empire is now currently stronger than it has been ever before, with it's major rivals defeated, and no internal or external threats.
The totalitarian government of this empire can make it's citizens do whatever it pleases. The empire has built pyramids, great walls, canals, bridges, aqueducts, and roads without too much difficulty, and zero social protests. Now they choose to go the the double planet "Luna". The emperor gave his word, to employ all the resources of the entire empire for achieving the singular goal of landing people on the "Luna" as representatives of the empire.
Assuming that the atmosphere and the biosphere of the "Luna" is compatible with "Terran" life, including humans, who do not need a special suit or anything to live there. "Terran" animals and plants can survive in "Lunan" environment, and vice versa. Sure the animals and plants of both these double planets have different evolutionary histories, but they still have the same DNA cell based biological structure. Perhaps they were descended from the same microbes which seeded both these double planets.
Just like medieval China, the empire has knowledge of rockets, having used them successfully in warfare to conquer less advanced civilizations. The plan is to somehow be able to get people, animals, and plants from the empire up to the "Luna", have them survive the landing (or use parachutes which are known by then), then establish a colony for the empire, and after some period of time march to a certain region, and light up a huge fire that could be seen from the "Terra" as a sign of success. Because the "Luna" is easily seen from the "Terra", maps of the landscape have been made in advance. It is a one way trip only, and other than lighting up large fires there is no method of communication. The empire doesn't have electromagnetic communications technologies yet.
Assume that the government is determined to get humans up to the other planet, using all the economic, human, and technological resources that they have available, and can try to extend their resources by encouraging progress in the related fields. Assume that there are little to no inefficiencies in the government, no social unrest, and the people can be brainwashed to do almost absolutely anything. Also assume that this is a long term goal. It's not a space race. The empire can work on this for hundreds of years, gradually advancing their technology through the industrial evolution. But they will not give up until they can see the outlines of towns on the other planet. Either the emperor is extremely long lived, or the entire dynasty has the same mindset.
**Actual Question**
Could such an empire realistically achieve such a task? If so, how would they do this? I mean, what would be the absolute minimum level of technology to establish a colony on the "Luna". If they need to wait hundreds of years until they develop cold war era rockets, they will do just that. But can they get to the "Luna" before reaching that level of technology though? Can they do it using (medieval China style) solid fuel rockets alone? Can we think of any other alternative launching systems that can be made with pre-industrial or early industrial technology? And what about landing on that other planet? And they also need to lift not just two men, but a whole population of men, women, farm animals, and plants in order to establish a colony on the first try. There is no way of going back for the colonists.
If there is a way to modify the planets to make this story more plausible, such as decrease the gravity, or make the planets closer together, that is acceptable, but it has to be science physics based.
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**No. It can't be done.**
A medieval civilisation, let alone an imperial system, lacks the materials technology to build the large rockets needed to travel the distance from Earth to the Moon (as is the case in your scenario). They also lack the resources and the knowledge to understand the problems they need to circumvent for translunar travel.
The USA had to devote roughly 5% of its GDP in the 1960s to fund, service and complete the Apollo Project. Now it might be possible to imagine the empire on Terra developing industrial technology and eventually mechanical forms of transportation such as railways, steamships, aviation and jet aircraft. This will transform the empire into a twentieth century industrial society. Such a society could devote the intellectual capital, the scientific and engineering innovation, and material resources necessary for travel to Luna. In our world we cannot contemplate dispatching a colonizing expedition to our Moon. While your Luna has the advantages of being a habitable planet, the same physical and technical obstacles exist.
Basically travel to and dispatching a colonial expedition to Luna by even a global medieval empire would be far beyond their capability.
Would moving the planets in the binary planet system closer together make it easier? Also, would reducing the planets' gravity make it easier?
In the principle, yes. Although you don't want to move both planets too close. This might put them in each other's Roche Limit and tidal forces would tear the planets apart. Rocket propelled vehicles would only need lower values of their top velocities to travel between the double planets. Planets with lower gravities will require rockets with lower escape velocities.
This all looks good, but unfortunately it's not. All the science, technology, industrial capacity, engineering and resources will still be far beyond any medieval civilization. A global-spanning empire on Terra may command greater resources and knowledge than any medieval civilization in our history, but it will still far short of what is required to travel to the other world of a binary planet system.
Once such a civilization has progressed beyond the medieval and developed modern technology and science it would be capable of such travel. Possibly their version of early twentieth century could begin travel to Luna, at least, experimentally. Having a habitable planet beckoning in your sky for all of their history will provide a ready impetus to develop space travel and its technologies much earlier than in our history.
Is there another science-based solution? Strictly, no. Since this is a work of fiction it is possible to imagine a medieval version of antigravity, Say, the equivalent of Chinese alchemists inventing something like Cavorite. Then using for manned flight and eventually space travel. But this is a science-fictional solution to what is otherwise an impossible problem.
CONCLUSION: Spaceflight between planets separated by the equivalent distance from Earth to the Moon is unobtainable by medieval societies. The technology is beyond their capacity. It is a practical impossibility. The alternative solution is to bypass the science and employ an impossibility (antigravity or a "magic" space drive) to permit medieval space travel.
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**The Basics of a Binary world**
As it just so happens to happen, i too work on a Visual Story about a Binary System. Only in my case it´s the Sisters Hela and Vesna. But the General idea for both of us is the same. Two VERY close Planets. Like this:[](https://i.stack.imgur.com/3Cee1.jpg).
The only really important information about such a world for this question is the lack of Movment between the worlds. This means you can, in theory, just go up and will land on the other plant.
**The Problems**
Now for a Modern Civilisation, this sort of set up is a dream. Going between words takes less than a day and the Math is super simple. Not to mention of the stripped down Life Support and so on.
But
For a Civilisation such as your´s the Planet might as well be on the other side of the Universe. Sure, IF you can Build a Rocket with 8km/s of Delta V you will reach the other Planet. But then what ? You fall on this world. Which means you might enter the Atmosphere at 8-9km/s. Even modern Spaceships cant do that.
IN addition to that, your people have no way of knowing if a Mission worked or what went wrong. So there is no way to improve anything. And this does not even mention that they cannot build a Deep Space ready craft. Anything they send up will either be Destroyed by the heat of the Rocket and lack of Radiators, Explode or Freez.
And again, when something goes wrong, they have no way of knowing WHAT happened.
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If your civilization has gunpowder, then [this](https://space.stackexchange.com/questions/815/can-gunpowder-get-you-to-the-moon) discussion at Space SE might be of interest. Using our Earth-Moon as reference, it would take a lot of gunpowder. And that assumes you fire the ship from a cannon, which would kill the astronauts. To have a ship that accelerates at a tolerable rate, and also has extra gunpowder to allow landing on the other planet, would take a lot more.
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Unless you are willing to MASSIVELY reduce the size of your "Earth", thus greatly reducing the velocity required to orbit it, no deal.
Using our Earth and history as a template, the *absolute earliest* we could aspire to get to space would be in the 1910-1920's. This is on the assumption of infinite goodwill and cooperation being available. Think something like a massively scaled up and complexified German A4 rocket.
You need a pretty good metallurgy, moderate chemistry, and a stonking huge infrastructure of manufacturing and supply chain.
No, a gunpowder cannon, even of city size, simply *cannot* the velocities needed. Not to mention it turns any passenger into strawberry puree at launch.
Sorry, but mere motivation, even at global and religious-fanatic level of support, cannot facilitate space access without the required technologies.
P.S.
I refer to "getting to space", as that is a necessary step to reaching another planet, AND is by far the hardest and most dangerous part of the job. Once you are in orbit, you can use much more leisurely ways to get to the other planet. And landing on a planet with atmosphere is as simple as wrapping your lander in a nice thick layer of cork, then once slowed down dumping the cork heatshield and deploying parachutes. (no return option!!!)
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The problem you have is the gravitational pull. You have to break out of Earth's (thier earth not ours ) Gravity well. Doing this requires a lot of energy. Much more then what a primitive civilization probably couldn't accomplish on our Earth. However we don't know enough information about your planet there are theoretical ways For planet to be formed that make escaping the gravity well easy I recommend the you go to YouTube and look up Isaac author as he has a whole video on this I will summarize one of his propositions here
Mountains it's hard to imagine a mountain large enough to get you into low orbit but we must remember that even within our own Solar System There are mountains that make mount Everest look like it tiny pile of pebbles. So it's possible that a planet could have amounted tall enough that it counts the energy cost of breaking out of orbit
Spaceship The complexity of your spaceship is dependent on how long you need it to stay in space by Lowering the cost of getting out of orbit You have already minimize the complexity considerably. At the very least You'll need something that is airtight everything beyond that depends on how long you gonna be there (in space) and how many people you're bring. I would look at some of the very old subs designs I had to make a guess I would say you'd need at least that Tech level.
I strongly however recommend you watch the video as It goes into a lot more detail then my failing memory If I have time I will edit this post and add the link to the video.
<https://m.youtube.com/watch?v=FEV5r8jdBvQ>
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### If stars align with a tonne of factors - yes:
You haven't specified exactly:
* how close they are to each other, just "Closer than the moon".
* whether they're tidally locked
* the mass of the planets
* the speed of rotation
So I'm free to fine tune these. If I tweak these by taking [this wonderful maths](https://worldbuilding.stackexchange.com/a/21344/78800) and stating that the planets are close enough to share an atmosphere, but not without crossing their respective Roche limits. (Eg - the air flows, but they don't rip each other to shreds).
The planets are also distorted by each other into ellipses, bringing the surfaces closer to each other by several hundred km.
[](https://i.stack.imgur.com/uc89U.png)
The distortion of the ellipses also affects the atmosphere and results in increasing the air density in the region between the two planets. The entire atmosphere will thinner on the outside, and there'll a permanent low tide on the outside.
It looks like its quite feasible that the surface-surface distance is only ~100-200km. Since the air density is higher between the planets, you may not even need supplemental oxygen for the trip.
This should be possible in a hot air balloon. If you reduce your buoyancy right as you approach the midpoint, you'll transition into the other planets gravity well and start slowly falling onto the other planet. This may need some wiggling or ballast tossing, and could take a lot of skill to get right.
Spider silk strands have a [breaking length of about 110km](https://en.wikipedia.org/wiki/Specific_strength). Once again, if all the stars magically align and the world is ideal for this mathematically, you could run a spider-silk woven rope between the two and use it to guide your hot air balloons as a primitive space elevator.
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Before the snows came--back when Luna was large in the sky every day, and not just during the Festival of Tango--there were great flying creatures that we could ride on. The air that covers Terra doesn't extend high enough for us to fly there, but those among us with a cruel streak would tax their beasts nearly to death trying to get as close as possible.
Then The Interloper came. Nobody saw it strike Mnemos No More--then the smallest moon of Theia--but we saw the havoc in its wake and our best arithmancers agreed that it was heading towards The Twins Luna and Terra.
Our ancestors hid underground and prayed--and it is well that they did. But the greedy, and the insane... They took to the skies to meet The Interloper head-on.
By some twist of fate, the Interloper split the gap between The Twins without striking either one. The three bodies danced a fleeting chaotic tango of near destruction. The Interloper was visible with the naked eye for just two days, but the earthquakes lasted for years, and our orbit changed forever. Then the snows came, and the great beasts of the sky died away.
Just a year ago, not even the wildest among us would have believed that any of the fools that took flight against The Interloper had survived. In fact, many would tell you that it never existed. They say it's just a story used by the Pharaohs to keep us in line. (They're fools too). Memory fades too easily since the sky lost Mnemos.
Last month the Imams completed the largest telescope built since the snows came. During the Tango festivities, the Highest used it to survey the surface of Luna. He saw it spangled with festival pyres--and everyone knows that he cannot lie.
The children of the lunatic fliers survive, and they too celebrate Tango.
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Actual Answer: No. Outside primary school, such a civilisation could not realistically achieve such a task… and please remember “empire” is a purely political term but you Asked about culture and technology; by which way, Worldbuilding SE suggests doing some basic research first.
If you want to build a world where it’s simply stipulated that a rocket can reach the moon, why not follow Wells, Herge or Wibberley, among others? It shouldn’t take hand-waving to make it obvious that visitors to your world will no more challenge what you say about your rockets than they would the true rules of real rocket science, provided only that your building is worth its own while.
If medieval-Chinese solid-fuel rockets could reach the moon why would even the Nazis, let alone America or Russia, modern China or India or Europe spend squillions replacing them? Similarly, your empire will need to wait hundreds of years to develop cold-war era rockets, by which time it will not be the same empire. Politics might endure; technology and society will change. Think Teflon and ball-point pens, among many.
Without cars or trains, why might your society be tempted to go to the Moon? “Because it’s there?” Does “pre-modern” allow telescopes, or can the people not see forests, oceans, rivers, etc? Either way, how would it be known at all that the other was “just another planet”, or that the humans’ home was a sphere?
If your objects are closer than our Moon and Earth and both “planet sized” why will they not collide?
How would you use parachutes for planetary landing - not splash-down; moving from orbit? Why is this trip one-way only?
If any of medieval China and Imperial Rome, renaissance Italy or Hellenistic Egypt are comparable, what lets them jump the century or two into an early Industrial Age? What makes you think employing geniuses gives access to knowledge, rather than wisdom?
When “One planet has humans and the other animals”, where did you find ”Terran" animals? Are the humans vegetarian, or what?
Didn’t medieval China famously not use rockets - or gunpowder - in warfare? Wasn’t the first use of firearms in 15th Century Europe, and of military rockets in the Napoleonic wars a lot later? Come to that, what less advanced civilizations did medieval China conquer? Wasn’t it too protectionist to be interested in foreign expansion?
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## How do you simulate tidal currents in an O'Neill Cylinder to maintain a healthy biome for aquatic life?
The O'Neill Cylinder contains artificial rivers, freshwater lakes, and "Oceans" which are just 60m deep large bodies of saltwater simulating continental shelf biomes.
This question has a lot of possible answers so to narrow it down I am looking for a solution that addresses the following in order of importance:
1. Consumes the least possible energy and resources to maintain.
2. Can be built in as many different kinds of places as as possible.
3. Would be the least expensive to build in the first place.
To estimate the relative cost of power, assume this civilization has easy access to hydrogen and/or helium fusion and solar power technology. Also assume they can convert power to propulsion at approximately a 1:1 ratio. Also assume this civilization can not violate the Conservation of Mass and Energy, Thermodynamics, or other such well established scientific principles.
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I'm wondering how much energy it would cost to just ebb + flow the spin of the whole cylinder once per day.
Let's see:
The moon is $7.34 \times 10^{22}$ kg in mass, and perigee is 362,300 km from the center of the Earth. Deduct the radius of the Earth (6,371 km) to get the "feel" at the surface and $a = {{GM} \over {r^2}}$ the moon exerts a change of ${{6.67 \times 10^{-11}
7.34 \times 10^{22}} \over ({355,929,000})^2 } = 3.86 \times 10^{-5}$ m/s/s. Or, in context of centrifugal spin producing 9.8 m/s/s of "force", a 0.000004% change in cylinder spin.
Now, you actually get the drop for free. You can use regenerative braking, braking the rotational energy into a flywheel, that you can then re-provide during spin-up. You could design-in the friction drop to occur smoothly over the course of 12-hours, and then computer control the spin-up over the next 12-hours.
As El Duderino pointed out in the comments, having a global change in the "centrifugal" force won't produce a tide. Tides are caused by uneven dynamic forces (tidal effect is weakest directly under the moon, a spot that moves constantly as the world turns).
I wonder if this can still work, however, with the radial part of the acceleration causing clockwise and counter-clockwise "tides"; helped a little by the reduction (or increase) in the ground-pulling force.
* $ E = mgh = \sqrt{(ma\_{\perp}h)^2 + ({{1 \over 2} mv\_{\parallel}^2})^2}$
* $a\_{\parallel} = \alpha r$
* $a\_{\perp} = {\omega}^2 r = {\alpha t}^2 r$
The mass of the ocean and the height don't change, so m and h can be dropped. The change in g we're looking for is $3.86 \times 10^{-5}$
* $3.86 \times 10^{-5} = \sqrt{({\alpha t}^2 r)^2 + ({{1 \over 2} ({\alpha r t})^2)^2}}$
You can still use regenerative braking to catch most of the braking energy for recycling into spinning back up. However, it's not *quite* like tides work on Earth.
Cost:
* Consumes the least possible energy and resources : costs you nothing you weren't going to have to spend already to keep the cylinder spinning (although perhaps you had even lower-friction spinning; maybe costs you that).
* Can be built in as many kinds of places as possible : the "tidal" effect is global; merely need to add water.
* Would be the least expensive to build in the first place : only costs a few lines of software putting some timing into the re-spin schedule.
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You need currents for two main purpose:
* oxygenate the water
* recirculate the nutrients
Waterfalls and artificial rain can help you with the first one, while thermal circulation can help you with the second and also in distributing the oxygenated waters. You can use the dump heat from the activities hosted in the cylinder to create a density differential in the water bodies, which then following the gravity will induce flow in the water itself.
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Inside the cylinder you are free to arrange the hydrography as you like, so a couple options are:
1. Make the water run in a circuit and use [wave pool](https://en.wikipedia.org/wiki/Wave_pool) mechanisms to keep it circulating.
>
> Wave pools replicate the movement of the ocean one of two ways, depending on the size of the pool and the size of wave desired. In small wave pools, pressurized air is blown onto the surface of the water, or a paddle creates force in the water, creating small ripple-like waves. Other techniques utilize an "accordion mechanism" which opens and closes in order to suck water into its belly (opening) and push it out (closing) to cause waves. However, in high-volume wave pools, a large volume of water is quickly allowed into the far end of the pool, forcing the water to even out, generating a sizeable wave. In these large wave pools, the excess water is removed by being channeled through a return canal where it can be used again to generate another wave.
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Make gentle waves that all flow in the direction of the circuit, and you will have an artificial current. The waves may be used for surfing too, which gives more options for leisure and fitness to the crew and passengers.
If you make the whole machinery run at really, really gentle levels you can even turn it into a [lazy river](https://en.wikipedia.org/wiki/Lazy_river), but that is not as much fun:
>
> A lazy river is a water ride found in water parks, hotels, resorts, and recreation centers, which usually consists of a shallow (2½ ft. to 3½ ft.) pool that flows similarly to a river.[1] There is generally a slow current, usually just enough to allow guests to gently ride along lying on rafts. There may also be scenic elements added, such as small waterfalls on the edge of the river. Some connect or lead into swimming pools or wave pools, while others are self-contained courses that simply complete a circuit.
>
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>
> A torrent river, or wave river, is a related concept. Torrent rivers feature wave machines similar to those that are in wave pools; the waves then push riders (who are on rafts, as they are in a regular lazy river) around the river faster than they would be traveling in a regular lazy river.
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**Add a different kind of spin.**
An object can have only one axis of rotation as I learned here:
<https://physics.stackexchange.com/questions/322200/how-many-different-axes-of-rotation-can-coexist>
But for ease of thinking let us think about 2 axes, realizing in our hard physics heart that there can be only one.
[](https://i.stack.imgur.com/WE6hv.jpg)
The cylinder spins along its long axis to simulate gravity. Yes, yes. Left image. Your left, not the images left.
Now let us also spin the cylinder along its short axis, like a propeller. Right image. This propeller spin is much slower than the long axis "gravity" spin. The effect of this gentle slow spin is to produce a vector force out towards the ends of the cylinder.
One could imagine this centrifugal force to simulate a change in altitude. Now it is "downhill" from the cylinder center to the ends. Water will tend to flow out towards the cylinder ends.
The cylinder ends admit more radiation than the central cylinder. Possibly a lot more. Water that reaches the end heats up and hot gases rise. The hot gases from the cylinders end will rise because of the same forces that pulled the water to the edges - gases are also pulled by this force, and hot, less massive gases will float atop cold. The evaporated water will make its way back to the relatively cool cylinder center and fall as rain.
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At a guess? Try placing the cylinder in orbit around a suitably sized planetary body at the appropriate distance and have the cylinder rotate so that each ends moves first closer to then father away from the larger body.
Other than that pumps and weirs and power driven hydro mechanics. If you can build an O'Neil cylinder electric power shouldn't be a problem
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James Cameron's *Avatar* featured floating mountains which stayed aloft due to the Meissner effect; they contained large quantities of the room-temperature superconductor unobtainium, which, due to their strong electromagnetic fields, were suspended above the ground.
Would this really work though? I've seen the concept criticized - see [here](https://www.scienceforums.net/topic/44200-avatars-floating-boulders/) - and I was wondering if you could help me overcome the flaws in the movie's floating islands; namely the fact that
* A superconductor can't just give off a magnetic field without a current
* The magnetic field would have to be so big, dense and strong that it could be uninhabitable for humans
* I'd rather not just magic an RC superconductor onto the periodic table unless it theoretically could exist on my planet but not Earth
I would also like to know how such a huge magnetic field could be produced naturally. Some requirements:
* The floating boulders I want have to be able to exist as large as houses
* The planet must be habitable to non-extremophilic animal life
* It is a planet, not a moon of a gas giant - so no help from Jupiter-like planets with metallic hydrogen outer cores
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1. Only those pieces of rock which contain a current can produce a magnetic field adequate to float in the planetary magnetic field.
2. Rocks will float at different distances from the surface depending on the strength of their internal current. Some might not float, but just be lighter than would be the case without the current. Some will be very high.
3. Some rocks obtain their initial current through lightning.
4. Rocks can maintain their current through induction. A conductor moving (falling or rising) thru a magnetic field will have a current induced within it. This induced current will produce a magnetic field opposing the one that produced it.
5. I conclude from videos of small animals being levitated that a magnetic field adequate to oppose gravity is not itself lethal.
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ADDENDUM: Maybe Pandora floating rocks are very light?
I recently had opportunity to see the simulated world of Pandora in Orlando. They have some cool "floating" rocks.
[](https://i.stack.imgur.com/yw2fn.jpg)
I conclude that the "rocks" are a lot lighter than they look. Pumice is a tenth the mass of the same volume of limestone. Mayne the levitating rocks are light too.
A do not think there is an upper limit to magnetic fields. Magnetars have a lot. Questions about how much magnetic field can a given volume of mass host, or how much can a given magnetic field (or interacting magnetic fields) lift can be answered. One would need to understand magnetic flux density and I do not.
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***Avatar* was a fun movie to watch, but a lot of it was fantasy**
Can you float a superconductor without an external current? [Sure you can](https://www.youtube.com/watch?v=qYhnt6Q_dXg). What you need is a strong enough magnetic field to induce the necessary current in the superconductor. for example, in that Youtube video, a neodymium magnet floats atop a super cold superconductor.
The problem you have is that planetary magnetospheres are *insanely weak.* The magnets holding your child's drawings on your fridge are [200X stronger than Earth's magnetosphere](https://worldbuilding.stackexchange.com/a/96550/40609) and you can't float a superconductor with a fridge magnet.
**Does this stop you?**
Not necessarily. You simply need to justify a strong enough magnetosphere that it would magnetize the fillings in a visitor's teeth.
Or do what Cameron did: ignore the details and tell a good story.
*But, according to your question you don't want a magnetosphere of that strength. That leaves one answer: sorry, it can't be done based on the science we know today.*
BTW, for fascinating insight into the idea of lethal magnetism, check out [this post from our sister site, Physics.SE](https://physics.stackexchange.com/questions/119999/is-it-possible-to-kill-a-human-with-a-powerful-magnet).
**And then my memory kicked in**
After answering this question, I realized it's a duplicate of [Floating cities with a new superconductor v2](https://worldbuilding.stackexchange.com/questions/137948/floating-cities-with-a-new-superconductor-v2). But since I've already answered this question, I'm not going to VTC.
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The magnetic force is much stronger than the gravitational force. Even a small magnet will easily hold a metal object a few times its mass.
Here is a video of common household objects being levitated:
<https://www.youtube.com/watch?v=1gMMM62NC-4>
On top of that the gravity on Pandora might be lower than that on Earth, and the rock less dense.
You can imagine layers of magnetic unobtanium separated by layers of ordinary rock. When the rock erodes, the like charged layers on unobtanium repel each other, thus resulting in floating rocks.
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Mobile cities are a common sci-fi setting. They are a staple ingredient in novels like "Mortal engine quartet" and "The inverted world"
Plot set aside, what justifies mobile cities *on land*?
[Giant excavators](https://worldbuilding.stackexchange.com/questions/136070/could-a-giant-excavator-like-bagger-293-breach-an-armored-wall-in-a-siege) are real machines which can be used as such. Still, examining them reveals some flaws:
* large footprit (track print), i.e. it leaves in its wake a smothered natural habitat. This was frequently mentioned in Mortal engine quartet. The smothered lands the tracks left behind were named "the hunting grounds".
* difficult to maintain. Replacing Large metallic chassis parts that corrode involves hard work. Indeed, One of the mobile cities in the novel was built haphazardly.
* guzzle lots of fuel when moving
* may still be dependent on land-based farmland, hence the need to plan trips ahead of time.
* may need traffic control, similar to that of ships. This is where a caravan of smaller units, or even motorhomes ("private" houses) may prove more useful, as they may use existing roads *and* traffic control.
* cannot handle all terrains.
Repurposed ships, aircraft carriers and cargo ships may solve most of those problems, but the question was narrowed down to land-faring societies: *Would mobile cities be practical or justifiable enough to be so appealing? Do they have an advantage over classical nomadic societies?*
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If the planet is in the process of becoming tidally locked, there will be a period of time where the day-night terminator moves, but slowly enough to make noon and midnight still be deadly. Your city might need to move to follow dawn/dusk.
Note that this is an exceedingly unlikely scenario. On cosmic timescales, tidal locking is the blink of an eye. For example, scientists think the Moon formed 4.5 billion years ago, and took only 16 million years to become tidally locked. And the time frame in which the day-night terminator moves dangerously slowly is a minuscule fraction of that.
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I'm a bit of a fan of the Mortal engines series, and many of these questions are answered in in the prequel "Scriveners Moon" and supplementary book "The Traction Codex".
According to that story line, the ancients (people near-future from us with orbital weapons etc.) nuked the world into oblivion, including managing to crack the earths crust, or in some other way destabilize the ground. This meant that there were lots of earthquakes, tidal waves, volcano's and semi-sentient weapons sweeping around the world.
To deal with this, people became nomadic and wandered around in tribes. But because they were still reasonably advanced they could build vehicles. The vehicles started small, more akin to a bunch of camper-vans, but because there was combat over surviving resources, these advanced into "traction forts". From there it was an arms race of bigger and bigger until the monstrosities you come across in the main Mortal Engines quartet. Eventually the earth re-stabilized (with a few new mountain chains) but the traction cities now existed and didn't want to go away.
So, with this backstory:
* They didn't care about the exological impact because the earth was already a wasteland from war
* People can change car tires while in an operating vehicle. If you design your moving town right or have the right equipment, you can design it so parts can be replaced without stopping.
* They had more efficient engines (if I recall correctly this was a plot-line in "Fever Crumb" or "A web of air" - I can't remember which)
* The towns were big enough they had farms on their towns (and algae tanks on smaller towns)
* You don't need traffic control if you're actively trying to hunt the other guy.
* If you're big enough, you can handle most terrains. If you've got a footprint of a square kilometer and have enough weight, most ground is very quickly "flat". In the traction codex it is revealed that "the big tilt" that killed Toms parents happened while London was driving up and over a mountain range: the whole town was at an angle.
So in this case, what was their advantage over other nomadic tribes? You could scavenge for resources of a dying world better if you were in a mobile armored fortress....
Practically, building a mobile city is something we would struggle to do with modern tech, and is almost certainly a terrible idea. But that doesn't stop authors making it sound plausible.
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In the history of mankind, there have been a lot of nomadic societies, whose caravans could be considered a kind of mobile city. They used to settle for a time to exploit the resources of a place (basically for hunting or pastures, since this way of life isn't compatible with agricolture), then when resources were depleted or the climate became unsuitable, they moved to other places
In the modern society, since all land (and relative resources) is owned by privates and/or part of a state, it is basically impossible to move freely to look for new resources to exploit (even because all worthy places are densely populated).
Since what you want is a city that can translate itself, not a group of carriages/tents, it is necessary to have a society with a suitable level of technology.
So the best scenarios to allow for a mobile city would be
- colonization of a new planet
- aftermath of a catastrophic event (like Mortal Engines)
- a steampunk scenario, with a new run for colonies in underpopulated lands
A mobile city would be necessary if you have to exploit a fast-to-deplete resource (precious wood, places to scavenge in a post-apocalyptic situation), a highly seasonal resource or a mobile resource (migrating animals).
Of course, since on land it would be far easier to use temporary and easy-to-mount-and-dismount housing and trucks rather than translate a complete city on wheels, a mobile city would require some additional reasons to justify.
The best reason that come to my mind (paired with the first and most essential prerequisite, which is a reasonably flat land, like desert, prarie or tundra) would be a big external menace (carnivorous animals, predons, mutants, extreme atmospheric events...) that could attack the city with no notice: a mobile city, with walls and defenses always ready, would be less vulnerable during the shifts
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The planet Mercury is close to being tidally locked, but has a 3:2 resonance with the Sun. A city build on a railroad track that would keep the city safely inside day-night terminator safe zone would not only be practical, but necessary.
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I would like to have an Earth-like planet (~Earth gravity, ~Earth day, ~Earth year, and liquid water oceans) with extreme variance in its tides. I want the lowest tide to reveal about 30 miles of floodplain, and I want there to be occasional massive tidal waves. I understand that, in theory, this might be achieved by giving the planet several relatively large moons with different orbital periods, such that sometimes they are spaced out, so they balance out the tides (a kind of medium tide), and sometimes they are all together on one side of the planet so that they create a highest / lowest tide.
The star and other solar system features can be placed under whatever side conditions to improve stability, if they can improve stability.
I am building animal life cycles so that they correspond to different tidal conditions. As such, knowing the approximate frequency of high/low tides and tidal waves would be really handy.
Is there a way to set up the orbits of the moons in a stable way such that tidal waves occur predictably and that high/low tides are relatively rare? (Of the order of every 30-40 days.)
Added bonus, if you can provide any spitballed numbers for viable orbital periods and tidal patterns.
[Answer]
Using the comment "The tides are the story-significant feature. The rest can be adjusted." I recommend **a single massive moon** (relatively massive compared to most natural moons that we know of) **on a highly elliptical orbit, making a close approach to the planet every 30 - 40 days**. When it gets close, you have the awesome tides you want. The rest of the time, the lesser tides are caused by the star.
Using the Earth and Moon as examples, because the influence (using loose terms here, not specific scientific ones) of gravity increases exponentially as distance decreases, if the Moon were to change to an orbit where it was only half as far away from Earth, its gravitational influence wouldn't be doubled, but quadrupled. This wouldn't necessarily mean that tides would be 4 times as dramatic as they are now, because there are many other factors, besides simple gravity (such as coastline shapes and arrangements, wave frequencies and resonance, etc) but it's a good starting example to explain it.
If you decrease the average distance by half like that, but without changing the shape of the orbit (which is currently pretty close to circular), you get a much faster orbit, maybe a complete orbit every 10 days, instead of the current 28 or so. But if you then stretch the orbit to a long thin oval, increasing the average distance again, so that it goes back to a 30 or 40 day orbit, you can have a close approach MUCH closer than it currently comes (massive tides for a few days or so), and then it will retreat much farther than it currently does as well (diminishing tides while it retreats, increasing when it starts approaching again).
[Answer]
**You can't achieve what you want with reality**
I should have explained this clearly when I first wrote the answer. I apologize for not having done so. I do not believe it is possible to achieve the effects you describe with reality. Moons large enough to create the tidal waves and the tidal shifts you're describing would make life on the planet miserable (volcanism, for one thing) and tidal waves would occur all the time. There is no coincidence of smaller moons that can bring them about, either.
This leaves you only two options: walk away from what you want for your story, or happily live with suspension of disbelief.
**For the purpose of suspension-of-disbelief, yes you can**
"Suspension-of-disbelief" describes the balance between detailed reality and fiction such that your reader enjoys the story without being distracted by the "unreality" of what you're describing. To be honest, you really want to simply use whatever schedule you want for your story. If you want that rare event to occur only once a month or so, then do so. You need a believable solution — not necessarily a scientifically accurate solution.
*Having said that, don't let our science fans on this site get too out of control. Every once in a while they get so wound up in saying "you can't do that!" that they forget that you're writing a story and not a textbook about lunar orbital mechanics.*
**So, what can I do?**
You can create a believable condition for nearly any kind of tide structure you want with three moons.
**Moon #1** is a bit smaller than our Luna and about at the same distance. It orbits the world in roughly 30 days and the world rotates in one day, which is what's creating the daily tides. It's a good starting point.
**Moon #2** is a larger moon. How much larger depends on how much greater tidal difference you need. You don't need to go wild here. We're not talking anything more than 1.5X the size of Luna. It's a bit further out in orbit and it orbits more slowly than Moon #1 such that the two moons line up only about every 30-40 days. Now, your planet is turning once a day and that means that the water directly beneath *either moon* is getting pulled toward said moon as the planet rotates it beneath said moon. Your tides are pretty complex now. The larger moon is further away, so its overall effect is more-or-less the same as the closer, smaller moon. Basically, you now have two tides per day. But when those two moons line up, you get HUGE tides. You do need to remember that as the two moons get closer to each other (and, subsequently, further away from one another), the effect gets slowly worse. So, while the worst day is when they're lined up, you do have the week ahead and the week behind of ugly tides.
*Thanks to @Eth for pointing out that my original comment about M2 moving a hair more slowly isn't believable. When considering how fast each moon is moving, think about it this way: Moon M1 orbits once every 30 days and we want them to cross every 40 days or so. M2 will travel some amount of its orbit in the same M1 travels up to 133% of its orbit. The lower the number (which must be less than 100%), the more believable the scenario.*
**Moon #3** Those first two moons are on the same orbital plane. This moon is not. It's tilted like Pluto. This has a bunch of complex effects, but to simplify them: (a) the tides for this moon are pulled *away* from the tidal pulls of the other moons. The tides will be complicated, but they'll also be "smoothed out" a bit. (b) Remember that tides are due to the pull of water toward the moon, and this pull is closer to the Tropics of Capricorn and Cancer where Moons #1 and #2 are pulled at the equator. But here's the fun part: (c) Now you have a condition where *all three moons can line up.* Due to the orbital inclination, that line up has a dramatic effect. You can now get your tidal waves via suspension-of-disbelief (the three moons in reality can't do this. No moon or combination of moons can. But you're looking to tell a good story, not write a textbook.)
Using any combination of these three moons, their size, and their orbital speed allows you to basically create any believable tidal system you want. Don't worry about being mathematically correct. If you want a larger tidal wave, make Moon #2 or Moon #3 a little bigger. If you want them to line up more rarely, make Moon #2's or Moon #3's orbital speeds a little faster. Tweak it just enough that people can believe what you're telling them and focus on the story you really want to tell.
[Answer]
I commented on another answer by Brythan & Dalila. They pointed out that an elliptical orbit will produce massive tides only at the close approach.
Orbital period depends only on the major axis of the orbital ellipse. So you lower the perigee by say 150,000 km, and raise the apogee by the same amount, the period will remaint the same 28 days we have now. There's a square root of axis cube in there. So if you double the length of the axis, the period goes up by the square root of 2^3 or about 3 -- ballpark 90 days.
However this has some side issues:
A: Really massive tides are going to have a huge erosion component. You put 50 feet of water over and over again, and the currents that move that water to and from the ocean are going so scour the land. You will not have mud flats. You will have bare rock. If 30 miles of flats are exposed during an 11 hour tide cycle then you have average tide speeds of 60/11 -- about 5 miles an hour. First approximation they are sinusoidal, so the peak speed would be roughly 7.5 miles per hour. That would mean tides come in at a speed most people can't run at for extended distances. That's better than a 4 hour marathon.
Look up tides in the English Channel. Look up tidal currents too. Multiply by 8. Getting on/off shore is going to be a challenge.
Tides are affected by the shape of land. The Bay of Fundy funnels the tides and so instead of 4-6 feet it has places with tides of up to 40 feet. The Pacific Coast near Kitimat has 15-25 foot tides now.
B: It's not just the seas that have tides. The air does too. Google lunar fluctuation air pressure. (4 mb?) Pretty small right now. Same factor will apply to those changes. Even now there is a slightly greater chance of storms at new and full moons, in part to the larger air tide. You can use this to make a few more disasters.
C: The air tides will skim off the atmosphere. You need to have a natural process that regenerates the atmosphere. Look up atmosphere origins.
D: The earth's crust will also be deformed by tides. This flexing generates heat. You are going to have a lot more earthquakes and a lot more vulcanism. Vulcanism generates lots of CO2. Several of the Earth's extinctions are blamed on major volcanic events either as principle or triggering events. This solves your air problem, but you will run out of Nitrogen. This also will help rebuild the eroded coasts.
E: Because of the greater distance variation, tide tables are going to be a lot more complicated.
F: Choose your distance right, and the moon at peragee will slow and stop. The moon will be orbiting at the same speed as the earth turns. This will lengthen the period of high tide. To do justice to this you need to invest in decent orbital simulator.
G: Right now the moon's orbit is thirty and change degrees tilted to the Earth's rotation. This has a stabilizing influence on the the earth's tilt. Putting at an even steeper angle would make the tidal wave pattern not repeat as often.
H: Earth at one point had a 6 hour day. The tugs of the tides have slowed down the earth, with the energy increasing the diameter of the Moon's orbit. This would happen faster with the elliptical orbit. The process tends to make the orbit more circular since more of the energy transfer occurs at perigee. You need to explain why it's not rounder. (You can leave it as an unsolved mystery. Then in a sequel, posit some Engines of God that power the station keeping. Niven had to do this when MIT students found that the Ringworld wasn't stable.)
[Answer]
The simplest way to model wave propagation and dispersion is through a sine wave. Let's start by modeling the effect by an individual moon in 1 constant position using the following equation:
>
> WaterSurfaceElevation = Amplitude × *sin*(( Frequency × T ) + Phase)
>
>
>
For our purposes:
Amplitude = The strength of the moon during its peak
Frequency = How many times the moon completes an orbit in a unit of time
T = Time since the start of the Moon's cycle
Phase = Phase at T(0) with 360 equating to one 1 full cycle
Moon red has: an amplitude of 1.5, frenquency of 1.2, and Phase of 0
Moon blue has: an amplitude of 1, frenquency of 0.7, and Phase of 90
[](https://i.stack.imgur.com/T6Ma2.png)
The green line represents the net effect of both moons. This process can be used for any number of moons.
---
On the possibility of 3 moons orbiting 1 planet, this is very possible. First we arrange the orbits in such a way that satisfies the [3 Body Problem](https://en.wikipedia.org/wiki/Three-body_problem). While this is very complex task, The Institute of Physics Belgrade has compiled a demonstration of the various "families" of [solutions](http://three-body.ipb.ac.rs/). Any of these solutions can be modified to solve this problem. To counteract gravitational pull from a central object the initial velocities could be proportionally scaled. While extremely unlikely, the physics do check out.
[Answer]
Reality check:
I have asked on this forum, physics.SE and several other science based forums if multiple significant moons are possible.
Criteria:
* Had to have a visual diameter of at least 1/2 degree (same as Luna)
* Roughly same density.
All of the existing examples of multibody systems in the solar system the primary is MUCH more massive than the satellites.
So far all of the answers have either been, "No" or didn't get an answer at all.
I've played with a simulator, trying one moon the size of luna, and one 1/2 the diameter (= 1/8 the mass) at 1/4 the distance. This gives the same sized tides as Luna, is visually larger than the moon.
I spent some time tweaking the orbits either trying to hit or avoid resonances. Most either threw the smaller moon out of the system, or crashed it into the earth.
As a counter example, we have Mars with two moons in fairly close orbit, but with small masses -- small enough that even if Mars had oceans, the tides would be insignificant.
] |
[Question]
[
## Context
To revive the Carboniferous period of earth one man and a group of other scientists have been genetically engineering and breeding land arthropods into giant sizes and exotic shapes since the 50s. The second part of the plan is to release the arthropods starting in Georgia and spreading them throughout the globe. But to accomplish this there needs to be a vacuum in a large number of ecosystems that can only be left by a mass extinction of a lot of animals (mostly vertebrates).
## Question
What can someone do to cause a mass extinction that will transform the environment to be beneficial to giant arthropods?
[Answer]
**Wipe out rodents.**
Rodents are the bane of giant insects. Consider the weta.
<http://www.sciencemag.org/news/2017/06/saving-god-ugly-things-new-zealand-battles-bring-back-its-rodent-sized-insects>
[](https://i.stack.imgur.com/EiMIN.jpg)
>
> But it and other weta have been losing ground to invasive mammal
> predators until recently. Flightless and stingless, the odorous weta
> are easy prey for rats and even mice. "Their smell is so strong that
> any rodent just goes ‘Boom!’" says researcher Danny Thornburrow, who,
> like Watts, works at Landcare Research, a public-private research
> institute in Hamilton, New Zealand. As a result, several species of
> weta, like New Zealand's flightless birds, have had brushes with
> extinction.
>
>
>
So too the [tree lobster](https://en.wikipedia.org/wiki/Dryococelus_australis)
[](https://i.stack.imgur.com/0f8o6.jpg)
>
> The stick insects were once very common on Lord Howe Island, where
> they were used as bait in fishing. They were believed to have become
> extinct soon after the supply ship SS Makambo ran aground on the
> island in 1918, allowing black rats to become established. After 1920,
> no stick insects could be found.
>
>
>
The same story holds for other giant insects found on the marsupial side of [Wallace's line](https://en.wikipedia.org/wiki/Wallace_Line), the geographic boundary setting apart the regions where placental mammals did not get established (except bats) from the rest of the world where placental mammals rule. Marsupial predators, hungry birds and even reptile predators like snakes monitor lizards are all compatible with big bugs. Not rodents.
How exactly rodents might be wiped out en masse is definitely something that humanity has considered long and hard. Maybe some bioengineered rodent virus?
[Answer]
**Eliminate lots of habitat.**
The easiest way to cause a mass extinction is to, well, keep doing what we're already doing.
Replace diverse habitats with a few cultivated species. Separate habitats to prevent migration. Dispose of hazardous chemical in unwise manners. Change the climate and the sea level. Selectively eradicate species from the foodweb. And more....
[Answer]
One reason that large arthropods were common in the Carboniferous was that vertebrates had not yet got the hang of eating plants. Vertebrates which could eat plant matter as a primary food source didn't happen until the early reptiles cracked the problem. The food chains we have currently (diverse plants eaten by diverse vertebrate herbivores, eaten in turn by diverse vertebrate carnivores) did not dominate until the end of the Permian period.
Prior to that the vertebrates were all carnivores (think giant amphibians and early reptiles) which ate fish, arthropods and each other. So the food chain would be like these:
Plant ➜ invertebrate ➜ big invertebrate ➜ big amphibian or reptile ➜ huge amphibian or reptile.
Plant ➜ rotting plant (easier to digest) ➜ invertebrate ➜ big invertebrate ➜ big amphibian or reptile ➜ huge amphibian or reptile.
It'll probably be a bit more mixed up in the middle of those food chains, with adult big invertebrates also eating small or juvenile reptiles.
**So to reset to the Carboniferous, vertebrates have to 'forget' how to eat plants. In realistic terms, this means that the plants have to become inedible in some way.**
Possible reasons:
* You do a *Death of Grass* scenario, as in the John Christopher novel of the same name, and all plants in the grass family (Poaceae) are killed off by a fungal blight. All the grazing animals die (or have population crashes), as do all carnivores and omnivores who depend on them. This includes human civilisation falling over, as all the staple cereal crops such as rice, maize and wheat are no more.
* The gut microbes which enable vertebrates to digest the tough bits of plants (cellulose, lignin), become extinct. For instance, ungulates (hoofed animals), kangaroos, and elephants. There are LOTS of different microbes and single-celled organisms doing this, so I don't know if killing them all off is plausible. The mammal herbivores such as cows, antelopes and zebras would then be getting a fraction of the nutrition out of plants that they used to. Some species are going to die out. Some habitats, where it was difficult to get nutrition even with all the right microbes (e.g. Australia's spinifex grasslands) become uninhabitable for mammalian herbivores.
* The plants evolve (or have been genetically engineered to have) some toxin or tough material to replace cellulose, which mammals and their microbes can't cope with — but the new 'Carboniferous' arthropod herbivores and their microbes can. Again not sure how plausible this is, because there are hundreds of thousands of plant species in the world!
[Answer]
Engineer flesh-eating insects.
Big problem with the original suggestion is that surface arthropod's size is limited. Without boosting Earth's atmosphere oxygen content, there's not so much that can be done about it. As a result, vertebrate's sizes will always be considerably bigger than arthropod's and vertebrates will likely be the apex predators. Even if some extinction event would wipe out most vertebrates, after a while they will grow back into this ecological niche.
Possible solution is to turn tables on large animals. Insects' strength is in their numbers. A swarm of bees is capable of taking down almost any animal - but a swarm of bees has little incentive to do so. A new class of insects may specifically hunt down animals and eat them (not just suck some blood now and then). This will see animals' numbers plummet, even those who, like bears, are heavily insulated and able to stand against a swarm of bees, because their food chain will be compromised.
Eventually, mammals' evolution will favor armored types like anteater, but they would not likely regain their unquestioned dominance.
[Answer]
Just like the scientist were able to modify the arthropods, they could modify a certain plant that releases poisonous spores that only affect vertebrates. That could be implemented in small quantities throughout woods, forests, fields, etc... and they would multiply naturally.
You see, fungi can synthesize penicillin to fight off bacteria, but has no effect on other fungi. Enough chocolate can kill a large dog while we can feast on it and nothing happens (apart from diabetes). With enough DNA engineering, the plant could release in the air and water a deadly substance that would affect a targeted species or multiple species.
[Answer]
**Destroy the ozone layer**.
Arthropods have two advantages when resisting radiation.
1. They have an **inert** and **replaceable** outer layer to absorb radiation. This should at least make them more resistant than soft bodied animals and much better than super squishy amphibians. While a cockroach cannot survive an atomic blast they are supposed to be very resistant to the radiation produced.
2. They can retreat underwater.\* A few metres of water can block radiation.
The world is populated by large arthropods who spend the day in pools underwater sheltering from the worst of the radiation. During the night they come onto the land to forage and their carapace protects them from the residual radiation.
**Bonus Points:** Find some way to make the planet more humid/tropical so there are more pools around the world for the arthropods to shelter. Otherwise they won't get anywhere near the arctic circle.
\*This is not true for all arthropods. In general arthropods breath through gills that must be kept moist at all times. Woodlice for example cannot survive underwater for a long time but their gills are close enough to their aquatic ancestors' that they can last an hour or so submerged. It is not far-fetched that an aquatic version of the woodlouse and other land based creatures develop or some already aquatic arthropod takes its place.
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[Question]
[
Living in Budapest I see almost everyday the Budapest Castle. Being into zombies I often wonder how useful could be a castle of this kind in a world where zombies taken over.
Most, if not all, the zombies movies and tv shows are set in America, where solid buildings aren't common as in europe, and medieval castles aren't present. So there aren't chances to see survivors try to adapt this kind of buildings to survive against zombies.
The castels I'd like to take in consideration are the ones in good status, without flaws in the walls and generically easy enough to be further fortified to defense their entries.
How plausible would be for a group of survivors , in a post apocalyptic world full of zombies (like the ones of the most common movies: slow and unorganized) to fortify a castle and live there for an undefined period of time?
I'd like to see all the possible factors covered: other groups of hostile survivors, demography (and related number of potential zombies) of the areas near the most famous castles and so on.
The timeframe should be modern days (2017).
---
This question is different from [Castle Moat Full of Zombies](https://worldbuilding.stackexchange.com/questions/67826) because I'm not asking how to keep the moat empty, I'm asking about the feasibility of living inside a medieval castle during a zombie apocalypse, with all the concerned problems considered.
[Answer]
**Short answer**: absolutely.
## Long answer:
Given that castles are, by their nature, fortifications, you would be hard pressed to find a more defensible building in the world (other than in an operational military base, at least). Using a castle in a zombie apocalypse scenario would have several pros and cons, as expressed below.
### Pros:
A castle is made entirely of strong walls, which are designed to deter entry and keep enemies out. Zombies, being of minimum intelligence, will be unable to penetrate strong walls so long as they are in good condition.
Almost every medieval style castle was built with active defense in mind. This means that man castles have ports to fire arrow from. Also, there tend to be locations to drop hot oil or other substances onto intruders. These ports and holes can be modified or used outright for rifle-wielding people, and if they are close enough to the ground, pole-arms and bayonets are also an option.
Castles tend to have high points, which are made for increased vantage for intelligence gathering. For the most part, any intruder is visible for miles, and slow moving zombies could be watched for days as they move either towards away from your fortification.
Castles tend to have multiple layers of defenses. This is known as defense-in-depth, and means that even if zombies make it past one layer, you have another ring of walls to fall back behind and continue defending with as of yet unbroken defenses.
### Cons:
Castles are large. Large buildings require either highly mobile or a lot of defenders to properly defend from active threats. If humans got involved, you'd be hard pressed to keep the whole thing defended.
Castles tend to be somewhat complex. If there are weak points anywhere that a zombie could get through, several of them could be in your castle before you even know it.
Many castles are not well ventilated or very modern in terms of human safety. You run the risk of such things are mold and other growth making the humans that live there sick and less effective as defenders.
Most castles are old, and lack certain design features like power distribution and plumbing. Most of those services won't really work in the apocalypse scenario anyway, but having them just in case sure would be nice.
## Conclusion:
I'd say, assuming you had no better options, a castle would be a wonderful place to set up for a long defense against zombies. Perhaps the closest modern analogue would be jails, although jails are mostly designed to keep people in, not always out.
There is a series of zombies that uses a jail as its location for several episodes (The Walking Dead, seasons 3 and 4) and this series manages to outline some great pros and cons to the hard-building approach to survival.
[Answer]
Two things about castles that make them less effective against zombies than people:
1. All that stuff that protects against siege engines and sappers is wasted on zombies. They don't do intelligent things like pick up trees to slam into the wall or gates. They don't try to dig under the walls. A castle is not nearly as much better than a brick house against zombies than as if it were defending from people. That said, any building where the doors can be locked is an advantage against zombies.
2. A major part of how zombies work is infiltration. Someone gets bit and doesn't tell anyone. Then they die inside the castle and turn into a zombie. Then they bite a second person. Now there's two zombies. Repeat until everyone's dead. Walls don't protect from a danger that is already inside. Under **Walking Dead** rules, the person doesn't even need to get bit. It's enough to die inside.
Beyond that, what happens when zombies surround the castle? Sure, they can't get in. But if you can't get out, you die of starvation.
A jail is a safer place in a zombie apocalypse. Lock yourself in the cell at night. Keep a supply of food in the cell. If something goes wrong, you're in a locked room. Stab the zombie(s) through the bars. Use the security system to track whether a zombie ended up inside. Keep the section doors locked to limit the scope of any problem.
If you do find yourself defending a castle in the zombie apocalypse (perhaps others took all the jails in the housing raffle), try to make the castle more like a prison. Make it possible to lock each room's door. Add chokepoints inside the castle halls that are easy for people to open but difficult for zombies. Add security cameras so as to monitor the halls (a castle that was a museum would work). Add a garden inside the walls. Keep the doors closed at all times. Open only when you have good visibility.
Try for a castle with a gate with a double portcullis. Open one to let some zombies into the vestibule. Drop it behind them (perhaps on some of them). Then stab them with spears through the other portcullis. Eventually open it and clean out the vestibule. Repeat until there are no more zombies blocking the gate.
Castles have solid walls. They are protected from attack from the outside. These walls are better than most fences against zombies, as they were built with the possibility that there might be attacks by pressing against them from outside. That may make them slightly more effective than more modern fortifications, which assume weapons capable of piercing them. Zombies don't have that ability. Their power is in massing together and brainlessly pushing.
[Answer]
As has been pointed out, castles are great for defense but rely on stored food and water in times of siege. The better castles have wells. Also, castles are usually situated on high ground and have good line of site.
Some strategies to make this work:
Use hand weapons to clear the zombies from the walls and gate. After entering the castle, close the outer gate and every internal door you find. Slowly do a section search (securing doors behind you) of the castle to clear it.
Once clear, start clearing the outside with hand weapons. If you can reach their heads from the top of the walls, great. Otherwise, use the human bait method to lure groups of zombies into kill zones (the double portcullis works well for this). Roam the local area in packs and lure more and more zombies into the trap.
Now, you can start growing food. If watch is kept on the walls/towers of the castle, you can spot zombies before they get to the farmers (just don't farm past the castle's field of view).
If, in your world, zombies only eat humans and leave animals alone, you can even raise sheep or cattle.
Everyone sleeps in locked rooms. At night, zombies can't get in and someone who does in their sleep doesn't get to go on a killing spree. The injured should be isolated.
Building forts on nearby high spots will let you expand. They can watch farmland further out and provide bolt holes for the farmers so they don't have to make it all the way to the castle.
A solvable problem will be getting rid of the smelly corpses but carrying them downwind once the area is cleared will work.
As has been mentioned, your biggest threat after starvation are any other humans who think that living in a castle is a good idea and who either don't want to share or think that they should be the ones running things.
Of course, that's the thing that castles were actually designed for.
[Answer]
Well...
[](https://i.stack.imgur.com/Bzh0p.jpg) *picture taken from "World War Z"*
Your group of survivors is doomed to die.
---
Okay, only slow and unorganized zombies:
Sure, they can survive. These castles were able to defend against armies of organized soldiers, why would they fall to some zombies?
But while they can't overthrow you, they can besiege you. And
>
> the most common [zombie] movies
>
>
>
tend to give them decades of lifetime after their transformation. So food and water will be your biggest problems. **Starvation** will kill your survivors. Especially because these castles hadn't todays methods of food preservation.
But stay relaxed, if your guys are lucky enough to find a full food storage all for themself, I'll give them about two years or so. As it is your world, you can let your zombies rot away in that time.
] |
[Question]
[
In a story I'm writing, the setting is a **tidally locked planet** with a moon a fifth its size in a binary system of a mature **red dwarf** and much smaller second sun. I haven't decided the planet's exact **orbital period** (30-40 earth days) at 0.5 AU from the larger sun, but its inhabitants experience slightly stronger gravity than on earth, and it is larger than earth with a large **molten iron core** for a protective magnetic field and tectonic activity.
While designing a map of the planet's surface, I've hit a point in my internet research where **I can't decide how to go about placing mountains**, which impacts flow of rivers, ice build up, terrain lighting, wind, etc. I've been looking up **plate tectonics** and found that the mantle could flow away from the sunny apex, sliding the crust along through convection toward the sub stellar hemisphere, and the crust might buckle and fold along the way. I thought this would make the mountains on the planet look like they were leaning away from the sun but also wondered whether this scenario creates so many mountain ranges parallel to the twilight band so as to interfere with the water cycle and air currents.
So I dug farther, looking for a planet tectonic simulator I could enter valid information into. If there is one out there, please link me to it. I found one, but the poles are set like Earth's, so I improvised and attempted to slide the equatorial region to the base and the poles to the top...which is difficult to describe, so I'm including a drawing of this and the first model I found. [](https://i.stack.imgur.com/cRESX.png)
Up to this point I've had a pretty good feeling about all my research in planet building where the laws of physics are at least fairly realistic. But I'm at a loss as to how to plop mountains about the planet surface, unless I should just pick any ol' environmentally ideal, plot strategic or even scenic location. Usually I stem my creativity from factual research conclusions.
[Answer]
As of 2016, we have evidence that Mercury is tectonically active (<http://www.nature.com/ngeo/journal/v9/n10/full/ngeo2814.html>) and it is also in a spin/orbit resonance. While it's not a perfect analog to your scenario, it's probably the closest example currently available.
The map in Figure 3 shows the locations of (known) tectonic scarps, which do not seem to be clustered around the twilight band.
My general intuition about such a situation is that the day/night disparity would not be a major factor in tectonic activity, because the Earth's core is hotter than the surface of the sun. Any difference in external solar heating would be dwarfed by the temperature differences within the planet itself which drive tectonic activity here on Earth. Nature's Figure 3 map is consistent with this intuition.
Based on this, I would tend to just run tectonic simulations normally and not apply any modifications to that stage of the simulation related to the planet's tide-locked condition.
[Answer]
# The heat of your planet's core is (sort of) independent of the sun
Your planet is tidally locked to the sun. You do not specify what the temperature regions are (is the sunny side habitable? the twilight zone?), but I think it is safe to assume parts of your planet have Earth like temperatures, and therefore no part of the planet is as hot as Venus.
The temperature of the Earth's surface is about 290 K, while the inferno on Venus is a sintering 750 K. However, the core of the Earth is in the 6000-7000 K range, while the mantle is around 900-1200 K.
Considering the basic laws of thermodynamics, it should be apparent now that the mantle is heated by the core of the Earth, not by the sun; the radiant energy that the sun deposits in the oceans, atmosphere, and lithosphere does not transfer to the hotter mantle.
The conclusion is, **as long as your planet's core is similar to Earth's, the convective forces of the mantle are (mostly) driven by the core, not the sun**. This means that plate tectonics will work as they do on Earth.
The reason I say sort of and mostly is that there will be a gradient in temperature loss form the mantle, where more energy will be lost on the dark side of the planet than the light side. However, if you are planning on an Earth-like planet with a thick atmosphere and lots of water, the temperature delta will be relatively small compared to the temperature delta between the mantle and the surface . For example, even a 100 K difference between light side and dark side is less significant compared to a 500 K difference between the mantle and the lithosphere.
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I'd simply add a massive mountain range on the dark side, and an elevated mesa on the sunlight side (because of tidal force) and be ok with that. We know so little about exogeology - hell, we almost know nothing about our own planet's core - that you are entitled to almost any amount of handwavium here.
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**This question already has answers here**:
[What are some tips for designing symbols for a constructed language?](/questions/49385/what-are-some-tips-for-designing-symbols-for-a-constructed-language)
(6 answers)
Closed 6 years ago.
I could spend weeks trying to make a script and the glyphs are still either extremely ugly or just a bunch of scribbles. Then, I look at things like Moonsong and Sun Script and I have no idea how people make anything like that. So, I was wondering. Does anyone have any tips or strategies for making a nice-looking script?
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I started with some principles: writing could go in any direction and glyphs can be written with any orientation or reflection, so they had to be distinct and not differ due to symmetry only.
For alien numerals, each glyph is written in a square bounding region. It touches the sides of the bounds. Each digit (0 through 8) is the simplest curve that has n intersections or endpoints.
I don’t remember what I did for other glyphs. But, one idea is to make the drawing structure based on the underlying sound (or whatever), like [Tengwar](https://en.wikipedia.org/wiki/Tengwar#Regularly_formed_letters). In my alien commerce-interchange code, there were a set of A and a set of B and a “syllable” used one of each set. For us we would use consonants and vowels for A and B. Another sound-based species may have different ideas of what sounds to make. A gesture based language for example uses tenticle joints and postures.
So, syllables had glyphs that *systematically* encode one A and one B value.
A series of posts on the [Artifexian YouTube channel](https://www.youtube.com/channel/UCeh-pJYRZTBJDXMNZeWSUVA) goes over some ideas, and he settled on something that was also a “structural” system, not arbitrary glyphs but some architectural correspondence to their sounds.
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# My favourite method:
(Works best if you have very non-neat handwriting, go to school, and have a teacher who dictates a lot.)
Get someon to dictate a long text quickly. Don't try to write neatly, as that ruins the point of the excersise. After you have a page of ugly text, you can finish, as you probably have a lot of random letters that look fine in the word, but completely alien out of context. Just look through the page for anything strnge, and copy it out. There will be similar letters, but you should have some nice, relatively random glyphs.
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You could use a calligraphy pen to draw them, almost anything looks cooler when it's not just thin lines.
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Cuneiform writing was called that because a wedge shaped tool pressed into clay was used to make all the characters. I think it looks cool.
From [reference.com](https://www.reference.com/hobbies-games/can-clay-cuneiform-tablet-made-55e725bfcde21d6e)
[](https://i.stack.imgur.com/YXv2J.jpg)
Maybe each of your characters is made using a curved tool pressed into clay. That would look cool and also be reproducible.
You might wind up with something that looks like the Tamil alphabet. Or you could just steal the Tamil alphabet, which I think is awesome.
[](https://i.stack.imgur.com/eutnN.jpg)
If you do, you should have the actual words say "Tamil readers I hope you will forgive my using these sweet letters for my story!"
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There are many theories about how teleportation could work (warning: [tvtropes](http://tvtropes.org/pmwiki/pmwiki.php/Main/Teleportation)). One of them is that the body is completely disassembled on a molecular level and reassembled at the target destination. This leads to ethical problems like “Am I still *me*, even after I got completely disassembled and the original *me* has been destroyed?”.
What I am interested in is not the ethical implications of teleportation by **disassembling and reassembling**, but the **applicability to shapeshifting.**
Shapeshifting is the changing of ones body from one form into a different one (again: [tvtropes](http://tvtropes.org/pmwiki/pmwiki.php/Main/ShapeShifting)). An example that is often used is the Werewolf – a human that can change into the form of a wolf and vice versa. There are already a few questions on [WorldBuilding](https://worldbuilding.stackexchange.com/questions/26001/anatomically-correct-werewolves) that deal with the transformation, but nothing about disassembling a human on a molecular level and reassembling all of his molecules to form a wolf.
For this scenario, we will disassemble a roughly average European human and say that this human is about 1,70 metres tall and weighs about 70 kg. Only the molecules and compounds of this humans body can be used. The machine that is used will not disassemble the body into single atoms, but into the existing molecules and compounds (e.g. glucose, water, ...). There are no clothes or other materials that could influence this little experiment in any way. This includes things that could potentially be in the stomach of the person, other organisms, piercings, ...
**How big would the wolf be that I could create from the molecules from this human? What differences to a normal wolf would this one have, if I were to use all of the molecules from the human?**
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The difference between humans and wolfes is in a few percent of DNA and maybe some proteins. Since you deconstruct the human body into lower elements that DNA and proteis, you will end up with the same "bricks", since DNA and proteins are made by the same basic assemblies.
In principle you could reshuffle the very same bricks to make a 70 kg wolf, or 2 35 kg wolves...
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I'll extend this a bit by providing a potential method for the shape-shifting that takes this molecular reordering into account.
You can use [Stem Cells](https://en.wikipedia.org/wiki/Stem_cell)
If the shape-shifter is able (consciously or not) to devolve its current cells into stem cells, they can be used to recreate the new shape while staying "biological", possibly doing it in stages, one organ at a time.
Of course, it would have to be very accelerated.
As a bonus, you can include something about the tidal pull of the full moon to prompt the transformation hormone.
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Well, the DNA of a human is complicated. Humans likely have a gene in them that makes low amount of hair. Take it out and you have a hairy human. If you mix and match other human genes, such as the length of a tailbone to become longer resulting in a tail, you could get a werewolf like human. But it would cost tons and likely many generations to get there. if you want some more info on this you could check out:
<https://theconversation.com/safe-and-ethical-ways-to-edit-the-human-genome-73110>
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I had to think this one through, and even now I don't know if it belongs here, hopefully you guys can help.
Most scifi media has the World War II approach to combat, chasing and maneuvering in dogfights or "running silent" when it comes to larger ships.
What I want to know for now is:
Is "jousting", in the terms of running at each other guns blazing repeatedly, a viable tactic against other combat vessels or, would extreme Ranged Combat still reign king?
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This is possible in some extreme situation, but I think, that it's less effective than ranged weapons.
Missiles and long range lasers are quite likely to disable the craft which tries to run on the other before it could use it's close range weaponry.
But one can make up situations, for example:
Hard sci-fi like:
1) Enemy ship with powerful laser weaponry is on very low orbit around celestial body having no atmosphere. (like moon.) Our ship is docked in a subsurface hangar, and has weaker power generation. Both ships have well aimed but low damage missile defense systems. Our ship takes off when the enemy is on the other side, and sets a retrograde intercept orbit relative to the enemy. They have a very high relative velocity encounter, and when they are only 200m away, we fire our computer aimed machine guns, and destroy the key systems of the enemy. Thus it's possible to minimize the time spent in line of sight, and giving less chance to their lasers to bake us.
2) The primary objective is to capture the enemy intact. We have to go close to launch our space marines. We will choose a decent velocity, since the rockets placed on the spacesuits of the marines have to compensate for it, (otherwise they would smash into the enemy hull.) but the faster we come, the less time does the enemy have to fire on us.
Handwavium like:
1) Both sides have powerful energy shielding, which are superior to beam and simple kinetic weapons, but can only be mounted on larger ships. But the unstable warhead of QWERTZUIOP-torpedoes is able to penetrate the shields. But the warhead quickly disintegrates after launch and/or is vulnerable to enemy point defense. So the ships try to get close to each other to minimize the chances of the enemy to destroy or manover out their torpedoes.
2) We are capable to FTL travel and combat, but engaging in FTL requires close proximity/warp field frequency matching...
Scrap like:
1) Both sides have combatants, which weren't originally designed for warfare. They have high dV, but weak power generation, are fragile, and they don't have access to professional weapon systems. So their tactic is to charge towards the enemy, and immediately before flyby release a massive piece of metal (A tungsten mining drill for example.) and hope to score a kinetic kill.
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# This will never work in hard science fiction
The that differentiates space combat from WWII combat *a la* Star Wars, is that shots fired never stop going wherever they are going.
For example, in the Return of the Jedi, we see a tightly clumped formation of Star Destroyers near the Death Star around Endor. Any shot fired into that group will undoubtedly hit something. There is no concept of range, as there is with a battleship on the ocean. A battleship at sea can fire short, or fire over the target. In space, if you fire a laser or mass driver or non-maneuvering torpedo, you can't fire short, or long.
If you are charging someone to 'joust' them, in space, your direction of motion has to be directly at them. Therefore, any shot fired from the target of the joust at you will hit you. It can't miss short or long.
Given the potential destructiveness of space based weapons (especially relativistic kinetic projectiles, or nuclear/anti-matter torpedoes), being hit is probably a bad thing. Shields don't really exist as such in science-based sci-fi, and armor doesn't stand much of a chance against the aforementioned weapons. To avoid being hit, you would want to fire on your target from long range, so that projectiles fired at you take a long time to get to you, and you have a chance to not be there when they arrive. If you are at ramming speed, you don't really have that chance, and you are probably going to be annihilated.
# How to make jousting work
That being said, if you aren't sticking to strictly hard science fiction, anything is possible. There could be powerful energy shields, or even impenetrable ones like the impeller wedges of the 'Honorverse.' But the point still remains: If in your universe weapons do a lot of damage, and they have computer guided aim, the chances of successfully jousting seem to be small.
The best way to make jousting reasonable is to make space combat similar to other methods of warfare that involved the 'joust' (which also, keep in mind, wasn't a real combat tactic so much as a form of entertainment). You could have spaceships like knights with heavy armor, limited visibility, and no long range weapons. You could have spaceships like age of sail ships-of-the-line, with lots of small weapons of short range and high damage, thereby giving people a reason to close and board. Or you could have ships like galleys with no real effective way to damage each other than by ramming.
How realistic those are in your universe is up to you.
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EvE Online would be a great place to test this idea out... well by test I mean observe because it is already tested by players XD. Truth is, ships that are charging into the front are usually built with a ton of armor and shielding. Even then, the hard part about this is that the ships are built to defend against KNOWN weapons. In other words, if they are going against unknown alien technology, there is a good chance that even these tanker ships are going to be torn up. Armor'd plating is good vs kinetic weaponry... shielding, well in theory, disperse laser fire due to being calibrated to the right frequencies.
If you also think about naval combat.... the old days of the gallons they would go guns blazing at each other side by side and completely knock the crap out of each other.... even if your ship won, you might as well lost. Even with today's destroyer's and battleships, they attack at range or with aircraft / torpedoes. ships are designed to output damage and take minimal risks. You didn't mention anything bout costs, however, warships are not cheap to produce. So if economics plays a factor, having to constantly repair/replace ships would get costly.
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Assume that beam weapons are relatively weak. Missiles and gun/railgun slugs do the killing. Their destructive potential depends on the relative velocity. If the warhead is fast enough, even a tiny splinter would be lethal, so a warhead can be explosively fragmented into tiny splinters to increase the hit probability. Many weapons in the setting are optimized for moderate to high relative velocities for the tactic outlined below.
Assume that there is an efficiency of scale effect for engines. Big ships are much faster than little missiles (or little fighters), or at least they have more delta-V.
Ships and fighters can and do fight in a furball [dogfight](https://en.wikipedia.org/wiki/Dogfight), especially if that happens near a station, planet, wormhole, or whatever is stationary and important. But it is an effective tactic to keep a few warships out of close combat and to have them make a [high-speed firing pass](https://en.wikipedia.org/wiki/Basic_fighter_maneuvers#High-side_guns_pass) through the furball.
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Sure- if the combatants set themselves up in the same orbit, but traveling in opposite directions, they could "joust" repeatedly while expending minimal delta-v. A very elegant and chivalrous way to fight a space battle!
It still wouldn't look very movie-like; the range of weapons in space is going to be much higher than for WWII-era warplanes, so they're going to start shooting well before a combatant's human eyes could pick out their foe. Also, the sheer relative velocity that their projectiles are impacting with will guarantee it's likely to be a short fight (and both sides are liable to be taken out!) unless extremely strong armor/forcefields are available.
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For spaceships from Earth, computer navigation technology would make any form of jousting or even combat with ranges close enough to see your target completely redundant.
However, perhaps an alien species that has highly advanced space-travel technology but very primitive computer technology might use jousting as a means of fighting effectively - if your missile can only fly bullet-like in a straight line, then a tactic would be approaching from the direction of their nose getting as close as possible, to minimise the effect of your bullet taking time to get to them and them not being where they were when you pulled the trigger.
Having said that it might be only useful against inexperienced impetuous enemies. An experienced pilot would recognise when you have the advantage over them and just steer away, calling off the joust.
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In my narrative several people can hear a soft buzzing when it is very quiet. It's almost unintelligible, but discovered it is what's on the radio. The people aren't related, but they may be very distant relatives.
I'm thinking there's a trigger gene that, say, when they hit their head a certain way an eardrum could 'suddenly' receive and translate the waves. Or a genetic mutation (not likely in, about 1,000 people around the world). A bug?
**Can a human naturally, in pseudo-science, or preferably real science, adapt to hearing what's on the radio?**
**What would be required to be in the ear, and how did it get there?**
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# Radio Is Never Heard, Only Seen
No ear can ever hear the radio, because it is transmitted with light waves. If you can see into the radio part of the light spectrum, you could "see" radio! Note that the visible part spectrum is far from the radio part of the spectrum; this would take some severe alterations to do this. Bees and other creatures do see different parts of the spectrum, but I'm not aware of any that go that far.
[](https://i.stack.imgur.com/OnfyG.png)
# Picking Up Radio?
Now, if these people developed something in their ears which gets ionized by radio waves alone (which is very hard to do), they could then "hear" the radio. It seems it would be easier for eyes to adapt to this, since they pick up light already. An organism would need a [new chemical in their eye](https://en.wikipedia.org/wiki/Photoreceptor_cell), which reacts with radio waves, so they can see the radio. Alternatively, they need something that can change state when hit with a radio wave, which their neurons can then translate into a signal in the brain.
It should also be mentioned that FM and AM radio waves use different codes to carry sound information:
[](https://i.stack.imgur.com/ct9Xj.gif)
So even if an organism was capable of detecting FM or AM radio, they would have to figure out how to de-code the message to understand it. Human brains have [amazing processing powers](http://www.extremetech.com/extreme/163051-simulating-1-second-of-human-brain-activity-takes-82944-processors), so I am confident a human could adapt to understand the input of a new sense. It is just that getting a new sense alone does not guarantee the ability to understand what is sensed.
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Yes, they can.
Electric current passed through the head might be perceived as sound - surprisingly, even by deaf people. It's called [electrophonic hearing](https://en.wikipedia.org/wiki/Electrophonic_hearing).
Here's one of the [articles](http://www.stopthecrime.net/Chou-Auditory-perception-of-radio-frequency-electromagnetic-fields%20(1).pdf) on auditory perception of radio frequencies. I don't know if that's a valid study, but at least it looks sciency enough for soft sci-fi. According to the article:
>
> Microwave hearing is most easily explained by the mechanism of
> thermoelastic expansion, i.e., absorption of microwave energy produces
> nonuniform heating of the exposed head; a thermoelastic wave of
> pressure is then launched, presumably through bone conduction, to the
> cochlea where it is detected. After auditory-nerve excitation in the
> high-frequency portion of the cochlea, transmission of the
> microwave-induced neural response follows the same auditory pathways
> as do all of the acoustically induced responses through the brainstem
> and thalamus to the auditory cortex.
>
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>
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You know how some of our own real world crackpots wear tinfoil hats, either makeshift, or real hats with a tinfoil layer inside?
If they used a regular mesh of wire instead of foil, they would stop hearing things that aren't there.
No, seriously!
Except that what they hear is not the greys trying to brainwash you into obeying the illuminati or whatever it is that conspiracy theorists are claiming these days. Humans can "hear" electromagnetic radiation, though it is on the microwave range rather than regular radio. [I present you the Frey Effect](https://en.wikipedia.org/wiki/Microwave_auditory_effect).
Of course, you won't hear your router talking to your cell phone this way. You're more likely to experience the Frey effect if you work with radar, or with radio masts.
[And the quote about how wire mesh blocks it:](https://en.wikipedia.org/wiki/Tin_foil_hat#cite_note-Elder_.26_Chou_2003-10)
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> In 1962, Allan H. Frey discovered that the microwave auditory effect, i.e., the reception of the induced sounds by radio-frequency electromagnetic signals heard as clicks and buzzes, can be blocked by a patch of wire mesh (rather than foil) placed above the temporal lobe.
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>
Now of course, in the real world, we only hear noise. But now that you know this, it doesn't take a lot of handwaving nor suspension of disbelief to come up with a fictional way to enhance our natural capacity to hear electromagnetic radiation.
I don't know, maybe a mutation causes iron or tin to accumulate in high(er) contentration in human bones. This could cause the cranium (where the brain is located) to act like a resonance chamber, amplifying the signal and making it much louder and perceptible for those who have the gene. These people would be able to tell the best spots to place a wi-fi router in their home, by ear!
A little more handwaving and you can change the "audible" spectrum from microwave to regular AM/FM radio. That would be really cool too!
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You can check out simple radio electronics, and design one using nanotechnology...
So, Graphene is used for the antenna, it's a tiny long graphene ribbon implanted somewhere rigid, because it has to be as long as a radio wave, i'd say an endoscopic implant in the top of the head. The capacitor would be a few microns, made of a futuristic ceramic perhaps, and the diode would be a few microns of germanium. describe a radio circuit in nanotechnology and connect it to the ear/the brain.
Radio-Waves travel far, because they interact very little with matter. If there was a radio wave signal on earth that helped survival, for example weather forecast or food that transmitted radio waves, I believe animals could have evolved to hear them, but it would be as complex as ocular apparatus.
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It happened on Gilligan's Island.
It happened on the Partridge Family.
Lucille Ball claims to have done it in real life.
Generally, blame metal dental work, and people will find it beleivable. A crystal radio is quite easy to make, can even use a razor blade.
I don't think it ever really happened, but it's *plausible* to pick up AM radio on a piece of metal embedded in the head.
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It's possible that an alien race would evolve to sense radio waves if it enabled them to survive and thrive in their environment. That is not any more outlandish than our race of beings being able to pick up the part of the EM spectrum we call "visible" with eyes. This is a good explanation of that:
<https://biology.stackexchange.com/questions/35337/why-is-human-vision-restricted-to-400-700-nm>
But in your story you wish for it to be a human on earth, living amongst other humans? It'd have to be some crazy mutation, Marvel Comics territory, brought about by exposure to some radioactive material or something.
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I am designing a world where humans have achieved FTL by means of the Alcubierre warp drive and are colonizing the stars.
Originally I had communication pegged as being done with quantum entanglement and the like, but I recently heard of the no-communication theorem that, seemingly, prevents this from coming to fruition. Now, from a narrative perspective it is not strictly speaking necessary that communication is fairly instant, but it's a ton more convenient. Therefore I'd to find a way for it to be so using existing theories or reasonable speculation.
* Is there a hole in the no-communication theorem that can be exploited to permit it anyway?
* Is there other, speculated methods of instantaneous communication?
Otherwise I am relying on communication being done with warp drives, that is, every settled planet will have a comm station in orbit that every day/hour/minute sends out a comm drone through warp space with the most recent and updated info to other settled planets, likely in a branching fashion so that A sends to B and then B sends to B1-B9 and B1 sends to B1,1-B1,9 and so on. Now, warp isn't instant, it takes about a week or two to travel across inhabited space (approximately 400 ly in radius), so that creates a lot of delay
* Is there a more efficient solution when you use warp as a basis for interstellar communication?
I don't want to have to rely on a lot of "magic" technology, but if something is reasonable speculated/theorized to be possible within the realm of physics (albeit past the capabilities of humans to reproduce at all anno 2015), I'm interested.
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Just reading up on what an Alcubierre drive is, and it seems to work by shrinking space in front of an object to allow the object to travel through the space faster than light.
Could you use the same principle for sending data? i.e. instead of a "warp bubble", have a warp tunnel? An almost infinitely thin (to minimise the size of it and therefore the energy required) line of shrunken space between the transmitter and the receiver through which data can be sent.
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It's simple, just invent a widgit that corrects for the quantum issues and use quantum entanglement for communication. Keep in mind that the Alcubierre drive itself has all sorts of issues within physics. As a nod to Star Trek you could even call them Heisenberg Compensators, since they did exactly that to explain how their teleporters work with the Heisenberg Uncertainty Principle.
Another option would be to say that the unmanned drones can travel much faster than crewed ships (maybe due to small size, lack of need to keep squishy organics alive, etc) so you could use drones and adjust the time delay to suit your needs.
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**As mentioned in your question**, quantum entanglement can't actually be used to send non-random information, as a result the only way to send things or information FTL is by using a warp drive (which still relies on theoretical negative energy that may not even exist).
**The warp drive is what you need to get FTL travel**, but it is also the only way to do FTL communication, if you had another way you could probably use it for travel as well.
**It seems the only way to do communications FTL** is going to be communication drones, but the drones would probably send their information in radio waves once they dropped out of FTL near their target.
**Intercepting communications** or stopping them would be tricky, at FTL speeds intercepting anything would be nearly impossible, but once they have dropped out of FTL messages would probably be sent with radio waves, which would entail using the same methods we use today.
**In addition** we *know* that the basic idea behind a warp drive doesn't break any laws like many other proposed FTL. We already know that space itself isn't limited to the speed of light, only matter and energy is. Galaxies sufficiently far away will never have their light reach us due to the expansion of space due to *dark energy*, to us they are effectively using a warp drive go FTL.
Warp drives are dependent on whether we can harness negative energy, but we already suspect that the fabric of space has negative energy as dark energy, but that would probably be impossible to harness since it's evenly distributed.
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Well, this kind of scifi is bending the laws of physics. Thus, you can fully legit use hypothetical particles which aren't proofed to exist yet.
So your solution is as simple as it can be:
[Tachyon](https://en.wikipedia.org/wiki/Tachyon)
>
> A tachyon /ˈtæki.ɒn/ or tachyonic particle is a hypothetical particle that always moves faster than light. [sic]
>
>
>
[...]
>
> They have been used as a standby mechanism upon which many science fiction authors rely to establish **faster-than-light communication**
> [sic]
>
>
>
A common mechanic is sending a tachyon beam to the communication target.
Behaves pretty much like any light beam (Just faster), can be detected or blocked by objects on their way.
**But even Tachyons would have a big problem.**
When the tachyon wants to reach a spacecraft from behind, it has to pass streched space, which will make it relatively slow, maybe so slow, that it needs aeons to reach the spacecraft.
**There are two solutions for this:**
1. Warp-drive is slower than tachyons by the manner that the time a tachyon beam needs to pass the negative warp-space is reasonable.
2. Spacecraft has to stop or throttle warp-drive to get the tachyon-delay reasonable.
First solution has the disadvantage, that the spacecraft has to move slower than it might could.
Second solution has the disadvantage, that you can't tell the crew "hey guys, I wanna talk to you, throttle down please." due you can't communicate currently. Thus, the spacecraft would have to throttle down periodic and the in-warp communication would have a protocoll like:
Once in t(xy) the spacecraft throttles to speed v(tachyon)-xyz), then communication is done, then the spacecraft accelerates again.
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Wormholes. Yea, wormholes. Some theories have them being created and destroyed at the quantum foam level ([Quantum Dynamics of Lorentzian Spacetime Foam](http://arxiv.org/abs/gr-qc/9309017)). For most things, this isn't practical. Its too small to even push atoms through - on the order of 1000x smaller than a proton.
However, one might be able to push light through it and allow for communication with the other end of the wormhole.
So, what you would do is grab one of these wormhole pairs that is constantly forming, and prevent it from being pulled back into where it came from. You put one end in the communication center on one planet, and take the other end to the communication center to the other planet.
There are some odd effects that would happen with wormholes that can cause some causality problems which one should be aware of. Lets take a wormhole and do a four year relativistic speed loop (that to the passage only takes a year). Now, the wormhole that traveled is three years younger than the one that stayed home. If you look through it, you would see three years ago (and on the flip side, if you look through the one that stayed home, you would see three years into the future). There are suggestions that this would cause it to [blow up before anything could happen](https://en.wikipedia.org/wiki/Chronology_protection_conjecture). There are possibilities of chronology violation with [rings of wormholes](https://en.wikipedia.org/wiki/Roman_ring) too where each end is not causality violating, but the combination is.
A system that wasn't causality violating would be a communication hub. Each colony has one, and only one, wormhole link to Earth (the location of the hub). Furthermore, colonies are prohibited to have wormhole links to other colonies (if they did, it would form a loop, and with FTL in there would have some causality violation and the virtual particles would pile up on a closed space time curve and cause an excess of energy density which, well, goes 'boom'). This would allow for some imperial censoring and such.
References of hard science fiction with wormholes:
* [The Light of Other Days](https://en.wikipedia.org/wiki/The_Light_of_Other_Days) Stephen Baxter based on a synopsis by Arthur C. Clarke (the wormholes are photon sized)
* [Time Master](http://rads.stackoverflow.com/amzn/click/0595197590) by [Robert Forward](https://en.wikipedia.org/wiki/Robert_L._Forward) - full of temporal paradoxes and larger than photon wormholes but has interesting bits on the wormholes (it starts out with "If I receive a letter from this sort of person complaining about the "impossibility" of the time machines in this novel, I will throw the letter in the nearest wastebasket . . . *unless* the letter is accompanied by a reprint of a scientific paper published in *Physical Review* (or any other reputable, refereed scientific journal), written by the person writing the letter, which *proves* that the paper "[Cauchy Problem in Spacetimes with Closed Timelike Curves](http://authors.library.caltech.edu/3737/)" by Friedman, Morris, Novikov, Echeverria, Klinkhammer, Thorne, and Yurtserver, is erroneous.")
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Superstring theory postulates that said "strings" are producing worm holes. While too small and volatile to send humans through, information COULD potentially be transmitted through said strings. This kind of goes along with @colmde in relation to small tubes/tunnels instead of bubbles.
Here is a quoted segment on this topic, but Michio Kaku:
"...as a string moves in time, it warps the fabric of space around it, producing black holes, wormholes, and other exotic solutions of Einstein’s equations."
And a useful page of information with more on the topic where the quote was found:
<http://mkaku.org/home/articles/blackholes-wormholes-and-the-tenth-dimension/>
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The bulk of communication can be carried by untrusted traveler ships at reasonable prices, with drones as an expensive fallback in case no-one is going.
Cryptography (heck, even *today's* cryptography) can guarantee no eavesdropping and no tampering with messages. The worst a malicious ship can do is not deliver, in which case it won't get paid.
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This is an idea I was going to use in an erstwhile project. It's softer sci-fi than Alcubierre drives, but it might suit.
A special device opens a tiny wormhole to a microscopic pocket universe. These devices are such that a connection can be opened to the same pocket from anywhere in the universe. EM waves can be sent and received, but nothing larger goes in or out.
Again, I'm not sure if this is too soft for you; wormholes are postulated to be possible, as are subatomic black holes, and white holes. Put them all together and there you are.
It also opens some interesting possibilities from a narrative perspective - can they be hacked, how much energy does it take to open the connection, are there limitations in creating/discovering pockets, etc.
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It's true that quantum entanglement cannot be used to send messages. The problem is well explained elsewhere, so I'm not going to dig too deep into it. However, there is a way around this - all you need is a device that destroys the universe.
Say you want to send a message `110`. You have a particle pair that's entangled, so by reading your particle in the pair, you know what the *other* end will read. You'll need to read the particles at predefined intervals and find a way to prevent the entanglement from propagating (it's not really entangled-not entangled, it's more like entangled with one or two other particles versus entangled with billions) - that's a great place for some handwaving. But let's suppose that's solved - you simply found a way to isolate the partice well enough that you only have the two entanglements - one to your sensor device, and another to the other side of the telegraph.
Now, you only have a reader. How do you use it to send messages? Simple!
Read your particle. Does it show `1`? Awesome, bit of data "sent". Does it show `0`? Destroy the universe. This way, the only universes that survive are the ones where the other side reads exactly the data you wanted to send! It may sound brutal, but don't forget that an infinite number of universes dies every second anyway, so you're just exploiting the natural behaviour for your own purposes ;)
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You could use the Well-established sci-fi technology: the ansible.
The technology is based on the idea that dimensionality is fictional under some restricted mathematical topologies, which provides an opportunity for non-transit communication.
Your deliberations are correct. Quantum physics requires that a breakdown of causality causes a singularity, and therefore superluminal communication of any sort is barred.
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Consider a scenario where there is an over-populated solar system (not necessarily *our* solar system). Several other rocky planets and moons in this solar system are inhabited by the same humanoid race, and every planet's population is reaching its [Malthusian limit](http://en.wikipedia.org/wiki/Malthusianism). It's not too hard getting things into space (via a space elevator, or something like it). Travel between planets is also relatively easy, but travel outside of the system is not feasible. Attempts have been made, but nothing successful has come of it. Limits on reproduction are enforced, but population culling would be considered unethical and war is uncommon.
Besides over-crowding, every planet in this system has had a serious waste management problem. In order to combat this, for the past 50-ish Earth years, each planet has been shipping its garbage into space. Let's assume that this "cosmic dump" lies outside the effective reach of any nearby gravity well, and the trash itself isn't really moving through space at all.
Leaders and committees of the various planets have come up with an idea to deal with the rubbish that is filling up space *and* perhaps help relieve the population crisis.
The idea is this: take all the garbage that is floating around space and bring it to a massive asteroid. Using the asteroid as a core, they'll dump all the garbage onto the surface, making it somewhat larger.
For some rough Fermi estimations, let's assume we have:
1. 50 earth years worth of trash
2. 10 billion people on each planet
3. 10 inhabitated planets
4. Each person produces 2 tons of waste per year
This comes out to be about 10 trillion short tons, or 9.07185x10^15 kg of material. The largest asteroid in our solar system, Ceres, is 946x10^18 kg. Using that as a figure, and adding the waste our trash planet would be about 9.4600907x10^20 kg. Let's also assume that the contents of the waste are distributed as per <http://www.epa.gov/epawaste/nonhaz/municipal/>.
I'm guessing gravity would be pretty low on trash planet. Feel free to play with the numbers a bit to make it larger, if necessary. Also, please don't focus on the holes in my scenario - it can change...my main question is, could trash planet support a population? What if we added nuclear waste, let's say 1 billion kg of it? How would that change habitability? If trash planet is habitable, would the population it could support even really help reduce the strain on the other planets?
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**Could the trashteroid support life?**
Your trash planet (Well, not really a planet, since it isn't big enough to clear its orbit. We'll call it a trashteroid.) is as habitable as Ceres is. Covering Ceres in trash still leaves it as a lifeless, atmosphereless lumpy asteroid being baked by solar radiation. Ceres would be, as it is now, completely inhospitable to life. Solar and cosmic radiation would quickly bake all of the trash you dumped there into sterility, while it was simultaneously frozen and dehydrated by the icy vaccum of space.
You would not want to go there for summer vacation.
Unless, of course, you had a space station built there.
**Life on the trashteroid (in a space station)**
You could, of course, life there in a space station. Life on a space station on Ceres could be enjoyable, in a sense. You'd effectively be living in space, but with a tiny amount of gravity to hold you down to the floor. Ceres has a gravitational pull of $0.27 m/s^2$, which is about 1/40th that of earth.
You couldn't really enjoy jumping around in that gravitational constant all that much, since you'd be stuck inside all day, and your space station wouldn't be likely to have high ceilings. You could, of course, go outside in a space suit, but why would you want to? Everything outside is covered in trash.
**How much trash would you need to make an inhabitable planet?**
Let's assume that our trash is gassy enough to form an atmosphere in which a Mars-sized planet could be inhabited. Mars is about 1000 times as massive as Ceres. Ceres is about 100,000 times as massive as the trash we've already dumped there, so we'll just need to dump around 100,000,000 times as much trash to have a reasonably sized planet. (Let's assume we're using worm holes to dump the trash of every planet in the Milky Way on Ceres.)
Our new planet, based on the composition of garbage, will have a *ton* of carbon, and as such will probably be able to support a large, healthy biome, once it cools off. Why does it need to cool off? Well, dumping that trash onto the planet is going to release lots of kinetic energy. The first few thousand loads will go on easily, since the gravity is so low, but the more garbage we dump, the higher the gravity will be, and the more energy the trash will release as it drops from space onto the surface of the planet. That energy will turn to heat, which will be further increased by the billions of kilograms of radioactive waste you're planning on dumping as well. They planet may well liquify, but it should cool down in a few million years into a nice habitable planet. (Provided you stop dumping garbage on it!)
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Yes, that planet could support population. But population would need independent life support system, aquaponics, etc, exactly as if it was build in empty space. Trash will support only gravity and nothing else (maybe some radiation pollution to boot).
But it would be rather expensive way to build a planet: lifting all that trash up the gravity well will take lots of resources. Even with space lift, lifting trash up is easy but not free. Spending rocket fuel to direct all that trash flying in space to target asteroid is not free either. Recycling trash on the planet would be much more energy efficient, and better use of planet's limited resources.
And if you want to use resources and material, you can get more livable space by building more traditional orbital space colonies, where gravity is provided by rotation. You can settle more people for ton of material spent (but that material cannot be trash)
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When a civilization reaches that point, recycling all those useful atoms would be much more likely than throwing them all away.
At this point I would also expect in order to get more living space that they would start making a ring around the planet or a Dyson swarm, this would also help in catching energy from the sun. A ring around the planet could have a huge living surface at a fraction of the wasted material churning away in the center of the planets. Rolling earth out like pizza dough to a thin couple hundred feet would give plenty of living space for a much larger number of citizens.
So while you could 'make' a planet with garbage, it would be as pleasant as building your house on a land fill and actually fairly wasteful.
[Answer]
**Intrastellar Nuclear Waste Disposal Company**
Founded 22-feb 2103 by Sophia Musk. The urgency of global nuclear waste disposal created a market. Most countries could not afford a Tokamak and had to resort to nuclear fission plants, replacing fossil fuel and providing electricity. A stack of nuclear waste had grown in 80 years, the sixth generation of nuclear plants..
**The sun is no option**
Until then, governments had considered shooting waste into the Sun, but they were reluctant to use heavy space transports, for fear of responsability claims, when something would go wrong. So they had "stored" their nuclear waste in controlled facilities, on Earth. *Expensive* facilities.
Part of the problem was political. A solution for Uranium and Plutonium would also need to serve the wishes of fission-believers, who assumed that in due time, all nuclear waste could be recycled. So they wanted to keep it at hand, not waste it by shooting it into the Sun.
**Orbit**
Musk filled the need, by providing a very safe launch procedure, and a huge load capacity. Their ships were launched off the Greenland south coast, filled up with high active nuclear waste. With Musk's method, there was no need to travel all the way to a Lagrange point, to push the waste into the Sun. The containers were released in a 3800 km equatorial orbit above the surface, stable.. they hoped
**The Sydney disaster**
In 2134, after the third Civil war, without any means to prevent disaster, one of the containers came down, as a result of an unfortunate meteorite impact. In most cases, falling satellites end up in the ocean somewhere, not in newspaper headlines. But now, the container impacted the suburbs of Sydney. 400 square kilometers and 12 million inhabitants of Sydney had to be evacuated, permanently. A major economic crisis hit Australia.
**Let's repair the situation**
Musk's company, which was destroyed now, spawned a few experts that were happily employed by NASA. They set out a plan to tug the remaining containers into a higher orbit. The new orbit was 120.000 km, about half way the Moon. The containers were moved to a single location and in the years, all kinds of additional waste was dropped on the assembly. Chemical waste, fracking waste from the past, mining waste, frozen CO2..
By the year 2409, the "new moon" had grown considerably in volume. Tugging it toward the sun would be a very expensive operation now. Earth had a useful second moon, visible from the surface. A Venus-lookalike celestial object between Earth and moon, weighing about 1.6x10e15 kg.. glistering in various colors.. because of the dust clouds surrounding it.. *ever growing*..
[](https://i.stack.imgur.com/JIR4K.png)
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This was spawned from this [question](https://worldbuilding.stackexchange.com/questions/4190/being-cooked-for-dinner-or-what-danger-of-blueshifting-em-into-x-rays-and-beyon) about Blueshifting (BS) when traveling near the speed of light.
I had found this while learning about the other question.
@99.99995 percent c
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> And interestingly, the students also realized that, when traveling at such an intense speed, a ship would be subject to incredible pressure exerted by X-rays — an effect that would push back against the ship, causing it to slow down. The researchers likened the effect to the high pressure exerted against deep-ocean submersibles exploring extreme depths. To deal with this, a spaceship would have to store extra amounts of energy to compensate for this added pressure.
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So then I began to wonder, I am assuming the higher the EM energy to begin with the more 'pressure' is exerted back, starting with X-Rays, they'd be BSed to Gamma and they would cause more pressure than visible light pushed back to soft X-Ray.
If that assumption is correct would a star going nova with a gamma ray burst cause enough pressure to throw a ship way off course? And would it be (reasonably) possible to cause a 'burst' large enough to push a ship off course (assuming we already have the tech to go near the speed of light).
On top of that, if you have a gamma ray machine and point it at a ship going at .9999995 light speed would Newton's 3rd law kick in with an equal and opposite reaction? Because if so, then we have an other issue, Mass increases with speed and near the speed of light it would be downright dangerous for anything in its path.
[Answer]
Let's first do some math, the first part taken from [this pdf](http://www.webassign.net/question_assets/buelemphys1/chapter22/section22dash3.pdf) regarding (solar) radiation pressure (the formulas should be applicable from any source of electromagnetic radiation).
The intensity $I$ depends on the power $P$ and the distance from the source $r$. We can write the expression
$$I=\frac{P}{4 \pi r^2}$$
The force $F$ depends on the intensity and the area $A$ of the object being buffeted. It is
$$F=\frac{2I}{c}A$$
and, substituting, we get
$$F=\frac{2P}{4 \pi r^2c}A$$
which is
$$F=\frac{P}{2 \pi r^2c}A$$
Given the mass of the ship $M$, we find that the acceleration $a$ is
$$a=\frac{P}{2 M\pi r^2c}A$$
How much power does a gamma-ray burst emit? From Wikipedia:
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> Because their energy is strongly focused, the gamma rays emitted by most bursts are expected to miss the Earth and never be detected. When a gamma-ray burst is pointed towards Earth, the focusing of its energy along a relatively narrow beam causes the burst to appear much brighter than it would have been were its energy emitted spherically. When this effect is taken into account, typical gamma-ray bursts are observed to have a true energy release of about 10^44 J, or about 1/2000 of a Solar mass energy equivalent—which is still many times the mass energy equivalent of the Earth (about 5.5 × 1041 J).
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We have to divide this number by two to account for the fact that only one of the two beams is hitting the ship - and this is still a little inaccurate, as it assumes the ship is hit by the whole beam. Anyway, gamma-ray bursts, on average, can last from [anywhere between less than a second to 30 seconds](http://en.wikipedia.org/wiki/Gamma-ray_burst#Classification). Let's say ours lasts for 10 seconds. Because the definition of power is $\frac{E}{t}$, where $E$ is work and $t$ is time, we can say that the power here is
$$P=\frac{E}{t}$$
$$P=\frac{5 \times 10^{43}}{10}$$
$$P= 5 \times 10^{42} \text{ Watts}$$
Plugging into our earlier equation for acceleration, we get
$$a=\frac{\frac{E}{t}}{2 M\pi r^2c}A$$
$$a=\frac{ 5 \times 10^{42}}{2 M\pi r^2c}A$$
Assuming a mass of the ship similar to the [Space Shuttle Orbiter](http://en.wikipedia.org/wiki/Space_Shuttle_orbiter) (109,000 kilograms) which is admittedly an unlikely comparison, we make this
$$a=\frac{5 \times 10^{42}}{2 \times 1.09 \times 10^5 \pi r^2c}A$$
$$a=\frac{5 \times 10^{37}}{2.18 \pi r^2c}A$$
If you want, you can plug in the area of the underside of the Space Shuttle Orbiter (a stat I can't find, at the moment) and discover that the space shuttle would take quite a hit if it was near a gamma-ray burst.
*Note that this is only valid for a ship traveling at a slow speed. At near-light speeds, the relativistic mass would increase (although I don't know if this is valid perpendicular to the direction of its initial motion). This would impact your calculations; I'll try to figure out the corrections later.*
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**Belated Conclusion**
The answer is a definitive yes. A ship moving at "normal" speed (i.e. something we could make today - think a successor to the space shuttle) would meet some severe buffeting if it was anywhere near a gamma-ray burst and was hit by one of the beams emitted from the progenitor. If it was hit full-on, it would be severely pushed back; if it was hit partially on, it could be sent spinning. Either way, things wouldn't turn out well.
Your ship, though, is a bit more advanced and is traveling at a speed pretty close to $c$. This means that it is highly unlikely that it would get hit with the beam for an extended period of time if it was anywhere close to the source. If it was further out, the cross-section of the beam would be a lot larger, though (eventually, on the order of hundreds of thousands of miles), and the ship could continue to travel through it for the duration of the burst. The downside is that the energy would be greatly dissipated over the beam's cross-section.
But the answer is yes, the sip would be buffeted if it was reasonably close (i.e. about an AU away, though that's an estimate) to the source, and would most likely be impacted in some way if it was further out.
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SJuan76 and Oldcat pointed out that [Lorentz contraction](https://en.wikipedia.org/wiki/Length_contraction) would impact the area of the side of the ship receiving radiation pressure if the ship was moving tangentially to the beam. At speeds nearing $c$, this phenomenon would have huge implications for the pressure on the ship. This answer is already math-heavy, so I figure adding a few more equation can't hurt. Haters of algebra beware.
The length of an object due to Lorentz contraction can be found by
$$L=L\_0 \sqrt{1-v^2/c^2}$$
This means that the area (previously the height times the length, $A=H \times L$) is now written as
$$A=H \times L\_0 \sqrt{1-v^2/c^2}$$
and so the original equation becomes
$$a=\frac{5 \times 10^{37}}{2.18 \pi r^2c} \times H \times L\_0 \sqrt{1-v^2/c^2}$$
[Answer]
I suppose I should take my comments and make them a response.
First - if a gamma ray burst has no effect on changing the course of a ship at rest, it will not have any greater effect on a ship at near-light speed. So lets assume this burst would not shove a ship at rest at all. What about all the blue-shifting?
The blue shifted extra momentum will all be in a direction that *opposes* the flight of the near-C ship. When you change frame to the rest frame of the ship, the energy and direction added will be directly opposing the flight path. So if this blue shift does anything, it merely slows down the ship and does not 'knock it off course'.
Second Case - The burst *would* add a significant kick to an at-rest ship.
When the ship is traveling at near C, the impact of this kick is **reduced** in a number of ways: first the mass is greatly increased, reducing the sideways velocity resulting. The Lorentz contraction reduces the apparent area of the ship, which might reduce the ability of the storm to push the ship off course.
It would take an amazing impact to still push the ship off course, but it could possibly happen. But the near light speed does not make it worse.
The one thing that *would* be massively increased is the in-line "braking" momentum of anything that the fast ship ran into in flight. But I wouldn't consider a slowing, or a requirement to fire the engines more to overcome it "knocking the ship off course".
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Imagine a world with a very wacky magnetic field, the magnetic poles are not aligned at the top of the axial tilt and the sun is active enough to cause huge northern lights each night.
I know electronic systems would fail but would a compass still point at the magnetic pole or would it be rendered useless by the major solar activity?
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Yes, it would mess up your compass systems. [Geomagnetic storms](https://en.wikipedia.org/wiki/Geomagnetic_storm#Navigation_systems) (which is what high solar activity is called) mess up compass navigation. These storms are what cause the auroral display to be seen at lower latitudes, and they have been proven to throw compasses off. They may not be entirely useless, but it could be thrown off by several miles.
This behavior of compasses was first noticed by Alexander von Humboldt. Humbodldt recorded compass bearings in Berlin for a year, from May 1806 to June 1807. On December 21, 1806, he noticed that his compass had become erratic during an auroral event.
Note that a stronger magnetic field would help protect against these magnetic storms.
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I know I'm late to this but it needs a map.
The problem is that simple magnetic compasses are fairly approximate anyway, they don't show direction by the global magnetic field but rather by the local one. For it to be truly useful over large distances you also need a map of [Magnetic Declination](http://geokov.com/education/magnetic-declination-inclination.aspx). An up to date map shows how wrong your compass is at your current location.[](https://i.stack.imgur.com/733Wv.jpg) (Map source is link above)
As you can see, the magnetic fields on our planet are pretty wacky even at the best of times.
It's well known that the magnetic poles move, so it's important to have an up to date map, however:
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> New research shows the pole moving at rapid clip—25 miles (40 kilometers) a year.
> <http://news.nationalgeographic.com/news/2005/12/1215_051215_north_pole.html>
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It was previously thought to be about 10km/year.
and just to add to your troubles:
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> On any given day, the magnetic pole may be as much as 80 kilometers away from its average position, depending on the geomagnetic disturbances in the ionosphere and magnetosphere.
> <http://www.scientificamerican.com/article/are-the-earths-magnetic-p/>
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In answer to your question, your simple magnetic compass is pretty useless without a lot more data.
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If a planet had such a large imbalance of protons and electrons that it possessed a net negative or positive charge what would happen to it and its solar system?
First, could it be stable, or would it simply disintegrate? Would the charge act against the pull of gravity and make everything on the surface weigh less?
Second, what effect would the charged planet have on its moons, neighboring planets, or sun? Would it polarize them, and how would it affect their orbits?
Third, what would the chemistry and biology be like on the planet's surface? Could life develop. Would the chemical reactions possible be radically different? Would elements exist in different forms?
Finally, what would happen to something that got too close like an explorer's spacecraft?
[Answer]
I don't mean to disappoint you but planets are already charged - all bodies in space have a voltage that depends on their immediate environment to the degree that they interact with it through the interplanetary medium, which transfers charge to an extent.
Being isolated most of the time, they develop a potential compared to other objects due to the balances within their immediate environment being satisfied but by not having contact with other objects, their relative potential doesn't balance because their charges don't interact.
This is why in electronics and electrical engineering, two points cannot be compared in terms of their voltage, unless they share a point, usually ground. An example would be two batteries - while the voltage between their ends can be approximately the same (lets say 5V), if they're isolated from each other completely and you place a wire near them with a high enough voltage to overcome air resistance (say, 50 kV), against one there might be a spark, but not against the other, at the same distance (provided you kept the wire at a constant voltage). While this is unlikely to happen in the same room, due to the air balancing out charges through interaction and friction, it *is* possible to observe this difference experimentally. The ground in England is not the same ground as in Italy - but the voltage between the ends of batteries will be.
In much the same way, if two celestial objects where to pass close enough to each other to interact electrically, there would be huge lightning bolts. You don't see this often with asteroids because they don't often pass close enough to other objects and because given enough time in the same environment, their effective potential balances out.
But to answer the question, a planet *can* and *does* have a net charge - it's not something exotic, it would be exotic if it didn't.
1. Celestial objects are too far from each other to interact electrically this way, although they do interact through the interplanetary medium, albeit at a much smaller degree
2. Electricity and gravity don't interact the same way with matter. If a planet had a net charge, everything on it would share that net charge. Unless we're talking about a huge volcano (where events are violent enough to cause lightning), a thunderstorm, a tornado or an earthquake (where separations are again violent and there's a lot of friction involved), you wouldn't see much of a difference. Also magnetism is not electricity - they're related but not the same effect - unless the magnetic poles shifted dramatically (which does happen but never abruptly), you wouldn't notice much changing.
3. It would have as much an effect as it has now, on other bodies - the Sun controls most of what happens with charge within the solar system as it has the most powerful charge flows and emissions. It's hard to imagine a planet having a stronger effect on the charge of its surroundings than the star they orbit. Even if it *were* to happen, only the planet would face the consequences, not even moons.
4. Life would be no different - in fact, lightning is considered to be part of the necessary ingredients to get life and in the primordial Earth, we probably got tons of it all the time. With time, life adapts, the atmosphere stabilizes and things work out fine. The elements would also be the same, chemistry would be the same.
5. If the spacecraft entered the planet's environment too fast, it could get struck by lightning when it enters the higher (near space) layers of the atmosphere. But that would be easy to mitigate by just slowly adjusting its orbit until the potential is equalized, provided the pilot was prepared for this case.
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> *Also, check Richard Tingle and supercat's comment's down below for more perspective.*
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[Answer]
The [earth](https://physics.stackexchange.com/questions/91556/is-the-earth-negatively-or-positively-charged) already has a minor negative charge. This is what causes [lightning](https://answers.yahoo.com/question/index?qid=20100929082548AA6zwU8). However, overall the planet is very close to neutral when combined with the atmosphere.
I do not believe that an electrically charged planet would be stable. The electromagnetic force is orders of magnitude stronger than gravity. If the planet were charged, I believe the planet would immediately stabilize. There are so many free electrons and other particles coming from the sun that the planet could use to revert to neutral.
Even if a planet didn't quickly revert to a neutral charge, how could you create a charge on a planet? The electromagnetic force is [effectively conserved](http://en.wikipedia.org/wiki/Charge_conservation). (Technically you can could chuck unwanted charge into a black hole and get an imbalance that way but that's a whole other can of worms.) Electrons and protons come in a pair and the electromagnetic force is very strong. What force would strip the protons and electrons apart, leaving one on the planet and driving the other far enough away that it didn't merge back into the planet? Given this, I don't know of any way to generate a large enough charge on a planet to be interesting.
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Sure, a planet could have “a few” too many or too few electrons to be exactly neutral, but such would be on the same order of magnitude as the separation of charges within different parts of the planet.
If you're thinking of a charged planet throwing lightning bolts to other worlds, or having electromagnetism play a noticeable role in its orbit (like in some of the later works of James P. Hogan), that would not happen. A strong charge would neutralize itself far faster than geologic time scales.
Consider an airless body like our moon. It is bombarded by particles from the solar wind, and UV radiation can knock out electrons. Why doesn't the moon build up a charge that keeps growing for billions of years? At some point incoming charged particles won't stick but bounce away, and charged particles are shed.
In a body like the Earth, the geomagnetic field shields against most of the solar wind, but if the Earth somehow had a large charge, it would preferentially lose charged particles in the air that slowly leaks away to space; or would strongly repel charged gas molecules and outgas quite rapidly.
[Answer]
Other answers are correct in saying that (a) celestial bodies generally do have a non-zero charge and (b) if a planet were very strongly charged then it would quickly suck opposite-charged particles from the solar wind until it was approximately neutralised.
But suppose an Earth-like planet *did* magically have a strong permanent negative charge. You have a surplus of electrons, which repel each other, so broadly they will try to spread out as thinly as possible. If the charge is completely evenly distributed, then things aren't so different to Earth, except that the ground voltage is much lower than on Earth, though you wouldn't know it unless you ran a cable between the two planets.
The excess electrons mean that the formation of negative ions is easier, and the formation of positive ions is harder. So I guess, crudely speaking, the planet will be a little more alkaline. The relative rates of various chemical reactions will be slightly different, but all the same chemistry will exist.
Weather would be different. Because different gases can hold different amounts of charge per unit mass, I believe the movement of wind would cause the excess charge to become unevenly distributed, resulting in lightning. Also, the atmosphere would eject more gas into space – the negatively charged planet will repel negatively-charged gas ions. (This is also one of the ways the planet would shed its excess electrons IRL, but we are stipulating that the electrons get replaced somehow). Because of this, the atmosphere would be thinner.
[Answer]
While the other answers covered this realistically I think you can take another spin on it. For a **large** net charge I believe you'd have some interesting effects. (the following is based off logical reasoning on the bold item scaled up to planetary sizes).
**Thinking of the atom:**
It would be stable up to a very large charge just due to the weight. At larger charges the the center might become less dense but the surface gravity would not be effected.
**Thinking of an electric generator:**
If objects were oppositely charged they'd probably generate magnetism in the negative object, huge electrical storms, and possibly arcs if close enough. They would at the very least generate an ion stream. It would change the distances and speeds of the orbits but would not effect the shape.
**Thinking of Ionizing Radiation:**
Life doesn't like ions and you have a lot of them flying around, especially if the flow is *from the planet* instead of *from the sun*. So you'd probably have none of it. As the percentage of charged particles increased the chance of forming compounds would go down as nothing would be forming ionic bonds and two ions don't really like to form covalent ones. I don't know about planetary-sized objects, but at least for star-sized ones you'd have some very different materials than normal in the core, as they would bond despite charge.
**Thinking Dust Wiper:**
We have materials such as microfiber which exhibit electrostatic adhesion (there's a name for this type of material if someone can find it), and your charged objects would behave just like them, pulling in oppositely charged objects and probably trying to ionize the other object and end up pulling it in anyway (like amber does when it exchange charge). So expect any passing ships to stick to your planet like tape.
[Answer]
Well, if you live in Europe, you might see three holes in the plug in the wall.
The bottom one is GND (Ground). It is connected to earth. It is meant to be so, so if a lightning strikes the building, it will not pass the charge to US but to EARTH.
The earth's core is filled with liquid metal, and this generates some electric charge, mostly negative one - it has more protons that electrons. The earth itself is generating electricity, and some of it comes from our activity as humans, and lightnings.
Best of Regards,
Itay
Tip: In a lightning storm - never play golf :)
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> **NOTE:** The offered "duplicate" question ***IS NOT WHAT I AM ASKING.*** Alternative methods of navigation ***ARE NOT ACCEPTABLE*** as answers. I am specifically asking whether or not a ship traveling in the method described could re-identify the destination star on approach because the perceived light of the star with each jump is "aging" as the ship approaches the "current age" of the star. Don't let @SlowlySwift's obsession with navigation fool you (he deleted his answer) and don't let the reason *why* I'm asking the question distract you.
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In the future, humanity develops what we'll call "hyperspace technology." Basically, a starship can "jump," whether it be via wormhole or any other fanciful idea, from one location to the next a considerable distance away in a very short period of time from Earth's frame of reference. Please accept this as a given. The technology and the rules of that technology are not relevant to the question.
A ship decides to travel from Earth to a world eight-billion light years away. From Earth at the time the ship is launched, we're seeing light that's been in transit for eight-billion years.
The ship must make 100 jumps to get from Earth to that distant world (an arbitrary number for the purpose of the question). No navigational technology is perfect because no knowledge of everything between here and there can be perfect. Therefore, the ship arrives at the termination of each "jump" and must re-determine its location in space before plotting and executing the next jump.
*If you're thinking this sounds a lot like space travel in Asimov's "Foundation" series... I've been re-reading it recently and it's definitely an influence on the question.*
With each jump of approximately 80 million light years, the light from the star the ship is approaching gets "younger," meaning that it's traveled less distance, and it represents a star that's getting perceptually "older," meaning it's true age from day #1 of the universe vs. the very young age we see through a telescope from Earth.
**Question:** Since the age of the star in question is getting older as the ship gets nearer jump-by-jump, is the spectral description of the star stable enough or predictable enough to remain entirely identifiable and therefore useful for navigation? In short, can I find it and point my ship at it after each jump?
My goal is to choose how "local" a star chart must be based on today's understanding of solar physics. In short, can someone travel the entire distance without the need of a star chart other than the data acquired on Earth? Or must they pick up the local star chart at, worst case, each jump to have their destination re-identified?
I recognize that a second problem is that over that distance, the star is "moving," meaning where is is "today" when the ship launches from Earth is very different from where it is "then" when the ship arrives, eight billion years into the star's future as perceived by its light from Earth. I'm ignoring that right now because (in my world, if not in reality) the motion of stars is more predictable than the motion of a space ship. I recognize that if the answer is along the lines of, "finding that star at each jump would be whomping difficult," that it would means very-long-distance travel without the aid of localized/regionalized star charts from earlier (and much slower) exploration would be next to impossible as all of the stars's apparent ages and locations are changing substantially over that distance.
I also recognize that at that distance it's plausible that the star has gone nova or some such fairly inconvenient thing, which the travelers will discover as they jump. Or would they? As a bonus question, but one no one is obligated to answer, can the original star be detected in the nova remains for the purpose of navigation? We'll assume the travelers still want to get there. Hopefully they'll be in a hyperspatial jump when passing the advancing cloud of destruction.
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Let's start with what we know about [stellar evolution](https://en.wikipedia.org/wiki/Stellar_evolution). Stars coalesce from a mass of gas, mostly Hydrogen, with some Helium and other trace elements, and begin to fuse Hydrogen to Helium. As they age, the Hydrogen runs out, and they begin to fuse their Helium to heavier elements, until they get to Iron. Depending upon their mass, they then either become a dwarf star, or a supernova that leaves behind a neutron star or a black hole.
The time that it takes a star to do all of this depends largely upon its mass; the more massive a star, the faster it fuses its fuel, and the shorter its life. Stars with classes O, B A and some F - blue to white stars - have been determined to have lifespans under 8 billion years.
Thus, if one of these stars was selected as the target for our ship, *it would most likely no longer exist by the time the ship arrived.* Whatever was left would be so different that there would be no practical way of determining that it had once been the star the ship was aiming for.
Alternatively, if the navigator on the ship was aware of this, and aimed for a high-F or any G, K or M star, whose lifespans are expected to exceed 8 billion years, and in the case of M-class stars may be trillions of years, then matters are a little different.
To answer the question if one of *these* stars is selected, we must understand [stellar spectroscopy](https://en.wikipedia.org/wiki/Astronomical_spectroscopy). Put in simple terms, the elements present in the atmosphere of a star emit and absorb radiation in such a way that its spectrum can be used to determine its chemical composition. We can say that a star contains whatever percentages of H, He and other elements.
However, we know that over the lifetime of a star, fusing of elements from Hydrogen to Iron results in lighter elements being consumed and heavier elements being created. This will result in the spectrum of the star changing over time.
Now, humans have been studying the spectra of stars since the 1800s... for maybe 200 years. That is a miniscule drop in the bucket of even a short-lived star's lifespan. We can *speculate* but cannot *know* how the spectrum of a star will change over its lifespan, because we have not been studying stars long enough to observe any significant changes. M-class stars, being very long lived may not change significantly, but hotter stars may.
The next problem that we will encounter is a result of the 80Myr jumps. Over this amount of time, the positions of the stars within the selected galaxy will change significantly, dependent upon local gravitational effects and the gravity of the central super-massive black hole. The chaotic movement of the stars will mean that it will be difficult to locate a single specific star within a galaxy, especially if it is a M-class star, which are the most common type of star. It'd be like trying to locate a single, specific piece of hay in a haystack... where vermin regularly nibble on the hay.
So, my answer is that unless a great many more shorter jumps are made, so that a specific star can be tracked with a reasonable expectation of success, the lack of definitive knowledge as to how the spectrum of a star will change over this amount of time will mean that it is unlikely to be possible to use it as a navigational reference... if the star even still exists by the time the ship arrives.
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I say quite a ton of imagination is required to outline such a journey, but I have gathered enough data over my astronomy reading to say this:
**Not possible**
First, from 8 billion light-years you do not see individual stars, only galaxies and in rare cases globular clusters of new stars (usually new, as they are the brightest), because of low light intensivity and general angular proximity of various objects contained in a galaxy to each other when viewed from this far. Even if you'd assemble a galaxy-wide interferometer out of several million ships, even assuming they know the distance between them and can use smaller shuttles to carry over information in essential FTL connectivity by pigeons, you won't be able to discern a single star, let alone a planet around it. Assuming that you did that...
Second. After the very first jump you are no longer able to receive interferometry larger than what you've brought with you, thus you would be left with only a general direction to the galaxy with your world, together with any gathered data about its spectre, distance from center (if discernible, assuming yes) and probable orbital period in the galaxy (assumed no, as discerning a star could be done via spectral filtering, but detecting its lateral velocity would require orders more magnitude of sensitivity). So you will no longer see the star. Also you will likely be hitting an issue of changing Hubble constant, so that everything around would get slightly shifted to blue end of spectrum, as the current hypothesis is that the universe is expanding with acceleration. Such an adventure would require exact knowledge of Hubble constant's behavior over the life of the universe.
Next, after three or so jumps of 80 MLY each, you will no longer be able to use galaxies in the local group for exact positioning, as well as directing yourself forward, because they would have been detected at wrong (moved backwards) positions in the local sky sphere, that alone would require recalibration of the entire model of the universe, and using the recorded data won't do much to provide your exact location in the space, since everything would have moved, sometimes unpredictably, as exact motion reversion is impossible due to error accumulation. Yet the journey would still be far from over, as you would still be able to discern the target galaxy among its neighbors, and advance in its general direction.
However, you might have encountered an issue that a close (angularly) galaxy would obscure your target after another jump, so that you might mistake that one for your target and start approaching it instead. Also your target galaxy also moves, and the closer you get, the farther it would be visibly moved from being dead center, thus you would be required to verify if your target is still "there", and the "there" you see is still the galaxy you're about to visit. This would prove sequentially harder, as stars in that galaxy would change over time as fuel in them would burn out, nova/supernova events could cause minor disruptions to the overall galaxy image, etc.
There is another thing you might not have foreseen with that 8BLY galaxy, that is galaxy collision event, like what happened to M32 when it came close to M31. Stars in there were partly dispersed into open space due to galaxies not being uniformly dense, and with initial measurements you won't be able to determine relative speeds of galaxies in the local group of the target, if any, so that another event that would spoil your mission would be another galaxy coming close to the target one, causing some stars to change their course and even be thrown out of both of them. Not just that, but during the collision of two galaxies many stars end up in the active center of either galaxy, essentially getting eradicated into a central black hole, and with the initially scarce information about your world you will be pretty unsure at where to seek the star should this happen.
But, assuming no galaxy-wide destruction has happened to the target galaxy, you will essentially be at a loss at the very last jump, because from 80 MLY away from destination you don't have enough data on the target galaxy's own revolving motion, and given that Milky Way's revolving (at our distance) about 1 full circle over 225 million years, you won't be able to predict where should the star exactly be when you jump into the galaxy (but, you will be able to find it from this distance using some large interference grid of telescopes, if there's still something to find), as 80 million years would translate into abot a quarter to a half of a revolution of the galaxy, if it's similar to Milky Way, and a random but significant number otherwise. Your ship would have to spend some hundred years determining the actual revolution speed of the target star with enough accuracy to not miss the destination with the next jump, or use several smaller jumps gradually reducing the distance to the target in order to increase final jump's precision. (EDIT: 1/4 of a revolution is largely predictable, say doing a jump 79 MLY instead of 80 to leave 1 MLY left, or say leave half a galaxy radius between the ship and the estimated area where the target star would likely be, to properly discern the star from above the galaxy plane - quite doable. So this part of the argument is eliminated, yet there could be troubles when properly employing this part of the plan, so let it still hang in here for analysis.)
But even then... will you ever have something to find out there? 8 billion years is about the entire length of a star's existence in the main sequence, thus if your star was initially anything other than a red/brown/white dwarf, aka something that would remain stable over 8 billion years, it would have evolved either gradually as a main sequence star, or rapidly after being involved in an intra-galaxy star formation event, like getting hit by a close nova, thus its spectre would not be predictable from whatever data you gather over the journey, assuming what you have discerned from the Milky Way was correct and about the target and not a star that was indistinguishably close to the target to mistake them. Also 8 billion years is about two star generations' worth of a timelapse, so the target galaxy should have experienced about two waves of star generation after you've seen it from 8 BLY, rendering it probably unable to get discerned at earlier jumps.
This totals to about 100% of nonexistence of your target where you would arrive with your FTL. So, better search for similar stars in the local group, they are about thousandfold closer and more data is available to gather about them to actually reach their current location rather than ending up at a complete loss in the midst of alien stars.
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# This would only work for the smallest and dimmest stars
Large bright stars have relatively short lifespans, and change a great deal over the timescales your talking about for your jumps.
However, small stars are very stable and can stay in their main sequence, with relatively stable spectroscopy, for perhaps trillions of years (this is theoretical as the universe isn't even 14 billion years old yet). The problem, of course, is: "How do you see a dim star from 8 billion light years away?". But provided that the star itself is over 8 billion years old, and that, for some reason you can see it from 8 billion light years away (seeing it at this distance does guarantee its age), then you should be able to find that star by its spectrograph, the helium line will brighten as you approach and the hydrogen line will dim, but this should be predictable enough to identify.
As for the Nova bonus question, the stars that we're talking about would be far too small to ever go Nova. They may not be as flashy as their much larger and brighter neighbors, but these are the stars that will still be shining billions of years after these supernova have gone dark.
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Stars have predictable life cycles, shifting their core up the periodic table. That doesn't mean that they won't receive input from outside, or that their aging can't be disrupted by gravitational forces. Passing through a nebula could easily change a spectrum enough for it to become less like you'd expect than some of its siblings.
Let's solve this as a Fermi problem. Fermi (of the Fermi Paradox) was notorious for breaking complex problems into sets of discrete variables. The Drake Equation is the most famous of these formulations.
Variables:
V (ly3): The volume of space that the star might pass through over that period of time, based on your ability to predict the motion of all of the stars near it.
D (count/ly3): The density of stars in the vicinity of your star. If your star is in the galactic core, you're going to have issues.
T (0.0 to 1.0): The percentage of stars in the galaxy of your star's general spectral type. Smaller stars have a higher T.
N: (ly3nebula / ly3non-nebula) The percentage of the volume that the star is expected to pass through which is occupied by Nebulae. This determines how much the star's spectrum can be expected to drift.
X: (0.0 to 1.0, where 1 = strongly unique) This is a rating for eccentricity, essentially a statement of how unusual the spectral lines are, and how vibrant they are. Is there a strong chlorine spike in its atmosphere? If so, this will create a recognizable absorption line in the spectrum. Unfortunately, these lines wouldn't be visible from 8 billion ly away because it would be overlaid by all of the dust the light has to pass through on the way there. Maybe they have magitech that allows quantum-pipeline of light from a specific area. That's pretty much the only way they could differentiate a single star from that distance in the first place. Or maybe someone handed over coordinates and a spectral signature for the star?
V \* D will give you the locational variability of your star over the 80 million year jumps. Denser stars mean more dancing around.
D*T*X/N is the difficulty of differentiating your star from the others around it. Thus, the total formula would be (V \* D2 \* T \* X) / N.
All of this needs to be adjusted for scanner technology. If you have the precise spectral signature recorded, and you can simultaneously sample and process the spectral type of every star in the target galaxy, then the only real variables are X / N, which states the probability that a nebula will smear the original spectral type out of recognition.
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It sounds like your ship has to use [Dead reckoning](https://en.wikipedia.org/wiki/Dead_reckoning). When there is too low of visibility, pilots and ships captains will use the knowledge of where they were combined with speed and time to determine where they are.
Since you'd be relying on dead reckoning to determine the position of the destination AND the position of the ship it is absolutely vital that:
1. The measurements of the stars are ABSOLUTELY accurate. Since you're extrapolating over billions of years the tiniest error will get your crew lost in space.
2. The consistency of the warp drives movement. Again, this most be ABSOLUTELY consistent in order for your dead reckoning to be accurate.
In terms of world building this would mean that the hundreds of stops are at closer planets in order to verify that dead reckoning is successful. The Alpha Centauri system is about 4.37 light years away, so it could be used to ensure that the dead reckoning is accurate, from there your crew could just warp exponentially further each time while constantly checking to make sure they're ending up in their expected destinations.
**The big problem:
It is impossible for us to know how accurate our measurements of stars are**
Since we won't live long enough to see the results of the experiment, all our hypotheses about the direction and speed of a galaxy are educated guesses that can never be proven or disproven. I can think of some ways around this:
1. Perhaps the ship your crew is on is the first ship to travel long distances and they test the accuracy of the measurements using the process described above.
2. Perhaps dead reckoning has already been tested by other ships or space probes using the warp drive and the process is commonplace in the future.
3. If this is REALLY far in the future you could say that they found our current day star charts and by comparing them to their they could accurately extrapolate out the movement.
Overall it would be a process of trial and error, but given the invention of a warp drive I see the navigation method you're describing as a perfectly valid method of space navigation.
**EDIT:**
It seems like the main question is the precision of the warp engine. If it can instantly get you where you want to go every time you don't need navigation. If it's inconsistent you should explain more about why it is inconsistent and how inconsistent it is.
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The Cult of the Holy Mother is a female-dominated sect within a larger religious organization led by a male patriarch. Although the cult is small, it retains a significant role in the imagination of the populace. The cult is made up of priestesses that enter into holy matrimony with their deity. These women have taken vows of chastity to devote themselves to the study and correct observance of religious rituals. There rituals are deemed necessary by the organization and forbidden for others to carry out. As such, they are regarded as fundamental to the continuance and security of the state. Occasionally, a supernatural event will be triggered which is described by the org. as a miracle. A priestess will be chosen by their deity to give birth to a son, who will grow up to be ordained as the next leader of this faith. These miracles occur anywhere from every few decades to every few centuries. They serve as an expression of the god's power and authority over nature, as well as a reminder to the people of the contract between the deity and mankind. This event symbolizes the holy trinity that the religion bases itself upon, with God the father in heaven, God the son as his representative on Earth, and God the Mother as the intermediary between both worlds.
Miracles can be used to legitimize the authority of religious leaders and authenticate the special relationship between them and the deity they worship. These supernatural events confirm the truth of the faith's teachings and secures their place in society. If done too often or on too big a scale, the populace can begin to take them less seriously as miracles and more like magic. They may even begin to demand "magic on demand" from their leaders to solve specific issues, and may even turn on them if they can't deliver. The trick is too make them rare enough so that they are seen as powerful events when they happen, but common enough to remain in public memory. However, other factions within a religion who desire more influence over the faith's direction may claim their own "miracles" as a source of their legitimacy. This can be marketed through events that retain some significance in public consciousness, or lost "sacred artifacts" that have suddenly been re-discovered, such as a shroud or an ark containing golden tablets. This can ultimately lead to a schism within the faith, with the religion breaking up into various factions spread throughout the nation, declaring themselves as the true faith and the others as heretics. In addition, rivals outside the faith would question the legitimacy of the cult's miracles to weaken their image in society, suggesting that the priestesses simply broke their vows and that they are merely fraudulent acts meant to deceive the public. As there is no simply way to disprove this, it can be a blow to their legitimacy.
How can the cult of the Holy Mother use their supernatural miracle to prevent schisms within a religion and keep it unified?
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**The Miracles are Unmistakable**
Every miracle is different. What they have in common is that every miracle is accompanied by a fortnight of tidal waves, earthquakes, strange stellar phenomena, virgin births, everyone having the same dreams, and the creation of some really really bad pop music. So it is hard for the sects to disagree about which are the legitimate miracles.
In 12324 the miracle was the Drying up of the Inland Caustic Sea.
In 12379 the miracle was the sudden Re-Wettening of the plains of Arab into the now Sea of Arab.
In 12399 the miracle was the eradication of the Yellow Leg Plague. Every infected person suddenly got out of bed with all their sores and delerium gone. No one has caught Yellow Plague since.
In 12425 the miracle was the discovery of a new source of fuel in the Northern Tundra.
In 12525 the miracle was the birth of a particularly large and ugly baby.
In 12800 the miracle was a bumper harvest where every potato plant in the land produced yummy live snakes (in addition to potatoes).
In 12867 the miracle was the first indisputable proof that we are standing on a big disk hurtling through space.
In 12925 the miracle was the invention of a new way to treat tobacco to make it less dangerous to smoke.
In 13120 the miracle was the big ugly baby -- now a big ugly grownup -- fought Mothra for forty days and forty nights and won despite not having very good kung fu.
In 13190 the miracle was the sudden ceasefire between two armies. The troops on both sides simply decided they'd rather not slaughter each other. They put down their weapons, kicked out their generals, and went back to their farms. Hooray!
They are all different. What they have in common is that every miracle was accompanied by a fortnight of tidal waves, earthquakes, strange stellar phenomena, virgin births, everyone having the same dreams, and the creation of some really really bad pop music.
This makes it very difficult for two sects to disagree on when a miracle happens. They don't look for the miracle itself. They look for the accompanying signs.
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Assume that miracles have an immediate, physical effect. Instead of "remission of cancer through prayer" you get the movie-style "parting of the Red Sea," or "real Manna from Heaven," or "fortress walls literally crumbling to dust." There should be clearly no natural explanation for what has happened.
These miracles only happen when senior leaders of the faith publicly pray for divine intervention. Not always, that would turn the deity into a vending machine for benefits on demand. The purpose has to be aligned with the divine plan, and faith leaders must be truly sin-les.
And the group doing the praying, and fasting, must be inclusive. All legitimate sects must be present, or it doesn't work. So this defines what a "legitimate" sect is. Any sect that is not required is, by definition, a heretic splinter cult. Any sect that is required is, by definition, mainstream.
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## Concensus
Never let locals come up with miracles, make it a central decision of your priests, with unanimous vote. Else, your miracle will become only of local importance and *cause* a schism, or it would be used as a token of war.
If your religion wants to prevent schisms, *everyone should agree* upon the miracle and its workings. Make sure the peaceful character of God's power shines through, the miracle should not divide, it should unite. Its workings be for the common good.
**End wars**
Allow miracles that end wars. To be acknowledged as a true miracle, the fighting parties should immediately stop all hostilities and return home as a result of the miracle. Any credible phenomenon can be used. There's e.g. a solar eclipse, priests will declare the miracle happened, ceremonially end the war.
**Prevent disaster**
Once in a century, you'll have a storm costing thousands of lives. Just halt the storm, or divert it into a desert, by calling upon divine intervention. When it actually ends, it will be an official miracle. Else it should be classified as fake news.
<https://en.wikipedia.org/wiki/Hurricane_Dorian%E2%80%93Alabama_controversy>
**Execute corrupt leaders**
A miracle may direct the priesthood to perform a task. There's a king who has been sitting there for ages and becoming more cruel and corrupt every year. When a comet appears in the sky, a miracle will be declared and a priest will ceremonially execute the king in public.
**Manna from heaven**
The above occur 1-2 times in a generation. It would be very convenient, marketing-wise, to have a more frequent miracle too. Suppose priests are able to call upon the heavens to let manna rain down. Hungry people will highly appreciate that and join the religion.
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In designing your own god and religion, you can draw from the way most authenticate their miracles. The way miracles stay in memory is by prophecy and scripture. A miracle that is prophesied is very tough to fake. Any event that is a stochastic process, and occurs according to a large enough prophecy while violating accepted scientific probabilities, will be seen as a miracle by the populace at large. There will always be skeptics, however; absolute proof is a scientific impossibility. But you want an *authenticated* miracle. Most religions rely exclusively on eye-witness accounts rather than periodic reminders. In fact, I don’t think any religion places a faith on some scheduled events. So this is a unique animal, but your god has a right to run the show however they want.
The current falsification method of modern science makes your request very challenging. Consider the claim that cold fusion was recorded in a jar, by reputable scientists. In 1989, two electrochemists, Martin Fleischmann and Stanley Pons, reported that their apparatus had produced anomalous heat ("excess heat") of a magnitude they asserted would defy explanation except in terms of nuclear processes.
## Authentication requires repeatability
The problem is that when other scientists used their carefully detailed lab notes, the excess heat did not occur. The report is considered today to be an error. Repeatability is an inseparable component of any theory.
This makes true miracles impossible to detect scientifically. If it can't be repeated, it didn't happen. No matter what miracle your god demonstrates, no matter how many camera angles caught it and how many witnesses saw it, the simple fact that it can not be repeated, after recreations and supercomputer simulations and witness interviews, a scientifically valid explanation will in all cases become accepted. We can easily see this with non-miracles such as 9-11 attacks. Huge splinter cells spawn ideas of conspiracy and government fakes. Thousands of people dying will not convince us away from our beliefs. The scientifically valid explanation may be radical and nearly impossible, but it will become the accepted explanation in society before anyone believes it was a supernatural miracle. This is a fundamental property of science, because science only studies the natural world of causalities.
## Personal contact is the authentication
Just like Gabriel was sent to authenticate the virgin birth to Mary, your deity needs to personally communicate the miracle to whomever it impacts. The message will need to be a simple prophecy that can’t be scientifically predicted. Today, that might mean knowing the exact time that three tornadoes will strike and their exact location. Your single priest predicts the event, the followers leave the towns, but the skeptics stay. The tornadoes fall on cue, your miracle has been authenticated.
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The miracles need to be predicted in advance by the leaders of the church, with specifics and unambiguous details. They shouldn't be predicted too far in advance, days (maybe weeks at the outside) and not months.
The other cults' inability to predict these miracles, or to do so only as often as chance would allow marks them as inferior and imposters.
Note: If there is the possibility that their predictions might fail for whatever reason, this can de-legitimize the religion. It might not survive even a single misprediction, but it certainly couldn't survive multiple mispredictions.
If the schismatic cult does predict a miracle, all is not lost as long as repeat successes can be prevented or sabotaged. The ready-made answer being, of course, that the schismatics have stolen or misappropriated the writings of a prophet or seeress, and were later smote for it. This get-out-of-jail-free card can't be overused, as it suggests that either the deity or the church itself is incompetent. The church can appeal to their human fallibility, but it raises the question of why the deity entrusts the church to them... some scapegoating might be in order.
Those who attempt the fraud of false miracles likewise need to be punished. Though, it may be true that they can have multiple successes before punishment is doled out. (Note: this is only for truly fraudulent miracles, not other supernatural events cooked up by someone other than the deity.) The church then needs to prove how the fraud was committed (sleight of hand, trickery, etc.) and the fraudsters harshly executed (burning at the stake seems sufficient, though other methods could certainly work). Bonuses for tortured public confessions.
With all that said, it's not important to explain the basic premise... the church/religion itself has no power to command a miracle. They can't decide on one happening tomorrow, so miracles aren't rewards for the biggest donor. They come at their own pace, the church can't hurry them along. They have no power over the nature of the miracle. And they only give warnings of an imminent event on a short timescale (if they have more warning, say years in advance, then they are careful to not reveal this, or leave writings laying around to be stolen).
This works because the actions of the church strongly suggest that they have a superior understanding of the universe that is unmatched by anyone. Not only that, but they do have a red phone to the deity, who presumably is capable of ignoring the physical laws of that same universe when it suits him, and that he favors the church enough to let them in on the joke. Nothing more is required for them to keep their religion unified and powerful.
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I have this idea for a world orbiting a type O star, a particularly active kind of star producing intense radiation. As a form of adaptation, the microbial life has become bright white so to reflect the radiation. This makes the planet look like it's covered in ice when it's actually pretty lukewarm. They've formed a thick film over most of the whole planet beneath which most all of the other life lives to feed off of it. Some of the more advanced life can come out on land for a little while, but only at night to avoid the radiation. Does this ecosystem work? Would white autotrophs even be feasible?
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**Each plankton organism carries a crystal.**
Just as earthly plankton might grow a shell, your world's plankton will grow a crystal. The crystal is precipitated out from the seawater and used as a bulk shield by the organism, which keeps its DNA and most of its mass on the underside. The crystal absorbs most of the radiant energy, and what gets thru and is scattered / refracted back is fine for the organism. Crystal composition varies from organism to organisms - sodium / magnesium chloride is most common but in polar regions there are organisms which purify water and carry a water ice crystal. Some organisms carry a crystal of insoluble white calcium salt - which is converging on a shell or test.
The crystals of salt or ice generally look white. Thus your white plankton sea.
After a storm, great rafts of plankton wash up. On rotting, piles of their crystals remain.
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Adapting white would mean they're reflecting visible light spectra. O-type stars emit tremendous amounts of ultraviolet. Sunscreen (which can contain zinc, making them white) is often transparent. My eye glasses block UV, and they're transparent, too. So, the "intense radiation" isn't what's causing the critters to be white. On the other hand, what UV radiation does to skin here on Earth is cause it to produce melanin, turning the skin tan. What this does (among other things) is make the skin opaque to the UV light, reducing the damage it can cause.
However, O-type stars are also very bright and tend to be blue. Let's chase that for a moment. Plants are green because they reflect the blue and green spectra, absorbing instead the red spectra that's more efficient for photosynthesis. But in this case, the plants need to absorb the green and blue spectra because it's mostly what's available (this isn't quite true, but it's true enough for government work). The consequence would be *black* plants in that they're absorbing everything they can for photosynthesis.
So, in humans the skin darkens in the process of becoming more opaque to block light and in plants they'd turn (IMO) black to absorb as much of the spectra as possible for photosynthesis.
I know your planet doesn't have plant life, but I needed to make the point. On your planet, what we have is the primoridal ooze that's just beginning to create complex life forms. Now that I think about it, you likely do have plants on the surface already. But what would turn them white?
That's actually a problem. Energy needs to come from *somewhere* or life doesn't find a way. All life begins with the sun, and that means absorbing energy, and that means reflecting nothing or very little.
But let's run for suspension-of-disbelief rather than science-based. What if we assume the creatures in your ooze (not the plants, you're kinda stuck with the plants) developed a skin that needed to act in the *opposite way* to how skin reacts here on Earth? Rather than blocking or reflecting spectra, we want to absorb it — but not like plants.
What if your creatures developed an epidermal skin layer that worked a bit like glucose-generating *solar panels.* What you really want is a mirrored surface (aka "white") under the transparent skin so that the skin simply gets *baked* by that glorious and short-lived star! Now we're cookin' with gas! The star may be hotter than Heather Locklear back in the 80's but your planet is ***cold!*** (Oh, all right... lukewarm.) And what this mirrored (white) dermal layer is doing is injecting heat into the body by warming the epidermis and allowing the blood to take the heat inside.
So, lukewarm planet, but critters still need to be warm — especially if the early life forms are cold-blooded!
* Transparent epidermis.
* White dermis.
* Thread-thin blood vessels (so the overall view is white, not pink).
But your plants are still black or very dark red. Sorry.
] |
[Question]
[
I would like to have a zero-g spaceship factory in orbit, and would like to know if this is a viable way to work:
I imagine melting metal into a big blob, then inserting a tube and pumping in gas to inflate it. Perhaps external struts and molds can push and pull on the form to shape it as it expands and cools.
Some questions.. would this actually work and be controllable? how long would it take for the metal to cool? How could a quenching technique to rapidly cool the metal be implemented? A good answer would provide details on how this whole forging process could work.
Assume a near-future level of technology.
[Answer]
**Vacuum deposition**
This is ideal for space. Micro-gravity will ensure an even deposition and space is already a vacuum!
You would use a carefully crafted spherical mould of light but rigid materials (it doesn't have to stand up to gravity and you could even use an actual inflated balloon as the mould).
Use the process from the inside of the mould. The slow atomic/molecular deposition will make the resulting sphere incredibly pure, strong, and the thickness will be exact to nano-meters. You can even build up layers of different metals for extra strength. Hull openings are simple: they are just built into the mould - no drilling or cutting.
>
> *Vacuum deposition (or vacuum evaporation) is a PVD process in which the atoms or molecules from a thermal vaporization source reach the
> substrate without collisions with residual gas molecules in the
> deposition chamber.*
>
>
> <https://www.sciencedirect.com/topics/chemical-engineering/vacuum-deposition>
>
>
>
[Answer]
While, as others have already pointed out, using glass-blowing techniques on steel is impractical to say the least (not to mention the fact that it'll radiate nearly 300 kilowatts per square meter in infrared radiation when molten) and that bulk metallic glasses are somewhat of an exotic medium.
***However***, that's not to say that there is no application for inflatable metals, may I introduce you to the main intake fan blades of the Rolls Royce Trent 1000 jet engine. I'll let Rolls Royce explain...
[](https://i.stack.imgur.com/n1YPl.jpg)
[](https://i.stack.imgur.com/ok9Vc.jpg)
It's a kind of middle ground between blow molding and stamping, titanium panels come in as a stack of flat sheets with a special bonding pattern which are them inflated like a balloon inside a mold. Probably as close as you're realistically going to get to an inflatable metal ship.
You could make the outer shell of your space ship really strong by using large pre-fab panels which both frees up the inside (less internal bracing needed) and as a bonus, the finished structure closely resembles a whipple shield which gets you some extra protection from asteroids and hyper-velocity balistic projectiles.
[](https://i.stack.imgur.com/nd3KG.png)
Whipple shields work by having multiple layers to break up and spread out impactors. After all, a cloud of sand is easier to stop than a bullet with the same total mass and speed.
[Answer]
**Your ships are made of metallic glass.**
<https://en.wikipedia.org/wiki/Amorphous_metal>
>
> An amorphous metal (also known as metallic glass or glassy metal) is a
> solid metallic material, usually an alloy, with disordered
> atomic-scale structure. Most metals are crystalline in their solid
> state, which means they have a highly ordered arrangement of atoms.
> Amorphous metals are non-crystalline, and have a glass-like structure
>
>
>
These alloys are unusual hybrids, with some properties of metal and some properties of glass. You can blow mold metallic glass as though it were plastic.
[Thermoplastic blow molding of metals](https://www.sciencedirect.com/science/article/pii/S1369702111700189)
>
> Blow molding of bulk metallic glass Even though fast cooling and
> forming are decoupled during TPF of BMGs, thin sections with a high
> aspect ratio remain challenging to create when using techniques where
> the BMG is in physical contact with the mold. This is due to stick
> conditions between the BMG and the mold and the resulting parabolic
> flow patterns16. In order to eliminate such stick conditions, physical
> contact between the BMG and the mold must be avoided, at least while
> significant tangential strain is generated. We will show that this can
> be achieved by TPF-based blow molding.
>
>
>
[](https://i.stack.imgur.com/ZkWe2.jpg)
There is a lot of seriously non-fictional materials science behind this. I could imagine there might be reasons you want a thin bubble of conductive metallic glass for your spacecraft. Less mass to move, for one. It might be possible to imbue a charge to this thin metal skin which will deflect charged cosmic rays. Or have a series of these bubbles one within the next Russian doll style, with charged vacuum between.
[Answer]
Your biggest challenge would be keeping it warm, not cooling it down. I'm assuming that you are seeking large bubbles. Think about how fast you would have to blow to get it to size in a minute or two.
What you might actually want to do is inflated it with a low pressure high temperature has to keep it warm while inflating.
The biggest challenge would be that there is a natural instability in blowing. Once a bubble gets thin, it wants to stretch more, making it thinner. Glass blowers have to bring a lot of skill to the table to keep things in check. They use a lot of gravity as a tool. You would need a new tool
[Answer]
You need a mold, and rubble may be the answer. No matter what you do you need a mold of some kind,otherwise with a hard vacuum on the outside you will never get a regular shape. The best idea would be to use something that you will leave on it, as it will be nearly impossible to remove a mold from metal deposited in a vacuum without damaging it. Ideally something that will act as a radiation shield since a thin layer of metal will not be very a good radiation shield.
Take a hollowed out asteroid, which are naturally full of cracks and micro-holes and inflate a balloon of molten metal on the inside let pressure differential drive metal into all those openings and seal the inside. Rock makes for a very good radiation shield.
Alternatively you don't even have to start with a whole asteroid, you can fill a net/mesh shell or a second balloon with stony rubble (mining leftovers) and use the metal balloon on the inside to seal and bind it into a solid. This also means you are not limited to spheres as you can get any shape you can build the net in. basically you are using the rubble like a mold to blow the balloon up into.
You will need two things you may not have considered, a very hot gas to fill it to keep it hot as it expands as the gas will cool drastically as it expands, and computer controlled pressure to regulate the internal pressure as it inflates, you need to be able to back off the pressure when you reach the desired shape.
[Answer]
This is a variation of a technique Dandrige M Cole thought about in the 1960's, although he was speaking in terms of heating an entire asteroid and "blowing" the molten asteroid into a hollow bubble as a colony.
The problem with "blowing" is that there is very little means of controlling the process. Glassblowers use centrifigal force and gravity to control the size, shape and thickness of the end product, a zero G bubble has a very distinct possibility of bursting and tumbling out of control.
Many of the other posters have the right idea, use the heat energy to use vapour deposition on a form to make a seamless pressure vessel or hull.
] |
[Question]
[
Some background: I'm developing a world that could, theoretically, be inhabitable by humans (with a high enough recruitment success to at least keep a stable population), randomly determining environmental parameters based on the range our physiologies can tolerate. This world has [50 atm of pressure](https://en.wikipedia.org/wiki/Saturation_diving#Underwater_habitats) at the inhabited area I'm designing, and a mass of just $0.11M\_{\oplus}$ (so a surface gravity of 0.48g). It's too small for plate tectonics, but has enough residual heat to create a magnetic dynamo.
Based on what I've been able to find online, in order for the atmosphere to be breathable, I need something like:
* 90% He
* 4.6% N2
* 3.8% H2
* 0.8% O2
* 0.6% Ne
* 0.18% Ar
* 0.01% CO
* 0.01% CO2
* +0% to 0.2% H2O (based on vapor pressure at habitable temperatures, which are probably on the warmer side since helium conducts heat so quickly)
The reasoning behind such a high concentration of helium is in line with heliox mixtures used in [saturation diving](https://en.wikipedia.org/wiki/Saturation_diving), where the inert gas helium is used to "dilute" oxygen to a breathable partial pressure. It's the partial pressure of oxygen (here 50 atm x 8% = 0.4 atm, or almost twice the partial pressure in Earth's atmosphere), not the volume or molar percentage, that determines hypoxia or hyperoxia.
Hydrogen might be a major constituent of the atmosphere if the planet was originally a [mini-Neptune](https://en.wikipedia.org/wiki/Kepler-138) [that](https://en.wikipedia.org/wiki/Mini-Neptune) [lost](https://en.wikipedia.org/wiki/Gliese_436_b) most of its hydrogen and a lot of its helium. Oxygen shouldn't be much higher than the noted percentage due to flammability risks and oxidative stresses on life. The big concern with nitrogen, neon and argon is nitrogen narcosis (and similar nasty effects); nitrogen is pretty much maxed out here. [CO and CO2 should be more common in a helium-dominant atmosphere](https://www.nasa.gov/jpl/spitzer/pia19345/how-to-make-a-helium-atmosphere/), but are directly toxic to life, so we probably can't raise them any more.
(As a minor sidebar, some envelope calculations based on equation 1 in [this article](https://iopscience.iop.org/article/10.3847/1538-4357/aa8137) give me an atmosphere loss rate (instantaneous $\frac{dm}{dt}$) of $2.61\times10^5$ kg/s, which if projected out geometrically would give about 16 million Earth years until the atmosphere is gone. So uh, definitely not a stable situation in geologic time.)
One of the explanations I've considered for having a thick helium atmosphere despite the current low mass is that the planet was originally a gas giant (mini Neptune-type) that got knocked into a lower orbit by some sort of prehistoric collision/slingshot effect, where it began bleeding off its gas envelope like a giant comet. I'm not sure if the planet could have *formed*, though - would it make sense for it to have such a small rocky core?
How else could a breathable high-pressure atmosphere form?
[Answer]
## TL;DR
You should be able to get this sort of helium-dominated atmosphere to form naturally by exposing the planet to the proper levels of ultraviolet radiation from its star. By tweaking the orbital and physical parameters, you should be able to strip the planet of its hydrogen while retaining most of its helium. A planet with a cold, dense atmosphere might be the optimal solution.
---
[Gliese 436 b](https://en.wikipedia.org/wiki/Gliese_436_b), as you mentioned, is an interesting case study and possibly the best example of a helium-dominated atmosphere like the one you're looking for. It weighs in at around 21 Earth masses, and the vast majority of that is likely to be solid, with an atmosphere-to-planet ratio of $M\_{\text{atm}}/M\_p\sim10^{-3}.$ This is far out of your desired range, but it's worth looking at anyway.
[Hu et al. 2015](https://ui.adsabs.harvard.edu/abs/2015ApJ...807....8H/abstract) argue that Gliese 436 b, a Neptune-sized exoplanet, began with an envelope dominated by hydrogen and helium, as is expected for planets of that mass range. It orbits a red dwarf, and as such, it receives a healthy dose of both extreme ultraviolet (EUV) radiation, as well as x-rays (though these are, for our purposes, relatively unimportant). This EUV light energizes atoms and molecules in the atmosphere, increasing their kinetic energy until some have thermal speeds greater than the escape velocity. These then move free of the atmosphere, in a process called *hydrodynamic escape*. Hydrogen is lighter than helium, and so it is stripped away much more easily. Hu et al. calculated that by this process, Gliese 436 b could have had its hydrogen and helium atmosphere converted to a helium-dominated atmosphere on a timescale of about 10 billion years.
Unfortunately, low-mass planets are unlikely to maintain such high helium/hydrogen ratios! Figure 4 of the paper shows a plot of what Hu et al. call the *fractionization factor*, $x\_2$. $x\_2$ can range from 0 to 1; a value of $x\_2=0$ means that the atmosphere is completely dominated by helium, while a value of $x\_2=1$ means that the two gases are well-mixed. We can see that low-mass planets have severe difficult reaching low fractionization factors; even at $M\_p=1M\_{\oplus}$, the best we can do is $x\_2\approx0.6$:
[](https://i.stack.imgur.com/NQgrh.png)
For an even lower-mass planet, I think $x\_2\approx0.8$ is, unfortunately, reasonable.
Let's see if we can tweak things a bit. The energy-limited$^{\dagger}$ escape rate is
$$\Phi\_{\text{EL}}=\frac{L\_{\text{EUV}}\eta a^2R\_p^3}{4Kd^2GM\_p}$$
where $R\_p$ and $M\_p$ are the radius and mass of the planet, $L\_{\text{EUV}}$ is the EUV luminosity of the star, and $d$ is the planet's semi-major axis. We see that for our planet, $M\_p=0.11M\_{\oplus}$ - fairly low. This should mean that the planet will easily lose both hydrogen and helium. We can mitigate this by, say, reducing the EUV luminosity (perhaps by making the star a K or G star) or increasing the semi-major axis, leading to a lower $\Phi\_{\text{EL}}$.
We want this lower $\Phi\_{\text{EL}}$ because then helium loss will be energy limited but hydrogen loss will be *diffusion-limited*, and will therefore depend on a different set of atmospheric physics. We may then be able to find-tune the hydrogen escape. The paper indicates that the scaled helium flux will be greater than the scaled hydrogen flux by the quantity
$$\phi\_{\text{DL}}=\frac{GM\_p(m\_{\text{He}}-m\_{\text{H}})b'}{R\_p^2kT}$$
with $T$ temperature and $b'$ the binary diffusion coefficient. We see that we can retain even more helium compared to hydrogen if we 1) increase the initial helium mass somehow or 2) decrease the temperature, as $\phi\_{\text{DL}}\propto T^{-1}$. This should make sense; a colder atmosphere will make it harder for gases to escape.
On the other hand, thanks to the ideal gas law, a cold atmosphere means that we'd likely see lower pressures unless we drastically increased the atmospheric density. We could attempt to make ourselves a cold but extremely dense atmosphere, with high-density maintained perhaps by a high surface gravity and some method of replenishing helium. A massive rocky core would certainly help.
---
$^{\dagger}$ *Energy-limited* means that the escape rate is limited by the EUV flux from the star; *diffusion-limited* means that the flux $\Phi\_{\text{EL}}$ is so low that diffusion suddenly becomes limiting factor.
[Answer]
I think you are mixing two aspects here: the formation of the atmosphere and its enrichment in oxygen.
In order to have free oxygen you need to have some process continuously producing it, else it will be depleted by the reaction with other species. And since you have hydrogen, you don't need much to have a lot of water. On Earth that process is called photosynthesis and it's carried out by plants and algae. Before that it is accepted that our atmosphere was not so oxidant.
You can follow a similar path also here: this planet, initially with a reducing atmosphere (noble gases, hydrogen, methane and water), developed life which ended up enriching the atmosphere with oxygen.
[Answer]
Here‘s another alternative: the planet‘s solid core contains lots of reservoirs of frozen/condensed hydrogen, helium, nitrogen, etc. Perhaps the planet initially had *no* atmosphere and was just a ball of frozen rock until an alteration to its orbit (as you mentioned) or a change in the size of its star caused it to be heated up. At this point, frozen and condensed substances at its surface begin to melt and evaporate, forming an atmosphere (that is gradually diffusing off into space at the same time).
You would just need to make sure that the planet is receiving enough heat for these reservoirs to evaporate faster than the atmosphere can escape from the planet.
Good news: the heat of vaporization of helium is $21.125$ joules/gram, which is very low (compare this with water‘s $2257$ joules/gram). This means it should be able to melt and evaporate quite quickly, and possibly even outpace the disappearance of the atmosphere.
Bad news: this still isn‘t what you would call “geologically stable.” Eventually, the reservoirs will run out and the atmosphere will disappear. Even worse, as the reservoirs empty out, the planet’s mass decreases, causing gravity to lessen and the atmosphere to vanish at an even faster rate. However, it should last much longer (and be more believable) than a planet with nothing but a preexisting atmosphere.
[Answer]
Let's dive into the physics and see where that gets us. A the outset, I assert that I will make no attempt to estimate any ingredient to better than $\pm 10\%$ and the result may be off by a small factor because of this. I use the subscript "Coel" to reference the planet you describe.
You don't state the radius of your planet or its density, but you do tell us the mass and the acceleration due to gravity at the surface. The gravitational potential from a point mass (or from a collection of concentric spherical shells of mass), $m$, at a distance $r$ from the center (and outside the mass) is
$$ V(r) = \frac{-m G}{r} \text{,} $$
where $G$ is the [gravitational constant](https://en.wikipedia.org/wiki/Gravitational_constant) ($6.674 {\dots} \times 10^{-11} \frac{\mathrm{m}^3}{\mathrm{kg}\,\mathrm{s}^2}$) and the magnitude of the acceleration is the magnitude of the gradient of the potential,
$$ |a| = \frac{m G}{r^2} \text{.} $$
You give $|a\_{\text{Coel}}| = 0.48 |a\_{\text{Earth}}|$, so with $r$ the distance from the center of your planet to its surface,
$$ \frac{m\_{\text{Coel}} G}{r^2} = 4.713{\dots} \frac{\mathrm{m}}{\mathrm{s}^2} \text{.} $$
Solving for $r$, we find that the radius of your planet is $r\_{\text{Coel}} = 3.049{\dots} \times 10^{3} \,\mathrm{km}$. (And as a sanity check this makes the average density of your planet and Earth the same to within a couple of parts per thousand.)
Escape velocity from the surface of your planet is
\begin{align\*}
v\_{\text{escape}} &= \sqrt{ \frac{2 m\_{\text{Coel}} G}{r\_{\text{Coel}} }} \\
&= 3.79{\dots} \,\frac{\mathrm{km}}{\mathrm{s}} \text{,}
\end{align\*}
which rounds to $3.8$ kilometers per second.
Checking the Wikipedia's [chart](https://en.wikipedia.org/wiki/File:Solar_system_escape_velocity_vs_surface_temperature.svg) for [atmospheric escape](https://en.wikipedia.org/wiki/Atmospheric_escape), at $300 \,\mathrm{K}$ (around room temperature), xenon won't go streaming off your planet, but carbon dioxide, oxygen, nitrogen, water (vapor), ammonia, methane, helium, and hydrogen will all escape (in rough order of increasing rapidity). From the chart, retaining helium requires temperature below about $150 \,\mathrm{K}$, which is quite a bit colder than I want to breathe.
One of the [sources](http://ircamera.as.arizona.edu/astr_250/Lectures/Lec_05sml.htm) for that chart writes
>
> It is also important to keep in mind that most of a gas will escape even if only a small fraction (say 5%) has a velocity higher than the escape velocity -- this assumes that there are no new sources of the gas from within the planet and that you are interested in times long after the planet has formed.
>
>
>
[Having produced a number of models, it is clear that having a stable atmosphere with this high pressure and low gravity is very tricky. It's far too easy for the (tightly) compressed spring of atmosphere to throw large fractions of the atmosphere off in the time it takes the compression wave to propagate down to the planet, reflect off the surface, and return to the outer layers, raising their speeds to greater than escape velocity. Having a stable column of gas 50-times heavier than that on Earth with half the surface gravity at reasonably close to livable temperatures is ... **hard**.]
[Answer]
# A wizard did it
>
> [Clarke's Third Law: Any sufficiently advanced technology is indistinguishable from magic.](https://en.wikipedia.org/wiki/Clarke%27s_three_laws)
>
>
>
It might be the case that a very advanced civilization terraformed the planet that way, maybe because they originally come from a place with a very thick atmosphere. The low gravity might be because the place was a spa, retirement home or kindergarten (less gravity means less strain on the heart(s), less damage from knocking things and people over), or maybe because changing gravity too much is more expensive than changing just the atmosphere. This gives you the planet you want while keeping your Occam razor sharp.
That civilization may then have vanished (they died out, moved on to other venue, or hid in an iceberg when the fire nation attacked).
[Answer]
I believe certain bugs can breath underwater by using surface tension to wrap an oxygen bubble around them. The bubble then exchanges carbon monoxide and oxygen with the surround water to give them effectively unlimited breathing capability (I don't pretend to understand this well, see <https://phys.org/news/2008-07-insects-oxygen-underwater.html> for more).
Your atmosphere could do something similar, maybe a certain combination of the elements would "cling" to a human (maybe due to a static charge? I'm not sure if surface tension is applicable at this scale) and cause a few centimeters of breathable zone around them that constant renews itself?
] |
[Question]
[
So, I decided to replace elves with tengu, a race of six-limbed humanoid birds.
Firstly, because I'm tired of seeing Legolas everywhere. Second is that compared to a bog-standard human-elf romantic subplot the fact, that a tengu is an anthro bird that can slice you open with their talons when angered enough, would make a relationship more "interesting".
However, there's a problem. Tengu are one of the most mobile and intelligent races, gifted with a long lifespan, however, they're also frail and physically weak. If they were to conquer any land, they wouldn't be able to hold it for long. They don't really have any interest in conquering, though, and that's okay.
The problem comes when holding their own lands against invading [filibusters](https://en.wikipedia.org/wiki/William_Walker_(filibuster)) and other unwanted elements. They live in hardly accessible parts of mountain-ranges, though their agriculture requires some flat space. Their buildings use a mixture of wood and dirt, and most of their settlements (roughly the size of a larger medieval town) have a vertical separation, with the innermost layer sitting at the highest and subsequent layers deeper than the previous one.
Tengu replace elves in this setting's tropes, consequently, they have a long lifespan, low population, and birthrates. They don't really compete with other races over resources. In terms of export, their light armor design became a hit among the other races who were quick to adopt it.
Tengu are mostly isolationists in the sense that they normally don't initiate communication with others. Though others might want to employ tengu as messengers or scouts, still, the demand is low and tengu are picky when it comes to contracts, filibusters or their affiliates are an obvious no-no.
Also, they fly now, but it's mostly gliding (ratio: 15/1) with flapping-bursts that top at 90 seconds.
Tengu use pole weapons and light armor (hard linen plates over a thin gambeson and steel helmets). Regardless, they prefer to stay away from their enemies and pepper them with various ranged weapons when possible.
Sounds like a real hassle to take over, IMHO. However, I'm unsure if having the high ground is enough to deter mercenaries and various human nations from trying to invade the tengu. **What else could ensure that tengu wouldn't be invaded by a foreign power?**
**The less additional details or unobtainium you have to introduce to make it work, the better.**
The technology level is towards the end of the high medieval period. Society (except for the filibusters) is medieval as well.
[Answer]
# Sounds like a fair fight
The biggest problem that you indicate is that the tengu are physically weak. Fortunately for them, by the high medieval period, defending an area did not necessarily require the defenders to by stronger than the attackers. Depending on how you define that time period, you could have crossbows with cranks and other devices.
[](https://i.stack.imgur.com/Ge0gz.png)
And that glide ratio is a big deal. The tengu could glide over a valley and drop stuff on the enemy. Don't underestimate the effectiveness of a medium-sized rock dropped from 100 feet and crashing into enemy forces at [58 miles per hour](https://www.wolframalpha.com/input/?i=10%20pounds%20falling%20100%20feet). If they attack near dusk or dawn, they could drop rocks on enemy tents without facing much risk. Then they could land on the far side of the valley, climb to the highest point on that side, and repeat the attack the next time conditions are right.
Your enemies are [filibusters](https://en.wikipedia.org/wiki/Filibuster_(military)), which were irregular forces that lacked the full support of a government. And the tengu hold the high ground. If they build castles and other fortifications, it would be difficult for anyone to conquer them, even a proper army. The key would be building strong enough defenses to hold off the attackers until they gave up and went home. Check out this well-written [guide to siege warfare](https://www.ancient.eu/article/1230/siege-warfare-in-medieval-europe/) for a detailed description. The below excerpt is doubly true against filibusters lacking supply chains and relief troops:
>
> Sieges were expensive and troops might be on a fixed term of service
> (40 days in English armies, for example) so time was also a factor to
> consider. In addition, the campaign season was typically limited to
> spring and summer, and the longer the attackers remained cooped up in
> their own camp, the more prone they were to attack from a relief
> force, disease, or even starvation themselves from lack of supplies in
> a hostile territory.
>
>
>
So you have a group of irregular troops trying to take the well-defended high ground, unsure when the next meal is going to arrive through their haphazard supply chain, and every night facing the fear of silent gliding enemies dropping rocks on their tents. Sleep tight!
[Answer]
Mountains + defense + an even sort of airborne intelligent race makes any sort of invasion absolute suicide. Mountains are full of narrow passes and paths flanked by nearly vertical rocky cliffs. Your Tengu don't need to be great at flying as long as it helps them take the high ground. Your invading army will need to walk through countless passes where tengus above can hurl a steady stream of missiles down on their heads while perched safely up on the cliffs. Since they can land up high, this means they are not limited by the weight of missiles they can carry with them
Your army will have no way to out maneuver said attacks, nor will they be able to move as wide enough of a unit to quickly bypass the ambush and just accept the attrition. Bows also don't shoot up very well. Most historical war-bows maxed out at 140-160 fps meaning when fired upward, by the time they reach 50m they would lose about 90% of their stopping power; so, your humans/orcs/whatever will not be able to return fire. Finding 50m worth of high ground in the mountains is not hard as the below image makes pretty clear.
[](https://i.stack.imgur.com/BudwS.png)
This kind of situation is so asymmetrical that even a few dozen tengu could conceivably defeat an entire army without risking a single warrior.
[Answer]
**They have got jack squat.**
So no-one is interested in taking them over. The tengu spend most of their time meditating and discussing mediation with one another. They do not accumulate treasure and make nothing of any value, instead trading self-composed songs and poems (about meditation) which other races find cringingly painful. They make terrible slaves because they are prone to die for no apparent reason, and even if you take great care to keep them alive they will not do as they are asked, or screw it up if they try, and blame you. Plus they smell like frumunda and are covered with jumping bird lice the size (and shape, and color) of a Hot Tamale candy.
Legolas, please come back!
[Answer]
If they have gunpowder, they'd be invincible.
Have you considered how much damage they can do, with 3 arms on each side, thus able to aim and reload even black powder revolvers with paper cartridges, on BOTH sides at the same time AND dual-wielding at the same time? Continuous volley like a slow machine gun. Yikes. I won't ever bother giving them Winchester Repeaters. (3 rifles firing together, it'd be like a f\*\*\*ing LMG)
Or give them repeating crossbows. Imagine one side of arms fires and re-cocks, while the other side reloads.
You gave them six-limbs. I just made use of them. :D
[Answer]
Kamikaze, fires, boiling oil, explosives and chemical warfare.
No matter if you use a "medieval" setting, bombs, flame throwers and various types of grenades where invented around the 4th century or even earlier.
King X wants to invade the Tengu village/city/citadel/nation because his country is starving due to overpopulation and they need more fertile land for crops and farming to feed their people, what can the tengu do to save themselves and maybe not becoming food? Solve the overpopulation problem in the first place by dropping dead rats on the population to spread disseases or living rats and other rodents on enemy farms and crops so they die of hunger before they are able to form a military.
Or bomb drop the king's castle, the structure might be intelligently built to not be reached by trabuchets or catapults but tengu can just fly over it.
Another option is to take ill and sick tengu and send them to infect civilians, doesn't matter if they are killed as long as they spread the dissease to the enemies, a proud tengu will willingly sacrifice himself to protect his family.
Because rember, there's nothing scarier than losing in a fight where you are defending your family, that's the meaning of pure terror, the idea that someone you love died because you were either too scared or too weak, this is the worst feeling a creature can experience.
[Answer]
as described by others they possess incredible advantages for defence, but IMO their best way to defend their land is to never have to...
As a long-lived creature, long term planning should be more prevalent than In human society. They have a consistent diplomatic effort to ally with neighbours. If diplomacy is not working they rely on black ops to be sure that only lord and king that like them stay long in power.
De facto they made a defensive alliance league with their neighbours.
Their wisdom help them to keep the alliance strong and to answer any threat military, commercial but also cultural.
Their professionals' warriors have incredible experience after centuries of training and war. Dispatching a few hundreds can really turn the table, they can help ally commander to find an original and bold solution to problem that may appear unsolvable. And they don't like to fight because losing a soldier is very tough for them, but when they do they are incredibly effective. For example, a couple of spartan saved the siege of Syracuse by the Athenian.
[Answer]
Tengu, or Tenku, are a real Japanese mythological being with a firm grounding in reality.
The myth is that tenku are bird-people, anthropomorphic ravens, known for living in the mountains and other inaccessible places. They were renowned for their skill at arms, including the spear and swords.
The reality of this myth would have been based in reality and the peculiarities of the Japanese warriors' code of honor, Bushido. In Bushido, the main differences between it and the Western military code of honour is the stance each takes on death and surrender. In the Western code, surrender was considered honorable, and required that the party accepting the other party's surrender treat them according to certain standards. In Bushido, surrender is *dis*honorable, and brands the person surrendering as a coward; the honorable course of action is to fight and die.
So, in medieval Japan, there were many wars between the rulers of the provinces. The majority of the soldiery were *ashigaru*, poorly trained and equipped peasant conscripts. However, there was typically a cadre of *samurai*, members of the warrior caste, who literally spent the majority of their lives either practising for or engaging in combat.
In these wars, one lord might be defeated in battle and be left with no escape where he could retreat, regroup and return to battle again. In such circumstances, the defeated lord was expected to die honorably, either in battle, or by *seppuku*, ritual suicide. His senior *samurai* would also be expected to either die in battle or commit *seppuku*. However, *samurai* as a group were people, and not universally paragons of virtue. So, some of these senior *samurai* would have fled the scene of their lord's defeat and retreated to make a life for themselves... Where? In the most defensible places in Japan: the mountains.
Of course, if it became known that a notable defeated *samurai* was hiding out in the mountains, the lord who defeated his master would likely send troops to dispose of this dishonorable holdout. However, if this *samurai* wore a mask, and dressed in a feather raincoat, he might go unrecognised, even if troops were sent to investigate.
If troops were sent to investigate stories of someone wearing a *daisho* (a *katana* and *wakisashi*, which were a pair of long and short sabres restricted to the *samurai* and forbidden to anyone else), the troops sent might have been a few younger *samurai* and some *ashigaru*. In most cases, the *daisho* wearing individual might have been a *ronin*, an unemployed samurai. Ronin frequently resorted to banditry to support themselves, and so had a bad reputation. However, some of these *ronin* may have been more than mere no-account unemployed *samurai*, but former senior retainers.
In the event of discovery, these former senior retainers would likely have fought for their lives, retreating to their inaccessible mountain dwellings if necessary. Given their likely skills, they would be able to defeat a disproportionate number of foes, especially *ashigaru*. On the other hand, if the *samurai* leaders of tbe detachment were to be defeated (i.e. killed), *ashigaru* were not noted for their bravery. It is entirely possible that they would flee rather than fight a man of such skill who would surely kill them, and by reporting this person as "a tenku" rather than a specific former senior retainer of a defeated lord, their own lord would have reason to ignore this person rather than spend more men trying to kill him... persons including the *ashigaru* who witnessed the first fight.
So, the arguments for *real* tengu living in the mountains is the same as for the historical tenku/ronin: the locations are very easily defended and very difficult to assault with a lot of men, making defeating a foe living there without a ruinous cost unlikely. A few highly skilled individuals in such a location could hold off an army. Before long, any advantage that might be gained from taking the objective could be outweighed by the cost of taking the place.
] |
[Question]
[
In many movies, alien species often have the ability to impregnate "every and any" species and have their mutant offspring.
I have a story setup where some, not so conscientious, scientists decide to make that happen, for whatever reasons.
But I wish to explain "how it worked", what's the biology mechanic behind it that make such thing "plausible"!?
Because in real world, crossbreeding often failed. Even if they do succeed, they often produce an infertile offspring.
What possible ways for the alien species to "guarantee" a success and produce, preferably fertile, offspring!?
[Answer]
Your species reproduces by attaching to any sperm and/or egg cells, but doing so like a virus which lays dormant in a [lysogenic cycle](https://en.wikipedia.org/wiki/Lysogenic_cycle).
Viruses replicate using either the [lytic cycle](https://en.wikipedia.org/wiki/Lytic_cycle) (where virus cells are produced very quickly and destroy the host cell), or the [lysogenic cycle](https://en.wikipedia.org/wiki/Lysogenic_cycle) (where the viral DNA is implanted into the host cell which continues to reproduce normally, but in doing so creates more of the viral DNA).
Diseases like chickenpox/shingles can lay dormant for years - decades even - by simply replicating in the lysogenic cycle. Eventually it can be "activated" - meaning the viral DNA in all the replicated cells start reproducing in the lytic cycle, consuming the host cells. Basically, it's the stuff of nightmares.
So your originating alien species doesn't reproduce by implanting sperm or eggs; it injects "venom" (a virus) into any living species. The "venom" finds and attaches to the host sperm or eggs. The species then goes on and reproduces normally, but the viral DNA exists not only in the parent, *but in the child as well*, thereby creating a type of hybrid. The dormant virus either (a) includes the genetic information of the host species (looks, features, etc), or (b) becomes "activated" - not by destroying the child DNA but by "taking over" the chromosomal features.
To better understand this process, look at [this image from wikipedia](https://en.wikipedia.org/wiki/Lysogenic_cycle#/media/File:Lysogentic_cycle_diagram.svg):
[](https://i.stack.imgur.com/U6wCY.png)
This would allow the host DNA to match up on different chromosomal layouts - perhaps including plants. There's some hand-waiving here, as there are no real-world examples of viruses which attach to sperm/egg cells in this way, but the concept of this type of virus is very well studied (again: chickenpox/shingles), so it's "plausible" in that sense.
[Answer]
### If you're talking about combining DNA to produce viable offspring - not a chance.
I've already gone over this in a [similar question](https://worldbuilding.stackexchange.com/questions/70471/can-a-reproductive-system-that-allows-interspecies-breeding-be-made-believable), so I'll just copy that part to here.
>
> The problem with this is that even if there is a mechanism for
> combining DNA arbitrarily, you can't plug bits of DNA into another
> species with a different evolutionary path and expect to come up with
> something meaningful. Even supposing they happen to look like humans,
> they will be completely different on a chemical level. They will
> probably not be able to produce proteins from our DNA, and if they
> can, said proteins will most likely be either useless or toxic.
>
>
> The reason why mating makes sense biologically is because you're
> combining your DNA with that of another organism whose genes are close
> enough to your own that the child will be able to benefit from those
> good (or at least viable) genes. Here, the child will not benefit from
> the fact that the other species has good (or at least viable) genes,
> so what's the point? You could say it's just randomly mutating to
> prevent the child from being a clone, but in that case you might as
> well just randomly mix up DNA and hope something comes of it, saving
> the tedious difficulty of mating.
>
>
> Some bacteria do swap genes randomly with bacteria of other "species",
> but this only makes sense because #1 bacteria are much more
> structurally simple than multicellular organisms and therefore
> producing a new protein has a much lower chance of simply killing them
> and a fairly decent chance of providing some benefit, and #2 bacteria
> reproduce so fast that they can afford to take these risks.
>
>
> All this is without even getting into the issues of the species being
> alien. They might not even *have* DNA.
>
>
> Now of course since these organisms are both alien and artificial you
> could say that they have a completely different chemistry. Maybe they
> even have "smart" DNA that is somehow able to analyze the DNA of its
> partner and pick out bits that might be useful. But this is getting
> into realms of bio-engineering so far beyond feasible speculation that
> it might as well be magic. Not that there's anything wrong with that.
>
>
>
Forget about making an interspecies *impregnator*. Instead, try and figure out how to make an interspecies *parasite* - a creature that injects its own offspring into the host, which develops and (somehow) acquires traits of its host. Basically, you want a Xenomorph.
Of course, the Xenomorph is *also* completely implausible. Endoparasites are, by nature, incredibly specific to their hosts. They need to feed off of exactly what the host is providing and fight off all of the host's defense mechanisms, which will be different for every species. And that's just on Earth, where most organisms share similar biochemistry, since they all come from a common ancestor. On other planets, even this is unlikely. Aliens probably wouldn't even be able to *eat* us and gain nutrients from it, let alone impregnate us.
But since the species is engineered, we can bend the rules a little. Let's say this is a species that can take *any* complex molecule, break it down, and construct its body atom-by-atom. (This means it should be able to "eat" *anything* with the right elements in it.) It will probably need energy to accomplish this, so let's say the parasitic embryo is injected with a high-energy "yolk" that it actually feeds on, using the host's body for mass alone. It also must be incredibly hardy to avoid being broken down by the host's immune system.
Now comes the even harder part - assimilating the host's traits. Analysis of DNA or biochemistry won't work, since the host is completely alien on a chemical level. Instead, the parasite must analyze its host on a physical level. Perhaps it produces a swarm of tiny blood parasites that swim through the body, collecting information, and then bring it back to the main body. The main body must also possess a knowledgable brain - perhaps the parent passes on actual pieces of its brain, unlike Earth animals that grow from a single cell. (This also means that the child will have some of its father's "knowledge" when it is born.)
The parasite must then take that information and use it to construct its body *consciously*, creating something similar to the host. It then must figure out how best to exit the host without causing harm (unless it doesn't care about this).
No, this is not plausible at all. But it might be able to help you produce something that sounds *almost* possible.
[Answer]
It really depends on how alien that "every and any" alien species may be.
If they all depend on DNA for genetic information, it becomes more plausible (if still unlikely). This could even be [extended DNA with five bases](https://www.nature.com/news/2005/050314/full/050314-8.html) or more rather than the four we see on Earth. Then, feasibly, the impregnating alien could place an 'egg' of a sort inside the host creature, and the egg then siphons off DNA from the host and combines it with its own. This would have to happen in some kind of structured fashion, or you would get gibberish. Maybe only certain impregnator genes can be replaced with host genes.
More complicated, the 'egg' could be a creature of its own with enough intelligence of a sort to be able to analyze the host's DNA and decide what parts need to be overwritten/combined to create a hybrid. Maybe mainly genes that express general morphology are taken from the host, while deeper functions all depend on impregnator genes. Possibly, the imprenator's vital organs can all be placed more or less anywhere inside the morphology of a host body.
Without a common genetic molecule, I really can't see how it could happen. At best (or worst) I could see an alien parasite using a host body as a structure to grow into, slowly transforming that body into a hybrid - sort of like how hermit crabs take over mollusc shells. The result wouldn't be an offspring per se, though.
[Answer]
I wouldn't call it hard science, but [this](https://avp.fandom.com/wiki/Facehugger) could be one possible approach, depending on what you mean by "impregnate".
] |
[Question]
[
I was hypothesizing an organism that could create it's own fire with the use of a flamethrower-like organ. I was thinking that this animal has a oxygen-free organ that hold diethylzinc and when the animal feels threatened or such, its sprays out the diethylzinc with instantly ignites when in contact with air, practically acting as a flamethrower. I mainly wondering if this seems like a plausible scenario and if diethylzinc would be a good substance to use.
[Answer]
**Mix the diethylzinc with oil.**
1. Oil (think whale oil, or spermaceti) can be produced using biology with no problem.
2. A hydrophobic light oil would also tend to exclude oxygen. The oil reservoir would be a safe place to store your diethylzinc igniter molecules.
3. A stream of viscous oil would be an easy thing to use as a breath weapon.
4. Mixing the diethylzinc with the oil would mean on contact with air, not only the diethylzinc ignites but then it also ignites the oil. You get a lot of added value from the zinc - once the zinc oxidizes it is gone, but when the oil ignites it will burn fiercely.
[Answer]
Your general idea is definitely possible and the use of Diethylzinc is a creative and possible one.
Nevertheless I would go an easier route as this is the one evolution often takes.
Diethylzinc combust with contact to oxygen which means that you would need a bladder like organ to produce and store your fuel without having any Oxygen in this organ (also not in the cells of the organ). Therefore I would go with a fuel which does not self-ignite.
The first think which comes to mind is Methane as this is something a lot of [animals are already exceptionally good at producing](https://www.newscientist.com/article/2208449-we-could-breed-climate-friendly-cows-that-belch-less-methane/).
Now that you need a source of ignition I would propose [electroplaques](https://en.wikipedia.org/wiki/Electric_organ_(biology)) to create a biological spark plug.
Your average [electric eel](https://en.wikipedia.org/wiki/Electric_eel#Physiology) does "only" produce about 1 Ampere at 500Volt but you could give your flame thrower animal just a bit more power to get to the Voltage you need to ignite fuel.
Now you have a safe flame throwing animal which produces it's fuel as a byproduct of it's digestion.
This is an efficient solution which, to me, sounds like something evolution would like.
---
If you want to precisely figure out how much you need to ignite Methane, [here is a paper](http://conference.ing.unipi.it/ichs2009/images/stories/papers/125.pdf) about the ignition of methane-hydrogen-air mixtures (which also examines the ignition energy of methane-air mixtures).
[Answer]
Nature is ahead of you -- the bombardier beetle uses a mix of hydroquinone and hydrogen peroxide to similar effect. And it works!
<https://en.wikipedia.org/wiki/Bombardier_beetle>
[Answer]
Personally, I like your idea of Diethylzinc. According to wikipedia:
>
> Diethylzinc (C₂H₅)₂Zn, or DEZ, is a highly pyrophoric and reactive
> organozinc compound consisting of a zinc center bound to two ethyl
> groups.
>
>
>
Now, this is the case in STP conditions (I think), so if your dragon was to go around doing burning people, it would have to do it in standard conditions. I think the main thing is that the dragon must somehow maintain its internal physical conditions. Basically its fire-chamber's temperature, pressure, chemical balance has to be very regulated, especially if your dragon wants to set things on fire in deserts and tundra. Otherwise, this power would be localized to areas where conditions allow it to, and nowhere else.
My only critique of Diethylzinc is where it's found: in the real world it must be synthesized, and is often found commercially as a solution in hexanes, heptane, or toluene, or as a pure liquid. So unless you can figure something else out, your dragon's fire chamber has a lot in common with an oil tanker or fracking operation.
**EDIT:** Bombardier beetles use both a fuel, hydroquinone, and an oxidizer, hydrogen peroxide. A pair of organs to produce and store the fuel and oxidizer, plus a third organ to catalyze their mixture and safely direct the resultant plasma, would make sense to get around diethylzinc's reliance on standard temperatures and pressure.
Now the limitation here is that although this could help, the beetles themselves release something that feels like hot, boiling water, which could change the nature of the fire being produced by your dragon. So, maybe copy the beetle's containment system, but definitely change the chemistry inside. Or, mix the two and you can effectively construct a more efficient way to set fires as a dragon.
*Source*: @Ghedipunk's comment
[Answer]
I'd personally go with a binary that produces an exothermic reaction (like the bombadier beetle) rather than a single pyrophoric material. That gives you a safety margin; you could imagine the two reservoirs of material have individual orifices that each spray their respective chemicals out so they only ignite once they mix outside of the animal.
For instance, potassium permanganate will ignite when mixed with glycerine or ethylene glycol (in fact, it's sold in survival kits as a firestarter). If you have the potassium permanganate in an organic oil or water suspension, spray that and spray the other chemical along with it, the fine mist should create a nice fireball.
] |
[Question]
[
## How Long?
In the 1960s, unknown to most, the United States set up a secret base on the moon manned by an "extra" aboard each Apollo lander. NASA architects decided that the base must be built into the native rock, taking advantage of [lava tubes](https://www.space.com/32795-moon-lava-tubes-protect-astronauts.html) to quickly conduct themselves below the surface - granting them protection from the heat, cold, and radiation behind dozens of yards of hard rock. The station was powered by a radioisotope thermo-electric generator.
Unfortunately, the base ended in tragedy. Planners had overestimated the quality of air and water scrubbers and also badly underestimated the need for spares. Changing political fortunes at home caused the base and crew to be left for dead. By accident, towards the terrible end the pressure seal on the base was ruptured exposing the crew and structure to the void.
How far forward in the future might it be possible for a future explorer, armed with a map and old government records, to find moonbase Snoopy and still be able to find any of the technology (LED lighting? Computer systems?) still operational?
Would it be possible that anything would be left after centuries? Millenia?
[Answer]
**First what does this base look like?**
Taking earth as an analogue [lava tubes](https://en.wikipedia.org/wiki/Lava_tube) are about 1-15 metres below the surface. Lets presume the base was the safest possible at 15 metres down.
Now [Mars One](https://www.mars-one.com/faq/health-and-ethics/how-much-living-space-will-the-astronauts-have) are projecting a living space of a 1000 square metres for their habitat. So how about a roughly straight section of tube 10 metres wide and 100 metres long.
**Danger list:**
* Gamma Radiation
* Extreme Heat/Cold
* Space Vacuum
* Asteroids
* The Sun
* Humans
**Gamma Radiation**
Radiation is all around us, but Gamma Radiation is some of the most high energy. It has a nasty effect on electronics [particularly computers](https://hps.org/publicinformation/ate/q11162.html). While it may not destroy the computers it will corrupt their running software, which might cause an automated self-destruct sequence to run, or the generators to run too high, etc...
[Fortunately a few centimtres of lead](http://www.bbc.co.uk/bitesize/standard/physics/health_physics/nuclear_radiation/revision/3/) or a metre of concrete will save the day. That 15 metres of rock should do the trick.
Also keep explosive things away from the habitat itself, and pipe/cable them.
**Extreme Heat/Cold**
Being 15metres below the ground this base won't be exposed to the extremes at the surface. Now 1 metre below the surface has a temperature of [roughly -21.6 centigrade](https://space.stackexchange.com/questions/19906/constant-lunar-sub-surface-temperature). At 15 metres we are talking somewhere between -20 and -40. Our equipment regularly survives these temperatures in the arctic/antarctic.
Given that there would be little fluctuation once the heating system failed, this would be unlikely to damage anything in the base. (Aside from initial cooling).
**Space Vacuum**
Worthy of note, but mostly harmless.
Space being a vacuum means that it has nothing to affect the moon base. The real problem in this scenario is in fact self-harm. The moon base being pressurised could explosively depressurise. Roughly 3000 cubic metres of air (3 metres high by the 1000 metre squared living space) would attempt to vent out one end. The air reserves and any liquid water might decide to do the same thing. Water can boil in space due to lack of air pressure.
As bad as this might sound, structurally speaking the base would be mostly fine. There would be a much larger hole in the habitat were it depressurised, and some amount of mess caused by the rapid air movement. Some things would likely have exploded due to air trapped inside them during manufacture, such as wires, batteries, and computer devices. Some of these may have survived if the government thought to manufacture space worthy versions, instead of using cheaper components presuming the habitat would protect them.
Over time the moon base will leak atmosphere, reducing the amount within. What will cause explosive depressurisation is if a hole forms.
This could be because of some external damage, it is after all in an underground tube, a disturbance could cause rock to hit the habitat and make the hole.
Alternately the most likely culprit is some chemical reaction happening within the habitat. This could be something like acid or a solvent eating through its container, and then affecting the habitat. The more likely is the oxygen in the atmosphere. It loves to react with just about everything. Fortunately your astronaut already dealt with this issue by breathing it in and leaving it as relatively inert carbon dioxide.
**Asteriods**
The moon gets hit by a lot of rocks, and it has no atmosphere to dissolve them before they hit.
There are a lot of [different sized impact craters](https://cosmoquest.org/x/blog/2012/02/how-many-craters-are-on-the-moon/). Depending on how you try to count it we get around 20 million above the size of 1 km. This is pretty worrying for the moon base because even if the crater is only 2 or 3 metres deep the shockwave could collapse/damage the tunnel, and [NASA is worried about that precedent too](https://www.nasa.gov/centers/marshall/news/lunar/lunar_impacts.html). Turns out the moons is being hit a lot and often.
If we do some [rough calculations](https://www.forbes.com/sites/quora/2016/12/29/how-often-do-meteoroids-hit-the-moon/#3026f63c6f2b). A musketball impact roughly every 1380 years for an area of 752 square meters. That is a direct hit to this moon base, and quite likely catastrophic.
**The Sun**
... will swallow the earth, or come pretty close in about [7.6 Billion years](https://www.smithsonianmag.com/smart-news/earth-will-die-a-hot-horrible-death-when-the-sun-expands-and-swallows-us-and-now-we-know-what-that-looks-like-28965223/).
So either the Earth (and its moon) are now parts of the Sun, *or* the sun is sitting so close that the moons surface starts to liquefy/erode.
**Humans**
Somewhere between now and the sun killing us all. Humans will want to move.
If we are tardy, the moon is a great mining opportunity for making our trans-solar space ship. I doubt the base would be preserved.
If we are enthusiastic, the Moon will be mined, settled, and used for space ship construction in the not so distant future. It is hard to determine how quickly we would find and/or destroy this base. Most human settlement occurs above the top 10 metres of ground, and it would take numerous generations to get a full population going, presuming that 1/6g is habitable by reproducing humans. Then again, presumably a 15 metre deep lava tube might make a very convenient location to setup, and be found if not immediately then shortly after.
**Long answer Short**
You have till the first human settlements on the moon, assuming they look for magma tubes too, because they are poorly funded/have to look for cost efficiencies.
Otherwise you probably have 1380 years, maybe a bit more if the site is luckier than expected, or the humans install an atmosphere/laser defense system.
Otherwise you have till the humans need to strip mine/convert the moon sometime later.
7.6 Billion years is the cap, excepting the serious good luck to be missed by those who fly the moon off into deep space.
[Answer]
Space scientists strive to get samples from comets and asteroids to better understand the history of our solar system. This because anything which is kept away from the nasty solar radiation is going to take way less damage and thus bear more information.
And if this applies to some icy/rocky body formed few billions of year ago, it has to apply also to tech leftovers produced less than a century ago.
If they are buried deep enough they will get no UV or X-ray from the sun. They might get occasional high energy cosmic rays, but those events do not bring macroscopical damage. Add to this that electronic from the 60'es was much more bulky than present day, thus while a cosmic ray impact might disrupt a 7 nm track today, would just tickle a 0.05 mm track dating back to those times.
The buried artifact will just be subject to the lunar core heat flow, which is small but still sufficient to keep the temperature above the few K of deep space.
Wrapping up, I would say that:
* the exterior aspect of all the items would be preserved pretty well for geological times.
* the functionality might be affected in some cases: cold welding of dry metallic couplings, demagnetization of magnetic elements are just some of the examples that come to my mind.
[Answer]
**How Long?**
I concur with the other two answers in that everything could be potentialy functional if sufficientley shielded from hard radiation and strikes by macroscopic particles.
However we need to look at several potential problems:
**[Tectonic activity on the moon](https://news.nationalgeographic.com/news/2012/02/120221-moon-recent-tectonic-nasa-molten-space-science/)** - until recentley it was thought that there hadn't been any since the moon's formation roughly 4.6 billion years ago.
The current best theory however is that the most recent scars formed roughly 50 million years ago, and no further activity is expected. No worries here then.
**[Thermo-electric generators](https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)** are potentialy going to last that long, still producing energy, depending on what they're made with:
Plutonium oxide was used in the Cassini and the Galileo mission's TEGs - but:
>
> Plutonium-238 has a [half-life](https://en.wikipedia.org/wiki/Half-life) of 87.7 years
>
>
>
Which is not sufficient to provide appreciable power over a millenium. However:
>
> Am241 (Americium) has a half-life of 432 years and could hypothetically power a
> device for centuries.
>
>
>
**The equipment was *[left switched on](http://www.vias.org/transistor_basics/transistor_basics_07_05_01.html)*:**
>
> The usual transistor failure occurs gradually over a long period of
> time and after thousands of hours of operation. The performance
> degradation generally shows up as an increasing saturation current ...
> the (device's) efficiency and gain suffer.
>
>
>
As to the monitors - I couldn't find specific figures for Cathode-Ray-Tube electron-gun life-expectancy, but the heater coils show gradual evaporation till they finaly fail - not to mention the gradual wear and tear of the phosphor - if you've ever seen an old multisync monitor you'll remember the permanent silhouette of the default screen etched there.
**[Electrolytic capacitors.](https://www.eevblog.com/forum/beginners/does-an-electrolytic-capacitor-work-in-vacuum/)**
These are ubiquitous in electronic equipment, they rely on a water based solution inside them to work, so if they're not sealed properly it would evaporate and cause them to fail - and since any rubber seals would have degraded on this timescale... they screw things up for you.
**Hot Equipment.**
Any equipment that relies on fans or convection currents to keep cool is going to melt if it doesn't trip.
## Conclusion.
Providing:
* It had adequate shielding.
* There are no catastrophic collisions from above.
* There's sufficient redundancy in the generators.
* The power tripped "off" when the base became abandoned.
* NASA had the foresight to use rugged tantalum-bead capacitors.
I see no barrier to securing the hatch, repressurising, brushing off the thin layer of dust that's formed and booting up, one system at a time, carefull not to overload these museum pieces. Even after 1000 years in semi-hard vacuum. Difficult to test in our lifetimes though, so even if I'm wrong I can still bet the farm with impunity.
] |
[Question]
[
We do not know how exactly it happened, but poor John Doe made a space-time trip along a three dimensional analog of a Möbius strip (a Klein bottle). He is now back on Earth, but he is now the mirror image of his former self: His heart beats on the right side, he is left-handed now, and even worse: All the molecules in his body (peptides, sugars, DNA and RNA) are mirrored, too.
Water is still drinkable and air is still breathable, but all the food on Earth is inedible or even poisonous to him.
Scientists quickly diagnose and confirm John's state, but how can he be fed?
I am asking about a plan to prepare food for him, not only noticing the fact that normal food is not available for him and he's in trouble. That I know already.
To be realistic, any programme to feed poor John Doe must be set up in reasonable time before he dies of starvation. You may use mirror bacteria extracted from John's skin or from John intestinal tract.
Doing the space-time trip again or going back the way he has gone is unfortunately not an option.
[Answer]
* If all that's happened to John is that the sugars and amino acids in his body flipped to the other chirality, then we can feed him without too much trouble. (But it will be expensive; I'm hoping he's rich or has a gold-plated insurance.)
>
> *Without a chiral influence (for example a chiral catalyst, solvent or starting material), a chemical reaction that makes a chiral product will always yield a racemate. That can make the synthesis of a racemate cheaper and easier than making the pure enantiomer, because it does not require special conditions.* (Wikipedia, on [Racemic mixture](https://en.wikipedia.org/wiki/Racemic_mixture))
>
>
>
In plain words, many chemical reactions which produce chiral molecules will produce equal amounts of the [enantiomeres](https://en.wikipedia.org/wiki/Enantiomer). This is actually a problem when trying to synthesize such substances, because biology only wants one of the enantiomeres.
That's why we need a way to separate the enantiomeres; this is called [chiral resolution](https://en.wikipedia.org/wiki/Chiral_resolution). There are several well known methods of chiral resolution; see for example "[Simultaneous Enantioseparation of Monosaccharides Derivatized with L-Tryptophan by Reversed Phase HPLC](http://www.jsac.or.jp/analsci/data/pdf/30/07/a30_0739.pdf)" by Mami Akabane, Atsushi Yamamoto *et al.*, in *Analytical Sciences*, Vol. 30, July 2014. It's not economic to do so, because normally we get the right chirality food from nature, but we *can* do it. If more and more people end up in John's condition it is likely that efficient methods will be developed.
So, long story short, John will have to eat synthetic sugars and amino acids synthesized from scratch; natural fats and minerals are all right. We can feed him the racemic mixes, and his body will assimilate the right molecules and pass the others; or we can feed the mix to ordinary bacteria and feed him what the bacteria could not assimilate.
* Ah, and what has this to do with quantum [parity](https://en.wikipedia.org/wiki/Parity_(physics))? Nothing -- both ordinary D-glucose and exotic [L-glucose](https://en.wikipedia.org/wiki/L-Glucose) are made of atoms containing protons and neutrons and electrons with their ordinary parities. If the question is seriously asking what would happen to John is the parity of his constituant electrons and protons and neutrons was reversed, then the answer is we don't know. There is a lot of speculation about [mirror matter](https://en.wikipedia.org/wiki/Mirror_matter), but nobody has ever seen it.
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I don't know if that suita your settings, but i am going to give it a try.
Cultivate huge ammounts of bacteria from his bowels and skin. Have you seen those leather funghi stuff? That ammount.
Well, the bacteria can't feed on normal stuff, YET. They are survivalists and adapt to many environments, so even though not all population will survive, some individuals of each generation might do a little better and you select those until you have a mix of mirrowed baxteria feeding from normal stuff.
Then, just make a ration of it, purify the toxines and stuff. Gnarly ration, but better than starving.
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In my military scifi novel the military is, obviously, very concerned with security aboard its spaceships. They don't want other people to be able to receive any information about what happens on their ships. They also don't want other spaceships to be able to send any signals to the computers and other devices used by the crew on the ship, at least no signals that didn't go through the "comm tower" that handles normal ship-to-ship or ship-to-planet communication and data transfer.
For ship sizes think [modern destroyers/cruisers](https://en.wikipedia.org/wiki/Zumwalt-class_destroyer) up to [aircraft carrier size](https://en.wikipedia.org/wiki/Gerald_R._Ford-class_aircraft_carrier) in space, just with a big engine at the back and all around armor plating.
Combat happens through missiles at distances between one and sixty lightseconds.
Technology is closer to [The Expanse](https://en.wikipedia.org/wiki/The_Expanse_(TV_series)) than Star Trek, i.e. no shields, no FTL communication and no teleporters.
Groundside on todays earth that might mean that wireless communication is forbidden, because the signals might be detected outside and someone with a powerful enough computer might eventually decrypt whatever was transferred through the wireless connection.
There are a few emissions that can't be prevented, e.g. heat and engine, but what other kinds of emissions could give information about what happens on the inside of the ships away? How would EmSec work in space?
My current idea:
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You're in a steel box, it shields internal wireless communications from the outside by virtue of being a big steel box. See [Faraday Cage](https://en.wikipedia.org/wiki/Faraday_cage) for details. I work in a steel frame building, we basically have no mobile signal inside. Your only external comms is through the comms tower because all other signals are blocked by the nature of the hull.
What's going to be far more interesting is tracking the [tiny vibrations in the outer hull caused by people and equipment moving around inside](https://www.sciencedirect.com/science/article/pii/S0263224116000178). They're going to know when your shifts change, they might even be able to track individuals moving around in the ship depending on how sensitive their equipment is.
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# Do not make a problem where there is none, or you will be ridiculed
I am sorry but this...
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> They also don't want other spaceships to be able to send any signals to the computers and other devices used by the crew on the ship, at least no signals that didn't go through the "comm tower" that handles normal ship-to-ship or ship-to-planet communication and data transfer.
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...is an almost nonsensical concern.
Getting communications to work is not an easy task, especially not in the digital age. For reasons too long to explain here, I will state the following as a given fact:
**You cannot "send a signal" to a device unless it is *explicitly listening for one***
If we were to rip out the radio units of your phone (4G, WiFi, Bluetooth), there is no way in hell you can "send a signal" to that phone without being physically connected to it. [Magic Hollywood Hacking](https://tvtropes.org/pmwiki/pmwiki.php/Main/HollywoodHacking) has led us to believe that we can access any device anywhere just because we want to but reality / realistic fiction begs to differ. Your readers will **laugh at you** if you create an environment where intruders can access computers at a distance and at will if those computers do not have a wireless communication interface.
# That said...
...even if [Eve & Mallory](https://en.wikipedia.org/wiki/Alice_and_Bob) cannot intrude on systems that are not actively listening for outside communications, you still have the comms tower, and you still have devices that are listening for **internal** communications.
This means you must have **communications protocols** that are specifically made to avoid unauthorised communication and to reject intrusions. Especially [**handshaking**](https://en.wikipedia.org/wiki/Handshaking) is required to set up a communications channel before you can start moving any data. But — again — the device must have been set to listen for the signals to begin with.
The comms tower is set to listen. There you need to have protocols that are made so that no handshaking is being performed until the incoming transmission has authenticated themselves. Otherwise Eve & Mallory could fool your ship to reveal its location by broadcasting transmissions in the blind and triggering a handshake attempt. This however is not a big issue and can easily be automated.
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Same thing for internal devices: they must be set to not trust any old transmission, but only those that can be authenticated. Again: this is not much of an issue, even present day communication protocols are designed for this (although [not always successfully](https://www.theguardian.com/technology/2017/oct/16/wpa2-wifi-security-vulnerable-hacking-us-government-warns)).
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> Eve & Mallory have gotten their hands on such a device that was not set to lock itself or self-destruct.
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# EMCON
Finally there is [EMCON... emissions control](https://en.wikipedia.org/wiki/Radio_silence#Military). This is good old fashioned **radio silence** and behaviour procedures for that are in effect even today. And — again — [these are not always successful](http://securesense.ca/fitness-app-causes-security-risk-high-ranking-military-officers-spies/).
You had the notion that internal communications should be made only over wired devices.
**That is a good idea, and is used in real life**
Personal anecdote: I did my military service in the Swedish Airforce. My task was to ready aircraft. When military aircraft are on the ground and being serviced in a war-like situation, it is procedure to hook them up to a land-line. In our case the connector was clipped to an eye in the concrete pad the aircraft was being serviced on. So when the plane started rolling, the connector with be yanked out by itself. That way the plane could be radio silent the entire time it was on the ground, no confidential orders would leak, and it would not even announce its presence through its emissions.
Apart from that there are several schemes to make artificial emissions disappear among the natural noise, for instance [LPI radars](https://en.wikipedia.org/wiki/Low-probability-of-intercept_radar). But out in space, any emission from a point source is likely to arouse suspicion.
# Levels of EMCON
Just like [submarines have different "rigging" when it comes to sound management](https://en.wikipedia.org/wiki/Silent_running_(submarine)) — which can be anything from We Do Not Care If We Sound Like A Rock Festival, in various levels all the way down to Do Not Even Talk Loudly — your space ships most likely also have that. The EMCON can take many levels from Noisy (all comms operative, space radar/lidar, jamming) to Quiet (no active comms, low intercept mode) to Stealth (everything that can emit is shut down).
In order to enforce this, I would recon that all emitting devices on-board can be turned off down by a "shut up" command from the ship itself.
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It's not beyond contemporary technology to create a series of shells that collect, convert and direct 'emissions' to a given point wherein they can be released into a high energy environment (the exhaust) that effectively neuters any attempt to listen in on emissions.
Such systems don't need to be passive, electrically active and reactive phases could be charged to switch an entire material layer to shed/gather in a sequence that would void any attempt to pass useful information through the hull. Such an arrangement would likely be expensive in any non techno-magical era, but then, in an era of routine spaceflight every polity can be 'genocided' with ridiculous ease if their spaceborne protectors are compromised, so one imagines quite an effort would be made to ensure they aren't.
<https://www.nuclear-power.net/nuclear-power/reactor-physics/atomic-nuclear-physics/radiation/shielding-of-ionizing-radiation/shielding-gamma-radiation/>
<https://physics.stackexchange.com/questions/43063/what-is-the-highest-possible-frequency-for-an-em-wave>
The designers would know perfectly well what ranges they couldn't shield against/contain and take account of that in any decisions re: what format/wattage onboard devices might take.
Moreover building a warship intended for space operations without equipping it with sensors capable detecting all bands of emissions in all directions would have to go down as a bad idea. Algorithms attached to the sensors can be used to detect any attempts to garner information on the internal workings by 'radar' returns and create 'noise' to match the return frequencies.
This is assuming of course the ships are operating in the light of day and not attempting more general stealth.
General stealth would be a matter of materials tolerances, absorbing man-made wavelengths whilst emitting natural ones shouldn't be too hard a design challenge with technology that routinely sends people flying about space though.
Have you thought about how your missiles are guided btw? I imagine in the 2xth century it would be trivial to blind missiles and even ship sensors before missile launch, that is, they have to have an idea of where their target is. The speeds ships and projectiles would have to be moving to outmaneuever simple tracking mechanisms on wide band emitters designed to overwhelm enemy sensors would need to be post-star trek, i'd think.
'Stealth-by-blinding'
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[Van Eck phreaking](https://en.wikipedia.org/wiki/Van_Eck_phreaking) of some kind will always be an issue with space craft, even one with a [Faraday Cage](https://en.wikipedia.org/wiki/Faraday_cage), which you want your ship hull to be for the protection of the crew from incoming radiation anyway. The Faraday Cage lights up, a little, at certain frequencies when EM radiation hits it, whether from the inside or the outside. In theory you can read the response of the Faraday Cage, AKA the hull of the ship, to the radiation hitting it and differentiate the internal signals. Then if you know the layout of the vessel and how the ship's display systems work you can work out what is being displayed. This is an extremely advanced technique that would require very discerning sensory systems but it is possible. To avoid this kind of surveillance [direct retinal displays](https://en.wikipedia.org/wiki/Virtual_retinal_display) are your best bet as they are extremely, personally, directional rather than being in fixed positions within the hull and they put out very little signal to start with.
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I'm writing a short story that takes place on an imaginary planet that is 88% ocean. The planet has two moons and one continent that is regularly flooded under 500 to 1500 feet of water. The tides are only extreme once or twice a month. I'm trying to work out the parameters for a two-moon system that produces such an effect. I'm working from the bottom up. This regularly flooding continent is essential to the story, so what is the best way to make this work?
I'm thinking one moon orbits at a very high velocity, while another moon is very large and further away, but when they align the flooding gets to be bad. Does this make sense?
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Look at planet Earth: also there [tides](https://en.wikipedia.org/wiki/Tide) are extreme only when the Moon and the Sun (the main attractors when it comes to the tides) are aligned with the Earth.
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> Approximately twice a month, around new moon and full moon when the Sun, Moon, and Earth form a line (a configuration known as a syzygy), the tidal force due to the sun reinforces that due to the Moon. The tide's range is then at its maximum; this is called the spring tide. When the Moon is at first quarter or third quarter, the Sun and Moon are separated by 90° when viewed from the Earth, and the solar tidal force partially cancels the Moon's tidal force. At these points in the lunar cycle, the tide's range is at its minimum; this is called the neap tide, or neaps.
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If you want to change the height of the tides, just work with the distance between the moon and the planet, or the mass of the moon.
A second moon added to this system would introduce a further pulsation and would likely not make possible the effect you want
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As mentioned in other answers, for the purposes of tides, the earth already has two 'moons', i.e. the moon and the sun. The difference in their gravity pull between the near side and the far side of Earth determines their influence on the tides. For nearby bodies this will be a much bigger difference.
The height of the tides however is much more determined by the shapes of the oceans and continents. There are places in the middle of oceans where there is nearly no tide at all. The strongest tides are at coasts where tides are funneled into a bay or similar body that has the right size to resonate with the pull of the moon. Tides in the oceans are more comparable to a bathtub on wheels that is being shaken and in which standing waves form, than with water flowing around the world following the moon's pull. So for a planet that is mostly water, with small continents that do not block the east to west flow of oceans like earth's continents do, the tides would be lower than on earth.
Another thing to note is that not just the oceans experience tides, the earth mantle does too. On the scale of the entire planet, the crust and mantle rock is flexible enough that you don't notice it. [Earth tide](https://en.wikipedia.org/wiki/Earth_tide) is about a meter high. A closer moon will also increase the earth tide, which reduces the relative increase in ocean tide. Since water is lighter and much less viscous than rock I would still expect the ocean tide to increase if you put the moon closer, but I'm not sure about the details.
The best way I can think of for creating once-a-month very large tides would be to have a large moon in a very elliptic orbit. When it comes close to the planet you will have a single high tide (depending on how close the moon comes and how fast the planet rotates), when the moon is far away for a long part of its orbit, tides will be much smaller. One gotcha with such an orbit is that it is probably not stable over astronomic time scales, the tidal forces will act to circularize the orbit over time. So you can't have this configuration for the age of your planet if the planet is billions of years old as the earth is. But the moon could have been slung in this orbit by an encounter with another body a few 100000 or million of years ago. Given the previous paragraphs I'm not sure how high a tide this could create. My guess would be that you could still have higher tides, but you still need to make sure the continents are rather flat. My guess would be tides of a few hundred meters would be possible, but not kilometers. And your continents will need to be small and with big ocean inlets. Water still takes a lot of time to flood the land, and a big continent where the closest ocean is thousands of km away from the center would not have enough time to flood in a day.
Another note: a planet system with multiple large moons would also be unstable on astronomic time scales. One moon is fine, multiple small moons is also fine, but multiple large moons only works for a long period of time if the central planet is much larger, e.g. gas giants, so that the moons are small compared to their host planet.
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As L.Dutch pointed out, the alignment of the Moon and Sun cause the biggest variation in tidal range but the largest of this on Earth is about [17m (50feet)](https://en.wikipedia.org/wiki/Tidal_range).
Interestingly, in a large open body of water the actual difference in level is minimal (usually less than a metre) and is instead caused by the [geography of the land](https://www.sciencedirect.com/topics/earth-and-planetary-sciences/tidal-range).
Even if you were to have two moons on opposite sides of the planet to cause as much spring tide as possible, 500 feet is way too high. The coast may suffer from high tide but as mentioned before, the shift in a body of water is too small to account for flooding an entire continent.
A possible solution around this might be to have the continent abnormally flat and close to that of sea level. Then even a slight change in ocean height could cause serious issues, but not enough to cause 500 feet worth of flooding.
Bring the Moon closer! Accounting for the [Roche Limit](https://en.wikipedia.org/wiki/Roche_limit), what if you moved the Moon closer to Earth? After a bit of [reading](https://astronomy.stackexchange.com/questions/19926/how-wide-is-earths-roche-limit) it looks like roughly 6000 km surface to surface would be a good ballpark figure for how close we can place the Moon in a "consistent" orbit. But at this distance its orbit speed would be much higher so now you have the pull on the Earth (and thus tides) would occur more often.
Using this [calculator](https://keisan.casio.com/exec/system/1360312100) the difference in gravitational pull of a Moon at this distance would increase by over 750% its current value. So maybe 500 feet isn't so unlikely as I first thought...
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Just have one moon (about the mass of ours; call it Moon A) in a **highly eccentric orbit** around the planet (perhaps it got flung into this orbit due to a collision with a Pluto-mass object, since the orbit, as mentioned in other answers, is unstable over billions of years). Then one can add a smaller one (around the mass of asteroid/planetoid Ceres which is about 0.03x that of our Moon) in a close in inclined orbit.
Then when the moon A reaches perigee at about 6x closer than our Moon is to Earth, the tidal range will be (IIRC) 6^3 ~ 200x higher than on Earth over that one small time period (less than a day). These tides can easily get over 1500 feet (and depending on the time of day, its maximum can go as low as 500, especially considering the geography of the land).
The purpose of the second moon, Moon B, is to be in roughly a geosynchronous orbit (closer in than A's perigee) so the planet will get tidelocked over geologic time with *it*, not with Moon A's much longer orbit on the order of a month (ensuring a comfortable day length).
Of course, one major side effect is that, during that day every month that the tides swell to 1000+ feet, the tidal forces will create massive volcanic eruptions and earthquakes.
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An entirely different way of creating your occasionally flooding land, you could also consider the land being made of floating mats of plants. You'll need to invent a story on why they sink occasionally, but since we're now talking biology there could be lot of reasons. Perhaps the plants evolved this behavior to get rid of the land creatures that feed on them, and the land creatures adapted to this leading to a kind of biological arms race.
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Does the continent have to flood just by the moons affecting the tides?
You could always make the continent that floods be below sea level. This would introduce a different problem on what drains it so it wouldn't just hold the water and be a lake.
If it was bowl-shaped with a "hole" in the bottom it could effectively drain back out.
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I am the new king of Earth. All current wars have ceased, and the whole planet operates as one kingdom. We have also decided on a currency. However, in order to pay off debt/create more buildings and roads/create more public services, I'd like to print off more money. That, in the normal world, would cause hyper-inflation, and drop a country's monetary value. It'd also mean prices for everything would go up. However, I want to stop this occurring. So, how do I get away with printing off more money and stopping inflation?
A tax on inflated goods might be a good idea, however that would also mean prices would go up even further to get profit. I'd also want my system to be humane, and keep the majority happy. Fortunately, because the whole world is a united kingdom, the problem of trading between countries with different currencies is nonexistent.
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I think you simply cannot.
If currency is a reflection of the total wealth of a country, printing more money has the mathematical consequence of bringing inflation.
Example:
* your nation only good are bananas.
* Your entire nation has only 10 bananas.
* you print a currency, let's call it bananero. You print 10 bananeros.
As a consequence, 1 banana is worth 1 bananero, or 1 bananero buys 1 banana.
Now you want more money, so your print 90 bananeros more. You end up with a total of 100 bananeros, but you still have 10 bananas.
This means 1 banana is now worth 10 bananeros, or 1 bananero buys 1/10 of a banana.
The only way out of this mathematical tyranny is to have more bananas, so that the ratio money/goods stays the same.
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# Theory 1
If you managed to add enough growth to the economy with your new infrastructure, then it should avoid inflation. That is, if your roads involved doubling the money in circulation, but made production so darn effective that people produced twice the number of widgets, the widget price would be about the same.
# Theory 2
You fix the prices of everything, by law, at what they are today. This will cause some people to have N dollars for a loaf of bread but not be able to afford it. This is similar to concerts in the real world, and will likely lead to scalping
# Theory 3
You could back the new money by national (or nationalized) assets. E.g. "petrobucks" entitling the bearer to a dollars worth of petrol from the nationalized oil industry. In this case, it's almost preselling, but youy establish an exchange rate earlier. It means cutting into your future revenue. You can look into the various gold backed currencies where they were redeemable for what was, at the time, an equivalent amount of gold.
# Theory 4
You probably don't want to hear it, but there doesn't seem to be a reason to print money. You can use debt, taxes, or even the profits from nationalized industries to fund your projects. You can literally have people spending time working on the buildings/roads. Similarly, you can decide you no longer owe debt.
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# It's a balancing act.
There are times when you have to print more money, in fact you should keep printing money, a steady rate of inflation is good for an economy as it stops people keeping large amounts of cash under the mattress.
What you need to keep away from is the idea that you can print money to pay your bills, you absolutely cannot do that.
# What you do is borrow money
I'm sure you've noticed that the majority of economies are in debt. Lots of debt, and interestingly they never seem to pay that debt off. That's not strictly true, individual debts are paid off, but the overall debt keeps growing. Don't worry about that, just keep going with your safe steady plan, you print a little money every year to keep steady inflation, You keep investing to maintain some growth. You borrow money at a rate lower than the sum of inflation and growth, ideally you borrow at a rate lower than inflation. What this means is that the debt is devaluing faster than it's increasing, but lending money to you should be the safest thing the lender could possibly do with it. You're always in debt, the debt is apparently growing, but as a proportion of your income debt is shrinking.
Always pay your debts.
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You are the despotic ruler of the entire world. This means that you have absolute rule over what is and is not law and can set any arbitrary policy you see fit. Importantly, as you are the undisputed ruler of the entire world, you have no competition or outside influences upon your kingdom. With this in mind,
**You have the sole last say on the value of currency**
Your money cannot be devalued relative to another because there is no other currency. If it is backed by a real resource (like oil or gold) then its value can be taken at face value as being equivalent to whichever exchange it is backed by. If it's not backed by a real resource, then its worth is solely determined by the value assigned to it by people, with you the absolute monarch being able to dictate that value. In short, the money is worth as much as you say it is, because no one is around to tell you otherwise.
Mind you, this is something that will work better the less scarcity there is. If there is significant scarcity, then people will likely skirt your restrictions, possibly forming black markets and other bad stuff that you don't want. Re-sellers and smugglers will always exist.
But why stop there? You have absolutely authority, so start seizing the means of production. Take apart artificial scarcities that do not benefit your new world order, flood the market with goods and put resources into transportation infrastructure to control local scarcity as much as possible as well. Hire as many middle men as needed to micro-manage the whole world's economy and set prices, wages, interest rates and other economic indicators to whatever place you need them to be.
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Forget about money. Yes, you'll have to frame it in terms of capital at some point, but forget about it at first.
Fundamentally you are trying to control 3 things:
* Who "owns" things.
* What activities are done (think "services")
* Things which are some mixture of ownership and services.
You simply cannot have more control over what is owned/done without having more control over what is owned/done. And, as it turns out, people don't mind the loss of little green pieces of paper. What they mind is that those green pieces of paper represented their control over what is owned/done.
It is on this level that you decide what makes your kingdom mostly happy. In the most general of senses, citizens are okay losing a lot of control if the government is doing things they want to see. If their loss of control is instead to permit some king to have a lavish lifestyle, they are less happy with it. If you can convince your citizens that it's a good thing to spend effort and allocate ownership the way you want to, then you can use any instrument you please to accomplish the goal, including printing money.
Once you are at that point, then you can start looking at vehicles to make it happen. Income taxes, consumption taxes, tariffs (even in a "whole Earth kingdom"), printing money, and even physical highway robbery can be valid vehicles, depending on what you need to make the citizens happy with what is owned/done.
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Yes there is one way, print more money only when total production increases, that is print more money only when the amount of available labor, services, and goods increases. By doing this you can keep the relative value of your current the same, of course this is difficult to manage becasue total production is difficult to measure, and rarely does everything increase at the same time.
Basically if you want to print more money you have to invest in research and infrastructure first to increase production so you can then print more money to keep up.
this is especially important for you since if you are in debt, it is to your own populace, thus if the money you give them is worth less you are killing your own economy.
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Ultimately, money is used to buy people's time.
You might think you are paying for a road; in fact you are paying for people to spend time with shovels and jackhammers, people to quarry stone and drill for oil, people to build and maintain the machinery, and people to transport the raw materials to the site. Not to mention yet more people to decide precisely where and how it should be built in the first place.
Some people value their time more than others; there are only so many waking hours in each day, and fatigue sets in quickly if you try to stretch them, or if you try to work through too many days in a row. Most people will try to earn as much money for their time as their education and training permits.
You can influence people to spend their time on projects that are important to *you*, by offering contracts to do so at a high enough price. Some (possibly much) of that money will be spent on supplies; the rest will be distributed among the workers and managers on the spot. At this stage, where the money comes from is irrelevant; if you control the Treasury, you can print it out of thin air, and it will be accepted at face value.
The above marks about as far as your current understanding reaches.
One must also understand that people working on your project are *not* working on *other* projects as a consequence. Other roads will develop more potholes, farms will go uncultivated, cars and computers will not be manufactured - because the people who would normally see to them are instead working on this new project of yours that earns them more money.
Yes, unemployment has also gone down a bit, but not everyone is inherently suited to construction work, and there's a finite supply of the unemployed. In fact, in many places [the construction industry is concerned about a shortage of skilled labour](https://yle.fi/uutiset/osasto/news/survey_majority_of_finnish_smes_say_govts_activation_model_failing_to_deliver/10194058). The same goes for the mining, chemical, transport and high-tech industries which feed into your project.
For a single project that's not a very large effect, but it adds up when you initiate a global programme of them. The result is that the supply of goods goes down a bit.
All these newly-enriched people then want to spend their money in order to benefit from it. To begin with, they buy food - construction work is hungry work, after all. With financial security, they move to larger homes, start families, and buy cars and computers and kitchen appliances. They travel to see the world, and need good roads to do so.
In short, demand for goods goes up a bit. But supply of goods has been going down at the same time. **The net effect is an increase in prices and a reduction in consumer satisfaction.**
The increased prices help to rebalance the economy. The price of food goes up, so being a farmer becomes worthwhile again. Profit margins on gaming computers go up, so chip fabs shift production to CPUs and graphics cards instead of industrial microcontrollers and sensors. Car manufacturers increase their wages and salaries, to bring in enough labour to increase production to meet demand.
Workers begin to leave your project behind, because they feel you're not paying them enough any more - even though your terms are still nominally as generous as they originally were. In order to entice them back, you must increase your own offers still further - and print yet more money to fund them.
This is a vicious cycle. This is how inflation happens.
If it happens quickly enough, the price increases become so noticeable that the *perceived* value of your currency goes down even faster - **people start charging higher prices because they believe prices will increase further before they can spend their earnings** - which leads directly to *hyperinflation*.
The root cause, though, is that you've been increasing the money supply faster than the supply of work hours and productivity. To avoid it, **you must fund your projects without increasing the money supply**.
Taxation is one of the traditional answers to this problem. Conveniently, one of the major expenditures normally funded by taxation - the military - can now be downsized, since you are so confident that wars will no longer occur (though I suspect you might be wrong in practice). So you can keep taxation roughly constant, and **redirect trillions of dollars per annum from the military-industrial complex into public works**.
Job done.
[Answer]
There are several ways you can try to solve this problem.
### Modern Monetary Theory
The closest proposal to this by real economists is that you can add as much money as you want into the system, if you also take it out.
Conventionally, countries pay for things by taxing and borrowing, but this theory holds that it could equivalently print money and prevent inflation by taking some of it back. If the money isn't in circulation, it won't raise prices. You still tax and sell bonds, but the purpose of it isn't to raise revenues (You did that by printing money.) but to reduce inflation.
Something like this was seriously proposed during the US debt-ceiling crisis in 2011. Without going into the ins and outs, because only the economics and not the politics are of interest here, the US government was caught in a bind where it had expenses to pay, only so much money in its accounts, and there was a law on the books saying it could not borrow more. One idea that was suggested to get around this was a loophole that said the Treasury could mint platinum coins, without any limit on the face value. So, it was suggested, the US could mint a trillion-dollar platinum coin and deposit it at the Federal Reserve. The Federal Reserve then had far more than a trillion dollars' worth of bonds in its portfolio, essentially IOUs from Uncle Sam to itself, so it would sell a trillion dollars' worth of Treasury bonds. It would then return the coin to the Treasury, which would melt it down. The overall result would be that the money supply would remain the same, and the net public debt would increase by a trillion dollars. That would have been exactly equivalent to borrowing a trillion dollars!
This isn't a free lunch, of course. If you sell real assets to absorb the monetary expansion, you lose them. If you sell bonds you can print, you're on the hook to repay those bonds (and if you keep rolling over the entire debt, it grows exponentially and you'll get inflation when you try to repay them). If you try to take money out of circulation with, say, a sales tax or VAT, then you've raised prices just like you were trying to avoid.
We don't know how well this would really work in practice, because nobody's ever tried it.
### Conventional Monetary Policy
Most central banks today have an inflation target and try to make the money supply hit it, mostly by reducing how much money banks lend out. The main alternative, peghing the value of your currency to another currency, isn't available to you because there are no other currencies in the world. Formerly, most countries were on a gold or silver standard, but mainstream economics no longer considers this a good idea.
### How Much New Money is Enough?
Central banks look at a number of indicators of inflation, including growth of wages and asset prices, but one important modern tool is the spread between fixed-rate and inflation-indexed bonds. In theory, this tells you how high the markets, with real money at stake, expect inflation to get. That is, if people are buying and selling a bond that pays out 1% above inflation like an equally-risky bond that paid 4%, they implicitly are betting that inflation will be 3%, and this should be true when they make long-term contracts as well.
### Some Other Considerations
Another unconventional economic-policy idea that gained some adherents in the last recession was *nominal-GDP targeting*. That is, you specify that the goal is for the money supply to grow by 5%. So if 3% of that is real growth, inflation should be 2%, but if real growth is only 1%, inflation should be 4%. Some economists believe this will mitigate the impact of recessions: if businesses expect to make 5% more in revenue next year, whether the economy is hot or cool, they can invest with confidence.
You don't have any exchange rates to worry about, with one global currency, but the world is not an optimal currency area. Since countries with uncompetitive industries won't see their currencies get cheaper, you will have to notice this and fix it yourself.
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[Question]
[
When you write about the world you built, you have to immerse the audience on it by describing the environment. I'm on the process of worldbuilding a world with lots of deserts in it.
Problem is: I've never been to a desert. And don't have the economic means to travel to one just to know how to describe it.
I know how to google images, but I am still wary of describing a place I've never been and that may be recognizable to other people, because I may commit imprecisions (for example, describing the color of a sunset or the feeling of the sand).
Do other worldbuilders have any suggestion regarding available resources that they use to mitigate these gaps on their perceptions?
[Answer]
Also, I would watch documentaries on those climates. There is always something on national geographics. Youtube videos even. As you are watching, listen to the sounds. Look up plants you see and read about them. Do they give off any smells? What would it feel like to be in that kind of climate? Humid? Dry? If you can't go there, bring it to you. Network and ask people who have been or lived in those places to describe what the environment is like! For your desert issue, I wouldn't mind helping you out if needed as I have lived in the desert for 20 years now both in Arizona and Saudi Arabia (both deserts but very different). Try to go on forums and ask around. Plenty of ways to figure out the climate culture without traveling :)
[Answer]
If you want to see video of an area, and can't find any documentaries, you can always check out Shutter Stock. They have a ton of videos of just about anything, and their search is pretty good.
You can preview any of them without buying them.
As an example, here are the search results for [desert sunset](https://www.shutterstock.com/video/search?search_source=base_landing_page&language=en&searchterm=desert+sunset).
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If you want to something a bit less superficial than looking at images, try reading accounts of desert travellers. This will take rather more research than you might wish, but can provide all sorts of entertaining anecdotes which you can steal. Try, for instance, T.E. Lawrence's books.
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Start with what you do know: The world around you. Use your 5 senses.
For a sunset, look at a sunset at your home then start thinking about how it would look. Is the sun the same color? Is there more or less pollution? Fog? Dust?
What types of buildings do you see when you look at the sunset? Would those types of buildings be there? Different buildings; what type? What do the buildings look like in your world? Maybe there aren't any buildings. What is there instead?
Now start going into detail, look at the pieces of what you see:
For Example, look at the roofs of the buildings. How would the roofs be different?
What kinds of sounds would they here? On a space ship, would the life support be silent or where there be a constant background noise? How about the sound of the engines, if any? Are the doors silent or do they make noise? How far away can you hear the noise? Huge metal doors can be heard from quite a distance and the clang would be transmitted through the hull. Characters might be able to identify different doors on their ship from sound. A Star Trek door makes sound but one wall between you and it would block that sound.
Think of the smells. The midwest smells different from the west coast because the moisture and soil are different. Pollution has a smell. Wood cook fires have a smell. Plastic has a smell.
For touch, does the ship have a constant vibration? Is it hotter or colder? Drier or damper?
You can probably forget taste, unless your character likes to lick the scenery (I am **not** reading **that** story).
Go down to as much detail as you can. Not all of this detail needs to go into the story but it'll be there, influencing the characters.
Remember that people, thus your characters, tend to focus only on what is immediately important to them.
You can start with a scene where someone is fixing an engine. Then he feels a breeze that provides a welcome relief from the heat but it has the smell of moisture in it. Now, can he finish the front left nacelle of the hovercar before it rains or should he spend his time dragging the tarp over it? He looks up in the sky and sees....
[Answer]
Visit a pet shop or zoo.
Environments established to house animals do what they can to replicate the environment. If you go to a zoo, you can stand in the exhibits and often get a pretty good feel for the real place. Pet shop terrariums aren't as immersive, but the backdrop projections combined with seeing the animals/plants that go into a given terrarium can get you started.
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[Question]
[
I'm trying to create a nation that is greedy, opportunistic & obsessed with profits and trade. They are cunning, treacherous schemers that will swindle you despite all the pleasantries and assurances to the contrary. If they had any religion it would be [Ferengi rules of acquisition](https://projectsanctuary.com/the_complete_ferengi_rules_of_acquisition.htm)
Basically a I'm constructing humans that have combination of psychological traits from fictional races (Ferengi, Hutts, Goblins, Toydarians) and stereotypes about [middleman minorities](https://en.wikipedia.org/wiki/Middleman_minority) (Jews, Chinese, Parsi, Lebanese, Indian).
How should Volto parents educate their children in the art of scheming, hyprocrisy and taking advantage of others?
**1st Edit**
Just to make something clear, Volto are hypocrites. Honesty for thee, not for me. There's nothing wrong with doing something illegal as long as you don't get caught. In public every Volto would present themselves as honest and trustworthy, but that's only a facade. They will stab you in the back the first moment it's to their advantage, and can get away with it. As long a you outlived your usefulness, they'll drop you like hot potato.
No successful Volto will ever tell how they really earned their fortune. They might (shadow)write a book how they worked hard and had a foresight to invest in the right time. But you could be sure that's only intended for gullible fools. The only way that Volto could learn how their things are really done is through experience, from close family and **extremely rarely** from good friend or mentor.
**2nd Edit**
Volto are humans.The story is set in Earth, with technological level of near past. Discrimination of women is on a Mad Men level.
[Answer]
I think the fundamental (though not insurmountable) problem with such a people (and the thing that always bothered me about the Ferengi) is that **lies are parasites of truth**. Truth can exist without lies but not vice versa. For lies to function properly they depend on a culture of honesty.
The apprentice system mentioned by AlexP for example could only work, if the apprentices can reasonably hope that they somehow get more out of the deal than they lose by being exploited. The state rewarding those businessmen with the largest margins depends both on the state not being so utterly corrupt, that it siphons off those margins to get paid for the reward; and that there is an honest way for determining how much money the company made. Importantly: money itself is dependent on honesty. Rampant counterfeiting or excessive printing by the state would rapidly cause their economy to collapse.
There is no way of getting around the problem that they need honest communication to exploit. If you can't trust anyone there is no need to even listen to them.
Personally, I think the best way of going about the problem is by letting them have some form of modest nationalism along with a state that strictly enforces basic rules of commerce. Even the Ferengi could rely on the contracts that they made. If their internal laws are very strict, if supervision and enforcement are functional, they can have enough reason to believe one another to conduct business.
They might also have a disinclination to screw over other Volto. A part of this would be esprit de corps, but also because Volto are much more vigilant. The economy could then be based on screwing over other nations: they would be naturally inclined to head out into other places with softer targets. There are millions upon millions of suckers out there! If they are then “patriotic” enough to send a portion of their earnings back to their homeland – then you have a parasitic people living in a nation that is itself parasitic. They could, of course, also do this for their families, for some sort of prestige back home or for benefits that other nations might not be able to supply as easily. You say they treat women like crap? Perfect! Have them earn more wives back home in a world that is largely monogamous. Even compared to a modestly polygamist society, they could hope for ludicrously large harems of imported slaves back home.
Over time, other nations would come to trust them about as much as a Nazi trusts a Jew – they are, after all, the worst stereotypes of Jews come to life. This would be precisely where their education system gets involved: **They would depend on being recognized as anything but Volto**. This naturally entails learning a variety of foreign languages and foreign customs, extensive theatrical training, being assigned a new identity, learning to create identities of their own etc. – they would basically be spies acting primarily in their own interest. Maybe they employ the strategy of assuming a nationality other than the one of the country they're infiltrating: If you don't want to be recognized as an American in Turkey, fooling Turks into believing that you're an Italian is easier than fooling them into believing that you're a Turk.
This would of course be connected with more obvious economy/mendacity focused education, including knowing the legal framework of the countries they want to specialize in and just a variety of games of deception (think of all the traitor games that are popular today like The Resistance – or games of bluffing like poker of course).
The strategy is basically this: liars need the reservoirs of truthfulness to flourish, so they cut back on lying back home and try to exploit the honesty of others.
[Answer]
Are you trying to describe a nation which actually *is* "greedy, opportunistic & obsessed with profits and trade", or are you trying to describe a nation which is *perceived* to be so?
If the nation is truly supposed to be made up of greedy, opportunistic etc. people then I suggest that it depends on the *degree* of greed, opportunism and obsession with profits. In moderation, those are admirable qualities, the basis of capitalism. Look at the education systems (at home and at school) of nations which are exceptionally successful in international commerce; America, China, England, Israel, or Japan come to mind.
In excess, those character traits will surely doom the nation; since the nation is already doomed, your imagination may be limitless. You may imagine that parents will teach their children to dissemble and to speculate sentimentalism; you may imagine that schools teach sophistic techniques, that teachers will track their pupils ability to cheat (at exams, at homework, and so on), that their religion resembles [prosperity theology](https://en.wikipedia.org/wiki/Prosperity_theology), that the society and the state reward the traders with the largest margins -- for example, the traders with the largest margins are seen as social stars, or the state uses a stack evaluation system, where the traders which obtained the largest margins get to enslave those who lost the most money. Young people may be apprenticed to successful traders and serve a term as unpaid interns to learn how to sell. The society may show an extreme case of interest in upward mobility, with a corresponding disdain and shunning for those who show a decrease in revenue.
If the nation is only to be *perceived* as greedy, opportunistic and obsessed with trade, then the situation is much more nuanced, because essentially any nation which is successful at creating wealth will be so perceived by the less successul nations. The Dutch in the 18th century, the English in the 19th, the Americans in the 20th were widely perceived as greedy, faithless opportunists obsessed with trade. See "[nation of shopkeepers](https://en.wikipedia.org/wiki/Nation_of_shopkeepers)" and "[perfidious Albion](https://en.wikipedia.org/wiki/Perfidious_Albion)". In this case, the education system of the nation will simply be a *good education* system; depending on the historial analog you want to make, you can model it on the English, German, or American system. Children will be educated to be independent, enterprising spirit and initiative will be encouraged, the society will praise success in all forms, risk-taking will be seen as a positive attitude, and so on.
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Why would a scheming, greedy, profits-driven opportunist ever educate their children? Education costs money and resources and risk revolution; much better to impress a basic trade skill on your children and lock them into indentured servitude to the family. (The Ferengi have been mentioned to do something like this). You want your slaves to be just intelligent enough to speak and do their menial tasks, but not so intelligent that they have second thoughts about their rightful place in the grand scheme of things (in a dingy factory, pulling levers).
Children would be born prolifically, probably in vats or some other bulk-production system, as the only employees these merchantilists\* would have full control over, for their entire lives, are family members.
So, to answer the question directly: **The Volto educate their children by brutal example (natural selection).** Many of their children will just make the best out of it that they can, learning quickly that pulling the lever faster gets one some minor increase in benefits (closer to an air vent, or a less-squeaky lever). Strong arming other workers into pulling their levers faster gets one a promotion to Supervisor and a plasma whip. They'll naturally learn to use their brute force to take what they need. Supervisors who don't punish their crews enough will be demoted back into ranks, where the next Supervisor will literally whip them into shape. Supervisors who are too brutal will decrease the productivity of their crew, and likely be terminated. The harsh (plasma pistol) firing will serve as a lesson to other Supervisors.
And some of those children, maybe one out of every vat-load, will be born with extra intelligence. When a Volto parent discovers one of their children organizing the other children into working for them (think Tom Sawyer, not labor union type organization), they pull that kid out of the mines and move him or her into Management (before they damage the Prole worldview too much). The ability to manipulate their fellows without force, but with the invisible hand of economic theory would be taught to them, on the job. They'll learn, or they'll go back to the mines, and their bretheren will be all too happy to get their hands on the "suit" who reduced their water rations to save on repair parts for the water pumps.
This, in fact, will be the biggest weapon used by the Management class against their own staff: do what I tell you to do or you go back to the mines to die at the hands of the Proles. Life in Management is a swift learning experience because your life is one check-mark on a form away from ending brutally at the hands of your oppressed under-family. One will learn how to manipulate their fellows, wring every drop of profit out of their under-family, and backstab each other to gain rank or cover their butts. Only the most backstabby, vile members of the family will survive to be a Parent, the C-levels of society.
Many will fail back into the mines as scapegoats or victims of purges, some will settle in the middle ranks as a headcount, doing just enough to keep their berth and having so little motivation for upward advancement that their supervisors never have to kill them off for safety. And those with the best biological makeup to be the scum of the scum will be the only members with enough pull to make it to the C-Level and become part of the next vat's gene pool, thereby building those features in to their family's DNA. Proles mate with Proles to fill out the working class, and C-levels mate with C-levels to increase the efficiency of the Management class.
(\* Many writers make the mistake of having uber-evil Capitalists, but that falls apart, as many features of Capitalism run contrary to the very overbearing, backwards minded concepts of these societies. For an example, take Star Trek: DS9. The Ferengi didn't even let their females wear clothing, and consigned them to the house, thereby pre-emptively shutting down half of the workforce (and half of the available market for goods! Women not buying clothing?! I couldn't not buy shoes!) A whole season's worth of Quark episodes surrounded the Ferengi Grand Nagus turning into a banking and industry genius, only for Quark to find out that his mother was the actual intelligence behind the throne! All those middle managers, marketing executives, and (yes) shuttle mechanics being forcefully excluded from the market? That's not Capitalism!
That's more like Mercantilism. Keep your resources internal. Exploit your workers to the bone. Refuse imports, focus on exports. Your aliens are more Mercantillist than Capitalist. Just a little detail to write in.)
[Answer]
Clearly, if one could pass along only one key skill to the next generation of schemers, it should be the careful, clever means of subverting complex systems (whatever the underlying technology) -- namely hacking.
So Computer Science skills are foundational, as is programming in the broadest sense. According to <https://en.wikipedia.org/wiki/Greenspun's_tenth_rule>, our prospective schemer will inevitably plumb the UrLanguage Lisp... but in what form?
<https://en.wikipedia.org/wiki/Scheme_(programming_language)>
is the obvious choice -- and thus must be avoided by a schemer at all cost. If not Common Lisp then I'd suggest a nice, open-source basis for scheming, namely <https://www.gnu.org/software/guile/>
;-)
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[Question]
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**How can I make a colonizable planet/moon that receives intense UV/x-ray radiation on parts of its surface while receiving much less on the rest of it?**
The most obvious way of doing this is to have the atmosphere over most of the planet significantly reduce the received radiation, but to have one spot where much more radiation gets through because of atmospheric changes (similar to the [fears about ozone depletion](http://www.nytimes.com/1988/10/11/science/new-ozone-threat-scientists-fear-layer-is-eroding-at-north-pole.html?pagewanted=all).) Specifically, I need enough radiation to cause severe damage to even hardened electronics exposed to sunlight for less than a day, and substantially raise the cancer risk for even sheltered organic life. And no, just having it in a tidally-locked orbit around a white dwarf or neutron star won't do. I need less than a third of the surface to receive this intense radiation.
There are three major components to this question:
**1. A star that produces significant amounts of UV and x-ray radiation:** The simplest way of doing this would be to make the star massive, since large and bright stars [tend to have high-energy emissions](https://www.nasa.gov/mission_pages/hubble/science/ultra-blue.html). Unfortunately, larger stars die much sooner, and I need a system that can survive long enough to produce mature planets and be able to keep them for at least another 500 million years. An [x-ray binary](https://en.wikipedia.org/wiki/X-ray_binary) is probably my best option for this, though the supernova necessary to create the neutron star it requires might hurt the chances of the system's planets managing to hold onto enough atmosphere to make this work.
**2. An atmosphere that can block most of this radiation:** [Ozone](https://en.wikipedia.org/wiki/Ozone) is great at blocking UV rays, and thick atmospheres [excel at blocking intense radiation](https://www.physicsforums.com/threads/why-are-x-rays-absorbed-in-the-atmosphere.525931/). [Smog](https://en.wikipedia.org/wiki/Smog) and other physical blockers reduce a wide variety of radiation. What other naturally-occurring chemicals/compounds/substances would block radiation? The more efficient the better.
**3. An area of the atmosphere that blocks much less radiation than the rest:** This is where it starts to get tricky. [CFCs](https://en.wikipedia.org/wiki/Chlorofluorocarbon) can break down ozone, but I'm not sure about the rest of it. The best candidates are ways to either break down the blocking agents or else move them out of the way. Of course, this needs to be kept local so that it doesn't propagate through the entire atmosphere. A couple of possibilities:
* Volcanic activity could probably disperse smog, and may or may not be able to able to move other blocking agents out of the way. There is also the possibility that it could break some of them down.
* Clouds on rapidly rotating planets [tend to arrange themselves in bands encircling the planet](http://www.astrobio.net/alien-life/rotation-planets-influences-habitability/). This might be a good way of channeling smog and other heavy blocking agents to certain latitudes, though I'm not sure whether they would end up concentrated near the equator or near the poles.
Or maybe I'm on the complete wrong track, and there's a way to make only part of a planet receive intense radiation despite having a uniform atmosphere.
*Optional requirements for bonus points:*
* Do this with as little radiation as possible (in other words, make the atmosphere as effective at blocking radiation as possible, while making the unprotected area let through as much radiation as possible.)
* Do this for a planet that would be a terrible candidate for terraforming while still being plausible to colonize with advanced technology.
A follow-up to [this](https://worldbuilding.stackexchange.com/questions/63778/making-a-planet-seem-uninhabitable) question. The basic premise is to make a planet (or moon) that seems completely uninhabitable from a certain point on its surface but is much more hospitable (though not necessarily friendly to organic life) beyond that point. Additional relevant details copied from the original:
>
> There can't be anything that would make mining or research seem to be worth the risk. Obvious signs of abundant rare elements, scientific anomalies, alien civilization, or native life would all be too interesting. I want anyone who discovers that the planet is inhabited to wonder why the inhabitants bothered. Planets with really unusual dangers are cool, but I want explorers to be saying "Wow, this place sucks!" rather than "Wow, I wonder what's up with this place!"
>
>
> 'Colonizable' means the following:
>
>
> * Temperatures between -250° and 200° C.
> * Surface pressure ranging from vacuum to 3 atms.
> * Gravity at or below 2.5g.
> * No conditions that would frequently destroy buildings dug into the crust.
> * At least 75% of the time, external conditions wouldn't cripple or kill a human in a hardened space suit.
> * Flooding, tides, or underwater land aren't an issue unless the liquid would be hazardous long-term to a deep-sea submersible.
> * The presence of enough metals and carbon for at least low-scale industry, and enough power options (solar, geothermal, volatiles, fusion, etc.) to support a colony.
>
>
>
**Please note: Any answer that would make scientists seriously question whether the conditions on this planet arose naturally and abiotically is not a good fit for this question.**
[Answer]
You could have a concoction of uniquely badass magnetosphere, oddly powerful solar wind and highly elevated (perhaps due to an icy plate floating on a deep ocean) northern pole.
Our own magnetosphere [channels charged particles](https://en.wikipedia.org/wiki/Magnetosphere_particle_motion) flung from the sun, the stars, and other cosmic entities along it's field lines to the northern (and some to the southern, lets not get chargeist) poles. There they interact with the atmosphere and cause [pretty pretty lights](https://en.wikipedia.org/wiki/Aurora)!
They also ionise the atmosphere, and the channelling effect causes higher levels of cosmic radiation at the poles. The higher up you are, the more likely you are to be exposed to higher doses. If your pole is high enough then you can put yourself in a worrying situation. Bump up the magnetosphere and the solar wind and you'll have a planet with planetwide aurora (aurorae?) and particularly vicious radiation conditions at the North Pole.
Or, if your atmosphere isn't too thick, just a stream of cosmic plasma bombarding the North Pole. Ho Ho Ho.
[Answer]
There are actually a couple ways to do this even with a star & earth similar to ours such as:
1. Make the magnetic poles point towards/away from the star (earth's equator equivalent). This would mean that when facing the sun the pole would get bombarded by the radiation with minimal protection while the rest of the planet would be relatively safe. As well, due to this bombardment, the O3 would break down more rapidly here such that it's an actual hole. Due to the magnetic field lines and unless the planet was tidally locked, it'd only be dangerous for x amount of time depending on the planet's rotation.
2. Either as it's own planetary feature or in conjunction with 1 which would make it worse: Is have an atmospheric circulation that prevents ozone from collecting easily around a point/band of the planet making it dangerous. This is actually part of the reason the Antarctic has an ozone hole in the first place as certain times of year the jet stream circling that continent tightens and prevents ozone created by storms and other atmospheric conditions from distributing there. I can't find the papers, but it's been theorized that our ozone "hole" (not complete yet or likely ever) is actually partially due to this atmospheric feature in conjunction with the CFCs and the natural breakdown due to blocking the high energy radiation.
Thos are just the couple I came up with quickly. There are probably other ways too, but these can both exist in worlds very similar to earth (and plenty of dissimilar worlds too).
[Answer]
1. Have a solar system like ours
2. Have a nearby x-ray pulsar or some other extremely energetic star located perpendicular to the plane of the solar system, along the axis of orbit of the planets
3. The northern (or southern) hemisphere of the affected planet would be bathed in life-threatening bad juju rays.
4. Bonus option. Modify axial tilt control exposure to the x-ray star. If the axial tilt is 90 degrees, for example, the entire star gets heavy radiation and at some point and there is no life. However, in a planet with an earth-like 23.5 axial tilt, the x-ray radiation coming from the northern hemisphere never extends farther south than 23.5 S - the southern Tropic of Capricorn. Now life can develop in the un-radiated part of the world.
5. Double-bonus option. Modify day length to control time of exposure. Unlike the seasons caused by the earth's rotation around the sun, the exposure to a star above the North pole will be controlled by day length. So in an Earth-like axial tilt situation, everywhere north of the Tropic of Capricorn gets hit with radiation at least once per day. If you make the day length equal to a year, then everything gets hit once a year with radiation.
6. Modify strength of radiation to control size of no-go zone. If the radiation is relatively weak, then maybe only the areas that are *permanantly* exposed to it are no-go zones. For example, if we have an earth-like 23.5 degree tilt, then only the areas north of the Tropic of Cancer are permanantly exposed to radiation, while areas in the tropics get some partial exposure, and areas south of the Tropics get none.
[Answer]
Start with [pulsar planet](https://en.wikipedia.org/wiki/Pulsar_planet) like the ones that formed around the pulsar [Lich](https://en.wikipedia.org/wiki/PSR_B1257%2B12), but a little further out and tidally locked so that it becomes something like a hot eyeball world:
[](https://i.stack.imgur.com/oOXYx.jpg)
Set the planet at just the right distance from a pulsar, which are very hot, but not very bright, and most of their energy is in the form of radiation.
Because of being tidally locked the back side would be cold, and the front would be blasted by radiation, but around the terminator would be a band of clouds and storms that would reflect some of radiation. Air from the front would be heated and pour around the planet toward the the cold back side, where it would cool down and rush back around to the front side bringing moisture with it and causing the storms.
The back side would be colder, but because of the circulation not freeze completely.
As to how life got there in the first place in only 1 billion years, it was seeded by the travelers that left the gates.
[Answer]
How about a ring system, like Saturn, where the rings keep the sunlight filtered except in a gap? This answer is inspired by this question: [By what mechanism could a planet be locked into permanent solar eclipse?](https://worldbuilding.stackexchange.com/questions/4363/by-what-mechanism-could-a-planet-be-locked-into-permanent-solar-eclipse)
This answer explores the idea of a tidally-locked binary pair of planets such that one keeps the other always in shadow. If the inner one is more dense, it would be smaller, allowing it to remain on the inside of the orbit and only allow full sunlight in a ring onto the larger planet. There is some debate in the answer about the orbital mechanics. Seems like it might be worth trying to set up in a simulator.
[Answer]
>
> How can I make a colonizable planet/moon that receives intense
> UV/x-ray radiation on parts of its surface while receiving much less
> on the rest of it?
>
>
>
**Up from the below.**
UV radiation is tricky, but you can have your world get lots of [ionizing radiation](https://en.wikipedia.org/wiki/Ionizing_radiation) in the form of X-rays and gamma rays by having your crust enriched in radioactive elements that emit this type of radiation.
[The earth contains elements which emit ionizing radiation](https://cemp.dri.edu/cemp/workshop2009/presentations/Hurley-Radioactivity_Geologic_Environ.pdf); the radioactive decay of these are responsible for heating the deep earth and generating radon gas in the crust. You could have a lot of radioactive elements in one area of your world, including some with shorter half-lives like americium. You could have these elements arrive on your world in meteors from some distant supernova - a few of these breaking up on entry would enrich parts of your world with radioactive isotopes while sparing the rest.
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[Question]
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According to a [recent National Geographic article](http://news.nationalgeographic.com/2016/11/nasa-astronauts-eyeballs-flattened-blurry-vision-space-science/), astronauts returning home after longer missions suffer **permanently impaired vision**. This is a problem that must be addressed in [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'") worlds if realism is desired - yet it is often overlooked.
Some of the other problems associated with microgravity are easier to deal with - muscle atrophy can be reversed by exercise, bone can be replaced or strengthened over time, the immune system can heal, coordination comes back, and cancer (from radiation exposure) is treatable.
---
**But how do you prevent vision from becoming permanently impaired?**
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**Context of the Condition**
*From the article linked at the top*
* Called "visual impairment intracranial pressure"
* Not fully reversible (**even by surgeries**) **when you get back to Earth**
* Occurs when cerebrospinal fluid builds up behind the eyes, which happens when gravity is reduced
* Eyeballs are literally "flattened"
* The [solution](https://www.washingtonpost.com/national/health-science/the-mysterious-syndrome-impairing-astronauts-eyesight/2016/07/09/f20fb9a6-41f1-11e6-88d0-6adee48be8bc_story.html?tid=pm_pop_b&utm_term=.27260dedf752) scientists have proposed is "clunky" and entails being hooked into a machine to draw fluid throughout the body
**Criteria for Solutions**
* Artificial gravity would fix the problem but it is not and will not
be present for all (if any) missions; **it will not be accepted**
* Will optimally be noninvasive (tubes running into the skull aren't great) but this is not a necessity
* Should be portable (being hooked into a large machine might help, but when mining asteroids or traversing the moon, there really isn't time)
* Should be [science-based](/questions/tagged/science-based "show questions tagged 'science-based'")
* Should not involve modifying the human genome
* Should focus on preventing the syndrome as opposed to correcting it after it occurs; it's not viable to do multiple missions, then get a new prescription and/or have a new surgery after each one
[Answer]
**Centrifuge** looks like an answer, and actually was used in few books I've read. Fluid builds up due to lack of force pulling it down, right? It does not mind if that force is not strictly gravity.
First solution is to build ring-shaped living area. Even for relatively small craft, I'd say at least 10m diameter, centrifuge could simulate gravity well enough to prevent build up of the fluid. Coriolis effects would be weird, but ultimately fluids would be pulled down, and that's what we need.
Another one would be sessions in one-man centrifuge at 2 or 3G, just to draw fluid that accumulated between these sessions. This is less convenient for the crew, but also more portable.
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Our bodies doesn't have any mechanism for sucking liquid from behind our eyes, except the gravity-based. This leaves us with centrifuges, and things that won't work:
* Needles, like [Eye Anesthesia Retrobulbar block](https://www.youtube.com/watch?v=eSrR2gYbGPs), but sucking instead of injecting. Not practical due to build up of scars and high risk of infection. Not to mention eye damage if it's fellow miner performing this on you.
* Pipe implanted there permanently. Bad for eyeball muscles, high risk of infection, risk of not sucking enough or sucking too much.
* Pipe implanted, but going via different route. High risk of infection and complicated implanting. A tiny bit better than pipe on the front, but still really far from safe, and shares most of the risk.
* Drugs - but there is no mechanism drugs could stimulate. For now these drugs are in the realm of fiction. Not yet science-fiction.
[Answer]
You could look at alternative treatments involving eye exercises. Mainstream doctors are often unaware of the work done by [behavioural optometrists](http://pavevision.org/what-is-behavioral-optometry/).
I have used the techniques in the book [Natural Vision Improvement](http://rads.stackoverflow.com/amzn/click/0890878390) with surprisingly good results (but of course my issues were not caused by microgravity displacing cerebrospinal fluid - I am just suggesting this as an avenue for finding a possible treatment.)
There is also a body of knowledge from India (with all the caveats about lack of controlled studies). I know someone who was able to correct reasonably significant myopia using something similar to [these techniques](http://www.stylecraze.com/articles/effective-baba-ramdev-yoga-exercises-for-eyes/), but he eventually decided it was not worth doing the hour a day of yoga practices - it was easier to put on glasses!
However, if the distortion of the eye shape was caused by fluid movement, rather than the original shape of the eye, then these practices (along with headstand, which is not on the list I referenced above) could theoretically displace the fluid back to where it should be, and then you wouldn't have to keep spending an hour a day practising these techniques for the rest of your life.
[Answer]
For a story that needs to mention this, just have them take drugs while in space designed to address it. If increased pressure is the problem, then the same treatments used today for other causes of that condition ought to work.
## update:
Since the available drugs that would suggest themselves *have* been tried and don’t work, some new drug would need to be found in time for your story.
You can remark that it was developed soon after long-duration missions started, or go into a backstory on how it required long duration mice studies in space, to discover the underlying mechanism well enough to start targeting drugs.
[Answer]
you could go with a mechanical solution, there are lots of things that you can't do in microgravity, or they are very difficult, set up stations where these needs can be met. for the eye a flexible microscopic tube could be inserted under the eyelid and through the fatty tissue around the eye and used to draw out the fluid periodically. It will be scary and uncomfortable but if you are in space you are already dealing with both of those, you can't do it forever, but you can't have people in microgravity forever either.
Honestly microgravity causes so many problems periodically spending time in artificial gravity, via centrifuge or other means, may really be the only solution. They will have to have gravity eventually, fluid build up around the heart, they eyes develop cataracts form the radiation, and breeding is impossible in microgravity.
You either A. have alter humanity, either genetically or a frankenstein's monster of surgeries and implants that won't be permanent fixes anyway, or B. provide the conditions humanity need, those really are your only options if you want hard science.
[Answer]
An option is to cancel out the microgravity by simply adding iron pieces to astronaut's suit and a magnetic field (on the ship), or charged suit (DC) and a electric field.
I prefer having gravity based on 2001: A Space Odyssey, good reference to hard science fiction. Circular ship, gravity generated by circular motion. But you dislike of artificial gravities and stuff.
You seems to be looking for hard science fiction here, but a it is difficult to answer as it is not a solved problem even on real life.
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The Hoatzin is a jungle bird whose only remarkable trait, other than looking fabulous, is that their wings have fingers.
[](https://i.stack.imgur.com/PWBsv.png)
Is it possible that these wing fingers could evolve into arms? What about legs? What pressures would lead to such an evolution?
[Answer]
I don't know exactly why you want the hoatzin to evolve hands, and the birds already have legs, but the best answer is to make the birds need to climb. At present, only the chicks need to climb, so only the chicks have claws, but the adults are pretty bad fliers, so it wouldn't take too much to push them to stop flying all together. This simplest way for this to happen would be for the climate to change a little.
Let's say we have a rain-forest just perfect for the modern hoatzin. It's got lots of trees with lots of branches perfect for hoatzin nests, and lots of leaves for the birds to eat. Now, hoatzins really only glide from branch to branch, they don't really flap much because their muscular structure really isn't set up for flapping. If the hoatzin didn't have a lot of branches fairly close together, it would have a right difficult time getting about. Of course, in a rain-forest there are lots of trees with lots of branches all very close together because there is plenty of sunlight and water for all of them. What would change this could be a climactic shift, I would propose to a wetter but cooler climate.
All this would take is some cloud cover.
With less sunlight, the trees devote all their energies to being taller and they put all their branches up top, where they can gather sun. The lower levels of the jungle are plunged into almost total darkness, very bad for plants, so the trouble of branches all over the place is cleared up. When the birds fall out of the nests, or out of the trees, or end up in the water for whatever reason, they *have* to climb to get back up into the trees. There is no longer the option to fly up, especially not out of the water.
Then, with clouds comes rain. Lots of rain. The hoatzin already lives where there is a lot of standing water, so it wouldn't take too much to flood the rain-forest floor. This would take care of all that pesky underbrush that the birds might use to hop-fly back up into the trees. Think swamp: tall trees sitting in water, not too much cluttering up the way-up from the ground-level.
The hoatzin sits on its eggs more to keep them cool than to keep them warm, so the birds can't be away from the nest for too long. Climbing up and down the trees isn't the fastest thing to do, so a cooler climate would help select for climbers, or at least, not select against climbers.
The original needs for climbing (get back to the nest, climb out of the water) are still present and are exaggerated. What's more, this shift in climate can occur with some rapidity. It wouldn't take eons and eons for a jungle to turn into something of a swamp, which means that the birds will be forced to select for a right-now trait (like claws that remain into adult-hood) instead of a slower trait (like a progressively better flight muscular structure), but it will take long enough that the birds would have time to evolve, not just be wiped out by the sudden change in conditions.
As the rain-forest becomes more and more swamp-like and the foliage changes, the hoatzin will have even less need or opportunity to fly. In the beginning, the birds will still fly between the tops of the trees, but with the expanding breadth of the tree-tops, they won't have to. As the trees strive to collect as much light as possible, their canopies will become less vertical and more horizontal, so the hoatzin will be able to hop more than fly, and its progressively longer-lasting claws will help it to do so. When these original trees die, the dark ground level will not permit as many saplings to take hold, so in perhaps a hundred years or more, when the first trees have died and the second generation has begun to rise, the forest will be less dense, meaning the trees don't have to compete as much for the light and their canopies will thin out again. At this point, the hoatzin has experienced some 30-40 generations since the environment began to favor adult claws. That's not a lot, but it's enough to give the hoatzin 2.0 a good basis of flightlessness because along side the selection for claws, the hoatzin is experiencing a lack of selection for flight structures. The reason the modern hoatzin does not fly well is because the structures needed for it to eat leaves conflict with the structures it would need to fly, so when the balance is tipped, relieving the need for flight while holding the need for digestion steady, we will see the worsening of flight structures. With the trees becoming farther apart, the hoatzin will have to get from one to the other, but it's flight ability has been reduced to clumsy gliding at best. The birds will have to climb back into the trees when they attempt to glide and miss, but they will also have to start developing better ways to get about in the trees. There will be a die-off as the second generation of trees replaces the first generation, and birds with longer wings will be selected for because they can reach farther to get from branch to branch. The half of the wing that follows the claws will get shorter as the part that precedes the claws gets longer, bringing the wing into a more arm-like appendage. The same pressures will select for longer legs as well, leading to a long-armed, long-legged, clawed bird that spends almost all of its time in the tree-tops. Eventually, it might be necessary for the swamp to begin to return to the rain-forest conditions (as we know, monkeys do not live in swamps {except the Allen swamp monkey, but it dives, so I'm not counting it} for the same reason: nothing to swing from/to) which will provide the hoatzin 2.5 the structures needed for flightless, grabby locomotion. The end result will be the hoatzin 3.0, a feathery, egg-laying creature with long scaly legs,and long arms with claws at the ends that swings through the jungle almost like an ape. If you then wanted the hoatzin to evolve into a human-oid, you need simply follow the ape-to-human evolutionary track.
Granted, this all involves a lot of time, a lot of things happening *just right*, and a lot of assumptions, like that the trees the hoatzin eats would survive this kind of change long enough for the hoatzin to switch foods, but it is, in theory, given ideal circumstances, possible.
[Answer]
Quick note: Only hoatzin chicks have claws on their wings; these claws are lost after maturity.
**What pressure could lead to further development of claws?** Well, it appears that the claws have emerged because of the pressure of local predators. Hoatzin chicks will run away from the nest when the alarm call is given, using their claws to climb more effectively. They'll also drop into the water, then use their claws to climb back up to the nest. Thus once the chicks are able to fly, they no longer exhibit the behavior that encouraged them to emerge in the first place. You'd need a use for those claws in adults to encourage them to be retained and developed further.
Perhaps a flightless species of hoatzin might develop a need for hands for the same reason primates have them - climbing and gathering food. Finding a food source that benefits from more dexterous tools than just a beak might be a good stimulant for such a change as well.
[Answer]
As pointed out the real question isn't how to further develop the claws, there is plenty of pressure for that already, climbing helps them in many ways. What you need to do is remove the pressure to keep flight capable wings. to really push it you could have them increases in size, the bigger they get the less flight is going to be achievable. Lack of predators could easily do both, a mass extinction freeing up lots of niches and killing off all the large predators would be enough.
One interesting feature, the creature will have 3 fingers, birds lost the 4th and 5th finger long before they were birds.
[Answer]
"Whose only remarkable trait, other than looking fabulous, is that their wings have fingers"? I'd have to heavily disagree with you there- Hoatzins have a couple of other remarkable traits as well. The Haotzin is the last surviving member of an order of birds which recent genetic studies have now shown branched off in its own direction more than 64 million years ago, literally as the ashes were settling shortly after the extinction event which wiped out the non-avian dinosaurs. And their most remarkable feature, IMHO, isn't the fact that juvenile Hoatzins possess finger claws.
Even more notably, the Hoatzins are the only birds to have ever evolved a digestive system which utilizes bacterial fermentation to break down the vegetable material they consume, in the same manner as cattle and other mammalian ruminants do. In the place of the mammalian ruminants' rumen (a specialized stomach for bacterial fermentation), in a case of parallel evolution, the hoatzin has evolved an unusually large crop instead, folded in two chambers, along with a large, multi-chambered lower esophagus. Its stomach chamber and gizzard are much smaller than in other birds. Their crop is so large as to displace the flight muscles and keel of the sternum, much to the detriment of their flight capacity.
And you might also be interested to know that the fossilized remains of an extinct species of Hoatzin has been found in Namibia, some 18 million years ago, proving that indicating that, in the African-South American interchange which faciliated the colonization of South America by new world monkeys, rodents, bats and other species, at least a few Hoatzins went the other way and successfully colonized Africa too (along with at least one species of terror bird). As such, full flightlessness seems like an extremely likely evolutionary path for the Hoatzins to take.
So, how's about this for a scenario; over in Africa, as the climate gets increasingly arid, and the mangroves and rainforests begin to be replaced by savannah, instead of simply dying out as they did, some of these African *Namibiavis* Hoatzins manage to cling on by abandoning their arboreal lifestyle and adopting a more terrestrial lifestyle instead; rapidly losing their flight ability in the process, and becoming fully terrestrial. Their unique pseudo-ruminant digestive system bestows them a tremendous evolutionary advantage as avian browsers and grazers, potentially enabling them to outcompete contemporary ostriches.
And without the limitation to their maximum size imposed upon them by retaining their vestigial flight ability, with their far more efficient digestive systems granting them access to more nutrition, and with the considerable evolutionary pressures placed upon them by African predators, these African hoatzins rapidly grow to become far larger than even ostriches; large enough to rival the mass and height of the largest ruminants, the giraffes (which they could also conceivably compete on a level footing with), and feasibly, even some of the dinosaurs of old (with mummified hadrosaur remains indicating that they also possessed enlarged crops most closely resembling those of Hoatzins). As a result, these end up looking something like this;
[](https://i.stack.imgur.com/rzB3d.jpg)
The original purpose of these Hoatzins' finger claws, for climbing, has long been rendered redundant by this stage. But these African Megahoatzins still re-evolve arms, and refine their finger claws, in an evolutionary development paralleling those of the gigantoraptors, ground sloths and calicotheres when they all took the same evolutionary path. Equipped with increasingly large and developed claws, they use them to strip leaves, tear off branches, and as potent and formidable defensive weapons against any predators who attempt to attack them or their nesting sites.
Perhaps even also as legs, with a sub-order evolving to become semi-quadrupedal as an adaptation to ground-feeding grazing, just like hadrosaurs did; with this semi-quadrupedal stance also enabling these Megahoatzins to become larger and heavier still, conceivably rivaling the size of the largest ornithopods. What do you reckon; does it sound interesting?
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[Question]
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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.
In a world similar to ours, a mad scientist is bent on preventing the ascendance of one certain individual over the rest of the people inhabiting the northern part of the continental America, also called U.N.A. (the Unity of Northern America). The U.N.A. hold presidential elections similar to those of the earth USA and are currently in the final phase of their elections.
Our scientist has tried everything from social media, over press publications over appealing to the common sense of people, but he failed nonetheless. In a last resort he gathers the funds to transport 30'000 members of the species of the Rhinocerotidae to the southern border of the U.N.A. hoping to be able to disrupt the election process and stop people from committing, what he deems to be, a mistake of global consequence.
The scientist gathers all the Rhinocerotidae in the eastern part of Europe and wants to transport them all as silent/stealthy as possible to the southern border of the U.N.A. using Soviet Era transport planes.
How would he have to go about it and how many planes would he require?
[Answer]
### 500 planes
If we consider the large [Antonov](https://en.wikipedia.org/wiki/Antonov_An-225), we have planes that weight 285 tons, and can carry 355 tons of load. They have dimensions for the load of $44\times6\times4.4\mbox{ m}^3$
Now a few facts about the [rhinos](https://en.wikipedia.org/wiki/Rhinoceros). They can be up to $4\times2\times2\mbox{ m}^3$, and weight 1 to 3 tons depending on the species.
So buy building a deck within your cargo area, you'd be able to place about 60 rhinos within each plane. You might get to more, if you pack them more tightly. The weight of the rhino alone would amount to 60-180 tons. Which is well below the maximum weight. You'd still need to add the structure, pack, food, etc. But we would probably stay within the limit.
But on the base of 60, you'd get $30000/60 = 500$ planes.
But do note, that summing up the number of rhinos of the various species, we barely come to 30,000 rhinos in the whole world!
It's going to require some planing for your stealthy operation.
[Answer]
**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.
**Use ships.**
While 500 planes would be hard to gather and hard to hide, the small number of ships would be much less noticeable. Even relatively small ships would hold 5,000-10,000 20ft containers, each easily capable of holding a rhino and a substantial amount of food. The container acts as a built in cage. People are used to seeing large numbers of containers being moved around, so having the ships unload onto trucks which then drop them at the desired location shouldn't even raise an eyebrow, especially if rumours of a 'big construction project' are spread. You might need to forge some import documents, and even bribe a few inspectors who want to open the containers, but that's definitely easier than trying to hide 500 transport planes.
Ships do of course take longer than aircraft, but in this world the US elections take forever - easily enough time to float a few mono-horned behemoths across the Atlantic.
The best thing is that when you want the rhinos to actually do their thing (whatever that is) you just remote trigger a hidden door in each container and the rhinos wander out. Spectacular.
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I was reading [this question](https://worldbuilding.stackexchange.com/questions/51387/how-to-convince-readers-to-accept-tolkien-esque-fantasy-where-people-of-color-ar) last night about people of colour in fantasy stories. I've read so many fantasy stories where any mention of colour is associated with the negative/animalistic/barbaric that I had long decided to include all types of colour in my story (and try to avoid the stereotype, 'black man - bad!'). The way they described how their races came about got me thinking how my story world's different ethnic-groups\* would 'survive' over a period of 2000-3000 years without 'dilution'.
\*For this purpose I'm using ethnic-group to mean people who share a similar physical appearance; so [ethno-racial](https://en.wikipedia.org/wiki/Ethnic_group) rather than religious or lingual ethnic-groups.
**Edit** to those who may wish to downvote because I'm asking how to keep my races 'separate'. I'm not at all worried about explaining people of colour to my readers. If they can't accept that, they can go read another book. Maybe it will have lots of pictures and big writing. What my question is about, is how to retain distinct physically different looking groups, until my main story begins; 2000-3000 years after my world's history begins. No use, trying to have black, Indian, Asian, Mediterranean, and /or pasty white folk arrive on planet only for them to have all lived happily ever after before my actual story begins. I want to throw race in people's faces. I want to make them see, everyone is the same, I want them to root for the 'other'. Can't have that if everyone is already caramel.**Edit** sorry, rant over....
In the linked example above, the backstory was that the world was created and the gods put everyone on the world about 6000 years ago as separate racial groups. No evolution, I think DNA didn't even exist!
In my backstory, I have a similar setup where everyone is placed on a planet and then the story evolves. I don't have any gods/magic doing the placement though, normal genetics and evolution still apply. In my setting an entire planet was being evacuated, sort of a Dunkirk sort of scene where everyone is helping out with all shapes and sizes of spacecraft; this way I can get many different ethnic groups for my story. There is an accident and several ships are transported to another location and cut off from the main civilisation for thousands of years. I had already established that I wanted people of different colours and cultures to have to work together to survive. But at the same time to retain some ethnic individuality. Especially as most of my story is actually set a long time after their arrival on the planet.
This question about the [minimum number of people needed for a sustainable colony](https://worldbuilding.stackexchange.com/questions/3/what-is-the-minimum-human-population-necessary-for-a-sustainable-colony) is very useful, as well as this one about [repopulating the earth after an apocolypse](https://worldbuilding.stackexchange.com/questions/18275/how-many-people-are-required-for-a-healthy-re-population-of-the-earth-post-apoc?noredirect=1&lq=1). However that is all about cross breeding and sharing genetic material to avoid inbreeding. In my mind that means mixing and balancing features out until everyone is somewhat 'similar' in appearance. So if you start with some really pasty folks and some really dark folks, over time you will end up with some really mixed folks with very few retaining the original physically distinct appearances of their forebears!
To avoid this I gave my different groups, different areas of the new planet to colonise; based on who were on the different ships, and where those ships ended up landing/crash-landing on the new planet. Mostly on the same continent. A lucky few land in the Hawaiian Islands equivalent (and are unfortunately isolated for much of my story). So they are not so much working together to survive but rather as several distinct groups working to survive separately, with some trade between them. I don't want them completely isolated from each other, frequent interaction will occur over the years. This will obviously lead to some racial conflicts when they do interact with each other (which will essentially revolve around who controls what resources). Which is fine, from a story telling conflict creation point of view but completely wrong ethically :)
To keep my groups, or at least a portion of them, distinct enough from the others over a period of time, they would have to develop some taboos about intermarriage and mixed-race children. But at the same time I do want and need mixed relationships to happen. Frequently enough that the children of such relationships are not considered 'too much' of an odd/unique curiosity. How strict/lax must their taboos about mixed marriages/relationships be? I don't want to start a war because Desdemona decided to run off with Othello!
While in real life this hasn't been a problem over the last 2000-3000 years, we still have plenty of pasty white folk and plenty of dark skinned folk with a fair few mixed folk walking around. But this new world would be a different scenario with a limited number of people at the origin point. Integration is more likely to happen as people work together/fight each other for resources.
So I believe my question is twofold:
**How do I keep my different groups physical appearances distinct enough over a time span of 2000-3000 years? (without creating extreme widespread racism; there can be a *few* rednecks...but I would prefer not too many Trumps)**
AND
**How large a population of each ethnicity would be needed to avoid 'dilution' while staying genetically viable?**
Or have I covered everything already and I have nothing to worry about; do I just take the [minimum viable population](https://www.britannica.com/science/minimum-viable-population) and multiply it by how ever many ethnic groups I want?
[Answer]
1) Taboo on intermarriage based on different religion. Very effective, think about Jews. Actually based on caste / nationality may also work, think about Roma (Gypsies) they tend to adopt local religion, but still are disgussed by idea of intermarring with local population.
2) Make really unprofitable to leave the landing place. Ex. the nuclear core of ship still works and provides effectively free electricity in huge quantity for centuries. It would keep population dispered. If they are any prefabricated factories/hydroponic plants on the ships make them constructed soon, with no coordination with other groups.
3) Provide political division. Just separate and uncooperative local governments what makes everything harder. Boost it by language problems.
4) Geographical bariers. Deserts, mountains, huge distances...
5) Designer babies / artificial insemination. Lot's of fun:
-the race of ones kids would be actually determined by asthetic preferences, not necessary by genes of parents. (there is no need for racial supremacists, when all you need is parents who think blond hair and blue eyes are cute)
-solves problem of inbreeding, if you one is somewhat unlucky only gamets of one ethnic group are present on the ship. (not necessary fitting outlook of parents)
6) Make resources locally abundant while transport cost high.
[Answer]
One way is: simply make travel long, difficult and expensive - and only ease it "recently".
That way, only the richest, or most risky, would do it. And they don't produce many children.
They may suddenly find out that planet they are on has no oil, no coal, no radioactive isotopes suitable for their technology, and limit all power to agriculture. After few hundred years everything on another continents would be legends.
You may make oceanic weather way too hard to cross.
Either way, after some centuries they wouldn't have a common language. They would look different. They will share memory of international, multicultural past, but that's it. Language barrier might be the best barrier you can get.
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Other way to go, would be to mix groups like Orthodox Jews, Muslims and Rastafari. Different beliefs, different, but deeply rooted taboos, some hatred. Common fight for survival would smooth some edges all right.
Food taboos, made stronger by what you can get on your side of planet, are very good against mixing nations. Jews have [distinct genetics](https://en.wikipedia.org/wiki/Genetic_studies_on_Jews) - it seems it worked for them for millennia all right.
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**TL;DR** it's either geography + lack of technology, or religion. That's what worked on good old Earth.
[Answer]
Strongly diverging language. If your nations have extreme differences in language, then communication will make it extremely hard for any person from one distinct group to integrate (marry) into another simply because they lack the means to communicate with them.
Some ideas:
* Tonals. If you are not born into a tonal language, it's very hard to pick out the subtleties here
* Clicks. Tongue and throat clicks can be produced that are very hard for a non-native speaker to reproduce
* Hand / visual cues. The difference in a statement vs a question could simply be the way a persons right hand is being held at. An integration between sign language and verbal language
* Consonant cluster f's. My screen name is a good example, the pronunciation of twelftheds is a tongue twister in a more literal sense and it takes a native speaker used to the tongue motions to get that out.
Basing each language on it's own distinct alphabet would also badly hinder communication.
As technology advances, these differences can be overcome, but early on this can completely inhibit cultures/peoples from integrating.
[Answer]
**Your "races" are actually different species.**
[](https://i.stack.imgur.com/djcqJm.png)
<https://allthingsfoxes.com/can-foxes-breed-with-dogs/>
On our world race is a sociocultural construct - all human races are the same species and we merrily interbreed. On your world, there are genetic barriers to interbreeding as with the fox and dog. If you want some interbreeding to occasionally occur you could have mule (horse x donkey) or liger (lion x tiger) equivalents. Mules are infertile and ligers have their own issues but both exist and are the products of 2 different species.
Foxes stay foxes and dogs stay dogs, even if they are friendly and living together.
[](https://i.stack.imgur.com/dPBUS.png)
<https://omnibus.home.blog/2020/04/13/damn-dirty-apes-planet-of-the-apes-1968/>
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If there were some way (sub question: IS there some way?) to get neutron star material out of the gravity well of a neutron star, -say maybe a high-speed collision of two such stars- how would that material behave away from the gravity well?
Would it continue to be as dense? What dangers would it pose if you were to approach or touch it?
[Answer]
Neutron stars are not very well understood, unfortunately. The matter on the surface is theoretically different from the matter in the core, due to the increased pressures at depth, but we can examine each layer in detail.
**Atmosphere**
There is actually an atmosphere around a neutron star, or there could be at least. It would be veeery thin, perhaps only a few micrometers, and likely composed of hydrogen and helium. If returned to "normal space" these gasses would likely exist as normal.
**Crust**
Beneath the atmosphere will be solid matter (or possibly liquid if the temperature exceeds about 10^6 Kelvin). The matter will still be mostly charged atomic nuclei crushed into a dense lattice swarming with electrons. This structure would behave metallically, and is thus theorized to be made perhaps of Iron, due to Iron's high binding energy. Iron could be too dense, though, which means the crust could be metallic Hydrogen and Helium. If we lifted this material off the surface, it might expand back into a more recognizable form, either solid Iron or gaseous Hydrogen/Helium. Due to the possible temperatures this material might become plasma.
**Inner Crust**
Proceeding inward we'd encounter more and more pressure, and so nuclei would be composed of more and more neutrons due to the process of Electron Capture. This process turns a Proton + Electron into a Neutron, at the expense of an escaped Electron-Neutrino. Once these neutrons are formed, they are permanent, and will not turn back into a charged duo. The nuclei at this depth become increasingly unstable, since the Strong Force cannot cope with the number of neutrons. The only thing keeping them in place is the immense gravitational pressures. If we scooped out some of this gunk and set it free most of the nuclei would decay rapidly, releasing radiation and turning into more stable heavy elements. This could potentially become an interesting source of exotic elements if you wanted to risk the process of mining in such conditions.
**Outer Core**
At this depth the Neutrons are becoming ubiquitous, and electrons and charged nuclei become smaller and more rare. The gravitational pressures involved completely overwhelm the Strong Force binding the nuclei together. Any remaining nuclei would probably still be stable if we removed them, since they have become so small, but there could be some very radioactive isotopes in there somewhere. Mostly all you'd pull out of this goo would be pure neutrons, which are not terribly exciting.
**Inner Core**
At this point there are ONLY Neutrons present. The Electron-Capture process has eliminated all charged particles, and no nuclei exist. If you could somehow get to this depth to remove this material, it would expand as the pressure was released, and the Pure Neutrons would decay rather rapidly into more stable nuclei.
There is a possibility that the core is composed of some sort of quark/gluon plasma. The neutrons are basically dissolved when subjected to the conditions in the core, but such a material is exotic and not well understood. I would probably want to stay away from it in case it expanded violently upon release.
[Answer]
If a neutron star material came out of a neutron star then it would immediately create a lot of energy. This is because neutrons would decay into a proton, electron, and an electron antineutrino. The only reason neutrons are stable in a neutron star is due to enormous gravity holding the neutrons and forcing them not to decay. Touching neutron star matter would be bad as neutrons can turn into protons and release energy. Also, strange star matter in the core of neutron star comes in contact with any matter to turn it into a strange matter also.
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[Question]
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I'm not going to go into the magic in my story in much detail here, because it's hard to put into words. But basically, magicians say what they want and if they are concentrating hard enough, it happens (Sorry for the run-on sentences, I've been studying Biblical Greek recently).
If you teleport an object what would the effects (on the object, the area it was teleported from, and the area it was teleported to) be?
I'm pretty sure that there would be a sharp increase of air pressure where the item was teleported to, possibly damaging nearby objects. Could living organisms survive this without specifically warding the creature or human from harm?
And what additional effects would there be?
**UPDATE**
Please ignore the fact that the teleportation is done using magic. Let me reframe the question as: What would the effects be of an object disappearing and reappearing somewhere else?
[Answer]
Imagine that you call a cab. It arrives and you step in. You tell the driver your destination. He drives there, deals with the traffic, maybe you have a little chat. You arrive, the driver tells you the fare and you pay it, and you step out at your destination.
That is teleportation in action. Your magical teleportation differs from this in following, non-essential, ways. You call it with magic. It doesn't look like a cab. It is much faster. And it can presumably pass thru intervening space without interacting with it noticeably. Although most settings do have some methods for blocking teleportation, so some interaction with intervening space can be assumed.
So basically your question can be answered by answering the question: "How do you notice that the (invisible) cab has arrived." The most obvious ways are the sight and sound of the cab, in your case these would be special effects you can freely choose and can be ignored here.
With a cab there would be also exchange of air, but the fact that teleportation skips interaction with intervening space causes an issue here as it requires a change to some non-interacting phase at the origin and back to normal at the destination. This requires either that the destination is linked to the origin **before** departure or that teleportation works like some sort of accelerated astral travel where interaction needed to "shift back" is possible in transit.
Usually these two forms of travel considered separate and only the former is considerde teleportation. That means that two points are connected in advance of the teleportation and the arrival or departure of the teleporter would be preceded by a a gust of wind caused by the pressure difference possibly causing scents or even light objects being carried to the point with lower pressure. In that way it would be more like stepping thru a doorway than using a cab.
You can ignore the motion vector issues, any plausible form of teleportation has to match the frames of reference. If it doesn't it isn't teleportation, it is a cannon blasting the target with sub-atomic particles thru obstacles. Pretty useful but not really relevant. And using metal for ammunition is cheaper than forcing people to step in such a device.
As for limits, you can model these thru the cab analogy. Reasonably knowing the teleportation spell would be like owning a car. It would require maintenance and refueling **between** uses. It would have maximum carrying capacity in both the size and mass of what it can carry. And it would have a maximum usable range based on the amount of fuel in the tank. So you could do a second jump right after a short hop, but would have to split long distances to shorter hops with refueling stops. It would also have a maximum speed that would drop with mass carried, but it is probably not worth modelling that, unless the plot requires carrying somethin near the maximum mass limit.
[Answer]
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> I'm pretty sure that there would be a sharp increase of air pressure where the item was teleported to, possibly damaging nearby objects.
>
>
>
Why? Your magic works by visualization. Why would it have undesirable side effects like that? You don't visualize yourself teleporting and being damaged. Well, maybe you would. But the typical wizard won't. The magic system that you describe would work because that's the way that the users see it. Ironically, learning more about the way that it works would actually make it harder to make it work. Knowing what could go wrong would make it more likely that you would visualize it going wrong--and then it would.
If you want things to go wrong, then you may want to consider having magic discovered in a relatively advanced society. Well-educated members would have a much better understanding of what could go wrong. Perhaps only ignorant members could be successful wizards.
Note that even skipping purely magical explanations, you can easily get around this by switching the air where you are going to return to where you have been. And this wouldn't be much of a problem if you simply pushed the air out of your way. Unless you are in a small, enclosed space, the higher pressure will quickly disperse.
[Answer]
\*Possibility regarding air pressure: if you're going to go there as a realism point, but have the person *instantaneously* displace a person-volume worth of air when he rematerializes, then the air breaking the speed of light would be more destructive to the fabric of space-time than just making some people's ears pop.
Perhaps re-materialization takes the form of an infinitesimal point of energy that grows into the size/shape of the person, turns back into the person's matter when the size/shape is correct, and the person - in teleport-energy form - can consciously control the speed of this transition?
That way, the person can stop the pressure spike from (at the low end) making him sick and/or (at the high end) triggering the nuclear fusion of atmospheric nitrogen/oxygen.
\*Secondary note: does the person end up completely naked every time he teleports, or does he bring his clothing with him? If his clothing teleports too, then that would mean that an enemy could wait for him to teleport, then force something like a crowbar or a brick into the energy bubble where the person is going to "land."
The person's vital organs might re-arrange around the object, but that would still be at least as dangerous as penetrative injury, and the person cannot teleport himself and leave the object behind (which would otherwise return his vital organs to a safer positioning) because he would bring the object inside his body when he teleports for the same reason he brings his clothing outside his body.
Is this the kind of side effect you're looking for?
[Answer]
@Wick, I suspect many, if not most, of your concerns with respect to the theory and practice of teleportation are addressed in Larry Niven's essay [EXERCISE IN SPECULATION: THE THEORY AND PRACTICE OF TELEPORTATION](http://www.e-reading.club/chapter.php/75689/7/Niven_-_All_The_Myriad_Ways.html).
The essay is adapted from a talk Niven gave at [Boskone](http://www.boskone.org/), the New England Science Fiction Association conference which is reliably packed with MIT students. So Niven knew he couldn't get away with non-rigorous handwaving, and had to look fairly carefully at the various scenarios. Since he has a good working knowledge of physics and has read a lot of science fiction, there's a lot of good solid speculative science in it.
Among other things, Niven goes into a good amount of detail about the kinds of issues @JonOfAllTrades raises: conservation of momentum and energy.
My own favorite zany speculation is the design for the "end-teleport drive", a spaceship that teleports itself onto its own front end. That's just glorious.
[Answer]
Rather than teleporting by "moving yourself there," you could "exchange your body with the air there." Then the volume your body filled "there" would be void of air, so no pressure effects "there," and the volume your body left behind would be filled by the air from "there." You might get some small aerodynamic effects in the location you departed from because of air pressure differences, but they'd be minimal.
Kip
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[Question]
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Imagine a world much like ours, except our ape ancestors decided they liked the trees and never climbed down and decided to try out these 'tool' things. sapient apes never evolved. Instead a predominately aquatic race evolved (race with limited ability to go on land, such as just long enough to lay eggs, count for this question).
My question is what sort of aquatic species would be the most likely to develop sapience, and what forces would encourage and lead to that development? By sapience I include regular tool use and at least second generation tools (ie, they build tools who's sole job is to build better tools). Communication and basic language of some form should also existed.
What forces would encourage sapience to evolve, despite the caloric expense of it? how would tool use develop, in a land without traditional hands what would be the means of creating and manipulating tools (unless your answer is that the most likely species to develop sapience already has some hand-like features, such as otters).
How would your species adapt as it developed sapience to look/behave different from it's non-sapient ancestor?
This world must be very close to earth, but need not be exactly like earth. It's okay to hypothesis minor differences from our earth; however, the world should predominately look and feel like our planet earth, with most of the same creatures evolving in the same ways and the same habitats and biomes. However, it's perfectly acceptable, for example, to assume that a species split off from a common ancestor of modern animals thousands of generations ago and that species is the one that ultimately achieved sapience.
Any species that predominately lives in and utilizes water, and can not live long term on land, counts for this question. Fish, mammals, aquatic reptiles etc etc all count as potential sapient species.
[Answer]
Well [dolphins](https://en.wikipedia.org/wiki/Dolphin) are already pretty smart along with killer whales, appear to be the smartest sea animals. Of course nether at this time seem to have a need for tools, the closest I know of are dolphins using their sonar to stun fish.
Since you mentioned the [Otter](https://en.wikipedia.org/wiki/Sea_otter), they already use tools. I've seen videos of them using rocks to crack open clam shells for an afternoon snack. They also happen to be fairly bright.
One thing both dolphins and otters have in common is a sense of play and often seem to be having fun.
[Cephalopods](https://en.wikipedia.org/wiki/Cephalopod) are one of if not the most intelligent invertebrate on the planet. Considering the appendages they have available my bet would be they would be the most likely sea critter to reach sentience.
With all of their appendages and the [chromatophore](https://en.wikipedia.org/wiki/Chromatophore) they already need a bit of brain power to keep all this coordinated. They are great at hiding both from predators and prey.
[Answer]
For tool using marine sapients we need three main things:
1. Dexterous appendages
2. A technological substitute for fire
3. A way to dominate their natural marine predators
Hands:
Try this for a hand:
<http://www.popsci.com/technology/article/2010-10/coffee-filled-balloon-makes-best-robotic-gripper>
Note that you don't need to settle for a single ball - have multiple balls on many tentacles, or branched tentacles each with a ball. Also a mix of large and small balls.
Fire:
Make tools using biotechnology and symbiotic processes instead of industrial ones. Maybe your lifeform has evolved glands to excrete chemicals to put marine life like corals and plankton to work fashioning tools (knives grown as coral reef formations etc). Or maybe they have symbiotic helpers.
Dominating Predators:
Give your lifeform a serious power up like a huge bio-electricty ability to give eel-like shocks to enemies. The same trait can be used for communication.
Using tools to fight predators underwater is less effective than on land due to the damping effect of water on missile and hand weapons. But an ability to coerce other marine species biologically or whatever may give them an edge.
Developing all the above would require intelligence to make the best use of them.
[Answer]
# My question is what sort of aquatic species would be the most likely to develop sapience, and what forces would encourage and lead to that development?
[Dolphins, by a decent margin](http://www.nbcnews.com/id/35013555/ns/technology_and_science-science/t/dolphins-second-smartest-animals/#.VeCjZ2K9KSM). They are believed to communicate as much as us and [use tools already](http://www.onekind.org/be_inspired/animal_sentience/tool_use/tool_use_in_dolphins/). While they don't design and use "hand made" tools, it is not too far fetched of a concept that some clever dolphin somewhere could be driven by competition and lack of resources to such a degree that it figures this out and spreads the technique.
Since you want this world to lack humans, I suggest you find some way to put extreme selective pressure on Dolphins. A lack of food caused by a natural disaster of some sort could put the pressure on Dolphins to adapt or die. If they adapt, they will likely pass the technique on to their progeny, who will gain an edge over other dolphin groups.
# How would they create and manipulate tools?
At first they would use their beaks to move things, however, this isn't the best way to manipulate your environment. The dolphins have fins that used to be legs before they entered the oceans, but these are useful in the ocean so they are likely not going anywhere. Dolphins are pretty accurate with their beaks and tails, so unless you want these animals to develop advanced technology ([computers](https://worldbuilding.stackexchange.com/questions/3722/how-would-an-aquatic-race-develop-computers)]) which you haven't specified, it should work just fine.
[Answer]
An aquatic sapient could evolve from a species that manipulates or "farms" the coral reefs' plant life. A species that learned to manipulate the coral so certain plants would grow in certain areas to facilitate better positioning for hunting the animals that feed on the coral or better growth of the plant life to consume. The need for better methods of altering the plant life and hunting the animals that feed on it could lead to greater intelligence. They could even use the smaller animals to bait the larger animals and use a pack mentality to kill those.
There are no ocean animals that even attempt at manipulating the plant life, nor are there any ocean animals that have a "pack" mentality. (That i could find anyways) I think the main reason that sapient life did not evolve in the ocean is due the the difficulty of "farming" and the individual hunting style that is predominate.
[Answer]
Group bonding: Communication and teamwork are a vital part of the secret sauce.
Tool usage: Difficult, as aquatic environments reward non-tool use (streamlined appearance, low weight) and no fire. So a programable corral that grows tools or precursors would be needed for a civilization to develop further.
Protection from predators: Predators are always there and they threaten intelligences, so areas were the knowledge is transported (schools) must be protectable. Cages, barbwire, high trees, fire, name your weapon.
In a way we developed at the bottom of a gas ocean too.. so if we can do it.
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