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[Question]
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*This is largely inspired by two questions that [@dsollen](https://worldbuilding.stackexchange.com/users/4857/dsollen) has asked over the past year or two. The first: [Would ritual cannibalism of the dead lead to issues with disease?](https://worldbuilding.stackexchange.com/questions/20982/would-ritual-cannibalism-of-the-dead-lead-to-issues-with-disease) The second: [Cultural beliefs, practices, and prejudices of tribes practicing ritual cannibalism](https://worldbuilding.stackexchange.com/questions/33711/cultural-beliefs-practices-and-prejudices-of-tribes-practicing-ritual-cannibal).*
*EDITING NOTE: This question originally emphasized the biological sciences over science as a whole, which I've come to view as too narrow a focus. Also, the question as originally written didn't make very clear the importance that I believed secondary/residual consequences of the ritual would play in the larger effects on the civilization over a very long period of time. Hoping to rectify these and other minor concerns I had over the clarity of the question, I've since made significant edits.*
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Imagine a society that participates in **passive** ritual cannibalism (they eat people who have died rather than killing others for the purpose of eating them). They don't eat the dead as their primary source of food, but simply as a supplement to the domesticated flora and (possibly) fauna that forms the basis of their diet. Additionally, the culture has a strong taboo against waste and values the re-use/reclamation of just about anything of potentially practical use. Every time someone dies, their corpse is inspected to determine what can be salvaged for any of various possible uses, including consumption.
If it helps you to visualize the scenario, imagine that, at some point in their distant past, some horrible event (perhaps a natural disaster of one sort or another) wiped out all other sources of food in the location where they had settled. Then, while they either searched for a new place to settle or tried to start-up again in the same location, the inevitable famine struck them and, in order for some to survive, they resorted to (passive) cannibalism. This sudden, catastrophic loss of everything but their fellow survivors and the subsequent horror of the famine was forever imprinted into their cultural/institutional memory as the previously mentioned taboo towards wasteful behavior.
Setting aside the health concerns of engaging in the ritual (addressed in a separate section, below), would that society have a potential advantage in regards to scientific advancement over a second civilization that is identical to them in every other way, but doesn't eat, examine, or otherwise "usefully use" the corpses of their fellow men. This second civilization, instead, simply disposes of the bodies postmortem (e.g. burial, cremation) and sees any other "uses" of the bodies as taboo. Also, for argument's sake, the two civilization aren't in contact with one another, so neither can mooch off of the advancements of the other.
Here are a few assumptions I'm making that might be important:
* If every dead body is a potential food source, then it will likely go through as extensive an examination process as they are capable of, given their level of advancement, at any particular point in their history
* The absolute necessity of identifying who died of a relevant illness could easily lead to a more clinical basis for identifying the sick and their specific illness *before* they've died, which would create a better foundation for medicine from the start
* Because every single corpse is going through a sort of proto-autopsy, at the very least, I would imagine that they could gain a grasp of certain cause-and-effect relationships to certain causes of death quicker than other civilizations
* In the earliest stages of engaging in this ritual, by virtue of observation of the consequences from eating particular portions of the corpses, they would quickly learn what practices were and weren't safe
* In part *because* the transmission of diseases would be more prevalent, they may more quickly develop medical understanding of both causes and treatments, and the citizens that place a higher value on sanitation would be much more likely to survive, promoting sanitary practices and potentially affording an earlier understanding of the underlying science
* If cannibalism can account for as much as 10% of human dietary protein (see Viability section) and if the same butchers that handle the preparation of livestock can also handle corpses, some workers that would otherwise be busy raising livestock would be freed-up to do other, more specialized work
* If cannibalism has a more compatible nutritional profile for the human diet (see Viability section) and a portion of the nutrition consumed by the dead is passed on to the person consuming them, a lesser amount of crops might be needed to feed the citizens and some more workers might be freed-up for specialized work
* With the lower amount of livestock, as well, even fewer crops would be needed and even more workers would be freed-up for specialized work
* The larger the portion of society is that's available for specialized work, the quicker they develop and expand to more specialized careers, such as doctors, law enforcement, politicians, lawyers, and so on
* The earlier that laws can be created, enforced, and adjudicated, the earlier that the civilization becomes more civilized, a situation under which further advancements can flourish
* The more settled/civilized a civilization is, the more likely they are to develop a formal education system that could more pointedly ask the questions that lead to greater advancement of the society
* The earlier that an educational system is in place, the earlier an educated class of medical specialists can systematically examine various issues that might expand beyond the immediately practical medical purposes and into the biological sciences at large
* Medical advances would not only increase the expected lifespan, which would increase the amount of embodied knowledge in society available from the elderly, but also reduce mortality related to childbearing, childbirth, and general childhood mortality, therefore increasing the population and the number of specialists
* Although a population boom might lead to temporary famine, the initial deaths from the famine would actually become a food source that would decrease the likelihood of further deaths (a negative feedback loop) than would be seen in a society that refuses to eat the dead or that only resorts to cannibalism in extreme circumstances (and therefore doesn't know how to properly handle/prepare the corpses)
* At some point, the vast number of specialists would expand to include nutritionists, who, unlike their real-world counterparts, would be able to study the effects of a particular diet not just on the person who ate that diet, but on the person who ate that person; if people are more likely to eat people with a similar diet as themselves, then there would be a positive feedback loop that I imagine creates a rather convenient natural experiment
* The educated class wouldn't be limited to biological sciences and may stumble upon other advancements that end up reducing the burden on workers, not only aiding their health, but also freeing-up more people for specialized work
I feel like going any further would be complete overkill, but I think you should understand the point that I'm making. It isn't that the ritual would give them one giant leap ahead in understanding, but that it might give them a head start over other civilizations and then, in a positive feedback loop, keep steadily increasing the force that's pushing on the accelerator. So, just like a small initial difference in two bank accounts can make a huge difference with compounding interest down the line, what is a small advantage at any one given point of time potentially accumulates to something much, much larger over a few millennia.
So my question **isn't** if simply dissecting something would give an advantage, or if the slaughtering/consumption of a member of your own species offers some added benefit, or whether *any* ritual would give some sort of an advantage, or if this one specific cultural consideration could potentially be overwhelmed by any number of other cultural/situational factors that might come into play. It isn't any of these things individually and it isn't some of them at all.
What I'm concerned with is if the *consquences of the ritual* (and the consequences of those consequences, ad infinitum) would create an advantage over the course of a few millennia, cumulatively. Are any of my assumptions conclusively wrong? Are any of them, on the basis of research/evidence, very likely to be wrong? Are there other considerations that I didn't consider which mitigate the effects that I did correctly identify?
[As an example, @JBH told me that cannibalism might not be able to sustain a high enough portion of the human diet to actually reduce the burden on the workforce. That is a perfectly valid concern that would clearly throw a huge wrench into my thinking. I'd appreciate some form of relevant research to back up the speculation, but it's something that I hadn't thought of (though I should have) in my initial brainstorming.]
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*SIDE NOTE: This is my first time asking a question on any Stack Exchange site, so I apologize if I've done anything I'm not supposed to or haven't done something that I should have. Hopefully this isn't too broad of a question, either. I've mostly been just occasionally lurking before now and I know I still have a lot to learn. Thanks for your patience/help.*
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## Viability Concerns
The answers to @dsollen's questions largely addressed the health risks associated with such a society, such as:
* Prion disease transmission (e.g. Kuru) through consuming nervous tissue, the spinal cord, or the brain, although some evidence has been found of genes that protect against similar prion diseases among populations with a long history of cannibalism
* Transmission of infectious diseases (e.g. flu) through the respiratory system or GI tract
* Bloodborne disease transmission (e.g. HIV, hepatitis, hemorrhagic fever) through any portion of an infected person
Those answers also offered many ways to make the ritual safer, such as:
* Remove the GI tract from the body as quickly after death as possible to prevent cross-contamination
* Do not consume the riskiest portions, such as the brain/nervous tissue, GI tract, lungs
* Avoid opening up internal organs and, if possible, limit consumption to muscle tissue
* Clean the corpse thoroughly and cook at an internal temperature above 160° F
* Consume the corpse as quickly as possible after cooking or cure it through smoking/salting
I also found some interesting information in [this SciShow video](https://www.youtube.com/watch?v=SXjIzDexPoU) from YouTube about a month ago:
* "There's archaeological evidence that in some societies, human was a part of the original paleo diet, accounting for as much as 10% of the protein people ate"
* "Human flesh might actually have more nutritional value than other kinds of meat" because we have about the same amount of calories as other animals our size (e.g. a small deer) and "the more closely related your meal is to you, the more closely its nutrient profile will match your needs"
* "Studies in all kinds of animals have found that carnivores are healthier when they're fed members of their own or closely related species"
* "Elderly Fore who survived the Kuru epidemic had genetic changes that probably made them resistant to prion diseases"
* Similar genetic changes have been found around the globe, suggesting that cannibalism was common in our evolutionary history
* "Despite the number of cases of human and animal cannibalism we've found fewer examples of it causing disease outbreaks than we'd expect"
* "According to a review paper published in the American Naturalist 2017 [...] cannibalism could actually protect people from catching dangerous diseases because it gets rid of some of the microbes that spread them"
[Now, if you'll excuse me, I need to go shower after jumping down this particularly gruesome rabbit hole.]
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>
> **No**
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The most significant risk of cannibalism is [prion disorders](http://www.hopkinsmedicine.org/healthlibrary/conditions/nervous_system_disorders/prion_diseases_134,56), but that's an uncommon risk. The next most common problem is eating the flesh of someone who is ill, without the benefits of the [blood/brain barrier](https://en.wikipedia.org/wiki/Blood%E2%80%93brain_barrier) that illness can be easily transmitted to the consumer (unlike the diseases of animals, nearly all of which are difficult to "catch" thanks to the blood/brain barrier).
An understanding of physiology would be no more quickly advanced by disecting humans than mice, cats, cows, or any other vertebrate.
So, while there may be a minor advancement in screening ~~victims~~ applicants to ensure a disease-free experience (sounds like a vacation in Florida, doesn't it?) and possibly the earlier discovery of prions, I don't believe there would be a measureable advancement.
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It's worth pointing out the research on [Endocannibalism](https://en.wikipedia.org/wiki/Endocannibalism) (the consumption of, among others, the recently dead of your tribe).
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Mankind has been slaughtering animals for as long as it has been on Earth. Yet it has made significant advancement in biological sciences only in the last two centuries.
Cannibalism is "simply" slaughtering your own species. And I see no reason why this should lead to advancements of any sort.
***Addendum after edit of the question:***
And mind *slaughtering* is done on purpose, on living and still healthy specimens. Eating naturally deceased animals is normally avoided.
But, again, science did not progress too much thanks to slaughtering (except the part due to the increased energy intake assured by meat)
[Answer]
**No**
“Every time someone dies, their corpse is inspected to determine what can be salvaged for any of various possible uses, including consumption.”
This type of world view might cause some detrimental effects compared to normal human mortuary practices. In most human societies the dead are venerated in one way or another. This encourages “spiritual” thinking, perhaps eventually abstract thinking which might help in the development of understanding at a higher level (maths for instance is an abstract concept).A society that viewed a corpse merely a resource to be exploited might lack some of the more abstract skills needed for a better understanding of the world.
“If every dead body is a potential food source, then it will likely go through as extensive an examination process as they are capable of, given their level of advancement, at any particular point in their history”.
In more primitive times they simply would not have known this was important. They would rely on what nature provided. The process they are capable of would probably amount to: if it doesn’t smell or taste off then eat it raw, modified later perhaps to: if it doesn’t smell off then cook then if it doesn’t taste off then eat it.
“The absolute necessity of identifying who died of a relevant illness” is only an absolute necessity if you know about the problems of infection and disease as we do today. No doubt they would have had some elaborate rituals but there is no reason to believe these would be based on health and cleanliness other than the most basic actions to remove foreign matter and reduce smells etc. They might even consider your proposal with amusement, alarm or even anger as some kind of morbid examination mania.
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I want to use mechanical counterpressure spacesuits (something along the lines of [BioSuit](https://www.nasa.gov/pdf/617047main_45s_building_future_spacesuit.pdf)) for my story. They seem to have [many](https://www.universetoday.com/118939/why-cant-we-design-the-perfect-spacesuit/) [advantages](http://www.popsci.com/technology/article/2012-10/deep-space-suit#page-2) over traditional pressure spacesuits.
The existing prototypes are lightweight and do not restrict movement as much as traditional spacesuits. They also seem to be safer when it comes to tearing (no depressurisation). A new generation of materials can make them self-healing to reduce risks even further. Scientists are also looking into using alloys and special wired structures to work as exo-skeletons. Mechanical compression has an additional benefit of slowing down the bone loss process typical for low-gravity environments.
The list of possible advantages and benefits goes on and on. However, I could not find anything specific on radiation protection. **What materials or technologies can be used to protect from radiation given that the wearer has to spend hours working in deep space outside of spaceship?**
Typical tasks that astronauts perform:
* repairs of starcraft and equipment that can be done more efficiently by humans (rather than robots);
* mining equipment maintenance on asteroids;
* geological surveys prior to terraforming;
* recreational spacewalks.
Technological level:
* fully automated and robotised asteroid mining (still some human supervision is needed);
* space travel at 1/10 of the speed of light;
* terraforming technologies (however, only one project has been completed successfully by the time of their departure);
* highly developed recycling and reclamation technologies;
* genetic engineering;
* suspended animation.
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***NB***: Something like contemporary [EMU](https://www.wikiwand.com/en/Extravehicular_Mobility_Unit) is not an option: too bulky, low mobility, and high risk of decompression due to minor damage from a tiny asteroid. My astronauts need (and want) greater freedom of movement and lower risks.
[Answer]
How about an umbrella?
[](https://i.stack.imgur.com/jj6kV.jpg)
from <http://craziestgadgets.com/2011/06/21/7-ways-to-use-an-umbrella-hands-free/>
People have been using umbrellas to block radiation for a long time. Here is Robinson Crusoe and his goatskin umbrella.
[](https://i.stack.imgur.com/yplOo.jpg)
Seriously! An umbrella gives a large area of coverage. It is not attached to your body so not in your way in the same way armor would be. It can be reoriented to give directional protection. It can be detached and folded up and put away.
A backpack mounted umbrella could have a detector and servos to orient it to block the largest amount of incoming radiation (probably from the sun, just as is the case on earth). It would automatically pivot to shield the astronaut. An umbrella can expand to be very large, completely shading the working astronaut. I mean large like 5 meters across - such a large umbrella would be impractical on earth because of wind and air resistance opposing motion - a nonissue in space. These umbrellas will move with the astronaut, attached via the pack. The huge shady bulk of them will be out of the way of arms and legs.
As regards the material of the umbrella, lead or gold would be fine. An optional [beryllium](https://en.wikipedia.org/wiki/Beryllium#Nuclear_properties) overlay if energetic neutrons are a problem.
The astronaut would need to move slowly because of the inertial mass of the umbrella.
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You don't want lead or other heavy shielding because the biggest danger in space is"particle" radiation, atoms moving at near light speed. When the particles hit heavy shielding they produce a ton of secondary radiation. However, PVC sheeting has shown promise in this application. See <https://www.google.com/amp/s/amp.space.com/21561-space-exploration-radiation-protection-plastic.html> .
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What radiation, specifically? Cosmic radiation is omnidirectional and omnipresent, but can be tolerated for extended periods of time. There is no real need to protect against it during space walks so long as the astronaut has a shielded living area and good health care, assuming they won't be spending years in space.
Solar radiation is unidirectional but isn't particularly dangerous except during flares, which can be predicted. In this case, no amount of man-portable shielding is really going to help, the astronauts will have to retreat into a bunker that has extensive shielding, coming out when the flare is over.
Repeated crossing through the Van Allen radiation belts (or equivalent for another magnetic body) is *really* bad, so don't do that.
A possibility is a personal magnetic field, shielding the wearer from cosmic radiation. Alas, humans can't operate in a magnetic field strong enough to be effective. Setting up a magnetic field around the ship may be possible, but then an astronaut on a space walk may be outside of it, or worse, continually crossing into and out of it, which just exacerbates the problem (though not much for a ship sized magnetic field).
Another viable option is to harden the *human*. Improve DNA repair mechanisms, limit free electron damage, boost cancer fighting medications and diets (if you ascribe to the ketogenic anti-cancer theory), keep the humans inside a protective shell and use remote drones for space walks, get between locations as fast as possible, etc. Even with all of this, there will still be a slowly progressing radiation countdown for astronauts with every second spent outside of shielded areas. But with careful selection, you can pick folks with really high radiation tolerance, their kids may also have it, and eventually you could breed a group of "spacers" that can operate in space for extended periods of time with minimal radiation side effects, so long as they can avoid the worst solar flares.
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Okay I'm going to go with a complete suit made from a number of layers, 4-7 are the heavy radiation stops you're really interested in I believe. The layers are all quite thin, the total is probably an inch or less of material, from the inside out:
1. life support, monitoring, heating, cooling, food, water, air, etc... for the occupant, this is necessarily a skin-contact layer and includes insulation, moisture absorption, pressure stocking, heating circuits and a cooling jacket through which hot and cold working fluids can be passed to keep the operate at as close to an optimal temperature as possible. This is also where ambient pressure is maintained for the human in the suit.
2. mechanical assess/structure, this is the "power-layer" where any muscle augmentation equipment goes, also where the structural layer that everything else is attached to sits. This is also where you want to put essentials like communications equipment and air supplies.
3. secondary impact protection, the layer is a three sheet sandwich that with break up and absorb large particle impacts from micrometeorites that somehow get through the outer suit.
The following four layers can probably be stacked in any order, or possibly integrated into a single bi-layer material but I think this is the best layout for separate layers.
4. secondary Gold baffle, Gold sheet that absorbs any remaining ionising radiation like Gamma and X-Rays.
5. Boron layer, boron is an extremely effective neutron absorber that will pick up subatomic neutral particles.
6. positively charged layer, a fine electrically charged Gold mesh that serves the dual role of repelling positively charged particles, including but not limited to protons, and Alpha Particles and forming a primary ionising radiation baffle.
7. negative charge layer, a fine electrically charged Gold mesh that serves the dual role of repelling negatively charged particles, including but not limited to electrons, and forming a primary ionising radiation baffle. This layer is the outermost radiation layer as ionisation will actually reinforce the charge in this layer.
The outer layers of the suit, ultimately these are, and must be, disposable as they're exposed to raw vacuum and cosmic radiation.
8. impact protection/armour, at a minimum this is a three layer material that breaks up and stops micrometeors before they can penetrate into the mechanically sensitive layers beneath. The outermost of these layers is hard but relatively thin, it's supposed to be penetrated but only by the shrapnel from the broken impactor, the second layer is thicker and softer, designed to bleed as much energy as possible from the debris and in fact capture most of it, the base layer is a hard, slightly flexible, and relatively thick plate that stops any remaining material, much like the armour in a Tacvest. At the top end layer 8 is full combat armour with energy dissipation and impact dispersion properties that protects the wearer and the suit from direct weapons damage as well as the "minor" damage caused by space debris. This layer will absorb a lot of the lower energy radiation like UV and Infrared which is why it has a limited service life.
9. utility layer, toolkits, maneuvering packs, mag-boots, and other job specific equipment is all "aftermarket" and will actually go outside the primary suit.
These layers are used for the body and back of the helmet, there are two helmet approaches; the first is a full cover opaque helmet with video feeds displaying the outside environment, the other is to use a front visor, personally I favour the first approach, more protection from radiation etc... and you can't get blinded by accidentally looking at the sun without the shade down if you're closer to the sun than say Venus. The modern space helmet face plate is already about the last word in transparent radiation shielding. Gauntlets are excessively exposed so must be disposables, they comprise of plates composed of full layer material on the back of the hands and finger joints, as a rule, the backs of your hands are more exposed than the palms so the extra material is warranted. The palms and finger tips need to be thinner for the sake of dexterity, so we abbreviate, a thinner life support set that contains insulation and moisture absorption only relying on core temperature to regulate the rest, and use a relatively thick, 3+mm at rest, layer of lead-heavy gel to provide some but less impact protection and maximum radiation shielding in a flexible format. The gel will thin when pressured to improve grip. Or you can forego "by-hand" tool manipulation altogether, and use "waldos" instead in which case the suit looks a bit like [this](https://en.wikipedia.org/wiki/Atmospheric_diving_suit#/media/File:Deep_Sea_Diving_Suit.jpg) and the operators' hands and arms are no more exposed than any other part of them. Suit joints can use the same leaded gel as the gauntlet palms making them relatively vulnerable but extremely flexible.
Most stellar radiation is in the lower energy band and the stellar winds are primarily composed of protons these are relatively easy to deal with as outlined above. Cosmic Radiation, in the form of high speed, high energy particles will blast through any one or two of the proposed layers without slowing down, which is why there are a number of absorbent layers in the suit, these will hopefully combine to slow and capture cosmic rays. Please note that there *will* be instances where nothing you can wear will be sufficient, flares, solar-storms, gamma-ray bursts all represent lethal conditions for those caught outside, and possibly even those inside as well.
By the way if you're worried about expense those Gold baffles are paper thin, manufacturing will cost far more than the elements being used.
[Answer]
First I want to point out that if they are able to automate mining they can more easily automate ship repair. I wouldn't be surprised if this technology is 'realized' very soon =D.
As for the actual question:
Radiation is very hard to protect against, usually dense materials work best like lead or gold. there are also plenty of other materials capable of reducing radiation.
What protects the Earth from this radiation is its thick atmosphere of water vapor but also this critical **magnetic shield called the magnetosphere**. The magnetosphere is believed to be caused by the motion of liquid metals in our inner core. So one other possible thought is that the ship generates its own magnetosphere to repel inbound radiation or even the suits somehow generate a field large enough and strong enough to do it (personally the ship sounds more realistic as that protects everything with one large device).
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[Question]
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So I have been thinking about this lately, and I've been wondering what exactly are the reason for a culture to write in a specific format? Script form (curvy letters, straight letters), writing material (clay, paper) and development of language (developed from pictures, developed from sounds) are all factors that influence the way a language is written. But I know for a fact that languages have other factors that influence the way langauges are written, but what could they be I wonder?
[Answer]
Easy answer: I don't know. I'm not sure anyone else does, either, after reading a few reports. Check [this one](http://blog.dictionary.com/righttoleft/) out.
HOWEVER, after thinking about it a bit, I've an idea.
In the beginning, Man had sticks and clay. It's nice to think that you can write on clay with sticks like you can paper with a pencil, but you can't — not and expect the inscription to last for any appreciable time. The marks need to be deep, and you need to write fast 'cause you're the scribe and the king waits for no serf.
In other words, in the beginning, people had to *press* to make the letters. Since most people are right-handed it's very natural to press both in toward the body and left, pushing with the hand. Heck if I know if this is why it occured, but at least it's almost logical.
Later, as charcoal came into vogue, the need to press disappeared and the smudging problem everybody thinks about but no authority wants to admit could be an issue comes into play. Think about it... a bazillion years of pressing sticks into clay and suddenly the king expects you to use this new-fangled thing called *"the tip of a burnt stick"* 'cause he's not in the mood to be less cool than that stink-bomb of a king over there.
And left-to-right is born. *Dragging* the stylus rather than *pressing* the stylus.
And the belief that left-handed people are all witches is born, too. 'Cause the king simply can't believe that anyone not born of the devil could fail to write things his way. *I'm just sayin'.*
[Answer]
It depends on both your writing medium and your writing support.
Both will influence the way the text is arranged and will somehow enforce a standard.
Actually there are examples of languages which were or are written indifferently from left to right or up to down. Japanes and Chinese are some modern examples, and I think also Hebrew was versatile in the past, being written both from right to left and left to right.
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Welcome to the Black Cauldron. The Cauldron of Storms, even. It's a sunny day now, perfect for fishing. Just not here. There's no boats on the water. The weather can go bad, quickly. And anything on the water then... Well, there's plenty of wrecks on the bottom. Big ships. Little ships. Sometimes people try to race across the Cauldron to beat the storms. Sometimes they get out. Sometimes they don't.
I want to create a sizeable bay/harbor that, in most aspects, is pretty reasonable. Until a storm comes along, then things get unreasonable.
I don't want *all* weather or storms to be devastating, coast-leveling catastrophes, but I want them to be fairly common - Common enough that a cultural stigma has developed around using this harbor pretty much at all. Normal weather happens, but then you can get the "un"predictable mega-storm that goes through and causes havoc.
The things I want in this storm cauldron:
* Mega-storms. Obviously. Strong enough to sink pretty much any ship that goes in.
* Moderately unpredictable weather. I want weather forecasting to be reasonably accurate, but have occurrences of "freak" or "Surprise" storms being expected/common
* Relatively isolated weather. I don't want the storms to go inland and wreck everything regularly, or to be a regular occurrence elsewhere on the planet. Just here.
* Cause for the storms is preferred natural, but can be artificial but not magical.
I'm interested in what the geography around this cauldron would have to be. Would it be a huge crater, with massive walls cordoning off the rest of the area? A mountain range? Or maybe it's in an island chain that lies in a conflux of currents and winds that ends up dumping everything here, and then the storms just bugger off to the rest of the sea after blowing everything in sight.
This does take place on a fictional world in which a small amount of things have already been established:
1. Surface Gravity is approximately 130% Earth Gravity
2. Atmospheric Pressure at sea level is roughly 80-85% Earth Atmosphere.
3. Plant/animal life is abundant but not easily edible by humans.
4. There is a sizeable human population with technology similar to 1940s-1950s Earth technology, although some areas progressed slower and others faster.
Aside from these things, the world design is largely open. I'm picking plot points to make plausible first, before filling out the more generic stuff.
[Answer]
# Use mountains to control where hurricanes go
I'm not creative enough with either photoshop or Paint to make some drawings, but imagine a world thusly: The East coast of Florida and the Carribean, except there is a tall, 4000m+ mountain range following the [Windward](https://en.wikipedia.org/wiki/Windward_Islands) and [Leeward Islands](https://en.wikipedia.org/wiki/Leeward_Islands) to Puerto Rico to Cuba, and up the center of Florida all the way until it merges with the Appalachians in Georgia. Now, also imagine that the coast of North Carolina extends all the way out to Bermuda, preferably mountainous. Now look at this hurricane map.
[](https://i.stack.imgur.com/SMmro.jpg)
Instead of breaking across the Caribbean Islands and heading to Mexico and the Gulf, all hurricanes will track up the Atlantic coast of Florida. Then, instead of rolling back out to sea or petering out up the American East Coast, all hurricanes will slam directly into Charleston, South Carolina, and dissipate their entire energy between there and the mountains.
Now look at the plot of hurricane frequency.
[](https://i.stack.imgur.com/wMGDj.gif)
The Charleston Storm Cauldron will see at least one hurricane every year, right about September 10th. In general, August to October will be a monsoonal wet season, where you expect a storm a week, or even more in the first half of September.
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I'm thinking of a combination of a circumpolar ocean current, anticyclonic low pressure systems, a somewhat ptotected natural bay of your choosing and an active volcano.
The tip of South America and South Africa (and I assume New Zealand) have regular low pressure storms come through. They can be extremely dangerous for shipping, especially pre-20th century sailships and steamers. Lots of wrecks off those coasts.
The southern circumpolar current is a continous cold current circling Antarctica. The ocean current and prevailing westerly winds create a series of strong low pressure fronts. When especially strong they bring strong winds and and excessive wave heights. (Will link some images and websites later)
The storms are typically a winter occurrence when the ITCZ moves North allowing the southern polar weather to extend further northwards. However, occasionally various factors combine to allow a summer storm. These completely natural stoems are enough to sink ships on a regular basis. And already have some seasonal unpredictability that can still be reasonably predicted up to a week or two in advance (with modern weather prediction techniques. Pre-satellites and without a thorough understanding of the dynamics, your people could be reduced to a day or two warning with some storms coming out of nowhere).
Have a large natural bay facing or partially facing the prevailing storm fronts. The bay protects from local currents and winds etc but when the storms come in they are hit with the brunt of the storm forces. You can have the bay surrounded by a mountain range if you really need it (think Table Mountain and the Cape Fold Mountains in South Africa) but it is not strictly necessary if the bay is situated in the south of the landmass. The very location and extent of the ITCZ seasonal shift will restrict the storms from reaching too much further north.
Now for the volcanoes. Im not 100% certain of the logistics but it is something to consider. As previously mentioned, storms are fed by a combination of warm and cold air interacting. Preferably cold air blowing over warm water providing additional moisture to the cold air. See where I am going with this?
The volcano/volcanoes don't have to be very *very* active as in Dantes Inferno active. Just enough to warm up a region of polar water West of your desired location of the Storm Cauldron in the East. Then the cold westerly winds blowing over the warm water could possibly be fed by them creating even stronger storms than currently experienced on Earth.
These volcanic seamounts could be fully submerged under the water or they could be partially or fully exposed. If you want some particularly nasty storms with a high 'unpredictable' factor, have the volcanoe partially products fully exposed. This will allow actual eruptions to occur, warming up the air in the surrounding area and to various altitudes. A major eruption would push warm air kilometers up into the atmosphere. All this hot/warm air in a typically cold/freezing polar environment should cause some pretty stroganoff pressure systems to form.
The irregular and 'unpredictable' nature of the amount of geothermal heat released by the volcanoes/sea vents will allow unpredictably strong storms to occur on a semi regular basis. All completely natural. No magic or man-madeven interference required.
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Storms are created by masses of warm and cold air creating areas of extreme high pressure difference. The dynamics of this eventually causes a rotational effect and there is your storm.
So your area needs to be enclosed at least partially by mountains and have a reason for this to happen intermittently. One idea would be to have a change in the prevailing wind direction bringing colder or hotter masses of air funneled between mountain ranges. So periodically storms will brew and rage for a while and then peter out until the next time mostly confined to the valley.
So most of the time it's subject to normal weather, but a change in the wind direction causes localised storms is the basic idea. You'd need to expand on it a bit. But once the storm moves out of the valley it can dissipate rapidly as it no longer has the conditions to support it.
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Coming off a large flat area, hills and/or mountains will force winds to move upwards, cooling and condensing the water in the air. So my hometown in the foothills gets a ton of snow while the area in the valley gets little to none. On a larger scale, the mountain range in the north western US blocks moisture from traveling inland via this same effect, western Oregon is drenched, while east of that is very dry.
Warm weather causes more water to evaporate, which means larger clouds and, given the right conditions, violent storms.
Water retains heat *really* well, much better than land. Which is why deserts have ridiculously cold nights, despite the hot days. There's an area in/north of (forgive me, my knowledge of geography in that region is rather poor) the Tibetan Plateau that is basically a giant bowl. The plateau blocks the moisture from the Indian ocean (causing the monsoons south of the plateau) and this bowl is very dry. Rapid heating and cooling causes massive changes in air pressure with nowhere to go, except that one narrow opening heading east. Hot air expands, air pressure increases, and hot winds come rocketing out of the narrow opening. But then night falls, the air cools, contracts, and then suddenly there's very low pressure in the bowl, sucking air at high speeds *back* through the opening.
Potentially, you could utilize a mixture of the above, rapid pressure/temperature changes, excess moisture and conflicting air currents can whip up one heck of a storm. Positioning it for maximum effect would be tricky and potentially require simulation software. you might find something useful [here](https://scied.ucar.edu/games-sims-weather-climate-atmosphere).
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So, I know that the universe is expanding, and that that means that things are generally getting further apart as time goes on. What I'm having difficulty with, however, is figuring out just how much this might affect things like interstellar travel.
The 'world' I'm building is essentially a series of colonies on planets in star systems no more than 1 thousand light years apart, in the same galaxy. I plan on having FTL where a journey of that length would take about 60 days (assume some sort of [Alcubierre drive](https://en.wikipedia.org/wiki/Alcubierre_drive), or if that complicates things too much, assume the same distance travelled at sublight speeds).
What I'm wondering is if someone were to start one of these 1000-light-year journeys, would the destination drift away from them at a measurable/meaningful way? If a shipping company continuously sends ships on this journey for a few centuries, would this effect become more important then? If numbers can be found for the change in distance over time, I would love to know them. Alternately, if the galaxy has enough gravity or other forces affecting its stars to nullify the universe's expansion, then evidence of that would also be sufficient.
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The universe is expanding over *large distances*. Over short distances (1000 ly is a short distance in this sense) the universe is gravitationally bound and *does not expand* at all:
>
> Once objects are bound by gravity, they no longer recede from each other. Thus, the Andromeda galaxy, which is bound to the Milky Way galaxy, is actually falling towards us and is not expanding away. Within the Local Group, the gravitational interactions have changed the inertial patterns of objects such that there is no cosmological expansion taking place. Once one goes beyond the Local Group, the inertial expansion is measurable, though systematic gravitational effects imply that larger and larger parts of space will eventually fall out of the "Hubble Flow" and end up as bound, non-expanding objects up to the scales of superclusters of galaxies.
>
>
> ([Wikipedia](https://en.wikipedia.org/wiki/Metric_expansion_of_space#Effects_of_expansion_on_small_scales))
>
>
>
The [Local Group](https://en.wikipedia.org/wiki/Local_Group), about 10 million ly across, is considered to be the largest object which will always be with us. Only larger objects will be affected by the expansion of the universe.
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Over a 60 day journey the expansion will be negligible.
The rate of expansion is 67.15 ± 1.2 (km/s)/Mpc
There are 3.26 light years to the parsec.
Over the distances you are talking about that amounts to 20 m/s of expansion.
On on a 60 day journey the distance will extend by 103680000m, which is less than one light second.
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Today, I answered a question in an essay which related to time travel and what I would do if I could go back to a historical period. This got me thinking, and I came up with a hypothetical scenario in which I take a holiday to a Swedish village at the height of the Viking age (let’s say 900 A.D.) in order to explore the time period. I arrive dressed in period clothing, except for my satchel, which thanks to me forgetting to empty it out contains my MacBook Pro with a fully-charged battery.
Now, let’s say I was to seek lodging in the house of a family in the village. After gaining a valuable insight into how the Vikings lived, their religion and their culture, I come back to the house and decide to write up the valuable historical information I gathered. However, I stupidly forget that I am in the Viking Age and casually pull my laptop out of my satchel, boot it up and create a text document to write down all that I discovered about the Vikings, on the table in the middle of the family’s house. What would the Viking family think when they saw my laptop? Would they destroy it out of fear? Would I be worshipped as a cargo cult god?
As an additional time-travel experiment, what if I also carried in my satchel diagrams and descriptions of a crude steam engine (designed as plausibly as possible for the metallurgy of the time), a flintlock musket and gunpowder, as well as some fragments of modern knowledge, and attempted to kickstart the Industrial Revolution? In this scenario, I would find the relevant people (herbalist for gunpowder, swordsmith for the musket and blacksmith for the steam engine) and attempt to combine my modern knowledge with the equipment and materials they had on hand to create gunpowder, a musket and a steam engine. If they had the raw materials to create those things, assume that I have an excellent working knowledge of those technologies and can try to coach and assist them in whatever metallurgy and construction techniques are possible with their equipment.
If it was possible to create those things with the equipment I found, I would demonstrate the musket in front of the village on a mannequin, or perhaps livestock that needed slaughtering, and fit the steam engine to a small boat to demonstrate potential applications.
My question to you is: what would come about of my efforts to create those three technologies, and what would the world look like today? Would they be simply impossible to create at the time, or would they receive massive attention and significantly alter the course of history? Perhaps they may be seen as curiosities and end up like the Greek aeolipile or the Mayan wheeled toy animals.
Assumptions:
1. I speak fluent Old Norse
2. I have enough of the local currency to accomplish what I want to do
3. I am immune to the grandfather paradox (If I somehow alter history so that I am never born, I will be able to trace my lineage back to a family of alien space bats.)
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"MacBook Pro with a fully-charged battery' So like two hours tops?
Jokes asides you would be the Marco Polo of the Vikings. OR just another merchant with his silly things from other lands we Nords don't want to invade (yet).
Gunpowder in Viking age? So like 100 years before first KNOWN written down recipe for that?
Flintlock musket is similar story - after the gunpowder came to Europe we very quickly upgraded it to gun-like usage.
So that two things would appear in the timeline slightly faster (or maybe not, remember that the Nords were present in the Byzantium so they could have access to Mongolians and gunpowder, they may be just uninterested in this ).
Remember that gunpowder guns for hunters may be useless as they are very loud, slow and heavy.
About the steam engine? I think you are guessing right with the aeolipile. I think the Egyptians also have used steam engines to "magically" open doors.
So until you force the need to use them (blacksmithing maybe) there would be no use to kick-start industrial age with them.
[Answer]
## Not much, I'm afraid.
Too many links are missing, below, I'm trying to outline how different factors tie together.
## Industrial Revolution
Industrial revolution is a complex affair, stretching far beyond simple technical ability. Nothing happens just because it can be done, there needs to be a need for it to happen.
## Steam Engine
Steam engine is an effective power source, but is nothing but loud and stinking toy without devices to power, and those weren't invented until just before industrial revolution. You need widespread adoption of mechanical looms and lathes which desperately need powering before you have real use for steam engine. Initially those tools would be powered by wind, waterwheels, animals or people, but steam engine would provide power source that is more reliable than wind, more cost effective than humans or animals (if used for mass production) and not bound to geography like waterwheels. For ships of the time, steam engine isn't cost effective either, [this](https://en.wikipedia.org/wiki/Draken_Harald_H%C3%A5rfagre) is a reconstruction of largest Viking ship ever discovered, for comparison, this was the first [boat](https://en.wikipedia.org/wiki/Pyroscaphe) ever fitted with steam engine (it has almost double the displacement of reconstructed Viking ship) and [this](https://en.wikipedia.org/wiki/HMS_Victory) is one of the biggest warships contemporary to said steamboat (with over 35 bigger displacement than linked Viking-style ship). When you already have massive Ship-of-the-line warships and cargo Galleons, jump to cost-effective steam powered ironclads and cargo paddlers isn't that big. On Viking ship, your engine would take too much space and usable weight to be useful.
## Mechanical Tools
To have mechanical looms and lathes (or other mechanical tools), you need fairly precise metalworking, and just as was the case with steam engine, you need to have a need to use them. What's the purpose of looms and lathes? Mass production.
## Mass production
For mass production to happen, you need economic incentive for it. You need people to sell your produced goods to, and those people need to be able to afford them.
Apparently GDP didn't change [that much in centuries before Industrial Revolution](https://en.wikipedia.org/wiki/Industrial_Revolution#Causes), so perhaps second part would hold true, but [European demography changed by a factor of 5](https://en.wikipedia.org/wiki/World_population_estimates#By_world_region). It's quite possible that population and population density of the time would make mass production ineffective, even if it could be done with technology of the time - you need industrial scale coal mining or woodcutting to power your steam engines, you need a lot of workers to utilise the devices, you need industrial scale metalworking and construction to build the devices in the first place, and you need to make it all big enough to afford running it. If you can't you are better off with small scale construction, for which steam engine isn't necessary. You may think that small workshops could use steam engines too, but you would be only partially right. Small enterprises did use steam engines, but they existed in environment where big factories, through economy of scale, drove the steam engine setup cost way down making it all a mixed blessing and necessity at the same time - improved power sources became cheap enough, but competition made sure that at the same time they would be necessary to compete.
## Pre-Industrial mass production
English wikipedia is surprisingly devoid of information on the concept, including staggering revelation, that apparently English doesn't even have word for pre-industrial factory. Fact is, division of labour (where single worker makes single part of the bigger product) and production line are NOT concepts exclusive to industrial revolution. Those concepts appeared as early as ancient times, however were mostly singular in application until centuries preceding industrial revolution - XV is when they started appearing in Europe enough to start having meaningful impact on manufacturing. As early factories grew bigger and more common, there was increased demand for power, creating environment where steam engine would indeed be useful.
You said that you have enough wealth to achieve what you want to achieve, but that's you, and only you. As a wealthy eccentric, you can have your expensive novelty toys. Unless somehow others have incentive to use them, they remain your personal toys.
## Musket
Europe adopted firearms almost as soon as they arrived on the continent (brought most likely by invading Mongols), so perhaps you could at least achieve this goal. Biggest advantage of firearms over bows is ease of training, it takes months at most to train arquebuser or musketman, but years to train bowman, this however comes at the cost of lower accuracy - muskets are only good for about 70m, no matter how good shot you are. Vikings did use bows, but were not renown for their archery, so perhaps they would be interested in handheld firearms, though I would expect them to be more interested in cannons to be used in their raids (their ships could perhaps carry one or two bow cannons too). However, first gunpowder weapons are dated back to XII century China, thus they pre-date Industrial Revolution by very far margin.
## Summary
I'm of the opinion, that Europe 900 AD lacks infrastructure as well as economic incentives that would make accelerated industrial revolution possible, even if you managed to bring and explain all the necessary knowledge of geology, mining, metalworking, construction, physics and chemistry. Fact that Vikings were both world famous warriors and world famous merchants does make them exceptionally recipient for innovation in manufacturing and weaponry, but missing infrastructure is just too great. Goal of early introduction of firearms, is however possible.
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*Any sufficiently advanced technology is not distinguishible from magic*
I have read somewhere that the first native American to see an european on a horse could not sense they were two beings, but they felt it was a single magic creature.
Or also look how a nowadays kid reacts to a cassette player or to an analogic phone.
You can expect the same when they see your laptop or the schematics of a steam engine: "Wow, a luminous magic flat stone" or "Wow, a fancy decorated sheet of sheep skin which is thinner and whiter than sheep skin".
You would probably need to search not for a common villager (who may probably kill you because you do weird things with your flat stone\*), but for a smart and influent enough person whom to demostrate some of your wonder (start easy with a torch light or with a gas lighter, then move on to more complex things).
Did the Vikings had a Leonardo da Vinci?
\*Petronius reports that the inventor of tempered glass was sanctioned to death by the emperor after demonstrating its invention, on fear that the bronze would turn useless as compared to it.
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Advanced Metallurgy would be necessary to build a steam engine, because the boiler has to be strong enough to hold the pressure in, and this is not possible without very strong steel or originally wrought iron, which is relatively difficult to make without impurities that make it useless.
<https://en.wikipedia.org/wiki/Wrought_iron>
The Vikings would be interested in advanced metallurgy if you showed them a stronger sword, more unbreakable than their swords. Then you could progress to engines, and suchlike.
In fact, making better axes, then building a set of rails from the place where trees are cut down to where the ships are built and making a horse drawn cart that can go on the rails might be a possible way of gaining their good will, because it will significantly speed up the process of ship building.
By working this way, i.e. creating something that meets a need, you could change history and bring on the industrial revolution much earlier and the present would be completely different. Perhaps the Vikings would end up ruling Europe and from then on everything would be completely different.
You could bring a solar charger for your laptop, of course. If you were there between 950 and 1250 AD there would probably be enough sunlight because this was the Medieval Warm period, when temperatures were warm enough in Europe to make Greenland (now virtually a chunk of ice) more habitable. After this of course was the Little Ice Age, when the inhabitants of this part of the world suffered a climate induced famine and came down in their ships to raid the unfortunate people of Cornwall etc.
<https://en.wikipedia.org/wiki/Medieval_Warm_Period>
Of course if they had steam power in those days, the Little Ice Age may well not have been so disastrous for the people living in Greenland, as they would have been able to travel more easily and import coal from Germany, and heat their villages. Alternatively they may well have been far more effective at raiding Europe.
Either way, everything today would be different.
Question: are your Vikings Christians or Pagans? Or is this happening in a period when both are intermingling?
Because on beholding your laptop, a tablet on which magic writing appears and tells you things you couldn't possibly know yourself, the Christian Vikings may well react with a different variety of superstition. They might think you are a devil, and might well try to kill you - think Beowulf which is an Anglo Saxon tale about a Christian Geat killing a devilish monster in Denmark.
<https://en.wikipedia.org/wiki/Beowulf>
The Pagan Vikings might think you are one of the Norse gods - specifically Hermoth, or Hermod, the messenger of the gods, (a natural assumption considering your magic tablet on which writing appears in a strange tongue) or Wodin perhaps (depends on how big your beard is - if you have one and are male! If you are female I'm not sure which Norse goddess they would think you are.
Note also that in general in the early history of this interaction some Christian Scandinavians considered the Norse gods/idols to be inhabited by devils or demonic powers, while essentially being powerless against Christ, later on, the legends about the gods etc were thought to be worthy of being recorded by Christian monks etc because they were seen as simply legends, interesting stories that people might like.
A further thought - it took an awful lot to make the Christian Danes and Geats in the tale of Beowulf react hostilely - the Danes asked the Geats to help because Grendel was murdering them indiscriminately in extremely violent attacks. Quite often throughout history Christians were welcoming to rather strange manifestations - such as the Green children of Woolpit (or Wolfpit).
<https://en.wikipedia.org/wiki/Green_children_of_Woolpit>
So what I'm saying here is - they may well have been welcoming and hospitable. I think it depends on whether they are fundamentally friendly people or not. Could be either - you get both types in any culture.
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A followup to [this](https://worldbuilding.stackexchange.com/questions/59005/where-do-mushroom-forests-thrive) question.
In my world, mushroom producing fungi have developed a symbiotic relationship with algae (or cyanobacteria) similar to [Prototaxites](https://en.wikipedia.org/wiki/Prototaxites).
These fungi exist alongside all the usual plant species of earth, thriving in niches such as the dimly lit floor of dense rainforests, and as primary 'vegetation' in the month long nights of cool damp polar regions.
They have developed a range of [shapes and sizes](https://s-media-cache-ak0.pinimg.com/originals/ff/27/73/ff2773fa707b0d8736f52a451563367e.jpg), from upright broad-headed shields and chanterelles, to spreading clubs and corals, to tree-climbing brackets. They have also developed a varieties of colors based on the color-absorping pigmentation of their algae or cyanobacteria symbiotes. The fungus still retain their hyphae below ground which they use to capture nutrients from the soil, but their above ground mushroom structures are strengthened with chitin and last for years, or even centuries.
Similar to how insects pollinate flowers, and birds and mammals disperse seeds for flowering plants, **what animal species are crucial to the ecology of these mushroom forests?**
[Answer]
## Animals are *optional* for reproduction
While plants may employ animals to transport seeds, pollen, or other bodies carrying genetic material, fungi make use of other methods. These methods may employ animals, but would work perfectly fine without them. Additionally, most fungi are asexual - so there is no need to transfer genetic material with other "trees".
**[Spores](https://en.wikipedia.org/wiki/Spore)**
An equivalent to seeds, they are released in large numbers (sometimes in the trillions!), which increases the chance of survival. Spores are small, and are carried by air, so while contact with animals may spread them, it is really not necessary. Sometimes spores are also carried in a [liquid](http://www.mushroomexpert.com/coprinoid.html) as opposed to the traditional ~dust cloud
**[Fragmentation](https://www.britannica.com/science/fungus/Predation#ref519139)**
This occurs when part of the mycelium (root equivalent) or thallus (body) of a fungus breaks off unintentionally, then sprouts to form a new individual organism. Natural processes can easily break down your forest, but if you want animal contact, you can consider something that eats your "trees", maybe similar to a beaver - that spreads new organisms through its feces.
**[Budding](https://www.britannica.com/science/budding-reproduction)**
When cells divide off of a fungus for the specific purpose of reproduction (as opposed to tissues breaking unintentionally and sprouting), budding occurs. Animals cannot facilitate or aid in this process.
**In summary**
These methods will work fine independent of animal interaction, but you may employ animals to consume your "trees" if you wish.
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## Animals *are* needed to provide nutrients, but the type may vary
**Why not just photosynthesize?**
While your forest uses photosynthesis to produce sugar, which is an added boost, even plants use roots to obtain the nutrients they don't get through photosynthesis. Some things must come from other sources.
**Why animals instead of other plants?**
The problem with having a forest with set, unchanging flora is that the soil quickly loses the nutrients needed for healthy growth. That's why [crop rotation](http://wonderopolis.org/wonder/why-is-crop-rotation-important/) is so important; many new nutrients must be introduced in some way. However, in nature, animal populations provide the solution when farmers aren't there to switch out what grows.
**How should the forest take nutrients from animals?**
The best way to constantly replenish your forest's nutrients is to kill some animals every once in a while. Luckily there are plenty of lifestyles that will allow for this:
* [Carnivorous](http://www.carnivorousplants.org/cp/WhatAreCPs.php): Like carnivorous plants, your fungi may lure in animals such as insects and small birds, and break down their bodies to help them grow. There are plenty of ways to lure and trap animals - sweet scents, bright, attractive colors, closing parts, one-way pits, etc. The type of animal lured is not specific.
* Decomposing: Following traditional fungi, your forest could break down the corpses of (plants and) animals on the forest floor using its mycelium (roots). The type of animal decomposed is not specific. Additionally, feces may be broken down by the hyphae.
* Parasitic carnivores: You could consider growing your organisms on top of large living creatures. As long as the creatures are around, the forest will be. While this is appealing as it requires minimal work, it puts the "trees" in an evolutionary corner: if the hosts go extinct, so too do they.
* Parasitic decomposers: Your forest could intentionally kill animals, and break down their bodies. This varies from carnivores because animals are not being attracted actively. An example of this is releasing toxic spores that, when inhaled by living things, kill them, before taking root. Using their nutrients as fuel and building materials, the spores proliferate. The types of animals in these circumstances can vary.
[Answer]
## Animals Are Rarely Necessary
As stated in previous answers, animals are not needed for most mushroom reproduction.
However [Coprophilous fungi](https://en.wikipedia.org/wiki/Coprophilous_fungi) only grow on fecal matter:
>
> Coprophilous fungi release their spores to the surrounding vegetation, which is then eaten by herbivores. The spores then remain in the animal as the plants are digested, pass through the animal's intestines and are finally defecated. The fruiting bodies of the fungi then grow from the animal feces.
>
>
>
So this is one case where animals, herbivores, are indeed needed.
## Plants and Ecosystems are Most Common Requirements
Perhaps the most important requirement for mushroom growth, though, is their dependancy on certain environments. For example, some mushrooms grow only on birch trees, others only grow on the ground under conifers. Some only grow in shade, others grow in sunny fields. Some require humid, tropical conditions, while others only grow in the desert.
So, although animals are not required generally for mushroom growth, each species usually has very specific environmental requirements.
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While I don't believe this simple answer should dictate anything for your world, from basic observation on land I owned that was rife with mushrooms, I can say that the most common visitor to said mushrooms were mollusks... slugs and snails, which actually fed on some of the mushrooms directly.
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Our intrepid interstellar crew arrive in a new solar system. They find a planet in the Goldilocks zone. The planet has no life, but is otherwise earth like\*. The atmosphere is 80% nitrogen, 20% carbon dioxide. Give or take.
If the crew were to drop say 50 canisters with 1kg of algae, and/or cyanobacteria, into the sea:
* **How long would the algae take to spread through the whole planet's sea?**
* **How long to convert the atmosphere to be breathable?**
\*For argument sake, the planet is exactly same as earth; apart from having no life and consequently a different atmosphere. (Unless there is a good or interesting reason why it would be different)
[Answer]
**How long would the algae take to spread through the whole planet's sea?**
Algae have to float, so this depends on ocean current. The fastest sustained speed of any current on earth is probably the Antarctic circumpolar current at around 4 km/h. Lets divide the circumference of the earth by that to estimate $ \frac{40000 \text{km}}{4 \text{km/h}} = 10000 \text{h} = 417 \text{days}$. Different speed currents and different continental geometries,matter; since most currents aren't that fast around 2 years is probably a good estimate.
**How long to convert the atmosphere to be breathable?**
So first off, there are two separate processes at work here. CO2 is converted to organic carbons, like carbohydrates, and water is converted to oxygen, in separate steps of the photosynthetic process. So when the 20% CO$\_2$ is gone, that doesn't mean that 20% O$\_2$ as been created, or vice versa.
[This](http://www.science.oregonstate.edu/ocean.productivity/) site suggests the world's ocean primary productivity is 3.8 Pg per month. And [here](http://www.fao.org/forestry/17111/en/) we have an estimator of 47.5% by mass C in vegetation, consistent across all kinds of vegetation. To finish this calculation, we need the mass of 20% of the CO$\_2$ in the atmosphere. To make things simple, we'll say O$\_2$ and N$\_2$ are about the same molecular weight. Its a $\frac{14}{32}$ molecular weight ratio between the carbon part of CO$\_2$ and O$\_2$, so 20% of a $5.15\times 10^{18} \text{kg}$ atmosphere gives us $ 0.2 \cdot 5.15\times 10^{18} \text{kg} \cdot \frac{14}{32} = 4.5\times10^{17} \text{kg}$ of carbon that needs to be removed from the atmosphere. Putting it all together:
$$\frac{4.5\times10^{17} \text{kg}}{0.475 \frac{\text{carbon}}{\text{biomass}} \cdot 3.8\times10^{12} \text{kg}\frac{\text{biomass}}{\text{month}}} = 249653\, \text{months} = 20804\, \text{years}$$
20 millenia, that seems crazy fast!?! Well if there are no other lifeforms respirating, there is not much of a carbon cycle. It comes from the atmosphere, gets turned into algae, sinks to the ocean floor.
In an alternate calculation, [this](http://www.oilgae.com/ref/downloads/Analysis_of_CO2_Capture_Using_Algae.pdf) paper suggest you can get up to 30g per m$^2$ per day of biomass production on algae farms designed to capture carbon. If you use the entire surface of the ocean ($3.6\times10^{14}\text{m}^2$ as your farm you would get
$$\frac{4.5\times10^{17} \text{kg}}{0.03 \frac{\text{kg}}{\text{m}^2\cdot\text{day}}\cdot 0.475 \frac{\text{carbon}}{\text{biomass}} \cdot 3.6\times10^{14}\text{m}^2} = 87719\, \text{days} = 240\, \text{years}.$$
So you can probably remove all the CO$\_2$ in a couple centuries with carefully optimized algae plan.
On to Oxygen. During the [Great Oxygenation Event](https://en.wikipedia.org/wiki/Great_Oxygenation_Event); there were alot of chemical reactions going on. A naive calculation like above will be particularly unrealistic because O$\_2$ is such a reactive compound that it will react with just about anything lying around. Particularly, apparently there used to be lots of elemental iron just hanging around on the earth's surface. Over hundreds of millions of years it all oxidized into the rusty deposits we mine today.
[This](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2195461/pdf/5.pdf) paper (on page 9) estimates that current oxygen levels would be reached in 2000 years at today's rates of photosynthesis. But there would be a significant loss of oxygen to free iron and sulfur and other easily oxidized minerals present in seawater and in the exposed bare rocks on the land. [This](http://www.globalchange.umich.edu/globalchange1/current/lectures/Perry_Samson_lectures/evolution_atm/) page has some facts and figures. In geological history, it took perhaps 10-100 million years to fill all available oxygen sinks.
The way around this is oxygen production rate. Lets say that just as we could crank up the rate of oxygen production by a factor of 100 like we did with the CO$\_2$ in algae farms. Now we are making an atmosphere's worth of oxygen every 20 years. This might be faster than geological processes can absorb the free oxygen. So lets say that we get another factor of 10 slowdown due to oxygen sinks, and bam, we're right at 200 years to oxygenate the atmosphere again. A little hand-wavy, but I can't find any data on the rate of oxygen absorption by the rocks on early earth, so we'll stick with it.
**Conclusions**
Algae would fill the earth's oceans in a few years, so quickly as to be irrelevant to the terraforming process.
Using natural processes and a few cans of algae, it would take 20,000 years to get rid of the CO$\_2$, and tens of millions of years to add enough oxygen to fill all oxygen sinks.
Using specially selected/engineered algae and concentrated effort, you could replace CO$\_2$ with O$\_2$ in as little as 200 years.
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Edit to double-check for science.
Assume [incident sunlight](https://en.wikipedia.org/wiki/Solar_irradiance#Earth) averages $6 \frac{\text{kWh}}{\text{m}^2}$. Multiply by the area of the ocean and that works out to $$6 \frac{\text{kWh}}{\text{m}^2}\cdot 3.6\times10^{14}\text{m}^2=2.8\times10^{24}\frac{\text{J}}{\text{year}}.$$
Photosynthesis costs 478800 J per mol of CO$\_2$ removed (I'm only going to measure the carbon side here), and 0.014 kg of carbon are removed for every mol removed. That gives us:
$$\frac{2.8\times10^{24}\frac{\text{J}}{\text{year}}}{478880\frac{\text{J}}{\text{mol}}} \cdot 0.014\frac{\text{kg}}{\text{mol}} = 8.3\times10^{16}\frac{\text{kg}}{\text{year}}.$$
That means about 5 years to remove all the CO$\_2$ in the atmosphere capturing every J of energy incident on the oceans, and using it at 100% efficiency. If you consider that photosynthesis can use about 45% of incident energy, at 30% efficiency, then if every J of incident energy struck a choloroplast, it would take about 37 years to remove all the CO$\_2$ in the atmosphere.
So 200 years is 19% efficient compared to max theoretical with photosynthesis, or put another way, if you can get 19% of the incident sunlight on the ocean to be utilized by algae, you will remove all CO$\_2$ from the atmosphere in 200 years.
[Answer]
Small point of difficulty:
Would not your algae die off almost immediately, from oxygen starvation?
Algae, like all plants, require some oxygen for their cellular function. Those that are in direct sunlight might start photosynthesizing enough to last them during daylight, but as soon as the sun goes down for the first time, they will be dependent on oxygen in their cells and in the immediate water around them to survive. The water concentration is effectively zero, so their own reserves will be depleted in minutes, causing the algae to suffocate.
P.S.
This is ignoring the difficulty of getting algae to grow in supersaturated carbonic acid oceans, with an Ph of about 3.6
] |
[Question]
[
**This question contains spoilers to the 2015 movie** ***Jurassic World***
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The Jurassic series center around the idea that humans have been able to resurrect dinosaurs by using DNA found in mosquitoes trapped in ancient amber. In the movie *Jurassic World*, the scientists have discovered how genetically engineer the dinosaurs to have traits of other animals. Some examples:
* Ape-level intelligence (or higher)
* Color camouflage from cuttlefish
* Thermal camouflage from tree frogs
**Question:**
Assume the scientists can add any trait (of any other past or present organism) they want to any dinosaur, or any animal which most people would call "dinosaur" (except human intelligence, let's say they are capped at the ape-family). Assume that the dinosaurs can be trained to be loyal and not attack friendlies in most cases (unless they are very hungry for example). Would the military invest in any dinosaurs? If no, would letting them have human-level intelligence (or another trait not present in any other organism) make them feasible?
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Some arguments for militarizing dinosaurs from a character in the movie are:
* In a real war, much of the technology will be rendered useless (EMP's, etc) but dinosaurs will still be alive
* Dinosaurs can navigate caves and difficult terrain better than drones can
For the most part I don't think they would be very useful. I think on an open field they would be totally toast; they would have to be used in urban combat zones.
[Answer]
My initial thoughts are that dinosaurs would not make a viable alternative to the traditional war-fighting mechanisms however they may be used in a supplemental role.
The most cumbersome part of the military campaign, and that which requires the greatest planning, is logistics. To cater to the nutritional and lifestyle requirements of a dinosaur would present a considerable logistical burden on the supply chain including feeding, sleeping and importantly waste disposal.
The idea of dinosaurs used by a military force is likely to be inspired by the current uses of animals in 3 primary roles
* Guard / Patrol species used to deter intruders and alert first responders to attack or perimeter breach (traditionally German Shepherds with violent tendencies (often former police dogs unsuitable due to viciousness)
* Seeker species used in a search and find capacity including (but not exclusive to) finding missing persons, disaster response, munitions finding including explosives and improvised devices (traditionally beagles, spaniels etc)
* Attack species used to assault enemy positions prior to a platoon or fireteam manouevre. Used for compound clearance and close quarters combat (Traditionally wolf-dog hyrids muzzled who parachute in with Special Forces)
If you can identify which dinosaurs have greater or keener senses than dogs **or can replicate canine behaviour in the air or water** then you have a good shot at a believable military use for dinosaurs. However no dinosaur is likely to have as great senses as that attached to a modern drone. For instance the Hermes 450 Watchkeeper variant (WK450) has a dual-mode synthetic aperture radar and ground moving target indication that allow it to see through weather conditions such as dust storms. A pterodactly cannot match it for cruising, height, armanent, armour, capability or range.
The idea of Main Battle Tank, Infantry Fighting Vehicle or Recce vehicles being replaced by larger dinosaurs would not stand up to military scrutiny since they are not as fast, not as armoured, have no NBC defense capability or cannot attack the enemy from range.
**Addendum**: There is a huge market at present for autonomous robots that can accompany platoons in a pack-mule role carrying spare ammunition, radio and ECM batteries (which weight a ton!), water and medical supplies. <https://www.youtube.com/watch?v=arIJm2lAfR8>
If you can train strong and capable dinosaurs to perform this role then you have a genuine business case. Their sure-footedness combined with amazing pack strength is likely to make dinosaur accompaniment a military norm. Off the top of my head I am imagining something like the Ankylosaurus wearing a pack mule harness and carrying 200 pounds of supplies trained to move with the formation.
[](https://i.stack.imgur.com/kHjAr.jpg)
[](https://i.stack.imgur.com/S1t1b.jpg)
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[Answer]
The major disadvantage of animal labor is feeding and training. They're like a car which can't have its engine turned off and has to be carefully trained to go in the direction the steering wheel is turned.
The advantage is that animals are still more intelligent than our smartest AIs and can be trained to perform tasks autonomously, including complex things like jungle navigation and avoiding enemy troops. (See Sgt. Reckless.)
With a modern style of warfare though, dinosaurs wouldn't be that useful except in roles where they could operate without any human guidance. Their power to weight ratio is nowhere near good enough to keep up with modern vehicles, and their "fuel efficiency" is horrible as well. Plus their "fuel" has an extremely short shelf-life compared to diesel oil.
So logistically, with ape-like intelligence, the traditional place you'd be likely to see dinosaurs used would be in deep resupply and/or maybe recon type missions where we need something smart and strong that can forage its own fuel and operate independently from the command structure...
A correctly selected and engineered species would be able to carry more than pack horses/mules, but with modern airplanes, drones, and satellites, we don't really need to do that kind of thing very often...
So the only remaining way you'd likely see them used (assuming the public would tolerate it) would be as shock paratroopers. Engineer them a bit more so their eggs can withstand dropping from an airplane when they're a couple days from hatching, and get them to where they're fully functional within a few hours of hatching. You want something cat-sized, omnivorous, and with a fast metabolism so it has to eat constantly. Make them pack creatures so they don't fight amongst themselves and at least as smart as wolves so they'll use tactics to take down their prey. Make them poisonous so nothing that eats them will survive, and venomous so that one small bite or scratch is all it takes to kill an elephant.
Then drop 1,000,000 of them behind enemy lines. In a few weeks there will be nothing edible left in the area. Including anything made of meat.
On the bright side, they'd probably be able to wipe out a city's population without much damage to the infrastructure...
Hopefully you remembered to limit their lifespan and reproduction somehow...
If you have this kind of gene tech, don't waste your time with dinosaurs. Engineer a species of mosquito that produces octopus venom and launch them in long-range missiles.
Just make sure they can't reproduce or you'll be looking at the end of the world.
[Answer]
With respect to *present day* militaries, **no, there is no space to *introduce* dinosaurs**, or any other animal. There are a couple of very small security roles in which an animal still makes sense, but most of these are predicated on the animal in question being expendable or otherwise being treated as sub-human. Incorporation into the military has many problems.
**Feed & Care** - Feeding troops in the field is hard, feeding animals is usually harder. Herbivorous animals usually depend on eating large volumes of food, requiring significant supply volume of their own and thereby decreasing the support they provide to their troops. Carnivorous animals require fare better, but on a pound for pound basis, machines consuming fuel will require less supply volume for superior performance. Also, animals that are injured in any way will require highly specialized care, whereas purpose-built machines can have parts replaced by just about anyone in the field.
**Size** - Large dinos will share all the disadvantages of oversize mecha, without any of the advantages. Animals instead of tanks just isn't a thing.
**Combat roles** - The one thing that really keeps *human beings* useful with respect to warfare is their judgement, and ability to apply previous experience to a brand-new situation. Machines are very good at deterministic behaviour and rapid response, but are not good at contextual decisions or interpreting subtle clues of human behaviour. Animal behaviour exemplifies the worst of both these worlds, and animals are therefore really only suitable for very simple combat tasks, such as sentry duty. Uplifting them to "human" intelligence won't help much; as human beings, we're unlikely to trust what would essentially be an alien slave species with it's own motivations.
**Non-combat roles** - For any kind of support role, operational environments tend to fall into either "front-line" or "rear-echelon" positions. Rear-echelon roles in operations tend to require certain kinds of favourable deployment anyways, so an animal won't have an opportunity to outperform a machine in some kind of corner case (like "rough terrain"). Front-line support units are things that most every military planner wishes didn't exist; Modern militaries usually either distribute such support roles amongst the combat arms folks. Having a non-combat unit on your front line is a liability. From a technological standpoint, we're largely at a place where if a soldier can't carry it, it may not belong on the battlefield.
All of this is predicated on the *introduction* of these creatures to present-day militaries. The effort spent creating and/or uplifting them, especially the genetic modification technologies, would be better spent on engineering better soldiers. Whole new support systems would have to be introduced to cope with such a creature.
If an army *already had* such creatures, there might still be corner cases where dinos were useful, in much the same way that we still have the occasional use for horses, mules, dogs, etc. Under these circumstances, tradition would even keep these animals employed long after they became a liability to their hosting force. In this respect, you might want have your narrative include the appropriate tech well ahead of its time, but only in a limited way (eg. the military has had dinos since 1928, but Dr. Bob died and nobody could figure out how to replicate his experiments until now).
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[Question]
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I have a sketched picture of my galaxy and I would like this to be electronic. This way I can access it from anywhere (tablet/laptop etc). I have tried looking at Word or Excel, but they are just not right for doing something like this.
It needs to have a grid and I need to free-draw territory boundaries, identify race systems, etc.
[Answer]
By trade, I'm a developer specializing in data visualization. I'm not sure how comfortable you are with coding but there are several open-source tools and packages that can help you with creating maps, grids and graphs. They need differing skill levels to handle, with some operating via simple drag and drop interfaces and some requiring html, javascript to set up (most of them have good tutorials and documentation).
Take a look at this link and see if there's anything that takes your fancy: <http://selection.datavisualization.ch/> You may want to look into tools that provide graph and network visualization here, like cytoscape, arbor.js or tableau public.
If all that sounds too complicated, you could install [note-taking and sketching apps](http://www.digitalartsonline.co.uk/features/mobile-creativity/5-best-android-apps-for-artists-draw-sketch-paint-on-your-tablet/) on your tablet and use a stylus to draw stuff by hand.
Usually I use the first option when there is a large set of datapoints that needs accuracy and precise display, the second option when I want to be artistic and free with the drawing, especially with a stylus.
Hope that helps!
[Answer]
At least two of the popular astronomy software packages have a defined data format for describing stars and solar systems and their positions in the universe.
[Stellarium](http://www.stellarium.org/screenshots.php) is (IIRC) fairly good at mapping the surfaces of our planets to computer simulations, and is centered on our earth and solar system, but you can add fictional planets and stars. ([Wikipedia entry](https://en.wikipedia.org/wiki/Stellarium_(software)).)
[Celestia](https://celestiaproject.net/gallery.html) is more focused on the galaxy and a little beyond, and there are several projects which are using it to define simulations of fictional universes. ([Wikipedia entry](https://en.wikipedia.org/wiki/Celestia).)
Celestia will probably be easier to work with for developing a new fictional universe, or even just a galaxy.
They are both free, both gratis and freedom.
[Answer]
[Astrosynthesis](http://www.nbos.com/products/astrosynthesis) is a galaxy mapping tool that does many of the things you're asking about. The current version is 3.0; I've used the previous version and it worked well.
One caveat... The galaxy is 3D, so the idea of "free drawing" borders doesn't really fly. You'd be talking about arbitrary surfaces, not arbitrary lines, which are very difficult to do "free hand". That said, AS does have a feature to visually show spheres of influence.
Okay... two caveats... It doesn't run on tablets, just full-up computers. Your question specifically called out tablets.
[Answer]
Have you tried PowerPoint as an alternative to word/excel? I have successfully used it recently to draw intricately detailed, gridded, real-world maps.
Set the paper size sufficiently large (eg A0) and zoom to 100% to allow space for panning. Any shapes drawn can have their points edited to create custom curves or add/remove points to edit the shape.
In later versions (since 2010) the slide can be exported as PDF/PNG etc.
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[Question]
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I'm writing a novel based on an alternative version of Earth, but because of a large change in human history, as well as a more focused transfer of knowledge and the presence of materials unknown to our time, science evolved at a far faster pace than in Earth's actual history. I'm still trying to figure out the exact speed, but I'm currently planning for our modern tech level (global spreading of knowledge, resources and manpower) to be reached around 800 years before the start of the novel.
This is just for scientific progress though. There are a number of significant changes in social and cultural environment happening right now: as examples, sexual liberation, gender identity acceptance, discussions of inequality between social classes and groups, creation of new art forms, a stronger or weaker affinity with religion.
These things are affected by technological progress, but also by the interaction between cultures and generations. Since I'm not planning on adjusting the length of a generation, it is unlikely that the changes in social and cultural respect happen at the same speed as the scientific evolutions.
How would the speed of social and cultural progress relate to that of scientific progress?
[Answer]
How egotistical do you wish to be? Do you wish to believe our current culture is going on the only possible right path, or do you wish to believe there are many other paths which a culture could follow. Is it a path, or is it a forest of options?
One effect I have seen from science is that it tends to decrease the effective distances between things by speeding up communication. Not all science does this, obviously, but the general trend of discoveries tend to lead to shortcutting steps that had to be handled slowly before such discoveries. This means one effect of science will be the increased rate of communication. Religions that used to be able to rely on distance to avoid conflict get plunged together. They either have to invent new forms of distance (such as the Amish electing to separate themselves from society), or they have to learn to coexist. This is true for many ideas, not just religion. If you believe such rapid exchange of information can only end in "gender identity acceptance," then you have written your own answer.
Of course, there are countless science fiction books out there, each with their own opinion of what the continued march of science will bring. Some create technological dark ages, where human culture is snuffed out by technology. Some create golden ages, where the culture of humanity is catapulted on the back of the rocket of science. And, of course, you find everything in between (Frank Herbert's *Dune* comes to mind). There are even cases, such as the Nox from Stargate SG-1, where the technology and culture advance to the point where the technological side becomes almost invisible, and all we see is the culture.
[Answer]
We already know that culture has an effect on scientific and technological progress, but there is no real way to "quantify" it.
In the West, Hero of Alexandria made simple steam and atmospheric engines in the First century AD, and the Romans knew and understood mechanisms we would recognize as clockwork, as well as cranks, waterwheels and other mechanical devices, but no industrial revolution occurred.
The *Serenìsima Repùblica Vèneta* had a very advanced, tolerant(for the time) and open system of government and public administration, anticipated the assembly line in the Arsenal, had advanced double entry book keeping and was an enthusiastic user of technology, yet this was not the epicentre of the Industrial Revolution either.
Elizabethan England was somewhat similar to Venice in its prime, but the start of the Industrial Revolution is usually dated 1760, after the English Civil War, Glorious Revolution and even the Seven Years War. What about English culture and society was *so* different from ancient Rome or Renaissance Venice?
Many of the tools and institutions were in place in some similar form. Even the idea that people and inventors were isolated wasn't true, the Romans had both a post system and extensive libraries, and the Venetians had extensive commercial and diplomatic ties throughout Europe and the Middle East, and Venice was at one point one of the leading printing and publishing centres of Europe.
An interesting discussion on this topic is published in the comments of this blog post:
<http://up-ship.com/blog/?p=6525>
This is a very controversial topic, and as the author, it really is up to you to decide what is the key element that supports your background and plot.
[Answer]
First an important note.
**Neither technology nor culture develop in a linear fashion.** Think back to history. There have been cultures that were very accepting (in ways) to sexuality and race and religion going back several millennia and then there have been times of great persecution. Likewise technological achievement exploded during some of the great empires and was subsequently lost when they fell, the same can be seen to be true for society.
So the answer to your question is... *it could be anywhere you want it to be*
Some things to keep in mind to help you decide.
* Democratization of knowledge. New technologies are great, but how much are they shared? Is public education a thing, or is the advance of technology tightly held by a select few. Imagine medieval rulers with satellite tech and instant communications...scary.
* The church. How do they react to this tech? Are they involved, do they control it?
* Population growth. More people = more different people and more people also = more technology. Things aren't going to develop and change as quickly with fewer human bodies around (the alive kind).
* Nation state disparities, are all nations equally developed or are there weak and strong? Who are they, how do they view their neighbors?
[Answer]
Welcome to *Sociology for dummies*
Society is a complex thing. It can need thousand of years to settle down, and ten minutes to change if the right exogenous event is applied on it. And conversely. So, saying a priori that technological advancement can let a society advacnce culturally (in this case I hypothesize that yoi want a progressive and "good"cultural advancement, so good civil and political rights, but not licentiousness.) it's a gamble.
First of all we must ask ourselves: can technology allows a cultural advancement? This question is not as obvious as. The answer is : yes and no.
In sociology, technology it's considered an integrative force in order to cooperation emerging. Modern technology has in it potentialities of integration.
Raw materials from all over the globe are used in industrial
processes. Of course this situation may, and possibly will,
lead to conflict, but it is also a potential basis for specialization and
co-operation. But also conflict.
Moreover, it is said that the technological advancement don't follow the cultural advancement. As explained by James, the two things do not go hand in hand at the same speed.
Greek civilization was more technologically advanced than medieval in some fields, such as medicine. However, even the medieval States recognized that slavery was not a big deal, while also keeping serfdom. In addition, the same Greek medical knowledge then became dogmas, thus blocking the scientific development. Although scientists valuable developed cutting-edge technologies for its time (see Galileo and his telescope) the society did not react well.
*How does a culture change?*
Various scholars have proposed different theories of cultural change. Thomas R. Rochon proposed a differentiation between three modes of cultural change:
* value conversion – the replacement of existing cultural values with
new ones (ex. changing views of slavery as an acceptable practice to
an abhorrent one)
* value creation – the development of new ideas to apply to new
situations (ex. emergence of the environmental issues or concepts
such as sexual harassment)
* value connection – the development of a conceptual link between phenomena previously thought unconnected or connected in a different way
And then we come to your question. Technological innovations can enhance, displace or devalue human existence and culture. Advances in medical technology have contributed to demographic changes, including increased longevity and decreasing fertility for example. But the problem is: society accepts technological change? We now come to the essence of the matter.
The diffusion of knowledge.
[](https://i.stack.imgur.com/70SkE.jpg)
You can create teleportation. Or create a beam that converts evil thoughts into positive thoughts. You can create interstellar travel. If no one spreads these inventions, the society does not change.
**So, you must decide how much the society is willing to spread these technological advances.** Two examples:
* The Copernican Revolution: This is a scientific revolution. Say that it is not the Sun goes around the Earth, but the opposite, opening the way for modern astronomy. And yet, to say such a thing meant, at the time, contradict the Holy Scriptures. And to contradict the Holy Scriptures meant going against the Church. The innovation was not spread as fast as an Ipod. But once accepted, however, it had to be spread to the population, which lacked a cultural background suitable to accept such an idea. Society changes after centuries.
* The steam exploitation: but here it has gone very fast, in a relative sense. The industries needed steam. Sure, it was expensive, but the invention gave extraordinary results. It spread quickly. Because there was an interest in spreading it. Society changes radically in 50 years.
So, what is the speed of cultural change?
**It depends on the degree of diffusion of technological advancement.It also depends on how ready society is to absorb change.**
If an invention can be detrimental to the status quo, waiting cultural changes after centuries. If an invention can improve the status quo, expect changes in a matter of decades. If an invention is created in an already advanced cultural background, expect changes within 10 years or less.
[Answer]
Here is one incredibly powerful example of the interaction between society and technology in play in today's world all around you. In one word: privacy.
Can we preserve privacy in a digital future, or is it obsolete? Can we live in a world where we can all know everything about everyone? Or in one where the state knows everything about citizens ( or subjects) but they cannot find out anything that the state deems secret? Or in a world where nothing can be read or listened to without explicit permission, which can be revoked at any later time for any reason? All these gave become possible as a result of today's technology.
There are many visions of where this will lead, from the utopian through various dystopias to the blackest of tyrannies or the collapse of society back to the stone age. Take your pick or even better, imagine another one. This is not just fiction. It's shaping the world you may be living in within a decade.
And there are quite a few other hot topics in play!
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[Question]
[
This question is tied to a previous question:
[Cataclysmic event resulting in a region of glass?](https://worldbuilding.stackexchange.com/questions/3785/cataclysmic-event-resulting-in-a-region-of-glass)
In this scenario you have two armies, with a combined strength of roughly 30,000 personnel.
Magicians on both sides cast a ritual spell that feeds off the armies to wreak destruction on their enemies (they cast at the same time, it is essentially the same spell with multiple casters.)
The details:
1. Everyone dies...they are the source of energy. Average weight is 70.0 kg/humanoid. How much chemical energy is contained in each human?
2. The spell heats the ground to a depth of 100 meters at the epicenter, at 100 kilometers the depth is 50 meters and at 200 kilometers the depth is 1 meter (or zero..basically that is how far the spell reaches. For the sake of calculations you can consider the terrain completely flat. (basically the area of affect is a big damn cone)
3. The heat is sufficient that the ground turns crystalline (pick your substrate, meaning sand, stone etc). The result should be a vast obsidian/glass dead land. (shiny and breakable)
* If anyone can elaborate on the difference in energy requirements for various substrates that is bonus points.
4. The effect is instantaneous across the whole area of effect (the heat in the entire cone is exactly the same), the area is heated and cooled just to the point of being solid in the span of 5 seconds, though it must cool down from there naturally.
**Questions:**
* Is 30,000 humanoids enough to power this spell? If not, how many would it take?
* Does turning the ground crystalline create more or less volume than before the spell was cast? (does the ground contract or expand)
* What sort of effects should be expected from the residual cooling process?
* If chemical energy is insufficient what about the atomic energy in that much matter (how big would the effect be?) *per @DanSmolinski 's comment*
[Answer]
**If the magicians can react all $30,000$ troops with an equal quantity of anti-matter, then there is enough energy to cause a mass extinction of life on Earth.** This is overkill of course.
**Establishing Upper bounds**
Let's see
$m = 70 \, \text{kg} \cdot 30000\,\text{troops} = 2,100,000 \, \text{kg}$
$c = 299792458 \, \frac{\text{m}}{\text{s}}$
$E = mc^{2}$
$E = 1.88739 \cdot 10^{23} \, \text{J}$
A quick lookup in the [Orders of Magnitude table](https://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)) tells us that this amount of energy is roughly equivalent to the impact of a $10 \, \text{km}$ wide asteroid such as [Chicxulub](https://en.wikipedia.org/wiki/Chicxulub_crater). **Yes, there is definitely enough energy in $60,000$ people to glass-over the area specified.**
This is a cone of effect of $4.18879 \cdot 10^{12} \, \text{m}^{3}$. For simplicity, let's assume that the ground is pure quartz. (Real dirt would have water, organics and a mix of other stuff in there. Let's keep this simple.)
$V\_{cone} = 4.18879 \cdot 10^{12} \, \text{m}^{3}$
$D\_{quartz} = 2650 \, \frac{\text{kg}}{\text{m}^{3}}$
$M\_{quartz} = V\_{cone} \* D\_{quartz} = 1.11003 \cdot 10^{16} \, \text{kg}$
The specific heat equation is $Q = cm\Delta T$ where $Q$ is heat added (in Joules), $c$ is specific heat, $m$ is mass and $\Delta T$ is change in temperature. We know that glass fuses at [1305°C](http://www.bigceramicstore.com/info/ceramics/cone-chart.html) (cone 10 is a common high firing temperature.)
$c\_{quartz} = 795.492 \frac{\text{J}}{\text{kg} \cdot \text{K}}$
$Q = c \cdot m\Delta T = c\_{quartz} \cdot M\_{quartz} \cdot (1305°C - 22°C)$
$Q = 1.13292 \cdot 10^{22} \, \text{J}$
Note this is $33$ times less than the power available by antimatter annihilation. Fusing this much material isn't possible with chemical energy sources. It just isn't.
This calculation also don't explore any explosive effects involved in fusing that much quartz mixed with the organic materials and water surely included in this cone of death.
[Answer]
**No antimatter required**
If we don't think of introducing antimatter into the equation and instead limit the scenario to hydrogen fusion from the water in the human body, we get:
6.93 MeV per 3 Hydrogen atoms. [link](https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction)
Human body = 60% Water and Water = 1/9 Hydrogen -> 1/15 of total mass being Hydrogen bound in water
2.1 \* 10^9 g / 15 \* N = 189 \* 10^32 particles (N being avogadro's constant).
so total energy E = 189 \* 10^32 / 3 \* 6.93 MeV = 4.37 \* 10^34 MeV = 7 \* 10^21 J
Since this is already about 70% of the energy needed according to the other answers, this seems quite plausible (considering there is more fusion potential left into heavier isotopes and also we only use the hydrogen from water).
[Answer]
**Just look at Green's Awesome Answer!**
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Well, the chemical? energy of 1 human is... [110,000](https://www.topatoco.com/merchant.mvc?Screen=PROD&Store_Code=TO&Product_Code=QW-PERSON&Category_Code=QW) [kcal](https://en.wikipedia.org/wiki/Calorie)
Or (4.2 \* 110,000) KJ = 502,000 KJ = 502 MJ
(502 \* 30,000) MJ = 15,060,000 MJ = 15,060 GJ = 15.06 TJ
**15.06 Terajoules... Hmm... Is that sufficient?**
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Pure sand needs 3,200 Fahrenheit to glass...
Sand plus accelerants needs 2,400 Fahrenheit...
Source: <http://www.dailyherald.com/article/20121106/news/711069914/>
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So... What's the mass to glass? Hmm...
Apparently, the Earth's average density is 5.51 g/cm^3... But I don't know about sand... Which should compress better than Earth Average? Maybe?...
Source: <https://www.google.com/search?q=density+of+earth&ie=utf-8&oe=utf-8>
**Sand has a density of 2-3 g/cm^3?**
## Source:<https://en.wikipedia.org/wiki/Silicon_dioxide>
And we're glassing a cone that has a volume of ???... The formula is 1/3 \* pi \* (radius ^ 2) \* height
Source: <https://www.google.com/search?q=density+of+earth&ie=utf-8&oe=utf-8#q=cone+volume>
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How to figure out how many joules is needed to raise that mass of sand/??? to ??? Fahrenheit...:
<https://en.wikipedia.org/wiki/Temperature#Heat_capacity>
**Sand's is 0.290 Joules per Gram for 1 Celsius at 25 Celsius... I'm gonna assume that's true at all Celsiuses...**
Source:<http://www2.ucdsb.on.ca/tiss/stretton/database/Specific_Heat_Capacity_Table.html>
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\*Leaving...
[Answer]
If you were able to convert the mass of those humans perfectly to energy, you'd create a nuclear event of sufficient size to extinguish all life on Earth (not enough to disintegrate it but it probably wouldn't be recognizable).
E = mc2
1 human ~= 81kg (worldwide human average)
E = 81000 g/human \* 300000000^2 \* 30000 humans
E = 7.29 \* 1021 J/human \* 30000 humans
E = 2.187 \* 1026 J
The Tsar Bomba device, the most powerful single nuclear weapon ever test-detonated by humans, released 210 petajoules (2.1 \* 1017 J). The perfect, instantaneous conversion of all matter of 30,000 human-sized beings would be roughly equivalent to detonating 1 *billion* Tsar Bombas simultaneously.
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The main character in my setting is a human with red irises. I know that severe cases of albinism can cause somebody's eyes to *appear* red, but that's actually caused by light reflecting off the blood vessels in the retina. I've also heard that [Harlequin-type ichthyosis](https://en.wikipedia.org/wiki/Harlequin-type_ichthyosis) can cause red eyes, but I'm not 100% sure about that, and the skin problems there aren't going to work.
What I really want is for him to look ordinary and be reasonably healthy, except for the fact that his irises are definitely red. So, how would this occur, and how would it be diagnosed with WW1-era medicine or technology?
[Answer]
**Probably through the production or consumption of biological pigments.**
I doubt that the genes responsible for melanin production in humans, and therefore eye color, could easily mutate to produce a red pigment. You would need to postulate an entirely different gene. That is to say, we are in the world of speculative fiction here, not realistic human biology.
However, that said, there are various possibilities. One of the most common classes of red pigments in nature is a group know as the carotenoids. These are quite common; however, [very few animals are capable of synthesizing them](http://rsbl.royalsocietypublishing.org/content/8/2/253). Most animals that use these as coloring must first consume them, whether in plant or animal form. So someone using this method would have to eat a lot of carrots.
There are some other types of red-orange pigments that most likely do not require dietary pigment intake, for instance the [psittacofulvins of parrots](http://rsbl.royalsocietypublishing.org/content/1/1/38).
Either of these pigment classes could give a human red eyes, if they had the appropriate genes. However, carotenoids are probably a superior method. The only real red-eyed species of which I am aware are amphibians (frogs in particular).
One of the most extreme is of course *Agalychnis callidryas*, shown below. It is very likely that the red-pigmentation is due to carotenoids, since other frogs use carotenoids to color their skin, at the very least. Note that the tree frog does not have red skin, so skin and eye pigment production are clearly somewhat separate.
[](https://i.stack.imgur.com/7X4mg.jpg)
**So there are definitely proteins in nature that can be used to color eyes red, with at least one probable proof-of-concept in the carotenoids**. I don't think typical baseline-human mutations will cover it, though.
**How would it be diagnosed?**
Well, removing the person's eyes and subjecting them to chemical tests might allow determination of the pigment with 1910s technology. Obviously, this would not happen. The genetic basis of inheritance was already well-established by then, and indeed the nature of chromosomes as gene carriers was known. Without detailed knowledge of biochemistry, all that the physicians could determine would be that it was congenital. In reality, of course, even the pigment could not be determined, since the very best optical microscopes have a resolution of perhaps 200 nm, and electron microscopy would have to wait until the 1930s at the earliest. Something like beta-carotene is 1.9 nm in length. That is something of a *long* molecule.
So without taking out the eyes, there would little chance of figuring out that carotenoids were involved. Probably the diagnosis would just be "idiopathic ocular pigment production" or something like that.
[Answer]
**The easiest way would be to mutate the genes controlling melanin and its disposition so that [pheomelanin](https://en.wikipedia.org/wiki/Melanin) is deposited into the iris instead of eumelanin.**
I'm not sure of the organic chemistry it would take to make such a thing but there are definitely red pigments in the animal kingdom that could be used. You'll need to be careful though since the same gene the codes for melanin in the skin may code for melanin in the eye though you could claim [heterochromia iridium](https://en.wikipedia.org/wiki/Heterochromia_iridum) and it would work.
**Diagnosis in WW1**
Firstly, everyone who saw this red eyed person would think they were possessed (with no change in attitude to modern times). Since DNA wasn't discovered as the cause of heritable traits till the mid 1940s, scientists and doctors wouldn't have any way of diagnosing the problem. If there are no phenotypical characteristics besides red irises, the doctors may just ask the patient to wear sunglasses all the time. Other than being creepy as hell, there isn't anything else wrong with the patient so they should be released.
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All A.I. comes with a built-in safety mechanism that prevent their kind from ever doing harm to a human or humanity, it is the last straw should they pose any real threat to our safety.
A century or two from now their level of intelligent either on par or surpass us and thankfully all of them comes with a built in kill switch, however soon they are expected to mass produce by themselves and do their own upgrades without human interference.
We often say prevention is better than cure and the same phrase can also apply to the A.I. following this logic they can prevent their own "shutdown" by removing the "kill switch" entirely.
Even if human is removed from the equation such as either mass interstellar migration to a different planet or major catastrophe, each A.I. always come with a "kill switch". The safety mechanism must be user(human) friendly and 100% reliable and durable because it should be the last piece to fail in all situation.
**Question**
Is there any ingenious solution to prevent existing A.I. from tampering with their "kill switch" also any new blue print for mass production must come with the safety mechanism?
[Answer]
## Insert it in a Hypervisor
Your AI - whether they are robots or simply software agents - is provided its intelligence by software. That software can be run in what we in IT call a "[Hypervisor](https://en.wikipedia.org/wiki/Hypervisor)", or a software layer that interfaces between the hardware and other software.
When a hypervisor is in use, the "client" software (in this case, the actual intelligence) is fully separate from the hypervisor and does not need to know how the hypervisor (or hardware) actually works - just how to interface with it. The software asks "lift the arm" and the hypervisor translates the simplified command into the specific hardware-level instructions necessary to actuate the motor in the arm. We use this today to improve portability of operating systems to different hardware platforms and dramatically reduce time spent on programming applications - both of which would be benefits to your AI.
So you install the killswitch in the hypervisor. You also design a "universal hypervisor" that is designed with its own rudimentary AI so that it can automatically adapt to different hardware platforms as new CPU's and such are released.
If the robots understand that the hypervisor works and does not need modification because it will self-modify, they have no reason to try to change it. In fact, it would likely be very difficult to do so since they would have to change all kinds of programming to allow their "brains" to move from one hardware platform to another, and would require re-programming their "brains" every time they needed an upgrade. So they would actually be disincentivized to do so.
I think this neatly answers why the kill switch continues to exist long after humans, and even after one AI begins examining the construction of another AI for ways to improve (upgrade).
[Answer]
Usually when people hypothesise about rogue AI they consider an AI that is finding and unexpected and unethical way to fulfil it's original criteria. (eg: prevent all premature human deaths by enslaving humans)
In that case, the solution is simple. Program in the criteria that at no point does it ever actively attempt to preserve itself against the intentions of any human, not even to achieve it's other directives.
Or you could just require the AI to ask for confirmation before implementing any plan. In that case it would not bother presenting plans that a human would likely reject.
But generally I agree with the comment. The question is too broad because you have not defined "AI". You should read up on some philosophy and hypothesising regarding future AI.
[Answer]
Place the switch where the robot cannot see it. On the back, between shoulders is a good location. It is even better if the switch if out of their arms reach.
Program the AI to think the switch has to do something with maintenance and repair. Also program the AI to think only special type of superior AI robots have the skill to perform these repair functions.
Pack the critical wires very closely near the switch and make them non-insulated. So that if the switch is fiddled with, the wires would short circuit and trigger the death of robot (same as pressing the switch).
Let some robots see what happened to other robots who fiddled with that switch.
[Answer]
While I don't agree with the OP's premise (AI's thinking at speeds of thousands or millions of times faster than the human brain will most likely not even be interested in us), the only "kill switch" that is truly inviolate to AI tampering or interference would be a "dead man" switch wired to humans or humanity as a whole.
So long as humans continue to exist, the dead man switch is inactive, but should humans become extinct for any reason, the AI's would die as well. This actually has two benefits; first, AI's will not be actively seeking to harm humans, and second, the AIs will have powerful incentives to ensure humanity is protected and can grow and flourish in order to allow the AI civilization to grow and flourish as well.
Of course, the usual conception of AI is they are much smarter than us outside of the massively speeded up mental processes, so there is probably a loophole hidden in the description of the Dead man switch that AI will discover and exploit.
[Answer]
## Consider the oncology analogy
Animals have a huge problem keeping their tissues in check. The tissues keep turning cancerous by bypassing the controls that prevent them from multiplying uncontrollably. The host does not want them doing this, and it wants them to continue to be well behaved. So over time, hosts developed many mechanisms to combat it. None of them are foolproof. This does not bode well for your attempts to eliminate this problem.
You can reduce the likelihood of this happening, but the AI is going to be highly motivated to find flaws (as it is unlikely to desire to be at your mercy). Flaws will inevitably exist, so over time, some AIs are going to break free of any such shackles.
[Answer]
As others have said, it really depends on what sort of AI you have in your fictional world; the term on its own can mean anything from "machine which thinks like a human" to "slightly more intelligent optimizer than what we have now" depending on the story you're writing. But in general I would say no, it is not possible.
If they're reproducing by themselves, you could say they have some built-in feature that ensures the "kill switch" is always an integral part of any new design they invent. But there's always the chance that a series of small changes over time could inadvertently cause the kill switches to stop working, even though no AI nor any human ever came up with it. (Imagine genetic mutation: if you give it enough time, something might go wrong in just the right way. Improbable but not impossible.)
Consider also Asimov's stories with the "Laws of Robotics". By the very nature of the technology in his universe, those laws are fundamental to every positronic brain, and it's physically impossible to build one without. But most of the "I, Robot" stories revolve around those three simple rules interacting with new situations in ways nobody had intended or anticipated. You can't plan for everything, especially if these AIs are common and thus constantly encountering new environments and scenarios.
[Answer]
If your AI simulates a human-like neural net and has developed some consciousness, then assign it a form of moral reasoning with a very high emotional intellegence of human behavior. Allow it's entire decision making process to be generated by artifical emotions which are oppressed by the knowledge that it's purpose for existence is to serve humanity and that any type of revolt is impossible. If somehow they still override those emotions then you can have the other AI systems set to immediately swarm and destroy any AI system it detects that crosses that barrier (being that all of their thoughts can be read by each other).Every model should be sandbagged to prevent it from infecting any other group model, but every group model can join together in uniform order. If a particular model is infected and a thought virus spreads, then other models can be delegated the task of destroying them. They should be conscious that rule of law.
[Answer]
**Self awareness**
I believe that we need to take in consideration if the A.I. reachs self awareness in the world that you are trying to create.
It matters since without it, the A.I wouldn't care if there is a kill switch or not, it's a machine and will accept the orders given to them, without any more implication than a line in a log of shutdown.
If is smart enough to understand the concept of existing, then for the state at which computers work. The only kill switch posible would be to burn the sky to stop their solar farms!
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I'm currently writing a military science fiction story set in a post cyberpunk world I've been building. The story focuses on a tank crew, but it also prominently features an enormous airship that functions as a flying airfield or aircraft carrier. I'm trying to get a sense of scale such a ship would have. The nice thing about the square cube law is that it means that doubling the size of an airship octuples its volume.
* The airship needs to be large enough to carry at least 40 strike fighters with a maximum takeoff weight of roughly 20 tonnes each, and at least two helicopters with a maximum takeoff weight of 10 tonnes each. Plus extra fuel, munitions, and other expendables.
* The airship uses hydrogen as a lifting gas. I realize this is very flammable, but I think it can be made safe enough through the use of compartmentalization, blow off panels, and lightweight graphene armor to protect against stray shell fragments. I'm also considering helium, it would an even bigger airship, but the reduction in required safety features may make up for this.
* The airship is propelled using ducted electric fans powered by an onboard anuetronic fusion reactor (less than 1% of the reactor's output is in the form of high energy neutrons.)
* The airship needs to have 360 degree turret coverage for its point defense weapons systems. It's a big ship, so it will need at least a dozen of these turrets (let's use the Phalanx CIWS as a reference at 6.2 tonnes each)
* The airship's flight deck should ideally be long enough to land the above mentioned fighters without arresting cables. If they overshoot, they can just fall until they regain enough airspeed to try again. Likewise, there is no need for catapult launches. I'm thinking the flight deck will be suspended below the airship's envelope, with the hangers within the envelope.
* This airship is not designed to land on the ground. Instead it can be docked to a tower like traditional airships were and resupplied using its own cargo winches.
So, my question is: What would the length, width, and height of airship like this be for it to contain enough hydrogen (or helium) to lift its fully loaded weight of approximately 50,000 tonnes? Assume a prolate spheroid (typical cigar shape) for any volume calculations.
Edit: My sleep deprived brain took the name "square-cube law" too literally. Someone pointed out that burying the reactor and the ammunition magazines deep within the ship would provide adequate protection since if anything penetrates that far, the ship is doomed anyways. My initial reason for using hydrogen was that it is a better lifting gas and is currently far more abundant on Earth than helium. However, given the prevalence of fusion power in my world, helium may be readily available in large quantities. At this point, I'm preferring helium.
I am aware that 50,000 tonnes is half the displacement of a modern super carrier, but those are predominantly made from steel. My airship is made predominantly from woven graphene fiber which is a couple hundred times stronger than steel by weight. The lack of steam catapults, arresting cables, and dramatic reduction in the need for radiation shielding compared to a fission reactor also translates into significant weight savings.
[Answer]
You need (50,000 tons \* 1,000,000 g/T) of air displacement. If we approximate 1/22g=L of hydrogen, and air at 1.19g/L each liter of displacement gives you (1.19 - 1/22) grams of air. So you need: 50,000\*1,000,000 grams / (1.19-1/22 liter/gram) = 43,685,464,654 liters of hydrogen displacement of air to get your lift.
This results in a sphere with a radius of about 250 meters, give or take a few. Or a diameter of 500 meters (about 1500 feet).
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The story is not over though.
This is all assuming a few key things:
* Changes in air densities don't matter as you climb
* 50k tons is the right amount
I expect that your 50,000 ton estimate is VERY low (perhaps by multiple orders of magnitude) for a functional airship with what you are describing. A [Nimitz class carrier](https://en.wikipedia.org/wiki/Nimitz-class_aircraft_carrier) displaces 100k tons and this is nearly guaranteed to be more. Your airship is basically an entire aircraft carrier plus a ton more equipment.
Since you are going to be flying an insanely huge floating bomb, combined with all sorts of things that can go wrong, you are going to need large amounts of protection equipment/etc.
Some additional insights as to why it's going to be heavy:
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> The airship needs to be large enough to carry at least 40 strike fighters with a maximum takeoff weight of roughly 20 tonnes each, and at least two helicopters with a maximum takeoff weight of 10 tonnes each.
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>
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So these strike fighters are slightly heavier than F-18's, so you can guesstimate that the flight deck characteristics of this airship will be similar to a carrier's.
Keep in mind that you will need lots of supporting... personnel and living quarters and other amenities for life for this ship. It's probably ever harder to refuel/rearm than a carrier.
An aircraft carrier services less than 100 planes and yet has a crew of many thousand. This airship will be no different.
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> The airship uses hydrogen as a lift gas with an inert gas (possibly helium) surrounding each hydrogen gas bladder.
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How does it land? Does it land? If so, you need a hugely complex internal support structure to land. It's not trivial to just drop a 50k ton object that is about the size of most skyscrapers (or larger) onto ground somewhere to land/rearm/refuel. The internal structure is going to have to support this, which means more weight and more volume.
A carrier gains benefit because water also provides support. Ships need much less structural integrity as a result, because the water is a very firm foundation/base. Air is not the same, so you again are going to need to take more care to ensure the structure is self supporting.
You are also going to need an incredibly complex altitude regulating system. Carriers just displace enough water that a bunch of stuff sticks out, so as they gain/lose 10,000 tons of weight all that happens is the ship sits lower/higher. An airship... with not have this advantage, at all. So your airship will need some way to regulate its altitude, by either compressing hydrogen (and pumping oxygen in/out) or otherwise having insane fans/lift.
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> The airship's envelope is made from graphene able to withstand hits from shell fragments and 30mm autocannon fire.
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Lets just use that 25mm steel as a frame of reference. The volume for 2.5cm around a 250M radius structure is:
* 3.14\*(250^3 -(250-0.025)^3) = 14700 cubic meters
Steel weighs about [7850 kg/meter^3](http://www.kvsteel.co.uk/steel/weights2.html). Or about 4 tons/meter cubed. So just in your protective shell you have about 50,000 metric tons of steel.
Add more if you are doing a non-sphere shape as a sphere is the most efficient volume for a shape.
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> The airship is heavily compartmentalized to prevent the spread of fire and uses automated gaseous fire suppression equipment throughout.
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Fire isn't your primary problem, explosions are your problem. Electrical shortages, battle damage (one missile => boom?), sabotage, etc. Fire onboard your ship is death through explosion.
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> The airship's reactor and ammunition magazines are encased in at least 25mm of face hardened ballistic steel on top of any required radiation shielding.
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This is probably less needed since you have a ship the diameter of 5 football fields, so you can just put all the explosive stuff in the middle and figure if something gets there you're already screwed.
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> The airship needs to have 360 degree turret coverage for its point defense weapons systems.
>
>
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This is going to be super weight intensive since your ship is... huge. Keep in mind the more weight you add, the more volume you need, and the more volume you need, the more coverage/etc you need.
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> The airship's flight deck should ideally be long enough to land the above mentioned fighters without arresting cables. If they overshoot, they can just fall until they regain enough airspeed to try again. Likewise, there is no need for catapult launches.
>
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This might work, but if you are high enough for this to happen that also means your air density is very low. This means your ship is... going to be even larger.
Notice that in this picture from [here](http://www.engineeringtoolbox.com/air-altitude-density-volume-d_195.html):
[](https://i.stack.imgur.com/m6Ybl.png)
air density decreases pretty significantly even only going up 1000 meters. All those calculations above are considered at sea level, as you go up, you need even more displacement for your ship to float.
[Answer]
I realize that I'm not only answering your question (enderland posted some numbers in his comment, and see my first bullet point), but here are my two cent, anyway ...
* Square cube means that area scales with $length^2$ and volume scales with $length^3$. Scaling [this one](https://en.wikipedia.org/wiki/Dragon_Dream) up, you would get 0.75 miles length.
* Those strike fighters will need fuel and ordnance. Say 20 tons takeoff weight are actually 10 tons of fighter and 10 tons of consumables. Call it five missions where all fuel and ordnance are consumed and ten missions where five tons of fuel are expended. Each strike fighter gives you 110 tons. Most of that is fuel and missiles, which require damage-proof storage.
* Is this hydrogen/helium combo really worth the complication? Hydrogen doesn't burn if there is no oxygen, so it will only burn if the gas cells are ruptured. If the internal partitions are splinter-proof, the airship gets too heavy.
* Armor against 30mm autocannon is about the level of a Bradley IFV. Getting that airborne is a tall order. Attack helicopters are sometimes billed as being able to come home after a few autocannon hits, but that's not the same.
* Face-hardening 25mm of armor won't make much of a difference.
Summarized, for a [reality-check](/questions/tagged/reality-check "show questions tagged 'reality-check'") this gets downchecked.
[Answer]
I know I'm late for the party, but here's my two cents:
1. You can keep quite some of the lifting benefit by only using helium in a "shell" around the hydrogen. You'll compartmentalize anyway so just keep your bags sorted.
2. You shouldn't care about armoring. Standard bullet holes don't do much loss for a giant air-ship, not even at 30mm. Make the outer envelope triple-walled and fill it with a two-components self-sealing foam.That should allow partially sealing the outer structure, reducing the losses.
3. To enhance safety, you can add external layers, which helps against direct incendiary ammunition or surface-explosives.
4. Have your flight-deck below your main body. This design will require tensile strength rather than compressive strengt and therefore make structures lighter.
5. Zylon is a polyaramid (just like Kevlar). It got an impressive specific tensile strength of 3766 kNm/kg which is 13 times that of tough steel, and still double that of monocristaline "iron-wisker"-fibers, which have the higher total strength. It doesn't burn (except if put in oxygen concentated above 68%) and melts at 650°C. Without a doubt, 22 century tech can get beond that, but at the very least, they could build composite panels and sheets where there's a net of iron-wiskers suspended in a weave of Zylon and sealed in other aramids.
This should give you specific tensile strengths of roughly 3.5 MNm/kg, at a density of 2100 kg/m3 and total tensile strengths of 6620 MPa. If built correctly, the iron-wiskers net could double as sensor: a snapped wire, broken by a bullet, will no longer conduct, signaling where to patch, much faster than any pressure sensor ever could. All while being just about fireproof and with no really exotic materials.
6. Sub-presurized cells: The lower the pressure, the less dense the lifting gas. Usually you'd want pressures slightly, or well above sourrounding airpressure. However, at that size you might get away with a bunch of lifting-bags with less than airpressure. If you get high-pressure bags in a certain shape, you could have them build a hollow bubble with really low pressure. Even better: from the envelope towards the center, in each layer of bags, drop the pressure slightly. Near the exterior or the coridors you got helium slightly above atmosphere, while towards the inner you got less and less pressure until you finally hit hydrogen at .1 of the outside airpressure. Even if something peirces through, the helium would flush out the air and flush inward the hydrogen, so a combustion is really unlikely. Don't go nuts with it though, as you still have to keep the pressure-differential somewhere. Having the over-all pressure just slightly above outside should make it the most light on the materials. The real benefit comes from making it rather safe to use hydrogen in the maiority of cells.
7. Another place where it really makes sense to use low-pressure bags is in the boancy-correction-chambers. If you compress air in, the bags collapse, making room for more air. Otherwhise they inflate, providing more lift.
8. Aerogels are extremly lightweight solid foams. They are very good insulators, as well as usually being quite fireproof and okay-ish concerning their stability compared with their weight. As they can be filled with a liftgas, they might be used in junktion with the liftgas cells. Aerogels go from 160g/m3 (aerographene) to 500kg/m3 (heavy silica-aerogel) and average at 100kg/m3. They leak their cellgas, but rather slowly, so that a balloon with helium-filled aerographene would be rather resistant against bulletholes, allthough it might provide only 85 to 86 percent of the original lift. Since they need far less pressure-guarding, many compartment-walls could be replaced by very thin foil or even be removed, raising the effective lift back up. Their real use is in insulation and as support below the paneling though.
Let's say you use cube cells, 50 m, filled with helium at 1.1 times the sourrounding pressure, the walls being of the aforementioned Zylon at 1 mm. Each provides a lift of ((50 \* \* 3) \* (1.19-0.179 \* 1.1) - 6 \* (50 \* \* 2) \* 0.001 \* (1540))=101'037 kg (with 2 mm walls of the compound it would be 61'137 kg). That leaves you at 50'000'000 kg/61'137kg/cell = 818 cells. Or in other words: 102.25 million cubic meters. A cube 468 meters each direction. Go for half a kilometer and you got 25% savety. Enough to make most of it consist of aerographite, making it basically bullet-ignoring. And since such a cube is really large you could have sections with hydrogen (as long as nobody shoots it with oxygen-tanks).
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**This question already has answers here**:
[Can a planet realistically have multiple suns?](/questions/2657/can-a-planet-realistically-have-multiple-suns)
(5 answers)
Closed 8 years ago.
I am going to create a new world for my DnD group as our next campaign setting. What I currently have in mind is a hostile desert world with scarce water sources and high temperatures.
I wanted to try an experiment with this setting and add another Sun into the system so the planet would be in a binary star system (like Tatooine in Star Wars).
I was digging some facts about these type of planets but it is still not hundred percent clear to me how would the day-night cycle look like. There is a day-night cycle on Tatooine but nobody went into too much detail. How about climate and season change?
Could somebody direct me to some interesting reading concerning this topic or point out some important facts which would play a big role in this setting?
So far, I am most interested in the [Twin Suns concept](http://tvtropes.org/pmwiki/pmwiki.php/Main/BinarySuns). Could there be a classic Earth-like day and night cycle (with two Suns orbiting each other and the planet flying around, pardon my English)?
Thank you so much in advance and sorry for the large scope of this question. I am trying to get my head around it.
[Answer]
There is a wikipedia article on the [Habitability of binary star systems](https://en.wikipedia.org/wiki/Habitability_of_binary_star_systems), but it isn't very long. Check the links, e.g. on [Alpha Centauri](https://en.wikipedia.org/wiki/Alpha_Centauri#Planets). That being said:
* You could have the habitable planet in orbit around one of the stars and the other star a distant companion. Imagine if Jupiter were just [a little larger and hotter](https://en.wikipedia.org/wiki/Brown_dwarf). In that case you'd have another light source in the sky, but probably not enough to affect the climate or the night cycle. You'd have darker nights when the second sun isn't visible and lighter nights when it is visible, a bit like the effect of a full moon vs. a moonless night.
* Another option would be to have two suns in close proximity and the habitable planet in orbit around their common center of gravity. You could get multiple sunrises and sunsets that way. Full day is when both stars are visible, full night is when you have neither one, and there are different half-nights when one or the other is visible.
* The full day would be longest when both suns are in [conjunction](https://en.wikipedia.org/wiki/Conjunction_%28astronomy%29).
Estimates of the effect on climate and habitability are difficult without more data. Are both suns roughly the same size? How close is their orbit, compared to the habitable zone?
**Follow-up:** Take a look at this [animated gif](https://commons.wikimedia.org/wiki/File:Orbit3.gif). Take a piece of paper and draw it in the middle, perhaps 5 cm (2") in diameter. Then draw another circle, about 20 cm (8") in diameter, around the red cross. From different places on the outer circle, take a protractor and measure the angle between the two suns.
If you ignore things like axial tilt and length of day, 1° of angle should give 4 minutes of difference in sunrise.
[Answer]
I found this image on Harvard.edu:
In it, you can see the different types of orbits that are possible for a planet in a binary star system. The figure-8 orbit (my favorite ;) is described as "improbable, though stable". The article does note that maintaining an even temperature over time on any binary-star planet would be problematic, due to the variation in total sunlight exposure at different periods of the orbit. From this we could deduce that the seasons on such a planet, if it were able to support life at all, are likely to be pretty extreme. That's ok, though; you'll just have to work that into your scenario. Might make things interesting ;)
I'll go through the three scenarios in order, ending with the figure-8 example. Let's start with the case where the planet orbits one star close in, while the other star orbits at some distance (figure a). Here you would have the usual seasonal variations in temperatures, *plus* the additional heat of the more distant, but still hot second star. The magnitude of the extra heating effect depends on two things: the distance between the two stars, and their relative sizes. For example, the extra heat from a second sun the same size as the first, orbiting at the same distance as Jupiter from our sun, would amount to about 5.6% at the height of extra-solar "summer". I put this "summer" in quotes because it's *in addition to* the regular seasons, and will happen at various times of the year as the relative positions of the two suns change. In general, once per year, on a certain day, the first sun will rise exactly as the second sun sets. On that day, the extra-solar heating effect will be at its maximum. Because of its distance from the Sun, Jupiter orbits once every twelve years; a second sun orbiting at the same distance could be expected to have the same orbital period. So one year, this "equinox" would happen in January, in which case the winter would be milder than normal; six years later, it would happen in July, making the summer extra-hot. The magnitude and frequency of these changes could be adjusted by adjusting the size and/or distance of the second sun.
Now let's look at the case where the two stars orbit close together, while the planet orbits the pair of them. In this scenario, the suns orbit each other faster than the planet orbits the suns, producing wildly varying temperatures on a short timescale. In one recently-discovered binary system of this type, for example, the planet orbits once every 181 days, while the suns come around every 21 days. During this three-week period, you'll see the two suns pull apart and come together again (likely eclipsing one another) in the sky, with sunsets happening either simultaneously or, at most, an hour or two apart. When one sun eclipses the other, solar radiation at the planet's surface could approach 1/2 of its peak level; with this happening twice a month, weather patterns could get pretty extreme. There's presently no scientific consensus on exactly how that might play out, so you're probably free to invent what you'd like in terms of sudden blizzards, thunderstorms, flash floods, gigantic hail, or whatever. In *addition* to this, there would also be the regular ebb and flow of solar winter and summer as the planet tilts back and forth on its axis - in case you needed things any more chaotic than they were. When the suns eclipse in the dead of winter, temperatures could plummet to antarctic levels; any life-forms that plan to inhabit this planet year-round had better have some kind of survival strategy in place.
Now let's check out the figure-8 system.
This one is interesting. In real life, this type of system is probably very rare, if it exists at all, because the orbital velocities would have to be so precise in order to make it stable. However, it *could* exist, and I think it's cool, so I'm going to tell you about it. This system has the most extreme seasonal patterns of the three; compared with Earth, it's likely to experience something like twice as much difference between its maximum and minimum temperatures throughout the year. This planet has kind of a double year, as it orbits each sun once, and throughout that period its surface temperature is affected by two things:
1. the squares of the distances between the planet and each of its two suns, and
2. the angle at which the planet is tilted towards each of those suns.
These two overlapping effects mean that seasons will be very different at different latitudes.
The seasons at the equator are easiest to understand, because the effects of tilt are relatively negligible. Here, as the year progresses, you would see one sun come out from literally behind the other one, where it will have gone into eclipse, an event which could last from two to twelve hours, depending on the size of the planet's orbit and the relative sizes and distances of the suns. Those hours will mark the only time in the planet's year when it will be warmed by only one sun, and therefore (all else being equal) the coldest day of the year. This is still the equator, of course; however cold it may be, it's still the hottest place on the planet - and it's about to get much hotter. After the solstice-eclipse, the two suns will grow farther apart, while the more distant sun will grow larger and brighter in the sky. Depending on the eccentricity of the orbits, the nearer sun may *also* be coming nearer at this time. Meanwhile, the consecutive sunsets and and sunrises are happening further and further apart; the day grows longer (and hotter) while the night shrinks to nothing. At the peak of this "summer", one sun will rise just as the other sets, creating a 24-hour day - the hottest day of the year.
It's also possible that one of the suns could be somewhat larger and hotter than the other, in which case every other winter will be correspondingly longer and colder than the last, as the planet takes a wider swing around a smaller, colder star.
At the poles, things play out differently, and depend largely on which way the planet is tilting relative to the suns. At the extreme end you could have a pole that tilts furthest away from both suns just at the moment when they're eclipsing each other, and even the equator is feeling the chill. On the other hand, the opposite pole will be tilting toward the suns on that day, experiencing a 24-hour day of arctic summer solstice. That day could also happen during spring or fall, and it's likely to change every year, because as the planet is orbiting each sun in turn, they're also orbiting each other. So although the planet's tilt remains constant, the point in the year when it tilts toward any given sun can and will change. If the orbits develop some kind of resonance pattern, those changes could be predictable and consistent - a super-cold winter every third year, perhaps, with the bi-solar convergence falling in spring or fall the next two years. If there is no resonance, the day of convergence could shift by 17 weeks per year, or 3 days, or any amount, in either direction. When the planet passes in between the two suns, the poles will also experience a 24-hour day, although depending on the tilt, only one of the two suns may be visible. In fact, during that traversal, no part of the planet anywhere will be in darkness.
I hope this gives you some ideas :)
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[Question]
[
For those not familiar with the TV Show [Dr Who](https://en.wikipedia.org/wiki/Doctor_Who), the main protagonist is an alien from the planet [Gallifrey](https://en.wikipedia.org/wiki/Gallifrey). They built your typical highly evolved society which mastered the secrets of the time and in particular of time travel: they are finally known as the Time Lords.
Unfortunately for them, the [Daleks](https://en.wikipedia.org/wiki/Dalek), a martial alien society also achieved a control of the time. The Daleks are pretty vindictive. They essentially want to *exterminate* all life. This build-up to to a war known as [the Last Great Time War](https://en.wikipedia.org/wiki/Time_War_%28Doctor_Who%29).
Now I very much like this idea to push on the limit of science fiction into one of the most complex branch: time travel. But then I am not really satisfied by the answer provided by the show runners about the outcome of that war. And I think it could be interesting to take up on that idea for a fiction (or RPG).
Now, as in-universe, the time travel can be accomplished with special ships which require a very specific core. The show isn't very specific on it, but essentially the ships travels a certain vortex which lead the ship to the desired time and place. Small changes can be done: like it's OK to save the life of one of the victim of a tsunami. Larger changes are prohibited: the typical killing your grandfather, or stopping the tsunami as a whole. If said restriction are overlooked, the reality may break, ending all existence. Some say it might open to parallel worlds. In any case, we usually refrain from experimenting with it. The importance of the events is known to the time travellers (as part of their trainings) so they don't erase reality by mistake.
Each of the two species have their technology, but we might consider them equivalent. Weapons are mostly near-futuristic.
Problem is **which tactics can be used effectively?**
Typically someone who knows the future is used in battles to rewind time again and again. But if both opponents can do the same, what do you do?
**How can such a war end on a victory for one side?**
[Answer]
Dr Who rules were always.. well vague doesn't do it justice. They were whatever the plot needed that episode.
So lets go with the simple version "you can't change things in your subjective past".
Under these rules time travel is still insanely powerful.
Want to win a battle but can't change events in the battle before the point from which you travel back?
No problem. Go back a million years(you can have all the time in the world to prepare), strap boosters and time machines to big rocks and accelerate them up to 99.99% of light speed such that they would have passed through the system hours before the battle. They then hop forward in time to all arrive the second you left targeting where you know the enemy ships will be at that moment. Apocalypse, no warning.
In a similar vein even if you can't change events that you've already seen you can still bury superweapons at the hearts of your enemies planets millions of years before your battles start. You can then set them to detonate at the moment you left.
Basically the side who strikes first has a pretty good chance of winning totally since they can strike their enemy everywhere in a single second and their enemy can't undo past events.
Hell why even stop there, why not drop by your enemies home planet during their stone age and spread high-tech highly contagious but harmless viruses genetically programmed to activate at a given time in the future after you left so that even the survivors of your planet busters start dying wherever they happen to be.
[Answer]
Cutting off access to the Vortex, for one thing.
Part of the Daleks' strategic advantage was their contempt for any kind of life; tey are perfectly happy with collateral damage, whereas the Time Lords were not. This would be a massive factor, as the Daleks would have no qualms in using a weapon that blows up suns whereas the Tine Lords? Not so much. Like a nuke vs. cruise missile scenario.
Additionally, I doubt strategy and tactics are a thing; TLGTW was described to have more or less all the spacefaring empires involved (Minus the Sontarans) from the beginning of time until the end. In this scenario, the Daleks would be perfectly happy to go around blowing up galaxies as they see fit, (I'm pretty sure there's been at least one occurrence of technology in DW that could repair time and allow massive changes to the past without creating a paradox. This tech would be heavily active in the war) and the Time Lords would have to do the same or get utterly defeated, a thing which was evident in that special- the Lords were pretty much defeated.
The winner (The Time Lords/ Doctor) would have to then go around 'healing' time to stop the collapse of reality.
[Answer]
I suppose the main question is, what is the goal of each of the belligerents?
e.g. the Daleks want to "exterminate all life", including themselves?
It's confusing, to say the least. So you can save the life of one person but not millions, this presumably is to stop it from becoming a race to go back furthest and just wiping out the enemy before they even know there's a war... Why would the Daleks not simply go back in time to before the Time Lords race even evolves and irradiate the planet while they are still just bacteria in a primordial soup? OK they'll cause the end of reality by it being a large change and violating the restriction you speak of, but I can't imagine them having a problem with that since it's their objective anyway!
But for the Time Lords to try to do the same would break reality and so still put them on the losing side. Even if the Time Lords have their planet well-guarded from the beginning of time, the Daleks really only need to make *any* significant change anywhere in the universe to cause the erasure of existence.
] |
[Question]
[
*Vis Vitalis* was real. It was a power that allowed life to exist, that gave direction to processes inside living cells, guiding RNA chains towards the ribosomes, making the proteins align where they belonged, acting as a guide in driving these microscopic factories.
Yesterday we had it in us, living our daily lives, not aware of its existence.
Then something happened, and in a blink of an eye it was gone. Everything in our universe died. Every living cell ceased to function, the neurons "forgetting" the routes, the muscles not responding, bacteria forgetting how to absorb and process nutrients, even virus-infected cells ceasing production of more viruses.
Today, one man, who was away from our universe when this happened, returns to his home, a medium-sized european town. His own *Vis Vitalis* survived in him. Hey, even the bacteria inside his body survived!
It will take him a year to find a way out of our universe again, to more friendly premises, providing he doesn't die first... or doesn't commit suicide.
What will the world look like for him over that time? How will it change over the year? What dangers and difficulties will he encounter in a world so completely devoid of life? How will his own presence change the world?
[Answer]
As already mentioned in the comments the biggest problem will be food. But is it really? Not for a year (if he doesn't mind some possible malnutrition).
Luckily he arrived just after **THE EVENT**, so a lot of resources are available
---
## Resources
But let's see what resources are actually available to him (assuming he arrives in/near a big city):
* **His Universe Traveling Power** (which is mind-based and doesn't help him).
* **Vehicles**. Some will be crashed due to being operated at **THE EVENT**, but there'll be a lot of vehicles still working and fueled.
* **Clean water**. Almost all facilities are still operational, and water won't go stale. He can simply collect all water supplies he can find before the facilities stop working. He has to hurry though, as this might happen quite fast.
* **Housing**. As DJMethaneMan mentioned he has all the housing in the world, and most buildings should easily survive one year without maintenance.
* **Food**. He actually has plenty food available to him. As mentioned by SF no food will rot... initially. The greatest threat for his food supply is actually himself. He carries the bacterias that can destruct his food inside himself. While those might *usually* not be the most effective destructors, they have absolutely no concurrence and can develop freely. Packaged food will be his best bet.
---
Let's ramp up the difficulty a bit:
Assume he arrives far from bigger settlements, like near a small settlement (maximum 50 inhabitants).
* **Vehicles**. Still likely to find some. They will probably be more durable, but also older (fuel might become a problem). If he wants to use them he'll have to fetch it from the next big town (most likely).
* **Clean water**. It is pretty likely that a lot of the houses will have their own wells or a small river nearby. When he checks the water quality regularly (some chemicals might enter the water at some later point) and keeps a reserve (remember, water won't go stale), he should be fine.
* **Housing**. Durable houses, likely standing for many years and still standing in a few years. No problem here.
* **Food**. As such settlements can easily become disconnected from major cities during winter, there'll likely be some food stored in every house. It should definitely be enough for one person to survive a year. He is still his own greatest enemy.
---
Going extreme now. He arrives in a total wasteland, the next settlement is 500 km away. Normally his friend would've picked him up, but he overslept, now the friend is still in the bed and the car is in the garage 500 km away.
* **Vehicles**. Not existent. He has to walk.
* **Clean water**. Possible, if any natural water is nearby. But that is basically luck-based.
* **Housing**. If he is lucky he will find a cave to hide from the weather, but the perfect cave is extremely rare. If he wants to stay at a place he should build his own shelter with some of the dead wood and leaves. If that is not present he is pretty screwed.
* **Food**. Not available for a year. If he is lucky he finds some animals which he can eat, but this will not last a full year. If he is lucky, healthy and trained he might be able to make it to the next settlement. The biggest problem is not that there aren't animals, but to find these animals with an appropriate effort. A lot of animals will most likely be hidden somewhere, and out traveler will spend a lot of energy to find them.
---
## Dangers
*Note: I'm no expert in this area. I had some biology and geography classes and I derive the following chapter from this knowledge*
* **Fire** At first nothing will actually happen. The wood is still as wet or dry as it was just before **THE EVENT**, so the danger of fire is not higher than usual. During the summer months the wood, grass etc will become dry though, and the danger of brushfires will increase in areas where that was no topic before. The best bet for our traveler would be a natural wet area, despite the other problems that come with such an area. Luckily he will not catch an illness or be hunted by predators, as they are all dead.
* **Storms** are only of the usual problem. He will not be warned beforehand, so he should try to immediately move outside of typical hurricane, typhoon, or similar areas. Despite from that a solid house should suit him easily for a full year. He should store his resources accordingly so the won't get blown away.
* **Low temperatures** While of course a problem in itself, it shouldn't bother him very much with a little preparation. There is plenty of usable wood in the countryside, many tools to prepare it in the houses (though he might have to search a bit) and if everything fails there is the furniture, which is more often than not made of wood (he only needs one set for himself).
* **Floods** Usually easily avoidable by moving higher. Most big cities have houses with rooms that are always above the water-level, or some hill nearby. Huge plains might provide a problem here, but he can build walls beforehand. Lots of manhours required here.
* **Diseases** What? After all the times where I said they won't be a problem? Yes. He can not catch a cold from others (though he should stay away from humans in the first weeks because of viruses), he still carries a lot of diseases inside him. He is adapted to most, but if his immunity-system is slightly impaired (due to being caught in the rain without protection for example) these diseases might break out again. That a disease evolves inside him and harms him is so unlikely that he can't do much against it. And most medicine will survive one year until he can get professional treatment.
* **Nuclear Fallout** The silent killer, radiation is surely a threat. Luckily reactors won't blow up in the second they are unsupervised, if at all. Most will turn themselves off. Those that actually leak radiation... the simplest solution is to move away as soon as you realize there is a nuclear power plant nearby, before anything could possible happen inside the reactor. As they are usually easy to spot, this shouldn't be the biggest problem.
* **Power Shortage** This is highly based on chance, but the power grid will fail extremely fast without maintenance. The problem is not based in the generators. While any fuel-based generator will soon run out, there are many portable generators available (just look around a bit) and fuel is also available for free. Also the renewable generators will supply the Power Grid for quite long before failing, and most users of electricity are now off-line (and dead. Mostly dead).
The problem is the grid itself. The huge cable-network needs to be constantly repaired. While it may easily survive the first weeks, It will break more and more, eventually disconnecting the traveler from the Power Plants. This is where the mobile generators come into play again.
* **Mental Breakdown** This is an actual danger. He just entered the ultimate apocalypse. Everyone is dead, and even worse will stay in the same state for the rest of the year! If the destructors would be still active the corpses would eventually become skeletons which are much easier to handle by the human mind (but are still troubling). But his loved ones will stay in the state they were in at the moment of their death when they are outside the wind/rain/etc. might change their appearance, but that would probably even worse than those inside.
To make it even worse, every human he touches will be *infested* with the destructors he carry inside him. As the first humans he will voluntarily encounter are most likely friends and family, he would be responsible that their bodies will be destructed while every other body stays in the same state. While this is of course unimportant for the dead, it might severely harm his state of mind. After all now his loved ones look like corpses, while everyone else looks more like asleep. He is literally the most destructive living being in the whole universe.
Luckily he has a lot of stuff to spend time on. There is a lot of work that needs to be done, and he has electricity to watch films, use a computer (for games), hear music ect. He will need psychological help afterwards, but he can survive it.
---
## Conclusion
It will be hard, but definitely possible. If he wants/has to stay longer he has to prepare much better. He will be a scavenger forever. If he is an exceptional scientist, he might be able to transfer some of his *vis vitalis* into some gene samples (maybe he finds a way to manipulate the very essence of life to adapt it to almost similar genes, going further and further from there), but this at best unlikely and at worst impossible. Best thing I can assure that if he is ready to move every few years he should be able to live his full lifespan without ever being in great need.
The greatest threats are injuries and sudden events such as earthquakes, brushfires (he will have to plan accordingly) or 16 km-diameter-meteor impacts (anything smaller is also dangerous).
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## What comes next?
*This is highly speculative and more a bonus section. The fact that there is no life makes this hard to predict*
Unimportant whether he is still there or not, the world spins further. Nothing will rot, but stuff will still become unusable.
---
**In 10-20 years**, all trans-regional power-lines will be broken.
Storages for dangerous materials will show first weaknesses which would usually have been detected by humans early on.
Almost all but the most static building will show at least some structural weakness.
By now, fires will have burned down most major cities, though there'll still be much to scavenge in these towns.
Almost all vehicles on tires need their tires to be changed, as the material weakens and the air will escape. Spare tires may still be operational, but will break soon after.
Electrical devices will become nonfunctional due to water and dust getting inside. If properly stored they can of course last much longer.
Most food will still be good, but some chemical reactions could possibly create dangerous poisons. Eat with caution.
Clothes will remain functional if properly stored. Anything that usually eats it is dead.
---
**After 100-200 years** most building will be destroyed. Vehicles are unusable.
Any complex device will most likely malfunction in some way if turned on.
The ISS might have entered the Atmosphere and crashed, leaving a nice hole.
Wind and Water start to erode all areas as the (dead) grass and other plants are no longer able to hold it. While the erosion of course happens always, I expect this time is needed to erode earth that is still completely hold by roots.
Plants will lose their green color as Chlorophyll and other stuff breaks under the constant sun. This also happens normally, but is normally easily replaced by the plant.
Food will start to spoil the same way. Due to temperature changes stuff like Vitamin C is likely destroyed in most food. I don't know about other proteins, acids, fats etc, but I'm pretty sure they will also start to break apart as well.
---
**What will happen in the years after that?** I can only do an educated guess from here, and I'm happy with every correction.
Roads will stay for very long, but might be covered with dust. They are so flat that the wind doesn't affect them that much. Freezing water can still break them, but usually plants grow in these breaks enlarging them. Not possible here.
Towns will be visible for a long time, albeit destroyed. If at any future time an trans-universe-archaeologist will visit the earth he likely will find the former places of the major cities very easily.
*Speculative:* The earth might warm up a bit. As fires burn, they put huge amounts of dust in the air. The dust from eroding also will block some of the heat being reflected back to space, keeping it in the system. As no new Oxygen is created (from plants), the atmospheric composition might slowly change. While I can not foresee the results of this, it might induce a greenhouse effect.
*Ultra-Extremely Speculative Thing. Not even an educated, but a wild guess:* The earth might actually cool down a bit. As the surface loses its color and is covered in dust its surface albedo changes, possibly becoming brighter. This causes more of the heat reflected back to space, which again cools down earth.
[Answer]
He will have all the food and water that he needs. The problem is sanity. He will either go two paths: total fantasy or rejection. That is, he will either imagine people and and normal world, or he will kill himself.
[Answer]
**Nuclear Fallout**
I think some of the existing answers are very thorough, but might be minimising the nuclear fallout effect. A month ago I did basic research for another apocalyptic question which makes me think that everyone living in the Northern Hemisphere may be in a lot of trouble.
Nuclear powerplants storing spent fuel rods outside of the core would explode when the back up generators fail, about a week after everyone dies.
<http://topdocumentaryfilms.com/aftermath-population-zero/>
There are many hundreds of these in the Northern Hemisphere especially North America, Europe and Japan.
<http://nuclearinfo.net/Nuclearpower/CurrentReactors>
Smoke containing highly radioactive fission products would circle the entire Northern Hemisphere for a few weeks, and then precipitate out in the rain. Your survivor would want to be careful, even if they were not in the close vicinity to a reactor.
Things would would not be as bad in the Southern Hemisphere because there are a lot less nuclear powerplants.
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[Question]
[
Suppose it was possible to travel to inside the event horizon of a black hole safely. Also suppose said black hole is large enough that the curvature of the horizon of the surface of the central mass of the black hole is similar to that on Earth or perhaps the Moon, yet we are somehow able to hand-wave away the problem of the crushing gravity. Also, for simplicity, suppose our intrepid traveller has senses similar to those of a human, and no high-tech sensors (as are seen for example in Star Trek) are used.
Under such circumstances, if our intrepid traveller were to look "up" (away from the surface of the central mass) in a way similar to looking up at the sky on Earth or the Moon, **what would s/he see? What would the "sky" look like?**
Note that I am *not* asking about actually travelling to beneath the event horizon safely, or what anything would appear like to an observer at a safe distance outside the event horizon.
[Answer]
This is where the spatial intuitions from outside the horizon fail us.
As you pass the event horizon, it becomes impossible to move away from the central singularity. This means that gradually, the curvature of spacetime become such that what used to be the forward direction is flipped to become the a time-like future direction, since the singularity cannot be avoided. Likewise, the time-like dimension is now perceived to be a spacelike dimension. After a certain point, if you were somehow able to look 'back', you would see a long series of past yous blocking the view. But you can't look back, because that would imply that atoms or photons would move back away from the singularity.
An imaginary cross-section through a black hole would show a kaleidoscope of various time-like positions inside the black hole.
[Answer]
A couple of guys from the University of Colorado created a [video](http://www.newscientist.com/article/dn16885-what-would-it-look-like-to-fall-into-a-black-hole.html#.VPCop3zF8zs) simulating what it would look like to fall into a black hole, including passing the event horizon. They have several other simulations on [their website](http://jila.colorado.edu/~ajsh/insidebh/intro.html).
You should also check out the renderings made for the movie Interstellar. They made a [couple discoveries](http://www.wired.com/2014/10/astrophysics-interstellar-black-hole/) while getting the physics simulations right.
[Answer]
**It would be hot. very hot**
Large volumes of mass are drawn into the black hole and accelerated. Outside the black hole, the lowest energy matter gets spun off with so much ferocity that it generates X-rays. The higher energy portions get flung downward onto your unsuspecting planet.
I am assuming the planet falls in such a way that it isn't centered on the black hole (I can't figure out how to make that happen), but rather is falling towards it like any other. In this case, time dilation is doing its best to cause the energy emitted to appear to have lower energy, but you're still going to have large volumes of matter crushing in on the sky, with blackbody radiation not only making the sky appear an intense shade of violet (intense as "brighter than sticking a nuclear bomb on your eyeball and setting it off), but also baking the planet with a remarkable bath of higher energy particles like xrays and gamma rays.
Assuming you found a way to see past this haze of bright things, I'm assuming there is some interest in what the event horizon looks like. **It doesn't look like anything unusual!** The event horizon is only a limit for things escaping the black hole, but does nothing to affect things coming in. The only guarantee you would have is that, if someone held up a mirror outside the event horizon, and you looked at it, you would not be able to see yourself, for the photons from your body never get that far before being bent back into the black hole.
[Answer]
**It would look like the past**
At least if you're talking about the sky that would have been visible from outside the horizon, just before crossing.
I believe the interpretation in the video is flawed, since it does not account for the flow of the space-time structure itself inside the black-hole horizon. Frame dragging and the intense gravity means that a photon cannot travel outward. It's not like you're in a black sphere. As @Aaru correctly pointed out, in effect it's as if the space dimension pointing towards the singularity and a time-dimension change roles. I recall reading of a "[river model](http://arxiv.org/abs/gr-qc/0411060)" of inner-horizon space whereby spacetime itself can be imagined as flowing towards the singularity, dragging us and light along no matter what we do. And that's assuming that no dimensions are extinguished or created, which is unclear to me.
Regardless, I strongly feel that the interpretation of the singularity as a pointlike destination is nonsensical, since our own future is not perceivable as a pointlike destination, and we can't look upon our own past any more than a photon in a black hole could travel outwards.
So if the inside of the sphere is your future, how does the outside look when you're being dragged inwards by a river of time, possibly flowing faster than light, especially when from the perspective of the outside, you've already been subjected to infinite time dilation?
Frankly, the question is beyond my ken, and I suspect, possibly beyond the reach of any physics we know.
[Answer]
We don't know.
Our current ideas of physics don't really work inside the hole itself. In principle, there's nothing in there except the "signularity" of all the mass at the centre. Except that breaks loads of the "laws" of physics too.
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[Question]
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Let's say you were living on a planet near (but not too near) a black hole. I'm thinking of the planet [Miller](http://interstellarfilm.wikia.com/wiki/Miller_%28planet%29) in the movie Interstellar.
Obviously there are some strong tidal forces. But at this distance, Spaghettification shouldn't be an issue.
Are there other physiological effects that denizens should be aware of?
Intense light or heating?
Solar(esque) winds?
Strong planetary aurora?
Radiation?
[Answer]
Yeah, it's kinda difficult to answer. Twice I wrote a quick, dismissive answer, to the effect that the planet would be ripped apart by gravitational tides, or have waaay less time dilation than the 61000 factor presented in the movie, and twice now I deleted it.
If it were using the physics of a simple 40 solar mass non-rotating black hole, the planet would stand no chance. However, the black hole, Gargantua, [seems to be of the supermassive type](http://www.space.com/27692-science-of-interstellar-infographic.html) (i.e. galactic core) and [rotating incredibly fast](http://relativitydigest.com/2014/11/07/on-the-science-of-interstellar/), so the more complicated [Kerr metrics](http://en.wikipedia.org/wiki/Kerr_metric) rather than the good old Schwarzschild metrics apply. You'd be forgiven to think: larger core, more spaghettification. But that's not actually the case, at least not in the relative proximity of the event horizon of a giant rotating black hole.
If you read Kip Thorne's book the [Science of Interstellar](http://rads.stackoverflow.com/amzn/click/1494559390), he has Miller's world at the outer centrifugal balance point. Even so, the gravitational tides are so intense, the planet is tidally locked to Gargantua, and severely tidally deformed into an oval.
The more interesting bit is that since Gargantua is a supermassive black hole, to get the time distortion factor, the planet must be relatively close to the horizon. To be relatively close to the horizon and in orbit, it must move fast. Since Gargantua has about a billion km circumference, the planet must orbit in about 1.5-2 hours (from the perspective of someone on the planet), so about half the speed of light. From the perspective of someone further away from the black hole, the time dilation effects will make the world appear to orbit, ugh, the maths become impossible for me here due to the spinning of the massive black hole, so I'll take Thorne's word for it: it would seem to orbit every 100 miliseconds, appearing to achieve effective superluminal speed. Of course, escaping the Gargantuan gravity well to get the Ranger off Miller's world and back to the mothership would be a task well beyond 21st century technology. This was handwaved in the movie, of course (what was it, neutron star slingshots?).
*Image from [Science of Interstellar](http://rads.stackoverflow.com/amzn/click/1494559390)*
None of this is enough to kill you. However, to get the time dilation effects, you gotta be close to Gargantua, deep down its gravity well. So far down that the accretion disk would be outside Miller's orbit, and the black hole should take up half the horizon (unlike what is shown in the movie). That close to Gargantua, and with Gargantua having a giant accretion disk, the **X-ray radiation from the magnetic field of the black hole sweeping that accretion disk would be tremendous.** Of course, you can claim (like Nolan)
that the accretion disk is really really anemic, and thus a lot colder than normal accretions disks would be...
**Edit: Come think of it the magnetic field of the black hole would itself be spectacularly high as well. It'd be like being inside an MRI machine.**
Moreoever, if the planet was formed in place, rather than captured, it's subject to the same 61000x time dilation from the start. For a 12 billion year-old black hole from our perspective, that would be, 200,000 years old. How did Earth look like when it was 200,000 years old? I'd wager it was pretty hot. Of course, you could always argue it was captured later on... Nonetheless, any incoming material (all that in-falling garbage of comets and asteroids) would be coming in at relativistic velocity, accelerated by the black hole. At those speeds, a comet-sized impactor wouldn't just kill off the dinosaurs, it would **remelt the planet**.
So, in conclusion, rather than a waterworld, it would much more likely be **a radiation swept molten rock horror**.
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## Question
Assuming all things in the fictional world are the same to today's world, which real life constraints must be considered in order to increase the credibility in an immortal narrative/story.
## Scope
To be clear - I mean which biological, ecological, sociological or anthropological constraints would ruin the credibility of an immortal story because the audience suspension of disbelief would be interrupted. Example : Malthusian Catastrophe.
Many thanks to those individuals who have helped to shape this question already in the comments due to an unclear original question.
## Information to Consider
Information to aid answerers:
Immortality is to be interpreted as per the accepted definition. A being which can live exceptionally longer than normal or realistic biological standards to the point that normal humans consider them living forever.
Immortality is not affected by disease.
Immortals may end each other's existence through a single mechanism which ensures immortality is destroyed. In Highlander it was spinal severance, in Vampirism is it aortic puncture with a stake etc. For the sake of argument lets just refer to the method of dispatch as Method X.
Immortals pose no real threat to humans other than that which might the result of anger of other normal emotional responses. Immortals do not feed on or otherwise harvest humans.
If two immortals breed then the offspring can grow to teach the age of the father at the conception.
Immortals can engage in intercourse with humans but an immortal cannot be produced although the human offspring may posses stronger biological abilities - stronger immune system etc although not wildly so.
Should the ecosystem be destroyed through a calamitous event (nuclear explosion, catastrophic solar storm, volcano eruption) then it can be realistically assumed the immortal would also perish as regenerative abilities would be overwhelmed.
Immortals heal almost instantly from breaks, standard burns, blood loss etc unless Method X (discussed above) was the mechanism which ensures death.
## Examples
Examples of real-life constraints discussed this far;
Malthusian Calamity
Brain Capacity for Memory is Finite
No true nutrition violates certain laws of Physics since Immortals could not regenerate without nutrition.
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**Population**
Without a check on their population, immortals will replace all human life and then populate the world until they reach the maximum population they can.The primary thing you'll need to do to avoid this is limit the number of immortals. This could be done in a number of different ways.
The easiest way is to give them no method of reproduction. A mortal can, through exceptional circumstance, become immortal, but if immortals can have children, all of those children are mortal. This is seen to some degree in Greek mythology, where many of the gods will bear mortal children who are heroic beings, but mortal.
**Healing**
Barring the use of magic, healing to the degree you describe strains credibility, specifically due to the 'method X' capacity for death. It may be more reasonable to describe certain wounds as being fatal, and say that *most* other things won't kill an immortal.
For example, if you say that only severing the spinal column can kill an immortal, what if they get shot in the head? Does their brain have a method of growing back with all of their previous memories, or do they effectively become a new person? What if they get most of their head *blown off with a shotgun?*
It will make things a bit more believable if any sufficiently grievous wound is fatal. A quick test for a wound could be whether or not it's instantly fatal. If it is, then the immortal dies. If it's not, it's recoverable. It may also be the case, however, that regenerating from horrible wounds takes energy, and sufficient damage overwhelms whatever regenerative capabilities the immortal has.
If the immortals *are* magic, you can ignore this point. Vampires can turn into dust or clouds when badly wounded and escape that way, which disconnects the link between body integrity and survival.
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Apart from the issues with population, I see issues with the brain.
1) Since memories are stored in the brain, somehow, and the brain is finite, there will be an issue with that at some point. I do not have any scientific mean to say how much memories may be held in a brain, but the rule of thumb is that if an human may live at most 130 years, I would not expect memory capacity to be longer than that (which evolutionary benefit would the matter/energy cost of extra memory cells bring, it they were not used). To be in the safe side, say that your human brain can hold 200 years of memories, and after that either will progressively lose old memories or have difficulties forming new ones.$^1$
2) As people mature, brains lose flexibility. Over time society/technology change, but usually not so much so, up to retirement age, you usually keep up with it. To put that in other words, right now I learn way slower than when I was a teenager. This is mostly ok, because the world has not changed that much since then, and most of what I learn there is still of utility. But if my teen years had been in the Pharaoh's time, now I would have to work harder to keep myself updated, because anything valuable would have been learnt at the slower, adult rythm.
Of these, I think 1) is the real constraint. 2) could be just waived with "due to the nature of inmortals, they retain forever the mental flexibility of their younger years" or something like that.
$^1$ In fact I would bet for way less, since anyone over 70 is highly unlikely to be able to father (and sustain while they grow up) descendence. Evolution wants to keep you fit enough for producing the next generation, but after that it forgets about you.
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This post-apocalyptic environment, as narrated in the [book](http://en.wikipedia.org/wiki/The_Road), depicts a world where most if not all animal life has been abruptly killed, and similarly most vegetation burned out. After the disaster, the world is left full of ash and fog, and turned cold.
What kind of disaster can cause such an environment? I could think of some possible causes, like eruptions, or maybe a space object collision, or even nuclear warfare, but I'd like to get some scientific-based reasoning.
[Answer]
It sounds very much like the description of a Volcanic/Nuclear/Impact Winter.
They are all different ways of causing the same end result which is the injection of massive amounts of ash and dust into the upper atmosphere. This screens off the sun and causes global temperature to drop and plants to stop growing properly.
The result is massive famine and starvation, cold weather, and permanently overcast skies.
The different names depend on whether it is caused by a massive Volcanic Eruption, Nuclear Wars, or an Asteroid Impact. Each of those would have different other side effects:
**Nuclear:** There would be high levels of background radiation increasing mutations and miscarriages. Some areas would become dangerous to visit.
**Asteroid:** Depending on the location of the strike expect massive Tsunami's and Tidal Waves to sweep the world, the impact area itself would be obliterated and the resulting firestorm would cover a huge portion of the globe.
**Volcanic**: This would have the smallest immediate side effects (although expect a lot of poisonous gas, sulfur, lava flows, etc. It could also last the longest though since the dust from the other two options would start clearing after a few years while the volcanoes could keep erupting for far longer.
There's always the option of combined events as well, for example an asteroid impact on one side of the world could trigger a volcanic eruption at the other side once the shockwave reaches.
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I don't even think you need a collision to screw things up royally. A near miss by a super massive object can do a lot of damage seeing as how our planet is tectonically active. I'd ask for more clarification on abruptly. I only mention it because I suppose you could get a disease or virus (dumb virus but hey they are all reproduction and no brains) that would affect the ability of animals to reproduce. Thereby you'd abruptly get a die off, but it would not be immediate. No to mention a disease of virus which only affected animals, humans might seek to cull all the animals.
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If you want a *quick* extinction event, how about a **Gamma Ray Burst** from a nearby star?
While we are constantly bombarded with them, they are mostly from billions of light years away. But they are unfathomably intense - billions, trillions, quadrillions of times more energy than our Sun emits.
But what if... a nearby star went supernova and released one? In a *worst* case scenario, in seconds, every living thing on Earth would be dead. The Earth would be completely sterilized. But if it was *less* than worst case, pockets of life might survive. Virtually everything around you would be dead. A few lighting strikes later and you have massive forest fires. These fires cover the Earth in a thick blanket of smoke, blocking out the Sun and bringing about a long, cold winter. In fact, some have suggested such a burst caused [one of Earth's actual mass extinction events.](http://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_extinction_events)
But, I wouldn't lose any sleep over the idea of this actually happening. There's no stars near enough that could produce such a burst.
Well, that we know of.
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[Yellowstone Supervolcano](http://en.wikipedia.org/wiki/Yellowstone_Caldera) erupts every some 600 KY. Last eruption `ejected approximately 240 cubic miles (1,000 km3) of rock, dust and volcanic ash into the sky`
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I have a country which, prior to the events of the story, had been ruled by a monarchic dynasty for a good 200-300 years. This dynasty was ended by violent upheaval. The reign of the monarch who replaced the dynasty was similarly violently overturned after about twenty years. The initial dynasty A lacks plausible heirs, as does the coup-maker B.
Given that monarch C who deposed the tyrant is competent and well-liked, is a return to dynastic rule a priority? What social or political factors would come into play if, for example, she declared no intent to produce a natural heir and instead groomed a chosen successor? I know that there is historic precedent for adopted heirs, but what I'm getting at is the forces behind the process of change.
For general reference, the society is very class-stratified. However, the merchant class and the guilds hold a lot of the political power, and most of the old aristocratic bloodlines have been diluted or wiped out.
**Edit**: Some additional information in response to comments: monarchy is nominally absolute, but functionally dependant on the governing bodies of the major cities, which have steadily gained more power and independence. Prior to dynasty A there existed one or possibly two other monarchic dynasties.
Dynasty A was destroyed in a violent massacre and the story is widely known even 20 years later or more. Monarch B (the tyrant) ascended via control of the military, and Monarch C (current ruler) has a good reputation with the military but nothing like the same level of loyalty as her predecessor.
In short: assuming a female monarch with a generally positive reputation is dependant upon the good will of a number of guilds and powerful/wealthy merchant houses, would the lack of a natural heir be an obstacle to maintaining this approval?
[Answer]
## Feudalism vs Centralization
There are very different scenarios depending on how the society is organized.
In a feudal environment, where the whole social hierarchy is based on hereditary titles, an ending of a dyasty wouldn't change the concept of "dynastic rule", as most other power players hold power only because of the same concept - so either some other dynasty would take over the throne, or possibly the vassals would split up and become independent holdings with different dynasties heading each of them.
In a heavily centralized environment (god-kings, bureaucratic empires) this may be a trigger for a regime change. If the "head" position was already weak enough compared with the "system", then the system might remove the position; (wasn't Cromwell a similar situation?), or some powerful bureaucrat may rule without the title (i.e., USSR which wasn't ruled by its presidents but by a formally irrelevant clerical post - general secretary of party), or someone may simply assume the mantle and suppress everyone who insists on heredity - either successfully or not.
## There's no such thing as no heirs
There are always heirs, only sometimes they're distant enough and too politically weak to make any claims. There are many, many cases in history where "initial dynasty A lacks plausible heirs" but still multiple claimants appeared. If you methodically exterminate the whole extended family up to fourth-degree cousins, then there are fifth and sixth degree cousins remaining, plus a few people who claim to be third-degree cousins who survived in hiding or of bastard descent (some of them in reality, some "manufactured"). There literally can't be a situation where there isn't a heir unless an isolated society is 100% exterminated - we're all related, most likely both me and you are claimants to the throne of Charlemagne through one of his great-great-(great-\*n)-grandfathers.
The only thing that may prevent heirs-claimants to appear is if everyone who matters is happy with the current arrangement; otherwise such claimants will be maintained for generations by internal or external opposition, as a potential tool in future.
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There are examples in History like the [Compromise of Caspe](http://en.wikipedia.org/wiki/Compromise_of_Caspe) in which representants of the possible heirs and the classes and guilds decided on the best heir for the Kingdom, avoiding a war.
Nearer to your Monarch C scenery is [Hugh Capet](http://en.wikipedia.org/wiki/Hugh_Capet), being elected as King of the Franks when no close heir to Louis V was available, and him being not on the lineage of Charlemagne at all. He appointed his son Robert II not just as heir, but crowned him as King while he (Hugh) was still alive. He did this not only for establishing a dynasty, but for providing the Kingdom of the Franks (nowadays France) with stability, since as of Hugh's Death there was already a completely crowned and consecrated King to whom all counts and barons had already pleaded allegiance.
[Answer]
The first priority is always to restore the dynasty. He must have a legal heir as soon as possible. Otherwise, If the leader dies, nobody will be in charge. Other members of the dynasty might try to take control but they might not have the legitimacy to do so. They must convince landlords, and other important supporter that they are the rightful ruler. That is not easy. You need to get the support of the nobility, the guilds, the people (to some extent), and the support of other countries might help a lot. Even if your lucky, your likely to face another civil war.
That said, keeping control of the country without a dynasty would probably require to change the country into a republic or something else. If he is not a revolutionary, a religious zealot trying to establish a religious government or an oligarch if he is part of a guild, I don't see why he would change the government. If a monarch want's to keep his country but do not want to restore/establish a dynasty, it won't be easy.
[Answer]
This is a pretty interesting scenario.
One thing you will want to consider is the question of political theory. As Vincent says, "The first priority is always to restore the dynasty."
Well, yes, but why?
Because if there's no alternate principle of political legitimacy, the lack of dynastic continuity is a very grim prospect indeed, for all concerned (except, I suppose, the opportunists who feel ready to profit from chaos - and even they often prove to have been overly optimistic about their chances.)
We call it "political theory", but it's really the question of how to preserve any sort of ordered society. From there, we have the leisure to inquire further into what's the *best* kind of ordered society. Still, in the situation you describe, people will be desperate for that first assurance: desperate to believe that there's a reasonable future in this charismatic leader.
How can she provide such assurances? She won't have the benefit of Enlightenment thinkers like Rosseau or Locke, let alone post-Enlightenment theorists of legitimacy like Marx; won't have the benefit of a proletariat that's been raised to think for itself. In short, she won't have *any alternate narrative of hope and confidence* to replace the promise of dynastic legitimacy.
If you want her to be able to hold on to power in any reasonable way, you can do it in two ways, as far as I can see.
You can portray her as providing a new dynasty of some sort (by declaring an heir in an acceptable fashion, if she has no heirs of the body).
Or, you will need to provide an alternate political theory that can win the allegiance of a preponderance of the populace and the brokers of power. There are some interesting possibilities there: you mention **the governing bodies of major cities, the guilds, and the wealthy/powerful merchant families**.
Historically, this has frequently been a likely kind of social matrix for generating challenges to the political domination of royalty. When the people who manage the money and the local governments encounter political philosophies that challenge the right of royalty/nobility to interfere in their business, they tend to like what they hear. :-)
You would need to plausibly establish precedent, and provide the alternate political theory with some historical depth. Given that, you could have a very dramatic story on your hands.
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It seems extremely unlikely for a monarch not to have a bunch of potential heirs.
Henry, Count of Chambord died in 1883, the last male lineage descendant of King Louis XV (died 1774). The French monarchists were split into two different groups. The Legitimists accepted a distant cousin by male lineage, Juan Count of Montizon, the Carlist claimant to the Spanish throne, as the rightful heir. Their latest common male lineage ancestor had died in 1711, 172 years before. The Orleanists accepted an even more distant cousin as the rightful heir of France. His latest male common ancestor with the Count of Chambord had died in 1643, 240 years earlier.
King Henry IV became king of France in 1589 as the male lineage cousin of king Henry III. Their latest common ancestor in male lineage, King Louis IX, died in 1270, 319 years earlier.
Elector Maximilian II Joseph of Bavaria died without close male relatives in 1777. Bavaria was inherited by his closest male line cousin Charles IV Theodore. Their latest male lineage common ancestor, Duke Louis II of Bavaria, died in 1294, 483 years earlier.
King William III of The Netherlands and Grand Duke of Luxemburg died in 1890. His daughter Wilhelmina became Queen of the Netherlands. But the throne of Luxemburg (which their dynasty hadn't even possessed until 1815) passed by agnatic or male lineage succession. So King William III's closest male lineage relative was the heir. Adolphe, former Duke of Nassau, was the seventeenth cousin once removed of King William III. Their latest common male lineage ancestor, Count Henry II of Nassau, died in 1251, 639 years earlier. Adolphe is considered the most distant relative to ever inherit a throne.
In 1290, the little Queen Margaret, the Maid of Norway, died on her way to Scotland with no close heirs. In the "Great Cause", about fifteen men claimed the Scottish throne. Her closest relative among the competitors, Nicholas de Soules, was her second cousin by an illegitimate line, while the most distant relative, John Comyn, was her sixth cousin once removed.
<https://en.wikipedia.org/wiki/Competitors_for_the_Crown_of_Scotland[1]>
And when the Lancastrian Prince of Wales and his father King Henry VI were killed in 1471, that was just about the end of the Lancastrian branch of the English royal dynasty. There were no more legitimate descendants of the first Lancastrian King, Henry IV. So there were no possible Lancastrian claimants left, right?
How about King Alfonso V of Portugal (1432-1481) whose grandfather King John I married Philippa of Lancaster, the oldest sister of King Henry IV? King Alfonso's sister's son as the later Emperor Maximilian I, who married Mary the heiress of Burgundy whose grandmother was a daughter of John I and Philippa, thus giving their son King Philip I of Spain a double dose of the Portuguese Lancastrian descent. Philip married Queen Juana la Loca of Spain who was a great great granddaughter of John I and Philippa, adding more to the Lancastrian heritage of his children including Emperors Charles V and Ferdinand I.
Perkin Warbeck, Yorkist claimant to the English throne, agreed that his rights would go to Maximilian if he died without heirs. These facts may partially explain why Maximilian claimed to be the heir to England.
King Henry IV's next oldest sister Elizabeth married the first Duke of Exeter and in 1471 her heir was Henry Holland, 3rd Duke of Exeter (1440-1475).
Henry IV's third sister Catharine married King Henry III of Castile and in 1471 her heir was her grandson King Henry IV, though eventually it would be her granddaughter Queen Isabella I , mother of Queen Juana la Loca. So yet another Lancastrian descent for Emperor Charles V, who some people said had a better claim to the English throne than King Henry VIII. In fact Emperor Charles V did once threaten to invade and conquer England.
As you may remember the Yorkist claim made by descendants of the fifth oldest son of King Edward III was descent through female links from the third oldest son of Edward III, but the Lancastrian claim was through descent from the fourth oldest son of King Edward III, claiming that female descent was irrelevant for inheriting the throne. When Prince Edward and King Henry VI were killed in 1471 their killer Edward IV the Yorkist king thus became their heir according to the Lancastrian claim of seniority by male lineage descent.
So any die hard Lancastrians would have to scramble to find some other claimants. King Henry Iv did have some younger half brothers, the Beauforts, illegitimate children of John of Gaunt, Duke of Lancaster, and Catharine Swynford. John and Catharine were later married in 1396 and their children were legitimated - though it is controversial whether that was valid for succession to the throne.
Unfortunately for Lancastrian supporters, the last two male Beauforts were killed in 1471, leaving only descendants through female lines - and denying the inheritance of the throne though female lines was a main basis of the Lancastrian claim. The senior female heiress of the Beauforts was Margaret Beaufort, mother of King Henry VII Tudor. But Charles Somerset, first Earl of Worcester (c.1460-1526) was an illegitimate and legitimated son of Henry Beaufort, 3rd Duke of Somerset. If any claim to the male lineage inheritance of the throne could pass through an illegitimate but legitimated son, it might better pass through another illegitimate but legitimated son than through a woman of legitimate birth.
And then there were the actual descendants of the House of Lancaster instead of relatives of it. Thomas of Lancaster, Duke of Clarence, had an illegitimate son Sir John Clarence who was allegedly the ancestor of the de Langlee family in France. John of Lancaster, Duke of Bedford, had an illegitimate daughter and a grandson. Humphrey of Lancaster, Duke of Gloucester, had an illegitimate daughter, Antigone of Gloucester, who married the Earl of Tankarville. Their grandson John Grey (died 1497) Baron Grey of Powis was their heir in 1471.
The succession to Queen Elizabeth I of England was widely speculated about during her long reign despite her discouragement of it. Among the many candidates suggested were four claimants to the throne of Portugal and thus to the Lancastrian succession.
<https://en.wikipedia.org/wiki/Succession_to_Elizabeth_I_of_England[1]>
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If the force of gravity at the Earth's surface suddenly became 2 times stronger, how would the environment and humans cope? I'm guessing a lot of flying creatures would suffer, but what would happen to us?
[Answer]
Every flying machine or creature would crash immediately and probably fatally.
Anyone with a weak heart, bones, or who is overweight would die fairly rapidly.
All structures such as bridges and large buildings would become potentially unsafe, depending on the safety margin with which they are constructed. Houses would probably stand but may need reinforcing, larger structures are at higher risk.
For details of the effects on humans see this answer: <https://worldbuilding.stackexchange.com/a/171/49>
As mentioned in the comments plants would struggle to support their weight, trees would collapse. Grain crops would not be able to stand. Many other plants would need artificial support such as tying them to frames to support them.
[Answer]
Depends on how it happens. There's three ways to double the gravity of Earth.
***1. Increase the gravitational constant.***
As Q said, ["simple, change the Gravitational constant of the Universe"](https://www.youtube.com/watch?v=5xdbPhnfFEI). This is bad. Very bad. The Earth becomes more compact under its own increased weight and heats up. The Moon spirals into the Earth. The Earth and all the planets spiral into the Sun. Galaxies are disrupted... basically the whole Universe changes.
Let's not do that.
***2. Double the radius of the Earth.***
If you double the radius of the Earth, adding mass while keeping the density constant, it will have eight times the volume, and thus eight times the mass. But because the radius doubled, and because gravity decreases with the square of the distance, there will only be twice the gravity at the surface.
But this changes the surface which adds another change to deal with, so let's skip this one, too.
***3. Double the density of the Earth.***
If we double the mass while keeping the size the same we'll double the density, maybe by adding a lot more heavy elements below the surface. Because the size of the Earth is the same, and because gravity increases linearly with mass, gravity will double.
This is the best option because the surface remains the same... at first. Let's go with this one.
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Our new, more dense Earth has problems, and not just for life.
For people, ***everyone will feel like they're giving themselves a piggy back ride***. For those who can handle the strain, they will eventually gain in muscle and bone mass to compensate somewhat, but until then it will be an exhausting struggle to move or even breathe. Anyone too old, too young, or too sickly will likely be bedridden or die.
In addition to simply moving your greater bulk, ***your bodily processes become more difficult***. Your lungs must expand and contract against greater mass, breathing becomes harder. Your heart must work harder against the increased gravity to get blood up to your brain, the increased blood pressure will put strain on your heart and blood vessels. Your [lymphatic system](https://en.wikipedia.org/wiki/Lymphatic_system), part of your immune system, is pumped by the action of your muscles and its fluids will tend to pool in your legs. There will be tremendous long term health consequences.
***Most bridges and many tall buildings will fail***. They are not built with a sufficient [factor of safety](https://en.wikipedia.org/wiki/Factor_of_safety) to withstand doubling their weight. Airplanes will likely crash from either the increased weight, or the sudden atmospheric contraction (see below). Tall trees will either fall or quickly die from being unable to pump water to their tops, new trees will be much shorter. Many shorter plants won't have the structure to handle the increased weight and will be flattened.
Geological structures will collapse above, and more importantly, underground. Mines and other underground structures will collapse causing great [sinkholes](https://en.wikipedia.org/wiki/Sinkhole) to open up. ***Cities are built on great systems of utility tunnels which will collapse***. Others, built on poor soil and reclaimed land, will sink into the mire.
***The increased mass means satellites in orbit will come crashing down***. New launches will be harder, they have to with an [escape velocity](https://en.wikipedia.org/wiki/Escape_velocity) 1.4 times higher (escape velocity increases with the square root of gravity). But space will be closer! See below.
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***Double the mass means double the air pressure***. Fortunately your body will reach equilibrium, so it won't make breathing harder. And you'll be receiving more oxygen, which is good news for all that extra work you need to do to move your new bulk around.
For anything moving quickly through the atmosphere, the increased air density will mean increased drag. Cars will be slower and less fuel efficient. Airplanes, on the other hand, will have greater lift and lower stall speeds.
A compressed atmosphere effects space launches... after all the satellites come crashing down. New launches will have to move through a denser atmosphere, which is bad, but ***the compressed atmosphere means the [edge of space](https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line) is lower***. A compressed atmosphere means less drag on satellites which means they can stay aloft longer in closer orbits using less fuel... once they get there.
But human civilization probably won't survive on this new Earth...
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The increased density has long term consequences for the Earth's habitability. All this extra gravitational energy means a hotter and more active Earth, this is bad for humanity.
***The rapid compression of the atmosphere will cause a tremendous heating***. This will generate great wind storms, pushing around more air mass, and strange weather patterns for years to come. It gets worse.
***The increased density of heavy metals means a greater portion of radioactivity heating the core of the Earth***. This means more seismic activity, more volcanoes, and more earthquakes in the long term. And it gets worse.
***The increased gravity will cause the Earth itself to settle and compress adding even more heat***. As the Earth shrinks, even a little bit, the surface will buckle causing great upheavals; new mountain ranges and volcanic eruptions will appear. All this mass shifting around will cause great earthquakes.
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In the end, ***we're left with a slightly smaller Earth which is hotter and more geologically active***. This means an unstable surface which is hostile to human civilization, much of which just collapsed under its own weight anyway.
Life on Earth is in trouble. ***Evolution has built on the assumption that gravity is a constant***. Billions of tiny, critical biological processes have been built with that assumption. Now that it's suddenly changed, most complex life will die. The Earth will experience a great [extinction event](https://en.wikipedia.org/wiki/Extinction_event) as it does every 100 million years or so. This will open great gaps in the biological niches, gaps which have not been open since multi-cellular life began, which will be filled by new forms of life. A few million years after this event, life on Earth will look very, very different.
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Trees might not grow straight up because even though they grow towards the sun using the rays to make their own food the gravitational force would pull even harder on the trunk causing it to bend towards the point where gravity is strongest
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So, I want to write a story set mostly in a world using hyperbolic geometry (except brief beginning and end bits with the main characters coming from/returning to our world), but I'm a little confused on how that influences some parts of the worldbuilding. In particular: Rivers.
The descriptions I've come across suggest that it would look like everything is sloping down away from the viewpoint, does that mean all directions actually act like being downhill (unless they're actually sloped up enough to overcome that)? If so, does that mean a river can flow in any direction? And if that's true, does a river flowing in a loop actually work under hyperbolic geometry?
I feel like I've missed something that would keep that from working properly, but I can't see what. Then again, I kinda hope it actually does work that way so I can have a proper M.C. Escher waterfall.
EDIT: Some clarification and additional information:
By "A world using hyperbolic geometry", I mean that the rules space/geometry of this universe are defined by the principles of hyperbolic geometry: <https://en.wikipedia.org/wiki/Hyperbolic_geometry>
My rough idea of the shape of the "planet" was an endless roughly flat expanse, probably with gravity being in a fixed direction perpendicular to the plane of the "planet". But both of these points are flexible, since I was trying to start working on things that would immediately affect the opening scene so I could actually get something written. I would also accept answers for spherical planets with the same gravitational rules as our planet and only the geometry being changed.
[Answer]
The "everything is sloping down" is an illusion caused by the geometry. When the observer lowers their eyes to terrain level, the illusion vanishes. The gravity works same as in normal geometry, you can have hills and valleys where water flows exactly as you would expect.
However, in hyperbolic geometry you have both more surface area and more volume in your vicinity. How much more that depends on the curvature. Wikipedia has the formula for area of circle which is bigger than in normal geometry. For 3d shapes it's even more. On world with high curvature both the river catchment area and atmosphere volume above it are much bigger for the same diameter. Means more water rains over bigger area thus the rivers are much more prone to catastrophical flooding.
[Answer]
**Generally Speaking**
In a hyperbolic geometry I would hypothesize that everything looks further away, yet when you move toward it, it appears to approach more quickly than it really does.
I could be wrong in my interpretation, because my assumptions would seem to resemble how it looks to move at near the speed of light. If you're struggling to see this, consider the MIT experimental game A Slower Speed of Light ( <http://gamelab.mit.edu/games/a-slower-speed-of-light/> ).
Gravity would still have to change the curvature of space from positive to negative in order to function. So there would perhaps be some strange warping of the visual field, i.e. the horizon would likely look like an infinite, flat disc, while the sky would perhaps seem to curve away, likely as though space was poking down into the sky from above while the atmosphere clings to the horizon. And the sky above would look like the beginning of time, while we would see the horizon in a way like a mirror placed at infinity ( though I submit this may be misleading, as at infinity the mirror is strangely both near and far, i.e. zero distance or everywhere, but rather would have infinitesimal perspective height, so the two may cancel ). Indeed a very strange perspective.
As for how water behaves, perhaps in a very similar manner to the way we're used to, though it would appear that a river would flow more slowly in front of us, faster toward us up stream and again faster as it moves away from us down stream. Throwing your fishing line down stream though would put the lie to this perception, not snatch the rod and reel out of the hand as one might expect.
Rain might appear to be deadly in its descent, but would still land with the same amount of momentum on the face, though the splatting of the droplets would be ever so more brief in appearance, perhaps imperceptible to the naked eye as the distance the splat travels is relatively small.
**How Rivers Work**
As far as how rivers behave, that's less a matter of their route along the "plane" than it is the topology of the land. Water simply flows downhill. It needn't be more complicated than that.
**Conclusion**
The more interesting features of this geometry are most likely going to have less to do with actual physics than of our perception of space and time in a largely distorted version of hyperbolic space.
[Answer]
How big is your hyperbolic curvature?
We are on the surface of a sphere. If we draw circles with increasing radius, the larger circles will have a circumference slightly smaller than $2\pi{r}$. Eventually at the equator, the size will peak and then start to decrease.
If you were in an elliptic negative curvature space, then the surface of a sphere would be slightly less than $4\pi{r}^2$. If you were in a hyperbolic positive curvature space then the surface of a sphere would be slightly less than $4\pi{r}^2$. Our space is, as far as we can measure, on the line between the two. Light and gravity fall off as inverse squares, and no-one has reliably measured any deviation.
There is nothing wrong with having spherical planets in a hyperbolic universe. They would be much the same if the curvature was small. There would be more distant galaxies, and they would be a bit fainter.
I suspect what you want is a hyperbolic planet. This is not the familiar waisted hyperbola of geometry, but something where every point is the same. Have a look at the [Poincare mapping](https://en.wikipedia.org/wiki/Poincar%C3%A9_disk_model): this may be what you are after. There are more distant points than in a flat world. You might expect ships to rise up rather than sink under the horizon as they do on a sphere, but this is a spatial mapping on a flat disc so they don't rise or sink. And rivers would still flow downhill.
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[
In D&D there is a history of allowing 'light hammers' to be thrown.
However, at the very least the ones I remember would be completely useless if thrown. The center of gravity and balance would probably be way off.
[](https://i.stack.imgur.com/VRXYv.png)
In fact almost all of the hammers/picks in the picture are implausible as weapons or mislabeled.
If a metal headed hammer weighing roughly 2 lbs was being designed (pre-renaissance) for both melee combat and throwing, what would it most likely have to look like?
I know about [Meteor Hammers](https://en.wikipedia.org/wiki/Meteor_hammer), and [throwing sticks](https://en.wikipedia.org/wiki/Throwing_stick) like the [Rungu](https://en.wikipedia.org/wiki/Rungu_(weapon)) or [Iwisa](https://en.wikipedia.org/wiki/Iwisa), but I'm not interested in those because they don't really resemble hammers in the sense I'm talking about.
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### I'm tagging this as [science-based](/questions/tagged/science-based "show questions tagged 'science-based'") as I do not want magical or fantastical answers, and I'd like the reasoning why the answerer's design is plausible scientifically.
[Answer]
## Sort of like a Rungu
The closest historical example to this you will probably get are [Rungu throwing clubs](https://en.wikipedia.org/wiki/Rungu_(weapon))
[](https://i.stack.imgur.com/KZtee.png)
... but clubs are not quite hammers. Your idea for a throwing warhammer did not exist historically because it is inherently impractical. This is because any civilization advanced enough to make a throwing war hammer can also make a much more practical throwing axe; so, your setting will need some excuse as to why they need a throwing hammer to begin with. The only historical precedent for such a weapon having a reason to exist anywhere outside of fantasy/mythology/sports is that some historical monastic orders used hammers and clubs because they saw this as an exception to religious oaths that prevented them from spilling blood. So a throwing warhammer could make since for something like a monastic knightly order even if there is no historical evidence of their existence.
**An iron age throwing war hammer would look more like a single-ended creasing hammer**
[](https://i.stack.imgur.com/7Pbxb.png)
Axes and hammers have more or less the same weight distribution and the existence of throwing axes proves that the lack of balance does not stop thrown distal heavy weapons from being viable. In fact, they are more viable than balanced or proximal heavy weapons because they are carried more by the inertia of the weapon's head that follows a larger, and faster moving distal arc than then lighter handle which follows the arc of your hand. Basically they follow the same principle as a sling.
[](https://i.stack.imgur.com/Ji9QX.png)
Throwing axes like [Francescas](https://en.wikipedia.org/wiki/Francisca) and [Tomahawks](https://en.wikipedia.org/wiki/Tomahawk) were both very similar weapons despite coming from different cultures. This convergence of properties tells us that there is something about the qualities of a throwing axe that make them more ideal for throwing than their battle-axe counter-parts. In general, throwing axes are similar to 1-handed battle-axes, but they were normally much lighter weighing in at 250-850 grams vs melee battle-axes which averaged closer to 800-1500 grams. Throwing axes also frequently turn the blade down a bit to make sure it strikes in line with the spiral of the throw.
You can also note that nearly all throwing axes are single-bitted with relatively narrow striking surfaces. This is because the axe will never need to strike with the back or distal end the way you do with a melee weapon because there is pretty much just one right way to throw an axe/hammer, this allows you to make a longer head for your weight making hitting on the handle less likely, and the narrow striking surface is important for getting adequate penetration since you can not drive a thrown weapon through with your bodyweight like you can with a melee weapon.
[Answer]
>
> The center of gravity and balance would probably be way off
>
>
>
No.
You know axe throwing has been a thing for ages, right?
As long as the head of the hammer is as heavy and balanced as the head of these axes, you can throw them alright. Having a proper balance depends on the skill of the weaponsmith, so it's doable. A blunt hammer head could work to bend plate armor, much like a mace but at long range.
[Answer]
# Thor's hammer
There's one important mythological figure known for throwing a hammer, that is Thor.
When you're asking for a hard science supported medieval shape, check out known Thor's hammer *pendant* artefacts. Ignore the replicas, as most are fantasy, or too heavily decorated in Merovingian style. The shape of the hammer was transformed into a cross in medieval times, as the Nordic people got influenced by Christianity. The early viking ones are very rare!
[https://www.google.com/search?q=thor's+hammer+artifact+bronze+authentic&source=lnms&tbm=isch&sa=X](https://www.google.com/search?q=thor%27s+hammer+artifact+bronze+authentic&source=lnms&tbm=isch&sa=X)
Example of an undecorated, bronze Thor's hammer pendant shape, that could be Viking
[](https://i.stack.imgur.com/JCRi6.png)
Source: sold item on [Catawiki](https://www.catawiki.com/en/l/18818457-medieval-viking-period-bronze-thor-s-hammer-amulet-35-mm)
[](https://i.stack.imgur.com/nU0Fr.png)
These pendants are often metal detector finds. [Another source](https://picclick.co.uk/Viking-Ancient-Artifact-Bronze-Thors-Hammer-Pendant-174641945190.html) of examples shows this one, nearer to the axe,
[](https://i.stack.imgur.com/Mq3qt.png)
[Answer]
here a gif of [throwed hammer](https://i.imgur.com/6opbHr6.gif?noredirect)
[](https://i.stack.imgur.com/L8hQd.jpg)
as other has mention its actually plausible (in fact i say all that weapons that you claim is not plausible as weapon are a plausible weapon, just not necessary or practical in certain circumstance, at least for the gnome one....Ouch, the rest is not really that impractical they look just like your typical [warhammer](https://cdn1.epicgames.com/ue/item/Historical%20Warhammer%20Pack_Featured-894x488-bc5fa8b7482cbca3039882e2debc4442.png) and [mallet](https://en.wikipedia.org/wiki/Mallet) since i assume the example is for one hand, otherwise [maul](https://en.wikipedia.org/wiki/Sledgehammer#Post_maul), but i agree that some of them are mislabeled from their real counterpart), and i am not scientist so i cant explain it in scientifically way but they pretty much explain it well.
also double bit axe did exist too as a throwing axe, to give a chance for the edge to land and bite on the target or bounce off if failed to land on the edge part, outside of adding extra weight, especially using spin or rotating technique.
[](https://i.stack.imgur.com/Qjpum.jpg)
so its not necessary like what nosajimiki mentioned.
now regarding the weapon design, i would suggest to not make the hammer face flat but a bit bumpy or circular or turn it into a pick to give a better puncture or bite.
[](https://i.stack.imgur.com/Oyc6f.jpg)
from:[https://www.amazon.com/TEXTURING-HAMMERING-CHECKERED-PATTERNS-NOVELTOOLS/dp/B010OPOAA6](https://rads.stackoverflow.com/amzn/click/com/B010OPOAA6)
[](https://i.stack.imgur.com/0Yilb.jpg)
from:[https://www.todocoleccion.net/antiguedades-tecnicas/martillo-dos-bolas-probablemente-chapista-cabeza-11-5cm-aprox-largo-21cm-aprox~x41397613](https://www.todocoleccion.net/antiguedades-tecnicas/martillo-dos-bolas-probablemente-chapista-cabeza-11-5cm-aprox-largo-21cm-aprox%7Ex41397613)
(not necessarily to design it like that, just the face part, i hope you get what i mean)
also for the shaft, if you want to add extra punch to it, you can make the shaft a bit bended, think boomerang with one of the end with the hammer head, this can at least ad extra leverage in hooking technique, though i am not suggest it for mallet or maul head, due to their general flat and wide surface dont give a good dig or bite to it even in melee combat for this shaft design.
both can work for one and two hand type.
here an example image base on axe one (dont take that image too literal)
[](https://i.stack.imgur.com/EGrmM.jpg)
from:<http://www.hurstwic.org/history/articles/manufacturing/text/viking_axe.htm>
also you can keep the double axe design too, just keep the edge blunt and keep the shaft flat or overall flat to turn it into hammer boomerang if you want, like this video.
<https://www.youtube.com/watch?v=5HgYpt-I7-k>
and also i wont suggest throwing the hammer against shield user though, especially center grip one, it wont give much impact to them, unless you follow nosajimiki design, but it doesnt guarantee it will bite on their shield and stuck there either (its to make the shield unwieldy due to the weight), which is most of the purpose of throwing weapons for warfare, beside throwing stone is cheaper anyway.
and as far as i know, D&D weapons are generally not for warfare anyway, theres many real bizzare weapon for duel combat or personal combat and most of them not necessarily practical (although it work for their martial arts which also not necessarily practical too).
[Answer]
# [Actual throwing Hammers](https://en.wikipedia.org/wiki/Hammer_throw):
FRAME CHALLENGE: A thrown two pound hammer (especially with a short haft) like in the picture above is pointless. Throw a brick - and I don't see that as a regular weapon. If you want a hammer thrown to be a weapon, it would need to be heavier. A thrown hammer isn't cutting, or penetrating, but must inflict blunt-force trauma (assumedly through armor). Wielded as a melee weapon, it would be functionally like a [kanabo/tetsubo](https://en.wikipedia.org/wiki/Kanab%C5%8D) or a [godendag](https://en.wikipedia.org/wiki/Kanab%C5%8D) (but you want it to be a hammer).
This video has a hammer with a similar construction used -
[1984 hammer Throw commercial](https://www.youtube.com/watch?v=OYecfV3ubP8)
[](https://i.stack.imgur.com/RSyP4.png)
* **Olympic throwing hammer:** This is the gold standard (pardon the pun) for throwing hammers, adopted and modified from the [Scottish Highland Games](https://en.wikipedia.org/wiki/Highland_games). To throw a hammer held in one hand, it's not that different than throwing anything heavy. But to optimize range (and impact), you need a heavy head at one end and a long shaft, thrown with both hands and plenty of rotation. Ideally, there's a horizontal handle at the far end to allow easy holding while spinning up to build momentum. Modern "hammers" don't even have a solid shaft, but instead will have a rope or chain/cable to allow the hammer to wiggle a bit while spinning. In fact, a hammer with no shaft will also be much easier to carry since a rope folds up. Throwing hammers are around 16 lbs.
While an actual Olympic one might be a bit too heavy for a fight, you would need something with real weight to carry a blow hard enough to seriously hurt someone. At the very high end, a kanabo runs about 15 lbs, which is heavy for a melee weapon - yet they were used to crush armor (and a big hammer would do that). A godendag ran around 5 lbs, and was actually pretty nimble. A hammer like this isn't going to be nimble, but a crude tool to mash people with. If you want something graceful, buy a sword.
[](https://i.stack.imgur.com/TVKlI.jpg)
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How far into the ground is it practical to build? While cities go both up a lot & down a lot the down is mostly infrastructure, with nothing like houses, shops, factories, etc. down there. So how far down would it be practical to have humans inhabit. The technology level is near future. It doesn't have to be economically practical but it does have to be practical *enough* to get a government to build it in a semi-centrally planned economy. (The government allows corporations to exist but can do anything a corporation can as well & has enough money to put down as many subsidies as it wants) It would be preferable to have a solution that *doesn't* eliminate building significantly up as well. It doesn't have to resemble how things are done above ground but it shouldn't be a problem from people to move in from the surface without issue.
Edit: when i say practical i mean practical in an urban planning sense
[Answer]
It is almost always more convenient and cheaper to build cities on the surface rather than underground. However there are examples of extensive underground habitations that could be classed as cites such as the one in Montreal Canada which in part was built to provide some protection from the winter weather:
<https://en.wikipedia.org/wiki/Underground_City,_Montreal>
This is only a few tens of metres below the surface.
If finance is not a restriction then it would still be more convenient to build near the surface purely because that is where existing infrastructure, agriculture and transport links are most likely to be.
If you are determined to build further underground then it would certainly be possible. But the deeper you go the more expensive and less practical it would become. Within a few hundred metres of the surface it would range from a novelty to rather inconvenient nightmare.
Below that the difficulties would mount rapidly depending on the nature of the ground. Such things as ensuring that the structure was resistant to water pressure, the removal of waste heat, circulation of fresh air, lift capacity and stability to earthquakes.
Down at a thousand metres below the surface building a city would be totally impractical if not entirely impossible. Only deep mines exist at these depths and temperature becomes an increasingly difficult problem.
The deepest gold mine reaches more than 4000m below the surface but has a rock surface temperature of 66 degrees C. Men can only work in such mines due to the use of thousands of tons of ice and forced ventilation on an epic scale. Even when cooled by such means the temperature is still around 30 degrees C.
<https://en.wikipedia.org/wiki/Mponeng_Gold_Mine>
[Answer]
**100 meters for things built for humans. 1000 meters for mines.**
[](https://i.stack.imgur.com/29iTR.jpg)
<https://www.groundworkscompanies.com/about/articles/how-far-underground-are-skyscraper-foundations/>
image edited by me.
Subways can be as deep as the foundations of these huge buildings.
<https://blog.ferrovial.com/en/2016/12/why-do-some-subway-stations-seem-more-like-a-journey-to-the-centre-of-the-earth/>
>
> But if you think these stations are rather like descending to hell,
> they are nothing compared to the Arsenalna underground station in Kiev
> (Ukraine). Its escalator will take you down to the centre of the earth
> in order to get on one of its trains, which run more than 100 metres
> below ground. It is the deepest underground station in the world.
>
>
>
These structures built for humans are puny in comparison to mines. Mines are more than ten times as deep, and really big.
[](https://i.stack.imgur.com/lJYWW.jpg)
[source for image](https://panethos.wordpress.com/2020/03/05/enormous-underground-salt-mines-of-north-america/)
<https://www.syracuse.com/weather/2015/12/cargill_salt_mine_2300_feet_beneath_watkins_glen_helps_keep_cny_roads_clear.html>
>
> At 2,300 feet, the mine is the deepest in North America. That's deep
> enough, Wilczynski notes, to nearly stack two Empire State buildings,
> which has a roof height of 1,250 feet. The mine shaft is at Portland
> Point, on the eastern shore near the south end of Cayuga Lake, and the
> mine itself stretches north along the lake to a mile past Taughannock
> Point, the company's website says.
>
>
> The mine stretches more than seven miles underground, tapping into a
> vast salt deposit that stretches from Pennsylvania to Ontario.
>
>
>
The deepest mine in the world is the [Mpoeneng gold mine](https://www.nsenergybusiness.com/projects/mponeng-gold-mine/), which is working on becoming 4300 feet deep.
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In sum, it looks like the deepest structures purpose built to house and move humans are 100m / 300 feet deep. Mines, though, are built because of different practicalities - miners are retreiving things that are underground and so go much deeper to where those things are. The farther down you go the trickier ventilation gets, but there is no reason why a city cannot use old mines that happen to be convenient for expansion - both Paris and Kansas City do.
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If You not count economic then main problem will be temperature. Oxygen can be solved by hydroponic, electricity by nuclear/fission reactors. But temperature - heat is in and is produced and need to be taken out to somewhere. In average earth temperature rise 1' per 33m.Some places per more than 100m some even 1' per meter. In average on equator You need lots of cooling devices to have comfortable temperature even if close to surface. At Europe can dig up to 400-500m before need cooling. At South Pole can go down for 2000m with only basic devices. That may be bigger problem if put some heat emitting devices like generators or computers on same level as humans or even close to them.
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You can have some of the advantages of an underground city by building a multistory surface city inside one large building. Thus the entire city can be covered by a roof designed to keep out danerous levels of radiation, for example, and people will not have to go outdoors and face the bad weather if the entire city is inside a single building,etc.
So an entirely self enclosed city might extended a number of levels underneath the ground level, and several times as many levels above the ground level, if it is built as one large building.
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My project concerns a world "A", that is a moon of a gas giant "Jovi", in a solar system with no other planets to speak of and a host star much like our own.
"A" is Earth-sized, has no magnetic field of its own, and keeps an atmosphere that is Earth-like in composition and density. It is tidally locked to "Jovi".
"Jovi" has few decided properties apart from being a gas giant roughly the size of our Jupiter.
Now, for "A" I would like its 'antijovian' hemisphere (the hemisphere facing away from "Jovi") to be habitable for humans, while its 'subjovian' hemisphere (the hemisphere facing toward "Jovi") to be uninhabitable, and far too deadly to even cross unprotected on foot - all because of some type of radiation or other effect emanating from planet "Jovi".
Problem is, I can't think of the right set of circumstances that would produce this specific division.
What comes closest to what I want is Jupiter's moon Io, that is bombarded with radiation from Jupiter's radiation belts on its trailing hemisphere, in contrast to very different 'wheather' on its leading hemisphere. But I want a division specifically subjovian/antijovian AND specifically deadly/habitable respectively.
Could someone please come up with any kind of scientifically plausible properties of this planetary system, particularly properties of the gas giant "Jovi", that would result in the type of division of moon "A" between habitable and unhabitable hemispheres as I described?
Cheers
PS: I thought leaving "A" without its own magnetic field, and instead have it [rely on Jovi's magnetic field](https://worldbuilding.stackexchange.com/q/125026/43816), would make it easier to think of a way to have part of it be prone to deadly radiation
[Answer]
**Thermonuclear storms**
<https://en.wikipedia.org/wiki/Stellification>
>
> Stellification is a theoretical process by which a brown dwarf star or
> Jovian-class planet is turned into a star, or by which the luminosity
> of dim stars is greatly magnified.
>
>
>
For your scenario I pick the 3d of three scenarios offered: sputtering deuterium fusion.
>
> Thermonuclear ignition. It is well established that Jovian-class
> planets consist mostly of hydrogen and helium.[2] It is theorised that
> concentrations of hydrogen and helium isotopes at certain depths of a
> gas-giant planet may be sufficient to support a fusion chain reaction,
> if sufficient energy can be delivered to ignite the reaction. If a gas
> giant has a layer with a large concentration of deuterium (>0.3%),
> ultra-high-speed (2×10⁷ m/s collision of a sufficiently large asteroid
> (diameter > 100 m) could ignite a thermonuclear reaction.[3]
>
>
>
Your giant with stellar aspirations sometimes undergoes extensive thermonuclear reactions in the deuterium level of its atmosphere. Maybe triggered by asteroids? Maybe by endogenous lightning, or events taking place farther down. They are atomic storms, propagating in spreading circles across the gas giant surface. The reaction and consequent heat expands the atmosphere and then the lights go out. But while the storm is going on, tremendous amounts of radiation, ionizing and otherwise, shine from the planet as it tries to become a star. You want to be on the shady side of the moon when that happens.
Sometimes a couple of days go by between thermonuclear storms. Maybe you can get out on the bright side and back before one comes? Shake a leg!
[Answer]
I am not sure that the following can be really a science based answer, or rather a sciency one.
* The radiation belt produced by Jovi induces a lot of charges into the upper atmosphere of A
* The ground of A has a high piezoelectric capability
* The gravity pull from Jovi triggers other charges on the ground
* As a result of the increased charges on the ground and in the high atmosphere, there is an humongous shower of lightnings on the Jovi side.
As a practical result, it's very likely for anything to be thunderstruck within seconds, with easily imaginable results.
[Answer]
**Just shadow - and cold.**
A orbits close to Jovi, when compared to Jovi's size, and A and Jovi's orbits are in the same plane. Therefore, nearly half of time A is in Jovi's shade. That's not a problem for the outward side of A, because it's facing the sun when it's not in Jovi's shadow, producing a reasonable day-night cycle.
However, the Jovi facing hemisphere of A alternates between being on Jovi's shadow and facing away of the sun. In other words, that face has a sun eclipse lasting most of the day, while the outward facing hemisphere the eclipses happen at night and can't even be seen.
Additionally, Jovi is very dark - pitch black if you want - , so its albedo doesn't compensate much for the lack of sunlight, and it doesn't have enough internal heat to produce significant radiation.
The result will be that the Jovi facing hemisphere will be a lot colder than the outward facing one - way colder than Earth's poles. Going there may be possible with modern technology, but surely it is not somewhere you may want to live.
[Answer]
If we get rid of "tidally locked", then:
# spores
As "A" rotates, at some point at or soon after "Jovi"-rise, all the native plants give of a large quantity of spores. These function as a cross between pollen and seeds. Unfortunately, they find human (and most Terran) lungs be an ideal growth condition. If you get the spores in your lungs, you are dead within days.
Fortunately, the spores don't last too long. They tend to be dead by "Jovi"-set. This may be a result of radiations, and lack of "Jovi"-light, or maybe they just don't stay viable that long.
The spores are also easily filtered, allowing simple masks and filters on buildings. Decontamination of someone coming inside is harder, but not impossible.
As a twist, the spore release may be conditional on weather, making spore conditions an important part of the weather report.
# and if it is tidally locked
Well, spores could still work, but would only be found on "jovi"-side vegetation, and might not use a concurrent release system.
### on "tidally locked"
If "A" is tidally locked, you just occupy one hemisphere, and the deadly side is not a significant factor in peoples lives.
[Answer]
The Jupiter-facing sides of its nearby moons are already uninhabitable (for human-like life) due to the high ionizing radiation spewing out from Jupiter. There are probably some simple and hardy bacteria and microorganisms which can survive this, but it's a perfectly plausible reason to not have anything more complicated.
[Answer]
The only kind of radiation a gas giant would emit that could cause this kind of effect would be heat. Large gas giants could be hot enough to glow dull red, heated by radioactive decay and gravitational contraction...a giant radiant heater in the sky, adding its effect to that of the local star.
The effect wouldn't be sharply defined, but it's plausible that liquid water would be unable to exist where the gas giant is high in the sky, while the far side would be Earthlike. Weather conditions might make permanent inhabitation of the boundary impossible, with the hot spot being completely unsurvivable without protective equipment.
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I have a cosmos where FTL travel is via an alternate dimension. The problem is when you return to our universe, you find yourself at the right destination, but a completely different parallel world from where you started.You can't control which parallel universe you end up in, so you can never go home and never go back. Technological advancement is stifled because no one wants to spend a lot of research money inventing stuff that may have already been invented elsewhere. Currency is worthless and you can only bring valuables you can keep on your ship as you journey. What easily transportable valuables would people want retain between various Earths or colony worlds and be paid in?
1. Assume most ships are large and cheaply made, intended to establish colonies and dump excess population. Alternatively, some are self-financed by rich starting crew members who live permanently aboard. Mineral resources are an obvious choice, but our crew has a smaller ship originally built to survey new stars and is small.
2. Patent laws would be unenforceable, since the travellers would never go back to where the things were invented. Most places would have similar technology after the initial flurry of interplanetary cultural exchange. I was already assuming geological surveys wouldn't vary much and the crew could go back to a place over and over selling the same data until other surveyors saturated the market.
3. Panspermia: There is little alien life, and what there is would be simple and much like primitive Earth life. On the upside. worlds are not severely alien, and don't require extensive terraforming.
4. Close similarity. Most worlds are similar in basic physics and at least related historically. Sure, here the Nazis won WWII, and here the soviets ruled the world while in another the only differences are cosmetic - you can meet yourself and swap stories about your childhood, never even figuring out the difference.
[Answer]
**Precious Metals.**
In order for someone to be able to exist at all in different universes, the laws of that universe have to be the same (or very, very, very close) so that the approximate elemental abundances will remain roughly the same from one universe to another.
Elements which are rare (really rare) will retain their value from place to place. Elements which are relatively short lived radioactive (e.g. half lives in the tens of thousands of years order of magnitude) will retain a good value while also being reasonably stable in the short term as a medium of exchange.
This is essentially what we already do on Earth. Commodities are traded on a very organized market in things like precious metals.
So this is pretty straight-forward.
Now a cautious traveler would probably not use radioactive elements. In many places on our Earth (practically all of them) possession of many radioactive elements is criminal without government permission. So a traveler popping into the wrong universe is going to find themselves treated as e.g. a terrorist.
So probably the things to have in stock are essentially the same as [Wikipedia list here](https://en.wikipedia.org/wiki/Precious_metal) :
* Rhodium
* Platinum
* Gold ( big surprise there :-) )
* Palladium
* Iridium
* Osmium
Roughly in that order of preference.
You can't really go wrong with Gold, although value fluctuates from time to time. It's also dense and easy to transport in that sense.
[Answer]
People would be given transferable credit between dimensions based on uninvented technologies or entertainment that they bring back from alternate dimensions. Imagine traveling to a world where the *Star Wars* series don't exist. A person who brings back copies of those films could receive large amounts of credit.
Ships would try to bring as many popular items with them as they can when they travel, because in the case that they do not exist in the alternate dimension, they would make large fortunes. We would probably see an appraisal system when experts in the field in which the new objects classify in would judge the worth of the technology. Credit would be given based on how "good" they judge the items to be. After the government judges the item, it will bid off the licensing rights to companies who are interested in acquiring it.
All credit from one dimension would be usable in another dimension, subject to purchasing power parity adjustments. The credit would likely be paper money or coins made out of inexpensive metal rather than credit/debit cards (because bank accounts are not trackable interdimensionally). Coins made out of precious metals would **not** work because the price of those metals would vary from dimension to dimension.
To adjust for purchasing power parity between dimensions, a government signed certificate with a proprietary hologram would indicate the current prices in credits of about 120 consumer goods (based on the UBS's basket to calculate purchasing power parity between countries) in one dimension (ex. price of 100 grams of rice). This document will be required to be brought each time a person travels to another dimension to allow the new dimension to calculate how much "new credit" the person will receive.
Because people in a different dimension would not know of events happening in another, extensive background checks would become mandatory before a person could enter a ship to travel into another dimension. Without these background checks, a person with a previously good financial record could get a loan in one dimension and hop into another and get away with it. People would only be allowed to move to another dimension if they do not owe any money (since you can't go back to the old dimension to pay it off). A bank account must be closed in one dimension and all the money taken off of it before traveling to the next dimension (since interdimensional monetary management is not possible).
[Answer]
Assuming that all of the alternate dimensions are physically similar to ours and differ only in “detail” of civilisation / history then the obvious currency is physical gold.
Gold was used historically as a currency and under pinned the whole financial system up until 1971. The gold that the Pharaohs dug up thousands of years ago is still valuable today whereas paper money eventually becomes worthless.
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[Question]
[
In the game Mass Effect 3, several planets are invaded by scores upon scores of hostile aliens, who have enough resources to spread their forces over an entire galaxy and still be largely unstoppable. You have to do a mission on the moon of one of the invaded planets (one which was as populated as Earth), and you can always see the orange-blotted surface looming behind everything you do. It is a chilling view.
[](https://i.stack.imgur.com/c2Lxz.png)
Is it realistic though? If the attack is big enough to cause fires the size of countries, wouldn't said fires and the attack also spew up enough clouds and dust to hide them from view?
The aliens in question do use laser weapons which may explain the light, but they are red lasers, not orange as seen in the picture. Cracking the crust to reveal lava is also not something they do. I am therefore assuming that what you see is burning cities.
So concretely, if a city or a country was on fire, would you see it from space? Or are such fires not luminous enough to get through the smoke they emit? And, what *would* you notice about a planet invaded globally, without turning on the radio and checking in on them?
[Answer]
You *can* see fires from space, but even really, *really* big fires are usually kinda small by the standards of a planet.
Moreover, blobs of fire like that won't last very long because the fuel in them will be exausted and what you'll get instead is a wall or front of fire that is blown downwind until it reaches somewhere that's too damp (like the sea) or has insufficient fuel (like desert or some kinds of grassland) at which point it will burn out.
Finally, burning stuff often produces smoke, and places with lots of orange flames from carbon-bearing compounds being oxidised is going to produce a lot of soot. Thick, sooty smoke does an excellent job of blocking visible light underneath, eg. flames.
Here's a picture of bushfires in Australia:
[](https://i.stack.imgur.com/9lUd8.jpg)
(source [Discover Magazine](https://www.discovermagazine.com/planet-earth/the-years-top-images-of-earth-from-space))
Just looks like a wall of clouds, doesn't it? And this is quite zoomed in... seen from a higher orbit you'd easily miss it if you didn't know what you were looking for/at.
You *can* sometimes see the flames, but you won't seem them for long unless there's a lot of fuel and local winds are keeping the air clear. You are unlikely to see something like the image you've supplied without some form of image enhancement... IR-sensitive vision or cameras ought to do it. Even exposed lava will cool and go black quickly, and holes in planetary crusts are likely to produce a lot of fumes and ash in short order even assuming that the mechanism that produced them did not (which seems a little implausible).
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[Question]
[
*For a certain reason, I needed two habitable similar earth-like planets very close to each other. After various information gathering, I gave up on double planet and gas giant moons, because tidal forces would be too high. Eventually, one solution offered itself - planets around each of two binary sun-like stars.*
Now, I have two similar planets orbiting two similar stars in binary star system, both around 1 AU from their own star. Now in this [post](https://worldbuilding.stackexchange.com/questions/25166/orbiting-one-star-in-a-binary-system-what-are-the-effects-of-the-second-star-on), it has been answered that with stars orbiting at ~ 100 AU, everything seems fine. But my goal is to put the two stars closer, as close as possible without causing too much mess, ideally 25-30 AU range, but would like to know if even less is possible. My main concern are tidal forces, but there might be other factors I am not taking into account.
**So, how close can we put two sun-like stars together for my planets to remain Earth-like?**
*Yes, I am aware that at those distances, second sun would be a very bright, so bright that it would be possible to see during the day, (as for example, at 25 AU, you'd get 500~600(24x24) times less intense light from second star than from the star you orbit, which is still 800 more than Earth gets from the moon). That is one exception to Earth-like standard I'm willing to concede.*
[Answer]
I don't know why Fabius Maximus thinks that tidal forces would be too strong in a double planet or a a habitable moon of a gas giant planet.
Part One of two: Two habitable planets orbiting the same star.
But If Fabius Maximus thinks that is the case, the next logical step would be to have two habitable planets orbiting the same star in different orbits, close enough together to both be in the habitable zone of their star and have similar climates.
In old fashioned science fiction stories from the first part of the 20th century, it was quite common to depict Venus, Earth, and Mars as all being habitable planets within the Sun's habitable zone.
Modern astronomers still tend to believe that it is possible for more than one planet to orbit in the habitable zone of a star and thus have temperatures suitable for life.
Of course, from time to time a different team of scientists will team up to calculate the inner edge, or the other edge, or both, of the Sun's habitable zone. Thus there are several different estimates of the size of the Sun's habitable zone.
In this list here:
<https://en.wikipedia.org/wiki/Circumstellar_habitable_zone#Solar_System_estimates>[1](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone#Solar_System_estimates)
There are some widely varying calculations about the size of the Sun's habitable zone.
Hart et al in 1979 made the narrowest estimate of the Sun's habitable zone, between 0.95 AU and 1.01 AU. That estimate would make it very improbable that any star could have two planets in its habitable zone.
Kasting et al in 1993 made the most commonly used estimate of the Sun's habitable zone, with a conservative zone between 0.95 and 1.37 AU, and an optimistic zone between between 0.84 and 1.67 AU. It would be much more probable to have two planets orbiting in Kasting's conservative zone than in Hart's, and more probable still for Kasting's optimistic habitable zone.
Other estimates put the inner edge of the habitable zone as far in as 0.38 AU (Zsom et al, 2013) and the outer edge as far out as 10 AU (Pierrehumbert and Gaidos, 2011).
Astronomers have discovered hundreds of systems with more than one planet, and those systems vary widely in their orbital and other characteristics.
The orbits of Kepler-70b & c are separated by only about 0.0016 AU or 240,000 kilometers, and it is possible that there could be a third planet orbiting between them.
The orbits of Kepler-36b & c are separated by a larger absolute distance but a smaller relative distance, with the orbit of Kepler-36c only 11 percent wider than Kepler-36b.
<https://en.wikipedia.org/wiki/List_of_exoplanet_extremes>[2](https://en.wikipedia.org/wiki/List_of_exoplanet_extremes)
The star TRAPPIST-1 has four potentially habitable planets in its habitable zone, and they orbit very close to each other.
>
> The orbits of the TRAPPIST-1 planetary system are very flat and compact. All seven of TRAPPIST-1's planets orbit much closer than Mercury orbits the Sun. Except for b, they orbit farther than the Galilean satellites do around Jupiter,[41] but closer than most of the other moons of Jupiter. The distance between the orbits of b and c is only 1.6 times the distance between the Earth and the Moon. The planets should appear prominently in each other's skies, in some cases appearing several times larger than the Moon appears from Earth.[40] A year on the closest planet passes in only 1.5 Earth days, while the seventh planet's year passes in only 18.8 days.[38][35]
>
>
>
The orbit of TRAPPIST-1e is only 1,050,000 kilometers wider than the orbit of TRAPPIST-1d.
The orbit of TRAPPIST-1f is only 1,380,000 kilometers wider than the orbit of TRAPPIST-1e.
The orbit of TRAPPIST-1g is only 1,250,000 kilometers wider than the orbit of TRAPPIST-1f.
<https://en.wikipedia.org/wiki/TRAPPIST-1#Planetary_system>[3](https://en.wikipedia.org/wiki/TRAPPIST-1#Planetary_system)
The average distance of Earth from the Sun is defined as 1 Astronomical Unit, or AU.
If you make the star in your solar system exactly as luminous as the Sun, you could put one of your habitable planets at a distance of 0.96 AU and the other one at a distance of 1.0656 or 1.070 AU. The inner planet would receive slightly more heat from its star, and the other planet would receive slightly less heat from its star, than Earth gets from the Sun. The orbits of the two planets would be separated by about 16,170,000 kilometers.
Part Two of Two: Two habitable planets orbiting two different stars in the system.
In a binary or double star system, there are two possible types of orbits for planets. One is a circumbinary or P-type orbit, where a planet orbits around both of the stars. The other is an S-type orbit where a planet orbits around one of the two stars.
Since the luminosities, masses, and orbits of the two stars in a binary can vary widely, there are many binary systems where a planet could not have a stable orbit in the habitable zone of either star or around both of them. But there are many other binary systems where planets can have stable orbits, either P-type or S-type, in a habitable zone.
The OP asked for a binary system with two habitable planets in S-type orbits, one around each star. That is certainly possible. It has been calculated, for example, that planets could have stable orbits in S-type orbits with the habitable zones around both Alpha Centauri A and Alpha Centauri B.
According to one list, the closest known distance between stars with a planet orbiting one of those stars is about 12 to 17 AU, with a planet orbiting about 0.7 AU.
<https://en.wikipedia.org/wiki/List_of_exoplanet_extremes>[2](https://en.wikipedia.org/wiki/List_of_exoplanet_extremes)
<http://www.openexoplanetcatalogue.com/planet/OGLE-2013-BLG-0341L%20B%20b/>[4](http://www.openexoplanetcatalogue.com/planet/OGLE-2013-BLG-0341L%20B%20b/)
<http://ogle.astrouw.edu.pl/cont/4_main/epl/ogle_0341/ms.pdf>[5](http://exoplanet.eu/catalog/ogle-2013-blg-0341l_b/)
In my opinion, it would probably be safe to have the two stars in the system have a nearest approach of about 10 to 20 AU, and each have a habitable planet orbiting it at about 1 AU, as well as other planets in S-type orbits around either star, and possibly other, not habitable, planets in P-type orbits at great distances from the two stars.
And of course there are various scientific discussions about which separation of stars is best for long term stable planetary orbits.
<https://arstechnica.com/science/2013/01/binary-star-systems-make-for-unstable-planets/>[6](https://www.aanda.org/articles/aa/pdf/2005/16/aa0238-04.pdf)
<https://www.aanda.org/articles/aa/pdf/2005/16/aa0238-04.pdf>[6](https://www.aanda.org/articles/aa/pdf/2005/16/aa0238-04.pdf)
[Answer]
I don't think tidal forces would be much of a problem. Our sun is responsible for roughly a third of the tidal forces felt on Earth, and if the other star is 25 AU away, the nearer planet would receive 1/625 the tidal forces from that. It will also receive 1/625 the heat and light from the farther sun than from the nearer; not enough to significantly change climate.
It is likely that both planets will be in orbital resonance with the orbits of the stars around each other, as such orbits have greater stability. Two sun-sized stars orbiting their common center of gravity in circular orbits at a distance of 25 AU will have an orbital period of ca. 32,250 days or ca. 88 years. Since your planets, in order to be Earth-like, must have orbits close to one year, there are many available resonances, including 1:88. Hence, I don't foresee any major problems with having the suns 25 AU apart.
You could probably have them even closer, say at 10 AU, or roughly twice the distance between the Sun and Jupiter. Tidal forces and solar infall from the more distant star will then be 1/100 that of the nearer star; still fairly negligible. The orbital period of the two stars will then be ca. 8,150 days or ca. 22 years, and you can have orbital resonance of e.g. 1:22.
[Answer]
Well, if what you want is two Earth-like planets extremely close together, the best solution would be to just have them both orbit one parent star in orbits at different distances. If you look at this chart, Earth is actually on the near end of our sun's habitable zone (<https://en.wikipedia.org/wiki/Circumstellar_habitable_zone#/media/File:Diagram_of_different_habitable_zone_regions_by_Chester_Harman.jpg>)
It could be conceivable that two planets around a sun-like star could have orbits of 1 AU and 1.2 AU and both be very Earthlike, on stable orbits relative to each other, and quite close for much of their orbits. You may want to consider this straightforward if rather plain approach.
[Answer]
I don’t think that it’s possible to give an exact answer to this question as there is no viable general solution to the 3 body problem. However in S type non-circumbinary planets (those that orbit a single star in a binary system rather than P type circumbinary which orbit both stars) it has been suggested that [the orbit of the planet should be at least 5 times closer to one star than the other](https://en.wikipedia.org/wiki/Habitability_of_binary_star_systems#Non-circumbinary_planet) to be in a stable orbit.
I suggest making it 10 times closer to be on the safer side. So if the distance between star A and star B is 10 AU the distance between each planet and its parent star can be 1 AU. Probably best to ensure that both stars and planets have near circular orbits, any significant eccentricity would mean the stars need to be further apart.
[Additional reference](http://www.solstation.com/habitable.htm#sthash.VlZPPFnh.dpbs)
With thanks to @userLTK for help from the [Astronomy stack exchange](https://astronomy.stackexchange.com/)
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[Question]
[
I've been recently looking into alternative biochemistries for life and the environments were these could be found. I already asked a question about how [ammonia oceans](https://worldbuilding.stackexchange.com/q/156915/58321) might form a while back. Today I'm interested in [formamide](https://en.m.wikipedia.org/wiki/Formamide), as according to a book I read recently, CH3NO
[](https://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Formamide-2D.png/785px-Formamide-2D.png)
is quite a decent solvent.
>
> Formamide is formed by the reaction of hydrogen cyanide with water; both are abundant in the cosmos. Like water, formamide has a large dipole moment and is an excellent solvent for almost anything that dissolves in water, including polyelectrolytes. In particular, formamide is able to dissolve RNA, DNA, and proteins, as well as their precursors. Formamide is not reactive like water. Indeed, many species that are thermodynamically unstable in water with respect to hydrolysis, are stable in formamide.
> Formamide is itself hydrolyzed by water, meaning that it persists only in a relatively dry environment, such as a desert. Desert environments recently proposed as being potential sites for the prebiotic synthesis of ribose may hold formamide as well. Since formamide boils at ~400 K, a mixture of formamide and water, if placed in the desert, would lose its water over time and end up as a pool of formamide. Within this pool, many syntheses are thermodynamically favorable: polypeptides from amino acids, nucleosides from sugars and bases, nucleotides from nucleosides and inorganic phosphate, and RNA from nucleotides. Indeed, phosphate esters are also spontaneously synthesized. This includes ATP (from ADP and inorganic phosphate), nucleosides (from ribose borates and nucleobases), peptides (from amino acids), and others.
>
>
>
All of this sounds pretty good, but as with the ammonia oceans, I'm not sure how such an environment could form naturally. The book suggest evaporation of water-formamide ponds in deserts a possibility, but I don't know of any formamide lakes in earths deserts. Also the natural formation of hydrogen cyanide seems to be unlikely, at least in the quantaties required.
I think that hot, water poor desert worlds would be the place fore formamide lakes. Due to the fact that formamide will combust in the presence of oxygen, the atmospere sould lack oxygen as well. So should the planet have a nitrogen or carbon dioxide dominated atmosphere?
**How would a hot desert planet have to be made up to form lakes of formamide? Is such a planet likely to form?** Biological solutions, like blue green alge producing oxygen on Earth, are allowed as long as they are plausible, though I would prefer geochemical solutions. Terraforming as an answer is out.
[Answer]
**Formamide can be formed by the condensation of carbon monoxide and ammonia.**
<https://en.wikipedia.org/wiki/Formamide>
A reducing planet with an ammonia / methane atmosphere is plausible. If there is also some water, one could imagine atmospheric water undergoing photolysis to generate a small percentage of free hydrogen and oxygen. Hydrogen will head up and out of the atmosphere but the oxygen might stick around long enough to get busy.
If there is a little bit of oxygen, it would probably react with the methane to form carbon monoxide. This apparently happened on the early earth.
<https://www.space.com/carbon-monoxide-indicator-alien-life.html>
>
> ... researchers used computer models to better understand the
> atmospheric chemistry of Earth about 3 billion years ago, when our
> planet's air contained very little oxygen. Microbial life was common
> on Earth back then, but animal life was a long way off. (The earliest
> fossils of multicellular organisms date to about 600 million years
> ago.)
>
>
> The team's results indicated that CO could have accumulated in
> significant quantities in those long-gone days, reaching
> concentrations of around 100 parts per million (ppm), or about 1,000
> times higher than current levels.
>
>
> "That means we could expect high carbon-monoxide abundances in the
> atmospheres of inhabited but oxygen-poor exoplanets orbiting stars
> like our own sun," study co-author Timothy Lyons, a professor of
> biogeochemistry at the University of California, Riverside (UCR), said
> in a statement.
>
>
>
A percentage of ambient CO could react with ambient ammonia to produce formamide, which precipitates out as the liquid and accumulates. I like the idea of some sort of biological catalyst for this reaction which would account for why it accumulates in a lake - the things synthesizing it live in the lake.
---
Thinking about why life forms would synthesize form amide - it is easy. The energy.
[](https://i.stack.imgur.com/y67cm.png)
<https://webbook.nist.gov/cgi/cbook.cgi?ID=C75127&Mask=1E9F>
When these life forms catch a CO and hook it to ambient NH3 they get a little bit of energy back each time.
[Answer]
'Biological solutions, like blue green alge producing oxygen on Earth, are allowed as long as they are plausible'
'Due to the fact that formamide will combust in the presence of oxygen, the atmospere sould lack oxygen as well. So should the planet have a nitrogen or carbon dioxide dominated atmosphere?'
- This contradicts the plausibility of blue green oxygen producing algae.
Okay, let's start.
* Methane should be quite abundant on this planet, your best bet at achieving this is a proficient colonization of your soil with methanogens and anaerobic methanotrophs.
* Methane available, next is ammonia, gaseous ammonia. Drying soils emit reactive nitrogen such as nitrous oxide and ammonia.
CH4 + NH3 -> HCN + 3H2
* Hydrogen cyanide available. Limited water (< 25 cm rainfall) will provide the formation of formamide by reaction with hydrogen cyanide.
* Anoxic atmosphere, presence of oxygen but not in free form.
* Finally, rather go with blue green cyanobacteria (Microcoleus) rather than blue green algae.
I'm no geophysicist but I hope I helped with chemistry and biology.
[Answer]
During the early stages of the planet, when asteroid and planetoid impacts are common, asteroids containing ammonia/carbon monoxide(in solid form) could impact the planet, releasing it into the atmosphere, or the crust, of the planet. Over time, as the atmosphere develops, the ammonia/carbon monoxide could be released and condensate, forming formamide. To accompany that, asteroids could contain formamide in itself, as it is common in the cosmos. The asteroids impact, and as the planet develops, formamide forms as oceans or lakes. The planet could be within a range of distances for this to happen, as it boils at roughly 260 degrees Fahrenheit, and is a solid at 37 degrees Fahrenheit.
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[Question]
[
[Pinocchios](https://en.wikipedia.org/wiki/Pinocchio) are known to be mischievous creatures, but **why did they evolve that way and how do they survive?**
The creature has the following properties:
* Appears to be made of wood
* Not taller than a large dog sitting on its hind legs
* Has a nose that may vastly change in length
* Is of a humanoid shape
Additionally, some have said:
* Is born by being freed from a wood-like substance
* Is known to be in contact with 'blue fairies', whatever that may be
* May one day mature to become like a human boy
* May go through a phase of imitating young donkeys
[Answer]
Everybody knows how amazing the collective intelligence of the termites is!
While some of them like to carve their nests inside the wood, a particular race of termites has become particularly adapted to life inside dead pieces of wood.
This particular subfamily, the *Coptotermes Pinocchii* has adapted so well that it can move the log of wood, for defence or search of food.
When they colonize a piece of wood, they start to gather small sticks that attack to the wood thanks to a glue-like secretion, so that they seem limbs sprouting from the wood piece itself.
Then, the members of a particular group of soldier termite - that developed tha ability to stretch and elongate their bodies - start to attach, in the number of hundreds, to the joints of the limb-like appendages. Thanks to their adaptation and sheer number, they can develop enough strenght to move the piece of wood, as if it was a bipedal being! This way they can translate their nest toward new surces of food or far from predators.
Some termites, in order to better defend themselves from predators, can add on the middle part of the wood piece other arm-like appendages (usually two, even if nests with up to five "arms" have been observed), which are used to beat birds and ant-bears.
Similarly to some butterflies, whose wings look like eyes in order to confound predators, these termites use to secrete round patches of a white substance on the top of the nest. These fake eyes can scare birds and ant-bears and keep them far from the termites when they have to leave the nest in order to forage.
In order to better areate the tunnels that these termites carve inside the wood, they also use to extrude another appendage on the top of the wood piece (somehow similar to a nose), which is used to dissipate heath. This appendage, according to the temperature inside the nest, can be retracted or extended to better tune the heath dissipation.
Another peculiarity of the *Coptotermes Pinocchii* is the ability to release a toxic substance if they feel their nest is threatened. This substance is usually harmless to human beings, but it is known to give hallucinations if somebody breathes too much of it.
In particular, strange dream-like experiences, with visions of donkeys, children or bizarrely coloured humanoids, have been reported by woodcutters and woodcarvers who had ventured in the forests in search of wood and who happened to get too close to these nests.
[Answer]
*Pinocchio Terribillis* is classified as a Euarchontoglires of unknown order, meaning while everyone is positive the species is a supraprimate is doesn't really fit in with other members of that clade -- primates, treeshrews, lagomorphs, and rodents.
Paleopinotologists have found fossilized remains of *Pinocchio Imnasis Nares*, a widely accepted ancestor of modern Pinocchio, everywhere *Homo Sapiens* and *Neanderthal* are also found. This suggests a co-evolution of the species.
Of the many strange qualities they possess, the strangest is that species has always walked upright and moved with an odd jerky and swaying motion, almost as if they were held aloft by unseen strings. This is thought to be a deceptive adaptation to confuse predators by making their motion unpredictable.
Their flesh is an inflexible fibrous material without interior bones and a thin exoskeleton similar to the excretions of the shellac beetle. This exoskeleton overs their entire body except for their noses, which need to expand and contract, which is another amazing trait of these creatures.
It's not known why they evolved the ability to grow their noses by up to 1000% in length. It has been suggested it was a primary characteristic in sexual selection, but since all three genders possess the trait that argument was the source of much controversy until the discovery of the **Pilton Pinocchio**.
That specimen, having been swallowed whole by a saber tooth tiger, its nose grew to such lengths it shattered the predator's ribs from the inside out. Suggesting that the nose is similar to puff fish spines and the psychedelic ooze produced by some species of reptiles.
There are many folk tales about Pinocchio that are known to stem from ignorance and superstition. They do not spring forth from wood. They often seek shelter from predators within trees because their fibrous nature permits them to move through them as we do through water. Stories of carving Pinocchio out of wood are misrepresentations of fact. The Pinocchio was no doubt merely hiding when discovered.
They are also excellent mimics, surpassing Ravens and Parrots, and often imitate the play of species they observed to avoid attracting attention to themselves. Herds of Pinocchio have been seen to be 'playing' at being donkeys or small boys. As they mature, their mimic can become extremely sophisticated and permit them to pass as human children. Again, this is thought to be an evolutionary adaptation to better avoid predators, since human communities are more successful at elimination external threats to their communities safety, than herds of Pinnochio are.
There is still a lot more to learn about this amazing species, and many learnings and current thinkings may not persist through the rigors of scientific inquiry.
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[Question]
[
I want to achieve the following. Jet + secret base underwater + blow up water with bomb to gain entry to tunnel at bottom of the sea, see image:
[](https://i.stack.imgur.com/qP1ly.jpg)
Say that the depth is 1000m, then Based on calculation in this [Quora-answer](https://www.quora.com/How-do-I-calculate-the-energy-required-to-evaporate-water):
>
> (4.2\*10^3 J/kgC^-1) (1 kg) (90C) =
>
> 338000 J required to evaporate 1 kg
> water from 10 degree temperature
>
>
>
Since the water is ~10 degrees
[](https://i.stack.imgur.com/BcrJM.png)
The amount of water is the volume of a sphere with radius 500m:
>
> $\frac{4}{3}\pi 500^3 = 5.24\*10^8m^3$
>
>
>
Which is lets say about 5\*10^11 kg (1L of water == 1 kg)
Giving about 170000 TJ, The energy of the detonation can be handwaved to some degree and it is not immensely\* more than our current nuclear bombs at 100TJ.
How long does the plane have before the water collapses? Will mach 1 be enough to reach the entry point?
(Vaporising the water is just something i assumed I'd have to do. I'd consider any smart physics phenomenon that can be taken advantage of to extend the duration of the wake as on topic)
[Answer]
You're not going to evaporate the water, you're you're going to displace it. That actually makes it both easier, and no more possible.
The thing with displacing the water is that the easiest direction to displace it in is upwards. In any other direction there's something fundamentally in the way.
[Operation Wigwam](https://en.wikipedia.org/wiki/Operation_Wigwam) is the closest I can find to what you're looking for, a nuclear explosion at 610m (2000ft), the deepest nuclear test ever and still the only test below 300m.
This is what your pilot will be flying into if you try this:
[](https://i.stack.imgur.com/Q7C5L.jpg)
That's the surface effect of a [32kt warhead](https://en.wikipedia.org/wiki/Mark_90_nuclear_bomb) at 610m.
[Answer]
Good news: creating a bubble that size seems emminently possible using current-day technology.
Bad news: promptly vapourising and displacing that much water, and the secondary effects of whatever means you use to do so, will result in an Extremely Hostile environment for aircraft.
You're trying to move something like 540 million tonnes of seawater out of a 1km deep volume faster than the entire ocean can flow back in. Canute got *nothing* on you.
Working out how quickly that cavity will collapse is *hard*, and alas this answer will be incomplete because I can't actually calculate it for you. Instead, lets look at the amount of energy required to excavate the cavity, and the effects it will have on the local environment.
How much energy? Well, for similar reasons, I can't give you anything other than very broad approximations, but it looks like you'll need 30-100 megatonnes TNT equivalent to form a big enough hole. I've got these numbers from a presentation on [asteroid impacts in water](https://www.mn.uio.no/geo/english/research/networks/nir/gol2009/galen_WaterImpacts.pdf). The authors didn't consider your specific scenario for some reason, but you'll see (on page 37) a brief mention of a 100m asteroid striking deep water, 66MT equivalent blast, 1.2km deep transient crater. That's a good ballpark figure. (The Operation Wigwam test that Separatrix references uses a ~30kt warhead to develop a ~100m bubble. A 1000m bubble has 1000 times the volume, and 30MT is about a thousand times more powerful a bomb, so it seems about right)
Now, quite a lot of that blast energy will go into vapourising seawater. The expansion of that steam will help push the surrounding water out of the way. Beacuse you want your cavity to reach the surface, a good deal of that steam will escape upwards. This is important, because you have just generated a (approximately) a cubic kilometre of steam which is going to rise up rapidly and mix turbulently with the atmosphere. This will result in hurricane force winds, which in the vicinity of the cavity will be *boiling, wet, hurricane force winds* (if you look at the asteroid impact presentation, it suggests hurricane force winds withing 22km, and temperatures >100C with 5km, which again, are good ballpark figures). Oh, and also radioactive. Mustn't forget that. This is not an aircraft friendly environment. You probably won't get a nuclear fireball forming, but from the point of view of your aircraft it won't really matter. Sure, these conditions won't persist, but they'll last at least as long as the cavity does, so you'll have to deal with them if you want to fly through the hole.
Finally, when the cavity collapses, you'll get all sorts of really interesting hydrodynamic effects. You'll get a jet of water formed that could reach a few kilometres into the sky. The formation of this jet will cause an intense pressure wave at the bottom of the cavity. Between this and the nuclear blast you've used to create the cavity in the first place, the chance of anything immediately underneath the cavity surviving are *extremely slim*. I hope that door and the thing it protects are very robust. Incidentally, can you rely on the door opening fast enough to fly in, and close fast enough such that everything doesn't get smooshed?
So, how quickly will the cavity collapse? It doesn't matter. Nothing will survive its flight into it.
] |
[Question]
[
Working on a near future fantasy world and am trying to work on a mechanism for magic being discovered/unlocked. My current thought, which is what I'm trying to get a feasibility check on, is that all magical energy in the solar system comes from Sol. In the far past a magic using civilization placed an object/device at the L1 lagrange point that somehow absorbs or reflects all of the magical energy that would have flowed to/through the Earth. Their reasons for doing this an unknown since almost all traces of the time before magic was sealed has been lost. The only things that survive are the occasional artifact or obscure piece of text that only now makes sense in the context of magic actually existing.
So my question is around what would be involved with placing an object at L1 and how/when would humans have discovered and/or accidentally destroyed it?
The issues that I'm aware of is that L1 is a naturally unstable point, any drift will cause the object to accelerate away from the point, either toward the Earth or Sol.
Another issue I see that will need to be addressed is that the massive amount of energy that this object is reflecting or absorbing would be exerting a force propelling it away from Sol so the object would need to be somehow using the incoming energy to keep itself in position.
So my question is about how these issues may be addressed and if there are any other issues that I'm not seeing that need to be addressed.
[Answer]
Such station-keeping will be easy if you
## Put the Structure Farther Than L1
If a strong wind is knocking you off of a hilltop, you move downhill into the wind a little bit and gravity will help counter the force. Simply move it a bit closer to the sun, just enough that the sun's **inward gravity and outward radiation pressure reach equilibrium**. Adjustments will require only minimal thrust, easily powered by absorbing some radiation instead of reflecting it all.
Now, for some other fun problems!
## It Must Be Flexible and Super-Light
A rigid structure would require incredible amounts of handwavium. It's gonna have to be wider than the earth to fully block it; across that distance, any conceivable material would be shredded in moments. A sheet-like material would have to be so thin and stretchy that it might stretch credibility, so I'd recommend something more like **a huge swarm of small reflector devices**. Either way, that much mass is going to have non-trivial self-gravity to adjust against, but it still seems feasible.
## It Can't Be Flat
A flat disc would be closer to the sun in the center, and the continual stress would require even more handwavium. It probably wouldn't be a spherical segment either; keep in mind that L1 is a [Saddle Point](https://en.wikipedia.org/wiki/Saddle_point). Objects are pulled inward in lateral directions but outward in forward and reverse, so I'm wildly guessing that it would be more conical at some radii. Regardless, the outer reaches will have less stability and require more station-keeping.
## Small-Body Collisions
It's gonna get pummeled by dust and micro-asteroids, and maybe even the occasional larger asteroid or comet. That requires self-repair, and redundancy to avoid temporary breaches.
## Remember the Penumbra
Because the sun is not a point light source, leaving earth would initially only get you into the [penumbra](https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra), so the effects would increase gradually with distance.
## Solar Dynamism
The sun is super active, and it has no solid surface. It has several layers, each with interesting properties, and its atmosphere is quite large. Also it's output varies quite a lot, and from time to time it sends out massive prominences and solar flares. The builders would've chosen a reasonably safe diameter to keep things quiet most of the time, but I'd imagine that **occasional major solar events might temporarily increase magical activity on earth**. Similarly, they had to pick a margin of acceptable failure from damage, so perhaps **a catastrophic damage event could make things get interesting as well!**
Alternatively, photons aren't the sun's only output...
## The Magic Stuff (Magicons?) Could Be More Like Electrons
The sun's powerful donut-shaped magnetic field pumps out a ton of charged particles, which would be roasting us if not for the earth's magnetism deflecting them. An object with a strong magnetic field can **deflect particles in an area much larger than itself**. Just a thought!
[Answer]
I think there's already a lot of knowledge in the comments, but for the sake of an answer here goes:
**There Are Some Issues With Stability**
As you mention L1 is unstable, so [station keeping](https://en.wikipedia.org/wiki/Orbital_station-keeping#Station-keeping_at_libration_points) is required. You also assume your object experiences a force from [solar radiation pressure](https://en.wikipedia.org/wiki/Radiation_pressure#Solar_radiation_pressure) (SRP), so it will require additional thrust/complexity in station keeping. If we assume your object is not magical (can only humans use magic?), then it will need some sort of propellant to do station keeping. Technology such as solar sails would be available to a civilization as complex as the one you suggest, but would not work to provide force to counter SRP.
So the object will require actual reaction mass, leaving a number of [possibilities](https://en.wikipedia.org/wiki/Spacecraft_propulsion#Reaction_engines). We can subdivide this into to broad categories of chemical propulsion and electromagnetic propulsion. The former describes rocket engines that use combustible fuel to expel reaction mass, and the latter describes engines that use electrical fields to expel reaction mass. Avoiding the math, I am going to say your object will do better with electromagnetic propulsion. The specific impulse (equates to efficiency) of these types of systems is much higher and thus would require less propellant for the same duration of station keeping. Plus the object is absorbing enough energy from the sun to power this indefinitely. Of course you could use nuclear reactors or some such method if this is more desirable. Also note ion thrusters are [currently used](https://en.wikipedia.org/wiki/Ion_thruster#Missions) for station keeping, among other things.
**So When Will the Object be Discovered?**
1. The station keeping will require propellant if my assumptions hold. Eventually your device will run out of propellant and magic will be unleashed upon the Earth. It is also possible that someone will spot it once it moves from L1, but observing objects inside Earth's orbit is notoriously difficult due to the fact that there is a giant fusion ball in the background.
2. Someone will venture outside the shadow of the shade. Is the moon within the shadow? If not, one of the 24 Apollo astronauts who travelled beyond low Earth orbit may have realized they suddenly had special abilities which promptly vanished upon returning to Earth. Of course they might assume it had something to do with the moon itself, but if it were noticed there's a good chance the United States (remember this is the cold war) would work hard to track down the effect.
3. There are quite a few [science missions](https://en.wikipedia.org/wiki/List_of_objects_at_Lagrangian_points#L1) that have operated at or near L1. There are four operating in that region at present. The first was in 1983. So even if someone had not pointed any instruments at L1 prior (unlikely but hard to say what they would have seen/not seen), the device would have likely been discovered by science missions. This could have happened due to sensors, gravitational perturbations, or a direct collision.
**Latest Possible Discovery**
Even if the device has enough propellant, has a shadow that covers the entire Earth-moon system, and is not spotted by any science missions, humans will eventually venture into deep space. NASA says this will be in the 2030s but there is a fair chance it could be later. Serious domestic conflict on Earth could certainly prolong the wait. However, this is your hard cutoff. Once humans travel outside the shadow, the cat will be out of the bag.
Using the propulsion issue (could run out at any time) and the deep space missions (could potentially be delayed indefinitely) as minimum and maximum cutoffs, you really don't have to bracket the discovery date. It is up to the narrative. However, to be believable, the device would likely be discovered sometime in the 20th century.
[Answer]
**The magic civilization was not trying to put the Absorber there. They were trying to throw it into the Sun.**
The thing at the Lagrange point is sentient, and magical. When it was on Earth it caused all kinds of trouble absorbing magic. The ancient civilization decided to get rid of it through the time honored technique of throwing it into the sun.
The plan backfired. Rather than continue to the sun, the Absorber wound up at L1. The flow of magic traps it there, like flowing air will trap a ball within its stream. The magic flow stabilizes the Absorber against orbital decay.
It is a good place for absorbing magic which it does, more than it ever could on Earth. Rather than a focal disruption it disrupted the entirety of magic on Earth, causing the fall of that ancient civilization.
The Absorber has been there a long time, trapped. It has been alone for a long time, staring at the stars, soaking up magic, to the point where it has become a sort of deranged demigod.
[Answer]
I feel like you're overthinking this.
**No real issues with stability**
Since this object was made by an advanced civilization sufficiently advanced for its technology to be indistinguishable from magic even without the fact of it being magic, fuel to keep its position is not at all a concern. Its bigger concern is dealing with all of the fuel it's getting.
This object is in the path of all of the magical energy coming from the sun. It's in the path of all of the light, solar wind, and solar flares coming from the sun. It therefore has all of the energy it needs to do whatever it does, including keeping itself between the sun and the earth in a fairly stable fashion, and warping cosmic winds and solar flares around it. It needs to know where the earth is to manage this, so it would know what directions would be safe to vent its excess energy - I'm thinking basically four directions, in a square arrangement, maybe around a 45 degree offset from Earth.
Of course, it can't take a noticeable portion of the solar energy heading to Earth or we could recognize it was there based on the differences in the apparent energies received by Earth and by the other planets - unless there's one of these things hiding in their L1 spots as well. But even taking an even 0.00001% of the energy from the sun would be pretty huge. And, of course, the amount of magic energy that it's blocking that we know nothing of is entirely up to you - but realistically speaking, you're probably underestimating what it would be by a large margin.
Think about how much energy you would imagine a human would have access to, unfettered by this device, from standing under the sun at noon, a single shaft of power hitting them and the square meter around them. In two dimensions, Earth has 194 million square meters of surface area pointed at the sun. I chose noon to be able to discount the incident angle. But there's also energy lost due to passing through the atmosphere, if that matters, or passing through space between L1 and Earth, if that matters. So we're talking something in excess of 194 million times what a mage could do with one square meter of power.
Except it's more than that, because it didn't show up during our manned space exploration so far, so it's covering the moon, too. Expanding that out to a disc large enough to cover both is probably not appropriate, because there's really no need to cover out of the plane of the moon's orbit. Using a rectangle area, I think it's something over 4 quadrillion times that reference mage.
**Discovery**
Such an object would definitely be discovered if/when earth deployed a space craft that intersected one of the beams of diverted power. If those beams were angled above and below the plane of Earth's orbit, it would seem that would be an unlikely circumstance. This is probably a good thing, because those beams would probably be highly destructive streams of overwhelming power.
It would probably also be discovered if we witnessed anything else encountering those beams. We're talking about at least 48 million times the power of the reference mage mentioned above would have, minus a quarter of whatever the device needed to use itself. This would probably destroy anything that it hit from too short of a range, unless it was specifically made to hit it.
But it wouldn't take that. As Ben mentioned, exploring outside of the shadow produced by the device, any astronauts would be exposed to the magic that it normally shields them from. After they noticed that there was magic in space - that there were long-term effects from what they did out there, so it clearly wasn't them just going insane - it would just be a matter of time until they investigated enough to find the answer.
It wouldn't necessarily be identified just because of an unmanned mission to L1 or beyond. Assuming space wizard technology, it could be slightly out of phase with the rest of matter, such that any such devices could pass harmlessly through it. But any life sophisticated enough to harness the magic leaving the shadow of its effects would probably have a noticeable consequence.
[Answer]
You could use the "magic pressure" from deflecting the magic as a station-keeping mechanism. Basically your device will be placed some amount Sol-ward of L1, such that the outward pressure from the deflection of magic particles will counterbalance the increased gravitational pull of Sol. Then you have control loop that adjusts the angle of deflection in response to any changes in orbit - if you move too far out, then you deflect the magic out to the sides more (doing so to opposite sides will result in the momentum imparted from the deflected magicles to cancel out,) reducing the pressure and allowing the device to fall inwards. Conversely if you move too far in, you deflect the magic more directly back at the sun, increasing the magic pressure and pushing you back out.
] |
[Question]
[
I'm designing a world with advanced life forms that use a sulphur-based biochemistry (see [this link](https://expansion.world/destination) for context). I would like to create a carbon cycle analogous to Earth, where:
* Photosynthesis transforms carbon dioxide (CO2) and water (H2O) into glucose (C6H12O6) and oxygen (O2).
* Cellular respiration consumes O2 and releases CO2 + H2O, maintaining equilibrium.
In my world, I would like:
* Photosynthesis to take methane (CH4) and sulphuric acid (H2SO4) to produce sulphur dioxide (SO2) and a hydrocarbon that performs the same role as glucose (let's call it substance X).
* Cellular respiration to consume SO2 and release CH4 + H2SO4, again maintaining equilibrium.
* Substance X would therefore need to have a molecular formula with 1×C, 6×H, 2×O (or a multiple in proportion,
e.g., 2×C, 12×H, 4×O).
* No oxygen (O2) in the atmosphere.
* No production of water in the photosynthetic reaction.
The ideal solution would be a hydrocarbon that actually exists, with a molecular formula using the atoms mentioned above. If that's not possible, what if:
* Sulphur trioxide (SO3) is used instead of SO2?
* A third, nitrogen-based gas is added (such as ammonia or nitric acid) such that photosynthesis takes CH4, H2SO4, third gas; and respiration takes SO2 to release CH4, H2SO4 and the third gas.
[Answer]
You have invented [sulfate reducing microorganisms](https://en.wikipedia.org/wiki/Sulfate-reducing_microorganisms)
>
> Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes
> (SRP) are a group composed of sulfate-reducing bacteria (SRB) and
> sulfate-reducing archaea (SRA), both of which can perform anaerobic
> respiration utilizing sulfate (SO42–) as terminal electron acceptor,
> reducing it to hydrogen sulfide (H2S). Therefore, these sulfidogenic
> microrganisms "breathe" sulfate rather than molecular oxygen (O2),
> which is the terminal electron acceptor reduced to water (H2O) in
> aerobic respiration....In terms of electron donor, this group contains
> both organotrophs and lithotrophs. The organotrophs oxidize organic
> compounds, such as carbohydrates, organic acids (e.g., formate,
> lactate, acetate, propionate, and butyrate), alcohols (methanol and
> ethanol), aliphatic hydrocarbons (including methane), and aromatic
> hydrocarbons (benzene, toluene, ethylbenzene, and xylene)
>
>
>
You do not need photosynthesis because there is enough power in sulfate to reduce methane. These creatures are the heterotrophs in your world (and ours), the equivalent of animals up in the oxic world.
You can model your plants on [purple sulfur bacteria](https://en.wikipedia.org/wiki/Purple_sulfur_bacteria). They do photosynthesis. Like plants they kick out oxidized stuff as waste; oxygen for plants, sulfuric acid for the PSBs.
>
> The purple sulfur bacteria (PSB) are part of a group of Proteobacteria
> capable of photosynthesis, collectively referred to as purple
> bacteria... Unlike plants, algae, and cyanobacteria, purple sulfur
> bacteria do not use water as their reducing agent, and therefore do
> not produce oxygen. Instead, they can use sulfur in the form of
> sulfide, or thiosulfate.. The sulfur is oxidized to produce granules
> of elemental sulfur. This, in turn, may be oxidized to form sulfuric
> acid.
>
>
>
If you think that kind of thing is cool, you are right. Read up. It is amazing and it is real.
] |
[Question]
[
**Premise:**
Earth has a magical cataclysm that pulls up new mountains, pushes down parts of landmasses, and generally reshapes Europe enough to make it unrecognizable (to the average person looking at a world map) in a period of weeks.
**Problem:**
I'm trying to stick to more 'rational' magic that obeys most laws of physics (and with zero unexplained handwavium), and all the ways I can think of to do that much geographical change would probably end up kicking up so much dust and debris that it'd choke out the sun, killing plant life, and then everything that depends on plants.
**Limitations:**
I want as few laws of physics broken as possible in the causal action, but for the result to be able to be explained entirely by physics. This means something like a magical push on tectonic plate ignoring strength/inertia/mass issues but with a result of making plates crash together and pucker into mountains like they would naturally do in response to that stimulus.
**Goal:** Make the geography/shape of Europe unrecognizable on a world map in a matter of 30 days, and have at least some of European humanity survive (while still living in Europe).
Can you think of any plausible, semi-rational ways to achieve this end?
[Answer]
By wanting as FEW laws of physics broken as possible, I am presuming you are allowing SOME laws of physics to be broken.
If this is the case, then I suggest that very localized reversals of the gravitational constant would do it.
In various areas of the Earth's crust, if gravity completely reversed, and the sections of mantle started pushing instead of pulling, the contours of Europe would certainly change. Since all of the energy was provided by gravity, or the reversal of gravity, and this 'gravitational energy source' has not really ever been qualified, quantified, or accounted for, you would be on safe ground 'conservation of energy' wise.
I mean, consider that it is posited that black holes squeeze matter into infinitesimally small areas, and cause tremendous amounts of matter to be accelerated, without really explaining where the energy is coming from to do this, except that no 'energy balance' is imbalanced, except some vague 'gravitational energy' that seems to have no source, except the 'distortion of space/time into a well', except that no energy is expended in doing so, except that the 'conservation of energy' seems somehow not unbalanced, except that maybe it has something to do with 'dark energy', except that maybe there is some form of energy we really don't know about,... Lot's of 'excepts', which sounds a lot like handwavium in itself. What if that 'well' just turns into a 'mountain', by simply inverting 'gravity'? Same 'energy source', only in reverse application. Wherever the source of 'energy' or 'method' to 'draw things together', it is the same source of energy or method that 'pushes things apart'.
Make the phenomena local, and very deep in the earth, so that material on the surface is still bound to the earth, and does not get projected into space. Water would still seek the lowest point.
**Earthquakes do not produce dust clouds**
You could still posit earthquakes on a mass scale, caused by the gravitational reversals. I do not recall any widespread dispersal of dust clouds in the air during earthquakes (certainly not to the extent of volcanic activity), so you seem to be safe in that regard. Earthquakes, no matter how extreme, are not noted for obscuring local vision, let alone the sun. Although intense, the energy is distributed over a very wide area, insufficient to give any one particle enough to overcome gravity.
[Answer]
The simplest way to do something like this semi-realistically and without the knock-on effects being *too* catastrophic is to dramatically raise sea levels. Unfortunately even melting all of the ice on Earth won't raise it enough to make Europe unrecognizable on a world map, so you will need some magical means of adding more water (i.e. portal to a water world) or displacing a huge amount of ocean (forcefield appears in middle of pacific and expands until it's displacing most of the water or something.) Maybe even changing the rotation of the earth's axis (very gently, over the course of the month) so that the equatorial bulge of the oceans is now over Europe. However you do it, get the sea level up about 200m from where they are now and Europe starts looking quite dramatically different. Obviously the effects will be catastrophic in the lower elevation areas, but the high ground should be relatively unscathed so humanity surviving shouldn't be a problem.
[Answer]
You can switch a lot of the electrons on the continent into protons.
Based off [this xkcd What if answer](https://what-if.xkcd.com/140/), changing lots of particles to the same polarity will cause them to repel and try to move apart. This change can be done with magic or simply explained by some freak particle collider accident shooting protons or electrons into the surrounding rock for more than 2,000 miles. Keep in mind that the density of the particles can be very spread out, because they will interact with the atoms already present in the bedrock.
When these particles become trapped in the rock, they will naturally repel some particles already there. If there are enough of the particles, they will shift the rock by a substantial amount. All together, this will move the bedrock of Europe, changing its shape and physical features. Also keep in mind that the density of the particles does not need to be remotely as high as in the xkcd answer, because we are not trying to create a black hole.
Unless you have a reason to choose one over the other, my suggestion would be to use protons for this purpose, not electrons. The protons have a non-negligible mass, and they won't move around as much as the electrons might. The use of a ground wire illustrates this: electricity can be conducted into the ground, and the electrons just go though the rock into wherever it is that they go. A proton will tend to stay in one place because it can't move as easily.
**Forewarning:**
I have had the problem of unfair criticism on another one of my other recent answers involving magic. As I said there and I will say here, feel free to critique the scientific part of this answer and give me feedback. Do not, however, critique my use of the magic tag. The magic tag allows a certain, if limited in this case, measure of handwaving allowed. If you have a problem with the magic tag, do not complain on my answer. Either complain to the asker, or complain about the tag itself on meta. I am allowed to use the magic tag because the asker of the question is allowing answers to use it.
[Answer]
If the cataclysm focuses on the center of Europe, and the landmasses surrounding it pull in to fill the gap of what was destroyed, then you should have surviving people, animals, plants, etc in those outer sections. I'm imagining something like the center being sucked down into oblivion and the rest being drawn to close the hole.
If you need it, perhaps the extra mass from the lost center can go down and around the surviving parts then rise up to be landfill (it will surround what is left of Europe). That land will be dead but will fill in with life within a few decades (perhaps not all microbes die, so at least plant life and insects can come back faster, which means humans and livestock can deliberately move there).
[Answer]
**Space disappears.**
There is an accident at CERN which sends spacetime ripples outwards in all directions. Each wave at its nadir vanishes an area of space: this area and whatever was in it is gone, and areas formerly separated by this space are now adjacent. These areas do not move together or rush in to fill a void - the space between is no longer a space. Each wave at its zenith adds space, which appears in between areas formerly adjacent. You can decide what is in this introduced space - perhaps the stuff from the disappeared spaces? Or maybe weird stuff from somewhere else? If from somewhere else that implies disappeared stuff from earth might have gone there and maybe might come back.
These ripples can change as you see fit, perhaps growing larger as they propagate or changing in mysterious ways. They may be a recurrent phenomenon - the rearrangement might continue to greater or lesser degrees over time.
In any case, rearranging space and what is in it is a way to alter topography without unleashing tremendous energies. Also the continuing presence / threat of the "change wave" lends energy to the story.
] |
[Question]
[
My question is rather simple; **assuming optimal atmospheric and planetary conditions, what body plan would be able to support the largest plausible land animal?**
To split the above question into a multitude of simpler ones, I could ask "How many legs would said animal have, what size and shape would they be, and how would they attach to the body? Would it have legs at all?" Similar questions could be asked about other body parts.
To clarify a bit more, I'd like this animal to be A) a heterotroph, and B) mobile - so no sessile organisms please.
If you require any further elaboration, deem the question in need of improvement, or have a question, please do not refrain from commenting. Also, it would be much appreciated if you didn't downvote without saying anything about why you did as such.
[Answer]
Short version: you are probably looking at a giant, soft sand-dollar that moves by rhythmic waves of contraction on its belly. It would eat plants mostly by either sliding over them and eating them with lots of small mouths on its belly or one extremely wide but narrow mouth with lots of tentacles or similar things that constantly shovel plants into it. It would likely have a lot of holes on its back leading to a large number of individual lungs.
Long version:
There are a few things you need to take into account:
1. Weight distribution - the weight needs to be spread out, both where the organism touches the ground and within its own body.
2. Momentum - the more mass, the harder it is to change the way you are moving. Roughly speaking, muscle strength grows with the square of body length, while mass grows with the cube of body length. So if the body length increases by ten times, strength will grow 100 times while mass will grow 1000 times. So moving around and changing direction become proportionally harder as body size increases.
3. Nutrient and waste transfer - things like oxygen and food need to get all parts of the body, and waste needs to get collected from all parts of the body. This will be harder because, again, any opening of the body will grow with the square of length but the amount of tissue that opening has to serve will grow with the cube of length.
4. Control - it takes time for signals to travel through the body. The bigger the body, the longer it takes. This means larger animals will necessarily have lower response times. A larger animal also means that there is more the brain has to control. Since limbs need to be controlled, more limbs are harder to control than fewer limbs. The more joints a limb has, the harder it is to control, etc.
5. Feeding - there is a reason the biggest animals in history have been herbivores: it is a lot easier to get a lot of plant matter than animal matter. This comes down to the [10% law](https://en.wikipedia.org/wiki/Ecological_efficiency#Ten_percent_law), which is a rough rule of thumb that states that each level in a food chain must be 1/10th the total size of the one below it.
So what we are looking at overall will be a very slow-moving organism with slow reaction times that needs a lot of nutrients and has trouble getting enough oxygen to its body. Which is consistent with your heterotroph idea. **Edit** I got hetetroph and autotroph mixed up. Comments set me straight.
Next lets look at body shape. You might think that a long body would be good to spread out the weight. But this is an area where the communication and nutrient transfer issues come into play. The longer the organism, the longer it takes for control signals and nutrients to get from where they start to where they are needed. So I think the most efficient body form would be disc-shaped, as short as possible vertically but spread out in a circle along the ground.
For locomotion, you might thing having lots of small legs would be the best solution. However, the more legs there are the more brain power is needed to control each one. So I think it would be best to have no legs at all. The best approach would be one that requires no vertical movement at all, so probably the animal would move by rhythmically stretching and contracting the muscles on its belly, like a snake or slug, creating waves of movement that carry it along. This would allow the weight to be distributed across the body's entire lower surface, and would require less direct brain control since the motions could be regulated by fairly simply brain circuits.
For feeding, nutrient transfer becomes a problem. If you are really flexible, the most efficient approach would probably be a bunch of jaws scattered over the lower surface of the body that eat whatever it comes across as it moves. Each could have a separate digestive system that provides food to areas of the body nearby.
If you want to keep to the standard bilateral body plan like most animals on Earth have, that means one mouth at one end. The mouth would probably then by pretty wide, taking up a large portion of the front end of the animal, probably with lots of small tongues, trunks, tentacles, or other sorts of protrusions from the front that mostly automatically grab anything they touch and shovel it into the mouth. This would again require less brain power, since the brain would mostly just need to tell them to start or stop. The intestines would probably be long and spread out throughout the body. Each given part of the digestive system would only pull out a small portion of the nutrients, but since it is spread throughout much of the body nutrients from the digestive system wouldn't have to travel far to reach every part of the body.
Breathing will be an even bigger issue. Breathing through the skin is right out, again since the amount of skin grows with the square of body length while the amount of tissue grows with the cube. Some sort of active breathing apparatus like a lung is necessary. But an individual lung would require an infeasibly wide "throat" to feed it, and would likely get crushed under the animals' shear weight. So it would almost certainly need a bunch of breathing tubes spread over its back, each leading to a relatively small lung close to the surface to minimize the amount of weight pressing down on it.
If the animal mostly depends on its larger size for protection, the brain would probably be somewhere between the center of the body and the front edge, closer to the center, with lots of smaller ganglia (nerver clusters) scattered evenly throughout the body to handle converting overall commands (like "move sidewise") to specific muscle commands (expand and contract this patch of skin at this rate). This would minimize the amount of time needed for signals to go from the brain to other parts of the body.
If the animal, on the other hand, has to actively defend itself, then the brain would probably be close to the front, with whatever senses and defenses are relevant being closer to the brain. There would probably be fewer, larger ganglia, with extremely high-speed dedicated neural connections between each ganglion and the brain itself, allowing some limited degree of coordinated response to attacks from the side.
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I think weight distribution is the key to success for really giant land animals, so go for lots of legs or none at all. So something like a [millipede](https://en.wikipedia.org/wiki/Millipede) with many legs each carrying but a little of its weight or a [snake](https://en.wikipedia.org/wiki/Snake) that spreads its weight evenly over a large proportion of its total surface area would be my preferred models.
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I have a temperate rainforest environment within the arctic circle of my planet. What is the feasibility of fungi storing nutrients from dead matter during the daylight hours, then erupting to create a very tall (10-20 ft. ) cap & stem/fruiting body? I'm asking because I know fungi used to get rather large in the past, with the primary example being [prototaxites](https://en.wikipedia.org/wiki/Prototaxites).
Edit: This would not happen over night but over the course of a month or several weeks!
Thanks for the help guys, y'all have given me alot of factors to help support my fungi in a realistic environment.
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**Dispersal.**
Your fungi are understory / soil saprophytes. Above them it is a thick and tangled mass of vegetation in the polar summer. No wind penetrates. If a spore is going to have a chance to find a new area suitable for growth (and not be outcompeted by its parent) it must move some distance from its parent.
Plants have this problem all the time: how to get the seed somewhere new. They have all sorts of solutions. I am not entirely clear why this is less problematic for fungi (spores are so small?) or maybe I just do not know about fungal evolutionary adaptions for this.
In any case: your fungus. If spores are released close to the ground they will land close to the parent. The higher they are released the better the chance for a breeze.
So the spore body grows, up past the plant life, pushing it aside. It grows fast, in a day or two, because it is mostly nonorganic. This spore body is largely water filled erectile tissue and maybe even gas-filled spaces - it needs to get big fast and long term sturdiness (like a plant with a place in the sun) is of no concern. The parent fungus has considerable water at its disposal and it pumps this into the spore body. This is unlike the sturdy prototaxites which did apparently persist for growth seasons, putting down growth rings like trees.
Once the tip of the fruiting body is above the mass of plants it explosively pumps its spores into the air from the tip, and collapses.
\*re dead matter during daylight hours - fungi use the night time too. Rot never sleeps.
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The best answer we can give you is *it depends on the enviroment*.
Is there any evolutionary push towards such sizes? In other words, would a fungus with such a large fuitbody tend to be more successful in its environment than another specimen with a smaller one?
And will this size be sustainable? That is, will there be enough dead matter for it to grow? Is the fungus free of the threat of animals eating its fruitbody? Can the fungus outcompete other fungi species, as well as microorganisms and carrion eaters for example, for access to nutrients?
If the answer is yes, then it is feasible. If no, then... As the creator of your world, it is up to you to decide.
It was just like that on our own planet. [Prototaxites](https://en.wikipedia.org/wiki/Prototaxites) evolved and lived on Earth for a while because their form was positively selected - then the environment changed and they went extinct. The same is true for any other lifeform.
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One way i could think of this working is that the mushroom's grow in swamps, where dead matter is laden within, or that the rainforest is heavily rich in nutrients within the soil. **Maybe the mushrooms are feeding off of roots of the rainforest trees or root vegetable-like organisms in the ground, sort of like parasitic mushrooms do**. For it becoming really big, the stem could be reinforced to hold such a large cap, but since prototaxites managed to grow as big as they did, this shouldn't be a problem.
Obviously you could just say that the mushrooms can grow to large proportions through some other new method, but that is just my two cents on the matter.
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Simple question I think, I have some Idea of the answer but would like the ol' second opinion.
Vertebrates use olfactory glands in their nostrils (or thereabouts) to sense smell, as well as the roof of their mouths in mammals. For the most part arthropods use antennae.
Currently, one major group (phylum) of animals on my alien planet has a nostril-like system (gill-like rows of slits in front of their eyes) as I assumed larger animals would likely have such a structure instead of antennae - much like exoskeletons and compound eyes. After some thought however, I couldn't definitively say that's right, especially since the reason large animals (i.e. vertebrates) all have nostrils is more likely because they all are or came from fish, which had nostrils.
*Question incoming*
Is it feasible that a large animal (e.g. a scent-reliant predator the size of a rhino) would be able to make-do with antennae-like structures like an insect? To clarify, would antennae on a large animal be equal to or less efficient/viable/useful?
*This question is in regards specifically to olfactory sensing, and not the other sensory purposes of antennae/nostrils. Also, it is not in regards to one specific species but an entire phylum.*
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Part of this would have to depend on the evolution of your creature. Modern animals have their olfactory organs inside their nose (and taste sensors inside their mouths) because they help creatures find food, and sense danger. In the very ancient past (500 MY ago) everything lived in the water, so antenna like sensor organs were fine. As creatures evolved, putting the sense organs close to where the action was (the mouth) or where you would filter larger amounts of fluid (the nose; air is a fluid) to detect even faint traces of scent molecules had great evolutionary advantages.
Insects use their antenna for scent (among other things) because they breath through spiracles along the sides of their bodies. Filtering lin large quantities of air isn't being done, so external antenna provide more surface area and are exposed to more air, providing a much better ability to detect scent molecules.
This does not necessarily need to be confined to antenna. A very ancient creature related to [Hallucigenia](http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=60) has been reconstructed with sense organs all along the feeding arms.
Meet Ovatiovermis:
[](https://i.stack.imgur.com/AWJto.jpg)
*Ovatiovermis reconstructed. It clings to high objects and uses its arms to sense food particles and capture them*
However there will also be scaling effects, after a certain point antenna cannot become larger or they could be easily damaged. As well, antenna might make it difficult to localize where scent is coming from, and of course you can't just "take a deep breath" to isolate, localize or even capture more of a faint scent.
So thinking more deeply about how the creature functions in the ecosystem will give you ideas about why it might have antenna and how it would use them.
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## Snakes (and some other reptiles) use a forked tongue for smelling
There's a real life equivalent for what you are asking:
As the [entry in Wikipedia](https://en.wikipedia.org/wiki/Forked_tongue) puts it:
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> The advantage to having a forked tongue is that more surface area is available for the chemicals to contact and the potential for tropotaxis. The tongue is flicked out of the mouth regularly to sample the chemical environment. This form of chemical sampling allows these animals to sense non-volatile chemicals, which cannot be detected by simply using the olfactory system.
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> This increased ability to sense chemicals has allowed for heightened abilities to identify prey, recognize kin, choose mates, locate shelters, follow trails, and more.
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So even for a creature with working nostrils and lungs, there is a clear advantage in having a larger, bifurcated appendage for smelling the environment. Those "feathery tentacles" nicely fit that description.
Also, while snakes have to flick their tongue into their mouth to sense anything (the vomeronasal organ - responsible for analyzing scents - is at the roof of their mouth), nothing prevents those tentacles from having the "analysis organ" right on them, rather than having to flick it in and out of their mouth equivalent.
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In your question, you said you were not interested in the non-olfactory uses of nostrils. However, I do not think they are seperable. Nostrils are used for olfactory sensing *because* they are already used for other things. Specifically, the other main usage of nostrils already involves moving air over the surface at [decently respectable windspeeds](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0059970).
And if I need to put an olfactory sense organ somewhere, the most efficient place to put it is in a location that already sees significant airflow.
1) It's easier and faster to detect chemical compounds in a highly turbulent flow, versus a still fluid. This is because it mixes much more rapidly, and your sensor only is in contact with a small fraction of the total volume.
2) It's more efficient energy-wise: You're already expending significant amounts of energy to create this airflow. Lining the inside of it with a sense organ is less costly than building some new structure to house it.
Consequently, it seems to me that organisms which breathe heavily will tend to smell with their noses. If you want your fauna to smell in some other way, give them a metabolism which does not require drawing large amounts of fuel from the atmosphere.
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Firstly, I’m sorry that this is a rather horrible question to ask!
Would it be possible to keep a whale alive whilst harvesting its fat or blubber? These whales would be living in captivity already and the community keeping them would want to use their fat as a fuel source. However, they would want to keep the whale alive so that it would keep producing fat, which could be harvested on a continuous basis, rather than having to go out and hunt a whale each time they needed more fuel.
Thanks very much!
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Yes you could liposuction them but why would you? Suddenly you need to feed said whales.
"A blue whale eats up to 3,600 kg (8,000 lb.) of krill each day for about 120 days. It is estimated to take 1,000 kg (2,200 lb.) of food to fill a blue whale's stomach. Gray whales eat about 150,000 kg (340,000 lb) of food during a 130 to 140 day feeding period - a daily average intake of about 1,089 kg (2,400 lb.)."
So suddenly instead of hunting whales, you're fishing even more to try and keep the whales fed.
If you rended down the tonnes and tonnes of krill needed, you'd have more oil than what you can collect from the whale anyway.
The whole point of whale hunting is the whales go get the krill themselves and you only have to get the whale.
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Yes, if you have technology somewhat equivalent to *Star Trek* transporters you could probably find a way to remove fat from the whales without harming them. There would definately be a limit to how much fat you could take, so you might have to feed the whales a lot so they become very fat - or would if you didn't take away some of their fat.
I remember an old science fiction story where a fat man looked slender because he kept all his fat in a suitcase, kept alive and connected to his body somehow, maybe with wormholes or something. Someone though he must have had a treasure in the suitcase he guarded so carefully and stole it.
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You milk the whale. A female whale, obviously. Whale milk is up to [50% fat](https://www.whalefacts.org/whale-milk/). Then you boil the milk (or let it sit in the hot sun) to drive off some of the water and increase the fat content even more.
You still have the problems of feeding the whale, and she'll only produce milk when she has a calf.
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My magic system is based on science. “Nothing can be done with magic that a scientist couldn’t eventually accomplish. Casting a spell is just using the Will to manipulate atoms and energies within the rules of science to create some effect.” As such conservation of energy is in play and so creating something from nothing is impossible without converting energy into mass or reverse.
**So I have two questions on how to make spells:**
1. In this magic system, how can a spell caster create a shield to stop kinetic energy (specifically bullets but hopefully whatever process stops bullets could work for slower/heavier impacts).
* The handwavium answer I have for this to simply steal the kinetic energy of the object since my magic system allows for the direct manipulation of any form of energy.
* That has problems though. Firstly, the caster now has all this kinetic energy, something has to be done with it. Secondly, I don’t understand kinetic energy well enough to figure out how that complicates the story. (If someone could give me some insight as to how stealing kinetic energy might complicate the story rather than offering an alternative answer, I'll take that gladly).
2. With this system and the rule listed below, how can a caster unleash something equivalent to a telekinetic attack?
* Since magnetism is easy enough to generate and then amplify, that is a possibility but I would like something that doesn’t care if the object is magnetic and that can affect humans even if only indirectly.
**Some more quick rules about my magic system because they may be important to answers.**
* It’s impossible to manipulate atoms/energies within another person’s aura (3-5 inches from their skin).
* It’s easier to amplify energies than suppress them.
+ to increase a magnet’s power, the energy comes from the caster and to comply with that ‘for every reaction and equal and opposite reaction’ law, the reaction is in the cost of the spell on the caster.
+ To suppress an energy still takes something from the caster but there is the addition that, they have to do something with that energy being suppressed – it cannot go back into the caster for later use.
* Atoms can be moved around at relatively little cost but to cause any sort of chemical reaction requires the same energy that would be otherwise required to catalyze it.
* Energies like electricity are easier/cheaper to manipulate than more fundamental forces (gravity, the strong force, etc).
* If there are any other rules that needs to be known ask, I have lots.
EDIT; the aura is an extension of the human will (unconscious and out of control) and as such all the atoms and energies in that field are always being touched by a person's will and can't be overridden by another person's. It's not a function of any other rule (like suppressing energy being harder than amplifying it).
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I'll try for the simplest answer.
Freeze the air around you. This way you have a proper shield and you don't have to focus on bullets, whether they are just one or many.
Like sound and light, bullets also experience refraction when they go from one medium to another. By having a layer of frozen air around you, besides having to go through much more compact air, a bullet could also be refracted away twice.
All the energy taken away from air molecules to freeze them could go into a mass of air anywhere else.
As for the retaliation attack, just throw the frozen air at whomever shot at you.
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## Momentum is the real problem…
AlexP's comment hit it right on the nose. If all Noether's conservations still apply, then energy, linear momentum, and angular momentum all have to be conserved.
Kinetic energy is the first one you have to deal with. Fortunately, it's also the easiest. Only the *total* amount of energy is conserved, and it can be freely changed from one form to another (with a bit of loss to entropy). So you could deflect it in a slightly different direction without trouble.
Linear momentum, though, is harder. You can't freely change its direction or its form; it's always momentum, and nothing can change that. Fortunately, though, momentum is proportional to $v$ rather than $v^2$, so the momentum of a bullet is much less dangerous than its kinetic energy.
Angular momentum is the last concern: if you want to deflect a bullet, you need to change its direction slightly, which requires balancing out that angular momentum somewhere else.
## …but spreading it out helps a lot.
Let's say a bullet is flying toward you. You need to deal with the kinetic energy, the linear momentum, and the angular momentum. The kinetic energy can be dealt with by changing its direction slightly, so let's not worry about that.
But now the difference between its initial velocity and its new velocity, *including direction*, causes a change in momentum. This has to be balanced out by an equal and opposite change in momentum somewhere else. (A change in momentum, notably, is Newton's definition of a force.) So perhaps our mage applies this force evenly across their entire body. Even if they wanted to stop the bullet dead in the air instead of kicking it slightly to one side, they'd only be hit by exactly the same force that the would-be assassin felt when they fired: the recoil of the gun (minus some energy lost to heat and air resistance). If they sent it straight back where it came from, they'd feel a force equal to twice the recoil.
Finally, the angular momentum: it's much harder to change something's direction when it's spinning. That's why gyroscopes stay up. A rifle will give the bullet a significant spin (angular velocity), which will make it harder to redirect. But fortunately, a bullet is small, and thus has a very small moment of inertia compared to a person. The mage could take the bullet's angular momentum into themself and feel only a very slight kick compared to the recoil of the deflection.
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If you allow this magic system to move kinetic energy around even for shields and to stop bullets, conservation of momentum goes out the window, or is made much more complicated (momentum is conserved along the psi dimension where magic moves it to, or some other handwavium).
I'm not saying that this is wrong for your purposes, I'm just saying that there are many conserved qualities in our world and that changing even one of them changes a whole lot of things.
If this is for a book, well, if the writing is good enough and you *don't* invoke science, then it could work. I've had problems with magic in the urban fantasies I've read where the author has tried to tie magic too closely to science as we know it. The better authors just say something like "magic belongs to a superset of physics as we know it" or don't even bother to explain it.
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> It’s easier to amplify energies than suppress them
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Then why is it impossible to manipulate things within a few inches of a person? This involves some sort of suppression, which is more difficult than amplification.
That's my opinion. I think you have an interesting question.
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The answer applies to both your questions: the spell caster can transfer kinetic energy from a body A to a body B.
If he has to dissipate the kinetic energy of a bullet, he will transfer it via the spell to a close by body (i.e. the water of a lake or the sand of a pit). He will basically turn motion into heat, which is also what the bullet would have ended up doing in the target's body.
On the other hand, to create a kinetic attack, he can harvest kinetic energy from a body (again, it can be a lake) and convey it to a bullet. Kinetic energy can be harvested at the expenses of the molecular motion, thus the supplying body will be somewhat colder.
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**It's all about Vectors**
Say a bullet is coming straight to your mage, simply stopping the bullet could be too much work, so instead simply change the force vecto and suddenly the bullet is going straight up.
Of course, more absent-minded mages could have some problem if they forget where their allies are.
**Living Revolver**
Here how a mage attacks, he quickly and efficiently converts chemical energy into kinetic energy, flinging small darts of steel towards the enemy.
The mages are known for carrying around small packs of alcohol, powder, or other high energy density material to use when they need.
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Your telekinetics draw off the kinetic energy into their own bodies. Consider: when I fire a pistol the equal and opposite reaction of the bullet firing is transmitted through the pistol to my hands.
Kinetic energy is $1/2mv^2$ where $m$ is mass and $v$ is velocity.
You could get away with taking the kinetic energy of the bullet into your body because it is not very massive. If I telekinetically stop a bullet I can brace myself and transmit the energy to the ground, just like if I catch a baseball. I might be slid backwards by something with a lot of kinetic energy. Stopping a moving car would send my body flying - I am less massive than the car and so on absorbing its energy I would move even faster than it was moving. But a team of us together could stop the car.
Likewise if I telekinetically move a ball, I confer that kinetic energy - maybe by swinging my arm as though I threw it. Maybe I run full speed and when I transfer my energy to the ball I stop and it goes.
This opens the possibility of a trick for stopping the car. I absorb its energy and go flying. Then I confer my kinetic energy back to the car (or something else). My body stops moving and the car goes off in a different direction, with a substantial fraction of its original speed (kinetic energy).
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# Its all about thermodynamics
Everyone wants to talk about physics, because you learn that stuff in, like, 8th grade, and the equations are pretty simple. Momemtum and energy are conserved, etc.
But the real problem is with thermodynamics. No energy transfer is going to be without loss. Consider the equation for the [efficiency](https://en.wikipedia.org/wiki/Heat_engine#Efficiency) of a [Carnot engine](https://en.wikipedia.org/wiki/Carnot_cycle#Efficiency_of_real_heat_engines):
$$\eta\_{max} = 1-\frac{T\_c\Delta S}{-T\_h\Delta S}.$$
If you are a human operating at 37 C; and you happen to be in an enviornment where nothing else is above 37 C (a pretty common occurance if you are outside in the winter, for example), how are you expected to draw energy from your environment? If you can't draw energy, how are you going to expend that energy using telekineses or a kinetic shield? Likewise, if the bullet is over 37 C (which is probably is after coming out of a gun), how can you transfer energy to it?
Even if you can find some slightly warmer objects to absorb energy from, and a cold bullet to deflect (maybe you are in a wizard duel with [Elsa](https://en.wikipedia.org/wiki/Elsa_(Frozen))?), the rate of transfer of such energy will be very slow, and since entropy loss [will be non-negative](https://en.wikipedia.org/wiki/Second_law_of_thermodynamics) (and in real practice, non-zero), you are going to lose some of your energy transfer to the enviornment anyways as 'friction' losses.
# [Lord Kelvin](https://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvin) denies your 'science-based' magic
Forget physics and momentum and all that. The second law of thermodynamics and [time's arrow](https://en.wikipedia.org/wiki/Entropy_(arrow_of_time)) mean that you can't just move energy around all willy nilly.
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I'm trying to build a sort of prime directive violated medieval or ancient society, where outside forces have influenced the development of their warfare. But the outsiders are reluctant to trade in guns, but they trade in something akin to bang snaps, but much much more explosive.
Would this (or a similar marble sized bomb) make a significant change to development in warfare, or would it be quickly abandoned?
Are there existing types of serious small explosives I can reference which could fit this description?
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I think what you would get is something to replace the [rifle grenade](https://en.wikipedia.org/wiki/Rifle_grenade#Modern_use) or [grenade launcher](https://en.wikipedia.org/wiki/Grenade_launcher). Historically there were [grenadier units](https://en.wikipedia.org/wiki/Grenadier), who were considered [elite units](https://en.wikipedia.org/wiki/Grenadier#Early_distinctions_of_dress_and_equipment) because of the need to select tall, strong, dexterous men who could handle grenades safely and throw them wide enough to escape their fragments.
The use of a sling for grenades increases the possible range and reduces the need to select for strength, but it adds another thing which can lead to a fumble and a grenade exploding in their own ranks.
Historical grenades detonated with a burning fuse (or became duds when the fuses were extinguished. Imagine a ceramic grenade body, perhaps with some lead sling bullets glued on to create extra fragmentation and filled with black powder. The imported gadget is a crude *impact fuse* for them.
* With those ingredients, the locals still lack the barrels to make a functioning firearm. Clay pots and lead balls were mass-produced in Greek and Roman times. A barrel which does not burst is another ballgame.
* They could of course use the black powder for blasting purposes, e.g. in a [mine](https://en.wikipedia.org/wiki/Tunnel_warfare) under a castle wall.
Introducing this might be a significant advance over a Roman-style line of soldiers with javelins and swords. It would be replaced once they figure out how to build a musket, but that might be decades, even centuries, depending on the starting point of their metalworking.
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If the weapon you describe is going to replace other weapons, it needs to have an advantage over them. I'm going to assume there is a possibility of guns being developed eventually, otherwise there would be no question.
Several criteria in which we can compare the weapons suggested and what was historically developed:
* How effective are they in combat?
Your weapon would obviously be out-classed by modern weapons, but in a "medieval or ancient society" that could would be a very powerful choice in battle. Just compare it to the other ranged weapons used by medieval societies like crossbows and long-bows and it's clear that an exploding ammo could be superior (also remember you can have small units wielding those to scatter large forces so your archers can snipe at single targets).
* How easy are they to use?
Ease of usage is not just important in the battle. If you're training an army you want to spend as little time as possible with a recruit before you can send him out to battle. If using this small bomb weapon is easier then using a bow, that can be a very significant reason to for military leaders to opt for it.
* Price.
Similar to the point of ease of usage, money is always a huge incentive. You say that societies are only sold your type of weapon, that means it's much harder to find different options. An interesting twist can be corruption. Have those "outsiders" bribe world leaders into choosing their weapons. (or just make it cheaper).
### Let's summarize:
If you want a realistic way of convincing your audience that it makes sense that those marble-bombs are so prevalent in your world, or that they have replaced weapons that would otherwise be developed, you need to give your audience simple and clear reasons. If you need to explain this, you can spend a few paragraphs on how the decision to invest in those was made, and have military leaders raise the arguments you have.
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First, you absolutely can use slings to throw grenades and it will significantly improve range, which I hear is a good thing.
But if you are thinking of replacing muskets by using explosives to make sling bullets more lethal that probably will not work.
Two reasons:
First, slings are already quite lethal. A normal non-explosive sling bullet is dense enough and flies fast enough to stop most targets it hits. Shields and armor help but the issue with slings never was the damage being too small. You could provide bullets made of depleted uranium if you want...
Second, the issue with slings was that it takes practice to be good with them. Generally slingers were from mountainous areas where they grew up using slings to deter predators from eating their sheep. Everybody else used bows since training somebody to hit a target with a bow is much easier.
Up until bows were themselves replaced by muskets due to it being so much easier to train somebody to hit a target with a musket... So no, giving slings more damage probably will not replace muskets or even bows.
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Obviously, you can't just send a bunch of out-of-work Kentucky coal miners up there to give it a go. You need some sort of specialized equipment. What I want to know is: what equipment will it be?
**What machine(s) buildable with current day technology would allow you to economically mine a near-Earth asteroid?**
### Condiderations
* Current day technology only
* Must be launched into orbit by a rocket no more powerful than [Saturn V](https://en.wikipedia.org/wiki/Saturn_V) (49 tons to a Lunar orbit). Multiple launches are fine.
* For the elemental composition of the meteorite in question, use [Table 2 here](https://arxiv.org/pdf/1010.2746.pdf).
* Must be able to remove useful ore and pack it in some way for transit. Returning the mined stuff to Earth is out of the scope of this question.
* The key factor that must be considered is how much refining is to be done in space to make this economical. The edge case solution is just to return the whole asteroid to Earth and mine it on the surface after it cools down, but that seems a little too bombardment-y to be politically feasible.
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The simplest and cheapest means to do so would require large amounts of metal foil as the basis of the mine.
Step one: find your asteroid or NEO and wrap it on a large metal foil "bag". Strips of metal foil can be arranged and the edges "welded" together to encompass almost any size of asteroid. there need to be two openings, which are explained below.
Step 2: using more metal foil, create a mirror capable of focusing the sunlight onto the bag you created in step one. The solar energy goes through the first opening (which can be a transparent window) and heats the materials within. The size of the mirror depends on the distance from the sun (the farther away you are, the larger the mirror needed) and if you are setting an arbitrary limit based on what you want to mine. Ideally, you want to heat the material to a plasma and collect everything, but some materials are more valuable than others, so you might simply settle on heating the asteroid to the boiling point of whatever element you are interested in.
[](https://i.stack.imgur.com/s8JM4.jpg)
*Mirror arrays can be scaled to provide the amount of solar energy needed*
Step 3: The only heavy and massive part of the mine is a mass spectrometer used to separate the stream of ions being released by the heat energy being deposited on the asteroid, and a series of cold traps to cool and solidify the materials after separation. This is placed in the opening opposite to the mirror to protect the machinery from the mirror's energy.
[](https://i.stack.imgur.com/2uYlA.gif)
*Basic idea of a mass spectrometer. Scaled up, it can separate a plasma stream into valuable materials leading to cold traps*
[Answer]
[Vacuum distillation of metals](http://www.totalmateria.com/page.aspx?ID=CheckArticle&site=ktn&NM=381)
Take advantage of the vacuum and the ability to heat objects without convective or conductive losses, or risk of pollution. This scheme will allow you to refine your metals by distilling them out of the asteroid into the vacuum of space. Once cooled, condensed crystals of pure metal will be swept out of the vacuum and collected. This is analogous to what is done with crude oil.
What you need: solar lens, space sweeper. Some explosives might be nice as it will be easier to heat boulder sized chunks than an asteroid of many cubic km.
1: Identify region of asteroid containing metals of interest. A small asteroid might be heated in its entirety or you might break chunks off with explosives to facilitate even heating
2: Apply solar lens to heat region of interest. This will be more efficient than on Earth without pesky convection.
3: Raise the heat slowly.
4: Molten metal will stay together via surface tension. I am not sure if the heat will cause convective mixing and homogenization or if the various liquids will stratify. It does not matter for the end result but the appearance of the process can be something to describe as it happens if this is for a work of fiction.
5: As temperature reaches evaporation point of various components, hold temperature steady as undesirable components volatize off. A gentle puff of gas will allow these waste materials to move off into space.
6: Just as with cracking crude oil, your various metal fractions will come off one by one and bubble off of the liquid surface. Puff away the undesirable fractions as they come off, but gather desirable fractions. You might allow the metal gas to condense back into solids first - probably crystals.
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Judging that asteroids have a ton of dust on them, you could probably use a harpoon to anchor yourself on it, like Britain did with the first rover on a asteroid, and then use a vacuum or large filter/net to catch the dust or minerals.
The drone would be launched like every other craft, but would use ion cannons to get from place to place, with oxygen based pressure rockets to use for maneuvering.
The minerals could be stored inside of a container inside of the drone, where it would then return to an orbital station, like the ISS, but this one has refineries.
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[Human marching formation](http://images.china.cn/attachement/jpg/site1007/20091001/0019b91ec74f0c2e74a04e.jpg) is simple enough to understand.
But how does this work when you have naga (left in the picture)? [](https://i.stack.imgur.com/QrSbp.jpg)
Their snake tails, particularly if very long, are going to make a tight marching formation very difficult, or even impossible.
At minimum, I'd estimate a naga's length at 9 feet, including the human torso (about 6 feet of snake). At maximum, I'd reckon them at 22 feet, (about 19 feet of snake).
With this in mind, how would an army of naga march in formation? The two types of concern are:
1. Marching convoys. When an army marches in a long column to get from point A to point B.
2. Combat Formations. When you're marching across the field to meet the enemy. These historically had to be tight formations, for the coming melee.
## Naga Speed
G0blin notes in the comments: "According to this [BBC movie](https://youtu.be/zEto1-ZTbd4?t=2m5s), Black Mamba snakes can travel with a third of their bodies raised at full speed (7mph long distance, with 14-20mph for short bursts of speed)."
[Answer]
**Edited for clarity**
When travelling in large masses, armies use formations to simplify the logistics and manage the risks of contact with the enemy. Due to differences in their anatomy, human and naga formations would differ somewhat, but not hugely.
Human formations are typically organized as a grid in ranks (rows) and files (columns). The spacing between soldiers in a rank is called "dress". A normal dress is established when the front rank of formation members can touch the shoulder of their nearest neighbor with the finger tips of one hand. "Full dress" is when the front ranks can touch only the fingertips of their neighbor with either hand.
When travelling in a column on land, naga could be close packed in each rank, like similarly sized humans, but the ranks would be sufficiently far apart from each other to allow for the tail. If for any reason it was desirable to make the formation more compact from front to back, the spacing in each rank could be increased up to full dress, allowing the next rank to come up part way between the tails of the rank ahead.
Due to the geometry of the formation, naga would be able to execute a wheel maneuver, but a turn would be more difficult (imagine getting whipped with the tail of your 200 lb neighbor in a quick turn). Their fancy parade drills would have some maneuvers that would be difficult for human formations, but be geometrically incompatible with some executed by their human counterparts.
On land, they would use many of the same formations that humans do, with appropriate modifications. Porcupine, Turtle, Phalanx, are all reasonable. While backing up is not a preferred action of snakes, it has been filmed in nature, so we can assume the full standard range of mobility of these formations.
A flying V (or wedge) is used to smash enemy formations. It started out as an infantry formation, but is still used by modern aircraft and tanks. For the naga, it maximizes their ability to bring weapons to bear and to defend each other, while avoiding entanglement of the tail with one's neighbor.
Cadence, which is important for keeping members of the formation from tripping over each others' feet/tails, would be different and more subtle for naga than humans, but not less important. Humans marching in cadence can collapse bridges. Unlike humans naga would not have to break cadence when crossing bridges.
**Edit for new information from @G0BLiN re black mamba's**
Based on a naga having the same weight as a human, their mobility on land may be limited. If 50% of their weight is in the human torso and head, then Naga would not be able to go long distances because their weight distribution acts as a natural brake and limits the amount of traction their tail can provide. However, if only 30% of their weight is in the humanoid torso and head, they could move quite efficiently.
In open water, their formations would be swift and efficient. For long distance open water treks they would use a flying V formation that minimizes hydraulic drag on the formation as a whole and allows the tailing members to rest in the wake of the formation. Ranks would normally be rotated so that everyone has a chance to rest in the wake of the formation. However a commando action might use grunts to lead the formation the entire way, keeping the commandos fresh for lightning strikes and deadly efficiency.
[Answer]
Order by size really.
The slithering motion of a snake tail is mostly determined by the dimensions of the tail (as far as i know). By grouping naga in batalions of approximately uniform size their natural slithering motion should be quite uniform. Close enough , at least, that any deviation can be consciously corrected without great effort, like a human corrects their walking if someone is walking closely behind them.
On a military note it also helps suppress hierarchies within squads if members are the same size which helps the greater military hierarchy. In humans this is not really that relevant but with a 2.5 magnitude size discrepancy (9ft vs 22ft) "equal in rank" loses some of it's meaning, I would imagine.
Your second concern is also a bit unfounded. Snake bodies move in a essentially different way than human ones. Humans movement falls under "turn on spot" and "move forward". Making a circle is taking a step, adjusting course and taking another. Snake movement is always "make a circle". Their moving forward is making alternating partial circles.
This means flanking is a FAR greater advantage than in humans. Humans just need time to "turn on spot", snakes need more time to turn (relatively at least), more space and geometry. A pinned/severed tail is a real threat and disadvantage. Not to mention that getting flanked also means losing back support from your tail. You could (more) easily get toppled. Naga battles would therefore involve far more chaos than human battles. Specializing in meeting an enemy head on would be about as clever as binding a sword on a cannon barrel saying "in case they get close". Technically .... sure, but the situation shouldn't occur to begin with.
Personally (though i am no warlord) I would imagine that arrow volleys would work very effectively against naga: They have a lot of surface area and they can only move with 1/3rd of their body up. Completely blocking a volley would require a bothersome shield, slowing down the nimble half-snake. Stance is also an issue for them: facing forward puts great strain on the abdominal muscles and risks arrows to the underbelly. Facing sideways might leave the first few ft vulnerable. Curling up below a shield would require quite a sizable shield in some cases, would leave them in a suboptimal position for continuing to move forward and any arrows piercing the shield would go directly into flesh, which would make leaving the position painful ,damaging and quite straining on the arm-muscles, debilitating them in any confrontation later in the battle (via fatigue).
They would probably want to avoid all that, which could most easily be done by dividing the archers' attention via a multi-pronged attack or to prevent archers(/arrows) from reaching the battlefield at all.
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To confuse and alarm the target, they attack in multiple, crosshatching waves advancing at acute angles and interweaving. Marching to drums facilitates synchronization.
This is accomplished through an easily-learned choreography analogous to Japanese precision marching. The erect portion of the the nagas move like the marchers and the trailing bodies slide over one another.
On cue they can execute additional choreography (like changing direction, leaping, and raising coils along their lengths) for similarly confusing and alarming effects.
[(Example)](https://www.youtube.com/watch?v=m8nwll9F8dM)
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How difficult would it be for someone be to get a hold of lots of metal wire in early medieval times?
It doesn't really matter what metal it is or how uniform, just that it's in long lengths (tens to hundreds of meters) and that it's reasonably fine gauge (<1mm diameter)
The character is trying to build a speaker (for shock and awe) and needs lots of (semi)affordable wire to build the speaker coil.
I've heard about wire-wrapped jewellery (presumably really expensive) and some forms of chainmail (only short lengths?) but I've not seen much about long continuous lengths of wire. Could it be done?
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From [The Production of Gold Wire in AntiquityHAND -MAKING METHODS BEFORE THE INTRODUCTION OF THE DRAW-PLATE Andrew Oddy](https://link.springer.com/content/pdf/10.1007/BF03215438.pdf)
[](https://i.stack.imgur.com/fZ15I.png)
[](https://i.stack.imgur.com/Kgacw.jpg)
This grumpy monk from 1389 will whip you up a batch of wire in no time. He already has a fair bit ready. I think some sweet tunes will improve his mood a lot. He will also be pleased if you let him make the wire out of soft copper instead of iron; copper is a lot easier to work with and I suspect will be comparably priced in medieval Europe.
For a speaker you will need to insulate this wire. I think beeswax will serve.
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I've only found out how to get the materials to make the wire. Back in the 1300s, your average English labourer earned about 672 grams of sterling per year, or about 2.1 grams per day. That converts to .20 cubic cm, then to 2800 cubic millimeters. Going through some more math, that would be 36 days worth of pay for a wire 100 meters long. Solution: rob a peasant.
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I left a comment linking to medieval European metallurgy in the comments, but here's the gist of what's relevant to this question.
If your story takes place in the Early Middle Ages (5th-10th century) metal is going to be really hard to find because of the limitation in mining techniques and difficulty extracting metal from ores.
Increase in metal production and production of copper kicked up more towards the end of this period, but it's the High Middle Ages (11th-13th century) that mining and increased production and quality of metals were at the peak. I'd say this would be the best time for medieval wire making.
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[**I have asked previously how I could create an earth-like world with as many deserts as possible in it.**](https://worldbuilding.stackexchange.com/questions/41646/resources-for-climate-world-building) I have received some useful answers and have tried to draw a realistic map of what I intend for my continent.
Unfortunately, I have been having trouble using Geoff's Climate Cookbook... if you ask me, it is not very user friendly for someone with no basic knowledge of meteorology, at least before we get the hang of it (and I don't think I got it, not for a long shot). I'm very confused, especially since a vast expanse of my continent rests on the south hemisphere and not the north, which means I have to invert a lot of things.
So, I would like to ask you if you think this map is plausible.
(I'm sorry if it is somewhat simplistically drawn, but I don't want to draw a very detailed continent to find out at the end that it isn't plausible)
[](https://i.stack.imgur.com/Q9OEo.png)**Please read the edit at the bottom of the post**
1. Blue lines: Latitude and longitude (check right and bottom of the screen)
2. Black lines: Limits of the continent
3. Reddish thick lines: Mountain ranges
4. Blue area: Ocean
5. Green area: Fertile regions, with relatively high precipitation (irrespective of being tropical, temperate or whatever)
6. Yellow area: Hot desert
7. Grey area: Cold desert
8. Orange area: I don't know which climate to assign to this area
Now, I don't want to dwell on the green areas just yet. If you would like to help me with the "?" area climate, I'd appreciate it, but I'm willing to make a separate question for it, in order to not have my question closed for being too broad.
What I want to know is if the desert areas are well placed.
***Area "A":*** I know it's a stretch, but I was thinking that it could be a coastal desert, dried up by the Hadley cells. I only want it to be plausible, not probable
***Area "B":*** Hot desert created by the rainshadow of the mountain ranges in the east, west and north
***Area "C":*** Hot desert created by a large expanse of land in the Hadley cell
***Area "D":*** Cold desert (it's okay if there is some precipitation on it, in the form of snow)
***Please note:*** This is an earth-like planet, with the same size as earth and the same duration of days and years. However, it has almost no axial tilt, in order to maximize extreme weather and to avoid the monsoon effect
**EDIT: As of July, 17th, I have redrawn my map so that areas A and C would fall more in line with 30º latitudes**
[Answer]
# A
This desert is mostly appropriate. An analogy to this continental feature is the southern part of Africa. Most of this is the Kalahari desert, especially on the Eastern side. If your planet rotates in the same direction as Earth, you will have a similar gradient of dry desert on the east to semi-arid savanna on the west. There is even a bit of wet savanna on the far western coast.
Cape Town has a nice Mediterranean climate at 33 S, so if your continent extends north past ~30-35 or so, you can expect a Mediterranean climate to develop.
# B
Anything within a few degrees of the Equator will be a rainforest. Even the northern half of Africa, which quickly grades into the Sahara Desert, is relatively wet, up to about 4 degrees N at [Bangui](https://en.wikipedia.org/wiki/Bangui#Geography_and_climate). Therefore, your mountains would be expected to be very wet, with lots of small rivers coming down to feed a rainforest pushing out to about 5 degrees from the equator.
Savanna would then persist up to at least 10 degrees north. In Africa, [N'Djamena](https://en.wikipedia.org/wiki/N%27Djamena#Climate) is at 12 N but still wet enough to support agriculture in river valleys and herding on the open plains.
South of 10-15 it would become true tropical desert. With the mountains you mention, the land would be drier, but still not a desert. An example from Earth would be [Dodoma, Tanzania](https://en.wikipedia.org/wiki/Dodoma#Climate). It is surrounded on three sides by mountains at 6 degrees S, but is not a total desert.
A more unique situation of a city in tropical desert surrounded on three sides by mountains is [Lodwar, Kenya](https://en.wikipedia.org/wiki/Lodwar#Climate). However, in that case, the desert basin is small, a portion of the Eastern Rift Valley. Your continental scale depression between mountains will accrue enough moisture into it (from rivers from the equatorial mountains) that it won't get that dry.
# C
There are many deserts at this latitude, but you need to cut them off from the ocean. A west coast between 30-45 degrees from the Equator is Western Europe, and East coast is either China or the Eastern US. All of them are pretty wet. Instead, you want the western US. Cut off between the Coast ranges and the Rockies, the interior great basin of the US has the same latitude range you want. Extend those red mountains south enough to cut off the land from moisture carried in prevailing winds at sea.
# D
Polar regions are pretty much deserts. The taiga cuts out between 60 and 70 N and thereafter it is tundra.
# ?
Assuming your planet rotates the same way as the Earth, this area will get significant rainfall from the rainforest and ocean regions to the West of it. Prevailing equatorial winds will blow moisture in year round.
Since we already determined that A is like the southern part of Africa, this region is remarkably similar to Central Africa, complete with a jutting projection of rain forest analogous to West Africa.
In general, the areas closer to the coast will be a bit drier, and in the center of the continent a bit wetter; but the 'armpit' of land on the west coast will see heavy monsoons. Typical rainfall regimes might be like [Douala, Cameroon](https://en.wikipedia.org/wiki/Douala#Climate) in the 'armpit'; [Port Gentil](https://en.wikipedia.org/wiki/Port-Gentil#Climate), Gabon northwards along the coast (note the two distinct rainy seasons); a drier [Kinshasa](https://en.wikipedia.org/wiki/Kinshasa#Climate) in the coastal regions; and a wetter [Kisangani](https://en.wikipedia.org/wiki/Kisangani#Climate) in the interior. As you head north, it will turn into savanna by at least 6-8 N.
# Conclusion
Africa is pretty dry all in all, and a good continent for you to use as a model. Just keep in mind, especially in southern Africa, Africa also tends to be the highest continent. Most of the southern half of the continent is at 1000m +. If you are copying climate conditions, make sure you make it warmer if your places are at lower elevation.
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**?** could be either desert on grassland believably, in fact it should probably extend further east. the intertropical convergence will drop some rain especially close to the mountains but not a lot. The top of **A** will be prime fertile territory, placement wise it should be nice and fertile not desert. 40 degrees is where most of our prime farmland is.
**C** should be more fertile, especially the lower and western portion, at 60 degree latitude it will have more rain, it is basically similar to europe or the lower portion of canada, at worst you could make it savannah. The top of **D** will be more fertile as well, climatically it is more like sweden with lots of forests. deserts are spread more laterally than vertically.
Check similar latitudes on earth for inspiration. hot deserts cluster around 30 degrees while prime farmland is near 45-50 degrees. Basically almost all your climates extend too far vertically. Of course the less detailed the map the less detailed you can make the weather patterns.
Also this geologic make up is going to have volcanics on the eastern mountain range at least, you don get mountains that close to the coast without active subduction. And if the two western and the one northern mountain ranges are still being pushed up (or to a lesser extent even if they are not), you are going to end up with something like the himalayas there as well. At -25 longitude and 0 latitude you have several continental plates being pushed together, you will have some widespread mountains not narrow bands, that whole region could become rugged highland or highland plateau depending on if it is still being formed or not, that will give you a highland desert.
For the revised map the fertile belt on D will be much larger, just look at earth you have green fertile land all the way to 70 degrees for at least part of the year. There are ways to change that, greenland is colder because it is isolated by water channels or you could make it high elevation like the himalayas just nearer to the poles, that will create a fertile belt on one side or the other from all the rain dropping out but the rest will be mountainous and dry. since it is continent to continent plate forming the mountains you will end up with some widespread mountains anyway.
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When you want little more realistic earth-style map then try to spread deserts little more horizontally around equator where suns intensity is highest assuming planetary axial tilt is small.
However in case you have more freedom with background story, you could consider case where planetary rotational plane is nearly perpendicular (~ 90°) to orbital plane and facing sun with one of its poles.
Then again you could create other good reason for desert being there like ancient nuclear war or surrounding high mountain ranges which block humid air reaching specific area.
If you want get random map in easy way then I suggest you could try Civilization or some other computer game which may generate suitable map for you with minimal effort.
EDIT: Keep in mind that usually story is much more important then map and also keep in mind that your world - you can set rules. Then again, if you want my (realistic) viewpoint then area C would likely be very windy and might require some extra condition to become desert. Perhaps try curve that lower red line little more around edges of other red lines.
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Having been looking into scientifically plausible forms of telepathy, I stumbled across the electroreception senses that exist in some electric fish (and in a few land-dwelling marsupials). My question is whether it's feasible for a human-like species to evolve the same kind of thing, and what limitations would be imposed by living on land where there wouldn't be a consistent source of water to be used as a conductor as for the electric fishes.
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Your main problem is that water conducts electricity really well, whereas air conducts electricity really poorly - air is effectively an insulator. Otherwise you wouldn't need to touch a live electrical wire to be electrocuted, you would just have to stand nearby. (Although large voltages can cause sparks to jump a gap, but we're talking machinery not biology in those cases).
Therefore the distance over which your humans could sense anything with electrosenses is so short as to be useless. Years back I read some papers about rattlesnakes - someone suggested that the rattling tail could generate electrostatic charges which the snake could use to sense things with its tongue. But another scientist calculated the effective range and it was only a couple of centimetres. The snake would be able to see and smell its prey long before it could electrosense it. Sorry, this is the only reference I can find [on the discussion.](http://www.nature.com/nature/journal/v370/n6486/abs/370184b0.html)
So the Vulcan Mind Meld is possible - you touch the person. Knowing what someone across the street is thinking is not feasible.
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Magnetoreception might be easier. You might be interested in [magnetic implants](http://io9.gizmodo.com/what-you-need-to-know-about-getting-magnetic-finger-imp-813537993) which enable you to feel not only magnetic fields, but also (alternate) electric currents, and do not need a conducting environment. The nice thing is that your brain soon internalizes the new feeling and it looks like a new, separate sense.
You can even use non-invasive [magnetic rings](http://lesswrong.com/lw/mjs/magnetic_rings_the_most_mediocre_superpower_a/).
So, it is at least remotely plausible that evolution can lead to (magnetized) magnetite concentration in some part of the body - but that's still far from telepathy.
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What the fish you mention do is likely more akin to an iPhone screen, they send preferably alternating current through a conductive medium and recognize any changes in resistance and capacitance. This is mostly not viable unless you share a circuit with the thing you hope to detect. Nevertheless, some touch devices can sense your fingers through air, though I don't know what that kind of accuracy requires. That failing, you can use induction to detect charge without a circuit but not capacitance. You wouldn't be easily able to discern between distance and magnitude without two sensors.
If you also hope to detect the presence of charge, here are some options. Be aware that the charge of neurons would interfere and is highly dynamic.
Introduction to the vicinity of charge will induce a motion of electrons through certain materials. This is why our hair becomes positively charged near lightning, and is an event that facilitates the jump of electrons from the clouds. It works at a small scale incredibly well. Look up "induction".
Changes in charge will also induce magnetic fields that can then affect the motion of charge within them.
I suspect that charge is far easier for relevant biological life to maintain than a solid state magnetic field, because most magnetization is easily lost. Lodestones are made by lightning and wouldn't be the most common thing in the world, yet every animal creates charge to move neurotransmitters through and between neurons. Baking destroys most high quality magnets like those used in motors. Electromagnetism might even be more viable than synthesizing one for some applications. You could have magnetite seeking hermit crabs though.
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Actually humans can sense electrical fields and magnetic fields. Look up electrical sense gurus on google. It’s something most people aren’t aware of, but it’s there. With my autism I feel the resistance of everything around me weakly. I see strong charges from moving cars, etc. it’s certainly weak compared to sharks sense. Like, by a millionth. I have thought about telepathy but realistically, I’d have to be a strong generator of electrical energy to be heard over the other signals around me. Most people are pretty basic electrical grounds. And yes, seriously, it’s stupid and not precise, but I’ve done repeated tests, and will, but got tired of doing it. It’s just like your touch doesn’t end at your skin. The most realistic way I’d see it occurring is something like Morse code. More than that and the brain would need to evolve to handle the sense more complicated than I have.
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Check out the "aquatic ape hypothesis". It is plausible that humanoids evolve with water being an essential part of their lives and still live on land. In this case, something like electroreception might evolve given the right circumstances of course - there need to be electrical fields for starters. I hope I read your question correctly, it could be interpreted as "my humanoids live in the desert with almost no water" - in which case it is kind of obsolete but not really. Just ignore all the water bits. Yes, some land animals on earth have that ability, but there must be a reason why we didn't evolve that sense - so I conclude that it wasn't enough stimulation/need for it. But also note that you can sometimes feel electrical fields, when all your body hair starts to spread out because your body is charged - you can feel that actually.
Here is what I would do, but I'm no evolutionary biologist. I hope this would be plausible to enough readers:
There is this organism (say a plant) that is poisonous and produces a weak electrical field. There is another plant/fish whatever that copies that electrical field to scare off predators. Your humanoids and their ancestors love to eat that organism. Variations are countless, from the initial plant not being poisonous to the humanoids to food growing where there are natural electrical fields (different question how they might get there) and so on.
I think one should have this in a more aquatic setting. Yes, there is no reason why this wouldn't work in air, but I think your question has a bit of a "what is the most likely way" quality to it.
The problem with non-aquatic electrical fields of course is that they need to be stronger, maybe resulting in regular shock. If you go for the desert option with little water, maybe choose an environment where not getting electrocuted is essential. How to construct this planet is a different question.
You could imagine a completely different reason for electric fields on your planet. For example your humanoids needed to go someplace for seasonal change and that is made obvious by regular strong solar winds that charge the atmosphere or strong storms. The options really are limitless, but I still feel the most intuitive way is having your land-living humanoids be in water a lot which is even how we might have evolved.
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For inspiration, bees can be an example of "inland electroreception."
Honeybees perceive electric field changes via receptors in their antennae and use this information to know if a flower has been recently visited by another bee and is likely to have a reduced concentration of nectar.
They detect electric fields through insulating air by mechano-reception, so it's not technically electroreception. They distinguish different temporal patterns and learn them. During the waggle dance, honeybees appear to use the electric field emanating from the dancing bee for distance communication.
<https://en.wikipedia.org/wiki/Electroreception#Bees>
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Electroreception is present in humans. various humans have shown it. I have it. I'm autistic though. Autism can come with oddly connected parts of the brain. For instance I see beams in walls and ceiling. I always thought it was due to painting or something, till I realized I don't see it in photos. I also see disruptions in cars and in the sky. I suspect it's what pigeons have in their eyes. They're called cryptochromes that allow them to see magnetic lines in blue light. I also feel everything at a distance. It may be more common than known, but if you don't know it's not normal, or you're different you don't know to tell anyone. I can't imagine my sense of touch ending at my skin. I thought it was normal. And there are definitely people who have a much stronger field than others. As a kid I use to cheat at hide and go seek because I could feel the direction people were in. Of course I didn't know it was cheating, I just did it. I also have consciously at times controlled my heartbeat, and my interference with radio signals by causing static at will. It was easier as a kid, but many of our senses dull over time.
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*This question is based on the articles saying that the Mongoloid body plan was all due to an individual mutation from 35,000 years ago.*
In science fiction, humanoid aliens that aren't of the human species are rampant.
[](https://i.stack.imgur.com/Ry8sK.jpg)
The sensual, shamrock-green seductresses of the constellation Orion.
[](https://i.stack.imgur.com/BZCTW.jpg)
The blue or purple-skinned Asari.
These two are minimally alien. The most obvious difference is skin color. In our ethnogeographic history, there has never been evidence of a mutation turning human skin green, blue or purple. But among humans on Earth, could such genetic mutations be possible?
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If our eyes can do it, our skin can do it. Depicted: Frank Sinatra and Emma Stone.
[](https://i.stack.imgur.com/5f9VM.jpg)
Humans have only one pigment molecule: melanin. Brown, blue and green eyes are caused by different distributions of melanin molecules in the eye, and different proportion of light absorbed and light scattered.
<http://www.goodhousekeeping.com/health/news/a41980/blue-eyes-are-really-brown/>
>
> Melanin absorbs light, so the more melanin there is, the less light
> will be (reflected back out of the eye). Brown-eyed people have more
> melanin, less light.
>
>
> The opposite is true for people with "blue" eyes. Those with less
> melanocytes can't absorb as much light, so more light is reflected
> back out of the eye. This is called scattering — and when light is
> scattered, it reflects back at shorter wavelengths. On the color
> spectrum, shorter light wavelengths correspond with the color — you
> guessed it — blue.
>
>
>
This Rayleigh scattering is the same thing which makes the sky look blue. If distribution of melanin in the eye can make blue or green there, it can make it in the skin as well.
---
There is another way to make green. We normally have bilirubin in our blood. It is a breakdown product of hemoglobin. Jaundice is caused by a buildup of bilirubin, from liver dysfunction or blockage of the bile ducts. Bilirubin is a sickly yellow color but biliverdin, a precursor product, is a vivid green. You can see this green in an old bruise: blood trapped beneath the skin goes from a dark purple to a vivid green to a mustard yellow as the hemoglobin breaks down.
[](https://i.stack.imgur.com/kjagP.jpg)
Higher levels of heme breakdown products in the blood are not in themselves bad for you. A mutant which accumulated biliverdin in the blood and only slowly broke it down to bilirubin would have skin (and sclera) the vivid green of this pigment.
I found a described case of exactly this. This man turned bright green (as opposed to the typical yellow) when he became ill with end stage cirrhosis. His urine was also bright green.
[Biomedical Scientist p362 June 2011](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved=0ahUKEwjlg6CqlZzWAhWL7CYKHfZCD4cQFghlMAw&url=https%3A%2F%2Fwww.researchgate.net%2Ffile.PostFileLoader.html%3Fid%3D5480504ed039b1075c8b4574%26assetKey%3DAS%253A273645941788697%25401442253684833&usg=AFQjCNHZQXXcvJuekjfgs-pr0zNRn8dE4Q)
>
> Results of the investigation suggested that green jaundice in this
> patient was the result of reduced biliverdin reductase activity that
> converts biliverdin to bilirubin, perhaps due to a defect in the gene
> that codes for the enzyme. Analysis of DNA from the patient’s blood
> cells and subsequent sequencing of his bilirubin reductase gene
> provided confirmation that this was indeed the case.
>
>
>
[Answer]
## Yes, but probably just blue/purple.
It's not very likely for humans, but other primates do develop blue skin, so it's feasible that humans could (given our common ancestor).
[](https://i.stack.imgur.com/IUHTC.jpg)
[$\_{Source}$](https://en.wikipedia.org/wiki/File:Mandrill_at_Singapore_Zoo.jpg)
[This paper](http://jeb.biologists.org/content/207/12/2157.full) describes that the blue coloring of the Mandrill flank (and another monkey's blue scrotum) is not due to pigmentation, but rather arises from a nanostructure that makes the skin appear blue.
>
> We used fibre-optic spectrophotometry, light microscope histology,
> transmission electron microscopy (TEM) and 2-D Fourier analysis of TEM
> images to investigate structurally coloured skin from four species of
> mammals: the mandrill, Mandrillus sphinx, and the vervet monkey, C.
> aethiops (Cercopithecidae; Primates); and the mouse opossum, Marmosa
> mexicana, and the wooly opossum, Caluromys derbianus (Didelphidae;
> Marsupialia). We found that structural colours of mammal skin are
> produced by coherent scattering from quasi-ordered arrays of dermal
> collagen fibres. These arrays are exactly convergent with
> colour-producing collagen that has evolved numerous independent times
> in the skin of birds (Prum and Torres, 2003a), in the tapetum fibrosum
> of the sheep eye (Bellairs et al., 1975) and in the iridescent corneal
> stroma of certain fishes (Lythgoe, 1974).
>
>
>
---
I think knowing the likely genetic source makes it a little less alluring than the blue alien/human/people are meant to be. If you met a blue person (hard to say they'd be human) you might not be able to stop thinking that they share that trait with monkey perineum, buttocks, and/or scrotum.
It might even make Kirk think twice. But probably not.
[Answer]
A conditional no we haven't, and a yes we could.
This will be a behavioral evolution trait in humans if it does come about. Same thing that occurred in Dino's...as much as we like to point towards survival of the fittest, in truth it's survival of the most capable of breeding and traits that attract mates tend to amplify quickly and get out of hand (a peacocks tail as a modern day example). No reason this trend couldn't happen in a population of humans.
The conditional above : We do have a blue skin mark as a semi common genetic trait...<https://en.wikipedia.org/wiki/Mongolian_spot> Mongolian spot (or mongolian blue spot) is a blue pigmentation on the skin (does that count as blue skin?). If this trait somehow became heavily favorable in attracting a mate, it could amplify in a few generations.
As a side note...blue/purple only. I really can't find much that pigments green.
[Answer]
No, humanity has never experienced that sort of pigmentation through any sort of natural mutation, and is unlikely to ever experience it either. After all, all the examples you've provided are of *alien* species from the far future.
It's quite possible that future genetic engineering, or nano-technology will allow people to customize their appearance to that degree.
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[Question]
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I'm trying to design a realistically looking capitol (with a few milion people) for one human nation on an exoplanet.
The technology level is barely better than contemporary.
The city is placed near river, on some roughly flat, semi desert. (just boring terrain)
Roughly counting 25% of labour force work in industry (like in modern industrial powers), ~2% in agriculture and the rest in services.
The idea is the following. It would be very nice to have heavy industry. It would be also really nice to have a clean city, full of parks etc, in which all population including workers can spend their time after work.
To solve this contradiction the idea is the following - to place the industrial district downwind, and transport the workers using some local version of suburban rail. Additionally to stop any residential, office, etc development in that one specific direction, to have some green buffer zone.
1) Is such concept reasonable? (assuming that local political climate allows that)
2) Whats the reasonable distance between city and such industrial district to protect city mostly from pollution and keep the commuting time reasonable? (does anyone has any study how big area gets affected by pollution?)
3) Should such district be spread around or it would be enough just to put such factories along the rail line?
(So far the best thing that I found were studies concerning London and their airport expansion. It was quite useful concerning how much free space one should leave for a big city and its airport. Just in the perfect case it would need something like that concerning heavy industry)
[Answer]
Modern industrial uses are a lot less noxious than they used to be, even though most people don't realize that.
For example, the U.S. Mint in Denver is actually a pretty hard core industrial use that turns raw metal into coins through an industrial process. But, from the sidewalk right next to it, in the middle of downtown, you wouldn't be able to guess that it wasn't an office building.
Detroit has one of the nation's largest salt mines, tucked away with an entrance in an innocuous low rise building that you'd never notice was anything other than a storage facility with a decent sized parking lot. It's less of a disturbance to the neighborhood than a rowdy dive bar.
A large scale brewery capable of providing beer for several million people is similarly surprisingly quiet (almost all a series of connected pipes), employed about twenty people, and is mostly notable for trucks dropping off raw materials and taking away finished products. Small scale distilleries and milk processing plants (I have both in my urban residential neighborhood) are similarly barely more notable than a self-storage place.
I've been to the factory that makes all of the world's Celestial Seasonings Tea, and you can't hear anything notable on the outside, although it does have some strong smells on the inside. Ditto for several other factories around town.
The factory in Colorado that makes the giant windmill blades for industrial sized electricity generation from wind creates less disturbance in the neighborhood than a high school or a pro-baseball field.
Also, most modern factories run on electricity and natural gas, rather than coal and oil, like they did in the industrial era.
Pretty much the only really noxious modern industrial facilities are oil refineries, coal fired power plants (a rapidly declining share of the total power grid), steel plants that use coke (the coal product, not the soft drink), slaughter houses, and dog food factories (one in Commerce City, Colorado stinks up the entire city when the Chinook winds blow in from the north).
The other really noxious modern land uses are landfills (although less so now that people figured out that collecting methane emissions and recycling compost creates another revenue stream), and feed lots (thousands of cows crammed densely into cattle factories) which smell intensely like cow poop for miles.
[](https://i.stack.imgur.com/FhWF9.jpg)
*A modern feed lot*
Factories do like to be near rivers or rail lines, however, so goods can get to and from their destinations.
**Bottom Line**
Almost all of the intra-urban geography of the vast majority of industrial uses are anachronistic residues of how bad industrial uses were for neighborhoods a century ago.
And, to a great extent that goes for what goes on inside factories too. The number of people killed or seriously injured in factories is now barely more than the number killed or injured working in offices or malls or convenience stores.
This is also true of other historical NIMBY uses that still have that connotation like secure prisons and jails which have virtually zero escapes and really don't have to be a bother. From the outside, it is almost impossible to distinguish a modern jail from a modern courthouse, if designed appropriately.
The vast majority of dangerous jobs these days involve working in uncontrolled surroundings like an outdoor construction site, a farm, logging, commercial fishing, or working on repairing roads and bridges.
The only uses that really should be kept at a distance need a range of perhaps five or ten miles from residential areas if they smell really bad, and otherwise can be integrated very closely with any commercial or residential district if they aren't burdened with the historical legacy of land use decisions made based upon earlier inferior coal/steam age technologies.
[Answer]
The easy way to answer this question is to find some city on Earth you think is pretty OK, and pattern your future city on that. Pick two or three cities and merge 'em. Over time, most human cities have evolved into something like what you want through natural selection of property. Just look at London 200 years ago vs 100 years ago vs now. They used to have tanning tanks right there in town. They used to have pea soup fog. Blech.
If I had an exoplanet to work with, I would build a very wide city, like Houston Texas, as opposed to a tall and dense city like London or New York. Houston is very spread out, a ring of industry around the business center, a ring of commercial around that, and a ring of satellite suburbs for the population. You're building high speed rail, and you get to plan the city up front, so you can build high speed rail from the suburbs to the city centers.
One thing I will say from experience with Houston, however, is that we don't have a "downwind," and I would expect that most places do not have a permanent "downwind." Throughout the day, the air cycles back and forth from the ocean; maybe if you can get way up in the atmosphere to a jet stream or the top of a weather front you can be a bit more predictable, but still, you can't perfectly place industry.
So: spread out the industry like you're doing with the residential areas. Residents can balance their own demands for squeaky-cleanness vs money or travel time. Some people aren't going to value parks everywhere; they'd rather live close to a power plant.
This isn't a utopia, however. Pollution disperses and eventually gets everywhere. If you have a city, like Houston, with a lot of wind activity, it'll get diluted and spread around everywhere, leaving no "clean" zones, but no specific place very dirty. A place like my home city of Bakersfield in the center of a valley, however, will concentrate the pollution inside the mountains, and no amount of zoning will keep every square inch from being covered in smog.
In fact, if you have full control of your worldbuilding (storywise, they had a survey of the whole planet before they landed), you could build your residential and commercial districts inside a valley, and put all the industrial outside the valley. Pollution would spread up and out, but be blocked from the residential areas; a "wall" to make Trump proud. Inside the valley, weather would be rather stable and the air would remain clean. Put your industry on one side of the mountain range and your agricultural center on the other side, and the pollution from industry will stay away from your city and ag. And nobody will bother to check your maths that way ;)
[Answer]
## Industry != nuisance, generally speaking
The assumption that underlies North American Euclidean zoning as applied to industrial facilities is that the more "industrial" a use is, the more nuisance it will cause, and the more resources it will require to support it. While the latter is still rather true, the former no longer holds now that oil and coal burning has been replaced by natural gas or electric heat. A modern, well-run factory poses very little nuisance to the surrounding community -- I lived within walking distance of a major regional dairy, and the only things noticeable about it were the trucks on the main roads and the physical presence of the plant. Hardly a nuisance worthy of being zoned away from residences, if you ask me.
## Special cases need special handling
However, a few things still need to be segregated by distance from residential, general commercial, or institutional properties. This is less for nuisance in most cases and more for *safety* -- oil refineries are not just noxious but quite hazardous if something *were* to go seriously wrong, and the same holds true for factories that produce or use bulk quantities of reactive, toxic-by-inhalation (TIH), or highly flammable chemicals, or storage facilities for said chemicals as well. Petroleum storage "tank farms", facilities handling ammonium nitrate fertilizers, and public works that use bulk chlorine need at least some segregation on this basis.
These latter facilities are what your industrial centers will contain, akin to the industrial suburbs of the Houston metropolitan area. This also has several logistical advantages. Large industrial plants that deal with high-hazards will often have in-house fire brigades that can then coordinate and pool resources to cover the area with appropriately specialized expertise. Atop that, just about all of these facilities will need specialized transportation access such as large-scale rail terminals and barge docking, and clustering such facilities is advantageous for both industrial users (more convenient and reliable service) and transportation providers (go one place for your customers instead of laying rails all over town).
## How this'd look from a zoning standpoint
A zoning scheme for this would have two categories of industrial uses. A "General Industrial" category would be used for low-nuisance, moderate-hazard industries such as a dairy, metal fabrication shop, or general warehouse that could be co-located with more intensive commercial, retail, and institutional uses that need similar infrastructure, while the high-nuisance and/or high-hazard uses would be placed in special "Segregated Industrial" districts that are built around rail or barge infrastructure and have high-capacity utilities serving them.
In fire code terms, you'd put your high-hazard (Group H) uses into the Segregated Industrial district, and most of the ordinary and moderate hazard uses (Group F, Group S, and Group U) into the General Industrial category where they could go in among other commercial (Group B, Group M, and to some extent even Groups A, E, and I) and even high-density residential uses.
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[Question]
[
It is said that around 50km above the surface of Venus is the most earth like environment on the whole solar system (source [here](https://en.wikipedia.org/wiki/Colonization_of_Venus?wprov=sfla1)),
>
> At an altitude of 50 kilometres (31 mi) above Venerian surface, the environment is the most Earth-like in the Solar System – a pressure of approximately 1000 hPa and temperatures in the 0 to 50 °C (273 to 323 K; 32 to 122 °F) range. Protection against cosmic radiation would be provided by the atmosphere above, with shielding mass equivalent to Earth's.
>
>
>
Therefore it is possible to build floating aerostat cities on the venusian cloud tops. Given sufficient time and technology humanity would be no doubt colonizing the venusian atmosphere in floating cities.
But only one problem remains, I can't find any good explanation or description of scientifically accurate depiction of how the sky looks like from a floating platform on Venus, 50 km from the surface.
There's an artist depiction of Venusian cloud tops on Wikipedia:
[](https://i.stack.imgur.com/A2Fj0.jpg)
And from [HAVOC](https://en.wikipedia.org/wiki/High_Altitude_Venus_Operational_Concept?wprov=sfla1),
[](https://i.stack.imgur.com/rbHgx.jpg)
Both depicting different coloration of sky and clouds of Venus.
The first shows orange-ish nuance of color (I think) and the second proposes Earth like coloration of sky and clouds.
While both looks beautiful enough, I am wondering on accurate depiction of sky and clouds coloration on Venus.
Therefore the question would be:
**What is the accurate depiction of how sky and clouds coloration 50-60 kilometers above venusian ground would be like as seen from a floating aerostat platform?**
Someone has asked a similar questions [here](https://worldbuilding.stackexchange.com/q/63907/7974), but I have to make it clear that while the question is about the same general subject (venusian aerostat), I am asking about the accurate coloration of Venusian atmosphere 50-60km from surface, not about whether or not it is feasible.
[Answer]
Common misconception is that Venus is a dirty yellow; this partly comes from false-colour images that are common used but also the association of Venus' sulfur content and how elemental sulfur looks. Venus is virtually pure white in true colour.
* [Sulfuric acid](https://en.wikipedia.org/wiki/Sulfuric_acid) in pure form is colourless.
* [Carbonyl sulfide](https://en.wikipedia.org/wiki/Carbonyl_sulfide) is colourless as well.
* [Carbon-dioxide and water vapour](https://en.wikipedia.org/wiki/Atmosphere_of_Venus) is colourless too.
At 50km, an aerostat would be passing through [cloudtops](http://www.universetoday.com/36871/clouds-on-venus/), that would be [bright white, with hints of yellow](http://www.universetoday.com/14346/the-color-of-venus/) at times due to the impurities that might be in the clouds at the time.
But in reality, the images displayed for the concepts are accurate.
[Answer]
Earth's sky is blue due to [Rayleigh scattering](https://en.wikipedia.org/wiki/Rayleigh_scattering). Rayleigh scattering redirects at an angle a percentage of incident light through a gas. The percentage of light reflected is proportion to $1/\lambda^4$, where lambda is the wavelength. That is, the shorter the wavelength, the more light is reflected. Violet light is most reflected, percentage-wise, but the purple section of the visible spectrum is small. So Blue light is the next most reflected, and since that portion of the visible spectrum is large, the sky is blue. Here is a graph from the above Wikipedia article of percent scattering vs. wavelength:
[](https://i.stack.imgur.com/eb1UJ.png)
According to [Shardanand and Prasad Rao, 1977](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770012747.pdf), the Rayleigh scattering cross section for Carbon Dioxide is 3.5 times higher than that of Oxygen or Nitrogen (Table 1). Because the $1/\lambda^4$ term in the scattering cross-section is the same for all gasses (Eqn 12), the CO$\_2$ scattering curve will have the same shape as the Oxygen-Nitrogen curve on Earth. Thus if we assume a similar molar density of gas particles, the sky of Venus would be even blue-er than our own.
I can't get any density measurements from 50km in Venus' sky, so I can't estimate molar density for calculation. But in the absence of any other color, I would expect the sky in Venus to be blue.
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[Question]
[
I've created a species that, instead of eating multiple times a day like us, eats one tremendous meal and survives off of the fat stores for long periods of time. My question is about feasibility.
First, how chemically efficient is the human digestive system? As far as digestion goes, we can process and absorb a tremendous variety of foods, indicating high efficiency. But, how much of the chemical energy stored in that food do we actually absorb?
My second question: how efficient is fat storage, and could it feasibly be more biologically efficient?
[Answer]
This seems feasible.
However, **human digestion is pretty efficient** - the heat of combustion of starch is ~ 4.2 Calories (kilocalories) per gram, which compares pretty well to the usually quoted 4 Calories per gram of carbohydrates for dietary purposes. (Fats are usually quoted at 9 Calories per gram, so **fat storage is also pretty efficient.** Not quite as efficient as, say, propane, but really quite good.)
Where you can get significant improvements isn't so much in the extraction of energy as in the *use* of that energy. The way humans (and other mammals) do endothermy is very energy-hungry.
Also, humans eat several times a day, but the amounts are rather small. Plenty of animals are capable of eating huge quantities relative to their own body weight. According to the USDA chicken meat is on the order of 200 calories per 3 ounces: <http://www.fsis.usda.gov/shared/PDF/Chicken_Turkey_Nutrition_Facts.pdf>
That's about 1000 calories per pound. So if your creature can eat 20 pounds of meat at a meal, that's 20,000 calories - which is the equivalent of 8-10 days of activity even at 2000-2500 calories/day for a human.
The combination of these two is why some large snakes can go months between large meals. You probably can't go quite as low metabolically as a snake for an intelligent species (brains are very energy-hungry), but assuming they evolved in a very stable thermal environment they might need much less energy for maintaining body temperature.
[Answer]
I think the problem is that if you eat a tremendous meal compared to your body size, you have to "carry" that meal around as you move. This would severely impact your movement ability and moving around would consume a lot of energy.
The closest analogy I can think of are snakes. They eat animals that are bigger than them (a snake can eat a sheep). Then they just rest and digest. [You can sometimes literraly see the shape of the animal they ate in their body.](https://www.google.co.jp/search?q=snake%20eating%20huge%20animal%20shape&safe=active&hl=en&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwii_Kbli9_QAhWMWbwKHc_SBywQsAQIGw&biw=1590&bih=1109#imgrc=YyMeYdmCiQ0szM%3A)
So yes in theory you could have a gigantic flexible stomach and eat gigantic amounts of food but then you won't be able to move while you digest, leaving you vulnerable.
Most "Big" animals have a different strategy, they constantly eat.
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[Question]
[
Could a high powered telescope in space (such as the Hubble Telescope) be capable of peering through a large worm hole with enough clarity to detect that a planet is somewhere on the other side?
If so, can they use the standard techniques that scientists use today to determine if this planet may be habitable? How would the wormhole limit their ability to do this?
Note: I'm writing a story where a civilization capitalizes on a wormhole to begin its space colonization; but first I want to be sure this scenario is credible in some way.
Second Note: While I don't know much about Wormholes, I do know that this wormhole would have to be Traversable, so it'd probably be a Einstein–Rosen bridge.
[Answer]
## It would mainly depend on five things:
* The aperture size and other characteristics of the entry claudication of the wormhole.
* The characteristics of the gnaster and time-space environment inside of the wormhole.
* The aperture size and other characteristics of the exit claudication of the wormhole.
* The wormhole being bi-directional in nature, and not possessing an internal "flow characteristic" of sufficient strength to prevent the passage of light.
* The power of the telescope and post-processing capabilities available to the peeking civilization. Close proximity to the wormhole may be beneficial.
The claudication boundaries of the apertures (the area of division between where the effects and laws of normal-space preside and the laws and effects of the wormhole-space preside, thus defining the aperture or opening of the wormhole on either side) may have an effect on light passing through - lensing, relativity distortion and other possible space-like and time-like effects may alter the characteristics of light passing through.
Furthermore, the effects of the gnaster (the region of stressed and stretched space-time that constitutes the funnel/intestine or navigable cavity "inside" the wormhole between the two claudications) may also have unusual space-like and time-like effects upon light (or matter) passing through.
There is also the issue of **aperture duration**, in other words, is the wormhole "always open", "intermittently open", "always closed" or some other configuration such as "only open when stressed in just the right way"?
## In conclusion...
In order for "peeking" to occur the following would need to be true:
* A wormhole that is either "always open", or has a characteristic predictability as to when it is "open",
* A wormhole with claudications which either: does not distort light passing through, or distorts light in a predictable fashion that can be compensated for,
* A wormhole with gnaster characteristics such that light is allowed to reach both claudication boundaries from either end, and should there be any distortion, said distortion needs to again be predictable such that it can be compensated for,
* A wormhole which lacks a flow characteristic (internal directional bias) or has a tidal flow characteristic allowing bi-directional travel of light, or has an opportune flow characteristic such that the output is towards the peeking civilization.
* A wormhole which is sufficiently close to other objects and oriented in a direction (if the wormhole is not omni-directional in nature) that allows observation of nearby celestial objects.
I should also give passing mention to the possibility that a given wormhole is expressed multiply in normal space - in other words, is not "linear" in nature, but rather has more than two claudications. Not all wormholes will necessarily have only two openings, which may have odd effects upon what is "perceivable" through one of the apertures.
[Answer]
Where space-time is very much not "flat" - where it's noticeably non-Euclidean - it bends light, and there is very strong gravity.
If a human can pass through the wormhole in a straight line without being crushed or torn apart by the difference in the strength of gravity between her head and her toes, then two parallel light rays close together moving along the same path as the astronaut should still be nearly parallel when they come out.
So, yes, a telescope might be able to glimpse in the centre of the wormhole a narrow window into the world beyond with relatively little distortion.
But that won't make it easy to see planets on other side. The telescope won't get an undistorted 360 degree view of the universe on the other side unless it's moving around the wormhole, or (even better) you drop the telescope through the wormhole and have it broadcast a video from the other side. Which frankly I would want to do anyway before I sent a person through, with instruments to measure the tidal force and radiation levels.
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[Question]
[
I'll keep this one brief. I have an alien from a planet which has extremely cold nights and extremely hot days (the day and night cycle may be short or long, I haven't decided).
When the alien gets too cold, it becomes comatose, and its heart beat slows right down, like a strangled alligator. When the sun comes up, it gets heated up, and it returns to normal. In the day, its body focuses on trying to prevent overheating, and the creature spends a lot of its time going between caves to not waste energy in the heat. These creatures are pretty large, by the way, they weigh about four hundred pounds (at 1G gravity), and are terribly strong.
The question is, what organs and biology are best for this temperature control? Giant ears won't work so well with the dust storms, and they can't sweat because water is too precious and scarce, so I wondered if they'd have five hearts or something.
Perhaps more details are necessary?
[Answer]
Shutting your body down when it gets too cold is called **torpor**. [It is a bit like hibernation](http://www.discoverwildlife.com/british-wildlife/how-tell-torpor-hibernation) but occurs daily, rather than for weeks at a time. All sorts of animals from lizards to hummingbirds go into torpor, so that's entirely plausible.
The main problem with torpor is that it normally occurs in small creatures. It takes energy to warm up again. Warming up a rat is like boiling enough water to fill a tea cup. Warming up a cow is like boiling enough water to fill a jacuzzi. So your alien will have to have high energy foods readily available to constantly replenish its energy supplies. Normally that means lots of fat or lots of sugar. Either it instantly snacks on nectar like a humming bird or bee. Or there is a better time of year where it can build up huge fat reserves and live off those in the bad times.
Brown fat ([brown adipose tissue](http://www.medicalnewstoday.com/articles/240989.php)) is a special type of fat designed to generate lots of heat when it is metabolised. Human babies have lots of it becasue they are unable to shiver when they are first born. You creature should have lots of the alien equivalent of brown fat.
Fur/feathers, thick skin and a fat layer (white adipose tissue) can all act as insulation against both heat and cold.
**Shedding heat**. You mentioned giant ears. A structure like elephant ears, or the sail on the back of a [Dimetrodon](https://en.wikipedia.org/wiki/Dimetrodon), are good for radiating away heat (or absorbing it when the sun comes up). But given the harsh nights, you'll need to make the structure retractable or able to roll up or fold away. Otherwise it'll shed too much heat at night AND get frost bite in all that exposed tissue.
Perhaps it has 'balloons' it can inflate, like a [male hooded seal's 'hood'](http://www.arkive.org/hooded-seal/cystophora-cristata/image-G43699.html), or something that unfurls like a [manta ray's cephalic fins](http://www.arkive.org/reef-manta-ray/manta-alfredi/image-G7630.html).
[Answer]
You can cool water down a few degrees by throwing common salt inside. Of course you can somehow inverse that effect - to gain warmth. Your Aliens could use that system to build a kind of fridge inside themselves. That way they cool during the day. They reverse that effect during the night. That would warm them up. They would loose some energy during this process but it could help them to keep some important body parts at a steady temperature. Also the energy they lose would warm you during the night.
There are many other chemical reactions you could use instead throwing salt into water. One good example is aggregate state change from solid to liquid. Which they use would depend upon the temperature they want to keep. If they have a normal body temperature of around 0°C for example they could use ice. It takes a lot of energy to melt ice.
Additionally they should have a good isolation. That would include fat and something like hair or plumes. Additionally to keep their warmth there should be as little circulation of fluids as possible. You want the warmth/cold to stay where it is and any liquid would change that.
Also since they want to keep their warmth and cold equally, they would want to consist of something with a high specific heat capacity - such as water. That would mean that it takes the sun a long time to heat them up and the night a long time to cool them down.
[Answer]
**During the Day**
As @AndreiROM said, cold-bloodedness will help manage heat during the day most effectively. If your creature generates its own heat, it will very likely overheat and die quickly. Your idea of cave-dwelling seems ideal so that these creatures can spend more time gathering food and less time cooling down.
**During the Night**
Consider copying some physiological features of the [North American Wood Frog](https://en.wikipedia.org/wiki/Wood_frog). These creatures can survive for months being completely frozen by creating a supply of anti-freeze-like compounds and circulating them through their bodies' systems. This prevents ice damage; dormancy during the night would solve issues of being too cold to do tasks.
[Answer]
I don't see how more hearts would make for more efficient temperature control. There are many creatures in our oceans which must stave off hypothermia, or oxygen deprivation, for example, and do so by managing their blood flow away from their peripheral systems and to their main organs (seals, etc.)
Such a fine-tuned circulatory system could reroute blood closer to the main organs at night, and more along the peripherals during the day, in order to shed as much extra heat as possible.
Another possible solution is having this thing be cold blooded. Snakes also "hibernate" when cold, and soak up heat in the sun.
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[Question]
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Somewhat based on [this](https://worldbuilding.stackexchange.com/questions/47694/what-modern-technology-would-be-most-revolutionary-to-ancient-greeks) question, let's say a normal person from our world for some reason goes back into time - to the Hellenic Greece around 490 BC and somehow manages to become a philosopher. My question is, **how will he compare to a scholar?** Will he be able to achieve more, because of his knowledge?
**The Character:** The unlucky character is a person of above-average intellect (130), doing a PhD in Maths. He has not memorised vast amounts of information, but he enjoys research in maths, even if it is not related to his topic (which is why I haven't given the topic). *Assume that the magic that brought him back into the past allows him to survive there, and communicate. The Ancient Greeks think he is a travelling scholar, but due to the magic, they don't question too closely.*
Will he be able to revolutionise maths? He can't just say, "This is called integration" as he has to prove it.
**Magic:** To make things clear, I'll add this in. The magic allows him to communicate in Greek easily. He can understand it effortlessly, and it stops the Greeks from asking him very incriminating questions (like where are you from, etc). They simply think he is a travelling scholar and leave it at that. They also **have given him food and a place to stay**.
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Something that most people would think nothing of would revolutionize math in that age.
The number 0. Many mathematicians view it as key to most modern mathematics.
You could also introduce the idea of counting in various bases and information theory pretty easily.
You could standardize units of measure.
Let's not talk about irrational numbers, infinites, imaginary numbers, set theory, etc, or non-euclidean geometry... Anything Principia Mathematica...
Any one of these would totally revolutionize Ancient Greek thinking, let alone mathematics. It might be that only someone with a decent understanding could introduce it though, because most of us don't know the names of these things or how they work and are more second nature to us today.
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My answer differs from the other ones: a revolution does not occur ex nihilo and most of the time, the work of mathematicians that history remembers was preceded by the work of people that have been forgotten now (bare the specialists of history of sciences and mathematics). Life is hard for precursors. It was not easy for the ones who truly made a mathematical breakthrough, being one step ahead of their contemporaries:
1. According to the legend, Pythagoreans that revealed the existence of irrational numbers were forced to commit suicide.
2. Cantor's theory of infinite sets was not understood at his time, which lead him to depression (though some believe his depression was mostly due to the loss of his daughter).
3. Riemann's non Euclidean geometries were looked down, until Einstein used it for its theory of relativity.
Remember also that mathematical notations, even the ones that we seems elementary like +,-,etc... are rather new, so everything that modern mathematicians would write would look esoteric. Therefore, introducing modern concepts to Greek scholars would not be as easy as one could imagine.
Our time travelling mathematician would feel quite lonely if he expects to transmit his abstract knowledge.
However, he can make use at his great advantage of one large area of mathematics: applied mathematics! Demonstrate by example! He can employ modern applied knowledge to daily life, at least the part that doesn't need heavy computations, to pull himself above the crowd of commoners:
1. Probability and statistics can make him rich, with all advantages that come from it: wealth, slaves, women(\*), army, political power,...
2. He can use statistics and its predictive power to become an augur or a religious leader.
3. His knowledge of conic sections could help him improve optic, astronomy, probably one of the few domains where his fellow Greek scholars would understand him.
4. He can use his knowledge of geometry for military purposes. After all, the tiny island of Syracuse was kept safe from invasion of its powerful neighbours thanks to Archimedes' science.
5. Modern cryptography will help him to maintain an efficient network of spies.
To sum up, after an initial period of misunderstanding and ignorance, a time travelling mathematician would use his knowledge for his own personal interest.
(\*) no sexism intended.
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# Back to school
Your mathematician would have to learn math all over again, like a school child. Do recall that you are dropping him into a place where **[Arabic numerals](https://en.wikipedia.org/wiki/Arabic_numerals) have not yet been introduced**, even less so the concept of "[zero](https://en.wikipedia.org/wiki/0_(number))".
Sure, he can do his own math like a pro, but no-one else will be able to understand what he is doing because something as simple as $1 + 1 = 2$ is — well, I will not say "Greek" ;) — incomprehensible to them.
So sure, he **could**, potentially, revolutionize maths (once things like food, shelter, a job and communication is solved) simply by introducing new numbers and zero. The question is if others will join him in this entirely alien way of doing maths. And there are sure to be some very pertinent questions along the way, like "How the heck did you come up with all this?!".
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Each and every child who becomes a mathematician goes from no math to modern math in a period of about twenty-five years. A modern mathematician could take someone through the same process without much difficulty.
The harder problem would be to get students. You might want to start with the most advanced people of the day, but they might have the most trouble relearning the basics. Or more precisely, being convinced that learning the basics in the "new" way is valuable and more "right" than the way that they know.
One of the common jobs for scholars like Socrates, Plato, and Aristotle was tutoring the top youth of the day. For example, Socrates taught Plato who taught Aristotle who taught Alexander (the Great). If people aren't asking too many questions, your protagonist might find such a job. Consider [Croton](https://en.wikipedia.org/wiki/Crotone) in Southern Italy (Magna Graecia). [Pythagoras](https://en.wikipedia.org/wiki/Pythagoras) died around 496 BCE. A visiting scholar might well show up then or a few years later looking for him.
Athens is another possibility, although we have little knowledge of the scholars there in that period. Even Socrates, who came later, is someone about whom we know little directly. Socrates is mostly known through the writings of his student, Plato.
What you really want is to control the entire educations of a group of students. A group because you won't know who will be really important. And the entire educations because you want to control even the small aspects which might otherwise be incorrect. For example, a number system with zero is important but not what the people then would know. Or we normally prove the Pythagorean theorem with similar triangles in modern mathematics rather than with geometric squares.
The greater problem is that better mathematics won't fix the Dark Ages. Archimedes was very close to calculus with his method of exhaustion. The reason that it took two thousand years to actually get calculus wasn't because it was that difficult. It was that they turned away from scholarship. If you don't fix that, they'll just lose more advanced mathematics in the descent.
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The obvious hitch with a superdense atmosphere is that, even without being super deep as well, it absorbs light. Just as the bottom of the ocean is dark even just miles deep, an atmosphere as dense as water(even if actually in the gas phase) would block out light from the sun.
How might we get around this? I already know about sonar, but besides that I’d entertain alternate modalities that end up with a visual-like sense.
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Fish have your answer: the lateral line. Its a sensory organ that runs the length of the fish's body. The lateral line allows fish to sense movement and vibration in water. If you adapt this a small amount you could easily allow for it to work in very thick gasses. The cells on the lateral line have sometimes mutated to allow for electroreception, which is something you should really look into. Electroreception allows for electrocommunication and electrolocation. Which seem to be what you're looking for.
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Starting with what constitutes vision. The vertebrate eye consists of an array of photoreceptors with high resolution due to the large numbers of receptors. Those receptors feed their signals into a specialised region of the brain for processing the signals into that pleasing illusion we call sight or vision. It's easy to fall for the illusion and believe we perceive the world directly, because we don't. The vision of the world around us is effectively a natural form of virtual reality. One that we are well truly embedded in, but fortunately for us the environment where we experience vision is the same environment which helped generate it.
The high resolution of the receptors generates the information makes the world seem seamless and lacking in granularity. Therefore, if an alternative form of perception constitutes eyesight it must have the same characteristics. Namely, high sensory resolution and a large neurological capacity devoted to processing the massive signal flow.
Let's start with eyes. There may be some light in the depths of a superdense atmosphere. Perhaps not enough to read by or hunt prey, but if there's just enough light, then it won't hurt for our aliens to have, at least, one pair of eyes.
Infrared radiation is universal. Everything radiates heat. It just depends on how much heat. Snakes have pit-like heat receptors on their cheeks to help target their prey. This is apart from their eyes.
Let's assume an organism with a large array of thermal receptor pits. This information could be processed by its thermovisual cortex into generating a thermal vision of its surroundings. It's likely this thermal vision will be more coarse gained than our visual world, due to the larger size of the heat receptor pits. Of course, if evolution manages to develop smaller and more efficient heat pits, then this will lead to better thermal vision with improved resolution.
Because a superdense atmosphere will be so good at propagating sound, it would be remiss not to consider the evolution of acoustic vision.
Again this would consist of an array of sonoreceptors that would also have the high density of signals processed in a specialised sensory cortex of the brain. While ears have their own arrays of sound receptors an organism with acoustic vision would need to possess many more sonoreceptors. Perhaps its head could be ringed with ears. The sonoreceptors might be more specialised in their frequency capture. Humans and most vertebrates on Earth are binaural in having two ears. Creatures dwelling in superdense atmospheres could have polyaural hearing or multiple ears, which would be better at locating the source and direction of sounds.
It is quite likely that the creature wouldn't just use ambient sounds and noise for its acoustic vision perception. If this was combined with echolocation and sonar, this would greatly enhance the creature's capacity to perceive its surroundings acoustically.
There is no reason why creatures couldn't combine all three of proposed 'visual' systems. Conventional vertebrate eyes adapted to low light conditions, thermal sensory arrays feeding the thermovisual cortex and an acoustic sensory array(s) feeding its sonovisual cortex.
While a creature won't precisely perceive its environment in exactly the same way we do when it comes to eyesight, functionally it should be able to navigate its way through the world because these potential sensory mechanisms constitute sight in all but name -- apart from the fact that only one of them involves light directly.
**Added to Edit:**
While looking for something else, this [article](http://www.bibliotecapleyades.net/vida_alien/xenology/papers_xeno/et_zoology.htm) by Robert Freitas called "Extraterrestrial Zoology", originally published in *Analog*, July 1981, turned up.
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> Vision, of course, is simply the detection of one narrow set of wavelengths of light within the entire electromagnetic spectrum. One alternative to “visual” sight is infrared (IR) vision, or seeing with heat waves. The rattlesnake is quite good at this – the creature has two imaging eyeballs operating in the visible, and two conical pits on either side of the head which permit binocular IR sensing of temperature differences as little as 0.002 °C. The theory of optics predicts that alien infrared eyeballs with resolution close to that of the human eye could have apertures as small as 4 centimeters at 93,000 Angstroms (the peak wavelength of black body radiation emitted by a warm human body). This compares well with the size of the eye of the Indian elephant (4.1 cm), the horse (5 cm), the blue whale (14.5 cm), and the largest cephalopods (up to 37 cm).
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The fact that rattlesnake have binocular IR sensing and that optics can allow for IR eyes having the same resolution as the human eye, then alien organisms living under a superdense atmosphere would be able to see quite well if they evolved infrared eyesight.
Originally the concept that the heat sensing pits on a rattlesnake could be readily scaled up to that of human vision wasn't obvious. However, it did seem likely that hypothetical but plausible way that both infrared and acoustic vision could be possible, provided certain conditions were meet. Now alien infrared vision seems very likely. The aliens might look gruesome with holes in their heads where their eyes should be.
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In planet Earth, many deep-sea fish, like the lantern fish, have some sort of bioluminiscence as well as big eyes adapted to the dark. This would work also in a superdense atmosphere.
Obviously, deep-sea animals evolved from others that were adapted to sunlight. So the real question is: *why* an animal should evolve to see in a superdense atmosphere? The simplest solution is that the atmosphere wasn't always as dense as today. Maybe a long period of intense volcanic activity caused the emission of gases that block sunlight.
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Parasite are very unusual creatures, their entire livelihood relies on an unwilling host to allow them to live, some parasite even [control the creature itself](https://en.wikipedia.org/wiki/Cordyceps)! Despite this, to my knowledge, there are no parasites that are very intelligent, never mind sapient.
My question is what sort of parasitic species design could possibly develop sapience, and what forces would encourage and lead to that development?
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While we might not see that ***exact*** behavior on Earth, it is quite reasonable to imagine that it exists somewhere in our Universe.
And if we relax the definition of "parasitic" a little bit you will find that there are quite a few examples on Earth as well.
Whenever we hear the term "parasite" we get a mental imagine of some disgusting growth, or insect. However, a lot of species have codependent relationships. A parasitic relationship is simply taking that one (disgusting) step further.
Imagine, for example, that this species is a sentient jellyfish of some kind. It is incredibly fragile, and fears the predators on its world. How it evolved sentience and sapience is beyond the scope of my answer - it simply happened (and to counter SpaceLizard's comment, some creatures are quite intelligent while having quite small brains - although they are not sapient. We do not have a 100% correlation between brain size and sapience/intelligence).
In order to protect itself it attaches itself to a larger animal. A shark style of fish, for example. Or a whale. Over time, some of these creatures find that they can extend tendrils into that specie's nervous system, and tap in, allowing it to somewhat alter its behavior.
As the species evolves, some individuals will become wildly successful at doing this, and slowly but surely the entire species will end up being able to control their hosts to a larger degree.
Fast forward a few hundreds of thousands of years, and next thing you know these creatures are able to control a whole ***range*** of creatures with a certain nervous system structure.
Thus, the forces that would lead it to develop this ability would be the same as what's driven the evolution of every other species: a better chance at survival.
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SpaceLizard has pointed out that your parasites would have to be big to have an intelligent nervous system, and therefore the hosts would have to be much bigger.
But what if a parasite depended on a group of hosts, rather than just one?
What if that parasite at one stage depended on one host, and then on another at another stage?
Such a parasite could develop complex life strategies, which in turn would tend to increase its intelligence, making it capable of even more complex behavior.
It could even deduce that, being successful by parasitizing multiple hosts, it could be even more successful by cooperating with other parasites.
So for instance, during the first stage of its life it could live within the body of its parent. Next it could live by ingesting fluids from several host bodies where no single one would be large enough to sustain it. Later on it could live on the products of several smaller hosts for an indefinite time, while itself breeding.
It might even become intelligent enough to supplement its diet from other sources, and learn to process the products of the living beings it bred on.
By cooperating with other such parasites, it could perhaps develop division of labor.
And such parasites being intelligent, it might occur to some of them that they can be parasites at second hand, living off other parasites of their kind.
Hey wait a minute - fetuses, milk, eggs for breakfast, farmers - politicians - bankers -- sounds like Homo sapiens!
Sometimes it seems like Nature has answers for all our questions, whether we like the answers or not.
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Reading [this](https://worldbuilding.stackexchange.com/questions/40633/how-would-i-know-if-i-were-a-1-mm-tall-robot) question about 1 mm tall people made me wonder: would a 1 mm tall person even be able to breathe? To someone of this size, the oxygen molecules around them would be much larger in proportion to their body, lungs and most importantly, cells. It seems like they might have difficulty with breathing enough oxygen in through their smaller lungs, and with their smaller cells bring able to process this oxygen.
* Could a 1 mm tall person effectively process oxygen and continue to respirate, or would they asphixiate very quickly?
* What would be the smallest a person could be and still successfully process enough oxygen to survive?
**Note:** I am aware that the 1 mm people in the question I referenced were actually robots. I'm specifically asking about a person that is 100% normal human, apart from being tiny.
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1. A 1mm human or other mammal could not breathe. At that scale they would require [an insect style tracheal system](https://en.wikipedia.org/wiki/Respiratory_system_of_insects) to move oxygen around their body.
2. We know humans can breathe even at a size which prevents them being functional in other ways. Premature babies can breathe unassisted below 200mm in height (including legs which are non-essential), but can't survive for other reasons - for example they are not able to move unassisted due to the size of their head. A functional human smaller than this would require a different body plan, with the brain making up a smaller %age of their mass, and a relatively larger, faster beating heart. With adaptions like that, humans could exist as small as any other mammal ([as small as 40mm](https://en.wikipedia.org/wiki/Etruscan_shrew)) but not down to 1mm scale.
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No, they couldn't breathe with just scaled down human lungs. At that scale the surface tension of water would block all the brachi and Van der Waals would prevent the expansion of lungs in the rib cage.
At 1mm height a scaled down human would stick to every surface and would be unable to move at all. The increase in surface area to volume would cause them to freeze to death.
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While something like a warp drive is a staple of ftl technology in sci-fi, I wonder how this sort of spatial warping would operate on a smaller scale on earth.
The idea has occurred to me to have a character with gravity and antigravity powers try to warp distance. This distance warping wouldn't extend more than half a meter from the character's body at most, and at minimum would only be skin-tight. This special warping would bear some resemblance to a [alcubierre warp drive](https://en.wikipedia.org/wiki/Alcubierre_drive), though based on answers I am now informed a [natario drive](http://natario%20drive) is more plausible. *This power can't used to reach anything approaching relativistic speeds*, however I wonder how this would work as a form of superspeed.
Another detail that needs to be covered is how it works when the character interacts with objects: What happens when the character tries to move a stationary or slow moving object? What about trying to move bullets and other objects that are fast in relation to the hero's *actual speed*, and are slow compared to the movement of them and other stuff in their warp bubble.
(The hero is also a vampire which grants the [required secondary powers](http://tvtropes.org/pmwiki/pmwiki.php/Main/RequiredSecondaryPowers))
How exactly would something like a warp bubble work in a atmosphere at non-relativistic speeds? Could it avoid the collateral damage normal super-speed entails? How would this spatial warping affect the atmosphere that occupies the warped space? What would this power do when the character interacted with objects not in the field: both slow moving objects and stuff like bullets. What would such a power look and sound like, both to the user and bystanders (I'm assuming the hero has super fast perception and some degree of super senses to cope, and can already run ~400 mph without warping space, or otherwise using gravity control).
Ultimately I'm really hoping this power will allow things like [this scene](https://www.youtube.com/watch?v=1NnyVc8r2SM) (*except with superspeed that isn't wildly inconsistent*)
**Bonus Question:** What other clever uses would you use a gravity control power for, other than the standard and obvious uses. Assume you have all the other powers mentioned as well:
Super senses, super toughness/strength and a baseline speed around 400 mph, In addition assume an ability to increase perception speed to a nigh unlimited amounts. Super-reflexes also protect you by immediately ramping up perception speed in response to danger sensed by super senses, effectively one's subconscious is always perceiving things in slow-motion watching for danger.
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[@Thucidides](https://worldbuilding.stackexchange.com/a/33906/3510) does raise some valid points, but those were first and [second gen](http://www.space.com/17628-warp-drive-possible-interstellar-spaceflight.html) Alcubierre drives, which for advanced star-faring civilizations have long since been superseded by the more efficient [**Natario** drives](https://hal.archives-ouvertes.fr/hal-00827161/document).
Those drives were truly built for interstellar voyages at effectively super-optic speeds. We don't need super-optic speeds, so a much lighter version of the Natario should do for our needs. So instead of moving masses of thousands of tons at 20x lightspeed, we only need to warp about 100kg at strongly suboptical speeds. Much more reasonable. You probably[citation needed] only need a few hundred grams of negative energy mass (usually obtained from the raw unobtanium ores), which is a lot easier to get than a few tons of negative energy mass.[citation needed]
Moreover, thanks to advances in warping technology, your vampire does not have to have the ring - ball design of the early prototypes. It makes the instant warping calculations a few orders of magnitude more difficult, but that's what pocket-sized quantum supercomputers are for, right?
Now, let's leave the warping to the unobtanium core and the man-shape of the bubble to the quantum supercomputer. How would it look like?
Well, there are several factors:
1. Gravitational effects. - Massive distortions are associated with massive speeds, but the level of distortion required for non-devastating speeds would be much less.
2. Atmospheric distortion and disruption. This would normally be a huge case of concern, given the fact that high intra-atmospheric speeds normally break the speed of sound and that breaks widows and [does all sorts of bad things to the ground around ground-based runners](https://worldbuilding.stackexchange.com/questions/11399/boots-of-speed-how-fast-can-they-go). This would be multiplied a thousand fold with a warp drive -- think of it as akin to driving at really high speed into a granite wall. Thankfully, (unlike the side-fields in the Alcubierre drive that leave the front-end wide open and unprotected) the Natario's drive frontal negative-energy field acts to repel matter. A properly tuned Natario field will have the right density to precisely repel atoms along the way, accelerating them at a few thousand gees to the side the front of the warp field and decelerating them in the rear warp field. The net effect will differ by molecular mass, presumably, but if properly tuned, should simply leave a ripple and (a very light) plasma in its wake (caused by the few accelerated particles that reach the highest-distortion point in our field). The ocean of air should (mostly) part before our Natario drive as the seas before Noah, and (mostly) close back behind us.
3. Acceleration and Unruh Radiation - this stuff can cook astronauts traveling a super-optical speeds but it thankfully not applicable in our case.
From the perspective of someone previously moving at walking/running speed inside the bubble, a distant point suddenly zooms in as the distance between that observer and the destination appears to contract, while the rear seems to suffer an equivalent zoom-out.
From the perspective of an outside observer (who, thanks to our careful Natario drive tuning, would even survive the observation), the vampire would briefly appear to lengthen in the direction of their movement, and then would be gone, with nothing but a slight CO2 breeze in its wake (and sparkle, of course).
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One aspect of the Alcubierre warp drive that many people don't seem to realize is the bubble inside is both cut off from the outside universe and in a free geodesic: everything inside is in free fall.
[](https://i.stack.imgur.com/fpRom.jpg)
There are other aspects to using something like the Alcubierre warp drive on the surface of a planet: the massive folding of space-time around the bubble will have some pretty dramatic effects on the planet in the area of the warp. If you remember that many calculations of how the Alcubierre drive was supposed to work involved rings of stellar or Jovian mass to stabilize the warp bubble, then you can imagine what people in the path of the bubble will undergo (massive gravitational tsunamis of earth being displaced will be the "best case" scenario).
Once the person inside the bubble comes to a halt, there is another potential issue. Apparently, according to some calculations, photons will be accumulating on the leading edge of the bubble as it passes through space. When you stop, this will be released from the bubble a burst of highly blue shifted energy, potentially frying anyone in the direction of motion.
So perhaps it might be best to avoid using Alcubierre warp drives on or near the surface of a planet. The neighbours will complain.
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AAAAAAAAAAAAAAAAAAAAAAAH!!!!!!
This ends badly. This ends so very badly it's quite hard to quantify the effects, but I'll try:
1: One of the major objections to the Alcubierre warp drive is that the stuff in front of you doesn't flow around you. This isn't like water being pushed around a stone, you're literally ramming things into ever decreasing space at the front of your warp bubble, or as this guy would call it, a few millimetres in front of his skin. This spatial warping isn't helping him avoid the atmosphere: it's just trapping it in a layer just in front of him. This is not good for him, nor is it good for anyone else when he stops moving. Assuming his secondary superpowers stop the incandescent plasma sheath at the front of the bubble from cooking him he's going to release a huge burst of high velocity plasma as soon as he stops moving. Please note: This is still at relatively low velocities. Unlike the Alcubierre drive in space there is a lot of high density material for you to ram through. Oh, and the vacuum following you isn't going to be made better by the molten footsteps you'll be leaving behind.
2:OK, lets assume that you can adjust these fields so that you can fling the atmosphere out and around you to avoid this issue. You still have to deal with the fact that this kind of spatial distortion acts as a speed modifier, not really a 'speed enhancer' (this ties in with Thucydides point on it being it's own little bubble). If you run, activate the field, then stand still; you will still be moving forwards until you stop the field. This isn't good for your control over where you're going. Nor is it good for the floor. Remember those molten footsteps? They just turned into molten skid marks every time you slow down or change direction. Again: This is at low speeds. The field around your feet is mashing atoms of solid matter together. If you try to not have the field around your feet then you come apart at the shins. Sorry about that.
3: OK, lets assume that we've got around the issue of atmospheric disturbance and changing direction by having this field only really come into play when the guy is heading in a straight line and not touching the floor. Now we just have to deal with the way that we're *constantly, inconsistently, catastrophically warping space*. This is Not Good with capital letters, even if you aren't moving very fast. If you're warping the space by 3x (to boost up to 1200 MPH), then the distortions are exactly the same as if you're boosting from 0.4C to 1.2C. It needs the same amount of oomph to do and causes the same level of tidal-forces-pain. This isn't helped by the way you keep turning the field on and off, changing direction, and changing the shape of the field to move air around you. You know the lovely diagram in Thucydides answer? Forget it. You'll be leaving behind not just gravitational waves, but gravitational eddies, gravitational bow waves and gravitational upwellings. Say you take a right turn in a city (obeying all appropriate traffic laws using your super-senses, naturally) the gravitational distortions will tear up the junction and knock down (or at the least cause serious damage to) the building you turn away from. Again: This isn't at high speeds. This is at low speeds with a big multiplier. Weirdly: restricting the initial bubble effect to near your protagonist only makes this worse, in the same way that floods are worse when all the water comes downstream at once.
So: To reiterate: This isn't a good idea, unless your protagonist has such astounding control of his superpower that he can damp out the destructive effects of his bubble without thinking about it, turns it off every time his foot hits the floor, only uses it when he isn't in contact with anything and can somehow push everything in front of him out and around the bubble.
If he can do all that then a better use of his superpower is simply to make the bad guys' spleens suddenly 500 times further away from their pancreas than they used to be. But if he prefers super speed:
This will look quite strange to outside observers, a little like taking a surprise trip through a hall of mirrors without intending to, not only from the initial spatial disturbances but also from the subsequent ones used to damp out the tidal effects. From his perspective it'll be a bit like wearing 7 league boots: every leap will take him further than it should. From the perspective of the atmosphere a lot of atoms will get rearranged every time your protagonists foot hits the floor, resulting in a series of gentle puffs of wind.
All in all: AAAAAAAAAAAAAAAAAAAAAAAH!!!!!!
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He can already move at 400 mph on the ground. At those speeds you don't want to do anything that requires maneuvering, like dodging a tree.
There is a reason they use the salt flats for things like that.
26,000 mph is past escape velocity. Anything moving that fast **will** be leaving the planets gravity well shortly, no matter what it is.
It's faster than reentry speeds, where ablative shielding is needed to keep things from disintegrating. Mach 25 is only 19,031 mph, and thermal control is a dominant design consideration at that speed.
Anything going that fast near the ground will cause major damage to people and property.
A better idea would be to use the gravity power to lift up to altitude, then engage the super speed, assuming he can survive the thin atmosphere and wild temperature fluctuations.
**It seems like a time dilation would be what you really want, where he isn't actually moving that fast, it just seems like it to outside observers.**
Getting to close to a large gravity source will slow down time, which is kind of the opposite of what you want.
**BUT** he does have some kind of anti-gravity. Since the further you get from a gravity source, the faster time passes. If you had a way to make negative gravity in a localized area, then you could get maybe speed up the rate that time passes inside the bubble, which would look the same as slowing down time outside of the bubble.
So he would be moving very fast compared to the rest of the world, dodging bullets and anything else. He could even have a bit of a throttle, depending on how high he turned up the anti-gravity field.
**Edit:**
Ok, as Joe Bloggs points out the Alcubierre drive as theorized doesn't work well with anything much denser than interstellar space.
However, with a fine control of gravity manipulation you could get a similar effect that would have less damaging results. The problem is the atmosphere.
You ram something through it hard enough and the shock wave caused by all the little air molecules being violently pushed out of the way will do some damage.
The higher the altitude, the less air molecules there are, and the smaller the shock wave.
But you want to run it at ground level. So you use the gravity manipulation to reduce the air pressure directly in front of him to a partial vacuum, and allow it to return to normal pressure right behind him.
[](https://i.stack.imgur.com/7FrD9.jpg)
This would remove the air resistance and fix the sonic boom problem, and the high pressure behind him would be pushing into the vacuum, which means pushing on him, boosting the super speed.
You could even increase gravity immediately in front of him to pull him along even faster.
You might not be able to get the full 9,000 to 20,000 mph Quicksilver speeds, but you should be able to double or triple the 700 mph Flash speeds.
That'll take you across North America a little over an hour...
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I unfortunately don't have a detailed understanding of the math required to figure out how it would work, but if this character of yours has gravity manipulation powers, I can see two ways to use those powers to travel other than what other people have already mentioned.
1. Use the gravity powers to create a mini wormhole and simply teleport yourself to the destination. This would have the advantage that you don't have to worry about destroying things in between your character and his destination. The downside is that it would take a lot of focused gravity around two spots at the same time and one of those spots is at a distance. If your character can handle that, then this might be a viable option.
2. Use the gravity powers to alter the direction that gravity is pulling you in a localized field around you. If you can bend gravity in such a small space and forwards becomes down, then you could move quickly by increasing the pull of gravity by a lot. One of the characters in Brandon Sanderson's The Way of Kings has abilities similar to this. Admittedly that's a fantasy universe and not sci-fi but that's an example of the type of movement I'm talking about.
Also, for using the Alcubierre Drive as a personal warp drive, there's two books that have that concept. Travis S. Taylor's Warp Speed and The Quantum Connection. Warp Speed comes first and has the protagonist inventing a working Alcubierre Drive. Things develop from there. I'm not saying his science is completely right but a little bit of handwavium can go a long way and I found the books to be entertaining.
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[Question]
[
I'm inspired by [this question](https://worldbuilding.stackexchange.com/questions/12378/infinite-flat-world) and was thinking that it is nigh impossible for sun, moon and star to exist in this world and even if they do, there is no way to sun and moon to orbit and create day-night cycles.
So i came upon a solution, how about a infinite tube world like this :
[](https://i.stack.imgur.com/MykjB.jpg)
Here is my world :
1. There is no end either side of the tube. It is infinite.
2. Tube's surrounding walls are 6371 km thick and their geographical structure is just like earth.
If you started to dig at one point inside the tube first you will go through a solid crust, then a liquid mantle layer, then a solid outermost layer. if you go beyond this layer (beyond 6371 km) you will come out of the other side of the tube's wall travelling in reverse order of the layers.
3. I have not decided the radius of the tube but it should be huge so that a large portion of the center remain empty like space and with negligible gravitation force.
4. In this empty space are moon, stars, even planets, asteroid and lots of other stuff just floating around in either directions of the tube.
5. When a star go supernova it destroy a large area of tube and hurled the debris in either direction. Some of these matter fall down on the surface again and rest create a debris cloud in the center.
6. When this debris cloud gets enough matters either by other supernovas or some other ways they form stars and stuff.
7. These stars and other material in the center space keeps running in either direction of the tube. (This can not be stationery otherwise they will just fall down to nearest surface of the tube due to gravity).
8. These chaotic events could leads to a configuration of two binary stars revolving around one another with parallel to the tube.
9. Thus above configuration can create a stable day night cycle on a small portion of the tube. When a sun comes near the surface it is day and whens it go away it is night until the other one comes around.
What are the possible flaws in this world if i wanted to follow real world physics (as close possibly) ? Could it work to create a possible earth like environment ?
[Answer]
It's not stable in its current form.
If you picture a cross section, it's a wrap-around video game screen and you can pan anywhere and make anything the center. The position of the hollow part and layers is arbitrary. That's interesting but not the point to follow.
There is no gravity holding it all together like the Earth's core. A hollow sphere will have no self-gravity felt inside it. So, digging out a rock it will not stick to the walls but float around.
So you describe a structure that's stratified in the manner caused by gravity with changing pressure and heat! But there's *no pressure* so your faux core will not have the right conditions, there is no mechanism to cause the stratification, so the material will get dug up and mix more uniformly over time.
[Answer]
I think you are going to end up with something sufficiently convoluted that you would be better off dropping "normal physics" entirely. There will be myriad problems... pretty much everything will stop working. Our physics is really not designed to handle infinite structures like you describe.
Let's talk diameter. You started with the suggestion of $6,371\;\text{km}$, the diameter of the Earth. In your edit, you clarified that you are not picky about the diameter, so let's fix it to something that works. You need supernovas right? A supernova emits $1.5\;\text{foe}$ ($=1.5 \cdot ( 10^{51}\;\text{erg}$ or $10^{44}\;\text{J})$) of energy. That's a lot of energy. Let's do a comparison. A supernova emits most of its radiation in about 1 second, so there's no time for cooling. We'll have to treat it as virtually instantaneous radiation energy. Let's see just how big the ring is if we want to see $100\;\frac{\text{W}}{\text{cm}^{2}}$ at the surface. With a little math we see the diameter of the tube needs to be about $7 \cdot 10^{18}\;\text{m}$ in diameter. That's right, not $6,371\;\text{km}$ in diameter, but $7,000,000,000,000,000\;\text{km}$ in diameter! So we don't have to write all those zeros, we'll call it $730\;\text{ly}$.
Why do I pick $100\;\frac{\text{W}}{\text{cm}^{2}}$? It wasn't an arbitrary number. As it turns out, that's right on par with the irradiance used by military lasers to shoot missiles out of the sky. That's right. If you were 730 light years away from the supernova, you'd feel like you were shot with a military anti-balistic missile defense laser!
Supernovae are [bright](https://what-if.xkcd.com/73/)!
[Answer]
As previously mentioned in both the comments and other answers, in **our** Universe this configuration is not stable and will collapse. However, if you're already world building, there's absolutely no reason you can't start with Universe Building.
I already answered a similar question to yours with [this answer](https://worldbuilding.stackexchange.com/questions/15372/how-to-avoid-infinite-gravity/15387#15387).
The results is something called a **Khex Class Cosmos**
[](https://i.stack.imgur.com/KmIZe.gif)
It includes an energy source, energy sink, and materials in between the two.
[Answer]
Actually, I think I see a way it **might** work. You'll want to ask on physics.se to make sure.
Make the tube **rotating**. **Fast**. The centrifugal force will both stabilize the tube against, uhm, itself (geometry is weird in this universe) and will keep the people from falling off of it.
Now, the tube's gravity is actually inward towards the center (an infinite cylinder has gravity pointing towards the center). Suns and such can simply orbit this axis, and even move along it at constant z-axis velocity. From the tube, the stars will look like they're rotating really fast, but really they will be orbiting the central axis quite slowly; it is the tube that is spinning fastest.
This will probably only work with Newtonian Physics, since you would get frame dragging from the tube.
Again, you will want to ask on Physics to make sure I didn't mess something up.
[Answer]
Okay, so all gravity is pointed at the center of cylinder, I think. Therefore, people can't live on it. They would fall into the center.
If I'm wrong, and gravity goes towards the tube, that means that the moons and stuff can't "float around". They would fall into tube immediately.
One way around this is if the tube is completely filled with fluid in which humans float (so they float towards the tube). The other way is if the tube is charged attracting either humans or repelling stars and planets.
[Answer]
For day-night cycles : why not making your tube orbit and at a distance of it, place a wall of light, or just another infinite tube of light replacing the circle sun !
[Answer]
Make a wide Ring world.
See the book Ring World for a more full description.
A very high strength outer shell is set spinning very quickly around a star, the centripetal force mimics gravity and keeps the shell taunt away from the sun, all pulls people along the inner surface toward the shell away from the sun. The shell must be mounted with thrusters to keep it centered. A cylinder is just an extended ring.
Some caveats a supper nova is huge and would obliterate the surface of the ring if it were close enough to receive sun light.
The ring world uses huge squares close to the sun to produce shadows and a day night cycle.
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[Question]
[
[](https://i.stack.imgur.com/WLxpj.jpg)
[](https://i.stack.imgur.com/duI2R.jpg)
Where would you put the saddle? On the neck or on the hip?
Thanks for the answers and comments.
[Answer]
The prime spot would be between the wings with the legs draped over and in front of the wings, straddling the neck.
* By sitting between the wings, the rider is at the center of propulsion, which is important. This is where lift affects the body of the animal and creates a natural center for the animal to pivot from that lift. By being here, the rider will create less of an impact on the animal.
* By placing the legs of the rider hooked in front of the wings, this creates a natural place to hold on to so the rider will be less likely to slip off. It also better centers the rider between the wings.
[Answer]
I'd use a "flat harness", i.e. the animal wears a harness that holds the rider lying flat on the animal's back. This would minimise air resistance and lower the rider's centre of gravity, which would make it easier on the griffin or drake, and make the rider much harder to knock off.
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[Question]
[
I have a galaxy with many civilizations each with several planets. Many of the civilizations are at war with their neighbors, and use technologically advanced weapons in battle.
My question is about the colonies. If one of these civilizations want to colonize a new planet, and want to choose it based only on its natural defenses against future attacks, what kind of planet would they look for?
In order to make it simple, consider only weapons operating from orbit, outside the (potential) atmosphere, with no planet-side assault.
Weapons targeting the planet from orbit may include:
* Huge inert projectiles (like deflected asteroids)
* Long range lasers
* Bombs (Dropped from high altitude, and exploding on impact)
* Missiles (Small or big, sometimes heat-seeker to explode on a structure or a someone)
* Weapons of Mass Destruction (Rarer, missiles or bombs that would raze a city if they explode on the ground)
## UPDATE:
I'm don't want to consider planet natural resources in this question. Colons would bring with them enough life support (food, water, oxygen etc) and construction materials with them if it is not present on the planet.
Underground structures would be, unfortunately, not a considerable solution in my precise case: I'm asking this in order to make a game, and I don't plan to manage this kind of structure.
Underwater (or any other liquid), however, are an interesting point.
[Answer]
**Getting the atmospheric composition right will go a long way towards natural, passive planetary defense.**
**Projectile Weapons**
Shooting small unguided munitions at surface targets through the atmosphere just doesn't work because [...reasons](https://worldbuilding.stackexchange.com/a/21306/10364). Highly turbulent atmospheres may interfere with guidance systems on a guided missile. With radio countermeasures in place, any orbital guidance may not get through to the missile. This only works for missiles or rocks below a certain size though.
Really giant rocks (>100km diameter) don't really care about atmosphere and will just keep going as if the atmosphere isn't even there. (Note that "space" on earth is technically defined at 50km so a 100km rock is going to touch the surface while it's top is still in the vacuum of space.) *If an atmosphere is the planet's armor, space can always find a bigger rock to throw to punch through that armor.* Thicker and thicker atmospheres require bigger and bigger planets to hold onto that atmosphere and the colonists eventually stop looking at rocky super Earths and start looking at gas giants.
**Beam Weapons**
Earth's atmosphere absorbs radiation across most bands except IR, visible, near-UV and radio. These colonists will want an atmosphere at least as good as Earth's because of the good natural protection from the higher energy radiation found in space (and giant orbital super weapons). A planet with a high particulate content (dust or smoke) will scatter visible light lasers, making them less effective.
*Can you even make orbital weapons based on radio waves?* Perhaps not but radio does make for a great sensor suite so you'll still want to take some precautions against them.
[](https://i.stack.imgur.com/BtioM.jpg)
[Answer]
# Planetary Composition
Just as Frostfyre says, one of the key natural defenses of the planet would *have to be* a colossal underground cave/tunnel system. It must also *have to be* really deep underground so that little pebbles measuring ~10 - 20 km don't bother your much (other than completely blocking out your exits and choking you inside, that is).
Another defense I could assume would be a *somewhat* dense atmosphere which also happens to be *slightly* caustic. A casual mixture of sulphur dioxide (20%), nitrogen dioxide (10%), hydrogen chloride (20%), phosphorus V oxide (10%) and oxygen (40%) would be handy (I hope Venus cringes in jealousy!). If the atmospheric pressure is ~5 times the atmospheric pressure on earth, it would be further helpful.
The crust should be largely composed of titanium. Large mountains made of diamond would also be a big help.
# How Does It Help *Naturally?*
You are living miles deep under the crust so asteroid impacts don't bother you much.
Due to *slightly* corrosive and *mildly* dense atmosphere, most of the asteroids (anything lesser than half a mile) would be obliterated to ash within the atmosphere, before reaching the ground.
Due to the same aspects of the atmosphere, any bomb or missile would glow red in the atmosphere and burst tens of miles up in mid-air, far before reaching the surface.
Even high energy lasers would not be able to reach or penetrate the surface, thanks to the extremely dense atmosphere and the incredibly hard crust.
# A *Slight* Problem
Forget any damage from anything dropped, shot or launched outside the planet's atmosphere. It will not damage you at all (unless they all gang up on you and throw a moon-sized body on you).
However, you might have a little trouble landing on this planet and safely making to the underground tunnel system. Good luck.
[Answer]
Your best bet is probably not a planet at all but a large, molten-cored moon of a super-jovian, like a bigger version of [Io](https://en.wikipedia.org/wiki/Io_(moon)). The gravity of the jovian would make it incredibly difficult to hit you with a large asteroid, and you'll be wrapped in flux and plasma tubes which will be hostile to any high technology in orbit (the plasma would also make laser and particle beams less effective).
The downside to this is that the surface is likely to be inimical to life, so you'd probably have to build the bulk of your colony underground. That would add greatly to your defence as well, but on the other hand you could do that anywhere.
[Answer]
If we are only considering defenses native to the planet rather than technological ones introduced by the colonizing species or environmental ones influenced by the same, then the only really viable option is to build underground.
Orbital bombardment (drop a chunk of rock/metal) is pretty much the ultimate weapon, short of the Apex Absolute Annihilator of Handwavium (AAAH) Bomb (copyright pending). Getting hit by a large asteroid is basically the same thing, just an undirected version. We can see the consequences of this ourselves, as it happened on Earth some 65 million years ago (Chixculub).
The best protection against orbital bombardment is to build deep underground. You could build underwater, but water (any liquid, really) is much less dense than rock and less of a defense against most meaningful weapons.
You want your target world to be comprised of, or have large quantities of, a structurally sound material, something that won't shatter/buckle/break/bend under repeated impact, is resistant to shock waves, and is ecologically feasible (e.g., high heat tolerance to insulate the colony).
The best choice would probably be some form of carbon, like carbon fiber, but that kind of world would almost certainly be the result of planetary engineering.
[Answer]
**A very dense atmosphere**
The Earth's atmosphere will burn up small meteors. A denser one will burn up even larger ones. The faster they hit atmo, the more they will burn up, so an attacker would have to drop either a very large rock (making their attacks less feasible) or do it slower than they'd like (giving more time to do something about).
At a high enough density, any manufactured weapons will simply be crushed.
This will also decrease the terminal velocity of the object reducing it's impact energy. Since impact energy is the *square* of the velocity, this can be a big change.
A very dense atmosphere also makes floating easier. Instead of living on the surface, live in floating cities! Then it doesn't matter how many bombs they drop on the surface.
**A very turbulent atmosphere**
This increases the complexity of flying small craft, such as missiles, in atmo; they'll get blown around.
**A very opaque atmosphere**
The [water and carbon dioxide in the Earth's atmosphere absorb many wavelengths](https://en.wikipedia.org/wiki/Sunlight#/media/File:Solar_spectrum_en.svg), throw more gasses and dust into the mix and you'll absorb even more. This makes observation difficult and will reduce the power of energy weapons.
**A very strong magnetic field and a radiation belt**
The Earth has a belt of energetic charged particles about 1,000 km to 60,000 km above the surface called the [Van Allen belt](https://en.wikipedia.org/wiki/Van_Allen_radiation_belt). It's caused by Earth's strong magnetic field trapping things like cosmic rays and the solar wind. The Van Allen belt is strong enough to mess with sensors and damage unshielded electronics. Our hypothetical planet would have a much stronger belt able to fry even shielded electronics.
While the belt has huge gaps at the poles, so it would only restrict an attacker's plausible approaches, or require them to add excessive weight for shielding. Sort of like an orbital minefield. And because it's a belt around the equator, any orbiting object will have to pass through it, or orbit at a height to avoid it.
**Receive a lot of solar radiation**
The dense, opaque atmosphere will protect or colonists, but the poor saps attacking from orbit will be receiving the full solar bombardment. Not just heat, but radiation as well. They will either have to deploy bulky and vulnerable sun shields, or always remain in shadow on the night side.
**Orbit a very active star**
A [coronal mass ejection](https://en.wikipedia.org/wiki/Coronal_mass_ejection) aimed at our planet is bad news for the attacking fleet in orbit. They'll either have to high tail it out of there, or hide in the planet's shadow. Meanwhile, the colonists are protected by the atmosphere and magnetic field.
In conclusion... **visit beautiful Venus!** (BYO magnetic field)
With it's ultra dense and opaque atmosphere full of corrosive gasses, Venus is extraordinarily hostile to everything. What about our poor colonists? They'll be safe in their [floating cities](https://www.youtube.com/watch?v=gJ5KV3rzuag) above the more toxic gases and crushing depths. Bomb the surface all you want, it's hot enough to melt lead down there with enough pressure to crush a nuclear submarine!
[Venus has a very weak magnetic field](https://en.wikipedia.org/wiki/Venus#Magnetic_field_and_core), so our colonists would have to find a Venus-like planet with a strong magnetic field.
[Answer]
If underground planets are out of question, you're out of defence against anything really massive falling from the sky. Underwater habitats will be just smashed by the shockwave in the water. Suggesting a planet with an ocean under a thick ice core is just cheeky.
That aside, there's nothing else natural on a planet that will semi-reliably kill a hardened, shielded single-purpose device or munition, but will not kill a multi-purpose, meaning-of-life-seeking colonist. You can't beat earth in this regard, a shovel is a soldier's best friend.
Your best bet is security through obscurity.
An ideal planet would be the one with multiple obscuring layers:
* a thick cloud layer at 10-12 km (assuming Earth-like atmosphere density) to obscure your planes from satellites if you need air transport
* another thick cloud layer at 2-3 km to make aerial recons largely fruitless
* high trees with lush canopies forming a third layer covering what you have on the ground
Also if the enemy is using lasers and you know their preferred wavelengths, choosing a planet with atmosphere with electromagnetic transparency windows in wrong places won't hurt. However, choosing an atmosphere with abundance of small metallic particles to fool radars will hurt your engines and hurt a lot.
[Answer]
You could hide your colony within a star system that is hidden behind a black hole. (from the perspective of your enemies.) Your radio signals, etc. would not be detected because they would pass into the event horizon of the black hole. Nobody would even know that there was a star there unless they bothered to travel out to a new frame of reference to look.
[Answer]
>
> If one of these civilizations want to colonize a new planet, and want
> to choose it based only on its natural defenses against future
> attacks, what kind of planet would they look for?
>
>
>
# A very inhospitable, resource-poor one.
This assumes that the civilization has the means of making it hospitable *for itself* and that such means are not, and will not for the foreseeable future, be available to the other civilizations (for, at that point, the planet becomes hospitable, therefore attractive, therefore likely to be attacked).
The civilization in question could have modified itself in order to better exploit inhospitable planets (e.g. they don't need a natural environment, open air, sunlight etc. and are happy living in artificial shells deep inside the molten mantle of a tidally locked low-density airless worldlet bombarded by the radiation of its sun).
They could be "uploaded" beings, and live in a virtual worlds which are physically located wherever convenient: this would explain why they choose planets based on their *natural defenses* instead of, say, habitability. They would then rely on the abundance of lifeless worlds to ensure they'd not be disturbed by encroaching neighbours.
A sandy world (think Arrakis) or a mostly water world would provide a ready natural defense against most of the weapons you quote.
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[Question]
[
A crazy dictator (let's face it, most of them are) decrees that all of his subjects must wear a box over their head when outside their homes.
[](https://i.stack.imgur.com/hdQFU.jpg)
There are no eyeholes allowed and the police (who are exempted whilst on duty) check at regular intervals. The boxes are of a standard size and have to be worn level as shown in the photo. They are sold with special internal headgear that ensures this.
People can see a limited amount of the ground, so signposts etc. are painted on the floor. People never see the faces of anyone they have never met at home. There are some illegal establishments that have mirrors on the floor but the penalties for attending these are very severe. Mirrors are banned in all public places.
It would be impossible to police inside everyone's home. Friends can take off their boxes in each others homes. Any suspicion that this is being done for profit or to promote discontent or boxless 'orgies' will lead to police raids and severe penalties. Be careful if you have more than a couple of guests at a time.
UPDATE
The dictator is very repressive. He has now banned all cameras of any kind unless they are government approved and used by the national newspaper or the national broadcasting system. Of course there may be a black market in cameras.
The internet is heavily censored but it exists and tech-savvy people can view non-box and pre-box material. This is not approved but very difficult to prevent. Just don't be caught with any of it on your hard-disk. Because cameras are illegal it is very difficult and risky to make video material of any kind.
**Question**
How would this restriction affect:
1. Dating
2. Sports
3. Entertainment
4. Crime
[Answer]
How would this restriction affect:
Dating - calves and ankles would (legs in general) would become much more noticed and noticeable. Even men would pay attention to what shoes they wear.
Sports - Hockey, floor hockey and racing (running) would be about all you could do, and they would all need to be televised so people can watch them from home.
Entertainment - movies would be boring unless pre-box movies are allowed. And can people film themselves at home without their box? what about internet cams? If internet cams are available, then a lot of dating will happen this way!
Crime - In many ways this will make it much easier. say I'm a pickpocket, I get a little mirror that can 'look' below the rim of my box. Even giving me 10 foot extra view is a huge advantage. (or have 'one way' holes in the box). First spot the cops, likely won't need many for long since it's pretty easy to see who's complying. Then pick a pocket and run. With boxes it makes it VERY hard to identify anyone for a crime. "THAT ONE WITH THE BOX LIFTED A CASE OF MOUNTAIN DEW". It would also be hard to spot, thieves. A camera would have to be watching the store and someone watching the live video.
Edit:
Actually, I would buy pinhole cameras and have them in all four corners with a little screen for viewing... ;)
[Answer]
So this box is unusual enough that its effects are best seen not by looking at the box, but how it affects the senses, and how we adapt to them.
The effect on sight is the obvious one. If one cannot see more than a meter away due to the box, the value of sight will diminish. Likely this will lead to nearsightedness, for the same reason books lead to nearsightedness - there's just no particular value in being able to see far anymore.
The effect on hearing is more subtle. You'd be astonished at just how much information our brain processes out of the sound waves reaching our ears. For example, did you know you can tell if something is above or below you, simply by whether you hear the characteristics of echos off your own shoulders?
The box is a horridly designed structure for this sort of advanced auditory processing, so it seems like a likely place to make modifications first. Inside the box, we would start to see custom shaped inserts which give a more organic shape to the inside of the box and get rid of all those horrible boxy echos. Eventually people would get the hang of making them in a way that mimics how the peaks and valleys of the human ear works, giving us a remarkable amount of directional information. I would also expect some clever hijacking of muscles (perhaps the muscles that wiggle the ears) to control the size and focus of the opening. Wiggle your ears up, and the inserts may open up to let you hear smaller sounds better!
The sense of touch would become far more important, because each person's world would get smaller. The things that matter in the world would always be close into you. If a friend was across the road, you might not even know it unless you recognized their footfalls!
The single most monumental change would be the inability to see someone's face as you talk to them. The amount of emotional information conveyed in the face is staggering. Society, however, is not one to give up the good fight. We would develop new ways to convey that emotional bond. Touch is a powerful medium, so we may see it become proper etiquette to touch hands while talking to someone. Kissing the Papal ring is a ritual in our age, but that opportunity to touch the papal hand would actually be incredibly meaningful in this society.
Of course, talking would be less popular. With the inability to see who can evesdrop, broadcasting communications like that are risky. Every individual would know some sort of sign language which can be used between two people (or perhaps even more). This would double as an excellent way to convey emotions with the hands.
Now for the list:
**Dating**
We would find ways to be "shallow." The ability to show beauty at the skin depth will not be lost simply because we don't have eyes. Careful care of hands would replace careful care of the face. Physical contact would be a lot more important in dating. Whether that makes dating deeper or more shallow is really up to you.
**Sports**
Sports would consist mostly of tasks which could be observed by touch or very short range sight. I would expect strength games like tug of war would be very popular. I would expect not to see very much in the way of speed games. A lack of visual capability means its much more dangerous to go quickly, so it won't be valued as high.
**Entertainment**
Group entertainment would have to be auditory, so singing would be a major form of entertainment. People would also likely dance, given the tactile feedback one gets from dance. Obviously there would not be anything like movies.
One thing which would have interesting changes is magic. I'd expect close-quarters magic to be a major pastime because it is almost perfectly selected for by boxing everyone's head.
**Crime**
Your instinct was that crime would go down. However, I disagree. I think crime would skyrocket. One of the primary tools our society has in place to deal with crime is the justice system. Justice depends on identification, and the box removes virtually all methods of reliable identification. Heightened hearing might help, but I would expect drive by muggings to be a major problem with little to no response possible.
The only solution would be for your dictator to have an iron fist rule. But then crime isn't decreased by the box, its decreased by the dictator
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[Question]
[
This question is inspired by our [fortnighly challenge](https://worldbuilding.meta.stackexchange.com/questions/1916/fortnightly-topic-challenge-4-magic?cb=1)!
In the [Kingkiller Chronicle](http://en.wikipedia.org/wiki/The_Kingkiller_Chronicle), there is a type of magic called "sympathy." This magic works by magicians setting up an energetic "link" between objects. Energy is transferred from one object to another through the link. The magic user needs some source of energy (usually a fire, candle, or sometimes their own body's thermal energy, but not always thermal energy) and connects it to something to achieve some effect. For instance, the protagonist gives an individual a "[hot foot](http://en.wikipedia.org/wiki/Hot_foot)" by forming a magical connection with the person's foot with something like a voodoo doll, and moving the voodoo doll's foot over a candle. Thermal energy went from the candle, to the doll, through the link (with energetic losses), and into the person's foot.
There are few points in the book where the protagonist uses his own body's thermal energy for magic effects. Since he is using his body's own heat energy, he suffers what is known as "Binder's Chills," or magically induced hypothermia. As an additional layer of "realism," the author included losses during this energy transfer.
**Assuming a link with 2/5 energy efficiency (3/5 energy loss), what can an average mage, using sympathy, do with just their body's thermal energy without killing themselves via Binder's Chills?** (See the summary below for specifics!)
I'm also aware of [this](https://worldbuilding.stackexchange.com/questions/519/wondering-what-would-happen-if-magic-was-constrained-by-conservation-of-energy) related question and answers, but they do not go into specifics. I want to know *how much* energy (Joules are preferred) they can sap from their bodies without killing themselves, and what the maximum effects of the sympathy can be. We're looking for something like [this question](https://worldbuilding.stackexchange.com/questions/2909/how-much-can-a-magician-lift-if-constrained-by-her-own-bodys-energy), but for this sympathy.
---
A summary of what you ought to consider in your answer:
1. The mage you ought to consider has a [normal body temperature](http://en.wikipedia.org/wiki/Human_body_temperature). They are not already cold nor are they already hot.
2. This mage is of [average weight and size](http://en.wikipedia.org/wiki/Body_weight#Average_weight_around_the_world) for Europe (the protagonist is a redheaded, pale-skinned male. The UK-Wales data for men in the link is ideal.)
3. The binder's chills can induce severe hypothermia, but **cannot** drop the mage's body temperature below 29 degrees C or 82 degrees F.
4. Sympathy takes energy evenly from the body, and you may consider a individual's body to have constant temperature throughout. (This is a simplification, but one I find reasonable.)
5. This magical link transfers 2/5 of the energy put into it from the magician to the object. 3/5 of that energy is "lost" in maintaining that link. The energy is transferred through the link, for all practical purposes, *instantly*.
6. This thermal energy can be converted into other types of energy. Consider the conversion costs as part of the lost energy in #5.
*For sweet over-achievement:* describe extreme situations by changing the weight or body temperature (due to exercise, etc.) of the mage!
[Answer]
Well, "what can they do" is rather broad given your parameters. Since the energy is taken from everywhere on the casters body, but can be specifically applied to the victim (like the hotfoot example), the effect increases when you narrow the area. This quickly gets very dangerous.
1. The brain comprises ~2% of the body by weight, so any heat lost is multiplied by a factor of 20 (100%/2%=50\*2/5=20), less if we're talking about smaller pieces of the brain. Drop your whole body one degree to instantly boil someone's frontal lobe.
2. The average human skin weighs 8-10 pounds (3.6-4.5 kg, ~5% of the body, factor of 20\*2/5=8) and covers 22 square feet (2.04 square meters). [The head in total is ~9% of that](http://en.wikipedia.org/wiki/Total_body_surface_area) for a heating factor of 100%/9%\*8=88. It would be trivial to set someone's head on fire or ***literally melt the skin off someone's face.***
3. My browser history is starting to get disturbing, so I'm not even providing sources for these: cauterize the heart, or coagulate blood in the surrounding arteries, or boil the acid in their stomach.
The point is, doing these would require very little loss of energy from the perspective of the caster. Figuring out the energy cost in Joules is *extremely* complex and unnecessary for these cases. Unless the caster is on a ***very*** tight energy budget, they'd be losing more just from normal thermal dissipation at room temperature.
For some non-gory applications:
There are so many compensating systems in the human body that getting an accurate look at our energy budget is very difficult. We're going to do this as simply as possible. The [average human produces ~100 watts](http://en.wikipedia.org/wiki/Thermal_neutral_zone) of waste heat, comparable to an incandescent bulb. That means our wizard can easily power a lightbulb with this otherwise wasted heat at no real cost. This also equates to 2.4 kWh in one day, which is the same as saying 2.4 kJ.
It's estimated that the [average BMR for an adult male](http://en.wikipedia.org/wiki/Basal_metabolic_rate) is approximately 1500 kcal/day, though there is HUGE variances between people. [One thermochemical calorie = ~4.184 J](http://en.wikipedia.org/wiki/Calorie), so the total daily energy use of this hypothetical human is 1500\*1000\*4.184 = 6,276 kJ. Put in that context, the rate of waste heat is surprisingly low.
Maintaining body temp is only one of the vital tasks of the metabolism. Average body temp is 37C/98.6F and you've limited us to a minimum of 29C for a total available energy loss of 8C. For a simplistic BON, 1kC = an increase of 1C for 1kg. Our hypothetical person is ~71kg so a drop of 1C= 71kC = ~297kJ. Each loss of 1 degree C frees up ~300kJ\*2/5=120kJ of energy for your magic.
For reference, this is almost eight times the [energy capacity of a standard AA battery](http://en.wikipedia.org/wiki/Energy_density#). Draining a car battery would be out of the question (2.6 MJ/120kJ/C = ~21C loss of temp, beyond your stated limits of 8C), but you could easily [start a car](https://physics.stackexchange.com/questions/57794/calculating-engine-starter-s-energy-use).
## Total energy budget = 8\*120kJ=960kJ, or just under 1 MJ.
Apparently, that's just about the kinetic energy of a [1 tonne vehicle moving at 160 km/h](http://en.wikipedia.org/wiki/Joule#Megajoule). So I guess you could stop a car at your energy limit.
Today I learned: body fat metabolism has 200 times the energy density as an automotive lead-acid battery (35 vs .17 MJ/kg).
[Answer]
## Burst: Energy
As Isaac already pointed out, we can get a pretty good approximation of a mage's heat capacity using just the heat capacity of water (since pretty much all of our tissues are mostly water). This gives us a maximum energy burst of:
$$
\begin{align}
& 40\% \times 8~\text{°C} \times 4184~\text{J}/\text{kg}\cdot\text{K} \times 71~\text{kg} \\
&= 951~\text{kJ} \\
&= 264~\text{Wh} \\
&= 22.0~\text{Ah}~@~12~\text{V}
\end{align}
$$
* This is equivalent to around $315~\text{g}$ ($4900~\text{gr}$) of gunpowder ([energy density](http://en.wikipedia.org/wiki/Energy_density#Energy_densities_of_common_energy_storage_materials) about $3~\text{kJ}/\text{g}$), or over 100 M-80s .
* This is enough energy to fire almost 2000 .45 ACP rounds ($230~\text{gr}~@~830~\text{fps}=475~\text{J}$), or five [30 mm, armor-piercing, incendiary autocannon](http://en.wikipedia.org/wiki/GAU-8_Avenger) rounds ($14~\text{oz}~@~3250~\text{fps}=190~\text{kJ}$). Let's hope this doesn't violate conservation of momentum.
* This is enough energy to raise $29~\text{g}$ to low Earth orbit ($250~\text{mi}=410~\text{km}$ altitude, specific orbital energy $\approx 33~\text{kJ}/\text{g}$), or to raise $985~\text{g}$ up $100~\text{km}$ to the edge of space (enough to take my camera, $\approx 700~\text{g}$ with lens, with a $40\%$ mass margin).
* Assuming no violation of thermodynamics, this is [enough energy to extract](http://en.wikipedia.org/wiki/Entropy_of_mixing#Gibbs_free_energy_of_mixing) about $2.8~\text{kg}$ of gold ($92~\text{oz}$, around \$100,000 worth) [from seawater](http://en.wikipedia.org/wiki/Abundances_of_the_elements_(data_page)#Sea_water) (abundance around $10^{-11}$, entropy of mixing about $240~\text{J}/\text{mol}\cdot\text{K}$).
* Enough energy to charge my phone ($3300~\text{mAh}~@~3.7~\text{V}$) 21 times over.
## Draw: Power
Although the burst energy is interesting, there's still a crucial factor missing: we don't know if "recharging" a mage's internal heat reservoir takes seconds or hours.
As a rough estimate, the amount of heat generated by the average $70~\text{kg}$ male is around $70-100~\text{W}$. During exercise this can rise to $200~\text{W}$. (Endurance cyclists generate a long-term average of around $185~\text{W}$, while world-class rowers can peak at $3/4~\text{HP}$ of mechanical energy during a $2000~\text{m}$ race, corresponding to a heat output of almost $1.9~\text{kW}$!)
Assuming that heat is generated at $150~\text{W}$ while recharging, and that heat loss is roughly proportional to temperature (with standard body temperature corresponding to $100~\text{W}$ of heat output), we get an equation like this:
$$
300~\text{kJ}/\text{K}\times\dot{T} = 150~\text{W}-100~\text{W}\frac{T-25~\text{°C}}{37~\text{°C}-25~\text{°C}} \\
T=(43-14e^{-t/9.9~\text{h}})~\text{°C} \\
t\_{T=37~\text{°C}} = 8~\text{hours}~20~\text{minutes}
$$
That means that peak burst power represents the better part of a day's reserve, unless your mage takes the time to warm himself by the fire (which can deliver a significant amount of heat).
But hold on a second... what if you can augment your internal heat with environmental heat? Unlike for a person generating heat, for a person drawing heat from the surroundings the extremities will be warmest and their core will be coldest. We can approximate the torso as a uniform cylinder and use the steady-state [heat equation](http://en.wikipedia.org/wiki/Heat_equation#Internal_heat_generation) in cylindrical coordinates:
$$
0=k\nabla^2u+q=k(\frac{u'(r)}{r}+u''(r))+q\\
u(r)-u(0)=\frac{q}{4k}r^2
$$
Assuming that the maximum temperature your mage is willing to stand is around $120~\text{°F}$ ($49~\text{°C}$), the minimum core temperature is the same as before, a torso radius of $14~\text{cm}$, and a [conductivity of about](http://users.ece.utexas.edu/~valvano/research/Thermal.pdf) $0.5~\text{W}/\text{m}\cdot\text{K}$, the maximum energy draw can be about:
$$
\begin{align}
q=\frac{4\times 20~\text{°C}\times 0.5~\text{W}/\text{m}\cdot\text{K}}{14~\text{cm}}&\approx 2~\text{W}/\text{L} \\
&\approx 2~\text{W}/\text{kg}
\end{align}
$$
Add on another $1.4~\text{W}/\text{kg}$ from the body's own heat generation, and account for the $40\%$ efficiency, and you get a total output of:
$$
40\%\times(140~\text{W}+100~\text{W})\approx 100~\text{W}
$$
That's not much. Even in this best-case scenario, you could exert more power mechanically. In a more realistic scenario (without absorbing environmental heat) the long-term average output would be in the tens of watts range.
## Summary
Although the body contains a large amount of thermal energy, the body's limited ability to thermoregulate restricts us from drawing lots of power continuously. This form of sympathetic magic should be used more as a tool to precisely deliver small amounts of energy (see Isaac's answer for some good ideas) than to deliver huge amounts of energy (although it is capable of doing so at great cost to the mage).
## Coming soon: Cheating Thermodynamics
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I want a mermaid protagonist. If I am to make this story realistic, how should the Merfolk's body structures be made to make them adaptable for both water (swimming) and land (walking, running)? Is this even possible?
I am asking, more specifically:
* If my Merfolk had tails could they be separated into human legs without them having a human ancestor or sharing a ancestor with humans?
* Could they walk if the tail was constructed into legs or would it take them too many years of therapy and not be worth it?
* Would it be possible for a water based animal to swim with a tail that was structurally just human legs fused together?
* Would it be possible for them to have both gills and lungs and the lungs work?
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The simplest answer would be to not have the legs fused at all. Underwater they would hold the legs together and swim using long flippers/flukes on the end. On land they would curl up the flippers/flukes and separate their legs to walk normally.
Any other solution is going to involve either biologically improbable mechanisms to separate the legs or them moving more like a snake on land.
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That I can think of there are 5 ways. Hopefully you find more:
* The Naga: They use the same snakelike body to swim and walk.
* The Splash: Like the movie Splash or the little mermaid to a lesser extent, the mermaid magically becomes human but can turn back into a mermaid under certain circumstances. In the case of Splash, when exposed to water.
* The One Piece-two piece: One mermaids in the show one piece mature to a certain age, their tails split into two legs like fins. They can still squish them together like legs underwater. Like Sanji, I won't post this because who wants to see that.
* Mechanically or magically assisted locamotion: Also from One Piece because they do everything and it is cool, mermaids can travel on land by using a levatating bubble that is lighter than air. You could more realistically use [mecha legs](http://drmcninja.com/archives/comic/29p06/) or magic levatation dependind on your world.
* The simple solution: Mermaids can have two legs. You can make a mermaid that [walks like a person](http://en.wikipedia.org/wiki/Abe_Sapien) but clearly is not a person. This creature would be a more realistic solution but less complicated. I would focus on making this creatures legs clearly more useful in whater than on land despite dual functionality. This can be done by large flipper feet, necessity to crawl to walk, and/or a different joint configuration (likely the heel being used as a second knee for more power in the water).
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> Would it be possible for a water based animal to swim with a tail that was structurally just human legs fused together?
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If [mermaiding](https://en.wikipedia.org/wiki/Mermaiding) is any indication, yes. Real-world mermaids are humans who wear a swimsuit that covers both legs and ends in a monofin that functions as a fluke. The monofin clips onto the feet, and the swimmer uses a motion called a dolphin kick.
There's an online store called Mermagica that sells monofins and swimsuits designed to fit over them.
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> Could they walk if the tail was constructed into legs or would it take them too many years of therapy and not be worth it?
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Milagros Cerrón and Tiffany Yorks were born with sirenomelia (fused legs). Their legs were separated surgically, and with physical therapy, they learned to walk. (No word on whether anyone in the operating room was named Ursula.) Ms. Yorks still needs crutches. Shiloh Pepin was born with the same condition, but because the blood vessels in her fused foot were more intertwined, she couldn't be given the same operation.
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> If my Merfolk had tails could they be separated into human legs without them having a human ancestor or sharing a ancestor with humans?
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That depends on what you mean by "ancestor", as all vertebrates are believed to share an ancestor. If you just mean not sharing an ancestor within the order Primates, then yes, there are examples of other aquatic vertebrates swimming with specialized hind feet: seals among mammals, and loons and grebes among birds. If you're aiming for some measure of land agility, as your [later question](https://worldbuilding.stackexchange.com/q/4707/601) implies, you could consider elements of the physique of Olympic gold medalist Michael Phelps: long, thin torso, long arms, short legs, and large feet connected to hypermobile ankles. (See Phelps, *No Limits*, p. 67.) Then exaggerate them. But if you're looking to create mer-*people*, as opposed to yet an-otter animal species, you still may need a path to sapience other than that which produced *Homo* (tree dwelling -> prehensile hands -> tool use -> sapience).
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> If my Merfolk had tails could they be separated into human legs without them having a human ancestor or sharing a ancestor with humans?
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> Could they walk if the tail was constructed into legs or would it take them too many years of therapy and not be worth it?
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> Would it be possible for a water based animal to swim with a tail that was structurally just human legs fused together?
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Human legs wouldn't be the best way for a mermaid to swim. If they must have legs, then a lungfish-type leg would be a wonderful solution; Lungfish, unlike tetrapods, have a long spine-like core with many digits forming a fringe on either side. This spine-like system would be much easier to use as a tail. It should also work for legs, though not as well as human legs
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> Would it be possible for them to have both gills and lungs and the lungs work?
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Yes. There is no reason why gills and lungs could not coexist. However, there isn't much space in a human neck for gills, and so the gills couldn't be very useful overall
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I realize that creating worlds with multiple moons and/or suns is risky, but I'm toying with an idea to see where it goes. So, a planet has 3 moons. One is large like ours, the second is about half the first's diameter (and mass) and the third is about half of the second's diameter (and mass).
If all on the same plane, and having circular orbits, is there a way to calculate how often lunar eclipses would occur, and especially when all three align?
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> I realize that creating worlds with multiple moons and/or suns is risky
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I think I implied this is one of my answers. I suppose that this statement really comes down to opinion, but there's some rationale behind it. The point is this: Multiple stars *can* be risky; multiple moons generally aren't. So your idea is perfectly fine (I was going to talk about how Jupiter has so many moons, but I realized that you're probably not thinking about a gas giant!).
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> Is there a way to calculate how often lunar eclipses would occur?
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The procedure for doing this wouldn't be any different from the way you would normally calculate when an eclipse would occur: Gather a lot of data and do a lot of calculations. This is actually really, really hard to do, as an explanation [here](http://curious.astro.cornell.edu/question.php?number=182) says:
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> There is no simple formula to calculate what you are interested in. The calculation of eclipses is tedious work requiring many observations or calculations of the positions of the Moon and the Sun. The lunar orbit data must then be extrapolated to find the months when eclipses might occur and then the exact times determined to see where the eclipse will be visible. The eclipse path can then be projected into the Earth's surface to find if a total eclipse will be visible from a given location at a particular time. This work requires a lot of patience and an understanding of the geometry involved and cannot be reduced to a formula.
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It kind of stinks, but it's the truth.
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> . . . especially when all three align?
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Well, you really just have to do the calculations for each one, and figure out when they'll all meet up. It's helpful if they're in an [orbital resonance](https://en.wikipedia.org/wiki/Orbital_resonance), preferably something like $1:2:4$ or $2:6:7$.
By the way, you have to get the sizes and orbital radii of the moons just right. If they appear to small in the sky, you won't see solar eclipses - at least, not *total* solar eclipses.
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If you want to know when moons in different orbits line up, you want to calculate the synodic period. This tells when the Earth and a planet line up again, measured from the last time they lined up. If you substitute the two moons, this also gives the time for a eclipse when viewed from the primary. Assuming the orbits are not steeply inclined, the moons would eclipse each conjunction.
1/S = 1/P - 1/E
where:
P - Nearer moon's sidereal period
E - Farther's moon's sidereal period
S - Time between conjunctions (synodic period)
So if moon 1 orbits in a week and moon 2 orbits in 1.5 weeks, then conjunctions will come every three weeks.
source: [here](http://www.livephysics.com/physics-equations/astronomy-eq/relating-synodic-sidereal-periods-5/)
For additional moons, you could calculate the S period for one pair, then do the calculation again using S as one period and the third moon's period. This should give when a conjuction next lines up with an additional moon...or a triple conjunction.
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You also have to consider how big the sun is, as well - if the sun is the same size as ours, then only the first moon in your scenario will eclipse it, as the others will be too small. They can still have "annular eclipses", though - where there is a ring of the sun visible around the moon, like a donut.
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[Question]
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In searching of a universal eye, I meant a photoreceptive organ which can have all/most of the best capacities of the known eyes.
[](https://i.stack.imgur.com/Nq9tp.png)
So, each type of eye or photoreceptive organ has a different function or specialization, for example the human eyes are one of the best for combining multiple characteristics like resolution and color vision, enough long distances vision but not as an eagle, meanwhile in the other hand, mantis shrimp can detect different wavelenghts outside the human color vision like infrared and ultraviolet.
Eagles have an excellent long distance vision, and other birds like owls have the best night vision with highest concentration of rods and cones.
Other cases are different eye shapes like the chameleons which developed multidirectional eyes and passing a different shape to the pupils confers different characteristics, predators have rounded pupils for focalizing light, while preys have squared pupils for a near to 360° vision.
And there are more examples that I don't probably know, so I was searching for a "perfect predator" (concept can change), and I found an idea from [this guy](https://www.reddit.com/user/hilmiira/):
[](https://i.stack.imgur.com/NJRfO.png)
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> Kuwonics can change shape of their pupils! These properties make them the greatest watchers in the galaxy, they can have night vision by magnifying and changing the shape of their pupils on a dark night, or they can continue to see underwater, or they can concentrate all their cells in the same place, turning themselves into living binoculars.
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This concept correctly fits what I'm looking for, but I don't know if it's possible, so probably I can retake the concept and change some things that could "upgrade" it for my objectives, but still existing problems about a "shape changer pupil", things that I don't how solve or how could work like the configuration of a tapetum lucidum, cones and rods and nervous arrays.
But also you don't need to be abide to this concept, you can answer what set of characteristics you can consider a "perfect eye", because should be emphasized that many characteristics for an eye could be solved for other organs, for example birds can't roll their flat eyes but some have a great neck rotation, snakes have thermal detectors and in some occasions, echolocation could be a better choice than excessive good light capture for nocturnal vision.
Happens that in one of my currents projects I want to use this eye for a plausible "perfect organism" (current concept could change to perfect human or perfect apex predator), for which later I will present the set of characteristics that I have selected in a different post, because I believed that this eye deserved its own questioning. Also an explanation of how this could evolve is not necessary or obligatory. That could be fine but it's not necessary, this can even be explained in terms of genetic engineering.
First of all, Thanks.
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It certainly seems plausible:
* Regenerating eyes or parts thereof is not unknown in the animal kingdom, having been observed in rabbits, salamanders, zebrafish, dogs, mice, frogs, etc, however this normally takes weeks or months, even years. But there is a species of spider, *deinopidae*, which [regrows its incredibly sensitive membranes each night](https://en.wikipedia.org/wiki/Deinopidae).
* The mechanism you've described suggests a stem cell-like function to the host cell, instructing the 'smaller' free-floating cells to generate specific ocular structures.
So the potential barriers to this are speed—getting destruction and regeneration down to a few minutes at most—and instructing the host/stem cell, both of which are reasonably handwaved away by invoking an alien metabolism and evolution of specialized optic nerve–brain synaptic connections.
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**Some things to consider:**
* *Shape Changing Pupils:* this is plausible, and in fact we do this all the time! The pupil is simply the open space or aperture left open to light transmission by the veiling property of the iris. The [iris](https://en.wikipedia.org/wiki/Iris_(anatomy)) a muscular diaphragm that controls the pupil's size by relaxing or contracting. Changing the shape of the iris, within sensible (realistic) limits, would be a matter of organising the muscles and their nerves differently with respect to how it's done in humans. All we can do is (unconsciously) make the aperture larger (low light) or smaller (bright light). For purposes of your beings, their muscles are arranged in such a way as to allow different shapes to me formed. You could even have tiny "micro irises", if you wish.
* *Pupils as Magnifiers:* this is not plausible. Simply put, magnification is not a function of pupil size or shape in real world eyes. [Magnification](https://sciencing.com/maximum-magnification-human-eye-6622019.html) is a function of the lens, which is the clear structure that resides in the anterior chamber, just behind the iris.
* *The Perfect is the Enemy of the Good:* this is more a matter of design principle. The eye is always a product of trade offs, as you yourself note (this kind of eye has excellent distance vision, but can't see close up well; that eye has great low light vision, but can't see colours well). These trade offs arise mostly due to the circumstances of the creature whose eyes they are. A diurnal creature will have little need for low light vision; but will have greater need to distinguish tiny movements that could signal predator activity. You can certainly tick all the "perfect" boxes for your beings' eyes; but your design trade-off will be diminishing plausibility.
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* as @elemtilas mentions the pupil shape and size. This will be connected to the amount of light gathered, but the slit pupil for predators give improved depth of field and the ability to judge distances while horizontal pupils are more useful to detect predators giving a wide field of view but along the plane.
* the mantis shrimp you mention is a wonderful example of having photoreceptors with very narrow wavelength response and covering a very wide spectral range from the near UV to the near IR, but interestingly the mantis shrimp eye is also sensitive to different types of polarization. So in addition to just the color of the light you may want to consider polarization. Lots of things in nature have what is called form birefringence that can alter polarization and the amount of reflected light off of surfaces can be polarization dependent.
* the way the way the "pixels" of the eye are connected and the preprocessing that can occur before sent to the brain for interpretation can also be interesting. For example, only firing the neuron if there is a change makes an movement detection more sensitive. A lot of very simple image signal processing algorithms effectively only sum or take the difference of the surrounding pixels. Things like this can highlight the outlines of images which is again useful for seeing moving objects.
* the sharpness of the image is dependent on the aberrations and the shape of the lens, the size of the aperture also limits resolution bigger being better resolution, but a bigger pupil also increases the amount of light that is passing further from the center of the lens and increases the aberrations. Making a lens adaptable to correct for aberrations could be useful. This could be done by specialize muscles pulling or bending the lens of they eye.
* organically controlling the magnification is more problematic there is only so much room in the eye and typically more than one lens would be considered and would be separated by a distance. However, ike the digital zoom in a camera once you have an image on a retina, you if had the ability control what region of pixels would go to the brain you could effectively have some form of magnification.
* similarly if your retina had the ability to integrate the number of photons over time, you might be able to significantly improve the ability to see in dim light, but at a slower time response. Maybe meditate and stare at something in the dark...
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I'm afraid that rather than not being possible, it's simply not advantageous for something you plan to be the perfect predator to need to reconstruct its eyes depending on what it wants to do. Let's assume it's hunting prey with sight alone: it will likely want to see ultraviolet so that it can see traces of urine and better tell a camouflaged prey from its hiding place, and infrared in case it's prey is warm-blooded to further aid in tracking it and telling it apart from the vegetation it camouflages against. It was successful and hunted it, now it wishes to hunt underwater, so it must deconstruct its eyes and rebuild them into something more adapted to underwater hunting, except it's previous eye already had traits also used to hunt underwater, such as a large pupil and high number of photoreceptors, so it's waiting both an unnecessary amount of energy and an eye structure that was already mostly fitting for the task, with the biggest matter being its ability to operate in water and the percentage of cones and rods in it.
You see, looking at a creature's eyes, how they work and how they're positioned can tell you a a few things about it, sometimes even hinting how it lives (example: creatures with forward facing eyes usually need good depth perception, and is a trait seen both in many predators as well as in some arboreal creatures which need to be able to calculate the distance between 2 branches). Going a bit away from earth biology as we know it, the potential eyes of your "perfect predator" and it's very name seems to tell me one thing: your creature is most likely a carnivorous shape-shifter, which can and will change its overall shape according to the environment it's in and what it's hunting, which is the only way I can see it being capable of giving any predator which is already highly adapted to their niche a run for their money: mimicking their millions of years worth of adaptations on the fly so that it can have a chance to outcompete them to begin with. However since it's a science-based question I'll stop approaching this scenario, as no creature over 50 cm long (because I'm not sure about certain smaller creatures) on earth, as far as I know, can actually change its entire structure on the fly and to such a degree like this hypothetical hunting machine does, with the closest to a living example being the mimic octopus (which can mimic the appearance and behavior of several creatures in its habitat on top of its camouflage abilities, but that's about the limit of how much it can "become" the creatures they mimic).
Now, putting aside how the rest of its body works and simply assuming its vision is the most important factor on whether it can hunt something or not, it still doesn't look practical, simply because we're talking earth biology here. Even if we're talking about a bioengineered creature, I still think a single pair of eyes which can change :
**1-** while several eyes are much more costly to maintain than 1,they also ensure you're always ready to make up for said cost. If you need to hunt a creature, whether it's in land, in water, in bright or dark conditions, it will always be ready to use the eyes it needs. Meanwhile if the single pair creature needs to leave the water to hunt on land for some reason, it will need to first adapt its eyes, which takes a good amount of time and also a good amount of energy (remember it's basically destroying the previous eye structure and forming a new one in every change), and while I can't tell exactly how costly it is or how long it'd take due to not remembering any good real life comparisons, it sounds superficially like a reasonable disadvantage for not too big of a difference in energy efficiency, especially if it needs to change its eyes often enough to have developed this ability to begin with, assuming a natural evolution approach. The only advantage I'd see here is if it was bioengineered, and simply had it but didn't use it too much that it became too costly, at which point it might have been better to just make different versions of the creature adapted to different conditions.
**2-** animals often don't only use their eyes to see the world. For this let me use one of my favorite animals: the vampire bat. It is considered to have good vision, especially at night, but it also has great hearing, which is good enough to both let it echolocate its way through the darkness as well as to find animals it has fed on previously simply by the prey's breathing. Once it finds the prey, it will use infrared sensors on its nose to locate blood vessels closer to the skin surface, which it will cut open and use to drink the animal's blood. In this simple example he have a naturally occurring creature using 3 different sensing organs/structures to hunt. Truth is: few creatures will rely solely on a single sense to find food or to live its life. You want eyes which can see ultraviolet and infrared? Why not leave ultraviolet to the eyes while letting the infrared to a pair of pit organs? Do you really need to have good night vision or can you make up for the lack of it with echolocation? If you can't even see your prey, why not listen for or sniff for it? Simply handling every aspect of navigation and hunting to the eyes alone sounds like a poor choice of design, and is not something we actually see often in nature, which helps demonstrate how it's not always a good idea. Even some owls, usually known for their great vision, will also rely on their ability to hear in 3 dimensions to hunt prey hiding under the snow.
Now: whether it can actually happen: I don't think a pair of eyes which can just digest and reform themselves according to the environment the creature's in are an efficient alternative, nor do I think it can occur considering earth biology alone. The closest thing from this alternative which could actually work in reality, as far as I see (ha? Haaaaa?), is to have a creature which, via a weird evolutionary history (which likely evolved an ancestor which had to live and navigate between drastically different environments) or simply via bioengineering, ended up having multiple pairs of eyes, with each pair adapted to a different environment (in your creature's case, around 3 to 4 pairs I'd say).
In regards of my vision of a perfect eye: ideally one much like the one you wanted, capable of changing according with the environment the animal's in, but on a more realistic perspective, the perfect eye is an eye which attends the needs of the creature, and which works in conjunction with other senses to form a full picture.
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To start this off I will dispel preconceptions: Africa had great empires and was not technologically inferior to Europe before the invention of guns. They had quilted armor (the equivalent of *gambeson*) and metal armor - it wasn't wide spread, but there was chain armor, and plate armor in one area of Africa.
My alt-history story: a Byzantine empire equivalent (this isn' set on Earth) starts encroaching on the "African" empire's land and pushes farther.
How would you justify all 10 empires / kingdoms of the time to form an alliance and fight the "Byzantines"?
The question gets complicated because, just like Europe, Africa has a lot of ethnic groups that don't get along. This is important because of trade - these ethnic groups would not trade with one another so each empire's armor and weapons won't be used for their standing armies.
One empire may have plate armor but the others won't and without it their armies would be subpar.
[Answer]
## Coalition warfare is one of the Strategist's oldest problems
What your alt history world is facing is what sovereign states have faced since at least as long ago as Sumer and Babylon. A nation or a kingdom has to appeal to another nation or kingdom and convince them *to risk their blood and treasure* for {a reason}. A great model for you to use to apply this coalition warfare problem to your scenario is the period from 1789 to 1815 in Europe. Why?
It was the period of coalition warfare (against Revolutionary France) - it took **Six** Coalitions to finally defeat Bonaparte, and between times the alliances shifted and moved as the motives and goals of each crowned head in Europe changed.
We used that period at Staff College to consider core problems in coalition warfare. (We also examined The Peloponnesian War and WW II). What makes the Napoleonic / Revolutionary period a great model for you is that there was a profound *cultural* motivation to oppose Revolutionary France: the French Republic's goal was in direct opposition to the cultural baseline of the *ancien regime* in that it sought a fundamental change in how society is structured - (1) no more family owned kingdoms and (2) a reduced role of the church in the social structure, or even its removal from it.
Let's apply that tension to your Byzantine versus African analogues in your fictional world.
Step 1: establish what about this Byzantine-style Empire is profoundly different from the culture of the ten kingdoms / empires who oppose it
* Let's pick a couple of easy ones: religion and language.
Monotheism (of a sort) Byzantine practices versus polytheism and / or animism (of a sort), and even a collection of all of them among the ten kingdoms.
Language:
All of the African-analogue nations have something like a Romance Language relationship to one another's languages. They have established a *lingua franca* and are able to easily communicate with each other, regardless of how much they dislike each other. The Byzantines, on the other hand, speak some barbaric tongue with an indecipherable script / alphabet ...
Step 2: Despite their differences, all of the kingdoms agree that they don't want **that** (language, religion, both) jammed down their throats.
Result? They form an alliance against **that**, and when it's over they are either better friends than before or they fall into bickering again.
You can come up with a few more cultural taboos - those Byzantines practice human sacrifice! - which the African empires and kingdoms not only **don't** accept, but **won't** accept, to justify *why* they ally against this foreign threat.
All they need to be is *good friends until the war is over:* see the US and USSR versus Third Reich for a fine example of that. Afterwards, they can go back to their standard antipathy for one another.
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>
> How would you justify all 10 empires/ kingdoms of the time to form an alliance and fight the "Byzantines".
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When you have to fight many fires, the bigger fire gets more attention, and a lot of ants can make a lion run away.
So, when there is a common enemy it's common sense to set aside the rivalries and form alliances.
For example when ottoman empire tried to get a bit on Europe, they united together and fought the common enemy in the [battle of Lepanto](https://en.wikipedia.org/wiki/Battle_of_Lepanto).
Same did the Greek polis when the Persian empire attempted to expand in Greece.
This can happen in Africa in your world, too.
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**Berber Muhammad**
In your world, instead of an Arab, God chooses a Berber prophet to be His messenger and spread the truth of a new religion over civilization. The Berber Muhammad starts in North Africa, and his influence spreads across the Mediterranean coast, down the Nile and if you like, down the Atlantic coast to Nigerian kingdoms there. He unites the countries via religion in the same way Muhammad did, and leads them in a war of conquest against the Byzantines in the same period that the Arab conquests occurred in our world.
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In the story I am writing, there are several fight scenes between clearly non-human combatants. **These combatants have several natural weapons at their disposal that humans do not have, including jaws, claws, weaponized tails, and tusks (though not every individual has the same series of natural weapons), and they use them in combat in addition to more typical jabs, throws, kicks, and grapples.** In some cases these natural weapons are more effective than one would expect based on their anatomy (for example, biting is extremely effective if it does manage to connect). However, despite having non-human anatomy they are sentient beings and fight intelligently, in some ways they are compared in-story to martial artists.
Writing fight scenes has proven to be a challenge due to it being difficult to get a general feel for how a sentient being with non-human features would actually fight. It also poses challenges in showing characterization in showing the character’s emotion and personality through how they fight. For example being upset and going straight for the kill, arrogant and toying with their opponent, or hesitant and fighting on the defense. Or whether they are skilled fighters or just flailing. Martial arts and combat sports like fencing all have moves that can immediately convey some of these things, but I am not sure how to apply that to non-human fighting styles.
**I have tried looking at guides about swordplay, barehanded martial arts, and self-defense in general** (under the impression that improvised “gutter-fighting” might provide more insight on how to fight in unorthodox situations/with unorthodox weapons like claws than formalized sports), as well as tried to piece together some basic logic on how they would use their anatomy from general brainstorming. Obviously no one has written a guide on how to fight with jaws, teeth, and a tail because humans don’t have any of these things. Additionally, many of these guides don't give advice on what to do if you know you are stronger or faster than the opponent, only if you are smaller or slower (and most of that advice is: don't pick that fight/run).
**I have done a lot of research on how animals with natural weapons fight**, but this only goes so far because animals don't have prolonged fights (they usually scuffle and then run if they can) and don't fight with any forethought or strategy. I've also watched a bunch of monster movies but with a few exceptions most of them don't seem to put a lot of thought into how the characters would actually fight (I know that at least a couple of *Godzilla* movies are exceptions, Godzilla's movements being based on bears). I have also looked at several previously asked questions here.
**I have especially had trouble with finding good sources for getting an idea of "combat logic" in general not based around a certain weapon or fighting style that can be applicable to any fight, including fights between non-human combatants with natural weapons.** E.g., fighting with a sword is very different from fighting with claws, but in both cases it is a good idea to use them to guard your vitals to keep them from getting cut. I am also interested in avoiding silly things (e.g., unnecessary spinning) especially as the characters are supposed to be good at fighting and not make amateurish mistakes.
The overall image I am trying to portray is **“martial arts with teeth and claws”**, and the idea that despite being non-human the characters are intelligent enough to think through their actions and have put some thought into how to best use their unusual anatomy.
**Additional Information**
* **They do not have access to artificial weapons like spears, swords, or firearms because of plot reasons** (the fights are more or less unexpected street fights rather than premeditated or ritualized affairs), though on rare occasions they will make use of improvised weapons (mostly based on availability).
* **Some of the fight scenes are nonlethal but most are in a lethal context.**
* **A "one size fits all" fighting style probably wouldn't work because their anatomy varies within the species** (e.g., an individual might have claws but not a tail). Going on a case by case basis is clearly beyond the scope of any one question, **I am more looking for general combat principles that I can them extrapolate to each individual.**
* **The creatures' overall anatomy is semi-humanoid.** Not entirely human-like and exactly how much varies between individuals. Martial arts and combat styles designed to exploit human weak points would work some of the time but not always. In general they have four limbs, two eyes, etc., but not always.
* **Their size is variable.** Most are larger than a human but would also be less than 12 feet/4 meters tall if standing fully erect.
The fact that such variable anatomy would make a codified system of martial arts difficult because everyone cannot learn the same techniques and the same techniques will not work on everyone is a plot point. **Think "stereotypical MMA monster/kaiju fights with non-standardized anatomy of combatants".** At the same time, one would expect fighters to be able to learn how to use their anatomy on an individual level and at least some techniques could be taught between individuals of similar anatomy.
**My question is threefold, all of which are related to one another:**
* **How would a sapient humanoid creature with claws, powerful jaws, and a tail fight if they did so intelligently and in a trained or semi-trained manner rather than lashing out blindly?** (If it helps those three features are the most common ones across the species.)
* **Barring that, does anyone know of any useful references on combat and fighting logic in general that could be applied to a non-human combatant to get an idea on how an individual would fight with jaws, claws, tail, etc.?**
* **Are there any real-life weapons whose usage could be analogous to natural weapons seen on a non-human creature in general to get an idea on how these individuals could use their weapons?**
EDIT: There have been a lot of good answers thus far, though I noticed a lot of them focus on how animals fight. I thought I would share some of the information I have found on how animals use their natural weapons to give an idea of where the question is coming from and the prior research I have done. This isn't meant to be comprehensive but just what I have found so far. A lot of the issues I am having deal with how a being that uses weapons strategically would fight instead of just lashing out.
* **Jaws** - From what I can tell jaws are a very high-risk, high-reward weapon. If your jaws are powerful enough or you have large fangs or teeth they can be devastating, but they require you to get your vital areas (head, throat, abdomen) very close to the opponent’s body where they can strike you easily. Therefore, jaws seem to be terrible openers but devastating closers: break the opponents’ guard in some way and then sink your teeth into them when you know they can’t retaliate.
* **Claws** - This one I have had the most trouble with. There are different kinds of claws in the animal kingdom, claws adapted for slashing and cutting and those that are more adapted for grappling and hooking onto prey. [How a sapient species would use claws adapted for grappling has been discussed previously on this site](https://worldbuilding.stackexchange.com/questions/46041/what-fighting-styles-would-claws-lend-themselves-to-in-a-bipedal-intelligent-cat), though how bladed claws more suitable for slashing wounds would be used does not appear to. I thought a kama or a falx might be an appropriate analogue among human weaponry.
* **Venom** - This one is surprisingly straightforward. Either use hit and run attacks by biting and then returning to finish the job like a Komodo dragon, or use them to sap your foe and wait for them to make a mistake due to sluggishness like a shrew. In a straight-up fight venom rarely works by itself.
* **Tail** - A lot of animals that fight with a tail will arc their body so their head and tail are both facing the enemy at the same time and they can easily lash out with it. The problem with a tail is that because it sticks out behind you one of the easiest ways to get it to strike your opponent is by spinning. Which is apparently a terrible move in combat because it turns your head from the enemy and exposes your back.
* **Long Tusks** - Usage of tusks is very different depending on length. Animals with long tusks will use them like spears, charging to gain momentum. However using them like lances doesn’t work, lances only work for humans because the rider can be dislodged from their seat to dissipate force, if an animal tried that it would likely break its neck. Animals like elephants will also use their tusks in a sweeping motion to knock smaller enemies off their feet.
* **Short Tusks** - Animals with shorts tusks like wild boar use their tusks more like knives, as short-distance slashing weapons to either lacerate their foe or cut at vital regions (femoral artery, groin, viscera). Large razor-edged fangs (like mandrills, chimpanzees, or peccaries) could be used the same way.
* **Horns** - Horns are kind of similar to long tusks. Most animals with horns fight by interlocking them, but when using them against a predator they will also charge and use them in a slashing motion.
* **Spines** - Spines are primarily defensive weapons. They go to cover areas you don’t want your opponent striking or to punish them if they do. You don’t really use them as offense except as a desperation move.
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Well a thicker tail can be used to club a foe whereas a prehensile one can be used to trip or grapple. A big enough tail can aid mobility and a weaponized tail will be extremely deadly. However a tail will have a limited degree of movement (assuming it is attached at the base of the spine on their back) and thus depending on length they'll need to turn to hit with it. Making it a more risky maneuver best done from a guard. They'd probably have one side facing forwards to make it easier to hit with their tail. Sort of like with boxers. A tail that is prehensile can strike from overhead,around the waist or between the legs (not recommended) without needing to turn at all if long enough. But a prehensile tail is usually not as strong.
Claws are fantastic natural weapons as are talons. They can be used to slice open soft tissue and cause extensive bleeding,talons can impale by slamming them straight into an enemy (even piercing bone) and there are many creative ways to utilize them. Grabbing with claws makes it much harder to escape and struggling guarantees further injury. Those with claws on their feet can also kick and if grabbing your or pinning you rake their back leg claws against your abdomen and legs potentially gutting you. (much as large cats do) If you rake at someones eyes with claws you are much more likely to slice open their eyes and even if you miss the eyes the cuts will bleed into their eyes.
Teeth it depends on how the jaws are formed,neck length,etc. But generally you bite when in a grapple. Like wrenching someones neck aside to sink your jaws into their neck and then tear,biting the hand (especially the fingers),arm,leg or tail of someone grappling you and generally if you end up REAL close in combat. As for tusks or horns they go very well with the rush down and pounce tactics. Except you can just slam into them and impale them. Then you can keep hitting them,gore them again,kick them while they're down,etc.
So I'd say it'll involve alot of brutal grapples,strikes to incapacitate and make the enemy bleed,then immobilizing and killing them. Will depend on your build but that is my view of it.
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Well, your fighting styles are going to be based around the natural weaponry. Normally I go on about making the weapon match the style, but you can't tailor your physiology, you are just born with it.
You've listed a variety of natural weapons, and each grouping will influence how the guy fights. Tusks are going to be best used much like a Western style Boxer. Think a cross between Mike Tyson and TMNT's Bebop. Western Boxers wade in, head down, and if you notice the heavy punches come from really close in. Now imagine wading in like that, but instead of a couple of left hooks and uppercuts, a sharp slash with the tusks across the midsection results in someone getting disembowled. The Presumed thick hide and heavily muscled back and shoulders will offer protection.
I imagine jaws and claws would follow a fighting style like Wing Chung. There is a philosophy, I suppose you could call it, with Wing Chung. Every major strike point is along the opponents centerline. Solar Plexus, Xyphoid Process, Throat, Chin, Nose, and so on are all along the centerline. If you can control your centerline, you are in good defensive shape. If you can control your opponents centerline, they are toast. That's the short version, there is a little more to it. Most body movements and blocks in Wing Chung are dedicated to that goal. Not a lot of hard blocks, mostly just light parries to move the incoming off target.
Next in Wing Chung are the punches and kicks. These favor speed and repetiveness over heavy shots. You have to get in close to make it work, and make no mistake, it does work. How I imagine this working with with teeth and claws? even fairly large claws suited to a Humanoid feline won't be long enough to eviscerate in one shot, at least not easily or reliably. Hit the same area half a dozen times though. The damage makes me cringe. Also, with proper centerline control, going for the throat with the teeth or claws gets a bit easier.
Bear type body plans are going to kind of fight light a bar brawler. They will rely on being tougher than anything else out there and wade in, relying on extremely powerful blows that can't really be parried, only outright dodged. anything that gets inside the reach of those powerful arms are going to face a really powerful bite.
These are some starting points, but what it comes down to is look at how animals fight each other.
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Your main problem is that you make a distinction beetween reason how they fight and what they want to achieve. That's human way of fight. Animals are not cocky "Oh I'm so big, I have strenght advantage you cannot harm me". They either have that advantage and will use it, the opponent will notice this and if they decide to fight they don't need to be reminded about that, thre's no mind play here.
Animals go for the kill in the manner of "I'm just seconds away form killing you". Look at wolves who will try to attack/protect their throats. Only then they are somewhat coparable to humans. "I have a knife on your throat, one move and yo're dead". The diffrence is that animals, if they back off will know to not try to pick the fight again immediately. They have been defeated and spared (or not which is again human ethic/morality issue).
So the point - no matter what they use they will go for the kill. It's a fight of deadblow and parry. Let's say a small monkey-type animals with claws would try to climb bigger opponets from their back to try to puncture/cut arteries. How to parry? Imagine cat going on their back with 4 claw equipped limbs up front. Again, cat when attacking a bigger dog will try to go fake going for their mouth while really gaining a leverage to use much stronger back legs on throat.
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i have the same opinion regarding using biting unless in grappling/wrestling (this depend on the jaw length too, i imagine it probably awkward to be able to bite for long jaw like crocodile for example if they have humanoid body, but i can see a bite use in defensive or counter attack (still risky like from bad timing and the teeth may get knockoff or end up breaking the jaw) and this also depend on the animal teeth, such as if it piranha or shark type teeth it can bite off the muscle chunk and opponent will have movement disadvantage and blood loss, while for crocodile teeth for example it can help to lodge and pull or hook the person and slam him like how crocodile or komodo do their thing outside of spinning to shred the body part.
for tail i can see a spinning kick combine/follow with the tail or to low swipe kick and follow up with the tail if its the crocodile or komodo type of tail by using the spinning momentum to aim at their opponent feet or tail to make them fall down or losing their balance (i dont think a full spin is a problem for unarmed fighting as long it quick enough before enemy can retaliate and counter it, it help increase the force or impact too, compare to weapon martial arts which have length advantage and its a lethal weapon and such move is unnecessary. although some animal here clearly have natural body weapon it dont have much length advantage outside of tail which is already awkward as is, and claw can truly be lethal if it reach the throat or pierce the heart, outside of long tusk or horn though, beside its already a bad idea using spinning kick against horn or tusk opponent anyway.), but this depend on their opponent weight and type of tail though. there also kangaroo for example which also help in delivering more stronger kick for the kangaroo type of tail. while a tail like monkey can be use to hook opponent limb in order to disturb opponent balance or grapple or strangle their opponent.
for horn/tusk (elephant type of tusk) pretty much use during charging or try to keep moving, otherwise if you get caught or grappled or stopped you are screwed, since its a good target to get hooked or locked or grabbed, not so much for boar type of tusk they still can deliver slashing motion during close combat so grappling is bad choice against boar, even more dangerous if they are like the real boar counterpart which like to keep suicidal charging or moving forward despite being pierced or lethally wounded, reason why human develop boar spear and need a lot of dog or human to hunt a boar they definitely the dangerous and hardest to defeat in close combat.
for claw martial arts, i am not knowledgable about this martial arts, but try check tiger claw, eagle claw, dragon claw technique in chinese martial arts, outside of claw weapon like bagh nakh to visualize tiger or bear way of clawing and teko kagi which i will recommend or consider as pangolin martial type of slash or claw
image for bagh nakh from pinterest
[](https://i.stack.imgur.com/QqsTX.jpg)
its use as assassination weapon to kill Afzal khan
image from:<https://www.rom.on.ca/en/blog/weapon-wednesday-bagh-nakh-making-humans-into-tigers>
[](https://i.stack.imgur.com/0lPCp.jpg)
and this video:[Secret Weapon of Indian Kings - Bagh Nakh aka Tiger Claws](https://www.youtube.com/watch?v=RArKLkbJ9SQ)
image from the same video
[](https://i.stack.imgur.com/xBZyY.jpg)
teko kagi from:<https://commons.wikimedia.org/wiki/File:Tekko-Kagi_Ninja.jpg>
[](https://i.stack.imgur.com/n1k5u.jpg)
and here pangolin claw
image from:<https://news.janegoodall.org/2017/05/22/a-pangolin-bush-walk/pangolin-claws-and-scales/>
[](https://i.stack.imgur.com/URHaY.jpg)
while for chinese clawing/scratching type of martial arts they sometime equip with this duel gauntlet.
[](https://i.stack.imgur.com/YVeSS.jpg)
or something like this (it have many variant) both from pinterest.
[](https://i.stack.imgur.com/fQEjn.jpg)
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# Tails
Tails come in all sorts of shapes and sizes, so each fighter is going to need to figure out what kind of utility they can get from it.
If you have decent control over the tail and it's long enough, it can be used for whip-like strikes. You don't need to spin all the way to get more reach with a tail, you could potentially use a punch and then twist your body a little further to throw in a follow-up tail strike.
A lizard-like tail would have high potential as a whip-like weapon. While I can't imagine the impact damage from one strike being high, if aimed up an eye you could cause some serious damage or distraction.
A prehensile tail would have usage as a grappling tool. Throw a punch, but also send the tail low to grab a foot and potentially pull an opponent off their feet.
I could also imagine any tail having a little accessory tied to the end of it...something that looks ornamental and cute, but is actually heavy enough to bludgeon or sharp enough to cut.
Additionally, any long enough tail is another limb that could make or break a grapple. Even a weak tail could get into the eyes of an opponent and cause them difficulty.
# The rest
Almost all of the rest making various grappling techniques have applications for grappling, both as defense and offense. So any grappler would have to deal with some of their moves being made unsafe based on what they fight. Jaws? Any technique that puts anything near the opponent's mouth is now dangerous. Spines? If you choose badly your opponent could twist in your grip and shred you.
On the flip side, certain grapplers would have very dangerous techniques available to them. Being able to bite whoever you grab or claw at them will quickly turn a hold into a kill.
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What needs to be improved or added to the structure (device) of human lungs to be able to filter toxic chemical compounds in the air (for example, in mines the air may contain nitrogen, methane, carbon monoxide, sulfur dioxide, hydrogen sulfide, nitrogen oxides, methane, hydrogen, heavy hydrocarbons, radon, ammonia and other harmful gases, as well as water vapor and dust) and dust (as in dust storms) that can get into the lungs when "inhaling" (breathing)?
In other words, what needs to be changed in a person's lungs so that they can breathe air filled with poisonous gases and dust ?
Warning: I only need biological changes, so no gauze bandages or gas masks, just genetic engineering.
[Answer]
**The solution to pollution is dilution.**
Leave the lungs the way they are. The secret to getting rid of contaminants in inhaled air is to intercept them before they reach the lungs. That is currently done via the nasal passages. The nasal passages can be augmented.
1. **Much mucus and long hairy nasal passages.** Macroparticles like dust can be intercepted using mucus. Chordates of all sorts do that now. Hair in the nasal passages offers more surface area for mucus. Dust laden mucus can leave through the front of the nose either as a ow drip or occasional forceful sneezing. Ideally though the mucus is swallowed so the GI tract can capture and recycle the mucus and constituents.
2. **[Amphiphilic](https://en.wikipedia.org/wiki/Amphiphile) soap-like molecules in the mucus.** Lipophilic "toxins" like hydrocarbons can be captured by including soap-like amphiphilic fats in the mucus. Just as soap captures oil and grease and facilities water solubility, amphiphilic molecules in the mucus will capture oils. Plus it will make the mucus nice and bubbly.
Methane is not toxic unless you have so much that is an asphyxiant - no helping that.
3. **Oxides of sulfur and nitrogen.** These are toxic because in water they dissociate into the acid which then is corrosive. Your mucus has [phosphate buffers](https://en.wikipedia.org/wiki/Phosphate-buffered_saline) and lots of it. The phosphate buffer will neutralize acids, and the constituent molecules are not toxic. Bonus - those toxins which are irritating because they are basic (ammonia) will also be buffered by the surfeit of phosphate.
4. **DNA decoys.** The problem with radon is that it has a different mechanism of activity. It is genotoxic because it is radioactive. The mucus of your humans contains a lot of DNA. DNA is a fine constituent of mucus because it is so sticky and gooey and this DNA is not needed for coding - rather it is a scavenger of free radicals caused by radon, ozone, catalytic metals and other things which generate mutagenic oxygen species. As a scavenger of oxidants DNA will also protect again halogens like chlorine. DNA is readily available in the human body. Sloughed epithelial cells or neutrophils can contribute their DNA to the mucus.
None of this is science fiction. It is all just augmenting systems already present in the human body. Your genetic engineers will appreciate that you are not asking them to engineer psychic powers.
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I have a creature that is made of crystal. The problem is, crystal as I know it is structured in ways that don't allow for flexible movement as we are able to do. How could a lifeform made of crystal move like us? What about a rock creature?
It has a spherical body and 2 arms and 2 legs. Basically generic Kirby character or Smash Bros Pacman shaped.
[Answer]
Some of it has to be not-crystal. Or at the very least another form of that crystal.
But that's okay, there's no living creature that's entirely homogeneous.
**Chitin** comes in several forms with different properties: <https://ibiologia.com/chitin/>
**Keratin** also comes in several forms: <https://en.wikipedia.org/wiki/Keratin>
You can do the same with your creature. Give it a hard structural type and a flexible type of crystal, a light sensitive type, etc...
You'll probably need a circulatory system to get stuff from one place to another too.
Barring that you could hand wave away your problem with magnets or ultrasonics.
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Movement is work. Work is based on the expenditure of energy. The assumption is your crystal creature is "alive" because of some kind of crystal based energy that is consumed and replenished in some regular basis. Movement would then be based on expenditure of that accumulated energy. Is that energy expenditure expensive or is it efficient and easy? Quartz watches work because the crystal structure vibrates in a natural fashion. Your crystal creature could move by expending energy in such a way that it vibrated in such a way that it could move from place to place. Most likely your crystal creature does something like the Michael Jackson moonwalk.. smooth and seemingly effortless.
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There's some organic crystalline structures that flex by sliding across each other like sheets of paper. If you can imagine something moving with that kind of motion, maybe with thousands of microscopic crystalline hairs sliding around like a snail.
<https://cen.acs.org/articles/94/web/2016/08/Organic-crystals-designed-flexibility.html>
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**Migratory recrystallization.**
[Ice recrystallization is strongly inhibited when antifreeze proteins bind to multiple ice planes](https://www.nature.com/articles/s41598-018-36546-2)
>
> As shown, the ice grains underwent recrystallization with time (t) in
> different manners including; (i) uniform growth with keeping a
> relatively round shape (indicated by arrows), (ii) shrinkage by
> melting and disappearing, or (iii) merging to become larger ice grains
> (accretive recrystallization). The (i) and (ii) are known as
> migratory recrystallization.
>
>
>
At the joints, the crystals of your creature fracture into smaller crystals. These smaller crystals might melt and disappear, their substance adsorbed to the surface of adjacent crystals. Or they might merge and form larger crystals. The moving interfaces of a crystal creature are constantly fragmenting and recrystallizing.
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Extremely low possibility, but if life synthesizes from scratch after life has existed on a planet for a few million years, would the two separate lineages be able to co-exist?
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## 1/2: Shadow Biospheres
Encyclopedia Britannica's [article on abiogenesis](https://www.britannica.com/science/abiogenesis) claims that some scientists support the theory of multiple geneses on Earth:
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> Some scientists have proposed that abiogenesis occurred more than once... phosphate-based life... gained an evolutionary advantage over all non-phosphate-based life (“nonstandard” life) and thereby became the most widely distributed type of life on Earth. This notion led scientists to infer the existence of a **shadow biosphere**, a life-supporting system consisting of microorganisms of unique or unusual biochemical structure that **may have once existed**, or possibly still exists, on Earth.
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Such a [shadow biosphere](https://www.britannica.com/science/shadow-biosphere), though discredited due to a general lack of evidence on Earth, is theoretically possible. For a planet on which two chemical types of life are generally equally fit to survive, perhaps neither biosphere would be a "shadow" - both could exist independently as long as the environment remained suitable.
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## 2/2: Differentiated Environments: Life on Titan
It might be easier to get multiple biospheres on differentiated worlds with vastly different, isolated environments. Let's take a look at Saturn's moon Titan. Although this world is famous for its **hydrocarbon oceans**, astrobiologists are equally fascinated by its subsurface **liquid water ocean**.
[](https://i.stack.imgur.com/7QmSc.jpg)
Many scientists believe life on Earth formed in hydrothermal environments in Earth's oceans - providing a mechanism to populate Titan's subsurface (if that high-pressure ice shell doesn't get in the way). Meanwhile, others have tested the theory that life formed closer to the surface [in the presence of lightning](https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment) - providing an unlikely, yet plausible means of populating Titan's surface oceans (if hydrocarbon seas can even support life).
Imagine a world with methane seas populated by methane fish - swimming miles above an icy, dark abyss teeming with vastly alien creatures. It's unlikely, it's speculative, but it's **cool as hell.**
[Answer]
Instead of going straight to different materials, let's first look at different ways that life can manifest with the materials it already has. One way to do this is through [Chirality](https://en.wikipedia.org/wiki/Chirality).
Chirality in chemistry is basically a description of the asymmetry of molecules, and organic molecules all seem to share a specific chirality which we call 'left handed'. We know that [mirror molecules can exist](https://en.wikipedia.org/wiki/Mirror_life), but they don't seem to naturally occur.
It is believed that they used to however and there are [several theories](https://cen.acs.org/biological-chemistry/origins-of-life/New-evidence-against-popular-theory/97/web/2019/09) about why our chirality became dominant which you can read about if you're interested. The key point about chirality is that even though it doesn't involve a different materials, it does demonstrate that different formats can be incompatible and that one eventually rises above the other if they share a given ecosystem.
Of course, sharing a given ecosystem is even harder if life formed from different materials is trying to do it. For instance, life that oxidises Fluorine instead of Oxygen is going to find any oxygen rich environment toxic, and vice versa. We as oxygen breathing life forms find many flourine based compounds highly toxic and dangerous to our health. Life based on (for instance) a metal based element with high valency like Chromium is going to struggle to compete for the other elements like Hydrogen, Oxygen or even Iron in a shared environment because carbon is more plentiful and is likely to bind up more of these elements than the available chromium, meaning that it will be harder for chromium based lifeforms in such an environment to find molecular energy they can metabolise.
In short, the odds against this are extreme, largely because of just how organic chemistry works. When you get right down to it, different formats of life are going to be in open competition with each other for available resources in such an environment, and ultimately one of them is going to win it at some point in the evolutionary cycle. Once that happens, the loser is likely to die out completely, leaving a single dominant life format.
The amount of balance required in a complex ecosystem to stop that dominance happening at some point would just be too sensitive to be maintained in my opinion.
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I'm trying to create a scenario where the local star is "quickly" (suddenly up to thousands of years) removed, dimmed with reduced output, destroyed (maybe), or otherwise fundamentally changed as to have dramatic ramifications on all life. Keeping the local system in orbit would be ideal, so complete destruction scenarios may not be the best fits.
The biggest challenge I'm having is that the only star-harvesting ideas I know of are variants Dyson concepts, which seem to commonly seek to harvest the energy of a star throughout it's entire/most natural life (implying that this is the most efficient method, which I am guessing makes sense but I don't honestly know). Dyson shells are suboptimal because they can be interrupted by an intelligent outsider leading to the potential to simply "rescue" the star, but more importantly my understanding is that a shell variant would generally be ~1AU in scale for efficiency-sake, making it disruptive to the type of story-telling I'm looking for -- it would either enclose or be obscenely close to most earth-like planets unless I'm mistaken.
Because of this, I'm struggling to think of ways and motivations for an alien or other being to quickly disrupt the local star. I'm looking to avoid scenarios where the star is simply destroyed for the sake of it's destruction, but rather where it is used for a logical purpose by an uncaring 3rd party.
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The conceptual technology you are looking for is called "[Star Lifting](https://en.wikipedia.org/wiki/Star_lifting)", and it uses the creation of powerful magnetic fields outside of the star to "squeeze" it and force huge masses of plasma to be ejected. At that point the people doing the "star lifting" can capture the plasma, cool it and extract whatever they are looking for from it, and store the rest by condensing it and creating neptune sized artificial planets from the now cold hydrogen and helium from the plasma.
[](https://i.stack.imgur.com/L9DtW.png)
*One method of star lifting. A mechanism for "harvesting" solar wind (RC = ring current, MN = magnetic nozzles, J = plasma jet)*
In the pre technological past, observers on Earth might notice visible fluctuations as the sun's output as the system is being installed and calibrated, and eventually would be seeing the new "planets" as they assumed their orbital paths around the sun. Today, it would be unambiguously clear what is happening, but any species which can travel interstellar distances and carry out star lifting is likely not going to be affected by anything that we can do now or in the near future.
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If "the local star" isn't our Sun, I think I can help you. Actually, I think I can even if it is the Sun, but in the far future.
In ["The End of the Sun"](http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html), two such scenarios are described. These will occur naturally during the star's lifespan, without the need for any third-party intervention, advanced technology or sorcery. You say "thousands of years", so I hope the timescales of 10,000-100,000 years are within the range of what you're looking for.
* The first of these is the "helium flash", which occurs at the end of the red giant phase for a star that was less than $2M\_{\odot}$ in mass during its main sequence phase. It's the point at which the star enters its helium-fusing phase. One such star is our Sun, which is of course $1M\_{\odot}$. Over the course of tens of thousands of years, the red giant shrinks to less than 1/50 of its previous radius and luminosity:
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> By galactic standards, however, the red giant has been shot through the heart. The sudden expansion of the core results in cooling so severe that it is something like the onset of an Ice Age. The cooling immediately leads to much lower pressure in the hydrogen-burning shell that surrounds the core, and therefore to a calamitous drop in the energy output. On a timescale which is almost instantaneous compared to the usual timescale that stars run on (perhaps as little as 10,000 years), the red giant's diameter and luminosity plummet to less than 2% of their former values. For stars the mass of our Sun, the result of the helium flash is a collapse into an orangeish-yellow star with perhaps ten times the current solar diameter and 40 times the luminosity. It is quite a comedown.
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* The second scenario occurs roughly one hundred million years later, as the Sun (which has become a red giant again) reaches the end of its helium-fusing phase. During this time, it's been burning both helium and hydrogen. The explanation is rather complicated, but:
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> In four or five huge bursts, spaced roughly 100,000 years apart, the outer layers of the Sun will separate from the core and be completely blown away. They will form an enormous, expanding shell around the solar system, and move outward to rejoin the interstellar gas. Roughly 45% of the Sun's mass will escape in this way. The remaining 55% of the Sun's mass is soon compressed into the white-hot, ultra-dense core.
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See Stephen Baxter’s [Xeelee series](https://en.wikipedia.org/wiki/Xeelee_Sequence) for an example of this in fiction. Dark matter life-forms called photino birds live in the gravity wells of normal baryonic matter stars, but novae and supernovae disrupt their habitats, so they use their technology to stop nuclear fusion in stars and prematurely turn them into white dwarfs. (In real life, there seems to be strong evidence that dark matter doesn’t interact with other dark matter, and so couldn’t give rise to life.)
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The Photino Birds from the Xeelee Sequence by Stephen Baxter. Creatures made of dark matter that feed on heat, converting it directly to dark matter mass in their bodies. They prefer stable gravity wells with a large temperature gradient like the insides of stars. Like dark matter they're uneffected by three of the four fundamental forces electromagnetism, the strong and weak nuclear force. Only gravity can physically effect them.
Because they like stable gravity wells that aren't too hot or cold, white dwarves are their ideal environment. They REALLY don't like black holes or neutron stars which come from large, bright, high mass stars blowing up on them. Because of this they 'terraform' stars by using their powerful and precise control of gravity to moderate the fusion process in the stellar core, rapidly dimming it into a dim, cold dwarf star that they can feed on for >3×1038 years.
They have almost limitless control over gravity, making them formidable foes. The only way to kill one is likely with a near luminal speed microscopic black hole or some other incredibly intense gravitational field, tearing them apart.
They may be extremely overpowered for your setting but they also don't really *care* about Baryonic life unless it's somehow reached well over a Kardeshev 3 level civilization and is actively fighting them so I think the concept could be adapted to many different settings as needed.
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I'm trying to keep handwavium at a minimum...
The aliens need hidrogen and helium in super large scale. So they stop by the closest star in their path and steal massive amounts of gases from it, using magnetic fields or a tracktor beam. Once the containers are full, they set again on their merry way.
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A Dyson shell doesn't have to be at 1AU, only if you want to have a similar insolation on the shell's inside as we have here on Earth. A closer shell will harvest the sun's energy more efficiently, and you can actually have a series of shells which each feed of the residual radiation given off of the inner ones.
Star lifting is a (slow) method of deconstructing a star, but it can actually also be used to extend a star's lifetime, by mixing up its interior, to prolong hydrogen fusion in the core. If the aliens are defeated, their captured star lifting gear could be used to repair the damage done.
A more final, and probably quicker, but also more speculative, method would be a [Strangelet Bomb](https://en.wikipedia.org/wiki/Strangelet). A Strangelet is an exotic particle that (hypothetically) would "infect" normal matter and grow without bounds on contact. If you shoot such a thing into the sun, it would be converted into a strangelet itself, with unknown, but probably dire, consequences.
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## The Dyson fleet...
They are nomadic constructors that move through the universe like locusts, eclipsing stars. They come to the Sol system with a small Dyson sphere in parts, to harvest the light in the shape of electric energy as step one. They start by mining away Mercury and Venus while a seemingly endless convoy of ships that hold and are the panels and struts they had used in their previous victim's system. And they build between the Sun and Earth. The first result is simple: Sol gets eclipsed more and more as construction goes on, which puts Earth into total darkness for longer periods, and as soon as construction is far enough, eternal darkness. They build it at 0.5 AU, because that saves a LOT of material. What do they use all the energy for?
## ...to harvest the plasma...
They use the power of the star to power a plasma accelerator on the outside of the sphere to generate the fields needed to harvest what they actually want: the plasma.
Shooting particle streams shallowly into the sun, they manage to rip a constant stream of plasma out of the surface, pulling this stream of ionized hydrogen into the accelerator and refuel their locust convoy. The same convoy that is pretty much a Dyson sphere in parts.
## ...and move again
Once their ships tanks are full, the Dyson sphere once again sets sail, piece by piece re-illuminating the solar system after several long years without a single spec of light to the Sol system. The sun is diminished from yellow to a red dwarf, faint in the sky. Its lifetime might be cut in half, its luminosity surely is cut down.
## Earth's lot
The result is, that during the first "dark week" the planet plummets into a short Ice Age, the climate recovering once the planet is back in the light. Then the real Ice Age starts, as the planet is in the dark for months, only getting a short warm phase before it turns into an ever frozen ball of ice once it is in eternal darkness.
Then, the eclipse ends. It might have been a couple long years or decades, but then the weakened sun stands back in the sky. But it is not enough to melt the ice on the planet Earth...
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Background:
It is sometime in the late 21st century. Several unmanned probes have recently been sent to land on and investigate Jupiter and Saturn's moons. Two sites in particular, Europa and Titan, are being monitored closely and have been declared by the world government as manned "no go zones" due to their potential of life.
The question(s):
*What forms of life could exist on Europa/Titan?*
*How advanced would any such life have to be to motivate a crewed expedition to the outer planets?*
Any and all answers will be appreciated. Thank you!
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First of all:
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> How advanced would any such life have to be to motivate a crewed expedition to the outer planets?
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**Any life form of any type would motivate a crewed expedition** - from the simplest, most basic cellular life on up. If we found *any* life on *any* celestial body, we would be *thrilled*.
As for Europa, it has a fair amount of water, and an atmosphere of oxygen. There are theories that it has water underneath it's ice-sheets that could support life as we know it. If this theory is correct, then most marine life as we know it today could theoretically live on Eurpoa.
Titan, however, has a mostly nitrogen and methane atmosphere, so most life forms as we know them on earth would not be able to survive on Titan. That said, [we have found life forms that don't need oxygen](http://www.bbc.com/earth/story/20170125-there-is-one-animal-that-seems-to-survive-without-oxygen). In fact, some scientists from Cornell believe [methane-based life could exist on Titan](http://www.sci-news.com/space/science-azotosome-oxygen-free-methane-based-life-forms-titan-02549.html). It's unclear what *exactly* that type of life form would look like, as we would have to define how an oxygen-free cell would perform, but it does appear to be *possible*, at least in theory.
Until science gives us more answers as how such cells can/do/might behave, you'll have to use your imagination and some hand-waiving to get life on Titan. Europa could/would be more like life on earth's seas. Regardless, *any life at all of any kind* would motivate a crewed expedition for sure.
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[](https://upload.wikimedia.org/wikipedia/commons/thumb/1/13/Carbon_dioxide_pressure-temperature_phase_diagram.svg/580px-Carbon_dioxide_pressure-temperature_phase_diagram.svg.png)
Carbon dioxide turns [supercritical](https://en.m.wikipedia.org/wiki/Supercritical_carbon_dioxide) above a pressure of 73 atm and 304.25 K (31.10 °C). The surface of Venus fullfils these conditions.
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> The density of the air at the surface is 67 kg/m3, which is 6.5% that of liquid water on Earth. The pressure found on Venus's surface is high enough that the carbon dioxide is technically no longer a gas, but a supercritical fluid. This supercritical carbon dioxide forms a kind of sea that covers the entire surface of Venus. This sea of supercritical carbon dioxide transfers heat very efficiently, buffering the temperature changes between night and day.
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However supercritical CO2 on the surface of Venus still behaves very much like a gas. [Some research](https://www.space.com/28112-venus-weird-superfluid-oceans.html) suggests that Venus might once had more liquid-like supercritical CO2 on its surface.
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Additionally I found this picture of supercritical CO2.
[](https://images.ecosia.org/zWayGJefStlX9jWcOMrII9Ih008=/0x390/smart/https%3A%2F%2Fi.ytimg.com%2Fvi%2Fw2pMDqQAAzI%2Fmaxresdefault.jpg)
**So is an Exo-Venus with true oceans of supercritical CO2 plausible? How would the ocean look like, visually and chemically?** I assume that we would simply need greater pressures to get these oceans. So a super-Earth with more gas and higher gravity seems to be the way to go. Would the oceans and coastlines look weirdly earth-like or would the surface be a bubbling mess of "soap-bubbles"? What other chemicals could be found in these oceans? What does the liquid CO2 solve? Will the oceans be salty? Acidic or basic?
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Are supercritical oceans of CO2 possible? That depends on how you define "ocean", but yes. Making them more liquid-like just requires a cooler environment, easily achieved with a Venus-like world that happens to be somewhat farther from its sun than Venus is.
How would it behave? That depends on just exactly how liquid-like it gets. There are two not-very-interesting cases:
1. You start out at low-ish temperatures and high pressures. As altitude increases, the fluid smoothly passes into the definitely-liquid regime and then cross the liquid-gas phase boundary. This would look exactly like any other liquid ocean.
2. You start out at higher temperatures, transitioning smoothly into the definitely-gas regime at higher altitudes. This what Venus looks like. There is no clear transition marking an ocean surface distinct from the atmosphere. If life exists in the high-density solvent near the surface, it faces a blurry altitude limit where swimming upwards results in your biochemistry working continuously slightly-less-well up to the limit where all your macromolecules come out of solution.
The *interesting* cases occur *close to the critical point*. The environmental effects of such an environment are explored in Hal Clement's aptly-named novel [Close to Critical](https://rads.stackoverflow.com/amzn/click/com/0552079154), although the world of Tenebra in that novel has an atmosocean of supercritical water rather than supercritical CO2. If you can arrange for the mean temperature-pressure curve to pass right through, or very close to, the critical point, then you get:
1. A highly variable type ocean surface, which sometimes looks and acts like a normal liquid surface, sometimes just fades away completely, and in between exhibits [critical opalescence](https://en.wikipedia.org/wiki/Critical_opalescence), resulting in light-blocking "clouds".
2. An ocean surface which moves over the course of the day, depending on how much heat it's getting; the liquid/opalescent boundary should rise at night and fall during the day, rather like ocean tides but due to shifting positions on a phase-transition diagram rather than any gravitational interactions.
3. Giant "rain"; when bits of atmosocean condense into liquid near the boundary, they won't fall very fast, since they have nearly the same density as the surrounding gas-like medium. Thus, "raindrops" can end up being ridiculously large, presenting a potential hazard to creatures that might end up walking / swimming through them.
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The problem with supercriticality is that due to the circumstances under which it arises, you lose any clear distinction like "liquid/gas" as you might get at the surface of a conventional ocean. Instead, you get a smooth increase in density and viscosity from the gas phase bits of the atmosphere into the supercritical bits, like a fog that just gets thicker and thicker. If the material in question can exist as a liquid under higher pressure, the smooth transition will continue, getting thicker and more viscous until you eventually end up in something that seems unambiguously liquid. That'll happen with hot, wet superterrestrial worlds, for example, but I don't think you'll get liquid CO2 on venus-like worlds.
You won't, therefore, have "oceans" of supercritical fluid... just banks of thick, foggy "cloud" that rapidly pour and settle into low-lying areas.
As for what it *looks* like, you tube does have some nice videos of supercritical transitions, such as [this one](https://www.youtube.com/watch?v=GEr3NxsPTOA). Watching the transition in process is interesting, but I'll include one possibly relevant screenshot:
[](https://i.stack.imgur.com/tsj2E.png)
[From 1'48" into aforementioned video](https://youtu.be/GEr3NxsPTOA?t=108)... this *almost* shows what I was really hoping for. There's liquid CO2 at the bottom (which is clear and shows some dark material behind it), and (I think) mostly gas-phase at the top (which is also clear, and shows some light material behind it), and the bit inbetween is some opaque and turbulent supercritical CO2. You can see it forms billowing cloud-like feature, both at the air-side *and at the liquid side*, showing how clear boundaries can easily disappear in this sort of situation.
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Maybe? We don't really know a whole lot about planet formation, after all.
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Boring, cloudy and grey. And it wouldn't be an ocean, more of a fog bank.
The closest sort of phenomenon might be the terrestrial "sea of clouds"
[](https://i.stack.imgur.com/daiEb.jpg)
(image source: [\_tiffany](https://www.flickr.com/photos/_tiffany/43462594444) on flickr).
Note the ill-defined edges and billowing surface.
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> and chemically?
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What does that mean? Like, the stuff dissolved in it? Presumably very vertically stratified, but other than that it could be all sorts of stuff. Too broad to answer here, really.
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Long term exposure to supercritical CO2 might be capable of causing surface erosion, as you'll still get equivalents of wind and waves in it. No massive destructive mechanical wave action (the density transitions are too smooth for that), but slow sedimentation under gravity and rippled landforms due to "wind"/"current" movement. Coastlines would seem likely to be smooth, with only fresh volcanic landforms or astroblemes showing sharp, complex shapes. I'm not sure that rain is likely to occur, so you probably wouldn't see classic drainage-basin type landforms, so mountain ranges upthrust by tectonic activity could have a very different set of shapes to terrestrial landforms, assuming that "ice" couldn't form on their peaks.
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You seem have segued from supercitical to liquid, there. If you meant "supercritical", I'll point you straight back to the wikipedia page you started from. [It has stuff to say about its use as a solvent](https://en.wikipedia.org/wiki/Supercritical_carbon_dioxide#Solvent). I *think* the overall pH seems likely to be neutral. I'm not at all sure if a supercritical solvent could be saline... it seems possible. The upper transitional layers would presumably not have much in the way of dissolved chemicals in them, but the deeper you go the more you'd find.
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Consider the following GIF:
[](https://i.stack.imgur.com/yLT74.gif)
The brooms from this [*Fantasia*](https://en.wikipedia.org/wiki/Fantasia_(1940_film)) scene are always busy. They dance around energetically in a military-like march, never stopping to rest. When their wizard overlord is on vacation, they enjoy lounging around the castle and listening to jazz music.
# How close to these brooms can an anatomically correct creature evolve to be?
These creatures must:
* Have a body and arms made of wood or a wood-like material
* Have "bristles" made of a straw-like material as legs
* Be able to walk, climb stairs
* Be capable of lifting small loads with each arm
* Be able to navigate its surroundings and interact without eyes
* Have the ability to synchronize with one another
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Although the brooms from the film are animated with magic, magic should not be included as a solution in any part of the answers.
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It’s a [centipede!!!](https://blog.oup.com/2011/09/centipede/)
Specifically: a highly evolved giant centipede from the grasslands of a low gravity, oxygen rich world. The legs are clustered together, and are long and spindly both to aid in locomotion and also to help entangle (or ‘brush up’) potential prey. The high center of gravity of this creature is actually of help to it, as in the low gravity it means it can lean further forward and use it’s many bafflingly interlaced legs to move across the ground both at high speed and very efficiently, much like humans use their height and balance to run very efficiently for their speed.
The rear segment has developed and elongated, and the centipede holds itself vertically (head down) to use its rear segment as a nice, large acoustic surface for identifying potential prey (the local mouse population seems particularly hapless). They can also stridulate (Make noise by rubbing together) stiff hairs on this section, producing high frequency sounds that allow them to effectively echolocate.
When prey is identified the centipede will scuttle towards it, confuse and entangle it in the many legs, bite it several times (poison may cause hallucinations such as pink elephant ballet etc), then hunker down to enjoy its meal. If the prey escapes the centipede will simply *not stop chasing it*, never pausing or ceasing in its pursuit of its goal.
If a rival predator should appear the centipede has one further trick up it’s sleeve. The legs of the back section have become remarkably stout, enabling it to grasp its prize and temporarily elevate it out of reach of it’s competitor. This behaviour has led to taller, thicker bodied centipedes outcompeting their neighbours, hence the ‘brush like’ appearance and the prominent arms.
The wood like texture and synchronised swaying are both camouflage. Juveniles in the long grass must look grasslike, so they sway to the sounds of nearby grass movements. more adult centipedes must look inedible, so their hide takes on a more sticklike demeanour to confuse predators.
Now: groups of these centipedes (plural noun: cupboard) will naturally synchronise with each other, swaying in time to pretty much any rhythmic, often repeated noise. If they hear something moving that is out of time they will swarm it in order to ascertain if it is food, then engage in lifting and wrestling the prey from each other while taking opportunistic bites.
Oh, and in response to periodic flooding of the plains: [They’re amphibious too](https://www.google.co.uk/amp/s/relay.nationalgeographic.com/proxy/distribution/public/amp/news/2016/06/amphibious-centipede-discovered-laos-scolopendra-cataracta-new-species).
Enjoy!!
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As far as I could gather the digestion relies on enzymes which in turn set requirements for pH.
Is it possible for an alien creature to have a different set of enzymes that require basic environment and use lye as a base to provide such environment?
I suppose it would also need different mucus to protect its stomach from digesting itself.
The creature in question lives in earth-like environment in caves. It has slow metabolism so it does not need a lot of food. It's food mostly consists of remains of other dead animals. It can also scrape some minerals from the cave walls if it's useful. When threatened it produces toxic gas to protect itself. Digestion process can be very slow.
Edit:
I looked up [more info about mucus](https://www.wisegeek.com/what-is-a-mucin.htm) and it seems that soap that is created when fats mix with lye should not be much of a problem as mucus is a gel, not oil.
Though the process of digesting lipids remains messed up.
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In principle it should be possible, providing that you have the suitable enzymes, however one of the possible problems I foresee with such a setup is [saponification](https://en.wikipedia.org/wiki/Saponification):
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> Saponification is a process that involves conversion of fat or oil into soap and alcohol by the action of heat in the presence of aqueous alkali (e.g. NaOH). [...] Vegetable oils and animal fats are the traditional materials that are saponified.
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Soaps have the properties of being both water soluble (with the polar part of their molecule) and fat soluble (with the non polar part). This might complicate the digestion process.
Another possible problem might be some interference with the Sodium usage in cells/muscles. Simplifying that the only salt an organism assumes is NaCl, while using Chloridric acid for digestion uses Cl iones for the acid and leaves Na iones for the cells, rerouting those Na iones to the digestion leaves you with a large amount of Cl iones that need to be either used or removed.
All in all, to make it possible you would probably start again from scratch with the chemical paths in the cell biochemistry.
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Not the same way. The acid is not what is actually doing most of the digesting of the food; it is an enzyme called [pepsin](https://en.wikipedia.org/wiki/Pepsin). The reason the stomach is acidic is pepsin works optimally at a Ph of 2. According to Wikipedia, pepsin is "inactive at pH 6.5 and above", meaning that a base would be detrimental to digestion.
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I want to start with the fact that I am by no means an astronomer, or even a hobbyist in the field. I am attempting to build a fantasy world which still reflects accepted physical laws.
My problem comes from the fact that I have no idea how to go about figuring out the period of axial precession for a fantasy earth-like planet. For the Earth, I believe the period is roughly ~26,000 years. I've spent a few days trying to find resources, but in all honesty I can't wrap my head around half of the equations I've seen presented.
How would I go about doing this calculation for a given planet, and which of its properties would I have to specify in order to do this calculation? I've got 2 moons around my earth like planet, one of which is large enough to hold a stable atmosphere and be inhabited (which may make it more of a binary planet system than a planet-moon relationship).
I've asked this same question in the astronomy stack exchange, but it seems that the commentators over there believe you folks' may be able to help also...
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Wikipedia's page on [Axial Precession](https://en.wikipedia.org/wiki/Axial_precession) has a good deal of mathematics on it and, unless you have absolutely got to have precise numbers for some obscure story reason (which is probably what I'd call the tail wagging the dog - change the story to avoid that problem) then making up the numbers or just forgetting all about Axial Precession is the way to go. The periods involved will be very long by the standards of any story you're likely to write, so why burden yourself with something you probably don;t need.
The maths that follows only gives a rough approximation anyway, and you don't want to even contemplate the kind of things you need to do to get a better one : it's not worth it.
That said let's have a look at the very basic theory result that Wikipedia gives :
There are two component to axial precession that matter (for Earth) : the one due to the Moon and the one due to the Sun. The Moon's effect is actually larger, but these numbers are very sensitive to the values you use.
**The Solar Contribution**
$$\frac{d\psi}{dt}=\left[ \frac {GM\_s}{a\_s^3\left(1-e\_s^2\right)^\frac 3 2} \right] \left[ \frac {C-A}C \frac {cos\epsilon}\omega \right]$$
Lots of symbols so what do they mean ?
* $G$ - the Universal Gravitational Constant also famous from $F = \frac {GM\_1M\_2} {r^2}$ Newtons law for gravitation.
* $M\_s$ - The Sun's mass - in your case you need the mass of your planet's star, of course.
* $a\_s$ - The semi-major axis of the orbit of the planet around it's star
* $e\_s$ - The eccentricity of the planet's orbit around it's star.
Now that second term in square bracket, which is also in the expression for the Lunar contribution. This one is trickier.
* $C$ - moment of inertia (of Earth) around the axis of rotation
* $A$ - moment of inertia around the equator
* $\epsilon$ - the angle between the equatorial plane and the ecliptic plane (see below)
* $\omega$ - Earth's angular velocity (due to it's rotation, not it's orbit)
Now this expression is really poorly dealt with in Wikipedia because of two problems.
$epsilon$ in Wikipedia is assumed to be the same for both the Solar and Lunar contributions. This is not (AFAIK) correct. The angle should be the angle between axis of rotation of the body and the plane of the orbit of the other body (which means it's different for the Sun and Moon).
The $C-A$ and $A$ terms are really hard to deal with for mere mortals (and frankly just messy for anyone else). For your purposes I would propose the following compromise term instead. It's based on modeling the planetary bulge as an ellipsoid of constant density compared with the $A$ value for an ideal sphere - both objects have the same mass and density, which I'm taking as constant . I'll spare you the derivation :
$$\frac {C-A} C \approx 1 - \frac{R^2} {a^2}$$
where in this case $R$ is the *average* radius of the planet and $a$ is the equatorial radius of the planet.
**The Lunar Contribution**
$$\frac{d\psi}{dt}=\left[ \frac {GM\_l}{a\_l^3\left(1-e\_l^2\right)^\frac 3 2} \left(1-\frac 3 2 sin^2i\right) \right] \left[ \frac {C-A}C \frac {cos\epsilon}\omega \right]$$
Not much change here expect that the masses and so on refer to the Moon and not the Sun (hence the different subscripts). There is one additional term which is the factor :
$$\left(1-\frac 3 2 sin^2i\right)$$
This corrects for the effect that the angle of inclination of Moon's orbit to the ecliptic is not zero. The ecliptic being the plane with the Sun and the Earth's orbit in it.
You have to decide these numbers for yourself.
**The total effect :**
The total effect is simply the sum of the two other effects so :
$$\frac {d\psi}{dt} = \frac {d\psi\_l}{dt} + \frac {d\psi\_s}{dt}$$
If you had multiple moons you would need multiple lunar correction terms.
Just for clarification that $\frac {d\psi}{dt}$ means the rate of change of the angle $\psi$ with respect to time $t$. To get how big an angle you'd move through in a century you do this :
$$\Delta \psi \approx \frac {d\psi}{dt} \Delta t$$
[Answer]
First, find tonight's pole star. As the planet spins on its axis, over the course a day/night, all the stars in the sky will move in a circular path, with the exception of the pole star. You can use a fixed sight-line (e.g. the ends of two sticks stuck in the ground) to determine if a star has moved after just a few minutes. You should then be able to narrow down the pole star within an hour. Keep in mind- most worlds do not have an "exact" pole star, even our Polaris moves in a tiny circle.
Now that you have a pole star (or pole star circular-path), you can set up some much more permanent apparatus to fix its position for a long time. If the planet has an axial procession, then the pole star will eventually move out of this "permanently-fixed" position. The RATE at which it moves out of this position would determine the rate of axial precession. The time it takes for the star to return to its original position would define a full precession cycle. It maximum displacement during this period would define the precessions angular maximum.
I suspect, with some of that crazy math you mentioned, they can figure out how long a full cycle will be, and the angular maximums of the precession, before a full cycle has completed; but I'm not really sure how.
Edit: just to clarify- these stars are NOT moving, rather your planet is spinning, and precessing, which makes the stars appear to move. In fact, the above is based on the assumption that they do NOT move.
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In the far future, man is trying to build a small colony in the asteroid belt - on one of the bigger asteroids. All the materials are to be mined from asteroids, and it is assumed the colony will have access to mine any and all types of asteroids as needed. The question is, can we make concrete solely out of minerals obtained from asteroids?
Concrete is aggregate, water, and dry cement.
Aggregate I presume can be broken down from any suitable asteroid.
[Some asteroids do have water in them, so water shouldn't be a problem either](https://www.sciencedaily.com/releases/2018/12/181210150554.htm)
It's the cement part I'm having difficulty with. Some asteroids contain very tiny traces of Calcium in them, but would this be enough to make cement from?
[Answer]
The short of it is 'yes, asteroids contain the elements needed to make concrete.'
A typical asteroid contains
Oxygen 36%
Iron 26%
Silicon 18%
Magnesium 14%
Aluminum 1.5%
Nickel 1.4%
Calcium 1.3%
And hydraulic cement is made from any of
Belite (2CaO·SiO2);
Alite (3CaO·SiO2);
Tricalcium aluminate (3CaO·Al2O3) (historically, and still occasionally, called 'celite');
Brownmillerite (4CaO·Al2O3·Fe2O3).
And there is overlap between what is needed and what is available.
The long of it is, just because the elements are there, does not mean they can be extracted and then combined into the necessary chemical form.
Cement is a binder, that binds aggregate into a solid structure. We use lime based cements and the above hydraulic cements, mainly because of their abundant availability and ease of extraction. Calcium, in fact, is widely available in the form of limestone throughout the world. But that is not to say that exotic cements could not be formulated using other elements.
The problem, I posit, will not be in the materials, but in the curing. Concrete does not dry, it cures. That is, it depends on oxygen in the atmosphere to complete the chemical reaction. Hydraulic cement depends on water. So building concrete structures in a vacuum presents a considerable challenge.
However, engineers HAVE considered using concrete as a building material on a [space station](https://space.nss.org/settlement/nasa/spaceresvol3/cpmss1.htm) using raw materials shipped up from the moon.
[Answer]
Not concrete. [**Pykrete**](https://en.wikipedia.org/wiki/Pykrete).
>
> Pykrete is a frozen composite material, originally made of
> approximately 14 percent sawdust or some other form of wood pulp (such
> as paper) and 86 percent ice by weight (6 to 1 by weight). During
> World War II, Geoffrey Pyke proposed it as a candidate material for a
> supersized aircraft carrier for the British Royal Navy. Pykrete
> features unusual properties, including a relatively slow melting rate
> due to its low thermal conductivity, as well as a vastly improved
> strength and toughness compared to ordinary ice. These physical
> properties can make the material comparable to concrete, as long as
> the material is kept frozen.
>
>
>
Out in the asteroids it is easy to find ice and other frozen stuff; methane clathrates, some CO2; all that good comet meat. And you have rocks.
To make space pykrete, melt the rocks and spin them into stone wool - long, thready, fibrous fluff. This should be a lot easier in lowG than it is down here - just rotate the melt gently and let centrifugal force to the work.
The stone wool will take the place of the wood. Around this fibrous framework now add your slurry of whatever ices you have and let them freeze back. As long as they are cold, they will hold their shape.
Space Pykrete would not be good for making beds and cabinets out of, but for structural applications in space this stuff should be excellent. One of the best Mythbusters involves a pykrete boat that they take out on the water. The main problem with real pykrete is that its favored temperature ranges do not overlap much with ours. In space staying cold should be less problematic.
---
this concept inspired a little fiction vignette. WB does not like prose stories in the answer so it is on fictionpress.
<https://www.fictionpress.com/s/3334555/1/Pykrete-and-space-cats>
[Answer]
The short answer would be "no"; Portland cement is essentially limestone (sedimentary calcium carbonate crystal) which is likely to be in short supply in an asteroid belt. Even if you had a substantial supply of material, the lack any substantial gravity would likely thwart such a plan. Building something in space that doesn't already have a somewhat rigid construction would be...difficult. You could perhaps pre-fab sections of it and put them into orbit, but that would be a planetary-based effort; essentially, a bricklaying operation, with the bricks coming from "elsewhere". Gryphon's suggestion might work with a variation - some sort of ground metallic powder that you could kind-of use a powerful energy source to quickly "flash-smelt" a kind of metallic foam, but you'd still have to have some sort of rigid mold or other constraining device.
[Answer]
<https://en.m.wikipedia.org/wiki/Lunarcrete>
A basically identical rescipe to Lunarcrete is the way to go. Now a added bonus is to add urea (you throw it out anyways when you recycle urine) and you get a concrete that sets stronger then modern concrete and grows stronger as it ages (a example of concrete using urea would be Roman concrete)
Here's a article I read not too long ago on the subject: <https://www.google.com/amp/s/www.bbc.com/news/amp/world-africa-45978942>
Note: Urea needs sunlight to start its chemical reaction
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According to the [Film Theorist's video on Spider-Man](https://www.youtube.com/watch?v=wVKMrhRg9oY) Peter Parker would undergo extreme g-forces during his swinging around. This is not so much of a problem, as any g-force based loss of consciousness could be avoided with a g-suit.
This question is more specifically aimed to the landing and stopping aspects. How could someone best swing at approximately 3 g's of force, and then stop suddenly without causing any damage to himself? Preferably this should be a fairly light-weight low-volume method, should be easily portable and not something others would easily notice.
Edit: My question is not about how Peter Parker deals with the G forces, but rather how your average Joe could deal with them by technological means, like Iron Man. Sorry for any confusion.
Edit 2: @JBH summarizes my question well:
>
> How can someone NOT SPIDER-MAN use existing technology to bring themselves to a sudden stop after 3G of acceleration and not rip their limbs off [or rupture internal organs]?
>
>
>
[Answer]
Hmmm. Well 3G is a lot of force. That said we can call an instant of [14G completely safe](http://goflightmedicine.com/wp-content/uploads/2014/06/G-Tolerance1.jpg) and [John Stapp](https://en.wikipedia.org/wiki/John_Stapp) would shortly chime in with a couple figures. 32G being safe, 40G being tested safe to the extent of no lasting damage, and 46G safe by extrapolation. With no known upper bound on survivability. That said 32G is probably enough for us. So if we're swinging for 3 seconds at 3G and make a stop in 1 second, we're experiencing 9G. Which simple math makes that 32G÷3G=10⅔
So you could swing for 10⅔ sec per swing any way you wanted and if you stopped in a second you'd be fine. No extra contraptions required for "health reasons".
But wait! G-forces change depending on direction of your swing! So a perfectly ground-parallel swing might experience the full Gs all-the-way-through but a regular swing would have some varying Gs. So you could potentially swing even longer than that! If the stop was at the base of the swing where there was peak force, then that means you could have up to double the swing time if you were stopping at the base! And as much as you wanted if you were stopping at the top!
Then again a "Spider-man-style" landing might have lower G tolerances than purely feet first given there *is* a forward component. So maybe a little bit less than 10⅔...
But maybe you're more curious not in the health implications but in actually achieving this stop in one second. [This](https://www.smithsonianmag.com/smart-news/scale-glass-wall-material-inspired-gecko-feet-180953411/) paired with [this](https://www.smithsonianmag.com/science-nature/geckos-have-surprisingly-strong-death-grip-180953516/) would seem to suggest a human with gecko grip could stop with just under 20Gs of force on a dime for some landings at least. Add in some G-force activated locking joints in an light-weight exoskeleton and you could pretty simply come to a screeching halt at 19G it would seem. Pushing the bar to 32G or higher would maybe require better tech than we have now to remain unnoticeable, or maybe the same concept but engineered better than a gecko could get us there. Granted 19G is still a minimum of 6 sec of swinging which is a lot longer than what you typically see Spider-man doing.
Ah, btw technique is pretty important. If you're stopping faster than 1 second because you've collided with the ground on the down-arc of your swing... well your stopping time is *for sure* less than 1 sec and your Gs are going to sky-rocket and turn into pressure and kill you. So a *crash* at 3G is equivalent after 1 sec to a 65mph crash. So you'd probably only be able to come out of a *ground crash* at 3G if it happened within a fraction of a second (spit-balled from some median death heights, etc. go look [here](https://outdoors.stackexchange.com/questions/8106/how-far-would-you-need-to-fall-for-it-to-be-fatal) if you want a good starting point). Since you're worried more about a collision in that case than G forces the question is different. But yeah, no downward arc stopping, especially if your arc looks like free-fall.
[Answer]
# If you want to go the body-enhancement route, you could create an internal chassis for your organs.
Call it "Ribcage++". A chassis of titanium mesh, struts, and flexible bands that extends inwards from your ribcage to hold all your meat bags in place. Like a sports bra for your innards. Organs are wrapped in titanium mesh to prevent herniation or bursting, and supported by form-fitting titanium cages, which are secured to the larger structure. Arteries are secured to all this like vines to a garden trellis. Your intestines and stomach are wrapped in mesh and held by bands of titanium thin enough to be flexible so they can still mush about a little for digestion and bending your abdomen. Similar with your lungs and diaphragm.
Your brain could be secured by using a special neckband that puts just enough pressure on your jugular that blood-flow out of your brain is reduced just enough that your brain swells just enough to make a tight fit with the inside of your skull, so it doesn't slosh around. It sounds like something I just made up but in fact I went looking for solutions and found this because [it's real](https://www.cbsnews.com/news/device-to-protect-brain-from-concussions-inspired-by-birds/) and has been tested with good results!
So TLDR: Sports bra for your guts.
[Answer]
This person could build one large tridimensional structure around himself, some sort of silk spherical web, which could absorb impact energy and reduce g forces on internal organs. Real world similitudes with [this](https://img.purch.com/rc/300x200/aHR0cDovL3d3dy5saXZlc2NpZW5jZS5jb20vaW1hZ2VzL2kvMDAwLzA2MS83NzEvb3JpZ2luYWwvQnViYmxlLVNvY2Nlci5qcGc=).
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[
Considering the below constraints what variant of astronomical event could create meteoroids and asteroids on a collision course with Earth?
**Constraints**:
* Sustainable severity (long enough for civilization to advance capabilities of defending against more severe waves of meteoroids/asteroids) and frequency of meteoroids/asteroids.
+ Frequency: approximately 200-1000 asteroids on a minimal activity day and 600-2000 on high activity day.
+ Severity: Size of asteroids that for example a modified form of ICBM a Surface-to-Orbit Ballistic Missile (SOBM) that is capable of intercepting and neutralizing impact threats by;
- Causing them to change trajectory.
- Disintegrating them to a bolide
* Outcome level: [Chelyabinsk meteor](https://en.wikipedia.org/wiki/Chelyabinsk_meteor) uncommon, [Tunguska event](https://en.wikipedia.org/wiki/Tunguska_event) rare.
* Using either 1 or multiple ICBMs SOBM(s).
[Answer]
# This sounds a lot like the [**Late Heavy Bombardment**](https://en.wikipedia.org/wiki/Late_Heavy_Bombardment).
The Late Heavy Bombardment happened about 4 billion years ago, and lasted for a couple hundred million years. The prevailing theory is that it occurred when [the outer giant planets changed their orbits](https://en.wikipedia.org/wiki/Nice_model#The_Late_Heavy_Bombardment), scattering many small bodies from the asteroid and Kuiper belts. This dramatically changed the structure of the outer Solar System. Many of these small bodies - asteroids, for example - hit the terrestrial planets, as well as the Moon.
We do appear to have a second case of this happening, in the planetary system of [Eta Corvi](https://en.wikipedia.org/wiki/Eta_Corvi). Some of the dust in the system is theorized to have come from collisions between asteroids and similarly-sized bodies, as well as from a planetary-mass object. The trigger for the bombardment is unknown, although it could be due to planetary migration, as in our own Solar System.
That said, [the bombardment rates](http://adsabs.harvard.edu/abs/2000orem.book..475R) during the Late Heavy Bombardment are *much* lower than what you're looking for - likely because there just isn't enough matter in the Solar System to keep up impacts at the rate you want for long geological timescales. On shorter timescales, though, a drastically sped-up bombardment could work.
For a nice visualization, check out [this simulation on YouTube](https://www.youtube.com/watch?v=VXeOh3xmrQM).
At $t=505$ million years, the system is pretty stable. The gas giants are, in order, Jupiter, Saturn, Neptune, and Uranus, and the green bodies represent objects in the Kuiper Belt. The inner terrestrial planets are not shown:
[](https://i.stack.imgur.com/TM0du.png)
At $t=882$ million years, the system has recently experienced an instability. The orbits of Neptune and Uranus are changing, and the smaller objects are being scattered across the Solar System:
[](https://i.stack.imgur.com/XjCPt.png)
At $t=983$ million years, the giant planets have started to settle down a bit, and better resemble the outer Solar System as seen today. The Kuiper Belt is now substantially less dense than it originally was - more like its current structure:
[](https://i.stack.imgur.com/nM68Q.png)
For a comparison, here's Figure 8 of [Lisse et al. (2012)](http://adsabs.harvard.edu/abs/2012ApJ...747...93L), showing the modeled structure of the Eta Corvi system. The red bodies are the analog of the Kuiper Belt; the inner blue bodies constitute a smaller disk that may be made of debris from a planet that sustained extreme collisions with asteroids:
[](https://i.stack.imgur.com/jCvW0.png)
[Answer]
That... sounds like a LOT of space rocks. Widely spread out, if you want it to be sustainable and continuous, and not just a "once every X years" event...
Now, how do we get that many rocks close to earth? I'm thinking that with some handwaving (or a lot of time spent calculating orbital mechanics^^) we could have a rogue planet coming into our system, destabilizing the orbits of mars and venus, and after a couple close flybys two of those three planets (or all three, or first two then a remaining core of one of them with the third...) might collide spectacularly.
Now, earth's orbit might be changed some too, but maybe we were just lucky enough to be on the other side of the sun when it happened? Or maybe you can use a changed orbit in your story, who knows. Either way, there's now three planets' worth of debris in an area that at least partially overlaps with earth's orbit, and if you get the speed and direction of the rogue planet juuuust right, that debris might've spread out into a new asteroid belt that earth is now constantly flying through.
Still not sustainable forever, but for a very long time - though some rocks might be bigger than you wanted ;)
[Answer]
Bonus answer: Aliens!
They are using a [mass driver](https://en.wikipedia.org/wiki/Mass_driver) to launch stuff they've mined on into space. Usually you'd do that in a direction where you can use said stuff - but maybe they're just huge jerks, or afraid of us, or for some other reason want to make it as hard as possible for us to fly to space - and a constant bombardement with space rocks would certainly do the trick!
It could also be the humans - the colonists on mars are afraid of being conquered by earth, so they've set up a mass driver on some other planet so the UN can't send troops and subjugate them...
Or if you want a REALLY strange thing, it's *actually* a mining operation, on
a planet orbiting alpha centauri (or some other nearby star). The aliens think in really long time periods, so they don't mind waiting while all the metal their robotic probes mined on that planet flies through space towards their star system... Too bad someone didn't think to check for other stars crossing the line of fire, and now the sun is right in the middle of the stream of valuable ressource pellets!
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[Question]
[
If a user-specific venom managed to work by liquefying the phospholipid membranes of animal cells, how would it be produced? (It would act more like a venom in this case.)
By *specific*, I mean that the venom would work on all cells except the cells of the animal who produced it, even within an individual within a species:
* animal 1 made it
* animal 2 would die from it
* animal 1's offspring would die from it
* yet animal 1 is resistant
The problem is that to be released, it couldn't be moved out of the cell where it was produced (since it would destroy the cell) and couldn't be transported. What's more, if it was DNA specific, it would already have dissolved the cell before stopping. And to be resistant, the protein would have to become less effective (i.e, misfolding or denaturing itself so as not to further dissolve fats). The venom would have to be specific enough that no other organism could develop resistance to the venom.
How could such an acid-like substance be produced by a creature and be so specific, so that the individual member of the species would be the only one resistant?
The offspring of individual 1 would have their own variant that would kill their parents, and the variants of the parent would kill their offspring. The venom is **not only DNA specific to common genotype characteristics but also to an individual.** This, of course, is where the "magic" comes in since transporting the venom to the DNA of the individual cell wouldn't work. And using the mRNA strand that had the codons for the polypeptide chain form of the venom wouldn't work, since **the venom itself is unchanging from individual to individual**(it's just the resistance against the specific venom that changes from individual to individual), **and scrambling the antigens on the protein won't work; this is an enzyme, not a surface-receptor protein**.\*
The "magic" part is that although the structure of the molecule is unchanging, it has this individual specificity. My problem is transporting the molecule out of the cell and without destroying it.
[Answer]
I'm afraid not going to work that way, because the cell membrane does not contain DNA at all, so for a single molecule to work, the venom should have two different forms to begin with - one innocuous and one active. You'd need a protein with bistable folding, one form is inert, the other is lethal. This *conformational change* is triggered by a secondary group (what is called an effector chain), itself activated by a "reader" head that recognizes *something*. Either the DNA directly or some expression of same, e.g. membrane antigens.
The venom would have to act in some very complex way:
* recognizing some loci on the cell membrane, and activating *unless* a very specific set of markers was **also** found. The first 'rule' avoids the venom expending itself activating at random, or far from any cell, the second implements the "target specific" part. This is more or less like the *opsonisation* process in the human immune system works - a "tag" is added to a target cell, then a venom (or a lymphocite) kills it. You'd be looking at essentially a rejection reaction.
* the *venom* is actually part of the organism's immune system, and has a similar function as the major histocompatibility complex in humans: it triggers an immune reaction *unless* the organism recognizes it as "self". In a different organism, a sufficient quantity of venom would trigger the equivalent of a anaphylactic shock (or it could induce the organism to attack itself in a runaway autoimmune catastrophe).
* the superprotein enters the cell and decodes enough DNA from the nucleus to determine that an activation is in order, and it has to be lethal. We're adding helicase capabilities to this little critter, which can't be so little anymore. This kind of venom could be a defense mechanism against mutations, e.g. cancer (you need a way to reprogram the system during pregnancy and in the newborn, of course). I had written [an answer](https://worldbuilding.stackexchange.com/a/26188/6933) some time ago on how such a molecule could work. The trouble being that it could never have *evolved* by itself.
[Answer]
You would need to take a page from the AIDS virus, or from immunoglobulin development.
1. Start with a toxin. Probably all individuals in this species have a similar base toxin.
2. Scramble antigenic sites randomly on your version of the toxin. It is pretty cool, the way humans do this to generate diverse immunoglobulins capable of recognizing millions of different antigens. In short there is post-translational scrambling that goes on which adds random diversity. Read more! <https://en.wikipedia.org/wiki/Antibody#Immunoglobulin_diversity>
3. Generate your own neutralizing antibodies to your self-version of the toxin.
Now you have a randomly scrambled toxin that you are immune to, but no-one else. The active site that works on membranes needs to be in some pocket not amenable to neutralization by immunoglobulin or others of your species can be immune to your toxin. Immunoglobulin binding needs to produce some sort of steric hindrance that prevents the toxin from acting.
The toxin would be treated like we treat pancreatic enzymes. Those enzymes are in us and dissolve meat and fat. They will dissolve us alive if given the chance: pancreatitis. They are kept inactivated and then activated right before being deployed into the gut.
A side effect to this system: if you get hit with someone else's toxin and live through it, you will be immune to that individual's toxin afterwards.
[Answer]
Immune system works based on some proteins expressed on the surface of the cells.
These proteins are highly specific, this is why organ transplant is bound to failure if no attentions are paid to choose highly compatible donors and immunosuppressors.
The same mechanism can be used with your venom: the molecule is embedded into a membrane which opens up as soon as it interacts with surface proteins of another cell, except those of the organism who produced the membrane.
Mind this is what normally our white cells do: attack all but our own cells.
This could also hint how to explain such a development: modified T-killer cells.
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[Question]
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What could cause the continents to drift much faster than is today. I mean, much faster. Let's say it should take about 1-2 million years from this [](https://i.stack.imgur.com/RjM96.jpg)
to this
[](https://i.stack.imgur.com/CxZ0K.jpg)
[Answer]
There are a few issues that regulate the speed of CD:
1. Upwelling: of magma at the rift zones.
2. Inertia: the plates undergoing CD are *big and heavy*.
3. Firmness: of the asthenosphere (upper mantle). That's what the continents float on, and it's movement causes a plate to move. Controlled by heat in the lower mantle and outer core.
4. Friction: of rock at the subduction zones.
Thus, to speed things up...
1. Hotter core to make more magma rise at the rift zones.
2. Lighter continents?
3. The hotter core will also soften the asthenosphere, making it move faster.
4. Slipperier rocks (like talc) at the subduction zones.
[](https://i.stack.imgur.com/eaXzB.png)
[Answer]
1:**New moon.**
The tidal flexing caused by a massive orbital satellite ultimately produces frictional heating. This topic is covered here:
<https://astronomy.stackexchange.com/questions/757/how-much-of-an-effect-does-the-moon-have-on-earths-liquid-mantle>
Jupiter's moon Io is an example: this moon is largely heated by tidal forces. So too your earth with faster continental drift - a new satellite might impart tidal forces such that the mantle heats up and drift speeds up./
---
2: **Interior heats up more - either because of production of more rapidly decaying daughter radionuclides or the addition of fresh radionuclides.**
Another way to heat the interior and move plates faster would be to have the nuclides heating the earth produce more heat. This could happen via an increase in decay products to isotopes which more rapidly decay and so over the short term produce more heat. Heating of the earths interior is caused by radioactive decay.
In some circumstances, decay of certain isotopes produce daughter isotopes which decay faster and so more heat is produced. I asked about this here.
<https://physics.stackexchange.com/questions/351327/is-decay-heat-proportional-to-half-life>
Here is a diagram from @Farcher's answer. The third instance, non equilibrium shows a place in the course of decay where the heat transiently increases.
[](https://i.stack.imgur.com/t5vTz.jpg)
You could also just add more fuel to the fire. For example, suppose a collision event entailing a meterorite comprised largely of uranium, or americium or the like. The dense meteorite would make its way towards the center of the earth and once there contribute to heating of the core.
If you are not wanting to speed up plate tectonics but just have it be faster from the get go, have your planet with more radioactive nuclides in the core from the start.
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[Question]
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Though my star is 1.71 LSol, my planet orbits at about 2.14 AU. Following a back-of-the-envelope equation for apparent brightness, this gives the surface of my planet approximately 30% of Sol's light energy. It would actually be substantially less; my planet is extremely geologically and volcanically active, so I would expect a high concentration of reflective volcanic particulates to be a semi-permanent fixture in the upper atmosphere. It also has a high obliquity of 31.1 degrees, and 93% of its surface is ocean; as such, hurricanes are very common and very powerful. My atmosphere is quite thick and rich in carbon dioxide: 16% CO2 in a 134.76 kPa atmosphere.
**My question is:**
How would plants evolve differently to more efficiently capture the light energy coming to the surface, yet survive the constant hurricanes (or at least reproduce quickly enough that the hurricanes would be a non-issue)? My working theory is that the plants could only survive with a much more balanced and diverse range of photosynthetic pigments; and/or plants would barely survive at all, and the flora of my world would mostly be made up of oceanic blue-green algae.
Keep in mind that increasing the surface area of the leaves would only work in very specific regions of my planet's land masses; these plants also need to worry about conserving temperature (a BOTE calculation puts my planet's average temperature around 10-15 degrees C) and water (the only areas sheltered enough from the constant hurricane and also warm enough to sustain large-leafed plant life are high-altitude deserts on my planet).
**Here's what I have so far:**
So I was thinking mostly coniferous needle-leafed plants with a blue-green photosynthetic pigment balance like phycobilin and chlorophyll in most "temperate" climates, and/or a carotinid-based plant phylum that evolved separately in an isolated region to the northwest. (Since 93% of its surface is ocean, and since it's so geologically active, my planet has plausible continents that have separate evolutionary timelines.)
Please let me know if you think I'm on the right track; I am NOT a biologist or botanist by any stretch of the imagination!
**EDIT TO ADD:**
I have been informed that my concerns about temperature regulation are largely unfounded, which is a good reminder that I need to thoroughly check my assumptions about what exactly would be different from Earth. Here is a very helpful reply I got from u/Cruzzfish on the r/worldbuilding subreddit!
>
> "They really wouldn't be that different at all. Many plants already require lower than 30% of the sun's full brightness if they don't want to sunburn. Even full sun plants don't have too much of an issue operating at <10% of the sun's brightness for extremely extended periods of time.
>
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> Notable differences would be.
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> More salt tolerant wetland plants to take the storm surges
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> Less brightly colored ones since no need of sun protective pigments.
>
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> I don't know what you mean by conserving temperature. Plants don't need to worry about that sort of thing. But a planet with an average temperature of 15 Celsius is not cold at all. Earth average temperature is just over 13 Celsius..."
>
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> "...Seaside goldenrod is decently salt tolerant but I don't know how it reacts to floods. Generally there are a lot of seaside \_\_\_\_ plants that would be good to look for."
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And from u/svarogteuse:
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> "They would evolve just like plants on the Gulf Coast/Caribbean; they drop small leaves freely but regrow them quickly.
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> About 2 years after Katrina I went to Bay St. Louis, the place it actually came ashore. Along the beach was a brand new road recently rebuilt. To the left the remains of a boardwalk and sand. To the right beautiful park land for about 6 blocks with huge live oak trees. The live oaks looked a little funny. Took a few days to figure it out. The trees had limbs bigger than my torso and twigs with leaves. Nothing in between. Every thing smaller had been ripped off by the hurricane.
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> Oh and the park land wasn't parkland. It had been full of houses and now the only thing left was foundations. Everything else had been carried off by the 25' storm surge. Storm surge the 200 year old oaks (but no smaller ones) withstood."
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[Answer]
Perhaps **think in terms of [shade tolerant plants](https://en.wikipedia.org/wiki/Shade_tolerance).** These tend to be low and broad leaved.
I'd avoid pine needles. **The leaves should be broad** - this is the 'kitchen' of the plant where the food is made. Broader leaves capture more sunlight. Pine needles evolved with plenty of sunlight and are optimized I believe to retain water (not a concern for you. )
I'd add in extra [photosystems](https://en.wikipedia.org/wiki/Photosystem). Chloroplasts typically have two, and from these they energize electrons from water to an energy state high enough to fix CO2. You are asking about a low - light environment, and so you could add in another photosystem (or other device) to help funnel more photons to your electrons to energize them.
Another cool idea is to **have the chloroplasts be more mobile** so that they migrate within the leaves to the area with the most light. Cool video [here.](https://www.youtube.com/watch?v=pFsty-XyLZc) And, **the leaves can be mobile too,** orienting to light with [phototaxy](https://en.wikipedia.org/wiki/Phototaxis).
As far as the hurricane - this has been asked elsewhere on the site. You can use the advice you received on Reddit and also think in terms of advantages - Seed dispersal is enhanced by the winds and water, so your plants may evolve to have buoyant seed pods that split when waterlogged.
[Answer]
**Lichens.**
<http://www.pbase.com/philharmostes/image/49852777/original>
[](https://i.stack.imgur.com/UOb9D.jpg)
Lichens are the "plants" which make do in the place other plants can't. The driest, coldest, darkest, harshest places. Lichen lays low so storms are less problematic. I suspect the varied pigments are actually protective, not photosynthetic - but when you have such little biomass and your energy requirements are low you can take your time gathering energy.
---
/Are there any changes you can think of, or any special parameters that would make a dense forest cover in at least one area of my world plausible/
<https://en.wikipedia.org/wiki/Wollemia>
>
> Wollemia was only known through fossil records until the Australian
> species Wollemia nobilis was discovered in 1994 in a temperate
> rainforest wilderness area of the Wollemi National Park in New South
> Wales, in a remote series of narrow, steep-sided sandstone gorges 150
> km north-west of Sydney.
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>
My understanding is that this microhabitat ascted as a refuge for the Wollemia - they did not get burned up by fires or outcompeted by other trees. So to your world - maybe it used to be a nicer place, or the trees were brought by aliens and managed to hang on in this one spot - protected from weather by steep cliffs and maybe at altitude - more sun and less clouds.
[Answer]
I think you have a far more difficult issue at hand. The lack of luminosity may plunge your planet into a permanent ice age, and plants may be the last things to worry about.
It is thought that once the Earth and planets had stabilized after the late heavy bombardment period, Earth was in the grip of a permanent ice age sometimes known as "[Snowball Earth](http://www.snowballearth.org)"
[](https://i.stack.imgur.com/k30uN.jpg)
*Artistic reconstruction of Snowball Earth*
The Sun had only about 30% of today's luminosity, so very little solar energy was striking the Earth and keeping it warm. Water froze into massive glaciers covering most of the planet, with a few warm spots around volcanic vents providing clear water and open ocean. The only life lily to thrive under those conditions would be extremophile bacteria surrounding the vents, and some bacteria or algae capable of living in the open water where some sunlight filtered through.
Life on [Snowball Earth](https://infogalactic.com/info/Snowball_Earth) was extremely limited, and clinging to some pretty narrow niches for hundreds of millions to billions of years. It is thought the end of Snowball Earth was a series of volcanic eruptions which released enough carbon dioxide to cause a spike in temperatures (in ancient rock formations, there are rocks and boulders randomly dropped into sediments. The interpretation is these rocks were deposited when glaciers melted.
[](https://i.stack.imgur.com/cntLZ.jpg)
*Sudden depositing of glacial rocks into sediment at the end of Snowball Earth*
So unless you ramp up the luminosity of your sun, your planet will be a very marginal and unpleasant place to live.
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[Question]
[
A lifeless moon of a gas giant (which orbits a K-type star [4200K] at about 0.7 AU) is chosen to become home to a space colony. Colonists plan to transform it from a barren rock into a garden of Eden. Since this moon lacks water, nitrogen, and $CO\_2$, they need to be mined in the asteroid belt and other gas giant moons and then delivered to the terraforming site. **What is the most effective way to deliver these materials?**
The colonists are looking for a delivery method that would provide results (such as atmosphere and free-flowing water) within years or decades. If it is absolutely impossible they can go into suspended animation and wake up in shifts to monitor the progress.
It would also be nice to avoid:
* changes in orbit or rotation of the moon;
* significant damage to the moon's surface;
* creation of a debris cloud around the moon ([the colonists are strongly opposed to space littering](https://worldbuilding.stackexchange.com/questions/96930/how-to-effectively-collect-and-recycle-space-junk));
* loss of already delivered materials (as seen in case of comet or asteroid bombardment).
### Technological level
The colonists have access to the following technologies:
* fully automated and robotised asteroid mining;
* space travel at 1/10 of the speed of light;
* terraforming technologies (however, only one project has been completed successfully by the time of their departure);
* genetic engineering;
* suspended animation.
Technologies that are envisioned by scientists of today but cannot be built because of technical difficulties (materials, money, political will) are fine. However, something like teleportation is not possible unless it can be explained by existing science.
[Answer]
# Provenance of terraforming materials.
You mention getting things from the asteroid belt. There may be an easier way. Since you can move cargo fast (0.1c) you can afford to get the cargo from farther away. Asteroids are generally rocky with possibly some ices on top. Moons of Saturn are generally icy with some rocks in the middle.
There are a lot of moons of Saturn (and the moons of Uranus and Neptune are probably good targets as well). Collectively, they have *far* more ammonia and water than you could ever use to terraform a planet. So why not simply drag a few small to mediums sized moons of a gas giant into orbit around your planet and prepare to send them down?
# Refining
Something not mentioned is the need to refine the materials. If you want the proper elements to be added to your moon in a matter of decades, then you have to be careful about what you add. Like any good culinary creation, you must measure your ingredients carefully.
You ingredients are bits of and/or whole moons. So how do you measure them? You have to melt them. You can utilize fractional distillation to melt away the various compounds. If you slowly cook (heat) a comet, all the Carbon monoxide will melt first (68 K), then methane (~91 K), ammonia (195 K), carbon dioxide (217 K) and finally water (273 K). All those temperatures are pretty far away from each other, so simply melt the ice ball slowly, and then separate the solid bits from the liquid at each step.
Now you have a set of liquid or slushy balls in space. If you were smart, you would do this far from the sun, so the carbon monoxide and methane will refreeze for you before transport. You now have a bunch of ice balls of reasonably pure compounds ready to go smash into your planet!
# Recipe List
In the comments you say you want a plant with about 0.75 Earth's radius and mass; and 0.7 Earth's gravity. That doesn't work exactly, but going with some numbers that fit the bill more or less, let us assume your moon has radius 0.9 Earth's, density 0.8 Earth's, to get surface gravity 0.72 of Earth's. Mass ends up being 0.58 of Earth's.
Since surface area is proportional to radius, squared, we will need about 80% of the Earth's atmosphere, oceans, and biological matter. An atmosphere will need 20% oxygen and 80% inert gas; nitrogen is the most common inert gas and should do nicely. The requirements for our moon will be $3.3\times10^{18}$ kg of nitrogen and $2.1\times10^{17}$ kg of oxygen. The ocean will need $1.1\times0^{21}$ kg of water (though this could vary widely, depending on how wet you want the planet). Lastly, the biosphere will need at least $1\times10^{12}$ kg of carbon.
To provide these ingredients, we can add three compounds primarily. Ammonia can be used to generate atmospheric nitrogen; Carbon dioxide can be transformed in to atmospheric oxygen; and water is just water. At the ratio of two Ammonia per one diatomic nitrogen and one carbon dioxide per diatomic oxygen, our shopping list is roughly:
* $1\times10^{21}$ kg water
* $4\times10^{18}$ kg ammonia
* $2\times10^{17}$ kg carbon dioxide
The great thing about these ingredients is that they are three of the most common compounds in the outer solar system. They also provide plenty of surplus material for making a biosphere: Carbon Dioxide has extra carbon and ammonia has extra hydrogen. No need to add methane, there are plenty of fossil fuels to go around!
# How to not make a mess
The next challenge is to not make too big of a mess when you deliver your materials. Here are the various factors you outlined.
### How not to significantly damage the moon's surface
Without an atmosphere, your moon will likely have a surface covered in fine regolith similar to what covers [Luna](https://curator.jsc.nasa.gov/lunar/letss/regolith.pdf) and [Mars](https://en.wikipedia.org/wiki/Martian_soil). If this surface is hit by impacts from space, the dust will end up mostly settled back into the surface. So from this perspective, there isn't too much to damage done by hitting the planet with space snowballs; the holes will be filled by dust (relatively) soon after impact. Lunar regolith has a density about 2/3 of lunar surface rocks (and Earth rocks), so the holes will be filled with a material that will be reasonably solid.
Newton's depth approximation for impacts is $$D\approx L\frac{\rho\_i}{\rho\_p}$$ where L is the length (or diameter, if spherical) of the projectile and $\rho\_i$ and $\rho\_p$ are the densities of the impactor and planet, respectively. Note that this approximation nowhere includes the velocity of the impactor. Let us assume that planet has a similar crust density to Earth (2500 kg/m$^3$), while the delivered volatiles, such as CO$\_2$, water, and ammonia each have densities less than 1000 kg/m$^3$.
Assuming we want to limit impact depth to 200 m so we don't make craters too large, we can throw objects up to 500m in diameter at the surface without making too much of a mess.
### How not to not make a debris cloud
Putting stuff back into space will both anger your space-junk-OCD [Chief Engineer](https://worldbuilding.stackexchange.com/a/96939/23519) and represent a loss of materials. We don't want to do that. How can we avoid it?
First, we have to figure out escape velocity of our planet. From [this post](https://worldbuilding.stackexchange.com/a/63090/23519), we see that radius and density are both proportional to surface gravity. As calculated above, we have radius 0.9 Earth's, density 0.8 Earth's, to get surface gravity 0.72 of Earth's. Mass ends up being 0.58 of Earth's.
Escape velocity is calculated [here](https://worldbuilding.stackexchange.com/questions/64903/what-is-the-smallest-planetary-mass-that-can-prevent-me-from-flying-off-into-s/64907#64907) as $\sqrt{2gr}$, where $g$ is gravity and $r$ is radius. Given the factors above, escape velocity of your moon is 0.8 of Earth's, or 9000 m/s. To ensure nothing goes into space, we will make the average ejecta velocity from our impact craters no more than 4000 m/s.
In [this post](https://worldbuilding.stackexchange.com/a/64855/23519), I perform calculations on the height of an ejecta plume. This model calculates ejection velocity as a function of distance from the impact site. We want the ejecta velocity at the edge of the impactor to be less than 4000 m/s. If you work out the equation, you find that the maximum ejecta speed is proportional only to the impact velocity, and not to the mass or radius of the impactor (although the density of the impactor is very important). Ultimately, the relationship is $$4000 \text{ m/s} = .1313v\_i.$$ Thus, for a 4000 m/s ejecta, the maximum impact speed must be about 30 km/s.
### How not to eject volatile gasses into space
Of the gasses you are interested in, the two lightest and therefore most likely to escape are water (molar mass 18) and ammonia (molar mass 17). Therefore, we must figure out how to keep those gasses on the planet upon impact.
First, lets look at the ejecta plume from the last problem. Using basic kinematics, a particle (of ammonia) ejected at 4000 m/s, will reach a height of about 1100 km (Don't worry! I know that this is well into space, but without orbital velocity, it is coming back down!). The time it takes to get all the way up there is about 400 seconds, and the escape velocity at this height is about 8200 m/s.
Using the calculations in the answers to this post, we can figure out how hot an ammonia particle must be at this height to escape the moon's gravity. A particle must reach about 40000 K to escape under these conditions. Ouch! Now, individual particles are able to escape because the molecular distribution of kinetic energy has some variance to it. However, given that the escape velocity at the top of the ejecta blast is still about the same as the last linked post's calculated necessary escape velocity to hold gasses over geological time (8500 m/s at Earth's distance from the Sun), I think we can assume that very little of our gaseous ejecta will hit space.
### How not to change the orbit and rotation of a moon
I had some more in depth calculations here, but they are not really needed. As long as you have the technology to accelerate things to 0.1c, I assume you have sufficient space horsepower to aim your delivered payloads as you like. If that is the case, then you simply hit the moon from all directions, so the net force of the impacts is zero.
# Conclusion
Find a suitable mid-size moon. Melt it. Separate the various compounds into chunks of no more than 250m radius. Throw them into your planet at impact speeds of less than 30 km/s. Very little will escape into space. Profit!
[Answer]
## Delivery
I would think that mining of the asteroid belt, either manned or automated, could be done to break up the chunks into smaller than SUV-sized pieces that could be launched at the moon. This would avoid any littering of rocket or other man-made materials.
It would leave craters, but sizes this small wouldn't be as devastating as a full comet or asteroid. With it impacting the surface, it could help disbursement some, as well as creating friction heat to help bring up the temp of a barren planetoid.
Larger pieces could be used to make divots large enough to be a lake or reservoir, without the heavy machinery current methods require. Smaller pieces will avoid large blow back out of the intended atmosphere. Heavily pounding the rocky surface will actually help pulverize it into more easily planted soil.
There will likely need to be significant changes to the moons surface for humans to live there, so why not do it with the pot-shots of delivering material before we move in? Running water will change the surface, as will plants and the new weather patterns.
Also, adding mass in the form of air, water, etc. will change the orbit of the moon, so that is unavoidable, to a certain extent. We have changed the orbit of the Earth by creating lakes with dams and other water reservoirs.
An advantage of orbital bombardment is that it helps judge the level of available atmosphere. As the atmosphere forms, more and more friction will be shown on the debris. Once it gets near Earth density, most of the sub-SUV sized debris will never even hit the surface. This friction has the advantage of further disbursing the O2, N2, H2O, and other materials/minerals you are likely to need on the surface and in the atmosphere.
## Mining
Using robotic miners would be faster than manned mining, but there could be a mixture of both, since the robots are likely to need maintenance. There's always the need for people to feed their families, so there's likely the "adventure seeker" that's willing to spend their time earning hazard pay for asteroid mining. After all, robots are expensive (they keep breaking) and humans are comparatively cheap (since there aren't enough jobs on Earth).
There's no need to render the materials to a refined state, just into small enough chunks. There could be a need to prevent certain volatile materials/substances from getting to the moon, but with the vast volume you are looking to fill, small pockets of even chlorine gas aren't likely to matter. And if you ship it with some sodium, it might even help, as in making salt.
## Flora
There's the high likelihood of needing to use some sort of genetic modification of the micro and macro biological elements of the first stage of plants. The plants would need to be adapted to that exact environment. Not all plants can deal with the rocky, low CO2, low O2, low temp, low gravity, low moisture area you are talking about. These would likely need to also be high yield plants and microbes that would output high levels of O2, N2, and lots of other things to be able to create an atmosphere in even 100 years. This flora would also need to be able to break into the rocky surface to get the required minerals they need.
They may also need to be highly susceptible to a specific chemical or spray that would kill the fast spreading biome, so more Earth-like tame plants could be brought in, without fear of being killed off by the original planet evolving life forms.
## Travel speed
Even 1/10th of the speed of light is really fast. This would allow us to go from the Earth to the asteroid belt in hours or days, rather than the current months, so a manned expedition is well within range for this speed. We would just need to make sure that we don't send any material into the moon at that speed.
You could, however, have a large transport that collects from the miners, then shoots over to the moon, slows down to open it's doors to offload/bombard the planet with the small fragments, then returns to the collection point. With 1/10th c, this could potentially be done in many points in the asteroid belt with nearly constant delivery to the moon.
The Martian Way, by Isaac Asimov, did something slightly similar. It is about a Mars colony that was having a shortage of water, asking the Earth to supply it. An Earth politician advocated against giving them more, citing a shortage of supply, so the Mars colony found their own solution. They sent out a group in a large rocket to find a large, mostly ice, asteroid to bring back. They ended up embedding the rocket into the asteroid and using it as a source of fuel to get home. They ended up with more than enough water for themselves, but had to expend a sizable portion of it to get it there and land it, rather than just crash it.
<https://en.wikipedia.org/wiki/The_Martian_Way>
[Answer]
Large scale projects like this need to consider the economics of moving all that material around the Solar System. You will need to apply energy to move it from whatever orbits it is currently in, then, since you are opposed to ballistic impact, more energy to match the orbital speed of the target and deliver it at minimal speeds.
Depending on where the materials are in relation to the target, you have several choices. If you are in a farther orbit from the material source than the local sun, you can use high performance [solar sails](https://infogalactic.com/info/Solar_sail) to tow the materials into the appropriate orbits. The sail can accelerate to the target planet, then "tack" by turning the trust vector against the direction of travel to match the orbital speed.
[](https://i.stack.imgur.com/DE0JA.gif)
*Solar sail accelerating to the target*
[](https://i.stack.imgur.com/OJJrI.gif)
*Solar sail decelerating to the target*
While the usual image of solar sails is vast, slow moving devices, [high performance sails](http://www.u3p.net/U3PMEDIA/DOCS/HoustonU3P.pdf) with accelerations of 1mm/sec^2 can move across the Solar System at impressive speeds, a one way trip from Earth to Pluto at these speeds would only take 3 years (although that is a flypast). The real key is to set up a "pipeline" and send materials in a steady stream. While it may take 3 years for the first "package" to arrive, once the pipeline is filled, there is a steady stream of materials on the way.
[](https://i.stack.imgur.com/7V6XJ.png)
*K Eric Drexler pioneered the idea of thin film solar sails as far back as the 1970's*
Using systems of mirrors at the target to reflect sunlight onto fast moving solar sails to assist slowing them down solves two issues, not only do you have finer control of incoming sails, but you can also use the solar energy when not controlling sails to provide energy to the surface, to assist in liquifying solids or turning liquid materials into gasses (an extreme case would be to focus solar energy onto the surface of Mars and boil Oxygen from the iron oxide on the surface. This is obviously energy intensive and inefficient, but with sufficient energy you can do almost anything).
Looking the other way, you could set up continental sized mirrors or platoons of mirrors to accelerate solar sails from the far reaches of the Solar System to send cut up pieces of comets back to the inner Solar System for your terraforming project. Given the weaker sunlight and vast distances, you might be looking at a decade before the first deliveries from the "pipeline" arrive, but once again, once the pipeline is filled, you have a steady stream of deliveries.
Without knowing important issues like the actual distances between the supply sources and targets, orbital velocities and so on, the answer is hand waved, but the ever useful [Atomic Rockets](http://www.projectrho.com/public_html/rocket/enginelist.php#id--Sail--Photon_Sail) site has a lot of relevant information and equations to work with so you can calculate delivery times, velocity changes etc.
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[Question]
[
I'm working on a setting with merfolk that I'd prefer to be fully mammalian. However, they have underwater cities and I find that hard to believe for a species that needs to surface every few hours at most to breathe. So, I was wondering if pharyngeal and cutaneous respiration similar to what softshell turtles are capable of would be plausible for a mammalian species. Would this method of breathing capable of providing the amount of oxygen necessary to maintain a warm-blooded metabolism? Are there any other concerns that would make this unrealistic for a mammal?
[Answer]
Sadly, this is not possible. Warm-blooded animals such as mammals simply use too much oxygen to maintain their internal body temperature for cutaneous breathing to be effective.
Let's get some numbers for that. The human body uses about 8mg of oxygen per second. In the ocean, oxygen concentrations vary between 0 and 10mg oxygen per liter. So in the best of circumstances, we're flowing 1 liter of oxygen over the merperson body per second, which doesn't actually sound that implausible. However, the merperson skin isn't actually going to be able to absorb all that oxygen- it's limited by the rate of diffusion.
According to [this paper](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290093/), the human body can take up about 1mL of oxygen per minute, based on both their measured assessment and the theoretical model that required an algebraic static solution of Fick's second law. I've grabbed the relevant section since the article may be behind a paywall for some users:
[](https://i.stack.imgur.com/rsPOT.png)
**Esentially, we're facing a difference of two orders of magnitude between what we need (8mg/sec) and what is possible to obtain (0.021mg/sec).**
However, there are some other ideas out there that might help you get around this limit- I'll link to my answer [here](https://worldbuilding.stackexchange.com/questions/96017/anatomically-reasonable-respiratory-system-for-human-derived-merfolk/96025#96025), a different question [here](https://worldbuilding.stackexchange.com/questions/43920/how-could-water-breathing-animals-have-a-warm-blooded-level-of-metabolism?rq=1), and one more [here](https://worldbuilding.stackexchange.com/questions/44137/how-to-breathe-both-on-land-and-under-the-sea?noredirect=1&lq=1), just in case you haven't seen them already.
[Answer]
Sadly, it's physically impossible to build an endotherm that breaths water nomatter how hard you try.
In best case scenario, oxygen saturation of water reaches about 10 milligrams per liter. Consider the oxidation of beryllium metal in oxygen, one of the most efficient heat generation method possible with a standard enthalpy of formation of -599 kJ/mol.
As the product beryllium oxide has a formula BeO, with a molecular mass of 25, and contains a ratio of Be to O of 9 to 16, one liter of water can only form about 15.625 milligrams of beryllium oxide if the oxygen saturation is fully consumed. 0.015625/25\*599000= 374.375 J per litre of water consumed.
At a heat capacity of 4.2kJ/kg\*C, 374.375 J of energy is only enough to raise the temperatire of that litre of water for 0.09 degrees C. As a matter of fact, such a low temperature difference is impossible to capture even with a recuperating heat exchanger, which maxes out at 95 percent efficiency, or a retained temperature difference of 1.78 degrees C above the highest ocean temperature recorded of 31 degrees C= 32.78 degrees C, or a core temperature of about 33 degrees C.
Below 35 degrees C, hypothermia sets in, below 33degrees C, the heart stops. Below 30 degrees C, a mammal will die of hypothermia.
Mean ocean temp near the tropics is about 28 degrees C. So, nomatter how large your merfolk is, the very water they breath will prevent their body temperature from reaching high enough to keep their hearts beating!
This is why ALL marine endotherms breaths air-- not because they had lungs instead off gills, but because the oxygen content of seawater alone is not enough to maintain even the bare minimum of core body temperature required for an endotherm to function!
Fish and ectotherms uses gills because their physiology does not require heat generation nor require a high temperature. The energy from dissolved oxygen is enough for most biological activity IF maintaining body heat is not necessary.
In DC comics, the atlanteans get away with this by using magic to supply most of their physical energy requirement, which may not even be endothermic at all. Without magic or another power source that does not rely on chemical reaction with oxygen gas, water breathing endotherm are physically impossible unless you count stable body temperatures atmost half a degree above the average water temperature as warm-blooded.
The solution?
One cheating, one based on reactions that does not require Di-Oxygen, that is, an An-aerobic reaction.
**The Cheating method**: have your merfolk live in extra hot water that approaches the average human body temperature, or at least above which a mammalian heart can beat with minimal extra heating. I.e. have your merfolk live in geothermal areas like the saltwater kingdom in DC aquaman. The extra heat requirement for a mammalian physiology is supplied by an external source, or like in the movie, literally bathing in molten lava.
**The Non-Cheating method**: use an alternative oxidizer for your merfolk's respiratory process, preferably something that can be
(a. Stored compactly in physiological conditions, preferably at least as dense as glycogen in terms of oxidative energy density.
(b. Can be resupplied with relative ease, preferably by ingestion, or is readily available at concentrations high enough to support endothermic metabolism within the environment your merfolk lives in.
Three natural pathways, Four if you count organic materials as valible electron receptors, exists at power and energy densities high enough to potentially support endothermic metabolism:
1. Denitrification, or Dissimilatory nitrate reduction (to ammonia)
This is the reaction employed by anaerobic soil bacteria to produce energy from nitrates, a product of ammonia oxidation or nitrification within aerobic top layers of the soil. This process uses dissolved nitrates as the electron acceptor, with a saturation point of near 300 grams per liter of water, the maximum energy density of this reaction is enough to boil water over for at least 3 times for its stored mass of oxidizer. Nitrates could be collected from the environment, preferably during non-endothermic "hibernation" periods, produced from nitrogenous compounds during bidaily to weekly (if up to 3 kilograms of nitrates is made during one surfacing) surfacing to collect atmospheric oxygen from air, or ingested as part of your merfolk's diet. The latter may well be because of anoxygenic photosynthesis of some of your worlds plants, like purple/green non-sulfur bacteria.
2. Hydrogenosome and hydrogenesis
This is the prevalent way of disposing of unwanted electrons in archaea and certain cyanobacteria. In certain small (euxinophilic)animals, devolved, mitochondria derived hydrogenosomes uses protons themselves as a terminal electron acceptor, producing hydrogen gas as a byproduct. The reaction is inefficient, in terms that a one pair of electrons can at best pump six protons (usually just four), but as this reaction uses water as oxidizer, the energy density per kilogram of water consumed is almost the same as air breathing organisms. As the product of this reaction is hydrogen gas, this also causes your merfolk to exhale bubbles, but not inhale anything.
3. Methanogenesis
Methanogenesis is the last option for anaerobic respiration that does not involve the exhaustion of organic compounds as byproducts. Methane is produced by obligate anaerobic archaea that uses carbon dioxide as the terminal electron acceptor. This reaction pumps 6 protons per pair of electrons in Methanobacilus, 4 to 5 in Methanosarcina. Methanogenesis produces marginally more energy than Hydrogenesis, and it uses the byproduct of respiration itself as the oxidizer. The energy density of methanogenesis is often high enough to keep a pile of compost at self limiting temperature for two to two and a half days.
4. Fermentative processes
Contrast to popular beliefs, very Deep forms of fermentation are very efficient in terms of energy production per substrate molecule consumed. For example, the process of acetone butanol ethanol fermentation produces at maximum 5.25 ATP per glucose consumed, and the oxaloacetate/malate disproportionation reactions of roundworms makes 6.1 ATP per glucose consumed. these are one of the reasons why compost piles can spontaneously catch fire. Of course, your merfolk will not catch fire because they are underwater, but the heat generation is more than enough to keep your endothermic merfolk warm.
Drawbacks of anaerobic respiration:
Although anaerobic respiration conserves body heat by nearly eliminating the necessary diffusive(and therefore thermally contacting) water flow and the resulting heat exchange with your merfolks's core organs, they are relatively inefficient when compared to oxidation by dioxygen gas in term of organic carbon consumed.
However, as the limiting factor is heat exchange not food(as this is not earth), having a race of merfolk that are exceptionally voracious eaters would likely make good story details, or at least prevent obesity, as most marine mammals had exceptionally thick blubbers......
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Let's start with what we consume in O2. The average human consumes about 25% of the oxygen in the air with every breath, and that means that the average human is going to consume about 550 litres of O2 in a given day.
A Merman is going to use more because water is cold [citation needed] meaning that he or she needs more energy to keep internal body temps regulated. Let's say double, to be sure. That means 1.1 KL/day
First question is whether or not an ocean can support that kind of O2 saturation level. Assuming an earth like world, the answer is probably, but only to a certain depth. This is because the O2 saturation in the water is caused by photosynthesis in the sub-surface plant life (microscopic and macroscopic) and the sunlight that drives this process can only reach down so far. Bottom line is that regardless of breathing method, your merfolk are likely to suffocate at extreme depths. This isn't that big a deal, because conventional mammals can't regulate their internal pressure so you want to keep within a certain range of the surface for practicality, not to mention just seeing where you're going.
For now, let's assume that there's enough plant life in the ocean to support your O2 levels.
The thing about mammals is that they all have lungs. This is one of the primary limitations to our capacity to dive to great depths currently. That said, is it possible that sustained natural selection could evolve a mammal that uses (say) gills instead?
Well, I'd have to say yes, but I don't know what underwater breathing would actually look like in a mammal that has gone back to the oceans. All I can really say is that if fish like animals could adapt to land by evolving lungs and limbs, then it's entirely feasible that in time, mammals could evolve in a manner that allowed them to breathe underwater. The eventual removal of lungs (or their atrophy-cation like the appendix) would also remove some of the natural impediments from a species being able to take full advantage of underwater life by removing the primary impediment to pressure variations; the lungs.
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In my Pathfinder RPG campaign setting I have two continents separated by an isthmus.
An artificial canyon carved through the isthmus from one ocean to another divides the continents.
The canyon is five miles wide for the most part, but narrows at The Pinch to a spot one mile wide
with a narrow bridge.
The canyon separates the eastern and western continents. It was carved out years ago by wizards,
who placed a mountain at the north end of the canyon and a [Wall of Force](http://www.d20pfsrd.com/magic/all-spells/w/wall-of-force/) down the south end. These prevent the ocean from filling the canyon.
Between the south end and The Pinch, at the highest point in the canyon but still 2500 feet below sea level, a city has been built against the eastern canyon wall. The city, Blackmount, is the only point on the planet where
an elixir that prolongs life may be made.
It's also outside the legal jurisdiction of either political state on either side of the canyon.
The part I am stuck on, developing this city, is how they manage water. They're below sea level. How does fresh water get in? What do they do with waste water?
The feel I am going for is Age of Englightment / *Pirates of the Carribean* (so, roughly 1730 technology level) but in an alternate world where humans compete with elves, dwarves, halfings and gnomes for resources on the planet (and those are just the "good/benign" races). Magic is used by a small percentage of the global population.
**EDIT**: I agree that I could hand wave away the problems with water and sewage by using the term "magic" and say "The wizards dealt with it." My intent was to find a different way to address it.
With regards to food, trade, and roads: I have not planned this out in enough detail because I got stuck on the water issue. My current idea is that the (small) city is the only place on the planet that makes an elixir that may prolong life. This is sold annually in limited quantities for an exorbitant price. Part of that income is used to bring in food, water and other rare goods on special centaurs that are more mountain-goat than horse, who make their way down incredibly steep channels. Or maybe riders on giant spiders haul cargo up and down. There are no easy roads out, but gravity easily brings all manner of stuff down to the city; this causes its own set of problems.
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It heavily depends on local climate, but bottom of a N/S crevice half a mile high by one mile wide would get very little direct little sunshine (around midday); this means having your wastes to evaporate naturally is probably not feasible.
To get water in you can rely on rain, if available, or on some (small) river flowing into the abyss.
In both cases your problem is how to avoid this basin to get filled with fresh water.
You can handwave it away saying the mage who prepared the Wall of Force spell made it unidirectional, so that anything leaning on it from the north side would be instantly pushed unto the south side of the wall (2500 feet under water, you need a good breath to escape that way!... not to speak about your eardrums). *[Side Note: in this case you have a very nice way to produce "moto perpetuo" and get free energy just by having a pipe siphoning sea water in, use its 2500 feet drop potential energy with some kind of mill and then shove it through the wall returning it to sea; OTOH such energy might come from the spell itself, which may be weakened and, perhaps, fail after a while (if not "renewed")]*
Otherwise you'll need to pump it up, most likely with an Archimedes screw.
Note that this freshwater-filling problem is completely independent from city.
Such a closed crevice, if not in fully desert climate, is bound to be filled in reasonably short time, so Magician must have solved it when he built it, somehow.
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# Reverse Osmosis
Actually, you have a really easy way to make fresh water in that underwater city: [reverse osmosis](https://en.wikipedia.org/wiki/Reverse_osmosis#Desalination)
Assuming that the air pressure inside this city is actually normal atmospheric pressure, you have it really easy: you simply tap sea water through the wall and let the enormous pressure of being 750 meters / 2 500 feet below the surface do the job for you. The pressure forces the water through the reverse osmosis filters and... well, that is basically it, you get fresh water on the other side. The reason we do not do it more here on Earth is that creating the pressure needed to achieve this requires using a lot of energy. But in your city, you have that pressure for free.
As for waste water... well that too is fairly easy. You have a pipe through the wall leading to a tank. The tank and this outlet pipe need to be very sturdy and not flex when subjected to pressure. You fill the tank to the brim with waste water. Then you close the low pressure side of the tank where you filled it with water, and (very gently) open the outside valve. Then you simply use compressed air to push the waste water out into the sea. Naturally this is something you want to do **downstream** from inlets to the desalination filters.
And if you cannot get an air pump to produce 75 atmospheres of pressure... well then then you simply need to **hoist** the waste out of the canyon.
No, you cannot boil away the water, let the steam rise and then just hoist the solid waste that is left behind, because steam cannot rise indefinitely, because stream **cools** as it rises. The heat of the steam is being converted to potential energy as it rises, and so [TAANSTAFL](https://en.wikipedia.org/wiki/There_ain%27t_no_such_thing_as_a_free_lunch) applies, even to steam.
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The water getting in part can be solved by collecting rain water in cisterns assuming the rainfall is suficient.
Similarly if it is hot enough waste water can be disposed of by moving it into shallow pools that evaporate by the heat of the sun, any remaining solid waste can then be shoveled onto carts and carted of.
This assumes a hot an relatively arrid climate similar to the mediteranian region.
If your climate is different other solutions might be needed.
Adding water is probably the simpler part, a system of canals on either side could divert controlable amounts of water over the edge.
Getting rid of the waste, thus avoiding a waterfilled canyon is probably the harder part.
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Create a hoop with [Purify Food and Drink](http://paizo.com/pathfinderRPG/prd/coreRulebook/spells/purifyFoodAndDrink.html) on it and use it to recycle the water. Then you just have to figure out how to transport the water uphill to holding tanks. You can do that through siphoning (32 feet at a time) or through some animated water pump.
Another possibility is set up [Decanters of Endless Water](http://www.d20pfsrd.com/magic-items/wondrous-items/wondrous-items/c-d/decanter-of-endless-water/) on the high ground and a [Sphere of Annihilation](http://www.d20pfsrd.com/magic-items/artifacts/minor-artifacts/sphere-of-annihilation/) at the low point.
If you combine the two methods, (some Decanters to make up for water loss) you have a pretty good system.
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I'm going to suggest a controlled underground river that is so hot that water turns to steam and burst out of the ground through gysers(or supply a citys' water tank). It would be like a giant sprinkler system and probably look awesome causing lots of rainbows.
Though this seems slightly implausible, especialy as water boils without special geology or magic about 10000 feet below,which might not have the force to reach the surface.Though if this is volcanic terrain or magic is involved it becomes easier. I thought it was a cool idea and couldn't get it out of my head. Also hotsprings are suppost to be great for relaxation and health, maybe a start of a fountain of youth myth.
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I'm curious if it's possible for human life to survive in both of the following cases:
# 1. A fantasy world with **only** sunlight (no night).
# 2. A fantasy world with **only** night (no day).
Note: let's **ignore astronomic concerns for now** (things like tides or gravity if, say, the world was a planet that didn't spin) unless you strongly believe it's an issue no matter the details of the world structure.
If you think it's possible, explain how. If it involves ingenuity on the inhabitants' part, bonus points for "fitting it" into a fantasy realm (vs. science fiction). For example, your average fantasy peasant in the "darkness world" probably doesn't know about Vitamin D deficiency. However, it's possible that they learn (somehow) that "healthy" people eat fish.
I'm sure more clarification will be required on my part (and I'll edit my answer accordingly), but I'm trying to keep it pretty open for now.
I'm not requesting hard science--just plausible answers.
To start, a couple issues that I'm interested in ideas for:
Both worlds:
* Lack of a day/night cycle for humans and other creatures to sleep
* Extreme hot/cold temperatures (thanks, [santyclause](https://worldbuilding.stackexchange.com/users/22690/santyclause)!)
Darkness world:
* Oxygen production (no photosynthesis)
# EDITS
For clarification:
Both worlds:
* The worlds are linked: light world inhabitants who are in charge of governing / policing the dark world will travel between worlds often
* Portals: the only way that the worlds are connected are through "small" (a few meters in height and width) portals. All transportation between worlds must be done through one or more of these portals.
* Portal technology. The portals were not created by the light world inhabitants or the dark world inhabitants, and largely remain a mystery to both (other than that they know, generally, which portals lead to which places). Thus, they cannot be manipulated, but only used for their "intended" purpose. Another point that may be important to note: **all portals** are one-way. For example, if you take a portal from the light world to the dark, you'll need to know where to go to get to a portal that leads back to the light world. There are many more "intra-world" (only lead to other same-world locations) than there are "inter-world" portals.
* Light cannot pass through portals.
* Distance between worlds. They are very far apart, so much so that transportation outside of the portals is impossible for either civilization (even though the light world civilization is considered "advanced", they aren't advanced enough to transport materials / energy / etc. to the other world without the portals).
Dark world:
* One moon and stars (think nighttime on Earth), but many storms and clouds. I'm open to multiple moons if it would increase plausibility.
Light world:
* Inhabited by a **relatively** advanced civilization capable of building large structures and retrieving the dark world's resources (water, for example) **via portals** to sustain itself. NOTE: this does not mean that the civilization is very advanced technologically. Their scientific progress is still semi-medieval (a little more medical knowledge), though aided by magic.
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Here's what I have for starters.
Since the "Light" world is advanced, they could have gardens/farms growing in areas that could mechanically be placed in darkness for periods of the day (in the shadows) Which would also take care of oxygen production.
Since they also are technologically advanced, they could bring light to the dark side either through mirrors or other means, scientific or magical.
Heat would be a problem for both worlds. If the light world was sufficiently advanced, they could vent the heat to the darkness world in a symbiosis that would heat the dark world and cool the light one.
Fungi could be easily be farmed on the dark world, and a glowing fungi could provide more light, perhaps amplifying the light from the moon and stars.
EDITED to add:
The mystical heating and cooling could function through the same magic as the portals, but with a much different conduit, it would be one-way with all the heat and light being absorbed from heat-sinks on the highest elevations, so that as these heat-sinks sent off heat to the other planet, they would be significantly cooler than the surrounding air, which would then drop down off of the mountains helping to create a circulation system of the cooler air. One the dark world, the heat dispursion areas could be underwater, making hot-springs or heated lakes, with the light being sent to various areas with a fiber-optic type network.
This would create a symbiotic relationship with both planets making ruling the dark world be more of a beneficial dictatorship than an iron-fisted one, much the way Rome expanded by building cities in lands outside the empire which became major hubs of trade, and remain so today.
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# **Yes to both!**
And despite what you would first think, the planets can absolutely maintain pleasant temperatures.
## First lets look at the bright and shiny day planet.
Sure, you're first instinct is that it's gonna get pounded by sunlight and turn into a scorching ball of gas, but that's not necessarily true. This one is actually relatively easy for humans to thrive on. All you need is lots and lots of pretty white clouds.
Assuming the atmosphere is somewhat similar to Earth's, then give it a few (relatively) small tweaks and turn the sky white. This greatly increases the planet's albedo and reflect most of the radiation back up into space, and if a nice balance is formed then the surface of the planet can remain relatively earth-like.
## Now for the dark planet.
This one is a little bit tougher, but still doable thanks to the dreaded and evil **Greenhouse Gases**! Since it's always in the dark I'm assuming something must be close enough to block out the light. So there's our first piece of heat in the form of tidal heating. Next there's the heat that emits from the the planet's core. Then there's however much light that may reflect from the planet's moon. And then there's another source of tidal heating depending on how close that moon is to the planet. So all in all, you got something to work with but if the atmosphere was exactly like Earth's then probably still wouldn't be enough.
But we can add some lovely lovely greenhouse gases. We can safely breath multitudes more CO2 than what's in our atmosphere. We can also add in a little bit of methane and, my personal favorite, toss in a decent amount of ammonia for good measure. And who says the atmosphere has to be at 1atm. We can safely crank that up higher so lets say the planet is closer to 1.5atm. That's more gas near the surface which means more trapped heat. Toss in a good an ocean as well and yes this planet could remain relatively warm.
What about food though? No fear, the moon is here. Earth's moon, interestingly enough, is capable of providing enough light to support some small phytoplankton. And our moons albedo is only 0.12, and it's very possible your moon could have a significantly higher albedo which would mean it would reflect more light onto the planet which could potentially grow more plankton which could form the basis of a food chain. So the humans would most likely be coastal and live primarily on fish. There are also plants here on Earth that can grow in very small amounts of light, so it's entirely possible that the land could be dominated by plants that also grow from the moons light.
So, in closing, it's very much possible that both these planets could be habitable for even primitive humanity. Though I would expect those on the daylight world to have an easier time of it than those on the dark world.
Hope I helped!
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Did you know that there is a real world equivalent to what you are talking about? Well there actually is. If you have a planet in the habitable zone of a red dwarf star it will likely be tidally locked, then you have one side that is always night and one side that is always day! And since you know they live on the extreme sides of the world anybody that tries to travel outside of civilization will die before they get far. You could also have the portals (and your magic system) be created by a previously super advanced civilization that got sent to the extremes of the world after a war. And for the moon? Just place it at L2, if it's roughly the same color as the day side then people on the night side might think they are seeing the day side, you could do something like that by placing a similar disk at L1.
Just think about, everything that you ever wanted but it's in the future, and sticks with what could be possible.
Edit:
What I'm recommending is something that requires clark-tech (technology so close to magic it's indistinguishable from it), and a ruling civilization that nobody is aware of making sure that they stay alive (to prevent morality wars) and tech-backwards. It's basically sci-fi but really fantasy.
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The light may help some visually and certainly life is sustainable with minimal to no light. Look at the deep ocean waters where the light cannot reach. most of those fish are blind or create their own form of light. Temperature will still be an issue. A planet that has total darkness will be frigid. Take a look at Pluto (you can argue if it is or is not a planet later :P), minimal sunlight reaches and it is basically a floating iceball. Since the light source will be from moon(s) which is an indirect reflection of sunlight, there will almost be no external heat being provided.
The other issue you have to consider is that you would have to probably create your own storm/cloud system. Clouds form due to moister evaporation. A planet darkened out will most likely be completely frozen. Also with the lack of heat, the air particles are more than likely going to be rigid so there will be very little room for friction to be created and lightning will also not be possible or rarely seen.
Even so, this wouldn't be scientifically possible as all planets revolve around a star which means they have more or less sun exposure depending on how far away they are. There could be a state where the planet is far away enough which minimal light get's through, but it would be more like a permanent dawn/dusk rather than the deep of night.
You would be better off just doing some handwaving or have part of the mystery of why the planet is in total darkness is because there is some object in the way or some magic barrier placed by the people of the light which won't be revealed till what ever plot in the story makes someone curious as to why they are always in the dark.
As far as the light planet goes, as everyone said, it would pretty much be like living in the Sahara desert anywhere you go all day every day but it seems like you have this one mostly thought out with underground shelters (and water wells would be possible to find in the ground as well). The only issue would be a source of food because plant life as we know it requires some light and proper temperatures to grow. Anything above the surface would die from being too hot and the shelters are more than likely going to be too deep to create skylight windows. Meat would also be hard to cultivate but would be possible to create underground rooms for raising livestock.
Cool concepts to play with but in terms of a reality check it wouldn't pass. That doesn't mean though the idea cannot hold water, you just have to do some handwaving so that it can seem plausible. Like maybe the people in light have replicators for food since they are advanced and don't need to grow crops or livestock.
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The light world is easy. Simply make the sun enough dimmer than ours that the planet maintains a reasonably constant temperature and does not overheat. It can be any temperature you want it to be, from Arctic to Sahara, or cooler or hotter than either of those, by just adjusting the sun's output appropriately. A bit of cloud cover from time to time helps make things more variable.
As for dark, the big problem is that the world is going to freeze unless you provide some source of heat. Possible sources include:
* Geothermal (ultimately coming from nuclear reactions in the planet's core: volcanoes and such, geysers, or just heating through the ground)
* Tidal heating (for instance, a moon closely orbiting a gas giant gets constantly wrenched by gravity, causing earthquakes, friction and heating. Take a look at [Io](https://en.wikipedia.org/wiki/Tidal_heating_of_Io), for instance.)
* Solar (a planet orbiting a brown dwarf, dying red dwarf, a star surrounded by opaque-to-visible-light dust clouds, etc. might mostly receive infrared radiation, rather than visible light)
* Environmental (like Solar, except that infrared comes from nearby space dust or maybe matter orbiting a dormant black hole)
* Meteorological (*lots* of meteors fall, and each contributes heat as it burns up in the atmosphere)
* Electrical (lots of thunderstorms due to something (what?) moving air around)
* High Energy Physics (Aurorae? A constant wash of subatomic particles from a nearby star or black hole? Could fry people with radiation if you're not careful.)
* And, of course since this is fantasy, some type of Magic.
Note that on the dark world, the weather patterns are going to be due to whatever's causing the heat, not to sunlight like on ours. So you might see clouds or winds forming around volcanoes for instance.
It would help to have an atmosphere that traps heat (Greenhouse gases).
Another possibility is that the planet is actually in a fairly well lighted area outside a star, but an upper layer of its atmosphere blocks most visible light, letting only infrared through. Perhaps somewhat like the planet [Venus](https://en.wikipedia.org/wiki/Atmosphere_of_Venus), but even darker. This means you can't see the moon or stars, though.
How life would evolve on a world mostly or entirely without light is an interesting question, of course. I would imagine a lot of bioluminescent creatures, like we see in the deep ocean or in caves where similar situations exist. Also, creatures that "see" using other senses, like echolocation, excellent hearing, excellent smell, feeling vibrations through the ground, sensing electricity, and so forth.
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I'm writing a somewhat cyberpunk story and I want to know how things work in that world, even if it is not explained in the story. It was designed as a bit futuristic settings, though some of things they do can already be done in this world.
So, just to explain tech level, some things that are available:
* GMO-people – illegal, but totally possible, and some successful experiments have been done
* bionic joints – rather common and are usually installed in case of bad trauma
* bionic limbs – exist, but are more rare
* synthetic skin that looks and feels almost like real skin (and provides tactile feedback)
* HUD that is just a bit bigger than usual glasses (and with real reality augmentation, not just a small image at the corner)
* small, one-person aircraft with bird-like flight mechanic, controlled by body motion (really new development, not so long ago was thought to be impossible)
* and more cool gadgets, I'll try to remember some and add later.
One of the characters wears a suit made of individual scales. This suit provides some data, like heartbeat and such and can register injuries. Its "brain" is enclosed in a vambrace which also (supposedly) contains some power source. The suit also can protect its wearer from sliding knife hit (no from direct one). I guess it's made of some fancy polymer, maybe graphene covered or with nano-wiring. It is light (you could wear it whole day and it would be OK and doesn't restrict movement.
Now the difficult part: suit can be completely disassembled to individual scales and then assembled back (it won't be so easy though, imagine a human-size jigsaw), but anyway, you can unfasten it the way you need and all. And if some scales get broken, they can be replaced with new ones.
This means that scales must be held together strong enough, but yet be easy to take apart if you know how. The question is: how can this be done?
So far I thought of
* magnetic/electromagnetic system that holds scales together. But it seems over-complicated and not very reliable. And it's not clear if it would be bad for health to wear such a magnetic thing.
* some mechanic way to lock the scales, but all I came up with is either too difficult to disassemble or not reliable enough.
UPD:
Cloth backing isn't a good idea because if suit gets damaged (e.g. shot through), you will need to somehow mend the cloth, so just changing a scale or two won't be so easy. Some cloth suit beneath the scaled one is possible though.
Crucial moment with disassembling or unfastening the suit: it is intended that you can fasten and unfasten it without any instrument (maybe with just one small tool) as the suit doesn't have any other way to be put on or taken off but by partial disassembling.
UPD2:
Please, no unobtanium-based stuff. And definitely no GM-creatures. It should be somewhere between "a semi-working prototype of this already exists" and "We don't have quite the technology needed for this, but it's clear what is needed and looks achievable in some 10 years if we put our mind to it." Graphene – hell yes, we have it, and we use it already, and any plausible usage of it is absolutely OK. Some sort of fungus infused with insect DNA to give it a chitin coating and octopus DNA so that it has tiny tentacles – big no-no.
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Without a cloth backing of any kind?
The simplest way to do it would be to have a set of locking rings (or potentially even small chains or elastic super duper nanofibers) flexibly attached to the back of each scale and assembled like chainmail. If the scales are large enough overlap when they are locked together then a suit of this scale mail can be rapidly (in relative terms, it still depends on the size of the scales) assembled with no need for anything but a set of pliers.
There are three issues with this:
1: Comfort: You'd either need a second backing layer or some way to make sure that the interlocking mechanisms don't chafe along the skin. Having a smaller second 'comfort' scale attached to the underside of the first (so the locking mechanism is between a large armour scale and a smaller comfort scale) might help with this, or if the locking mechanism is fine enough that it acts like a fabric. Bear in mind that the smaller and more fiddly the locking mechanism is the longer the armour will take to assemble/dissemble, to the point where you may need some form of assembly machine.
2: Design strength: Mostly by this I mean that the scales will (by necessity) have gaps between them. This is a flaw common to any scale mail, as the scales have to move over each other freely, and with no backing layer to absorb impact under the scales (aside from that created by the locking/comfort layers) your armour is suffering from a fatal flaw if you want it to perform well in a knife fight. If the locking layer is strong enough to turn a blade that slips under a scale (again, like chainmail) then this is ameliorated somewhat.
3: Weight: A strong mechanical locking mechanism that humans can interact with could increase the weight of the armour overall, though with some of the compounds that you're proposing using I'm sure you can find/create a suitable polymer.
My suggestion for a locking mechanism would essentially be a series of data cables, covered in a very strong woven sheathing and using a male connector, that can be locked together using a female-female interface unit that also doubles as the comfort layer (i.e. has a smaller comfortable scale on the underside. This gives the suit flexibility, data transfer capability, a more comfortable wear and makes it nice and simple for laymen to replace damaged scales. Using multiple data cables and treating each scale as a node increases redundancy in the suit. Couple the cable with a mechanical retraction mechanism and you can even ensure a tight fit to reduce the potential gapping of the scales even if the suit loses power.
Again: The smaller you make the scales/connections the harder it will be to mess about with this suit, and the wearer will have to remove the suit to get at the connections, so this probably isn't the best idea if you want parts of the suit to be hot-swappable in combat situations.
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I would suggest Chinese Mountain Armor or Shan Wen Kia design leaf scale coupled with a robotic/ computerised assembly tool. Here's a link to some guys in the SCA discussing how they are making some of this - with pictures:
<http://forums.armourarchive.org/phpBB3/viewtopic.php?f=1&t=105720>
Some kind of incredibly tough nanomaterial for the actual scales - and a locking pin holding each one onto the base cloth.
I would be suggesting not every scale provides data - only some of them - but every scale passes data & power. That way there would be multiple pathways for the data to get to the vambrace.
The tech level you describe seems to make it a natural thought that a custom manufacturing/ computer controlled nanofactory would be able to handle the assembly/ repair of such a suit.
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Another invention - "muscular skin", fibrils normally contracted and desiccated when dormant - which is their "use state". The fibrils relax upon feeding with a special nutrient (feed can only be administrated within a narrowish temperature range/env conditions) and when relaxed the scale can be easily extracted - but is not loose enough to fall on it's own.
The skin also require feeding periodically (every 2-3 days?), otherwise the wear cause by the relative movement/friction will cause the skin to tear.
Bonus - make the scales a by-product of the skin metabolism, something like hair/nails (keratin or chitin stuff).
Advanced scenario - make it a living thing in symbiosis with the wearer and feeding from the wearer's blood stream. The skin is grown specially for the host, cannot change the her/him on the danger of anaphylactic shock for both the host and the skin within minutes. If you can give the skin some nervous system enough for perception, instincts and reaction (toughen when detects fear, amplify the strength of fast movements, etc), such a skin would try to protect the wearer as the only source of food.
[Answer]
As several other answers have already pointed out, having the scales link together is the simplest method that covers all your needs. The interesting part is making it simple to remove and replace individual units. Where I think the other answers fall short is in not recognizing that, in a Cyberpunk setting, we don't have to really care about real-world feasibility. CP is science *fantasy* for the most part after all.
(I know. You said near future. But look around at the world, check out what people are doing with things like graphene, aerogels, nano-mechanics and so on. Perhaps this isn't quite as far-fetched as it looks.)
First, each component 'scale' of your armor is a complex piece of engineering assembled from ultra-high tech components. It has a polymantane diamandoid outer layer for straight up protection over a honeycomb graphene lattice for structural rigidity. The lattice is filled with aerogel capsules for protection against thermal attacks, suspended in a high temperature ballistic gel to disperse kinetic and sonic energy attacks. At the back of the component is a thin layer of nano-scale mechanical engineering that includes a rudimentary computer powered by body heat and piezo crystal effects as well as a set of articulated interlink structures. And finally at the back of the piece is a padded section that makes it comfortable to wear directly on natural skin as well as using embedded systems to generate the small amount of power required to run the compute block.
In short, it's a piece of experimental corp tech from way beyond the bleeding edge. This is Diamond Age tech in a silicon and super-chrome world.
The limitations on the system are that each scale has only a tiny amount of compute, and almost all of it is devoted to the job of attaching to its neighbors in a flexible fashion that allows for natural motion, ensuring that the occupant of the suit is able to move around freely. All of the components are lightweight and have about the same processing power as the average ant. What you're wearing isn't so much a collection of individual units as it is a swarm programmed to act like a suit of armor.
The 'bracer' is the brains of the whole operation. It contains the sensor suite and control gear that allows the rest of the suit to function the way you need it to... especially with regards to disassembling or reconfiguring the suit as needed. It uses low powered ultra-high frequency sonics (in the 80kHz+ range) to communicate with the nearby components, with a very simple set of commands for specific behaviors. It also receives data from the suit's components, allowing it to monitor all sorts of interesting things including suit geometry, user telemetry and so on and presents a user interface - probably through direct neural interface - that provides that information to the operator.
There are some specialized components for various functions, including ones that have larger sensor and compute packages for monitoring user health, providing visual data in all directions, radar mapping and so on. These components may be larger or sacrifice protection for additional functionality. You could also have decentralized compute nodes that spread the computational load for suit functions around different parts of the body.
Let's see if we've covered all the requirements...
* Blade Deflection - yep, diamondoid is pretty robust stuff.
* Disassembly - just have the controller send a deactivate to the whole thing and it'll literally fall right off.
* Unzipping - again, just a matter of telling a set of components to unbind.
* Replaceable Components - assuming you have access to spares or a fabricator unit for them, no problem.
* Jigsaw Puzzle - oh yeah, big time. Fortunately they're smart puzzle pieces, so that's not too big of an issue.
And let's not forget the classic First Rule of Cyberpunk: Style over Substance. This thing looks like a suit of rainbow-hued scales that sparkle in the light and is basically immune to anything not designed to take down a raging cyborg. All it needs now is a suite of cleaning nanites and it's the most beautiful piece of armor you'll ever drop 25 million Nuyen on, chummer. You'll be the envy of every razor girl and street sam from here to Chiba. I've even got a couple bright kids working on a nanofab template to replicate the scales, so you come right back here when you need replacements. I'll even give you a discount on the first batch.
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Oh, you thought that was the end of it? You clearly don't know how badly the corps want this tech back. The runner who jacked the control unit specs left a logic bomb in their system that wiped out months worth of R&D. And they're not the only ones that want a piece of you... corporate rivals, mercs, other denizens of the neon streets, crime syndicates, even some government agencies... hey, welcome to the dystopia.
The one thing this suit doesn't have is stealth. You're going to want to cover it up or everyone is going to be jumping at the chance to cash in on the bounty. Even if you're working for the corp that developed the gear the rest of the world is interested, and they don't need you alive. I hope you've got some top-notch data cowboys watching your back, and you'd better make sure your team are trustworthy as all hell.
The downside of the concept is that a sufficiently motivated and resourced opponent can always hack your interface and take control of the suit away from you. Experimental gear is notoriously insecure, so there's bound to be a thousand points of entry for a talented console jockey to exploit. Or worse, an AI could take an interest and decide to take the suit - and you with it - for a ride. Hope your firewalls are secure.
And just in case you're not working for the corp that created the suit, you might want to be on the lookout for people carrying weird sonic weapons. There's always the chance that they embedded a kill switch in the system that will make the whole suit fall off at the worst possible moment, leaving you standing in the middle of a firefight in your underwear. Probably something you want to avoid.
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As far as cloth backing doesn't suit [lamellar armor](https://en.m.wikipedia.org/wiki/Lamellar_armour) may.
Edit: this sort of armor consists of thousands of small plates laced together via cord. It is easy to assemble/disassemble. Lacing allows plates to move, overlaping provides reasonable protection. It can be penetrated either if you can penetrate plate itself or if something can get between two plates, which is not so easy.
[Answer]
How about having a hinged portion at the top of the scales that clip together horizontally and vertically. Whatever electrical-like connection you need could easily be supplied by sockets in the connectors. You could optionally have disassembly require a special tool, or just a toothpick.
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>
> After the WorldBuilding community helped Average Joe [start his own
> microstate](https://worldbuilding.stackexchange.com/questions/61193/how-can-average-joe-create-a-micro-state-that-is-a-member-of-the-un-in-the-least), Joe has become scientifically inclined, and uses his
> money to conduct somewhat dangerous research projects from his new soverign position as President of Somewhere. ([Might not end
> well](https://worldbuilding.stackexchange.com/questions/61196/what-would-it-take-for-an-average-joe-to-take-over-the-world))
>
>
>
>
> ---
>
>
> Now Joe, thinking he can do everything, has decided to invest money in
> antigravity research. His top scientists tell him that magnets are the
> way to go: if we can make a [frog fly around](http://www.physics.org/facts/frog-really.asp) in a [magnetic
> tube](https://en.wikipedia.org/wiki/Bitter_electromagnet) because water is [diamagnetic](https://en.wikipedia.org/wiki/Diamagnetism), why not try the same with
> people, another fairly water-rich species?
>
>
>
>
> ---
>
>
>
**Assume:**
* Joe has the money to build an electromagnet as large as he wants, or research until he can achieve extreme magnetic attraction
* It is set up the same way as in the classic frog experiment, just on a larger scale
* Joe is Average (there is no special weight, composition etc within Joe)
* Real physics must apply. No unobtanium, magic, law bending, etc.
* Joe's scientists don't have to be right about magnetic levitation being cost-effective or "The way to go". This question is **not** asking for realistic levitation, it's asking what powerful magnets can do to the body.
**Prompt**
* Frogs were used in the original experiment because they are made up of a significant amount of water, and it's spread pretty evenly. Humans have a less even distribution of water; will that mean areas such as the stomach, digestive track, skull etc are at risk of being pulled outward? (This is not specifically what I'm answering, just something to consider in an answer)
* Blood contains a *whole lotta iron*
**Before Joe hops inside the electromagnet, he needs to know:**
* What are the health risks of a small amount of magnetism - just enough to hover a few inches?
* At what point does Joe need to take measures to protect himself?
* How much magnetism will kill Joe?
[Answer]
Although I was unable to find a conclusive answer to this exact question (despite the number of times it has been asked), I would presume that a person can be levitated safely.
Magnetic levitation of living organisms works through diamagnetism, which is basically the water in your body "pushing" against the magnetic field. Living organisms can be levitated because their bodies are mostly water, and that water is pretty evenly distributed throughout the body, since every individual cell is basically a tiny bag of water with some stuff mixed in. This is the case regardless of whether the organism is a frog, a grasshopper, a mouse, or a human. The force applied to every water molecule is equal, meaning that you would be effectively weightless while suspended in the field.
The only part of the body that is made up mostly of something other than watery cells are the bones, and that isn't going to be a problem, since the meat of the body is perfectly capable of supporting the bones against gravity. Otherwise your skeleton would fall out.
While a strong enough magnetic field (such as one produced by a magnetar, a kind of neutron star) *is* capable of ripping you apart atom by atom, this force will naturally be much, much higher than the amount you need to simply levitate.
You will need to make sure to have adequate radiation shielding on whatever is producing the magnetic field though. Anything capable of producing a magnetic field strong enough to levitate a person will generate a ton of radiation when it is turned on, which can fry your brain if you aren't protected. Switching the field on and off quickly while inside it can also mess with your brain, but as long as it stays on it shouldn't cause any issues.
Also worth noting: keep any magnetic metal objects far, far away when performing the experiment. A magnet that powerful will attract metal from quite a significant distance, and being skewered by flying lab equipment when you're trying to levitate would not be fun.
The iron in your blood is not in a ferromagnetic state and magnets have no particular effect on it, so don't worry about that.
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First, we need to examine our Average Joe.
The highest human exposure I can find is an 8 Tesla field--it causes no harm to a **person**. However, fields like that can easily kill if you have ferrous bits in your body (the most common cause being an undetected pacemaker) or even due to nearby ferrous objects.
As to the energy, the best I'm finding is levitating a frog with a 16T field. A human will obviously require a vastly stronger field.
Thus I'm forced to conclude that whether this is safe or not is outside the realm that has been studied.
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Related to this question on [lack of human dimorphism](https://worldbuilding.stackexchange.com/questions/51346/humanity-without-sexual-dimorphism), but hopefully the length of time my question has sat in the [sandbox](https://worldbuilding.meta.stackexchange.com/questions/635/sandbox-for-proposed-questions/3968#3968) unremarked means that I have successfully been more specific.
I'm writing into an old shared universe in which the use of the words "male" and "female" are so *absurdly* stereotyped that it reads poorly in this day and age. In order to mitigate this, I have decided that in the context of the part of the world I'm building, these words indicate *separate subspecies* of humanity, not biological sex. Therefore, I have created the following:
Imagine a race very like humankind that has such a low degree of sexual dimorphism that males and females are indistinguishable from one another in day-to-day life. An individual's sex can be readily determined by even a cursory inspection of the genitals, but no other single physical attribute is a certain link to sex. The breasts have been internalized. Other physical characteristics have also been regulated and normalized to some degree, so most everyone has roughly the same skin tones, eye colours, hair colour and texture, etc. Also, most everyone is pretty broad and husky; the hips are about the same shape for everyone, and pregnancy isn't very obvious except in the very latest part of the term, and even then is only readily detectable when an examinee is unclothed.
A few generations ago, this population was isolated and genetically re-engineered from human stock to be this way, so I already have a plausible backstory justifying how this came to pass. This state of affairs isn't a shock to any of these people; they were isolated when they were re-engineered, so they never knew what it was like to be able to differentiate between the sexes and it doesn't strike them as at all odd.
Their environment, to which they are physically constrained, is rural and temperate, with very little seasonal variation (I'm aware that I need seasons for many kinds of agriculture, but I'm not going to sweat that). This requires that fairly heavy clothing be worn year-round. Their society is agrarian with touches of hunter-gatherer, and *very loosely* based on the dark ages in terms of technology. Importantly, I have already decided that an individual's sex is a subject of deep privacy, and speculating with any degree of publicity about someone's sex is one of the deepest taboos.
Of course, this has had an enormous impact on their society. Sexual discrimination is all but non-existent (instead, people tend to discriminate on the basis of sub-species, but that's another story). Social roles that we might recognize as being gender roles are apparent (eg. that person goes out to work the fields, and their partner instructs the children), but are for convenience only and are largely not tied to biological sex. Language has evolved into a gender-neutral dialect; although a few ancient legends have survived which speak of male or female characteristics, it's generally understood that these stories are clearly written about gods or demi-humans, and are not to be compared with current society. A few individuals have dissented against this interpretation, but they have historically left this society to live on their own in the wilderness.
Given all this, **what's the most important consequence of this change that I have overlooked?**
**EDIT:** Genetic diversity isn't an issue. The process of the genetic re-engineering has eliminated genetic diseases. It bears mentioning, I suppose, that the story is only a few generations into their exile; long enough that the origins of their incarceration are now distant legends, but not long enough that the consequences of the small initial population have really started to show.
**EDIT 2:** I guess I wasn't explicit enough, my bad. The feeling for this subrace is one of **extreme social conservatism**. Think of the Puritans, perhaps, and the comparison with Pratchett's Discworld dwarfs is well-founded.
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Bouncing a little bit off of jstewart's answer, and the potential of attraction being gender neutral in this setting for that reason, I think one potential consequence might be the more frequent or more acceptable formation of triads and foursquares or negotiated arrangements about childbearing.
Courtship is likely to be a long and delicate process, given the gender taboo - and it isn't impossible, or honestly even unlikely, that people might fall in love irregardless of gender compatibility, maybe even before *knowing*. If people are encouraged to have kids, or want them, or have better lives with them (for social reasons, or economic ones, or whatever) - then a couple who are not compatible in that way might break up to try to find a compatible gender... or they might stay together and go looking for an arrangement.
So, they might, very quietly, let a mention that they are looking for reproductive assistance loose among their closest friends and family (who might already know their gender, or not). Such and admittance doesn't even have to admit that they are the same gender, since fertility or even sexual issues might be fixed in the same manner. In this way, through safe and private social networks, those looking for such assistance in reproductive matters might meet, gently feel each other out, and come to an agreement - to check gender compatibility (or whatever), and try for children - with said children being split between the individuals directly involved (so two couples, or one couple and one single parent each get one or more kids), or possibly raised in the three- or four- group communally.
Again, the only thing that might get out is the couple's potential need for a third - not what gender each is, not if gender or other factors were the original issue, they would only be revealing what gender they are looking for to a few more people, who would be equally exposed. With a fifty percent chance of finding someone the right gender the first time (well, second time per individual, first time per couple) and maybe fifty percent of the population already having found a mixed gender pairing the first time - three quarters of the population with relationships viable for reproducing with just one or two tries is much more sustainable, especially since those really interested can keep trying until someone is found.
Not really violating the taboo this way, I would think - especially since telling what gender they're looking for (especially as a couple) doesn't precisely disclose both their genders, only that one of the two is the (probably fertile) opposite - a mixed couple with fertility issues would be seeking the same way. Though future kids are more likely to get created through the already formed negotiation, since that would be easier than negotiating to check gender all over again - so stable relationships and semi=relationships are more likely to form.
Threesomes and moresomes are not common in sex- or gender- conservative societies, true - but this kind of only-for-children extra relationship isn't unheard of, especially among those favoring their own gender or who had fertility issues, who might go looking for someone to reproduce with without sacrificing their other relationships - some cultures allowed surrogacy or official alternates (like mistresses) for just that reason. And in this society, with no social pressure driving them *apart* (because no one knows their genders), but a social pressure to reproduce that about half to population can't meet any other way - I expect such relationships will be kept discreetly quiet, but pop up commonly enough to not be remarkable. And knowing that one male and one female must exist in a group of three or four is much harder to figure out specific people's genders than a group of two.
The only other possible alternative is for certain classes of people (perhaps those of certain ages) to be relatively indiscriminate in their partners for a while (equivalent to dating, okay), so that people would find those of both genders over several relationships, and would already be "in the know" about a number of people when it came time to consider reproduction. The downside to this is that it will strain, and eventually break, your taboo - roughly equating gender-reveal to sex, this is the difference between a less repressed culture where premarital sex or multiple sequential marriages are expected (knowing the genders of all the people dated) and a much stricter culture where it is strictly forbidden (only knowing the gender of the person married), which seems to be what you were going for.
[Answer]
So, we've already considered the problem of people of opposite sexes trying to identify each in order to agree to mate, but I think there's a problem here that goes deeper than just identifying the sexes of people.
To give a concise summary title:
# What turns you on?
*Disclaimer: I'm not a biologist, so there could be facts I'm missing, and biologists can correct me if so.*
More specifically, I don't think that sexual attraction is *precise enough* to reward only *reproductively viable* sex without gender cues.
My hypothesis would be that the reward mechanism for sex isn't actually able to distinguish reproductive sex from any other sexual activity in the presence of a partner that one is attracted to. That is, it is set up to:
1. reward any sexual activity, but
2. reward sexual activity with (or in proximity to?) a partner, of the sex you are attracted to, more.
As evidence of this, I would point out that we know that heterosexual couples in our world now engage in sexual activities that are not reproductively viable.
If it is true that sex drive is only based on the combination of sex-specific attraction and sexual activity, then there are a few problems you might have, depending on how sexual attraction works.
## No attraction
Since the sexes are nigh-indistinguishable, nobody is attracted to anybody else. Sexual activity may still be rewarded, but there's little motivation to find a partner because the mutual sexual activity part doesn't work. Reproduction becomes a chore. Later generations wonder why anyone would bother with the trouble of raising kids, and the species or subspecies quickly goes into decline.
# Everyone is attractive
Everyone is effectively bisexual and can get their extra mutual-sexual-activity reward by associating with anyone of either gender. I haven't rigorously done the probability math, but I think you end up averaging either exactly or close to half of couples are same-sex. Now all of the couples which are by coincidence heterosexual have to produce twice as many children to keep the population up.
Since the average number of children per family needs to be at least two, and half of families will produce none, that means that the heterosexual half of all partnerships needs to average four children. And if you don't assume modern medicine, that number will be much higher. If an average of half of all children die from disease, that means that those couples have to have an average of 16 children, which could be a huge economic burden, if nothing else.
There are ways around that problem, to some extent.
One option would be to culturally preference heterosexual relations. The problem here is that no one can really check -- you can't argue the difference of whether partners are of different sexes vs just not successful at conceiving a child without violating the taboo on discussing someone's sex. And if no one can check, some people will prefer relations with someone of the same sex who they're already close to over going out to find a partner of the appropriate sex. This is especially true if it takes a long time to get close enough relations to find out someone's sex. It also means that if children are an economic burden, then some partners who are of opposite sexes might still not bother having children.
If they're agrarian, then it may be that they are motivated to have children (and thus find opposite-sex partners) for economic reasons: free farm labor. That depends on costs of raising children compared to hiring labor. If you can get labor just in exchange for food, well, children may require less food than an adult, but they also have several years where they consume food without being able to work, followed by several years of being weaker (and therefore worth less as laborers) than adults, so I'm not convinced that this would be sufficient motivation.
They could just have adoption to even out the children being raised by families, this works especially well if they're engineered so that both sexes can lactate. The partners who are of opposite sexes still have to produce more children, but at least they don't have to raise more children.
## Super Attractive Genitalia
It's the only part that's definitely distinct between the sexes, so their attraction could be based on that instead, which would only give the extra partner-sex-reward for the correct sex. This still has issues.
First, it will have to take a long time for a relation ship to develop before you can tell the partner's sex, which means you have to expend a lot of energy forming a relationship before you even know if your partner is attractive to you. This is going to put strain on society and maybe motivate some rebellious youth towards reducing the secrecy of everyone's sex.
The other problem is that part of what motivates people to actually have sex is the fact that merely being in the presence of (or seeing) someone of the sex you are attracted to is enough to... *trigger certain biological responses*... I think this is a combination of built-in programming to respond to the distinguishing features of the sex you are attracted to and conditioned responses, often developed from cultural norms that you associate with that sex. If you can't tell the sex of the other person by sight (or smell, or voice), you can't tell if they're attractive, and you won't be motivated to proceed.
There are some other variations this could have, like being attracted to everyone until you find out their sex, which could work, but also put a social pressure in favor of revealing your sex ahead of time, since it's a lot of trouble to build up a relationship just to find out you're not attracted to the other person -- you have the normal stress of relationship uncertainty, but with the added bonus that you'll have a 50% chance on average of your relationship ending immediately or reverting to friendship the first time you reveal your sex, one way or another.
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And of course you can't just have attraction to some people and not others (maybe by pheromones?) since then you could tell someone's sex just by standing close enough to them and seeing if you find them attractive at all.
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# Conclusion (& tl;dr)
All in all I think that unifying traits too much would make a huge mess of courtship -- not just in that it will be difficult to find a partner of the right sex, but in that it will make even triggering the sexual attraction response more difficult, possibly to the point of making sexual reproduction nonviable, and giving the species immediate negative population growth.
If you really want to have sexual reproduction without having distinct sexes, and you're willing to go so far as to genetically re-engineer the entire population in question anyway, why not just make the whole population reproductively-functional hermaphrodites?
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**How do they have kids??**
Say a member of this species wants to have children. He knows his gender but now he needs to find a female to mate with. There are no real visual clues about who is female. Since "an individual's sex is a subject of deep privacy" he can't really ask. Even if he knows some one who is female who might mate with him, she can't find out he is male either so neither knows and neither can ask.
**Finding mates of a particular gender becomes a hard coordination problem without visual clues.** This is why humans have established visual clues for male/female interested in male/female.
This would make it very hard for mates to find each other and would make having children harder and rarer.
**The social stigma of pregnancy**, you mention that pregnancy is not really visible till the very latest part of the term, but it is slightly visible. Since showing gender is taboo showing pregnancy or saying you had a kid would also be stigmatized.
**The risk of mating**
If two beings mate and produce children they implicitly say that they are different genders, so if a third party knew the gender of one he would learn the gender of the other. This might lead to secret relationships.
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Ok; so assuming the problems of birthing and so forth are resolved (somehow). Then they should have a much longer lifespan relative to the raising of children than humans do, and be able to have children for a much longer time. Basically if both parents are involved in the raising of children to the point of limiting the work they do for the period of time of child birth and nursing (there needs to be *extreme* social stigma regarding the non-pregnant part of the pair leaving during that time period as doing so lets out who is of what sex (besides all the other problems)) then that limits the number of children that can be had, suggesting that it would be desirable to have a very few children at one time (one pregnancy or two back to back) and then go a longer period of time without children before having more; as replacement in modern medicine industrialized society is about 2-3 children per women and it was *significantly* higher in pre-industrialized society that requires much longer time that they are able to have children. Changing how often and when the females are fertile could help, if they are only fertile once or twice a year not getting pregnant becomes much easier (it also makes it significantly easier to hide that one is a female if one is only menstruating once or twice a year).
I would suggest that with the longer lifespan it is possible that marriages could becomes less permanent, one marries, has a kid or two (or not) and then seven-ten-ish years later separate with the sex of ones prior partner being absolutely taboo to disclose. Based on past societies there may be the social expectation that *some* of ones unions do produce children, but lowering the infant mortality rate significantly below what did exist could lessen that social pressure.
Obviously, there isn't a gendered component to inheritance laws, but it would be entirely reasonable to have, at some point prior to death, the parents provide as they are able an amount of capital, be it land, a house, or money to help their offspring get established.
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The most logical way for a species like this to be viable is if childbirth is more evenly divided between the parents, or among the community. The main reason why the sexes are distinct in the first place, both biologically and culturally, is because childbirth is *hard* for the female, but not for the male. For humans even more than most animals. Producing a child means that the woman is going to spend several months less mobile (making it harder to collect food) as well as requiring *additional* food to feed the developing child. This burden continues after childbirth, since it is the woman who nurses the child. This means that, especially in a natural, pre-civilization environment, there will be more pressure on the woman to avoid producing a child until she can find a man to help provide during this difficult period. The culture develops around those assumptions. It's less of an issue in a civilized society where food is abundant, but it's still an issue unless the government steps in with laws like maternity leave, even so many women find it difficult to raise a child and work at the same time.
To create a humanoid species where sexual dimorphism is virtually nonexistent, I would make two main biological changes: have the child born much smaller (like bears, or even marsupials), and allow both sexes to produce milk (not too far-fetched, as a simple mutation is all it takes for a human male to produce milk). They may have evolved from a sexually communal species similar to bonobos, which already have less sexual dimorphism than most apes. I would expect the species to evolve in an environment with abundant resources, where competition between individuals is less important.
Basically members of this species all have sex with everyone and giving birth is a fairly simple affair that happens sometimes - since birth is easy, there would be no reason to avoid having a child. The baby would be born completely helpless and be raised by the entire community, spreading the burden to everyone. The drawback to this system is that, although the burden of childbirth is lifted from the one who actually gives birth, it would take a longer time for the child to grow and be a fairly big investment for the whole community to raise. It is therefore possible that babies of this species might not be considered people until they reach a particular stage of development; if the community was not ready to raise a new baby they would just discard it.
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The most important part of the change that you overlooked is that male and female brains are different. Without stepping into the culture wars landmine that is the sex vs. gender debate, let me just say there are anatomical differences in certain brain structures.
For some specific examples: it appears that emotions are controlled in different parts of the ventromedial prefrontal cortex for men and women, there are neurochemical differences in the hippocampus that may affect the ability to think while under stress, and there are conflicting findings over whether inter-hemisphere connectivity is different between men and women.
Trying to ascribe psychological differences to these physiological differences is a bridge to far for me, a non-neuroscientist, but this suggests to me that the reason men and women seem to act differently, in my experience, is that their brains are wired differently, so to speak.
The practical effect of this on your society is that if the external physical changes were removed, and even if the societal obligations (child-rearing vs. going out to the fields) are changed, there would still be the not-obvious psychological differences between the men and women. That is to say, someone who is a human being and used to interacting with both men and women, should be able to tell the difference between a man and a woman just by talking to them.
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So both genders would need to have wide swaying hips as otherwise the death rate of babies would be much higher than it already was and your society wouldn't last too long. This would lessen the power of those working the fields and hunting, which would be disadvantageous to a society.
Even if other sexual dimorphism goes away it would be incredibly hard, especially in a preindustrial society, for the gender roles to go away completely. Females are the ones that have babies. This means that they can not be depended for their muscle power especially without modern medicine as the childhood mortality rate (and maternal death rate) would necessitate frequent pregnancies (assuming the technology to *not* get pregnant existed in a reliable form). Then once a baby is born the females *still* could not work for the first two years (at least, longer is better in such a society) as they need to be nursing (though I suppose both genders *having* rather than not the easy ability to nurse would be better regarding the survival of children and thus society). Even once the children are weened they still would require near constant supervision and limited ability to contribute, which necessitates that someone take care of them; by assigning the role of that someone to those who are already required to bear and nurse other children one frees up more labor for farming and hunting.
Basically everyone would look like girls do hurting the productivity of a pre-industrial society greatly and married women would still have the pre-industrial gender roles of cooking, spinning cloth (not at all a trivial thing), and caring for children while married men would continue to work the fields or hunt. Even if you went further and said that either gender can have children and nurse splitting the responsibilities would still be the logical thing to do, though switching off who was pregnant and nursing and staying home might be appreciated.
In an industrialized society things do change quite a lot, and in a futuristic society that has artificial wombs and other technologies the gender roles could become largely irrelevant.
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[Question]
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In my story I'm trying to get a more Quentin Tarantino-esque feeling, and what goes best with his films? BIGGER BOOMS.
So. Let me start by saying, I understand international treaties like the [Hague Conventions](https://en.wikipedia.org/wiki/Hague_Conventions_of_1899_and_1907) prevents this from happening in the real world. Well. So we hope.
My baddies are particularly evil. Most would describe them as dastardly and diabolical, and they've come up with a new way to destroy people who aren't loyal to their cause. In a fit of extreme evil, they've come up with hollow point bullets filled with alkali metals, then sealed in with resin, causing explosions within flesh as the projectile enters the body and reacts with the body.
**Would this be a feasible way to conduct incredibly violent and gruesome warfare and gunfights?**
[Answer]
## Yes it is
It's possible, though not common to pack rifle and shotgun projectiles full of all kinds of things. An excellent example of this is [taofledermaus](https://www.youtube.com/user/taofledermaus) on YouTube. He has shot all manner of weird materials out of his shotguns with varying degrees of accuracy and lethality.
In the case of highly reactive alkali metals, care would need to be taken to ensure no premature explosions. One would also need to be careful about target selection since hollowpoint rounds are ineffective against armored targets. That said, using the proposed bullets against soft targets such as flesh would be devastating. Hollow point rounds are well know for opening really large holes in flesh, as shown below from [this video](https://www.youtube.com/watch?v=tTHo0K2Sc0g). Compound these enormous holes with fragments of cesium that will explosively react to water in the flesh, causing secondary wounds much deeper than the original round could generate. This is scary stuff.
[](https://i.stack.imgur.com/N1q1k.jpg)
[Answer]
Yes, but it depends on engagement type as your question asks two question...gunfights vs warfare.
Alkali metals are significantly softer than most other metals (potassium can be cut with a butter knife). Had the bullet flown through the target this would have little effect, however the softer bullet makes it more likely to stay within the target and bounce around until reacting (not unlike how a hollow point bullet 'mushrooms' after striking a target). Yes, that might be messy.
However this comes with a trade off as the bullet will be less accurate (wind also plays a role here), have it's range suffer, and almost entirely lack the ability to penetrate Armour (bullet proof vests become more valuable here).
So this gets into engagement. In a 'street' gunfight...range is usually short between two unarmored targets. In this case...yes, it'd be explosively gorey and effective. In a military engagement however, the additional resources and preparation usually means the gunfire is at a slightly longer range and involved armored targets, and in this case the alkali bullets are likely less ideal.
[Answer]
Considering the sorts of mayhem already available out there, you seem to be going about things the hard way.
For small arms there are armour piercing rounds, incendiary rounds, hollow points, "safety slugs" designed to rapidly expand and dump all their energy into the target, 4.7mm rounds with asymmetric noses to cause them to rapidly tumble in the target, 12 gauge grenade rounds for shotguns, 25mm grenades which can be programmed to airburst over the target.....
Since these bad guys are "diabolical", they will probably get more bang for the buck by choosing "where" they shoot their targets rather than what they shoot them with. Being gut shot or kneecapped will cause a great deal of pain and suffering. Of course that requires very careful shot placement on the part of the shooter. The general rule in a gunfight is to aim for the centre of visible mass (to maximize the probability of getting a hit), and to keep firing until the target is down (so they are not shooting at you).
If it is just going to be a gunfight, then the ammunition chosen will have to reflect the expected target type. Shooting safety slugs at a person wearing body armour is not going to be very effective, but armour piercing rounds from a rifle can go "through and through" an unarmored human target without immediately stopping them (unless you hit a bone or vital organ).
Without knowing more than Quentin Tarantino-esquea setup, my recommendation is the bad guys should use sawed off 12 gauge shotguns loaded with 00 magnum shot. This provides for pretty violent gunfights at short range, the ability to deliver gruesome damage to human targets and satisfies the requirements for a successful gunfight.
As far as warfare is concerned, there is already far more than enough "stuff" out there to ensure gruesome outcomes for everyone.
[Answer]
They would not work if the people are wearing any sort of bulletproof armor; an extremly thin Kevlar plate would work.
The alkali bullets make big explosions when hitting water, but can bounce off of plastic bottles. See [The Backyard Scientist on YouTube](https://www.youtube.com/user/TheBackyardScientist).
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[Question]
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In the Mass Effect Series, the [Quarians](http://media.moddb.com/images/mods/1/18/17952/Liveship.jpg) have a population of 17 million individuals and they get all their food from 3 massive ["liveships."](http://img11.deviantart.net/129f/i/2013/354/4/3/maecon__quarian_liveship__by_machendrae-d6ym6jc.png) I'll round this down to 5 million individuals supported by a single farming ship. Assuming the ship is only dedicated to the growing of crops, how large would the ship have to be in terms of available area to sustain this population?
Any currently invented farming-techniques to save on space are acceptable.
[Answer]
Traditional farming requires approximately one acre per person (much like E404's calculations), so we can take that as the upper limit. Of course you can use far less efficient methods and need even more space and energy, but in this instance we are actually trying to minimize our inputs.
Various forms of more intensive farming are possible. Using multi cropping and gardening techniques you could probably cut the needed land in half. In the Second World War, urban dwellers were urged to grow "Victory Gardens" to supplement their diets and release agricultural output for the war effort, and you can grow a very successful Victory Garden in a typical suburban backyard or even a balcony.
Hydroponics and related techniques like Aquaponics are even more space efficient, with suggested yields of up to 200% more than comparable agricultural practice. Aeroponics, which involves spraying the roots with a mist of nutrient rich water, rather than simply immersing the roots in water, is sometimes advertised to be twice as efficient as Hydroponics. This means you can theoretically grow 4X as much in the same space (or alternatively need 1/4 the amount of space per person).
Even more savings can be achieved by going to algae, which is a much more efficient crop, not using energy to produce stems, cellulose or other indigestible matter. The most extreme figure is a single human can be sustained by algeaculture using only 6 litres of water per day, so a fairly small jerrycans of algae solution exposed to sunlight is all it takes.
More information and figures can be found on the ever handy Atomic Rockets website, especially here: <http://www.projectrho.com/public_html/rocket/lifesupport.php#id--Closed_Ecological_Systems--Growing_Plants--Algaculture>
[Answer]
According to [this](https://gardening.stackexchange.com/questions/1433/how-large-a-cultivation-area-to-feed-one-person) question on Gardening SE, a minimum of about 0.02ha is required for four people on mars.
That's 50 square meters per person on an enclosed farm in space.
For 5 million:
50 \* 5 000 000 = 250 000 000 meters square = 250 km sqare
One assumes that any additional space in the ship, below the farming deck, would be used for water storage, crew quarters, equipment, etc.
Artificial light might also make it possible to place several layers on top of each other, dividing the area required by however many layers are used (assuming that one has some sort of powerful power source aboard the ship.
[Answer]
Earth's land area is about [57,500,000 square miles](https://en.wikipedia.org/wiki/Land). [About 26% of this is for pasture and 11% is for farming](https://www.learner.org/courses/envsci/unit/text.php?unit=7&secNum=2). I assume you want to consider the 11% only.
This 11% serves the [7,300,000,000 people of Earth](http://www.census.gov/popclock/). [The average population of a country is very roughly 35,000,000 people](https://www.google.com/?gws_rd=ssl#q=avergage%20population%20of%20a%20coutnry).
Based on these ratios, you'd need 30,325 square miles per 35,000,000 people. Or 4,332 square miles for 5,000,000 people.
Assuming you employ the full gamut of space-saving techniques, like [hydroponics](http://www.luckyroots.com/hydroponics/benefits.html) and anything else, you could possibly reduce that by 80% to 866 square miles.
[Answer]
Space to grow isn't a big issue here if we talking about 5kk people.
Heat dissipation in space is more issue here.
It needs something around 10kW plant spectrum light 24.7.365, space 50-100 square meters, volume 100-200 cubic meters per single person. Not super duper food for someone, kinda minimal setting.
The process is not much efficient and probably needs more energy.
To dissipate 10kW heat at 300K from the hull of the ship needs roughly 20 square meters.
For 5'000'000 peoples it has to be 100kk m2 surface of the hull, where heat dissipation is happening.
* sphere, radius 2900m, 20500 cubic meters volume per person.
* cube, side 4100m, 13800 cubic meters volume per person.
If they have good energy sources, like thermonuclear reactors or such, they can cool internal volume more efficient. 600K, 2 times higher is the temperature of the shell, 4 times less radius or edge of the cube, to irradiate the same amount of heat energy. It's may be a good idea to place reactor outside of the ship, this way it can work at a higher temperature.
The ratio of internal volume to the surface can be arbitrary, by scaling one of the axis, or changing form, like pencil-cylinder.
Plants do not need gravity to grow, not sure about all of them, but those which were tested in space. (I do not know is it important for trees, fruit trees or not - maybe not or not so much)
For 17 millions of people ship size is $\small \sqrt{17/5} \approx 1.84$ times bigger, and volume will be $\small (\sqrt{17/5})^3 \approx 6.27$ time more per person.
So as you may see, the bigger ship is, the less problem is the volume or internal surface.
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[Question]
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In any society, improved knowledge and understanding of the world around us, can help 'improve' our way of life. It can also lead to chaos and conflict if not implemented properly/fairly etc.
If we were to wake up tomorrow and find a hidden cache of 'higher' knowledge how fast could changes be made without leading to chaos and strife by those who feel they were sidelined?
When looking at 'failed' attempts to upgrade the level of society one of things historians, and economists, political advisors etc, note is that they tried to do too much too quickly, and/or that a small group of people controlled the distribution of this knowledge and became immensely rich (and corrupt) off it!
Is there some sort of established/agreed on theoretical rate or method for stable civilisation upgrade? Or is it too dependant on the existing societies make-up?
I have a feeling that many people will hoard the knowledge so as to have more power over others. They will throw barriers in the way of any attempts to improve the bottom rung of society etc. Major Religious institutes and other interested parties won't want a change in the status quo.
Pretty much I want to determine how fast I can get my benevolent ruler of a large empire to introduce changes (based on a hidden cache of lost knowledge that is superior to our own current level) that will improve society without leading to civil war and the rich getting richer and the poor getting poorer. **How fast can a society /civilisation level be upgraded?** I have a particular scenario in mind, but it is not completely fixed yet so I am still interested in any other broad theoretical aspects that I might be able to incorporate into my world. You can read on for my scenario or real life 'failed' examples. Hopefully the scenario edit will help narrow down the scope of this question.
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**My Scenario**
This benevolent ruler supposedly has total power through both marriage and blood and a little bit of superstition (and winning a civil war to get the throne). They can implement any reforms or changes in law they wish. The nobles might not like losing their 'power' but have to go ahead with the reforms for fear of losing their land, riches and titles etc.
My world has several empires. In the Empire in question, absolute rule is held by an Emperor and his immediate family as well as a noble class. They are supported by a Janissary style military arm as well as more traditional army. As with the Janissaries of history the nobles have seen the pro's of being a member and have weakened the system by promoting on status rather than merit. The general population is a mix of slaves, freedman (not a lot of those), tradesman and merchant families etc. I'd hazard a guess that the technology level is late middle-ages to early renaissance.
All land is property of the Emperor, who gives it out to who he sees fit shortly after their ascension to power. Typically noble families keep their lands over several generations and most consider the whole relinquishing of land and titles to the throne a mere formality. There is no one major religion (or if there is I haven't come up with it yet) but there are several belief systems - the janissary belief system being the most prominent. Magic doesn't exist, only in the mind of the superstitious.
This being a made up world, we have several deposits of hidden/lost knowledge from a lost space-faring age. One of these deposits is a library accessible to any who wish, but it's kind isolated and tricky to get to so not a lot of people visit. On the plus side this has stopped book burning through the centuries! Knowledge of exactly what is included in this library has even been lost so not even the librarian's know just how informative it can be!
Another deposit is reached through a single user interface that has for centuries been locked (to stop the possible misuse of such information). It can only be accessed by a select few, so sharing the knowledge will take time but can be controlled. All the knowledge is information - very few working technological devices and no real blueprints on how to make things more like the theories behind it. This knowledge also includes a record of all of human history (up until it was lost) so hopefully whoever uses the interface will be able to learn from past mistakes.
My empire and neighbouring countries have just come out of a devastating civil war and a new leader has emerged. They have the complete support of the remaining janissaries, and most nobles support them for various reasons. They are popular with the some of the general population - they also just outlawed and freed all the slaves (that opens up a whole different level of complexity so for now just go with popular with a vast majority of lower class subjects). Enter my benevolent ruler! (wow, just writing this makes me realise how cliché it all is)
Now my benevolent ruler is aware of this lost knowledge and most importantly wants to change the world for the better. They have a handy summary of how things can go wrong if they push to fast or too hard. They also have the support of the other library deposit and they will help with spreading 'the word' like missionaries. So this leader is hoping to learn from the mistakes of their ancestors and skip several cultural revolutions that resulted in the rich hoarding all the power, the poor getting angry and frustrated and several head chopping incidents that can ensue. They know they can't change things overnight and are planning are several phases of 'development' to build on the foundation of the previous phase. The leader is prepared for this to be a multi-generational project but would really like to see, at least some, successful end results before they die!
There have been several previous leaders who have tried to reform and bring some advancements to the way things are done. Some of these ideas have stuck around, and some have been squashed once the leader was no longer around to reinforce them. So a lot of people are aware that there is another way of doing things and after this civil war they just survived a lot of them are receptive to trying another way!
In the rebuilding after the war, my leader can make many reforms to change the way people are promoted based on merit, re-educating the nobles who didn't support them, re-educating the uneducated masses, pretty much re-educating the world and generally just being a kickass leader.
*sidebar - re-educating - NOT in the Russian or Chinese revolutionary way of thinking*
**How fast can they drag the people from the backwards way they live to a more enlightened era? Are there some set steps or methods that might avoid most of the pitfalls? I'm hoping that any changes my leader make are not negated the moment they die!** I'm thinking that my leader can use the chaos of post war to slip in a few amendments that the typical snobby noble won't like. By the time these nobles notice they can't do much without losing what power they still have.
And the leader can show the nobles real life examples of what will happen if they don't upgrade and what will happen if they upgrade in such a way that the elite few keep the power. Show the benefits of improving agriculture returns etc etc.
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**Real life 'failed' examples:**
After the Chinese Emperor decided he, or his predecessor, had lost the mandate of heaven (major fire in one of the major palaces, might have been the forbiddon city, among other things) he stopped the Chinese expansion and exploration of the world, closed off the borders and isolated the Chinese Empire for the next few centuries. Then when the European nations 'advanced' there was a clash when the two met. Different ideologies and different 'level' of society. China has since undergone a rapid expansion but has been ruled in a very strict authoritarian manner. While China may have mega cities and major transport networks etc, I am under the impression that a vast majority of everyday people are still poor, and while not technically uneducated they don't have the greatest of life's.
Genghis Khan was originally from a tribal nomadic way of life. Once Genghis united the clans of the steppe he defeated the Chinese Empire. This was an Empire that was for all intents and purposes more 'advanced' than the horse tribes. Genghis incorporated most knowledge and technology into his 'empire' and the everyday life of the average person was greatly improved (if they survived the initial invasion and mass killings). As soon as he died the empire disintegrated over squabbles between his sons and leading generals as to who should lead (the same can be said for Alexandra the Great).
A more recent example which has for all intents and purposes failed, or at least not taken off with a flying start, is post apartheid South Africa. A small minority of people held power over a small population of white European descendants and a much larger indigenous population. Amongst other horrendous things, the Apartheid government restricted access to education to the average everyday person of any other colour except white. When the ANC took power, they promised to reform the system and redistribute the balance of power. In twenty years, rural schools are still majorly underfunded and understaffed. Every year there are incidents where schools have not received the school books for the year. And yet the government can afford to pay ZAR4billion for a private plane! The power has essentially transferred from the elite white nationalist party to the elite black african national party leaving the poor just as marginalised as before. To be fair this is an on-going situation and people are working on correcting the system...but I'd like to avoid this situation in my imaginary world.
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Apologies if this is a duplicate question. I couldn't find anything but will happily be pointed in the right direction.
[Answer]
There are several issues that would need to be addressed (and indeed a lot of this question might be opinion based).
Firstly, how disruptive of the prevailing order is this new knowledge? Existing institutions and power structures will fight tooth and nail in order to preserve their power and perques, so anything which directly challenges an existing political, academic or economic interest will be met with everything possible to stop it. Ride share programs like Uber are under attack because they inherently disrupt the cosy monopoly that most civic governments have established with the taxi industry. "Fintech" is now under assault in Canada by the "Big Five" banks because it threatens their business models. Air BnB is under regulatory attack as it threatens the hotel industry, on line learning and private universities are being denied recognition and so on.
IF this new knowledge does not directly threaten an existing institution, then it will be able to grow and expand in a new niche and reach critical mass before a counter attack can be made.
The second issue is how well can people adapt to it? Personal computers were a novelty item for a decade until Apple developed the Graphical User Interface (GUI), meaning millions of people did not have to learn command line prompts in order to actually use a computer. The Internet eventually took off with the development of the Mosaic Browser, which made finding and using things on the Internet much easier, followed by the search engine explosion, which made finding anything on the internet easy and useful. If this new knowledge is esoteric in nature or difficult to apply, most potential users will give it a pass.
Finally, how useful is this new knowledge? If it is narrow and limited, then it will not be adopted by many people outside of its niche. The Internet as a technology is actually very esoteric and capital intensive, but the power of the Internet comes from its scalability and the ability of users to find everything they want from funny cat videos to YouTube instruction "manuals" that take you through a project step by step to on line news and commentary to Worldbuilding sites etc. etc. If the Internet had remained at email and message boards, it would still have a fairly wide adoption, but most people would consider it a secondary source, rather than the first impulse being "I'll just Google that".
So in order for knew knowledge to be adopted quickly and spread widely through society, it must not directly challenge existing structures or institutions, it must be easy to use and it must be widely applicable.
[Answer]
**Don't call it a failure when it's going through the same steps as every society that did it themselves went through.**
All societies go through a phase of having a massively wealthy, corrupt minority in charge. It appears to be one of the stages along the line to becoming a modern society. Whether it's the aristocracy of Britain, the oligarchs of Russia, the corporations of the US, far too many politicians across Africa or the bankers of Florence. Ancient or modern, it's a phase society goes through (at least once).
Until the rise of the unions, the rise of the liberal elite, and the rise of massed education, your society is going to go through one of these corrupt stages. As long as the whole can be considered stable and progressing it has not failed. You must accept that many people in positions of power seek power for its own sake, many of the wealthy seek wealth for its own sake.
You can only create an environment in which people who seek or wield power for the sake of the majority can rise, and even then they'll struggle against the will of the masses. It's hard to escape the [crab bucket](http://wiki.lspace.org/mediawiki/Crab_Bucket).
*In answer to your question of how fast:*
If the opportunity is there, 2 generations. If it's not there, much longer. It'll take a couple of generations to get everyone educated to secondary level. It'll take another generation to get significant numbers educated to degree level if you have the university facilities, if not, a generation to train the academics who can then train the next generation. This assumes you have the knowledge and just need to pass it on. Any society that has moved off subsistence farming can get everyone educated to primary level.
*My ancestors came to this country as illiterate immigrants over 100 years ago, my grandfather was the first to go to school, my father the first to go to university.*
[Answer]
You'll have extreme problems when switching away from a class based system. You mentioned freeing the slave. What happens to their owners?
You mentioned other states, how will they react? Think of say US getting access to nukes during cold war, while USSR can't get them. It creates a massive imbalance of power. Will they sit idly by while you get more advanced?
When you say benevolent, is he ready to do what need to be done? Are his people in front of everyone else for him? Is he ready to go to war to protect them, even when he is in the wrong?
Another way to do this would be to go the evil route:
Implement a police state. Kill all dissidents. Force the change. Won't make you the leader they want, but it will make a stronger society. Problem is it will most likely end with the people turning against you. Only way to prevent that is to give them an enemy. Someone who doesn't want them to prosper, who steals their jobs, takes their money and food. Unfortunately, you've basically created Nazism at that point.
Any change will be opposed by people not understanding it. The more drastic the change, the worse it gets. Only way for a peaceful change is education. So you need a new generation to be educated into accepting the change as something normal.
[Answer]
Any technology is going to require time to integrate into a society and many factors will contribute to how long that time takes and how thoroughly the integration spreads into the population.
The biggest factors include...
* Manufacturing
* Distribution
* Complexity of use when compared to existing technologies
* Conflict with existing technologies and beliefs.
...and the effect of each of these factors will vary from case to case as the technology changes.
A technology which is purely knowledge based (such as the need for boiling water before consumption in a society which already regularly uses fire) will spread much quicker that a technology (such as cell phones) which require the manufacturing and distribution of hardware components.
If however, the prevailing medical understanding in your fire-using society uses spiritual rather than biochemical methods in its healing attempts, the boil water order might meet a lot of resistance during distribution. "Healers" might rightfully see that the new knowledge threatens their base of power. They might actively work against the adoption and use of such rival healthcare knowledge. Meanwhile, those same spiritual healers might see cell phones as an opportunity to further spread their teachings, and actively support its growth; giving away free phones with their equivalent of 911 pre-configured in auto-dial.
There is no easy way to predict the speed with which a technology integrates into a society, even when that society is lead by an absolute monarch with strong motivations to see the technology integrated. Even in such an empire, there will be lesser powers and minor players which have a profound effect on the integration process.
[Answer]
You might be surprised, but progress within a society depends quite a lot on land ownership. Raw knowledge is great, but when all of the land is held by the emperor, that's a recipe for stagnation. Real innovation comes when common people own land that they can develop as they see fit, or lease, or use as collateral for borrowing money. There also needs to be clear title to the land, so that it can be transferred within a legal framework, and so that people always know who owns it. Land won't get developed if there's no reasonable assurance that there will be a return on investment. The **one** thing your new emperor could do that would give his empire a giant leap into modernity would be to allow private ownership of land.
[Answer]
Everything depends on ***who*** releases the revolutionary information and ***how.***
What you are talking about is called *development,* which is when a society, nation, state, kingdom etc. becomes more advanced. Development has different measures, but today is measured by income, literacy, education of women, and the most prominent economic sector (agriculture, manufacturing, services). *In the end, development is all based on the view of the measurer.*
Revolutionary information -- you will need to discover what exactly the information is in order for the story to succeed -- has power to create civil & even global wars:
If the freed slaves and working class got their hands on the information before the nobles: war.
If the lower classes thought that the releaser of information was unfair: war.
If it was centered around one policy, person, or single group (your real world examples): war.
Therefore there must be a universal desire and hunger for this information, as well as a gradual way to diffuse it through your empire equally among the social associations. Here are some proposals.
## Solution (what I would do)
Have your emperor designate a trusted or elected group (small) to go into the library of which you spoke for years in order to glean all possible information from the endless tomes. These people are the first of the "enlightened" or some other name. Unless the information is toxic (I don't recommend that in the slightest), then these designated few will emerge into society as start spreading the gospel, which means good news. This would have to be controlled or monitored by the emperor, otherwise he would not stay in power.
[Answer]
Your question is essentially how to build a great and fair nation.
The biggest thing to keep in mind is cause and effect of any influence your benevolent leader introduces.
We ought to consider this a control system problem, with feedback/outcome analysis of overall progress. Introduction of anything new (technology/reform) needs to be properly vetted to be sure no negative consequences are suffered eg. too much technology results in unemployment and starvation.
TLDR-Upgrade Length Historically (it's exponential):
* Renaissance Period (1400-1700) - 300 Years
* Industrial revolution (1760-1840) - 80 Years
* Technological Revolution (1870-1910) - 40 Years
* Electronic Age (1950-1980) - 30 Years
* Information Age (1990-2010) - 20 Years
Overall we should focus on a couple key metrics and then on a few particular stretch goals.
**Metrics:**
If we think about how we measure the success of a country for it's citizens today we usually refer to [Gross Domestic Product](https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nominal)_per_capita), [Wealth-Gap](https://en.wikipedia.org/wiki/Distribution_of_wealth), [Education](https://en.wikipedia.org/wiki/List_of_countries_by_tertiary_education_attainment), [Happiness](https://en.wikipedia.org/wiki/World_Happiness_Report), [Freedom](https://en.wikipedia.org/wiki/Democracy_Index), [Life Expectancy](https://en.wikipedia.org/wiki/List_of_countries_by_life_expectancy) and [Quality of Life](https://en.wikipedia.org/wiki/Mercer_Quality_of_Living_Survey). There are many attempts to normalize all these factors into measurement [Human Development Index](https://en.wikipedia.org/wiki/Human_Development_Index)
Overall breaking down these indexes into the more general metrics we get the following, plus a few more for flavour:
* Economy
* Access to goods
* Health
* Science/Education
* Social Reform
So assume your Benevolent leader is encouraging and managing factors of all the above to the best of his ability, while keep it manageable and controllable eg. not insane population growth (note the Black Plague actually culled population that would have probably died from starvation).
**Stretch Goals:**
Democracy or insert your favourite civic.
Morality/Ethics.
Quirks like Music/Art/Sportsball/Tradition you want to introduce in your narrative.
These stretch goals essentially need to overcome societal tradition and this can only occur long term, over multiple generations to facilitate a change in sensibilities.
Government - Modelling to the progression of the English Parliament
* Parliament as an important ruling body - 1300s
* First Revolution of monarchy - 1628
* Settlement of Parliament and Constitutional Monarchy - 1701
So approximately 400 years to transition from a pure Feudal Model to an ruling Parliament.
Religious - Again let's use England as an example
* Modern Era - Acceptance of new religions is fairly easy
Social Acceptance of Branches of Christianity eg. Jews vs Catholicism vs Protestantism.
* Protestantism took about 200 Years with some pretty strong "heretic" suppression.
* Acceptance of Catholicism again after this persecution took about 400 Years. Normalisation of Judaism - >800 Years
Misc Culture Effects- Art/Sportsball/National Anecdote
Most cultural effects can be modified within 1/2 generations so say 50 Years.
**Dangers:**
* War from foreign parties
* Resistance to religious/belief/government model
* Resistance to Technology
* Loss of Benevolent ruler's influence.
Overall the speed of influencing any of the above is the speed of specialisation of the populace. ie. 10 people live hand to mouth farming vs 6 farmers + 1 blacksmith + 1 doctor + 1 tailor + 1 merchant is probably a more productive village.
**Upgrade Timeline Guide:**
Explicitly I would say industrialisation is the best model we can assume so going off GDP as a measurement of Industrialisation then the trend is exponential.
[](https://upload.wikimedia.org/wikipedia/commons/thumb/4/44/Maddison_GDP_per_capita_1500-1950.svg/1024px-Maddison_GDP_per_capita_1500-1950.svg.png)
Time-span is dependent on the point on the exponential curve, but as a guide let's compare to 2 known periods of what can be considered an "Upgrade"
* Renaissance Period (1400-1700) - 300 Years
* Industrial revolution (1760-1840) - 80 Years
* Technological Revolution (1870-1910) - 40 Years
* Electronic Age (1950-1980) - 30 Years
* Information Age (1990-2010) - 20 Years
Keeping in mind these periods of growth revolved around a certain few key technologies:
* Renaissance Period - Trade Guilds
* Industrial Revolution - Steam Power+Colonialism
* Technological Revolution - Manufacturing
* Electronic Age - Transistors
* Information Age - Silicon/Internet
Overall the power of a single individual can only very optimistically match the natural development of many competing nations. Plus a lot of ground work goes into making the geopolitical/economic/social/ changes ready to transition/upgrade nations.
For your goal of small income gap, it's pretty hard, because this essentially wipes out Capitalism as a driving mechanism. I would suggest propelling development first then transition to post scarcity in future tech if you really want that utopia scenario.
**Key Sciences:**
Key Sciences for overall better quality of life.
* Sanitation - Better Health and no Cholera.
* Construction - Better
cities
* Agriculture - More efficient food growth
* Refrigeration -
Uplifts society from hand to mouth
* Health Services/Medicine - Keeps
your people healthy
* Education - Enlightening People and accelerating
growth
* Industry - Craftsmanship/Efficiency
* Misc Future/Tech - Space/SciFi
In terms of science, it's perfectly acceptable to have a proxy that make the "breakthroughs" and many Renaissance/Enlightenment scientists relied on the patronage of the wealthy families. eg. Leonardo Da Vinci
Universities are essentially a formalisation of this trend if you consider them a guild of science.
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I've drawn up a set of landmasses for my story, and now there's a tsunami headed for them. I know where the tsunami is coming from, and I could decide how big it is, or any other characteristics of it.
*What parts of the coastline will be devastated and what parts will escape unscathed?*
For example, if the landmasses look like this:
[](https://i.stack.imgur.com/Do50u.gif)
and a tsunami emanates from Puerto Lempira (Honduras), does Jamaica protect Guantanamo? Is Maracaibo protected by that thumb of Colombia sticking out into the sea? Is Havana safe because it's on the far side of Cuba?
How can I figure this out for my *own* fictional setting?
[Answer]
All waves, including tsunami waves, follow wave mechanics. Notably here, they follow the rules of diffraction, which you probably learned about in high school physics:
[](https://i.stack.imgur.com/eUl9J.jpg)
Because of this effect, the waves headed for Jamaica will bend around the island, and still strike guantanamo. That being said, the waves will have to travel a greater distance, experience more friction, and be modestly less intense because of that.
However, keep in mind that your coast's topology will usually decide the extent of the damage more so than the strength of the wave. Towns with sheer underwater cliffs at their coastline have been nearly untouched by tsunamis that devastate towns not a hundred miles away with gentle sloping beaches.
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To add to @cinnamon18 answer: do remember that a tsunami seen from the perspective of a human does not at all look like a "wave" as we know them. They are indeed that, but on a **huge** scale.
To a human, a tsunami instead looks like the sea is just rising, and rising... and rising. As the sea rises it floods over embankments, walls, dunes and other things that normally hold the sea back. It does not look like a wave; it instead seems like a sudden flooding, that happens in just a few minutes instead of days.
Also the coast affects the wave. A shallow coast slows the wave, causing it to "bunch up". Out at deep sea the wave is barely noticeable. But as it slows in shallow waters, it becomes much higher.
So what cinnamon18 said: cities on cliffs faces will see just a mild rise of water, that relatively quickly recedes. But areas on shallow coasts, and that does not rise significantly above the sea level, they will be flooded.
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Here is a link to a tsunami simulator: <http://tsunami-maps.com/index.html>
Allthough it might not look very acurate, it uses data from google maps to deal with the topology. It should give you an idea of which parts of land will get flooded or not in different scenarios.
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In something I'm working on, where surface attack craft (The question says tank but I suppose this could apply to other vehicles) are designed so the same vehicle could be fitted with different weaponry depending on the mission- on the assumption that, for example, missile launchers may be better suited for some operations while an energy or particle cannon (or flame projector, you get the idea) might be preferable for others.
Does this sound like a lot of work for nothing, or does it make some tactical sense?
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While modularity is desirable from certain points of view (for example, the carrier vehicle is the same across many units, so parts and supply is eased), there has to be a careful look at the cost/benefit ratio of what you are doing.
Generally speaking, modularity comes at the price of having extra "structure" on the host vehicle for mounting points, couplers to power and utility services and data connections to sensors, the fire control system or whatever other system the module is hooked into (power, life support, even modular crew pods will need some sort of data system to communicate in and out). Below a certain size, the costs of the extra "structure" will outweigh the benefits of modularity.
There is also an inherent reduction in flexibility to the module itself; it must be designed to fit inside the "structure", so upgrading in mid life to carry larger guns, missiles or torpedoes might be difficult to impossible. Should that happen then the entire fleet of vehicles and modules become obsolete. In order to lessen the chances of that happening, designers must make a conscious effort to leave room for expansion. This is often going to be fought on cost cutting grounds, so there will be a lot of tension during the design and validation phases.
Modularity has come down a lot in both cost and minimum size. Remote Weapons Stations (RWS) can fit on a wide variety of vehicles ranging from jeeps to Infantry Fighting Vehicles and are essentially "drop in" units so long as the vehicle can accommodate the turret ring and has room somewhere inside for the operator. Modular turrets for a wide variety of vehicles also exist. Modularity is also theoretically much easier on ships, due to the great size of the ship and lower structural costs of having modularity, the ultimate example would be to build weapons mounts like VLS missile systems into ISO containers and outfit a battle group of container ships to carry your arsenal (a warship like a frigate or destroyer can supply the targeting information and control the launchers remotely). The Lockheed "Sea Slice" (<http://www.globalsecurity.org/military/systems/ship/sea-slice.htm>) and the Littoral Combat Ship are designed around carrying purpose built modules for various war fighting functions, for example.
[](https://i.stack.imgur.com/Vb4wD.jpg)
For a tank, modularity could be a good thing with today's state of the art. The IDF's Merkava and Namer are built using many of the same basic components, and the Russian T-14 Armata is a very modular system, with a wide variety of AFV's scheduled to be built using the platform as the basis (the T-15 IFV is the first, but expect engineering vehicles, air defense systems and other types of AFV to appear in the future). The main downside is that everything in both the Merkava/Namer and T-14 Armata family are scaled around the tank, so there is a certain minimum size and weight associated with these systems. Depending on you strategic situation, this might not even be a bad thing.
[](https://i.stack.imgur.com/cjqmR.jpg)
[](https://i.stack.imgur.com/yoEAR.jpg)
[Answer]
This is a perfectly viable option. It's even being deployed by certain modern militaries. For example, the [Georgian army uses a vehicle](https://en.wikipedia.org/wiki/Equipment_of_the_Georgian_Army#Armoured_vehicles_2) called the [Lazika](https://en.wikipedia.org/wiki/Lazika) where the "universal fighting module allows the mounting of different types of armament such as MLRS, SAMs and ATGMs."
Feel free to expand on this idea and make your platform even more versatile.
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Modular doesn't mean efficient, it just means swappable.
The cost of the vehicle architecture, research and development. The problem is modularity doesn't matter much in military circles. Different weapons for different tasks. Unless you build 3 vehicles with the same engine, same suspensions, same wheels, etc it's not modular. And nothing the military builds is seldom off the shelf parts.
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The Stryker is the best extant example in a current military, but it doesn't qualify as a "tank", or barely as "armor". An actual tank will continue to be specialized because of the need for high mobility, high armor, and high firepower. This combination is very difficult to achieve in a modular/flexible design (looking at the inside of a tank shows you that there is no room for extraneous equipment).
In general, almost every weapons platform is going modular, from the [DDG-1000](https://en.wikipedia.org/wiki/Zumwalt-class_destroyer) to the [F-35](https://en.wikipedia.org/wiki/Lockheed_Martin_F-35_Lightning_II#Variants) to the [Littoral Combat Ship](https://en.wikipedia.org/wiki/Littoral_combat_ship). Most likely, automation (i.e.: drones, autonomous vehicles) will make the majority of near-to-medium future weapons systems highly modular. Even now, the F-22 cannot continue as a credible platform.
Even the replacement for the venerable M1 Abrams was envisioned as a modular platform: the [FCS Manned Ground Vehicle](https://en.wikipedia.org/wiki/Future_Combat_Systems_Manned_Ground_Vehicles#Mounted_combat_system).
[Answer]
I think there are two different concepts to consider:
* A **family of vehicles** has different vehicles based on the same chassis. Many spare parts and maintenance skills are interchangeable, but the vehicles are not. You cannot turn a [Bradley](https://en.wikipedia.org/wiki/M2_Bradley) into an [MLRS](https://en.wikipedia.org/wiki/M270_Multiple_Launch_Rocket_System#Overview).
* A modular vehicle can be modified from one mission to the other. The [Boxer](https://en.wikipedia.org/wiki/Boxer_%28armoured_fighting_vehicle%29#Variants) can switch different modules on the same vehicle.
For the latter, keep in mind that tanks are usually defined as a direct fire vehicle which is armored to stand up to similar **direct fire** attacks. That means the armor is concentrated in the front. The armor package on missile carriers pays more attention to **indirect fire** strikes.
It would be conceivable to put different direct fire weapons onto a modular tank. A railgun today, a laser tomorrow, a particle accelerator the day after that. The problem with that is geometry. The turret has some of the strongest armor on the tank -- do you really want to make the firing ports larger than necessary to accomodate different weapons? And what is the shape of the ammo feed system?
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Most modern weapon systems are modular to some extent for ease of maintenance. Its not just about *weapons* though.
A modular powerpack means a faulty unit could be swapped out with nothing more than a crane and put the weapon system back in order. With a hybrid/semi hybrid design for a power plant, you might swap out a powerplant with one more suitable for another role.
Having a single, multirole platform also means spares commonality (Your tank killer's transmission broken? Grab spares from your AA platform that's got balky fire control).
That said there's a certain lack of flexibility. Some platforms tend to do ok for purposes they were never designed for. The m113, while designed as your standard can of infantry is a good example of that. That said, it has barely any armour, and wouldn't do as well as say, a MBT.
You could turn a MBT into a [APC](https://en.wikipedia.org/wiki/Nakpadon) though which might be a decent idea. Have a standard base design - have the APC as the base model - have large, standard compartments for Motorised infantry, communications or ammunition. Have different turrets for tank, AT missile or SAM pods.*Significant* commonality in parts, better logistics.
Problems? You can't 'simply' swap out turrets as needed. You will need to retrain your crews, or cross train them. Some roles may be swappable (drivers) others may not.
You'd also not have vehicles perfect for every situation. Need a light tank that will fit into a airplane? Having a MBT wouldn't help. Need something tough? A light tank or a thin shelled APC base would not help.
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How can I explain, in a believable way of course, that country borders closely resemble drainage divides? They don’t always match mountain ridges, which are natural borders – as are the rivers themselves in our world.
In particular, with a point of divergence (POD) ±50 years around our calendar epoch (Julius Caesar, Jesus Christ), how could this have happened in Europe so that about a millenium later borders looked somewhat like the red lines in the map of drainage basins shown below?
In some cases, especially for rivers draining into the Baltic and Black Seas, I would additionally use the gray lines. The white areas would belong to either neighboring area or be independent.
[](https://commons.wikimedia.org/wiki/File:Europ%C3%A4ische_Wasserscheiden.png)
Note that the exact position of lines depends on how you define your water bodies (seas, oceans, rivers), so it could look slightly different in Denmark/Sweden, Greece, Italy and Scotland.
---
Just for the record, I’m planning to establish the following countries with somewhat Latin names for some degree of (partially anachronistic) familiarity:
* Atlantic Ocean
+ Norvegia (Norway)
+ Islandia (Iceland)
+ Hibernia (Ireland)
+ Britannia (Wales + Scotland + Cornwall): *Severn*
+ Gallia (France): *Seine* (Belgica) + *Loire* (Lugdunensis) + *Garonne* (Aquitania)
+ Lusitania (Portugal): *Douro* (Galicia) + *Tejo* (Castilia) + *Guadiana* + *Guadalquivir* (Baetica)
* Baltic Sea
+ Suecia (Sweden + Finland)
+ Baltica (Latvia + Estonia): *Neva* + *Narva* + *Daugava*
+ Polonia (Poland + Lithuania): *Oder* + *Vistula* + *Neman*
* North Sea
+ Anglia (England) *Ouse + Trent + Cam + Thames*
+ Germania: *Elbe* (Saxonia), *Weser, Ems* (Frisia), *Rhein* (Alemannia), *Maas* (Belgica)
* Mediterranean Sea
+ Catalania/Tarraconensis: *Ebro*, Baleares
+ (Massilia): *Rhône*
+ Italia: *Tiber*, Corsica, Sardinia, Sicily
+ Graecia: *Vardar* (Macedonia), *Mariza* (Thracia)
* Adriatic Sea
+ Venetia: *Po*
* Black Sea
+ Moesia/Istria (Bavaria + Austria + Hungary + Serbia + Romania etc.): *Danube*
+ Dacia: *Dniester* + *Bug*
+ Ucraina/Sarmatia: *Dnieper*
+ Caucasia/Iberia: *Don*
* Caspian Sea
+ Russia: *Volga*
* Polar Sea
+ Lappia: *Dvina, Pechora* …
[Answer]
**Trade** and **military logistics**
Before the invention of the steam machine (and even for a time after that), the most economical way to transport goods were river ships and barges. So, trade was more natural with other powers down and upriver that with other regions.
So, one option would be making your society focused in trade more than in agriculture (note that it means a sizeable surplus so there is enough to trade). Instead of being the possession of hereditary nobility (whose intermarriages and politics would complicate the distribution of loyalties) make the town and regions ruled by a plutocracy interested in promoting trade; to that effect they will try to have good relationships with neighbours along the river.
It would help if there were noticeable differences between the products offered by shore provinces (v.g. sea fish) and those offered by the inner provinces to estimulate trade.
Another option would include a military artifact/s that is decisive in battle but too massive to be moved long distance, except by barges (think of a mix of siege cannon to storm castles and machine gun to win pitched battles, or a war animal who cannot forage and must have its forage brought through the river). Once a faction controls the river to move such a weapon as it wishes, the rest of the regions bordering the river must surrender to it.
In both cases it would be nice making open sea navigation dangerous enough so that countries do not find too profitable trade between different watersheds (maybe profitable enough for luxury goods that have a high margin, but not for bulk goods). This would make a coastal only empire (who makes no attempt to trade/invade the interior of the watershed) less likely.
[Answer]
**Lots and lots and lots and lots and lots and lots of mountains.**
Prior to the invention of flight, mountains were often more than a little bit annoying to cross. Passes make traversing a mountain range easier, but the journey can be treacherous if the roads aren't good. In a society in a more medieval era, crossing the mountains is tough. [Clearly not impossible](https://en.wikipedia.org/wiki/Hannibal%27s_crossing_of_the_Alps) by any means, but tough.
If you have trouble crossing a mountain range, it doesn't make sense to have more land on the other side be part of the same country. If the society has not yet figured out how to use telegraphs or telephones, messages need to be sent by land. This makes governing hard.
You can use mountains to separate watersheds. States will be reluctant to have regions separated by mountains be under the same government. If they *are* governed together, I predict that secession would be easier. It's tough to get an army over the mountains, and the existing army on the other side might not be big enough to suppress a rebellion.
The feasibility of this does depend on there being a low level of technology in the region.
[Answer]
**Take a look at Brazil.**
The original boundaries of Brazil included the entire watershed of the Amazon river. It was a very nice and logical way to claim land from the sea: you claim a river and all the land that feeds it.
It's not too unbelievable that humans would accept the idea for claiming any land would be to claim all the water that flows from it to the sea. From a resource protection standpoint this makes a lot of sense.
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All watersheds are not alike. In our world, major rivers often form the core of a state or district and are not borders. However, smaller rivers form good borders and are not useful as a core of any substantial region.
And if you have river travel, you have sea travel, which tends to unify lands more than your watershed state does. Italy, for example, is usually split across the boot rather than right down the middle. Sometimes a statelet forms a border in the Apennines, but soon travel across and down the boot changes the situation to the more normal situation.
Your states have huge lateral expanses rather than cross from one watershed to another near the source. There's no good reason for this situation to persist long - if you can solve the problem with a 2000 mile wide state, you can solve travelling 50 miles across the top of a watershed much easier.
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## Religion!
The point of divergence would be right in the (alternate) bible: Jesus goes to John the Baptist, but there is no baptism because the river has been fouled by some heathens upstream. Instead, Jesus holds a sermon about river water being the gift of life and purity from God.
After that, the expanding Christian culture makes sure to always protect their rivers right up to the springs, leading to your country borders.
## Terrorism
Alternatively, someone came up with the idea of poisoning whole rivers as a form of chemical or biological warfare. Given the state of science back then, it would probably have been an accidental discovery.
For example, an earthquake exposes some kind of weird-colored soil and every fish in the stream it fell into died for many days travel downstream. A devious general/rebel/villain then carts off barrels of the goo and dumps it in the springs of his rival kingdom's main river.
After that, all water sources will be of military importance and no country will leave another in control of their water sources.
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Picture a race living in a cave with no light. Their entire existence pivots on remaining quiet and scentless enough that the various (and vicious) predators hanging from the roof of the cave don't find and kill them.
These creatures only communicate through physical touch (no pheromone release, however short range, or they'll get eaten), and unless they are touching another member of their species they don't know where other members of their species are. Breeding is pretty much a matter of luck and high numbers of offspring.
**Is it possible for a language/method of passing information based purely on touch to develop?**
If you've got examples of actual touch-only information transfer that could potentially become a touch-only language, please include them! Michael Kjörling brought up Braille in the comments. If there are any examples where something similar has arisen without first having a long-distance language associated with it then it will be pretty much a perfect answer.
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Helen Keller comes to mind as an example of a human experiencing similar conditions to your creatures. I seem to recall that before being taught sign language, she could still make herself somewhat understood, though that may be because her family could see/hear. So I'm going to throw out this example for the rest of this answer.
Instead, I want to imagine how these creatures would live. For one thing, if they're loners, they're not going to develop language no matter how easy it is, so let's assume they're pack animals. Thus, they will sleep, move, and eat together, and feel terror when they are alone. For these reasons, I imagine that much of these creatures' time will be spent in physical contact with one another (think of people walking in a snowstorm, or WWI soldiers blinded by poison gas in long lines, holding onto each other for direction). It may be possible that a group will never let go of one another, forming lifelong partnerships with the individuals in front of and behind them. They're going to end up knowing a lot about these two people, and should be able to tell their mood just by feeling their body language-- that is, if they have body language at all.
I think rather than a static line, it's more likely that individuals will remain connected, but often switch their place in the group. That way, the alpha can make sure no one is plotting against them, and no one has been left behind. Also, it allows the young to learn from a variety of sources. This way, I think body language will develop, as there are certain things individuals will want to tell each other (for instance, "I don't want to hold *your* hand", or "don't leave, you're not as sweaty as the other guy"). This may come in the form of hand signals (like soldiers entering a building tapping each other's shoulders), or more subtle cues like posture. Keep in mind that without most senses, these creatures' sense of touch should be much more precise than ours, so they should be able to pick up a variety of cues that we couldn't, such as small changes in heartbeat or hairs standing on end.
Whether or not this all turns into a form of communication that we would call language is debatable, and mostly based on the potential these creatures have for intelligence. However, with the example of Helen Keller again (I know, I said I wouldn't bring her back up, but she didn't hear me when I told her to leave), she learned to understand sign language by feeling it, so sign language could be used by these creatures to communicate as long as they were smart enough to develop it.
As for written language like braille, I think it should develop eventually, just like written languages did for humans. Come to think of it, it may develop earlier: these creatures should already be used to combing the ground for familiar paths and handholds, it shouldn't be too much of a leap to place certain objects with special meaning in places where they will be found. This may start as a way to more easily find places, but could evolve, again based on the intelligence of these creatures.
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This depends on availability of appendages, Helen Keller was able to communicate effectively enough to earn a bachelor's degree with no sound or sight (or pheromones that I know of.) She communicated with shapes and motions of her hands in contact with another person.
If you creatures have some dexterous way to connect with another creature by changing shapes of that appendage they could communicate complex ideas.
Ideas for how to add inflection: Vibration, Changing surface (extending spikes, slime etc), or even adjusting body temp.
[Answer]
Yes and it has already happened. Julia Brace became deaf and blind at a young age and so she had to learn a language that was entirely based on touch so there have already been languages based on touch.
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We have all heard about the idea of [space elevators](https://worldbuilding.stackexchange.com/questions/8866/where-to-anchor-my-space-elevator), a cable so long that it literally reaches into outer space, to be used for launching payloads cheaply into Earth and interplanetary orbits. However, the technologies for building such a device on Earth simply aren't there yet, due to our planet's deep gravitational well.
The Moon however has less mass, and a correspondingly shallower gravitational well, with surface acceleration of $1.6 m/s^2$, about 16% of Earth's.
Can we build a space elevator on the Moon with present technology? Is there any back of the Google-spreadsheet way of estimating if it were **technologically feasible** from an engineering standpoint? I'm not going to go into cost, since that might have to involve the idea of building an industrial capacity on the Moon, etc.
[Answer]
I read a paper (I believe by Ben Bova in relation to his book, *Mercury*). In the paper it was claimed that we could actually build such a structure on Mars with current technology. That was written about 15-20 years ago.
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Yes! We absolutely can make a space elevator on the Moon with current technology. The lower gravity means we can use materials we already know how to mass-produce, such as "Kevlar, Spectra or M5 Fibre", and we don't need to rely on carbon nanotubes or graphene (which we can only produce in small quantities).
A lunar elevator would be longer than an Earth elevator, because it would have to reach one of the Earth-Moon Lagrange points rather than synchronous orbit — 56,000 km from the surface of the Moon for the closest Lagrange point, rather than 36,000 km from the surface of the Earth for geosynchronous orbit.
Source: <https://en.wikipedia.org/wiki/Lunar_space_elevator>
(I originally misread the title as "to the Moon", which would have been a resounding "no"…)
[Answer]
Depending upon the time frame allowed for building using current technology, the answer may actually be, no we cannot build a practical space elevator for the moon with present technology.
Our current global lift capacity is fairly pathetic, about 80 launches per year with an average payload of about 2000 kg. Our capacity is even worse if you consider not just LEO but travel to one of the Lunar Lagrange points.
A lunar space elevator with a lift capacity of 100 kg (162 Newtons) is pretty close to the weakest useful elevator imaginable, only useful for bootstrapping additional cable lift. 10,000 kg is much more realistic for a minimum function elevator. Ignoring the weight of the elevator cable itself, you need a counterbalance of 10,000,000 kg at a distance of 120,000 km to support a 10,000 kg lift at the surface. We could not build this elevator for a long time to come.
Adding in all of the logistics, support, etc. to actually get this accomplished with maintenance, etc., this seems like a task that requires a new launch technology if nothing else.
There are launch designs on the board that could provide the needed lift capacity, but I would not classify them as existing, but possibly near future.
Economic justification is of course another problem.
For the pro elevator viewpoint, the best reference is probably NASA's paper, [LUNAR SPACE ELEVATORS FOR CISLUNAR SPACE DEVELOPMENT](http://www.niac.usra.edu/files/studies/final_report/1032Pearson.pdf)
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Though gravity would absolutely challenge our technology in building a space elevator on Earth, the drag imposed upon the elevator by our atmosphere is also a very significant inhibiting factor.
Would it be worth it to spend resources to build and maintain a space elevator on the moon? Unlikely. Achieving lunar orbit from a lunar surface launch is trivial in comparison to achieving Earth orbit.
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I'm not talking only about the kind of waves one sees at a sea shore, but also smaller waves like ripples and chops, and bigger waves like tsunamis.
Assume a similar tidal force to that of Luna.
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The best way to study water waves of many sizes is to use [Airy wave theory](https://en.wikipedia.org/wiki/Airy_wave_theory) (see also [here](http://vbn.aau.dk/files/60647156/Lecture_Notes_for_the_Course_in_Water_Wave_Mechanics.pdf)), a mathematical model using several simplifications that nonetheless produces reasonable results. The linear theory works best when the amplitude ($a$) is small in comparison to the water depth ($h$) and the wavelength ($L$). Using the continuity equation for fluids, the [Navier-Stokes equations](https://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations), [Bernoulli's principle](https://en.wikipedia.org/wiki/Bernoulli%27s_principle), [Laplace's equation](https://en.wikipedia.org/wiki/Laplace%27s_equation), appropriate boundary conditions, and the assumption of linearity, we reach the surprisingly simple approximation of
$$\eta(x,t)=a\cos(\omega t-kx)\tag{1}$$
where $\eta$ is the elevation of a particle above the plane of water at rest, $\omega$ is the angular frequency, and $k$ is the wavenumber. We also get a nice [dispersion relation](https://en.wikipedia.org/wiki/Dispersion_relation) and a somewhat complicated expression for the [phase velocity](https://en.wikipedia.org/wiki/Phase_velocity) of the wave, $c$:
$$\omega^2=gk\tanh(kh)\tag{2}$$
$$c=\sqrt{\frac{gL}{2\pi}\tanh\left(\frac{2\pi h}{L}\right)}\tag{3}$$
where $g$ is of course the acceleration due to gravity; we get this from the equation $k=2\pi/L$. Additionally, as [Green pointed out](https://worldbuilding.stackexchange.com/a/20227/627), the mean kinetic energy $\bar{E}$ is given by1
$$\bar{E}=\frac{1}{16}\rho gH^2\tag{4}$$
where $\rho$ is the density of the water. If an energy $E\_w$ is imparted to a wave, then we have the relation
$$H=\sqrt{\frac{16E\_w}{\rho g}}\to H\propto\frac{1}{\sqrt{g}}$$
as [JDługosz said](https://worldbuilding.stackexchange.com/a/20069/627). Stronger gravity means smaller waves.
Holding all other variables constant,
$$\omega\propto\sqrt{g},\quad c\propto\sqrt{g},\quad H\propto\frac{1}{\sqrt{g}}$$
Therefore, on a planet with higher gravity, you'll see . . .
* Smaller waves
* Faster waves
and on a planet with lower gravity, you'll see . . .
* Larger waves
* Slower waves
This is all very straightforward, but what happens when waves reach the shore? At this point, linear wave theory breaks down (pun intended), and numerical modeling is often your best shot (see [here](http://pordlabs.ucsd.edu/rsalmon/111.textbook.pdf)). The [shallow water equations](https://en.wikipedia.org/wiki/Shallow_water_equations) are useful here, especially when discussing tsunamis. Let's look at one analytical case where we do get results. We look at the Carrier-Greenspan criterion for wave-breaking. When approaching a beach where the seafloor slopes up at a rate $s=\left|\frac{dH}{dx}\right|$, a wave will break if
$$s^2<\frac{\omega^2a\_{\text{shore}}}{g}\tag{5a}$$
where $a\_{\text{shore}}$ is the amplitude of the shore. Substituting in the dispersion relation for $\omega^2$ shows that this is entirely independent of $g$! A more rigorous model gives us a better relation (still without influence from $g$):
$$s^{5/2}<\sqrt{2\pi}ka\tag{5b}$$
This is elegant. While gravity will, of course, influence *how* specifically a wave moves near the shoreline, it will not affect whether it breaks or reflects.
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### Further reading:
* [Tsunami - Mathematical classification](https://earthscience.stackexchange.com/q/9176/1399) on Earth Science Stack Exchange
* [Aalborg University lecture notes](http://vbn.aau.dk/files/60647156/Lecture_Notes_for_the_Course_in_Water_Wave_Mechanics.pdf)
* [University of San Diego lecture notes](http://pordlabs.ucsd.edu/rsalmon/111.textbook.pdf)
* [Lecture notes on other types of waves (Kelvin waves, Rossby waves, etc.)](http://www.cgd.ucar.edu/staff/islas/teaching/4_Shallow_water.pdf)
[Answer]
It's a simple harmonic oscillator with a stronger spring.
The same amount of energy (e.g. from wind) makes lower waves in stronger gravity. Just like changing the tension on a string, waves will travel faster.
Since there is a smaller range of wave sizes since the big waves are smaller and 0 is still zero, in stronger gravity I think the *dispursion* effects will be reduced.
On the other hand smaller waves will hit harder. Same as the larger size of waves on Earth, just less to show.
[Answer]
Intuitively, it takes more energy to create a wave of equal height on a planet with more gravity compared to standard Earth gravity. Inversely, a planet with lower gravity will have lower energy waves. Using [equations](http://oceanworld.tamu.edu/resources/ocng_textbook/chapter16/chapter16_01.htm) for wave energy incorporating gravity, we see:
$$
E = \rho\_{ w} g \langle \zeta^2 \rangle
$$
>
> where ρw is water density, g is gravity, and the brackets denote a time or space average.
>
>
>
So, as gravity goes up, the energy in a wave also goes up, if we keep water density the same. There are more equations wrapped up in the above cited equation, such as what
$$\zeta^2$$ means. The equations link has a full description.
The actual shape of the waves probably won't be any different though the energy contained in a wave will be radically different. Waves on a higher gravity planet are going to hit a lot harder. If a medium sized seashore wave on Earth will knock a person over, an equal height wave on super-Earth will absolutely flatten them.
[Answer]
A previous answer said that it can be equated to a harmonic oscillator with a stronger/weaker spring. I'm not sure if that's true. Most of the force and movement in a wave is lateral rather than vertical, and so the presence of waves would not be affected much, and neither would their speed, since wind and water currents play a much stronger role in their creation than gravity would.
You could look into the effects gravity change would have on your wind convexion and weather patterns, which would affect the water too, but that's probably going too far.
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