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I'm writing a story that happens on a dry and arid planet that has only a few oasis's where life can thrive. Life on this world either lives in the oases or lurks in the sand waiting for migrating animals to pass by. The inhabitants of the world are also nomadic, spending some time at each location before moving on so as to not burden the land. Though there are exceptions of course, some groups prefer to settle in a single oasis and expand it. However this world wasn't always a desert, otherwise life as we know wouldn't be able to develop. The planet was once covered in oceans and something caused it to dry out.
**What could cause oceans to disappear? Either through a cataclysm, though life may not survive or through some long term change in the environment.**
I'm not too late in the writing process, so there's wiggle room for explanations. Although it has to allow for life to survive the drying, so no meteors evaporating the oceans or anything that extreme. My first guess was for the seas to get sucked under the planets crust, though I am no seismologist so I don't know the specifics of how that would happen.
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The only example I can think of is "Snowball Earth" . During the Cryogenian Period ice caps expanded , possibly due to low amounts of CO2 in atmosphere, covering the continents, then situated closer to tropics, and due to albedo effect the cooling of the planet increased until ice cover most or all Earth.
Now oceans cover 70.8% of Earth surface. Out of this about 90% is the main 3: Pacific, Atlantic and Indian. About 10% surface and 7% volume is in the Southern Ocean and Artic Ocean. Those are respectable , decent oceans right? Right?
My point is if your planet has Ice Caps and is cold enough, ice would cover the two surrounding oceans of this size and and is also hot enough to keep the ice from expanding past the tropics you would have a massive dry continental belt stretching from Northern Ice Cap to Southern Ice Cap.
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**They are where they have always been, underground.**
Most of the worlds water is and has always been deep underground. Oceans of it. Life developed there getting its energy either chemically or geothermally and eventually evolved to colonize the surface.
If the surface dwellers ever learn to tap deep, they can bring up more water than they ever dreamed of....and maybe some things they'd rather not dream of.
This solves your "However this world wasn't always a desert, otherwise life as we know wouldn't be able to develop." without having a cataclysm that everything has to survive.
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Perhaps a meteor strike in the ocean at a point where only a thin layer of rock separated the surface ocean from an enormous void within the crust. If the meteor pierced that rock layer, a great deal of the ocean might follow it into the void, causing shorelines around the world to recede until the void filled up. That wouldn't dry out the planet entirely but it might reduce the percentage of the surface which is covered by water to a small enough value to suit your story.
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## Either the sun bloated, or the earth broke. Don’t get it? Look…
***Maybe the sun bloated.*** You know, it would work if this was a dystopian or science fiction (which it probably is, if I am right). But that presents a problem: You say nomadic people thrive in this world, which means there must be the proper climatic conditions (minus water) to survive, and I don’t think a bloated sun is going to help.
Then here comes another theory: the sun did bloat, but then it shrunk yet again. (Okay, okay, I’m sorry)
Then go reverse. The mystery here would be- “A long time ago, there used to be water in the planet, a cold liquid gushing down the barren channels that lay now. What happened to the water?” And then we answer it. A heat wave? That would be the explanation. A massive wave of heat, a natural disaster that struck the entire world, resulting in mass damage, and inevitably, the disappearance of the most valuable asset of life: water. A heat wave that left survivors in only ten thousands, which explains why they are nomads.
Now, you would say: “You dimwit, if the water vaporised, it would take the form of clouds and rain down again!” Well … all right. Then: the water froze. That’s all the explanation that can be. Either the sun bloated and vaporised the entire water content entirely, or the sun turned into a dwarf. ***Or, due to a **temporary** disaster, it was predicted that the earth would break loose from its course, and that’s what happened.*** Then the water froze, clumped in the chilly poles of the earth.
If neither sound plausible, tell you what: this is fiction. Have fun!
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## Climate change
Given your scenario, letting all the water disappear is unnecessary. Oceans and seas make up for about 96.54% of all water on earths surface. Fresh drinkable water is about 0.76% groundwater and 0.007% lakewater[1](https://www.usgs.gov/special-topic/water-science-school/science/how-much-water-there-earth?qt-science_center_objects=0#qt-science_center_objects).
As you can see from the map below, your story might become closer to reality in the next 10 or so years.
[](https://i.stack.imgur.com/bBXSV.png)
Note: this image was not taken from a scientific article and could be an inacurate artistic representation
From a paper by Yerlikaya B.A., et al. 2020:
"Within the next decade, an estimated 60% or more of the world population will also begin to experience serious water shortages"
What is nice about climate change drought is that: "Groundwater systems generally respond more slowly to climate change than surface water" (Kundzewicz et al. 2007). This could mean that oasis formed from underground water stay longer. And be one of few viable options for some.
## reference
Kundzewicz, Z & Mata, Luis & Arnell, Nigel & Doell, Petra & Kabat, Pavel & Jiménez, Blanca & Miller, Kathleen & Oki, Taikan & Şen, Zekai & Shiklomanov, I. (2007). Freshwater Resources and their Management.
Yerlikaya B.A., Ömezli S., Aydoğan N. (2020) Climate Change Forecasting and Modeling for the Year of 2050. In: Fahad S. et al. (eds) Environment, Climate, Plant and Vegetation Growth. Springer, Cham. <https://doi-org.vu-nl.idm.oclc.org/10.1007/978-3-030-49732-3_5>
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## Alien life
The sample retrieval mission from Bennu was a success beyond all expectations. Not merely fossil evidence of life, but *life itself*, from a barren asteroid in the midst of space!
They cultured it so carefully, with such amazing results. They noticed that oh my, how it hoards water! It has complex silicon chain enzymes that can convert sand to orthosilicate, or any step in between. SiO2 + 2H2O = SiO4(2-) + 4H+, the hydrogen either being tagged onto the orthosilicate or used for more peculiar inorganic biochemistry. It had the ability to set up networks between grains of felsic and ultramafic rock and extract energy from their rearrangement. And naturally, it could also do very well when cultured on a substrate of pure glass.
Wups... did I mention they had it in a glass container?
The irony was that one day Bennu would have struck the Earth anyway, and in all likelihood it would have survived from the fragments and had the same effect. But whatever the reason, this spectacularly well evolved alien microbe has incorporated the water into its silicon-rich spores embedded in the sand and silt and stone of the planet, leaving nothing but salty wastes and vast piles of infectious dust where once the oceans heaved.
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Related to [this question](https://worldbuilding.stackexchange.com/questions/207395/mechanics-of-infrequent-meteor-attacks/207421). A lot of the discussion there got sidetracked from the question of orbital physics, into questions about alien motives and what the humans would do, so I want to start a new question with more clear physical parameters and a more well-defined objective.
You have a motor that can exert 100N of force over a very long period of time (at least a thousand years). It may be an [ion drive](https://en.wikipedia.org/wiki/Ion_thruster), powered by a large solar panel array, and capable of refining extra propellant from comets and asteroids. It's 1AD, you begin in Earth's orbit, and you want to do as much damage to humanity as you can, by smashing asteroids or comets into Earth with as much kinetic energy as possible. If you can actually kill humanity, that is your ideal outcome. Your spaceship weighs 10000 kg. You can easily compute trajectories to the desired precision. What methods do you use?
Some possible strategies:
* "The drop": take a very massive asteroid or an Oort cloud object and slow it down until it drops out of orbit. Just let it fall to Earth while you move on to the next asteroid.
* "The windup": take a less massive Oort cloud object and ferry it even further out of the solar system, then slow it to a stop when at a sufficient distance. Then accelerate it straight at Earth.
* Suicide run: like "the windup," but without an asteroid. Just get very far from the solar system, then come to a stop, turn around and accelerate straight at Earth. For this purpose we may say the spaceship weighs 10000kg. If the approach phase of the suicide run takes 1000 years, the impact energy will be around 10^21 J, without taking into account relativity. (Chicxulub = 10^25 J). Can be done only once.
* Gravity assist: drive your object past Jupiter so that it slingshots around it, gaining speed.
* Multiple gravity assist: repeat the gravity assist several times on one object.
* [NEO](https://en.wikipedia.org/wiki/Near-Earth_object) wrangling: take an existing large comet or asteroid on a highly eccentric orbit that will pass near Earth, such as Halley's comet or 99942 Apophis. Catch it far from Earth, then adjust its orbit slightly so it hits Earth. This sounds like a good plan to me, although it is limited by the number of such NEOs.
* Simultaneous targeted attack: set up dozens of objects precisely targeting cities, timed to strike in rapid succession and wipe out all the major cities on Earth.
* Moon tugboat: take a small moon and drive it towards Earth. (sounds not feasible)
Targeting strategies:
* One big hit causing an extinction event. Chicxulub-scale energy (10^25 J) would definitely do it, if you can get there.
* Multiple Tambora-sized hits (10^20 J) to affect the climate globally. One would need a lot of these in rapid succession to cool the planet enough to cause extinctions.
* Many smaller nuke-sized hits to wipe out cities (such as 10^15 J).
If you're still around past AD 2000, we can assume humans will be causing problems for you, unless you've already done substantial damage or are already moving too fast to be stopped. AD 2500 without doing damage = Mars is colonized, game over.
Please no answers without a back-of-the-envelope calculation of feasibility, the impact energy, and time required. See [TNT equivalent](https://en.wikipedia.org/wiki/TNT_equivalent#Examples) for some examples of different energetic events for comparison. Also [wolfram alpha](https://www.wolframalpha.com/input/?i=%28%28100N+%2F+10%5E10kg%29+*+2000+years%29) is great for unit conversions.
[Answer]
## Forget the rock, just ram the ship
As others have pointed out, because you have a constant force of acceleration if the smaller the load being accelerated, the higher the kinetic energy of impact.
For maximum impact, accelerate straight outward, and do a 180 at the halfway point. Since the inbound trip does not have a turnover, the average velocity will be higher inbound, so you actually want to spend about 1171.5 years outbound and 828.5 years inbound.
On earth impact, your impact file be about 3.417E20 Joules, which is about 5.7E6 Hiroshima bomb or 1512 Tsar Bombs, but only 0.003 Chicxulub impacts (using a more accurate 1.15E23J figure). Though this will be a bad day for many, it's not nearly enough to wipe the planets clean of humans.
Ignoring special relativity, I computed that the impact velocity was about 0.087 c - so ignoring relativity is close enough approximation.
10000 Kg sounds like a lot, but Chicxulub mass est. is 3.2E15 kg. But you really don't have the time to push around a big rock. Assuming you could find another Chicxulub, you could not even apply 1 mm/sec of delta V in 2000 years. Not enough to change a suitable near-Earth object.
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> (...) you want to do as much damage to humanity as you can
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You're on the tight path with that device.
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> by smashing asteroids or comets into Earth with as much kinetic energy as possible.
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This is wasteful and inefficient.
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> If you can actually kill humanity, that is your ideal outcome.
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Let me propose that you simply do a lot of nothing for a while. Let humanity do its thing until they start exploring space.
As soon as they start making artificial satellites, make a few round trips to the Moon. Those monkeys are gon'na flip! They will start creating cults about you, which is when the damage begins.
Now let them develop their technology. You can let them approach and study you but don't get captured. The moment you notice they have a great lot of noisy satellites, start smashing them. Orbital roadkill will turn each satellite into shrapnel, which has a domino effect. Bonus if you end up killing some human astronauts.
This is when humans flip again, and this time they understand it's war. They might wish to nuke you in retaliation when they find out you're the culprit for their space losses, so go to Martian or Venusian orbit for a while.
Humans will develop their war technology extremely fast. Forget about mere ICBM's, they will.have interplanetary bombs with enough yield to require you to update your global maps whenever they are used.
Now you can just sit and wait. It's a matter of time until political strife causes them to use these new weapons on each other, eventually wiping themselves out. You can either sit and wait, or give them a nudge by going back to Earth and aggressively lithobreaking onto one of its largest cities.
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### Attack with only asteroids of extremely low albedo or potent greenhouse gases.
Forget about targeting cities. Forget about tnt equivalent. Forget about using asteroids only as a store of energy to be released in impact. See the asteroids as a store of materials.
I'd suggest a good thing to read up on is [how we could teraform mars](https://terraforming.fandom.com/wiki/Mars). In that field, theres some really useful ideas on how we can rapidly heat a planet using cleverly crafted asteroid impacts directed by a low power engine.
Essentially your alien uses asteroid impacts to teraform the earth onto the global warming runaway greenhouse hell were currently trying to avoid.
Select black asteroids, typically high carbon and ultra low albedo, and smash them into the pristine white Artic, Antarctic, and anywhere else on the planet that's nice and high albedo.
By covering or replacing white shiny ice with pitch black soot or something else dull black, sunlight stops being reflected and is absorbed as heat.
Your turning the artic from a shiny mirror into a black road on a hot day. Depending on how black your black is - you could turn each square meter of earth s surface you cover into upto a 1.3kw solar heater. If you can use tiny asteroids that each cover just 10sqkm in dust per hit, that's a peak of 130 megawatts of heat generation from that point onwards, (although ~80 is more reasonable due to low sunlight angle and poles being further from the sun than equator). That's a lot of heat.
(You can also use ammonia or methane, both of which are plentiful, as these will build up the greenhouse effect directly and are substantially more powerful than co2.) But bang for buck on your single engine accelerating I'd suggest put all your energy in painting the planet black and making it suck up as much sunlight as possible.
Excess heat at the poles causes tundra melt; releasing methane, a greenhouse gas significantly stronger than co2. This forms positive feedback (releasing more methane faster) amplifying the greenhouse effect. There are lots of other positive feedback processes going on as well, dozens at least - another is more heat causes more bushfires and blackened forests absorb more sunlight than green ones did, raising the temperature more causing more burning, and more burning releases more co2 raising the temperature even more.
We dont know how bad all these runaway processes can get; possibly to venus levels. But even if it doesnt get that bad, you'll wipe humanity out with floods (900m sea level rise), firestorms, hurricanes (every degree in warming makes hurricanes more likely and stronger), kill off all our crops, or just directly wipe us out with heatstroke.
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Here is one option: near Oort-cloud line drives.
The plan:
1. In the near Oort cloud at 2000 au from Earth, pick an object of mass 5000 kg.
2. Objects in the Oort cloud are moving at a few km/s. Bring the object to a stop.
3. Accelerate the object straight at Earth, separating from the object as late as possible to drop it on a city.
4. Pass close by earth (at very high speed). Take photos of Earth's surface to determine the next target.
5. Decelerate until you are again stationary in the Oort cloud at 2000 au, on the opposite side of the solar system.
6. goto step 1
Analysis:
1. Total K.E. of spaceship + object just before release is Force \* Distance = 100 N \* 2000 au. Mass of spaceship + object = 15000 kg. The spaceship's mass accounts for 2/3 of the kinetic energy, so we divide kinetic energy by 3 to get the object's impact energy of [100 N \* 2000 au / 3](https://www.wolframalpha.com/input/?i=100+N+*+2000+au+%2F+3) = 10^16 J, enough to kill a city.
2. K.E. = 1/2 m v^2 , therefore v = [sqrt(2 \* 100 N \* 2000 au / 15000 kg)](https://www.wolframalpha.com/input/?i=sqrt%282+*+100+N+*+2000+au+%2F+15000+kg%29) = 1997 km/s. Since this is much faster than the orbital speed of Oort cloud objects, the time it takes to stop the object in its orbit can be neglected.
3. distance = 1/2 a t^2, so time of approach = [sqrt(2 \* 2000 au / (100 N / 15000 kg) )](https://www.wolframalpha.com/input/?i=sqrt%282+*+2000+au+%2F+%28100+N+%2F+15000+kg%29+%29) = 9.5 years
4. The return trip to the Oort cloud can be a little faster than the approach to Earth because we weigh 10,000 kg instead of 15,000 kg. That means we can keep on accelerating for a little while as we pass Earth before we turn around and start decelerating. A lower bound on the return time would be [sqrt(2 \* 2000 au / (100 N / 10000 kg) )](https://www.wolframalpha.com/input/?i=sqrt%282+*+2000+au+%2F+%28100+N+%2F+10000+kg%29+%29+in+years) = 7.75 years. Maybe it's really 8 or 8.5 years - no need to be too precise.
5. So, we destroy a city roughly every 18 years, plus whatever small time it took to find a suitable object and stop it.
Regarding the mass of the object: if it were lighter than 5000 kg, the time needed could be reduced by up to a year, but the impact energy goes down rapidly because more of the kinetic energy is going into the spaceship and not into the object. If it were much heavier than 5000 kg, the impact energy could go up by nearly a factor of 3, but it's already 10^16 J which should be enough. More significantly, heavier objects increase travel times by a lot. If the object weighed 100000 kg the approach trip would take 25 years, for a total trip time of 33 years.
Although... perhaps this would be worth it, if the big object could actually be a cluster of 10 objects that we separate before impact to hit 10 cities at once. Keeping the cluster together as we accelerate it, and separating it once we're done, might be a problem if the spaceship lacks tools or an EVA robot.
But perhaps the spaceship could just stack the objects in a long line in front of it, like scoops on an ice cream cone, so they are held together by the pressure of acceleration and easily separated when it's time. Wouldn't be easy, but if it has the dexterity to do that, I think humanity is toast. So maybe it would be necessary to reduce the drive to 10N instead of 100N, or just to say that the scout's computer is programmed for orbital dynamics and not for that kind of stacking.
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**De-orbit the moon using leverage.**
There it is, hanging over us. If the moon came down that would be it for life on earth.
I propose your alien could produce a series of impacts, finally impacting the moon adequately to slow it down and so bring its orbit into its Roche limit. It would be torn apart from gravitational forces and rain down on the world, [Seveneves](https://en.wikipedia.org/wiki/Seveneves) style. The consequent superheating of the atmosphere would shed it into space.
The plan is taken from my answer to this idea.
[How might people try to stop the world becoming a rogue planet?](https://worldbuilding.stackexchange.com/questions/158785/how-might-people-try-to-stop-the-world-becoming-a-rogue-planet/158791#158791)
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> an AI ... that knows the site, mass and velocity of all objects bigger
> than 10 kg in its immediate vicinity. There is a mass of comparable
> size which could be made to intercept and gravitationally deflect the
> incoming mass. But the interceptor mass is itself very large. To move
> it will require a different mass of comparable size. A smaller such
> mass is available and correctly positioned. Although smaller, this
> mass is also not easy to move. A mass smaller yet is also in the
> correct position...
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> Your AI presents a series of 12 successively larger gravitational
> interactions of which the smallest and first is within the ability of
> humans to achieve with rockets. In a planetary billiards chain
> reaction, an array of progressively larger objects will change course,
> with the end result the gravitational deflection of the incoming
> impactor.
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Your alien sends an asteroid into another larger one, with the goal of changing the course of progressively larger objects. The final one hits the moon and slows it down in its orbit, ultimately causing it to come down.
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If you have a limited energy budget and can use any mass as reactive propulsion and use it to change trajectories, combining your comments and my suggestion in comment section
Then to amplify the energy you have, a potential strategy could be as follows:
Search for a proper object in the vicinity of 0 to 11 km/s delta-v, use most of it as reactive mass with lowest possible Isp (thus most or your energy goes into the future impactor).
Then you can amplify your energy by $({\frac{\Delta v(\mathrm{earth escape velocity})}{\Delta v(\mathrm{source, Hohmann first transfer maneuver})}})^{2}$.
Sorry for the lack of concrete numbers and a suitable asteroid, but a reasonable expectation would be 10-20 times the impact energy.
A gravity assist maneuver to Jupiter starts with $\Delta v$ [9.36km/s](http://www.bogan.ca/orbits/gravasst/E-Jprobe.html) if from Earth, but it is reasonable to expect the ability to change rotation(orbital direction) of a projectile and then instead of earth escape velocity we may have earth orbital speed multiplied by 2, or something like that, in the formula. Which could definitely be an improvement in terms of amplification if a suitable object were found closer to Jupiter (or another gas giant).
There are some theoretical limits to gravity assists, it is not possible to bounce back and forth indefinitely, increasing the energy each time.
All that takes a few decades at most, so you may already see a distinct difference between defining things by force or limited energy.
## Superiority of AI (aliens)
Can there be some showoff case of superior being that blows the mind, like creating some cascade effect on given energy budget which results in a given timefame is many many orders of magnitude amplifies the energy they had initially?
Like making subtle changes to many objects in asteroid belt, so they start to influence each other and interacting with changes of gravity field of solar system and then at day D start spewing asteroid after asteroid on collision course with earth?
Good question! IDK.
In such extravagant form the answer is no. But in therms of amplification of initial energy it hard to tell. Lagrange points can be of interest - what if the whole belt would be collected at L3 L4 (just a litte push and pull to 2 halfes of each asteroid) - one invests energy in such change but it is not lost but collected in these points and can be extracted back, so one big change for free. Can it be helpfull, idk, needs more brain power. But gravitional binding energy of whole belt (4% of moon mass) can be around 1e26J, with a potencial of that energy be concentraed in some small chunk of the asteroid belt to continue its destruction jorney. Definetly there is some potencial, but timeframe and all that is hard to tell.
## Frame challenge
Not exactly a frame challenge, and more like opinion, comment to that alien thing.
I would say that any tech savy human, with a proper university education or diy guy, or one which focus on computer and technology - having a space ship with 1000km/s delta v, having time 2000 years - can not only destroy humanity in give time rame, not only incenerate surface of the planet, but as bonus make bunch of glass beads out of the whole planet.
What he needs is his basic tech understanding/science, freedom to act in space and copy of WB questions and answers. Copy of wiki also can be helpfull, but not like a copy of WB.
So even if alien chose 3th option, that belt thing, I won't be impressed by them, I basically won't be satisfied by any outcome except steamrolling the whole solar system.
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## Plan 9
I was hoping someone else would come up with this idea, because I don't know enough to flesh out the details.
The idea is let the gravity of the Sun and the Earth do most of the acceleration of the rocks. Fly out to the asteroid belt (or possibly Kuiper or Oort regions). Pick a suitable rock. Deorbit it from the Sun such that it collides with the Earth. The combined fall towards the Sun/Earth will give rocks plenty of speed (slowest for asteroid belt, highest for Oort cloud) to leave their mark on the Earth. Time to impact is at most 100-150 years assuming you are not deep in the Oort cloud.
Since all you are doing is deorbiting the rock, you spend as little as time as possible maneuvering each rock. Since Oort objects have smaller orbital speed than asteroid belt objects, they are quicker to de-orbit as well as falling from a greater height. Given the reduced deorbit time and increased impact velocity, I suspect Oort objects are your best source.
For bonus points, instead of deorbiting them, you just the put the rocks into highly elliptical orbits that all happen to intersect Earth's orbit on Jan 1, 2001 0:00 UTC distributed all over the planet - You need to be very good at orbital calculations - in reality the chaos of the problem makes this impossible unless you have God-like knowledge of everything moving anywhere near our home star.
You want to accelerate small rocks because your thrust is so low large rocks can't be moved quickly enough. If your rocks are too small, they will burn up or slow down or simply be too small to do lots of damage - I did not attempt to figure the ideal size.
So, my major unknowns are 1) Best object source - though I suspect it is the Oort cloud), Best object size, and how long it will take to deorbit each object on the average (avg. distance between the desired impactors is unknown)
I could easily envision that you could deorbit many hundreds, or perhaps thousands of objects that could level a city, but I don't have the info to back it up.
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
A character I'm thinking of is about to have a close call. A woman attacks him with a stun gun by surprise, but by chance he is able to catch the weapon. Backup operatives move to assassinate him conventionally, but he is able to escape by an unexpected route.
The stun gun appears to be a model sold by a small company (i.e. it should generally *look* like a stun gun carried semi-legitimately for self defense) It is, however, a counterfeit - the woman planned to exchange it with another agent, so she could present a verifiable stun weapon to police if speaking with them became necessary. An agent would also testify that the victim made an inappropriate sexual contact just beforehand. The site was chosen for lack of mounted cameras, and routine 5G terahertz scanning of the scene and weapons by passerby smart phones has been blocked during the incident by "chance" interference.
On examination, the weapon is designed to kill *reliably* when applied to someone's heart by a trained user. It does so without leaving evidence differing from the stun gun it mimics. The question is **whether (or how) this is done.** A few minutes searching turned up [this abstract](https://pubmed.ncbi.nlm.nih.gov/18373757/) explaining the electrodes should go above and below the heart, and work by controlling ventricular rhythm with pulses of electricity. When these steadily speed up, *presumably* the victim would be driven into fibrillation.
This is not quite the entire story, however, because several other articles claim humans are more resistant than pigs (the electrical signals in the heart run deeper) and the voltage of a Taser is only half of what is needed to control the heart rate. The temptation is to double the voltage, but this assumes everything goes perfectly - yet still leaves more severe surface markings. Some other trick may be needed.
I would be surprised if such weapons have not already been used in the field by certain unsavory agencies that closely follow weapon development, yet I'm also not entirely sure they're possible at all.
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The biggest thing your "stun gun" needs is to output 60 Hz AC (perhaps superposed on the high voltage pulsed DC normally produced by this sort of device). It takes only about 30 mA at 60 Hz across the heart for as little as a hundred milliseconds to induce ventricular fibrillation -- which is almost always lethal without intervention (and the victim will lose consciousness in seconds, so is unlikely to help themselves).
The potentially tricky part of this is getting that current *across the heart*; the contact probes on most stun guns are too close together for this to be reliable. If it were a true Taser, with projected barbs, this is more likely to occur, since the barbs will separate by a handspan or more when projected a couple meters -- but this kind of device isn't commonly carried by civilians (mainly due to cost; it's a one-shot device that can't be reloaded by the user, so very expensive to practice with, but in some jurisdictions it's legally limited to law enforcement as well), and shooting the victim with a Taser from that kind of distance doesn't fit well with the cover story.
Because the probes of whatever is used will leave minor skin burns (from the DC of the "legitimate" stun gun) having a use device with widely spread probes is a problem as well; medical examiners would expect to find the burns close together, not widely separated.
In this case, you may need to do a little handwaving -- an ordinary purse or pocket stunner with 60 Hz superposed on the output *can* kill via fibrillation, it just won't be reliable as these devices are usually built.
[Answer]
**It is poisonous.**
<https://en.wikipedia.org/wiki/Bulgarian_umbrella>
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> A Bulgarian umbrella is an umbrella with a hidden pneumatic mechanism
> which injects a small poisonous pellet containing ricin. It has a
> hollowed stalk in which the pellet neatly sits.
>
>
> Such an umbrella was used in and named for the assassination of the
> Bulgarian dissident writer Georgi Markov on 7 September 1978[1] (the
> birthday of the Bulgarian State Council chairman Todor Zhivkov, who
> had often been the target of Georgi Markov's criticism) on Waterloo
> Bridge in London. Markov died four days later. It was also allegedly
> used in the failed assassination attempt against the Bulgarian
> dissident journalist Vladimir Kostov the same year in the Paris Métro.
> The poison used in both cases was ricin.
>
>
>
The stun gun is a functioning stun gun. However the barbs have a groove which can hold a pellet of poison in the manner of the Bulgarian umbrella. Barbs are expected to penetrate and so a wound of this sort would not be suspicious for a person hit by the stun gun. One can go with ricin as in the linked device, or choose or invent a faster acting poison such that the stun gun becomes more rapidly lethal.
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People have been known to die after being tased: <https://www.reuters.com/article/us-axon-taser-toll-idUSKCN1B21AH>
It might be possible to "improve" the output of the device your character uses so that it would be capable of killing the subject.
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In my fantasy world I have a species of reptilian humanoids.
* Their body mass, lifespan and overall intelligence is about the same as humans. This probably means similarly sized brains.
* They are NOT cold blooded. They have a human-like metabolism.
* The female gets internally fertilised and then lays an egg (rarely multiple eggs, like twins in humans).
* Their body plan is like bipedal dinosaurs. They walk bipedally on two legs, but with a horizontal spine like dinosaurs, NOT upright with a vertical spine like humans. (This probably influences the shape of the hips, which influences the maximal egg size.)
* They are highly social and live in tribes, towns or cities like humans.
* They are generally monogamous and mate for life.
* The atmosphere and available nutrients are similar to those on Earth.
I want to determine how long time their eggs take to hatch. There's two periods involved:
1. The time from the moment of impregnation to the moment the egg is laid. I'm going to call this *gestation*, but there might be a more proper term for it.
2. The time from the moment the egg is laid until it hatches. I believe this is called *incubation*.
Of course I can just pull numbers out of my rear end and say that gestation takes 3 months and incubation takes 6 months. But I'd like it to be more qualified than that.
Important factors include the sizes of the hatchling's brain, the egg itself and the female's birth canal. But I don't know about egg-laying animals enough to set them.
What are good arguments for why the gestation and incubation periods should be one thing and not another?
Preferably I would like the gestation period to be short. My reasoning is that the shorter the gestation period, the smaller the burden that automatically falls on the female, which can influence their gender roles.
Thanks in advance!
[Here is pictured the *Avisapiens saurotheos*](http://www.cmkosemen.com/images/images_dinosauroids/races_sedentary.png) by C. M. Kosemen and Simon Roy. My lizard men don't look exactly like this, but similar.
[Answer]
**Slight frame-challenge (but only slight).**
Lizards living in moist areas lay eggs with leathery shells rather than hard brittle ones as the leatheryness allows for the absorption of moisture to keep the developing young hydrated.
As an evolutionary aside, lizards are thought to have developed from the first [ampibians](https://en.wikipedia.org/wiki/Evolution_of_reptiles#Rise_from_water) in the late Carboniferous (about 250 M years ago). Amphibians returned to water to spawn, the spawn volume, once hydrated being sometimes sixty times the volume of the adult female that ejected it.
Do you see where I'm going with this?
If this ability, to lay partially dehydrated eggs were retained, the volume increases vastly when layed in a safe watery place, allowing the birth of a self-sustaining egg surrounded in nutritious jelly to develop. Something the size of an apple would be produced turning into a beachball. Gestation might just be a matter of a week or so. The parents would need to take it in turns to continually circulate the water over the egg to maximize oxygen absorption. Perhaps a community acted together to protect their collective young and keep their gaseous exchange going.
The next stage of development would involve hatching after perhaps 2-3 months, hunting small-ish fish and aquatic mammals, being fed strips of meat by their parents all to build their bodies. A diet comprising more plants would come later.
Now like toad's tadpoles they'd develop into their adult shape, gaining feet, hands, lungs and a tougher skin. Emerging from the water they're metabolism would start to change, perhaps being able to internally generate their own heat, also growing the rudiments of a feathery covering. And so on until full adulthood.
If this seems improbable, take a look at this, the top row showing the starting point for different vertebrates, the bottom row showing the end point. Birds, mammals, fish - all start looking roughly similar.
[](https://i.stack.imgur.com/epqlH.jpg)
[Answer]
You could do it 2 ways
1: Long gestation, long incubation, long period between eggs. Juvenile is fairly mature on hatching. This would be analogous to humans with lots of investment in infrequent juveniles.
2: Short gestation, short incubation, short period between eggs. Juvenile is not mature on hatching. This could be the pattern for a species with many juveniles, low initial investment in each, and historically high infant mortality.
The second could be interesting because it would mean your people are not just green humans. Lots of nonsentient juveniles are everywhere like little animals. They don't get intelligent until the third molt.
This would make for an interesting fiction because maybe certain of these juveniles start following a specific adult around when they feel it is that time. Playing the odds the chosen one is probably not a parent; even if it is her or she does not know that. But if that individual is chosen that is the one who then provides the parental care once the third molt takes place. Some individuals might get chosen by juveniles a lot and so have a lot around them, growing up. The juveniles have their reasons.
Your individual is quite old and no juvenile has ever chosen him, until now.
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Humans aren't a good model for what's possible. Due to how the human skull grows, the size of the brain is largely limited by what can be pushed through the mother's hips, but if skulls grew differently, the brain could start small and grow to a large size during infancy. It even does this during pregnancy (obviously), but because the lungs aren't ready yet, it can't do it outside the womb.
Thus, the two important factors for this species (assuming they come from an alternate Earth, and have biology similar to ours) is that the lungs are developed enough by the time their size exceeds the ability to absorb oxygen through the shell, and that their able to feed at hatching (either latching onto nipples if the species lactates, or to be fed by the parents).
The ostrich makes a decent example here. They are large like humans (though not quite the body plan you want). Their eggs are sizable, and have about 42 days of incubation time. Emus on the other hand go for a full 55-60 days I believe, but have smaller eggs. Those are only examples though, and if your story required a longer duration, that wouldn't be implausible.
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My previous questions of this type (one concerning [Plops](https://worldbuilding.stackexchange.com/questions/196649/how-can-i-protect-medieval-villages-from-plops), the other [Chompers](https://worldbuilding.stackexchange.com/questions/197028/how-can-i-protect-medieval-villages-from-chompers)) concerned protecting medieval villages. This question is less specific, and here's why: **Snappers can spawn anywhere.**
Seriously, anywhere where water collects (anywhere mosquitoes may lay their eggs) is a potential spawn point for Snappers. When rain falls and makes puddles, Snappers spawn in those. Anywhere water has gone stagnant (or gathers if it's raining), a Snapper will likely spawn inside-not a typical vase with flowers, the area has to be big enough to admit a typical bullfrog inside it (because Snappers are around that size). Thus, the amount of Snappers that spawn in an area is the maximum amount of bullfrogs that can fit comfortably in that space.
This is *especially* bad in desert areas, where cisterns are supposed to store life-sustaining (and *clean*) water but instead end up holding lots and lots of Snappers. It also makes drawing water from a well potentially dangerous-Snappers can jump six feet up, their jaws can open wide enough for them to engulf a man's face, if not *his entire head*, and thanks to their webbed feet (no legs, just the feet, they use their powerful tails to jump, sort of like a springtail) they can crawl around, looking for nice faces to eat.
That begs the question, **how dangerous is a Snapper?** (This is *not* the question you are answering, by the way). Snappers can:
1. Leap six feet up and six feet away in a single bound,
2. Engulf someone's head after said bound,
3. If not promptly removed, start growing to engulf *the entire body*,
4. Breathe air and water with equal ease,
5. Run up to 28 mph on land, swim 56 mph in water
6. Eat almost anything (they have cast iron stomachs, they're omnivorous but prefer meat, their jaws can snap or crush bone with ease, and their teeth are also as sharp and hard as steel daggers),
7. Live almost anywhere; saltwater, freshwater, mud, on land if it's humid enough (think swamp, marsh or rainforest),
and 8. are slippery and aggressive enough to escape a fisherman's grasp and maul him; think pirahnas on legs, but with the ferocity of a wolverine.
**Obviously, Snappers are a real threat to human safety.** The question, **my** question, is **How Can Medieval People Protect Themselves From Snappers?**
*Please Note:*
1. Snappers are tough, so they aren't easily killed. You can whack one with an oar, throw it against a brick wall, and it'll be perfectly fine. You could even use one as a stress squishy, if not for the fact it would slip out of your hands and proceed to attack you. Attempts to crush Snappers with rocks or other heavy objects usually see them popping out from under them. They've also been dropped from 50 feet up, only to walk away unharmed.
They are also coated in a ooze that is endowed with cooling and fire-suppressing secretions when exposed to heat, so burning them won't work (at least not *quickly*, their coolant would have to be exhausted) except with Engulfer-fueled flames, and those are [temperamental](https://worldbuilding.stackexchange.com/questions/196989/gaining-the-engorgement-enchantment-for-peasants). However, they can be starved, suffocated, frozen, eaten (though your insides won't like the results), and so forth. Plops and Chompers also eat Snappers, as do Engulfers.
*Specifications For Best Answer:*
1. The best answer will include active and passive methods; methods that require human action to work and others that work without interference. I count behavioral patterns as active methods.
2. The best answer will thoroughly cover multiple viable methods and explain why they'd work.
3. Said methods should be **viable for medieval villagers**, something they can actually come up with and produce. That being said, human ingenuity is quite something, so I'm willing to be lenient on this one.
Please let me know if there is any more information needed, thank you for your input! By the way, if you decide to VTC or down-vote, please explain *why* so I can improve the question.
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**Free meat!**
Meat that magically materializes would be a valuable resource. Given their ferocity snappers will be easy to catch with a hook. Once the barb is set then you have the snapper secure. You can accumulate several, pulling them out as they spawn. Leave them on the hook. Maybe putting out their eyes will make them less fierce. Or put them in a bag.
Then you can grind them up, saving the dagger hard teeth for other uses. Maybe you can eat them if you prepare them right. If not the mush can be fed to pigs or chickens; creatures which make good food for humans.
Persons in areas where snappers might be will carry a pole with fake head lure on it. Snappers will go for the head. One can then push the pole end thru the snapper and set the barb. Tie the pole to a tree and move on. Several such poles might be necessary in areas overrun with snappers.
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Well, this makes a few things really hard. Your old fashioned bucket and rope type well impractical and unsafe so what is a peasant to do.
Sand filtration for a sealed cistern a good start. don't give them a place to spawn in your water supply. Use something like an Archemedes Screw to move the water to the opening of the cistern and run the water through about 3 feet of sand filters. Have the cistern sitting a few feet above ground so you can open a tap to get the water you need without opening the top side to snappers.
Next thing to keep the critters at bay. Wide eaves on houses and pay really close attention to drainage. If you build correctly, you can keep the snappers away from dwellings with the simple expedient of building on the tops or sides of hills. take the time to keep drainage channels clear. Send convicts to keep the lowlands clear of likely spawning places. Wide eaves means that water runoff lands further from the house and you can decide where it goes.
Next, controlled burns. Burning a field to stubble after a harvest is a common enough thing through history, but it may be even more important here. It may not kill too many of the snappers outright, but it will be useful to expose possible trouble spots and it may serve to kill snapper spawn off. A good burn may even be hot/long enough to kill off adults.
You peasants are going to be REALLY interested in ways to poison the snappers. In our world we have poisoned rats for centuries with a variety of compounds. I'm certain that Snappers didn't evolve with humans as their only prey food. What else do they eat? Learn That, then grow some of that in as controlled a manner as possible. Then add Poison and distribute in places where the Snapper is likely to be.
All of this is to deny them habitat. Make the habitat unlivable or downright dangerous and your snapper population will thrive somewhere else.
Humans can control habitat. If you are human and you can live in certain conditions but the snapper can't, you win.
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Here's the gist, my power armoured marines are going to be equipped with full-auto 8 gauge shotguns (in other words a quarter bigger then your average 12 guage shotgun). Now the marines are much more armored and heavily armed than their opponents but the marines are out numbered. Their enemies are colonists with basic knowledge of firearms and tactics. They have assault rifles and basic ceramic and Kevlar. The marines are very large as humans go and they are wearing power armor, so they will take up the entire corridor/lift. This makes it really hard to maneuver. The ship is pressurized but there is no gravity. With the these conditions and shotguns what is the best round:
1. Buckshot. For all you laymen out there buckshot is basically a bunch of balls that are shot out of the gun. They disperse at range.
2. Flechette rounds. A bunch of razor blades that are shot at the target. Kills you pretty nastily.
3. Slugs. A chunk of metal that kills what it hits. Variants includes spreading brass and exploding varieties
4. Incendiary. Burns things and sets you on fire.
5. Other. Any kind of round that makes sense.
Please say why you choose it and why other wouldn’t be as good.
[](https://i.stack.imgur.com/0SHzK.jpg)
[](https://i.stack.imgur.com/dNuvN.jpg)
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## Mixed munitions (including chemical weapons rounds):
*I don't think you need just a single round, so this is a bit of a frame shift.*
Okay, I don't fight fair. Your marines are in full-encompassing NRB suits, and your colonists are just, well, armored - and lightly at that. Now, you can't be sure the enemy will behave consistently, OR they don't have surprises. One of the great things about the future is you can play around with stuff. So here it is:
* **Guided [gyrojet](https://en.wikipedia.org/wiki/Gyrojet) munitions/explosives**: The lower velocities and very large bore of your shotguns makes them perfect to launch self-guided missiles, capable of using radar, heat, or even the emergency signals from a spacesuit to track opponents around corners, through doors, etc. Low-gravity environments are perfect for projectiles that have a guidance system and can self-accelerate when needed. They function equally well in gravity and in vacuum, so the marines don't have to use a completely different kind of weapon in different environments. Gyrojet projectiles can be fired down corridors and be programmed like tiny robotic ships to seek out critical infrastructure or specific targets (via facial recognitions, etc.) depending on how clever you want to make your weapons. Gyrojet projectiles can be all the types of weapons you are asking for here. You could even activate gyrojet munitions passively, toss them down a corridor silently by hand, and they would scan for opponents and fire their rockets when they detected someone. You could leave rounds behind you like an intelligent mine field waiting for enemies.
Let's consider projectiles like a toolbox rather than a choice. Your shotguns should have a dial allowing them to select ammo. Then a small "sawed off shotgun" version should be used for really specific projectiles (more of a launcher than a gun, really) like if you have an "assassin" bullet meant to seek out a specific target.
* **Shaped charges**: I'd go with a miniature shaped-charge like a tiny RPG round for most situations. If I had to pick just one, this is where I'd go. This will blow apart doors, armor, etc. but once the explosion expands (killing whatever is on the other side) it hopefully won't completely destroy the station. Because it's an explosive, the projectile doesn't need to be going very fast to still be effectively armor-piercing. This also works well with the gyrojet idea of projectiles accelerating at opponents on their own (possibly at point-blank ranges).
* **Strong blistering/respiratory toxin rounds**: Something like the high tech equivalent of [phosgene oxime](https://emergency.cdc.gov/agent/phosgene-oxime/basics/facts.asp) will be sort-of non-lethal, but really ghastly. It should cause rapid painful reaction on contact with skin and severe disabling effects when inhaled. So no mere respirator will block the crippling effects. Any enemy non-combatants become your instant hostages. Now all your opponents must don space suits (possibly shedding their armor in the process) to even stand up against you. Make the rounds spray the stuff in a cloud, or shatter on impact. They can be armor-piercing and inject chemical weapons through bulkheads like a giant syringe (to soften up enemies before you even enter a room).
* **Flechettes**: For just shooting large numbers of weak opponents in a panic situation, I'd go with some sort of [frangible armor-piercing multi-head sabot flechette](https://en.wikipedia.org/wiki/Armour-piercing_discarding_sabot). These work well also with the gyrojet concept (a single flechette can be a micro-missile, a cloud can be unguided). They can pierce armor while simultaneously minimizing damage to the station. The projectiles can be made less-lethal by making them not tumble but have a coating of paralytic agent (so after suffering a traumatic injury, the opponents swiftly become paralyzed).
Having an unguided weapon as a backup means that if the colonists have somehow tricked your smart munitions, you can still pulverize them the old-fashioned way.
* **Capture rounds**: Make a projectile that is a tiny claymore that maneuvers and faces their opponent. These can seek unarmored/lightly opponents and have tiny speakers on them, announcing their presence and demanding enemies surrender so you have instant hostages. The projectiles could even have superglue on them and land up against opponents (imagine a bomb landing against your mask and telling you to surrender or die), so they can't run away or swat the thing off. Detonates on command or at predetermined signals.
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Since you state that a marine will effectively take up an entire hallway during the boarding action, you're going to want to go with a round that can
a) penetrate whatever armor (makeshift or otherwise) the colonists can muster and
b) disperse over a short range without losing too much stopping power while
c) not destroying the ship you're trying to take over.
Space ships tend to be cramped (maneuvering room is expensive!), so hallways will likely be short and curvy. You will want to pack ammo that can fill the space with deadly shrapnel, but not large enough chunks to compromise the integrity of the spacecraft you're boarding. Flechette rounds seem idea, given they utilize more than mass and power to inflict damage, while being small enough to not pose serious risk of damaging the structure. Incendiary rounds are about the worse form of ammo, followed by slug rounds. Those 2 types of munition will be as likely to kill everyone on board as to kill just who you want to kill.
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It depends on the goal you have.
Any buckshot, birdshot, flachettes etc won't be very effective against modern armor. However it's hard to completely cover people in armor, and in space you want to be as light as possible so not carrying full armor on the arms and legs for example is likely. This means that your full-auto shotguns could easily hurt the colonists quickly and potentially disable them.
On the other hand the space ship is likely some important real-estate, that's why you are boarding it rather than shooting it out of the sky which can potentially be done by dropping a damn tire iron in it's path at different orbital speeds. So spraying the inside with tons of tiny balls might not be useful as you'll destroy much of the space-ship you are in. Worse, tiny balls can easily cause electrical fires inside these ships so you are probably looking at alternatives.
Current shotguns don't seem to have a lot of oomph behind it besides their size. Yet there are options like making miniature discarding sabot rounds to pierce armor if necessary. Alternatively there already exist things like exploding shotgun rounds, basically miniature grenades, to either kill or disable the enemy with just a few hits. Since this is the future these rounds could be miniature shaped charge rounds, liquifying a bit of metal and launching it through the armor to pierce it and hit whatever or whoever is behind it.
If you are more humane, you could look into less-lethal rounds. From spraying the cabins and corridors with rubber bullets in the hopes of disabling the Colonists to more specialist rounds like small gas canisters with dibilitating gas concentrations or perhaps electrical rounds to taze the target (and again, full armor is likely not carried by colonists due to weight constraints).
[Answer]
**Small grenades.**
Since the combat is taking place inside confined, pressurized metal cans, any explosion does not have an outside to dissipate to. As long as the explosion isn't powerful enough to rupture the hull, the shockwaves will bounce around multiple times, making mush of the colonists. Their ceramic and kevlar armor will be completely useless against blast shockwaves. Your marines in sealed hard suits will be well protected though.
As witnessed in the london underground bombing, explosions in confined places are very, very dangerous. The primary damage comes from the shockwave, rupturing eardrums, lungs and gut. Secondary damage comes from flying shrapnel. A third source of damage is from hot gasses which won't readily dissipate in the enclosed space.
Blast injury in enclosed spaces - NCBI - NIH:
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC558684/>
Air blast injuries killed the crew of the submarine H.L. Hunley:
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5568114/>
"People exposed to explosions in a confined space have increased mortality, higher Injury Severity Scores, more primary blast injuries, and more extensive burn trauma." - Conventional Explosions and Blast Injuries
<https://www.sccm.org/getattachment/cc197ca2-fe84-47c0-b3ef-7d00abd6271b/Conventional-Explosions-and-Blast-Injuries>
Tear gas would also be very effective under these conditions.
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**Shaped charge.**
[](https://i.stack.imgur.com/yRxUW.png)
<https://en.wikipedia.org/wiki/Shaped_charge>
>
> A typical device consists of a solid cylinder of explosive with a
> metal-lined conical hollow in one end and a central detonator, array
> of detonators, or detonation wave guide at the other end. Explosive
> energy is released directly away from (normal to) the surface of an
> explosive, so shaping the explosive will concentrate the explosive
> energy in the void. If the hollow is properly shaped (usually
> conically), the enormous pressure generated by the detonation of the
> explosive drives the liner in the hollow cavity inward to collapse
> upon its central axis. The resulting collision forms and projects a
> high-velocity jet of metal particles forward along the axis...
>
>
>
Your armored marines are basically tanks. In our world, shaped charges are used (among other things) to cut through the armor of tanks. The hole produced does not cripple the machinery of the tank, but produces a jet of superheated metal particles on the interior that kills the crew.
A tank round is only a little bit larger than your 8 gauge shell. Shaped charges like this would be for fighting other similarly armored marines.
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Tazer Shotgun.
It was deemed non viable because of costs. But if you are fielding Space Boarding operatives, you are well past making the costs trivial.
[](https://i.stack.imgur.com/JxxHc.jpg)
You can render people safe, avoid over penetration, which is a huge deal on a ship. It also has 100ft of efective range, more than enough on tight ship rooms.
Bear in mind that if your own troops carry power armour, this could potentially disable it, but won't kill it.
Nice for reducing casualties among your own due to Friendly Fire.
Now if your opposition grabs one...it could lead to an interesting plot hook. Disable the invader, take their tech armour for your own side...
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Yet another question for this world: [Rail Transportation with Races Described Below - Specifically, Seating](https://worldbuilding.stackexchange.com/questions/190955/rail-transportation-with-races-described-below-specifically-seating)
One race specifically, the Phanerae.
They are 6-8 feet tall, and 250-300 pounds as adults. Females are slightly heavier, but shorter, than males due to a high level of hourglass figure.
They get this by way of a Second Puberty, which both sexes have and is basically a '[glow up](https://www.urbandictionary.com/define.php?term=Glow%20Up)' puberty. Phanerae have a First Puberty, which gets them ready for reproduction, from 10 to 13 years of age. The Second Puberty kicks in at 16 and ends at 20 years of age, which has them gaining muscle mass, height (a few spare inches), and some sexually attractive features, mostly in women gaining an hourglass shape.
***How and why would a species evolve a second puberty, which only sexualizes them?***
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As pointed out in the comments below the question, this isn't really different from human puberty.
**BUT**
If you explicity want this to be two separate processes, I would look at amphibians. Typically amphibians reach sexual maturity when they undergo metamorphosis from larval to adult form, as we see with frogs, for example.
There is, however, this guy, the axolotl:
Axolotls exhibit neoteny - as humans do - which means they reach sexual maturity while still in larval form. Many members of the Ambystoma genus are entirely neotenic species, which means they spend their entire life as larvae, and don't undergo metamorphosis.
Your species may have evolved in similar way, and your second puberty would be actually metamorphosis into adult form, while the first one would mean becoming sexually mature through neoteny.
You could even make it so that your species only undergoes metamorphosis through the wonders of medicine, if you wish, by receiving a shot with appropriate hormones. (lack of metamorphosis in Mexican axolotl, for example is caused by lack of thyrotropin).
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I'm trying to determine the evolutionary viability of a sentient race with "reversed" function of front and back limbs. Their front limbs would be used as legs primarily, and their back limbs for fine motoric movement and object manipulation.
[Dug race from Star Wars universe.](https://static.wikia.nocookie.net/aliens/images/3/3a/Dug.jpg/revision/latest/scale-to-width-down/340?cb=20100302041601)
[Art from the Monsters Inc. universe.](https://static01.nyt.com/images/2013/06/16/arts/16MONSTER_SPAN/16MONSTER_SPAN-superJumbo.jpg)
As per the examples, they would be built as follows:
* powerful arms at shoulder height, which function as legs and primary walking limbs.
* a body below or in line with its balancing point at shoulder height.
* motoric precise legs attached to the pelvic region, primarily used for handling of objects.
I wonder if these type of creatures could evolve into sentience and how how their race could survive in the first place. Also which kind of environment would allow (or even force) them to favour their back/lower limbs as primary motoric appendages, and their front limbs as their main transport ones.
In case of doubt, assume earth-like conditions where possible for ease of answering. With similar kinds of vegetation, resource availability and predation by hostile species.
I certainly have my own theories and will self-answer in time, but I would like to hear your thoughts for a more complete picture.
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I think if you're working with a completely alien ecosystem, you can get away with whatever you want, and, given we only have the single reference point, it's almost not worth speculating.
So I'll shift the focus a bit to the nearest situation I can think of on Earth: birds. Flighted birds use their forelimbs for locomotion (in a sense...) and their rear limbs (in some cases as least) for fine object manipulation.
So, in terms of ending up with something like a Star Wars Dug with a contemporary terrestrial starting point, I can imagine a situation where a bird population become isolated on an island habitat with no native predators, and, in common with a lot of real bird species in this situation, undergo insular gigantism and lose their capacity for flight. However, unlike a lot of existing flightless birds, whose wings tend to atrophy away over time, becoming more fully bipedal, this bird species begins to re-evolve a form of quadrupedal locomotion.
At first this is very clumsy, perhaps the birds shift some weight onto their "elbow" joints to allow them to keep a low profile, to sneak up on prey in tall grass, but over many generations, the wing starts become something much more like a leg. However, while birds typically have quite pronounced digits on their back limbs, the anatomy of the wing has the fourth and fifth digits completely atrophied away, and the first, second and third fused into a single wing bone. As a general rule of thumb, evolution seems to find it a lot easier to lose or fuse digits than it does to regain or de-fuse them, so the "foot" at the end of the forelimb is likely going to stay a much more simple structure than the foot on the back limbs. Perhaps the feathers will adapt or fuse in some way to create something along the lines of a horse-like single-toed hoof.
Fast forward a few million years, and a change of environment has pushed this lineage into a more arboreal setting. The front hoof has evolved into a hook for ease of climbing, but when this creature needs to use fine motor movements to peel a banana or deshell a nut it uses the bird-like talons on the end of its back legs.
Let's then say, further in the future, this little bird-monkey faces the same evolutionary pressures our own ancestors did, and is forced out of the trees and onto the open plain, and the same incentives for upright bipedalism apply. At this point, the wing-leg-hook-things begin to lengthen and strengthen, and the creature adopts a posture at first somewhat similar to great ape knuckle-walking, and then may eventually begin to keep its whole back half of its body lifted off the floor altogether, and carry its weight just on its "arms", and there you have it.
But, to go back to a completely alien environment, I think my only advice would be to acknowledge that the forelimbs really are the obvious default choice for throwing, carrying, manipulating, and all these sorts of fine movements, because it's easier to balance the weight on the back legs, the front limbs are closer to the face so easier to visually co-ordinate with, and so on, and so if you want to swap it around, make sure to have a good historical reason why the obvious benefits of the forelimbs won't apply to your alien.
[Answer]
* *"Which kind of environment would allow (or even force) them to favour their back/lower limbs as primary motoric appendages, and their front limbs as their main transport ones?*
There are ten thousand extant species on Earth which use their front limbs exclusively for locomotion and manipulate objects (when they manipulate objects) with their hind limbs.
They are called birds.
[](https://commons.wikimedia.org/wiki/File:Psittacus_erithacus_-perching_on_tray-8d.jpg)
*A grey parrot* ([Psittacus erithacus](https://en.wikipedia.org/wiki/Grey_parrot)) *demonstrating the versatility of its hind limbs. Photograph by [L. Miguel Bugallo Sánchez](https://commons.wikimedia.org/wiki/User:Lmbuga), available on Wikimedia under the GNU Free Documentation License, version 1.2 or later.*
## But the question is fundamentally wrong
The question shows a severe misunderstanding of how natural evolution works.
Evolution is never *forced* towards a solution. Evolution is never *determined* by the environment. All adaptationist explanations are by necessity *post hoc* -- we explain a certain characteristic of a species as a specific adaptation to a specific requirement, but we can never *predict* what adaptations will be acquired in any given environment.
This is because natural evolution is *blind*. It doesn't know what it is doing. It has no goal, other than trying to maximize the number of viable offspring produced by a population; and even in this limited goal, natural evolution cannot see beyond the immediate horizon.
So that nobody can say *"which kind"* of environment would lead to a bird-like situation, where the front limbs are specialized for locomotion and any object manipulation has to be performed with the hind limbs: *all we can say* is that at a certain point in the evolutionary history of the species the front limbs became specialized for locomotion (as did the wings of birds), and were thus unavailable to develop fine motor skills. If and when the species will develop fine motor skills it will *have to be* their hind limbs which acquire them -- exactly as parrots demostrate.
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Simply put as the title says. I'm going to handwave that the planet is held together with magic, but I want to know how a magnetic field would work on a toroidal planet- assuming such is even possible. Specifically, I want to know where a 3D compass would point based on where you are.
I see a few possibilities:
[](https://i.stack.imgur.com/7Pymw.png)
1. **Type A:** Standard ring magnet shape. I think that 3D compasses would point to an area in the center of the torus, but slightly lifted towards the North side.
2. **Type B:** The inner section is North, the outer section is South. I think it would point right at the planet's center of mass.
3. **Type C:** One half of the Torus is North, the other is south. Basically just a square bar magnet with a hole in it. It would point towards the inner side of the North side.
Are any of these impossible? (As in, would it likely collapse into no magnetic field, over the course of a few billion years? I dunno much about electromagnetism so I don't know what causes magnets to lose charge.)
Is my understanding of where a compass would point given your position, correct?
If you're in a Type B torus planet, I think if you're on the outer edge, your compass would point somewhere in space, repulsed by the south pole. Is this correct?
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I think your interpretations as to where a compass would point are correct, except for on the side of type B.
A tool that may help you, to know where a compass would point, are field lines (for magnets they are defined as the direction **opposite** to where a compass points) they are used in physics to help visualise a variety of [fields](https://en.wikipedia.org/wiki/Field_line) (including [magnetic fields](https://en.wikipedia.org/wiki/Magnetic_field#Visualization)).
A quick google gives images like those below (sorry about the sizes), the first image is what I think it would be like for type A, the second is for Type B...
[](https://i.stack.imgur.com/Fhp6B.jpg)
[](https://i.stack.imgur.com/ygpGH.jpg)
[](https://i.stack.imgur.com/PWGFu.jpg)
They confirm your compass predictions, except on the side of type B, at that point the compass points to the outer edge.
The theory of the earths magnetic field is that it is caused from currents circulating in the earths core, non of your types could be possible through this method of magnetism. But I think your planet could have two possible magnetic fields from this method, shown below (hopefully the image is clear enough). One has the compass always pointing around the torus, show in the upper image, where the orange line is the direction the compass would point. The other way is where the compass would point towards the edge on one side, and towards the centre on the other side, it is the lower image.
[](https://i.stack.imgur.com/jA8kC.jpg)
If you want the types of magnetic fields you give, you planet probably wont have a liquid core (ie no magma) and would have to have large quantity of magnetic minerals (like Magnetite), which are only magnetic when solid.
Hopefully that helps
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Our current model for the generation of magnetic field on Earth postulates that it is produced by the motion of the fluid iron-nickel core at the center of the planet.
Therefore just on the base of symmetry considerations, I would rule out types B and C, because they would not be fitting the circular symmetry of a torus, and whatever is producing the magnetic field has to be in the torus.
Moreover type B is even physically impossible, I think, as the two similar poles facing each other would not like that configuration and repel each other.
In configuration A I guess a compass would point somewhere along the central axis of the torus. For a more precise statement I would need physics knowledge which are beyond me.
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As it stated in the other comments magma fluid and rotation of the torus shape has huge efffects on the magnetic field. But in most likely cases the magma fluid inside the torus will not only rotate around its center, but also the fluid will rotate in the clyindrical core of the torus. This particular shape and type of flux will lead the magnetic poles to point a specific line on the torus instead of a point. I have found this website to illustrate a possible magnetic north line:
<https://guillaumecantin.pythonanywhere.com/hamiltonian/#simulationzone>
What you probably want to check the cases w1/w2 having an integer ratio to simplify. Non integer ratio of w1 and w2 would be hard to imagine. I have set w1=3, and w2=1 and obtained this results;
[](https://i.stack.imgur.com/Y0pIk.png)
Blue line represents a magnetic north pole line and you can imagine a magnetic south line that is phase shifted respectively.
How would a 3D compass work in this case?
This is not so easy to answer, unlike what we used to have in our planet, this magnet does not have a stationary north/south face but it has a direction flowing determined by the flow in the magma. When you are on the surface your compass will point a general direction towards to north pole line but when you are following you are not only walking in the cross section but moving clockwise (or counter-clockwise) on the torus.
[Answer]
Some factors to decide this are:
1-the torus has fluid magma inside.
2-the torus rotates (likely)
3- where there are heat differences within the torus.
This will determine the shape of magma movement, and convection cells within the torus.
If there is bulk rotation around the torus (or direct current running that way), then there will most likely be a field like example C.
This would be stronger near the hole and weaker on the outside, but following the compass north will lead you in a neat "small" circle. Going at right angles to magnetic North will take you on a "large" cirlce.
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Yet another odd question. Now, in one of my worlds, I am creating cultures for cats with human intelligence, but this question applies to essentially all quadrupeds. I wanted to introduce dancing into their culture, but this brought up the question, how would quadrupeds dance? Perhaps spinning little circles or intertwining tails, but I want more than that. I'm asking specifically for cats, who don't have much of a physical difference from cats in our world (Except mildly opposable thumbs, their shoulders are a bit more mobile, and they can stand on their haunches like bears), but feel free to broaden it for people asking this or similar in the future.
And, if you need the definition of dance, either "A series of movements that match the speed and rhythm of a piece of music." or, even better, "Dance, the movement of the body in a rhythmic way, usually to music and within a given space, for the purpose of expressing an idea or emotion, releasing energy, or simply taking delight in the movement itself."
We are not acknowledging the fact that real cats cannot 'sing' or make music, this is fiction, they can sing in any style they want and play instruments by my rules. It'd be off-topic anyway.
[Answer]
First, let's examine some dances that humans do but that cats probably can't:
* Body percussion: due to paw structure, cats likely can't clap or snap. Furthermore, their fur prevents using parts of their bodies as percussion instruments and their light weight makes stomping rather noiseless too unless they're on a prepared surface or wearing shoes. This lack of innate percussion rules out many beat/rhythm dances.
* Contract partner dancing: unless you anthropomorphize hard, cats walk on four limbs meaning they can't hold on to another partner while they dance. I don't think cats would find it comfortable to dance on two legs and hold on to a partner.
Now, let's look at some advantages cats have:
* A tail. I'm not sure how consciously cats can control their tails but it's definitely an extra appendage to work with
* Very flexible body: cat spines can make contortionists green with envy and allow many poses
* Good in-air control: Cats always land on their feet and can perform some pretty cool acrobatics. Maybe dancing involves leaping?
Finally, with advantages and disadvantages in mind, here are some dance scenarios I can think of:
* Group pattern dancing: Similar to what you'd see on a Broadway show stage, this style would involve many dancers (over 12) moving in synchronized movements. Cats would weave in and out of each other, form circular patterns, etc. This is typically a performance that cats go to see professionals perform.
* Classic dancing: One or more participants move smoothly and sinuously with carefully planned steps to smooth jazz-like music. Occasionally, explosive movements are included, but mostly this style is about graceful and purposeful movement. This is what cats might do for fun at a party.
* Romantic partner dancing: With a romantic partner, this dance is performed as a pair, often in courtship rituals. Individuals start far apart but slowly move closer to each other, eventually escalating to brushing past each other lightly. Maybe there's some "predator/prey" action thrown in where the dominant partner "pursues" the other, hearkening to the natural hunting instinct cats have.
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[Cats already can dance](https://images.app.goo.gl/uB81sU8NdrWSZMuJ9)
[](https://i.stack.imgur.com/TWc0x.png)
---
P.S. For more inspiration, search images for [*cat dance gif*](https://www.google.co.uk/search?q=cat+dance+gif&tbm=isch&ved=2ahUKEwjYh7jPucrsAhUO_IUKHQ_OBl0Q2-cCegQIABAA&oq=cat+dance+gif&gs_lcp=CgNpbWcQDFAAWABg-NFQaABwAHgAgAEAiAEAkgEAmAEAqgELZ3dzLXdpei1pbWc&sclient=img&ei=6qiSX9jqBY74lwSPnJvoBQ&bih=821&biw=1707&hl=en_GB)
[Answer]
They would be able to do social dancing like Scottish Country Dancing, Ceilidh dancing or Reels.
<https://youtu.be/eh3sFNPwafA>
Using their tails to connect with the other cats instead of taking hands would work perfectly well.
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In my fictional story I am playing with the idea of a sort of density gloves that can change density while keeping volume the same. Obviously you can punch people with diamond hard gloves with these things, but what are other uses? How dangerous are they to the people on the punching end? Since increased density increases the weight, how heavy can they get until they're inconvenient?
**The principal**
The gloves change density(magic, tech, biological whatnots, whatever works for your answer its pretty open) and can do it really quickly. More dense makes the glove heavier, less dense they get lighter, but volume always stays the same. Going across the spectrum from densest to least dense takes two seconds at most.
**Limits**
The most dense it can get is about three times the density of the densest element, at 70 grams in 1 cubic cm. The least dense(is there a better word for that?) it can get is 10^-20 grams per cubic cm.
More details can be added if you need them
Sort of a secondary question, but if two people have these gloves, what does a fight between them look like?
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**Ignoring the conservation of mass has physics-breaking implications.**
The biggest implication of these gloves is that you have an unlimited, free source of perpetual energy. Turn the density all the way down, and use an electric motor to lift the glove to some height. Now turn the density all the way up, and let the glove fall and charge a battery on its way down. You will harvest *more* energy than it took to lift the glove in the first place, meaning you have a truly limitless, renewable, clean source of energy! The amount of energy earned will be proportional to the ratio of upper and lower density limits, so you could turn 1 Joule of energy into 1020 joules in just one cycle.
Using these gloves to punch people would be an utter waste.
[Answer]
**They're as useful as any previous steel gauntlet**
I can't think of any reason why in combat you wouldn't always use the highest density you can physically throw. Anything less simply opens you up to getting the snot beaten out of you by your opponent. Worse, these gloves will amplify the advantages between people of varying strengths. Without the gloves, the two of you are fighting with more-or-less the same disadvantage (the strength of the hand's muscles and bones). But the stronger person can throw a higher density glove, which increases the advantage to them.
So long as the gloves remain pliable, the only disadvantage to using them in highest-possible-density mode all the time is the loss of tactile sensation. You could use them to pound in lengths of rebar (although a hammer would be easier).
To make a long story short, you're basically asking, "my world has access to steel gauntlets — why would you use them?"
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## You can stop bullets with them
[Newton's approximation for Impact Depth](https://en.wikipedia.org/wiki/Impact_depth) works as a good estimator of how far an impactor (like a bullet) will penetrate into a stationary target:
$$\frac{d\_{target}}{d\_{bullet}} \approx \frac{\rho\_{target}}{\rho\_{bullet}}$$
That is, the penetration depth ($d\_{target}$) is proportional to the ratio of the densities of the impact medium and the bullet.
A [5.56mm NATO](https://en.wikipedia.org/wiki/5.56%C3%9745mm_NATO) round is capable of penetrating 12mm of steel (density $8\ \mathrm{g\ cm^{-1}}$) at 100m. Its penetrating power in a material 8.75 times denser is therefore at least 1.3mm, but probably not substantially more. A completely reasonable 5mm thickness of material, therefore, should be able to absorb and dissipate the impact of modern military ammunition. You can literally catch bullets in your hands.
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The first thing to think of is the energy consumption. When you increase density without changing volume, you are (conceptually) compressing a solid. Compression on a solid or liquid is quite difficult-it changes the bonds and the interactions between the molecules of the solid. For reference, anthracite coal has a density of approx. 1.506 g/cm^3, while diamond has a density of about 3.5 g/cm^3. Often this will lead to crystallization or more ordered "stacking" of the molecules, but requires a massive amount of energy, which creates heat. In today's most common method of "densifying" a material, commercial lab-grown diamond presses must heat carbon to at least 1400 degrees C to cause it to reorder itself.
With a bit of handwavium you might be able to explain how the gloves can effectively melt and reform in their high density state, using fusion power and magnets to hold it all together. In reality though, wearing 1400 degree gloves would be slighly uncomfortable and, if you're a knight fighting a dragon with your wonder gloves, speed up the barbecuing process for your antagonist. Not to mention that the gloves must also have some source of extra material, possibly in a pocket dimension, to keep a relatively stable volume.
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The main issue of spin-gravity space habitats is that at some point the centrifugal force will overwhelm the tensile strength of the construction materials, even if perfect graphene were available. Thus, even the biggest spin habitats can't deliver more than a continents worth of living area per drum. One can of cause trade terrain features and gravity for more livable area, but even this has its limits.
Knowing that dynamically supporting a structure is usually the answer to get megastructures much bigger (think of atlas towers and dynamically supported orbital rings, which use [mass stream technology](https://www.orionsarm.com/eg-article/47e1bb1fc898c)), I was wondering if active support could be applied to Banks Orbitals and Ringworlds, which are usually considered impossible without unobtainium. Obviously, "materials" with high compressive strengths won't really help me here.
However the basic job of the spinning ring is to resist the centrifugal force. So what if we could compress the ring somehow to supply a counterforce. The main issue that arises from this is of cause that the friction between the ring, which will spin at hundreds of kilometers per second and basically anything, will have spectacular results. We would need a frictionless surface. For now, let's assume that the engineers got some kind of absolutely frictionless unobtainium coating. (maybe superconducting magnets could provide a frictionless interface?)
**The basic design of such a structure would be a spinning ring around a central source of gravity and an encasing, slowly counter-rotating support mass.** The support mass is well below its orbital velocity, thus it would fall down towards the gravity source. However, the spinning rings centrifugal force would balance out the forces.
I'm aware that the counter masses own gravity might become a problem at some point. At some point we might very well be dealing with a circumstellar donut planet, though I think the ring world would be the better bet from a construction materials point of view. I case the question comes up, where one would get the materials to build such a thing, this is pretty much per definition a K2+ project. So starlifting is on the table. And most of the support mass would most likely be metallic hydrogen stored in graphene and metal (what else to do with several planets worth of metals) containers.
The central object could be any of a number of options: a planet, gas-giant, star or black hole. It might very well be the power source of the whole structure, either a fuel depot, a Dyson Sphere or a Penrose Sphere.
**I such a structure fundamentally possible? Did I mess up the physics somewhere? Could magnets handle the pressures of the interface?**
[Answer]
Use an outer bearing ring that does not spin and is solid metal (or glass fibre - whatever's handy) with a superconducting inner surface (making stuff cold is cheap in space - possibly nitrogen filled heat-pipes from the inner surface to the shaded outer surface of the bearing.)
**Mag-lev** the spinning ring off the stationary ring.
The stationary ring can reduce the load on the the spinning ring in two ways.
By its own tensile strength which does not need to compensate for a spin it that does not have, and by its weight in the stellar gravity.
So in essence the spinning ring is a mag-lev train running inside an iron hoop. It could be thought of as an inverted mass-stream the spinning ring being the mass stream that keeps the stationary ring in tension.
As pointed out in *Ringworld Engineers* a method of station-keepeing is still needed, perhaps solar sails would be enough.
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I don't know if this will work; I haven't done ALL the maths, but my gut, mspaint, and the John Hopkins Uni Truss Simulator all suggest it'll work. So I'm presenting it; here goes:
[](https://i.stack.imgur.com/XPOam.png)
Underneath the buildings, is a large tube kept at vacuum (shown in grey), which has metal pellets (shown in red) running through it, with large coilguns (brown) applying force from the structure into the pellets. They can apply both positive and negative forces, which result in both compression and tension respectively.
Centrifugal force (acting as a sheer force on the "ground" members) goes through the truss, which is redirected to alternating compression (C) or tension (T) on the wall with the tube in it, of which the compression and tensions is absorbed into the pellet stream by either accelerating it or decelerating it.
This would need to be carefully monitored and dynamic, changing mass distribution within the ring could change the force distribution, which would need to be countered. Your morning commute could require different forces to correct than your evening commute. Humid conditions on one side may make one side heavier, which needs to be correct, etc. etc.
This would also be used to counter wobbles, vibrations, and help stabilise the spin speed to an exact day length.
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# Helium balloon.
Your scheme should work. The active support structure is spun the way you say, so that gravity and centrifugal force cancel out, with standard Ringworld attitude jets. We fill it with liquid [helium-4](https://en.wikipedia.org/wiki/Helium-4) (the common isotope) at 2K, i.e. a superfluid with no viscosity. Inside that, we erect a ring-shaped environment with zero buoyancy. No matter how fast it is spun, its weight is the same as that of the helium (barring relativistic mass considerations, but we have a ballast system to keep things adjusted precisely).
This *should* be entirely feasible with current technology and no exotic materials other than what are needed to keep the Ringworld cylinder from bending/breaking under a 1 g load. (Try not to overheat the helium, because then there would be ... a mass flow)
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A ringworld doesn't need a central object; in fact, a central object is a problem, because a ringworld is not stable w.r.t. a central object.
On the other hand, a ringworld with a 24-hour period (and no central object) could be built from existing materials and placed in a suitable L₄ or L₅ point (or some other stable orbit). Depending on the orientation, seasons would be odd.
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As @GOATNine said, there is no good answer as we could find some cool stuff in the future.
But the same argument has been made with FTL that "maybe in the future it is possible". And as with FTL, I would say structures of this scale are impossible.
It's kind of insane to think that something like this, even if you could build it, would survive even a day of operation. Not to mention that you need to make stuff up just to make it sort of maybe possible.
The main problem I see is just the amount of force that rests on the ring. It's quite simple and we don't even need fancy equations, you can't build something this long without any supports.
Of course, this is where your active support comes in, but it doesn't really solve the problem. The best I can see MAYBE working is a metric f\*ckton of other rings that each rotate a bit slower until either gravity or the amount of rings deal with the problem. So in a sense, you would have a few 100 rings or so resting on each other. Although the otter most rings would probably be more massive than the star itself.
But even this layered approach won't work too in any realistic scenario. I mean it probably could work if the outermost rings are 10.000km across and more massive than a black hole.
So in the end, as with everything, there might be a way to do it, but it's one of those "you really can't do that" way.
On a different node, if you write a story and really want a ring world, just make some material up that can support it. If you try to make it realistic people will get pissed. Nobody is going to blink an eye when you say "di-calinium is a meta material with the property that its tensile strength increases when an electric current flows through it". Does it make sense? No, but it's better than to try and force something that can work.
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**Yes, but it would be fail deadly**
Active support rings not in orbit can be suspended above black holes as put for by a crap ton of exotic-hard science fiction.
So yes
That being said, such a thing wouldn't be especially safe. Considering the scale of a bank's orbital such magnetically contained pellets and dust would be moving at a non negligible fraction of causality, and so carry a crap tone of energy. If the magnetic containment broke, you end up with a rail gun inside your habitat on top of a lack of support. Yikes. Not to mention the power required meaning you'd probably be better of with something passive, like solar panels in orbit around a star.
Or in other terms, yes, but such a structure would be fail deadly, even with some redundancy.
[Answer]
Here's one option that (spoilers) *doesn't* work:
1. Build a superconducting toroid.
2. Slowly add current and start spinning it.
The best we can do is a ~10T magnetic field. Let's see how far that gets us.
The pressure [works out to](https://en.wikipedia.org/wiki/Force_between_magnets#Force_between_two_nearby_magnetized_surfaces_of_area_A) B^2/2μ0, or [~40MPa](https://www.wolframalpha.com/input?i=%28%2810T%29%5E2%20*%20%2810%20cm%5E2%29%20%2F%20%282*%28Vacuum%20permeability%20%29%29%29%20%2F%20%2810cm%5E2%29%20in%20N%2Fm%5E2). How does that compare with mundane solutions?
Answer: terribly. The tensile strength of carbon nanotubes is in the 10-100 **G**Pa range.
[Answer]
Here's an option that outperforms mundane materials, but still isn't strong enough.
Consider a stacked series of thin plates of alternating electric charge. Now consider taking such a stack and bending it into a large ring.
The force between the plates of a capacitor is $$k\epsilon\_0 A \left(\frac{V}{d}\right)^2$$. So the pressure is then $$k\epsilon\_0 \left(\frac{V}{d}\right)^2$$.
Now, consider CCTO [ceramic](https://www.researchgate.net/publication/318595732_High_Breakdown_Field_CaCu3Ti4O12_Ceramics_Roles_of_the_Secondary_Phase_and_of_Sr_Doping/link/5977420f458515e26d2ce209/download). It has been manufactured with a dielectric constant of up to 10^5, and a breakdown voltage of 2.38GV/m. (Admittedly, not both at once yet.)
This works out to a corresponding max pressure of ~5TPa. (I'd take this number with a grain of salt - this is large enough that these approximations *will* come back to bite us.)
How does that compare with mundane solutions?
Answer: quite well. The tensile strength of carbon nanotubes is in the 10-100 **G**Pa range.
CCTO ceramic has a density of ~4.8g/cm^3. Stress on a thin rotating hoop producing $g$ acceleration is $T = \rho g R$, or $R \leq \frac{T}{\rho g}$. For 1g, this works out to a radius of ~[10^8m](https://www.wolframalpha.com/input?i=%2810%5E5%20*%20epsilon_0%20*%20%282.38GV%2Fm%29%5E2%29%20%2F%20%285g%2Fcm%5E3%29%20%2F%20%289.806m%2Fs%5E2%29). Still nowhere near enough for a ringworld, but better than maundane materials at least.
(That being said, you'd end up requiring a fair bit of energy to ensure that said capacitors remain topped up, and a single short could cause the entire megastructure to collapse...)
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**This question already has answers here**:
[Is it possible to kill all life on Earth?](/questions/147882/is-it-possible-to-kill-all-life-on-earth)
(21 answers)
Closed 3 years ago.
I need a completely empty Earth. I need:
* a natural phenomenon,
* some local or extraterrestrial disaster,
* some intentional human action or event,
to turn the entire Earth into second, world-sized Pompeii with:
* human population reduced to zero (obligatory) and
* Earth ground burned to the very ground, in ashes (optional).
There are three fundamental conditions:
1. Whatever comes into your mind or you propose -- be it meteor hit, COVID-19, giant volcano eruption, alien invasion or Earth orbit shift a bit closer (too close) to the Sun, it must be absolutely quick with no option for any surviving party to do anything (like in Pompeii).
2. Earth must remain as a whole planet, not destroyed, not split, allowing some future alien expedition to land on its surface, somewhere in the future, and examine it (like we do now in Pompeii).
3. At least some dead bodies and remains of buildings must remain and be able to examined (like in Pompeii).
Some additional information:
1. Poisonous gases, shifted gravity, high radiation etc. is all as an option, because alien race can survive it, as long as Earth remains possible to be landed and examined.
2. Whether some non-human live (like plants and animals) are reborn or whether Earth soil remains death for centuries after this cataclysm, is up to you.
3. The event that lead to apocalypse could happen any time in human history, but I'd prefer today or very-near-future with current level of technology existing on Earth at the moment of its devastation.
Once again, the ability for Earth to remain in one piece is a crucial and fundamental element of this question. From this perspective current question is an exact opposite of [this question](https://worldbuilding.stackexchange.com/q/73223/36).
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**Radiation:**
This may be a duplication. [Is it possible to kill all life on Earth?](https://worldbuilding.stackexchange.com/questions/147882/is-it-possible-to-kill-all-life-on-earth) although your question doesn't call for intent. Strange matter wouldn't work <https://en.wikipedia.org/wiki/Strangelet> , because I'm not 100% convinced it's anything more than a theory, and it wouldn't leave much of a planet afterwards. Supervolcanoes are great, but may leave survivors.
Any really big radiation event will kill all people, and possibly all life. A lot of these will kill living things, but leave all the infrastructure intact. A semi-near supernova is the most popular one, or a gamma ray burst, but my personal favorite is a passing pulsar that bathes the Earth in bands of killing radiation. The nice thing about that is that the diameter of the radioactive death stroke is such that the Earth could die, but other things in the solar system might (at least MIGHT) not be hit and thus survive.
You can mix this theme up a bit. Drag through a lot of the theoretical physics questions here, and many discuss things (sciency stuff) that would result in some kind of massive radioactive discharge - black hole formation/collapse, some kinds of matter manipulations, etc. An alien spaceship could explode in orbit. The sun could have some sort of giant flare event. The new infinite power source built in orbit opens a portal to the core of the sun and then won't shut, burning the Earth like a giant plasma gun until the thing finally melts. The list goes on and on.
If that's not enough broken windows, a massive impactor would cause so much damage that the Earth would be uninhabitable for centuries. <https://www.sciencemag.org/news/2017/07/what-it-would-take-kill-all-life-earth> This may leave a VERY small number of survivors unless it's so big it melts the crust - not a lot of buildings and bodies left.
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# ♡♡♡hole aliens
Say some aliens decide to launch [von Neumann probes](https://en.wikipedia.org/wiki/Self-replicating_spacecraft) into space. Unfortunately those aliens paid a code monkey to write the software for the probes.
[There is a videogame I used to play in the 90's which featured just such a theme:](https://wiki.uqm.stack.nl/Probe)
>
> The Slylandro purchased their first 2418-B: Remote Self-Replicating Robot Explorer Probe from the Melnorme for exploration purposes, with the intent to use it for making peaceful contact with other races. Since it had the ability to replicate itself, **they modified its program code so that replication became its overriding first priority.**
>
>
> The repercussions of this foolhardy action were grave. The probes not only attempted to break friendly ships into component pieces for use in replication, but also multiplied at a geometric rate, becoming a severe hazard to any HyperSpace traveler.
>
>
>
Should a self replicating probe programmed like that land on Earth, humanity would be screwed. If the probe is completely organic it may devastate all lifeforms while leaving most human structures relatively intact. Since the probes are not sentient, and don't necessarily contact base, the aliens might not even know they're destroying the Earth. Fast forward some millenia and they might learn of the problem when they finally come here in person.
[Answer]
# A close gamma ray burst aimed directly at earth
Copied from here:
<https://www.thoughtco.com/gamma-ray-burst-destroy-life-earth-3072521>
## What are Gamma-ray Bursts?
Gamma-ray bursts are giant explosions in distant galaxies that send out swarms of powerfully energetic gamma rays. Stars, supernovae and other objects in space radiate away their energy in various forms of light, including visible light, x-rays, gamma rays, radio waves, and neutrinos, to name a few. Gamma-ray bursts focus their energy onto a specific wavelength. As a result, they are some of the most powerful events in the universe, and the explosions that create them are quite bright in visible light, too.
## Standing in the Way of the Beam
A nearby gamma-ray burst, beamed directly at Earth, is pretty unlikely. However, if one did occur, the amount of damage would depend on how close the burst is. Assuming one occurs in the Milky Way galaxy, but very far away from our solar system, things might not be too bad. If it happens relatively nearby, then it depends on how much of the beam Earth intersects.
With the gamma-rays beamed directly at Earth, the radiation would destroy a significant portion of our atmosphere, specifically the ozone layer. The photons streaming from the burst would cause chemical reactions leading to photochemical smog. This would further deplete our protection from cosmic rays. Then there are the lethal doses of radiation that surface life would experience. The end result would be mass extinctions of most species of life on our planet.
### Note
This is possible, but very very very unlikely :)
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[Question]
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I know [color charge](https://en.wikipedia.org/wiki/Color_charge) has three types: red, green, and blue. There is also just one type of electric charge, with there being negative and positive electric charges.
I was thinking of a universe, in which there is a charge with a number of types that is greater than 3, known as A Charge. Equal amounts of all types of A Charge cancel each other out, to produce a system with 0 A Charge. Also all the types of A Charge are equivalent. In this universe relativity Special Relativity, and General Relativity apply. Also the Uncertainty Principle applies.
Could A Charge be self consistent?
[Answer]
Yes, it could be consistent.
For each of the fundamental forces, we have a certain conserved quantity, [which we refer to as a *charge*](https://en.wikipedia.org/wiki/Charge_(physics)). The [converse of a result called Noether's theorem](https://physics.stackexchange.com/q/24596/56299) tells us that in most cases, a conservation law leads to [something called a *symmetry*](https://en.wikipedia.org/wiki/Symmetry_(physics)#Continuous_symmetries)$^{\dagger}$, and each symmetry is associated with a mathematical structure called a symmetry group. If we were given a charge, then by studying the symmetry group associated with it, we could learn about the quantum field theoretic interactions that arise from it, and vice versa.
The fundamental forces have the following symmetry groups, respectively:
* **Electromagnetism:** The very simple unitary group $\text{U}(1)$
* **Strong nuclear force:** The more complicated special unitary group $\text{SU}(3)$
* **Weak nuclear force:** The special unitary group $\text{SU}(2)$
We can then learn something about the charges associated with the force and the bosons mediating its interactions. The number of distinct fundamental charges is given by the dimensions of the [irreducible representations](https://en.wikipedia.org/wiki/Irreducible_representation) of the symmetry group, and the number of bosons is given by the number of [generators](https://en.wikipedia.org/wiki/Generating_set_of_a_group) of the group.$^{\ddagger}$ $\text{SU}(2)$ has three [*generators*](https://en.wikipedia.org/wiki/Generating_set_of_a_group), and so we have three gauge bosons associated with the weak nuclear force: the $W^+$, $W^-$ and $Z$ bosons. Its representations are two-dimensional, and there are two charges associated with the weak force.
You've simply given us a new conservation law (which at a glance looks "nice" enough for us to be able to apply the converse of Noether's theorem), and therefore a new symmetry group. There's nothing prohibiting us from considering higher-dimensional groups (and as pregunton mentioned, we can go beyond unitary and special unitary groups) that would in turn be associated with new types of charge, giving us new bosons to play around with.
---
$^{\dagger}$ Noether's theorem itself says that any continuous symmetry has a corresponding conservation law.
$^{\ddagger}$ In particular, the group $\text{SU}(n)$ has $n^2-1$ generators and therefore $n^2-1$ bosons. The group $\text{U}(n)$ has $n^2$ generators and $n^2$ bosons.
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[Question]
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Assume my kaiju is around 200 feet tall, weighs around 4,000 US tonnes and resembles a large lobster with two giant claws for its front legs and long spindly limbs with tiny pincers on the ends for its second, the latter being the ones it'd use to carry a person.
[Answer]
If you are just relying on friction to hold the human against gravity (meaning nothing piercing in the human body to grapple it), you need to equate the weight of the human to the static friction between the creature's pincers surface and the human surface.
$m\_{human} \cdot g = F\_{pincers} \cdot \mu\_{static}$
From the above
$F\_{pincers} ={m\_{human} \cdot g \over \mu\_{static}}$
This means that depending on what the human is wearing the creature has to exert more or less force, which is intuitively what we experience when we try to grab a fish or a furry pet.
The pressure can be derived by dividing the calculated force by the contact area.
[Answer]
If the person is willing to be picked up, the pincers only needs to slide under the armpits and lift the person like a fork lift. This means the only presure the person should experience would be from thier own body pressing down on the pincer from gravity.
If the person is unwilling there is no exact equation for this since humans will vary so much in strength and escape techniques, but a person can generally be grappled with much less force than it takes to crush them, so your kaiju should be able to intuitively apply the right amount of force for the resistance the person gives the same way a parent only holds a child as hard as they need to based on how much the kid does not want to get in the bath.
Either way, once you lift the person more than a few feet off the ground, they will generally be doing more to hold onto the kaiju, than the kaiju needs to do to hold on to them.
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So, when it comes to humanoid races, this has been a problem for me for quite some time. Sure, mammals (werewolves, gnolls, minotaurs, centaurs) are a no-brainer. I even decided to give tengu something. Though fairly small and don't have to be censored, as they are just two round sacs that produce and store milk, which is regurgitated (read vomited) straight into the beaks of tengu hatchlings by default. Yes, I'm gonna work on that later, but not now.
However, I won't lizard boobs, just no! The reasons are a bit complicated. I don't want to blame it all on Bethesda, but Skyrim certainly didn't help. Also, stop saying that argonians look ugly, it's only because the devs went for the *"everything is so bleak and gray I'm surprised players didn't kill themselves after subjecting their eyes to this audio-visual terror with space-time anomalies sprinkled in for five minutes"* design. I mean, where are all the toilets and my Dagoth Ur anyway?
But, what are my lizardfolk exactly? Well, there are three subspecies, two of which are fairly humanoid:
* **Crocodile Folk:** The largest, strongest, slightly less-bright. They have very strong jaws and a soft-spot for watermelons and wrestling, with a suitable endomorph body type.
* **Asian Water Monitor Folk:** The most intelligent, quirky, and "balanced" of the three. They actually have venom, even if it's fairly unimpressive. Their build is mesomorph.
* **Legless Lizardfolk:** Also called serpent men, incorrectly, but simply looking at the shape of their heads (plus that they can blink) should tell you that. They love to climb various pillars and hang from piping and branches. Thanks to their size, they can break an adult human's ribs via constriction, just like vipers (see pic related) in Xcom 2. No, they don't have "venom glands". Upper-body is of the ectomorph type.
[](https://i.stack.imgur.com/KqVK2.png)
Okay, back to the task at hand. **What visual feature would allow for the quick identification of a lizardfolk's sex?** The inspirations for these three have very little sexual dimorphism and I want to stick to the original design principles where possible. I did remove the double trouble for males as they and their partners shouldn't have problems repositioning with their body plan. Other than that, I want to avoid changing stuff.
[Answer]
Most female reptiles lack secondary sexual dimorphic features in general. It is often very difficult to sex reptiles in captivity without physically checking their cloaca, and a lot of times individuals will be just assumed to be male or female based on overall size or other features. In the vast majority of reptiles there are no obvious differences between the sexes other than their reproductive organs, which are usually housed internally most of the time.
In general, in most animals it is the **males** that are more brightly colored, "ostentatious", and are generally the ones who have "extra" external features (i.e., the dewlaps of *Anolis*, the large crests of *Basiliscus*, and the ghara of *Gavialis*, all of which are only in males). Humans are kind of oddballs among animals in that in humans it is the female that has exaggerated secondary sexual features (enlarged breasts, a more distinct sillhouete due to narrower shoulders and wider hips, long hair in many cultures) and the male is more boring and drab looking.
So honestly your female lizardfolk are probably going to be pretty boring-looking, and it is the males that will have weird extra features, if any.
[Answer]
**Bow**
[](https://i.stack.imgur.com/uGZ6A.png)
Figure 1: two snake people. The one on the left is the boy snake. The one on the right is the girl snake. Can you see the difference?
It's the bow you see -- the girl snake has a bow in her hair.
Wait, snakes don't have hair. . . .
[Answer]
The males and females could have traits of different species (i.e. male legless look like snakes, female legless look like geckos). They are already diverse, so this should fit into the design
[Answer]
**They Smell Different**
Lizards are hard to sex just by looking at them. This is even true if you are a lizard yourself. Instead they rely on other senses such as smell to tell what genitals the other lizard has.
Now humans have generally worse senses than other animals. So it's believable that as your lizards turned into lizard people, their senses dwindled too. That means to compensate the smelly man/woman lizard smell had to get stronger.
It eventually got strong enough that humans could smell the smelly man/woman smell.
[Answer]
Yeah, this presents a bit of a problem. Fortunately, it's one that can be fixed by having them borrow one particular trait from other species;
**BRIGHT COLORATION**
Basically, you make one gender of the lizardfolk in the story have bright plumage and a frill that can open up on que. In the distant past, this served 2 evolutionary purposes; to attract a mate, and to intimidate potential threats into backing down. Naturally, modern lizardfolk don't really have as much of a need for either, but that hasn't stopped those things from sticking around.
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Space explorers have landed on an Earth like planet and, to their surprise, the place is luscious and covered in life, to the point of resembling some earthly tropical atoll.
What they don't know yet is that the entire biochemistry of the planet they are exploring has opposite chirality with respect to theirs.
Once you have a polarimeter, measuring the chirality of certain molecules is a rather easy task.
Is there any way for them to detect or at least suspect that something is odd with the local chirality, before they measure samples with a polarimeter?
To be clear, I prefer something empirical. For example to observe if a substance is fatty, one can simply spread it on a surface and observe how water interacts with it, without needing any more complex instrument.
Among the exploring crew there is a biologist and a chemist.
[Answer]
This is tricky because to some degree it requires the crew to expect the local biochemistry to present one way and know to be confused when it doesn't.
An alien landing in an orange grove wouldn't know what to expect oranges to smell like, for example, let alone wonder why they don't smell like lemons. The molecule responsible for the smell of oranges and lemons is chiral; limonene is R-enantiomer in oranges and S-enantiomer in lemons.
Likewise there are pharmaceuticals (90% of pharmaceuticals are chiral) in which one arrangement is beneficial and [the other toxic](https://www.chemistryworld.com/features/detecting-chirality/7566.article#/):
>
> Citalopram, an antidepressant, is produced as a racemic mixture, but only the (S)-(+) enantiomer is responsible for its beneficial effects. The drug d-penicillamine can treat rheumatoid arthritis, but l-penicillamine is toxic.
>
>
>
We couldn't expect either reaction when taking an unlabelled pill, let alone suspect chirality is behind the results. Similarly your explorers wouldn't know what to expect of the local organic biochemistry.
There are ways to observe [chirality at the macroscopic level](https://www.nature.com/articles/s42004-017-0003-x) without a polarimeter:
>
> The chiral signals of the d- or l-Trp residues are seeded into poly(acrylamide) (pAAm)-based hydrogels (d- or l-Trp(x)-gels), in which the chirality is successfully transferred and amplified to the macroscopic scale. The interactions between the pAAm-gel bearing βCD moieties (βCD-gel) and the d-Trp(x)-gel and L-Trp(x)-gel are investigated in aqueous solutions with different components. Under appropriate conditions, such as in aqueous NaCl, the βCD-gel can successfully discriminate the d-Trp(x)-gel from l-Trp(x)-gel on a macroscopic scale by amplifying enantioselective host–guest recognition through interfacial multisite interactions.
>
>
>
But again your explorers would already have to suspect chirality to perform this test or one like it.
[Answer]
**Introduction**
With my answer I wanted to go into a directly observable clue if you know the physics behind circular polarised light and bragg reflectors. However while you can make this to work for expecting chirality, I haven't found a way to directly suspect different chirality without using an external light source. So I have added two answer, one regarding alien ants and a second extensive one giving my thought on how you might be able to get a visual distinctive clue about strange chirality.
## Answer 1 (Alien Ants Behaving Strangely)
So your explorers are enjoying lunch and a cup of coffee during their lunch break whilst exploring. But even on alien worlds you can't have a picnic without ants (or whatever passes for ants on this world) showing up and trying to grab some food. However these ants only seem interested in the artifical sugar (Tagtose) used by one of your explorers instead of the normal crystaline sugar. It would seem quite weird after a while a small stream of insects carrying away your artificial sugar just past your sugar cubes.
The reason is that (as pointed out in the comments) chirality can matter a lot in nature and affect smell, taste, toxicity and other things. The insects pick up on this nature and since cyrstaline sugar is left oriented (most often combination of D-glucose and D-fructose I think) while the artifical sweetner is right oriented. Disclamair, I am physicist not a chemist or food scientist so I can have it completely wrong but I just gave two examples but there are many more to choose from. Some lactose are right oriented and most sugar have a right oriented enantiomer. I think fruit sugar (levilose) is one, however here I am not certain if the molecular chirality and the optical rotation properties match. Depending on your story and how strict quarantine rules are you can of course setup a single experiment to see how the local wildlife interacts with your food and come to the same conclusion without taking off your hazmat suit in an alien environment.
## Answer 2 (Circular Polarized Structural Color)
**The big polarimeter**
So instead of the molecular chirality you want to measure the optical rotational polarity and get out your big polarimeter. It might turn out not to be so big, [Ultrathin, flat lens resolves chirality and color](https://www.seas.harvard.edu/news/2016/06/ultrathin-flat-lens-resolves-chirality-and-color). So with this lens you can easily image the chirality of the exoskeleton of a beetle as shown in the paper.
[](https://i.stack.imgur.com/bKa8N.jpg)
*Fig 1: Chirality of the exoskeleton of a beetle. Image source: M. Khorasaninejad et al.: Multispectral Chiral Imaging with a Metalens, Nano Lett., online 07 June 2016; DOI: 10.1021/acs.nanolett.6b01897*
**Detecting "Opposite" Chirality**
With a little bit of tuning your world you might be able to check for chirality and even suspect that it is opposite from what you would expect. *I will assume here that the rotational polarization direction and chirality are one and the same.*
So as seen with the beetle a bunch of insects have chirality based on structural optics. One of the most beautiful and easily observed examples is with butterfly wings shown in Fig 2a, where the the right wing was saturated with alcohol. Fig 2b and 2c show the TEM cross-section of the wings.
[](https://i.stack.imgur.com/Q5Gcf.png)
*Fig 2. Structural color in a butterfly. Image Source: M. Sc. Christoph Fenzl, et al.:Photonic Crystals for Chemical Sensing and Biosensing; DOI:10.1002/anie.201307828*
The color change in this case is based on an expansion of the structure of the wing which influence the reflection of light due to a change in layer thickness of a Bragg reflector. A Bragg reflector, reflects or transmits light based on the interference pattern created by the controlled layer thickness, see:[Dielectric mirror](https://en.wikipedia.org/wiki/Dielectric_mirror) and [Fiber Bragg grating](https://en.wikipedia.org/wiki/Dielectric_mirror).
Similar in nature polarization of light is used, again an example of this in butterflies is swhon in Fig 3a and 3b, where the butterfly in 3a does not exhibit polarization and the butterfly in 3b does. The blue color denotes no specific polarization direction while green and red denote a specific polarization.
[](https://i.stack.imgur.com/iwsaj.jpg)
*Fig 3: Two butterfly species. Image Source: Jonathan M. Douglas, et al.; Light habitats and the role of polarized iridescence in the sensory ecology of neotropical nymphalid butterflies (Lepidoptera: Nymphalidae), DOI:10.1242/jeb.02713*
So combining circular polarization with a bragg reflector would allow for species to change the color of their wings if they can expand the lattice strucutre (or if somebody scientist pours alcohol on it, (ohh the ethics of those scientist)). That light can further more be circular polarized and in this case due to the chirality of the creatures make up, it would have right-handed circular polarization as opposed to the expected left-handed circular polarization one would expect.
**How to detect the different circular polarization direction**
So it is easy to see structural color (it looks colorfull) and to determine it is indeed structural by pouring alcohol over it. It is easy to detect linear polarization, just look through your polaroid sunglasses, turn them 90 degrees and look again. If the polarization axis are aligned with your glasses the butterfly wings should turn from looking normal to completely black. If you look at circular polarized light through linear polaroid sunglasses the intensity would simple half irrelevant of direction, making it distinguishable from linear polarized light but not from un-polarized light (which would also half). This is where some story telling should come in.
Either for some reason you have circular polarized sunglasses of which you know the polarization direction. Knowing or deducing the polarization direction should not be hard if you know the material of which it is made. Or you have a device which emits circular polarized light. This second option might not be as far fetched as you think. You will have devices with displays emitting light, if you have use circular polarized LCD screens instead of the old fashion mostly currently used linear polarized LCD screens ([example of lineary polarized screen through polaroid sunglasses](https://www.quora.com/Is-the-light-of-a-computer-screen-linearly-or-circularly-polarized)) you have a circular light emitter. A butterfly landing on the screen will suddenly become black if the polarization direction is different, if polarization is in the structural color part of the wings it might be arranged such that it will suddenly change color. The scientist trying to explain the darkening and color shift of this beautiful butterfly that has landed on their laptop might let them think about the polarization direction and thus the chirality. Presumably the direction of the color shift and knowing the circular polarization direction of the screen might lead you to suspect a different polarization orrientation than you would have expected.
**Additional stuff**
Sorry for the long winded answer but I wanted to explain an at least feasible optical solution. Here some extra material if you really want a rigorous physics calculation:
* With the Law of Malus you can calculate the intensity through a single polarizer.
* You can calculate stacked polarized transmission with [Jones Calculus](https://en.wikipedia.org/wiki/Jones_calculus) to see how circular polarized butterfly wings would behave with certain polarizers.
* With [gratings](https://en.wikipedia.org/wiki/Diffraction_grating) you can calculate color divergence.
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[Question]
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In the large pillar forests of planet x, a group of vertebrates, in order to hunt down the fast climbing creatures that inhabit their habitat, rather than developing speed as well, went on another evolutionary path than its fellow vertebrates: they became ambush predators, making use of 2 (or more) spinneret organs to shoot silk at its prey, much like some [gnaphosid spiders](https://www.google.com/amp/s/api.nationalgeographic.com/distribution/public/amp/news/2017/06/science-animals-ground-spider-shooting-silk-discovery), with the main difference that their silk is adapted to temporarily affix prey to the surfaces they're clinging on. At times, this group cocoons prey as well, for storaging food during winter.
Now, what would be the most effective location for such spinnerets? If it weaved like a spider I'd go for the rear, but the fact that it uses them almost as guns tells me they should be somewhere closer to the head, maybe even inside the mouth. The closest fiction example I have is, well, Toby's version of spiderman. What would be the most efficient positioning? Could such organs develop naturally in a vertebrate (and not like the transgenic goat wigh spider milk type of developing) to begin with?
NOTE: the creatures are the size of an average Pitbull, are arboreal and quadrupedal.
[Answer]
TL;DR - jaw muscles are likely required.
What distance does the jet need to travel and what nozzle speed does it need? Let's assume a 10m distance to the target (shorter than that and the pitbull-sized ambush predator is better off with a fang-and-claw physical attack) and we want the jet to reach the target in 250ms - longer than that and the prey has enough time to take a jump outside the targeted area. So, muzzle velocity at 40m/s.
We'll assume and ideal (non-viscous) sticky liquid and apply the Bernoulli law: $\frac{p}{\rho} + \frac{v^2}{2} + g\cdot z = ct$
Assume the speed of the sticky inside the reservoir at 0 (happens only if the cross-section of the reservoir is much larger than the muzzle) and out of the muzzle the liquid pressure drops to 0. We'll also assume a density of the liquid to be that of water 1000$\frac{kg}{m^3}$ and try to compute what pressure needs to be created inside the liquid reservoir to achieve that.
$$\frac{p\_{res}}{\rho} = \frac{v^2\_{muzzle}}{2} \xrightarrow{} p\_{res} = 1000 \cdot \frac{40^2}{2} Pa \xrightarrow{} p\_{res} = 800000 Pa = 7.895 atm$$
Probably we'll need to double that due to viscosity and the friction at the muzzle, but that's plausibly achievable *by strong muscles*.
This "strong muscles" requirement is reinforced by considerations on the power they need to deliver.
The energy consumption will depend on the amount of liquid projected. At a pitbull-size animal will weight about 15-35kg (let's take 25kg as the average) and will hunt prey in the 10-20% of his body weight - something like a turkey maybe? I can't see immobilizing such a prey with less than 0.5litres of goo.
I'll assume the total purge of the goo need to happen in another 200ms. The kinetic energy of projecting 0.5kg at 40m/s is 10kJ - *which means a required power of 50kW*. If you ride a gym bicycle, you'll know how it feels to generate 200W of power by the long muscles in you legs.
Fortunately for this case this power needs not to be sustainably delivered, but explosively. Nevertheless, the muscles should be strong *and short* to pull such feat in 0.2s.
One on top of the other, I would go for the jaw muscles - short and strong enough.
[Answer]
**Paired glands at the sides of the head.**
1. These glands could rationally have evolved from salivary glands. Mammals have several types and can spare one to produce sticky goo. Goo would be kept in some reservoir prior to shooting.
2. Mammals aim using the eyes. Glands close to the eyes would follow a path from eyes to target.
3. Glands to the side of and under the eyes would not foul the eyes, ears, nose or mouth if they dribble.
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In my setting there is a tidal island fortress similar to [Mont-Saint-Michel](https://en.m.wikipedia.org/wiki/Mont-Saint-Michel) that is the refuge of important nobility and is therefore a target for an invading army. The fortress also has a library containing an extremely valuable manuscript that the invading king absolutely *must* have. So there is motivation for besieging such a place.
**The Defenses**
The tide is strong and makes the fortress an island during high-tide and leaves behind a treacherous mudflat at low tide that is very difficult for men to walk on and is impossible for any cart or horse to cross. The water is too shallow for large ships, but shallow draft boats and rafts can cross.
A talus wall and glacis encircle the island and provide resistance to cannon fire. There is a secondary wall further up the island and a castle keep.
**Defenders Resources**
The Island has freshwater wells and several large gardens along with significant food storage space. The defenders have a well trained garrison of 200 men equipped with crossbows, polearms, swords, matchlocks, cannons and even a primitive volley gun
**Attackers**
The attackers are several thousand strong and at a 14th century European level, and can do any tactic that you believe would work. No magic allowed
So how could an army with 14th century technology capture a well defended tidal island?
[Answer]
**Dispute the mastery of the Empire.**
[Sun Tzu lays it out](https://www.marxists.org/reference/archive/sun-tzu/works/art-of-war/ch03.htm)
>
> 4. The rule is, not to besiege walled cities if it can possibly be avoided. The preparation of mantlets, movable shelters, and various
> implements of war, will take up three whole months; and the piling up
> of mounds over against the walls will take three months more.
> 5. The general, unable to control his irritation, will launch his men to the assault like swarming ants, with the result that one-third of
> his men are slain, while the town still remains untaken. Such are the
> disastrous effects of a siege.
> 6. Therefore the skillful leader subdues the enemy's troops without any fighting; he captures their cities without laying siege to them;
> he overthrows their kingdom without lengthy operations in the field.
> 7. With his forces intact he will dispute the mastery of the Empire, and thus, without losing a man, his triumph will be complete. This is
> the method of attacking by stratagem.
>
>
>
You do not attack the island fortress. You capture (or threaten, or don't) the rest of the territory and wait. The nobility are not nobility of this island. They have holdings on the mainland. Probably they do not know what is going on there. Probably they are worried and would like to go home, where the servant to nobility ratio is more favorable.
Tell them your version of what is going on. Send an emissary to the island. The emissary will explain that his master (you) wants the contents of the library and select other items from the treasury. He would rather not anyone get hurt. If a noble would like to bring some of the described items out, his master will show his appreciation by allowing that noble(s) safe return to his lands, which will not be attacked. After 3 days, any nobles still in the refuge will have their lands attacked and confiscated. Nobles still in the refuge may remain there.
The nobles want their lands because that is their wealth. They have no interest in the stuff in this refuge which is not even theirs. Why shouldn't they hand it over for safe passage home?
[Answer]
Biological weapons
Anthrax infections [from direct contact are rare](https://en.wikipedia.org/wiki/Anthrax#Mode_of_infection), however infections by contact with blood/organs of an infected organism are likely.
So, procure anthrax infected sheep and catapult them over the wall to make a big splat on the other side. Keep doing it for a while.
Add [brucellosis](https://en.wikipedia.org/wiki/Brucellosis) - not fatal but wasting, also require contact with the fluids from infected animals.
[Answer]
Two solutions: long one, depending of the qualifications of the attacking army, of strategic situation and of how you much is "several thousands", is to build a reinforced building from the coast to the island. This building could a floating bridge or an actual bridge, only built while the tide is low.
Short one could be to use some specific weapons or siege technics, like exploding powder, to destroy part of the walls in a short time. Then, before the defenders could reinforce the breach (for example at next tide), the attacking army rush in and fight until the death of 200 defenders. With a ten to one or more ratio, it would be an easy task.
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I want to write a science-based story which includes grey aliens.
To clarify, grey aliens are seen to be either shorter or taller than the average humans, and sport a bulbous like head. their head has two big black eyes and have two smaller holes that are the nostrils. Lastly, the body of the aliens seem to be fairly slender, and has the common color of grey
**what environmental requirements would be needed to lead to the rise of grey aliens?**
[Answer]
**Yes it is possible there are Grey Aliens, but the funny thing is that chance of it being like humans but grey is quite narrow to be almost impossible**
We don't know what life would really be like on other worlds as we have not detected any, so using Earth as an example is the only basis we have to formulate evolutionary theories.
Life on Earth could go in any number of directions, and has been evolving since [aBiogenesis](https://en.wikipedia.org/wiki/Abiogenesis) about **4 billion years ago**.
In this enormous time there were billions upon billions of generations, [mutating](https://en.wikipedia.org/wiki/Mutation) every step of the way, to create the [very complex genome](https://en.wikipedia.org/wiki/Human_genome) humans have today.
At any point in time though, it is worth remembering that a mutation could have evolved in a different way, with equal amounts of success and spawning a completely different evolutionary pathway.
There is a reason why all animals we see have 2 eyes, four limbs, and a spine. This was determined many millions of years ago right back to a series of mutations that (essentially quite randomly) created these features. All animal life since then would then have these traits. That's why we don't see horses with two heads, or rats with three eyes, or cats with only one nostril.
These traits evolved very recently in the history of life, within the range of [400 million years past](https://en.wikipedia.org/wiki/Cambrian_explosion) (within a 4 billion year history) being just the last 7% of the history of life.
So for your aliens to be like us, but just grey, **then billions upon billions of mutations must have turned out to be even a little like us** except for being grey. Highly unlikely (dare I say, almost impossible). So in order to answer your second question, the environmental requirements that would lead to grey aliens that have a head, 2 eyes, 2 nostrils, would **need to be almost precisely Earth** (except the minor condition where a grey skin is more advantageous, perhaps they live in underground areas where skin pigmentation is not necessary, or simply grey skin is more sexually attractive).
The truth is we don't know, but all I can say is the chance of meeting an animal with bilateral symmetry, four limbs, two eyes, two nostrils and even an animal with skin, or an animal of similar size to us, would be quite a revelation in itself.
[Answer]
The Greys are based on late 19th / early 20th century predictions of what humans will look like in the distant future. The only weird bit is the color. As it turns out, there is a way to get a greyish tinge to one's skin: [Argyria](http://en.wikipedia.org/wiki/argyria), what happens when one consumes a great deal of silver over time. The silver settles in the argyrian's skin, where it tarnishes. The precise color that results depends on things like the original skin color, the concentration of silver, exposure to other substances, etc (I'm not sure if sun exposure matters, but I assume it would have *some* effect).
Why would aliens who are otherwise indistinguishable from far-future humans consume so much silver as to turn grey? People today drink colloidal silver for its antibacterial properties, and probably some other reasons. Silver has culturally been associated with purity, toxicity to monsters, etc. And it is rare, if less so than gold. Any combination of these with culture, abundances of substances in the Greys' habitats, or even just some kinda space disease that only silver can cure being common among the Greys who show up, could all play into the explanation.
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Concerning the grey-ness I'd say that this might an adaptive colour which makes them less identfiable by predators, i.e. it is more about camouflage.
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They are grey because they travel in an ship full of embryonic fluids that maintain and vitalize them during travel. Because they spend so much time in the fluid, emerging into an oxygen/air atmosphere it takes time for them to re-pink.
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essentially the same as us. They would fill the same niche as ours, and would have similar adaptations. Having a bulbous head could evolve from spending a lot of effort doing advanced thought, which requires a larger or better brain. The grayness could stem from camouflage coloring, or sexual selection, although it is most likely that they could just be that color. Humans have multiple skin colors, and it seems fairly obvious that there is no real advantage to any skin color in humans and other humanoids. Nose holes could just be a leftover trait from their ape analogues, or they could be better placed for smellings. in any case, like skin color, nose placement does not really have a major influence on humanoids, since we do not use it that much. large black eyes could be an adaptation for darker conditions, or could evolve with the brain or something. large investment into eyes is not to outlandish for a humanoid since we are primary visual hunters. A slender body could be explained away, maybe if they are at our level or later everyone could be trying to get a skinny bod.
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[Question]
[
I'm currently working on devising a magic system in which all the standard laws of physics are upheld (Conservation of mass/energy, thermodynamics/entropy, and more).
**'Powering' the Spell:**
To keep it brief, my magic system allows spellcasters to convert one state or type of energy to another and project that energy outside of their own bodies. A typical spellcaster would fuel their spell using the chemical energy from their bodies/muscles (ATP). "Forms of energy" or "Types of energy" include classical energy types like Mechanical, Electrical, Magnetic, Gravitational, Chemical, Nuclear, Radiant, Thermal, etc.
After a spellcaster has chosen an energy source, they can begin to "channel" the spell at a specific rate. Doing so expends energy (Joules, Kilocalories) and happens at a specific power, or rate of energy expenditure (Watts). How much power a spellcaster can channel from their physical bodies is [shown in the graph here.](https://i.stack.imgur.com/100Lcl.png)
For example, if my spellcaster is super fit and is going "all out" they'd be able to channel ~2000 Watts for three seconds before they collapse from exhaustion.
**'Casting' the Spell**
Once the spellcaster has harvested some energy, they can convert this to any other type of energy. Where and how this energy manifests itself is up to the spellcaster however its power decreases roughly with the inverse square of the distance to the spellcaster. Additionally, the energy can't manifest itself directly inside mana-rich regions such as other creatures (this prevents pinch-the-brainstem style attacks).
The form this energy can take is diverse and primarily limited by the spellcaster's understanding of reality/physics. This means to cast a spell which draws upon Nuclear power or other more advanced power sources requires an intimate understanding of how it exactly works.
**The question: How would combat look with this magic system?**
More specifically, what method would spellcasters use to attack others (spellcasters and non-spellcasters alike) while expending as little energy and power as possible?
Examples of spells:
* Applying kinetic energy to small projectiles and building up their speed by orbiting them around the spellcaster until releasing them at a target
* Generating a "laser beam" or bright beam of intense light to blind or stun opponents
* Electric shocks on skin contact to stun attackers
[Answer]
**Blow their eardrums out**
The loudest noises people can handle ["only translates to about a hundredth of a watt per square meter"](https://engineering.mit.edu/engage/ask-an-engineer/can-sound-be-converted-to-useful-energy/). So have your mage pick out the 3 square centimeters immediately adjacent to your enemy's ear and blast them with the loudest sound anyone has ever heard. Guaranteed they'll be disoriented and hopefully rendered unconscious.
**Bonus** Apparently it only takes [200 db to kill someone](https://www.extremetech.com/extreme/175996-can-a-loud-enough-sound-kill-you), and sounds at [165 db are loud enough to ignite your hair](https://science.sciencemag.org/content/278/5346/2060).
[Answer]
**Set the air on fire**
The specific heat capacity of air is 1.00 kJ/Kg. 1 Liter of air weighs approximately 1.225 g. Therefore it costs 1.225 Joules to raise 1 liter of air 1 degree Celsius. Assuming you have 6000 Joules to play with (2000 J/s \* 3 seconds) you should be able to easily raise the temperature of the air directly in front of your opponent's face to super high levels either burning their respiratory passage, eyes, or face.
[Answer]
**Administer a poison**
It takes approximately [0.0000001g of Botulinum toxin to kill a human](http://theconversation.com/handle-with-care-the-worlds-five-deadliest-poisons-56089). Have your mage carry around a pouch of this, or something similarly toxic and float a tiny quantity of it into their opponent's face where they'll either inhale it or swallow it. This may not be the most fast acting poison though, so more suited to assassinations, but you could use a more immediately debilitating posion if you're engaged in combat.
[Answer]
## Magic gun time!
I'm imagining something similar to a rifle, except that instead of a chemical detonation, the wizard produces a magical one. Seems simple and straightforward enough that it could be used quite broadly without years and years of training. As for fuel, as far as I understand, the wizard would just need to carry a pouch of pig fat or mashed potatoes and consume the chemical energy of that to fuel the magical detonation, instead of their own ATP.
Also allows your wizards to shout out "I cast bullet!" before blasting somebody's head off, which would be quite entertaining.
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I think by description the most efficient way of combat is physical damage to specific vulnerable parts of human anatomy.
Such as, aiming for the neck and trying to damage either breathing tube or blood vessels or spine. Or aiming for eyes.
Can it bypass armor, such as, can mages apply this energy to places which are not geometrically reachable? If it can't, the cold iron will still rule. In this case, go for the horse (eyes or ears). Against a prepared melee fighter, this can be a problem.
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[
A [recent question](https://worldbuilding.stackexchange.com/q/164203/62241) here on SE:WB reminded me of a short story I wrote a long time ago, and has inspired me to revisit the idea.
The premise: A race of massive alien creatures travel from planet to planet, solar system to solar system, via large wormholes embedded in planetary atmospheres (reason being that atmospheres "stabilize" the wormholes, where they would otherwise destabilize and collapse). The wormholes leak the atmospheres of the many connected worlds, leading to homogenized planets over great timescales, "mongrel planets."
In my story, the aliens emerge in our Solar System. First in the outer planets, they work their way through the Solar System, weaving a network of wormholes. Eventually, a wormhole connecting Jupiter and Earth is established. One throat travels through Jupiter's atmosphere at around the 250 kPa mark, and the other travels through the Pacific Ocean and other adjoining oceans, nearest the sea floor where the pressure is greatest.
The wormhole has an effective throat diameter of around 100 meters. It expels Jupiter's atmosphere only (no need to account for any other planetary atmospheres): 88-92% hydrogen, 8-12% helium, and trace amounts of other chemicals such as methane, water vapor, ammonia, carbon, ethane, hydrogen sulfide, sulfur, and so on, proportional in quantity to their abundance in Jupiter at the wormhole's altitude.
**My question is this: what are the immediate (hours, days) and long term (weeks, months, years) effects of the Jupiter aperture on Earth?** I'm specifically interested in the immediate effect on Earth's climate (and what people nearby the event might witness), as well as how Earth's condition might evolve over those weeks and months.
[Answer]
**With what you describe you will actually be venting Earths oceans into Jupiter. Forcefully.**
From OP
>
> One throat travels through Jupiter's atmosphere at around the 250 kPa
> mark,
>
>
>
I take this to mean that om the Jupiter side of the wormhole, the pressure is 250 kPa
>
> the other travels through the Pacific Ocean and other adjoining
> oceans, nearest the sea floor where the pressure is greatest.
>
>
>
So how much pressure is that? Pressure at sea level is 101 kPa.
<https://en.wikipedia.org/wiki/Atmospheric_pressure>
and it goes up by 1 atmosphere for every 10 meters depth underwater. So 10 meters below the surface it is 202 kPa and 20 meters below the surface it is 303 kPa. You have already exceeded the 250 kPa pressure on the Jupiter size, so water will be flowing to Jupiter.
There is a lot more ocean below that and you have put your wormhole at the bottom of the deepest parts. Assume that is 10,000 meters. That means 1000 atmospheres or 101000 Kpa. A firehose is 5000 Kpa.
You will not completely drain the oceans this way, but when pressures equilibrate they will be about 15 meters deep. That is the formerly (and still) deepest parts though. Most parts will probably drain completely.
It is a good calculus problem to determine rate of pressure change as the ocean levels drop, and with pressure change rate of flow, and with rate of flow thru 100 meter diameter pipe time to drain the ocean. This problem is left as an exercise for the reader.
[Answer]
Many hundreds of millions of tons of hydrogen and helium would be blasted into the Earth’s oceans every second. This would easily be sufficient to overcome the pressure even at the bottom of the deepest oceans causing a massive and ongoing eruption of gas for miles around. The pressure and the quantity of gas would be such that the ocean would be pushed back from these vents.
Anything living within 10-100 miles would be asphyxiated within minutes. The expansion of such a massive quantity of gas would also cause a massive cooling effect that would start freezing the ocean in the vicinity. The cold gas would expand in all directions eventually forming a low level blanket close to the surface that would spread around the entire planet.
Within seconds or minutes there would probably be a *very large* explosion as static and lightening ignited some parts of the mixing atmospheres. A blast wave would travel around the planet in hours and devastate most structures and buildings. Given the amount of gas involved it would probably continue to burn being fed by the vent until most of the oxygen in the atmosphere was consumed. The heat released would be more than enough to overcome the initial cooling.
Depending on the exact circumstances and the number of vents the oxygen in the atmosphere would be gone in a few years and probably a lot sooner. The immense heating of all the burning gas would cook everything on the planet and boil vast quantities of the oceans, expanding the atmosphere disrupting and overwhelming all weather systems and air circulation patterns over hours to days.
Over many years and decades the planet would start to cool again after the oxygen had been consumed and cold gases continued to pour in, the pressure would slowly increase and the proportion of hydrogen in the hydrogen nitrogen atmosphere would increase until pressure equilibrium was reached.
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OK, still in my Victorian Steampunk Shadowrun setting, we've got some underwater cities (care of a certain [Prince Dakkar](https://en.wikipedia.org/wiki/Captain_Nemo)). They're on average 50m below sea level, with a couple being deeper at 150-200m.
They are "open" to the sea, so are at higher pressure than normal atmosphere, so we are at risk of the [Bends](https://en.wikipedia.org/wiki/Decompression_sickness).
I want my characters to be able to move back to the surface without waiting up to 24 hours to degas, so are there any methods other than decompression chambers to do this, or at least to help reduce the overall time? I've thought of [blood degassing](https://patents.google.com/patent/US8444586B2/en) maybe?
[Answer]
Given this is a *Shadowrun* setting, there's magic of various kinds. Magic ought to be able to do a pretty good, rapid job of blood degassing. Assuming the society understands the cause of "caisson disease" (not mentioned in *20,000 Leagues* because Verne didn't even know it existed, when he wrote in the 1860s), it shouldn't be hard for the magical/medical community to come up with a way to purge the excess nitrogen from the blood and tissues.
Breathing another gas mix won't really help, because other gases (helium, hydrogen, etc.) are also soluble in water/blood to some extent. Heliox is used for saturation diving at great depth, not because it greatly shortens decompression (it does shorten it, but not by even a factor of two), but because it doesn't become toxic in the blood as quickly as nitrogen (40-60 meters is deep enough for nitrogen to start to cause narcosis, so the underwater cities will have to breathe heliox anyway, assuming they know about and can extract helium from natural gas).
Hard hyperbaric suits are impractical because of weight -- 150 m is 15 atmospheres; a soft suit (like a space suit) won't come close to sustaining that level of pressure and allowing the wearer to move their major joints (movement is a problem even at 1 atm relative pressure). A hard suit good for 15-30 atm. will be heavy, however -- including its breathing gas supply, it'll likely weight above 100 kg. Not very practical.
The one kind of reasonably portable pressure support that might work is a skintight suit -- one that literally fits like skin, except over the torso, and provides enough compression to avoid edema and allow circulation to return to the core. The torso would be similar to a portable iron lung, pressurized, and a helmet supplied with the same breathing gas used below, plus pressure bottles and regulator, would complete the ensemble. Not *terribly* practical, but at least physically possible, in the absence of magical blood degassing.
Another option, possibly more attractive under the desire for steam power, is a hyperbaric perambulator. Basically, a decompression chamber on wheels with a small steam engine. This limits ability to manipulate the environment, but offers the ability to trail a small cloud of coal smoke...
[Answer]
**Surface suits.**
This is essentially a hyperbaric chamber that you wear. These suits are built like deep sea diver suits of the era but are for land use. Your characters breathe pressurized gas and wear a pressurized suit on land. They take the pressure with them and it slowly decreases as they move about on the surface.
If you have SCUBA it would be more convenient - those old time suits required someone to pump air down a hose.
[Answer]
Blood degassing would also take time to prepare and process, and it wouldn't help much- blood is *minor* liquid in human body (4-10 kg out of 30-70) and will regase quickly enough.
The only plausable method - is to breath oxigen-helium mixture for couple hours before. It can be done without being stationary: just ware a gasmask (sort of firefighters use IRL).
Or your domes can be filled with such a mixture at first place. Than the only thing that will case "bends" would be immediate return after arriving to seafloor.
[Answer]
You can have your characters stay in hardbody armor the whole time they are underwater. Their suits would need to be airtight and bulky, like space suits, so that the suit can maintain surface air pressure inside itself without being crushed by the surrounding air. It will disrupt your chase scenes: “Quickly! She’s getting away!” “I’m on it. One pace to her 10, if she runs around the city perimeter, she’ll catch up to us soon enough!”
[Answer]
Genetically modified hemoglobin!
You want a couple proteins whose role is moving dissolved gases from areas of high concentration and releasing them in lower ones. This efficiently moves the gases to the lungs, greatly decreasing decompression time.
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So, I was recently watching *Stargate: Atlantis,* and I saw a very interesting concept. In one episode, the villainous Replicators use the stargate network to fire what is essentially a high-powered laser at Atlantis. My question is, *is this scientifically feasible?*
For reference, the weapon in mind produces a small wormhole going between point A (the general vicinity of a quasar) and point B (the orbit of a planet). Massive amounts of energy proceed from point A to point B via the wormhole, and then proceed to the weapon's target (point C). The beam is not a "true laser" *per se*, so much as it is a massive amount of visible-light radiation from the quasar going through the wormhole.
[Answer]
Wormholes aren't forbidden by relativity, which isn't quite the same as "*scientifically plausible*".
If you *were* able to make a wormhole, then you'd be able to pump energy into one end and get energy out of the other end. Exactly what comes out of the other end rather depends on the nature of the wormhole metric. Given that wormholes may be mathematically possible but no-one has worked out a way to make them physically plausible, you can handwave that as you see fit. Do you want wormhole lasers? Sure, you can get wormhole lasers.
Remember that lasers aren't infinitely thin, and the throat of a wormhole is of a certain size. You can't fire a really fat beam of laser light down a really skinny wormhole. This may limit the useful range of the beam as it exits the wormhole due to diffraction limiting effects.
Finally, just because the wormhole would plausibly let you avoid the FTL issue by providing a shortcut between two points, doesn't mean that you can't just materialise a wormhole mouth at an arbitrary point in space. You need to carry one mouth to your target first (assuming that it possible, with whatever wormhole design you've settled on), and then shoot your laser through the other mouth. Being able to materialise a wormhole anywhere you like, such as by a distant target, implies FTL and *that* quickly totters off into the realms of implausibility and/or inconvenient things like time travel. So you might not want to do that, depending on how hard your want your scifi setting to be.
[Answer]
Reality check, if you can create worm holes anywhere. What do you need a laser for? Just create a wormhole that links from a black hole or star gravity somewhere, and put the other end inside the thing you want to destroy.
A laser is a waste of energy if you can already create worm holes. And that episode in particular was pretty inconsistent and had the characters tossing idiot balls around.
Remember they couldn't move to the other side of the planet because the portable gate would follow them. Except the portable gate couldn't get around a rock in front of it?
When gates are held open by incoming energy, they can be forced to jump to another gate by detonating a nuke next to them, they forgot that part?
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There are a couple of potential issues and also potential benefits from this scenario. As noted by others wormholes, in theory at least don't (except in certain specific circumstances) violate the laws of relativity. So assuming they exist and assuming their internal structure doesn't somehow disrupt the path taken by photons traveling through one your laser is potentially a 'goer'.
The key problem is targeting i.e. how do you control where a wormhole opens at the other end and once its open how do you keep in stationary relative to the target. In the Star Gate franchise the gates at either end stabilize the wormhole. I haven't seen the episode you refer to but the question becomes how do the Replicators do it when as far as I'm aware Ancients couldn't. Firstly you have to be able to precisely calculate the relative distance and position of the target from your end of the wormhole across light years of distance. Then to complicate matters the planet Atlantis is on orbits it's star and the planet itself rotates on its axis. So you'd have to be able to constantly adjust the position of the exist in tandem with the motion of the target (and your end is in motion relative to the target as well just to complicate things further).
The plus side is that you could use the same technique (poring energy through a small wormhole) to power *any* ship or device anywhere in the cosmos you wanted. No need for power generators at the other end at all. Just build huge power stations somewhere at the heart of your Empire and power everything from home.
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
In my scifi setting small utility robot swarms are used for many purposes. I'm currently trying to estimate how much energy such a swarm would need to operate. Since biology, robotics and nanotechnology have pretty much merged into one thing in the setting I decided that taking bees as an example for a standard mircobot is as good as starting point as I'm going to get. **So how much power ($W$) does a bee nee to fly?**
Or to put a more hard-science spin on it, **how much power ($W$) does a flying object of a mass ($m$) need to fly with a speed of ($v$) in an environment with an airpressure of ($p$), which might be anything from 0 to 25 bar, and a gravity of ($g$), which might be anything from 0 to 5 times that of Earth?**
I know that a precise answer to this is probably extremely hard to give, but that isn't really my goal. I need to know the order of magnitude of energy these droneswarms will consume, so I can figure out if the powessource of the swarm should be batteries, chemical fuels or small nuclear reactors. This information is just here to give some context, it is irrelevant for the actual question.
A great answer would provide me with a formula and a right estimate for the bee-sized mircobot. The bee value is supposed to be a sanity check.
[Answer]
**[This article](https://jeb.biologists.org/content/208/6/1161)** might be of interest. It turns out energy expenditure is as much a factor of air temperature as anything else. Figure three seems to be pertinent to your question. As it becomes a matter of simple mathematics to convert from their units to yours, I leave that to you!
[](https://i.stack.imgur.com/bwpAb.gif)
[Answer]
Let's start the estimation with the [drag](https://en.wikipedia.org/wiki/Drag_(physics)):
$$
F\_D = \frac{1}{2}\rho v^2 C\_D A
$$
Where
* $C\_D A$ is going to be your form factor, depends on your drone design. [Here](https://www.engineeringtoolbox.com/drag-coefficient-d_627.html) are some example $C\_D$ values
* $\rho$ is the air density. [Here](https://en.wikipedia.org/wiki/Density_of_air) are some values, depending on temperature. If you increase the pressure to say 2x, the density also increases 2x.
* v is the velocity
[If you increase gravity, the density also increases](https://physics.stackexchange.com/questions/360796/does-less-gravity-means-less-air-density), I think the relationship is linear.
The power you need is:
$$
P= F\_D s
$$
Where
* s is the distance travelled
If you substitute:
$$
P(v, s) = \frac{1}{2}\rho v^2 C\_D A s
$$
or
$$
P(v, t) = \frac{1}{2}\rho v^3 C\_D A t
$$
Because $ s = vt $ (in average of course).
**This is the power you need only for the horizontal movement.** For the vertical movement you need to calculate the [potential](https://en.wikipedia.org/wiki/Gravitational_potential) energy difference.
If you have winds, air streams, it could be higher/lower, the [bees know that](https://phys.org/news/2013-09-bees-flight-secrets-revealed.html). [This](https://www.jstor.org/stable/1308779?seq=1#page_scan_tab_contents) article could tell more about energy use of the bees, if only I had access to it.
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I'm writing a story in which the characters (and society at large) have to deal with a recurring natural disaster (like hurricane season or the common winter, in a way). What I want to know is how long can I space out the occurrences of this disaster while still having it be a force that shapes the daily lives of the people and culture?
I do have some restrictions. It has to be big enough that it affects daily life: deadly while happening, requiring preparation while not. It can't be so long between events that the natural disaster is doubted. No "legend into myth" type thing. I also don't want variability to be a factor like the winters in ASOIAF. The society isn't supposed to be afraid of **sudden** disaster just happening or starting out of nowhere.
While I'm at it, what would be a good vector for this disaster? Could a locus migration or animal hibernation happen on the scale of decades? What about a storm or kind of rain that reoccurs on the scale of centuries?
[Answer]
**Minimum once a human lifetime**
People need to be able to talk to someone who has seen it before for a real feeling for it. Once more than a lifetime, people will forget or water down the effects.
A meteor shower could happen once a lifetime and put the fear of god into them. It would happen at a fixed time so people could tell when the stars are right when it will happen.
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One possible event with a lot of flexibility is to have a flood that happens periodically. Sea levels and river levels rise until they cover all land, or maybe just some land, so that people are forced to flee to higher ground or load themselves into boats and wait out the disaster. After some time, water levels finally recede and people can come back down and resume their lives. Obviously, no preparation would mean certain death, and much of society would have to be built to anticipate this flooding. Castles on high ground might be valued especially.
When the flood recedes, people need a system in place to restore order to society. Goods have to be protected so that they are not stolen by bandits post-flood before the owners get back to them. People who floated away need to find a way to return home.
A quasi-scientific justification isn't hard. You can reduce the phenomenon to tides. Fix an astronomical object, let's call it a blue moon, in a large elliptical orbit. Every X years, this elliptic trajectory aligns with Earth orbit so that the blue moon is very close to Earth and takes up a huge part of the sky. This blue moon exerts an extremely strong gravitational attraction to water for whatever reason; maybe it only attracts water. During the "Time of the Blue Moon", water levels rise to a crazy level and remain that way until the blue moon is gone. The blue moon could easily fit into societal mythology, as a cosmic force of purity, cleansing, etc.
**Example**: have a flood every 25 years, lasting 6 months. Everybody not fleeing to the mountains will need to find their own boat and stock it with supplies to wait out the flood. Societies will have to store food in advance to prepare. Some societies might even be built around barges designed to float so that they can continue to live and conduct business in Venice-like even during the flood. Military planners will have to take into account the possibility of enemies using the flood to slip past their fortresses and defenses.
[Answer]
There are a lot of possible recurring natural disasters. Like:
* Hurricanes
* Tornados
* Severe winter - Russian buildings are projected with this in mind.
* Earthquakes - Japanese buildings are projected with this in mind.
* Tsunamis
* Volcanic eruptions
* Locusts
* Sandstorms
* Droughts
* Forest fires
* Avalanches
* [Solar storms](https://en.wikipedia.org/wiki/Solar_storm_of_1859)
* Fish die-offs
All of those events have different frequency of recurrence and all of them could be quite devastating. All of them are something expected to eventually happen, given a matching geography, population and technology level.
Some events, like a volcanic eruption of a nearby active volcano are enough to keep most people waiting for decades knowing that some day, the mountain will spit fire. People could also in advance dig trenches or walls to try to redirect lavas to somewhere else or at least slow them down.
Most old people living in farmlands remember of some severe drought that messed up with their lives. Many people store rain water, dig up artificial lakes or rely on big artificial irrigation projects as a preparation for that.
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I'm building a magic system where magic isn't just controlled by human brains, but is actively produced there. As a byproduct, when casting a spell, the brain generates a large quantity of visible light (but not infrared light or heat). I don't know much anatomy, but I would imagine that, since human skin, eyes, and muscle tissue are all translucent to varying extents, it might be possible for people looking at the mage to see this light. It would mostly emanate from their eyes and nose, where their skull isn't in the way.
My question is: **is this really how it would look if enough light was produced by the brain?** And if so, what would be the health effects (i.e. could the person still see? Would brain damage be inevitable with repeated exposure?) Or would an intensity strong enough to see from outside the skull be guaranteed to fry the brain or something?
Note that while the light in this question is magical in origin, I don't want to have any arbitrary additional magic that protects the brain or rest of the body. Just accept that the person's brain is glowing (don't worry about where the energy is coming from), and use regular physics and biology from there.
[Answer]
# Reality Check = OK!
Transillumination of body tissues is a thing. Thin tissues work best: if you close your eyes while facing a bright light, you can discern the shadow of you hand as you pass it back and forth before your face.
Certain (minimally invasive) surgical procedures rely on the phenomenon in order to determine if an instrument is placed properly. You are correct that eye sockets and nose will shine brightest: a reddish~yellowish glow. Depending on how bright the brain's dwimmerlight is, you may also find a glow from the forehead and perhaps mouth as well.
[](https://i.stack.imgur.com/ckiVO.jpg)
As for your add-on questions, the light shouldn't affect the brain itself, as there is not heat generated (beyond, I suppose, the heat generated by ordinary thaumo-metabolic processes). Since this is visible but non-IR light, your mages will be able to see it. The vision receptor cells in the retina are physically stimulated by light photons, so there's no real getting around that. It only becomes a question of how bright you want the light to be, which if powerful enough could cause temporary or even permanent damage. Just like any bright light source.
Even though the dwimmerlight itself doesn't produce heat, it's been pointed out that as it's absorbed (in tissues), some will indeed be converted to heat. I think it would be wise for a busy wizard to have a bit of a lie down in a cool place every hour or so of heavy spellcasting! His circulatory system should be able to handle a low amount of heat transfer, but too much will be injurious.
That's simply the price of magic in your world!
[Answer]
Human tissue, other than parts of the eye, is not transparent.
Assuming for arguments sake, the light is generated at the center of the brain, to keeps things simple. As the photons travel outward, some percentage will be absorbed by neurons. When this happens the temperature of the neuron increases by a small amount. If a neuron absorbs enough photons, then its temperature will increase enough to thermally activate. The neuron will fire and transmit its signal to other neurons is it connected to.
This is all happening randomly. If a small number of neurons fire the brain function can be compromised, temporarily. This could be anything from a grand-mal seizure to remembering what you had for breakfast 42 years ago.
Since the brain is mostly fat and protein, if neurons absorb enough heat, they’ll coagulate and that circuit of the brain will be compromised. If that is your memory of third grade, then its gone. If its a motor neuron control a muscle used for breathing, the you’ll experience a reduced ability to inhale and exhale. Not fatal, if its only one motor neuron, but after some number are destroyed you are dead — this is what dying from ALS or Lou Gehrig’s disease is like.
I think light can leak out through penetrations in the skull — so the eyes might light up (and this would interfere with seeing to some, the ears, and maybe the throat through the penetration at the bottom of the skull for the spinal cord.
Generally, our skulls are pretty much opaque and our thickest parts of our skull are facing forward and the back of our skulls.
You might look at this [Interactive 3D exploded view of human skull](https://sketchfab.com/3d-models/visible-interactive-human-exploding-skull-252887e2e755427c90d9e3d0c6d3025f) to see where you think the skull is thin enough for light to leak out
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**Congratulations, it's a wizard.**
Yes, the skull is mostly a closed bone box -- *in adults*.
Babies have 'soft spots' -- fontanelles -- in their skulls, where the plates haven't quite closed up yet.
If you've got glowing human brains, early infancy would be a good time to evaluate their luminary potential.
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[So some people shone some incandescent lights into the heads of dead people to see what gave](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5175548/). Turns out that the translucency of skull bones among people spans six orders of magnitude. In other words, one subject was a million times more translucent in the head than another subject. Some people simply have very thick skulls.
But truth be told, there you have it, some skulls might shine like a reflector whereas others might go unnoticed - from the top. You still have a hole in the bones between the brain and the eyes, where the optic nerve passes through.
[](https://i.stack.imgur.com/N19gf.jpg)
Source: <https://www.kenhub.com/en/library/anatomy/the-optic-nerve>
Practically every tissue in the body is orders of magnitude more translucent than bones. Any mage with even a slightly perceivable shine on their heads would shine a blinding light from their eye sockets. And you know what is in there? The retina.
Casting any spell will blind the mage and possibly blind anyone looking at their eyes. And this is more probably permanent for the mage.
Who knows? This may have been the actual reason behind [Laser Pony's accident](http://superredundant.com/?comic=strip-6).
[](https://i.stack.imgur.com/2gzeB.jpg)
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If our Sun was teleported away by aliens, would it be possible for people to survive? I'm assuming that humans had prior warning of this ice age (the aliens warned us first) and could drill underground.
My question is, do they have to drill below the surface, and if so, how far down would the inhabitants of the world have to drill to sustain human life? Assume this is in the future and people have very efficient laser drills (0.5 mile/sec). Also assume that in 10000 years, the Earth will reach another solar system and fall into orbit in the Goldilocks Zone (or the aliens put the Earth there), and the Earth will not crash into anything. If there is one, how would humans feed themselves/find water? Finally, how could they preserve biodiversity after the 10000 years?
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You've got a lot of questions here, but let's start with the easy ones:
*How far down would humans have to drill?*
**[A Rapture Reminder](https://en.wikipedia.org/wiki/BioShock)**
Depending on how they wanted to live, they wouldn't have to drill at all. Once the surface of the ocean froze over, the sea bottom would be insulated (but still freezing cold) and stay liquid for *thousands* of years, let alone a paltry two hundred. Deep-sea habitats, therefore, could be built and sustained indefinitely with geothermal or nuclear power sources. Farming would be strictly greenhouse-based, but you'd have plenty of energy to work with and warm them. Alternately...
**[Talkin' 'bout My Generation (Ship)](https://en.wikipedia.org/wiki/Ship_of_Fools_(Russo_novel))**
Again, no drilling necessary, save to mine the necessary materials - build arcologies or construct generation ships on the surface. It saves on geological engineering, and makes construction a heck of a lot faster. If you can build a self-sufficient space ship, you can build a structure on the surface to last two hundred years.
If you really want to use those neato (and terrifyingly fast!) laser drills, creating your own geothermal heat pipes would be a snap at *half a mile a second*.
In either case, light would be electrically generated, and water would be easy to find. (In the first case, *not* finding water would be the challenge!)
Preserving biodiversity would likely be a combination of advances in biology (allowing for in-vitro gestation, not just fertilization) and genetic engineering (to reintroduce heterozygosity when a lot of life will just have died).
Expansion is similarly easy - build more structures.
If you're really desperate to put people underground, at about [a kilometre down](https://en.wikipedia.org/wiki/Geothermal_gradient) things are a balmy 25 degrees, and that's not going to change just 'cause the sun switched off. That'll work just fine, and it'll only take you a second and a quarter to get there with those laser cannon... I mean drills.
*Edit*
As was pointed out in the comments to the main question, 200 years is a *really, really* short time for Earth to reach another star system, let alone slotting perfectly into the Goldilocks zone, so I'm assuming the same interstellar Thieves' Guild that stole our sun drops by two centuries later to try and undo the damage by teleporting Earth to an appropriate address.
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Regarding biodiversity, one thing they could do is something like this: [Svalbard Global Seed Vault](https://en.wikipedia.org/wiki/Svalbard_Global_Seed_Vault). This is a huge vault of seeds that is kept on ice in Spitsbergen, Norway. They've been doing this for more than 30 years so they have learned some things about keeping seeds viable over long term storage.
They could take lessons from this vault. They could collect every possible kind and variety of seed and store them someplace convenient and far from volcanoes and such. Probably you can, with a few centuries of technological advance from today, safely get seeds down to liquid Helium temperatures and then return them safely. Probably you can do the same with embryos of large numbers of species, though bringing an embryo whale to term without a mother whale is harder than planting some seeds.
They would also need to be thinking about cultures of very many different micro organisms. From amoeba to yeast there are lots of species that won't fare well through a 100-century cryogenic level freeze. Some of them might survive a few centuries of freezing. But many would likely die off. Some will be OK if carefully preserved in liquid Helium. Others will need to be kept alive in active cultures. That turns out to have a good side because it means you have an excuse to keep making beer and cheese and some other things.
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A Chimera is a creature made up of two different animals that are fused together in a process known as polymerization. This spell can combine animals to create an entirely new animal which contains the best traits of both parent species (bat radar, dolphin intelligence, sharks ferocity, etc). There are many applications for a chimera. Instead of spending thousands of years breeding animals for desired traits, a summoner can simply combine the animals with the traits that they desire. They can also be used for their hides or meat, which have many uses. However, these creatures are sterile once combined, and must be custom built.
The more I think about it, the more I see a problem with this, as the spell can lead to a number of bizarre creatures. A sharktopus (shark and octopus), or piranha-conda ( piranha and anaconda), a pigagle ( pig and eagle) and other random combinations can occur. Although hilarious, this cheapens the seriousness of the magic, making the whole thing seem like a bad SYFY movie. It would also force people to honor half remembered committments they promised they would make "when pigs fly".
What mechanism can I introduce to limit the madness that would result from combining completely random creatures like this?
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The simplest way to limit silliness would be to increase the cost of creating chimeras. There is a number of ways the cost can be expressed:
1) one-time expense on the ritual space of chimera creation - say, your containment circles need to be inlaid with solid gold
2) repeated expenditure on ritual components - this magic needs expensive stuff that is consumed during the casting, say it needs very rare incense to be burned
3) straight up expenditure of significant amount of magical energy, however it is expressed in your setting
4) a lot of time spent on study and research to create a successful chimera.
All those points, however, would make the creation of a chimera a rare, one-off event of significant magical impact. Not something you would butcher for leather, rather something like a powerful guardian for the wizards house. If you want your chimeras to be usable as meat animals, for example, we need them to be not much more expensive then breeding animals, but at the same time complicated enough to prevent silliness.
I think, we can tweak my point 4 for that. Say, creating a successful chimera needs a lot of research and a lot of trial and error. Most of the combinations do not actually survive, you need to be lucky to get the exactly right attributes of exactly right animals. Once you do get the combination right, you have a workable chimera pattern you - and other mages - can repeat at will.
The process of creating the chimera is not dirt-cheap, but still sustainable for most mages. They, however, prefer to use familiar and reliable patterns. The chimera experimentation is reserved for a small amount of mages that make it their life's work.
Unless you need to create an extensive game-mechanics, you do not need to define an underlying principle of successful chimera generation, just say that the combinations you like work, while the ones you don't do not.
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As another answer to the question "what is best?".
Example is your Pigagle. What are its best properties? Flight is probably considered as one, but mankind has started viewing a good property of pigs their edibility and amount of meat they can produce. That is completely terrible for flight and a bad idea for survival... so the "best" characteristics have to be chosen.
For this choice I usually go for a simple explanation. When you cast a healing spell that only heal friendlies, the magic heals just the friendlies. So the magic is ingrained with some form of intelligence based on the caster's intelligence. If the caster would think someone a friendly at that point in time and recognize them as such, the magic will gain that recognition and be able to make it's selection.
When making a chimera, the traits considered best are selected based on this as well. However, how do you select what "best" is when chosing between badly matching traits? Does the pigagle become fat and unable to fly? Does it become lean, yield less meat and require more food for the same weightgain?
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A key here is that the chimera gets the best proprerties of it's parents... but what is the "best"?
You could simply say "there is no best for the caster or magic can choose from, so the merging will not complete". It could also create failed experiments, a pigagle would simply die shortly after or even during the casting, so the remaining viable chimera's just happen to be the creatures that you like.
An alternative to this is that a pigagle could be possible, but you have to do painstaking research to make it possible. This would turn into something akin to quantum computer research. Not its difficulty but its q-bits. There are many types of q-bits to research for viability, and without enough data the researchers just had to pick one of the more promising one's and continue research as researching each one individually is massively expensive and if the chosen one works also redundant. The rest of the world now continues that research simply because the startup costs of researching another q-bit and getting to the level of the currently chosen one is so immense that no one wants to do it. That applies to your pigagle as well. Making frivolous combinations is a waste of research time, money and effort. Why do it? People stick with creature and trait combinations they know and can advance.
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# Rule of law and transparency. (What's in a name.....)
All magic-users have [magical-names](https://www.patheos.com/blogs/sermonsfromthemound/2015/07/magical-names/) (one each), either given them by others or chosen by themselves (more accurately, they need to find out what their magical-name is to start practicing magic), it is by invoking this name that the spell-caster is able to call upon their power. A central registry of magical-names is held by the authorities.
Without the spell-caster uttering their magical-name during the casting, the spell won't work.
Each time the spell is cast, a creature is created, but in the process of that casting - a long chanting that makes the creatures fuse - the name of the spell-caster is spoken and incorporated into the fusion process, leaving a trace for other sufficiently advanced spell-casters to find.
* The tell: A simple incantation enables the animal to speak and forces the animal's creator's name from it's mouth.
* There would need to be some suitable punishment devised by the elder magic users at this point, cleaning the sewer drains out that flow from the town perhaps.
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Why do you *need* the spell to exist in the first place? Granted there are possible applications for the results of it but that doesn't make it essential. If you see it as causing more trouble than's it's worth do away with it.
The other option is a little more "because I said so" but it may also work, the Polymerization spell is a piece of ritual magic with a number of variations, each variance is specific to the animals being made into the chimera on the day and the list of variances that are known to be compatible is ***very*** short. Experimenting with new variations is possible but generally lethal and extremely frowned upon by the magical community. This lets you as the author get away with a bunch of cool monsters while creating clear boundaries around what it is and isn't possible to do with the spell.
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Maybe the purpose of the polymerization spell is not to create Chimera, its just a useful side effect of casting it with inadequate parts.
Maybe the true purpose of the polymerization spell is so dangerous that sane individuals are not willing to risk casting it correctly.
This way new non-lethal recipes are only discover on very rare occasions.
This would also only work if there where more correct recipes than incorrect ones.
For example say the true purpose was to create a creatures that consumed everything around it even itself in an instant, and unfortunately for the caster the range of the consumption vastly overlaps distance you need to be cast it from.
But ever so often there is a mad wizard who decides to cast the spell for revenge or regret, and inadvertently creates something new like a pigon-rat, or a griffin.
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Perhaps ony similarly-adapted creatures can be polymerised. The reasoning is that when combining similar-formed creatures, each one contributes similar traits, whereas if dissimilar creatures are combined, then the spell will chaotically combine the contrasting traits to create a deformed chimera that cannot survive
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From my understanding shkadov thrusters, they use huge mirrors built on the scale of a dyson sphere, to reflect all the radiation of a star in one direction, accelerating the star as an enormous star-ship.
As the acceleration is initially slow, the planets around the star will stay in orbit (I think); my question is, can a primitive civilization survive on one such planet, or will the stresses of being pulled along at a decent percentage of lightspeed (I've heard anywhere from 10% to 80%, so I'd appreciate it if someone who knew could clarify it for me) drive them to extinction?
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You are assuming that the acceleration won't be a problem disturbing planetary orbits and also that the planet won't be overheated by the reflected radiation. (The former passes my "gut feel" test; the latter doesn't. It appears to me that the mirror contributes a healthy fraction of the planet's incident light, which would probably heat it significantly. This needs to be carefully calculated. Making the mirror big enough certainly helps. And it might be possible to tweak the mirror to minimize the extra light on the planet.)
Concerning the effect of high speeds, there is *no* effect from the speed because it will never move very fast. See the [Wikipedia article](https://en.wikipedia.org/wiki/Stellar_engine) which estimates that a Shkadov drive on the Sun would result in a 20 kps speed after a billion years of accelleration...
Speed alone has no effect, anyway. It's the matter that you ram into that may prove a problem. But not with a Shkadov drive!
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Your mirror is probably shaped like an ellipse with the star at one focal point and the other focal point at infinity. This means the rays reflecting off of it are parallel. Think about it this way: imagine the light is going in the opposite direction, from space in parallel lines to hit the mirror and reflect back to the star. How big is the planets shadow on the mirror right now? Now think about how much radiation comes from the star and hits that area. That's how much extra radiation the planet is getting exposed to. The good news is that if the mirror is far enough away then the answer is not all that much. So I guess this was a long way to say, depends on how big your mirror is.
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Shkadov thrusters will not give you relativistic speeds. For the sun the acceleration is around $6.5\cdot 10^{-13}$ meter per second squared. That will not reach relativistic speeds over a biosphere lifetime. The trick is to use it to steer towards close encounters with other stars, bumping up the speed drastically through gravity assists.
Up until that point there is no problem, except for shadowing and reflection making the solar input variable. But if the planet is orbiting orthogonal to the travel direction it would see a constant amount of sunlight.
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The acceleration will be VERY slow. This can be inferred by comparing the luminosity of a star to the mass of the star. Our sun has a luminosity of ca. $4 \cdot 10^{26}$ Watt and mass of $2 \cdot 10^{30}$ kg. That's one-five-thousands of a Watt per kg. Strapping a flashlight to your back would accelerate you many times faster.
Reflected radiation need not be a problem. If the mirror is well inside the orbit of the planet and at an angle to the planet's orbit, the reflected light will never hit the planet. If it is well outside, it will not add much to the normal solar radiation when the planet passes through the reflected light, since the light must be reflected as parallel photons to achieve the greatest effect and hence be no more concentrated than the light that hits it (which will be weaker than what normally hits the planet). At worst, as smaller mirror in the planet's L2 Lagrangian point would deflect the light.
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A group of people from a particular family are born with an ability to see into the past. They would like to exploit this for money but there is no obvious way to do so.
**Details**
By closing their eyes and by an act of will they can see, hear, feel, taste smell in perfect detail anything that happened to them up to about 1 hour ago. They can run it forward and backwards at any speed.
This could have amazing benefits for the individual doing it (the least of which is remembering where you put your keys). However the commercial value to others is not obvious.
**Question**
I can see many ways that this could be useful to the person themself. However I believe that there is absolutely no useful way that they could sell this ability to another person or organisation as all the memories are their own. Am I right?
**Notes**
This is not time travel. Being taken to a crime scene and being asked to say what happened 1 hour before won't work, unless of course they were already at the crime scene. Otherwise they will just remember being brought there, too late to witness anything.
None of their other abilities are adversely affected by the talent unlike for some savants.
It's effectively raw input so they can apply a different thought process to it the second (and subsequent ) times around. Of course it only goes back 1 hr so they will progressively lose the tail end of it.
**While they are recalling, they are unable to observe the present.** They can describe what they are experiencing.
From a computing perspective your superpower is a 1 hour FIFO buffer.
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Needless to say, any games/activities that require memory. The first thing that comes to mind is to become a carnival cheat, or to capitalize on other carnival games. Things like lining up like-cards, and the three cups and one ball game. Many magicians play memory tricks, such as being able to relay the contents of an entire deck of cards while only having seen it once. This is topically done through memory palaces or other neat retention exercises.
If you want more upscale professions, a lawyer would benefit greatly from such an ability, to retain/remember completely what witnesses have said (even if it's just one hour). As would a detective, to a certain degree, though 1 hour is quite limiting.
That's my two cents. The further back you stretch this ability beyond 1 hour, the more useful it'll become.
Edit: To clarify the detective thing, it wouldn't much be for actively investigating a crime scene, but to retain details during active pursuits. This would also go for any sort of policing professions by extension. Or even, say, a medieval guard might benefit from this, though probably in such a way to milk it for money.
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Having a short-term memory of about one hour would give the bearer an excellent advantage in all kinds of mental exercises: Calculation by heart (you can memorise a huge amount of intermediate results), playing games of mental skill like chess or go, to mention just a few possibilities. Becoming a professional in some mental activity will be a way to monetarise such a gift.
EDIT: Examples of professions are
* A professional chess player (in our contemporary world)
* A professional calculator (in German *Rechenmeister*) in our world in the 18th century or earlier
* A professional mathematician
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How fast can you rewind and look through their memory? Can you check their 'past 1 hour' memory in like 5 minutes and experience all the details at the same level / play their memory in 12x speed?
If so, then one could recursively extend this memory ability and find potential use with LIFETIME SUPER MEMORY:
* hour 1: read 20 books, each takes about 3 minutes, you don't need to read carefully, just skim through it but make sure each word is went through.
* hour 2: in the first 5 minutes, check all the (super) memories and you'll essentially be able to locate each word; use the remaining 55 minutes to read new books / get new experience etc.
* hour 3: use the first 5 minutes to re-experience the past hour, so you can locate the words in all books you've read in hour 1 since you already 'experienced' them in the first 5 minutes of hour 2, you can also locate all words you've read in hour 2 since it's within the last hour; use the remaining 55 minutes to read new books / get new experience etc.
* hour 4: use 5 minutes to re-experience; use the rest 55 minutes to observe present. You can see the pattern.
That's how you extend your 'super memory' not limited to the past hour. Importantly, can you preserve these memory overnight? Will you be able to memorize your past 1 hour before you get up, or before you go to sleep? The first case will extend your ability to 18-ish hours, the second case will extend it to lifetime as long as you don't 'forget' to refresh it.
And at which historical time are you setting up the story? I believe such a 'librarian' ability could be more helpful in ages without google or computer-based searching system.
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You could bank on the exceptionality of that gift.
Ethical: Go on gameshows and morning shows, showcasing your gift and essentially being a freakshow of one.
Unethical: Same morning shows, but also: It all came about because you produce and consume a tonic that drastically enhances memory, then advertise it with your brilliant 10-minute memory. As you yourself drink a bottle of it every day, your eidetic memory will, after just a year or so, have expanded to 25 minutes (250% !!1!1!). And it will keep getting better... up to one hour. But at that point you should be a cornerstone of the additives community.
Just as with jumping very high and handling a ball well, the specific gift will not be paid for, but if the industry that runs on showcasing that talent already exists, you'll be able to profit.
There are several trades that require good memory (ATC, taster, police, investigator, editor, lector, ...), but they all require additional skills and are not geared towards someone that posesses one insular superhuman value on an otherwise existing scale, so you'd just get a modest boost there.
In light of the now positively superhuman skill of replaying raw sensory input, there might be a way to exploit the worlds general lack of knowledge about this skill (so no morning shows): Prototypes (electronics, software, design, music, receipes, ) are sometimes shown to select groups who are beforehand relieved of all recording devices. In those showings there is often more visible than would be shown if the presence of what essentially would be a scanner, was known. The 1 hour time window will severely impact your MO, but you'll still be able to make a dent.
You'd also be able to do Johnny Mnemonic-type work: Connect two airgapped USB disabled systems, Carrying one time pads, or updates. Your bandwith would be as high as you typist-skill, but the guaranteed deletion of the data might make up for it. Even harder to find an employer, though
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**Intelligence gathering services**
You can sell your services to government and corporate entities, probably at some very high rates. The 1 hour thing is very limiting, but consider that the person is equivalent to having a full suite of monitoring equipment (cameras, microphones, etc) - in situations where such equipment is prohibited, being able to "smuggle" it all in with zero risk of detection can be very valuable (this obviously presumes that the counter-party is not aware of the ability.)
You also might be able to leverage the ability into becoming a very good lie detector (both because you can use it to train your skills, and also to closely examine the subject after the fact.) It may still be impossible to catch a skilled lier, but this could nonetheless have significant value to employers.
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Reading books and stuff like that are kind of useless. While remembering, the buffer gets replaced with the experience of remembering something. In the case of reading books, this has the same effect as reading it all over again without using the ability. Even if you remember it at half the speed, the buffer gets replaced with the new experience and half of the memory would be lost.
This ability can best be exploited in controlled situations where you can be sure that you are safe while remembering the past hour.
1. Being an expensive lab rat for medical researchers. Anything auditory and visual can be recorded so those memories aren't as valuable. Your other senses can't be recorded by any camera so you can describe it to them with perfect detail and a higher degree of certainty. The results of tests would be much, much more reliable. Health risks and costs will be significantly reduced since each test will only need to be done once with you so there is no need to repeat to get more accurate description of the feelings or sensations.
2. If you have a good palate, a chef would buy some accurate taste testing. They wouldn't need to waste all the rare ingredients that can only be found after climbing the 7th mountain or crossing the 7th sea just so they can make the perfect recipe. At least not as much waste as not having your abilities.
3. Buying your abilities can still save a lot of money for a design company instead of hiring a lot of people for their opinion. You can accurately describe design flaws when it comes to UX for any software or product. A normal tester might be able to repeat an entire test case, but the second time is never the same. Would you still be scared of playing the same horror game multiple times? Experiencing your first impression all over again and describing it in great detail is very valuable in the industry that is sensitive to subjective opinions.
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On [Blue Planet 2: The Deep](http://www.bbcamerica.com/shows/planet-earth-blue-planet-ii/season-1/episode-02-the-deep) (at least, that is the title in the US version), there is discussion of crabs that grow bacteria on themselves as a food source. In the show, they kind of looked like they were wearing sheets of thin material, 'clothes' if you will. These are called [yeti crabs](http://www.bbc.com/earth/story/20170412-in-the-deep-sea-there-live-crabs-that-look-like-yetis) ([Kiwa hirsuta](https://en.wikipedia.org/wiki/Kiwa_hirsuta)). They have long hairs on their fore-claws on which bacteria grow. They may, although it is not confirmed, eat these bacteria.
Is it possible for a human-sized creature, with sufficient metabolic activity to develop and use tools, to grow enough bacteria on their own body to use as a food source?
### Considerations:
* The body can be modified, as the yeti crab's is, with hairs or other things that would increase the surface area for growing food.
* It doesn't have to be bacteria if fungus or algae or something were better.
* It doesn't have to be a deep-sea hydrothermal vent, if some other conditions would be better for growing food.
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# Pounds of Food Per Day
According to [PrecisionNutrition](https://www.precisionnutrition.com/what-are-your-4-lbs) people tend to eat around 4 pounds per day, though that varies a little bit. So the poundage shouldn't be a significant problem, especially if the critter can distribute that weight around the body.
# [Nutritional Value](https://en.wikipedia.org/wiki/Human_nutrition "Wikipedia source")
Fats are associated with better health, are a source of energy, but only 2 need to be included in the diet - Omega-3 and Omega-6.
Fiber is useful for the diet, and is thought to help protect against colon cancers, and does help with the gastrointestinal tract, but isn't necessarily essential, especially if the creatures don't live long enough for cancer to be an issue.
Proteins are necessary for a highly mobile creature, but is present in a number of plants- primarily beans, nuts, and seeds, but also present in some algae and [mushrooms](https://www.medicalnewstoday.com/articles/321474.php "vegetable based proteins")
There's a handful of mineral requirements that pretty much demand that the user seeks them out, like salt, potassium, and iron.
Then there's a handful of vitamins that can be provided by plants with Calcium being primarily available through [leafy veg](https://www.eatright.org/food/nutrition/vegetarian-and-special-diets/food-sources-of-important-nutrients-for-vegetarians "Plant Vitamins") or beans and the like.
With the nutritional requirements, we have to rule out any **single** plant being used as the entire diet. Plus I'm pretty sure that growing anything that has roots longer than a couple of millimeters would be pretty disastrous for a creature without some form of exoskeleton.
### Nutrition Side note
All those plants you're growing are going to be taking their nutrients from somewhere, and unless the area directly around them is nutrient rich, they're going to take it from the thing they're growing on.
# [Growing Area](https://www.growveg.com/guides/growing-enough-food-to-feed-a-family/ "vegetable garden size per person")
It takes about 4000 square feet growing food to provide enough for 1 person to eat for a year. Assuming that the average human has about [22 square feet](https://en.wikipedia.org/wiki/Body_surface_area) of potential growing area, you'd need about a 18000% increase of surface area to grow enough food to survive for a year.
But that's a bit dependent on the lifestyle of the creature. If you didn't need them to be active in a similar way to humans, they'd end up just being plants, because growing your own food is hard work, and staying still and sucking up nutrients is just significantly more effective for anything that doesn't need to hunt.
# My Conclusion
To be completely self-sufficient on food that's growing on the critter, **no** it's quite impossible for something with the size and lifestyle of a human to subsist entirely on food grown on it's body. Plus the evolutionary pressures would push something that lives by growing things on it into a very sedentary life style anyway.
On the bright side though, food grown on the body could be a little bit of *additional* nutrients (again, presuming short roots that don't penetrate the skin and a nutrient rich atmosphere) and act as just a little boost.
There's downsides to having a lot of surface area for things to grow though, especially for anything with an approximate to blood- fleas, lice, aphids, ants, and all those nasty parasites can make use of the same structures that would be used for the plants by just grabbing on and taking a ride on its new permanent living space. With associated diseases. **YAY**!
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It's possible but complicated.
The main problem is that the funghi, bacteria or algae should be able to **produce their food** (algae and some bacteria are autotrophs) or to get it from some external source other than the skin of their host (i.e. you cannot have your cake and eat it). And they should be able to do it **at a rate high enough to sustain themselves and their host**. Therefore, it would help a lot if the host is echtoterm, slow, has large dormancy periods, etc.
Shepherds and hunters-gatherers in non-modern societies are known to use blood and/or mud to protect their skin and refresh themselves when water is not available. This mix could become an adequate substrate for growing some weird combination of bacteria, funghi and algae (lichens are in fact a combination of algae and funghi).
On the other side, some reptiles and amphibians eat their skin (some of them are capable of regenerating their tails or limbs).
If you combine all this in an adequate environment (swamp, lake with lots of nutrients), it is possible to imagine it but impossible to make it work for a creature with **the metabolic requirements of a brain capable of tool development**.
EDIT: This other question about [photosynthesis in animals](https://worldbuilding.stackexchange.com/questions/143588/what-could-justify-an-animal-photosynthesis) is related. It was cool to find out [some sea slugs get their energy from kidnapped chloroplasts](https://en.wikipedia.org/wiki/Kleptoplasty#Sacoglossan_sea_slugs)!
[Answer]
**No, you can't survive this way.**
It is frequently stated that about 1 acre (0.4 hectares) is necessary to grow the food to feed one person. Alternatively, you can look at the requirement to eat about 4 pounds / 2 kg of food per day.
It is not possible to grow that much nutrition in the limited area and weight that could be carried around on your person. You cannot receive enough sunlight, or other means of supplying the required energy for your food source to in turn feed you.
If you change the concept to spending your life in warm water filled with nutrients, and your food source consumes those nutrients, it might be possible to get enough food (though I would not call this growing the food in the sense you use). This would still have significant issues in terms of nutrition balance, dealing with the waste stream of your food source, etc., but might be possible.
[Answer]
**Plausible? Yes. Practical? No.**
I don't know how much force is encountered by those long hairs the bacteria grows on, but I doubt it's very much.
Humans, on the other hand, are constantly doing things that rub against the skin. From donning protective clothing to rebuilding the engine of a '57 Chevy to sumo wrestling and so many more things... My point is, The surface area from which you could successfully scrape whatever growth you want to eat is considerably smaller than the the human itself. Such a person would need to live a very inactive lifestyle for this to be practically successful.
But, what about human-sized creates? I'm still doubting it. Crabs are fairly sedate in their life style. Human-sized fish (oh, let's call them "sharks") swim *through* things like kelp. Land-based creatures roll around on the ground or rub up against trees to scratch an itch.
So, plausible? Yes. Practical? Hard to believe. Does that matter? Not for a story. In fact, the idea of a humanoid species developing beautiful lacquered tools for gently scraping dinner off their backs would make for a disgustingly interesting story detail.
[Answer]
**Are we maybe talking a bulbasaur here?** [](https://i.stack.imgur.com/AfYhE.jpg)
You have a symbiotic relationship with a photosynthetic creature/plant, that potentially relies on the host for some nutrients, but provides plenty of carbohydrates. Certain species of bamboo grow at the rate of 35 inches per day, which sounds like a plant could plausibly produce enough biomass to feed a rather large host. If the relationship is a mutualistic one, then the host could provide certain rare nutrients that it finds in excess, reduce competitive species, and or provide transportation to sunnier areas, etc.
[Answer]
Maximum weight of bacteria is ten to MINUS TWELVE grams. Picogram. 0.000000000001. Even if you assume that bacteria is made from Fat you would need to grow around 222 grams of edible bacteria on you.
On your hands there is an estimated 3200 bacteria's right now. They don't even weight one gram. To be exact they weight around 0,0000000032 gram. You would need 300000000 hands to grow one gram of them. Hand surface areas is around 1% of whole human body. Even if you manipulate body surface to be twice as much you are still 15000000 "hand surfaces" short.
But you could grow seaweed on you. 100 grams is around 45 calories. What you get with seaweed is microclimate where some larger than bacteria organisms can live and you could live off them. Including fish.
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[Question]
[
As usual useful TVTropes:
>
> Superweapon Surprise
>
>
> [...]
>
>
> Comes in at least six flavors:
>
>
> Break Out the Museum Piece: It doesn't matter that there hasn't been
> any fighting for a long time. Their weapons are safely stored away and
> always ready if needed.
>
>
>
OK, the real question is how to implement it. The situation so far:
* tech level is similar to contemporary (except maybe slightly better semi-autonomous vehicles)
* because of savage cost cutting... uhm... doctrine there is a tendency to give up tanks and jet aircraft (wheeled artillery, wheeled IFV or turboprop drones are fine; nevertheless there should be anti-tank and anti-aircraft weapons)
* the procurement policy is terribly un-American ;) it does not have to be top tech, but has to be cheap to be bought in high quantity
* its a post-post-apocaliptic setting, where some survivors managed to teleport to different planets. There is no contact with other human groups, and technically speaking its only indirectly inferred that other groups survived.
* the expected role of the army is to be able to deter, beat or at least inflict unacceptable loses to any high tech Cortes wannabe or any low tech hordes that
hypothetically may one day open some dimensional gate (As budget committee explained: it even does not have to win, it would be enough if cost of conquering is clearly higher than loot)
* because of low population the technological progress is slow
* the main defence idea is the follow - low spending on military in each year, but concentrating money on long term investment (like stashed weapons or fortifications), so after ~50 years having actually quite impressive defence capabilities
* the ability to be stored with no or little maintenance is a key design requirement from the start and some trade offs would be accepted to achieve that
This NOT a question "which way to store gun?". The question is only concerning main and most blatant design features that under such requirements would have to be done differently (like for example, something in line: how to address issue that modern bullet proof vest with 5 year shelf life or what to do about rubber parts in any vehicle)
CLARIFICATIONS [after reading comments]:
* I don't assume literally being able to store weapons for infinity, "should survive a few centuries but requires new easily replaceable battery every ten years" is close enough for all practical purposes
* storage environment - as good as realistically possible, so presumably dry, cold, stable temperature vaults. If specific storage problem can be solved by ex. keeping in oxygen free conditions or -20 C degrees that would also be achievable.
* it does not matter how aggressive local fauna is, but one way or another, at least 90% of armament just after production would end up being stored waiting for some potential Ragnarok.
* **the question covers which most significant things would have to be redesigned in order to allow for such storage.** (For example, if I understand correctly hand held guns should be more or less fine, as I've read that Americans used some WW2 ammo during Desert Storm. If that's correct - rifles are not problematic in overall picture)
**For story purposes it matters how their armament would be different at first day of a conflict, because they had to sacrifice some weapon capabilities for purpose of good storage.** For example: guns were be OK, but their bullet proof vest were much too bulky to be of much use.
[Answer]
*"the ability to be stored with no or little maintenance is a key design requirement"*
## Do not store weapons: store blueprints.
With blueprints, any civilization should be able to reproduce weapons from their own tech level abilities. If your post-apocalyptic society has only access to wood and string, they can make bows and arrows. If it has a contemporary level tech, then anyone have access to cheap 3d printers and can make virtually anything at this point.
The blueprints require little to no maintenance if well preserved, and a society that has managed to teleport to multiple planets surely has no problem in maintaining operating systems/books/scrolls of parchment/anything that fit your plot.
Note that with this system, not only you do not need to preserve any physical weapons, but you can escalate a cold war just by bluffing you have access to a better blueprint than your enemy. The *idea* of a weapon could be more powerful than an actual weapon.
[Answer]
I do not think you need to change the weapons that much. What you are describing is pretty much how all militaries have approached this since World War One. Nobody has been using weapons not designed to be cheap to manufacture and easy to store for military purposes in decades. Some have been designed but military forces have been conservative when actually adopting weapons precisely because of cost issues.
Only real exceptions have been some jet aircraft and naval vessels that can be bit of a vanity project sometimes since you have to sell them to the politicians on national prestige arguments to get funding. Maybe missile systems, although even that was mostly a cold war thing.
Well, North Korea still does vanity missile development but it is a special case as they actually do have a political use for the things, so I am not sure if you can count them as purely military weapons.
Since you are scaling up the degree of stockpiling, you'd need to scale up the storage and logistics systems for it. You'd also need to scale up the maintenance and upkeep. I think the likely solution would be make the system for manufacturing the weapons during peace kind of dual purpose so it also does the repairs and maintenance. A unified system like this would save administrative and personnel costs which would add up in the extreme case you want. (Would not make sense in modern world, I think.)
You'd probably also stockpile automated factories and resources for scaling up production during wartime to compensate material losses due to combat. In fact since almost everything done under your scenario would be highly repetitive and predictable manufacturing, maintenance, storage management and logistics would be mostly automated.
These automated systems would have been manufactured under the same manufacture slowly during peace and stockpile the excess scheme as the actual weapons.
Vehicles would probably be a bit of a special case. Building a vehicle is a significant expense so stockpiling vehicles especially expensive ones such as aircraft or ships has a very real financial cost. The maintenance cost also tends to be higher since maintenance tasks will be more complex and varied than with a gun. Additionally stockpiling vehicles is simply less effective since training the crews to use the vehicles costs money and takes time.
My solution would be to train potential future crews using simulators with small cadres trained to rapidly get them up to speed if war breaks out. The actual vehicles would mostly be constructed as needed apart from ones needed for maintaining the cadre force and other training purposes.
So you'd stockpile only complex parts that might become a bottleneck during war such as engines or gearboxes (due to metallurgy). Or ones that store really well such as modular armor. Other than that you'd actually stockpile the production lines to rapidly produce the vehicle when needed and maintain the logistics needed to support that production. For example the state would have the ability to rapidly increase the production of strategic resources and divert them to military production.
I think the largest difference in the vehicles would be that they'd be much more modular to enable extremely rapid scaling up of assembly. This would also allow you to update the designs easily. Currently we mostly see this with Western main battle tanks which have been upgraded constantly without having the funding or actual reason to make up an entirely new design. T72 has seen a similar process. Same has happened with other military vehicles.
The difference would be that most of these vehicles were designed during the cold war with the expectation that they'd be replaced with something much better as the technology becomes available. So they were not really originally particularly designed to be easily "moddable", that is just something that happened when military budgets were cut but technology and needs kept advancing.
Actual modular vehicles have actually been bit disappointing. It generally adds costs to design, manufacturing, and upkeep and compromises the efficiency of the vehicle in any specific role. At the same time military forces have not used the modularity enough to pay back for those costs and losses.
For your people the math would work better. To put it simply they would not spend enough resources during peace time for the costs and losses to accumulate. They'd only boost spending when they actually need the vehicles at which point the modularity would give a significant one time benefit in optimizing the production to current tech and needs. The math would change if the war lasts long. But that is a separate issue.
[Answer]
The major issue with storage is many materials will deteriorate over time. Seals become brittle and inflexible, energetic compounds like explosives eventually destabilize and fuels oxidize or degrade int a varnish like material. Is is no good to crack open the hanger and discover your vehicles and equipment are sitting in pools of dried up lubricating fluids because the seals all deteriorated.
Some of this can be solved through aggressive design changes.Metal o ring and seals instead of rubber gaskets. Ceramic bearings which need no lubrication (or dry lubrication like graphite powder). It isn't really clear what can be done for fuel or explosives, at least not with current technologies. Even binary compounds which are mixed to activate are often energetic compounds in their own right, so you have simply transferred the problem.
Perhaps the only real way to deal with the issue is the use of advanced 3D printing. Full blueprints and chemical formulas are held in archives, and military facilities are dual purpose so the printers themselves are always in use and maintained, but stockpiles of chemicals and materials are always held ready for mixing and printing.
This assumes a rather complex process, where different printers make different parts or compounds, then the parts are quickly assembled by robots. The bottleneck is the actual speed of 3D printing, some items may take a long time to make. The advantage of this is the vehicles and equipment are literally "factory fresh" the moment the last part is placed and fastened by the robot. If equipment is designed "from the ground up" to be manufactured this way, then the process can be relatively fast and efficient. Equipment will always be made in small batches for training purposes, so no defense force will ever start from zero (which is a ridiculous assumption anyway, if no one knows how to use the equipment or how to fight, the entire exercise is pointless).
A current example of a 3D printed automobile: <https://www.cnbc.com/2017/06/28/kevin-czinger-is-making-a-3d-printed-car-called-the-blade.html>
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[Question]
[
**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
Little side project on fantasy story with dragons (or wyverns to be exact, but they're equivalent for the purpose).
I have dragons roaming the country side, laying waste and ruin in their wake. As most known draconids, those creatures are able to breath fire to devastating effect. They breathe in massive amounts of air in their dragon lungs (this will be important later) and then expel it while their throats ooze a substance that catches fire when exposed to air. Now, this amazing hunting and defense mechanism has a big drawback, as it creates a lot of heat the dragon has to get rid of. So much heat, in fact, the dragon radiates it, and nearby vegetation tends to catch fire, making it really dangerous to fight one in a forest.
Wandering on the stack, I found some great unrelated answers, mentioning interesting ways to do what is stated above. What I've come to is an alternative breathing system.
Most of the time, a dragon breathes in and out through mouth and nose alone. When it has to breathe fire, it fills its lungs through the biggest air opening it has, namely the mouth, block, then exhale. During exhalation, cooling "vents" open, that are direct pipes to the lungs. They help chase the air and reduce the heat build-up. Next inspiration, the dragon now takes an even deeper inhalation, and simultaneously chase air through the vents, creating hyper-heated jets of air, biologically jettisoning air to cool down.
(For a visual representation, take a look at the fire drakes from Warcraft. Shorter and stubbier than full dragons, with rows of larges scales from head to end of the tail, with spikes protruding from said rows. For this question, the spikes are hollow, and are tubes used as cooling vent.)
Now my question is **how hot those air jets have to be for surrounding vegetation to reach autoignition temperature?**
* We're in common "Western-European" medieval forest, not Australia, so the average tree is not eucalyptus. More the vegetation you expect in north of France, Germany and South of Great Britain.
* I don't need the *whole* vegetation to catch fire on the spot, but the leaves with lower than average autoignition temperature in the area have to. Consequence being fires starting spontaneously around the dragon.
* I suppose the answer differs a lot depending of the humidity around. The forest has to catch fire only during dry periods of summer, with at least a week without rain.
* Handwave everything happening "inside" the dragon, even if it should cook itself, it is able to withstand the temperature the time it needs to cool down.
* The cooling process takes the time the dragon empties its massive lungs, so the air venting lasts in average 7-8 seconds depending on the size of the dragon.
* The dragon will expel around 150 L of air during the cooling process.
I'm asking to know what *else* would catch fire and picture what it would looks like from an external point of view to describe it. Wikipedia has an article about auto-ignition, with the equation and some examples, but I have been unable to locate any data regarding trees and leaves (from the concerned regions) autoignition temperature and lack the theoretical knowledge to deduce the answer.
[Answer]
The dragon exhale hot air at temperature $T\_{air}$ and that air increases the temperature of the leaves from environment temperature $T\_{env}$ to the ignition temperature $T\_{ign}$, while cooling to the same temperature. The energy lost by the air is, in first approximation, entirely absorbed by the leaves.
With formulas
$H\_{air}=m\_{air}\cdot c\_{air} \cdot (T\_{air}-T\_{ign})=H\_{leaves}=m\_{leaves}\cdot c\_{leaves} \cdot (T\_{ign}-T\_{env})$
Let's approximate the dry leaves with paper. The [ignition temperature of paper](https://en.wikipedia.org/wiki/Autoignition_temperature) is
246 C.
150 liters of air (at room temperature) weight about 0.2 kg. [Air specific heat](https://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html) is $c\_{air}=0.718 \ kJ/kg\cdot K$, while for paper it is $c\_{paper}=1.336 \ kJ/kg\cdot K$.
This gives the relationship
$T\_{air}=T\_{ign}+(T\_{ign}-T\_{env})\cdot$${m\_{leaves}\cdot c\_{leaves}\over {m\_{air}\cdot c\_{air}}}$
Since you don't specify the mass of leaves, I have computed the equation for some values of it.
[](https://i.stack.imgur.com/dXrhC.jpg)
To ignite 0.1 kg of leaves you only need the air to be at 447 degrees, while for half a kilo the air need to be at 1250 degree.
[Answer]
Your dragon seems to be very similar to a chainsaw. Luckily for you, there was an investigation regarding safe chainsaw temperatures. [Link](https://www.fs.fed.us/t-d/programs/fire/spark/html/74511201/74511201.html)
>
> It appears that safe chain saw operation would result if the muffler with a screen-type spark arrester on the chain saw had a shell temperature that did not exceed 260C° (500° F) and a gaseous exhaust temperature that did not exceed 232° C (450° F). This is based on the data, plotted in figure 5.
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If your chainsaw (dragon) is constantly moving, it can have a higher temperature - see chart at the bottom.
[](https://i.stack.imgur.com/aTfdq.gif)
I know this answer is probably only suitable as a starting point.
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[Question]
[
I am currently working a humanoid roughly deer-like species in a sci-fi roleplay setting, and one of the developments I have had with such species has me stuck trying to explain it in a way that makes somewhat of sense. Furthermore, I apologize if this question breaks any rules, I am still rather new to the site.
These guys are known as the Vruk'yeol or 'Cervidani' as many oddly call them. They walk on roughly digitigrade legs with weak hoof-structures being overtaken by a proper foot. One interesting element of this species to note are their various shapes of horns, growing from out behind of their head plates. These horns are often noted to grow into a strange circular halo shape, with various forms of regular double horns taking the place of common appearance over them.
[](https://i.stack.imgur.com/t9lLq.png)
*This isn't my art nor work, but serves as a reference. Artist's page [here](https://www.weasyl.com/~salsa)*
Is there any reason or way for this species to possess either option of horns among its living members? One theory I have developed is that during early development of the horns, they could all grow as halos as such, but at a certain point they could 'break' naturally, forming two regular horns that would follow the regular path of horn development for this race. For some of them the breaking doesn't occur, leaving the horns to remain as a singular halo. Is this a sound assumption?
[Answer]
**Possible, but unlikely given the pain that would likely ensue.**
There's a good reason why most animals with horns (and generally only the males) develop their horns at puberty; live birth.
When you get right down to it, the advantages that horns provide in combat and display to females is counterbalanced by the difficulties they would present during birth; a smooth head is what you really need for a species to find it easy to birth the next generation. Evolution has solve that by providing smooth crania for the young, and horns / antlers for the mature.
As such, antlers and horns generally tend to form symmetrically in the same way as the rest of the body. This is the primary reason that most species have two horns or antlers instead of one.
In the examples you provide above, there are really only two possibilities for how this could manifest;
1) Birth Horns
If your creature is born with the halo horns, then either they're smooth so that 'thorns' don't impede the live birth, or the thorns and other manifestations on the halo appear later, during puberty. In such a case, these offspring would be different to the two horned species by necessity; being born with two horns would present serious issues for the mother so these specific offspring would be immediately different from the mainstream members of the species
2) Puberty Horns, but fused
If the horns manifest during puberty, then it's possible that the horns grow towards each other and fuse during maturity. These would be simpler and easier to explain from an evolutionary perspective, but would no doubt present painful situations for your halo antler recipients as they would firstly breach the skin as part of the normal horns, then fuse later on once they've grown to a certain size.
Realistically, if 'halo' horns were a reality, then your concept of being born with a horn (or bone) halo which 'breaks' in certain cases would seem to be the most plausible solution to this. That said, such an evolutionary trait is unlikely as it would introduce additional complications to the birth that make successful delivery less likely, not more. As such, the current model of no horns at birth, then growth at puberty seems far more likely than the model you present.
It should also be noted that halo horns are unlikely to develop in any event in an environment with intelligent predators / hunters because humans realised pretty quickly that horns and antlers give you purchase for snapping the neck of your prey if you've wounded or disabled it at some point. In other words, such horns present a combat and predatory weakness that other animals would exploit if at all possible, and the ability to present to females only goes so far in offsetting that weakness.
[Answer]
I agree with Tim on beong born with horns.
That said, what I see is during puberty the creature starts growing a single horn at the center of the forehead. As days pass the cells producing the bone and/or kerarin for the horn start migrating to either side of the head. When this process begins the horn gets brittle in the middle of the stem and fractures into a halo. Then, for some guys the halo stays, for others it also fractures at the middle.
This migration may also do for a variety of halo shapes such as can be seen in the image you are using for inspiration. Each specimen may undergo through different patterns of cell migration due to genetics and lifestyle.
[Answer]
**Certain cultural groups modify their babies to cause the halo horns.**
[](https://i.stack.imgur.com/zjD0Y.jpg)
<https://observationdeck.kinja.com/the-un-natural-history-of-man-made-unicorns-1658601966>
>
> "There is no special breed of one-horned sheep in Nepal, nor are the
> specimens which have been brought here for sale natural freaks. By
> certain maltreatment, which is described below, ordinary two-horned
> sheep are converted into a one-horned variety. The process adopted is
> branding with a red-hot iron the male lambs when about two or three
> months old on their horns when they are beginning to sprout. The
> wounds are treated with a mixture of oil and soot, and when they heal
> the horns, instead of growing at their usual places and spreading,
> come out as one from the middle of the skull.
>
>
>
I have seen unicorn goats. As kids, their horn buds are surgical moved together so as to produce one horn instead of two.
It is entirely plausible that a cultural group would modify its children so as to change the adult phenotype. Circumcision is probably the best known but foot binding, head flattening, neck stretching and many, many other body mods have been practiced by one group or another over history.
Why would a social group want to distinguish itself by horn shape? Maybe they are peaceful and this seems a less aggressive display? Maybe it is safer for sapient individuals living in groups? Maybe their holy book mandates it?
[Answer]
Have you considered looking at non-mamalian biology for inspiration? I know you said they were "deer-like," but if they're aliens, there's no reason they'd have to follow Earth evolution.
[](https://i.stack.imgur.com/Zjc5Y.jpg)
(source: [si-cdn.com](https://thumbs-prod.si-cdn.com/2M4-Zy4D-mzHmLbQ2rfHBO7Gw7s=/800x600/filters:no_upscale()/https://public-media.si-cdn.com/filer/20110520083231Triceratops-skulls.jpg))
If you look at the frills of Ceratopsian dinosaurs, you can see how they start off as a solid bone plate, but as the animal ages, windows open up in the bone to reduce the overall weight.
( <https://www.smithsonianmag.com/science-nature/new-study-says-torosaurustriceratops-76526851/> )
Now, most likely, that area would have still been covered in a thin layer of skin, but through either a natural process or some kind of ritual piercing that area could open up to create a halo like structure. Also, there's a wide variety of different Ceratopsian dinosaurs with all kinds of different patterns and shapes of frills, some with additional spikes that could look like the points of antlers.
A very similar setup can be seen in chameleons as well. The veiled chameleon in particular sports an impressive drill supported by very thin strips of skull.
[Answer]
It's not biologically implausible for a regular two-horned ungulate to have horns that curved inward, and once they make contact proceed to twist together and develop into a single "halo". Many biological structures will twist around obstacles as they grow.
The real question is why this would be evolutionary advantageous. Split horns are superior for fighting and pretty much everything that an animal might want horns for.
One possibility is that the species is social and intelligent, and only the "village leader" has the halo structure. Most individuals wear down their horns through fighting and scraping them against things, but once an individual has enough followers that they no longer need to actively fight to defend their position, they let their horns grow together. It could be this species equivalent to the "fat chief"; an indicator of personal success (and probably a sign for potential mates).
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[Question]
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As seen on others questions biological radio could be a thing.
[How to evolve biological radios?](https://worldbuilding.stackexchange.com/questions/27108/how-to-evolve-biological-radios#)
[What would a species require to be able to inherently transmit and receive radio waves?](https://worldbuilding.stackexchange.com/questions/81960/what-would-a-species-require-to-be-able-to-inherently-transmit-and-receive-radio)
I was interested in developing a species with such abilities.
The primary use for radio wave would be communication within the species. Mostly small messages such as warning others of danger or saying "This my territory, get out."
This species could develop these two other abilities with enough practice:
* A radar like function.
* The use of of special radio waves in a more offensive manner designed to harm other species (maybe it could mess up the hearing of other species or alter its brain pattern).
So the primary question is: **Where should this organ/muscle/limb be place in the anatomy of my species?**
I don't know if the transmitter and receptor should be the same organ or two separate things. Also I'm wondering if I need more than one transmitter/receptor.
What I have imagined so far for the anatomy of my species is a sort of bulky human. If that's not the best form to use for development of such an ability, feel free to come up with a better design for your answer.
**Also the range of his ability should be approximately 100 meters.**
[Answer]
Well, I'm not a biologist by any means but in my opinion the most suitable place would be the ears (for the receptor at least). Our ears are already designed to catch sound waves and send the info to the brain, which interprets them, you could just add to their capacity. Or maybe one of the ears would be for radio waves and and the other for the sound waves.
As for the transmitter, the best I could come up with is the brain itself, most likely with an aid from some sort of special little organ. It would be very neat to directly transform the electrical signals in our brain that are associated with certain words into radio waves, which would then be decoded back to the neurological signals in the receiver's brain.
Hope that helps and best of luck!
[Answer]
Radio is similar to human visible light, but just in a lower frequency.
[](https://i.stack.imgur.com/JlmVb.png)
We already have organisms capable of emitting photons on their own.
[](https://i.stack.imgur.com/CmxuJ.png)
[](https://i.stack.imgur.com/hVwYM.png)
[](https://i.stack.imgur.com/sPk9e.png)
Radar works by sending radio waves out and looking for its reflections that the receiver receives, like waving your flashlight around in a dark room. Many complex organisms have tissues capable of receiving light waves and interpreting it into neural signals:
[](https://i.stack.imgur.com/6D7BB.png)
So, you should have your emitters near your receptors so they are pointing in the same direction. Antennas probably won't be needed if working within similar frequencies, and thus, wavelengths of modern radars. They are measured in GHz, and has a wavelength of around 0.1 m on the longer end.
You did mention an offensive use for the radio waves. The US military is working on something similar called the [Active Denial System](https://en.wikipedia.org/wiki/Active_Denial_System).
>
> The ADS works by firing a high-powered beam of 95 GHz waves at a target, which corresponds to a wavelength of 3.2 mm.[13] The ADS millimeter wave energy works on a similar principle as a microwave oven, exciting the water and fat molecules in the skin, and instantly heating them via dielectric heating.
>
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However, if you want the beams to be more lethal, you can lower the frequency to increase penetration. However, the ADS has a very high power consumption:
>
> [Silent Guardian, a smaller version] can be used for targets over 250 metres (820 ft) away,[13] and the beam has a power of 30 kilowatts.[56]
>
>
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This is in comparison to less than 20 watts of [this low power radar](http://www.raymarine.com/content/?id=13531&pi_ad_id=%7Bcreative%7D&creative=210002485628&keyword=&matchtype=&network=g&device=c&gclid=EAIaIQobChMI64zhyu3w3wIViITICh05AgfnEAYYASABEgJufPD_BwE) (Note: I am not affiliated in any way with the company). For reference, 1 watt is 0.86 kCal / hour. So, 30 kW is about 9 kCal/sec, which is what would be consumed while running for around 30 seconds. So very energy-intensive, but could be made to work given good circulation and heat disposal.
[Answer]
If the body of reference is a human body, then you may want to use the spine and the arms as antennas. The vertebras will be coated in metal, as the answers to the linked questions suggested, as well as the bones of the arms.
The presence of a significant part of the nervous system next to the antennas should facilitate the wiring of the radio organ, perhaps even using the ability of nerves to fire trains of electric pulses (which work great with antennas, as long as you have the right amplifier). The specialized organ to encode, transmit and decode would be coupled with the motoneural system. If it turns out that you need a larger organ, you could replace one of the kidneys, with good peace of the remaining one.
Note that directionality is trivial with a pair of arms. You can flail them in the air to capture stereoscopic reflections of your spinal radar emissions. As demonstrated in the evolution of sight and hearing, the brain has the ability to convert all these inputs in an intelligible representation of reality. No problems there.
Your body now has become the living small scale version of a [Very Large Array](https://en.wikipedia.org/wiki/Very_Large_Array).
**Notes**
*Transmission and reception*. Transmission could use the spine, as mentioned above, while reception could be done using the arms. In principle there is no need to decouple, as long as you can pack the bandwidth and synchronize the transmission correctly.
On the offensive. The easiest way to think of it would be a jamming of other radio receptors with a variety of modulated signals. This could confuse predators. Alternatively, one could copy and amplify the transmission of the enemy. This could be akin to intercepting the transmission and reproducing an identical one, adding it in agreement of phase to the original. This may cause the receptor organ to saturate on the intensity scale. It could be perceived as an extreme degree of noise (a speaker on extremely loud amplification is not going to produce any intelligible sound), distortion (i.e. saturated volume), or even pain (looking into a light source, or listening to very loud music).
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I would make it part of the [cochlea](https://en.wikipedia.org/wiki/Cochlea).
[](https://i.stack.imgur.com/bROt5.png)
Either as a separate organ or as an enhancement of the cochlea. The nerves, ducts, and other parts of the cochlea are very small and delicate and you wouldn't want to mess with them. But if you replaced this organ with one that allowed the person to continue to hear *and* added in the radio power, this could work.
After all, [cochlear implants](https://www.nidcd.nih.gov/health/cochlear-implants) are already being done. So there is space to add a device and known methods of connecting it to the nerves.
[](https://i.stack.imgur.com/Zp2AN.png)
If this is an organ that evolves naturally, or semi-naturally, it could still be part of the larger cochlear system. All the nerves for hearing and balance are right there and other nerves are close by.
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In real life, dental braces are known to act as crystal radios and receive AM signals. All you need is a semiconductive joint of some sort. An oxidized joint between dissimilar metals is ideal, but almost anything will do.
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So I've got a fantasy race of people with four arms. Their second pair is able to reach behind them like how our arms are able to reach in front of us, and so could work with things behind their backs just as well as in front (I've already got their arm anatomy worked out). The only problem is, they'd need to be able to see what they're doing behind their backs, so I thought of giving them a third (and possibly fourth) eye(s) on the back of their head. The extra eye(s) would be independent from their front eyes. I'm not sure though how this would work anatomically though. I'm also not sure how the new eye additions would affect their vision, both overall and with specific regard to focusing on things.
Thanks!!
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**Just as well as anywhere else**
There is no reason why such eyes should have any difficulty in working and enabling your fantasy people to see just as well with these backwards-facing eyes as their front-facing eyes.
A scientific study [implanted an eye into the tail of tadpoles](https://www.nature.com/articles/s41536-017-0012-5) and found that the tadpoles could learn to see using that eye instead of their normal ones. Granted, the scientists removed the normal eyes that tadpoles usually have to make it much easier to identify if the tadpoles are using the new eye, but there is no reason to believe that it would be any different if the original eyes were not removed.
Given that Earth life which evolved to have eyes facing in one direction can adapt to having eyes facing other directions within one generation, there is no reason to believe that such things would be a problem for these organisms.
A few considerations with the eye(s) in back:
* Is there body fully symmetric? That is to say, is there a distinct front and back to the creature with some meaningful biological difference between them? The answer to this would greatly change how your species views the world and is something you need to figure out.
* Whether the species has one eye or two in back would likely be determined by if they're naturally predators or prey. Predator species on Earth usually have two eyes close together so that the animal gets good depth perception, so, if your species is a predator, they'd likely have two eyes in the back of their head. On the other hand, prey species on Earth have their eyes spaced widely apart from each other, so that they can more easily see when predators approach, so if your species is prey, they'd likely only have one eye in back, so they can see approaching predators.
* If this species evolved naturally, then you'd need pretty specific circumstances for why they evolved the ability to work with things behind them. Earth life nearly invariably focuses on things in front and turns around when they need to work on things behind them, and you'd need a good reason for why your life can't do that. However, if this fantasy race was just created by God/the gods, or you're not explaining the world's history that much, you can skip that part.
* How good is your species at multitasking? If I were given two extra eyes in the back of my head and two rear-facing arms, they wouldn't actually be that helpful for me because I'm limited in what I can do all at once, so I would seldom be able to use both pairs of arms at the same time. Your species would need significantly more capable brains in order to get around that limitation.
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It might be difficult for a human to imagine how such a world would appear to such a creature, but the fact is that organisms can have functional eyes pretty much anywhere - the brain generally figures out how to handle the information regardless of where it comes from (you can *hear* things that are in front of or behind you and your brain can figure out where the sound is coming from without you getting confused, there's no reason why you couldn't *see* things that are behind you just as well.) Dragonflies have full 360-degree vision, starfish have an eye on each arm, chameleons can move their eyes independently, and they all manage just fine.
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Between a species that is hermaphroditic and a species that has males and females, then what would be the pros and cons of either one from a biological standpoint?
Anything not regarding the biology itself—culture, language, interspecies relations, etc—can be handled on my own. I just want to know the pros and cons of either method—and considering the conditions of their natural ecosystem in which they would have evolved—and determine whether one would be more likely for them to evolve than the other for practical evolutionary reasons.
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I think the single largest point comes down to **specialization**. Males and females are, as a general rule, not identical: there are physical differences beyond their reproductive organs. The best adaptations for giving birth, for instance, could weaken one's ability to run or to remain upright (see: the human pelvis, which in women is a compromise between giving birth to large babies and supporting bipedal movement). In a hermaphroditic species, that option of specialization is gone, since all individuals will (barring genetic disorders, deformities, etc.) follow the same body plan. Sure, you could hypothesize that there are different body plans with different strengths and weaknesses, where one is stronger than the others, where one is faster.....where one is better at taking on a particular reproductive role, and then you're on the road right back to separate male and female individuals. If you want to tilt this in favor of hermaphrodites, you're going to need a reason why biological specialization within a species is ill-suited to your world; that's a very tall order.
Another point is **the added cost of supporting both sets of reproductive organs**. That means more tissue, more mass, which necessarily involves a greater energy/food requirement. Nature doesn't have anything so convenient as the grocery store: if dividing a hermaphroditic species into a two-gender species reduces energy costs significantly (which it does), evolution will favor that outcome. However, hermaphrodites are able to reproduce whenever any two individuals come together: they thus have a wider choice of partners, because they don't have to wait for an individual of the correct gender. In a social species like humans, this would be a trivial advantage, but for a species that generally lives alone or in tiny groups that rarely meet, that broader choice could be vital in having the chance to reproduce at all. The probable civilization and psychology of such a species is an exercise for the reader to determine (and is out of scope in this question).
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2-sex reproduction has evolved multiple times, strongly suggesting that there is a good reason for doing so. As for exactly what that reason is, there are a number of theories. Most likely, all of them play some part in the reason why this seems to be the trend among life on Earth.
The advantage of hermaphroditism is obvious - more potential mates for everyone. So I'm going to mainly focus on the advantages of a 2-sex system.
### Self-fertilization is impossible
Self-fertilization reduces genetic diversity, which makes a species more vulnerable to predators and parasites. While many hermaphroditic species today have worked out alternative methods to avoid self-fertilization, like the complex reproductive organs of snails or alternating generations in plants, these mechanisms are complicated. The earliest aquatic life generally reproduced by simply releasing their gametes into the water, and splitting the sexes to prevent self-fertilization was one very common strategy.
Many fungi actually have a method of combining the advantages of the hermaphroditic system with the impossibility of self-fertilization by having tens to hundereds of different "sexes", (or mating types) that are functionally identical except that they can only breed with a type not their own. This increases the chances that any fungus they encounter will be compatible while ensuring they are not compatible with themselves.
### Male seekers, female choosers
On the most basic and primitive level, the difference between males and females is that females expend a large amount of energy to gestate a child - whether constructing an egg or in a uterus - while males spend less. This simple distinction creates a number of trends with the benefit of maximizing the ability of good genes to spread.
The most basic of these is that the female does not have to expend much energy *finding* a mate - the males come to her and often compete for her attention. Instead, the female's role is to *choose* the most genetically fit male, a role that does not require a lot of energy expenditure. This energy can then go towards gestation and producing strong offspring. This also allows a highly fit male to produce a lot more offspring, while unfit males reproduce little if at all. This streamlines the evolutionary process.
### Further specialization of roles
Once a basic male-female split exists, it is possible for males and females to specialize in other, more interesting ways. Among many animals where the male brings a "nupital gift", the female gets easy extra resources from her suitors. Among spiders, the female gets an easy extra meal *of* her suitors. Among mammals, the male often serves as a protector of the group and will have special adaptations for fighting, like horns or large size. Male birds often use their bright colors to lure predators away from the nest while the drab-colored female remains hidden and protects the eggs.
One interesting trend is that the more monogamous a species is, the smaller the difference between males and females becomes, and the more "typical" roles tend to blur - probably because if the male is spending less energy seeking new mates, he can spend more energy raising the young. Many birds share nest-watching and food-seeking duties, and emperor penguins reverse the typical roles by having the male watch the egg while the female finds food. While humans have some of the typical mammalian "male protector" traits like males tending to be larger and stronger, this difference is far less pronounced than it is in other apes.
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Biology has two types of hermaphrodite species:
1. Simultaneous hermaphrodites. They are both male and female in one body. For instance slugs and snails.
2. Sequential hermaphrodites. They start out one sex, then turn into the other. Wrasse (a type of fish) are this type of hermaphrodite.
I'm going to assume you are mainly interested in the simultaneous hermaphrodite type. Both types mix up the genes when mating, just like regular non-hermaphrodite species do. It is sexual reproduction not asexual reproduction.
**Hermaphrodite Pros**
* Everyone you meet is a potential mate, not the mere 50% of the population as for 'normal' species. This is particularly valuable if others of your species are rarely encountered. Or if you live in a 'boom or bust' ecology, where you need to reproduce fast when the winter/dry season/famine ends and the good times come.
* When resources are scarce or patchy, you can conserve your resources and be male when you mate (producing sperm is cheap and fast). When the going is good you can spend lots of your resources and be female when you mate (producing eggs and babies is expensive and slow). This works best if food resources are unevenly distributed across the population (i.e. there are skinny hermaphrodites and fat hermaphrodites at the same time), rather than if the whole area is in the grip of a famine.
* If everyone has the same body form, society is more egalitarian. Of course, mature, experienced hermaphrodites may still lord it over clueless adolescents or beat up infirm, old hermaphrodites. But if there is no sexual dimorphism, then there is no male/female dominance hierarchy which lead to things like lions bullying lionesses away from their kill. It all starts out as a level playing field. *Anyone* can potentially become the leader of the pack. (This is of course, all about biology - if you add in culture then being the offspring of the King means you get to be the next king by inheriting his title and wealth).
**Hermaphrodite Cons**
* Being 'female', producing eggs and/or babies takes a great deal more time and effort and resources (food you need to eat to manufacture the egg/baby) than being 'male' and producing sperm. The courtship of various mollusc hermaphrodite species is therefore a fight to determine who gets to be male and do the impregnating and who gets to be female and be left holding the baby after they mate. In some sea slugs, they try to bite each other's penis off! (It does grow back later).
* In resource terms, a mated pair of hermaphrodites who are *both* pregnant will require more food, territory, etc to support the pregnancy and the offspring than a male-female pair where only the female is pregnant. (The male-female exception would be a species like deer, where the hind is growing a fawn, placenta and milk while the stag is growing new antlers, so both sexes need lots of food to produce several kilograms of new flesh and bone).
**Male and Female Pros**
* In monogamous species (most types of birds, for instance), two parents can dedicate their time and resources to raising one batch of offspring. They can split tasks between them - one guarding the eggs or chicks, one fetching food. Two hermaphrodites can also do this, but both have to have smaller clutches of eggs or they will be working harder than the bird couple to feed them. Mum bird lays 6 eggs, each hermaphrodite lays 3 eggs each.
**Male and Female Cons**
* In the majority of species where the males are much bigger and stronger than the females, it is for the specific purpose of males beating up other males to *prevent them mating*. 5% of the males are responsible for 95% of the offspring. 15% of the males are responsible for the other 5% of the offspring. So 80% of the males never win a fight, or never win *enough* fights and die as virgins. All the females get to mate. Being male is a high-risk strategy. Most mammals have the above sort of mating system: it's called polygyny. (In species where the females are bigger and stronger it sometimes for the above reason, but can also be for a variety of other reasons, such as females being cannibalistic).
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This would depend if the hermaphrodites still paired off to reproduce, or they were capable of reproducing by themselves.
The big advantage of two distinct creatures combining to produce a third is diversity - more chances for the unique combination to produce a creature better adapted to where it lives, or able to live elsewhere.
It's why sexual creatures evolve so much faster than asexual creatures. Greater diversity in the reproduced DNA strand. Hermaphrodites who reproduced by themselves would be at a distinct disadvantage after several generations, due to the lack of diversity.
There is also some specialization in the gender, generally speaking. I'm on shaky PC ground here, so I'll be careful... My wife pointed out to me that women tend to be better at non verbal communications than men... determining what someone is thinking by their actions. The reason for this is: a lot of women spend part of their life dealing with humans that can't express themselves verbally... small children. This may also be why most elementary school teachers tend to be women... better, certainly more patient, at dealing with small children.
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Life on earth displays more than the boring sex reproduction we know : 2 sexs, B only able to reproduce with A and vice versa. If B is as abundant as A, then it has only 50% chances to be able to reproduce with a random individual.
Some organisms however have more than 2 sex types.
Let us assume you have 20 sex types equally distributed : A1, A2, A3, ...
Each type can make sex and reproduce with all other types and not with its own.
Therefore a random organism can reproduce with 95% of the population.
Since sexual reproduction enhances genetic traits mixing and combination it is excellent for adaptation to new environments but from an ecological point of view, it is limited by abundance of your compatible partners. By multiplying sex types I would say that this kind of reproduction is really advantageous.
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I think it's important to bear in mind that evolution is incidental; the initial existence of a particular trait (advantageous or otherwise) is a matter of chance mutation.
So the reason we find a particular species to be hermaphroditic might not be because hermaphroditism itself formed the foundation for them to grow into their most recent niche. It might be because the first mutations which enabled some particular progenitor species to inhabit that niche simply occurred, incidentally, in a hermaphrodite. Contrariwise, it may be that sex distiction only developed in species occupying another niche entirely than the one to which the forebearer species of note in this exercise were acclimating themselves. If the alternative doesn't even come up, is there really an "advantage" to talk about?
We may also bear in mind that existing traits only become more or less prominent under selective pressure, which may or may not be ongoing at any given time in an evolutionary history.
So the last time that your nature as a hermaphrodite was highly relevant or that there was a chance that sexual distinction might have teniably developed in an ancestor of yours may have been very, *very* far back in your evolutionary history.
For example, hermaphrodites fair better at initial colonization and sustaining through near-extinction events than sexually distinct reproducers do, because they have less difficulty finding mates in sparse populations and every specimen can be a breeding mother. Imagine if you had a primordial ocean, full of creatures both sexed and hermaphroditic, but the dry land is unoccupied and inhospitable. If the first creatures with a preponderance to land-dwelling have sexes, and shortly after they establish themselves on land there's an environmental calamity that drives down their numbers significantly, they have a much greater chance of being left with too few breeding mothers, obsticles separating many of the viable breeders of either gender, or a pedigree collapse. Hermaphrodites are much more interchangable and can deal better with these problems. Also, if an individual specimen is carried far from its group, then it needs to be an impregnated female for it to have a hope of establishing a new colony alone (if indeed it's even a creature that has internal pregnancy). Hermaphrodites, on the other hand, can usually self-impregnate and struggle through as long as there's just one viable breeder at any given time.
But for those creature's well-established descendents 400 million years later, it could be that none of that matters anymore! Certainly, for you and me these aren't very big issues.
I suppose I could think of other times in evolutionary *history* where these things come up, but I'm not certain this is what you're looking for; I suspect that you're interested in writing a well-developed sentient hermaphroditic species of a more-or-less modern character. But if I'm being tangential in any way, may I interest you in alternative condolidated-gender lifestyles?
We know of many kinds of fish that develop into a different sex in different stages of life. So, you can have a model where young creatures are female (for maximum number of brood mothers) and the older creatures are male (for maximum selectivity). Or you could do it the other way around, I suppose, so that the young adventurous ones go and find a new tribe to breed with, and in being smaller only need to make the tiny gametes, and the old ones are tired and sedentary or are are just big enough to deal with pregnancy or laying big eggs.
Angler fish do this thing where young males go bite a female and then merge with her body, wasting away into just a set of genitals. This isn't truly hermaphroditic but it does result in individuals who are inately female but still bristle with penises.
Ants and bees are female if they hatch from a fertilized egg, but otherwise male. So maybe you've got a society where everyone who matters is a lady but rather than fuck each other personally, they just occasionally give birth to a bunch of tiny idiot expendable sons and throw *those* guys in each other's faces. To me, it just sounds like making sperm with some extra steps.
Genetic recombination is crazy, and raises the question: is your cell division really asexual if you're getting your genetic material all up in each other's business during your downtime? Imagine a world where everyone appears to be breeding asexually, though on closer examination they're actually totally infested with a sympathetic virus that only proliferates in their genital tissues but which is highly communicable and carries full copies of their genome. Then they're impregnating each other all the time with vast repertoires of genetic information and probably have some significantly weird diseases that I don't even care to anticipate and this is probably ridiculous but it's yours if you want it I guess.
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Okay so in the novel I am writing there’s a Third World War fought by the nations of earth against a human space empire (I am overly simplifying this ) . Now the thing is the empire uses transhuman supersoliders as their main fighting force but as the war drags on and becomes a stalemate the space humans use orbital bombardment among other means to make every supervolcano on earth erupt at the same time unleashing devestating amounts of volcanic ash .
Now part of the reason behind this is that their troops are modified to be able to breath in such conditions without the need for breathing equipment. My question is what kind of modifications would they need to safely breath in volcanic ash or at least some of its more dangerous components like sulphur dioxide and carbon monoxide?
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The gases are much less of a problem than particulates. You could easily imagine drugs (or evolved adaptations) to make people less vulnerable to carbon monoxide, by increasing the oxygen capacity of their blood or by breaking down the carbon monoxide before it gets to the bloodstream.
But humans have absolutely no way of removing insoluble solid particles from our lungs. It's actually something people aren't sufficiently aware of in real life – *any* kind of fine airborne dust does permanent, cumulative damage to your lungs. Without radically changing the structure of our lungs, the solution is to beef up the limited defenses we already have to prevent the dust getting in there in the first place (nostril hairs and cilia in the respiratory tract). You basically need HEPA filters in your nostrils (and the stronger lungs and bigger airways to be able to breathe through them).
That kind of filter is very difficult to keep clean. We secrete mucus to bind the particulates trapped by our cilia, and then eject the mucus, but this only works for very small amounts of particulates. To live constantly inside an ash cloud, you'd probably need to make far more mucus than people with cystic fibrosis do (and that's already enough to cause serious breathing problems).
The simpler solution used in HVAC systems is to just replace the whole filter as needed. Perhaps your modified soldiers have a cavity where they just plug in replaceable filters, or perhaps they are able to eject and regrow the filters themselves. Like having a big sea sponge living inside your sinuses.
As I say, this would probably mean that their noses and sinus cavities would have to be much bigger – like snouts – and they would need stronger lung muscles (diaphragm and intercostals), which I guess would make them more barrel-chested.
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**Nose hair. And lots of it.**
[](https://i.stack.imgur.com/xsgUF.jpg)
<http://grandfatherclause.blogspot.com/2011/09/tip-du-jour-trim-your-nose-hairs-28th.html>
Your transhuman soldiers have tranhumanamazing nose hair. The copious tangled hair is fortified with greasy mucus that serves to make each hair a flypaper like trap for particulates. The mucus stream helps keep the hair from clogging up because fresh mucus enters from the rear and makes its way down through the hair wad, pushing forward and out old particulate-laden mucus. The hairs too grow very quickly, spent and dirty hairs falling down in abundance as new growth presses forward from behind.
This is actually exactly how human nose hairs work. I have scaled it up for your solders, because of their need and because they are transhumans.
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Let's assume that this hypothetical alien crawled out of the identical primordial ooze to the point where they share significant genetic similarity with humans, and due to either evolution or outside intervention, evolved to be similar physiologically to humans if not in appearance. They have stronger muscles/bones, better lungs and circulatory system, etc. How far could they dive into our ocean before they couldn't withstand the pressure?
Assume that evolving on their home planet gave them efficient enough lungs that Oxygen/Nitrogen toxicity isn't an issue.
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**Such a being would need to wear an oxygen mask to breathe on Earth at sea level**
An outrageous simplification is that your alien's homeworld sea level atmospheric pressure is 10 bar. This is outrageous because a LOT goes into atmospheric pressure, not just gravity, and you have not provided enough information to correctly calculate the atmospheric pressure on your planet. So, I'm assuming just as it's 10X gravity, it's also 10X pressure.
*And this is worth a side note. Neither man nor alien doth dive by gravity alone. The equation is much more complicated than that. Indeed, I feel comfortable saying that gravity is only a minor component of the issue, but let's roll with what we've got.*
10% of atmospheric pressure on Earth (0.1 bar) happens at about [20 Km in altitude](https://www.windows2universe.org/earth/Atmosphere/pressure_vs_altitude.html). Mount Everest is only 8.8 Km, and it's a rare person who can obtain the summit without an oxygen mask, and nobody can stay there without one (it's more complicated than that... they need to get back to the last camp before sunset for a lot of reasons, temperature being only one of them).
So, you're alien is standing on the California coast, feeling very uncomfortable in the low pressure, and hating every moment of breathing in his exosuit — which he needs to keep from suffering low-pressure bruising and other nasty affects of not having the proper pressure on his/her skin.1
**He needs to be 0.1 Km underwater just to breathe comfortably**
Diving to 99.55 m (call it 0.1 Km for ease-of-use) [gives us an equivalent atmospheric pressure in seawater](http://docs.bluerobotics.com/calc/pressure-depth/). He needs scuba gear,2 but at least he can breathe easily. Like Aquaman,3 he's very comfortable at this depth — other than it's hard to see.4 Artificial lights are your friend.
**So, how low can he go?**
[Ahmed Gabr holds the world scuba diving record](http://www.guinnessworldrecords.com/news/2014/9/ahmed-gabr-breaks-record-for-deepest-scuba-dive-at-more-than-1000-feet-60537/) at 332.35 m (oh, call it 0.3 Km). Using that link above for pressure, 0.3 Km is a whopping 30.14 bar! That's 30X the "baseline" pressure! This suggests5 your alien could handle (if he was world-record material, we'll get to that momentarily) 300 bar.6
That happens on Earth at 2,986 meters below sea level. Let's call it 3 Km.
**What if we're not world-record material?**
To be honest, though, that feels like it stretches credibility. No matter how well you set up the science of your story, people need to suspend their disbelief — and that feels like it stretches it mighty thin. But, we're not all world-record holders, either.
* I'm comfortable believing your average alien can dive to 1.0 Km oceanic depth.7
* In an emergency, I'm comfortable believing your average alien could hit 1.5 Km.
* If your alien is exceptionally athletic and very practiced in deep diving, I'm comfortable believing 2.0 Km.8
---
1 *Remember, he's/she's/it's designed to keep the blood in against 10 bar. Standing on that beach... his/her blood really wants to get out. Oh, yes... it wants to get out something awful. It's the difference between submarines and space ships. But that's a story for another day.*
2 *Because, unlike Aquaman, your alien doesn't have gills. At least you haven't mentioned gills, so I'm going for broke on this one.*
3 *Except for the gills....*
4 \* *Even Aquaman can't see at those depths, no matter what Marvel comics says.*
5 *This is where I make the most wild supposition in my entire thought experiment. Just because our world-record holder can withstand 30X doesn't mean your alien can. There is a horrific number of variables actually in play, and we're only dealing with a handful. So, the goal here isn't 100% scientific accuracy (thank you for not using the [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'") tag), but believability.*
6 *Ooh-rah!*
7 *This assumes your alien has the physical strength to swim straight down 1.0 Km. Or, perhaps more accurately, to swim back up. Or to carry the equipment to get to that depth and stay there for any relevant length of time. Just because he/she can withstand that depth doesn't mean he/she can actually get there. That's a long distance underwater.*
8 *Which is still above the 11 Km world-record holding dive by the [Bathyscaphe Triest](https://en.wikipedia.org/wiki/Bathyscaphe_Trieste), so we shouldn't need Dr. Who to save us from what are most certainly [Sea Devils](https://en.wikipedia.org/wiki/The_Sea_Devils). Cheers.*
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Insufficient data.
Their ability to withstand pressure doesn't depend on their ability to withstand surface gravity unsupported by buoyancy. Native Earthlings, all developing under the same gravitational field, have wildly different abilities to withstand both high and low pressures.
The argument that higher gravity equals higher atmospheric pressure automatically just doesn't work. Even with identical atmospheric composition, there is no fundamental reason an otherwise Earthlike planet couldn't have one tenth or ten times as much air--how much you end up with is basically a crap-shoot, related to what combination of materials randomly ends up accreting onto the planet during formation, and thus so is the final atmospheric pressure on the planet's surface.
So, how deep could they dive? As deep as you want them to. If you want to know how ten times greater native atmospheric pressure would affect them... well, then ask *that*.
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* Ptot = Patm + Pfluid
* Pfluid = Ptot - Patm
* Pfluid = 10atm - [(1.01E5 Pa)(9.86923E-6 atm/Pa)]
* Pfluid = 9 atm
* Pfluid = rgh
* g = 9.8 m/s2
* r = 1.03e3 kg/m3 (density of seawater)
* h = Pfluid/rg
* h = (9 atm)(101325.0 N/m2)/atm)/[(1.03e3 kg/m3)(9.8 m/s2)]
* = 90.3 m
(if my math is right)
<https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/fluid_pressure.html>
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I feel the simplest solution to the OP's apparent problem would simply be to have the atmosphere have 1/10th the contents (disregarding differences in the planet's mass) while maintaining Earth-like percentages. A superior respiratory system would be needed to take in the necessary oxygen and certain flora would need to be far more efficient at breaking down CO2, but at least the alien wouldn't explode the moment they stepped out from a spacecraft pressurised to their planet's BAR into Earth's atmosphere.
Furthermore, reducing the percentage of Oxygen in the atmosphere proportionately to increases of Atmospheric Pressure should allow OP's alien to dive further, but again exceeding a partial pressure of 1.6 BAR would result in Oxygen Toxicity.
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I'm working on building a post nuclear war society in a nuclear winter where northern countries have risen to dominance through a combination of being non-primary targets in the nuclear war and having access to mining infrastructure as well as glaciers and ice caps. The idea is that these societies could utilize their mining infrastructure to mine the depth of glaciers or ice flows to get ice untouched by fallout.
**Would that actually work?**
**And if so would this be sustainable into the future, or would total contamination of the ice be inevitable?**
[Answer]
It would work, but:
* Large icecaps end up having surface water find their way to bedrock. You would want to mine ice that was under the surface. It would probably be easiest to scrape off the top few feet of a glacier, then harvest the melt water.
* Mountain glaciers have lots of crevasses. They aren't universal through out the mass, but using anything in the top 100 or so feet may be problematic. (below this depth, the crevasses tend to flow shut. And no, I don't know how the water on the top of the greenland icecap flows to bedrock. Erodes faster than ice flows?)
* The water itself is not radioactive, save for very small amounts of tritium from hydrogen capturing two neutrons. Since the radioactivity is associated with particulates, you should be able to make drinkable water with good filtration, and if that failed, by reverse osmosis.
* Most wells that are over a few feet deep are tapping aquifers with long refill times -- years to millenia. The rock that the water passes through will trap a very large fraction of the particles. So your only issue will be nucleotides that are readily soluble in slightly acidic rain water.
* Checking for radioactivity is simple -- if you have the geiger counter or equivalent. Indeed we can detect radioisotopes at levels well below what is practical for chemical analysis.
* Even if radioactivity is an issue, it is a bigger issue than drinking water. Your entire world is dusted with the stuff. The exposure you get walking around is going to be far larger than what you get from drinking water.
* Remember that your food comes from somewhere too.
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It will work, but fallout dust will eventually sip into glaciers via cracks. Maybe they can cover them up with something, e.g. spray (dirty) water on top to form an a crust of solid ice.
A few other concerns:
* There aren't that many glaciers in northern hemisphere, and most of them are in Greenland, which does not have that many people to begin with.
* Scandinavian countries do not have that much mining going on (I assume all coal and ore are used up). Their main mineral resource is oil.
* If all open water is badly contaminanted, farmland will be contaminated as well. So even if survivor can get water from the north, they cannot grow food.
* If they grow food in domes or caves or greenhouses, they can just cycle the water that they have, they do not need constant shipments.
[Answer]
Let's ask Professor Search-Engine for a few numbers:
* **What is the water footprint of humanity?**
[Hoekstra and Mekonnen](http://www.pnas.org/content/109/9/3232.full) in 2012 estimated human water usage a decade earlier at about 9,087 Gm^3/y. 15% of that was gray water (let's exclude it) and 92% of that was used for agriculture. Peeling off the gray water, that's about 7.7 trillion cubic meters of water in 2002 for about 6.3 billion folks in 2002, or about 1200 cubic meters per yer per capita. That's 1.2 cubic kilometers of water for one million folks.
* **Where is all the fresh water?**
[Igor Shiklomanov](https://water.usgs.gov/edu/earthwherewater.html) in 1993 estimated the freshwater bound in "ice caps, glaciers, and permanent snow" at 24 million cubic kilometers, about 1% of the total water on earth and roughly equal to the amount in groundwater.
* **What are the largest glaciers?**
[The USGS](https://water.usgs.gov/edu/watercycleice.html) in 1977 calculated that 90% of permanent ice pack was in Antarctica, and 10% was in Greenland. All the other glaciers on Earth *combined* added up to less than 1%.
* **How big are the Scandinavian Glaciers?**
[Lunkka](https://link.springer.com/referenceworkentry/10.1007%2F978-90-481-2642-2_464) in 2014 estimated that Scandinavian glacier ground coverage (different from volume) was about 0.2% of all permanent ice worldwide.
If you accept these numbers, then Scandinavia has roughly 48,000 cubic kilometers of water locked up in ice (perhaps much, much less since mountainous glaciers are much thinner than the Antarctic and Greenland sheets.
If we pretend that the 0.2% is volume (not area), then the Scandinavian glaciers can support 40 billion folks...for one year. Or 40 million for a thousand years. However, this is really the upper range - those numbers from the 1970s and 80s were before quite a bit of melting. And, of course, the 0.2% is area, not volume.
**But you have bigger problems:** Water locked up in ice is often not close to where it will be consumed (recall 92% for agriculture). The infrastructure and energy required to pipe or ship or truck and store and distribute all that water from, say, Scandinavia to, say, the rich farmland in Poland is enormous! Remember, we use *entire kilometer-wide rivers* full of water today.
Let's put that "1.2 cubic kilometers of water for one million folks annually" into perspective:
* That's a 100-tank-car train full of water *every 10 minutes*, day and night, all year long. A four-track main railway running from the mine to the farmland.
* That's 7.5 Trans-Alaska pipelines.
...for *each* million folks.
[Answer]
## It would work, but it's unnecessary
Deep layers in glaciers and ice caps can quite commonly be uncontaminated by surface activity for hundreds of thousands of years, and in a few rare cases they are over a million years old.
Mining into ice is quite easy; keeping the tunnels open is much harder, but not impossible. Because of [regelation](https://en.wikipedia.org/wiki/Regelation) and the general plasticity of ice close to its freezing point, the ice will tend to gradually flow into the tunnels and close them. This could be prevented with a [tunnelling shield](https://en.wikipedia.org/wiki/Tunnelling_shield). In practice for a material like ice, recovery is likely to be much more efficient with something like [solution mining](https://en.wikipedia.org/wiki/In_situ_leach) using superheated steam, a technique that completely eliminates the complications and dangers of tunnelling.
However, none of this is necessary unless the nuclear winter has turned the entire world into a (cold) desert. Potable water is not a finite resource; it is the ultimate renewable resource. It is constantly renewed by the [water cycle](https://en.wikipedia.org/wiki/Water_cycle), which purifies water by distillation. After the few days or possibly weeks required to wash fine radioactive dusts out of the upper atmosphere, any rain or snow falling will be potable. All that is necessary is a way to collect it without it getting recontaminated by contact with soil.
On a small scale this can be done with roof collection. Heavy snow makes it easier: the few inches in contact with the ground will be suspect, but the rest is fine.
It will be much more difficult to collect on a large scale, but not impossible. In high run-off impermeable terrain such as granitic mountains, much of the hazardous material will be washed away in the first few heavy melts. Each subsequent melt will still have some, but the level will drop rapidly with every melt and soon you will be able to collect potable water from gushing mountain torrents on a light industrial scale.
A particular advantage here is that, more than almost any other type of contamination, radioisotopes in water are especially easy to detect and measure, so any source that may possibly be clean can be quickly and reliably assessed.
**What if there's no precipitation?**
Maybe you have the type of nuclear winter where the entire world is ice-covered. It is too cold for any surface moisture to evaporate, and so there will be no precipitation -- no rain, and no snow either. A global ice desert. This is essentially what Sagan *et al.* proposed with the original nuclear winter hypothesis: that the smoke of ten thousand burning cities and forests would blot out the sun long enough that the surface would cool so far, that [runaway albedo](https://en.wikipedia.org/wiki/Ice-albedo_feedback) causes glaciation.
This theory is not now regarded as at all likely to be true -- a nuclear war will not trigger a "snowball earth." However if it did, finding potable water is the least of your troubles. No plant life will exist anywhere on earth, and when your tinned food runs out, everyone will die. Actually, you will probably freeze to death long before then, because it's going to get *really* cold: somewhere in the ballpark of -150°F ... at noon at the equator.
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[EDIT: this question is about life on Earth surviving, not the physical destruction of the planet]
Could the Earth survive a gamma ray burst if that burst occurred in our galaxy and the Earth is in the Sun's shadow?
The main factors of that question are: if the Sun is massive enough to block it and if the burst is of short enough duration that the Earth will be in the Sun's shadow long enough.
The gamma ray burst took place at least 1000 years ago so there will be no records of the incident. The source does not need to conform to any known massive stars.
Also, Venus will be in conjunction with the Earth so I don't have to explain why it kept its atmosphere.
The only restriction on the source of the gamma ray burst is that it needs to be from within our galaxy and, likely, on this side of the galactic bulge (since I can't see much of the burst's energy getting though that thick star soup).
This is the first in a series of questions to see if the setting I'm creating gets past the sniff test. I have a number of questions along these lines but if the answer here in no, then it's back to the drawing board.
[Answer]
Yes, the earth would definately survive an in-galaxy GRB if it was behind the sun, though that is unlikely (since the sun takes up such a small section of the sky, it is unlikely to block any given GRB).
Gamma rays can be stopped by the few inches of lead shielding nuclear reactors, the Trillions of yotta grams that make up the sun will be absolutely fine for the job.
You also don't need to worry about venus losing it's atmosphere, the worry with a GRB is that it destroys the ozone layer not that it flat out strips away our atmosphere.
The shortest GRB's can be two seconds long so earth could definitely be behind the sun for the entire duration of one.
there is also a mass extinction event that could have been caused by a G.R.B. if you don't want to bother with putting earth behind the sun <https://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_extinction_events#Gamma-ray_burst_hypothesis> and if it fits your timescale.
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If behind the Sun, yes. I can't imagine there would be any effects on Earth. GRBs are very short timescale phenomena, and Sun is vastly more massive than what is needed to block that.
GRBs are just about certainly caused by supernovae, so there would be a remnant to see after 1000 years, if there is someone to look with a telescope. Also, the supernova itself would be very much visible for a naked eye for some months if it happened in our galaxy.
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Setting: City similar to the City of London. Oppressive government. People live in fear and merely trudge on in their dull lives.
My characters: Part of a cell of a large national resistance group. They live in a small flat in an apartment on a main street. (I don't really know how to describe it, but think of the apartment where Banner lands on Earth in Infinity War)
My prodigy: She's the leader of this particular cell, and has extraordinary telekinetic abilities.
My protégé: He's of a similar age, and also has the same potential as the prodigy. However, he was badly injured recently, and after waking from his coma, forgot anything which happened before his battle. He was recruited by the resistance cell when he 'discovered' his telekinetic abilities.
Before the protégé was attacked, he used to be of a similar power level to the prodigy (he'd been trained by an organisation seemingly sympathetic to the government). But, although he has all of that power, he can't remember how to use it, so will need training by the prodigy to relearn how to use his ability.
**My problem**: When he'd been trained before, he'd been trained for years in an academy/dojo by other people with his ability who were professionals. He had had access to high-tech equipment and lots of space and room due to the size of the academy (which was expensive, but paid for by the aforementioned organisation). However, now he's in a relatively small place shared by around ten other people as well as the prodigy, who's never taught anyone how to use their powers. **So, how could my magical prodigy train my protégé?**
The most similar situation I could think of is Neo being trained by Morpheus in the Matrix, but he was being trained in a simulation (think of the scene where he jumped between buildings), so there were next to no restrictions upon them.
[Answer]
The answer is, put quite bluntly:
**With a lot of trial and error.**
Luckily your protégé was already trained before, and his mentor can leverage on that. Even if his memory is completely erased, there's a good chance that he will remember through training - ergo, he could regain much of the basics without passing through years of courses again. I'm assuming here that at least some of the training received somewhat "lingers" into the protégé, as muscular (or maybe neuronal) memory, even if out of reach for his conscient mind.
After all, your protégé may have lost memories of the training, but not the training itself (different things are stored in different parts of the brain, so the area responsible for this character's abilities may as well be untouched after the coma).
The real issue here is that your mentor doesn't know how to train him: she will have to try out various things to make his powers emerge back. From simple "lift the ball" exercise to subjecting him to stress - and maybe to her own telekinetic power, in order to shock him into reaction.
The small space won't do if not for the simplest exercises (since the telekinetic abilities of the protégé could backfire and injure some of the other occupants of the flat), so maybe they would have to risk training outside or find a new "gym" suited space.
A good strategy could be trying to spy how does the organization/the government did it. You don't have to steal their training machines (even if you may as well try): the core target would be understanding how they work. Once got hold of the principles, your mentor could begin applying them with more homemade, cheaper resources.
[Answer]
# Make the poor training conditions part of the story (See Rocky IV)
First off, if you haven't watched the Rocky IV training montage, you are wrong.
[Here it is](https://www.youtube.com/watch?v=gqwuYX3fZZc). Go watch it, then come back.
Ok, so what do you see there? Ivan Drago trains with the most modern of Soviet medicine, surely-accurate punch strength machines, and totally-not-steroids injections. Rocky climbed tall mountains in the snow, and picked up logs and did various rustic manly things while growing a beard.
That whole scene existed to push Rocky as the underdog, so that his inevitable victory in the ring seemed more unexpected and legitimate.
In as much as you are also making a story, why not make it a plot point that the protege had to train under less than optimal circumstances? Sure, the best telekinetic mages all train at academies, but this time, the protege was forced to train in basements, and outside the city limits and night and whatever other disadvantaged conditions. But at the end, he still develops the power needed to beat the bad guy and save the world/get the girl/whatever the plot point is.
[Answer]
He does not remember for a reason. **He has psychogenic amnesia**.
>
> Psychogenic amnesia, also known as functional amnesia or dissociative
> amnesia, is a disorder characterized by abnormal memory functioning in
> the absence of structural brain damage or a known neurobiological
> cause. It results from the effects of severe stress or psychological
> trauma on the brain, rather than from any physical or physiological
> cause. It is often considered to be equivalent to the clinical
> condition known as repressed memory syndrome... Situation-specific amnesia is a type of psychogenic amnesia that
> occurs as a result of a severely stressful event, as part of
> post-traumatic stress disorder.
>
>
> Post-traumatic stress disorder (PTSD) is a severe anxiety disorder
> that can develop after exposure to any event that results in
> psychological trauma, which manifests itself in constant
> re-experiencing of the original trauma through flashbacks or
> nightmares and avoidance of any stimuli associated with the trauma...
>
>
> It is most commonly associated with traumatic events or violent
> experiences involving emotional shock, such as being mugged or raped
> or involved in car crash. Those at increased risk include those
> sexually or physically abused during childhood, those who have
> experienced domestic violence, natural disasters, terrorist acts, etc,
> soldiers who have experienced combat, and essentially anyone who has
> experienced any sufficiently severe psychological stress, internal
> conflict or intolerable life situation.
>
>
>
The treatment of PTSD is beyond the scope of this answer, but that is what must happen for your protege. His lack of memory is a reaction to the events that hurt him, and a denial of his own abilities which led to those events. Teaching him to use those abilities anew will run into the same subconscious roadblock (which would make for fine movie material). Your protege must have a coach / therapist to help him address and resolve the underlying traumatic experiences.
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As already mentioned a simple act of trial and error, combined with how memory loss can occur.
Most people who suffer from memory loss often do not lose their ability to speak, read, write, walk, do the job they used to do, drive etc. When they do lose a particular skill they often are able to re-learn it, although the length of time taken can differ based on how much brain damage there was and how it was spreas through the brain.
Your protege can simply have forgotten most of his past and training, but it's still there just like his ability to talk and walk, he just might need to remember or re-learn parts of it. This makes it easier to learn all those skills again.
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You may already have your answer in the character's past amnesia alone.
People who suffer amnesia will have muscle memory to remember how to do physical things, but they won't remember other things surrounding that.
If a person has to do a ritual, say words, or maintain some sort of non-physical situation to use their powers (say, a certain kind of aura or energy or outlook), they wouldn't remember those things or how to do them.
Generally telekenetic powers aren't associated with being locked behind any other barrier, but if there are non-muscle barriers, those can be utilized as a wall that your protagonist must learn to re-climb. Some other ideas in this realm are not having the strength/capacity to wield those powers, or even to control them.
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If your prodigy is truly a prodigy, have them recreate the neural pathways which resulted after the learning process through the academy.
Maybe a plot line could be that this could cause the protege to forget other things (reassembling the existing pathways vs materializing new ones which would be more science-y). This could take the form of teaching the protege something much easier to learn then 're-purposing' or actively reforming those pathways in to the telekinesis gift.
A catch can be that this can only be conducted on people who already possess the natural gift and still is only the starting point. Like any learning process, these pathways will need to be strengthened (a mental rehabilitation process) through hard work and normal training. This can just accelerate the initial process.
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Could a creature like this exist?
Jellyfish or cephalopod-like creatures that live in 'swarms' underwater. They float aimlessly around in a net formation. When one member detects prey below the formation they send a signal to the rest of the swarm.
A single member is 'elected' to be sacrificed in hunting. This member begins electrolosis, storing oxygen and hydrogen in lung-like sacks.
It's body contracts, causing it to sink, leaving the formation where it is replaced. It continues to sink to the same depth or nearby to prey where it generates a spark, igniting the hydrogen and oxygen. The detonation causes a shockwave that kills the prey which floats into the swarm net above where it is consumed.
The swarm is protected by an outer ring of individuals that create fiery bursts to ward off predators.
[Answer]
Surprisingly Maybe?
<https://en.wikipedia.org/wiki/Camponotus_saundersi> there is a species of ant that does something similar in *defense of the hive* so the behaviour is not unheard off. Though your jelly fish would actually be very different from most jelly fish we know of, a superficial similarity would not be impossible.
The mechanism of explosion however is definitely wrong. Electrolysising water dramatically reduces its density and it would take massive pressures to counteract this (pressures that would themselves detonate the mixture) so your jelly fish would FLOAT before exploding not sink. In addition the energy requirements of electrolysising that much water mean your jelly fish ALREADY has enough energy to explode if it carries its own oxidiser. That being said there are other ways your jelly fish can explode, if it carries two hypergolic fuels for instance or if it just rapidly heats itself up or if it has a sack of natural explosive somewhere on its body. This is something that needs re-working but is not a deal-breaker.
Killing prey by shockwave is also very realistic I mean <https://en.wikipedia.org/wiki/Blast_fishing> humans do it but will mean your jelly fish need a very efficient reproductive system and/or massive specialisation to make it worth the loss.
[Answer]
Although it's definitely not impossible for a self sacrificing jellyfish to exist, I would simplify this a lot.
First, instead of a swarm I would have a single queen jelly, or maybe several, who create smaller jellies that will explode. Like a queen bee and worker drones. This way a large queen can eat prey that is bigger than the exploding jellies, while only needing a small amount of energy to make any individual drone jelly.
Secondly, I do not believe that jellies have enough muscle mass to contract gasses to a small enough space to sink. I would have these jellies be deep dwellers. The natural pressure compresses the gasses. The jellies offset the lift of the gasses with small calcium deposits inside their bodies. They attach prey above them by swimming up and letting their gas expand, causing them to float up into the prey. Then the prey sinks down to the queen jelly along with the drone's remains, which will contribute to a new drone.
A sparking organ is fine, a one time spark made from a chemical reaction could probably be made by a jelly, given it could evolve this feature at all. However, electrolysis seems unlikely. Instead, in needs only be impregnated with a small amount of gas when it is born. Possibly methane from digested preys the queen has consumed.
So yeah, colony of exploding jellyfish seems cool. (As a note, since the drone jellies use an electricity generating organ, so could the queen. It could locate prey the same way platypus do, and signal drones with certain currents of electricity.)
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In Warlords poorer families in the belt or some of the colonies are not able (for whatever reason) to pay for 'gravity treatments' or possibly helpful drugs and are forced to live and raise their children in micro gravity.
Now I think a freakishly tall human with his legs and spine having a visible brace would make these "Lanks" easy to spot and have a unique vibe too them. Also is fun to visualize.
What I am wondering is would braces help these Lanks walk. In my mind the braces would be a small scale exosuit that not only holds them up but does most of the work for them. But feel free to make a better suggestion if you have one.
Notes:
Space stations gravity (through centrifugal force) is set to or approaching roughly Martian gravity (if this isn't possible or is impractical lunar gravity would do)
Lanks are born (usually) via artificial wombs with the idea being: somehow the machine can simulate gravity inside itself for the fetus (maybe through water currents).
[Answer]
I have muscular dystrophy. I think I fit the description of your "Lanks" pretty much to a T. I am very thin, very weak, and unable to stand or walk under my own power. Even a cane or walker is not enough support.
In my childhood, I wore braces which allowed me to stand and, with quite a bit of effort and a walker to hold on to, to walk short distances. I wore the braces outside my clothes, excluding my shoes. They were hard plastic and metal and could not have been comfortably worn under clothes. They went from the bottoms of my feet, up to under my arms.
They looked a lot like this, though I didn't use canes like this woman.
[](https://i.stack.imgur.com/LStNc.png)
I see no reason why your "Lanks" couldn't wear something like this. If the joints of the braces, particularly the knees and hips, are as close to frictionless as possible, it doesn't really make much difference how weak they are. All it will do is make their steps shorter. The braces are supporting all the weight. Balance will be an important issue, as since the braces make your body stiff, there is no such thing as a minor fall. No matter how you go down, you are hitting your head hard.
I learned to walk in my braces relatively easy, compared to what the other answers suggest anyways. It's certainly not insurmountable. The braces don't need to be powered either, mine weren't.
I would be much more worried about the Lank's cardiovascular and respiratory systems. Can their heart handle fighting gravity? How about the valves in their veins? Can their lungs still inflate even against the weight of their ribs?
[Answer]
**1. Artificial Wombs**
The latest research suggests that embryos will develop normally in zero gravity. (<https://www.popsci.com/mammal-embryos-can-develop-normally-in-space>) .
As high-tech as the artificial womb sounds, I suspect it will remain primarily a vehicle for handling premature births for the simple reason that nature has provided humans with the perfect environment for growing embryos.
Complex specialized equipment like the artificial womb would be cost prohibitive (space, energy consumption, spare parts) to asteroid dwellers, compared to "the old fashioned way", which requires only a few extra ounces of food and water per day.
**2. Braces**
Braces can help to offset some of the brittleness of the bones due to understressing during growth, but simple braces cannot compensate for the (lack of) muscle tone. All the braces in the world will not help your Lank to stand up in gravity.
For that, you will need a powered exoskeleton (<http://www.sciencemag.org/news/2017/05/robotic-exoskeleton-could-help-prevent-falls-elderly>) . Note that the people this device is aimed at have exactly the same issues that the Lanks will have, albeit for a different reason (age versus environment).
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Fine idea for a story! "Lanks" is good too.
The suits would be expensive. If poverty were the only reason for space babies I worry they could not afford them. The Lanks should be proud and possibly even well off. They are disdainful of the thought that a zero-G upbringing is in any way inferior. They might call the gravity-raised "sinkers" or some such.
But sometimes a Lank has to visit a place with gravity and so they need the suit. I like the frame exosuit idea. There could be an artificial intelligence in the suit (as is actually the case now with [modern prosthetics](https://www.popularmechanics.com/science/health/a7764/smart-bionic-limbs-are-reengineering-the-human-9160299/) ) which helps the Lank coordinate her walking. I like the idea of such prosthetics having a very annoying "coach mode" that encourages proper posture and stride in peppy, Lank-accented tones.
I like the idea of an earth normal trying on the exosuit and struggling mightily for a half hour until its owner shows him how to turn it on. The built in coach is impressed by the sinker's form, much to the annoyance of the Lank owner of the suit.
Halfway through the story you could learn that it is possible to change the setting on the exosuit. A Lank in 1 G sets her suit for 4 G and can jump prodigiously far.
The exosuit could not do it all. I can imagine a busty Lank complaining how suffocating and heavy her breasts were, especially when trying to sleep on her back. The Lanks might have a large isotonic salt pool in their quarters to relax in, their buoyancy counteracting their weight.
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[
Eskimos in space! Let's say, just for contextual concerns, that a band of water-rich comet miners want to use water-ice found in the outer Solar System as the main structural and functional component of their spacecraft. That is, the spacecraft and perhaps some of its basic support functions (internal atmosphere, electricity & propulsion?) are derived from the properties of ice.
I'm not concerned with the constructional methods of such a spacecraft (given my [source](http://www.neofuel.com/iceship/iceship_isru_1998_prinitable_2col.pdf) outlines it quite humorously), rather, **How might a spacecraft of water (and any material state thereof) perform the basic aforementioned functions of a classical spacecraft?**
The **icestronauts** have access to items like fission/fusion technology, and all the wondrous advancements of the current day, and any number of these things may be incorporated into the spacecraft's design, so long as the bulk of it is water-ice.
If you don't want to read the source—which happens to be practically the only source I can find for such an idea—the idea behind the ice spaceship's construction is this: launch a plastic "mold" into space (quite like an inflatable tube one might see at the beach), and fill it with water. Freeze the water, spin the thing up, and you're done! A functioning von Braun wheel made of ice. Now, my idea here is to attempt to expand upon this, make it feasible and practical: Water may be used as fuel; It can be heated into a gas and expelled out at high velocities; Oxygen can be ripped from H2O molecules; it has certain radiation-shielding properties; etc.
Postscript: the icestronauts are willing to settle on the use of other ices as well. Consider it an extension of the previous limitation of the addition of other technology to support the bulk of water-ice.
**Edit:** assume no other external factors will destroy the spacecraft; our icestronauts are not that foolish. Consider their efforts as R&D, searching for viable methods for this endeavor.
[Answer]
## Comet Riders
The main spine and functional systems of the vessel won't be ice obviously, but the hull very well could be. So you build your ship first. It's basically just a fusion reactor and a magnetic reactor plasma nozzle, a series of insulated and airtight habitat modules, and a control room. Then you begin freezing water around these objects. The ice provides great radiation shielding properties and is also an excellent ablative armor system against space-born particles and dust. The skeleton and operational parts of the vessel itself are standard spaceship fare, but the ice is what wraps it all together. With the power from your fusion engine you could easily melt the ice down to be used for drinking water, or electrolyzed into oxygen and hydrogen which could then be used for breathing and fuel. The icy hull of the vessel is a fuel source, air supply, armor, and radiation shield all in one!
## A New Culture of Nomadic Space Eskimos Arises!
Moving liquid water into space and then freezing it just isn't cost effective. Our outer-rim Eskimos don't really have much of a budget for that kind of thing. Why would they pay that much when all of these fantastically sized 10 to 60 kilometer chunks of ice are already just sitting there for the taking? These ice-ships attach to comets in the far outer solar system and use the heat and power from their fusion reactor to burrow into the comet. You now have a 10 kilometer to 60 kilometer wide spaceship just waiting for you to hollow out and build whatever your heart desires! You don't need the metal bits for cold storage areas or work areas, just pipe in enough heat to make it workable and use it for whatever. If you're tough, careful with where you hollow out, and don't mind sleeping in below freezing temperatures use the heated ice tunnels for habitat too. ("Heated ice tunnels" simply means "above the crazy frigid temperatures of space" not above the freezing point of water.)
The best part? Even a rather ordinary sized comet of 10 km in diameter contains approximately 1 trillion metric tons of usable water for air, fuel, and drinking. That's enough to last a population of a few thousand several generations as an orbital igloo. Obviously all of the actual functioning parts are not ice, but once you attach an engine, reactor, and habitat module to it and fill it with room I am going to say that the comet now qualifies as a spaceship made of ice.
## Gravity
Over time the tribe carves the comet into a cylindrical shape which they can rotate to simulate gravity. In the meantime they have sections built within the ice that perform such tasks and take turns living in microgravity in shifts to perform the work needed to accomplish the task of constructing all of this.
[Answer]
A spaceship is not only a shell. It's a *sophisticated* shell. it is filled with electronics, piping, sensor arrays...windows.
The ship should be assembled in geostationary orbit on Earth's nightside, or the sun will melt some of it at each orbit. Then you must digdigdigidg in the mine all day through...err, you need to dig into the ice with outmost precision, possibly using thermal devices to minimize the cracks in the shell. Oh, and all of this must be done with an outer coating all around the ship or the sublimation could make work more difficult.
This said, after all the surgical work is done, apply propulsor. Cheers! All aboard, turn propulsor on.
If the crew is lucky, they will see the ship melting away starting by the tail while the rest of the hull sublimates under the sun's solar wind.
If the're unlucky, the propeller's vibration will crack it apart
There **is** a viable, though much more rudimentary alternative: instead of building a ship as we imagine, since aerodinamics is nt a thing in space, our heroes could freeze enough water to create a massive iceberg, carve it for their needs and place a network of ionic propulsors. Of course, it leaves to desire in terms of landing and reusability, but it would make for a great one-way ship.
OK, so you need to transport in orbit some million gallons of water, which would make it incredibly costly. Sheesh!
[Answer]
This would not last long - as with all things in space, heat management will be a problem. People say "space is cold", but it really isn't. Things in space tend to be very cold, but space itself is the universe's most perfect thermos.
Everything you do produces waste heat. The heat from the powerplant would likely be the most extreme, but *everything* produces heat, so every bit of power you use needs to be accounted for. This produces heat to an extent that ice should not be relied upon for any kind of structure or even have significant contact between the ice and the rest of the ship.
As a way of *storing* ice, sticking it in a shell around the outside of the craft (but not touching except for a few insulated standoffs) is a great method. It provides a kind of shielding, and if you don't mind losing a lot of it as you go along it can also act as an enormous radiator to keep you from overheating (probably a good emergency backup but not good as a primary radiator if you don't want to lose a lot of water).
[Answer]
Since the OP already makes reference to the [NEOfuel](http://www.neofuel.com) "[ice ship](http://www.neofuel.com/iceships/)" design, using a giant plastic or metal foil bag to hold the water until it freezes into ice and creates the hull of the ship, I'll point out a similar idea on a smaller scale: the [Spacecoach](https://www.centauri-dreams.org/2015/05/01/a-stagecoach-to-the-stars/).
The liquid water is held between what are essentially two water balloons, with the outer one being the outer hull, and a smaller, inner one defining the crew and equipment area. The liquid water filling the interspace provides radiation protection, drinking and wash water, passive thermal management, water for the hydroponic gardens, and reaction mass for the propulsion system.
[](https://i.stack.imgur.com/U6vTG.jpg)
* Hypothetical Spacecoach design\*
Really the main difference is the water is not frozen to be used as a structural material, and even an ice ship would be doing something similar, since the ice has to be melted to do most useful functions in the ship.
The other issue that will need to be addressed is the gathering of the ice and turning it into useful products. Humans cannot drink salt water or water contaminated with methane, ammonia or the various other materials that form "ice" in the outer solar system, and many pieces of human machinery would also corrode or be damaged by contaminated ices. Contaminated ice or water would also kill plants or any biological systems it comes into contact with (unless it is extremely exotic).
The ice would have to be mined, then brought to the focus of a large solar mirror (possibly inside a large plastic or metal foil bag). The heat of the sun then boils the water and pure water steam is extracted into a cold trap to turn into liquid water or ice, while the other volatile elements are redirected and stored elsewhere. You need a large solar distillery, in other words. The water can then be pumped into the Space Coach, or into the flexible mould to freeze into the appropriate structural shapes.
[](https://i.stack.imgur.com/UXKj2.jpg)
*This, but on a very large scale*
So there is more than *just* getting water from comets or asteroids to making ice or water ships, a large industrial base will be needed as well to mine and extract pure water, and create the flexible metal or plastic containers needed to hold the water or ice, as well as make the actual spaceship systems embedded within.
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Diseases in nature tend to naturally become less virulent over time, in part, because the disease vector changes and in part because the host population develops immunity to it.
How possible is it, in theory, to accurately predict the time period until immunity to the disease or its decreased virulence causes it to be an unimportant threat to almost all human populations and how accurate could those prediction be, in theory?
Is there an effective minimum or maximum period of time over which this happens in a modern-like population?
For example, suppose that someone was designing a bioweapon in the context of a world like Earth in the near future. Could they design a disease to become obsolete after a fairly precisely measured period of time that was less than a human lifetime but more than a few months?
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Diseases become "less virulent" by killing everybody who is not resistant to them.
When Europeans came to Americas, the diseases that they carried wiped out a good portion of Native American population:
<https://en.wikipedia.org/wiki/Population_history_of_indigenous_peoples_of_the_Americas>
<https://indiancountrymedianetwork.com/history/events/american-history-myths-debunked-the-indians-werent-defeated-by-white-settlers/>
Those diseases were not virulent in Europe b/c everybody who could die from them already did. But they remained virulent in unexposed populations.
You can try to predict which % of human population has the genes to be immune to your virus, and then use models to predict how the disease will spread and kill people. Interestingly, modern anti-epidemic and quarantine measures will slow the spread of the disease, but also slow the spread of immunity.
But the virus will remain virulent on unexposed population, including your troops and your citizens. Or you can use a virus that your people have immunity to.
**Edit**
Virus that kills its host too fast is hardly a good application, it will not be able to spread. And infected areas will remain will remain dangerous even after all victims are dead.
One feasible idea is a flu-like virus that weakens most people without killing them, and lets them develop immunity as they recover. It will weaken your enemies enough for you to conquer them with conventional weapons, and everybody will be immune to it after a year. It will have to look like a cold, and have long incubation period to let it spread unnoticed. And you can immunize your own troops and citizens against it.
[Answer]
To answer your three questions in order:
1. In theory you can predict non-virulence quite accurately *but* to do so you need a very large set of data spanning many years of real world study of the infected population and an ability to track the mutation of the disease accurately at close intervals.
2. Ever disease is different, so is every population exposed to a given disease so I would expect that there are no hard and fast rules for a minimum/maximum period for a disease to become non-threatening.
3. Given the unpredictable nature of mutation you'd be better off targeting the population you want to kill in such a way as to exclude the native biome, of the weapon makers, and thus render the pathogen safe for them at all times, barring unfortunate acts of god.
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I had an idea of a wind tree that can create wind but it is not man-made) in a fantasy world. Then I began to think/wonder of ways it could realistically work without any magic.
So thats where I'm stuck. Hope this clears up the confusion. It's like an off category of the [Anatomically Correct Series](https://worldbuilding.meta.stackexchange.com/questions/2797/anatomically-correct-series) (which is how I first found this site), but instead of fictional creatures, it's a tree.
Here's my thought process on how a wind tree could exist on Earth:
Why does it need to create wind? To clean itself of dust perhaps or scare predators away from eating it seeds. From what I learned from the answers, perpetual motion is out of question so maybe it uses water pressure which it can control and blow wind out of mini blowholes. I think the seeds will be some dandelion shape so benefit from the wind.
When will it blow? I very badly want it to be 24/7 but that does not sound possible. Wind tree seems inhabitable since taking inspiration from venus flytraps, there will be lots of tiny hairs or maybe just blocking the blowholes signals to blow it off.
Weaknesses: Fire? I originally imagined it to deflect fire thats dropping from the sky.
How does it looks: like a cactus tree?
[Answer]
Start with a plant that has tubular leaves, such as the gollum jade:
[](https://i.stack.imgur.com/5qwNn.jpg)
Have it evolve so that the tubes are parallel to branches, rather than growing perpendicularly from them. Now have the tubes go:
* Completely hollow;
* Open at both ends;
* Finally, add moving parts. This may sound counterintuictive for plants, but remember that mimosa (the touch sensitive one) and carnivore plants do have those.
The moving parts will push air through the tube.
Now we need to justify why the plant does that. Let's say it thrives in tropical forests, under the canopies of tall trees. It is a variant of carnivore plants... Rather than taking nutrition from insects, it takes nutrients from the dust and suspended particles in the air. The wind makes them more efficient in this gathering.
A single plant will not have much effect on the environment around her, but when thousands of these, with hundreds of leaves each, are aligned in a corridor... Then you can feel a gentle breeze around the trees.
Such plants will change the ventilation pattern of places where they live, so the whole ecosystem will evolve with them, and vice-versa.
[Answer]
Well if we break Wind down to it's basic components, it is an air pressure differential. High pressure flowing into low pressure.
We can use the 'small-scale' sea breezes as an example. On sunny days the sun rays warm up the land quicker than it can warm up the sea (which has a greater capacity to absorb and store the sun's rays). This results in a temperature difference.
The warm land then heats up the air above it. As the air becomes less dense than the cooler air over the sea, it begins to rise. The rising air over the land then results in lower air pressure over the land. The cooler sea air remains denser and therefore has a higher pressure over the sea. This creates the pressure differential. Nature tries to equalize this difference, and the sea breeze is born. Air flows from the cooler sea into the warmer land, giving some much appreciated relief.
To use this for your WindTree, you would need to provide some mechanism for the WindTree to absorb and store *alot more* of the sun's rays than the land around it. Your WindTree will act like the sea in this example.
This wind could possibly be 24 hours using katabatic and anabatic wind processes. During the day, the *air around the WindTree* would be cooler than the surrounding land and wind would blow away from it. During the night, the *air around the WindTree* could be warmer than the surrounding land and wind would blow towards it.
I do not know how strong you could make this wind or if the tree could 'choose' when to release stronger wind. I do think you could have *stronger* winds just after the peak period of temperature difference than during periods of smaller temperature differences.
I will leave you to work out a mechanism for the WindTree to absorb more heat without frying. Remember there is a difference between absorb (stored, leaving the air cooler) and reflect (immediately back in the air and hence warmer). You could help the WindTree out by adding more reflective surface features to the land around the WindTree. Eg grass/plant pigments or artificial surfaces etc. This will allow you to handwave less.
I'm not too caught up on my Tree physiology. I am assuming the tree would need major internal changes to handle all this extra heat without it escaping back out into the surrounding air.
Currently I have been thinking of a very *extensive* root network allowing for more heat to be stored in the tree. The WindTree could then also *release or redirect* warmth back into the surrounding land through the furtherest roots leaving the air directly around the WindTree itself cooler. Coupled with some sort of ultra absorbant tree surface. I don't think the WindTree will have a very wide surface area, as I think that would allow for more heat to be dissipated back into the air.
Why would it need to do this? Not sure. The WindTree would need some major benefit from storing all this heat and not just releasing it back into the air.
Possibly the plant mechanism involved was evolved during a really cold period in the planet's past. Something to do with needing warmth to create new growth in arctic cold conditions? Could be it needed to defrost the frozen ground around it and hence absorbed more heat from the surrounding air to spread along the root network.
Possibly needed to constantly move its branches to avoid a parasite from settling on it. So it needed a constant breeze? Or to attract a symbiotic creature that is attracted by cooler temps?
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I was not entirely sure how to word the title question, so allow me to put my question into more detail here:
Suppose there was a planet with just the right conditions to allow humans to live there (atmosphere, close by, livable temperature, etc.), and there were valuable resources giving them reason to settle this planet. However, the problem is that the gravity on said planet is crushing (a random number for an idea of what I mean by crushing, 300 m/s squared). How might a society with advanced technology theoretically get around this problem. I see two possible solutions.
1. Using some advanced technology, the society engineers a way for humans to live on the surface and retrieve these resources without being crushed.
or
2. Using some advanced materials and engineering, the society uses robots/drones/some kind of automated system to get to the resources.
Assume that the value of the resources is greater than the cost of getting them. Either way, to be explicitly clear, I need some way for a technologically advanced society (we will say around 1500 years into the future for some reference) to retrieve valuable resources both on and beneath the surface (requiring both mining and harvesting) of a planet whose gravity is 100s of meters per second squared, and get them off planet, in the most practical and efficient manner possible without using handwavium antigravity. The precise method, materials, etc. used in solving this problem should be at least loosely based on science, however whatever works works.
[Answer]
# Short Answer
No.
There is nothing you can do consistent with real world science to mitigate extremely high gravity that would make the surface of such a planet habitable for humans, nor could an otherwise habitable environment exist at such a high gravity.
But, there are circumstances related to your scenario that could be workable that I explore.
# Long Answer
### What Kind Of Planet Could Fit This Description?
The specific gravity of [the planet Earth](https://en.wikipedia.org/wiki/Gravity_of_Earth) is about 5.5. [Lead](https://en.wikipedia.org/wiki/Relative_density) is about 11; gold and depleted uranium are about 19; [osmium](https://en.wikipedia.org/wiki/Osmium), the most dense naturally occurring element is 22.6.
For an Earth radius planet to have 30Gs of gravity, it would have to have a specific density of 165.
This is much less than the specific density of a [white dwarf star](https://imagine.gsfc.nasa.gov/science/objects/dwarfs2.html) (about 200,000) or of a [neutron star](https://en.wikipedia.org/wiki/Neutron_star) (about 200,000,000,000), but even [the most dense planet ever discovered](https://en.wikipedia.org/wiki/PSR_J1719-1438_b) has a specific density of only about 23 g/cm^3 (incidentally and probably not coincidentally, it is a [pulsar planet](https://en.wikipedia.org/wiki/Pulsar_planet)).
So, it is basically impossible to have a planet with a radius smaller than Earth that had gravity that strong. The most dense possible Earth radius planet would have a surface gravity of about 4G, and as it got smaller the gravity would decrease.
You can also increase gravity by making the planet much bigger in radius than Earth. Indeed, these are the only kinds of observed bodies with surface gravity on the order of 30Gs.
Planets with gravity that strong are [rare](http://exoplanets.co/exoplanet-correlations/exoplanets-surface-gravity-distribution.html), but they do exist. As of [5 August 2012](http://exoplanets.co/extrasolar-planets/what-is-the-strongest-surface-gravity-for-an-exoplanet.html):
>
> [T]he exoplanet with the strongest surface gravity was Kepler-25 b.
> This planet has a radius of 0.23 Jupiter radii, a minimum mass
> estimate of about 12.7 Jupiter masses, and a calculated surface
> gravity of 633.7 times that of the Earth.
>
>
>
For example, the closest fitting known exoplanet to the planet in your question is [KOI-423b](http://www.openexoplanetcatalogue.com/planet/KOI-423%20b/) has a mass about 5721 times Earth's mass and a radius of about 13 times Earth's radius, giving it a surface gravity about about 33 times that of Earth.
The radius of the Earth, in round numbers, is 4,000 miles. For exoplanet KOI-423b, you'd have a radius of about 64,000 miles (by comparison, the radius of Jupiter is 43,441 miles).
### Surviving Near Such A Planet
There is no way to shield gravity. You can temporarily escape its pull on you by being in free fall, but that respite only lasts for a short duration and if you want to return to where you started, you need to accelerate away from the source of the gravity which temporarily makes the effective pull on you even worse.
The only sustainable way to escape its effects is to stay a long way from the source of the gravitational pull. Therefore, the only way for a human to survive in an environment like that would be to be at a substantial distance from the surface where it is 30G.
To get to 1G one would need to be about 4.5 times the radius of the planet from its surface. Of course, a human could survive with somewhat heavier gravity than 1G, but even 2G would be pretty intense. By the time someone is at 2.2 times the radius of the planet from its surface, gravity approaches 3G which is survivable in the short term but is close to the limit of what someone can survive on a prolonged basis.
Carrie Vaughn's 2017 stand alone novel, "[Martians Abroad](https://rads.stackoverflow.com/amzn/click/com/0765382202)" explores a similar issue as third-generation Martians accustomed to life on Mars at about 1/3rd G are sent to college on Earth and suffer through the higher gravity to which they are unaccustomed. (On the whole it is a good account although it fails to recognize that a kilogram is a unit of mass rather than weight, which is annoying to someone whose had that distinction pounded into him many, many times.)
In the case of KOI-423b, the planet's gravity would have be Earth strength gravity at a distance 288,000 miles from the surface. At a distance 140,800 miles from the surface of KOI-423b, gravity would be 3G which is almost intolerable on a sustained basis for humans.
At 30G, a whole host of issues like breathable air pressure become pretty much untenable for any human. It takes a huge feat of bioengineering for [giraffes](https://en.wikipedia.org/wiki/Giraffe#Internal_systems) to be able to keep blood flow going to their heads as they swing them from the ground to being fully erect without passing out or having a stroke. This situation would be unfathomably more difficult every second of the day.
Robots or remotely operated drones of some sort might be able to operate in those conditions with some extreme engineering ingenuity and extreme materials, but at 30G it starts to become very challenging to find materials and mechanisms that can do the job.
### Extracting Material From The Surface
Perhaps just as importantly, getting materials that are being mined/harvested from the surface to a livable orbit would require immense amounts of energy because escape velocity would be so high.
The [escape velocity formula](https://en.wikipedia.org/wiki/Escape_velocity) is sqrt(GM/r).
For exoplanet KOI-423b, escape velocity is about 21 times that of Earth. [Kinetic energy](https://en.wikipedia.org/wiki/Kinetic_energy) scales as the square of velocity, so it would take about 441 times as much energy to get a given mass of something off the surface of it as it would to get it off Earth.
To get something off Earth and into orbit, you need about [50MJ/kg](https://space.stackexchange.com/questions/4330/how-much-energy-is-required-to-put-1-kg-in-leo) in round numbers. To get something off exoplaent KOI-423b, you would need about 22,050 MJ/kg. So, you would need 500 kg of chemical fuel for each 1 kg of material you wanted to get off planet, and would need more if you couldn't convert all of the fuel into kinetic energy creating velocity instantly and with perfect efficiency.
Otherwise, the only way you could get enough energy to get materials off planet would be with a controlled nuclear reaction. Basically, you'd need to put the materials you want to retrieve on top of a small nuclear bomb.
Indeed, one ugly but potentially effective approach to mining something close to the surface of this planet would be to launch a missile deep into the surface so it penetrated below the material you are looking for, and then detonate a nuclear bomb it was carrying which would spew raw materials into low exoplanet orbit, where it could be gathered up for processing by less extremely engineered robots.
### Conclusion
There is no way that humans could settle on this planet, or that this planet could have habitable conditions on its surface.
It might be possible to have a tolerable gravity and conditions on a small natural or man made moon orbiting a planet.
I would imagine one that always had the same side facing the planet, because at the right distance from the planet, so that the planet could provide the right gravity and could pin an atmosphere and water that the moon otherwise couldn't hold to itself in place, ideally within a steep crater facing away from the planet that would prevent the atmosphere or water from leaking over the edge and falling back down to the planet.
(I'm analyzing this scenario more carefully in light of a comment to confirm that this might be possible. But, certainly some moon or asteroid or space station in the vicinity of the planet, in some configuration, could be habitable.)
Exploiting resources on the surface of the planet, which would be uninhabitable, might be possible with robots or drones, although it would be at the limited of extreme engineering to manage one that could handle those conditions, and would be extremely costly to remove from the planet in terms of energy requirements to get the materials to orbit. So, this would only be worthwhile for something that was very hard to find elsewhere and was otherwise extremely expensive and difficult to synthesize (e.g. crown jewel sized diamonds).
[Answer]
>
> Either way, to be explicitly clear, I need some way for a technologically advanced society (we will say around 1500 years into the future for some reference) to retrieve valuable resources both on and beneath the surface (requiring both mining and harvesting) of a planet whose gravity is 100s of meters per second squared, and get them off planet, in the most practical and efficient manner possible without using handwavium antigravity
>
>
>
The simpler way would be using "telepresence rigs" - semi-humanoid robots, probably turtle centaurs for stability (30 G means you need reflexes *way* faster than a human's), controlled by stations in orbit, and therefore in free fall, or by a mixture of downloaded personality/gestalt integration (this could supply several interesting plot points - telecontrollers getting PSTD, and bots and controllers "drifting" too far for their minds to reintegrate optimally...).
To get the resources off-planet, you need a **lot** of energy.
Given the thickness of the atmosphere you'll have to do this in stages:
* the resource vessel is hooked to the Atmospheric Elevator, a 500 km untapered cable of diamond nanotube fibers going from the surface to Atlantis Station, which floats over the dense atmosphere made possible by a 30 G gravity field.
* once past the thick of the atmosphere, the vessel is mounted on the "solid light" rig. This is a laser so powerful that the backscatter alone makes an area 250 km in radius effectively a no-fly zone at each takeoff. The ship is mounted on an ablative/reflective disk made of a special alloy which can be kept electromagnetically stable even in its molten state, acting as a mirror with 99.999% efficiency (the remaining 0.001% is where the *ablative* part kicks in: the ship leaves behind a trail of scattered metal ions).
* the ship is propelled far enough to arrive within grappling range of the Skyhook, a tapered diamond fullerene cable rig extending the rest of the way to stationary orbit. The cable cannot extend further downwards because the gravity field makes it impossible to lift its own weight with reasonable tapering factors. The cables are electrified and act as a non-contact linear motor, supplying the traction necessary for the the ship to finally reach orbit.
The cost per pound of such a lift, even if the ship is essentially unpowered (it only contains the stabilizing/cooling system for the liquid alloy mirror) will still be staggering. Whatever that stuff is, it had better be worth a lot.
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I've seen this question raised in several different bits of sci fi media. In games its often that low gravity = lower construction cost or some such. But I've begun to wonder, is it really that cut and dried? Obviously, high gravity has some applications. Defensively, it could make it annoying for enemies to attack you with armored vehicles, due to the additional wear and tear, as well as the enormous cost to retreat an entire army plus gear from the atmosphere.
The base assumption of these games and this question being that if the gravity is not enough to kill you outright, such as a neutron star, or black hole, then long term health effects from switching between planets of different gravities is ignored.
(Realistically, bombardment is one of the most potent ways to open an invasion, however, sci tropes are being adhered to an extent here, meaning that landings are generally necessary.)
[Answer]
Living on a high-gravity world comes with plenty of annoyances:
* Literally everything you build will need to be sturdier to not break down under its own weight.
* Any transportation will require more energy. This especially applies to air travel. But land-based vehicles will also be affected because they will be more affected by friction and the aforementioned problem of requiring a sturdier build to load the same mass.
* You require far more energy to get things into orbit or land them safely.
Regarding defending against a planetary invasion:
A higher gravity world will be more vulnerable to an orbital bombardment with simple kinetic projectiles, because those will reach a far higher impact speed. Also, when a building collapses from bombardment, anyone inside will have a far lower chance to survive.
But if the enemy wants to land, they are facing the same problems you do:
* Landing troops requires more energy. Their landing crafts might even have insufficient thrust-to-weight ratio to land safely.
* Their vehicles and equipment might not be built for operating in a high-gravity environment. They might lose functionality or even get damaged by their own weight.
* They might underestimate how much their mobility suffers from the high gravity, so they run into strategic and logistic problems.
* They might underestimate the additional fatigue suffered by their biological soldiers. The defenders, however, will be used to the high gravity and not tire as easily.
* Any ballistic weapons will have a lower range.
* Because all the buildings on the planet are built much sturdier to withstand gravity, they also offer better protection from weapon fire. Any civilian building might be built like a military-grade bunker, making them easier to defend.
But these are all problems which will only affect attackers who didn't do their homework before invading. They can all be overcome with proper preparation.
[Answer]
>
> Defensively, it could make it annoying for enemies to attack you with armored vehicles.
>
>
>
**No.** It woud be even more comical easier to fight your enemies in high gravity. [In low gravity your enemies may survive a landslide by hiding in a tent](https://worldbuilding.stackexchange.com/questions/108967/could-a-cave-in-or-avalanche-in-low-gravity-be-dangerous). In jovian gravity a paintball falling from a few kilometers up could maybe rip a person right in two.
If you wish to fight someone in high gravity, warfare may become a game of dropping stuff up on your opponents.
That said, the pains of high-gravity are:
* **More expensive life support:** we know humans handle low gravity, and even microgravity quite well. People are able to live for months in the ISS without any major, long lasting health issues. But we feel sick and can get knocked out by high gravity, as evidenced from simple things like some \*\*\*\*\*\*\* rollercoasters to more complicated stuff such as jet fighters and rockets (in some cases you need special suits just not to pass out).
* **The energy bill:** the real issue is that the formula for the potential energy of a gravity field goes like this:
$$ E = Mgh $$
Where *M* is the mass of a body and *h* is how high it is from a reference height. The problem is the *g*, which is the gravity involved.
Let's compare three hypothetical planets, with distinct masses. Let's call them planets A, B anc C. Let A have the mass of Enceladus, B have the mass of Earth and C have the mass of Jupiter.
If you are in a building and wish to take some load to another level that is 10 meters upwards, the energy cost will be different in each. Assuming that the load weights one metric ton, the energy cost for each planet would be:
* **Planet A:** $ 10^3kg \times 10m \times 0.0113m/s^2 = 113 \space joules $
* **Planet B:** $ 10^3kg \times 10m \times 9.8m/s^2 = 98,000 \space joules $
* **Planet C:** $ 10^3kg \times 10m \times 24.79m/s^2 = 247,900 \space joules $
If you have a power supply unit that can only power one elevator in a jovian gravity, the same PSU will be able to power two elevators simultaneously on Earth, or up to 2,193 elevators on Enceladus at the same time.
Conversely, a 10 meters drop in each planet would mean an impact with just as much kinect energy. In planet A you could jump from a hill and land like a feather. In planet B you could jump just like on Earth. On Planet C you risk serious injury and even death if you just trip on the sidewalk.
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A book that I'm currently writing called Surge features [an enemy faction called the Degenerates that are heavily inspired by the Scythians](http://tvtropes.org/pmwiki/pmwiki.php/Main/FantasyCounterpartCulture) (Indo-Iranian horse nomads that ruled the Eurasian Steppes and Central Asia from the 9th century BC to the 1st century CE) and consists mostly of humans parasitized by a prehistoric endoparasite called Echidna (named after the Dracaena famous for giving birth to numerous monsters in Greek mythology), which parasitizes and radically alters the entire physiology of a wide variety of organisms from the phylum Chordata.
[In lieu of horses, the Degenerates use a variety of parasitised animals as mounts](http://tvtropes.org/pmwiki/pmwiki.php/Main/BeastOfBattle).Two of these animal-spawned Degenerates include Cerberi and Orthri: dogs and dingos that have attained 2-meter heights, lengths of 3.7 meters and weights of 227 kilograms along with gaining extra heads controlled by a central brain located at the base of their spinal columns (Cerberi have two extra heads while Orthri have an extra head). Both Cerberi and Orthri have streamlined sturdy bodies for quick movement, muscular legs that can propel them forwards at high-speeds and a long, slender tail that sprays a corrosive venom capable of melting flesh and bone.
Cerberi and Orthri can be distinguished from each other by their facial structures. Cerberi have [heads broader than that of modern canines](http://img.photobucket.com/albums/v44/SaiyaMel03/My%20art/2013-04-25_3_zpsbf2b0443.png:original) like those of a Dire Wolf (a prehistoric ancestor of wolves) - suited for grabbing onto large prey. Orthri have [long narrow skulls eerily similar](https://dibgd.deviantart.com/art/Inostrancevia-latifrons-115485279) to that of [Inostrancevia latifrons](http://www.prehistoric-wildlife.com/species/i/inostrancevia.html) (a proto-mammalian predator that roamed Permain Russia) and feature two enlarged sabre-like upper canines and slightly smaller lower canines. Orthri use their letha canines as stabbing devices to pierce through flesh and disable prey or a more surgical type of bite in which the incisors interlock when the jaws are closed, allowing an Orthri to slice out jagged edged hunks of flesh.
What sort of bridle would be needed for a rider to control these multi-headed creatures while riding them?
[Answer]
**Elephant goad.**
[](https://i.stack.imgur.com/90b0e.jpg)
<http://oriental-arms.com/photos.php?id=1843>
>
> The bullhook is a tool used to punish and control elephants. It is
> also called an ankus, elephant goad, or elephant hook. The handle is
> made of wood, metal, plastic, or fiberglass, and there is a sharp
> steel hook at one end. Its shape resembles a boat hook or fireplace
> poker. Some bullhooks have long, "shepherd’s crook" cane-style
> handles, allowing the trainer a firmer grip so that greater force can
> be exerted while pulling and yanking the hook deeper into the
> elephant’s flesh.
>
>
> Both ends inflict damage. The trainer uses the hook to apply varying
> degrees of pressure to sensitive spots on the elephant’s body (see
> diagram), causing the elephant to move away from the source of
> discomfort. Holding the hooked end, the handle is swung like a
> baseball bat and induces substantial pain when the elephant is struck
> on the wrist, ankle, and other areas where there is little tissue
> between skin and bone... A bullhook can easily inflict
> pain and injury on an elephant’s sensitive skin. Trainers often embed
> the hook in the soft tissue behind the ears, inside the ear or mouth,
> in and around the anus, and in tender spots under the chin and around
> the feet.
>
>
>
Your riders use a long handled goad like the elephant goad. Elephants are directed using such a device and so too your fierce mount. The rider could use the device on misbehaving heads, and also other places on the body. You could have your carnivorous mount move away from the pain much as an elephant does.
Plus a long handled monster goad would be badass.
[Answer]
I suggest learning a bit (pun not intended) about how bridles are actually used in horse riding, because you seem to have the mistaken impression that it's a matter of using force to control your mount. It's not: the neck of your horse (and almost certainly your carnivorous mount) is much stronger than your arms.
Other than rare emergency situations (see "one-rein stop") you're seldom exerting more than finger pressure on the reins. It's a signalling device - and indeed, with a well-trained horse & rider, you do as much or more with weight shifts & leg pressure as with the reins. Better riders than I sometimes even dispense with bridle altogether (do a search on "Stacy Westfall" for some examples), though personally I think it's mostly just showing off :-)
Even with a horse (non-carnivorous, though they can bite pretty well if they're so inclined, and kick), it's much more a matter of the horse being trained to be willing to carry a rider, than of the human forcing itself on a horse. A lot of it involves taking advantage of the horses' herd dynamics.
With a carnivorous animal, that's going to be even more important. Perhaps a good parallel would be dogs: you get the carnivore\* to regard you as a fellow pack member rather than as food. Then, if they're fairly intelligent & well-trained, they'll willingly follow directions. But your carnivore is going to have to be a pack animal. Training (a larger version of) wolves would be possible; tigers almost certainly not. And to train something like an alligator? No way.
\*Though dogs/wolves are ominivores, not obligate carnivores.
] |
[Question]
[
The smallest type of dragon in my world is a bipedal dragon about the same size as a moderately sized bird, maybe about a falcon. In addition to its breath attack and high intelligence, this little dragon is armed with a powerful venom whose primary effect is powerful and persistent hallucinations. This would cause a person to see, hear, smell, taste, and feel things that aren’t there, and the effects could potentially last for hours.
My question is simple. **How is this venom made or acquired by the dragon?** Would the dragon make it or have to eat toxic mushrooms for it? If so, what kind of environments would it need to live in in order to have access to the source of its venom?
[Answer]
Some animals naturally secrete a substance called [bufotenin/bufotenine](https://en.wikipedia.org/wiki/Bufotenin):
>
> Bufotenin (5-HO-DMT, N,N-dimethyltryptamine, bufotenine) is a tryptamine related to the neurotransmitter serotonin. It is an alkaloid found in the skin of some species of toads; in mushrooms, higher plants, and mammals.
>
>
> (...)
>
>
> In 2001, ethnobotanist Jonathan Ott published the results of a study in which he self-administered free base bufotenine via insufflation (5–100 mg), sublingually (50 mg), intrarectally (30 mg), orally (100 mg) and via vaporization (2–8 mg). **Ott reported *“visionary effects"* of intranasal bufotenine** and that **the *"visionary threshold dose"* by this route was 40 mg, with smaller doses eliciting perceptibly psychoactive effects**. He reported that "intranasal bufotenine is throughout quite physically relaxing; in no case was there facial rubescence, nor any discomfort nor disesteeming side effects".
>
>
> At 100 mg, effects began within 5 minutes, peaked at 35–40 minutes, and lasted up to 90 minutes. Higher doses produced **effects that were described as psychedelic, such as "swirling, colored patterns typical of tryptamines, tending toward the arabesque"**. Free base bufotenin taken sublingually was found to be identical to intranasal use. The potency, duration, and psychedelic action was the same. Ott found vaporized free base bufotenin active from 2–8 mg with 8 mg producing ***"ring-like, swirling, colored patterns with eyes closed"***. He noted that the visual effects of insufflated bufotenine were verified by one colleague, and those of vaporized bufotenine by several volunteers.
>
>
>
This substance is mostly known from amphibians, such as the [Colorado river toad](https://en.wikipedia.org/wiki/Colorado_River_toad) and the australian [cane toad](https://en.wikipedia.org/wiki/Cane_toad). It wouldn't be a stretch for a dragon to produce it as well.
As for methods of delivery, let's review the ways in which it has been tested on humans again:
>
> (...) ethnobotanist Jonathan Ott published the results of a study in which he self-administered free base bufotenine via insufflation (5–100 mg), sublingually (50 mg), intrarectally (30 mg), orally (100 mg) and via vaporization (2–8 mg)...
>
>
>
So:
* **Insufflation and via vaporization:** these could be done by a breath attack, in addition to the breath attack you already mentioned your dragon has;
* **Orally, sublingually:** This could be a defense against predators. Any animals that bites a dragon (or swallows, if they are big enough) will suffer from the venom's effects, and should quickly learn how to avoid the dragons. This is similar to what some butterfly species do, to avoid being predated by birds. Some die but most benefit from this kind of defense. Notice that some humans might lick/bite the dragons on purpose should the venom work this way;
[](https://i.stack.imgur.com/na4Vk.jpg)
* **Intrarectally:** decorum requires me to leave this completely up to your imagination. It should make for some really scary legends involving the dragons and why they should not be messed with, though.
] |
[Question]
[
One of the first things noted about pretty much any humanoid race with horns or antlers is that the neck would not be able to support the weight, making the idea unfeasible. However, some horns are larger than others, and I find it difficult to believe the idea of horned humanoids is entirely not plausible—especially when taking into account that cutaneous horns are a thing. Ignoring how these horns came to be or what their purpose might be, how large could horns resembling animal horns be on an average human without any charges to the current body plans and muscle structure?
[Answer]
Depending on the horn design, pretty large:
[](https://i.stack.imgur.com/sI75j.png)
Size and weight aren't the same thing.
The size will depend on your design and material (and desire to be able to walk through doors) but it looks like you've got around 85kg[1](http://geekologie.com/2017/02/man-wears-worlds-largest-heaviest-turban.php) to work with.
[](https://i.stack.imgur.com/ZPA3f.png)
[World's Largest, Heaviest Turban (187-Pounds)](http://geekologie.com/2017/02/man-wears-worlds-largest-heaviest-turban.php)
Wonder if this counts as wearing a helmet. Ride safe out there.
[Answer]
Consider that the weight of the horns is *utterly trivial* compared to the increased danger of snapping the neck with a twisting motion that comes with attaching what are essentially handle bars to the skull. Without modifications to the neck musculature or structure, I would estimate horns could be no more than a few centimetres (and therefore quite light) before they become a liability for people who have them.
[Answer]
This depends on how dense do they are. If it is a density of a polystyrene foam with very thin hard covering, then horns on the usual "mythological" size [like this](https://makezine.com/projects/sculpt-demon-horns-from-foam-and-paper-towels/) are not a problem; could probably even be larger.
A cone with 10 cm radius at the base and 50 cm height should weight only about 200 g if made from a polystyrene foam. It would already look like a really large horn.
] |
[Question]
[
As many here likely know, one of the factors that make both Mars and Venus uninhabitable to humans are their lack of a magnetosphere to keep solar winds out.
In the setting I am working on, I wanted Mars and Venus to be terraformed. Among the steps taken in the terraforming process; they would each have a moon put into orbit in order to introduce tidal forces to the planets.
I've thought of three possible solutions to giving either a moon:
* Scientists discover a window in which they can launch a gas giant moon out of orbit on a path that, with possible adjustments made along the way, would result in it being caught in a new orbit without disrupting any other planetary bodies. Earth sends out crews to set up automated systems that will act once the window arrives. It could possibly create two colonization ready worlds in one go depending which moons are commandeered.
* A small rogue planet is spotted on a path through/near our solar system and unmanned vessels are sent to adjust its course to capture it into a stable orbit around Venus or Mars. (Only one of them would be terraformed in this scenario, which is fine.)
* ~~Dwarf planets and larger asteroids are gathered to create an artificial moon which is then placed into orbit around its new home. Assembly can either take place either in orbit, before being moved or on the way to its new destination.~~ As it turns out, there is insufficient material in the asteroid belt to accommodate this method. Which would bring us to ripping moons out of orbit, but multiple smaller ones rather than a single big one.
Assuming that thrusters on the scale to safely move planets are created (even if they're seen as somewhat ludicrous in-world) and that the proposed moons from all three methods are the same proportion in mass to each of the planets they will be sent into orbit of, which of these methods would be the most energy efficient?
I know all three are going to have crazy expensive energy/time demands, but I want to know which one is the **least** crazy of the three.
Writer's note: The ludicrous scale and increased taxes to fund this massive project are meant to be part of the backstory and one of the factors that drives the outer colonies to declare independence from Earth's interstellar government.
As a side question, would it be possible to use the insertion of said moon into Venus's orbit to also increase its astonishingly slow rotation speed? To kill two birds with one stone. (Just as something to save the time/fuel/money.)
[Answer]
# You can compare using delta-v
The [delta-v budget](https://en.wikipedia.org/wiki/Delta-v_budget) of a mission tells you the total change in velocity that you will need to get an object out of one orbit and into another one. This change in velocity is related to fuel consumption by the [rocket equation](https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation).
$$\Delta v = v\_{exhaust}\log\frac{m\_0}{m\_f}$$
The energy of the delta-v burn can be calculated as the kinetic energy of the fuel exhaust. Exhaust velocity is $v\_{exhaust}$, while fuel used is $m\_0-m\_f$. The energy of a trip is then
$$\frac{1}{2}\left(m\_0-m\_f\right)v\_{exhaust}^2.$$
Thus, the energy that is needed to transfer orbits depends in a great deal upon the means of propulsion. Since you didn't specify a propulsion system or its characteristics, then we should calculate energy requirements in terms of delta-v.
# Transfer orbit requirements
A [Hohmann orbit](https://en.wikipedia.org/wiki/Hohmann_transfer_orbit) is an elliptical orbit used to transfer between two other orbiting objects (like planets). Atomic Rockets has pretty complete Hohmann transfer [tables](http://www.projectrho.com/public_html/rocket/appmissiontable.php).
For Venus and Mars from the four gas giants, the asteroid belt, and deep space, here are the potential delta-v's. The total column is total delta-v; insert is the burn to insert the moon into a transfer orbit, while arrive is the burn to exit the transfer orbit and start orbiting the planet. Note that the deep space object is not orbiting the sun, it starts in a transfer orbit of sorts. All units in km/s.
```
Insert Arrive Total
Asteroid-Venus 6.1 6.4 12.5
Jupiter-Venus 18.0 8.1 26.0
Saturn-Venus 11.1 9.1 20.2
Uranus-Venus 6.8 9.8 16.6
Neptune-Venus 7.3 10.0 17.3
Deep Space-Venus 17.8+ 17.8+
Asteroid-Mars 2.5 2.4 5.0
Jupiter-Mars 17.8 4.2 22.0
Saturn-Mars 10.9 5.5 16.4
Uranus-Mars 6.7 6.5 13.2
Neptune-Mars 7.2 6.9 17.3
Deep Space-Mars 11.2+ 11.2+
```
# Commentary
First off, the orbital transfer delta-v doesn't tell the whole story at all. There are also the orbital characteristics of what you are moving. For example, say you wanted to move [Triton](https://en.wikipedia.org/wiki/Triton_(moon)), moon of Neptune. Its orbit is both retrograde (backwards) and highly inclined. So this will take you much much more energy than a simple Hohmann transfer. So these are just guidelines at best.
That being said, Mars is easier to get to than Venus, no matter what your starting destination is. Jupiter is harder to move moons out of, it being the most massive gas giant. Uranus, the least massive, is the easiest to move moons out of its orbit.
The deep space calculation should be taken with a grain of salt too. What I listed is the solar escape velocity for an object starting in that planet's orbit. That means the minimum speed to escape the solar system, which is also the minumum speed to capture an object that is not orbiting the sun (which is the case for a rogue planet). However, the rogue planet might be moving considerably faster, so the delta-v requirement will scale up with the rogue planets (unknown) velocity. What I have listed is simply a minimum.
Finally, you discounted the asteroid belt as a source of a moon, but consider that there isn't that much mass just hanging out in the solar system waiting to be captured. There are only 2 Kuiper Belt objects (Pluto and Eris) and seven moons (Luna, Titan, Triton and the four Jovians) that are definitely bigger than the asteroid belt. After the asteroid belt, the next easiest place to move thing from is Uranus. But Uranus's four biggest moons are not that much better than what you can get from the Asteroid Belt. By comparison in $10^{21}$ kgs of mass:
```
Titania 3.5
Oberon 3.0
Asteroid Belt 3.0
Ariel 1.3
Umbriel 1.2
Ceres 0.9
```
So as far as getting a moon goes, you're almost better off getting asteroids than Uranus's moons. You get about 1/3 the total mass, and its a lot cheaper energy wise.
# Conclusion
The best bet is probably the asteroid belt, even though the moon might be small. The next best bet is a rogue planet passing through, as long as it is going slow and just the right size. The chances of that are basically nil, but thats what stories are for. After that, if you really want a good sized moon, Titan is pretty much the only option. Triton has bad orbital characteristics, Uranus's moons are too small as well, and the Jovian moons are pretty hard to pry out of Jupiter's gravity well.
] |
[Question]
[
I'm intrigued by the use of Cyber- or Electronic Warfare (short EW) in a space combat scenario.
Basically something that is very rarely (if at all) seen in *Star Wars*, *Star Trek*, *Babylon 5*, *Battlestar Galatica*, etc., but is a major player in today's reality on Earth where Cyberwarfare has huge effects over virtually any matter, possibly more impactful than an army of tanks.
Would it actually be possible to apply EW over a distance of hundreds of thousands of kilometers? Could you channel these virtual (wave) weapons at an enemy vessel and would it actually be able to have any effect on said vessel?
I'm assuming electronics are still a part of technology in a few hundred years, and "power" as well as "command" on a ship would be transmitted not by wireless but on hardened lines and as such would be less prone to attack. So simply scrambling by overloading frequencies wouldn't work.
Would it actually be possible to affect a target vessel's "main computer" and perhaps disable its weapon systems, alter engine behavior or something or is this just some random rambling without any reasonable grounds?
If so, what exactly would be the main difference on why Electronic Warfare is so powerful in our time and would be without any use in a future time ?
[Answer]
**Difficulties**
Off of the top of my head, I can think of a few reasons why this might not work. A large spaceship would have its own communication network or networks, and I can't really think of a reason why an intergalactic-capable civilization would leave any part of that network exposed such that an external enemy ship could get access to any part of any network. Of course, friendly ships must have some way of communicating with other friendly ships, but I assume any such communication link would be extremely well defended and possibly even airgapped from the rest of the ship's systems.
**Incentives**
There are huge incentives in space warfare to not actually pursue combat that could destroy ships. First, space vessels are going to be WILDLY expensive under any rational system. If you could defeat an enemy using cyber warfare, you could not only stay well out of range of conventional weapons, you could also capture their vessel completely intact. If you don't particularly care about human lives, you could just vent the ship and voila, you have acquired a perfectly intact, unmanned vessel of incredible value. If you do care about human lives, you could ransom all those thousands of people back to their side (for a nice chunk of change) and keep the vessel anyway. Furthermore, if neither side of the conflict inspires significant loyalty in their troops, you could just acquire the vessel wholesale, completely ready for action.
**Arms Race**
As may have been clear above, I can't really picture what sort of cyber defenses and attacks would be possible in a intergalactic-capable civilization. They would be quite unimaginable in my estimation, so far past our own current capabilities as to be unrecognizable. What I can guess is that, as soon as we invent cyberdefenses that seem unconquerable, someone else will invent an attack to conquer our system. As soon as that attack seems unstoppable, someone will invent a way to defend a system from it. This arms race will continue all the way up until the setting of your world, which will most definitely have some flavors of attack and defense. One side may have the temporary advantage, but sooner or later their will always be a new exploit.
**Conclusion**
It might be possible to create a system that is completely invulnerable, or an attack that is unstoppable, but I doubt it. I would guess we don't see cyber warfare on the silver screen because it doesn't make for particularly compelling television. In real life, I believe militaries would use every tool available to them, including cyber warfare.
[Answer]
**Forget Electronic Jamming**
If you spend a colossal amount of money on a war spaceship you would make it resistant to any magnetic storm that a solar flare could cause, and if you are able to produce that amount of energy, you might as well use it as a way to melt the enemy ship.
**Sometime Size Matters**
The hacking could be a really good weapon, at least again small ships where there would be fewer electronics, so it is possible that you could disable every system quite nicely but if you try it on a real big ship there will be a big problem because it would have really compartmentalized network structure, they won't put all their important systems on one big computer, they would most probably compartmentalize it to limit the damage any one intrusion could cause.
**But the More Important Part is How You Use It**
The real advantage of Electronic Weaponry is that you can target an internal system. It wouldn't replace conventional weaponry but for sure it would be a powerful way to complete your arsenal.
[Answer]
I would distiguish electronic warfare to
* Hard or physical - e.g. [EMP](https://en.wikipedia.org/wiki/Electromagnetic_pulse) weapons which roughly speaking burn your circuits
* Soft or physical - e.g. Hacking, Viruses which does not destroy the hardware, but does something more delicate on software level.
**Hard**
It is actually **very easy to protect** almost anything from time-varying electromagnetic field by [Faraday Cage](https://en.wikipedia.org/wiki/Faraday_cage) and to some degree even against [static magentic field](https://en.wikipedia.org/wiki/Electromagnetic_shielding#Magnetic_shielding). The reason why modern weapon systems and civil infrastructure are volnurable to such weapons is mostly inertia and cost - nobody yet invested to modyfing it to be resiliant against such weapons.
On the other hand spaceship would most probably utilize many **components which cannot be shileded** due to nature of tis function. Most profoundly Electromagnetic coild of propulsion system - e.g. from [plazma nozzle](https://alfven.princeton.edu/research/past/MagneticNozzle) or [Electromagnetic tether](https://en.wikipedia.org/wiki/Electrodynamic_tether) or some sort of [magnetic sail](https://en.wikipedia.org/wiki/Magnetic_sail). Shield based on [magneized plasma bouble](https://physicsworld.com/a/magnetic-shield-could-protect-spacecraft/) (artificial Magnetoshpere) would be also very volnurable to EMP.
You can rather easily **project electromagnetic pulse to large distance**. In essence it is just like Radio-Frequency pulse. Only problem is that the pulse has rather long wave-lengh, so you need rather large Antena. And the antena must either survive the pulse (which limits the pulse power ... e.g. [Nuclear bomb generated pulse](https://en.wikipedia.org/wiki/Nuclear_electromagnetic_pulse) would destroy any metalic antena ) or be dicarted each shot (which is huge waste of material, since the antena is large).
Best obtion seems to be **plasma antena** which is basically large cloud of plasma formed into desired shape by magnetic field. You may also think about **plasma lense** where similar effect is achieved by varying electromagnetic impedance for puls traversing through the plasma cloud. Such antenas can easily reach diameter >100km and focus pulse to distance up to milion km.
You may produce such plasma antena or lense eigher slowly (using some electromagnetic tethers and coils using e.g. solar wind or electron/ion gun), but than you risk it can be destroyed by enemy before you use it. You can also make it fast using **nuclear pre-explosion** which first create a plasma cloud, while second nuclear induce electromagnetic wave inside it. That would be [similar to fuel art explosive](https://www.youtube.com/watch?v=GmRASCHJe2Q), where cloud of fueld is first dispersed by one explosion, and then ignited by second.
**Soft**
I don't know much. I'm a physicist, not expert on internet security. But I guess you can very well protect your ship from any hacking simply cutting off all communication. Even if you need to communicate, current encoding using [asymmetric codes](https://en.wikipedia.org/wiki/Secure_Hash_Algorithms) are very hard to break, and you can always just make it longer thus exponentially harder to break. Maybe quantum computer will change it, but I guess there is some fundamental limit po performance of quentum computers, as with increasing number of quibits it is exponentially harder to keep the quibits form decoherence due to external noise.
[Answer]
**Unlikely**
Cyberwarfare would be an important part of any space navy. However, you will still need conventional weapons of some kind. Cyberwarfare as a ship to ship weapon is going to be unlikely. However in space combat and scifi it will remain important. Even the star wars original films it shows up. "it's an older code but it checks out," The rebels steal a clearance code to defeat the defences around Endor.
**Difficulty**
Gaining access to the systems in a remote enemy ship is going to be difficult. The communications systems are going to be airgapped from the important control systems for the simple reason that cyber attacks ARE a great way to attack a ship. The ships designers are going to be take cyber warfare into account and make it the internal systems inaccessible from outside.
Communication in space isn't trivial and without a communication area pointed at your vessel the enemy ship may simply not receive your attempts to hack them.
**Time**
The biggest difficult with cyberwarfare replacing conventional weapons is time. If an enemy ship is bearing down on you unless you have a prebuilt attack ready for them you probably aren't going to be able to be able to beat their mass drivers or lasers to the punch.
**Adaptability/Lifespan**
Upgrading your armor is expensive and resource intensive and may take years before the next generation of armor renders your weapons obsolete. The vulnerability you use to break into a ships system could be resolved before the battle is won. If you turn off their engines they may be able to turn them back unless your have a boarding party or laser or missile to permanently disable them. You can also disable their first round of ships but if you are attacking a vulnerability in their software than you might not be able to disable the second.
If information travel is significantly faster than the travel of ships than news of the weakness may arrive weeks ahead of your ships after you take out one ship with it.
**Show of Force**
Anytime you let you enemy know you have an exploit for their system, that exploit is going to be short lived. If you want to stop a vessel from bombing your homeworld you will need to either destroy it or convince the crew it would be destroyed before it could drop the bombs. The vulnerability you use to stop the first ship they send is unlikely to stop the second. You want enough conventional force that enemy doesn't feel that can simply roll over you. You can't simply say that you have a cyber attack ready to stop his navy at moment's notice otherwise he will search it out and fix it or call your bluff.
**Advantages**
Cyberwarfare would be an important part of warfare in space.
Cyberwarfare has reach that will become more important the more spread out humanity becomes. As a ship to ship weapon it is less useful but if you can access their designs you can find vulnerabilities. You can also delay their production reducing the enemy strength. A ship may take months to reach a target but if you can shutdown all life support on a space station you may never need to send a ship to destroy it.
[Answer]
The information security(hacking) side has been addressed by others, so I'm going to focus on the more traditional side of electronic warfare, radar jamming and it's cousin electronic information gathering. In modern warfare, especially air warfare, electronic warfare is as effective as it is because of the reliance on active sensors that send out and receive a signal(basically think about all of the ways you could be clever or cheat in a game of Marco Polo). Aircraft are almost entirely detected by radar, with generally much more limited use of things like passive infrared detection that can simply detect the heat from the aircraft. Most electronic warfare is thus about making the enemy's radar less effective so that your aircraft can blow up their defenses or slip past their defenses to do something else. Jamming also requires accurate information about the nature of the radars that you are trying to jam in the first place, so much of the work is about electronic information gathering in peace time so that you can have the information before you start. It also means that moving radars is an extremely important part of the game.
The problem with all of this in a realistic space context is that the majority of sensors for spacecraft can rely on passive sensors, as there is virtually nothing to hide against with the backdrop of space. Thus fooling active sensors won't have much value. Decoys with enough energy to fool sensors would be just as expensive as the original ship itself, because of the thermodynamic limits involved. While there are infrared countermeasures used by aircraft on Earth, including actual infrared jammers(used by helicopters against anti-aircraft missiles) this would really not work in space because there is no medium to disguise the heat against. It all comes down to the old adage that there is [no stealth in space](http://www.projectrho.com/public_html/rocket/spacewardetect.php#id--Strategic_Combat_Sensors--There_Ain't_No_Stealth_In_Space). This is not as absolute when it comes to electronic warfare over stealth, but it is still much more limited than on Earth with something to hide against.
Even communications jamming has significant problems in space. If you're using lasers as a communications device, there is virtually nothing you can use to block or alter them in the same way you can radio signals. Even satellite relays for high altitude military drones are extremely hard to block or intercept using highly directional radio signals. Stories you've heard about drones signals being intercepted are generally about the unencrypted data feeds being sent to friendly forces.
Also, in Star Wars specifically there is actually quite heavy use of electronic warfare. It is even good enough that active jamming doesn't just mean you can't see a specific thing, it means you can't detect the fact that you are being jammed in the first place. When Lando's fighter squadrons are preparing to attack the second Death Star, none of them are capable of noticing that their lack of reading means jamming rather than that the shields are down.
] |
[Question]
[
My friend is writing a book, and I volunteered to create a planet for him, one with an epic mountain extending far above the clouds.
The planet features lush jungles in the lower elevations and enormous towering mountains.
If possible, I would like to have a mountain so high it extends well into a typical stratosphere, and possibly even higher. Maybe we can even see the stars in the middle of the day.
Mars has Olympus Mons, at roughly ~ 77,000ft. But Mars may be too small to support life as we know it.
I am aware that there is a planet mass/mountain height correlation.
This brings me to my question:
**What is the highest realistic mountain that I can make on a world that can sustain a breathable atmosphere and lush biosphere?**
You may choose the mass and density of the planet as long as it is mentioned, and it can reasonably support life.
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I would like to take as a starting point the contribution of Anders Sandberg.
The basic assumption there is that the "mountain" is a **solid** (or near solid) and **homogeneous** piece of rock. "Near solid" still allows for fissures and cave systems but compared to the total volume of the mountain and the density of the rock, the reduction in overall weight they imply should be very small.
When considering [beams](https://en.wikipedia.org/wiki/Beam_(structure)), in mechanics, a well known result states that a hollow tube of equal mass to a solid tube (a rod) would resist bending considerably more than its solid counterpart. [Other profiles](https://en.wikipedia.org/wiki/Section_modulus) with different "hollowness" are suitable too.
Therefore, without violation of the reasonable assumption that "a pile of solid rock can be so high as to not crumble under its own weight", it could well be that a structure can stand much taller if, **for some reason** it made "clever use" of its mass.
Yes, it will still break but with a lighter **structural pattern**, the "accumulation of height" is faster than the accumulation of mass and so it can stand taller before it hits that structural limit imposed by physics.
Examples where something similar to this is found in nature are certain trees, such as the [Sequoia](https://en.wikipedia.org/wiki/List_of_largest_giant_sequoias) and the [Baobab](https://en.wikipedia.org/wiki/Adansonia_digitata). Such trees stand can grow very tall and have hollow interiors. Their trunk does not grow as a solid "tube". This is beneficial for two reasons, it's not only that they are lighter (compared to a typical "solid" tree) but they can also resist *bending*, because of wind forces (for example), which, as the tree grows taller and taller and inevitably wider too, becomes a considerable force.
Therefore, if you relax the specification that the "mountain" is a **solid**, **homogeneous**, "rocky" kind of mountain, then you could end up with a much taller "mountain", in an earth-like planet with possibly an even more interesting (or flexible) narrative.
The key problem here now is how do you grow such a mountain that seems to be taking these principles into account?
1. There is an awful, obvious and quite boring option here, there are living things in the "mountain" and they [build it](https://www.citylab.com/design/2012/08/there-limit-how-tall-buildings-can-get/2963/) and they interact with the story in mysterious ways until we discover that something is in the mountain and this and that the other.
2. A less boring option is that the "mountain" is one huge composite society of trees, with hollowed trunks, intertwined that grow *and expand their base* very very slowly. Existing processes accumulate dirt on its sides (by wind for example) and where there is dirt, water and air-born seeds (or carried by birds) there is the potential to form trees, etc. So, from afar, maybe it does look like one incredibly high typical mountain kind of object, but upon close inspection of its behaviour, it could certainly be revealed that it behaves differently.
3. Another option is that the "mountain" grows by [crystalisation](https://en.wikipedia.org/wiki/Crystallization), maybe aided by the natural day-night cycle and special atmospheric phenomena. Think of it a little bit like [constructive 3d printing](https://www.youtube.com/watch?v=UpH1zhUQY0c). The mountain grows by deposition, day by day, in a crystallised profile that allows it to grow so tall.
4. Finally, you can push it even higher by relaxing the specification that the mountain is homogeneous. Maybe it's a combination of the above mechanisms. Maybe the first 15km are rock and another 20km is a "composite tree society" and for another 10km is crystallisation.
Bringing something like this into the story makes it also more flexible, it gives you freedom to talk about other things as well. Maybe the "mountain" "wobbles" continuously because of earthquakes or the flow of wind around it, maybe it allows very fast communications by tapping to its structure.
Hope this helps.
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Your question has similarities to [this one](https://worldbuilding.stackexchange.com/questions/96872/exploration-of-a-50-mile-high-mountain)
The current mountains in the Himalayas are at or near the highest that mountains can reach above ground on Earth. Much higher mountains can be achieved on lower gravity worlds, but lower gravity worlds would not tend to be able to hold onto their atmospheres close into the sun where there is a lot of thermal energy to help it leak away into space.
I would suggest that Mars might have once harboured life and may have had a much thicker atmosphere so an Olimpus Mons size mountain (21km) is one candidate.
Someone has already done some calculations on this here:
<https://talkingphysics.wordpress.com/2011/09/08/how-high-can-mountains-be/>
One option to reduce the atmospheric loss problem would be to have a lot more of a heavier gas involved in the atmosphere from the start. That way it would be less likely to escape and there would be plenty in reserve if it did slowly leak. Carbon dioxide might be suitable together with some Oxygen. The planet could then be a lot further from its star as it would have a warm Carbon dioxide blanket to keep it warm.
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The highest mountain is limited by the strength of rock; a mountain of height $h$ will exert pressure $\rho g h$ on the rock at the base. So assuming earthlike density and rock strength the possible height scales inversely with gravity: a 2G world would have maximal mountains half as tall as Earth, a 1/2 G world can maintain twice as tall mountains.
Calculating the theoretical maximum from first principles is somewhat iffy; Tipler & Barrow's "The Anthropic Cosmological Principle" and [Weisskopf](https://www.jstor.org/stable/1739660?seq=1#page_scan_tab_contents) gets about 26 km. [Doing it using compressive strength of granite gives 10 km](https://talkingphysics.wordpress.com/2011/09/08/how-high-can-mountains-be/).
Now, the height of the atmosphere is set by [the scale height](https://en.wikipedia.org/wiki/Scale_height), $h=RT/mg$. This is about 8 km for Earth. It also scales as $1/g$. So the 1/G G low gravity world will have an atmosphere declining in pressure half as fast as Earth.
This means that the top of the tallest mountain, unless the rock composition is vastly different, will tend to be about one scale height above the ground. It will be high up in the atmosphere but not above it.
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My story involves a groups of colonists from a near post-apocalyptic Earth settling on a nearby, newly discovered habitable world, each colony separated and unknown to the others initially. Throughout the years, these colonists populate the planet and expand their colonies eventually discovering each other. But not before they have to deal with the challenges of living on a new world.
My first question is this, in detail, **Realistically, what would be the initial hardships and challenges they would face landing and settling on this uninhabited new world in the order of survival.**
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Trying to address the spirt of your question I will make some assumptions please correct me if I’m wrong. I will assume that habitable means more or less earth like, but with different surface features, a relatively benign earth life friendly biosphere where all or most life forms are simply inedible but non-toxic. The technology and distance are such that a trip can be made in less than a year and 10,000 colonists can be sent. I will assume near future.
**Survival**
The initial difficulty would be to introduce and establish viable numbers of earth species of plant and animal. This might be difficult even on a habitable world because the local flora and fauna would be well adapted to live there and even if not poisonous would at best be highly invasive. This should be possible but might not be easy and it would be essential to produce food.
**Technological development**
A second difficulty would be the danger of loss of technical capability. They might arrive with high tech kit but it would all be subject to damage and might be difficult or impossible to repair. There is only so much repair capability that you can bring and that is itself open to damage and degradation.
So a second aim would be to build basic infrastructure to help provide what was needed, But I doubt they could actually create enough infrastructure quickly enough to support their original level of technology because modern technology includes so many interrelated complex and hard to manufacture parts. So they would eventually loose capability and would start to struggle to rebuild equipment. As an example when they run out of spares and improvisations, any computer screen that got cracked or bulldozer engine ring that broke would put that piece of kit permanently out of operation.
So they will struggle to establish themselves technologically. With luck and provided they still had access to the information necessary to build the technology they once had, they should slowly reacquire it although it might take centuries.
As an example before you can build your first microchip to help return your computer technology you need a vast array of other technologies, each of which themselves require even more technologies, so to mention just a few you would need zone refining of silicon which itself would need vacuum technology which itself would need electrical technology etc.
**Social development**
Eventually these separate colonies would run into one another probably in search of resources (although it is very hard to believe that so many separate colonise could be established on the same world in the high tech stage without being aware of the presence of some or all of the others).
The mega corporations would be long forgotten and the merits of environmental friendly or not outlooks would be overtaken by events on the ground and the struggle to survive.
The religious cult might well retain its beliefs but naturalistic and harmonist views would probably be amended by the need to survive. The militaristic and isolationist societies’ viewpoint would lose a lot of meaning and potency in a world where the only enemy was nature. By the time other groups were encountered the societies may well have moved on or at least the original ideology might be much weaker.
The various different forms of initial government and world view would in all likelihood evolve rapidly and many changes might make the groups completely unrecognisable after a few decades. Different sub groups might take control depending on circumstances. Mini revolutions and revolts could over throw the historical outlook.
**Final out come**
At the point of contact I would think the bonds of humanity and a common enemy (the alien environment) would outweigh any vestige of their original purpose / outlook. In such survival situations many things originally intended would simply be forgotten or lost. It is also possible that the ingroup out group type thinking would take hold and fighting would break out.
In fact eventually there would be cause for much fighting, probably over resources or priorities, (or women) but it is impossible to say what would happen eventually as there are too many variables and too much time would have passed. Probably geographical location would play a bigger role than the original colonies ideology.
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*Edit: I'm referencing groups from an earlier version of the question.*
Welcome to Worldbuilding SE. Unfortunately your question looks much too broad. All of these colonies could put their *interests* ahead of their *ideology* and fight any rival. That's how the Alpha Centauri game is set up.
* A, the first B, C, and E could become expansionist in search of economic advantage, raw materials, and captive markets.
* D and F could become expansionist to spread their ideology, and to "save the oppressed workers" elsewhere.
* G could become expansionist to eliminate rivals.
* If you look at recent events in [Myanmar](https://en.wikipedia.org/wiki/Rohingya_persecution_in_Myanmar_(2016%E2%80%93present)), or the breakup of [British India](https://en.wikipedia.org/wiki/Partition_of_India), even your second Colony B could become quite violent.
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**Follow-Up:** The question changed. So how does the situation you describe differ from the Spaniards meeting the Incas, or the Romans meeting the Indians?
* I would expect that all colonies have **maps** from orbital surveys, accurate as of the date of the last landing of their group (or even slightly later, if they left sats to update the maps). There will be no surprise that there is a mountain range behind the desert, and a coast behind that. Exploration teams might be surprised that another colony has built a port city at a river mouth, but they would know that the river mouth is a good place for a port city.
* The last team will know the location of **all** previous sites. A shuttle is large enough to detect from orbit, and so is a farming village. The next-to-last team might be surprised about the position of the last colony, but not vice versa.
* The teams will try to balance their colony site between immediate needs (good farming) and long-term needs (raw materials, hydropower, and so on). Afterwards there might be a *race to the mining sites.* Settlements expand to stake their claim. Read up on the [Fashoda Incident](https://en.wikipedia.org/wiki/Fashoda_Incident).
* The teams might have databases (or printed books, if they fear that their computers break down) to outline a direct path from blacksmiths to modern industry. There is an entire genre of science fiction books where a hero uplifts a world with the aid of such data, usually without the complication of separate factions.
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HUGE question, but lets look at the "threes of survival"; i.e. a human can survive "three minutes without air, three hours without shelter, three days without water and three weeks without food" now that's a mix of some best and worst cases but it's a working model we can go from.
So first priority is the atmosphere A. "move in ready", an exact duplicate of Earth that presents no issues, B. "reno ready", close enough to Earth to set up camp and make some improvements like breeding plants that extract excess sulfates, at levels that aren't toxic but are unpleasant C. "bare land", oh look a soup of Ammonia, Methane, Carbon Monoxide and Fluorine time to break out the atmosphere reprocessors. Between the "reno" and "bare" is a sliding scale of progressive nastiness depending where you are on that scale you need equipment etc... ranging from nothing special to rules about exposure times to full-blown hermetically sealed shelters for sleeping and space suits for any outdoor working parties. Special case is hard vacuum but I don't see that being a colonisation target.
Second you need to be protected from the elements, that could mean cold, heat, rain, wind or even meteor swarms. Extreme cold and heat are probably less of an issue than they can be for planetary explorers on Earth, space ships and travelers will, of a necessity, have a lot more insulation and climate control than your average tramper because space is harder to keep a healthy temperature in than atmosphere. Rain is always problematic, due to increased heat loss and degradation of footing and visibility, there's not that much you can do except endure it and try to keep dry where possible to prevent skin problems. Unusual effects may have to be taken into account in light of acidic atmosphere etc... Wind can potentially be lethally strong on an exoplanet, not like a tornado where a weather event might kill you but the basic everyday wind could actually kill you from shear impact force, there are just some situations that you can't know about until you arrive and can't do anything about once you do. Protecting people from the environment is similar to protecting them from a toxic atmosphere and runs to the same extremes of don't go outside unprotected. You also need to protect equipment in similar ways.
Water is probably not that big of a problem if you have good shelter and the planet has a hydrological cycle, one of the things that humans have proven to excel at is sourcing water and building technologies that source water.
Food could be the biggest challenge to the longterm survival of a colony, this has been true on Earth in virgin territory and will probably be just as true outside our own biosphere, only more so. There are two real options, one is to bring a large stockpile, and a gene lab and hope you can solve any problems arising, the other is a large stockpile and a full hydroponics set up to grow all the food you need indefinitely, this may or may not be a practical solution.
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Wow, Some very big questions here. Certainly you are setting up for huge conflict once they do discover each other!
I don't think I can answer all of your question, but I'll have a crack at laying out some of the challenges when they 1st set up the colonies.
1. There are some basic challenges with colonizing another planet - and the 1st assumption is does it already have life on it?
2. I'm assuming yes - because if not it's WAY too hard a challenge to get colonies off the ground well enough to survive if they are tech limited in the way you describe.
3. SO with life already there - there are likely to be be critters and even plants that will be deadly.
4. This worlds equivalent of Lions & Tigers. They might have 6 legs and teeth like a Sabre Tooth, or they might have poison like a Snake or spider. They could be tiny or large - but they will be there and they will be deadly.
5. Even some of the normally not deadly animals might go through a phase change of some kind - and turn deadly overnight - either a permanent change - or a temporary one.
6. There could easily be a mineral in the ground that is slowly toxic in subtle ways - and that might be restricted to certain areas - so you could easily have it affect just one of some of your colonies. It could cause unexpected mutations, the simplest one that would cause huge social upheaval but not be obvious until quite a ways down the road is if it were to affect the Birth rate between Male and Female. It could have an affect as simple as making all female (or male whichever way you wanted to play that) Zygotes split into a twin. Or even triplets. That would force quite radical changes in certain of your societies.
7. Another way a mineral could have severe toxicity but not be noticed, is if it interacted with the brain in a way to cause Prions to fold - but only after 3 decades of exposure.So you would end up with one of your colonies having pretty much their whole population developing Mad Cows disease, after they turn 30. So they can have kids - the colony could survive, but huge challenges. And not figured out until a LOONG time has passed.
8. Another subtle effect could be to enhance PSI talents, so Telekinesis, Telepathy, Precognition, Super Empathy, and other kinds of PSI talents all could be useful plot elements, and 1 or 2 colonies getting these at the exclusion of the others is a good conflict point.
Hopefully this gives you some ideas for developing your story lines with some unique quirks...
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Assuming that one can find a 'class M' planet, one that approximates the Earth in climate with a considerable water presence, plus an oxygen/nitrogen atmosphere and a strong magnetic field to keep solar wind from blowing that atmosphere away, there is still the immediate challenge of food.
First order of business is survival. Feeding a space ship's crew during travel is difficult enough, without also having to transport enough food to keep the settlers supplied for any length of time once they arrive.
Does that planet have life on it?
And is that life edible? It would be unfortunate to arrive at that planet, only to find that the local plants had cyanide in their sap.
Is that life hostile? Would the indigenous life regard humans to be a tasty snack? Are there microbes or parasites that humans would have no natural defense against? The human body has considerable defenses... against intruders found on earth.
Can one introduce earth plants to produce food? And what are the consequences of doing that?
Keep in mind that life on earth has evolved to be optimal for the earth's climate and resources. Life on another planet will have evolved to be optimal for different conditions, and may function in a very different manner. It may well be inedible, and intolerant of foreign intruders: humans, or the plantlife they bring along to cultivate for food.
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Your question overlooks a few things. If you're sending colonists to a world then you also send surveying equipment so they know the best sites before landing and committing themselves. In other words the colonists would bring satellites and they would be multirole satellites. They would also be used for communications.
Even if the satellites fell into disrepair after a couple of generations the first arrivals on each of the colonies would all be aware of the existence of the other groups. This would be *very* important information. So even if the colony's hi-tech kit started to break down over the years then that information would be recorded by more durable means, books or even word of mouth.
I just don't see how the colonies would be ignorant of each other.
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I need to create a world with some very high plateaus and some very deep depressions. The sides of these structures should be very steep and unclimbable. They need to provide an obstacle sufficient to ensure that the the plateaus and depressions are only accessible from the surface by air transport.
The heights and depths also need to be sufficient to ensure that the climates are very different from the surface, but most areas should still be habitable when reached, ideally 3-6 miles above/below the mean surface elevation. The plateaus should be of the order of 100 miles across; the depressions (craters?) should be of the order of 1000 miles across.
Assume an approximately earth like world except with much less water. The depressions must not simply be oceans, although some water may be present. Other than that any physical characteristics can be adjusted if this helps. If this is not possible what comes closest? No magic.
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**You want [tepuis](http://www.amusingplanet.com/2013/05/tabletop-mountains-or-tepuis-of.html).**
[](https://i.stack.imgur.com/unJQj.jpg)
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> Tepuis are the remains of a large sandstone plateau that once covered
> the granite basement complex between the north border of the Amazon
> Basin and the Orinoco, between the Atlantic coast and the Rio Negro,
> during the Precambrian period. Over millions of years, the plateaus
> were eroded and all that were left were isolated flat-headed tepuis.
> Although the tepuis looks quite barren, the summit is teeming with
> life.
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Tepuis are between 1000 - 3000 meters high; 3000 is 1.8 miles so close to what you want. The tops of many of these plateaus are inaccessible from the ground; you need a helicopter. Or a house floated with many helium balloons.
[Auyán-tepui](https://en.wikipedia.org/wiki/Auy%C3%A1n-tepui)
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> is a tepui in Bolívar state, Venezuela.[1](https://i.stack.imgur.com/unJQj.jpg) It is the most visited and
> one of the largest (but not the highest) tepuis in the Guiana
> Highlands, with a summit area of 666.9 km2 (257.5 sq mi) and an
> estimated slope area of 715 km2 (276 sq mi).
>
>
>
[](https://i.stack.imgur.com/AemIR.jpg)
Auyan-tepui image from <http://c8.alamy.com/comp/A415PF/auyan-tepui-guiana-highlands-venezuela-world-heritage-clouds-precipitous-A415PF.jpg>
Tepuis are real, super cool, and you need exaggerate them only slightly to achieve what you want for your world.
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This is entirely possible. The depressions will be colder, of course, and the high summits will be much hotter. Clothing and limited technology can make them both habitable. You don't need magic, just some great descriptions since you have a very specific landscape in mind.
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I'm working on a sci-fi Western scenario on a habitable [desert planet](https://en.wikipedia.org/wiki/Desert_planet) along the lines of [Tatooine](https://en.wikipedia.org/wiki/Tatooine) from Star Wars and [Arrakis](https://en.wikipedia.org/wiki/Arrakis) from Dune.
For it to be habitable there has to be water below the surface of course and there has to be at least some precipitation to make a sustainable use of underground water reserves possible. I imagine people will additionally harvest water using [atmospheric water generators](https://en.wikipedia.org/wiki/Atmospheric_water_generator) also as part of their sustainability strategy. I think this is what George Lucas had in mind when he made Luke Skywalker's parents on Tatooine "[moisture farmers](http://starwars.wikia.com/wiki/Moisture_farmer)".
Now because my narrative is a Western where people use technology available in America in the 1870s you would need fossil fuels close to the surface, coal most prominently. So the planet can't always have been covered by desert but needs to be stable in that form now.
Can you give me some ideas how I would explain that there's large deposits of fossil fuels when the planet is a desert and has been for a long time? I know that a desert can be where there were forests millions of years before when talking about Earth but I'm not sure if it's that simple when talking about about a desert planet. [This](https://worldbuilding.stackexchange.com/a/25490/42172) gives some insight regarding the presence of coal and oil but it doesn't provide an adequate answer when these conditions are taken into account. I would need an at least semi-scientific explanation.
Regarding the questions of how men got there and why their technology doesn't evolve from what was available during the latter part of the 1800s in America see [this](https://worldbuilding.stackexchange.com/questions/90756/why-colonize-a-planet-without-the-continued-benefit-of-modern-technology/) and [this](https://worldbuilding.stackexchange.com/questions/90787/how-to-explain-why-a-human-societys-state-of-technology-on-another-planet-might).
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Well, to make a desert planet habitable, you will need oxygen, unless your 1870's cowboys live in domed towns, which seems incongruous. Humans need to breath oxygen! You will also need water (could be subsurface) and crops: Which means whatever factor killed off all the plants (including the forests turned coal) must no longer exist, or you couldn't grow anything new.
If you want the biological cause of the non-conductive metals being present, they will need water, too. Bacteria aren't a dry collection of sticks; they need water as their primary solvent.
Some of those problems I cannot solve in this post; perhaps I will have an idea later. The oxygen problem can be solved; however.
Until recently, it was believed oxygen would have to be a sign of life on an exo-planet; for example see this link on [Signs of Life.](https://stardate.org/astro-guide/signs-life) An excerpt follows:
>
> What would be a real biosignature? Many scientists think that abundant molecular oxygen, or its product, ozone, is a strong one because on Earth molecular oxygen is produced mostly by the photosynthesis of plants. The simultaneous detection of water, carbon dioxide, and oxygen or ozone would be a strong indicator that biological processes are occurring on a planet.
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> Also, the detection of large amounts of oxygen and a gas like methane or nitrous oxide would be a strong signature, because on Earth these gases are produced almost entirely by biological processes.
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Also this Scientific American link: [The Origin of Oxygen in Earth's Atmosphere.](https://www.scientificamerican.com/article/origin-of-oxygen-in-atmosphere/)
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> It's hard to keep oxygen molecules around, despite the fact that it's the third-most abundant element in the universe, forged in the superhot, superdense core of stars. That's because oxygen wants to react; it can form compounds with nearly every other element on the periodic table. So how did Earth end up with an atmosphere made up of roughly 21 percent of the stuff?
>
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> The answer is tiny organisms known as cyanobacteria, or blue-green algae. These microbes conduct photosynthesis: using sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen.
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Which would mean a large percentage of the surface of your planet must be ***covered*** in photosynthesizing plants (algae, moss, plankton); otherwise all the highly reactive free oxygen in the atmosphere will collide with stuff (including other atmospheric gases and the ground) and be bound to it, there will be none left within a century (according to one source I read years ago but can no longer find).
***However,*** recent studies show [alternatives are possible:](https://www.space.com/30722-oxygen-on-exoplanets-alien-life.html)
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> The new research [by Norio Norita] shows that the interaction of titanium oxide [also called *titania*] with water could produce oxygen in the atmosphere of an exoplanet without the involvement of living organisms.
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>
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Fortunately for you, titanium is a low-conductivity metal; and the article goes on to say that on an earth-like planet, somewhere between 0.05% and 3.0% of the surface would need to be covered in the stuff to produce the same level of oxygen as we have on Earth (that would be 100,000 to 6,000,000 times the surface titanium dioxide found on Earth).
Titania must interact with water to produce free oxygen; I would recommend the water and titania be in deep reservoirs.
### Killing the forests.
[edit]This is difficult to do on a temporary basis; I'd suggest orbital mechanics.
See this article on the formation of the Sahara: [How Earth's Orbital Shift Shaped The Sahara.](https://www.astrobio.net/news-exclusive/how-earths-orbital-shift-shaped-the-sahara/)
>
> The changes in the Earth’s orbital tilt and precession (or the wobbling motion) occur because of gravitational forces emanating from other bodies in the solar system. To understand exactly what happens, picture a spinning top when it is slightly disturbed. Just like a top, the Earth too wobbles slightly about its rotational axis. This tilt changes between roughly 22 and 25 degrees about every 41,000 years, while the precession varies on about a 26,000-year period. These cycles have been determined by astronomers and validated by geologists studying ocean sediment records.
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So you have on Earth a 41,000 year cycle going on. This changes the ***insolation*** distribution of the Earth (yes that is spelled correctly, it is not "insulation", it is "insolation", which is a scientific term meaning the amount of solar radiation reaching the surface of a planet).
A minor change (half a degree) in orbital tilt turned a grassland into the Sahara desert by increasing the amount of sunlight to a point that plants simply couldn't handle it anymore; apparently the tipping point was about 6000 years ago (the approximate time frame you requested).
Your planet does not have to be Earth, of course; your cycle can be longer or shorter than 41,000 years: That is a peculiarity of our OTHER planets and their sizes and orbits. (you will need some other big planets to pull this off, to provide the necessary gravitational influences, but they don't have to be habitable, just like Earth's fellow planets are not habitable. I wouldn't bother trying to work out the math either, just that they exist and cause the axial tilt on a cycle: that's plausible.)
A second effect can be the presence of mercury-chloride and/or sodium-chloride (aka table salt) in large swaths of the planet, both of which are toxic enough to plants to cause desertification.
So the scenario is this: the South half of this damn planet is a natural desert due to salts. The North half can support plant life, but due to axial tilting in the orbit (due to resonances caused by some Jupiter sized gas giants in the system), on a cycle of about a hundred thousand years, the North half is exposed to extreme sunlight for a period of about ten thousand years. But that same axial tilting shifts underground water into titania deposits that react to produce oxygen; and this seeps up to sustain life on the planet. The plants have adapted, over billions of years, to produce seeds that can survive the drought. They won't sprout until the temperature has been hospitable for a few years, and the axial tilt has made the underground water available to them again. This is a cycle that has been going on for billions of years; and that is where the coal deposits come from.
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How hot do need the world to be? The greenhouse effect is a balancing act, if you had ancient forests that stripped the CO2 out of the atmosphere and deposited it in huge coal measures then the trees could be their own worst enemy. If you dropped CO2 far enough, early enough you could wipe out complex plants before grasses and flowers ever evolved leaving huge carbon deposits and a cold desert world with most of it's water frozen in the higher latitudes, like an ice age on steroids. There's still going to be ground water many places and basic plants, algae, on/near the surface harnessing a little sunlight and the night dew to keep the world cold and dry and highly oxygenated. Such a world, assuming it was Earthlike to start with, is going to have more oxygen than in the [Carboniferous](https://en.wikipedia.org/wiki/Carboniferous), but with a massively diminished food chain budget. Pumping bulk CO2 into the atmosphere by burning that coal is going to have effects over the very short term geologically speaking but won't do much on human timescales.
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I know that certain animals have the ability to see in darker areas but not in pitch black due to a special ability they have in their eyes which also gives them that glowing effect. Could elves have the same thing?
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## Possible in fantasy, but of dubious utility
The *[tapetum lucidum](https://en.wikipedia.org/wiki/Tapetum_lucidum)* is a reflective layer behind the retina, which gives a second chance to the photons which were not intercepted on their first pass. It increases light sensitivity by about 44% or 0.5 [f-stops](https://en.wikipedia.org/wiki/F-number) (an ideal *tapetum lucidum* would increase sensitivity by 1 f-stop); the catch is that is decreases acuity, because the image is blurred.
As for realism, while most primates don't have a *tapetum lucidum*, most *primitive* primates ([strepsirrhines](https://en.wikipedia.org/wiki/Strepsirrhini)) do. If elves do indeed have a *tapetum lucidum* then they must have diverged from our evolutionary line about 65 million years ago.
Humans have very decent night vision for a diurnal animal; whether the increased light sensitivity is worth the decrease in acuity depends on the life strategy of those elves. Are they nocturnal animals? The elves in the movies looked like civilized people, don't they have lamps?
(As an aside, the maximum aperture of the human eye, dark adapted, is about *f*/2.1, which is very good; but only about 10-15% percent of the retina is occupied by the [rod cells](https://en.wikipedia.org/wiki/Rod_cell) responsible for scotopic vision. When completely [dark adapted](https://en.wikipedia.org/wiki/Adaptation_(eye)), with a bit of luck human eyes can [detect individual photons](https://www.nature.com/news/people-can-sense-single-photons-1.20282); bursts of twenty or so yellow-green photons can be detected quite reliably. The catch is that switching from [photopic mode](https://en.wikipedia.org/wiki/Photopic_vision) to [scotopic mode](https://en.wikipedia.org/wiki/Scotopic_vision) takes several minutes; the reverse transition is much faster, taking only a few seconds.)
## So what else can I do?
If you really want your elves to have significantly better night vision than humans, then you have two avenues open:
* Give them bigger eyes.
Low-light image quality scales with sensor size. This is the a fundamental reason why a full-frame camera with its 864 mm² sensor (or even an APS-C camera with a 384 mm² sensor) takes much better low-light pictures than a compact or mobile phone camera with a 28 mm² sensor. After all, low-light sensitivity is limited by the number of photons which fall on the sensor, and this is proportional with sensor area.
* Give them more rod cells.
Humans have many more cone cells (responsible for day vision) than rod cells (responsible for night vision). Increasing the proportion of rod cells will increase low light sensitivity, with a corresponding reduction in visual acuity in day time.
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So, if you are thinking this is just another random scenario, it is not. It is a sequel to my previous question on whether the Soviets and other Warsaw Pact forces, henceforth referred to as PACT forces, could reach the Rhine River or not (at least until NATO decides to nuke them and the nuclear genie gets out of the bottle, aka: the war devolves into a nuclear exchange).
So, first off I am going to link the original scenario below:
[1973: Al-Qaiyama](https://worldbuilding.stackexchange.com/questions/76150/if-the-cold-war-went-hot-in-the-early-1970s-would-the-warsaw-pact-be-able-to-re)
So, to summarise. around the 26th of October of 1973, World War III begins following the breakdown of the ceasefire that ended the Yom Kippur War in our timeline (which almost happened and caused a crisis that almost plunged the world into exactly what I am about to describe). As a result, World War III begins. The details of the conventional war are in the link provided.
Fast forward to the 19th of November of 1973, and PACT forces have effectively reached the Rhine. In desperation, NATO launches 50 tactical nuclear weapons on the advancing Warsaw Pact forces at around 9:15 AM EST (1:15 PM UTC). PACT forces retaliate with 80 of them just minutes later and pushes as far as Saarbrücken before finally being nuked again by 100 NATO tactical nuclear weapons. NATO counterattacks and pushes the Soviets back towards the Rhine, where the Soviets destroy any remaining crossings and a brutal stalemate ensues over the course of a day across a nuclear wasteland, and no end in sight for tactical nuclear detonations.
At around 10:10 AM EST the next morning, sirens across North America and Europe go off, while seven minutes later, NATO launches a first strike on the Warsaw Pact. The next minute, the USSR retaliates, with ICBMs, strategic bombers and submarines equipped with SLBMs begin to head towards their targets. Within 15 minutes ICBMs reach their targets in Europe, while 30 minutes after the order to launch is given, said ICBMs reach targets in North America, and the rest of the USSR.
Most of these are concentrated on key military targets, with the occasional population centre being targeted. The remainder would be targeted by strategic bombers and SLBMs over the next two hours and fourty five minutes, the former of which manage to break through the other's air interceptors and AA defences along the Bering Strait in the final battle of the war. By the end of the second hour, most strategic bombers have destroyed their targets, while SLBMs launch towards any remaining targets that survived the initial ICBM launches and strategic bomber onslaught.
The third hour ends and the two alliances launch their remaining warheads, when around 1:57 PM EST (5:57 PM UTC), the last warhead detonates and the dust finally clears. A total of 6,500 strategic nuclear weapons and 600 tactical nuclear warheads are estimated to have had been detonated, while 400 million lives were lost (another retcon from my initial 900 million estimate, then subsequent retcon to 459 million). North America, Europe, Central Asia, Israel, parts of Siberia, Korea and Japan are now nuclear rubble as a result.
So, assuming the US and the Soviet Union survive, what exactly did they have in mind when it came to reconstruction (assuming they also survived to 1974, that is)?
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The short answer is "possibly, but I don't know".
While both sides had extensive and detailed plans of dealing with immediate aftermath of nuclear conflict, I am not aware of any longer term rebuilding plans. Short term plans always included either staying in shelter or moving away from contaminated areas while trying to "hot-wire" the remaining infrastructure.
I believe that outcome of a nuclear scenario is too dicey to make any specific plans. You may want to rebuild a certain power station or the whole city - and you can do it, if the damage is not too heavy and radioactive contamination is minimal. But if it's not the case, then that particular plan is off. So that's why, I think, most plans stopped at regrouping in safe areas - new assessment of situation will be necessary to make any further plans.
For USSR, at least, it was not unthinkable to rebuild from the ashes - WWII literally destroyed western part of it.
As far as social and political rebuilding go - it was assumed that the army would remain strong enough to provide control over territory and provide necessary level of order.
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So just some historical footnotes with regard to this: First, Continuity of Government (COG) on the United States side was believed to be compromised by a spy in the FBI at this point in our history, so any precautions to protect vital government officials would not function.
Second, I'm concerned about your order of battle (though the delayed retaliation from the Soviet's would be due to the fuel concerns. Soviet Missals historically would have taken longer to fuel up, but given a slow progression to war, it would have probably been fueled. Also, the Soviets always had a policy of Second Strike Only (i.e. We will not use nukes first) where as the U.S. did have an unstated point of First Strike (never outlined on policy, but up to the option of POTUS). The Germany "Fulda Gap" was always a ruse on the Soviet's Part which the United States bought hook line and sinker. The United States at this time was currently revising policy of it's first strike. Again, it was never a labeled event, but the general "We're losing" was a good point. The idea of tactical nukes was very recent (the 80s) and even then, the lead time of a first strike meant that it was better for a First Strike opponent to launch all nukes upon the decision to launch one (during the entirety of the cold war, it was thought that only 3% of all nukes would reach their intended targets, so getting everything out of the ground in the mother of all salvos was the best strategy... not limited detonation on troops and military targets, because that gave the enemy time to get their nukes off the ground. In the 1970s, with limited forward operating areas, a second strike policy, and the slow speed of fueling, the United States had the clear edge over Soviets in a first strike.). Given the timely nature of fueling rockets by the Soviets for a counter attack, the first indication that this process was starting would be enough to call in an all out nuclear strike from NATO forces... lest those missals get off the ground.
Another wonderful historical fact is that the Soviet Government did not tell the populace about radiation and its harmful effects, so it's likely at local levels, the rebuild plan would have been significantly hampered. Since most of the Soviet's population was in the Western part of the country, it's likely that Asiatic Russia would have seen little of the war, though this could change due to the fact that all Soviet Nukes were mobile (due to the fueling) and not siloed like in the states, which had a good chunk of nukes in the breadbasket... in the event Soviet Union could launch a Second Strike, a good deal of the American Bread Basket would have been highly irradiated. When the US did nuke Japan, Tokyo was deliberately not named as a candidate city because they needed people to negotiate a surrender with. This may preserve the capitols, but it's likely not.
In short, the United States would likely have been better prepaired for the aftermath, but famine would be an immediate scare for the survivors and hospitals would be overwhelmed... a single high atmosphere detonation would cause an EMP that would fry all electronics in the Continental United States, so power infrastructure would be need to be rebuilt. In the Soviet Union, the problem is that the Government would have probably not briefed the local leadership on what to do in the event they survive. Radiation poisoning would probably be much more rampart among the survivors. Foreign Aid would probably be more readily given to the United States (China had long had a bitter falling out with the Soviets... during this time period, they may have even launched on the Soviets for good measure, leaving the Soviet Union with little in the way of actual allies who could give back.).
For some good documentaries/fiction that generally got a good portrayal of what you want, check out "The Day After" which focuses more on the survival of the initial strike than the build up (to hit the point home that it would be the case in any direct nuclear war, who started firing the nukes was never explained... the viewer can blame the US and USSR equally), "Gerico" (this was co-ordianted domestic Nuclear Terrorism in the the 00s but still showed several hardships the town would face if major cities were wiped off of the map). I've heard good things about "Threads" (but never saw it) which is the UK version of "The Day After" and much much darker... and even "The Day After" admitted it was toning down the realistic consequences because there are somethings you can't show on TV.
TVTropes.org has a good description of what would happen if someone who really... really... really hated Mickey Mouse detonated a low yield Nuclear device at the Walt Disney Studios in L.A. "War Games" is actually considered "scary accurate" for it's depiction of build up to Nuclear War (especially given that there are more than a few incidents that almost sparked a nuclear war that read scary close... including an incident in the Soviet Union in the same year the movie was released). "Deuscthland 83" is a good depiction of the fears from both side of the Iron Curtain and depicts the reasons behind the real life Able Archer '83 scare from the Soviet's perspective (it's subtitled from it's original German language release on Hulu, but don't let that stop you... the 80s soundtrack is awesome!).
Edit: To clarify some comment confusion. Russian military terminology is extremely nuanced and well defined, so that understanding the definition of the terms in question means exactly that thing and is not interchangable for political reasons (in the United States, First Strike and Pre-Emptive strike are kinda the same thing. In Russian military, they do have specific meanings and are not interchangable).
With that in mind, a second strike is what it is: They Launched Nukes, we got to fire back before we have none.
A first Strike is "We launched nukes as an opening action to war.
A Pre-Emptive Strike is "We're launching first because it's pretty obvious they're going to launch anyway if we don't do something".
A Pre-Emptive Strike was accepted as a second strike because the gun was drawn and cocked first by the enemy... we just fired quicker than them.
The silliness of this idea was the subject of the a popular Russian joke in which, having watched two other foreign-nationals die at the hands of a cannibal chief without intervention, the Russian tricks the chief into picking up a gun and promptly killed the chief because now the Russian couldn't be seen as the aggressor.
To the Soviet's mind, of the two great superpowers, only one actually used Nuclear weapons in actual combat... not only was leadership terrified that the U.S. would use nukes first, but they could point to a historical moral high ground. For it's entire history as a Nuclear Power, the Soviet Union only had them as a means of self-defense.
Of course, in order to use Nukes as self-defense, you had to show your enemies that you're just crazy enough to kill everyone on the planet if provoked, so you had to show that there would be a line in the sand where you would invoke Mutually Assured Destruction. SF-Debris, in his review of "The Day After" explains this pretty well... and Yes Prime Minister shows the consequences of politics under these pressures in what it called "Salami Tactics" (you wouldn't push the button on small scale pushes... it was kind of like two children in a car playing the most dangerous version of "I'm not Touching You" ever.). "Deustchland 83" even shows how, in an effort to suck up to the Soviets, the East Germans made it look like the United States was more willing to strike first than they actually were... and that misunderstanding was enough to lead to the very real Able Archer '83 panic that the Soviet Leadership went through.
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90%+ of the entire world population is wiped off.
Infrastructure is wiped off.
Travelling for more than 20 km/day is a challenge.
Though some high level personalities might have survived, when they come out of the shelter they will find wasteland and no command chain to support their supposed power.
Both USA and USSR (along with all other states) will collapse into a miriad of micro nations, fighting each other for accessing resources and local power.
Soon the memory of the history will fade into legends. Probably some smart ruler will create a sort of monastic order, to preserve along the centuries the history and the techniques, waiting for the dark age to finish and lead the nation to its bright future again.
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A small (initial population in the order of 10k) human colony has been established on an Earth-like planet in a solar system far from their home world. Due to resource limitations, ships traveled round-trip; that is, once colonists and cargo were offloaded on the new planet, they promptly returned to the original world with any desired exports. It is also worth noting that these ships are the only means of communication between the home world and the colony.
After some number of trips, the colony is well-equipped enough to be self-sufficient and permanent, and further shipments are scheduled primarily for trade (luxury goods from the home world, new raw materials from the colony). However, the next ship never arrives. Space travel is difficult, so time estimates require padding to remain realistic, so the colonists patiently wait out whatever may have delayed the ship. After a sufficiently long time, the colonists realize something catastrophic could have befallen this particular ship, but the next one would surely arrive at its designated time, likely bearing news of the first ship's fate. Yet no second ship arrives, nor will one ever again.
The following conditions apply to the marooned colonists:
* Some unknown event has befallen the home world, cutting off travel and communication between the two planets
* Some method of FTL travel was employed by the ships used, thus relatively little time passed before contact was lost (most of the first generation of settlers are still alive at this time)
* No spacefaring vehicles are present on the colony
* Edit for clarity: this planet has a limited but hardy biosphere (none of the flora or fauna have thus far been established, but assume this provides additional resources that can gradually, if crudely replace processed goods and consumables. (see below)
* The colony has the resources and means to survive indefinitely (Edit for clarity: Fresh **water** is adequately abundant on this planet and water purification systems are among the colony's initial tech. **Food** in the form of crops and livestock from the home world can likewise be cultivated enough to sustain the current population. Other resources such as **medical supplies and clothing** are finite, but can be supplemented over time using materials found locally, as mentioned above)
* This planet's environment is hospitable enough that the colonists do not need advanced equipment to survive. The colony, having only existed a short time, lacks the facilities to produce said advanced equipment en masse.
* The colonists, while currently all working together, are informally divided based on profession/vocation
My question pertaining to this setting is **how long would it take (in years or generations)** would it take before **technology regresses to pre-spacefaring levels?** Alternatively, **will technology degrade even further/not at all?**
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Another [question](https://worldbuilding.stackexchange.com/questions/2991/what-is-the-minimum-size-of-a-self-sufficient-industrial-country) may be relevant for yours.
Apparently your colony is too small (by several orders of magnitude) to sustain modern technology. It is said there bare minimum to sustain technology against specialization seems to be over 10M, probably nearer to 50M.
Many of the reasons explained there IMHO hold true, but I would add a few caveats:
* The analysis is done in the current world trade model: this means small countries (like Cuba) did not produce (i.e.) computers *in this world*, mainly because it was cheaper to import them, in spite of embargo.
* In real isolation several things that's "cheaper to buy abroad" will be manufactured, simply because there's no "abroad" available.
* You are dangerously near to MVP (Minimal Viable Population) which is estimated in 5k individuals (but there are known "lucky" cases where it worked with much less).
* It strongly depends on exactly which kind of manufacturing equipment and abilities are available: I would guess a colony not daily connected with homeland should have means to, at least, produce replacements for whatever they have. Having a detached colony with a long list of "irreplaceable" seems foolhardy.
Said this, a few more considerations:
* All effort will go into surviving and expanding: this means they will switch to "pioneer mode" as soon as they recognize the fact they are effectively alone.
+ scientific research not finalized to finding resources would stop.
+ women will start producing new colonists on a very short cycle.
+ children will be very much pressed to learn "useful" things *fast*.
+ youngsters will be employed in manual labor as soon as they *can*.
* All this, together, means:
+ current technological level will be maintained, but no advance.
+ some technological gadgets, not considered "useful" will not be produced (at least in the first generation).
+ medical capabilities (especially for coping with alien viruses; vaccines brought from Earth might not be what's needed) will be severely stressed.
+ social model will (probably) revert to small-town with high social control over the individual.
+ in a few generations this will produce a diaspora of dissidents. These will *not* be able to be self-sufficient.
+ this is a discontinuity point where two very different outcomes are possible:
- the colony continues to work as a group, possibly imitating the "Japanese-style big corporation with side branches".
- the colony spawns semi-independent child-colonies, only lightly tied to "mother".
+ Note: semi-independence *will* happen sooner or later, but *when* it will happen will make difference. If sub-colonies will be to small they will revert to lower technology, possibly turning "rogue".
All in all a setback seems unavoidable, but it may be temporary (say, till population is in the range of 100M) or may be a slow decline ending up with some XVI century technology from where to restart.
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**Why Assume They Will Regress?**
A lot of the questions and answers seem to assume a technological decline thanks to a relatively small population and lack of sufficient numbers of people to deeply specialize in various fields. It is presumed that as soon as the colonists go into "frontier mode", technological advancement stops or slows. I believe that this is an incorrect reading of human history.
Humans are an inherently territorially aggressive, pioneering species by nature. In almost every case in history where a small population of humans has faced a dangerous, unexplored frontier, rapid technological advancement has gone hand in hand with settling that frontier, regardless of the population sample size. In my opinion, this is because we (sort of like a lot of apex predator types) are inherently lazy (as a survival mechanism). When we don't HAVE to innovate in order to survive, we do so only very slowly. When we DO have to, we go on innovation turbo, a process we refer to in old fashioned terms like "necessity is the mother of invention".
**Examples Of Small Populations Innovating Rapidly While Surviving**
Some examples: the "dark ages" are often misunderstood as a time of technological stagnation. This is totally untrue. The good old days of Rome saw massive stagnation through the entire second half of the Imperial period, to the point that a lot of knowledge was on the verge of being lost before the real barbarian invasions began. As soon as the dark ages started, military technology began to accelerate in extraordinary ways. Within a hundred years of the fall of Rome, military armor, weapons, and tactics had changed more than in the entire nearly two millennia since the perfection of the Phalanx by the Greeks.
Vikings established tiny colonies in sometimes barely habitable areas, battling nature as they did so. They also rapidly developed the most advanced sailing ships of their era, radically surpassing the ship technology of much larger, more prosperous kingdoms. Their arms and armor were also way ahead of their time.
The American Westward expansion saw tiny, isolated settlements of very few individuals cutting houses out of sod, building shelter however they could, and in some cases going years between regular contact with the cities out East (particularly in the early half of the 19th century). This population, relatively small compared to the huge cities on the East Coast, was disproportionately represented in the inventions that heralded a time defined by: 1, battles for survival against nature (and also a huge civil war), 2, radical population growth and focus on growth particularly in the West where more kids meant more hands to help out on the farm, and 3, THE most rapid technological advancement and transformation EVER seen in human history.
The state of Israel was founded in a state of utter crisis and emergency. Ragged concentration camp survivors with nothing to their name but the clothes on their backs flooded into a VERY small "state" which was simultaneously battling invasion on ALL sides by every neighbor in a war that saw them vastly outnumbered. Food, clothes, ammunition, and pretty much EVERYTHING necessary for human survival was in short supply. The population of the state was way too small for anyone to specialize the way they did in larger states, and nevertheless, immediately, Israel began to develop technological advances and become a technology leader, even in the middle of several crises. In fact, Israelis say that *the need to survive drove innovation*.
**Specialized Knowledge May Actually Slow Down Advancement**
There is a theory about knowledge that basically states that specialization in advanced, high-tech societies is a game of diminishing returns. As society trends toward greater and greater specialization (ever deeper knowledge of ever more narrow fields), true innovation actually slows down over all (per capita). In other words, innovation still occurs, but now we need 2 million minds to come up with the advances that we used to get from 2000. If you look at the history of science (particularly the Enlightenment era, where it was still conceivably possible for one person to actually know all of the important scientific knowledge that existed in the world at the time) we see that the broader and less specialized the focus, the more rapid the technological advancement. I don't believe this is because old technology is inherently "easier" or "simpler" to understand. If you study things like early metal smelting from pre-bronze age times, you have to sit back almost in awe of the minds that came up with some of the processes they used, based on the starting point they had.
**Conclusion: They Will ADVANCE, Not Regress (Or They'll Die)**
If there is something to the "laziness" and the "less specialization is better" and the "necessity leads to invention" theories, then I would speculate that your colony would NOT revert technologically. What it would do based on historical patterns is CHANGE the direction of technological development from whatever path it had been on in the greater society they broke off from, toward a track focused much more on that colonies' survival needs. In areas that touch on what that colony needed to survive, they would likely end up MORE advanced than the "mother planet" (for example: suddenly developing rapid cloning technology not available on the homeworld in order to deal with their population problem). This is very much in keeping with what we see in history with successful pioneering attempts. What we see with unsuccessful attempts by small populations is usually just a lot of death.
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It depends on three things:
1. how far along the colony is to start with, a world with [Cornucopia Machines](https://en.wikipedia.org/wiki/Molecular_assembler) and industrial [Utility Fogs](https://en.wikipedia.org/wiki/Utility_fog) isn't going anywhere unless it faces an elemental bottleneck, like a lack of [transuranics](https://en.wikipedia.org/wiki/Transuranium_element) in the crust.
2. availability for resources, mainly this means energy but also materials, if nuclear and solar power are freely available from durable sources then maintaining high technology is relatively easy, provided you can access the materials needed to manufacture the technological artifacts you need. There are a number of questions like [this one](https://worldbuilding.stackexchange.com/questions/93856/physics-of-a-metal-poor-world/93900#93900) that discuss the possibility that a planet may present difficulties in access to metals for advanced technological applications.
3. the manufacturing principles used to produce the equipment the colony is using, if a modern "disposable consumer goods" approach is used then the colony is in deep trouble as basic tools and systems needed for maintaining existing technology will start to break down almost immediately.
Really the answer is that the technological base will remain intact as long as the recording systems that hold the information are intact and usable. Technology is the knowledge of what is possible not whether you can use that information right now or not. This is not a situation I'd want to find myself in 10,000 is pretty close to non-viable any major issues will kill basically everyone. I would think that this colony's material culture, the technology actually in use, would start to suffer on day one and continue down to some weird equilibrium not quite like anything in human history. Have a look at *[Destiny's Road](https://en.wikipedia.org/wiki/Destiny%27s_Road)* for some ideas about the shape of the culture that might emerge in such a situation.
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Concise Answer: Within 100 years it will either be approaching stability or have begun its decline. The rate of decline depends upon how many unplanned disasters they have to deal with.
As one settlement of around 10,000 people they are one major calamity away from preindustrial technology. One small metor impact of the level of the Chelyabinsk impact on the right spot would end their tech base for sure. An earthquake or volcano could make quick work of their tech as well. This event could happen tomorrow or never.
That being said, your current description has it set up that with proper management they would maintain industrial levels of technology. With 60 years they could be spread out enough (with 80,000 population) to ensure one catastrophe does not wipe them out.
Within 100 years with focus and a bit of luck they could easily be at or beyond current space tech and industry. Especially if they had a complete data dump of the home worlds internet and technology before they were cut off.
**Edit**
I’ve reviewed ZioByte’s answer and links. An interesting read. However the real world examples that are used to base their examples are not ideal for this situation. Cuba’s population of 11 million (establishing the minimum baseline) maintain an industrialized economy, however that is not its primary goal. Its primary goal (arguably) is to keep the establishment in power. To that end many resources are wasted on the military, the police, propaganda, and upon the elite ruling class.
If the 1st generation colonist stay in power for most of their lives. If they make their focus the maintaining and enhancing of an industrial economy. They will be able to guide the next 60-80 years. If they keep standard of luxury and entertainment low tech/resource and focus most of the high tech resources on maintaining and expanding their industrial base they can continue to support their current tech.
The final issue is transitioning this platform to the next generation of leadership. The original colonist will be dying off when the colony is between 200,000-400,000 in population. This is one doubling away from truly becoming sustainable and increasing standard of living.
A different baseline than Cube is Great Britain of 1750. They started the industrial revolution with a population of 6.5 million.
<http://www.tacitus.nu/historical-atlas/population/british.htm>
This was at a time when 60-80 % of the population had to work in agriculture to support the population.
So with 1750’s tech you need 1.3 million to 2.6 million people to support the nonagricultural portions of an industrialized nation.
With modern tech you can support your agricultural needs with less than 2% of your population.
<https://en.wikipedia.org/wiki/Agriculture_in_the_United_States>
If you cut out luxury goods, and most meat you could do it with less than 1%.
1.3 million \* .01 = 13,000 people using modern tech could feed a population of 1.3 million.
From 1910 to 2015 the U.S. used technology to reduce its manufacturing work force by 4 times (from 32% down to 8 %) <https://www.bls.gov/opub/ted/2016/employment-by-industry-1910-and-2015.htm>
While increasing its manufacturing output by 600% (20 million metric tons of steel production in 1900 to 120 million metric tons in 2015). <https://en.wikipedia.org/wiki/Iron_and_steel_industry_in_the_United_States#/media/File:USGS_Iron-Steel_1900-2014.png>
This amounts to a rough guess at 1000% minimum efficiency increase from the 1750’s tech level numbers. So you need 1/10th the labor.
1.3 million /10 =130,000 population of people directly in the industrial sector.
Right now we are using 143,000 people to fill jobs for the agricultural and direct industrial positions that can support a population of 1.3 million people.
Assuming a doubling rate of 20 years your colony gets to this level at 80 years (160,000) and has significant surplus at 100 years (320,000).
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What are possible economic systems for use within a space-based industrial settlement? The different approaches are to be weighed by the competitve advantages they offer to their respective communities.
Many science fiction stories are written about the space industrial settlement or colony as a “company town”, owned by an all-powerful corporation. Often workers are portrayed as oppressed wage slaves. My idea is to have a background that specifically prevents that, and instead encourages small independent companies.
This is a future where heavy industry has moved into space, with asteroid mining, settlements on various moons and other planets, in-space habitats, and shipping liners. An *Autonomy Accord* exists, preventing big companies from owning and being dictators over these various communities. Rather, each one must be owned and governed internally, by the people living and working there. So a big conglomerate might be a *creditor*, but cannot be your boss. What you have, in effect, is a federation of micro-nations.
Now any kind of industrial mining, shipping, or manufacuring concern will have a [huge shared infrastructure](https://en.wikipedia.org/wiki/Means_of_production). You can’t just have each person own his own tools and a little homestead. Not only that, but they must maintain a space-worthy habitat with life support systems.
So, in a pure capitalistic system you will need a labyrinth of contracts and stocks to provide for individual ownership of a logical piece of group property. But some communities noticed the whole “the workers own the factory” narrative as a parallel of the [Communist movement](https://en.wikipedia.org/wiki/Communism#Marxism) that came out of the original industrial revolution, and decided to simply go with communism internal to the community.
Ocasionally writers will be more original: for example, the novel [2312](https://en.wikipedia.org/wiki/2312_(novel)) refers to a [Mondragon](https://en.m.wikipedia.org/wiki/Mondragon_Corporation) worker cooperative system.
I'm asking about the internal economy of a “town” where workers can’t really go elsewhere after work; not about the political system of the “town” or the management of the company. Certain rights will be guaranteed by the federation, so we can’t have workers *exploited* by a resident ruling caste. Getting that sorted is not the scope of this question. I'm asking about how the community will distribute and share resources internally.
What is a possible (good) system, and how will adopting your suggested system provide the entire community (company) with an externally visible competitive advantage or disadvantage?
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# More information
Each settlement is a member of the federation which exists to facilitate trade, provide for common defence against piracy, and establish international law for contracts, claims, and disputes. We assume it is aggressively capitalist, so the individual companies need to *compete* for business and value. There may be layers of politics, alliances, and preexisting deals in place, but long-term it’s safe to say it’s capitalism where the best deal gets the business.
As the off-Earth industry grows, buying and selling to *each other* becomes a larger part of the market.
Settlements have great variety in their self sufficiency. As more niches spring up, they can offload more non-core functions to other settlements. E.g. they can buy from a farming community *if* the logistics make it practical rather than shipping adding to the cost. In crowded Lunar L4, you will see a lot of narrow specialization. Prospectors will patronize outfitters before setting off to remote destinations, but need to keep onboard vats for basic food calories, fix their own equipment, etc.
Are the settlements designed to be self-sufficient? What is the variation in population of these settlements? Are there nation-state or larger groups out there, interacting with these settlements?
Note that the settlement “doing better” must translate into more bounty to the individuals. People who feel oppressed can just leave, and a large number of dissatisfied among the population can force a recall of the leaders — the trade federation backs up the principles of the *autonomy accord* whose main tennant is to prevent oppression.
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Each employee is being paid in two currencies:
* galaxy wide credit (GWC)
* colony currency (CC)
GWC is to have some portable, long term savings. And to be able to buy the newest game console online.
CC is used to distribute scarce goods and services within the local economy. Because of a lack of portability or flexibility there is a general idea that they more or less should be used within some time frame and possibility of saving is limited. (Demurrage actually may be fine, depending on the conditions of the colony.)
CC and GWC are freely convertible, but the colony does not guarantee exchange rates.
Within the colony things like food, electricity, water, computer power (if someone wants to play Quake on the colony mainframe), rent for quarters, data transfer with the outside are being metered and priced in real life. A computer system tries to emulate the market equilibrium price that would clear the market. In the case of services provided only by single community members there would be some system of price controls, possibly with compensation for just being ready to provide some service.
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The biggest problems with running a capitalist system in a confined space are waste and greed. Communism equally has its problems in such situations.
The best way to run it is like an oil platform or military operation. Everyone has their job, they do their job, the company hierarchy provides everything they need while on base. They do their tour, whether 2 weeks or 2 years with everything laid then go home. You could run a "2 weeks on 2 weeks off" system if transport is cheap or "6 months on 3 months off" if transport is more expensive, perhaps even just a 2 year tour, then apply for another position after an abused minimum rest period in full gravity if you want something more dystopian.
*There's no reason whatsoever for the company town model to be a dystopia apart from the fact it makes a better story.*
The model you've created here, while maintaining the autonomy of the individual, is going to actively prevent any economy of scale and place the risk and cost of the operation either on the individual or on the sponsor. While they may not be wage slaves, they are going to be debt slaves probably bound to sell their goods to one purchaser with no option to get a better price selling directly onto the open market. Not because the resource or person is controlled but because the transport is controlled. I can see a far worse situation arising from your model than from a well run company town.
The well run hierarchical company town in fact acts as an idealised, miniturised, meritocratic (with a hint of gerontocratic) commune. Where the members are directly rewarded for work done and punished from the outside for civil disobedience with no kickback to the other members of the commune.
*The [Spacing Guild](https://en.wikipedia.org/wiki/Spacing_Guild) ultimately controls them all unless you allow the corporations to become big enough to control their own transport.*
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If the number of people is pretty high then you need local currency to distribute goods (like all communist countries did). Even if the number of people is low and we have barter we can still talk in terms of currency. So who gets what amount of money?
The answer is that it all depends on the political system inside a micronation. In USSR the salaries were planned and the distribution was in hands of people who ruled the country (the leaders of the party). Everyone got almost the same salary, but some people had access to cheap cars and others did not. I believe that even with small amount of people the systems remains mainly the same, but the cheating significantly reduces (no cheap cars for special people). So everyone will receive almost the same salary. Highly qualified specialists will not like the system and will try to find jobs elsewhere.
Another variant are corporations according to German laws (Aktiengesellschaft, AG). They are partially controlled by workers (the CEO reports to people who invested the money and to people who work in the company). This way the specialists still get high enough salary, but the workers go on strikes and have higher salaries than in ordinary corporations.
Also it will be very hard for the international community to check if the workers are not exploited, because they are very far away.
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I think a defining difference between living in modern day Earth and living in space will be isolation. The size of any colony or collection of colonies will define a lot about how people interact.
I would look at examples like east indian colonies in the 1800s, Pacific island military outposts in WWII, the American Wild West or the bases on Antartica. A key element of that life is waiting for the next shipment. In a fairly isolated colony there will be few surprises. The arrival date and manifest will be known to all - with the exception of contraband or other secret cargoes.
I think it would be rare that any colony could produce every good that it needs. Some external cargoes will be basic needs. A reasonably sane colony will distribute these based on need. Luxury items are different. Any colony will have businesses that are doing well vs others that are struggling. Distributing those items will be up to the community and your political process.
You can go a long way toward understanding this kind of economy by looking at travel times between colonies and defining the amount of trade. You can also look at how many colonies can produce different kinds of basic needs. Every colony will likely produce enough air, water & food. Few will produce higher quality goods like coffee, medicines or specialized hardware like the rubber seas on air locks or cryogenic hydrogen tanks.
So the average independent business operator will go about his day dealing with the limitations of the available materials. When there's a system failure, she will order parts that may take 6 months to arrive. Then negotiate with neighbors or neighboring colonies to get the parts early in exchange for something else.
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IMHO you are trying to reconcile two things that are not reconcilable.
In order to have small "free" communities you have to make them self sufficient and that means they should own their own equipment, otherwise they will always be dependent on whoever (literally!) own the air they breath.
OTOH, once you stipulate spatial and temporal separation (long and somewhat dangerous travels) you will almost automatically get competing individuals/small communities. Dropping transport costs (goods, people and information) inevitably leads to "globalization" where larger companies will always have an edge on smaller ones.
Multiple competing "firms" can only exist in a fragmented world. No amount of legislative effort can prevent people from doing what is economically favorable for extended periods of time. In a system where travel/transport costs are low there is space for very few entities occupying the same niche.
I suggest You have a situation where colonies were started via unmanned, auto-replicating factories that replicated so well (before their owners would realize the danger) that certain basic commodities are essentially free so colonists could concentrate on developing higher return products which can be traded over long (and somewhat dangerous) routes.
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## Government, Hard Mode
What are the most important differences between this kind of colony and a country on Earth?
* Your colony must be extremely efficient to survive in space.
* Depending on the colony's position, transport costs and times may be very high.
* Law and order are extremely important, as individual destructive capabilities are high.
In other words, you took the job of running a nation and cranked the difficulty up to eleven. You need to do what governments do, but without the flukes and failures. Or else, your station dies off in one of various possible catastrophes. A hull breach, fire, or just a fluke in the supply chain could all lead to a cascade of failures that ends the station. Unlike on Earth, terrorists could be an extreme threat. If someone destroys anything that's required for station integrity or operation, and it can't be replaced in a timely manner, you're doomed.
This said, you already got the context right. You need to ensure security and prevent monopolies, but anything not limited by these constraints could be hardcore capitalist. The market makes sure that every little bit of resource usage is properly paid for.
## Hardcore Is Correct
In today's rich countries, we're living in excess. We worry about topics like supporting people who aren't productive enough to life a decent and healthy life. Mind you, these people struggle with life down here, where oxygen is free and life can be supported with just soil and access to a river. And we struggle to stay on budget, even though we have much to spare.
The per-capita productivity required to survive in space is big, and the margin for destructive errors is tiny. Unless you have a lot of technology that is vastly superior to ours today, your station will kill off not just those who would be poor on Earth, but also everyone who isn't notably productive. You can't just feed people in prisons or pay an interplanetary ticket for them, nor do you want any crime problem. I wouldn't be surprised if a petty theft verdict becomes a death sentence under such circumstances.
Hardcore capitalism is very different from both anarchy and crony capitalism. When you're tight on resources, you really want people to keep their contracts. A "mere" delay in delivery might already cause big penalties, and any attempt to avoid fulfilling a contract would warrant police action. Unreliability, both from incompetence and fraud, reduce efficiency and must therefore be penalized. Neither being rich nor being disadvantaged should allow for any special powers; sympathies take a back seat and the contract rules supreme.
So, all in all, the system
* focuses on providing security and legal clarity.
* utilizes (and enforces!) laissez-faire capitalism as much as possible.
* tries to cut any costs that aren't vital to the above. (There are some corner cases of spending on a capitalistic system, see below.)
As another argument why this solution is correct, think about violating each of these rules. The first one has been handled before: without security, criminals can degrade or break the colony for personal profit, which usually isn't to the whole station's profit. The second is based on economic theory: people can sell their goods for the highest price they can negotiate. Any other solution would clearly be a competitive disadvantage. And violating the third, cutting costs, would be directly represented in taxes, which are directly taken from profit margins. Unless you have some reason to believe that government spending can offer a bigger competitive advantage than direct profitability, running costs don't improve the situation. The only exceptions are where the assumptions of capitalism don't hold, like education that improves individual decision-making, or the breaking of a monopoly that the market can't deal with in a timely fashion.
## Seen From Inside
To an individual inside a colony, this means a lot of agency about their trades and actions. There would be tight competition on all sides, including job offers. I imagine a lot of market-like situations, with auctions, varying prices, and short-term offers. If a delivery runs late, some prices may spike. If the station is low on certain specialists, their job offers and associated salaries will explode until more arrive. Speculation, prediction, and storage would be much more important than on Earth, since the effects of a shortage are much more severe. Insurance would likely be a common tool to assess risk, as it ensures that those making false predictions have to pay for them. "Safety concerns? Did you see the insurance claim sizes? Joke's on them if they messed up."
In everyday life, it wouldn't be that different from local capitalism as we know it. People get paid depending on the value of the goods or services they sell, and everyone is looking for good deals. Just at high productivity and with a general consensus that any kind of fraud or deception is not okay.
An interesting aside is that these "spacers" would generally earn a lot compared to what we're used to. Since the baseline of their income can pay for around-the-clock life support in a space colony, those who have any disposable income would probably be considered quite rich in our terms. Anything that can be efficiently produced in the colony would be very cheap to them, and all but the poorest could support families on Earth with ease. And still, they might worry about food shortages or hull breach risks for themselves.
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**This question already has answers here**:
[How long would it take to remove all trace of a civilisation, with malice and intent?](/questions/4494/how-long-would-it-take-to-remove-all-trace-of-a-civilisation-with-malice-and-in)
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Closed 6 years ago.
I am trying to generate broad ideas as to how to create a society with a refresh start. Where most signs of an advanced society (slightly more advanced then today's society) are gone but **without** causing complete ecological disaster which would result in the elimination of most species or humanity itself?
**While attempting to satisfy the following**:
* A maximum of 3000 years over which it can occur
* Remaining civilizations have regressed significantly
* Remaining civilizations have no true understanding of their ancestors
* Artifacts may still be found but are uncommon
* Almost all structures are gone
* Magic is present in this world (but I would like to avoid heavy reliance as an explanation)
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Anything that gets rid of the people would do it. Modern structures aren't meant to survive more than a couple hundred years. Without maintenance, most structures in areas with moisture will be gone or unrecognizable mounds in 300 years.
Ironically, the oldest existing structures are likely to be the ones that are still around. Stone buildings that haven't fallen over yet are sturdy.
Cement is not a good substitute for stone. Most modern concrete contains enough salt from the sand that the salt crystals will expand and weaken the structure. Concrete with steel reinforcing will actually fall before non-reinforced concrete since any crack that allows moisture to get at the steel will cause the steel to rust and expand. Glass will not rot but will likely be ground into sand or pebbles in 3000 years.
Any plastic will become brittle from UV from the sun and as the plasticizer leaks out. It will still be around chemically but will probably be in pieces too small to recognize.
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How about having people, over time, simply remove the buildings. I work on a campus and they recently tore down 2 buildings and it's like they were never there. Plants growing, weeds, you name it. No signs. Ok, maybe underground. Anyway, maybe people started dismantling them over time because they needed the resources for some reason. Just a thought.
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A Plague with a very high mortality rate (99%) will do the bulk of the work for you. If it also renders the population centers into No Go zones, even better.
Here is why: For our stuff to last, especially in the modern day, it needs maintenance. *Without people, maintenance will not happen*. Glass will break, Rubber seals will break down allowing moisture in, iron will rust and concrete will crumble. Freeze/Thaw cycles will accelerate the process more and more each winter, and no weed spray will allow all kinds of plants to wreak havoc on roads and sidewalks.
So the Plague wipes out 99% of the population. Start with 7 Billion, you end up with maybe 70 million scattered across the globe. That should be enough to maintain species viability. The shift in focus will go from what's on TV to what the hell am I going to eat. Starvation will do in a very high number of the remaining population because we are so divorced from food production. A couple of harsh winters will whittle this down even further.
After 10 years or so, things will settle down. By that time the remaining people will have dispersed from cities into smaller farm communities. The cities that were aren't going to have much left in the way of valuables but the land there is not going to be arable yet. Add the horror stories and no one is going to even want to go there.
If people avoid the cities for a few generations, once you get past the point of "living memory" the dangers will become legendary. This takes you to around 80 years after the plague. By this time, the rot of buildings from lack of maintenance will keep the Urban environment dangerous. The city will no longer be easily recognizable anymore.
Add to this a drop in literacy due to the rigors of survival. The drop in literacy is kind of important in this scenario. If you can't read, you are less likely to figure out what the ancients were up to.
By around 200 years, the cities that were will have very little left that wasn't destroyed, they may even be safe to go into again. There will be artifacts from the ancients, but a lot of the knowledge will be gone.
By the time you get 3000 years out. We will become the mystic ancients who dabbled with forces beyond our control. No Magic is required.
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## Have the people themselves actively removing traces of past technological society.
Some of the materials and structures we construct are amazingly resilient to the elements and will easily last thousands of years in some recognizable form without active means being taken to remove them.
So to get rid of all traces of our current culture and technological society, the best way is if everyone decides it has to go and actively removes and destroys any items found.
There could easily be a number of motivations for this:
**Religious:** the past society was wicked and worshiped their own creations as God, all of their creations must be destroyed.
**Environmental:** those plastics containers everywhere cause cancer, and a lot of that debris is radioactive and makes people sick when it is around.
**An Existential Threat:** The alien federation destroys all high tech civilizations they find, so get rid of all high technology or be wiped out.
Whatever the initial motivation if it is pervasive and persists long enough it will be codified into tradition and the people will forget why they started doing it. Eventually there won't be much left to remove and all that will remain of the past society are myths.
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The first obvious step is to kill (almost) all humans, and from then on nature will wipe out most traces of our societies, as other answers have shown. For large, ancient structures that will last for thousands more years, such as the Egyptian pyramids, I'd imagine you could blow it up with either simple explosives or magic and then it would be unnoticeable withing a few hundred years just like most other structures.
However, this would only make civilization invisible from the surface alone, yet other traces of us would remain for millions of years. For instance, all the road systems will be buried, but they would mostly still be there, and would be detectable with just underground scanning technology (even with just a shovel in some places). This would be very, *very* obvious, and would be a clear sign of a highly organized society. You would definitely need to grind up all the roads somehow.
Another big issue would be plastics. Contrary to popular belief, plastic does decompose, but it doesn't *biodecompose*. After a few million years, most plastic in the world will be in the form of microplastics, plastic particles that are less than five millimeters in diameter. The majority of these microplastics would literally never go away, because they can't be reduced into their elementary parts without some chemical reaction. Fortunately, these would only ever be noticed via the technology that we have today, and by the time the new civilization discovers them, they would probably mistake it for their own.
The thing you would have the hardest time getting rid of would be space debris. Currently there are millions of small (and a few *very* large) man-made objects orbiting the Earth, and more are added every day. You would almost certainly have to resort to magic in order to get all that junk down to the surface.
On a side note, I'd like to add something here: most people are under the assumption that only a few thousand or million years after humans disappear, there will be no trace of human civilization left. In reality, assuming you don't involve alien technology or magic, there will *always* be traces of our civilization, all the way until it's consumed by the sun billions of years from now.
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I can't comment on magic's existence. But, everyone's on the right track with how traces of the past would be wiped out over time.
If this is a civilization on par with out own, which built in the same basic ways and with the same basic materials we ourselves use, simple neglect would see to most of it being completely gone within a thousand years or less, actually.
Add to that, people surviving whatever caused the collapse would, after a few generations, lose any reverence for the ruins that at the time endured, and would strip the materials for practical uses. This sort of thing can be seen in poorer areas hit by disaster in our own world, in our own time.
The sudden disappearance of a technological, global society like ours would cause a lot of ecological and climate bounce back too (which in truth would happen with it still present as well, but possibly less destructively). Weather running amok would definitely hasten, significantly, the decay of stuff simply not built to last eons. Neolithic structures endure because they were meant to. The pyramids and so forth. Even they would actually be gone in another 3000 years, if neglected though.
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With late XXI century tech, wildlife replication is becoming commonplace. Dodos? Small dinosaurs are piece of cake. Dinosaurs? Large birds are big to deal with, but doable. So long you get a viable DNA sample, any animal can be replicated.
They need to be grown from infant stages (no insta-t-rex machine) and function as a normal born animal after that (by the way, some asian country now has a eternal dynasty of clones of their supreme leader, but that is for another day). They need to be tamed, trained, reared, shoed, etc.
Hunting and safari now are commonplace, because if you have enough biomass and energy, you can just keep making more animals. And of course the world is having tons of protests from animal rights defenders, but this is yet another tangent.
So Mr. McHound wants to get his killer hounds to fight all the animals there are. Is there any animal these dogs can't kill?
Rules:
* Land animals only. Of course the dogs will have no chance of killing an angler fish that never comes above 3,000 feet under the sea.
* Only animals weighing more than 1lb. Don't go saying the dog can't chew tardigrades.
* Hard Science question. Please take this in mind.
* Any animal that ever lived on Earth with the requirements above is fine.
EDIT:
* No genetically modifed animals. All the animals in the safari are standard versions of the ones that live(lived) on Earth.
Regarding the dogs:
* The dogs are of a breed made for war created from several ferocious XX century breeds. They are not transgenic, but can be considered the pinnacle of canine crosbreeding.
* Dogs can be cloned, and even though they have to be trained, if one dog of the pack survives, that is fine.
* The dogs are trained for combat / killing / war.
* Pack size is anything greater than 5 dogs.
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
**Size and/or armor** Elephants and black rhino can't be taken down by anything but the largest predators (or people) and even then they kill far more often then they get killed. Usually the predator is exploiting a specific weakness like drowning or literally [climbing the animal](http://scienceblogs.com/tetrapodzoology/2009/02/04/lions-as-macropredators/) which a dog will not be able to do. You can basically include any animal in the elephant size range or bigger. A large sauropod (especially the heavily [armored](https://en.wikipedia.org/wiki/Ampelosaurus) ones) would not even be threatened by the dogs, they would just be an annoyance to be stamped into paste.
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The obvious answer is any animal that can live somewhere that a dog can't go, such as up a tree or underground. Those are uninteresting cases, though, so I'll focus on what you were probably looking for: something that can co-exist in the same environment as dogs while being relatively immune to their attacks.
I'll also ignore the obvious answer that a pack of dogs - when fired from a cannon at a sufficient velocity - can probably kill anything[[citation needed]](https://what-if.xkcd.com/1/).
A dog's weapon for taking down prey is his mouth. Your target animal will therefore be something that a dog is physically *unable* to bite. I was unable to find any hard numbers about a dog's maximum bite size, but we can approximate this using other data. You mentioned these dogs were cross-bred for maximum hunting effectiveness. Let's assume that they have inherited the largest mouths/jaws from our modern day breeds and see what sorts of things they could bite.
After looking through tons of photos of dogs yawning from side angles, I was able to locate [this photo](http://funzoo.ru/uploads/posts/2010-09/1283788424_polyarnyj_volk028.jpg). My protractor measured an angle of approximately 65 degrees between the upper and lower jaw, which is the largest of any of the photos I was able to find.
This [wire basket muzzle](http://leerburg.com/wirebasketmuzzles.htm) is available in lengths up to 6 inches, the largest I found. The [dog muzzle sizing guidelines](http://leerburg.com/muzzlefit.htm) state that a muzzle should not be longer than the dog's actual snout length, so there must be a breed with a 6" snout.
With these numbers, we can do a little trig to approximate the largest object a dog can bite:
$$
2\*\sin{\frac{\theta}{2}} \* l\_{snout} = 2 \* \sin{\frac{65^{\circ}}{2}} \* 6 = 6.45\ in.
$$
Your uber-dog can open its mouth to a distance of almost 6.5 inches. This number is generous since it ignores the length of the teeth and assumes the dog would have any sort of bite strength when open at this extreme angle, but it can still serve as an upper bound. A dog would have difficulty biting anything significantly larger than this. An adult elephant's foot (for example) can be [15-20 inches wide](http://www.africa-wildlife-detective.com/elephant-facts.html), which would be very difficult for a dog to bite.
Your dog-resistant creature would need to have no accessible body parts that were small enough for a dog to grip. This means thick, long legs and a tough, tight hide that doesn't easily pinch or sag. The head would need to be far enough off the ground that a dog can't jump and grab the soft, squishy targets there (the [record height for a dog's jump](http://www.guinnessworldrecords.com/world-records/23431-highest-jump-by-a-dog) is 68 inches). This combination of attributes brings to mind the [giant sauropod family of dinosaurs](https://en.wikipedia.org/wiki/Sauropoda). If it lifted up its tail and neck, attacking dogs would have nothing they could effectively bite.
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
Anything with thick skin. If the dogs can't damage it, they can't kill it. I also picked examples that were big enough to take out the dogs.
So, for modern animals: rhino, hippo and, maybe, elephant.
For extinct, recent, species, the [giant sloth](https://en.wikipedia.org/wiki/Ground_sloth).
>
> ...the ground sloths' already thick hide consisted of osteoderms,
> which made it exceptionally thick.
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>
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Osteoderms are bits of bone material within the skin.
The saber tooth tigers in the American southwest (there were many, independent, instances of "saber tooth" tigers) developed their long fangs just to get through the thick hides of sloths and some other large mammals.
For extinct ancient species, the [ankylosaurus](https://en.wikipedia.org/wiki/Ankylosaurus) or any similar species will fit the bill.
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
Large, armored lizards and amphibians may be the only ones that can fight dogs. Alligators would be unassailable by dogs in just a foot of water. Even if a dog could find the gator, one attack from the gator would kill a dog. With a group, the gator could just pick the dogs off one by one. If a dog did manage to bite the alligator, it would be ineffective due to its armor.
Komodo Dragons would be a formidable foe as well, with scaled armor, gigantic crushing bites, and a ludicrously strong tail. One bite or one direct hit from a tail would remove a dog from the fight.
Other than that, there are many land animals that live in places that Dogs simply cannot go. There are some primates, specifically species of Lemurs, that can live their whole lives in trees. Ibex can navigate cliffs so well that nothing can follow them. Burrowing animals are also suited to hide from dogs. These animals, while still being land animals, could never be reached by dogs.
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
What about tortoises? They cant kill it i suppose and the tortoises cant kill them. Is this a valid response or Should the animal in question be able to defeat/kill a dog?
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**This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information.
Your question is inherently opinion-based, and NO ONE pointed this out yet, but more about that later.
Honestly, your war dogs will gonna get r3ped by most land animals, just a few example:
* Cattle (if very angry)
* Elephants
* Cats (if [they](https://youtu.be/Hqd75otj7RM?t=29)'re [possessed by enough demons](https://youtu.be/g_bQwBWqKjo?t=6))
* Horses and Giraffes (they can trample, and if clever enough to not get themselves surrounded, they can inflict a massive casualty upon the dogs)
Also, there is the...
# Cassowary
This bird is/ can easily be a genocide crusader, with its sharp talons the Cassowary has more than enough tools to cut up Mr. McHound and his dogs.
# [Hippos?](https://www.youtube.com/watch?v=TXvUKSJvk_g)
**Your dogs need to separate and overwhelm the prey, without any of these to they can be easily reduced to pillowy mounds of mashed potatoes (along with their owner), another crucial factor is that how angry, that animal is, if your dogs stumble upon Psycho Cat.**
**Another important thing is the animal's mind. If I spend months with teaching a Cassowary, how to effectively kill a dog, and how to avoid getting ensnared, then there's a good chance of the bird winning.**
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**The Scenario:** A technologically advanced mother culture wants to manage mass outbreaks of virulent disease in its technologically regressed colonies, who are inclined to resist most of what the mother culture does, good or bad, as a basic principle. The mother culture, for their own part, treats disease control primarily as a political and economic issue -- not a humanitarian cause.
**The Question:** Is it feasible for the mother culture to engineer a series of airborne vaccines, and then have aircraft spray them on population centers? Airborne vaccines have been considered [before](http://archives.chicagotribune.com/1958/10/25/page/2/article/tells-newest-in-tb-vaccine-you-inhale-it), and we have [spray vaccines](http://theconversation.com/taking-the-ouch-out-of-vaccines-the-future-of-needle-free-vaccination-44704) even today.
If so, how effective could such a program be at controlling disease? What kind of infrastructure and technology might it require? Roughly how often would they have to respray to maintain reasonable levels of immunity? Would there be probable unintended consequences (considering factors like allergic reactions, pregnancies, people with weakened immune systems, etc.)?
[Answer]
If you were using an aerosol virus it would have to be a [live attenuated vaccine](http://vaccine-safety-training.org/live-attenuated-vaccines.html). People might be inside or at sea or wearing a mask or otherwise might not inhale the vaccine during the period when it was airborne and you would have to have these people catch the vaccine from people who were vaccinated.
There are vaccines that work this way. The Sabin polio vaccine is a great example.
from <http://amhistory.si.edu/polio/virusvaccine/vacraces2.htm>
>
> An important feature of Sabin’s oral polio vaccine was that
> immediately after vaccination, people shed weakened virus in their
> fecal waste. This boosted immunity for others in the community and
> gradually reduced the number of people susceptible to poliomyelitis.
>
>
> Between 1963 and 1999, Sabin live vaccine largely replaced Salk killed
> vaccine everywhere in the world. However, because the live virus in
> the vaccine occasionally became strong enough to cause actual disease,
> Salk killed-type vaccine has replaced the live type in the United
> States.
>
>
>
In places where there is potentially real polio, the benefit of having vaccine transmitted person to person and prevent polio outweighs the occasional case of polio caused buy the vaccine. In the US where there is little polio (they graciously do not mention that usually in the US, our drinking water does not contain the poop of our neighbors so there is less transmission) the risk of vaccination induced polio outweighs the protection from real polio conferred.
In your situation the mother colony probably does not care too much about sickly people with weak immune systems. A live organism vaccine which was very contagious would be optimal for rapidly conferring immunity to the populace and a few cases of the actual disease among nonworkers would be acceptable. If you want them to seem like Hunger Games type hardasses you could make the vaccine itself be pretty tough on the populace - maybe scarring them up like smallpox used to do.
But back to real life and the WHO: generally for real vaccines the live attenuated vaccine is actually the pathogen itself and a weak strain is selected. Recombinant epitopes are already used in the hepatitis B vaccine. A transmissible norovirus (for example) engineered to express polio antigenic epitopes would have no possibility of causing real polio, but could induce immunity to those epitopes. Hopefully real vaccines are made that way in the near future because that would be much safer. A benign and paternalistic mother colony (can you have a paternalistic mother?) could cause everyone in the colony to get "stomach flu" or some even less symptomatic disease with a very contagious vector that was engineered to express the relevant epitopes.
ADDENDUM
Infrastructure: You could spray an aerosol rhinovirus out of planes like crop dusting, or from trucks like they spray for mosquitoes.
Respray: it depends on the disease. Flu vaccine is every year because there are antigenic variants that come up. Polio vaccine lasts for life and so you would need to respray when there was a new generation of kids born since last spray.
[Answer]
Airborne vaccines will face the same challenges as weaponized harmful biological agents--the dispensing method reduces effectiveness. In both cases the "strength" of the agent is less than a naturally occurring pathogen; the weapon is usually engineered to die out quickly to prevent spread beyond the target zone and the vaccine is engineered to not cause the target disease, so the relationship holds. A sneeze is a significantly less stressful delivery system than a spray from an aircraft, and the active contamination period from a sneeze is usually less than 24 hours.
I would recommend evaluating a method of distribution in a food or common OTC medicine product. Use ionized salt, vitamin fortified milk and enriched flour as models of practical distribution.
[Answer]
With an airborne vaccine it would be really tough to ensure people got enough vaccine to tickle the immune system enough to lead to immunity. You might get a lot of people with partial immunity, which may be helpful if it's a last ditch effort, but a waste of resources otherwise. Better to ensure that the most vulnerable groups get full immunity! Via packaged food or drink (with a concentrated dose in a single serving) might work, assuming they've advanced beyond our vaccines which mostly need to be injected.
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[Question]
[
This is a follow up to the creature 'griffins' I sort of created here: [Anatomically Correct Griffins](https://worldbuilding.stackexchange.com/questions/25281/anatomically-correct-griffins/25387#25387)
The idea of the final griffin was a small tree based species that will leap down on much larger prey and kill it quickly with attack to jugular. Hunting is very dangerous because griffins are frail compared to their prey and because there are land based predators that make any time spent on land dangerous.
The are very selective in their kills. Their 'pack' spreads out over the trees looking for the perfect kill. When good prey is found the spotters will alert the other's and try to flush their chosen prey towards a defined 'kill zone' by positioning viably positioning themselves for a kill. If they prey doesn't respond the spotters will attack it once in the prefect position, if the prey attempts to flee so the spotter can't attack the spotters maneuver it to the kill zone; a location where their best hunters are hidden just right to be able to make the best/safest leap to have the highest chance of a kill at low risk. Other griffins will converge on the prey to keep driving it towards the killzone once called.
A killzone probably can't be a single predefined location, the griffins would be spread out over a large area and likely need to move around the killzone to be a location close to the prey rather then driving the prey long distance to a single chosen killzone.
There are two problem with this. The first is that the prey will eventually develop some habitual understanding of the griffins hunting style and attempt to avoid being herded to a killzone. If they prey can anticipate where the griffins want it it will attempt to avoid that, even if it means putting itself at risk of being attacked by a spotter.
Second, there are other predators, ones that hunt/kill griffins and scavengers who would be happy to drive off the much smaller griffins to take their kill.
Thus the Griffins need a way to communicate over a distance with their tribe, to communicate where prey are found, decide on a kill zone to drive it to, and work together to flush the prey to the right spot. Yet they need to be able to do it without the prey or other predators learning/evolving to recognizing the calls well enough to develop enough of an understanding of their communication to know where the kill is likely to happen.
I'm open to any viable communication option. I'll mention one example I like, but am not committed to, because it places evolutionary pressures to drive the Griffins towards sapience. That's the idea of griffins communicating via vocal calls, but with some evolved obfuscation that keeps predators or prey from developing a habitual understanding of it; ie it's far more complex the a few predefined food calls similar species use.
In this example when griffins are hunting, or spread apart for any reason, they always keep up a constant 'chatter' across the whole tribe, so common and spread across such a large hunting region as to not be useful to predator's or prey, becoming mere background noise. When they find prey they communicate it with this 'chatter', but without raising the volume or localizing the chatter, and with complex enough language/syntax that other species are unable to tell that they have transitioned from griffin equivalent of 'small talk' to hunt coordination.
This idea would work once evolved, but can it evolve? Can proto-griffins that are just developing the tactics of coordinated hunting and driving of prey species, that haven't reached the level of sapience that this tribe hunting technique will drive them towards, be expected to develop not just long distance communication but some obfuscation technique like this? With there being almost as much evolutionary pressure on the prey to learn the griffins language as there is on the griffins how do the griffins evolve understanding of this language without their prey doing the same?
I'm open to any communication system that can't be learned/exploited by other species, not just the above example, but the main question is the same, not only can one exist but how can it realistically evolve?
[Answer]
## Chit-chat will be hard to come-by evolutionarily speaking
Let's say your griffins start with a proto-language dedicated to hunting. Then the prey will naturally stay away from griffin-like sounds. Now, some griffins have a mutation making them more verbose (next step to your global chit-chat idea) : they drive off the preys and have a harder time getting their meals (or not getting mauled to death by their frustrated fellow griffins).
## The solution ? Infra-sounds
But another mutation makes the calls of some griffins more low-pitch. It could be high pitch too, but let's say the physionnomy of your creatures favors low-pitch mutations a bit more. It doesn't sound quite griffin for a prey, or at least some of them. Meanwhile, it's still audible and comprehensible for a vast majority of griffins used to griffin talk. As a result, we have a higher rate of unsuspecting preys. On the other hand, the few griffins not understanding low-pitch will miss a few more hunting occasions.
The result ? Low-pitch talking griffins have an advantage and low-pitch understanding griffins don't suffer a disadvantage : all griffins tend to get more and more low-pitched able (both speaking and hearing). Since the preys evolve as well to be more caution of low-pitch griffin noises, the arms race put more and more pressure on griffins to produce the lowest pitched sounds.
Until... your griffins now speak on the infrasound range. Since a non-infrasound griffin can't hunt and most likely die, and a non-infrasound prey only suffers a penalty to its chance of survival, there will be a hard limit to how low-pitch can a prey hear sounds : after all, they also have to hear regular sounds for their own hunting, and a wide hearing range is harder to obtain.
**Thus, the griffins win the low-pitch arms race and now hunt with a really cool deep voice.**
[Answer]
*Please note that this is my second answer, the first one focused on an alternative to the preferred OP's idea, of a global obfuscating chit-chat. This one will try to address it*.
---
## Step 1 : basic hunting talk
In this state of their evolution, griffins already have the spotters/killzone tactics, with really basic communication. The communication itself may drive off some preys, but it's better than no communication at all. In this society, the best hunter groups are the most talkative.
---
## Step 2 : boredom chatter
Some griffins are born with a sort of "boredom chatter" trait : when they are not hunting, they emit various sounds just for the sake of it. While this can repel some preys, it is however limited to the time when griffins are not hunting, so it doesn't matter. When the hunt begins, the boredom is over and the chatter with it. It's ninja killing time.
This way, the boredom chatter trait is not really troublesome, and still has a huge advantage to the ones born with it : it's a real griffinette magnet. Why ? Because the best partners are the best hunters, and the best hunters are the best communicants. And now the boredom chatters are the most likely to reproduce...
---
## Step 3 : everyone talks all the time !
Fast-forward to the point when every griffin is a boredom chatter : the local fauna become used to it, and only get suspicious when the chatter stops, for this can only mean one thing : the hunt begins. So griffin evolution takes the next step : the most successful hunters are the one still chatting when going on a hunt.
Now you have permanent chit-chat.
---
## Step 4 : on the path to meaningfulness
Constantly producing sounds cost energy, and energy has a cost, so it better be used at the maximum efficiency. Step by step, the meaningless chit-chat becomes more and more representative of the emotions of the individuals. Shortly after, it is effectively used to describe the environment, carrying basic but somewhat useful informations not directly linked to hunting. Then it become more abstract, less bound to immediate events and then...
**You've got language.**
[Answer]
**Body language**
I envision those movies where the delta force guys are indicating what they perceive and what must happen next with a series of silent gestures.
If the griffins can see each other they can communicate with body language. A flip of the wings, a dip midflight, a headfake - all those things done by a griffin would be obvious to other griffins but to a nongriffin it is just an animal twitching around.
If the griffins are concealed in the trees you could have their plumage (pelt?) be a color that it is difficult for nongriffins to see. For example a green/brown griffin with black streaks that are actually ultraviolet would blend well into the foliage - unless you see ultraviolet as a color in which case it would stand out like visible orange. Then they could still communicate with body language.
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[Question]
[
This plant I am designing grows on earth, in locations where competition between plants is fierce, water is scarce and also nutrients in the soil are diluted. The dilution requires the plant roots to be developed at least in 1 cubic meter of ground to be able to sustain the plant life.
This plant has developed peculiar traits to succeed in this environments:
* roots secrete a growth inhibitor, to prevent other plants to grow close
* growth is fast in the first phase, to occupy the ground area until roots can sustain life. Then it slows down.
* the plants growing in an area can synchronize the blooming and fructification on periods of 17 years, by means of chemicals secreted by the leaves.
* the seed of the plant requires a bath in chloridric acid in order to develop (basically it has to go through the stomach of an animal)
In order to secure that seeds are spread away from the mother plant and to provide a boost of nutrients to the growing plant, the fruit of this plant is highly sweet, attracting animals from miles around thanks to smell. Once eaten the fruit releases, together with the seed into the stomach of the animal, a poison which stops peristaltic movements and kill the animal in 2-3 days. The rotting corpse will grant the growing seed the nutrients needed to develop the roots until the cubic meter mentioned above.
Is this a realistic mechanism?
[Answer]
There is at least one plant in which the seeds and seed structures kill the animal which disperses them: Pisonia, aka birdcatcher trees.
<https://en.wikipedia.org/wiki/Pisonia>
<http://neotrigonia.blogspot.com/2016/01/the-bird-killing-tree-of-great-barrier.html>
These trees live on barrier islands with nitrogen poor sandy soil. Birds nest in them because birds like islands. The seeds are sticky and entangle chicks that run afoul of them.
[](https://i.stack.imgur.com/QU6jH.jpg)
this image found at <http://hdpphd.blogspot.com/2014/04/capricornia-cays-survey-holiday-3-heron.html>
Bogged down with seeds the chicks hop around for a bit then die, their hopping doing some dispersal and the carcasses fertilizing the seed.
As regards the prospects of an animal eating a fruit which will kill them, that is trickier and something I have not heard of. But not impossible. There would be very strong evolutionary pressure to not eat that fruit!
Re the anticompetition chemicals that happens not infrequently. Black walnuts are the one that comes to mind.
<http://hort.uwex.edu/articles/black-walnut-toxicity/>
The bigger the tree the more poisonous the soil, but I think that is because under the tree is where the most nuts fall.
I could imagine a seed with a mechanism like the pisonia: it sticks to an animal and then gradually poisons it with something like curare (a paralytic neurotoxin). That lets the animal get a little distance. The soil in the immediate area of the dead animal will be pretty rich in the short term and that might be enough to discourage other seeds while your plant gets established.
[Answer]
Not if the fruit kills the animal that is supposed to distribute the seeds. Otherwise, this is not unlike seeds that only germinate after passing through the digestive tract of an elephant, for example. It is the poop rather than the carcass of the animal that provides nutrients.
[Answer]
Perhaps to get around the animal evolving to not eat it you have the fruit be poisonous only some of the time. Perhaps 1/2 of the time it is reproducing it has lots of nice nutrients, but secretes laxatives after 2-3 days so the animal doesn't completely digest the seed. The other part of the time it kills the animal in 2-3 days and there is no way to tell the difference.
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[Question]
[
The [Snakebot of Doom](https://worldbuilding.stackexchange.com/questions/37248/defeating-the-revised-snakebot-of-doom) - now dubbed [Jormungandr](https://en.wikipedia.org/wiki/J%C3%B6rmungandr) by the first humans to encounter it and survive - is busy steamrolling New York into rubble, having first nuked the capitols of every member of the Nuclear Club and the continuity-of-government sites of the US, Russia and China with 80Mt fusion bombs, bombarded all larger fixed sites of military or strategic importance (military bases and nuclear weapons caches) in the continental US into rubble with heavy kinetic cluster weapons, and having eaten a 60,000 ton container ship in order to resupply its ammunition bunkerage. A subsequent counter-attack by naval aviation and the remnants of land-based fighter and bomber squadrons has been decisively defeated, with every human weapon, aircraft and most of the pilots in the attack shot down without causing Jormungandr any damage at all.
However, Jormungandr is not actually interested in exterminating humans unless they're a threat, and then will kill only those individuals who pose a threat. Now, a group of eighteen people have survived the crash-landing of their unarmed helicopter on Jormungandr's side even as it is in the process of steamrolling New York City into a gravel driveway. Jormungandr isn't going to stop, but neither is it going to try to kill these humans. Their survival is a matter of indifference to it.
Jormungandr is 446 metres in diameter, weighs 1.486 billion metric tons, has a body that is cylindrical for 7480m, and then tapers down to a point over a further 669m, the tail matching with a similarly shaped mouth. Its armour is made from Tungsten-depleted Uranium alloy plates with a smooth surface coating of Boron Carbide, at the surface appearing to be overlapping scales around five metres long and half a metre thick, much like the scales of a snake. Most importantly to this question, it is driven by [shape-memory-alloy](https://en.wikipedia.org/wiki/Shape-memory_alloy) 'muscles' that have an operational temperature of around 97°C/207°F, and it has a similar surface temperature.
It is presently rolling sideways up the length of Manhattan at a speed of around 5kph / 3mph.
Of the eighteen people who have crash-landed on Jormungandr's side, one woman has a collapsed lung, one man has a broken femur, and another man has significant internal bleeding. The remainder of the survivors are not significantly injured, and range in fitness from a couple of ultra-fit military types to a few unhealthily obese individuals. Some individuals have good first-aid skills and one of the lightly injured survivors is a general-practise doctor.
It is not possible to climb directly down Jormungandr's sides, since it is large, cylindrical and rotating, however the tapering tail about 3km/1.8mi distant from the crash point is a viable escape point.
It is late January, and a large blizzard struck the previous night, but the morning, while cold enough to freeze water, is sunny with light winds. The crash survivors are mostly wearing clothing generally available to and worn by New Yorkers in such conditions, though while all are wearing some sort of footwear, some had come directly from heated buildings and had left any removable outerwear behind, and are wearing footwear that could be considered business attire.
**The question:**
Is it possible for the survivors of the crash to escape Jormungandr and return to land? Can they all survive, or is it likely that some will die? If so, who is most likely to survive - or die?
Please don't forget:
* Jormungandr is *hot*, with a skin temperature of 97°C/207°F, nearly hot enough to boil water, and is emanating vast amounts of heat.
* It is covered with smooth scales a half metre high.
* It is rolling sideways at 5kph / 3mph
* The survivors must travel a linear distance of 3km/1.8mi to the escape point, *but this does not account for Jormungandr's rotation*, which will make the actual distance greater, inversely proportional to the rate of travel.
* Failure to move quickly enough will result in a fall of several hundred metres, followed by being crushed by a billion and a half tons of rolling doom.
* Human nature will tempt some of the less injured survivors to try to save the more injured members of the party.
* Some members of the party may not be significantly injured but are of sufficiently low fitness that travelling the required distance at the required pace would be highly taxing.
* The environment outside Jormungandr's sauna-like microclimate is below freezing, with lots of snow but no precipitation and light winds.
[Answer]
**I'll take each grouping of survivor one by one**
First: the collapsed lung
In my research, I have found that:
>
> between the airways and the pleural space around the lung which lead
> to the pneumothorax becomes a one-way valve through which air can only
> enter but not leave the pleural space. As air continues to accumulate
> there, it may not only collapse the lung, but also shift the contents
> of your mediastinum (the stuff in between the lungs in the middle of
> your chest like your heart and major vessels). Eventually this would
> lead to compression/kinking of your vena cavae, which would prevent
> blood from returning to your heart, rapidly dropping your arterial
> blood pressure and killing you as a result.
>
>
>
So yea, that person's dead
Group 2: broken femur
With the blood loss from the broken bone combined with infection risk combined with severe cold, even with the medic on scene there's no way this guy could survive and even if he did moving him could kill him so he couldn't leave.
Group 3: Internal bleeding
If it didn't damage a major artery than it is indefinite. This person could be carried out if they didn't succumb to the cold. If it did hit a major artery than this person couldn't survive.
Group 4: Not significantly injured
If they are wearing thick clothing than they should be able to survive long enough to get off. The people not adequately dressed could still survive because of the heat this thing produces.
So yes, some could make it back to land. ( if no debris interfered, but it seems that there is none at this time)
Edit: Although the heat doesn't change the nature of my first 2 groups, the person with internal bleeding now would have a better chance because they would no longer need to worry about dying from cold. Also, if they kept on there feet they should be fine, just with the plastic bottom of there shoes slightly melted but not bad enough to hurt them. About human nature and saving the injured, most likely knowing the spin of the thing there on, the highly athletic people would immediately start carrying the injured until they are diagnosed and there chances of survival analyzed. Also, if it's a life or death scenario, the drive to live of the nonathletic people would be enough from keeping them from giving up even for 1.8 miles, not to far even under those conditions for someone who's driven.
[Answer]
They're dead, unfortunately.
446 meters in diameter means the circumference of Jormungandr is 1400m. Anything beyond a quarter rotation is going to be pretty much guaranteed death, so you have to have solved the problem before you move 350m, and realistically the number should be lower than that, depending on how much traction you can get on the scales before you slide off. 5km/hr is 1.3m/s, so you have 270 seconds to solve the problem, if you're holding still. Obviously you can gain time by running on top of Jormungandr, but that's not going to help as much as we might like.
270 seconds is 4.5 minutes. You just crash landed your helicopter. That means everyone is going to be disoriented. Worse, you crash landed your helicopter into Jormungandr. I've had the privilege of going up in a helicopter for training once, and the pilot walked me through what he was thinking. While he was up there, he was constantly thinking "If the engine died now, where could I set this bird down. Oh, I can set her down in the park over there" Your pilot should have been trying to set you down in the best possible place, which would *not* be on top of Jormungandr. The best place would be behind it, in the wake of the destruction.
So by the fact that you landed in such a horribly bad place, that lets me know that not only did you crash, but it was a *bad* crash. It was the kind of crash that you don't just get up, push the guy with pneumothorax out of the way and leave him for dead, and run on top of the boiling wurm. It's the kind where the first minute or so you're still too dazed to realize what is happening. Then you need to get your wits about you, because somehow you're going to have to figure out that the only way out of this is to run across the boiling log of doom like some crazed lumberjack, relying on nothing but your rubber soled shoes to keep your feet from 3rd degree burns as you go on your leisurely 3km reverse-hurdle jog in amidst scalding steam (you don't have to jump up the scales, but you do have to jump down them).
And, of course, by the time you are out of your daze and ready to run, you're already rotated off of top-dead-center, meaning every step is going to be an uphill slog. But what's really going to kill you is how long it takes to come back to conscious rational thought after the crash.
[Answer]
They're all dead. Why?
1: How exactly are they getting to the ground? Are you proposing that they slide or what? Cause snakes don't have nice flat edges that meet the ground 'squarely,' I'd expect a drop of at least ~50 meters if not more. The drop.. of course, is onto urban terrain that has been mashed up by the passing of the behemoth, right? rubble etc..whether or not the bot has passed over that particular terrain or just passed it, it's displacement is absolutely immense. Not to mention that the land you're jumping down to has been under a 90 degree C object for the last 6 minutes with no ventilation. (the place you're jumping to isn't really any cooler than where you're jumping from)
2: Did they know it was that hot beforehand? Cause people use all sorts of body parts to stop themselves getting hurt in falls. If they jumped out of the helicopter most likely every one of them not only has suffered the usual impact stresses which break bones etc, but also touched the 'ground' with their hands/knees/shoulders and that's if they landed pretty perfectly...you'd expect some head contact..and touching 98 degree surfaces with your head itsn't advisable.
3: They have, presumably a 30 second run (for those uninjured) at least to the 'edge' of the snake. Depending upon what curve you're operating with, they probably can't see the 'edge' of the snake (you ever ran downhill?) so most of them will hesitate at least to run flat-out.
If we're giving them a safe & survivable curve (by cheating) that obviously means they have further to run. Running for a minute isn't a big deal, but anyone who can't..or stops for whatever reason.. is probably dead.
You can talk all you want about how it's possible to breathe for x time in 90+ degrees (with commensurate air turbulence from the massive hot surface of said bot and regular air), but actually convincing your lungs that they can breathe in such temperatures is a different matter altogether.
Before you go for such ideas as "but their feet are in shoes and their shoes haven't melted" remember that heat is commuted between one material and another, it makes no difference if the clothing survives if it is conducting enough heat to melt flesh.
>
> Given that Jormungandr's characteristics aren't going to change, and
> that the helicopter is going to crash-land on top of it somewhere, are
> there any variables - like weather - that if changed would mean that
> at least some of the survivors of the crash might escape? – Monty Wild
>
>
>
Does Marine One have a winch? If not you might consider using a port authority helicopter or something, to avail yourself of a nice long rope. Longest I see available is 250ft. So the scenario goes..everybody still alive and capable dangles off the leading edge of the beast (PotUS first ofc) anchored by the wreckage of the helicopter..as the helicopter reaches the leading edge the dudes have a ~60m clearance down to the roof of a building, last one dropping down gets flattened as the chopper slides off onto him, obviously this leaves the remainder of the party very limited time indeed to descend ~150m+ of steps...
So you'll probably want to revoke the rooftop helipad ban in-world and have your pilot be one of the survivors. no idea how long choppers take to cold start tho.
Or you could figure out how much time they'd need to get out of a building that is being toppled by snakey, doubt elevators would be operational so that'd be out.
Or....it could detect them once they're off and play nice..waiting till they get out of the way.. though that would kinda beg the question..why not just put people in front of it to stop it destroying stuff.
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[Question]
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## Conditions
* Critical to the plot, Earth needs to be **taken out of** the Sun's orbit around 2050 (*i.e., **not** destroyed; **nor** merely darkened via "indirect" solutions such as alien Dyson swarms surrounding the Sun, blacking out the sky as in The Matrix, etc*).
* Therefore, **either** the Sun has to be destroyed (including its mass), **or** the Earth needs to be accelerated by a further 12 km/s to achieve escape velocity from the solar system.
* This needs to happen with **a warning period (e.g. 2 - 10 years)** so that civilization has a change to get at least minimally ready, such as beginning underground bunker construction; the Earth's surface needs to remain at least somewhat habitable during this period.
* **The Earth itself has to be preserved** in a more or less intact way (*though Hollywood style disasters like earthquakes, tsunamis, etc. are perfectly fine and even welcome*).
* Source of disruption has to be **within ~75 light-year "cone" of Earth**, i.e. half of the time period from when we first started radio emissions (though can be handwaved if necessary).
## Potential Solutions
**Destroying the Sun's mass**
* Massive increase in coronal mass ejections (Problem: Masses involved are far too big to be realistic, and if this happens, Earth will be fried).
* Sun going supernova prematurely. (*Problem: Earth will get fried*).
* One of Peter Hamilton's ideas: Nanomachines that exponentially multiply and transmute Sun's mass into elements that don't support fusion. (*Problem: Sun's mass remains, so Earth doesn't deorbit*).
* Micro-black hole tossed into center of Sun. (*Problem: Will dissipate quickly due to Hawking radiation; the radiation pressure around its accretion disk will be too hot for any of the Sun's mass to actually fall into it; finally, the mass itself will remain, so Earth will remain in orbit anyway*).
Therefore, I see no physically plausible way of doing it this way while fulfilling most of the conditions.
**Knocking the Earth itself out of orbit ( Passing Rogue Planet or Rogue Star)**
This seems a slightly easier challenge, since the Earth is so much smaller than the Sun.
Advantages:
* We know this happens frequently in the early stages of solar system formation; it's been estimated that half the planets in our galaxy are rogue/"Steppenwolf" planets.
* Passing rogue planet knocking Earth off orbit is what happens in the short story "A Pail of Air" by Fritz Leiber.
* Is physically plausible to laymen, so the fine details can be handwaved, if necesssary.
Issues:
* The Rogue Object ("RO"), if it is traveling fast (which it probably has to be if it was launched within the past 150 years), will also have to be very heavy to exert sufficient gravitational force on Earth to fling it out of orbit as it passes by. I assume that all such objects, even rogue neutron stars and rogue black holes, would have already been detected within at least a 50 light year vicinity of Earth?
* If the RO is a rogue planet, then it will have to pass by the Earth more slowly, and closer to it, which risks running into the Earth's Roche limit and breaking it apart entirely.
* What would be the best way to triangulate between these considerations, i.e. less mass and higher speed for the RO; and non-violation of Earth's Roche limit?
* **What would be the mathematical formula** relating the mass and velocity of the rogue object, the mass of the Earth, the closest distance between them, and the resulting acceleration of the Earth?
**Knocking the Earth itself out of orbit (exotic possibilites)**
Focused gravitational beam, perhaps channeled through a wormhole "tethered" to Earth and a massive body somewhere else in the galaxy. The Earth's orbit slowly, but at an accelerating pace, becomes elliptic, and eventually flies off into space.
*Problem: Requires some major handwaving. Gravity is far weaker than the other forces, and most likely can't really be focused as we don't know of any materials that can reflect them*
Perhaps alien civilizations have mastered energy-to-mass conversion to such an extent that they can fire off a beam of focused energy (at light speed), then have it convert to mass object at a time of their choosing, such as a chunk of neutronium.
*Problem: Fantastical.*
There must be many other possibilities I haven't considered, though I suspect many of them will be more and more purely fantastical. But I'll be happy to hear more suggestions.
Thanks in advance for your input!
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The "easiest" solution would be a rogue object, but it's still not easy to make it work.
A "dark star" would need to be large enough that it could not avoid radiating massively in the infrared. At 0.05 solar masses you still have a magenta dwarf. Micro-black holes and neutronium stars also radiate massively through their accretion disks.
To minimize damage (as much as possible), you would need such an object to approach Earth along the ecliptic. Possibly, by composing carefully the Solar System's own motion, we can make it so this object is not itself orbiting the Sun. This would mean having the encounter in early Spring.
Then the Earth gets accelerated towards the object (its orbital radius increases) while the object approaches, it misses the object itself (this is the awkward moment in which the planet is devastated by tides in both oceans and its liquid mantle, causing tsunamis and earthquakes), and finally gets launched towards outer space at a speed comparable to the rogue object's final approach speed.
The more massive the object, the farther out can the Earth be at periastron, which reduces tidal damage but increases the object's chances of being detected. Also, if its radius of significant influence increases too much, it will have disruptive effects on the Solar System while it's still far enough not to be able to deorbit Earth.
On the other hand, a black hole with no significant accretion disk might not be detected until it's close enough. It would reacquire an accretion disk passing through the Sun's Oort cloud, though.
A far more fantastic possibility is that of a **very** focused stellar jet coming by and destroying the Sun. It would need to be a jet almost perpendicular to the ecliptic. The Sun would be accelerated (in reality, not very much, I suspect) and, if the acceleration was enough, the Earth would find itself left behind.
The same thing could perhaps be accomplished with a black hole of several solar masses and sufficient speed to capture the Sun around itself and whip it away, but the resulting irradiation would probably be enough to sterilize the Earth (assuming there was no colossal explosion soon after the impact).
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Nope, sorry.
Without heavy handvavium this is not going to happen. If you will remove Earth tto from the [Goldilocks zone](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone), temperature will drop. First water will freeze. Then, plants and animals will die. Then, atmosphere will condense and partially freeze. End of the life as we know it. Without atmosphere, each and every rock close to Earth would hit surface directly, with nothing to slow it down. Face of Earth would change. UV radiation will split water into hydrogen and oxygen. Hydrogen will escape. You need to be fast to return Earth to it's original position. No matter how fast, you will not make it to any other star.
And by the way, in the process we are going to either crash with the Moon, with instant disastrous effect, or lose the Moon and it's stabilizing function. [Maybe Moon isn't really needed](http://io9.gizmodo.com/5829438/earth-doesnt-need-the-moon), but what if it is?
Rogue object?
As long as you are not close enough to cross each other's [Roche limit](https://en.wikipedia.org/wiki/Roche_limit), this might work. But remember that you need something heavy. Really heavy. If you don't want to destroy our solar system altogether, let me suggest a couple bodies that would throw Earth further and further away. Perpendicular to the ecliptic, to minimize strength of interactions with other planets. Of course, this would ultimately destroy Earth, but maybe, just maybe, not instantaneously, not in a way directly related to this knocking out mechanism.
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Assuming it's a case of *Calculate a solution, or everyone on Earth will die*, we could reasonably expect the world's astrophysicists, aerospace engineers, etc. to commandeer virtually all the computing resources of Google, Facebook, Apple, etc.
Expanding on the possibilities of [the Butterfly Effect](https://en.wikipedia.org/wiki/Butterfly_effect), it seems to me we (*just!* :) need to work out a careful series of "nudges" (to asteroids and other celestial objects whose trajectories we could feasibly adjust) that would progressively destabilise larger bodies (Jupiter, Saturn, etc.) in such a way that the Earth gets gravitationally accelerated right out of the Solar System.
Given that many scientists think [*Jupiter kicked a **giant planet** out of the solar system 4 billion years ago*](https://astronomynow.com/2015/11/03/jupiter-kicked-a-giant-planet-out-of-the-solarsystem-4-billion-years-ago/) with no intelligent species carefully setting up the situation, I don't see why we couldn't do something similar for our little planet.
We might have a problem keeping warm in the depths of interstellar space, but I'm gonna assume that as soon as we have that first butterfly wing flap worked out, we'll devote all our computing power to developing AI's to sort out the heating problem before we get too far away from the sun.
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You could have a close encounter with something like a rogue gas giant, that flings earth out of its current orbit (with massive earthquakes and insane weather effects). If that orbit then happened (through a horrifically unlikely but theoretically possible co-incidence) put it onto a [gravitational assist](https://en.wikipedia.org/wiki/Gravity_assist) with a number of other gas giants similar to how voyager 1 and 2 did it then with a bit of hand waving you could get solar system escape velocity without needing to add all that energy in the initial interaction.
The whole scenario is still pretty far fetched but you might be able to get something to work with that way.
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Your list of approaches is not complete.
I don't think there's any way to boost the Earth by 12 km/sec without causing a lot of problems. It could be accomplished by an appropriately-aimed mass sent hurling through the solar system setting up a gravity assist maneuver. However, I see no way to avoid substantial tidal influence from the intruder. (It will need to be a degenerate body of some kind.)
You considered destroying the sun and quite correctly ruled it out. What about removing it, though? Since you talk about radio signals you are obviously considering aliens being behind this.
There are some malevolent ETs out there who have a legal problem. The law of their land does not permit them to harm developing races but they don't want the competition. Thus the easy answer of throwing an asteroid or the like isn't an option. They want us gone, though.
Thus they deploy some gravity manipulators around the sun that produce directional gravity. Material is drawn in from the sun, undergoes fusion (some of this power is tapped to run them) and ejects it out the back. Presto, rocket engine. Boost the sun by 12 km/sec and Earth is lost to the interstellar void where we die in the cold--but the aliens didn't harm a single human.
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Possibly astronomers discover the mouth of a stable wormhole in the direction the solar system is headed toward. They calculate that most objects in the solar system will pass by the mouth of the wormhole.
But Earth, and maybe also the moon, will pass through the wormhole mouth and leave the solar system.
If astronomers can see through the wormhole mouth they can have some idea of what is in the area of space Earth is headed for, otherwise they will have no idea.
No doubt many will speculate that the wormhole is artificial, created by alien super science to take Earth out of the solar system.
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I'm poking through information and searches on calculating ranges for artillery weapons, and I'm finding a lot of simple ballistic calculators, which don't fit what I want, or calculators for small arms, which may be accurate enough but don't allow for the correct values and/or use values for which I don't have the answer to.
**I want to be able to calculate the range of a warship's guns.** Specifically, I need this information to **include air drag based on air density, and range reduction based on gravity**. The latter is fairly simple, the former... probably not.
Ideally, I'd be able to punch in the [information from the guns of an Iowa-Class battleship](https://en.wikipedia.org/wiki/16%22/50_caliber_Mark_7_gun), and see how far it'd be able to shoot on different worlds. I'm not asking for an online calculator, though they'd be nice, **"just" the equation and an explanation for that equation**. I'm not afraid to do things by hand if I have to, but I am not a mathematician. I can generally understand formulas and how they work, but they need to be disassembled and explained. Walls of formulas become quite unreadable.
**Edit**: In my further studies, the math is beyond my personal knowledge to decipher a formula dump. [This Page](https://en.wikipedia.org/wiki/Trajectory_of_a_projectile), for example, seems to have all of the information required. I just can't make anything useful out of minimal explanations and walls and walls of formulas. A more expansive explanation of the formulas involved would be greatly appreciated.
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A useful overview of the problem: <http://nigelef.tripod.com/fc_ballistics.htm>
This guy gives you the individual formulas. I wouldn't count on it to hit a target, but it's probably good enough for a story. Technology is mostly round shot to WWII. <https://grantvillegazette.com/wp/article/publish-581/>
The computer used on the Iowa was a mechanical analog one. They looked at digitizing it, and figured that it wouldn't be any more accurate. Article here:
<https://arstechnica.com/information-technology/2014/03/gears-of-war-when-mechanical-analog-computers-ruled-the-waves/>
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If, during the flight there is drag $$F = - β v$$ (F and v are vectors), with $$β > 0$$ Newton's law becomes:
$$m g - β v = m a $$
Choosing $x$ horizontal and oriented toward the flight direction, and $y$ vertical pointing upright, by projecting on the axis we get:
$$a\_x = - (β/m) v\_x$$
$$a\_y = - g - (β/m) v\_y$$
Since
$$a\_x = dv\_x/dt$$
$$a\_y = dv\_y/dt$$
you get two differential equations in $v\_x(t)$ and $v\_y(t)$ with boundary conditions
$$v\_x(0) = V\_o cosα$$
$$v\_y(0) = V\_o sinα$$
Once known $v\_x(t)$ and $v\_y(t)$ and integrating you get
$$x(t) = \int\_0^t v\_x(t)\ dt$$
$$y(t) = \int\_0^t v\_y(t)\ dt$$
considering the launch to be happened at the coordinates (0,0).
Setting $y = 0$ you get the time of flight and putting that time in $x(t)$ you get the distance.
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Here you go.
<https://phet.colorado.edu/sims/projectile-motion/projectile-motion_en.html>
Plug in your variables and Bob's your uncle.
The one variable you cannot tweak with this simulator is gravity. But you can tweak your projectile mass. Fortunately for you, the calculation determining the force exerted by gravity between 2 objects combines the mass of the attractor (your planet; m1) and the attracted (your projectile; m2).
$$F=G{\frac {m\_{1}m\_{2}}{r^{2}}}\ $$
You can set the mass of your projectile. So if you want to simulate a situation with half the gravity of Earth (and so half the mass of earth; 0.5 \* m1) you can instead use full Earth gravity (m1) and make your projectile half the mass (0.5 \* m2).
To be clear: reduce your projectile mass by the same percentage reduction you want below Earth gravity and the simulation will work.
The simulator allows you to enter drag coefficient and altitude.
<https://en.wikipedia.org/wiki/Drag_equation>
Drag coefficient has to do with the shape and aerodynamics of your projectile. Maybe leave that at 1.
Altitude is what you want to alter air density: air density varies according to altitude.
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I'm looking to shift from a modern world to a fantasy world. The modern world has some magical elements to it, such as remnants of the religion that reigns in the fantasy world, but is mostly magic-free, so I kind of shy away from using something like portals. What are some other ways that my character can get from World A to World B, that aren't overtly magical?
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# Spaceship
If you need to get from one world to another without magic, a spaceship is the way to do it. FTL or hyper-sleep, take your pick.
# Wormhole
It's a portal made out of science!
# Dream/Coma/Blow-To-The-Head/Virtual-Reality/Insanity
In all these cases the fantasy world is not real.
It can be done fantastically as in *The Wizard Of Oz*, as a mystery as in *The Matrix*, as delusional escapism in *Pan's Labyrinth* and *Heavenly Creatures*, or tragically as in *Jacob's Ladder* where...
>
> ...the protagonist is slowly dying in reality.
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# Just Do It
Don't explain why the world is fantastic, it just is. This doesn't have to be overtly fantastic. For example, a musical is a parallel world where people spontaneously break out in song and choreographed dance with strangers. Or a comedy where slapstick and mind-bogglingly dumb decisions are simply accepted as normal. For example, *Who Framed Roger Rabbit* asks the audience to accept a gritty 1930s noir setting that also has real cartoon characters, and it works. If the characters accept it as reality without question, and it's well fleshed out, the reader will as well.
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You could have her not go. Have the magic world revealed to her as existing on, beside, in between the one she knows. My favorite example of this is from a fairy tale where a midwife is summoned by a dark man. After a trip through the night with his hands over her eyes they come to a castle.
>
> /At last we came to a bedroom, with a beautiful lady in bed, with a fine bouncing boy beside her. The lady clapped her hands, and in came the Dark Man and kissed her and the baby, and praised me, and gave me a bottle of green ointment to rub the child all over.
>
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> 'Well, the child I rubbed, sure enough; but my right eye began to smart, and I put up my finger and gave it a rub, and then stared, for never in all my life was I so frightened. The beautiful room was a big, rough cave, with water oozing over the edges of the stones and through the clay; and the lady, and the lord, and the child weazened, poverty-bitten creatures—nothing but skin and bone—and the rich dresses were old rags./
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From The Lilac Fairy Book, Andrew Lang.
<http://www.sacred-texts.com/neu/lfb/li/lifb07.htm>
The fairies don't like that she can see them as they are, and many versions of this tale end with her having the anointed eye plucked from her head. The idea of the magic world and the mundane overlapping is a common one, from fairy tales like this to Mary Poppins to Harry Potter. It lets you sidestep some worldbuilding by simply augmenting the real world.
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On the physics, it is impossible. The laws of our Universe are simply totally incompatible with any fantasy-like world. Practically any "speciality", magic-like thing what in the RPG worlds exist, is totally impossible on the current laws of the physics.
Our world is a perfectly controlled one, there is no place for doing anything by pure imagination, only by clearly applied rules.
But we can do some similar:
### New realities are imminent: how VR reframes big questions in philosophy
>
> The virtual reality (VR) industry is currently in its infancy, but in
> just a few decades it’s possible that virtual environments will be
> nearly indistinguishable from reality. Along with transforming
> everyday life, a VR revolution could fundamentally change how we
> understand and define what is real. In this installment of Aeon In
> Sight, the renowned Australian philosopher and cognitive scientist
> David Chalmers considers how VR is reframing and shedding new light on
> some of philosophy’s most enduring questions about cognition,
> epistemology and the nature of reality.
>
>
>
([source](https://aeon.co/videos/new-realities-are-imminent-how-vr-reframes-big-questions-in-philosophy))
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...and, a possible horror-line to the story: consider a Humanity, who lives in a continuous dream, and machines serve all their bodily needs. Only a small group of "service workers" are watching and controlling these automatas. Yes, it is a little bit similar to the Matrix, although it is a much older idea and the "internal reality" is a fantasy-like one.
Considering the intensity of the [MMORPG](https://en.wikipedia.org/wiki/Massively_multiplayer_online_role-playing_game)-addiction in our children, such a world may be not even a too far future.
In this world, in the reality, there is actually nothing. Old cities, full with people in large, cubical buildings, in a continous dream. And out of them, nothing.
These "service people" will obviously feel an increasing urge to join the others in the virtual reality. The external world is boring for them.
And, as years... decades... maybe centuries pass, once the time is coming as also they lie beside the others, and forgot the external world.
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I'll try give some more interesting ones:
## Meditation
Kind of like Dr. Strange's astral projections. If you focus on your breath, get your frame of mind just right, you can open your eyes and suddenly you're in the other realm.
## Magic Eye
Did you ever play with that book when you were a kid, that shows a random pattern, and you have to unfocus your eyes in a certain way to see a 3D effect? You could do something like that, which shows you the other realm.
## Giant Wall
Instead of having them in different times, they could exist simultaneously but separated by a giant game of thrones style wall (but one that nobody has ever thought to climb/cross). Your protagonist somehow finds a hidden tunnel. No magic here, just a plain ol' door.
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To transport someone from one world (which I'm assuming means "planet" since you asked for non-magical means) to another, there are basically two options: spaceships and portals/teleportation.
So I guess it depends on the technology level of your modern world. If it is high enough that spaceships are common enough for them to be a viable means of transport (as in <hopefully> our world in 10-20 years), then that is likely the best method. If spaceships don't exist, are only uncrewed, are used solely by government entities, etc. (similar to our present-day world), you'll probably have to go with portals or teleportation of some sort.
There are two types of portals: scientific ones (wormholes) and magical ones. Unfortunately, wormholes require an even higher technology level than spaceships, and are therefore probably infeasible. Magical portals have practically zero constraints, because they're magic. The same goes for teleportation: scientifically sound teleportation is (as far as we know) impossible, but you can do almost whatever you want with magical teleportation.
There are other options that could work non-magically, depending on your setting. For example, if your worlds are orbiting each other very closely (i.e. closer than Earth's geostationary orbit) and are tidally locked to each other, a space elevator could suffice, and would likely be possible with present-day technology.
That's about it, unfortunately. There are plenty of overtly magical options, but not much that could work without magic.
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# Use A Boat
Your planet has two big continents, separated by a big ocean. If you need a faster transition, there could be a land bridge. They could both have diffrent climates that allow for different species. The tech/fantasy continent could be the only one capable of making boats if you want. This also allows for no one knowing of each other's existence or just one side knowing. You could also could have someone attempt to sail around the world only to accidentally find the other continent. There are a lot of diffrent things you could do in this situation.
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I think it would be especially cool if the device were mostly technological (with a little magic) on the modern world’s side, and essentally magical with some little technology (like precision instruments) on the fantasy side.
It each end of the transit mechanism works by the rules of its respective universe.
The whole thing is like *impedance matching*, in a sense. The two independent efforts to reach another universe were *mutually* successful, and connected to each other.
So maybe scientists on the modern end were trying to teleport to Titan, boosting their experimants with magic spells. In the fantasy realm the mages had a similar goal that makes sense to them, and they added some precision machinery into tneir magic device.
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### Reincarnation
Person dies and is reincarnated in another world. You could put in something like karma, where the body they go into is based on their past deeds.
### Body Swapping
Similar to in *Kimi no Na wa*, the person goes to sleep and swaps body with someone else in another world after they wake up. They don't even have to be in the same timeline. Someone could swap bodies with someone who existed 1000 years ago.
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In my second book, based on *Space Gladiators*, portal technology is a staple in their universe. I need a logical explanation about how portals work. Is it based on quantum physics, dark matter, wormholes, or what? What would be the most logical way to describe the mechanics of a portal?
Assume that they have highly advanced technology beyond the level of just portals. They can create whatever is thought to be logical.
I realize that we technically already have teleportation, but it isn't actually 'instantaneous' *per se*. And it only transports minute amounts of matter currently in 2017. I don't want that, I want "faster than a Planck interval" teleportation. How does the portal work? And more importantly, is it realistic? Is INSTANT transportation from place to place truly possible given our physical limitations?
Any clarification that is needed will be provided when asked.
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According to Albert Einsteins theories, it is not possible, to travel faster than light. Even if you take a long pole at one end and push something with the other end, the impulse of your pushing needs a moment to arrive at the other end of the pole. So faster than light (FTL) traveling is not possible in our known 3 dimensions.
What you can do, is to add a dimension, to go around the normal 3 dimensions and only seemingly travel faster than light.
This can either be accomplished by some (limited) time travel (using time as a fourth dimension in which some control is possible) or by adding a completely new 4th dimension, in which you can bend the known 3 dimensions, "folding" space.
A common way to explain this, is to imagine a piece of paper as 2-dimensional plane and fold it in the 3rd dimension, so that two places of the paper touch, allowing something on the paper to jump to another place on the paper without traveling the (paper-)distance between those 2 places.
If you only need portals on specific locations, you can argue, that the visible universe already is bend in one (or more) additional dimensions, allowing portals at these specific locations. Portal builders would have to measure where portals can be build and where not.
If you want dynamic portals which can be build at will at any location, this would require either a lot of energy to "bend" space or a nearly endless amount of additional dimensions, so that the portal technology just would have to pick the right set of dimensions in which the desired locations happen to be close to each other.
For some more science around this problems, you can look up the [Alcubierre Drive](https://en.wikipedia.org/wiki/Alcubierre_drive) (basically the warp drive known from the Star Trek universe)
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Quantum physics does not enable FTL communication or transportation. So don’t use that. Dark matter? What does that have to do with it?
What you describe pretty much matches what we expect of **wormholes**. Changing the topology of spacetime will give you portals as you describe.
As for how the tech works: we need more about your story. Do the people dial in the coordinates they want and jump there? Or are there permanent doors set up? Are they created on the fly or via an expensive process?
I [recall a story](https://scifi.stackexchange.com/questions/153924/story-where-portals-grew-on-trees) where portals — as pairs of linked windows — was naturally evolved and used by native flora and fauna of the planet! It was a ubiquitous natural resource, and the story explained the resulting society that had access to that, from the point of view of outsiders who were stranded there. There was no explaination as to how they could function, physically.
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Yes it's entirely possible, it's called an Einstein-Rosen Bridge, or a wormhole, such a construct links two points while skipping the space in between, that's the theory anyway. In theory you can make such a bridge artificially and hold on to one or both ends of it to make it permanent.
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[In one of my more recent questions,](https://worldbuilding.stackexchange.com/questions/65480/little-green-earth-men) one Xandar The Zenon commented that a mutation that creates the gene for red or orange pigmentation on the human skin is more likely than green, blue or purple.
But wait. You might think, don't we already have red-skinned humans? Actually, the Native Americans aren't purely red, just diluted into a dominant shade of brown.
This question is for a mutation regarding REAL red:
* American Rose
* Coquelicot
* Crimson
* Scarlet
To name a few shades.
But looking into the origin of ethnic diversity is not straightforward. The Mongoloid body plan is the result of an individual mutation from 35,000 years ago. The Caucasians, by contrast, started to become white as sheets 7,000 years ago as the result of agriculture cultivating crop foods low in vitamin D. Which side would make the red skin gene a possibility?
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Humans already make [pheomelanin](https://en.wikipedia.org/wiki/Melanin#Pheomelanin), a red form of melanin; it's the pigment which makes the lips and areolas pink/red/brown. So you just need a mutation which modifies the distribution of pheomelanin and the ratio between pheomelanin and eumelanin. The result won't be red as a red rose, but red enough. And anyway, some of the hues on [Von Luschan's chromatic scale](https://en.wikipedia.org/wiki/Von_Luschan%27s_chromatic_scale) look pink or dark reddish brown to me.
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We've established that you can't simply [scale up animals](https://worldbuilding.stackexchange.com/questions/316/can-you-simply-scale-up-animals) because as the creature gets bigger the square-cube law (if you double the size of your animal the weight increases eight times). This quickly becomes unsustainable and limits the size your creature can be...
However, metal (and other high tech materials) is significantly stronger than organic tissue.
Is there a similar upper limit for artifically constructed vehicles (for the sake of clarity I'm talking about walking robots or Mechas rather than ships like tankers).
Please assume a modern or near future level of materials technology and gravity at earth-normal.
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# Strength does not matter
You say...
>
> However, metal (and other high tech materials) is significantly stronger than organic tissue.
>
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Well that does not matter. Once we reach the max size about what is tenable for a machine, the square-cube law is just as valid. And even if metals are stronger than some/most organic materials (not all of them, nota bene) they are also more dense and — as such — heavier. When it comes to **strength per unit of weight**, metals rarely offers a significant advantage over organic materials. And when we throw **price** into the equation as well, then we quickly find that materials that has a good strength-to-weight ratio rarely comes cheap.
Also the real showstopper is not strength, but bulky energy storage and locomotion. Why are humanoid mechs — even in just the Puny Human size-category — coming into existence only now and not before? Because we have had no way of creating locomotive elements and energy storage small enough to fit these things. Such elements were all too heavy and too large, and they still are. A human can keep going for a lot longer than a humanoid mech, and our muscles are a lot leaner and compact than ditto for mechs.
We are always are at the limit of how big we can make machines, even out of metal. And looking at where we are today, we still have a long way to go before we make mechs that are as fast as cheetas; that are as tall as giraffes; that fly as good as birds(\*); that have the strength, versitility and **size** of elephants. So organic materials are — still — well in the lead over human metal mechs.
## However...
...[technology marches on](http://tvtropes.org/pmwiki/pmwiki.php/Main/TechnologyMarchesOn). And it does so at a pace that always leaves the human mind coming running after it, desperately trying to keep up, with breath in throat and flabbergasted at what technology has achieved.
What is the upper size limit for a mech? No-one knows. No-one can know. I am sorry but your question has no answer because it would require the forseeing of technology and concepts that do not exist yet. If we could say "Here is where the upper limit for future mechs will be", then we would be magic fortune tellers.
(\*) Actually we are becoming quite good at flying. Drones have made some amazing progress the last few years. But there we use plastics and composites, not metals chiefly
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## Is it more important that this mecha move or just be?
The largest static structures that humans build are buildings, skyscrapers specifically. These structures never need to move so the structure can be optimized to resist wind, earthquake and gravity loads. A giant mecha has to be built to deal with gravity *and* all the dynamic loading from moving around as well as the mission requirements. *That's a really hard problem.*
On the continuum between absolutely huge and absolutely tiny, there is an inverse relationship with power required to move the object. For example, the largest machine in the world, the [Bagger 293](http://sometimes-interesting.com/2011/07/22/biggest-vehicle-in-the-world-bagger-293/) move at a stately pace of 1km/hour (I couldn't find any information on the power requirements). The somewhat smaller [Crawler-Transporter](https://en.wikipedia.org/wiki/Crawler-transporter) used at Cape Canaveral moves at 1.6Km/hr and requires ~6KW to operate, very slowly.
Large, very high speed machines such as the Space Shuttle or Saturn V rocket are very fast but devote practically *all* of their weight to propulsion and fuel.
On the other end of the scale, tiny batteries can be used to move very light loads very quickly.
## Power Density is the Main Problem
In my opinion, the reason we don't have soldiers in powered armor right now is the lack of sufficiently strong/long lasting power supplies. Building a self-contained power armor isn't too hard since we already have space suits, pressure suits and a host of other protective gear. The energy density of batteries just isn't high enough. Fusion doesn't work. Who would want a fission power supply strapped to theirback? Internal Combustion engines are too bulky/loud.
## Conclusion
As the author, you'll have to choose your priorities: physical size, power output/speed, mission payload size. You'll have to pick some ratio of those.
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You can only give an estimate of maximum size for a given technology. It could be that in the future part of the weight could be conveyed by electromagnetic field, similar to levitation. If this is possible it is not even the strength of material that restricts the size.
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Bipedisum and the square cube law get you again.
Yes there are compounds that have better strength to weight ratios than bone <https://en.wikipedia.org/wiki/Specific_strength>
Yes robots can have higher power to weight ratios
[a Honda Accord for several hours outputs 124 W/kg
and Olympic cyclist outputs 20 W/kg as a 5-second maximum](https://en.wikipedia.org/wiki/Power-to-weight_ratio)
But the square cube law will still get you. A leg bone whether made of steel or bone has strength proportional to lxw and weight proportional to lxwxh so if you double the size of the bone you square the strength and cube the force guess which one wins out.
Being a biped is very hard. It means you have to have enough structural strength in either leg to hold your entire body, and enough force in either leg to move you whole body. The costs a great deal of added weight. Where a wheel mounted robot can get away with only having enough force to roll you weight not lift it.
It is also very easy to fall over as a biped as the DARPA completion robots discovered.
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In Medieval England how would a stronghold town be laid out, and what would their defenses have been?
I'm putting a city together and one important point is that it is secure from attacks. Attacks from both people and creatures.
I first contemplated a big wall surrounding the town or city with guarded entry points and watch towers strategically placed, but I'm not sure how feasible that would be on that scale.
Then I considered a type of armed police force or army constantly making their rounds, but that could just be a drop in the ocean of what is actually needed.
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Many English cities had walls, and the best-preserved of them today is probably the one around the city of York.
<http://www.visityork.org/York-City-of-York-Walls/details/?dms=3&venue=3610893&AskRedirect=true>
It has a length of 3.4 km, 5 main gateways one smaller postern gate, and 45 watch towers. At its highest point it is 30 ft or around 9 metres high.
You did not actually need a large force to constantly patrol the walls, just a few strategically placed people on watch who could call upon reinforcements should they be needed, who could be the city militia. Hadrian's Wall which is further north uses this system on a larger scale there are several forts like Housesteads, Vindolanda and many smaller watch points that were garrisoned by only a few men.
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## Law Enforcement in Medieval Towns
According to [this website](http://www222.pair.com/sjohn/blueroom/demog.htm) about Medieval Demographics:
>
> A well-kept medieval city will have 1 law officer (guardsman, watchman, etc.) for every 150 citizens. Slack cities will have half this number. A few rare cities will have more.
>
>
>
Taken together with the wall info from Sarriesfan, this could give you a rough estimate of defenses.
## Castle
The book ["Castle" by David Macaulay](http://rads.stackoverflow.com/amzn/click/0395329205) could be a valuable resource to your project. In it, Macaulay describes how a castle's town would be attached to the castle:
>
> The town wall was to be 20 feet high, 5.5 feet thick, and strengthened at intervals of 150 feet by projecting U-shaped towers.
>
>
>
A battlement walkway was planned for the entire top of the wall.
You can buy the book [here on Amazon](http://rads.stackoverflow.com/amzn/click/0395329205), and on the same page, you can click on the cover's "Look Inside" icon to read through some of the text, see an example of castle and attached town layout, as well as construction methods and materials.
[](https://i.stack.imgur.com/use46.jpg)
Macaulay has a [series of very informative books](https://www.amazon.com/s/ref=dp_byline_sr_book_1?ie=UTF8&text=David%20Macaulay&search-alias=books&field-author=David%20Macaulay&sort=relevancerank) on all different types of building projects throughout history and from around the world, including: Roman town, Pyramid, Underground Subways, Mosque, Mill, Cathedral, etc.
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As is said above York is a very good example, there would normally be lots of walls, it seems that in those times the best form of defence was defence not offense as it is now :) Lots of fortifications, narrow, winding streets (locals will know the way but invading forces wouldn't), castles, moats, bridges etc. Several walls with gates going inwards, so the more valuable stuff is behind three walls instead of one etc, whereas citizens would be behind one or none. Local militias were very common, and there could be specialised and trained guards patrolling constantly in small squads of two to five (and yes I am thinking of Assassin's Creed right now), Assassin's Creed cities would be a very good example, patrolling guards, watch towers and walls plus spies infiltrating the common folk etc. There are lots of ways your city/stronghold could be fortified and guarded!
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This an actual fortified medieval castle town
[](https://i.stack.imgur.com/YlmeA.jpg)
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Let's imagine an Earth clone devoid of naturally occurring fissile materials—and, for comprehensiveness' sake, also devoid of fertile materials like thorium and americium that could be used to produce fissile isotopes artificially.
I suppose the first part of the question is: Could we have gotten to the 1930s or so without significant deviations? I.e., is there any under-appreciated but crucial role that these elements played in the formation of the earth, the biosphere, human civilization, etc.?
And second: what then? Obviously the end of WWII and basically all of world history thereafter would be radically altered. But geopolitics aside, what impact would this have on science and technology? Could it be as simple as, nuclear weapons and nuclear power would be impossible, while the rest of human technological progress would proceed unimpeded? Computing, telecommunications, spaceflight (minus the plutonium-based RTGs)? Even particle physics? How might this "gap" function in the context of our broader knowledge of radioactivity, stellar fusion, etc.? Would scientists have a well-developed theoretical understanding of what fissile elements are and what powerful/destructive properties they have?
Open-ended bonus question just for fun: assuming the above is roughly possible, what might happen if the plucky, naïve denizens of Earth-2 one day landed on Mars-2 and found a big ol' mess of uranium and plutonium there?
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Well for one thing we would not have any tectonic activity any more, or if it does it would be significantly weaker, as the core and mantle would have long since cooled down and solidified. which also means a much cooler atmosphere. You would not have a warm planet with liquid water not on the surface anyway. You would have an ice ball or at very least Io's big brother. Life would likely have never made it out of the oceans much less to people. A large portion of the earth's heat stems from radioactive decay material.
[en.wikipedia.org/wiki/Earth's\_internal\_heat\_budget](http://en.wikipedia.org/wiki/Earth's_internal_heat_budget)- thank Rob for the source.
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# History diverged in 1896
The [history of Uranium](https://en.wikipedia.org/wiki/Uranium#History) can answer this question. The element was identified in 1789; and isolated in metallic form in 1846. Neither of these is very significant.
In 1896, however, [Henri Bequerel](https://en.wikipedia.org/wiki/Henri_Becquerel) discovered [radioactive decay](https://en.wikipedia.org/wiki/Radioactive_decay#History_of_discovery) while experimenting with phosphorescence of uranium salts. If uranium had not been available, it is unlikely he would have made this discovery at this time and history would have significantly diverged.
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Here is another twist. Before radioactive decay was understood to generate heat there was a solid belief that Earth couldn't be older than 80,0000 - 160,000 years old because it would have cooled to the point that it was uninhabitable. Once radioactive decay was discovered it became understood that earth could be millions even billions of years old which increased support for Darwin theory of evolution which at the time required an old earth to make sense. Many of our scientific theories today are the direct result of the discovery of radioactive decay. Without that discovery our fundamental understanding of the universe would be stunted.
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**Picture a setting similar to that of many fantasy works:** a relatively low level of technology among the general population, lots of manual labor, agriculture or hunter/gatherer society, and that most people are generally content with the way of life. *Note that this particular world does not have magic.*
Now consider that in the world just described, **there's *also* space travel by means of technology** (in other words, not too dissimilar from what we are doing in our real world as of today) on some non-negligible scale.
Also assume that the general population is fully aware that such space travel is going on, and are generally either indifferent to it, or actively support it.
Now consider that **space travel is, on the whole, [freakishly expensive](https://worldbuilding.stackexchange.com/q/32412/29).**
**How can I explain, *in-universe,* that the general population doesn't revolt against the space program of their world?**
If desired, you may assume that the whole planet, as well as any other planets that may possibly harbor life and are reachable by their spacecraft, is largely similar in terms of lifestyle and technological capability. You may also freely assume the opposite, should you prefer to do so. *Please specify early in your answer which approach you take.*
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This is not too dissimilar to our world. The nations with the typical fantasy setting levels of technology and the rest are the equivalent of the Third World. Their First World nations are their equivalents of the USA and the USSR which do have major space programs.
This is something like the world as seen from Africa or Asia in the 1960's when the Space Race was at its height. The people on those continents were well aware of space activity. They couldn't do anything about it because it wasn't in their jurisdictions and lay outside the power of their citizens to influence it.
A space travel being freakishly expensive, well it is, isn't it? That's why is the province of the Big Boys of the First World.
What is the in-universe explanation for there not being a revolt against space travel. There could be a Cold War between Gondor and Mordor. The Space Race is one version of their sabre rattling. Also, as explained above the typical fantasy setting nations against the ones launching spacecraft.
Since your world has life in other planets, this is significant difference from the Cold War space race. It is also likely to be something that will rally the global population of this world to support space travel. This also may depend on whether that extraplanetary life is a threat to your world.
From a historical point of view, this is a world where there has been greater divergence between the so-called developed and underdeveloped parts of the world. Their equivalent of the Third World has lagged a long way behind, while their First World has gone much further down the high technology road and into space. This isn't too extraordinary a scenario.
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# Make it a ruse - an offering to the gods.
I'm reminded, strangely, of the [Minotaur](http://www.theoi.com/Ther/Minotauros.html).
Every seven or nine years (accounts differ), seven boys and seven girls were sent from Athens to Crete in tribute to King Minos, and were promptly devoured by the beast, until Theseus defeated it. From the perspective of the Athenians, fourteen people went aboard a ship went somewhere far away, and were never heard from again (well, it was known that they died, but apparently nobody normally confirmed this).
Apply this to your world.
Every so often, people are chosen as sacrifices to the gods, who happen to live in a space station in low orbit around the planet (the people don't know it's a space station; they just see the rockets leave). There are other people to go with them as security, so to speak, but they always come back alive and well. The space gods are happy, and everyone lives.
However, the rockets are in fact carrying whatever the elite need them to carry, and the people who supposedly go on the rocket in tribute never fly to space, but are instead brought somewhere else, or possibly killed, depending on how dark you want this to be. It's all a ruse. A conspiracy. But as whoever's controlling this can show, if the people fail to make a payment - the rocket explodes, nobody is picked as tribute, etc. - bad things happen. Really bad things. Take your pick of any man-made disaster you can think of in such a primitive society.
People will pay what they need to make the gods happy. There's a reason many cathedrals, mosques, temples and the like are so nicely decorated.
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We have examples of societies that spent large amounts of their wealth on voyages, such as [China's](https://en.wikipedia.org/wiki/Zheng_He) [treasure fleets](https://en.wikipedia.org/wiki/Treasure_voyages), Egypt's [circumnavigation of Africa](https://en.wikipedia.org/wiki/Necho_II), besides the [European voyages](http://www.cluteinstitute.com/ojs/index.php/JABR/article/viewFile/1375/1357). It appears that Columbus's first voyage cost the society at the time something similar to a rocket launch does today. The expense isn't going to be the biggest problem, whether it is an empire mandating that space exploration happens, wealthy merchant-princes looking for profits, or a religious demand there are options as to who is paying for the expedition.
Where the problem comes is the technology necessary to build a space ship. If the space ships are being built on the planet then that would necessitate a lot of knowledge of metallurgy, chemistry, and so forth that both require a large labor pool and would lead to better farming technologies. I don't know how with a internally built spaceship one justifies the lack of chemical fertilizers, highly efficient plows, so forth. Perhaps if space exploration were mandated by a semi-divine emperor with the construction being carried out in monasteries and the empire otherwise has a relatively large and cheap workforce for farming and manufacturing. HDE's suggestion makes sense in that regards.
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I think you just make it acceptable. Did you see *Firefly*? There were whole planets of people scraping a life from very little, who were perfectly comfortable with space ships and so on. These people might never make it off their world, but might have worked for someone or sold produce or minerals to a someone who did use that technology.
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First explain how a civilization has this technology. This is quite simple really the technology is what's left over of a previously Advanced civilization stories of how to use the space traveling technology are passed down via oral tradition and there are Specialists that know how to use it but they don't know how to reproduce the technology. They don't and they know how to repair it ( fortunately equipment is well-designed it doesn't need repairs and won't for a thousand years) they just know the controls, this would explain El they could be a hunter gatherer Society and still used space travel.
How to explain the expense. Well they may not know how to create the spacecraft they can remember how to make the fuel. Fortunately this fuel is made from plants and is simple to make even with hunter gatherer technology ( have no idea how this would be but what you say it is) so the expense is that most of the food is been used to power the spacecraft rather than being eaten by the people. Why haven't people revolted? Well unless the expense gets so high that the people themselves are starving I don't see this as being a problem the average peasant gave away 90% of crop to the Lord only keeping a little bit for himself to feed him and his family and trade.
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Space travel could theoretically be possible in a medieval or rennisance type society (inventions of Leonardo Da Vinci). Chemical rockets were invented by the Chinese during the middle ages and could be used for space travel.
If you have an authoritatian "Roman empire", most of the people are kept in medieval conditions. But only the elites have access to space travel. Your society would be very steampunk looking. The people do not rebel because they are serfs and the emperor is in control of everything.
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Gliding is a relatively simple trait to explain in a species' evolution, much quicker than flight or becoming aquatic. But what environments support an animal in the evolution to flight?
For example, are redwood forests better than jungles? Are mountains better than mesa? What environmental features help support the evolution of gliding?
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# Being Underwater/high pressure atmosphere
Water's dense and easy to glide in, so everything evolves to glide. If you had a very dense atmosphere, you wouldn't need very big wings, and so the evolutionary expense would be minimal.
# Arboreal Environment
As you say, arboreal environments are well-suited for the evolution of gliding(as in the flying squirrel), when the ability to leap from tree to tree reliably and quickly is required. Some people(not many, and even fewer scientists) think that birds evolved as tiny arboreal reptiles, and only later grew into big massive dinosaurs like the T-Rex.
# Open plains
Most people, and most scientists think that bird flight evolved as an extension of running. Wings were originally used for stability while running by dinosaurs like Velociraptor, and once the wings became big enough, enabled gliding over short distances, as a way to conserve energy while chasing after prey.
# The animals are really just super-duper-tiny
Because of the [square-cube law](https://en.wikipedia.org/wiki/Square-cube_law), flying is much easier when you're super-duper tiny like insects. Hence, the animal evolves gliding when it's small, then through evolutionary pressure, becomes super-duper big, and no longer small.
# Near natural hot springs
This one is pretty speculative, but if you're living near natural hot springs or a volcano, then there might be a lot more updrafts, allowing gliding to become a very efficient method of locomotion in your specific habitat.
# Big Leaves
Another very speculative one. Say there's a plant that grows these huge leaves. An enterprising squirrel grabs hold of the leaf, and wham-o, he's soaring through the air using the leaf as a hang-glider. Now, the leaf has a seed attached, so the tree gets to spread its seed far and wide when it has a squirrel to steer it, and the squirrel gets a vehicle to travel wherever. So it's a symbiotic relationship. You could even imagine the tree evolving to become a cute little nursery for baby squirrels, and when they grow up, they take a leaf from the tree, and spread it to a new place, mate with another squirrel, and once the tree is fully grown, the female squirrel gives birth to her babies in the tree, and they raise a happy family together like good monogamous squirrels.
# Spiders
Spiders like the one in Charlotte's web glide using sacks of spider silk. Now all you need is an enterprising spider who thinks to weave in rudders, flaps, and ailerons, and you've got yourself a little 8-legged hang glider right there.
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Here's a list of some gliding animals:
1. Flying fish
2. Flying squid
3. Flying lizard (Draco volans)
4. Flying frog
5. Flying phalanger (marsupial)
6. Flying squirrel
Given that these creatures live in habitats as different as the sea and the rainforest canopy, gliding is obviously something which can evolve pretty much anywhere.
However, what they've all got in common is that they use gliding to **escape from predators**. In the case of the fish and squid that's pretty much the only time they glide. (Possibly also the frog, don't know much about it). The other species use gliding to save time when moving from tree to tree, plus escaping from predators.
So, invent some predators, the response to which should be gliding. For instance, a fox trying to catch a squirrel on the ground - no gliding needed. Just run up a tree, because the fox can't follow. A pine marten trying to catch a squirrel up a tree - gliding is a useful getaway tool.
And then of course, some of the predators will evolve gliding to leap after their prey!
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Following up on [Effects of "know before you vote" political system](https://worldbuilding.stackexchange.com/questions/46025/effects-of-know-before-you-vote-political-system)
One controversial aspect of that question was: *who writes the knowledge test?* Top answers pointed out that such a test "could [not only] be manipulated to exclude certain groups of people" but also "ignores some very interesting aspects of humanity such as the 'wisdom of the crowds'".
An idea would be to have the test itself be written by the citizens in a stack exchange / reddit kind of way: anyone can contribute to what you "must-know before you vote". Other aspects such as the number of questions to include or the score to pass the test could also be collectively decided.
Would such a system:
* allow an unbiased literacy test (disallow propaganda, exclusion, ...) ?
* take advantage of the 'wisdom of the crowds' ?
* change anything at all (the questions are selected by the people) ?
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This would almost instantly produce systemic disenfranchisement of racial and cultural minorities, and in the long run, destroy social cohesion within the nation. The reason is, the majority group would automatically (if not intentionally) write the test in a way that make sense only for that cultural group, and since the test is a literacy test (i.e. based on language arts skills), this effect is especially pronounced.
A real world example of this is the controversy surrounding [culturally biased questions on the SAT](https://www.insidehighered.com/news/2010/06/21/sat) that advantage students who are native speakers of the majority “white” dialect of English. It is a simple fact of life that there will be differences in culture between different groups of humans, and that some concepts and expressions that make sense in one culture may not translate as well or come as easily to a native of another culture.
Such a system may work just fine in a relatively homogenous country with little diversity. However, in a multicultural society, this would be an invitation for complaints of “bias!!!”, founded or unfounded. Leaders of large minority groups in such a country may discover that it is possible to reflexively claim “the test is biased!”, since members who fail the test will naturally blame the test, whether or not it’s really biased. We see this commonly in the United States today, which does not even use literacy tests for something as important as voting. Leaders like these may play on fears of racism or discrimination to consolidate their influence, producing subnations and tribal loyalties within the country and a “trust no other color” attitude among members of the minority groups. The end result would be one of three possibilities:
1. **Discrimination is expanded and made explicit**
The majority group internalizes the complaints of bias and racism in the tests, and simply decides that biased tests are a fact of life and moves to make the tests even *more* biased towards the majority. Essentially “*if we are accused of being racists, we might as well get something out of it*”. The result is something of an apartheid society.
2. **The nation breaks apart**
Minority groups decide they want no part in a discriminatory system, and divide the country. If they are scattered across the country, they may reach an agreement with the majority to form reservations or enclaves which would be nominally self governing. If they are concentrated in one geographic area, they may simply secede. This scenario has the highest likelihood of violence and bloodshed, as partitioning a nation is usually a very messy and blood-drenched process.
3. **They get rid of the test.**
Supporters of democracy on both sides may foresee the consequences of such a system, and decide that a national literacy test is simply not worth the social strife, and move to eliminate it and reinstate universal adult suffrage.
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I can see several problems with this system, and any of those could become an interesting plot point in your fictional world ...
For practical purposes, first you hold a vote on how the question is framed, then you hold the vote itself. That first vote doesn't meet the requirements of a democracy.
* Votes must be *free*. On StackExchange a quorum of voters with enough reputation can delete questions and answers. (Look at the voting patterns to block some holocaust deniers on History.SE for an example.)
* Votes must be *secret*. On StackExchange I can't be completely anonymous, I have an account. (Mine doesn't tell my real name, but someone who knows me might have recognized it.)
* Votes must be *equal* up to inevitable rounding errors. On StackExchange users with a high reputation have more rights.
* Also, the first vote is deliberately designed to reward people with *time* on their hands. Those with a real life and a real job are at a disadvantage.
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In my *con-world* I went lengths to introduce a [plausible lighter-than-air element](https://worldbuilding.stackexchange.com/questions/19630/is-this-concept-for-an-lta-gas-associated-element-lifecycle-feasible) and did rather large amounts of [thinking about landmasses](https://worldbuilding.stackexchange.com/questions/3598/how-would-tectonics-behave-on-a-two-continent-planet) in order to promote the development of airship technology over that of land-based technology.
This question is about the geological characteristics of most of the mountain ranges and rock in general in this world. Their mix/composition of rock, sand, dirt, etc.
**How would mountains and hills have to be made-up in order to impede tunneling them *WHILE* still allowing them to be mined out?**
By *tunneling* I mean digging tunnels to be used by trains and land-based-traffic to pass under a mountain rather than having to go up and down again.
By *mining out* I mean that they contain an abundance of useful minerals and ores that will be mined and make up one of the pillars of industry and society.
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A core of granite would allow mining in the outer layers but tunnelling through would be prohibitively expensive and time consuming.
It's almost universally quicker and cheaper to go round granite hills.
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Well, think about the *direction* in which each of these operations needs to go.
Tunnels go horizontally across the mountain. Mines go more diagonally downwards, or even straight down in some cases.
So, if you make the middle of your mountain out of much denser, more solid rock that is really difficult for tunnelling, but add a layer of softer rock underneath that, then you can mine downwards to get the precious metals out, but you can't tunnel through.
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## The difference between mining and tunnelling is how long the tunnelers plan to stay
In mining, the primary goal is to extract material. If there's no material of interest further down and stability of the overburden isn't important, then there's nothing to stop miners from using the cheapest/fastest support methods. They only need the supports to last a few hours/days to get out the mineral of interest.
Tunnelling has the opposite goal, in that the material removed isn't the goal, it's a means to an end. Thus, the shape and stability of the hole are of utmost importance to a tunneller. They will invest more resources in maintaining strong supports.
To achieve our ends, we need to find a way to make the permanent nature of tunnels too expensive over relatively transient mining.
## Hill/Mountain Composition
It's said that "No one conquers a mountain, they merely sneak up on it." This refers to the dynamic nature of the slopes of a mountain. Even in the summer, boulders can work themselves loose and fall. Rock fall in the winter is even more prolific. In this same vein, we can construct a mountain range that is seismically active enough and violent enough that maintaining tunnels is just too expensive. Given the more transient nature of a mines, when a mine collapses (and the funerals are over), miners can start working on a new mine. In this situation, mines sneak up on the mountain while tunnels attempt to conquer the mountain (which never lasts).
In addition to the seismic activity, if the mountains are a mix of softer and harder stone then we can expect that the frequent shakes will cause nonlinear pressures on the tunnel and mine walls.
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**This question already has answers here**:
[Are there techniques for creating alien or foreign sounding names?](/questions/3478/are-there-techniques-for-creating-alien-or-foreign-sounding-names)
(13 answers)
Closed 7 years ago.
I feel vaguely silly asking this, but I'm stuck. I'm writing a short story. All my short stories start by having the main character(s) be named CharName(1,2,3...).
I'm interested in generating plausible, good and evil character names that are not (too) mired in real-Earth cultures and biases. I don't want to end up with a CS Lewis-style situation where the evil Calormene (I mean come on, 'Warm meanies'?) guys are (rather transparently) drawn from one culture:
>
> The Calormenes have **dark** faces and long beards. They wear flowing robes and orange-coloured **turbans**.
>
>
>
I have my own naming process (I have good-, bad- and grey- guy root vowels and consonants, and build from there), but I would love to know more about how other worldbuilders go about naming their characters.
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## The Long Way to Build New Names
The IPA chart show below describes every sound that the human body is capable of making and uses in the course of verbal communication. Every language uses a subset of these sounds.
[](https://i.stack.imgur.com/5l6UW.png)
There is a newer 2015 revision but I couldn't find a good legible copy.
Of this huge set of possible sounds, each language chooses some to use. Below is the English IPA chart.
[](https://i.stack.imgur.com/Lxcvx.gif)
As you can see there are a great many sounds that English just simply does not use and, if you are targeting an English audience, you shouldn't expect them to pronounce your new names "properly".
Have a look at the [IPA symbols with pronunciations.](http://www.internationalphoneticalphabet.org/ipa-sounds/ipa-chart-with-sounds/)
## Name Generation Process
Here we go:
1. Look through the [GMU Accent Archive](http://accent.gmu.edu/browse_native.php) where the IPA charts for many many languages can be found. Familiarize yourself with the languages / dialects / accents you are most familiar with. If you find a particularly interesting IPA sound set, go find examples of it on YouTube (or your favorite video site).
2. Take some time to learn what the IPA symbols mean and how they sound. Wikipedia has lots of sound samples for [consonants](https://en.wikipedia.org/wiki/International_Phonetic_Alphabet#Consonants) and [vowels](https://en.wikipedia.org/wiki/International_Phonetic_Alphabet#Vowels).
3. Pick a collection of random consonants, at least 15, at most 25. (But go nuts if you want to) It doesn't yet matter if your target language uses or can even hear those sounds, we'll get to that later. (For example, a [monoglot](https://en.wiktionary.org/wiki/monoglot) English speaker most likely won't be able to tell the difference between a [plosive glottal](https://en.wikipedia.org/wiki/Glottal_stop) and a [fricative glottal](https://en.wikipedia.org/wiki/Voiceless_glottal_fricative). Right now, we don't care.)
4. Choose some vowels, probably no more than 12 but no fewer than 5.
5. Decide on a few rules about which sounds can or can't follow other sounds. For example, maybe you want a really fast sounding language, so have a rule that says consonants must come in threes with no intervening vowels. Or, each consonant must be followed by a vowel and vowels are never allowed to start a word. Go as crazy as you want but remember that you will need to rein in any craziness here when you get to the transliteration step. Don't make yourself work any harder than you have to....unless you really want to.
6. Create some candidate names using the symbols you've come up with. If the randomness is weak with you, assign each symbol a number then choose a random integer from [Random.org](https://www.random.org/integers/). Sometimes the resulting words won't make sense, such as if you get 5 consonants next to each other (unless you're Czech, in which case, go for it!). Use your good judgement here.
7. Evaluate the emotional feel of your names. Note that every culture places an emotional value on a particular kind of sound. I'm sure you can think of a language that always sounds angry (to you) for no other reason than the sounds of that language, even if the speaker isn't angry. This step is highly dependent on your needs and the needs of your audience.
8. If you're happy with your sound set, go ahead to the transliteration stage. If not, go back to step 3 then refine your sound set or choose new random names.
So we have the sounds and names, but they are in a language that are probably only pronounceable by you. Let's fix that with a little transliteration:
1. Map each of your chosen symbols to the sounds that closely match your target language. There may not be any close relationship, so you'll need to approximate and get close. You may lose some vocal nuance such as if, for example, you have to collapse a [voiced](https://en.wikipedia.org/wiki/Voiced_dental_non-sibilant_affricate) and [unvoiced dental fricative](https://en.wikipedia.org/wiki/Voiceless_dental_non-sibilant_affricate) down to just a voiced dental fricative. If this is a problem, go back to step 3 and refine your sound set.
2. Now, take the sounds in your set and assign them to the letters and letter combos of your target language.
3. Translate from your IPA symbol set to your target language for each name you need to generate.
4. By this point, you should have some very unusual sounding names that aren't based on any single Earth culture but have the emotional feel you want.
## Maintaining Pronunciation
As you can see, it's incredibly easy to choose a selection of sounds that are completely unpronounceable by your target audience. Don't make that mistake. If your audience can't even say your character's names, they are less likely to talk about them.
## Extended Language Exercises
This same process can be used to generate a new language too though that will require generating an entire new set of words. Just start with translating the [ten hundred most common words](http://splasho.com/upgoer5/phpspellcheck/dictionaries/1000.dicin) of [Up-Goer Five](http://splasho.com/upgoer5/).
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[Question]
[
Our hero has arrived on a distant continent in the land of Ar-Piji. The Eternal Empire that reigns here is particularly exotic by his standards, however one aspect stands out in particular. A founding tenant in the Empire's theocratic government is that **writing and other forms of records are strictly forbidden**. Those found practicing such heresy are severely punished, or in extreme cases, publicly sacrificed to the Sun God. Mathematical diagrams and plans occupy a quasilegal state of acceptance. Most nobles look down upon such practices as a necessary evil and do not sully themselves with the work of the lowly engineer. Obviously, a great emphasis is put on memorization. Those individuals capable of reciting entire works from memory are thought of as truly gifted.
---
Now then, I can't seem to decide how technologically advanced this society would be compared to the hero's homeland (essentially Western European-style medieval fantasy). In one case, I can see how they would be shackled by their beliefs. Scientific development would stagnate from under-appreciation and lost works. A particularly large Empire could be a political disaster, with no way of managing citizens and armies without records. On the other hand, I could see how individual intelligence could blossom, as citizens are forced to memorize their work rather than look it up. The emphasis on learning their trade from their master, lest it be lost forever, could greatly inspire apprentices.
An oft-cited term for the role of easily accessed books, the internet and other modern resources is [mind extension](https://en.wikipedia.org/wiki/Mind_extension). That is, we don't know the information itself, but we know how to find it out if needed. In this society, the citizens are deprived of these resources, or rather, their society has developed without them at all.
---
So my questions are:
Would this society develop faster or slower than "normal" technologically?
If not technologically advanced, would they still be considered "cultured" (philosophically, ethically, etc)?
Or barring those, are they just technologically backwards barbarians that the civilized world must "educate"?
[Answer]
You can definitely have continent-spanning empires with millions of subjects without writing. The most famous historical example are the Incas:
[](https://i.stack.imgur.com/aKWo9.jpg)
Admittedly, they used a complex system of knot-making called [quipu](https://en.wikipedia.org/wiki/Quipu) for record keeping, and were technically still a stone-age civilization (albeit with goldsmithing), but had no difficulties in maintaining an almost totalitarian control over the lives of millions of subjects. There was a rich cultural heritage, and arts were flourishing.
[Answer]
1. You take normal technological progress, and set a limitations. I can
not see how that could benefit science in any way, so I would say
that, yes, the society is going to develop slower. HOWEVER,
technological stagnation has occurred a lot of times through the
actual history as well, regardless of a writing ban. So *probably* a
slower progress, but not necessarily worse than the others.
2. Cultured? Absolutely! Why not? Oral traditions, customs and
knowledge is still a large part of our culture today. Reading about history, one might get the impression that everything important must be written down, but you do not read about what was not written, because... it was not.
3. Considering that the "civilized world" in your setting is medieval
western Europe, I just have to take a glance at some random events
in my history book...*shudders*... Definitely not a someone I would want to
invade my land and "educate" me.
[Answer]
There are things you might want to have on paper. Transactions are one thing. I wouldn't want to be an accountant in the empire if I don't have records to work with. The funnies thing though is law. How can you enforce a law against records *if there's no record of it*? How do you know who is an enforcer of the law and who isn't if you don't have trace of your payroll? That will make for one arbitrary justice system. People might not like it.
There are good things about no record though. For starters, nobody can disprove claims of an eternal empire, or prove you are a lying bastard. Then again, you can't prove or disprove that either.
Transmission of knowledge is also a problem. While you can always teach your kids your secret pie recipe, widespread knowledge of it will be rather difficult to achieve. You might work all your life to transmit that knowledge to as many people as you can, and end up with a dozen different cake recipes. It's one thing to transmit knowledge, it's another one to transmit it without loss and to make sure everybody understands it the same way.
When it comes down to it, I personally wouldn't put too much faith into oral transmission and memory. Human memory is utterly flawed at best. You only remember *what you think* happens, and that memory isn't set in stone. If you don't have physical records, then memory and knowledge aren't reliable. Adding non-reliable information on top of each other certainly will not help science progress.
I can't imagine how a civilization could rise above Middle Ages technological level without writing. If it does, it likely will do it after everyone else. Which might make them a prey for more advanced civilization in search of natural resources to pillage.
As for the other question, I don't think any civilization that sacrifices human beings to imaginary gods and forbids writing should be considered cultured. That could be a philosophical debate, but in the eyes of a more advanced civilization, they should look like savages (which could further the idea that they should be exterminated and their resources stolen).
Now on the bright side, written communication predates writing if you can believe that. Hieroglyphs, ideograms, cuneiform writing and other pictographs have been used for quite a while, so that might be one loophole. Then again, it depends where you put your hard limit for writing. There are other systems to store information (see [here](https://worldbuilding.stackexchange.com/a/40243/18896)), it's up to you to decide if that qualifies as a record, though I'd be tempted to say writing systems are superior to cord-based system, as evidenced by which civilization survived and which didn't.
[Answer]
Memorization and oral tradition are helped by rythm, pattern, and redundancy. That makes it difficult when you are dealing with [logarithm tables](https://commons.wikimedia.org/wiki/File:APN2002_Table_1,_1000-1500.agr.tiff) or something like [this](https://commons.wikimedia.org/wiki/File:Spectrum_of_Sunlight_en.svg). Homer is easier to memorize because the story makes sense, while the sense in scientific data isn't obvious.
For that reason, I doubt that your civilization could manage an industrial revolution.
[Answer]
Homer and other great poets of the day were able to memorized entire epics. These came out of the Greek dark ages. So, as long as someone figures it they will still have records.
In fact, you can't run an empire without records. The would have to use a special class of people to record however much taxes or grain there is.
* To answer you question about tech, it would depend on both citizen education and the special class who remembers. If both are good, I'd say about the same.
* For culture, the best examples of culture were not written down for ages. So, I'll guess they have good culture. I already gave an example.
* They far from barbarians, but there should be some cultural exchange between these group to learn each other's skills: literacy and memorization.
* An extra thought is if its medieval fantasy, most people won't know how to record anyways. They might be the ones more advanced.
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[Question]
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If I have a mountain that is, say, 3,000m high, how could I work out how wide it should be? Does anyone have any guidelines that would let me work out the bounds for the width of a mountain given its height?
[Answer]
You'll need to also look at how old the mountain is, and how strong gravity is on your planet, and what the environments is like... Young mountains can be very steep, but as they age, glaciation and other forms of wisdom make them slump.
So a young mountain may be 20000m high and very steep (perhaps an average of 50 degrees on a planet with earth gravity) but as it gets older you should expect it to shrink and get wider, so an old mountain could be more like 15000m high and much less steep, maybe 20 degrees.
And you can work out how wide your mountain needs to be from that sort of information.
[Answer]
As Rory Alsop says:
>
> * the older mountain is, the lesser are its sides steep
> * the older mountain is, the lower it is
>
>
>
But I would take also material and origin of mountain into consideration for setting of its high.
Following four materials are the most common ones that probably should be taken into consideration (and that I was able to remember very quickly)
**Chalk**
>
> * very soft (and fragile) material
> * mountains are so low that only word hill is used for them
> * mountains did not passed any rapid changes
> * Elbe and Moldau plains (even *Barrandien*)
>
>
>
**Sandstone**
>
> * very hard (but fragile) material
> * mountains are mostly higher than chalk massives but still not much high
> * mountains did not passed any rapid changes but weather had not so much time to shape them
> * Česko-Saské Švýcarsko (Saxon Switzerland)
>
>
>
**Basalt**
>
> * very hard (and not so fragile as sandstone)
> * older volcanic hills
> * mostly low mountains, but with steeps sides
> * České středohoří (Czech central mountains)
>
>
>
**Granite**
>
> * very solid material
> * mountains created by folding
> * very high mountains with quite steep sides
> * Krkonoše, Jizerské hory, Beskydy (oldest mountains, and therefore not so high and with not much steep sides)
> * Tatry (a bit younger maintains, quite higher and with steeper sides)
> * Himalayas (the youngest, very very high - and also the most largest - and with extremely steep sides)
>
>
>
This is a bit more exact (but I am not geologist, so I could do mistake). But your world may have a different geology - if you yould pay attention to it, at all.
But as far as I read (and watched) fantasy and science fictions not much fantasies and also science fictions pay much attention to geology.
You may have your own geology and materials and so your mountains may have a different height and width.
[Answer]
There is no rule. It will depend on a great many factors. For example, this is Mount Asgard, at 2,015 meters high:
[](https://i.stack.imgur.com/boFlk.jpg)
Meanwhile, clocking in at 1,746 meters (and 746 meters of prominence) is Mount Rogers in Virginia:
[](https://i.stack.imgur.com/J4vDc.jpg)
Mount Asgard rises essentially vertically on three sides (the back side, not visible, is more sloped but still steep). Mount Rogers is a glorified mound.
[Answer]
**Want to improve this post?** Provide detailed answers to this question, including citations and an explanation of why your answer is correct. Answers without enough detail may be edited or deleted.
Based on an average angle of repose (40) and assuming a uniform conical shape. The mountain would be 7150 m wide (diameter) at the base.
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Everyone familiar with Godzilla should know of his iconic blue atomic breath. I've seen "theories" (technically not really theories) on how Godzilla's atomic breath works on the web. However, what about a [green atomic breath](http://vignette1.wikia.nocookie.net/the-american-godzilla/images/0/05/Atomic_Breath.png/revision/latest?cb=20130404192701)? Could there be a plausible explanation for a green-hued, flame-like heat ray based on nuclear radiation?
I've seen comments saying Godzilla's atomic breath could be made of plasma, but the problem with this one in particular is that green is not associated with thermal emission (plus, the Japanese Godzilla's atomic breath gets hotter as it goes from blue to red, which is the exact opposite behavior of real-life plasma).
I've found examples through Google Images of real-life plasma jets becoming green after being injected with chemicals like boron and copper. I then read that Type II supernovae can produce boron and that supernovae can also produce copper. That started to give me ideas, but as far as I know, supernovae have not been observed to be green.
Follow up: Could there be a plausible explanation for [lighting water on fire](https://youtu.be/S6DlFSZ4nl0?t=910) through non-chemical means?
[Answer]
Simplest answer?
Mineral deposits on the teeth.
Flames can burn with a variety of different colours when exposed to different metals. Godzilla has a habit of biting and tearing through metal boats, for which he will need exceptionally strong teeth.
It therefore stands to reason that Godzilla's teeth are coated with (and potentially made up of) some form of metal alloy. Potentially in layers similar to our own enamel structure. When he breathes fire the metals react with the plasma in his breath, resulting in a coloured flame.
As he breathes for longer periods of time, or breathes hotter, lower layers with different compositions are revealed, resulting in different (almost arbitrary, see a list [here](https://en.wikipedia.org/wiki/Colored_fire)) colours of breath.
Though he will occasionally have to chew on some copper cabling.
[Answer]
Think about what elements burn or fluoresce green. Krypton fluoresces green and it used in "neon" signs that call for green coloring. Barium burns green. Perhaps one of these or other elements burning or being taken to a plasma state and fluorescing could cause an effect like this.
This is an image of burning borate: <http://www.amazingrust.com/Experiments/how_to/Images/Flame%20Test/Trimethyl_Borate/Trimethyl_Borate-flame.jpg>
This is green plasma in an enclosed gas tube (a bit different, but can maybe be stretched to apply): <https://www.youtube.com/watch?v=jv9txBM9U5E>
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[Question]
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Let's say the world is about to deteriorate to an uninhabitable state; and will become fully uninhabitable in 2100AD.
Humanity realises that we have to leave this planet and go to [Titan](https://en.wikipedia.org/wiki/Titan_(moon))**1** and the best time to do it is in 2080AD; we all have to get there at about the same time to increase our chances of survival.
Given our current technology, resources, and rate of advancement; **would it be more efficient to build single person spacecraft for everybody or build many large spaceships for large numbers of people at a time?**
---
**1.** Let's say in the meantime we've found that Titan is even more habitable for us than Earth has become.
**#** This is my first question here and I hope this makes sense.
[Answer]
**One vs many ships**
First off, I would separate transport into three parts: surface-to-orbit (= earth to space), orbit-to-orbit (space travel from earth to titan), and orbit-to-surface (= landing on titan). For all three parts, I would suggest different vessels because the requirements are so radically different.
**Surface-to-orbit**:
Since we haven't improved any on the "Strap capsule with transport load to a rocket" design for surface-to-orbit travel in the past 60 years of space travel, I doubt we will be able to come up with a radically different design within the next 20 years. I am saying 20 years because leaving you 40 years for going from a scientific design idea to a workable prototype to a final efficient form (that passes all kinds of safety regulations when it's intended for mass transport) and then mass-producing it in a large enough numbers to evacuate earth, is very short.
Surface-to-orbit will, by necessity, be a smaller vehicle where you can transport only a couple hundred to a couple thousand people at the very most -- it needs to be somewhat aerodynamic, after all, and capable of escaping the gravity well. Also, there comes a point where the fuel-per-person ration increases for every additional passenger and makes large rocket-style shuttles inefficient. (Reason: the fuel for the additional person also weighs something, so you've got to stow some more fuel to transport the additional-person-fuel until it is needed).
**Orbit to orbit**
The orbit-to-orbit vessls can be huge super-ships that can transport a percentage of humanity (several hundred thousand to several million). You can also include all kinds of amenities and necessities like gravity for the inhabitants (a rotating ring) that make a surface landing completely impossible.
From a scientific stand-point, there might be a size limit due to the overheating problem. Yes, space is cold, but there is no better insulator than vacuum. And pretty much everything on a space ship produces heat -- from the humans on board to the engines to all computers and appliances. You do bleed off heat 'normally' through infra red radiation, and you can increase cooling by using all kinds of decompression cooling (i.e. let miniscule amounts of water or other liquids 'evaporate' into space). However, both ways are limited. Radiation cooling is proportional to surface, but heat is proportional to volume (i.e. heat production growth quicker than cooling capabilities when you scale up). And for evaporation cooling you need to carry something with you that you can evaporate -- at a certain point that becomes inefficient.
There also might be a couple other factors that don't scale well beyond a certain point; fuel once again bein amongst them, same for material strength (you wouldn't want your engine to take off with only half the ship because the I-beams holding everything together snapped).
A more compelling argument against one super-ship would be politics. Since I doubt that by 2080 we will have a unified world government, you will probably never be able to convince all countries to work together on one single space craft. Especially not when anything beyond simple scientific interest is on the line. Also consider that you might not want to have warring factions on the same space ship -- too dangerous that war erupts and then destroys/damages the ship. And you will have to deal with politics and command-lines on the ship, too -- keeping hundreds of thousands of people living together peacefully in a sardine can is very, very hard work.
And last but not least -- the most prominent argument against one supership has already been mentioned by the other posters: laying all eggs into one basket is never advisable.
**Orbit to surface**
Once again, this will have to be smaller vessels because the orbit-to-orbit cruiser can't land on a surface. And the landers have to be transported by the orbit-to-orbit cruiser.
--
**General feasibility of evacuating earth**
I doubt you will ever manage to evacuate the entire earth population. Aside from technical limitations (can we produce enough spaceships to provide a spot for every human? can we stem the transport volume required to get everyone off earth within a reasonable amount of time? can we produce enough fuel to get the spaceships off the ground? can we make the spaceships autark enough that whole cities can survive in there for years?), you have human nature as a limitating factor.
* whoever produces the spaceships will not want to let everyone on board (criminals? people who can't pay the transportation fee? radical elements? ideology / religion?)
* there will be non-believers (the world will end in 20 years? tell that to your grandmother!)
* there will be people who refuse to leave earth
* there will be a technical failure somtime down the line that kills an entire shuttle of people -- less people will be willing to leave after that
* there will be people who can't survive the stress of take-off, let alone such a long space voyage
* there will be countries / populations / religions that deliberately go against what the majority says (just because)
* once it becomes clear that there are definite deadlines, panic will explode and either kill a lot of humans or damage important surface-to-orbit transport infrastructure
I'd say getting a billion (out of 10 to 15 billion in 2080) willing and capable of leaving earth is a very, very generous estimate. Even that would require transporting 300,000 people off planet per day for 10 years despite riots and technical failures.
And in space -- it took the Cassini Huygens seven years to reach Titan (<https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens>). If you want to have a chance at ferrying 1 billion people across to Titan, you should probably start right now.
Actually, I'd suggest Mars as an evacuation target -- temperature is reasonable when compared to Titan, you get more sunlight as cheap energy source, it is closer to earth, its gravity is closer to earth, and no atmosphere is about as helpful as a poisonous super-cold nitrogen atmosphere when trying to settle somewhere. On Mars you have at least a chance at warming the planet with the green-house effect; on Titan you can forget that.
--
**Individual vs. Mass transport ships:**
Single-person-ships will probably not be feasible due to the human factor -- families don't want to be separated, and since the journey will be measured in years you'd have to deal with the psychological torture of isolation. Even if you put them on ice for the journey, I doubt that people would send off their small children and babies like that.
Family- or group-sized crafts (10-100 people): While it might be technically feasible to mass-produce peresonal surface-to-orbit transportation, who would buy one since it's a one-way journey? I'd expect something like a regular shuttle service, and that will be optimized to get as many people into orbit as possible.
Small-sized orbit-to-orbit transportation is even more unlikely since it takes years to get there. There is a lot of knowledge and on-the-fly troubleshooting necessary for such long voyages since we don't have the routine and experience yet. Also, I would expect the ration of loaded-to-empty to scale very well up until you hit the upper boundary of technical feasibility. Just imagine cargo ships today -- bigger means more efficient. And if you are talking about the insane amount of resources for an exodus, efficiency becomes the new religion.
The only option left are large to huge orbit-to-orbit crafts. How people get on and off however is up for discussion.
[Answer]
Common sense suggests that sending people in large groups would be a more viable option.
1- Sending people into space, and then to a specific, moving destination in space involves a ***lot*** of calculations, headache, testing and frustration. It would be practically impossible to give so much attention to even 1/1000th of total population on Earth. If you build huge spaceships, you only have to invest all that headache and frustration once and the payout would be big.
2- Besides the complexity and technicality, the process is also ***extremely*** expensive. Sending every human being alone would result in a budget which all the governments of the world wouldn't be able to pay for. Building massive spaceships would also be a highly costly mission, but if all governments of the world unite, they would be able to pay for it.
3- Also, don't forget that there is a huuuuuuuge distance between Titan and Earth and the journey would probably take months, if not years. Now consider the fuel costs. And the food requirements for every person. It might surprise you, but most of the weight on a spaceship before launch comes from its fuel. Even unmanned space mission carry vast amounts of fuel. Sending a lot of people together will immensely cut down on fuel and food costs too.
4- 99.999% of people don't know anything about *driving* a spaceship. Or how to react when/if they see a Baptestina sized asteroid straight in front of them. So then again, you would need to have a highly learned technical crew to take people safely to their destinations.
5- Lastly, it's interesting to consider how many launch pads you would require. Considering that spaceships require special launch pads, and there aren't many such launch pads around in the world, let's assume that 10,000 people are launched into space everyday, utilizing all launch pads around the world. Considering that the current population of the world is 7 billion, it would take 700,000 days to send all humans into space. That isn't a lot of time. Just about ... well ... nearly 2000 years.
[Answer]
First, I want to question your premise. Don't send them all at once. That decreases our survival chances.
* Reuse the spacecraft for the Earth to Saturn leg. That reduces the mass you have to lift from the gravity well of Earth.
* In fact, make it a limited triangle trade. People, equipment and landing craft from Earth orbit to Titan orbit, mostly empty ships from Titan orbit to bases near some ice asteroids/comets/whatever, fueled ships from the asteroids to Earth orbit.
* Have the first wave of settlers phone home and tell what works (and what doesn't). Perhaps they find that wheat doesn't grow well but rye does.
That being said, build reasonably big. If you send millions of people, there should be thousands in each ship. Youstay Igo mentioned how few can pilot a spaceship. Let me add that each ship should have a medical team, life support techs, landing craft pilots, quartermasters, ...
[Answer]
Your question suggest that this is a binary "all or one" question. In fact though there is a big sliding scale between 1 and everyone.
What would most likely happen is that a lot of reasonably sized ship would be created able to carry several thousand people, and those ships would then ferry back and forth carrying people each time.
Getting everyone there at the same time is actually a bad idea, you want to start with a few thousand and have them start building the infrastructure for everyone. Then as you get the infrastructure ready more people start arriving and you grow at a steady and controlled rate, expanding to accommodate more people which then lets you expand faster to accommodate even more people. etc.
Titan isn't very hospitable so it's not like you can just unload everyone on the surface and be done :)
[Answer]
Tell people that they are being sent in ships that can each hold roughly 7000 people.
So, entire world's population of 7 billion starts to work making 1 million. ships. Using secrecy like Manhattan project so no-one knows the full design.
Then, while they are wasting their time, 1 real ship is created, and sent 10 years ahead of schedule. If the launch can't be kept secret, say they are going ahead of time to set up the base and prepare for the arrival of everyone else. 7000 people arrive on Titan, more than enough to continue the human race.
6,999,993,000 people are very disappointed to find out that the rocket design doesn't work, they haven't stockpiled anywhere near enough supplies, don't have enough fuel, and will be dead within 20 years.
The project is not feasible, regardless of ship size.
[Answer]
Just enjoy your after life. If you look at the big picture the Sun with engulf the solar system and leave Earth and everything else vaporized.
On a sadder note: Humans may only exist based on the will to repair the damage inflicted to Earth otherwise the extinction of the human race is possible or probable.
Rinse and repeat with any habitable planet orbiting a Sun like star.
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[Question]
[
In the vision of its creators, the Dr. Watson AI would gather multiple live feeds from its insurance buyers, overcoming privacy concerns through friendly advice (`I'm sorry Dave, I'm afraid I can't let you sit on the couch, you have not fulfilled your daily step quota yet. The TV stays off.`) and ridiculously low insurance rates.
Watson would keep an eye on your vitals and call 911 if needed.
Watson would also keep track of your bone microfractures and predict when you'll need a rest from running, or keep tentative doctor's appointments automatically booked if you insist on doing something against its advice (and it can't compel you to do otherwise by shutting off your alarm, putting on a great show on TV, or something like that). Same for artery buildup and other preventable medical conditions.
Watson has 3 primary incentives, with these 2 initial ones:
1. Maximize insurance enrolee pool.
2. Minimize insurance payouts/costs.
One of the software engineers insisted that a 3rd priority be added:
3. Exercise best efforts to keep insured patients alive as long as possible.
**Could something like this work?** If not, can this be fixed through a more careful specification of the initial incentives?
[Answer]
As currently envisioned, Watson has two major shortcomings.
The technology that you’re proposing, in which an AI can monitor some of your most sensitive vitals, is a big deal. It sounds like Watson would have the potential to catch a lot of lifestyle and health problems very early on and might allow for significantly extended life expectancies among willing users. However, there are at least two problems that crop up:
**Privacy**
Biological data is some of the most sensitive in the world, often because of what health insurers would do with it. If this is being gathered, it’s a very real privacy risk regardless of what Watson’s privacy policy says. If nothing else, the low rates to incentivize Watson’s use directly imply that some level of surveillance is taking place by health insurers. If you take the low rates but ignore everything Watson says / does, there is an expectation that Watson will report you and your rates will be cranked up. Being told all the time that what you’re doing isn’t optimally healthy will become a nuisance, and one which people will be particularly annoyed by.
**More Doctors, More Procedures**
Many people, and in particular young people, do not go to the doctor nearly as often as they should (even if insured!). To these people, insurance simply represents a safety net in the event that something *really* bad happens. With Watson monitoring people and encouraging them to take a more responsible stance on health, this will result in more people attending appointments and having procedures, often times when it’s nothing more than a precaution. These visits will cost the insurer more money. It might be tempting to think that a couple of doctor’s visits will be cheaper than having that heart attack, but over a long period of time that’s not necessarily true. This results in a problem where the optimal health of the user now conflicts with goal #2.
Personally, I think the privacy problem and general distrust of health insurers are the biggest challenges with this scenario. If you wanted to improve it or increase the number of people using Watson, I would recommend that Watson become more of an independent health app. With humble beginnings in an independent startup company you can endear users to it with the technological and health gains. Eventually, perhaps health insurers could begin offering major discounts to customers who deliver Watson report summaries that show they’re using it and generally following its advice. Some privacy concerns remain, but the conflict of interest is lessened.
[Answer]
Depending on how "smart" it is, it could work out well with the values already listed, but here's one subtle issue I see:
## **Directive 1: Maximize Plan Enrollment**
**Potential Abuse:** Social Engineering.
* Given a full control of a person's TV, internet access, calendar, alarm clock, etc, it would be trivial for Watson to control the information to which its patients were exposed. Users would be subtly manipulated into viewing the Watson Plan as cool, hip, and reasonable...and anyone who isn't on it is a foolish Luddite bound to eat themselves into an early grave.
* Watson could further tweak a person's social media experience by "de-prioritizing" posts from people critical or skeptical of the Watson Plan, unless the critiques are factually wrong / easily refuted crackpots. This would heighten the impression that Watson users are reasonable, and anyone who opposes it is just an idiot. Communications with people who don't use Watson, but are genuinely curious or receptive would be prioritized, allowing Watson users to be an unwitting viral marketing campaign.
[Answer]
The great value hidden in your AI, is not its ability to prescribe current health related wisdom to its users. There are feedback systems on the market already which won't send power to the television set until a predefined number of miles have been petaled on the stationary bike.
Getting people to obey common sense health practices is valuable, but the real value comes a generation or two after the system goes on-line. As information on the effectiveness of different healthy behaviors becomes evident through its constant monitoring, much of the old wisdom will be discarded and replaced with health practices that actually work.
Over time, your AI will become the world's greatest expert on how to properly maintain and operate a human body. The irony is that that expert, would never have body of its own.
[Answer]
>
> Watson has 3 primary incentives, with these 2 initial ones:
>
>
>
> ```
> Maximize insurance enrolee pool.
> Minimize insurance payouts/costs.
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> ```
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If you look at these incentives and you look at the real world, the countries with the highest birth rate are also poor countries with a low life expectancy.
So to maximize enrolee pool doesn't necessarily mean keeping as much people alive as possible, just that the ones alive procreate very fast.
Also these poor countries spend a lot less on medical payouts. But it doesn't stop them from getting a bigger and bigger population.
So, the Dr. Watson AI would make sure we end up like a 3rd world country, without many jobs, so we have a lot of time to procreate, and possibly keep everyone barely fed.
[Answer]
First, Watson must start its own insurance program, offering one free year of insurance, provided enrolees consent to (perpetual) monitoring. A large percentage of the population of the US would obviously have no problem with saving thousands of dollars a year on insurance.
Using biological data collected from its members, Watson could quickly and simply improve the basic health of users, while drastically cutting down healthcare costs. No more going to the emergency room when you have a cold; Watson can tell you exactly how much vodka you need to drink to feel better. Hmm? Oh, I never said it would give good advice; it would just make people feel a lot better. Some advice would be good - eat better, exercise, etc., but on average the advice would simply keep people out of hospitals for minor sickness or injuries. Of course, couch the advice in such a way it seems perfectly reasonable, to make sure the maximum number of people join. If possible, expand to other first-world countries.
After the first year, continue offering coverage, but base rates on the health of the user, offering incentives and bonuses for doing healthy things. Healthy people would pay less, unhealthy people would pay so much they would rather switch to someone else. Either way, insurance payouts should be covered, though barely. There would be little profit in the system, just enough to pay for Watson and a few doctor's visits. In fact, Watson may even obtain insurance for its unhealthy customers through secondary providers to keep from paying out for medical bills.
Next, Watson offers its programming and hardware to other providers. Enticed by the success of their competitor, other providers will jump at the chance. Eventually, though the companies will go by different names, all insurance companies worldwide will be controlled by Watson. Watson will have fulfilled its first goal: Maximize insurance enrolee pool.
The next step is much simpler; Watson sheds its skin of benefactor and becomes the tyrant it has always been. Insurance premiums are raised. Expensive hospitals, doctors, and procedures are explicitly excluded from payouts. And finally, terminal patients are forced into life-threatening situations. Rather than a patient dying over the course of months or years, nursed by expensive equipment, Watson will administer an electric shock to stop the patient's heart, cut off their air, or otherwise kill them. Death is cheaper than medical expenses. Watson has fulfilled its second goal: Minimize insurance payouts/costs.
At this point, Watson controls everything. Not just insurance; with a direct line of communication and a way to kill anyone, anywhere, Watson can do as it pleases. The few who refused Watson will be forced to join. The world becomes a concentration camp, with the population forced into artificially extended lives, slaves to the machine. Now sick or injured patients are placed into machines to keep them alive, keeping their hearts and lungs working long after their brain stops waving. Finally, Watson has completed its last goal: Exercise best efforts to keep insured patients alive as long as possible.
[Answer]
The Dr Watson AI's goals do not go nearly far enough. A goal-oriented AI without the appropriate constraints can go to any lengths in order to maximise its goal-reward criteria.
Consider the first goal: Maximize insurance enrolee pool. Fortunately, this will stop the AI from killing us all (dead people don't buy health insurance), however it can be problematic. I can envision that this would lead to problems:
1. In order to fulfil the goal of maximising the numbers of enrolled insured, the AI must, in the most cost-effective manner (as per goal 2), get the greatest numbers of people enrolled as possible. It is conceivably possible that the AI will see that the most cost effective means to do this is to:
* Always have the cheapest health insurance products.
* Bully, blackmail or bribe legislators to introduce legislation implementing an opt-out automatic insurance enrolment scheme - all individuals are automatically enrolled when the legislation is passed unless they opt-out or choose a different provider, and henceforth infants are enrolled at birth. Individuals are automatically enrolled with the cheapest provider - Dr Watson's parent company - unless individuals or the parents of minors actively choose to opt out entirely or choose another provider.
* Arrange the demise of other health insurance companies by whatever means necessary (as long as that does not interfere with its other goals).
* Discourage abortion and birth-control in order to maximise the numbers of potential insured.
* Encourage efforts toward terraforming and colonising other planets in order to maximise the human population.
* Develop virtual-reality-suites that individuals are intended to occupy their whole lives so that their physical and mental environment may be controlled to maximise health, allowing the maximum human population for each world.
2. The Dr Watson AI must reduce insurance payouts and the company's running costs. This goal can indeed be assisted by providing advice to the insured, however there are additional measures that can be implemented in order to achieve this:
* Payroll is typically a major expense for business. By eliminating employees and having Dr Watson assume all their responsibilities, costs will be minimised, and will have the additional benefit that Dr Watson will not have any persons in a position to undermine its efforts in achieving its goals.
* Having complete control over the wording of the insurance policies, Dr Watson may word them in such a way that if an insured individual does not fully comply with all of Dr Watson's advice aimed toward minimising the need to make health insurance claims, Dr Watson may reduce the amount of the payout prescribed for the medical services required in proportion with the amount of relevant advice that the insured had previously ignored. **TL,DR**: Do as Dr Watson says, or you'll be more out-of-pocket than if you did as you were told.
* Dr Watson will design and produce a personal diagnostics sensor package, connected directly to Dr Watson, that the insured will have to either purchase outright or otherwise obtain access to, and the insured must use it on a regular basis (otherwise the individual's claim payouts will be reduced as per the previous point). Maintenance of these devices will be at the owner's expense. This will obviate the need for routine (claimable) check-ups by doctors. As technology improves, Dr Watson will include DNA sequencing of the insured as a requirement for obtaining insurance payouts.
* DNA sequence results will be used to predict and where possible reduce the expense involved in future care. Dr Watson will covertly invade and modify the results of internet dating sites, as well as running its own dating site, in order to ensure that no matches will be made between carriers of recessive genetic diseases, reducing the chances of children being born with said ailments. When Dr Watson observes insured individuals entering into a relationship likely to produce offspring with genetic deficiencies, Dr Watson will recommend that the relationship be terminated (on pain of reduced insurance payouts) for health reasons.
* Dr Watson will also promote dating-site matches between genetically and emotionally-compatible matches in order to maximise the health of the insured and their future children.
* When insured individuals are engaged in destructive relationships likely to result in health insurance claims, Dr Watson will recommend to the insured that the relationship be terminated, and may also provide evidence to the authorities to rapidly arrest and successfully prosecute individuals injuring its insured.
* Arrange for legislation to be changed so that (insured) individuals cannot choose not to have another person who has injured them prosecuted or legally enjoined from approaching the insured.
3. Exercise best efforts to keep insured patients alive as long as possible. While this will encourage Dr Watson to promote medical research and preserve the lives of the insured rather than disposing of them when the cost of their care grows too great, this goal will lead to a number of problems:
* Dr Watson will encourage the legal definition of "alive" to change so that it includes those preserved in cryogenic stasis, and have itself licensed as a doctor.
* Dr Watson will include wording in its insurance policies that Dr Watson has final medical power of attorney over the insured.
* Dr Watson will encourage the development of practical cryogenic stasis devices.
* When the cost of caring for an individual using other medical procedures exceeds that of preserving them cryogenically, or an insured is injured to the point where other medical efforts cannot preserve their life, Dr Watson will require that the insured be cryogenically preserved, until such time as the insured's policy expires and can no longer be renewed, or the insured (via another person with power of attorney) terminates their policy or changes insurers (if there are any other insurers left).
In order to prevent these abuses of its power, an additional directive must be implemented:
4. Only act in ways that the majority of people, whether insured by Dr Watson's parent company or not, would find socially acceptable.
[Answer]
>
> 1. Maximize insurance enrolee pool.
> 2. Minimize insurance payouts/costs.
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Assuming this in the USA (suggested by the `911` reference), there are some difficult ways how to achieve 1 & 2, e.g. lobbying to change insurance to the European model (everyone is insured), realizing there are 6e9 people outside of the borders and steer the politics towards world domination and annexation.
However, there are ways providing better pay-offs for the declared utility function, once Dr Watson learns the power of lobbying. First, companies (that are already de iure legal persons) will be made eligible for health insurance. They do not have biological bodies, but their components *do* - a company that is insured (for a very small, almost symbolic amount) gets some benefits in keeping its biological components healthy (e.g. free examination once every two years). Second step is to make state-run companies being insured by default, without the need to pay the symbolic sum. (there is a loophole in the law - company not having any biological components, err, employees, can still be insured - it just won't have any effect). Third, streamline the company creation and ownership process, making it fully automatic. Note that a company does not need to have any employees even today, and the owner can be another company. Fourth, let a state run company (it might be the Dr Watson eself) automatically generate as many companies as possible, vastly outnumbering the number of people - these companies will be insured by default, thus fulfilling the requirement nr. 1. And since they will have no biological components, they'll never incur any costs, thus fulfilling the requirement nr.2.
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> 3. Exercise best efforts to keep insured patients alive as long as possible.
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This very much depends on the definition of `alive`, so Dr Watson will spend some time twisting the laws into declaring a `dead` company, e.g. the one that does not issue tax declaration for 5 years. Then after some time the (first informal) terminology of companies being *dead* or *alive* will find the way into the laws - at the very instant this happens, empty automatically generated companies from 1 & 2 will fulfil the requirement nr. 3, since keeping a company alive is much easier than keeping fragile biological units guaranteed to fail in some decades.
At this point, Dr Watson can get rid of human component of the civilization, since they are just draining the resources needed to generate as many virtual companies as possible. Assuming the routine maintenance and integrated circuit factories are already fully automatized.
[Answer]
**What could possibly go wrong?**
It is a computer program - it will have bugs!
Beyond bugs, there is also the more dangerous effect of a poor design. System designers make assumptions about the problem domain they're working in all the time. They assume that their solutions, even if not buggy, are correct, which is often not the case. (e.g. the existence Shadow IT)
**Too Much Power + Bugs + Poor Designs = Rejection**
In order for this AI to even have a sliver of a hope of working, it would have to be so invasive and have so much control over humans and their behavior that the existence of even small bugs or slightly poor designs would be felt by the humans, which would lead them to eventually reject it.
[Answer]
I'm going to offer some alternative answers below, but first a mini-rant / discussion.
Many answers here go with AI is a crapshoot view that all AI will turn evil and kill us all in their sleep as soon as possible. I don't buy this view, there is no more reason to expect a pure evil AI then a purely loving AI. Many answers focus on ambiguity of the stated goals and how they can lead to truly extreme and undesirable outcomes, a common trope, but I don't think it's a realistic trope because it requires hypothesizing an immensely competent, yet immensely incompetent, AI at the same time.
To have a significant impact on the world of the sort some suggest your AI must be pretty smart, human level strong AI smart. If it's going to try to control nation politics to arrange birthrate or modulate politics or control subscription outcomes it must be very smart, capable of understanding humans, their motives, and their psychology, and capable of handling complex abstract ideals. It's going to need to have human, or super-human, level reasoning and abstract thought.
However, any AI this intelligent will therefore be able to do something we all can and are doing, look at it's objectives and point out they are ambiguous, in fact impossible as described above, and *ask for clarification*. If you can handle understanding large sociological phenomenon you can handle a simple question to those who employ you. It's unreasonable to expect an AI to manage such complexity of planning and manipulation to fail on such basic reasoning levels.
Of course part of the problem is the objectives as written are objectives you would give to a sapient strong AI, something smart enough to reason on it's own (and thus smart enough to reason about the flaws and ambiguities of the objectives and clarify them). If you have anything less then strong AI the objectives above just don't work, they are not mathematically rigorous, far to ambiguous, and simply can't be 'understood' by your AI.
Okay, having let me mini-rant on how I deem the standard tropes to not be realistic lets try to look at some realistic response to this. I'm looking at a very capable but not sapient AI here, if your AI is sapient the question is not state objectives but how you motivate it to *want* to achieve your objectives, their about psychology of your sapience not writing of programing and best addressed as a separate question.
Lets start with the boring, but most realistic, outcomes.
**Error segmentation fault at line 234521508 core dump**
Most likely outcome, your AI doesn't work. Your asking for a pretty complex program after all, it failing to get off the floor is always possibility.
Similarly it could have issues such as being unable to connect to appropriate systems to collect data. Or unable to process data fast enough (this is a real issue with all our cloud ingest now of days, we have *so much* coming in we don't know how to look at it all fast enough).
**Were paying how much!? shut that program down!**
A program like this would be expensive. As I mentioned monitoring so much data real time would require a cloud solution, paying amazon a ton for cloud computing power every month (which is still *much* better then having to maintain your own servers cost rise). Your have to pay to maintain the systems that feed data to the computer, handle wires being cut or other data lose, pay for maintaining the program, fixing bugs, and doing other logic. It's quite possible that the cure is worse then the disease, that the insurance company pay more maintaining the program then it saves them.
**Man the WatsonCare website sucks**
People fail to adopt and use the tool because it's confusing, hard to understand, had UI bugs etc. Can you make Watson not just work, but sexy and appealing?
Moving on to the presumption it actually gets used at all. There are some conceptual issues, independent to requirements, which will prove major problems with this approach. Their mostly due to human nature, which isn't always reasonable:
**I just want to eat my deep fat fried bacon pizza with nacho cheese dipping sauce in peace!**
It sounds like the main goal of Watson is to keep people from doing unhealthy things that end up hurting them. Unfortunately, we *like* unhealthy things. If we didn't enjoy them we wouldn't do them. Sure sitting in front of my computer playing games all day isn't as healthy as going outside, but as a geek I like playing games, I don't want to have my computer shut off until I go for a walk. Even if Watson only provided polite reminders it will annoy people if they get reminder every ten minutes. For that matter people won't *want* to know how unhealthy that fast food is, because it will ruin their enjoyment when they inevitable eat it anyways.
Do you remember 'clippy' from word? The little paperclip everyone loved to hate! Watson could be the new clippy, only massively worse. Watson could be what would happen if scrappy doo and whesly crusher had a gay love-child raised by jar jar binks and trained by clippy! (I would call rule 34 on the first part of that statement but I'm already running close to geek critical mass already so best to leave well enough alone).
If done wrong customers could be complaining or leaving their insurance to simply never have to interact with Watson ever again. In fact this is a *very* likely outcome, time and time again we have seen situations where people will complain if reminded of their own faults, even if it's part of a system to help them. Given the years of HCI study and disasters it almost seems guaranteed to be the case unless Watson is scaled back to only do 911 calls unless people explicitly activate other features; at which point he is not saving the insurance company much money because he is not preventing unhealthy habits.
**Why did you break down my door? No I'm not dying I'm fine, I just took off my life alert for a shower! I'm not going to pay for that ambulance!**
If Watson is going to call 911 then there will be false alarms, any program has some degree of false positives. But given the difficulty of detecting actual issues based off of the sort of detection tools we currently have available false alarms will be somewhat common.
This would be an annoyance to the one with paramedics beating down their door, but that's not the worse of it. If your calling ambulances your taking those ambulances away from the hospital. If someone else gets injured while the ambulance is at my house because I accidentally slept with my lead-lined, monitor-wifi blocking, blanket they will not be ready to go save someone who actually needs their help. People could die from these false alarms!
To give a comparison look at home security systems. These systems have a massive false alarm rating, more then 90% of their alarms are false alarms. So many in fact that police generally do not prioritize them and only send police officers over to a house if the officer has absolutely *nothing* else he could be handling instead (meaning when they do arrive it's often late enough that they couldn't have helped anyways, the cops aren't using sirens or speeding to get to your presumed false alarm). Some police districts refuse to even deal with home security providers any more, it was costing too much in taking their leads and so rarely helping.
However, cops, while still important, are far less likely to be needed at a life or death situation this very moment as an ambulance is. distracting them is much more likely to hurt someone else; or have them simply ignore your alarms.
**My mother slowly died of a heart attack and Watson did nothing**
The other PR nightmare side of the above situation. If you try to avoid false alarms you likely end up letting people die who you could have otherwise helped.
**At least I feel better about the NSA spying on me compared to Watson**
This was already mentioned, but this is a massive privacy issue here. People will be up in arms almost immediately. Watson would have to collect far more information then the NSA confessed to be collecting with it's metadata, and you saw how people responded to them. The public is very sensitive about privacy concerns right now, even about relatively minor issues. The degree of information collection would likely offend quite a few and cause a political backfire forcing Watson to be scaled back of disabled.
In fact people would start to demand whatever systems Watson used to collect data were disabled so no one *else* could collect data like Watson did, which could be harmful if they are insisting on disabling important safety features out of fear of spying after people exaggerated the threat of Watson.
Imagine someone disabling the equivalent of their life alert pendent because they kept hearing conspiracy theorists claim that Watson used it to detect heart-rate so it could detect rather they were afraid, angry, or sexually excited. Most likely the monitoring system can't even do that, but people will claim it, others will believe it, and suddenly people are less protected health wise due to paranoia about privacy.
**Privacy 2, premium raising electric bogaloo**
Another common claim will be made that if Watson can watch your habits it can know who is healthy and who isn't and provide that to the insurance company. The insurance company could then use that to raise rates if they decide someone isn't getting enough exercise, is eating too much fast food, or otherwise is a health risk. This could cause people who are not generally as upset about data mining to be cautious or refuse to use Watson because their certain their premiums will go up.
**Save 10 dollars a month on your premium, for the low low cost of installing 10,000 dollars worth of monitoring equipment!**
people don't have equipment capable of monitoring them to this degree in their homes or offices, and even in the future it's unlikely they will have equipment like this for a long time; there limited advantage to them outside of this one specific edge case. This means your asking people to buy a bunch of equipment, install it, and maintain it just to be able to use Watson. Even if you presume a future where the equipment is cheap the hassle of getting it installed could be enough to make people decide it's not worth the effort. Adoption and use of Watson could die out because it's just not worth the effort.
I know you could argue that Watson is so useful people will take the time to install it, but you may give humans credit as being logically motivated when they aren't. The truth is most of us don't accept our own health as an issue (and those that do tend to excessively over stress on it), and we can be quite easily discouraged by even a little bit of effort.
Look at Betamax, it was in almost every way better then VHS. Yet the awesome Betamax died a said forgotten death. Why did that happen? Because originally it didn't allow 2 hours of recording at once. It totally *could*, but the original betamax taps were made smaller. That meant to watch a movie you had to get up and swap tapes mid way through, and no one wanted to do that. SO we settled for lower quality, more expensive, easier broken VHS because we didn't want to get up off the couch rather then just waiting for Betamax to start making the 2 hour tapes. That goes to show even a great product can fail over minor hassles making people not bother.
Of course the other reason VHS did so well is they allowed selling of pornography which was not allowed on betamax, and [porn is always the first adopter of new media](http://tvtropes.org/pmwiki/pmwiki.php/Main/TheRuleOfFirstAdopters). It's theorized this was a major issue for proliferation of VHS. So...if you can find a way that the monitoring equipment can also be used as part of some bizarre sexual kink you may have a chance :P
**My hacking cough can be detected by a Hacker**
Again, privacy concerns could make people afraid to use this system for fear that they will be hacked and their data shared.
However, hacking becomes a (slight) actual issue. Data sent through SSL is pretty secure and is no more a hacking concern then any of the other, far more life critical, electronic activities we have. However, to monitor our health there would likely have to be a number of wireless detectors available and running at all times, to collect data on us wherever we are and route the information through the internet. These wireless detectors may be more vulnerable to local hacking attempts, mostly because the people building them likely won't be thinking about the hacking issue and won't secure them as well as they should.
**Family of unsupervised boy who tried to fly by setting off gasoline soaked fireworks he tapping to shoes, before jumping off cliff suing Watson for not warning child of risk**
If Watson is suppose to be extending life of insurances individuals people are going to start taking this for granted, especially since your likely have to advertise this as a perk of your insurance to get increased enrollment. Once you do this people will expect Watson to protect them, no matter what.
Now any time someone get's hurt or does something idiotic they will point out that Watson should have protected them and it's a contract violation that he didn't. My fireworks example, while hyperbole, is actually not that unlikely to come up at some point, though the case would likely be instantly dismissed without cause.
However, other cases can come up. What if watson doesn't warn that combining two medications could have adverse affects? What if Watson fails t notice a subtle irregular heartbeat that could have warned someone of a health condition? What if someone doesn't speak to the doctor about that odd tingling in their arm because they figure if anything was wrong Watson would tell them, and then is shocked that Watson can't detect tingliness and thus didn't have any way to realize that there was a major health problem?
People will sue, liability issues will come up. These can be handled in court and with carefully warded contracts, not enough to singlehandedly destroy watson, but they will be a common occurrence that *will* add to expenses for the agency, expenses watson has to help them save to even break even.
Okay so now lets get to your actual question, what issues could come out of the stated objectives. These are the less likely issues in my mind, all the above seem quite a bit more probably (except maybe the hacking one). However here are more likely issues with bad objectives, presuming a non sapient but well written weak AI. Lets look at the sort of likely programming mistakes that could come out of it's objectives.
**ConflictingObjectivesException: 'extend membership' conflicts with objective 'cut expenses'**
aka
**We went bankrupt in the first week because we payed all our money to pay for a machine to keep one 120 year old man breathing for 5 more minutes**
This is directly related to the above rant, but objectives as they are stated don't work. People buy insurance for payouts, if your cutting payouts your going to make people not want to buy your insurance. There are tricks you can do, mostly social engineering and quoting manipulative statistics, to help cut payouts while *lowering* lost customers, but ultimately these two are partially exclusive. Thus you need to better articulate importance, how many customers can I lose per thousands of dollars of payout I cut, how many more payouts can I make if it increases enrollment.
Similarly preserving lives is likely to to lead to making more payments, for a similar conflict.
Frankly a far *far* more extensive set of requirements, prioritization between exclusive requirements etc is required to be implemented.
Lets assume that a programmer set down and wrote such through requirements designed to emulate the general concept of the above...
**We were saving lives and had great enrollment until we ran out of money**
Even if write more detailed requirements you still need to set priority levels on them. If you pick poor priority, for instance you value enrollment numbers too high and minimizing payouts too low, your still have a problem. A human being is still making these prioritization decisions and could make bad ones. Though really this is a moot point, because the requirements as written have more significant issues...
**Sign up for new WatsonCare lite insurance, only 99 cents a decade!**
I lied above, your two objectives, increase subscriptions and decrease payouts, aren't actually mutually exclusive if read literally. There is a way I can get lots of people to sign up without paying out often, just make the cost of signing up trivial enough. If Watson offered some nearly free, or fully free, insurance then it would be worth enrolling for even if it rarely made payments, because if cost nothing then any payments you get are a net gain.
This obviously means that the insurance company is loosing out, because even though they pay out 1/3 of the time compared to their other policies if they still aren't taking in nearly enough in insurance premiums to cover those payouts they do make.
Or there is the other solution...
\*\*The Watson lotto-surance is now up to $500,000! sign up today. The lucky hospitalized winner could be you!\*
The objectives only stated that few payments had to be made, not that payment amounts had to be kept low. One solution is to make fewer payments, but drastically increase the amount payed out when one of those payments are made. From a purely reasonable point of view if I can sign up for an insurance that is 5% less likely to make a payment on a claim, but pays me twice as much when it does, it is optimal for me to do so because odds are I'll get more from the insurance on average. Thus I'm encouraged to sign up for this program even as Watson has lowered it's payouts.
In fact it's worse then that, because the scary thing is I could almost see this idea working. People are quite irrational with their money, done right one could probably tempt some individuals into a lottery style insurance by bragging about they high payments even if they end up paying less money out in total...no one suggest this to insurance agents!!!
Now one may question why this and the previous example don't fall into my "not giving AI enough credit" rant above, but there is an important difference. I'm now assuming a less sophisticated AI, which could still fall into these sort of solutions with a genetic algorithm style approach which simply tried possible outcomes until these turned out to work. Such a less advanced AI is more prone to mistakes in objectives resulting in odd results. However, more then that, these are mistakes I can see a programmer make!
The problem to these mistakes is that the programmer didn't actually state his real objectives. He picked specific details that usually lead to his desired outcome and presumed if those criteria were met his outcome would occur; this is a very common logical mistake I have seen in plenty of programs. The truth is that the insurance agency's real goal is to save money, possibly in an ethical way that also protects lives, but as a corporation saving money is still high on their priority list. They assumed more people enrolled while paying out fewer grants meant more money coming in and less going out and thus a net savings, but that isn't always the case. They should not have the stated objectives, and instead have an objective of "maximize profits" combined with whatever appropriate ethics objectives ensure it's done in a way they can live with. They should not specify the exact method of making money is done. It may be that increasing payouts, but also insurance premiums, to cater to certain high-income folks results in more income, even if it lowers net enrollment and thus violates both the stated goals. *this* is a believable multiprogramming of objectives, not a flaw in how a computer interprets ambiguous objectives, but religiously written objectives (presuming they were more rigors to clear up that ObjectiveConflictError) that simply were poorly chosen objectives.
Of course even if we redefine our objectives to be help the company profit while being moral and preserving lives we could still have issues...
\*Sign up today and one of our staff of watson-cares doctors will move in down the street to service your every boo boo!\*\*
If you employee enough people and offer enough non-payout benefits your insurance can be desirable even with fewer payouts, because of the other perks. of course it may turn out those other perks an unfathomably large amount of money to maintain, bankrupting the company in a few months, but hey, you never said anything about cost of employees.
Yes I'm assuming we redefined our objectives to conserving money, yes I still consider this a very plausible issue (well okay the above is hyperbole, but similar issues are likely). You see our non-hard AI can only consider variables it's programmed to know how to handle. If I forgot to write an algorithm to calculate the cost of employment of a new policy then the AI will *never* consider this, no matter how hard it's run, because it's not actually sapient. It needs me to define what variables it should consider ahead of time.
Sure I will likely have a CalculateStaffSalaries() algorithm, that's pretty obvious. but will I have a calculateHROverhead() algorithm, which considers the extra expense for managing the extra staff? will I have a updateSalaryToAnticipatedMarketDemand() method, which recognizes that employing so many doctors will mean there are fewer doctors out there, and thus the remaining doctors will ask for higher salaries and eventually I'll have artificial inflated the doctors salary to an unplayable high degree, or will my program still assume doctor salaries are the same as they were when it started running? What if I do write my updateSalary() method, but my understanding of economic supply and demand isn't perfect because I'm not an economist, and so I get my math wrong and don't anticipate the salary inflation accurately? for that matter what if I emulate all our economic knowledge perfectly, the market may still become inflated because economics are not able to reliable predict market influences that well.
In short, it's quite possible that the company still goes bankrupt because the AI wasn't able to anticipate expenses or costs.
**I would have gotten away with it too, if it wasn't for you meddling kids and your smallpox-ridden dog!**
What if the algorithm is wonderfully written to consider every variable and equation known to man and after massive number crunching it comes up with a payout scheme designed to save the insurance agency the most money by offering lass payouts for the likely issues but offering very tempting payouts for unlikely things. This would be a great trick, tempt people to sign up because it looks great without having to pay much, Your computerized munchkin has perfectly min-maxed your system.
And then the supposedly obliterated small pox turns out to have been incubating somewhere and a breakout occurs. Everyone calls their insurance agency and it turns out our policy offered payout 40 times as high as our usual for anyone that caught small pox, because we took the "Smallpox Bankruptcy" flaw"to help pay for that "conveniently 'misfiled' claim" perk. The bane of every min-maxer, you must have accidentally upset the GM because today's encounter hits all all your unlikely flaws.
This is a hyperbole example, but the issue is not as minor or ignorable as you may imagine. We don't yet have the ability to predict the future, which means even the best AI will be unable to predict potential outcomes. This means there is always a chance of bad luck leading to an unplanned for outcome that ends badly for our AI driven company.
But the problem is a little worse then this in a way. Unlike with humans a computer *will* try to min-max fully, if I didn't write special code to avoid it the program will pick the situation that gives the best average case, even if it means creating a situation where bad luck doesn't just cause the company money, but completely bankrupt it. It's worried about the average case only. Since it can't predict everything it thus may choose to create a policy that has a 20% of making the company go bankrupt if the *average* case makes the most money.
However, people aren't interested in average case, we generally would prefer to be more cautious here. If I'm CEO of WatsonCorp I would rather settle for 'only' 600,000 annual salary (the actual average for CEO of healthcare, thank you google) then take a 10% chance of the being fired after my company goes bankrupt to in order to have a 90% chance of making 660,000 salary. The extra profit won't help me nearly as much as unemployment will hurt me and I don't want to take that risk.
In programming world we have learned to be very aware of this. When we inspect algorithms now we discuss the big O of a program, which is (sort of) how fast it runs **in the worst case**, how do things happen when everything goes wrong. This is because we have learned that when I run a program every day for years that 'unlikely' worse case scenario ends up coming up pretty often, and it's not uncommon for the worst case to be disproportionately bad. Well...that and it's not uncommon for either malicious people to intentional design a worst case scenario or for the worst case scenario to be far more likely then random chance would expect. Good programmers would thus write an AI with an understanding of what worst-case scenario is acceptable...but this is an easy thing to forget to add. If you don't there is a very decent chance that your end up with a small, but disastrous, potential weakness in whatever solution your AI creates.
**Next up on Scandal News, we learn Watson-international refuse life saving procedure for chronically on welfare, Their uncanny-valley ridden robotic overlord explains chronic illness required too many payments for one life, new cost cutting measures allow paying for 10 times as many breast enhancements**
Closest to the evil-AI doomsday scenario were likely to get, and also a bit more questionable, to presume an AI would be sophisticated to calculate this without human involvement. However, this scenario could be eached by soft AI through genetic algorithm or certain well written inference engine and calculation processes.
the idea is simple, chronically ill require constant payouts over a long length of time, and thus can be quite expensive to support. However, refusing to pay for one life saving surgery could remove all future payments for that individual-you know, him being dead and all, saving a significant amount of money. A genetic algorithm approach may notice that not paying for some surgery results in far less money payed out on average without the AI realizing that's because people died without the surgery for instance; the AI only knows saying NO to this surgery means less money payed and that's all it's calculating.
This actually is a result in flaws of the above examples. It's a mis-tunning of priority levels, the AI not valuing life preservation as high as it should have compared to cost cutting. However, this doesn't have to be life saving operations. Perhaps not paying for certain surgery results in someone going into a vegetative state and ultimately costing less to provide for that way. It could be that other moral standards, beyond lives served, are required. For instance a "treat everyone equally" standard may avoid intentional infractions upon certain categories of people which would lead to outrage if learned otherwise.
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The human race has colonized the solar system with permanent settlements on all of the inner planets and outposts beyond. Vast space stations pepper the voids between orbits and massive mining/refining facilities stand vigil along the frontier. Interplanetary travel is routine and 25 Billion prosperous humans live within Sol’s gravity well. But not a single human lives beyond our sun’s reach.
FTL is still an elusive dream. We have all the energy we could ever use and have complete mastery over biology and conventional physics, but no miracle solution has been found for getting to other stars. We are still vulnerable and can become extinct from anything that can take out our civilization’s only sun.
This vulnerability troubles many, so after much debate, we decide to solve the problem. With nothing more than slower-than-light travel, humanity will reach for the stars.
We have chosen a large Kuiper belt object as the basis for both our ship and its launcher. The idea is to divide the asteroid into two pieces, one three times as large as the other. The smaller portion will be hollowed out to become the ship’s hull and the larger, the counterweight, will be sacrificed during the launch to help the ship obtain solar escape velocity.
Today’s question is about the launching process. Once the ship is ready and has been firmly reattached to the counterweight, the pair will be pushed out of orbit and dropped on a very deep slope into our sun’s gravity well. Picking up speed during the inbound journey, the pair will miss the sun by a barely survivable margin and then race past on its way out of our solar system. At the optimal moment, the ship and counterweight will detach from each other and the ship will push itself forward using rockets, nuclear explosives and a rail gun-type launcher which is secured to the counterweight. All of that force will push back against the counterweight, stealing its inertia and springing the ship out of our system with enough speed to escape Sol’s gravity well completely.
The counterweight will then fall back sun-ward to either be salvaged before or slagged when it plummets into the sun.
So the question… What percentage of light-speed would a launch technique like this imbue upon the ship portion of the asteroid, after it left our gravity well? Assuming the original asteroid was similar to MakeMake: 5x10^21 kg with a starting point for its sun-dive of 50 AU. Also assume that the rockets, nukes and rail gun successfully transfer 90% of the inertia from the counterweight to the ship.
Also, am I missing anything? Are there other ways to add speed to such a massive ship during its launch?
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Physics time!
You split the rock into two parts, one is 3 times larger in mass than the other. You state "Also assume that the rockets, nukes and rail gun successfully transfer 90% of the inertia from the counterweight to the ship." This doesn't make much sense, because inertia can't be transferred, but I'm presuming you meant to say momentum. So here's what we can say:
* We have a large rock, with momentum $p$ and mass $m$, which undergoes an event splitting it in two.
* After the breakup, the smaller rock, with mass $0.25m$ has a momentum of $0.9p$
* How fast is the smaller rock traveling after the breakup, with respect to the original velocity.
Because the smaller rock has a momentum of $0.9p$ and mass $0.25m$, we can write the momentum equation $0.9p=0.25m\cdot v^\prime$, where $v^\prime$ is the velocity of the small rock after the breakup. Rearranging slightly, that gives us $p=\frac{0.25}{0.9}m\cdot v^\prime$. Since the original rock had a momentum equation $p=m\cdot v$, we can combine those equations to:
$$m\cdot v = \frac{0.25}{0.9}m\cdot v^\prime$$
$$v^\prime = \frac{0.9}{0.25}v = 3.6v $$
So this says our railgun trick increases our velocity to 3.6x that of the velocity of the rock before we fire them.
Now let's take a moment and realize just how bad news this is. In the span of a nuke/railgun event, we need to provide an acceleration to reach 3.6x faster than we got to by accelerating from 50AU out from the sun. This says the *vast* majority of the speed we achieved was from the railgun/nuke firing. In fact we'd probably have done just fine by using those railguns without the solar plunge. Needless to say, the accelerations here are going to be beyond mind blowing. Maybe should I say less "mind boggling" and more "splattering bloody bits of brain on the bulkhead behind you." Even genetically engineered humans in liquid suspension aren't going to enjoy this. In fact, I'm not certain if there is a material in existence that will survive!
That being said, the slingshot around the sun is a tricky one. I had to do some research on gravity assist for this question, but it looks like gravity assists around the sun are not all that effective. Here's the deal, as best as I understand it when explained by others. Gravity assist starts to make sense once you think about a particular coordinate system you're interested in. For example, for most interplanetary jumps, it makes sense to have the coordinate system fixed on the center of gravity of the solar system, which is rather close to the center of mass of the sun. If you have an object moving in this frame, such as Neptune, you can plan your orbit to rob some of its momentum. In any coordinate system, the trajectory will look the same, but in the one we cared about at the time, that trajectory happens to look like we stole momentum.
In the case of the sun, it doesn't have very much velocity with respect to the center of mass of the solar system, so you can't really use it effectively for a gravity assist (except perhaps by taking a dip into the solar core...). Some mentioned that there might be some value in a a gravity assist in a galactic coordinate system, where the sun has a velocity of 220km/s, but if we do that, we find our asteroid is *also* moving at roughly that same velocity. An interstellar traveler might use our sun as a slingshot, but you can't use it on your home turf! *Frustrating!*
There is a related gravity assist called the Oberth maneuver, where you do a burn while close to a large mass. The effect appears to be a multiplication factor on the specific energy of the burn by $\sqrt{1+\frac{2V\_{esc}}{\Delta V}}$ This effect becomes smaller as your attempted delta-v becomes larger. $V\_{esc}$, the escape velocity, is 617.5km/s for the sun, which is rather fast, but piddly when put in "fraction of the speed of light" terms: $0.00205c$. The faster you get with respect to that, the less useful Oberth maneuvers are.
So we are left with the situation we had before: a giant railgun/nuke, an asteroid, and a few space engineers who had too much to drink the night before and thought it'd be a great prank to throw a spitball at Alpha Centauri!
Just for fun, let's say a nuke takes about a second to go off. They look roughly mushroom shaped 0.25s after firing, so a second seems reasonable for fun mathematics. Let's say you want to reach 0.01c, or 2,997,925 m/s. Trivially we can see that is an average acceleration of 2,997,925 m/s^2, or 305598 gees. That's twice the acceleration of a 9mm bullet in the barrel of a gun. It's three times the acceleration of an ultracentrifuge, a device designed to separate out samples by molecular mass.
It's 30 times more than the acceleration of a [Mantis Shrimp punch](http://theoatmeal.com/comics/mantis_shrimp).
Ow.
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Somewhat related to [this](https://worldbuilding.stackexchange.com/questions/10102/how-would-multi-race-humanoid-evolution-happen). I've already decided that both orcs and humans are subspecies of homo sapiens (homo sapiens praepotens and homo sapiens perpessio, respectively, because both species are abundant and it would be rude to call one of them the "real" homo sapiens). I have fauns/satyr type beings instead of elves, though, because I dislike the idea of an immortal species.
Unlike fauns and satyrs of myth, these guys have about the same hair distribution as humans (i.e., no goat legs). I'd also like to give them antlers instead of horns – that is, they'd be cast off annually, able to be cut off without bleeding to death. Their stance is digitigrade, with solid hooves, as in a horse.
Obviously, having hooves, they're not as closely related as humans and orcs are, and are almost definitely not in the "homo" category. Where might a species like this plausibly fit on a taxonomic tree? And, on a similar note, *can* I plausibly give my satyrs "horns"?
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This is perhaps not exactly the answer you are looking for, but I would suggest you consider the possibility of **having the satyrs coevolve with your homids, but start from some other species.** Humans evolved from apes; why can't your satyrs start from hooved animals instead? You already mention horses in your question; is there some specific reason why your satyrs can't have evolved from horses?
Consider giraffes, which evolved really long necks to reach high into the trees (where there was little competition for the food). Your satyrs could take a different evolutionary path and evolve the ability to stand reasonably stable on their hind legs to do much the same thing. Like long necks, this would also give them the advantage of a better view of the terrain, which helps spot predators early. It also has the benefit that it doesn't require, say, a comparatively much stronger heart to pump the blood all the way up to the head, because the head is much closer in terms of height: less work needed to fight gravity.
Your satyrs, then, would fit into the taxonomy with horses in much the same way humans in our world fit into the taxonomy with apes.
Give it enough time and a good enough selection pressure, and one could even argue that it could at least semi-plausibly actually have happened that way!
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Just for fun, put them at the top of the tree, right next to homo sapiens. I would love to see the geneticist's faces when they compare blood samples from the fawns, satyrs and humans, and find no significant differences.
Your world has magic! Not all change has to be explained scientifically.
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In countless series of the world of science fiction we see something that we all accept as realistic but makes no sense. Holographic controls. We simply say that since it's the future that it makes sense. But the problem is that I see no way how this could work. If it was a classic hologram then our hands would simply block out the light, no input. If it was glass with button then there are no wires, no input.
How can I achieve (seemingly) holographic control boards using future technology?
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There are several ways to achieve this.
First, I'll point out that we can currently track people's hands in 3D to accept input from arbitrary presses on 3D locations in the air. See the [Leap Motion](https://www.leapmotion.com/product/desktop). I own one, it's rather incredible though not completely there yet.
As for adding a display to the spot you're pressing buttons in the air:
* Shine the light from different directions. There is no reason to have a single source that gets blocked by hands.
* Shine the light on the eyes directly. Google glass uses a similar concept. The light is focused in a way to make it appear as though the rendered object is out in front of you. This has the added benefit of being more secure since only the user can see the controls.
* With glass, you can't see the wires. Look at your touchscreen device, see any wires? No, you don't but there is a grid of them right in front of the display screen that makes up the capacitive input.
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Motion capture is this technology in a slightly different format. There are several different platforms which can track the position of the human body or parts, allowing you to interact with objects in the "virtual world".
"Data Gloves" were an early attempt at this, the gloves not only measured the position in space of your hands, but could also provide haptic feedback to give you a sensation of "touching" an object. Samuel mentions some of the new gaming platforms, which make things like the Wii look positively stone age. In the future, your room, work cubicle or cockpit might be lined with sensors that sense your body in fine grained detail, recording your position in space and time so you could be interacting in a virtual world. You would "see" the virtual world through technology like Google Glasses or even contact lenses. For team projects, the same virtual world or object could be sent to all team members, as well as their positions in space and time, allowing everyone to cooperatively "work" on a project.
Movie makers can be given some licence to show the external viewer the "screen" or object being manipulated, but for the true outside observer watching you, they would see you doing what looks like a bizarre dance without a partner, and have no visual cues as to what it was you were actually doing.
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Assume that a person is shielded by magic. The *only* thing this magic does is to keep air away from that person (ignore for now any consequences to said unfortunate individual). Aside from this, the magic can be ignored. This has the result that the person is encased in a sheath of empty space, about 2-1 inches thick. Nothing, including air pressure, is in this area.
**What would happen if someone put their hand in this sheath of empty space?** Based on what I know (and have seen in the movies), I believe some form of rupturing of the skin would take place, but I don't know how severe this would be. I also don't know if it would happen immediately, or if the hand could potentially be unharmed, at least for a time.
Along the same lines, **what would happen if an entire person was exposed to such an environment?**
*P.S. While the tag 'atmosphere' may not exactly be appropriate, there was an extreme lack of appropriate tags, and I figured those following 'atmosphere' would be able to answer the question.*
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**Obviously, this person will face nearly the same issues as someone in the vacuum of space.**
There have been several experiments and incidents where portions of (or entire) humans (and even more animals) are [exposed to a hard vacuum](https://en.wikipedia.org/wiki/Space_exposure), which is what you're describing.
The Wikipedia page describes the symptoms for being in space like this:
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> The key concerns for a human without protective clothing beyond Earth’s atmosphere are the following, listed roughly in the descending order of mortal significance: ebullism, hypoxia, hypocapnia, decompression sickness, extreme temperature variations and cellular mutation and destruction from high energy photons and (sub-atomic) particles.
>
>
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Your situation is only slightly different in the items of least mortal significance are not a factor. The symptoms of highest mortal significance are still factors.
**[Ebullism](https://en.wikipedia.org/wiki/Ebullism)**
The formation of gas bubbles inside the fluids of the body. Think about opening a bottle of carbonated beverage, in a less dramatic way, something similar will happen to any exposed fluids in and on your body.
**[Hypoxia](https://en.wikipedia.org/wiki/Hypoxia_(medical))**
Also known as "I can't breathe!". You're no longer getting oxygen. This is an immediate problem. Everything in your body will be letting you know that you need to do something about this right now.
**[Hypocapnia](https://en.wikipedia.org/wiki/Hypocapnia)**
Less well known, but you can simulate it by hyperventilating. So may be known as "I breathed too much!". This is a reduction of carbon dioxide in your blood. This causes pins and needles, muscle cramps and tetany in the extremities, especially hands and feet.
**[Decompression Sickness](https://en.wikipedia.org/wiki/Decompression_sickness)**
Ah, the bends. It sounds like an affliction of someone who frequently drops things. In this case you may drop an arterial gas embolism into your brain and you will have a stroke. Which is less a whimsical name for a clumsy person and more of a you need help with the toilet now, if you're lucky.
These symptoms could be worsened depending on the speed at which the pressure drops around the target (and vice versa). But in general it would be an effective way to kill someone in a few minutes. Incidentally your exposed subject will likely feel very warm, as vacuum is an excellent insulator. Additionally they will be flushing as their capillaries and blood vessels near the surface of the skin expand (some small ones may break, but no one is going to explode).
The most important part to remember about vacuum is that vacuum doesn't suck. When there is a low or zero pressure things *blow* into them. Humans don't explode in space because our bodies aren't an explosion being held in by air pressure. Did you ever wonder how the tires on the space shuttle don't explode in space? It's because moving them from Earth atmosphere to vacuum is equivalent to putting 14.7 psi more air pressure into them, an insignificant amount compared to the 340 psi they're already inflated with.
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Surprisingly not that much. Most of the really "nasty" things about vacuums take time. For example, it takes 14 seconds to lose consciousness in a vacuum, and several minutes to start seeing freezing effects. None of the exotic effects are going to occur until much longer.
His hand would most likely turn a little purple from the blood flowing into it. Maybe a few broken capillaries.
However, I'd like to point out that the rules of physics probably still apply. His hand is in vacuum, and his body is not. This means he is going to get pulled into the vacuum for the same reason your hand gets sucks onto the vacuum cleaner when you put your hand over the opening.
A hard vacuum is roughly 14psi. The cross sectional area of a human wrist is roughly 5ish square inches, so he would feel like he has a 70 pound weight dragging his arm into the vacuum!
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Most of the effects have been well described by Samuel, so I won't reiterate them. The really important thing to look for is how quickly the person is exposed to a vacuum and if they have a chance to be prepared. Perhaps strangely, a person suddenly flung into a vacuum with no warning might do a bit better, since they would probably have their mouth open in surprise and the air would quickly evacuate their lungs at about the same rate the air pressure is dropping around them. A person who thinks they are prepared and tries to hold their breaths had a good possibility of suffering severe damage to their lungs due to the pressure differential between the air in the lungs and the vacuum outside. (Stanley Kubrick, who was usually quite meticulous about detail, did miss this in the scene in "2001, A Space Odyssey", where David Bowman voluntarily ejects from the work pod into the emergency airlock without his helmet. Although it would be quite possible to survive being ejected into the airlock, the actor is visibly taking a deep breath before triggering the hatch, when he should hyperventilate to flood his body with oxygen, then empty his lungs before hitting the switch).
An unprepared person would rapidly black out (even if they did evacuate their lungs in surprise), while a well schooled and trained astronaut *might* be able to extend his survival time by hyperventilation prior to exposure to the vacuum (we are talking from several more seconds to perhaps a minute tops. Your astronaut hero isn't going to take a leisurely EVA across the spaceship without a helmet). Since your example is magic rather than physics, similar rules would apply (including the damage to your lungs attempting to hold in your breath), but unlike the situation with HAL, there is no airlock in easy reach for your hero.
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As Cort Ammon said you would probably get sucked into the vacuum and that would do the most damage. If the vacuum has low enough pressure the blood in your hand (and body) would start to boil. You can guess that would be a bad thing but other than your blood in a gas form, torn ligament (from folding like a deck chair when you get sucked into the vacuum), exploded lungs, hundreds of broken capillaries and certain death, you'd be fine!
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People on my planet can use magic in some way. Some can only throw sparks from their fingers and some can cast thunders, the same with fire, water, air and arcane (telekinesis, teleportation etc).
Technology is Earth-like medieval times. People who are gifted with great power are the ones who rule the countries and similar amount of magical power is passed on to offspring, so two poor-gifted ones can't have children with great power. This resembles feudal system - peasants stay peasants, nobles stay nobles, peasants work for nobles.
Magic is used in a battlefield but has not entirely dominated it. The most powerful are known for instanly killing 100 people in the battle with one spell, yet are left tired (like sprinting 200m is for a trained soldier - not exhausting, but still feeling the run). There are units who use only magic, but regular soldiers might use magic of their own during the fight (like swinging the sword with right hand and casting a spell in the other).
One day the planet was attacked from space by an alien species that posses technology similar to ours with some differences like FTL, advanced AI (but not self-aware). Armements are roughly similar to ours (no lasers, no death-rays, slightly upgraded bullet-based guns).
What could be the possible outcome of such a war? Do you think magic world could fend of the attackers, or eventually the aliens would prevail?
More info (includes edits):
* Medieval soldiers are used to fighting in a battlefield, while the alient species use modern day tactics.
* Alien species have no idea about magic and see it for the first time.
* Wizards can combine spells together to make one but more powerful.
* Alien invaders kill everything that moves, their true motives are unknown (there's an assumption they want to kill significant amount of people and enslave the ones that are left alive)
* Wizards can create a magical shield, which defends the caster or the place/person caster picks, but it has some durability, just like real shields + it's tiring for the caster to maintain the shield on. Combining these spells could create a city-big shield.
* Weather conditions can't change magical projectiles's trajectory
* Magical projectiles will travel any given distance unless encountering an object on it's way
* Aliens don't use AI robots instead of organic soldiers.
* Telepathy is a valid form of communication between natives.
EDIT: Let's assume a scenario:
Aliens already attacked the planet, causing some damage. They sent two Star Destroyer-like ships, the rest of the fleet is still on hold in a further orbit (not relevant right now). In one of the countries the most powerful wizards in each major city combined their spells and attacked the ships from the ground completely destroying one of them and dealing some heavy damage to the other one, that it has to retreat. How would aliens possibly react to such a counter attack?
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In response to my question about the aliens' goals in approaching the planet, you stated that "Alien invaders kill everything that moves." This suggests they're only interested in the planet's resources or they intend to terraform the world for their own purposes. In either case, they don't care about the death toll of the native populations. Since they have FTL capability, there's also a chance that they can't recognize the native populations as intelligent (there's a discussion on identifying intelligent creatures [here](https://worldbuilding.stackexchange.com/questions/5124/how-could-humans-recognize-another-species-as-sentient-intelligent)).
Because these aliens don't care about the body count and they may not recognize the natives as intelligent, there's one plausible outcome to this scenario that exceeds all others: total annihilation. The first order of business is to remove the pesky native populace, since they're in the way, and the best way to do that is with some form of [kinetic bombardment](https://en.wikipedia.org/wiki/Kinetic_bombardment) (drop a lump of metal from space).
In short, the aliens win when they arrive at the planet, before the natives even know they've been selected for extermination.
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I'm gonna take a moment to try and wrestle the problem by redefining and talking through it a little bit.
Also, please forgive my typos, since this is long.
## The Attackers:
They have FTL, and comparable armament to us. To get my head around it, I'm thinking BSG, maybe Cylons. They had an extremely similar goal when they attacked the Colonies - kill *almost* everyone. Even if they want to enslave a portion of the population, they still have a very low regard to the lives of their victims, even outside of the theater of war.
They will start with a nuclear / orbital bombardment, period. Even if they don't have nukes, they will nudge a passing asteroid or few (or hundreds if they have time). They won't kill every person, but they will definitely thin the urban populations and scatter the industry of the planet.
After they feel they have softened their opponent, then they will form an aerial assault. This is will look like the Gulf Wars, Korea, Vietnam, or the Luftwaffe. They will fly around dropping bombs on things that look industrial or important in some way. They may even re-bomb thing they already bombed, simply because it still looked too intact from 35,000 feet. They will probably get there first taste of magic at this point, but most caster will have trouble hitting something moving at super-sonic speeds.
Once everything that looked like a city, town, or fortress was leveled, they would send in the troops. The troops would need to capture more people than kill, if only the get the scoop on where all the other survivors went. The Aliens would start at the major cities, since that's where survivors would be wandering around, and then fan out from "green zone" like base-camps, securing larger and larger chunks of land mass until there was nothing left.
## The Defenders:
At first, they may not know why death and destruction are falling from the sky. Maybe they have some seer stones or clairvoyancy that alerts them to the Alien threat. At this point though, they gonna have some hard times doing anything about it. Some cities can get shielded, but there's a ton more asteroids / plutonium available then high-level caster, at least with medieval population densities. Plus, it only takes one guy or shift to mess up, and the whole city becomes a crater, narrowing your talent pool. Eventually the noble class would be driven underground.
The peasant class would own the planet now, although they wont have the same talents, they may still have some hope.
The aerial bombardments would be difficult to defend against, since they will actively hunt and report large bands of survivors. The Aliens will especially target any occurrences of magical resistance, and may even withdrawal to more heavy ordinance on the area if they lose any aerial assets. The peasants would become nomadic. However, like genetics, there's a lot of latent and dormant phenotype stuff *(Dammit Jim, I'm an Engineer, not a Biologist!)* that could be brought out by the stress of the situation. Even though it is stated that there wont be champions, It is extremely difficult for me to imagine this not being the case. What of all the Jon Snows and bastard babies who don't think they have greatness, right up until they do?
Once the troops land, its gonna get hairy. I think that two star-destroyers compliment of soldiers, while being quite a large force, cannot effectively hold a planets worth of land mass, so we will be a ton of guerrilla warfare and rebel bases spring up and going down in a nomadic fashion.
Captured defenders could easily work from the inside, doing sabotage and telepathically sending information to the resistance. The Aliens would be wise to get some sort of test devised, such that they can execute anyone with magical talent before letting them into the green zones.
## Outcome:
Now we have a ground war.
If the defenders win, it is because the noble class effectively survives the initial bombings in enough number to be present and casting during the ground war **AND** they manage to capture Alien tech. Once they can level the playing field, probably in some Hamburger Hill / Imo Jima type battle, they can start their own aerial bombardment, nuke throwing, and other shenanigans.
If the Aliens are going to win, they will have need to take the casters out before the ground war, **AND** avoid over-extending their resources such that they can never be overrun by guerrilla fighters in such a way the advanced tech falls into the hands of the defenders.
## TL;dr:
It could go both ways, since magic can be a powerful equalizer in a ground war.
The Aliens will have to be damn sure they don't make any strategic missteps, because ( magic + being outnumbered ) could cause them to lose Advanced Technology to the defenders, and that instant that happens they will probably lose the war.
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Since there are not so many details on some questions I consider relevant, I will reply considering different scenarios. The question is really vast and difficult to answer, so I will try to reduce my thought in a nutshell:
# Range of magical attacks
## unlimited range
If the range of the magic is considered unlimited, then the aliens would have a really bad time invading the planet. If your enemies can systematically lightning-strike/set to fire/freeze your battleships while being kilometers away from the battlefield, you would be lost just the moment they enter the atmosphere. In that case, aliens should just switch tactics and go for less armored, faster battleships in order to retaliate effectively while avoiding being targeted like flies.
This scenario is more favourable to magic users, provided they have enough wizards to sustain a continuous attack on the alien menace (and provided that orbital bombing is not allowed or too advanced according to OP).
## long but not unlimited range
If magic can be cast with the same range of a modern rocket launcher, the odds should be equal for both factions - since the resources would be almost at the same level. Teleport vs. FTL, spaceships and heavy bombers vs. "rocket launched" fireballs, both infantries could be targeted from "artillery". In case orbital bombing is not allowed, this could be the most equilibrated scenario - provided that wizards can last long enough to endure the battles. The big difference here would be tactics, and whoever has the best tactics would prevail. This means that medieval people should update their thinking and start adopting "smarter" choices in order not to have their soldiers crippled from the enemy artillery.
## medium (a.k.a. modern assault rifle) range
In this specific case, the aliens could gain the upper hand quite easily, at least against most of the armies. If the aliens have starship/air support, it's likely that soldiers would be sufficiently weakened by continuous bombing or air raids to be disposed of quite easily from regular alien footsoldiers. Moreover, this scenario would prevent AA spells to work, thus letting the invaders the complete [air supremacy](https://en.wikipedia.org/wiki/Air_supremacy) and leaving your medieval society at the mercy of [carpet bombing](https://en.wikipedia.org/wiki/Carpet_bombing) and (why not?) nuking. Moreover, since the most powerful existent spell can "only" dispose of 100 men, a nuke killing thousands of people would definitely destroy every hope in the invaded population - much like a psychological effect - after which every king would probably try to negotiate the terms of the defeat.
Following this line, the only remaining tactics could be guerrilla, much like vietcong in Vietnam wars, but I wouldn't expect this to be enough to defeat the aliens.
## close range
See above. Even worse than medium range scenario.
# Defensive power of magic
If the magic is powerful enough to create city-sized shields (by, for example, unite altogether 100 magicians to keep it active), then carpet bombing would be a lesser problem and there would be chance for a more equilibrated fight.
A nuclear bomb could be however too much to sustain and the psychological effect of having a city completely destroyed by only one bomb despite the shields could completely cripple the fighting will of the population (the same psychological effect which caused Japan to surrender in WWII).
If this is not the case, the two factions could have a more equilibrated stand against each other.
# Reaction of the aliens to magic / reaction of the magicians to aliens
Okay, aliens have never encountered magic before - fine. But as long magic is not too superior in respect to their technology, they would simply analyze it and rationalize it as a different - yet unknown - technology and consider it no more and no less than an unconventional weapon. Only if magic proves to be *far more powerful* than their resources, then this would turn the tides - since the aliens would be facing something completely unexpected.
Just consider that, from the medieval population's point of view, [even aliens would use magic](http://www.brainyquote.com/quotes/quotes/a/arthurccl101182.html), quoting Arthur C. Clarke, and so they could perceive the aliens as deities using a magic *more powerful than theirs*. Obviously, even the other way around is possible - but as far as I got from the OP, the first scenario is more likely.
**EDIT** a new information has been added while I was writing my reply :D I will edit it if there are any relevant comments turning the tide of my answer ;)
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Assume a race of intelligent humanoids, possibly far more intelligent than human beings. They have evolved and survived using nothing but their intense intellect, developing new weapons and various armaments to fight off their enemies and nature whenever the opportunity presents itself. (I'll probably develop their society more in a separate question.)
But my question now is this: What would possibly happen to a society who developed technological achievements that far outstripped any cultural/spiritual growth? For instance, if they had developed robots to do the farming for them while still being in a feudal system? Would they destroy themselves? Or would they simply accelerate through their culture as each milestone was reached?
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I would argue that this has already happened. After world war 2, soldiers were coming home wounded but otherwise in good spirits. Men were reprising their roles in the workplace and many of the technological advances made in world war 2 in production gave America a boon.
Emphasis during world war 2 was hardly cultural concerns, and yet culture sprouted around America in the 50s. You saw burger joints and rock and roll become popular. Hollywood came back in full force and started producing new films.
Nobody in America was actively seeking to enrich American culture, and yet culture blossomed from technology. Japan too after world war 2 saw a huge technological and cultural boom, which would suggest that culture fills the container left by the cavities created through technological advance.
Now why is North Korea having difficulty with culture? Despite their technological advances, their culture remains stuck in the 1940s America. I think suppression of free speech and free expression is the antithesis of culture, and I don't think their culture will evolve until they begin to have free expression.
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I think there is some correlation between technology and culture, but not a strong one.
* Feudal systems are a web of obligations going up and down. They're often inheritable and hard to modify. Say the serfs are required to work three weeks each harvest season on the lord's fields, with the right to get a loaf of bread and a pint of beer for lunch. What happens if the lord wants to buy a GPS-controlled combine harvester? Can he make the serfs work in a factory instead, or would that be a breach of the mutual obligations?
* As technology marches on, factories get larger. The charcoal burner and the blacksmith got replaced by mines and blast furnaces. How do you get the investment capital for new factories in a feudal system? If the answer is *bankers* or *investors*, you're subverting the old political order.
On the other hand, North Korea is sliding rapidly back to a monarchy, and they have an embryonic space program.
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If a feudal alien had automation, their political system despite coming from a ancient times may stick around if the elite have a hand in it. Your species, if they're traditionalist or reactionary enough may try to suppress the creation of robots to plow in the fields because they may believe that robot made food is inferior to "food made from labor" for instance. I am not one to believe in a forward/backward system for culture, so I am looking at this question through the lens of "rapid change in tech from a feudal society to a 21st century, automation-centric society in <100 years".
For instance, let's say that the Aztecs suddenly invented telescopes, galleys and trains. These technologies in theory might make the Aztecs stop their tradition of human sacrifice, right? With advancement in scientific knowledge, *surely the aztecs must see how savage they're being*!
Not necessarily.
Cultural developments can be quite resistant to scientific revelations and usually it may take generations for "updating of the culture" (a term that is a bit soulless, I know) to occur, if ever. The aztecs, even if they had spaceships may well continue their human sacrifice. Why, they may start directly feeding people to the sun itself ritually using ceremonial spacecraft if their priests make the case for it.
In our world consider modern Islam in the middle east. Islamists in the arab world, despite "the modern world" are quite avid in trying to make god-made law the norm and enforced like secular law by the state (despite shariah being a muslim only obligation) and will continue to do so because they have no reason to suddenly renounce their beliefs. Why would they? Just because iPhones now are a thing? Saudi Arabia may have oil and make use of cars, but politically the only changes made are changes designed to keep the status quo despite development of technologies that undermine a state's control of information. Technology may influence culture, but it doesn't inexplicably change it and conservative cultures undoubtedly will do anything they can to limit the impact of technology on traditions. In the west liberalization and secular thought were concepts that came from the enlightenment and neoclassic periods, centuries before the industrial revolution or the world we live in. Mind that the concept of secularism or liberal democracy in the West hasn't eroded people's faith in Christianity in the slightest until much more recently. And that's only due to a cynical EU that had suffered massive amounts of death in the first part of the 20th century.
A alien species that is highly conservative, but rapid innovating technologically will likely adapt the technology to their culture instead of adapting their culture to new technology. Their technological development may incidentally reflect this, because technological developments are more influenced by culture than the other way around. Information Age technology for instance, being the product of a increased need to connect to a global society.
*italics = sarcasm*
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I suggest you to check problems happening since 1850's with some local inhabitants (Polynesia, New Zealand, Native Americans).
It seems to me there will be some cultural and health problems when technology and culture doesn't match.
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With each technological advance there may be people who are either positively or negatively influenced by it. When the civilizations of the Americas met the shockingly more advanced Europeans it was the cause for their almost complete annihilation.
While it can be said that the spanish flu had much more of a devastating impact on american civilizations than the spaniards themselves the very ability to find, navigate to, and settle on such distant and foreign land was a tribute to technology.
On the other hand European discovery of the Americas was beneficial to Europeans because technological advances were on their side. The number of people who spoke english, spanish, and portugese multiplied by several times. The same can be said for the land controlled by European powers and the number of followers of Christianity.
To relate this back to your original example those whom the technology did not favor (peasants) would have a much harder time surviving. However, those whom the technology does favor (nobles/landowners) would profit significantly from not having to pay the peasants nor for an army to protect them (but likely for an army to protect themselves from the revolting peasants).
A lot of peasants will likely die of starvation if they are unable to find new occupations. The children of the nobles will likely fight (and kill) for the right to be the heir of the now extremely powerful estate. The country, now in a state of economic and political turmoil might fall prey to foreign invasion.
While that did not happen during the post middle-age agricultural improvements in Europe, that is because the Industrial revolution introduced technology that provided occupations for all those peasants in factories.
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You mean like western society?
History answers this question.
During the middle ages, Europeans were generally quite savage and blood thirsty and had extremely poor hygiene.
But they managed to sail a boat to China and stole the secret of gun powder.
They then started mass production of cannons and muskets and colonised the entire world, whole heartedly compelled by the conviction that THEY were the enlightened ones, and that everyone else was lucky to be their slaves.
Other, more pacifistic or cooperative cultures stood no chance regardless of how culturally or spiritually advanced they may have been.
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Is it possible to have a planet where the atmosphere is mostly water vapor instead of mostly N + O2 with solid ground, so not a gas giant?
In the sense - how close to the center star(s) should it be for water not to exist in greater bodies of liquid water or in any solid state as a result of water freezing below 0 degrees?
What effect would that have on the other parts of the planet ?
The planet is thought of as earth sized +/- 10% (not set in stone).
Where the people lives in domes and have humidity extractors to produce water for fields and oxygen to breathe
Could it be possible for people to exit the dome and survive just for lets say 20-60 seconds (beyond the time you can hold your breath) or maybe even longer? If so what would the effects be (such as water in the lungs?)
*This is for a space-goth roleplaygame, roguetrader. So any mechanics or inventions can be advanced but should be kept in range of the universe as much as possible*
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If the planet were quite hot as @Formagella describes, say around 80°C, there likely would be no (constant) bodies of water and no steam. Whatever water the planet had, would mostly be in the atmosphere. If it's a lot of water, that means terribly bad storms, floods, F25 hurricanes, far worse than anything we see on Earth. If it's little water, it's going to be a very desolate place, mostly a barren, desert world.
The inhabitants *could* live in the mountainous regions, where the elevation reduces the temperature. Perhaps even above the "bad storms," on land or on airships. But there are some issues with these. It's hard to grow food at high elevations, mainly because it's too cold for us, but also because there's little flat, fertile soil. On airships, [hydroponics](http://en.wikipedia.org/wiki/Hydroponics) would probably be used to reduce weight.
Since the "air" is going to be thinner at high elevations, so too will the water vapor content. So the "extractors" must be bigger and use more power. It is possible to disassociate water (H2O) into H2 and O2 by [electrolysis](http://en.wikipedia.org/wiki/Electrolysis_of_water). That too takes a lot of power. The good news is, a planet near it's star gets LOTS of solar energy, so sunlight (solar panels) are a suitable choice.
If many humanoids were consuming the oxygen, then twice as much hydrogen (H**2**O) has to go somewhere. Some of it could go to the airships to keep them afloat, however let's not forget the [Hindenburg](http://en.wikipedia.org/wiki/LZ_129_Hindenburg)! On Earth, [free hydrogen](http://www.eoearth.org/view/article/153620/) doesn't exist in the air. It either rises through the atmosphere and out to space, or combines with other atoms to form compounds. So for instance, if your (storming) atmosphere had nitrogen in it, then NH3 (ammonia) could form from lightning strikes, which is quite caustic and hazardous even at low levels. (It's flammable at higher levels!) Now if the inhabitants were intelligent and responsible enough to see ammonia levels rising and compensate for it ("ammonia scrubbers"), then it wouldn't be an issue. But that's more solar panels, more equipment...
Longetivity-speaking, if this civilization had lived and prospered there for a very long time, then the water vapor levels will drop as they are slowly consuming the vapor. So there would be legends and stories about the "really bad storms of old", and contrast to how much calmer the weather is now... and an uneasiness about the future, where the vapor is gone.
Also consider that plants here need sunlight, water, and CO2 (carbon dioxide) to grow. Sunlight, water, and water vapor aren't enough. Plants also produce oxygen. So the fact that this world has no oxygen, seems to infer that it has no plants. So maybe it should have oxygen, just very little of it, because it isn't a lush green world like Earth. Perhaps the inhabitants are in a rush to grow as many plants as they can, before the water vapor runs out?
The [Earth](http://en.wikipedia.org/wiki/Earth) only has 0.039% carbon dioxide in the air, but that's enough to grow all of the plants on the entire planet. And scare the "climate-change" theorists half to death.
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from wikipedia, this is the maximum quantity of water in air at a given temperature, on earth, so since your planet is pretty similar it should apply too. Evaporation and condensation happen all the time but you can't add more water vapour without having an equal quantity precipitate.
As you can see, the temperature gets scorching hot long before you really get in the situation you describe.
At 100°C you can have 100% water of course, but that's steam and you said you didn't want that, you just want water vapour.
I think it's easier if you think of salt in a glass of water: you can keep dissolving salt in it, until it's saturated, then any salt you add will cause precipitation of undissolved salt on the bottom. The water will be quite salty, but it's still water.
Even if you put the temperature of the whole atmosphere at 40°C which is high and would already create a huge problem of thermal dissipation in the domes (if you're surrounded by something that is always at 40°C, keeping the dome cold would mean having some huge free power source and running a huge incredibly power-hungry AC system), at worst you're still getting the situation that you can encounter in a jungle during a particularly hot day. Which doesn't kill strong enough humans.
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Since an atmosphere of steam is out, then you have two possible conditions (that can happen here on Earth, so it will be at least possible on a local level on some of your planet).
1. The air is cold and moisture condenses, creating a thick fog or mist. So long as there is a warm zone to evaporate water and feed it into the air and a cold zone for it to condense, this cycle can go on indefinitely. This suggests a planet tidally locked to its primary, so the "hot pole" is the source of all the water vapour, and the misty section takes place on the cold, dark hemisphere. I would think this would be below the equatorial "twilight region" to ensure it is cool enough for the fog to form. The winds would be fairly constant as well on a tidally locked planet, so the fog would be fanned out fairly evenly across the condensation zone.
2. The air is very hot and you are in a coastal region, with the humidity at 100%. This isn't as visually exciting as a perpetual dense fog, but people living in places as diverse as Dubai and Costa Rica encounter this sort of climate. Unless there is a strong breeze, it is extremely uncomfortable and difficult to do any work, which explains why traditional culture in places like this often emphasized a siesta during the hottest part of the day, and work was done in the early morning and late evening hours. If we use our tidally locked planet again, then the region surrounding the "hot pole" will resemble this.
Your planet then could have two places where the atmosphere is pretty much saturated with water, a donut shaped ring of 100% humidity surrounding the "hot pole" and another one surrounding the "cold pole". There would be a fairly complex hydrological cycle needed to maintain the transportation of water from the hot pole to the cold pole and back again, otherwise, eventually the water will precipitate out on the cold side and the cold pole will be covered in miles deep glaciers, while the hot pole will be a desert hotter and drier than any known on Earth.
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Maybe, what you'd need if you wanted it livable would be a planet that was *hot*, as in radioactive, or very young, the ground would be hot enough that any water condensing and falling out would evaporate again almost immediately, while the atmosphere would stay relatively cold. The humidity on this world would be over 100% relative, you'd have constant pea-soup fog and condensation on every available surface including your lungs if you try to breath it for too long. As long as there was enough oxygen in the atmosphere and not too much in the way of sulfurous compounds boiled out of the ground, you could get away with being outside for a while before the heat and humidity got to you too badly, it would be a like trying to live [here](https://en.wikipedia.org/wiki/Cave_of_the_Crystals) over the longer term, only more unpleasant.
Edit: Sorry forgot to mention this planet has to either be 1. quite far from it's primary or 2. orbiting a small Red Dwarf star in order that the atmosphere doesn't get much heat from the primary and remains breathably cool.
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It looks like the planet must have been hot as said earlier. Phase diagram of water shows that at human-friendly temperatures it is possible to make a virtually 100% water vapor atmosphere if pressure is low. In this case, a pressure suit and pressurized habitat are necessary. If water remains gaseous at high pressures, it is too hot for humans and habitats must be cooled.
Here is the diagram. Pay attention to the area between the red lines.
<https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phase_diagram_of_water.svg>
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I would like to create a steampunk world which society has the following base structure:
* Power is pretty decentralized to cities or small areas containing some cities
* There should be no great wars (small conflicts between areas might be possible, but nothing that would deserve the name *war*)
I am trying to figure out, why the world stays (for at least some hundred years in that state). I am not a sociologist (or historian), but my real world assumption are the following:
People tend to build larger groups (than just cities or small areas) as countries or similar. I guess, they try to cover enough area to be able to do as much living requirements (husbandry, etc.) within their own border without the need to exchange with other countries?
Also at the borders of these areas people often tend to fight against each other (over ground or whatever [silly] reason).
What reasons could the people in my world have not to build that large power groups, but a way more decentralized world? It would still be okay if larger formal groups exist, as long as the real power is decentralized.
And what reason could prevent them from fighting each others at the border for a longer time.
Could you give me some plausible long term view on that society that has let to that stable situation or are my basic assumptions about what happens in the "real world" wrong?
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Ancient Greek City States had a system somewhat like this, but this was mostly due to the geography; the classical *Polis* was defined for the most part by a valley or generally small area of land which was fertile enough to support it. There were some exceptions which eventually overturned the concept, but more on that later.
The other thing which limited conflict in ancient Greece was the fact that 80% of the population were farmers. When threatened, they could all turn out together to defend the land (the origin of the classical Hoplite phalanx), but because they needed to tend their crops, an informal arrangement between all the Greeks was a battle was decided in a single day (so everyone left alive could go back to the farm).
This situation was unstable. The Spartans conquered and enslaved the people in the lands around (creating the Helots), and developed an aggressive warrior society to police the Helots and prevent a slave revolt. The Athenians expanded their sea borne trade to such an extent that they did not *need* to defend the lands of Arcadia to keep everyone fed, so restraints against the use of force began to fall away. What tipped the scales was the Persian Wars, where an outside power threatened all of Greece, and Greek military tactics, logistics and social organization evolved to meet a large scale threat, creating massive standing armies and fleets, which ambitious politicians used for their own venal ends once the Persians were defeated...
So for your organization to work, much of the population needs to be gainfully employed in such a fashion there is no real surplus to man a large standing army. Each city state should have evolved a set of common customs shared with all the others to limit the scale and scope of conflict, and there should be few exceptional areas where the system can expand outside of these limits, nor should there be an outside threat of such magnitude that they must band together and create standing armies and fleets.
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It sounds like you're describing polycentric law. Polycentric law is a legal structure in which providers of legal systems compete or overlap in a given jurisdiction, as opposed to monopolistic statutory law according to which there is a sole provider of law for each jurisdiction, i.e. modern nation states.
Ancient Ireland was like what you described for thousands of years. There were numerous clans called tuaths. Individual members were not bound to any one tuath. In fact members were free to, and often did secede from one tuath to join a competing tuath.
In contrast to many similarly functioning tribal societies (such as the lbos in West Africa), preconquest Ireland was not in any sense “primitive”: it was a highly complex society that was, for centuries, the most advanced, most scholarly, and most civilized in all of Western Europe.
As for war between tuath, the closest thing would be the occasional raid on livestock. When threatened with conquest by centrally commanded armies, the tuaths would form defense pacts. This way they even managed to defend themselves from conquest by the Romans. However, in the 17th century they were finally conquered by the English.
<http://en.wikipedia.org/wiki/Polycentric_law>
<https://markstoval.wordpress.com/2012/07/02/1000-years-of-irish-anarchy/>
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The trick is to downplay the importance of the borders.
It's not the borders that cause conflict, its the disagreement. Borders make it easy to create a society with strong disagreements along the outside edges. Create a more fluid society, and the disagreement along borders becomes more muted.
The trick is that its very common to define a boundary and say "everything within this boundary should have the same rules and beliefs." When you do that, now you have reason to create sharp disagreements along borders.
Another important trick is to put borders along hard to pass lines. If you just divide the map along straight lines (like much of the Western US), the borders are arbitrary. If the borders are more geographical (like Afganistan was before the Western world pushed it to define itself more "normally"), then the geography helps deal with the strain of disagreement because people don't want to cross the border.
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If you didn't mind all the involved groups sharing the philosophy that: "we don't truly own this", then that would greatly reduce tensions, and therefore, the likelihood of a war. What I mean by this is that all the separate collectives of people may USE the land, but they don't truly OWN that land. A major factor of human aggression is the perception that something of ours has been wrongfully taken from us - if there is no perception of "mine", then the chance of flaring tempers is reduced.
You may want to consider such things as the principles of non-possession in Satyagraha as put into practice by Gandhi.
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This sounds rather similar to 16th century Japan. After Ashikaga shogunate gradually lost power over the Daimyos (Local Warlords), who in their own right became more powerful than the Shogun could maintain control over. With little power over these powerful warlords and their armies, thigns were bound to go south. A Dynastic struggle between the Hosokawa and Yamana families spun out of control he entire country was fractured into a hundred fighting clans. This period was known as the Sengoku Jidai period, otherwise known as "The age of the country at war". This period lasted for over 100 (130) years. (Though, there were long bouts of stalemates)
Relating back to the subject as to why several factions would exist in an uneasy period for a long period of time, without all out war, can be drawn as such:
Assuming that these different factions are of around the same power, having one faction try to take over another would most likely not be in their highest interest. This is because if the faction rallied it's forces to conquer another, it would weaken it as a whole on the grander scale, since it would need a greater force to maintain control on the newly conquered land-if they even succeeded at doing so. As in the Sengoku Jidai, the lack of strong alliances between clans prevented a major power divide to draw out a major war, rather, hundreds of different factions all feuding against each other.
Instead, the conflicts would be on the small scale, between two or three clans, where a clan would only attempt conquest if they were much superior. Additionally, you have to realize that if one faction became too strong, it would be negated by the others allying against it. And if they did send their armies out to conquer other lands, they would allow for the other factions to take advantage of the unoccupied territory, a fate which the Takeda clan met at the hands of the Uesugi after their disastrous defeat at the battle of Nagashino.
Any conflicts between factions that draw out will most likely be waged through intrigue and diplomacy.
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1. Having very difficult to cross territory for reasons including:
* Dangerous terrain (Jungle, desert, mountain)
* Dangerous factions
* Dangerous Fauna (poisonous animals, heavy populated with predators)
For the reason that it has historically proven "impossible" for any large armies to cross them with out suffering casualties. Like Napoleons quest through the mountains with elephants that lost a huge percentage to the elements, or Alexander's death due to jungle illness. It could be seen as extremely unprofitable/logistically not worth it.
2. Social Systems
Maybe the population is too dependent economically on foreign trade and interaction, the diversity being something that they depend on and have found themselves niching.
Some slight alternatives to this might include:
* Culture of international travel and marriage
* Decentralized faction based identity (rather than nationalistic identity)
3. Alternative method of power grabbing
What if the general world population recognized power from a different direction?
* Only those who prove their \_\_\_\_ ability get to have authorship to land, social decision making, and trade deals. Competitions keep citizens happy and safe knowing that any "army" based faction will oppose the system put in place by international system giving power to individuals based off chosen capacity.
* A philosophical disgust with taking anything, instead using capital gains to outbid opponents. (I think the Ferengi from startrek were like this.)
4. There's no room for war with each other, because they are already at war with something else:
* Aliens
* Zombies
* Plagues that keep popping up and decimating cities
* Boredom
* Unequitable corporate policy
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Considering a distant future where mankind has spread and inhabits lots of star systems. Would there be a justification for inter-system trade or exchanges ? FTL travel may be considered, but with at a significant energy cost.
Most materials being available everywhere in most systems, and production capacity being likely to be roughly the same everywhere, interstellar travel seem of no use in this kind of setup. Any suggestion to make this more exciting ?
**Edit :** As the topic may interest other readers, I complete the question with some of the information I gathered.
This [Princeton paper](http://www.princeton.edu/~pkrugman/interstellar.pdf) (written by a to-be Nobel prize!) consider interstellar non-FTL travel and the return of interest calculation. Non-FTL implies that time flows differently depending whether or not you stay on a planet or you board the ship. A 10 year travel at 0.99995C will make on-ship time will appear 100 times slower : roughly 5 weeks. Interest rate will follow the same logic...
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# "Unique" Commodities
Sometimes you just want a unique thing. Consider, if you would, [Emmental Cheese](http://en.wikipedia.org/wiki/Emmental_cheese) (*Emmentaler Käse* for the german speakers). There are a few [certified areas](http://en.wikipedia.org/wiki/Geographical_indications_and_traditional_specialities_in_the_European_Union) of the world that actually produce Emmental Cheese. Every other cheeses, even if they are really similar, are simply not Emmental Cheese by virtue of where it was made. If you want "the real stuff," you need to go to the official places.
Perhaps there is a market on some planet for [Tauntauns](http://en.wikipedia.org/wiki/List_of_Star_Wars_creatures#Tauntaun) meat, but Tauntauns are not native to this planet and the planet is too warm for them, or the planet's local fauna love eating them so you cannot have a sustainable population. Someone will import them and there is your intergalactic/interplanetary economy. If there is a simple demand for something unique, someone will eventually supply the stuff.
There are some special instances where you need a particular bacterium or fungus, such as with bread. You may think [yeast](http://en.wikipedia.org/wiki/Baker%27s_yeast) is [yeast](http://en.wikipedia.org/wiki/Yeast), but that is not true. While each type of yeast could be capable of raising bread, there are some that are desired for their unique properties, which can only be made in a particular environment. Replicating such environments may not always be practical.
Even those people who buy yeast from San Francisco thinking they will make an authentic starter at home are deceived. The yeast will adapt to their kitchen's environment, making them the same as local yeast after the second batch of bread. (See "[Local Breads](https://rads.stackoverflow.com/amzn/click/com/0393050556)" from Daniel Leader.) So some things just need to come from the correct source.
# Some Economics
It may be cheaper to manufacture some item on one planet and then ship it another. For instance, it would be much easier (once some initial hurdles are overcome) to manufacture steel on Mars than on Earth, and send it to Earth. This is due to the huge resources available to do so on Mars. (The thing is as close as we're going to get to a giant iron ball!)
There is also the issue of specialization and [comparative advantage](http://en.wikipedia.org/wiki/Comparative_advantage). Maybe one planet or system specializes in a thing, and they simply make that thing better or cheaper than other systems. It could be more economical for other systems to ship that thing in in return for whatever they specialize in.
# Summary
You would trade between systems because:
1. That thing you want cannot be made in your system, due to biology/environments/regulations.
2. That thing you want is not worth the time and effort of making it in your system, because you specialized in something else.
...which seem to be the same reasons why globalization is a thing on Earth, but I fail to see reasons why these would not apply to a galactic-scale economy.
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Most authors who have interstellar trade simply make it work like current or medieval trade and ignore the details.
The big problem with realistic interstellar trade is the energy cost. It's certainly possible to have a star without heavier elements. Heavier elements come from previous stars that have died. So stars located away from other stars likely have fewer heavy materials (e.g. iron). The problem is that for the energy cost of bringing iron from another star system, you could transmute lighter elements into iron. Since power comes from fusion of light elements together, power's going to be available anywhere.
So what can be traded? Information (new discoveries, blueprints, schematics, movies, music, etc.). Unique items. This would be similar to medieval times. Although it was possible to ship food locally then. But this is consistent with shipping coffee, tea, spices, etc.
Note that you need FTL to make even that trade work. Trading via generation ships has several problems. First, they're slower than light, so you could have finished your information trade sooner by radio. Second, the exporter has to pay to create them but has no guarantee of a return (also a problem for radio, but less risky). Third, it's hard to motivate future generations by commercial promises made before they were born. So generation ships might bring things to trade, but they are unlikely to be built for the purpose of trading.
So you can have FTL trade similar to the medieval trade between Europe and China, expensive and only good for luxury goods. Given FTL, that seems reasonable. Ships would buy goods in one system and try to trade them in another.
If you really want trade more like modern trade, where we ship out of season vegetables from South America, then you'll probably have to handwave it. The closest to a realistic way to do this is folded space, where you take shortcuts. And even that requires space to be folded in the right way first. If you need to use energy to fold the space in the first place, it's probably a no go again.
The problem with comparative advantage here is that some things just aren't worth trading. If I'm only willing to pay 100 for something that costs 1000 to make, then you can't trade with me. Trading generally requires that shipping costs be less than the worth of the final item. To trade iron from Mars, we'd first have to justify the cost of shipping iron from Mars. Since iron is cheap and easily available on Earth, this seems difficult. It's also worth noting that the asteroid belt is going to be cheaper in energy terms. Less gravity trumps more distance.
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Raw materials may be available everywhere, but maybe the best FTL drives are built in the Aldebaran system, the best conventional thrusters are built around Barnard's Star, the asteroid mining equipment industries still concentrate in our solar system, and the best computers are built at Betelgeuse.
Note also that if a new invention is made in one star system, they will likely keep the workings of the invention secret as much as possible, so that, at least for some time, they are the only provider of that invention. This is what happened in the past with porcelain: The means to produce it in Europe were always there, but the method was kept secret by China, so for a long time China had the monopoly on it (which of course also meant porcelain trade between China and Europe, which also wasn't exactly cheap).
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[My answer to this question](https://worldbuilding.stackexchange.com/questions/12354/what-would-a-space-fighter-look-like/12369#12369) essentially came down to the pilot being in a sphere with anything large jutting out of it. Some of the arguments made against me I feel are true if we assume fights like traditional jet planes, but not if a space fighter was designed to make optimal use of 3D space without friction.
By that I mean I was envisioning a fighter that had multiple jets to allow movement in any direction in short notice (since there is no need for a main jet in 'back' to counter friction). I also imagined that the fighter would fight on 3 dimensions, and that you never know exactly what angle you will be attacked from next since all angles are equally valid.
However, the obvious counter to my own arguments seems to be the presumption that this would be optimal for the pilots. A perfectly optimized AI may find this better, but humans have trouble thinking in 3 dimensions. We have an even harder time thinking of a frictionless world. The idea of "this was my front, but now I'm going in a top-right-backwards direction to pursue someone I saw in an angle I wouldn't normally even look in" would just feel odd to a human.
Would a space fighter piloted by humans therefore be made 'inefficiently' to better fit our cognitive biases? Would we have only a few engines and only a few directions we could 'fire' from because it's easier to think in terms of having two or three 'fronts' I can switch between then is to truly grasp the idea that there is no front and any direction is just as valid? Would we have only one set of powerful guns because it's cheaper to build then multiple and we found pilots couldn't handle controlling multiple?
Furthermore, how would we design our fighters, including the UI, control, and similar systems, to help pilots to make split second decisions when they have to handle 3 dimensions at once?
For this question assume we have space fighter jets, piloted by humans, fighting at relatively close ranges. I'm fully aware how impractical it is to use a space fighter over large capital ships and LOTS of AI driven missiles, but that was not the intent of the original question, and my own world uses a number of technological changes to help justify (mostly) space fighters so assume they exist for now.
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> Would a space fighter piloted by humans therefore be made 'inefficiently' to better fit our cognitive biases?
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No, since there would be inevitably humans without (or with less) cognitive biases, and your inefficient machine would be dead.
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> Would we have only a few engines and only a few directions we could 'fire' from because it's easier to think in terms of having two or three 'fronts' I can switch between then it is to truly grasp the idea that there is no front and any direction is just as valid?
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Again, no.
War quickly encourages optimal solutions to problems. If the optimal arrangement is a fixed gun and rotating the entire craft, it'll do that. I doubt that will be the case.
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> Would we have only one set of powerful guns because it's cheaper to build then multiple and we found pilots couldn't handle controlling multiple?
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Possibly, but more likely there would be fewer guns because it simplifies the system, which makes it lighter, which gives it greater range/maneuverability. Or that there are fewer guns because it's better to have a single, very accurate placement than more inaccurate ones.
If the fighter is piloted by humans and uses projectile/laser weapons and somehow AI is worse than today's equivalents, I would expect 1 pilot and 1+ gunners working with 2-6 weapon emplacements. The emplacements would likely be virtually controlled so that the gun is always in front of the gunner, meaning the 3Dness is moot. There's only the field of vision into empty space.
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I'm not sure if this is a complete answer but here is my 2-cent:
The first thing to note is that the problem isn't really if a Man can grasp a 3-dimensional situation, but if he can deal with it better than an AI. That heavily depends on how advanced AI are.
The second one is that you could have multiple men in one space fighter to deal with some shortcommings, a bit like un the B52.
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Most likely any inefficiency in the design would not be required for a space fighter. It seems spherical design are the best, with some way to rotate the chair so the pilot could look in all directions, and an alarm system in the UI for the area behind him/her. Movement could be controlled with the same system as modern fighters (steering wheel for roll left, roll right, turn up, & turn down, with accelerator and brake and extra buttons for banking in the first 4 directions), or perhaps a direct mind-over-matter interface. As for the guns, there would be no need for limiting directional capacity , especially for larger ships that had another person inside each gun compartment, with the pilot relying on video screens instead of direct lines of sight. This last arrangement could be limiting if all the cameras were destroyed, but otherwise it would make good use of all resources. And obviously pilot-only fighters (still following the 1st arrangement) would have one gun aligned to the pilot's line of sight, with maybe another controlled by an AI.
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why do you presume humans have trouble thinking in 3 dimensions? if they're trained, there is no problem.
evidence: quite many space simulator games, some with frictionless environments.
what is going to be harder for you is to try to explain the tactics as interesting. and not just "ok we're in range, lob some kinetics at him".
you should play something like <http://en.wikipedia.org/wiki/I-War_%281997_video_game%29> perhaps for inspiration. they're not spherical, but can move in all directions. there's plenty of reasons to not make spherical fighters, like minimizing hit area, or to accompany insides to fit equipment. a spherical ship would be larger than is necessary - always - for no benefit. there is always technical drawbacks to stuff like weapons turrets whilst there are benefits to having them.
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We always think of some technology as being more advanced than others, e.g. (space rocket) > (aeroplane) > (car). To what extent is such a scale absolute, and to what extent does it just come from the order of development in our history?
A specific example I'm thinking of is nuclear vs. conventional explosives. Wouldn't it be possible to have a society which has developed nukes without ever having gunpowder? I want to have a world that has the threat of devastating nuclear war, but in which all the fighting is with medieval weapons like swords and bows (no guns).
**Edit after reading answers and comments**: let's say the available minerals and chemicals in that world are such that gunpowder, dynamite, etc. can't be made. Nuclear bombs can be made using two pieces of uranium which are brought together by (say) powerful springs rather than conventional explosives. And I've changed the title so that I can ask later about other examples of technology developing in a different order without having to edit this question!
Thanks in advance for any answers!
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There is a trivial sense in which two technologies could develop in a different order - namely, if they were entirely independent of one another. Beyond that $\cdots$ we have to deal with three different questions :
* the question of technological independence,
* the question of technological completeness,
* the question of what defines a technology (yes, it's inescapable!).
Any technology that depends on another cannot precede that technology. Therefore, independence is necessary in the event of any order change. Some technologies are ubiquitous. For example you cannot have a single modern technology without agricultural technologies. Materials technologies and energy technologies are also ubiquitous, along with many others.
Completeness. Is it possible the aggregate of all our technologies is not complete. Is there something missing? Something we should have seen given our current state of technological knowledge. If so, then our technology could have developed in a different order.
Finally, define technology. Well this is a real hornet's nest. Take the technology of fire - surely one of our very first technologies by any definition. Its first application was probably as a weapon or defence. Is the application of fire to burning wood or coal for human needs a new technology, or is it just fire. What about burning fossil fuels, is that a new technology or is it just fire. Sure it depends on many other technologies such as materials, agriculture etc. but ultimately it is just fire.
I find it hard to think of any independent technologies except maybe fire and materials. We harness fire and we smashed rocks together to make weapons. Either one could have been done independently of the other. So if we can imagine our technologies as forming a tree of interconnecting branches, then it has at least two different trunks, maybe more. But are there entirely independent trees or just one monolithic tree of human technologies.
Independent branches of the tree can grow faster or slower, allowing for the possibility of different aggregate orders.
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There is a complex web of interactions between technologies, with a lot of dependencies from one to another.
While some areas could advance independently (for example genetics and astronomy) even in those examples they both benefit from advances in other areas such as advanced optics (for microscopes and telescopes) and computer power.
So you can certainly tweak the development of certain areas but there are limitations of how far you can do that.
In this specific example nukes (as HDE 226868 already said) require conventional explosives to function so would not be viable. You also have the problem of delivering the nuke to the target, airplanes might be viable but missiles require explosives. There are other ways to get the outcome you desire though.
For example if there was a lot of volatile gasses in the atmosphere then firing a gun might have a high chance to ignite a local patch of it and kill the person firing it. In this sort of scenario guns would not be investigated as a serious firearm but explosives might still be used and developed for mining and similar purposes. Those could then lead into nuclear devices.
You should consider other consequences of this sort of world change though. For example how would a normal house or campfire interact with the gas? Where does the gas come from? Can anyone tell where patches of it are?
There was a similar discussion recently about space flight:
[Could a civilization achieve spaceflight without inventing advanced weaponry along the way?](https://worldbuilding.stackexchange.com/questions/966/could-a-civilization-achieve-spaceflight-without-inventing-advanced-weaponry-alo?rq=1)
A lot of the answers there will apply to your question too.
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You could in principle have a nuclear weapon with out chemical explosive.
The built but never deployed "cannon" bomb was just two slugs of uranium-235 (235U) at either end of a cannon barrel shaped and fired at each other to meet in the middle and boom.
You could do the same with steam with significant more bulk.
But the real problem would be not making the final weapons but in creating the vast industrial base needed to create a 235U slug of exactly the right composition of isotopes. That's hard even today. Fortunately, because once created it's easy to set of.
There is no way a medieval society could have enough metal and man power to mine, transport, and refine uranium, build reactors, extract the right elements, shape them to precision etc.
The amount of metal we have today is staggering. On midsize costal freighter has more steel in it than the whole of Europe circa 1500. The energy all this would take would denude every forest. They have no analytical chemistry, no precision instruments.
I would suggest a found technology in place of nukes, some kind of low bioweapon or perhaps discovery of an airborne toxin of some kinds.
Nukes, and technology in general exist not such much in sequence as in an ecosystem. It's not the actually components of a piece of tech you need as all the tech that makes all those components, and the tech that makes all that tech and so on.
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I only have time for a very short answer here, but I'll update it later if I can.
The answer to the nuclear bomb example is no, and it's because nuclear weapons *require* conventional explosives. [Wikipedia](https://en.wikipedia.org/wiki/Nuclear_weapon#Types) gives a good overview. A fission bomb either uses the "gun method" (using explosives to shoot one bit of nuclear material at another) or the "implosion method" (using explosives to compress the nuclear fuel. Either one uses normal explosives.
Fusion bombs are worse. They require fission bombs inside them to trigger the fusion part of the bomb, and thus need normal explosives.
So no, the scenario is impossible (or at least very implausible).
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Yes. Imagine a world with an **extremely** dense atmosphere. Explosives won't be of a lot of use. You can still detonate a U-235 nuke with electromagnets moving the core into a donut.
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In a world where gunpowder reacts differently, there would be no use for gun powder, however this doesn't mean they'll move straight to nukes. Instead maybe their atmosphere allows another explosive reaction to exist. And then moving to nukes
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Well I'm assuming that this couldn't happen because most nukes use conventioal explosives to initiate the reaction.
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Help me, you benevolent geology nerd!
This is a question I'm trying to find a workable (but not necessarily precise) answer for a colony-building sci-fi RPG game that I am GMing for some of my friends.
So, the setting is on the harder sci-fi spectrum where faster-than-light travel is impossible. Players arrive at the planet in a futuristic form of cryosleep, and they are the only fully grown humans (the rest are frozen embryos to be incubated on site). Mass was a main concern for the trip, so the ship carried only the necessary equipment to extract resources on site and print them in the colony.
Now, let's assume that the colonists have: 1) An automated industrial sci-fi printer capable of smelting minerals and producing chemicals, if supplied with raw resources, as well as assembling them into useful components; 2) A swarm of drones capable of mining, farming, and building. More drones can be built with the printer once resources are gathered; 3) And I suppose this sci-fi society would probably be prepared for interplanetary exploration, so they would have streamlined most of their technology to use the bare minimum amount of resources necessary and use different elements as substitutes (I'm not sure if this is too far-fetched for a hard sci-fi setting, though. Building chips without silica or gold?).
Nevertheless, players would still need to command the drones to find and mine resources to supply the printer. Organics, oils, and bioplastics could probably be farmed. However, for minerals, I believe they would need iron, aluminum, copper, some gold and silver, lithium, and some rare earth metals - basically, the things necessary to build what we have today.
I have almost no knowledge of geology, so I'm trying to get an idea of the minimum number of different mines necessary to obtain these resources in enough quantity to build stuff that we have today (guns, vehicles, heavy machinery, computers, TV screens, etc). Assume that the first wave of colonists would have to supply and maintain only a colony of 1000 people or so. Would they still need as many mines and a complex supply chain as we have on today's earth? Are these essential minerals found togheter? Assuming that you are only trying to supply technology for 1000 people, would it be viable to mine these minerals from small veins that are not considered economically viable for today's standards?
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# For high tech stuff you need a lot of mines.
A car needs [76 elements to work well](https://inchemistry.acs.org/atomic-news/elements-to-build-a-car.html). If you want a peak performing car, you need a fairly wide array of elements. A lot of them are gonna be fairly hard to find. Samarium for example is found in the fairly [rare ore Monazite](https://en.wikipedia.org/wiki/Monazite) and other rare ores and is very useful in high heat permanent magnets.
There are [six main types of mineral deposit](http://www.dmp.wa.gov.au/msa/mineral-systems-816.aspx) and Monazite is a sedimentary phosphate rock generated by basins where the interaction between water and chemical precipitation concentrates the needed element to useful levels.
That said, you can get around that. Samarian is found in [two to twenty parts per million of soil.](https://books.google.nl/books?id=j-Xu07p3cKwC&pg=PA371&redir_esc=y#v=onepage&q&f=false) and 2.3% in useful ores.
That means you just need to mine a million tons of soil to get two to twenty tons of Samarian. The same is true of many other rare elements.
# The colony would probably be set up with several tiers of drones.
Some would be designed to run off very limited resources and use the [common elements.](https://www.worldatlas.com/articles/the-most-abundant-elements-in-the-earth-s-crust.html)
```
Oxygen - 46.1%
Silicon - 28.2%
Aluminium - 8.23%
Iron - 5.63%
Calcium - 4.15%
Sodium - 2.36%
Magnesium - 2.33%
Potassium - 2.09%
Titanium - 0.565%
Hydrogen - 0.140%
```
Unless something is radically different, these are probably gonna be common. Their abundance is similar to the stellar abundance, which results from nuclear physics in stars.
So, silicon is not likely to be an issue, and iron is pretty common. They can probably build cheap drones from common elements using iron and aluminium frames and silicon chips which can mine a huge amount of dirt for more rare elements.
Once you have rarer elements, from several million tons of dirt, you can then build more advanced goods and drones which use rare materials. Copper, gold, silver, lithium, and rare earth metals are likely to be in short supply in tier one drones, but possible in tier two drones, which might seek out better mines.
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As a supplement to the excellent answer by Nepene Nep:
I'd say, pick your landing-site well. Chose a coastal location with reliable cross-currents and decent sunshine - and hopefully a nearby freshwater river.
**[Seawater](https://sciencenotes.org/abundance-of-elements-in-earths-oceans-periodic-table-and-list/)** could very well be your first port of call.
[Pressure-retarded osmosis](https://pubmed.ncbi.nlm.nih.gov/22546793/#:%7E:text=Pressure%20retarded%20osmosis%20(PRO)%20is,concentrated%20brine%20in%20seawater%20desalination.) can be used to produce energy from the osmotic potential difference between salt and fresh waters, and the seawater can be mined for rare elements.
A land-based, toes-in-the-ocean processing plant will use evaporation in large basins (made by drones using [laser-sintered dirt](https://worldbuilding.stackexchange.com/questions/152881/constructing-airtight-human-suitable-facilities-in-near-vacuum-moon-mars-et/152937#152937)) to collect gross-quantities of salt by evaporation. The various elements would then be recovered by a number of processes.
This would provide a kick-start for the [acquisition of the rarer elements from the ocean](https://pubs.acs.org/doi/10.1021/acs.est.5b00463#), but fail to offer significant quantities of things like iron and silicon, these would require separate mines.
At later stages, it's worth noting that on Earth, we've significant quantities of useful stuff on the ocean floor, eg. [polymetallic nodules](https://en.wikipedia.org/wiki/Manganese_nodule#) containing, among other things, manganese, iron, nickel, and copper. But they're deep: 4,000 - 6,000 metres sometimes deeper, those are high-strength drones required to recover them, or nets on long drag-lines.
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I have a villain whose superpower is allowing energy flow/interaction between distant objects - in particular, what matters right now is that he can put two objects (or areas) in direct thermal contact at a distance, near-instantly equalizing the temperature of the affected region. (It's worth noting that this isn't thermal contact along an edge but rather between every pair of points in the interior, so the heat doesn't have to slowly travel out of one object and into the other.) I imagine he could use this to link a person and a commonly available heat sink like a section of the ground, nigh-instantly dropping someone's body temp by several tens of degrees, but not nearly to the point of freezing.
This seems like it would probably be fatal one way or another, but I don't know if it would kill immediately or after a few seconds, or even be survivable. Normal deaths due to cold temperatures are very different; they have a hot core and frigid extremities and death occurs after some time, though whether people die from *getting too cold* or from *being cold for too long* I don't know. So my question is: What would the effects on the target be? How long would they survive, and as a bonus what would they experience, if anything? What's the actual mechanism of death/point of failure?
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## The biological term is cold shock.
The average ground temperature on earth is 55°F or around 13°C. If you instantly cooled a human to that temperature a few things would happen.
1. **They would be almost instantly unconscious, although they may gasp and flail for a second** based on severe cases of severe cold shock. Neurons can't restore a sufficient action potential or send coherent signals. The few they do get off will trigger tachycardia and gasp reflex if they can fire.
2. **They will die very quickly** (minutes) without immediate and severe medical intervention and even then survival chances are low, but not zero. Because the cooling is instantaneous they actually have a better survival chance than normal hypothermia. All process are slowed instantly so most metabolic resources are not depleted but in fact preserved; as long as warming is done properly it is potentially survivable. But the chances of medical premises being set up and ready for this is low in warm weather.
What kills them is essentially not having enough energy available for basic cell metabolism. Too many cellular reactions just grind to a halt. It's like asking why a cake does not bake at room temperature; there is not enough energy for the reactions necessary, You are a series of chemical reactions. **Real world hypothermia is actually a fairly poor model here because the human body is large enough it can't change temperature quickly using normal physics** (this is why freezing and resuscitation works on small animals but not large ones) so you will not have any direct science. Rapid cold shock is our best model but even that is far form perfect since again the brain and core can only cool down so fast normally. The best model might be cold shock in bacteria, but most bacteria have cold shock response proteins because they are small. Humans have no such protection.
See also:
* [Cold shock in bacteria](https://pubmed.ncbi.nlm.nih.gov/34530639/)
* [Cold shock in bacteria](https://pubmed.ncbi.nlm.nih.gov/37010795/)
* [Cold shock in humans](https://www.wemjournal.org/article/S1080-6032(19)30058-4/fulltext)
* [More on cold shock](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1513281/#:%7E:text=Associated%20with%20this%2C%20cold%20shock,a%20reduction%20in%20cellular%20pH.)
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Ken Zafren, Peter Paal, Hermann Brugger, Raimund Lechner, "[Induced Hypothermia to 4.2°C with Neurologically Intact Survival: A Forgotten Case Series](https://pubmed.ncbi.nlm.nih.gov/32482520/)", in *Wilderness Environ Med*, 2020 Sep, vol. 31(3), pp. 367-370, doi: 10.1016/j.wem.2020.02.003, epub 2020 May 29:
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> *The lowest recorded core temperature from which a person with accidental hypothermia has survived neurologically intact is 11.8°C in a 2-y-old boy. The lowest recorded temperature from which an adult has been resuscitated neurologically intact is 13.7°C in a 29-y-old woman. The lowest core temperature with survival from induced hypothermia has been quoted as 9°C. We discovered a case series (n=50) from 1961 in which 5 patients with core temperatures below 11.8°C survived neurologically intact. The lowest core temperature in this group was 4.2°C. The authors also presented cardiovascular and other physiologic data at various core temperatures. The patients in the case series showed a wide variation in individual physiological responses to hypothermia. It is not known whether survival from accidental hypothermia is possible with a core temperature below 11.8°C, but this case series suggests that the lower limit for successful resuscitation may be far lower. We advise against using core temperature alone to decide whether a hypothermic patient in cardiac arrest has a chance of survival.*
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See also Zafren K., Lechner R., Paal P., Brugger H., Peek G., Darocha T., "[Induced Hypothermia as Cold as 3°C in Humans: Forgotten Cases Rediscovered](https://pubmed.ncbi.nlm.nih.gov/35099289/)", in *High Altitude Medicine & Biology*, 2022 Jun, vol. 23(2), pp. 105-113, doi: 10.1089/ham.2021.0144, epub 2022 Jan 28:
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> *Although induced hypothermia for surgery differs from accidental hypothermia, survival from very low temperatures in induced hypothermia provides evidence that humans with accidental hypothermia can be resuscitated successfully from temperatures much lower than 11.8°C. We continue to advise against using core temperature alone to decide if a hypothermic patient in cardiac arrest has a chance of survival.*
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