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[Question] [ Suppose such an organism had evolved from using sound like most life we know to use different intensities, wave lengths, and hues of light to communicate. This is assuming that these creatures are as or more intelligent as humans currently and emit the light themselves from their face, these organisms are humanoid. What effect would such a change have on the rest of their physiology? [Answer] The first and most obvious requirement is that they would need light sensitivity, so vision is a must. Beyond that there are some differences between the way light and sound work, for example hearing is 360 degree coverage, if someone shouts behind you then you can still see it. Equally sound can be used for communication around corners or over hills. As a result light is actually quite weak to use as an early warning signal, so it is likely that there would be some auditory communication as well even if it's restricted to alarm and distress signals. One advantage of visual signalling is the available bandwidth, if you had a creature with the ability to change its skin dramatically and rapidly in various patterns and shapes then it could well be able to transmit information far faster and at longer ranges than speech. Multiple creatures could all be "speaking" in the same area at the same time without interference and conversations would not need people to wait for each person to finish. Instead even in a multi-way conversation each person could constantly talk all the time, so expect them to be better at multi-tasking and processing multiple information streams simultaneously than humans are. In general their visual processing would be superior to humans but their auditory processing would be weaker. Technology would take different routes from our own, as the telephone and radio would both be pointless. Early remote communication would most likely be something like the telegraph and writing could well be hieroglyphics designed to look like the skin patterns used to "speak". They may well develop independently mobile eyes so that they can watch people they are talking to at the same time as working. For example a conversation while sewing would require two eyes to watch the sewing process and another to watch the conversation. A group conversation may require either one eye on each person in the conversation or some sort of signal that causes everyone to switch attention to the person who is going to speak. [Answer] We already have animals that communicate by light. The one most people have seen are lightening bugs. Granted it's mostly for 'lets propagate' but it is a form of communication. There are plenty of animals in the deep that use light for different things. However, the closest and most intelligent animal that uses light is the octopus (and it's cousin the cuttlefish). They use their [chromatophores](http://en.wikipedia.org/wiki/Chromatophore) for quite a few different things. They will use it as camouflage, but it can also be used to threaten predators, mesmerize prey, and attract a mate. The cuttlefish have some absolutely amazing displays that are very incredible. They can even appear to be trying to communicate with divers. So I would think the [cephalopods](http://en.wikipedia.org/wiki/Cephalopod) are a good place to start for ideas of light as communication. At least as primary communication, as someone pointed out, sound would likely still needed to be used for warnings and such, but the bandwidth of the light could be much, much higher allowing for a much more exact transfer of information between individuals. [Answer] If light was the dominate form of communication then I would expect the physiology to reflect the dependence on light. Unlike us they may have additional "eyes" that allow them to receive messages from other directions. Think like the compound eyes on most insects or an arachnids multiple (6-8) eyes that form a photo sensitive "wreath" around their heads. Eye stalks might be another option, rather then a single directional approach like our eyes take maybe a complex compound eye sits atop a couple of eye stalks (much like long rabbit ears or antenna). The other thing to consider might be what what range of light for them is visual and which is "auditory" can they see the same wavelengths we do? If so they may then use a more invisible (to us anyway) light wavelength for communication like infrared or x-ray. This gives such a species some interesting angles for making communication difficult; perhaps the "speech" wavelength is just plain red so this species is effectively red color blind and is very confused by some of our lights. The flip side to this is that using a wavelength in the x-ray spectrum may cause damage to species less able to deal with the "radiation" of their speech. [Answer] This is not an exact answer like the others. But, if there exists such a creature, everything around them will produce "sounds" in terms of light and they probably will name objects according to their colors. The ambient color would affect their mood and psychology. It is also possible to use lower frequency electromagnetic waves (since visible light is as such but at a very high frequency). Lower frequencies can be used to communicate longer distances and would be broadcasted to a larger area (like radio signals). This would allow them to communicate long distance without any equipments. ]
[Question] [ [Maelstroms](http://en.wikipedia.org/wiki/Maelstrom) are ginormous whirlpools. They can exist continuously in an area. They're cool. The question is, how large can they get? As large as an island? Could a maelstrom have a diameter of `60` or `100 km`? If so, could they be formed or maintained by natural causes and structures so that one could encircle an island constantly (as big as [Jamaica](http://en.wikipedia.org/wiki/Jamaica) for example)? As in, having an effective source beneath the island? (I know islands don't have sea under them, I'm talking about the effective center of the whirlpool) What about a group of islands, where a massive maelstrom has a source between them? Could the tides encircle an island group (like the [Seychelles](http://en.wikipedia.org/wiki/Seychelles) in size)? I'm asking if such a thing could exist with contrived (if necessary) but natural causes. [Answer] Using a little power-scaling math because simulation at this scale is difficult, and the rules break down at large scales anyway: No, No island. At least not for Earth-typical conditions and continuous existence. First, a [free vortex](http://en.wikipedia.org/wiki/Free_vortex) is needed. But it needs to be physical and have room for Jamaica in the center, so we'll choose a [Lamb-Oseen vortex](http://en.wikipedia.org/wiki/Lamb-Oseen_vortex) which can get a stable center. Based on that you need a viscosity much much higher than water to get a center region larger than 1 meter. For water you'll have an edge velocity close to Γ/188.5 km. Γ is an integral that is larger at larger radial distances. Assuming you could ignore the slowing effect of a central landmass, you still need additional extra input to keep the whole thing spinning against the losses from viscosity. Near the equator you can pull about another 1 meter/sec from the [Coriolis effect](http://en.wikipedia.org/wiki/Coriolis_effect) at 50 km radius and Earth's Coriolis Parameter. As far as tidal forces and pressure forces, at [Saltstraumen](http://en.wikipedia.org/wiki/Saltstraumen) you have the strongest tidal forces on earth at 41 km/h yet they only create 10 meter whirlpools. If we increase that number by 300 km/h for some of the strongest thermal currents on Earth, [the Katabatic wind](http://en.wikipedia.org/wiki/Katabatic_wind)). And then if we scale linearly, we could possible walk away with 83 meter diameter whirlpools. If instead of instead of a singular whirlpool you can accept a chain of smaller ones then I don't think there is an effective limit as you just need more turbulence. The vorticity at high energies in a turbulence will create little whirlpools everywhere. Yes, If you toss the island requirement then your 100 km region is very doable. The [Great Red Spot](http://en.wikipedia.org/wiki/Great_Red_Spot) can have several Earths fit inside it for example. I can also see turbine-shaped mountain ranges from pole to pole that gradually smooth out. A rapidly spinning planet would have the water forced towards the poles from the mountains and the centrifugual force would tend to force the water towards the center. Circulation would form a whirlpool I would imagine. The setup balancing Roche limit, pressure, and centrifugal forces would be tricky to compute because calculating pressure would be hard. [Answer] Saltstraumen and Moskstraumen can both be up to 8km wide. I know of no reason why they could not be bigger. The terrain needs to be correct, such that water is trying to move very fast through an opening which is relatively small. In the case of some whirlpools, the constraining passage can be underwater. I do not believe that a landmass could be engulfed in a maelstrom though. The existence of an island inside of it would make the vortex more difficult to form. Try it at home... If you take a pan full of water and start swirling around the edges, a little whirlpool will form. Now try it with a bundt pan. Moving the water around is much more difficult, and the water will slow down faster. FYI - Whirlpools can be caused by non-natural events as well. [Lake Peigneur](http://www.losapos.com/lakepeigneur) in Louisiana was the site of a maelstrom resulting from aberrant drilling. I'm surprised no Bond villain has tried this... [Answer] This almost deserves to be a comment, but too long for that format. I have no clue on the feasibility of this. Lets take an impact crater lake...impact craters tend to leave glass bottoms which won't let water through. Put a hole at the bottom of said impact crater that drains into underwater passages and eventually out to an ocean. This should create a decent sized whirlpool. Gives it a nice uniform round/cone shape as well. Lets scale this up and feed a couple rivers into the system...if the rivers enter the crater at the right angle, the flow of the river will help power the rotation of the whirlpool. Now lets take another mass of land and drop it into the vortex so it sits touching the edges of the crater without actually blocking the drainage hole at the bottom (sadly, this would kinda look like a raised stopper in a bathtub). This mass of land would have to be one solid chunk and large enough that the top of it is your island. Would be best if it was resistant to erosion as well if you wanted a decent lifespan on this setup. Possible that this setup leaves you with a crater lake and a spinning whirlpool around it. I'm really not sure if this setup is feasible from a 'how did that land get there' standpoint, nor can I really prove this setup would perpetuate a whirlpool. This wouldn't really be a series of islands in the ocean (unfortunately the ocean setup always leaves the question of 'where does the water drain to then?')...just a crater lake with a whirling mass of water spinning around it. \\how about the Flash is running around in circles at the bottom of the ocean around the Seychelles? ]
[Question] [ Closed. This question is [off-topic](/help/closed-questions). It is not currently accepting answers. --- This question does not appear to be about worldbuilding, within the scope defined in the [help center](https://worldbuilding.stackexchange.com/help). Closed 9 years ago. [Improve this question](/posts/546/edit) Life on Earth is protected by Earth's magnetic field, which deflects high energy charged particles that arrive from the sun and from outside the solar system. This prevents damage to organisms. For a habitat in orbit around the sun, how much energy would be required to generate a magnetic field providing sufficient protection for the inhabitants (humans, animals, plants) from direct damage from charged particles? Would it be possible to power this magnetic field using only solar power? That is, can sufficient solar power be gathered by a habitat? I'm interested in the range of sizes of habitat (if any) for which this would be possible. I understand this is likely to be different for different sized orbits, due to different levels of charged particle bombardment and different amounts of sunlight available. Assume a roughly circular orbit. This can be somewhat closer to or further from the sun than Earth is, or potentially at the same distance as Earth, if one of these options allows for the possibility of a solution. [Answer] We need some facts to get this right. Solar Energy from the Sun at 1 AU Wikipedia says that we receive about [1361 watts per meter squared](http://en.wikipedia.org/wiki/Solar_constant#Calculation). (The power flux through a given bit of space varies with the sun's solar cycles, but I'm ignoring that.) Needed Energy for the Magnetic Field Once again, wikipedia suggests that the [largest threats](http://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays) to "deep space" travel are protons, helium nuclei, and [HZE nuclei](http://en.wikipedia.org/wiki/HZE_ions). NASA (and wikipedia) also suggest [various ways](http://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays#Shielding) to overcome this. Specifically for magnetic shielding, your power consumption will look like [10 gigawatts to 10 kilowatts](http://www.islandone.org/Settlements/MagShield.html), depending on your design. Solar Cell Efficiency Solar cells have a [demonstrated maximum efficiency of 44.7](http://en.wikipedia.org/wiki/Solar_cell_efficiency)% [The maximum thermodynamic limit is around 86%](http://en.wikipedia.org/wiki/Solar_cell_efficiency#Thermodynamic_efficiency_limit). Let's assume you have those nice ones that were actually made. The Calculation (10 kw / 1.361 kw/m^2)\(1/.447) = ~32.843 m^2 If you go for the 10 kilowatt design, you need ~32 square meters of very high-end solar panels. That's about a 5.73m x 5.73m square, which is large, but doable. For reference, the solar array on the [ISS puts out ~84 kw](http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html#.VCXKhSldWv0) and has ~73m of solar panels. [Answer] Solar wind is the least dangerous thing the sun emits. Anything outside the earth's magnetosphere for very long would require shielding for the higher energy charged particles emitted during solar flares and other CME events. According to Wikipedia solar energy at 1AU is 1367 watts per square meter. That's a lot of energy. The next question: is it even possible to build a (launchable) electromagnet array capable of deflecting X-Rays and Gamma Rays? I don't know enough about the physics of magnet fields to answer this part of the question. On the surface, you have a relatively large energy budget (you get 854 KW from just a 25 x 25 meter array (at 100% efficiency)). So it really comes down to building and launching the magnets. Then you probably want to give some consideration to the crew living in such a high magnetic flux environment. Though, you also have a really big space* budget. The magnets could be placed by trusses or booms at some distance away from the crew module so that it sits in the magnetic null. Again, no idea how far away that would be but it seems probably no more than 10s or 100s of meters. [Answer] I don't believe that an enclosed habbitat would actually need a magnetic field to survive. The main danger of the solar wind is stripping the atmosphere of the earth away. Inside a ship with metal ways, there is no danger of that. I believe that ships walls alone provide sufficient protection from solar winds to allow the ship to survive. As long as the ship isn't close enough to the sun to melt, the metal should be enough. We already send astronauts to the moon and ships out of the solar system. Purely metalic shielding can be designed without the need to a magnetic field. ]
[Question] [ Obviously flint and similar stones are much more fragile than tool or weapon quality bronze and steel, but while writing I find I don't actually have any idea what this means in practice. I use steel tools every days, so I have a decent intuitive understanding of how different steep alloys and designs can take different types of use, but I have absolutely no idea what the abilities of stone tools are. Basically, I want to know how long a stone weapons can last, while being in regular use, if it is properly treated. Are they almost certainly one battle tools? Or is that only a possibility? Are they reliable weapons if there isn't metal armor? Or would a trained fighter still break his axe if he makes a slight mistake? [Answer] Flint is sharp but brittle. It's slightly more durable than kitchen glasswear. A microlith projectile point will go through skin and tanned leather, but won't reliably penetrate any form of metal armor. You can expect a flint arrowhead to shatter if it hits stone. You can't form flint into anything resembling a sword, although you can make a wooden sword with a flint edge. Flint on flint impacts will almost always destroy an edge. Once a flint edge is damaged, it might be impossible to re-shape it into something useable. It takes a lot more skill to fix a damaged flint edge than it takes to re-sharpen a steel or bronze weapon. In response to the "one-battle weapon" concept, a stone knife can do a lot of killing and skinning. With a stone arrowhead, it's always a gamble when you let it fly, but they were treasured and conserved. It's probably doomed if it hits rock, and even bones can make one snap. Stone axes were apparently tougher, but I wouldn't think it would last long against metal armor. [Answer] ## Using stone tools mostly means being more careful with the tool and not using one tool for everything. A lot depends on what you are doing with it. A stone knife can be used a lot, you just need to be more careful with it. The extreme sharpness actually helps reduce wear, but after a month or two of using it every day you will need a new blade. Or what often happens, that knife gets used more for things were sharpness is less important, and you make a new one for skinning or the like. It is hard to describe how much difference that sharpness makes in use, the first time I used one I almost cut my hand open because being used to a steel knife I expected way more resistance than it had. A flint axe has a very different type of blade but will need care after cutting down any tree of size, but can be sharpened in a few minutes. A flint scraper could last for one use of years depending on what you are doing with it. in war a single battle weapon is fine, flint bladed weapon either use flint that can be easily replaced (macuahuitl or spears) or are treated as single use (arrows) and any extra uses you get are just bonus. Also a dull or chipped flint blade still cuts really well as a weapon, a weapon does not need to be that sharp. You can find a lot of videos of people using stone tools I suggest watching some of them. ]
[Question] [ After the Great Nuclear Apocalypse, the skies clouded over with dust and the world froze. Expectedly, most plants died out, and were then replaced with radiotrophic fungi, originating from all sorts of fungal clades Unlike plants, which absorp light from above, these fungi take up radiation from the contaminated earth and water. This radioactivity is quite evenly spread, but some areas (such as the ancient bombed cities) have more than others With this unique source of energy, they will have unique modes of growing. What general shapes (like trees or shrubs in plants) would be likely for these fungi to take on? [Answer] Ramifying subsurface hyphae. [![fungus hyphae](https://i.stack.imgur.com/3zGZk.png)](https://i.stack.imgur.com/3zGZk.png) <https://symsoil.com/mycorrhizal-fungi/> Plants maximize surface area exposed to light, balanced against needs to conserve water and preserve structural stability. For an organism that gets energy from soil and water radioactivity, the energy collecting apparatus needs to be large and diffuse. Radiation can be blocked by soil and water also. Hyphae will need to ramify out and occupy as large an area as is possible to maximize collecting area. Structural stability is not an issue underground. Conservation of water is not an issue. Competition with other organisms trying to occupy the space would very much be an issue. Fortunately for the fungi of your world all of these things are true for the lives they lead today. Radiotrophic fungi would look like fungi. Above ground, we would see fruiting bodies - mushrooms. [![mushrooms](https://i.stack.imgur.com/G9wwP.png)](https://i.stack.imgur.com/G9wwP.png) [Answer] They would likely take the form of [lichen](https://en.wikipedia.org/wiki/Lichen) or [slime mold](https://en.wikipedia.org/wiki/Slime_mold), sprawling over the ground and other surfaces. Most trees or shrubs have the form they do to compete with other plants for their food source (which is light). Growing tall allows them to compete for sunlight, but it is energetically expensive to make structures to support weight and grow tall. However, since the sunlight comes from above, there is a benefit from height. For background radiation, much comes from ground-based sources, with only ~[15-20%](https://en.wikipedia.org/wiki/Background_radiation) coming from the Sun. After the Great Nuclear Apocalypse, the proportion coming from the ground would likely be even greater. Thus your main benefit comes from occupying the space near to the ground and other surfaces. Your organism will want to capture as much radiation as possible, and once it is too far from a surface the benefit is small. There could be some differences in terms of which type of radiation the fungi utilize - Alpha-[radiation](https://en.wikipedia.org/wiki/Radioactive_decay) will mean organisms that form a very thin film over surfaces, while Beta-radiation allows for a few centimeters of thickness to generate energy throughout its depth. If there were organisms that utilized gamma radiation, they could extend up to bush height or tree height and still gain some energy. Alpha radiation is more likely to be predominately found in fallout, while the others are just as common in normal ground materials. So perhaps the full ecosystem could have some paint-like slime mold extending over surfaces where Alpha-rich fallout has come to rest (roofs, benches, any horizontal surface), while masonry buildings and the ground have more lichen or mushroom-like fungi, that capture more beta or gamma radiation. They would generally be blobby-looking shapes, as there is little benefit to building support structures, but could easily pile on top of one another. ]
[Question] [ ## Jumps between floating cities. In this setting floating cities exist because of floating rocks and people already live in them for a long time. Jumpers, jump between close leveled cities carrying packages. They do it by running in a track and jumping at the end, but, at the moment of the jump someone hands off an object that makes them 95% lighter. How would that go? Would they be able to make jumps? What perils would they face, like wind gusts and such? Different objects changing their weight in different percentages would result in longer jumps? Ps. Jumpers have "winged" suits that help control the trajectory. Ps2. When landing they would probably release the object and slow their running. [Answer] You will need to better define your world physics to get a reliable answer. Depending on how the hand-held object makes them ‚Äúlighter‚Äù will determine what your dangers are and how dangerous it is. I will ‚Äúguess‚Äù a few options and share the consequences: # The object Reduces the Jumper‚Äôs Mass If this is the mechanism you use, then you will certainly allow longer jumps, but the jumper‚Äôs moment of inertia will become 5% of what it was. Air friction, a slight breeze, and even the position of you hands and legs will make your trajectory completely uncontrollable for any normal human. Think of wrapping a rock in a piece of paper, then throwing it as hard as you can. When the object leaves your hand it has lots of momentum. But when released, the paper falls away. Your jumper will bee like the piece of paper, flitting around chaotically. You will not stay on the same trajectory like the rock does. You are welcome to try this experiment for yourself in a field. So it would boot be recommended to literally make the jumper ‚Äúlighter‚Äù by reducing their mass. # The Object Reduces Gravity For The Jumper This presents a more workable solution because your jumper still has all their inertia, and consequently, momentum. It sounds like this was the benefit you were after. The drawback here is that you will loose an ability to control your landing. You will run and jump with normal force and speed, then you will get far more altitude than planned, and fall at a much greater speed than planned; but when you land, your feet will try to stop all that energy with only the friction of a small dog! The effect would be very much like you just throwing a small dog or cat with all your stength, then hoping they land on their own feet alright. Very likely to break some bones this way. Now, with perfect timing, you could have gravity ‚Äúturn on‚Äù at the instant your feet hit the ground. If your jumpers were machines, this would work well. But they aren‚Äôt, and they have human reflexes and human reaction times. Their brains will be expecting a certain amount of impact on the landing, then you will surprise it. Your jumpers will need to be extensively trained, like what a professional football player needs. Just this past Superbowl game one of the Bengals tore his ACL tendon with no one near him, he merely placed his foot at a slightly bad angle, the weight of his body was not aligned perfectly, and his ligament got torn. Your brain REALLY needs to be able to predict the forces it is about to react to, and this is all done subconsciously. So jumpers need constant training and conditioning to override their natural instincts. # The Object Creates an Upward Force This is similar to turning off gravity but slightly different; it is adding a new force pushing upward. But in this case, you may select what is being pushed upward. Is it the whole jumper? In that case the effect would be identical to reducing gravity. But if you provided lift at the jumper‚Äôs shoulders, for example, the jumper would have the sensation like they were strapped into a harness at their shoulders. Or you could have it push only on their feet and they would have to balance on a sort of flying skateboard. There is an infinite number of ways you could manipulate this, and your normal human body would feel mostly comfortable with it because all the normal forces it is conditioned to are still working; it just has to figure out this invisible harness-thing. Another option is that the force only pushes up on their hands, feeling like you are riding a zip-line but it‚Äôs impossible to let go or fall because the force is actually your hands. Doing this wrong can risk wrist injuries however, so training is important. For this option, grabbing the jumper above their center of gravity would be safest and provide the least challenges. # The Hover-Scooter Here the object is actually the handlebar of a hovering invisible scooter. This object, when you hold it in a human hand, creates a hard, flat force field 75cm below it. A scooter needs to be pushed every few seconds unless going downhill, but you can‚Äôt push off in mid air! So, the jumper gets good speed, grabs the handlebars, and JUMPS off the edge. His feet land solid on a flat force field that projects exactly 75 cm below the bar. It goes all the way around the handlebars like a frisbee ü•è, and also resists air so the jumper can ‚Äúsurf‚Äù across the sky. His suit has a tail wing to maneuver; if he needs to steer right, he moves his footing a little to the left and angles the fin in his back. The force disk repels the ground like a magnet üß≤, so on landing, the jumper‚Äôs legs don‚Äôt feel a big impact; it‚Äôs like landing in a sponge. When he lets go of the bar, the field disappears and the jumper drops to the ground. [Answer] Yes - depending on how far they need to jump Jumping in a similar setting is already very feasible if they need to jump straight down - the thing called parachute is actually very safe for experienced jumpers. Jumping horizontally and down is also feasible, although definitely more risky - it is much more easy to crash with a wingsuit rather than with a parachute. Having an opportunity to lower your weight (or mass) to just 5% changes this calculation. Now it's becoming possible for a human to propel himself/herself on own muscle power, and this power would not even need to me strained. Even distant lateral jumps, as well as jumps up would become possible. However, if human mass is reduced to 5%, there comes an issue of wind. If jumper's entire mass (including cargo) is that low, any strong wing would blow this jumper off course. At high altitudes, high winds are rather common, and it is unclear whether muscle power would be sufficient to compensate for this wind. I believe that jumping in this setting would be practical and even safe if wind is not an issue, and risky (though still practical) if the wind needs to be accounted for. ]
[Question] [ I've been doing research for my speculative evolution project, and I am currently mapping body plans for the main lineages of organisms I'm going to feature in this project. One of them has an endoskeleton derived from subdermal armor structures and I was wondering whether it would be possible for it to have an endoskeleton made of cellulose, or chitin, or some kind of combined hybrid material of those two. Of course it wouldn't be pure chitin/cellulose and there would be proteins and such incorporated into it to alter its quality, but I think it's an interesting question nonetheless. This idea came from the fact that cellulose and chitin are similar in their structure. For reference, this spec evo project is on a mostly Earth-like planet with the differences being a binary red star system and a planet with 1.5x Earth's gravity. [Answer] Cellulose and chitin are both hard materials, but are inferior to bone when it comes to building an endoskeleton. They are softer and offer less support than bone - the trade-off being that because they are a little flexible, they can handle impacts that would chip or dent bone. This is why chitin, rather than bone, tends to be used for exoskeletons, since they are on the outside of the body where they are more susceptible to direct impact. Bone is shielded with layers of fat and muscle, so it can be harder and more brittle. That doesn't mean it's impossible for a creature to have a chitinous endoskeleton, but it would be weaker than a bone one. And on a planet with higher gravity, you probably want skeletons to have more strength, not less. ]
[Question] [ If there was a double planet with each mutual satellite being the mass of the Earth could they still maintain Earth-like magnetic fields despite being tidally locked to each other? [Simulations of how double gas giants might form](https://arxiv.org/abs/1504.06365) in a separation of 3-5 radii after orbit circularization by tides ends with mutual locking. Because larger bodies will lock to each other quickly, within a few million years, it does seem that hypothetical double planets of near equal mass ratios won't recede very far from each other. So while locked they should spin reasonably quickly. A double Earth pair would have to be about 8.3 radii apart in order to orbit each other in around 24 hours. Each planet being tidally locked is then spinning around on its axis within 24 hours also. So I had a look into this myself. Is it then correct to assume this is directly equivalent to the spin of the regular Earth as regards the generation of a magnetic field, or is this a naive assumption? Perhaps double planets with Earth strength magnetic fields would funnel particles into each other, making stronger auroras. [Answer] Earth's magnetic field is generated by [the spinning of our iron core](http://www.geomag.bgs.ac.uk/education/earthmag.html), not by the spinning of Earth in space. Theoretically, you could have a non-spinning planet with a spinning iron core, which would still have a strong magnetic field. On the opposite side, Mars is a planet [which spins almost as fast as Earth](https://solarsystem.nasa.gov/planets/mars/in-depth/), but without that spinning core, its magnetic field is weak. So, your real question should be "can a tidally locked planet have a spinning iron core?" While we still don't know for sure, exoplanet researchers [think that it's possible](https://exoplanets.nasa.gov/news/217/earth-like-exoplanets-may-have-magnetic-fields-capable-of-protecting-life/); the theory is that the amount of tidal heating would offset the drag on the core by the tidal partner. Note that this research seems to be targeted at planets tidally locked to their suns, and tidal locking to another planet may be slightly different (not a scientist). [Answer] I don't know if it is possible for a double planet to have 2 Earth like planets as close together as you want. Being separated by about the Earth-Moon distance seems more plausible to me, so you might need to get someone to do calculations. There would be great views of one planet from another if they were as close as you want them to be, but I don't knowhow possible that is. You may have to worry about the Roche limits of the planets. If the planets ae within their Roche limits they will disrupt each other. As a rule the Roche limit of the denser or more massive object is used to calculate if the less dense or less massive objects is disrupted. Your planets are twin planets, very similar. But I don't know if you can plausibly make them identical enough to avoid having one break up. The Moon becaem tidally locked to the Earth by a process of tidal interaction which also is slowing down the Earth's rotation rate and pushing the Moon farther from Earth. If you want your two Earth like planets to be habitable for humans, and/or have native life with similar requirements including multicelled animals and maybe native intelligent beings, the planets will have be billions of years old. And over those billions of years the processes which slowed down their rotation and tidally locked them will have also have forced them farther and farther apart. So if they were moving farther and farther apart for billions of years, how could they end up not much farther apart than their Roche limits? You may need to have someone do calculations. Do the planets need strong magnetic fields to retain their atmopsheres, or could their escape velocities be enough without magnetic fields? Titan, the moon of Saturn, has a dense atmosphere without a magnetic field of its sown, and also has a very low escape velocity. > > Titan has no magnetic field, although studies in 2008 showed that Titan retains remnants of Saturn's magnetic field on the brief occasions when it passes outside Saturn's magnetosphere and is directly exposed to the solar wind.[33] This may ionize and carry away some molecules from the top of the atmosphere. Titan's internal magnetic field is negligible, and perhaps even nonexistent.[34] Its orbital distance of 20.3 Saturn radii does place it within Saturn's magnetosphere occasionally. However, the difference between Saturn's rotational period (10.7 hours) and Titan's orbital period (15.95 days) causes a relative speed of about 100 km/s between the Saturn's magnetized plasma and Titan.[34] That can actually intensify reactions causing atmospheric loss, instead of guarding the atmosphere from the solar wind.[35] > > > [https://en.wikipedia.org/wiki/Atmosphere\_of\_Titan#:~:text=Titan%20has%20no%20magnetic%20field%2C%20although%20studies%20in,some%20molecules%20from%20the%20top%20of%20the%20atmosphere.](https://en.wikipedia.org/wiki/Atmosphere_of_Titan#:%7E:text=Titan%20has%20no%20magnetic%20field%2C%20although%20studies%20in,some%20molecules%20from%20the%20top%20of%20the%20atmosphere.) But if Titan was at Earth's distance from the Sun the solar wind would be much stronger and knock off gas particles much faster. The atmospheric gases would alos be much hotter and faster and would escape faster. Ganymede, the largest moon of Jupiter, is the only moon in the solar system with a measured magnetic field. Ganymede is tidally locked and has a day 7.154 Earth days long. Io and Europea have shorter days and rotate faster but are smaller than Ganymede. Callisto and Titan rotate slower than Ganymede and are less massive. And I don't kow if that is the reason why only Ganymede has detected magnetic field. I note that if your planets ae supposed to be habitable for humans, there may be an upper limit to how long their days can be. Sephen H. Dole, in Habitable Planets for Man, 1964, discusses what is necessary for a planet to be habitable for humans. <https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf> On pages 58 to 61 he dicusses the rotation rate for a habitable planet and guesses that between 2 to 3 Earth hours and 96 Earth hours per day would be the habitable range. You should find out if you agree that 96 Earth hours would be the longest possible day for a planet to remain habitable for humans. You may need to increase the separation between your planets, and thus the lengths of their orbits and days, to make a plausible astronomical situation, but you shouldn't make the length of day longer than the uper limit, whatever it may be, for a habitable planet. I note that a large moon orbiitng a giant planet that orbits in the Circumstellar Habitable zone of a star would be similar in most respects, though not all, to a double planet of twin Earth-like planets orbiting in the Circumstellar Habitable zone of a star, And there have been scientific studies of the hypothetical habitabilty of hypothetical exomoons, as they are called. "Exomoon Habitability Constrained by Illumination and Tidal Heating", Rene Heller and Roy Barnes, Astrobiology, Volume 13, number 1, 2013 discusses various factors affecting the potential Habitability of hypothetical exomoons. They discuss the magnetic fields of exomoons whch may depend on their rotation rates. Most such exomons would be tidally locked to the planet and not to the star, so their day would equal their month orbiting the planet and not their year orbiting the star. > > However, considering an Earth-mass exomoon > around a Jupiter-like host planet, within a few million years > at most the satellite should be tidally locked to the planet— > rather than to the star (Porter and Grundy, 2011). This configuration would not only prevent a primordial atmosphere > from evaporating on the illuminated side or freezing out on > the dark side (i.) but might also sustain its internal dynamo > (iii.). The synchronized rotation periods of putative Earthmass exomoons around giant planets could be in the same > range as the orbital periods of the Galilean moons around > Jupiter (1.7–16.7 d) and as Titan’s orbital period around > Saturn (&16 d) (NASA/JPL planetary satellite ephemerides)4 > . The longest possible length of a satellite’s day compatible with Hill stability has been shown to be about P)p/9, > P)p being the planet’s orbital period about the star (Kipping, > 2009a). Since the satellite’s rotation period also depends on > its orbital eccentricity around the planet and since the > gravitational drag of further moons or a close host star could > pump the satellite’s eccentricity (Cassidy et al., 2009; Porter > and Grundy, 2011), exomoons might rotate even faster than > their orbital period. > > > <https://faculty.washington.edu/rkb9/publications/hb13.pdf> It is interesting that in some cases an exomoon might rotate even faster than its orbital period. The faster a world rotates, the more likely it would be to have a strong magnetic field. So if an exomoon could avoid becoming tidally locked to either its planet or its star it would retain a rotation rate closer to its original rotation rate, and thus rotate faster than if it was tidally locked tothe planet, let alone to the star. So you need to find out whether planets part of double planets mighht also possibly be able to rotate faster,and thus in les time, than their orbital periods around the center of gravity. Thus it may be possible for a planet in a double planet to have moved far enough away from its partner to be consistent with the tidal interactions over the billions of years it should have taken to develop an oxygen rich atmosphere, while still rotating faster than the slowest possible rate consistent with remaining habitabel, and also fast enough to generate a strong agnetic field. Or your story could involve a double planet which was terraformed by an advanced civilization to become habitable, and while the two planets in the pair were still yung and orbiting close together. And for the purpose of your story it might not matter how many hundeds of thosuands or millions of years ago that terraforming was, or how many more millions or billions of years the planets can remain habitable in the future. ]
[Question] [ Vampires are no exception to the phenomenon of evolution. In my world various species or races or breeds of these creatures can be observed. They can interbred as much as neanderthals can breed with sapiens or French men with Saxons or coyotes with wolves. Which means easily and with no ill effects. They are not mystical creatures, lacking the magical powers usually portrayed in books and movies. Yet some cultures of vampire can do feats which might seem impossible to the top level elite human. One city in my world, a multicultural human-vampire city has a formidable military force of vampires. They make for excellent warriors due to their innate tolerance to cold climates, endurance, night vision and being able to quench their thirst and fill their bellies with the flesh and blood of enemy lines. And some say that an army marches on their belly. On top of everything, the weakest vampires can also surpass top human athletes both in strength and power. But in time of peace warrior vampires still need to be fed. They require only 350 grams of blood per week to maintain idle activities. Fighting and other heavy work increases the thirst. Vampires in this city are not slaves, they can decide to not be warriors. But there's little to no incentive to not go to war, especially since warriors are paid in both coin and blood taxes. These vampires are weaker than other "breeds" of vampires but require less resources. Conflicts between warrior vampires and other vampires are rare but it's always a fight of numbers versus quality. Outcomes are never easily predictable. I have many questions to make, but I'll split it in multiple threads. First question: What is the ratio of human citizens and vampire citizens the city must have in order to feed all warriors? The more vampire warriors, the better is the city protected from foes. This also increases the blood requirements thus human cost of shelter and feed. Also consider that in cold climates blood can be stored for an entire year, but there's a weaker agricultural production. Extra details: Vampires can breed only with other breeds, races, cultures, species of vampires not with humans. The first section might be confusing but I thought it will be useful in the fure to connect the next questions I'm planning to make. Vampires can ingest other foods as a hobby to savor the taste, but they only require human blood to survive. Human flesh is often eaten as filler food during war. Vampires are born from sexual reproduction, not created. Vampires are humanoids but not related to humans. They look like humans due to convergent evolution. The same way the ancient reptile Ichthyosaur looks and behaves similarly to the mammal dolphin even though they are not closely related or how bats and pterodactyls evolved similarly. Some types of vampires are photosensitive and nocturnal, but those vampire warrior specifically can sunbathe if they want. [Answer] 2 vampires for every 1000 humans. Let us work backwards from the Aztecs, a society that practiced large scale human sacrifice. We will have your society have the same amount of human sacrifice but all sacrifices are used to feed vampires. <https://en.wikipedia.org/wiki/Human_sacrifice_in_Aztec_culture#Scope_of_human_sacrifice_in_Aztec_culture> > > Michael Harner, in his 1977 article The Enigma of Aztec Sacrifice, > cited an estimate by Borah of the number of persons sacrificed in > central Mexico in the 15th century as high as 250,000 per year which > may have been one percent of the population. > > > 250000 being 1% means a population of 25 million. Assume you have a similar population. If every one of these 250,000 sacrifices is used for blood then that is 250,000 x 5000 ml blood each = 1250000 liters of blood a year for vamp feed. 1 gram blood = 1 ml. Vampires need 350ml /week when idle, more when active so I will say average 400ml week; 400 \* 52 weeks = 20800 ml or 20.8 liters per vampire per year. 1250000 available liters /20.8 liters = 60096 vampires can be sustained by this number of human sacrifices. 60096/25000000 = 0.00296 or 0.29% of the population. 2 vampires per thousand humans. Or 2.9 if you allow fractional vampires and I think you should. Maybe those ones are short, or missing parts but I like to think they suffer no discrimination for being fractional. As regards where these sacrifices come from, the Flower War method sounds like a good match for your warlike society. Read up: <https://en.wikipedia.org/wiki/Flower_war> --- You have me thinking now about an Aztec society in which sacrifices are used to feed vampires. Pretty cool. And when I go out Flower Warring to collect sacrifices I would definitely want some of my own bloodsuckers along with me. I think vampire on vampire combat is going to happen in these contests. When I see the enemy vampire coming to capture me I am definitely going to run toward my own friendly neighborhood vampire (we call him Sucko) as fast as I can. Hopefully everyone around settles down with the warring to watch Sucko bust out his moves on that jerk because that is the most fun part of Flower Wars. [Answer] ## ~56:1 Ratio Using Blood Taxes will be Most Common A single unit of blood is 525 mL which a healthy donor can give about once every 8 weeks. This means you need 5.3 healthy donors to support a vampire. The caveat here is that not everyone can be a doner, so you will not be able to just say you need 5.3 humans per vampire. The old, the young, the sick, the pregnant, and people with certain disorders can not safely donate blood. This number could be even smaller if your Vampires are at risk for bloodborne diseases like HIV or hepatitis. According to the Red Cross only 38% of people are eligible blood donors. Using these figures, your ratio of vampires to humans will depend a lot on how you are getting the humans to participate in these donations. * If blood is only harvested from volunteers then you will only get about 1/200th of this capacity based on current volunteer blood center figures giving you ~2800 people per vampire. * If you do a paid volunteer system, then you get about double that assuming you pay your volunteers the current market rate of 20-50 USD per unit. This yields ~1400 people per vampire. That said, the more you pay for blood, the more volunteers you will probably get. An average human spends ~140 USD/week on groceries meaning the value of a unit of blood in a vampire society is more like 210 USD. I can not predict how much this will increase your supply, but I suspect it will be significant. I would ballpark this system putting you in the 500-1000 humans per vampire range. * Human sacrifice following Willk's Aztec model will give you ~416 humans per vampire. While his idea definitely wins the cool contest, the fact that it is less efficient than the following models without being any less cruel makes it pretty unlikely for any civilization to go along with IMO. The Aztecs did human sacrifices because they believed they would all die without appeasing the gods. Vampires on the other hand are known to be mortal in this setting, even with their superior physical prowess, Vampires would have a hard time stopping a human uprising that outnumbers them over 400 to 1. * Next, you mentioned a blood tax. How a blood tax is levied will require a lot of consideration but can yield a lot more vampires than previously mentioned methods. Blood donations make a person weaker and more prone to sickness. If you try bleeding everyone at their maximum capacity, then your human workforce will not be able to do any heavy labor for itself. This makes important tasks like farming, construction, etc. unsustainable. To this end I would suggest limiting the blood tax to 6 donations per year. This gives every human 9 healthy months, and 3 months a year where they will be weakened by their donations. Most professions, particularly those than involve heavy labor, have a down season. In winter your farmers can donate. In summer, you'll get a lot of contribution from teachers and outside heavy-duty laborers. Then in spring and fall you collect taxes from your white collar and light duty laborers who don't really need to take an off season. Using a responsable blood tax like this, I would estimate a population of ~56 humans per vampire. * Your next most aggressive option is to keep humans as livestock. In this case you can bleed them year round since the Vampires would be doing most of the work of sustaining the humans. In this case you will get somewhere around 10-14 people per vampire depending on how aggressively you cull your herd. Keeping in mind that even with aggressive culling, you will still have a significant number of humans who can't donate at any given time because they are either children, pregnant, or acutely sick. * Lastly, you have your most aggressive option where you keep humans as slaves. In this case you only keep humans that can actively donate year round, and when they die, you go out and get more. This will give you about the 5.3:1 ratio. Considering that different societies will probably experiment with various techniques, you will likely see those that pick better techniques drive others out of existence. Volunteer & Paid Volunteer methods would allow for a large healthy human population, but very few vampires; so, they would be at risk of being conquered by smaller civilizations with more vamps. Human sacrifice would cause major discourse between the humans and vampires. The humans being so much more numerous than the vampires could easily overthrow their blood-thirsty masters at which point they would probably have to merge with another civilization that sustains more vampires more humanely, or be conquered by one that allows a smaller human to vampire ratio. Keeping humans as livestock makes sure that the humans stay few enough in numbers that they can not rebel, but humans take a lot of work to feed. Your vampire society would be forced into sustenance level conditions putting all of their work into producing enough food for their humans. Such a society would be kept from technologically advancing until it is overwhelmed by superior technology. Slaving means you don't have to work too hard to keep a viable human population, but you'd be reliant on needing a constant source of "wild" humans to replace your attrition. Here, your vampire society would need to be so constantly at war that they will eventually have enough enemies that they are taken out. This just leaves blood taxing. Blood taxing allows human societies to grow large and self sufficient while also maintaining a large population of vampires. In the end, most nations will probably turn to the blood tax method or be wiped out for one of the afore mentioned reasons. [Answer] You have a few things to consider first. How do the Vampires feed under normal circumstances? Does it have to be human blood? You already mentioned that in colder climates blood can be stored, so I am assuming it does not have to be purely fresh. The whole point is that your Vamps, as a different species, are what would be called "The Other" They are different than us. They are not like us. Why should they Rule us? This happens all the time, even in modern society, when "The Other" is still the same species, just a different skin color or religion. That means the Vamps are going to have to downplay the bits about them that make them seem inhuman. No showing off superior strength unless you have to. Don't drink blood in front of humans. Come by the backyard BBQ. Don't gravitate towards positions of power and do not abuse that power if you have it. I would guess that you would want your vampires to be around 1% of your population. this might be lower than the human population could actually handle if this was a pure predator/prey situation, but remember they have to live in at least some sort of harmony. Asking someone for a 500 gram donation to the blood pool once every year and a half (I'm accounting for minors not being eligible to donate) is not so onerous as to cause revolt of humans against the Vamps. You also want to make sure the donation is impersonal, like a modern day local blood bank situation. That will be far more tolerable that having to go somewhere to have somebody chew on your neck. In the case of a sudden attack, the vamps will always be in slightly better than subsistance level feeding conditions. Of course, then they will have victims to eat, so you would be even better off. In the case of a war, you could ask for a lot more blood to be donated without harming your populace, but you have to be very careful in not extending the heightened levels beyond what is actually needed. Other Societal notes: Make sure that if a Vamp gets to a position of power and authority, they do it through open, honest, and merit based means. Make sure all vampires are subject to the same laws as everyone else. As a matter of fact, Hold them to a higher standard. Make military service for a Vamp mandatory for at least a couple of years before leaving them to make the choice whether to continue to serve or not. You want to take away the arguments for the Vamps being Other as much as you can so you can integrate them as deeply as possible into your society. [Answer] I'm trying a scientific answer for the fun of it, but you threw me a curve with the "resistance to cold". A fairly well known study tried to estimate if dinosaurs were cold or warm blooded based off of the ratio of predators to prey in the fossil record. I put a good overview below, but a short take away is that as cold blooded predators require far less energy and eat less, the ratio of predator to prey can be close to 1:1, while for warm blooded predators the ratio may be more like 1:10. <https://blog.everythingdinosaur.co.uk/blog/_archives/2009/11/18/4383513.html> The curve I mention is that cold blooded animals are most certainly not resistant to cold. Otherwise, the vampires could fit this description nicely. They would have to be relatively inactive most of the time, but be capable of enormous feats for short periods when needed. (think alligators on the hunt) I'm not sure how far I would take it, but this could form a sort of symbiotic relationship where the humans are industrious workers, but the vampires are a real terror on the battlefield and can end rebellions. ]
[Question] [ Can an adult human with no underlying medical conditions survive on these foods alone for 24 months without severe malnutrition? Here is the list of foods: * Water * Plain crackers * Canned beans Assume an unlimited amount of these foods. The human must be able to walk and pull a cart containing these foods for 2 years in a Mars-like environment. In addition, could the human fully recover afterward? [Answer] If you got some sun you would be ok. [![bean vitamins](https://i.stack.imgur.com/AVS6b.png)](https://i.stack.imgur.com/AVS6b.png) <https://nutritiondata.self.com/facts/legumes-and-legume-products/4303/2> You will note that for vitamin C the % daily value is 5%. That is % in one serving of beans which is about 200 kcal. If you were living on beans you would eat 10x that much which is 20mg/day; 50% of the recommended daily allowance but enough to not die of scurvy. If you were eating more beans you would get more vitamin C; for example 3000+ kcal/day is reasonable for a person doing physical labor. Beans (and crackers) have no vitamin D and no B12. [It takes 3-5 years to exhaust normal bodily B12 stores](https://www.merckmanuals.com/home/disorders-of-nutrition/vitamins/vitamin-b12-deficiency) so even a diet devoid of B12 would be ok for 6 months or 2 years. Vitamin D deficiency could get you in trouble but you can synthesize that yourself when sunlight (ultraviolet light actually) hits your skin. If you knew that was an issue and took pains to get some sun then vitamin D would be ok. But even profound vitamin D deficiency is tolerable for adults - it messes with your bones and really that is about it. [Answer] The character would probably die almost instantly. The original question asks: > > The human must be able to walk and pull a cart containing these foods for 2 years in a Mars-like environment. > > > Everything that people have suspected about a Mars-like environment in the 20th century, and all they have learned about a Mars-like environment since 1964, says that the atmosphere of Mars has only a tiny fraction of the atmospehric pressure necessary to maintain human life. A person would loose conssciousness and suffer fatal injuries with seconds of exposure to the Martian atmosphere, or even an atmosphere which was several times as dense as the Martian atmopshere. And the Martian atmosphere has only trace amounts of oxygen, so if it was concentrated to the same pressure as Earth's atmosphere, someone would still suffocate quickly when breathing it. No environment which is even remotely Mars-like can be survivable for an unprotected human. So maybe the human is not unprotected. Maybe they wear a full spacesuit when they pull their cart around on the Mars-like surface. That means that a lot of the space and weight capacity of the cart would have to be used to extract oxygen from the Martian atmosphere or soil somehow to replenish the oxygen supply of the person's spacesuit, and the power source for the oxygen device. That leaves a lot less room for food in the cart. I believe that I eat several pounds of food and water each week. So for about 2 years or about 100 weeks someone would need a load of several hundred pounds of food and water to carry around in their cart. So how does the space suit wearing human actually eat and drink the food and water they pull around in their cart? How does the food and water get from outside the spacesuit to inside the spacesuit without the human losing air and dying? And how do they excreate while wearing the spacesuit? It would be a lot more plausible if the human lived in a pressurized habitat where they didn't have to wear the space suit, and only went on long trips outside the pressurized habitat pulling the cart when they had missions requiring them to be out of the habitat for several days at a time. I note that in a spaceship or a large habitat in space or on a planet, an advanced enough technology would enable the recycling of all waste products via complex chemical reactions powered by a powerful energy source into breathable air, drinkable water, and nourishing foods. And possibly after such recycling becomes common in space ships and large habitats, centuries of improvement and advances will enable such recycling equiment and its power source to be miniaturized small enough to be built into a spacesuit, so that someone could survive in a spacesuit for months or years without ever taking it off. And possibly before that recycling equipment becomes miniaturized enough to be used in a spacesuit, a slightly less miniaturized version would become available which could be installed in a cart pulled by a human in a spacesuit with various umbilical hoses connecting the cart and the spacesuit, so that the cart is effectively a vital part of the spacesuit. But in that case the recycling system would synthasize air, water, and nutritious foods for the human, and they would not need to carry hundreds of pounds of air, water, and canned(?) food with them in the cart. As I wrote, any environment which is "Mars-like" would be almost instantly lethal for a human without the protection of a pressurized habitat or a spacesuit. But possibly the question means an environment with Mars-like gravity for making pulling a cart loaded with years of food in it easier, but with an Earth-like atmosphere which is breathable for humans. Thus the human wouldn't need a spacesuit, heavy oxygen bottles, or a device to extract and concentrate oxygen from the atmosphere or the ground. And so they might not have devices to recycle wastes into synthasized food, and thus might need to rely on canned(?) food and water supplies which they have to pull behind them in a cart. But is a planet with low, Mars-like gravity and a breathable atmosphere possible? The important atributes to consider here are the surface gravity of a planet and its escape velocity. The surface gravity of the planet should be low enough that movement and pulling heavy loads is much easier than on Earth, while high enough to avoid problems with movement and avoid the long term bad health effects of microbravity. And the escape velocity of the planet has to be high enough to prevent oxygen and other necessary gases from escaping. The surface gravity of a planet can be calculated from the equations here: [https://en.wikipedia.org/wiki/Surface\_gravity#Relationship\_of\_surface\_gravity\_to\_mass\_and\_radius[1]](https://en.wikipedia.org/wiki/Surface_gravity#Relationship_of_surface_gravity_to_mass_and_radius%5B1%5D) And the escape velocity of a planet can be calculated from the equations here: <https://en.wikipedia.org/wiki/Escape_velocity#From_the_surface_of_a_body> [2](https://en.wikipedia.org/wiki/Escape_velocity#From_the_surface_of_a_body) And I have noted that for planets, moons, and other objects less massive than Earth, the listed surface gravity decreases faster with a decrease in mass than the escape velocity does, so that the escape velocities of those smaller bodies are higher, proportional to Earth's escape velocity, than their surface gravities are proportional to Earth's surface gravity. Which helps a bit in having planets with lower surface gravity retain their atmospheres. There is an estimate about how small a planet could be and still have an atmosphere breathable for humans. Habitable Planets for Man Stephen H. Dole, 1964, 2007, is a scientific study of the requirements for a planet to be habitable for humans. [https://www.rand.org/content/dam/rand/pubs/commercial\_books/2007/RAND\_CB179-1.pdf[3]](https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf%5B3%5D) Pages 13-19 discuss the atmospheric requirements, and pages 53 to 58 discuss the mass requirements for a planet to retain a breathable atmosphere for geological amounts of time. On page 54 Dole calculates that the minimum escape velocity for a planet to retain a breathable atmosphere is 6.25 kilometers per second, corresponding to a mass of 0.195 Earth and a surface gravity of 0.49 Earth. But Dole believed such a planet would be too small to produce enough oxygen for humans to breath. Dole made two different estimates of the minimum mass of a planet that could produce an oxygen rich atmosphere, 0.25 Earth and 0.57 Earth. Dole decided that the correct minimum mass should be between those figures, and thus about 0.4 times the mass of Earth, which corresponds to a planet with a radius of 0.78 Earth radius and a surface gravity of 0.68 Earth. However, discoveries since Dole wrote indicate that it might, repreat might, be possible for a world with lower surface gravity than that to have a breathable atmosphere. Titan, the largest moon of Saturn, has a very surprisingly dense atmosphere considering its low surface gravity & escape velocity. Its surface gravity is only 0.36 that of Mars, while its escape velocity is only 0.52 That of Mars. But Titan has an atmosphere many times as dense as that of Mars. In fact, Titan's atmosphere has a atmopshere 1.45 times as dense as Earth's, despite Titan having a surface gravity 0.137 that of Earth and an escape velocity 0.235 that of Earth. So perhaps it is possible for a planet to have a surface gravity like that of Mars, temperatures similar to those on Earth, and a breathable atmosphere. However, part of the reason that Titan has a dense atmosphere is because it is so far from the Sun, and way too cold for unprotected humans to survive. Humans would need very warm clothing to survive on Titan. And while Earth's atmosphere is about 78 % nitrogen and 20.9 % oxygen, Titan's atmosphere is about 97 % Nitrogen and 2.7 % methane, with no oxygen detected. So humans would have to use breathing apparatus on Titan. Titan offers hope that a planet with Mars-like surface gravity and Earth-like temperatures might have a breathable atmosphere, but not proof that is possible. Another possibility might be a story set in a vast artificial space habitat, a hollow cylinder which rotates to provide Earthlike gravity. So perhaps a vast cylindrical space hapibtat has been constructed and has been supplied with an atmosphere, and is being slowly spun to provide Earth-like gravity for the eventual settlers. But it will take years or decades to get the vast mass spinning fast enough to avoid long term health problems for the settlers, so the station is deserted at the moment. But maybe two people have snuck into the station to fly with artifical wings attached to their limbs, which is practical near the center axis of a rotating space habitat but not near the surface where the gravity is too high. Inside this station the gravity is not yet too high at the surface for human powered flight, so they can land and take off from the inner surface, which they couldn't do in a habitat ready for occupation. So maybe the two people are flying low over the surface and can easily land when they want to, unlike in an inhabited habitat, when suddenly some interior storm strikes them and scatters them. They land separately too far apart for each to see or guess where the other has landed, and the protagonist's wings are broken beyong repair. But the station has a hundred levels of interior space below the inner surface they were flying around above. Those levels wiil be interior spaces for people to live in and for all the food synthiszers and other life suppport equipement which will be installedin the future. The surface area will be reserved for parks and other recreational purposes. Those lower levels were built in many thousands of airtight segments that were joined together to form the giant cylinder. And the airtight airlock doors between each segment are locked and won't be unlocked until the station is made ready for habitation. And the protagonist knows that there are emergency supplies in each segment for workers who might be stranded due to accidents. So he opens a door to a ramp down into the lower levels, and finds the emergency cache, which is in the same location in every one of the shousands of segements. He finds a cart and loads it up with all the water and food he can pull in the very light gravity, leaves a note for anyone who might happen to come there, and pulls the cart back up the ramps to the inner surface of the cylinder. And then he sets out across the inner surface until he reaches one of the ends of the cylinder. Then he pulls the cart up ramp after ramp after ramp, the elevators probably not being powered yet, up kilometers to the central axis of the habitat, where their space ship is parked. His partner isn't there. He waits for the partner as long as he can stand to, and then leaves a note at the spaceship and returns to the inner surface of the cylinder. And then he searches the inner surface of the cylinder for his partner who could be dead or injured, and goes down to the emergency supply place in each seqment, checks to see if any supplies have been taken, and leaves a note for anyone who might find it. And it may take him years to search the entire habitat, replenishing his supplies from the emergency supply places, until he either finds his partner or the work crews arrive to begin readying the habitat for the colonists. And this is the best I can think of to justify someone pulling a cart loaded with food and water through a "Mars-like" enviroment. [Answer] Most likely.... But you need to think about the deficiency on Vitamin D. Above the Earth’s atmosphere the solar irradiance is slightly more than 1300 watts per square metre. The Earth’s atmosphere is not perfectly transparent to sunlight and about 1/4 of the Sun’s light scattered before it reaches the surface. At Earth’s surface, with the Sun directly overhead at local noon (clear dry atmosphere), the solar irradiance is reduced to 1000 watts per square metre. This value is highly variable depending upon such things as the amount of dust and water vapor in the atmosphere. At local noon on Mars, with Sun directly overhead, the solar irradiance 590 watts per square metre. Mars atmosphere is very light, like 0.5% as of earth with no ozone layer. So, there are too much UV rays that will burn a space traveller skin quickly. And if they can have enough protection, rickets will quickly affect them and their bones will be weak. So they will need Milk for getting Vitamin D. Plain crackers and Canned beans (if cooked in oil) will provide fat. [Answer] Crackers and beans are, imho, not very healty food, lack of vitamins, too many plant protein from beans with absense of dietary fibres (from fruits and vegetables). I think your character can have dramatic stomach problems from diet like this. But if we consider character found stash of Military Grade Emergency Rations (each of them have enough food to keep grown up human for full day), things are not so dramatic. Lets consider this tourist grade ration: [![tourist grade food ration](https://i.stack.imgur.com/UZlCI.jpg)](https://i.stack.imgur.com/UZlCI.jpg) Kits like this are popular among Russian hikers. It has various porridges with meat, preserved vegetables, dried bread, some snaks and food warming systems. Water not included. All this kit weights around 4 lb or 1.5 kg. So, to survive 6 month, character needs 6\*30 = 180 kits, or 270 kg / 720 lb of this kits. Its possible to carry all this weight in hand pulled cart. If we had Mars like environment with lower gravity, task is much easier. But, humans requires ~ 2-3 kg of water per day, so your character needs big flask and access to drinkable water sources once per few days. Also, humans requires oxygen. And there is no oxygen in Mars atmosphere. [Answer] If this is a survival mode with a lot of physical activity, exposure to the sun, then you can survive with one type of food. Moreover, the brain involved in nutrition accepts that this is the only way to get energy. Ultimately, this will [change our body structure](https://gut.bmj.com/content/gutjnl/27/Suppl_1/9.full.pdf) and how the brain works differently. But if there are other food options, it's very difficult to convince the brain. Moreover, in order to think, learn and behave in today's social conditions in an extremely competitive world, all nutrients are needed in order to cope with others. In this [article](https://workoutplan.org/lose-30-pounds-in-30-days/), it is said that malnutrition of your daily allowance for a long time will definitely cause micronutrient deficiency. When the body does not get enough essential vitamins and minerals from food. Micronutrient deficiencies can impair health and development. [Answer] Survival is impossible: By "plain crackers" I assume soda crackers. Vitamin A = 0. Beans, Vitamin A = 0. ]
[Question] [ > > NOTE: This question is inspired by my own answer to a previous question. > There is no duplication. See > [What do stranded astronauts eat in space](https://worldbuilding.stackexchange.com/questions/178874/what-do-stranded-astronauts-eat-in-space) > > > --- Scenario On a mining planet where there are vast deserts/wastelands. Food is supplied from the main base. Small vehicles carry mining-scouts long distances from the base. The planet is subject to huge storms that can make rescue impracticable for long periods of time. In case of vehicular breakdown, lack of food can become a problem. The scouts vehicles have many metal parts but a lot of the interior furnishings (the seats etc.) are made of a durable but edible substances. This is sufficient to sustain the occupants for many weeks. Historical examples In all of the following, partly edible vehicles could have been highly advantageous. 1. On Oct. 13, 1972, a Uruguayan air force plane, carrying the Old Christians Club rugby team, crashed in the Andes mountains of Chile. Facing starvation and death, the survivors reluctantly resorted to cannibalism. Among the 45 people on board, 28 survived the initial crash. After 72 days on the glacier , 16 people were rescued. Uruguayan Air Force Flight 571 <https://www.britannica.com/event/Uruguayan-Air-Force-flight-571> 2. There are anecdotes of polar explorers being forced to kill and eat their sled-dogs when rations ran low. 3. During the Lunar landing, "the descent stage was left on the moon, while the ascent stage crashed into the moon’s surface once the astronauts returned to the Command Module" <https://apollo11space.com/nasas-apollo-11-lunar-module-basic-facts/> Had those stages been edible, the space shot would have been feasible with a smaller payload. Question An edible vehicle would require many of its parts to be highly durable but nutritious when eaten directly by humans. Is there already a substance available that would fulfil this role? If not, how difficult/easy would it be to develop? Note In response to comments, this substance is for emergency meals only. It is only deployed when normal food runs out and there is danger of starvation. Whether it tastes good is irrelevant as long as it keeps the crew alive long enough to be rescued. Part of the substance's specification is that it does not go rotten but is structurally strong. I'm asking if such a substance is feasible with modern technology or could be in future. [Answer] Why not use a horse or similar mount? It has low maintenance and can self-refuel, and , in times or dire need, can be eaten. Obviously the animal will be engineered to the specific environment. [Answer] I think is a really good idea. In [this](https://www.acs.org/content/acs/en/pressroom/newsreleases/2016/august/edible-food-packaging-made-from-milk-proteins-video.html#:%7E:text=These%20casein%2Dbased%20films%20are,are%20biodegradable%2C%20sustainable%20and%20edible.) article you can find how with actual technology it is possible to develop an edible plastic-like substance that is used to make food wrapping. Edit... At the grocery store, most foods come wrapped in plastic packaging. Not only does this create a lot of waste, but thin plastic films are not great at preventing spoilage. To address these issues, scientists are now developing a biodegradable film made of milk proteins and you can eat it. Led by Peggy Tomasula, the team at the U.S. Department of Agriculture developed an environmentally friendly film made of the milk protein casein. These films are up to 500 times better than plastics at keeping oxygen away from food and, because they are derived from milk, are biodegradable, sustainable and edible. The researchers presented their work at the 252nd National Meeting of the American Chemical Society. Although the researchers’ first attempt using pure casein resulted in a strong and effective oxygen blocker, it was relatively hard to handle and would dissolve in water too quickly. So they made a few improvements, adding citrus pectin into the blend to make the packaging even stronger, and more resistant to humidity and high temperatures. The material has a number of unique applications. In addition to being used as plastic pouches and wraps, this casein coating could be sprayed onto food, such as cereal bars or flakes. Right now, cereals keep their crunch in milk due to a sugar coating. Instead of all that sugar, manufacturers could spray on casein-protein coatings to prevent soggy cereal. Co-leader of the study, Laetitia Bonnaillie, says the team is currently testing applications such as single-serve, edible food wrappers. Individual dried soup portions, or instant coffee wrapped in the film can be added to hot water where the film readily dissolves, eliminating the packaging waste. Because single-serve pouches would need to stay sanitary on store shelves, they would have to be encased in a larger plastic or cardboard container to prevent them from getting wet or dirty. Tomasula and her team hope in the future their casein based film helps foods keep fresh during shipping while decreasing the amount of plastic waste entering landfills. So I suppose that this technology is an really early stage from developing some really rigid and sturdy material that can have many uses. [Answer] Utility Rovers for Remote Operations have been a staple of prospecting across many millenia and many worlds. They can be made of many substances; on a partially terraformed world with Earth-origin plants, the Biological Utility Rover for Remote Operations has proven popular and is edible. Additional chemical processing is required to make it palatable, but many Earth-origin shrubs have woody cores that can be used to construct a carbon-based plasma that will trigger the Maillard reactions. Advantages of the BURRO approach: * Unlimited range in terraformed areas with water. * Effective on uneven terrain. * Waste products can be combusted to produce a morale-enhancing contained plasma reaction. * Builds morale by empathic connection with pilot. Disadvantages of the BURRO: * Limited to terraformed areas with drinkable water * Low maximum speed * Small temperature and atmospheric composition range * Empathic connection with pilot renders consumption traumatic. * Can go off course at night if not properly secured and it thinks somewhere else is more interesting than where you are. For a high tech society, the possibility of a bioengineered lifeform that can consume alien organisms and convert them to human-suitable food comes up. That would, of course, have to be tailored to the ecology of the particular host world. For the next step up, the pilot could be modified to be able to consume alien life. This still needs to be host world specific, and is likely two-part: the miner has modifications that make it easy for them to host symbionts, and only the symbionts need to be swapped out per-world. Now, for a mechanical rover of some sort, the first question is always "why not just make it bigger and add an extra pemmican compartment?". If scouting normally involves bringing a lot of ore/samples back to base and the weather is predictable enough that the satellites can tell you when a dust storm is coming far in advance, that really seems like the best option. But that's not at all what you were asking for. Light, durable, and strong, dried balsa meat has been used to construct the frames of small aircraft, tent poles, and rovers for centuries. An early product of genetic manipulation, its impact on culture cannot be understated; there is even a Terran tree named after it. You can eat it, though it takes a very long time to soften up enough to chew. It tastes much, much better than the leather hull of your rover or the wings of your glider do. In a pinch the balsa meat wheel-rims can be eaten, though they can lead to poisoning if you've driven through particularly toxic terrain. The repair kit includes several extra panels of hull leather, a full set of six new balsa meat rover wheels, and several balsa meat spars. The contoured grip on the rover gearshaft and the buttons on your keyboard are made of dried shelf fungus (the internet assures me that I can eat some shelf fungi today), carved into the desired shape and coated with a biologically inert shellac which, while it contains no nutritive value, is perfectly safe to eat. The seat cushions are a plastic foam honeycomb, each cell containing approximately a single meal's worth of various Foods™, perfectly nutritionally balanced. These don't actually taste bad - the deterrent to eating them is the fact that the seat will be a lot less COMFORTABLE once you've eaten all the Szechuan Cream of Wheat, Spicy Minty Peas, and Professional Rose Chili (genetic engineering produced non-flatulence-inducing beans centuries ago, but it turned out that what the market really wanted was not a reduction of flatulence but rather an improvement of aroma.). Note that atmospheres with high O2 aren't stable in nature; if an unmodified human can breathe the air, there's an ecosystem or some sort of HUGE terraforming engine on the planet - in which case foraging may become relevant. If the atmosphere is not breathable, the scout is going to need very high quality atmosphere regeneration tech. The atmosphere regenerator might also have the ability to output some catalytic chemicals that convert tough and inedible construction materials to digestible form. Also, while a mining-dominated planet already implies cheap space travel (difficult to imagine raw materials worth taking from Mars to Earth in large amounts, for instance), a single-industry planet only works if space travel is RIDICULOUSLY cheap - say, a giant wormhole with trains to Earth running through it. There will be plenty of other industries at the main base, at least for domestic consumption - farming, for example. If the planet is also in the process of being terraformed the manual for strandees may include instructions for optimum distribution of terran-ecosystem fertilizer and seeds of the seventeen useful plants. [Answer] I can't say how long it sustained them but IRL people have eaten leather to ward off starvation. ]
[Question] [ I can imagine the proliferation of Alcubierre drives in the distant future, which would distort space so it takes the shape of a Mexican hat in 4D map. I am wondering, what would the gravitation wave output from such a drive looks like? How many chirps would occur between turning he warp drive on and off? Can the warp drive be passive? If so, would there be any gravitational waves, however feeble? [Answer] Alcubierre's solution to the Einstein field equations ([Alcubierre 1994](https://ui.adsabs.harvard.edu/abs/1994CQGra..11L..73A)) gives us a metric - an expression describing how spacetime curves - of the form $$ds^2=-dt^2+(dx - v\_s(t)f(r\_s)dt)^2+dy^2+dz^2$$ where our drive is moving in the $x$ direction at a speed $v\_s(t)$. $f(r\_s)$ is a function encoding the size of the bubble itself. When we talk about an Alcubierre drive, we are usually talking about this solution to the field equations, rather than a device that has more freedom to behave in different ways. Gravitational waves are generated by any object with an accelerating mass quadrupole moment. What that means is that we require certain kinds of acceleration to produce gravitational waves. Sure, any object with mass or energy will bend spacetime, but to actually produce gravitational waves we need acceleration. The upshot of all this is that an Alcubierre drive, while in operation, will not produce gravitational waves if $v\_s(t)$ is constant. (If a constant speed drive is what you mean by "passive", then this is the key bit for you!) In the case where $v\_s(t)$ is not constant, I'm not sure what the gravitational wave signature would look like, because I don't think anyone's investigated it. The problem is that the Alcubierre metric describes a universe with just a moving drive and nothing else outside it - we assume that $f(r\_s)$ goes to $0$ outside the bubble, and so we have flat Minkowski space. In other words, the metric behind the drive assumes that there are no gravitational waves. It's a toy model, not necessarily an accurate representation of reality. When we talk about an Alcubierre drive, we think about the metric - it's not like we have a physical object and calculate the properties of spacetime (i.e. the metric and its perturbations) based on that. Regarding chirps: [The gravitational wave chirp of two inspiraling masses](https://www.ligo.org/science/GW-Inspiral.php) occurs because the gravitational wave output itself is changing. In the final milliseconds before coalescence, the two bodies rapidly get closer and closer, drastically increasing their orbital frequency. As gravitational waves [are emitted and twice the orbital frequency](https://astronomy.stackexchange.com/a/36312/2153), we would therefore expect the frequency of the waves to change in time - producing a chirp. We would, then, only detect a chirp if there was a change in the acceleration; presumably, this would not be significant in an accelerating ship if that acceleration was roughly constant, and so we would detect no chirp. The only way to produce a sequence of chirps would be if the ship was repeatedly accelerating and then decelerating, which is strange behavior for an object trying to reach high speeds. [Answer] Your best answer would be to look Dr Alcubierre's original paper or summaries of it to get a description of how 'space' is curved before and behind a ship using this drive (it's not a gate). The drive 'bends' local space around the ship severely so as per General Relativity there should be gravitational wave effects (I think). If you insist on a 'gate' then I don't know a possible answer. Dr Alcubierre's paper relates strictly to a hypothetical object moving at FTL speeds when surrounded by an effect the object generates itself as it moves, not a generator that imparts 'motion' onto other objects while staying fixed in place itself. Your 'gate' would have to travel with the ship to be a true Alcubierre drive. For a true gate you are better off with wormholes. ]
[Question] [ In world building it is often interesting to consider extreme landscapes – how tall can a mountain be on Earth for example. But what is the tallest mountain possible in any gravitational environment? Formation of the mountain may be unlikely in the extreme, but it must be at least theoretically possible to form by natural processes. For the purposes of this question a mountain's height is the distance between the mountain peak and the average radius of the object it is physically joined to. [Answer] Step 1: maximizing planet size Having the largest potential body gives us the most space to work with. I'm going to assume a rocky planet because gases generally don't form mountains very well, and massive wind speeds will work against our goal. Wikipedia directed me to [this paper](https://arxiv.org/abs/1311.0329), which suggests that 1.75 Earth radii is the upper limit for rocky planets. 5 Earth Masses is the round number floating around this size of planet, which gives us a surface gravity of about 1.6g. Step 2: building a mountain I'm going to run with the idea of a shield volcano, since that category includes the largest mountain in the Solar System and the largest base-to-height mountain on Earth. According to wikipedia, these are usually pretty shallow, with a typical height/width ratio of 1/20. Olympus Mons on Mars is steeper with an about 1/11 average slope, but it only has to handle 0.4g instead of out mountain's 1.6. I will be running with 1/25, because I can assume some optimization on our lava composition and don't know how I would calculate the exact ratio But how wide can we make the mountain? Since the layers form in a liquid state, I think it's reasonable to assume that the shape can be scaled up without breaking. In this case, we are limited by the size of the planet, since after that point we are just increasing the planet radius. In other words, our maximum width is half the planet's circumference, and our maximum height is 1/25 of that, or 1401km. Step 3: minmaxing The tallest mountain on Earth by your criterion is neither the tallest base-to-height mountain, nor is it the mountain with the highest altitude. This is because the Earth's rotations cause the shape to be squashed such that the equator is farther out. There doesn't seem to be data on how fast a large rocky planet can spin, and the actual effect is hard to calculate because planets have a non-uniform composition, so I'm going to assume that we manage to get the same flattening as Earth (1:300), and position our globe-spanning volcano on the equator. This isn't a large amount, but it'll add a couple extra meters. result: 1413 km Note that this is not a peak by any stretch of the imagination, it's a very shallow bulge that takes up the entire planet. [Answer] A mountain is a lot of rock placed atop other rock. So, you need for the lowest layer of the rock to not crumble and flow outward (beyond a certain point, the rock will behave like a slow-flowing liquid); you want a very high compressive strength. Since you seek to maximize the (roughly speaking) mass of the mountain and the F=ma equation tells us that m = F/a, you not only want to maximize the compressive strength (which equates F) but also minimize a, which in this case is the gravitational acceleration "g". Then again you do not want to maximize the mass, you want height, so, a huge volume for any given mass. You want a mountain that is not too dense. The weight of the mountain is proportional to density multiplied by the volume, which is $1/3 \cdot S \cdot h$ for a conical mountain with base S. The downward pressure is then $\rho \cdot g \cdot h/3$ and we want it to equate the material's compressive strength: $\rho gh/3 = c$ so $h = 3c/(\rho g)$ with c = compressive strength, $\rho$ = density, g = surface gravity. Simply plug in the parameters for the material (c and $\rho$) and the planet's surface gravity and you ought to be done. With c measured in Newton over square meters, $\rho$ in kilograms over cubic meters and g in meters over seconds squared, you will get the maximum height expressed in meters. [Answer] I would suggest that volcano formed islands would be the "tallest mountain possible in any gravitational environment". "For the purposes of this question a mountain's height is the distance between the mountain peak and the average radius of the object it is physically joined to." By this definition, many of the Earth's tallest mountains are well below sea level. Beyond Earth, look at Olympus Mons on mars, 13.6 miles tall. ]
[Question] [ I am an alien from outer space who is visiting a planet called Earth. The species living here, humans, have a very primitive and strange culture. They seem to spontaneously burst into dance and song, performing long musical performances at random notice. The topics involving these musical numbers can involve anything ranging from love in a relationship to discovering a magic lamp. This can grow to be very irritating, as a simple conversation with one of these idiots can erupt into a long musical number when a simple answer would have sufficed. This bizarre nonsense usually starts off with one person at a time. They normally complain about their woes or some aspect of their life, and begin singing loudly. This could occur in an isolated spot or a heavily populated area. This singing eventually leads to body movements which I interpret to be what passes for dancing in this species. The effect seems to be contagious, as any passers-by are affected and join in, extending the range and effect to others. Soon, hundreds or even thousands of random strangers join in the number, despite having no relation to each other. The performance appears to have been perfectly choreographed, as everyone is on cue and NSYNC with each other, despite having no previous contact. This can go on for minutes, until the performance is over and everyone goes back to what they were doing before. This strange occurrence is unique compared to all the other species I have observed. I am currently studying them to discover why this happens, and whether the effect stems from something biological, mental, or cultural in their society. It may simply be a mix of all three in some way. How can I explain this bizarre behavior? [Answer] The Dancing Plague is back and better than ever. This phenomena was [first observed](https://www.britannica.com/event/dancing-plague-of-1518) in 1518 in Strasbourg. Perhaps it was demons, or contaminated rye, or an entirely psychological phenomenon - but for several months, people were inexplicably compelled to burst into dance. Combined with the rise of musical theater as an art form among humans, it's no wonder why isolated performances propagate through the population today. [Answer] Why would you write a poem, or a heartfelt letter to your loved one? A simple affirmation of love would convey the same meaning without using so many words. Why would you speak to your boss politely and ask for a raise, instead of just bluntly stating that you want it? As humans, we do value other humans putting more effort into their communication than just stating the facts. Using formal, or even literary language is then a kind of kindness we extend to others - we show that the other person is worth us expending the extra energy on communicating with them. Various societies on Earth have different ideas of how much and what kind of formality is appropriate in which situations, but the overall idea is similar - the more you have to think about your words, the more effort you put into them, the kinder and more polite you appear. And putting our thoughts into verse, arranging a melody around them, and punctuating that with a choreographic routine certainly does take a lot of effort. And with that kind of communication being common, other ideas grow around it. Just like holding the door open for someone is viewed as nice even if they don't require the help, so is joining in as a backup singer or a part of the dancing crowd. Don't be alarmed then, stranger - they're just being kind to you. Maybe a bit overly kind, but I'm sure you'll get used to it. [Answer] First of all - if you call the culture, you're "studying", behaviour - a "bizarre nonsense" you might be in the wrong field. You are not only biased toward them but also prejuiced and with very narrow defintions. You interpret the thing as "dance" because it's what in your culture is called (not even on your planet). But it's a language. A language shared by a lot of people, hence they all know rules of it. Rules on with whom they might share it, to whom story they might add a little reverb/echo by participating in the background. What stories are performed solo and what are a group effort. Make an experiment - think if you can "dance" the sentence "whip the mashed potatoes for the nana". Also observe some more species. This is not unique. Blue Footed Boobies do that in pairs. Blue Manakins in little groups of four. Andean Flamingos in dozens. [Answer] Over the life of every human they have been trained to associate singing and dancing with happiness. This species seems to be the most happy when they sing and dance, especially in groups. Many of these songs and dances are ritualistically taught starting at birth. Everyone knows the newest song and dance as it is broadcast on TV or on the internet. Everyone strives to become the newest song and dance sensation as the most famous of this species are singers. Oddly enough, the most common place for humans to sing is in the shower. Or maybe futuristic musical brain chips installed at birth. ]
[Question] [ Assume that space warfare is dominated by gamma and x-ray lasers (Wakefield-Plasma and Free Electron Lasers) capable of killing targets several light-seconds away. Stealth in space is possible due to optical metamaterials and cooling tech, this is a set assumption. However stealth is rendered useless by x-ray phosphorescent scanning. Antimatter mass-production and fusion are well understood technologies and are easy to use. The setting is nonetheless supposed to be hard-scifi. While conventional projectiles will be vaporised quickly by the lasers, and throwing kilometer sized asteroids at them to overwhelm them isn't really an option, a black hole would be a projectile utterly immune to laser fire. Ultra small Kugelblitz black holes with lifetimes in the days or hours seem to be suited best for this, due to their relatively low mass and the fact that they will give off enormous amounts of energy as gamma radiation. Scale the black holes right and even a near miss can evaporate an enemy spacecraft. The only way to counter this would be evasion or point-defense with defensive black holes, which perform a flyby maneuver to deflect the incoming black hole. The Kugelblitze are generated using the laserstars laser and mirror essemblies, either tuned down to lower wavelengths or using [x-ray mirrors](https://www2.lbl.gov/Science-Articles/Archive/multilayer-mirror-optics.html). Basically the mechanism just puts enough photons in one place to create a black hole of the desired mass. The issues begin after the Kugelblitz is generated. How do I move a Kugelblitz black hole? I know that gravity, meaning a [gravity tractor](https://en.m.wikipedia.org/wiki/Gravity_tractor), would work, but the performance would be pityful. Can the black hole be manipulated by electro-magnetic fields? If that where the case, would building a coil-gun or a missile out of it be possible? [Answer] You have an issue with evaporation of black holes. A black hole of mass 228 tonnes has a life time of about [1 second.](https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_evaporation) The life is roughly proportional to the cube of the mass. So to get 100 seconds you'd need just over 1 thousand tonnes. Or 4 thousand tonnes for roughly 2 hours. So producing 4 thousand metric ton black hole from radiation (the meaning of Kugelblitz) would be a challenge. And then it would only have 2 hours to reach its target. During that 2 hours it would be radiating at a truly astronomical intensity, with the intensity rising quite rapidly. Being nearby your bullet just before you shot it would be a challenge. Possibly the original radiation to produce the black hole, projected at the enemy in a not-particularly-tight beam would be nearly as harsh a weapon. And probably a lot easier to direct at the opposition rather than into some kind of mad focus on an absurdly small object. (If I did the math right, a 4000 tonne black hole has a radius of 6E-21 meters.) So producing such a thing would be a lot harder than tossing around anti-matter. Very much a lot harder. However, leaving that aside, black holes have mass, charge, and angular momentum. So you could chuck in some extra electrons and use electro-magnetic fields to push it around. Of course, the magnetics to push a 1000 tonne projectile around would themselves be a challenge to work with and around. Your red blood cells, for example, are subject to being [affected by extreme magnetic fields.](https://physicsworld.com/a/magnetic-fields-reduce-blood-viscosity/) To say nothing of the effects on any metalic components in your nearby ships. [Answer] At first, it may seem crazy, but yes. Alexander Bolonkin seems to have an idea on how to do this: <http://vixra.org/pdf/1309.0200v1.pdf> ]
[Question] [ One of the major sources of conflict in my story is that, in my story's modern-day world, two to three times a year, a week-long supernatural effect is globally applied to everyone on Earth over the age of 13. These can range from relatively minor things like rendering them all mute, to the far more dangerous effects like making them all fall sideways instead of down. Now, one thing that occurred to me early on with this concept is that there's a heck of a lot of human upkeep that needs to be done every day to keep society moving. Too much global disruption to everyone's work week, it stands to reason, could result in lasting damage to society and its various systems. But given that there's a lot more going on in my story's world than just these periodic week-long events, asking about the consequences of any of the specific scenarios is going to be insanely complicated. So I thought I'd high-ball things to get something close to a worst-case-scenario in terms of how much an event like this could leave society unattended, then see what the various consequences of that would be and how long it would take to fix them. So here's the scenario, and to keep things simple let's focus on America: One Saturday afternoon, every single person on Earth who at that moment is 13 or older suddenly turns into a ghost. They're all still audible and visible (though semitransparent), can fly at about 20 mph in any direction they like, don't get hungry, tired, or have any biological needs at all, and are still wearing whatever they were wearing when it happened, but they cannot physically interact with anything, ghost or non-ghost, apart from their own body. Also, they can't leave the confines of the Earth's atmosphere, and when not flying are locked to the planet's general inertia and won't drift off into the sky as the planet moves. Before this happens, everyone on Earth who would be affected is struck by a vague dizzy feeling, just enough to make them want to stop doing anything potentially dangerous like driving a vehicle. So assume no massive traffic accidents caused by millions of suddenly-unmanned vehicles. Also, assume no planes are flying when this happens. This will last a week, after which everyone will turn back to normal(after being gently pushed upward out of any solid matter they may have been ghosting through at the time), and due to past experience with this world's magic system the fact that it will last a week is common knowledge. And it won't affect anyone who turns 13 during the week, only those who were already 13 or older when the event happened. Basically, every single adult (and teenager) on Earth is rendered physically incapable of doing their jobs, and if they need something to be done during this week, they need to get a child to do it for them. Now, that's the scenario. The first question about this scenario that I'd like to ask is what it would do to our electrical infrastructure. Power plants, power lines, everything that's involved in getting electricity to people's houses and keeping the America's lights on. How much damage is this forced neglect of the world's infrastructure going to do to the power grid, what can the people, ghost adults and physical children, do while it's happening to mitigate the damage, and how long will it take before the power grid is back to normal? [Answer] *The grid will not survive intact.* A significant amount of technical knowledge and experience is required to keep an electrical grid functioning. First, you need trained linesmen who can physically maintain the equipment. This job cannot be done by untrained 12 year-olds, even with ghost supervision. They will be electrocuted before the day is out. Second, you need experts in grid control, current management, and switching. Without these, instabilities in current usage will result in [cascading failures](https://en.wikipedia.org/wiki/2016_South_Australian_blackout) and ultimately render the grid inoperable. I estimate this will happen within 48 hours. Sooner if there is any kind of inclement weather. 12 year-olds, even with ghost supervision, will not have the required training or software familiarity to operate the control room. At least these children won't die. Thirdly, you need to keep the generation sites running. Power stations suffer from both of the issues described above; They are both maintenance heavy, and need constant management of elements such as current flow and switching. Depending on your type of power station, it may automatically shut down, or it may suffer a catastrophic failure and explode. For reference, a pentane-based binary cycle geothermal powerplant supplying 25 megawatts contains sufficient flammable pentane that a failure causing a leak has the potential to detonate with a force similar to a small nuclear weapon. [Answer] It’s already fairly obvious the power grid will not survive intact; there are too many jobs in this sector that require actual experience for ghosts to conceivably guide 12 year olds through. I think the main reason for that does not lie in a twelve year old being capable of the job, especially if it’s just to mitigate problems for systems that mainly need programming or technical support, but because the twelve year olds of today’s generation are significantly less responsible than say, those from medieval times. The biggest issue would be for the ghosts to actually convince the children to even go do their jobs. They would have to first find the children responsible enough to do the job, which would already be somewhat difficult. Secondly, they would have to convince the child to do the job, which would be nearly impossible. With all the children running rampant, with no clear hierarchy, the children will probably adopt a mob mentality, making it difficult for any adult (or anyone, persay) to easily control them. In a handful of cases the parents of the children could perhaps have enough authority, but this means that the number of children available to be employed for the task is very limited. Children will also be much more timid, and be influenced by stereotypes or other notions developed during school. It may be hard for parents to convince their children to do dangerous tasks, and more likely, they wouldn’t force their children to do these in the first place. As such, the power lines across the country will fall completely into disrepair for the next week. These two issues of limited manpower and the inability to do most of the dangerous physical work will lead to a fairly comprehensive collapse of the power grid, but optimistically, some of the damage can be prevented by the small number of responsible children. [Answer] There are two takes on this in my mind. If your described ghost event suddenly happened in today's world the grid would fail as described in other answers, so I won't rehash that. However if these events as your question suggest happen several times a year, and have been for some time, the entire infrastructure system, and even the way society is structured would likely be designed around the lack of adults for a week. With a divergence from what we have today depending on how long these style of events have been happening. So it makes a big difference how long ago the events first started in relation to the timeline of your story. For example, if these events have only been happening for a year or so, started in a 2018 version of our timeline, the main concern is going to still be getting through event with minimal damage, turning off the major power suppliers ahead of time and relaying on local power sources that require less over sight. So individuals or communities may have solar or wind power that can continue mostly unsupervised while the adults are ghosts. An easy to prepare weeks of rations would be stashed for the older kids to prepare for themselves and younger kids. At this point people are still adapting to the new normal, and some disruption is likely to occur, but the pieces get picked up afterwards. If the events have been happening for decades instead, 1950 start time in our line, you will start to see more extreme changes, communal child reading is very likely. Essentially a boarding school for everyone from infants to 13. With the older kids 10+ being trained and trusted with running the school during gap the occasional weeks that the adults are ghosts. From a power standpoint the country will have started to move away from or have moved away from a national network. Passive power generation and effective ways to store it will take priority, and the grid will break into smaller units that can stand on their own of one does fail during an event. If these events have been happening long enough, on the order of centuries, it is likely that society would have developed in a much different way than it did in our timeline and while the setting could be modern from a tech standpoint great liberties could be taken with what techs did or did not develop. ]
[Question] [ How would you design a saddle for a giant turtle (think rhino size) and a bridle, and how would you make it go, given that spurs or whip wouldn't really be an option with the shell? [Answer] Turtles as a mount certainly wouldn't be fantastic for cavalry, but they may make ok pack animals. To start with a Saddle. Think of the saddles and big curtained affairs that go on elephants. Have the straps go around from front right to rear left and the opposite on the other side. The round nature of the shell should help maintain tension so the saddle or chair or whatever doesn't move around much. The turtle isn't going to be running at a gallop, so this should be fine. Next your bridle. This is harder. Since most turtles have a beak like affair, you would seriously have trouble with a traditional bit like is used with horses. In a horse, the bit fits in the tender part of the mouth behind the teeth. I don't know that much about the skull and musculature of a turtle's mouth, but beaks might be like giant shears. Sadly, that means we might have to get inhumane. You know the trope about the ring in a bull's nose? That was used as a control and lead point because it hurt the bull to pull against the ring. Find a spot on either side of the turtles head that is sensitive and pierce it to hold the reins. Maybe along the lower jaw or something. As a spur, you could use something like a prod to reach to the back legs. Maybe a mechanical contrivance that can poke up underneath the shell to the back legs. That way the poor fellow can't just tuck himself up under the shell to stop the poking. A turtle isn't going to be able to pull huge loads, but they can probably lift quite a lot. Build an area like a truck bed connected to the saddle part to carry cargo. I hope you can find some very patient trainers. [Answer] You don't provide any context on the type of Tortoise you are referring to but something that might make it feasible is [long neck tortoises/turtles](https://upload.wikimedia.org/wikipedia/commons/0/0e/Common_snakeneck_turtle_(Chelodina_longicollis).jpg) these animals have necks so long they can't be retracted into a shell or only partially retract. So you can have classic saddle like you would for a horse mounted on the neck but as these necks are usually used for snapping at things such as with a snapping turtle they would have enough muscle strength to support a rider but if it decided to snap the rider would have a terrible time. With this long neck style tortoises you could also strap a saddle to the edge of the shell, perhaps something like a [camel stool saddle](https://i.ytimg.com/vi/e28pUtVdGtw/hqdefault.jpg) and use extended steering ropes (not too familiar with harnessing terminology) to pull the head side to side to guide the animal in the direction you want to go. This style of harnessing should also work with the shorter neck variant of tortoises or turtles. [Answer] The saddle would be like a full chair, strapped all the way around the turtle. If the turtle has a good hard rim around the top shell, you might be able to hook the straps onto that, and tighten them against straps hooked on the opposing side. It might be best to motivate the turtle with food on a stick, but turtles also have sensitive shells, so "spurring" it might not be totally out of the question. You could touch the rear top of the shell with a hot poker, or you could set something up so that when the rider pulls a cord, a spike is driven into the rear underside of the turtle's shell, prompting it to move away from the harmful spike underneath it. The shape of a turtle's shell is also heavily affected by the turtle's nutrition intake as it grows. For many breeds, malnutrition leads to a more spiky looking and less rounded shell. That spiky shape might make it easier to keep straps in place, so a turtle being raised for mount might be kept on a careful diet while growing, and then fed an improved diet for strengthening the turtle when it gets big enough to ride. Turtles' natural defensive behaviors would make them a suboptimal mount for battle. Turtles can be fast, but they also tend to be contemplative. It may just be the case that anyone mounting a turtle must also be patient, and ok with the turtle making random stops here and there. ]
[Question] [ Assume that an [Alcubierre drive](https://en.wikipedia.org/wiki/Alcubierre_drive) is feasible. In fact, assume that one has been built. A superluminal starship can propel itself through space by distorting space in front of it and behind it. However, other than an Alcubierre drive, there are no other known technologies that allow anything to travel faster than light (no wormholes or anything). Utilizing this same technology, is there any way to make a communications system that does not involve a vessel? An electromagnetic wave carrying information (like modern radio or cell phone signals) won't have any feasible way to bend space around it; you would need a drive and power source, themselves inside a vessel. If Alcubierre drives exist, does this imply that communications can travel no faster than the Alcubierre driven vessels, just as news could not travel faster than sailing ships in ~1700? [Answer] Not necessarily. The Alcubierre metric merely describes a space-time that is compressed in front of your spacecraft and expanded behind it. The assumption has always been that the warp field comes from the craft inside the bubble, but this isn't required to be the case. An interesting thing about the Alcubierre metric is that it looks almost identical to the shockwave produced by aircraft traveling at supersonic speeds. An aircraft has air compressed in front of it because the air can't get out of the way fast enough, and rarefied behind it because it hasn't had time to diffuse back into the wake created by the aircraft. The difference with an Alcubierre drive though is that this compression/expansion is actively created by the drive itself and used to carry the ship along, whereas a sonic boom is just a side effect of exceeding the speed of sound. If you imagine taking a string or a rug, and whipping it to create a traveling wave in it, this would be equivalent to your FTL communicator. It might be possible to derive a solution to the Einstein equation where this "wave" travels faster than the speed of light, as there is no limit on how fast space-time itself can expand (in fact the current research suggests at the edge of the Universe's visible horizon galaxies are moving away from us at 3x the speed of light). The caveat here is that what I've described is also essentially a gravitational wave, and we know gravitational waves move at the speed of light, so it's questionable whether or not you could do this without a vessel. However, even if it's possible, what this does mean is that your comms system is point to point. It's essentially like a laser beam, and wouldn't be able to do broadcast like we do with radio waves. In order to communicate with a space colony or a ship, you'd have to know where it is to send your FTL beam. For colonies, the motion of planets are known well in advance, so it's not as big a deal, but attempting comms with a ship if you don't know where it is would be an issue. I would imagine in this case FTL comms would be similar to how submarines work, in that the spaceship would be out of communications except for certain windows where the ship is in a known location or it drops out of FTL to call home. Since the ship knows where the home base planet is, they'd have no problem setting up their point to point comms, and could radio back their position to allow the planet to communicate back. Now, assuming what I've described is possible, there are some things we can say about the physics involved: * The amount of negative mass density you need to form an Alcubierre bubble is related to the size of the warp bubble you need to create. If we're just creating warp bubbles around photons in our beam, the amount of mass needed would be drastically smaller than that needed for a ship, it just has to be bigger than a few wavelengths of your photons. * More than likely you would have to send this negative mass density along with your photons, so we might think of a kind of "exotic energy" used to carry information instead of photons. In this case, your Alcubierre bubble itself becomes the information carrier. There are only two things we know of that exhibit this exotic matter/energy property: The Casimir effect and Dark Energy. The Casimir effect can only occur between small plates, and is more akin to how holes/electrons function in a semiconductor than what we might call "real" exotic matter. Dark energy however is prevalent in the Universe itself and is our best guess at what is driving the accelerating expansion of the Universe. If you can find a way to harness dark energy, you can not only build your warp drive, but you can use the "dark quanta" of the energy to send information faster than light. In your story you might say scientists have discovered an exotic matter particle that is responsible for Dark Energy, and manipulating these particles is how they form a warp bubble. You could then go on to say that sending beams of these particles is how your civilization communicates at FTL speeds, perhaps by "bundling" dark energy into a long-lived packet that travels at FTL. The "range" of this packet would depend on how long it can stay together. [Answer] > > If Albucierre drives exist, does this imply that communications can travel no faster than the Albucierre driven vessels? > > > Yes. But that doesn't actually mean anything. Because Alcubierre drives can travel through time. If the only technology in your setting not backed by modern hard science is the Alcubierre drive, then there is no other technology in your setting for FTL communication, by definition. You could easily add one, of course, but that's getting off-topic. Any FTL travel technology can send matter and information backward in time if and only if it is capable of making FTL jumps in different directions in different frames of reference moving relative to each other. Alcubierre drives are actually one of the hypothetical FTL drives most amenable to exploitation in this manner, since the simplest way for them to work is for each FTL jump to take place in the ship's proper frame (that is, the reference frame moving with the same velocity as the ship, in which the ship is stationary) before the jump. Thus, a ship could fire up its Alcubierre drive, zip off into interstellar space, drop out of warp (moving at the same speed it was before the jump), fire up its conventional thrusters, accelerate away from Earth to nearly the speed of light, hit the Alcubierre drive again, and return to Earth several years before it departed. Because special relativity. That explanation made no sense at all, so [here's](https://www.youtube.com/watch?v=HUMGc8hEkpc) a video from PBS Space Time that explains the FTL time travel process much more clearly. I will note that, with this system, it is much easier to send small packages back in time, since that crucial conventional-thruster step in the middle will require burning a huge amount of propellant. Your engineers may find that sending people back in time by this method is economically infeasible, but sending a couple of SSDs in a tiny Alcubierre-enabled ship could be profitable. If you want to forbid FTL time travel, you need to ensure that all FTL travel occurs in the same universally agreed-upon frame of reference. This is probably easier to justify with a technology that teleports ships instantaneously from one place to another, a lá the Teraport in Schlock Mercenary. Just declare that all teleportations are instantaneous in the same specific frame of reference (e.g. the frame of the cosmic microwave background), and you're good to go. If you're OK with FTL time travel, well... go wild. [Answer] One detail about Alcubierre drives, which we handwave away as quickly as the setting allows for convenience, is the trouble with controlling the warp from within the warp. The most "practical" way to achieve this (for definitions of "practical" that involve megastructures) is to build what amounts to a tunnel or track, or analogous system, that controls the warping of space along its path. This would function like an FTL railroad, and would therefore be point-to-point, but could be used for both cargo and communication. Now, building such a thing that could fit cargo would doubtless be absurdly expensive compared to building one for communications. So you could have both communications networks and free-roaming vehicles, since the costs and benefits involved would vary enough to conceiveably justify both. ]
[Question] [ I know there are similar questions on here already, yet this is different because I don't care about traditional farming in this question. Environment This meant for food production on interplanetary and interstellar vessels, space stations and remote outposts. Assume that: * energy is not an issue * fertilizers and materials are not an issue due to recycling and mining * all variables are under control and optimized (CO2, temperature, humidity, ...) * automation makes labor intensity irrelevant Given the availability of genetic engineering, vertical farming, bioreactors (for synthetic meat), insects, mushrooms, aquaculture, ... What is the minimum space(1) required to provide a healthy and diverse diet to one person? (1) Any answer should give the space estimate in $m^3$, $m^2$ requirement only if relevant, and in addition to this a mass requirement in $kg$. [Answer] First we need to set a standard, given that crew selection criteria should eliminate people who have specialised needs the [RDI](https://en.wikipedia.org/wiki/Reference_Daily_Intake) will do. That means we need 2000 food calories worth constituted as 50g of assimilable Proteins, 275g of assimilable Carbohydrates, 80g of assimilable Fats, about 30g of Dietary Fibre and a bunch of minerals that, to my thinking, fall under "materials" and we don't need to worry about them. The vitamins we'll get at the same time as the major constituents as well. Micoculture is going to be the key to minimising the space and weight needed, we're talking about [Fusarium venenatum](https://en.wikipedia.org/wiki/Fusarium_venenatum) for a start, because it's the most intensive protein production method we know of. But we're looking at it as the foundation for creating a GM yeast that forms a whole food. We need approximately 500g a day of Micoproduct Complete FoodTM that's about 10% Protein, 55% Carbohydrates, 16% Fat, and 6% Fibre, the remainder being additives like salt, potassium, flavours, water, etc... Given [certain recent advances](https://newatlas.com/muufri-synthetic-milk/34415/) we should be able to engineer yeasts to produce any extra vitamins, flavours or texturing compounds we need to add. As we're going to retain Fusarium venenatum's growth rate and it doubles in mass every five hours under ideal growth conditions you're talking about about 0.034g of yeast culture per person per day plus support equipment, and another 2000g liquid water per person or a bit more depending on the humidity and temperature in the vessel for hydration. This is the minimum, don't expect people to enjoy this diet. ]
[Question] [ I'm working on a game with combat between spaceships. It will not be hard sci-fi, but I'd like to base the mechanics on (simplifications of) real physics. When it comes to laser-weapons, I would like to include lasers of different wavelengths, preferably in the microwave (maser), visual (laser) and x-ray/gamma-ray range (graser). I wish to know what the realistic effects the wavelength would have on a laser's effectiveness as a weapon are. I know (but correct me if I'm wrong) that the beam of a shorter wavelength laser retains its focus for longer and would thus have a larger effective range. Also, there currently aren't any "mirrors" that reflect x-rays/gamma-rays which means such lasers can't use a resonance cavity, which means you need a longer "barrel" and/or get less energy output. And obviously the shorter wavelength beams carry more energy per photon, but I don't know if that has any significant effects. To split off my general question in three more concrete examples: * Assuming a laser designed to output a fixed wavelength, what are the advantages and disadvantages of such a laser with a shorter or longer wavelength? Are there any performance characteristics (for example, range, damage on target, size/mass of the laser, cooling/recharge time) that would be significantly changed between, say, a 100 MW maser, laser or graser? (Or is there a limiting factor that prevents you from pumping a large amount of energy in one particular wavelenght of laser?) * Assume a Free Elector Laser, which can output different wavelength laser beams. With the design of the laser fixed for all different wavelengths (though minor mechanical tweaks when changing between wavelengths, like sliding mirrors in and out of the beam, is allowed), does this have different effects on the effectiveness of the laser than in the fixed design per wavelength above? * Are there any effects exclusive to the very high or low end of the wavelength spectrum, such that the visual wavelength laser's isn't simply the midpoint between the microwave and x-ray/gamma-ray laser in terms of performance? [Answer] The question was slightly editted and clarified in the original post and some comments, so my original answer has been replaced and you can find it in the edit history if you were interested. I've ignore some parts of the original question, because it was too broad. > > what are the advantages and disadvantages of... [a] 100 MW maser, laser or graser? > > > Masers may be generated simply and efficiently. We can do that well enough nowadays... something like a [gyrotron](https://en.wikipedia.org/wiki/Free-electron_laser) is decades old design, and I believe we can get efficiencies of at least 50%, which is pretty good. The range of a maser is more limited than devices that emit shorter wavelengths due to [diffraction issues](http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/synchrotron.html). (note that in really old scifi, masers may have been used simply because there were no lasers yet, and there was a time when lasers might have been called "optical masers") Lasers (by which I'm choosing to mean "things that emit visible and near-visible light") are harder to generate (read: needs more clever engineering, generates more heat, etc etc) but have the advantage that they have a much longer potential range as they suffer less from diffraction due to their shorter wavelengths. We also have a good knowledge of optics, and there are plenty of ways to bend and focus visible light. Efficiencies are likely to be lower than masers, but needn't be terrible, especially in a fancy future scifi setting. Grasers aren't quite scifi... bomb-pumped nuclear lasers have been around in theory for decades. The biggest problem with them is that as the beams can't reasonably be reflected, and any attempt to focus them is probably going to require something like a [zone plate](https://en.wikipedia.org/wiki/Linear_particle_accelerator) which means you either have to put up with unfocussed beams (read: short range) or losing at least 50% of your emitted power to the opaque bits on your zone plate. Efficiencies are likely to be very poor... maybe only a few percent. As a weapon, they might be found on nuclear missiles which can get close enough to the target to zap it, rather than trying to build one onto a warship. > > what the difference is between, say, a 100 MW x-ray laser vs a 100MW visual light laser fired at a ship > > > There are a number of important differences. An obvious one is potential range... the radius of the focussed spot at the target (which you want to be as small as possible) is proportional to the wavelength of the light the laser emits. X-ray light has less than a twentieth of the wavelength of visible light, which gives a massive potential range advatange. Both lasers, when they're in their killing range will generate plasma when they hit their target. For the visible light laser, this is inconvenient because the plasma will be opaque to the radiation it is emitting, and so the laser will have to stop, wait for the plasma to dissipate, and then start again so as not to waste power on heating the plasma instead of zapping the target. The x-ray laser is under no such limitation, and can keep firing for as long as you like, and pulse as fast as is practical. The drilling speed of an x-ray laser at shorter ranges is likely to exceed the speed of sound in the target's armour. Each pulse of the laser will generate a shockwave in the armour, and these shockwaves will all merge together at the back face of the armour producing quite a bang. At any range, an x-ray laser of suitably short wavelength will ionise material it is incident upon. This will damage the chemical and crystalline structure of the target (important for handwavium "thermal superconductors") and interfere with electrical and electronic systems. X-rays are obviously highly penetrating. They have a measurable [attenuation length](https://en.wikipedia.org/wiki/Synchrotron) in matter, meaning that the energy deposited in the target drops off exponentially with depth. This means that it may be possible for a beam to shine straight through thin or low density materials and cook whatever is underneath (eg. the meatbags flying the ship), even if it isn't actually powerful enough to melt the armour. --- Finally, and this is perhaps the most important thing... X-ray lasers are going to be big, and they're going to be inefficient. You pretty much have to use a [free electron laser](https://en.wikipedia.org/wiki/Free-electron_laser), and those things get pretty hefty if you want small wavelengths. You have two choices... a [linear particle accelerator](https://en.wikipedia.org/wiki/Linear_particle_accelerator) (aka a LINAC) or a [synchrotron](https://en.wikipedia.org/wiki/Synchrotron). The former can be very, very long... the [European XFEL](https://en.wikipedia.org/wiki/European_XFEL#Accelerator) is over 2km long, for example, though you could probably get away with a more modest accelerator a mere few hundred metres long. You can wrap this around into a doughnut-shaped [synchrotron](https://en.wikipedia.org/wiki/Synchrotron) to be more compact, but whenever you bend the electron beam you will lose energy to [synchrotron radiation](http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/synchrotron.html), and that means lower efficiency, more heat output and larger power requirements. You might think that you could use a super-compact [wakefield accelerator](https://en.wikipedia.org/wiki/Plasma_acceleration) (with accelerations to GeV energy levels over metres instead of over hundreds of metres), but alas current designs are not actually very efficient (certainly no more than 30%, excluding seed beam, FEL and optics losses) so again: more heat, higher power requirements, lower output. TANSTAAFL. Its enough to make you just throw up your hands in despair and just use a normal laser instead. [Answer] I was going to ask this question but you beat me to it. I have the sneaking suspicion that microwave lasers are secretly very good, efficient, and critically underrated, as they are good for frying electronics and making the recipient's craft inoperable while having a low energy per photon. If energy shields are a thing, it's a common sci-fi video game convention that EMPs wreak havoc on them. X-rays and gamma rays may very well be an energy inefficiency trap if mirror plating isn't allowed (in which case you might prefer a more efficient visible-spectrum or infrared laser). If mirror plating is a problem, then definitely use an X-ray laser. A common misconception is that "higher frequency = more energy = more damage". In practice, what's more important is that the energy interacts with (is absorbed by) its intended target. In theory, if you used extremely high-frequency EM radiation, the energy cost will be prohibitive and a good amount of the blast might simply punch through whatever you're aiming at. Sure you might do a lot of damage, but it's a horrid waste of energy when you could have used a simple microwave laser and nixed the enemy's electronics. An extreme example of "energy input != damage": Neutrinos. Particles that hardly interact with matter. You could have a particle beam that fires massive bursts of neutrinos, and chances are they will simply pass through the recipient. My overall answer to this question: X-ray laser paired with a microwave laser. This thwarts mirroring defenses while giving you the option of punching holes in hostile craft or simply disabling them. Interestingly enough, I've been playing a lot of Freespace 2 lately, and I often pair the Akheton SDG (EMP bolt/system disruption) with Subach X-ray lasers. ]
[Question] [ Imagine a device implanted inside the body which can detect when your heart has stopped and, in such a case, burns fat rapidly to generate enough energy to shock your heart into restarting, in a similar way to a modern defibrillator. How much fat would need to be burned to power this, without the need for a battery? I had a quick google and found that the average defibrillator uses 200-360 Joules of energy, and 1g of fat burned can generate 3.6kJ but I think my research is poor or my understanding is poor, because 1g of fat to power a defibrillator unit seems like too little. [Answer] Your research is correct. 5 mg fat would suffice to provide the energy. [Energy requirements for defibrillation.](https://www.ncbi.nlm.nih.gov/pubmed/3536158) = 200J 1 mg beef fat has 0.04 kj or 40 J, so 5 mg = 200J. <https://www.aqua-calc.com/calculate/food-weight-to-volume> It takes a miniscule amount of electricity to affect a heart, especially if it is delivered right to the heart by a device. You are not jumpstarting it or powering it up. The electricity does not go to power a contraction. It is just a signal to reorganize confused myocytes that have become disorganized. Kind of like shouting at a bunch of rowers to get rowing together again. The shout does not itself move your boat. It does not even have to be that loud if they can all hear you. Those external defibrillators deliver more of a jolt because they are not delivered right to the heart but to the skin, with insulating dry skin, fat and tissue between energy source and heart. [Answer] Note¹: Everything that's written in this answer is heavily simplified, if someone is interested in learning more about human physiology I recommend reading "Guyton and Hall Textbook of Medical Physiology", I used the 12th edition as a reference for most of the answer; regarding the osmotic power generator I'm by no means an expert in the field, so my approximations may not be correct, feel free to correct me in the comment section ### The device Such a device may sound like science fiction but we already use those in medical practice everyday, what you're refering to is an [implantable cardioverter-defibrillator](https://en.wikipedia.org/wiki/Implantable_cardioverter-defibrillator)(ICD), it's a kind of pacemaker but it's capable of defibrillating. It basically consists of a battery, multiple capacitors in series (to achieve high storage charge), electrodes that are implanted in the myocardium (the heart muscle) and a small computing unit to identify both the rythm (how the heart is beating) and the cardiac frequency (how many times in a minute the heart is beating). The batteries that are used in these devices must be capable of outputting high energy pulses of at least 2-3A in order to quickly charge the capacitors, while also having a low drain current in order to power the computing unit. The capacitors are in [series](http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capac.html#c2) so they can achieve a high storage charge (up to 850V). They also must be capable of emiting their stored energy (usually 30 to 80J) in a few miliseconds (20ms) in order to defibrillate. ### Using fat as a power source The main issue of using fat as a power source is that metabolic energy isn't directly translated to power. The energy stored in fat can be used either by simple oxidation (not very effective) or by processing it, through a complex series of reactions, into Adenosine Triphospate (ATP) (there's a net gain of 146 molecules of ATP during the complete processing of 1 molecule of "fat"). The energy generated via theses processes isn't the type that electronics can use, and in the body it's only used in other chemical reactions. So, how would we use the energy currency of the body (the ATP) to generate energy for an electronic device? Electrical potentials exist across the membranes of every cell of the body, this is because of the difference in the concentration of ions of the extracellular and intracellular spaces, the mainstays of this difference are Na+ (extracellular space) and K+ (intracellular space) but other ions play a role as well. There are cells that are capable of rapidly generating a greater potential in order to create eletrochemical impulses ([action potential](https://en.wikipedia.org/wiki/Action_potential)) at their membranes, namely neurons (nerve cells) and muscle cells. These potentials usually vary between -90mV (resting state) up to +50mV (action potential) depending on the cell, and they are created with the rapid influx of ions from one side of the membrane to another in a process that's called depolarization. 1. The depolarization begins with the opening of multiple channels that make the membrane permeable to a cation (Na+), then the resting state is neutralized by the quick influx of those ions. The change of the membrane potential initiates the repolarization 2. The repolarization begins with the closure of the sodium channels and opening channels for a different cation (K+) in order to create an efflux of those ions to the extracellular space. This leads to a big potential difference in a period that's called refractory period (because the cell can't depolarize in this period) 3. During the refractory period Na+-K+ pumps start working in order to normalize the membrane potential to the resting potential * The depolarization and the polarization are both passive processes (facilitated diffusion), there's no energy expenditure (see [Diffusion](https://en.wikipedia.org/wiki/Diffusion) for more information), while the "pumping" uses energy because it goes against the chemical potential [![Approximate plot of a typical action potential](https://i.stack.imgur.com/iP1Wu.png/1024px-Action_potential.svg.png)](https://i.stack.imgur.com/iP1Wu.png/1024px-Action_potential.svg.png) The membrane potential can be considered as a Nernst potential (EMF) and can be calculated using the following formula (this is the Nernst equation modified to calculate the potential of the intracellular portion of a membrane at 37ºC): \begin{equation} EMF\text{(millivolts)} = \pm61\log\frac{\text{Concentration inside}}{\text{Concentration outside}} \end{equation} Now that we established that there's a physiological way to generate a difference of potential that could possibly be used as power for an electronic device (using pumps that require ATP to function, and ion channels) I suggest using some kind of osmotic power generator that is constantly recharged using the energy provided by the body - not just fat but any energy that the body has available, because it's very complex to activate the pathway to "burn" fat using an external device more so one that has no other means to be energized. ### An osmotic power generator Note²: In order to simplify the calculations I won't take into account the increasing ammount of work that's needed by the Na/K ATPase while the potential difference increases, If you're interested in reading more about it you can find the formulas and precise values in "Lehninger's Principles Of Biochemistry". Also, I'm clueless about electronics so my estimations may be wrong.* Such a device generates electricity when ions pass through a membrane, so it harnesses the membrane potential turning it into electricity. Let's consider that we have a perfect membrane with attached electrodes, with optimal resistance of 2mΩ, and capable of conducting osmotically induced current that's generated from ion flux from one side of the membrane to another via a channel that has simillar properties as the ion channels described before. This generator would need to have two different cells divided by the aforementioned membrane (red), one of the cells (1) would have a more concentrated solution while the other (2) would not. There's a simple membrane (black) surrounding those cells and it should have both Na/K pumps (orange) and voltage dependent ion channels (green). [![Simple osmotic power generator schematic](https://i.stack.imgur.com/J4vHS.png)](https://i.stack.imgur.com/J4vHS.png) The Na/K pump only works against the concentration gradient while the energy of the hydrolysys of ATP (34kJ/mol) is greater than the potential energy of the given gradient. Therefore the maximum average fluid density at (1) should be equivalent of 34kJ/mol of the solution. Let's consider that we have a synthetic variant of this pump that's capable of hydrolyzing 1mmol/l ATP/s, so we can charge 34W/l per second, and also increase the concentration of (1) by 2mmol/l of K+/s while reducing Na+ concentration by 3Na+/s. In order to generate enough current (3A) to power the capacitors we would need at least a concentration difference of at least 10x (61mV). This difference is the physiological difference of K+ (V = I(A) x R(Ω)). Considering the capacitance 150μF the capacitors will charge in 1.5μs ([T = R(Ω) x C(F); Time to full charge = T \* 5](http://www.learningaboutelectronics.com/Articles/How-long-does-it-take-to-charge-a-capacitor)). As you can imagine the discharge rate would be very low and the ions would be replenished quickly. The energy expenditure of this device would be around of 7.5cal/s while in usage, with some peaks after discharges. ### Side note A key piece of information is that not all cardiac arrests, or as you put "the heart stopping", are defibrillatable only the ones that the heart activity hasn't come to a halt, so there's still a rythm - but not an effective one (think of it as the heart only shaking), i.e. the heart isn't capable of pumping any blood whatsoever. Thus this device won't save everybody from this dire situation, e.g. when somebody drowns and their heart stops all the activity ceases so it's not shockable, but when someone has a Myocardial Infarction the organ keeps "shaking", so it's possible to defibrillate. [Answer] Your math is correct. It's just your intuition that is off. Our bodies are amazingly good at storing energy. The body needs roughly 10,500,000 J of energy every day, and 1kg of fat has 37,000,000 J of energy in it. Put that together, and in a day, you only burn 1/3 of a kg of fat (or the equivalent in food calories). Losing weight is hard! For another intriguing comparison, consider the deadlift. [![enter image description here](https://i.stack.imgur.com/4g9p5.jpg)](https://i.stack.imgur.com/4g9p5.jpg) The world record deadlift is 500kg. Eddie Hall did that, lifting the bar 0.45m. A quick run through E=mgh shows that he outputted 2,200 J of energy doing that. That's about 2/3 of a gram of fat's worth of energy. In other words, the energy used to start someone's heart is roughly 1/10th of the energy outputted by the world-record dead-lift, and that's just a few milligrams of fat's worth of energy. In hind sight, it should not surprise you that the energy stored in fat is so much larger than the energy we see from our muscles. Think of how many times you have to contract your leg muscles to walk. If that took a substantial amount of energy compared to our fat stores, we'd starve! [Answer] Defibrillators don't work on a stopped heart to get it going again; they work on a heart that is working, but not functioning correctly, with the shock meant to essentially reset it into properly beating. If you use a modern portable defibrillator, once you apply the electrodes or the pad and activate it, the unit will first perform an analysis of the patient's heart. If it says something like "No shock advised, resume compressions" that means it hasn't detected any activity in the heart and therefore shocking it is pointless. I've used a unit on multiple occasions where that has been the case; it doesn't detect any cardiac activity so doesn't waste time trying to shock it into starting. ]
[Question] [ My world is far away exoplanet with water and some oxygene, but without life or plants, which means without coal and organic materials inside. High tech people from Earth come there and made some quick (and succesfull) terraforming but after that, and after building the cities, vast majority of them cannot survive the planet conditions and people starts to die slowly due to health complications. Planet is classified as dangerous and deleted from future missions from Earth. Those few people who survives starts wars for goods and tech era is finished in three or four generations after all machines will run out of energy and get destroyed. After hundreds of medieval years they just adapt for the planet, and start to rise again. They start new industrial revolution (with some historic books written by wise people from first era, so they have handwritten historic step-by-step guide to some crutial inventions, which speeds things up). They will use hydropower, got lots of mining, got steam engines, railways, boats, cars, ethanol engines instead of classic fuel. People gets to 1850 - 1900. But what about planes in such era? 1) Materials: can be such a strong conventional engine built without steel? Can it be just an iron engine, or lithium / aluminium or whatever unorganic metal? Does any material have such good behavior like steel, but not based on organic materials? 2) Fuel: can it runs on etanol, whale oil or some bio fuel instead of classic fuel? Or it should only be sort of eletric / solar engine and thus produced quite later? \note: this is max reality world. The only made-up thing should be the apocalypse. Everything other should be real, like we were really there and tryin to survive with everything we have. Really thanks for answers. [Answer] The fact that they have ethanol means that as part of their terraforming efforts, they have a thriving plant life, probably terran based, established on the planet after colonisation. This is the only way this planet makes scientific sense anyway, because without photosynthesis going on there would be no way that the oxygen would be replenished after animals breathe it. Mind you, the amount of free oxygen in a non-plant based planet would also indicate very low levels of iron near the surface of the planet, otherwise it would oxidise and take the oxygen out of the atmosphere, but for the sake of argument let's say; 1) biofuel is a thing because there are now* plants there, and 2) all metallurgy has become possible only through deep mining So the question is whether or not planes are possible. The answer is of course yes, but your biome does put some constraints on them. WW1 planes (for instance) were largely built with wood frames, and many of the early ones had canvas coverings. The wright brothers engine also contained a lot of aluminium to keep it light. It's entirely possible with the technology base you're talking about though that a lot of it could have been built using ceramics. This is assuming you have an internal combustion engine in the first place. Iron, steel and other metals and alloys are a challenge because of weight, and I'd argue that building planes out of wood frames and a heavy material covering would get planes with a suitable engine up and running. Given that there are even parasail ultralights (essentially engine frames with a seat in front and a parachute above it for lift) means that you could get people flying on this world. But, these technologies and building materials don't scale well. At our current level of technology we can't run a jet engine on biofuel, although it's coming I believe. Internal combustion engines could do it certainly, and many ultralights run on standard car fuel which in many cases now contains 10% ethanol anyway. So, it's arguable that you'd be able to get small planes up and running in your world, but you're not going to be able to scale up to something like an Airbus A380 with that building design. Internal combustion engines are certainly the order of the day if you want to follow an Earth analogue, but it's also possible to design an electric engine that spins a propeller if you're not that interested in speed. In modern times, the batteries for these are getting lighter and lighter, but in your world I'd argue that the lack of chemical energy in the form of oil and coal would have meant that your industrial revolution would never have followed the same technological path as the industrial revolution on Earth was driven by cheap and accessible energy in the form of fossil fuels. On your planet, I'd argue that they would have gone down an electricity / solar or wind generation model, and battery storage, simply because it would have been the most convenient model in the first instance, especially if they needed most of their initial crops for food. So; simple, lightweight planes that are probably slow but designed with wings that make them much more energy efficient, that don't scale up very well but could be used as personal transport for couriers, scouts, et al is what I suspect would be the order of the day, along with either an electrical or biofuel engine of some kind. [Answer] If metals are scarce I would suggest wood and cloth as main construction materials. This was done historically and successfully [1]. My guess why it never became mainsteam is that wood is a natural material, thus has unpredictable features and is not uniform. Aluminium is just easier to work with and more predictable. Concerning steel free engines I was only able to find this [2] they only discuss the pistons, but those are the parts taking the most stress. So if the pistons can be made with these other materials, so can the entire engine. Yet there is an issue. Why would your planet lack steel? You mentioned terraforming and I assume you meant establishing an earth like biosphere. To have a functional biosphere you need hydrogen, oxygen, nitrogen, sulfur, phosphorus and carbon. (and a bunch of trace elements) These elements are the basis of organic chemistry, which is somewhat crucial to life. Steel is an alloy of iron and carbon. Do as soon as your planet has any lifeforms on it you will have carbon. (using human remains for steel production sounds like a intriguing story idea) This article [3] disscusses steel production and how to do it without coal very detailed. Using biofuel for aircrafts seems plausible, although there seem to be a number of issues [4]. Production seems to be difficult uneconomical compared to fosdile fuel, but on your world that would hardly be an issue. Have you considered alternative aviation methods? Airships might be more popular if planes are hard to construct. Yes they are slower, but imagine a airship covert in thin solar panels or sheets to travel the planet somewhat slowly, yet hyper efficient. [1] <https://www.aircraftsystemstech.com/2018/09/history-of-wooden-aircraft.html?m=1> [2] <https://www.google.com/amp/s/www.researchgate.net/post/what_is_the_best_material_that_can_internal_combustion_engine_piston_made_from_to_get_best_result/amp> [3] <https://coalaction.org.nz/carbon-emissions/can-we-make-steel-without-coal> [4] <https://en.m.wikipedia.org/wiki/Aviation_biofuel> [Answer] As to the engine: Ford has been using aluminum engine blocks for a while now - the aluminum is alloyed with strengthening metals but the key is that it can contain the combustion pressure without blowing out one or all of its spark plugs - losing compression, stalling and crashing. I guess it might be possible to use other metals, Magnesium is common in aircraft because of its high rigidity and low weight but its not very heat tolerant. Tungsten is heat tolerant but brittle and may degrade from the combustion stresses. If you can get a lighter weight material then you improve your thrust : weight ratio which allows bigger or more heavily armed aircraft or longer range aircraft. A big limitation to this kind of engine will be the amount of oxygen in your planet's atmosphere. If it is lower than Earth then the intake section will need to be more powerful to deliver enough pressurized combustion air to the combustion chamber. This could get challenging because if you have an outlandishly large intake that may create parasitic drag. As to the airframe: it has to be able to withstand the stresses of fixed wing flight. The fuselage, wing spars and stabilizers are all going to be subject to twisting, torsion, compression and many other forces during maneuvers. A lighter weight material like wood probably cannot stand up to a ton of punishment like that. A steel framed fusleage and steel wing spars will allow higher G maneuvers, but also means more weight and so calls for a stronger or more numerous engines.. you're beginning to see how tough it is to engineer fixed-wing combat aircraft. what you might want to consider instead if this is late 1800s / early 1900s equivalent is airships ]
[Question] [ Researching for a science fiction novel. My character loves math + I have dyscalculia = Problem. Therefore, I need your help. In my story, there are aliens we can see, but we can't hear or touch. They appear like ghostly monsters to us. Somehow these aliens became trapped 'on' earth in a so-called parallel dimension. They want to go home, but they need our help. If you watched Star Trek, you might consider this a Tykins Rift or Gravity Well. However, it doesn't affect humans/earth, only the aliens' so-called dimension. My mathematician character needs to find a way to send these guys home using math (and tech of course, but the foundation of the solution has to come from math). Can you think of a semi-plausible mechanism for both what is trapping the aliens on earth, and what mathematical solutions my character could come up with to help them get home? Links to interesting hard-science and math theories are good. You'll get A+ for imagination and super-cool jargon. Extra bonus points for anything that would make an actual mathematician laugh when reading the story (not laughing AT me, but laughing WITH me). I appreciate your time in advance. Cheers! EDIT: After reading the answers to my question so far (which are really great, thank you), I have come to realize it's probably not possible for JUST math to fix this. Maybe my character needs to be interested in another science as well as math (probably physics). Because math is theoretical. (I just loved the image of the astronauts having all these "computers" in the 1950s and 60s and my character madly doing math and coming up with something that actually sends the beings home. haha!) So my edited question would be: if there was a dimensional rift (wormhole), and the aliens needed to be blasted away from earth (not violently, but in a friendly way) by some kind of machine -- what could the science behind something like that look like? Thank you! [Answer] From a somehow formal point of view, math is totally abstract from reality. This is why once a mathematical theorem is demonstrated, nobody bothers invalidating it. When math starts to mess with reality becomes physics, and there the problems start. Think of Pythagoras theorem in Euclidean geometry and General Relativity: nobody is trying to find rectangular triangles which fail to fulfill the theorem, but a plethora of scientists is trying to find way to find wrong previsions given by General Relativity. Now, coming to your problem: you want some math-sounding problem which can be used to justify some beings being trapped and needing to escape. Luckily, your story is not going to be submitted to any Mathematical publications, where it would undergo the scrutiny of mathematicians, but you want just some barely plausible reason to maintain the suspension of disbelief in the readers. I can suggest you watching the movie [Moebius](https://en.wikipedia.org/wiki/Moebius_(1996_film)), which makes use of a similar concept: > > On one 4 March, the controllers of the Buenos Aires Underground discover that train number UM-86 (a Siemens-Schuckert Orenstein & Koppel train), along with its passengers, has gone missing in the network of tunnels. After searching the entire network (which in the film is shown as being much larger than in reality) they fail to find both the train and its passengers. > > > In an attempt to hide the incident from the public, the director of SBASE contacts the engineering firm responsible for the construction of the line where UM-86 went missing in order to investigate the incident. The firm then sends a young topologist Daniel Pratt, rather than an experienced engineer, which displeases the director. > > > [...]Pratt reveals his complex theory: that the construction of the perimeteral line has turned the network into a form of [Möbius strip](https://en.wikipedia.org/wiki/M%C3%B6bius_strip) which, under the right conditions, caused the missing train to pass into another dimension. > > > ]
[Question] [ [This question here](https://worldbuilding.stackexchange.com/questions/137160/would-moores-law-apply-to-mechanical-computers) brought up interesting points on what kind of distribution we could expect for the increase in computational power of mechanical computers in a world relying solely on such non-electric computation devices. A [related question](http://Just%20How%20Powerful%20Could%20a%20Mechanical%20Computer%20Be?) is asking about theoretical limits to mechanical computing. I am wondering on what realistic computational limits exist on mechanical computers given a certain level of mechanical expertise - i.e. how small can we make the actual gears/shafts/springs/cogs/... What is the maximum amount of computational power we could expect from a mechanical computer? Some limitations: * Let's assume that the level of mechanical expertise is what we see in exquisite (and expensive) mechanical watches today - so in effect mechanics on a scale that a person can manufacture at with hand tools. * As a size limit let's pick the size of some of the earliest large computers (maybe similar to ENIAC and consorts): the mechanical computer still needs to fit into a medium sized building. As a measure of computational power I'm interested in FLOPS, i.e. floating point operations per second, which is still the standard in measuring computational strength of cluster systems nowadays. Exact numbers would of course be dependant on the system, but some rough order-of-magnitude estimation should be possible. For reference: * [Z4](https://en.wikipedia.org/wiki/Z4_(computer)) reached about 0.27 FLOPS * [ENIAC](https://en.wikipedia.org/wiki/ENIAC) reached about 500 FLOPS Bonus: If possible I'd also be interested in the power consumption (in Watt) of such a computational machine, but this could also be hand waved. [Answer] Propagation of mechanical signals into solids is basically limited by the speed of sound in that solid. Therefore, assuming that the length over which you want to transfer a mechanical signal is $L$ and the signal propagates with velocity $s$, neglecting inertial effect you cannot switch the signal before a time $t\_{min}=L/s$, which gives a maximum operating frequency of $F\_{max}=1/t\_{min}=s/L$ Also here we see that reducing the dimension of the features is a good way to increase the frequency of the device. Just to throw some numbers in, let's say the device is made of steel and the critical size is 1 cm, this means that the maximum frequency would be $F\_{max}=5900 [m/s]/0.01 [m]=590 kHz$ Giving the equivalent in FLOPS goes beyond my capability, and I suspect the architecture of the device should be known, too. ]
[Question] [ This is my first time using this site and i'm excited to get answers to roadblocks that have prevented me from finishing my writing in the past. However, you may have to excuse some mistakes I make along the way, internet communication isn't exactly my forte. For starters, I've been trying to develop a character whose skin is not only immune to burning via acid, but also has a seemingly infinite supply of acid withing herself which she secretes all over her body uncontrollably. My questions are as follows: * What type of acid should she secrete? I know hydrochloric acid is in our stomachs but that's not strong enough, it needs to be able to burn through skin and metal (kinda like alien, I guess). Some light research introduced to me hydrofluoric acid and fluoroantimonic acid, but I don't know enough about acids. * Where does she store the acid inside her body and how does she get it out? It's possible she could store it in her stomach and it could come out her pores but I'm open to plenty of other ideas, because mine doesn't make a whole lot of sense. * Finally, what could she wear to protect the things she comes in contact with? At first I was thinking thick rubber but then I came across Teflon, a material that apparently stops acid, but again I really have no idea. I hope my questions are easy enough to answer. If you can think of any other problems with my character you would like to answer, then feel free. Your help is much appreciated. A.L [Answer] Teflon is your best bet for what could make her skin acid proof, but honestly hydrochloric acid is your best bet, unless you wanted her to violently react with water, which is what most of the stronger acids do. Be advised though, that without aqua Regina you will almost certainly be unable to corrode gold, and possible platinum as well. But Aqua Regina doesn't dissolve other commoner metals, so you'd need a combo. Trifluoromethanesulfonic acid seems like a good candidate as well, seeing how its so strong. [Answer] Disclosure: I'm a Chemist, not a biologist. One of the harder parts of acids is that a lot of them are too harsh for biology, so it's challenging to have an organism use them offensively without hurting itself. You can basically rule out every -fluoric acid, they're way too strong for biology to still function. The -chloric acid approach is reasonable - Hydrochloric Acid is common in humans at a low strength (<0.8 Molar) or (< 0.8 grams/Liter). Assuming you can purify it biologically with [inorganic salts](https://en.wikipedia.org/wiki/Magnesium_sulfate) somehow (or some handwavology) , you'll be able to dissolve some metals pretty well at 6-7Molar. HCl gets [azeotropic](https://en.wikipedia.org/wiki/Azeotrope) at around 13 Molar, so you likely won't be able to get beyond that. Furthermore, you can make aqua regia: a mixture of Hydrochloric Acid and Nitric Acid ([HNO3](https://en.wikipedia.org/wiki/Nitric_acid)) which is what I use to chemically purge Nickle from contaminated surfaces in lab research. It's so nasty that we use it only in a ventilation hood with a splash/blast shield, no exposed skin, and never more than 100mL. It'll get the corrosive job done. The body can store it in the stomach just fine (assuming you have stronger mucus to contain it), and pipe it out to pores with dedicated vasculature. While Teflon is an effective anti-acid polymer, it has to be coated on most surfaces, and its got a LOT of [fluorine in it](https://en.wikipedia.org/wiki/Polytetrafluoroethylene). You breathe in teflon while it's being applied, it will kill you. The mutant is better off wearing protective rubber gloves to contain its corrosives. For its own protection: another solution would be to have your mutant constantly secrete a oily non-polar mucus that would both hydrate its skin and protect it from the strong acids it has. Most mucus is [alkaline](https://en.wikipedia.org/wiki/Alkaline_mucus) anyways, so you have a biological basis for it. ]
[Question] [ Saturn and it's moons, minus a few rogue colonies, are under the control of the Saturnine Syndicate. Long have they wanted to turn Mimas into a communication, technology, and data hub. But I've run into a problem: I don't honestly know if a massive satellite dish on Mimas (taking up the Hetrschels crater) would have any use. My question is: Is there any practical use for a large satellite dish on Mimas? Or would it be better to not use a massive satellite dish, another location is better, etc. Note: Yes, Mimas would really look like the Death Star with this satellite dish. Which would be a funny reference in my mind. [Answer] So, there are sort of two answers to this. Answer number one is that this has already been done on earth, although not QUITE to the scale you're envisioning. Telescopes in general have better resolution and performance based on the diameter of the viewing aperture (either the recieving dish for radio telescopes, or the lens for an optical telescope). The [Arecibo Observatory](https://en.wikipedia.org/wiki/Arecibo_Observatory) is built in a sinkhole, rather than an impact crater, but in the 1960s it was cutting edge for radio telescopy. China has since built [an even bigger one](https://en.wikipedia.org/wiki/Five_hundred_meter_Aperture_Spherical_Telescope), although Arecibo still wins in my book because they have [space cats!](https://www.space.com/41619-arecibo-observatory-space-cats-fundraiser.html). So, there are absolutely good reasons to build a Really Huge Dish in an impact crater. Now, that said, those reasons have mostly been superseded by the introduction of high speed data transfer abilities allowing a technique called [Aperture Syntheisis](https://en.wikipedia.org/wiki/Aperture_synthesis). Instead of buliding a dish 500m across, you can get the same effect by building two smaller dishes 500m apart from each other. If you're thinking of building a dish on Saturn in the first place, whatever result you're looking for is going to be met far more effectively by putting a constellation of smaller dishes in orbit AROUND Saturn. A dozen networked telescopes in geosynchronous orbit around Saturn would give you an effective dish size of almost 200,000 km, if I have my math right. [Answer] Using a crater for building a satellite dish has a big disadvantage: you cannot choose where to point it, and moreover wherever you are point in the sky is moving following the rotation of the planet, so you can have a window of few seconds of link with any other transmitting station. This is for example what happened for the notorius [Wow signal](https://en.wikipedia.org/wiki/Wow!_signal) > > The Wow! signal was a strong narrowband radio signal received on August 15, 1977, by Ohio State University's Big Ear radio telescope in the United States, then used to support the search for extraterrestrial intelligence. The signal appeared to come from the constellation Sagittarius and bore the expected hallmarks of extraterrestrial origin. > > > The entire signal sequence lasted for the full 72-second window during which Big Ear was able to observe it, but has not been detected since, despite several subsequent attempts by Ehman and others. > > > If this short window can be unpractical for astronomical observation, it also makes the use of the dish for two way communication practically impossible. Unless, of course, you have the following conditions satisfied all together: * your celestial body and its companion are mutually tidally locked * the location of the crater faces the other body of the pair * you have a suitable location for building a transmitter/receiver on the other body. In this case you can build a radio connection between the two bodies. ]
[Question] [ I've been thinking about writing a fantasy novel set on an [earth-like](/questions/tagged/earth-like "show questions tagged 'earth-like'") world with Saturn-like rings. I've been doing some research here by looking up questions about worlds with rings, of which there is a surprising amount. [One answer I found](https://worldbuilding.stackexchange.com/a/82476/6620) indicated that: > > The area under the rings will be an exclusion zone because the material will continue to fall to the earth for millions of years. Expect lots of craters and volcanism due to damage to the tectonic plates. > > > Such a phenomenon isn't mentioned in any other question/answer about rings which I've found, leading me to wonder if it would, in fact, be the case. That answer dealt specifically with the evolution of a ring, which I am not interested in, but it did mention that debris would continue to rain down for "millions of years". It doesn't sound like things will be letting up any time soon. Is the fall of debris just an 'early-stage' thing which will let up after a few million years? The answer doesn't specify. I don't want a planet with an equator being pulverized by rocks big enough to wipe out nearby civilizations every 20-ish years. So my question is, if an earth-like planet (or simply Earth, for that matter) had Saturn-like rings, would there be any debris-fall beneath them? For all details, assume the rings are identical to the rings of Saturn, just scaled down so the proportions are the same for Earth as they are for Saturn. Note that I am aware this question has been answered in the question above. This is not a duplicate question, because I am asking whether or not that answer can be backed up/special circumstances explained, due to the fact that no other questions/answers about rings which I have found even mention such a phenomenon. [Answer] If the Earth had Saturn-like rings, you would not have to worry about falling debris. As you mentioned, the area under rings that were created (relatively) recently could be hazardous due to falling debris landing on the planet. However, this is not the case for [Saturn's rings](https://en.wikipedia.org/wiki/Rings_of_Saturn#Physical_characteristics): Size of debris: Saturn's rings are mainly composed of particles measuring 1cm to 10m. [Nasa claims](https://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html) that any rocks smaller than 25 meters generally burn up in the atmosphere, and that the Earth gets about 100 tons of new space-dust added to the surface every day. However, because the ring particles will be moving significantly slower than most asteroids, larger amounts of smaller objects/dust would now be landing on the Earth. This actually isn't much of a problem, because of what this extra material actual is. What the debris is: 99.9% of the material in Saturn's rings is just (frozen) water. Because the melting point of this ice is much lower than the material in rocky-asteroids mentioned previously, the amount of solid ice that will make it to the surface will be very small as most of it will simply melt before it gets too far down. So, if the Earth (or any planet) had Saturn-like rings, a steady supply of water will be added to the atmosphere with an occasional small meteor making it to the surface. At worst, the upper atmosphere around the equator may be cloudy and the world will be more humid, but there would not be any periodic civilization-ending debris falls. Do note that this only applies to Saturn's old, powdered, watery, stable rings. Newer, rockier, chunkier rings likely would result in more frequent debris landings, as you mentioned, though their speed would be much slower due to coming from orbit. ]
[Question] [ Disclaimer: By human-like, I am referring mostly to limb proportions similar to ours. Would it be reasonable for the average member of a bipedal species with proportions similar to those of humans to be stronger than the average chimpanzee? The species I am working on in particular is a semi-arboreal species that reentered the forest after evolving efficient bipedal walking. Unlike chimpanzees, the legs are quite long as the legs of humans are. The average height of this species is about 196 centimeters, and the individuals are rather lean with a body fat content of around 12%. The diet of this species contains many energy rich fruits and some meat with other foods such as eggs when the opportunity arises. Currently, I am thinking of a catlike build for individuals of this species, and by this I mean increased flexibility and the ability to react very quickly. Some things in particular I am wondering about are: * If the bones would need to be more dense * If tool use would be hindered * An approximate weight (would this species be very heavy or light?) * If this would take away from intelligence * Would endurance be decreased * Around what weight could be lifted * Would this species be able to react quickly * Would the jump height be very high During my research on the comparative musculature of humans and chimpanzees, I have found claims that involve the chimpanzees having fewer larger muscles and humans having more small muscles. I have had trouble with considering how this would work on a spindly human frame. Overall, I am wondering what limitations or possibilities there are if this was applied to a human frame. I do not at all expect an exact answer. [Answer] A recent study I read [here](https://www.smithsonianmag.com/smart-news/why-are-chimpanzees-stronger-than-humans-1379994/) states that the reason chimpanzees are comparatively stronger than humans is because their muscles sacrifice control for efficiency. I don't know if the whole fewer but larger muscles element is relevant to this but it would make sense. If you replaced human musculature with equivalent chimpanzee musculature, your questions would have the following answers: * Greater bone density isn't a necessity but would be a benefit. * Like I said, chimpanzee musculature would sacrifice control for power. * The difference in weight would probably be negligible without denser bones. * I have no idea what role muscle plays in the brain, but I'm guessing intelligence would be about the same. * Humans are actually among the most endurant animals in the world and replacing our muscle structure with that of a chimpanzee would definitely reduce that endurance. * The World Record for most weight lifted by a human goes to [Paul Anderson](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwj1yJHYgafZAhVESK0KHTevCmAQFgg0MAI&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPaul_Anderson_(weightlifter)&usg=AOvVaw29drvYlKeQOQKPJ9fZZIyK) when he lifted 2.85 tonnes with a back lift. Chimpanzees are supposedly at least twice as strong per-weight as humans so, while your species doesn't sound like it could produce a Paul Anderson, the possibilities are incredible, especially in fist fights. * Likely, since this is more down to the capacity of the nerves than that of the muscles. * They would definitely be good jumpers. In fact, I would argue that jumping should be a very normal way of getting into trees. One more thing, for an arboreal species, shorter is actually better. Why do you think chimps are half the size of humans? [Answer] lets answer in order. 1. not significantly, bone density is not a really good measure of strength. 2. tool use will be hindered by a climbing anatomy, you can have a hand optimized for climbing or for tools not both, it may be hindered if you make the muscles stronger as fine motor control may be affected. 3. since the only information we have is "stronger" their weight is kinda up to you. I will say with that height they will not be great climbers, humans are already too heavy for it. 4. intelligence and climbing do not appear to be related so no. 5. Yes endurance will suffer, human endurance is so good becasue we evolved for long distance bipedal travel, these have evolved in the opposite direction. 6. Again with just "stronger" this is up to you. 7. reaction time is not related to any of this so they will reacts as fast as humans which is normal for animals our size, size is the major factor as it controls the length of the nerve signal, smaller animals react quicker becasue the signal has a shorter distance to travel. of course they will be a bit slower in the limb but that is a fairly minor thing unless they a throwing something, and will not impact reaction time. 8. this depends entirely on how much you change them to be better climbers, long legs are not good for chimp style climbers but good for jumpers. Humans are good jumpers, chimps are not, so if they still have human like legs they will be good jumpers. Likely around the same as a humans. "Stronger" is not much help you would have ot say how they are stronger (greater muscle recruitment, larger muscles, better leverage, etc.) [Answer] The only thing I'd consider in terms of how strength would affect intelligence would be the size of the jaw muscles. The major difference between humans' and other primates' muscles and bones of the head and neck is a larger cranium that sacrifices muscle volume in the jaw area. This led to our much weaker bite but gave us room to develop a very large forebrain. Hope this helps! ]
[Question] [ A rich nation, constantly embroiled in warfare and more often than not being invaded, has built, about a couple decades ago, a grand city over the old capital. It houses a very large population of 300 thousand, and it's very well strategically placed, about 50 kilometers from the city lies the coast, with another, albeit much smaller, similarly built city acting as port, this is great because the ocean in which the coast is set brings very rich trade, which made both cities major trade hubs in the continent. The city is built on top of fertile plains and has a particularly thick river running through town. The technology available to the civilization is similar to that of the late 16th century and early 17th, along with the architectural / engineering knowledge of the Romans (not sure if the Romans would be able to rival that of the 16th century Europeans in this aspect, but the Rome was the first city to achieve a population of one million in Europe [133 B.C.], a feat only seen in Europe again after nearly two millennia [London 1810 A.C.], and they had a pretty awesome sewage system, which I intend to mimic in the city). As already mentioned, the nation is constantly warring, so the city has huge, thick walls, with many bastions around it, similar to the walls of star fortress, made to deflect cannon fire, allowing the city to hold besiegers at bay if their only hope of conquest is through an invasion on the city. The city is also built to withstand a long siege, it has huge underground storehouses that store food and supplies, and I thought of having large farms and estates inside the city, but I think that it would take up too much valuable space and would not be cost-effective or efficient. I also thought of some sort of vertical farming mumbo jumbo but I'm not sure of how that would work. The city is also a knowledge hub, it has three universities, four military schools, an observatory, many schools and it houses the central government, the royal palace and the court, and contributing more to the scholarship of the city, the community is, as already mentioned, an economic center, attracting merchants from all over the world, and many markets and banks have been built on the city, attracting even more traders. Last but not least, I'm aware that the city would be VERY expensive to built, but that won't be a problem, for the kingdom has since long been wanting to build a grandiose capital, and has hoarded money / goods / resources for centuries to build such city, and even then that nearly wasn't enough, the government almost got in debt and lost a lot of influence because of the construction, but eventually, it paid off, so finances won't be much of a problem here fellows. So, with this information in mind, how large would be this city? Keep in mind that it was also built with a small "extra space" to allow growth. P.S. - I'm an architecture illiterate, so please explain your ideas to me, and point out my mistakes. P.S. 2 - If anyone has a cool sounding name for the city, I'm all ears. [Answer] # Large cities of ~1500 Wikipedia conveniently has a [list](https://en.wikipedia.org/wiki/Historical_urban_community_sizes#Early_Modern_era), and it is well sourced from Chandler, Modelski, Morris and others in the field. Lets run down some of the largest cities from 1500-1600. I rank all cities above 200,000 by their median estimate in the time range. I skipped pre-Columbian estimates for New World cities. ### Beijing 700,000 Beijing's [city walls](https://en.wikipedia.org/wiki/Beijing_city_fortifications) were completed in 1553, right in the middle of this time period. It had two sets of walls, the 'Inner Wall' and 'Outer Wall.' Interestingly, the Inner Wall was not inside the Outer Wall, but directly north of it. The inner city wall was 24 km long, and the outer wall was 28 km long. Together, I estimate they enclosed about 50 km$^2$. This makes the total density within the walls about 14,000 per km$^2$. ### Istanbul 600,000 The [Theodosian walls](https://en.wikipedia.org/wiki/Walls_of_Constantinople) still stood as the boundary of the city in the 1500s. There was some suburban development outside the walls, and a lot of development across the Golden Horn in [Galata or Pera](https://en.wikipedia.org/wiki/Galata). The modern area inside the walls is the [Fatih](https://en.wikipedia.org/wiki/Fatih) district; combined with [Beyoglu](https://en.wikipedia.org/wiki/Beyo%C4%9Flu) to the north to represent the suburban areas, that gives an area of 22 km$^2$ for a density of about 27,000 per km$^2$. ### Vijayanagar 500,000 The modern [Hampi](https://en.wikipedia.org/wiki/Hampi) archaeological site is 41 km$^2$. The inner city walls were somewhat smaller than this, but since there were [more wells](https://en.wikipedia.org/wiki/Hampi#Water_infrastructure) outside the walls than inside, this larger number is likely more accurate. This gives a density of about 12,000 per km$^2$. Medieval travelers claimed that there was a second outer wall that enclosed a large area of farmland, around 500-750 km$^2$. So an alternate lower density could be calculated for this city. ### Cairo 300,000 Old Cairo has largely been buried under the new, so there isn't a lot of good information on how big the old city was. According to (unsourced) [Wikipedia](https://en.wikipedia.org/wiki/Old_Cairo), by the end of the 15th century, Cairo was composed of Old Cairo, Downtown Cairo, Bulaq, and Azbakeya. Measuring these areas on Google Maps, I get a total area of around 20 km$^2$; for a density of 15,000 per km$^2$. ### Kyoto 300,000 Wikipedia has a [1696 map](https://en.wikipedia.org/wiki/Heian-ky%C5%8D#/media/File:1696_Genroku_9_(early_Edo)_Japanese_Map_of_Kyoto,_Japan_-_Geographicus_-_Kyoto-genroku9-1696.jpg) of Kyoto (a little after our time period), where it covers what is the modern day [Kamigyo](https://en.wikipedia.org/wiki/Kamigy%C5%8D-ku), [Nakagyo](https://en.wikipedia.org/wiki/Nakagy%C5%8D-ku,_Kyoto) and [Simogyo](https://en.wikipedia.org/wiki/Shimogy%C5%8D-ku,_Kyoto) wards. These wards have a total area of 21 km$^2$. Since we measured the city in 1700, we ought to use the 1700 population of 350,000, giving us a density of 16,000 per km$^2$. ### Paris 250,000 [Paris](https://en.wikipedia.org/wiki/Paris_in_the_16th_century)' city walls for this time period were finished in 1383 (the [Wall of Charles V](https://en.wikipedia.org/wiki/Wall_of_Charles_V)) and covered 4.4 km$^2$. Maps made in this period (like [this one](https://en.wikipedia.org/wiki/File:Munser1572.jpg) from 1572) show some development outside the walls. If we estimate the actual city size as the 1st through 6th [arrondissements](https://en.wikipedia.org/wiki/Arrondissements_of_Paris) of modern Paris, we get an area of 10 km$^2$ for a density of 25,000 per km$^2$. ### Hangzhou 250,000 Several sources list Hangzhou as being this big, but it had been much larger in the past, up to a million people and probably the largest city in the world for most of the 1200s. It was sacked by the Mongols in 1276 and declined, though it was still bigger than Beijing when Marco Polo and Ibn Battuta visited in roughly 1290 and 1345, respectively. The problem is, smaller 1500s Hangzhou with only a quarter of the population certainly didn't fill out its old size, and it is difficult to estimate the occupied area of the city was at this point. There must have been substantial ruins surrounding the occupied parts of the city center. ### Tabriz 250,000 I can't find any useful information on Medieval or Early Modern Tabriz. ### Naples 200,000 I couldn't find much information on the old walls of the city, but based on the location of the gates, I estimate that the old city occupied what is now [San Ferdinando](https://en.wikipedia.org/wiki/San_Ferdinando_(Naples)) (which was explicitly developed by the Spanish in the 16th century) and the [2nd municipality](https://en.wikipedia.org/wiki/2nd_municipality_of_Naples) (which includes the old port town along with [Avvocata](https://en.wikipedia.org/wiki/Avvocata), another area developed by the Spanish). Summed together, these areas are about 6 km$^2$, for a density of 33,000 per km$^2$. ### Agra 200,000 This is another one that is tough to adjudicate. Agra was only founded in 1504. Agra fort, a 0.4 km$^2$ walled city was built on the location at that time, and served as the capital of Sikandar Lodi's empire until the death of his son in battle in 1526. Then there were years of chaos and the fortress was ruined until [Akbar](https://en.wikipedia.org/wiki/Akbar) re-united Northern India and made it his capital again, completing a rebuild of the fort in 1573. But then Akbar moved his palace to [Fatehpur Sikri](https://en.wikipedia.org/wiki/Fatehpur_Sikri), about 35 km to the southwest, in 1571 and stayed at that site until the local water supply ran out in 1585. After that, the emperors finally moved back to Agra. The conclusion is, the population was probably in a lot of flux over time, and there were never proper city walls, just a small fort. # Conclusion: 10-30 km$^2$ Our density estimates for the largest cities of the 16th century range from 12,000 to 33,000 per km$^2$. Thus, if you want a city of 300,000 people, it should have a geographical area anywhere from 10 to 30 km$^2$, based on real world precedents. ]
[Question] [ When Ghenghis Khan was establishing his great empire, he felt that it was important to allow information to travel quickly. He created a postal system which allowed everyone from commoners to the military to send messages from one important location to another. My question is, how long would it take to send a high-priority message from one major population center to another near one? Now, let's table that answer. We have an interstellar empire highly resembling the Mongols. We don't have any ansibles or whatnot, so information has to travel on ships (FTL ships, luckily). Assuming standard interstellar distances (3-10 ly), how quickly would the Empire's ships have to travel in order to have similar information lags? [Answer] The Mongols established defined routes called a [Yam](https://en.wikipedia.org/wiki/Yam_(route)) much like the Pony Express routes of 19th century western America. > > Relay stations were used to give food, shelter and spare horses for > Mongol army messengers. Genghis Khan gave special attention to Yam > because Mongol armies traveled very fast, so their messengers had to > be even faster, covering 200–300 km per day. > > > (between 100 and 200 miles). Another [entry](https://en.wikipedia.org/wiki/Mongol_Empire#Mail_system) gives an overall time: > > When the great khan died in Karakorum, news reached the Mongol forces > under Batu Khan in Central Europe within 4–6 weeks thanks to the Yam. > > > So 4-6 weeks to cross the earth based empire. You might assume similar time to cross your star empire, then divide by that distance to get your FTLs rate of travel to produce similar delays. --- An example extrapolation (I'll make some assumptions): Our Galactic Mongol Empire controls this arm of the galaxy, with Earth as its capital, and we need to send a message to a general near the galactic core, and this will take the same time (4-6 weeks) as the above mentioned message. * Earth to core [distance](https://imagine.gsfc.nasa.gov/features/cosmic/milkyway_info.html) = 8000 Kpc = 26,092 LY (round to 26100) * Time for Mongol message (pick 5 weeks) = 5 \* 604800(seconds per week) = 3024000 seconds gives us 26100/3024000 = 0.0086309523809524 LY/sec multiply by 60 gives us 0.5178571428571429 LY/minute The last value we can round(if desired) to 1/2 LY per minute or 2 minutes / LY, so the OPs example of 3-10 LY separation means travel between typical worlds will take 6 to 20 minutes, to simulate an expansion of Mongol rates of travel to a galactic empire stretching from earth to the galactic core. Note your mileage may vary. [Answer] About the speed of a horse ( about One Horse power) with short breaks this speed produces about 30 to 50 miles a day depending on the horse . That's over flat terrain. Longer over mountains. Faster overseas or traveling along rivers it really depends on the terrain. ]
[Question] [ Conceiving of a moon with a similar ecology and atmosphere to Earth, but with a gravity level equivalent to the moon. This is essentially a terraformed analogue to Earth's moon in terms of size and orbit along with a rotation of 60 hour days. My question is what would rain storms look like on this world? Would it be more like mist? Or would it just be similar to Earth. the idea for this came from an article i will post below. Does not go into a few things, among them, how rain behaves on a terraformed moon, so was trying to get an idea how rain storms would work. <http://www.slate.com/articles/technology/future_tense/2014/07/terraforming_the_moon_it_would_be_a_lot_like_florida.html> [Answer] I'd guess drops would be larger, as they fall more slowly and have more time to accrete and grow. The speed of rain depends on drops' terminal velocity, which depend on air density and gravity. Density depends on the overall quantity of air together with gravity, so you can have an atmosphere as dense as Earth's. No changes there. The density gradient would be gentler. So I suspect clouds would tend to form at a higher altitude and also be taller in general. On the other hand, they might be less dense since the same quantity of water vapour would be diffused on a larger volume. Rain frequency might then be different from Earth, you might even not have rain at all -- but I'm already far outside the boundaries of my meteorological knowledge. ]
[Question] [ Short variant of question: 1. I have few big natural caves (really big). 2. I want to transform it into shelters capable of keeping ~2.000.000 humans in hibernation, sleep, suspended animation or other thing - so they can sleep for 5000-10.000 years and wake up on one day being mainly healthy and sane (and being THE SAME person they descended to sleep). 3. This system does not need to be fully automatic - we can wake up some members for maintenance of sleeping ones' live support system and performing cave entrance guard duties. 4. Ideally, it can all be done with 20th-21th century technologies (we assume we have few biology breakthroughs happened earlier in 19th century). 5. Shelter inhabitants are not 100% humans, they have more skills in biology than us, and can alter themselves a little before going to sleep. 6. We need at least 80% percent of sleeping population survive in 5000 years and at least 60% survive in 10000 years. 7. There is bronze age population evolving on surface, we need to keep if away from our shelters. The question is - what breakthroughs in biology do we have to achieve in the 19th century for this shelters be build-able in the 21th century? Long variant of question: In my story there is a human nation. Lets call them Forest Confederation. They are on technology level of early 20th century (but with a few additional breakthroughs in biology) - their analogue of the First World War just finished recently and they are victorious - they used quite clumsy, by our standards, [aeroplanes](https://en.wikipedia.org/wiki/Wright_Flyer) loaded with bacteriological based weapon spreading airborne. Of course the people of the Forest Confederates have all undergone proper vaccination, but not their rivals - they have lost 90% population turned into short living [turbozombies](https://en.wikipedia.org/wiki/28_Days_Later) killing the remaining 9%, and sparing the most lucky 1 percent. In long time this 1% can recover at least to Medieval level. Unfortunately, the Forest Confederation has no choice but to perform this forced genocide, because their more industrial advanced rival would give them no chances. Also killing 99% of the population granted attention of a nearly omnipotent Mother Nature Goddess (the Forest Confederation has a strong faith). Or at least the Forest Confederation interpreted a few dark omens as occurences by the will of their goddess. So, the will of the goddess is clear - "I will perform major climate change in 200 years from now and all of you will either die or degrade back to stone ages." The Forest Confederation treated this like real danger and started building underground shelters to survive the climate change. I have posted the requirements to this shelters in the short version of the question above. I have read this [question](https://worldbuilding.stackexchange.com/questions/66391/alternative-to-cryogenic-sleep-deep-hibernation), but it has 23th century technology level and I want something more simple. I do not want `You might want to consider transporting digitised copies of the people, and then 3D printing them new bodies at the other end.` as pointed by Jnani Jenny Hale (<https://worldbuilding.stackexchange.com/a/66404/2763>), I want something more close to Zxyrra's answer (<https://worldbuilding.stackexchange.com/a/66452/2763>) with tech level close to present day, maybe with some handwavium. I want the Forest Confederates leaving their shelter after 10.000 years being the same ones who entered it. UPD 1: power is not such a drastical problem - we can receive power using [geothermal energy sources](https://en.wikipedia.org/wiki/Geothermal_energy) even using 20th century technology. [Answer] If they aren't human just make their reproduction system different? Creature has capacity for sexual reproduction, but not necessity. Sexual reproduction creates a conjunction of the participating parents, a new being. Asexual reproduction essentially clones the existing material of the parent. You could include with this process a change in neural formation in the organism that creates a more definite & closely defined template than that of humans to the point where their personality is essentially identical.. Or instead of that some 'handwavium' neuronal transfer so you're effectively the same person, but not actually the same body. Treat the memories of the species as a virus/prion, sorta. If you want them to be biologically human in ancestry at least, use some epigenetic effect of the local environment or..like bacta tanks in star wars.. it's not a technological discovery, but a use of a natural resource. Actually making an underground settlement is pretty simple. People need: Heat regulation & Regular provision of certain chemicals & compounds. So you need..heat source, heat exchangers, water source, organisms that live underground whose products or byproducts are useful. upper chambers could be filled with a fungus/bacteria/tree roots that convert co2, there's nothing banning inland caves from having subterranean access to water tables or even the sea. bred or natural organisms that can filter saline, no problem? Thirdly, surround all your cave entrances with something that's extremely poisonous to whatever this bronze age species is (human also?) well, learning how to and having the will to remove said poisonous flora could well take 10,000 yrs if the species is comparatively retarded. Bear in mind how long the move from bronze age to powered flight took humanity..and probably nothing your 19th/20th century civ is going to do is going to last 10,000 yrs and remain effective, your poisonous organism might die from drought or evolve to be less poisonous or bronze aged peoples find it's particularly useful for poisoning other bronze age peoples and start harvesting it with slaves for use in war or w/e. [Answer] If you want to build a structure to last for 10 000 years you really have only one option: pile rocks on top of rocks the way they did in Ancient Egypt; essentially, build a small hill. Nothing else will last that long. Build it in a hot desert -- temperate or subarctic latitudes are a no-no, especially with water around. Don't have anything electronic in it; no way the materials used in electronic circuits will last for 1000 years, let alone 10 000. In short, the millions of hibernating humans will never get a chance to wake up. Alternatively, don't build the facility to last 10 000 years. Instead, built a small country, complete with farms, factories, schools, universities, hospitals and an army. Task the country with the maintenance of the cryofacility. A population of a few million may be sufficient; say 10 million. In favorable conditions (good climate, good agricultural land, sufficient rain but not too much, access to the sea and natural resources such as iron and copper and tin and zinc and gold and petroleum), a country of 10 million people does not need more than 50–60 000 km², which is about 250×250 km or 150×150 miles. Small enough to make it plausible that the rest of the world can just ignore it; for example, the island of [Madagascar](https://en.wikipedia.org/wiki/Madagascar) is 500 000 km² and is very inaccessible for people lacking modern technology—in the real history it was the last large landmass to be populated by humans, and that did not happen before the 3rd century BCE (or CE, opinions vary) and the human population remained very low until the 6th century CE. How to make those millions of people to (1) not multiply to excess and (2) stay focused on the mission for 400 generations is another problem. Please note that the entire history, from the very first cuneiform tablets in Sumer to this day, is about 5000 years: your intention is to make a facility and support structures lasting for two times the duration of the entire history. [Answer] There's no way that anything more complex than a nail created with early 20th century technology would survive 100 years of continuous work, much less 5,000 or 10,000. Even if you have some people awake to make maintenance, they'll run out of spare parts and replacements quickly, not to mention power sources or food and waste disposal for the awaken. [Answer] The keeping of a specimen alive and as it is longer than its lifespan should be the main issue. That can be solved by: * Self-replication: Making copies of oneself to survive longer (asexual reproduction as already suggested) * Negate Aging: By means of cryogenization or suspended animation (if technology allows) If we can get a source of water and convert whatever power we get (geothermic for example) into something processable by the species, sustaining life wouldn't be a problem either. ]
[Question] [ Assume the observer was on the ground, 4 km from the base (bottom) of the Space Elevator. Assume a "standard" Earth Elevator "tethered" at <= 20 degrees of equator, made of diamond nanothread, with an elevator "top" in LEO and a final tether in geosynchronous orbit. Please take into account oscillation and differing rotational momentum between Earth and the geosynch tether. How long would it take for the effects of the severing to be noticed, as well as what the observer on the ground would see? I add this to "world-building" as I need specific numbers to play around with for both Earth and a different world for a piece I'm writing. [Answer] Breaking at the bottom would be the best way for it to break. A couple of notes: The space elevator needs to have a top at geosync orbit, and a counter balance extending above geosync orbit. You can't use a space elevator to get into low Earth orbit, because at low Earth orbit heights you aren't going fast enough to be in orbit. Not having the elevator on the Equator is possible, but adds to stresses as there is now bending in the elevator cable. Now the elevator will be under a lot of tension. If it breaks at the base, the whole thing will lift off and be flung off the Earth, and probably end up in solar orbit. The bottom part will be dragged at high velocity through the atmosphere, probably fragmenting and the fragments will fall in the neighbouring districts. If the elevator breaks higher up, the lower part will fall down, wrapping itself around the equator. God help anyone living on the Equator. Although the broken elevator won't hit the ground at very high speeds (thank you atmosphere) it will cause a line of destruction through Brazil, Congo, Indonesia and other countries on the Equator. These breaks can be simulated: Blaise Gassend has done some animated gifs of an elevator break at various altitudes. <http://gassend.net/spaceelevator/breaks/index.html> His model assumes "The elevator that is simulated is an equatorial uniform stress elevator with Brad Edwards' standard parameters. Length is 91000 km, density is 1300 kg/m^3, strength is 130 GPa with a factor of safety of 2, Young's modulus is 1 TPa." [Answer] Visually, 1 second for every 186,000 miles, because that's the speed of light. A geostationary equatorial orbit (GEO) is a circular geosynchronous orbit in the plane of the Earth's equator with a radius of approximately 42,164 km (26,199 mi) (measured from the center of the Earth). A satellite in such an orbit is at an altitude of approximately 35,786 km (22,236 mi) above mean sea level. Because it's only 22,236 high, even if you severed it at the tippy top, they would notice pretty much instantly (or near to) if they have a clear view. (I assume they'd be able to look through a telescope). [(source)](https://en.wikipedia.org/wiki/Geosynchronous_orbit) But, Because of the slow rate of rotation of the Earth (only one revolution per 24 hours) the cable has to be very long - theoretically at least 25,000 miles, and in practice closer to 60,000 miles. [(source)](http://www.spaceward.org/elevator-what) Still, even at 60,000 miles, it will take less than a second for the light to travel and show us that it has happened. Now, non-visually, the effects are going to depend on HOW you handle the severing. Is it a large explosion? Is a line mechanism just cut? Let's also talk about how elevators are handled in large buildings. Most of the time, the elevators go to certain floor, then you have to change elevators to go up the rest of the way. For safety's sake, I would expect it would be handled this way. So maybe 1/2 way or a 1/4 of the way up, the doors open and you go to another elevator in the same bay, switching sides as you go. If the elevator doesn't work, you'd be stuck at the second to last elevator up. Now, some of these proposed space elevators don't work this way--they are a single elevator that travels up at a high speed, but this is the way I'd build it, mainly because segmented systems can be easier to maintain. There are lots and lots of models for this, so I can't answer this question fully without knowing the method of design (there's the ski-lift version that involves multiple cars, and I'd expect that this would be segmented in some way as well). I also think that the speed is important to the design as well. See [this answer as to the top speed of the elevator](https://space.stackexchange.com/questions/5603/how-long-would-it-take-to-ride-to-the-top-of-a-space-elevator). That's because if you have people travelling in the elevator for 2-3 days, those people are going to have NEEDS. Like eating and going to the bathroom. Will there be a bathroom on the elevator? Will the elevator(s) have stops on tiny platform to allow for eating and drinking? How large will each one be? Is it one single car, or several sent in a row? If it's several, the car that doesn't make it might procedurally send a message down on arrival, and that will be noticed, or the system simply won't take them up any further and they might radio for help. Answering this question can only be fully accomplished once you've done a lot more research on how these things work and how your operating system is going to work. This determines how communication works, how many stops there are and all that--since I am sure the ground likely communicates with the elevator(s) along the way. If many are being sent up, one right after another, that changes things vs. one single car, (because that will take 2-3 days to reach the top) as will stops and communication with people on the top. [Answer] Look online for videos of a slinky toy being dropped. The top starts falling when it is released, but [the bottom does not move yet](https://www.insidescience.org/news/secrets-levitating-slinky)! The bottom is still supported by material that is not itself supported. The loss of tension is noticed by other parts of the system at the speed of sound in that material. The space elevator, assuming it’s under tension and cut at the bottom, is the same thing. Various cars gripping it will notice the lack of tension after a delay ed on the speed of sound. Likewise, this is the time scale at which it will start to bend and whip around. A ground observer can’t see the tension. He won’t notice anything until it moves far enough to resolve. How fast the cut end snaps up depends on the specific design and tension, and can vary by orders of magnitude! Newer concepts [don’t need an anchor at all](https://en.wikipedia.org/wiki/Space_elevator#Base_station), but hang in the air and normally don’t touch the ground. So at one extreme you won’t see anything happen; at the other it will shoot up at supersonic (in air) speed. ]
[Question] [ Now I love huge living creatures and fantasy settings, this just might be reflected in my questions, so I had the idea to make a massive living island. I saw a similar question, but unfortunately it asked not how it would work, but how it would evolve and play out, so I still need an answer. Now to start I said plant, so its flight will have to be passive, so lighter than air gases are needed. My ideas both include giant gas bladders so will that work and how? For my idea the roots would hang down all the way into the ocean, the plant would grow up from the ocean floor. Eventually forming an island which as the bladders are made and start to fill up with the lighter than air gases slowly lifts off. Will this work and if no, how else? PS: For size something massive like the isle of Wight. [Answer] Air bladders (as found in sargassum weed) plus methane-producing bacteria. The plant or alga grows in shallow seas (shallow enough that the light that reaches the bottom is sufficient for photosynthesis), and spreads largely by budding from its 'root' or holdfast. It grows into a kelp-like frond which reaches the surface. The frond's tip is an air bladder, holding it at the surface (for maximum photosynthesis). Most of these plants (due to budding) have identical DNA, and as their fronds make contact, sometimes they grow into one another. In some cases the air bladders merge, while in others they remain separated by a wall of tissue. Eventually, a giant, convoluted mass of photosynthesizing air bladders floats at the surface. Some such colonies develop a symbiotic relationship with methanogenic bacteria which live inside the air bladders. They eat nutrients provided by the plant colony, and in return, excrete methane gas which makes the bladder float higher in the water - allowing it to shade out & outcompete neighboring surface flora. As this process continues, the (now gigantic) colony eventually becomes buoyant enough to rise out of the water entirely. It is still linked to the bottom of the sea by its stems, and the result resembles a giant green brain (the surface is crenelated & convoluted due to all the separate air bladders) linked to the water by thousands of green nerves. [Answer] Having it be ONE plant, or one single gas bag, connected by one single line, seems limiting for the organism. It's not very easy for them to propagate or evolve or anything. Therefore, I am going to go with a model that features lots and lots of these plants. So, let's say helium is the element you'll be using to float your plants. In this case, you'll have to find a way to have your plants manufacture helium. > > Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of helium-4 nuclei. [(source)](https://en.wikipedia.org/wiki/Helium) > > > Since it comes from radioactive materials, these will have to be present in abundance for the plant to process. This may change the entire ecology, and so should be approached with caution. Helium might not be the way you'll go. There are other options, such as: * methane, which is far easier to produce, although more often for animals than plants * hot air, which will need a mechanism for heating, and thus will be difficult for a plant to achieve. * Hydrogen, which is present in water, and is perhaps the easiest, but your plants will need a mechanism to separate the oxygen from the hydrogen. They will be very flammable. EDIT: This may be a problem, because if there is any kind of fire on this island, many will explode, causing the island to dip lower or fall into the ocean. In fact, this could be part of the natural life cycle, and the island needs to fall in so that the process can begin again. Like [pine cones](https://en.wikipedia.org/wiki/Serotiny) You could also have it so that sections of the island can break off and fall away resulting in holes in the middle of your island or breakaways at the edges. This will depend on growth pattern. (They can grow in rings so that the edges are stronger and the center is empty, filling in as they go, or randomly, or out from a center point). First, you must decide the mechanism and type of gas you want to use. That determines a lot of other things and factors. Next, let's look at how the ground will be built. Are people meant to walk across the top of the plants and that forms the ground of your island? Or are you looking at having the plants grow up THROUGH this "ground" basically as balloons over the ground? If it's the second one, that means the plants have to have a way to form the ground, and once it is formed, a way to poke through it. Forming the ground is a matter of lattice work between plants, and falling leaves from the plant, which will create soil. How stable it will be will depend on how it's built. Once a lattice work of plants is formed, and the ground is too solid, I would expect that it would be difficult for the ones underneath the island to be be able to get above this newly created ground. So you'd have to find a mechanism for that, and you'd likely have immature ones beneath, that are gas filled but haven't come out yet. EDIT: You could have any mechanism to get this done, but if parts of the plants burn if it's hydrogen, you can have these searching for the "holes" or weak spots created by this. There's other ways to do this too--the gas bag plants have phases, in which they can grow directly on the created soil (and don't have to have a line down to the ocean). I would have them start in clusters, over miles of ocean, for sure, so that there's multiple lines down to the ocean. Edit: Even better, they start as one or a cluster with the line to the ocean, but eventually that falls away and it just floats free in a particular stage of development, such as when the island reaches a certain size. Then, all the plants on it grow from the "soil" produced by the main plants. Additions to the soil will come from birds (their poo, nests, and carcasses) and other plants which grow on that soil. It eventually won't be tethered to the ocean, but the weight will keep it from floating into the atmosphere. [Answer] Entry eighteen, day 52 "Being low on supplies, Faraday called the suggestion that we make anchor on a nearby island to collect water and food. It was on gathering from a selection of fruiting trees that we detected a foul odour on the breeze - something akin to sulphur or decay. On checking our baskets, we found none of the fruit to be bad, nor could a place be found for the smell's origin. "As the weather closed in and took a turn for the worse, we gathered underneath a branching tree. Overhead, a large, dense cloud drew in, carried on the breeze. "It soon became apparent, however, that it was not a cloud, but a continent-sized growth of lichen - wiry as beard-hair and as light as spider webbing - which descended upon us like a snow. Light wisps at first, followed by large clippings. It soon threatened to engulf us, and we had to make a concerted effort to prevent it from compromising our shelter. On attempting to shift it with our bare hands, we found our skin to become rashed and chemical-bitten. "As the wind picked up again, the lichen was blown away in large patches - the hairy barbs caused it to clump together and take with it patches of fruit and bark from the nearby trees. It would appear that this is how the colony of lichen fed and received moisture, moving across the land like a travelling blight or cloud of locusts. "Large patches were left like carpet in the aftermath of a barber's shop, where the dry lichen had become too damp or laden to be carried by the wind. On the return journey to the ship, we were careful to avoid contact. Indeed, we saw some creatures which had not been as lucky as we had been to find shelter, and they had died of their afflictions." TL;DR: a lichen which, when dry, can be borne on the wind in large quantities resembling a mobile island without need for a root system [Answer] Entry 22, day 102 "We were travelling the gulf when we came across a rather quaint thing. We could neither decide on plant or creature - but from here on we shall describe it as a plant. Details on this shortly. "As we had encountered it, the plant was floating above the water at a degrading altitude. We caught it before it had become submerged and thoroughly inspected it. "Its stems were knotted and bulky, yet tubular and empty like plumbing pipe, perhaps like a succulent bamboo - which made capturing it with the barge hook from the port side of our boat an easy task. On its apex, a single, withered grapevine split like hollow veins to encapsulate a partially filled ballooning membrane. On the dexter side of these veins, small holes with wrinkled grape-like valves which must have, in a previous evolution, been stomata. "After our analysis and samples were taken, Charles released the plant into the water - at which point this seemingly dead plant sprung back into life. "The roots and stems began to swell (you could see the water being drawn up through the pipe-like stems) and the outsize plant stomata began viciously gulping air by action of their fluctuating turgidity. The weather-balloon at its topmost point began to inflate and it was not long before (now laden with water) the plant began to ascend into the firmament. "It was only later on this trip that we discovered this plant to be a juvenile, as indicated by its nut-hatchings and partially discarded shell. Fully grown plants, in our experience, might reach the size of a small continent - given that it does not drown itself under its own weight first." TL;DR: Strange mechanical action is sometimes stumbled upon in nature - the valves of the heart, the undulations of jellyfish or, even in the plant world, the exploding cucumber or the sensitive plants. [![exploding cucumber](https://i.stack.imgur.com/fRgWz.gif)](https://i.stack.imgur.com/fRgWz.gif) [![sensitive plants](https://i.stack.imgur.com/5k71Z.gif)](https://i.stack.imgur.com/5k71Z.gif) While most plants have 'nervous systems' which trigger in one direction only (Venus fly traps close, sundew plants curl up etc) - it's not impossible to imagine a mechanism where the Bernoulli principle causes a fluctuation of parts, which in turn, through another development of kelp-like gas sacs - allows a mechanical suction and storage of air. ]
[Question] [ Suppose a civilization in which every possible appliance is a bio-machine. There are automobiles, but each one has a human-like head under the hood. Each datacenter is a bunch of over-grown brains. There are artificial udders that produce milk without a cow. Each house is living as well. When you sit in a chair it embraces you with its hands etc. Everything is based on mutated animal and/or human genomes, but the civilization evolved from human society. There are no steel/plastic machines, there is no use of mains electricity. There is no internet (but neural networks are possible). What conditions may lead a human civilization to pursue advances in bio-engineering but reject other technologies? [Answer] Lots of this is very sci-fi, but I figure without a hard-science tag, I can let fly with the theories. Funtastic!!! Here's my list that I could think up. * Once they had regular tech, and that turned out badly, so they bioengineered everything. * Extreme gene plasticity is present and any material can be produced. * All the movie stars started using bio houses in the 1930s and it just took off! * There was a "naturalist" social movement. * Everything growing on this earth is already sentient, so the people took advantage of it. * A memetic, living bio gel was found which took on characteristics of whatever it touched. This lead to many discoveries, but first, some horrors... * Rolling EMP waves are present on this planet that would knock out anything run by electrics. * Anything on this planet WITHOUT a bioorganic base quickly degenerates and disintegrates. For some reason the bonds between atoms don't work properly without LIFE installed, so there's a need for bio-based steel. * Free market competition! There were solid, non-bio based technologies, but an important discovery made bio-based cheaper, easier to produce AND better at handling certain jobs, and it just took over the whole market. * Survival of the fittest. So someone invents bio-whatevers, and the bio-whatevers want more of themselves to be produced. The bio-whatevers actually send out spores or something like to either destroy anything that's merely matter or INFECT IT! Everything is bio-based because there isn't much that isn't infected with bio-smutz and for some reason, any matter material that humans work with starts to become bio-based. Humans figured out quickly that it was best that they guided the process rather than letting it run wild. * Like @Zxyrra says--maybe some crazy dude in power decided this was the way. And it was. * So, computers reached their zenith. We found we could not do more without incorporating bio-tech. And so, we did. And then we kept doing it. [Answer] ### Trendy cosmetics The cosmetics industry grew tenfold after many advancements in biomedical technology, genetics, and general surgical procedures. The trend of self-modification spiraled out of control, and people became effective enough to do most tasks. This technology was then applied to other fields. ### Employment / economic competition After machines became more skillfull and more prevelant than most humans, upsetting the global economy, some scientists took matters into their own hands. So what if you're an abomination when you can compete with the machines and feed your family? ### Biodegradability While the climate changes, plastics and other synthetic products we push out do not. In an effort to create green infrastructure and industry, biological machines became the norm. ### Computation As @CameronLeary said, organic tissue - especially the brain - is incredibly good at small-scale tasks, such as computing. Supercomputers are big, bulky, and expensive, but people can do the job at a lower cost. And so they do. ### No good reason After a cruel, demented dictator took charge of society, they implemented these changes as a way of suppression - and to instill great fear. It worked. [Answer] I see some good answers here, but I'll add one more that deals with the motivation of moving away from existing technology: perhaps they had a bad time with purely mechanical robots, and learned the hard way that [AI is not to be trusted](http://tvtropes.org/pmwiki/pmwiki.php/Main/AIIsACrapshoot) (TV Tropes link, be warned). A civilization that had intelligent robotic creations rebel against them would not be keen on rushing to recreate anything similar. There are many instances of this in fiction, but I'll point out the [Geth](http://masseffect.wikia.com/wiki/Geth) from Mass Effect as a particular example of this scenario; the in-universe result of that rebellion was for all races to utterly ban research and development related to true AI. Warhammer (the 40K version) actually has what you're looking for, to an extent: the Imperium uses servitors (lobotomized humans, usually criminals, with robotic augmentation) instead of purely mechanical robots because of an ancient rebellion by artifically intelligent robots (the Men of Iron) that is believed to have effectively wiped out humanity's power in the galaxy at the time. As a result, it is a grave crime to attempt to develop artificial intelligence; robotic creations like the Titans are built to have pilots, not think for themselves. For more detail, look at that universe's [Dark Age of Technology](http://warhammer40k.wikia.com/wiki/Dark_Age_of_Technology). For your scenario, you can easily hypothesize a similar rebellion that resulted in a more extreme answer: banning all purely mechanical technology, intelligent or not. If biotechnology exists, this sort of thing would be motivation enough to drive it into the forefront, and countless trillions of dollars (or credits, or whatever the currency of the time is) would be thrown at it [Answer] Situation 1- global warming If the planet had, in the past, had issues with global warming and so found no way to maintain there current technological status without ruining their planet. Noticing this, they may use a combo of plant and animal genes to recreate and even improve upon all of the technology they had. As well as stopping global warming, the reason I mentioned plant genes would be that this would actually undo the harmful effects they have bestowed upon their planet by using water and carbon dioxide to fuel themselves. Removing carbon from their atmosphere. Situation 2- technological advancement If these new technology's worked as you have explained, the technological advancement would be huge. The computing power of the human brain is already very powerful. If you were to tweak this and recreate it on a magnitude equivalent to that of millions of individual brains then you gave it all the information your civilization possessed, it would be beyond all current computing capabilities. [Answer] What it takes is simply for messing around with Biology to be easier than it is in the real world. Imagine Biology turned out to be much like Chemistry, there are relatively simple things you can try to get reasonable and reproducable results, and eventually you can create theories to predict how things will work before you even try them. It could be as simple as mixing some cells from one organism into another during development, with trial and error until you get a viable strain which you can then just breed. No plastic is easy to consider, there are few uses for plastic you couldn't get from simply growing something in the right shape. Steel is harder, because it's... harder. There isn't an organism with the strength of steel, but you could perhaps simply have things grow out of hardwood but thick enough that it's strong enough anyway. Brains might turn out to be super easy. Perhaps you just transplant them (after growing in vats) and they automatically create connections to any loose nerve ends you've built into your device. You'd have to say there is no such thing as biological rejection, all biological things by default likes to grow into each other (or perhaps theres an easy way to turn such protections off temporarily). [Answer] I think one variant can be fear of technological singularity. In the past there were very complicated electronic machines who rebelled against humans. The humans managed to win the war, but since then prohibited any non-biological machines because they can unpredictably interact and be hacked. [Answer] Genetic engineering: Creation of 1. XNA (artificial DNA - already accomplished.) 2. XNA has already been encoded with 100 bits of data can be attached to the DNA of bacillus subtilis, (a common soil bacteria) and shows great potential for data processing. 3. Modified E. coli can already be used to produce polyester for carpet (DuPont.) 4. Genetically modified silkworms have also been made to produce "Dragon Silk," which is 10 times stronger than conventional silkworm silk, and is being investigated by the US military (It's tougher than Kevlar.) 5. The seeds of a vultivated hybrid strains of a plant called "jatropha" is currently being produced in the laboratory as a biofuel (essential fulfilling the need for any petroleum based product.) 6. Using genetic engineering to modify animals for transport, scouting (slightly "enhanced" canine), enhanced milk production etc. So: data storage and processing; pollutionless materials fabrication (from carpets to armor); and specialized chimeras. I suggest that all the basic "building blocks" you need can be extrapolated from these. [Answer] You say the civilization 'evolved from' human society, is this on Earth? Metal - poor world: If not, one possibility is a planet which is very poor in the elements needed for 'conventional' technology -- iron, aluminum, titanium etc. for structural uses and machines, copper/silver/gold for wiring, silicon/germanium for electronics, platinum group metals for a catalysts used for a wide variety of things, thorium/uranium for nuclear power, praseodymium/neodymium for strong magnets, etc. etc. Of the above listed elements only iron, copper, and maybe silicon are biologically essential for humans, and only in very small quantities that wouldn't require the existence of practical ores of those metals on a planet. No access to ores: Or those ores might exist, but not be accessible -- if a planet was, say, almost entirely covered by deep oceans with the only land being biologically deposited limestone islands, and all the useful ores are under five miles of ocean. Or maybe the people even live on living, "floating islands" (island sized water lilies or something... a situation like this is found in Jack Vance's The Blue World). In that case the ocean could be something like 200 miles deep (a hypothetical ocean planet: <https://en.wikipedia.org/wiki/Ocean_planet> ). Or the setting might be in an artificial environment - either a space habitat of some type (O'Neill colony, "Halo" type ring, Niven ring, Dyson sphere) or even a sealed 'arcology' type environment on Earth. Such a structure wouldn't allow access to ores, etc. unless that was intentionally incorporated in the design. (This problem is discussed in the original Ringworld by Larry Niven.) Competition: Accessible ores exist, but if you make steel or aluminum structures or copper wiring, etc., they become extremely attractive food for some local pest. (The iron, copper, etc. in the human body isn't in metallic form but part of proteins, so wouldn't necessarily be a target just because the pure metal is.) ]
[Question] [ Let's use a Mars-like as an example of a planet that interstellar travelers may settle on. Assume that the spacecraft will provide Earth gravity and atmosphere. Comparing this new planet to Earth, it has .5g (1/2 the gravity) and has .5bars of atmosphere, or 1/2 the pressure of Earth. Everything else is the same. Water, light, heat, techtonics, length of day and gases in the atmosphere. In building this world, my travelers build a settlement, and begin having children. My questions may be basic, but in this first generation that is born on this planet: 1) Will they grow taller? And by how much? 2) Will their lungs develop the capacity to breath unaided? 3) Will their muscles and bones develop naturally for the new world conditions, or will genetics get in the way? If so, how and what? My last question is we know humans in zero gravity or even on Mars will lose bone and muscle, heart weakens. We suspect if humans born on Earth were to find such a planet, they will need to be aided in breathing like mountain climbers. Is it realistic to believe that human muscle/bone loss will stop when it reaches what it needs to function at .5g and .5bars of atmosphere, or will our genetic code continue the signal of bone/muscle loss? It may be a lot to think about, but the scenario I am looking at is what life will be like for the first generation born on a new world that is different from Earth. And if anyone has ideas on whether the second generation will have it easier, I'd like to hear about that too. [Answer] 1. They will grow slightly taller. Genes won't allow any huge differences - our spines are still stuck at a relatively set height - but less compression will allow a few inches of growth, according to [this](http://www.livescience.com/33082-would-humans-born-on-mars-grow-taller-than-earthlings-.html) source. 2. Their lungs will not catch up. Such low gravity and pressure are survivable, as clarified by the comments, but pressure suits and masks may be more comfortable. People can acclimate to survive - their bodies can respond and stay that way - but there is no reason for our genes to change. Evolution is driven, along with other things, by natural selection. What can survive will, what isn't fit to survive won't, and over time, whole species change to be better suited to the environment. However, if humans are at the point where they can colonize other planets, those "unfit" to survive will survive anyways. Nothing prevents those unable to breathe as easily from being able to reproduce. If an individual is not able to acclimate, they can get a pressure suit and a mask - and reproduce just like everyone else. Therefore, there is no evolutionary pressure, or incentive, to adapt. It's not impossible for it to occur with mutations, but when there's no reason to adapt, don't expect adaptation. 3. Their muscles and bones can adjust. People on your world will definitely appear smaller - they don't need heavier bones or stronger muscles, so they will not develop them. This probably isn't a problem if they don't try to go back home, but in the event that they must, excercise and nutrition can help rebuild what has been "lost". ]
[Question] [ I recently learned about a chemical known as [chlorine trifluoride](https://en.wikipedia.org/wiki/Chlorine_trifluoride). This utter abomination of chemistry reacts to almost everything, setting glass, sand, asbestos, and rust on fire (to name only a few), and can only be loosely contained in a fluorine-treated metal container (the fluorine layer must not be damaged, at risk of explosion). This chemical is deadly beyond reason... ...and, as is typical with me, I started trying to combine it with other things. My question is this: Can a dragon-like creature be biologically designed to create and excrete this substance as a breath weapon? How many biological processes would have to be redesigned or completely handwaved to allow this? Can such a creature even exist in our atmosphere? [Answer] So the trick is to create a separate space for the chlorine and the fluoride in the dragon. Set up the dragon's system so that it separates fluorine from the atmosphere (there are tons of fluoride compounds floating around up there) and stores it in a specialized air sack along one side. The same system is necessary for the chlorine, which will be gotten from sea-water. The dragon can separate the chlorine from the sodium and will store both. The chlorine will be stored in another air sack on the other side of its body, which will need to be coated in strong mucus because Cl2 will form hydrochloric acid if it comes into contact with water, the sodium will be stored in a special oil gland. When the dragon wishes to breath ClF3, it simply expels both fluorine and chlorine at the same time. The fluorine will coat the dragon's mouth, preventing ClF3 from hurting it. The gases will mix, yielding ClF3 and excess chlorine gas, which is also toxic. The fluorine that coats the dragon's mouth can be reused. The sodium the dragon extracts from the sea water can be used as a separate attack. The dragon can expel clumps of sodium, which reacts violently with water. These bombs could be spat out with force, or simply dropped down on people or ships. ]
[Question] [ I am writing a book, and I want to create either a sentient fungoid or plant and I wish for it to use hormones instead of neurons to transfer information. I'm not sure how this would work and affect the capacities of the plant/fungoid? [Answer] It's possible, doable, and [there is real world research on plant intelligence](http://news.nationalgeographic.com/2016/02/160221-plant-science-botany-evolution-mabey-ngbooktalk/). There are a few "problems" with this kind of intelligence, though. Comparative problems, having to do with speed. Let us talk about something more basic than sentience. I think we can agree that consciousness is a prerequisite - you have to be aware before you can think "I am". We still know little about consciousness, but [it's all about computing and how data is moved around a colletion of parts](http://www.scientificamerican.com/article/consciousness-might-emerge-from-a-data-broadcast/). In our case, we use neurons. It may be that one day we will replace them with electronic parts. What neurons and electronics have in common is that they use electricity. For neurons, this means a signal can travel up to 120 meters per second (1 meter is about 1.1 yards, or a bit more than 3'3"). With electronics instead of neurons, an electrical impulse will move at a considerable fraction of the speed of light. In very laysman terms, it means that if I step on your foot, the pain signal will reach your brain in really short time, and you will be able to react practically instantly. A plant or a fungus, though, which can't rely on electrical impulses and must communicate solely through chemical signals... Well, that might take some time. If I kick the ankle of your fungoid, its ankle will start to produce the chemicals that signal pain. Now it doesn't matter if it has a brain somewhere or if its processing elements are spread wide over its body, it will take a lot of time for its circulatory system to distribute those signaling chemicals to its "neural" network. For a human sized fungus monster, this could take from minutes to hours, depending on your design - but it could be faster if your creatures have a heart to pump their fluids. Now, the signal doesn't just have to reach the "neural" network. Each element must process its input, and communicate its processing result to the elements connected to it, many times. Your fungoid might start calling me names days after I've kicked it. For a creature like this, a mobile lifestyle would be a no-no. It's no good moving around if you'll only react to the simplest obstacle in your path only on the next day. Of course, this is all assuming that your creatures are human sized. If they are small, the distance the chemical signals will have to travel before a reaction can be taken will be shorter too. Remember, bacteria and protozoa have no neurons, and they react to their environment in reasonable time (usually - [but not always](https://www.youtube.com/watch?v=pvOz4V699gk)). ]
[Question] [ This question already has an answer here: [How to make a flying human](/questions/23145/how-to-make-a-flying-human) (1 answer) Closed 4 years ago. How would it work for a human to have wings and how would they be able to fly? What wings would make the most sense, feathered, webbed etc.? How would it make sense for it to connect to their own body and would there be a way for them to hide it on a day to day basis? What adaptations would have to be made for said human to fly? [Answer] ### Human Wings If you wanted it to be "natural" then they would look similar to the wings used by other mammals. Namely webbed like a bat's (or a Batman's !) wing. [![Bat wing](https://i.stack.imgur.com/Pu9JG.jpg)](https://i.stack.imgur.com/Pu9JG.jpg) Also the wing membrane would be stretched between highly specialized fingers. [A bat has much more maneuverability than birds do from this arrangement.](http://www.livescience.com/1245-bats-efficient-flyers-birds.html) ### Could Humans Fly & How to Connect Wings to the Human body? On an Earth like planet (same atmospheric density & gravity) humans can not fly. Our configuration makes us too massive to fly given our skeletal-muscular structure. For a human to fly in a terrestrial environment, you'd need to completely reconfigure the body. * Replace solid bones with hollow bones (like birds). * Deepen the chest to give the wing muscles a proper breast bone anchor. * Remove most of the mass of the legs (you'll be flying most places). * Add a bunch of muscles in the chest, shoulders, and upper arms. * Also since humans descend from quadrupedal animals, our arms are what will turn into or be used as our wings. However, if you put the plot of your story [on the terraformed Moon with Earth pressure atmosphere then humans could fly with their existing arm structure and musculature.](https://worldbuilding.stackexchange.com/questions/28386/architecture-of-richest-persons-house-on-the-moon) They would need to change outfits into a special flying suit with appropriate wing shape. ### Keeping wings hidden If using a human adapted to fly in a terrestrial environment, the only way to keep this hidden from others would be to move around in a wheel chair and keep your arms close to your sides. The rest of the deformities might be explained to the public as some sort of degenerative disease. You might have your character move around in a wheel chair to keep the stunted legs (probably still useful for moving around but they'll obviously be different than normal human legs). If using the terraformed Lunar setting, the character could keep their wings hidden by simply changing clothing from normal clothes to flying suit and back. The flying suit need not be particularly bulky. Also you would not need to modify the human body (other than the flying suit) at all to allow them to fly. [Answer] Firstly, feathered wings would be a nightmare on humans, mainly cos we're naturally not feathered. We have skin, and so our wings should also be covered in skin, yep, like a bat. Otherwise, you'd have an overload of biological and logistical issues, like how can the winged human take a shower/bath with soap? The feathers would get gummed/ruined. How would the blood circulation in the body work out? And what happens if the human falls down in mud on a rainy day? Mud would cake the feathers... So to be realistic, skin-covered wings would be better for humans. Also, the wingspan would have to be very long. About 15 feet from wingtip to wingtip for the average-height human adult. How best to connect it the body, well, it would be better if it connected directly to the spine, like all our other limbs. So maybe the wings could connect either directly in the middle of the back or spaced slightly apart (but must be between shoulder blades, otherwise arm movement would be impeded). The connecting area between the wing and the back could be from shoulder-height down to maybe mid-back or three-quarter ways down. Any less and the wings would be liable to tearing off when faced with a strong force. Blood circulation would, of course, have to include the wings. As to hiding it on a day-to-day basis, the best way would be if you could draw out a design for your wings so that it can support the human's weight, and yet it can also fold neatly along the back. The batwing design would be a little difficult here because the long 'fingers' make it difficult to fold easily. You can see a picture of man's arm, bird's wing, and bat's wing [here](https://askabiologist.asu.edu/sites/default/files/resources/articles/bats/homology_550.jpg). What would be ideal is the skin-covered wing of a bat, but with the bone structure of a bird. Windbreakers with special slits in the back can be used, so that the wings can be hidden while the jackets are worn, yet in an emergency, the wings can snap out of the slits. With regards to adaptations in the human body, of course, the bones would need to be lighter. Maybe not hollow, because our skeleton would need to still support our bodies, significantly less dense. Muscle structure, also less dense, and the human must have very little fat or he/she'd be lugging around a lot of extra weight. Heart compressions must come faster to support the beating of the wings (which need to be very strong), and so diets would need to change too. On average, the human-bird would need maybe twice to three times as many calories as a normal person. Also, birdlike air-sacs in addition to lungs would be very useful, as well as something that may allow them to breathe in the lower-pressure atmosphere when they fly. Basically, the human has to be as light as possible, and yet strong. [Answer] The biggest issues are attaching the wings in a way that would give them the necessary range of motion (between the shoulder blades is way to restricted), and the weight of a human-in some birds the total weight of their feathers is more than their skeleton. In regards to the first problem, you'd need to deepen the chest to make room for muscles, but you'd also need to lengthen the torso. (Side-note, the deeper chest will need to include room for a bigger heart, lungs, and possibly air sacs) This is because, if you still want arms, you're going to need a second set of shoulder blades below the first and still have the flexibility to move and bend. This will remove the arms in the way issue completely, and allow for the new muscles, tendons, and ligaments to attach to the wings in way that will compensate for the stress of lifting the entire body. As to the issue of weight, the legs will definitely need to drop a lot of power. They're so heavy in the first place because we are running animals. Our bones would have to be hollow with inner supports to increase strength (same as birds), and we'd probably need to be shorter overall. Feathers weigh a lot, and produce a ton of problems (as pointed out by another answer) so skin would the way to go. Also, look at how a bat's skin reattaches to the body a human's would have to way down to achieve the same thing. If you want to still wear clothes, you'll probably want a tail for the skin to attach to instead of your legs. No idea how you'd hide it, and you probably wouldn't be able to carry much weight when flying. Should work though. ]
[Question] [ So, after multiple users informed me that my [previous question](https://worldbuilding.stackexchange.com/questions/32372/is-my-flying-fish-world-plausible) was a little to broad, I decided to narrow my focus a little bit. Using only hard science, could there be a planet composed, with the exception of a small, rocky core, entirely out of gas, that could support human life? I don't just mean one in which spacecraft could venture. No, I mean a fully breathable, habitable, earth-like world; One which you could live in without any sort of advanced equipment (assuming you had food to eat, water to drink, and solid ground to stand on). This doesn't mean the entire planet has to be livable; Just a small, verticle sliver or localised area would be fine. The main things to take into consideration are... * Radiation: The solar wind streaming through space would normally turn the planet into an inhospitable wasteland. This radiation would, somehow, have to be low enough that a stable population could exist, even if it suffered from higher rates of birth defects and a shorter average lifespan. * Gravity: The reason I said "Planet made of gas" instead of "Gas giant" is because any human on the latter would crumple under their own weight. To avoid this, the new planet would have to be comparitively small, making the gravity roughly that of Earth's, so that the denizens wouldn't be to stout/elongated, and of more normal preportions. * Pressure: The pressure has to be within reasonable means for a human to survive, although, in the case of scuba divers, the addition of certain gases would increase this. * Air: Gases, especially reactive ones like oxygen, don't like to stay in neat, precise bands but instead mingle. It would have to be a high enough percentage for a working, active person to safely breath for years on end, and of course free of any dangerous or toxic substances like Carbon Dioxide. * Cold: The level of heat, due the specific story I'm working with, is more variable, with anything that a society living today endures acceptable. Please comment if you need any clarification. [Answer] From a hard science perspective, a planet made of gas that is small enough to avoid the problems associated with a gas giant would be too small to hold a gaseous envelope unless it was extremely cold (in which case gasses like oxygen and nitrogen would have frozen out, leaving you with an atmosphere of hydrogen and helium). The alternative would be to look at engineered worlds instead. The closest thing to what you are looking for that I can find is the "gravitational balloon", which is pretty much what it sounds like: a balloon filled with breathable gasses which is inflated inside an asteroid and uses the gravitational "pressure" of the asteroid to maintain its integrity (not to mention the mass of the asteroid provides shielding, protection from micrometers and a degree of temperature control). There is an entire site devoted to the mechanics and mathematical exploration of the idea here: <http://gravitationalballoon.blogspot.ca> Note that you can build a gravitational space balloon as large or small as you like, the author envisions large asteroids riddled with voids filled with these balloons and housing billions of people, but there will be a range of balloons of all sizes depending on the materials available, population to be housed and the political, social and economic conditions of the setting. The ultimate size of a gravitational balloon was calculated by Dani Eder, and is pretty fantastic. Technically, this is a construct entirely filled with gas (a central core of hydrogen in this case), using some membranes to prevent the gasses from mixing and an outer shell of steel to provide counter pressure for the balloon, the maximum size is 240,000km in radius, providing something like 1400 X the usable surface area of Earth, plenty of room for your setting.... <http://yarchive.net/space/exotic/bubbleworld.html> [Answer] Do you actually require a planet? If not, read The Integral Trees and The Smoke Ring by Larry Niven. Both are set in a gas torus being pulled off an uninhabitable planet, the whole thing kept in check by being pretty close to a neutron star. It's not permanently stable and probably couldn't evolve an intelligent species before it dissipates but if it were seeded from elsewhere things could evolve. [Answer] # Radiation Need not be a problem, if the planet orbits quiet, settled down star. Note that even in our Solar system, Sun radiation is pretty survivable unless there is a solar flare. So you are looking at K or M stars (you might wait a trillion years or so for the flares to settle down — but on the upside, you'd have very stable star with many trillions of years ahead). Alternatively, change your "small rocky core" to a "small metallic core" and you can have a full featured magnetic field, making it a non-issue even for Sun-like stars. # Gravity Let's take Saturn as a model — its "surface" gravity is $10.44 m s^{-2}$, which is practically the same as Earth. Note that gravity does not depend on the size of the planet alone, but on its mass (linear) and radius (inverse square). Assuming compatible density distribution (which is not true, especially when under pressure gasses undergo phase change into metallic form, but anyway), mass depends on the volume, which is radius cubed. $r^3$ for mass is cancelled by $r^{-2}$ for the radius and the dependency is nicely linear — for planets with the same density, gravity increases linearly with the radius. Since the mass is density times volume, gravity depends linearly on density (at the same radius). Therefore, if you increase the (average) density of the planet, you need to scale down the radius by the same amount to keep the gravity the same. # Pressure No problem, just pick the height you need. Remember the [barometric formula](https://en.wikipedia.org/wiki/Barometric_formula). Changing temperature will make it more complicated, but you can still pick up comfortable pressure. # Air This is where things become interesting. Let's assume (for simplicity) a planet made of oxygen. Taking Saturn as an example, it consists mostly of hydrogen, which has a density $0.09 kg\cdot m^{-3}$ (at 1 bar and "normal" temperature). Oxygen's density is $1.4 g\cdot m^{-3}$ (its atomic weight (16) times the hydrogen density). Thus in order to keep the gravity at $1g$, recall that the planet's radius should be 16 times smaller than Saturn's — that is $60000 km/16 \approx 3750 km$, i.e. about 60% of Earth. Now, you do not want to live at 1 bar of pure oxygen atmosphere — it is unhealthy and [dangerous — anything combustible will combust rather violenly](https://en.wikipedia.org/wiki/Apollo_1). You'd need 0.2 bar partial oxygen pressure, which means moving upwards just by 12km or so. Or you can mix in 75% nitrogen, and it will not change the numbers much and make the atmosphere very Earthlike. # Cold Again, let's take Saturn — at 1 bar pressure, the temperature is 134 K, way too low for unaided human life. But since the planet's gravity and dimension is quite comparable to the Earth, so just increase the insolation to Earth level (or slightly more, due to the absence of greenhouse gasses). # To summarize You have a planet made of oxygen (and some other gasses, like water vapour which you'd rather need for survival), slightly (60%) smaller than Earth, with Earth like insolation. It's perfectly habitable, if you manage to float at the correct level (i.e. using hydrogen or helium balloons). If you drop anything, it will be crushed by the pressure — but long before that, increasing oxygen pressure will make it burn (if combustible) rather explosively. At the pressures at the centre, oxygen will likely turn into metallic form, which is going to create some magnetic field, useful (but not absolutely necessary) to protect from solar flares. Now the question is, could such a planet occur naturally? The answer is almost certainly no. You'd need a protoplanetary disc consisting primarily of oxygen (and nitrogen), but no or little hydrogen (which will burn in the oxygen planet, providing much needed water vapour). It is difficult to imagine such circumstances. The planet would have to be deliberately constructed. Also, any life will lack solid materials (such as carbon), since everything will fall down to the core (although, carbon will combust and at least part of it will be recycled in the form of $CO\_2$). It would have to be imported and kept floating. [Answer] You can forget about radiation and gravity as problems, if you want to. As others have pointed out already, a magnetic field could deflect the radiation (just like Earth's), and gravity at the surface of a gas giant isn't necessarily that extreme. As for the other factors: it seems that what you'd need is a situation where pressure is approximately one bar, gravity is approximately on G, and oxygen content is approximately 20%, and for all of these conditions to occur at the same altitude within the planet's atmosphere. Saturn actually comes reasonably close, except for the oxygen content (it has practically none). Making a semi-educated extrapolation, we could guess that a planetary body could exist that would fulfill all your requirements. It would be smaller than Saturn, closer to its sun, and have an atmosphere more similar to Earth's, with nitrogen, oxygen, water vapor, and carbon dioxide. Humans could survive there by floating around in the layer where pressure ~ 1 bar. I don't know if there is a plausible way for such a planet to form; it certainly hasn't happened in our solar system. If you can't think of anything either, just say aliens did it, or ignore the question altogether. One would assume that, in order for humans to live in this environment, there would have to be (at least) some kind of plant that has adapted to live here, too. An organism like a living zeppelin, which breaks down water molecules using photosynthesis and collects the hydrogen inside a membrane for buoyancy, could provide both a food source and a stable platform for people to float on; a rich enough ecosystem of these zeppelin-plants would allow humans to survive with any level of technology down to and including zero. If tapped carefully, a large enough zeppelin-tree could be made to "leak" a small amount of hydrogen to be used as a cooking flame or energy source. I say "carefully" because tapping hydrogen faster than it can be replenished would cause the tree to sink, and of course if it overheats, the whole thing could go down like the Hindenburg. Interesting features of this world: * It's much, much bigger than Earth. Habitable surface at least 100x greater. * Metals and heavier elements, even trace metals to support body chemistry, may be hard to come by, since they normally don't float around in the air. Perhaps some of the largest, oldest "trees" have sunk roots all the way to the surface, or close enough to gather some of these trace minerals and transport them to their leaves, which humans must then eat in order to get calcium for their bones, iron for their blood, etc. This would also tend to keep technology limited to naturally-occurring materials. Human bone might be the hardest substance available, which would have interesting cultural implications. ^o^ * The most primitive people would have no control over their movement through the atmosphere; they'd float around wherever the air currents take them, drifting with the trees. They could thus experience more extreme seasonal variations than if they existed at a fixed latitude, because they drift sometimes near the polar regions, sometimes near the equator. ]
[Question] [ I have a city built on the peak of a 3 km-high mountain that moves from place to place on a daily basis, the whole mountain appearing in a new place each dawn. Typically, the place in which it appears is or has experienced winter conditions, or at least colder conditions than usual. The city survives by trading with people who live in the places it appears - these places trade goods such as foodstuffs, timber and other raw materials for magical or technological items that are produced on the city, or for services provided in the city. The city's technological level is similar to renaissance Europe, and the magic is similar to that depicted in the [Ars Magica](http://www.warehouse23.com/products/ars-magica-4th-edition-core-rulebook) RPGs, though with much less restraint of trade as imposed by that RPG's Order of Hermes. I have people who are interested in setting up at two or three new businesses in this city, and who are looking for businesses that have closed down or are no longer prospering so that they can make an offer for the properties. They are looking in the middle-class to upper-class areas (not coincidentally also the mid to upper levels of the city), so the businesses that they are looking to displace must once have been moderately to highly profitable. What sorts of businesses could initially prosper but ultimately fail in such an environment, and for what reasons? [Answer] A few things come to mind. 1. Change of fashion or culture in high society. If you're a powdered wig manufacturer and suddenly people decide wearing powdered wigs to pretend that they're older and more mature than others is silly and stop buying them, you're out of luck. Historically, short-lived fashions have spawned short-lived but prosperous businesses that died as soon as the fashion did (look at any disco studio ever after the mid '70s) 2. New technology, or magic, has rendered a service unneeded any more. Someone who trained homing pigeons will find themselves out of work when someone invents magical long distance communication. Someone who uses leeches for healing will sure have trouble making a profit once people realize leeches sure don't work like that. Maybe blacksmiths are going out of business once people found a way to magically make hotter fires with less effort which allowed a few good blacksmiths to produce products faster, running the 'somewhat good' blacksmiths unneeded because the really good ones now have time to do all the work. 3. Owner lost favor with the nobility or ruling class. If the business owner offended the king or queen with some minor slight he may find that royalty either forbids him from working or expresses their displeasure causing all nobles to avoid him and put him out of business. Maybe a business owner lost their nobility, or were proven to not be a noble in the first place, and everyone decided that they didn't want to work with a non-noble! 4. Death of the owner of the business. At this tech level deaths would be much more common, leaving more businesses without owners. In addition at these times many businesses required a specific craftsman to run them, you must have years of training to be a blacksmith, or cobbler, or glass blower etc, which means even if the owner of the business had family members they may lack the craftsman skills necessary to continue the business after the craftsman passed away. In a closely related note many injuries can make one unable to ply their trade for much the same effect, since many trades were very physical and any number of even minor injuries could make it difficult or impossible to adequately perform your job. 5. Odd travel locations. You said yourself that the mountain appears randomly, so they don't know where they would end up. Maybe you had a fluke and appeared at a large number of locations that did not need a certain craftsman. If you have someone who sews winter coats and your last 6 months of jumps were all to desert he is going to have a hard time continuing to turn a profit. Maybe weavers were shocked that they appeared above a country known for fast cheap crafting of materials. Business men often have limited amount o savings, particularly at this time where banking wasn't as available to the common trader, so even a few months of 'dry spell' with little business can kill a previously thriving bushiness. Actually this option may suit your needs well, because it could result in a number of businesses all going broke at the same time, meaning many cheap business locations up for grabs at the same time setting up a situation where a business man can quickly start up many locations cheaply. 6. Odd travel locations 2, electric boogaloo. Imagine the mountain jumped to a rather unique location that sells products that are usually hard to get hold of. Many speculators bought up large quantities of these products on the assumption that they would soon leave for another region where the product doesn't exist and they will be in high demand. However, the mountain either didn't jump for awhile, or soon jumped to another location where the usually-scarce product was sold even cheaper. The speculators who committed large amount of their savings to stock piling this product will find themselves unable to sell it for awhile due to the lack of scarcity, causing them to lose a huge amount of money in opportunity cost and be unable to keep up with regular bills. This is particularly true in the second situation, where the mountain later jumped somewhere where the product was sold even cheaper, since the product would now flood the market and the investors would either have to sell everything at a lost or hold on to the product for an extremely long time before selling, during which they will have little money for other investments. 7. Lack of raw materials required for a business. Perhaps the equivalent to a drought has killed all of a certain type of crops. A florist finds all the delicate flowers were killed when they appeared in a much colder region then usual, there are now too few flowers, and those that exist are so outrageously expensive, that a simple florist can't compete. 8. A superstore appeared. Someone proved exceptional at a craft to the point that they drove all others out of business. This would likely mean either your equivalent of wal-mart, a company that works as a giant in mass numbers and economy of scales to out compete smaller companies, or one person with a potential talent. Maybe someone has a unique magical gift that allows him to, say, make glass figurines absurdly fast by shaping them with magic rather then blowing them. The glass blowers will find that this one person can produce as good or higher quality figurines at a fraction of the rate that tedious glass blowing techniques can, putting many of them out of business. To go the second route you need to stress the person out competing others has a unique magical gift, something that isn't easily recreated or else this is more an example of 2 above. 9. A minority group has become a political scapegoat for some reason and no one wants to ask them for help any more, causing stores run by these minority group to fail due to lack of customers. This may sound extreme, but it's happened quite often in our history. The most obvious being the Jewish in Nazi Germany, but everyone from Christians in biblical times, to Irish in the US industrial revolution to Islam in modern America have gotten the unfair scapegoat status for some social ill and been run out of business because of it in our past, to name just a few off the top of my head. This is far more common then you may imagine. 10. Recent urbanization. A previously less populated 'country' area has had people expanding out into it, rapidly building houses and urbanizing it. This would change the types of people who live in it, and thus the types of stores needed. Someone who use to sell farming or hunting supplies to mostly country folk may find that with the place rapidly growing more urban, farms shutting down and being replaced with stores etc there simply isn't enough people who need the sort of supplies he use to sell. 11. Recent 'nobilization'. Similar to the above, nobles started to expand out into previous more 'middle class' areas, driving up property values and rapidly driving the former middle class people out (both because they can make so much money selling to new nobles, and because nobles likely took action to drive out the 'dirty peasants' from their new area). This would likewise cause stores that catered to middle class folk, but not nobles, to shut down. This sort of thing happened often in the past, as new nobility couldn't buy houses that existed in old nobles families for generations they would instead build houses on the outskirts of the previous nobles area, expanding the 'nobility area' out to include their new houses and driving those how use to live there further back. This also means the stores may be relatively cheap, since new nobles are only now taking over the area the property values may not be as high as the more established noble districts yet, and new nobles tend to be younger and potentially more interested in taking advantage of new unique business ideas as opposed to the 'old nobility' which tend to be more set on tradition and the old ways. ]
[Question] [ Came up with this question when I read [this](https://worldbuilding.stackexchange.com/questions/25658/how-would-a-war-between-immortals-be-fought). Would Immortals feel pain? Pain is our bodies reaction to a stimulus, telling us that something is wrong and that we should stop doing what we are doing because it is detrimental to our health. With an immortals ability to be able to heal from any injury, would there actually be a reason for an immortal to feel pain from a physical injury? Secondary questions; If they don't really feel physical pain, would they feel emotional pain more? How would this effect how they interact with each other? [Answer] This really depends on the nature of their immortality. There may be no reason for someone who can't be hurt to feel pain, but there's no reason for humans to have hair, tonsils or an appendix, either. There's a lot about living organisms that doesn't really do much any more; evolution doesn't really have any grand designs in mind, it just selects whatever traits keep the most organisms alive and reproducing. That said, pain is very useful for getting people to stay alive. It gets you to stop hurting yourself or being hurt, and thus usually gets you away from further danger. Now, the fact that humans have become immortal means they no longer have to flee danger, but that doesn't mean that they'll suddenly stop being afraid of things. Evolution is a slow process, and it'll probably take hundreds of thousands of years before humans can kick the habit of being scared. It's possible immortality developed in parallel with this diminishing fear response, or maybe it was an instantaneous magical change; if the latter, you could say that some similar magic removed human fear, but that's beside the point. Now, as to your point about emotional pain, you must note that with immortality, humans have one less basic desire to worry about. Well, two, actually, if immortality means they don't have to eat. All that's left is the desire to have sex, and make/raise babies. So yes, I would say that evolution would start favoring the fearless romantics over the timid loners. But as before, this would be a gradual change. [Answer] Why would immortal feel pain ? Why wouldn't they ? While I don't really agree with DaaaahWhoosh answer, he pointed out that pain is really usefull. > > That said, pain is very useful for getting people to stay alive. It > gets you to stop hurting yourself or being hurt, and thus usually gets > you away from further danger. > > > I think (I may be wrong) that pain is a powerful stimulus that indicates the body that some threshold have been reached. In that way it is just a feed-back from the body that tells, if the situation remains as it is, there will be a risk of damage to the body. (Damaging a body is different from killing it). Also, pain is really useful for learning processes. For example, in computer science, when you try to teach a neural network something, you have to recompense him when it does good, and punish him when it does not good. So, I can't find any reason why immortals won't feel pain as it is a useful tool to learn the limits of one's body. As of emotional pain, obviously I think it necessary for them. I see that trait as part of empathy and what would be immortals without empathy but psychopaths ? Again, emotional pain is useful to avoid hurting oneself and to understand why it is wrong to hurt someone else. Two statements bother me from DaaaahWhoosh's answer : > > Now, the fact that humans have become immortal means they no longer > have to flee danger > > > Being immortal just means you can not die. But there still exist conditions they want to flee (like being imprisoned for decades), so danger still exist for them. > > All that's left is the desire to have sex, and make/raise babies > > > I think the opposite. Some unicellular bacteria are "immortal" but can not reproduce. In fact, would it be sustainable over long-term if immortals could reproduce? There would be virtually an infinite amount of children who cannot die and would have children of there own. Considering infinite life time, when would they stop being a child and becoming adult ? [Answer] If a normal human gains immortality, there no innate clause that says his nerves no longer work like they used to. He is the result of evolution. And pain is a result of successful breeding in a world where feeling and reacting to pain is very useful. Meaning it's in his genes. Pain and emotional pain are both ways your subconsciousness is telling you that you are in perceived danger. A species that were immortals from the get-go might have never gained the ability of feeling pain. Therefore, I think the answer can lie in the origin story of the Immortal in question. Or, perhaps, it's a medical question. There's a Kung-Fu style called Iron Shirt. The student's body is beat meticulously several hours every day, and at the end, the nerves in his skin is so worn out that he doesn't register superficial pain on the skin. (practical for ignoring pain in combat, obviously). Without knowing the practical benefits of your story's variant of immortality, maybe the Immortal will be less and less subject to pain over long periods of time. Maybe his curse is that he's slowly losing feelings, first physical, then emotional. [Answer] This depends on their genetics. If they belong to a race of immortals (talk about Greek and Roman gods), their supreme genetics would probably have shifted towards a painless physiology during the eons long course of their evolution. However, if you are talking about a human who attained immorality due to some quirk, unless you also change their genetic information in a really outrageously precise and accurate way, they will continue to feel pain as humans do. ]
[Question] [ I imagine a world like Earth, only without easy mineable copper (say, where copper was as rare as gold). That means no brass nor bronze too (they are copper alloys). I presume prehistoric humans could discover metallurgy using other easily melted metals (tin, lead). So they would pass directly from stone age to iron age. I don't know if steam engines would be feasible. Do they require any significant amount of copper, brass or bronze? Electricity could be discovered using batteries based on zinc or lead, but without copper wiring it would remain little more than a scientific curiosity. Electric motors and generators require large amount of wiring, so they are impossible to build on large scale in this world. Some small units could perhaps be made using silver wiring in place of the copper ones. Possibly, wiring in internal combustion engines could also be made out of silver. That would make them very expensive, though. Aluminum, which requires large amount of electricity to be refined from ore, would be a rare metal, therefore airplanes, if ever developed, would be made out of wood. In sum, that would mean a world fixed at a tech level of the late 1800, gaslit and with very few cars, with very expensive air travel, no telegraphs nor phones, nor radio, with only mechanical computing machines. Edison would be mainly known for the phonograph. Any other thoughts ? UPDATE: if there is no economical way to produce and distribute electricity, a lot of conseguences would follow for the organization of society. Instead of huge power plants that serve millions of users located perhaps hundreds of miles away, there would be small plants serving a single building or city block, distributing energy in form of steam or compressed air. There would probably be no "NIMBY" movements, given that there would be no alternative to a plant in each backyard. I wonder if this would lead to a more or a lesser "green" society. Also living "off the grid" would be the norm, not the exception. [Answer] Humans would find a way to compensate. Take your airplanes example - why would airplanes have to be limited to wood? What about composites? Wood can easily lead, through a different technology path to materials like graphite. Pona wood from the Amazon has a cross-section and properties that are practically identical to graphite. And there are plenty of other metals that are ductile enough to make wire, but even without wiring, I can see technology going down a different path. Rather than transmitting electricity, what about skipping the whole electrical network technology, and going right to self contained devices that require no flexible wiring. Electricity and magnetism are such ubiquitous, useful, and powerful forces/fields/concepts that we'd find a way to make them work. Now, take iron out of the equation and you may have something. Taking iron out would probably also take Nickel out, at least any significant deposits of it to be mined. Nickel is found, in mines, mixed with iron, likely because of the way stars and worlds form. So that takes out the two most common ferromagnetic materials. Take out the ability of an intelligent race to interact with magnetism, and you've just handed them a very intractable technological hurdle. [Answer] You are not only limiting copper, but are also limiting silver and gold too! This isn't quite fair (I think). In a copper-less world, actually copper could be used for ornamentation and jewellery while gold might be available in much larger lodes and be used for electric wiring. Gold is one of the best metallic conductors of electricity (even better than copper) and if it is available in large quantities on the said planet, it would be cheap enough to be used for electrical wiring. What about silver, tungsten and platinum? On earth they are rare and very expensive, but in a fantasy world, it doesn't have to be that way. ]
[Question] [ # Background: Human Origins: We originated from a space-faring civilization. A breakaway faction that hates advanced space level tech traveled here and set up shop before destroying their advanced tech. They were unprepared for the large animals on Earth before the Ice Age and they quickly lost the ability to make any reasonable tech. A few generations later and they were unadvanced. They retained their ability to solve problems though and eventually out competed the native proto-Hunan Neanderthals. NOW: In 3096 we have reached interstellar travel using a combination of wormhole (govt. access only) and considerably slower warp drive. We send colony ships out and quickly find that we are totally surrounded by alien colonies. We soon find out that these aliens are genetically related to us. While some conspiracy nuts (yes, they still exist in 3096) expected this, most of humanity is shocked. The aliens are genetically different from us in many areas however as they have had to use gene manipulation to adapt to new worlds. My main character falls in love with the High Princess of the alien empire (which is by its own nature peaceful). They decide they want to escape the obvious difficulties that would be caused by their union by fleeing known space. They want to have children. # Question: How much genetic variation would allow offspring? The offspring do not have to be viable from the standpoint of reproduction. [Answer] It mostly depends on how long ago your humans came to Earth. The process you are referring to is known as Allopatric speciation. It's the process of forming a new species by geographical isolation (in this case separate planets). The classical definition of a species (although not strictly adhered to by biologists) is the most inclusive group of organisms capable of interbreeding and creating viable offspring. So if your humans and aliens have diverged sufficiently to no longer produce viable hybrids they will be considered separate species. So how long does allopatric speciation take? How long does it take after separating two genetically identical groups until random genetic drift causes them to no longer be able to interbreed? It turns out it can range anywhere from a few generations to many thousands. All it takes is one strong mutation (say one chromosome breaking into two to give a simple example, but much more subtle mutations would work as well) to create an insurmountable reproductive barrier between two organisms. However, the chances of such a mutation occurring are quite small. The estimates I've seen suggest at least hundreds of thousands of years and more likely millions of years between isolation and speciation. It's well within reason that your humans (unless they showed up many millions of years ago) will not have drifted too far to interbreed with your aliens. As for the aliens and their genetic manipulation, I think that part of their society actually makes them much more likely to be capable of interbreeding. If they have multiple races on different planets it would be important for them not to drift far apart or they would become separate species. If they care at all about inhabitants of different planets being able to procreate with one another then they would need to develop a galactic standard of reproduction. They would take special care in all of their genetic manipulations to not change their ability to reproduce with the rest of their species. As a result the aliens may closely resemble the original ancestors of the humans in terms of reproduction. [Answer] The answer lies in the genetic difference of a horse and a donkey. They can have a baby (although infertile) called a mule :) There are some interesting articles on horse and donkey genetics on Google. This is just an analogy but it may point you to the right direction. My GUESS is that horse and donkey diverged from a common ancestor no more than 100,000 years ago. And if the analogy holds and your humans and aliens have a common ancestor around the same time, then you should be able to have human-alien hybrid. [Answer] Homo Neanderthal is not an ancestor of Homo Sapiens but a cousin who lived at the same time and went instinct. If you want a species that can evolve into Homo Sapiens, go for Homo Erectus. However, there is some proofs that homo sapiens and homo neanderthal had children since we -Homo Sapiens- have some of the DNA of homo neanderthal. So you have the proof that viable hybrid human existed in the past. Second, hybridation is a very particular science and it is very difficult to know what will happen so you are free to do what you want. You can check the Hybrid page of wikipedia. [Answer] Don't forget differences of environment. All of the examples of hybrids have been on planet Earth, subjected to the same gravitational pull, the same lunar phases (tides, body fluids, menstrual, etc) and the same carbon based food source. If you have the same species dropped off on different planets to survive, I would suggest they would separate much faster than the proposed 100,000 years of earth only examples. If you have a group living in space, with no lunar/solar pull on the body, it will be considerably different from a body needing to adapt to a multi-moon or red giant sun planetary environment. Even if you dropped off a group on Earth, and one on Mars, they would diversify faster because the body would become dictated by the two rock moons on Mars (they emit a gravitational pull of sorts) and the one moon on Earth (that also emits a gravitational pull). Now that I think about it, if the same species was dropped off on Earth AND the moon, would they divide quickly too? I would take a guess and say more than likely. Technology may be grand, but it can only get so far, it's no match against the forces of the universe. ]
[Question] [ Before the double helix DNA was discovered by Watson and his colleague, they theorized the existence of a triple-strands DNA and its properties. Is multiple-strands DNA possible perhaps by manipulating the structure of a double helix DNA with science? Multi means more than 2 [Answer] There has been a claim that 4-strand DNA structures exists in nature, in fact in human cells. [University of Cambridge article](http://www.cam.ac.uk/research/news/four-stranded-quadruple-helix-dna-structure-proven-to-exist-in-human-cells). The link to the the original paper in Nature seems to be broken though. I am pretty think the Nature paper was more detailed, but it is not my field. I should also note that there is no evidence of a complete organism based on using triple or higher strands of DNA. But the scientists claimed they had stablized the quad strand DNA, so it would appear to be viable at a molecular level. Though the Cambridge article is limited (as were the others I checked), there were some interesting details: > > The findings mark the culmination of over 10 years investigation by scientists to show these complex structures in vivo – in living human cells – working from the hypothetical, through computational modelling to synthetic lab experiments and finally the identification in human cancer cells using fluorescent biomarkers. > The research, published today in Nature Chemistry and funded by Cancer Research UK, goes on to show clear links between concentrations of four-stranded quadruplexes and the process of DNA replication, which is pivotal to cell division and production. > > > ... > > “The research indicates that quadruplexes are more likely to occur in genes of cells that are rapidly dividing, such as cancer cells. For us, it strongly supports a new paradigm to be investigated – using these four-stranded structures as targets for personalised treatments in the future.” > Physical studies over the last couple of decades had shown that quadruplex DNA can form in vitro – in the ‘test tube’, but the structure was considered to be a curiosity rather than a feature found in nature. The researchers now know for the first time that they actually form in the DNA of human cells.\* > > > ... > > While quadruplex DNA is found fairly consistently throughout the genome of human cells and their division cycles, a marked increase was shown when the fluorescent staining grew more intense during the ‘s-phase’ – the point in a cell cycle where DNA replicates before the cell divides. > > > [Answer] It is possible but impractical. Double-helix DNA's structure is something like this: $$ \text{B — (A/C/T/G) : (T/G/A/C) — B} $$ where B is a backbone molecule, A/C/T/G is adenine/cytosine/thymine/guanine, `—` is a molecular bond, and `:` is a hydrogen intermolecular bond. What's important here is the molecule connecting the strands: since it's only connecting 2 backbones, it's a relatively simple molecule. --- 3-way DNA I can't accurately represent with MathJax, so here's a picture: ![3-way DNA](https://i.stack.imgur.com/SIooy.png) In this diagram, a line is a molecular bond, a dotted line is a hydrogen intermolecular bond, B remains the same, H and N are hydrogen and nitrogen, and (AF/CF/TF/GF) is some variation of (A/C/T/G) where the molecule must incorporate a fluorine molecule on the outside of the molecule. The part in the center is $\text{NH}\_3$, which I have picked purely because it has 3 outer hydrogen molecules. These hydrogens form hydrogen intermolecular bonds with the fluorine atoms in (AF/CF/TF/GF). There are relatively few 3-way molecules like $\text{NH}\_3$, so 3-way DNA is more difficult and more fragile than 2-way. --- 4-way DNA is also possible: substitute $\text{NH}\_3$ in the diagram for $\text{CH}\_4$, methane, which has 4 outer hydrogens and can thus form intermolecular bonds with 4 `(AF/CF/TF/GF) - B` groups. --- The major point to note here is that DNA is the way it is because it's simple: 2-way DNA does not require another molecule in the middle like my representations of 3- and 4-way DNA do. While my ideas are probably not optimal, 2-way DNA is both simpler and stronger than any other type. (Also, DNA helicase (one of the enzymes that process DNA) would have a hard time adapting for 3- or 4-way DNA.) [Answer] It is possible to produce [triple stranded](http://www.wikipedia.org/wiki/Triple-stranded_DNA) genes using some variation of DNA, PNA, XNA, etc. I recall reading about PNA as a third strand as a possible means to bootstrap our modern DNA scheme. I doubt three-stranded genes would be found in a life system of a mature planet ecosystem. It would evolve toward simplicity, and lose one. But, that's a way of having an intermediate step offering the possibility of changing the encoding system. E.g. an asymmetric Peptide-Ribo two strand system is good for early days because it is easy to emerge from RNA-world and has high matching affinity. But symmetric DNA is better after various other mechanisms mature and the cell gets more complex. So it first gains a 3rd strand, changes the RNA to DNA, then loses the PNA. [Answer] The real problem with multi strand DNA isn't so much if it is possible (Dr Science can do some pretty freaky stuff in the lab), but how it would work in the natural environment. To put it bluntly, if there were some evolutionary advantage to 3 stranded DNA, then there would need to be some means of combining it during reproduction: 3 parents would be needed. If this means 3 different sexes are needed is probably up to you as an author, a more likely scenario is two "male" parents and a "female" parent. (Star Trek gets it wrong with their "Species 8472" since they claim 5 genders but only 3 strand DNA. Unless their reproduction includes phases where they burrow into a host like parasitic wasps, this is hopelessly inefficient, and since two of the genders are not represented in the DNA, why would they evolve in the first place? A five gendered species would have 5 strand DNA.) ]
[Question] [ So, just read a good number of the answers over at [Is a jet dragon possible?](https://worldbuilding.stackexchange.com/questions/8962/is-a-jet-dragon-possible), and it seems that a jet dragon doesn't make much sense due to supersonic flight pre-jet engine being required. Rocket engines function differently from jet engines, in that they don't require external airflow (i.e., are not necessarily air-breathing). Given that, what would be required for a rocket powered dragon to exist? The bombardier beetle seems to be an example of a very small scale type of rocket engine, albeit a very short lived one. What inherent difficulties exist in attempting to scale that design up, as well as what might be some possible evolutionary paths for a rocket-propelled dragon? As for some parameters, lets try a scale of 6-foot nose to tail length minimum (below which, I'm not sure it qualifies as a "dragon"), and 1000-foot nose to tail length maximum (I'm not interested in a planetary scale rocket spaceship creature). It must be able to fly it's own weight (passengers not required), and must be able to travel for at least 6 seconds of active thrust. [Answer] Yes, this is just as possible as a jet dragon, though rather more limited in range due to the need to store both oxidiser and fuel. The most efficient form of rocket engine would be a liquid-fuelled type. Then, as this is a biological rocket, the oxidiser and fuel would best be HCNO-derived chemicals, those being the most readily available to carbon-based organisms. Fuel: Given the requirement for HCNO-derived chemicals for both oxidiser and fuel, and that we must presuppose that these fuels are not externally obtained and must be synthesised by the organism. Of the many fuels and oxidisers, [Hydrogen peroxide](http://en.wikipedia.org/wiki/Hydrogen_peroxide) and [Monomethylhydrazine](http://en.wikipedia.org/wiki/Monomethylhydrazine) are probably the most likely combination, as both are liquid at body temperature and standard air pressure, making them easy to store, and both can be biosynthesised. I don't believe this combination is hypergolic, but providing an ignition source such as an electric arc would be feasible. Storing these fuels would be a minor issue, since they are ordinarily toxic, but it has been shown that animals are capable of storing toxic substances safely. Reaction Chamber and Exhaust: The reaction chamber must be strong and temperature resistant. There exists the possibility that our rocket dragon could be able to precipitate metals or graphite sheets that would allow a strong, temperature-resistant combustion chamber and nozzle to be formed. The reactants could be passed through the walls of the combustion chamber prior to mixing to both pre-heat them and cool the chamber walls, preventing excessive heating of the creature's body. Provision of other insulation would reduce further heat transfer, as would strategic positioning of the organ so that it would not dump its waste heat directly into the creature's core body. The combustion chamber might best be located at the end of a short, strong tail. The concept of a combustion chamber like an extra anus and co-located with said orifice would lead to heat management issues in much shorter order. Evolution Since the reactants involved can be and are biosynthesised in various organisms, and have benefits other than propellants (such as protective toxicity in the case of MMH), they could occur. Then, if, like a bombardier beetle, this organism evolves a defensive heat source on its rear end, it is not too much of a stretch to progress to using that to assist flight by adding extra reactants. This system would have the added advantage that it would not only provide a means of rapid escape from one or more predators, but would also be highly likely to injure or kill at least one predator if triggered at close range. As to size, the most efficient, manoeuvrable flyers are small, so these rocket dragons would most likely be in the 6-foot range specified in the question, and quite lightly built, save for a large propellant-storing belly. However, larger fliers have less parasitic drag, and induced drag decreases with speed, so a larger size is not out of the question, especially as rocket assisted take-off is a given. The duration of the rocket burn would be dependent on the power of the thrust. It may be possible to maintain sufficient thrust to maintain altitude for some minutes, or to expend the available reactants in a few seconds to provide a rapid getaway or increase in altitude. The main issue would be the synthesis of the reactants. It would take significant energy input and time to synthesise the reactants, so the reactants for the minimum six-second full-power burst might take days and a very high energy input to synthesise. This would preclude any herbivorous lifestyle. However, having a rocket would make for a predator that could not be outrun, only outmanoeuvred. ]
[Question] [ Going off of my other question [here](https://worldbuilding.stackexchange.com/questions/8772/can-a-nonspherical-planet-exist-and-can-it-be-habitable), I guessed that a cube planet could work out. BUT, would it be possible for the planet to exist and function as a (relatively) normal planet with life on it without having tectonic plates? I know that tectonic plates with a cube don't really work out too well in life's favor. [Answer] Artificial planet made by Ancients is your only option. If your planet was "nature made", without plate tectonics and with crust thick enough to support your gigantic mountains, such planet would have very little mantle (melted core). But turbulence of such core creates magnetic field protecting the atmosphere. Mars has no atmosphere because its atmosphere was swiped away by solar wind: Mars also lacks strong enough magnetosphere (protective magnetic shield) - which is direct consequence of its cold core (which prevents mountains from sinking into the mantle). So Ancients need to take care for magnetic field - not only to protect atmosphere from solar wind, but also protect life from radiation from space. Yes, such planet is very carefully engineered project - most likely PhD in planet engineering from advanced race. Some interesting reading about [why mountains on Earth have theoretical limit on height](https://skeptics.stackexchange.com/questions/5848/can-mountains-on-earth-grow-higher-than-49-000-feet-15-000-m) of about 49K feet (15km). Another unexpected (for me) force grinding mountains down: glaciers eroding valleys. [Answer] The cube would have to be artificial and relatively recent. It can't be created by natural process and eventually tidal forces will break it apart. As such any life on it would have to be either created artificially or imported from elsewhere. You can simply assume that the planet was created or given maintenance recently enough that the planet still works as planned. [Answer] Forget about cube planets, by now, and go for a real planet: Mars. Mars has no tectonic plates, but for it being habitable it just needs some more atmosphere and heat. In fact, if Mars were where Earth is, it would surely have basic life (at least) on its own, since polar caps would be smaller and there would be more water on them. A lake is enough to create life, from where bacteria would have colonized the planet's soil. ]
[Question] [ 1. How would plants be affected by a 48 hour day, instead of 24 hour? Would plants be larger to store more energy for photosynthesis? 2. Also, how about the temperature of the earth be different on both day/night? 3. How would the different temperature affect plants? (Note: this is a more precise question, based off of a much more broad question I asked that I've since deleted.) [Answer] 1. You can actually try this with regular plants by keeping them in a room in which they are given a full day of light and a full day of darkness in turns. I haven't done this long term, but in the short term (weeks) they do not seem to suffer at all. It would not be unreasonable to assume somewhat greater energy storage as a long term evolutionary outcome though. 2. It really depends on the extremity of the temperature change, but on Earth we see plants that have to survive in extremely cold climates being much smaller than those in more temperate zones. If the temperature extremes are reasonable, then there might not be much change at all. Consider plants in one of Earth's hot deserts - they experience excessive temperature swings most days due to their environment but do not have any particular adaptations to those temperature swings. (To be clear, they do have a great many adaptations for heat both on a macroscopic and microscopic scale, but I cannot find anything related to daily temperature changes.) 3. The answer to this question depends very much on the environment. In the American Southwest there are regions where the day/night temperature difference for a 24 hour day is 40°F (22°C) and in Hawaii it's only 10-15°F (6°C.) On Venus, which has a 2802 hour day, the temperature is believed to be nearly uniform from equator to pole, day or night. In general though, for a temperate climate, you would expect the temperature swings to be somewhat more extreme in both directions. [Answer] Plants can grow with no problems beyond polar circle, where sun does not set during summer, and no sun during winter. Plants do not store energy for photosynthesis - they use it if available, and live off reserves (sugar they produced by photosynthesis) during night (exhale CO2). With longer nights, temperature differences would be bigger, but plants would adapt. [Answer] Plants survive the night by producing excess energy during the day. This excess they then convert to starch and store. [Research shows](http://news.discovery.com/earth/plants/plants-do-math-to-survive-the-night-130624.htm) that chemical reactions in the plant's cells then calculate, based on their energy store and the rough length of the night, how to proportion their starch stores to last them the night. In the experiment linked above, scientists shut off the light early, giving the plants a shorter day and much longer night (8/16 hrs instead of ~12/12). Still, the plants managed to have enough starch left over in the morning. Given that plants can adapt to a change in day/night cycle like this, they can easily adapt to a simple double. The day/night proportions remain the same, it's just the time that has changed. Since the daytime has also doubled, the starch the plants store in the day also doubles, so they have twice as much to use at night - meaning they can use the same amount per unit time. The temperature differences wouldn't have too much effect. A longer night would mean a greater drop in temperature and a greater rise in the morning, but given that we have desert plants that survive +40oC to -20oC, our current plants would either just survive or adapt to the change. [Answer] An aspect of this not yet covered by other answers: Some plants measure the length of night-time darkness and use this to decide what time of year it is i.e. is it time to flower, is it time to drop leaves. etc. The behaviour is called [photoperiodism](http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Photoperiodism.html) and a switch to a 48 hour day/night cycle could be bad news for the long term prospects of those plants which rely on it. BTW the link, and others I looked at, suggests the mechanism involves measuring actual elapsed time rather than just day/night proportions, and the plants are using an innate 24 hour circadian rhythm that is tuned to but not controlled by the actual day length. ]
[Question] [ Scenarios for a [technological singularity](http://en.wikipedia.org/wiki/Technological_singularity) usually seem to wait for machine intelligence to [exceed](http://en.wikipedia.org/wiki/Superintelligence) human intelligence. Say the consumer [needs](http://en.wikipedia.org/wiki/Basic_needs) of humans are food, clothing, shelter, transportation, communication, sanitation, education, healthcare. Say specialized, relatively [dumb](http://en.wikipedia.org/wiki/Weak_AI) machines are developed to perform all steps necessary to provide those requirements, without human interaction: mining, refining, manufacturing, planting, harvesting, distribution, fishing, construction, disposal, and so on. Say machines exist to [build, maintain, and repair](http://en.wikipedia.org/wiki/Self-replicating_machine) themselves and all other machines. At that point, the world is automatic and mechanized enough that all humans can be idle consumers only, and not employed producers. If population growth is then restricted to less than [zero](http://en.wikipedia.org/wiki/Zero_population_growth), either through deliberate human-instigated or machine-instigated policy, or because of some [disaster](http://en.wikipedia.org/wiki/Global_catastrophic_risk), hasn't the transition from humans to machines then been achieved without superintelligence ever happening? [Answer] This is not singularity but total automation. I doubt that machine capable of designing and running new mine (and repair all broken equipment) would be dumb. It would have to have AI comparable with human's, would have capabilities to detect defects, design equipment needed to accomplish goals, and modify itself. Modification may include improving. Maybe (if this was the smartest AI and human died out quickly) this AI would go on to make more mines, and then it would invent space travel to be able to mine even more - asteroids and other planets. Pretty funny way to settle all Galaxy - just to mine it out. [Answer] Typically people are talking about the point where progress of technology becomes incomprehensible to us. The point where all our current preconceptions of society and technology break down. Note that "us" refers to people discussing the topic now and the issue is about understanding. So what future people understand or do and even whether they exist, is not really the point. This presumes that there are actors working on society and technology that are capable developing concepts we can't understand. Often this means those actors are either AIs or enhanced humans with super-intelligence. The super-intelligence can also be the collective intelligence of the society as a whole. A billion humans can think up more than any single person can understand. If the efficiency and applied resources of technological development increase enough, the rate of development might become higher than individual human can understand. Still, "technological singularity" does not exclude a scenario where the reason we cannot understand the speculated future is simply because the technologies their society relies on are not understood by us. Most common example is nanotechnology. We do not currently know the real limits of nanotechnology, thus a society with good enough nanotechnology could rely on applications that simply have never occurred to us. This society would also be beyond our current ability to understand as would be their technology. So the correct answer would be, depends on your definition? [Answer] I can't see how non-intelligent machines could "take over." I can see that a group of people who control those machines could take over. In another option, people could give more and more of their tasks to the machines to the point that everyone is a couch potato but, even then, that only persists because people continue to choose it. ]
[Question] [ Closed. This question is [off-topic](/help/closed-questions). It is not currently accepting answers. --- This question does not appear to be about worldbuilding, within the scope defined in the [help center](https://worldbuilding.stackexchange.com/help). Closed 1 year ago. [Improve this question](/posts/231455/edit) I have a pet rock that I bought from a store. It is about the size of my fist and is smooth with no features. I named it Rocky. Rocky seems to be sentient and it follows me around everywhere I go. It doesn't make any noise, but I can tell it is watching me. It is getting really annoying. I have tried everything I can think of to get Rocky to stop following me, but nothing works. I have tried putting it outside, but it just rolls back in. I have tried putting it in a box, but it just waits until I take it out. I have even tried putting it in the fridge, but it just sits in there until I take it out. I am getting really frustrated. How do I get my pet rock to stop following me around? [Answer] Place Rocky into a sturdy terrarium with a padlocked lid. Hang this terrarium from a chain in your garage, so that Rocky can't bump into its walls from the inside to roll it after you - since Rocky is suspended above the ground, there's no surface for it to roll the box along. You may wish to furnish this terrarium with amenities such as padding, food or water dispensers, hamster wheels, wood chips, plants, or additional pet rocks, so as to maintain Rocky's physical and mental health. When you want to take Rocky out of the terrarium, unlock the padlock, open the lid, and take Rocky out of the terrarium. Unfortunately, there are no means of stopping you from taking Rocky out of the terrarium that don't involve Rocky's death or your simultaneously becoming physically disabled and somehow incapable of telling other people to take Rocky out of the terrarium. After all, if you want to take Rocky out of the terrarium, you'll take Rocky out of the terrarium if you have the capability to do so. I am unsure how to overcome this actuality. If Rocky is some kind of compulsive [memetic hazard](https://scp-wiki.wikidot.com/understanding-memetics) that makes you take Rocky out of a box against your will, please let me know, so that I can revise my answer. ]
[Question] [ A Banks Orbital requires some form of unobtainium, with tensile strength much greater than any known substance. I'm trying to figure out how that substance would stand up to impacts and explosions. To be specific, say the material in question is, to coin a word, paraneutronium, basically 'as strong as neutronium would be if it were a solid instead of liquid, and stable at zero ambient pressure'. Or, like a single layer of graphene, except with neutrons in place of carbon atoms. Per <https://en.wikipedia.org/wiki/Nuclear_binding_energy#The_nuclear_force> > > The nuclear force is a close-range force (it is strongly attractive at a distance of 1.0 fm and becomes extremely small beyond a distance of 2.5fm) > > > Assuming the neutrons are spaced 1.0 fm apart (and effectively assuming a square grid, ignoring the possibility of a hexagonal lattice like graphene; it doesn't matter for current purposes of order of magnitude estimation). The measured binding energy of the deuteron is 2.2 MeV. Not the same thing, but a plausible proxy; say that's the bond energy we are looking at here. That's 3.5e-13 J. Force = energy/distance = 3.5e-13/1e-15 = 350 N. That seems plausible; the above Wikipedia page gives the repulsive force between a pair of protons close to each other as 40 N, and the strong nuclear force must overcome the electromagnetic repulsion in nuclei containing tens of protons. A square meter of paraneutronium contains 1e30 neutrons, has a thickness of ~1e-15 m, and a mass of 1675 kg. A meter-wide strip of paraneutronium has a tensile strength of 3.5e17 N. The maximum length of paraneutronium that could support itself in 1 g = 3.5e17 / (1675 \* 9.8) = 2.13e13 m = 2.13e10 km, twenty billion kilometers. That compares favorably with the radius of a Banks Orbital = 1.8 million kilometers; we have a little over ten thousand times the minimum necessary tensile strength. That means a single layer of paraneutronium could support, say 1 km thickness of rock ~= 3000 tons/m^2, and still have a severalfold safety margin. All well and good when nothing goes wrong, but in a science fiction story, something always goes wrong or there wouldn't be a story. So what happens when the load-bearing shell suffers an unexpected impact? What happens if it gets hit by a 1-meter rock at 100 km/s? Or a 100-km asteroid at that speed? Or a 1-megaton nuclear warhead? [Answer] Here's a few alternative calculations: --- You will have problems when the speed of sound is insufficient to carry the information of the impact far enough to dissipate said impact before the material is moved far enough to break. (You may have problems before this; this is an estimate of an upper bound.) The speed of sound in a taut thin membrane is just $c = \sqrt{T/\sigma}$. $T=3.5\10^{17} N/m$. $\sigma = 1675 kg/m^2$. Overall, this works out to a speed of sound of ~14.5 km/s. Let's say that the membrane breaks when it stretches 2.5x (from 1fm spacing to 2.5fm spacing). Consider a massive point hitting the membrane. It ends up stretching out a cone shaped 'depression' in the membrane. The base of the cone can grow in radius at no more than 14.5km/s. The sides of the cone aren't snapping, and so can grow at no more than 2.5\14.5km/s. This then constrains the speed of the point to no more than ~33km/s. (You can also imagine a disk hitting the membrane, and the truncated cone resulting.) Do note that this is after the collision of the point and the membrane. 1675kg/m^2 isn't negligible. Take your 1m rock at 100km/s. Or rather, let's call it a 0.5m radius 1m cylinder of magnetite (~5g/cm^3). If it was somehow zero thickness, or a rigid body even at these speeds, would it penetrate? Yes. 5000kg/m^2 is more than enough; it would still be traveling at ~75km/s after initial impact. Unfortunately, these speeds are well above the speed of sound in mundane materials, so you can't just consider the impactor a rigid body. And when you do the estimate for non-rigid bodies, you're fine. That being said, this does indicate that you have to worry about collisions with other things made of neutronium. --- Alternatively, consider high-speed lead colliding with said membrane. Each individual lead nucleus is ~5.5fm in radius. This means that each lead nucleus should collide with ~1 neutron. Breaking 4 of the bonds in said neutronium requires 1.4e-12 J. Corresponding velocity of a lead-208 nucleus is 2,847 km/s. This puts an upper bound on things - lead traveling at 1% of c or faster or the equivalent will destroy it (or at least poke holes in it). (That being said, there 'should' be all sorts of interesting nuclear reactions that also occur...) [Answer] # Boom. The biggest problem I see with your paraneutronium is that it has no repulsive force. Neutron is stuck to neutron somehow, every femtometer. If a piece of matter hits it, the electrons sail through the barrier, and the nuclei aren't far behind. If they're more than a centibarn in cross-sectional area, they're guaranteed to "interact" with the neutrons. For many nuclei that would be energetically unfavorable and I suppose nothing would happen ... but what if forming the higher isotope releases more than 2.2 MeV? Then a lot of energy gets loose, even as a hole is formed in the pattern. Now this might not add up quickly, if the violence of interaction drives back anything that would strike... but it seems like it should do something eventually. [Answer] Okay, it seems to me we can reason roughly as follows. Take the case of a 1 m object impacting at 100 km/s (around the high end of expected natural impact speeds, assuming an object coming from interstellar space). That's on the order of 1e3 kg, that must be decelerated from 1e5 m/s in 1 m (being the size of the impacting object), in other words in 1e-5 s. So for about ten microseconds, the exerted force would be on the order of 1e13 N. A meter-wide strip of paraneutronium has a tensile strength of 3.5e17 N. On the face of it, that's four and a half orders of magnitude safety margin. In practice somewhat less because the material has limited elasticity etc. Say it's three orders of magnitude. A quick dimensional analysis suggests, and experience with guns versus armor confirms, that the amount of armor a projectile can penetrate, is a linear function of its diameter. That means at that speed, a kilometer-sized asteroid would punch a hole in the structure. That sounds plausible, and means the active meteor defense system only needs to deal with objects that can feasibly be spotted at interplanetary range. ]
[Question] [ A dark hycean world is supposed to be a hot water world with a thick atmosphere around a red dwarf star. This means it's tidally locked with one side forever facing the sun and the other forever facing space. These red dwarves do tend to flare often so proper shelter would be a must. Would just going beneath the clouds suffice or would submerging beneath the ocean be required to avoid the solar radiation? [Answer] ## Hard to see, the dark hycean is... An [article](https://earthsky.org/space/hycean-planets-exoplanets-habitability/) on this made the rounds recently, based on [this paper](https://iopscience.iop.org/article/10.3847/1538-4357/abfd9c). Note that "Dark Hycean" is defined in terms of "habitable zone" - it is said life cannot exist on these worlds except on the far dark side of the tidally locked planet. Avoiding direct solar radiation is, therefore, not a priority as they envision it. To be sure, there is not really such a thing as a habitable zone, only a habitable planet. The poles of Mercury have comfortable temperatures while the "seas" of Neptune are likely much too hot for any life we imagine. Even with the narrow definitions given, the dark hycean planets might allow for temperate upper layers of the atmosphere as on Venus or Saturn, or cool deep layers of ocean far below. The flyers of such a world should be well evolved to withstand radiation, like some organisms on Earth; if anything, they come seeking the flares to harvest their energy. For the night side, I would divide up the organisms as with my musings on Saturn, into Earthlike life and filamentous life. The Earthlike life relies more on biochemistry, and uses anti-solar cells (there's such a thing!) to gain some energy by radiating heat out to space. Filamentous life embraces the turbulence of the air and sea, consisting primarily of long filaments of graphene, carbon nanotube ... apparently [diamond](https://phys.org/news/2022-03-easier-flexible-diamonds.html) is on the list now. Stretching the filament generates piezoelectricity, which is captured and used to generate electromagnetic waves along the filament to supply the organism's biosynthetic energy. On most planets these two geneses of life work together symbiotically. For example, the daytime flyers rely on filamentous life to form the large flight surfaces needed to move efficiently and safely at high altitude in a hydrogen atmosphere, but rely on Earthlike photosynthesis to absorb the solar radiation. [Answer] It may not be necessary to seek shelter during a red dwarf star's flares at all. [Recent research](https://earthsky.org/space/red-dwarf-stars-superflares-red-dwarf-planets-habitability/) shows that red dwarf flares are emitted from the poles of the stars, away from the star's equator and planetary orbital plane. So, if shelter is required at all, it's unlikely that much will be needed. If the only threat is the greatly increased luminosity during the flares, this could be mitigated by sheltering behind the clouds or on the dark side of the planet. [Answer] Given the projected depth and density of the atmospheres of hycean worlds there may be no need for additional shelter from radiation. I would be more concerned with building habitats that can survive the extremes of weather that are thought to be the norm on a tidally locked water world. Actually you'd have to build with flares in mind there as well, the weather would be made more violent by flare activity due to the increased energy flux raising the thermal gradient. ]
[Question] [ I'm currently creating a setting with a large culture that takes a lot of inspiration from Zoroastrianism and the Ancient Near east and Mediterranean. It's going pretty good I'd say, but I've realized that all of my cultures, barring linguistics and rituals specifically relating to magic, are one-to-one identical with the real world cultures I've taken inspiration from. In every way. From their interactions to their clothing. I've taken too much inspiration, you could say. I've tried to look up guides online about this, but most of them relate to cultural appropriation. Which is a valid issue (I'm not gonna debate this in the comments because it's not the point of my post btw) but that's a separate discussion, and partially irrelevant to me as I'm working off of cultures that don't really exist anymore, like the Minoans, or exist now but in much different forms, like Achaemenid Iran. In the case of Iran I make sure not to use any aspects relating to modern Islamic Iranian culture, for example. But still my question remains, the peoples I've created are far too similar to their analogs for my liking. This is supposed to be fantasy not historical fiction. Please don't give me the same "just mix and match" solution, I've tried that and I don't like the results personally. [Answer] Much of what looks like copy/paste of a culture are things which can be described superficially. The real roots of a culture are harder to pin down. Those roots are what you want to capture the essence of a culture without feeling like a copy. For any superficial aspect of the culture ask "why is this the way it is?" But don't just ask it from your perspective. Ask it from the perspective of someone from that culture. Then, when there is an answer to that, ask why that is the answer for why it is the way it is. Again, do it from their culture. At some point, the native member of that culture will start to struggle with answering "why." It may become too tedious or too nuanced of a topic. That's the point where you are at a kernel of the culture which can be used without it feeling like copy/paste. Then, build the culture up from those kernels, which you may take from multiple societies if you desire. The result will feel more organic. And, if you do it very well, the native members of those societies will be impressed at how you captured them. (if they aren't impressed, you may need to do a bit more work!) [Answer] You need to mix and match features of different cultural models so that you aren't, and are seen to not be, copying a single culture. The trick is to pick the right features to create a cohesive whole, this isn't necessarily a matter of avoiding traditions that seem to be in opposition to each other, many cultures have paired rituals that appear to be in opposition to each other; for example the Bedouin find no fault with killing a stranger who doesn't announce their arrival but also venerate outsiders guesting in their camps. The key to creating a cohesive culture from a number of different sources comes from justifying those tensions and from having rituals/traditions to deal with most/all aspects of everyday life that make sense as a cultural whole and also in the physical environment and technological context in which those practices started. [Answer] ## TL:DR - change something I mainly world build for role playing games, so this is a technique I use myself a lot. It has a lot of advantages! You can get a lot of detail quickly, and people meeting your world for the first time already have some familiarity with it. I start with a rough idea of the kinds of traits I want the culture in my world to have and then pick a real world culture that fits the bill. Then I change one thing. Make a bronze age culture iron age, polytheistic to monotheistic, patriarchal to matriarchal, whatever. (In a high fantasy setting just adding magic is usually enough to thoroughly transform any real world historical example). Then I work through all the consequences of that change. The (usual!) result is cultures that are recognisable enough for my players to use their familiarity with the real world, different enough that they are surprising and unique, detailed enough I can tell interesting stories, and didn't take eight years and a PhD in Anthropology to come up with. One other thing that is important to consider is that cultures do not exist in isolation. The cultures around them shape them. Caesar's Romans never met Sengoku period Japanese - what if two similar cultures had been neighbours? (And what, if anything, do we have to tweak in both cultures to account for the time difference between them?) [Answer] Exclusion helps Take essentially any culture that is dominated by one or another thing and remove its influence entirely. Like generally arabic cultures for example, they're hugely dominated by the influence of islam, just imagine how different they'd be if they weren't? The resulting culture would be as different from its source as night and day. Now you can't just leave an empty space where there once was something as big as something as religion, or land ownership customs, or whatever the heck you exclude, so naturally you need to fill it with something else. It could be something as simple as believing the world was hatched from an egg that was laid by some great beast. How would such a belief change things? Well, you might get buildings with high egg-like domes within which another floor could be built into. You could have the priesthood where hats that symbolize their belief, a hat that looks like the top of an egg, or you could even have jewelry become more oval or have the crowns of your rulers have more rounded and heighty tops after having been influenced by such as thing, or have a preference for shields to be more egg-shaped over round ones(kite shields already are sort of like this with an extended bottom tip, just make its tip more round/shorter). Egg-laying creatures might get held in higher regard over others, and whether or not eggs would still be included in a person's diet would hugely depend on whether they believe the eggs from 'not as great' creatures to be sacred. You can have hugely different cultures if you simply remove one aspect about it and put another aspect or in its place. Of course, it'll also be up to you to actually account for how an altered, excluded, or otherwise replaced aspect will affect the culture of your world. [Answer] Cultural copying, transmission and evolution has taken place plenty of times, so finding similarities between cultures is not unusual. The Abrahamic religions all influenced each other. They underwent several periods of divergence and convergence due to the cultural and political interactions between them. Chinese culture influenced Korean and Japanese cultures. Indian culture influenced SE Asian cultures, and many of the European cultures share significant portions of their culture with their neighbors. I would say, if you worry that your cultures are too copied, do a quick thought exercise. Develop the base culture you transmitted, then focus on a unique place, item or characteristic that only exists in this other culture's area. Then develop some lore about that item and think about how it would evolve over 100's of years. Christianity diverged from Judaism over a single man. It then developed in the sea of sin that is Rome, causing an aversion to vices, and were persecuted in its initial years to create a martyrdom worship. Now, the Christian and Jewish communities are pretty different, based on a coule minor tweaks early on. ]
[Question] [ PROJEKT ' *ABYDOS* ' The (as of yet pretty ill-defined) setting of one of my worldbuilding projects is the Vārẽn Sea (working title). It's a large gulf that opens into waters with a large amount of small islands, similar to the South China or Agean Sea, or to a lesser extent the Gulf of Mexico or Hudson Bay. There isn't very much wind in the sea itself, with stronger winds in the open sea that facilitate trade with faraway civilizations to the North and South. The dominating society of the region (the Vārẽn) are seafarers and traders, and as a result also make long journeys outside of the sea to nearby nations further north and south. My question is: what would be the most likely design of their ships? Would they use oar galleys to navigate the many islands and calm seas? Would they just use sailing ships intended for the rougher journeys on open seas even in the small island chains around their homes? If they do use sails, I'm also struggling with how they might actually rig them. They need maneuverability in the islands, ability to operate in both strong trade winds in the open ocean and softer breezes in the gulf, and the resilience to withstand these long journeys. I've been considering several Philippine ships, or galleys similar to the Ancient Greek design, but nothing has really stuck well yet. The reliance on oars for both is especially problematic for me, since their larger ships will be regularly sailing over long stretches of open ocean, and i kind of just don't like them. Following some suggestions posted here since, I'm considering designs closer to Viking longships and several smaller Asian trading vessels. I'm split between Junk or Square sail rigging, and I've since cut out my previous idea of possibly having outriggers. [Answer] # Viking-line of ships: The kind of ships built by a culture are very dependent on the available materials, technology, and very specific usage requirements, so any suggestions will perforce have some opinion. I would look to cultures that had similar geographic distributions, where towns/villages are separated, trade via ships is central, and land transport is low/non-existent. The Vikings built a family of ships with similar designs, but slightly different for specialized functions. They were fairly small, often easy to pull up on shores without a formal port, yet quite robust for long sea voyages. For a culture that is disparate (spread across numerous islands) with both local trade and oceanic voyages, these vessels seem optimum, barring specific technological or magical requirements/alternatives/restrictions. Common vessels included the [karve](https://en.wikipedia.org/wiki/Karve_(ship)), [knarr](https://en.wikipedia.org/wiki/Knarr), and [longship](https://en.wikipedia.org/wiki/Longship). They share [clinker-built](https://en.wikipedia.org/wiki/Clinker_(boat_building)) design, allowing a light, flexible hull. Many of these vessels COULD be operated by oars, but generally didn't require oars for routine operations. The cargo ships usually had small crews, while those used for military roles used more people and more oars. If this isn't to your liking, consider ships from cultures with similar requirements, like the [Polynesians](https://en.wikipedia.org/wiki/Polynesian_navigation) and their double-hull canoe/outrigger canoe family of similar ships for various functions. The Chinese [Junk](https://en.wikipedia.org/wiki/Junk_(ship)) was also an extremely versatile design base, allowing many functions in one basic engineering set and made of soft woods, yet it proved very seaworthy. [Answer] ## Specialization leads to Profit With a wide variety of needs and external conditions, you will probably see a wide variety of solutions. ## Outriggers Small, catamaran style vessels with hybrid oar / sail set ups allow for quick transport in relatively calm waters. Outriggers could be used in the Gulf and Islands for transport of people and perishable goods. They are cheap to build, use oars when it's calm or near shallows, and use sails whenever they can. ## Barges For bulk transport in the Gulf, barges are a good fit. Large, simple, sail powered vessels, you might need to use outriggers to unload them if the destination has reefs or tricky harbors, but again, these are cheap, easy, and "good enough" for relatively protected waters. Downsides - it's slow, and these would be terrible in a storm. ## Ocean Going Vessels Large sailing ships are really your only good option for long sea voyages. You need storage for your own supplies, as well as your trade goods, which all pushes towards a larger ship. Above a certain size sails are really your only option for propulsion in a pre-steam power world. ]
[Question] [ Closed. This question is [opinion-based](/help/closed-questions). It is not currently accepting answers. --- Want to improve this question? Update the question so it can be answered with facts and citations by [editing this post](/posts/194863/edit). Closed 2 years ago. [Improve this question](/posts/194863/edit) Nice to meet you all. Inspired by Star Trek: Discovery's Season 3 and "The Burn", I've been re-reading materials where there has been a "Fall of Civilization" scenario and it seems most writers opt for a singular point of origin. Examples include: * Gene Roddenberry's Andromeda: The Nietzschean Uprising and the subsequent FALL OF THE SYSTEMS COMMONWEALTH; * The aforementioned Star Trek: Discovery: THE BURN titular event; * Dragon Age: Inquisition: THE BREACH of the magical Veil; * Warhammer 40,000: The birth of Slaanesh and the instantaneous fall of the Eldar/Aeldari Civilization, as well as the Horus Heresy and subsequent loss of "The God-Emperor of Mankind" There are plenty of others, of course. What has gotten me curious and eager to beseech your assistance is this: even in our own History, the fall of the Roman Empire did not happen with a single event, but instead a sequence of them. Same thing for the rise and fall of several Chinese dynasties, which even fractured the Yellow Kingdom at one point into the Three Kingdoms period. The fall of civilizations seem not to occur overnight, but instead a period of transition. How could I make a "believable" model of such a catastrophic (to some) scenario in a RPG? Assuming an Interstellar body of government divided into central "Core Worlds" full of opulence (and decadence) as well centralized military bases, and "Fringe/Frontier Worlds" often left to their own devices by sheer bureaucracy, inefficiency and red tape, how would such a political beast "fall"? Is it more likely to be slowly eaten away at the fringes by invading forces while the Core worlds are too slow and sluggish to even recognize an invasion? Can a plague bomb be detonated within its Capital cities, cutting the snake's head off so to speak? I feel that most writers focus too much on a singular point of origin for these catastrophes and it seems to be too convenient to "undo" the disaster: just magically or scientifically time travel to that event in time, prevent it or contain it quickly and ALL issues are solved. Whereas, in real-life, such events only portray a "tip of the iceberg" and slowly bring to light long-ignored underlying issues. [Answer] ## A "Fall" is Just One Day in a History Book: There was a day before the fall of Rome where it looked like there was still hope. But already by then, the empire had split into two, and the dependence of Rome on mercenaries (who really just wanted to have what Rome had) seeded the core of their own destruction. There was a day after the fall of Rome when the "barbarians" thought they could salvage the city, or Attila perhaps thought he could make everything better now that he had loot in place of his pay. That same day, a centurion believed he could still rebuild the city and reestablish the Western empire, if only X, Y and Z would happen. Empires are not points on a map, but big, living things that breath and ebb and flow. They almost never just "fall" one day, but there is always a process going to it, and a flow of things coming out of it. It's a huge mélange of individual people's stories all coming together. The best stories about a fall center around a person who can see the critical failures going on, but do nothing to stop it. The whole thing is a house of cards, and the critical people know it. The fall can seem inevitable, with all the citizens scrambling to position themselves for what happens after. If the consequences are bad enough, that may include fleeing the universe (I've read at least two of those). Or people can be in denial. Even after the fall, they still hold out (often reasonable) hope that things can still be fixed, and the responsible people can be made to act for the better interests. Imperial districts hold together, maintaining civilization in one region, while anarchy and chaos tear another apart. A single fall is a consequence of either events portrayed in the distant past, or the need to wrap up a story in 30 min less commercials. To write about a real fall, you need to have a rich detail of events leading up to it, and a rich mix of all the consequences. Leaders try to keep order; often successfully. A new emperor is named, and might keep things up - for a time. A district becomes a prosperous kingdom, or a separate empire. But every great story about a fall needs that one singular thing that happens which makes people believe that things are over. Rome sacked, with flames pouring out. The empire may still exist, but the dream of empire has fallen. [Answer] No-one remembers why. [![castle in the sky](https://i.stack.imgur.com/rddRC.jpg)](https://i.stack.imgur.com/rddRC.jpg) [source](https://www.ebay.com/itm/Castle-in-the-Sky-Poster-Studio-Ghibli-Anime-Poster-High-Quality-Prints-/264218393136) Castle in the Sky does this so well. There is a world of people and their tech, farming fields, working mines, fighting wars. But from the very beginning there is a feeling that things used to be better; greater. The foundry building includes many ruins and only some parts are now used. The mine is depleted and the machines are worn and unreliable. There used to be more. The world used to be more amazing. Over the course of the movie, relics appear - a necklace, a robot - an abandoned flying city. We are never told why all but one of the flying cities fell from the sky or what happened to the civilization that built such wonders. There are parallels all over the real world - people live in the vicinity of amazing ruins built by forgotten people for forgotten reasons. I am sure those people wonder because I do. You do not need to know exactly what happened to marvel at the works of these lost civilizations. In some ways the mystery makes it more marvelous. ]
[Question] [ I have a magic system with very specific physical rules (hence why the question is [science-based](/questions/tagged/science-based "show questions tagged 'science-based'")), but I need help working out a specific scenario. Also feel free to suggest better terminology where it can use improvement; explaining this system has always given me difficulties. Ground rules It works like this: a witch can make the [normal force](https://en.wikipedia.org/wiki/Normal_force) apply without physical contact. For example, imagine that you are an evildoer walking up towards a witch you want to murder. If she is inside a building, then she can take the wall behind her, and manifest its physical presence in front of your nose. You'll bump into what feels like solid rock to you, and probably break your face. And a witch can go on the offense too. She needs to make a slight hop, and then as she is about to land, projects her own body right on top of your head. If you didn't anticipate it, then the sudden impact of the mass of a human body on your head can break your neck. There's more sophisticated uses of this force; a skilled witch in active combat will seem to be doing parkour in the air whilst people around her are kicked without ever coming into physical contact - at least not in a way you can perceive with your eyes. Other aspects and limitations: * This kind of sorcery only carries over the normal force on the super-atomic scale, not photonic interaction, chemistry, etcetera; so the projections are tangible but invisible. * A projected surface has all the friction of its source object (at least the amount of friction resultant from physical ridges in the object, not that from any chemical bonding or whatnot). * It does not create a vacuum where you project the item; a projection is an infinitely thin shell. * You can make interactions with the projections as if they were the real objects; project a small cup and you can fill the projection with water, and see water hovering in the air, whilst the source cup feels heavier. * Force on the projection can move and/or destroy the source object as if it were interacting with the source object. This also works vice versa. * The direction of any forces involved is never changed by the magic. * The projection ceases to be once a witch stops actively maintaining it. Let me know if this makes sense so far. Flight Now, the specific use case I want to figure out is flight. One of the things a witch can do is seemingly walk on air, by actually walking on the floor below, which she projects higher up, right below her feet. That way she can create staircases anywhere. But she can also change the scale of the projections. Surgery is made much easier by projecting an upscaled version of the patient's body, covering the projection with some sand so she can see it, and then manipulating the enlarged body with her bare hands, allowing high precision. And that allows for a much cooler form of flight. A witch can walk on the air itself; if she projects an enormous surface of air below her feet. It should be a large enough surface that she can step on the air, push herself off it, and take another step with her other foot before the first foot sinks too far. And because this projection is perfectly smooth (it is an artificial gathering of air along a perfectly flat, slightly inclined plane), it is frictionless. Once reaching cruising altitude (basically just high enough not to bump into buildings), a witch can lie down and glide on the projected air, and traverse the sky at hawk speeds. She only occasionally needs to get up and gain more altitude; even more skilled witches can use the (projected) wind for that instead and basically take off without expending any energy. How large is the stairway to heaven? The stepping process is the specific use case I need to sort out. The question is: in terms of horizontal surface area, how much air is needed to walk upon, particularly to lift oneself up? Think of it like the witch wearing enormous sandals, perfectly stiff and weightless, of such an area that you can step on the air the way you can walk on snow with [snowshoes](https://en.wikipedia.org/wiki/Snowshoe). I want to sort this figure out because it will allow me to put an upper limit on the size of both projections and source objects. A formula with as input an arbitrary weight would be most useful, as I am also considering the witches building "boats" to fly on the frictionless projected air, and then I would need to know the required surface area to support the boat too. [Answer] Fascinating question! Your magic scheme seems to make total sense to me. So the witch is exerting a force of 700N (about 70 kg seems reasonable? I've never asked a witch her weight, seems terribly impolite) on the air, and we need to find out what area of 'snowshoe' would resist that force for long enough for her to step upwards on it - she's always going to be falling, but needs snowshoes big enough that the falling is very slow. When we say 'very slow', if she stands still, she'll constantly be accelerating under gravity: there's no-way that anyone could float by standing on a (flat, weightless) platform, no matter how big it was. Now I can walk up stairs at about 0.4 m/s. If the witch put in the same effort, it'd feel like walking up stairs - or on one of those stepper machines at the gym. Now using the drag equation (<https://en.wikipedia.org/wiki/Drag_equation>), with air density of 1.2 and imagining the snowshoes as a thin disk which would give them a drag coefficient (<https://www.engineeringtoolbox.com/drag-coefficient-d_627.html>) of about 1.1 gives: $700 = 0.5 \times 1.2 \times 0.4^2 \times 1.1 \times Area$ $Area = \frac {700} {0.5 \times 1.2 \times 0.4^2 \times 1.1} = 6628.788 m^2$ which is a snowshoe of approximately 92m diameter ($2 \pi r^2$) If your 70kg witch was prepared to expend the effort of someone sprinting up stairs at (2m/s), she could fly on the level with only 18m snowshoes. If she was super-powerful at projections, she could fly level using stroll-up-a-wheelchair-ramp levels of energy (slope 1-in-12, so lets say 0.0833 m/s) on snowshoes that were 440m across. Of course it would take more energy to accelerate up into the air in the first place, and remember that stairway is always going to be like climbing up sinking sand. Hope that makes sense... [Answer] Your magic system sounds like your witch can somehow blow a lot of air in a given direction to exert a force. I think we can model it with the equation of [drag force](https://en.wikipedia.org/wiki/Drag_equation) $F\_D \approx P\_d \cdot A $ To sustain the body of a witch on a walk you would need to equate their weight on the surface of their feet. Assuming the area of a witch's feet is $2\cdot 0.25 \cdot 0.10 = 0.05 \ m^2$ and their weight is 700 N, you would need a dynamic pressure of the order of $700/0.05=14000 \ Pa$ Note that this is assuming that the witch is standing. Should the position change, i.e. laying on the belly, that pressure would be harmful. On the contrary, going from laying to standing would require an adjustment to avoid falling. If we calculate the dynamic pressure as $P\_d=$$1 \over 2$$\rho u^2 $ we can get an estimate of the amount of air needed per second, as the volume of air contained in the footprint surface times the air velocity. [Answer] This is a pretty complex question. The plates you're suggesting, being infinitely thin, would be infinitely light, so exerting any force to them would send them off at light speed. In this case, you have just air to keep them in place as you step on them. ### Amount of Air How much air you need depends on how fast you want to go, as I'll get into. Overall, I guess you need at least the same weight of air as the weight you're exerting with your step. Every cubic foot of air weighs about 0.0807 lbs. So, for a 100 lb witch, you'd need 1,239 cubic feet of air, and more for jumping. But air is a gas, so if you put any pressure on it it'll compress/move.... ### Balloon If the witch can make a box of air, that might work, so the air can't escape. Since the box is weightless, it wouldn't cause the air to fall, under the weight of the witch was added. Of course, no matter how much air you use, you'd cause it to accelerate downwards, until it reached an altitude where it's at neutral or positive buoyancy despite its weight. Actually, with a big enough box, you could basically make the equivalent of a balloon. But the issue with that is air is not lighter than air, so any added weight and it sinks. If you could capture specific gasses out of the air, that'd be different. With a large enough air balloon, still, you could get a moment to jump from one to the other, the balloon sinking as you jump off of it. ### Conclusion So, when you jump off it, it'll be moved at the same velocity as yourself, so half your energy would be moving the box. However, it does have a lot more drag, being a giant box, so you'd get more than half your speed/energy jumping off of these things. A larger box would mean more energy goes into your running, but you can never get 100%, so it just depends how fast you want to run up this staircase, as to how much air you want. This would be quite an exhausting climb, as climbing ordinary steps is already great exercise, but you could do it. Hope this was helpful. ]
[Question] [ Light travels at different speeds through different types of media, which causes phenomena such as [refraction](https://en.wikipedia.org/wiki/Refraction) and [Cherenkov radiation](https://en.wikipedia.org/wiki/Cherenkov_radiation). However, in most cases, the light still travels through the medium pretty darn fast. If we possessed a material that was capable of slowing the propagation of light to a tiny fraction of light speed, we might actually be able to notice the delay between light entering and leaving the material. If I walked past an screen covered with this material, someone looking through the screen might see me walk past a few minutes after it actually happened. If the material is even more powerful (or fashioned into a thick slab), one could observe events that took place days, months, or even years in the past. Is such a material theoretically possible? If so, what other strange properties (e.g. refractive properties) would this material have? Is there a limit to how much a medium can slow light down? [Answer] We can do this on timescales on the order of 1 minute at the moment, if you'll allow me to stretch the boundaries of the question a bit. There are essentially [two ways to do this](http://physics.wm.edu/%7Einovikova/slowlight.html): 1. Slow light, where the refractive index of a medium is drastically increased, in the process slowing down the pulse velocity of a beam of light. 2. Stored light, where the quantum states of photons in a laser beam are mapped onto atomic states in a crystal with the help of a second laser, and then converted back into photon states. The second example is potentially more fruitful, and it is this method which enabled physicists ([Heinze et al. 2013](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111.033601); pdf [here](https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.111.033601)) to "store" light for one minute inside a 3-millimeter Pr3+:Y2SiO5 crystal: [![Diagram of the Heinze et al. experiment](https://i.stack.imgur.com/fGPvJ.png)](https://i.stack.imgur.com/fGPvJ.png) Figure 1(a), Heinze et al. 2013. The setup for light storage is much more complex than you presumably want, and involves many different optical elements. Part of the reason the team was able to achieve such long storage times was their use of evolutionary algorithms to find an optimal pulse shape; these algorithms could potentially be extended in the future to reach longer timescales. Unfortunately, any storage mechanism will be subject to optical losses, and will be limited by the simple fact that it isn't an ideal environment. There are, of course, some caveats. For example, the light being stored comes from a laser, so you would need a large bank of lasers to slow down complex images. You also have the issue that only one pulse is being stored in each crystal at once, and that pulse doesn't represent a long snapshot of time. Plus, the storage efficiency is not great - 0.4% by Heinze et al., with the possibility of doubling it to 1% if certain technical problems can be accounted for. The upshot, though, is that yes, we can indeed see store light for noticeable timescales. The efficiency is poor, and the light has to come in the form of a laser, but it can be done, and it can presumably be improved upon. [Answer] Read Bob Shaws SF Novel 'Other days Other Eyes' which revolves around the invention of a product called 'Slow Glass' - sheets of a transparent glass like material that slow the speed of light down so that events that occurred on one side of the 'glass' can take days, weeks. months, years or decades etc depending on the thickness of the sheet and other factors to reach the other side. The implications turn out to be both intriguing and at a human level tragic. ]
[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. I've been working on designing how an ammonia-ocean world might work and I've settled basically everything except one. I cannot for the life of me find any sources that actually provide a decent way to estimate how strong a greenhouse effect is with an alien atmosphere. The topic gets touched on here and there, but nothing I felt I could easily use. I've gathered that ammonia is a greenhouse gas, just one not long-lived on Earth. This brings up something important. Ammonia has a big vapor pressure. The partial pressure of ammonia even on a cold world would be quite significant. I'm also assuming a lot of methane for biological reasons. What sort of greenhouse effect will you get on a world with as much or more partial pressure of NH3/CH4 as Earth has nitrogen? I don't need absolute precision, I just want to be sure I'm not giving ammonia worlds air mixes and orbits intended to leave them chilly enough for ammonia but would actually turn them into Venus. A rule a thumb, an estimate, would be awesome. [Answer] Ammonia is a greenhouse gas. Not the easiest question because although you can find data that absorbs energy in the infrared spectrum (one of the qualifies for a greenhouse gas), it is not considered in publications dealing with the greenhouse effect because ammonia has such a short residence time in our atmosphere. Our current atmosphere, that is. I found this fine article by Sagan and Mullen. It is very approachable and qualitative; I would expect nothing less from Carl Sagan. [Earth and Mars: Evolution of atmospheres and surface temperatures](https://www.jstor.org/stable/pdf/1733927.pdf) This is 1972. They consider how warm earth is and note that it would be colder if it were not for the trapping of infrared emissions from the Earths surface by atmospheric gases - the greenhouse effect. They note that the sun has gradually been getting brighter. They then consider the ancient Earth when the sun was cooler - with current atmosphere the sea would be frozen. Adding more CO2 does not help because apparently you reach maximal absorption pretty fast. Adding NH3 does help and they lay out (in lay terms!) the properties of NH3 that make it a good greenhouse gas. Then they show how cold the earth would be with and without NH3 over time. [![graph](https://i.stack.imgur.com/aGs88.jpg)](https://i.stack.imgur.com/aGs88.jpg) Red boxes are mine. I encourage anyone interested to check out the linked paper. It is a good thing that NH3 went away with the Great Oxygenation or the seas would be boiling by now! In any case - NH3 is definitely a greenhouse gas. But there is plenty of wiggle room for you to make your planet how you want it to be. You could assert that NH3 infrared absorption also maxes out. You could make the atmosphere more or less dense. You could cool the planet by increasing albedo - maybe even increasing it with a haze of atmopsheric ammonia ice. ]
[Question] [ What are two non lethal substances that will combine to create a strong poison when ingested close together? Hopefully my character would be able to drink one of the substances mixed in to a wine or whiskey that is shared out with a few people, but does not kill anyone (yet!). Soon afterwards the character goes upstairs and takes some form of pill, which should have the other half of the poison in it. The pill could have been switched out weeks in advance, without detection. This combination kills them - but as multiple people drank the wine, and they have been taking the pill for days without being poisoned, it is difficult to piece together how they have been killed. Preferably the two ingredients would be naturally occuring as it is a low-tech world, and without taste to help avoid detection, but I know that's very unlikely so no worries if it has some taste/smell! I'm sure I can find a way to play it off! I have thought of sulphur tablets with Isopropyl aminoethylmethyl phosphonite in the wine, which creates a VX (a strong nerve agent), however I'm having trouble thinking of a way of the character being able to get hold of Isopropyl aminoethylmethyl phosphonite with only fantasy technology... Am also unsure of the quantaties needed etc. Another option is an overdose of a certain chemical, with one half being in the wine and the other in the pills, but again I'm unsure of quantity and what would work best. Edit: sorry forgot to say, the context is a murder mystery story in a fantasy world. Thank you all so much! [Answer] [Coprine](https://en.wikipedia.org/wiki/Coprine) is a mycotoxine, found in the mushroom [Coprinopsis atramentaria](https://www.mushroomexpert.com/coprinopsis_atramentaria.html), thus being obtainable in low tech setting, if you know what to look for. The substance is toxic when mixed with alcohol - how to make the unsuspecting victim drink enough alcohol in wine is left as an excercise for the reader... [Answer] # Grapefruit juice and Codeine (etc) There is a lovely [long list](https://en.wikipedia.org/wiki/Grapefruit%E2%80%93drug_interactions#Affected_drugs) of medication that should not be mixed with Grapefruit Juice. One large subset of these are prodrugs, which are not active medication when consumed, but become active when digested. They are transformed by chemical reaction during digestion, Grapefruit juice (and a number of other compounds) can substantially increase how much active medication is produced from the prodrug. Thus triggering an overdose. A common example is [Codeine](https://en.wikipedia.org/wiki/Codeine#Mechanism_of_action). Codeine is a fairly common painkiller, hard to notice if you are taking it on its own. it functions via being converted into morphine in the liver. Grapefruit juice increases how much morphine is made. So you dose someone up with a large (but sublethal) does of codiene (e.g. in the food). Then serve grapefruit juice with the meal. They get to die of an opiod overdose [Answer] Alcohol and Opiods Alcohol can react badly with other drugs and be potentially lethal. In the modern world it is dangerous to take alcohol with Codeine painkillers. These are available without prescription. Opiods can be derived from plants like the poppy. The Victorians are famous for their opium dens. So modern technology is not needed to concentrate the important chemicals. [Answer] [Monoamine oxidase inhibitors (MAOI)](https://en.wikipedia.org/wiki/Monoamine_oxidase_inhibitor) and anything from the long list of substances they are known for their possibly lethal interactions. MAOI occur naturally and have nasty, potentially lethal interactions with a lot of other substances. This is also a problem. If you put MAOI in the wine some guests may eat aged cheese and get the nasty symptom themselves. If you put it in the pill, the victim may experience the interactions on random days before the attack. [Answer] You can build up tolerances to some poisons over the long term. Famously, this has been used for poisoning since the Renaissance era (IIRC) , so you can drink from the same bottle as your victim and survive. Now go for the reverse: everyone else has built up immunity (because they grew up in an area which has lots of the relevant poison in the local water) but your victim, who came from elswhere did not. Hence, one person dead, everyone else baffled as to what killed him. ]
[Question] [ I want to have a somewhat realistic setting where space fleets have to close in to short distances, probably around 1000 km or less, in order to inflict damage. This will be only a few hundred years into the future. Also, I don't want a direct translation of a naval fleet to space if it'll require too many justifications. I'm fine with doing away with fighters for example. What's important is that small and large ships have a reason to gather into a formation and engage at relatively short ranges. I thought about what a setting would need to accomplish this and I've come up with the following 1) Armor, engines, and heat sinks are really efficient in this setting, made possible by unobtainium if need be 2) Lasers are out. Maybe diffraction is too high, or perhaps the armor mentioned in the first point deals with lasers very well. For whatever in-universe reason lasers are not effective 3) Missiles are the only way of striking at long range With these 3 rules in effect what I envision would happen would be ships sticking close to one another. Small ships would protect capital ships with their overlapping point defense. With such an effective defense fleets will have to move close enough to use kinetic weapons like railguns, whose projectiles are too fast to intercept. Then, once enough of a fleet has been destroyed and their point defense compromised, the other fleet would seek to finish off their heavily armored capitals (which presumably are resistant to railguns) with nukes. All in all, a nice long fight with lots of opportunities for maneuvering. So, what are the ramifications of my rules? Are my assumptions reasonable? Or would some other tactic be the standard? If the latter is true then what else would I have to change in order to make the premise realistic? [Answer] I think your arguments for naval battlegroups work fine in space. As for why the ships wouldn't be all of a similar size, the answer is gravity wells. Maybe your capital ships aren't structurally sound enough to actually make landfall on any planet. So if you want to land, you need smaller ships. Maybe the capital ships would collapse under the weight of their own armor, but smaller ships have less armor and can handle it. You need bigger ships than just surface-to-orbit ferries though, because you want to loiter over the target to provide air support. A hovering ship experiences just as much gravity as one on the ground, so the above argumentation still applies. It's kinda like the difference between littoral warships and ocean-going warships in real life. Little gunboats can go up rivers which would be too shallow for a full-size destroyer, but the gunboats are no match for a full-size destroyer out on the open sea. [Answer] If the distances are really far in your universe, your excuse might be chain of comand and relativity. If the distances between places are huge and you need multiple ships to a combat. I m imagining various types of especialized ships. You need to be really close to your allies to send messages that are useful. So you have this clusters of vessels that have a chain of command and some level of autonomy. Let's say each one of them have a person from the goverment or some sort of general or leader, the battles will be taking place in more than light second distances between those clusters. But between each ship from the same cluster there will be a short distance [Answer] Are my assumptions reasonable, or would some other tactic be the standard? I think that the capital ships might just be large railguns, not a typical capital ship, to maximize firepower with a low material cost. I don't see the reason for small ships when you can just mount an extra gun onto the capital ship. If the latter is true then what else would I have to change in order to make the premise realistic? Make it very hard to mount point defences onto the ships. Maybe the armour could interfere with radio/electrical signals. Maybe the ships are primitive and are spun to generate gravity, but the outside shell spins with the ship, complicating controls. [Answer] If weapons are traveling at significantly less than the speed of light, then the ability to calculate the other ships trajectories might play a part. If computers aren't powerful enough to calculate trajectories - or if they are so powerful they can send their own ships on unpredictable paths - most shots would miss because they simply weren't aimed at a fleet's current position. These problems would get worse with distance, so maybe close range is the only way to reliably damage enemy ships. If the ships are also able to survive multiple hits, I could see a complex game of chicken emerging, with each fleet trying to make the enemy misjudge their paths or maneuver into a bad position. [Answer] A reason for which close range combat may be absolutely necessary could be the existence of deflection/jamming technologies. A spaceship using space distortion for FTL travel (e.g. Alcubrierre drive) should be able to use this ability to jumble the geodesics of spacetime in such a way aiming from long range becomes totally unreliable (e.g. from large distances you see those ships like through the heat raising from a sealed road on a hot afternoon) ]
[Question] [ So, one thing we didn't talk about was the political ramification that'd arise from kingdom A using a dragon in battles. Kingdom A seems to be able to make the dragon do just about anything they say. The Dragon can rebel to a degree and choose his own method of doing things, but he can't disobey a direct order (without punishment). The most reliable way to determine if having a dragon would just make more enemies is to look at what nobles and the church are thinking. ## A quick rundown on the dragon Combat value: While nowhere near as malicious or powerful as your typical Smaug, the Dragon is obviously much more powerful than any individual human he may encounter. He usually isn't fighting on the front lines, as his ability to fly allows him to wreak havoc deep within enemy territory then get out fast. So, he usually does stuff like attacking supply lines and tracking enemy movement. Obviously, the Dragon isn't invincible, he can still get exhausted and poison works on him, though usually to a lesser degree when compared to humans. Social Standing: Despite that, the Dragon is considered to be a pet at best and a slave at worst. The only people who treat him like an actual person are his handlers, who themselves are nobles, but are still pretty low in the hierarchy. Reputation outside of combat: While the Dragon indeed likes to appear regal and is actually pretty smart, he's too stubborn and confident for his own good. He also does not understand human social norms often talking down to people that are several rungs above him and sometimes he also ends up being accidentally lewd when he forgets he isn't supposed to sniff strangers, lick friends in the face, or preen them, even if those are perfectly acceptable for dragons. The general opinion considers him to be a beast/monster that's ultimately below humans. His handlers consider him to be simply childish and the church thinks he's a demon from hell. Reputation in combat: Though he's willing to spare just about anyone who surrenders (read: runs away), there are three big problems: 1. If someone manages to make him angry enough (usually by threatening his loved ones), he won't care if they're a noble, or even a king and tear them to shreds. 2. His breath weapon is concentrated sulfuric acid that's sprayed in a fine mist, while usually not lethal, it can quickly cause permanent eye damage, blindness and lasting respiratory problems. The dragon will use it when his life is in danger, regardless of the target. 3. Though the Dragon has no incentive to and takes no pleasure from hurting humans, that's completely irrelevant to people who are afraid that kingdom A might send him on terror missions like a Red Wedding. --- Other than the Dragon, the setting has no fantastical elements (as far as humans know, there's only one dragon) and is more or less a carbon copy of high medieval Europe. How could kingdom A minimize the "bad press", using the Dragon would give them? [Answer] > > Other than the Dragon, the setting has no fantastical elements (as far > as humans know, there's only one dragon) and is more or less a carbon > copy of high medieval Europe. > > > In medieval Europe, dragons were typically seen as evil and malevolent beings on par with or analogous to demons. In christianity, Satan himself is called a "dragon" in the Book of Revelation which the people of the time would have taken very literally. Best case scenario, dragons would be viewed with the same level of mistrust as black cats, and anyone who tries to domesticate them would risk being accused of witchcraft. Worst case scenario, commanding a dragon would be considered irrefutable proof that you've sold your soul to the devil, and being subsequently tortured to death is pretty much guaranteed. There being only 1 dragon is actually much worse than there being many since people are more likely to assume that the dragon is THE devil rather than a naturally occuring animal that symbolizes the devil. For a king, the prejudice would be far worse. A world leader who commands the one and only dragon would so closely resemble Christian belief in the end times that religious scholars from across Europe would accuse him of being the Antichrist himself. Fear and superstition would lead to his excommunication, which in Medieval times, strips a leader of the Divine Right of Kings. Without this protection, his enemies would have no qualms about killing him in battle or having him assassinated. Even if he does somehow maintain his status as king, his lords will likely rise up against him given the first chance, and crusades will be launched against him from all across Europe. A Norse or Muslim King would not be much better off. Pretty much every religion in Medieval Europe considered dragons to be the enemy of both God(s) and man. How to minimize bad press? The only really positive depiction of dragons in a medieval setting is the White Dragon. In British mythology, there is the conflict between Albion the White Dragon and Ddraig the Red Dragon. In this mythos, both good and evil are represented by dragons. If your king were to paint his dragon white, he may be able to convince enough people that his dragon is the living embodiment or champion of goodness, and that he must raise this dragon up and make it ready for the day that its evil counterpart arrives. In this case though, he must be very careful about how he deploys his dragon. If it uses it to raid and destroy his political rivals, the public image of it being a champion of goodness won't last for long. However, if he uses the dragon in religious wars such as the Crusades or the 30 Years War, the dragon could come to be a symbol that God is with the king in question and help him rally allies of the same Creed to help him destroy the heretics/infidels. Another option to convince people that the dragon is the "good" type is to constrict its use to defensive and political affairs. If the dragon's only military duties are to guard the capital city and greet political guests, then neighboring kingdoms would feel a lot less actively threatened and be more likely to choose an uncomfortable peace than to risk threatening this kingdom to the point that deploying the dragon offensively becomes necessary. [Answer] I'll call the army with the dragon Team Dragon and any army they are opposing Team Toasted. It's hard to imagine what poor public image Team Dragon could be concerned with. Warfare in this time frame was beyond brutal. Forces sieging a city would hurl carcasses -- animal or human -- over the walls with the hope of starting an epidemic. When bio-war is your starting point, and you pay your troops with the promise of rape and pillage after a city falls, the leaders are not viewing the world through the same lenses of morality and ethics that we judge societies today. Given that Team Dragon is using the beast in the fashion of a very modern strategic air campaign the number of people that will come in direct contact with it will be small. Assuming some live to tell the tale, the fast strikes and their vulnerability to attack from the sky should cause the moral of draymen and teamsters moving the food and livestock to Team Toasted to be very low. And, if the War on Logistics of Team Toasted is effective, then troops the will likely be very demoralized as well. I would like this to the US invasion of Iraq in 1991. The month-long air campaign denied the Iraqi soldiers food, water, and fuel. When the ground attack came, most just gave up. If Team Dragon moves on a city or fortress after cutting off their resupply for a month or two, the city will likely be not inclined to sustain a siege they know they are going to lose. In the 13th century Scottish War's of Independence, the sight of the trebuchet Warwulf would cause fortified cities to surrender. There was no point in fighting if you had no chance of withstanding the siege. [![enter image description here](https://i.stack.imgur.com/bYKN2.png)](https://i.stack.imgur.com/bYKN2.png) So, how Team Dragon is perceived politically will be determined by the degree they use their winged WMD directly against the non-fighting folk of the lands that they are attacking. If they minimize the carnage and loss of life and property ‚Äî and it sounds like they are since they attacking Team Toasted‚Äôs supply trains ‚Äî then I‚Äôd think they‚Äôll be regarded more in the vane of Richard the Lionhearted or Henry the IV (Shakespeare‚Äôs version) and less like Vlad Tepes or William Longshanks (Braveheart version) [Answer] ## Who controls the spice dragon, controls the universe. The political troubles you have aren't going to be external. As usual, the threat is inside. The dragon represents a lot of concentrated military, and therefore political, power that resides more or less solely in its handlers. If they tell it to eat the king, will it do it? As the king, do you believe them when they say it wouldn't? Having a large, organized bloc of military force that can remove the government on a whim is, to put it mildly, not the most stable form of governance. For instance, it gave Rome the [Year of the Four Emperors](https://en.wikipedia.org/wiki/Year_of_the_Four_Emperors), mostly because of successive emperors displeasing the Praetorian Guard (nominally their bodyguards) and other legions, which led to them being deposed in short order. Your kingdom could easily devolve into a similarly troubled state. Any tension between the king (or other noble leaders) and the dragon's handlers could erupt into violence. The usual method of smoothing out these troubles is to have so many nobles that anyone who upsets the status quo will almost certainly be hauled back into line by the sheer numbers of the opposition... but in this case the opposition doesn't really matter. Only the dragon matters, at least if you want to continue sleeping in your own bed at night without worrying about a faceful of acid coming through the roof. Your international political outlook would be similarly rough. If you're the country next to the man-eating dragon, do you really trust them not to invade? Especially when their political situation starts looking dicey? And if you have the opportunity to remove that threat, say by covertly backing the nobles who want to kill the dragon handlers in their sleep, wouldn't you be tempted to take it? Having too much concentrated military force (viz, a dragon) in one place destabilizes the status quo that a medieval kingdom relies upon. People will fall over themselves to seize control of this power and use it on their rivals, before their rivals do the same to them. And since a dragon (unlike, say, a Roman legion) can't be disbanded or bought off, this cycle seems likely to continue until it dies or escapes into the wild... or someone manages to control a second dragon in a balance of terror. Edit: since @Nosajimiki was kind enough to point out to me that this question is about solutions rather than problems. If your world doesn't have enough dragons to go around, you can work on the next step, his handlers. If these people are actually calling the shots - and people trust that they can do that - then "all" you have to do is make them not partisan. Of course, this is easier said than done. One option might be to gather a diverse set of handlers from around the kingdom, say, one from each noble house. If each house thinks that their scions among the handlers will stop the dragon from attacking them, that might go some way towards calming their fears. However, this solution revolves around the dragon remaining passive if there are conflicting orders from multiple handlers. If the dragon doesn't, this could just make things more dangerous. Another option is to get someone completely outside the political squabbles of the kingdom. Mercenary fighters were popular for a lot of reasons, but one of them was that they didn't have any loyalty to any particular faction. As long as you paid them, they'd fight for whoever. (This was, incidentally, the eventual solution to the Praetorian Guard problem, with the Eastern Roman Empire phasing out elite local troops for foreign mercenaries like the Varangian Guard.) A group of mysterious foreigners also provides a simple answer to the question of why there aren't any other dragons around: this is the only one that's been brought this far into civilization. ]
[Question] [ (Note: This is a follow-up question to my previous one: [Moved into further orbits to protect them, how much damage do Earth and Moon take when the Sun expands?](https://worldbuilding.stackexchange.com/q/166627/61035)) Thanks to clever stellar engineering by a group of aliens (see below.), the Sun has been induced to end its red giant stage early by turning into a blue-white (B-type) subdwarf. These have lifespans of less than 200 million years, plus another 20-40 million as a bluer O-type subdwarf, before cooling toward the white dwarf stage. One of my questions on Astronomy.SE notes that sdB stars originate from main-sequence stars with mass in the range $0.5M\_{\odot} \leq M \leq 2M\_{\odot}$. Certainly our Sun is in that range, though I'm trying to find out if tighter bounds are known to astronomers! I'm assuming the subdwarf is a fairly typical star of that type. Mass between $0.29$ and $0.53M\_{\odot}$, surface temperature between 27,000 and 36,000 K (I don't know why stars at the higher end of that range weren't filed as O-type instead of B, but they exist.), luminosity $22.9-34 L\_{\odot}$, and the star is rotating (though as I type this, I don't have a range of values for just how fast to consult.) My question: *How soon after the red giant Sun lost its hydrogen envelope and turned into this star would it take for the damaged Earth from my previous question (which had been moved to a 1.15 AU orbit) to cool down enough that there is once again a solid crust, with continents people can walk on? (Probably wearing protective clothing.)* Notes: 1. The stellar engineering involved stealing either: * a gas giant similar to Saturn - but much larger, somewhere between 1 and 5 times the size of Jupiter, or * a brown dwarf. and parking it close enough to the main-sequence Sun to form a binary. The planet's core survived engulfment, but its presence inside the star caused the Sun to lose its hydrogen envelope prematurely, turning it abruptly from a red-giant into a B-subdwarf. This is what was meant to have happened with Kepler-70 (aka KIC 05807616). The exoplanets were the remains of the core or cores of the Hot Jupiter gas giants involved. Though more recent research has suggested that they may not in fact exist. 2. These are not the alien explorers from my previous question, they're another group. But the explorers have realised "This star shouldn't have reached the white dwarf stage so soon!" and are getting ready to travel back in time and find out what happened. 3. I do have some information on how long the Moon took to solidify when it was intially formed, thanks to a [2011 paper](https://www.higp.hawaii.edu/~gjtaylor/GG-673/Moon/Elkins-T%20et%20al_MO,petrology,ages(2011).pdf). According to this, 80% of the Moon's magma ocean solidified in about 1000 years, however the plagioclase crust that had formed atop it acted as a "conductive lid". Counterintuitively, this slowed the remainder of the cooling process down significantly. Tidal heating from the Earth slowed down the remainder of the process even more significantly, melting portions of the crust and causing new eruptions. The total time was approximately 220 million years, but would have been only about 10 million without the tidal effects. The 220 million may still be an underestimate - a later [2015 paper](https://websites.pmc.ucsc.edu/~fnimmo/website/Kamata_Moon.pdf) suggests that it may be roughly 300 million. In another question on this site, I discuss the geology of the exposed layer of the smaller moon. You can see it at: ([The Earth and Moon resolidify under a bluer star, their outer layers evaporated and burned away. What do they look like now?](https://worldbuilding.stackexchange.com/q/167234/61035)) In brief, the plagioclase is now burned away, and there isn't enough aluminium left in the iron-rich remains of the moon to form another plagioclase crust. From the [2011 paper](https://www.higp.hawaii.edu/~gjtaylor/GG-673/Moon/Elkins-T%20et%20al_MO,petrology,ages(2011).pdf), we discover that there isn't another way for the Moon to form a conductive lid, so the solidification process should now be faster than before. How much faster isn't clear, but the aforementioned papers plus [a 2010 paper](http://web.mit.edu/wisdom/www/coupled.pdf) and a paywalled 2008 paper suggest that even with the tidal effects it should be a few tens of millions of years at most. Sources: [Dorman, B., Rood, R., & O'Connell, R. (1993). Ultraviolet Radiation from Evolved Stellar Populations--I. Models. arXiv preprint astro-ph/9311022.](https://arxiv.org/pdf/astro-ph/9311022) For a version that includes the diagrams but doesn't allow you to select text, [see here](http://adsabs.harvard.edu/full/1993ApJ...419..596D). Elkins-Tanton, L. T. (2008). Linked magma ocean solidification and atmospheric growth for Earth and Mars. Earth and Planetary Science Letters, 271(1-4), 181-191. I'm afraid this one's paywalled. [Heber, U. (2009). Hot subdwarf stars. Annual review of Astronomy and Astrophysics, 47, 211-251.](https://web.archive.org/web/20110721003323/http://www.sternwarte.uni-erlangen.de/~heber/araa/araa_revised.pdf) There are also [slides](http://astro.physics.ualberta.ca/rockies14/sites/default/files/conference_presentations/u71_present.pdf). [Østensen, R. H. (2010). Observational asteroseismology of hot subdwarf stars. Astronomische Nachrichten, 331(9‐10), 1026-1033.](https://arxiv.org/pdf/1010.3214) [Meyer, J., Elkins-Tanton, L., & Wisdom, J. (2010). Coupled thermal–orbital evolution of the early Moon. Icarus, 208(1), 1-10.](http://web.mit.edu/wisdom/www/coupled.pdf) [Elkins-Tanton, L. T., Burgess, S., & Yin, Q. Z. (2011). The lunar magma ocean: Reconciling the solidification process with lunar petrology and geochronology. Earth and Planetary Science Letters, 304(3-4), 326-336.](https://www.higp.hawaii.edu/~gjtaylor/GG-673/Moon/Elkins-T%20et%20al_MO,petrology,ages(2011).pdf) [Charpinet, S., Fontaine, G., Brassard, P., Green, E. M., Van Grootel, V., Randall, S. K., ... & Telting, J. H. (2011). A compact system of small planets around a former red-giant star. Nature, 480(7378), 496-499.](http://www.astro.umontreal.ca/~doyon/PHY6795O/Revues/Revue5/Charpinet2011.pdf) This is the paper which announced the discovery of the Kepler-70 exoplanets, before research in later years provided a strong counterargument and suggested that they didn't in fact exist. It also reveals that Kepler-70 has been a B-subdwarf for 18.4 million years so far. [Bear, E., & Soker, N. (2012). A tidally destructed massive planet as the progenitor of the two light planets around the SDB star KIC 05807616. The Astrophysical Journal Letters, 749(1), L14.](https://arxiv.org/abs/1202.1168) This is the one that suggested the Kepler-70 exoplanets might not be the remains of two separate Hot Jupiter gas giants, but one. The theory being that the core of that planet did not completely survive engulfment, and was split into two. [Suckale, J., Elkins‐Tanton, L. T., & Sethian, J. A. (2012). Crystals stirred up: 2. Numerical insights into the formation of the earliest crust on the Moon. Journal of Geophysical Research: Planets, 117(E8).](https://sigma.stanford.edu/sites/g/files/sbiybj11581/f/publications/suckaleetal_stirredcrystals2_jgr2012.pdf) [Schindler, J. T., Green, E. M., & Arnett, W. D. (2015). Exploring stellar evolution models of sdB stars using MESA. The Astrophysical Journal, 806(2), 178.](https://iopscience.iop.org/article/10.1088/0004-637X/806/2/178/pdf) This one's particularly relevant to the question of Subdwarf B lifespans. [Planetary candidates around the pulsating sdB star KIC 5807616 considered doubtful. J. Krzesinski A&A, 581 (2015) A7 DOI: https://doi.org/10.1051/0004-6361/201526346](https://doi.org/10.1051/0004-6361/201526346). This is the one which provided evidence that the things which had seemed to indicate exoplanets in 2011... probably didn't. As someone who loves the idea of planets orbiting blue stars, you have no idea how disappointed I was to read this! [Kamata, S., Sugita, S., Abe, Y., Ishihara, Y., Harada, Y., Morota, T., ... & Matsumoto, K. (2015). The relative timing of Lunar Magma Ocean solidification and the Late Heavy Bombardment inferred from highly degraded impact basin structures. Icarus, 250, 492-503.](https://websites.pmc.ucsc.edu/~fnimmo/website/Kamata_Moon.pdf) [Heber, U. (2016). Hot Subluminous Stars. arXiv preprint.](https://arxiv.org/abs/1604.07749) [Sleep, N. H. (2016). Asteroid bombardment and the core of Theia as possible sources for the Earth's late veneer component. Geochemistry, Geophysics, Geosystems, 17(7), 2623-2642.](https://doi.org/10.1002/2016GC006305) [Deca, J., Vos, J., Németh, P., Maxted, P. F. L., Copperwheat, C. M., Marsh, T. R., & Østensen, R. (2018). Evolutionary constraints on the long-period subdwarf B binary PG 1018–047. Monthly Notices of the Royal Astronomical Society, 474(1), 433-442.](https://arxiv.org/pdf/1710.07327) [Analysis of putative exoplanetary signatures found in light curves of two sdBV stars observed by Kepler. A. Blokesz, J. Krzesinski and L. Kedziora-Chudczer A&A, 627 (2019) A86 DOI: https://doi.org/10.1051/0004-6361/201835003](https://doi.org/10.1051/0004-6361/201835003) [Answer] Okay... it's not a precise answer, but here goes. I'll start by discussing my research into the Moon's solidification, since it's relevant, especially as the Moon took longer to solidify than the Earth originally. (I edited all this into the question as supporting information.) Then I'll go from there to the case of the Earth. According to a [2011 paper](https://www.higp.hawaii.edu/~gjtaylor/GG-673/Moon/Elkins-T%20et%20al_MO,petrology,ages(2011).pdf), 80% of the Moon's magma ocean solidified in about 1000 years. However, after this point, the plagioclase crust that had formed atop it acted as a "conductive lid". Counterintuitively, this slowed the remainder of the cooling process down significantly. Tidal heating from the Earth also slowed down the remainder of the process significantly, melting portions of the crust and causing new eruptions. The total time was somewhere roughly in the time range of [220 million years](https://www.higp.hawaii.edu/~gjtaylor/GG-673/Moon/Elkins-T%20et%20al_MO,petrology,ages(2011).pdf) to [300 million years](https://websites.pmc.ucsc.edu/~fnimmo/website/Kamata_Moon.pdf). If the tidal effects were not present but the conductive lid was, it would only have been [about 10 million years](https://www.higp.hawaii.edu/~gjtaylor/GG-673/Moon/Elkins-T%20et%20al_MO,petrology,ages(2011).pdf). I don't have any figures for a situation where the tidal effects are present but not the conductive lid. In another question on this site, I discuss the geology of the exposed layer of the smaller moon. You can see it at this link: [The Earth and Moon resolidify under a bluer star, their outer layers evaporated and burned away. What do they look like now?](https://worldbuilding.stackexchange.com/q/167234/61035) In brief, the plagioclase is now burned away, and there isn't enough aluminium left in the iron-rich remains of the moon to form another plagioclase crust. From the [2011 paper](https://www.higp.hawaii.edu/~gjtaylor/GG-673/Moon/Elkins-T%20et%20al_MO,petrology,ages(2011).pdf), we discover that there isn't another way for the Moon to form a conductive lid, so the solidification process should now be faster than before. How much faster isn't clear, but the aforementioned papers plus [a 2010 paper](http://web.mit.edu/wisdom/www/coupled.pdf) and a paywalled 2008 paper ("Linked magma ocean solidification and atmospheric growth for Earth and Mars.") suggest that even with the tidal effects it should be a few tens of millions of years at most. I don't feel able to use a stronger word than "suggest", though. According to a [2012 paper](https://wesfiles.wesleyan.edu/courses/E&ES-471-mgilmore/Elkins-Tanton2012.pdf), these conductive lids aren't expected to form on most planets. In addition, [a 2005 paper](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.466.4451&rep=rep1&type=pdf) shows in Table 3 that the Earth's mantle doesn't have much aluminium in it to form a plagioclase lid anyway. (I should warn you, Table 3 of that paper can be a bit hard to understand - I've posted on a Wikipedia talk page because I thought it contradicted something in that article, when in fact it didn't.) Moving from the Moon to the Earth, we now come back to our 2008 paper, "Linked magma ocean solidification and atmospheric growth for Earth and Mars." This one is behind a paywall, and if anyone has a non-paywalled link to it, please edit it into this answer! It's a very highly cited and interesting paper that I think will be of interest to several worldbuilders. Table 3 of that paper (Ooh, we've got a lot of Table 3s here!), in a case where there's no initial $H\_{2}O$, gives various scenarios relating to the depth of the magma ocean and the amount of $CO\_2$ in the atmosphere. Importantly, some of these cover cases where there's no water vapour in the atmosphere or magma ocean. The Earth takes longer to solidify in these cases, carbon dioxide being a more powerful greenhouse gas than water vapour. But anyway, the longest the Earth takes to reach 98% solidification in these is 5.3 Myr. (Mars takes 2.8 Myr under similar conditions.) It's said that it should be at least five million, and at most some value on the order of tens of millions of years, to reach "clement" conditions after that's happened. The no-water-vapour case wasn't one of a few cases modelled in more depth than the others, but the paper does seem to be referring to all possible cases when it claims this, especially in the abstract at the start. With the lid, [the 2010 paper](http://web.mit.edu/wisdom/www/coupled.pdf) by Elkins-Tanton et al explicitly states that the Moon took longer than the Earth to resolidify, and that the lid was the reason. That language suggests that without the lid, the tidal effects wouldn't have slown down the Moon's cooling by enough to keep it molten much longer than the Earth. As seen in my comments on Zeiss Ikon's answer, the smaller blue Sun is probably supplying less than a third as much heat to the Earth and Moon as before. A typical B subdwarf with 1/5 the Sun's radius has 1/25 the surface area. They are hotter - the Sun has $5772K$ surface temperature, the hottest sdB star I know about has $\leq 36,000K$, and that's a 6.237-fold temperature difference, but once you divide that by 25 you get about 0.25. Now, I have seen an unsupported claim that O-type subdwafs can go up to 100,000K, but even then the reduced surface area means that it's still supplying less heat to Earth than the original Sun did. (Only about 0.693 times as much as before). So that should also help the Earth cool and solidify faster than it did the first time. As should the fact that there's no Theia impact or Late Heavy Bombardment this time. Finally, we take another look at the [2012 paper](https://wesfiles.wesleyan.edu/courses/E&ES-471-mgilmore/Elkins-Tanton2012.pdf) I mentioned earlier. In section 5, the author makes the assumption that it took Earth roughly 50 million years to cool down to "clement" (inc. solid) conditions after the Theia impact. I don't know if there's a scientific consensus on whether Earth actually had solidified prior to the Theia impact energy melting the crust again, though. Figure 7 gives a total cooling time of 55 million years, relying on a very steep temperature dropoff in the final 5 million. I think I may have to increase this for the no-water-vapour atmosphere, though, especially if a carbon dioxide atmosphere isn't convective enough. Anyway... at this point, there's a lot of evidence for "on the order of tens of millions of years" as the answer for full solidification, although I don't think it's proven conclusively for this particular scenario. And for large amounts of partial solidification but a world too hot for humans to inhabit unprotected, it's even less, 5.3 million years at most, maybe sufficiently solid in only 1000 years! So my answer is "on the order of a few tens of millions of years, probably quite a bit less than 100 million years, but even then I'm still not 100% sure." Sources: [Workman, R. K., & Hart, S. R. (2005). Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters, 231(1-2), 53-72.](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.466.4451&rep=rep1&type=pdf) Elkins-Tanton, L. T. (2008). Linked magma ocean solidification and atmospheric growth for Earth and Mars. Earth and Planetary Science Letters, 271(1-4), 181-191. I'm afraid this one's paywalled. [Meyer, J., Elkins-Tanton, L., & Wisdom, J. (2010). Coupled thermal–orbital evolution of the early Moon. Icarus, 208(1), 1-10.](http://web.mit.edu/wisdom/www/coupled.pdf) [Elkins-Tanton, L. T., Burgess, S., & Yin, Q. Z. (2011). The lunar magma ocean: Reconciling the solidification process with lunar petrology and geochronology. Earth and Planetary Science Letters, 304(3-4), 326-336.](https://www.higp.hawaii.edu/~gjtaylor/GG-673/Moon/Elkins-T%20et%20al_MO,petrology,ages(2011).pdf) [Elkins-Tanton, L. T. (2012). Magma oceans in the inner solar system. Annual Review of Earth and Planetary Sciences, 40, 113-139.](https://wesfiles.wesleyan.edu/courses/E&ES-471-mgilmore/Elkins-Tanton2012.pdf) [Suckale, J., Elkins‐Tanton, L. T., & Sethian, J. A. (2012). Crystals stirred up: 2. Numerical insights into the formation of the earliest crust on the Moon. Journal of Geophysical Research: Planets, 117(E8).](https://sigma.stanford.edu/sites/g/files/sbiybj11581/f/publications/suckaleetal_stirredcrystals2_jgr2012.pdf) [Kamata, S., Sugita, S., Abe, Y., Ishihara, Y., Harada, Y., Morota, T., ... & Matsumoto, K. (2015). The relative timing of Lunar Magma Ocean solidification and the Late Heavy Bombardment inferred from highly degraded impact basin structures. Icarus, 250, 492-503.](https://websites.pmc.ucsc.edu/~fnimmo/website/Kamata_Moon.pdf) [Sleep, N. H. (2016). Asteroid bombardment and the core of Theia as possible sources for the Earth's late veneer component. Geochemistry, Geophysics, Geosystems, 17(7), 2623-2642.](https://doi.org/10.1002/2016GC006305) [Answer] Given that the inner Solar System has been pretty thoroughly cleaned by the swollen red giant phase of the Sun's senescence, there could be no Late Heavy Bombardment to remelt the intial crust that begins to form almost immediately after the engulfment that cause the melting is halted. Whatever primordial crust Earth had predated the Moon-forming event. We have no Theia impact to form the Moon (in the process, completely or almost completely remelting the Earth), no (currently in dispute) millions of years of asteroidal bombardment -- in fact, I'd question whether the existing crust would melt completely from a few million years orbiting inside the fairly rarified (albeit pretty hot) outer envelope of the Sun. [Dating of the oldest known rocks](https://www.sciencedirect.com/science/article/pii/S0009254119304280) on both Earth and Moon suggests the Earth had begun to reform a crust less than a hundred million years after the Theia impactn -- and given that nearly all of that "second crust" has since been recycled by erosion and subduction, that figure might well have been much shorter. On that reasoning, I'd say there ought to be a solid surface to land and walk on within, at most, a few million years of the Sun's induced sub-dwarf collapse (because of the small radiating surface, the radiation of the blue to blue-white sub-dwarf would be trivial compared to the cooling effect of the magma surface radiating to space). Fresh magma flows form a weight bearing crust in days or weeks, though that surface is still hot enough to melt boot soles for many times that span. The far deeper heat beneath the surface of a fully melted crust would extend that figure significantly, but rock isn't a very good heat conductor -- hence why there are still rocks hot enough to boil water hundreds of thousands of years after the most recent eruption at Yellowstone. Best wear heavily insulated vacuum suit boots; the ground will be nearly as hot as the crust on a fresh magma flow. Also be careful where you land, as there might be thin spots in the crust that aren't up to supporting a starship or heavy lander, and plate drift might locally be real-time visible. ]
[Question] [ Taking into account the some limitations of the square-cube law, biology, and aviation, I have tried to make a dragon-like creature and a hominid that participate in a symbiotic relationship. For starters, the dragon is reptilian, and related to varanids (possibly in the varanoidea superfamily). In particular, I researched varanoidea as an evolutionary candidate because of the air-sac like structures seen in varanids and already impressive and diverse evolutionary history (if mosasaurs could take to the sea, with a little hand-waving, perhaps these guys could take to the air.) I would call the dragons wyvern-like and small, compared to other fictional beasts. For the sake of stats, I would put their general size and weight in the category of quetzalcoatlus (150-250kg mass and a wingspan of around 11m). I would say that convergent evolution would be our friend here, as most characteristics are similar to that of quetzalcoatlus, save for the tail and head anatomy. These varanid-like dragons have an aerodynamic, flattened tail and a squamate-based head. Perhaps the wings could be larger, but I would like to leave a lot of physiological qualities vague and up to interpretation because I suck at math, and I'm not any kind of aviation specialist. For takeoff, the creatures could probably vault themselves into the air using their wings, and because the largest 'dragon' species live in alpine environments, they could rely on the altitude to take off from peaks over valleys as well. One crucial detail for the dragons is their ability to lift prey. They generally prey on goat-like animals such as tahr and sheep that are typically less than 45kg. This is the characteristic that I expect would help the case of dragon riders. Only the mature adults would make good mount material. The riders themselves are smaller than humans with the larger men usually less than 55kg. They are human-like primates that have adapted to high altitude environments, hence why taking a ride on a dragon's back may be alright for them. TL;DR: Could tiny people ride a quetzalcoatlus thing? Considering physics and biology (I'll save the issues of taming the 'dragons', culture, saddles, etc. for later), would these tiny people be able to ride these wyvern-like beasts? Could the weight the dragons would have to endure be too great for powered flight? As far as handwaving goes, a little is welcome if needed as you see fit, but the more scientifically plausible, the better. Of course, if no math could line up and/or this is completely unsalvageable science-wise, please do say so. [Answer] Your dragon riders are children. The largest dragons can carry some extra weight, but not too much more and not for any great length of time. A 20 kg child, however, is not a great strain. These are 6 and 7 year olds. From the time children can walk they are around the dragons, riding them with their older brothers and sisters until they are strong enough to ride alone. The riders are immensely valuable to their society during the few years that they are small enough to ride. They know it and they take it seriously. But they are still kids, and sometimes they mess around. [Answer] The general rule of thumb for eagles is that they can carry up to half their own body mass in prey. <https://www.quora.com/What-is-the-maximum-weight-a-bird-can-carry-while-flying> This means that a 250kg mass dragon can probably be physically handwaved to carry a 55kg adult warrior, plus equipment. The bigger concern is probably how such an animal might be tamed enough to be ridden. One suggestion could be that these dragons typically carry young on their own back until they ready to fly on their own, and so a rider-dragon relationship might develop out of the humanoids playing the role of the young, especially seeking out female dragons that have failed to breed for whatever reason. ]
[Question] [ I wish to create a world such that it can support the following plot point: the world experiences gravitational waves that are directly noticeable to the human population (i.e. they can feel or see the effects themselves without instruments) without being so strong that everything gets spaghettified. The most obvious way to arrange this seems to be to have a pair of black holes undergo a merger at a suitable distance: not so close that everything gets ripped apart, and not so far away that the gravitational waves have become un-noticeably weak. My question has 2 parts but they are directly related so it wouldn't make sense to split this into 2 separate questions: (a) assuming a pair of 30 solar mass black holes as detected the other year by LIGO, what distance from the event would provide gravitational waves of the weird but not deadly strength that I need; and (b) at such a distance from the event, would you be safe from other consequences of the black hole merger, or would something else such as the intensity of high energy particle emissions kill you anyway? I'm open to any kind of habitat for my world, it could be a planet or a deep space habitat or generation ship or whatever. If the gravitational waves would rule out particular kinds of world then I'd be keen to hear why (e.g. maybe waves strong enough to be noticeable to humans would shatter a planet but a space habitat might be small enough to survive). In my story I may make limited use of unobtainium for interstellar travel, but I want the physical effects of the black hole to be as hard science as possible. If a black hole merger is out of the question as too dangerous, I'd be happy to receive reality-check level suggestions of alternative events that could safely create the kind of noticeable gravitational wave I want. [Answer] I think I can now answer my own question, having come across some decent references I hadn't found before asking it. I found the equation for the gravitational strain $h$ - the proportional change in length of an object due to gravitational waves from a mass $M$: $$h \approx {{GM} \over c^2} \times {1 \over r} \times {v^2 \over c^2}$$ [(Source of formula)](http://www.tapir.caltech.edu/~teviet/Waves/gwave.html) The first term is of the order of the size of the black hole, or about 45 km for a 30 solar mass ($M\_{\odot}$) black hole. Near collision the black holes move close to the speed of light so the last term is $\approx 1$. Then the strain falls off as $1 \over r$, so even if you could sense a brief stretching of 1 part in 10,000 (about 0.2 mm along the length of your body) you would need to be 450,000 km (about 1.9 times the average distance between Earth and the Moon) from two 30 $M\_{\odot}$ black holes orbiting each other at near light speed. My takeaway is really just how weak gravitational waves are for the amount of energy that goes into them (for the LIGO 60 $M\_{\odot}$ collision about 3 $M\_{\odot}$ was converted from mass energy into gravitational waves). For an object orbiting 60 $M\_{\odot}$ at that distance the orbital period would be 11.2 minutes. The gravitational tidal acceleration across a body of length d is given by: $$a={{2 G M d} \over {r^3}}$$ which works out as 5.8 micronewtons, so the astronauts would be safe from spaghettification at a range where they could experience noticeable but not intrinsically fatal gravitational waves. At that distance I guess it's still highly likely radiation from accreting matter would be fatal, so my scenario would rely on the black hole pair being located in an almost perfect void, which leads to other questions (how did they end up in such a perfect void, how did the characters end up at just such a perfect distance from them?) (Edited to remove erroneous statement about centripetal acceleration.) [Answer] When gravitational waves reach Earth, [they usually give a strain](https://en.wikipedia.org/wiki/Gravitational_wave#Difficulties) of $\delta L \over L$$=10^{-21}$. If we assume that they scale with the distance the same way electromagnetic waves do, thus following the inverse square law, we can get an estimate of the distance needed. LIGO detected the [first merger](https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves) of black holes at 1.3 billion light years away. If we would get to 1 light year away from the merger, under the above hypothesis we would get a strain of $10^{-21} \times (1.3 \cdot 10^9)^2=10^{-3}$. This means that on 1 meter length we would notice a 1 mm oscillation, which is something we are able to sense. On the other hand, supernova explosions are lethal well beyond 1 light year, and though extremely powerful they are probably tiny when compared with black hole merger. Wrapping up, there is probably a distance at which our body can feel gravitational wave produced by merging black holes, but that feeling would probably we quickly swept away by a shower of high energy particles, unless the two black holes have both no accretion disk. Addendum after Starfish Prime's comment: If instead the scaling goes like $1/r$, then at a distance of 1 light year the strain would be $10^{-21} \times (1.3 \cdot 10^9)=10^{-9}$. Thus too low. To make it back to $10^{-3}$ the observer would need to be to $1/1000$ of a light year, or $9 \cdot 10^9$ km, twice the distance between Neptune and the Sun. ]
[Question] [ Is there a way to make retractable tusks anatomically plausible in a creature design without relying on an articulated bone structure? Basically, relying fully on musculature instead of articulation like a cat's retractable claw. The tusks would be able to slide in and out of the creature's mouth through sheaths near the gums, maybe leaving the tips exposed rather than sheathing fully. An articulated structure would completely break the evolution line for vertebrates in my headworld, so I really wanted to avoid that. Update: based on the comments and also feedback from a friend of mine, I thought about this: * Given the tusks would be used mainly for threat display and defense, they aren't functional for eating and/or killing prey. Their function is more comparable to appendages such as stingers and spikes. This means they don't need to be anchored in the jawbone and instead can be stored in a very thick, bulky head/throat separately. * The muscles would work like a mix of the retracting musculature you see in [bird tongues](https://www.birdwatchingdaily.com/wp-content/uploads/2013/12/Flicker-Tongue-660x403.jpg) and [pharyngeal jaws](https://upload.wikimedia.org/wikipedia/commons/c/c2/Pharyngeal_jaws_of_moray_eels.svg), though a bit simplified. It's a matter of a muscle pulling it forward and a tendon pulling it back to the resting position naturally. * In order to prevent the tusks from being pushed back, they would slide in at a slight angle and lock into a crevice of the jaw, similar to how horses lock their legs to rest standing up. There would be a little muscle that pulls the tusk back to the straight alignment which allows the tendon to bring it back into resting position [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. Would natural gears be acceptable? If so, the tusk could be drawn/withdrawn through a gear slider mechanism. Hope this helps :) <https://www.youtube.com/watch?v=Q8fyUOxD2EA> (Edit for clarification) Sorry about that Lilian and Dutch (I am new here). A "gear slider mechanism" is a term used to describe a gear rotating that activates another gear attached to a rod in such a way as to slide the rod back and forth. in your case the gears could slide not a rod but a tusk back and forth, with the halting of the gears determining the length of exposed tusk. Depending on what you mean by articulated bone structure this may or may not be valid. This is partially present in nature already as bodily functions of some bugs have these partial gear shapes to aid in certain locomotions. Since it would be difficult for a fully circular gear to operate in nature these are partial gears that work in a shorter distance but no less effectively. A google search of "Gear Slider Mechanism" will bring up various simple videos of this (<https://www.youtube.com/watch?v=CbFPxpRHyRI>), including external and internal variations. Hope this clarified it somewhat :) Edit again: [![I drew a very crude and not to scale picture with what abysmal Paint skills I have.](https://i.stack.imgur.com/En8Fm.png)](https://i.stack.imgur.com/En8Fm.png) More info. This is basically the "Gular sac" of a cone snail with the "radula harpoon" being replaced by a tusk fired with a combination of the "ballistic energy" of both the potential energy barely being held back by the tendons and the modified natural counter rotating mechanical gear of certain jumping insects (Planthoppers) used an "Internal gear slider mechanism". These two types of potential energy could result in a lightening fast and powerful thrust of a tusk that would not be pretty to be hit by. Essentially a sharpened jackhammer that would hit once and slowly build the potential energy back up for the next strike. This all is of course poorly explained and probably not feasible for an obvious reason im missing entirely but this would be pretty d--n awesome if it was accurate and compact enough to fit in the throat,base of jaw, roof of mouth...etc. all the quotated words are google searches or at least they were for me. Im done haha [Answer] The [Onychodus](https://en.m.wikipedia.org/wiki/Onychodus), a prehistoric fish, had a pair of laterally compressed tusks at the front of the lower jaw. These tusks were not attached to any other bone, but fit into a pair of deep cavities on the palate and were free to move. The lower jaw was connected with the upper jaw in a way that made the tusks thrust out as a dagger when the head was raised. So yes, it is possible. [Answer] Moray eels have a second set of jaws (pharyngeal jaws) in their mouth which they can retract with muscles. Or rather, the retracted position is the normal condition, and they can extrude the jaw to grab an unfortunate victim. But still, the mechanism is the same. [![enter image description here](https://i.stack.imgur.com/Tuwjz.jpg)](https://i.stack.imgur.com/Tuwjz.jpg) So, since these are only tusks, you can do away with a few of the muscles that morays use to open and close their jaws. In the end, you only really need 5 of the eels' muscles - 3 for protracting and 2 for retracting. Those muscles are the levator internus and externus and the rectus communis to pull the tusk out, and then the dorsal retractor and pharyngocleithralis for pulling it back in. So, there is the mechanism by which your creatures will retract their tusks without any osteological articulation. Needless to say, the muscles involved don't have to be literally homologous with the fish muscles of the same name, they just need to resemble them and function similarly. [Answer] Well as you mentioned, cat’s claws function in a similar way. It is not too great of a leap to assume this would be possible with tusks. Plausible is a different story though. However, i suggest retractable gums rather than tusks. The tusks themselves would stay in place, attached to the jaw. The muscles in the gums would contract, and pull upwards, revealing the tusks which could now be used. The tips of the tusks may protrude past the gum line, assiting in eating, but when the tusks are needed to attack, the gums would be able to move to unsheath the tusks (similar to how you move your lips to bare your teeth). ]
[Question] [ In actual history, the Supreme Court ruled in 1971 in New York Times v. US that prior restraint is illegal, upholding its earlier decision in 1931 in Near v. Minnesota. In my alternate history, the Supreme Court rules that the US does not have to prove that publication would cause irreparable harm to national security in order to prior restrain publication. This does not overturn Near v. Minnesota, but rather broadens the scope of its exceptions. Nixon, still fearing a left-wing radical conspiracy to delegitimize his administration following the publication of the Pentagon Papers, sends a bill to Congress called the News Management Act. This calls for the creation of the Department of News Management (henceforth DNM), which would require all newspapers to submit their copies and get pre-approval from the government before publication. Likewise, news channels need to send scripts to the government before going to air. If they report without pre-approval, they risk being shut down. This gets approved in late 1973.1 Of course, the newspapers sue on the grounds of violation of the First Amendment. Shortly before the Watergate break-in, the Supreme Court rules that the DNM is legal, as it only prevents national security-related matters from being published; all other articles are still able to be published, and so freedom of the press is preserved. The government being the government, this freedom is used for political gain, under the guise of national security. ("If that person gets elected, the whole country will be invaded by Commies!") And how can anyone complain - what are they going to do, print it in the papers? That would delegitimize the sitting President, leading to national security issues. The first major change would be Nebraska Press Association v. Stuart in 1976, where, in actual history, the Supreme Court ruled that, since prior restraint is illegal, the media is free to print whatever they want about ongoing court cases without worrying about influencing the jury. Because in this alternate timeline prior restraint is perfectly legal for "national security," the government is free to influence cases by choosing which ones the news can report on. As a corollary to the previous point, I don't think Chappaquiddick (which I'm aware happened before Nebraska) or Whitewater would have ended differently. Neither Nixon nor Bush 41 would feel it's worth censoring. Nixon probably would make sure that Chappaquiddick gets aired so that Ted Kennedy doesn't run in '72 and '76, as actually happened. Really, I think history would overall remain the same (except for the public distrust of the media) until the late 2000's, with the advent of social media. Now people are getting their news online in the masses. The government doesn't like this loophole and passes the Internet News Management Act in 2007, extending the DNM's censorship to the Internet. This means that any news site or social media platform must be moderated by the government before anything is published. As the Internet gets larger and larger, the government struggles to keep up. A new division of the DNM is opened to work on this problem specifically. Because of this new problem, AI research is advanced by several years, and in late 2012, the DNM begins to employ new algorithms to help with the monitoring. The entire Internet is monitored by early 2016. Websites operating inside the US are blocked from publishing certain content and are taken down if they find a way to bypass the filters. Ones operating outside the US are simply blocked from entering. Because the Internet, television, and print media are all being censored, Snowden no longer has a way to send PRISM to the masses in 2013, and we remain in the dark about the NSA's spying. (He could post it on blogs or whatever, as it's not until 2016 that the entire Internet is moderated, but it wouldn't become as widespread.) I think the privacy vs. security debate would start eventually, probably with 2016's San Bernardino case. The one thing I'm unclear about is the 2016 election. There's no more election meddling, and I strongly believe that, because of Obama and Clinton's relationship, the media would be heavily slanted to the left at that point. What I'm unclear about is how this impacts the election: does Clinton now get elected, or would those who'd vote for Trump anyway still land him the majority in the electoral college? 1In an earlier draft, I said that the DNM was established fairly quickly, in early 1972. At first I thought that Watergate would happen pretty much the same way; the only thing that changes is that Woodward and Bernstein are unable to publish their articles in the Post about it. The burglars still plead guilty to perjury under pressure, and the case is led toward Nixon, who eventually resigns. However, I'm not sure anymore how important the Post's articles were, and to avoid this issue, I'm now saying that since bureaucracy takes time, the DNM doesn't get established until later 1973 - after Watergate has already sufficiently broken that covering up the story makes him look worse. Nixon still resigns in 1974, succeeded by Ford. --- My main question is: is this a plausible timeline resulting from the Supreme Court ruling that prior restraint is legal? I'd especially like to hear the legal ramifications of this, as while I've done a bit of legal research, is it likely that the theoretical 1972 lawsuit regarding the legality of the DNM would be ruled in favor of the government, given that the Pentagon Papers ruling was also ruled in favor of the government? --- Some of you in the comments theorized that the Presidents elected in the interim may not have been elected in such a world. I'll have to look into their respective platforms, and especially their relationships with the candidates of the succeeding elections, but at the moment I feel secure in saying that, besides the 2016 election, the Presidential roster remains the same. [Answer] The timeline is plausible (even if the premise is questionable). I don't see any catastrophic issues with the details of your timeline as you've laid it out. So in short, my answer to your question is yes. I'm sure you'd like some more feedback than that, though. So first, here's a few points I would like to address about your scenario: 1. "Neither Nixon nor Bush 41 would feel it's worth censoring." Politicians will do whatever benefits them politically. If the fallout from censoring is less than the fallout from not censoring, they will choose the former if it's within their power. 2. The government already has tools to to examine Internet data, and it would be possible to pass laws to further ease their ability to do so. For example, requiring network hardware manufactures to include software allowing government back door access into systems (which is obviously a potential weakness that a third party could exploit). Such technology already exists so it's demonstrably possible. Enforcing the use of "government approved" network hardware could involve validation of this software's existence in internet requests. It would still be possible to fool, but it's a potential element to consider. But that doesn't stop sources outside the US from releasing the information. The government would still block anything it didn't like regardless of it's point of origin, but there's nothing stopping Snowden from bringing a flash drive to a WikiLeaks-esque organization based outside of the US for the rest of the world to see. And once something's out of the bottle, it's hard to put it back in. 3. The 2016 election outcome: Tough to say. For starters, you can be sure that essentially any and all of the negative press Sen. Clinton received for her ill-advised communication practices would have been quashed. Speaking generally, I would incline toward a left-leaning press having an even easier time propping up liberal candidates and negatively portraying conservative candidates (that is to say, objectively speaking, the majority of news media tends to lean toward the liberal side of things, and I'm assuming the political climate in your scenario is comparable to our present day environment). So, if you would prefer a Clinton victory in your story, it would be believable, though I still see it being a tight race. Personally, I would think a Trump victory was still likely; without any smoking guns from some particularly shady hypothetical dealings by the Trump campaign, I feel the US is too polarized at this point for almost anything to sway too many people one way or the other, but serious enough matters could still affect turnout. Now, the premise itself of more lax prior restraint restrictions is problematic. Something like a News Management Act is inherently against the spirit of the First Amendment. It's not an accident that that's the first amendment in the Bill of Rights. Don't underestimate the importance of protecting speech in America, throughout its history. (I can easily imagine a heated debate among your bill's authors over whether the very term "news management" itself would garner too much public opposition.) I would suggest that in order to make this scenario more believable, you devise some new occurrence (or alter the details of New York Times v. US) to create a situation not directly related to national security, yet with a strong possibility of an indirect implication that is difficult to prove with certainty, yet significant enough to lead the court to decide to play it safe. This might be a good explanation for an alternative ruling to the 1971 case or something like it. All in all, this is a very thoughtful scenario, and certainly a plausible one for a work of fiction. I encourage you to continue with it. Well done! ]
[Question] [ This question already has answers here: [Could a gas giant's moon have stable rings?](/questions/96187/could-a-gas-giants-moon-have-stable-rings) (4 answers) Closed 3 years ago. I'm currently fleshing out a sci-fi universe and always looking for fun new locales to populate it with, and I saw this phenomenon in a video game I've been playing recently, and it made me curious... the world on which the story takes place appears to be Earth-Like (albeit the setting is a fantasy one), but when you look at the moon, it seems to have very faint "rings" made of dust or particulate, like Saturn's; however, as far as I can tell, the actual main PLANET doesn't have rings of its own? While I'm not certain that an Earth-Like planet with an Earth-Like Moon would have the right kind of gravity or positioning for this to occur, I was wondering what sort of planet/moon arrangement might be able to cause a Moon with Rings. Is it even possible? Or would the host planet's larger gravity well prevent the moon from gathering enough stuff in its orbit for visible rings to form? (The planet doesn't need to be habitable by humans or anything, I just want to know if this effect could be plausibly caused ANYWHERE, by ANY means, or if this was just a touch of whimsy on the game developer's part XD). [Answer] Saturn’s moon Rhea [may have rings](https://en.wikipedia.org/wiki/Rings_of_Rhea), and while it’s not been confirmed, the fact that astronomers are considering it shows that they believe it’s possible for a moon to have rings. ]
[Question] [ How could I calculate the habitable bounds, in relation to temperature, near the twilight zone of Gliese 667 Cc? Assuming an Earth-like atmosphere and no tidal working. Here are the numbers that I have been using: * Parent star Temperature = $3350\text{ K}$ * Distance from star = $25.4\times10^6\text{ km}$ * Radius = $9\,800\text{ km}$ * Surface area = $1.2\times10^9\text{ km}^2$ I have little experience in astrophysics, or basic physics for that matter, so my understanding of heat dissipation through space is poor at best. In my mind, since I have the temperature of a heat source, a distance to the center of the planet, and the planet's farthest points from the center (25.4 million km ± 9,800 km), it wouldn't be difficult to calculate if you understood radiant flux and such. [Answer] ## Radiant Power Equilibrium Per Stefan-Boltzman $$ {P \over A} = \sigma T ^4 $$ Where: * P/A = watts per meter squared of radiated power * $\sigma$ is the Stefan-Boltzaman constant, $5.67 \times {10^{-8}} {W m^{-2}} {K^{-4}}$ * T is temperature (in Kelvin). 3,350 K in your original post That is the power emitted ($7.1 {MW \over m^2}$) at the surface of the star, which for Gliese 667C is $.42 R\_{sun}$, about $2.92 \times 10^8 m$ Area expands as a factor of $r^2$, but at $25.4 \times 10^6 km = 2.54 \times 10^7km = 2.54 \times 10^{10} m$. Dividing the distance by the radius to the surface of Gliese667C(c) gives ${2.54 \times 10^{10}} \over {2.92 \times 10^8}$, or very roughly 100 $R\_{surface}$ There is a shortcut that will eliminate our need for calculating that wattage. Get the cross-sectional area of Gliese 667C(c) $ A\_{cross} = \pi r^2 $ Get the surface area of Gliese 667C(c) $ A\_{surf} = 4 \pi r^2 $ We don't actually need to calculate either of those values because what's important is $ P\_{absorbed} \over P\_{radiated} $ which is a function of cross sectional area on the top half, and surface area on the bottom half. So, the equilibrium Wattage is one-quarter the absorbed amount. Putting it all together : $ {1 \over {4 \dot (100)^2}} \sigma T\_{star}^4 = \sigma T\_{planet}^4 $. Lose the $ \sigma $ and calculate $ \sqrt[4] {(3,900K) ^4 \over 40,000}$. The result I get is about 295 degrees Kelvin ## Gravity and Gasses The next important thing is to calculate the gravity of Gliese667C(c) and figure out, for the temperature what kinds of gasses the planet can hold on to. Like Mars and Venus, the planet may be in the process of venting away lighter material. The escape velocity is $\sqrt { 2 G {M \over R} },$ where $$\begin{align} \text{G} &= 6.67 \times 10^{-11}\\ \text{M} &= 3.7 M\_{earth} (5 \times 10^{24} \text{ kg}) = 1.85 \times 10^{25} \text{ kg}\\ R &= 9800 \text{ km} = 9800000 \text{ m} \end{align}$$. Escape velocity would be 17 km/s. Since that is much than the escape velocity for Earth, but your temperature is roughly the same, it stands to reason Gliese 667C(c) has a generous atmosphere of whatever you'd like to imagine it having. ## Convection Given a tidal locked planet with a twilight zone, but having a good atmosphere for carrying convection currents. Winds will moderate the temperature by driving up and over the night-side cool air. You need a good carrier of thermal energy (moisture) for convection to work. With good convection, you will get a nearly constant cooling breeze on the ground level from the night side, which might pick up speed as it moves to fill in the higher high pressure regions facing the star. You can use the pipe equation to estimate how much the global maximum and minimum temperature of Gliese 667C(c) will vary from the mean. ${{\Delta P} \over L} = {128 \over \pi} \dot {{\mu Q} \over D^4}$. Q, the volume flow rate, is ${1 \over 2} \pi D^2 v$; so you can simplify to ${{\Delta P} \over L} = {32 \over \pi} \dot {{\mu v} \over D^2}$. This is the pressure loss over distance. Plugging in the 9,800 km radius of Gliese 667C(c), neglecting the velocity term, and picking an arbitary 2.7 meter height (not completely arbitrary, used to obtain 150C swing seen on Earth), $\Delta P$ = 3,564 Pascals. Use the Bernoulli equation to convert that to temperature: $ PV = \rho R T $. The gas constant is $8.314 J (mol \dot K)$. The density of air is $1.225 kg / m^3 $. Assume V (volume) is a unit volume (1.0). A maximum pressure loss of 3,564 Pascals is equal to about 250 K. Given the mean temperature of 236K $\pm $ 125K, the temperature should range no lower than 111K (-162 C/-259 F) at the coolest, and no higher than 361K (88 C/190 F) at the hottest. With a range that wide, steady density is not a valid assumption - reality will be a lower swing, because phase transitions (solid to liquid to gas) will smooth things out. ## Coordinates For the rest, it helps to know what part of Gliese 667C (c) we're talking about. I'll choose to call the point that receives the most direct heating the tropics, and run circles of latitude 171 kilometers per degree from the tropic to the equator/twilight zone, calling the tropics 90 degrees north latitude and the middle of the night zone 90 degrees south. ## Effect of Water and Other Greenhouse Gasses If there is plenty of water, it can moderate the temperature of the planet. According to [this](http://www.waterencyclopedia.com/Ce-Cr/Climate-Moderator-Water-as-a.html) article, water on Earth provides 33 degrees Celsius of additional warmth by trapping and transporting thermal energy. At the tropics radiant power is 710 Watts/sq.meter. Around 86% of this (610 W/sq-m) makes it to the surface. Provided enough water vapor in the atmosphere, [greenhouse gasses (of which water vapor is 60%) trap nearly 90%](https://en.wikipedia.org/wiki/Earth%27s_energy_budget#/media/File:The-NASA-Earth%27s-Energy-Budget-Poster-Radiant-Energy-System-satellite-infrared-radiation-fluxes.jpg) of what would be re-radiated into space from the ground. Per [here](http://www.biocab.org/Overlapping_Absorption_Bands.pdf), the emissivity of air and water vapor mixed is 0.3128. More carbon dioxide (which has a partial emissivity of 0.04) can further decrease the amount of energy being re-radiated into space, nudging all temperatures up. If you plug the radiant heat equation into the equation for specific heat capacity, as someone else has already done [here](http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/cootime.html) you can get a more precise cooling model, and wind speeds. Wind speed is important, because it establishes the upper limit for this model (wind speed can not be supersonic $ a = \sqrt(\gamma R T)) $ ) Noting that you can substitute N k in the model with $ \rho R $, the equation becomes $ t = (\rho R\_{water} / (2 \epsilon \sigma A)) \* (1/T\_{final}^3 - 1/T\_{start}^3) $ Unfortunately, I could not find a nice model to just determine the change in temperature, so you have to try values. Wind speed is $ \sqrt(2 R \delta T) $, which should be lower than the speed of sound. Some of the following below is a first-draft pass at the model, which produces a lower-resolution answer than the final answer given. A 10 km high column of cool water vapor traveling from the equator/twilight zone at 0 degrees north latitude to the tropics at 90N at 10 m/s (36 km/hr), then turning around back to the equator would take 855 hours to make the trip, picking up ~57 degrees C of temperature along the way (simultaneously cooling the ground by that same amount). This global air current would then travel to the southern latitudes past the equator/twilight zone, depositing this ~57 degrees before turning back around. Similarly, an ocean current in the daylight region (200 m deep) making the same global circuit would warm by two degrees in the warming part of the trip and drop by two degrees in the southern part of the circuit. But how would currents develop on a planet with no tides? There is more than enough temperature difference for [Rayleigh-Benard convection cells to develop](https://en.wikipedia.org/wiki/Rayleigh%E2%80%93B%C3%A9nard_convection). These cells are unstable, so you might have something like weather - more moderate temperatures when convection is strong and more extreme temperatures when convection is weak. Past the equator, ice may further insulate against heating loss. Above the ice would be extreme, but like the arctic and antarctic, circulating and insulated running water (and underground) would be kept near 0 degrees C. ## Habitable Region At a guess, the habitable region extends from the tropics (90 North / 30 to 80 Celsius) to the equator (0 N/S, 0 to 15 C). The south pole might be accessible in good weather, but would be mostly ice, subsurface water/ground and extreme surface conditions (90 South / 0 (subsurface) to -111 (surface) Celsius). In the complex setting, you'd have both convection driven weather and climate change. Region Tropics : 0 to 30 degrees latitude * Surface Area : 301718558 square kilometers * Ground Temperature : 418-403K (145-130C / 293-267F ) * Water Temperature : 299-298K (26-25C / 79-77F ) * Air Temperature : 312-306K (39-33C / 102-92F ) Temperate : 30 to 60 degrees latitude * Surface Area : 220873314 square kilometers * Ground Temperature : 403-352K (130-79C / 267-174F ) * Water Temperature : 298-297K (25-24C / 77-75F ) * Air Temperature : 306-301K (33-28C / 92-83F ) Daylight Equatorial : 60 to 90 degrees latitude * Surface Area : 80845244 square kilometers * Ground Temperature : 352-6K (79--267C / 174--448F ) * Water Temperature : 297-296K (24-23C / 75-73F ) * Air Temperature : 301-296K (28-23C / 83-73F ) Night Equatorial : 90 to 120 degrees latitude * Surface Area : 80845244 square kilometers * Ground Temperature : 6-5K (-267--268C / -448--450F ) * Water Temperature : 296-295K (23-22C / 73-71F ) * Air Temperature : 296-290K (23-17C / 73-63F ) Night Temperature : 120 to 150 degrees latitude * Surface Area : 220873314 square kilometers * Ground Temperature : 5-5K (-268--268C / -450--451F ) * Water Temperature : 295-294K (22-21C / 71-69F ) * Air Temperature : 290-285K (17-12C / 63-53F ) Night Polar : 150 to 180 degrees latitude * Surface Area : 301718558 square kilometers * Ground Temperature : 5-4K (-268--269C / -451--451F ) * Water Temperature : 294-292K (21-19C / 69-67F ) * Air Temperature : 285-280K (12-7C / 53-44F ) ]
[Question] [ In the science fiction setting I'm working on, one of the factions are supposed to be using naturally occurring antimatter because the systems they reside in have sufficient natural sources of it. I've explored the idea of chasing positrons in gas giant storms, but found that antiprotons can be found in the radiation belts of worlds. Antiprotons have more mass and are not trapped in the hostile environment of a gas giant's atmosphere. Unfortunately, they do not seem to be in sufficient quantities to power a fleet. From what I've read, the Van Allen radiation belt of our planet have somewhere between 100-200 nanograms of antimatter to work with. I think it came out to less energy than a quarter gallon of gasoline. The concept seemed sound enough that I wanted to see if there were conditions that could affect the abundance of antimatter in the radiation belts of a planet. While this planet does not have to be habitable, it at least has to exist in the same star system as a habitable world. So, I'm curious to what conditions could create a radiation belt that would produce/contain an abundance of antimatter sufficient to power starships and what properties the planet with such a belt would have, particularly its atmosphere and size. Since this antimatter is formed during interactions with a planet's atmosphere and cosmic rays, I imagine the star(s) of a system also being a factor which could potentially make a habitable world in that system a little more difficult to have. [Answer] I read through the discovery paper ([Adriani et al. (2011)](http://adsabs.harvard.edu/abs/2011ApJ...737L..29A)) about antimatter in Earth's Van Allen belts, and I just want to lay out a few points before we begin: * The antimatter in the Van Allen belts consists mostly of antiprotons, as you stated. Antineutrons may be initially produced, but free neutrons (and antineutrons) are unstable, and thus decay into protons (and antiprotons). * The main creation mechanism for antiprotons in the Van Allen belts is the CRAND process,[[1]](https://www.jstage.jst.go.jp/article/jgg1949/43/4/43_4_255/_pdf) where galactic cosmic rays (GCRs) collide with particles to produce neutrons and antineutrons. only GCRs - not cosmic rays from other sources, like the Sun - have enough energy to do this. These neutrons and antineutrons decay, creating protons and antiprotons. On Earth, the flux should be $\sim4000\text{ m}^{-2}\text{ s}^{-1}$[[2]](http://www.niac.usra.edu/files/studies/final_report/1071Bickford.pdf). * A secondary mechanism involves GCRs colliding with the interstellar medium to produce neutron-antineutron pairs. These particles then decay, sending antiprotons and other particles speeding off. The flux on Earth is $\sim3\text{ m}^{-2}\text{ s}^{-1}$[[2]](http://www.niac.usra.edu/files/studies/final_report/1071Bickford.pdf). * Antiprotons are lost through interactions with the atmosphere and instabilities in the magnetic field. As with production, these losses depend on the angle of entry into the atmosphere. At high altitudes, collisions with hydrogen and helium nuclei dominate. * The magnetosphere of a planet can shield it from cosmic rays, thus reducing the production rate of antiprotons. This is in part why Jupiter does not receive as high an antiproton flux as Earth. In a gas giant (notably Saturn), this can be mitigated by antiproton production in the rings through other mechanisms, but likely not significantly. It seems, then, that the obvious thing to do would be to place the planet somewhere with a higher flux of galactic cosmic rays. I don't think we can decrease antiproton loss rates without affecting production via the atmospheric collision pathway. You could try to introduce a very strong cosmic ray source into the planetary system, but I don't have any ideas what that could be. It could also be detrimental to the habitability of other planets. One problem is that we don't have a great idea of where all of the galactic cosmic rays come from. There are quite a few possibilities out there (and all of these could produce different components of the GCR flux on Earth): * Supernovae might be a source,[[3]](http://adsabs.harvard.edu/abs/1934PNAS...20..259B) although some observations of the GCR spectrum dispute this. Putting your system somewhere in the vicinity of a stellar nursery could place it near quite a few supernovae, because the massive stars that are supernova progenitors have such short lives that they hardly move from their birthplaces. However, having a lot of supernovae nearby tends to make worldbuilders nervous - I think 10 parsecs is the closest you'd want to go if you want to preserve habitability. * Active galactic nuclei[[4]](https://arxiv.org/abs/0906.2319) are also an option, albeit one that you can't control much by moving your planetary system throughout the galaxy. These might be a source of the highest-energy GCRs, which would be quite good at penetrating magnetic fields and the atmosphere. Now, one thing you could do is lower the activity of the central star. The Sun blocks GCRs during coronal mass ejections and similar eruptions, leading to something called a [Forbush decrease](https://en.wikipedia.org/wiki/Forbush_decrease),[[5]](http://adsabs.harvard.edu/abs/1937PhRv...51.1108F) which is simply when fewer GCRs reach Earth. We also see modulations in the GCR flux [during the Sun's 11 year cycle of activity](https://physics.stackexchange.com/a/286385/56299). The latter leads to changes in flux of around 10-20%, at is peak. However, keep in mind that this is measured from a baseline level of activity; reduce stellar events (coronal mass ejections, stellar flares, long-term fluctuations, etc.) significantly, and you could really make an impact. Therefore, I have two proposals to make: 1. Put your planetary system at a safe distance from a star-forming region, where you might see larger GCR fluxes. 2. Make the central star one with low stellar activity. Perhaps you can increase the quantity of antimatter in the radiation belts by an order of magnitude or so - maybe more. I'm not sure just how strong the effects would be. ]
[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. I'd like to explore some details on a so-called water-ball planet (i.e. a planet in the habitable zone of a sun, covered by a 100 km deep ocean). I am particularly interested where life could develop on such a planet. I am afraid that it will be a planet full of de-mineralised water where no life form can survive. * Will there be enough salts and other minerals in the ocean for it to be able to host life forms? * What kind of atmosphere do we expect? It could be oxidizing like Earth's atmosphere containing oxygen and nitrogen gas, reducing containing methane, or neutral with almost only water vapor ? * What is on the ground of the ocean? I can think of rock, some kind of ice, or methane hydrate. [Answer] As you can read in this [paper](https://www.nature.com/news/exoplanet-hunters-rethink-search-for-alien-life-1.23023), a planet only water is not the best place for life. > > It turns out that water worlds may be some of the worst places to look for living things. One study presented at the meeting shows how a planet covered in oceans could be starved of phosphorus, a nutrient without which earthly life cannot thrive. Other work concludes that a planet swamped in even deeper water would be geologically dead, lacking any of the planetary processes that nurture life on Earth. > > > On Earth, rainwater hitting rocks washes phosphorus and other nutrients into the oceans. But without any exposed land, there is no way for phosphorus to enrich water on an aqua planet over time [...] There would be no ocean organisms, such as plankton, to build up oxygen in the planet’s atmosphere, she says — making this type of world a terrible place to find life. > > > So your water would likely host no life. You may have dissolved salts in the water, sure, but no life for the lack of phosphorus. Lack of life means also no oxidizing atmosphere, as you will have no mechanism to replenish the oxygen involved in oxidation. With no life will come also no methane (not in big amounts, at least) for the bottom of your ocean. [Answer] You are thinking about nutrients and salts being washed off dry land and into the sea. But you could have those nutrients and salts expelled from the crust up into the water. You can have life arise at hydrothermal vents on the sea floor. It turns out there are a lot of those on our own planet. <https://www.sciencenewsforstudents.org/article/seafloor-hosts-surprising-number-deep-sea-vents> [![lots of deep sea vents](https://i.stack.imgur.com/N72ZO.jpg)](https://i.stack.imgur.com/N72ZO.jpg) People think that something like this could give rise to life on Jupiter's ocean moon Europa. <http://www.divediscover.whoi.edu/ventcd/vent_discovery/index_sr_future_et.html> It could work on your watery world too! --- Other idea: Pumice raft! <https://en.wikipedia.org/wiki/Pumice_raft> [![Pumice raft](https://i.stack.imgur.com/ia5l7.jpg)](https://i.stack.imgur.com/ia5l7.jpg) These are floating mineral islands spewed up from undersea volcanoes. They can be big. This [Home Reef](https://en.wikipedia.org/wiki/Home_Reef) is a related floating island phenomenon and it looks plenty big. If your world has undersea volcanoes, in addition to powering hydrothermal vents as above they could create floating pumice islands to serve as a substrate for life in the sun. Would the islands last long enough? If you had them continually replenished they might. Would there be enough of them? You can make up as much of them as you want! ]
[Question] [ Is there a limit (and if so, what is it) to the size (mass) of terrestrial planet that could be "captured" as a moon by a migrating gas giant? I'm writing a novel where a colony ship crashes on such a moon. My research tells me that a moon around a gas-giant is not likely to be larger than 1:10,000th of the mass of its parent. If this is true, an Earth-like moon is unlikely to form around anything with less than 30 Jupiter masses, which puts the parent planet in the brown dwarf range. Not what I want. So, can I get round this by having the gas giant migrate into the inner system, snaring a rocky world approximately the size of Earth, as it goes? I'm not too concerned about other issues - I'm happy to fudge tidal locking, and have the gas giant only have a couple of other moons to avoid tidal heating, and stick the Earth-like moon 10ish million kms out to avoid the worst of the radiation. But I feel like I can't fudge the mass of the related bodies. Any help, or related thoughts, would be greatly appreciated. SOURCES: <http://phl.upr.edu/library/notes/themassandradiusofpotentialexomoons> <https://www.reddit.com/r/askscience/comments/32ixle/is_there_a_clear_maximum_gas_giant_moon_size/> This is indicative of similar sites and forums where I got the figures. I've struggled to find anything concrete anywhere else; language is vague, but supports the notion that there is a mass limit for moons forming around gas giants, and that an Earth-mass moon would require a gas giant of several multiples of Jupiter. One site I read suggested that Earth-sized ice moons might form past 10 Jupiter masses, but that any terrestrial moon would be considerably smaller. Obviously, I'm looking for an Earth-mass, terrestrial planet, not a slushie world, and I want to avoid small terrestrial worlds because of the low-gravity. I'm grateful for the response re the Roche Limit. I did wonder about two planets orbiting a mutual gravitational center, but I don't know how to figure out what kind of effects that might have on the Earth-like planet, and whether I could keep it far enough outside the gas giant's radiation belts. Thanks for all the replies so far. [Answer] I'm not sure where you are looking, but first look here: <https://www.reddit.com/r/askscience/comments/23a96x/could_an_earth_sized_object_orbit_jupiter/> The answer is Yes; any two objects can orbit each other, include Earth and Jupiter. You need to be concerned about the [Roche Limit](https://en.wikipedia.org/wiki/Roche_limit), which tells you how far apart they must be in order to do so. And be aware that gravity works both ways, even for smaller objects: The Earth is pulled into a rotation by our Moon just as much as our Moon is pulled into a rotation by Earth: It isn't just the tides moved by the Moon, but the center of Earth is moving in small circles due to the moon. So planets of equal mass would circle each other. But Jupiter is 318 x the mass of Earth, and the [most massive known planet in the Universe](https://en.wikipedia.org/wiki/List_of_most_massive_exoplanets) is about 30 x the mass of Jupiter. (FWIW our Earth is 81 x our Moon). Look up the Roche Limit; that should also tell you what your minimum orbit should be around your big planet (but actual orbit can be thousands of times bigger). Roche Limit says Earth cannot be any closer than about 67,000 miles to Jupiter without breaking up. However, your planet can be quite a bit further, our Moon is about 40x its rigid body Roche Limit from Earth. But what this means is you can put it about where you like; it does not have to be extremely far from the gas giant. If you want tidal heating of your planet (and lots of earthquakes) put it close; if your planet is warmed otherwise and you want it calmer; I'd keep it at least twenty Roche units away, say 1.4 million miles from Jupiter. [Answer] You are better off with a habitable moon than a captured terra. One scenario would be [a massive moon which migrated in towards its planet, while the planet migrated in towards its sun](https://astronomynow.com/2015/06/01/habitable-exomoons-will-need-to-be-bigger-than-mars/). The migration is explained by universal "shrinkage" so it's consistent, and there are no improbable catcher's mitt or billiard physics necessary. The problem is your gas giant and terra planet were not formed in the same part of the solar system. The current thinking is there's a defining [frost line created when the solar nebula formed into planets](https://en.wikipedia.org/wiki/Frost_line_(astrophysics)). Within the frost line you get the rocky terrestrial planets, beyond it are the gas and ice giants. A migrating terra planet is possible – knocked from its orbit by a brush with another planet, but to later be gently plucked by a gas giant into a stable orbit is improbable – like knocking a baseball 10,000 miles to gently land a catcher's glove. You probably don't want your planet to be in the outer solar system, even if it could hold its atmosphere during cosmic billiards. A migrating gas giant is believable because it could easily [migrate in towards the sun](https://www.cfa.harvard.edu/news/su201635), but then what made it stop migrating – assuming your terra planet isn't being dragged into a death spiral? The answer would be another even bigger gas giant in a [resonance orbit](https://en.wikipedia.org/wiki/Orbital_resonance), but again this set of circumstances seems like improbably cosmic billiards, now involving three planets. Resonance orbits are unstable, they don't "settle" an object into a stable groove so much as fling the other bodies away. The definitions of a planet is how they clear their own orbit of all other objects (the 1:1 resonance ratio), and Jupiter is [theorized to have been the big baby that threw all the toys out of the pram](https://en.wikipedia.org/wiki/Nice_model). As your gas giant approaches the inner system, it would send your terra planet flying out of the solar system long before it got close enough to be captured. Getting captured by a [rogue planet](https://en.wikipedia.org/wiki/Rogue_planet) also seems impossible, the rogue would tear through the solar system at escape velocity. That's not going to gently snag a planet either. A habitable moon is the only reasonable way you could end up with something stable. [Answer] > > My research tells me that a moon around a gas-giant is not likely to be larger than 1:10,000th of the mass of its parent. > > > The theoretical mass limit between a planet and a brown dwarf is about 13 Jupiter masses, or about 4,131.4 times the mass of Earth. Thus if a moon can be no more than 0.0001 times as massive as a gas giant, it can have no more than 0.41314 times the mass of Earth. Jupiter has a mass 317.8 of Earth. Its most massive moon, Ganymede, has a mass of 0.025 of Earth. Thus the mass of Jupiter is 12,712 times the mass of its most massive moon. Saturn has a mass 95.159 of Earth. Its most massive moon, Titan, has amass of 0.0225 Earth. Thus the mass of Saturn is 4,229.28 times the mass of its most massive moon. Uranus has a mass 14.536 of Earth. Its most massive moon, Titania, has mass 0.0005908 of Earth. Thus the mass of Uranus is 44,603.926 times the mass of its most massive moon. Neptune has mass of 17.147 of Earth. Its most massive moon, Triton, has mass 0.00359 of Earth. Thus the mass of Neptune is 4,776.3231 times the mass of its most massive moon. So according to the examples of gas giant planets in our solar system, a moon with the mass of the Earth could orbit around a gas giant planet with a mass of 4,229.28 or 4,776.3231 times the mass of Earth, which would be 13.307992 or 15.029336 times the mass of Jupiter. That would be a little bit above the theoretical lower mass limit for a brown dwarf. > > The largest and most massive moon in the Solar System, Ganymede, has a radius of only≈0.4R⊕ (R⊕ being the radius of Earth) and a mass of≈0.025M⊕. The question as to whether much more massive moons could have formed around extrasolar planets is an active area of research. Canup and Ward (2006) showed that moons formed in the circumplanetary disk of giant planets have masses ≲10−4 times that of the planet's mass. > > > <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/>[1](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/) Canup R.M. Ward W.R. A common mass scaling for satellite systems of gaseous planets. Nature. 2006;441:834–839. [PubMed] > > Mass-constrained in situ formation becomes critical for exomoons around planets in the IHZ of low-mass stars because of the observational lack of such giant planets. An excellent study on the formation of the Jupiter and the Saturn satellite systems is given by Sasaki et al. (2010), who showed that moons of sizes similar to Io, Europa, Ganymede, Callisto, and Titan should build up around most gas giants. What is more, according to their Fig. 5 and private communication with Takanori Sasaki, formation of Mars- or even Earth-mass moons around giant planets is possible. Depending on whether or not a planet accretes enough mass to open up a gap in the protostellar disk, these satellite systems will likely be multiple and resonant (as in the case of Jupiter) or contain only one major moon (see Saturn). Ogihara and Ida (2012) extended these studies to explain the compositional gradient of the jovian satellites. Their results explain why moons rich in water are farther away from their giant host planet and imply that capture in 2:1 orbital resonances should be common. > Ways to circumvent the impasse of insufficient satellite mass are the gravitational capture of massive moons (Debes and Sigurdsson, 2007; Porter and Grundy, 2011; Quarles et al., 2012), which seems to have worked for Triton around Neptune (Goldreich et al., 1989; Agnor and Hamilton, 2006); the capture of Trojans (Eberle et al., 2011); gas drag in primordial circumplanetary envelopes (Pollack et al., 1979); pull-down capture trapping temporary satellites or bodies near the Lagrangian points into stable orbits (Heppenheimer and Porco, 1977; Jewitt and Haghighipour, 2007); the coalescence of moons (Mosqueira and Estrada, 2003); and impacts on terrestrial planets (Canup, 2004; Withers and Barnes, 2010; Elser et al., 2011). Such moons would correspond to the irregular satellites in the Solar System, as opposed to regular satellites that form in situ. Irregular satellites often follow distant, inclined, and often eccentric or even retrograde orbits about their planet (Carruba et al., 2002). For now, we assume that Earth-mass extrasolar moons—be they regular or irregular—exist. > > > <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/>[1](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/) Sasaki T. Stewart G.R. Ida S. Origin of the different architectures of the jovian saturnian satellite systems. Astrophys J. 2010;714:1052–1064. Ogihara M. Ida S. N-body simulations of satellite formation around giant planets: origin of orbital configuration of the Galilean moons. Astrophys J. 2012;753 doi: 10.1088/0004-637X/753/1/60. Triton has a mass 2.0936 times as great as a moon formed in the circumplanetary disc of Neptune should have according to Canup and Ward. Triton is believed to have been captured by Neptune. Titan has a mass 2.3644 times as great as a moon formed in the circumplanetary disc of Saturn should have according to Canup and Ward. Thus Titan should have acquired its mass by one or more of the processes suggested to enable moons to exceed the mass limit postulated by Canup and Ward. But why are gas giants and their moons the only models for the satellite systems of gas giants? The Earth is 81.300813 times the mass of the Moon. Using the Earth-Moon system as a model, a moon with the mass of Earth could orbit a gas giant planet with a mass 81.300813 times the mass of the Earth, less massive than Saturn. The dwarf planet Pluto has a mass of 8.1967 times its largest moon, Charon. Using the Pluto-Charon system as a model, a moon with the mass of Earth could orbit a gas giant planet with a mass 8.1967 times the mass of the Earth, less massive than Uranus. ]
[Question] [ We've built a nice, sturdy enclosure to house one of our drydocks to do covert work on a battleship without people easily spying on us. As such, there are no significant windows. Additionally, it's not a quick and dirty coverup - This dock has been used a few times for such purposes, so the construction is fairly robust and sturdy. Then we're attacked. We were actually planning on launching the ship soon, so the drydock is actually full, and the ship is armed and ready. The enemy doesn't know this, so we figure we can surprise them with the battleship's guns. What happens to and inside the building? To the battleship? I'm not concerned with actually hitting anything with the shells, or what the shells would do to their target. I'm mostly concerned with what happens to the interior - And possibly the squishy people inside. While not 100% accurate to my world, let's just use the [USS Maryland (BB-46)](https://en.wikipedia.org/wiki/USS_Maryland_(BB-46)) as our baseline. As battleships rarely fired all turrets at once, it'd probably be a single turret of three guns firing at once. [Answer] ## It really depends on the structure... So now, you already know it is a bad idea to fire a (huge) gun in a confined space... Soft shell: To conceal a ship you don't need to build a big heavy thing. A wooden of steel frame can be made. Covered with wooden planks, corrugated steel or even burlap can be used to hide it from view. Like the Japanese did with the building of the [Yamato](https://en.wikipedia.org/wiki/Japanese_battleship_Yamato#Design_and_construction). It might even allow you to move the guns out to the side where the enemy is. When the guns fire you don't want to be near. I don't have good numbers, but some video will give you an idea. First start with small Leopard 2 [gun](https://www.youtube.com/watch?v=WrZni_qAorQ) firing, only 120mm. You don't want to be in front of that. Or anywhere near without ear protection. Now here is a nice video about the workings of those lovely big guns: [Firing Operations of Heavy Battleship 16"/406mm Guns](https://www.youtube.com/watch?v=Dg-cNmLRgiU), 7:25 for the shooting part. So with a light structure, everyone near, let keep it to [Danger Close](https://en.wikipedia.org/wiki/Fire_discipline#Call_for_fire) distances. (I know this is for explosions, but firing a 16" guns is a big explosion, just very directed.) So, that makes 2000 meters for every one to have big hearing problems. If not outright deaf. And every thing that is not bolted down will move. The closer to the gun, the more. One big shotgun blast of dirt and debris, if not for the bullet itself. Yes, people will be blown over and break things. And your ship will be covert with that is left of the building. Hard shell: So you want big, hard and somewhat secure. Sure, we have the thing for you! Let build an oversized [Submarine pen](https://en.wikipedia.org/wiki/Submarine_pen). This thing is going to be huge, battle ships are no where near as small as submarines. And I don't think you can move the guns too much to the sides, it will be cramped in there. But if a gun goes off here it will be much worse, as the whole structure will work as a gun barrel itself and the sheer pressure of the blast will not dissipate as much as in the open. It's probably not good for the structural integrity of the building as well. In the end we are just talking about an [explosion](https://en.wikipedia.org/wiki/Explosion), either in the open or in an enclosed space. Notes: In both cases you will need to find a way to power your ship to be able to aim and fire the guns. And unless you have updated and automated lots of it, you will need quite a crew on hand to do so. As with aircraft and tanks, there will be few if any locks and keys to stop someone gaining access to your toy. Most often you will find guards with weapons and backup. [Answer] Since large naval guns could kill people who got too close enough to their muzzle blast firing it indoors would be bad news. Any glass in the building or on the ship would be shattered by the pressure wave. Depending on how enclosed and sturdy the structure is hearing loss and ruptured eardrums are likely from the sound waves being reflected off the walls. There's probably enough space so that there aren't any more serious injuries caused by shockwaves. Luckily by the 1920s naval shells had a time delay after firing before they armed themselves. So while its velocity and mass would be impressive when it collides with the walls, it wouldn't explode. ]
[Question] [ For starters, allow me to define more carefully what I am asking. For now I am not worried about any of the following, as if this question is answered they will be covered in later questions: * The aerodynamics or feasibility of its flight, covered [Here](https://worldbuilding.stackexchange.com/questions/76422/could-this-very-specific-dragon-fly) * Metabolic requirements. * How such a creature evolved or the plausibility thereof. What I am asking is: How well will my proposed adaptations work and what other adaptations may the dragon need? I figured that whether or not my dragon could get off the ground, this question and subsequent answers might supply the basis for others who come to this site who are interested in devising large flying creatures. *Warning - Math Ahead - Warning - Product of Someone with to much Free Time* A Drawing of the dragon in question. [![enter image description here](https://i.stack.imgur.com/nbTFL.png)](https://i.stack.imgur.com/nbTFL.png) Height: 6.5 meters Length: 19 meters Volume: 11.9 cubic meters Head/Neck Volume: 1.3 cubic meters Average Density: 0.614 g/cm^3\* Weight: 7310 kilograms Wingspan: 38 meters Wing area: 304 square meters Wing loading: 23 kg/m^2 Wings+Legs+Tail muscle cross-section: 43,000 cm^2 Muscle strength\\\* newtons/cm^2: 35 n/cm^2 Wings+Legs+Tail muscle strength: 1,474,900 watts Liftoff time: 1 second Height leaped in Liftoff\\: 20.6 meters Liftoff force on body: 2.1 gravities Wing muscle cross-section: 21,600 cm^2 Wing muscle strength: 756,000 watts Flap time: 2 seconds Flap acceleration\\: 21 meters a second Adaptations Facilitating Large Size + Flight: Strength giving minerals in bones replaced by Graphene Foam, Giving enormously increased strength and reducing density from 700 kg/m^3 (bird density) to 650 kg/m^3.\* Collagen replaced by material similar to dragline spider silk,Giving enormously increased strength and reducing density from 650 kg/m^3 to 614 kg/m^3.\\ Carbon Nano-tubes worked into the nervous system, allowing for increased signal relay speed. And into the Connective tissue where greater stiffness then the dragline adaptation would allow for. Lungs Like those of a bird, considerably more efficient at gas exchange than most tetrapod lungs. Because of the increased connective tissue strength, the patagium may remain quite thin, allowing for gas exchange to be preformed across the area of the wing, as occurs in bats. Are there any issues with these adaptations, or will they work as I would expect? What other adaptations might the dragon need in order to survive and function as such a large flying organism? \The body is ~15% bone, which is ~50% mineral, the primary constituent of which is calcium, with a density of 1.54 g/cm^3, as opposed to graphene foam with a density of 0.06 g/cm^3. \\* The dragons body should be ~16% protein, ~35% of which is collagen. Collagen has a density of 5 g/cm^3, as opposed to the density of dragline silk, at 1.3 g/cm^3. Question: How well will my proposed adaptations work and what other adaptations may the dragon need? [Answer] # This is not a dragon. This is an aircraft This series of questions is fundamentally flawed. What we have here is a 7 tonne entity shaped sort-of like a bird, with structural members made of exotic materials ("graphene foam"), with flight surfaces made of silk, with signal conduits made of carbon nanotubes, capable of producing 2600 horsepower. This is an aircraft, not a biological entity. Yes, we know that aircraft of this size can fly, there is no question about that. No, there is no way for this to be a living thing. Living things are not made of graphene foam. 2 MW (2600 hp) is 478 kcal/sec. Let's say that in flight the entity uses 50% maximum power; that's about 240 kcal/sec. [Muscles](https://en.wikipedia.org/wiki/Muscle) have an efficiency of about 20%, that is, to produce 1 W of mechanical power they consume 5 W of chemical energy, of which 4 W are dissipated as heat. Let's say that the dragon has better muscles with 33% efficiency, and let's say that it eats bacon (5000 kcal per kilogram). For five minutes of flight the dragon needs 300 × 240 / 0.33 = 216 000 kcal, or about 43 kg of bacon (or 80 kg of lamb): it needs to eat one pig for 5 minutes of flight. It must dissipate 2 MW; let's say that it has a superb heat transfer system able to dissipate 40 W/m² per degree centigrade, and it has 400 m² of area available: the temperature difference between the blood and the air would need to be 2 000 000 / 40 / 400 = 125° C; it the air is at 20° C then the blood must be at 145° C... And that's above and beyond its basal metabolism; by necessity it must be warm-blooded in order to be able to regulate its internal temperature; a 7 tonne warm-blooded animal dissipates somewhere around 7 kW (1.67 kcal/sec) at rest. In one day it requires 24 × 3600 × 1.67 = 144 516 kcal, or about 30 kg of bacon (or 60 kg of lamb) per day just to keep on living. [Answer] Adding graphene will make the bones stronger but it will not make them any lighter. You can't reduce the animal's weight by switching out the bone material because then it needs to store that calcium and phosphorous in some other fashion, you can't eliminate them only move them. living things with muscle need a very narrow range of calcium concentration in the body to function. Having a solid mass of calcium's distributed around the body is the most efficient way to do that. Dinosaurs, birds, and pterosaurs, make bones hollow to make a larger structure for the same weight, the total ratio of bone surface area to body mass remains the [same](http://www.journals.uchicago.edu/doi/10.1086/283367). In fact you really can't change that ratio very much because the bone surface area (exposed to body tissue) cant change much. <http://rspb.royalsocietypublishing.org/content/early/2010/03/13/rspb.2010.0117.short> So your dragon bones will be stronger, but you won't drop any weight. ]
[Question] [ In some environments (think of the Faerunian Underdark for a fantasy example, or a planet orbiting a pulsar for sci-fi folks), high-energy (UV and up, but I'm mostly concerned about UV and very soft X-rays here as hard gammas are going to make animal life impossible anyway) radiation predominates over visible light in the environment in question. Assuming that other issues (food chain is solvable, see [this answer](https://worldbuilding.stackexchange.com/a/36539/3097) for details)) are taken care of, would terrestrial animal (or better yet, sapient) life in that environment evolve melanism (i.e. very dark skin) as a result of the radiation-heavy environs? Or would this be counterproductive as an evolutionary adaptation? Am I already talking about a point where the environment is too radiation-rich for even a basic lizard to evolve, never mind intelligent, terrestrial life? (Oceanic life has it easier as water is a pretty good radiation shield, so I'm putting it out of scope for this question.) [Answer] Fungi adapt to ionizing radiation by expressing more melanin - they are "melanized". This form of adaptation has been noted in a variety of environments. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2677413/> So if you are talking about a fungus, yes. But fungi might be doing something different - they might be using melanin to capture energy from the radiation and then use it for their own purposes. <http://www.asmscience.org/content/journal/microbiolspec/10.1128/microbiolspec.FUNK-0037-2016> In vitro work shows that introducing melanin into animal cells decreases damage from ionizing radiation. <https://www.ncbi.nlm.nih.gov/pubmed/10789895> This would lead one to expect a survival advantage for an organism with more melanin in the context of ionizing radiation. Given what an easy experiment this would be to do, I was surprised how hard it was to find results. I finally did. <http://www.rrjournal.org/doi/abs/10.2307/3578834?code=rrs-site> Melanin does protect against mutational damage from ionizing radiation and higher levels of melanin are associated with less damage in experimental organisms exposed to radiation over many generations. /would terrestrial animal life in that environment evolve melanism as a result of the radiation-heavy environs/. They might, unless some superior method evolved that took away the adaptive advantage of melanism. Of note is the fact that UV does not penetrate very deeply and so the skin / integument is the place animals accumulate melanin. Because ionizing radiation does penetrate one might expect a more generic distribution of melanin throughout the cells of the body; i.e. they would be darker through and through. [Answer] Short answer: No. Longer answer: Firstly, melanism tends to develop within the natural world as a form of camouflage from other animals, predator or prey, rather than by light exposure, so it's more a matter of whether or not melanism would help the animal avoid detection. Secondly, if UV is the dominant form of radiation, then it is more likely that, like bees, the lifeforms of this universe will see in that part of the spectrum, and as such will likely appear transparent or blandly coloured to us. If the radiation is strong, they will likely develop skin tissue of a 'colour' that reflects most UV light as white reflects most visible light. Given the high energy of UV, this seems quite likely to me. As such, melanism, or its equivalent within the UV band, is even less likely because they would be absorbing rather than reflecting the radiation. [Answer] More than melanism it is likely that they would develop a suitable exoscheleton, to act as physical barrier against the radiation. Life on heart developed first in water, where the UV radiation from the sun was reduced to a bearable level. Then, as ozone started to develop and filter UV, life migrated on dry land. If melanism would be a "tweak" to tolerate high UV, life on our planet would have already used it. ]
[Question] [ Specifically, how many 5 to 10 kilometer asteroids could you fit around the Earth-Moon Lagrangian points? Does the number change depending on which Lagrange point it is? [Answer] From [Wikipedia:](https://en.wikipedia.org/wiki/Lagrangian_point#Stability) > > # Stability > > > Although the L1, L2, and L3 points are nominally unstable, it turns out that it is possible to find (unstable) periodic orbits around these points, at least in the restricted three-body problem. These periodic orbits, referred to as "halo" orbits, do not exist in a full n-body dynamical system such as the Solar System. However, quasi-periodic (i.e. bounded but not precisely repeating) orbits following Lissajous-curve trajectories do exist in the n-body system. These quasi-periodic Lissajous orbits are what most of Lagrangian-point missions to date have used. Although they are not perfectly stable, a relatively modest effort at station keeping can allow a spacecraft to stay in a desired Lissajous orbit for an extended period of time. It also turns out that, at least in the case of Sun–Earth-L1 missions, it is actually preferable to place the spacecraft in a large-amplitude (100,000–200,000 km or 62,000–124,000 mi) Lissajous orbit, instead of having it sit at the Lagrangian point, because this keeps the spacecraft off the direct line between Sun and Earth, thereby reducing the impact of solar interference on Earth–spacecraft communications. Similarly, a large-amplitude Lissajous orbit around L2 can keep a probe out of Earth's shadow and therefore ensures a better illumination of its solar panels. > > > Emphasis mine. Example is about Earth-Sun, but for Moon-Earth it's the same, only proportionally smaller. This means that around these points you can have a semi-stable orbits far larger than your intended spacecrafts. As long as you keep masses irrelevant in comparison to the mass of Earth and Moon, and not enough to create measurable gravity or other forces between them, there is no practical limit on how many you can fit. Just note that the more of them, the more fuel you would use to stay away, avoid shadowing each other, and keeping "in orbit" - but the difference shouldn't be dramatic. For L4 and L5, as far as I understand, such orbits are not so easy, impossible even, and you would need to have all your vessels actively track each other and use fuel almost constantly. Still, it is possible there [already are clouds of interplanetary matter](https://en.wikipedia.org/wiki/Kordylewski_cloud) there. If cloud can be relatively stable long term, anything you can fit into that cloud could, too. Practical limits are a bit too hard for me to calculate - the less fuel you are willing to spend, the closer to the point you have to be and / or the higher drift and less stability you have to accept. ]
[Question] [ On a world I am building, the day/night cycle last 9 years, meaning that there are interesting forms of life. Plants are the most interesting of these living things, which have many interesting forms of keeping themselves alive. The problem is that I am unaware of what the effects of 4 and a half years of daylight would even do on plant life. Keep in mind that rain and storms do occur, just that night is absent. Would they grow much quicker with constant food or dry out from the constant heat of day? What are the effects of years of daylight on plantlife [Answer] The effects will not be universal, for one. it will depend on the plant, and the adaptations that species has undergone to survive the day/night cycle. Plants (in our world) rely on the day/night cycle to regulate their seasonal growth, [among other things](https://en.wikipedia.org/wiki/Circadian_rhythm#In_plants) - without that cue, they may not adapt correctly. There are two kinds of plants, those that regulate themselves by the length of day and those that depend on the length of night. I recall reading about some experiments back in biology class, where the light or dark cycle of plants was briefly interrupted (a flash of light when it was "supposed" to be dark, the lights turned off for a bit when "supposed" to be light) - to figure out which part the plants were keeping track of. I think the results were that different plants kept track differently, depending on their purposes. Leaves will want to know about sunlight, flowers or [pest control](http://www.popsci.com/blog-network/our-modern-plagues/do-plants-sleep) will want to track dawn and dusk, and so on. Some were highly [dependent on the night-length](https://en.wikipedia.org/wiki/Photoperiodism), and whether it was shorter or longer than the day length, while others relied on different factors like temperatures. So, if this world began with plants or acquired plants which were adapted to our world, any of those which relied on the day/night cycle would die off rapidly, irregardless of other factors, since they couldn't control certain kinds of responses. Day-neutral plants would have a better chance of surviving, though. I suspect desert plants, and tropical plants, would likewise adapt better to the daylight years - being accustomed to plenty of sun and warmth, though they would die back sharply in the night years, so annuals with an extra nine-year cycle. Polar plants would also perhaps survive well, being accustomed to long day/night cycles anyway - and the temps would likely be more, hm, stable at the poles. Temperate zone plants would not adapt well, though, I assume, since daylight cues would be all messed up, with much wider variances ("yearly" summers and winters will likely stack up on top of the "day" and "night" temperature variances, which will exaggerate the heat and cold). Of course, if you're starting with plants that are already adapted to this world... they will likely be adapted, that is, it will be normal to them. I would expect big seasonal variations, as I mentioned, and there will be annuals (which will run rampant when they can, and seed and re-sprout when the temp is too bad), and plants which persist through all temp variances with slower and more steady growth, evergreen-alikes which stay alive and deciduous-analogues which hibernate through the worst temp changes. Just, they may have to hibernate through worst heat as well as worst cold, "day-summers" will be desert-like, night-winters will be frozen solid. Plants will need to store up food for the night-winters, especially. I sort of expect that the "winters" will act more like nights (shorter periods of less productive, colder time) and the "nights" more like winters (long bleak periods where there's no food, and survival is questionable), for the plants. The planet's rotation is quite slow, if it orbits the star eighteen times before it has rotated on its axis once - it is very nearly tidally locked, yes? I expect the "dawn" and "dusk" areas will end up acting like de-facto spring and fall, months or even a year of warming up and cooling down the plant growth. [Answer] See (e.g.) [Why Vegetables Get Freakish In The Land Of The Midnight Sun](http://www.npr.org/sections/thesalt/2014/08/20/341884706/why-vegetables-get-freakish-in-the-land-of-the-midnight-sun) among others I found with the Google search `alaska giant vegetables`. ![photo from NPR link](https://i.stack.imgur.com/Xm3RN.jpg) > > Giant Cabbage Weigh-Off 2013 winners (with placards, left to right): Scott Rob (92.1 pounds), Keevan Dinkel (92.3 pounds) and Brian Shunskis (77.4 pounds). The growers are joined by the cabbage fairies, a group of women who for 15 years have volunteered at the cabbage competition. > > — Clark James Mishler/Courtesy of Alaska State Fair > > > ]
[Question] [ I've wanted my fantasy world to be as realistic and science-based as possible (aside from magic), but I also want there to be dinosaurs or creatures that are very similar to dinosaurs. So what would be required to realistically have dinosaurs inhabiting the same world as humans? For example, what climates would this world need, how separate would the mammals and dinosaurs need to be, and could there be any ice ages? And, please, no "dinosaurs are already here" answers. I'm asking about [these](http://islanublar.jurassicworld.com/media/dinosaurs/tyrannosaurus-rex/tyrannosaurus-rex-info-graphic.png) dinosaurs, not [these](http://www.gourmetsleuth.com/images/default-source/articles/big-white-chicken.jpg?sfvrsn=8) ones. [Answer] You're probably gonna hate me for this...but suppose that you just go with the obvious solution: the asteroid misses, and non-avian dinosaurs don't go extinct. Could humans evolve in an environment such as this? Well...probably? [![Purgatorius, a proto-primate that lived during the Late Cretaceous.](https://i.stack.imgur.com/d0rjS.jpg)](https://i.stack.imgur.com/d0rjS.jpg) See, proto-primates did exist during the Late Mesozoic. The question is, could they have evolved into proper primates, then apes, then hominids with dinosaurs running around? Well, considering that most arboreal dinosaurs ended up becoming actual birds, it's probable that Primates and other mammals could have "beaten" the dinosaurs to the punch in evolving a primate-like form. So considering this, there's a veeeeeeerrrrrrrry slim chance that, assuming they all kept out of reach, Humans could have evolved. Ultimately, it'd depend on which groups of dinosaurs made it to the present day. Since humans never would've evolved in Asia/the Americas, Tyrannosaurs and Deinonychosaurs could safely exist in this world, as could Ankylosaurs, Therizinosaurs, Hadrosaurs (heck, they're everywhere), and Ceratopsians. African Sauropods and Chacharodontosaurs might make this scenario harder, but hominids were able to last alongside Deinotherium and the like, so whose to say they couldn't against larger beasts? Bigger isn't always better, eh? As for those theories stating dinosaurs would probably stick closer to warmer climates, I say NAY! Assuming you have properly feathered dinosaurs, you could have dinosaurs in all climates, cold to hot, dry to swampy, high and low. Ultimately, for a world where humans and dinosaurs coexist, one of three things would need or have happen. [![ye Olde Tyrannosaure](https://i.stack.imgur.com/Icz6T.jpg)](https://i.stack.imgur.com/Icz6T.jpg) 1. Assuming you're using "Ye Olde Dinosaurs", then those forementioned climactic limits would probably be more in effect. While even Herbivorous dinosaurs could have some extra blubber for those lean times, it wouldn't be enough to live in arctic environments. That'd be where humans would have to set up cities. Farming spots would be prime competition with destructive herbivores; humans would either need to take up herding/ranching, or would be stuck as hunter/gatherers, in small tribal communities. [![Dinotopia](https://i.stack.imgur.com/5iwOr.jpg)](https://i.stack.imgur.com/5iwOr.jpg) 2. Humans could take a page from Dinotopia, and basically have mobile towns atop Sauropod herds. Imagine houses on individual dinosaurs. Traveling together in a herd. The humans could hunt smaller species which hang around sauropods, or even take a couple of the great herbivores for themselves once in a while, and in turn protect the herd from other threats. ...fanciful, I know, but hey. It could fit in your world! :) [![Grr!](https://i.stack.imgur.com/eAJ9z.jpg)](https://i.stack.imgur.com/eAJ9z.jpg) 3. While I myself am not one for violence or senseless hunting/killing, selectively reducing the populations of large dinosaurs in given areas could give humans room to build up stable and sturdy fortifications. Whether they can KEEP those locations is another matter. Like I said, a lot of this depends on which groups of dinosaurs you have in this environment, and how they have evolved. 65 million years is a long time to make evolutionary advancements, so there's a lot to consider here. Hope this helps. [Answer] Organize the geography and plate tectonics so that there has been a super-continent full of dinosaurs and another continent where humans evolved separately. Continental drift eventually brought the two land masses into contact with each other. Now you have a continuous land-mass where humans and dinosaurs co-exist. Basically evolution has worked its magic on two isolated populations of organisms in two different environments. One environment favoured dinosaurs and their continuing survival into the same epoch where humans had evolved too. Because this is an imaginary world, you can assume whatever dinosaurs you like are present. You can, for example, assume the Age of Dinosaurs started, at least, sixty-give million years later on this planet than it did on Earth. This brings humans and dinosaurs together. Don't worry about K-T impactor asteroid, in this world it didn't happen. That may have happened to Earth, but this isn't part of this world's history. Simply forget about it. Essentially allow two separate evolutionary biomes. One with dinosaurs, and the other with humans. For the purposes of your story they can brought together recently in terms of geological history. The world now has both dinosaurs and humans. ]
[Question] [ Based off [this question](https://worldbuilding.stackexchange.com/questions/55260/reasons-to-not-allow-an-uploaded-brain-to-be-conscious), since it also involves brain uploading. My Magnificent Bastard villain is a cognitive neuroscientist with his own lab who has interest in knowing how brains would work in a computerized environment. For that, he has built the following cycle: * Murder an individual and take their central nervous system out; * Connect the CNS to a high-end mainframe that will fool the spinal cord into thinking it's connected to real body nerves. The mainframe preserves the CNS on a long-term basis; * He will not bother studying the "whys" of brain functioning; he puts together a hardware device, which is part of the mainframe, that will simply convert chemical and electrical brain activity into binary data and vice-versa. This process is black-boxed; * He puts together a robotic construct capable of communicating with the mainframe through a mobile network. The construct contains artificial nerves throughout the body, which will respond to incoming and outgoing data from and to the mainframe. This is because the villain doesn't want to risk having the CNS inside the construct, since he personally considers human brains the "epitome of general-purpose problem-solving devices"; * He constructs an artificial neural network powered by a genetic algorithm, which evolves the neural network, based off the binary data input, into a human being. The algorithm designs the structure of the neural network into being able to learn through supervised learning; the villain himself will manually tell the neural network whether its behaviour is human, by watching how the robotic construct behaves. This process takes a very long time, obviously; * After the genetic algorithm reaches local optima, a new brain is needed and the cycle loops over. We can assume the following points: * The mainframe's processor is capable of processing data in humongous proportions; the villain might even plan to connect several CNSs to the same mainframe. * He will do anything to make a mobile network capable of transmitting the necessary data between the robotic construct and the mainframe. If he can't use a current mobile network service, he will come up with his own; * The mainframe generates additional binary data based off the transmitted data between mainframe and robotic construct. Data acquired by each brain is kept for the villain's research purposes and is kept isolated; the data must not be mixed; * The villain's reputation in the scientific community is extremely high; he is regarded as a lead figure in the cognitive psychology field, gives numerous speeches and has written several highly-acclaimed papers. He's middle-aged, very charismatic and has a well-toned body. * His true objective is to build a new human species by giving them the "immortality" specified in the previous points and, hence, enough time for them to find a way to "transcend" themselves into a superior human race. The villain is willing to die for this cause and will gracefully accept them as superior beings. Of course, nothing in this is possible without a reliable mobile network. How can the villain find or come up with a mobile network fast and efficient enough for his objectives? [Answer] --- ## Bit rate The paper [The Limiting Information Capacity Of A Neural Link](http://www.sns.ias.edu/~tlusty//courses/InfoInBio/Papers/MacKayMcCulloch1952.pdf) says: > > the mean frequency would be about 670 impulses > per second and the average information content about 4.3 bits per impulse. > > > That would be 4.3\670 bits / second = 2881 bits/second. We know that there are 24 cranial nerves and 30 spinal nerves. So we have to connect 30 + 24 = 54 streams of data of 2881 bits/second = 2881 \ 54 = 155574 bits/second = approx. 19.45 kB/second. --- Edit: later in the paper the figure of 6 bits per impulse in introduced, givin us: 6\670 bits / second = 4020 bits/second. So, 54 streams of 4020 bits/second = 54\4020 bits/second = 217080 bits/second = approx. 217.1kB/second. --- It is not that much. It is over GSM bit rate, but any 3G, WiMAX or LTE connection will do. --- ## Latency According to the question [How long does a signal from the brain take to reach the limbs?](https://biology.stackexchange.com/a/21801) the latency of the nerves is between 100 ms to 300 ms. According the research [Measuring mobile broadband performance in the UK](http://consumers.ofcom.org.uk/news/4g-significantly-outperforms-3g/) by ofcom.org.uk latency in 3G connections is between 63.5 ms and 85.1 ms. So, again, any 3G connection will do just fine. [Answer] ## Bandwidth isn't the killer problem, latency is. Bandwidth Requirements There are 640 muscles in the human body, each with a range of values from totally relaxed to totally constricted, zero to one. Floating point values are stored in 32 bits. 640 \* 32 = 20480 bits/second. Assuming that the same amount of data needs to be uploaded as download, then we're talking about 5 kilobits per second. Add required overhead such as packet headers and you're to 10Kbps. But....muscle state isn't enough. To work the construct, we will also need continuous streaming video/audio as well as sensory data to the mainframe. Netflix recommends a minimum of [3.0 megabit/second](https://help.netflix.com/en/node/306) for SD quality streaming video. They recommend 25 megabit/second for Ultra HD quality streaming. Verizon claims that LTE can carry between [5 and 12 megabits/second](https://www.verizonwireless.com/archive/mobile-living/network-and-plans/4g-lte-speeds-compared-to-home-network/). Under ideal circumstances of full bars in a dense urban environment, the construct could stream SD quality video back to the mainframe. During periods of high usage on the LTE network (outside of the construct's control), streaming video may stutter or stop, effectively rendering the construct blind and/or deaf. Kind of a big problem if the construct is driving a car or operating heavy machinery. Or, if not the public cellular networks, our villain could make his own wireless network and build it specific to his needs. Latency kills The problem with remote administration of a construct without any kind of central nervous system is the time it takes to get state info from the construct back to the mainframe, process it and send commands back. This is true, even if the villain builds his own wireless network. There are several sources of latency: * Video processing: It will take some amount of time to translate the binary data coming from the construct into electrical impulses on the optic nerve. * Audio processing: Same as visual processing. It will take some time to translate. * Sensor synthesis: If any amount of processing needs to be done on the sensory data coming, this will add to the delay. * Network latency (the speed of light gets you every time) Note that the fastest recorded reaction time for a human being was [0.101 seconds](http://www.humanbenchmark.com/tests/reactiontime/statistics) and a median reaction time of 0.266 seconds according to HumanBenchmark.com. If the combination of the construct, cellular network, mainframe and CNS cannot respond in less than a quarter a second, the construct will appear clumsy, uncoordinated and slow. [Answer] I guess the obvious solution here would be to have multiple mobile connections between host and client. This increases the bandwidth and provides for some redundancy in case one or more of the connections drop for some reason. ]
[Question] [ In the [latest Artifexian video](https://www.youtube.com/watch?v=t6i6TPsqvaM), he talked about terrestrial moons, bringing up great ways they could and would exist. But the video ended with an interesting concept, Horseshoe Habitable Moons. From [Wikipedia:](https://en.wikipedia.org/wiki/Horseshoe_orbit) > > A horseshoe orbit is a type of co-orbital motion of a small orbiting body relative to a larger orbiting body (such as Earth). The orbital period of the smaller body is very nearly the same as for the larger body, and its path appears to have a horseshoe shape in a rotating reference frame as viewed from the larger object. > > > The loop is not closed but will drift forward or backward slightly each time, so that the point it circles will appear to move smoothly along the larger body's orbit over a long period of time. When the object approaches the larger body closely at either end of its trajectory, its apparent direction changes. Over an entire cycle the center traces the outline of a horseshoe, with the larger body between the 'horns'. > > > Artifexian pointed out the interesting features twin habitable worlds in a coinciding horseshoe orbit and it made me wonder, What would Seasons and day/night cycles on habitable worlds be like if they existed in a horseshoe orbit? [Answer] TL;DR: The seasons will have different lentghs depending on the "side" of the horseshoe it is in (there is a slow and a fast "side"), and the day/night cycle will be unchanged. --- For more info on horseshoe orbits, [there's this Q&A on physics.SE](https://physics.stackexchange.com/q/8340/48721). > > From the perspective of an inertial frame in heliocentric coordinates this asteroid [that has a horseshoe orbit] is in a circular orbit (topologically a circle) around the sun. > > > This means that the seasons will be the same. It has a moment when it will be nearer the sun (summer) and another when it will be farther away (winter). Depending on its rotational tilt, it will probably also have autumn and spring seasons. But the length of the seasons will be different, and the order may change too. More on that below. It [probably will have rotation](https://physics.stackexchange.com/a/26749/48721), so day / night cycles are a given. Since it is habitable, it is crucial for the cooling of the planet surface to have a day/night cycle. Again, the horseshoe orbit won't affect it for the most of the time. When it approaches the main planet, things change a bit: > > It will eventually catch up with the Earth, but it is not necessarily gravitationally drawn into the Earth. It interacts with the Earth’s gravity field in its frame with an effective and repulsive potential (...). The gravitational potential plus this effective potential pushes the asteroid into a higher orbital radius. The Lagrange points L4 and L5 act then as attractor points in the rotational frame of the asteroid. Its orbital velocity is now smaller and recedes away from the Earth. Eventually the Earth approaches the asteroid and the process is repeated. [ref.](https://physics.stackexchange.com/q/8340/48721) > > > The tides will probably become stronger due to their gravity interaction. Because it will change its orbital velocity as it "rotates" around L4 and L5, the length of the seasons will change also. It will have a faster and a slower season cycle. Relative to the sun, the planet never changes direction, only speed. On the slow cycle, the main planet catches up from behind and accelerates the horseshoe-orbit planet. It enters the fast cycle, when it goes around the orbit and approaches the main planet from behind, when it has its speed reduced and goes back to the slow phase. All of this while both bodies orbit the sun. > > This is a “hunter-chaser” type of orbit. The thinner the horseshoe is the smaller the angular momentum L is with respect to the Earth at close approach. This means the gravitational attraction can become larger. [ref](https://physics.stackexchange.com/q/8340/48721) > > > [Answer] Interesting question. HEre is what the setup looks like for Saturn's moons Janus and Epimetheus (from <https://en.wikipedia.org/wiki/Epimetheus_%28moon%29#Orbit>) [![enter image description here](https://i.stack.imgur.com/LzRnl.png)](https://i.stack.imgur.com/LzRnl.png) The key thing to know is that planets on horseshoe orbits don't strongly affect each other's spin. Both Janus and Epimetheus are tidally locked to Saturn, meaning that they always show the same face to Saturn. So, relative to the Sun, each moon spins once for each orbit it makes around Saturn. Imagine a more general setup, where the central body is a star and two planets share an orbit in a horseshoe configuration. If the planets are close to the star it is likely they will be tidally locked such that the same side always faces the star. But the planets could well spin at a different rate and that would not be affected by the horseshoe setup. The only really interesting thing is what Artiflexian pointed out, that the other planet would get big in the sky and then retreat. This is likely a very rare setup -- in running thousands of simulations of planet formation (my day job) I have only encountered this once or twice. Much more common are Trojan planets: configurations where two planets share the same orbit and remain roughly 60 degrees apart -- FYI see the second part of this post: <https://planetplanet.net/2014/05/22/building-the-ultimate-solar-system-part-4-two-ninja-moves-moons-and-co-orbital-planets/> ]
[Question] [ Let's assume that the dictator of a large and rich country is approximately 70 years old, and that signs of old age are showing, meaning that his death is not very far. Let's assume that the people of the country want to keep this person alive for the longest possible period at any price. Let's assume that the dictator is a healthy person who does not have cancer, is not obese and exercises regularly. All medical and biological resources (bioengineering, genetic engineering, etc...) of a large and rich country are available. My question is: * What is the most effective method to keep the dictator alive for the longest time possible, using modern or near future state-of-the-art medical and biological technology and surgical procedures? By "alive" I do not mean cryogenics or any other type of stasis - the dictator should be able to live a (largely) normal life and fulfill his duties and obligations. [Answer] I would say [Heterochronic parabiosis](http://stemcellassays.com/2014/08/parabiosis/). Basically, a young person and an old person share a circulatory system. This means that the factors which make a person young get into the old person along with the [dilution of factors which make a person old](http://www.nature.com/cr/journal/v24/n12/full/cr2014107a.html). One could possibly have young people feed their plasma into the old person to rejuvenate them. As well, [senolytics](https://en.wikipedia.org/wiki/Senolytic) may be useful, clearing out damaged cells and the factors that they circulate which make people old. See [here](http://onlinelibrary.wiley.com/doi/10.1111/acel.12344/abstract). Edit: Heterochronic parabiosis is the procedure of surgically joining two organisms of different ages so that they share a similar circulatory system. Because aging is a systemic disease (it affects all parts), a significant percentage of the factors which govern again are quite often found in one's circulatory system. There are factors which rejuvenate people and keep them young and their are factors which contribute to aging. By linking circulatory systems, the old people get the 'youth' factors, while offloading the 'aging' factors onto the young organism. This leads to the old organism rejuvenating (though it must be said that the young organism gets the short straw as it ages). So inserting blood plasma from younger people -- which some researchers are currently testing or about to test -- may be a way to get a young person old again. Senescent cells also influence aging. These cells are cells that are dysfunctional but have not been cleared through apoptosis (cell death). They exist in a senescent state where they give off aging factors into the local environment and blood stream. Removing these cells through various chemicals called senolytics has been shown to increase cardiac output and reverse other signs of aging in mice. One could imagine that a person may be given senolytic compounds to rejuvenate them. Edit 2: I also want to say that one could potentially isolate the factors that make organisms young and basically have a drug cocktail. Such factors like GDF11 show promise to do so. The problem is that there are so many factors which govern aging and youth so coming up with a complete list is very hard and very tricky. You can though, dependent upon how technical you need it to be, say something like 'a drug cocktail to extend aging which included GDF11, blah, and blah.' [Answer] If you throw morals and ethics into the nearest black hole (and start early enough), you might be able to get a cloning and organ harvesting setup going. It's reasonable to assume that we could clone a human today, and even if only 1% of clones are viable, the rich country could afford it. Then, raise the children and once they're of age (or the dictator suffers a kidney failure or whatever), harvest their organs to replace the failing ones of the dictator. [Answer] There are a few options for your ailing dictator. * Pump him full of [nanites](https://worldbuilding.stackexchange.com/questions/32577/how-many-nanobots-can-i-have-in-my-blood) that take over most if not all of his body's functions. * Do what Plinth said (Heterochronic parabiosis). * Upload his mind into a quantum (or any other type that could handle the job) computer. that's all I can think of for now. P.S. Why do the citizens of a dictatorship want their (most probably) cruel oppressor to live for ever?! [Answer] Ivan Stepanovich Filimonenko, one of the founders of nuclear physics and the developer of the project to neutralize radiation, did not try to create an elixir of eternal youth. The discovery made by this outstanding scientist is not just sensational, but, at first glance, fantastic. Knowing that the main source of radioactive contamination is the isotope potassium-40, Ivan Stepanovich calculated that the duration of our life is inversely proportional to the amount of radioactive elements contained in the body. It is this isotope that decays in the human body and destroys all living cells. The body, however, restores them, but the action of the isotope does not stop, and the cells die again and again. The human genetic program is designed to replace cells no more than a hundred times, and, having spent its limit, the body concedes to the radioactive monster. Thus comes the inevitable old age and death. So, since we get radiation exposure from the environment, the fewer sources of radiation there are in this very environment, the higher the average life expectancy will be. Ivan Stepanovich did some calculations and determined that if the human body throughout its life contained 245 grams of potassium-40, the duration of its life will be equal to 61 years and seven months. If you reduce the content to seven grams, the average is 2531 years , and at 0.7 grams of potassium-40, the life expectancy will increase to 25,300 years! He created the world's first radiation neutralization unit 50 years ago, and it successfully passed all the tests. But as is often the case, he was not allowed to put this installation into practice. But Ivan Stepanovich so dreamed of conducting his experiment on some territory and reducing the content of radioactive substances, if not to the level that was on the land of the ancient Sumerians, then at least by half. However, such an experiment would have to be strictly classified, otherwise thousands and thousands of pilgrims would rush to this territory in the hope of prolonging their lives. For" a place in the sun " they would have trampled each other for sure. According to the scientist, the powerful even then offered to equip him with miracle installations in special underground cities, ]
[Question] [ I'm retouching the idea discussed in detail here [Evolution of species with separate sapient and non-sapient forms?](https://worldbuilding.stackexchange.com/questions/10131/evolution-of-species-with-seperate-sapient-and-non-sapient-forms). I like the discussion had there, but want to focus in on one specific question, the biggest difficulty of the question. Context and some ideas already come up with can be found there. To give the short version, I had the idea of a species that had a separate sapient and non-sapient phase/lifecycle to combine R and K reproductive strategies. When the species mates, it produces lots of non-sapient young which are initially left to fend for themselves to live or die; I use the analogy of tadpoles produced by frogs, and in fact refer to these individual as T phase for tadpole. The species will eventually come back to pick a small number (1-4) of the 'strongest' of the remaining tadpoles and raise them as sapient adults. Those chosen to be raised by their parents will trigger a metamorphosis which leads to developing an increased brain and sapience, but requires years of rearing from the parents as any human child would. I refer to these as S-phase, for sapient. However, those T phase that survived and were not chosen by their parents to be raised will continue to grow & develop on their own. A small number will grow into adults, while still being T-phase, meaning they are not sapient, being more animal the 'human', think the difference between semi-complex heard species like wolves and something between human and bonobo for difference in intellect between T and S phase, very roughly speaking. The idea is that a batch of children can lead to both T and S phase young surviving and potentially later reproducing, thus allowing the parent a choice between S and T reproductive strategies. They can choose to produce lots of T phase young, or focus on S phase with fewer matings producing T phase as needed. I'm specifically looking at the transition period where Sapience is evolving, so the S phase is at or beyond bonobo/chimp's level of intellect, However, they have not developed intellectually/culturally further then say caveman & stone users, they don't yet have sufficient technology to be modifying their mating strategies. For this to work, T phase must be able to grow up and mate. Either phase is capable of mating with the other phase, and two T phase can mate to produce T phase children, but only S phase parents will be able to trigger the mutation that leads T phase young to grow into S phase. My original question was very open-ended. I want to focus this question specifically on gene-flow; as such I'm less worried about the other (non-trivial) questions of how they evolved to reach this point, or the viability of the species (I acknowledge justifying a species like this is hard evolutionarily, though I don't think impossible with work). I want this species to have an evolutionary stable mating strategy, meaning it does not lead to either only S or T phase being produced and it does not lead to T and S phase becoming separate species. The biggest problem with this is having T phase adults able to produce S phase young. While S phase adults are capable of producing many T phase young if those young do not eventually produce now S phase then evolution will not 'reward' S phase adults for producing the T phase young and thus they would evolve to focusing on producing more S phase children and less T phase ones. Thus I'm looking for good explanations for how to ensure gene flow between the two phases, specifically with T phase adults able to produce S phase young. A few presumptions: * S phase have a much higher reproductive success, to justify the energy expenditure. * An S adult would presumably prefer to have S children with an S mate, since it's easier to judge the fitness of s-relevant traits (like intelligence and social interactions) in a mate who is also S phase and thus demonstrating the traits. I'm more than open to S choosing to raise S young from a T mate, but some justification for why this offers genetic fitness over focusing on S children with S mates despite the lack of ability to judge relevant traits as easily must be provided. * The vast majority of the time an S phase adult will be required to provide for a young in order for it to develop into S phase adults, K species simply are not self sufficient as young without parental investment. Ideally: * At least some T phase will mate with other T phase as adults to produce 2 gen T young. * T phase are not dependent on S phase to care for them, unless part of an instinctual symbiotic relationship (ie, not something S phase engineered through technology & training or intentional domestication of T phase) I'm looking for all possible methods to encourage gene flow, specifically from T adult to producing S young. I'll start with some key points which I likely will be using to get out of the way, though I don't consider them enough. 1. Cuckoldry from T phase. T phase will attempt to fertilize the eggs of, or later add their own eggs into, the 'clutch' of S phase parents, in hopes that one of the S phase parents will raise the T children's child parent by mistake. This could be with support of the female ('cheating' on the male, possible to get a fit T phase child with help of an unfit S phase male in raising it) or without. I think this actually is a great potential starter towards justifying gene flow actually! But S parents would likely have evolved pretty effective methods of avoiding cuckoldry quickly, and cuckoldry will have to be limited in occurrence or the S phase would eventually disappear entirely (why invest energy in producing S phase young over lots of T if there is a non-trivial chance that energy is expended on a child that isn't yours?). So while I'll likely use this as at least a partial explanation I don't think it can be a full one. 2. Adults, particularly males, who can not find or do not want a mate may mate with T phase and raise a smaller number as S children as a 'single parent' so to speak, most common with young males who can not yet convince females to mate with them or with males/females who have something 'wrong' with them to make it hard to convince an S adult to mate with them. However, it seems like it would be rare that committing the time investment of raising a S phase child alone is better than waiting a year or two to try to get an S phase mate. 3. Occasional rare occurrence of S phase adult simply choosing to raise an unrelated T young (ie adoption); I don't see this adding up to a significant number to add much gene flow. * However, a system when S adults raise T young that is closely related to them (grandchild, nephew, half-sibling) could potentially result in 'adoptions' being frequent enough to have an effect. Though I'm not certain how to justify this happening frequently, raising a half-sibling is only 50% as effective as raising your own, why would this become evolutionarily common? Only excuse I can think is in situations where the parent cannot produce children themselves. The only example f that to occur frequently enough to matter in less culturally advanced sapient would seem to be infertility due to old age; but wouldn't evolving to stay fertile longer, or assist your S phase children in producing children, make more sense then evolving an extensive system for tracking and choosing the young of T phase to raise? 4. Some sort of quid-pro-quo where parents raise, or take a chance of raising, the child of a T phase in exchange for some resource the T offers. For instance a T male will guard the 'clutch' of S parents if it is allowed to fertilize a small number of the eggs in it, with the female then piking children to raise knowing some of them will be from the preferred S male and some from the possible less preferred T male, but the advantage of a 'clutch gaurd' for her clutch is worth the risk of picking the less desirable males child? There are likely a few variants of this idea, but I've yet to get one that felt viable and evolutionarily stable, particularly if one assumes males help in raising of S phase children since they would evolve to avoid agreeing to raise a child that isn't genetically theirs. Possibly combine this with cuckolding idea could work though.. Some more 'extreme' options I've debated but am not certain are ideal which someone may be able to expand on. 1. Sequential hermaphrodites, with T phase all being female and S phase all male. Geneflow is guaranteed, but this would almost certainly result in 'wife husbandry' sort of harems being genetic/instinctual in males that I'm not certain rather or not I want in regards of making an interesting species I'd enjoy writing. I want the sapient species interacting socially as humans due, not in constant competition over winning the other male's females into his harem. * Many other variants of unequal distribution of sexes I've considered. If I can get a system with s females, but more S males then females, it can work well, but fisher principle makes that difficult. 2. Some natural symbiotic relationship between T and S such that the two are not mostly separate outside of mating season, though doing it as naturally symbiotic and not 'domesticated' T's being husbanded by technologically developed S is harder, and it doesn't solve gene flow as simply allow some interesting variants for how mating can occur due to the inherent closeness. [Answer] I feel like this type of breeding behavior would make the most sense if there were specific points in time when T-phase offspring were optimal to produce and other points in time when S-phase offspring were optimal. If these two reproductive strategies were both critical to the success of the species, both would be preserved. One way to obtain such a pattern would be with a cyclical climate, which altered between an incredibly lush climate, where plentiful resources made survival and reproduction easy and an incredibly harsh climate which favored highly intelligent individuals. In the plentiful season, rapid reproduction would give individuals a huge advantage in numbers, quickly outnumbering individuals who chose a slow reproductive strategy. During the 'fall' season, individuals would switch to a slow reproductive strategy to produce intelligent, competent offspring who could adapt to the challenges of winter. There would be some tradeoff in when individuals would switch strategy, so the two strategies would overlap to some extent in the spring and fall, while summer would be almost exclusively a time of fast reproduction and winter a time of slow reproduction. If only S-phase individuals are capable of having S-phase children, the optimum behavior strategy would be to produce lots of T-phase individuals under good conditions, and then for S-phase males to produce lots of S-phase children with T-phase females before winter arrived. While Earth-like seasons are too quick to lead to this sort of behavior, it could easily evolve on a planet with much longer years, where it would make sense for reproduction to continue year round, rather than being seasonally driven. [Answer] I was thinking about the mention of an S-phase adult choosing to adopt a T-born offspring, as a strategy to ensure the gene flow, and how to make that more likely. Adoption may be much more likely if there are advantages to having S-phase offspring that are more immediate than competitive genetic legacy. If your S-adults are slightly more social, with a social structure that's based around a slightly larger pack or family instead of individuals, then adoption becomes more likely to maintain a larger group. One idea that struck me was the possibility of S children helping parents or family when ill, injured, or old. This behavior might include families helping each other forage for food, or banding together to ward off predators. This gives an advantage to raising a child even if unrelated, since it improves the adopting parent's chances of survival and later reproduction, or (depending on social structure) improves the chances of survival for a whole family. Other factors that might play into adopting rather than depending on their own offspring - if there is a gender divide, perhaps those of one gender are 'adopted' into the family of their mates... so a family who tends to produce that gender may need to adopt to keep their own numbers up as their offspring mature and leave. Or those whose family becomes dangerously small, from predators or illnesses, trading the effort of raising unrelated offspring for numbers to survive long enough to reproduce later. Another option may be that perhaps adults leave their parents once they are mature, and so only a still-dependent child will assist their parents... and so adoption will happen when an S-adult is already injured or ill, so it is not dependent on having had young of just the right age... and if the parent dies before the child is independent, the loss of the effort involved in raising an unrelated child is less expensive than all the effort lost if their own S-offspring were to be orphaned (including extra time maturing to adoptable age and the effort spent reproducing). Or, to play off of ckersch's idea of cyclical climate - it might be that at certain times of the year, more pack-mates (or family members) are helpful to forage for food or fight predators, and at other times the fewer the better to conserve resources... adopting would therefore be equivalent to seasonal labor, unrelated t-born being adopted and raised when resources are plentiful and higher numbers are safer (perhaps more frequently than actual reproductive cycles allow?), and abandoned or driven away when resources become scarce. This "less expensive loss" idea may also be a reason for a young adult to adopt T-born before attempting to reproduce and raise their own offspring, if a larger family increases the odds of the children's survival a great deal. The extra effort of raising the t-born (and making newbie mistakes) is balanced by a lesser cost if they are lost, and the extra protection when the young adult is ready to raise their own offspring in the larger family. Alternatively, once you have advantages to raising a child regardless of actual parentage... maybe you can emphasize the differences in your R and K strategies. Tadpoles are, after all, rather difficult to trace the lineage of - they all exist in the same ponds, and don't look much like their parents. R strategy species don't tend to track their own lineage, its about reproducing many offspring and letting the fittest survive... so maybe the R phase of your species likewise can't tell whose tadpoles are whose. Rather than having your curiously mixed stage, of producing lots of offspring but also tracking the lineages (and/or caring for them) until adoptable age, have your tadpoles simply be indistinguishable from each other, and the T-born or S-born lineages unclear at this stage. S-adults will then choose from all the tadpoles of adoptable age, looking for those most likely to have successful S-traits, and choosing successful offspring is then as much a survival strategy as reproducing lots of offspring. The families, or clans, are then solely based on adoption and mutual support - and the better survival of the clan means more chances for each individual to breed, and therefore more chances for their offspring to be adopted by any clan or survive as T adults. There might be some benefit to identifying relatives (by scent? or markings?) and adopting those preferentially, but it would not be required. Credit where it's due, I think I might have read a similar scenario in a book, maybe in the "Reteif!" or "Interstellar Patrol" series. This scenario would probably lead to fairly quick evolutionary process - the tadpoles are selected for survival fitness, the survivors evaluated for S-traits, the adults (both S and T) are selected for survival fitness again. The free intermingling of genes during tadpole phase would keep the populations intertwined, and the S-adults selecting among all the offspring for S-traits would increase the selection pressure for those traits (selecting for individuals, not just families). Also, I would expect a heavy cultural emphasis (once they get that far) on being strong or useful, competing heavily, and surviving at all costs - since cooperation is not rewarded through a major portion of their lifestyle. Side note - whatever mechanism you choose, you might want to relax your requirement that only S-adults can trigger S-offspring, otherwise the question of where the first S metamorphoses came from is quite puzzling. Having the possibility of T-born occasionally managing to hit the right cues for the metamorphosis would answer that question, while sneakily helping to keep the genes intermingling. That these occasional converts have a much lower chance of survival due to lack of training and care while young, keep the possibility from disadvantaging your S-families too much, while giving a slight advantage to T-adults having S-trait offspring and answering how the whole setup came to be. ]
[Question] [ I've just read [this article](http://www.gizmag.com/laser-light-propulsion/41980/) and watched the accompanying video. Heady stuff, for sure. I'm particularly intrigued by the concept of a "solar gravitational lens telescope" somewhere out near the heliopause. I'm surprised this isn't bigger news. I don't know how to effectively read the charts, nor interpret what they're telling me even if I did. Conceptually I grasp it, though; at least I think I do. So, let's say we got really serious about sending a manned mission to a nearby star. In this scenario, we've determined without a doubt that there is an advanced civilization living on a planet orbiting 61 Virginis, which is (per Wikipedia) 27.9 light years away. Many questions come to mind, and I need to break this idea up into several "questions", but here they are a few that are related: 1. Given sufficient funding to build and deploy up to three space-based lasers in the solar system, where should they be "placed" (orbited) to best accelerate a ship? 2. Given the above placements, how large are the launch windows to use the lasers? 3. How often do the launch windows come around? [Answer] Using light to launch an interstellar probe has a number of things going for it, but it's not all peaches and cream. Most importantly. it's wildly inefficient in the short term. For a light beam bouncing off a mirror, the thrust applied to the mirror amounts to 150 MW of optical power per newton of force. Note that a newton isn't much. For the video's proposed 70 GW array, that amounts to about 467 N, or about 100 pounds of force. Of course, the advantage is that the thrust just doesn't stop. The linked video talked about sending a package to Mars in 8 hours, and this is correct. What you may not have realized is that the package under discussion is a CubeSat, and these things have a maximum mass of 1.33 kg. For such a light object, the acceleration is about 35 g's so yes, it really does get moving. Also note that nothing is said about how to slow it down once it reaches target. This is not, in principle, difficult: you just have another 70 GW array orbiting Mars which applies deceleration. It is unfair to ask how the target array got there in the first place. So, there are (at least) 2 things to ask about an interstellar launcher. How big is the laser array, and how big is the probe? Let's say, just as a starting point, that the probe has a 1 $km^2$ light sail, and weighs 1000 kg. This is clearly not a manned probe, and the technology is beyond what we can do (if nothing else, we can't guarantee reliable operation for a century or more, and that assumes average velocities of about 0.3 c - more on that later). Let's say that the laser arrays are the video's 70 GW. As the video points out, solar power makes the most sense, especially for long-duration power production. Conceptually, each array consists of a 10 km x 10 km solar cell array which will orbit oriented to point directly at the sum. The back side of the platform is a phased-array of laser emitters producing a total of 70 GW, with a beam steering capability of +/- 60 degrees. This limits the illumination time for an object to about 1/3 of the array's orbit. Fortunately, you specified that 3 launchers will be built, so if the 3 arrays are in solar orbit at 120 degrees spacing, one will always be available for use. An obvious requirement in this case is that the array orbit must be inside earth's orbit, since the arrays can only fire outward from the sun. With a probe mass of 1000 kg, acceleration will be nominally about 0.467 m/$sec^2$. How long will the array be able to supply power? Assuming a 1 um laser wavelength, the diffraction angle for the beam is the Rayleigh criterion $$\theta = 2.44\frac{\lambda}{D} = \frac{2.44 \times 10^{-6}}{10^4} = 2.44\times10^{-10}\text{ radians}$$ and this will produce a spot size of 1 km at $$ R = \frac{d}{2 \theta} = \frac{1000}{2\times 2.44\times 10^{-10}}= 2\times10^9\text{ meters}$$ or about 7 light-seconds. After this range, the thrust will drop off as the square of the range, since the beam will get larger and large and the mirror will intercept a progressively smaller portion of. The high-boost phase will take$$ t = \sqrt{\frac{2s}{a}}= \sqrt{\frac{4\times10^9}{.467}}=857,000\text{ sec}$$, or about 10 days and velocity at that point will be $$ v = at = .467\times 8.57\times10^5 = 4\times10^5\text{ m/sec}$$ I am, frankly, too lazy to do the math for the post-peak acceleration, but let's round up the final velocity to about $10^6$ m/sec. Note that this is only about 0.3% of c, and time to 61 Viginus is about 8600 years. It's clear that we need bigger guns. Now, as promised, the question of how to slow down at journey's end. It's very, very clear from the previous that there is no way affect the final trajectory with the specified array. It simply will not produce an appreciable power density over 30 light years. But let's say that we could, somehow, do this. Does that help? The answer is yes. During the voyage the probe turns around and ejects a second, much larger mirror which precedes the probe. The braking beam impinges mostly on the secondary mirror, accelerating it, but the reflected beam hits the probe mirror and provides a braking force. This is not exactly a friendly move towards the target system, since it produces an expended secondary mirror which whips through the target system at (for a secondary mirror equal in mass to the payload probe) about twice the transit velocity. Admittedly, the braking mirror is presumably some extremely lightweight material, but still... Assuming a launch acceleration adequate to produce low-relativistic velocities, launch window is fairly forgiving, about 4 months/year. The immediate issue is to eliminate the cross-target velocity of the probe. Doing this immediately will, of course, result in a small radial velocity for any probe launched with a velocity near Earth's escape velocity, since the orbital velocity of the earth is about 30 m/sec. The ideal launch point occurs when the sun/earth vector is about 45 degrees to the target vector. Then the cross-target velocity is relatively small, and angling the mirror to eliminate this will also produce decent down-range acceleration. The exact optimum and window will depend on the thrust available and the launch velocity of the probe from earth. In principle, there is nothing to prevent using the laser beam to provide all of the thrust and the probe assembled in low earth orbit, but the numbers need to be worked out. EDIT - Oh yes, and about the gravitational lensing thing. You can probably forget it. I haven't been able to get at the underlying calculations, but it seems pretty clear that the author simply doesn't know what he's talking about. A discussion of this is beyond the scope of this question, but I'm fairly certain that it won't work. His claims and explanations are to some degree self-contradictory, and he seems to have overlooked a few very important issues. I could be wrong (as history has shown) but I'm fairly sure I'm not in this case. [Answer] This sort of system was used by the book Rocheworld, a.k.a The Flight of the Dragonfly. <https://en.wikipedia.org/wiki/Rocheworld> The author had a very well thought out system where collector stations orbiting Mercury (and crewed by people working from a sunhook in Mercury's shadow gathered up the power and sent it out to a lens further out in the solar system. That lens then focused the light and sent it on to the lightsail. With modern laser technology the lens stage may not even be needed, so we could just send the power directly from Mercury. This would be quite a dangerous thing to have and control though, be careful where you aim it! In that example the ship got up to 0.2c, which is similar to that in your article which mentions 0.26c. Even at those speeds though it would still take 107 years. This is not fast enough for relativity to really kick in either, elapsed time for people on board would still be over 100 years, especially once you factor in acceleration and deceleration times. For "launch windows" you need Mercury to be on the right side of the sun as the sail and the target, and stay in it for a while, which means that traveling to a target in line with the plane of the solar system you would be able to launch for say 20 days out of each 88 day Mercurian year and have enough acceleration time before you lost the laser. Multiple sails could be launched to different destinations though and the lasers would switch between them in turn as the planet orbited so you could keep continuous uptime accelerating something. If you were launching up or down then that would not be a problem and you could launch at any time. [Answer] The logical place for the lasers is near the Sun, so they can absorb the maximum amount of solar energy. Many proposals suggest they orbit Mercury so the gravity of the planet keeps them aligned, and also has the advantage of providing raw materials for building the project in the first place. Since the amount of energy needed increases exponentially as the ship gets farther away, the construction site will be busy building and launching lasers around Mercury, starting with a 43,000TW array and finishing with a monster 73,000TW array. Authorities on any inhabited planet will be watching this very closely, since you are building a real life Death Star that could fry any planet crossing the beam..... [Answer] The lasers will need energy. A lot of energy. Possibly several terawatts of energy each. So you'll need to put them somewhere they can get energy. So put them in orbit around one of the gas giants, probably Saturn because of how hostile Jupiter's radiation is, and use the gas giant as fuel to power the laser. The lasers will be in orbit, which means that you'll have between 1 and 2 with line of sight to the space ship at all times. So as they get line of site they will aim their laser at where the ship will be when the light gets that far. Maintenance can happen while the laser is behind the planet. The people working on the lasers can live on Titan, which actually has a dense atmosphere, though it's very cold. The ship will be traveling toward where Virginis will be a thousand years, give or take, but the lasers will only really be pushing them for the first hundred or two, before they get to far away for the light to do much good. ]
[Question] [ One of the great problems in designing an Artificial Intelligence [we can control](https://worldbuilding.stackexchange.com/questions/6340/the-challenge-of-controlling-a-powerful-ai) is our own lack of sufficient intelligence. Partial failure here (success as designing an AI, failure at control) would result in a future where we're all dead [or pets to greater beings](https://worldbuilding.stackexchange.com/questions/6550/humans-as-pets) at best. It would be helpful if biological humans were smarter. [Nick Bostrom](http://rads.stackoverflow.com/amzn/click/B00LOOCGB2) discuses a cognitive-enhancement process through repeated genetic selection. He argues that if the heritable genetic characteristics of intelligence can be assessed by large-scale correlation studies, a 1 in 100 selection pressure (select the "best" out of 100) towards correlates of higher cognitive function repeated over 10 gamete (sperm + egg) generations can result in massive IQ boosts in the selected individuals (upwards of 100 IQ points total gain at the end of the selection process compared to the baseline - i.e. us). If Bostrom's scenario is realistic, what would be the social implications of such a selective process if there were, say, 1% adoption of this method among the population? In other words, how smart can we get, and still retain a viable society? [Answer] I think that some governments might create a very secret, well controlled group of highly intelligent super-scientists who's jobs it would be to gain them tremendous advantages over their competition. These people could be depended on to figure out issues which would otherwise take decades to research and understand, as well as design weapons systems, and other technologies which would put that that country ahead of everyone else. The way in which you'd keep these people from effectively becoming our overlords is by keeping them on a tight leash. Indoctrinating them from birth seems like a logical first step, however anyone truly intelligent will likely outgrow their conditioning. At that point having a good-ol fashioned goon with a gun aimed at their head will help maintain control. Even then, these people may very well figure out how to gain control. Depending on how they view the rest of us (insects to be crushed vs their disadvantaged cousins) they may or may not make better leaders than the ones we have today. [Answer] This would certainly increase the number of 'geniuses' that are produced rather significantly, and after a few more generations, redefine what we consider genius. Many smart people are already looked on as odd frequently because of how they interact with others. Somewhere I read a quote that we can really only effectively communicate with people within a certain IQ range of our selves. I think it might [30 IQ](https://georgiebc.wordpress.com/2010/11/15/the-30-iq-point-bridge/) points. So as you get people who are smarter and smarter they will by default tend to separate themselves from us (and us from them). We would have two separate societies emerging. Eventually they might take over governing us, since they would be smart enough to manipulate us like pets. Now if they became despotic, they would likely be overthrown and maybe wiped out, but being that much smarter than us, more likely they would take the road of benevolent dictators and making sure everyone is taken care of the the 'burden' placed on an one individual it 'relatively' light. If people are comfortable and occupied, they don't riot or resent (as much). If the super intelligent don't flaunt their money and power, then there would be even less reason for discontent. Eventually they would likely get themselves a space vessel to leave us dirt diggers behind to our own devices. [Answer] The problem is in how we define "intelligence." If we limit it to "what is measured by IQ tests," then we can possibly increase this factor significantly, but at what cost. Note that many super-intelligent people are also very anti-social. [Grigori Perelman](https://en.wikipedia.org/wiki/Grigori_Perelman) is perhaps one of the most famous. [Paul Erdos](https://en.wikipedia.org/wiki/Paul_Erd%C5%91s) was friendly but eccentric. Thus, high IQ alone might not save us from the tyranny of AI, since the high-IQ individuals might not care a whit about that problem. Today, our political leaders can hardly be considered the smartest in the pack. Even our CEOs tend towards [sociopathy](http://www.patheos.com/blogs/drishtikone/2013/10/are-ceos-and-entrepreneurs-psychopaths-multiple-studies-say-yes/?repeat=w3tc) moreso than [high IQ](https://lionoftheblogosphere.wordpress.com/2014/10/12/ceos-of-big-corporations-only-have-iq-of-115-on-average/). So it is not exactly clear how high-IQ individuals would actually save us from the Robot Overlords, unless we employed them as defensive hackers in the NSA. ]
[Question] [ In previous questions on this topic, I've devised a [genetically-diverse creature](https://worldbuilding.stackexchange.com/questions/33040/multiple-dna-one-creature?lq=1) that uses a [cold fusion internal engine](https://worldbuilding.stackexchange.com/questions/33243/internal-organic-cold-fusion-engine) to provide tremendous amounts of short-term (sprint) energy. However, there have been several concerns raised about such an internal engine. So I am asking the community, what would be the best solution to the problem of sprint energy? Constraints: * Must be able to produce copious amounts of energy on demand * Must be able to produce energy for up to 10 minutes at a time * Must be organic * Must be scalable to creature size (size ranges from caterpillar to whale) [Answer] As a starter for ten: Sugar is actually pretty darn good. It diffuses well, can be broken down immediately by cells needing a boost, and it's pretty simple to get hold of. If your hypothetical creatures have 'sprint cells' (like the exact opposite of fat cells) lining their cardiovascular system that contain high concentrations of a glucose syrup/oxygen/adrenaline mix (built up over time), then when they're in need of a boost a special hormone/chemical can be released into the bloodstream. This chemical would cause the walls of the sprint cells to break down, releasing huge amounts of sugar (which cells need for high performance), oxygen (which cells need for high performance) and adrenaline (or something similar). The advantages: Instant high energy, a feeling of heightened alertness, crazy strength (adrenal surges can do really weird things), and a general feeling of invulnerability. This also scales at the same speed as the cardiovascular system of your creature and can be 'tuned' for varying energy release patterns based on hormone strength/number of sprint cells etc. Potential side effects include: Epic crash after the buzz wears off, Liver failure, Kidney failure, Irreparable brain damage, Cardiovascular disease, Increased risk of stroke, Hyperglycaemic shock, muscle strain and diabetes. Use with caution. [Answer] The power source [![enter image description here](https://i.stack.imgur.com/2rSjE.jpg)](https://i.stack.imgur.com/2rSjE.jpg) There are existing biological power sources that your DNA chimera could use to "power" the muscles, like the organs of an [electric eel](https://en.wikipedia.org/wiki/Electric_eel#Physiology). The organs could produce electricity and provide an electric shock to stimulate the muscle. Multiple organs could be fired in sequence to provide a sustained burst over a period of time. I remember a lecturer a while back talking about how frogs have a different type of muscle in their legs that is really good for fast movement. (White muscle maybe? it's been a long time.) Since your creature has multiple DNA types, it's believable that it would have different types of muscle, possibly layered on top of each other. The normal "red" muscle would be used for normal movement, and the "white" fast twitch muscle would be used as a speed and strength enhancer when needed. ]
[Question] [ Ogre, a sci-fi tabletop wargame from 1977, used the development of an extraordinarily strong composite armor called 'biphase carbide' (BPC) as a technobabble justification for the widespread deployment of nuclear munitions in conventional warfare and a resurgence of tanks as the primary combatants of world powers. The intro to the game states that the armor is so light that even a ground-effect vehicle can carry several centimeters of protection, which is still enough to require 'the equivalent of a ton of TNT' to breach. Armored vehicles protected by layers of BPC are effectively invulnerable to anything short of a contact nuclear detonation. It seems to me that widespread development of this material would have implications beyond being used simply as armor. While the game is deliberately vague about the material beyond stating that it's both very tough and very light, I'd think that a material that is so strong that it requires tactical nukes to breach while being lighter than steel should be useful for more than just armoring tanks. The focus of the game is on the AI-controlled supertanks, but I'm curious as to what the wider applications of this material would be. Lighter engines? More stable architecture? Should the implied materials science translate to civil applications, or do properties that make for good armor not necessarily have wider uses (eg, nobody makes buildings out of Chobham)? Or am I missing some obvious, world-changing application? What would be the world-changing implications of widespread access to an extremely strong, but extremely light composite material? Criteria and constraints for this material. I'm not a materials scientist so please bear with me. * I've [read](http://www.plasticsnews.com/article/20140805/NEWS/140809971/price-keeping-carbon-fiber-from-mass-adoption) that carbon fiber is currently about eight times more expensive than steel, and that price has thus far limited its adoption, so let's put the overall price for manufacturing (tooling, production costs, etc) at roughly four times that of steel. So cheaper than carbon fiber, and much more capable for the same roles (high strength, light weight), but still more expensive than steel. * It's not particularly difficult to produce, or reliant on exotic materials. I'll say comparable to carbon fiber. * It's not able to survive sitting on a nuke. It's strong enough to render conventional weapons ineffective, not invulnerable. Given that the Chobham armor of an M1 Abrams is speculated to be around five times more effective than a steel equivalent, I'll say that this material is fifty times tougher than steel per unit mass. * Its density is a fifth that of steel, so a given volume of this material is ten times stronger than steel at a fifth the mass. * Given the above, I know that this is pretty much an impossible wonder-material. Let's say it runs on the magic of handwavium and try to focus on the implications rather than the physical implausibility. These are all ballpark figures, but I think may help narrow down the parameters. It's more expensive than steel, but far stronger despite less density. It has limits, especially cost-related, but it's physical capabilities are pretty high. So, what are the practical applications? Where will this technology change the world in immediately noticeable ways? [Answer] The purpose of armor is not to 'stop' a bullet, but to spread the kinetic force of a projectile (bullet, missile, knife, sword, shrapnel) into a non-lethal (preferably non-wounding). This might be by having a surface that cause the the energy to be redirected, such as a ricochet, or a sliding glancing blow. Others, like reactive armor have layers to absorb a direct hit and reduce the kinetic energy before it hits the next layer. However the first layer is reduced in effectiveness each time and a hit in the same spot will penetrate much deeper. Now with a light substance that is almost impossible to penetrate, it really means it is EXTREMELY good at spreading out any kinetic energy applied to it, and maybe even able to channel/direct it. Because if I'm in a car that get's hit by a depleted uranium round from an Abrams tank, even if it doesn't breach the car, (especially with light armor) the impact will still rattle me around inside, possibly making a mess, like hitting a semi head on (a little hyperbole there!) So most vehicles and other forms of personal transport would likely have this 'armor'. However just because a material can take a hit, does not mean it can actually support a large structure. It might crumble under the mass of a large building, so might only be a skin on the outside. Now, taking into account the kinetic dispersal capabilities of this material, lots of sports might be made even more extreme. Why have a parachute, when you can put yourself in a sphere, and just 'bounce' after jumping from a plane, or off a mountain top? Why worry about a helmet for bike racing when a small bubble around the vehicle will save your life? [Answer] One thing which was not explored in the game was "how" the armour works so effectively. Some possible forms of armour absorb the energy of incoming blows by shattering or breaking, such as ceramic "strike plates" in body armour. The bullet hits the plate, and the energy is converted into creating a pile of fragments and dust inside the carrier. Unless you are exceptionally unlucky and get hit in the same place again, you survive the bullet strike by picking yourself off the ground and putting in a new plate. Prior to the introduction of composite armour in modern tanks, many experiments along these lines were conducted, including ideas like putting panes of glass between two armour plates, with the glass shattering and taking the energy of the incoming round. I believe other materials tested were various types of salts as well (the salt also had the property of absorbing and dissipating much of the energy of things like HEAT rounds). As you can imagine, while things like this might work once, to properly protect a vehicle the armour would have to be in the form of "scales" so damaged pieces can be replaced. As well, much like dealing with Explosive Reactive Armour (ERA) bricks, multiple warheads on the same round (tandem warheads) are used to clear a path through the ERA so the main charge can get through the tank and kill the crew. Going a different way, spider silk is about 5X stronger than steel by unit weight. Armour made of super fibres has been mentioned in other comments and answers, but because the strength is in tension, it has to be used in different ways than ordinary materials which are strong in compression. The properties of these sorts of armours don't really lend themselves to other uses like structural support or engine blocks for vehicle motors, so while you can have an insanely light and strong material which might even need the use of nuclear firepower to breach, it might not have much of an effect on other industries. ]
[Question] [ ## Premise Imagine a world in which magical healing exists. A healer may heal wounds very quickly until his energy is exhausted (at peek performance they can heal someone severely wounded back full fighting force on the field). In this world front line soldiers may get rapidly healed from severe injuries and expected to immediately return to battle, occasionally even multiple times in one battle (although due to limited healing resources solders can't expect infinite healing, and could still die from the wounds, or at least need to be taken back to a hospital for slower/regular medical treatment) ## How It Works Healing requires a mage to make physical contact, and takes anywhere from half a minute to 4-5 minutes depending on how serious your injuries, and how experienced the mage. Super experienced mages are limited in number. Due to the flow of battle a soldier has no way of being certain that a healer will reach him, or be 100% certain that he will survive. If a mage does reach him, they may not be able to heal the soldier completely on the spot - maybe just enough to save his life. Alternatively, the mage may be completely exhausted, and only apply regular bandages and healing salves. ## My Question(s) I want to focus on the psychology of front-line soldiers in this situation. 1. What might the impact on a soldier be from seeing himself brought back to full ability from the very brink of death? Will that encourage recklessness? being super careful in the future? 2. What emotional impact might the uncertainty of whether you will survive or not have on soldiers in these situations? What about the uncertainty of whether you will suffer for months while recovering, or be healed on the spot? 3. Will soldier's fighting styles/tactics/bravery remain the same after such an experience? Will fear of getting wounded again affect their ability to continue fighting, or will they be hardened? To tie it all into one: What psychological effects might a soldier in this situation experience? [Answer] This would cause similar but more extreme versions of psychological trauma currently seen in combat today. Militaries would take precautions to prevent psychological damage when possible. Most modern militaries would not expect or promote soldiers returning to the front lines immediately after being healed. The pain and trauma induced will be serious, and they would still be pulled back whenever possible to get out of harms way. The big benefit here is that soldiers who would otherwise be dead, maimed, or simply put out of action would now be able to get back with their unit within days (depending on the level of rest deemed necessary to ensure the soldier’s mental well-being). The potential to be severely wounded several times within a short timespan will still present psychological risks, but military doctors will go to great lengths to do what’s best for the soldiers. Now, there will definitely be some other psychological effects. It is likely that some soldiers, after being healed back to full health, will not be willing to leave their unit in the thick of the battle. Commanding officers would probably be compelled to order them back behind the lines, but this won’t always happen. Similarly, if a unit is surrounded or otherwise unable to get to safety, having the ability to heal someone back to proper health is extremely valuable — they would most likely stay put, take a minute or two to collect themselves, and then continue their mission for better or worse. Triage will still happen. With such limited resources to heal, the presence of these healers has a single critical goal: to save soldiers who would otherwise die on the battlefield. There would be a major effort to manage the available resources to heal, which means some gunshot wounds or maiming injuries would be ignored in favor of saving lives. This will create a very challenging psychological scenario for soldiers and healers alike — when your friend is begging you for help, do you continue to follow orders and intervene only in the event of a life-threatening injury? This has a lot of implications, possibly resulting in healers being shuffled through different units to avoid bonding too closely with their compatriots. The worst psychological risk will be to the healers. Unlike traditional medics today, they have the ability to not only save lives that may otherwise be lost, but could also potentially save soldiers from having life-altering wounds (particularly missing limbs). The temptation to help a soldier with such an injury would be strong, but it risks the future death of one of your other comrades. Some of this same difficulty is present in modern-day combat, but this would be a more extreme version. [Answer] When you train as a soldier, there's a lot of focus on not getting hurt. You hone your reflexes so as to automatically avoid risks that can be avoided. Train enough and these techniques become ingrained, you apply them without even thinking about them. That's the deal about training: you learn both how not to die and how to become an efficient cog in the military machine. There's comfort and pride in this. Now imagine you've been gravely wounded and healed. Then you have a problem. All your training is put in question. You now know in your bones that you can take more risks than you've trained for if the outcome warrants it. But the problem is that the decision is now yours. You have to weigh the risks you can take every single moments, and you're constantly pushed to take more risks by your experience (after all, you're a good soldier who wants to succeed). The psychological pressure would break the exact type of soldiers who were comforted by the lack of responsibility that the army provided them. And for those it won't break, it will be worse. The veterans willing to risk more will infect young recruits with a sense of heroic recklessness that could totally derail their esprit de corps. Those recruits who would be hurt and healed would see this attitude reinforced, while deaths due to recklessness would be deemed worth it, so that they can distance themselves from the survivor's guilt (and from their own responsibility). The army would rot from the inside until it changed how it trained its soldiers. But this would require redefining its values and culture. After all, how much sacrifice for you comrades is worth if you can be revived? [Answer] I expect it would have much the same impact as the near-misses soldiers have in the real world. Imagine getting shot, but the bullet hits your bulletproof vest and you're merely bruised. Imagine a bullet whizzes right past your head. Now imagine you take a sword to the chest, but it doesn't hit anything immediately fatal, so the mage heals you back up. The last outcome is a bit more painful but otherwise these experiences are very similar. Obviously different people react differently, but I think for the majority of people, when this happens it is a wake-up call: "I nearly died; I could have actually died. I should be more careful." If the soldier can identify a way that they were acting sloppy, and fix it so they won't die that way again, the outcome is a better soldier. If the soldier can't identify a way to prevent getting nearly killed again, the outcome is mental stress. --- I'm confused about the notion of "slower standard treatment". If the world has magic healer mages in it, why would anyone need standard treatment? They'd just wait a few days until a mage was available to fully heal them. (And I expect that, in an actual battle, the front line mage would focus on keeping everyone alive. Healing one soldier back to fighting condition now is worse than healing two soldiers just enough to be in fighting condition in a week.) [Answer] One idea to reduce the amount of mental trauma would be to use short term amnesiacs/hypnotics to remove or reduce the mental impact of the injury. It's one thing to head back into battle with the memory of being shot still fresh, vs. having the memory missing or really weak. It wouldn't remove the need to keep a solder out of combat, but it might shorten it, especially if the use of healing removes all the outward signs of injury. > > "I kind of remember getting hit, but it's real fuzzy and I don't hurt anywhere. Not even any scars." > > > [Propofol](https://en.wikipedia.org/wiki/Propofol) is one drug that could work to remove memory of being injured, though a dose of morphene might work just as well. In your scenario the biggest emotional impact might be survivors guilt, if my buddy died because I got healed and tired the healer out. ]
[Question] [ The [Worlds largest ant](https://www.youtube.com/watch?v=ipkHrzKK110) is around 1 inch long give or take. I wanted to know how large an ant could grow assuming conditions are perfect. Below are the conditions of their environment; 1: The gravity is equal to or less than earth 2: They would live in rain forests 3: They will have access to large amounts of meat and fallen (or rotten) fruit 4: This worlds oxygen content is 23% 5: Air pressure is equal to earth The only goal here is to make the ant as large as possible in the conditions above. [Answer] Two things limit insect size: 1. Their respiration system which is based on using passive circulation via tubes called Trachae. 2. The load bearing capacity of an exoskeleton and the fact that as the exoskeleton cavity gets larger, the internal organs tend to slosh about. For insects such as ants, item 1 is the limiting factor, placing an upper limit of about 3-4 inches for the truly giant insects. There are but a few examples of such beasts on earth. Unfortunately, since you have mentioned that your atmosphere is blessed with only 3% higher oxygen content, the lower gravity doesn't change anything. Studies suggest that oxygen levels may have been higher during various past epochs including the carboniferous, maybe as much as 15% higher. However even then, the best nature managed was a massive dragonfly with a 30 inch wingspan. Its actual body would not have been much more than maybe 6 inches long I would guess. Many insects of this period appear to have been unchanged in size from now, for obvious reasons. Now give the insect some branchiostegal lungs so solve that problem, which technically makes your critter a crustacean, rather than an insect. The largest known land dwelling crustacean (a Coconut Crab) is about 16 inches. However its a slow mover - too fast, or a bad fall and body parts start to slosh about. Lower gravity will help a bit here, but probably not enough to confer a decent evolutionary advantage for very large crustaceans. My suggestion is to invent an insect/crustacean hybrid that looks like an ant, and increase the oxygen by 20%, and reduce the gravity by one half to two thirds. Maybe also use internal exoskeleton partitions to hold critical organs in place. Then you could get something nasty. ]
[Question] [ I'm thinking of a character who is cursed (magical in nature) so that everything organic that enters his vision is immediately turned to ash, with the exception of his own body (ie, he won't reduce his own eyelids to ash). The effects of the curse: When I say "everything organic", I mean everything that is, or once was, living. So the assertion that the character would probably starve is correct, though he would still be able to drink water. He would not extinguish stars by looking at them, nor would he turn the Earth itself into ash (though he could kill any grass and insects on the surface). Since microscopic organisms are, by definition, too small to see, they would be spared from the direct effects of the curse. If the character only sees part of an organic object, then only the part that he sees will be ashed. Reflections are more complicated; I was initially going to say that reflections would not trigger the effect, but I need a specific scene where the character uses a coin-operated telescope and sees nothing but devastation. If I rule out all reflections, then the character would be able to use binoculars without triggering the effect. Similarly, I like the idea of the character seeing a person's reflection in a glass door, but finding nothing but ash when he rushes over to them. So my final ruling for now is that reflections do trigger the effect, unless I can think of a way to consistently allow certain reflections (doors/windows/water), but not others. Video does not trigger the effect. If he sees something on a live video feed, it will not be destroyed. Though any organic (using my above definition of the word) components of the monitor which are visible from the outside would be destroyed. Being a magical curse, the process defies the laws of physics by being completely instantaneous and silent. There is no radiation or other energy which is emitted from the character, or the objects turned to ash. The effect covers everything to the very edge of his peripheral vision, and the range extends as far as he can discern (if he uses lenses to view farther, the effect will carry farther). \\Question 1: \\ Assuming that this character is an average middle-class person living in a modern city, and the effect just starts when they wake up one morning, how long would it take them to determine that they are the cause of the destruction they now see? What would be the sorts of things that would tip them off? Question 2: Similarly, what sort of radius of destruction would such a person have (assuming they have average vision)? EDIT 2: Removed my question about the world's reaction. I'm more specifically curious about the radius of damage that would be caused by a person in this situation. In a city environment, I would think that people higher up in offices and skyscrapers might be able to look down and see the carnage, while still being far enough from the character's "cone of vision" to be affected by it. However, if they tried to shout a warning at him, he'd instinctively look in their direction, which would instantly kill them. Any non-artificial fabrics would be instantly destroyed, but I'm thinking that things like dental fillings and surgical implants (ie pacemakers and bone pins/screws) would just drop to the ground, covered in ash, with whatever momentum they still had. I know that car tires would be destroyed, but I'm not sure about paint or ink...ie, whether someone would be able to spray-paint a message for him to see. [Answer] I'm assuming that "everything organic" means everything with carbon in it according to the chemical definition of "[organic](https://en.wikipedia.org/wiki/Organic_chemistry)". Question 1: Assuming no pets and no roommates/significant other and no breakfast and a very unusual apartment, it wouldn't take more than two or three steps along the sidewalk to realize that he's the one causing it, especially if this is as an instantaneous effect. Just looking around from the plants on the sidewalk to the trees should prove it. The first person or two he looks at is going to be horrific. If he has a significant other, after his pillow and sheets, they will be the first thing to go. I'm not sure what this kind of trauma would do to a person. You reach over to touch the person you love, hear them happily moan at your touch, open your eyes and....Ash. Nothing but ash. If he lives in a timberframe home, then he will be homeless, as will everyone else in his neighborhood as he looks around. If he lives on the bottom floor of a timberframe apartment building, he'll be crushed to death by the weight of the collapsing building as he takes out the surrounding loading bearing walls. What happens after the initial discovery depends on the character of this cursed individual. If he's malicious and has a bone to pick with society, he can happily go on a walk and wipe the surrounding area clean. Wooden doors offer no resistance so home invasions are easy. Initial police resistance will be futile because most conventional tactics are within the kill zone of a kilometer. However, a SWAT sniper could easily pick him off from beyond the kill zone. The [Barret M82 50 caliber rifle](https://en.wikipedia.org/wiki/Barrett_M82) has an effective range of 1800 meters. Military and police threat assessment continues to improve so it won't take them long to figure out the max range of the kill zone or how the power works. Someone with a curse like this is too dangerous to keep alive so they will act to terminate as quickly as possible. If he doesn't have any kind of mental illness, then he's not going to leave his apartment but will have difficulty making contact with anyone because most phones and computers are made of organic compounds and will turn to ash. Certainly, keyboards and mice are plastic. Question 2: Without visual obstructions, the maximum range of devastation is about 1.1km. Humans have a [visual resolution](http://www.clarkvision.com/articles/eye-resolution.html) of about [0.1 degrees](http://www.kylesconverter.com/angle/arcminutes-to-degrees). To be safe from this curse, a person just needs to be far enough away that their apparant height is less than 0.1 degrees. Thus, the kill zone is [1.146km](http://www.1728.org/angsize.htm). In a city, it's rare to see that far and most people are hidden away in buildings. Initial death toll might be in the hundreds if he decides to go for a walk. However, larger objects such as trees can be seen from much farther away. It's up to the author to decide how he wants to handle trees at distance. Conclusion He's either going to kill himself, be killed by the military or police, put out his own eyes or have his eyes put out. Either way, he's dead or blind in relatively short order. Or he starves to death. ]
[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. Based on this [question](https://worldbuilding.stackexchange.com/questions/22676/can-a-human-sized-organism-survive-eating-only-textile-fibers) and [answer](https://worldbuilding.stackexchange.com/a/22687/10364) about a human sized creature that lives completely on textiles, how feasible is it for a creature to consume [nylon](https://en.wikipedia.org/wiki/Nylon) and [polyester](https://en.wikipedia.org/wiki/Polyester) to derive fats/lipids useful for building cell walls? Whether the creature performs the transformation itself or special gut bacteria perform the transform is irrelevant to the question. Assume an approximately human sized creature that requires between 1500 and 2000 calories per day. We have established that this creature can synthesize its own amino acids and vitamins, so it doesn't need to consume those from the textiles. Mineral consumption has been handwaved a bit because there just isn't much mineral content in the dyes and fabric of textiles. Remember, this is a [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'") so equations, journal entries, or official sources are required in the answer. [Answer] Like termites, they'll probably need some help. Termites have a gut bacteria that produce cellulase which helps them digest cellulose. Your cloth eating creature might need something similar, a bacteria that produces [nylonase](https://en.wikipedia.org/wiki/Nylon-eating_bacteria). Nylonase is an enzyme capable of biodegrading polyamides, like nylon, as discussed in [this paper](http://www.jbc.org/content/287/7/5079.full.pdf). Similarly, [polyester eating fungi](http://aem.asm.org/content/77/17/6076.full) and [polyester eating bacteria](http://www.sciencedirect.com/science/article/pii/S0964830598000511) (paywall, sorry), use a polyurethanase–protease enzyme to biodegrade polyester. Both groups of bacteria are anaerobic, so would prefer to live in a gut. With a nice community of these and similar bacteria in the gut, this creature has the opportunity to digest both nylon and polyester. Nutrition is a bit harder to determine. We're not even sure how the [metabolic pathways work inside a termite gut](http://www.caltech.edu/news/new-gut-bacterium-discovered-termites-digestion-wood-40332). But nylon and polyester, like cellulose, are high in energy and degrade back into sugars and fatty acids (or natural versions [can be made from the same components](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3535385/) by some quite different bacteria). Given the [energy content of polyester](http://www.aquafoam.com/papers/selection.pdf) (6,214 kilocalories per kilogram), the creature would probably need to eat around a kilo every day, though that's a wild guess on digestion efficiency. ]
[Question] [ Set in the late 21st century AD, tensions in South China Sea is high, especially since China already constructed its third nuclear aircraft carrier. During the last decades, mishap and tragedy occurred frequently near international water shared by Philippine and China. There have been many reports of broken arrows in the troubled water, and many nuclear subs owned by both China and US come close to a nuclear catastrophe. While the Chinese are developing stealthier and quieter submersibles running on electricity, the Philippines and the US turn to taming nature's most skilled diver, the sperm whale. My question is, in order to search and destroy a submarine, what kinds of weapons are needed to arm the sperm whale? Particularly, how do you train the animal to search for enemy submarines? [Answer] Right off the bat, I'll note that animals can be curious. If a sperm whale sees a submarine, s/he may approach it and investigate. [This happened to a scientific submarine](http://www.telegraph.co.uk/news/newstopics/howaboutthat/11551083/Amazing-sperm-whale-footage-Mammal-circles-submarine.html) earlier this year (although the research submarine was much smaller than a typical nuclear submarine!). I found another story about a whale being even more aggressive, but a five-second skim convinced me that it was a spoof. How could you get a sperm whale to find a submarine? Well, first you have to get the whale near one. I've modified [an image](http://commons.wikimedia.org/wiki/File:Sperm_whale_distribution_(Pacific_equirectangular).jpg) of sperm whale breeding grounds to note the main sperm whale distributions near the South China Sea: ![](https://i.stack.imgur.com/gtZYv.png) Image modified from [this](http://commons.wikimedia.org/wiki/File:Sperm_whale_distribution_(Pacific_equirectangular).jpg) Wikipedia image, courtesy of Wikipedia user Kurzon under the [Creative Commons Attribution-Share Alike 3.0 Unported license](http://creativecommons.org/licenses/by-sa/3.0/deed.en). Modifications consist of adding in freehand colored lines using Microsoft Paint and cropping the image. I've circled the South China Sea in blue, and identified two sperm whale hotspots in orange. On the whole, the sea appears to be relatively sperm whale-free, with the obvious exception of areas firmly in Filipino/Indonesian waters. I assume that the confrontations will take place in international waters. Here's a map of territorial claims in the South China Sea: [![](https://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/South_China_Sea_vector.svg/816px-South_China_Sea_vector.svg.png)](https://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/South_China_Sea_vector.svg/816px-South_China_Sea_vector.svg.png) Image courtesy of Wikipedia user Cmglee under the [Creative Commons Attribution-Share Alike 3.0 Unported license](http://creativecommons.org/licenses/by-sa/3.0/deed.en). Chinese claims do not appear to extend towards the central western edge of the Philippines, where sperm whales are prevalent. This makes it clear that any confrontations will likely be to the west. Therefore, for the whales to be of any use, they must be lured there. [Wikipedia](http://en.wikipedia.org/wiki/Sperm_whale#Distribution) states > > Populations are denser close to continental shelves and canyons. Sperm whales are usually found in deep off-shore waters, but may be seen closer to shore, in areas where the continental shelf is small and drops quickly to depths of 310–920 metres (1,020–3,020 ft). Coastal areas with significant sperm whale populations include the Azores and the Caribbean island of Dominica. In Asian waters, for examples, whales are also observed regularly in coastal waters such as at Commander and Kuril Islands, Shiretoko Peninsula, off Kinkasan, vicinity to Tokyo Bay and Boso Peninsula to Izu and Izu Islands, Volcano Islands, Yakushima and Tokara Islands to Ryukyu Islands, Taiwan, Northern Mariana Islands, and so on. > > > I modified [this Wikipedia image](http://commons.wikimedia.org/wiki/File:South_China_Sea.jpg) to show the area in more detail: ![](https://i.stack.imgur.com/ooxoy.jpg) Image modified from [this](http://commons.wikimedia.org/wiki/File:Sperm_whale_distribution_(Pacific_equirectangular).jpg) Wikipedia image, courtesy of Wikipedia user Rex; however, the image is in the public domain. Modifications consist of adding in freehand colored lines using Microsoft Paint and cropping the image. Here, purple indicates what I think is the edge of the continental shelf, orange denotes sperm whale grounds, red denotes the target area - right in the middle of China's claims - and black shows the paths the whales need to follow. I don't know how long the paths are, but I do know that they're pretty long. I don't think that the odds of forcing a significant amount of sperm whales to go that far are too good. Assuming you get a large amount of sperm whales into the red area, though, could they successfully attack a nuclear submarine? It's something of a tough question to answer, given that the technology is decades ahead of the present day. I'll try to extrapolate based on the toughest nuclear submarines we currently have. The [Ohio Replacement Submarine](http://en.wikipedia.org/wiki/Ohio_Replacement_Submarine) (I'll abbreviate it as ORS-class) seems like a good choice, as it is expected to remain in service until about 2085. Who knows - perhaps this is one of the submarines the United States uses in this scenario! True, the whales will be attacking Chinese submarines, but their advanced ones are either still in early development stages or currently in use and most likely not active in the late 21st century. [This pdf](http://www.senedia.org/wp-content/uploads/2014/09/Ohio-Replacement-Program-Defense-Innovation-Days-5-Sep-2014-Final.pdf) (linked to in Wikipedia) gives a good overview of ORS-class submarines. The submarine will have * Electric propulsion * Trident-variant nuclear missiles * Modular construction * "Sufficient stealth to address the projected threat through the 2080s" * Other cool stuff The bit that worries me is the fourth bullet I listed: stealth. Submarines are generally considered "stealthy" because they can go deep underwater, where it is harder to track them. I'm unaware how deep ORS-class submarines can go, although it seems likely that sperm whales could go just as deep. That said, I assume that more measures are being taken to make these submarines as stealthy as possible, making them hard to find. Assuming a sperm whale could find a submarine, could it attack it? I say no. Take the hull, for example. [The hulls of many nuclear submarines](http://science.howstuffworks.com/nuclear-submarine5.htm) were/are made of HY-80, or some variant thereof. [Some basic statistics](http://www.aasteel.com/hy-80-100.html) correspond with Wikipedia's yield strength figure of 550 MPa (note that materials will not snap, break or be punctured at their yield strength). That's enormous - 550,000,000 Newtons per square meter. Sperm whales themselves can weigh up to about 410,000 Newtons - peanuts in comparison! I doubt they would have the strength to seriously damage a nuclear submarine. [Answer] A sperm whale could be taught to hear and respond to sounds, so if they were equipped with sonar then they could respond to a sound and swim towards it. Even better is if enemy subs returned a unique sound which notified to swim closer and attack, while a friendly sub/ship would indicate to swim away or not attack. As far as weapons, a sperm whale is not magnetic a submarine is. This sounds a bit wacky but wrap the whale with a belt that holds magnetic mines. On the expose side have a magnet more powerful then whatever holds the mine to the belt. The whale could hear a sound swim toward and nudge the sub allowing for the mine to attach to it. Once the magnet is activated it emits an over riding sub for the whale to swim away allowing it to then detonate safely and not take the whale with it. ]
[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. This is the first question in a series on the physical limits of the human body. > > The intent of this series is to, illustrate the upper and lower limits of human biology for the purpose of building worlds on which they can (or cannot) survive. > > > Other Questions: (obviously this will get updated as other questions are asked in the series.) > > > Questions: What are the maximum possible and minimum required for the human body to function properly, in percentage of the atmosphere near the sea level. 1. Oxygen Future Questions will cover: 2. Nitrogen 3. Hydrogen Restrictions: * Humans must be able to function at least efficiently enough to provide food, water, and shelter for themselves without the aid of hydrocarbon fuels (basically pre-industrial, pre-gunpowder technology). This can be in the form of farming or hunting. Humans still need to be able to exert themselves physically without the atmosphere causing undue limitation on their ability to do so. [Answer] Just ask NASA, they have [already studied](https://web.archive.org/web/20221114011217/https://history.nasa.gov/conghand/mannedev.htm) it pretty carefully. The key chart is [![](https://i.stack.imgur.com/1Noe0.gif)](https://i.stack.imgur.com/1Noe0.gif) (source: [nasa.gov](https://history.nasa.gov/conghand/fig15d3.gif)) As long as you keep hydrogen concentration below about 4% (at normal earth atmosphere pressure and temperature) it is not flammable mix. Don't know where you can find flammability limits in chart form, but the [Wikipedia article on flammability limits](https://en.wikipedia.org/wiki/Flammability_limit) lists the formula for estimating this based on different atmospheric compositions. For low H2 concentrations (to avoid fire) you can see that lines are close to flat at the right edge of the chart, so you can probably ignore hydrogen pretty much for environmental tolerance. --- Reading some specific values from the chart, for sea level pressures, an oxygen content from about 12% to 62% is considered safe, i.e., a human of normal health can survive indefinitely without negative consequences. In the range 9% to 12% people who have been acclimated to low oxygen environment will be OK as the body will adapt by changes in the blood and lungs to survive lower oxygen levels. Also note at low oxygen levels there may be some discomfort, (shortness of breath), but nothing of real consequence although your athletic abilities will be curtailed. Above 62% the increased oxygen (at sea level pressure) is at least somewhat toxic, though at much higher pressures pure oxygen can also be quickly fatal. As the chart shows, 24 hours of even pure oxygen won't be a serious problem (though fire risks are severe). Nitrogen is safe in any amount at sea level (assuming your still have enough oxygen). At higher pressures, narcosis becomes important, i.e., nitrogen (almost all inert gases too) puts you to sleep, makes you intoxicated, etc. The exact level of the inert gas required for narcosis varies by type. A small amount of CO2 is also required for breathing regulation, etc. ]
[Question] [ It is said that the Moon plays a significant role on stabilizing the obliquity of Earth (or call it the axial tilt). Without it, the tilt of the planet is subject to great variations causing unpredictable climatic conditions on the planet. This is not ideal for life. Scenario: An advanced civilization discovers a perfect planet that is just like Earth except that the planet doesn't have a natural satellite. They really want to settle the planet and they are planning for a long term investment. How can they minimize the changes in the planet's obliquity over long periods of time? [Answer] Probably the most straightforward solution is to grab some nearby asteroids and build yourself a new moon. It would take a lot though, It's estimated that our entire asteroid belt combined together would mass about the same (or in fact a little under) the mass of our moon. However if you want a long term safe environment harvesting all the rogue, orbit crossing asteroids and compressing them into a moon would kill two birds with one stone (sorry for the pun). It keeps you safe from asteroid impacts and fixes your planetary tilt. [Answer] If the aliens (or us, for that matter) have superscience, then one answer would be to grab a moon from a Gas giant planet in the system and place it in orbit around your planet. Playing a game of planetary billiards with comets from the system's Kuiper belt and using flypasts to add or subtract orbital velocity from the moon you want gets the job done, although it takes a long time and an insane amount of computational power. The constant stream of comets through the inner solar system wold make for a spectacular night sky, but interplanetary transportation would be rather hazardous. Plan "B" would be to forget the moon and use the incoming comets directly to apply a gravitational torque to the planet. This might be sub optimal if there is a lot of space infrastructure, since the traffic control system would have to ensure clear space for the incoming comet to pass the planet, and the water vapour and dust from the comet's tail would have long term effects on the orbital infrastructure and possibly the planetary climate (reflecting sunlight away and dropping the average temperature). With a bit more superscience, Plan "C" might be to create a very small artificial moon using ultra dense materials. A slug of Neutronium the mass of the Moon would be incredibly tiny (and probably unstable). A miniature black hole might be created to do the job (one of lunar mass would probably be stable enough to last for geological ages), and careful observers would see an "Einstein ring" in the sky every time the miniature black hole passed in front of a star. Finally, if the superscience is sufficiently advanced, they might simply warp space near the planet to create the same effect. [Answer] Does your perfect planet need to NOT have a moon? My scientific knowledge is probably lacking, but I would think it unlikely that the planet would be perfect without a moon at all. Perhaps your planet has a moon but its current orbit is eccentric or orbiting it in such a way that the planet cannot have stable seasons or a proper day/night cycle. Assuming you have the means to travel to this planet and set up life on it, there would probably be a way to engineer the moon into a better orbit that life would be possible on your perfect planet. ]
[Question] [ I am trying to make a digital world map (preferably vector graphic but it's definitely not essential) for my planet but I don't know which projection to use and how to go about actually making it. I want to be able to define shape and size of the land with minimal distortion. Furthermore, how would I go about converting from one projection to another? I'd rather not have to spend money on software but I could if necessary. I use Windows 8.1 primarily, but could use Linux if no Windows versions of a program are available. [Answer] To make experimentation with different map projections, you can use NASA's [G projector](http://www.giss.nasa.gov/tools/gprojector/). It's free and it come with a large number of projections. It can import an image, change the projection and export it. But there is a size limit for exporting the file, so it's best to do it on a rough version of the map. Otherwise you will lose some details. I would recommend doing some tests before getting into the actual mapping as is might be better to do most of the job after converting the map to the right projection. You can use any software you want as long as you use these file extensions : JPEG, GIF, PNG and BMP. These files are compatible with the software. * Another more advanced software: [Flex projector](http://www.flexprojector.com/) let you play with the different parameters and you can create your own projection. The base set of projection is more limited and it's most useful if you know what you are doing. For vector based software, the most used are probably Inkscape (free) and Illustrator. They do a great job for planing the world and adding elements but they can't manage textures. To find a good map projection, you need to know what the map will represent and what is the goal of the map. Some maps are not appropriate to map a whole world and some are not. For example: the [azimuthal equidistant](http://en.wikipedia.org/wiki/Azimuthal_equidistant_projection) projection is good to map poles but not the rest. But most projection can do a good job to represent a world depending on the other criteria. Minimal distortion: you will need to figure out what you want to keep intact. You can keep the angles/directions (conformal), the shapes, the size and the distance, but not everything at the same time. * Conformal projection are good for navigation but like the Mercator projection, they all distort the size awfully. It makes Greenland almost as big as Africa. in reality, it is only the size of Algeria. * Equal area keep the size intact but distort the shape. Here, some of the most used projections: Hammer, Mollweide, distort the outer parts of the map. This makes New Zealand look too stretched. All projections in this category try to address this issue but it is not possible to solve it. * Equidistant : The equirectangular projection is widely used in amateur map making because it is the simplest. > > As [smithkm](https://worldbuilding.stackexchange.com/users/30/smithkm) pointed out: > An equidistant projection preserves distances toward or away from a > particular point and its antopode. In polar aspect azimuthal or normal > aspect cylindrical/conic these two points will be the poles in which > case it preserves distances along meridians rather than between them. > In such a case the distance between parallels will be the same, > because they are equally spaced north to south. > > > * Compromise projections: these projections try to minimize the total distortion by accepting some distortions on the size, shape, or conformity. In this regard, they might be the best for someone trying to minimize distortion without working on a globe. A globe would have no distortion but it requires a 3D software. National Geographic have used these projections for more than 100 years. Including: Van der Grinten, Robinson and now Winkel tripel. They have the advantage to look more round and natural than other projections. It is more eye pleasing but they still are distorted in some ways. ]
[Question] [ Start: * Normal planet, very similar to Earth. The main difference is that the continents are placed differently. * Magic could play a role in the formation of mountains but I prefer a scientific explanation. Process: * The activity inside the planet makes surface plates move. At a specific place, two plates are colliding and this creates a large mountain range. * It is a subduction zone of several thousand kilometers long. Result: [This question already addressed the maximum height of a mountain.](https://skeptics.stackexchange.com/questions/5848/can-mountains-on-earth-grow-higher-than-49-000-feet-15-000-m) But what about the size of a mountain range? Given sufficient time and tectonic activity the rock will keep compressing and will form several parallel mountain ranges. How large could it get with peeks over 4000m? [Answer] The maximum vertical height is already addressed so the question is then the maximum width and/or length of the mountains. A subduction zone could be the maximum of half the planet for a solid plate or the whole planet's circumference for soft plates forming [bernard cells](http://en.wikipedia.org/wiki/Rayleigh%E2%80%93B%C3%A9nard_convection) (which is essentially a torus-shaped planet with a small inner diameter in the limit of size). These could be extended temporarily by instabilities (wiggly edges). Those limits are for a linear mountain range. It's perfectly plausible to have a circular one or a network though if that counts. In such a case you could have a checkerboard pattern of upthrust and subducted plates. There's no real limit if you don't limit the planet's size. A lower amount of "instabilities" increases likelihood of larger ranges while reducing the chance of the super long "wiggly-extrema". An example of instability would be rock having a non-uniform shear strength or non-uniform plate sizes. As we drag our maximum shear strength lower and widen the range of values within a plate we get more cases where "edge wear" can occur on the mountain range. The "edge-wear" in a plate collision would be the tips of the mountain range being scraped off the plate or a wiggly mountain proper being flattened against a subduction zone. So length is kinda variable. A solid upper limit would be the setup with the most bernard cells you could get for your given material strength. But a lot of specifics can drag the limit all the way down to just half the circumference (our basic hard plate case). Maximum width of a mountain is already set by the material strengths and was covered in the answer to the tallest vertical height. When you achieve the maximum height you'll have the largest width. Anything wider next to the mountain will be past an inflection point in the slope that measures our true width. Example: You have a pile of sand and make it as tall as you can by adding to the peak. It will have a specific angle of slope. It will be a convex mountain. If you add material at the base around it then it will not be structurally part of the sand pile. The part where your added sand at the base makes the mountain convex and is under its own separate structural support. ]
[Question] [ [This question](https://worldbuilding.stackexchange.com/questions/2629/what-happens-if-the-sun-disappears-and-then-reappears-some-days-later) asks what would happen to the solar system if the sun vanished for about three days, the mass and energy of the sun simply ceasing to exist. [This answer](https://worldbuilding.stackexchange.com/a/2632/447) (as of this question, anyway) notes that for the most part, the solar system will remain unchanged. If Ragnarök has already happened, and the sun has already been eaten and replaced, is it possible to use the current eccentricity, positions, and speeds of the various planets in our solar system to determine how long ago that occurred? As for an explanation of why this is in World Building rather than Physics: The events in Ragnarök result in sentient life on Earth being effectively wiped out; after the cataclysmic event, only two people remain, and civilization restarts through them and their children. There would be no written history of the event, and oral tradition is unreliable at best. There may not even be any archaeological evidence. However, the physics would remain, and "proving" that the sun vanished for three days is a pretty good step towards building a magical, unknown history into a normal, mundane world - through science, no less! [Answer] The simple answer is no, we would never know. Not unless there are records from that time we could refer back to or we can use FTL travel to go far enough away that we can look back and see. The resulting orbits afterwards are stable and we have no way of knowing that they were not always that way. Additionally anything that is odd in orbital configurations can be far more readily explained by something like a rogue planet passing through the system and disrupting things than the sun disappearing. Essentially there are no tracks in space so we have no way of knowing that something odd happened at a certain point unless we have measurements both before and after that odd thing happened. The only way it might be possible is if there were records from the pre-ragnarok civilization that were discovered and included precise details of the orbital tracks of the planets. Comparisons between those records and now might make it possible to work out that the sun disappeared and how long it was gone for but it would take advanced astronomical and mathematical knowledge and detailed records from before. [Answer] I'll give a try, but screw physics, I'm using Geology to look for it. The heliosphere (or heliomagneticsphere, both terms hated by spell check apparently) is the suns magnetic field as our solar system travels through the galaxy. Ions travelling around 99% the speed of light or faster dominate this interstellar space (space between stars). This heliosphere deflects the majority of the particles coming at us, some possessing energy with an upper limit of 5J (which is an exceedingly silly amount of energy on an atomic level, being hit by 30 of these atoms is the same force most of us exert when we jump as high as we can) . I would have to venture that the removal of the sun for 3 days would allow these particles free access to earth...at this speed and with this energy, the effects to life on Earth would be beyond catastrophic. Quite literally Ragnarok would only need to be the sun being devoured as the resulting impact from interstellar solar winds would destroy our atmosphere, almost all life on earth, and quite likely scar the planet. Proof of Ragnarok should be discoverable in our geological record or ice cores as a massive earth altering event. [Answer] Yes, but you'd have to get lucky. If you want to use celestial bodies, you're best bet would be to study the effects of something that closely interacts with the Sun. Really, this rules out much of the solar system. Even [Mercury](https://en.wikipedia.org/wiki/Mercury_(planet)), the closest planet to the Sun, is 46 million kilometers away from the Sun - at its closest approach! The difficulty here is that almost all the bodies in the solar system have orbits with small [eccentricities](https://en.wikipedia.org/wiki/Orbital_eccentricity), and are pretty far from the Sun. Fortunately, there are exceptions. [Comets](https://en.wikipedia.org/wiki/Comet) have fairly eccentric orbits, so they're an interesting choice. They can closely interact with a body and then zoom off somewhere else, and we can study the effects that other body had on them based on orbital perturbations. For this, we can look at [sungrazing comets](https://en.wikipedia.org/wiki/Sungrazing_comet). I think these are the coolest bodies in the solar system, partly because of their crazy orbits but also because "sungrazing" has a nice ring to it. Sungrazing comets swing out from the far reaches of the solar system, coming in extremely close to the Sun - sometimes only a few thousand kilometers away! Think about it - that's one one-thousandth the distance between Mercury and the Sun! How does this help us? Well, think about what happens to these comets when they pass the Sun: * They may undergo orbital perturbations * They develop a long tail and related features (although this happens with all comets, this can be fairly prominent on sungrazers) If the Sun disappeared for three days while a sungrazing comet (let's say a [Kreutz sungrazer](https://en.wikipedia.org/wiki/Kreutz_Sungrazers), because these ones come really close) was near the Sun, the comet wouldn't interact with the Sun. It would continue on its merry way in space. Our best shot at figuring out that the Sun wasn't there for three days would be to trace back the orbits of these comets using a simulator. It would be very hard to accurately model the orbits, but if the comet went straight through the location the Sun was supposed to be in, was otherwise not perturbed, we would know that something odd had happened. ]
[Question] [ I'm looking for a rock from which my island is constructed. It needs to be: * Either created from the sea or via intense pressure/heat * Capable of trapping layers of gas beneath it * White(ish) I was thinking about limestone but I'm not sure if islands with large quantities of limestone are realistic. Also could a softer rock such as limestone trap large quantities of natural gas (methane and hydrogen) beneath the surface? [Answer] ## Previous answer aimed for trapped air You want something that contains feldspar and/or quartz to make it light and granite often does but its color varys based on the source. You want it to be rapidly cooled igneous rock. I have a hard time seeing how something high in carbonates could survive in the ocean long term as water would degrade carbonates over time. you could possibly make the same arguement with feldspars but they will hold up better than carbonates. Felsite is high silica igneous rock. igneous rock can have cavities depending on the way it cools (see pummice). It contains large quantities of quartz which is, of course, white. Noe though that rhyolite is often a type of this and the rhyolite I mine is pink. Pumice is, of course, porous and light but not as light as Felsite. Tonalite looks exactly the right appearance but is rare enough I don't think you will find a whole island of it. If you want a volcano on the island, you want a volcanic igneous rock. If you don't want there to have every been volcanic activity, you want a plutonic rock. Sedimentary rocks will be too soft and porous for you. (Pores trap things but can let things slip through expecially gases) Metamorphic rock will prevent trapped gasses. ## New answer for lighter than air gases While most of the above holds true, it doesn't allow for why trapped gases are there. There are two lighter than air gases: Hydrogen and Helium. Hydrogen does not get trapped as a gas in rock much at all. It is, however, common in chemicals that can be mined. Hydrocarbons are trapped in sedimentary rocks and are made of carbon and hydrogen. While buring these causes the oxygen to react with the hydrogen producing water, reforming these to make double bonds/soot/etc. by heating in a oxygen free environment can cause hydrogen to be released but it is still reactive so... yeah.. do some research. With some oxygen present, this can be done with out input electricity. Hydrogen can be produced easily by passing an electric current through water. This is hydolysis and is the most likely way to make lighter than air gas on an island. As natural gas is often mined from the sedimentary rock at the ocean floor, it doesn't matter what you bedrock is much does it? Choose any very high silica igneous rock to make the island more stable and volcanic or some kind of sandstone or marble and say it happend via an upheval. Helium can actually be mined as a gas but is far more rare than hydrogen. Almost all of the helium on earth was formed by the radioactive decay of uranium. There needs, therefore, to be a deep bedrock of high urnaium granite. The helium diffuses through grain boundaries (i think) in the granites into areas with a higher porosity (often sedimentary rocks). If you want an island (kind of hard as helium would want to get into the water), propose the following. You have a high silica/high uranium baserock that is heated and coming to the surface as magma (but I don't actually want it to become lava). Above this is a metamorphic upheval brought up by the tentonic activity which is marble. This marble is chosen so they can form it as the greeks/romans did. The other white alternative are harder to sculpt. Water leaking beneath the marble at some point caused an area of the lava to cool quickly and form a porous region. This is now largely sealed by the lava flow. Radioactive decay of the uranium forms helium gas which concentrates in the porous region of the rock under the largely non-porous marble. [Answer] Natrocarbonatite is a rare form of lava (only known to come from a volcano in Tanzania). It bubbles to the surface as a muddy black color, and then turns white as it cools. Theoretically, if such a volcano existed in under the sea, perhaps an entire island could be made out of it. ]
[Question] [ Disclaimer: the overall idea of the world as presented is basically lifted from Strugatsky Brothers "[Inhabited Island](https://en.wikipedia.org/wiki/Prisoners_of_Power)". The details of the question are for a derivative work in that universe. Imagine a planet whose atmosphere has an unusually large refraction, resulting in the observer getting the impression that the surface of the planet is concave. The upper atmosphere is very dense and opaque, constantly, phosphorescent, resulting in no observable sun or stars from the planet's surface. If a sentient species with civilization developed on such a planet (without - to date - access to high level atmospheric flight, but otherwise, a 1900-1940 level of overall scientific/technological development - what would be the likely cosmology be for such a species? Their direct visual experience is that they live on an inner circle of a large bowl or a sphere. Would they likely be able to detect that they indeed live on an outer surface of a spheroid, by gravitational observation/experiments? Geographical travels? Would they be able to somehow deduce the existence of extra-planetary space, their solar system/sun, or other astronomical bodies/structures? Assume that all the physical laws of the universe are 100% identical to Earth, aside from whatever needs to be minimally bent to produce such an unusual atmosphere. Desired answers will be based on physics/astronomy/cosmology, as well as history of science. [Answer] # The Ship in the Distance One of the early arguments for a spherical earth went something like this: > > You are on a large sea, and you see a ship approaching you. Why do you see the masts first, and not the ship all at once? If the earth (and ocean) was flat, you'd always be able to see it, all at once. > > > Now, if they would see the same ship in the sky, this argument still works. Why can we see the sky-ship all the time, but the real ship shows up as described above? Someone would figure this out eventually, and it would make a good argument for a convex planet surface. I am sure there must be other ways to figure this out, but this is simple and came to mind. # Cosmology Now, not being able to see stars, their cosmology would be very geocentric. Assuming they could see nothing but the sky above them, they would have no choice but to conclude the planet is the universe. The discovery of the non-visible spectrum is going to be a big deal for them, especially if portions of this non-visible spectrum can pierce the atmosphere. (Odds are, some wavelengths will!) If they attempted to get into the sky, they may have a big surprise when they get through it! This is especially true if the sky acts like a rather large mirror; earth-people would want to get to the sky-people, only to find out that they don't exist. Some people may observe that such sky-people mirror our every actions, and that could have huge effects on philosophy and religion. It could also be exploited for communication as well, but that's off-topic here. Tides will, of course, be a huge mystery to them. It was a huge mystery for us, after all, [until heliocentrism took off](http://en.wikipedia.org/wiki/Tide#History_of_tidal_physics), despite the fact that Seleucus of Seneca proposed the idea around 150 BC. Since our atmospheres can require certain depths (and temperatures) to refract light correctly, there is a possibility that high mountains may allow them to see (or hint at) the existence of their sun or moon. This could be leveraged to learn about the sun and moon much in the same way that humans have. Really, the more technology they have, the more likely they'll figure out that they live on the outside surface of a sphere, not the inside of one. Advances in flight and optics will be key to figuring this out. [Answer] I believe they would figure out they're really on a ball. 1) At that tech level they understand refraction and would be able to figure out that the atmosphere refracts. Thus they could calculate where the light rays really went. 2) Ballistics. Artillery rounds would go long. Someone would figure out what was up. (Note: There might not be artillery on such a world. Consider Venus--it looks like a bowl. The atmosphere is dense enough artillery isn't going very far.) 3) Gravity. Climb a hill, gravity goes down. 4) The travel time of electromagnetic radiation in the atmosphere. Like with the ballistics issue everything would take a little longer than it should because it's actually taking a longer path than it looks like. ]
[Question] [ The international phonetic alphabet system contains all sounds that a human can make. However, humans are not lizards, but mammals, and hence have many features that let us make more complex sounds The basic example will be an intelligent lizard that speaks through its mouth. Its mouth has the following features: * Its lips are fused to its jaws, and cannot move independently from them. There is also no gap between the lips and jaws * Its front teeth are sharp, but not sharp enough to cut the tongue during normal speech * It has no alveolar ridge * Its tongue is thick and can move around the mouth or become deeper or shallower, just as a human tongue can * It has no soft palate, and its hard palate is divided down the middle into two halves and cannot be closed * It has a larynx, which functions similarly to a human larynx Based on this anatomy, what sort of phonemes could a lizard with such an anatomy produce from its mouth? [Answer] ## A Narrow Answer About Lizard-Human Pidgin Sure, the broadest interpretation of this question may be unanswerable. If you're creating a fantasy creature, you could give it all sorts of exotic signalling apparatus or linguistic instincts. (Maybe their language consists mostly of skin-color changes.) But we can answer a narrower question: What kind of phonemes could be spoken both by humans and by a fantasy species with the specific anatomical features you describe? In other words, what phonemes would humans and your lizans use to speak to each other? Well, you specify that this creature has: * a human-like tongue (which can presumably block air flow for plosives and the like) * a human-like larynx * teeth which can be used in speech. So it sounds like you've designed them to be able to use dental and laryngeal consonants (except for the nasals), and some form of vowels. That seems like enough to form a humanesque language. The tongue does a lot of the work for vowels, but the lips and other bits are also important for shaping them. Let's just assume there's some subset of vowels found to be mutually comprehensible and move on, though, since I'm not sure how specific we can be there. The dental consonants give you both th sounds, variants on t,d,l,s,z, as well as the dental ejective and click. The dental versions of s and z sound hissy when I say them, so that's on-theme. The laryngeal consonants are also on-theme because a snake's hiss is glottal (it's more of a 'hhhhh' than a 'sssss'). If I were designing this language, I'd lean hard into the pharyngeal and glottal sounds. But even just sticking to English phonology (or sounds which are close to English's), you'd have 9 consonants, including the glottal stop. That's small, but not unreasonably so. Hawaiian only has ~8 consonants, for example. ... Actually, that gives me an idea for a horrifically lazy bit of language building. Just take Hawaiian and do a swap the consonants to make them purely dental/laryngeal. (K to T, M to S, N to Z, P to D, and W to TH,. H/L/' stay the same.) Though it might stretch suspension of disbelief if your lizards greet each other with "aloha". ]
[Question] [ So 5-6 million years ago, the strait of Gibraltar closed due to plate tectonics. Because of this the Mediterranean dried up (maybe leaving a couple small very salty lakes). This would have made Europe much drier, maybe even gave it a desert. This event is expected to happen again in the future. So 5-10 thousand years ago, a combination of Milankovitch cycles stuff, topography, and albedo-by-vegetation feedback loops caused the Sahara desert to become a vast grassland. This event will also happen in the future, as the Greening and Deserting of the Sahara happens in a 41000 year cycle. I am thinking of a world in the future where both of these events happen at the same time. However, these conditions are obviously contradictory. The Salinity Crisis happened mainly because the strait of Gibraltar closed, which prevented the Mediterranean from being able to receive water from the Atlantic (The Mediterranean evaporates much of its water, and Atlantic Ocean is it's main source of water.) Green Sahara happens due to Axial Changes over time, the Northern Hemisphere would receive more energy, which means more evaporation, which means more rainfall, which is the seeds for plants to grow. Plants draw out groundwater and most of it is evaporated off leaves, more water. The plants increase the albedo which means more energy which means more rainfall and- oop we have got a feedback loop. As you can see, with a grassy Sahara that receives rainfall (and the seasonal monsoon), it seems a little weird that there could be a very dry Mediterranean Basin next door. So what I want to ask is, would it be plausible for a Green Sahara to co-exist right next to a dried up Mediterranean Sea (with the exception of some small lakes of brine)? Notes: * There must be a Green Sahara in the Sahara (with its rainfall and its monsoon) * There must be a desiccated (dried up) Mediterranean Basin (going through something similar to the Messinian Salinty Crisis), with the exception of some small very very salty lakes collected at the deepest parts. * To be more specific about the Mediterranean Basin, it should not be receiving much rainfall, however the Sahara must receive a nice dose of it, for it to be grassland. The Mediterranean sea can permit a small amount of it, as evaporation will take care of it [Answer] It would be not just plausible, but likely. For Sahara to be green, you need the Intertropical Convergence Zone (ITCZ) to move further northwards during the summer than it does today. Milankovich cycle and other mechanisms cause that periodically, as you described. ITCZ effectively collects moisture from all over the tropics into a narrow(ish) band, providing plenty of rain as a result. So this is the easy bit. The even easier bit is that the bottom of a dried out Mediterranean will always be dry, precisely because it lies at such a low elevation. Any air reaching it would necessarily have to descend, and will become hot and dry as it does that. The exact mechanism is that as the air descends, its pressure increases (because there is then more air above it, weighing down on it); the increased pressure causes the air's temperature to rise; and the warmer air can hold ever more water vapor as it keeps descending, which prevents cloud formation and therefore rain. It's the same mechanism that keeps Death Valley brutally hot and dry, but on a much larger scale in all dimensions. ]
[Question] [ In my setting, there is an area that is usually filled with water at high tide and a land bridge at low tide. One day, a magical wall appeared that does not let water through, but does let through anything else. The shape of the wall is a vertical cylinder (with radius high enough that locally, it as well may be a vertical plane). The wall appeared during hight tide, so at low tide, there is now a vertical water surface. 1. What is the safest way to cross this wall for a human during low tide in each direction? I can imagine that if a human is partially submerged in the water, then the water pressure would only create force on one of his sides and thus might try to eject him rather forcefully. 2. How dangerous is it to cross in an "improper" way by a person who has no experience with this wall but is otherwise fit? I figured when you would swim on the surface, you wouldn't be ejected sideways with a large force, but you will then fall form a really awkward position. On the other hand, trying to swim deep in the water will create a lot of sideways force but probably much more manageable fall. Still, you would be shot across the rough sea bed. Things you can assume: * The water at the border is about 10 feet deep. * The floor is your average rocky beach, relatively lifeless, there aren't any large rocks but some of the smaller ones can be pointy. * The people crossing it are a (relatively) weak high fantasy heroes in vaguely medieval setting (in fact, it's a low level DnD 5e party, but I am interested more in an real-world physics answer than a 5e mechanics answer, thats why I ask here. Assume Earth gravity, Earth-like salt water, regular physically fit human with no modern gear, also no other magic than whatever created the wall.) * The wall behaves the way you'd expect it to without thinking too hard about it, eg. it lets through any liquid that is part of body of a living creature, and also the scenario where the hero gets hurt by a last drop of water that doesn't have anywhere to escape when it's pressed between the hero and the wall just doesn't happen. It also doesn't let through anything that is too small to be visible with a human eye (no pile of microbes/originally dissolved stuff right at the border) and the stuff that's dissolved in water doesn't sediment on it. At any time there aren't any major currents at either side of the wall, even if it would make sense for them to be present. [Answer] ## You can get past it using something very buoyant. Have a hatch in the object that can be opened and closed from a ways away. Tie a rope to the object, preferably with knots in it to climb. Take the object and throw it over the edge. Very quickly open the hatch and then close it after letting a small amount of water in. The water will then prevent the buoyant object from being able to cross over, allowing you to climb the rope up to the other side. In order to hold your weight, the object would need to be large, meaning more than one person could sometimes be needed to get it over and then execute the process. [![basic diagram](https://i.stack.imgur.com/ByY5c.png)](https://i.stack.imgur.com/ByY5c.png) This diagram I made in ms paint should explain how it works. The reason a jug wouldn't work is that your weight would push it down and then you couldn't get up. The shown design is simplified. The danger would not be excessive, it would push you away before you could get far enough in. That said, it would push you away (based on my rough assumptions and calculations) so you probably couldn’t just swim through it. [Answer] BUILD A RAMP OR SCAFFOLD AND LAUNCH A BOAT 10 feet isn't very deep. It would be a work of an hour or less to build a makeshift construction up the side of the wall. Then lift a boat to the top and put it in the water, where the side of the construction prevents it from slipping over the edge. Then board the boat and row or sail where you want. When you reach your destination (assuming it is still low tide), have two rowers keep the boat from the edge while the others climb down a rope. Then the last two can swim to the edge and jump down to be caught by the people on the ground, possibly in a big blanket. The construction can be quite simple. You can use the buoyancy of the water to your advantage by building a wooden ladder or A-shaped structure and lean it on the edge of the water, perhaps propped up by inflated bladders. You may even be able to pull this up once you are in the boat and drag it with you to your destination for easy descent. Lacking access to wood, you pile rocks to get you to the top. Lacking a boat, you could swim, possibly aided by swimming bladders or similar. If this is a regular occurence, somebody could even have pulled a rope through the wall all the way to the destination. Then it is just a matter of pulling yourself through the wall by the rope. Away from the ends of the wall, this rope would float, propped up by air bladders or air-filled jugs or flasks. ]

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