66

Large dinosaurs are like elephants. Very strong, but the one thing they can't do is jump. Their massive body weight increases with the cube of their size, meaning that large dinosaurs are at the limit of what their body can physically support. Trying to jump is impossible for them. So forget about trying to build a strong wooden fence, build a ditch. That's ...


63

I'm going to respond to this with a framing challenge, because as it stands I think you're asking the wrong question. The issue is that the modern industrial world is a product of population DENSITY rather than total population. This may seem semantic but in a post-apocalyptic environment it's very meaningful. Modern industrialism depends on and benefits ...


45

An assembly hall (town hall). The reason those churches get used for other things is that there are reasons other than worship for everybody to gather at times. A church's main hall is only in use for a few hours a week, so gatherings at other times are feasible. Your need for those gatherings doesn't go away just because your society doesn't have ...


42

/Their lives are to be miserable./ I know a recipe for miserable. Flies everywhere. https://en.wikipedia.org/wiki/Black_fly The flies are a genetic modification attempt gone wrong. They are everywhere and they attack anything that moves, biting and chewing and drinking. They cause blindness and carry other diseases as well. Attempts to control them ...


37

A year isn't going to cut it, you're looking at about a generation at least for any noticeable progress. The problem is the lack of industrial base. Medieval society is a hair's breadth above subsistence farming. Technology is largely driven and supported by population pressures, without that they don't have the need to progress nor to maintain anything you ...


32

The situation you describe is almost exactly (part of) the plot from the book "A Fire Upon the Deep". Which in my opinion presents a very plausible level of success. In fact the specifications you offer (1 year-ish time period, lack of homeworld contact for the high tech people) match the conditions in the book very closely. https://en.wikipedia.org/wiki/...


31

It is already too late. Any decision you make will either be a) one you have been gently guided towards by a posthuman superintelligence (with or without your realisation of this fact) or b) one that the posthumans have noted and decided to be entirely compatible with their other aims. You can't wriggle out from under the unblinking omnidirectional gaze of ...


30

Wood You said they don't have access to fossil fuels, but not to a forest. Using wood as fuel can be a good way to start gathering energy, in form of steam engine if you are looking for mechanical energy instead of heat. For the link: A common hardwood, red oak, has an energy content (heat value) of 14.9 megajoules per kilogram [...] Wood as fuel can be ...


30

Presumably the insects swarm, gorge, breed, then either die or hibernate. Then come out in force 20 years later after the eggs have hatched and the larvae mature into adults who can fly and who need human blood in order to support breeding. Humans have 20 years to find and kill the eggs or to kill the larvae. If the eggs are grouped together, then fire ...


30

Gray Goo Nanobots that can break down anything and use the raw materials to make copies of themselves go out of control. They literally devour the surface of the Earth. Things get back to normal when for some reason the bots decide to stop replicating and decay naturally. Source: https://xkcd.com/865/


30

Your question includes the answer: they have prehensile feet. As long as their body plan allows for balancing on one foot and manipulating objects with the other, or sitting and using both feet as we'd use hands, there are few barriers to their ascent to a technological civilization. Carrying objects in their mouths will have to suffice until bags and ...


30

would it be feasible for there to be a unique but similar civilisation on each 'Plane'? Define "similar". Given how thoroughly you've cut off each face, there's no guarantee that inhabitants of different faces would have the same set of amino acids, let alone anything more complex in common. You'd need to set up some means for information (cultural or ...


28

Man-eating dinosaurs should be relatively easy to keep at bay. A tyrannosaurus is a little under 4 meters tall, so it should be possible to hold it back with a good wooden wall at about that height. The villagers should keep a bell to ring when one is spotted to that everyone can run back to the walled fort to hide. Some flaming arrows might help persuade it ...


27

I've used a personal analogy for this, which I call "The brake pad problem." I estimate (without any serious research) that maybe a few hundred people around the world really know what it takes to manufacture an automobile brake pad. If you kill them all off, we're in serious trouble at least until a new process (or a reconstruction of the original) can be ...


27

Measurement units have followed a fairly standard pattern. Originally things are compared to something that both parties recognise. It could be a specific thing (the Washington monument) or a general thing (a banana). No one is really measuring anything accurately, so this is good enough. Next people start to measure things against their own standard. ...


26

No advancement at all Let's assume "very nearly destroyed" (a very vague description) means less than 5% of the population survives every attack. Those attacks occur every 20 years. Let's make an outrageous assumption that the only remaining people are distributed 19:1 in favor of women and all the women are prime childbearing (18-20 years old). In 10,...


20

A significant increase in global volcanism would satisfy your requirements: The devastation would be widespread, varied, and continuous. Think of something on par with the formation of the Siberian Traps. Such eruptions can last millennia. The resulting volcanic winter would wreak havoc on the biosphere and agriculture, necessitating greenhouses and ...


20

Sure, why not? The Soviet Union had mandatory military service pretty much EXACTLY like what you're describing with a population that size. The factors that would make it difficult to have nationwide combat training have everything to do with politics (your population refuses to participate) and economics (you can't afford to have all those people not ...


20

A better and more grounded question is not with mountain-sized animals but by comparing a society of humans and small +/-18mm long creatures, which if I didnt mess up my unit conversion again would be 1/100th the size. Lets say intelligent scorpions and fairies live with us. Smart though these creatures would be, would humans really pay enough attention all ...


20

They are simply too dull to attract attention from others. Think of ants or of other insects/bugs. As long as they don't become a direct nuisance, we don't really bother with them. We don't kill ants just because they are ants, but only when they start colonize our houses, we don't kill wasps just because they are wasps, but only when they become a danger ...


19

The Four Horsemen Global warming is making crop failures look likely. Famine can kill large numbers of people and historically has done so often. Tens of millions died in the midcentury famines in China and the USSR. If global warming makes the tropics unsuitable for agriculture that would lead to famine in Africa and India for sure and possibly China. ...


19

As opposed to men, animals are much more reasonable. They don't stubbornly go in places where they experience discomfort. Therefore walls, fires and smoke, topped with loud noises will be good dissuasive means. Keeping food away to remove any rewards for facing the troubles will also help.


18

Nearby Supernova. Dr. Mark Reid, a senior astronomer at the Harvard-Smithsonian Center for Astrophysics stated: … were a supernova to go off within about 30 light-years of us, that would lead to major effects on the Earth, possibly mass extinctions. X-rays and more energetic gamma-rays from the supernova could destroy the ozone layer that protects ...


15

It doesn't matter Both will be able to get manual labor jobs unavailable to the other. The elephant will be favored for jobs requiring strength while the mouse will do better with jobs requiring fine detail. But neither of those jobs will pay well. The best paying jobs will be those that require thinking. Unless the physical size comes with different ...


15

You give your own answer! When that size variation was a problem, they could standardize, somewhat, by using the body part of a ruler/monarch/lord/etc. instead of just some random individual. There is some historic individual who has made a big impression on all of these involved races. Measurements reference body parts and famous exploits of this ...


15

Every society needs to have multiple functions, so if you can only build one building for general civic use, it needs to accommodate all these functions You cannot just focus on one purpose for one building, you need to incorporate as multiple functions as possible. This is because if you group more than a few people together, they need to: Governance: ...


14

Poop! Poop! And more Poop! But seriously, dried animal dung is a very common fuel, even today in some places. You can burn it like wood. Dry dung fuel (or dry manure fuel) is animal feces that has been dried in order to be used as a fuel source. It is used as a fuel in many countries around the world. Using dry manure as a fuel source is an ...


13

Basic sanitation, including the germ theory of many diseases. Animal husbandy and plant improvement based on Mendelian genetics. If they have the data and sensors, mid-term weather forecasts. Imagine a serf knew that there would likely be two more dry and sunny weeks before the harvest is due. Food preservation technologies like canning (this requires jars ...


12

Insects are both bane and boon... and much worse for low-tech than for high-tech. They're not ever going to knock people back down the technological totem pole, because 20 years is well within living memory. Any technology is going to be build with the assumption of once-every-20-years horrible insect swarms. Mostly, then, it adds another thing to the ...


12

First, welcome to Worldbuilding, halp! Let me preface this by saying that this answer @rek gives about volcanism is a good start, and it was my first thought, as well. But in considering the additional details you've given, you may want to go another route (that is, depending on how realistic you want to be). I'll expand on some of the finer points below. ...


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