michael_cain writes "One of the plot elements implicit in much speculative fiction is the size of the population required to support a given level of tech. Generation ships, colonies on new planets, Earth after some sort of semi-collapse. In many cases, small groups maintain a level of tech beyond what we have today: assume self-repairing self-programming super-computer AIs and it doesn't take a whole lot of humans. For today's tech, it couldn't just be eggheads; there would need to be doctors and farmers and police officers and bricklayers and... you get the idea. How big/small a "closed" society would it take to support — and be supported by — today's tech?"