I don't think it is impossible. And humans have a way of doing things that really seem impossible at first. I'm sure a hundred years ago no one would have thoug

I don't think it is impossible. And humans have a way of doing things that really seem impossible at first. I'm sure a hundred years ago no one would have thought it possible to walk on the moon. We now have workable methods to turn the dirtiest of water into pure drinking water. Agriculture is a long, long way from being as efficient as it could be; we find ways all the time to quadruple the food output of a plot of land, and there will continue to be innovation in this area. Our diets are largely wasteful around the world as well, it is possible to live on much less food than the typical American eats, for example. And as for space, the world average population density per land is actually not that high; certain places are, but when spread out, there is tremendous room for physically placing more people. So I'd say it is well within possibility to make 100 billion people stay alive. But, a lot would change to do so.