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You're all considering the universe as matter expanding within infinite void. That's not correct. The universe is space expanding within nothingness. Nothingness is not the same thing as void; "void" needs a space to be empty, while there's simply no space outside the universe. If there are other universes, there must be nothingness between them; if it doesn't, it's still one universe. You don't need to continuously give energy to the expansion. It's still powered by the night infinite energy of the big bang. Remember, if you move something and there's no opposite force to stop it, it will keep going forever. Without friction in a void space, you could kick a tin can from orbit to another galaxy. It would just take a little time (if the galaxy isn't expanding in another direction more quickly than the can, in that case it will never reach it). Expansion could stop only if the gravitational total force of all the matter in all the universe is enough to counter it, leading to a big crunch. Apparently, there's not enough gravity according to the latest experiments, but it's still under some debate. Space expands faster than light, by the way. Things can't move in space faster than light, but space isn't expanding "in space". Not making this up, read Scientific American. So the question is, what do you see if you fly to the edge of the univese ? If spacetime is curved enough, you'll never see it as in a pac-man game; you could keep walking forever on Earth, for an infinite time, but you'll never find an "edge" because you're walking on a curved space. If it isn't curved enough, you'll see simply nothing. Space expands far faster than matter or energy. At a point, you'll be the moving edge of the universe, I guess.
""For every complex problem, there is a solution that is simple, neat, and wrong.""
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