Well, the current understanding is 1. The universe was created by the big bang, which created all the energy and matter in an instant. In the first few moments

Well, the current understanding is 1. The universe was created by the big bang, which created all the energy and matter in an instant. In the first few moments, this soup of energy and matter was near-uniform, but tiny imbalances caused matter to start clumping up into larger clumps. 2. Fast-forward 14 billion years, and those tiny imbalances and the resulting forces appear to have distributed the matter (including dark matter) into a fairly even, consistent structure across the entire universe, with galaxies mostly collecting together in clumps separated by huge filaments (see e.g. [1]). Our own galaxy seems to be in a bit of a void between some of these clumps. So that's our understanding of how the universe came to be, and how it came to be the way it is now. It seems that things are, as I said, "pretty much the same" no matter how far out you go, and this has an explanatory reason: the near-uniformity of the matter and energy created by the big bang. You're saying that it could be that, somewhere, outside the reaches of our telescopes, things are totally different. But we have no theories of how that could possibly have come to be, given our assumption #1 above. It just doesn't seem plausible, given our understanding of the big bang, that somewhere on the "other side" of the universe there's, say, nothing at all. Or a pure carbon crystal the size of our own observable universe. Or a Library of Babel. You're free to say "well, scientists don't know that there isn't," yes, of course, but without some kind of explanatory hypothesis, it makes far more sense to go with the data and theories we have. 1. https://www.space.com/37191-we-live-in-a-cosmic-void.html https://www.space.com/37191-we-live-in-a-cosmic-void.html