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I m having difficulty understanding what is after the "Future Horizon" as defined per wikipedia
I read the similar "If the universe is expanding, what is it expanding into?" question and answers. I might have misunderstood the answer but I fail to understand what is meant by the answer "the universe isn't expanding into anything".
What exactly happens when the universe extends. Does extending mean fill vaccuum with something? Does this vacuum outside of our future horizon extend infinitely? I thought that infinity was not possible in physics.
I searched for answers here but most answers were using analogies of a circle in a 2D world or a sphere in a 3d world but I m not satified by these answers as in each case there is always a higher dimension which "contains" the universe. The question is then what is at the boundary of this higher dimension.
Maybe there is something I don't understand. Could someone come up with a clear explanation?