Eli5 if the universe is everything but it is constantly expanding, what is it expanding into?
In: 22
There’s a theory that the universe is locked onto itself like pacman where you exit through the left and appear on the right. Given that we’re used to three-dimensional thinking it is hard to imagine 3d space being somehow twisted in a way so that it behaves this way.
My way of imagining it is this. Consider a one-dimensional space — a finite line. You can move left and right. The only way for it to lock onto itself is to close the line in a loop, say a circle. If you follow the line you still move one-dimensionally, but the line that got locked onto itself gets another dimension by becoming a circle.
Now if you were to live in a two-dimensional space, say a circle, locking it onto itself would turn it into a sphere of a sort. Your movement would be two-dimensional, but the shape would have three dimensions.
Hence, locking our 3d universe onto itself would add a fourth dimension, which we can’t feel or see and are not able to comprehend.
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