The_elk00 t1_iy7d37j wrote on November 29, 2022 at 7:52 AM

Reply to comment by Radiant_Nothing_9940 in what would be different if we had two moons by Any_Palpitation_3110

Space is such a crazy concept to think about. If it's not infinite, what's the end or edge like? Does time move at an insurmountably slow speed at the edge? Is space infinite but there's just nothing there? Is it a wall? Does all matter become more tightly packed that it acts like a wall but can expand?

Aekiel t1_iy7hyfh wrote on November 29, 2022 at 9:03 AM

There's a lot of debate about this.

The prevailing theories at the moment are that the universe is either infinite or finite. If it is infinite then there is no question of whether it is bounded or not (it is unbounded as you can't name two points within the universe and have the distance between them encompass everything within it).

If it is finite then the question is whether it has an edge or not. If it has an edge it is referred to as a bounded universe and we have little idea what could be at or beyond the edge of such a universe.

If it is a finite but unbounded universe then there's a definable volume to the universe (that is growing all the time due to expansion), but it doesn't have an edge. This is where the common balloon analogy comes in (a balloon doesn't have an edge, but as it expands the surface area of the balloon and distance between two points expansions).

Current thought rules out a finite bounded universe as it violates homogeneity, but there's no settled consensus on whether we live in an unbounded infinite universe or an unbounded finite one.

EDIT: If we do live in a bounded finite universe there's also debate as to the geometry of it (is it like a sphere? a torus? something weirder?).

Radiant_Nothing_9940 t1_iy8c0ym wrote on November 29, 2022 at 2:42 PM

There’s also the theory that it’s a 4d hypersphere, meaning reaching one “edge” will just be the same as making it to the opposite side and nothing else. I love this theory as it adds both an explanation for the expansion of space (the sphere itself is expanding, so all the 3d things are getting further apart) as well as possibly leaving a scientific space for a god. I am an atheist, but if we live in a 4 dimensional (or more) universe, a god could easily exist outside the 3d bounds of it, and would therefore be able to see and interact with any part of it.

Too bad this universal theory is likely untrue and these days not considered a prevailing theory. It just explains so much for me, and could even let string theory exist, but I think the math just doesn’t work out.