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According the the Big Bang theory, the universe started as a 0-dimensional point of infinite density. Shortly thereafter, it underwent inflation and grew to some measurable size, and continues growing to the present day.

If, when inflation started, the universe was a "ball" of some measurable size, that implies that some of the matter-energy was close to the "outside" of the ball and some was close to the "center", even if there is no "outside" of the ball.

Why is it not possible to determine how far something is from that "edge"? If the answer is that the "edge" is farther away than light travels in 13.7 Gy, I can accept that. It is still some finite distance away, albeit too large to measure.

Am I completely off in my thinking? What is wrong with my logic?

Qmechanic
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Ralph
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    How do you know that the universe is of finite size in the first place? We've never had any conclusive evidence that such a thing is true. The current measurements still allow a "flat" universe, which is of infinite extent. For an explanation of how an infinite universe works with the Big Bang theory, see https://physics.stackexchange.com/q/136831/ – probably_someone Jun 13 '18 at 14:35
  • Yes, you are completely off. The universe has no centre or edge, even if it is finite, which it may well not be. –  Jun 13 '18 at 14:44
  • Possible duplicate of Did the Big Bang happen at a point? –  Jun 13 '18 at 14:52
  • @probably: According to this answer, if we assume that the "size" of the universe is the distance that a photon could travel since the big bang, then it has a "size" and is not infinite. – Ralph Jun 13 '18 at 16:01
  • @Ralph Most of the time, including in the referenced answer, that quantity is called the size of the observable universe. This doesn't necessarily have anything to do with the size of the universe at large; at best, it's a lower bound on the size. – probably_someone Jun 13 '18 at 16:10
  • Ok. I understand that. Therefore we can be 46+ GLy from the edge of the observable universe, but we have no idea how far it extends beyond that. This stuff is pretty "meta" :-) . – Ralph Jun 13 '18 at 16:13
  • @Ralph Also, the concepts of the "center" and "edge" of the universe don't really make much sense, either. The universe is not expanding outward from a point; rather, everything is moving apart from everything else. No matter where you stand in the universe, on average you'll see galaxies moving away from you in all directions, so there's no center. If the universe is infinite, there is obviously no edge; if it's finite, space is curved such that traveling in any direction will eventually get you back to your starting point. So there's no edge, but space is finite, like on a sphere in 2D. – probably_someone Jun 13 '18 at 16:29
  • @Ralph You can certainly say that the observable universe, observed from a particular point, has a center (it's where you're standing) and an edge (it's the sphere of first light), but the observable universe changes every time you move, so the center and edge don't have any physical significance. – probably_someone Jun 13 '18 at 16:33
  • This answer helps a lot. – Ralph Jun 13 '18 at 16:39

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