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?

  • 1
    $\begingroup$ 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 physics.stackexchange.com/q/136831 $\endgroup$ – probably_someone Jun 13 '18 at 14:35
  • $\begingroup$ Yes, you are completely off. The universe has no centre or edge, even if it is finite, which it may well not be. $\endgroup$ – tfb Jun 13 '18 at 14:44
  • $\begingroup$ Possible duplicate of Did the Big Bang happen at a point? $\endgroup$ – tfb Jun 13 '18 at 14:52
  • $\begingroup$ @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. $\endgroup$ – Ralph Jun 13 '18 at 16:01
  • $\begingroup$ @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. $\endgroup$ – probably_someone Jun 13 '18 at 16:10