In explaining why the universe is isotropic, physicists theorize that the infantuniverse expanded in a virtual instant by a factor of 10 to the 26th power. What size was the universe at the end of the inflationary expansion? Also, several sizes are given for the universe today, with 92 billion light years being a more-or-less credible figure. However, the source I read confuses the issue by using the terms “visible” and “observable,” which do not appear to interchangeable. How large is the entire universe thought to be, not just the visible or observable parts?
There is no way to know how big the universe is beyond the observable universe since light (and therefore nothing else has been able to reach us from there to give us any idea. There is at least one theory that the universe may be infinite in extent and consist of parallel* branes which collided to give a local big bang.
*I say parallel, but they are parallel in an unobservable dimension not one of the three (or four counting time) that we cannot perceive.
Isn’t one theory that the universe (or our universe, if you believe in there possibly being numerous universes) is constantly expanding and therefore there is no exact measurement because the universe will have expanded again after your “measurement” of the universe.
After this, the two theories I think I know of are that the universe after billions and billions of years may suddenly stop expanding and snap back the around the size of pre-big bang universe (and then maybe explode out again?), or that the universe will continue expanding and continue expanding until everything separates from itself including atoms, quarks, until everything is too far apart to actually be anything (then keep expanding?) So basically, thinking about the theories I’ve heard (from Discovery Channel’s Scientific show about the universe) it is impossible to figure out how large the universe is or will be.
I hope that was understandable.
The simplest theories to account for the best data which we currently have all say that the Universe is infinite. If it is infinite, then it’s always been infinite, and will always be infinite. We can’t rule out the possibility that it’s finite, though: It would just require a slightly more complicated theory.
I’m not following. How is this consistent with there having been a Big Bang?
The Big Bang has two essential properties: expansion of the space-time of universe, and cooling of the matter-energy within it. Neither of those require a finite universe, although it makes thinking about it easier.