It is entirely likely that the Universe is not infinite. Most cosmologists would probably bet against it being so. But the details of inflation, and the exact geometry of the Universe make it impossible to know for certain its true extents.dlw wrote:When I was a little boy I looked up at the stars and wondered what all was up there and how far it went. That's why I've been an avid APOD follower for many years. I was (and still am) puzzled by the notion that the super-universe is infinite - literally without edge and not curved so that going far enough would bring you back to where you started.
It shouldn't. It should only suggest the possibility that the Universe itself is larger than the part we can see from here. That certainly doesn't imply it is infinite.The notion that there is a 13.7 BLY "sphere of observability" from any point in the universe reinforces the concept of an infinite universe.
Really, a single point in spacetime. Thus, a point that is outside the three-dimensional spatial universe we observe.Perhaps then the conceptual mistake is thinking of the "big bang" as occuring at a single infinitely small point. Perhaps a better way to think of it as occuring at a single point in "time" (for some definition of time) but physically everywhere (for some definition of those things).
I'd say both your terms are the same thing. There is a large universe, presumably many times larger than 91 billion ly. From any point in this universe you have an observable sphere with a diameter of 91 billion ly, a diameter dictated by the speed of light and the expansion rate of space. Beyond any observable universe is just more space, the same as anywhere. Don't get confused by the fact that what we see at the edge of the observable Universe is very young; we're just seeing photons that took a long time to get here. What is really out there "now" isn't younger than what is here. Everything in the Universe is the same age, 13.7 billion years old. It's not like you could travel outwards billions of light years and see your surroundings get younger.But then what "meaning" does the 91 BLY have? The notion of "observable universe" versus "sphere of observability" is confusing. I understand the latter but not the former if indeed there is a 13.7 BLY SoO from any point in the OU. What's beyond the OU or is there a 91 BLY OU around every point as well?
As already noted, the Wikipedia articles on cosmology, the Universe, the age of the Universe, and the observable Universe are all good starting points.Is there a good reference on this subject that a layman might understand?