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The universe seems to be infinite in size, both now and at t=0.
It certainly isn't spherical
talking about the surface of the universe, and an inside and outside is nonsense
Do you mean "infinite" or "boundless"?
If it is only boundless, there could be something outside.
The original question requires that we accept the B B as the beginning of the Universe. If it had a beginning it must be finite.
There are theories involving weird geometry in which the universe is finite but unbounded
How would you go from the outside to the inside without crossing a boundary?
I don't think the question does assume that the BB is the origin of the universe - it could be infinitely old, with the BB representing the end of a collapse.
why couldn't the universe be infinite in size when it began? If it is infinite now then it must have been infinite a finite time in the past.
Why the need for weird geometry? Surely, if the Universe had a beginning, it is finite. It might go on expanding for ever (unbounded), but it could never become infinite.
Bouncing universe? BB would still be the beginning of the universe we perceive. How would we know that earlier universes were "the same universe" as our's, or even that they occurred as a sequence, rather than all at once?
Are you using "infinite" as though it were synonymous with "unbounded"?
I am using "infinite" in the sense of an infinite straight line.
The infinite straight line, like the infinite series, is a mathematical construct which has no "reality" outside the, presumably finite, minds of mathematicians.
That doesn't mean that it is an invalid way of describing the universe. We think about the universe in mathematical terms all the time!
We continue for ever, ie the infinite universe, which seems to be the best bet.
I was assuming that the laws of physics as we understand them today are still in effect.
This seemed way to small to me
I see no reason why the laws of physics should apply in such conditions
I had originally thought of this question after reading an article about the big bounce. I was imagining all the matter and energy in the universe coming together at the moment of the big bounce.I was assuming that the laws of physics as we understand them today are still in effect.Which would mean that the very tightest you could pack the matter and energy would be to cram a planck mass into a space of planck length.
perhaps even smaller than the Planck Time
This idea that the universe poped into existence from a minutely small point whether a planck mass is a little hard to accept.
This idea that the universe poped into existence from a minutely small point whether a planck mass is a little hard to accept. You could then ask the question what were the conditions prior to the expansion event. The key to explaining the origin lie with understanding the unity theory of gravity and it's existence prior to the big bang. !
physics necesserily breaks down at the singularity
A singularity is simply somewhere that an infinity occurs, it need not be a point in space. The Big Bang was a singularity that occurred throughout space, with the density virtually infinite.
Quote from: QuantumCluephysics necesserily breaks down at the singularity Obviously a singularity can exist in theory, but has anyone established that it is a physical possibility?
Surely, by its very nature, an infinity must be everywhere, and include everything; unless you are talking about a Cantor type mathematical infinity, which is a very different "creature".
Quote from: Bill S on 15/11/2010 22:36:47Quote from: QuantumCluephysics necessarily breaks down at the singularityObviously a singularity can exist in theory, but has anyone established that it is a physical possibility? Yes.Is that yes a singularity is proven possible. I don't think so.Current opinion on the universe creation is speculative. However i will accept a big bang event occured from the decay of an ancient universes dark matter collapse. When a universe eventually disperses far enough into (space*) it is reduced to dark matter ( dark matter is made up of base sub atomic elements fragments of atoms ) clusters with minimal gravitational forces. All matter whatever it is will eventually decay to sub atomic components. When the (dark) matter attractive forces exceed the expansion gravitational forces the universe collapse begins. However not all matter is consumed. This is not unlike a black hole however a black hole occurs in an active galaxy in our universe. The collapse event consumes a different type of matter which in theory creates this singularity event. When the explosion occurs (big bang) the energy release is unimaginable in size and triggers development of galaxies from the remnants of a much older universe. The varieties of these remnants gives us today the many different galaxy types which if you think about it explains a lot. These remnants form galaxies of all different types and shapes and would give evidence that the contents of our universe is older then the singularity event itself. One day to be proven. My interest is more on the period prior to the universe creation.