Solanalos

I want to understand it better. I would appreciate corrections to the following (my understanding of it) if need be.

1. The Big Bang occurred everywhere in the universe and everything that now exists (matter, energy, spacetime) comes from it.

2. The Big Bang began at a point of singularity and expanded from there.

3. The universe in it's early stages was small.

How can the universe be infinite if it was at one time finite?

If my above understanding of the early universe and the Big Bang is correct, that is the question that sticks out at me. Here's what I need to know: Does spacetime come from the Big Bang or not? Is the Big Bang an explosion in spacetime or is spacetime within the Big Bang?

The only way I can see the possibility of an infinite universe is if spacetime preexisted the Big Bang and was already infinte. I can't understand how something can "make the jump" from finite to infinite?!

I'm probably missing something fundamental, but that's why I made this post. Thanks in advance for filling me in.

Kalkin

Yes, you are missing something fundamental. According to modern cosmology, the universe is not infinite. (I think.)

Solanalos

I'm under the impression that the jury is still out on this.

wade-w

I'm certainly no cosmologist, but mathematically, a space can be infinite, but still be bounded.

Lobstrosity

I believe it is considered infinite by modern cosmology in that there's no boundary out there that we'll one day reach if we go far enough. The universe is assumed homogeneic and isotropic, which, as far as I know, would proclude the existence of boundaries. The only way it could be finite in extent is if the universe were closed (geometrically speaking). In such a universe you would (in theory) eventually come back to where you started if you travel far enough in a "straight" line. The only caveat is that such a universe would collapse in on itself more quickly that it would be possible to complete a round trip, so in practice you'd never be able to pull it off. At any rate, WMAP seems to strongly indicate that the universe is flat, which according to modern cosmology means an infinite Euclidian 3-space. (The third possibility is an open universe, which would be a 3-dimensional hyperboloid embedded in an abstract 4-dimensional Lorentzian space. An open universe would also be infinite in extent, in theory.)

Kat_Somm_Faen

Naw,

the Universe ( at least the observable to the surface of last scattering ) is quite finite. It is just reeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeeeeeeeeely big ( well its bigger than that I just did not feel like putting in all the billions of e using up all the space on the boards ).

Yeah it should be in the teens of billions light years across. I believe 14-16 billion light years range. Someone please feel free to correct me if I am wrong. Its a closed system, flat geometry and apparently bound to be forever expanding.

Solanalos

Are you talking a closed infinity like ending up where you started if you went far enough? I guess I can kind of see that. Even then, though, it would seem an added, unnecessary condition of spacetime. Then again, I'm no cosmologistm, either (or mathematician for that matter) - just your run-of-the-mill armchair scientist. I know common sense has little place in the realms of quantum mechanics and cosmology.

Kat_Somm_Faen

I believe wade is thinking of infinite sums ( or parts ) still making a finite quantity... Kinda like one of the Zeno's paradox explanations.

Am I right, wade?

Solanalos

I must be missing something. If everything was once in the finite conditions of the early universe, how is it a flat infinity now?

Edit: Why isn't it just an ever expanding finity?

EGGO

I guess we can look at a seed growing into a giant redwood as a parallel?

Well maybe not...the seed DOES need some sort of nurturing.