(September 19, 2012 at 5:03 am)FallentoReason Wrote:genkaus Wrote:Currently, we are sort of hard-wired to think in 3-d terms. When we talk about whether the universe if finite or not, what is going on in our minds is that if we go far enough, we'll either find some sort of membrane that we just can't cross, which defined the limit of this universe or we won't find any such membrane, in which case we can call it infinite. But as we know from our practical experience with circles and spheres, it wouldn't really be infinite. So the question of whether the universe is infinite or not would boil down to understanding what boundary conditions are applicable. And since we are not built to think in those terms, trying to imagine it gives me a headache.
You were treading on a solution to being able to answer the question. What would help us would be to better understand the shape of the universe. From what I've read (although I'm quite rusty on the topic) the sum of all the energy in the universe is 0, which means that it's linear i.e. 'flat' in a nutshell. It means that everything did begin at a single point and expanded out. I think this would suggest that the universe can't be a sphere type shape which is infinite but something else. But like I said, I'm quite rusty on this topic.
On a bit of a tangent: I find it quite interesting and somewhat chilling that the universe began at a 'single point'. This literally means that the beginning of the universe happened where you and I are sitting simultaneously. The singularity expanded, therefore creating the world we know, which means all this space is the space that came from the singularity. So the big bang technically happened everywhere in the known universe only that it was all squeezed into a singularity.
The shape of the universe is calculated using CMB, and the basic geometry of a triangle. Using earth as one apex, and measuring the largest fluctuations in the CMB we can determine the shape of the universe. If the universe was spherical, the angles would be more than 180 degrees, if it had a negative curvature, then it would be less than 180 degrees. Neither of these have turned out to be the case.
