Is the universe bounded or unbounded?

[otseng]

In the Light, stars, and creationism thread, I proposed a theory to reconcile a young earth with being able to see stars that are billions of light years away. The theory assumes that the Big Bang is true, however, it also assumes that the universe is bounded. In typical cosmology, it is assumed that the universe is unbounded.

Bounded means that the universe has a boundary to it. There exists an "edge" to the universe in which beyond this boundary, our universe does not exist.

In an unbounded universe, there is no "edge". The universe "wraps" around itself. So, if you are to go in any direction in a straight line, you will eventually come back to the starting point.

This is hard to conceptualize, but can be explained like a surface of a sphere. On the surface of a sphere, if you start at any point and then go in a straight line, you will eventually come back to the starting point. Now, instead a 2-D surface on a sphere, the universe is a 3-D topology that curves in on itself.

The ramifications of either of these two assumptions make for drastically different cosmological conclusions.

So, the questions are:
1. Is the universe bounded or unbounded? Why?
2. What are the ramifications of whether it is bounded or unbounded?

[otseng]

You know what, I now understand your angle! I think this is illustrative of how difficult it is for someone who comes from one angle to grasp the meaning of another's angle. Well, at least it's not always so easy for me.

So what was the point of all of this discussion? ... I think it was about gravitational red/blue-shifting. I had said that a bounded universe would cause light to be redshifted. Shouldn't this be the case with both our models? In both our models, the mass that would not be cancelled out would be greater as the object approaches the border. So, there would be a greater gravitational force as an object goes farther from the center.

[QED]

You know what, I now understand your angle! I think this is illustrative of how difficult it is for someone who comes from one angle to grasp the meaning of another's angle. Well, at least it's not always so easy for me.

No worries. I could probably have explained it better if I had realized sooner that your intuition was leading you astray. Understandably human intuition is only geared towards our typical daily experiences. Most interesting science lies outside this experience and I really can't resist this opportunity to express my opinion that most of the honest incredulity held by creationists towards evolution stems from the counter-intuitive and far from human-scale events taking place in nature.

So what was the point of all of this discussion? ... I think it was about gravitational red/blue-shifting. I had said that a bounded universe would cause light to be redshifted. Shouldn't this be the case with both our models? In both our models, the mass that would not be cancelled out would be greater as the object approaches the border. So, there would be a greater gravitational force as an object goes farther from the center.

I think you were referring to the red-shifting of photons climbing out of "gravitational wells". Due to the inverse square law, this is usually only a local effect -- realised in proximity to hyper-massive objects like black holes. Only if mass were to be concentrated to black-hole densities in one region of the outer-shell could photons coming from that direction be red-shifted. This is not possible in a homogeneous model as Gauss's law sees to it that the photon's velocity is compensated by the mass in the remainder of the universe.

This takes us back to the standard cosmological model and the associated cause of super-luminal red-shift -- which is metric expansion. The theory that space and time are elastic was promoted to fact following the experimental confirmation of general relativity in the nineteen-twenties. Metric stretching of space is fact.