Quote:
Originally Posted by dcl
speedfreek: M-Theory proposes the possible existence of multi-dimensional membranes which interacted, causing our universe.
dcl: Let's not lose sight of the fact that, as attractive as M-theory may be in some respects, there is absolutely no evidence for or against it. So let's remember that at best it is only a hypothesis awaiting the first evidence that it may be valid. I'm under the impression that the same must be said for loop quantum gravity.
speedfreek: As for Loop Quantum Gravity, Abhay Ashtekar and Martin Bojowald have released papers stating that according to loop quantum gravity, the singularity of the Big Bang is avoided. What they found was a prior collapsing universe.
dcl: I, too, think it plausible that the present expansion was preceded by a bounce from a previous contraction, but I'm not aware that there is any evidence for a bounce, so we should not seize on the idea that there was one.
|
Of course, both M-Theory and Loop Quantum Gravity are hypotheses awaiting a mechanism to test them with. I agree we should not seize upon the idea that
either is correct, as we have no evidence. I presented them simply as valid possibilities (ones being pursued seriously, rather than pie in the sky ideas), hence my repeated use of the term "
perhaps" in my post above.
Quote:
|
Originally Posted by dcl
I feel that further investigation in some areas is pointless. For example, the idea that the Universe has the shape of a cube, a 3-torus, a doughnut, or a dodecahedron is pointless because the suggestion that the Universe has any of those shapes seems preposterous to me. The shape that seems plausible to me is that of an expanding four-dimensional hypersphere.
|
The idea that any shape other than a four-dimensional hypersphere seems implausible
to you and is therefore preposterous
to you is essentially irrelevant. Cosmologists are searching for evidence of a shape, and one method is to look for matching areas in the WMAP data.
Any valid shape with a non-trivial topology (and that includes a hypersphere, amongst others) might show up as repeated inhomogeneous regions in the CMBR, where these non-uniform regions were introduced during inflation. The relative positions of these regions would indicate the topology involved, but only if the fundamental domain of the universe was smaller than our observable universe.
It may indeed seem doubtful that the fundamental domain (the whole universe) is smaller than our observable universe, but we have to do what we can to test for it and the least we can do is search our observable universe for evidence for it so that we can count it out. So far we have only counted it out across a co-moving diameter of 78 billion light years and our observable universe has a co-moving diameter of 92 billion light years so there is a little way to go yet before we can confidently state that the whole universe is larger than our observable portion of it. Until we can, there remains the possibility that we might find evidence for a non-trivial topology.
Should we only look for evidence for the most plausible model? Is that good science?
As you are so convinced that the hypersphere is the only plausible shape for the universe I must assume you have studied the mathematics of hyperspheres and so you should be familiar with both the
Poincaré conjecture and, perhaps more pertinently, the
Poincaré homology sphere, which is also known as
Poincarés dodecahedral space.