(Darn you, Chronos! It takes me time to babble like that! No fair slipping in front of me.)
(I know I know - “preview reply” is my friend…)
There appears to be a new and better theory than the Big Bang, and it’s called Brane New World: http://www.arxiv.org/list/hep-th/new
The way I heard it didn’t involve (require) expansion of the universe at all. It went like this:
Using well known and well verified orbital calculations, if we plug in the mass of a galaxy we can get the speed of its rotation, and if we plug in the speed of rotation we can get the mass. We can accurately measure its speed of rotation, however, that gives us a mass figure that is much, much larger than the mass we can observe. So either
a) our orbital calculations are totally wrong,
b) our measurements of the orbital speed are totally wrong,
or
c) there’s a lot of mass out there that we can’t observe.
Cosmologists have strong evidence that it’s not a) or b), thus it is most likely it’s c). Hence, Dark Matter. There’s no need to invoke the Big Bang, curvature of space, etc.
Of course, this is likely a really simplistic explanation (from high school physics, filtered through fifteen years of foggy memory).
As for Dark Matter being clouds of hydrogen, wouldn’t we expect to see evidence of emmision/absorption, which we’re not?