Einstein wins again

Despite the bit of knocking that Einstein has gotten recently over the speed of light, one aspect of his work appears to have checked out: the general of theory of relativity.

Said theory states in part that the wavelength of light from a distant galaxy will shift a small amount due to the galaxy's gravitational mass, a phenomenon known as "red shift" in astronomy.  Turns out this is correct.  As stated in the linked article on Space.com:

 "The effect is very difficult to measure, because it is the smallest of the three types of redshift, with redshift also being caused by the movement of the galaxies and the expansion of the universe as a whole. To disentangle the three sources of redshift, the researchers relied on the vast number of galaxies in the Sloan Digital Sky Survey sample, which allowed them to perform a statistical analysis."

And it does indeed seem that gravity can and does affect the wavelength of light, bearing out Einstein's notion that not are space and time related but the presence of mass warps space-time itself.  A significantly large mass such as a galaxy or a galaxy cluster will alter space-time to a point where time will actually move faster.  So...I have to ask.  If light is subject to the forces of gravity, i.e. speeding up or slowing down according to the presence of mass, wouldn't that indicate that the speed of light is not the constant Einstein thought it to be?  That alone is tough to get my head around but then toss in the idea of dark matter and it all gets real noodlely, real fast.

It is currently suspected by camps of astronomers that the universe contains far more mass than is visible.  This x quantity has become known as "dark matter."  If dark matter exists, and more and more space scientists think this likely, then what occurrences is it responsible for?  How is this mass exerting itself upon light and other aspects of the universe.

Sure wish Einstein was still here to tell us.  Heck, Carl Sagan wouldn't be bad, either.

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