On Nov 22, 10:13*pm, Tom Roberts wrote in
sci.physics.relativity:
Dark matter is a potential problem for GR. Dark energy is a puzzle for
GR, and cosmology in general. We most definitely would like to identify
the former and understand the latter; or find a theory with the domain
and explanatory power of GR, but which does not need one or both of
them. And we would like to unify GR with quantum theory. Current guesses
are that these are all inter-related, in some manner not at all
understood at present.

Master Leonard Susskind is starting to see the solution to the
problem, Honest Roberts:

http://www.sciscoop.com/story/2008/10/30/41323/484
"Does the apparently constant speed of light change over the vast
stretches of the universe? Would our understanding of black holes,
ancient supernovae, dark matter, dark energy, the origins of the
universe and its ultimate fate be different if the speed of light were
not constant?.....Couldn't it be that the supposed vacuum of space is
acting as an interstellar medium to lower the speed of light like some
cosmic swimming pool?"

Pentcho Valev