Maybe it’s not dark matter, just gravity leaking in
The visible stars and other bodies do not move in the manner we would expect, given the gravitational pull of the matter visible to us. This has led to the theory of “dark matter” as the source of the remaining gravity, even though we don’t know what this dark matter is, and cannot even detect it beyond its gravitational effects on the celestial motions of visible bodies.
Perhaps it is not detectable because it is not there, at least not in this universe. When discussing extra-dimensional travel and its consequences on time travel (20 May, p 34), it was mentioned that in string theory the graviton, the hypothetical carrier of the gravitational force, is represented by a closed loop. As such it is not bound to this “brane” and is free to leave and travel into the 10-dimensional “bulk”. This is suggested as the reason why gravity is so weak compared to other forces: it leaks away out of this universe.
If gravity can leak out of this brane, then why shouldn’t it be able to leak in as well? If so, the dark matter which holds galaxies together could in fact be galaxies (or some other collections of mass) in other, neighbouring branes from which gravity is leaking into our own. This would explain why dark matter is undetectable and has a consistent pattern to its distribution.
But do we need dark matter at all? Maybe general relativity explains it all.
UPDATE: That last link references a paper that has serious problems. So we do need dark matter—or some other explanation—after all.