It's believed that the excess gravity observed in the local galaxy (and in all the others as well) arises out of matter/energy which we can neither sense or manipulated ('cause it's in an adjacent or nearby universe).
Recently an evaluation of the location of dark matter in a nearby galaxy was consistent with a string theory hypothesis regarding what happens to dark matter when regular matter accelerates.
Thought that was a neat photo.
Incontrovertible? Drs.Michio Kaku and Lane Collins state there is “not a shred of experimental evidence”that has been found to confirm superstring theory. Neither is there evidence to support inflationary cosmology. The fact that some appeal to the theoretical existence of many universes to avoid the implications of the finely-tuned circumstances of the universe at hand, still requires explaination of design.
The skeptic needs to invent a whole new set of physicl laws and a whole new set of mechanisms that are not a natural extrapolation form anything we know or have experienced. If a theist profered such theories to explain a theology they would be run out of town on a rail.