How the Edge of Our Galaxy Defies Known Physics

One thing I've been wondering gets into M Theory, the theory that "isn't even wrong."  If our universe is described holographically as a d-brane with strings dancing on the "surface" describing everything in our universe, one thing I haven't seen anyone speculate about is, what about the other "side" of the d-sheet?  Is there a parallel or mirror universe with its own physics where Dark Matter and Energy exist, and the gravity effects leak through the d-brane to the other side?  Both Light and Dark matter would be mutually attracted to each other in the "same" location.