According to the theory of Lisa Randall the gravity is leaking from another dimension towards ours , beeing stronger in
the other dimension and weakening as it enters ours. Seeing that almost, if not all galaxies have a black hole in the middle
and according to M theory that matter was created by another universe coliding with ours , could it be that the black holes,
, where gravity manifests in a stronger way, are the points where the two universes colided ?