After recently seeing Brian Greene's "Elegant Universe," I was struck by an idea - maybe not an original idea, but an idea nonetheless. If gravity is a weak force because it is not stuck to the "brane" of this universe, then gravity from our universe can influence others and vice versa from distant galaxies, right? If matter is in adjacent universes could that influence ours via gravity(?), it would appear to us that some invisible form of matter, "dark matter", was exhibiting a gravitational effect. Has anybody investigated this concept further than I?