For decades astronomers have been perplexed by so-called "dark matter" in our universe. It might be slightly more accurate to call dark matter "excess gravity," as what astronomer actually observe is gravitational force pulling stuff together where no matter appears to be present. This dark matter is currently measured to make up more than 90% of the mass of our universe, and has such intimate affects as holding our Milky Way galaxy together.
Is this extra gravity in fact coming from another brane, an entirely different universe? When we map the distribution of dark matter around our galaxy, are we in fact creating the first map of a parallel universe? Did the pull of gravity from another brane influence the way the structure of our universe formed and evolved? In the end it will all come down to gravity, and what its weakness tells us about the structure of reality.
Comments? How popular is this notion? I have read about this quite a few times...and Kaku often references this point.