Throughout the Universe, there are lots of signs that there's more gravity out there than there is visible matter to produce it. Over the last few decades, physicists have slowly come to the conclusion that it is not the laws of gravity that need to be changed, but rather that a massive particle is responsible for the extra gravity. Now, it should be pointed out that this is not a whim. The distribution of dark matter describes all manner of gravitational phenomena at all scales, including some really weird things, like the Bullet Cluster. So, understandably, particle physicists and cosmologists get a bit touchy when people say that we should just modify gravity instead. Erik Verlinde, a Dutch