On Gravity, Oreos and a Theory of Everything - New York Times: "They began by drawing pictures and making crude estimates over ice cream and coffee in that ice cream parlor, which is now a taqueria. What they drew pictures of was a kind of Oreo cookie multiverse, an architecture similar to one first discovered as a solution of the string equations by Edward Witten of the Institute for Advanced Study and Petr Horava, now at Berkeley. Dr. Randall and Dr. Sundrum's model consisted of a pair of universes, four-dimensional branes, thinly separated by a five-dimensional space poetically called the bulk.
When they solved the equations for this setup, they discovered that the space between the branes would be warped. Objects, for example, would appear to grow larger or smaller and get less massive or more massive as they moved back and forth between the branes.
Such a situation, they realized to their surprise, could provide a natural explanation for the hierarchy problem without invoking supersymmetry. Suppose, they said, that gravity is actually inherently as strong as the other forces, but because of the warping gravity is much much stronger on one of the branes than on the other one, where we happen to live. So we experience gravity as extremely weak.
'You can be only a modest distance away from the gravity brane,' Dr. Randall said, 'and gravity will be incredibly weak.' A result was a natural explanation for why atomic forces outgun gravity by 10 million billion to 1. Could this miracle be true? Crazy as it sounded, they soon discovered an even more bizarre possibility. The fifth dimension could actually be infinite and we would not have noticed it."
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