I just went to hear Lisa Randall speak at Laurence University in Appleton Wisonsin, and very much enjoyed it.(adsbygoogle = window.adsbygoogle || []).push({});

I have her book,Warped Passagesand in both the talk and the book she introduces an intriguing phenomenon. Assuming a (3+1) dimensional brane embedded in an extended higher dimensional spacelike bulk, she calculated the Einstein equations assuming the source was localized on the brane, and discovered that while the resulting gravity obeys the approximate inverse square law on the brane, it falls off as a sharp exponential orthogonal to the brane in the bulk space. Since in the Einstein theory gravity is identical to curved or warped geometry, this allows her to describe the bulk as warped. Hence her title.

This exponential fall-off recalls Yukawa's theory of a force carried by a massive boson, which was also characterized by an exponential decay. So the Randall theory is "as if" the graviton, massless on the brane, acquired mass when it left the brane.

She then imagines that the world we live in is one brane - she calls it the weakbrane after the weak energy scale, which characterizes our experimental physics - and there is a parallel brane, some distance away orthogonally in the bulk, which is the source of gravity. Since the strength of gravity has fallen exponentially by the time it encounters the weakbrane this accounts for the fact that gravity is so feeble at the weak energy scale.

A pretty model, and she claims it will be testable at the LHC. She even showed a slide which portrayed her, very fetching in a hard hat, examining the construction there.

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# Lisa Randall's Warped Passages

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