The standard model of particle physics is a very successful theory, spectacularly consistent with a vast range of experimental results. Nonetheless, most particle theorists believe that it is not a fundamental theory. They are confident that experiments in this decade—particularly at the Large Hadron Collider and the Tevatron—will discover some dramatic extension that sheds light on the origin of the many parameters that nowadays have to be put into the standard model “by hand.” But the incorporation of gravity into an all-encompassing theory has generally been regarded as a more distant goal.
Since 1974, the guiding principle for building extensions of the standard model has been the so-called desert hypothesis. 2 Its premise is that there is no new physics between the energy scales of electroweak unification (103 GeV or 1 TeV) and the vicinity of the Planck mass M Pl (1019 GeV). That implies an enormous “desert,”...
