  The search for a theory of quantum gravity faces two great challenges: the
incredibly small scales of the Planck length and time, and the possibility that
the observed constants of nature are in part the result of random processes. A
priori, one might have expected these to be insuperable obstacles. However,
clues from observed physics, and the discovery of string theory, raise the hope
that the unification of quantum mechanics and general relativity is within
reach.
