7 Applications in Quantum
Gravity
As discussed in the introduction, laws of black hole mechanics,
discovered in the early seventies, provided a concrete challenge to
candidate quantum theories of gravity: Account for the
thermodynamic, black hole entropy through a detailed, statistical
mechanical counting of appropriate micro-states. Indeed, this is
essentially the only concrete quantitative hint we have had about
the nature of quantum space-time geometry. The isolated horizon
framework has been used to address this issue systematically and
has led to the only available detailed calculations within a
full-fledged approach to quantum gravity that encompass realistic
black holes (which carry no or negligible gauge charges and may be
distorted). As we will discuss in Section 8, what
we know about dynamical horizons does suggest that there should be
interesting generalizations of these results also to
non-equilibrium situations. But so far there has been no work along
these lines.