What have we learned from two-dimensional models of quantum black holes?

Abstract

The two-dimensional black hole provides a theoretical laboratory in which the quantum nature of black holes may be probed without the complications of four-dimensional dynamics. It is therefore natural to ask, what have we learned from this model? Much recent work has focused on the semi-classical limit where the black hole is similar to the Schwarzschild solution. However, in this essay, we demonstrate that theexact two-dimensional quantum black hole is non-singular. Instead the singularity is replaced by a surface of time reflection symmetry in an extended space-time. The maximally extended space-time thus consists of an infinite sequence of asymptotically flat regions connected by timelike wormholes, rather analogous to the Reissner-Nordstrom space-time. The implications of this to the apparent loss of quantum information arising from black hole evaporation are also briefly discussed.