The black hole interpretation of string theory
For scattering processes in which both s and t are significantly larger than the Planck mass we have string theory on the one hand, and on the other hand the physics of black hole formation and decay. Both these descriptions are as yet ill understood. It is argued in this paper that a lot of insight is to be gained by insisting that black holes and strings should be “unified”. Just like string theory, the horizon of a black hole is governed by some conformal operator algebra on a two-dimensional surface, where the in- and out-going particles are represented as vertex insertions, so here we have a starting point for a unified description. Only the “physical picture” is very different. Rather than a quantized string, a black hole is seen to be a classical statistical ensemble defined on a membrane, its horizon. The former requires a minkowskian surface; the latter a euclidean one. These two are known to be related by a Wick rotation. We stress that black holes are as fundamental as strings, so the two pictures really are complementary.