Black holes, string theory and quantum coherence

On the basis of recently discovered connections between D-branes and black holes, I show how the information puzzle is solved by superstring theory as the fundamental theory of quantum gravity. The picture that emerges is that a well-defined quantum state does not give rise to a black hole even if the apparent distribution of energy, momenta, charges, etc. would predict one on classical grounds. Indeed, geometry - general relativistic space time description - is unwarranted at the quantum microstate level. It is the decoherence leading to macrostates (average over degenerate microstates) that provides on the same token - the loss of quantum coherence, the emergence of a space time description with causal properties and, thus, the formation of a black hole and its Hawking evaporation. (C) 1999 Elsevier Science B.V. All rights reserved.