Black holes and quantum cosmology

Abstract

The work of this thesis falls into two parts: a discussion of decoherence in quantum Kaluza-Klein theories and a study of some of the properties of general black hole metrics in de Sitter spacetime. Kaluza-Klein theories permit a variety of compactifications and arbitrary scales for the internal space. There must be no quantum interference between these different possibilities. In chapter one it is demonstrated that in the Salam-Sezgin compactification interference between differently scaled interenal spaces is suppressed. In chapter two new gravitational instantons are presented which are related to charged, rotating black holes with a cosmological constant A. These instantons correspond to black holes in de Sitter space with identical Hawking temperatures. Their action contributes terms of order A-1/2 to path integrals with quantum wormholes. The metrics of these general de Sitter black holes show that the spacetimes have wormholes connecting different asymptotic regions. In chapter three the theory of black hole perturbations is extended to these metrics. It appears that the holes are stable even at the Cauchy horizon. This implies that cosmic censorship is violated. The stability of the spacetimes also implies the existence of a cosmological no hair theorem.