Approaches to Quantum Cosmology

TL;DR

This paper reviews various proposals for the wave function of the universe in quantum cosmology, focusing on tunneling, path integrals, boundary conditions, topology change, and third quantization, comparing their theoretical foundations and implications.

Contribution

It provides a comprehensive analysis of different quantum cosmology approaches, clarifying their relationships and addressing key conceptual issues.

Findings

Equivalence between Lorentzian path integral and outgoing-wave proposals

Clarification of boundary conditions and topology change effects

Discussion of third quantization and its implications

Abstract

Different proposals for the wave function of the universe are analyzed, with an emphasis on various forms of the tunneling proposal. The issues discussed include the equivalence of the Lorentzian path integral and outgoing-wave proposals, the definitions of the outgoing waves and of superspace boundaries, topology change and the corresponding modification of the Wheeler-DeWitt equation. Also discussed are the "generic" boundary conditions and the third quantization approach.