Decoherent Histories Analysis of Minisuperspace Quantum Cosmology

TL;DR

This paper develops a formalism within decoherent histories quantum theory to assign probabilities to cosmological histories, improving upon heuristic methods by using class operators derived from complex potentials, applicable to minisuperspace models.

Contribution

It introduces a rigorous operator-based approach to compute probabilities in quantum cosmology, linking decoherent histories with the Wheeler-DeWitt equation using complex potentials.

Findings

Class operators constructed via complex potentials are consistent with classical limits.

Probabilities derived match heuristic results in semiclassical regimes.

The formalism applies to questions about regions of configuration space in minisuperspace models.

Abstract

Recent results on the decoherent histories quantization of simple cosmological models (minisuperspace models) are described. The most important issue is the construction, from the wave function, of a probability distribution answering various questions of physical interest, such as the probability of the system entering a given region of configuration space at any stage in its entire history. A standard but heuristic procedure is to use the flux of (components of) the wave function in a WKB approximation as the probability. This gives sensible semiclassical results but lacks an underlying operator formalism. Here, we supply the underlying formalism by deriving probability distributions linked to the Wheeler-DeWitt equation using the decoherent histories approach to quantum theory, building on the generalized quantum mechanics formalism developed by Hartle. The key step is the construction of class operators characterizing questions of physical interest. Taking advantage of a recent decoherent histories analysis of the arrival time problem in non-relativistic quantum mechanics, we show that the appropriate class operators in quantum cosmology are readily constructed using a complex potential. The class operator for not entering a region of configuration space is given by the $S$-matrix for scattering off a complex potential localized in that region. We thus derive the class operators for entering one or more regions in configuration space. The class operators commute with the Hamiltonian, have a sensible classical limit and are closely related to an intersection number operator. The corresponding probabilities coincide, in a semiclassical approximation, with standard heuristic procedures.