A Review of the Decoherent Histories Approach to Quantum Mechanics

TL;DR

The decoherent histories approach to quantum mechanics offers a framework for assigning probabilities to histories of closed systems without relying on measurement or wave function collapse, explaining the emergence of classicality.

Contribution

This review synthesizes the decoherent histories approach, highlighting its application to closed systems and its relation to other quantum interpretations like quantum state diffusion.

Findings

Provides a consistent framework for probabilities in closed quantum systems

Explains emergence of classical behavior from quantum mechanics

Connects decoherent histories with quantum state diffusion

Abstract

I review the decoherent (or consistent) histories approach to quantum mechanics, due to Griffiths, to Gell-Mann and Hartle, and to Omnes. This is an approach to standard quantum theory specifically designed to apply to genuinely closed systems, up to and including the entire universe. It does not depend on an assumed separation of classical and quantum domains, on notions of measurement, or on collapse of the wave function. Its primary aim is to find sets of histories for closed systems exhibiting negligble interference, and therefore, to which probabilities may be assigned. Such sets of histories are called consistent or decoherent, and may be manipulated according to the rules of ordinary (Boolean) logic. The approach provides a framework from which one may predict the emergence of an approximately classical domain for macroscopic systems, together with the conventional Copenhagen quantum mechanics for microscropic subsystems. In the special case in which the total closed system naturally separates into a distinguished subsystem coupled to an environment, the decoherent histories approach is closed related to the quantum state diffusion approach of Gisin and Percival.