Time symmetry in wave function collapse

TL;DR

This paper demonstrates that dynamical wave function collapse models can be described in a time-symmetric manner, with the apparent time asymmetry arising only from initial and final boundary conditions.

Contribution

It shows that collapse models are fundamentally time-symmetric and that observed asymmetry results from boundary conditions, not the dynamics themselves.

Findings

Collapse models admit time-symmetric descriptions

Empirically equivalent forward and backward in time models

Time asymmetry arises from boundary conditions

Abstract

The notion of a physical collapse of the wave function is embodied in dynamical collapse models. These involve a modification of the unitary evolution of the wave function such as to give a dynamical account of collapse. The resulting dynamics is at first sight time asymmetric for the simple reason that the wave function depends on those collapse events in the past but not those in the future. Here we show that dynamical wave function collapse models admit a general description that has no inbuilt direction of time. Given some simple constraints, we show that there exist empirically equivalent pictures of collapsing wave functions in both time directions, each satisfying the same dynamical rules. A preferred direction is singled out only by the asymmetric initial and final time constraints on the state of the Universe.