Time reversal symmetry and collapse models

TL;DR

This paper demonstrates that collapse models in quantum theory, despite their apparent time asymmetry, are fundamentally time reversal symmetric when considering the real physical parts and boundary conditions, challenging previous assumptions.

Contribution

It shows that collapse models can be time reversal symmetric when focusing on the physical locations of collapses and boundary conditions, countering the belief that they inherently break time symmetry.

Findings

Collapse models are time reversal symmetric when considering physical collapse locations.

Observed time asymmetries are due to boundary conditions, not the dynamical laws.

Models satisfy the Born rule in both forward and backward time directions.

Abstract

Collapse models are modifications of quantum theory where the wave function is treated as physically real and the collapse of the wave function is a physical process. This appears to introduce a time reversal asymmetry into the dynamics of the wave function since the collapses affect only the future state. This paper challenges this conclusion, showing that in three different examples of time asymmetries associated with collapse models, if the physically real part of the model can be reduced to the locations in space and time about which collapses occur, then such a model works both forward and backward in time, in each case satisfying the Born rule. Despite the apparent asymmetry of the collapse process, these models in fact have time reversal symmetry. Any physically observed time asymmetries that arise in such models are due to the asymmetric imposition of initial or final time boundary conditions, rather than from an inherent asymmetry in the dynamical law. This is the standard explanation of time asymmetric behaviour resulting from time symmetric laws.