The arrow of time in operational formulations of quantum theory

TL;DR

This paper investigates the apparent time asymmetry in operational quantum theory, arguing it arises from assumptions about users and information flow rather than fundamental physics, highlighting the difference between knowns and unknowns.

Contribution

It demonstrates that the time asymmetry in operational quantum formulations is due to implicit assumptions about users and information, not fundamental physics.

Findings

Operational formulations are time-oriented due to assumptions about users.

The asymmetry reflects differences between known and unknown information.

Microscopic physics remains fundamentally time-symmetric.

Abstract

The operational formulations of quantum theory are drastically time oriented. However, to the best of our knowledge, microscopic physics is time-symmetric. We address this tension by showing that the asymmetry of the operational formulations does not reflect a fundamental time-orientation of physics. Instead, it stems from built-in assumptions about the $users$ of the theory. In particular, these formalisms are designed for predicting the future based on information about the past, and the main mathematical objects contain implicit assumption about the past, but not about the future. The main asymmetry in quantum theory is the difference between knowns and unknowns.