Einselection, Equilibrium and Cosmology

TL;DR

This paper investigates whether einselection, the process that leads to classicality from quantum states, can occur in equilibrium systems and explores implications for the arrow of time and cosmological initial conditions.

Contribution

It demonstrates through Caldeira-Leggett model calculations that einselection can happen in equilibrium, challenging the notion that an arrow of time is necessary for classicality emergence.

Findings

Einselection occurs in equilibrium systems despite detailed balance.

Equilibrium einselection is linked to histories that exhibit an arrow of time.

Implications for cosmology and initial conditions are discussed.

Abstract

Our observed Universe has a very strong arrow of time rooted in its low entropy starting point. This low entropy start can be related to various "tuning puzzles" about the early state of the Universe. Here we explore the relationship between the arrow of time and the emergence of classical from quantum in the hopes of ultimately gaining insights into cosmological initial conditions. Our focus is on einselection, the process whereby interactions with an environment select preferred states for a quantum system. This process plays an essential role in the emergence of classical from quantum. Studies of einselection have so far been limited to cases that exhibit an arrow of time. Here we study the ability of equilibrium systems to exhibit einselection -- and investigate whether detailed balance prevents this -- motivated by the question of whether classicality requires an arrow of time. We present calculations in the adapted Caldeira-Leggett model which demonstrate that einselection can indeed take place in equilibrium systems, and show how this phenomenon is tied to histories which express an arrow of time, despite the global equilibrium. We discuss some interesting implications of our results for cosmology and cosmological initial conditions. We are intrigued and a bit surprised by the role the consistent histories formalism has ended up playing in our analysis.