Entropy Production and Thermodynamic Arrow of Time in a Recollapsing Universe

TL;DR

This paper demonstrates that the thermodynamic arrow of time, characterized by increasing entropy, persists universally in a recollapsing universe due to matter-gravity interactions, despite the universe's time-symmetric evolution.

Contribution

It provides a quantum mechanical analysis showing entropy production in a recollapsing universe, highlighting the universality of the thermodynamic arrow of time.

Findings

Entropy increases monotonically despite time-symmetric Hamiltonian

Thermodynamic arrow of time is universal in recollapsing universe

Matter-gravity interaction drives entropy production

Abstract

We investigate the thermodynamic arrow of time in a time-symmetrically recollapsing universe by calculating quantum mechanically the entropy production of a massive scalar field. It is found that even though the Hamiltonian has a time-reversal symmetry with respect to the maximum expansion of the universe, the entropy production is generic and the total entropy of the scalar field increases monotonically. We conclude that the thermodynamic arrow of time is a universal phenomenon even in the expanding and subsequently recollapsing universe due to the parametric interaction of matter field with gravity.