Local detailed balance

TL;DR

This paper reviews the concept of local detailed balance in nonequilibrium mesoscopic systems, emphasizing its relation to fluctuation relations and entropy flux, and clarifies its physical and mathematical foundations.

Contribution

It clarifies the physical meaning and mathematical implementation of local detailed balance and its connection to fluctuation relations in nonequilibrium processes.

Findings

Local detailed balance is equivalent to fluctuation relations for entropy flux.

Steady average entropy flux corresponds to the mean entropy production rate.

The paper emphasizes the foundational role of local detailed balance in nonequilibrium thermodynamics.

Abstract

We review the physical meaning and mathematical implementation of the condition of local detailed balance for a class of nonequilibrium mesoscopic processes. A central concept is that of fluctuating entropy flux for which the steady average gives the mean entropy production rate. We repeat how local detailed balance is essentially equivalent to the widely discussed fluctuation relations for that entropy flux and hence is at most "only half of the story."