Thermodynamics of Active Matter: Tracking Dissipation across Scales

Abstract

The concept of entropy has been pivotal in the formulation of thermodynamics. For systems driven away from thermal equilibrium, a comparable role is played by entropy production and dissipation. Here, we provide a comprehensive picture of how local dissipation due to effective chemical events manifests on large scales in active matter. We start from a microscopic model for a single catalytic particle involving explicit solute molecules and show that it undergoes directed motion. Leveraging stochastic thermodynamics, we calculate the average entropy production rate for interacting particles. We then show how the model of active Brownian particles emerges in a certain limit, and we determine the entropy production rate on the level of the hydrodynamic equations. Our results augment the model of active Brownian particles with rigorous expressions for the dissipation that cannot be inferred from their equations of motion, and we illustrate consequences for wall aggregation and motility-induced phase separation. Notably, our bottom-up approach agrees with the “naive” result from Onsager’s principle for the local dissipation rate. Published by the American Physical Society 2025