Symmetry, Thermodynamics and Topology in Active Matter

TL;DR

This paper discusses open questions and new directions in active matter research, focusing on phenomena like active turbulence, topological defects, non-reciprocal interactions, and the thermodynamics of active systems, with implications for biological tissues.

Contribution

It provides a personal perspective on emerging research directions in active matter, highlighting connections to non-Hermitian quantum mechanics and biological relevance.

Findings

Spontaneous flows and active turbulence are prevalent in active matter.

Topological defects play a significant role in ordered active systems.

Progress has been made in formulating the thermodynamics of active systems.

Abstract

This article summarizes some of the open questions in the field of active matter that have emerged during Active20, a nine-week program held at the Kavli Institute for Theoretical Physics (KITP) in Spring 2020. The article does not provide a review of the field, but rather a personal view of the authors, informed by contributions of all participants, on new directions in active matter research. The topics highlighted include: the ubiquitous occurrence of spontaneous flows and active turbulence and the theoretical and experimental challenges associated with controlling and harnessing such flows; the role of motile topological defects in ordered states of active matter and their possible biological relevance; the emergence of non-reciprocal effective interactions and the role of chirality in active systems and their intriguing connections to non-Hermitian quantum mechanics; the progress towards a formulation of the thermodynamics of active systems thanks to the feedback between theory and experiments; the impact of the active matter framework on our understanding of the emergent mechanics of biological tissue. These seemingly diverse phenomena all stem from the defining property of active matter - assemblies of self-driven entities that individually break time-reversal symmetry and collectively organize in a rich variety of nonequilibrium states.