Time-(ir)reversibility in active matter: from micro to macro

Abstract

Active matter encompasses systems whose individual consituents dissipate energy to exert propelling forces on their environment. This rapidly developing field harbors a dynamical phenomenology with no counterpart in passive systems. The extent to which this is rooted in the breaking of time-reversibility has recently triggered an important theoretical and experimental activity which is the focus of this review. Building on recent progress in the field, we disentangle the respective roles of the arrow of time and of the non-Boltzmann nature of steady-state fluctuations in single-and many-body active systems. We show that effective time-reversible descriptions of active systems may be found at all scales, and discuss how interactions, either between constituents or with external operators, may reveal the nonequilibrium nature of the microscopic source of energy. At a time when the engineering of active materials appears within our reach, this allows us to discuss to which extent methods stemming from equilibrium statistical mechanics may guide us in their design.

Distribution of the time of the maximum for stationary processes

“…As an example, this method has been employed to show the nonequilibrium nature of red blood cells [68]. Several other methods, based, e.g., on the detection of probability currents in the phase space or the breakdown of time-reversal symmetry, have also been developed [36,42,64,[69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85].…”

Tuning Nonequilibrium Phase Transitions with Inertia

“…However, assessing the success of effective temperature ideas to describe nonequilibrium steady states remains largely empirical. Recent work by O'Bryne and Tailleur demonstrated that the dynamics of tactic active matter can be rigorously mapped to effective passive systems at a hydrodynamic level [34,35]. On a microscopic level, active forces under certain limits can act as traditional thermal forces by satisfying an effective fluctuation-dissipation theorem (FDT) [36,37].…”

Play. Pause. Rewind. Measuring local entropy production and extractable work in active matter

“…Time reversal symmetry breaking (TRSB) in active matter systems arises from the self-propelled motion of individual particles, driven by the continuous injection of energy into the system [1,2]. TRSB is linked to the emergence of steady-state currents in phase-space, a clear signature of a system's departure from equilibrium, which can be quantified in terms of the global rate of entropy production [3][4][5][6][7][8][9][10].…”