A method for detecting nonequilibrium dynamics in active matter

Abstract

Active force generation is an important class of out-of-equilibrium activity in cells. These forces play a crucial role in vital processes such as tissue folding, cell division and intracellular transport. It is important to determine the extent of such nonequilibrium activity during cellular processes to understand cell function. Here we present a framework for measuring nonequilibrium activity in biological active matter using time reversal asymmetry based on the Kullbeck-Leibler Divergence (KLD), also known as relative entropy. We estimate the KLD from a stationary time series using a k-nearest neighbors estimator, comparing the time-forwards process to the time-reversed process Using time series data of probe particles embedded in the actin cortex, we establish a lower bound for the entropy production of cortical activity. Our results demonstrate a reliable way to measure the breaking of detailed balance in mesoscopic systems.