Systems in thermodynamic equilibrium are not only characterized by time-independent macroscopic properties, but also satisfy the principle of detailed balance in the transitions between microscopic configurations. Living systems function out of equilibrium and are characterized by directed fluxes through chemical states, which violate detailed balance at the molecular scale.

I will report on a method to probe for broken detailed balance and demonstrate how such non-equilibrium dynamics is manifest at the mesosopic scale. The periodic beating of an isolated flagellum from Chlamydomonas reinhardtii exhibits probability flux in the phase space of shapes. With a model, we show how the breaking of detailed balance can also be quantified in stationary, non-equilibrium stochastic systems in the absence of periodic motion. We further demonstrate such broken detailed balance in the non-periodic fluctuations of primary cilia of epithelial cells. This analysis provides a general tool to identify non-equilibrium dynamics in cells and tissues.