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Broken Detailed Balance in Living Systems 

What distinguishes animate from inanimate matter? In his famous 1944 book What is Life?, Erwin Schrödinger noted the need for living systems to avoid thermodynamic equilibrium. Once any system reaches thermodynamic equilibrium, the rates of forward and backward transitions between any two microstates must be equal. This is the principle of detailed balance. An important consequence of this is the impossibility to construct a Brownian Ratchet to extract useful work from thermal fluctuations, as discussed by Feynman in his 1960s lectures.

Detailed balance is strongly violated by the imbalanced reactions of living systems as they consume metabolic energy to avoid equilibrium and death. Whether and how this lack of molecular-scale detailed balance is manifest at the macroscopic or even whole cell level has been the subject of intense recent interest. A collaboration involving the VU, Göttingen, MIT and Munich has developed a new, non-invasive method to probe violations of detailed balance, with which violations have been demonstrated at the supramolecular scale in the stochastic dynamics of hair-like cilia of cells.

A stylized Feynman Ratchet, driven not by molecular collisions, but by hair-like cilia of cells. (Image: C. Hohmann, Nanosystems Initiative Munich (NIM) & M. Leunissen, Dutch Data Design.)



C Battle, CP Broedersz, N Fakhri, VF Geyer, J Howard, CF Schmidt and FC MacKintosh, Broken detailed balance at mesoscopic scales in active biological systems. Science, 352: 604 (2016).