Abstract
The first lecture presented a brief introduction to matter outside thermodynamic equilibrium and to the physical methods that allow us to identify systems that are not at thermodynamic equilibrium, in particular living systems.
An essential property of all physical systems at thermodynamic equilibrium is the fluctuation-dissipation theorem, which relates, for a given frequency, the system's response to an external disturbance to the thermal fluctuations in the system and to the temperature that characterizes the amplitude of these fluctuations. One method of discriminating between an equilibrium and a non-equilibrium system is therefore to measure both the response function and the thermal fluctuations as a function of frequency. If the fluctuation-dissipation theorem is not verified, the system is not in thermodynamic equilibrium. This approach was used for red blood cells, for example, by Timo Betz's team at the Institut Curie, who measured the response of the red blood cell shape to a mechanical perturbation and the shape fluctuations. The conclusion is that the fluctuation-dissipation theorem is not verified and that a red blood cell really is a living system, which had been disputed by some authors. Note that many generalizations of the fluctuation-dissipation theorem have been made recently, notably the so-called fluctuation theorems, which were the subject of a recent lecture by Bernard Derrida at the Collège de France.
Another classic approach to identifying out-of-equilibrium systems is to study the breakdown of the detailed balance when the system cycles in phase space. This approach was used by Christoph Schmidt and colleagues to study the cilia of the alga Chlamidomonas.
