FLUCTUATIONS IN OPEN SYSTEMS

The probability of occurrence of fluctuations around nonequilibrium steady states or states slowly varying in time is discussed from a kinetic viewpoint. The limitations of the thermodynamic theory of fluctuations are investigated. It is shown that in a large class of far-from-equilibrium systems, described by a discrete set of variables, it is possible to extend the classical Einstein fluctuation formula, provided one uses suitable steady-state parameters rather than equilibrium quantities. This conclusion is shown to be in agreement with the results of recent work by Prigogine and Glansdorff.