Equality governing nonequilibrium fluctuations and its information theory and thermodynamic interpretations.

The master equation is cast in the form of an equality involving the variation, in the course of a transformation, of a quantity playing the role of a generalized potential, weighted with the probability of allowable transformations emanating from different initial states. In the most general case this equality cannot be formulated entirely in terms of thermodynamic variables and state functions. Some conditions under which such a reduction becomes possible are identified and a comparison with fluctuation and work type relationships previously reported in the literature is carried out.