Nonequilibrium Fluctuation Theorems and Thermodynamic Second Laws

Most processes in nature are nonequilibrium (NEQ) processes, which include key dynamic processes in biological cells and social networks, as well as the usual physical phenomena. Nevertheless, our understanding of NEQ dynamic processes, except for those near equilibrium (EQ) has been quite primitive. Recently, various interesting results have been reported regarding phenomena far from EQ. These have opened a new understanding of NEQ processes. Among many others, the most dramatic advance was achieved on the issue of the thermodynamic second law, which is known as the law of entropy increase or irreversibility. First, the inequality relation of the thermodynamic second law, S 0, was replaced by the equality relation, eS =1, through which the inequality relation could be automatically derived. Detailed information on the probability distribution function of S was given by using the so-called Gallavotti-Cohen symmetry. More surprisingly, the total entropy production could be divided into two distinct terms, each of which satisfies its own thermodynamic 2nd law. This implies a more intricate structure in the irreversibility. In addition, many other new thermodynamic second laws and corresponding equality relations have been established. These equality relations are called the fluctuation theorems.