The Second Entropy: A Variational Principle for Time-dependent Systems

The fundamental optimization principle for non-equilibrium thermodynamics is given. The second entropy is introduced as the quantity that is maximised to determine the optimum state of a non-equilibrium system. In contrast, the principles of maximum or minimum dissipation, which have previously been proposed by Onsager, Prigogine, and others as the variational principle for such systems, are shown to be incapable of fulfilling that role.