# Statistical physics of machinery: forgotten middle-ground

## Abstract

Statistical physics long concentrated on the equilibrium state in the thermodynamic limit, and small deviations from that state. Machinery is spatially inhomogeneous, non-linear, and operates far from equilibrium. After our field expanded to face these problems, they were soon displaced by still newer fashions. It is symptomatic of this situation that the real resolution of Maxwell's demon, in the 1980s, passed almost unnoticed. We revisit a number of subjects, emphasizing the need for concern with the detailed kinetics of the system at hand and the difficulties posed by magic short cuts. The maximum entropy formalism, minimal entropy production, and the difficulties in identifying the most likely state among competing states of local stability will be taken up. The blowtorch theorem demonstrates that relative stability cannot, in general, be decided by examining only the neighborhood of the competing states. The kinetics along the pathway connecting the states must be taken into account. The latter point will be connected to biological evolution. Circulating currents, set up by the simultaneous presence of force fields and temperature gradients, will be described. © 1993.