Entropy Production — Nonequilibrium Steady State

Fluctuation Theorem: In a nonequilibrium steady state driven by two heat baths at T_hot and T_cold, entropy is produced at rate σ = J·(1/T_cold − 1/T_hot) where J is the heat flux. The Gallavotti-Cohen fluctuation theorem states P(Στ = A)/P(Στ = −A) = e^A — entropy-decreasing fluctuations occur exponentially rarely. The histogram shows ln[P(+σ)/P(−σ)] should be linear with slope 1. Particles collide with walls, exchanging heat according to Maxwell-Boltzmann sampling at each reservoir temperature.