Intrinsically nonequilibrium state of gravitational redshift

In a gravitational field, at equilibrium, because of the covariant conservation of stress-energy, the locally measured temperature and photon frequency are nonuniform along height. By themselves, these phenomena do not cause any significant thermal effects. In current research, we show that if thermal radiation and thermal conduction are both considered, remarkably, a heat flux can be spontaneously generated with no energetic penalty, effectively breaking the boundaries of the second law of thermodynamics. The root cause is the lack of photon-photon interaction. As photons are non-interacting, the redshifted photon gas is intrinsically nonequilibrium. Because the photon trajectories are nonchaotic, Boltzmann's H-theorem is inapplicable. While counterintuitive, this finding is consistent with the basic principle of maximum entropy. The classical mechanical counterpart of the model has been accepted for publication by Physical Review E [1].