Second law of thermodynamics: Spontaneous cold-to-hot heat transfer in a nonchaotic medium

TL;DR

This paper demonstrates that in nonchaotic media, such as a Knudsen gas, spontaneous heat transfer from cold to hot can occur, challenging the traditional second law of thermodynamics and enabling work extraction from a single heat reservoir.

Contribution

It reveals that nonchaotic, intrinsically nonequilibrium systems can violate the second law of thermodynamics through specific setups, a phenomenon previously not considered in thermodynamics.

Findings

Cold-to-hot heat transfer can occur spontaneously in nonchaotic media.

Such systems can produce work from a single thermal reservoir.

The phenomenon challenges the traditional understanding of the second law.

Abstract

It has long been known that, fundamentally different from a large body of rarefied gas, when a Knudsen gas is immersed in a thermal bath, it may never reach thermal equilibrium. The root cause is nonchaoticity: as the particle-particle collisions are sparse, the particle trajectories tend to be independent of each other. Usually, this counterintuitive phenomenon is studied through kinetic theory and is not considered a thermodynamic problem. In current research, we show that if incorporated in a compound setup, such an intrinsically nonequilibrium behavior has nontrivial consequences and cannot circumvent thermodynamics: cold-to-hot heat transfer may happen spontaneously, either continuously (with an energy barrier) or cyclically (with time-dependent entropy barriers). It allows for production of useful work by absorbing heat from a single thermal reservoir without any other effect. As the system obeys the first law of thermodynamics, it breaks the boundaries of the second law of thermodynamics.