Heating and Cooling are Fundamentally Asymmetric and Evolve Along Distinct Pathways

TL;DR

This paper demonstrates that heating and cooling are fundamentally asymmetric processes with distinct pathways, especially far from equilibrium, confirmed through experiments with colloidal particles and supported by a new theoretical framework called 'thermal kinematics.'

Contribution

It introduces the concept of 'thermal kinematics' to explain the fundamentally different pathways of heating and cooling, supported by experimental validation.

Findings

Heating is faster than cooling far from equilibrium.

Heating and cooling follow distinct pathways.

Experimental confirmation with colloidal particles.

Abstract

According to conventional wisdom, a system placed in an environment with a different temperature tends to relax to the temperature of the latter, mediated by the flows of heat and/or matter that are set solely by the temperature difference. It is becoming clear, however, that thermal relaxation is much more intricate when temperature changes push the system far from thermodynamic equilibrium. Interestingly, under such conditions heating was predicted to be faster than cooling, which we experimentally confirm using an optically trapped colloidal particle. More strikingly, we show with both experiments and theory that between any pair of temperatures, heating is not only faster than cooling but the respective processes in fact evolve along fundamentally distinct pathways, which we explain with a new theoretical framework we coin "thermal kinematics".