Negative Absolute Temperatures

TL;DR

This paper clarifies the concept of negative absolute temperatures, arguing they are not physically attainable through reversible processes and are often a result of applying thermodynamics incorrectly to irreversible systems.

Contribution

It demonstrates that negative temperatures are not achievable via reversible processes and are due to improper application of thermodynamics to irreversible phenomena.

Findings

Negative temperatures are not attainable through reversible thermodynamic processes.

Negative temperature states result from incorrect application of thermodynamics to irreversible processes.

Upper limits in system states do not imply the existence of negative temperatures.

Abstract

The concept of negative absolute temperature, introduced by Ramsey based on the study of a nuclear spin system by Purcell and Pound in 1951, has been subject to continued debate. According to a recent analysis by Struchtrup, the apparent negative temperature states are temperature unstable states for which no temperature-positive or negative-can be defined. Ramsey was aware of the potential problem with his treatment of the negative temperature by pointing it out that the apparent negative temperature states cannot be achieved via any reversible process. In this paper, we demonstrate that the existence of an upper limit in the allowed states of the system is not a sufficient condition, albeit a necessary condition, for the appearance of negative temperatures. A thermal system cannot move into any negative temperature state via reversible thermodynamic processes. Negative temperature of a system is a direct outcome of incorrectly applying thermodynamic functions to an irreversible process.