Principle of Unattainability of Absolute Zero Temperature, the Third Law of Thermodynamics, and Projective Quantum Measurements

TL;DR

This paper clarifies the distinction between the Third Law of Thermodynamics and the Principle of Unattainability, exploring their implications for reaching absolute zero temperature and examining potential conflicts with quantum measurement postulates.

Contribution

It distinguishes the Third Law from the Principle of Unattainability and discusses how non-adiabatic processes and quantum measurements relate to reaching absolute zero.

Findings

The Third Law is only equivalent to unattainability via adiabatic processes.

Non-adiabatic means could potentially attain absolute zero without violating the Third Law.

Quantum projective measurements might allow zero temperature states, challenging classical principles.

Abstract

The Principle of Unattainability rules out the attainment of absolute zero temperature by any finite physical means, no matter how idealised they could be. Nevertheless, we clarify that the Third Law of Thermodynamics, as defined by Nernst's heat theorem statement, is distinct from the Principle of Unattainability in the sense that the Third Law is mathematically equivalent only to the unattainability of absolute zero temperature by {\em quasi-static adiabatic} processes. This, on the one hand, leaves open the possibility of attainability of absolute zero by non-adiabatic means, without violating the Third Law. On the other hand, we point out some apparent incompatibility between the Postulate of Projective Measurement in quantum mechanics and the Principle of Unattainability in that projective measurements of energy could result in zero temperature.