Quasi-Carnot cycles, negative Kelvin temperatures, and the laws of thermodynamics

Abstract

It is maintained that the impossibility of moving a thermodynamic system adiabatically and reversibly (isentropically) from the domain of positive Kelvin temperatures to the domain of negative Kelvin temperatures (and vice versa) is a consequence of (an extended form of) the Third Law of thermodynamics and not of the Second Law alone; it is further maintained that Schöpf’s apparent proof to the contrary is inconclusive. In the course of the discussion the properties of a quasi-Carnot cycle (two adiabatic steps coupled with two steps involving floating temperature heat reservoirs) are explored.