Fundamental Thermodynamics Since Carathéodory

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Scientific article / Rev. Mod. Phys., 1968, Vol. 40, No. 3, p. 556–563.The uneasiness prevailing in thermodynamics is the inevitable result of the absence of clearly understood basic concepts. Since thermodynamics, the doctrine of equilibrium, encompasses parts of all branches of the physical sciences, its basic concepts must be explained in ordinary language, free from all references to a specific branch. Moreover, the general applicability of the concepts must be demonstrated.Carathéodory has introduced new ideas of fundamental importance. But his shortcomings concerning basic concepts have been repeated and intensified by his successors in axiomatics.A properly constructed basis of thermodynamics elucidates the fundamental distinction of generalized coordinates and generalized forces from each other and from other properties. As an accessorial result one notices a unique quality of the generalized forces (and the temperature): They can be measured only if equilibrium has been established.The so-called 'zeroth law' is neither a law nor a generalized observation. The clarification of its significance contributes to the epistemological understanding of thermodynamics.