David Anthony Lavis

The aim of this text is to provide an account of the fundamentals of thermodynamics which is accessible at graduate level to physicists, mathematicians and philosophers of physics. The bulk of the book (Chapters 2-9) is based on the algebraic approach of Lieb and Yngvason, but extended to encompass both positive and negative temperatures and systems in which entropy increases and decreases in adiabatic processes. We show that these four possibilities are already present in Carathéodory's version of the Second Law which arises as a theorem from the axioms. We develop generalized versions of the Kelvin-Planck and Clausius formulations valid for the same range of systems. The parallel development in Chapter 10 takes a geometric approach. We discuss the limitations associated with the local nature of Carathéodory's Principle and present the resolution of this problem due to Boyling. Part of the aim here is to substantiate the claim of Arnold that the mathematical structure of thermodynamics is contact geometry. The last two chapters of the book extend the scope of the discussion to, respectively, critical phenomena and non-equilibrium systems. Chapter 11 is a presentation of phase transitions and critical phenomena in which we discuss universality and use scaling theory to derive scaling laws. Chapter 12 contains a generalization to non-equilibrium. We present the extension of Lieb and Yngvason's work to non-equilibrium and also give a brief account of classical irreversible thermodynamics (CIT). The latter enables a possible understanding of the way that the lack of a unique entropy function in the Lieb and Yngvason non-equilibrium approach can be resolved. The book is completed by a set of appendices which provide mathematical and physical support to the work in the main text.

One of the consequences of the derivation of single-system entropy in the previous chapter was an assignment, to every state X∈Ξ[M]\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\pmb {X}}\in \varXi [M]$$\end{document} of the system Σ[M]\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varSigma [M]$$\end{document} a number SΣ(+)(X)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$S_\varSigma ^{(+)}({\pmb {X}})$$\end{document} or SΣ(-)(X)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$S_\varSigma ^{(-)}({\pmb {X}})$$\end{document}, according to whether the system is i-simple or d-simple; this being the value of the single-system entropy at X\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\pmb {X}}$$\end{document}.

We have, up to this point in our discussion, availed ourselves of a supposed prior knowledge of thermodynamics on the part of the reader to present our primary example of a fluid system. Otherwise, however, the thermal nature of thermodynamics has played a relatively minor part. It has mainly intruded in a negative way, in that non-adiabatic processes involve an increase or decrease in the internal energy of a system not attributable to work done, but rather to a flow of ‘heat’Heat between the system and its environment. Here we edge a little closer to the thermal in thermodynamics by discussing and defining thermal equilibriumThermal equilibrium between systems. However, we are still able to do this without introducing the primary thermal variables of thermodynamics, entropy and temperature, which are introduced in Chaps. 6–8.

This paper presents an in-depth analysis of the anatomy of both thermodynamics and statistical mechanics, together with the relationships between their constituent parts. Based on this analysis, using the renormalization group and finite-size scaling, we give a definition of a large but finite system and argue that phase transitions are represented correctly, as incipient singularities in such systems. We describe the role of the thermodynamic limit. And we explore the implications of this picture of critical phenomena for the questions of reduction and emergence.

We show that both positive and negative absolute temperatures and monotonically increasing and decreasing entropy in adiabatic processes are consistent with Carathéodory's version of the second law and we explore the modifications of the Kelvin–Planck and Clausius versions which are needed to accommodate these possibilities. We show, in part by using the equivalence of distributions and the canonical distribution, that the correct microcanonical entropy, is the surface (Boltzmann) form rather than the bulk (Gibbs) form thereby providing for the possibility of negative temperatures and we counter the contention on the part of a number of authors that the surface entropy fails to satisfy fundamental thermodynamic relationships.

It is well-known that the invocation of `equilibrium processes' in thermodynamics is oxymoronic. However, their prevalence and utility, particularly in elementary accounts, presents a problem. We consider a way in which their role can be played by sets of sequences of processes demarcated by curves carrying the property of accessibility. We also examine the vexed question of whether equilibrium processes are necessarily reversible and the revision of this property in relation to sets of sequences of such processes.

The Boltzmann and Gibbs approaches to statistical mechanics have very different definitions of equilibrium and entropy. The problems associated with this are discussed and it is suggested that they can be resolved, to produce a version of statistical mechanics incorporating both approaches, by redefining equilibrium not as a binary property but as a continuous property measured by the Boltzmann entropy and by introducing the idea of thermodynamic-like behaviour for the Boltzmann entropy. The Kac ring model is used as an example to test the proposals.

This chapter defends and refines a specific objectivist interpretation of probabilities in statistical mechanics. For ergodic systems, probabilities are defined as time-averages. For other systems, ergodic decomposition is applied, and stochastic nomological machines are used to assign probabilities over the members of the decomposition. The relevance of this analysis to the Boltzmann and Gibbs approaches to statistical mechanics is discussed. The chapter shows that the proposed definition of probabilities matches a Boltzmann-like approach particularly well if the sharp distinction between equilibrium and non-equilibrium is given up and if more emphasis is laid upon the global time profile of entropy. The chapter furthermore argues that the alleged weaknesses of the time-average definition of probability are avoided.