The great German physicist Arnold Sommerfeld, in the preface to his book Thermodynamics and Statistical Mechanics, had this to say: “In contrast to classical mechanics, thermodynamics has withstood the quantum revolution without having its foundations shaken.” A similar sentiment is echoed in the American physicist Arthur Wightman’s tribute to Gibbs that “his contributions have survived 100 years of turbulent developments in theoretical physics.”

It is this resilience that makes a study of thermodynamics such a rewarding experience. In fact, not only did thermodynamics survive the revolutionary developments of quantum theory, it, in the hands of the great masters Planck and Einstein, played midwife to the very birth of quantum theory. Behind this resilience lies the great generality of the principles of thermodynamics.

Usually when principles are too general, their effectiveness gets limited. But in the case of thermodynamics, its impact both on scientific thought as well as its practical impact have been unmatched by any other field of science. As for the latter aspect, the applications of thermodynamics range over physics, chemistry and engineering, and of late over biology and even black holes! With the epoch-making developments in Statistical Mechanics, there is an increasing trend among physicists to treat thermodynamics as some sort of a second fiddle.

This is unfortunate indeed as in reality the powers of thermodynamics remain undiminished. Of course, the two complement each other, making both of them even stronger. It is also unfortunate in another sense that young readers get the mistaken impression that statistical mechanics is easier while thermodynamics is nearly incomprehensible. This is partly because at that level, statistical mechanics is almost algorithmic, while thermodynamics seems to require constant revision of its basic tenets.

In fact, one often needs, as for example in the case of magnetism, the guidance of thermodynamics in proper applications of statistical mechanics. In this book the focus is entirely on what Pippard calls Classical Thermodynamics. My intention is certainly not to belittle the greatness of statistical mechanics. It is more to highlight the elegance, power, and conceptual economy of thermodynamics. To see how much of natural phenomena can be comprehended, even highly quantitatively, by thermodynamics on its own. I find it gratifying that Max Planck, Fermi, and Pippard have written their great books in a similar spirit.

That this classical thermodynamics can be succesfully applied even to a manifestly quantum state like the Bose-Einstein condensate is yet another example of the resilience mentioned above. All this granted, I am sure many would like to ask “Why yet another book on thermodynamics?.” It is true that there are many many books on this subject, and some of them are classics. I would say, in response, that first of all there should always be space for more books. No two serious authors will have the same perspective and emphasis.

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