Of all the outpouring of books, symposia and special issues commemorating Einstein in this International Year of Physics, * Einstein's Other Theory * may make the least connection to the great man's persona. You must look elsewhere if you are interested in Einstein stories and pictures.

But the one point that it makes about Einstein is a significant one: that his contributions to quantum mechanics, and particularly to quantum statistical mechanics, are arguably at least as revolutionary as those he made via his much more famous relativity theory. For instance, one can argue that the route from his discovery of the stimulated emission of radiation to the laser, as it is described in this book, is much more direct than that from * E=mc² * to the atomic bomb. One could make the point that, at least so far, the laser has changed our lives at least as much as the bomb.

After doing just that in a preface, Donald Rogers jumps into textbook mode. The book's jacket suggests he is writing for advanced undergraduates or graduate beginners in physical chemistry or materials science. The book is approximately on the level of Charles Kittel's * Thermal Physics * but with a more historical approach, and also emphasises quantum statistics particularly and their modern manifestations in Bose-Einstein condensation and superconductivity. * Einstein's Other Theory * is a true textbook, with a problem set after each chapter and no dearth of equations, at least in the first part, although esoteric subjects such as superfluidity and stopped light are treated more qualitatively.

More than half the book is devoted to developing the physics necessary to understand the foundational era of statistical physics - Boltzmann, Planck, Einstein, Debye and Nernst. Because of my own interests, I found the very historical slant intriguing and unusual. A student would come out with a fairly deep and perhaps excessively detailed knowledge of where the equations he uses every day come from. The book then jumps, in a progression that may be logical but might be bewildering to the student, from these hoary topics to Bose-Einstein condensates, the idea of order parameters, and then superfluidity and superconductivity; it hardly mentions most developments between Einstein in 1917 and the 2001 Nobel prize.

I should think that it would be most suitable as background reading for a course in which more modern topics such as electron band theory, phase transformations, defects in solids, polymers and other amorphous phases and the like are introduced from some other source. Whether and to what extent the summation of a geometrical series to get the Planck distribution, or the derivation of the Stefan-Boltzmann law from thermodynamic identities, will be of much practical use for a student in his professional life is something of a question.

On the whole, * Einstein's Other Theory * is a book I would enjoy teaching from, but I found myself wondering exactly what that course might be. Perhaps an optional seminar for bright undergraduates? Perhaps, wonder of wonders, a seminar for science journalists who would like to learn the real fundamentals of modern physics and where they came from?

Philip W. Anderson, Nobel laureate, is emeritus professor of physics, Princeton University, New Jersey, US.

## Einstein's Other Theory: The Planck-Bose-Einstein Theory of Heat Capacity

Author - Donald W. Rogers

Publisher - Princeton University Press

Pages - 181

Price - £32.50

ISBN - 0 691 11826 4

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