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Physics of the Universe, by Mendel Sachs

on the use of the Density Matrix, and Chapter 4 the theory of susceptibility of matter, first in classical and then in quantum terms. Chapter 5 concerns phenomena such as selfinduced transparency, photon echo and superradiance. These are generally satisfactory, although the idea of coherent states is introduced in a brief and confusing manner, with a definition of such states left until much later in the book. This omission constitutes a major weakness, given the way in which the analysis of such states plays an important part in present day work. The two longest chapters, 6 and 7, concern nonlinear optics and what the authors call ‘statistical optics’ – covering the field more often referred to as photon optics. The first gives a careful analysis of the various nonlinear phenomena, first in classical and then in quantum mechanical terms. Chapter 7 gives a basic introduction, but obviously does not include a detailed discussion of the work on squeezed states which has taken place in the last twenty years. Of course the book’s main and crippling weakness (recognised by the editors) is the lack of any connection with the wealth of experimental work that has taken place in this field over the last quarter century, furthermore many references are to works in Russian which would not be easily obtainable. The editors have added some later references, but these are mainly to textbooks or monographs. Although this book was obviously an excellent one in its time, and provides a clear analysis at a basic level which could form useful back-up material, it has to be said that it would not be suitable as a basic text for a course at later undergraduate or early postgraduate level.