Early in his career, Albert Einstein spent two years as a professor at the German University in Prague. His office overlooked a beautiful park belonging to the insane asylum of the province of Bohemia, where patients who were not confined were allowed to walk. When Philipp Frank first visited, Einstein showed him the view and remarked playfully, "Those are the madmen who do not occupy themselves with the quantum theory." It is well known that Einstein, whose profound insights had been so crucial to the development of the quantum theory, ultimately came to regard it as incomplete. While he recognized that it was the "most successful physical theory of our time", he could not accept the idea that probabilities must replace strict causality.

Einstein's debates with Bohr concerning the concept of complementarity at the 1927 and 1930 Solvay Congresses are legendary. Although Bohr was able to respond to almost all of Einstein's clever arguments, the Einstein-Podolsky-Rosen (EPR) paradox, published in 1935, was a profound critique that even Bohr could not answer. Einstein was joined in his distaste for the statistical aspects of the quantum theory by Schrödinger, who in 1935 published his famous cat paradox. The success of the quantum theory, however, was not to be denied, and the debates over its foundations slipped into the background as the theory became an integral part of normal science.

With the development of powerful computers and sophisticated programs, quantum mechanics has become an everyday tool in chemistry, essential in the interpretation of experiments, and increasingly useful as a predictive method for molecular design. Elementary quantum mechanical ideas are introduced in high school and general chemistry courses and then further developed and used throughout the chemistry curriculum. It seems, however, that every time I teach some aspect of quantum mechanics I am stopped short by a question about the foundations of the theory asked by a precocious student who really wants to understand the wave-particle duality or one of the other paradoxical ideas in the theory. Up to now it has been difficult to find an accessible treatment of the important issues in the foundations of quantum mechanics to help me or the student find an answer to these profound questions, but Greenstein and Zajonc have come to the rescue.

George Greenstein and Arthur Zajonc, both professors of physics at Amherst College, have written a wonderful book for those madmen who do occupy themselves with the meaning of the quantum theory. They present the most important contemporary problems in the foundations of quantum mechanics in clear language, using only elementary mathematics. Since this is a book about science and not philosophy, all the conceptual issues are discussed in an experimental context. The details of very sophisticated contemporary quantum optics experiments that probe important theoretical questions are lucidly explained.

The questions explored in this book include the wave-particle duality, the uncertainty principle, complementarity, the EPR paradox and Bell's theorem, Schrödinger's cat paradox, and the measurement problem. After placing each question in a historical context, the conceptual issue is framed and then explored in terms of recent experiments. Only simple nonrelativistic quantum mechanics is used; no knowledge of advanced topics such as Hilbert spaces or quantum electrodynamics is required. While the authors are careful to point out the limitations of each experiment, the enchanting mysteries of the quantum theory are brought into focus in the discussion of these clever experiments.

This volume is part of the Jones and Bartlett "Challenge Series", which is intended to introduce undergraduate science, mathematics, and engineering students to exploration of the important unsolved problems of our time. I think this book admirably accomplishes the goal of the series. It can be read, though with some effort, by an undergraduate who has a basic understanding of quantum mechanics such as that gained in a physical chemistry course. The questions raised are profound and exciting. I came away with a deeper understanding of quantum mechanics, but also with a clear sense that there are important issues still to be resolved.

This is a book to which I will return, and one that I will enthusiastically recommend to both students and colleagues.