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March 7, 1982, Page 6 The New York Times Archives

Robert P. Geroch is a professor of physics and mathematics at the University of Chicago. His latest book is ''General Relativity From A to B.''THE COSMIC CODE Quantum Physics as the Language of Nature. By Heinz R. Pagels. Illustrated. 370 pp. New York: Simon & Schuster. 17.50.By ROBERT P.GEROCH

SERIOUS obstacles confront the nonscientist who wants some insight into what theoretical physics is all about and what theoretical physicists do with their time. Many of the popular books on science prove to be no help; in fact, they are part of the problem. The fundamental ideas of theoretical physics are not hopelessly intricate; there is no need for a ''gee whiz'' treatment.

Heinz R. Pagels's ''The Cosmic Code'' is part of the solution. Its theme is the structure and implications of quantum mechanics, but the book is far broader than that. It touches on much of 20th-century physics: statistical mechanics and entropy, special and general relativity, the nature of atoms and elementary particles. The author's approach is partly historical, in that we are given a glimpse of the personal styles of the participants and the puzzles they wrestled with. But his perspective is a thoroughly modern one; he places the early developments in the context of what we know of physics today. This marvelously effective blend is further enhanced by Mr. Pagels's style. He avoids jargon and does not talk down to the reader.

The book begins at the opening of our century, at the time of the two great revolutions in modern theoretical physics - quantum mechanics and relativity. Mr. Pagels starts with Albert Einstein and gives us a brief tour through his special and general theories of relativity. There follows the main course - quantum mechanics. Mr. Pagels's treatment includes an exposition of the photoelectric effect, perhaps the first observation of a quantum phenomenon, and matrix and wave mechanics, the two original versions of quantum mechanics. And it extends to issues that are of active interest today, such as differing interpretations of quantum mechanics.

A number of topics not normally discussed in a popular book are treated here in some detail. The seemingly innocent notion of probability is an example. Probability has a somewhat different meaning in quantum mechanics than it has in classical physics or in everyday life. In classical physics, probability reflects mere ignorance of the initial conditions - of things that could in principle be known. But in quantum mechanics, probability reflects uncertainty inherent in the description of the physical world. Is it not possible that probability in quantum mechanics actually reflects, but in some more roundabout way, the same sort of ignorance underlying classical physics? The answer is no. There is a theorem to the effect that there is no way to reformulate quantum mechanics excluding probability.

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Another example of the kinds of topics discussed in this book is a comparison of the various interpretations of quantum mechanics. (An interpretation seems to be required by the new meaning of probability.) It is not widely known that a competition among interpretations continues to this day. (I must confess that I wish the one I lean toward - that of ''many worlds'' - had been treated more generously!)

Next Mr. Pagels explores some implications of quantum mechanics in the world of the very small. Our understanding of this world has opened up in layers: first the atoms, later their nuclei, then the constituents of the nuclei (the particles known as hadrons, leptons, quarks, etc.). The study of these particles is at the forefront of physics today, and the basic tool of that study is quantum field theory - the combination of relativity and quantum mechanics. We just do not understand these particles and their interaction. A number of attempts at an understanding are clearly presented in the book: the boot-strap picture, in which no particles are regarded as fundamental, but rather as composed of one another; the eightfold way, a remarkably successful classification scheme for certain elementary particles; even, briefly, the hot topic of the day - gauge theories. This section of the book concludes with a discussion of cosmology, the study of the universe as a whole, and in particular its role in attempts to understand why these are the particles we can observe.

The final section of ''The Cosmic Code'' deals with the nature of physical theory and the character of theoretical physics itself. Chapter 1 of Part III, in particular, is a very nice discussion of what a physical theory actually consists of. If you read nothing else in the book, read that.

One might infer from my description that ''The Cosmic Code'' requires of the reader a background in physics, but that is not the case. It can be read by anyone. The book makes liberal use of analogies, which is entirely appropriate since analogies are a key tool of the working physicist in thinking about the world. There is virtually no mathematics in this book. Despite its broad sweep, it gives the flavor of the many areas of physics it touches, and the reader's understanding of what scientists do is actually helped by some vivid accounts of the eccentricities of the better-known physicists.

The one misgiving I have about the book is perhaps an unavoidable consequence of its scope and style. Its treatment of several technical issues leaves what I would regard as misimpressions. For example, the view is expressed in the first chapter that quantum mechanics substitutes a discrete character for what was a more continuous classical physics. Yet there is a substantial body of opinion that holds that quantum mechanics is better regarded as the more continuous of the two. (Thus, the ''discrete'' classical bouncing off of a particle from a barrier is replaced, in quantum mechanics, by continuous wave behavior.) We are told that the entropy law is essentially nonclassical. But I would have thought that statistical mechanics -including the entropy law - without quantum mechanics is fully consistent. My strongest reservation concerns the discussion of special versus general relativity, explained in the book in terms of one twin on a train and another stationary on the ground. The author says: ''Einstein's special theory of relativity applies only to uniform motions, and the motion of the train is not always uniform. Only by Einstein's general theory of relativity, which applies to nonuniform motions like that of the train, can one show that the twin on the train has actually aged less.'' I submit that virtually no practicing relativist would agree with this statement. Special or general relativity is applicable according as space-time is flat or curved. This feature of space-time is intrinsic to it and is not dictated by the motion of a particular observer.

But these are quibbles. ''The Cosmic Code'' provides a great deal of insight into the working of physics and the thinking of physicists. I heartily recommend it.

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