American Scientist

The Inflationary Universe: The Quest For a New Theory of Cosmic Origins. Alan Guth. 368 pp. Helix Books, Addison-Wesley, 1997. $25.

Since 1977 Steven Weinberg's explanation of the origin of the cosmos, The First Three Minutes, has been matchless in its simplicity, clarity and scientific accuracy—until now, that is, when The Inflationary Universe by Alan Guth elegantly and engagingly makes a compelling case for his inflationary universe theory.

Although the big bang theory is very successful in describing the evolution of the universe, it fails to address some very fundamental questions: What is the origin of all the matter in the universe? Why is the universe so flat? Why is cosmic background radiation so uniform? Guth's theory of the inflationary universe was invented to answer these questions and others by postulating a very brief moment of hyper-rapid expansion ("inflation") in the very early universe. His purpose is not so much to replace the big bang theory as to refine its description of the universe's first fraction of a second by explaining the "bang" in the big bang.

In the very early universe, the problems of cosmology are intertwined with those of the theory of elementary particle physics, and Guth delves into various aspects of both fields. He weaves into the physics discussion his own scientific autobiography, a chronicle of the dramatic discovery, and his account of the roles various people played in motivating and developing the theory of cosmic inflation. In this, he is helped by his diary. Guth is gracious in admitting his particular debt to his former Cornell collaborator Henry Tye, first for arousing his interest in cosmology, and second for making a crucially important remark that would help him relate the expansion rate of the universe to a phase transition in the early universe, the very cause of cosmic inflation. This is a historical document and personal memoir as well as a book on the science.

It is remarkable that Guth uses no equations to explain the esoteric concepts encountered in particle physics and cosmology, relying instead on diagrams and ingenious analogies. To remain faithful to the physics, Guth provides further explanations in an unusually large number of footnotes and a very helpful glossary.

As an improvement on the big bang theory, the theory of inflation could become the new paradigm in cosmology. But we should keep in mind that the details of the theory have yet to be worked out—if only for want of correct theories of quantum gravity and particle physics. It is even possible that when the correct theory of nature is available, all the problems in cosmology will disappear of their own accord without the need to invoke inflationary theory. This is not just idle speculation. After all, theoretical physics is still beset by the cosmological constant problem, which arises from the discrepancy between the theoretical expectation of vacuum energy (a monstrously huge value) and the empirical observation (a minute value). A large value of this vacuum energy in the early universe is precisely what is necessary to give cosmic inflation. On the other hand, the idea of inflation is so simple and, indeed, such a natural consequence of phase transitions, that many physicists believe that the correct theory of nature will not contradict the inflationary-universe scenario.

In his preface, Guth writes that "the book is aimed primarily at the nonscientist with an interest in science." But he warns that "some of the ideas described in the book are complex, so the reader will need some patience." Indeed, patience is probably needed for a full appreciation of the book. However, even an impatient nonscientist reader will still grasp the most important ideas and will appreciate the enormous philosophical implications of cosmic inflation. Near the end of the book, Guth discusses, in the framework of inflation, the thought-provoking questions of whether other big bangs are happening far away, so that there is an infinite number of other universes that are completely disconnected from our own, and whether it is possible to recreate the big bang in a laboratory. If inflation is correct, we may finally understand where matter and energy come from and why there is something rather than nothing. What could be more profound?—Y. Jack Ng, Physics and Astronomy, University of North Carolina at Chapel Hill