Although not well known to the general public, British physicist Paul Dirac (1902-1984) is indisputably one of the giants of modern science. More specifically, he was one of the founders of quantum mechanics, the theory that, together with Einstein’s theory of relativity, defines the modern physical world picture at its most fundamental level. Dirac probably contributed more profoundly to the quantum revolution than any other physicist. His amazing outbursts of scientific brilliance were essentially confined to a decade-long period starting in 1925, after which his creativity and interest in mainstream science declined.

Dirac acquired fame not only for his contributions to physics but also because of his peculiar personality, including such traits as extreme reticence and taciturnity. Social skills were not his strong side. His younger contemporary, Richard Feynman, another quantum genius, was once described as “a second Dirac, only human.”

This book offers a condensed account of Dirac’s life and science or, more specifically, his life in science. Despite his reserved personality, he was very well connected and during his long career, he interacted with physics luminaries such as Niels Bohr, Werner Heisenberg, J. Robert Oppenheimer, and others. The book is to some extent based on a more detailed and technically demanding monograph I published in 1990, in which one can find further information (Dirac: A Scientific Biography, Cambridge University Press). It also includes material from a more recent, and even more detailed biography by Graham Farmelo (The Strangest Man, Faber and Faber).

While Dirac is primarily—and for good reasons—known as the quantum theorist par excellence, he also made other noteworthy contributions to the physical sciences. These were not as successful as his early work in quantum theory, but they are nonetheless of considerable interest. I describe in one of the chapters Dirac’s unorthodox and highly original cosmological theory, based on the hypothesis that the gravitational constant varies in time—and hence is not a constant. Dirac’s cosmology is erroneous, but his more general ideas concerning the constants of nature and their possible variation in time are still alive and part of modern physics.

A thorough understanding of Dirac’s work requires more than average expertise in physics and is therefore beyond the reach of most people. However, this should not discourage a curious reader from exploring Dirac’s thoughts—it is possible to grasp the main ideas of some of his theories without the use of mathematics. This is what I have tried to do. The book requires almost no prior knowledge of mathematics and physics, just an open mind and a little imagination. On the other hand, some basic knowledge of physics and its history is not a disadvantage.

Dirac’s life and science can be dealt with in a rather narrow, biographical perspective or a broader, more contextual one. Likewise, it can be dealt with in strictly chronological order or in a more thematic one. I have chosen the two latter options, which I believe are better suited to explain what made Dirac such an outstanding and remarkably creative physicist. Also, they allow more room for the biographer to point out connections that were scarcely recognized at the time. The book is slim enough to be read from beginning to end in a relatively short time span, allowing the reader to remember the material from one chapter to another. For this reason, I have no qualms about referring in some of the early chapters to topics that will be mentioned only later on in the book.

Although the chapters roughly follow a chronological pattern, a few of them cover much of Dirac’s life—and some beyond it—focusing on themes that were not time-sensitive or specific to a particular scientific work. Some parts of a scientist’s work, as well as its historical significance within a broader context, can only be properly evaluated with the passage of time.

As I did in my 1990 monograph, here too I have chosen to pay attention to aspects of a more general, methodological, and philosophical nature. Dirac was not a philosopher, but one does not need to dig deeply into his work to find assumptions and guiding themes that can best be characterized as philosophical. The most original of these themes and the one he felt most committed to was the so-called “principle of mathematical beauty.” It is more than a little surprising that the emotionally restricted Dirac, an almost inhuman worshiper of rationality and logic in science as well as in life, should develop such a strong commitment to the nebulous concept of beauty. He seriously believed that a theory of great mathematical aesthetic should be preferred over a less beautiful rival theory, even if the latter were empirically superior. But isn’t beauty in the eye of the beholder?

Helge Kragh
Copenhagen, Denmark