The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom, by Graham Farmelo
Basic Books, 2009

When Niels Bohr calls you strange, you know you're in rare company. Niels Bohr, as director of one of the great institutes of theoretical physics, came to know almost every one of the oddballs who populated the early 20th century physics community, and he rated Paul Dirac as "the strangest man" he ever met. Hence the title of Graham Farmelo's excellent new biography of this major physicist.

Dirac's eccentricity was due to his extreme reticence in conversation, and his apparent inability to relate to the emotional give-and-take that makes up most human relationships. The many legendary stories of Dirac's behavior give the impression of a man who was a cross between Farmer Hoggett and Raymond Babbitt. It is likely that today, as Farmelo discusses, Dirac would be classed somewhere on the autism spectrum.

In fact, Dirac's life illustrates one tragic dimension of autism spectrum disorders (ASDs): not long ago, they were attributed to poor parenting, especially by the mother. Dirac himself strongly felt that he was emotionally crippled by his home life. His father was emotionally unavailable (he may also have suffered from an ASD), his brother committed suicide, and his mother was desperate for some sort of emotional contact from her family. For much of Dirac's lifetime, medical science would have blamed this family situation on some moral failing of Dirac's mother. Today, it is not difficult to see that it was likely a genetic disorder that was largely responsible for the Dirac family dynamics and the desperate and tragic situation of Dirac's long-suffering mother.

Both physicists and the British love their eccentrics, and Dirac did not lack friendships, although they were always on his own terms. He formed long-lasting relationships with the other giants of 20th century physics, relationships that were fascinating to observe and often the source of the Dirac legends that have circulated in scientific lore. One is told by Heisenberg, who took a two-week steamer trip with Dirac from San Francisco to Yokohama in 1929. In contrast to the reticent Dirac, Heisenberg loved to cut it up on the dance floor. Dirac asked Heisenberg a classic Dirac question: 'Why do you dance?' Heisenberg replied, 'When there are nice girls it is a pleasure to dance.' Dirac followed up with what was to him the next obvious question: 'How do you know beforehand that the girls are nice?'

Dirac was famous for this kind of literal-mindedness. After a lecture at the University of Wisconsin in Madison, the moderator asked for questions. One member of the audience stated that 'I don't understand the equation on the top-right-hand corner of the blackboard.' As Farmelo writes:

Dirac said nothing. The audience shuffles nervously, but he remains silent, whiling away the time of day, looking unconcerned. The moderator, feeling obliged to break the silence, asks for a reply, whereupon Dirac says, 'That was not a question, it was a comment.'

A great scientific biography effectively conveys not only the personality of its subject, but also attempts to explain what makes a successful scientist. Farmelo's book highlights several elements of Dirac's phenomenal success as a physicist. One is that Dirac was obviously extremely intelligent. But there was more to his success. Dirac himself felt that his training, which today we would call multidisciplinary, was key. He began his education at a technical school, where he was trained in engineering. As an undergraduate, he continued his engineering studies, which he complemented with studies in pure mathematics. Thus he came to physics with some formidable mathematical tools, and with an engineer's feel for the practical. Dirac also emphasized that, in spite of his reputation as an extremely mathematical physicist, he approached problems visually, aided by his early training in what is known as projective geometry. (True to form, he wouldn't give an example of just how he applied projective geometry to quantum mechanics.)

Another of Dirac's traits, held in common with most successful scientists, was ambition. In science, productive ambition means the judicious selection of important research problems. Dirac was driven to tackle fundamental problems in physics, and after some searching, managed to find a niche right at the heart of quantum mechanics. He completed one of the first successful efforts to develop a relativistic quantum mechanics applied to electrodynamics (called quantum electrodynamics), developed an equation that predicted the existence of anti-matter, and wrote one of the most influential textbooks on quantum mechanics.

Dirac's style was to seek out solitude. He worked alone, and would rarely share any of his latest struggles or results with even his closest colleagues. His approach was driven by his belief that, physics had reached the point to where its advances will be driven by innovations in theory subsequently tested by experiment, and not theory driven first by experiment. As he put it in a 1931 paper (PDF):

There are at present fundamental problems in theoretical physics awaiting solution... the solution of which problems will presumably require a more drastic revision of our fundamental concepts than any that have gone before. Quite likely these changes will be so great that it will be beyond the power of human intelligence to get the necessary new ideas by direct attempts to formulate the experimental data in mathematical terms. The theoretical worker in the future will therefore have to proceed in a more indirect way. The most powerful method of advance that can be suggested at present is to employ all the resources of pure mathematics in attempts to perfect and generalise the mathematical formalism that forms the existing basis of theoretical physics, and after each success in this direction, to try to interpret the new mathematical features in terms of physical entities.

Farmelo's balanced book is an excellent study of Dirac's approach to science, his personality, his place in the physics community, and his difficult and sometime tragic home life. Biography of 20th century physicists is an extremely worked-over genre. It is difficult to make a significant new contribution, but that is exactly what Farmelo has done.

Join me next month for the Sunday Science Boook Club. We'll be discussing Darwin's Voyage of the Beagle on November 8th.

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