PAUL DIRAC (1902-1984)
Raised in humbler circumstances than his posh Georgian predecessor, Paul Dirac grew up in Brighton, the son of a librarian and a tyrannical strict French teacher. His classmates remember him as a tall, quiet, “un-English-looking” boy in unfashionable knickerbockers who virtually lived in the library, maintaining a “monomaniacal focus” on science while seeking refuge from his father’s pedantry in adventure novels and comic books.
His uncanny aptitude for math showed itself early. A teacher once sent young Dirac home with a set of problems designed to keep him occupied all evening and was shocked when he had solved them by the afternoon. Even as a boy, he preferred a life of contemplation to the hurly-burly of the schoolyard. When he was nine, his teachers at the Bishop Road School awarded him with a telling prize: a copy of Daniel Defoe’s Robinson Crusoe, the fictional autobiography of a castaway marooned for twenty-eight years on a remote island.
Lacking an aristocratic father to introduce him to potential mentors in science, Dirac trained at a technical school to become an electrical engineer. In his first year, he distinguished himself so highly that Cambridge offered him a scholarship to its prestigious math program. At St. John’s College, his diffidence and taciturnity became “the stuff of legend,” writes Graham Farmelo in a biography of the physicist The Strangest Man. The newly matriculated Dirac would sit stiffly in the dining hall, hesitant to ask the person eating beside him to pass the salt and greeting every question posed to him with blank silence or a stark yes or no. Incapable of bluffing his way through the protocols of polite conduct, he came across as cold, rude, disinterested, or uncaring, though he didn’t intend to.
A classmate once tried to break the ice with him by casually remarking, “It’s a bit rainy, isn’t it?” Dirac’s strictly empirical response was to march over to the window, peer out, return to his chair and reply, “It is not now raining.” Inspired by his extreme verbal parsimony, his fellow students at St. John’s invented a unit of measurement for the number of words that a person might utter in conversation, christening the minimum rate one “Dirac” – one word per hour. But, like Cavendish lurking in the shadows at the Monday Club, he would often eavesdrop inconspicuously as his peers swapped stories.
Oblivious to contemporary modes of dress, Dirac wore cheap, unstylish suits in all weathers until they were threadbare, even after securing a generous salary as the Lucasian Chair of Mathematics at Cambridge (the position later held by Steven Hawking). His mother practically had to beg him to buy a winter coat so she could stop fretting about his health. Though he seemed impervious to freezing temperatures, he was acutely sensitive to sounds – particularly the barking of dogs, which were permanently banned from his household. Dirac’s motor skills were notoriously poor; a classmate described his method of wielding a cricket bat as “peculiarly inept.” Yet he was as devoted as Cavendish was to taking long walks on a regimented timetable, holding his hands behind his back as he efficiently ticked off the miles in his “metronomic” stride.
In an era when physicists like Einstein and Max Planck were feted as international heroes in the press, Dirac had no interest in being a public figure. He routinely turned down honorary degrees because he felt they should be awarded strictly on merit, and he refused a knighthood because he didn’t want strangers chummily referring to him as “Sir Paul” rather than “Mr. Dirac.” Upon winning the Nobel in physics with Erwin Schrodinger in 1933, he told a reporter from a Swedish newspaper, “My work has no practical significance.”
His life path diverged from Cavendish in at least one important way: he married a bubbly Belgian extrovert named Margit Wigner – nicknamed “Manci” who urged him to supplement his pop-culture diet of comic books and Mickey Mouse cartoons with novels and occasional foray to the ballet. (As Farmelo puts it, “He had wed his anti-particle.”)
The newlyweds honeymooned in Brighton, where the love-struck groom rigged up a camera with a string so he could click the shutter himself. In one shot, the gawky physicist reclines beside his bride on the beach, attired in his usual three-piece suit, with a thicket of pencils sprouting from his pocket. “You have made a wonderful alteration in my life. You have made me human,” Dirac gushed shortly after the wedding. This turned out to be an ongoing job. When Manci complained that he habitually ignored her questions, he pasted her queries into a spreadsheet and filled it in with his replies.
As a theoretical physicist, Dirac didn’t need a lab to do his work; all he needed was a pencil because his most finely calibrated instrument was his mind’s eye. When he was young, a teacher told him that she felt he was cogitating not in words but in “another medium of forms and figures.” He once described his own thoughts as essentially “geometrical.” While visiting an art gallery in Copenhagen, he turned to fellow Nobel laureate Niels Bor and said that he liked a certain painting because “the degree of inaccuracy is the same all over.” He told journalists who asked him to make sketches of his highly abstract concepts for their readers that they would melt away like “snowflakes” if he tried.
The breakthrough that assured him of his own eponymous place in history is known as the Dirac equation. Worked out on a scrap of paper at a schoolboy’s desk in his sparsely furnished room at St. John’s in less than a month in 1927, his formula bridged a seemingly impassable gulf in physics by reconciling quantum mechanics and Einstein’s special relativity in a single concise line of variables. His equation also implied the existence of a previously unsuspected form of particle – antimatter – three years before a scientist named Carl Anderson glimpsed the ghostly arcs of positrons passing through a lead plate in his lab.
Dirac made only one miscalculation in the course of his career: understanding the practical applicability of his work. The relationships between matter and energy that he described made possible the development of semiconductors, transistors, integrated circuits, computers, handheld devices, and the other innovations in microelectronics that ushered in the digital age. By capturing the ephemeral snowflakes in his mind in the universal language of mathematics, this man who found communication so arduous a task made it much easier for everyone else to communicate.
But even in a field in which absent-minded professors are the rule rather than the exception, Dirac’s colleagues were left unsettled and confused by his behaviour. Einstein confessed, “I have trouble with Dirac. This balancing on the dizzying path between genius and madness is awful.” Bohr claimed that Dirac was “the strangest man” he had ever met, finishing Farmelo with a title for his biography. Like Cavendish, he was a walking riddle to everyone who crossed his path.
Addition from Wikipedia:
Family. In 1937, Dirac married Margit Wigner (Eugene Wigner’s sister). He adopted Margit’s two children, Judith and Gabriel. Paul and Margit Dirac had two children together, both daughters, Mary Elizabeth and Florence Monica.
Margit, known as Manci, visited her brother in 1934 in Princeton, New Jersey, from their native Hungary and, while at dinner at the Annex Restaurant, met the “lonely-looking man at the next table”. This account from a Korean physicist, Y. S. Kim, who met and was influenced by Dirac, also says: “It is quite fortunate for the physics community that Manci took good care of our respected Paul A. M. Dirac. Dirac published eleven papers during the period 1939–46… Dirac was able to maintain his normal research productivity only because Manci was in charge of everything else”.
Personality. Dirac was known among his colleagues for his precise and taciturn nature. His colleagues in Cambridge jokingly defined a unit called a “dirac”, which was one word per hour. When Niels Bohr complained that he did not know how to finish a sentence in a scientific article he was writing, Dirac replied, “I was taught at school never to start a sentence without knowing the end of it.” He criticized the physicist J. Robert Oppenheimer’s interest in poetry: “The aim of science is to make difficult things understandable in a simpler way; the aim of poetry is to state simple things in an incomprehensible way. The two are incompatible.”
Dirac himself wrote in his diary during his postgraduate years that he concentrated solely on his research and stopped only on Sundays when he took long strolls alone.
An anecdote recounted in a review of the 2009 biography tells of Werner Heisenberg and Dirac sailing on an ocean liner to a conference in Japan in August 1929. “Both still in their twenties and unmarried, they made an odd couple. Heisenberg was a ladies’ man who constantly flirted and danced, while Dirac—’ an Edwardian geek’, as biographer Graham Farmelo puts it—suffered agonies if forced into any kind of socializing or small talk. ‘Why do you dance?’ Dirac asked his companion. ‘When there are nice girls, it is a pleasure,’ Heisenberg replied. Dirac pondered this notion, then blurted out: ‘But, Heisenberg, how do you know beforehand that the girls are nice?’”
Margit Dirac told both George Gamow and Anton Capri in the 1960s that her husband had said to a house visitor, “Allow me to present Wigner’s sister, who is now my wife.”
Another story told of Dirac is that when he first met the young Richard Feynman at a conference, he said after a long silence, “I have an equation. Do you have one too?”
After he presented a lecture at a conference, one colleague raised his hand and said: “I don’t understand the equation on the top-right-hand corner of the blackboard”. After a long silence, the moderator asked Dirac if he wanted to answer the question, to which Dirac replied: “That was not a question, it was a comment.”
Dirac was also noted for his personal modesty. He called the equation for the time evolution of a quantum-mechanical operator, which he was the first to write down, the “Heisenberg equation of motion”. Most physicists speak of Fermi–Dirac statistics for half-integer-spin particles and Bose–Einstein statistics for integer-spin particles. While lecturing later in life, Dirac always insisted on calling the former “Fermi statistics”. He referred to the latter as “Bose statistics” for reasons, he explained, of “symmetry”.
Views on religion. Heisenberg recollected a conversation among young participants at the 1927 Solvay Conference about Einstein and Planck’s views on religion between Wolfgang Pauli, Heisenberg, and Dirac. Dirac’s contribution was a criticism of the political purpose of religion, which Bohr regarded as quite lucid when hearing it from Heisenberg later. Among other things, Dirac said: I cannot understand why we idle discussing religion. If we are honest—and scientists have to be—we must admit that religion is a jumble of false assertions, with no basis in reality. The very idea of God is a product of the human imagination. It is quite understandable why primitive people, who were so much more exposed to the overpowering forces of nature than we are today, should have personified these forces in fear and trembling. But nowadays, when we understand so many natural processes, we have no need for such solutions. I can’t for the life of me see how the postulate of an Almighty God helps us in any way. What I do see is that this assumption leads to such unproductive questions as to why God allows so much misery and injustice, the exploitation of the poor by the rich, and all the other horrors He might have prevented. If religion is still being taught, it is by no means because its ideas still convince us, but simply because some of us want to keep the lower classes quiet. Quiet people are much easier to govern than clamorous and dissatisfied ones. They are also much easier to exploit. Religion is a kind of opium that allows a nation to lull itself into wishful dreams and so forget the injustices that are being perpetrated against the people. Hence the close alliance between those two great political forces, the State and the Church. Both need the illusion that a kindly God rewards—in heaven if not on earth—all those who have not risen up against injustice, who have done their duty quietly and uncomplainingly. That is precisely why the honest assertion that God is a mere product of the human imagination is branded as the worst of all mortal sins.
Heisenberg’s view was tolerant. Pauli, raised as a Catholic, had kept silent after some initial remarks, but when finally he was asked for his opinion, said: “Well, our friend Dirac has got a religion and its guiding principle is ‘There is no God, and Paul Dirac is His prophet. ‘” Everybody, including Dirac, burst into laughter.
Later in life, Dirac’s views towards the idea of God were less acerbic. As an author of an article appearing in the May 1963 edition of Scientific American, Dirac wrote:
It seems to be one of the fundamental features of nature that fundamental physical laws are described in terms of a mathematical theory of great beauty and power, needing quite a high standard of mathematics for one to understand it. You may wonder: Why is nature constructed along these lines? One can only answer that our present knowledge seems to show that nature is so constructed. We simply have to accept it. One could perhaps describe the situation by saying that God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe. Our feeble attempts at mathematics enable us to understand a bit of the universe, and as we proceed to develop higher and higher mathematics we can hope to understand the universe better.
In 1971, at a conference meeting, Dirac expressed his views on the existence of God. Dirac explained that the existence of God could be justified only if an improbable event were to have taken place in the past:
It could be that it is extremely difficult to start life. It might be that it is so difficult to start a life that it has happened only once among all the planets… Let us consider, just as a conjecture, that the chance of life starting when we have suitable physical conditions is 10−100. I don’t have any logical reason for proposing this figure, I just want you to consider it as a possibility. Under those conditions … it is almost certain that life would not have started. And I feel that under those conditions it will be necessary to assume the existence of a god to start off life. I would like, therefore, to set up this connection between the existence of a god and the physical laws: if physical laws are such that to start off life involves an excessively small chance so that it will not be reasonable to suppose that life would have started just by blind chance, then there must be a god, and such a god would probably be showing his influence in the quantum jumps which are taking place later on. On the other hand, if life can start very easily and does not need any divine influence, then I will say that there is no god.
Dirac did not commit himself to any definite view, but he described the possibilities for scientifically answering the question of God.
Dirac biographer Graham Farmelo came to the same conclusion as Sachs did with Cavendish. “Nearly all” of the Dirac stories that physicists have been telling each other for years, he wrote in The Strangest Man, “might also be called ‘autism stories.’” After interviewing 30 people who knew Dirac very well (including two members of his close family) he concluded that his behaviour was so singular that he very clearly passed every criterion for autistic behaviour.
