British Poets, Scientists, Mathematicians, Actors, and Comedians have often gone serenely their own way, doing the things that interested them personally as if they were playing cricket for their personal amusement only, with a self- satisfied disregard, for what others shouting at the top of their lungs have assured the world is of supreme importance. This has been the case with Shakespeare, Newton, Maxwell, Lawrence Olivier and Charlie Chaplin in their respective fields.
Paul Adrian Maurice Dirac, the English physicist like the others referred to above is cast in the same mould.
Dirac was one of the pioneers of quantum theory. He received the Nobel Prize for Physics in 1933, jointly with Erwin Schrodinger.
Dirac was born on 8 August 1902, in Bristol, England. Dirac first went to Bristol University, where he took a degree in electrical engineering, graduating in 1921. He stayed on to complete a mathematics degree in 1923. He then went to Cambridge to work for his PhD under the supervision of Ralph Fowler. It was only when he arrived in Cambridge that Dirac learned anything about quantum theory.
In July 1925, Werner Heisenberg gave a talk in Cambridge, where Dirac was in the audience. Heisenberg did not discuss his new ideas about quantum physics in that talk, but he mentioned them privately to Fowler, and followed up by sending Fowler an advance copy of his first paper on the matrix mechanics approach to quantum theory. Fowler showed the paper (which had not yet been published) to Dirac. Then Dirac used his mathematical background to develop his own version of quantum theory (known as operator theory or quantum algebra), which was published in the proceedings of the prestigious Royal Society in December 1925.
Dirac obtained his PhD in 1926. He then visited Niels Bohr’s institute in Copenhagen, where he showed that both Heisenberg’s matrix mechanics and Erwin Schrodinger’s wave mechanics were special cases of his own operator theory, and were therefore exactly equivalent to one another. In the same year he married Margit Wigner, the sister of the Hungarian Nobel Laureate Eugene Wigner. He also visited the University of Gottingen before returning to England.
In 1927 Dirac introduced the idea of second quantisation to quantum physics, pointing the way for the development of quantum field theory. In the same year, he became a Fellow of St. John’s College and a university lecturer In Cambridge, but also taught in the United States and visited Japan over the next few years. What is widely regarded as his greatest contribution to physics came in the following year, when he found an equation which incorporates both quantum physics and the requirements of the special theory of relativity to give a complete description of the electron. One of the most remarkable features of this equation was that it had two sets of solutions, corresponding to negatively charged electrons and positive energy electrons, now called positrons. Dirac had predicted the existence of antimatter, although even Dirac was not entirely clear what the equations meant until the positron was discovered by Carl Anderson in 1932. Dirac received his Nobel Prize a year later.
It was also in 1932 that Dirac was appointed Lucasian Professor in Cambridge (it may be mentioned that the Lucasian chair in mathematics is the most prestigious in mathematics in the world). Newton was a Lucasian professor. Other great scientists are Stephen Hawking and Sir James Lighthill the world’s most brilliant fluid dynamicist.
Dirac also worked out the statistical rules which describe the behaviour of large numbers of particles which have half-integer spin, such as electrons. Because the same statistical rules were worked out independently by Enrico Fermi, they are now known as Fermi-Dirac statistics, and the particles whose behaviour they describe are called fermions.
In 1930 Dirac published a book, “The Principles of quantum Mechanics”, which was the first systematic treatment of the subject and became the bible for generations of physicists (for example, it was an inspiration to the young Richard Feynman), and, revised down the years. It is still in use.
Dirac made no major contributions to physics after that ( although in an obscure paper published in 1950 he did suggest that fundamental particles might have string-like properties), and was extremely unhappy about the process of renormalisation which became an integral part of quantum field theory …
Dirac was a great traveller, and worked as a visiting lecturer in several American universities (and at the Institute of Advanced Study in Princeton) during his time as Lucasian Professor.
There are several anecdotes concerning Dirac.
When Dirac retired from Cambridge in 1969, he became a research professor at Florida State University, in Tallahassee, where he died on 20th October 1984. Someone asked him why he was visiting Cambridge university in England often, Dirac replied ” Sometimes I like to be in the centre of things”.
Once a group of professors visited the great man in his chambers. One of the professors commented that it was raining outside. Dirac got up from his chair, drew the curtains and said” yes, it is indeed raining”. Dirac was essentially conveying the idea that in science, if you make a comment, it must be backed by evidence,
One day Dirac was going up in a lift with Lee and Yang, two brilliant physicists. They asked him what was the secret of his success. He replied” moderation”
Dirac believed that it was important to have beauty in an equation. If there was beauty, the equation could be considered correct.
In the year 1958, Dirac had come to Madras to give a series of lectures at MATSCIENCE. My uncle Ramakrishnan who was the founder director of MATSCIENCE HAD put him up in Ekamra Nivas, the ancestral house built by my grandfather Sir ALLADI, where we all stayed.
Shortly after dinner Dirac went up to his room upstairs. My uncle and I were curious to know why Dirac was remaining there for a long time. After about forty five minutes my uncle politely asked Dirac’ wife why he had still not come down. She answered ” after dinner Paul likes to lie in bed for about an hour and think.My uncle and I simultaneously asked her” what does he think about ? “She replied” these days he is thinking about two questions that are bothering him. He is wondering whether the so-called ” constants” in Physics are really constant. He is also wondering whether ether exists..
Dirac is generally regarded as the only English theorist who can rank with Issac Newton, and Maxwell in the pantheon of physics.