Paul Dirac - Physicist

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Paul Dirac was known for being: a Nobel-Prizewinning physicist, a genius, a 'strange man' (he was possibly on the autistic spectrum) and a fan of Mickey Mouse cartoons.

A Difficult Childhood

Paul Adrien Maurice Dirac was born on 8 August, 1902 in Bristol in the UK. His father Charles had been born in Switzerland but was working in the UK as a language teacher. Paul's mother Florence (née Holten) had been a librarian. Paul's brother Felix had been born in 1900 and his sister Betty was born in 1906.

Charles was keen for his children to work hard and get a good education. As his first language was French, he encouraged Felix, Paul and Betty to become bilingual by speaking French to them while Florence spoke in English. However, Paul remembered this as an ordeal because he didn't have a particular talent for languages - he recalled that Charles wouldn't let him leave the dining table until he spoke a sentence free of grammatical errors. Paul struggled with eating at the best of times1 so he made mistakes and often became ill.

Paul went to the same primary school as Cary Grant (or rather Archibald Leach as he was then) and then won a scholarship to study at the Merchant Venturers' School where his father worked. He studied a range of subjects including English, German and Technical Drawing, but particularly enjoyed Mathematics - his maths teacher encouraged his enthusiasm by giving him books on geometry and other topics that he could study by himself. Paul contemplated studying Mathematics at university, but as the main career option for mathematicians at that time was teaching, which was something he was not interested in doing, he chose Engineering. The University of Bristol's Engineering department was based in the Merchant Venturers' Technical College that adjoined the School of the same name so that was very convenient for him when he transferred there at the age of 16.

University Life

The Engineering course gave Paul a broad range of knowledge, incorporating topics in Physics, Chemistry and even accounts management and patent law. His favourite lectures were the theoretical ones2 - he often went to the library to work on problems by himself, aiming to find the most elegant solutions, rather than simply the most practical solutions.

In his final year, Paul specialised in Electrical Engineering, and learned about the work of Oliver Heaviside. In his spare time he studied Relativity, as Albert Einstein's theory entered the popular realm in 1919 following experiments that supported its conclusions. In 1921 Paul graduated with a First Class degree, having scored the highest marks in the class in all but one3 of the subjects he studied.

Charles encouraged Paul to apply for a scholarship to Cambridge University. Paul was successful, but was not awarded enough of a bursary to be able to live there without additional funds. His father was not willing to provide financial support so he was forced to give up the place. He applied for various engineering jobs but was not successful, so when he was offered the opportunity to do a Mathematics degree free of charge at the University of Bristol, he accepted. He learned mathematical topics such as Hamiltonian Mechanics but also attended Physics lectures in his spare time, in particular learning about the structure of atoms and the new field of Quantum Theory.

Paul again graduated with First Class Honours and in 1923 he was able to take up his scholarship at Cambridge as his continuing academic success secured him more bursaries for his living expenses. He studied Relativity along with the atomic theory of Niels Bohr and wrote papers linking the two theories together. He then moved on to studying Quantum Mechanics. In 1925 he found an elegant equation to describe concepts that Heisenberg had developed and went on to write a paper entitled 'The Fundamental Equations of Quantum Mechanics'. His thesis 'Quantum Mechanics' summarised his understanding of the subject as a whole and he was awarded the title of Doctor of Philosophy on 19 June, 1926.

In the months after his graduation ceremony, Paul got to grips with the work of his contemporary and fellow quantum theorist Erwin Schrödinger, who had taken a different but related approach to the subject. He also published a paper about the topic that would come to be known as Fermi-Dirac Statistics. In September 1926 he travelled to Europe to meet other men working in the field of Quantum Mechanics.

New Horizons

In Copenhagen, Denmark, Paul wrote a paper that brought together the work of Heisenberg and Schrödinger as special cases of a more general theory of Quantum Mechanics. In it he introduced what would be called the Dirac Delta Function4. He also considered wave-particle duality and wrote a paper that built on James Clark Maxwell's work on electromagnetic waves and Einstein's Nobel Prize-winning work on the particles called photons.

In 1927 he attended the Solvay Conference that would become legendary as a gathering of 29 the finest minds in the world at that time - the names of 17 of the delegates can now be found on the list of Nobel Prize winners. Double-Nobel winner Marie Curie was there along with Einstein, Bohr, Schrödinger, Heisenberg, and others famous in the field of Physics.

Back in Cambridge, Paul's efforts to link Relativity and Quantum Mechanics together yielded what would become known as the Dirac Equation to describe the behaviour of electrons5. He published the results in a paper entitled 'The Quantum Theory of the Electron' in 1928. The fame of this paper meant he was invited to visit Physics departments around the world. In 1930 he was elected as a Fellow of the Royal Society and his book The Principles of Quantum Mechanics was published.

In 1931 Paul turned his attention to Electromagnetism and its relationship with Quantum Mechanics. His theory described Magnetic Monopoles (like half a magnet on its own, with just a north pole and no south pole or vice versa) as a way to explain why magnetic field strength and electrical charge are both quantised (so they can only exist as whole number multiples of a minimum amount, not fractions of that amount). His paper 'Quantised Singularities in the Electromagnetic Field'6 also described his prediction for the existence of 'anti-electrons' and 'anti-protons' to explain the holes in his understanding of the physical reality underpinning his Dirac Equation (indeed he had previously called the unknown aspects 'holes').

At the age of just 29, in 1932 Paul was appointed Lucasian Professor at Cambridge, following in the footsteps of Isaac Newton. And in 1933 he was awarded the Nobel Prize in Physics jointly with Schrödinger, for 'the discovery of new and productive forms of atomic theory'.

Family Life

Whether because of his opinion that he once expressed to Heisenberg - 'You are now past 30 and you are no longer a physicist' - or for other reasons, Paul took more of an interest in matters outside of theoretical physics in the mid-1930s, becoming more involved with experimental physics and even learning Russian. In 1934 he went to Princeton in the USA and met Margit 'Manci' Balázs, the sister of the Hungarian physicist Eugene Wigner. She was an extrovert while Paul was very much an introvert, but they got on well. When Manci returned to Hungary a few months later, she wrote him letters but complained that he didn't answer all her questions in his letters. In response, he created a table of the questions with his answers beside them, including 'Do you know how I feel like? - Not very well. You change so quickly'. They spent Christmas 1936 together in Hungary and Paul met Manci's two children from her first marriage (she was a divorcée) - the more time he spent with her, the more he realised he loved her. Paul and Manci married on 2 January, 1937 in London.

Paul and Manci settled into married life in Cambridge. Their daughter Mary was born on 9 February, 1940 and Florence Monica was born on 29 September, 1942.

War Work

For a time Paul turned his attention from the smallest parts of the universe to the largest, focusing on Cosmology. However, during World War II Paul's atomic expertise was put to use when he was asked to investigate methods for separating isotopes of elements from one another. It had been found that the radioactive element Uranium has two isotopes and the lighter one, 235U, was unstable enough to undergo nuclear fission and release large amounts of energy. Paul also worked on the theory behind how such a reaction could be used to create a bomb. Even so, it would be Robert Oppenheimer7 and the Manhattan Project in the USA that would be credited with the devices used in the bombing of Hiroshima and Nagasaki.

Post War

In 1947 Paul and Manci visited the USA and spent time in Princeton University. They felt at home there so when Paul was offered a sabbatical a few years later he decided to return. However, his application for a visa was turned down in 1955 as he had visited Russia in the past so that put him under suspicion during the McCarthy era. This caused an outcry amongst his fellow scientists and the visa refusal was reviewed, but Paul and Manci decided to visit India instead. There Paul gave lectures and was honoured, even meeting the Prime Minister Jawaharlal Nehru, but he contracted an illness that affected his liver. He spent time in hospital in Hong Kong and then travelled to Canada where he met Oppenheimer again (Einstein had recently died, and Oppenheimer had had his security clearances revoked so they had a lot to talk about). To get the best medical treatment, Paul was allowed to travel to the USA.

After he recovered, he spent some more time at Princeton University. There he did work visualising electrons as short pieces of string rather than as particles or waves, which foretold the development of String Theory in the 1990s. In the 1960s he gave lectures aimed at non-specialist audiences and wrote an article 'The Evolution of the Physicist's Picture of Nature' for Scientific American magazine in 1963. In 1965 he appeared on television in conversation with Heisenberg in an episode of the BBC's Horizon science documentary series.

Paul often went to the cinema, and was known to particularly enjoy James Bond films and Disney Classics. In 1969 Paul was captivated by Stanley Kubrick's film 2001: A Space Odyssey - he even watched it three times in one day.

By 1971 Paul and Manci's daughters had both moved to the USA, so the couple officially emigrated to join them that year. Paul took up a professorship at Florida State University and gave lectures on Einstein's General Theory of Relativity. He spent less time on quantum mechanics even though the Standard Model of Particle Physics had been developed and included a quantity named the Dirac Constant in his honour.

Paul was also honoured by being accepted into the Order of Merit in 19738. In 1975 he gave a series of four lectures and they were filmed for posterity. In 1979 he participated in the celebrations of Einstein's 100th birthday year and travelled from the USA to Europe on Concorde. In contrast, demonstrating his insecurity in the achievements of his career, in the 1980s Paul wrote an paper on 'The Inadequacies of Quantum Field Theory'. However, by then his health was failing - in 1983 he had an operation to remove one of his kidneys and recovered well enough to work on the paper and meet his doctoral student, but he was still weak. On 20 October, 1984 Paul Dirac died of heart failure at the age of 82.

Celebration

Paul's archive of work was transferred to Florida State University and Manci opened the Dirac Science Library there in 1989.

In 1995, Paul's life and work was celebrated at a ceremony in Westminster Abbey. Prof Stephen Hawking made a speech and Sir Michael Atiyah, President of the Royal Society, unveiled a stone engraved with the words: '1902 P. A. M. Dirac OM Physicist iγ.δψ = 1984'.

1It was only when he was in his 70s that it was discovered his stomach didn't produce enough acid to digest large amounts of food, so it was no wonder he had always felt uncomfortable during meals. Acid supplements cured the problem.2He particularly admired David Robertson, who used a wheelchair and whose Electrical Engineering lectures (delivered on projected slides rather than a blackboard) focused strongly on the theory behind the subject.3In that subject, he was second in the class.4This function is zero at all but one point, so it could roughly be visualised as a needle standing on its end on a flat surface.5This equation, (iδ-m)ψ = 0 would go on to be elected the most beautiful equation in 2016.6Note the early version of autocorrect in the paper - 'Pauli' has become 'Fault' in the third paragraph of the Introduction!7Whom Paul had met in Germany in the 1920s when Oppenheimer was a PhD student.8He had declined a knighthood in 1953 - a possible reason was because he generally preferred to be known as 'Mr Dirac', not even taking the title of 'Dr' or 'Prof', so 'Sir Paul' was out of the question.

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