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Important Scientists

PAUL DIRAC (1902 - 1984)
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Paul Dirac
Paul Dirac

Paul Dirac was a British theoretical physicist who made fundamental contributions to the development of quantum mechanics, quantum field theory and quantum electrodynamics, and is particularly known for his attempts to unify the theories of quantum mechanics and relativity theory. His Dirac Equation, which was formulated in 1928 and describes the behaviour of fermions like the electron, predicted the existence of antimatter such as the positron. He shared the 1933 Nobel Prize in Physics for 1933 with Erwin Schrödinger "for the discovery of new productive forms of atomic theory” and is regarded by some as one of the greatest physicists of all time.

Paul Adrien Maurice Dirac was born on 8 August 1902 in Bristol, England. He was brought up in an unusually strict and authoritarian household by his Swiss immigrant father, and was educated at the Merchant Venturers' Technical College (where his father was a French teacher), an institution attached to the University of Bristol which emphasized scientific subjects and modern languages.

Dirac went on to study at the University of Bristol, completing his degree in electrical engineering in 1921, and then earning a BA in applied mathematics in 1923. He obtained a grant to conduct research at St John's College, Cambridge, where he would remain for most of his career, pursuing his interests in general relativity and in the nascent field of quantum theory, initially under the supervision of Ralph Fowler.

He began working on quantum mechanics almost as soon as it was introduced by Werner Heisenberg in 1925, and he earned a PhD in 1926 for his canonical quantization of classical mechanics based on Heisenberg's recently proposed matrix formulation of quantum mechanics. His independent mathematical equivalent to Heisenberg's matrix formulation consisted of a non-commutative algebra for calculating atomic properties.

Building on Wolfgang Pauli's work on non-relativistic spin systems, he proposed the “Dirac equation” in 1928 as a relativistic equation of motion for the wave function of the electron. This work also led him to his prediction of the existence of the positron (the antiparticle of the electron, identical to it in every aspect but its charge, the existence of which was later observed and confirmed by Carl Anderson in 1932) and matter-antimatter annihilation, as well as contributing to the explanation of the origin of quantum spin as a relativistic phenomenon. He was also responsible for developing “bra-ket” notation (or Dirac notation), the standard notation for describing quantum states in the theory of quantum mechanics, composed of angle brackets (chevrons) and vertical bars.

Dirac travelled extensively, especially in his younger years, and studied at various foreign universities, including Copenhagen, Göttingen, Leyden, Wisconsin, Michigan and Princeton, as well as visiting the Soviet Union several times. In 1929, after having spent five months in America, he continued around the world, visiting Japan (together with Heisenberg), and then returning across Siberia.

His 1930 book “Principles of Quantum Mechanics” is considered a landmark in the history of science, and it quickly became one of the standard textbooks on the subject (and is still used today). In the book, Dirac incorporates Heisenberg’s previous work on matrix mechanics and Erwin Schrödinger’s work on wave mechanics into a single mathematical formalism. He earned his share in the 1933 Nobel Prize in Physics largely as a result of the book.

He became Lucasian Professor of Mathematics at Cambridge in 1932, a post he held for the next 37 years. In the early 1930s, Dirac introduced the idea of vacuum polarization and developed the field of quantum electrodynamics (he was the first to use that term). In 1933, he showed that the existence of a single magnetic monopole in the universe would suffice to explain the observed quantization of electrical charge (although to date no convincing evidence has yet been found for the existence of physical magnetic monopoles). In 1937, he proposed a speculative cosmological model based on the so-called “large numbers hypothesis” which, although it has not gained acceptance in mainstream physics, has been highly influential among proponents of other non-standard cosmologies.

Dirac married Margit “Manci” Wigner (sister of the Hungarian-American physicist and mathematician, Eugene Wigner) in 1937. He adopted Margit's two children, Judith and Gabriel, and the couple went on to have two more children together, Mary and Florence. He was known as a very precise and ordered man but shy, modest and taciturn, and it has been argued that his autism was crucial to his success as a theoretical physicist. His important contributions to physics were largely motivated by principles of mathematical beauty and he once said, "God used beautiful mathematics in creating the world". However, he is quoted as saying, “I do not recognize any religious myth, at least because they contradict one another”, and he strongly criticized the political manipulation of religion.

Dirac shared the 1933 Nobel Prize in Physics with Erwin Schrödinger “for the discovery of new productive forms of atomic theory”. He was also awarded the Royal Medal (in 1939), the Copley Medal and the Max Planck Medal (both in 1952) among other honours, and was elected a Fellow of the Royal Society in 1930, and of the American Physical Society in 1948, and was made a member of the British Order of Merit in 1973.

During World War II, he worked on uranium separation and nuclear weapons, but his work moved increasingly out of the mainstream in later life. In the 1960s, he developed a theory of “constrained quantization”, identifying the general quantum rules for arbitrary classical systems, and his quantum field analysis of the vibrations of a membrane in the early 1960s has proved extremely useful to modern practitioners of superstring theory and its closely related successor, M-theory.

After teaching as Lucasian Professor of Mathematics at Cambridge from 1932 to 1968, he moved to Florida to be near his daughter Mary, spending his final teaching years at the University of Miami in Coral Gables and Florida State University in Tallahassee. Dirac died on 20 October 1984 in Tallahassee, Florida, where he is buried.

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