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Paul Adrien Maurice Dirac, (August 8, 1902 - October 20, 1984)
was a British theoretical physicist and a founder of the field of quantum physics.
Biography
Paul Dirac was born in Bristol, Gloucestershire, England. His father, Charles Dirac, was an
immigrant from the Valais Canton in Switzerland who taught French for a living. His mother was originally from Cornwall and the daughter of mariner. Paul had an elder brother and an younger sister. His early family life
appears to have been unhappy on account of his father's unusually strict and authoritarian nature, but he never publicly
expressed his feelings on the subject. He was educated first at Bishop Primary School and later at Merchant Venturers Technical
College. The latter was an institution, attached to the University of Bristol, that emphasized scientific subjects and modern languages (an unusual
arrangement at a time when secondary education in Britain was still dedicated largely
to the classics, and something for which Dirac would later express gratitude).
Dirac studied electrical engineering at the University of Bristol, completing his degree in 1921. After
working briefly as an engineer, Dirac decided that his true calling lay in the mathematical sciences. He completed a degree in
mathematics at Bristol in 1923 and then received a grant to conduct research
at St. John's College, Cambridge,
where he would remain for most of his career. At Cambridge he became interested in the general theory of relativity and in the nascent field of quantum physics, and worked under the supervision of Ralph Fowler.
In 1926 he developed a version of quantum mechanics that incorporated the previous work of Werner Heisenberg on “Matrix Mechanics” and of Erwin Schrödinger on “Wave Mechanics” into a single mathematical formalism that associates
measurable quantities with operators acting on the Hilbert space of
vectors that describe the state of a physical system. For this seminal work he was awarded a Ph.D. from Cambridge.
In 1928, building on Pauli's work on nonrelativistic spin systems, he derived the Dirac equation, a relativistic
equation describing the electron. This work led Dirac to predict the existence of the positron, the electron's antiparticle, which he interpreted in terms of what came to be called the Dirac sea. The positron was subsequently observed by Carl Anderson in 1932. Dirac also contributed to explaining
the origin of quantum spin as a relativistic phenomenon.
Dirac's Principles of Quantum Mechanics, published in 1930 became one of the
standard textbooks on the subject and is still used today. It introduced the Bra-ket notation, in which |ψ>, ket, denotes a state vector in the Hilbert space of a system and <ψ|, bra, its dual vector. <ψ|ψ> denotes an inner
product. Dirac also introduced Dirac's delta function.
In 1931 Dirac showed that the existence of a single magnetic monopole in the universe would suffice to explain the observed quantization of electrical charge. This proposal received much attention but there is to
date no convincing evidence for the existence of magnetic monopoles.
Paul Dirac shared the Nobel Prize for physics in 1933 with Erwin Schrödinger "for the discovery
of new productive forms of atomic theory." Dirac was Lucasian
professor of mathematics at Cambridge from 1932
to 1969. The Dirac Prize is awarded in his honour.
Dirac spent his last years at Florida State
University (FSU) in Tallahassee, Florida. The
Dirac-Hellman Award at FSU was endowed by Dr. Bruce Hellman (Dirac's last Ph.D. student)
in 1997 to reward outstanding work in theoretical physics by FSU researchers. He died in Tallahassee, where he is buried. In 1995
a plaque in his honor was unveiled at Westminster Abbey in
London.
He married Eugene Wigner's daughter, Margit Dirac in 1937.
Views
Dirac was a committed atheist. After being asked about his thoughts on Dirac's
views, Pauli remarked "If I understand Dirac correctly, his
meaning is this: there is no God, and Dirac is his Prophet".
Dirac was known among his colleagues for his precise and taciturn nature. When Niels Bohr complained that he didn't know how to finish a sentence in a scientific article he was writing, Dirac
famously replied: 'I was taught at school never to start a sentence without knowing the end of it.' While visiting the U.S.S.R., he was invited to lecture on his philosophy of physics. He merely stood up and
wrote on the board: 'Physical laws should have mathematical beauty and simplicity.'
When asked on some occasion about his views on poetry, he replied that 'in science one tries to tell people, in such a way as
to be understood by everyone, something that no one ever knew before. But in poetry, it's the exact opposite.'
Dirac was also noted for his personal modesty. He called the equation for the time-evolution of a quantum-mechanical operator,
which Dirac we was in fact the first the 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 'Einstein statistics' for reasons, he explained, of symmetry.
See also
External links
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