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Paul Dirac

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   CAPTION: Paul Dirac

              Paul Adrien Maurice Dirac
   Paul Adrien Maurice Dirac
          Born        August 8, 1902
                      Bristol, England
          Died        October 20, 1984
                      Tallahassee, Florida, USA
       Residence      UK
                      USA
      Nationality     English- Swiss (to 1919)
                      English (after 1919)
         Field        Physicist
      Institutions    Cambridge University
                      Florida State University
       Alma mater     University of Bristol
                      Cambridge University
   Academic advisor   Ralph Fowler
   Notable students   Homi Bhabha
                      Harish Chandra Mehrotra
                      Dennis Sciama
                      Behram Kurşunoğlu
                      John Polkinghorne
                      Per-Olov Löwdin
       Known for      Quantum physics
     Notable prizes   Nobel Prize in Physics (1933)
        Religion      Atheist
   Quantum physics
   Quantum mechanics

   Introduction to...
   Mathematical formulation of...
   Fundamental concepts

   Decoherence · Interference
   Uncertainty · Exclusion
   Transformation theory
   Ehrenfest theorem · Measurement
   Experiments

   Double-slit experiment
   Davisson-Germer experiment
   Stern–Gerlach experiment
   EPR paradox · Popper's experiment Schrödinger's cat
   Equations

   Schrödinger equation
   Pauli equation
   Klein-Gordon equation
   Dirac equation
   Advanced theories

   Quantum field theory
   Quantum electrodynamics
   Quantum chromodynamics
   Quantum gravity
   Feynman diagram
   Interpretations

   Copenhagen · Quantum logic
   Hidden variables · Transactional
   Many-worlds · Ensemble
   Consistent histories · Relational
   Consciousness causes collapse
   Orchestrated objective reduction
   Scientists

   Planck · Schrödinger
   Heisenberg · Bohr · Pauli
   Dirac · Bohm · Born
   de Broglie · von Neumann
   Einstein · Feynman
   Everett · Others

   Paul Adrien Maurice Dirac, OM, FRS ( IPA: [dɪ'ræk]) ( August 8, 1902 –
   October 20, 1984) was a British theoretical physicist and a founder of
   the field of quantum mechanics. He held the Lucasian Professor of
   Mathematics at the University of Cambridge and spent the last ten years
   of his life at Florida State University. Among other key discoveries,
   he formulated the so-called " Dirac equation," which describes the
   behaviour of fermions and which led to the prediction of the existence
   of antimatter. Dirac shared the Nobel Prize in physics for 1933 with
   Erwin Schrödinger, "for the discovery of new productive forms of atomic
   theory."

Biography

Early years

   Paul Dirac was born in Bristol, England and grew up in the Bishopston
   area of the city. His father, Charles Dirac, was an immigrant from
   Saint-Maurice in the Canton of Valais, Switzerland and taught French
   for a living. His mother was originally from Cornwall and the daughter
   of a mariner. Paul had an elder brother, Felix, who committed suicide
   in March 1925, and a younger sister, Beatrice. His early family life
   appears to have been unhappy due to his father's unusually strict and
   authoritarian nature. He was educated first at Bishop Road Primary
   School and then at Merchant Venturers' Technical College (later Cotham
   Grammar School), where his father was a teacher. The latter was an
   institution, attached to the University of Bristol, that emphasized
   scientific subjects and modern languages. This was 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. He then decided that his true calling
   lay in the mathematical sciences and, after completing a degree in
   mathematics at Bristol in 1923, he received a grant to conduct research
   at St John's College, Cambridge, where he would remain for most of his
   career. At Cambridge, Dirac pursued his interests in the theory of
   general relativity (an interest he gained earlier as a student in
   Bristol) and in the nascent field of quantum physics, working under the
   supervision of Ralph Fowler.

Middle years

   Dirac noticed an analogy between the old Poisson brackets of classical
   mechanics and the recently-proposed quantization rules in Werner
   Heisenberg's matrix formulation of quantum mechanics. This observation
   allowed Dirac to obtain the quantization rules in a novel and more
   illuminating manner. For this work, published in 1926, he received a
   Ph.D. from Cambridge.

   In 1928, building on Wolfgang Pauli's work on non-relativistic spin
   systems, he proposed the Dirac equation as a relativistic equation of
   motion for the wavefunction of 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's equation also contributed to explaining the origin of quantum
   spin as a relativistic phenomenon.

   The necessity of electron matter being created and destroyed in Enrico
   Fermi's 1934 theory of beta decay, however, led to a reinterpretation
   of Dirac's equation as a "classical" field equation for any point
   matter of spin ħ/2, itself subject to quantization conditions involving
   anti- commutators. Thus reinterpreted, the Dirac equation is as central
   to theoretical physics as the Maxwell, Yang-Mills and Einstein field
   equations. Dirac is regarded as the founder of quantum electrodynamics,
   being the first to use that term. He also introduced the idea of vacuum
   polarization in the early 1930s.

   Dirac's Principles of Quantum Mechanics, published in 1930, is a
   landmark in the history of science. It quickly became one of the
   standard textbooks on the subject and is still used today. In that
   book, Dirac 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 to
   operators acting on the Hilbert space of vectors that describe the
   state of a physical system. The book also introduced the bra-ket
   notation and the delta function, which are now universally used.

   Guided by a comment in Dirac's textbook and by Dirac's 1933 article
   "The Lagrangian in quantum mechanics" (published in the Soviet journal
   Physikalische Zeitschrift der Sowjet Union), Richard Feynman developed
   the path integral formulation of quantum mechanics in 1948. This work
   would prove exceedingly useful in relativistic quantum field theory, in
   part because it is based on the Lagrangian, whose relativistic
   invariance is explicit, while the invariance is only implicit in the
   Hamiltonian formulation.

   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.

   He married Eugene Wigner's sister, Margit, in 1937. This took some
   courage on his part, because he was unused to solving problems that
   would not yield to reason. But once he had noted that the relapses in
   his favourable inclinations towards Margit were getting less and less
   as time went on, the matter was settled quickly. He adopted Margit's
   two children, Judith and Gabriel. Paul and Margit Dirac had two
   children together, daughters Mary Elizabeth and Florence Monica.

Later years

   Dirac was the Lucasian Professor of Mathematics at Cambridge from 1932
   to 1969. During World War II, he conducted important theoretical and
   experimental research on uranium enrichment by gas centrifuge. In 1937,
   he proposed a speculative cosmological model based on the so called "
   large numbers hypothesis." Dirac would write, "I am very disturbed by
   the situation because the so-called good theory quantum theory does
   involve neglecting infinities in an arbitrary way. This is not
   sensible. Sensible Mathematics involves neglecting a quantity when it's
   small; not because it's infinitely great and we do not want it." Dirac
   became unsatisfied with the renormalization approach to dealing with
   these infinities in quantum field theory and his work on the subject
   moved increasingly out of the mainstream. After having relocated to
   Florida in order to be near his elder daughter, Mary, Dirac spent his
   last ten years (both of life and as a physicist) at Florida State
   University (FSU) in Tallahassee, Florida.

   Amongst his many students was John Polkinghorne who recalls that Dirac
   "was once asked what was his fundamental belief. He strode to a
   blackboard and wrote that the laws of nature should be expressed in
   beautiful equations."

Death and afterwards

   In 1984 Dirac died in Tallahassee, Florida where he is buried. The
   Dirac-Hellman Award at FSU was endowed by Dr Bruce Hellman (Dirac's
   last doctoral student) in 1997 to reward outstanding work in
   theoretical physics by FSU researchers. The Dirac Prize is also awarded
   by the International Centre for Theoretical Physics in his memory. The
   Paul A.M. Dirac Science Library at FSU is named in his honour. In 1995,
   a plaque in his honour bearing his equation was unveiled at Westminster
   Abbey in London with a speech from Stephen Hawking. A commemorative
   garden, in his honour, has been established opposite the railway
   station in Saint-Maurice, Switzerland, the town of origin of his
   father's family.

Honours and tributes

   Paul Dirac shared the 1933 Nobel Prize for physics in with Erwin
   Schrödinger "for the discovery of new productive forms of atomic
   theory." Dirac was also awarded the Royal Medal in 1939 and both the
   Copley Medal and the Max Planck medal in 1952.

   He was elected a Fellow of the Royal Society in 1930, and of the
   American Physical Society in 1948.

   Immediately after his death, two organizations of professional
   physicists established annual awards in Dirac's memory. The Institute
   of Physics, the United Kingdom's professional body for physicists,
   awards the Paul Dirac Medal and Prize for "outstanding contributions to
   theoretical (including mathematical and computational) physics". The
   first three recipients were Stephen Hawking (1987), John Bell (1988),
   and Roger Penrose (1989). The Abdus Salam International Centre for
   Theoretical Physics (ICTP) awards the Dirac Medal of the ICTP each year
   on Dirac's birthday (August 8).

   The street on which the National High Magnetic Field Laboratory in
   Tallahassee, Florida, is located was named Paul Dirac Drive. There is
   also a road named after him in his home town of Bristol, UK. The BBC
   named its video codec Dirac in his honour. And in the popular British
   television show Doctor Who, the character Adric was named after him
   (Adric is an anagram of Dirac).

Personality

   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 replied, "I was
   taught at school never to start a sentence without knowing the end of
   it.". When asked about his views on poetry, he responded, "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".

   Eugene Wigner, Dirac's brother-in-law, once described Richard Feynman
   as "a second Dirac, only this time human".. It is suspected that Dirac
   may have suffered from Asperger syndrome.

   Dirac was also noted for his personal modesty. He called the equation
   for the time-evolution of a quantum-mechanical operator, which Dirac
   was in fact 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
   "Einstein statistics" for reasons, he explained, of "symmetry".

Religious Views

   Dirac did not believe in a personal God. He once said "God used
   beautiful mathematics in creating the world," but here he may have used
   "God" as a synonymous with nature.

   Werner Heisenberg recollects a friendly conversation among young
   participants at the 1927 Solvay Conference about Einstein and Planck's
   views on religion. Wolfgang Pauli, Heisenberg and Dirac took part in
   it. Dirac's contribution was a poignant and clear criticism of the
   political manipulation of religion, that was much appreciated for its
   lucidity by Bohr, when Heisenberg reported it to him later. Among other
   things, Dirac said: "I cannot understand why we idle discussing
   religion. If we are honest - and as scientists honesty is our precise
   duty - we cannot help but admit that any religion is a pack of false
   statements, deprived of any real foundation. The very idea of God is a
   product of human imagination. [...] I do not recognize any religious
   myth, at least because they contradict one another. [...]" Heisenberg's
   view was tolerant. Pauli had kept silent, after some initial remarks,
   but when finally he was asked for his opinion, jokingly he said: "Well,
   I'd say that also our friend Dirac has got a religion and the first
   commandment of this religion is 'God does not exist and Paul Dirac is
   his prophet.'" Everybody burst into laughter, also Dirac.

Legacy

   Paul Dirac is widely regarded as one of the greatest physicists of all
   time. He was one of the founders of quantum mechanics and quantum
   electrodynamics. Many physicist consider Dirac as the greatest
   physicist of 20th century. Physicist Antonino Zichichi, a professor of
   advanced physics at the University of Bologna, believe that Paul Dirac
   had a much bigger impact on modern science in the 20th century than
   Albert Einstein.

   The work of Dirac in the early Sixties proved extremely useful to
   modern practitioners of Superstring theory and its closely related
   successor, M-Theory.
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