Paul Dirac Totally Explained

Everything about Paul Dirac totally explained

Paul Adrien Maurice Dirac, OM, FRS (August 8, 1902 – October 20, 1984) was a British theoretical physicist and a founder of the field of quantum mechanics. Dirac made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics. He held the Lucasian Chair of Mathematics at the University of Cambridge and spent the last ten years of his life at Florida State University. Among other discoveries, he formulated the so-called Dirac equation, which describes the behavior 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

Birth and education

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, Félix, who later committed suicide in the March of 1925, and a younger sister, Béatrice. 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 BA in applied mathematics at Bristol in 1923, he received a grant to conduct research at St John's College, Cambridge, where he'd 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 delta function. Following his 1939 article, he also included the bra-ket notation in the third edition of his book, thereby contributing to their universal use nowadays.
   In 1933 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's to date no convincing evidence for the existence of magnetic monopoles. However, in 1975, intriguing evidence of a moving magnetic monopole was announced by P. Buford Price based on the discovery by the lead researcher W.L. Wagner of ionization tracks in over 30 sheets of a particle detector that were equivalent to an electric charge of 137, the same as predicted by Dirac. No known particle plausibly explains those tracks.
   Dirac's extensive work was key to the development of quantum mechanics by the next generation of theorists, and in particular Schwinger, Feynman, Sin-Itiro Tomonaga and Dyson in their formulation of quantum electrodynamics.
   He married Eugene Wigner's sister, Margit, in 1937. 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 isn't sensible. Sensible Mathematics involves neglecting a quantity when it's small; not because it's infinitely great and we don't 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's buried. The Dirac-Hellmann Award at FSU was endowed by Dr Bruce P. Hellmann (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 honor. 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 has been established opposite the railway station in Saint-Maurice, Switzerland, the town of origin of his father's family.

Honours and awards

Dirac shared the 1933 Nobel Prize for physics with Erwin Schrödinger "for the discovery of new productive forms of atomic theory." The first three recipients were Stephen Hawking (1987), John Stewart 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".
Some psychologists, including Simon Baron-Cohen have speculated that Dirac may have suffered from Asperger syndrome, an autistic spectrum disorder, due to his taciturn nature, and logical rather than emotional mindset. Dirac himself wrote in his diary during his postgraduate years that he concentrated solely on his research, and only stopped on Sunday, when he took long strolls alone.
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". Jane Hawking, first wife of Stephen Hawking, remembered that Dirac introduced his wife Margit not by saying "This is my wife," but instead "This is Wigner's sister."

Religious views

Dirac had a characteristically balanced position on God. For some physicists "God" isn't a personal deity in the usual religious sense, but rather a metaphor for nature. Dirac once said "God used beautiful mathematics in creating the world".
   Here he used "God" as a metaphor for nature at the same time as adhering to his own rules for complete specificity and “never starting a sentence without knowing the end of it. The sentence can mean belief in God or belief in Nature or neither or both.
   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 can't understand why we idle discussing religion. If we're honest—and as scientists honesty is our precise duty—we can't 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 don't 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 doesn't exist and Paul Dirac is his prophet.'" Everybody burst into laughter, including Dirac.
   According to Margit Dirac, Paul's wife, he believed in an intelligent creator. Although an atheist early in life, he became a Christian later in life, attending church on Sundays.

Legacy

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 physicists consider Dirac the greatest physicist of the 20th century. Physicist Antonino Zichichi, a professor of advanced physics at the University of Bologna, believes that 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.

Selected bibliography

Principles of Quantum Mechanics (1930): This book summarizes the ideas of quantum mechanics using the modern formalism that was largely developed by Dirac himself. Towards the end of the book, he also discusses the relativistic theory of the electron (see Dirac equation) which was also pioneered by him. This work doesn't refer to any other writings then available on quantum mechanics.
Lectures on Quantum Mechanics (1966): Much of this book deals with quantum mechanics in curved space-time.
General Theory of Relativity (1975): This 68 page work summarizes Einstein's general theory of relativity.

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