Paul Adrien Maurice Dirac, OM, FRS (pronounced /dɪˈɹæk/; 8 August 1902 – 20 October 1984) was a British theoretical physicist. 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 fourteen years of his life at Florida State University.
Among other discoveries, he formulated the 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."[2]
Early years
Paul Dirac was born in Bristol,[3] 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. His mother was originally from Cornwall and the daughter of a mariner. Paul had an elder brother, Félix, who committed suicide in March 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 School), where his father was a French teacher. The school was an institution attached to the University of Bristol, which 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 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, under the supervision of Ralph Fowler.
Career
Dirac noticed an analogy between the 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.[4] 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.[5] The positron was 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 fermions i.e. 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 particle of spin ħ/2, itself subject to quantization conditions involving anti-commutators. Thus reinterpreted as a (quantum) field equation accurately describing quarks and leptons i.e. all elementary matter particles, this Dirac field 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. This 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.
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,[6] he also included the bra-ket notation in the third edition of his book,[7] thereby contributing to its universal use nowadays.
In 1933, following his 1931 paper on magnetic monopoles, Dirac showed that the existence of a single magnetic monopole in the universe would suffice to explain the observed quantization of electrical charge. In 1975[8], 1982,[9] and 2009[10] [11] [12] intriguing results suggested the possible detection of magnetic monopoles, but there is, to date, no direct evidence for their existence.
Dirac was the Lucasian Professor of Mathematics at Cambridge from 1932 to 1969. In 1937, he proposed a speculative cosmological model based on the so-called large numbers hypothesis. During World War II, he conducted important theoretical and experimental research on uranium enrichment by gas centrifuge.
Dirac's quantum electrodynamics made predictions that were - more often than not - infinite and therefore unacceptable. A workaround known as renormalization was developed, but Dirac never accepted this. "I must say that I am very dissatisfied with the situation," he said in 1975, "because this so-called 'good theory' does involve neglecting infinities which appear in its equations, neglecting them in an arbitrary way. This is just not sensible mathematics. Sensible mathematics involves neglecting a quantity when it is small — not neglecting it just because it is infinitely great and you do not want it!"[13] His refusal to accept renormalization, resulted in his work on the subject moving increasingly out of the mainstream. After having relocated to Florida in order to be near his elder daughter, Mary, Dirac spent his last fourteen years (of both life and physics research) at the University of Miami in Coral Gables, Florida and Florida State University 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."[14]
Personal life
Dirac 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, both daughters, Mary Elizabeth and Florence Monica.
Margit, known as Manci, visited her brother in 1934 in Princeton from her native Hungary and, while at dinner at the Annex Restaurant (1930s–2006[15]), met the "lonely-looking man at the next table." This account came from a physicist from Korea who met and was influenced by Dirac, Y.S. Kim, who has also written: "It is quite fortunate for the physics community that Manci took good care of our respected Paul A.M. Dirac. Dirac published eleven papers during the period 1939-46.... Dirac was able to maintain his normal research productivity only because Manci was in charge of everything else."[16]
A reviewer of the 2009 biography writes: "Dirac blamed his [emotional] frailties on his father, a Swiss immigrant who bullied his wife, chivvied his children and insisted Paul spoke only French at home, even though the Diracs lived in Bristol. 'I never knew love or affection when I was a child,' Dirac once said." She also writes that "[t]he problem lay with his genes. Both father and son had autism, to differing degrees. Hence the Nobel winner's reticence, literal-mindedness, rigid patterns of behaviour and self-centredness. [Quoting the biography:] 'Dirac's traits as a person with autism were crucial to his success as a theoretical physicist: his ability to order information about mathematics and physics in a systematic way, his visual imagination, his self-centredness, his concentration and determination.'"[17]
Personality
Dirac was known among his colleagues for his precise and taciturn nature. When Niels Bohr complained that he did not 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."[18] He criticized the physicist J. Robert Oppenheimer's interest in poetry: "The aim of science is to make difficult things understandable in a simpler way; the aim of poetry is to state simple things in an incomprehensible way. The two are incompatible."[19]
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.[citation needed]
An anecdote recounted in a review of the 2009 biography tells of Werner Heisenberg and Dirac sailing on a cruise ship to a conference in Japan in August 1929. "Both still in their twenties, and unmarried, they made an odd couple. Heisenberg was a ladies' man who constantly flirted and danced, while Dirac—'an Edwardian geek', as [biographer] Graham Farmelo puts it—suffered agonies if forced into any kind of socialising or small talk. 'Why do you dance?' Dirac asked his companion. 'When there are nice girls, it is a pleasure,' Heisenberg replied. Dirac pondered this notion, then blurted out: 'But, Heisenberg, how do you know beforehand that the girls are nice?'"[17]
According to a story told in different versions, a friend or student visited Dirac, not knowing of his marriage. Noticing the visitor's surprise at seeing an attractive woman in the house, Dirac said, "This is... this is Wigner's sister". Margit Dirac told both George Gamow and Anton Z. Capri in the 1960s that her husband had actually said, "Allow me to present Wigner's sister, who is now my wife."[20][21]
Dirac was also noted for his personal modesty. He called the equation for the time evolution of a quantum-mechanical operator, which he was 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".[citation needed]
Religious views
Dirac once said: "God used beautiful mathematics in creating the world." 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, which was much appreciated for its lucidity by Bohr, when Heisenberg reported it to him later. Among other things, Dirac said:[1]
| “ |
I cannot understand why we idle discussing religion. If we are honest—and scientists have to be—we must admit that religion is a jumble of false assertions, with no basis in reality. The very idea of God is a product of the human imagination. It is quite understandable why primitive people, who were so much more exposed to the overpowering forces of nature than we are today, should have personified these forces in fear and trembling. But nowadays, when we understand so many natural processes, we have no need for such solutions. I can't for the life of me see how the postulate of an Almighty God helps us in any way. What I do see is that this assumption leads to such unproductive questions as why God allows so much misery and injustice, the exploitation of the poor by the rich and all the other horrors He might have prevented. If religion is still being taught, it is by no means because its ideas still convince us, but simply because some of us want to keep the lower classes quiet. Quiet people are much easier to govern than clamorous and dissatisfied ones. They are also much easier to exploit. Religion is a kind of opium that allows a nation to lull itself into wishful dreams and so forget the injustices that are being perpetrated against the people. Hence the close alliance between those two great political forces, the State and the Church. Both need the illusion that a kindly God rewards—in heaven if not on earth—all those who have not risen up against injustice, who have done their duty quietly and uncomplainingly. That is precisely why the honest assertion that God is a mere product of the human imagination is branded as the worst of all mortal sins. |
” |
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, including Dirac.[1]
Death and after
In 1984, Dirac died in Tallahassee, Florida where he is buried.[22]
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 Paul A.M. Dirac Science Library at FSU is named in his honour.
In 1995, a plaque in his honour bearing the Dirac 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
Dirac shared the 1933 Nobel Prize for physics with Erwin Schrödinger "for the discovery of new productive forms of atomic theory."[2] 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.
In 1975, Dirac gave a series of five lectures at the University of New South Wales which were subsequently published as a book, Directions of Physics (Wiley, 1978 – H. Hora and J. Shepanski, eds.). Dirac donated the royalties from this book to the University for the establishment of the Dirac Lecture Series.[23] The Silver Dirac Medal for the Advancement of Theoretical Physics is awarded by the University of New South Wales on the occasion of the Public Dirac Lecture.
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".[24] 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 (8 August). Also, the Dirac Prize is awarded by the International Centre for Theoretical Physics in his memory.
The street on which the National High Magnetic Field Laboratory in Tallahassee, Florida, is located was named Paul Dirac Drive. A second location on the Florida State University campus, the Paul A. M. Dirac Science Library, also bears his name. 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.
Legacy
Dirac is widely regarded as one of the world's greatest physicists. He was one of the founders of quantum mechanics and quantum electrodynamics.
His early contributions include the modern operator calculus for quantum mechanics, which he called transformation theory, and an early version of the path integral. He formulated a many-body formalism for quantum mechanics which allowed each particle to have its own proper time.
His relativistic wave equation for the electron was the first successful attack on the problem of relativistic quantum mechanics. Dirac founded quantum field theory with his reinterpretation of the Dirac equation as a many body equation, which predicted the existence of antimatter and matter–antimatter annihilation. He was the first to formulate quantum electrodynamics, although he could not calculate arbitrary quantities because the short distance limit requires renormalization.
In an attempt to solve the quantum divergence problem, Dirac gave a classical point particle theory combining advanced and retarded waves to eliminate the classical electron self-energy. Although these classical methods did not immediately solve the problems in quantum electrodynamics, they did lead John Archibald Wheeler and Richard Feynman to formulate an alternative Green's function description for light, which eventually led to Feynman's point particle formulation of quantum field theory.
Dirac discovered the magnetic monopole solutions, the first topological configuration in physics, and used them to give the modern explanation of charge quantization. He developed constrained quantization in the 1960s, identifying the general quantum rules for arbitrary classical systems.
Dirac's quantum-field analysis of the vibrations of a membrane, in the early 1960s, proved extremely useful to modern practitioners of superstring theory and its closely related successor, M-Theory.[25]
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 (the Dirac equation), which was also pioneered by him. This work does not 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.
- Lectures on Quantum Field Theory (1966): This book lays down the foundations of quantum field theory using the Hamiltonian formalism.
- General Theory of Relativity (1975): This 68-page work summarizes Einstein's general theory of relativity.
- The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom (2009): A comprehensive biography including a focus on the private side of Dirac's life. Written by Graham Farmelo, 539 pages.
See also
Notes
- ^ a b c Werner Heisenberg (1972). Physics and Beyond: Encounters and Conversations. New York: Harper & Row. ISBN 0061316229.
- ^ a b "The Nobel Prize in Physics 1933". The Nobel Foundation. http://nobelprize.org/nobel_prizes/physics/laureates/1933/. Retrieved 2007-11-24.
- ^ Register of births at Family Records Office
- ^ Dirac, P. A. M. (1928-02-01). "The Quantum Theory of the Electron". Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 117 (778): 610–624. doi:10.1098/rspa.1928.0023.
- ^ Dirac, Paul A. M. (1933-12-12). "Theory of Electrons and Positrons". The Nobel Foundation. http://nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-lecture.html. Retrieved 2008-11-01.
- ^ Paul Dirac, A New Notation for Quantum Mechanics, Proceedings of the Cambridge Philosophical Society, Vol. 35, p. 416 (1939)
- ^ François Gieres, Rep. Prog. Phys. 63:1893 (2000) arXiv
- ^ P. B. Price; E. K. Shirk; W. Z. Osborne; L. S. Pinsky (1975-08-25). "Evidence for Detection of a Moving Magnetic Monopole". Physical Review Letters (American Physical Society) 35 (8): 487–490. doi:10.1103/PhysRevLett.35.487.
- ^ Blas Cabrera (1982-05-17). "First Results from a Superconductive Detector for Moving Magnetic Monopoles". Physical Review Letters (American Physical Society) 48 (20): 1378–1381. doi:10.1103/PhysRevLett.48.1378.
- ^ "Magnetic Monopoles Detected In A Real Magnet For The First Time". Science Daily. 2009-09-04. http://www.sciencedaily.com/releases/2009/09/090903163725.htm. Retrieved 2009-09-04.
- ^ D.J.P. Morris, D.A. Tennant, S.A. Grigera, B. Klemke, C. Castelnovo, R. Moessner, C. Czter-nasty, M. Meissner, K.C. Rule, J.-U. Hoffmann, K. Kiefer, S. Gerischer, D. Slobinsky, and R.S. Perry (2009-09-03). "Dirac Strings and Magnetic Monopoles in Spin Ice Dy2Ti2O7". Science, DOI: 10.1126/science.1178868. http://dx.doi.org/10.1126/science.1178868. Retrieved 2009-09-04.
- ^ S. T. Bramwell, S. R. Giblin, S. Calder, R. Aldus, D. Prabhakaran & T. Fennell (2009-10-15). "Measurement of the charge and current of magnetic monopoles in spin ice". Nature, DOI: 10.1038/nature08500. http://www.nature.com/nature/journal/v461/n7266/full/nature08500.html. Retrieved 2009-10-15.
- ^ Helge Kragh (1990). Dirac: A Scientific Biography. Cambridge University Press. pp. 184. ISBN 0-521-38089-8-1. http://books.google.com/books?id=5ajhJGdL0J4C&pg=PA184. Retrieved 2008-06-08.
- ^ John Polkinghorne. 'Belief in God in an Age of Science' p2
- ^ "Last call at The Annex: Nassau Street institution closes doors after more than 70 years" by Sophia Ahern Dwosh with reporting by Euphemia Mu, The Daily Princetonian, 10 March 2006. Retrieved 2009-02-06.
- ^ "Wigner's Sisters" by Y. S. Kim, Department of Physics, University of Maryland, College Park, Maryland 20742, U.S.A.; written in 1995, article in Web site dedicated to Paul A. M. Dirac. Retrieved 2009-05-08.
- ^ a b "Anti-matter and madness: British physicist Paul Dirac had a brilliant mind, but the joys of daily life flummoxed him" Review of The Strangest Man by Graham Farmelo by Robin McKie, The Observer, 1 Feb. 2009. Retrieved 2009-02-06.
- ^ "Paul Adrien Maurice Dirac". University of St. Andrews. http://www-history.mcs.st-and.ac.uk/Printonly/Dirac.html. Retrieved 2007-11-24.
- ^ Kragh op. cit., 258, citing Jagdish Mehra (1972). "The Golden Age of Theoretical Physics: P. A. M. Dirac's Scientific Works from 1924–1933". in E. P. Wigner and Abdus Salam. Aspects of Quantum Theory. Cambridge: University Press. pp. 17–59. ISBN 0521086000.
- ^ George Gamow (1985). Thirty Years That Shook Physics: The Story of Quantum Theory (1966 ed.). Courier Dover Publications. pp. 121. ISBN 0-486-24895-X. http://books.google.com/books?id=L90_wY1VCW0C&pg=PA121. Retrieved 2008-06-08.
- ^ Anton Z. Capri (2007). Quips, Quotes, and Quanta: An Anecdotal History of Physics. World Scientific. pp. 148. ISBN 981-270-919-3. http://books.google.com/books?id=GfmR0mHxeZkC&pg=PA148. Retrieved 2008-06-08.
- ^ See this web site from Florida State University for his burial site. The gravesite for Dirac and his wife is located on the hill at the back of the cemetery.
- ^ "Public Dirac Lecture 2008". University of New South Wales. http://www.phys.unsw.edu.au/phys_news/Dirac.htm. Retrieved 2008-06-05.
- ^ "The Dirac Medal of the Institute of Physics". Institute of Physics. http://www.iop.org/activity/awards/Premier_Awards/The_Dirac_Medal_and_Prize/page_1731.html. Retrieved 2007-11-24.
- ^ Britain's answer to Einstein[1][dead link]
References
- The Second Creation: makers of the revolution in twentieth century physics by Robert P. Crease and Charles C. Mann, 1986 Macmillan Publishing, New York, 1996 (revised), Rutgers University Press. Entertaining personality-based history of particle physics/quantum mechanics in the twentieth century.
- QED and the men who made it: Dyson, Feynman, Schwinger, and Tomonaga by Silvan S. Schweber, Princeton University Press, 1994. Includes a chapter on Dirac as the founder of quantum electrodynamics.
- "Paul Adrien Maurice Dirac"
- The Strangest Man: the Life of Paul Dirac by Graham Farmelo, Faber and Faber, London 2009.
Further reading
Dirac videos
External links
- Dirac Medal of the International Centre for Theoretical Physics
- O'Connor, John J.; Robertson, Edmund F., "Paul Dirac", MacTutor History of Mathematics archive .
- Dirac Medal of the World Association of Theoretical and Computational Chemists (WATOC)
- The Paul Dirac Collection at Florida State University
- The Paul A. M. Dirac Collection Finding Aid at Florida State University
- Photocopies of Dirac's papers from the Florida State University collection, held under Dirac's name in the Archive Centre of Churchill College, Cambridge, UK
- Letters from Dirac (1932-36) and other papers, held in the Personal Papers archives of St John's College, Cambridge, UK
- Annotated bibliography for Paul Dirac from the Alsos Digital Library for Nuclear Issues
