Julian Seymour wrestler

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Julian S. Schwinger, 1965

Julian Seymour Schwinger (born February 12, 1918 in New York City , † July 16, 1994 in Los Angeles ) was one of the leading American theoretical physicists . Along with Richard P. Feynman and Sin-Itiro Tomonaga he received the 1965 physics - Nobel Prize "for their basic performance in quantum electrodynamics , with deep implications for particle physics ."

life and work

Schwinger had an early talent in the field of physics and mathematics. He studied at the City College of New York and at Columbia University in New York, where he received his doctorate under Isidor Isaac Rabi in 1939 . He then went to Robert Oppenheimer in Berkeley and also taught at Purdue University. In the 1930s he became one of the leading theorists in the field of nuclear physics, which was then “booming” . Even then he developed a preference for working at night when he was undisturbed. In nuclear physics, for example, he developed the effective-range theory in 1950. He derived the tensor component of nuclear forces from the quadrupole moment of the deuteron and studied their spin - isospin structure.

During the Second World War he worked at the "Radiation Lab" of the Massachusetts Institute of Technology on the radar project. He developed the theory of wave propagation in waveguides . He later successfully applied the variation methods developed in the process in quantum field theory and scattering theory (working with Lippmann, Physical Review 1950, " Lippmann-Schwinger equation "). His work on waveguides resulted in the book "Discontinuities in wave guides" in 1968 and in 2006 with Milton the book "Electromagnetic radiation - variational principles."

After the Second World War, he turned to quantum electrodynamics (QED) and was the first to derive the important predictions of the theory of the Lamb shift and the anomalous magnetic moment of the electron at the 1-loop level (1948). He continued these calculations in the early 1950s with his assistants Robert Karplus and Abraham Klein . The concept of renormalizing the QED essentially comes from him, but was also developed independently of Shin'ichirō Tomonaga in Japan. His "variation methods" were not as popular as Richard Feynman's diagram methods , but they were no less powerful. They could be described as “differential”, based on the differential equations for Green's functions , in contrast to Feynman's “integral” methods, where the Green function appears as a “propagator” in the integrand. The always polite Schwinger sometimes frowned when his students and staff used Feynman's more vivid methods, but ignored them. The keywords here are, for example, the Schwinger-Dyson equations .

In the long series of works “Theory of quantized fields” (Physical Review 1951–1954) he developed his approach to the quantum field theory (“quantum action principle”) and also introduced Grassmann variables and “ coherent states ” (which his student Glauber later examined and had already been discovered independently by Erwin Schrödinger in 1926).

He taught at Harvard University from 1945 to 1972 . His lectures in the 1940s to 1950s were legendary and he also formed a large school of theoretical physicists (unlike Feynman), including Nobel Prize winners Roy Jay Glauber , Ben Mottelson , Sheldon Glashow, and Walter Kohn . Other undergraduate and graduate students included Kenneth A. Johnson , Abraham Klein, Fritz Rohrlich , Laurie Brown , Stanley Deser , Bryce DeWitt , Richard Arnowitt , Gordon Baym , Jeremy Bernstein , Eugen Merzbacher , Roger G. Newton , Kimball Milton , Raymond Stora and Paul C. Martin . Robert Karplus did not do his doctorate with him, but was his student and assistant.

In the 1950s he was the first to point out the “Euclidean structure” hidden in the relativistic quantum field theory (Proceedings National Academy of Sciences 1958, 1959). This was mocked by Wolfgang Pauli (in the sense of the simplest application of complex numbers: rotation by 90 degrees by multiplication with "i"), but in retrospect it turned out to be an important observation - all calculations of the lattice range theories are in "Euclidean" continuation of the underlying Minkowski space carried out. There is such a connection between relativistic quantum field theories and classical statistical mechanics.

With his student Paul Martin, Schwinger laid the systematic foundations for a quantum field theoretical treatment of many-body systems of statistical mechanics. After Murray Gell-Mann and Francis Low , he also developed the Bethe-Salpeter equation for bound states, first in lectures at Harvard. He also dealt with the theory of diffraction in optics and acoustics with variation methods (work with Levine, Physical Review 1948, 1949) and the classical (and quantum theoretical) theory of accelerated electrical charges ( synchrotron radiation, etc., Physical Review 1949, but he came back to it several times later ).

In “Lectures on angular momentum” from 1952 he gave a “bosonization” (representation by harmonic oscillators) of the angular momentum algebra.

In several works in the late 1950s and early 1960s, he anticipated many important developments in elementary particle physics. He was one of the first to predict the existence of different types of neutrinos. Schwinger worked with William Rarita (1907–1999) in the early 1940s on the elucidation of the tensor nature of nuclear forces, with Rarita mainly doing the numerical work. As early as 1941 they jointly published the first quantum theory of spin 3/2 particles (later important in supergravity ), formulated in the Rarita-Schwinger equation . The Schwinger terms as commutator anomalies in quantum field theory are named after him (Physical Review Letters 1959).

According to his own statements (Selected works), in “Theory of fundamental interactions” he deals with charged heavy vector mesons, an early electroweak union theory (his student Glashow also carried out similar work in the early 1960s), chiral transformations, Higgs theory, vector-axial vector Theory. He found evidence of the chiral anomaly in quantum electrodynamics as early as 1951.

In Physical Review , Volume 125, 1962 and Volume 128, 1962 he developed an exactly solvable model of quantum field theory with dynamic mass generation (the Schwinger model is a two-dimensional QED with a massless Dirac spinor).

In the 1960s there was also work on magnetic monopoles , dyons (particles that carry both magnetic and electrical charges) and the quantum theory of gravitation.

Again and again he proved himself to be a master in the development of new formalisms, although he always attached great importance to close contact with experimentally observable things. His invention of "source theory" in the mid-1960s was also an attempt to focus on observable quantities in formalism. In his hands and those of his students, it turned out to be a powerful tool, but could not prevail overall (or is used as a "spectral representation"). He developed the theory in three books "Particles, sources and fields" 1970, 1973, 1989.

In 1972 he went to the University of California in Los Angeles .

In the 1970s he tried to give an interpretation of quantum mechanics with the help of "measurement algebra" ("Quantum kinematics and dynamics" 1970, "Quantum mechanics - symbolism of atomic measurements" 2001 (Englert ed.)). He and his students also deal with the most diverse problems (from “deep inelastic scattering” in the high-energy scattering experiments to the Casimir effect) with his “source theory”.

In the 1980s he worked, among other things, on the statistical theory of the atom (" Thomas Fermi theory ") and from 1989 also developed an interest in the work on " Cold Fusion " by Fleischmann and Pons, which later turned out to be flawed . Schwinger kept an open attitude to this area and tried to accommodate some publications. When these were rejected by leading journals, he saw it as unjustified censorship and resigned from the American Physical Society in protest. Another controversial area in which he was most recently active is the theory of sonoluminescence , which he tried to understand as the dynamic Casimir effect .

Schwinger had been married since 1947.

Memberships

In 1948 Schwinger was elected to the American Academy of Arts and Sciences . In 1949 he was accepted into the National Academy of Sciences .

Works

  • Classical Electrodynamics (The advanced book program) . Westview Pr., 1998
  • Selected papers . Reidel, 1979 (edited by Flato, Fronsdal, Milton, with a (very) short comment by Schwinger himself).
  • A quantum legacy - seminal papers of Julian Schwinger (editor Kimball Milton). World Scientific, 2000.
  • Einstein's legacy . Spektrum Verlag (popular, but nevertheless exact, book on relativity theory, first published in 1985).
  • as editor: Selected papers on Quantumelectrodynamics , dover (first 1957, the classical works by himself, Schwinger, Feynman).
  • QED - an individual view . In: J. Physics , Volume 43, 1982, and in L. Brown, Hoddeson: The birth of particle physics . 1983.
  • On Quantum Electrodynamics and the Magnetic Moment of the Electron . In: Phys. Rev. Band 73 , February 15, 1948, p. 416 , doi : 10.1103 / PhysRev.73.416 ( aps.org [PDF]).
  • On the spin of the neutron . In: Phys. Rev. Band 52 , December 15, 1937, p. 1250 , doi : 10.1103 / PhysRev.52.1250 ( ihep.su [PDF]).
  • On angular momentum , Technical Report, US Atomic Energy Commission 1952, online
  • Some of Schwinger's work in the Proceedings of the National Academy of Sciences is available on the PNAS website .

literature

  • Jack Ng (Ed.) Julian Schwinger , world scientific 1996 (with contributions from Freeman Dyson and Schwinger himself, in which he pays tribute to George Green, "The greening of quantum field theory - George Green and I").
  • Jagdish Mehra , Kimball Milton Climbing the mountain - the scientific biography of Julian Schwinger . Oxford 2000. Robert Finkelstein: Review. In: Cern Courier
  • Silvan S. Schweber QED and the men who made it , Princeton 1994
  • Silvan S. Schweber The sources of Schwingers Greens functions . In: Proc.Nat.Acad. , Volume 102, 2005, p. 7783.
  • Paul C. Martin, Sheldon Glashow, obituary in physics today October 1995.
  • Martin, glass show: Biographical Memoirs National Academy. (PDF) 2008
  • Jeremy Bernstein : A theory of everything . Springer, 1996 (with essay on Schwinger).
  • Gerjuoy: Memories of Julian Schwinger . In: Asian Journal of Physics , Volume 23, 2014, pp. 5–15, arxiv : 1412.1410

Web links

Commons : Julian Schwinger  - Collection of images, videos and audio files

Individual evidence

  1. ↑ Burt A. Folkart: Obituaries - Julian Schwinger; Nobel Physicist, Professor at Harvard and UCLA . In: Los Angeles Times . July 19, 1994 ( Julian Schwinger; Nobel Physicist, Professor at Harvard and UCLA [accessed February 5, 2018]).
  2. ↑ Physical Review , Volume 115, 1959
  3. ↑ published in Lawrence Biedenharn , van Dam “Selected Papers on the Quantum Theory of Angular Momentum”, Academic Press 1965
  4. ↑ Annals of Physics , Volume 2, 1957, p. 407
  5. ↑ Physical Review , Volume 82, 1951, p. 664.See Bertlmann: Anomalies in Quantum Field Theory , Clarendon Press 1996, p. 2
  6. ^ J. Zinn-Justin: Quantum Field Theory and Critical Phenomena , ISBN 0-19-851873-0
  7. ^ Members of the American Academy. Listed by election year, 1900–1949 (PDF). Retrieved October 11, 2015
  8. ^ Member Directory: Julian Schwinger. National Academy of Sciences, accessed December 10, 2015 (Biographical Memoir by Paul C. Martin and Sheldon L. Glashow ).
personal data
SURNAME Schwinger, Julian Seymour
BRIEF DESCRIPTION American physicist
DATE OF BIRTH February 12, 1918
PLACE OF BIRTH new York
DATE OF DEATH July 16, 1994
Place of death los Angeles