Julian Seymour Schwinger (; February 12, 1918
– July 16, 1994) was a Nobel Prize winning
American theoretical physicist. He is best
known for his work on the theory of quantum
electrodynamics (QED), in particular for developing
a relativistically invariant perturbation
theory, and for renormalizing QED to one loop
order. Schwinger was a physics professor at
several universities.
Schwinger is recognized as one of the greatest
physicists of the twentieth century, responsible
for much of modern quantum field theory, including
a variational approach, and the equations
of motion for quantum fields. He developed
the first electroweak model, and the first
example of confinement in 1+1 dimensions.
He is responsible for the theory of multiple
neutrinos, Schwinger terms, and the theory
of the spin 3/2 field.
== Biography ==
Julian Seymour Schwinger was born in New York
City, to Jewish parents originally from Poland,
Belle (née Rosenfeld) and Benjamin Schwinger,
a garment manufacturer, who had migrated to
America. Both his father and his mother's
parents were prosperous clothing manufacturers,
although the family business declined after
the Wall Street Crash of 1929. The family
followed the Orthodox Jewish tradition. Schwinger
attended the Townsend Harris High School and
then the City College of New York as an undergraduate
before transferring to Columbia University,
where he received his B.A. in 1936 and his
Ph.D. (overseen by Isidor Isaac Rabi) in 1939
at the age of 21. He worked at the University
of California, Berkeley (under J. Robert Oppenheimer),
and was later appointed to a position at Purdue
University.
=== Career ===
After having worked with Oppenheimer, Schwinger's
first regular academic appointment was at
Purdue University in 1941. While on leave
from Purdue, he worked at the Radiation Laboratory
at MIT instead of at the Los Alamos National
Laboratory during World War II. He provided
theoretical support for the development of
radar. After the war, Schwinger left Purdue
for Harvard University, where he taught from
1945 to 1974. In 1966 he became the Eugene
Higgins professor of physics at Harvard.
Schwinger developed an affinity for Green's
functions from his radar work, and he used
these methods to formulate quantum field theory
in terms of local Green's functions in a relativistically
invariant way. This allowed him to calculate
unambiguously the first corrections to the
electron magnetic moment in quantum electrodynamics.
Earlier non-covariant work had arrived at
infinite answers, but the extra symmetry in
his methods allowed Schwinger to isolate the
correct finite corrections.
Schwinger developed renormalization, formulating
quantum electrodynamics unambiguously to one-loop
order.
In the same era, he introduced non-perturbative
methods into quantum field theory, by calculating
the rate at which electron-positron pairs
are created by tunneling in an electric field,
a process now known as the "Schwinger effect".
This effect could not be seen in any finite
order in perturbation theory.
Schwinger's foundational work on quantum field
theory constructed the modern framework of
field correlation functions and their equations
of motion. His approach started with a quantum
action and allowed bosons and fermions to
be treated equally for the first time, using
a differential form of Grassman integration.
He gave elegant proofs for the spin-statistics
theorem and the CPT theorem, and noted that
the field algebra led to anomalous Schwinger
terms in various classical identities, because
of short distance singularities. These were
foundational results in field theory, instrumental
for the proper understanding of anomalies.
In other notable early work, Rarita and Schwinger
formulated the abstract Pauli and Fierz theory
of the spin 3/2 field in a concrete form,
as a vector of Dirac spinors. In order for
the spin-3/2 field to interact consistently,
some form of supersymmetry is required, and
Schwinger later regretted that he had not
followed up on this work far enough to discover
supersymmetry.
Schwinger discovered that neutrinos come in
multiple varieties, one for the electron and
one for the muon. Nowadays there are known
to be three light neutrinos; the third is
the partner of the tau lepton.
In the 1960s, Schwinger formulated and analyzed
what is now known as the Schwinger model,
quantum electrodynamics in one space and one
time dimension, the first example of a confining
theory. He was also the first to suggest an
electroweak gauge theory, an SU(2) gauge group
spontaneously broken to electromagnetic U(1)
at long distances. This was extended by his
student Sheldon Glashow into the accepted
pattern of electroweak unification. He attempted
to formulate a theory of quantum electrodynamics
with point magnetic monopoles, a program which
met with limited success because monopoles
are strongly interacting when the quantum
of charge is small.
Having supervised 73 doctoral dissertations
, Schwinger is known as one of the most prolific
graduate advisors in physics. Four of his
students won Nobel prizes: Roy Glauber, Benjamin
Roy Mottelson, Sheldon Glashow and Walter
Kohn (in chemistry).
Schwinger had a mixed relationship with his
colleagues, because he always pursued independent
research, different from mainstream fashion.
In particular, Schwinger developed the source
theory, a phenomenological theory for the
physics of elementary particles, which is
a predecessor of the modern effective field
theory. It treats quantum fields as long-distance
phenomena and uses auxiliary 'sources' that
resemble currents in classical field theories.
The source theory is a mathematically consistent
field theory with clearly derived phenomenological
results. The criticisms by his Harvard colleagues
led Schwinger to leave the faculty in 1972
for UCLA. It is a story widely told that Steven
Weinberg, who inherited Schwinger's paneled
office in Lyman Laboratory, there found a
pair of old shoes, with the implied message,
"think you can fill these?". At UCLA, and
for the rest of his career, Schwinger continued
to develop the source theory and its various
applications.
After 1989 Schwinger took a keen interest
in the non-mainstream research of cold fusion.
He wrote eight theory papers about it. He
resigned from the American Physical Society
after their refusal to publish his papers.
He felt that cold fusion research was being
suppressed and academic freedom violated.
He wrote: "The pressure for conformity is
enormous. I have experienced it in editors'
rejection of submitted papers, based on venomous
criticism of anonymous referees. The replacement
of impartial reviewing by censorship will
be the death of science."
In his last publications, Schwinger proposed
a theory of sonoluminescence as a long distance
quantum radiative phenomenon associated not
with atoms, but with fast-moving surfaces
in the collapsing bubble, where there are
discontinuities in the dielectric constant.
The mechanism of sonoluminescence now supported
by experiments focuses on superheated gas
inside the bubble as the source of the light.Schwinger
was jointly awarded the Nobel Prize in Physics
in 1965 for his work on quantum electrodynamics
(QED), along with Richard Feynman and Shin'ichirō
Tomonaga. Schwinger's awards and honors were
numerous even before his Nobel win. They include
the first Albert Einstein Award (1951), the
U.S. National Medal of Science (1964), honorary
D.Sc. degrees from Purdue University (1961)
and Harvard University (1962), and the Nature
of Light Award of the U.S. National Academy
of Sciences (1949).
=== Schwinger and Feynman ===
As a famous physicist, Schwinger was often
compared to another legendary physicist of
his generation, Richard Feynman. Schwinger
was more formally inclined and favored symbolic
manipulations in quantum field theory. He
worked with local field operators, and found
relations between them, and he felt that physicists
should understand the algebra of local fields,
no matter how paradoxical it was. By contrast,
Feynman was more intuitive, believing that
the physics could be extracted entirely from
the Feynman diagrams, which gave a particle
picture. Schwinger commented on Feynman diagrams
in the following way,
Like the silicon chips of more recent years,
the Feynman diagram was bringing computation
to the masses.
Schwinger disliked Feynman diagrams because
he felt that they made the student focus on
the particles and forget about local fields,
which in his view inhibited understanding.
He went so far as to ban them altogether from
his class, although he understood them perfectly
well. The true difference is however deeper,
and it was expressed by Schwinger in the following
passage,
Eventually, these ideas led to Lagrangian
or action formulations of quantum mechanics,
appearing in two distinct but related forms,
which I distinguish as differential and integral.
The latter, spearheaded by Feynman has had
all the press coverage, but I continue to
believe that the differential viewpoint is
more general, more elegant, more useful.
Despite sharing the Nobel Prize, Schwinger
and Feynman had a different approach to quantum
electrodynamics and to quantum field theory
in general. Feynman used a regulator, while
Schwinger was able to formally renormalize
to one loop without an explicit regulator.
Schwinger believed in the formalism of local
fields, while Feynman had faith in the particle
paths. They followed each other's work closely,
and each respected the other. On Feynman's
death, Schwinger described him as
An honest man, the outstanding intuitionist
of our age, and a prime example of what may
lie in store for anyone who dares to follow
the beat of a different drum.
=== Death ===
Schwinger died of pancreatic cancer. He is
buried at Mount Auburn Cemetery;
α
2
π
{\displaystyle {\frac {\alpha }{2\pi }}}
is engraved above his name on his tombstone.
These symbols refer to his calculation of
the correction ("anomalous") to the magnetic
moment of the electron.
== See also ==
List of things named after Julian Schwinger
== Publications ==
Schwinger, J (1948). "On Quantum-Electrodynamics
and the Magnetic Moment of the Electron".
Phys. Rev. 73: 416–417. Bibcode:1948PhRv...73..416S.
doi:10.1103/PhysRev.73.416.
Schwinger, J (1948). "Quantum Electrodynamics.
I. A Covariant Formulation". Phys. Rev. 74:
1439–1461. Bibcode:1948PhRv...74.1439S.
doi:10.1103/PhysRev.74.1439.
Schwinger, J (1949). "Quantum Electrodynamics.
II. Vacuum Polarization and Self-Energy".
Phys. Rev. 75: 651–679. Bibcode:1949PhRv...75..651S.
doi:10.1103/PhysRev.75.651.
Schwinger, J (1949). "Quantum Electrodynamics.
III. The 
Electromagnetic Properties of the Electron
Radiative Corrections to Scattering". Phys.
Rev. 76: 790–817. Bibcode:1949PhRv...76..790S.
doi:10.1103/PhysRev.76.790.
Feshbach, H., Schwinger, J. and J. A. Harr.
"Effect of Tensor Range in Nuclear Two-Body
Problems", Computation Laboratory of Harvard
University, United States Department of Energy
(through predecessor agency the Atomic Energy
Commission) (November 1949).
Schwinger, J (1951). "On Gauge Invariance
and Vacuum Polarization". Phys. Rev. 82: 664–679.
Bibcode:1951PhRv...82..664S. doi:10.1103/PhysRev.82.664.
Schwinger, J. "On Angular Momentum", Harvard
University, Nuclear Development Associates,
Inc., United States Department of Energy (through
predecessor agency the Atomic Energy Commission)
(January 26, 1952).
Schwinger, J. "The Theory of Quantized Fields.
II", Harvard University, United States Department
of Energy (through predecessor agency the
Atomic Energy Commission) (1951).
Schwinger, J. "The Theory of Quantizied Fields.
Part 3", Harvard University, United States
Department of Energy (through predecessor
agency the Atomic Energy Commission) (May
1953).
Schwinger, J. Einstein's Legacy (1986). Scientific
American Library.
== References ==
== Further reading ==
Mehra, Jagdish, and Milton, Kimball A. (2000)
Climbing the Mountain: the scientific biography
of Julian Schwinger. Oxford University Press.
Milton, Kimball (2006-10-09). "Julian Schwinger:
Nuclear Physics, the Radiation Laboratory,
Renormalized QED, Source Theory, and Beyond".
Physics in Perspective. 9: 70–114. arXiv:physics/0610054.
Bibcode:2007PhP.....9...70M. doi:10.1007/s00016-007-0326-6.
Revised version published as (2007) "Julian
Schwinger: From Nuclear Physics and Quantum
Electrodynamics to Source Theory and Beyond,"
Physics in Perspective 9: 70-114.
Schweber, Silvan S. (1994). QED and the Men
Who Made It: Dyson, Feynman, Schwinger, and
Tomonaga. Princeton University Press. ISBN
0-691-03327-7.
Ng, Y. Jack, ed. (1996) Julian Schwinger:
The Physicist, the Teacher, and the Man. Singapore:
World Scientific. ISBN 981-02-2531-8.
Julian Seymour Schwinger (2000), Kimball A.
Milton, ed., A quantum legacy: seminal papers
of Julian Schwinger, World Scientific series
in 20th century physics, 26, World Scientific,
ISBN 978-981-02-4006-6
== External links ==
Nobel Museum Biography
O'Connor, John J.; Robertson, Edmund F., "Julian
Schwinger", MacTutor History of Mathematics
archive, University of St Andrews.
