A boy with Physical Review
Julian Seymour Schwinger was born on February 12, 1918, in Manhattan, New York City, the younger son of Benjamin Schwinger and Belle Rosenfeld. Both parents came from Ashkenazi Jewish families in the clothing trade, and the household followed Orthodox Jewish tradition. His father, who had emigrated from Poland, was a well-known designer of women’s clothes. The Depression cost him his business, and though other designers valued him enough to employ him, the family lived less comfortably than before.
Julian idolised his brother Harold, seven years older, who later became a successful lawyer and claimed to have taught Julian physics until he was thirteen. Julian discovered the subject first in Harold’s Encyclopaedia Britannica and then in the New York Public Library. As a teenager he was reading the latest research papers from Europe, including those of Paul Dirac, in the original journals. His first scientific paper appeared when he was about sixteen.
Rescued by Rabi
Schwinger depended on New York’s free public education. After Townsend Harris High School he entered the City College of New York, where he largely stopped attending lectures. In physics and mathematics he worked out the problems from first principles, often baffling his professors, but his grades in history, English and German were poor, and he might have failed out.
A City College instructor, Lloyd Motz, introduced him to the Columbia physicist Isidor Isaac Rabi. During a conversation between Rabi and Motz about the famous Einstein-Podolsky-Rosen paper, the young student joined in and resolved a difficulty. Rabi had him transferred to Columbia with a scholarship. Schwinger took his bachelor’s degree in 1936 and by 1937 had published seven papers, enough for a doctorate, which Columbia awarded in 1939 when he was twenty-one. One of these early papers laid foundations for the theory of nuclear magnetic resonance, the effect later used in MRI scanners. A winter in Wisconsin confirmed a lifelong habit of working through the night.
His early research was remarkably wide. During the winter of 1937 in Wisconsin he laid the groundwork for his prediction that the deuteron, the nucleus of heavy hydrogen, has an electric quadrupole moment, a slight departure from a perfectly round shape, which his experimental colleagues at Columbia confirmed independently a year later. At Berkeley, with Oppenheimer, he showed that an anomaly in the decay of fluorine could be explained by vacuum polarisation, the fleeting creation of electron-positron pairs, an insight that gave him a head start when quantum electrodynamics came to the fore. With William Rarita he also wrote a prescient paper on particles of spin 3/2 that became influential decades later.
Radar, not the bomb
After two years with J. Robert Oppenheimer at Berkeley and a teaching post at Purdue University, Schwinger joined the Radiation Laboratory at the Massachusetts Institute of Technology in 1943 to work on radar. Although he was seldom seen, going home in the morning as others arrived, he quickly became the laboratory’s theoretical leader. He developed powerful mathematical methods for designing waveguides and complicated microwave circuits, and expressed the results in quantities engineers could use. Radar was vital to the Allied victory, and his wartime lectures were later published as a textbook on electromagnetic radiation and waveguides.
Unlike most of his colleagues, he did not go to Los Alamos to build the atomic bomb. Later in life he most often explained this as moral repugnance: radar was a primarily defensive technology, while the bomb’s destructive power repelled him. As the war ended he turned to the design of new particle accelerators and worked out in detail the theory of synchrotron radiation, the intense light given off by electrons forced to travel in curves at nearly the speed of light, at a time when many physicists expected it to be negligible.
Taming quantum electrodynamics
In 1945 Harvard University appointed him associate professor, and in 1947 he became the youngest full professor on its faculty to that date. That year he married Clarice Carrol of Boston. A week before the wedding he attended the famous Shelter Island conference, where physicists heard of new experiments showing that the electron’s behaviour differed slightly from the predictions of Dirac’s theory. Existing theory could not calculate these small effects, because its equations produced infinite answers.
Schwinger found a way through. He showed how the infinities could be absorbed into the measured mass and charge of the electron, a procedure called renormalisation, and in late 1947 he calculated the first correction to the electron’s magnetism, a tiny extra amount equal to the fine-structure constant divided by 2π. It matched experiment. Richard Feynman and Sin-Itiro Tomonaga reached equivalent results by different routes, and the three shared the 1965 Nobel Prize in Physics for their fundamental work in quantum electrodynamics. The formula α/2π is engraved on his headstone in Mount Auburn Cemetery in Cambridge, Massachusetts.
Why it matters
Quantum electrodynamics, or QED, is the theory of how light and matter interact. It explains the behaviour of electrons and photons that underlies chemistry, electronics and lasers, and its predictions agree with experiment to better than a part in a billion, making it the most precisely tested theory in science. Its methods became the template for the Standard Model of particle physics. Schwinger himself proposed in 1957 that there are two different kinds of neutrino, later confirmed by experiment, and sketched an early model unifying the weak and electromagnetic forces that his student Sheldon Glashow developed further.
His practical legacy is just as real. His radar work contributed to a technology that had already helped save Britain and went on to serve the Allies throughout the war. His theory of synchrotron radiation describes the light produced by the synchrotron light sources now operating around the world, giant machines built since the 1980s that scientists use to study the structures of proteins and new materials.
The great teacher
In the late 1940s and 1950s Harvard was the centre of theoretical physics, and students and professors crowded into Schwinger’s lectures, which ranged brilliantly over electrodynamics, nuclear physics and quantum mechanics. He supervised about seventy-three doctoral students, among the most of any physicist. Four went on to win Nobel Prizes: Roy Glauber, Ben Mottelson, Sheldon Glashow and Walter Kohn, the last in chemistry. Many others became leaders in science and industry.
He was shy, private and disliked the limelight. He saw his large flock of students only one afternoon a week, but those admitted to his office were never rushed, were listened to with respect and treated with kindness, and often left with insights that kept them going for months. His biographer and former student Kimball Milton called him a very private yet wonderful human being.
Jewish background
Schwinger grew up in an Ashkenazi Jewish family that kept Orthodox traditions, part of the great community of Jewish immigrants and their children in New York’s garment trade. Like many of them, he owed his start to the city’s free schools and colleges, and to the Jewish physicist Rabi, himself an immigrant from Galicia, who recognised his gift and opened Columbia’s doors to him.
He did not write publicly about religion, and his life centred on physics. He is listed among Jewish Nobel laureates in physics by JINFO.org, which cites the Encyclopaedia Judaica.
Later years
In 1971 Schwinger left Harvard for the University of California, Los Angeles, partly for his health; he had taken up tennis, skiing and daily swimming. There he developed his own approach to particle physics, called source theory, which anticipated later effective field theories, and made lasting contributions to the theory of the Casimir effect. He received the first Albert Einstein Award in 1951, shared with Kurt Gödel, and the National Medal of Science in 1964.
In his final years he championed unpopular causes, including the possibility of cold fusion, and resigned from the American Physical Society after its journals refused his papers on the subject, writing that the pressure for conformity was enormous and that such censorship would be the death of science. Most physicists did not accept his cold fusion ideas. Julian Schwinger died of pancreatic cancer in Los Angeles on July 16, 1994, aged 76.
Legacy
Schwinger is less famous with the public than his co-laureate Feynman, partly because of his reserved nature and partly because his elegant mathematics was harder to popularise than Feynman’s diagrams. Yet equations bearing his name, such as the Rarita-Schwinger, Lippmann-Schwinger and Schwinger-Dyson equations, and many methods credited to others, run through modern physics.
His legacy reaches well beyond the blackboard: in the radar that helped win a war, in the synchrotron light used to study the molecules of life, in the precise theory of light and matter on which modern physics and technology rest, and in the generations of physicists he trained.
His rivalry with Feynman was one of style, not hostility. Schwinger favoured formal, powerful mathematics and banned Feynman diagrams from his own classes, joking that they brought computation to the masses. When Feynman died in 1988, Schwinger called him an honest man and the outstanding intuitionist of the age. He was also a sponsor of the Bulletin of the Atomic Scientists, which campaigns to reduce the dangers of nuclear weapons.
Sources & further reading
Julian Schwinger, Biographical, NobelPrize.org · Julian Schwinger (1918–1994), by K. A. Milton, arXiv · Julian Schwinger, Wikipedia · Jewish Nobel Prize Winners in Physics, JINFO.org · Researched from the sources above and checked against them. Spotted an error? Tell us.
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