Julian Schwinger

A New York prodigy who read Dirac in the library

Julian Seymour Schwinger was born in Manhattan on the 12th of February, 1918, the second son of Ashkenazi Jewish parents who had come from Poland. His father Benjamin ran a garment business; his mother Belle ran the household. The Wall Street Crash of 1929 took much of the family’s money, but it did not touch the boy’s reading habit. By the time he entered the public-school system he was already the kind of student teachers learn to be careful around: precocious, fast, and largely uninterested in the parts of school that bored him.

He went to Townsend Harris High School in 1932, a free school for gifted boys housed on the campus of City College of New York. The library at City College stocked Physical Review, the American research journal, and the fourteen-year-old Schwinger started reading it. He worked his way through papers by Paul Dirac, the most forbiddingly abstract theorist of the day, and understood them. He published his first physics paper at seventeen. He had not yet finished his bachelor’s degree.

CCNY accepted every Townsend Harris graduate automatically, so in the fall of 1934 Schwinger walked across the courtyard from one to the other. His grades told two stories. In physics and mathematics he sailed. In English he sank, because he could not be bothered. His brother Harold, a CCNY graduate, asked an old classmate named Lloyd Motz to keep an eye on Julian. Motz was a physics instructor and a Columbia PhD candidate. He took one look at Julian’s notebooks and called Isidor Isaac Rabi at Columbia for help.

Julian Seymour Schwinger (; February 12, 1918 – July 16, 1994) was an American theoretical physicist. He shared the 1965 Nobel Prize in Physics with Richard Feynman and Shin'ichirō Tomonaga "for their fundamental work in quantum electrodynamics (QED), with deep-ploughing consequences for the physics of elementary particles". He developed a relativistically invariant perturbation theory, and renormalized QED to one loop order. Schwinger was a…

Rabi rescues him into Columbia

Rabi (later a Nobel laureate himself, the man who invented the magnetic-resonance method that lets us see hydrogen atoms in a brain scan) met Schwinger and instantly knew. The boy was the real thing. But CCNY’s transcript stood in the way of a Columbia scholarship: bad grades in subjects Schwinger had refused to study. Rabi did not give up. He grabbed an unpublished QED manuscript that Schwinger had written and waved it at Hans Bethe, the German theorist passing through New York. Bethe read the paper, said yes, this kid is serious, and the scholarship came through. Schwinger transferred to Columbia in the middle of his sophomore year. By 1936 he had his BA. By 1939, at twenty-one, he had his PhD, with Rabi as adviser.

During graduate school Rabi sent him on a travelling fellowship to visit Gregory Breit and Eugene Wigner. Schwinger, already a confirmed night-owl, took the trip as an opportunity to make the inversion total: he began working through the night and sleeping through the day. He kept the schedule for the rest of his life. He once said, with the deadpan honesty he was famous for, that the night shift was a way of avoiding being “dominated” by Breit and Wigner. If you keep opposite hours from your seniors, you have to think for yourself.

In the fall of 1939 he went west to Berkeley as a National Research Council fellow, working under J. Robert Oppenheimer. He stayed two years. By 1941 he had landed his first real faculty job, at Purdue.

Radar, then the magnetic moment of the electron

The Second World War scattered American physicists across two great projects, Los Alamos and the MIT Radiation Laboratory. Schwinger went to MIT, not Los Alamos. He worked on the theory of microwave waveguides for radar, a problem nobody romanticises but one that turned out to matter for his postwar physics. The mathematics of waveguides is the mathematics of boundary-value problems and Green’s functions, and Schwinger came out of the war with a fluency in those tools that almost no other theorist had.

He moved to Harvard in 1945, age twenty-seven. The next three years were the most productive stretch of his life. The Lamb shift, an experimental anomaly in hydrogen reported in 1947, made it obvious that the existing perturbation theory of quantum electrodynamics was inadequate: the corrections to the electron’s energy levels and magnetic moment came out infinite. Schwinger, drawing on his waveguide-era affection for Green’s functions, set up QED in a relativistically invariant way, isolated the infinities into the electron’s mass and charge, and showed that the finite leftover matched the experiment.

In a calculation he later asked to have engraved on his tombstone, he worked out the leading correction to the electron’s magnetic moment: the anomalous moment is α/2π, where α is the fine-structure constant. This number, roughly 0.00116, is one of the most precisely tested predictions in the history of science. The agreement between Schwinger’s theory and modern experiment now runs out to twelve decimal places. It is, by any sane standard, the best-confirmed quantitative prediction humans have ever made.

Julian Seymour Schwinger was born in New York City, to Ashkenazi Jewish parents, Belle (née Rosenfeld) and Benjamin Schwinger, a garment manufacturer, who had emigrated from Poland to the United States. 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. Julian's older brother Harold Schwinger was born in 1911, seven years before Julian who…

Schwinger and Feynman, two languages for the same physics

In 1948 the American Physical Society held a small conference at Pocono Manor in the Pennsylvania mountains. Schwinger spent most of a day at the blackboard, writing dense, formal equations in his slow careful hand. Then Richard Feynman got up and drew pictures: little squiggles and arrows that he called diagrams. Almost nobody in the room understood Feynman, and almost nobody could keep up with Schwinger. They were saying the same thing in different languages, and it took the young Freeman Dyson, working through the next year, to prove that the two formalisms gave identical answers. Tomonaga in Japan had developed a third version of the same calculation during the war, in isolation. The three of them shared the 1965 Nobel Prize.

Schwinger and Feynman could not have been more different in style. He worked in suit and tie, drove a Cadillac, lectured in elegant complete sentences without notes, and treated the algebra of local quantum fields with the reverence other people give to scripture. Feynman wore no tie, told dirty jokes, and trusted his diagrams to tell him what the physics was. Schwinger banned the diagrams from his Harvard classroom, not because he could not draw them (he understood them perfectly) but because he felt they tempted students to think in particles when they ought to be thinking in fields. “Like the silicon chip of more recent years,” he later wrote, “the Feynman diagram was bringing computation to the masses.” It was, for Schwinger, not quite a compliment.

Seventy-three students, four Nobels, and a pair of old shoes

For thirty years Schwinger held the most powerful seat in American theoretical physics, the Eugene Higgins chair at Harvard. In that time he supervised seventy-three doctoral dissertations, more than any other theoretical physicist of his generation. Four of his students went on to win Nobel Prizes of their own: Roy Glauber for quantum optics, Benjamin Mottelson for the structure of atomic nuclei, Sheldon Glashow for the electroweak theory, and Walter Kohn (in chemistry) for density-functional theory. Glashow’s prize was for an idea Schwinger had handed him: in 1957 Schwinger had been the first to suggest unifying electromagnetism and the weak nuclear force into a single broken gauge theory. Glashow worked out the SU(2) details, Weinberg and Salam brought it home, and the trio shared the 1979 Nobel.

His relationship with his colleagues was harder than his relationship with his students. Schwinger was a private man who pursued his own problems in his own way and resented faculty meetings, departmental politics, and the polite consensus of post-war physics. In the late 1960s he developed what he called source theory, a reformulation of quantum field theory designed to bypass the infinities of renormalization entirely. His Harvard colleagues thought he was chasing ghosts. The friction grew until 1972, when he resigned the Higgins chair and moved to UCLA. The story goes that Steven Weinberg, inheriting Schwinger’s old paneled office in the Lyman Laboratory, found a pair of worn shoes left under the desk, with the implied question: think you can fill these? Weinberg, ever generous, said the answer was no, and credited Schwinger for the inspiration that became effective field theory.

The last years, and a stubborn faith in cold fusion

Schwinger taught at UCLA from 1972 until his death. He kept publishing through his sixties and seventies, mostly elaborations of source theory. In 1989 Stanley Pons and Martin Fleischmann announced the discovery of cold fusion at the University of Utah. Within weeks the mainstream community had dismissed it. Schwinger, almost alone among Nobel laureates, did not. He thought the experiments deserved a careful theoretical look, wrote eight papers proposing mechanisms, and was so infuriated when the Physical Review refused to publish them that he resigned from the American Physical Society in protest. 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.” Whether or not the cold fusion idea was right (it almost certainly was not), the principle was the same one that had driven him in 1948. Trust the algebra. Do not trust the room.

He died of pancreatic cancer in Los Angeles on the 16th of July, 1994, aged seventy-six. He is buried at Mount Auburn Cemetery in Cambridge, Massachusetts. Above his name on the headstone is carved the symbol α/2π, the small fraction he calculated in 1948 that opened the modern era of precision physics.

What he means to the quantum story

Schwinger gave the theory of quantum electrodynamics its first complete, finite, relativistically invariant form, and in doing so showed every physicist after him how to extract sensible predictions from a field theory that, taken naively, gives infinity. Most working physicists today read Feynman and skip Schwinger, because Feynman is easier. But the calculations they do are Schwinger’s calculations, in Feynman’s notation, and the answer they trust to twelve decimal places is the one Schwinger first wrote down in the autumn of 1948.