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This article is from the In-Depth Report Celebrating The Nobel Prizes

Profile: Yoichiro Nambu in 1995

Strings and gluons--The seer, this year's physics Nobel laureate, saw them all



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Editor's note: This story was originally posted in the February 1995 issue, and has been reposted to highlight the long intertwined history of the Nobel Prizes in Scientific American.

I first saw Yoichiro Nambu almost 10 years ago, from the back row of a graduate seminar in physics at the University of Chicago. A small man in a neat suit, he was sketching long, snaking tubes on the blackboard. Sometimes he said they were vortex lines, found in superconductors; other times he called them strings, connecting quarks. Mystified, and yet fascinated by a bridge between such disparate realms, I later asked him to be my thesis adviser.

Face to face, Nambu was still hard to understand. I was clearly not the first to try. Bruno Zumino of the University of California at Berkeley once recounted his own attempts: "I had the idea that if I can find out what Nambu is thinking about now, I'll be 10 years ahead in the game. So I talked to him for a long time. But by the time I fi- gured out what he said, 10 years had passed." Edward Witten of the Institute for Advanced Study in Princeton, N.J., explains: "People don't understand him, because he is so farsighted."

Nambu was the first to see that when a physical system such as a superconductor --or an ocean of quarks--defies the symmetry imposed by physical laws, a new particle is born. Along with Moo-Young Han, then a graduate student at Syracuse University, he proposed the existence of gluons, the objects that hold quarks together. He also realized that quarks act as if they are connected by strings, an idea that became the foundation of string theory. "Over the years," remarks Murray Gell- Mann of the Santa Fe Institute, "you could rely on Yoichiro to provide deep and penetrating insights on very many questions."

The roots of Nambu's originality may lie in a singular childhood in prewar Japan. Born in Tokyo in 1921, he was two when the city was destroyed by an earthquake. (He still has a vague recollection of flames.) Kichiro Nambu, his father, had run away from home to attend university and there had met his bride, Kimiko. The earthquake forced him to return to his hometown of Fukui, near Kyoto, with his wife and young son.

The prodigal was forgiven (although his wife never was). Retaining traces of defiance, Kichiro Nambu became a schoolteacher and built his house on the outskirts of town--an act that was later to save him from Allied bombs. From Tokyo he had brought back an eclectic library. Browsing there, his growing boy learned of ideas that allowed him to flee, at least mentally, the excruciating regimen at the local school.

Fukui, in those days, prided itself on having the most militaristic school in Japan. The boys dressed in scratchy army uniforms and were taught to march, shoot and salute. "If you didn't see a senior boy and so didn't salute him, he would punch you out," Nambu recalls. "You had to keep one eye on every person." At 4:00 A.M. in midwinter, he would walk a mile to school to learn Samurai sword fighting, barefoot on bare floors in unheated halls. To the frail child, school proved as trying as, later, the real Imperial army.

Nor did the school neglect the mind. Heroic deeds-- notably, that of a schoolteacher who died saving the emperor's picture from a fire--embellished the curriculum. Nambu was protected from such teachings by his father's antiestablishment diatribes. Yet they also prevented him from fitting in. "I had a longing to be like the other boys," he smiles ruefully. As he grew, he came to realize that his father's opinions were dangerous in an increasingly warlike Japan.

Thus, Nambu learned to keep his thoughts to himself. This trait served him well later, through years in the army--and perhaps even as a physicist. His originality might come from having to think everything through for himself, from being aware of, but ignoring, ideas in the world outside.

Moving on to a premier college in Tokyo in 1937, Nambu discovered a freer intellectual atmosphere and smart classmates who awed the country boy. Of his courses, physics caused him special trouble: "I couldn't understand entropy and flunked thermodynamics." Yet, possibly inspired by Hideki Yukawa, the pioneer who realized that particles transmit force, Nambu chose to aim for a master's in physics at Tokyo University.

Among his new classmates, he found some underground radicals. Japan was fighting China. "We were told of the victories, " Nambu says, "but these communists somehow also knew about the massacres and defeats." The academic program turned out to be short: the class graduated six months early so that its members could be drafted.

In the army Nambu dug trenches and carried boats. "Physically it was hard," he shrugs, "but inside I was free. As long as you said, 'Yes, sir, yes, sir,' they left you alone." After a year he was assigned to help develop shortwavelength radar. The navy already had such radar, but the army had no confidence in that equipment. Nor was Nambu's team especially successful: "To test our system, I set it up on a hilltop and hired a boat to take a metal rod out into the ocean. You could see it with your bare eyes--but not with our radar."

He was then ordered to steal a secret navy document, a paper on field theory by Sin- Itiro Tomonaga, who was applying his discoveries on particle waves to radar waveguides. (Werner Heisenberg's publications on field theory had arrived from Germany shortly before, after traveling by submarine for a year.) Obtaining these papers--simply by asking a professor--Nambu became acquainted with some of the newest ideas in physics.

Life was quite easy. The unit was housed in a golf club, and romance was budding between Nambu and his assistant, Chieko Hida. For the most part, the war seemed far away. Yet one night Nambu watched a fleet of B-29s fly over Osaka. For a change, they did not drop their bombs on the city but moved on to Fukui. Nambu lost his grandparents; his parents were spared.

After the war, Nambu and Hida married, whereupon he left for Tokyo to take up a long-promised research position. (Hida stayed on in Osaka to look after her mother.) Housing was scarce, and Nambu moved into his laboratory for three years. Gas and electricity were free, and he could bathe in the water basin intended for extinguishing air-raid fires. But his of- ficemate, Ziro Koba, a diligent young man (he once shaved his head for missing a calculation), would come in early and often embarrassed Nambu, who was sleeping across both their desks.

"I was hungry all the time," Nambu says. Finding food took up most of the week. For the rest, he thought about physics, calculating on rolls of cashregister paper. Koba, a student of Tomonaga, kept Nambu informed about the latter's work. A group of solid-state physicists in a neighboring office also provided stimulating company.

All that these researchers knew of scientific developments in the West came from sporadic issues of Time magazine. Later, journals in a library set up by the Occupation forces helped to fill in the gaps. Yet much had to be reinvented by the Japanese physicists. Sometimes they got there first. After moving to Osaka City University in 1949, Nambu published a formula describing how two particles bind, now known as the Bethe-Salpeter equation. Along with others, he also predicted that strange particles should be created in pairs, a discovery usually attributed to Abraham Pais.

Describing Nambu's early work, Laurie M. Brown of Northwestern University writes of its "exuberant sense of play." As his student, I enjoyed Nambu's sheer pleasure in ideas and his ready laugh (even if I did not always get the joke). In the belief that too much work is harmful, he urged me to attend baseball games and to read the exploits of V. I. Warshawski, the fictional Chicago sleuth.

In 1952 Nambu was invited to visit the Institute for Advanced Study. There he found many brilliant and aggressive young men. "Everyone seemed smarter than I. I could not accomplish what I wanted to and had a nervous breakdown," Nambu wrote to me decades later, trying to bring comfort during my own travails as a postdoctoral fellow. In 1957, after having moved to Chicago, he proposed a new particle and met with ridicule. ("In a pig's eye!" Richard Feynman shouted at the conference, Brown recalls. The omega was discovered the next year, in an accelerator.) Meanwhile Nambu had heard J. Robert Schrieffer describe the theory of superconductivity that he had just devised with John Bardeen and Leon N. Cooper. The talk disturbed Nambu: the superconducting fluid did not conserve the number of particles, violating an essential symmetry of nature. It took him two years to crack the puzzle.

Imagine a dog faced with two bowls of equally enticing food. Being identical, the bowls present a twofold symmetry. Yet the dog arbitrarily picks one bowl. Unable to accept that the symmetry is entirely lost, Nambu discovered that the dog, in effect, cannot make up her mind and constantly switches from one bowl to the other. By the laws of quantum physics, the oscillation comes to life as a new particle, a boson.

Nambu points out that others, such as Bardeen, Philip W. Anderson, then at Bell Laboratories, and Gerald Rickayzen, then at the University of Illinois, also saw that a superconductor should have such a particle. It was Nambu, however, who detailed the circumstances and significance of its birth and realized that the pion, as well, was born in like manner (by breaking the chiral, or leftright, symmetry of quarks). While he searched for more of its siblings in nature, Nambu circulated his findings in a preprint.

Jeffrey Goldstone, then a postdoctoral fellow at CERN, the European laboratory for particle physics, realized the import of this work and soon published a simpler derivation, noting that the result was general. Thereafter the new particle was dubbed the Goldstone boson. ("At the very least, it should be called the Nambu-Goldstone boson," Goldstone comments.) When Nambu finally published his calculations in 1960, his paper also showed how the initially massless particle mixes with a magnetic field in a superconductor to become heavy. Recognized by Anderson, Peter Higgs, then at the Institute for Advanced Study, and others as a general phenomenon, it later became the Higgs mechanism of the Standard Model of particle physics.

In the years that followed, Nambu studied the dynamics of quarks, suggesting they were held together by gluons carrying a color quantum number to and fro. "He did this in 1965, while the rest of us were floundering about," Gell-Mann says. (Nambu, however, believed the quarks to be observable and assigned them integer electrical charges, an error that Gell-Mann and others corrected.) In 1970, perusing a complex mathematical formula on particle interactions, Nambu saw that it described strings. In the 1980s his "string action" became the backbone of string theory.

"He has an amazing power of coming up with pictures," says Peter G. O. Freund, a colleague at Chicago. While working with Nambu, I noticed that he would look at a problem from several different, yet simultaneous, points of view. It was as if instead of one mind's eye he had at least two, giving him stereoscopic vision into physical systems. Where anyone else saw a flat expanse of meaningless dots, he could perceive vivid, three-dimensional forms leaping out.

Over time, Nambu became known as a seer, albeit a shy one. "I can think of no one who gives such good advice," Witten says. Pierre M. Ramond of the University of Florida observes that the directions of particle physics were often predicted by Nambu's papers--encrypted in the footnotes.

These days Nambu puzzles over how quarks acquire their diverse masses. He suggests they might come from historical accident, such as the quarks being born at different stages of the early universe. His thoughts have also turned to biology and to an old bane, entropy. Nambu calculates that virus-size particles, when placed in a cusp-shaped container, seem to violate gravity and entropy. Perhaps they conceal a clue as to how life-forms defy entropy and become ever more organized. Prophecy or quixotic fancy? Ten years from now, we might know.

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