Genius (53 page)

The blueprint, retrieved from the files and laid out over the photograph, showed that his pencil had found the exact spot. An ordinary proton had struck the bolt and scattered backward into the picture. Later, experimenters at Caltech felt that Feynman’s very presence exerted a sort of moral pressure on their findings and methods. He was mercilessly skeptical. He loved to talk about the famous oil-drop experiment of Caltech’s first great physicist Robert Millikan, which revealed the indivisible unit charge of the electron by isolating it in tiny, floating oil drops. The experiment was right but some of the numbers were wrong—and the record of subsequent experimenters stood as a permanent embarrassment to physics. They did not cluster around the correct result; rather, they slowly closed in on it. Millikan’s error exerted a psychological pull, like a distant magnet forcing their observations off center. If a Caltech experimenter told Feynman about a result reached after a complex process of correcting data, Feynman was sure to ask how the experimenter had decided when to stop correcting, and whether that decision had been made before the experimenter could see what effect it would have on the outcome. It was all too easy to fall into the trap of correcting until the answer looked right. To avoid it required an intimate acquaintanceship with the rules of the scientist’s game. It also required not just honesty, but a sense that honesty required exertion.

As the particle era unfolded, however, it made other demands of top theorists—whose ranks, meanwhile, were expanding. They had to demonstrate new kinds of flair in sorting through the relations between particles. They competed to invent abstract concepts to help organize the information arriving from accelerators. A new quantum number like isotopic spin—a quantity that seemed to be conserved through many kinds of interactions—implied new incarnations of symmetry. This notion increasingly dominated the physicists’ discourse. Symmetry for physicists was not far removed from symmetry for children with paper and scissors: the idea that something remains the same when something else changes. Mirror symmetry is the sameness that remains after a reflection of left and right. Rotational symmetry is the sameness that remains when a system turns on an axis. Isotopic spin symmetry, as it happened, was the sameness that existed between the two components of the nucleus, the proton and the neutron, two particles whose relationship had been oddly close, one carrying charge and the other neutral, their masses nearly but not exactly identical. The new way to understand these particles was this: They were two states of a single entity, now called a nucleon. They differed only in their isotopic spin. One was “up,” the other “down.”

Theorists of the new generation had not only to master the quantum electrodynamics set forth by Feynman and Dyson. They also had to arm themselves with a rococo repertoire of methods suited to the new territory. Physicists had long utilized exotic variations of the idea of
space
—imaginary spaces in which the axes might represent quantities other than physical distance. “Momentum space,” for example, allowed them to plot and to visualize a particle’s momentum as though it were merely another spatial variable. One grew comfortable with such spaces, and now they were multiplying. Isotopic spin space became essential to understanding the strong forces acting on nucleons.

Other concepts, too, had to become second nature. Symmetries suggested that various particles must come in families: pairs, or triplets, or (as physicists now said) multiplets. Physicists experimented with what they called “selection rules”—rules about what must or must not happen in particle collisions on account of the conservation of quantities like charge. A physicist Feynman’s age, Abraham Pais, guessed at a rule called “associated production”—certain collisions must produce new particles in groups, preserving some putative new quantum number, the nature of which was unknown. Feynman had had a similar idea in Brazil but had not liked it enough to pursue it diligently. For a few years associated production became an important catchphrase. Experimenters looked for examples or counterexamples. In the longer term its main contribution to physics was that its popularity rankled a younger theorist, Murray Gell-Mann. He thought Pais was wrong, and he was jealous.

Murray

At fourteen he had been declared “Most Studious” and “wonder boy” by his classmates at Columbia Grammar, a private school on the Upper West Side of New York, and that was the last they saw of him, for he was already a senior, and he started at Yale that fall. Gell-Mann’s surname was subtly difficult to pronounce. It was wrong to unstress the second syllable, as if the name were Gelman, although Murray’s older brother, Benedict, had chosen that simpler spelling. Many people leaned the other way, toward a pedantic, European style of pronunciation, the accent on the second syllable and the
a
broad:
gel
-MAHN. This, too, was wrong. Later, when he had secretaries, they sometimes upbraided malefactors: “He’s not German, you know.” Of course the
g
was hard, despite the unconscious tug of the soft
g
in the word
gel
. Natives of New York and other regions that distinguish between the
a
’s of
man
and
mat
suspected rightly that the second, flatter
a
must be better for Gell-Mann. It was safest to stress the two syllables almost equally. By then anyone who knew anything about Gell-Mann knew that his own pronunciation of names in any language was impeccable. Supposedly he would lecture visitors from Strasbourg or Pago Pago about the niceties of their own Alsatian or Samoan dialects. He was so insistent about differentiating the pronunciations of Colombia and Columbia that colleagues suspected him of straining to bring references to the country into conversations about the university. From the beginning most physicists simply referred to him as Murray. There was never any doubt which Murray they meant. Feynman, preparing for a cameo performance as a tribal chieftain in a Caltech production of
South Pacific
, taught himself a few words of Samoan and then resignedly told a friend, “The only person who will know I’m pronouncing this wrong is Murray.”

Gell-Mann attended Columbia Grammar on full scholarship. His father, born in Austria, had learned to speak a perfectly unaccented English and so, in the early 1920s, decided to start a language school for immigrants. It was the closest to success that he came, as his son saw it. The school moved several times—once, as Murray recalled, because his mother was afraid that his brother would catch whooping cough from someone in the building—and went out of business a few years later. It was his brother, nine years older and so adored by his parents, who taught him to read and to take pleasure in language, science, and art. Benedict was a bird-watcher and nature lover before nature became a practical field of interest; dropping out of college at the height of the Depression, he stunned his parents and left a complicated impression on his younger brother.

Murray did not find his way immediately to physics, talented as he was in so many subjects. When he applied to the Ivy League graduate schools, he was widely disappointed: Yale would take him only in mathematics, Harvard would take him only if he paid full fare, and Princeton would not take him at all. So he made a half-hearted application to MIT and heard directly back from Victor Weisskopf, whom he had not heard of. Gell-Mann decided to accept Weisskopf’s offer, though grudgingly. MIT seemed so lumpen. The joke he told ever after was that the alternatives did not commute: he could try MIT first and suicide second, whereas the other ordering would not work. He reached MIT in 1948, close to his nineteenth birthday, just in time to watch the exploding competition in quantum electrodynamics from the vantage point of an office near Weisskopf’s. When Weisskopf advised him that the future belonged to Feynman, he studied the available preprints. Feynman’s struck him as a cuckoo private language, though correct; Schwinger’s version struck him as hollow and pompous; Dyson’s as crude and sloppy. He was already inclined toward scabrous assessments of his famous fellow physicists, though for now he kept them mostly private.

His own work was not quite living up to his severe expectations, though he was finally beginning to impress other physicists. After a year at the Institute for Advanced Study he joined Fermi’s group at Chicago. He was in time to join the tumultuous effort to find the right concepts, the right ordering principles, the right quantum numbers for understanding the many new particles. There was confusion and there were regularities—coincidences in the experimental plots of particle masses and lifetimes. There were mesons that seemed to exist, and mesons that seemed plausible but absent. There were even more mysterious particles called V-particles. The problem with these enormously massive items was that particle accelerators produced them copiously, with relative ease, yet they did not decay with corresponding ease. They lingered for as long as a billionth of a second. Pais’s approach to associated production had reached toward the heart of some of the regularities in need of explanation. It contained the crucial idea of another hidden symmetry. It was also reaching a peak of popularity: in the summer of 1953 Pais created such a stir at an international conference in Japan that
Time
magazine called him at his hotel. His roommate answered the phone—it happened to be Feynman, attending the same conference to present his liquid helium results. Feynman felt a flicker of envy when he realized that
Time
had no interest in him. Gell-Mann, in Chicago, felt even more, particularly since he now saw a far more powerful answer.

Physicists had learned to speak comfortably about four fundamental forces: gravity; electromagnetism, which dominated all chemical and electrical processes; the strong force binding the atom’s nucleus; and the weak force, at work in the slow processes of radioactive decay. The quick appearance and slow disappearance of V-particles suggested that their creation relied on strong forces and that weak forces came into play as they decayed. Gell-Mann proposed a new fundamental quantity, which for a while he called
y
. This
y
was like a new form of charge. Charge is conserved in particle events—the total going in equals the total coming out. Gell-Mann supposed that
y
is conserved, too—but not always. The algebraic logic of Gell-Mann’s scheme decreed that strong interactions would conserve
y
, and so would electromagnetic interactions, but weak interactions would not. They would break the symmetry. Thus strong interactions would create a pair of particles whose
y
had to cancel each other (1 and – 1, for example). Such a particle, having flown away from its sibling, could not decay through a strong interaction because there was no longer a canceling
y
. That gave the slower weak interaction time to take over.

Artificial though it was, Gell-Mann’s
y
qualified as not just a description but an explanation. As he conceived his framework, it was an organizing principle. It gave him a way of seeing families of particles, and its logic was so compelling that the families had obvious missing members. He was able to predict—and did predict, in papers he began publishing in August 1953—specific new particles not yet discovered, as well as specific particles that he insisted could not be discovered. His timing was perfect. Experimenters bore out each of his positive predictions (and failed to contradict the negative ones). But this was only part of Gell-Mann’s triumph. He also injected a piece of his fascination with language into the temporarily befuddled business of physics nomenclature. He decided to call his quantity
y
“strangeness” and the families of V-like particles “strange.” A Japanese physicist, Kazuhiko Nishijima, who had independently hit upon the same scheme just months after Gell-Mann, chose the considerably less friendly name “?-charge.” Amid all the -
ons
and Greek-lettered particles,
strange
sounded whimsical and unorthodox. The editors of the
Physical Review
would not allow “Strange Particles” in Gell-Mann’s title, insisting instead on “New Unstable Particles.” Pais did not like it either. He pleaded with the audience at a Rochester conference to avoid loaded terms like “strange.” Why should a broad-minded theorist consider one particle stranger than another? The quirkiness of the word had a distancing effect: perhaps this new construct was not quite as
real
as charge. But Gell-Mann’s command of language had an unstoppable force. Strangeness was only the beginning.

The winter Fermi died, just before Christmas 1954, Gell-Mann wrote to the one physicist who seemed to him utterly genuine, free of phoniness, the one who did not worship formalism and superficialities, whose own work was always sure to be interesting and real. Some of Feynman’s colleagues were already beginning to think that he had drifted away from the mainstream of particle physics, but it did not seem that way to Gell-Mann. On the contrary, he knew from their few conversations that Feynman was thinking about all the outstanding problems, all the time. Feynman responded in a friendly way. Gell-Mann visited Caltech to give a talk on his current work. The two men met privately and spoke for hours. Gell-Mann described work he had done extending Feynman’s quantum electrodynamics at short distances. Feynman said he knew of the work and admired it enormously—that in fact it was the only such work he had seen that he had not already done himself. He had pursued Gell-Mann’s line of thinking and generalized it further—he showed what he meant—and Gell-Mann said he thought that was wonderful.