Genius_ The Life and Science of Richard Feynman - James Gleick [234]
Once again Gell-Mann trusted his scheme enough to predict, as a consequence of broken symmetry, a specific hitherto-unseen particle. This, the omega minus, duly turned up in 1964—a thirty-three-experimenter team had to canvass more than one million feet of photographs—and Gell-Mann’s Nobel Prize followed five years later.
His next, most famous invention came in an effort to add explanatory understanding to the descriptive success of the Eightfold Way. SU(3) should have had, along with its various eight-member and ten-member and other families, a most-basic three-member family. This seemed a strange omission. Yet the rules of the group would have required this threesome to carry fractional electric charges: ? and – ?. Since no particle had ever turned up with anything but unit charge, this seemed implausible even by modern standards. Nevertheless, in 1963 Gell-Mann and, independently, a younger Caltech theorist, George Zweig, proposed it anyway. Zweig called his particles aces. Gell-Mann won the linguistic battle once again: his choice, a croaking nonsense word, was quark. (After the fact, he was able to tack on a literary antecedent when he found the phrase “Three quarks for Muster Mark” in Finnegans Wake, but the physicist’s quark was pronounced from the beginning to rhyme with “cork.”)
It took years for Gell-Mann and other theorists to generate all the contrivances needed to make quarks work. One contrivance was a new property called color—purely artificial, with no connection to everyday color. Another was flavor: Gell-Mann decided that the flavors of quarks would be called up, down, and strange. There had to be antiquarks and anticolors. A new mediating particle called the gluon would have to carry color from one quark to another. All this encouraged skepticism among physicists. Julian Schwinger wrote that he supposed such particles would be detected by “their palpitant piping, chirrup, croak, and quark.” Zweig, far more vulnerable than Gell-Mann, felt that his career was damaged. The quark theorists had to wrestle with the fact that their particles never appeared anywhere, though people did begin a dedicated search in particle accelerators and supposed cosmic-ray deposits in undersea mud.
There was a reality problem, distinctly more intense than the problem posed by more familiar entities such as electrons. Zweig had a concrete, dynamical view of quarks—too mechanistic for a community that had learned as far back as Heisenberg to pay attention only to observables. Gell-Mann’s comment to Zweig was, “The concrete quark model—that’s for blockheads.” Gell-Mann was wary of the philosophical as well as the sociological problem created by any assertion one way or the other about quarks being real. For him quarks were at first a way of making a simple toy field theory: he would investigate the theory’s properties, abstract the appropriate general principles, and then throw away the theory. “It is fun to speculate about the way quarks would behave if they were physical particles of finite mass (instead of purely mathematical entities as they would be in the limit of infinite mass),” he wrote. As if they were physical particles; then again, as if they were conveniences of mathematics. He encouraged “a search for stable quarks”—but added with one more twist that it “would help reassure us of the nonexistence of real quarks.” His initial caveats were quoted by commentators again and again in the years that followed. One physicist’s typically uncharitable interpretation: “I always considered that to be a coded message. It seemed to say, ‘If quarks are not found, remember I never said they would be; if they are found, remember