Free My Life as a Quant by Emanuel Derman Page B

acronym for Junior Achiever, Somewhat Older Now—English for ex-wunderkind , I guess.
    In late 1969 I finally began my PhD thesis. Just at that time, the particle physics world I was entering was agog over two momentous new developments. First, experimentalists were discovering the earliest hints of the actual existence of quarks, and second, theorists were beginning to understand the origin of the subtle similarity between the weak and electromagnetic forces.
    Gell-Mann’s version of the Eightfold Way had predicted that the proton, the neutron, and all the other thus-far observed strongly interacting particles could in principle be made out of three smaller subparticles called quarks. Quarks, if they existed, had to be almost unbelievably peculiar; they had to carry a fractional electric charge of either one-third or two-thirds the charge of the proton, but no one had ever seen a particle of fractional charge. Although the Eightfold Way implied their existence, physicists were reluctant to take them seriously. Instead, avoiding the reality behind their mathematics, they had come to think of quarks as mathematically consistent but fictitious components that could never be observed. It was as though the only coins you had ever seen in circulation were nickels, dimes, and quarters, and you had concluded that somewhere there had to be a one-cent coin.
    If a proton really contained three hard little quarks deep inside it, one should be able to “see” them experimentally by shooting a fast electron at a proton and observing it recoil sharply when it struck a quark head-on. The method is a little like looking for bits of eggshell in a sponge cake—once in a while, as you chew, you hear a sharp crack as your teeth hit a fragment of shell.
    Robert Hofstadter, my cousin’s City College friend of the 1930s, had observed no such sharp recoils, and everyone had concluded that the proton was pure sponge and no eggshell. Hofstadter’s experiments, however, were limited. He had kept an eye only on the so-called elastic collisions, those in which the target proton remained intact as it recoiled like a struck billiard ball. Now, in the late 1960s, a later generation of physicists at the Stanford Linear Accelerator Center (SLAC) began to watch so-called inelastic electron-proton collisions in which the proton disintegrated rather than recoiled after being struck. Amazingly, in these collisions, many of the electrons did in fact recoil sharply, as though they had struck something very hard and small. Somewhere deep inside there truly were bits of eggshell.
    Feynman, from his base at Caltech in Pasadena, had developed a simple phenomenological picture of the proton as a closed bag of hard little quark-like constituents which he called its “partons.” In Feynman’s picture, the energetic electrons that scattered off the protons at SLAC provided a metaphorical X-ray view of the partons inside the proton, much as an ordinary X-ray or a CAT scan uses high-frequency radiation to provide a view of our internal organs. Using the information from the SLAC X-ray of the partons, one could calculate many other properties of the proton itself.
    More and more, we began to believe that protons, long thought of as unsplittable, might be composite—they might contain quarks. But this was not all that excited us; we were also increasingly becoming aware of the similarity between the weak and electromagnetic forces. Since the 1930s, physicists had been aware of an intriguing analogy between Maxwell’s 1873 theory of electricity and magnetism and Fermi’s 1934 theory of the weak force. However, no one had yet been able to extend this analogy into a consistent theory of the two forces. Then, in the 1960s, Glashow, Weinberg, and Salam, all working independently, accomplished this unification by creating what is now called the “standard model.” They based their theory on Yang’s symmetry principle of