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The parton model was oversimplified. It explained nothing that Bjorken could not explain, although Bjorken’s explanation seemed less fundamental. Partons required considerable hand-waving. Yet physicists clutched at them like a lifeboat. Three years passed before Feynman published a formal paper and many more before his partons finally and definitively blended with quarks in the understanding of physicists.

Zweig’s aces, Gell-Mann’s quarks, and Feynman’s partons became three paths to the same destination. These constituents of matter served as the quanta of a new field, finally making possible a field theory of the strong force. Quarks had not been seen or detected in the direct fashion of more venerable particles. They became real nonetheless. Feynman took on a project in 1970 with two students, assembling a vast catalog of particle data in an effort to make a judgment about whether a simple quark model could underlie it all. He chose an unconventional model once again, using data that let him think in terms of the electromagnetic field theory of the last generation, instead of the hadron-collision data that interested most theorists. For whatever reason, he was persuaded—converted into a quarkerian, as he said—although he continued to stress the tentativeness of any one model. “A quark picture may ultimately pervade the entire field of hadron physics,” this paper concluded. “About the paradoxes of the quark model we have nothing to add, except perhaps to make these paradoxes more poignant by exhibiting the mysteriously good fit of a peculiar model.” Younger theorists learned how to explain confinement—the quark’s inability to appear as free particles—in terms of a force that grew rapidly with distance, in strange contrast to forces such as gravity and electromagnetism. Quarks became real not only because ingenious experiments gave an indirect look at them, but because it became harder and harder for theorists to construct a coherent model in which they did not figure. They became so real that Gell-Mann, their inventor, had to endure the after-the-fact criticism that he had not fully believed in them. He never understood why Feynman had created his own alternative quark and maintained a distinction that faded in the end. He missed no opportunity to call Feynman’s particles “put-ons.” Like Schwinger years before, he disliked the fanfare over a picture that he thought was oversimplified—anyone could use it.

Quarks were real, at least to physicists of the last years of this century. Partons were not, in the end. What is real? Feynman tried to keep this question from disappearing into the background. In a book assembled from his lectures, Photon-Hadron Interactions, he concluded:

We have built a very tall house of cards making so many weakly based conjectures one upon the other… . Even if our house of cards survives and proves to be right we have not thereby proved the existence of partons… . On the other hand, the partons would have been a useful psychological guide … and if they continued to serve this way to produce other valid expectations they would of course begin to become “real,” possibly as real as any other theoretical structure invented to describe nature.

Once again Feynman had placed himself at the center of modern theoretical physics. His language, his framework, dominated high-energy physicists’ discourse for several years. He wanted to move on again, or so he told himself. “I’m a little bit frustrated,” he said to a historian soon after he published his first parton paper.

I’m tired of thinking of the same thing. I need to think of something else. Because I got stuck—see, if it would keep going it would be all right, but it’s hard to get any new results… . This parton thing has been so successful that I have become fashionable. I have to find an unfashionable thing to do.

Feynman routinely refused to recommend colleagues for the Nobel Prize, but he broke his rule in 1977—after Gell-Mann had already won the prize once—and quietly nominated