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But in Feynman’s tentative question the answer had emerged. Lee and Yang undertook an investigation of the evidence. For electromagnetic interactions and strong interactions, the rule of parity conservation had a real experimental and theoretical foundation. Without parity conservation, a well-entrenched framework would be torn apart. But that did not seem to be true for weak interactions. They went through an authoritative text on beta decay, recomputing formulas. They examined the recent experimental literature of strange particles. By the summer of 1956 they realized that, as far as the weak force was concerned, parity conservation was a free-floating assumption, bound neither to any experimental result nor to any theoretical rationale. Furthermore, it occurred to them that Gell-Mann’s conception of strangeness offered a precedent: a symmetry that held for the strong force and broke down for the weak. They quickly published a paper formally raising the possibility that parity might not be conserved by weak interactions and proposing experiments to test the question. By the end of the year, a team led by their Columbia colleague Chien Shiung Wu had set one of them up, a delicate matter of monitoring the decay of a radioactive isotope of cobalt in a magnetic field at a temperature close to absolute zero. Given an up and down defined by the alignment of the magnetic coil, the decaying cobalt would either spit out electrons symmetrically to the left and right or would reveal a preference. In Europe, awaiting the results, Pauli joined the wagerers: he wrote Weisskopf, “I do not believe that the Lord is a weak left-hander, and I am ready to bet a very large sum that the experiments will give symmetric results.” Within ten days he knew he was wrong, and within a year Yang and Lee had received one of the quickest Nobel Prizes ever awarded. Although physicists still did not understand it, they appreciated the import of the discovery that nature distinguished right from left in its very core. Other symmetries were immediately implicated—the correspondence between matter and antimatter, and the reversibility of time (if the film of an experiment were run backwards, for example, it might look physically correct except that right would be left and left would be right). As one scientist put it, “We are no longer trying to handle screws in the dark with heavy gloves. We are being handed the screws neatly aligned on a tray, with a little searchlight on each that indicates the direction of its head.”

Feynman made an odd presence at the high-energy physicists’ meetings. He was older than the bright young scientists of Gell-Mann’s generation, younger than the Nobel-wielding senators of Oppenheimer’s. He neither withdrew from the discussions nor dominated them. He showed a piercing interest in the topical issues—as with his initial prodding on the question of parity—but struck younger physicists as detached from the newest ideas, particularly in contrast to Gell-Mann. At the 1957 Rochester conference it occurred to at least one participant that Feynman himself should have applied his theoretical talents to the question he had raised a year earlier, instead of leaving the plum to Yang and Lee. (The same participant noticed a revisionists’ purgatory in the making: theorists from Dirac to Gell-Mann “busy explaining that they personally had never thought parity was anything special,” and experimenters recalling that they had always meant to get around to an experiment like Wu’s.) Publicly, Feynman was as serene as ever. Privately, he agonized over his inability to find the right problem. He wanted to stay clear of the pack. He knew he was not keeping up with even the published work of Gell-Mann and other high-energy physicists, yet he could not bear to sit down with the journals or preprints that arrived daily on his desk and piled up on his shelves and merely read them. Every arriving paper was like a detective novel with the last chapter printed first. He wanted to read just enough to understand