Джеймс Глик - Genius - The Life and Science of Richard Feynman

The year before, Schrieffer had listened intently as Feynman delivered a pel ucid talk on the two phenomena: the problem he had solved, and the problem that had defeated him. Schrieffer had never heard a scientist outline in such loving detail a sequence leading to failure.

Feynman was uncompromisingly frank about each false step, each faulty approximation, each flawed visualization.

No tricks or fancy calculations would suffice, Feynman said. The only way to solve the problem would be to guess

the outline, the shape, the quality of the answer.

We have no excuse that there are not enough experiments, it has nothing to do with experiments. Our situation is unlike the field, say, of mesons, where we say, perhaps there aren’t yet enough clues for even a human mind to figure out what is the pattern. We should not even have to look at the experiments… . It is like looking in the back of the book for the answer …

The only reason that we cannot do this problem of superconductivity is that we haven’t got enough imagination.

It fel to Schrieffer to transcribe Feynman’s talk for journal publication. He did not quite know what to do with the incomplete sentences and the frank confessions. He had never read a journal article so obviously spoken aloud. So he edited it. But Feynman made him change it al back.

New Particles, New Language

In the mere half-decade since the triumph of the new quantum electrodynamics the culture of high-energy physics had made and remade itself again and again. The language, the interests, and the machinery seemed to undergo a new transformation monthly. Experimentalists and theorists assembled yearly for meetings cal ed Rochester conferences (after their initial site, Rochester, New York), descendants of the already mythic-seeming Shelter Island–Pocono–Oldstone meetings, but far larger and better financed, scores and then hundreds of participants. By the first of these meetings, at the close of 1950, quantum electrodynamics itself was already passé; it was so perfect experimental y and so far from the frontier of new forces and particles. That year had seen a kind of

milestone, the discovery of a new particle not in cosmic rays but in an experimentalist’s accelerator. This was a neutral pi meson, or pion—“neutral” because it carried no charge. Actual y, the experimenters did not so much detect the neutral pion as the pair of gamma rays into which it immediately decayed. This particle’s ephemerality made it less consequential in the everyday world of tables and chairs, chemistry and biology, than on this exciting frontier: it typical y vanished after a lifetime of a tenth of a mil ionth of a bil ionth of a second. This qualified as a short time by 1950 standards. Yet standards were changing. Within a few years particle tabulations would list this fleeting entity in the category of STABLE. And meanwhile the legions of cosmic-ray explorers, many of them British, hoisting their photographic plates skyward with bal oons, would find their specialty declining as spectacularly as it had risen.

“Gentlemen, we have been invaded,” one of their leaders declared. “The accelerators are here.”

Of necessity physicists dispensed with their earlier squeamishness about the prospect of adding yet another particle to the already rich stew. On the contrary, an experimentalist could hardly aspire to more than the creation and discovery of a new particle. What it meant to measure these particles had also changed dramatical y since the days when electrons had held center stage.

Inferring the mass of a particle from the arcing traces left in a cloud chamber by its second- and third-generation decay products was not so simple. An enormous range of error had to be tolerated. It had become a serious and worthwhile intel ectual chal enge merely to identify the particles, to name them, to write down the rules of which particles could decay into which other particles. These rules were pithy new equations: π + p →π0 + n, , a pion with negative charge and a proton produce a neutral pion and a neutron. Never mind assessing the mass; it was hard enough to identify the objects of study. Declaring the

existence or nonexistence of a certain particle became a delicate rite imbued with as much anticipation and judgment as declaring a rain delay at a basebal game.

This was the experimenters’ art, but, as the accelerator era began, Feynman took a special interest in the methodologies and pitfal s. He was influenced by Bethe, who always wanted to ground his theory in his own intuitions about the numbers, and by Fermi, the field’s last great combination of experimenter and theorist. Bethe spent time working out formulas for the probabilities of various wrong curvatures in cloud-chamber photographs.

One experimentalist, Marcel Schein, set off a typical commotion with the announcement that he had discovered a new particle in cyclotron experiments. Bethe was suspicious. The energies seemed far too low to produce the kind of particle Schein described. Feynman forever remembered the confrontation between the two men, their faces eerily il uminated by the glow from the light table used to view the photographic plates. Bethe looked at one plate and said that the gas of the cloud chamber seemed to be swirling, distorting the curvatures. In the next plate, and the next, and the next, he saw different sources of potential error. Final y they came to a clean-looking photograph, and Bethe mentioned the statistical likelihood of errors. Schein said that Bethe’s own formula predicted only a one-in-five chance of error. Yes, Bethe replied, and we’ve already looked at five plates. To Feynman, looking on, it seemed like classic self-deception: a researcher believes in the result he is seeking, and he starts to overweight the favorable evidence and underweight the possible counterexamples. Schein final y said in frustration: You have a different theory for every case, while I have a single hypothesis that explains al at once. Bethe replied, Yes, and the difference is that each of my many explanations is right and your one explanation is wrong.

A few years later Feynman happened to be visiting

Berkeley when experimenters excitedly thought they had discovered an antiproton—a particle clearly destined to be found at higher energies, but impossible, Feynman thought, at the mere hundreds of mil ions of electron volts available that year. As Bethe had, he went into a dark room to examine the photographs, a dozen questionable images and one that seemed absolutely perfect, the cornerstone of the discovery, with its track curving backward just as the antiparticle must.

There must be matter somewhere in the vacuum chamber, Feynman said.

Absolutely not, the experimenters told him—just thin glass wal s on either side.

Feynman asked what held the upper and lower plates together. They said there were four smal bolts.

He looked again at the white arc curving through the magnetic field. Then he jabbed his pencil down onto the table, inches away from the edge of the photograph. Right here, he said, must be one of those bolts.

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 Mil ikan, 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.