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

Feynman and Welton, juniors, showed up in a room of excited-looking graduate students. When Morse saw them he demanded to know whether they were planning to register. Feynman was afraid they would be turned down, but when he said yes, Morse said he was relieved.

Feynman and Welton brought the total enrol ment to three.

The other graduate students were wil ing only to audit the

class. Like quantum mechanics, this was difficult new territory. No textbook existed. There was just one essential text for anyone studying nuclear physics in 1938: a series of three long articles in Reviews of Modern Physics by Hans Bethe, a young German physicist newly relocated to Cornel . In these papers Bethe effectively rebuilt this new discipline. He began with the basics of charge, weight, energy, size, and spin of the simplest nuclear particles. He moved on to the simplest compound nucleus, the deuteron, a single proton bound to a single neutron. He systematical y worked his way toward the forces that were beginning to reveal themselves in the heaviest atoms known.

As he studied these most modern branches of physics, Feynman also looked for chances to explore more classical problems, problems he could visualize. He investigated the scattering of sunlight by clouds— scattering being a word that was taking a more and more central place in the vocabulary of physicists. Like so many scientific borrowings from plain English, the word came deceptively close to its ordinary meaning. Particles in the atmosphere scatter rays of light almost in the way a gardener scatters seeds or the ocean scatters driftwood. Before the quantum era a physicist could use the word without having to commit himself mental y either to a wave or a particle view of the phenomenon. Light simply dispersed as it passed through some medium and so lost some or al of its directional character. The scattering of waves implied a general diffusion, a randomizing of the original directionality. The

sky is blue because the molecules of the atmosphere scatter the blue wavelengths more than the others; the blue seems to come from everywhere in the sky. The scattering of particles encouraged a more precise visualization: actual bil iard-bal col isions and recoils. A single particle could scatter another. Indeed, the scattering of a very few particles would soon become the salient experiment of modern physics.

That clouds scattered sunlight was obvious. Close up, each wavering water droplet must shimmer with light both reflected and refracted, and the passage of the light from one drop to the next must be another kind of diffusion. A wel -organized education in science fosters the il usion that when problems are easy to state and set up mathematical y they are then easy to solve. For Feynman the cloud-scattering problem helped disperse the il usion. It seemed as primitive as any of hundreds of problems set out in his textbooks. It had the childlike quality that marks so many fundamental questions. It came just one step past the question of why we see clouds at al : water molecules scatter light perfectly wel when they are floating as vapor, yet the light grows much whiter and more intense when the vapor condenses, because the molecules come so close together that their tiny electric fields can resonate in phase with one another to multiply the effect. Feynman tried to understand also what happened to the direction of the scattered light, and he discovered something that he could not believe at first. When the light emerges from the cloud again, caroming off bil ions of droplets, seemingly smeared

to a ubiquitous gray, it actual y retains some memory of its original direction. One foggy day he looked at a building far away across the river in Boston and saw its outline, faint but stil sharp, diminished in contrast but not in focus. He thought: the mathematics worked after al .

Feynman of Course Is Jewish

Feynman’s probing reached the edge of known science.

His scattering calculations had immediate application to a problem that was troubling one of his professors, Manuel S.

Val arta, concerning cosmic rays. These had become a major issue. Not just specialists but also the public worried about these unknown rays of unknown origin, streaming through space at high energies and entering the atmosphere, where they left trails of electric charge. This ionization first gave their presence away. It occurred to scientists just before the turn of the century that the atmosphere, left alone, ought not to conduct electricity. Now scientists were sending forth ray-detecting equipment on ships, aircraft, and bal oons al around the globe, but especial y in the neighborhood of Pasadena, California, where Robert Mil ikan and Carl Anderson had made the California Institute of Technology the nation’s focal point of cosmic ray research. Later it began to become clear that the term was a catchal for a variety of particles with different sources. In the thirties the detective work meant trying to understand which of the universe’s constituents

might emit them and which might influence their timing and direction as seen from earth. At MIT Val arta was puzzling over how cosmic rays might be scattered by the magnetic fields of the galaxy’s stars, just as cloud droplets scatter sunlight. Whether cosmic rays came from inside or outside the galaxy, should the scattering effect bias their apparent direction toward or away from the main body of the Milky Way? Feynman’s work produced a negative answer: neither. The net effect of the scattering was zero. If cosmic rays seemed to come from al directions, it was not because the stars’ interference disguised their original orientation. They wrote this up together for publication as a letter to the Physical Review —Feynman’s first published work. Unrevolutionary though the item was, its reasoning turned on a provocative and clever idea: that the probability of a particle’s emerging from a clump of scattering matter in a certain direction must be equivalent to the probability of an antiparticle’s taking the reverse path. From the antiparticle’s point of view, time was running backward.

Val arta let his student in on a secret of mentor-protégé publishing: the senior scientist’s name comes first.

Feynman had his revenge a few years later, when Heisenberg concluded an entire book on cosmic rays with the phrase, “such an effect is not to be expected according to Val arta and Feynman.” When they next met, Feynman asked gleeful y whether Val arta had seen Heisenberg’s book. Val arta knew why Feynman was grinning. “Yes,” he replied. “You’re the last word in cosmic rays.”

Feynman had developed an appetite for new problems—

any problems. He would stop people he knew in the corridor of the physics building and ask what they were working on. They quickly discovered that the question was not the usual smal talk. Feynman pushed for details. He caught one classmate, Monarch Cutler, in despair. Cutler had taken on a senior thesis problem based on an important discovery in 1938 by two professors in the optics laboratory. They found that they could transform the refracting and reflecting qualities of lenses by evaporating salts onto them, forming very thin coatings, just a few atoms thick. Such coatings became essential to reducing unwanted glare in the lenses of cameras and telescopes.

Cutler was supposed to find a way of calculating what happened when different thin films were applied, one atop another. His professors wondered, for example, whether there was a way to make exceedingly pure color filters, passing only light of a certain wavelength. Cutler was stymied. Classical optics should have sufficed—no peculiarly quantum effects came into play—but no one had ever analyzed the behavior of light passing through a parade of mostly transparent films thinner than a single wavelength. Cutler told Feynman he could find no literature on the subject. He did not know where to start. A few days later Feynman returned with the solution: a formula summing an infinite series of reflections back and forth from the inner surfaces of the coatings. He showed how the combinations of refraction and reflection would affect the phase of the light, changing its color. Using Feynman’s theory and many hours on the Marchant calculator, Cutler