Genius (14 page)

In their spare time Feynman and Welton used the same machines to earn money through a Depression agency, the National Youth Administration, calculating the atomic lattices of crystals for a professor who wanted to publish reference tables. They worked out faster methods of running the calculator. And when they thought that they had their system perfected, they made another calculation: how long it would take to complete the job. The answer: seven years. They persuaded the professor to set the project aside.

Shop Men

MIT was still an engineering school, and an engineering school in the heyday of mechanical ingenuity. There seemed no limit to the power of lathes and cams, motors and magnets, though just a half-generation later the onset of electronic miniaturization would show that there had been limits after all. The school’s laboratories, technical classes, and machine shops gave undergraduates a playground like none other in the world. When Feynman took a laboratory course, the instructor was Harold Edgerton, an inventor and tinkerer who soon became famous for his high-speed photographs, made with a stroboscope, a burst of light slicing time more finely than any mechanical shutter could. Edgerton extended human sight into the realm of the very fast just as microscopes and telescopes were bringing into view the small and the large. In his MIT workshop he made pictures of bullets splitting apples and cards; of flying hummingbirds and splashing milk drops; of golf balls at the moment of impact, deformed to an ovoid shape that the eye had never witnessed. The stroboscope showed how much had been unseen. “All I’ve done is take God Almighty’s lighting and put it in a container,” he said. Edgerton and his colleagues gave body to the ideal of the scientist as a permanent child, finding ever more ingenious ways of taking the world apart to see what was inside.

That was an American technical education. In Germany a young would-be theorist could spend his days hiking around alpine lakes in small groups, playing chamber music and arguing philosophy with an earnest
Magic Mountain
volubility. Heisenberg, whose name would come to stand for the twentieth century’s most famous kind of uncertainty, grew enraptured as a young student with his own “utter certainty” that nature expressed a deep Platonic order. The strains of Bach’s D Minor Chaconne, the moonlit landscapes visible through the mists, the atom’s hidden structure in space and time—all seemed as one. Heisenberg had joined the youth movement that formed in Munich after the trauma of World War I, and the conversation roamed freely: Did the fate of Germany matter “more than that of all mankind”? Can human perception ever penetrate the atom deeply enough to see why a carbon atom bonds with two but never three oxygen atoms? Does youth have “the right to fashion life according to its own values”? For such students philosophy came first in physics. The search for meaning, the search for purpose, led naturally down into the world of atoms.

Students entering the laboratories and machine shops at MIT left the search for meaning outside. Boys tested their manhood there, learning to handle the lathes and talk with the muscular authority that seemed to emanate from the “shop men.” Feynman wanted to be a shop man but felt he was a faker among these experts, so easy with their tools and their working-class talk, their ties tucked in their belts to avoid catching in the chuck. When Feynman tried to machine metal it never came out quite right. His disks were not quite flat. His holes were too big. His wheels wobbled. Yet he understood these gadgets and he savored small triumphs. Once a machinist who had often teased him was struggling to center a heavy disk of brass in his lathe. He had it spinning against a position gauge, with a needle that jerked with each revolution of the off-kilter disk. The machinist could not see how to center the disk and stop the tick-tick-tick of the needle. He was trying to mark the point where the disk stuck out farthest by lowering a piece of chalk as slowly as he could toward the spinning edge. The lopsidedness was too subtle; it was impossible to hold the chalk steady enough to hit just the right spot. Feynman had an idea. He took the chalk and held it lightly above the disk, gently shaking his hand up and down in time with the rhythm of the shaking needle. The bulge of the disk was invisible, but the rhythm wasn’t. He had to ask the machinist which way the needle went when the bulge was up, but he got the timing just right. He watched the needle, said to himself,
rhythm
, and made his mark. With a tap of the machinist’s mallet on Feynman’s mark, the disk was centered.

The machinery of experimental physics was just beginning to move beyond the capabilities of a few men in a shop. In Rome, as the 1930s began, Enrico Fermi made his own tiny radiation counters from lipstick-size aluminum tubes at his institute above the Via Panisperna. He methodically brought one element after another into contact with free neutrons streaming from samples of radioactive radon. By his hands were created a succession of new radioactive isotopes, substances never seen in nature, some with half-lives so short that Fermi had to race his samples down the corridor to test them before they decayed to immeasurability. He found a nameless new element heavier than any found in nature. By hand he placed lead barriers across the neutron stream, and then, in a moment of mysterious inspiration, he tried a barrier of paraffin. Something in paraffin—hydrogen?—seemed to slow the neutrons. Unexpectedly, the slow neutrons had a far more powerful effect on some of the bombarded elements. Because the neutrons were electrically neutral, they floated transparently through the knots of electric charge around the target atoms. At speeds barely faster than a batted baseball they had more time to work nuclear havoc. As Fermi tried to understand this, it seemed to him that the essence of the process was a kind of diffusion, analogous to the slow invasion of the still air of a room by the scent of perfume. He imagined the path they must be taking through the paraffin, colliding one, two, three, a hundred times with atoms of hydrogen, losing energy with each collision, bouncing this way and that according to laws of probability.

The neutron, the chargeless particle in the atom’s core, had not even been discovered until 1932. Until then physicists supposed that the nucleus was a mixture of electrically negative and positive particles, electrons and protons. The evidence taken from ordinary chemical and electrical experiments shed little light on the nucleus. Physicists knew only that this core contained nearly all the atom’s mass and whatever positive charge was needed to balance the outer electrons. It was the electrons—floating or whirling in their shells, orbits, or clouds—that seemed to matter in chemistry. Only by bombarding substances with particles and measuring the particles’ deflection could scientists begin to penetrate the nucleus. They also began to split it. By the spring of 1938 not just dozens but hundreds of physics professors and students were at least glancingly aware of the ideas leading toward the creation of heavy new elements and the potential release of nuclear energies. MIT decided to offer a graduate seminar on the theory of nuclear structure, to be taught by Morse and a colleague.

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 enrollment to three. The other graduate students were willing 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 Cornell. 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 systematically 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 mentally 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 all 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 billiard-ball collisions 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 well-organized education in science fosters the illusion that when problems are easy to state and set up mathematically they are then easy to solve. For Feynman the cloud-scattering problem helped disperse the illusion. 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 all: water molecules scatter light perfectly well 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 billions of droplets, seemingly smeared to a ubiquitous gray, it actually 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 still sharp, diminished in contrast but not in focus. He thought: the mathematics worked after all.

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. Vallarta, 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 balloons all around the globe, but especially in the neighborhood of Pasadena, California, where Robert Millikan 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 catchall 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 Vallarta 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 all 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.

Vallarta 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 Vallarta and Feynman.” When they next met, Feynman asked gleefully whether Vallarta had seen Heisenberg’s book. Vallarta 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 small 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 also found a way to make the color filters his professors wanted.