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

When he was a boy, he spent many hours poring over the drawings in a book cal ed Ingenious Mechanisms and Mechanical Devices . He made adding machines and automatic pistols with gears and levers whittled from wood, and his blackboard il ustrations of the most foggy quantum paradoxes retained that ingenious flavor, as though the world were a wonderful silvery machine. Wheeler grew up in Ohio, the son of librarians and the nephew of three mining engineers. He went to col ege in Baltimore, got his graduate degree at Johns Hopkins University, and then won a National Research Council Fel owship that brought him to Copenhagen in 1934 via freighter (fifty-five dol ars one way) to study with Bohr.

He and Bohr worked together again, as col eagues this time, in the first months of 1939. Princeton had hired Wheeler and promoted the distinguished Hungarian physicist Eugene Wigner in a deliberate effort to turn toward nuclear physics. MIT had remained deliberately conservative about rushing to board the wagon train; Slater and Compton preferred to emphasize wel -roundedness and links to more applied fields. Not so Princeton. Wheeler stil remembered the magic of his first vision of radioactivity: how he had sat in a lightless room, staring toward the black of a zinc sulfide screen, counting the intermittent flashes of individual alpha particles sent forth by a radon source. Bohr, meanwhile, had left the growing tumult of Europe to visit Einstein’s institute in Princeton.

When Wheeler met his ship at the pier in New York, Bohr was carrying news about what would now rapidly become the most propitious object in physics: the uranium atom.

Compared to the hydrogen atom, stark kernel with which Bohr had begun his quantum revolution, the uranium atom was a monster, the heaviest atom in nature, bulked out with 92 protons and 140-odd neutrons, so scarce in the cosmos that hydrogen atoms outnumber it by seventeen tril ion to one, and unstable, given to decaying at quantum mechanical y unpredictable moments down a chain of lighter elements or—this was the extraordinary news that kept Bohr at his portable blackboard al through the North Atlantic voyage—splitting, when slugged by a neutron, into odd pairs of smal er atoms, barium and krypton or tel urium and zirconium, plus a bonus of new neutrons and free energy. How was anyone to visualize this bloated nucleus?

As a col ection of marbles sliding greasily against one another? As a bunch of grapes squeezed together by nuclear rubber bands? Or as a “liquid drop”—the phrase that spread like a virus through the world of physics in 1939

—a shimmering, jostling, oscil ating globule that pinches into an hourglass and then fissures at its new waist. It was this last image, the liquid drop, that enabled Wheeler and Bohr to produce one of those unreasonably powerful oversimplifications of science, an effective theory of the phenomenon that had been named, only in the past year, fission. (The word was not theirs, and they spent a late night trying to find a better one. They thought about splitting or mitosis and then gave up.)

By any reasonable guess, a liquid drop should have served as a poor approximation for the lumpy, raisin-

studded complex at the heart of a heavy atom, with each of two hundred–odd particles bound to each of the others by a strong close-range nuclear force, a force quite different from the electrical forces Feynman had analyzed on the scale of whole molecules. For smal er atoms the liquid-drop metaphor failed, but for large agglomerations like uranium it worked. The shape of the nucleus, like the shape of a liquid drop, depends on a delicate balance between the two opposing forces. Just as surface tension encourages a compact geometry in a drop, so do the forces of nuclear attraction in an atom. The electrical repulsion of the positively charged protons counters the attraction. Bohr and Wheeler recognized the unexpected importance of the slow neutrons that Fermi had found so useful at his laboratory in Rome. They made two remarkable predictions: that only the rarer uranium isotope, uranium 235, would fission explosively; and that neutron bombardment would also spark fission in a new substance, with atomic number 94

and mass 239, not found in nature and not yet created in the laboratory. To this pair of theoretical assertions would shortly be devoted the greatest technological enterprise the world had ever seen.

The laboratories of nuclear physics were spreading rapidly. Considerable American inventive spirit had gone into the development of an arsenal of machinery designed to accelerate beams of particles, smash them into metal foils or gaseous atoms, and track the col ision products through chambers of ionizing gas. Princeton had one of the nation’s first large “cyclotrons”—the name rang proudly of the future—completed in 1936 for the cost of a few automobiles. The university also kept smal er accelerators

working daily, manufacturing rare elements and new isotopes and generating volumes of data. Almost any experimental result seemed worthwhile when hardly anything was known. With al the newly cobbled-together equipment came difficulties of measurement and interpretation, often messy and ad hoc. A student of Wheeler’s, Heinz Barschal , came to him in the early fal of 1939 with a typical problem. Like so many new experimenters Barschal was using an accelerator beam to scatter particles through an ionizing chamber, where their energies could be measured. He needed to gauge the different energies that would appear at different angles of recoil. Barschal had realized that his results were distorted by the circumstances of the chamber itself. Some particles would start outside the chamber; others would start inside and run into the chamber’s cylindrical wal , and in neither case would the particle have its ful energy. The problem was to compensate, find a way to translate the measured energies into the true energies. It was a problem of awkward probabilities in a complicated geometry.

Barschal had no idea where to start. Wheeler said that he was too busy to think about it himself but that he had a very bright new graduate student …

Barschal dutiful y sought out Dick Feynman at the residential Graduate Col ege. Feynman listened but said nothing. Barschal assumed that would be the end of it.

Feynman was adjusting to this new world, much smal er, for a physicist, than the scientific center he had left. He shopped for supplies in the stores lining Nassau Street on the west edge of the campus, and an older graduate student, Leonard Eisenbud, saw him in the street. “You look

like you’re going to be a good theoretical physicist,”

Eisenbud said. He gestured toward Feynman’s new wastebasket and blackboard eraser. “You’ve bought the right tools.” The next time Feynman saw Barschal , he surprised him with a sheaf of handwritten pages; he had been riding on a train and had time to write out a ful solution. Barschal was overwhelmed, and Feynman had added another young physicist to the growing group of his peers with a weighty private appreciation for his ability.

Wheeler himself was already beginning to appreciate Feynman, who had been assigned to him—neither of them quite knew why—as a teaching assistant. Feynman had expected to be working with Wigner. He was surprised at their first meeting to see that his professor was barely older than he was. Then he was surprised again by Wheeler’s pointed display of a pocket watch. He took in the message.

At their second meeting he pul ed out a dol ar pocket watch of his own and set it down facing Wheeler’s. There was a pause; then both men laughed.

A Quaint Ceremonious Village

Princeton’s gentility was famous: the eating clubs, the arboreal lanes, the ersatz-Georgian carved stone and stained glass, the academic gowns at dinner and punctilious courtesies at tea. No other col ege so keenly delineated the social status of its undergraduates as Princeton did with its club system. Although the twentieth century had begun to intrude—the graduate departments were growing in stature, and Nassau Street had been