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

In this first report the agent tried diligently to understand the exculpatory opinion of the informant that “this was not indicative of any criminal tendencies on the part of Feynman but was merely one of the works of a bril iant mathematical mind chal enged by a device considered practical y impossible of solution by an ordinary individual.”

Nevertheless, the suggestive combination of opened safes containing atomic secrets and socialized with Klaus Fuchs proved irresistible to the anonymous authors of memorandums, special inquiries, and secret airtels that swel ed Feynman’s file for years to come.

The bureau monitored one other incident with particular interest. The Soviet Academy of Sciences invited Feynman to a conference in Moscow, where he would have had a chance to meet the great Lev Landau and other Russian

physicists. Nuclear physics, particularly in its sensitive guises, was not on the agenda. Stil , the cream of Soviet physics was engaged in a weapons program quickly catching up with the Americans’. That year the Russians exploded an advanced, portable thermonuclear bomb over Siberia. (One of its principal architects, the future dissident Andrei Sakharov, watched from a platform on the snowy steppe, miles from ground zero. Having read an American primer cal ed the black book, he decided it would be safe to remove his dark goggles.) Feynman accepted the invitation enthusiastical y, the Soviet Academy having offered to cover his travel expenses. Then he had second thoughts. He wrote a careful letter to the AEC to ask for the government’s advice. “I thought you would be interested,”

he said, “because I was connected to the Los Alamos project during the war, so the danger that I might not be able to return, or the attitude of public opinion must be considered.” After a delay, officials at both the commission and the State Department replied, asking him to turn the Soviets down. His presence might be exploited for

“propaganda gains.” Feynman acquiesced. He wrote the head of the Soviet Academy that “circumstances have arisen which make it impossible for me to attend.” The government also forced Freeman Dyson to withdraw, warning him that under the McCarran Immigration Act he might not be al owed back into the United States. Dyson did not surrender so quietly, however. He told newspaper reporters, “This is a clear case in which the law has been proved stupid.”

In their basic, nonweapons research, Russian physicists eagerly pursued the latest developments in the United States and Europe. Yet a faint difference in outlook between East and West was already unfolding. The triumph of the atomic bomb had been an American triumph, had won the American war, and had not ingrained itself so firmly into the Soviet psyche (obsessed though policymakers

were with the arms race). Although an international-class synchrocyclotron went up in Dubno, money was not so readily available for giant particle accelerators of the kind now under construction in the United States. And the most influential single figure in Soviet physics was Landau, famous for the catholicity of his interests across the whole breadth of phenomena that could be cal ed theoretical physics. He had devoted his greatest work not to elementary particles but to condensed matter: the dynamics of fluids, transitions between one phase of matter and another, turbulence, plasmas, sound dispersion, and low-temperature physics. Fundamental though al these subjects were, in the United States their status was beginning to dim slightly next to the glamour of particle physics. Not so in the Soviet Union, where physicists were particularly eager in 1955 to meet Feynman. For his first major work since quantum electrodynamics, he had turned away from particle physics after al and chosen instead a subject close to Landau’s heart: a theory of superfluidity, the frictionless motion of liquid helium cooled to near absolute zero.

A Quantum Liquid

By then science-fiction writers had learned an interesting rule: not to let their imaginations run too freely, too widely. It was often better to be conservative. To create a strange new world, they had only to alter one or two features of the usual reality and let the manifold unexpected implications play themselves out. Nature, too, seemed capable of adjusting a single rule and thereby creating the most bizarre phenomena.

Superfluid helium showed what happens when a liquid can flow with no friction—not just low friction, but zero friction. Resting in a beaker, the liquid spontaneously glides

in a thin film up and over the wal s, apparently in defiance of gravity. It passes through cracks or holes so microscopical y smal that even a gas would not fit through.

No matter how perfectly a pair of glass plates are polished to a smooth surface, and no matter how hard they are pressed together, superfluid helium wil stil flow freely between them. The liquid conducts heat far better than any ordinary substance, and no amount of cooling wil freeze it into a solid.

When Feynman talked about fluid flow, he knew he was returning to a childlike, elemental fascination with the world as it is. The pleasure of watching water in bathtubs or mud puddles on the sidewalk, of trying to dam a curbside rivulet after a rainstorm, of contemplating the movement in waterfal s and whirlpools—that was what made every child a physicist, he felt. In trying to understand superfluidity, he began once again with first principles. What was a fluid? A substance, liquid or gas, that cannot withstand a shear stress, but moves under the force. The tendency of a fluid to resist the shear is its viscosity, its internal friction—honey being more viscous than water, water more than air.

Nineteenth-century physicists creating the first effective equations for fluid flow found viscosity especial y troublesome, so uncomputable were its consequences. For the sake of simplicity, they often created models that ignored viscosity—and for that John von Neumann later mocked them. Modelers always tried to omit unnecessary complication—that was one thing. But classical fluid dynamicists had omitted what seemed an essential, defining quality. Sarcastical y von Neumann cal ed them theorists of “dry water.” Superfluid helium, Feynman said, resembled that impossible idealization, fluid without viscosity. It was dry water.

Superfluidity

had

an

equal y

bizarre

twin,

superconductivity, the flow of electricity with no dissipation or resistance. Both were phenomena of low-temperature

experimentation. Superconductivity had been discovered in 1911; superfluidity not until 1938, because of the difficulties of watching the behavior of a liquid inside a pinhead-size container in a supercooled cryostat. Esoteric though they were, by the fifties this pair of phenomena had become crown jewels of the side of theoretical physics not devoted to elementary particles. Little progress had been made in understanding the perpetual-motion machinery that seemed to be at work. It seemed to Feynman that they were like “two cities under siege … completely surrounded by knowledge although they themselves remained isolated and unassailable.” Besides Landau, the chief contributor to the theorizing on superfluidity was Lars Onsager, the distinguished Yale chemist whose notoriously difficult courses in statistical mechanics were sometimes cal ed (in al usion to Onsager’s accent) Norwegian I and Norwegian I .

Nature had exhibited another kind of perpetual motion, familiar to quantum physicists: motion at the level of electrons in the atom. No friction or dissipation slowed electrons. Only in the interactions of crowds of atoms did the energy drain of friction arise. Were these super phenomena somehow escaping the incoherent tumult of classical matter? Was this a case of quantum mechanics writ large? Could the whole apparatus of wave functions, energy levels, and quantum states translate itself onto macroscopic scales? The most basic clue that this was indeed large-scale quantum behavior came from the apparent unwil ingness of helium to freeze into hard crystals at any temperature. Classical y, absolute zero was often described as the temperature at which al motion ceases.