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

Workshops were converted according to happenstance and convenience. At Princeton no more than a few thousand dol ars was available for Wilson’s project. To get help with the electronics he resorted to throwing a near tantrum in I. I. Rabi’s office at the MIT Rad Lab. Including shop workers and technicians, his team grew to number about thirty. The experimental division amounted to one ungainly tube the length of an automobile, sprouting smal er tubes and electrical wiring. The theoretical division comprised, in its entirety, two cocky graduate students sitting side by side at rol -top desks in a smal office.

They found they were able to bear the pressure of working on the nation’s most fateful secret research project.

The senior theoretician crumpled a piece of paper one day, passed it to his assistant, and ordered him to throw it in the wastebasket.

“Why don’t you ?” the assistant replied.

“My time is more valuable than yours,” said Feynman.

“I’m getting paid more than you.” They measured the distances from scientist to wastebasket; multiplied by the

wages; bantered about their relative value to nuclear science. The number-two man, Paul Olum, threw away the paper.

Olum

had

considered

himself

the

best

undergraduate mathematician at Harvard. He arrived at Princeton in 1940 to be Wheeler’s second research assistant. Wheeler introduced him to Feynman, and within a few weeks he was devastated. What’s happening here?

he thought. Is this the way physicists are, and I missed it?

No physicist at Harvard was like this. Feynman, a cheerful, boyish presence spinning across the campus on his bicycle, scornful of the formalisms of modern advanced mathematics, was running mental circles around him. It wasn’t that he was a bril iant calculator; Olum knew the tricks of that game. It was as if he were a man from Mars.

Olum could not track his thinking. He had never known anyone so intuitively at ease with nature—and with nature’s seemingly least accessible manifestations. He suspected that when Feynman wanted to know what an electron would do under given circumstances he merely asked himself, “If I were an electron, what would I do?”

Feynman found a vast difference between intuiting the behavior of electrons in rarefied theoretical contexts and predicting the behavior of a bulky jury-rigged assemblage of metal and glass tubing and electronics. He and Olum worked hastily. They could see from the start that Wilson’s idea sat somewhere near the border between possible and hopeless—but on which side of the border? The calculations were awkward. Often they had to resort to guesswork and approximation, and it was hard to see which pieces of the work could accommodate guesses and which demanded rigorous exactitude. Feynman realized

that he did not completely trust theoretical physics, now that its procedures were put to such an unforgiving test.

Meanwhile the technicians moved forward; they could not afford to wait for the theorists’ numbers. It was like a cartoon, Feynman thought; every time he looked around, the apparatus had sprouted another tube or a new set of dials.

Wilson cal ed his machine an isotron (a near-meaningless name; his old mentor, Ernest Lawrence, was cal ing a competing device a calutron, Cal ifornia + tron ). Of al the separation schemes, Wilson’s isotron owed the least to ordinary intuition about physical objects. It came the closest to treating atoms as denizens of a wavy electromagnetic world, rather than miniature bal s to be pushed about or squeezed through holes. The isotron first vaporized and ionized chunks of uranium—heated them until they gave up an electron and thus became electrical y charged. Then a magnetic field set them in motion. The stream of atoms passed through a hole that organized it into a tight beam. Then came the piece of wizardry that set the isotron apart from al the other separation schemes, the piece Feynman was struggling to evaluate.

A particularly jagged, sawtooth oscil ation would be set up in the magnetic field. The voltage would swing sharply up and down, at radio wavelengths. Some of the uranium atoms would hit the field just as the energy fel to zero. Then some later atoms would enter the field as the energy rose, and they would accelerate enough to catch up with the first atoms. Then the energy would fal off again, so that the next atoms would travel more slowly. The goal was to make the beam break up into bunches, like traffic clumping on a

highway. Wilson estimated that the bunches would be about a yard long. Most important, the uranium 235 and uranium 238 atoms, because of their differing masses, would accelerate differently in the magnetic field and would therefore bunch at different points. If the experimenters could get the timing right, Wilson thought, the bunches of each isotope should be distinct and separable. As they reached the end of the tube another precisely timed oscil ating field, like a flag man at a detour, would deflect the bunches alternately left and right into waiting containers.

Complications appeared. As the ions’ own momentum pushed them together, their tendency to repel one another came into play. Furthermore some atoms lost not one but two or more electrons when ionized, doubling or tripling their

electric

charge

and

sabotaging

Feynman’s

calculations. When experimenters tried higher voltages than Feynman had initial y calculated, they found that the bunches were springing back, the waves rebounding and forming secondary waves. It was with something like shock that Feynman realized that these secondary effects appeared in his equations, too—if only he could persuade himself to trust them. Nothing about the isotron project was simple. The physicists had to invent a way of feeding the machine with uranium powder instead of uranium wire, because the wire had a tendency to al oy with the electrodes, destroying them spectacularly. One of the experimenters found that, by setting a flame to the end of the uranium wire, he could create a shower of dazzling stars—an unusual y expensive sparkler.

Meanwhile the project’s worst enemy was proving to be its closest competitor, Lawrence, at Berkeley. He wanted to

absorb the isotron into his own project, shutting down the Princeton group and taking on its staff and equipment for his calutron. The California-tron similarly used the new accelerator technology to create a beam of uranium ions but accelerated them instead around a three-foot racetrack.

The heavier atoms swung farther out. The light atoms made the tight turn into a careful y positioned col ector. Or so they would in theory. When General Leslie R. Groves, the new head of the Manhattan Project, first made the drive up the winding road from San Francisco Bay to Berkeley’s Radiation Hil , he was appal ed to find that the entire product of Lawrence’s laboratory could barely be seen without the aid of a magnifying glass. Worse, the microgram samples were not even half pure. Even so, they outweighed the total output of the Princeton group.

Feynman carried the isotron’s flyspeck sample by the train to Columbia for analysis late in 1942; Princeton had no equipment capable of measuring the proportions of the isotopes in a tiny piece of uranium. Wearing his battered sheepskin coat, he had trouble finding anyone in the building who would take him seriously. He wandered around with his radioactive fragment until final y he saw a physicist he knew, Harold Urey, who took him in hand. Urey was a distinguished physicist who, as it happened, had delivered the first scientific lecture Feynman had ever heard, a public talk in Brooklyn on the subject of heavy water, sharing the bil with the wife of the Belgian bal oonist Auguste Piccard. More recently Feynman had come to know Urey by attending meetings of the Manhattan Project’s de facto steering committee. In that way he also met for the first time I. I. Rabi, Richard Tolman, and the