by James Gleick
“This preoccupation with …” he wrote—then reconsidered.
“This desire for a principle of least action is besides the simplicity gained that, when the motions can be so represented, conservation of energy, momentum, etc. are guaranteed.”
One morning Wilson came into his office and sat down. Something secret was going on, he said. He was not supposed to reveal the secret, but he needed Feynman and there was no other way. Furthermore, there were no rules about this secret. The military still did not take the physicists completely seriously. Physicists had decided on their own not to discuss certain matters, and now Wilson had decided to take it on himself to discuss one. It was time for Feynman’s initiation.
There was a possibility of a nuclear bomb, Wilson said. British physicists had heard the message of Bohr and Wheeler about uranium 235 two years earlier and had arrived at a new estimate for the critical mass of material that would be needed. An expatriate German chemist on the British team, Franz Simon, had made the Atlantic crossing by “flying boat” with the latest news from their Birmingham laboratory. Perhaps a pound or two would be enough. Perhaps even less. The British were working hard on the problem of separating the uranium isotopes, winnowing the rare lighter isotope, uranium 235, from the far more common chaff, uranium 238. The two forms of uranium are chemically indistinguishable—a chemical reaction sees just one kind of atom. But the atoms of different isotopes have different masses, a fact that theorists could exploit in several plausible ways. Simon himself was investigating a scheme of slow gaseous diffusion through metal foil riddled with pinpoint holes; the uranium 238 molecules, ever so slightly heavier, would lag behind as the gas drifted through. Secret committees and directorates were forming around the uranium problem. The British had a code name: tube alloy, soon contracted to tubealloy. The Americans were building a nuclear reactor; other Princeton professors were involved. And Wilson said he had come up with an idea of his own. He had invented a device—so far existing only in his head—that he hoped would solve the separation problem much faster. Where Simon was thinking about holes in metal—one morning he had gone into his kitchen and attacked a wire strainer with a hammer—Wilson had in mind a combination of novel electronics and cyclotron technology.
He had persuaded Harry Smyth to let him assemble a team from among the instructors, graduate students, and engineers. A sort of countrywide “body shop” trading in the available technical talent was taking shape with the help of the National Defense Research Council; that would help him find some necessary staff. Graduate students were being pressed into service with the help of a simple expedient—Princeton called a halt to most degree work. Students were asked to choose from among three war-related projects: Wilson’s; an effort to develop a new blast gauge for measuring explosive pressure; and a dully irrelevant-sounding investigation of the thermal properties of graphite. (Only later did it become clear that this meant the thermal-neutron properties of a material destined for nuclear reactors.) Wilson wanted to sign Feynman first. It occurred to him that Feynman’s persistent skepticism, his unwillingness to accept any assertion on authority, would be useful. If there was any baloney or self-deception in the idea, he thought, Feynman would find it. He wanted Feynman in place when he presented the plan to the other graduate students.
To his dismay Feynman turned him down flat. He was too deep in his thesis; also, though he did not say so, the Frankford Arsenal had left him slightly disillusioned with war work. He said that he would keep the secret but that he wanted no part of it. Wilson asked him at least to come to the meeting.
Long afterward, after all the bomb makers had taken second looks back at their moments of decision, Feynman remembered the turmoil of that afternoon. He had not been able to go back to work. As he recalled it, he thought about the importance of the project; about Hitler; about saving the world. Elsewhere a few physicists already guessed, making delicate inferences from university rosters and published papers, that Germany was mounting no more than a cursory nuclear-weapons research project. Still, among the physicists who had disappeared from view was Werner Heisenberg. The threat seemed real enough. Later Feynman remembered the decisive physical act of opening his desk drawer and placing in it the loose sheets of his thesis.
The Manhattan Project
Chicago, Berkeley, Oak Ridge, Hanford: the first outposts of the Manhattan Project eventually became permanent capitals of a national nuclear establishment. To produce purified uranium and plutonium on a scale of mere pounds would require the rapid establishment of the largest single-purpose industrial enterprise ever. General Electric, Westinghouse, Du Pont, Allis-Chalmers, Chrysler, Union Carbide, and dozens of smaller companies combined in an effort that would see giant new factory towns rising from the earth. Yet in the first uncertain months after the attack on Pearl Harbor nothing in the modest scale of nuclear research even remotely foreshadowed the impending transformation of the nation’s war-making capacity. Workshops were converted according to happenstance and convenience. At Princeton no more than a few thousand dollars 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 smaller tubes and electrical wiring. The theoretical division comprised, in its entirety, two cocky graduate students sitting side by side at roll-top desks in a small 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 brilliant 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 called his machine an isotron (a near-meaningless name; his old mentor, Ernest Lawrence, was calling a competing device a calutron, California + tron). Of all 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 balls 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 electrically 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 all the other separation schemes, the piece Feynman was struggling to evaluate.
A particularly jagged, sawtooth oscillation 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 fell 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 fall 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 oscillating 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 initially 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 alloy 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 unusually 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 carefully positioned collector. 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 Hill, he was appalled 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 finally 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 bill with the wife of the Belgian balloonist 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 physicist, so like Feynman and yet so unlike him, who would control his destiny for the next three years, J. Robert Oppenheimer.
Soon after Feynman’s trip to Columbia bearing uranium, these men made their final decision on Princeton’s adventure with the isotron. On the recommendation of Lawrence, nominally in charge of all electromagnetic separation research, they closed the Princeton project down. Operationally the calutron seemed a full year ahead, and money had to be committed as well to the more conventional diffusion approach, with pumps and pipes instead of magnets and fields, the atoms drifting in random trajectories, at ever-so-slightly different speeds, through many miles of metal barriers pricked with billions of microscopic holes. Wilson was stunned. He thought the committee was acting not just hastily but hysterically. To his senior colleagues it seemed that Wilson had lost to the personal strength and promotional skill of his former mentor Lawrence. Smyth and Wigner both felt privately that, given a fuller trial, the isotron might conceivably have shortened the war. “Lawrence’s calutron simply used raw brute force to pry the beam a little way apart,” a younger team member said. “Our method was elegant.” Blown up to the scale needed for mass production—thousands of giant machines—the isotron promised a yield many times greater. Feynman had produced detailed calculations for the design of a vast manufacturing plant, with isotrons working in a “cascade” of increasing purity. He took into account everything from wall-scrapings to uranium that would be lost in workers’ clothing. He conceived arrays of several thousand machines—yet that proved a modest scale, in light of the later reality.
For Feynman one legacy of the Princeton effort was the friendship with Olum, a friendship, like many that followed, intellectually rich and emotionally unequal. Encounters with Feynman left marks on a series of young physicists and mathematicians, in the glare of a bright light, out-thought for the first time in their lives. They found different ways of adapting to this new circumstance. Some subordinated their own abilities to his and accepted his occasional bantering abuse in exchange for the surprising pleasure that came with his praise. Some found their self-image enough changed that they abandoned physics altogether. Olum himself eventually returned to mathematics, where he was more comfortable. He worked with Feynman throughout the war and then Feynman drifted away. They met only a few times in the next forty years. Olum thought of his old friend often, though. He was president of the University of Oregon when he heard of Feynman’s death. He realized that the young genius he had met at Princeton had become a part of him, impossible to extricate. “My wife died three years ago, also of cancer,” he said.
… I think about her a lot. I have to admit I have Dick’s books and other things of Dick’s. I have all of the Feynman lectures and other stuff. And there are things that have pictures of Dick on them. The article in Science about the Challenger episode. And also some of the recent books.
I get a terrible feeling every time I look at them. How could someone like Dick Feynman be dead? This great and wonderful mind. This extraordinary feeling for things and ability is in the ground and there’s nothing there anymore.
It’s an awful feeling. And I feel it—— A lot of people have died and I know about it. My parents are both dead and I had a younger brother who is dead. But I have this feeling about just two people. About my wife and about Dick.
I suppose, although this wasn’t quite like childhood, it was graduate students together, and I do have more—— I don’t know, romantic, or something, feelings about Dick, and I have trouble realizing that he’s dead. He was such an extraordinarily special person in the universe.
Finishing Up
Absent from Princeton’s nuclear effort was John Wheeler. He had already departed for Chicago, where Enrico Fermi and his team at the Metallurgical Laboratory—that enigmatic laboratory emplo
ying no metallurgists—were driving toward the first nuclear reactor. They intended to use less-than-bomb-grade uranium to produce slow fission. In the spring of 1942 Chicago was the place where it was easiest to gain a sense of what the future held. Wheeler knew how deeply his former student was mired in the isotope-separation work. In March he sent Feynman a message. It was time to finish his thesis, no matter how many questions remained open. Wigner—who was also more and more a part of the Chicago work—agreed that Feynman had accomplished enough for his degree.
Feynman heard the warning. He requested a short leave from the isotron project. Even now he did not feel quite ready to write, especially under such pressure. Later he remembered spending the first day of his leave lying on the grass, guiltily looking at the sky. Finally, writing with fountain pen in his fast adolescent scrawl, he filled sheaves of scratch paper—but paper was expensive, so he used the stationery of the Lawrencian, the Lawrence High School newspaper (Arline Greenbaum, editor in chief) or surplus order forms of G. B. Raymond & Company, sewer pipe, flue linings, etcetera, of Glendale, Long Island. He had now thoroughly assimilated Wheeler’s revolutionary attitude, the stance that declared a break with the past. When the quantum mechanics of Max Planck was applied to the problem of light and the electromagnetic field, he wrote, “great difficulties have arisen which have not been surmounted satisfactorily.” Other interactions, with more recently discovered particles, were creating similar difficulties, he pointed out: “Meson field theories have been set up in analogy to the electromagnetic field theory. But the analogy is unfortunately all too perfect; the infinite answers are all too prevalent and confusing.” So he disposed of the field—at least the old idea of the field as a free medium for carrying waves. The field is a “derived concept,” he wrote. “The field in actuality is entirely determined by the particles.” The field is a mere “mathematical construction.” Just as radically, he deprecated the wave function of Schrödinger, the now-orthodox means of describing the full state of a quantum-mechanical system at a given time. It was practically useless, after all, when the interaction of particles involved a time delay. “We can take the viewpoint, then, that the wave function is just a mathematical construction, useful under certain conditions”—no, “certain particular conditions … but not generally applicable.”
