Genius (20 page)

Waves forward and backward in time. Wheeler and Feynman tried to work out a consistent scheme for the interactions of particles, and they embroiled themselves in paradoxes of past and future . A particle shakes; its influence spreads outward like waves from a stone thrown into a pond. To make their theory symmetrical, they also had to use inward-traveling waves-implying action backward in time.

They found that they could avoid unpleasant paradoxes because these normal and time-reserved waves ("retarded" and "advanced") canceled each other out-but only if the universe was arranged so as to guarantee that all radiation would be absorbed somewhere, sometime. A beam of light traveling forever into infinite, empty space, never striking an absorber, would foil their theory's bookkeeping. Thus cosmologists and philosophers of time continued to consider their scheme long after it had been supplanted in the mainstream of quantum theory.

He described it to his graduate student friends and challenged them to find a paradox he could not explain his way through. For example, could one design a mechanism with a target that would shut a gate when struck by a pellet, such that the advanced field closed the gate before the pellet arrived, in which case the pellet could not strike the target, in which case the advanced field would not close the gate after all … He imagined a Rube Goldberg contraption that might have come straight from Wheeler’s old book of ingenious mechanisms and mechanical devices. Feynman’s calculations suggested that the model was surprisingly immune to paradox. As long as the theory relied on probabilities, it seemed to escape fatal contradictions. It did not matter where the absorber was or how it was shaped, as long as there were absorbing particles off at some distance in every direction. Only if there were “holes” in the surrounding layer, places where radiation could go forever without being absorbed, could the advanced effects make trouble, arriving back at the source before they had been triggered.

Wheeler had his own motive for pursuing this quixotic theory. Most physicists were now persuaded that the atom embodied at least three irreconcilably different particles, electrons, protons, and neutrons, and cosmic rays were providing intimations of several more. This proliferation offended Wheeler’s faith in the ultimate simplicity of the world. He continued to cherish a notion so odd that he was reluctant to discuss it aloud, the idea that a different kind of theory would reveal everything to be made of electrons after all. It was crazy, he knew. But if electrons were to be the ultimate building blocks, their radiative forces would have to provide the key, in ways that the standard theory was not prepared to explain. Within weeks he began pressing Feynman to write a preliminary paper. If they were going to make grand theories, Wheeler would make sure they publicized the work properly. Early in 1941 he told Feynman to prepare a presentation for the departmental seminar, usually a forum for distinguished visiting physicists, in February. It would be Feynman’s first professional talk. He was nervous about it.

As the day approached, Wigner, who ran the colloquiums, stopped Feynman in the hall. Wigner said he had heard enough from Wheeler about the absorber theory to think it was important. Because of its implications for cosmology he had invited the great astrophysicist Henry Norris Russell. John von Neumann, the mathematician, was also going to come. The formidable Wolfgang Pauli happened to be visiting from Zurich; he would be there. And though Albert Einstein rarely bestirred himself to the colloquiums, he had expressed interest in attending this one.

Wheeler tried to calm Feynman by promising to field questions from the audience. Wigner tried to brief him. If Professor Russell appears to fall asleep during your talk, Wigner said, don’t worry—Professor Russell always falls asleep. If Pauli appears to be nodding, don’t assume he agrees—he nods from palsy. (Pauli could be ruthless in dismissing work he considered shallow or flimsy: “
ganz falsch
,” utterly false—or worse, “
not even
false.”) Feynman prepared carefully. He collected his notes and put them into a brown envelope. He entered the seminar room early and covered the blackboard with equations. While he was writing, he heard a soft voice behind him. It was Einstein. He was coming to the lecture and first he wondered whether the young man might direct him to the tea.

Afterward Feynman could remember almost nothing: just the trembling of his hand as he pulled his notes from the envelope and then a feeling that his mind put itself at ease by concentrating on the physics and forgetting the occasion and the personalities. Pauli did object, perhaps sensing that the use of advanced potentials merely invoked a sort of mathematical tautology. Then, politely, Pauli said, “Don’t you agree, Professor Einstein?” Feynman heard that soft Germanic voice again—so pleasant, it seemed—saying no, the theory seemed possible, perhaps there was a conflict with the theory of gravitation, but after all the theory of gravitation was not so well established …

The Reasonable Man

He suffered spells of excessive rationality. When these struck it was not enough to make progress in his scientific work, nor to rectify his mother’s checkbook, nor to recompute his own equivocal balance sheet (eighteen dollars for laundry, ten dollars to send home … ), nor to lecture his friends, as they watched him repair his bicycle, on the silliness of believing in God or the supernatural. During one occurrence he wrote out an hourly schedule of his activities, both scholarly and recreational, “so as to efficiently distribute my time,” he wrote home. When he finished, he recognized that no matter how careful he was, he would have to leave some indeterminate gaps—“hours when I haven’t marked down just what to do but I do what I feel is most necessary then—or what I am most interested in—whether it be W.’s problem or reading Kinetic Theory of Gases, etc.” If there is a disease whose symptom is the belief in the ability of logic to control vagarious life, it afflicted Feynman, along with his chronic digestive troubles. Even Arline Greenbaum, sensible as she was, could spark flights of reason in him. He grew concerned about the potential for emotional disputes between husbands and wives. Even his own parents fought. He hated the battles and the anger. He did not see why two intelligent people, in love with each other, willing to converse openly, should get caught in arguments. He worked out a plan. Before revealing it to Arline, however, he decided to lay it out for a physicist friend over a hamburger at a diner on the Route 1 traffic circle. The plan was this. When Dick and Arline disagreed intensely about a matter of consequence, they would set aside a fixed time for discussion, perhaps one hour. If at the end of that time they had not found a resolution, rather than continue fighting they would agree to let one of them decide. Because Feynman was older and more experienced (he explained), he would be the one.

His friend looked at him and laughed. He knew Arline, and he knew what would really happen. They would argue for an hour, Dick would give up, and Arline would decide. Feynman’s plan was a sobering example of the theoretical mind at work.

Arline was visiting more and more often. They would have dinner with the Wheelers and go for long walks in the rain. She had the rare ability to embarrass him: she knew where his small vanities were, and she teased him mercilessly whenever she caught him worrying about other people’s opinions—how things might
seem
. She sent him a box of pencils emblazoned, “Richard darling, I love you! Putzie,” and caught him slicing off the incriminating legend, for fear of inadvertently leaving one on Professor Wigner’s desk. “What do you care what other people think?” she said again and again. She knew he prided himself on honesty and independence, and she held him to his own high standards. It became a touchstone of their relationship. She mailed him a penny postcard with a verse written across it:

If you don’t like the things I do
My friend, I say, Pecans to you!
If I irate with pencils new
My bosom pal, Pecans to you!
…
If convention’s mask is borne in view
…
If deep inside sound notions brew
And from without you take your cue
My sorry friend, Pecans to you!

Her words struck home. Meanwhile she had nagging health worries: a lump seemed to come and go on her neck, and she developed uncomfortable, unexplained fevers. Her uncle, a physician, had her rub the lump with a nostrum called omega oil. (This style of treatment had had its heyday a hundred years before.)

The day after his presentation to the physics colloquium in February, Richard went up to Cambridge for a meeting of the American Physical Society, and she took the train from New York to Boston’s South Station to join him. An old fraternity friend picked her up and they crossed the bridge to MIT, catching a ride on a horse-drawn junk wagon. They found Richard in the corridor of building 8, the physics building. He walked by in animated conversation with a professor. Arline made eye contact with him, but he did not acknowledge her. She realized that it would be better not to speak.

When Richard returned to the fraternity house that evening he found her in the living room. He was ebullient; he grabbed her and swung her around, dancing. “He certainly believes in physical society,” one of the fraternity boys said. At Wheeler’s prodding Feynman had presented their space-time electrodynamics a second time, to a broader audience. The talk went well. After having faced a public of Einstein, Pauli, von Neumann, and Wigner, he had little to fear from the American Physical Society rank and file. Still, he worried that he might have bored his listeners by sticking nervously to his prepared text. There were a few polite questions, and Wheeler helped answer them.

Feynman had enunciated a set of principles for a theory of interacting particles. He wrote them out as follows:

1 The acceleration of a point charge is due only to the sum of its interactions with other charged particles… . A charge does not act on itself.

2 The force of interaction which one charge exerts on a second is calculated by means of the Lorentz force formula, in which the fields are the fields generated by the first charge according to Maxwell’s equations.

Phrasing the third principle was more difficult. He tried:

3 The fundamental equations are invariant with respect to a change of the sign of the time …

Then, more directly:

3 The fundamental (microscopic) phenomena in nature are symmetrical with respect to interchange of past and future.

Pauli, despite his skepticism, understood the power of the last principle. He pointed out to Feynman and Wheeler that Einstein himself had argued for an underlying symmetry of past and future in a little-known 1909 paper. Wheeler needed little encouragement; he made an appointment to call at the white clapboard house at 112 Mercer Street.

Einstein received this pair of ambitious young physicists sympathetically, as he did most scientists who visited in his last years. They were led into his study. He sat facing them behind his desk. Feynman was struck by how well the reality matched the legend: a soft, nice man wearing shoes without socks and a sweater without a shirt. Einstein was well known to be unhappy with the acausal paradoxes of quantum mechanics. He now spent much of his time writing screeds on world government which, from a less revered figure, would have been thought crackpot. His distaste for the new physics was turning him into, as he would have it, “an obstinate heretic” and “a sort of petrified object, rendered blind and deaf by the years.” But the theory Wheeler and Feynman described was not yet a quantum theory—so far, it used only classical field equations, with none of the quantum-mechanical amendments that they knew would ultimately be necessary—and Einstein saw no paradox. He, too, he told them, had considered the problem of retarded and advanced waves. He reminisced about the strange little paper he had published in 1909, a manifesto of disagreement with a Swiss colleague, Walter Ritz. Ritz had declared that a proper field theory should include only retarded solutions, that the time-backward advanced solutions should simply be declared impermissible, innocent though the equations looked. Einstein, however, could see no reason to rule out advanced waves. He argued that the explanation for the arrow of time could not be found in the basic equations, which truly were reversible.

On his bicycle in Far Rockaway.