Genius (64 page)

The course was a magisterial achievement: word was spreading through the scientific community even before it ended. But it was not for freshmen. As the months went on, the examination results left Feynman shocked and discouraged. Still, when the year ended, the administration pleaded with him to keep on for a second year, teaching the same students, now sophomores. He did, finally trying to teach a thorough subcourse in quantum mechanics, again reversing the conventional order. Another Caltech physicist, David Goodstein, said long afterward, “I’ve spoken to some of those students in recent times, and in the gentle glow of dim memory, each has told me that having two years of physics from Feynman himself was the experience of a lifetime.” The reality was different:

As the course wore on, attendance by the kids at the lectures started dropping alarmingly, but at the same time, more and more faculty and graduate students started attending, so the room stayed full, and Feynman may never have known he was losing his intended audience.

This was the world according to Feynman. No scientist since Newton had so ambitiously and so unconventionally set down the full measure of his knowledge of the world—his own knowledge and his community’s. With intensive editing by other physicists, chiefly Robert B. Leighton and Matthew Sands, the lectures became the famous “red books”—the three-volume
Feynman Lectures on Physics
. Colleges and universities worldwide tried to adopt them as textbooks and then, inevitably, gave them up for more manageable and less radical alternatives. Unlike true textbooks, however, Feynman’s volumes continued to sell steadily a generation later.

Adorning each volume was a picture of Feynman in shirtsleeves, gleefully pounding a bongo drum. He came to regret that. “It is odd,” he said after hearing himself introduced yet again as a bongo player, “but on the infrequent occasions when I have been called upon in a formal place to play the bongo drums, the introducer never seems to find it necessary to mention that I also do theoretical physics. I believe that is probably because we respect the arts more than the sciences.” And when yet another request came in for a copy of the photograph—from a Swedish encyclopedia publisher who wished to “give a human approach to a presentation of the difficult matter that theoretical physics represents”—he exploded. “Dear Sir,” he scrawled,

The fact that I beat a drum has nothing to do with the fact that I do theoretical physics. Theoretical physics is a human endeavor, one of the higher developments of human beings—and this perpetual desire to prove that people who do it are human by showing that they do other things that a few other humans do (like playing bongo drums) is insulting to me.

I am human enough to tell you to go to hell.

The Explorers and the Tourists

“When you have learned what an explanation really is,” Feynman had said, “you can then go on to more subtle questions.”

Creeping philosophy. What is an explanation? Science and scientists had commandeered the practice of explanation, but the theory they left mainly to philosophers. The
why
seemed to fall in their domain. “With this question philosophy began and with this question it will end,” Martin Heidegger had recently said, “provided that it ends in greatness and not in an impotent decline.” Feynman, who believed that the impotent decline was well under way in the academies that supported philosophers, realized that he had had to develop a view of what constituted explanation, what legitimized explanation, and which phenomena did and did not require explanation.

His understanding of explanation did not depart far from the modern philosophical mainstream, though its jargon of
explanans
and
explanandum
was an alien language to him. Like most philosophers, he found explanations most satisfactory when they called upon a generalizing, underlying “law.” A thing is the way it is because other things of its kind are all that way. Why does Mars travel around the sun in an ellipse? Feynman explained—and ventured deep into philosophical territory—in an invited lecture series at Cornell University in 1964. He began by speaking, nominally, about the law of gravitation. In reality his subject was explanation itself.

All satellites travel in elliptical orbits. Why? Because objects tend to travel in a straight line when left alone (the law of inertia) and the combination of that unchanging motion and a force exerted toward a center of gravity—by the law of gravitation—creates an ellipse. What validates the law of gravitation? Feynman expressed the scientist’s modern view, a blend of the pragmatic and the aesthetic. He cautioned that even so beautiful a law was provisional: Newton’s law of gravitation gave way to Einstein’s, and a necessary quantum modification eluded physicists even now.

That is the same with all our other laws—they are not exact. There is always an edge of mystery, always a place where we have some fiddling around to do yet. This may or may not be a property of Nature, but it certainly is common to all the laws as we know them today.

Yet in its unfinished form the law of gravitation explained so much. To a practicing scientist, that validated it. The same small parcel of mathematics
explained
Tycho Brahe’s nightly observations of the planets in the sixteenth century and Galileo’s measurements of balls rolling down inclined planes, timed against the beat of his own pulse. The planets are falling, Newton reasoned; the moon feels the same force as an earthly projectile, the force weakening with the square of the distance. A law is not a
cause
—philosophers still wrestled with this distinction—yet it is more than merely a description. It precedes the thing explained, not in time but in generality or in profundity. The same law explained the earth’s symmetrically bulging tides, rising both toward and away from the moon, and the newly measured orbits of the moons of Jupiter. It made new predictions that scientists could confirm or disprove with experiments on balls hanging delicately in a laboratory or observations of majestically rotating galaxies a hundred million million times larger. “Exactly the same law,” Feynman said, and added—having struggled to find the right wording—

Nature uses only the longest threads to weave her pattern, so each small piece of the fabric reveals the organization of the entire tapestry.

Meanwhile,
why
does an object in motion tend to travel forever in a straight line? That, Feynman said, nobody knows. At some deep stage, the explanations must end.

“Science repudiates philosophy,” Alfred North Whitehead had said. “In other words, it has never cared to justify its truth or explain its meaning.” Feynman’s colleagues liked to think of their gruffly plain-spoken pragmatist hero as the perfect antiphilosopher,
doing
rather than justifying. His own rhetoric encouraged them. He lacked patience for the now-popular
What is reality?
brand of speculation arising from quantum-mechanical paradoxes. Yet he could not repudiate philosophy; he had to find ways to justify the truth that he and his colleagues sought. The modern physics had banished any possibility of discovering a system of laws unambiguously tying effects to causes; or a system of laws deduced and conjoined with perfect logical consistency; or a system of laws rooted in the objects that people can see and feel. For philosophers, these had all been marks of a sound explanatory law. Now, however, a particle might or might not decay, an electron might or might not pass through a slit in a screen. A minimum principle like the principle of least action might be derived from laws of forces and motion, or those laws might depend on the principle: who could say with logical certainty? And the basic stuff of science had grown inexorably more abstract. As the physicist David Park put it: “None of the entities that appear in fundamental physical theory today are accessible to the senses. Even more … there are phenomena that apparently are not
in any way
amenable to explanation in terms of things, even invisible things, that move in the space and time defined by the laboratory.” With all these traditional virtues removed—or worse, partly removed while still partly necessary—it fell to science to build a new understanding of the nature of explanation. Or so Feynman argued: the philosophers themselves, he said, were always a tempo behind, like tourists moving in after the explorers have left.

Scientists had their own forms of blindness. It was often said in the quantum-mechanical era—Feynman had said it himself—that the only true test of a theory was its ability to produce good numbers, numbers agreeing with experiment. The American pragmatism of the early twentieth century had brought forth views like Slater’s at MIT: “Questions about a theory which do not affect its ability to predict experimental results correctly seem to me quibbles about words.” Yet Feynman now felt a hollowness in the purely operational view of what a theory means to a scientist. He recognized that theories came laden with mental baggage, with what he called a philosophy, in fact. He had trouble defining this: “an understanding of the law”; “a way that a person holds the laws in his mind …” The philosophy could not be discarded as readily as a pragmatic scientist might suggest.

Consider a Mayan astronomer, he suggested. (In Mexico he had grown interested in the deciphering of the great ancient codices, hieroglyphic manuscripts that employed long tables of bars and dots to set down an intricate knowledge of the movements of sun, moon, and planets. Codes, mathematics, and astronomy—eventually he delivered a lecture at Caltech on deciphering Mayan hieroglyphics. Afterward, Murray Gell-Mann “countered,” Feynman said, with a series of six lectures on the languages of the world.) The Maya had a theory of astronomy that enabled them to explain their observations and to make predictions long into the future. It was a
theory
in the utilitarian modern spirit: a set of rules, quite mechanical, which when followed produced accurate results. Yet it seemed to lack a kind of understanding. “They counted a certain number and subtracted some numbers, and so on,” he said. “There was no discussion of what the moon was. There was no discussion even of the idea that it went around.”

Now a “young man” approaches the astronomer with a new idea. What if there are balls of rock out there, far away, moving under the influence of forces just like the forces that pull rocks to the ground? Perhaps it would make possible a different way of calculating the motions of the heavenly bodies. (Feynman certainly had memories of a young man confronting his elders with new, half-formed physical intuitions.)

“Yes,” says the astronomer, “and how accurately can you predict eclipses?” He says, “I haven’t developed the thing very far yet.” Then says the astronomer, “Well, we can calculate eclipses more accurately than you can with your model, so you must not pay any attention to your idea because obviously the mathematical scheme is better.”

The notion that alternative theories could account plausibly for the same observations had slipped into a central position in the working philosophy of scientists. Philosophers called it
empirical equivalence
, when they began to catch up. The recent history of quantum mechanics had pivoted on the empirical equivalence of Heisenberg’s and Schrödinger’s versions. The empirical equivalence of very different-seeming theories could be demonstrated mathematically, as Dyson had shown for Feynman’s and Schwinger’s quantum electrodynamics. Scientists knew, usually without thinking about it, that empirically equivalent theories could have different consequences, mathematics and logic notwithstanding.

For Feynman, especially, the tension between alternative theories served as a creative force, an engine for generating new knowledge. Perhaps more than any living physicist, he had made a specialty of learning what models could be derived from which principles, and what models from each other. To Dyson’s astonishment, he had stood at a blackboard one day in 1948 and interrupted their heady discussions of quantum electrodynamics to show him something different. Sketching quickly, he derived the nineteenth-century Maxwell field equations—the classical understanding of electricity and magnetism—backward from the new quantum mechanics. Einstein had started with the Maxwell equations and then shifted the perspective of the observer to arrive at his theory of relativity; Feynman went the other way in a fit of ahistorical perversity. He began with a void, no fields or waves, no concept of relativity, not even a notion of light itself, just a single particle obeying quantum mechanics’ odd rules. Before Dyson’s eyes he traveled back mathematically from the new physics, with its riddles of uncertainty and immeasurability, to the comforting exactitude of the previous century. He showed that Maxwell’s field equations were not a foundation but a consequence of the new quantum mechanics. Startled and impressed, Dyson urged him to publish. Feynman just laughed and said, “Oh, no, it’s not serious.” As Dyson understood it later, Feynman had been trying to create a new theory “outside the framework of conventional physics.”

His motivation was to discover a new theory, not to reinvent the old one… . His purpose was to explore as widely as possible the universe of particle dynamics. He wanted to make as few assumptions as he could.

A theorist who can juggle different theories in his mind has a creative advantage, Feynman argued, when it comes time to change the theories. The path-integral formulation of quantum mechanics might be empirically equivalent to other formulations and yet—given less-than-omniscient human physicists—find more natural-seeming application to realms of science not yet explored. Different theories tended to give a physicist “different ideas for guessing,” Feynman said. And the century’s history had shown that when even so elegant and pure a theory as Newton’s had to be replaced, slight modifications could not suffice.