Genius: The Life and Science of Richard Feynman

by James Gleick

  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.

  To get something that would produce a slightly different result it had to be completely different. In stating a new law you cannot make imperfections on a perfect thing; you have to have another perfect thing.

  He understood explanations as a surgeon understands knives. He had a set of practical tests, heuristics, that he applied when reaching a judgment about a new idea in physics: for example, did it explain something unrelated to the original problem. He would challenge a young theorist: What can you explain that you didn’t set out to explain? He knew that why? is a question without an end and that our knowledge of things is inextricable from the language we use. The words and analogies from which we build our explanations are culpably linked with the things explained. Explanans and explanandum are inextricable after all. An interviewer for the British Broadcas
ting Corporation, Christopher Sykes, once asked him to explain magnets: “If you get hold of two magnets and you push them you can feel this pushing between them… . Now what is it, the feeling between those two magnets?”

  “What do you mean, what’s the feeling?” Feynman growled. His hair, swept back in dramatic gray waves, had receded high atop his head, leaving a statue’s high brow above a pair of heavy eyebrows that curled more impishly than ever. His pale blue shirt was open at the collar. A pen and eyeglass case rested in his front pocket, as always. Off camera, a defensive note entered the interviewer’s voice.

  “Well, there’s something there, isn’t there? The sensation is that there’s something there when you push these two magnets together.”

  “Listen to my question,” Feynman said. “What is the meaning when you say there’s a feeling? Of course you feel it. Now what is it you want to know?”

  “What I want to know is what’s going on between these two bits of metal.”

  “The magnets repel each other.”

  “But what does that mean? Or why are they doing that? Or how are they doing that?” Feynman shifted in his easy chair, and the interviewer added, “I must say I think that’s a perfectly reasonable question to ask.”

  “Of course it’s a reasonable—it’s an excellent question, okay?” Reluctantly, Feynman now stepped into metaphysics. Particle theorists were toying with a “bootstrap” model, in which no particle lies at a deepest level, but all are interdependent composites. The name bootstrap paid homage to the paradoxical circularity of having to build each fundamental particle from all the others. Feynman, as he now made clear, believed in a kind of bootstrap model of explanation itself.

  You see, when you ask why something happens, how does a person answer why something happens?

  For example, Aunt Minnie is in the hospital. Why? Because she went out on the ice and slipped and broke her hip. That satisfies people. But it wouldn’t satisfy someone who came from another planet and knew nothing about things… . When you explain a why, you have to be in some framework that you’ve allowed something to be true. Otherwise you’re perpetually asking why… . You go deeper and deeper in various directions.

  Why did she slip on the ice? Well, ice is slippery. Everybody knows that—no problem. But you ask why is ice slippery… . And then you’re involved with something, because there aren’t many things as slippery as ice… . A solid that’s so slippery?

  Because it is in the case of ice that when you stand on it, they say, momentarily the pressure melts the ice a little bit so that you’ve got an instantaneous water surface on which you’re slipping. Why on ice and not on other things? Because water expands when it freezes. So the pressure tries to undo the expansion and melts it… .

  I’m not answering your question, but I’m telling you how difficult a why question is. You have to know what it is that you’re permitted to understand … and what it is you’re not.

  You’ll notice in this example that the more I ask why, it gets interesting after a while. That’s my idea, that the deeper a thing is, the more interesting… .

  Now when you ask why two magnets repel, there are many different levels. It depends whether you’re a student of physics or an ordinary person who doesn’t know anything.

  If you don’t know anything at all, about all I can say is that there’s a magnetic force that makes them repel. And that you’re feeling that force. Well, you say that’s very strange because I don’t feel a force like that in other circumstances… . You’re not at all disturbed by the fact that when you put your hand on the chair it pushes you back. But we found out by looking at it that that’s the same force… . It turns out that the magnetic and electric force with which I wish to explain these things is the deeper thing that we would start with to explain many other things… .

  If I said that magnets attract as if they were connected with rubber bands, I would be cheating you, because they’re not connected with rubber bands… . If you were curious enough you’d ask me why rubber bands tend to pull back together again, and I would end up explaining that in terms of electrical forces—which are the very things I was using the rubber bands to explain, so I have cheated very badly, you see.

  So I am not going to be able to give you an answer to why magnets attract. Except to tell you that they do … I really can’t do a good job—any job—of explaining the electromagnetic force in terms of something you’re more familiar with, because I don’t understand it in terms of anything else that you’re more familiar with.

  He sat back and grinned.

  To the professionals Feynman’s musings were not philosophy but a charmingly naive folk wisdom. He was both after and ahead of his time. Academic epistemology was still wrestling with unknowability. What choice did they have, in light of scientific relativity and uncertainty, the abandonment of strict causality and the pervasiveness of ever-qualified probabilities? No more certainties, no more absolutes. The Harvard philosopher W. V. Quine mused, “I think that for scientific or philosophical purposes the best we can do is give up the notion of knowledge as a bad job… .” Not knowing had its ironies as well as its pleasures. For philosophers this was “the post-scholastic era,” as a later physicist, John Ziman, put it, “when it seemed essential to (dis)prove the peculiar (un)reality of scientific knowledge (theories/facts/data/hypotheses) by analysing (deconstructing) the arguments on which it was (supposedly) based.” Scientists themselves, in the knowledge business, had no use for this mode of discourse. Judged by results, their understanding of nature seemed richer and more efficacious than ever, the quantum paradoxes notwithstanding. They had rescued knowledge from uncertainty after all. “The scientist has a lot of experience with ignorance and doubt and uncertainty,” Feynman said. “… we take it for granted that it is perfectly consistent to be unsure—that it is possible to live and not know. But I don’t know whether everyone realizes that this is true.”

  Feynman’s gift to his coworkers was a credo, accreted over time and disbursed both formally and informally, in lectures and books like the 1965 Character of Physical Law and in a stance, an attitude, that seemed too natural to constitute a philosophy.

  He believed in the primacy of doubt, not as a blemish upon our ability to know but as the essence of knowing. The alternative to uncertainty is authority, against which science had fought for centuries. “Great value of a satisfactory philosophy of ignorance,” he jotted on a sheet of notepaper one day. “… teach how doubt is not to be feared but welcomed.”

  He believed that science and religion are natural adversaries. Einstein said, “Science without religion is lame; religion without science is blind.” Feynman found this style of accommodation to be intolerable. He repudiated the conventional God: “the kind of a personal God, characteristic of Western religions, to whom you pray and who has something to do with creating the universe and guiding you in morals.” Some theologians had retreated from the conception of God as a kind of superperson—Father and King—willful, white-haired, and male. Any God who might take an interest in human affairs was too anthropomorphic for Feynman—implausible in the less and less human-centered universe discovered by science. Many scientists agreed, but his views were so rarely expressed that in 1959 a local television station, KNXT, felt obliged to suppress an interview in which he declared:

  It doesn’t seem to me that this fantastically marvelous universe, this tremendous range of time and space and different kinds of animals, and all the different planets, and all these atoms with all their motions, and so on, all this complicated thing can merely be a stage so that God can watch human beings struggle for good and evil—which is the view that religion has. The stage is too big for the drama.

  Religion meant superstition: reincarnation, miracles, virgin birth. It replaced ignorance and doubt with certainty and faith; Feynman was happy to embrace ignorance and doubt.

  No scientist liked the God of Sunday school stories or the “God of the gaps”—the last-resort explanation for
the unexplainable, called on through the ages to fill holes in current knowledge. Those who did turn to faith as a supplement to science preferred grander and less literal gods: “the ground of all that is,” as John Polkinghorne, a high-energy physicist turned Anglican priest, said: “Those who are seeking understanding through and through—a natural instinct for the scientist—are seeking God, whether they name him or not.” Their God did not fill gaps in the sense of particular lacunae for evolutionary theory or astrophysics—how did the universe begin?—but hovered over whole domains of knowledge: ethics, aesthetics, metaphysics. Feynman conceded the existence of genuine knowledge outside the range of science. He admitted that there were questions science could not answer, but grudgingly: he saw a danger in tying moral guidance to unpalatable myths, as religion did, and he resented the common view that science, with its merciless unraveling and explaining, was an enemy of the emotional appreciation of beauty. “Poets say science takes away from the beauty of the stars—mere globs of gas atoms,” he wrote in a famous footnote.

  I too can see the stars on a desert night, and feel them. But do I see less or more? The vastness of the heavens stretches my imagination—stuck on this carousel my little eye can catch one-million-year-old light. A vast pattern—of which I am a part… . What is the pattern, or the meaning, or the why? It does not do harm to the mystery to know a little about it. For far more marvelous is the truth than any artists of the past imagined it. Why do the poets of the present not speak of it? What men are poets who can speak of Jupiter if he were a man, but if he is an immense spinning sphere of methane and ammonia must be silent?