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

Particle physicists were awed by the effectiveness of their theories. They adopted a rhetoric of the “grand unified theory,” a concept with its own acronym, GUT. Progress in science had long meant unification of phenomena that previously had been treated separately: Maxwel ’s electrodynamics had begun to unify electricity and light, for example. Steven Weinberg and Abdus Salam had unified the realms of electromagnetic and weak interactions with their (inevitably so-cal ed) electroweak theory; however, this latter unification of such distant realms seemed more a mathematical tour de force than a demonstration that the two realms were two sides of one simple coin. Quantum chromodynamics attempted to embrace the strong interactions as wel ; however, experimental support seemed remote. Physicists now talked as though they could extend unification to cover everything, as though they could conceive of a time when physics would be able to close shop, its work complete. They could imagine—they

could almost see —“the ultimate theory of the universe”;

“nothing less than a complete description of the universe we live in”; “a complete unified theory of everything.” The inflation of rhetoric accompanied a noticeable reversal of the physicists’ political stature. The aura that had come with the success of the atomic bomb project was fading. To carry out increasingly high-energy experiments, physicists needed exponential y more-expensive machinery, and the question of financing such projects became political y divisive among scientists.

In the year of Feynman’s death, a pair of experimental physicists introduced a text with the simple declaration,

“Fifty years of particle physics research has produced an elegant and concise theory of particle interactions at the subnuclear level.” Particle-physics outsiders could be less generous. Elegant and concise? Why, then, did so many particle masses and other specific numerical parameters have to be fed into the theory, rather than read out? Why so many overlapping fields, so many symmetries broken—it seemed—as necessary to fit the data? Quantum numbers such as color and charm might be elegant simplifications, or they might be last-minute rubber bands applied to joints that had threatened to spring loose. And if theorists explained quark confinement, justifying a kind of particle that could never stand on its own, they surely could explain anything. Was the theory rigged—as one critic put it provocatively, “a contrived intel ectual structure, more an assembly of successful explanatory tricks and gadgets …

than a coherently expressed understanding of experience”?

Although each piece of the theory might have been tested against experiment, the whole theory—the style of theory making—had become resistant to disproof. It was hard to imagine phenomena that could not be explained with a new symmetry breaking, a new quantum number, or a few extra spatial dimensions. Perhaps the spare-parts department of modern physics was so wel stocked with ingenious devices that a serviceable engine could now be devised to handle any data the particle accelerators could offer.

This was a harsh critique—not Feynman’s. Stil , in another time, Feynman had spoken of the search for the fundamental laws of nature. No longer:

People say to me, “Are you looking for the ultimate laws of physics?” No, I’m not… . If it turns out there is a simple ultimate law which explains everything, so be it

—that would be very nice to discover. If it turns out it’s like an onion with mil ions of layers … then that’s the way it is.

He believed that his col eagues were claiming more success at unification than they had achieved—that disparate theories had been pasted together tenuously.

When Hawking said, “We may now be near the end of the search for the ultimate laws of nature,” many particle physicists agreed. But Feynman did not. “I’ve had a lifetime of that,” he said on another occasion. “I’ve had a lifetime of people who believe that the answer is just around the corner.”

But again and again it’s been a failure. Eddington who thought that with the theory of electrons and quantum mechanics everything was going to be simple

… Einstein, who thought that he had a unified theory just around the corner but didn’t know anything about nuclei and was unable of course to guess it… . People think they’re very close to the answer, but I don’t think so… .

Whether or not nature has an ultimate, simple, unified, beautiful form is an open question, and I don’t want to say either way.

In the 1980s a mathematical y powerful and experimental y untestable attempt at unification emerged in the form of string theory, using stringlike entities wrapped through many dimensions as their fundamental objects. The extra dimensions are supposed to fold themselves out of the way in a kind of symmetry breaking given the name compactification . String theory relies on Feynman’s sum-over-histories method as an essential underlying principle; the theory views particle events as topological surfaces and computes probability amplitudes by summing over al possible surfaces. Feynman kept his distance, sometimes saying that perhaps he was too old to appreciate the new fashion. String theory seemed too far from experiment. He suspected that the string theorists were not trying hard enough to prove themselves wrong. In the meantime he

never adopted the rhetoric of GUT’s. It made him uncomfortable. He retreated into the stance that he himself merely solved problems as they came along.

When a historian of particle physics pressed him on the question of unification in his Caltech office, he resisted.

“Your career spans the period of the construction of the standard model,” the interviewer said.

“‘The standard model,’” Feynman repeated dubiously.

“ SU (1) × SU (2) × U (1). From renormalization to quantum electrodynamics to now?”

“The standard model, standard model,” Feynman said.

“The standard model—is that the one that says that we have electrodynamics, we have weak interaction, and we have strong interaction? Okay. Yes.”

The interviewer said, “That was quite an achievement, putting them together.”

“They’re not put together.”

“Linked together in a single theoretical package?”

“No.”

The interviewer was having trouble getting his question onto the table. “What do you cal SU (×3) SU (2)× U (1)?”

“Three theories,” Feynman said. “Strong interactions, weak interactions, and electromagnetic… . The theories are linked because they seem to have similar characteristics… . Where does it go together? Only if you add some stuff that we don’t know. There isn’t any theory today that has SU (3) × SU (2) × U (1)—whatever the hel it is

—that we know is right, that has any experimental check… .

Now, these guys are al trying to put al this together.

Now, these guys are al trying to put al this together.

They’re trying to. But they haven’t. Okay?”

Particle physicists were his community. They were the elite who revered him, who passed along his legend, who lent him so much of his prestige. He rarely dissented publicly from their standard dogma. For the past two decades, he had worked on their problems: try though he might to disregard , in the end he had accepted their agenda.

“So we aren’t any closer to unification than we were in Einstein’s time?” the historian asked.

Feynman grew angry. “It’s a crazy question! … We’re certainly closer. We know more. And if there’s a finite amount to be known, we obviously must be closer to having the knowledge, okay? I don’t know how to make this into a sensible question… . It’s al so stupid. Al these interviews are always so damned useless.”