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

Schweber. “The divergences that had previously been considered a disastrous liability now became a valuable asset.” Gel -Mann and younger theorists applied the notion with real success. “We very much need a guiding principle like renormalizability to help us pick the quantum field theory of the real world out of the infinite variety of conceivable quantum field theories,” said Steven Weinberg years later—recognizing, however, that he was begging the question of why ? Why should the correct theories be the computable ones? Why should nature make matters easy for human physicists? Feynman himself remained nearly as uncomfortable as Dirac. He continued to say that renormalization was “dippy” and “a shel game” and “hocus-pocus.”

By the 1960s he seemed to be withdrawing from the most esoteric frontiers of high-energy physics. Quantum electrodynamics had achieved the quiet stature of a solved problem. As a practical theory it had entered applied, solid-state fields like electrical engineering, where, for example, quantum mechanics gave rise to the maser, a device for creating intense beams of coherent radiation, and its successor, the laser. Feynman drifted into the theory of masers for a while, using his path integral methods to lay some of the foundation. He had also worked persistently on another solid state problem, the problem of the so-cal ed polaron, an electron moving through a crystal lattice. The electron distorts the lattice and interacts with its own cloud of distortion, creating, as Feynman realized, a kind of case study for examining the interaction of a particle with its field.

Again his diagrams and path integrals found fertile ground.

Yet this was minor work, not the special outpouring of someone already regarded as a legend (though each fal , it seemed, younger men won the Nobel Prize).

He could not find the right problem to work on. His Caltech salary passed the twenty-thousand-dol ar mark—

he was the highest paid member of the faculty. He started tel ing people jovial y that that was a lot of money to be paid for theoretical physics; it was time to do some real work . He had a sabbatical year coming. He did not want to travel. His friend Max Delbrück, himself a physicist turned geneticist, was always trying to lure physicists into his group at Caltech, saying that the interesting questions now lay in molecular biology. Feynman told himself that he would go into a different field instead of a different country.

In biology the theorists and the laboratory workers were stil largely one and the same. Feynman began in the summer of 1960 by learning how to grow strains of bacteria on plates, how to suck drops of solution into pipettes, how to count bacteriophages—viruses that infect bacteria—and how to detect mutations. He planned experiments at first to teach himself the techniques. Much of Delbrück’s laboratory devoted itself to the genetics of such microcreatures: tiny, efficient DNA-replicating machines. The most popular virus when Feynman arrived in the upper basement of Church Hal was a bacteriophage cal ed T4, which grew on the common strain of E. coli bacteria.

Less than a decade had passed since James Watson and Francis Crick had elucidated the structure of DNA, the molecule that carried the genetic code. Code was one word for this storing of information; geneticists also thought in terms of maps and blueprints, printed text and recording tape—the mechanics were far from clear. Mutations were known to be changes in the DNA sequence, but no one understood how a developing organism actual y “read” the altered map, text, or tape. Was there a biological copying, splicing, folding? Feynman began to feel at home in the

basement laboratory. He took comfort from the knowledge that everything around was made of matter. He felt wel acquainted with the essence of evaluating experiments—

as he said, “understanding when a thing is real y known and when it is not real y known.” He could see at once how the centrifuge worked and how ultraviolet absorption would show how much DNA remained in a test tube. Biology was messier—things grew and wiggled, and he found it difficult to repeat experiments as exactly as he wished.

He focused on a particular mutation of the T4 virus cal ed r I. This mutant had the useful quality of growing abundantly on one strain of the E. coli bacteria, strain B, while not growing at al on strain K. So a researcher could infect strain K bacteria with the mutants and watch for signs of T4.

If any appeared, it must mean that something had happened to the r I mutation—presumably, it had reverted back to its original form. Such “backmutation” was relatively rare, but when it happened, giving the virus the ability to grow again in the K bacteria, it could be detected with extreme sensitivity, rates as low as one in a bil ion.

Feynman compared finding a T4 backmutation to finding one man in China with elephant ears, purple spots, and no left leg. He col ected them, isolated them, and injected them back into bacteria of strain B to see how they would grow.

Odd-looking plaques appeared. Among the normal, backmutated T4, he began to see phages that did not grow as they should have. He cal ed them “idiot r ’s.” He could only guess what might be happening at the level of the DNA itself to create the idiot r’ s. He saw two possibilities: the site of the r I mutation in the DNA strand might have undergone a second, further mutation. Or a second mutation might have occurred at a different site, somehow acting to partial y cancel the effect of the first mutation.

Tools for directly examining the genetic sequence, letter by letter, base pair by base pair, did not exist. But by

painstakingly crossing the idiot r’ s with the original virus, Feynman was able to show that his second guess was correct: two mutations, situated close to each other on the gene, were interacting. Furthermore, he showed that the second mutation had the same character as the first; it was a no t he r r I mutation. He had discovered a new phenomenon, mutations that suppressed each other within the same gene. Friends of his in the laboratory cal ed these

“Feyntrons” and tried to persuade him to write up his work for publication. Elsewhere, discovered independently, the phenomenon came to be cal ed intragenic suppression.

Feynman could not explain it. The Caltech biologists had no clear model for understanding how the genetic code was read, how the information encoded in DNA actual y transformed itself into working proteins and more complex organisms. And Feynman’s time as a geneticist had come to an end. He desperately wanted to return to physics.

When he was not grinding microsomes, he had been working more and more intently on a quantum theory of gravity.

Without realizing it, Feynman had come to the brink of the next great breakthrough in modern genetics. The specialists had an advantage after al : a year later, Francis Crick’s team at Cambridge, England, used the discovery of intragenic suppression as the touchstone for an explanation of how the genetic code was read. They guessed, correctly, that the mutations actual y added or deleted a unit of DNA, thus shifting the message back or forward. One mutation threw the message temporarily out of phase; the next mutation put it back in phase. This interpretation suggested

—or perhaps Crick already had it in mind—one of the simplest, yet strangest, mechanical models for genetic decoding: that the message of the gene is read in linear fashion, one base pair after another, from beginning to end.

By 1966 Crick was declaring, “The story of the genetic code is now essential y complete.”

Ghosts and Worms