Quantum Man: Richard Feynman's Life in Science (19 page)

Nowadays, the violation of reflection symmetry in the weak interaction is most easily displayed by a simple statement: the exotic particles called neutrinos, the products of beta decay so-named by Fermi, which are the only known particles to interact solely by the weak interaction, are “left-handed.” As I have described, most elementary particles carry angular momentum and behave as if they are spinning. Objects that spin one way would be observed to be spinning in the opposite direction if viewed in a mirror. All other known particles can be measured to behave as if they were spinning either clockwise or counterclockwise, depending on the experiment. However, neutrinos, the elusive weakly interacting particles, maximally violate mirror symmetry, at least as far as we know. They only spin one way.

Tsung-Dao Lee was actually alluding to this implication when he was describing his work with Yang at the 1957 Rochester Conference, and it grabbed Feynman’s attention. Back in the early days, when Feynman was trying to first reproduce Dirac’s equation as an undergraduate with Ted Welton, he had missed the boat, coming up with a simpler equation that didn’t properly incorporate the spin of the electron. Dirac’s equation had four different components, to describe the two different spin configurations of electrons and of their antiparticles positrons.

Feynman now realized that by using his path-integral formalism, he could naturally come up with an equation that looked like Dirac’s but was simpler. It had only two components. This excited him. He recognized that if history had been different, his equation could have been discovered first, and Dirac’s equation derived from it later. Of course, his equation ended up having the same consequences as Dirac’s—his equation described one spin state of the electron and one for its antiparticle, and there was another similar equation that described the other two states—so it was not really new. But it did offer a new possibility. For neutrinos, which appeared to have only one spin state, his equation would, he felt, be more natural.

There was one problem, however. If one tried to mathematically incorporate this kind of equation to describe the weak interaction that led to beta decay and the production of neutrinos, it would yield results different from those that experimenters seemed to be unearthing with their experiments. The strange thing, though, was that these experimental results were inconclusive, and inconsistent with a single force at work. If one classified all the different mathematical forms one could write for the interactions of a neutron, proton, electron, and neutrino (the latter three the products of the decay of the former), one would find five different possibilities:
scalar (S), pseudoscalar (P), vector (V), axial vector (A),
and
tensor (T)
. This mathematical classification scheme describes the properties of the interactions under rotations and parity flips. Each interaction has different properties. The fact that the weak interaction violates parity meant that it had to combine at least two different types of interactions, each with different parity properties. The problem was that beta-decay experiments suggested the combination was
S
and
T
, or
V
and
T
, whereas Feynman’s two-component picture required a combination of
V
and
A.

Feynman wasn’t the only one thinking about these questions. Gell-Mann, who had been contemplating parity issues for some time, was also keen to unify the various weak decays, having been scooped by Lee and Yang and perhaps more bothered by that than Feynman. While Feynman was once again off in Brazil cavorting for the summer, Gell-Mann remained in California working.

But there were also others, and a particularly tragic case involves the physicist E. C. G. Sudarshan, a young Indian physicist who had come to the University of Rochester in 1955 to work with physicist Robert Marshak. In 1947 Marshak had suggested that two different kinds of mesons had been observed in experiments, one, the pion, that corresponded to the strongly interacting particle that physicists had expected, and a different one, the muon, that is now known to be simply a heavy version of the electron. Marshak was also well known in the community as the originator of the Rochester Conferences, where the central problems of the day in particle physics, like the tau-theta problem, and parity violation were hashed out.

As a graduate student Sudarshan had gained a thorough knowledge of nuclear physics, and neutron beta decay in particular, and after parity violation was discovered, he and Marshak investigated the current experimental data and decided that the conventional assignment of
S
and
T
for nuclear beta decay had to be wrong. They realized that all weak decays, including the decays of muons, could be unified together only if the interaction had a
V-A
form.

Remarkably, Sudarshan was set to present these results at the seventh Rochester Conference in 1957, where Marshak was the chair. Marshak, however, decided that as a graduate student, Sudarshan was not a delegate to the conference, and since he, Marshak, was giving a review talk on another subject, he felt he could not speak on the subject, so a prime opportunity to announce their proposal to the community was lost. As the data related to muon decay into pions, which also subsequently have weak decays into electrons and neutrinos, was not very solid, Marshak was probably hesitant to make any definitive claims at this time.

Instead, over the summer Marshak and Sudarshan completed a systematic analysis of the data up to that time, and prepared a paper proposing a
V-A
universal form of the weak interaction that Marshak would present that fall in Padua, Italy. It was a brave claim, as it required no less than four different experimental results to be wrong. During this period Marshak and Sudarshan were in California, at UCLA, and they dropped by to talk to Gell-Mann, who also set up a meeting for them with Caltech experimentalist Felix Boehm. They explained to Gell-Mann, who had been thinking about
V-A
but dropped the idea because it disagreed with some data, that they felt these experiments could be wrong. Boehm reassured them by explaining that his experimental findings were now consistent with
V-A
.

Gell-Mann, who had also realized that
V-A
was the only sensible form for a universal weak interaction, if there indeed was one, told the anxious duo of Marshak and Sudarshan that he was not planning to write a paper on the subject, but might mention the possibility in a paragraph of a long review he was writing on the weak interaction. He then headed off for a vacation, and Marshak and Sudarshan headed home.

Meanwhile Feynman had been obsessed with the idea of a universal weak interaction, perhaps his last hope for discovering a fundamental law. The confusing state of the different experiments, however, remained a stumbling block. Upon returning to Pasadena while Gell-Mann was on vacation, he learned that Boehm and Gell-Mann had been talking about the possibility of
V-A
satisfying the experimental constraints after all.

That, for Feynman, was when a bell went off. If this was true, his idea about describing neutrinos by two components in a simple mathematical form that could accommodate beta decay was right. As he later put it, “I flew out of the chair at that moment and said, ‘Then I understand everything. I understand everything and I’ll explain it to you tomorrow morning.’ . . . They thought when I said that, I’m making a joke. . . . But I didn’t make a joke. The release from the tyranny of thinking it was S and T was all I needed, because I had a theory in which if V and A were possible, V and A were right, because it was a neat thing and it was pretty.” Feynman was so excited that he convinced himself he was the only person in the world who understood that
V-A
would produce a universal form for the weak interaction. Indeed, he had his own peculiar reasons for thinking so, due to, as usual, his own unique formalism. With uncharacteristic speed, he proceeded to draft a paper—his great hope for a new theory of nature, he thought.

Gell-Mann, in the meantime, returned back to Caltech to learn that Feynman was writing up his proposal, while Gell-Mann had had his own reasons for thinking of
V-A
, having to do with the symmetries of the
currents
, or the flow of charges that were associated with the particles entering and leaving the reaction. He decided, in spite of his assurance to Marshak, that he had to write his own paper.

In one of the moments that make the life of a department chairman less than fun (moments that are only too familiar from my own twelve years in such a position), the chair of the Caltech physics department decided his two stars shouldn’t be playing dueling papers, and told them to team up and write a single paper. Surprisingly, Feynman and Gell-Mann agreed.

The Feynman–Gell-Mann paper was an interesting kluge of styles, but a masterpiece nevertheless. It had the best of both, Feynman’s two-component neutrino formalism (which later would become useful, though at the time it seemed contrived) and Gell-Mann’s brilliant thoughts on conserved quantities and symmetries associated with weak currents (which would prove useful far beyond understanding beta decay for years to come).

Needless to say, word of the Feynman–Gell-Mann paper quickly spread, and poor Sudarshan had to endure talk after talk where he heard the idea for
V-A
attributed to these two leading lights. It was true that Gell-Mann had insisted on an acknowledgment in their paper to discussions with Marshak and Sudarshan, and he always tried to write supportive letters for Sudarshan, and Feynman later acknowledged to Sudarshan that he had since been told that Sudarshan had had the idea for
V-A
before anyone else, and subsequently admitted such in public. But for years, the Feynman–Gell-Mann paper became the classic and only reference people quoted when discussing the idea.

This might have been the only time in his career that Feynman felt so driven and so excited by an idea that he wanted to publish it as his own. It was, he felt, perhaps his proudest moment, or as he put it, “There was a moment when I knew how nature worked. It had elegance and beauty. The goddamn thing was gleaming.” And it was a beautiful piece of work, as one might expect from the two most creative minds in particle physics of their era. Though not earth-shattering, nor even completely surprising, and certainly not a complete theory of anything (the full theory of the weak interaction would take another decade to be written down, and another decade after that to be accepted), in spite of Feynman’s subjective assessment, for the world it seemed to signify that the partnership which had started in 1954 when Gell-Mann moved to Caltech to be near Feynman had reached a kind of fruition that promised great things to come.
Time
magazine profiled the two of them among the leading lights in U.S. science: “At the blackboard the two explode with ideas like sparks flying from a grindstone, alternately slap their foreheads at each other’s simplifications, quibble about the niceties of wall-length equations, charge their creative batteries by flipping paper clips at distant targets.”

But this was not the beginning of a beautiful partnership. It was closer to the end. Just as their collaboration had been a forced marriage, the two geniuses, while never losing their respect for each other’s abilities and ideas, carried out their future work on parallel tracks. Sure, they would consult each other for advice and periodically bounce ideas off each other. But never again would they collaborate to “twist the tail of the cosmos.” Gell-Mann was soon to make his greatest contribution to physics, and Feynman was to focus on other things for almost a decade, then returning to particle physics and ironically helping to convince the world that Gell-Mann’s mathematical invention, quarks, might actually be real.

CHAPTER
14

Distractions and Delights

The Prize is the pleasure of finding things out.

—R
ICHARD
F
EYNMAN

A
t last Feynman had written up a brilliant idea in a timely manner and was satisfied—incorrectly it turned out—that he had finally been the first to unveil for the world a new law of nature. He could now revel in the pleasure of both sharing the limelight with Gell-Mann and being at the center of the physics universe.

With Gell-Mann and Feynman at Caltech, it became a place where physicists went to learn, to collaborate, or simply to reflect their own ideas off the combined brilliance of the two greatest physics minds of their generation. A succession of fertile young theorists would study there and then move on to seek out brave new worlds. Feynman himself had almost no graduate students, but the combined attraction of Feynman and Gell-Mann was enough to lure both students and postdoctoral researchers, numerous future Nobel laureates among them, to the institution.

Some were shocked at the attention they received. Barry Barish, then a budding young experimentalist from Berkeley and later a colleague of Feynman’s at Caltech, gave a seminar there and was overwhelmed to see Feynman and later to be peppered with questions by him. Barish recently related to me how self-satisfied and important he felt at the time. That is, until others told him that Feynman attended all of the seminars and was full of questions—there was nothing special about his visit.

At the same time the place could be intimidating. Gell-Mann could be cutting, usually in private. On the rare occasions when Feynman thought little of one’s work, he could be openly dismissive or worse. What would set him off would not always be clear. Certainly he had little patience for nonsense, but he also clearly reacted negatively to approaches that were valid, perhaps even brilliant, but reflected a style he didn’t like. An example is the reception a young theorist, Steven Weinberg, received when he went to Caltech to present a seminar on his ideas. Weinberg, who later became one of the world’s most respected and accomplished physicists (and later shared the Nobel Prize for coming up with a full theory of the weak interaction, unifying it with electromagnetism), often sought out detailed formal solutions, working from the general to the particular—the opposite of how Feynman often worked. This physicist of such obvious substance was so mercilessly questioned by both Feynman and Gell-Mann that he almost could not finish his talk.

Feynman’s wrath was normally restricted to those who he felt were abusing physics by making unfounded claims, usually on the basis of insufficient evidence. To Feynman, the physics came first, and it didn’t matter who the culprit was. Perhaps the most famous example that I am personally aware of involved a future Nobel laureate, Fred Reines, who in 1995 won the prize for a 1956 experiment that first verified the existence of neutrinos. Reines had continued his work on neutrinos coming from nuclear reactors, and much later, in 1975 claimed to have evidence that neutrinos, which come in several types, were oscillating from one type into another as they traveled outward from the reactor. If true, this result would have been hugely significant (it turns out that neutrinos do oscillate—just not in the way Reines had claimed). Feynman examined the data and demonstrated that the claimed effect was not substantiated and publicly confronted Reines with his results, ultimately putting to rest this false positive. This embarrassment might have contributed to an almost forty-year delay in awarding Reines the Nobel Prize for his original discovery.

In any case, back in 1957 Feynman’s work with Gell-Mann on the weak interaction released him from a burden he had carried with him over the years as his fame in the community had continued to increase even as he remained personally skeptical about the significance of his work on QED. While he never lost interest in particle physics, he seemed freer to wander further afield and try his talents elsewhere.

At the same time, his mind was also wandering over other domains. His personal relationships were getting messy again. In 1958, in Geneva to present an overview of weak interaction physics at one of the first Rochester Conferences held abroad, he had planned to travel with the wife of a research associate at Caltech, with whom he had apparently been having an affair. This was happening even as another affair was coming to a brutal end, also with a married woman, and one whose husband was prepared to sue for damages. Ultimately that uproar died down, and the spurned lover eventually returned to Feynman both a gold medal he had been awarded as a part of the Einstein Prize in 1954 and some drawings by Arline.

In Geneva, Feynman found himself alone, since his lover had decided she would avoid Switzerland and meet him later in England. On the beach he met a young twenty-four-year-old Englishwoman, Gweneth Howarth, who was traveling around the world as an au pair, and at the time was in possession of no less than two other boyfriends, so in that sense they were even. Not surprisingly, he took her to a club that night, but much more surprisingly, before he left Geneva he invited her to come work for him as his maid in the United States, and he offered to assist with the necessary immigration procedures. (Whether he went on to meet with his other lover in London is not recorded.) There were, of course, inevitable delays, and even as Feynman continued to deal with the consequences of his other spurned lover, with whom he had considered marriage, Gweneth got involved in several romantic liaisons and periodically changed her mind about coming. Thus, while there had clearly been a spark between them, it is hard to know exactly what Feynman, or Gweneth, had in mind with all of this.

It was brought to Feynman’s attention that given the circumstances it might seem inappropriate at best, or illegal at worst, for a forty-year-old man to help transport this twenty-four-year-old woman to live under his roof, so his colleague, a delightful and free-spirited experimental physicist named Matthew Sands, arranged the paperwork in his name. Finally, after more than a year of delays, Gweneth arrived in Pasadena in the summer of 1959, and helped convert the house of this clearly lonely bachelor into a home. While she dated other men—whether a pretense or not, it is hard to say—this behavior too declined, and she would eventually accompany Feynman to social events, often leaving separately to keep up appearances. A little over a year after her arrival, Feynman asked her to marry him.

This story was the stuff of B-rated movies, not real life, and there was every reason to suggest that Feynman’s rash behavior would end up, like so many of his other romantic escapades, in disaster. But it didn’t. Two years later they had a son, Carl, and a dog. Richard’s mother moved out to live nearby, and he purchased a home close to his colleague and collaborator Gell-Mann and his new British bride. Feynman had become a family man. He and Gweneth later adopted another child, their daughter Michelle, and remained happily married until his death.

Feynman’s personal life finally settled down—it would after all have been impossible to have become more unsettled than it had been—but his mind remained restless. He considered moving into another field and toyed with genetics, egged on by his friend, physicist-turned-biologist and future Nobel laureate Max Delbrück. But that didn’t take for long.

He continued to work with Gell-Mann on the weak interaction and to tease him at seminars (though the sparring perhaps became a little more pointed over time), but his heart didn’t seem to be in this work. The two of them had an idea that there might be two different kinds of neutrinos in order to explain a puzzling experimental result, but Feynman lost interest in it and refused to write it up. Subsequently Leon Lederman, Melvin Schwartz, and Jack Steinberger won the Nobel Prize for experimentally verifying that this was indeed the case. On another paper, with Gell-Mann and several other colleagues, Feynman agreed to collaborate, and then after the preprint was sent out, he begged, successfully, to have his name removed before publication.

In 1961 an unusual opportunity came along that opened up his creative energy in a totally new way and helped catapult Feynman to a new rank within the physics community and beyond. It did not involve discovering a new law of nature, but rather discovering new ways to teach physics.

Undergraduates at Caltech were required to take two years of introductory physics courses, and like most such courses they were a disappointment, especially for the best and brightest students who had been excited by physics in high school and wanted to learn about relativity and the modern wonders and didn’t want to start over studying balls rolling down inclined planes. At the instigation of Matthew Sands, who had been discussing the idea with Feynman for some time, the physics department, and eventually the chair, Robert Bacher, the same one who had enforced the shotgun marriage of Feynman and Gell-Mann, decided to revamp the course. Again, at Sands’s suggestion, it was agreed that Feynman would take one entering class through the entire introductory sequence. Even though Feynman was not widely recognized for his teaching, his teaching reviews at Cornell had been very good, and he was well known in the community as a uniquely gifted expositor when he put his mind to it. His remarkable energy, his colloquial manner, his physics intuition, his Long Island accent, and his inherent brilliance gave him a riveting aura behind any podium.

Feynman took up the challenge and then some. He had tirelessly devoted his whole life to rebuilding in his own mind the entire edifice of physical law. The adventure of personal understanding had driven him since his childhood. Now was an opportunity for him to put this picture out there for others. (I have since discovered, while reading through Matthew Sands’s memoirs, that he used almost this same language to convince Feynman to teach the class.) He could put his own brand, not just on physics at the forefront, but on the very basic ideas that form the heart of our physical understanding. Over the next two years he devoted more intense energy and creativity into developing his lectures than he had put into anything since the war.

The timing was perfect. This expenditure was possible at that time in part because his wanderlust had subsided. With the stability of his marriage and domestic life, he was able to focus less on his own needs and desires, had fewer motivations to seek out adventures to mask his loneliness, and more importantly, could settle down in one place for the time required to sketch out a completely new introduction to the fundamentals of physics. He could show others not only how he personally understood the world, but also what had excited him enough to learn about it. He could make new connections, which is what science is all about, in unraveling the mysteries of the physical universe. He wanted to quickly take students to the exciting forefront mysteries, but at the same time show that they were not all esoteric, that many were connected to real phenomena as immediate as boiling oatmeal, or predicting the weather, or the behavior of water flowing down a tube.

Every day he arrived at class before the students, smiling and ready to regale them with yet another totally original presentation of everything from classical mechanics to electromagnetism, gravity, fluids, gases, chemistry, and ultimately even quantum mechanics. He would march back and forth behind a huge demonstration table and in front of a mammoth blackboard, yelling and grimacing and cajoling and joking. And by the end of the class he would make sure not only that the entire chalkboard was full, but that he had completed the circle of ideas he had set out at the beginning of class to discuss. And he wanted to show students that their lack of knowledge didn’t need to compromise their understanding, that with hard work even freshmen could address, in exact detail, some modern phenomena.

Most of all, he wanted to present a guide for understanding or, as he almost called it, “a guide for the perplexed”—after the title of the famous tract by the eleventh-century philosopher Moses Maimonides. As he said,

I thought to address them [the lectures] to the most intelligent in the class and to make sure, if possible, that even the most intelligent student was unable to completely encompass everything that was in the lectures—by putting in suggestions of applications of the ideas and concepts in various directions outside the main line of attack. For this reason, though, I tried very hard to make all the statements as accurate as possible, to point out in every case where the equations and ideas fitted into the body of physics, and how—when they learned more—things would be modified. I also felt that for such students it is important to indicate what it is that they should—if they are sufficiently clever—be able to understand by deduction from what has been said before, and what is being put in as something new.

In his excitement he also wanted to connect physics with the rest of science, to show that it was not an isolated island. He introduced the physiology of color vision and the very mechanical engineering applications that had so interested him when he was a student, and of course he described his own discoveries as well.

The department realized something special was happening, and Feynman was given great support and encouragement. Every week he would meet with other faculty who were assigned, under the supervision of Matthew Sands and Robert Leighton, to devise problem sessions and extra recitations to help the students. Since Feynman wasn’t teaching out of any textbook, it was necessary to have these meetings, and these instructors and assistants had to work full-time, both to keep up and to develop appropriate teaching materials to complement the course.

Soon, word of what was going on in the large lecture hall at Caltech spread, and graduate students and faculty began to trickle in to listen, even as the terrified and overwhelmed undergraduates stopped coming. As perhaps might have happened only at a school like Caltech, the department urged him to continue lecturing for a second year, in spite of the fact that many of the students couldn’t pass his exams.

The lectures were also recorded so that Sands and other colleagues, chiefly Leighton, could transcribe and edit them. Ultimately a three-volume set of “red books” appeared for sale around the world. Never before in modern times had someone so comprehensively or so personally re-created from scratch and reorganized the entire knowledge base and presentation of the basic principles of physics. This was reflected in the name given to the set:
The Feynman Lectures on Physics
.