by John Gribbin
The recovery from the trough he had experienced after the award of the Nobel Prize had begun in 1967, when he visited the University of Chicago. The slump in Feynman’s creative physics activity had really begun in 1961, when he had finished most of his work on gravity and made the commitment to two years’ concentrating on the Lectures. It had been the longest more-or-less fallow period of his life in physics; but it is somehow an appropriate part of the Feynman legend that what put him back on the track to real scientific creativity was not an encounter with a new idea in physics, but an encounter with a molecular biologist, James Watson.
Feynman had got to know Watson during the sabbatical year that Dick had spent as a ‘graduate student’ in biology. He had an opportunity to renew the acquaintance when he visited Chicago early in 1967, and when they met Watson gave Feynman a copy of the typescript of what was to become his famous book The Double Helix, about his discovery, together with Francis Crick, of the structure of DNA.21 Feynman read the book straight through, the same day. He had been accompanied on that trip by David Goodstein, then a young physicist just completing his PhD at Caltech, and late that night Feynman collared Goodstein and told him that he had to read Watson’s book – immediately. Goodstein did as he was told, reading through the night while Feynman paced up and down, or sat doodling on a pad of paper. Some time towards dawn, Goodstein looked up and commented to Feynman that the surprising thing was that Watson had been involved in making such a fundamental advance in science, and yet he had been completely out of touch with what everybody else in his field was doing.
Feynman held up the pad he had been doodling on. In the middle, surrounded by all kinds of scribble, was one word, in capitals: DISREGARD. That, he told Goodstein, was the whole point. That was what he had forgotten, and why he had been making so little progress. The way for researchers like himself and Watson to make a breakthrough was to be ignorant of what everybody else was doing, and plough their own furrow.22 In a letter to Watson that is preserved in the Caltech archive, Feynman wrote ‘you are describing how science is done. I know, for I have had the same beautiful and frightening experience.’
In fact, what Watson was describing was how science is done not by ordinary scientists, but by those rare individuals who have the ability to achieve new insights and make major breakthroughs. Watson himself had the ‘beautiful and frightening experience’ once, and earned a Nobel Prize for his efforts. Such a singular achievement is far beyond the realistic aspirations of the great majority of scientists. Even Dirac reached the pinnacle only twice, first with his version of quantum mechanics, then with the equation of the electron. Yet by the time Feynman wrote those words, he had already had that beautiful and frightening experience three times, in his work on QED, on superfluidity and (best of all, in his own eyes) on the weak interaction. And now, he was about to experience it again, as he stopped trying to keep up with the scientific literature or compete with other theorists at their own game, and went back to his roots, comparing experiment with theory, making guesses that were all his own, and coming up with an insight that would give an enormous impetus to the development of particle physics in the 1970s. He would show that there was, indeed, life as a theoretical physicist of the top rank beyond the Nobel Prize.
Notes
1. But still, very well known in the world of physics. Interviewed by JG in October 1995, Norman Dombey, who was a graduate student in physics at Caltech in the early 1960s, said that at that time ‘Feynman was the guy in the subject, and had been since Los Alamos. The only other person on a par was Landau, and Feynman thought that too; he regarded Landau as his Soviet equivalent.’ The reference is to Lev Landau, of liquid helium fame.
2. Sands, foreword to volume two of The Feynman Lectures on Physics, hereafter referred to as the Lectures.
3. Leighton, foreword to volume one of the Lectures.
4. See Most of the Good Stuff.
5. Interview with JG, April 1995. This is similar to the way in which Feynman honed his anecdotes about his own life to tell the truth, but to tell it in an entertaining way.
6. Six Easy Pieces (see Bibliography).
7. See Most of the Good Stuff.
8. David Goodstein, interview with JG, April 1995.
9. Thanks to notes taken by two of the graduate students who attended those lectures, the first sixteen of them, roughly covering the work up to the point where Feynman ran into a brick wall, were eventually published, in 1995, as Feynman Lectures on Gravitation. Their significance today is discussed in Chapter 14.
10. Jagdish Mehra says that exactly the same thing occurred when Dirac was offered the Nobel Prize. He wanted to turn it down, but was advised by Ernest Rutherford that he would get more publicity by refusing the prize than by accepting it. Several times, Dirac commented to Mehra that the prize had been ‘a nuisance’.
11. Mehra.
12. Nobel lecture, Science, volume 153, page 699, 1966.
13. Surely You’re Joking.
14. Mehra.
15. Leighton, interview with JG, April 1995.
16. See contributions by Carl and Richard to No Ordinary Genius.
17. Letter in Caltech archive; also quoted by Schweber.
18. See Zorthian’s contribution to No Ordinary Genius.
19. Surely You’re Joking.
20. Surely You’re Joking.
21. The best available edition of Watson’s famous book is the ‘critical edition’ edited by Gunther Stent (Weidenfeld & Nicolson, London, 1981). This includes all of Watson’s text (originally published in 1968), plus reviews, commentaries and reprints of some of the original scientific papers.
22. David Goodstein, interview with JG, April 1995; see also Gleick.
* Our emphasis.
10 Beyond the Nobel Prize
Albert Einstein was almost unique among the physicists of modern times in making major contributions to fundamental physics in each of three separate decades – the 1900s, the 1910s and the 1920s. Born in 1879, he completed his last important work, involving the application of Bose–Einstein statistics, in the mid-1920s, a couple of years short of his own fiftieth birthday. But his achievement is only ‘almost’ unique because it has been matched by one other physicist, Richard Feynman, who made major contributions to fundamental physics in the 1940s, 1950s and 1960s. Indeed, Feynman’s last great work continued well into the 1970s, and occupied him until only just before his own sixtieth birthday. In the words of David Goodstein, ‘even among Nobel Prize-winners, he was extraordinary. Long before he won the Nobel Prize, he was a legend in the community of scientists.’1
Feynman made his name in the 1940s with his work on QED, providing a theory of one of the four fundamental forces (or interactions) of nature, electromagnetism. In the 1950s, as we have seen, he made a major contribution to developing physicists’ understanding of another fundamental force, the weak interaction, and then went on to make a major contribution (only fully appreciated in the 1980s and 1990s) to the understanding of a third force, gravity. His work in the late 1960s and early 1970s provided profound insights into the workings of the fourth force, the strong interaction. Nobody else has made such influential contributions to the investigation of all four of the interactions – even Murray Gell-Mann, for example, made significant contributions only to the study of two of the interactions (the strong and the weak), and he is generally regarded as a remarkable genius.
Gell-Mann, who worked in the office just down the hall from Feynman at Caltech, was closely involved in theoretical investigations of the particle world in the 1950s and 1960s, and helped to bring some sort of order into the chaotic confusion of particles that had been discovered as the new particle accelerators had probed to higher and higher energies. Although he and Feynman had collaborated, in memorable fashion, on one important piece of work concerning the weak interaction, their styles and approaches to physics were so different that it was inevitable that they would largely go their own ways, although it was convenient for each of t
hem to have the other to bounce ideas off on occasion. Was there a rivalry between them which helped to spur each of them on? Norman Dombey, one of Gell-Mann’s former students, says that ‘I think it spurred Gell-Mann on. He couldn’t stand anybody beating him.’2 If so, he was certainly spurred on to good effect.
Back in the early 1930s, physicists had known of just four fundamental particles, to set alongside the four fundamental interactions. All you needed to explain the properties of everyday atomic matter were the proton, the neutron and the electron, together with the neutrino, which had never been detected directly, but was needed to explain details of beta decay. Then, ‘new’ particles began to turn up – very short-lived particles, which quickly decayed into the familiar stable particles and intense pulses of electromagnetic radiation, but real none the less, with distinctive properties (such as mass and charge) that could be measured during their brief lives. The first of these particles were found in showers of cosmic rays. Then, after the Second World War, physicists began to build the ‘atom smashing’ machines in which they could create exotic particles more or less at will.
This work involves using electromagnetic fields to accelerate particles such as electrons and protons to high velocities (a sizeable fraction of the speed of light), and then smash the beams of high-energy particles into either a target of ordinary matter, or into another beam of particles going in the opposite direction. When some of the particles in such a beam arc brought to a sudden halt in the resulting collisions, their energy of motion (the kinetic energy) is released, and is available to manufacture other particles, in line with Einstein’s equation E = mc2.
It is important to stress that the exotic particles are manufactured out of pure energy. If a fast-moving electron collides with a neutron, say, and produces a shower of particles, this does not mean that those particles were in any sense hidden inside the neutron waiting to be liberated; in such experiments, the combined mass of the particles produced in the collision may be many times more than the mass of the neutron, and all this mass has come from the energy of motion of the colliding particles.
By the end of the 1950s, dozens of different kinds of particles were known that could be produced out of energy in this way, live their brief lives, then decay into a mixture of high-energy photons and ordinary stable particles. How could such a profusion of particles be regarded as in any sense ‘fundamental’? How could some sort of order be brought into the chaos?
The first step was to group the particles according to their common properties. There are two key criteria. Particles which are affected by the strong force (such as protons and neutrons) are called baryons. Particles which are not affected by the strong force (such as electrons) are called leptons. Baryons and leptons are all fermions. In each case, there are force-carrying bosons (such as the photon), with the ones that carry the strong force generally referred to by the overall name of mesons. And mesons and baryons are together often referred to as hadrons. The embarrassing proliferation of particles in the 1950s chiefly involved hadrons, with both new baryons and new mesons turning up by the handful.
In 1961, Gell-Mann and the Israeli physicist Yuval Ne’eman (then working at the University of London, in England) independently hit upon a way of arranging hadrons in accordance with their properties (mass, charge and so on) in a pattern that Gell-Mann dubbed ‘the eightfold way’, because it grouped the particles in octets. The approach was very similar to the way Dmitri Mendeleyev had grouped the chemical elements into the pattern that we now call the Periodic Table, back in the 1860s. Just as Mendeleyev’s arrangement of chemical elements only worked if certain gaps were left in his table, corresponding to elements that had not yet been discovered, so the eightfold way classification only worked if certain gaps were left in some of the octets, corresponding to particles that had not yet been discovered. And, just as Mendeleyev was triumphantly proved correct when new chemical elements were found with exactly the properties required to slot them into the gaps in his table, so Gell-Mann and Ne’eman were triumphantly proved correct when new particles were found with exactly the properties required to slot them into the gaps they had left in their classification. For this and his other work on the classification of fundamental particles, Gell-Mann received the 1969 Nobel Prize for Physics; surprisingly, the Nobel Committee overlooked Ne’eman.
The order in the Periodic Table of the Elements is explained, of course, because atoms are not indivisible. The properties of atoms are determined by the number and nature of the particles they are made of – the electrons, protons and neutrons. It was natural to guess that the order in the eightfold way classification might be explained if hadrons were also composed of different arrangements of some sort of truly fundamental particles. But physicists were so used to thinking of protons and neutrons, in particular, as indivisible fundamental entities that it took a long time for the idea that they might be composite entities to become accepted. It was in making this concept (of protons, neutrons and other baryons being composite particles) acceptable that Feynman made his next great contribution to physics. But he was not the first on the trail, because in the early 1960s he was finishing up his work on gravity and becoming deeply immersed in his undergraduate lectures.
The first tentative steps towards the idea of a deeper layer of particles within the hadrons was made in 1962 by Ne’eman (then working for the Israel Atomic Energy Commission) and his colleague Haim Goldberg-Ophir. They wrote a paper suggesting that baryons might each be made up of three more fundamental particles, and sent it to the journal Il Nuovo Cimento, where it was mislaid for a time, but was eventually published in January 1963. The paper attracted little attention, partly because the eightfold way itself had not yet been fully accepted, but also, as Ne’eman has acknowledged, ‘because it did not go far enough. The authors had developed the mathematics resulting from the eightfold way, but they had not yet decided whether to regard the fundamental components as proper particles or as abstract fields that did not materialize as particles.’3
One person who had no such inhibitions was George Zweig, a PhD student at Caltech. Zweig had been born in Moscow in 1937, but moved to the United States in the 1950s and obtained a BSc in mathematics from the University of Michigan in 1959. He started his research career at Caltech as an experimental particle physicist, but after three years struggling with a recalcitrant experiment on an accelerator called the Bevatron, he decided that experiment was not his forte and turned to theoretical physics, under the nominal guidance of Richard Feynman but actually working largely on his own. Zweig was immediately taken with the beauty and simplicity of the eightfold way, and quickly realized that the pattern of octets could be explained if mesons and baryons were composed, respectively, of pairs and triplets of fundamental entities, which he called ‘aces’. Zweig regarded these, from the outset, as real particles, not ‘abstract fields’, and he was unfazed by the fact that in order to make the scheme work each of his aces would have to have a fraction of the charge on the electron – either ⅔ or ⅓, in units where the electron’s charge is 1.
Although Zweig wrote up his ideas for publication, they met with such a violent response that the papers were never formally published in their original form. In 1963, on a one-year visit to CERN, Zweig prepared two papers which were circulated in the form of CERN ‘preprints’, but as he later recalled:
Getting the CERN report published in the form that I wanted was so difficult that I finally gave up trying. When the physics department of a leading university was considering an appointment for me, their senior theorist, one of the most respected spokesmen for all of theoretical physics, blocked the appointment at a faculty meeting by passionately arguing that the ace model was the work of a ‘charlatan’.4
As if this were not bad enough, Zweig’s work was soon to be overshadowed by Gell-Mann, who had hit on the same idea, completely independently, back at Caltech. But Gell-Mann was much more cautious, and trod a path almost exactly halfway between the confident espousal of
aces as real by Zweig, and the dismissal of the ‘fundamental components’ as ‘abstract fields’ by Ne’eman and Goldberg-Ophir. Like Zweig, he gave the fundamental entities a name (‘quarks’); but like the Israeli team he expressed reservations about their reality. In a paper that was published in Physics Letters in 1964, Gell-Mann said:
It is fun to speculate about the way quarks would behave if they were physical particles of finite mass (instead of purely mathematical entities as they would be in the limit of infinite mass) … a search for stable quarks of charge –⅓ or +⅔ and/or stable diquarks of charge –⅔ or +⅓ or +4⁄3 at the highest energy accelerators would help to reassure us of the non-existence of real quarks!5
This is an astonishingly oblique way of presenting a great new idea in physics, and one which Gell-Mann lived to regret. With hindsight, it is probably unfortunate that Zweig was away from Caltech when he developed the theory of aces. Back in Pasadena, he would have had the chance to discuss the idea with Feynman, and almost certainly the Caltech authorities would have urged a joint publication with Gell-Mann, just as Feynman and Gell-Mann had been forced into a fruitful shotgun marriage with their work on the weak interaction. A joint paper by Gell-Mann and Zweig, less overtly cautious than Gell-Mann’s paper but not triggering the same knee-jerk reaction as Zweig’s preprints, and endorsed by Feynman, might well have made more of a splash in 1964 than either of their solo efforts. As it was, it took a long time for physicists to become convinced that anything was going on inside the hadrons. When physicists did become convinced of the reality of these entities inside the baryons, it was Gell-Mann’s name, not Zweig’s, that stuck. According to Gell-Mann,6 he chose the name as a made-up nonsense word, meaning it to rhyme with ‘pork’, and only later realized the relationship to the passage in James Joyce’s Finnegans Wake, referring to ‘three quarks for Muster Mark’, which suggests a pronunciation to rhyme with ‘bark’. But since Gell-Mann had previously read Finnegans Wake several times, the association may have been there in his subconscious all along. Either way, both pronunciations are used today.
