My three interactions with the physicist Wendell Furry, all of which were memorable in their own way, took place within a period of seven years. The first was in the fall of 1948 when I was a sophomore at Harvard. I took a semester of freshman physics, which was taught by Furry. The second was on January 15, 1954 at a courthouse in Boston. I was in attendance when Furry testified before Senator Joseph McCarthy’s Permanent Subcommittee on Investigations.1 The hearing was concerned with “Subversion and Espionage in Defense Establishments.”2 My third and final interaction with Furry was a little over a year later at Harvard. He was one of the examiners when I defended my PhD thesis. Furry asked a question that I could not answer and I almost failed the examination.
Wendell Hinkle Furry was born in Prairieton, Indiana, on February 18, 1907. After graduating high school, Furry enrolled at DePauw University in nearby Greencastle. He began his studies hoping to become a chemist, but soon switched to physics and mathematics. Furry’s professor at DePauw suggested that he should do his graduate work at the University of Illinois.3 To cover his expenses, he applied for a teaching assistantship that paid seven hundred dollars a year.
In 1929, while Furry was a graduate student, F. Wheeler Loomis became the chairman of the physics department at the University of Illinois and set about making it one of the best in the country. With the help of Loomis, Furry was able obtain a postdoctoral fellowship from the National Research Council. Loomis later became the associate head of the wartime radar project at the MIT Radiation Laboratory in Cambridge, Massachusetts. Furry began working on the project as a researcher in 1942. The presence of Loomis may well have played a role in his recruitment.
A decade earlier, in 1932, having obtained his PhD at Illinois, Furry turned down an offer to become an instructor at Harvard. Instead, he decided to work with Robert Oppenheimer at the University of California, Berkeley. Some of Furry’s most significant and enduring work dates from the two years he spent with Oppenheimer.
In the following Feynman diagram, the wiggly lines represent photons and the arrows represent electrons or positrons, depending on the direction in which they are pointed.
Figure 1.
The odd number of photons is significant. Furry’s theorem for quantum electrodynamics states that Feynman diagrams with an odd number of external photons must vanish.4 I do not know how Furry proved his theorem since I have not read his original paper, but physicists would now use arguments based on charge conjugation invariance.
An electron at rest has a mass energy, but no kinetic energy. The bare mass is a parameter in the formalism of quantum electrodynamics, but it is not the mass one would actually measure. The electron is constantly interacting with its own electric field, illustrated in the Feynman diagram below.
Figure 2.
This interaction between the electron and its electric field produces an inertial effect that is reflected in a change to the mass. The first perturbative calculation of the electron’s self-energy was published in 1934 by Victor Weisskopf.5 He found that it was quadratically divergent. Furry checked the calculation and found that Weisskopf had made a mistake. The divergence was, in fact, only logarithmic. Furry asked Oppenheimer what he should do next. Oppenheimer told Furry that he had to decide whether to inform Weisskopf before publishing. Furry duly informed Weisskopf, who was able to publish his own correction.6
In 1934, Furry accepted an assistant professorship at Harvard and returned to Cambridge.7 Further significant results were to follow. Physicists still refer to his paper on neutrinoless double beta decay, “On Transition Probabilities in Double Beta-Disintegration.”8 At the time, beta decay was not described in terms of intermediate weak boson transmitters; the interactions were supposed to be direct contacts. Consider the following diagram, which shows a process first discussed by Maria Goeppert Mayer in 1935.9
Figure 3.
Two electrons emerge without any accompanying neutrinos. Furry’s contribution was to indicate what the observation of this process would say about neutrinos. If a particle is electrically neutral, it is not necessarily identical to its antiparticle. The neutron and its antiparticle are not identical, while the opposite is true for the neutral pi meson, or the pion and its antiparticle. What of the neutrino and its antiparticle?
In 1927, Enrico Fermi’s group in Rome, the Via Panisperna boys, was joined by a gifted young theorist, Ettore Majorana.10 Fermi later proclaimed Majorana the most brilliant physicist he had encountered. In 1933, Majorana spent a year working in Leipzig, where he became acquainted with Werner Heisenberg, among others. When he returned to Italy after his time in Germany, Majorana was transformed. He became a recluse, no longer published any new results, and continued his work alone. It was not until 1937 that he finally decided to rejoin the physics community and compete for a professorship. As part of this process, Majorana was required to submit a published work. In what was to become his most famous paper, “Teoria simmetrica dell’elettrone e del positrone (A Symmetric Theory of Electrons and Positrons),” Majorana showed that a Dirac neutrino would differ from its antineutrino, and a Majorana neutrino would not.11 Neutrinoless double beta decay, Furry observed, is only possible for Majorana neutrinos. This observation is the subject of ongoing experiments.
If anyone had asked me about Furry’s political inclinations, I would likely have described him as a midwestern Republican. When I learned that he had joined the Communist Party in 1938, I could hardly believe it. That he was allowed to work at the MIT Radiation Laboratory during the war seems remarkable: it was widely believed at the time that radar was far more likely to win the war than the atomic bomb. Still more puzzling is the fact that Furry was not the only Party member that worked on the radar project. Surely this situation must have been known to the FBI from their background checks? I am not aware of any espionage that took place among the radar group at MIT. The espionage cases at Los Alamos, on the other hand, are well known.
The hearing I attended at Boston in 1954 was, of course, chiefly concerned with espionage. I went because I thought Furry might welcome the sight of a friendly face. While I still retain a copy of the stenographic transcript of the hearings, which was printed by the Harvard University printing office, I cannot recall how it came to be autographed by Furry, McCarthy, and Leon Kamin. Furry signed “Best Regards.” Conspicuously absent is the signature of Roy Cohn, who was the chief counsel for the committee.
In relation to the hearings, Harvard had taken the position that in order to keep his job, Furry was not obliged to name names, but he was required to answer questions about his own activities. McCarthy’s overriding concern, on the other hand, was obtaining a list of the names of other party members. A game of cat and mouse ensued, of which the following exchange is typical:
The Chairman: Do you know of any one connected with Harvard who is or was a member of the Communist Party?
Mr. Furry: Sir, I am not sorting people for the committee.
The Chairman: Answer the question.
Mr. Furry: Well, I would like to make this statement, and that is that I have never at any time known anyone who held a permanent position on the Harvard faculty with the exception of myself or who has since come to hold or who now holds a permanent position on the Harvard faculty, to be a member of the Communist Party. Apart from that, I will refuse to answer the question.12
McCarthy summed up the proceedings:
This, in the opinion of the Chair, is one of the most aggravated cases of contempt that we have had before us, as I see it. Here you have a man teaching at one of our large universities. He knows that there were six Communists handling secret Government work, radar work, atomic work. He refuses to give either this committee or the FBI or anyone else the information which he has. To me it is inconceivable that a university which has had the reputation of being a great university would keep this type of a creature on teaching our children. Because of men like this who have refused to give the Government the information which they have in their own minds about Communists who are working on our secret work many young men have died in the past, and if we lose a war in the future it will be the result of the lack of loyalty, complete immorality, of these individuals who continue to protect the conspirators.13
Furry was indicted for contempt of Congress, but the charge was eventually dropped. The Harvard Corporation was minded to fire him, but many of his colleagues in the physics department threatened to resign in protest. Ten years later, Furry was appointed chair of the department of physics, a position he held between 1965 and 1968.
My final encounter with Furry took place in the spring of 1955. He was a member of the committee that examined me on my thesis. Indeed, apart from my thesis advisor Abraham Klein I think he may have been the only other examiner.14
At the time, quantum electrodynamics seemed to me to be a settled subject. The weak interactions—beta decay and the like—appeared almost an irrelevance. This, of course, changed dramatically a few years later when it was discovered that the weak interactions did not conserve parity. There were also a few strange particles that had been described, but no one quite knew what to make of them.
The real action at the time was thought to be the interactions of pions and nucleons, for which there were new experimental results. Yet the theorists were stuck. It was, more or less, a trivial matter to write down Feynman diagrams. But these were expansions in a coupling constant that was greater than one, as opposed to quantum electrodynamics where the expansion constant was around 1/137. A new expansion had been proposed by Igor Tamm and Sidney Dancoff. Their idea was to ignore all the diagrams containing loops and to expand the number of particles in intermediate states. Some fairly sensible results had already been achieved. Klein, my thesis supervisor, had become an expert and proposed a problem for me to work on involving the deuteron, the nucleus of heavy hydrogen.
One might imagine that the charge distribution of the deuteron in the ground state would be a sphere, representing the fact that the ground state, an S state, has no orbital angular momentum. It follows that there should be no quadrupole moment. This is not the case, which means that some other angular momentum state must mix with the S state. The next possibility is an angular momentum one state, a P state. This has the wrong parity, so the S state must mix with an angular momentum two state, a D state. Suppose one considered the exchange of mesons; how would this effect the situation? The exchange occurs when the neutron and proton are in close proximity, which changes the shape of the charge distribution. This is what I had been assigned to calculate using the Tamm–Dancoff method. I spent weeks doing numerical integrals on a mechanical calculator. It was a waste of time, but supplied some sort of answer—one that I am ashamed to say became my first physics publication.
Then came my thesis defense. Furry posed the question that would have been obvious to any good physicist: how big is the next term in the expansion? Klein had no idea, and, of course, neither did I. Klein said something that seemed to satisfy Furry and he left the room. I never saw him again. I got my degree and learned a lesson from a very good physicist.
Furry retired from Harvard in 1977. He died in 1984.
