The absence of any Italian was a source of continuing irritation for the leaders of Italian physics. Not even the famous Guglielmo Marconi received an invitation, probably because he was considered more of an inventor than a scientist. Other distinguished Italians might have merited inclusion, such as Corbino in Rome, Garbasso in Florence, and even Levi-Civita, who, though not a physicist, had developed much of the mathematical framework for Einstein’s theory of general relativity. Lorentz ignored them all. Italian physicists were simply not part of the highest-level dialogues in the field.
Feeling shunned, Corbino came up with an idea that he thought would alter the playing field. If Italians could not get invited to Solvay, he would hold a conference of his own. He had two major assets on his side. First, of course, was Fermi, already known to many of those invited to Solvay. The other was the natural beauty of Italy’s Lake District. Breathtaking lakes nestled in the valleys of the Italian Alps could, he imagined, provide an attractive place for Italy’s own conference on physics. He chose the town of Como for the site of his conference. The hundredth anniversary of the death of famed Italian physicist Alessandro Volta, who invented the electric battery, provided a credible reason to bring the world’s great physicists together.
And so it did. Among those who attended the conference in mid-September 1927, just one month before the fifth Solvay conference, were Niels Bohr, Max Born, Walter Bragg, Maurice de Broglie, Werner Heisenberg, Wolfgang Pauli, Max Planck, Ernest Rutherford, Arnold Sommerfeld, Pieter Zeeman, and even Solvay director Hendrik Lorentz himself. The Italians were there in full force, of course, with Corbino and Fermi acting as hosts for the events.
From an historical perspective, the most important presentation was that of Bohr, who took the opportunity to share some initial thoughts on his concept of complementarity, thoughts that he developed in greater detail a month later at the Solvay conference. Fermi, Heisenberg, and Pauli presented no papers of their own, but they did comment on Bohr’s paper and on a variety of other issues relating to quantum theory.
On a social level, it was an opportunity for Fermi to meet and greet many of the great names of the field. It was the first time Fermi met Pauli in person. Heisenberg introduced the two of them by saying something to the effect of “May I introduce the applications of the exclusion principle to each other.” Rasetti memorialized the moment in a photograph he took of the three young quantum theorists sharing a boat ride on Lake Como. In the photo Heisenberg is clearly the happiest, arms folded and beaming. He had just made an historic introduction and was probably quite pleased with himself. Pauli looks happy enough as well. It is Fermi who looks the most awkward; perhaps because Rasetti caught him just at a moment when the wind was whipping his thinning hair up and away from his head. Or perhaps it was the conflict he felt as host, colleague, and competitor with respect to his companions on the boat. Rasetti’s photo is one of the iconic images of twentieth-century physics, showing three of its greatest minds at the height of their intellectual powers.
FIGURE 7.3. Left to right: Fermi, Heisenberg, and Pauli, Lake Como, 1927. Photograph by Franco Rasetti. Courtesy of AIP Emilio Segrè Visual Archives, Segrè Collection.
Years later, Rasetti, reflecting on the importance of the Como conference, noted that in general Italian physicists were not aware of Fermi’s significance until Sommerfeld underscored the impact of Fermi’s work on statistical mechanics at this conference, in particular, pointing to its ability to explain the behavior of electrons in metals. The conference also made clear to the Italian physics community just how far behind it was because many of its senior physicists refused to adopt the new quantum theories of 1925–1926. It was, in Rasetti’s view, the moment when Italy began to recognize Fermi’s standing.
It was too late to invite Fermi to the fifth Solvay conference just a month later, and it is not clear just how much the Como conference influenced the organizers of Solvay, but they invited Fermi to attend the conferences in 1930, 1933, 1936, and 1939 (although the last one was canceled owing to the outbreak of World War II).
FERMI’S ARRIVAL IN ROME WAS NOT MET WITH UNIVERSAL WELCOME in the corridors of Via Panisperna. In particular, Antonino Lo Surdo, an older experimentalist with offices at Via Panisperna, resented the newcomer. Corbino and Lo Surdo were personal rivals and had been feuding for years before Fermi arrived on the scene. Lo Surdo had made some important discoveries but was overlooked for a Nobel Prize in 1919, perhaps in part because Corbino had worked hard to undermine his scientific reputation in Italy. By the time Fermi arrived in Rome Lo Surdo was a bitter man who resented the appointment of this prodigy to a new professorship at the institute.
Lo Surdo may not have won a Nobel Prize, but he was a member of the distinguished Accademia dei Lincei (Academy of Lynxes), the oldest scientific society in the Western world. Founded in 1603, among its earliest members was Galileo. By the early twentieth century, its status as Italy’s most prestigious scientific organization was unquestioned. At this point in Fermi’s career, it would have been natural for Corbino to nominate his protégé to the Accademia, and it would also have been natural for Lo Surdo to block the nomination. But the accepted narrative of these events, as told by Laura Fermi, does not cohere. As she would have us believe, Corbino prepared a nominating letter on behalf of Fermi and, because he would be traveling during the annual election meeting, entrusted this letter to Lo Surdo, who promised to submit it in Corbino’s absence. When Corbino returned, however, Fermi was not on the list of those elected. When he confronted Lo Surdo, the latter insisted he had forgotten to submit the nomination letter—an unlikely excuse, to say the least.
It is genuinely difficult to believe that, given their historic enmity, Corbino would have entrusted Fermi’s nomination to Lo Surdo. Their feud had lasted over a decade, and Corbino was highly sophisticated and politically adept. Further, the process of nomination was a complex, lengthy one, and many people would have been involved by the time an election was held; members would have been aware that Fermi was up for election well before the election date. The story does not hold up. Corbino probably had a different agenda.
Mussolini had long been planning to establish his own institution to rival the Accademia dei Lincei in prestige and importance. The Reale Accademia d’Italia (Royal Academy of Italy) was Mussolini’s brainchild, and the bill to establish it passed the Senate in 1926. Setting it up was complicated because the fascist dictator wanted to include the greatest cultural and intellectual figures in all of Italy, across all disciplines. He also wanted, somewhat naïvely, to include individuals who were not completely enamored with his fascist regime. Under the circumstances, it took until March 1929 for the government to compile a slate of inaugural candidates for the new academy. Corbino, no fan of the dictator, was nevertheless able to persuade Mussolini to place Fermi on the list of academicians.
Lo Surdo had expected to be named and was deeply disappointed to have been passed over. Corbino had in fact won a double victory. Not only had he influenced the naming of Fermi over Lo Surdo; he had done so at a time when he must have known that, owing to Mussolini’s new high-profile academy, the Accademia dei Lincei would soon fade in importance. Fermi was delighted. On that date he wrote in large capital letters in his notebook: “INCIPIT VITA NOVA—GAUDEAMUS IGITUR!” (Now begins a new life—let us rejoice!).
Newly appointed members of the Accademia d’Italia were celebrated in the press, and ceremonies of great pomp and elegance were held to honor them. Of far greater importance to Fermi, membership included a significant annual stipend of 36,000 lire for life, more than doubling his salary from the university. This enabled him to drop other distracting commitments he had made to supplement his income, most notably an editorship in Treccani’s Enciclopedia. It entitled him to be known as “His Excellency,” a title whose pretentions endlessly amused him. It also included a new uniform designed especially for the honor, with flowing robes and faintly ridiculous headgear. Self-conscious of appearing in public so
dressed, Fermi would drive himself in the bébé Peugeot to the meetings of the Accademia d’Italia and dress when he got there. On one occasion, he was challenged by a guard who was certain that such a car did not belong at an august meeting of the Reale Accademia. Fermi explained—truthfully, he would later recount with a smile—that he was the driver of His Excellency, Enrico Fermi. The guard waved him through.
The public was fascinated. Fermi was by far the youngest academician. Before his induction he was known by physicists throughout Europe for his work in quantum physics. His fame within Italian physics spread as a result of Sommerfeld and others’ comments at Como. As a result of his elevation to the Accademia, he was now known more broadly. He had become, as he would later say, “a great man.”
He was certainly willing to play Mussolini’s game, lending his name and his scientific prestige to the new fascist institution. He may well have thought that it was essential for continuing government funding for Italian physics. Corbino, no Fascist himself, probably felt the same way. Although the honors fed Fermi’s ego, he considered the various functions and receptions a waste of time. Every hour spent at the Reale Accademia was an hour away from his work at Via Panisperna. There was never any doubt about his priorities.
In this way an uneasy symbiosis was established between Fermi and the fascist regime. However readily he accepted the radical ideas of the new physics, he was personally conservative and may at some level have approved of the stability that Mussolini brought to Italy, despite the regime’s use of thuggery and violence. Fermi played the game and was trotted out as an example of the brilliant science sponsored by the regime. In return, his work was supported without interference. It was, to be sure, a deal done with the devil, but it served Fermi’s purpose. His trips to America, beginning in 1930 and continuing throughout the decade, showed him what opportunities lay abroad under a freer, more prosperous form of government, and he fully appreciated those opportunities. Laura’s resistance, however, prevented him from making a move.
IN THE END, THE IMPORTANCE OF THE ROME PERIOD HAD NOTHING to do with Fermi’s election to the Accademia d’Italia, nor to his growing celebrity, nor even to his ability to attract the best young talent to Via Panisperna. The importance of these years can only be measured by the discoveries made by Fermi and his little group perched on a hill overlooking Via Panisperna. The work in Florence had made him famous among physicists. The work in Rome would make him a legend.
CHAPTER EIGHT
BETA RAYS
ENSCONCED AT VIA PANISPERNA, FERMI BEGAN EXTENDING HIS work on statistical mechanics and then turned to quantum electrodynamics, a process that led him to his theory of beta radiation, considered by many today his most important contribution to physics.
Fermi’s first important paper of 1928 extended his work on statistical mechanics from a monatomic gas to the much smaller world of electrons around an atom. A monatomic gas is one in which only one type of atom is present, like an idealized helium-filled balloon. Fermi imagined that the cloud of electrons around a nucleus could be viewed as a gas with one type of particle. Fermi could apply his new statistical methods because electrons obey Pauli’s exclusion principle—no two can share the same quantum state. Pauli himself had used his exclusion principle to explain the way electrons fill up each orbital and why each orbital can contain only a finite number of electrons. Building on this, Fermi wanted to find an entirely probabilistic description of these orbitals to calculate the probability of finding electrons at any given place within the atom at any given time. Where the probability density was great, one was more likely to find an electron. Where the probability density was low, the probability of finding an electron would be lower. Fermi’s approach would also, in principle, give results consistent with Pauli’s rules regarding how many electrons could occupy each orbital.
The idea was an example of Fermi’s enthusiasm for taking ideas developed in one context and applying them in another. It had some usefulness in analyzing complex atoms and also had applications in calculating how charged particles would behave when moving through matter—the so-called stopping power of matter with respect to these charged particles. Eventually, it gave rise to density functional theory, which has proven sufficiently useful in condensed matter physics and computational chemistry that Walter Kohn and John Pople shared the 1998 Nobel Prize in Chemistry for its development.
There were, however, two problems with Fermi’s extension of his statistics to the electrons surrounding an atom. First, the technique as originally presented by Fermi had limited accuracy in a variety of important applications, a problem that was eventually overcome through the development years later of the Kohn-Pople density functional theory. The second problem was that someone else had beaten Fermi to the idea.
Llewellyn Thomas, a young British mathematical physicist who received his degree at Cambridge, read Fermi’s 1926 statistics paper and decided to see whether Fermi-Dirac statistics could model the electron’s behavior around the nucleus from a statistical perspective. His article, “The Calculation of Atomic Fields,” using the assumptions of Fermi-Dirac statistics as a starting point, came out in the Proceedings of the Cambridge Philosophical Society in January 1927, some eleven months prior to Fermi’s paper published in the journal of the Accademia dei Lincei. How Fermi missed Thomas’s paper remains a bit of a mystery. Fermi was, at this point, still reading the international journals on a regular basis, and it is difficult to imagine him glossing over Thomas’s work. Some have speculated that the physics department did not subscribe to the journal, which is true, but the Istituto Superiore di Sanita, located in the basement of Via Panisperna, certainly did. The journal itself was an important one, publishing the top British physicists and mathematicians of the day, people Fermi followed. It is possible, as some Italian historians point out, that he was indeed aware of the article but considered his own work to be sufficiently different to obviate the need for a direct reference.
In any event, Fermi’s attention soon turned to another, far more challenging and far more important issue. In 1927, Dirac continued his exploration into quantum theory and produced something monumental—a quantum theory of the electromagnetic field, known today as “quantum electrodynamics,” or QED. Because Dirac’s achievement laid the foundation for Fermi’s theory of beta radiation, it is essential to understand what Dirac achieved and how Fermi integrated Dirac’s accomplishment into his own thinking.
TO APPRECIATE THE MAGNITUDE OF DIRAC’S BREAKTHROUGH, IT helps to understand what his predecessors meant by an electromagnetic field. This concept of a field is the great contribution of the experimental physicist Michael Faraday, a high school–educated Englishman who conducted a series of experiments in the 1840s and 1850s to explore the relationship between electricity and magnetism. His concept of a field was quite simple: a region contains a field if objects therein feel a force without a direct physical connection. Observing how magnets and electricity flowing in a current affected each other, he posited a relationship between the electric field and the magnetic field. A Scottish physicist named James Clerk Maxwell subsequently put this relationship into a mathematically rigorous form. The eponymous Maxwell’s equations define the characteristics of the electromagnetic field.
Maxwell’s equations are classical, with three major characteristics that quantum mechanics would completely undermine. First, if one understands the strength of the field at any point, one can predict with certainty how a charged particle will behave at that point within the field. If one can characterize the field as a whole, one can predict the behavior of a charged particle at any point in the field—if it is moving in one direction at a particular moment, one can predict with absolute certainty where it will be at the next moment, irrespective of how soon that next moment is. Second, in classical electromagnetic theory, a field exerts a force that varies continuously throughout the field, influenced by such factors as the distance between a point and the source of the field, that is, electric currents and
charges or magnets. In fact, it is analogous to Newton’s laws of gravity, although unlike Newton’s gravitational field, Maxwell’s equations allow for repulsion as well as attraction between two charged particles or magnets. Finally, in classical electromagnetic theory, the particle itself is not a manifestation of the field. This seems so obvious at first glance that it might hardly be worth commenting on, except that it is not actually true, as Dirac would discover.
The quantum revolution changed forever the way physicists think about the world around us. The world is not perfectly predictable. Though predictions can indeed be made, there is an inherent uncertainty in these predictions that must be taken into account when calculating the behavior of very small objects like atoms or subatomic particles. Furthermore, the world is not continuous. Energy comes in the form of irreducible packets, imparting a granularity to a world previously thought of as smooth. An analogy might be the way we observe a body of water versus a sand dune. Significantly, a particle and its associated field are not independent. A particle is indeed a manifestation of the field with which it is associated. Any conception of an electromagnetic field that accords with the principles of quantum theory would have to incorporate these new insights.
Between 1900 and 1925, the theory of quantum mechanics developed apace, culminating in the 1925 work of Pauli, Heisenberg, and Schrödinger. Dirac followed these developments closely and wrote an astonishingly sophisticated thesis on the subject. Not content to rest there, however, he decided over the next two years to apply his insights into a reformulation of classical electromagnetic theory. In particular, he became interested in how Einstein’s theory of the photon—the particle of light that is created or absorbed during the shift in electron energy levels—could be interpreted in a general quantum theory. By 1927, he had done it. In an historic paper published in March 1927, he gave a new account of electrodynamics based on the idea of a quantum field, which treats the particle and the field not as two separate entities but rather as a single system consisting of the energy of the atom, the energy of the radiation field, and a “coupling” factor that connects the two. His mathematics, arcane and difficult even for seasoned physicists to follow, developed a model of the electron’s behavior that integrated the matrix mechanics approach of Heisenberg, Born, and Jordan with the wave formulation of Schrödinger. It also incorporated the special theory of relativity developed by Einstein in 1905, necessary because electrons nearest to the atomic nucleus travel at speeds approaching the speed of light. At these speeds, the weird effects of Einstein’s theory become relevant.
The Last Man Who Knew Everything Page 12
