The 'physicist with a capital F'

Enrico Fermi - Fermi Remembered
March 11, 2005

Chris Llewellyn Smith finds Fermi a brilliant scientist with inscrutable politics

Enrico Fermi played a key role in designing and building the world's first nuclear pile. By scientists he is remembered as the last great physicist to make major contributions to both theory and experiment.

Gilberto Bernardini, in his mangled English, called Fermi "a physicist with a capital F", referring to his outstanding qualities and unique versatility as a physicist and teacher, and his focus on physics. Fermi was a cultured man and an enthusiastic - and aggressive - sportsman, who enjoyed climbing, swimming and skiing. But he was also the man who tried to teach his wife Maxwell's equations on their honeymoon (as she recalls in her book Atoms in the Family ), and someone who showed little ostensible interest in politics despite the events in which he was involved.

These books were produced to celebrate the 100th anniversary of Fermi's birth in 1901. Enrico Fermi: His Work and Legacy (first published in Italian in 2001) contains essays by distinguished Italian physicists on Fermi's contributions and their influence on subsequent developments. It also contains a year-by-year summary of his work and talks given soon after Fermi's death by his friend and fellow student Enrico Persico, and his collaborators Edoardo Amaldi and Franco Rasetti.

Fermi Remembered derives from a symposium in 2001 at Chicago University, where Fermi spent the years from 1945 until his death in 1954. It contains letters and documents relating to the development of nuclear energy, items from Chicago University archives and reminiscences by colleagues and students at the university.

By his own efforts, Fermi acquired a wide and deep knowledge of physics and mathematics before he entered the Scuola Normale Superiore in Pisa in 1918.

He achieved star status with his 1926 paper on what would come to be known as Fermi-Dirac statistics, shortly before he was appointed to the chair of theoretical physics at the University of Rome. The simple but remarkably successful Thomas-Fermi statistical model of the atom followed in 19.

Fermi continued to work on atomic physics until 1930, when - considering it essentially finished - he deliberately reoriented the work of the Rome group towards nuclear physics.

This shift involved a move to experimental physics, but Fermi remained very active as a theorist. His 1932 (re)formulation of the quantum theory of radiation, which influenced an entire generation of physicists, was preparation for his stunning theory of the creation of electrons in nuclear beta decay. This theory successfully organised a vast wealth of data, although his first (1933) paper on the subject was rejected by Nature as being "too remote from physical reality to be of interest to the readers".

The Rome group's big breakthrough in nuclear physics occurred in October 1934. Puzzled by various measurements of radioactivity induced by neutrons, Fermi decided to study what would happen if he placed a piece of lead in front of the neutron source. As he described it: "At a certain point I said to myself: 'No, I do not want a piece of lead here; what I want is a piece of paraffin.' And that is how it was, without prior warning or conscious reasoning." To everyone's surprise, the presence of paraffin increased the induced activity. According to Bruno Pontecorvo, who was present, Fermi quickly explained the effect, adding: "What a stupid thing, to have discovered this phenomenon by chance without having known how to foresee it."

In the next 18 months, the Rome group established the basic features of the interactions of low-energy neutrons with nuclei, for which Fermi won the Nobel prize in 1938. This work was perhaps the first example of a major group contribution to physics, although Fermi - known by his collaborators as the "Pope" - was the clear leader.

In response to the Fascist racial laws, which affected his wife Laura (who was Jewish) and deeply offended his sense of justice, Fermi decided to accept the offer of a chair at Columbia University. The award of the Nobel gave him a pretext to leave Italy without fear of reprisals, and the couple travelled directly from Stockholm to New York.

It seems likely that Fermi would have left neutron physics for another subject had it not been for the sensational news of the discovery of fission, which was brought to the US by Niels Bohr on January 16, 1939, a fortnight after Fermi's arrival. Fermi quickly set up an experiment and on January 26 announced the observation of fission fragments produced at the Columbia cyclotron.

At Columbia, with Leo Szilard, who had thought about the possibility of a nuclear chain reaction since 1933, Fermi initiated a series of experiments to study the viability of a fission reactor, or nuclear pile. Fermi, Szilard and collaborators moved to the University of Chicago in early 1942, where Fermi led the construction of the world's first pile. The dramatic scene when it went critical on December 2 is described in Enrico Fermi (which also reveals the origin of the term "scram" to describe the emergency shutdown of a nuclear reactor: Fermi added a third, redundant, safety rod attached to a rope over a pulley - scram stood for "Safety Control Rod Ax Man", who stood with an axe, ready to cut the rope if necessary).

For further studies, the pile was improved and reconstructed 20 miles away in the Argonne Forest. There, Fermi and his collaborators carried out many experiments in 1943 and 1944, including the first study of crystal lattices using neutron beams.

Fermi moved to Los Alamos for the final year of the war. He witnessed the first bomb test at Alamogordo on July 16, 1945, from a distance of 10,000 metres. Characteristically, he immediately and accurately estimated the energy released by dropping a few small pieces of paper and measuring the displacement produced when the shock wave reached his observation point.

On returning to Chicago, Fermi wanted to get back to pure science. He made fundamental contributions to cosmic ray physics. With John Pasta and Stanislaw Ulam, he carried out computational experiments on coupled systems that produced a stunning surprise: the approach to equilibrium is non-trivial and involves emergent structures and collective excitations that can persist indefinitely. He performed experiments at the Chicago synchrocyclotron, commissioned in 1951, that established the fundamental properties of low-energy pion-nucleon interactions.

Having created the first modern school of physics in Italy, essentially from scratch, Fermi built in Chicago what was perhaps the world's greatest-ever school of theoretical and experimental physics. His prestige and prodigious powers as a teacher attracted an extraordinary faculty and many outstanding students: ten Nobel prizes were eventually awarded to physicists who had been under Fermi's tutelage.

Fermi was at the height of his powers when he died of cancer, with little warning, in 1954.

These books give complementary insights into Fermi's work in Italy and the US. Enrico Fermi contains some gems - articles by Giorgio Parisi on Fermi statistics, Nicola Cabibbo on weak interactions and Ugo Amaldi on nuclear physics - which could profitably be read by undergraduates. Fermi Remembered provides fascinating insights into Fermi's style and the beginning of the Manhattan project.

Politics remain in the background in these books, but readers will inevitably wonder about Fermi's political views and his attitude to the consequences of his work. The unhappy political atmosphere in which the Rome group worked is evoked by Laura Fermi's description of Emilio Segre asking Fermi in 1936: "Can you tell me why we are now accomplishing less than a year ago?" To which he replied: "Go to the physics library. Pull out the big atlas that is there. Open it. You shall find your explanation." Of its own volition, the atlas opened at the map of Ethiopia. But there is no evidence that Fermi, who might be described as having been a right-wing nationalist who accepted authority (his father was a civil servant), would have emigrated in 1938 had Laura not been affected by the Mussolini regime's anti-Semitic laws, although sooner or later better funding might have lured him to the US.

In mid-1945, Manhattan Project scientists in Chicago and at Oak Ridge petitioned the President not to drop the bomb on Japan, at least not without first demonstrating it on uninhabited territory (scientists at Los Alamos, where there was less time for reflection, did not participate, apparently trusting Robert Oppenheimer to deal with "political" issues).

Fermi, however, with Oppenheimer, A.H. Compton and E.O. Lawrence, was a member of an official group that recommended the military use of the bomb.

But, in 1949, he also served on a committee that recommended against developing an H-bomb in response to the Soviet Union's explosion of a fission bomb. In an addendum to the committee's report, Fermi and Isidor Rabi wrote: "It is clear that the use of such a thermonuclear weapon cannot be justified on any ethical ground which gives a human being a certain individuality and dignity even if he happens to be a resident of an enemy country. The fact that no limit exists to the destructiveness of this weapon makes its very existence and the knowledge of its construction a danger to humanity as a whole." Nevertheless, Fermi, who "was not the sort to take to the streets to oppose a perceived national need", contributed when President Harry Truman began a crash H-bomb programme, seeing it as "a fascinating physics problem", according to M. Goldberger.

Fermi's students and associates report in Fermi Remembered that they were left to infer his attitudes. They gave him the benefit of any doubts. Jack Steinberger writes: "As best I know, he did have a real sense of social responsibility as a scientist, in particular on the questions raised by the atom bomb and its evolution, but these questions he did not discuss with the students." While Nina Byers writes: "Since he did not express himself to us on these issues, we do not know what he thought or felt about them.

One cannot but believe that as a scientist and teacher he was a deeply humane man." In a particularly interesting essay, Byers contrasts the attitudes of Fermi and Szilard, who was devoted first to defeating fascism and developing the bomb before Hitler, and second to limiting the spread of nuclear weapons. Fermi took his feelings to the grave, although on his deathbed he told Richard Garwin that he regretted not having been more involved in public policy.

These excellent books left me with enormous admiration for Fermi as a physicist with a capital F. They also left me feeling that a comprehensive biography of Fermi, putting his work in its scientific and political context, is overdue.

Sir Chris Llewellyn Smith is director, UK Atomic Energy Authority, Culham Division.

Enrico Fermi: His Work and Legacy

Editor - Carlo Bernardini and Luisa Bonolis
Publisher - Springer
Pages - 409
Price - £30.50
ISBN - 3 540 22141 7

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