Nuclear Forces: The Making of the Physicist Hans Bethe

Hans Bethe (1906-2005) was the first human being to understand why the stars shine in the sky. Hugely admired in his field of theoretical physics, he did pioneering work applying quantum mechanics, was the chief theorist on the Manhattan Project and later became an effective campaigner against nuclear weapons. In 1995, he called for scientists to take a modern version of the Hippocratic oath, pledging not to work on weapons of mass destruction.

Yet Bethe is little known outside his subject. Scientific biographers - or rather their publishers - have neglected him, preferring instead to write the umpteenth life of Albert Einstein, Richard Feynman, Robert Oppenheimer and a few other bankable names. It is a pleasure, then, to see the spotlight turn at last to the theoretician described by Freeman Dyson as “the supreme problem-solver of the twentieth century”.

Silvan Schweber wrote about Bethe 12 years ago in a short book that compared and contrasted his reaction to the ethical and moral challenges of the Bomb with those of Oppenheimer. Now Schweber returns with a detailed and thoroughly researched study of Bethe’s development as a scientist and as a human being.

Nuclear Forces begins on an apologetic note, with a reminder that biography has always been considered the poor relation in the discipline of history. The anthropologist Claude Levi-Strauss condescendingly remarked in La Pensée Sauvage (1962) that biographical and anecdotal history is “at the bottom of the ladder” of historical studies and is “weak history that does…not contain its own intelligibility, which it gets only when it is transferred en bloc into a history stronger than itself”. There is something in this, although well-written biographies will have a place in literature so long as readers are interested in individual human beings as well as their culture and development. Biographies of the calibre of Richard Ellmann’s Oscar Wilde (1988) and David Cairns’ two-volume life of Hector Berlioz can, I suggest, be counted among the finest writing about the 19th century.

Scientific biographies are especially problematic for scholars. One reason for this is that science is above all a communitarian activity - individuals rarely matter much, as their work is always dispensable in the long run. If Marie Curie or Einstein had never lived, their contributions would have been made by others, probably sooner rather than later. Yet the notion that these great scientists are just high-profile actors who got lucky in the socio-political pageant will not wash. As the community of scientists is always aware, a small number of them are almost unfathomably gifted and productive, as outstandingly creative as J.S. Bach or Jane Austen. Such figures hold a fascination not just for their peers but also for non-specialists, who quite reasonably want to understand why.

Schweber amply justifies this biographical project by pointing repeatedly to the “off-scale” ability of Bethe and makes it clear that he is interested mainly in finding out how his ability was nurtured to fulfilment. As usual with many high achievers in science, it was obvious in Bethe’s early life that he was extremely bright, although it was far from clear that he would go on to pre-eminence in physics. Apart from his experiences as a young student, he immersed himself in the culture of three scientific institutions that, Schweber argues persuasively, shaped Bethe as a theoretical physicist.

Most important for Bethe was the influence of his thesis adviser at the University of Munich, Arnold Sommerfeld, who is often underrated in histories of quantum theory, although his hypercritical former student Wolfgang Pauli rated him as one of the greats. It was Sommerfeld who impressed on Bethe the importance of the mysterious harmony between mathematics and physics and, at the same time, of testing candidate theories by using them to make clear-cut predictions. Bethe would become a theorist with his feet firmly on the experimental ground, ingeniously applying the new quantum theory to atoms, molecules and solid materials. His PhD thesis on X-ray diffraction by crystalline solids impressed almost all his colleagues except Pauli, who told him when they first met in 1929: “After Sommerfeld’s tales about you, I had expected much better…”

After he left Munich, Bethe worked at Ernest Rutherford’s Cavendish Laboratory at the University of Cambridge and in Enrico Fermi’s group at the Sapienza University of Rome, becoming a world expert in the new discipline of theoretical nuclear physics. Schweber brilliantly underlines the importance to Bethe of being part of the collegiate atmospheres that Rutherford and Fermi set up. Blessed with a first-rate analytical mind, a nose for good problems and a knowledge of his limits, Bethe was ideally placed to thrive. Sure enough, in the late 1930s he identified the complex series of nuclear reactions that power the stars, work that led to his Nobel Prize in Physics in 1967.

By the time Bethe was well established, he had made two friendships that played a large part in his life - with the Hungarian-born Edward Teller and the German-born Rudolf Peierls. All three fled Europe in the 1930s and played crucial roles in the development of nuclear weapons, Bethe and Teller eventually settling in the US, Peierls in the UK. Schweber sheds a good deal of light on these friendships, drawing on the illuminating letters between Bethe and Peierls, which continued until they were separated by death. Schweber has trawled this correspondence, together with Bethe’s voluminous archive, with the finest of gauzes, and the result is a richly detailed picture of his life. Schweber tells it with compassion and admiration, although Nuclear Forces is no hagiography. It is painful to read his account of how the blazingly ambitious Bethe suddenly abandoned plans for a wedding, an act the jilted fiancee still remembers bitterly. One of her friends, the much-lionised Danish physicist Niels Bohr, was distraught by this news - as a result, it seems, Bethe was never admitted into the Great Dane’s charmed circle.

Schweber ends his story around 1940, when Bethe had lived about a third of his life. Many more achievements were to come, including work on the American H-Bomb that he hoped would fail, campaigns on Capitol Hill against nuclear testing and a glorious career at Cornell University. Even in his nineties, he was publishing and giving inspirational lectures, some of which are available online. Much remains to be explored about his life, not least how Bethe went from being a pioneer of the Bomb to one of the most eloquent opponents of nuclear weapons.

Quite apart from offering insights into Bethe’s early career, Schweber riffs on a host of other subjects, including the role of mathematics in physics, the work of Sommerfeld and the strange climate of Europe in the 1930s, glorious years for fundamental physics but terrible ones for many living under the rule of dictators. Of all the first-rate European physicists who fled totalitarianism to emigrate to the US and work on the Bomb, few had a more intriguing trajectory than Bethe.

This is a deeply rewarding book, especially for physicists, and non-scientists will be amply rewarded if they are willing to skip the sometimes intimidating equations and technical details. Readers who persevere will be rewarded with an insightful account of how Hans Bethe became, in the constellation of 20th-century physicists, one of its most luminous stars.

The Author

“When I was 10 or so, I developed a great interest in mathematics,” recalls Silvan Schweber, emeritus professor of physics at Brandeis University. “An outstanding physics teacher in high school and another in my senior year in college made me gravitate to that subject. Theoretical physics became the substitute for the Orthodox Judaism I was raised in and gave up - in that it too sought an answer for the Leibnizian question: ‘Why is there something rather than nothing?’”

Born in France, Schweber has lived in Boston most of his adult life: “I have had the benefit of the stimulation and intellectual resources that its many universities offer: Boston is its universities.

“For the past 10 years I’ve lived half the year in Tel Aviv, where my partner lives, and have deeply appreciated its enormous cultural vitality.”

Officially retired but still active, Schweber notes: “Many colleagues of roughly the same age are as active as, and some more productive than, I am. It is a myth that one ceases to be productive or innovative as one grows older.”

He has found all his academic posts to be “challenging, stimulating and very rewarding. I have always thought my interactions with students, and the lives I touch thereby, to be more important than the articles or books that I write.”