Hans Albrecht Bethe

German American physicist

• Born: July 2, 1906; Strassburg, Germany (now Strasbourg, France)
• Died: March 6, 2005; Ithaca, New York

Hans Albrecht Bethe’s work in theoretical nuclear physics explained how stars convert mass to energy and broadened the scientific understanding of subatomic events. Long an influential advocate for restraint in the proliferation of nuclear weapons, Bethe laid the theoretical groundwork for the explosion of the first atom bomb.

Primary field: Physics

Specialty: Nuclear physics

Early Life

Hans Albrecht Bethe (BAY-tuh) was the only child of Albrecht Theodore Julius Bethe, an eminent German physiologist, and Anna Kuhn, a musician and playwright. His father’s family was Protestant and his mother’s was Jewish. As a child, Bethe was frail, lonely, and perhaps overprotected by his mother. At an early age, he found that he loved numbers; at age seven, he filled a notebook with the powers of two and three. However, Bethe’s father did not want him to progress too far beyond the mathematics appropriate to his grade in school.

The family moved to Frankfurt, Germany, in 1915 when Bethe’s father was invited to start a department of physiology at the University of Frankfurt. In Frankfurt, Bethe attended the gymnasium, a nine-year school. He felt estranged from the other students, having received private tutoring up to that point, and found solace in mathematics, especially algebra. In his last few years at the school, Bethe’s physics courses convinced him to pursue the subject further at the University of Frankfurt. He enrolled in 1924, and upon discovering that he had little facility for experimental physics, his interest in mathematics drove him to take up theoretical physics. One of his teachers, spectroscopist Karl Meissner, persuaded Bethe to study under Arnold Sommerfeld, professor of theoretical physics at the University of Munich.

Bethe left for Munich in 1926. Under Sommerfeld, he found himself at the center of a great ferment in theoretical physics. Quantum mechanics was replacing the classical model of the atom. The old model pictured electrons orbiting around a hard central core, or nucleus. In the quantum theory, however, electrons were represented as if they were waves, explaining subatomic phenomena. In 1926, Sommerfeld shared with his students a new paper by Austrian physicist Erwin Schrödinger that developed equations for quantum wave mechanics; subsequently, Sommerfeld encouraged Bethe to apply these insights to the effect of electron scattering, which takes place when a beam of electrons is directed against a crystal. This study formed the basis of Bethe’s doctoral degree in physics, granted in 1928.

Life’s Work

Bethe spent some time as an instructor in physics at Frankfurt and Stuttgart. In 1929, Sommerfeld invited him to return to Munich to work as a privatdozent, a university lecturer whose fees are paid by students. During this time, Bethe wrote a paper that gave mathematical expression to the passage of charged particles through matter. He considered the paper, which appeared in a physics journal in 1930, to be among his best work.

In the early 1930s, Bethe used a fellowship from the Rockefeller Foundation International Education Board to study at Cambridge University in England and at the University of Rome. In Rome, Bethe was profoundly influenced by the personality and theoretical approach of Enrico Fermi, from whom he learned a kind of experimental insight into theoretical problems, and he coauthored a paper with Fermi on electron-electron interaction that was published in 1932. In 1933, Bethe and Sommerfeld published an article, “Die Elektronentheorie der Metalle” (The electron theory of metals), published the next year in the Handbuch der Physik, which provided the foundation for theoretical work on the solid-state basis of metals.

That same year, Bethe took a position as assistant professor at the University of Tübingen. When dictator Adolf Hitler came to power in 1933, Bethe was forced to resign from the university, since his mother was Jewish. The Nazis seemed less concerned with the activities of older researchers such as Sommerfeld, so Bethe went to work for Sommerfeld once again. The next year, he was offered a permanent position at Cornell University in Ithaca, New York. He immigrated to the United States and in February 1935 joined Cornell’s physics department, where he remained until his retirement in 1975. At Cornell, Bethe found both the students and the professors eager to learn about nuclear physics but lacking sufficient background. Eventually, Bethe wrote three long articles for the journal Reviews of Modern Physics; “Bethe’s Bible,” as the articles came to be known, provided the basic textbook on the subject for a generation of scientists.

At an astrophysics conference in 1938 in Washington, DC, Bethe met theoretical physicists George Gamow and Edward Teller, who were working on the big bang theory and the theory of the expanding universe. Bethe was inspired to take up the problem of how the sun produces energy through thermonuclear reactions. His findings were first published in a 1939 article entitled “Energy Production in Stars”; in 1967, Bethe was awarded the Nobel Prize in Physics on the basis of his work in this area. In September 1939, Bethe married Rose Ewald, the daughter of one of his Stuttgart professors, who had immigrated to the United States in 1936. They would later have two children, Henry and Monica.

After becoming a naturalized citizen of the United States in 1941, Bethe received a security clearance and soon afterward began work on radar for the Massachusetts Institute of Technology (MIT) Radiation Laboratory. In 1943, he received a call from J. Robert Oppenheimer to assist in the production of an atom (fission) bomb. That top-secret endeavor was called the Manhattan Project, and its goal was to beat the Germans in the building of an atomic bomb. At the urging of Teller, who was also on the project, Bethe accepted, even though he had written a theoretical paper doubting the feasibility of fission reactions.

From 1943 to 1946, Bethe was chief of the Theoretical Physics Division at Los Alamos Laboratory in New Mexico, charged with developing the theoretical base for a fission explosion. Teller, working under Bethe in the Theoretical Physics Division, insisted on the development of what he called the super-bomb (later known as a hydrogen bomb, or H-bomb), which would use the power of a fission explosion to trigger a hydrogen-fusion reaction. Far from embracing the idea of a super-bomb, Bethe was a reluctant participant in its creation. After the successful test of the first plutonium bomb at Alamogordo, New Mexico, in July 1945, Bethe began to consider the need for international control of atomic weapons and civilian control of atomic energy in the United States.

After World War II, Bethe developed a world-class physics department at Cornell University, bringing with him Richard Feynman, Philip Morrison, and Robert Wilson from the Manhattan Project. Their research led to fundamental breakthroughs; for example, the group first devised crucial calculations that led to the theory of quantum electrodynamics (QED).

Teller convinced Bethe to return to Los Alamos to work on the H-bomb after the Soviet Union tested their first atomic bomb in 1949. He finally agreed to go, reasoning that since there was no global mechanism for arms control, the United States ought to develop the hydrogen bomb for its own defense. However, Bethe became increasingly concerned with public policy regarding nuclear energy. In 1955, he served as a technical adviser to the United States delegation to the International Conference on the Peaceful Uses of Atomic Energy held in Geneva, Switzerland. He was a member of the President’s Science Advisory Committee from 1956 to 1959 and played a large part in the negotiations that led to the atmospheric Nuclear Test Ban Treaty in 1963. In 1983, when President Ronald Reagan called for a Strategic Defense Initiative (dubbed the Star Wars program), Bethe was swift to call the proposal unworkable and destabilizing, arguing that the development of weapons that could destroy the satellites used to monitor atomic testing around the world would defeat a system of checks and balances that Bethe claimed had been effective for decades.

Bethe’s worry about the misuse of scientific knowledge twice prompted him to make public protests. In 1995, he published an open letter urging fellow scientists to withdraw from all work relating to nuclear weaponry; in 2004, upset with President George W. Bush’s attitude toward science, Bethe joined forty-seven other Nobel laureates in signing a letter of endorsement for Senator John Kerry in that year’s presidential election.

Into his eighties, Bethe continued to pursue research in theoretical astrophysics, publishing an influential article about the mysterious absence of the predicted flow of neutrinos from the sun. He also studied the processes that produce such phenomena as type II supernova explosions, neutron stars, black holes, and stellar mergers.

Impact

Bethe died at his home in Ithaca on March 6, 2005, at the age of ninety-eight, survived by his wife, son, and daughter. Cornell honored Bethe by naming a new residential hall after him. An asteroid was also named for him. Among the many other honors he received throughout his life are the Henry Draper Medal (1947), the Max Planck Medal (1955), the Eddington Medal of the Royal Astronomical Society (1961), the Enrico Fermi Award (1961), the Albert Einstein Peace Award (1992, with Joseph Rotblat), and the Bruce Medal (2001).

Bethe championed the prudent use of atomic energy, though he deplored nuclear arms proliferation. As an influential arms-control advocate, he believed that the mutual superpower reduction of nuclear warheads from tens of thousands down to around two thousand would serve to maintain nuclear deterrence, but at a safer level.

Bibliography

Bethe, Hans Albrecht. Selected Works of Hans A. Bethe with Commentary. River Edge: World Scientific, 1997. Print. A collection of Bethe’s twenty-eight most important scientific papers, each accompanied by a brief note describing its relation to previous research and its effects on subsequent theory.

---. “The Technological Imperative.” Bulletin of the Atomic Scientists 41.8 (1985): 34–36. Print. Evaluates contemporary technological developments in weapons research and concludes that, on balance, they have produced greater world instability.

---, and Edward Teller. “Face-Off on Nuclear Defense.” Technology Review 87.3 (1984): 38–39. Print. Excerpts from a debate between Bethe and Teller on President Reagan’s Star Wars proposal, held at the Kennedy School of Government at Harvard in November 1983.

Brown, Gerald E., and Chang-Hwan Lee, eds. Hans Bethe and His Physics. Hackensack: World Scientific, 2006. Print. Collection of essays by scientists, friends, and colleagues of Bethe, discussing his work in solid-state physics, nuclear physics, astrophysics, nuclear energy, and atomic weapons. Includes an appreciation and obituary.

Schweber, S. S. In the Shadow of the Bomb: Bethe, Oppenheimer, and the Moral Responsibility of the Scientist. Princeton: Princeton UP, 2000. Print. A comparison of the lives and careers of Bethe and Oppenheimer, focusing on how they came to terms with the nuclear weapons they helped create.