Hans A. Bethe

Staff Biography

Hans Bethe was one of the great physicists not only of the twentieth century, but of all time. During his long life, he uncovered the secrets powering the stars, published the standard work on nuclear physics, built atomic weapons, and called for a halt to their proliferation. Bethe's dual legacy is one of genius and conscience.

On July 2, 1906, Hans Bethe was born in Strasbourg, Alsace (then part of the German Empire), to Albrecht and Anna Bethe. Bethe attended a private school in Kiel, Germany, on the eve of the Great War, before entering the Goethe Gymnasium at Frankfurt in 1915. During his years at the gymnasium, Bethe demonstrated a remarkable talent for processing numbers. His outstanding performance won him acceptance to the University of Frankfort, where he studied from 1924-26. He transferred to the University of Munich, where he studied under the great physicist, Arnold Sommerfeld. In 1928, the university awarded Bethe a Ph.D. in physics.

Over the next several years, Bethe would produce some of his most important work. In 1930 and 1931, he enjoyed stints working with Enrico Fermi at his laboratory in Rome. During this time, he also maintained contact with Sommerfeld as a research associate at the University of Munich. This collaboration culminated in the joint publication of a long article, "Elektronen-theorie der Metalle," in the prominent Handbuch der Physik. By 1933, Bethe was regarded as one of the great physicists of his generation. He was only 27 years old.

This year was a watershed in Hans Bethe's life. The year before, Bethe had been offered a post at the University of Tubingen. Despite his great ability and reputation, Bethe was dismissed from the university less than a year later, a victim of Hitler's first round of racial laws. Though Bethe was raised in a Protestant household, his mother Anna, a Lutheran convert, was Jewish. The influential Sommerfeld immediately began searching for jobs, particularly in England, on behalf of his disenfranchised colleagues. Probably as a result of his mentor's efforts, Bethe was awarded a fellowship by Bristol University. This job would last until 1935, when he accepted an assistant professorship at Cornell University. Bethe continued his research during the 1930s, focusing on nuclear reactions and cross sections. This work led to his discovery of the carbon-nitrogen cycle and, thus, his theory that this process powers the stars.

During his years at Cornell, he also worked with Robert F. Bacher and M. Stanley Livingston to produce a series of three articles on nuclear physics. These articles redefined the field by consolidating existing concepts and filling voids in the literature. The collected articles soon became known as the "Bethe Bible," a work that is still relied upon decades later.

The 1930s had been a decade of great triumphs for Bethe. He had established himself as one of the world's leading physicists. The advent of the '40s opened up a whole new realm of deadly new applications for his field of nuclear physics. In September 1939, Hitler's armies attacked Poland, initiating World War II. Many physicists, with Leo Szilard at the fore, realized the wealth of scientific talent at the disposal of the Third Reich and called for action in the United States. The National Defense Research Committee was established in response to this plea, and Bethe was recruited by the group as a consultant. He was also hired as a staff member by the Massachusetts Institute of Technology's Radiation Laboratory. The most notable of Bethe's activities in the early '40s was his participation in the 1942 Berkeley summer study. J. Robert Oppenheimer, a University of California physicist, organized the group to investigate the feasibility of an atomic weapon. Beside Bethe, the group included many other talented physicists such as Edward Teller, Felix Bloch, and Emil Konopinski. These discussions established a theoretical basis for the construction of the atomic bomb.

Over the winter of 1942-43, Project Y came together at Los Alamos under the leadership of General Leslie R. Groves and Oppenheimer. Hans Bethe emerged as a primary candidate to work at the Los Alamos project. Edward Teller, his old friend and Berkeley summer colleague, urged an ambivalent Bethe to join the project. Bethe finally gave in, and Oppenheimer made him chief of the Theoretical Division, a position Teller sorely coveted. This slight marked the beginning of a feud that would last for decades.

Bethe quickly settled into his new post. A few weeks before the Trinity shot, he chronicled his work on the Manhattan Project for a biographical data questionnaire. When asked to provide a detailed description of the work he performed, he wrote:

Supervision of the work of the theoretical division of the Los Alamos Project. The work of the Division in the first year was mostly concerned with the prediction of the critical mass and multiplication rate of a fission bomb....The larger fraction of the effort since Nov. 1943 was devoted to the theoretical study of the hydrodynamics of implosion. From March to June 1944 I had direct charge of the group concerned with implosion hydrodynamics. The emphasis of my own work shifted with that of the division....In 1945 I worked on the theory of the initiator.... and most recently on the hydrodynamics connected with the propagation of radiation in the nuclear explosion....The largest fraction of my time was concerned with the correlation of the work of the division.

Bethe's efforts helped lead to the production and successful testing of the world's first nuclear weapon.

After the war, Bethe returned to Cornell but became a very public figure. He argued for civilian control of atomic energy before the Senate, and wrote papers and gave talks on the dangers of nuclear war. Bethe also returned to intellectual pursuits. In 1947, he offered a theoretic calculation of the Lamb Shift, an explanation of the electron's changing energy levels in the hydrogen atom. Bethe's work led directly to the creation of a new field, quantum electrodynamics.

In 1949, the Soviet Union successfully tested its first nuclear bomb. It was basically a copy the "Fat Man" bomb based on plans Klaus Fuchs, a German expatriate and Project Y physicist, had passed on to the Soviet intelligence. In the United States, the Soviet test led to the crash program to build the hydrogen bomb, or "Super." As had been the case in 1943, Edward Teller again tried to persuade Bethe to join the H-bomb effort. Bethe initially refused. He was adamantly opposed to building weapons of that magnitude and was not convinced that one could even be constructed. When the Korean War broke out, however, Bethe agreed to join the project, explaining, "...my chief desire was to clinch the argument that the H-bomb would not work." Indeed, Teller's original design proved impractical. However, in early 1951, Teller and Stan Ulam devised a method to detonate a hydrogen bomb. With the realization that a hydrogen bomb was possible, Bethe agreed to dedicate himself to the cause. He relates, "I was convinced that the thing could be done, and since it could be done we had to be afraid that the Russians could and would do it, too." The first hydrogen bomb was detonated on November 1, 1952. Though the Mike shot, as it was called, was simply a test of the hydrogen bomb principle (not a weapons test), it ushered in a new era, an era Bethe would devote himself to ending.

Bethe became a member of President Eisenhower's Scientific Advisory Committee (PSAC) a few years later in 1956. One of Eisenhower's great ambitions was to conclude a test ban treaty with the Soviets. In Bethe, he found a sincere, articulate proponent of his plans. Although a treaty was not concluded by the end of the Eisenhower administration, Bethe continued to argue for such an agreement into the early 1960s. Finally, his efforts paid off in 1963 when President Kennedy signed the Limited Test Ban Treaty, outlawing atmospheric tests.

Nobel Prize In Physics

In December 1967, Hans Bethe was awarded the Nobel Prize in Physics for his work on energy production in stars. Professor O. Klein of the Swedish Academy of Sciences presented Bethe to the academy, stating: "...your solution of the energy source of stars is one of the most important applications of fundamental physics in our days, having led to a deepgoing evolution of our knowledge of the universe around us." Bethe humbly accepted the prize from the King of Sweden, his only regret being that the prize for peace was not awarded that year: "Unfortunately it is not surprising in the present world that the Norwegian Parliament could not find anybody who has contributed sufficiently to peace to merit the Prize. I believe I express the hope of all of us that a Peace Prize can be given next year." In addition to his Nobel Prize, Bethe was awarded several other very prestigious awards, including the President's Medal of Merit, the Max Planck Medal, the Enrico Fermi Award, and the Los Alamos National Laboratory Medal.

Bethe retired from Cornell in 1975, emeritus. After retirement, he was an active advocate for arms reduction aimed at the ultimate goal of disarmament. In an open letter to the scientific community in July 1995, he made the following appeal: "I call on all scientists in all countries to cease and desist from work creating, developing, improving and manufacturing further nuclear weapons and, for that matter, other weapons of potential mass destruction such as chemical and biological weapons." In 1999, at the age of 93, Dr. Bethe argued at length against the Senate's decision to reject the Comprehensive Nuclear Test Ban Treaty in a letter to the president of that body. Until his death in 2005, he continued his decades-long crusade to make the world a safer place for all its inhabitants.