Hans Albrecht Bethe (pronounced Bay-tuh; July 2, 1906 – March 6, 2005), was a German-American physicist who won the Nobel Prize in Physics for 1967 for his discovery of stellar nucleosynthesis. During World War II, he was head of the Theoretical Division at the secret Los Alamos laboratory developing the first atomic bombs. His team worked out the critical mass of uranium-235 necessary to sustain the fission reaction that would enable the bomb to explode.

The first atomic bomb was detonated at the Trinity site in the Jornada del Muerto Desert, southwestern United States, on 16 July 1945. Witnessing it, Bethe claimed concern only for the smooth running of the test and was not concerned with the implications for the world. "I am not a philosopher," he explained. He also played an important role in the development of the larger hydrogen bomb in the early 1950s. Bethe later campaigned together with Albert Einstein in the Emergency Committee of Atomic Scientists against nuclear testing and the nuclear arms race. He influenced the White House to sign the ban of atmospheric nuclear tests in 1963 and Anti-Ballistic Missile Treaty (SALT I) in 1972.

Biography

Bethe was born in Strassburg (then part of Germany, now Strasbourg, France). He studied physics at Frankfurt and obtained his doctorate from the University of Munich with supervisor Arnold Sommerfeld, after which he did postdoctoral stints in Cambridge and at Enrico Fermi's laboratory in Rome. He left Germany in 1933 when the Nazis came to power and he lost his job (his mother was Jewish) at the University of Tubingen, moving first to England where he held a provisory position of Lecturer for the year 1933-1934 and in the fall of 1934, a fellowship at the University of Bristol. IN England, Bethe worked with the theoretician Rudolf Peierls on a comprehensive theory of the deuteron.

In 1935 Bethe moved to the United States, where he joined the faculty at Cornell University, a position which he occupied throughout his career. At Cornell, Bethe became known as one of the leading theoretical physicists of his generation, and along with other upcoming physicists like Stanley Livingston (a cyclotron pioneer) and later, experimentalist Robert Wilson and theoretician Robert Bacher, put Cornell on the world physics map. He published a series of articles on nuclear physics, summarizing most of what was known until that time, an account that became informally known as 'Bethe's Bible', and remained the standard work on the subject for many years. In this account, he also continued where others had left off, and filled in gaps from the older literature. From 1935 - 1938, he studied nuclear reactions and reaction cross sections (carbon-oxygen-nitrogen cycle), leading to his important contribution to stellar nucleosynthesis. This research was later useful to Bethe in more quantitatively developing Niels Bohr's theory of the compound nucleus. In 1941 he became a naturalized citizen of the United States.

When the war began, Bethe wanted to contribute to the war effort. Following the advice of the Caltech aerodynamicist Theodore Von Karman, Bethe collaborated with his friend Edward Teller, then at George Washington University, on a theory of shock-waves which are generated by the passage of a projectile through a gas. This work was later useful to researchers investigating missile reentry. Bethe also worked on a theory of armor penetration.

During the summer of 1942, he served as part of a special session at the University of California, Berkeley at the invitation of Robert Oppenheimer, which outlined the first designs for the atomic bomb. Initially, Bethe had been skeptical about the possibility of making a nuclear weapon from uranium (in fact, in the late 1930s, he had written a theoretical paper that argued against fission), but when Teller showed him the atomic pile that Enrico Fermi was building in a squash court under the football stands at the University of Chicago, he became convinced that such a project might actually be feasible. When Oppenheimer started the secret weapons design laboratory, Los Alamos, he appointed Bethe as Director of the Theoretical Division, a move that irked Teller who had coveted the job for himself. During the project, Klaus Fuchs who was leaking nuclear secrets to the Russians, was also in Bethe's division. Like everyone else, Bethe never had the slightest idea that Fuchs was a spy. When the first atomic bomb was detonated in the New Mexico desert in July, 1945, Bethe's only immediate concern at the time was for its efficient working, and not for its moral implications.

After the war, Bethe argued that a crash project for the hydrogen bomb should not be attempted, though after President Truman announced the beginning of such a crash project, and the outbreak of the Korean War, Bethe signed up and played a key role in the weapon's development. Though he would see the project through to its end, in Bethe's account he personally hoped that it would be impossible to create the hydrogen bomb.

In 1967, Bethe was awarded the Nobel Prize in Physics "for his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production in stars" . He had postulated that the source of this energy are thermonuclear reactions in which hydrogen is converted into helium (stellar nucleosynthesis).

Bethe was also noted for his theories on atomic properties. In the late 1940s, he provided the first way out of the infinities that plagued the explanation of the so called Lamb shift. This work was the impetus for the pioneering later work done by Richard Feynman, Julian Schwinger and others which marked the beginning of modern quantum electrodynamics.

In 1954, Bethe testified on behalf of Oppenheimer, who was on trial for being labeled a security risk. During this event, Bethe and his wife also tried hard to convince Edward Teller against testifying. However, Teller did not agree, and his testimony played a major role in the repudiation of Oppenheimer's security clearance. While Bethe and Teller had been on very good terms during the pre-war years, the conflict between them during the Manhattan Project, and especially during the Oppenheimer episode, permanently marred their relation.

In 1960, Bethe, along with IBM physicist Richard Garwin, wrote an article criticising in detail the new anti-ICBM defense system that the Government was planning to install. In the article that was published in Scientific American, the two physicists described in detail how almost any countermeasure that the US could take would be futile, as the enemy would be able to thwart the system through the use of suitable decoys. He was one of the prime scientific voices behind the signing of the 1963 Partial Test Ban Treaty which prohibited atmospheric testing of nuclear weapons.

During the '80s and '90s Bethe campaigned for the peaceful use of nuclear energy. After the Chernobyl accident, Bethe put together a committee of experts that analysed the incident, and concluded that a similar episode would not happen in any good US reactor, as the Russian reactor suffered from a fundamentally faulty design and human error also had significantly contributed to the accident. Throughout his life, Bethe remained a strong advocate for electricity from nuclear energy. In the 1980s, he, along with other physicists widely opposed the Strategic Defense Initiative missile system that was being conceived by the Reagan administration, arguing against the enormous sums of money spent on it and the feelings of instability and animosity that it would foster. In 1995, at the age of 88, Bethe wrote an open letter calling on all scientists to "cease and desist" from working on any aspect of nuclear weapons development and manufacture. In 2004, he signed a letter along with 47 other Nobel laureates endorsing John Kerry for president of the United States citing Bush's misuse of science.

He continued to do research on supernovae, neutron stars, black holes, and other problems in theoretical astrophysics into his late nineties. In doing this, he collaborated with Gerald Brown of SUNY-Stony Brook. In his 80s, he wrote an important article about the solar neutrino problem.

Bethe's hobbies included a passion for history and also stamp-collecting. About the latter, he wryly remarked that it was the only instance where all the countries in the world could coexist by each other's side in peace. Bethe was also known for his great sense of humor. He was coauthor of the legendary Alpher-Gamov-Bethe paper about the big bang and nucleosynthesis and he published a spoof paper 1931 "On the Quantum Theory of the Temperature of Absolute Zero" (Beck, Bethe, Riezler) where he calculated the fine structure constant from the absolut zero Temperature (in Celsius units!) causing a scandal in the scientific world. This second spoof paper intended to characterize a certain class of papers in theoretical physics of these days which are pure speculative and based on spurious numerical agreements (e.g. Sir Arthur Eddington claimed to have calculated the fine structure constant from fundamental quantities in an earlier paper).

Hans Bethe died in his home in Ithaca, New York. At the time of his death, he was the John Wendell Anderson Professor of Physics Emeritus at Cornell University. He is survived by his wife Rose, his son Henry and his daughter Monica.

Honors

Awards

Henry Draper Medal (1947)

Max Planck medal (1955)

Eddington Medal of the Royal Astronomical Society (1961)

Rumford Prize (1963)

Nobel prize in physics (1967)

Bruce Medal (2001)

Named after him

Asteroid 30828 Bethe

Hans Bethe Prize of the American Physical Society

Quotes

"I am not a philosopher" - comment on his work on the first nuclear bomb explosion, 1945.

"Just a few months before, the Korean war had broken out, and for the first time I saw direct confrontation with the communists. It was too disturbing. The cold war looked as if it were about to get hot. I knew then I had to reverse my earlier position. If I didn't work on the bomb, somebody else would -- and I had thought if I were around Los Alamos I might still be a force for disarmament. So I agreed to join in developing the H-bomb. It seemed quite logical. But sometimes I wish I were more consistent an idealist." - 1968 (in Schweber, p.166)

"After the H-bomb was made, reporters started to call Teller the father of the H-bomb. For the sake of history, I think it is more precise to say that Ulam is the father, because he provided the seed, and Teller is the mother, because he remained with the child. As for me, I guess I am the midwife." - 1968 (Schweber, p.166)

References

• Bernstein, Jeremy, Hans Bethe, Prophet of Energy, 1980
  
• Bethe, Hans A., The Road from Los Alamos, NY: Simon and Schuster, 1991, ISBN 0671740121, some collected essays on nuclear topics.
  
• Schweber, S. S. In the shadow of the bomb: Bethe, Oppenheimer, and the moral responsibility of the scientist. Princeton, N.J.: Princeton University Press, 2000.
  

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