Hans Bethe

Hans Albrecht Bethe (pronounced ; July 2, 1906 – March 6, 2005), was a German-American physicist who won the Nobel Prize in Physics in 1967 for his work on the theory 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. There he played a key role in calculating the critical mass of the weapons, and did theoretical work on the implosion method used in both the Trinity test and the "Fat Man" weapon dropped on Nagasaki, Japan.

During the early 1950s, Bethe also played an important role in the development of the larger hydrogen bomb, though he had originally joined the project with the hope of proving it could not be made. 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. His scientific research never ceased even into the later years of his life; He is one of the few scientists that can claim a major paper in his field every decade of his career which spanned nearly sixty years.

Biography

Bethe was born in Strassburg (then part of Germany, now Strasbourg, France) to a Christian father and a Jewish mother. He was raised a Christian, and studied physics at Frankfurt. Bethe 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 was influenced by Fermi's simplicity and Sommerfeld's rigor in approaching problems, and these qualities influenced his own later research. Bethe left Germany in 1933 when the Nazis came to power and he lost his job at the University of Tübingen, 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, and 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, after the war, experimentalist Robert R. 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.

Manhattan Project

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 at the urging of Teller he agreed to join the Manhattan Project. When Oppenheimer was put in charge of forming a 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.

Bethe's work at Los Alamos included calculating the critical mass of uranium-235 and the multiplication of nuclear fission in an exploding atomic bomb. After November 1943, when the laboratory had been re-oriented to solve the implosion problem of the plutonium bomb, Bethe spent much of his time studying the hydrodynamic aspects of implosion, a job which he continued into 1944. In 1945, his work concerned working out the workings of the neutron initiator, and later on radiation propagation from an exploding atomic bomb. (see Nuclear weapon design)

During the project, Klaus Fuchs who was leaking nuclear secrets to the Russians, was also in Bethe's division (often doing work which had originally been assigned to Teller). Like everyone else, Bethe had no knowledge that Fuchs was a spy.

When the first atomic bomb (an implosion weapon) was detonated in the New Mexico desert on July 16, 1945, at the Trinity test, Bethe's only immediate concern at the time was for its efficient working, and not for its moral implications — "I am not a philosopher", he was reported as saying at the time.

Hydrogen bomb

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. He would later remark (in 1968) on the apparent contradiction in his stance, having first opposed the development of the weapon and later helping to create it:

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. (quoted in Schweber, p.166)

As for his own role in the project, and its relation to the famous Teller-Ulam priority dispute, Bethe later said that:

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. (quoted in Schweber, p.166)

In 1954, Bethe testified on behalf of Oppenheimer during the latter's high-profile security clearance hearing. Specifically, Bethe argued that Oppenheimer's stances against developing the hydrogen bomb in the late 1940s had not hindered its actual development, a topic which was seen as a key motivating factor behind the hearing. Bethe contended that the developments which led to the successful Teller-Ulam design were a matter of serendipity and not a question of manpower or logical development of previously existing ideas. During the hearing, 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 revocation 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.

Political stances

In 1968, Bethe, along with IBM physicist Richard Garwin, wrote an articleR. L. Garwin, H. A. Bethe, Sci. Am., March 1968, p. 21. 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 1980s and 1990s, 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 (with considerable support from Edward Teller), 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 George W. 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 the State University of New York at Stony Brook. In his 80s, he wrote an important article about the solar neutrino problem. Physicist Kurt Gottfried says that he does not know anyone in the history of modern physics, who has done work of such calibre in his 80s.

Awards and legacy

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 is 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. Although his calculation was a non-relativistic one, it was a definite starting point. This work provided the impetus for the pioneering later work done by Richard Feynman, Julian Schwinger and others which marked the beginning of modern quantum electrodynamics.

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-Bethe-Gamow Paper about the Big Bang and nucleosynthesis, and he published a spoof paper in 1931, "On the Quantum Theory of the Temperature of Absolute Zero" (Beck, Bethe, Riezler) where he calculated the fine structure constant from the absolute zero temperature (in Celsius units!), causing a scandal in the scientific world. This second spoof paper was intended to characterize a certain class of papers in theoretical physics of the day, which were purely speculative and based on spurious numerical arguments (e.g. Sir Arthur Eddington's claim 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. Since his death, Cornell has announced that the third of five new residential colleges, each of which will be named after a distinguished former member of the Cornell faculty, will be named the Hans Bethe House. 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)
Enrico Fermi Award (1961)
Rumford Prize (1963)
Nobel Prize in Physics (1967)
Lomonosov Gold Medal (1989)
Oersted Medal (1993)
Bruce Medal (2001)

Named after him

References

Bernstein, Jeremy. Hans Bethe, Prophet of Energy. New York : Basic Books, 1980.
Bethe, Hans A. The Road from Los Alamos. New York: American Institute of Physics, 1991.
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.

External links

Hans Bethe at Nobel lectures
Hans Bethe at World of Science
Hans Bethe at Britannica Nobel Prizes
Text of the Eddington Medal award speech
Bruce Medal page
Three Lectures by Hans Bethe videos on Quantum Mechanics given at Cornell University in 1999.
Obituaries
- Hans Bethe obituary from (Wikinews)
- Hans Bethe obituary from Scientific journal Nature
- Hans Bethe obituary from The Economist magazine
- Hans Bethe obituary from The Guardian Newspaper
Hans Bethe And His Physics
his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production in stars.
Annotated bibliography for Hans Bethe from the Alsos Digital Library for Nuclear Issues

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