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Hans Albrecht Bethe2.7.1906

Wikipedia (27 Jun 2013, 07:57)

Hans Albrecht Bethe (July 2, 1906 – March 6, 2005) was a German and American nuclear physicist, and Nobel laureate in physics for his work on the theory of stellar nucleosynthesis. A versatile theoretical physicist, Bethe also made important contributions to quantum electrodynamics, nuclear physics, solid-state physics and astrophysics. During World War II, he was head of the Theoretical Division at the secret Los Alamos laboratory which developed 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. For most of his career, Bethe was a professor at Cornell University.

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 the 1972 Anti-Ballistic Missile Treaty, SALT I. His scientific research never ceased even into the later years of his life and he was publishing papers well into his nineties. He is one of the few scientists who can claim a major paper in his field every decade of his career, which spanned nearly 70 years. Freeman Dyson called Bethe the "supreme problem solver of the 20th century."


Early years

Bethe was born in Strasbourg, which was then part of Germany, on 2 July 1906, the only child of Anna (née Kuhn) and Albrecht Bethe, a Privatdozent of physiology at the University of Strasbourg. Although his mother, the daughter of a professor at the University of Strasbourg, was Jewish, he was raised a Christian in the religion of his father, and was confirmed at age 13. Despite having a religious background, he was not a religious person in later life, and described himself as an atheist.

His father accepted a position as professor and director of the Institute of Physiology at the University of Kiel in 1912, and the family moved into the director's apartment at the Institute. He was initially schooled privately by a professional teacher as part of a group of eight girls and boys. The family moved again in 1915 when his father became the head of the new Institute of Physiology at the University of Frankfurt am Main. His father turned down a subsequent 1918 offer of a position at the University of Strasbourg, because he foresaw Germany's defeat in World War I and Alsace-Lorraine being ceded to France.

Bethe attended the Goethe-Gymnasium in Frankfurt. His education was interrupted in 1916, when he was diagnosed with tuberculosis, and sent to Bad Kreuznach to recuperate. By 1917, he had recovered sufficiently to attend the local realschule, and the following year he was sent to the Odenwaldschule, a private, co-educational boarding school. He attended the Goethe-Gymnasium again for his final three years of secondary schooling, from 1922 to 1924.

Having passed his abitur—his matriculation examinations—Bethe entered the University of Frankfurt in 1924. He decided to major in chemistry; the instruction in physics was poor, and while there were excellent mathematicians at Frankfurt like Carl Ludwig Siegel and Otto Szász, Bethe disliked their modernist approach, which presented mathematics without reference to the other sciences. Bethe found that he was a poor experimentalist who shredded his lab coat by spilling sulphuric acid on it, but he found the advanced physics taught by the associate professor, Walter Gerlach, more interesting. Bethe dated a number of young women there, including Fips Böhm, Käte Feiss and Hilde Levi. Gerlach left in 1925, and was replaced by Karl Meissner, who advised Bethe that he should go to a university with a better school of theoretical physics, specifically the University of Munich, where he could study under Arnold Sommerfeld.

Bethe entered the University of Munich in April 1926, where Sommerfeld rook him on as a student on Meissner's recommendation. Sommerfeld taught an advanced course on differential equations in physics, which Bethe enjoyed, and a seminar series one evening a week. Because he was such a renowned scholar, Sommerfeld frequently received advance copies of scientific papers, which he put up for discussion at the seminars. When Bethe arrived, Sommerfeld had just received Erwin Schrödinger's papers on wave mechanics. For his PhD thesis, Sommerfeld suggested that Bethe examine electron diffraction in crystals. As a starting point, Sommerfeld suggested Paul Ewald's 1914 paper on X ray diffraction in crystals. Bethe later recalled that he became too ambitious, and, in pursuit of greater accuracy, his calculations became unnecessarily complicated. When he met Wolfgang Pauli for the first time, Pauli told him: "After Sommerfeld's tales about you, I had expected much better from you than your thesis." "I guess from Pauli," Bethe later recalled, "that was a compliment."


Early work

After Bethe received his doctorate, Erwin Madelung offered him an assistantship in Frankfurt, and in September 1928 Bethe moved in with his father, who had recently divorced his mother. His father met Vera Congehl earlier that year, and married her in 1929. They had two children, Doris, born in 1933, and Klaus, born in 1934. Bethe did not find the work in Frankfurt very stimulating, and in 1929 he accepted an offer from Ewald at the Technische Hochschule in Stuttgart. While there, wrote what he considered to be his greatest paper, Zur Theorie des Durchgangs schneller Korpuskularstrahlen durch Materie (The Theory of the Passage of Fast Corpuscular Rays Through Matter"). Starting from Max Born's interpretation of the Schrödinger equation, Bethe produced a simplified formula for collision problems, which is known today as the Bethe formula. Bethe submitted this paper for his habilitation in 1930.

Sommerfeld recommended Bethe for a Rockefeller Foundation Travelling Scholarship in 1929. This provided $150 a month, twice what he has been earning, to allow him to study abroad. In 1930, Bethe chose to do postdoctoral work at the Cavendish Laboratory at the University of Cambridge in England, where he worked under the supervision of Ralph Fowler. At the request of Patrick Blackett, who was working with cloud chambers, Bethe created a relativistic version of the Bethe formula. He also, with Guido Beck and Wolfgang Riezler, two other postdoctoral fellows, created a hoax paper poking fun at Arthur Eddington's attempts to the explain the value of the fine structure constant. They were forced to issue an apology.

Bethe next chose to go to Enrico Fermi's laboratory in Rome in February 1931. He liked Rome, and considered the food in Italy to be vastly superior to that of England. He was greatly impressed by Fermi who, he told Sommerfeld, "immediately sees the solution to every problem that is put to him". Bethe regretted that he had not gone to Rome first. After touring Italy for three weeks with Käte Feiss, he proposed marriage to her, but she turned him down. While in Italy, Bethe developed the Bethe ansatz, a method for finding the exact solutions for the eigenvalues and eigenvectors of tof certain one-dimensional quantum many-body models. He was influenced by Fermi's simplicity and Sommerfeld's rigor in approaching problems, and these qualities influenced his own later research.

The Rockefeller Foundation offered an extension of Bethe's fellowship, allonging him to return to Italy in 1932. Bethe accepted an request from Karl Scheel to write an article for the Handbuch der Physik.

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 at the University of Manchester 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 for the rest of his career. During 1948–1949 he was a Visiting Professor at Columbia University. At Cornell, Bethe became known as one of the leading theoretical physicists of his generation, and along with upcoming physicists such as cyclotron pioneer Milton Stanley Livingston, and later, after the war, experimentalist Robert R. Wilson and theoretician Robert Bacher, put Cornell on the world physics map. Together with Robert Bacher and Livingston, Bethe published a series of three articles which summarized most of what was known on the subject of nuclear physics 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 left off, filling 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.

Bethe became a naturalized citizen of the United States in 1941. He was an honorary member of the International Academy of Science.


Manhattan Project

When the war began, Bethe wanted to contribute to the war effort. Following the advice of the Caltech aerodynamicist Theodore von Kármán, 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 ballistic reentry. Bethe also worked on a theory of armor penetration, which was immediately classified by the Army, making it inaccessible to Bethe, who was not an American citizen at the time.

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 was skeptical of the possibility of making a nuclear weapon from uranium. In the late 1930s, he wrote a theoretical paper arguing against fission, but was convinced by Teller to join the Manhattan Project. When Oppenheimer was put in charge of forming a secret weapons design laboratory, Los Alamos, he appointed Bethe 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. Along with Richard Feynman, he developed a formula for calculating the explosive yield of the bomb. After November 1943, when the laboratory had been reoriented 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, he worked on the neutron initiator, and later on radiation propagation from an exploding atomic bomb.

During the project, Klaus Fuchs, a German scientist spying for 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 design) was detonated in the New Mexico desert on July 16, 1945, at the Trinity test, Bethe's immediate concern was for its efficient operation, and not its moral implications. He is reported to have commented: "I am not a philosopher."


Hydrogen bomb

After the war, Bethe argued that a crash project for the hydrogen bomb should not be attempted, though after President Harry 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 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, published an article criticising in detail the anti-ICBM defense system proposed by the Department of Defense. The two physicists described in the article that nearly any measure taken by the US would be easily thwarted with the deployment of relatively simple decoys. Bethe was one of the primary voices in the scientific community behind the signing of the 1963 Partial Test Ban Treaty prohibiting further atmospheric testing of nuclear weapons.

During the 1980s and 1990s, Bethe campaigned for the peaceful use of nuclear energy. After the Chernobyl disaster, 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 and other physicists opposed the Strategic Defense Initiative missile system conceived by the Ronald Reagan administration. 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.


Later work

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". His postulate was that the source of this stellar nucleosynthesis was thermonuclear reactions in which hydrogen is converted into helium.

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 provided the impetus for later work done by Richard Feynman, Julian Schwinger and others which marked the beginning of modern quantum electrodynamics.

Bethe 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. At age 85, he wrote an important article about the solar neutrino problem, in which he helped establish the conversion mechanism for electron neutrinos into muon neutrinos proposed by Mikheyev and Smirnov to explain a vexing discrepancy between theory and experiment. 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.

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. He loved the outdoors, and was an enthusiastic mountain climber all his life. Bethe was also known for his sense of humor, and once published a parody in 1931, On the Quantum Theory of the Temperature of Absolute Zero where he calculated the fine structure constant from the absolute zero temperature in Celsius units, causing a scandal in the scientific world. This second parody 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 such as Sir Arthur Eddington's claim to have calculated the fine structure constant from fundamental quantities in an earlier paper. He has also, wrongly, been credited for allowing his name to be used in the Alpher-Bethe-Gamow paper in which he did not participate; in fact, George Gamow added Bethe's name without consulting him, and against Ralph Alpher's wishes.

Bethe died in his home in Ithaca, New York on March 6, 2005  of congestive heart failure. At the time of his death, he was the John Wendell Anderson Professor of Physics Emeritus at Cornell University. He also was, reaching the age of 98, the third-oldest Nobel laureate ever. 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.

While lecturing at Duke University in 1937, Hans Bethe met Rose Ewald, who was a daughter of his former professor Paul Peter Ewald. They were married in September 1939. The Bethes, who had two children, Henry and Monica, spent most of their lives in Ithaca.

   
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