Portions of this entry contributed by Leonardo Motta

Portions of this entry contributed by Michel Barran

German-American physicist who was born in Strasbourg, in the French province of Alsace-Lorraine (at the time, occupied by Germany), on July 2, 1906. His father was the physiologist Albrecht Bethe. He was educated at the Goethe Gymnasium (1915-24),the University of Frankfurt am Main (1924-1926), where he studied for two years, then finished his studies at Munich (1926-1928). He obtained his Ph. D. in theoretical physics under Arnold Sommerfeld in 1928. He was then appointed instructor of physics at Frankfurt for one semester, at Stuttgart for another semester, finally becoming Privatdozent at the University of Munich in 1930, a position that he held for only three years.

After the rise of the Nazis in Germany, Bethe emigrated to England in October 1933, holding a temporary position as lecturer at the University of Manchester (1933-1934) and at University of Bristol (1934-1935). In February 1935, he was appointed assistant professor at Cornell University in Ithaca, New York. He was subsequently promoted to professor in 1937, a position he has held even since (as professor emeritus since 1975). Bethe subsequently became a U.S. citizen in 1941.

During the World War II, Bethe worked on microwave radar at the Radiation Laboratory of the Massachusetts Institute of Technology, and then he served as director of theoretical physics of the Manhattan Project at Los Alamos (1943-1946). At the end of the War, Bethe worked, along with Edward Teller , on the development of the hydrogen bomb. At the same time, he became an active proponent of the peaceful exploitation of nuclear energy.

In 1934, Bethe and Peierls developed a theory of the nucleus of the deuteron, which he further extended in 1949. Also in 1934, Bethe and Heitler developed the quantum mechanical theory for bremsstrahlung of relativistic electrons, and initiated the theory of electron and proton showers in cosmic rays . He resolved some contradictions in the nuclear mass scale 1935.

During 1935-1938, he studied nuclear reactions and predicted many reaction cross sections, research that was useful to him to develop Bohr's theory of the compound nucleus more quantitatively. This work was summarized in three articles in Reviews of Modern Physics which for many years served as a textbook for nuclear physics, sometimes known as "Bethe's bible." Bethe's main achievement in astrophysics is considered to be the exclusion of many possible interactions than can happen inside the stars, leaving just two possibilities (the carbon-nitrogen cycle for massive stars and proton-proton reaction that powers fainter stars like the Sun). His work on nuclear reactions led him to the discovery of the reactions which supply the energy in the stars, now called the Bethe (or Bethe-Weizsäcker) cycle, or more commonly, the carbon-nitrogen (or CNO) cycle. Bethe was awarded the 1967 Nobel Prize in physics "for his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production in stars."

Bethe also conducted theoretical research on atomic and molecular physics, studying the behavior of groups of atoms and molecules, their interactions (collisions), and on solid-state physics. In 1947, with Marshak he anticipated the discovery of the pi meson . The same year, Bethe was the first to explain the Lamb shift in the hydrogen spectrum, thus laying the foundation for the modern development of quantum electrodynamics. In 1948, as a joke, Bethe contributed with Ralph Alpher and Georges Gamow to the famous "alpha-beta-gamma" paper on the origin of the chemical elements at the time of the big bang. In 1955, Bethe returned to the theory of nuclei, and worked then on the theory of nuclear matter. Bethe also did some work on solid state theory, and discussed the splitting of atomic energy levels when an atom is inserted into a crystal. He also worked on the theory of metals, and especially developed a theory of order and disorder in alloys.

Bethe was a member of the President's Science Advisory Committee from 1956-1964. In 1958, he headed a presidential study of nuclear disarmament and and was scientific adviser to the United States at the Geneva nuclear test-ban talks. In 1957, he became a member of the National Academy of Sciences.

Bethe (Albrecht), Feynman

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