Hans Bethe

Hans Bethe grew up in Strasbourg and Frankfurt, the son of a physiology professor and a mother of Jewish descent, in a household that was Protestant by practice and increasingly secular by inclination. He earned his doctorate under Arnold Sommerfeld at Munich in 1928, then spent two restless years learning from the best physicists in Europe — Cambridge's Cavendish Laboratory, Rome with Enrico Fermi — before landing an assistant professorship at Tübingen in 1932. The Nazi civil service law reached him within a year: because his mother was Jewish, the university dismissed him in 1933. He taught briefly in Manchester, then accepted an assistant professorship at Cornell University in February 1935, for a salary of $3,000, and stayed there for the rest of his career.

At a 1938 conference in Washington he worked out the nuclear reactions that make stars burn — the proton-proton chain for small stars, the carbon-nitrogen-oxygen cycle for large ones — winning the 1967 Nobel Prize almost 30 years later. In 1942 Oppenheimer put him in charge of the Theoretical Division at Los Alamos, where he calculated the critical mass of uranium-235 and the plutonium-implosion physics tested at Trinity in July 1945. He opposed a postwar crash program to build a hydrogen bomb, reversed himself once the Korean War started, and led the work that made it possible anyway, calling his own role the midwife's, not the father's. In 1947, riding a train to Schenectady, he solved the Lamb shift problem in an afternoon, a calculation Feynman called the most important discovery in the history of quantum electrodynamics.

The contradiction he spent the second half of his life trying to resolve was his own. He had calculated how to build the atomic bomb, then helped work out how to make one a thousand times more destructive, and afterward campaigned for decades against the weapons he had helped design — joining Einstein's public warnings, helping negotiate the 1963 Test Ban Treaty and the 1972 Anti-Ballistic Missile Treaty, and testifying for Oppenheimer at the 1954 hearing that stripped his former boss of his clearance, at real risk to his own standing in Washington. He kept publishing physics into his 90s and kept lobbying against weapons programs just as long, writing an open letter at 88, in 1995, asking scientists to refuse further weapons work. He never resolved whether Los Alamos had been necessary; he worked both sides for 60 years.

He died at home in Ithaca in 2005, still holding his Cornell professorship after 70 years, having published papers in every decade of a career that started before quantum mechanics was 10 years old. Cornell named a residential college after him; an asteroid carries his name. Colleagues did the ranking instead of historians: the physicist Freeman Dyson called him the supreme problem-solver of 20th-century physics, and the astrophysicist Edward Kolb described him as the last of the old masters, spanning a career from the discovery of the atomic nucleus to the hydrogen bomb and beyond. The stellar physics he worked out in 1938 is still the textbook explanation for why the sun keeps burning.

Hans Bethe's life against the full span of the corpus.

• CNO cycle and proton-proton chain discovery
  Explained how stars generate energy; the basis of the 1967 Nobel Prize 1939
• Los Alamos Theoretical Division mission
  Led wartime calculations for the atomic bomb's critical mass and implosion design 1943
• Lamb shift calculation discovery
  First successful quantum electrodynamics calculation, worked out on a train 1947
• Open letter against nuclear weapons work speech
  Signed at 88, urging all scientists to refuse further weapons research 1995

• July 2, 1906 aged 0 Born in Strasbourg, then part of the German Empire
• 1928 aged ~22 Earns his doctorate at Munich under Arnold Sommerfeld
• 1933 aged ~27 Dismissed from his Tübingen post under the Nazi civil service law His mother was Jewish.
• February 1935 aged 28 Joins Cornell University as an assistant professor
• March 17, 1938 aged 31 Works out the nuclear reactions that power stars at a Washington conference
• July 16, 1945 aged 39 The Trinity test validates his Los Alamos calculations
• 1947 aged ~41 Solves the Lamb shift problem on a train to Schenectady
• 1967 aged ~61 Awarded the Nobel Prize in Physics
• March 6, 2005 aged 98 Dies at home in Ithaca, New York

• J. Robert Oppenheimer 1904–1967
  Theoretical physicist who led the Manhattan Project and became known as the father of the atomic bomb. testified on his behalf
• Richard Feynman 1918–1988
  Theoretical physicist known for his work in quantum mechanics and his accessible teaching style. Los Alamos colleague
• Albert Einstein 1879–1955
  German-American theoretical physicist whose theory of relativity revolutionized modern physics. campaigned with him against the arms race
• Edward Teller 1908–2003
  Physicist and advocate of the hydrogen bomb whose work and policy influence shaped Cold War science and defense. hydrogen bomb rival
• Enrico Fermi 1901–1954
  Italian-American physicist who built the first nuclear reactor and won the Nobel Prize in Physics. mentor in Rome