Hans Bethe explained how heavy stars shine, and kept publishing into his nineties
In 1939 Hans Bethe worked out that heavier main-sequence stars are powered by a cycle of reactions involving carbon, nitrogen and oxygen, which earned him the 1967 Nobel Prize in Physics. His career lasted nearly seventy years, and he produced at least one major paper in each of those decades.
Bethe was born in Strasbourg, then part of Germany, in 1906, the only child of a physiology lecturer. A bout of tuberculosis in 1916 sent him away to recover. At Frankfurt he began in chemistry but proved a clumsy experimenter who ruined his lab coat with sulfuric acid, and a professor steered him to Munich to study theory under Arnold Sommerfeld. His doctoral thesis on electron diffraction in crystals grew overcomplicated; when Wolfgang Pauli, famous for his sharp tongue, said it fell short of Sommerfeld's praise, Bethe took the remark as a compliment by Pauli's standards.
At Stuttgart in 1930 he wrote what he regarded as his finest paper, a simplified formula for how fast particles lose energy passing through matter, still known as the Bethe formula. A Rockefeller scholarship worth 150 dollars a month took him to Cambridge. In 1931 he devised the Bethe ansatz, a way to solve certain one-dimensional quantum systems exactly. He spent most of his career as a professor at Cornell.
During the Second World War he headed the Theoretical Division at Los Alamos, calculating the critical mass of the first atomic bombs and developing the implosion theory used at the Trinity test and in the weapon dropped on Nagasaki in 1945. After the war he again led theory for the hydrogen bomb, having joined partly hoping to show it could not be built. He then campaigned with Albert Einstein against nuclear testing and helped persuade American governments to sign the 1963 Partial Test Ban Treaty and the 1972 Anti-Ballistic Missile Treaty.
His 1947 calculation of the Lamb shift, a tiny displacement in hydrogen's energy levels, transformed quantum electrodynamics. Later work helped solve the solar neutrino problem and explain supernovas. Freeman Dyson, who had studied under him, ranked him the greatest solver of physics problems of his century. He died in 2005.
Source: Hans Bethe
