Goodbye, quantum mechanist

Bethe was famous for his ability to make calculations quickly, a useful talent in the days before computers. It was this that allowed him, in a mere six months, to figure out a problem that had foxed other physicists, and explain what drove nuclear fusion the process by which two atomic nuclei join and release energy in the core of the sun. His colleagues could not understand how, as the temperatures of stars increased, they very rapidly became more luminous, so that a star that was ten times as hot would be thousands of times as bright. Bethe saw that only a chain of six reactions, in which carbon acted as a catalyst for the fusion of two hydrogen atoms, would explain what scientists were observing. He was to win the Nobel prize for his calculations.

With the advent of the second world war, Bethe, along with a crowd of other physicists, turned from studying the sun to creating a new one. The Manhattan Project did not start until 1942, three years into the war, when Robert Oppenheimer assembled his extraordinary team in the high desert of New Mexico, north-west of Santa Fe, to devise an atomic bomb. One of his first acts was to appoint Bethe head of the theory division, the obvious man for the job. Among the geniuses working under Bethe was Edward Teller, then one of his close friends. The two men fell out in later years: first about the hydrogen bomb, on which Teller was a hawk and Bethe sceptical, and then about the politically motivated persecution of Oppenheimer, who was stripped of his security clearance. Teller was among those leading the attack, while Bethe steadfastly defended the man who had recruited him.

Excerpted from an obituary from 8216;The Economist8217;, March 18