Martin J. Sherwin

“Frank himself is a sweet, lovable person,” observed the physicist Leona Marshall Libby, a friend of both brothers. She called him a “delta function,” a mathematical device used by physicists in which delta is defined as zero—except at a specified place or time, at which point it becomes infinity. When called upon, Frank always possessed an infinite reservoir of goodwill and cheer.

Another graduate student in physics at Caltech, William “Willie” Fowler, used to say that the reason he was a physicist was that he didn’t want to have to worry about people—and now he was upset because he was being forced by the Depression to do just that.

Bethe had an inkling of Oppenheimer’s political loyalties, so he was struck one evening when his friend gave a “beautifully eloquent speech” about how the fall of Paris to the Nazis threatened all of Western civilization. “We have to defend Western values against the Nazis,” Bethe recalled Oppenheimer saying. “And because of the Molotov–von Ribbentrop pact we can have no truck with the Communists.”