Nor were the men close during World War II, when Oppenheimer headed up the Manhattan Project to build the atomic bomb. True, Einstein had written to President Franklin Roosevelt in 1939 warning of Nazi Germany’s potential to develop “a single [atomic] bomb, carried by boat and exploded in a port, which might very well destroy the whole port together with some of the surrounding territory”. But the Manhattan Project did not start for a further three years, and Einstein was denied security clearance for the program on the grounds of his leftist political beliefs. It was not until after the...