he had lived long enough to see his predictions substantiated by experiment, Oppenheimer might have won a Nobel Prize for his work on gravitational collapse, concerning neutron stars and black holes. In retrospect, some physicists and historians consider this his most important contribution, though it was not taken up by other scientists in his lifetime. The physicist and historian Abraham Pais once asked Oppenheimer what he considered his most important scientific contributions; Oppenheimer cited his work on electrons and positrons, not his work on gravitational contraction. Oppenheimer was nominated for the Nobel Prize for physics three times, in 1946, 1951 and 1967, but never won. Private and political life During the 1920s, Oppenheimer remained uninformed on worldly matters. He claimed that he did not read newspapers or listen to the radio and had only learned of the Wall Street crash of 1929 while he was on a walk with Ernest Lawrence six months after the crash occurred. He once remarked that he never cast a vote until the 1936 presidential election. From 1934 on, however, he became increasingly concerned about politics and international affairs. In 1934, he earmarked three percent of his annual salary—about $100 ()—for two years to support German physicists fleeing Nazi Germany. During the 1934 West Coast Waterfront Strike, he and some of his students, including Melba Phillips and Bob Serber, attended a longshoremen's rally. Oppenheimer repeatedly attempted to get Serber a position at Berkeley but was blocked by Birge, who felt that "one Jew in the department was enough". Oppenheimer's mother died in 1931, and he became closer to his father who, although still living in New York, became a frequent visitor in California. When his father died in 1937, leaving $392,602 to be divided between Oppenheimer and his brother Frank, Oppenheimer immediately wrote out a will that left his estate to the University of California to be used for graduate scholarships. Like many young intellectuals in the 1930s, Oppenheimer supported social reforms that were later alleged to be communist ideas. He donated to many progressive causes that were branded as left-wing during the McCarthy era. The majority of his allegedly radical work consisted of hosting fundraisers for the Republican cause in the Spanish Civil War and other anti-fascist activity. He never openly joined the Communist Party USA (CPUSA), though he did pass money to leftist causes by way of acquaintances who were alleged to be