The 1930 Solvay Conference was the last Solvay Einstein attended. The next one took place in 1933, and by then he was in the United States, a refugee from the Nazi government that was voted into office in March 1933. Einstein lived 25 years beyond Solvay 1930, Bohr more than 30. They had one more long-distance dispute. In 1935, Einstein published an article pointing to a problem he saw entangling quantum theory, but Bohr answered him sharply and for many decades was considered triumphant. Only in the twentieth century’s final quarter did physicists realize that Einstein had been back in his crow’s nest spotting still more unanticipated trouble from quanta. Most importantly, the great equations of the quantum revolution never failed. Schrödinger’s equation, Dirac’s equation, and Heisenberg’s principle have all withstood the tests of decades. Nothing hidden has been found, nothing extra has been needed, nothing exceptional has been acknowledged. The accuracy of the equations has survived the ever-improving precision of measurements, and nobody expects them to falter. Even the puzzle of negative energy in Dirac’s equation proved correct when “antimatter” was discovered.
Bohr and Einstein never met again in Europe but did meet several more times in America. After 1930, however, matters between them were never the same. Bohr’s idea of complementarity and his Copenhagen Interpretation enjoyed a monopoly over quantum phys-
ics for another generation. In the 1950s, however, the kind of quarreling over physical meaning that had seemed to end with Newton returned when a series of rival interpretations of the same logical laws started to appear. Perhaps the most famous, or notorious, of these is the “many worlds interpretation” in which the universe keeps splitting into as many alternate realities as are required to produce every possible outcome for each quantum event. The “sum over histories” interpretation proposes that photons, electrons, and other quantum entities follow all their possible trajectories at the same time. Meanwhile, “hidden variable” interpretations propose that reality still determines what happens as firmly as it did during the reign of Newton, but the details of these determinants are hidden from us. This last interpretation builds on ideas Louis de Broglie had proposed at the start of the quantum revolution.
Of course, there were some proud moments yet to come for the quantum revolutionaries. De Broglie had won the 1929 Nobel Prize. Heisenberg won it in 1932. Schrödinger and Dirac shared 1933’s prize. Pauli finally landed his in 1945. Max Born did so much for the quantum revolution yet was somehow overlooked by the Swedes until 1954.
Despite these honors, our history’s final scene in Holland smells of doom. Ehrenfest was rocked with despair and would, in three years, kill his son, Vassik, and then himself. The other professors in the room would be scattered to the earth’s corners. The Jews among them would have no choice but to flee. Others, like Schrödinger, could have stayed and been honored, but they fled as well. The heritage of Göttingen, preserved by Napoleon, would quickly be destroyed by the Nazis as its brain power was chased abroad. German nationalists had done what Planck had said no enemy could do, rob German science of its position in the world. The forgotten figures of Philipp Lenard and Johannes Stark would suddenly move to the top of Germany’s scientific bureaucracy.
Elsa died in 1936 while Einstein looked on in helpless misery. “I never thought he was so attached to me,” Elsa wrote a friend in amazement over her husband’s worry, “That, too, helps.” But Einstein did not live alone for long. His secretary, Helen Dukas, remained with him
and he brought some of his family over. Matters were growing more terrible in Europe every day. He got his oldest son, Hans Albert, and his family out in 1937. His sister, Maja, who had not played much part in the Einstein story since his boyhood, joined him in Princeton in 1939 and stayed until her own death in 1951. During all his years in America Einstein pursued both his physics and his humanist politics. His anti-fascism, pacifism, enthusiasm for democracy, and support for civil rights brought him to the attention of America’s policeman-in-chief, J. Edgar Hoover. The FBI complied a fat dossier on him but never acted on it. As had been the case 30 years earlier in Germany, America’s leading politicians thought he was a malodorous flower, but, after he became a U.S. citizen in 1941, they proudly showed him off in their buttonholes.