In 1921 Aided by his fame, Einstein championed the fledgling German republican government and other liberal causes. Partly as a result of this, he and his theory of relativity came under vicious attack from anti-Semites. He began travelling, attended an International Trade Union Congress in Amsterdam, and visited the United States to help raise funds for the Hebrew University in Jerusalem. The following year he received the Nobel Prize.
Einstein in motorcade on occasion of his arrival in New York City, 1921.
In 1924 Einstein contributed to the struggling new quantum theory. Meanwhile, he searched for a way to unify the theories of electromagnetism and gravity. In 1929 he announced a unified field theory, but the mathematics could not be compared with experiments; his struggle toward a useful theory had only begun. Meanwhile he argued with his colleagues, challenging their belief that quantum theory can give a complete description of phenomena.
In 1933 Unwilling to live in Germany under the new Nazi government, Einstein joined the Institute for Advanced Study in Princeton, New Jersey. He turned away from strict pacifism, and warned world political leaders to prepare for German aggression. He also worked to rescue Jewish and other political victims of the Nazis.
Einstein in Berlin,In 1939 Einstein signed a letter that informed President F. D. Roosevelt of the possibility of nuclear bombs, warning that the Germans might try to build them. The next year Einstein became an American citizen.
"How I wish that somewhere there existed an island for those who are wise and of goodwill! In such a place even I would be an ardent patriot."
In 1952 Einstein was asked to become the second President of the State of Israel, but declined. He was supporting many causes, such as the United Nations and world government, nuclear disarmament, and civil liberties.
"The feeling for what ought and ought not to be grows and dies like a tree, and no fertilizer of any kind will do much good. What the individual can do is give a fine example, and have the courage to firmly uphold ethical convictions in a society of cynics. I have for a long time tried to conduct myself this way, with varying success."
In 1955 The search for a true unified field theory for a more profound understanding of nature continued to fill Einstein's days. While corresponding about a new anti-war project and writing a speech for Israel, he was stricken and died.
"One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike – and yet it is the most precious thing we have."