(1879-1955) a physicist, born in Germany, who was possibly the greatest scientist of the 20th century. In 1905 he published his theory of relativity. This led to the equation giving the relationship between mass and energy, E=mc2, which is the basis of atomic energy. Einstein suggested how it could be used for making weapons, but after World War II he spoke publicly against nuclear weapons. By 1917, he had become famous all over the world. He was given the Nobel Prize for physics in 1921. When Hitler came to power, Einstein, who was Jewish, went to live in the US, becoming a US citizen in 1940. In 1933 he wrote a book called Why War?with Sigmund Freud. He became a professor at Princeton University in 1934, and he spent the rest of his life looking, without success, for a theory that combined those of gravitation and electromagnetism. In 1952 he was offered the presidency (= the position of president) of the state of Israel, but did not accept it.