German-born, Albert Einstein was the leading physicist of the 20th century. His theories on the relationship of time, space, and matter changed our view of the nature of the universe. His research provided the theoretical basis for the development of the atomic bomb. Einstein won the Nobel Prize for physics in 1921. In 1933, he fled Nazi Germany and accepted a professorship at Princeton University, where he lived until his death. An outspoken humanist and philosopher, Einstein wrote works such as Why War (1933, with Sigmund Freud) and About Zionism (1930). In the year of his death, Einstein signed a document, along with six other Nobel Prize winners, that appealed to the world to seriously consider the dangers of nuclear war.