Albert Einstein (German/English: Albert Einstein; March 14, 1879 – April 18, 1955) was a Jewish physicist who held dual U.S. and Swiss citizenship. Born in Ulm, Baden-Württemberg, Germany, Einstein graduated from the Swiss Federal Institute of Technology in Zurich in 1900 and later acquired Swiss nationality. In 1905, he earned his Ph.D. in Physics from the University of Zurich and proposed the photon hypothesis, successfully explaining the photoelectric effect—which earned him the 1921 Nobel Prize in Physics. That same year, he formulated the theory of special relativity, and in 1915, he developed the theory of general relativity.