# Albert Einstein

### theoretical relativity energy theory

**Einstein, Albert** (1879–1955), German-born U.S. physicist, one of the greatest scientific figures. He received the Nobel Prize in physics in 1921 for his services to theoretical physics, especially the discovery of the law of the photoelectric effect. While still a youth he taught himself calculus and science. In 1896 he entered the Swiss Federal Polytechnic School in Zurich, where he trained as a teacher of physics and mathematics. He became a Swiss citizen on receiving his diploma in 1900. Unable to find an academic position, Einstein worked for the Swiss Patent Office while studying for the Ph.D. degree, which he received from the University of Zurich in 1905. In 1905 he published 4 scientific papers, each containing a great discovery: (1) the first presentation of the special theory of relativity; (2) the statement of the equivalence of mass and energy (the famous E=mc^{2} equation, stating that energy equals mass times the velocity of light squared), which later provided the theoretical basis for the atom bomb; (3) a theoretical explanation of Brownian motion, the incessant erratic movement of tiny particles suspended in a fluid; and (4) his application of Planck's quantum hypothesis to the investigation of the nature of light, in which he showed that light behaved as if it were composed of independent quanta (tiny units) of energy called photons, and not simply of waves. In 1914 he became professor at the University of Berlin and director of the Kaiser Wilhelm Physical Institute, resuming his German citizenship. In 1916 he published his general theory of relativity. Much of the rest of his life was spent in an unsuccessful effort to produce a *unified field theory*, that is, to show that both gravitational and electromagnetic phenomena derive from the geometrical properties of space-time. The task has still not been completed. With the rise of the Nazis, Einstein, a Jew, found his position in Germany impossible, and in 1932 he resigned from his post at Berlin. In 1933 he moved to the Institute for Advanced Study at Princeton, N.J. He became a U.S. citizen in 1940. Just before World War II, Einstein wrote a letter to President Franklin D. Roosevelt, pointing out the theoretical possibility of a nuclear bomb and warning of the danger that Germany might develop the bomb first. This resulted in the establishment of the Manhattan Project. He retired from the institute in 1945 but continued to work there until his death in 1955.

*See also:* Relativity; E=mc2.

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