Einstein, Albert

Einstein, Albert (1879–1955) German-born US theoretical physicist, founder of the theory of relativity, often regarded as the greatest scientist of the 20th century. In 1905 he published three outstanding papers dealing with the photoelectric effect, Brownian motion, and his special theory of relativity. Relativity abandons the idea of absolute space and time as a reference framework for all bodies; instead a distinction is made between the framework of the observer and that of the object. Among the theory's most important conclusions is that mass and energy are interconvertible, expressed by the equation e = mc² (c being the speed of light). In 1915 Einstein published the general theory of relativity. This extended his ideas to gravitation, which he treated as a curvature of the space-time continuum. The general theory was vindicated when the predicted deflection of light rays passing through a substantial gravitational field was confirmed by observations during the solar eclipse of 1919. As a Jew, Einstein decided to live in the USA when Hitler came to power in 1933. For the remainder of his life he sought without success a unified field theory embracing electromagnetism, gravitation, and quantum mechanics. In 1939 he wrote to President Roosevelt about the military potential of nuclear energy, greatly influencing the decision to build an atom bomb. After the war he spoke out passionately against nuclear weapons.