E=mc2

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One of only three existing manuscripts (two of them are housed at the Albert Einstein Archives) which contain Einstein's famous formula, E=mc². Einstein's formula, which describes the relationship between energy (E), mass (m) and the speed of light (c), derives from Einstein's special theory of relativity. This theory postulates that time and space are relative - how we measure time and space depends on our state of motion relative to other observers. The formula E=mc² first appeared in an article by Einstein in 1905, using a different notation, and in 1907 he fully generalized the concept to the equivalence of mass and energy. The implication of the formula thus became that a small amount of matter could, in principle, be converted into a vast amount of energy. The realization of this principle in practice became a possibility in the 1930's with the discovery of nuclear fission, which led ultimately to the development of nuclear weapons. After the Second World War, Einstein's formula became synonymous with the nuclear age. The popular science magazine, Science Illustrated, asked Einstein to write this article. In his choice of the title, "The Most Urgent Problem of Our Time", Einstein alluded to his support for the nuclear disarmament movement.