E=mc2 is the theory of relitivity,which is the theory of the speed of light and whether or not the speed of light is constant or not.
Y' wot? E=mc^2 is an equation to convert matter to energy or vice versa.
Relativity is:
"a set of two theories in physics: special relativity and general relativity. The core idea of both theories is that two observers who move relative to each other will often measure different 'time' and 'space' intervals for the same events, but the content of physical law will be the same for both."
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I'm not evil, just morally challenged