E = mc² where E denotes energy, m denotes mass, and c is the speed of light in a vacuum. This is the equation proposed by Albert Einstein as part of the special theory of relativity showing the relationship between mass and energy. The implication of this equation is that mass can be considered as potential energy, though it is extremely difficult to make the conversion and release the stored energy. Two such methods are nuclear fusion and nuclear fission, both of which involve creating a new molecular structure from existing molecules where the new structure contains less mass, with the difference being converted into energy.