Einstein's Theory of Relativity

In physics, mass-energy equivalence is the concept that all mass has an energy equivalence, and all energy has a mass equivalence. Special relativity expresses this relationship using the mass-energy equivalence formula

E = mc²

where

E = the energy equivalent to the mass (in joules),

m = mass (in kilograms), and

c = the speed of light in a vacuum (celeritas) (in meters per second).

Several definitions of mass in special relativity may be validly used with this formula, but if the energy in the formula is rest energy then the mass must be rest mass or invariant mass.

Origination of the formula is popularly attributed to Albert Einstein in 1905 in what are known as his Annus Mirabilis ("Wonderful Year") Papers, though Einstein was not the first to propose a mass-energy relationship, and the formula appeared in works predating Einstein's theory (see Contributions of others, below).

In the formula, c² is the conversion factor required to convert from units of mass to units of energy, i.e., the energy density. In unit-specific terms, E (joules or kg·m²/s²) = m (kilograms) multiplied by (299,792,458 m/s)2.

For more information, visit http://en.wikipedia.org/wiki/E=mc²