The Exchange Rate between Mass and Energy

Because the speed of light squared is a very large number when expressed in appropriate units, a small amount of mass corresponds to a huge amount of energy. Thus, the conversion of mass to energy could account for the enormous energy output of the stars, but it is necessary to find a physical mechanism by which that can take place.

Mass and Energy

Until the time of Einstein, mass and energy were considered to be two separate things. In the special theory of relativity, Einstein demonstrated that neither mass nor energy were conserved separately, but that they could be traded one for the other and only the total "mass-energy" was conserved. The relationship between the mass and the energy is contained in what is probably the most famous equation in science,

E = mc2

where m is the mass, c is the speed of light, and E is the energy equivalent of the mass.