is a formula in special relativity that relates the relativistic energy, E, rest mass, , and momentum, p, of a particle. From it the momentum of a photon can be derived and so to the famous equation E=mc2.
The relativistic equation for momentum is:
The equation for relativistic energy is:
These can be rearranged into the forms:
Subtracting the momentum equation from the energy equation an rearranging gives:
The energy of a photon can be derived by setting the rest mass, , equal to zero, so:
Mass energy equivalence can be derived by setting the momentum, , to zero. This gives us one of the most famous equations in physics,