AQA A-Level Physics/Mass and energy

The mass-energy equivalence principle theorised by Albert Einstein describes the relationship between mass and energy through the equation $E=m{c}^2$. As $c^2$ is constant, $E\alpha m$. For example, 1kg of matter is equivalent to around $3\times 10^8$J of energy. This principle can be used to calculate the rest mass of a pair of particles which are produced through pair production, or the energy of a gamma photon produced through annihilation.