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 ${\displaystyle E=mc^{2}}$. As ${\displaystyle c^{2}}$ is constant, ${\displaystyle E\ \alpha \ m}$. For example, 1kg of matter is equivalent to around ${\displaystyle 3\times 10^{8}}$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.