In particle physics, antimatter extends the concept of the antiparticle to matter, wherein if a particle and its antiparticle come into contact with each other, the two annihilate or cause the equivalent to a nuclear explosion, similar to nuclear fission —that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. This gives rise to high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle-antiparticle pair, which is often quite large.