n.
In physics, a reaction in which a particle and its antiparticle (see antimatter ) collide and disappear.
The annihilation releases energy equal to the original mass m multiplied by the square of the speed of light c , or E = m c 2 , in accordance with Albert Einstein 's special theory of relativity . The energy can appear directly as gamma rays or can convert back to particles and antiparticles (see pair production ).