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In physics, a reaction in which a particle and its antiparticle (seeantimatter) 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 = mc2, 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 (seepair production).
This entry comes from Encyclopædia Britannica Concise. For the full entry on annihilation, visit Britannica.com.