Antimatter is a type of matter predicted by Paul Dirac when he attempted to write down a version of quantum mechanics that incorporated Einstein's theory of special relativity. In the Standard Model, every particle has a corresponding antiparticle that has the same mass but opposite electric charge, baryon number, and strangeness. When a particle meets its antiparticle counterpart, the pair annihilates: they disappear, and their total energy is converted into other particles.