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A subatomic particle that has the same mass as another particle and equal but opposite values of some other property or properties. For example, the antiparticle of the electron is the positron, which has a positive charge equal in magnitude to the electron's negative charge. The antiproton has a negative charge equal to the proton's positive charge. The neutron and the antineutron have magnetic moments opposite in sign relative to their spins. The existence of antiparticles is predicted by relativistic quantum mechanics. When a particle and its corresponding antiparticle collide annihilation takes place. Antimatter consists of matter made up of antiparticles. For example, antihydrogen consists of an antiproton0 with an orbiting positron. Antihydrogen has been artificially created in the laboratory. The spectrum of antihydrogen should be identical to that of hydrogen. It appears that the universe consists overwhelmingly of (normal) matter, and explanations of the absence of large amounts of antimatter have been incorporated into cosmological models that involve the use of grand unified theories of elementary particles.

Subjects: Physics.

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