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出典:『Wikipedia』 (2011/06/08 19:03 UTC 版)

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In particle physics, an elementary particle or fundamental particle is a particle believed not to have substructure; that is, it is believed not to be made up of smaller particles. If an elementary particle truly has no substructure, then it is one of the basic building blocks of the universe from which all other particles are made. In the Standard Model, the quarks, leptons, and gauge bosons are elementary particles. Historically, the hadrons (mesons and baryons such as the proton and neutron) and even whole atoms were once regarded as elementary particles. A central feature in elementary particle theory is the early 20th century idea of "quanta", which revolutionized the understanding of electromagnetic radiation and brought about quantum mechanics. For mathematical purposes, elementary particles are normally treated as point particles, although some particle theories such as string theory posit a physical dimension.