ELEMENTARY PARTICLES en.wikipedia.org/wiki/Elementary_particle In particle physics, an elementary particle or fundamental particle is a particle whose substructure is unknown, thus it is not known to be composed of other particles.[1] Known elementary particles include the fundamental fermions (quarks, leptons, antiquarks, and antileptons), which generally are matter particles and antimatter particles, as well as the fundamental bosons (gauge bosons and Higgs boson), which generally are force particles that mediate interactions among fermions.[1] A particle containing two or more elementary particles is a composite particle. Everyday matter is composed of atoms, once presumed to be matters elementary particles—atom meaning indivisible in Greek—although the atoms existence remained controversial until about 1910, as some leading physicists regarded molecules as mathematical illusions, and matter as ultimately composed of energy.[1][2] Soon, subatomic constituents of the atom were identified, although as the 1930s opened, only the electron, photon, and proton were known.[1] By then, the recent advent of quantum mechanics was radically altering conception of particles, as a single particle could seemingly span a field as would a wave, a paradox still defying satisfactory explanation.[3][4][5] Via quantum theory, protons and neutrons were found to contain quarks—up quarks and down quarks—now considered elementary particles.[1] And within a molecule, the electrons three degrees of freedom (charge, spin, orbital) can separate via wavefunction into three quasiparticles (holon, spinon, orbiton).[6] Yet a free electron—which, not orbiting an atomic nucleus, lacks orbital motion—appears unsplittable and remains regarded as an elementary particle.[6] Around 1980, an elementary particles status as indeed elementary—an ultimate constituent of substance—was mostly discarded for a more practical outlook,[1] embodied in particle physics Standard Model, sciences most experimentally successful theory.[5][7] Many elaborations upon and theories beyond the Standard Model, including the extremely popular string theory, double the number of elementary particles by hypothesizing that each known particle associates with a shadow partner far more massive,[8][9] although all such superpartners remain undiscovered.[7][10] Meanwhile, an elementary boson mediating gravitation—the graviton—is generally presumed, but remains hypothetical.[1]
Posted on: Thu, 21 Nov 2013 19:38:37 +0000
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