quasi-particle

quasiparticle

[kwey-zahy-pahr-ti-kuhl, kwey-sahy-, kwah-see, -zee-]
noun Physics.
an entity, as an exciton or phonon, that interacts with elementary particles, but does not exist as a free particle.

Origin:
1955–60; quasi- + particle

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Encyclopedia Britannica
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quasi-particle

in physics, a disturbance, in a medium, that behaves as a particle and that may conveniently be regarded as one. A rudimentary analogy is that of a bubble in a glass of beer: the bubble is not really an independent object but a phenomenon, the displacement of a volume of beer by carbon dioxide gas, but, because of the characteristics of the surface of liquid in contact with the gas, the bubble retains a certain identity as it rises and floats. It, like a quasiparticle, carries properties characteristic of objects, such as size, shape, energy, and momentum. Two bubbles can bounce off each other; quasiparticles, too, undergo collisions. Some specific quasiparticles are the exciton, phonon, magnon, and polaron (qq.v.).

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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