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photon
A particle of light or, more precisely, a quantum of the electromagnetic field. It has zero rest mass and a spin of 1. Apart from its obvious role as the carrier of virtually all the information that we have so far been able to ascertain about phenomena beyond the solar system (with the exception of cosmic dust, cosmic rays, neutrinos, and, possibly, gravitational waves), the photon is also the gauge boson that mediates the force of electromagnetic force acting between any two charged particles. In their role as force-carriers, photons, known as virtual photons, can adopt an effective mass for a short period in accordance with Heisenberg's uncertainty principle.
The name "photon," which comes from the Greek photos meaning "light," was coined by the American physicist G. N. Lewis in 1926.
Related entry
• electromagnetic radiation
Related category
• PARTICLE PHYSICS
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