Glossary
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Definition
Photon
The photon is the elementary particle that carries the electromagnetic interaction (force). Each electromagnetic wave (visible light, but also infrared, ultraviolet, X-rays, etc.) carries photons, which have a precisely-determined energy (according to the 'colour' or wavelength of light). This energy can be transferred to matter in packets or quanta.
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The photon has a special status in the classification of particles, since it was discovered well before the development of the current standard model. After it was predicted by Planck's work, Einstein confirmed its existence in his 1905 article on the photoelectric effect: the photon interacts with the electrons of atoms and exchanges energy. Its discovery formed the basis of quantum mechanics. Light is both a wave that propagates and a particle (the photon), which has an impact on a detector. The photon has zero mass: it moves at the speed of light and the range of electromagnetic force is infinite, unlike the strong and weak interactions.
