Photon

Elementary particle or quantum of light

A photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual particles). The photon has zero rest mass and always moves at the speed of light within a vacuum.

Properties

Photons are massless, so they always move at the speed of light in a vacuum, 299792458 meters per second. The photon is also responsible for carrying electromagnetic force, one of the four fundamental forces.

Wave–particle duality

Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles.

Physical properties

Photons are massless, so they cannot slow down; they move at the speed of light in a vacuum. This speed is a constant of nature and is one of the fundamental constants in the theory of relativity.

Applications

Photons have many applications in technology. These include night vision goggles, spectroscopy, and highly accurate atomic clocks.

See also

• Quantum mechanics
• Electromagnetic radiation
• Speed of light
• Elementary particle
• Electromagnetic force

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  Photoelectric effect in a solid - diagram
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  1926 Gilbert N. Lewis letter which brought the word "photon" into common usage
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