photon

American  

[foh-ton] / ˈfoʊ tɒn /

noun

1. a quantum of electromagnetic radiation, usually considered as an elementary particle that is its own antiparticle and that has zero rest mass and charge and a spin of one. γ

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photon British  

/ ˈfəʊtɒn /

noun

1. a quantum of electromagnetic radiation, regarded as a particle with zero rest mass and charge, unit spin, and energy equal to the product of the frequency of the radiation and the Planck constant

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photon Scientific  

/ fō′tŏn′ /

1. The subatomic particle that carries the electromagnetic force and is the quantum of electromagnetic radiation. The photon has a rest mass of zero, but has measurable momentum, exhibits deflection by a gravitational field, and can exert a force. It has no electric charge, has an indefinitely long lifetime, and is its own antiparticle.

2. See Note at electromagnetic radiation See Table at subatomic particle

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photon Cultural  

1. The quantum, or bundle of energy, in which light and other forms of electromagnetic radiation are emitted. (See atom.)

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Etymology

Origin of photon

First recorded in 1900–05; phot- + -on ¹

Explanation

In physics, a photon is a tiny bundle of matter that transmits light. You can also think of photons as little bits of electromagnetic energy. Light is made up of small amounts of energy which are known as photons. You can tell how much radiation is being emitted by the number of photons — think of a dimmer on a light switch, with the brighter light emitting more photons. Albert Einstein was instrumental in developing the photon theory of light, although he used the term "the light quantum," rather than photon, which was first used in this sense around 1926.

Example Sentences

In these states, a photon is not simply detected as arriving "early" or "late," but exists as a combination of both possibilities.

From Science Daily • Apr. 1, 2026

This means that roughly 1.3 molybdenum-based metal complexes were activated for every photon absorbed, exceeding the usual limit and demonstrating that more energy carriers were produced than incoming photons.

From Science Daily • Mar. 28, 2026

However, it could become detectable at the highest photon energies, specifically in very-high-energy gamma rays.

From Science Daily • Jan. 8, 2026

This hybrid approach is the key to success: it combines the extreme sensitivity of photon detection with the ability to "recover" the calibration capabilities of the Autler-Townes method even for the weakest signals.

From Science Daily • Dec. 13, 2025

Equally, if a real photon collides with an atom, it may move an electron from an orbit nearer the nucleus to one farther away.

From "A Brief History of Time: And Other Essays" by Stephen Hawking