photon

noun pho·ton \ ˈfō-ˌtän \

|Updated on: 11 Jun 2018

Editor's Note: Science and the photon

Definition of photon

1 : a quantum of electromagnetic radiation

Should a substance happen to have a lot of electrons in a higher level, and a lower level is mostly empty …, then a photon can cause an electron to transfer from a higher state to a lower one. This change releases energy and creates a new photon, in addition to the one which caused the transfer. This photon can in turn induce more electrons to fall to a lower state.
—Robert Gilmore

2 dated : troland

—

photonic

play \fō-ˈtä-nik\ adjective

See photon defined for English-language learners

See photon defined for kids

Recent Examples of photon from the Web

There are many fabric additives available, and these include molecules that absorb a high-energy ultraviolet ray, siphon off a bit of heat energy, and then re-emit the rest as a lower-energy photon: one that’s blue.

— helen czerski, WSJ, "Behind Sparkling White Uniforms, an Optical Trick," 24 May 2018
Particles like photons, on the other hand, are bosons.

— chris lee, Ars Technica, "Giant atom hides its neighbors under a single-electron skirt," 7 Mar. 2018
Water in a new state, how CRISPR can fight Huntington's disease, photons cozy up and more.

— lacy schley, Discover Magazine, "Building Blocks," 18 May 2018
Nestled in the Rocky Mountains inside a facility for the National Institute of Standards and Technology, the photon-generating behemoth spans an entire building.

— sophia chen, WIRED, "Quantum Mechanics Could Solve Cryptography’s Random Number Problem," 11 Apr. 2018
The intense x-ray emissions from these disks would be exceedingly faint when viewed from Earth’s vicinity, sending only one photon apiece into Chandra’s optics every five or 10 minutes.

— lee billings, Scientific American, "Astronomers Spy Swarms of Black Holes at Our Galaxy's Core," 4 Apr. 2018
For the moment, microwave photons are the keys to many quantum computers: Physicists use them to program, read out, and otherwise manipulate the machines' quantum bits.

— adrian cho, Science | AAAS, "Weird vibrations poised to control quantum computers," 14 Mar. 2018
In new research, Johnsen and colleague Karen Osborn discovered how complex nanostructures in the fishes' skin trap incoming photons, absorbing almost all the light that touches them.

— sonke johnsen, National Geographic, "How Deep-Sea Fish Are So Exceptionally Black," 18 Apr. 2018
Both electrons and positrons have a small mass unlike photons, which have no mass.

— aristos georgiou, Newsweek, "Physicists Are Trying to Turn Light Into Matter to Prove the 'Impossible'," 21 Mar. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'photon.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Science and the photon

It was Albert Einstein who first theorized that the energy in a light beam exists in small bits or particles, and scientists today know that light sometimes behaves like a wave (somewhat like sound or water) and sometimes like a stream of particles. The energies of photons range from high-energy gamma rays and X-rays down to low-energy infrared and radio waves, though all travel at the same speed. The amazing power of lasers is the result of a concentration of photons that have been made to travel together in order to hit their target at the same time.

Origin and Etymology of photon

phot- + ²-on

NEW! Time Traveler

First Known Use: 1916

in the meaning defined at sense 2

See Words from the same year

PHOTON Defined for English Language Learners

photon

noun

Definition of photon for English Language Learners

physics : a tiny particle of light or electromagnetic radiation

Medical Dictionary

photon

noun pho·ton \ ˈfō-ˌtän \

medical Definition of photon

1 : a unit of intensity of light at the retina equal to the illumination received per square millimeter of a pupillary area from a surface having a brightness of one candela per square meter — called also troland

2 : a quantum of electromagnetic radiation