Photon
A photon is the quantum of the electromagnetic field, the smallest indivisible unit of light and of all other electromagnetic radiation. It carries energy proportional to its frequency, has zero rest mass, moves at the speed of light in vacuum, and is a boson with spin equal to one.
The idea originated with Albert Einstein, who in 1905 proposed that light energy comes in discrete quanta in order to explain the photoelectric effect, work for which he received the 1921 Nobel Prize in Physics. Arthur Compton's scattering experiments in the early 1920s confirmed that these quanta carry momentum like particles, and the name photon was adopted later that decade. The photon is the clearest example of wave-particle duality: the same entity produces interference patterns like a wave yet registers as discrete detection events like a particle.
Sources
- The Nobel Prize in Physics 1921 (Albert Einstein) (The Nobel Foundation, 1921)
- The Nobel Prize in Physics 1927 (Arthur H. Compton) (The Nobel Foundation, 1927)
Cite this entry
"Photon." postquantum.wiki. Updated July 11, 2026. https://postquantum.wiki/photon@misc{pqwiki-photon,
title = {Photon},
howpublished = {\url{https://postquantum.wiki/photon}},
year = {2026},
note = {postquantum.wiki, updated 2026-07-11}
}