Photon

This article is about the elementary particle or quantum of light. For other uses, see Photon (disambiguation).
Photon
CompositionElementary particle
StatisticsBosonic
FamilyGauge boson
InteractionsElectromagnetic, weak (and gravity)
Symbol γ
TheorizedAlbert Einstein (1905)
The name "photon" is generally attributed to Gilbert N. Lewis (1926)
Mass0 (theoretical value)
< 1×10−18 eV/c2 (experimental limit)[1]
Mean lifetimeStable[1]
Electric charge0
< 1×10−35 e[1]
Color chargeNo
Spin1 ħ
Spin states+1 ħ,  −1 ħ
Parity−1[1]
C parity−1[1]
CondensedI(JP C)=0,1(1−−)[1]

A photon (from Ancient Greek φῶς, φωτός (phôs, phōtós) 'light') is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that always move at the speed of light measured in vacuum. The photon belongs to the class of boson particles.

As with other elementary particles, photons are best explained by quantum mechanics and exhibit wave–particle duality, their behavior featuring properties of both waves and particles.[2] The modern photon concept originated during the first two decades of the 20th century with the work of Albert Einstein, who built upon the research of Max Planck. While Planck was trying to explain how matter and electromagnetic radiation could be in thermal equilibrium with one another, he proposed that the energy stored within a material object should be regarded as composed of an integer number of discrete, equal-sized parts. To explain the photoelectric effect, Einstein introduced the idea that light itself is made of discrete units of energy. In 1926, Gilbert N. Lewis popularized the term photon for these energy units.[3][4][5] Subsequently, many other experiments validated Einstein's approach.[6][7][8]

In the Standard Model of particle physics, photons and other elementary particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass, and spin, are determined by gauge symmetry. The photon concept has led to momentous advances in experimental and theoretical physics, including lasers, Bose–Einstein condensation, quantum field theory, and the probabilistic interpretation of quantum mechanics. It has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Moreover, photons have been studied as elements of quantum computers, and for applications in optical imaging and optical communication such as quantum cryptography.

  1. ^ a b c d e f Amsler, C.; et al. (Particle Data Group) (2008). "Review of Particle Physics: Gauge and Higgs bosons" (PDF). Physics Letters B. 667 (1): 1. Bibcode:2008PhLB..667....1A. doi:10.1016/j.physletb.2008.07.018. hdl:1854/LU-685594. S2CID 227119789. Archived from the original on 2018-12-25. Retrieved 2010-04-09.
  2. ^ Joos, George (1951). Theoretical Physics. London and Glasgow: Blackie and Son Limited. p. 679.
  3. ^ "December 18, 1926: Gilbert Lewis coins "photon" in letter to Nature". www.aps.org. Archived from the original on 2019-05-02. Retrieved 2019-03-09.
  4. ^ "Gilbert N. Lewis". Atomic Heritage Foundation. Archived from the original on 2015-04-16. Retrieved 2019-03-09.
  5. ^ Kragh, Helge (2014). "Photon: New light on an old name". arXiv:1401.0293 [physics.hist-ph].
  6. ^ Compton, Arthur H. (1965) [12 Dec 1927]. "X-rays as a branch of optics" (PDF). From Nobel Lectures, Physics 1922–1941. Amsterdam: Elsevier Publishing Company. Archived (PDF) from the original on 12 May 2024. Retrieved 3 January 2019.
  7. ^ Kimble, H.J.; Dagenais, M.; Mandel, L. (1977). "Photon Anti-bunching in Resonance Fluorescence" (PDF). Physical Review Letters. 39 (11): 691–695. Bibcode:1977PhRvL..39..691K. doi:10.1103/PhysRevLett.39.691. Archived (PDF) from the original on 2020-11-25. Retrieved 2019-01-03.
  8. ^ Grangier, P.; Roger, G.; Aspect, A. (1986). "Experimental Evidence for a Photon Anticorrelation Effect on a Beam Splitter: A New Light on Single-Photon Interferences". Europhysics Letters. 1 (4): 173–179. Bibcode:1986EL......1..173G. CiteSeerX 10.1.1.178.4356. doi:10.1209/0295-5075/1/4/004. S2CID 250837011.