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A '''photon''' is a particle of light. The term was coined by the American physical chemist Gilbert Newton Lewis.<ref>{{cite web |title=Should creationists accept quantum mechanics?|author=Jonathan Sarfati|publisher=CMI|url=http://creation.com/creationists-quantum-mechanics#txtRef15|accessdate=August 1, 2013|quote=Einstein called this Lichtquant or light quantum, but the American physical chemist Gilbert Newton Lewis (1875–1946) coined the term photon which stuck}}</ref>

A '''photon''' is a particle of light. The term was coined by the American physical chemist Gilbert Newton Lewis.<ref>{{cite web |title=Should creationists accept quantum mechanics?|author=Jonathan Sarfati|publisher=CMI|url=http://creation.com/creationists-quantum-mechanics#txtRef15|accessdate=August 1, 2013|quote=Einstein called this Lichtquant or light quantum, but the American physical chemist Gilbert Newton Lewis (1875–1946) coined the term photon which stuck}}</ref>

Photons are [[bosons]], that is, particles that have integer [[Quantum field theory#Field Bosons Mediate Action At a Distance|spin]]. In [[quantum field theory]], photons are the mediators of the [[electromagnetic force]].

Photons are [[bosons]], that is, particles that have integer [[Quantum field theory#Field Bosons Mediate Action At a Distance|spin]]. In [[quantum field theory]], photons are the mediators of the [[electromagnetism|electromagnetic force]].

==Historical development==

==Historical development==

Since Newton's publication of his [[Opticks]] in 1704, his corpuscle theory of light dominated the world of physics. However, this changed in the 19th century with experiments done by [[Fresnel|Augustin-Jean Fresnel]] and [[Young|Thomas Young]], which supported [[Huygens|Christian Huygens]]'s wave theory.  One of the proofs for this is that light experiences [[Optics#Physical optics|interference]] and [[Optics#Physical optics|diffraction]], which would not be displayed if light were a classical particle. Furthermore, [[James Clerk Maxwell]] theoretical prediction of electromagnetic waves, together with [[Hertz|Heinrich Hertz]] experiments led to conclude that light was an electromagnetic wave.

Since Newton's publication of his Opticks in 1704, his corpuscle theory of light dominated the world of physics. However, this changed in the 19th century with experiments done by Augustin-Jean Fresnel and Thomas Young, which supported Christian Huygens's wave theory.  One of the proofs for this is that light experiences [[Optics#Physical optics|interference]] and [[Optics#Physical optics|diffraction]], which would not be displayed if light were a classical particle. Furthermore, [[James Clerk Maxwell]] theoretical prediction of electromagnetic waves, together with [[Hertz|Heinrich Hertz]] experiments led to conclude that light was an electromagnetic wave.

However, a phenomenon called the [[photoelectric effect]] led to a different conclusion. The photoelectric is the emission of electrons from a metal which is illuminated with light. This by itself is in no contradiction to the wave theory of light, but certain peculiarities of it were. For example, it was observed that no electrons were emitted unless the frequency of light was greater than a threshold frequency, regardless of how intense the light beam was. Also, the energy of the emitted electrons was dependent only on the light frequency, not in its intensity. Since the energy of a wave depends on its amplitude, which in turn is related to its intensity, this was in contradiction with the wave theory of light.  

However, a phenomenon called the [[photoelectric effect]] led to a different conclusion. The photoelectric is the emission of electrons from a metal which is illuminated with light. This by itself is in no contradiction to the wave theory of light, but certain peculiarities of it were. For example, it was observed that no electrons were emitted unless the frequency of light was greater than a threshold frequency, regardless of how intense the light beam was. Also, the energy of the emitted electrons was dependent only on the light frequency, not in its intensity. Since the energy of a wave depends on its amplitude, which in turn is related to its intensity, this was in contradiction with the wave theory of light.  

In standard interpretations of quantum mechanics, light behaves both as a wave and as a particle. The existence of photons is now well accepted by the physics community, and its implication has gone well beyond the photoelectric effect.  

In standard interpretations of quantum mechanics, light behaves both as a wave and as a particle. The existence of photons is now well accepted by the physics community, and its implication has gone well beyond the photoelectric effect.  

==References==

==References==

[[Category:Physics]]

[[Category:Physics]]