Light quantum | Wikipedia audio article
Channel: wikipedia tts
Date: 05/06/2019

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Photon


00:04:10 1 Nomenclature
00:07:36 2 Physical properties
00:09:52 2.1 Experimental checks on photon mass
00:11:38 3 Historical development
00:11:49 4 Einstein's light quantum
00:15:46 5 Early objections
00:18:20 6 Wave–particle duality and uncertainty principles
00:21:01 7 Bose–Einstein model of a photon gas
00:23:26 8 Stimulated and spontaneous emission
00:24:44 9 Second quantization and high energy photon interactions
00:28:25 10 The hadronic properties of the photon
00:37:43 11 The photon as a gauge boson
00:39:24 12 Contributions to the mass of a system
00:51:09 13 Photons in matter
00:59:18 14 Technological applications
01:00:48 15 Recent research
01:03:32 16 See also
01:06:10 17 Notes
01:08:47 18 References
01:12:22 19 Further reading
01:13:51 20 External links



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SUMMARY
=======
The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual particles). Invariant mass of the photon is zero; it always moves at the speed of light within a vacuum.
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens and exhibit wave interference with itself, and it can behave as a particle with definite and finite measurable position or momentum, though not both at the same time as per Heisenberg's uncertainty principle.  The photon's wave and quantum qualities are two observable aspects of a single phenomenon—they cannot be described by any mechanical model; a representation of this dual property of light that assumes certain points on the wavefront to be the seat of the energy is not possible. The quanta in a light wave are not spatially localized.
The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical wave model of light. The benefit of the photon model is that it accounts for the frequency dependence of light's energy, and explains the ability of matter and electromagnetic radiation to be in thermal equilibrium. The photon model accounts for anomalous observations, including the properties of black-body radiation, that others (notably Max Planck) had tried to explain using semiclassical models. In that model, light is described by Maxwell's equations, but material objects emit and absorb light in quantized amounts (i.e., they change energy only by certain particular discrete amounts). Although these semiclassical models contributed to the development of quantum mechanics, many further experiments beginning with the phenomenon of Compton scattering of single photons by electrons, validated Einstein's hypothesis that light itself is quantized. In December 1926, American physical chemist Gilbert N. Lewis coined the widely-adopted name "photon" for these particles in a letter to Nature. After Arthur H. Compton won the Nobel Prize in 1927 for his scattering studies,  most scientists accepted that light quanta have an independent existence, and the term "photon" was accepted.
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 this 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 ...