Photon

photonslight quantaincident photonlightaethereal spheresAntiphotonbetween lightcorpusclesdiscrete wave packetsenergies of light
The photon is a type of elementary particle.wikipedia
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Electromagnetic radiation

electromagnetic waveelectromagnetic waveselectromagnetic
It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles).
In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space, carrying electromagnetic radiant energy.

Quantum

quantaquantizedquantal
It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles). The word quanta (singular quantum, Latin for how much) was used before 1900 to mean particles or amounts of different quantities, including electricity.
For example, a photon is a single quantum of light (or of any other form of electromagnetic radiation).

Elementary particle

elementary particlesparticleparticles
The photon is a type of elementary particle.
Subatomic constituents of the atom were identified in the early 1930s; the electron and the proton, along with the photon, the particle of electromagnetic radiation.

Albert Einstein

EinsteinEinsteinianA. Einstein
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. In 1905, Albert Einstein published a paper in which he proposed that many light-related phenomena—including black-body radiation and the photoelectric effect—would be better explained by modelling electromagnetic waves as consisting of spatially localized, discrete wave-packets.
He also investigated the thermal properties of light and the quantum theory of radiation, the basis of laser, which laid the foundation of the photon theory of light.

Matter

corporealsubstancematerial
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.
However it does not include massless particles such as photons, or other energy phenomena or waves such as light or sound.

Compton scattering

Compton effectinverse Compton scatteringeffect named after him
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.
Compton scattering, discovered by Arthur Holly Compton, is the scattering of a photon by a charged particle, usually an electron.

Light

visible lightvisiblelight source
It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles).
EMR in the visible light region consists of quanta (called photons) that are at the lower end of the energies that are capable of causing electronic excitation within molecules, which leads to changes in the bonding or chemistry of the molecule.

Static forces and virtual-particle exchange

staticexchanging other particlesPath-integral formulation of virtual-particle exchange
It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles).
Pions, photons, and gravitons fall into these respective categories.

Electromagnetic field

electromagnetic fieldselectromagneticEMF
It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles).
Experiments reveal that in some circumstances electromagnetic energy transfer is better described as being carried in the form of packets called quanta (in this case, photons) with a fixed frequency.

Quantum mechanics

quantum physicsquantum mechanicalquantum theory
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles.
Einstein further developed this idea to show that an electromagnetic wave such as light could also be described as a particle, or quanta (later called the photon), with a discrete quantum of energy that was dependent on its frequency.

Gilbert N. Lewis

Gilbert Newton LewisG. N. LewisLewis
In December 1926, American physical chemist Gilbert N. Lewis coined the widely adopted name "photon" for these particles in a letter to Nature.
Lewis also researched on relativity and quantum physics, and in 1926 he coined the term "photon" for the smallest unit of radiant energy.

Quantization (physics)

quantizationquantizedquantize
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.
Also related is field quantization, as in the "quantization of the electromagnetic field", referring to photons as field "quanta" (for instance as light quanta).

Particle physics

high energy physicsparticle physicisthigh-energy physics
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.
Modern particle physics research is focused on subatomic particles, including atomic constituents such as electrons, protons, and neutrons (protons and neutrons are composite particles called baryons, made of quarks), produced by radioactive and scattering processes, such as photons, neutrinos, and muons, as well as a wide range of exotic particles.

Electron

electronse − electron mass
The word quanta (singular quantum, Latin for how much) was used before 1900 to mean particles or amounts of different quantities, including electricity.
Electrons radiate or absorb energy in the form of photons when they are accelerated.

Electric charge

chargeelectrical chargecharged
The intrinsic properties of particles, such as charge, mass, and spin, are determined by this gauge symmetry.
The study of photon-mediated interactions among charged particles is called quantum electrodynamics.

Quantum field theory

quantum field theoriesquantum fieldquantum theory
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.
Building on this idea, Albert Einstein proposed in 1905 an explanation for the photoelectric effect, that light is composed of individual packets of energy called photons (the quanta of light).

Photoelectric effect

photoelectricphotoelectronphotoemission
In 1905, Albert Einstein published a paper in which he proposed that many light-related phenomena—including black-body radiation and the photoelectric effect—would be better explained by modelling electromagnetic waves as consisting of spatially localized, discrete wave-packets.
Because a low-frequency beam at a high intensity could not build up the energy required to produce photoelectrons like it would have if light's energy were continuous like a wave, Einstein proposed that a beam of light is not a wave propagating through space, but rather a collection of discrete wave packets (photons).

Laser

laserslaser beamlaser light
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.
When an electron absorbs energy either from light (photons) or heat (phonons), it receives that incident quantum of energy.

Photon energy

photon energiesenergyenergetic
In chemistry and optical engineering, photons are usually symbolized by hν, which is the photon energy, where h is Planck constant and the Greek letter ν (nu) is the photon's frequency.
Photon energy is the energy carried by a single photon.

Wave–particle duality

wave-particle dualityparticle theory of lightwave nature
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles.
Einstein's "light quanta" would not be called photons until 1925, but even in 1905 they represented the quintessential example of wave-particle duality.

Speed of light

clight speedspeed of light in vacuum
The invariant mass of the photon is zero; it always moves at the speed of light in a vacuum.
In this theory, light is described by the fundamental excitations (or quanta) of the electromagnetic field, called photons.

Quantum cryptography

cryptographyquantum cryptographicquantum
Recently, photons have been studied as elements of quantum computers, and for applications in optical imaging and optical communication such as quantum cryptography.
In this paper he showed how to store or transmit two messages by encoding them in two "conjugate observables", such as linear and circular polarization of photons, so that either, but not both, of which may be received and decoded.

Spin (physics)

spinnuclear spinspins
The intrinsic properties of particles, such as charge, mass, and spin, are determined by this gauge symmetry.

Chemistry

chemistchemicalApplied Chemistry
In chemistry and optical engineering, photons are usually symbolized by hν, which is the photon energy, where h is Planck constant and the Greek letter ν (nu) is the photon's frequency.
The particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon.

Photon polarization

polarization transversalitylight polarization
A photon has two possible polarization states.
An individual photon