Difference between revisions of "Photon"

Latest revision as of 10:09, 30 August 2016

A photon is an elementary particle, the quantum of all forms of electromagnetic radiation, including light.

Description

It is the force carrier for the electromagnetic force, even when static via virtual photons.

The photon has zero rest mass and as a result, the interactions of this force with matter at long distance are observable at the microscopic and at the macroscopic level.

Like all elementary particles, photons are currently best explained by quantum mechanics but exhibit wave–particle duality, exhibiting properties of both waves and particles.

For example, a single photon may be refracted by a lens and in doing so exhibit wave interference with itself, or it can act like a particle that has a definite position and momentum that can be measured.

The photon's wave and quanta qualities, are two observable aspects of a single phenomenon, and cannot have their true nature described in terms of any mechanical model, thus a representation of this dual property of light, which assumes certain points on the wavefront to be the seat of the energy, is also impossible.

The quanta in a light wave cannot be spatially localized.

The modern concept of the photon was developed gradually by Albert Einstein in the first years of the 20th century to explain experimental observations that did not fit the classical wave model of light. The benefit of the photon model was that it accounted for the frequency dependence of light's energy, and explained the ability of matter and electromagnetic radiation to be in thermal equilibrium.

The photon model also accounted for anomalous observations, including the properties of black-body radiation, that others, most notably Max Planck, had sought to explain using semiclassical models. In that model, light was described by Maxwell's equations, but the material objects that emitted and absorbed light were found to do so in amounts of energy that were quantized (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 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles.

After Arthur H. Compton won the Nobel Prize in 1927 for his scattering studies, most scientists accepted that quanta of light have an independent existence, and the term photon for light quanta 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 the properties of this gauge symmetry.

The photon concept has led to momentous advances in experimental and theoretical physics, such as 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.

Recently, photons have been studied as elements of quantum computers and for applications in optical imaging and optical communication such as quantum cryptography.

See also

• Advanced Photon Source at Argonne National Laboratory
• Ballistic photon
• Dirac equation
• Doppler effect
• Electromagnetic radiation
• EPR paradox
• High energy X-ray imaging technology
• Laser
• Light
• Luminiferous aether
• Medipix
• Phonon
• Photography
• Photon counting
• Photon energy
• Photon polarization
• Photonic molecule
• Photonics
• Quantum optics
• Single photon source
• Static forces and virtual-particle exchange
• Two-photon physics

External links

• Photon @ Wikipedia