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Encyclopedia > Photons

In physics, the photon (from Greek φως, "phōs", meaning light) is the quantum of the electromagnetic field; for instance, light. The term photon was coined by Gilbert Lewis in 1926. A Superconductor demonstrating the Meissner Effect Physics (from the Greek, Ï†Ï…ÏƒÎ¹ÎºÏŒÏ‚ (physikos), natural, and Ï†ÏÏƒÎ¹Ï‚ (physis), nature) is the science of the natural world dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. ... The word quantum, pl. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. ... Lewis in the Berkeley Lab Gilbert Newton Lewis (October 23, 1875-March 23, 1946) was a famous physical chemist. ...

The photon can be perceived as a wave or a particle, depending on how it is measured

The photon is one of the elementary particles. Its interactions with electrons and atomic nuclei account for a great many of the features of matter, such as the existence and stability of atoms, molecules, and solids. These interactions are studied in quantum electrodynamics (QED), which is the oldest part of the Standard Model of particle physics. Little pretty representation of photons made from scratch File links The following pages link to this file: Photon Timeline of the Universe Categories: GFDL images ... Little pretty representation of photons made from scratch File links The following pages link to this file: Photon Timeline of the Universe Categories: GFDL images ... This is a list of particles in particle physics, including currently known and hypothetical elementary particles, as well as the composite particles that can be built up from them. ... Properties The electron is a fundamental subatomic particle that carries a negative electric charge. ... A stylized representation of a lithium atom. ... Properties In chemistry and physics, an atom (Greek Î¬Ï„Î¿Î¼Î¿Î½ meaning indivisible) is the smallest possible particle of a chemical element that retains its chemical properties. ... In general, a molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. ... In jewelry, a solid gold piece is the alternative to gold-filled or gold-plated jewelry. ... Quantum electrodynamics (QED) is a quantum field theory of electromagnetism. ... The Standard Model of Fundamental Particles and Interactions The Standard Model of particle physics is a theory which describes the strong, weak, and electromagnetic fundamental forces, as well as the fundamental particles that make up all matter. ... Particles erupt from the collision point of two relativistic (100GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...

In some respects a photon acts as a particle, for instance when registered by the light sensitive device in a camera. In other respects, a photon acts like a wave, as when passing through the optics in a camera. According to the so-called wave-particle duality in quantum physics, it is natural for the photon to display either aspect of its nature, according to the circumstances. Normally, light is formed from a large number of photons, with the intensity related to the number of them. At low intensity, it requires very sensitive instruments, used in astronomy or spectroscopy, for instance, to detect the individual photons. In particle physics, an elementary particle is a particle of which other, larger particles are composed. ... A camera is a device used to take pictures (usually photographs), either singly or in sequence, with or without sound recording, such as with video cameras. ... The concept wave is related to a disturbance that propagates through space, often transferring energy. ... See also: List of optical topics Optics (appearance or look in ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. ... In physics, wave-particle duality holds that light and matter can exhibit properties of both waves and of particles. ... Fig. ... In physics, intensity is a measure of the time-averaged energy flux. ... In physics, intensity is a measure of the time-averaged energy flux. ... Lunar astronomy: the large crater is Daedalus, photographed by the crew of Apollo 11 as they circled the Moon in 1969. ... Extremely high resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines) Spectroscopy is the study of spectra, that is, the dependence of physical quantities on frequency. ...

## Contents

A photon is usually given the symbol $, gamma$, the Greek letter gamma, although in nuclear physics this symbol refers to a very high-energy photon (a gamma ray). Note: This article contains special characters. ... Gamma (upper case Î“, lower case Î³) is the third letter of the Greek alphabet. ... Nuclear physics is the branch of physics concerned with the nucleus of the atom. ... This article is about electromagnetic radiation. ...

## Properties

Photons are commonly associated with visible light, but this is actually only a very limited part of the electromagnetic spectrum. All electromagnetic radiation is quantized as photons: that is, the smallest amount of electromagnetic radiation that can exist is one photon, whatever its wavelength, frequency, energy, or momentum, and that light or fields interact with matter in discrete units of one or several photons. Photons are fundamental particles. They can be created and destroyed when interacting with other particles, but are not known to decay on their own. The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Legend: Î³ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves: EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultrahigh frequency VHF = Very high frequency HF = High frequency... Electromagnetic radiation can be conceptualized as a self propagating transverse oscillating wave of electric and magnetic fields. ... In physics, quantization is a procedure for constructing a quantum field theory starting from a classical field theory. ... The wavelength is the distance between repeating units of a wave pattern. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... In physics, momentum is the product of the mass and velocity of an object. ... In particle physics, an elementary particle is a particle of which other, larger particles are composed. ...

A photon of a definite frequency is not a localized particle. Photons thus exhibit a position/frequency uncertainty relation similar to that of matter particles and exactly analogous to the bandwidth theorem of classical optics. Photons have zero mass and zero electric charge, but they do carry energy, momentum and angular momentum. Photons are always moving, and photons in a vacuum always move at a constant speed with respect to all observers, regardless of the observers' own velocities. This speed is called the vacuum speed of light. The energy and momentum carried by a photon is proportional to its frequency (or inversely proportional to its wavelength). This momentum can be transferred when a photon interacts with matter. The force due to a large number of photons falling on a surface is known as radiation pressure, which may be used for propulsion with a solar sail. In quantum physics, the Heisenberg uncertainty principle states that one cannot assign, with full precision, values for certain pairs of observable variables, including the position and momentum, of a single particle at the same time even in theory. ... Mass is a property of a physical object that quantifies the amount of matter it contains. ... â€¹ The template below has been proposed for deletion. ... In physics, momentum is the product of the mass and velocity of an object. ... In physics the angular momentum of an object with respect to a reference point is a measure for the extent to which, and the direction in which, the object rotates about the reference point. ... For other uses, see vacuum cleaner and Vacuum (musical group). ... Cherenkov effect in a swimming pool nuclear reactor. ... Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. ... Concept image of a solar sail spacecraft in the process of unfurling sails. ...

The actual upper limit of the photon rest mass compatible with observations depends on additional assumptions. A conservative consensus limit of the Particle Data Group is 6×10-17 eV based on changes in magnetohydrodynamics which would contradict solar wind observations. An electronvolt (symbol: eV) is the amount of kinetic energy gained by a single unbound electron when it passes through an electrostatic potential difference of one volt, in vacuum. ... Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics), is the academic discipline which studies the dynamics of electrically conducting fluids. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ...

Photons are deflected by a gravitational field twice as much as Newtonian mechanics predicts for a mass traveling at the speed of light with the same momentum as the photon. This observation is commonly cited as evidence supporting Einstein's theory of gravitation, general relativity. In general relativity, photons always travel in a "straight" line, after taking into account the curvature of spacetime. (In curved space, such lines are called geodesics). The gravitational field is a field that causes bodies with mass to attract each other. ... The original version of the physical discipline of mechanics, due to Sir Isaac Newton, who developed the theory over a period from about 1664, until the publication of his great work, known as the Principia, in 1687. ... Mass is a property of a physical object that quantifies the amount of matter it contains. ... To meet Wikipedias quality standards, this article may require cleanup. ... In physics, gravitation or gravity is the universal force of attraction between objects with mass. ... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ... Curvature is the amount by which a geometric object deviates from being flat. ... World line of the orbit of the Earth depicted in two spatial dimensions X and Y (the plane of the Earth orbit) and a time dimension, usually put as the vertical axis. ... In mathematics, a geodesic is a generalization of the notion of a straight line to curved spaces. Definition of geodesic depends on the type of curved space. If the space carries a natural metric then geodesics are defined to be (locally) the shortest path between points on the space. ...

### Creation

Photons are produced by atoms when a bound electron moves from one orbital to another orbital with less energy. Photons can also be emitted by an unstable nucleus when it undergoes some types of nuclear decay. Furthermore, photons are produced whenever charged particles are accelerated. Properties In chemistry and physics, an atom (Greek Î¬Ï„Î¿Î¼Î¿Î½ meaning indivisible) is the smallest possible particle of a chemical element that retains its chemical properties. ... Properties The electron is a fundamental subatomic particle that carries a negative electric charge. ... Electron atomic and molecular orbitals In atomic physics, an electron orbital (or simply orbital) is the description of the behavior of an electron in an atom or molecule according to quantum mechanics. ... A stylized representation of a lithium atom. ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles. ... In physics, a charged particle is a particle with an electric charge. ... Acceleration is the time rate of change of velocity, and at any point on a v-t graph, it is given by the slope of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of velocity. ...

Atoms continuously emit photons due to their collisions with each other. The wavelength distribution of these photons is thus related to their absolute temperature. The Planck distribution determines the probability of a photon being a certain wavelength when emitted by a collection of atoms at a given temperature. The spectrum of such photons is normally peaked in the range between microwave and infrared, but sufficiently hot objects (such as the surface of the Sun or a lightbulb filament) will emit visible light as well. As temperature is further increased, some photons will reach even higher frequencies, such as ultraviolet and X-ray. // Physical collision Dynamics Deflection happens when an object hits a plane surface In physics, collision means the action of bodies striking or coming together (touching). ... The wavelength is the distance between repeating units of a wave pattern. ... In mathematics, a probability distribution assigns to every interval of the real numbers a probability, so that the probability axioms are satisfied. ... Absolute zero is the lowest temperature that can be obtained in any macroscopic system. ... Black body spectrum as a function of wavelength In physics, the spectral intensity of electromagnetic radiation from a black body at temperature T is given by the Plancks law of black body radiation: where: I(Î½) is the amount of energy per unit time per unit surface area per unit... The word probability derives from the Latin probare (to prove, or to test). ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... In mathematics, physics and signal processing, the frequency spectrum is a representation of a signal or other function in terms of frequency (in the frequency domain). It is the projection of the function onto a set of sinusoidal basis functions. ... Microwave image of 3C353 galaxy at 8. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of microwave radiation. ... For other uses, see Sun (disambiguation). ... The incandescent light bulb uses a glowing wire filament heated to white-hot by electrical resistance, to generate light (a process known as thermal radiation). ... The visible spectrum is the portion of the optical spectrum (light or electromagnetic spectrum) that is visible to the human eye. ... UltraViolet is a 2006 action film in the science fiction genre. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...

Radio, television, radar and other types of transmitters used for telecommunication and remote sensing routinely create a wide variety of low-energy photons by the oscillation of electric fields in conductors. Magnetrons emit coherent photons used in household microwave ovens. Klystron tubes are used when microwave emissions must be more finely controlled. Masers and lasers create monochromatic photons by stimulated emission. More energetic photons can be created by nuclear transitions, particle-antiparticle annihilation, and in high-energy particle collisions. M*A*S*H , see Corporal Walter (Radar) OReilly. ... Antenna tower of Crystal Palace transmitter, London A transmitter (sometimes abbreviated XMTR) is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ... BlackBerry 7100t Telecommunication refers to the communication of information at a distance. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. ... In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ... Electrical conduction is the current (movement of charged particles) through a material in response to an electric field. ... A cavity magnetron is a high-powered vacuum tube that generates coherent microwaves. ... Something which is monochromatic has a single color. ... Microwave oven A microwave oven, (or microwave), is a kitchen appliance employing microwave radiation primarily to cook or heat food. ... A klystron is a specialized vacuum tube (evacuated electron tube) called a linear-beam tube. ... A Hydrogen RF discharge, the first element inside an Hydrogen Maser (see description below), courtesy NASA/JPL-Caltech. ... Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other physics experiments. ... In optics, styimulated emission is the process by which, when perturbed by a photon, matter may lose energy resulting in the creation of another photon. ... Nuclear physics is the branch of physics concerned with the nucleus of the atom. ... Particles erupt from the collision point of two relativistic (100GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... Particles erupt from the collision point of two relativistic (100GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...

### Spin

Photons have spin 1, and they are therefore classified as bosons. Photons mediate the electromagnetic interaction; they are the gauge bosons of quantum electrodynamics (QED), which is a U(1) gauge theory. A non-relativistic spin-1 particle has three possible spin states (−1, 0 and +1). However, in the framework of special relativity, this is not the case for massless spin-1 particles, such as the photons, which have only two spin projections, helicities, corresponding to the right- and left-handed circular polarizations of classical electromagnetic waves. The more familiar linear polarization is formed by a superposition of the two spin projections of a photon. In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is generated by the motion of its center of mass about an external point. ... Boson (game) Bosons, named after Satyendra Nath Bose, are particles which form totally-symmetric composite quantum states. ... Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ... Quantum electrodynamics (QED) is a quantum field theory of electromagnetism. ... In mathematics, the unitary group of degree n, denoted U(n), is the group of nÃ—n unitary matrices with complex entries, with the group operation that of matrix multiplication. ... Gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... Albert Einsteins theory of relativity is a set of two theories in physics: special relativity and general relativity. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is generated by the motion of its center of mass about an external point. ... Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. It replaced Newtonian notions of space and time and incorporated electromagnetism as represented by Maxwells equations. ... Mass is a property of a physical object that quantifies the amount of matter it contains. ... In particle physics, helicity is the projection of the angular momentum to the direction of motion: Because the angular momentum with respect to an axis has discrete values, helicity is discrete, too. ... In electrodynamics, polarization (also spelled polarisation) is a property of waves, such as light and other electromagnetic radiation. ... Quantum superposition is the application of superposition principle to quantum mechanics. ...

### Quantum state

Visible light from ordinary sources (like the Sun or a lamp) is a mixture of many photons of different wavelengths. One sees this in the frequency spectrum, for instance by passing the light through a prism. In so-called "mixed states", which these sources tend to produce, light can consist of photons in thermal equilibrium (so-called black-body radiation). Here they in many ways resemble a gas of particles. For example, they exert pressure, known as radiation pressure. In mathematics, physics and signal processing, the frequency spectrum is a representation of a signal or other function in terms of frequency (in the frequency domain). It is the projection of the function onto a set of sinusoidal basis functions. ... If a shaft of light entering a prism is sufficiently small such that the coloured edges meet, a spectrum results In optics, a prism is a device used to refract light, reflect it or break it up (to disperse it) into its constituent spectral colours (colours of the rainbow). ... In thermodynamics, a thermodynamic system is in thermodynamic equilibrium if its energy distribution equals a Maxwell-Boltzmann-distribution. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. ...

On the other hand, an assembly of photons can also exist in much more well-organized coherent states, such as in the light emitted by an ideal laser. The high degree of precision obtained with laser instruments is due to this organization. In quantum mechanics a coherent state is a specific kind of quantum state of the quantum harmonic oscillator whose dynamics most closely resemble the oscillating behaviour of a classical harmonic oscillator system. ... Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other physics experiments. ...

The quantum state of a photon assembly, like that of other quantum particles, is the so-called Fock state denoted $|nrangle$, meaning $, n$ photons in one of the distinct "modes" of the electromagnetic field. If the field is multimode (involves several different wavelength photons), its quantum state is a tensor product of photon states, for example: A quantum state is any possible state in which a quantum mechanical system can be. ... A Fock state, in quantum mechanics, is any state of the Fock space with a well-defined number of particles in each state. ... In mathematics, the tensor product, denoted by , may be applied in different contexts to vectors, matrices, tensors, vector spaces, algebras and modules. ...

$|n_{k_0}rangleotimes|n_{k_1}rangleotimesdotsotimes|n_{k_n}rangledots$

Here $, k_i$ denote the possible modes, and $, n_{k_i}$ the number of photons in each mode

### Molecular absorption

A typical molecule, $, M$, has many different energy levels. When a molecule absorbs a photon, its energy is increased by an amount equal to the energy of the photon. The molecule then enters an excited state, $, M^*$. In general, a molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). ...

$M + gamma to M^* ,$

## Photons in vacuo

In empty space (vacuum) all photons move at the speed of light, c, defined as 299,792,458 metres per second, or approximately 3×108 m/s. The metre is defined as the distance travelled by light in a vacuum in 1/299,792,458 of a second, so the speed of light does not suffer any experimental uncertainty, unlike the metre or the second, which rely on the second being defined by means of a very accurate clock. For other uses, see vacuum cleaner and Vacuum (musical group). ... Cherenkov effect in a swimming pool nuclear reactor. ... Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ... The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. ... In mathematics, defined and undefined are used to explain whether expressions have meaningful, sensible output. ... For other uses, see vacuum cleaner and Vacuum (musical group). ... Look up second in Wiktionary, the free dictionary. ... // Relation between uncertainty, probability and risk In his seminal work Risk, Uncertainty, and Profit, Frank Knight (1921) established the important distinction between risk and uncertainty: â€¦ Uncertainty must be taken in a sense radically distinct from the familiar notion of Risk, from which it has never been properly separated. ... Atomic clock Chip-Scale Atomic Clock Unveiled by NIST An atomic clock is a type of clock that uses an atomic resonance frequency standard as its counter. ...

According to one principle of Einstein's special relativity, all observations of the speed of light in vacuo are same in all directions to any observer in an inertial frame of reference. This principle is generally accepted in physics since many practical consequences for high-energy particles in theoretical and experimental physics have been observed. Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. It replaced Newtonian notions of space and time and incorporated electromagnetism as represented by Maxwells equations. ... Observation is an activity of an intelligent living being, to sense and assimiliate the knowledge of a phenomenon in its framework of previous knowledge and ideas. ... An inertial frame is a coordinate system defined by the non-accelerated motion of objects with a common direction and speed (as opposed to a non-inertial reference frame). ... A Superconductor demonstrating the Meissner Effect Physics (from the Greek, Ï†Ï…ÏƒÎ¹ÎºÏŒÏ‚ (physikos), natural, and Ï†ÏÏƒÎ¹Ï‚ (physis), nature) is the science of the natural world dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. ... Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. ... Theoretical physics employs mathematical models in an attempt to understand Nature. ... Experimental physics is the part of physics that deals with experiments and observations pertaining to natural/physical phenomena, as opposed to theoretical physics. ...

## Photons in matter

When photons pass through matter, such as a prism, different frequencies will be transmitted at different speeds. This is called dispersion of colors, where photons of different frequencies exit at different angles. A similar phenomenon occurs in reflection where surfaces can reflect photons of various frequencies at different angles. Matter is commonly defined as the substance of which physical objects are composed. ... If a shaft of light entering a prism is sufficiently small such that the coloured edges meet, a spectrum results In optics, a prism is a device used to refract light, reflect it or break it up (to disperse it) into its constituent spectral colours (colours of the rainbow). ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... Dispersion of a light beam in a prism. ... This article is about angles in geometry. ... The reflection of sunlight on water Reflection is the abrupt change in direction of a wave front at an interface between two dissimilar media so that the wave front returns into the medium from which it originated. ...

The associated dispersion relation for photons is a relation between frequency, $, f$ , and wavelength, $, lambda$, or equivalently, between their energy, $, E$, and momentum, $, p$. It is simple in vacuo, since the speed of the wave, $, v$, is given by The group velocity of a wave is the velocity with which the overall shape of the waves amplitude (known as the envelope of the wave) propagates through space. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... In physics, momentum is the product of the mass and velocity of an object. ...

$v=lambda f = c,$

The photon quantum relations are:

$E=hf ,$ and $p=h/lambda ,$

Here $, h$ is Planck's constant. So one can also write the dispersion relation as A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ...

$E=pc ,$

which is characteristic of a zero-mass particle. One sees that Planck's constant relates the wave and particle aspects. A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ...

In a material, photons couple to the excitations of the medium and behave differently. These excitations can often be described as quasi-particles (such as phonons and excitons); that is, as quantized wave- or particle-like entities propagating though the matter. "Coupling" means here that photons can transform into these excitations (that is, the photon gets absorbed and medium excited, involving the creation of a quasi-particle) and vice versa (the quasi-particle transforms back into a photon, or the medium relaxes by re-emitting the energy as a photon). However, as these transformations are only possibilities, they are not bound to happen and what actually propagates through the medium is a polariton; that is, a quantum-mechanical superposition of the energy quantum being a photon and of it being one of the quasi-particle matter excitations. Excitation is the amount of energy (energy in a general sense, not energy as defined in physics) that something or someone has. ... In physics, a quasiparticle refers to a particle-like entity arising in certain systems of interacting particles. ... In physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the atomic lattice of a solid. ... An exciton is a bound state of an electron and an imaginary particle called an electron hole in an insulator (or semiconductor), or in other words, a Coulomb correlated electron-hole pair. ... Generally, quantization is the state of being constrained to a set of discrete values, rather than varying continuously. ... This article is in need of attention. ... Quantum superposition is the application of superposition principle to quantum mechanics. ...

According to the rules of quantum mechanics, a measurement (here: just observing what happens to the polariton) breaks this superposition; that is, the quantum either gets absorbed in the medium and stays there (likely to happen in opaque media) or it re-emerges as photon from the surface into space (likely to happen in transparent media). Various meters In classical physics and engineering, measurement generally refers to the process of estimating or determining the ratio of a magnitude of a quantitative property or relation to a unit of the same type of quantitative property or relation. ...

Matter excitations have a non-linear dispersion relation; that is, their momentum is not proportional to their energy. Hence, these particles propagate slower than the vacuum speed of light. (The propagation speed is the derivative of the dispersion relation with respect to momentum.) This is the formal reason why light is slower in media (such as glass) than in vacuum. (The reason for diffraction can be deduced from this by Huygens' principle.) Another way of phrasing it is to say that the photon, by being blended with the matter excitation to form a polariton, acquires an effective mass, which means that it cannot travel at c, the speed of light in a vacuum. To do: 20th century mathematics chaos theory, fractals Lyapunov stability and non-linear control systems non-linear video editing See also: Aleksandr Mikhailovich Lyapunov Dynamical system External links http://www. ... In mathematics, the derivative is one of the two central concepts of calculus. ... Diffraction is the bending and spreading of waves when they meet an obstruction. ... Wave Refraction in the manner of Huygens. ... In solid state physics, a particles effective mass is the mass it seems to carry in the semiclassical model of transport in a crystal. ...

## References

• Lewis, G.N. The conservation of photons. Nature 1926, 118, 874-875.

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