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Encyclopedia > Graviton
Composition Elementary particle Gravity Hypothetical 0 Stable 0 2 2 This box: view • talk • edit

In physics, the graviton is a hypothetical elementary particle that mediates the force of gravity in the framework of quantum field theory. If it exists, the graviton must be massless (because the gravitational force has unlimited range) and must have a spin of 2 (because gravity is a second-rank tensor field[clarify]). A graviton is a hypothetical elementary particle that transmits the force of gravity. ... For the novel, see The Elementary Particles. ... A fundamental interaction or fundamental force is a mechanism by which particles interact with each other, and which cannot be explained in terms of another interaction. ... Gravity is a force of attraction that acts between bodies that have mass. ... The invariant mass or intrinsic mass or proper mass or just mass is a measurement or calculation of the mass of an object that is the same for all frames of reference. ... Given an assembly of elements, the number of which decreases ultimately to zero, the lifetime (also called the mean lifetime) is a certain number that characterizes the rate of reduction (decay) of the assembly. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... For the novel, see The Elementary Particles. ... Gravity is a force of attraction that acts between bodies that have mass. ... Quantum field theory (QFT) is the quantum theory of fields. ... The term mass in special relativity can be used in different ways, occasionally leading to confusion. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... In mathematics, physics and engineering, a tensor field is a very general concept of variable geometric quantity. ...

Gravitons are postulated because of the great success of the quantum field theory (in particular, the Standard Model) at modeling the behavior of all other forces of nature with similar particles: electromagnetism with the photon, the strong interaction with the gluons, and the weak interaction with the W and Z bosons. In this framework, the gravitational interaction is mediated by gravitons, instead of being described in terms of curved spacetime as in general relativity. In the classical limit, both approaches give identical results, including Newton's law of gravitation. The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... This box:      Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... In particle physics, gluons are subatomic particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei. ... The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. ... In physics, the W and Z bosons, colloquially known as Weakons, are the elementary particles that mediate the weak force. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... The classical limit is the ability of a physical theory to approximate or recover classical mechanics when considered over special values of its parameters. ... The law of universal gravitation states that gravitational force between masses decreases with the distance between them, according to an inverse-square law. ...

However, attempts to extend the Standard Model with gravitons run into serious theoretical difficulties at high energies (processes with energies close to or above the Planck scale) because of infinities arising due to quantum effects (in technical terms, gravitation is nonrenormalizable.) Some proposed theories of quantum gravity (in particular, string theory) address this issue. In string theory, gravitons (as well as the other particles) are states of strings rather than point particles, and then the infinities do not appear, while the low-energy behavior can still be approximated by a quantum field theory of point particles. In that case, the description in terms of gravitons serves as a low-energy effective theory. In physics, Planck units are physical units of measurement originally proposed by Max Planck. ... In physics, the adjective renormalizable refers to a theory (usually a quantum field theory) in which all ultraviolet divergences, infinities and other seemingly meaningless results can be cured by the process of renormalization. ... Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ... This box:      String theory is a still developing mathematical approach to theoretical physics, whose original building blocks are one-dimensional extended objects called strings. ... In physics, an effective field theory is an approximate theory (usually a quantum field theory) that contains the appropriate degrees of freedom to describe physical phenomena occurring at a chosen length scale, but ignores the substructure and the degrees of freedom at shorter distances (or, equivalently, higher energies). ...

## Gravitons and models of quantum gravity GA_googleFillSlot("encyclopedia_square");

When describing graviton interactions, the classical theory (i.e. the tree diagrams) and semiclassical corrections (one-loop diagrams) behave normally, but Feynman diagrams with two (or more) loops lead to ultraviolet divergences; that is, infinite results that cannot be removed because the quantized general relativity is not renormalizable, unlike quantum electrodynamics. In popular terms, the discreteness of quantum theory is not compatible with the smoothness of Einstein's general relativity. These problems, together with some conceptual puzzles, led many physicists to believe that a theory more complete than just general relativity must regulate the behavior near the Planck scale. Superstring theory finally emerged as the most promising solution; it is the only known theory with finite corrections to graviton scattering at all orders. In physics, a classical theory usually refers to a theory that does not obey the principles of quantum mechanics (classical theory vs. ... The term tree diagram is used in different ways in different disciplines. ... In physics, the adjective semiclassical has different precise meanings depending on the context. ... In physics, a one-loop Feynman diagram is a connected Feynman diagram with only one cycle (unicyclic). ... In this Feynman diagram, an electron and positron annihilate and become a quark-antiquark pair. ... In physics, an ultraviolet divergence is a situation in which an integral, for example a Feynman diagram, diverges because of contributions of objects with very high energy approaching infinity, or, equivalently, because of physical phenomena at very short distances. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... In physics, the adjective renormalizable refers to a theory (usually a quantum field theory) in which all ultraviolet divergences, infinities and other seemingly meaningless results can be cured by the process of renormalization. ... Quantum electrodynamics (QED) is a relativistic quantum field theory of electrodynamics. ... Discrete mathematics, also called finite mathematics, is the study of mathematical structures that are fundamentally discrete, in the sense of not supporting or requiring the notion of continuity. ... In mathematical analysis, a differentiability class is a classification of functions according to the properties of their derivatives. ... â€œEinsteinâ€ redirects here. ... In physics, Planck units are physical units of measurement originally proposed by Max Planck. ... Superstring theory is an attempt to explain all of the particles and fundamental forces of nature in one theory by modeling them as vibrations of tiny supersymmetric strings. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ...

String theory predicts the existence of gravitons and their well-defined interactions which represents one of its most important triumphs. A graviton in perturbative string theory is a closed string in a very particular low-energy vibrational state. The scattering of gravitons in string theory can also be computed from the correlation functions in conformal field theory, as dictated by the AdS/CFT correspondence, or from Matrix theory. This box:      String theory is a still developing mathematical approach to theoretical physics, whose original building blocks are one-dimensional extended objects called strings. ... For other uses, see Interaction (disambiguation). ... In quantum mechanics, perturbation theory is a set of approximation schemes for describing a complicated quantum system in terms of a simpler one. ... A closed string is a one-dimensional fundamental object in string theory that has no end-points, and therefore is topologically equivalent to a circle. ... In quantum field theory, correlation functions generalize the concept of correlation functions in statistics. ... A conformal field theory is a quantum field theory (or statistical mechanics model) that is invariant under the conformal group. ... In physics, the AdS/CFT correspondence is the equivalence between a string theory or supergravity defined on some sort of Anti de Sitter space and a conformal field theory defined on its boundary whose dimension is lower by one. ... It has been suggested that this article or section be merged with matrix string theory. ...

An interesting feature of gravitons in string theory is that, as closed strings without endpoints, they would not be bound to branes and could move freely between them. If we live on a brane (as hypothesized by some theorists) this "leakage" of gravitons from the brane into higher-dimensional space could explain why gravity is such a weak force, and gravitons from other branes adjacent to our own could provide a potential explanation for dark matter. See brane cosmology for more details. This article or section is in need of attention from an expert on the subject. ... For other uses, see Dark matter (disambiguation). ... Brane cosmology is a protoscience motivated by, but not rigorously derived from, superstring theory and M-theory. ...

Some proposed quantum theories of gravity do not predict a graviton.

## Experimental observation

Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector. The reason is simply the extremely low cross section for the interaction of gravitons with matter. For example, a detector the mass of Jupiter with 100% efficiency, placed in close orbit around a neutron star, would only be expected to observe one graviton every 10 years, even under the most favorable conditions. It would be impossible to discriminate these events from the background of neutrinos, and it would be impossible to shield the neutrinos without the shielding material collapsing into a black hole. In nuclear and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles. ... For other uses, see Jupiter (disambiguation). ... For the story by Larry Niven, see Neutron Star (story). ... For other uses, see Neutrino (disambiguation). ... For other uses, see Black hole (disambiguation). ...

However, experiments to detect gravitational waves, which may be viewed as coherent states of many gravitons, are already underway (e.g. LIGO and VIRGO). Although these experiments cannot detect individual gravitons, they might provide information about certain properties of the graviton. For example, if gravitational waves were observed to propagate slower than c (the speed of light in a vacuum), that would imply that the graviton has mass. This box:      In physics, a gravitational wave is a fluctuation in the curvature of spacetime which propagates as a wave, traveling outward from a moving object or system of objects. ... 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. ... LIGO stands for Lesser Inner Greater Outer. ... Virgo (Latin for virgin, symbol , Unicode â™) is a constellation of the zodiac. ... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ...

## Is gravity like the other forces?

Some question the analogy which motivates the introduction of the graviton. Unlike the other forces, gravitation plays a special role in general relativity in defining the spacetime in which events take place. Because it does not depend on a particular spacetime background, general relativity is said to be background independent. In contrast, the Standard Model is not background independent. In other words, general relativity and the standard model are incompatible. A theory of quantum gravity is needed in order to reconcile these differences. Whether this theory should itself be background independent, or whether the background independence of general relativity arises as an emergent property is an open question. The answer to this question will determine whether gravity plays a "special role" in this underlying theory similar to its role in general relativity. For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... For other uses of this term, see Spacetime (disambiguation). ... Background independence is a condition in theoretical physics, especially in quantum gravity, that requires the defining equations of a theory to be independent of the actual shape of the spacetime and the value of various fields within the spacetime. ... Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ... Emergence is the process of deriving some new and coherent structures, patterns and properties in a complex system. ...

To meet Wikipedias quality standards, this article or section may require cleanup. ... Results from FactBites:

 Graviton - Memory Alpha, the Star Trek Wiki (422 words) The opposite of a graviton is an antigraviton. The graviton was postulated by Earth physicists in the 20th century as an outgrowth of quantum gravity theory. Gravitons were apparently harnessed in the 20th century since the Vulcan ship in ENT: "Carbon Creek", the SS Botany Bay in TOS: "Space Seed", and the 20th century cryogenic satellite ship in TNG: "The Neutral Zone" clearly show artificial gravity usage.
 Graviton (comics) - Wikipedia, the free encyclopedia (1677 words) Graviton (Franklin Hall) is an elemental supervillain in the Marvel Comics universe, and an enemy of The Avengers and the Thunderbolts. Graviton is an extremely powerful villain with the power of gyrokinesis; the superhuman ability to control gravity in the area around him. Hall is a gravitokinetic, able to manipulate gravitons for various uses, including the projection of concussive blasts, formation of force fields and levitation, and has also proven capable of generating gravitational fields in various objects, making them attract any nearby matter (or individuals) not heavy enough or physically strong enough to resist.
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