- Induced gravity
Induced gravity (or Emergent gravity) is an idea in
quantum gravitythat space-time background emerges asa mean field approximationof underlying microscopic degrees of freedom, similar to the fluid mechanicsapproximation of BEC. The concept was originally proposed by Andrei Sakharovin 1967.
Sakharov observed that many
condensed mattersystems give rise to emergent phenomena which are identical to general relativityquantitatively. Crystal defects can look like torsion, for example. His idea was to start with an arbitrary background pseudo-Riemannian manifold(in modern treatments, possibly with torsion) and introduce quantum fields (matter) on it but not introduce any gravitational dynamics explicitly. This gives rise to an effective actionwhich to one-loop ordercontains the Einstein-Hilbert actionwith a cosmological constant. In other words, general relativity arises as an emergent property of matter fields and is not put in by hand. On the other hand, such models typically predict huge cosmological constants.
The particular models proposed by Sakharov and others have been proven impossible by the
Weinberg-Witten theorem. However, models with emergent gravity are possible as long as other things, such as spacetime dimensions, emerge together with gravity. Developments in AdS/CFT correspondenceafter 1997 suggest that the microphysical degrees of freedom in induced gravity might be radically different. The bulk space-time arises as an emergent phenomenon of the quantum degrees of freedom that live in the boundary of the space-time.
* [http://www.slac.stanford.edu/spires/find/hep/www?j=SPHDA,12,1040 A.D. Sakharov, "VACUUM QUANTUM FLUCTUATIONS IN CURVED SPACE AND THE THEORY OF GRAVITATION", 1967.]
* [http://relativity.livingreviews.org/Articles/lrr-2005-12/ Carlos Barcelo, Stefano Liberati, Matt Visser, "Living Rev.Rel." 8:12, 2005.]
* [http://online.itp.ucsb.edu/online/strings05/berenstein D. Berenstein, "Emergent Gravity from CFT", online lecture.]
* [http://arxiv.org/abs/0710.4153 C. J. Hogan "Quantum Indeterminacy of Emergent Spacetime", preprint]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Gravity turn — A gravity turn or zero lift turn is a maneuver (see trajectory optimization) used in launching a spacecraft into, or descending from, an orbit around a celestial body such as a planet or a moon. This launch trajectory offers two main advantages… … Wikipedia
Loop quantum gravity — Not to be confused with the path integral formulation of LQG, see spin foam. This article is about LQG in its Canonical formulation.. Beyond the Standard Model … Wikipedia
Conformal gravity — is a generic name for gravity theories which are invariant under conformal transformations in the Riemannian geometry sense; more accurately, they are invariant under Weyl transformations where gab is the metric tensor and Ω(x) is a function on… … Wikipedia
Massive gravity — In theoretical physics, massive gravity is a particular generalization of general relativity studied by Hendrik van Dam, Martinus J. G. Veltman (1) , and Vladimir E. Zakharov.(2) One assumes that physics takes place in Minkowski space and gravity … Wikipedia
Composite gravity — In theoretical physics, composite gravity refers to models that attempted to derive general relativity in a framework where the graviton is constructed as a composite bound state of more elementary particles, usually fermions.A theorem by Steven… … Wikipedia
Anti-gravity — Antigrav redirects here. For the EyeToy video game, see EyeToy: AntiGrav. Anti gravity is the idea of creating a place or object that is free from the force of gravity. It does not refer to the lack of weight under gravity experienced in free… … Wikipedia
List of episodes in Gravity's Rainbow — The following is a list of episodes in Thomas Pynchon s Gravity s Rainbow.Part 1: Beyond the ZeroEpisode 1Set in London at the home of Pirate Prentice on Monday, December 18, 1944, the episode begins with Pirate dreaming about the evacuation of… … Wikipedia
Modified Newtonian dynamics — MOND redirects here. For other uses, see Mond. In physics, Modified Newtonian dynamics (MOND) is a hypothesis that proposes a modification of Newton s law of gravity to explain the galaxy rotation problem. When the uniform velocity of rotation of … Wikipedia
Weinberg-Witten theorem — Steven Weinberg and Edward Witten consider the so called emergent theories to be misguided. During the 80 s, preon theories, technicolor and the like were very popular and some people were speculating that gravity might be an emergent phenomena… … Wikipedia
General relativity — For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. General relativity Introduction Mathematical formulation Resources … Wikipedia