Quantum gravity Quantum gravity In some branches of physics, including acoustics and fluid mechanics, a classical signal horizon (e.g. an acoustic horizon) can radiate weakly and "leak" information. This effect is analogous to the Hawking radiation behaviour predicted by quantum mechanics for the region of curved spacetime around a black hole. ...more on Wikipedia about "Acoustic Hawking radiation"
In mathematical physics, a metric (mathematics) describes the arrangement of relative distances within a surface or volume, usually measured by signals passing through the region – essentially describing the intrinsic geometry of the region. An acoustic metric will describe the signal-carrying properties characteristic of a given particulate medium in acoustics, or in fluid dynamics. Other descriptive names such as sonic metric are also sometimes used, interchangeably. ...more on Wikipedia about "Acoustic metric"
In physics, there is a speculative notion that if there were a black hole with the same mass and charge as an electron, it would share many of the properties of the electron including the magnetic moment and Compton wavelength. ...more on Wikipedia about "Black hole electron"
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. ...more on Wikipedia about "Composite gravity"
A dark-energy star or gravastar is a hypothetical compact astrophysical object which a minority of physicists feel might constitute an alternative explanation for observations of astronomical black hole candidates. ...more on Wikipedia about "Dark energy star"
In theoretical physics, it is often important to study theories with the diffeomorphism symmetry such as general relativity. These theories are invariant under arbitrary coordinate transformations. Equations of motion are generally derived from the requirement that the action is stationary. There are special variations that are equivalent to spatial diffeomorphisms. The invariance of the action under these variations implies non-dynamical equations of motion i.e. constraints. These equations must be satisfied or, at least, they must annihilate the physical states in a quantum version of the theory. ...more on Wikipedia about "Diffeomorphism constraint"
In the theory of discrete Lorentzian quantum gravity, space itself is modeled by a lattice instead of a manifold. ...more on Wikipedia about "Discrete Lorentzian quantum gravity"
Euclidean quantum gravity refers to a Wick rotated version of quantum gravity, formulated as a quantum field theory. The manifolds that are used in this formulation are 4 dimensional Riemannian manifolds instead of pseudo Riemannian manifolds. It is also assumed that the manifolds are compact, connected and boundaryless (i.e. no singularities). Following the usual quantum field-theoretic formulation, the vacuum to vacuum amplitude is written as a functional integral over the metric tensor, which is now the quantum field under consideration. ...more on Wikipedia about "Euclidean quantum gravity"
In theoretical general relativity, a geon is an electromagnetic or gravitational wave which is held together in a confined region by the gravitational attraction of its own field energy. They were first investigated theoretically in 1955 by Wheeler, who coined the term as a contraction of "gravitational electromagnetic entity." ...more on Wikipedia about "Geon (physics)"
In astrophysics, the Gravastar theory is a proposal by Pawel Mazur and Emil Mottola to replace the black hole. Instead of a star collapsing into a pinpoint of space with virtually infinite density, the gravastar theory proposes that as an object gravitationally collapses, space itself undergoes a phase transition preventing further collapse, being transformed into a spherical void surrounded by a form of super-dense matter. ...more on Wikipedia about "Gravastar"
Gravitational instantons fall into a few classes, such as asymptotically locally Euclidean spaces (ALE spaces), asymptotically locally flat spaces (ALF spaces). There also exist ALG spaces whose name is chosen by induction. ...more on Wikipedia about "Gravitational instanton"
The gravitino is the hypothetical supersymmetric partner of the graviton, as predicted by theories combining general relativity and supersymmetry, i.e. supergravity theories. If it exists it is a fermion of spin 3/2. ...more on Wikipedia about "Gravitino"
In physics, the graviton is a hypothetical elementary particle that transmits the force of gravity in most quantum gravity systems. In order to do this, one theory posits that gravitons have to be always-attractive (gravity never pushes), work over any distance (gravity is universal) and come in unlimited numbers (to provide high strengths near stars). In quantum theory, these requirements define an even- spin (spin 2 in this case) boson with a rest mass of zero. ...more on Wikipedia about "Graviton"
This is a list of researchers in quantum gravity. ...more on Wikipedia about "List of quantum gravity researchers"
In black hole theory, the black hole membrane paradigm is a useful " toy model" method or "engineering approach" for visualising and calculating the effects predicted by quantum mechanics for the exterior physics of black holes, without using quantum-mechanical principles or calculations. It models a black hole as a thin classically-radiating surface (or membrane) at or vanishingly close to the black hole's event horizon. ...more on Wikipedia about "Membrane paradigm"
In theoretical physics, quantum cosmology is a young field attempting to study the effect of quantum mechanics on the earliest moments of the universe after the Big Bang. Despite many attempts, the field remains a rather speculative branch of quantum gravity. ...more on Wikipedia about "Quantum cosmology"
Quantum field theory in curved spacetimes is an extension of the standard quantum field theory to curved spacetimes. The theory studies the dynamics of quantum matter fields that propagate in static curved backgrounds. Thanks to the equivalence principle the quantization procedure closely resembles that of Minkowski spacetime once the proper formalism is chosen; however, interesting phenomena not present in flat spacetimes occur. ...more on Wikipedia about "Quantum field theory in curved spacetime"
In theoretical physics, quantum geometry is the set of new mathematical concepts generalizing the concepts of geometry whose understanding is necessary to describe the physical phenomena at very short distance scales (comparable to Planck length). At these distances, quantum mechanics has a profound effect on physics. ...more on Wikipedia about "Quantum geometry"
Quantum gravity is the field of theoretical physics attempting to unify the theory of quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. The ultimate goal of some is a unified framework for all fundamental forces—a theory of everything. ...more on Wikipedia about "Quantum gravity"
In topology, quantum mechanics and geometrodynamics, rolling-ball arguments are used to describe how the perceived geometry and connectivity of a surface can be scale-dependent. ...more on Wikipedia about "Rolling ball"
The Ultimate Ensemble is a speculative possible feature of theories of everything (TOEs), suggested by Max Tegmark. Related to the Anthropic principle and Multiverse theories, the Ultimate Ensemble suggests that not only should worlds corresponding to different sets of initial conditions or different physical constants be considered real, but also worlds ruled by altogether different equations. The only postulate in this theory is that all structures that exist mathematically exist also physically. In those mathematical structures complex enough to contain self-aware substructures (SASs), these SASs will subjectively perceive themselves as existing in a physically "real" world. Tegmark observes that this simple theory, which has no free parameters at all and may thus be preferred over all other TOE's by Occam's Razor, is not observationally ruled out. ...more on Wikipedia about "Ultimate ensemble"
I wish I had a shortopedia.
(Weinberg-Witten theorem) * A 3 + 1D QFT with a conserved 4-vector current J (see four-current) which is Poincaré covariant (and gauge invariant if there happens to be any gauge symmetry which hasn't been gauge-fixed) does not admit massless particles with helicity |h| > 1/2 that also have nonzero charges associated with the conserved current in question. ...more on Wikipedia about "Weinberg-Witten theorem"
In theoretical physics, the Wheeler-DeWitt equation is an equation that a wave function of the Universe should satisfy in a theory of quantum gravity. An example of such a wave function is the Hartle-Hawking state. ...more on Wikipedia about "Wheeler-deWitt equation"
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