Hořava-Lifshitz gravity
Encyclopedia
Hořava–Lifshitz gravity is a theory of quantum gravity
proposed by Petr Hořava
in 2009. It solves the problem of different concepts of time in quantum field theory
and general relativity
by treating the quantum concept as the more fundamental so that space and time are not equivalent (anisotropic
). The relativistic concept of time with its Lorentz invariance emerges at large distances. The theory relies on the theory of foliation
s to produce its causal structure
. It is related to topologically massive gravity and the Cotton tensor
. It is a possible UV completion
of general relativity. The novelty of this approach, compared to previous approaches to quantum gravity such as Loop quantum gravity
, is that it uses concepts from condensed matter physics
such as quantum critical phenomena
. Hořava's initial formulation was found to have side-effects such as predicting very different results for a spherical Sun
compared to a slightly non-spherical Sun, so others have modified the theory. Inconsistencies remain.
Quantum gravity
Quantum gravity is the field of theoretical physics which attempts to develop scientific models that unify quantum mechanics with general relativity...
proposed by Petr Hořava
Petr Horava
Petr Hořava is a Czech string theorist. He is currently a professor of physics at the University of California, Berkeley, where he frequently teaches courses on quantum field theory and string theory...
in 2009. It solves the problem of different concepts of time in quantum field theory
Quantum field theory
Quantum field theory provides a theoretical framework for constructing quantum mechanical models of systems classically parametrized by an infinite number of dynamical degrees of freedom, that is, fields and many-body systems. It is the natural and quantitative language of particle physics and...
and general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
by treating the quantum concept as the more fundamental so that space and time are not equivalent (anisotropic
Anisotropy
Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
). The relativistic concept of time with its Lorentz invariance emerges at large distances. The theory relies on the theory of foliation
Foliation
In mathematics, a foliation is a geometric device used to study manifolds, consisting of an integrable subbundle of the tangent bundle. A foliation looks locally like a decomposition of the manifold as a union of parallel submanifolds of smaller dimension....
s to produce its causal structure
Causal structure
In mathematical physics, the causal structure of a Lorentzian manifold describes the causal relationships between points in the manifold.- Introduction :In modern physics spacetime is represented by a Lorentzian manifold...
. It is related to topologically massive gravity and the Cotton tensor
Cotton tensor
In differential geometry, the Cotton tensor on a -Riemannian manifold of dimension n is a third-order tensor concomitant of the metric, like the Weyl tensor. The concept is named after Émile Cotton...
. It is a possible UV completion
UV Completion
In theoretical physics, ultraviolet completion, or UV completion, of a quantum field theory is the passing from a lower energy quantum field theory to a more general quantum field theory above a threshold value known as the cutoff...
of general relativity. The novelty of this approach, compared to previous approaches to quantum gravity such as Loop quantum gravity
Loop quantum gravity
Loop quantum gravity , also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity...
, is that it uses concepts from condensed matter physics
Condensed matter physics
Condensed matter physics deals with the physical properties of condensed phases of matter. These properties appear when a number of atoms at the supramolecular and macromolecular scale interact strongly and adhere to each other or are otherwise highly concentrated in a system. The most familiar...
such as quantum critical phenomena
Quantum Critical Point
A quantum critical point is a special class of continuous phase transition that takes place at the absolute zero of temperature, typically in a material where the phase transition temperature has been driven to zero by the application of a pressure, field or through doping.Conventional phase...
. Hořava's initial formulation was found to have side-effects such as predicting very different results for a spherical Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
compared to a slightly non-spherical Sun, so others have modified the theory. Inconsistencies remain.