Gravity as an Emergent Phenomenon| Gravity as an Emergent Phenomenon |
In General
> s.a. emergence [including spacetime from entanglement]; entropic
gravity; gravitation; gravitational thermodynamics;
models for spacetime.
* Idea: The gravitational field
as a metric, and its dynamics, are not fundamental but arise as an effective
theory from some other microscopic degrees of freedom; The first widely known
proposal was Sakharov's 1967 induced gravity, but many other theories have
been proposed since.
* 2016: A popular idea is that
spacetime and gravity emerge together from the entanglement structure of an
underlying microscopic theory.
* Issue: Arguments against emergent
gravity have used the Weinberg-Witten Theorem, but many current proposals are
based on theories that are not Lorentz-covariant.
@ Reviews: Padmanabhan AIP(07)-a0706;
Sindoni Sigma(12)-a1110 [overview];
Carlip a1207 [challenges];
Padmanabhan AIP(12)-a1208 [conceptual aspects];
Padmanabhan MPLA(15)-a1410.
@ Conceptual: Padmanabhan IJMPD(08);
Linnemann & Visser SHPMP-a1711 [comments on emergence of gravity].
@ General references: Hu gq/96-conf [geometro-hydrodynamics];
Barceló et al IJMPD(01)gq;
Jenkins IJMPD(09)-a0904-GRF [difficulties];
Lee IJMPA(09)gq/06 [from interacting simplices];
Padmanabhan a0910-conf,
JPCS(11)-a1012;
Hu IJMPD(11)-a1010-fs [and non-equilibrium thermodynamics of classical matter];
Sindoni a1105 [group-field-theory perspective];
news dw(11)aug;
Kolekar & Padmanabhan PRD(12) [action principle from fluid-gravity correspondence];
Wetterich PLB(12)-a1203 [ambiguity in which collective field is the effective metric];
Consoli & Pluchino a1311 [experimental signatures];
Marolf PRL(15)-a1409 [need for kinematic non-locality];
Bhattacharya & Shankaranarayanan IJMPD(15)-a1505-GRF;
Zatrimaylov JCAP(20)-a2003 [critique].
@ Phenomenology, tests: Brouwer et al MNRAS(17)-a1612 [using weak gravitational lensing];
Diez-Tejedor et al MNRAS(18)-a1612 [vs MOND, and dwarf spheroidals];
Iorio EPJC(17)-a1612 [and anomalous perihelion precessions];
Lelli et al MNRAS(17)-a1702 [and the galaxy Radial Acceleration Relation];
Tortora et al MNRAS(17)-a1702 [and early-type galaxies];
Pardo JCAP(20)-a1706 [isolated dwarf galaxies];
Tamosiunas et al JCAP(19)-a1901 [at galaxy cluster scales].
@ Analog gravity phenomenology:
Klidis & Spyrou CQG(00) [in astrophysics];
Faccio et al ed-13.
> Related topics: see Deformations;
duality; lensing; non-commutative
gravity and spacetime; topology change;
Weinberg-Witten Theorem.
> Related theories: see Induced
Gravity; Matrix Models; modified electromagnetism;
non-commutative gauge theories [electromagnetism].
> Online resources:
see Wikipedia page.
Effective Metrics and Analog Gravity Models > s.a. lorentzian
geometry; qft effects in curved spacetime; sound.
* Idea: The propagation
of perturbations in certain condensed matter systems is equivalent to
the dynamics of quantum fields in curved spacetimes.
@ Reviews: Barceló et al LRR(05)gq;
Unruh & Schützhold ed-07;
Visser & Weinfurtner PoS-a0712;
Visser & Molina-Paris NJP(10)-a1001;
Barceló et al LRR(11);
Leonhardt et al NJP(12) [focus issue];
Visser LNP(13)-a1206;
Jacquet et al PTRS(20)-a2005.
@ General references: Barceló et al CQG(01)gq [field modes in non-trivial background];
Visser et al GRG(02)gq/01-proc;
Barceló et al NJP(04)gq [causal structure];
Okninski gq/05 [from scalar field];
Weinfurtner et al JPA(06)gq/05-conf [analog of Klein-Gordon field in curved spacetime];
Milgrom PRD(06) [particles and mass];
Liberati et al a0909-proc [general aspects, diffeomorphism invariance];
Smolyaninov & Hung JOSA(11)-a1104 [modeling the flow of time];
Chaline et al LNP(13)-a1203 [surface waves and dispersive horizons];
Fewster & Liberati GRG(14)-a1402 [GR20 report];
Hossenfelder & Zingg CQG(17)-a1704 [the class of metrics that have an analogue];
Crowther et al a1811 [what we cannot learn];
Iorio a2005-conf [Dirac materials];
> s.a. Elasticity; finsler geometry;
Lorentz-Fitzgerald Contraction; optics [optical
geometry]; perfect fluids; sound [acoustic geometry];
spacetime [geometry]; types of quantum field theories.
@ Quantum gravity simulation: Conti PRA(14)-a1406 [non-paraxial non-linear optics].
@ In a dielectric: De Lorenci & Klippert PRD(02) [electromagnetism in non-linear media];
Novello & Perez Bergliaffa AIP(03)gq [flowing dielectric];
Cacciatori et al NJP(10) [refractive index perturbations];
Thompson & Frauendiener PRD(10)-a1010 [general metrics];
Fathi & Thompson PRD(16)-a1602;
Schuster & Visser CQG(19)-a1808.
@ In a boson gas / BEC: Chapline & Mazur APPB(14)gq/04 [superfluid condensate model, and spinning cosmic strings];
Liberati et al PRL(06),
CQG(06)gq/05 [quantum gravity analog from BECs];
Weinfurtner et al PRD(07)gq [boson gas, signature change];
Bravo et al EPJQT-a1406,
Hartley et al PRD(18)-a1712 [simulation of gravitational waves];
Szpak a1410-GRF [ultra-cold atoms in optical lattices];
> s.a. bose-einstein condensates.
@ From non-linear field theory:
Novello & Goulart CQG(11)-a1102 [Lagrangian for field + analog metric];
Goulart et al CQG(11)-a1108.
@ Other models: Sepehri et al EPJB(16)-a1606 [f(R) analog from defects in graphene];
Datta PRD(18)-a1804 [analog metric for gravitational wave];
Kishore Roy et al a2011 [granular matter].
> Specific types of metrics: see black-hole analogs;
de sitter space; FLRW models [condensed matter analogs].
Emergent Gravity Proposals
> s.a. approaches; models of spacetime
[including internal relativity]; renormalization; time.
@ General references: Hu gq/06-talk [and stochastic gravity];
Hedrich a0902;
Hu JPCS(09)-a0903;
Mannheim GRG(11)-a0909,
MPLA(11)-a1005-conf
[intrinsically quantum-mechanical gravity and cancellation of cosmological-constant and zero-point energies];
Yang MPLA(10)-a1007 [using a spacetime symplectic structure],
JPCS(12)-a1111 [and background-independent quantum gravity];
Mandrin a1505 [non-dynamical approach];
Erlich CQG(18)-a1807 [stochastic framework];
> s.a. gravity theories.
@ Bose-Einstein condensate:
Consoli CQG(09);
Jannes PhD(09)-a0907;
Sindoni PRD(11)-a1011 [multi-BEC hydrodynamics];
Belenchia et al PRD(14)-a1407.
@ Other condensed-matter-type proposals:
Volovik 03 [low-energy behavior of Fermi liquids];
Girelli et al PRD(09)-a0806;
Jannes in(09)-a0810 [collective excitations];
Xu & Hořava PRD(10)-a1003 [Bose Liquid on an fcc lattice];
> s.a. quantum-spacetime proposals.
@ From entanglement, Verlinde theory:
Verlinde a1611 + news es(16)nov [and additional, dark gravitational force];
Hossenfelder PRD(17)-a1703,
Dai & Stojković PRD(17)-a1706 [covariant version], JHEP(17)-a1710 [inconsistencies];
> s.a. entanglement in field theory and spacetime.
@ U(1) gauge fields on a non-commutative spacetime:
Lee et al JHEP(12)-a1206;
Yang IJMPA(15)-a1312 [quantization].
@ From fundamental spinors: Kober PRD(09)-a0812;
Finster a1409 [causal action principle, system of relativistic fermions].
@ Other proposals: Sernelius IJMPA(09)-a0804 [as Casimir interaction];
Padmanabhan ASL(09)-a0807-in [from a theory of null vectors, and the cosmological constant];
Kabe a1002/PRD;
Marin a1206, a1206 [from "arrangement field theory" on a non-ordered space-time];
Sexty & Wetterich NPB(12)-a1208 [2D non-linear σ-model, numerical simulations];
de Souza a1212 [from discrete interactions, and cosmological acceleration];
Matsueda a1310 [from the Fisher information metric];
Anastasiou et al PRL(14)-a1408 [as convolution of left and right Yang-Mills theories];
Diaz et al a1609 [gravity from bilocality];
Mohan a1802 [tracing out fermions from an interacting quantum field theory];
Gallego Torromé IJGMP(20)-a2005;
Das & Sur a2105-GRF
[quantum universe with matter and a cosmological constant];
> s.a. cosmological expansion.
Gravity is the thermodynamic limit of the statistical mechanics of "atoms of spacetime."
— Thanu Padmanabhan, during a talk at Perimeter Institute.
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