Locality |

**In General** > s.a. localization; Reference
Frame [accelerated]; Ultralocality.

* __Locality principle__: Roughly,
a physical system can only interact with other systems in its immediate surroundings;
A measurement on one particle cannot affect the properties of another particle before
the appropriate light travel time; More generally, spacelike separated events cannot
causally influence each other.

* __Remark__: The only strictly
local theories are classical special-relativistic ones.

* __Branch locality__: An operational
physical locality principle, similar to non-signaling but applicable to single systems;
> s.a. Box World.

@ __General references__: Mashhoon PLA(90);
d'Espagnat PLA(92);
Hunter et al ed-98;
Mashhoon in(03)gq [limitations];
Gisin qp/05-conf [history];
Doplicher JMP(10)-a0911-conf;
Di Lorenzo a1105 [different definitions];
Dahlsten et al nComm(14)-a1206 [branch locality];
Weinstein a1211-FQXi [challenging the locality assumption];
van Hateren EPL(15)-a1505 [how non-locality can arise from strictly local interactions].

@ __Consequences, uses of non-locality__: Hoyle & Narlikar PRS(93) [infinities in field theory];
Bennett et al ht/95.

@ __And fundamental physics__: Oeckl a1412-proc [approach based on locality and operationalism].

> __ Online resources__:
see Cornell Instrinsic Localized Modes site;
Wikipedia page.

> __Mathematical notions__: see distributions.

**In Classical Physics**

* __Formal role__: It is
important in special relativity (finite speed of propagation), but even more
in general relativity (spacetime and laws are locally Minkowskian – see
the principle of equivalence – and there is no distant parallelism),
and similarly for gauge theories.

@ __In field theory__: Carati & Galgani NCB(99),
Frisch BJPS(02) [non-locality in classical electrodynamics];
Fewster & Verch AHP(12)-a1109 [scalar field, dynamical locality];
Benini a1503-PhD [Abelian gauge theories];
> s.a. types of field theories.

@ __In general relativity__:
Mashhoon in(01)gq/00,
gq/01-proc;
Chiao gq/03-proc [vs quantum mechanics].

@ __Non-local theories__: Ohira PhyA(07) [in time];
Mashhoon AdP(11)-a1006 [accelerated observers and necessity of non-locality].

> __Non-local theories__:
see causality [action at a distance]; higher-order lagrangians;
special relativity [non-local]; non-local field theories.

> __Related topics__:
see huygens principle; temperature [local definitions];
wave phenomena.

**In Quantum Physics** > see locality in quantum mechanics
and in quantum field theory.

**Relative Locality** > s.a. rainbow gravity.

* __Idea__: An approach to physics
in which momentum space is taken as a primary object, and spacetime is emergent,
motivated by the fact that we interact with the physical world by measuring energies
and directions of incoming photons, rather than making measurements of spacetime itself;
In this framework, momentum space is not flat; There is also a dual picture in which
one gets spacetime non-commutativity from relative locality.

@ __General references__:
Amelino-Camelia et al PRD(11)-a1101 [principle],
PRD(11)-a1104,
GRG(11)-a1106-GRF;
Gubitosi & Mercati CQG(13)-a1106 [and the *κ*-Poincaré Hopf algebra];
Smolin talk(11)feb;
Amelino-Camelia et al IJTP(12)-a1107 [transverse relative locality];
Carmona et al PRD(11)-a1107 [beyond special relativity];
Amelino-Camelia PRD(12)-a1110 [fate of Lorentz symmetry];
Smolin GRG(11);
Loret et al JPCS(12)-a1207 [summary];
Amelino-Camelia et al PRD(12)-a1206 [and deformed Lorentz symmetry, in a curved spacetime];
Arraut a1301;
Kowalski-Glikman & Rosati MPLA(13)-a1303 [in curved spacetime];
Banburski PRD(13)-a1305 [twisting loops and global momentum non-conservation];
Cianfrani et al PRD(14)-a1401 [generally-covariant formulation];
Amelino-Camelia et al PRD(15)-a1401 [causality and momentum conservation];
> s.a. minkowski spacetime;
Observers; Soccer Ball Problem.

@ __In specific models__: Amelino-Camelia et al PLB(11)-a1102
[and speed of particles in *κ*-Minkowski spacetime];
Banburski & Freidel PRD(14)-a1308 [Snyder momentum space];
Ivetić & Mignemi a1711 [Snyder model].

@ __Related topics__: Oliveira MS-a1110 [point-particle interactions];
Kowalski-Glikman & Szczachor a1212-proc [and the *G* → 0 limit of gravity];
Chen PRD(13) [causal loops];
Smolin a1311 [and twistor geometry].

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