Causal patch

Short description: Special region of spacetime

A causal patch is a region of spacetime connected within the relativistic framework of causality (causal light cones).

## Background

After Leonard Susskind proposed the black hole complementarity conjecture for black holes in quantum gravity, he realized it would also apply to a de Sitter universe with a positive cosmological constant with the cosmological horizon in place of the event horizon. The region within the horizon is the causal patch,[1][2] and it is self-contained. This means we may neglect what happens beyond the cosmological horizon. A consequence of this radical conjecture is that the total number of states of the universe is finite.

## References

1. ↑ Dyson, Lisa; Kleban, Matthew; Susskind, Leonard (October 2002). "Disturbing Implications of a Cosmological Constant". Journal of High Energy Physics 2002 (10): 011. doi:10.1088/1126-6708/2002/10/011. Bibcode: 2002JHEP...10..011D.
2. ↑ Goheer, Naureen; Kleban, Matthew; Susskind, Leonard (July 2003). "The Trouble with de Sitter Space". Journal of High Energy Physics 2003 (7): 056. doi:10.1088/1126-6708/2003/07/056. Bibcode: 2003JHEP...07..056G.

## See also

* Black hole complementarity
* de Sitter space

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Quantum gravity

Central concepts|

* AdS/CFT correspondence
* Causal patch
* Gravitational anomaly
* Graviton
* Holographic principle
* IR/UV mixing
* Planck scale
* Quantum foam
* Trans-Planckian problem
* Weinberg–Witten theorem

Toy models|

* 2+1D topological gravity
* CGHS model
* Jackiw-Teitelboim gravity
* Liouville gravity
* RST model
* Topological quantum field theory

Quantum field theory
in curved spacetime|

* Bunch–Davies vacuum
* Hawking radiation
* Semiclassical gravity
* Unruh effect

Black holes|

* Black hole complementarity
* Black hole information paradox
* Black-hole thermodynamics
* Bousso's holographic bound
* ER=EPR
* Firewall (physics)
* Gravitational singularity

Approaches|

| String theory|

* Bosonic string theory
* M-theory
* Supergravity
* Superstring theory

|

Canonical quantum gravity|

* Loop quantum gravity
* Wheeler-DeWitt equation

Euclidean quantum gravity|

* Hartle-Hawking state

Others|

* Causal dynamical triangulation
* Causal sets
* Noncommutative geometry
* Spin foam
* Group field theory
* Superfluid vacuum theory
* Twistor theory
* Dual graviton

Applications|

* Quantum cosmology
* Eternal inflation
* Multiverse
* FRW/CFT duality

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