Cosmological event horizons, thermodynamics, and particle creation

Gibbons, G. W.; Hawking, S. W.

doi:10.1103/physrevd.15.2738

Cited by 2,863 publications

(2,681 citation statements)

References 29 publications

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“…To obtain the field equations, one either has to cancel out the variations in the surface term by adding a suitable counter-term [11,39] or use special boundary conditions. In either case, the field equations arise essentially from the variation of the bulk term with the boundary term of the action playing absolutely no role.…”

Section: Gravitational Action As Free Energy Of Spacetimementioning

confidence: 99%

Emergent perspective of gravity and dark energy

Padmanabhan¹

2012

Res. Astron. Astrophys.

117

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There is sufficient amount of internal evidence in the nature of gravitational theories to indicate that gravity is an emergent phenomenon like, e.g, elasticity. Such an emergent nature is most apparent in the structure of gravitational dynamics. It is, however, possible to go beyond the field equations and study the space itself as emergent in a well-defined manner in (and possibly only in) the context of cosmology. In the first part of this review, I describe various pieces of evidence which show that gravitational field equations are emergent. In the second part, I describe a novel way of studying cosmology in which I interpret the expansion of the universe as equivalent to the emergence of space itself. In such an approach, the dynamics evolves towards a state of holographic equipartition, characterized by the equality of number of bulk and surface degrees of freedom in a region bounded by the Hubble radius. This principle correctly reproduces the standard evolution of a Friedmann universe. Further, (a) it demands the existence of an early inflationary phase as well as late time acceleration for its successful implementation and (b) allows us to link the value of late time cosmological constant to the e-folding factor during inflation.

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Section: Gravitational Action As Free Energy Of Spacetimementioning

confidence: 99%

Emergent perspective of gravity and dark energy

Padmanabhan¹

2012

Res. Astron. Astrophys.

117

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“…Quantitative insights into the Hilbert space of inflationary spacetimes come from the thermodynamics of black holes [25][26][27][28][29][30] and de Sitter spacetimes [31]. The black hole entropy derived from thermodynamic reasoning appears to be complete, in the sense that it includes all possible degrees of freedom of mass-energy that make up the hole.…”

Section: Holographic Bound On the Information Content Of Inflatiomentioning

confidence: 99%

Holographic discreteness of inflationary perturbations

Hogan

2002

Phys. Rev. D

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The cosmological holographic principle, which states that the total observable entropy of de Sitter space (including gravitational quanta) is bounded by S < π/H 2 , where H is the expansion rate, is used to estimate the magnitude of quantum-gravitational effects on inflationary perturbations. The constraint is shown to imply that the initial states of the vacua for perturbation modes are not independent, and that field theory is not a reliable tool to study transplanckian effects on mode amplitudes and phases. It is argued that holographic discreteness alters the continuous, random-phase gaussian distribution predicted by standard field theory for fluctuations in the inflaton field that lead to cosmic background anisotropy. A toy model, applied in the context of scalar inflaton perturbations produced during standard slow-roll inflation, and assuming that horizonscale perturbations "freeze out" in discrete steps separated by one bit of observable information, predicts discrete steps in anisotropy separated by ∆T ≈ 10 −10 K. It is conjectured that the Hilbert space of a typical observable perturbation is equivalent to that of no more than about 10 5 binary spins (approximately the inverse of the final scalar metric perturbation amplitude, independent of H and other parameters), and that some manifestations of this discreteness may be observable.

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“…This horizon, like a black hole horizon, is associated with thermodynamic properties [7]: the Hawking temperature T and entropy S,…”

Section: Introductionmentioning

confidence: 99%

First Law of Thermodynamics and Friedmann Equations of Friedmann–Robertson–Walker Universe

Cai

Kim

2005

J. High Energy Phys.

730

779

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Applying the first law of thermodynamics to the apparent horizon of a FriedmannRobertson-Walker universe and assuming the geometric entropy given by a quarter of the apparent horizon area, we derive the Friedmann equations describing the dynamics of the universe with any spatial curvature. Using entropy formulae for the static spherically symmetric black hole horizons in Gauss-Bonnet gravity and in more general Lovelock gravity, where the entropy is not proportional to the horizon area, we are also able to obtain the Friedmann equations in each gravity theory. We also discuss some physical implications of our results.

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Cosmological event horizons, thermodynamics, and particle creation

Cited by 2,863 publications

References 29 publications

Emergent perspective of gravity and dark energy

Emergent perspective of gravity and dark energy

Holographic discreteness of inflationary perturbations

First Law of Thermodynamics and Friedmann Equations of Friedmann–Robertson–Walker Universe

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