Hawking radiation of an apparent horizon in a FRW universe

Cai, Rong-Gen; Cao, Li-Ming; Hu, Ya-Peng

doi:10.1088/0264-9381/26/15/155018

Cited by 275 publications

(290 citation statements)

References 49 publications

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“…the field equations become T dS = dE + P dV ) continues to hold for a very wide class of theories! In the more general class of theories, one can define a natural entropy for the horizon called the Wald entropy [17] and we again get the same result with correct Wald entropy (for a sample of results see [18][19][20][21][22][23][24][25][26]). …”

Section: Gravitational Field Equations As a Thermodynamic Identitymentioning

confidence: 54%

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 Field Equations As a Thermodynamic Identitymentioning

confidence: 54%

Emergent perspective of gravity and dark energy

Padmanabhan¹

2012

Res. Astron. Astrophys.

117

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“…There are two definitions for the temperature of apparent horizon of FLRW universe [6-9, 15, 16], called the Hayward-Kodama temperature [6][7][8] and the Cai-Kim temperature [9,15], and both of them, whenever they are combined with the Bekenstein entropy relation, are in agreement with the Friedmann equation as well as the unified first law of thermodynamics. It is useful to note here that although the Bekenstein entropy is in line with the current accelerating phase of universe expansion and the second and generalized second laws of thermodynamics [17,18], some authors show that a dark energy candidate, due to its unknown nature, may modify the horizon entropy (the Bekenstein limit in the Einstein general relativity framework) [19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Implications, Consequences and Interpretations of Generalized Entropy in the Cosmological Setups

Moradpour

2016

Int J Theor Phys

121

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Recently, it was argued (Eur. Phys. J. C 73, 2487 (2013)) that the total entropy of a gravitational system should be related to the volume of system instead of the system surface. Here, we show that this new proposal cannot satisfy the unified first law of thermodynamics and the Friedmans equation simultaneously, unless the effects of dark energy candidate on the horizon entropy are considered.In fact, our study shows that some types of dark energy candidate may admit this proposal. Some general properties of required dark energy are also addressed. Moreover, our investigation shows that this new proposal for entropy, while combined with the second law of thermodynamics (as the backbone of Verlinde's proposal), helps us in providing a thermodynamic interpretation for the difference between the surface and bulk degrees of freedom which, according to Padmanabhan's proposal, leads to the emergence of spacetime and thus the universe expansion. In fact, our investigation shows that the entropy changes of system may be equal to the difference between the surface and bulk degrees of freedom falling from surface into the system volume. Briefly, our results signal us that this new proposal for entropy may be in agreement with the thermodynamics laws,

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“…However, in order to get a thermodynamic description of the universe evolution based on the Jacobson formalism, it has been shown that the choice of the cosmological apparent horizon as the holographic boundary [21,34] is more convenient. Such conclusion comes from that fact that, at the apparent horizon, the Friedmann equations have been shown to be equivalent to the first law of thermodynamics [47][48][49]. It occurs not only in Einstein's gravity, but in other scenarios such as braneworld models [50][51][52][53], Horava-Lifshitz gravity [54], Lovelock gravity [47,55] and f (R) gravity [56].…”

Section: Friedmann Equations From Thermodynamicsmentioning

confidence: 99%

“…which was obtained in the reference [48,49] through tunneling methods. From the equations above, we obtaiṅ…”

Section: Friedmann Equations From Thermodynamicsmentioning

confidence: 99%