Journal ArticleDOI
Universal upper bound on the entropy-to-energy ratio for bounded systems
TLDR
For systems with negligible self-gravity, the bound follows from application of the second law of thermodynamics to a gedanken experiment involving a black hole as discussed by the authors, and it is shown that black holes have the maximum entropy for given mass and size which is allowed by quantum theory and general relativity.Abstract:
We present evidence for the existence of a universal upper bound of magnitude $\frac{2\ensuremath{\pi}R}{\ensuremath{\hbar}c}$ to the entropy-to-energy ratio $\frac{S}{E}$ of an arbitrary system of effective radius $R$. For systems with negligible self-gravity, the bound follows from application of the second law of thermodynamics to a gedanken experiment involving a black hole. Direct statistical arguments are also discussed. A microcanonical approach of Gibbons illustrates for simple systems (gravitating and not) the reason behind the bound, and the connection of $R$ with the longest dimension of the system. A more general approach establishes the bound for a relativistic field system contained in a cavity of arbitrary shape, or in a closed universe. Black holes also comply with the bound; in fact they actually attain it. Thus, as long suspected, black holes have the maximum entropy for given mass and size which is allowed by quantum theory and general relativity.read more
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Revisit of the interaction between holographic dark energy and dark matter
TL;DR: In this article, the authors investigated the possible direct, non-gravitational interaction between holographic dark energy (HDE) and dark matter and found that the data slightly favor an energy flow from dark matter to dark energy, although the original HDE model still lies in the 95.4% confidence level.
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Light sheets and Bekenstein's entropy bound.
TL;DR: From the covariant bound on the entropy of partial light sheets, a version of Bekenstein's bound is derived, where S, M, and x are the entropy, total mass, and width of any isolated, weakly gravitating system.
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Entanglement interpretation of black hole entropy in string theory
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Holography, a covariant c function, and the geometry of the renormalization group
TL;DR: In this paper, a covariant geometrical expression for the c function for theories which admit dual gravitational descriptions is proposed, and a c theorem with respect to this quantity is proved.
Journal ArticleDOI
On the corpuscular theory of gravity
Andrea Giusti,Andrea Giusti +1 more
TL;DR: The corpuscular theory of gravity as discussed by the authors provides a way to unify most of the experimental observations (from astrophysical to galactic and cosmological scales) in a single framework, solely based on gravity and baryonic matter.