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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Emergence and Fundamentality in a Pancomputationalist Universe
TL;DR: It is argued that if one adopts pancomputationalism (the idea that the world is a computer of some sort) as a metaphysics for the universe, then there are higher-level structures which are just as fundamental for computation as anything from microphysics.
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Entropy, inflation and the arrow of time
Dalia S. Goldwirth,Tsvi Piran +1 more
TL;DR: In this article, it was shown that inflation is generic in the expanding phase but exceedingly unlikely in the collapsing phase, which introduces an asymmetry in the evolution of the universe which resembles to a large extent the asymmetry that appears in the growth of entropy.
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Contracting Cosmologies and the Swampland
TL;DR: In this article, the cosmology obtained using scalar fields with a negative potential energy, such as employed to obtain an Ekpyrotic phase of contraction, was considered and the relative slope of the potential was bounded from below by a constant of the order one in Planck units.
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Notes on quantum corrections of swampland and trans-Planckian censorship conjectures
TL;DR: In this article, the de Sitter swampland and trans-Planckian censorship conjectures were discussed from the entropy bound with quantum corrections, namely quantum version of Bousso's bound and energy conditions, and the typical contributions from the entanglement entropy in quasi-de Sitter spacetime.
Journal ArticleDOI
Geometric Inequalities for Quasi-Local Masses.
TL;DR: In this article, lower bounds are obtained for quasi-local masses in terms of charge, angular momentum, and horizon area, and a localized version of the Penrose inequality for the static Wang-Yau mass is obtained.