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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Weak gravity conjecture for effective field theories with N species
TL;DR: In this article, an intrinsic UV cutoff for the effective field theory with a large number of species coupled to gravity was conjectured in four dimensions, where the UV cutoff takes the form {lambda} =gM{sub p}/{radical}(N) for N scalar fields with the same potential {lambda}{phi}{sub i}{sup 4}, i=1,...,N.
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Entropy, energy and temperature–length inequality for Friedmann universes
TL;DR: In this article, the authors apply the modified black hole entropy formula to Friedmann expanding spacetimes with zero, negative and positive spatial curvature and obtain the correct result that F is stationary only for physical systems in isothermal equilibrium, i.e. a de Sitter expanding universe.
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Asymptotic Symmetry Algebras in Non-Anti-de-Sitter Higher-Spin Gauge Theories
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First law of thermodynamics for dynamical apparent horizons and the entropy of Friedmann universes
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Vindication of quantum locality
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