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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Living with L
Marek Nowakowski,I. Arraut +1 more
TL;DR: The return of the cosmological constant A to explain the accelerated stage of the universe has brought back many puzzles and misteries surrounding this constant and its role in quantum gravity as mentioned in this paper.
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Bounding violations of the weak gravity conjecture
TL;DR: In this article , it was shown that a small violation of the weak gravity conjecture is consistent with unitarity and causality, which vanishes in the limit where gravity decouples and also depends logarithmically on an infrared cutoff.
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Entropy bounds for uncollapsed rotating bodies
Gabriel Abreu,Matt Visser +1 more
TL;DR: In this paper, it was shown that the entropy of uncollapsed matter inside a region enclosed by a surface of area A is bounded from above by S = max kappa(FIDOs) / (2 pi).
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There is plenty of time at the bottom: the economics, risk and ethics of time compression
TL;DR: In this article, the authors review reasons to believe computation will continue to become faster in the future, the economic consequences of speedups and how these affect risk, ethics and governance, and conclude that speedups can lead to loss of control owing to inability to track fast change, emergent or systemic risk and asynchrony.
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Quantum corrections to a finite temperature BIon
TL;DR: It will be observed that these quantum fluctuations produce logarithmic corrections to the entropy of this finite temperature BIon solution, which correct the internal energy and the specific heat for this finiteTemperature BIon.