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Entropy
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Entropy and Spacetime
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Entropy and Spacetime

A special issue of Entropy (ISSN 1099-4300).

Deadline for manuscript submissions: closed (31 January 2015)

Special Issue Editor

Dr. Hiromi Saida

E-Mail
Guest Editor
Department of Physics, Daido University, Nagoya 457-8530, Japan
Interests: quantum aspect of black hole; Quantum statistics of gravity; black hole thermodynamics; relativistic dissipative hydrodynamics; theory for direct astronomical observation of black holes

Special Issue Information

Dear Colleagues,

A black hole is an empty region. Anything in a black hole region cannot stay at a constant, proper distance from the center, but has to fall towards the center. In ordinary laboratory physics, we cannot regard an empty region solely as a system that forms some physical state (such as a thermal equilibrium state). Therefore, Hawking’s discovery that thermal radiation is emitted from the surfaces of black hole regions (i.e., black hole horizons) is astonishing. The black hole has to be regarded as a thermal equilibrium system. The fact that Hawking’s radiation is predicted by quantum field theory in the context of black hole spacetime implies that the black hole is a thermal equilibrium state of the underlying quantum gravity.

It is expected that the black hole is regarded as some thermal equilibrium system composed of microscopic constituents of spacetime. Such microscopic constituents should cause the black hole’s entropy. Bekenstein's proposal implies that black hole entropy is given by a quarter of the surface area of the black hole horizon (in Planck units). This is the entropy-area law of black hole. This law should include at least the following two ingredients: (1) the nature of microscopic constituents of spacetime (in other words, microstates of underlying quantum gravity), and (2) the statistical mechanical property of long range interaction systems, since gravity is a long range interaction.

This Special Issue “Entropy and Spacetime” can be a meeting place for statistical mechanics, thermodynamics, black hole, and spacetime physics. Further, both classical and quantum approaches are possible. Contributions from both gravitational and statistical physics are welcome.

Dr. Hiromi Saida
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Entropy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • black hole thermodynamics
  • black hole entropy
  • entropy-area law
  • quantum gravity approach to black hole entropy
  • statistical mechanics approach to black hole entropy

Published Papers (4 papers)

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Research

331 KiB  
Article
Losing Information Outside the Horizon
by Samir D. Mathur
Entropy 2015, 17(6), 4083-4109; https://doi.org/10.3390/e17064083 - 12 Jun 2015
Cited by 1 | Viewed by 4464
Abstract
Suppose we allow a system to fall freely from infinity to a point near (but not beyond) the horizon of a black hole. We note that in a sense the information in the system is already lost to an observer at infinity. Once [...] Read more.
Suppose we allow a system to fall freely from infinity to a point near (but not beyond) the horizon of a black hole. We note that in a sense the information in the system is already lost to an observer at infinity. Once the system is too close to the horizon it does not have enough energy to send its information back because the information carrying quanta would get redshifted to a point where they get confused with Hawking radiation. If one attempts to turn the infalling system around and bring it back to infinity for observation then it will experience Unruh radiation from the required acceleration. This radiation can excite the bits in the system carrying the information, thus reducing the fidelity of this information. We find the radius where the information is essentially lost in this way, noting that this radius depends on the energy gap (and coupling) of the system. We look for some universality by using the highly degenerate BPS ground states of a quantum gravity theory (string theory) as our information storage device. For such systems one finds that the critical distance to the horizon set by Unruh radiation is the geometric mean of the black hole radius and the radius of the extremal hole with quantum numbers of the BPS bound state. Overall, the results suggest that information in gravity theories should be regarded not as a quantity contained in a system, but in terms of how much of this information is accessible to another observer. Full article
(This article belongs to the Special Issue Entropy and Spacetime)
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2748 KiB  
Article
Space-Time Quantum Imaging
by Ronald E. Meyers and Keith S. Deacon
Entropy 2015, 17(3), 1508-1534; https://doi.org/10.3390/e17031508 - 23 Mar 2015
Cited by 5 | Viewed by 6196
Abstract
We report on an experimental and theoretical investigation of quantum imaging where the images are stored in both space and time. Ghost images of remote objects are produced with either one or two beams of chaotic laser light generated by a rotating ground [...] Read more.
We report on an experimental and theoretical investigation of quantum imaging where the images are stored in both space and time. Ghost images of remote objects are produced with either one or two beams of chaotic laser light generated by a rotating ground glass and two sensors measuring the reference field and bucket field at different space-time points. We further observe that the ghost images translate depending on the time delay between the sensor measurements. The ghost imaging experiments are performed both with and without turbulence. A discussion of the physics of the space-time imaging is presented in terms of quantum nonlocal two-photon analysis to support the experimental results. The theoretical model includes certain phase factors of the rotating ground glass. These experiments demonstrated a means to investigate the time and space aspects of ghost imaging and showed that ghost imaging contains more information per measured photon than was previously recognized where multiple ghost images are stored within the same ghost imaging data sets. This suggests new pathways to explore quantum information stored not only in multi-photon coincidence information but also in time delayed multi-photon interference. The research is applicable to making enhanced space-time quantum images and videos of moving objects where the images are stored in both space and time. Full article
(This article belongs to the Special Issue Entropy and Spacetime)
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199 KiB  
Article
Geometric Thermodynamics: Black Holes and the Meaning of the Scalar Curvature
by Miguel Ángel García-Ariza, Merced Montesinos and Gerardo F. Torres del Castillo
Entropy 2014, 16(12), 6515-6523; https://doi.org/10.3390/e16126515 - 11 Dec 2014
Cited by 16 | Viewed by 6451
Abstract
In this paper we show that the vanishing of the scalar curvature of Ruppeiner-like metrics does not characterize the ideal gas. Furthermore, we claim through an example that flatness is not a sufficient condition to establish the absence of interactions in the underlying [...] Read more.
In this paper we show that the vanishing of the scalar curvature of Ruppeiner-like metrics does not characterize the ideal gas. Furthermore, we claim through an example that flatness is not a sufficient condition to establish the absence of interactions in the underlying microscopic model of a thermodynamic system, which poses a limitation on the usefulness of Ruppeiner’s metric and conjecture. Finally, we address the problem of the choice of coordinates in black hole thermodynamics. We propose an alternative energy representation for Kerr-Newman black holes that mimics fully Weinhold’s approach. The corresponding Ruppeiner’s metrics become degenerate only at absolute zero and have non-vanishing scalar curvatures. Full article
(This article belongs to the Special Issue Entropy and Spacetime)
148 KiB  
Article
Is Gravity Entropic Force?
by Rongjia Yang
Entropy 2014, 16(8), 4483-4488; https://doi.org/10.3390/e16084483 - 11 Aug 2014
Cited by 12 | Viewed by 6504
Abstract
If we assume that the source of thermodynamic system, ρ and p, are also the source of gravity, then either thermal quantities, such as entropy, temperature, and chemical potential, can induce gravitational effects, or gravity can induce thermal effects. We find that gravity [...] Read more.
If we assume that the source of thermodynamic system, ρ and p, are also the source of gravity, then either thermal quantities, such as entropy, temperature, and chemical potential, can induce gravitational effects, or gravity can induce thermal effects. We find that gravity can be seen as entropic force only for systems with constant temperature and zero chemical potential. The case for Newtonian approximation is discussed. Full article
(This article belongs to the Special Issue Entropy and Spacetime)
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