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Quantum Information in Quantum Gravity
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Quantum Information in Quantum Gravity

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Quantum Information".

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 11626

Special Issue Editors

Dr. Charis Anastopoulos

E-Mail Website
Guest Editor
Department of Physics, University of Patras, ‎Patras, Greece
Interests: quantum foundations; relativistic quantum information; black hole thermodynamics
Dr. Ntina Savvidou

E-Mail Website
Guest Editor
Department of Physics, University of Patras, ‎Patras, Greece
Interests: quantum foundations; problem of time; quantum gravity

Special Issue Information

Dear Colleagues,

Quantum theory and general relativity are the fundamental theories of modern physics, and are both highly successful in their domains. However, they are ultimately incompatible: their mathematical and conceptual structures are very different. A unifying theory of quantum gravity is necessary. However, despite many decades of effort, no consistent and predictive theory of quantum gravity exists.

In recent years, a seemingly unrelated development has begun to make an impact on quantum gravity research: the development of quantum information theory. Quantum information focusses on features of quantum theory that have no analogue in classical physics, like superposition and entanglement. While quantum information theory is mostly discussed in terms of non-relativistic quantum mechanics, there is a strong effort in placing quantum information within the more fundamental framework of relativistic physics, including general relativity and gravitational effects.

The effect of quantum information on quantum gravity is stronger in the field of black hole physics, where the issue of information loss has been viewed either as a blessing or as a paradox ever since Hawking’s discovery that black holes radiate. It is also important in (quantum) cosmology, especially in relation to the emergence of a classical world (or realized universe) from a quantum description. Additionally, it is directly relevant to the very structure of quantum gravity programs, as researchers try to incorporate physical assumptions that are fundamentally informational (like the holographic principle).

Furthermore, there are new proposals for testing the relation of quantum theory and gravity, not in the very high energies traditionally ascribed to quantum gravity but by exploring the interplay of gravity with quantum entanglement and superposition at large distances. Relevant experiments promise to be within reach in the near future. They include tests of gravity-induced modifications of quantum mechanics; probing gravitational fields generated by quantum sources; understanding the effect of gravity on entanglement; and, in some proposals, even testing whether gravity is fundamentally quantum or not.

Dr. Charis Anastopoulos
Dr. Ntina Savvidou
Guest Editors

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

  • quantum gravity
  • entanglement
  • superpositions
  • decoherence
  • quantum cosmology
  • quantum information
  • black holes

Published Papers (4 papers)

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24 pages, 427 KiB  
Article
Unitarity and Page Curve for Evaporation of 2D AdS Black Holes
by Mariano Cadoni and Andrea P. Sanna
Entropy 2022, 24(1), 101; https://doi.org/10.3390/e24010101 - 08 Jan 2022
Cited by 9 | Viewed by 1760
Abstract
We explore the Hawking evaporation of two-dimensional anti-de Sitter (AdS2), dilatonic black hole coupled with conformal matter, and derive the Page curve for the entanglement entropy of radiation. We first work in a semiclassical approximation with backreaction. We show that the [...] Read more.
We explore the Hawking evaporation of two-dimensional anti-de Sitter (AdS2), dilatonic black hole coupled with conformal matter, and derive the Page curve for the entanglement entropy of radiation. We first work in a semiclassical approximation with backreaction. We show that the end-point of the evaporation process is AdS2 with a vanishing dilaton, i.e., a regular, singularity-free, zero-entropy state. We explicitly compute the entanglement entropies of the black hole and the radiation as functions of the horizon radius, using the conformal field theory (CFT) dual to AdS2 gravity. We use a simplified toy model, in which evaporation is described by the forming and growing of a negative mass configuration in the positive-mass black hole interior. This is similar to the “islands” proposal, recently put forward to explain the Page curve for evaporating black holes. The resulting Page curve for AdS2 black holes is in agreement with unitary evolution. The entanglement entropy of the radiation initially grows, closely following a thermal behavior, reaches a maximum at half-way of the evaporation process, and then goes down to zero, following the Bekenstein–Hawking entropy of the black hole. Consistency of our simplified model requires a non-trivial identification of the central charge of the CFT describing AdS2 gravity with the number of species of fields describing Hawking radiation. Full article
(This article belongs to the Special Issue Quantum Information in Quantum Gravity)
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16 pages, 513 KiB  
Article
Quantum Information in Relativity: The Challenge of QFT Measurements
by Charis Anastopoulos and Ntina Savvidou
Entropy 2022, 24(1), 4; https://doi.org/10.3390/e24010004 - 21 Dec 2021
Cited by 9 | Viewed by 2977
Abstract
Proposed quantum experiments in deep space will be able to explore quantum information issues in regimes where relativistic effects are important. In this essay, we argue that a proper extension of quantum information theory into the relativistic domain requires the expression of all [...] Read more.
Proposed quantum experiments in deep space will be able to explore quantum information issues in regimes where relativistic effects are important. In this essay, we argue that a proper extension of quantum information theory into the relativistic domain requires the expression of all informational notions in terms of quantum field theoretic (QFT) concepts. This task requires a working and practicable theory of QFT measurements. We present the foundational problems in constructing such a theory, especially in relation to longstanding causality and locality issues in the foundations of QFT. Finally, we present the ongoing Quantum Temporal Probabilities program for constructing a measurement theory that (i) works, in principle, for any QFT, (ii) allows for a first- principles investigation of all relevant issues of causality and locality, and (iii) it can be directly applied to experiments of current interest. Full article
(This article belongs to the Special Issue Quantum Information in Quantum Gravity)
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16 pages, 307 KiB  
Perspective
Gravity, Quantum Fields and Quantum Information: Problems with Classical Channel and Stochastic Theories
by Charis Anastopoulos and Bei-Lok Hu
Entropy 2022, 24(4), 490; https://doi.org/10.3390/e24040490 - 31 Mar 2022
Cited by 6 | Viewed by 2026
Abstract
In recent years an increasing number of papers have attempted to mimic or supplant quantum field theory in discussions of issues related to gravity by the tools and through the perspective of quantum information theory, often in the context of alternative quantum theories. [...] Read more.
In recent years an increasing number of papers have attempted to mimic or supplant quantum field theory in discussions of issues related to gravity by the tools and through the perspective of quantum information theory, often in the context of alternative quantum theories. In this article, we point out three common problems in such treatments. First, we show that the notion of interactions mediated by an information channel is not, in general, equivalent to the treatment of interactions by quantum field theory. When used to describe gravity, this notion may lead to inconsistencies with general relativity. Second, we point out that in general one cannot replace a quantum field by a classical stochastic field, or mock up the effects of quantum fluctuations by that of classical stochastic sources (noises), because in so doing important quantum features such as coherence and entanglement will be left out. Third, we explain how under specific conditions semi-classical and stochastic theories indeed can be formulated from their quantum origins and play a role at certain regimes of interest. Full article
(This article belongs to the Special Issue Quantum Information in Quantum Gravity)
22 pages, 4350 KiB  
Concept Paper
Towards Unification of General Relativity and Quantum Theory: Dendrogram Representation of the Event-Universe
by Oded Shor, Felix Benninger and Andrei Khrennikov
Entropy 2022, 24(2), 181; https://doi.org/10.3390/e24020181 - 25 Jan 2022
Cited by 4 | Viewed by 3605
Abstract
Following Smolin, we proceed to unification of general relativity and quantum theory by operating solely with events, i.e., without appealing to physical systems and space-time. The universe is modelled as a dendrogram (finite tree) expressing the hierarchic relations between events. This is the [...] Read more.
Following Smolin, we proceed to unification of general relativity and quantum theory by operating solely with events, i.e., without appealing to physical systems and space-time. The universe is modelled as a dendrogram (finite tree) expressing the hierarchic relations between events. This is the observational (epistemic) model; the ontic model is based on p-adic numbers (infinite trees). Hence, we use novel mathematics: not only space-time but even real numbers are not in use. Here, the p-adic space (which is zero-dimensional) serves as the base for the holographic image of the universe. In this way our theory is connected with p-adic physics; in particular, p-adic string theory and complex disordered systems (p-adic representation of the Parisi matrix for spin glasses). Our Dendrogramic-Holographic (DH) theory matches perfectly with the Mach’s principle and Brans–Dicke theory. We found a surprising informational interrelation between the fundamental constants, h, c, G, and their DH analogues, h(D), c(D), G(D). DH theory is part of Wheeler’s project on the information restructuring of physics. It is also a step towards the Unified Field theory. The universal potential V is nonlocal, but this is relational DH nonlocality. V can be coupled to the Bohm quantum potential by moving to the real representation. This coupling enhances the role of the Bohm potential. Full article
(This article belongs to the Special Issue Quantum Information in Quantum Gravity)
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