Information Puzzle Research Articles

IMAGINEA EROILOR ÎN ERA DIGITALĂ – HAIDUCII BABA NOVAC ȘI GRUIA LUI NOVAC

The fascinating stories of the outlaw Baba Novac and his son Gruia can be found dressed up in various versions and in digital format. By accessing the Internet, we will come across texts (stories, ballads, legends) that help us much more easily discover, through a pertinent analysis, what are the main moral and physical features of these popular heroes. It is interesting to watch how the two historical characters become contemporaries by accessing specialized websites, and not only that, and how they can positively influence the virtual collective mind. Thus, this information puzzle represents a real support in the current endeavor, which consists in the contemporaneous placement of information regarding the outlaws Baba Novac and Gruia Novac

Discreteness Unravels the Black Hole Information Puzzle: Insights from a Quantum Gravity Toy Model.

The black hole information puzzle can be resolved if two conditions are met. The first is that the information about what falls inside a black hole remains encoded in degrees of freedom that persist after the black hole completely evaporates. These degrees of freedom should be capable of purifying the information. The second is if these purifying degrees of freedom do not significantly contribute to the system's energy, as the macroscopic mass of the initial black hole has been radiated away as Hawking radiation to infinity. The presence of microscopic degrees of freedom at the Planck scale provides a natural mechanism for achieving these two conditions without running into the problem of the large pair-creation probabilities of standard remnant scenarios. In the context of Hawking radiation, the first condition implies that correlations between the in and out Hawking partner particles need to be transferred to correlations between the microscopic degrees of freedom and the out partners in the radiation. This transfer occurs dynamically when the in partners reach the singularity inside the black hole, entering the UV regime of quantum gravity where the interaction with the microscopic degrees of freedom becomes strong. The second condition suggests that the conventional notion of the vacuum's uniqueness in quantum field theory should fail when considering the full quantum gravity degrees of freedom. In this paper, we demonstrate both key aspects of this mechanism using a solvable toy model of a quantum black hole inspired by loop quantum gravity.

The universality of black hole thermodynamics

The thermodynamic properties of black holes — temperature, entropy and radiation rates — are usually associated with the presence of a horizon. We argue that any extremely compact object (ECO) must have the same thermodynamic properties. Quantum fields just outside the surface of an ECO have a large negative Casimir energy similar to the Boulware vacuum of black holes. If the thermal radiation emanating from the ECO does not fill the near-surface region at the local Unruh temperature, then we find that no solution of gravity equations is possible. In string theory, black holes microstates are horizonless quantum objects called fuzzballs that are expected to have a surface [Formula: see text] outside [Formula: see text]; thus the information puzzle is resolved while preserving the semiclassical thermodynamics of black holes.

Evaporation and information puzzle for 2D nonsingular asymptotically flat black holes

We investigate the thermodynamics and the classical and semiclassical dynamics of two-dimensional (2D), asymptotically flat, nonsingular dilatonic black holes. They are characterized by a de Sitter core, allowing for the smearing of the classical singularity, and by the presence of two horizons with a related extremal configuration. For concreteness, we focus on a 2D version of the Hayward black hole. We find a second order thermodynamic phase transition, separating large unstable black holes from stable configurations close to extremality. We first describe the black-hole evaporation process using a quasistatic approximation and we show that it ends in the extremal configuration in an infinite amount of time. We go beyond the quasistatic approximation by numerically integrating the field equations for 2D dilaton gravity coupled to N massless scalar fields, describing the radiation. We find that the inclusion of large backreaction effects (N ≫ 1) allows for an end-point extremal configuration after a finite evaporation time. Finally, we evaluate the entanglement entropy (EE) of the radiation in the quasistatic approximation and construct the relative Page curve. We find that the EE initially grows, reaches a maximum and then goes down towards zero, in agreement with previous results in the literature. Despite the breakdown of the semiclassical approximation prevents the description of the evaporation process near extremality, we have a clear indication that the end point of the evaporation is a regular, extremal state with vanishing EE of the radiation. This suggests that the nonunitary evolution, which commonly characterizes the evaporation of singular black holes, could be traced back to the presence of the singularity.

A dialog on the fate of information in black hole evaporation

We present two alternative perspectives for the resolution of Hawking's information puzzle in black hole evaporation. The two views are deeply contrasting, yet they share several common aspects. One of them is the central role played by the existence of the interior singularity (whose physical relevance is implied by the singularity theorems of Penrose) that we expect to be replaced by a region described by a more fundamental quantum gravity formulation. Both views rely on the notion that the standard effective quantum field theoretic perspective would require some deep modifications. In this respect, both of our scenarios are deeply influenced by ideas that Penrose has advocated at various times and, thus, serves to illustrate the lasting influence that his deep thinking on these and related matters continues to have on the modern thinking about fundamental aspects of both quantum theory and gravitation. Despite that, there is of course no claim that Penrose would agree with any of the concrete proposals that will be discussed here.

The elastic vacuum

The quantum gravity vacuum must contain virtual fluctuations of black hole microstates. These extended-sized fluctuations get “crushed” when a closed trapped surface forms, and turn into on-shell “fuzzball” states that resolve the information puzzle. We argue that these same fluctuations can get “stretched” by the anti-trapped surfaces in an expanding cosmology, and that this stretching generates vacuum energy. The stretching happens when the Hubble deceleration reduces quickly, which happens whenever the pressure drops quickly. We thus get an inflation-scale vacuum energy when the heavy GUTS particles become nonrelativistic, and again a small vacuum energy when the radiation phase turns to dust. The expansion law in the radiation phase does not allow stretching, in agreement with the observed irrelevance of vacuum energy in that phase.

Unitarity and Information in Quantum Gravity: A Simple Example

In approaches to quantum gravity, where smooth spacetime is an emergent approximation of a discrete Planckian fundamental structure, any effective smooth field theoretical description would miss part of the fundamental degrees of freedom and thus break unitarity. This is applicable also to trivial gravitational field (low energy) idealizations realized by the use of Minkowski background geometry which, as with any other spacetime geometry, corresponds, in the fundamental description, to infinitely many different and closely degenerate discrete microstates. The existence of such microstates provides a large reservoir q-bit for information to be coded at the end of black hole evaporation and thus opens the way to a natural resolution of the black hole evaporation information puzzle. In this paper we show that these expectations can be made precise in a simple quantum gravity model for cosmology motivated by loop quantum gravity. Concretely, even when the model is fundamentally unitary, when microscopic degrees of freedom irrelevant to low-energy cosmological observers are suitably ignored, pure states in the effective description evolve into mixed states due to decoherence with the Planckian microscopic structure. Moreover, in the relevant physical regime these hidden degrees of freedom do not carry any “energy” and thus realize, in a fully quantum gravitational context, the idea (emphasized before by Unruh and Wald) that decoherence can take place without dissipation, now in a concrete gravitational model strongly motivated by quantum gravity. All this strengthens the perspective of a quite conservative and natural resolution of the black hole evaporation puzzle where information is not destroyed but simply degraded (made unavailable to low-energy observers) into correlations with the microscopic structure of the quantum geometry at the Planck scale.

Editorial

Black holes play a very prominent role in nowadays physics. For the discovery of a supermassive black hole in the center of our galaxy and for the theoretical description of black holes, the three physicists Reinhard Genzel, Andrea Ghez and Roger Penrose were honored by the Physics Nobel Prize of the year 2020. However, black holes are still very mysterious objects, both seen from theoretical, fundamental physics and concerning their role in astrophysics and the evolution of the Universe. There are several key questions: What is the quantum nature of black holes? In particular can one derive, possibly based on the holographic principle, a quantum description of black holes that provides a clue to the black hole information puzzle? New calculations of the so-called Page-curve, which describes the entropy of a decaying black hole, including the contribution of entanglement islands and gravitational wormholes opened up a promising avenue in the better understanding of Hawking radiation. Black holes and black hole decays also play a very prominent role in the ongoing swampland discussion about quantum gravity. Furthermore, can primordial black holes serve as viable dark matter candidates? We expect that the field black holes and their interrelation to quantum information, astrophysics and cosmology will further evolve during the next years and will give further new insights into the quantum nature of black holes and their role in the evolution of the universe. I wish all authors and readers of "Fortschritte der Physik” a happy and successful new year 2021.

Information recovery from pure state geometries in 3D

It is a well-studied phenomenon in AdS3/CFT2 that pure states often appear ‘too thermal’ in the classical gravity limit, leading to a version of the information puzzle. One example is the case of a heavy scalar primary state, whose associated classical geometry is the BTZ black hole. Another example is provided by a heavy left-moving primary, which displays late time decay in chiral correlators.In this paper we study a special class of pure state geometries which do not display such information loss. They describe heavy CFT states created by a collection of chiral operators at various positions on the complex plane. In the bulk, these take the form of multi-centered solutions from the backreaction of a collection of spinning particles, which we construct for circular distributions of particles. We compute the two-point function of probe operators in these backgrounds and show that information is retrieved.We observe that the states for which our geometric picture is reliable are highly extended star-like objects in the bulk description. This may point to limitations of semiclassical microstate geometries for understanding the information puzzle and to the need for including quantum effects.

Variations in the use and availability of formal and informal care at the end of life over time and space

Background In light of increasing death rates and a high need for palliative care at the end of life, it is important to plan formal care resources and understand in what ways informal care may alleviate the pressure on healthcare services. A piece to this information puzzle is understanding spatial variations in the use and availability of formal and informal care and how these develop over time.
 Aim This paper explores spatial variations in place of death and living arrangements (as proxy for informal care availability) in the last year of life in Scotland, comparing two time points.
 Data Analysis is based on population data from the Scottish Census 2001 and 2011 that was linked with NHS data and death records data for everyone who passed away within a year of census enumeration. Geographic data includes the Scottish urban-rural classification and healthboards.
 Methods Data was linked via probability linkage. Descriptive analysis and regression models will be presented.
 Results and Conclusions The study population comprises 49,356 cases from 2001/02 and 46,473 from 2011/12. Understanding how care use has changed over time and varies spatially is key to health and social care resource planning and social policy making.

The averaged null energy condition and the black hole interior in string theory

Recently it was shown that folded strings are spontaneously created behind the horizon of the SL(2,R)k/U(1) black hole. Here we show that these folded strings violate the averaged null energy condition macroscopically. We discuss possible consequences of this observation on black hole physics in general, and on the information puzzle in particular.

Emergent gravity from relatively local Hamiltonians and a possible resolution of the black hole information puzzle

In this paper, we study a possibility where gravity and time emerge from quantum matter. Within the Hilbert space of matter fields defined on a spatial manifold, we consider a sub-Hilbert space spanned by states which are parameterized by spatial metric. In those states, metric is introduced as a collective variable that controls local structures of entanglement. The underlying matter fields endow the states labeled by metric with an unambiguous inner product. Then we construct a Hamiltonian for the matter fields that is an endomorphism of the sub-Hilbert space, thereby inducing a quantum Hamiltonian of the metric. It is shown that there exists a matter Hamiltonian that induces the general relativity in the semi-classical field theory limit. Although the Hamiltonian is not local in the absolute sense, it has a weaker notion of locality, called relative locality : the range of interactions is set by the entanglement present in target states on which the Hamiltonian acts. In general, normalizable states are not invariant under the transformations generated by the Hamiltonian. As a result, a physical state spontaneously breaks the Hamiltonian constraint, and picks a moment of time. The subsequent flow of time can be understood as a Goldstone mode associated with the broken symmetry. The construction allows one to study dynamics of gravity from the perspective of matter fields. The Hawking radiation corresponds to a unitary evolution where entanglement across horizon is gradually transferred from color degrees of freedom to singlet degrees of freedom. The underlying quantum states remain pure as evaporating black holes keep entanglement with early Hawking radiations in the singlet sector which is not captured by the Bekenstein-Hawking entropy.

The Hawking paradox and the Bekenstein resolution in higher-dimensional spacetimes

The black-hole information puzzle, first discussed by Hawking four decades ago, has attracted much attention over the years from both physicists and mathematicians. One of the most intriguing suggestions to resolve the information paradox is due to Bekenstein, who has stressed the fact that the low-energy part of the semi-classical black-hole emission spectrum is partly blocked by the curvature potential that surrounds the black hole. As explicitly shown by Bekenstein, this fact implies that the gray-body emission spectrum of a (3+1)-dimensional black hole is considerably less entropic than the corresponding radiation spectrum of a perfectly thermal black-body emitter. Using standard ideas from quantum information theory, it was shown by Bekenstein that, in principle, the filtered Hawking radiation emitted by a (3+1)-dimensional Schwarzschild black hole may carry with it a substantial amount of information, the information which was suspected to be lost. It is of physical interest to test the general validity of the “information leak” scenario suggested by Bekenstein as a possible resolution to the Hawking information puzzle. To this end, in the present paper we analyze the semi-classical entropy emission properties of higher-dimensional black holes. In particular, we provide evidence that the characteristic Hawking quanta of (D+1)-dimensional Schwarzschild black holes in the large D≫1 regime are almost unaffected by the spacetime curvature outside the black-hole horizon. This fact implies that, in the large-D regime, the Hawking black-hole radiation spectra are almost purely thermal, thus suggesting that the emitted quanta cannot carry the amount of (non-thermal) information which is required in order to resolve the information paradox. Our analysis therefore suggests that the elegant information leak scenario suggested by Bekenstein, which is based on the effective gray-body (rather than a black-body) nature of the black-hole emission spectra, cannot provide a generic resolution to the intriguing Hawking information paradox.

Editorial

The first discovery of gravitational waves in September 2015 has spectacularly exhibited the merging of two black holes, each of about 30 solar masses. For this discovery, which was a fantastic confirmation of Einstein's prediction of gravitational waves, the three physicists Barry Barish, Kip Thorne and Rainer Weiss were honored by the Physics Nobel Prize of the year 2017. However, black holes are still very mysterious objects, both seen from theoretical, fundamental physics and concerning their role in astrophysics and the evolution of the Universe. There are several key questions: What is the quantum nature of black holes? In particular, can one derive, possibly based on the holographic principle, a quantum description of black holes that provides a clue to the black hole information puzzle? Can newly discussed classical BMS-like symmetries, related to soft graviton emission, help to shed more light on Hawking radiation and the black hole entropy. Can astrophysical measurements reveal deviations from general relativity that hint at quantum effects? Can primordial black holes serve as viable dark matter candidates? We expect that the field of gravitational waves, black holes and their interrelation to quantum information will further evolve during the next years and will give further new insights into the quantum nature of black holes. We wish all authors and readers of “Fortschritte der Physik” a happy and successful new year 2018. Dieter Lüst (Editor) Wolfgang P. Schleich (Co-Editor)

Coarse Graining Shannon and von Neumann Entropies

The nature of coarse graining is intuitively “obvious”, but it is rather difficult to find explicit and calculable models of the coarse graining process (and the resulting entropy flow) discussed in the literature. What we would like to have at hand is some explicit and calculable process that takes an arbitrary system, with specified initial entropy S, and that monotonically and controllably drives the entropy to its maximum value. This does not have to be a physical process, in fact for some purposes it is better to deal with a gedanken-process, since then it is more obvious how the “hidden information” is hiding in the fine-grain correlations that one is simply agreeing not to look at. We shall present several simple mathematically well-defined and easy to work with conceptual models for coarse graining. We shall consider both the classical Shannon and quantum von Neumann entropies, including models based on quantum decoherence, and analyse the entropy flow in some detail. When coarse graining the quantum von Neumann entropy, we find it extremely useful to introduce an adaptation of Hawking’s super-scattering matrix. These explicit models that we shall construct allow us to quantify and keep clear track of the entropy that appears when coarse graining the system and the information that can be hidden in unobserved correlations (while not the focus of the current article, in the long run, these considerations are of interest when addressing the black hole information puzzle).

Relativistic collapse dynamics and black hole information loss

We study a proposal for the resolution of the black hole information puzzle within the context of modified versions of quantum theory involving spontaneous reduction of the quantum state. The theories of this kind, which were developed in order to address the so called "measurement problem" in quantum theory have, in the past, been framed in a non-relativistic setting and in that form they were previously applied to the black hole information problem. Here, and for the first time, we show in a simple toy model, a treatment of the problem within a fully relativistic setting. We also discuss the issues that the present analysis leaves as open problems to be dealt with in future refinements of the present approach.

Sub-Saharan red cell antigen phenotypes and glucose-6-phosphate dehydrogenase deficiency variants in French Guiana.

Background The treatment of Plasmodium vivax infections requires the use of primaquine, which can lead to severe haemolysis in glucose-6-phosphate dehydrogenase (G6PD)-deficient individuals. However, most of the Latin American countries, which are still endemic for vivax malaria, lack information on the distribution of G6PD deficiency (G6PDd). No survey has been performed so far in French Guiana. Herein, 80 individuals of the French Guianan Noir Marron population were scrutinized for red cell surface antigens of six blood group systems (ABO, Rh, Kell, Kidd, Duffy and MNS) and G6PD genetic polymorphisms. First, the sub-Saharan origin of the red cell phenotypes was assessed in relation with the literature. Then, given that the main sub-Saharan G6PDd variants are expected to be encountered, only the G6PD sequences of exons 4, 5, 6 and 9 were screened. This work aims at appraising the G6PD gene variation in this population, and thus, contributing to the G6PD piecemeal information in Latin America.ResultsNinety-seven percent (97 %) of the red cells are Fy(a− b−), either D+ C− E− c+ e+ or D+ C+ E− c+ e+ and 44 % exhibited the Fya−/Jkb−/S− combined phenotype. Noteworthy is the detection of the G6PD(Val68Met) variant characterized by c.202G > A transition, G6PD(Asn126Asp) variant characterized by c.376A>G transition and G6PD(Asp181Val) variant characterized by c.542A>T transversion of the G6PD gene in 22.5 % of the sample, characteristic of the A−(202), A and Santamaria G6PDd variants, respectively.ConclusionsFrench Guianan Noir Marron population represents a pool of Rh-D antigen positive, Duffy-negative and G6PD-deficient erythrocytes, the latter accounting for one in every eight persons. The present study provides the first community-based estimation of the frequency of G6PDd polymorphisms in French Guiana. These results contribute to the G6PD genetic background information puzzle in Latin America.

Quantum-gravity effects outside the horizon spark black to white hole tunneling

We show that there is a classical metric satisfying the Einstein equations outside a finite spacetime region where matter collapses into a black hole and then emerges from a white hole. We compute this metric explicitly. We show how quantum theory determines the (long) time for the process to happen. A black hole can thus quantum-tunnel into a white hole. For this to happen, quantum gravity should affect the metric also in a small region outside the horizon: we show that contrary to what is commonly assumed, this is not forbidden by causality or by the semiclassical approximation, because quantum effects can pile up over a long time. This scenario alters radically the discussion on the black hole information puzzle.

Stringy horizons and UV/IR mixing

The target-space interpretation of the exact (in $\alpha'$) reflection coefficient for scattering from Euclidean black-hole horizons in classical string theory is studied. For concreteness, we focus on the solvable $SL(2, \mathbb{R})_k/U(1)$ black hole. It is shown that it exhibits a fascinating UV/IR mixing, dramatically modifying the late-time behavior of general relativity. We speculate that this might play an important role in the black-hole information puzzle, as well as in clarifying features related with the non-locality of Little String Theory.

Estimation of K-WAIS-IV Premorbid Intelligence in South Korea: Development of the KPIE-IV

Objective: The accurate estimation of premorbid intellectual functioning in patients with known or suspected cognitive impairment is crucial for clinicians. However, there is no reliable method for estimating premorbid intelligence in South Korea. The purpose of this study was to develop the Korea Premorbid Intelligence Estimate (KPIE) as an estimate of the premorbid intellectual functioning. Method: Data from the Korean WAIS-IV standardization sample were used to generate several Full Scale Intelligence Quotient (FSIQ) estimation formulas using demographic variables and current WAIS-IV subtest performance. The standardization sample (N = 1216) was randomly divided into two groups: the first group was used to develop the formulas and the second group was used to validate the prediction equations. Age, education, gender, region of the country, and select subtest raw scores (Vocabulary, Information, Matrix Reasoning, and Visual Puzzle) were used as predictor variables. Results: Five KPIE-4 equations were generated. Estimated FSIQ derived from the KPIE-4 equation is highly correlated with K-WAIS-IV FSIQ. Conclusions: The resulting formulas for estimating premorbid FSIQ were highly significant and precise in predicting FSIQ scores of participants in the K-WAIS-IV normative sample. These equations provide a means for clinicians to estimate intellectual functioning in adults, and can be utilized as a method of estimating individuals premorbid functioning.