Simple holographic models of black hole evaporation (1910.00972v2)

Abstract: Several papers have shown a close relationship between entanglement wedge reconstruction and the unitarity of black hole evaporation in AdS/CFT. The analysis of these papers however has a rather puzzling feature: all calculations are done using bulk dynamics which are essentially those Hawking used to predict information loss, but applying ideas from entanglement wedge reconstruction seems to suggest a Page curve which is consistent with information conservation. Why should two different calculations in the same model give different answers for the Page curve? In this note we present a new pair of models which clarify this situation. Our first model gives a holographic illustration of unitary black hole evaporation, in which the analogue of the Hawking radiation purifies itself as expected, and this purification is reproduced by the entanglement wedge analysis. Moreover a smooth black hole interior persists until the last stages the evaporation process. Our second model gives an alternative holographic interpretation of the situation where the bulk evolution leads to information loss: unlike in the models proposed so far, this bulk information loss is correctly reproduced by the entanglement wedge analysis. This serves as an illustration that quantum extremal surfaces are in some sense kinematic: the time-dependence of the entropy they compute depends on the choice of bulk dynamics. In both models no bulk quantum corrections need to be considered: classical extremal surfaces are enough to do the job. We argue that our first model is the one which gives the right analogy for what actually happens to evaporating black holes, but we also emphasize that any complete resolution of the information problem will require an understanding of non-perturbative bulk dynamics.

An Analysis of Simple Holographic Models of Black Hole Evaporation

The paper "Simple holographic models of black hole evaporation" by Chris Akers, Netta Engelhardt, and Daniel Harlow explores the intricate relationship between black hole evaporation dynamics and entanglement in the context of holography. The authors aim to elucidate the ostensibly discordant results between classical and quantum approaches to black hole information frameworks, particularly by juxtaposing findings from different models of black hole evaporation. The paper leverages the framework of AdS/CFT correspondence and entanglement wedge reconstruction to propose novel models that depict scenarios of both unitary and non-unitary black hole evaporation.

At the core, the paper addresses a puzzling observation: results suggesting information conservation amid black hole evaporation, when evaluated using the entanglement wedge reconstruction in AdS/CFT, contrasted with traditional bulk dynamics indicating information loss. This apparent inconsistency arises from the divergence between quantum extremal surfaces, which suggest the expected behavior of the Page curve, and classical approaches following Hawking's prediction of information loss.

Key Contributions:

1. Unitary Black Hole Evaporation Model: The authors present a model where the emitted radiation leads to purification, in line with entropic expectations of unitarity. The entanglement wedge reconstruction supports this, proposing that the formation of a quantum extremal surface inside the horizon progressively aligns with diminishing black hole entropy, reflecting the Page curve. This model intriguingly maintains a smooth black hole interior throughout the evaporation, reinforcing the possibility of capturing quantum characteristics indicative of information conservation.
2. Information Loss Through Alternative Interpretation: In contrast, the authors hypothesize another model reflecting information loss, demonstrating that the bulk dynamics can be adjusted so that the entanglement wedge analysis corroborates the lost information scenario. This is particularly insightful as it advances understanding of quantum extremal surfaces' kinematic nature—how the computed entropy's temporal profile is contingent upon the chosen bulk dynamics.
3. Impetus on Classical Extremal Surfaces: Notably, both models operate without invoking bulk quantum corrections, relying instead on classical extremal surfaces to account for entropy calculations. This elemental approach crucially highlights how classical dynamics can still encapsulate significant complexity and meet the aforementioned quantum expectations.

Implications and Future Directions:

The paper's findings bear significant implications for theoretical physics, suggesting that the journey towards resolving the black hole information paradox may profit from focusing on bulk dynamics that transcend Hawking-style perturbative approaches. The need to incorporate non-perturbative effects to achieve a truly comprehensive understanding of black hole systems inherently demands a revisitation of classical dynamics vis-à-vis their quantum counterparts.

Furthermore, the work underscores the necessity of bridging discordant predictions between bulk and boundary theories to maintain a coherent holographic narrative—a critical step towards cementing our understanding of the Page curve and the ultimate fate of the information encoded within evaporating black holes.

By methodically deconstructing these models, the authors set a foundation that not only challenges conventional interpretations of black hole dynamics but also paves the way for future investigations targeting comprehensive, realistic models of black hole evaporation. As the quest for reconciling general relativity and quantum mechanics continues, such investigations are indispensable for progressing towards a theory of quantum gravity.