Quantum Compositeness of Gravity: Black Holes, AdS and Inflation

Abstract: Gravitational backgrounds, such as black holes, AdS, de Sitter and inflationary universes, should be viewed as composite of N soft constituent gravitons. It then follows that such systems are close to quantum criticality of graviton Bose-gas to Bose-liquid transition. Generic properties of the ordinary metric description, including geodesic motion or particle-creation in the background metric, emerge as the large-N limit of quantum scattering of constituent longitudinal gravitons. We show that this picture correctly accounts for physics of large and small black holes in AdS, as well as reproduces well-known inflationary predictions for cosmological parameters. However, it anticipates new effects not captured by the standard semi-classical treatment. In particular, we predict observable corrections that are sensitive to the inflationary history way beyond last 60 e-foldings. We derive an absolute upper bound on the number of e-foldings, beyond which neither de Sitter nor inflationary Universe can be approximated by a semi-classical metric. However, they could in principle persist in a new type of it quantum eternity state. We discuss implications of this phenomenon for the cosmological constant problem.

• The paper demonstrates that black holes, AdS spaces, and inflation emerge as composite states of soft gravitons near a quantum critical point.
• The paper introduces a large-N quantum scattering framework that reproduces classical gravitational phenomena and predicts novel inflationary corrections.
• The paper suggests that nearly-gapless Bogoliubov modes in the graviton condensate underpin holographic features, affecting black hole evaporation and cosmology.

Quantum Compositeness of Gravity: Black Holes, AdS, and Inflation

The paper "Quantum Compositeness of Gravity: Black Holes, AdS, and Inflation," authored by Gia Dvali and Cesar Gomez, endeavors to provide a quantum mechanical reinterpretation of classical gravitational phenomena. This work suggests that gravitational entities, such as black holes, anti-de Sitter (AdS) spaces, and inflationary universes, can be described as composite systems formed by soft gravitons, a view that departs from traditional classical treatments.

Key Concepts and Findings

1. Quantum Compositeness and Criticality: The authors propose that black holes, AdS spaces, and inflationary universes are composite states consisting of a large number of soft gravitons. These systems are described as being near a quantum critical point, which corresponds to the transition from a graviton Bose-gas to a Bose-liquid phase.
2. Emergence of Classical Gravity: The paper outlines how classical gravitational phenomena can emerge as large-$N$ limits of quantum scattering processes involving constituent gravitons. This framework provides an alternative to the traditional metric description of gravity, effectively bridging the gap between quantum mechanics and classical general relativity.
3. Novel Predictions for Inflation: The authors examine the implications of their approach for inflationary cosmology, noting that it can reproduce known inflationary predictions for cosmological parameters. Notably, the paper predicts new observable corrections informed by the complete inflationary history, suggesting that there exist effects sensitive to the entire inflationary timeline beyond the traditional last 60 e-folds. An absolute upper bound on the number of e-foldings is derived, beyond which neither a de Sitter nor an inflationary universe can maintain a quasi-classical description.
4. Holography and Quantum Mechanics: The paper suggests a potential quantum foundation for holography, emphasizing that near the quantum critical point, a system of gravitons exhibits a significant number of nearly-gapless Bogoliubov modes which behave conformally. This interpretation offers a new perspective on the holographic principle, particularly within the context of the AdS/CFT correspondence, attributing holographic features to the quantum compositeness of the gravitational systems.

Implications

Practically, this reinterpretation affects the understanding of black hole evaporation, AdS/CFT duality, and the nature of cosmological inflation. The consideration of these systems as quantum states consisting of constituent gravitons could provide new insights into gravitational entropy and information paradoxes, suggesting, for instance, that particle emission from a black hole is not a vacuum process but a result of graviton depletion. Theoretically, it pushes forward the idea that holographic principles may naturally arise from quantum characteristics of gravitational systems.

Future Developments

The findings and ideas presented in this paper invite further exploration, inviting research that explores:

• The robustness of the graviton composite model in different gravitational backgrounds.
• The implications of these ideas on the cosmological constant problem and the consistency of de Sitter space.
• The potential for this framework to solve longstanding challenges within quantum gravity, such as the quantum mechanics of black holes and the reconciliation of gravitational dynamics with quantum physics.

Overall, this paper proposes a paradigm shift in understanding gravitational systems, attributing classical gravitational phenomena to underlying quantum mechanical interactions involving soft gravitons and reshaping our comprehension of gravity at both macroscopic and microscopic scales.