The Quantum Structure of Black Holes and the Recovery of Information

Project Information

QBH Structure

Grant agreement ID: 787320

DOI

10.3030/787320

Project closed

EC signature date 28 June 2018

Start date 1 January 2019

End date 30 September 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 462 659,00

EU contribution

€ 2 462 659,00

Coordinated by

COMMISSARIAT A L ENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES
France

Periodic Reporting for period 4 - QBH Structure (The Quantum Structure of Black Holes and the Recovery of Information)

Reporting period: 2023-07-01 to 2024-09-30

Summary of the context and overall objectives of the project

This project addressed foundational issues about black holes and what happens to the matter that falls into them. Conventional combinations of general relativity and quantum mechanics lead to a deep conflict that is best characterized through the information paradox: Hawking showed that quantum black holes will ultimately radiate away all their mass, or evaporate, into a largely featureless cloud of thermal radiation. This radiation is independent of how the black hole formed and so it is impossible to use it to reconstruct the initial state of the matter that made the black hole. Such a loss of information is fundamentally incompatible with the precepts of quantum mechanics, and this is the core of the Information Paradox.

Since quantum mechanics and general relativity are essential to the technological functioning of modern society (through things like microprocessors and global positioning systems), it is essential to resolve conflicts between these two extremely important theories of Nature. By trying to resolve the conflict, we have learnt much about behaviour of black holes, the quantum properties of matter near black holes, and even some aspects of the quantum structure of space and time.

This project used string theory and higher-dimensional theories of gravity, to reveal the quantum properties of black holes through the construction and analysis of “microstate geometries.” The research focussed on the construction of such geometries and the dynamics of matter falling into them. We showed that microstate geometries can replicate the properties of black holes but without producing an information paradox. Indeed, microstate geometries can absorb infalling matter, much like black holes, but then the matter is scrambled into the structure of the microstate geometry. Ultimately the signatures of the matter become encoded into an analog of Hawking radiation. In this way one can ultimately recover all the information about how the black hole formed, and thus avoid the information paradox.

In this project we showed how this works for special classes of idealized black holes and developed a pathway to realizing these ideas and processes in more realistic astrophysical black holes.

One of the most important conclusions of this project is that new microstructure must be present at the horizon-scale of the black hole. We showed how this structure could be supported against the incredible gravitational forces at this scale, and showed how it results in new physics at the horizon scale. By exploring the similarities and differences in the predictions coming from the black holes of General Relativity and microstate geometries of string theory, we were able to compute and characterize potential macroscopic, measurable signatures of the horizon-scale microstructure. We also showed how black holes could be used as naturally-occurring particle accelerators to probe not only the horizon-scale microstructure but also to probe Planck-scale physics, and string theory in particular.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project progressed extremely well, realizing all its objectives. It led to 105 publications, of which 82 have already appeared in refereed journals. All of the publications are available on open-access servers.

We organized and held ten very successful Conferences/Workshops:

Black-Hole Microstructure Workshop – May 27-31, 2019
Black-Hole Microstructure Conference I - June 8-12, 2020 (23 speakers, 285 participants)
Black-Hole Microstructure Conference II - December 9-11, 2020 (17 speakers, 120 participants)
Black-Hole Microstructure Conference III - June 7-11, 2021 (20 speakers, 259 participants)
Black-Hole Microstructure Conference IV - June 6-10, 2022 (20 speakers, 138 participants)
Black-Hole Microstructure Workshop IV - June 13-17, 2022 (40 participants)
Black-Hole Microstructure Conference V - June 5-9, 2023 (20 speakers, 74 participants)
Black-Hole Microstructure Workshop V - June 12-16, 2023 (40 participants)
Black-Hole Microstructure Conference VI - June 10-14, 2024 (20 speakers, 89 participants)
Black-Hole Microstructure Workshop VI - June 17-21, 2024 (40 participants)

All the conference talks are freely available on YouTube.

We also organized three training programs/lecture courses for students, post-docs and researchers:

Lectures on Microstate Geometries: 4 x 2 hours of lectures with recordings and lecture notes. Given by Warner in May 2019
Lectures on Superstrata Construction: 4 x 2 hours of lectures with recordings and lecture notes. Given by Warner in October/November 2020
Virtual Workshop on Black-Hole Information conducted by Samir Mathur: 5 x 2 hours of lectures and discussions; May, 2021

Members of the QBHStructure team have given many plenary conference talks. Bena, Mayerson and Warner attended, and have given talks at meetings with members of the LIGO, LISA and EHT collaborations. We have developed dialogues about possible observable signatures of microstate structure. This initiative was greatly advanced in the six Black-Hole Microstructure conferences at which 20% of the time was dedicated to exploring how microstructure might give rise to observational signatures. The project led to multiple publications that calculated and explored how microstructure might ultimately be detected.

Warner did several public outreach activities on black holes and black-hole microstructure, ranging from interviews on YouTube to being a science consultant for NOVA, Universe Revealed: Black Holes.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The entire QBHStructure project was about breaking new ground and creating a paradigm shift in the analysis of black holes; going beyond the dominance of General Relativity to create more precise models based on theories (like string theory) that are not only viable theories of quantum gravity but are also able to go beyond the rigidity of uniqueness theorems and support horizon-scale microstructure.

In the last decade, the study of possible new horizon-scale physics has become a wide-ranging and growing enterprise pursued by many groups. Because of the highly visible achievements of the QBHStructure project, the Fuzzball and Microstate Geometry programs have become firmly established in black-hole physics, and in the planning for future observational detection strategies. Indeed, the QBHStructure project represents the state of the art when it comes to grounding horizon-scale physics in real mechanisms that can support new structures that are emerging at the horizon.

The QBHStructure project revealed new details of how Infalling matter interacts with black-hole microstructure to create extremely high-energy interactions at scales at which quantum gravity is expected to be important. Thus, a complete and accurate picture of black-hole microstructure must ultimately be framed in quantum gravity. The fact that Microstate Geometries emerge as coherent expressions of string theory (and Fuzzballs) means that they are ideally adapted to meet this challenge. Conversely, understanding Microstate Geometries in terms of string theory provides an immensely powerful platform for computing the detailed properties and consequences of the microstructure, especially when combined with the insights that are gained from another avatar of string theory: holographic field theory.

Simply put, the QBHStructure project has been instrumental in shifting the needle on the discussion, and computation, of possible new physics at black-hole horizon scales.

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