Island Hopping 2020: from Wormholes to Averages

16 Nov 2020, 09:00 → 20 Nov 2020, 22:00 Europe/Zurich

Virtual conference only (CERN)

Welcome to Island Hopping 2020, a workshop that will be held entirely virtually!

 

The focus will be on recent developments around the information paradox, quantum extremal surfaces and islands, generalized entropies, the Euclidean path integral in quantum gravity and the importance of spacetime wormholes, as well as the role of ensemble averages in holography. It will be held from November 16-20 2020.

Confirmed Speakers:

Ahmed Almheiri - Raphael Bousso - Alejandra Castro - Jan de Boer - Steve Giddings - Daniel Harlow - Tom Hartman - Daniel Jafferis - Kristan Jensen - Clifford Johnson - Hong Liu - Alex Maloney - Juan Maldacena - Henry Maxfield - Geoff Penington - Andrea Puhm - Suvrat Raju - Phil Saad - Edgar Shaghoulian - Julian Sonner - Douglas Stanford - James Sully - Mark Van Raamsdonk - Herman Verlinde - Ying Zhao

Recordings and Slides:

The slides of the presentations can be found in the contributions list, by clicking on a particular talk. Video recordings will be made available as the conference goes on, please see the appropriate tab.

 

Pre-conference tutorials

Coorganized with Jonathan Oppenheim, pre-conference tutorials were held on Friday Nov. 13 for younger students or participants who are less familiar with the topics of the conference. The lecturers are Raghu Mahajan and Dominik Neuenfeld. Please find additional information in the relevant tab, including a link to the recordings.

Schedule

Talks and panel discussions will be held in two sessions each day:

Central European: 16:00 - 18:00 and 20:00 - 22:00

Eastern:                 10:00 - 12:00 and 14:00 - 16:00

Pacific Coast:         07:00 - 09:00 and 11:00 - 13:00

The detailed schedule can be found in the programme tab on the right.

There will be opportunities for informal discussions and social interactions in between these 2 sessions, which will happen on gather.town.

 

Organizers: A. Belin, N. Engelhardt, R. Myers

 

The registration deadline is Monday November 9th. Please click on the registration tab.

This workshop acknowledges funding from the "It from Qubit" Simons collaboration.

 

Monday 16 November

16:00 → 17:00 Causal symmetry breaking: the EFT description of quantum chaos

Abstract:

Quantum chaotic systems are often defined via the assertion that their spectral statistics coincides with, or is well approximated by, random matrix theory. In this talk I will explain how the universal content of random matrix theory emerges as the consequence of a simple symmetry-breaking principle and its associated Goldstone modes. This approach gives a natural way to identify wormhole-like correlations, even for individual theories.
I will also discuss how to extend the Goldstone effective-field-theory approach to study operator correlation functions, and present some thoughts on how to understand causal symmetry breaking in holographic bulk gravity.

Speaker: Julian Sonner

CERNIslandHopping2020Final.pdf

Recording_JulianSonner

17:00 → 18:00 The time to the black hole singularity from thermal one point functions

Speaker: Juan Maldacena

Recording_JuanMaldacena

TimeToSingularity.pdf

18:00 → 20:00 Informal interactions/Virtual hanging

20:00 → 21:00 Global symmetry, Euclidean gravity, and the black hole information problem

Speaker: Daniel Harlow

islandhopping.pdf

Recording_DanielHarlow

21:00 → 22:00 Discussion Session: To average or not to average

Speakers: Douglas Stanford, Raphael Bousso, Steve Giddings

Recording_Discussion

Tuesday 17 November

16:00 → 17:00 Collision in the interior of wormhole

Abstract:

The Schwarzschild wormhole has been interpreted as an entangled state. If Alice and Bob fall into each of the black hole, they can meet in the interior. We interpret this meeting in terms of the quantum circuit that prepares the entangled state. Alice and Bob create growing perturbations in the circuit, and we argue that the overlap of these perturbations represents their meeting. We compare the gravity picture with circuit analysis, and identify the post-collision region as the region storing the gates that are not affected by any of the perturbations.

Speaker: Ying Zhao

Recording_YingZhao

slides.pdf

17:00 → 18:00 Islands beyond AdS

Abstract:

I will discuss the appearance of islands and replica wormholes in flat and cosmological spacetimes. I will also discuss general consistency conditions that guide the search for such nontrivial saddles in the gravitational path integral.

Speaker: Edgar Shaghoulian

IslandsBeyondAdS.pdf

Recording_EdgarShaghoulian

18:00 → 20:00 Informal interactions/Virtual hanging

20:00 → 21:00 Observations of Hawking radiation: the Page curve and baby universes

Abstract:

It has long been argued that black holes can be modeled as unitary quantum systems with density of states given by the Bekenstein-Hawking formula. It now seems that this idea is realised within semiclassical gravity, without using details of the UV completion or assuming duality. I will describe this in an asymptotically flat setting using Lorentz-signature gravitational path integrals, concentrating on the predictions for observables. However, for this semiclassical picture to be coherent, we are forced to conclude that there are superselection sectors for asymptotic observers. These sectors are associated with the states of baby universes, which appear when we consider the Hilbert space interpretation of replica wormholes.

Speaker: Henry Maxfield

20-11-IslandHopping.pdf

Recording_HenryMaxfield

21:00 → 22:00 Perturbative and Non-Perturbative Insights into Deformed JT Gravity using Random Matrix Ensembles.

Speaker: Clifford Johnson

Island_Hopping_Talk_November_2020_Johnson.pdf

Recording_CliffordJohnson

Wednesday 18 November

16:00 → 17:00 A general approximation scheme for addressing the black hole information paradox

Abstract:

We develop a general approximation scheme for calculating quantum informational properties of a pure state that has equilibrated in a non-integrable quantum many-body system. For gravity systems, such as those involving black holes, this approximation gives a prescription for calculating entanglement entropies using Euclidean path integrals which is manifestly consistent with unitarity. Applied to recent models of evaporating black holes and eternal black holes coupled to baths, it provides a derivation of replica wormholes, and elucidates their mathematical and physical origins. In particular, it shows that replica wormholes can arise in a system with a fixed Hamiltonian, without the need for ensemble averages.

Speaker: Hong Liu

Island1.pdf

Recording_HongLiu

17:00 → 18:00 To average or not to average

Abstract:
In this talk I will describe a possible interpretation of genus two wormholes in AdS3 in terms of a
suitable averaging procedure in the dual field theory, and connect this to random properties of
OPE coefficients. I will discuss possible lessons from this for the question whether or not gravity
is intrinsically an averaged theory. Mostly based on arXiv:2006.05499 with Alex Belin.

Speaker: Jan de Boer

islands1120.pdf

Recording_JandeBoer

18:00 → 20:00 Informal interactions/Virtual hanging

20:00 → 21:00 Gravity without Ensembles

Speaker: Jamie Sully

Recording_JamieSully

21:00 → 22:00 Discussion: Firewalls

Speakers: Ahmed Almheiri, Daniel Jafferis, Herman Verlinde

Recording_Firewallsdiscussion

Thursday 19 November

16:00 → 17:00 Holographic duality for averaged free CFTs

Abstract:
I will describe how the modular bootstrap leads us toward a holographic duality for 2d Narain CFTs averaged over moduli. The bulk theory is a 3d Chern-Simons-like theory of "U(1) gravity." Although this theory has no Einstein term, it has composite gravitons and other features similar to ordinary 3d gravity, so it may be a good place to test ideas about ensemble averaging in holographic duality.

Speaker: Tom Hartman

narain-island-hopping-2020.pdf

Recording_TomHartman

17:00 → 18:00 More on Holographic duality for averaged free CFTs

Abstract:
I will continue to explore the idea that certain theories of gravity in Anti-de Sitter space are dual to an average over an ensemble of quantum theories, rather than to a specific quantum theory. The average over Narain’s family of two-dimensional conformal field theories which describe free bosons is given by the Siegel-Weil formula, which can be computed at any genus and for disconnected boundaries. The result takes the form of a sum over geometries as one would expect in a theory of gravity. But the gravitational theory looks more like a Chern-Simons theory than like Einstein gravity, and several mysteries remain.

Speaker: Alex Maloney

Islands_Workshop.pdf

Recording_AlexMaloney

18:00 → 20:00 Informal interactions/Virtual hanging

20:00 → 21:00 Some comments on wormholes and factorization

Abstract:
Spacetime wormholes have played an important role in recent progress in black hole physics. However, in the context of AdS/CFT, these wormholes lead to a basic puzzle: the "factorization problem", introduced by Maldacena and Maoz. In this talk we will explore this issue in some simple models, including Marolf and Maxfield's topological model, JT gravity, and the SYK model. These models are described by ensemble averages of quantum systems; the factorization problem is solved by focusing on single members of the ensemble. In gravitational theories like JT gravity and the topological model, this involves introducing many additional spacetime boundaries in path integral computations. We find that there is a simple effective description common to these models, where the many additional boundaries are replaced by a single "dynamical" boundary. A variant of this effective description also applies to the SYK model. This effective description involves a peculiar modification to the sum over geometries; it requires us to identify a ``diagonal'' subset of the contributions of the dynamical boundaries with the wormhole. This rule has somewhat different origins in the full description of the gravitational theories and the SYK model. We briefly comment on how this might be relevant to conventional, non-averaged AdS/CFT.

Speaker: Phil Saad

Recording_PhilSaad

SlidesConference.pdf

21:00 → 22:00 Wormholes, random matrices, and (non-)factorization in d>2

Abstract:

In the first half of this talk, I will discuss wormholes in pure 3d Euclidean gravity with negative cosmological constant. We compute a wormhole amplitude, the path integral over Euclidean spaces which smoothly connect two hyperbolic regions with torus boundary and topology torus times line. This is a 3d version of the “double trumpet” of JT gravity. From this amplitude we extract the leading two-point fluctuation statistics of highly spinning BTZ microstates near threshold. These statistics precisely match a random matrix ansatz. This is evidence that, if 3d gravity is a consistent theory of gravity, then it is dual to an ensemble rather than a single CFT.

In the second half, I will discuss recent progress in constructing Euclidean wormholes in d>2 dimensional pure Einstein gravity. These configurations are also generalizations of the JT double trumpet, in particular they are not saddle points of the gravity action. They are instead “constrained instantons.” For fixed bottleneck size, we have shown that some of these wormholes are completely stable in Einstein gravity. These wormholes can be easily embedded into supergravity, in which they are generically unstable to brane nucleation. However, we find a class of wormholes with AdS-scale bottlenecks in EAdS_5 x S^5 supergravity which are stable against obvious potential brane instabilities. These wormholes may pose a factorization paradox for the duality between N=4 super Yang-Mills and IIB string theory on AdS_5 x S^5.

Speaker: Kristan Jensen

islands_jensen.pdf

Recording_KristanJensen

Friday 20 November

16:00 → 17:00 Gravitational Perturbations of Extreme Kerr Revisited

Speaker: Alejandra Castro

Kerr Perturbations Talk 2020.pdf

Recording_AlejandraCastro

17:00 → 18:00 Discussion: The Final State

Speakers: Andrea Puhm, Juan Maldacena, Suvrat Raju

Recording_FinalStateDiscussion

18:00 → 20:00 Informal interactions/Virtual hanging

20:00 → 21:00 Life without pythons would be so simple

Speaker: Geoff Penington

GeoffIslandHoppingSlides.pdf

Recording_GeoffPenington

21:00 → 22:00 Confinement, Wormholes, and Cosmology

Speaker: Mark Van Raamsdonk

IslandHopping.pdf

Recording_MarkVanRaamsdonk