Quantum gravity is concerned with unifying Einstein's general theory of relativity with quantum theory into a single theoretical framework. At Perimeter Institute, researchers are actively pursuing a number of approaches to this problem including loop quantum gravity, spin foam models, asymptotic safety, emergent gravity, string theory, and causal set theory. We are also particularly interested in experimental implications of these different proposals. As the aim is a unification of the laws of physics into a single theory, the search for quantum gravity overlaps with other areas such as cosmology, particle physics and the foundations of quantum theory.
Format results

62 talksCollection Number C16003
Talk


Gravity Basics  1
Veronika Hubeny University of California System

QI Basics  1
Patrick Hayden Stanford University

Entanglement  1
Robert Spekkens Perimeter Institute for Theoretical Physics

GR: Actions and Equations
David Kubiznak Charles University

A new perspective on holographic entanglement
Matthew Headrick Brandeis University

Bell’s Theorem
Adrian Kent University of Cambridge

QI Basics  2
John Watrous IBM (Canada)


Time in Cosmology
14 talksCollection Number C16016Talk

Welcome and Opening Remarks

Marina Cortes Institute for Astrophysics and Space Sciences

Lee Smolin Perimeter Institute for Theoretical Physics

Neil Turok University of Edinburgh


The origin of arrows and time I

David Albert Columbia University

Steve Weinstein University of Waterloo


The origin of arrows of time II

Sean Carroll California Institute of Technology (Caltech)  Division of Physics Mathematics & Astronomy

Marina Cortes Institute for Astrophysics and Space Sciences

Tim Koslowski Universidad Nacional Autónoma De Mexico (UNAM)


The origin of arrows of time II cont.

Sean Carroll California Institute of Technology (Caltech)  Division of Physics Mathematics & Astronomy

Marina Cortes Institute for Astrophysics and Space Sciences

Tim Koslowski Universidad Nacional Autónoma De Mexico (UNAM)


Testing time asymmetry in the early universe

Brian Keating University of California, San Diego

Andrew Liddle University of Lisbon

Richard Muller University of California System


The fate of the big bang

Abhay Ashtekar Pennsylvania State University

Neil Turok University of Edinburgh


Time as Organization – Downward Caustation, Structure and Complexity I
Barbara Drossel Technische Universität Darmstadt

Time as Organization – Downward Caustation, Structure and Complexity II

Stuart Kauffman Santa Fe Institute (SFI)

George Ellis University of Cape Town



Quantum Information in Quantum Gravity II
31 talksCollection Number C15041Talk

Gravity Dual of Quantum Information Metric
Tadashi Takayanagi Yukawa Institute for Theoretical Physics

A new perspective on holographic entanglement
Matthew Headrick Brandeis University

Universal holographic description of CFT entanglement entropy
Thomas Faulkner University of Illinois UrbanaChampaign

Geometric Constructs in AdS/CFT
Veronika Hubeny University of California System

Do black holes create polyamory
Jonathan Oppenheim University College London

Tensor Network Renormalization and the MERA
Glen Evenbly Georgia Institute of Technology

Entanglement renormalization for quantum fields
Jutho Haegeman Ghent University

Holographic quantum errorcorrecting codes: Toy models for the bulk/boundary correspondence
Fernando Pastawski California Institute of Technology


WeylAmbient Metrics, Obstruction Tensors and Their Roles in Holography
Weizhen Jia University of Illinois UrbanaChampaign


Asymptotic structure and the characterisation of gravitational
Jose Senovilla University of the Basque Country

Asymptotic structure and the characterisation of gravitational radiation at infinity
Jose Senovilla University of the Basque Country

Merged talks  An effective field theory for nonmaximal quantum chaos; 66 Effective description of submaximal chaos: stringy effects for SYK scrambling

Ping Gao Massachusetts Institute of Technology

Felix Haehl University of Southampton


Asymptoticsafety inspired results and ideas in causal set quantum gravity
Astrid Eichhorn University of Southern Denmark

BMS Field Theories with u(1) Symmetry
Max Riegler Technische Universität Wien

Wrap Up and Discussion: An inclusive roadmap for cracking Quantum Gravity
Steve Weinstein University of Waterloo

The emergence of spacetime is governed by a quantum Mach's principle
Lee Smolin Perimeter Institute for Theoretical Physics



Quantum Information in Quantum Gravity II
31 talksCollection Number C15041Quantum Information in Quantum Gravity II 
WeylAmbient Metrics, Obstruction Tensors and Their Roles in Holography
Weizhen Jia University of Illinois UrbanaChampaign
Weyl geometry is a natural extension of conformal geometry with Weyl covariance mediated by a Weyl connection. We generalize the FeffermanGraham (FG) ambient construction for conformal manifolds to a corresponding construction for Weyl manifolds. We first introduce the Weylambient metric motivated by the WeylFeffermanGraham (WFG) gauge, which is a generalization of the FG gauge for asymptotically locally AdS (AlAdS) spacetimes. Then, the Weylambient space as a pseudoRiemannian geometry induces a codimension2 Weyl geometry. Through the Weylambient construction, we investigate Weylcovariant quantities on the Weyl manifold and define Weylobstruction tensors. We show that Weylobstruction tensors appear as poles in the FeffermanGraham expansion of the AlAdS bulk metric for even boundary dimensions. Under holographic renormalization, we demonstrate that Weylobstruction tensors can be used as the building blocks for the Weyl anomaly of the dual quantum field theory.

Zoom link https://pitp.zoom.us/j/91781363979?pwd=NlhjTVlHTlhMSTcxYnk5eExkTWFqdz09

Creases, corners and caustics: properties of nonsmooth structures on black hole horizons
Harvey Reall University of Cambridge
The event horizon of a dynamical black hole is generically a nonsmooth hypersurface. I shall describe the types of nonsmooth structure that can arise on a horizon that is smooth at late time. This includes creases, corners and caustic points. I shall discuss ``perestroikas'' of these structures, in which they undergo a qualitative change at an instant of time. A crease perestroika gives an exact local description of the event horizon near the ``instant of merger'' of a generic black hole merger. Other crease perestroikas describe horizon nucleation or collapse of a hole in a toroidal horizon. I shall discuss the possibility that creases contribute to black hole entropy, and the implications of nonsmoothness for higher derivative terms in black hole entropy. This talk is based on joint work with Maxime Gadioux.

Zoom link: https://pitp.zoom.us/j/98839294408?pwd=cytNYThQaDV4Y2lob1REY0NyaTJNUT09

Asymptotic structure and the characterisation of gravitational
Jose Senovilla University of the Basque Country
With the main purpose of identifying the existence of gravitational radiation at infinity (scri), a novel approach to the asymptotic structure of spacetime is presented, focusing mainly in cases with nonnegative cosmological constant. The basic idea is to consider the strength of tidal forces experienced by scri. To that end I will introduce the asymptotic (radiant) supermomentum, a causal vector defined at scri with remarkable properties that, in particular, provides an innovative characterization of gravitational radiation valid for the general case with Λ ≥ 0 (and which has been proven to be equivalent when Λ = 0 to the standard one based on the News tensor). This analysis is also shown to be supported by the initial (or final) value Cauchytype problem defined at scri. The implications are discussed in some detail. The geometric structure of scri, and of its cuts, is clarified. The question of whether or not a News tensor can be defined in the presence of a positive cosmological constant is addressed. Several definitions of asymptotic symmetries are presented. Conserved charges that may detect gravitational radiation are exhibited. Balance laws that might be useful as diagnostic tools to test the accuracy of model waveforms discussed. An interpretation of the Geroch `rho' tensor is found. The whole thing will be complemented with a series of illustrative examples based on exact solutions. In particular we will see that exact solutions with black holes will be radiative if, and only if, they are accelerated.

Zoom link https://pitp.zoom.us/j/96816406686?pwd=eGZINlo2R0d1YkZMRGhackRNMzBVUT09

Asymptotic structure and the characterisation of gravitational radiation at infinity
Jose Senovilla University of the Basque Country
With the main purpose of identifying the existence of gravitational radiation at infinity (scri), a novel approach to the asymptotic structure of spacetime is presented, focusing mainly in cases with nonnegative cosmological constant. The basic idea is to consider the strength of tidal forces experienced by scri. To that end I will introduce the asymptotic (radiant) supermomentum, a causal vector defined at scri with remarkable properties that, in particular, provides an innovative characterization of gravitational radiation valid for the general case with Λ ≥ 0 (and which has been proven to be equivalent when Λ = 0 to the standard one based on the News tensor). This analysis is also shown to be supported by the initial (or final) value Cauchytype problem defined at scri. The implications are discussed in some detail. The geometric structure of scri, and of its cuts, is clarified. The question of whether or not a News tensor can be defined in the presence of a positive cosmological constant is addressed. Several definitions of asymptotic symmetries are presented. Conserved charges that may detect gravitational radiation are exhibited. Balance laws that might be useful as diagnostic tools to test the accuracy of model waveforms discussed. An interpretation of the Geroch `rho' tensor is found. The whole thing will be complemented with a series of illustrative examples based on exact solutions. In particular we will see that exact solutions with black holes will be radiative if, and only if, they are accelerated.
Zoom link: https://pitp.zoom.us/j/95879544523?pwd=MFl5UEtUZ0hUcU1hNk1SZ2R4MThxUT09

Merged talks  An effective field theory for nonmaximal quantum chaos; 66 Effective description of submaximal chaos: stringy effects for SYK scrambling

Ping Gao Massachusetts Institute of Technology

Felix Haehl University of Southampton
66  It has been proposed that the exponential decay and subsequent power law saturation of outoftimeorder correlation functions can be universally described by collective 'scramblon' modes. We develop this idea from a path integral perspective in several examples, thereby establishing a general formalism. After reformulating previous work on the Schwarzian theory and identity conformal blocks in twodimensional CFTs relevant for systems in the infinite coupling limit with maximal quantum Lyapunov exponent, we focus on theories with submaximal chaos: we study the largeq limit of the SYK quantum dot and chain, both of which are amenable to analytical treatment at finite coupling. In both cases we identify the relevant scramblon modes, derive their effective action, and find bilocal vertex functions, thus constructing an effective description of chaos. The final results can be matched in detail to stringy corrections to the gravitational eikonal Smatrix in holographic CFTs, including a stringy Regge trajectory, bulk to boundary propagators, and multistring effects that are unexplored holographically. 

Asymptoticsafety inspired results and ideas in causal set quantum gravity
Astrid Eichhorn University of Southern Denmark
I will argue that a fruitful strategy to make progress in quantum gravity is to connect distinct approaches and transfer methods and ideas from one approach to another. As a concrete example, I will explain recent results in causalset quantum gravity. The first, namely the construction of a higherorder curvature operator in causal sets, is motivated by the idea to use causal sets as a Lorentzian regularization of the gravitational path integral, in which one can search for asymptotic safety. The second, namely an upper bound on the mass of scalars is inspired by the "matter matters" program in asymptotically safe quantum gravity, in which observational tests of quantum gravity are based on gravity's interplay with matter. I will argue that a similar program for causal sets can provide new, observationally motivated constraints on causal set quantum gravity.To provide background and motivation for these results, I'll provide brief and pedagogical introductions into the key features and key open challenges of both asymptotically safe quantum gravity as well as causal set quantum gravity.
Zoom Link: https://pitp.zoom.us/j/99855484685?pwd=M0IvOFk1OWNCdVlZVDdkUFQ4MzZKUT09

BMS Field Theories with u(1) Symmetry
Max Riegler Technische Universität Wien
Quantum field theories in two dimensions (2d) with an underlying Bondivan der BurgMetznerSachs (BMS) symmetry augmented by u(1) currents are expected to holographically capture features of charged versions of cosmological solutions in asymptotically flat 3d spacetimes called Flat Space Cosmologies (FSCs). I will present a study of the modular properties of these field theories and the corresponding partition function. Furthermore, I will derive the density of (primary) states and find the entropy and asymptotic values of the structure constants exploiting the modular properties of the partition function and the torus onepoint function. The expression for the asymptotic structure constants shows shifts in the weights and one of the central terms and an extra phase compared to earlier results in the literature for BMS invariant theories without u(1) currents present. The field theory results for the structure constants can be reproduced holographically by a bulk computation involving a scalar probe in the background of a charged FSC.
Zoom Link: https://pitp.zoom.us/j/99205444635?pwd=Tk02UlgvcjJCU3JSWWphY1JQSlhFQT09

Wrap Up and Discussion: An inclusive roadmap for cracking Quantum Gravity
Steve Weinstein University of Waterloo

The emergence of spacetime is governed by a quantum Mach's principle
Lee Smolin Perimeter Institute for Theoretical Physics
"I describe a candidate for a fundamental physical theory called the causal theory of views. This describes a world constructed by a continual creation of events; where an event is a transition at which a small portion of the possible becomes actual. I first recall older results which includes the emergence of space and, with space, a nonrelativistic Nbody quantum dynamics. I next describe recent progress on this model including, in a different limit, a formulation of a cut off quantum field theory, which we describe in terms of an SMatrix formulation of amplitudes. The dynamics is specified by an action principle consisting of a kinetic energy and potential energy term. The former are based on measures of how quickly components of causal change do so with respect to averaged notions. The potential energy terms measure how much local moves alter an observer's ""view"" of the universe, as seen from their perspective. These results show that quantum dynamics is restored in an N to infinity limit. Measurable nonlinear corrections to quantum dynamics emerge to higher order in 1/sqrt{N}. "