Quantum Gravity

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.

Displaying 97 - 108 of 1337

Quantum hair and information loss paradox - VIRTUAL

Xavier Calmet
University of Sussex
October 26, 2023

PIRSA:23100067
Quantum Gravity
Open Discussion with today's speakers (Ashtekar, Surya, Vieira)
- Abhay Ashtekar
  Pennsylvania State University
- Sumati Surya
  Raman Research Institute
- Pedro Vieira
  Perimeter Institute for Theoretical Physics
October 25, 2023

PIRSA:23100012
Quantum Gravity
Panel Discussion - Cosmological Puzzles (Ashtekar, Brandenberger, Geshnizjani, Sakellariadou, Yazdi)
- Abhay Ashtekar
  Pennsylvania State University
- Robert Brandenberger
  McGill University - Department of Physics
- Ghazal Geshnizjani
  Perimeter Institute for Theoretical Physics
- Mairi Sakellariadou
  King's College London
- Yasaman Kouchekzadeh Yazdi
  Dublin Institute For Advanced Studies
October 25, 2023

PIRSA:23100011
Quantum Gravity
Where is String Theory

Pedro Vieira
Perimeter Institute for Theoretical Physics
October 25, 2023

PIRSA:23100066
Quantum Gravity
Glimpses into Loop Quantum Gravity

Abhay Ashtekar
Pennsylvania State University
October 25, 2023

PIRSA:23100009
Quantum Gravity
Panel Discussion - QFT vs beyond-QFT approaches (Buoninfante, Rejzner, Smolin, Vieira)
- Luca Buoninfante
  Nordic Institute for Theoretical Physics
- Benjamin Knorr
  Nordic Institute for Theoretical Physics
- Katarzyna Rejzner
  University of York
- Lee Smolin
  Perimeter Institute for Theoretical Physics
- Pedro Vieira
  Perimeter Institute for Theoretical Physics
October 24, 2023

PIRSA:23100008
Quantum Gravity
Open Discussion with today's speakers (Buoninfante, Eichhorn, Holdom, Knorr, Loll)
- Luca Buoninfante
  Nordic Institute for Theoretical Physics
- Astrid Eichhorn
  Universität Heidelberg
- Bob Holdom
  University of Toronto
- Benjamin Knorr
  Nordic Institute for Theoretical Physics
- Renate Loll
  Radboud Universiteit Nijmegen
October 24, 2023

PIRSA:23100007
Quantum Gravity
Form Factors - a unifying language for Quantum Gravity

Benjamin Knorr
Nordic Institute for Theoretical Physics
October 24, 2023

PIRSA:23100087
Quantum Gravity
The Case for Renormalizable Quantum Gravity: from local to nonlocal approaches (and back!)

Luca Buoninfante
Nordic Institute for Theoretical Physics
October 24, 2023

PIRSA:23100064
Quantum Gravity
UV complete 4-derivative scalar field theory

Bob Holdom
University of Toronto
October 24, 2023

PIRSA:23100006
Quantum Gravity
CDT as computational gateway to nonperturbative quantum gravity

Renate Loll
Radboud Universiteit Nijmegen
October 24, 2023

PIRSA:23100062
Quantum Gravity
Status, perspective and three challenges in the asymptotic-safety paradigm for quantum gravity - VIRTUAL

Astrid Eichhorn
Universität Heidelberg
October 24, 2023

PIRSA:23100005
Quantum Gravity

Quantum hair and information loss paradox - VIRTUAL

Xavier Calmet
University of Sussex
October 26, 2023

PIRSA:23100067
Quantum Gravity
In this talk I present our solution to the information paradox published in Phys.Rev.Lett. 128 (2022) 11, 111301 and Phys.Lett.B 827 (2022) 136995 (see EPL 139 (2022) 4, 49001 for a review). Long wavelength quantum gravitational effects allow the interior state of the black hole to influence Hawking radiation, leading to unitary evaporation. I explain why the Mathur theorem is evaded due to the complex nature of the Hawking radiation superposition state. --- The presenter will be joining via Zoom for this talk.
Open Discussion with today's speakers (Ashtekar, Surya, Vieira)
- Abhay Ashtekar
  Pennsylvania State University
- Sumati Surya
  Raman Research Institute
- Pedro Vieira
  Perimeter Institute for Theoretical Physics
October 25, 2023

PIRSA:23100012
Quantum Gravity
Panel Discussion - Cosmological Puzzles (Ashtekar, Brandenberger, Geshnizjani, Sakellariadou, Yazdi)
- Abhay Ashtekar
  Pennsylvania State University
- Robert Brandenberger
  McGill University - Department of Physics
- Ghazal Geshnizjani
  Perimeter Institute for Theoretical Physics
- Mairi Sakellariadou
  King's College London
- Yasaman Kouchekzadeh Yazdi
  Dublin Institute For Advanced Studies
October 25, 2023

PIRSA:23100011
Quantum Gravity
Where is String Theory

Pedro Vieira
Perimeter Institute for Theoretical Physics
October 25, 2023

PIRSA:23100066
Quantum Gravity
Glimpses into Loop Quantum Gravity

Abhay Ashtekar
Pennsylvania State University
October 25, 2023

PIRSA:23100009
Quantum Gravity
The organizers requested an overview of Loop Quantum Gravity (LQG). However, this is an impossible task, especially for a 30 minute talk, given that the subject is over three decades old with tens of thousands of papers. Instead, I will outline some of the key distinguishing features of LQG and discuss an illustrative application. Hopefully these topics will complement those that will be covered by Bianca Dittrich and Lee Smolin, without too much of an overlap.
Panel Discussion - QFT vs beyond-QFT approaches (Buoninfante, Rejzner, Smolin, Vieira)
- Luca Buoninfante
  Nordic Institute for Theoretical Physics
- Benjamin Knorr
  Nordic Institute for Theoretical Physics
- Katarzyna Rejzner
  University of York
- Lee Smolin
  Perimeter Institute for Theoretical Physics
- Pedro Vieira
  Perimeter Institute for Theoretical Physics
October 24, 2023

PIRSA:23100008
Quantum Gravity
Open Discussion with today's speakers (Buoninfante, Eichhorn, Holdom, Knorr, Loll)
- Luca Buoninfante
  Nordic Institute for Theoretical Physics
- Astrid Eichhorn
  Universität Heidelberg
- Bob Holdom
  University of Toronto
- Benjamin Knorr
  Nordic Institute for Theoretical Physics
- Renate Loll
  Radboud Universiteit Nijmegen
October 24, 2023

PIRSA:23100007
Quantum Gravity
Form Factors - a unifying language for Quantum Gravity

Benjamin Knorr
Nordic Institute for Theoretical Physics
October 24, 2023

PIRSA:23100087
Quantum Gravity
QFT's remarkable success lies in its ability to yield precise predictions through e.g. scattering amplitudes, capturing the essence of running couplings in a gauge-invariant manner. However, the introduction of gravity disrupts this straightforward notion of momentum dependence, posing a significant challenge to our theoretical framework. Enter form factors—an ingenious concept that extends the idea of momentum dependence to the curved spacetime of quantum gravity. They form the central ingredient when discussing quantum gravity in a QFT language. Furthermore, within an effective action, form factors offer a unifying language, allowing us to compare and contrast different quantum gravity approaches apples-to-apples. I will give an overview of the ideas underlying form factors, their application to scattering problems, and their potential to put different approaches on the same footing.
The Case for Renormalizable Quantum Gravity: from local to nonlocal approaches (and back!)

Luca Buoninfante
Nordic Institute for Theoretical Physics
October 24, 2023

PIRSA:23100064
Quantum Gravity
In the context of perturbative quantum field theory (QFT), the addition of quadratic-curvature invariants to the Einstein-Hilbert action makes it possible to achieve strict renormalizability in four dimensions. This theory exhibits unusual features due to an additional massive spin-2 ghost which, in general, may cause instabilities. In the first part of this talk, we focus on the possibility of giving up locality as a way to avoid ghost-like degrees of freedom and provide a critical assessment on open questions in nonlocal theories of gravity, such as the uniqueness problem. In the second part of the talk, we take a step back and argue that, despite the presence of the ghost and actually thanks to it, Quadratic Gravity can still provide a consistent local perturbative QFT description of the gravitational interaction and explain new physics beyond Einstein's general relativity, e.g., it offers a natural explanation for the inflationary phase. Finally, we argue that a type of nonlocality in gravity can still occur non-perturbatively and show that a new lower bound on scattering amplitudes indicates that the gravitational interaction is intrinsically nonlocal if black holes form.
UV complete 4-derivative scalar field theory

Bob Holdom
University of Toronto
October 24, 2023

PIRSA:23100006
Quantum Gravity
A scalar field theory with 4-derivative kinetic terms and 4-derivative cubic and quartic couplings is presented as a proxy for quadratic gravity. Unitarity and positivity appear as the key issues in the scalar field theory, just as they do in quadratic gravity. We have extended some calculations to show how these issues are resolved in the high energy limit of the theory. The results also show how it is that differential cross sections can have good high energy behaviour.
CDT as computational gateway to nonperturbative quantum gravity

Renate Loll
Radboud Universiteit Nijmegen
October 24, 2023

PIRSA:23100062
Quantum Gravity
Based on quantitative results on quantum observables in a Planckian regime, I will argue that using dynamical lattices `a la CDT to construct and explore the nonperturbative path integral over Lorentzian geometries is a bona-fide quantum field-theoretic "method" rather than an "approach" to quantum gravity. Its most important features are universality, unitarity and the presence of powerful numerical tools to directly simulate and measure a chunk of quantum spacetime of about 20 Planck lengths across. This small observational window is a preferred place to look for clues to what quantum gravity is all about. Despite the diffeomorphism-invariant and nonlocal character of the observables, qualitatively new and surprising UV properties have already been discovered, and compatibility checks with semiclassical expectations for several cosmological observables ("classical limit") have been performed successfully. The underlying new mathematics is that of random geometry and beyond-Riemannian geometry.
Status, perspective and three challenges in the asymptotic-safety paradigm for quantum gravity - VIRTUAL

Astrid Eichhorn
Universität Heidelberg
October 24, 2023

PIRSA:23100005
Quantum Gravity
In my talk, I'll review the key idea underlying asymptotically safe quantum gravity, before giving an overview of the current status and open questions. I'll then spotlight three challenges. The first challenge is how to test quantum gravity and I'll advocate that by linking quantum gravity to particle physics and cosmology, we can probe quantum gravity at all scales. The second challenge is how to connect to other ideas about quantum spacetime and I'll discuss effective asymptotic safety as a way to link to, e.g., string theory. The third challenge is the status of global symmetries and I'll discuss what we know about the preservation of global symmetries in asymptotic safety and what this implies for a broader perspective on the question. --- The presenter will be joining via Zoom for this talk.

Title	Speaker(s)	Date	Talk Type	Info link
Quantum hair and information loss paradox - VIRTUAL	Xavier Calmet	2023-10-26	Conference	View details
Open Discussion with today's speakers (Ashtekar, Surya, Vieira)	Abhay Ashtekar, Sumati Surya, Pedro Vieira	2023-10-25	Conference	View details
Panel Discussion - Cosmological Puzzles (Ashtekar, Brandenberger, Geshnizjani, Sakellariadou, Yazdi)	Abhay Ashtekar, Robert Brandenberger, Ghazal Geshnizjani, Mairi Sakellariadou, Yasaman Kouchekzadeh Yazdi	2023-10-25	Conference	View details
Where is String Theory	Pedro Vieira	2023-10-25	Conference	View details
Glimpses into Loop Quantum Gravity	Abhay Ashtekar	2023-10-25	Conference	View details
Panel Discussion - QFT vs beyond-QFT approaches (Buoninfante, Rejzner, Smolin, Vieira)	Luca Buoninfante, Benjamin Knorr, Katarzyna Rejzner, Lee Smolin, Pedro Vieira	2023-10-24	Conference	View details
Open Discussion with today's speakers (Buoninfante, Eichhorn, Holdom, Knorr, Loll)	Luca Buoninfante, Astrid Eichhorn, Bob Holdom, Benjamin Knorr, Renate Loll	2023-10-24	Conference	View details
Form Factors - a unifying language for Quantum Gravity	Benjamin Knorr	2023-10-24	Conference	View details
The Case for Renormalizable Quantum Gravity: from local to nonlocal approaches (and back!)	Luca Buoninfante	2023-10-24	Conference	View details
UV complete 4-derivative scalar field theory	Bob Holdom	2023-10-24	Conference	View details
CDT as computational gateway to nonperturbative quantum gravity	Renate Loll	2023-10-24	Conference	View details
Status, perspective and three challenges in the asymptotic-safety paradigm for quantum gravity - VIRTUAL	Astrid Eichhorn	2023-10-24	Conference	View details

Quantum Gravity

Format results