The Path Integral for Gravity

Conference Date: 
Monday, November 13, 2017 (All day) to Friday, November 17, 2017 (All day)
Scientific Areas: 
Quantum Gravity

 

Over the past three decades, the idea of a path integral over geometries, describing gravity in various dimensions, has become increasingly central to many areas of theoretical physics, including string and M-theory, holography and quantum aspects of black holes and cosmology.

In each of these areas, the path integral is frequently invoked as a formal device although, as practitioners will admit, except in very special cases the basic formula remains undefined. Typically, classical saddle points are discussed, whether real or complex, but the required integrals are left unperformed.

This state of affairs is untenable because it leaves the theory on a shaky footing and hence does not permit a sound comparison of theoretical predictions with observations. The time has come to critically reassess the foundational ideas of the path integral for gravity, including its definition, evaluation and interpretation; to identify problems with
existing uses and claims based on it, and to seek improvements. The workshop will focus on the continuum theory and its semiclassical limit, with applications to cosmology, black holes and holography. In particular, the notion of a “Euclidean path integral” for a “wavefunction of the universe” will be addressed.

To this effect we intend to revisit discussion of “quantum geometrodynamics” from the path integral viewpoint and to pursue various applications. The developments in this direction that took place in the late 1970's and early 1980's were not incorporated in subsequent efforts, where the emphasis shifted to using a classical background with quantum fluctuations superimposed on it, a split which although useful in particular approximations can hardly be imagined to lie at the  foundation of the theory. The revival of the discussion of the foundation of the path integral for gravity is made timely, we believe, by the introduction of new global methods such as Picard-Lefschetz theory.

The format of the workshop will be unusual. For the first three days, the mornings will begin with a longer, introductory lecture by each of the three organisers, setting out some of the foundational issues. This will be followed by shorter lectures by the participants, tackling the same foundational questions. The morning lectures, held in the Bob room, will be open to all Perimeter residents and visitors. They will be recorded and made available for viewing on PIRSA. Afternoons will be devoted to friendly and informal discussions, with participants invited to offer short contributions which follow up or develop points raised in the mornings, within a relaxed and highly conducive environment. Participation in these afternoon discussion sessions, as well as social events associated with the workshop, will be limited to registered workshop participants. The last two days of the workshop will be an opportunity for participants to continue discussions on topics which emerge as of greatest general interest, as well as to follow up in smaller groups on technical points or new ideas.

Registration for this workshop is now closed.

  • Claudio Bunster, Centro de Estudios Cientificos
  • Astrid Eichhorn, Heidelberg University
  • Steffen Gielen, Perimeter Institute & Max Planck Institute
  • Ruth Gregory, Durham University
  • Jonathan Halliwell, Imperial College London
  • James Hartle, University of California, Santa Barbara
  • Thomas Hertog, University of Leuven
  • Stefan Hollands, University of Leipzig
  • Jean-Luc Lehners, Max Planck Institute
  • Emil Mottola, Los Alamos National Lab
  • Viatcheslav Mukhanov, Ludwig Maximilian University of Munich
  • Roberto Percacci, Scuola Internazionale Superiore di Studi Avanzati
  • Rafael Sorkin, Perimeter Institute
  • Neil Turok, Perimeter Institute
  • Itzhak Bars, University of Southern California
  • Alice Bernamonti, Perimeter Institute
  • Beatrice Bonga, Perimeter Institute
  • Latham Boyle, Perimeter Institute
  • Claudio Bunster, Centro de Estudios Cientificos
  • Kevin Costello, Perimeter Institute
  • Bianca Dittrich, Perimeter Institute
  • Astrid Eichhorn, Heidelberg University
  • Job Feldbrugge, Perimeter Institute
  • Angelika Fertig, Perimeter Institute
  • Laurent Freidel, Perimeter Institute
  • Federico Galli, Perimeter Institute
  • Steve Giddings, University of California, Santa Barbara
  • Steffen Gielen, Perimeter Institute & Max Planck Institute
  • Jaume Gomis, Perimeter Institute
  • Ruth Gregory, Durham University
  • Hal Haggard, Bard College
  • Jonathan Halliwell, Imperial College London
  • Lucien Hardy, Perimeter Institute
  • James Hartle, University of California, Santa Barbara
  • Thomas Hertog, University of Leuven
  • Stefan Hollands, University of Leipzig
  • Achim Kempf, Perimeter Institute
  • Jean-Luc Lehners, Max Planck Institute
  • Sebastian Mizera, Perimeter Institute
  • Emil Mottola, Los Alamos National Lab
  • Viatcheslav Mukhanov, Ludwig Maximilian University of Munich
  • Roberto Percacci, Scuola Internazionale Superiore di Studi Avanzati
  • Alfredo Perez, Centro de Estudios Cientificos
  • Kasia Rejzner, University of York
  • Mehdi Saravani, University of Nottingham
  • Laura Sberna, Perimeter Institute
  • Barak Shoshany, Perimeter Institute
  • Vasudev Shyam, Perimeter Institute
  • Lee Smolin, Perimeter Institute
  • Rafael Sorkin, Perimeter Institute
  • Nadine Stritzelberger, University of Waterloo
  • Sumati Surya, Raman Research Institute
  • Neil Turok, Perimeter Institute
  • Alexander Zamolodchikov, Rutgers University

Monday, November 13, 2017

Time

Event

Location

8:30 – 9:00am

Registration

Reception

9:00 – 9:05am

Welcome and Intro

Bob Room

9:05 – 10:30am

Claudio Bunster, Centro de Estudios Cientificos
The significance of the proper time in the quantum mechanics of the gravitational field.

Bob Room

10:30 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 - 11:35am Viatcheslav Mukhanov, Ludwig Maximilian University of Munich
TBA
Bob Room

11:35 – 12:10pm

Bianca Dittrich, Perimeter Institute
Semi-classical evaluation of the 3D gravity path integral and quasi-local holography

Bob Room

12:10 – 12:45pm

Emil Mottola, Los Alamos National Lab
TBA

Bob Room

12:45 – 2:00pm

Lunch

Bistro – 2nd Floor

2:00 – 2:35pm

Astrid Eichhorn, Heidelberg University
An asymptotically safe point of view on the gravitational path integral

Sky Room

2:35 – 3:10pm

Stefan Hollands, University of Leipzig
The path integral for gravity and Fedosov quantization

Sky Room

3:10 – 3:25pm

Angelika Fertig, Perimeter Institute
Real time path integral for quantum tunnelling and pair creation I

Sky Room

3:25 - 3:40pm Laura Sberna, Perimeter Institute
Real time path integral for quantum tunnelling and pair creation II
Sky Room

3:40 – 3:55pm

Alfredo Perez, Centro de Estudios Cientificos
TBA

Sky Room

3:55 – 4:30pm

Coffee Break

Bistro – 1st Floor

4:30 – 5:30pm

Discussion

Sky Room

5:30 – 6:00pm

Ontario Tasting Adventure

2nd Floor Bistro

 

Tuesday, November 14, 2017

Time

Event

Location

9:00 – 10:30am

Neil Turok, Perimeter Institute
Surprises in the Path Integral for Gravity

Bob Room

10:30 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 – 11:35am

Jean-Luc Lehners, Max Planck Institute
Quantum incompleteness of inflation - part I

Bob Room

11:35 – 12:10pm

James Hartle, University of California, Santa Barbara
What is a No-Boundary Quantum State?

Bob Room

12:10 – 12:45pm

Thomas Hertog, University of Leuven
The No-Boundary Proposal: Alive and Well

Bob Room

12:45 – 2:00pm

Lunch

Bistro – 2nd Floor

2:00 – 2:35pm

Steffen Gielen,  Perimeter Institute & Max Planck Institute
Consistency of a quantum cosmological bounce

Sky Room

2:35 – 3:10pm

Hal Haggard, Bard College
The route to a Picard-Lefschetz Treatment of Black to White Hole Tunneling

Sky Room

3:10 – 3:25pm

Job Feldbrugge, Perimeter Institute
Quantum Incompleteness of Inflation I

Sky Room

3:25 – 4:25pm

Discussion

Sky Room

4:25 – 5:00pm

Coffee Break

Bistro – 1st Floor

5:00 – 9:00pm

Star Gazing Excursion

Meet at
Reception

 

Wednesday, November 15, 2017

Time

Event

Location

9:00 – 10:30am

Rafael Sorkin, Perimeter Institute
Why should (and why can) the path integral serve as the basis for quantum theory?

Bob Room

10:30 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 – 11:35am

Jonathan Halliwell, Imperial College London
Quantum-Mechanical Aspects of Quantum Cosmology

Bob Room

11:35 – 12:10pm

Roberto Percacci,  SISSA
The path integral of unimodular gravity

Bob Room

12:10 – 12:45pm

Lucien Hardy, Perimeter Institute
Intrinsic and extrinsic points of view

Bob Room

12:45 – 2:00pm

Lunch

Bistro – 2nd Floor

2:00 – 3:00pm

Colloquium
Caslav Brukner, University of Vienna
Bell’s Theorem for Temporal Order

Time Room

3:10 – 3:45pm

Ruth Gregory, Durham University
Gravity and Higgs

Sky Room

3:45 – 4:20pm

Latham Boyle, Perimeter Institute
CPT invariance in cosmology: predictions for dark matter and the matter/anti-matter asymmetry

Sky Room

4:20 – 4:45pm

Coffee Break

Bistro – 1st Floor

4:45 – 5:30pm

Discussion

Sky Room

5:30 – 6:00pm

Break

 

6:00 – 9:00pm

Banquet

Bistro – 2nd Floor

 

Thursday, November 16, 2017

Time

Event

Location

10:00 – 10:45am

Sumati Surya, Raman Research Institute
Covariant observables and (quantum)  extension theorems

Bob Room

10:45 – 11:30am

Coffee Break

Bistro – 1st Floor

11:30 – 12:45pm

Alfredo Perez, Centro de Estudios Cientificos
Space-filling branes of gravitational ancestry

Bob Room

12:45 – 2:00pm

Lunch

Note:  Perimeter Orchestra will perform a 15 minute Beatles Medley at 1:00 pm in the Atrium.  All are welcome          

Bistro – 2nd Floor

2:00 – 2:15pm

Lee Smolin, Perimeter Institute
Semiclassical states in loop quantum gravity

Sky Room

2:15 – 3:00pm

Chair:  Bianca Dittrich, Perimeter Institute
Discussion on projectors, inner products, convolution properties, unitarity

Sky Room

3:00 – 3:45pm

Chairs:   Itzhak Bars, University of Southern California &
Roberto Percacci, Scuola Internazionale Superiore di Studi Avanzati
Discussion on unimodular gravity, metric degeneration, Weyl "lifts", analyticity, applicability of Picard-Lefschetz

Sky Room

4:00 – 4:30pm

Coffee Break

Bistro – 1st Floor

 

Friday, November 17, 2017

Time

Event

Location

10:00 – 10:45am

Chairs:   Jonathan Halliwell, Imperial College London &
Jean-Luc Lehners, Max Planck Institute
Follow-up to debate on no boundary proposal

Bob Room

10:45 – 11:15am

Coffee Break

Bistro – 1st Floor

11:15 – 12:00pm

Chair:  Astrid Eichhorn, Heidelberg University
Discussion of contour rotation and the conformal factor problem

Bob Room

12:00 – 12:30pm

Chairs:   Itzhak Bars, University of Southern California &
Roberto Percacci, Scuola Internazionale Superiore di Studi Avanzati
Follow up discussion on unimodular gravity, metric degeneration, Weyl "lifts", analyticity, applicability of Picard-Lefschetz

Bob Room

12:30 – 2:00pm

Lunch

Bistro – 2nd Floor

2:00 – 4:00pm

Chair:   Rafael Sorkin, Perimeter Institute
Questions and comments arising from the workshop

Sky Room

 

 

 

Wednesday Nov 15, 2017
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Wednesday Nov 15, 2017
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Wednesday Nov 15, 2017
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Wednesday Nov 15, 2017
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In quantum cosmology wave functions are traditionally generated either from path integrals or from solving the Wheeler-DeWitt equation. In the first part of the talk I discuss what is required in these approaches in order to meet the usual requirements of Hilbert space quantum mechanics, namely, the specification of an inner product structure and classes of states and operators of interest.

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Tuesday Nov 14, 2017
Speaker(s): 

TBA

Collection/Series: 
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Tuesday Nov 14, 2017
Speaker(s): 

Contemporary final theories consist of a theory of the universe’s dynamics (I) like the avatars of string theory together with a theory of its quantum state (Ψ) like the no-boundary wave function of the universe (NBWF). This talk is concerned with the definition of a no-boundary quantum state at the semiclassical level where its predictions can be straightforwardly derived and compared with observation. A semiclassical no-boundary wave function is defined by an ensemble regular saddle points. The ensemble is restricted by simple considerations of symmetry such as time neutrality.

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Pages

Scientific Organizers:

  • Claudio Bunster, Centro de Estudios Cientificos
  • Rafael Sorkin, Perimeter Institute
  • Neil Turok, Perimeter Institute