Introduction To Loop Quantum Gravity

  • #301
In the previous post I mentioned the Relativity and Gravitation conference scheduled to take place in Prague this month.
http://ae100prg.mff.cuni.cz/program
at that point the title of Ashtekar's talk was TBA. Now it is listed on the program as:

Abhay Ashtekar (Institute for Gravitation and the Cosmos, Penn State University, University Park )
Loop quantum gravity and the very early universe

I certainly hope that the conference organizers will post PDF slide sets for the talks, online video would be even better. Two other talks could prove especially helpful:

Jerzy Lewandowski (Department of Physics, University of Warsaw, Warsaw)
Loop quantum gravity: The status report
...
Hermann Nicolai (Albert-Einstein-Institut Golm, Potsdam)
Quantum gravity: the view from particle physics
...

Back in May a PF member named Neutrino98 asked a basic question. How does Loop gravity work? This post is one possible very basic answer
https://www.physicsforums.com/showthread.php?p=3930796#post3930796
This occasioned a positive reaction from Tom Stoer, who knows quite a lot about LQG, so I take that as a good sign. Maybe the explanation is worth keeping track of, so I will copy it here and maybe we can fill out some more details---of the simplest possible entry-level account of the theory's basics.
==quote==
Loop gravity works first of all by focusing attention on geometric MEASUREMENT.

You know that the Einstein 1915 theory of gravity is actually a theory of geometry. How geometry evolves and interacts with matter. How a concentration of matter will cause geometry to curve around it. So gravity = geometry.

Any modern theory of gravity must be a theory of geometry.

What is geometry? It's about measuring things like areas, volumes, angles. And about relations among these measurements, which can change depending on when and what order you measure them. And about predictions concerning future measurements. On a cosmic scale geometry can be about the pattern of expanding distances people call "expanding universe" and all the stuff that goes along with that.

So Loop Gravity works first of all by setting up NETWORKS where each node corresponds to a volume measurement something might make, and the connections between nodes are labeled to indicate the AREA where those chunks of volume might touch. Another word for network is graph: something made up of a bunch of points (nodes) interconnected by lines (links). In this case it's a network of possible measurements and the nodes and links are labeled with volume and area numbers.

A network could have millions of nodes but to picture one of the simplest examples it might just be a square: four nodes at the corners, connected by 4 links which are the sides of the square.

So a network is an idealized STATE of the world's geometry representing the results of a bunch of interrelated measurements which some thing or somebody could be imagined making. (If matter measurements like particle detections are included, that means more labels on the network.)

Then, as a theory of dynamically evolving geometry, LOOP HAS TO SAY HOW THESE NETWORKS, these states of geometry, EVOLVE.

In a quantum theory the PROBABILITY of going from state A to state B is given by a complex number called an AMPLITUDE. So Loop has to say what the amplitude is of going from network state A to network state B.

At the current stage of development of the theory, the tool used to arrive at amplitudes is a kind of path leading from one network to the other. the path looks like a FOAM. To take a simple example, suppose both A and B are squares as described earlier. A path between the two squares could be pictured as a CUBE with A on the bottom or "start" and B on the top or "finish". A hollow cube is all you need to make continuous connection between the two squares. It can even be open on the top and bottom. Such a cube might be one part of a much more elaborate foam.
Loop has a rule for calculating amplitudes from foams. Given a foam that runs from network A (say at the bottom) to network B (say at the top) there is a way to calculate the amplitude of that foam---the probability amplitude of that path of evolution being taken from A to B.

That's the theory. That's how it works.

It gives results like replacing the BigBang "singularity" (where the old theory broke down) by a bounce. The present theory applied to cosmology predicts that a collapsing universe will rebound and undergo a brief very rapid phase of re-expansion. It let's us extrapolate backwards in time to before the start of our own universe's expansion and suggests things to look for as traces of the bounce (as a way of testing.)
==endquote==

The special issue of the journal SIGMA devoted to LQG and LQC now has 19 articles that have gone thru peer review and whose final versions are online. The special issue is still listed as "in progress" so there may be more articles in the pipeline, but I do not know of any. So this may turn out to be the near-final version of the special issue.
http://www.emis.de/journals/SIGMA/LQGC.html
A useful cross-section sampling of current research in the Loop Gravity&Cosmology community.
 
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  • #302
More complete information is now available about the lineup of talks at the Prague June conference Relativity and Gravitation http://ae100prg.mff.cuni.cz/program
It's a large conference covering a wide range of topics (observation, numerical work, theory, testing) with talks by major people from many fields. So to get a good idea of the scope you need to look over the whole program. I'll just give some selected excerpts where there is relevance to Loop gravity/cosmology or to provide context. Here's a sample of the program.

MONDAY June 25
...
...
Parallel Session

16:00 Jorge Pullin
A local Hamiltonian for spherically symmetric gravity coupled to a scalar field

16:15 Maite Dupuis
Loop Quantum gravity in terms of spinors and harmonic oscillators

16:30 Seth Major
On the Observability of Granularity of Spatial Geometry

16:45 Yuri Bonder
Quantum Gravity Phenomenology without Lorentz Invariance Violations

17:00 Break

17:15 Deborah Konkowski
Quantum singularities in static and conformally static space-times

17:30 Vladimír Balek
From 'nothing' to inflation and back again

17:45 Jakub Mielczarek
Signature change in loop quantum cosmology

18:00 Andrzej Gorlich
A transfer matrix model of volume fluctuations in 4D Causal Dynamical Triangulations

18:15 Igor Khavkine
Time delay observable in classical and quantum geometries

TUESDAY June 26

Plenary Talks in Blue Lecture Hall
8:40 Gary Gibbons
Links between general relativity and other parts of physics

9:20 Abhay Ashtekar
Loop quantum gravity and the very early universe

10:00 Coffee break

10:30 Misao Sasaki
Inflation and birth of cosmological perturbations

11:10 Alexei Starobinsky
f(R) gravity - the most straightforward generalization of the Einstein gravity

WEDNESDAY June 27

Plenary Talks in Blue Lecture Hall
8:40 Bernard Schutz
Gravity talks: observing the Universe with gravitational waves

9:20 Daniel Sudarsky
The quantum gravity interface and the origin of the seeds of cosmic structure during inflation

10:00 Coffee break

10:30 Helmut Friedrich
The large scale Einstein evolution problem

11:10 Hermann Nicolai
Quantum Gravity: the view from particle physics
...
...

Parallel Session in Yellow Lecture Hall
16:00 Alejandro Corichi
Effective Dynamics of Anisotropic Cosmologies in Loop Quantum Cosmology

16:15 Steffen Gielen
Spontaneous breaking of Lorentz symmetry for canonical gravity

16:30 Thomas Roman
Probability Distributions of Quantum Stress Tensors in Two and Four Dimensions

16:45 Florian Girelli
Geometric operators in loop quantum gravity with a cosmological constant FRIDAY June 29

Plenary Talks in Blue Lecture Hall
...
...
11:10 Jerzy Lewandowski
Loop Quantum Gravity - where are we?
=========================

In early July there will be another large conference, the MG13 (13th Marcel Grossmann) in Stockholm. For Loop and related QG there are several parallel sessions to check out. The chair of each session is supposed to list the lineup of talks in their brief descriptions, but this hasn't happened in all cases yet. I'll give the links to where the listing should appear.

http://www.icra.it/mg/mg13/par_sessions_chairs_details.htm#lewandowski
Parallel Session: QG2 - Loop Quantum Gravity, Quantum Geometry, Spin Foams

http://www.icra.it/mg/mg13/par_sessions_chairs_details.htm#mielke
Parallel Session: QG3 - Asymptotic Safeness and Symmetry Breaking in Quantum Gravity

http://www.icra.it/mg/mg13/par_sessions_chairs_details.htm#moniz
Parallel Session: CM4 - Quantum Cosmology and Quantum Effects in the Early Universe

http://www.icra.it/mg/mg13/par_sessions_chairs_details.htm#pullin
Parallel Session: QG4 - Loop quantum gravity: cosmology and black holes

http://www.icra.it/mg/mg13/par_sessions_chairs_details.htm#novello
Parallel Session: CM3 - Nonsingular Cosmology

http://www.icra.it/mg/mg13/par_sessions_chairs_details.htm#amelinocamelia
Parallel Session: QG2 - Quantum Gravity Phenomenology
 
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  • #303
The Prague "Relativity and Gravitation" conference starts in about 5 days and the abstracts of all the talks are posted. http://ae100prg.mff.cuni.cz/abstracts Here is a sample of the talks:

http://ae100prg.mff.cuni.cz/img/abstracts/25d99baef0860381a14c4b539cd744e6.pdf
Jerzy Lewandowski
Loop Quantum Gravity - where are we?
Abstract: For several models of gravity coupled to other fields, the algorithm of the canonical quantization has been completed and performed to an end. It gave rise to well defined, exact quantum theories. The Dirac observables are provided by the relational and the deparametrization frameworks. The quantum states, Hilbert spaces and concrete quantum operators are furnished by the canonical Loop Quantum Gravity framework. The models are not confirmed experimentally and admit ambiguities, but they are there, available for further study and applications.

http://ae100prg.mff.cuni.cz/img/abstracts/3be634f679c60019132a7a3b4e153470.pdf
Abhay Ashtekar
Loop quantum gravity and the very early universe
Abstract: Since the standard cosmological perturbation theory is based on QFT on curved space-times, it is not applicable in the Planck era. Using techniques from loop quantum gravity, the theory is extended to overcome this limitation. The new framework sharpens conceptual issues by distinguishing between true and apparent trans-Planckian difficulties and shows that the true difficulties can be generically overcome in the standard inflationary scenario, with interesting lessons for both theory and observations. The talk will be based largely on some recently completed joint work with Ivan Agullo and William Nelson.

http://ae100prg.mff.cuni.cz/img/abstracts/7f79ff4a754e798d850287e3abe1f296.pdf
Hermann Nicolai
Quantum Gravity: the view from particle physics
Abstract: In this talk I will review some facts and lessons that particle physics can offer to help in the search for a fully consistent theory of quantum gravity, including a brief discussion of recent LHC data from this perspective.

Jorge Pullin
A local Hamiltonian for spherically symmetric gravity coupled to a scalar field
Abstract: We present a gauge fixing for gravity coupled to a scalar field in spherical symmetry that leads to a true Hamiltonian that is the integral over space of a local density. We discuss its potential use to study black hole evaporation.

Maite Dupuis
Loop Quantum gravity in terms of spinors and harmonic oscillators
Abstract: Loop Quantum Gravity is an attempt to quantize general relativity. Its kinematical aspects are well understood and yield a description of space in terms of quanta. Spinorial tools provide a really nice geometrical picture of the classical phase space of Loop Gravity. Moving to the quantum level, spinors are simply quantized as harmonic oscillators. They are then the building blocks to define coherent states for Loop Quantum Gravity and to build spinfoam models which is a regularized path integral for general relativity. I will recall the main results of the spinorial formalism in the context of Loop Quantum Gravity and Spinfoam models and explain how it can be generalized to introduce a cosmological constant into the game.

Yuri Bonder
Quantum Gravity Phenomenology without Lorentz Invariance Violations
Abstract: In the last years the phenomenology of quantum gravity has been dominated by the search of violations of Lorentz symmetry. However, there are very serious arguments that led us to assume that Lorentz invariance is a real symmetry in Nature. This motivated us to construct a phenomenological model describing how a Lorentz invariant discrete structure of spacetime could become manifest. The proposal is fully observer covariant, it involves non-trivial couplings of curvature to matter fields and leads to a well defined phenomenology. In fact, an experiment specially designed to test the model has been performed by the Eöt-Wash group allowing to put bounds on some of the model's free parameters.

Jakub Mielczarek
Signature change in loop quantum cosmology
Abstract: The Wick rotation is commonly considered only as an useful computational trick. However, as it was suggested by Hartle and Hawking already in early eighties, Wick rotation may gain physical meaning at the Planck epoch. While such possibility is conceptually interesting, leading to no-boundary proposal, mechanism behind the signature change remains mysterious.
In this talk we show that the signature change anticipated by Hartle and Hawking may occur in result of the loop quantum gravity effects. Theory of cosmological perturbations with the effects of quantum holonomies is constructed. It is shown that such theory can be uniquely formulated in the anomaly-free manner. The algebra of quantum constraints turns out to be modified such that the signature is changing from Lorentzian in low curvature regime to Euclidean in high curvature regime. Implications of this phenomenon on propagation of cosmological perturbations are discussed. Possible relations with other approaches to quantum gravity are also outlined.

Alejandro Corichi
Effective Dynamics of Anisotropic Cosmologies in Loop Quantum Cosmology
Abstract: We present results of numerical evolutions of effective equations for anisotropic cosmologies with spatial curvature in loop quantum cosmology. We address the issue of singularity resolution for different types of initial conditions and study the behavior of geometrical scalar quantities.

Steffen Gielen
Spontaneous breaking of Lorentz symmetry for canonical gravity
Abstract: In Hamiltonian formulations of general relativity, in particular Ashtekar variables which serve as the classical starting point for loop quantum gravity, Lorentz covariance is a subtle issue which has been the focus of some debate, while at the same time being crucial with regard to possible experimental tests. After reviewing the sources of difficulty, we present a Lorentz covariant formulation in which we generalise the notion of a foliation of spacetime usually used in the Hamiltonian formalism to a field of ”local observers” which specify a time direction only locally. This field spontaneously breaks the local SO(3,1) symmetry down to a subgroup SO(3), in a way similar to systems in condensed matter and particle physics. The formalism is analogous to that in MacDowell-Mansouri gravity, where SO(4,1) is spontaneously broken to SO(3,1). We show that the apparent breaking of SO(3,1) to SO(3) is not in conflict with Lorentz covariance. We close by outlining other possible applications of the formalism of local observer, especially with regard to phenomenology of quantum gravity.

Florian Girelli
Geometric operators in loop quantum gravity with a cosmological constant
Abstract: Loop quantum gravity is a candidate to describe the quantum gravity regime with zero cosmological constant. One of its key results is that geometric operators, such as area, angle, volume, are quantized. Not much is known when the cosmological constant is not zero. It is usually believed that to introduce this parameter in the game, we need to use quantum groups. However due to the complicated algebraic structure inherent to quantum groups not much is known in this case. Apart from the area operator, the geometric operators are not yet defined. I will discuss how the use of tensor operators can circumvent the difficulties and allow to construct a natural set of observables. In particular, I will construct the natural geometric observables such as angle or volume and discuss some of their properties.

Franz Hinterleitner
Quantization of plane gravitational waves
Abstract: A long-standing problem in Loop Qauntum Gravity (LQG) is the semiclassical limit and the question of Lorentz invariance violation due to the "granularity" of quantum space-time. In full 3+1 LQG there are strong indications for such violations, but no definitve answer to this issue has been given so far.
Unidirectional plane gravitational waves are 1+1 dimensional fully general-relativistic systems, which are convenient for an investigation of possible dispersion of gravitational radiation, quantum fluctuations of flat space, and the speed of light in a quantum space-time environmant.
In a recent paper a classical canonical approach to plane waves was found, where the reduction from arbitrarily forth- and back running waves to unidirectional ones is formulated in terms of first-class constraints. This means that this step of symmetry reduction can be carried out after quantization. The presently ongoing work deals with the formulation of the corresponding quantum constraint operators and the construction of solutions.

More information about the schedule and program of the conference is here:
http://ae100prg.mff.cuni.cz/program
 
  • #304
The triennial Marcel Grossmann meeting "MG13" starts next week in Stockholm.
To see the QG-related talks to be given go to:
http://www.icra.it/mg/mg13/parallel_sessions.htm
Scroll down to the QG block
Clicking on QG4 A gives, for example, the first of two sessions chaired by Jorge Pullin, taking place Thursday 5 July and Friday 6 July.
CLICKING ON THE TITLE OF THE TALK links to a brief abstract.
http://ntsrvg9-5.icra.it/mg13/FMPro...tField=order2&-SortOrder=ascend&-Max=50&-Find

1) 14:00 - 14:30
Rovelli, Carlo
Recent developments in Black Hole physics

2) 14:30 - 15:00
Perez, Alejandro
Black holes in LQG, a local perspective.

3) 15:00 - 15:30
Bianchi, Eugenio
Entropy of Non-Extremal Black Holes from Loop Gravity

4) 15:30 - 16:00
Barbero, Fernando
The thermodynamic limit for black holes in loop quantum gravity.

COFFEE BREAK

5) 16:30 - 17:00
Diaz Polo, Jacobo
Testable predictions from loop quantum gravity in evaporating microscopic black holes

6) 17:00 - 17:30
Gambini, Rodolfo
Quantum scalar field in spherical quantum gravity: Standard and nonstandard techniques.

7) 17:30 - 18:00
Pranzetti, Daniele
Dynamical evaporation of quantum horizons

8) 18:00 - 18:30
Frodden, Ernesto
Toward the LQG quantization of rotating black holes
 
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  • #305
See also the previous post #304
The triennial Marcel Grossmann meeting "MG13" starts next week in Stockholm.
To see the QG-related talks to be given go to:
http://www.icra.it/mg/mg13/parallel_sessions.htm
Scroll down to the QG block and click on, for example, QG1A.
This will give the Tuesday 3 July session, the first of two Loop-and-allied sessions chaired by Jerzy Lewandowski. CLICKING ON THE TITLE OF THE TALK links to a brief abstract.

1) 14:00 - 14:30
Rovelli, Carlo
Covariant dynamics

2) 14:30 - 15:00
Lewandowski, Jerzy
Quantizable canonical LQG

3) 15:00 - 15:30
Ma, Yongge
Loop Quantum Scalar-Tensor Gravity and Cosmology

4) 15:30 - 16:00
Bianchi, Eugenio
Horizons in spin foam gravity

COFFEE BREAK (I've added some possibly incomplete place tags to help keep track of the next batch of speakers.)

5) 16:30 - 16:50
Vidotto, Francesca (Mars. Utr.)
Spinfoam Cosmology

6) 16:50 - 17:10
Puchta, Jacek (Wars. Mars.)
Operator Spin-network Diagrams in calculations of higher order amplitudes in dipole cosmology

7) 17:10 - 17:30
Zipfel, Antonia (Erl.)
Solving the Euclidean scalar constraint with Spin Foam methods

8) 17:30 - 17:50
Pawlowski, Tomasz (Wars. Mad. UNB Penn.)
Computable framework of Loop Quantum Gravity

9) 17:50 - 18:10
Alesci, Emanuele (Mars. Erl.)
A new perspective on early cosmology

10) 18:10 - 18:30
Duston, Christopher (FSU-Marcolli)
Topspin Networks and Loop Quantum Gravity

11) 18:30 - 18:50
Smerlak, Matteo (Mars. Perim.)
The shift symmetry in spin foam models of BF theory

12) 18:50 - 19:10
Ryan, James (AEI, Unam)
Tensor models and discrete quantum gravity
 
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  • #306
See also post #304 on the previous page.
I should note that session QG2 A, the first of two chaired by Giovanni Amelino-Camelia, has a talk by Bee Hossenfelder discussing the possibility of FTL exchange of information within the context of quantum gravity. Try clicking on QG2A and check out her abstract.

On the other hand, still in the QG block, clicking on QG4 B
will give Friday 6 July the second of two sessions chaired by Jorge Pullin
http://ntsrvg9-5.icra.it/mg13/FMPro...tField=order2&-SortOrder=ascend&-Max=50&-Find
Here as on the previous page, the abstract shows up when you click on the talk's title.

1) 14:00 - 14:30
Agullo, Ivan
A quantum gravity extension of the inflationary paradigm

2) 14:30 - 15:00
Wilson-Ewing, Edward
Lattice LQC

3) 15:00 - 15:20
Cailleteau, Thomas
Observational consequences of Loop Quantum Cosmology

4) 15:20 - 15:40
Vidotto, Francesca
Spinfoam for cosmologists

5) 15:40 - 16:00
Dapor, Andrea
Loop Quantum Cosmology for nonminimally coupled Scalar Field

COFFEE BREAK

6) 16:30 - 17:00
Pawlowski, Tomasz
Geometric time in quantum cosmology

7) 17:00 - 17:30
Velhinho, Jose
Uniqueness of the Fock quantization of scalar fields with time dependent mass

8) 17:30 - 17:50
Fernández-Méndez, Mikel
Hybrid quantization of an inhomogeneous inflationary scenario

9) 17:50 - 18:10
Martín-de Blas, Daniel
Approximated quantum solutions in inhomogeneous loop quantum cosmology

10) 18:10 - 18:50
Dapor, Andrea
Quantum Field Theory on LQC Bianchi Spacetimes

11) 18:30 - 18:50
Cianfrani, Francesco
Inhomogeneous Universe in Loop Quantum Gravity
 
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  • #307
The Marcel Grossmann triennial conference is a major indicator of what fields of research are active and people are interestied in hearing about in the areas of theoretical/experimental General Rel., Cosmology, Field theory on curved spacetime, Astrophysics, and suchlike. The last two meetings MG11 and MG12 averaged about 800 participants each---a big international gathering. This years's MG13 has 1021 registered participants.
http://ntsrvg9-5.icra.it/mg13/FMPro...astname_and_name&-max=1200&-token.0=19&-find=
http://www.icra.it/mg/mg13/parallel_sessions.htm

So it's interesting that Loop is making a strong showing in the MG13 parallel sessions.
Many more talks, for example, than other QG approaches and than are String-related.
Also I was interested to see several Loop people are giving talks at more than one session. Rovelli (2)
Bianchi (2) Pawlowski (2) Vidotto (2)...

QG is broadly represented in the Plenary Sessions.
Martin Reuter is giving a plenary talk:
http://ntsrvg9-5.icra.it/mg13/FMPro...&-max=1200&-recid=35110&-token.0=19&-findall=
And Jan Ambjorn as well:
http://www.icra.it/mg/mg13/invited_speakers_details.htm#ambjorn
To check for more look for links in the right hand column beside participants' names:
http://ntsrvg9-5.icra.it/mg13/FMPro...astname_and_name&-max=1200&-token.0=19&-find=

Tony Padilla's giving a talk, don't want to lose the link:
http://ntsrvg9-5.icra.it/mg13/FMPro...s&talk_accept=yes&-max=50&-recid=41805&-find=
 
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  • #308
In a little over a week there will be a QG summer school in Beijing---giving an introduction to Loop Quantum Gravity and related topics (Loop Cosmology, Spinfoam, Limits, LQG black hole, GroupFieldTheory, and Regge calculus). The speaker lineup can provide perspective on the current makeup of the field:
The 2nd BNU International Summer School on Quantum Gravity (Schedule)

13 Aug (Mon.) Coordinators: Yongge Ma, Sijie Gao
9:00-9:50 Jerzy Lewandowski: Canonical loop quantum gravity (1)
10:00-10:50 Jerzy Lewandowski: Canonical loop quantum gravity (2)
11:10-12:00 Benjamin Bahr: Introduction to Regge calculus (1)
2:30-3:20 Benjamin Bahr: Introduction to Regge calculus (2)
3:40-4:30 Jonathan Engle: Isolated horizon and BH entropy in loop quantum gravity (1)
4:40-5:30 Jonathan Engle: Isolated horizon and BH entropy in loop quantum gravity (2)

14 Aug (Tue.) Coordinators: Jinsong Yang, Bin Zhou
9:00-9:50 Jerzy Lewandowski: Canonical loop quantum gravity (3)
10:00-10:50 Jerzy Lewandowski: Canonical loop quantum gravity (4)
11:10-12:00 Benjamin Bahr: Introduction to Regge calculus (3)
2:30-3:20 Thomas Krajewski: Introduction to group field theory (1)
3:40-4:30 Jonathan Engle: Isolated horizon and BH entropy in loop quantum gravity (3)
4:40-5:30 Jonathan Engle: Isolated horizon and BH entropy in loop quantum gravity (4)

15 Aug (Wed.) Coordinator: Kinjal Banerjee
9:00-9:50 Jerzy Lewandowski: Canonical loop quantum gravity (5)
10:10-11:00 Abhay Ashtekar: Loop quantum cosmology (1)
11:15-12:05 Free Discussion (Chair: Jerzy Lewandowsk):
Loop quantum gravity, BH entropy, Regge calculus,…

16 Aug (Thu.) Coordinators: You Ding, Hong Lu
9:00-9:50 Etera Livine: Spinfoam representation of loop quantum gravity (1)
10:00-10:50 Etera Livine: Spinfoam representation of loop quantum gravity (2)
11:10-12:00 Abhay Ashtekar: Loop quantum cosmology (2)
2:30-3:20 John Barrett: Asymptotics of spin foam models (1)
3:40-4:30 Thomas Krajewski: Introduction to group field theory (2)
4:40-5:30 Thomas Krajewski: Introduction to group field theory (3)

16 Aug Public Lecture: Jingwen Lecture Hall
7:30pm-9:00pm Abhay Ashtekar: Big Bang and the Quantum: Einstein and Beyond

17 Aug (Fri.) Coordinators: Li Qin, Jonathan Engle
9:00-9:50 Etera Livine: Spinfoam representation of loop quantum gravity (3)
10:00-10:50 Etera Livine: Spinfoam representation of loop quantum gravity (4)
11:10-12:00 Abhay Ashtekar: Loop quantum cosmology (3)
2:30-3:20 John Barrett: Asymptotics of spin foam models (2)
3:30-4:20 John Barrett: Asymptotics of spin foam models (3)
4:40-5:30 Free Discussion (Chair: John Barrett):
Spin foams, Group field theory, Loop quantum cosmology,…
6:30pm Banquet

18 Aug (Sat.) Coordinator: Jerzy Lewandowski
9:00-9:50 Etera Livine: Spinfoam representation of loop quantum gravity (5)
10:00-10:50 Abhay Ashtekar: Loop quantum cosmology (4)
11:05-11:55 Free Discussion: (Chair: Abhay Ashtekar)-------11:55-12:00 Closing Session

I see that Lewandowski is giving 5 hour lectures on Canonical LQG. Livine is giving 5 on Spinfoam LQG, Ashtekar is giving 4 on Loop Cosmology, Engle 4 on Loop BH, Barrett 3 on Spinfoam limits, Bahr 3 on Regge, Krajewski 3 on GFT.
 
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  • #309
Webpages for Loops 2013 are online, it's interesting to see who they have on board for the International Advisory Committee, and who the local organizers are:

http://www.perimeterinstitute.ca/en/Events/Loops_13/Loops_13/

International Advisory Committee

Giovanni Ameliano-Camelia, University of Rome
Abhay Ashtekar, Pennsylvania State University
Fernando Barbero, Instituto de Estructura de la Materia
John Barrett, University of Nottingham
James Bjorken, SLAC
Martin Bojowald, Pennsylvania State University
Robert Brandenberger, McGill University
Alejandro Corichi, Pennsylvania State University
Fay Dowker, Imperial College, London
Rodolfo Gambini, Instituto de Fisica Facultad de Ciendias
Steve Giddings, University of California, Santa Barbara
Viqar Husain, University of New Brunswick
Ted Jacobson, University of Maryland
Kirill Krasnov, University of Nottingham
Jerzy Lewandowski, University of Warsaw
Stefano Liberati, SISSA
Etera Livine, Ens de Lyon
Renate Loll, Universiteit Utrecht
Joao Magueijo, Imperial College, London
Alex Maloney, McGill University
Matilde Marcolli, California Institute of Technology
Guillermo Mena, Instituto de Estructura de la Materia
Djordje Minic, Virginia Tech
Daniele Oriti, Albert Einstein Institute
Roberto Percacci, SISSA
Alejandro Perez, Centre de Physique Theorique
Jorge Pullin, Lousiana State University
Martin Reuter, Johannes Gutenberg Universitat
Vincent Rivasseau, Laboratoire de Physique Théorique d'Orsay
Carlo Rovelli, Centre de Physique Theorique
Thomas Thiemann, Institut für Theoretische Physik III
William Unruh, University of British Columbia

This is a Loops conference, but somebody has applied ecumenical outreach to the International Advisory Committee. We all know who Matilda Marcolli and Roberto Percacci are. It is great they are on board. And Rivasseau! And James Bjorken! And Ted Jacobson!
Alex Maloney is a young string star who has coauthored with Witten and made faculty at McGill. Probably everybody knows of Steve Giddings and Robert Brandenberger, who've been prominent in String Theory and in string-related Cosmology.
Wow this is Unitarian Universalist Loops 2.0
Maybe it is how it always OUGHT to have been. Am I dreaming?

To make the mix visual, I colored general QG phenomenology green, competing theories orange (Spectral Geometry, AsymSafe, CDT, CausalSets) and string magenta---with blue reserved for some all-purpose great people.
 
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  • #310
Who are the young Perimeter people who are doing the Local Organizer work for Loops 13?
Of course Lee Smolin is the main Perimeter host for the conference. But who else besides him is Local Organizing?
http://www.perimeterinstitute.ca/en/Events/Loops_13/Loops_13/
http://www.perimeterinstitute.ca/Events/Loops_13/Local_Organizers/ Local Organizers

Joseph Ben Geloun, Perimeter Institute
Eugenio Bianchi, Perimeter Institute
Valentin Bonzom, Perimeter Institute
Bianca Dittrich, Perimeter Institute
Astrid Eichhorn, Perimeter Institute
Cecilia Flori, Perimeter Institute
Laurent Freidel, Perimeter Institute
Steffen Gielen, Perimeter Institute
Florian Girelli, Perimeter Institute
Philipp Hoehn, Perimeter Institute
Mercedes Martin-Benito, Perimeter Institute
Flavio, Mercati, Perimeter Institute
Lee Smolin, Perimeter Institute
 
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  • #311
I misspoke in the previous post. The main hosts for Loops 2013 are THREE people: Bianca Dittrich, Laurent Freidel, and Lee Smolin.
Plus there is quite a large crew of Perimeter folk doing the local organizing. The International Scientific Advisory committee has an interesting makeup. If you haven't examined it yet please to scroll back a couple of posts and take a look.
===============
The next big triennial conference for quantum relativists will be "GR20" in Warsaw July 2013.
It actually comes a few weeks before Loops 2013. The announcement and conference webpages were just posted last week. I'll get the list of parallel sessions. This can help us get an idea of what the conference organizers think their research community is interested in, and where important developments are occurring.
http://gr20-amaldi10.edu.pl/index.php?id=18

Parallel sessions: Title (Chairpersons)
A1: Exact solutions and their interpretation (J. Bicak, J. Tafel)
A2: Mathematical relativity and other progress in classical gravity theory (P. Chrusciel)
A3: Modified gravity theories (P. Horava)
A4: Complex and conformal methods in classical and quantum gravity (M. Dunajski)
B1: Relativistic astrophysics (C. Miller, I. Mandel)
B2: Numerical relativity and astrophysical applications (N. Padmanabhan)
B3: Numerical relativity--methods, theoretical gravity and high energy applications (D. Garfinkle)
B4: Analytic approximations, perturbation theory, effective field theory methods and their applications (V. Cardoso, R. Porto)
B5: Observational cosmology (L. Verde)
B6: Theoretical/mathematical cosmology (R. Durrer)
C5: Experimental gravitation (J. Mueller, C. Laemmerzahl)
D1: Loop quantum gravity and spin foams (T. Pawlowski, B. Dittrich)
D2: Strings, branes and M-theory (R. Gopakumar)
D3: Causal sets, causal dynamical triangulations, non-commutative geometry,
and other approaches to quantum gravity (J. Jurkiewicz)
D4: Quantum fields in curved space-time, semiclassical gravity, quantum gravity phenomenology,
and analog models (C. Fewster, S. Liberati)

I'm struck by the fact that Dittrich and Pawlowski are chairing the LQG session. Dittrich has in progress what seems to me to be a bid to reformulate LQG spin foam dynamics in terms of holonomy spin foams offering the prospect of already well-developed coarse-graining techniques (among other expected benefits.) I think she now has a permanent or faculty position at Perimeter, possibly split with AEI-Potsdam, and a fair number of collaborators working with her on this project.
Tom Pawlowski has also been working in an interesting direction recently. Loop early universe cosmology and inflation. Andrea Dapor (one of his co-authors) gave two talks about this work recently at the triennial Marcel Grossmann meeting in Stockholm. Here for reference his most recent 4 papers:
1. arXiv:1207.4353
Inflation from non-minimally coupled scalar field in loop quantum cosmology
Michal Artymowski, Andrea Dapor, Tomasz Pawlowski
14 pages, 5 figures
2. arXiv:1112.0360
Positive cosmological constant in loop quantum cosmology
Tomasz Pawlowski, Abhay Ashtekar
36 pages, 6 figures
Phys. Rev. D 85, 064001 (2012)
3. arXiv:1108.1147
Dust reference frame in quantum cosmology
Viqar Husain, Tomasz Pawlowski
8 pages
4. arXiv:1108.1145
Time and a physical Hamiltonian for quantum gravity
Viqar Husain, Tomasz Pawlowski
5 pages, version to appear in Phys. Rev. Lett

I'm impressed that not only does GR20 provide a session for LQG/SF chaired by these two people but also there is a separate session devoted to: Causal sets, causal dynamical triangulations, non-commutative geometry, and other approaches to quantum gravity. The chairman Jurkiewicz has co-authored many CDT papers with Ambjorn and Loll.
 
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  • #312
Just a quick question. I thought formulation of loop structure was based on the idea using Giles's theorem and defining different colors via dimensions of solution to the connection's algebra. Here, the author says it's due to vibrations as in QFT. Thoughts?
 
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