New stuff happening in Quantum Gravity

[ensabah6]

The main Quantum Gravity and Quantum Geometry conference this year will be at Nottingham UK in early July.
Here is website:
http://www.maths.nottingham.ac.uk/r...ntum_geometry_and_quantum_gravity_conference/

There are 12 invited speakers listed so far:


Ali Chamseddine Connections between noncommutative geometry, spectral action and quantum gravity
]

marcus, Ali Chamseddine has co-authored many NCG papers with the man himself, Connes. AFAIK Ali Chamseddine hasn't published any QG papers, what type of QG does he with to show a connection to, as string theory is considered a QG and Witten-Seidberg has published papers connected ST with NCG, LQG, or something else?

 

[marcus]

It will be interesting to see how Ali Chamseddine draws the connection between QG and NCG---I expect it will be one of the more interesting talks at the conference. They now have around 120 registered participants and the list of speakers has grown since my last update on this.

http://www.maths.nottingham.ac.uk/r...ntum_geometry_and_quantum_gravity_conference/

the conference is slightly over two months away and shaping up nicely.
At the conference site, the dual topic (QG and QG) is summarized this way:
*
Quantum gravity, including loop quantum gravity, spin foam models, 1+1 and 2+1 quantum gravity, perturbative and discrete approaches. Quantum cosmology.


*
Quantum geometry, including physical aspects of non-commutative geometry, quantum groups and quantum topology. Non-commutative field theory and deformed special relativity.

 

[ensabah6]

It will be interesting to see how Ali Chamseddine draws the connection between QG and NCG---I expect it will be one of the more interesting talks at the conference. They now have around 120 registered participants and the list of speakers has grown since my last update on this.

http://www.maths.nottingham.ac.uk/r...ntum_geometry_and_quantum_gravity_conference/

the conference is slightly over two months away and shaping up nicely.
At the conference site, the dual topic (QG and QG) is summarized this way:
*
Quantum gravity, including loop quantum gravity, spin foam models, 1+1 and 2+1 quantum gravity, perturbative and discrete approaches. Quantum cosmology.


*
Quantum geometry, including physical aspects of non-commutative geometry, quantum groups and quantum topology. Non-commutative field theory and deformed special relativity.

I am wondering if there is a merger between the two, NCG and LQG.

Any invitations for Levin/Wen? He said he has some interest in showing up.

 

[marcus]

I am wondering if there is a merger between the two, NCG and LQG.

That is one of the things that you can see happening in the spotlight provided by these conferences. A lot of people have started thinking about this and talking about it. Jesper Grimstrup has actually co-authored several papers merging NCG and LQG. You can find them on arxiv. It is not clear if anyone has proposed the RIGHT way. Ashtekar has talked about it in a recent paper of his, in the conclusion section, as a possibility. And it is obviously what John Barrett has in mind and what the QG+QG conference is all about--the not-so-hidden agenda.

BTW the QG+QG conference is turning out to be the biggest QG conference ever. Well over 160 registered and must be approaching 200 by the looks of it now
http://www.maths.nottingham.ac.uk/r..._and_quantum_gravity_conference/participants/

I see that Renate Loll has confirmed that she will be giving a talk. It could be a condensed version of the minicourse she will be teaching at the Oporto Meeting later that month.

 

[marcus]

The confirmed speakers list for the QG+QG conference is currently as follows
(many more have registered but have not yet indicated that they will present a talk)

Aldaya Victor Instituto de Astrofisica de Andalucia-CSIC
Ashtekar Abhay Penn State
Aschieri Paulo Centro Fermi, Roma and U. Alessandria
Baratin Aristide Max Plank Institute
Barbero Fernando IEM-CSIC
Barnich Glenn University Libre de Bruxelles
Bianchi Eugenio CPT Marseille
Bonder Yuri UNAM Mexico
Borowiec Andrzej Wroclaw University & JINR, Dubna
Chamseddine Ali American University of Beirut & IHES
Fleischhack Chrstian Hamburg University
Freidel Laurent Perimeter
Giesel Kristina Albert Einstein Institute
Girelli Florian SISSA
Grosse Harald University of Vienna
Gurau Razvan Gheorghe LPT Orsay
Hinterleitner Franz Masaryk University, Czech Republic
Kay Bernard University of York
Klauder John University of Florida
Krajewski Thomas CPT Marseille
Lauda Aaron Columbia University
Lewandowski Jerzy University of Warsaw
Loll Renate University of Utrecht
Majid Shahn QMUL
Maloney Alexander McGill University
Martin-Benito Mercedes Instituto de Estrucura de la Materia-CSIC
Mikovic Aleksandar Lusofona University
Nelson William King's College, London
Noui Karim University of Tours
Oriti Daniele Institute for Theoretical Physics, Utrecht University
Pawlowski Tomasz IEM-CSIC
Perez Alejandro CPT Marseille
Picken Roger Instituto Superior Tecnico, Lisbon
Reuter Martin University of Mainz
Rivasseau Vincent University of Paris-Sud
Rovelli Carlo CPT Marseille
Ruiz Ruiz Fernando Universidad Complutense Madrid
Salminen Tapio University of Helsinki
Samanta Saurav S. N. Bose National Centre for Basic Sciences
Sarkar Subir Oxford
Schupp Peter Jacobs University Bremen
Schroers Bernd Heriot-Watt University
Skakala Jozef Victoria University of Wellington
Starodubtsev Artem CPT Marseille
Steinacker Harold Ludwig-Maximilians-University, Munich
Stephan Christoph Alexander University of Potsdam
Taveras Victor Penn State University
Tlas Tamer DAMTP, University of Cambridge
Vicary Jamie Imperial College London
Vignes-Tourneret Fabien University of Vienna

Quite a few of these are people whose work we have noted and sometimes discussed over the years since 2004 here at PF.
Those who have will in many cases find it not difficult to get an idea of the physics topics which will be discussed at conference, and some of the recent research to be presented.

 

[marcus]

Often people ask how is it proposed to merge LQG with Noncommutative Geometry. This is is specially interesting because NCG has achieved the Standard Model particle menu, and actually made some predictions of masses (measurable at LHC).

Jesper Grimstrup and co-workers has been working on this merger for some 3 years and has produced some three papers about it. One came out this year.

Presumably he will be talking about it at the July QG+QG conference. He is going to be there.
But there is something earlier. Just next week I think.
There will be a 29 May seminar talk at Perimeter.

http://pirsa.org/08050004
On Spectral Triples in Quantum Gravity
Speaker(s): Jesper Grimstrup - Neils Bohr Institute
Abstract: This talk is concerned with the existence of spectral triples in quantum gravity. I will review the construction of a spectral triple over a functional space of connections. Here, the *-algebra is generated by holonomy loops and the Dirac type operator has the form of a global functional derivation operator. The spectral triple encodes the Poisson structure of General Relativity when formulated in terms of Ashtekars variables. Finally I will argue that the Hamiltonian of General Relativity may emerge from the construction via the requirement that inner automorphisms vanish on the vacuum sector.
Date: 29/05/2008 - 4:00 am

Since it has a PIRSA number (Perimeter Institute Recorded Seminar Archive) I am expecting that the seminar will be recorded and made available like the other PIRSA seminars.
==================================

Pedro Machado got his PhD at Utrecht in Renate Loll group. He is now at Perimeter as a postdoc.
Loll's former PhD students are an interesting bunch so I also note that Machado will be giving a talk, in just a day or so actually
http://pirsa.org/08050042
Functional Renormalization Group Equations and f(R) Gravity
Speaker(s): Pedro Machado - Institute for Theoretical Physics
Abstract: After motivating and briefly reviewing the Functional Renormalization Group approach to gravity, we'll construct an FRG equation for gravitational f(R) theories. This allows us to extend the space of truncated effective average actions so far considered, giving us a better understanding of gravity FRG physics in the infrared and of the effect of non-local operators in our theories. To illustrate, we'll analyze the RG flow properties of the so-called ln(R) truncation, particularly in light of the asymptotic safety scenario.
Date: 22/05/2008 - 2:00 pm

This is in the general area of asymptotic safety that Martin Reuter works in, and Roberto Percacci, and Frank Saueressig.
Machado just did a paper with Saueressig while both were at Utrecht, and now Percacci is there. Utrecht obviously has quite a bit going in asymptotic safety as well as other approaches.
So if they record this talk too and put it online we will get a window on that as well.

Here is Saueressig and Machado's paper, to appear in Physical Review D

http://arxiv.org/abs/0712.0445
On the renormalization group flow of f(R)-gravity
Pedro F. Machado, Frank Saueressig
55 pages, 7 figures
(Submitted on 4 Dec 2007)

"We use the functional renormalization group equation for quantum gravity to construct a non-perturbative flow equation for modified gravity theories of the form $$S = \int d^dx \sqrt{g} f(R)$$. Based on this equation we show that certain gravitational interactions monomials can be consistently decoupled from the renormalization group (RG) flow and reproduce recent results on the asymptotic safety conjecture. The non-perturbative RG flow of non-local extensions of the Einstein-Hilbert truncation including $$\int d^dx \sqrt{g} \ln(R)$$ and $$\int d^dx \sqrt{g} R^{-n}$$ interactions is investigated in detail. The inclusion of such interactions resolves the infrared singularities plaguing the RG trajectories with positive cosmological constant in previous truncations. In particular, in some $$R^{-n}$$-truncations all physical trajectories emanate from a Non-Gaussian (UV) fixed point and are well-defined on all RG scales. The RG flow of the $$\ln(R)$$-truncation contains an infrared attractor which drives a positive cosmological constant to zero dynamically"

 

[marcus]

Links to check periodically as the summer meetings gain definition
30 June Nottingham
http://www.maths.nottingham.ac.uk/r...ntum_geometry_and_quantum_gravity_conference/
10 July Oporto
http://faraday.fc.up.pt/omgtp2008/
18 August Cern
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/workshops/strings2008/?site=content/talks.html
25 August Mit
http://www.rle.mit.edu/emergent/participants.htm

 

[marcus]

The question has been asked several times recently how are people going about merging LQG with NCG (noncommutative geometry, where Connes and Barrett have found a way to represent the standard model particles).

One approach is presented in this video talk by Jesper Grimstrup of the Bohr Institute Copenhagen
http://pirsa.org/08050004

We have four papers by Grimstrup et al that they have posted over several years, since 2005.
This talk may be helpful in understanding, because it has a bunch of Perimeter people asking questions.

Grimstrup will also be one of the participants at the Nottingham QG+QG conference that starts in one month from now (30 June). One of the main focus points of this conference is connecting Quantum Gravity with NCG. There may be several ways to do it and the approach of Grimstrup et al is one that has been worked on among the longest.
(It currently of considerable interest because it offers a way of including matter in theories like LQG.)

 

[marcus]

The QG2 conference starts 30 June. The speakers list has been updated. Here's the new list
==================

Aldaya Victor Instituto de Astrofisica de Andalucia-CSIC
Alexandrov Sergey Montpellier University
Ashtekar Abhay Penn State
Aschieri Paulo Centro Fermi, Roma and U. Alessandria
Baratin Aristide Max Plank Institute
Barbero Fernando IEM-CSIC
Barnich Glenn University Libre de Bruxelles
Bianchi Eugenio CPT Marseille
Bonder Yuri UNAM Mexico
Borowiec Andrzej Wroclaw University & JINR, Dubna
Chamseddine Ali American University of Beirut & IHES
Fleischhack Chrstian Hamburg University
Freidel Laurent Perimeter
Giesel Kristina Albert Einstein Institute
Girelli Florian SISSA
Grosse Harald University of Vienna
Gurau Razvan Gheorghe LPT Orsay
Hinterleitner Franz Masaryk University, Czech Republic
Kay Bernard University of York
Krajewski Thomas CPT Marseille
Lauda Aaron Columbia University
Lewandowski Jerzy University of Warsaw
Liberati Stefano SISSA
Loll Renate University of Utrecht
Majid Shahn QMUL
Maloney Alexander McGill University
Marciano Antonino CPT-CNRS
Martin-Benito Mercedes Instituto de Estrucura de la Materia-CSIC
Mikovic Aleksandar Lusofona University
Nelson William King's College, London
Noui Karim University of Tours
Oriti Daniele Institute for Theoretical Physics, Utrecht University
Pawlowski Tomasz IEM-CSIC
Picken Roger Instituto Superior Tecnico, Lisbon
Reuter Martin University of Mainz
Rivasseau Vincent University of Paris-Sud
Rovelli Carlo CPT Marseille
Ruiz Ruiz Fernando Universidad Complutense Madrid
Salminen Tapio University of Helsinki
Samanta Saurav S. N. Bose National Centre for Basic Sciences
Sarkar Subir Oxford
Schupp Peter Jacobs University Bremen
Schroers Bernd Heriot-Watt University
Singh Parampreet Perimeter Institute
Skakala Jozef Victoria University of Wellington
Starodubtsev Artem CPT Marseille
Steinacker Harold Ludwig-Maximilians-University, Munich
Stephan Christoph Alexander University of Potsdam
Taveras Victor Penn State University
Tlas Tamer DAMTP, University of Cambridge
Vicary Jamie Imperial College London
Vignes-Tourneret Fabien University of Vienna
==================
At this point there are 52 confirmed speakers.
There are some folks one would normally expect to present who haven't signed up to give a talk yet. This is a partial list in no particular order: a few names I remembered not seeing.
Martin Bojowald
Derek Vandersloot
Andy Randono
Derek Wise
Yidun Wan
Jesper Grimstrup
Dario Benedetti
Jeffrey Morton
Ruth Williams
Lee Smolin
This could in some cases be because their co-authors are presenting the work.
Going back over, I now see many more people whose work I have been following with interest, who are registered as participants, but not yet confirmed as giving a talk. Counting the above, maybe 20 in all. So I am wondering if there is a problem. Will there be parallel sessions to accommodate more talks, or is the number of talks limited to 50-some and there just isn't room in the conference for more? 30 June is just a month away.

 

[marcus]

The speaker list has been updated again. There are now 73 confirmed talks.
I listed some in the last post that I expected to be added, and several of these are now confirmed.
John Baez former PhD student Derek Wise is one.
Andy Görlich, one of Loll's collaborators will presumably be presenting the results on the emergence of a smooth deSitter background, from foam. He was involved in the detailed data analysis of quantum fluctuations, in the Monte Carlo simulations.
Bojowald is confirmed on board.

You can check the list out. I think it is going to be exciting, a lot of the speakers I know to have remarkable new results to report.

JESPER GRIMSTRUP IS TALKING! He is the guy at the Niels Bohr Institute Copenhagen who has been working since 2005 on welding Loop Quantum Gravity to Alain Connes Noncommutative Geometry----he and collaborators. We have discussed his work and given links to some four of his papers. This will be the first conference where Grimstrup Aastrup results are presented, if I remember right. He gave a seminar at Perimeter recently which is video online at PIRSA.

Jeffrey Morton, another John Baez PhD, has been added to the list. Aaron Lauda is already on---n-category application to QG probably.
It is shaping out that a lot of different sectors of nonstring QG (and QG) are being brought together. It is important for people to meet in conference partly because it helps them talk the same language. It helps them to converge on meaning the same things by the terms they use in communicating.

so here we are getting spinfoam, triangulations, noncommutative geometry, n-category stuff, quantum groups, LQG, Loop Quantum Cosmology, group-field-theory, asymptotic safety, and more, into the same conference

 

[marcus]

Many of the abstracts of talks scheduled for the Nottingham QG2 conference are now available:
http://www.maths.nottingham.ac.uk/r...ravity_conference/participants/abstracts.html

 

[marcus]

Many of the abstracts of talks scheduled for the Nottingham QG2 conference are now available:
http://www.maths.nottingham.ac.uk/r...ravity_conference/participants/abstracts.html

Today when I counted, 62 abstracts were posted so you can get a good overview of what the talks will cover. I was especially interested by the abstracts for two of the talks, Eugenio Bianchi's and that of Florian Conrady (on joint work with Laurent Freidel). Looks like a lot of progress towards confirming the classical limit of loop/spinfoam and also towards bringing together with triangulations (cdt) path integral approach. Probably this is a big year in quantum geometry/gravity.

Lee Smolin will be giving a talk. He has not posted an abstract so we don't know the topic.

There are a total of 75 talks confirmed-----the 62 where we have the abstracts already and the others where we mostly only have the titles.
http://www.maths.nottingham.ac.uk/r...y_and_quantum_gravity_conference/participants

 

[marcus]

There are now 66 abstracts posted.

In what appears to be a last minute change, Yidun Wan will be giving a talk on 4-valent braid-matter. It sounds like a pretty interesting talk, judging from the abstract.
==quote==
Yidun Wan
C, P, T, and Conserved Quantities of Braid Excitations in Quantum Gravity

We derive conservation laws from interactions of braid-like excitations of embedded framed spin networks in Quantum Gravity. We also demonstrate that the set of stable braid-like excitations form a noncommutative algebra under braid interaction, in which the set of actively-interacting braids is a subalgebra. We show that four-valent braids allow seven and only seven discrete transformations. These transformations can be uniquely mapped to C, P, T, and their products. Each CPT multiplet of actively-interacting braids is found to be uniquely characterized by a non-negative integer. Finally, braid interactions turn out to be invariant under C, P, and T.
==endquote==

Looks like Smolin can now sit back and let others of the Perimeter group present the new braid-matter developments----Jon Hackett and Yidun Wan, possibly others as well.

To me it looks suspiciously like the first stage of the braid-matter program has succeeded.

It's going to be a lively conference: counting some dozen or so plenary speakers not included in the abstracts list, the total comes to around 78 talks. Several of the talks are apt to present landmark results. (I mentioned Eugenio Bianchi and Florian Conrady earlier. It's worthwhile to have a look at the abstracts of their talks, among others.)

 

[marcus]

Here is what the program for the week looks like
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/QGsquared-timetable

Lee Smolin will be chairing a discussion at the end----Friday 11:30AM to 1:00PM---
apt to be a "Where do we go from here?" summary and prospects discussion.

Most days lunch starts at 12:30PM. On each of the five days, M-F, there will be 3 one-hour morning slots for plenary speakers-----the 14 plenary talks we know about plus the overview concluding discussion chaired by Smolin.

In addition there are 60 some parallel session talks, which are scheduled for the afternoons of three days
Monday:
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/Monday_Parallel_Sessions
Tuesday:
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/Tuesday_Parallel_Sessions
Thursday:
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/Thursday_Parallel_Sessions

These talks are alotted 30 minutes each. There are three lecture halls, each session runs 4 hours, from 2PM to 6PM-----allowing either for 8 talks or else 7 talks plus a halfhour discussion period at the end.

 

[marcus]

Here is what the program for the week looks like
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/QGsquared-timetable

...

On each of the five days, M-F, there will be 3 one-hour morning slots for plenary speakers-----the 14 plenary talks we know about plus the ... concluding discussion...

In addition there are 60 some parallel session talks, which are scheduled for the afternoons of three days
Monday:
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/Monday_Parallel_Sessions
Tuesday:
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/Tuesday_Parallel_Sessions
Thursday:
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/Thursday_Parallel_Sessions

These talks are alotted 30 minutes each. There are three lecture halls, each session runs 4 hours, from 2PM to 6PM-----allowing either for 8 talks or else 7 talks plus a halfhour discussion period at the end.

since I posted that, there has been a change. the discussion at the end of the conference will be chaired by Vincent Rivasseau
the QG2 conference website says that all the scheduling is complete, in final form to be printed out for inclusion in the information packets.
It looks to be a major success. Good luck to the organizers and participants!
===========================

Earlier I mentioned that Rovelli will be giving a talk on LQG at the annual strings conference "Strings 2008" to be held this year at CERN in August. I gave a link in Announcements to the list of summary and research talks.
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/workshops/strings2008/?site=content/talks.html
and there was some discussion here
https://www.physicsforums.com/showthread.php?t=235532
At that time only the speakers names were listed. Now many of the titles of the talks have been filled in.

There are 9 "survey" talks and 30 briefer "research" talks. Rovelli's is one of the latter.

It is remarkable that 4/9 of the lengthier "survey" talks are not about string.

Also that little or nothing is being said about the String Landscape and the speculation about "multiverses". No survey talk. Little or nothing of that sort evident yet in the research talk listing either AFAICS. What was fashionable and receiving much attention 2 or 3 years ago is no longer in evidence.

Also no talk by Susskind, or by Witten---neither have registered to attend so far. Gary Horowitz has not registered. Steve Giddings has registered but is not giving a talk. There is an odd sense that the face of the field has changed.

All the talks will be plenary session. Just one auditorium. No sessions running in parallel in different halls. The CERN hosts are running a nice tight format. And I can't overemphasize what a positive development I think it is for them to have included a talk about the Loop Quantum Gravity/Spinfoam approach by Carlo Rovelli.

somebody obviously thinks it is important for the two research communities to talk to each other.

 

[jal]

As a preview you might want to search for the work of some of the authors.
I looked up a few to see what they might be presenting.


Since CERN will be making a quark-gluon liquid/plasma/fireball then ALL models must eventually link their approach to what is being observed.
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/workshops/strings2008/?site=content/talks.html
http://arxiv.org/abs/0806.3796
String 2008 18-23 Aug
========
http://arxiv.org/abs/0806.3796
Zero Sound from Holography
Authors: A. Karch, D. T. Son, A. O. Starinets
(Submitted on 24 Jun 2008)
========
http://arxiv.org/abs/0705.3870v2
Metallic AdS/CFT
Authors: Andreas Karch, Andy O'Bannon
(Submitted on 26 May 2007 (v1), last revised 10 Sep 2007 (this version, v2))
======
http://arxiv.org/abs/0801.4566
Chiral Gravity in Three Dimensions
Authors: Wei Li, Wei Song, Andrew Strominger
(Submitted on 30 Jan 2008)

 

[marcus]

the next major workshop/conference that I know about, is the one in Sussex 17-19 September
I posted an announcement about this in the ANNOUNCEMENTS thread back in June, month before last.
What I want to do here is study the topics, focus, and lineup of speakers for clues about where the field is going
Continuum and Lattice Approaches to Quantum Gravity
http://www.ippp.dur.ac.uk/Workshops/08/CLAQG
Among other things it will feature talks by
* Jan Ambjorn (NBI Copenhagen)
* John Barrett (U Nottingham)
* Laurent Freidel (ENS Lyon and Perimeter Institute)
* Renate Loll (U Utrecht)
* Max Niedermaier (U Tours)
* Roberto Percacci (SISSA Trieste)
* Martin Reuter (U Mainz)
* Thomas Thiemann (AEI Golm and Perimeter Institute)

You can see the emphasis
Triangulations----Ambjorn, Loll
Asymptotic Safety----Reuter, Percacci, Niedermeyer,
Spinfoam---Freidel, Barrett
canonical LQG---Thiemann

The three days of talks will be preceded by a school 15-16 September, to provide extra preparation for participants who wish it
Non-perturbative Methods in Quantum Field Theory
http://www.ippp.dur.ac.uk/Workshops/08/NPMQFT
Some of the lectures will be as follows:

* Basics of the non-perturbative renormalisation group (D. Litim, U Sussex)
* Basics of the Renormalization Group for QCD and confinement (J.M. Pawlowski, U Heidelberg)
* Basics of QCD on the lattice (O. Philipsen, U Muenster)
* Basics of asymptotic safety for gravity (M. Niedermaier, U Tours)
* Basics of the Renormalization Group for quantum gravity (M. Reuter, U Mainz)
* Basics of lattice quantum gravity I (R. Loll, U Utrecht)
* Basics of lattice quantum gravity II (J. Barrett, U Nottingham)

have to go. I'll comment on this when I get back.

 

[marcus]

New stuff happening in Quantum Gravity (a break-out in terminology at Sussex)

... school 15-16 September, to provide extra preparation for participants who wish it
Non-perturbative Methods in Quantum Field Theory

* Basics of lattice quantum gravity I (R. Loll, U Utrecht)
* Basics of lattice quantum gravity II (J. Barrett, U Nottingham)

Lately in QG papers I've seen the acronym LQG stand for Lattice QG and also for Lorentzian QG.
====================

for several years I've seen people who don't have much direct firsthand familiarity with QG research assuming that it was somehow mostly SPIN NETWORKS or else SPIN FOAMS. Spin networks are a characteristic tool of canonical Loop QG as it developed some 20 years ago. Then starting around 1996 quite a lot of the Loop people moved over and started working on Spinfoam approaches---different but conceptually related.
So Loops gets used as a generic catchall term. And the annual conference sometimes gets called Loops. Even though a lot of the research is NOT related to spin networks or even in a lot of cases to spinfoams.

I can imagine that a fair number of QG researchers are now impatient with this outdated terminology of putting what they do under the general rubric of Loops----when that misrepresents, and allows misconceptions to persist.

Furthermore LATTICE Quantum Gravity is a more accurate description. Laurent Freidel just translated the leading Spinfoam models into 4D lattice path integral formalism.
It looks like you can simply start with glued 4-simplices, and go all the way without ever making a detour into spinfoam (the 2-complex dual).
And LATTICE QG was what Ambjorn and Loll were doing all along.

It is not a regular lattice they work with, but it is made of 4-simplex cells glued together.
As long as you don't imagine the lattice as a repetitive boring one, then it is OK to think lattice.

So this looks to me terminology-wise like an organized jail-break. they want out from under the Loops rubric. They want to fly a more accurately descriptive flag.

And one of the most successful areas of research that is actually bonafide Loop is the applied field LQC---loop applied to cosmology. And a lot of those papers are about what is called lattice-refinement. So we are all getting more lattice-conscious.

Plus Sussex included Thomas Thiemann, who does an evolved version of 1990s canonical Loop QG. So there is an all-inclusive tectonic plate movement in the works here. LQG is becoming Lattice QG.

The two-day school and the three-day conference/workshop are FREE. Any QG-minded person who is going to be in the UK in mid-September should consider seeing if you can still register. I think it is going to be a redefining event.

BTW notice the clever acronym CLAQG. Sounds like claque---I'd guess it's a Lollard pun. it contains LQG but avoids direct confrontation by spacing things out:

continuum and LATTICE approaches to QUANTUM GRAVITY...

Continuum and Lattice Approaches to Quantum Gravity
http://www.ippp.dur.ac.uk/Workshops/08/CLAQG
Among other things it will feature talks by
* Jan Ambjorn (NBI Copenhagen)
* John Barrett (U Nottingham)
* Laurent Freidel (ENS Lyon and Perimeter Institute)
* Renate Loll (U Utrecht)
* Max Niedermaier (U Tours)
* Roberto Percacci (SISSA Trieste)
* Martin Reuter (U Mainz)
* Thomas Thiemann (AEI Golm and Perimeter Institute)

You can see the emphasis
Triangulations Lattice people----Ambjorn, Loll
Asymptotic Safety Continuum people----Reuter, Percacci, Niedermeyer,
Spinfoam 4D Lattice---Freidel, Barrett
canonical LQG 3D Lattice---Thiemann

 

[marcus]

Quantum Geometry and Quantum Gravity conference
http://echo.maths.nottingham.ac.uk/qg/wiki/index.php/QGsquared-slides

slides and audio are available for the QGQG conference (July 2008 Nottingham)

most plenary talks have both slides and audio, but the plenary talks by Ali Chamseddine and by Aaron Lauda have only the audio

parallel session talks are slides-only

 

[marcus]

It will be interesting to see what Carlo Rovelli chooses to highlight in his talk to the Strings 2008 conference on Thursday 21 August.
There will be a live video starting at around 5:35 PM Cern time, which is 9 hours ahead of pacific. So for me on the west coast it will be around 8:30 in the morning.
Perhaps Cern will archive the video, in which case it will appear here:
http://cdsweb.cern.ch/collection/Webcast

But it may only be available once, in real time.
Here is the schedule of talks:
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/workshops/strings2008/schedule.php

To tune into the live broadcast, while it is happening, just go here:
http://webcast.cern.ch/live.py
Most of the time you just see a dark box because no talk is happening, but I tried it when Engeler was talking and it worked fine. Nothing to do, just click on it.

Rovelli's talk will be a first. Someone from the background independent QG community invited to speak at the annual strings conference.

 

[marcus]

slides for 14 out of the 40 Strings 08 talks are available here
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/workshops/strings2008/?site=content/talks.html
it looks like they may get all or nearly all the slides online

 

[marcus]

Slides for Carlo Rovelli's talk at Cern
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917

 

[MTd2]

Did anyone there really cared about Rovelli's talk? Lubos said he was completely ignored, but I guess his opinion concerning non stringy subjects are a bit strong.

 

[marcus]

Did anyone there really cared about Rovelli's talk? Lubos ...

He's not a disinterested observer and he wasn't there, so I reckon it doesn't matter what he said about the reception of Rovelli's talk. What interests me about the talk is two things:

1. It is a clear well-organized introduction aimed at a non-expert audience---people who don't know very much about non-string QG. It covers the whole field of loop/foam and sketches the recent results---the progress in just the last couple of years. So it's potentially useful as a current status report.

2. This year the string conference organizers were very selective about who got asked to present. There were only 30 talks in the whole conference. Five or so were about non-string topics. All the talks were invited---and all were presented in full session. There weren't any parallel sessions for contributed talks. The organizers chose to invite Rovelli to give a survey of loop/foam research.

As an indication of how selective they were, they excluded presentations about the anthropic principle, the string landscape, multiversalism, and suchlike stuff. They left it out of the conference even though it has been a fashionable string topic for several years (since 2003) and is favored by some prominent string folks.

To me it speaks volumes that they chose, for the first time, to invite a talk about loop/foam and to exclude the anthropic string landscape (as Susskind calls it) from the discussion.

 

[Micha]

You can find here on Lubos blog an exchange between Lubos and Carlo about Carlo's talk:
http://motls.blogspot.com/2008/08/strings-2008-thursday.html

I think it is very good that these guys talk to each other instead of insulting each other.

 

[Coin]

1. It is a clear well-organized introduction aimed at a non-expert audience---people who don't know very much about non-string QG. It covers the whole field of loop/foam and sketches the recent results---the progress in just the last couple of years. So it's potentially useful as a current status report.

Actually what was interesting to me was this comment by [URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/url] at Not Even Wrong, he discusses the question and answer session from the talk and then suggests Rovelli maybe assumed the audience was slightly more non-expert than they actually were:

My impression from watching the webcast of talk and question session: the audience was not ignorant about LQG and might have apprectiated a less introductory talk addressing more of the technical issues. It remains a bit frustrating to see Rovelli using up so much time to explain the bare idea of a “spin network” to an audience that is familiar with the concept of Wilson line and non-perturbative gauge theory on the lattice.

But, as I understand the mere presence of Rovelli at the Strings conference was vaguely unprecedented to begin with so I don't know if he could have done any differently than he did.

 

[marcus]

Slides for Carlo Rovelli's talk at Cern
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917

I just got a link to the video that goes with these slides.
http://cdsweb.cern.ch/record/1121957?ln=en

The resolution in the video is not great, so one cannot read the slides as they are projected up on the screen. So it helps to download the PDF file of the slides and scroll thru them as one is watching the video.

At the end of the video talk there are the questions from the audience and the camera turns around to take in the audience.
=================

I should note that it is customary at the corresponding Loops conference to have a featured invited string speaker in plenary session (there may also be contributed stringy talks contributed in parallel session, but at least one invited talk)

Loops '05 had Robbert Dijkgraaf
Loops '07 had Moshe Rozali
QGQG 2008 (the Loops for this year) had Alex Maloney---a collaborator with Edward Witten and Andy Strominger on 3D quantum gravity

there was no Loops '06 conference, so the tradition is so-far unbroken, and one can see their inviting Rovelli as an (intended or unintended) form of reciprocation

Rovelli got a lot of questions at the end, none hostile as far as I could see, and he obviously appreciated the expression of so much interest. Clearly a successful talk and a good move on the part of the organizers.

 

[marcus]

I've had a chance to watch the video several times. Good talk---a half-hour slide lecture---then followed by over 13 minutes of questions! I counted some 8 questions, all excellent. And at the end after a 43 minute session the moderator proposed that they continue the Q/A outside during the break. (People were not done asking questions, so it ran into the break.) I think this is great. Real dialog between research programs that don't have enough substantive interchange. In fact in the break afterwards, Rovelli says he talked some more with Ibanez, one of those who had asked a question earlier.

The hall was clearly packed too. People standing. Speaks well of the conference participants that they gave such welcome and attention to an outsider.

Here are the links again.
Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides:
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917

 

[marcus]

I should update this thread and record the new stuff that has happened since the July QG² conference and Rovelli's invited talk at Strings 2008.
A major development, I would say, is the planned launch of two new spacecraft observatories in April 2009---Planck and Herschel. I hope the current financial crisis does not delay the launch. These observatories present a challenge to the nonsingular quantum cosmology community to come up with predictions about structure formation in the early universe.

Bojowald in particular has begun to focus on deriving structure formation features from nonsingular (bounce) cosmology models.

A team consisting of Alexander, Ashtekar, and Bojowald won a FQXi grant for a two-year study involving deriving phenomenology (things to look for) from nonsingular QC.

In other areas, there was a conference at Sussex in September which had an interesting lineup of 2-day tutorials followed by three days of invited talks.

Martin Reuter (asymptotic freedom, UV fixed point) and his co-authors were strongly represented---at least four principal actors.

Renate Loll (triangulations, emergence of deSitter spacetime) and her co-authors were also present in roughly equal strength.

Laurent Freidel and Jerzy Lewandowski presented Spinfoam and Loop papers.

John Barrett was there. I don't know the actual subject of his talks but this month he gave a talk at Loll's seminar at Utrecht which was about the Geometrical Basis of the Standard Model. Here are some links:

Slide sets for the September Sussex QG school (John Barrett, Renate Loll, Martin Reuter,...)
http://www.ippp.dur.ac.uk/Workshops/08/NPMQFT/Programme/
Slide sets for the Sussex conference (John Barrett, Laurent Freidel, Roberto Percacci, Jan Ambjorn, Jerzy Lewandowski,...)
http://www.ippp.dur.ac.uk/Workshops/08/CLAQG/Programme/

I want to especially recommend people look at the slides for Percacci's talk "A particle physicists view of gravity"
http://www.pact.cpes.sussex.ac.uk/~dl79/CLAQG/Percacci.pdf
I think his view of gravity (with the LHC in mind) parallels and clarifies the perspective in Frank Wilczek's book The Lightness of Being.

There are probably other things to report but this is all that occurs at the moment. Maybe I will post more later.

 

[marcus]

There has been an order-of-magnitude change in Quantum Gravity since 2003 when I began watching the QG research community. I will explain using this example of a recent 5-day workshop at Utrecht organized by Dan Oriti:

http://www1.phys.uu.nl/wwwitf/MMQS/
Microscopic models of Quantum Spacetime
Utrecht, 15 - 19 Sept. 2008
Microscopic models of Quantum Spacetime

" Microscopic models of Quantum Spacetime " is a 5-days informal, technical workshop at Utrecht University, discussing some recent developments in our theoretical understanding of the fundamental, physical nature of spacetime at the Planck scale.
# The main themes of the workshop are loop quantum gravity and spin foam models, simplicial quantum gravity and discrete geometry, group field theories, non- commutative geometry. Sponsor of the event is FQXi- Foundational Questions Institute
. The workshop will consist of 2-3 long talks per day. Plenty of time will be set aside for in-depth discussion...

My comment is that in 2003 when I started to pay close attention there was not even on annual meeting of the background independent QG research community. Then in spring 2004 Rovelli held a loop/foam workshop, but there was still no suggestion of regular conferences. Then in 2005 the AEI (Albert einstein inst.) hosted Loops '05. The idea of an annual meeting emerged, and yet there was no Loops '06. However in 2007 there was the spring Zakopane school for young QG researchers and the Morelia Loops '07.

Abrubtly, in 2008, there is much more activity. Another Zakopane meeting, then QG-squared (an alternative name for Loops, more inclusive) in Nottingham. Then in September TWO exciting workshops, one at SUSSEX and one at UTRECHT.

These workshops are not exclusively loop/foam. They include Triangulations (cdt), Regge, GroupFieldTheory (gft), Reuter stuff (uv fixedpoint, asympt. safety) as well as Loop/Foam. The researchers, like Bianca Dittrich, are getting very good at crossing back and forth across the borders and comparing what they get with this and that approach. They have become specialists in the whole leading edge enterprise----a kind of freestyle swimming using any and all approaches. All this robust activity is nice to see. There is simply more happening than there was in 2003. Or so it seems to me as a sideline observer.

The lineup at these workshops can tell us trends. I already discussed the Sussex CLAQG workshop. Let's look at the other thing that happened in September, the Utrecht workshop.

 

[marcus]

http://www1.phys.uu.nl/wwwitf/MMQS/
Here are the participants. They are all second-generation. Postdocs or junior faculty who have in the past worked with some first-generation QG people (Williams, Ashtekar, Rovelli, Smolin, Barrett, Loll, Freidel, ...) This classification is not very good and I am leaving out mention of important people, but I want to give a rough idea of the generational cohort.
==quote==
Participants-speakers of the workshop Microscopic models of Quantum Spacetime

* S. Alexandrov, LPT - CNRS, Montpellier
* B. Bahr, Cambridge University
* E. Bianchi, SNS, Pisa
* B. Dittrich, Utrecht University
* F. Girelli, SISSA, Trieste
* K. Noui, LMPT, Univ. Tours
* D. Oriti, Utrecht University
==endquote==
Now here are the titles of some of the talks:

Karim Noui: Spin foams and LQG scalar product
Karim Noui: Spin foams and LQG scalar product
Sergei Alexandrov: Covariant view on loops and foams: SL(2,C) case
Eugenio Bianchi: Graviton propagator and simplicial QG
Bianca Dittrich: Area-angle Regge calculus
Florian Girelli: On the relationships between NCG and QG
Sergei Alexandrov: Covariant view on loops and foams: SU(2) case
Eugenio Bianchi: Spin networks and simplicial geometry
Bianca Dittrich: Discrete phase space, BF theory and LQG
Benjamin Bahr: Semiclassical LQG coherent states
Daniele Oriti: GFT and simplicial quantum gravity
Florian Girelli: On the relationships between NCG and QG discussion
Benjamin Bahr: SemiclassicalLQG coherent states
Daniele Oriti: GFT and simplicial QG

 

[marcus]

There was an important workshop this summer, and PDF slide files are available for some of the talks.
http://www.icms.org.uk/workshops/ndsr
The July 7-11 workshop at Edinburgh was funded in part by QGQG network (quantum geometry and quantum gravity)---an arm of ESF (euro science foundation). Remember the QG-squared conference took place the week before at Nottingham. The workshop came right on the tail of the main annual conference.

This workshop is relevant to a paper which Etera Livine indicated was in preparation (by Girelli, Livine, Oriti). There was this reference in a recent paper of his:
[8] F. Girelli, E.R. Livine and D. Oriti, Doubly Special Relativity from 4d Spinfoam models, in preparation;
E.R. Livine, Non-commutative field theories from 3d and 4d spin foam models, Talk at the “Noncommutative Deformations of Special Relativity” ICMS workshop (Edinburgh, July 2008)

the basic idea is why should momentums add? Why can't the momentum space be curved instead of flat, with momenta combining by a (slightly noncommutative) group multiplication
rather than by a dumb vector addition? If space space can be curved, then why not momentum space as well? That kind of thinking.

Well Freidel Livine and others gave the idea a chance in 3D (always good to start in lower dimensionality and work up) and amazingly enough in 2005 they got that DSR (deformed special rel) comes right out of 3D spinfoam! And they got matter born out of the geometry in a natural way. Matter's feynman diagrams were just flattened out spinfoams.

So this result intrigued people and ever since 2005 they are wondering if this would also work in 4D. Can you get matter, can you get feynman diagrams, can you get "noncommutative field theories from 4D spinfoam models"? And can you get DSR from 4D spinfoam? If it works in 3D, why wouldn't it work in 4D? And the first attempts met with frustration, which went on for some 3 years, so long that one could easily have given up on the idea (or so it seemed to me). But then there was this July 2008 workshop. John Barrett's ESF money helped keep the fire burning. After a long time the metal in the crucible looks like it might be melting. Or maybe not. We don't know.

So. to get a feel for how that line of research is progressing, check out the workshop lineup and some of the PDFs.
There's files for talks by (among other people):
Jerzy Kowalski-Glikman
Laurent Freidel
Florian Girelli
Michele Arzano
Dario Benedetti

And keep an eye out for the GLO paper Doubly Special Relativity from 4d Spinfoam models, in preparation.

 

[marcus]

It is always interesting to see the lineup at the major international General Relativity and Gravitation (GRG) conference take shape. This can be window not only on the current approaches to Quantum Gravity, but a lot more as well.

The GRG conference happens every 3 years. It is abbreviated GR18, GR19 etc.

GR18 was in Sydney in 2007 and about 600 people participated. Abhay Ashtekar was elected president of the GRG Society that organizes the conference.

Now we can watch GR19 take shape. It will be in Mexico in 2010. It already has a website which lists the members of the scientific organizing committee.

http://www.gr19.com/scicom.php

The point about this conference is that the scope is very wide. It has experimental gravity stuff, like gravity wave detection and much else. It has both classical cosmology and quantum nonsingular cosmology. It has classical General Relativity research and various approaches to quantum GR. The conference connects to a lot of different observational and theoretical research fields. So it gives an overall perspective that let's you see where the various subfields stand.

At each GRG conference they award the Xanthopoulos Prize which is a major GR-related prize. It is a way of telling what subfield of Gravitation research is seen as making especially good progress. For example, if gravity wave detection is making good progress by that time, then the prize might go to someone working in that field. Or if there are important developments in some theoretical area, it might go to someone in that line of theory.

So we'll see.