New stuff happening in Quantum Gravity

[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.