New stuff happening in Quantum Gravity

[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.