How do you see the next phase of background independent QG research?

[marcus]

How do you see things shaping up during the next few years in Quantum Gravity?

the last two years have seen a lot of change
there are some new approaches that have either just been discovered (like Smolin's group finding matter degrees of freedom in spin networks)
or have recently become prominent (like asymptotic safety approach of Reuter and Percacci groups)

there are attempts to get different approaches to CONVERGE---like A & G working for the past two years on unifying spin network LQG with Alain Connes Noncommutative Geometry.

and many people including Rovelli and Freidel working on making spinfoam so it has the right low-energy behavior and also matches LQG----if you read the "new spinfoam vertex" papers you see a major focus on unifying spinfoam with canonical LQG.

so there is a trend or a groping towards convergence and unification of approaches.

And Martin Reuter gave a very clear prescription for the next 5 years when they were asked at the end of Loops '07. He wants to see the dimension of the critical hypersurface around the renormalization group fixed point be the same as the number of ambiguities in LQG----some number like three: of parameters that you can nail down and then the theory is predictive. Seriously or not, he gave a vision of equivalence between the two approaches: his and Loop.

In the Q&A at the end of his Asymptotic Safety chapter for Oriti's book, Percacci also described various way the approaches could converge.

Those are some things I see happening or vaguely on the horizon. What do you see? Can you describe in better detail what is going on?

What are some other trends?

 

[ensabah6]

How do you see things shaping up during the next few years in Quantum Gravity?

the last two years have seen a lot of change
there are some new approaches that have either just been discovered (like Smolin's group finding matter degrees of freedom in spin networks)
or have recently become prominent (like asymptotic safety approach of Reuter and Percacci groups)

there are attempts to get different approaches to CONVERGE---like A & G working for the past two years on unifying spin network LQG with Alain Connes Noncommutative Geometry.

and many people including Rovelli and Freidel working on making spinfoam so it has the right low-energy behavior and also matches LQG----if you read the "new spinfoam vertex" papers you see a major focus on unifying spinfoam with canonical LQG.

so there is a trend or a groping towards convergence and unification of approaches.

And Martin Reuter gave a very clear prescription for the next 5 years when they were asked at the end of Loops '07. He wants to see the dimension of the critical hypersurface around the renormalization group fixed point be the same as the number of ambiguities in LQG----some number like three: of parameters that you can nail down and then the theory is predictive. Seriously or not, he gave a vision of equivalence between the two approaches: his and Loop.

In the Q&A at the end of his Asymptotic Safety chapter for Oriti's book, Percacci also described various way the approaches could converge.

Those are some things I see happening or vaguely on the horizon. What do you see? Can you describe in better detail what is going on?

What are some other trends?

LHC results may affect research directions, obviously if SUSY is observed, or Higgs, or new particles, or higher dimensions. Obviously if LHC finds evidence of both higher dimensions and SUSY, it's entirely possible LQG-BI interest will dry up and string's hegemony will continue unabated. Other results, including astronomical or even TEV are important (i.e speed of c)

I would like to see more research into condense matter models, , although Wen seems to think LQG could be a string net condensation convergence, Volvovik argues that quantizing GR is fundamentally the wrong approach, and that in his view, GR and SM arise from a fermionic vaccuum. (Though he regards string-M-theory as equally misguided as BI LQG)

There may be in the near future a convergence between Wen's string net condensation and work by Fotini in this direction in her "quantum graphity" papers.

 

[jal]

Hi ensabah6!
I like your assessment.
jal

 

[ensabah6]

Hi ensabah6!
I like your assessment.
jal

you and I are in substantial agreement.

 

[marcus]

Hi you two, thanks for your thoughtful input.

Just to clarify, I am not asking what you WANT to see happen but what trends you see actually in progress and looking ahead say 5 years. what you actually expect to happen in Background Independent QG research.

To give an example, I see a pattern of fights and arguments among close relatives. As the various QG approaches converge people will inevitably step on each other's toes more.

I don't think it is sensible for us to think of ourselves as PICKING WINNERS because that is not how QG is organized. Different approaches constantly MORPH. The things in the "race" don't ever stay the same. What we are watching is different trains evolving as they merge into each other.

Have to go, more later.
======================

Back now. Another trend is the emergence of cosmology as the proving ground.

Another is the rising prominence of nonstring QG at international conferences like the GRG, the Marcel Grossmann, and the upcoming ICGC (international conference on gravitation and cosmology).
For instance at the Spring 2007 APS meeting (american physical society annual meeting) there were an equal number of nonstring QG and string invited speakers. At the Sydney GRG (general relativity and gravitation) it was 2:0 and at the ICGC it will be 6:1---this is just counting the invited plenary speakers. At these big broadgauge meetings they cover a lot of areas including various kinds of observational astronomy, so if you lump nonstring QG and string together it is a small slice of the total. Within that small slice, however, the BI approaches have become much more prominent.
this means that working cosmologists are increasingly interested in what QG folks have to say. that means, in turn, that more will be expected of them.

There will be more pressure to answer questions about things like
dark energy
accelerated expansion
structure formation in early universe
resolution of hole and bang singularities
inflation alternatives to exotic matter

 

[Chronos]

I agree entirely, marcus. The universe is the ulitimate laboratory. No earthly device will ever compete with the energies attained by inspiralling binary neutron stars. Mathematical models will compete for centuries, IMO. Better telescopes will put the fora of mathematical models in their proper place.

 

[ensabah6]

Hi you two, thanks for your thoughtful input.

Just to clarify, I am not asking what you WANT to see happen but what trends you see actually in progress and looking ahead say 5 years. what you actually expect to happen in Background Independent QG research.

To give an example, I see a pattern of fights and arguments among close relatives. As the various QG approaches converge people will inevitably step on each other's toes more.

besides any research leads LHC, TEV, HEP, or astronomy may provide,

in addition to your list I would add:

1 more research into the Kodama state, with Randanomo and Eyo Ita leading the way, and
2 more research into condense matter models (i.e Wen, Markapolou's Quantum graphity, Volvovik) of gravity and SM. Oriti's GFT is inspired by Volvovik's condense matter models.

 

[marcus]

Remember we are trying to say what to expect to happen, not what this or that person WANTS. the thread is not about what's your favorite.

So say we're talking about the next 5 years. One way is to look back over the past 5 years.
To gauge the influence, see how many papers with say 10+ citations---ten or more is not a lot to ask! Maybe add up the total cites of these 10+ papers.

So go to Spires http://www.slac.stanford.edu/spires/hep/ and put this in
FIND EA WEN, XIAO GANG AND DATE > 2002
I think you will find just one paper-----it has 12 cites
Tell me if you do a more effective search and there are any besides this with 10 or more cites.

 

[marcus]

Hi Chronos! I am glad you agree. I will test a few names and see about their recent cites, as a pointer to how the immediate future may go. Let me know if you think of anybody.

As a benchmark we can use Ensabah suggestion of Xiao Gang Wen who in the past five years had ONE paper with 10 or more---and the total was 12 cites. (one, 12)

Reuter has TEN papers in the same period that each got over 10 cites.
He also caused a lot of excitment among the grad students and postdocs when he spoke at Loops 05, the Zakopane School, and Loops 07.
FIND A REUTER, MARTIN AND AFF MAINZ U., INST. PHYS. AND DATE > 2002
I totaled up what Spires gave me and got 256.
So we can gradually accumulate some benchmarks

In case anybody missed Satz blog
http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-3.html
http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-2.html
http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-1.html
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_12.html
ESPECIALLY THIS ONE:
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_10.html
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_08.html

Xiao Gang Wen (one, 12)
Martin Reuter (ten, 256)

In trying to get a realistic picture of the next 5 years it helps to gauge how influential someone has been recently and also how much enthusiasm among the young researchers there is, for what they do. I assume everyone here has read Alex Satz blog reporting on the Zakopane school and on Loops 07. If you are talking about Background Independent QG that is where it's at, so it would be naive to try to say anything about the field without carefully studying what went down there. Satz blog is called
REALITY CONDITIONS. He is a PhD student and knows the others, and he gives an idea of how the various research looked to them and what impressed them.

that is where the energy comes from to run QG for the next five years.

Percacci (five, 90)
he shares collaborators with Reuter, so whoever Reuter draws in will sometime be co-author of a paper with Percacci.

FIND A BOJOWALD AND DATE > 2002
Bojowald (thirtysix, 1139)
that is we are trying to predict the future so we look at RECENT work in background independent QG and with Bojo we find that he has thirtysix recent papers (past five years) that got 10 or more cites and the cites on just those papers totaled up to 1139.

Reuter, Percacci, Bojowald all have ways of explaining either accelerated expansion or inflation without dark energy or exotic "inflatons" or they have ways of getting over singularities, or both or all three. That is THEY ARE TALKING ISSUES OF CURRENT INTEREST and showing results. And they are moderately or highly influential. And they are attracting young researchers to collaborate.

So it is a good bet that they have some considerable influence on the next QG phase----the next five years.
I will try to think of others. Percacci and Reuter are, of course, the asymptotic safety approach. Bojowald and his associates run the quantum cosmology approach. there are signs of convergence, which should be lively to watch!Markopoulou (five, 90)
Percacci (five, 90)
Reuter (ten, 256)
Freidel (thirteen, 348)
Bojowald (thirtysix, 1139)

 

[ensabah6]

Ok,
So then why not just tell us which papers to date have the most cites and which topics have the most papers, and we can be done with this? How many Bi-LQG researchers are thoroughly trained in condense matter physics to expand on Wen's or Volvovik's work? (how many condense matter physicists can understand BI QG-SM research?)

regards,

BTW, there are a couple of papers on SUSY + LQG, as well as LQG + higher dimensions (Oekcel has published some), with possibly few citations. However, should LHC discover SUSY, current LQG papers that have been published detailing how to incorporate SUSY into LQG would get more citations, (i.e more citations to Oeckel's previously published paper on how to incorporate SUSY in Ashketar variables) and of course, more LQG papers will be focused on SUSY by Oeckel and other researchers (though I think in this event M-theory papers would get much bigger boost).

Likewise, while LQG DSR in 2+1 has been proved, DSR in 3+1 has not been proved, but should DSR be firmly established (i.e results of Markan be established with other observations) obviously linking LQG to DSR in 3+1 would be a future research direction.

So observational results, esp from LHC (i.e electroweak symmetry breaking, SUSY, higher dimensions) may determine the course of future LQG research.

Hi Chronos! I am glad you agree. I will test a few names and see about their recent cites, as a pointer to how the immediate future may go. Let me know if you think of anybody.

As a benchmark we can use Ensabah suggestion of Xiao Gang Wen who in the past five years had ONE paper with 10 or more---and the total was 12 cites. (one, 12)

Reuter has TEN papers in the same period that each got over 10 cites.
He also caused a lot of excitment among the grad students and postdocs when he spoke at Loops 05, the Zakopane School, and Loops 07.
FIND A REUTER, MARTIN AND AFF MAINZ U., INST. PHYS. AND DATE > 2002
I totaled up what Spires gave me and got 256.
So we can gradually accumulate some benchmarks

In case anybody missed Satz blog
http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-3.html
http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-2.html
http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-1.html
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_12.html
ESPECIALLY THIS ONE:
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_10.html
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_08.html

Xiao Gang Wen (one, 12)
Martin Reuter (ten, 256)

In trying to get a realistic picture of the next 5 years it helps to gauge how influential someone has been recently and also how much enthusiasm among the young researchers there is, for what they do. I assume everyone here has read Alex Satz blog reporting on the Zakopane school and on Loops 07. If you are talking about Background Independent QG that is where it's at, so it would be naive to try to say anything about the field without carefully studying what went down there. Satz blog is called
REALITY CONDITIONS. He is a PhD student and knows the others, and he gives an idea of how the various research looked to them and what impressed them.

that is where the energy comes from to run QG for the next five years.

Percacci (five, 90)
he shares collaborators with Reuter, so whoever Reuter draws in will sometime be co-author of a paper with Percacci.

FIND A BOJOWALD AND DATE > 2002
Bojowald (thirtysix, 1139)
that is we are trying to predict the future so we look at RECENT work in background independent QG and with Bojo we find that he has thirtysix recent papers (past five years) that got 10 or more cites and the cites on just those papers totaled up to 1139.

Reuter, Percacci, Bojowald all have ways of explaining either accelerated expansion or inflation without dark energy or exotic "inflatons" or they have ways of getting over singularities, or both or all three. That is THEY ARE TALKING ISSUES OF CURRENT INTEREST and showing results. And they are moderately or highly influential. And they are attracting young researchers to collaborate.

So it is a good bet that they have some considerable influence on the next QG phase----the next five years.
I will try to think of others. Percacci and Reuter are, of course, the asymptotic safety approach. Bojowald and his associates run the quantum cosmology approach. there are signs of convergence, which should be lively to watch!


Markopoulou (five, 90)
Percacci (five, 90)
Reuter (ten, 256)
Freidel (thirteen, 348)
Bojowald (thirtysix, 1139)

 

[jal]

ensabah6 ... I still agree with your assessment
jal

 

[ensabah6]

ensabah6 ... I still agree with your assessment
jal

You and I agree on everything :)

Where would you place Witten's work on AdS3/CFT2 gravity, in the BI camp or string camp?

 

[etera]

Without doing too much self-advertising, may i suggest also all the work on the semi-classical behavior of loop gravity and spinfoam model through the study of the "graviton propagator"... The goal of the program is to check whether our (dear?) loop quantum gravity has the right semi-classical limit (general relativity) and what are the unambiguous quantum corrections to the classical theory... actually, if any of you has any comment or opinion about the work in this direction, it'd be great/fun to hear what you think about it (see stuff by Rovelli, Speziale, Modesto... and even me).

also even i don't think the citations count gives a proper assessment of how promising some work is, but i felt like adding these to your counts:
Smolin (thirteen, 515)
Rovelli (ten, 208)
Livine (ten, 209) - sorry, after seeing the citation counts, i couldn't help but check what i was worth...

 

[jal]

ensabah6
Where would you place Witten's work on AdS3/CFT2 gravity, in the BI camp or string camp?

I have not given it any though.
I think along different lines.
I'm looking for the common pattern from all the approaches that indicate that there might be a quantum structured spacetime.
I could add more but it would divert this thread by too much.
jal

 

[marcus]

Without doing too much self-advertising, may i suggest also all the work on the semi-classical behavior of loop gravity and spinfoam model through the study of the "graviton propagator"... The goal of the program is to check whether our (dear?) loop quantum gravity has the right semi-classical limit (general relativity) and what are the unambiguous quantum corrections to the classical theory... actually, if any of you has any comment or opinion about the work in this direction, it'd be great/fun to hear what you think about it (see stuff by Rovelli, Speziale, Modesto... and even me).

also even i don't think the citations count gives a proper assessment of how promising some work is, but i felt like adding these to your counts:
Smolin (thirteen, 515)
Rovelli (ten, 208)
Livine (ten, 209) - sorry, after seeing the citation counts, i couldn't help but check what i was worth...

Etera! Great to hear from you!

thanks for supplying the citation counts. Obviously we are not thinking of cites as the only measure of influence, but it does help quantify a PART of the picture.

I will merge your list in with mine.

Markopoulou (five, 90)
Percacci (five, 90)
Rovelli (ten, 208)
Livine (ten, 209)
Reuter (ten, 256)
Freidel (thirteen, 348)
Smolin (thirteen, 515)
Bojowald (thirtysix, 1139)

I can hear Rovelli (your PhD thesis advisor i think) laughing if you would tell him that you scored one more point than he. Nobody should care about differences that aren't even an order of magnitude, but when we are trying to predict the progress over the next year or two, then what has just recently happened is a useful guide.

the work that just recently HAS been cited is more likely to characterize the work to be expected over the next couple of years, than work that so far has barely been noticed. I shouldn't have to say this, it is so obvious.

It's a reality check.

OK so what kind of progress can we expect in QG over the next couple of years?

Clearly the new work in spinfoam is the most or one of the most important developments. It finally solves many problems and gives a new dynamics. Good evidence suggesting that the semiclassical limit is satisfactory----last night I was reading your and Simone Speziale paper with Dan Christensen which means BEOWULF CLUSTER!
Anyway I think that this was supercomputer work using efficient algorithms that Dan and his group have developed.
I find this exciting and the results in that new paper were good. Pointing towards good behavior both IR and UV if I understand correctly. You said in the outlook section that the next step is to do the same analysis with the new spinfoam model. That all sounds really good. I logged the paper in our bibliography thread yesterday.

-----------------------------------------------
If you want a paper to read about that, an obvious one is to get the one by Etera Livine, Simone Speziale, and Dan Christensen that I refer to here. It was posted just last night.

That paper has references that will lead you back to a lot of work that has happened in the past year and a half or so.

This is partly in response to the next post by Ensa, and in case anybody else reading didnt notice the reference here to the Christensen, Livine, Speziale paper

 

[ensabah6]

Etera! Great to hear from you!

thanks for supplying the citation counts. Obviously we are not thinking of cites as the only measure of influence, but it does help quantify a PART of the picture.

I will merge your list in with mine.

Markopoulou (five, 90)
Percacci (five, 90)
Rovelli (ten, 208)
Livine (ten, 209)
Reuter (ten, 256)
Freidel (thirteen, 348)
Smolin (thirteen, 515)
Bojowald (thirtysix, 1139)

I can hear Rovelli (your PhD thesis advisor i think) laughing if you would tell him that you scored one more point than he. Nobody should care about differences of order of magnitude, but when we are trying to predict the progress over the next year or two, then what HAS just happened is a helpful guide.

the work that just recently HAS been cited is more likely to characterize the work to be expected over the next couple of years, than work that so far has barely been noticed. I shouldn't have to say this, it is so obvious.

It's a reality check.

OK so what kind of progress can we expect in QG over the next couple of years?

Clearly the new work in spinfoam is the most or one of the most important developments. It finally solves many problems and gives a new dynamics. Good evidence suggesting that the semiclassical limit is satisfactory----last night I was reading your and Simone Speziale paper with DAN CHRISTENSEN WHICH MEANS BEOWULF CLUSTER!
Anyway I think that this was supercomputer work using efficient algorithms that Dan and his group have developed.
That I find exciting and the results in that new paper were good. Pointing towards good behavior both IR and UV if I understand correctly. You said in the outlook section that the next step is to do the same analysis with the new spinfoam model. That all sounds really good. I logged the paper in our bibliography thread yesterday.

Hi Marcus,
I do agree that establishing spinfoam semiclassical limit is GR is probably the #1 priority, otherwise you don't have gravity, but I've not seen any progress that I'm aware of.


Which specific papers do you have in mind "Clearly the new work in spinfoam is the most or one of the most important developments. It finally solves many problems and gives a new dynamics. Good evidence suggesting that the semiclassical limit is satisfactory---- "

 

[marcus]

read my previous post please

Let's get back to work on this. Please only people who are actually familiar with the QG literature of the past couple of years or so! If you do QG research or follow the field closely enough to know what's been going on---the main papers of 2005-2007---the main areas where progress has been made. If you went to Loops 05, Loops 07 or the Zakopane school or read up on several of the talks. What I mean is, iff you know the QG scene I would very much like your opinion.

Let's make the horizon a little closer. Lets try to predict QG research TWO YEARS OUT.

that is, if you have a realistic idea of what's been happening in the past couple of years, and a feel for the momentum of the various approaches, perhaps you could make an educated guess about what will actually happen between now and October 2009.

So it's a reality check. If it gets to be October 2008 and nothing that you were predicting is happening yet, then it probably won't be happening by 2009 either and better luck next time.

I am more interested in hearing what other people think who know the situation, than making my own predictions, especially anybody who was at the recent school or conferences. Maybe none of them will help out with savvy guesses But Etera already did! So things are not so bad! Come what may. I'll go ahead and say what I see happening in the next couple of years.

 

[ccdantas]

Hi Marcus,

I'll not dare to make any guesses here, this is such an active field. But I'd say that I hope the GLAST mission will have an important role in shaping some directions. I hope.Christine

 

[marcus]

Hi Marcus,

I'll not dare to make any guesses here, this is such an active field. But I'd say that I hope the GLAST mission will have an important role in shaping some directions. I hope.Christine

Christine, congratulations on the publication of your Science Fiction novel Tempo Aberto which I gather just went on sale:
http://www.lulu.com/content/1100795
also thanks so much for putting in a word here! With a two-year horizon both GLAST and MAGIC will have an important impact on Quantum Gravity. Let me turn your hope into a prediction. I feel certain of this.

Regardless of whether the answer is yes or no about dispersion, it will make a big difference either way, and be good for the field. Both telescopes are sensitive enough to help decide the basic question.

As an astrophysicist, you may have a number of other ways in mind that gammaray observations can contribute to QG development, but I think primarily of the one big issue of energy-dependent speed of light.

I think with MAGIC it is just a question of their taking the time to observe more AGN flares. A sample of one (or one and a half ) flares is not enough. They must have more in the pipeline.

 

[ccdantas]

Christine, congratulations on the publication of your Science Fiction novel Temp Aberto which I gather just went on sale:
http://www.lulu.com/content/1100795
also thanks so much for putting in a word here!

Thanks! I'll see whether there is enough interest in my book so that it is worthy the effort of translating it into English. At present, only for the Portuguese speaking world... The title is "Tempo Aberto", which means "Open Time". The book was inspired by the idea of Laplace's[/PLAIN] demon, and the most part of it was actually written many, many years ago.

With a two-year horizon both GLAST and MAGIC will have an important impact on Quantum Gravity. Let me turn your hope into a prediction. I feel certain of this.

Right, thanks for reminding me of MAGIC as well. I hope they get more data. No need to say that anyone interested in QG must be very interested on the data that these telescopes will bring.

Christine

 

[Chronos]

It is a good time to be a young cosmologist. With so many terrific projects scheduled, or peaking, over the next few years [e.g., GLAST, LHC, LIGO, MAGIC, PLANCK, JWT], we live in the most exciting era of observational astronomy in the history of science. It will take decades to decipher the flood of new data, and no existing theory will emerge unscathed, IMO.

 

[Jim Kata]

Ok, since this is such an open ended question, I'm going to answer in kind of a stream of conscious way while including what I think about string theory too. Truly the answer to this question is largely dependent on what is found by the LHC.
It seems from a theoretical standpoint, that there are some problems with loop quantum gravity. One being the failure of the Barret Crane model to give the correct long distance limit. I find it also amusing that asymptotic safety is the new sexy theory of quantum gravity. I mean I agree with its line of thought. The problem with quantum gravity has always been its non renormalizability, and a better understanding of how to address this non renormalizability seems a far more reasonable strategy than creating a whole new physics from scratch. As far as the string landscape problem, and people making anthropic principle arguments, you might as well claim it's creationism. They're both presuppositions. One uses bayesian probability the other uses some other contrived argument.
So to summarize, the real answer lies in the LHC. Questions like what if the LHC creates baby black holes like the ones claimed to of been created at the RHIC, color glass condensate? Would this mean string theory is right? What would it mean to lqg or quantum field theory? What are other people's thoughts on this?

 

[marcus]

Jim, thanks so much for adding to the discussion!
In response to your comment, I think speculating what if the LHC sees evidence of extra dimensions (what effect on QG) is a bit like speculating what if the LHC sees little unicorns. It could happen and it would be surprising! But there has so far never been any experimental evidence of either SUSY or of extra dimensions so speculating that this particular machine will see them has low priority for me. It doesn't seem like a profitable exercise.

If any totally unexpected things are seen that will of course be wonderful and theorists of every stripe will scramble---and we may see unexpected new models.

The nonstring QG community is obviously already in a period of rapid change. the biggest effort is focused on new spinfoam formalism replacing the Barrett-Crane. For a long time there was no progress in this area and the field sort of went dormant, but then around 2006 progress started to be made and now a lot of researchers (by nonstring standards) are working on it.

You mention Barrett-Crane and also asymptotic safety! I think your argument is flawed when you say everything has to wait for the LHC---a lot is going on right now as it is! I personally am extremely interested to see how asymptotic safety will mesh with the various non-string QG approaches (loosely called "LQG"). Both Percacci and Reuter's recent papers mention some remarkable instances of convergence---some of which could simply be strange coincidence.

You express amusement at my excitement with asymptotic safety---or perhaps you have encountered this avid interest in other people as well, and are amused by it. Let me say that I have been watching Reuter's work since around 2004 when it was still rather tentative, he was saying that there MIGHT be a non-gaussian FP. He spoke at Loops 05 about the remarkable coincidence of certain dimensionality results with a simplicial model of gravity (something very different for sure) suggesting that both MIGHT be on the right track. After two more years, and much checking, he is considerably more confident about the existence of the FP. I feel it's time to address the consequences.

To me this poses a serious challenge to the "LQG"-related nonstring QG approaches. I think this is good. It puts additional demands on that small community of researchers. they are "getting it from all sides"----already working hard to establish the semiclassical limit with new spinfoam models they now face input from Reuter, and the imminent prospect of some relevant astrophysical observations. You could say it is amusing if you like, but what I get is a sense of intense excitement.

These people don't need LHC results, they are already in high gear. But any challenge, input, constraint is of course good and if LHC does actually produce something unforeseen (say in 2010 when it really gets going) that would be a nice bonus for them.

You asked for our reaction. That is my "stream of consciousness" in response to yours. Hope this is what you were looking for and that it's helpful.

 

[marcus]

Another way to anticipate the emphasis and directions of QG research over the next two (or few) years is just to look at which 2007 papers are most cited. The numbers are small because a paper that appeared in 2007 has often hardly even STARTED being cited yet. It can take a few months for results to be assimilated and become the basis of future research and for papers to be written that cite the given work. But even though the citation numbers are small they could suggest to us what kinds of QG are getting particular attention. As of 7 October, here are the QG TOP FIVE papers of 2007 ranked by cites:

1) An Introduction to Loop Quantum Gravity Through Cosmology.
Abhay Ashtekar (Penn State U. & Santa Barbara, KITP) . IGPG-07-01-02, NSF-KITP-07-05, Feb 2007. 20pp.
e-Print: http://arxiv.org/gr-qc/0702030
Cited 14 times

2) A New spinfoam vertex for quantum gravity.
Etera R. Livine (Lyon, Ecole Normale Superieure) , Simone Speziale (Perimeter Inst. Theor. Phys.) . PI-QG-45, May 2007. 25pp.
e-Print: http://arxiv.org/abs/0705.0674 [gr-qc]
Cited 9 times

3) The Loop-quantum-gravity vertex-amplitude.
Jonathan Engle, Roberto Pereira, Carlo Rovelli (Marseille, CPT) . May 2007. 6pp.
e-Print: http://arxiv.org/abs/0705.2388 [gr-qc]
Cited 8 times

4) Singularities and Quantum Gravity.
Martin Bojowald (Penn State U. & Santa Barbara, KITP) . IGPG-07-2-4, Feb 2007. 41pp.
Lectures given at 12th Brazilian School of Cosmology and Gravitation (XII BSCG), Rio de Janeiro, Brazil, 10-23 Sep 2006.
Published in AIP Conf.Proc.910:294-333,2007. Also in *Rio de Janeiro 2006, Cosmology and gravitation* 294-333
e-Print: http://arxiv.org/gr-qc/0702144
Cited 6 times

5) Gamma-ray Burst UV/optical afterglow polarimetry as a probe of Quantum Gravity.
Yi-Zhong Fan (Hebrew U. & Purple Mountain Observ.) , Da-Ming Wei (Purple Mountain Observ. & Nanjing U.) , Dong Xu (DARK Cosmology Ctr.) . Feb 2007. 4pp.
Published in Mon.Not.Roy.Astron.Soc.376:1857-1860,2006.
e-Print: http://arxiv.org/astro-ph/0702006
Cited 5 times The themes are very clear: two are about QG COSMOLOGY (Ashtekar and Bojowald)
Two are about spinfoam DYNAMICS (Livine Speziale, Rovelli et al) which is closely linked to establishing the semiclassical limit.
One is about OBSERVATIONAL TESTING (Fan et al)
Parenthetically, the Fan et al paper deals with a birefringence index derived from the standard LQG model in 1998 by Gambini and Pullin (http://arxiv.org/abs/gr-qc/9809038 ). QG effect on the polarization. This is an example of a kind of paper we could see a lot more of: looking for small cumulative effects on light, possibly energy-dependent, from lengthy travel perhaps on the order of a billion years. The MAGIC collaboration posted such a paper in August. Gammaray astronomy developments feed activity around observational testing of QG.