Strings Meets Loops at the Albert Einstein Institute

[marcus]

John Baez just posted this announcement and tentative schedule for a conference this month at the Albert Einstein Institute (Max Planck Institute for Gravitation Physics) on the outskirts of Berlin.

We have had several threads at PF studying work by AEI people---Hanno Sahlmann, Martin Bojowald,...
Here's John Baez announcement:
-------------------------

Announcement of AEI Symposium 29 - 31 October, 2003

"STRINGS MEET LOOPS"

Organizers: A. Ashtekar (PSU) and H. Nicolai (AEI)

The primary purpose of this meeting is to bring together researchers working on string theory on the one hand, and on canonical and loop quantum gravity on the other, and to enhance exchange of ideas between the two communities. The program will consist of talks that will not be too technical, and should be primarily addressed to the other community. Their main purpose is to serve as a concrete platform for subsequent discussions. Each one hour talk will be followed by half an hour of discussion. The discussion need not be restricted to the material presented by the speaker, but should cover the general area of the talk. We expect a lively and frank exchange of ideas and anticipate many probing questions from the audience and participants who may have a different perspective on the subject than speakers.

For further information concerning participation in this symposium,
contact M. Bojowald at mabo@aei.removethis.mpg.andthis.de




PROGRAM


Wednesday 29 October:

9:30 H. Nicolai: Introductory remarks

10:30 A. Ashtekar: Quantum geometry and its applications: an overview
11:30 Discussion

(Chair: H. Nicolai)

12:30 Lunch

14:00 K. Peeters: Supergravity description of string diagrammatics
15:00 Discussion

15:30 Coffee

16:00 M. Henneaux: Cosmological billiards and hidden symmetries
of gravitational theories
17:00 Discussion

(Chair: D. Giulini)



Thursday 30 October

9:00 B. de Wit: Supergravity, duality and BPS states
10:00 Discussion

11:00 J. Lewandowski: The Hamiltonian constraint
12:00 Discussion

(Chair: D. Maison)


12:30 Lunch

14:00 M. Bojowald: Loop quantum cosmology
15:00 Discussion

15:30 Coffee break

16:00 M. Douglas (by video link): Statistics of string vacua
17:00 Discussion

(Chair: S. Theisen)



Friday 31 October:

9:30 C. Rovelli: Spin foams
10:30 Discussion

11:00 J. Plefka: Supermembranes, M(atrix) theory and all that
11:30 Discussion

(Chair: L. Freidel)

12:30 Lunch

14:00 M. Niedermaier: Integrable quantum gravity in two dimensions
15:00 Discussion

15:30 Coffee break

16:00 A. Ashtekar: Closing remarks
16:30 Conference ends

(Chair: D. Luest)

_______________________________________________

 

[marcus]

Hermann Nicolai is a string/brane theorist who has, eg., authored or coauthored 9 stringy-type articles since January 2002. One of the active senior research people at AEI (Albert Einstein Institute, Golm right outside Berlin)

Abhay Ashtekar is a relativist who works in (Loop) Quantum Gravity. He runs the Center for Gravitational Physics and Geometry at Penn State (which was set up to get him to come there I believe)

This conference is a first in some respects. Actually when relativists like Ashtekar have set up conferences on classical and quantum general relativity they have regularly invited string theorists to come and present papers! And one sees from the schedules of past GR and QG conferences that string theorists have taken part. But my understanding is that the string theorists have, as a rule, not invited LQG people---they may generally be in denial about the growing success and importance of a neighboring field of research.

However now we have a conference where ONE of the organizers (tho not both) is a string theorist and, breaking with tradition, Loop Quantum Gravity people are invited to give papers and indeed are giving half the invited talks.

Golm where the AEI is is actually right next to Potsdam (where the University of Berlin and the MPI for Gravitation Physics are). It is all one place really. So this is a kind of "Potsdam Conference"
where important string people will formally take note of the recent advances in LQG. It may change the balance somewhat in future conferences and this could, it is remotely possible, eventually be reflected in the balance in research budgeting
and positions. It is, I feel, a hopeful development. Several of the names will be familiar to PF readers.

 

[Mentat]

This is awesome! Thanks for telling us about this, marcus.

 

[ranyart]

Originally posted by Mentat
This is awesome! Thanks for telling us about this, marcus.

And here is an awsome link:http://uk.arxiv.org/PS_cache/hep-th/pdf/0310/0310077.pdf

Carlo Rovelli.

 

[Mentat]

Originally posted by ranyart
And here is an awsome link:http://uk.arxiv.org/PS_cache/hep-th/pdf/0310/0310077.pdf

Carlo Rovelli.

Thanks for that, ranyart. I've just finished reading it, and it was most interesting. However, there are philosophical problems with Sal's argument that the Professor didn't notice (I can't blame him, since his field is just he physics and mathematics). We should devote a thread to this conversation, ranyart (though I wouldn't feel right starting it myself, and insist that you do so).

 

[ranyart]

Originally posted by Mentat
Thanks for that, ranyart. I've just finished reading it, and it was most interesting. However, there are philosophical problems with Sal's argument that the Professor didn't notice (I can't blame him, since his field is just he physics and mathematics). We should devote a thread to this conversation, ranyart (though I wouldn't feel right starting it myself, and insist that you do so).

Thanks Mentat, I would have to agree on the exploration of the paper and its interesting angles, but I can only suggest Working(in the spirit of a recent Hawking Paper) from the bottom up!

The last sentence form Rovelli, quote:The final words of Professor Simp were not heard. But he was seen smiling, and later heard
referring to Sal as stubborn, but definitely smart. By the way, Sal is still looking for a job. . .

has a bit of Philosophical Hidden Variables! for instance we can ask, who is in pursuit of a career over truth? at least this is one possible outcome. Is Sal career minded?..or is it his/her pursuit of truth, and based on his/hers own questions which is of importance?

As soon as I have re-read the paper, I will comit myself to the plus's and minus's of how I see it, but it is a great first read, one cannot help but delve a little deeper, and from a number of perspective angles.

 

[Mentat]

Originally posted by ranyart
Thanks Mentat, I would have to agree on the exploration of the paper and its interesting angles, but I can only suggest Working(in the spirit of a recent Hawking Paper) from the bottom up!

The last sentence form Rovelli, quote:The final words of Professor Simp were not heard. But he was seen smiling, and later heard
referring to Sal as stubborn, but definitely smart. By the way, Sal is still looking for a job. . .

has a bit of Philosophical Hidden Variables! for instance we can ask, who is in pursuit of a career over truth? at least this is one possible outcome. Is Sal career minded?..or is it his/her pursuit of truth, and based on his/hers own questions which is of importance?

As soon as I have re-read the paper, I will comit myself to the plus's and minus's of how I see it, but it is a great first read, one cannot help but delve a little deeper, and from a number of perspective angles.

Yeah, it's a great read, but I was a bit disappointed that the Professor didn't notice the logical errors in Sal's reasoning (some of the things that s/he was asking for from the theory were completely illogical, and they are not satisfied by LQG either!).

Like I said, you should start a thread on it, ranyart.

 

[marcus]

mi casa es su casa

Originally posted by Mentat
...<snip>...We should devote a thread to this conversation, ranyart (though I wouldn't feel right starting it myself, and insist that you do so).

Mentat and Ranyart you have already begun a thread on this conversation, right here!, please continue if you're so inclined. it is not in any way off-topic----I have nothing special to add right now about the opending announcement of a symposium (at which rovelli will be giving a talk).

as far as I am concerned, this is a friendly continuation and not a redirection of the thread!

 

[Mentat]

Originally posted by marcus
Mentat and Ranyart you have already begun a thread on this conversation, right here!, please continue if you're so inclined. it is not in any way off-topic----I have nothing special to add right now about the opending announcement of a symposium (at which rovelli will be giving a talk).

as far as I am concerned, this is a friendly continuation and not a redirection of the thread!

Alright.

Here are my notes on the conversation, which I took while reading (my comments are in bold):

My notes
Sal’s arguments basically hinged on the following points:

“Perche’ I nostri discorsi hanno a essere sopra un mondo sensible, e non sopra un mondo di carta” … “Our arguments must be about a world we experience, not about a world made of paper”.

This is utterly fallacious, since the two greatest theories of modern physics defy the modern "experience" for a "world of paper". How can Sal honestly hold this against SMT?

“[The search for a theory of everything] has never worked and may fail this time too”.

Of course it MAY fail this time too. So MIGHT LQG, that doesn't mean it's not worth pursuing.

“Is there a paper now that shows, blah blah blah?”

This really bothers me. Throughout this entire conversation, she's been asking him to present papers that give a complete understanding of some of the most complicated issues in Theoretical Physics today. If string theory had already produced such certainties, it would already be the ToE. As it is, we can still be very hopeful for it.

Continued notes, without commentary
She then contradicts her own points by asking us to abandon all of the tools of QFT, just to incorporate background indepence, which is not something we “experience” in normal life. She also points out that LQG does not follow unitary evolution, because it disregards that there is space (with stuff on it) and time (with stuff on it). This is in favor of the background-independence of GR but in complete contrast with what we “experience” in normal life.

Basically, the above is my using her own arguments (which I still don't like) against her own defense of LQG.

Now, I'm not saying that LQG isn't just as good as SMT (and I'm not saying it is, either ), but I am saying that most of her points against the Professors encouragements toward studying SMT instead of LQG were fallacious.

 

[sol1]

Standard Model

http://superstringtheory.com/basics/basic4a.html


In the nonrelativistic string, there was a clear difference between the space coordinate along the string, and the time coordinate. But in a relativistic string theory, we wind up having to consider the world sheet of the string as a two-dimensional spacetime of its own, where the division between space and time depends upon the observer.


If the photon becomes the undertsanding of longitudal directionU(1), and the transverse wavesSU(2) become the extension to the world sheet, then the idea behind following the logic, siads, that in the z directionSU(3) is rotation, and boson production? This follows the idea of information being released along with the photon where the photon can be held to mass considerations, while gravity is not.

The basis then of all determinations is a energy one(https://www.physicsforums.com/showthread.php?s=&goto=lastpost&threadid=6963 )

I am open to corrections.

Sol

 

[marcus]

The Symposium began today. The actual schedule posted on the web is essentially the same as the tentative schedule I posted at the start of the this thread, except that Laurent Freidel will give the talk on spin foams in Rovelli's place. Here's the schedule posted earlier with that change:

Originally posted by marcus
...conference this month at the Albert Einstein Institute (Max Planck Institute for Gravitation Physics) on the outskirts of Berlin.

We have had several threads at PF studying work by AEI people---Hanno Sahlmann, Martin Bojowald,...

-------------------------

Announcement of AEI Symposium 29 - 31 October, 2003

"STRINGS MEET LOOPS"

Organizers: A. Ashtekar (PSU) and H. Nicolai (AEI)

The primary purpose of this meeting is to bring together researchers working on string theory on the one hand, and on canonical and loop quantum gravity on the other, ...

For further information concerning participation in this symposium,
contact M. Bojowald at mabo@aei.removethis.mpg.andthis.de


PROGRAM


Wednesday 29 October:

9:30 H. Nicolai: Introductory remarks

10:30 A. Ashtekar: Quantum geometry and its applications: an overview
11:30 Discussion

(Chair: H. Nicolai)

...

14:00 K. Peeters: Supergravity description of string diagrammatics
15:00 Discussion


16:00 M. Henneaux: Cosmological billiards and hidden symmetries of gravitational theories
17:00 Discussion

(Chair: D. Giulini)



Thursday 30 October

9:00 B. de Wit: Supergravity, duality and BPS states
10:00 Discussion

11:00 J. Lewandowski: The Hamiltonian constraint
12:00 Discussion

(Chair: D. Maison)
...

14:00 M. Bojowald: Loop quantum cosmology
15:00 Discussion

16:00 M. Douglas (by video link): Statistics of string vacua
17:00 Discussion

(Chair: S. Theisen)


Friday 31 October:

9:30 L. Freidel: Spin foams
10:30 Discussion

11:00 J. Plefka: Supermembranes, M(atrix) theory and all that
11:30 Discussion

(Chair: M. Staudacher)

12:30 Lunch

14:00 M. Niedermaier: Integrable quantum gravity in two dimensions
15:00 Discussion
...

16:00 A. Ashtekar: Closing remarks
16:30 Conference ends

(Chair: D. Luest)

_______________

here's a link to the Institute's website that has the schedule

http://www.aei-potsdam.mpg.de/events/stringloop.html

 

[jeff]

Audio for LQG (along with string theory) lectures given during two conferences on the subject of strong gravitational fields held in 1999 at the KITP can be heard here:

http://online.kitp.ucsb.edu/online/gravity99/

http://online.kitp.ucsb.edu/online/gravity_c99/

Enjoy.

 

[sol1]

Originally posted by jeff
Audio for LQG (along with string theory) lectures given during two conferences on the subject of strong gravitational fields held in 1999 at the KITP can be heard here:

http://online.kitp.ucsb.edu/online/gravity99/

http://online.kitp.ucsb.edu/online/gravity_c99/

Enjoy.

What is nice about these links is that they lead to other avenues of information as well.

For instance: It lead me too...

http://relativity.livingreviews.org/Articles/lrr-2003-2/index.html

So thanks. It is deeply appreciated.

Sol

 

[helenb]

Could we say that strings are a constant and that they bind each and every thing in the universe at different levels?
HelenB

 

[ranyart]

Here is a Paper that has relevance to the meeting, having read it yesterday morning, no doubt others have allready done this, but we will leave comment for another day:http://uk.arxiv.org/abs/gr-qc/0311003

 

[marcus]

Originally posted by ranyart
Here is a Paper that has relevance to the meeting, having read it yesterday morning, no doubt others have allready done this, but we will leave comment for another day:http://uk.arxiv.org/abs/gr-qc/0311003

ranyart, thanks for the link. I didn't know about this paper---didn't look at arxiv yesterday, or yet today.

several things about the paper were interesting. It takes a microscopic look at the the classical big bang singularity----where the geometry of space becomes chaotic at a finer and finer scale (more and more "jagged" I guess you could say)-----and studies in more detail than was done earlier just how quantizing the model cures the singularity and stops chaotic development at a certain scale.

It was interesting also to see this collaboration between Bojowald and Date continue. Date is at India's Chennai institute. I recently found another loop cosmology paper by someone else at Chennai, named Hossain. It was about the quantum operator corresponding to the Hubble parameter in LQC. There are only a few places in the world where loop gravity research is done and it looks like Chennai may emerge as one of these centers. I don't know anything about Date or about Gossain either, aside from their papers.

thanks for keeping an eye out, enjoyed looking at this short (4-page) paper, even though certainly didnt understand much of the technical detail could still get some general idea from it

 

[marcus]

I'm especially interested to know what Freidel said about spin foams at the symposium last week

if anyone has a link or can provide a short abstract, would very much appreciate

I want to know how much coverage he gave Livine's thesis
and the spin networks in non-compact case (how they connect to spin foam) and the work by other people that connects with the topics in the thesis

 

[Urs]

Hi -

I have been at the symposium. I cannot give a decent summary of Freidel's talk but there were a couple of other things that caught my attention. We have been discussing some of this over on sci.physics.research.

One important point, that was however mostly discussed during coffee breaks and briefly in Ashtekar's final lecture, was the question whether the LQG computation of black hole entropy _assumes_ that the entropy (to leading order) is proportional to the horizon area, or whether it actually derives it. On s.p.r. several string theorists have expressed concerns about the fact that the counting of states is apparently restricted to the horizon by hand. So at the conference I have asked Ashtekar about this. He appreciated that he was made aware of the fact that string theorists think this is a problem. Here is my summary of what he answered:

<begin quote from s.p.r.>
I am currently at the "Strings meet Loops" symposium at the
Albert-Einstein-Institute in Potsdam, Germany, and I have taken the
opportunity to interview A. Ashtekar after dinner on the entropy
caclulation of black holes in LQG and other issues. John Baez has also
already answered this question, but I'll try to reproduce here what
Ashtekar said as I understood it.

Regarding the question of whether the proportionality (to first order)
of the entropy of a black hole to the area of its horizon is an
assumption or a result of LQG Ashtekar essentially made two points:

1) That the interior of the black hole does not enter the calculation
is a result of how the phase space of the system has to be
constructed.

I should have asked for further details on this point because I don't
understand it well. My impression was however that the interior of the
black hole can be removed due to purely kinematical considerations.
Apparently this step is trivial to those working in the filed, even
though to others it may contain the crucial information.

2) Even though it now follows that the entropy is entirely that of a CS
theory on the horizon, Ashtekar stressed that this does not imply at
all that we shoud automatically expect it to be proportional to the
area of the horizon. Rather, he said, the entropy of CS on a punctured
sphere depends crucially on the number of punctures, Since these
punctures are due to spin networks poking throught the horizon, the
nature of spin networks enters crucially into the calculation of the
area. Therefore it is nontrivial that the entropy calculated this way
for black holes really is propertional to the area.

We have talked about other things which I found highly interesting and
which I would like to discuss further on s.p.r., but right now I am
way too tired for that... :-)

<end quote from s.p.r.>

spr thread on black hole entropy

 

[dlouapre]

http://www.aei-potsdam.mpg.de/events/stringloop.html

The talks are online at AEI website...

David

 

[marcus]

Originally posted by dlouapre
http://www.aei-potsdam.mpg.de/events/stringloop.html

The talks are online at AEI website...

David

Thanks!