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Strings Meets Loops at the Albert Einstein Institute

  1. Oct 7, 2003 #1


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    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


    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


    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)

    Last edited: Oct 7, 2003
  2. jcsd
  3. Oct 7, 2003 #2


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    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.
  4. Oct 8, 2003 #3
    This is awesome!! Thanks for telling us about this, marcus. :smile:
  5. Oct 9, 2003 #4
  6. Oct 9, 2003 #5
    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).
  7. Oct 9, 2003 #6
    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.
  8. Oct 10, 2003 #7
    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.
  9. Oct 10, 2003 #8


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    mi casa es su casa

    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 Im concerned, this is a friendly continuation and not a redirection of the thread!
  10. Oct 11, 2003 #9
    Re: mi casa es su casa


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

    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 :wink:), but I am saying that most of her points against the Professors encouragements toward studying SMT instead of LQG were fallacious.
  11. Oct 11, 2003 #10
    Standard Model


    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(See Liminocentric Structures )

    I am open to corrections.

    Last edited by a moderator: Oct 11, 2003
  12. Oct 29, 2003 #11


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    Re: Strings Meet Loops at the Albert Einstein Institute

    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:

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

    Last edited: Oct 29, 2003
  13. Oct 31, 2003 #12


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  14. Oct 31, 2003 #13
    What is nice about these links is that they lead to other avenues of information as well.

    For instance: It lead me too.....

    Gravitational Waves from Gravitational Collapse

    So thanks. It is deeply appreciated.

  15. Nov 3, 2003 #14
    Could we say that strings are a constant and that they bind each and every thing in the universe at different levels?
  16. Nov 4, 2003 #15
    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
  17. Nov 4, 2003 #16


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    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 dont 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
  18. Nov 4, 2003 #17


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    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
  19. Nov 5, 2003 #18


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    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

    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
  20. Nov 5, 2003 #19
  21. Nov 5, 2003 #20


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