New stuff happening in Quantum Gravity

  1. marcus

    marcus 23,922
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    Simone Speziale is teaching an introductory course on LQG, and Perimeter has the videos online.
    Lecture #1, 5 February:
    http://pirsa.org/08020008/

    Lecture #2, 7 February:
    http://pirsa.org/08020012/
    =====================

    Lee Smolin is giving a more advanced QG course and there are about eight lectures online so far.
    Lecture 1
    http://pirsa.org/08010033/
    Lecture 2A
    http://pirsa.org/08010034/
    Lecture 2B
    http://pirsa.org/08010040/
    Lecture 3A
    http://pirsa.org/08010035/
    Lecture 3B
    http://pirsa.org/08010041/
    Lecture 4
    http://pirsa.org/08010036/
    Lecture 5A
    http://pirsa.org/08020024/
    Lecture 5B
    http://pirsa.org/08020029/
    ==================
    Kirill Krasnov has given a talk on SELF DUAL GRAVITY at the ILQGS, for which the slides are available.
    http://relativity.phys.lsu.edu/ilqgs/krasnov020508.pdf
    Here is the Spring 2008 schedule for the ILQGS
    http://relativity.phys.lsu.edu/ilqgs/schedulesp08.html
    Jan 22 Quantum gravity and the information loss problem Madhavan Varadarajan Raman Research Institute
    Feb 5 Self Dual Gravity Kirill Krasnov University of Nottingham
    Feb 19 Improved effective equations in loop quantum cosmology Victor Taveras PennState
    Mar 11 TBA
    Mar 25 Manifestly gauge invariant relativistic perturbation theory Kristina Giesel AEI
    Apr 8 TBA
    Apr 22 New developements in the definition of the spinfoam vertex, and the loop-spinfoam relation Carlo Rovelli Marseille
    May 6 QFT in Cosmological Space Times from LQC Speaker TBA
    For more information and links here is the main ILQGS page:
    http://relativity.phys.lsu.edu/ilqgs/

    ==================
    Yidun Wan's seminar on network braid matter states
    http://pirsa.org/08010044/
    ==================

    Renate Loll's group has recently posted two papers applying CDT (causal dynamical triangulations) to non-critical string (field) theory. "Extra dimensions" are not required in this approach.
     
    Last edited: Feb 9, 2008
  2. jcsd
  3. marcus

    marcus 23,922
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    The Utrecht Triangulations QG group, that Renate Loll belongs to, has been busy in the past 6 months and has come out with several papers some of which go in unexpected directions (at least not expected by me.) Here are some papers since September 2007.
    1. http://arxiv.org/abs/0802.0896
    Title: Topology change in causal quantum gravity
    Authors: J. Ambjorn, R. Loll, Y. Watabiki, W. Westra, S. Zohren
    Comments: 4 pages, proceedings of the workshop JGRG 17 (Nagoya, Japan, December 2007)

    2.http://arxiv.org/abs/0802.0719
    Title: A String Field Theory based on Causal Dynamical Triangulations
    Authors: J. Ambjorn, R. Loll, Y. Watabiki, W. Westra, S. Zohren
    Comments: 29 pages, 4 figures

    3. http://arxiv.org/abs/0712.2485
    Title: Planckian Birth of the Quantum de Sitter Universe
    Authors: J. Ambjorn, A. Gorlich, J. Jurkiewicz, R. Loll
    Comments: 4 pages, 3 figures

    4. http://arxiv.org/abs/0711.0273
    Title: The Emergence of Spacetime, or, Quantum Gravity on Your Desktop
    Authors: R. Loll
    Comments: 21 pages, 11 figures, write-up of plenary talk at GR18, Sydney, July 2007

    5. http://arxiv.org/abs/0709.2784
    Title: Putting a cap on causality violations in CDT
    Authors: J. Ambjorn, R. Loll, W. Westra, S. Zohren
    Comments: 17 pages, 4 figures

    I've highlighted a paper with Watabiki, dealing with a low-dimension case of string field theory.

    On 11 February Pedro Machado, a PhD student of Loll's, will give a talk at the Utrecht ITP on
    Exact RG flows, asymptotic safety and f(R) gravity
    It points up the close relation between CDT and the Asymptotic Safety approach of Reuter, Percacci, Saueressig, and others.
    Machado just posted a paper he did with Saueressig.
    http://arxiv.org/abs/0712.0445

    ====================================
    THIS IS NOT A NEW SOURCE but since a lot is happening recently with Triangulations QG some people might want to know the best quick introduction to this approach. Geoff C just reminded me of a 50 minute video of a November 2005 talk at Perimeter by Loll.
    http://pirsa.org/05110012/
    Loll has also written several review papers for nonspecialists, and some SciAm level stuff for general audience. These are listed at her website in either the Publications section or the Press section.
    http://www.phys.uu.nl/~loll/Web/title/title.html
    http://www.phys.uu.nl/~loll/Web/publications/publications.html
     
    Last edited: Feb 10, 2008
  4. Great, Marcus. I didn't know about the Speziale stuff.
     
  5. marcus

    marcus 23,922
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    UPDATE Simone Speziale is teaching an introductory course on LQG, and Perimeter has the videos online.
    Lecture #1, 5 February:
    http://pirsa.org/08020008/

    Lecture #2, 7 February:
    http://pirsa.org/08020012/

    Lecture #3, 12 February
    http://pirsa.org/08020009/
    =====================

    Lee Smolin is giving a more advanced QG course and there are about ten lectures online so far.
    Lecture 1
    http://pirsa.org/08010033/
    Lecture 2A
    http://pirsa.org/08010034/
    Lecture 2B
    http://pirsa.org/08010040/
    Lecture 3A
    http://pirsa.org/08010035/
    Lecture 3B
    http://pirsa.org/08010041/
    Lecture 4
    http://pirsa.org/08010036/
    Lecture 5A
    http://pirsa.org/08020024/
    Lecture 5B
    http://pirsa.org/08020029/
    Lecture 6A
    http://pirsa.org/08020025/
    Lecture 6B
    http://pirsa.org/08020030/
    ==================
    Kirill Krasnov has given a talk on SELF DUAL GRAVITY at the ILQGS, for which the AUDIO is now available.http://relativity.phys.lsu.edu/ilqgs/krasnov020508.mp3
    When I posted earlier only the slides were available.
    http://relativity.phys.lsu.edu/ilqgs/krasnov020508.pdf

    The audio has some noise problems for the first 2/5 or 3/8 of the talk. But this part is non-essential overview and introduction. You can drag the Quicktime button over about 40 percent and it will restart on the good part. This will correspond to around slide #17, as I recall, but that is where the equations begin. Equation (1) and (2) are right around slide #17, as I recall.

    It is an interesting talk. Ashtekar and Rovelli and Smolin were all asking Krasnov a lot of questions. I think the course of lectures that Smolin is now giving dovetails with Krasnov's new approach and provides background to it.
     
    Last edited: Feb 14, 2008
  6. marcus

    marcus 23,922
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    John Baez and Bertram Kostant each gave talks relating to E8
    at UC Riverside recently. Each talk was great in its own way and should get special mention. There should be a list of the best one-hour math videos, these would be on.

    Here's the Baez talk
    http://mainstream.ucr.edu/baez_02_12_stream.mov

    Here's the Kostant talk
    http://mainstream.ucr.edu/baez_02_12_guest_stream.mov
    and here are Baez' notes from Kostant's talk, which can help you understand the video
    http://math.ucr.edu/home/baez/kostant/summary.html

    Kostant has given the talk at a number of universities. At UC San Diego, the announcement of the talk said:
    Baez talk is a remarkably clear introduction to E8 in which you learn what a a Dynkin diagram is and how to use them and think about them.
    It starts with the densest way to lay out pennies on a table, and the densest way to stack oranges. In other words, a really intuitive visual down-to-earth approach to classifying Lie groups where you learn a lot more than you realize or bargained for.

    And the Baez talk is the best possible entrylevel one hour preparation to watch the Kostant video. Which is mostly too technical for me to follow but can give you a whiff of an idea now and then.

    It's good to have a reminder to check ILQG regularly for new online seminars:
    http://relativity.phys.lsu.edu/ilqgs/

    Victor Taveras recently gave a talk on Effective Equations for Loop Quantum Cosmology. The audio is not yet available but the PDF is here:
    http://relativity.phys.lsu.edu/ilqgs/taveras021908.pdf

    I'll update the Simone Speziale lectures listing. This is a really helpful introduction to Loop Quantum Gravity which treats
    constrained systems, the meaning of diffeomorphism invariance, loops and spin networks:
    Lecture #1, 5 February:
    http://pirsa.org/08020008/

    Lecture #2, 7 February:
    http://pirsa.org/08020012/

    Lecture #3, 12 February
    http://pirsa.org/08020009/

    Lecture #4, 14 February
    http://pirsa.org/08020013/

    Here are the Smolin lectures on Time in Quantum Gravity. I am guessing about the URLs of lectures 7A and 7B, which have not been posted yet as far as I know.
    Lecture 1
    http://pirsa.org/08010033/
    Lecture 2A
    http://pirsa.org/08010034/
    Lecture 2B
    http://pirsa.org/08010040/
    Lecture 3A
    http://pirsa.org/08010035/
    Lecture 3B
    http://pirsa.org/08010041/
    Lecture 4
    http://pirsa.org/08010036/
    Lecture 5A
    http://pirsa.org/08020024/
    Lecture 5B
    http://pirsa.org/08020029/
    Lecture 6A
    http://pirsa.org/08020025/
    Lecture 6B
    http://pirsa.org/08020030/
    Lecture 7A
    http://pirsa.org/08020026/
    Lecture 7B
    http://pirsa.org/08020031/
     
    Last edited: Feb 21, 2008
  7. marcus

    marcus 23,922
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    Pirsa fooled me! When the two Smolin lectures were posted, ones I expected would be 7A and 7B, they were listed as 6C and 6D.

    And they had different url numbers!

    Lecture 6C
    http://pirsa.org/08020048
    Lecture 6D
    http://pirsa.org/08020049

    So what I have in the previous post about Lectures 7A and B is wrong.
     
  8. I havn't been able to get the Baez link to work. Something about real player not working. Is anyone else having this problem? I'll erase this to keep the thread clean.
     
  9. marcus

    marcus 23,922
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    Richard, this is hardly clutter! Thanks for the alert. What Baez link doesnt work?
    (I have a mac)
     
  10. xristy

    xristy 116
    Gold Member

    problem links to Baez's and Kostant's videos

    Hello,

    The links are not working for me either. If I go to http://math.ucr.edu/home/baez/kostant/ and try the links for streaming the videos, the Quicktime viewer starts up and then after awhile reports a "400 Bad response" error from the streaming server - I'm using Mac OS X 10.5.1 and Safari.

    If I try either of the downloadable video links such as http://mediaserve.ucr.edu/baez/baez_02_12_stream.mov then after several minutes I get a timeout reporting that the file doesn't exist.

    X
     
  11. marcus

    marcus 23,922
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    I watched the talk by Baez twice all the way through, earlier. After i saw your post I decided to try it again. This time I could not connect to the UC Riverside server.
    Your guess is as good as mine. One possibility is the server is overloaded. Too many people trying to watch Baez lecture.
     
  12. Still no luck with the Baez vids. Maybe it is because I run Windows and the software (quick time) appears to be an Apple product.
     
  13. marcus

    marcus 23,922
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    I'm sorry to hear you are still having trouble. things were acting up for me too, but now are back to normal.

    BTW I just watched a PI talk by John Moffatt
    http://pirsa.org/08020047/
    It was quite interesting. Based on recent work with Toth he is making a number of
    astonishing claims for his Modified Gravity scheme MOG.
    It appears to cope with the Bullet Cluster data handily, and so not to be shot down in the general MOND debacle. He also says that once two parameters are fixed once and for all, there are no free parameters in the system----thus his MOG will make unequivocal predictions which can be tested.

    In case anyone is interested, here is the abstract:

    Modified Gravity and Its Consequences for Astronomy, Astrophysics and Cosmology

    John Moffat - Perimeter Institute for Theoretical Physics

    "The consequences of a modified gravity (MOG) are explored. I demonstrate how the solutions of the field equations obtained from the action principle of the MOG lead to a theory without any free, adjustable parameters or ad-hoc empirical formulae. The theory successfully explains solar system observations, the dispersion velocities of globular clusters, the rotation curves of galaxies, the mass profiles of X-ray clusters, the dispersion velocities of satellite galaxies, the Bullet Cluster and cosmological observations without exotic dark matter. The peculiar features of the recent data obtained for the merging cluster Abell 520 are discussed. MOG predicts agreement with data from the scale of the solar system to cosmological scales without dark matter. With no undetermined free parameters, the theory can be used to make firm predictions that may be verifiable in the foreseeable future."
    19/02/2008

    MUCH of the content of the talk can be found in a recent Arxiv posting, which makes good reading to go along with the video lecture.
    http://arxiv.org/abs/0712.1796
    Fundamental parameter-free solutions in Modified Gravity
    J. W. Moffat, V. T. Toth
    8 pages, 5 figures
    (Submitted on 11 Dec 2007)

    "Modified Gravity (MOG) has been used successfully to explain the rotation curves of galaxies, the motion of galaxy clusters, the Bullet Cluster, and cosmological observations without the use of dark matter or Einstein's cosmological constant. We now have the ability to demonstrate how these solutions can be obtained directly from the action principle, without resorting to ad-hoc parameter choices or empirical formulae. We obtain approximate solutions to the theory's field equations that, after the values of integration constants are determined from observation, show excellent agreement with data from the scale of the solar system to cosmological scales. With no undetermined free parameters, the theory can be used to make firm predictions that may be practically verifiable in the foreseeable future."
     
    Last edited: Feb 24, 2008
  14. Hi all:

    I cannot download Baez's video (baez_02_12_stream.mov) as well. I'm using a mac, safari, quicktime.

    Best,
    Christine
     
  15. I got the Baez vid to work on my machine by downloading a new copy of quick time from the Apple website. However, it played for a while and then broke up.....after several tries, I got about 3/4 through.

    Baez is teaching here at about my level of understanding. I wonder what course this is?
     
  16. turbo

    turbo 7,365
    Gold Member

    Try again, Christine. I just watched it, and though there is a nagging low-frequency hum in the audio, it was watchable.
     
  17. Hi turbo-1

    Just tried again, but all I get is a timeout. :frown:

    I have also sent a trackback to their blog from my post, but it did not appear there... :frown:

    Christine
     
  18. turbo

    turbo 7,365
    Gold Member

    I'm using a plain-vanilla PC running XP SP2 over a DSL connection and the video came up fine. Try purging your browser's cache and see if you can connect after that.
     
  19. I got through the whole Baez vid up until the last minute or so. I'd like to discuss some things about it. I am not sure about the method used to raise the dimension by adding "same sized" spheres to the spaces between spheres. I guess it works because the added spheres are removed in another dimension where the size is arbitrary. This is like when looking at a two dimensional print photograph of a three dimensional set of objects, we know that an object further away (in the third dimension) will look smaller. The new spheres look smaller, but that is because they are "farther away" in the 4th dimension.

    About the idea that they are all one unit from the origin, that seems to be part of the conditions of the definition.....closest kissing spheres will always be one unit from the origin, because the origin is defined as the center of the sphere, radius = 1.

    I think we are finally getting down to the bones of the dimensional questions which keep coming back. People want to know how we do geometry in higher dimensions. Well, now I see how it is done. I still have to validate the method in my own mind, because I do not intuitively see the logic of merely adding new (smaller) spheres to the spaces.

    I usually try to do dimensions by moving the minimal shape of a dimension in a new orthagonal direction. A point becomes a line in this way, a line becomes a plane, a plane becomes a volume. The minimum stack of spheres that requires three dimensions is the tetrahedral form, where the centers of each sphere in the group are the vertices of a tetrahedron. I try to imagine shifting that along a new orthagonal basis line, one which is at right angles to the other three. I usually choose time as the 4th basis line, and lay it down parallel to one of the 3 dimensional volumetric basis lines, so the shift is represented by a simple doubling. That part seems more or less to match the method Baez describes.

    Perhaps a better way to choose a fourth basis line would be to use scale as the new basis. Then we can imagine the shift being one of size. The cubeoctahedron (3 dimensional) is expanded until a new orange fits in the spaces between. The new orange is still the same size as the originals, but the original 'old' oranges have gotten large enough to admit the 'new' oranges.
     
  20. marcus

    marcus 23,922
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    Glad you got the Baez video to run! It is a wonderful talk. I think it may echo some TWFs from back around #63-65. I haven't checked. But if so, the online TWFs could serve as lecture notes for better understanding.

    Keeping up with the New Stuff theme. The program of the APS meeting in St Louis is out.
    http://meetings.aps.org/Meeting/APR08/Content/1034
    The meeting will be 10-15 April.
    Abhay Ashtekar is giving an invited talk, as is Jorge Pullin.
    http://meetings.aps.org/Meeting/APR08/APS_Invited

    Ashtekar, Abhay Session B7.00002 Singularity Resolution in Loop Quantum Gravity
    http://meetings.aps.org/Meeting/APR08/Event/82745
    Pullin, Jorge Session M7.00002 Recent developments in loop quantum gravity
    http://meetings.aps.org/Meeting/APR08/Event/83488

    They expect about 1200 physicists to attend the April 2008 APS meeting. For an overview see
    http://meetings.aps.org/Meeting/APR08/APS_epitome
    The sessions are in alphabetical order----B is on the second day, Saturday morning 12 April.
    M is halfway through the conference, Sunday afternoon 13 April.
    W is at the end, Tuesday morning 15 April.
     
    Last edited: Feb 26, 2008
  21. Wow. Right after finally seeing the first images of John Baez, my browser (Safari 2.0.4) disapeared and the program was shutdown.

    Then tried Firefox 2.0.0.6. The same happened! I'm using Quicktime 7.2.

    Maybe I need to upgrade, or perhaps it is because I'm running a simulation in my mac at the same time. I'll try again later.
     
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