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New stuff happening in Quantum Gravity 
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#1
Feb908, 10:27 PM

Astronomy
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PF Gold
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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 loopspinfoam 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 noncritical string (field) theory. "Extra dimensions" are not required in this approach. 


#2
Feb908, 11:11 PM

Astronomy
Sci Advisor
PF Gold
P: 23,226

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, writeup 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 lowdimension 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/publ...lications.html 


#3
Feb1208, 01:09 PM

P: 145

Great, Marcus. I didn't know about the Speziale stuff.



#4
Feb1408, 07:00 PM

Astronomy
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PF Gold
P: 23,226

New stuff happening in Quantum Gravity
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 nonessential 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. 


#5
Feb2008, 08:50 PM

Astronomy
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PF Gold
P: 23,226

John Baez and Bertram Kostant each gave talks relating to E_{8}
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 onehour 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: 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 downtoearth 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/ 


#6
Feb2208, 01:43 PM

Astronomy
Sci Advisor
PF Gold
P: 23,226

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. 


#7
Feb2208, 01:52 PM

P: 182

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.



#8
Feb2208, 02:41 PM

Astronomy
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PF Gold
P: 23,226

(I have a mac) 


#9
Feb2208, 10:12 PM

PF Gold
P: 116

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 


#10
Feb2308, 12:35 AM

Astronomy
Sci Advisor
PF Gold
P: 23,226

Your guess is as good as mine. One possibility is the server is overloaded. Too many people trying to watch Baez lecture. 


#11
Feb2408, 01:02 PM

P: 182

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.



#12
Feb2408, 03:27 PM

Astronomy
Sci Advisor
PF Gold
P: 23,226

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 systemthus 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 adhoc empirical formulae. The theory successfully explains solar system observations, the dispersion velocities of globular clusters, the rotation curves of galaxies, the mass profiles of Xray 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 parameterfree 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 adhoc 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." 


#13
Feb2408, 04:28 PM

P: 344

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


#14
Feb2508, 06:03 PM

P: 182

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? 


#15
Feb2508, 07:27 PM

PF Gold
P: 7,363




#16
Feb2608, 05:29 AM

P: 344

Just tried again, but all I get is a timeout. I have also sent a trackback to their blog from my post, but it did not appear there... Christine 


#17
Feb2608, 06:31 AM

PF Gold
P: 7,363

I'm using a plainvanilla 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.



#18
Feb2608, 02:36 PM

P: 182

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. 


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