Registration deadline for Loops '07 is coming up deadline for early registration is 25 April late registration in May. Looks like most splendid Loops conference yet (even includes string as a small auxilliary sub-department See Rozali's talk further down the page) TOPICS COVERED * Foundational questions of quantum gravity * Loop quantum gravity * Spin foam models * Dynamical triangulations * Causal sets * String theory * Cosmology related to quantum gravity * Phenomenology of quantum gravity http://www.matmor.unam.mx/eventos/loops07/index.html ==quote from provisional program for the June 2007 conference== Program At this time the program is in an early planning stage. Below is the list of plenary speakers with titles of talks. Abstracts can be displayed by clicking on the title of the respective talk or by going to the abstracts page. When more detailed information on the program is available it will be posted on this site. Jan Ambjørn Abhay Ashtekar "LQG: Lessons from models" Martin Bojowald "Loop quantum cosmology and effective theory" John F. Donoghue "Effective field theory and quantum general relativity" Klaus Fredenhagen Lucien Hardy "The causaloid formalism: a tentative framework for quantum gravity" James B. Hartle "Generalizing Quantum Mechanics for Quantum Spacetime" Sabine Hossenfelder "Phenomenological Quantum Gravity" Bei-Lok B. Hu "Stochasticity and Nonlocality in Quantum-Classical and Micro-Macro Interfaces" Fotini Markopoulou Daniele Oriti Alejandro Perez Jorge Pullin "Uniform discretizations and spherically symmetric loop quantum gravity" Michael Reisenberger Martin Reuter "Asymptotically safe quantum gravity and cosmology" David Rideout Carlo Rovelli Moshe Rozali "Background Independence in String Theory" Lee Smolin Rafael Sorkin* Artem Starodubtsev "Some physical results from spinfoam models" Jörg Teschner* Thomas Thiemann ==endquote== Abstracts of most of the talks with titles shown above are already available at the website. I have printed them out here as well https://www.physicsforums.com/showthread.php?p=1294958#post1294958
The list of plenary speakers at Loops '07 has been made more definite and some abstracts have been added. The plenary talks page was updated 18 April as follows: ==quote== Abstracts of plenary talks Abhay Ashtekar: LQG: Lessons from models In the last couple of years, several simple but physically interesting models were solved. Solutions led to concrete and detailed realizations of a number of ideas that have been heuristically expected for decades. There were also some surprises. These analyses suggest viewpoints and strategies for full quantum gravity. I will summarize some of them in broad terms. === Martin Bojowald: Loop quantum cosmology and effective theory Several models have been defined to study the broad framework of loop quantum gravity. We present a common perspective for cosmology where configurations are close to being isotropic. Effective techniques are then used to illustrate important features of the semiclassical limit and to show examples of correction terms to Einstein's equation. Applications include corrections to the Newton potential and to cosmological perturbation equations relevant for the CMB power spectrum. === John F. Donoghue: Effective field theory and quantum general relativity I will review the foundations and recent progress in the use of effective field theory to elucidate the quantum predictions of general relativity. === Lucien Hardy: The causaloid formalism: a tentative framework for quantum gravity General Relativity is a deterministic theory with non-fixed causal structure. Quantum Theory is an inherently probabilistic theory with fixed causal structure. A theory of Quantum Gravity must reduce, in appropriate limits, to General Relativity and Quantum Theory. It seems likely, therefore, that Quantum Gravity will inherit the radical aspects of these two less fundamental theories – namely that it will be a probabilistic theory with non-fixed causal structure. In this talk I will present the causaloid formalism which is a general framework for such theories. I will show how Quantum Theory can be formulated in the causaloid framework and provide tentative results for how it may be possible to formulate General Relativity in the framework. Finally, I will discuss the issue of formulating a theory of Quantum Gravity using the causaloid formalism. === James Hartle: Generalizing Quantum Mechanics for Quantum Spacetime Familiar textbook quantum mechanics assumes a fixed background spacetime to define states on spacelike surfaces and their unitary evolution between them. Quantum theory has been generalized as our conceptions of space and time have evolved. But quantum mechanics needs to be generalized further for quantum gravity where spacetime geometry is fluctuating and without definite value. This talk will review a fully four-dimensional, sum-over-histories, generalized quantum mechanics of cosmological spacetime geometry. In this generalization, states of fields on spacelike surfaces and their unitary evolution are emergent properties appropriate when spacetime geometry behaves approximately classically. The principles of generalized quantum theory would allow for further generalization that would be necessary were spacetime not fundamental. Emergent spacetime phenomena are discussed in general and illustrated with the examples of the classical spacetime geometries with large spacelike surfaces that emerge from the `no-boundary' wave function of the universe. These must be Lorentzian with one, and only one, time direction. The question will be raised as to whether quantum mechanics itself is emergent. === Sabine Hossenfelder: Phenomenological Quantum Gravity The search for a satisfying theory that unifies general relativity with quantum field theory is surely one of the major tasks for physicists in the 21st century. During the last decade, the phenomenology of quantum gravity and string theory has been examined from various points of view, opening new perspectives and testable predictions. I will give a short introduction into these effective models which allow to extend the standard model and include the expected effects of the underlying fundamental theory. I will talk about models with extra dimensions, models with a minimal length scale and those with a deformation of Lorentz invariance. The focus is on observable consequences, such as black hole and graviton production and modifications of standard-model cross-sections. === Daniele Oriti: Group field theory: spacetime from quantum discreteness to an emergent continuum Group field theories are non-local quantum field theories on group manifolds, and a generalization of matrix models. Having been first introduced in the context of simplicial quantum gravity, have gained attention as being potentially of much interest in the context of loop quantum gravity and spin foam models. After a brief introduction to the group field theory formalism, I review some of the results already obtained in this approach. I will then try to offer a new perspective on how group field theories should be interpreted and used towards a complete theory of quantum gravity. In particular, I will argue that group field theories can represent on the one hand a common unifying framework for loop quantum gravity, spin foam models and simplicial approaches, like quantum Regge calculus and dynamical triangulations, and on the other hand a consistent microscopic description of spacetime considered as a condensed matter system. From this, a novel approach to the issues of the emergence of the continuum and of General Relativity as an effective description of spacetime, in this approximation, is proposed. Finally, I will briefly report on some recent results and work in progress inspired by and supporting this new perspective. === Jorge Pullin: Uniform discretizations and spherically symmetric loop quantum gravity We discuss the application of the uniform discretization procedure to handle the dynamics of loop quantum gravity with spherical symmetry. === Michael Reisenberger: Canonical gravity with free null initial data Free (unconstrained) gravitational initial data variables are known for initial hypersurfaces consisting of two intersecting null hypersurfaces. Recently the Poisson bracket on functions of such data has been obtained. This opens the prospect of a constraint free canonical formulation of general relativity. The reasons for looking for such a formulation, and some of its features will be discussed. Martin Reuter: Asymptotically safe quantum gravity and cosmology The basic ideas and main results of the asymptotic safety scenario in Quantum Einstein Gravity (QEG) are reviewed and possible implications for the cosmology of the early universe are discussed. Moshe Rozali: Background Independence in String Theory I review several notions of background independence in quantum gravity: full or partial, manifest or not etc., and discuss the evidence for and against taking the notion seriously as a guide for research. I review the current status in string theory with regard to this question and discuss the extent to which existing non-perturbative formulations of string theory are background independent. John Stachel: Projective and Conformal Structures in General Relativity Our goal is to contribute to the development of a background-independent, non-perturbative approach to quantization of the gravitational field based on the conformal and projective structures. Physically the conformal structure is determined by the local behavior of null wave-fronts and rays; and the projective structure by the local behavior of freely falling massive test particles, respectively. In general relativity, these structures may be taken as fundamental, and the pseudo-Riemannian metric and affine connection derived from them. Various initial value problems in GR may be reformulated on the basis of the conformal-projective breakup-- in particular, null-initial value problems and the 2+2 decomposition of the field equations-- with the aim of investigating how best to isolate the two degrees of freedom of the gravitational field, a question of crucial importance for their quantization. The quantum of action sets limits on the co-measurability of various physically measurable quantities, and thereby determines their commutation relations. Hence, the co-measurability of quantities derived from the conformal and projective structures, such as the conformal 2-structure, will be analyzed as a heuristic guide to their quantization. We have already derived the connection and metric from a Palatini-type variational principle utilizing the conformal and projective structures, and will explore this and various other variational principles that could form the starting point for a Feynman type quantization of the gravitational field. === Artem Starodubtsev: Some physical results from spinfoam models Given the known mathematical fact that a spinfoam is a Feynman diagram the data relevant for particle scattering amplitudes could be identified in it. ==endquote==
Hey Marcus, Since you seem to be an insider, how does the list of who gets invited to talk gets chosen, for Loops 07? Is there any possibility Xiao-Gang Wen could be invited to Loops 07? Recent advances in condensed matter theory have revealed that new and exotic phases of matter can exist in spin models (or more precisely, local bosonic models) via a simple physical mechanism, known as "string-net condensation." These new phases of matter have the unusual property that their collective excitations are gauge bosons and fermions. In some cases, the collective excitations can behave just like the photons, electrons, gluons, and quarks in our vacuum. This suggests that photons, electrons, and other elementary particles may have a unified origin -- string-net condensation in our vacuum. In addition, the string-net picture indicates how to make artificial photons, artificial electrons, and artificial quarks and gluons in condensed matter systems. A local quantum bosonic model on a lattice is constructed whose low energy excitations are gravitons described by linearized Einstein action. Thus the bosonic model is a quantum theory of gravity, at least at the linear level. We find that the compactification and the discretization of metric tenor are crucial in obtaining a quantum theory of gravity. We give an example of a purely bosonic model -- a rotor model on the 3D cubic lattice -- whose low energy excitations behave like massless U(1) gauge bosons and massless Dirac fermions. This model can be viewed as a ``quantum ether'': a medium that gives rise to both photons and electrons. It illustrates a general mechanism for the emergence of gauge bosons and fermions known as ``string-net condensation.'' Other, more complex, string-net condensed models can have excitations that behave like gluons, quarks and other particles in the standard model. This suggests that photons, electrons and other elementary particles may have a unified origin: string-net condensation in our vacuum.
I'm the opposite of an insider but thanks for the compliment! I'm a bystander---like the people on the sidewalk gawking at the riggers putting up a building. Why couldn't X-G Wen just go to the conference and deliver a paper? They would surely love to have him show up! Judging by Loops '05, in a conference like this there is space for about 60 - 80 talks, of which only 20-some are "invited", and the rest are called "contributed". There are usually the invited plenary talks in the MORNING. This conference has around 22 invited speakers. they will somehow have to schedule them, which will use up about half the time (most likely the mornings) then the remaining time (e.g. afternoons and evenings) they run 2 or more PARALLEL SESSIONS. So at any given time, say 2PM, you have a choice of several different talks, and you pick one of them to go to. If X-G Wen would just register for the conference, they would quickly assign him a good spot in one of the parallel sessions. He is well known! Then he would give a talk and probably it would attract a big audience, in one of the afternoon sessions. If his talk was a hit, then next year, or next time they have a conference, the organizer committee (and their advisor committee) might well decide to ask Wen to give a plenary talk. Of course if you feel strongly about it you could write email to someone on the "scientific advisory committee" and urge that they invite Wen to give plenary talk THIS year. But they already have 22 confirmed plenary speakers and that really is a lot to squeeze into a week of morning sessions. I don't think it is a good idea to urge that, at this point, because plenary session time is at a premium. During the plenary session you cannot, by definition, be running parallel sessions. So every halfhour that you commit to plenary means two or more halfhour talks that you cannot be having in the parallel sessions. Plenary session time is costly in terms of how many other talks you can schedule. So I would not urge for Wen to give one of those talks---which they already have enough. Better he should just give one of the ordinary talks. Maybe he will! We have not seen the list of other speakers yet. There will be at least 50 others and so far we have no idea who they are.
Well Dan, I just checked the poster and I my initial guess was wrong. I thought they would be having 3 parallel sessions, but they say they will only have two. "Format: The conference will consist of four plenary talks each morning from Monday 25 to Saturday 30 June. After lunch two parallel sessions with contributed talks will take place Monday 25 to Friday 29 June. An exception is the afternoon of Wednesday 27 June which is free. We plan to offer social events for this day, including an excursion to the beautiful town of Patzcuaro." they seem to have maybe one morning spot left uncommitted because they say they are running 24 morning talks. Of course some might be WELCOME talks or Concluding talks by the hosts. My hunch is the morning is now full. And also they say they will only have TWO parallel sessions for the "contributed talks" and that will be just be the afternoon of Monday Tuesday Thursday Friday. So that is 4 days x 2 sessions x maybe 5 talks in an afternoon session so that is only room for maybe 40 contributed talks. So I was off some. ======================= BTW I think it is absolutely fantastic to have Lucien Hardy, and Jim Hartle, and Martin Reuter AS WELL AS so many more familiar top quantum gravity people. The mexican organizers have gotten a majorly heavyweight batting lineup. and they also have a fine choice of young people helping to give the plenary talks (in many fields only the prominent senior people do that but here they have Dan Oriti and Bee Hossenfelder and so on). the more i inspect the more intelligent it looks, how they are assembling Loops '07
Hi, So who should I email so they can contact Wen? His lattice graviton model is quantum gravity. Thanks
It's obvious, isn't it? If you are interested, email X-G himself and ask if he is planning to attend the conference. He may already have plans to go in June and deliver a paper! In case he doesn't know about the conference, give him a link to the announcement. http://www.matmor.unam.mx/eventos/loops07/index.html If he hasn't already registered, and you think he should go and give a talk, then remind him to register soon, because the deadlines are 25 April and then 30 May (for late registration). The lineup for the morning talks looks like it is already decided. So I would think it is counterproductive to be talking about that, at this late date.
Oh I can email him but his spam mail filter will treat my yahoo email as spam, probably. Still I can try.
I just checked the "Participants" list and there are already 86 people signed up, including a couple we know here at PF Beyond forum F-h and KEA It looks like this is going to be a popular conference (by quantum geometry- quantum gravity standards) because many people have hurried to register. There will be a lot of demand for the afternoon parallel session time---they may need to increase the number of parallel sessions from two (as planned) to three.
Early registration is now closed, late reg is possible thru 30 May. 126 participants registered so far. the titles of many of the plenary talks are now listed, most with abstracts available. title of Lee Smolin's talk is listed. it looks like an exceptionally interesting conference with new ideas and approaches not represented at the earlier Loops 04 and 05 in Marseille and Potsdam. I have highlighted several titles which were not on the list given in the first post of this thread, and so may not have been noticed. ==update list of Loops '07== Plenary Speaker Title Jan Ambjørn "4d quantum gravity as a sum over histories" Abhay Ashtekar "LQG: Lessons from models" Martin Bojowald "Loop quantum cosmology and effective theory" John F. Donoghue "Effective field theory and quantum general relativity" Klaus Fredenhagen Lucien Hardy "The causaloid formalism: a tentative framework for quantum gravity" James B. Hartle "Generalizing Quantum Mechanics for Quantum Spacetime" Sabine Hossenfelder "Phenomenological Quantum Gravity" Bei-Lok B. Hu "Stochasticity and Nonlocality in Quantum-Classical and Micro-Macro Interfaces" Fotini Markopoulou Daniele Oriti "Group field theory: spacetime from quantum discreteness to an emergent continuum" Alejandro Perez Jorge Pullin "Uniform discretizations and spherically symmetric loop quantum gravity" Michael Reisenberger "Canonical gravity with free null initial data" Martin Reuter "Asymptotically safe quantum gravity and cosmology" David Rideout Carlo Rovelli Moshe Rozali "Background Independence in String Theory" Lee Smolin "Chiral excitations of quantum geometries as a possible route to unification" Rafael Sorkin* John Stachel "Projective and Conformal Structures in General Relativity" Artem Starodubtsev "Some physical results from spinfoam models" Thomas Thiemann "Elements of Loop Quantum Gravity" ==endquote== I already mentioned some PF posters who will be at the conference, two more I didn't mention are Garrett Lisi and William Donnelly. WD has a blog ( http://williamdonnelly.blogspot.com/ ) so we might get some reports there. Alejandro Satz who has the blog "Reality Conditions" will be there so we might get some reporting from him too. Jan Ambjorn's abstract: 4d quantum gravity as a sum over histories "In this plenary talk I will review the attempts to formulate 4d quantum gravity as a sum over histories in such a way that computer simulations can be performed. I will report on computer simulations of a quantum universe with a positive cosmological constant as well as a quantum universe where test matter is included." I didn't yet see a preprint of any paper telling the results of computer simulations of this sort that included matter.
I'm delighted that Hardy is invited. I've been intrigued by the causaloid idea for a couple years. It's still in its infancy, but has great potential, IMO.
Hi Marcus. It's unlikely that I'll be blogging from Morelia for a couple of reasons. The first is that maintaining a blog is a lot of work (I have no idea how you manage to be so prolific on these forums). The second is that I probably won't have a laptop. I might write some kind of summary when I get back, either way I'll let you know.
Thanks, I've rarely found "live" blog reports as satisfactory as reports from when the blogger is back home and has had time to recollect and reflect and filter. For me, the best report from the QGQG school was what Alejandro Satz provided over the course of several days after he was back in England. A "live" report might have had vivid impressions but could have been confusing because of so much going on. I found your blog in the aftermath of Jerzy Kowalski-Glikman's seminar talk at Perimeter exceptionally helpful. If you have time and energy to provide anything like that from one or two of the talks in Morelia, I shall be grateful. It almost doesnt matter which talks you pick to report on. And if you don't have time in the days after the conference, that's fine too. Clearly there's not time for everything. Have you heard any reactions at Perimeter about the new formula spinfoam vertex proposed by Etera Livine and Simone Speziale? I think there's a chance it might be a substantial improvement over the B-C spinfoam model in general use.
Thanks Marcus. I'm not a student at Perimeter and don't know the authors, so I haven't heard anything about it. But it's likely that they will speak about it at one of the quantum gravity meetings.
It has been almost a month since I last updated the list of plenary talks. Some more have been added, including one by Carlo Rovelli. So let's take a look at the new lineup. It says "Last updated 18 May 2007" so it is fairly fresh information. Abstracts are available for nearly every talk by clicking on the title. I have highlighted some talk titles and some names, somewhat arbitrarily, to help me think about aspects of the program: Plenary Speaker Title Jan Ambjørn "4d quantum gravity as a sum over histories" Abhay Ashtekar "LQG: Lessons from models" Martin Bojowald "Loop quantum cosmology and effective theory" John F. Donoghue "Effective field theory and quantum general relativity" Klaus Fredenhagen "General covariance in quantum field theory and the background problem in perturbative quantum gravity" Lucien Hardy "The causaloid formalism: a tentative framework for quantum gravity" James B. Hartle "Generalizing Quantum Mechanics for Quantum Spacetime" Sabine Hossenfelder "Phenomenological Quantum Gravity" Bei-Lok B. Hu "Stochasticity and Nonlocality in Quantum-Classical and Micro-Macro Interfaces" Fotini Markopoulou Daniele Oriti "Group field theory: spacetime from quantum discreteness to an emergent continuum" Alejandro Perez "Regulator dependence in quantum gravity and non perturbative renormalizability: possible new perspectives" Jorge Pullin "Uniform discretizations and spherically symmetric loop quantum gravity" Michael Reisenberger "Canonical gravity with free null initial data" Martin Reuter "Asymptotically safe quantum gravity and cosmology" David Rideout "Can the supercomputer provide new insights into quantum gravity?" Carlo Rovelli "Vertex amplitude and propagator in loop quantum gravity" Moshe Rozali "Background Independence in String Theory" Lee Smolin "Chiral excitations of quantum geometries as a possible route to unification" Rafael Sorkin* "Quantum reality and anhomomorphic logic" John Stachel "Projective and Conformal Structures in General Relativity" Artem Starodubtsev "Some physical results from spinfoam models" Thomas Thiemann "Elements of Loop Quantum Gravity" In a certain way Artem Starodubtsev is standing in for Laurent Freidel. Freidel won't be there and Artem has co-authored papers on obtaining the Feynman diagrams of usual QFT---in other words MATTER---from spinfoam quantum gravity. Also Jan Ambjorn will be talking about work he has done with Renate Loll, who won't be there. He gives the Simplex Gravity talk. It is worthwhile reading the abstracts and thinking about what will be brought out in some of these talks.
http://www.matmor.unam.mx/eventos/loops07/index.html there are 158 registered participants (more even than Loops '05 at the Albert Einstein Institute, AEI, in Germany) the abstracts are now all available for the 20-some plenary talks David Rideout's talk about using supercomputers in numerical LQG seems particularly interesting. He posted a paper about this on arxiv in the past day or two. He and Brunnemann ran their work on the Peyote cluster at AEI. with a framework or operating system called "Cactus". their project used some 20,000 CPU hours on the Peyote cluster (as described on page 18 and following in http://arxiv.org/abs/0706.0469 ) Rovelli's talk covers things in a paper that he, Engle, Pereira posted on arxiv recently. One can get an idea of what many of the talks will be like by reading recent arxiv postings and comparing with the available abstracts.
Artem has not been working with Freidel on deriving the QFT Feynman diagrams from spinfoams.. i think you were thinking about Aristide Baratin. Artem has been focusing on the (spinfoam) quantization of the Mac-Dowell-Mansouri action for GR (plus particles)...
One can hardly fault Marcus. The program reads: "Artem Starodubtsev: Some physical results from spinfoam models Given the known mathematical fact that a spinfoam is a Feynmann diagram the data relevant for particle scattering amplitudes could be identified in it." I'm happy to hear he's continuing work on MM GR -- looking forward to his talk.
Hi Garrett! Yes I was looking at the abstract of Starodubtsev's talk and although he hasnt posted co-author with Freidel lately it did look as if among other things his talk would necessarily be reporting Freidel's recent work. Among the plenary talks, it seemed to come the closest. But "stand-in" was the wrong word. For anyone interested in how Loops '07 is shaping up: The day-by-day schedule of plenary talks has been finalized as of 11 June http://www.matmor.unam.mx/eventos/loops07/index.html click on "program" It is a six day conference and there are 4 plenary talks per day, mostly in the morning, with parallel sessions in the afternoons.