Loops 05 Programme

  1. marcus

    marcus 24,110
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  2. jcsd
  3. marcus

    marcus 24,110
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    a sample---picking names more or less randomly to see what that person is going to talk about:

    Speaker: Prof. John Baez
    Title: New Progress in Spin Foam Models
    Abstract: While the challenge of finding spin foam models with a well-behaved large-scale limit remains open, there has recently been interesting progress in a number of other directions. These include: relating spin foam models to the Feynman diagram formulation of ordinary quantum field theory on flat spacetime, finding a natural home for point particles in the spin foam formulation of 3d quantum gravity, and exploring a new background-free perturbative formulation of 4d gravity based on the BF formulation of the MacDowell-Mansouri theory. We hope to show that the ideas involved are beautiful and simple.

    Speaker: Prof. Robbert Dijkgraaf
    Title: Quantum geometry and topological strings
    [my comment: "quantum geometry" is Ashtekar's name for LQG, he might be relating LQG and topol. string. Dijkgraaf already has a paper that hints at some connection to LQG---one thing is a "topological sector" of another thing. or he might mean something else by "quantum geometry", like a Loll kind of thing, no way to tell in advance]

    Speaker: Dr. Laurent Freidel
    Title: Effective Field theory from quantum gravity
    Abstract: The Coupling of matter fields to spin foam models of quantum gravity will be discussed. We will show in the case of three dimensional gravity how the integration of quantum gravity degrees of freedom coupled to matter can be explicitely described in terms of an effective field theory. This theory is a new non commutative field theory obeying the principle of doubly special relativity. We will conclude on the extension of this approach to the four dimensional case.

    Speaker: Prof. Martin Reuter
    Title: Asymptotically safe quantum gravity: from the UV to the IR
    Abstract: The construction of a microscopic theory of quantum gravity in the asymptotic safety scenario is reviewed, and the nonperturbative renormalization group flow of Quantum Einstein Gravity from the UV fixed point towards macroscopic scales is described. Furthermore, the emergence of a fractal spacetime structure will be discussed.

    Speaker: Renate L:!!)ll
    Title: Emergence of Quantum Spacetime from Causal Dynamical Triangulations
    Abstract: In this talk, I will summarize and discuss some recent results on the emergent macro- and microstructure of quantum spacetime obtained in the Causal Dynamical Triangulations approach to nonperturbative quantum gravity. Particularly compelling is the finding of a dynamically generated scale-dependent dimension of this spacetime, interpolating between the classical value four on large scales and two at short distances.
     
    Last edited: Sep 9, 2005
  4. marcus

    marcus 24,110
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    more sampling (I bolded something in rovelli's, for emphasis)

    Speaker: Carlo Rovelli
    Title: GENERAL RELATIVISTIC QUANTUM PHYSICS: Background independent scattering amplitudes, boundary formalism, local particles and partial observables
    Abstract: (i) I present some preliminary results on background independent calculations of particle scattering amplitudes. In particular, I discuss the derivation of the graviton propagator, from loop quantum gravity and the spinfoam formalism. (ii) I illustrate the boundary formulation of quantum field theory, its role in a background independent context, and how "particles" emerge in this language. (iii) More in general, I discuss how systematic physical predictions can be extracted from a general relativistic quantum field theory: I illustrate the notion of "partial observable", and discuss the issue of the physical significance of the spectrum of these observables, which controls the interpretation of the area and volume discreteness.

    Speaker: Prof. Lee Smolin
    Title: Persistent puzzles in background independent approaches to quantum gravity
    Abstract: The talk is intended to be a provacative review of what we have NOT accomplished so far in LQG, CDT and other background independent approches to quantum gravity. I will describe then work with collaborators motivated by new hypotheses about some of these persistent problems.

    [COMMENT: I think by new hypotheses he means relatismo as laid out in "The Case for...", there is no denying that it does address some of the most persistent problems]

    Speaker: Prof. Abhay Ashtekar
    Title: Quantum Geometry and Space-time Singularities
    Abstract: General relativity provides a subtle and powerful interplay between gravity and geometry, thereby opening numerous possibilities for novel phenomena. However, this interplay also implies that the space-time itself ends when the gravitational field becomes singular. In loop quantum gravity, the interplay is elevated to the quantum regime through quantum geometry. I will present examples which strongly suggest that the physical space-time does not end at singularities. Quantum geometry can serve as a bridge between vast space-time regions which are classically unrelated. Thus, contrary to one's initial intuition, ramifications of quantum geometry can reach far beyond the Planck regime.

    [COMMENT: he could be talking about black hole gravitational collapse extending on into a kind of bounce----serving as a "bridge" to some other tract of spacetime. or he could have something else in mind. likes surprise]

    Speaker: Prof. Roy Maartens
    Title: COSMOLOGY AND QUANTUM GRAVITY
    Abstract: I will review the basic features of the standard, classical model of cosmology, which is based on General Relativity, and how this model accounts for observed properties of the universe. Modifications to General Relativity that are inspired by quantum gravity need to be tested against cosmological observations. This is one of the key tests for any candidate quantum gravity theory. I will discuss in general terms some of the difficulties involved in this aim, and what is needed from theorists in order to achieve this aim. In particular, I will compare some of the features of stringy cosmology and loop quantum cosmology.


    [COMMENT: selfAdjoint corrected a stupid mistake I made here.]

    Speaker: Dr. Hanno Sahlmann
    Title: On the measure theory underlying LQG
    Abstract: We review recent results on measures on spaces of connections in connection with LQG and discuss new questions and work in progress in this area, interesting both for LQG and from the viewpoint of standard quantum field theory.

    [COMMENT: measure theory is the bedrock of analysis. measures on spaces of functions and other geometrical objects. hardhat area]

    Speaker: Bianca Dittrich
    Title: Partial and Complete Observables for Canonical General Relativity
    Abstract: We will apply the concepts of partial and complete observables to canonical general relativity. We will show, that by using these concepts, one can calculate Dirac observables for general relativity by dealing with just one constraint. Furthermore we will introduce Abelian Hamiltonian constraints, invariant under spatial diffeomorphisms.

    [this is her good paper of the same title]

    Speaker: Dr. Etera Livine
    Title: Black Hole Entropy, Entanglement, and Area Renormalisation in LQG
    Abstract: One can model a LQG black hole at the kinematical level as a space region bounded by a closed surface -the horizon- whose geometry an external observer can acquire information about only through measurements on the surface. The black hole state is then given by completely coarse-graining the geometry of the bounded region, which defines a density matrix on the space of intertwiners i.e. the quantum state of the boundary horizon. I'll explain how to derive the black hole entropy law in that context and how to explain the logarithmic correction in terms of entanglement/correlation between parts of the horizon. This will lead to introduce a concept of surface renormalisationin LQG.

    [Livine and Terno, recent paper]

    Speaker: Prof. Dan Christensen
    Title: Finiteness and Positivity for the Lorentzian partition function
    Abstract: This talk gives an overview of recent results on the Lorentzian Barrett-Crane model, a spin foam model of quantum gravity. I will begin with a concise proof of the finiteness of the Lorentzian 10j symbol, which generalizes to other integral expressions of the same form, such as causal models. I then describe work of my student Wade Cherrington which uses the generalized finiteness result above to show that the Lorentzian partition function for a fixed triangulation is finite in the Perez-Rovelli normalization. Finally I will outline joint work with Cherrington which shows that the Lorentzian partition function is non-negative. In fact, we show that the Lorentzian Barrett-Crane model can be reformulated as a model with non-negative amplitudes, and this leads to the possibility of efficient computations of expectation values using statistical methods.

    [John Baez should be happy about this. there was worry about the Barrett-Crane model starting around 2002, which perhaps is being cleared up. Christensen does computer studies of spinfoam models so when he says "efficient computations" it is serious-----"statistical methods" could mean Monte Carlo. I think they have a good computer setup at Western Ontario where he is, or they use some other Canadian supercomputer installation---so this could be progress towards doing some of the same stuff Loll does, but with Foams instead of CDT. Cherrington recently posted a paper. quite a bit of this may be already available online]

    Speaker: Dr. Josh Willis
    Title: Computational Building Blocks for Lorentzian Spin Foams
    Abstract: I discuss recent work on efficiently computing the basic functions of Lorenztian spin foam models, from which the amplitudes themselves are calculated. The focus is on computing the 6-J and 10-J symbols, and I show how starting from the expression for these functions as integrals over copies of the group SL(2,C), one can develop an efficient algorithm for the 6J symbol, which can then be applied in calculating the 10J symbol.

    [Willis is also at Western Ontario, working with Christensen. Having the three researchers Christensen, Willis, Cherrington suggests that UWO is strong in the computational end of spinfoam research. The Loll example with CDT points up the critical importance of computer spacetime simulations and machine computation in quantum gravity.]

    Speaker: Rafael Porto
    Title: Fundamental gravitational limitations to quantum computing
    Abstract: Lloyd has recently considered the ultimate limitations the fundamental laws of physics place on Quantum Computers (QC). Based on ordinary Quantum Mechanics, he concludes in particular that for an 'ultimate laptop' (a computer of one liter of volume and one kilogram of mass) the maximum number of operations per second is bounded by 10^51. Here we consider additional limits that are placed by quantum gravity ideas, namely the use of a relational notion of time and fundamental uncertainty relations that exists on time measurements. We then particularize fot the case of an ultimate laptop and show that the maximum number of operations is further constrained to 10^47 per second. In addition it is shown that black holes QC face similar limitations.


    [Rafael Porto sometimes comes to PF and has posted here on some of our threads! Great going Rafael. I read this paper, that you are delivering! If you have time tell us something about the conference.]

    Speaker: Artem Starodubtsev
    Title: Scattering problem in background independent quantum gravity
    Abstract: Four dimensional topological field theory allows to define matter particles as charges of the gauge group breaking the gauge symmetry at a point. This is analogous to Deser Jackew and t'Hooft particles in 3d gravity. The degrees of freedom of General Relativity can also be introduced by symmetry breaking of the same topological field theory. This provides a framework in which gravity and matter can be considered from a unified point of view. In this framework we study scattering of matter particles due to quantum gravity effects.

    [OH MY! This sounds very interesting.]

    Well that is a sample. I have to stop sampling the talks. Many interesting ones left out. Other people if you look at the program and find something that piques your interest please post it.
     
    Last edited: Sep 9, 2005
  5. selfAdjoint

    selfAdjoint 8,147
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    Maybe we mean something different by Julia Sets? I mean the well-known classical fractal sets of that name; these were devised by Prof. Raoul Julia who fought in WWI and I don't suppose is around anymore.
     
  6. marcus

    marcus 24,110
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    to me it comes across as a galant gesture of hospitality that the main LQG researchers at Albert Einstein Institute (one could call them "senior" except that both are young) are not scheduling their own talks!

    Thomas Thiemann and Martin Bojowald have each originated major lines of LQG investigation and lead considerable amounts of research in their respective areas---but have chosen to play the host

    and NOT to put themselves on the programme WHICH THEY ORGANIZED AT THEIR AEI HOMEBASE.

    maybe that will change, if some scheduled speaker can't make it and they have to fill an empty spot

    but right now it looks very impressive

    one thing it means is that nowadays you can put on a Loops conference and voluntarily exclude a couple of the major players and you still have a good show---there is a depth and breadth of resources

    have to congratulate Drs. Bojowald and Thiemann for setting up such a program (it really looks very good, very exciting) and also thank Hermann Nicolai for deciding to have the conference at AEI!

    Where will Loops 06 take place?
     
    Last edited: Sep 9, 2005
  7. marcus

    marcus 24,110
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    thanks, mistake corrected :redface:
     
  8. This might sound like a silly question, but...
    Is the picture on their homepage a rendering of CDT?
     
  9. marcus

    marcus 24,110
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    it definitely is not a silly question


    the "icon" chosen for a line of research can be a helpful handle on it

    I think that the picture is actually a unification of two or more theories where in the FOREGROUND near the viewer I see the triangles of CDT
    and FURTHER AWAY more in the background, I see loops emerging, or perhaps they are nonperturbative strings and branes, as some largerscale structures, already kind of foggy or blurred, emerge out of the primitive small scale triangles.

    at least one of the pictures has this suggestive foreground-blending-into-background thing

    http://loops05.aei.mpg.de/

    If I were to meet hermann nicolai, I think I would ask him did he choose the artist or the pictures for this AEI website?
    I think he is a clever far-seeing man and although his specialty is string, I think he WANTS THE BEST for all approaches to quantum gravity and he believes that they can work in a synergistic way to test each other and so on. a man like Nicolai could have decided on that picture.

    (if anyone doesnt know: nicolai directs the Unified theories and Quantum gravity department of AEI-Potsdam where they are hosting the conference)
     
    Last edited: Sep 9, 2005
  10. One has to observe the interchanging three "logos" at the top left hand corner sidebar?..the one which emerges with a G ..where the tail-end is contained within a "background/foreground" !...the actual letter G goes through a 'loop' in its upper part. The bottom tail of G appears out of a fractal border of the 'white square'/'brown square, curve's around and back onto the brown square, which is embedded onto the "background"? :rolleyes: really cool and interesting.
     
  11. marcus

    marcus 24,110
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    The Loops 05 program schedule was posted Friday 9 September. I saw it around 7 AM California time and started this thread. Something I'd like to do is use this thread to collect insights and straws in the wind that we get SINCE AFTER they posted the programme of talks.

    whatever anyone sees or hears that in some way modifies the picture you get of current state of QG that is spelled out in the programme with its abstracts.

    Another thing we can do is connect the dots so that someone who is not going to the conference can READ recent articles posted on arxiv that are likely to correspond somewhat to the talks, in some cases.
    I can give some arxiv links, maybe other people can supply a few as well.
    so we can have a Threepenny Opera version of the conference. an ersatz substitute for stay-at-homes, which with a little imagination might not be so bad.
     
  12. marcus

    marcus 24,110
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    the most illuminating thing I have seen since Friday when the program came out (bearing on the current QG picture) is this comment on Woit blog by JB
    http://www.math.columbia.edu/~woit/wordpress/?p=251#comments
    this post is #53 in the comments.
    I can't easily copy the links so I put them as footnote at the end

    ---quote---
    John Baez Says:
    September 10th, 2005 at 10:19 pm
    dan writes:

    >Since Loll’s causal dynamic triangulation appears to have a
    >well-behaved semi-classical limit, with non-trivial predictions
    >on the planck scale, shouldn’t that excite you to doing research
    >in QG?

    It does excite me; I think it’s one of the most exciting things to come along in quantum gravity during the last few years! Everyone should read this for a less technical description of what Ambjorn, Jurkiewicz and Loll have done - or these for more detail. I talked about this stuff in the issue of This Week’s Finds covering the 2004 Marseille conference on loops and spin foams, so you can also read that.

    Unfortunately the most important work being done by these authors isn’t the sort of thing I’m good at. It involves lots of computer calculations. I’ve tried to get some computer whizzes interested, but so far nothing has come of it. So, I expect I’ll watch from the sidelines for a while.

    There’s one place I can *imagine* helping out. Their theory makes crucial use of a time coordinate. This should wash out when they take the continuum limit, but it might not - in which case they would be studying not quantum gravity, but some other theory in a different “universality class”.

    One can investigate this issue numerically. But it would be nice to find a variant of their model which did not make use of a chosen time coordinate, to simply sidestep this issue.

    That’s the sort of thing I can *imagine* being able to do… but I haven’t actually been able yet. Since I’m making so much more progress on various kinds of math, I’ve been doing more of that.
    ---end quote---

    "this" is The Universe from Scratch http://arxiv.org/abs/hep-th/0509010

    "these" is Loll's stuff on the arxiv http://arxiv.org/find/gr-qc/1/au:+loll/0/1/0/all/0/1?skip=0&query_id=e9777db1cb585b3b

    "that" is JB http://math.ucr.edu/home/baez/week206.html

    ---What this says to me---

    first of all the picture for me is focused on 4 main areas----(apologies to Fay Dowker, Alain Connes, Raphael Sorkin, Steven Hawking, Gerard 't Hooft...and everybody else who has their own very interesting QG ideas)---it's focused on LQG, SpinFoam, CDT, and Reuter's QEG.

    For me, THE OVERWHELMING FEATURE of the last two (CDT QEG) is that they are based on taking a limit. it is like the derivative is not defined in Calculus, you never actually get your hands on it, it only exists as a limit of ratios of differences. you never see it, all you see is an infinite SEQUENCE of approximations leading up to it.

    Another thing about CDT QEG , that may or may not be related to this, is that they NOW SEEM NOT AMENABLE TO CATEGORIES and other high algebra.

    I do not see anyone doing Category or Group Field with Loll triangles. So from a certain perspective it they are HARD TO MAKE SIMPLE AND BEAUTIFUL.

    I hear this. And this for me is very very interesting, because the possibility of new mathematics is above all when people come across some ideas that are hard to make simple and beautiful. And then after a hard uncomfortable experience they see a creative way to do it, and that is new---it doesnt just use already existing tools and ideas.

    So I like this situation and like to watch it develop. Hopefully it is not out of place for me to say this and I am not speaking out of turn. But in any case that is what I see as an onlooker and it is very interesting indeed right now.

    I am waiting for SOMETHING LIKE A CATEGORY or a group field or some other beautiful elegant gadget to be applied to Loll Triangle gravity and I am almost certain that it will be something nobody has seen before.

    There's no question Loll CDT is NOT MERE COMPUTER SIMULATION. I dont think anyone suggested that, so that is not exactly the issue. In fact the 2003 topology change papers with Westra for example are not computerish IIRC and have some rather neat combinatorics (what is it, Catalan numbers? and that's not all). It seems to me that the obstacle is not simply that computer simulations are involved------I would expect that in SpinFoam there will be more and more computer simulations as time goes on too. It seems to me that there is something deeper by way of an obstacle and it is that the model, as it stands, is not amenable to categories and algebra as they now are.

    But the first two QG I mentioned, LQG and especially SpinFoam possibly ARE amenable to making simple and beautiful by Category and Algebra methods which exist or are within sight on the horizon. I don't know about this but JB says something about a hope of this kind in the abstract of his Loops 05 talk. And he indicates a friendly disagreement with Carlo Rovelli over whether "Group Field" method or Category method might work best so simplify and beautify SpinFoams.
     
    Last edited: Sep 11, 2005
  13. marcus

    marcus 24,110
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    there is another thing that changes how I see the Loops05 programme, or shed some light on it for me and that is a passage from an earlier JB post on the same thread. it is hard to understand but points to something

    ---quote JB #29 in same thread---
    John Baez Says:
    September 5th, 2005 at 11:53 pm
    ... I have two grad students working on spin foam models: Derek Wise and Jeffrey Morton...

    Among other things, we’re working on Freidel, Louapre, Barrett et al’s ideas on how to describe particles in 3d quantum gravity as “spin networks with loose ends” - a wonderful realization of Wheeler’s old dream of “matter without matter”. Spin networks with loose ends are also mathematically related to D-branes, especially in topological string theory. We want to clarify these ideas using n-categories, following the strategy outlined in last year’s quantum gravity seminar at UCR (see my website). Crudely, there’s a 2-category with:

    particles as objects
    spin networks going between particles as morphisms
    spin foams going between spin networks as 2-morphisms

    and this fact, when worked out in detail, gives a rather beautiful new picture of how matter, gravity and spacetime could fit together - at least in 3 spacetime dimensions! Building a realistic theory along these lines would be a lot harder, since many of the details use mathemagical features special to 3d spacetime.

    But, to answer your question, what could get me working harder on quantum gravity is some evidence that we can find a mathematically elegant background-free quantum theory that can reduce to general relativity in a suitable limit. I see no reason why such a thing can’t be found if we drop the restriction on “mathematical elegance” - but I like things that use beautiful math.

    This is precisely why I mentioned Carlo Rovelli’s new paper...
    ---end quote---
    as a QG watcher I get several things:
    1. look out for Jeffrey Morton and Derek Wise in future, I recall that Wise is scheduled to give a late-afternoon talk at Loops05

    2. look out for Freidel and others incorporating matter into spinfoam spacetime, I guess by breaking the topology up a little, "loose ends".
    Freidel talks about this in the abstract of his Loops05 talk and indicates he will discuss EXTENDING IT FROM 3D TO 4D, he has a lot of recent papers dealing with the 3D case which you could say is for practice.

    3. look out for JB and others ideas of how to make this elegant---simpler and more beautiful---using category or other methods.

    4. "such a thing might be found" if one does not require elegance might contain an acknowledgement of promise in the direction of more socall-grubby analytical methods of CDT and QEG, but it also may refer to Rovelli work that is then discussed.

    right now I think that if I want a good picture of current state of non-string QG-----or one can say "nonperturbative/backgroundindependent" QG as the organizers of Loop05 say----that one way to make a good snapshot of the current situation is to look at the online programme abstracts, like those I copied earlier in this thread, and then TWEAK the picture slightly by thinking about this quoted passage from Baez.
     
  14. marcus

    marcus 24,110
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    The preceding post has a significant quote from John Baez
    elegance is an interesting standard. perhaps not entirely straightforward either, I think new and noble mathematics might sometimes sprout from a mere pragmatic contrivance---something cobbled together just to get it to work. I think the awkward could sometimes harbor the seeds of elegance. Maybe one just needs to understand the inelegant thing better.

    Some famous mathematicians are apparently not shy about visiting a dusty attic or the junkyard---I learned from Arivero posts ("graviton" thread) that Alain Connes has been concerning himself with the infinitesimals of Calculus, with limits of sequences of numbers, with the Nonstandard Analysis of Abraham Robinson (goes back to the 1960s, didn't catch on much IIRC).

    Maybe it is not appropriate to this context but I want to mention Rodolfo Gambini. here is what he is going to talk about at Loops conference:

    http://loops05.aei.mpg.de/index_files/abstract_gambini.html
    Prof. Rodolfo Gambini
    Consistent discretizations of totally constrained systems
    "I describe the consistent discretization scheme for the quantization of totally constrained systems and quantum gravity. As a first example I analyze the canonical formalism for Regge Calculus. I complete all the steps of the program for a reparameterization invariant system composed by a microscopic particle in a potential and a macroscopic clock. I define the physical Hilbert space of the discrete totally constrained theories, and I study the quantum evolution given by conditional probabilities defined in terms of quantum magnitudes associated to the clock and the system. I show how to recover the standard quantum mechanical continuum limit for the microscopic system."

    If you want to follow up and see what his thing is, here is a recent paper
    http://arxiv.org/abs/gr-qc/0505052
    Classical and quantum general relativity: a new paradigm
    Rodolfo Gambini, Jorge Pullin
    8 pages, one figure, fifth prize of the Gravity Research Foundation 2005 essay competition
    "We argue that recent developments in discretizations of classical and quantum gravity imply a new paradigm for doing research in these areas. The paradigm consists in discretizing the theory in such a way that the resulting discrete theory has no constraints. This solves many of the hard conceptual problems of quantum gravity. It also appears as a useful tool in some numerical simulations of interest in classical relativity. We outline some of the salient aspects and results of this new framework."

    http://arxiv.org/abs/gr-qc/0409057
    Consistent discretization and loop quantum geometry
    Rodolfo Gambini, Jorge Pullin
    4 pages
    Phys.Rev.Lett. 94 (2005) 101302
    "We apply the ``consistent discretization'' approach to general relativity leaving the spatial slices continuous. The resulting theory is free of the diffeomorphism and Hamiltonian constraints, but one can impose the diffeomorphism constraint to reduce its space of solutions and the constraint is preserved exactly under the discrete evolution. One ends up with a theory that has as physical space what is usually considered the kinematical space of loop quantum geometry, given by diffeomorphism invariant spin networks endowed with appropriate rigorously defined diffeomorphism invariant measures and inner products. The dynamics can be implemented as a unitary transformation and the problem of time explicitly solved or at least reduced to as a numerical problem. We exhibit the technique explicitly in 2+1 dimensional gravity."

    To offer an unqualified opinion, always risky, GAMBINI's way might not have the distinguishing STYLISTIC features of 21st Century mathematics. It might not be what one expects, but it looks like it kind of WORKS and Gambini thinks so. It has one or two odd gimmicks but maybe that's actually a good thing.

    AND THEN THERE IS MARTIN REUTER STUFF and it has signs of working too. And Loll. To generalize, all these approaches have the character of sticking very close to General Relativity, posssibly in some discretized lattice-like form, or some Regge triangles form, or taking the quantization that was the obvious thing to try in 1960 and stubbornly making the renormalization that didnt work then work now. But in whatever form they follow Gen Rel closely---and the indications are that these approaches might very well have the right classical limit, just because they stay so close to the original model.

    And Loll. She is using the original Einstein action put into Regge triangles form (which has been around since 1960) so how far off from the classical limit can she be?

    And Rovelli. Looks like he might have a handle on the vacuum and flat-limit gravitons and scattering amplitudes.

    So all these various people are converging on home base from different directions. And JB says

    I see no reason why such a thing can’t be found if we drop the restriction on “mathematical elegance” ...

    Baez hunches have often been a good guide---a compass needle in the QG wilderness. So I'm beginning to feel some nearness to the right classical limit (the behavior in the large scale, low energy, not terribly curved case that Gen Rel says you should have).

    And once SOMETHING works then even if it is awkward then its very awkwardness (when people confront and understand that) could point to some new mathematics.

    Let's put links to all the ones mentioned here, to their conference abstracts:

    http://loops05.aei.mpg.de/index_files/abstract_gambini.html
    http://loops05.aei.mpg.de/index_files/abstract_reuter.html
    http://loops05.aei.mpg.de/index_files/abstract_rovelli.html
    http://loops05.aei.mpg.de/index_files/abstract_loll.html
     
    Last edited: Sep 13, 2005
  15. Marcus, one of the main things to consider is what Olaf Dreyer:http://loops05.aei.mpg.de/index_files/abstract_dreyer.html

    appears to tackling?

    I have one or two things I would be very interested in finding out regarding Quantum to Macro transitions, having my own ideas, I am going to see how close I am to what the Theorists predict, but I ll leave that till about two days before the programme gets under way.

    Regarding the "new hypotheses" from Smolin,http://loops05.aei.mpg.de/index_files/abstract_smolin.html

    I wonder what it could involve?..I have a number of calculated guesses, but,again this will go onto my website no later than two days before the start date.
     
  16. marcus

    marcus 24,110
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    Hi Spin, I may have missed something you said earlier. How will we know anything about what they say at the conference until much later if at all? I am unable to attend---comes at the wrong time for me and it's far away. It would be wonderful of course if someone were to attend and put reports up on a website.

    I hope John Baez does a TWF soon after this exciting conference. But I have no certainty that we will hear an extensive report----may have missed something but I dont know of anyone who is, for example, live-blogging.

    Do you?
     
    Last edited: Sep 13, 2005
  17. Chronos

    Chronos 9,871
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    Loops 05 Day 1

    Since I have too much free time, here are the scheduled talks for Loops 05 day 1.

    Speaker: Carlo Rovelli
    Title: GENERAL RELATIVISTIC QUANTUM PHYSICS: Background independent scattering amplitudes, boundary formalism, local particles and partial observables

    Speaker: Prof. Lee Smolin
    Title: Persistent puzzles in background independent approaches to quantum gravity

    Speaker: Dr. John Barrett
    Title: Three-dimensional quantum gravity coupled to matter

    Speaker: Stefan Theisen
    Title:

    Speaker: Karim Noui
    Title: Creation and anhiliation of particles in 3D gravity: toward a background independant field theory

    Speaker: Florian Girelli
    Title: Higher dimensional perspective on DSR

    Speaker: Tomasz Konopka
    Title: A model of a scalar field theory with Lorentz-invariant energy scale

    Speaker: Simone Speziale
    Title: On the perturbative expansion of a quantum field theory around a topological sector

    Speaker: Florian Conrady
    Title: Yang-Mills theory and 3d gravity as string theories

    Speaker: Dr. Dorothea Bahns
    Title: The Invariant Charges of the Nambu-Goto String

    Speaker: Seth Major
    Title: A Discrete Machian Model: Fermions

    Speaker: Dr. Daniel Terno
    Title: The classical limit of a quantum tetrahedron

    Speaker: Prof. Fotini Markopoulou
    Title: Erorr-free quantum gravity

    Speaker: Olaf Dreyer
    Title: Classicality and Quantum Mechanics

    Speaker: Yidun Wan
    Title: 2-D Ising Model with non-local links - a study of nonlocality problem

    Speaker: Pierre Martinetti
    Title: An overview on the thermal time hypothesis

    Speaker: Aureliano Skirzewski
    Title: Effective Action From Geometric Formulation of Quantum Mechanics

    Speaker: Rafael Porto
    Title: Fundamental gravitational limitations to quantum computing [QIT]

    Speaker: Dr. Robert Oeckl
    Title: States on timelike hypersurfaces

    Speaker: Bruno Hartmann
    Title: An operational determination of the physical action

    Speaker: Ruediger Vaas
    Title: Before Time: Loop Quantum Cosmology and Philosophy of Science
     
  18. Chronos

    Chronos 9,871
    Science Advisor
    Gold Member

    Loops 05 Day 2

    Scheduled talks for L05 day 2:

    Speaker: Prof. John Baez
    Title: New Progress in Spin Foam Models

    Speaker: Prof. Robbert Dijkgraaf
    Title: Quantum geometry and topological strings

    Speaker: Dr. Laurent Freidel
    Title: Effective Field theory from quantum gravity

    Speaker: Alejandro Perez
    Title:

    Speaker: Prof. Dan Christensen
    Title: Finiteness and Positivity for the Lorentzian partition function

    Speaker: Dr. Josh Willis
    Title: Computational Building Blocks for Lorentzian Spin Foams

    Speaker: Dr. Suresh K Maran
    Title: Classical and Spin Foam Quantum Gravity for Complex, Real Orthogonal Groups and the Square of Area Reality Constraint

    Speaker: Dr. Etera Livine
    Title: Black Hole Entropy, Entanglement, and Area Renormalisation in LQG

    Speaker: Dr. Daniele Oriti
    Title: Parametrised group field theories and quantum gravity transition amplitudes

    Speaker: James Ryan
    Title: A group field theory for 3d quantum gravity coupled to a scalar field

    Speaker: Artem Starodubtsev
    Title: Scattering problem in background independent quantum gravity

    Speaker: Prof. Aleksandar Mikovic
    Title: [I am going to describe how to construct a spin foam model of quantum gravity based on the path integral quantization of the Palatini action of General relativity].

    Speaker: Dr. Kirill Krasnov
    Title: Lambda<0 Quantum Gravity in 2+1 Dimensions

    Speaker: Dr. Hendryk Pfeiffer
    Title: Two-dimensional open-closed TQFT from a state sum model

    Speaker: Federico Mattei
    Title: From 3-geometry transition amplitudes to graviton states

    Speaker: Aristide Baratin
    Title: Hidden quantum gravity in Feymnan graphs

    Speaker: Winston Fairbairn
    Title: Large N QCD and spinfoam models

    Speaker: Catherine Meusburger
    Title: Grafting and Poisson structure in (2+1)-gravity with vanishing cosmological constant

    Speaker: Eugeniu M. Popescu
    Title: Topological matter models in (2+1)-dimensional gravity

    Speaker: Jesper M. Grimstrup
    Title: Spectral Triples of Holonomy Loops

    Speaker: Dr. Mario Paschke
    Title: Causal Parametrices and Lorentzian spectral geometries
     
  19. marcus

    marcus 24,110
    Science Advisor
    Gold Member
    2014 Award

    Loops 05 Day 3 (in appreciation of Chronos doing 1 and 2)

    Speaker: Renate Loll
    Title: Emergence of Quantum Spacetime from Causal Dynamical Triangulations
    Abstract: In this talk, I will summarize and discuss some recent results on the emergent macro- and microstructure of quantum spacetime obtained in the Causal Dynamical Triangulations approach to nonperturbative quantum gravity. Particularly compelling is the finding of a dynamically generated scale-dependent dimension of this spacetime, interpolating between the classical value four on large scales and two at short distances.

    Speaker: Prof. Martin Reuter
    Title: Asymptotically safe quantum gravity: from the UV to the IR
    Abstract: The construction of a microscopic theory of quantum gravity in the asymptotic safety scenario is reviewed, and the nonperturbative renormalization group flow of Quantum Einstein Gravity from the UV fixed point towards macroscopic scales is described. Furthermore, the emergence of a fractal spacetime structure will be discussed.

    Speaker: Prof. Rafael D. Sorkin
    Title: Some Insights for Quantum Gravity Derived from Work on Causal Sets
    Abstract: Drawing on a range of results from the causet program, I try to extract some general lessons that can help guide future work on quantum gravity in general. Some of these insights are of long standing, but some are very recent, notably the indication that an "intermediate nonlocality scale" much greater than the Planck length might be required to make contact with local continuum physics.

    Speaker: Dr. Fay Dowker
    Title: Causal Set Phenomenology
    Abstract: The hypothesis that the discrete substructure of spacetime is a causal set suggests a straightforward model building technique: invent phenomenological dynamics for matter (particles or fields) on a background causal set that is well approximated by our continuum spacetime. These models can be analysed to see if they predict observable deviations from continuum models. I will describe two examples of such models: "particle swerves" and a model of detector response to the scalar field of a scalar charge source.


    that's all there is this day, because the organizers made Wednesday afternoon a free day with no talks.

    that means people can go into Berlin, a pretty good cultural city, or they can hang out in small groups and discuss the implications of the talks they have heard so far, and maybe make some contacts for possible collaboration on future research. I guess Wednesday afternoon could be one of the nicest times of the conference.
     
  20. Chronos

    Chronos 9,871
    Science Advisor
    Gold Member

    Day 1 looks like dynamite. Many interesting papers.
     
  21. marcus

    marcus 24,110
    Science Advisor
    Gold Member
    2014 Award

    Loops 05 Day 4

    Speaker: Prof. Jerzy Lewandowski
    Title: Loop Quantum Gravity

    Speaker: Dr. Alejandro Corichi
    Title: Towards semi-classical physical states in LQG

    Speaker: Dr. Rainer Verch
    Title: Generally covariant quantum field theory

    Speaker: Prof. Rodolfo Gambini
    Title: Consistent discretizations of totally constrained systems

    Speaker: Prof. Yongge Ma
    Title: On the Master Constraint Operator for Loop Quantum Gravity

    Speaker: Dr. Hanno Sahlmann
    Title: On the measure theory underlying LQG

    Speaker: Dr. Christian Fleischhack
    Title: Stone-von Neumann Theorem in Quantum Geometry In ordinary quantum mechanics

    Speaker: Dr. Jose A. Zapata
    Title: Loop quantization as a continuum limit

    Speaker: Kristina Giesel
    Title: Consistency Check on Volume and Triad Operator Quantisation in Loop Quantum Gravity

    Speaker: Bianca Dittrich
    Title: Partial and Complete Observables for Canonical General Relativity

    Speaker: Dr. Jorma Louko
    Title: Group averaging, positive definiteness and superselection sectors

    Speaker: Wayne Bomstad II
    Title: Linearized Gravity as the Rosetta Stone of Quantization Techniques

    Speaker: Hal Finkel
    Title: Stochastic Evolution of Graphs using Local Moves

    Speaker: Prof. Jorge Pullin
    Title: Classical applications of consistent discretizations

    Speaker: Dr. Gabriele Gionti
    Title: Discrete Theory of Gravity as a local Theory of the Poincare Group in the First Order Formalism

    Speaker: Dr. David Rideout
    Title: Spatial Hypersurfaces in Causal Set Cosmology

    Speaker: Dr. Sumati Surya
    Title: Recovering spacetime topology from a causet

    Speaker: Derek K. Wise
    Title: Discrete p-form Electromagnetism as a Chain Field Theory

    Speaker: Stefan Zohren
    Title: Taming the cosmological constant in 2D causal quantum gravity with topology change

    Speaker: Prof. Manfred Droste
    Title: Universal homogeneous causal sets

    Speaker: Dr. Jan-Markus Schwindt
    Title: Is there a minimal length in asymptotically safe quantum gravity?
    http://loops05.aei.mpg.de/index_files/abstract_schwindt.html

    Thanks to Chronos for entering the list of talks for days 1 and 2.

    I was intrigued by the abstract of J-M Schwindt's talk---it refers to Martin Reuter QEG (assympt. safe quantum GR, "quantum Einstein gravity") which has a sequence of metrics appropriate for finer and finer resolution, and so a sequence of "microscopes" with which to view spacetime. And Schwindt has the surprising result that there is a limit on the resolution of angle. with no-matter-how-fine a microscope one cannot see less than a certain angle. So he asks if there is a minimal length as well? weird. I did not expect this of Reuter QEG
     
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