Loops 05 Programme

marcus

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.

Chronos

Day 1 looks like dynamite. Many interesting papers.

marcus

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_file..._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

Chronos

I saw that abstract too, marcus, and found it intriguing. There could be some really good things emerge from this conference. I am greatly encouraged some very fine string theorists are participating. Theorists should build more bridges than they burn. These people are gifted, brilliant and deserve to be heard. IMO, they all have a viable claim to a piece of the puzzle. A 'united we stand' sort of thing...

marcus

Chronos you started this and I think it is a good idea because seeing the talks listed like this lets one scan down and perhaps see some themes or shared ideas that one could otherwise have overlooked. So I will finish the listing by doing Friday 14 October talks. the source is
http://loops05.aei.mpg.de/index_files/Programme.html
http://loops05.aei.mpg.de

Speaker: Dr. Bernard L. Julia
Title: Provisional title Dualization of gravity

Speaker: Hugo A. Morales-Tecotl
Title: On the top-down approach to quantum gravity

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.

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.

Speaker: Dr. Oliver Winkler
Title: Quantum Black Holes I: Kinematics
Abstract: We discuss a novel approach to a quantization of spherically symmetric black holes. We present the kinematical setup and focus in particular on a genuinely quantum definition of what a quantum black hole is which avoids fixing classical inputs such as boundaries a priori.

Speaker: Prof. Viqar Husain
Title: Quantum Black holes II: Dynamics
Abstract: I will describe an approach to studying gravitational collapse in quantum gravity. The model studied is the spherically symmetric gravity-scalar system, which is a 2D field theory. An ADM Hamiltonian formalism is utilised, together with an alternative quantisation scheme with similarities to loop quantum gravity. The calculational scheme allows an initial quantum state of matter and metric excitations to be followed to black hole formation, and beyond.

Speaker: Dr. Stefan Hofmann
Title: The Power Spectrum in Quantum Inflationary Cosmology
Abstract: We analyze fluctuations of a generic scalar field around its vacuum state in a singularity free quantum cosmology... In this framework we calculate the power spectrum and discuss its leading imprint from a quantum inflationary stage. [my comment: concern with testing]

Speaker: Johannes Brunnemann
Title: Singularities in LQG: A Status Report
Abstract: Loop Quantum Cosmology (LQC) has taken huge steps towards an answer to the question about sigularity (dis-)appearence in a quantum theory of gravity. The results look very promising, however they are usually obtained within the framework of symmetry reduced and thus simplified models....[comment: concern with BB and BH singularities, work with Thiemann]

Speaker: Dr. Leonardo Modesto
Title: Disappearance of the Black Hole Singularity in Quantum Gravity
Abstract: We apply techniques introduced in quantum cosmology to the Schwarzschild metric inside the horizon. The space-time inside the horizon is the Kantowski-Sachs space-time with space section of topology R x S^2. In particular, we use a mini-superspace quantization procedure suggested by Loop Quantum Gravity and based on an alternative to the Schroedinger representation. Using this quantization procedure, we show that the black hole singularity disappears and spacetime can be dynamically extended beyond the classical singularity. At this point we introduce the matter and we study the gravitational collapse of a star. We study the dynamic of the space time in the interior of the Schwarzschild radius. In particular in our simple model we obtain the evolution of the matter inside the star and of the gravity outside the region where the matter is present. When we impose the boundary condition between the two region we identify an unique time coordinate inside and outside the star.

Speaker: Gregory Vereshchagin
Title: From Semi-classical LQC to Friedmann Universe
Abstract: I will discuss basic phenomenological consequences of modification of Friedmann's equations in the semi-classical LQC. Such aspects as cosmic singularity problem, size of the Universe, generation of initial conditions for inflation and constraints on parameters of inflationary models will be considered. [comment: all these COSMOLOGY papers held until Friday!]

Speaker: Dr. Tomasz Pawlowski
Title: Isotropic universe dynamics from self-adjoint form of Hamiltonian constraint in LQC
Abstract: The self-adjoint form of the Hamiltonian constraint within Loop Quantum Cosmology framework is used to determine the evolution of an isotropic universe with massless scalar field. Its dynamics near classical big-bang singularity is analysed. In particular we are going to present the results on the evolution 'through' the singularity and analysis of the classicality of the universe re-emerging from deep quantum region.[comment: a co-author with Ashtekar, talking about the BB side of a BH-bounce, more cosmology, refers to future paper by Ashtekar-Pawlowski-Singh]

Speaker: Dr. Marek Szydlowski
Title: Dynamics of bouncing cosmological models
[comment: more bounce]

Speaker: Dr. Hector Hugo Hernandez
Title: Anisotropic perturbations in Isotropic Loop Quantum Cosmology
[comment: more cosmology]

Speaker: Jonathan Engle
Title: A full quantum theory and its symmetry reduction
Abstract: In loop quantum cosmology, a key issue regards the relation of the reduced quantum model to the full quantum theory. In the ideal scenario, the reduced model is isomorphic to the ``symmetric sector'' of the full quantum theory...

Speaker: Kevin Vandersloot
Title: Phenomenological implications of discreteness in loop quantum cosmology
Abstract: We discuss non-perturbative modifications to standard Friedmann dynamics implied by loop quantum cosmology. Particular focus is paid to effects arising from the discrete quantum geometry inherant in loop quantum cosmology. We show that these effects can imply bouncing behavior even in spatially flat models. We discuss the implications for pre big-bang and cyclic style models of string cosmology. Lastly we discuss how these effects can help provide sucessful initial conditions for inflation with a possibly measurable signature.

[comment: I was always wondering about this! LQC seems to want the universe FINITE and only almost flat, not perfectly flat. But Kevin now says it may be flat. Good. I notice again a concern for testing---an observable signature possibly in the Cosmic Microwave Background]

Speaker: Dr. Daniel Cartin
Title: Anisotropic homogeneous models in loop quantum cosmology
Abstract: Loop quantum cosmology is a simplified version of the full quantum geometry program,... the Hamiltonian constraint becomes a partial difference equation acting on the wave function. ...are not straightforward to solve; we discuss generic methods that can be used, and present results for various specific cases.

[Cartin works with Gaurav Khanna, they were both at Penn State. Khanna is at Dartmouth and does supercomputer, numerical relativity stuff. They have computational methods to contribute to LQG. Good idea IMHO]

marcus

I want a simplified schedule I can remember:

Monday is Carloday
Tuesday is Freidelday
Wednesday is Lollday
Thursday is Otherday (Rodolfo plus Jerzy et al on math. foundations)
Friday is Abhayday

Chronos

Terno and Markopoulou are giving presentations based on quantum information theory on Monday [Markopoulouday on my calender]. I'm a big fan of QIT. FM's presentation should be quite interesting

Title: Erorr-free quantum gravity
Abstract: We investigate the possibility that a background independent quantum theory of gravity is not a theory of quantum geometry. We provide a way for global spacetime symmetries to emerge from a background independent theory without geometry. In this, we use a quantum information theoretic formulation of quantum gravity and the method of noiseless subsystems in quantum error correction. This is also a method that can extract particles from a quantum geometric theory such as a spin foam model.

Instead of the usual 'sum of geometries' approach to quantum gravity, FM is suggesting the geometry itself may be emergent. How is that for background independence? This appears to build upon a presentation from late 2004. Here's a link if anyone is interested:

http://www.newton.cam.ac.uk/websemin...6/markopoulou/

Spin_Network

Chronos and Marcus thanks for the great thread, keeping everything in check.

Chronus, the above link you have provided is really,really interesting!
Thanks

john baez

Hi -

You can see the transparencies of my talk at Loops '05 here:

Towards a Spin Foam Model of Quantum Gravity

I've changed the title from what appears in the program. I've also changed my abstract. Here it is:

Spin foam models include several different classes of physical theories: lattice gauge theories, dynamical triangulation models of quantum gravity, "chain mail" quantum field theories, and topological string theories. Is there a spin foam model of quantum gravity in 4 dimensions? To address this question, we review recent work on causal dynamical triangulations and the renormalization group. This suggests that quantum gravity is a well-defined theory with the curious property that spacetime is effectively 4-dimensional at large distance scales, but 2-dimensional at very short distance scales. This is just what one might expect from a spin foam model, since spacetime is fundamentally 2-dimensional in these theories. We discuss properties a spin foam model should have in order to approximate general relativity at large distance scales.

I refer to a bunch of papers in my talk, but you can more easily get to those papers from my webpage.

My grad students Jeffrey Morton, Derek Wise and I are flying to Berlin this Saturday... this is gonna be fun!

marcus

thanks for keeping us posted!

be sure to ship us all the tidbits you can. it is an historical conference, and we crave news of it

marcus

you really have redirected! now it looks like focusing on work of Loll and Reuter and aligning spinfoam so it takes in CDT as a special case
my head is reeling slightly but it was not altogether unexpected
Bravo!
you will all have a great time for sure!

marcus

I have started on your lecture notes
they get hard around page 13
and interesting too

I hope other people here at PF study your notes and we can make a collective effort of understanding


I see that Tullio Regge is the hero of your pages 16, 17, 18
here's a picture
http://www.cicap.org/enciclop/at101249.htm

he's one of my heroes too. Tully (also the English nickname of Cicero)
http://plagiarist.com/poetry/3381/ Yeats said about the other Tully

Horace there by Homer stands,
Plato stands below,
And here is Tully's open page.
How many years ago
Were you and I unlettered lads
Mad as the mist and snow?

marcus

darn it, Berislav
you should be going to Potsdam next week!

but I guess you are busy beginning university studies,
how do you like the university?

selfAdjoint

And also Browning's "Tully's every word" from his "The Bishop Orders his Tomb at St. Praxed's Church in Rome"
http://eir.library.utoronto.ca/rpo/display/poem265.html

selfAdjoint

Which lecture notes are you reading? Can you give the link?

marcus

JB calls it a set of transparencies but I called it notes, it reads somewhat coherently, like 18 pages of lecture notes

it is here
http://math.ucr.edu/home/baez/loops05/
and you click on "Towards a..."

and IIRC you get this pdf

http://math.ucr.edu/home/baez/loops05/loops05.pdf

In fact you may already have been looking at this (which he calls his slides) and were confused by my calling it "lecture notes"

I didnt know that poem of Browning. It's good.

BTW won't you take a look at this site. some of the best translations into English that there are on the web I think:

http://www.brindin.com/main.htm

the site has over a dozen excellent translators working on the greatest poetry in over a dozen languages----often preserving some of the music (the rhyme, rhythm, general sound) of the original

the editors are an English couple, both verse translators themselves. the English seem to be more in touch with the European verse tradition than we are---maybe it is oldfashioned education. this site really deserves to be widely known

if you find some of the good stuff you will know what i mean
================
EDIT: I went to History and made a thread about it
http://www.physicsforums.com/showthr...322#post777322

getting close to voices from the past is a way to approach the past

Kea

Hey guys, the references in JB's slides greatly expand the 18 pages.