What QG to expect in next 6 months

marcus

[1] A. Baratin, L. Freidel Hidden Quantum Gravity in 4d Feynman diagrams: Emergence of spin foams, To appear.

(this was ref [1] in http://arxiv.org/gr-qc/0604016, Freidel has always delivered on his promises and going by past experience one could make a wild guess of a 4 month interval, so August or September 2006)

[3] J. C. Baez and A. Perez, Quantization of strings and branes coupled to BF theory, to appear.

(this is ref [3] of a revised retitled version of http://arxiv.org/gr-qc/0603085 available at Baez site. http://math.ucr.edu/home/baez/ Baez says he is "just finishing up" this work with Alejandro Perez)

Both these forthcoming papers are follow-on work of stuff that just appeared recently. By understanding what has just appeared we should get an idea of what to expect in the coming months

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Oh, this just appeared today. It might have a bearing
http://arxiv.org/abs/hep-th/0604181
Karim Noui and Philippe Roche are involved

marcus

I see that 3 new Freidel papers appeared today, have to evaluate them to see if any news about what to expect in next six months.

they are listed here, with the abstracts
http://www.physicsforums.com/showthr...791#post971791

here, for compactness, I omit abstracts and only give title and link:
http://arxiv.org/abs/hep-th/0604181
6J Symbols Duality Relations
L. Freidel, K. Noui, P. Roche
28 pages, 2 figures

http://arxiv.org/abs/hep-th/0604184
Towards a solution of pure Yang-Mills theory in 3+1 dimensions
Laurent Freidel, Robert G. Leigh, Djordje Minic
12 pages

http://arxiv.org/abs/hep-th/0604185
On pure Yang-Mills theory in 3+1 dimensions: Hamiltonian, vacuum and gauge invariant variables
Laurent Freidel
35 pages

marcus

here are links to other PF threads discussing recent Freidel and Shahn Majid papers, and also the Baez paper

"new Baez article, BF"
http://www.physicsforums.com/showthr...793#post943793

Majid thread
http://www.physicsforums.com/showthread.php?t=118079

marcus

One very simple lesson of the Baez paper that might escape people's notice is YOU DON'T NEED EXTRA DIMENSIONS TO HAVE "STRINGS".

Baez is working in 4D and he defines some flexible circles in 4D that he uses to poke around with and explore things, and then he says "I am going to call these things strings".

It sounds to me like he does it for good reason and knows what he's about, as you'd expect. But these are not quite the same things as strings in many extra dimensions that a superstring-thinker would be talking about. They don't vibrate or dance the Witten Polka or whatever "real" strings are supposed to do. They are used to explore the topology of some branching tubular membranes, which I guess you could call "branes", which also live in modest 4D.

So there is a refreshing change in the jargon weather here where simple unassuming things in familiar 4D are called by straightforward names

have to go, try to finish this thought later

Kea

Oooh, Marcus, careful! Someone might yell at you.

marcus

well I hope you admire my nerve, then. pip pip
stiff upper lip and all that

they will have to yell at Baez too, of course.

marcus

I think the next 6 months will be exciting. see a lot of changes. a new map of QG.

I'm still looking at the current papers to understand the direction things are going (or at least make a guess). A possible theme could be
4D UNIFICATION
(unification of spacetime geometry and matter in plain old 4D--wouldn't that be a novelty!)

Freidel is certainly doing that because he is getting matter (Quantum Field Theory) out of 4D spin foam. Already did it in 3D and has a paper in the works with Baratin doing it in 4D.

And Baez seems to be proceeding in that direction too. He has a 4D beef model ("be-eff") that he is discovering a wealth of exotic particles in. and he has these little flexy circles living in 4D which he (provocative as ever) calls LOOPS in the initial version of the paper on arxiv----and indeed they are loops-----and then turns around and calls STRINGS in another version of the paper at his website----and indeed that is a very good name for them because they are like little loops of string.

and why should the superstring-M-people own the word? computer scientists can say "string" when they mean string of ASCII characters, it isnt any one group's intellectual property.

Baez indicates that he and Alejandro Perez are bringing out a LAGRANGIAN for these exotic particles in 4D

dynamics part of the 6 month trend as I see it: Laurent Freidel also seems to be getting the DYNAMICS for his spinfoam/matter model not to mention THE CLASSICAL LIMIT.

So there is change in the Loop Quantum Gravity community, having to do with 4D unification, BEEF, SPINFOAM/MATTER, dynamics and the classical limit.

also it is very interesting that Freidel is writing stringy papers too, or what would you call this?

http://arxiv.org/abs/hep-th/0604185
On pure Yang-Mills theory in 3+1 dimensions: Hamiltonian, vacuum and gauge invariant variables

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[EDIT] Kea, I will reply to your #8 here, to save making an extra post. you say "plans for combinatorial magic"--------the atomic theory that forced its way in circa 1890-1905 or whenever, that was a combinatorial theory. or more than what went before, maybe fundamental theories tend to be that. Shahn Majid used the word in the first sentence of "Algebraic QG II"
Majid:"In this article we present noncommutative geometry(NCG) not as a ‘theory of everything’ but as a bridge between any future, perhaps combinatorial, theory of quantum gravity and the classical continuum geometry that has to be obtained in some limit."
Yes maybe a fundamental theory of spacetimematter will have to be combinatorial---graphtheoretical---but CLOTHED in decent algebra which will allow it to go out into society and join the country club and all the correct semiclassical and zerogravity limits.

Kea

As some of my non-physics West Coast friends say when people ask them what I'm doing these days: she wants to know how long is a piece of String. They launched this one gleefully on an actual, real, live mathematician recently, and were returned a serious and quizzical look.

Six months. Hmm, yes, sometimes a lot can happen in six months. 6j dualities and Langlands dualities and plans for combinatorial magic - on both sides. Where will they meet?

Chronos

I suspect Kea already has a related work in process and is holding out on us!