(UV finite)LQG @Strings 2008-Rovelli's slide #20

[marcus]

(UV finite)LQG @Strings 2008--Rovelli's slide #40

Rovelli was invited by the organizers of the annual strings conference, Strings 2008, to give a plenary session talk outlining the main features of Loop Quantum Gravity. The talk got an unusually lively response, prompting a number of interesting questions which spilled over into the break and had to be continued outside in the lobby. A video is available online at the CERN website, and there is a PDF of the slides. For this short, basic-level, talk, Rovelli used 40 slides. Here is slide #40, his summary---a kind of thumbnail sketch of LQG.
============================
IV. Summary

• Loop quantum gravity is a technique for defining Diff-invariant QFT. It offers a radically new description of space and time by merging in depth QFT with the diff-invariance introduced by GR.

• It provides a quantum theory of GR plus the standard model in 4d, which is naturally UV finite and has a discrete structure of space at Planck scale.

• Has applications in cosmology, black hole physics, astrophysics; it resolves black hole and big bang singularities.

- Unrelated to a natural unification of the forces (we are not at the “end of physics”).
- Different versions of the dynamics exist.
- Low-energy limit still in progress.
+ Fundamental degrees of freedom explicit.
+ The theory is consistent with today’s physics.
+ No need of higher dimensions (high-d formulation possible).
+ No need of supersymmetry (supersymmetric theories possible).
+ Consistent with, and based on, basic QM and GR insights.
=====endquote=====

Note that work on the low-energy limit is in progress, and different versions of the dynamics still exist. I think a key word in the second bullet is provide----the idea that LQG offers a platform on which the particle fields of QFT can be defined, and thus on which the standard model can be based. LQG is of course concerned with spacetime geometry and typically does not try to unify forces or contain the standard model. I don't fully grasp what he means in the second bullet.

I would welcome attempts to clarify not only the second bullet, but any of these points. You may wish to look through the full set of 40 slides. The 43 minute video explains and elaborates somewhat. It's interesting to see what questions the string audience had at the end.

Here are the slides:
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
Here is the video:
http://cdsweb.cern.ch/record/1121957?ln=en

The talk itself lasted 30 minutes, after which there were 13 minutes of Q and A, which the moderator cut short and said must be continued at coffee outside the hall. Interesting document

 

[Fra]

I couldn't see the link in Marcus post, but I googled the strings in the text.

http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917 seems to be it.

/Fredrik

 

[marcus]

Hi Fra, you beat me to it! You found the llnk and posted, while I was still hunting for it. I edited it into my post. Thanks.
(I see I initially typed the number of slides wrong. It should be 40, not 20. I corrected this to the extent possible.)

One thing that prompted me to ask for clarification was this recent exchange between Haelfix and Demystifier in the "Background Independence" thread:

...
LGQ has absolutely not been shown *yet* to be 'UV finite' however string theory is completely UV finite...

...
First, as far as I know, in string theory UV finiteness is shown rigorously only for 1 and 2 loops, while a rigorous proof for arbitrary number of loops is still lacking.

Second, as far as I know, UV finiteness of LQG is shown rigorously (LQG is defined non-perturbatively) to be a consequence of compactness of SU(2) or SO(3).

If LQG was UV finite, it would be a big deal. Last I check, no one had shown that...