New directions in Background Independent Quantum Gravity

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Marcus! Your find....
http://arxiv.org/abs/gr-qc/0703097
New directions in Background Independent Quantum Gravity
Fotini Markopoulou
Perimeter Institute for Theoretical Physics
Summary and Conclusions
One can start with a pre-geometric theory and look for the effective coherent degrees of freedom
along the lines described. Spacetime is to be inferred by them internally, namely, using only operations that are accessible to parts of the system. This is very promising for three reasons:
1) The emphasis on the effective coherent degrees of freedom addresses directly and in fact uses the dynamics. The dynamics is physically essential but almost impossible to deal with in other approaches.
2) A truly effective spacetime has novel phenomenological implications not tied to the Planck scale which can be tested and rejected if wrong.
3) A pre-spacetime background independent quantum theory of gravity takes us away from the concept of a quantum superposition of spacetimes which can be easily written down formally but has been impossible to make sense of physically in any approach other than Causal Dynamical Triangulations.
Good stuff.
How influential is Fotini Markopoulou?
Is anybody going to listen?
jal
 

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  • #2
marcus
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Marcus! Your find....
http://arxiv.org/abs/gr-qc/0703097
New directions in Background Independent Quantum Gravity
Fotini Markopoulou
Perimeter Institute for Theoretical Physics

Good stuff.
How influential is Fotini Markopoulou?
Is anybody going to listen?
jal
She is a key figure at Perimeter Institute. People will surely listen!
But just at the moment the game in B.I. QG is (IMHO as bystander) a free-for-all in which only the new RESULTS are influential, and people are not intrinsically influential. This is an abnormal temporary situation as I see it.
As a social system, there does not appear to be any clear ranking by who is influential.

To me, just to take an example, Ashtekar is very influential right now because his cosmology group is improving the quantum cosmology models and running computer simulations of various universes where quantum stuff replaces the big bang singularity. People want to have singularities resolved these days and Ashtekar team is delivering the goods. This is progressing rapidly and is what makes him influential. Thomas Thiemann is influential partly because his form of AQG fits together with Ashtekar and Bojowald LQC (as the 'full theory' supporting it).

Admittedly even without his new results Ashtekar is one of the senior people, enormously respected, and administratively powerful, but without the stream of results 2005-2007 he would not be so influential (IMO as humble observer)

I see a many-sided shifting free-for-all with no settled social hierarchy---perhaps in string-land there is more a settled hierarchy---I think I saw this in the Toronto 2005 video of "Strings '05" panel discussion---who was speaking authoritatively and being listened to and who not so much.

Markopoulou is brilliant original insightful and, I would like to say influential too but now I think in the rough-and-tumble who is turning out to be influential (besides Ashtekar/Bojowald Penn group) is actually what I would call the "French" team.

Alejandro Perez and Winston Fairbairn (Marseille)
Etera Livine (Lyon)
Laurent Freidel (Lyon and Perimeter)

I think people want that 4D spinfoam gravity-with-matter (or 4D BF gravity-with-matter) should develop into a theory of stringlike objects in 4D or 5D. It will not at all be usual "superstrings"---it may SOUND like stringery but it will not actually be that. It won't be stuff VIBRATING IN SOME KIND OF PRE-ARRANGED extra-dimensioned TARGET SPACE, it will be a background independent theory with no prearranged geometry but it will have ONE DIMENSIONAL OBJECTS plus their worldsheets and basically everything happening in 4D.

De Sitter space will be important, and DSR, in this picture. It is already turning out so.

Baez helped set up this collision of spinfoam with 4D stringlike stuff when he wrote this paper with Alejandro Perez last year.

Everybody wants this kind of collision to happen because it will make everybody's brain explode and they will think extra well for a few years.

Fotini deserves to have influence and to guide people's vision but I don't see how she can swim against this tide.

Maybe since I really am not knowledgeable I should have declined to answer your question but the atmosphere here encourages taking chances a bit and if I had to answer that would be my guess.:smile:
 
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jal
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LOL....
Taking chances is what makes progress... besides... I don't have anything to lose... THEY on the other hand have everything to gain.
We are using "play money" hehehe
jal
 
  • #4
marcus
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I am glad you liked the Fotini article. I thought it was exceptionally thoughtful and well-written. In part, it gives a clear survey of different B.I. approaches to quantum gravity-and-matter and the problems they encounter---which is worthwhile reading for overview even if one doesnt want to get into details of some of the sections.

Now I think Dan Oriti has all the chapters of his book! and Cambridge Press can go ahead and publish. I hope so! the Rafael Sorkin chapter is there too now.
 
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