What is the latest research on spin foam models of quantum gravity?

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Discussion Overview

The discussion centers around the latest research on spin foam models of quantum gravity, exploring various theoretical advancements, connections to other frameworks, and implications for understanding quantum spacetime. The scope includes theoretical insights, conceptual clarifications, and potential applications in quantum gravity and cosmology.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants highlight recent progress in spin foam models, including their relation to Feynman diagrams and the integration of matter fields into these models.
  • Prof. John Baez discusses challenges in finding well-behaved large-scale limits for spin foam models while noting advancements in related areas.
  • Dr. Laurent Freidel presents a new effective field theory approach for coupling matter to spin foam models, emphasizing its implications for three-dimensional gravity.
  • Prof. Martin Reuter reviews the nonperturbative renormalization group flow in asymptotically safe quantum gravity, suggesting a fractal spacetime structure may emerge.
  • Prof. Carlo Rovelli introduces background independent calculations of particle scattering amplitudes and discusses the emergence of particles in a quantum field theory context.
  • Prof. Lee Smolin provocatively reviews unresolved issues in loop quantum gravity and related approaches, indicating ongoing challenges in the field.
  • Prof. Abhay Ashtekar explores the implications of quantum geometry for spacetime singularities, suggesting that quantum geometry may connect classically unrelated regions of spacetime.
  • Prof. Roy Maartens emphasizes the need for testing quantum gravity modifications against cosmological observations and compares features of stringy cosmology and loop quantum cosmology.
  • Dr. Hanno Sahlmann discusses recent results on measure theory in relation to loop quantum gravity, indicating its foundational importance.
  • Bianca Dittrich applies concepts of partial and complete observables to canonical general relativity, proposing methods for calculating Dirac observables.
  • Dr. Etera Livine addresses black hole entropy and entanglement in loop quantum gravity, introducing concepts related to surface renormalization.

Areas of Agreement / Disagreement

Participants express a range of viewpoints, with some agreeing on the significance of recent advancements while others highlight ongoing challenges and unresolved issues. Multiple competing views remain regarding the implications and interpretations of the discussed models and theories.

Contextual Notes

The discussion reflects a variety of theoretical approaches and assumptions, with some claims depending on specific definitions and frameworks. Unresolved mathematical steps and the implications of certain models remain points of contention.

  • #31
marcus said:
I
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?

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
 
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  • #32
Marcus said:
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

Which lecture notes are you reading? Can you give the link?
 
  • #33
selfAdjoint said:
Which lecture notes are you reading? Can you give the link?

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
https://www.physicsforums.com/showthread.php?p=777322#post777322

getting close to voices from the past is a way to approach the past
 
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  • #34
marcus said:
JB calls it a set of transparencies but I called it notes, it reads somewhat coherently...

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

:smile:
 
  • #35
Kea said:
Hey guys, the references in JB's slides greatly expand the 18 pages.

:smile:

Indeed they do!
:smile:
 
  • #36
marcus said:
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.

If you have questions, ask them here and I'll try to reply! - probably after I get back from Berlin, though, unless I have time during the conference.

I see that Tullio Regge is the hero of your pages 16, 17, 18.

Yes! Actions speak louder than words, and his is one of the best.
 
  • #37
john baez said:
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 http://loops05.aei.mpg.de/" . 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 "[URL my webpage[/URL].

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

This was just posted to Xr :http://arxiv.org/abs/gr-qc/0510033

prior to their leaving U.S of A.

and this may be of interest as a historical reference?:http://groups.google.com/group/sci....group%3Dsci.physics.research#efe70e642e41021f
 
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