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The Twelfth Marcel Grossmann meeting is taking place this week in Paris. The meetings started in 1975 and occur every three years, to review recent developments in gravitation and general relativity.

http://www.icra.it/MG/mg12/images/poster_mg12.pdf

The expressed focus of the current MG12 is "recent developments in theoretical and experimental general relativity, astrophysics, and relativistic field theories."

Normally no single event, book, lecture, experiment, or conference would by itself redefine the scientific mainstream. And yet what constitutes the mainstream of research is constantly subject to redirection, and various things like a major international conference can help define it for us.

One has to look at the line-up of invited plenary talks, and how that compares with 3 years ago. Also there are the various parallel sessions---how well populated they are and what the titles of the papers indicate, again compared with MG11 in Berlin, three years back.

There has been a subtle change in the physics character and emphasis of the Marcel meeting. I have to run to make an appointment, but will continue this post later this afternoon.

BTW today (Tuesday 14 July) it was Abhay Ashtekar who chaired at the session of invited plenary talks. Two speakers of note at today's plenary session were Laurent Freidel, Juan Maldacena, and Herbert Hamber. To give a clue about Freidel's MG12 talk here's the abstract:

Abstract: In this talk I will give an overview of spin foam models which describe the dynamics of quantum gravity in a background independent context. I will focus especially and the recent developments which concerns the construction of these models in 4 dimensional gravity and present some of the key results obtained in this context like the construction of the model, the

Likewise to give a taste of Maldacena's talk:

Abstract: We will review the duality between gravity in negatively curved spacetimes and quantum field theories on the boundary. Black holes in these spacetimes represent finite temperature configurations for the theory on the boundary. The classical dynamics of these black holes can be used to get some insight into strongly coupled quantum systems.

And as a further sample, Hamber's talk:

Abstract: I will discuss how non-perturbative approaches to the problem of ultraviolet divergences in quantum gravity, similar in spirit and methods to what is done in the modern renormalization group treatment of non-abelian gauge theories, point to a possible weak scale dependence of Newton's constant at very large distances. I will then discuss ways by which such a scale dependence could in principle be verified observationally.

http://www.icra.it/MG/mg12/en/invited_speakers_details.htm#freidel

http://www.icra.it/MG/mg12/en/invited_speakers_details.htm#maldacena

http://www.icra.it/MG/mg12/en/invited_speakers_details.htm#hamber

http://www.icra.it/MG/mg12/images/Program_MG12.pdf

http://www.icra.it/MG/mg12/images/poster_mg12.pdf

The expressed focus of the current MG12 is "recent developments in theoretical and experimental general relativity, astrophysics, and relativistic field theories."

Normally no single event, book, lecture, experiment, or conference would by itself redefine the scientific mainstream. And yet what constitutes the mainstream of research is constantly subject to redirection, and various things like a major international conference can help define it for us.

One has to look at the line-up of invited plenary talks, and how that compares with 3 years ago. Also there are the various parallel sessions---how well populated they are and what the titles of the papers indicate, again compared with MG11 in Berlin, three years back.

There has been a subtle change in the physics character and emphasis of the Marcel meeting. I have to run to make an appointment, but will continue this post later this afternoon.

BTW today (Tuesday 14 July) it was Abhay Ashtekar who chaired at the session of invited plenary talks. Two speakers of note at today's plenary session were Laurent Freidel, Juan Maldacena, and Herbert Hamber. To give a clue about Freidel's MG12 talk here's the abstract:

*Spin Foam models: models of quantum dynamical space time*Abstract: In this talk I will give an overview of spin foam models which describe the dynamics of quantum gravity in a background independent context. I will focus especially and the recent developments which concerns the construction of these models in 4 dimensional gravity and present some of the key results obtained in this context like the construction of the model, the

**proof of the semi-classical limit**and the relationship with loop quantum gravity and SU(2) spin network states.Likewise to give a taste of Maldacena's talk:

*Black holes as a source of information*Abstract: We will review the duality between gravity in negatively curved spacetimes and quantum field theories on the boundary. Black holes in these spacetimes represent finite temperature configurations for the theory on the boundary. The classical dynamics of these black holes can be used to get some insight into strongly coupled quantum systems.

And as a further sample, Hamber's talk:

*Ultraviolet Divergences and Scale-Dependent Coupling in Quantum Gravity*Abstract: I will discuss how non-perturbative approaches to the problem of ultraviolet divergences in quantum gravity, similar in spirit and methods to what is done in the modern renormalization group treatment of non-abelian gauge theories, point to a possible weak scale dependence of Newton's constant at very large distances. I will then discuss ways by which such a scale dependence could in principle be verified observationally.

http://www.icra.it/MG/mg12/en/invited_speakers_details.htm#freidel

http://www.icra.it/MG/mg12/en/invited_speakers_details.htm#maldacena

http://www.icra.it/MG/mg12/en/invited_speakers_details.htm#hamber

http://www.icra.it/MG/mg12/images/Program_MG12.pdf

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