Effective Quantum Extended Spacetime of Polymer Schwarzschild Black Hole

Tuesday, Dec 3rd.
Fabio Mele and Johannes Muench, University of Regensburg

Title: Effective Quantum Extended Spacetime of Polymer Schwarzschild Black Hole
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By Jorge Pullin, LSU

When one crosses the horizon into a black hole the role of time and radius get interchanged. One is inevitably dragged into "the future" along the r direction towards the singularity at r=-0. The metric of the space-time, which outside the black hole depends on r, inside depends on t, it becomes time dependent as if it were a cosmological space-time. This in fact can be made into a mathematically precise correspondence. The space-time in the interior of a black hole is equivalent to a type of cosmology known as Kantowksi-Sachs. This led people to study it using loop quantum cosmology tools. In particular one finds that the singularity inside black holes gets replaced by a "bounce" into another region in space-time just like the Big Bang is replaced by a bounce in loop quantum cosmology.

This talk focused on some technical issues of these types of studies. In particular, when one studies physically observable quantities, mathematically one finds there are two of them, but only one has a physical interpretation, it is the mass of the black hole. Through a change of variables the authors were able to identify physically two observable quantities. They correspond to the mass of the black hole and the mass of the "white hole" that emerges once one bounces through the singularity. The new variables have several other advantages, in particular they simplify the dynamics quite a bit and it actually becomes exactly solvable.

Quasilocal holography in quantum gravity in 3 dimensions

Tuesday, Nov 5

Aldo Riello, Perimeter Institute

Title: Quasilocal holography in Quantum Gravity in 3 Dimensions
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Audio+Slides of the talk (220M)
SRT (Subtitles) of the talk (60K)

By Jorge Pullin

Holography in the context of gravitational physics refers to describing a region of space-time through a theory on its boundary. The idea arises in several scenarios, in particular in string theory in the so called AdS/CFT correspondence.

In this talk the concept of holography was first studied in three dimensions. General relativity simplifies considerably in three dimensions since the Einstein equations in empty space imply that space-times are all flat. This allows to make considerable progress and in fact there exists a quantum theory of gravity in three dimensions, it is known as the Regge-Ponzano model. In the talk the relation of this model with degrees of freedom on the boundary of space-time were discussed. Both the case with and without a cosmological constant were considered. Many parallels with other results in the literature were found. The relation of the dynamics in the interior with that on the boundary and its corresponding states was outlined. Connections with other boundary treatments that were discussed in International Loop Seminars recently by Dittrich and Bonzom and by Wieland were also presented.