Pennsylvania State University
Talks by Abhay Ashtekar
A New Perspective on Time Reversal Motivated by Quantum Gravity
Implications of the Quantum Nature Spacetime for the Big Bang and Black Holes
Bounce in Loop Quantum Cosmology and its Implications
The BMS group, conservation laws and soft gravitons
I will give a broad overview of this old subject which has come back to light recently in connection with the issue of black hole evaporation. It will be an informal, black board talk.
The fate of the big bang

Abhay Ashtekar Pennsylvania State University

Neil Turok Perimeter Institute for Theoretical Physics
Even a tiny positive cosmological constant casts a long shadow
Even a tiny cosmological constant casts a long shadow
Surprisingly, several basic questions in classical and quantum gravity, which were resolved some 4050 years ago for zero $\Lambda$, still remain open in the $\Lambda >0$ case. In particular, for $\Lambda >0$, we still do not have a satisfactory notion of gravitational radiation or Bondi 4momentum in exact general relativity, nor a positive energy theorem. Similarly, the standard constructions of `in' and `out' Hilbert spaces that we routinely use (e.g. in the analysis of black hole evaporation) do not extend to the $\Lambda >0$ case.
Loop Quantum Cosmology & The Very Early Universe Interplay between theory and Observations
Thanks to the spectacular observational advances since the 1990s, a `standard model' of the early universe has now emerged. However, since it is based on quantum field theory in curved spacetimes, it is not applicable in the Planck era. Using techniques from loop quantum gravity, the theory can be extended over the 12 orders of magnitude in density and curvature from the onset of inflation all the way back to the Planck regime, providing us with a possible completion of the standard model.
Promising Paths: What Have We Learned So Far About Quantum Gravity?

Abhay Ashtekar Pennsylvania State University

Carlo Rovelli Centre de Physique Théorique (CPT)
I try to make the point about what we know and what we do not yet know about the possibility of writing a quantum theory of gravity.