Discussion Meeting
Pallab Basu (International Centre for Theoretical Sciences), Suvrat Raju (International Centre for Theoretical Sciences) and Spenta Wadia (International Centre for Theoretical Sciences)
22 September 2013 to 23 September 2013
ICTS, Bangalore

This meeting which is ICTS-IISc joint program will discuss recent progress on the black-hole information paradox, and the question of whether AdS/CFT can provide a useful description of the interior of black holes.

Long ago, Hawking found that the thermal radiation from black-holes appeared to be in conflict with the unitarity of quantum mechanics. It was believed, especially after the advent of the AdS/CFT correspondence, that Hawking's calculation was not precise enough to provide a paradox, and that small effects in the CFT would reconcile Hawking radiation with unitarity.

Recently, there have been several claims, starting with the work of Mathur, and followed by the work of Marolf, Polchinski and others that this is impossible; rather unitarity implies that quantum effects modify the structure of the horizon of the black-hole.

This meeting will take stock of the claims and counter-claims in the literature. Broadly speaking, the following positions have been articulated:
1) quantum effects modify the horizon structure, and the interior of a black-hole has a firewall, or that AdS/CFT does not describe the interior at all.
2) quantum effects modify the horizon structure, but the black-hole is described not by the smooth Schwarzschild geometry, but by various fuzzball solutions.
3) subtle non-local effects restore unitarity, so that the interior of the black-hole is in, some sense, a rewriting of the degrees of freedom that reside in the far-away radiation.
4) Information loss really does occur in gravity.

These scenarios often require some departure from accepted principles. For example, in the first two, effective field theory is violated. In the third one, we require that the operator identified as the "local field" depends on the microstate of the black-hole. The fourth one is difficult to reconcile with AdS/CFT or even energy-momentum conservation.

pallabbasu  ictsresin