The quantum structure of black holes and the recovery of information
The detection of black-hole mergers in 2015 was a spectacular confirmation of General Relativity (GR). Yet, it is also in black holes that the fundamental conflict between GR and quantum mechanics (QM) is most acute.  Black holes are known to have a vast entropy.  Consistency with QM requires that the microstates giving rise to this entropy must be accessible at the horizon scale. However, GR coupled to field theory is incapable of supporting this horizon-scale microstructure!  My work has shown that Microstate Geometries (MG’s), based in string theory and higher-dimensional field theory, have all the essential elements for supporting and encoding microstate data:  MG’s are smooth, horizonless solutions in string theory that are identical to black holes on large scales but differ radically from the black holes of GR at the horizon scale.

I propose to launch a new, extensive study of the MG paradigm, focussing on the, as yet, unexplored dynamics of the microstructure in MG’s: (i) How infalling matter is absorbed and diffused into excitations of MG’s; (ii) How the excitations of MG’s, and the MG’s themselves, decay into some form of Hawking radiation that carries the microstructure data to infinity, thereby preserving quantum unitarity; (iii) How the large-scale, collective dynamics of microstructure interacts with matter in the horizon region and, particularly, how microstructure dynamics influences accretion disks and black-hole mergers. Progress will be achieved by analyzing the energy transfer between infalling probes and MG’s, computing the resulting excitations of the MG and the drag on infalling objects. The results will be re-expressed in a hydrodynamic form that can be applied to simulations of astrophysical black holes. 

This proposal will thus solve the information paradox by providing a microscopic description of black-hole entropy at the horizon scale and this should lead to macroscopic, measurable signatures of the horizon-scale microstructure.