Black hole microstates and a rough end to spacetime
The study of supersymmetric black holes in string theory has been a useful arena for the search for the correct microscopic description of black holes, with one of its greatest triumphs being the explicit stringy counting by Strominger and Vafa of the number of microstates of the D1-D5-P system which famously agrees precisely with the Bekenstein-Hawking entropy of the naive black hole solution. The fuzzball program is an attempt to describe these microstates at finite coupling with the extended objects of string theory modifying the structure of the black hole horizon by replacing it with an end to spacetime. An important open question is what fraction of these microstates is smooth, contains singularities corresponding to D-brane sources or is arbitrarily quantum and/or strongly curved. In this talk I will use entropic and dynamic arguments to address this question.