A black hole has entropy and must represent an ensemble of many underlying microstates. Clarifying the nature of these microstates is one of the most important problems in theoretical physics and will help us understand the microscopic workings of spacetime.
Among various approaches to black hole microphysics, the "black hole microstate geometry program", which is based on the fuzzball program, aims to understand how many of these microstates can be represented by solutions of classical supergravity. Recently, it was conjectured that there exist a new class of gravity microstates, called superstrata, which might account for a finite fraction of the black hole entropy, and some simple examples of them have been successfully constructed. Furthermore, there also is a proposal that generic microstates involve non-geometric microstates which are solutions of string-generalized supergravity. There are various other approaches to black hole microphysics, such as the AdS/CFT correspondence, self-consistent models of black hole formation and evaporation, numerical simulations, quantum information, and firewalls. The intuition into the microstructures of black holes can shed light also on the microstructures of spacetimes in general and may allow one to study microphysics of other spacetimes such as cosmological spacetimes.
The aim of this workshop is to bring together researchers working on the microstructures of black holes and, through talks and discussions, promote new directions of research in this exciting and developing field of research.