  The Schwarzschild metric has an apparent singularity at the horizon r=2M.
What really happens there? If physics at the horizon is 'normal' laboratory
physics, then we run into Hawking's information paradox. If we want nontrivial
structure at the horizon, then we need a mechanism to generate this structure
that evades the 'no hair' conjectures of the past. Further, if we have such
structure, then what would the role of the traditional black hole metric which
continues smoothly past the horizon? Recent work has provided an answer to
these questions, and in the process revealed a beautiful tie-up between
gravity, string theory and thermodynamics.
