6: The Inner Boundary
Causal structure of Black holes such that no boundary conditions are required at and inside the apparent horizon of the black hole.
Require a good choice of “coordinates” in order to take advantage of this
The only problems that we have been able to do, have been “model problems” which give us coordinate conditions for static rotating, moving black holes (Choice corresponds to the Kerr-Schild spacetime metric or ingoing Eddington-Finkelstein coordinates for Schwarzschild black holes)