6: The Inner Boundary (cont.)
The Schwarzschild (Ingoing Eddington-Finklestein) and Kerr spacetimes use the Kerr-Schild form of the metric:
- The metric is form invariant under a boost.
- The 3+1 decomposition are unique for boosted Schwarzschild or Kerr.
- 3+1 decomposition gives us initial data (gij, Kij) and coordinate conditions (a,bi) which we can then use.
- The analytical apparent horizon location is known everywhere.