Causal boundary for standard static spacetimes

It is shown how to construct the causal boundary of Geroch, Kronheimer, and Penrose, for a standard static spacetime: With (M, h) an arbitrary Riemannian manifold, the causal boundary for the spacetime V = (R, -dt(2)) x (M, h) is formed from a boundary construction on M: In addition to what amounts to the Cauchy completion on M, there are ideal points representing ray-like directions; all these together are called the Busemann boundary for M. The future causal boundary on V is a cone on the Busemarm boundary of M.