Observations and predictions from past lightcones

In a general Lorentzian manifold M, the past lightcone of point is proper subset M that does not carry enough information to determine rest M. That said, if globally hyperbolic Cauchy development vacuum initial data on surface S and there whose contains S, then contents such determines all (up isometry). We show some results describe what properties guarantee lightcones do indeed or at least significant portions Null lines observer horizons, which are well known features de-Sitter spacetime, play prominent role.