White hole
= White hole
A white hole is the time reverse of a <black hole>: causal trajectories can emerge from its past singularity, while exterior future-directed trajectories cannot enter through its past horizon. The maximal <Schwarzschild spacetime> contains both a future black-hole interior and a past white-hole interior. Both have the same areal-radius range, illustrating why a global time orientation and choice of extension are essential in causal statements.