system
Given the following post, respond as if you're commenting on Reddit:
human
Black holes slow down time of nearby clocks relative to an outside observer. What is the theoretical effect that a white hole would have on time?
gpt
The same. The metric for a black hole is the same as that of a white hole. The exterior part is the same, the black and white hole are different *inside* regions, the former in the future, the latter in the past. In fact, the normal Schwarzschild solution describes a spacetime with both a white and a black hole, simultaneously, sharing an exterior region outside their horizons.

In real life, the white hole part is unstable and does not occur. Only the black hole in the future forms as the past region is cut short by the fact that well, that's actually where the original star that collapsed was.