I know white holes probably don't exist, but I'm having trouble understanding how someone outside the white hole would perceive them. My understanding is that they are time-reversed black holes. I've read that nothing can fall into a white hole, that it is repulsive, and that it continually ejects things out. But... when I try to reason out what a time-reversed black hole would actually look like, I get a black hole. I mean, I get something which seems to behave the same as a black hole, at least from an observer outside the hole. It's possible to orbit a black hole. After all, the gravity outside a spherical planet is supposed to be the same as the gravity at the same distance from a black hole of the same mass. If you play a video of a stable orbit in reverse, you get a stable orbit. So it should be possible to orbit a white hole. So a white hole is not repulsive, but attractive, just like a black hole. Would we, in fact, be able to tell them apart? I looked at the diagram in: http://en.wikipedia.org/wiki/Kruskal–Szekeres_coordinates where black hole and white hole seem clearly different. But, can we actually identify the top and bottom singularities (topologically tie them together, so coordinate T loops around endlessly). Then a black hole and a white hole are the same thing.