We don't think white holes exist because if they did, we'd have seen them by now. A black hole is not absolutely only a one-way street. Unless the singularity is a gateway to another dimension. But then other black holes from other universes ought to be sending their stuff into our universe. And maybe that's what dark energy is. If we're dark energy, it would be coming in in a different way. We should find some sort of streams of energy that we should see. Neil deGrasse Tyson: Do you believe white holes exist? Have we found evidence of them or is this still just theoretical? Why does the event horizon always appear as a disc? Why