It seems to me that if we on the outside of a black hole never see things fall past the event horizon, then a white hole is just a black hole with stuff already rushing out from the event horizon. In other words, nothing can escape from inside a black hole, but then, nothing ever gets that far in anyway. An observer falling into a black hole continues past the event horizon onto a piece of paper that branches off from our history; I don't see why white hole ejecta can't have started on a similar side track-- except that both those tracks seem "non-falsifiable". I guess a singularity is a place where a scientific theory continues majestically past science? What I really want are gray holes, randomly absorbing and ejecting large chunks of matter contrary to all probability but consistent with "classical GR". It's hard to imagine a black hole forming after the big bang and *then* ejecting something. You have to imagine a very red-shifted thing accelerating from +.999...c to -.999...c -- how did it get up the gumption in such a short time? Was it actually in a tight chaotic orbit all along?
From: Rowan Hamilton <rowanham@gmail.com>
Classical mechanics is invariant under translations in time - this results in conservation of energy via Noether's Theorem.
Looking at http://en.wikipedia.org/wiki/Noether%27s_theorem it looks like the only kind of symmetries it applies to are transformations that you can have continuous versions of, like translation and rotation. Is this true? It makes me sad! I would have liked a conservation law to pop out of *every* kind of symmetry!
Classical mechanics is *not* invariant under time reversal, as others have pointed out, since this violates the Second Law of Thermodynamics.
I second the motion to marginalize the second law to statistics and revert to time-reversible physics. Surely a time-reversed black hole is allowed under a time-reversed Second Law. I'm curious how to tell whether the Second Law is working in forward or reverse. I can take two measurements of entropy, but looking at my log, how do I know whether the 1:01pm measurement was taken before or after the 1:03pm measurement? --Steve