Actually I think I just gave the Big Crunch hypothesis. The universe can be expanding so long as it eventually collapses. Even in a normal black hole forming out of a star, some particles will happen to be heading out as the star collapses and then be dragged back in after the black hole forms.
> Actually I think I just gave the Big Crunch hypothesis. The universe can be expanding so long as it eventually collapses.
Even in this case it's not correct to say that the universe is a black hole. The spacetime geometry is very different. A black hole, as I've posted elsewhere in this thread, is a region from which light can't escape to infinity. But in a universe that will end up in a Big Crunch, there is no infinity: space has a finite volume (which increases up to maximum expansion and then decreases back to zero).
