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So if it turns out that the whole universe is at least 64 times larger than the visible portion then we are in fact already in a black hole!
by OscarCunningham 10y ago
So if it turns out that the whole universe is at least 64 times larger than the visible portion then we are in fact already in a black hole!
- mlonkibjuyhv 10y agoIt would give an "intuitive" explanation to why we can only see the inside of the universe.
- kobeya 10y agoNo explanation needed if the age of the universe is finite.
- akvadrako 10y agoThe universe is expanding in volume, but not mass. Thus some years ago the current visible portion did fit inside a 14Bly radius.
- pdonis 10y ago> if it turns out that the whole universe is at least 64 times larger than the visible portion then we are in fact already in a black hole! No. The universe is expanding. If it were a black hole, it would not be expanding.
- OscarCunningham 10y agoActually 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.
- pdonis 10y ago> 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).
- OscarCunningham 10y agoThen can any black hole exist in such a universe?
- pdonis 10y agoIn a closed universe that collapses to a Big Crunch, no, no black holes can exist. Everything will eventually come back together at the crunch.