This is from Hawking's Brief History of Time: I don't see why the black hole is cut off from the rest of the universe. The black hole is still there and it's still made of ordinary matter, just a more dense than other matter. Is it because time stops in a black hole? Or that nothing can escape from it? Even if those two traits are true I don't see why those conditions qualify as cutting one's self off from the rest of the universe.