Sorry, noob question. On the Discovery channel I've seen a couple of programs where they had physicists trying to explain black holes. The physicists said that if you collapse matter to a small enough space, you would get a black hole. One of the Physicists examples was that if you collapsed Earth to the size of a marble, you'd get a black hole. I didn't think gravity had anything to do with density. Isn't the gravitational formula unrelated to density? I think it's something like ((M1 * M2)/D^2)*G; where the Ms are the masses of the objects in question, D is the distance between them, and G is the gravitational constant. Whether you stretch out Earth to be the size of Jupiter or you shrink it down to the size of a pinhead, gravity wouldn't change, according to this formula. Is this formula too old-school/obsolete? Does density play a part in gravity?