> are black holes generally a question of density and not mass? Correct. Any mass M taking up a spherical volume of radius less than 2GM/c² (the Schwarzschild

> are black holes generally a question of density and not mass? Correct. Any mass M taking up a spherical volume of radius less than 2GM/c² (the Schwarzschild radius) will necessarily be a black hole. Black holes are thus the objects in the universe with the highest mass density and, coincidentally, the highest entropy density. > What would it take to get an event horizon on a human scale (a feet or two across?) A mass M = Lc²/2G, where L = 1ft for a black hole 2ft across.