Black Holes

Juan Maldacena: "A black hole is an object that forms when you put too much matter in a small region of space so that the gravitational forces become so big that essentially nothing can escape. Not even light can escape, and that's why it's called black. It's one of the strangest predictions of general relativity: space-time can bend so much that it produces a hole in the middle of space." According to general relativity, once something crosses the surface or horizon of a black hole, it is lost forever.