The Basics of Black Hole Theory

Einstein said that space is bent by the presence of mass, but you can't see this bending directly. You shine light beams through space that's not curved, for example, and they just go through parallel. But because we can't see that curvature directly like with our own eyes, then it looks like there's a force there. So about a hundred years ago, people came up with this solution to Einstein's equations that predicted that if you got enough mass in one little spot, it would compactify itself so much that space would curve infinitely. And things that got really close to it would be trapped forever.