Black holes are the remnants after heavy stars burn out and collapse. The gravitational pull of a black hole is so strong that not even light can escape. Moreover, craters and other distinctive features are impossible because of the crushing forces exerted on matter in the black hole. The contrast between the initial complexity of a star and the final, apparently structureless state of a black hole is dramatic and puzzling. Indeed, if the black hole shows no hint of its complex past, there is an apparent conflict with determinism. According to determinism, the present state of the world developed from some past state that should be deducible from the present one, at least in principle. Theoretical physicists are strong believers in determinism and therefore are inclined to suspect that the complexity of the star has been transformed into some kind of internal structure of the black hole, rather than having disappeared. Recent research may have uncovered the appropriate hidden structure.