Einstein said that the most incomprehensible thing about the universe is that it is comprehensible. But was he right? Can the quantum theory of fields and Einstein's general theory of relativity, the two most accurate and successful theories in all of physics, be united in a single quantum theory of gravity? Two of the world's most famous physicists - Stephen Hawking and Roger Penrose - disagree. Here they explain their positions in a work based on six lectures with a final (...) debate, all originally presented at the Isaac Newton Institute for Mathematical Sciences at the University of Cambridge. (shrink)