pbFrom two of the world's great physicistsb--bStephen Hawking and Nobel laureate bbRoger Penroseb--ba lively debate about the nature of space and timeb pEinstein 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 into a single quantum theory of gravity Can quantum and cosmos ever be combined In iThe Nature of Space and Timei, two of the world's most famous physicists--Stephen Hawking iA Brief History of Timei and Roger Penrose iThe Road to Realityi--debate these questions. pThe authors outline how their positions have further diverged on a number of key issues, including the spatial geometry of the universe, inflationary versus cyclic theories of the cosmos, and the black-hole information-loss paradox. Though much progress has been made, Hawking and Penrose stress that physicists