Nature of Space and Time (Princeton University Press)

Einstein said that the most incomprehensible thing about the universe is that it is comprehensible. But was he right$892 Can the quantum theory of fields and Einsteins general theory of relativity, the two most accurate and successful theories in all of physics, be united into a single quantum theory of gravity$893 Can quantum and cosmos ever be combined$894 In The Nature of Space and Time, two of the worlds most famous physicists - Stephen Hawking (A Brief History of Time) and Roger Penrose (The Road to Reality) - debate these questions.

The 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 still have further to go in their quest for a quantum theory of gravity.