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? Can
quantum and cosmos ever be combined? On this issue, two
of the world's most famous physicists--Stephen Hawking
(A Brief History of Time) and Roger Penrose
(The Emperor's New Mind and Shadows of the
Mind)--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. How could quantum gravity, a theory that
could explain the earlier moments of the big bang and
the physics of the enigmatic objects known as black
holes, be constructed? Why does our patch of the
universe look just as Einstein predicted, with no hint
of quantum effects in sight? What strange quantum
processes can cause black holes to evaporate, and what
happens to all the information that they swallow? Why
does time go forward, not backward? In this book, the
two opponents touch on all these questions. Penrose,
like Einstein, refuses to believe that quantum mechanics
is a final theory. Hawking thinks otherwise, and argues
that general relativity simply cannot account for how
the universe began. Only a quantum theory of gravity,
coupled with the no-boundary hypothesis, can ever hope
to explain adequately what little we can observe about
our universe. Penrose, playing the realist to Hawking's
positivist, thinks that the universe is unbounded and
will expand forever. The universe can be understood, he
argues, in terms of the geometry of light cones, the
compression and distortion of spacetime, and by the use
of twistor theory. With the final debate, the reader
will come to realize how much Hawking and Penrose
diverge in their opinions of the ultimate quest to
combine quantum mechanics and relativity, and how
differently they have tried to comprehend the
incomprehensible. In a new afterword, the authors
outline how recent developments have caused their
positions to further diverge 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 much farther to go in their quest
for a quantum theory of gravity.
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