topics: |  physics | space-time

God does not play dice. - Einstein

God not only plays dice, he also sometimes throws the dice where they
cannot be seen.
	- Hawking (Quoted in Ponomarev:The Quantum Dice



Sixty years ago Einstein and Bohr debated whether quantum theory could be a
"final theory" - Einstein disagreed on the grounds that it was
"philosophically inadequate.  Now Stephen Hawking and Roger Penrose debate
whether quantum field theory can be united with the general theory of
relativity into a single quantum theory of gravity.  Their positions are
explained in alternating chapters (originally lectures), with a final debate,
that took place at Cambridge over six months in 1994.

from blurb:
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.  Their divergences cannot be unified, and in the
end they agree to disagree.