Three Roads to Quantum Gravity , Lee Smolin , Basic Books, New York, 2001. $24.00 (231 pp.). ISBN 0-465-07835-4
The 20th century witnessed two conceptual revolutions in physics; these in turn led to the most successful physical theories ever: general relativity and quantum mechanics. Immediately after their creation Oskar Klein in 1927 suggested that quantum mechanics should be applied to general relativity, and technical papers on the subject were written by Matvei Bronstein, Léon Rosenfeld, Wolfgang Pauli, Markus Fierz, Werner Heisenberg and others. These early investigations already suggested that something would go seriously wrong in this endeavor.
The difficulties did not go away when Peter Bergmann, P. A. M. Dirac, Richard Feynman and Bryce DeWitt applied the modern tools of quantum field theory to the problem in the 1950s and 60s. Since then, many people have considered the question to be one of the...
