Quantum gravity is notoriously a subject where problems vastly outnumber results. This is no surprise at short distances, on the order of the Planck length, where most of us expect quantum fluctuations in the metric to cause space-time itself to lose its meaning and gravity to be subsumed (along with the other so-called fundamental interactions) into some more comprehensive, consistent, and radical theory. However, even at larger scales, where one would naively expect quantum corrections to be small and controllable, reasonable people disagree not only on what are the right answers but also on what are the right questions. Recently there has been a flurry of activity in this area, inspired both by the importation of ideas from string theory and by speculations about connections between topology-changing quantum fluctuations and the vanishing of the cosmological constant. This last was the focus of the Seventh Jerusalem Winter School, on "Quantum Cosmology and Baby Universes", held from December 27 1989 to January 5 1990.
Lectures were given by S. Coleman (Harvard), J. Halliwell (M.LT.), J. Hartle (University of California, Santa Barbara), S. Hawking (Cambridge), A. Strominger (University of California, Santa Barbara), L. Susskind (Stanford), and C. Teitelboim (Centro de Estudios Cientificos de Santiago). Halliwell's "Introduction to Quantum Cosmology", Hartle's "The Quantum Mechanics of Cosmology" , and Teitleboim's "Hamiltonian Formulation of General Relativity" dealt with the foundations of the subject, while my "Wormhole Dynamics", Hawking's "Wormholes and Non-simply Connected Manifolds", Strominger's "Baby Universes" , and Susskind's "Critique of Coleman's Theory of the Vanishing Cosmological Constant" dealt with more recent developments. The more responsible lecturers submitted lecture notes to be published in this book.
Everyone involved in the school, both lecturers and students, displayed a very high level of energy and enthusiasm; I had a wonderful time and learned a lot, and I suspect others did also.
The success of the school owed much to the efforts of my co-directors, Jim Hartle and Steve Weinberg, and to those of the local organizer, Tsvi Piran. We are grateful to the Israeli Ministry of Science and to the Alfred P. Sloan Foundation for their support.