An introduction to quantum gravity

After an overview of the physical motivations for studying quantum gravity, we reprint THE FORMAL STRUCTURE OF QUANTUM GRAVITY, i.e. the 1978 Carg`ese Lectures in Levy & Deser (1979): Recent Developments in Gravitation pp. 275–322 by Professor B. S. DeWitt, with kind permission of Springer Science and Business Media. The reader is therefore introduced, in a pedagogical way, to the functional integral quantization of gravitation and Yang–Mills theory. It is hoped that such a paper will remain useful for all lecturers or Ph.D. students who face the task of introducing (resp. learning) some basic concepts in quantum gravity in a relatively short time. In the second part, we outline selected topics such as the braneworld picture with the same covariant formalism of the first part, and spectral asymptotics of Euclidean quantum gravity with diffeomorphism-invariant boundary conditions. The latter might have implications for singularity avoidance in quantum cosmology.