Book contents
- Frontmatter
- Dedication
- Contents
- Preface
- Acknowledgments
- Conventions and notation
- 1 Modeling the early universe
- 2 Blowing up the universe: inflation
- 3 Observing perturbative quantum gravity: fluctuations
- 4 Quantizing gravity: canonical approach
- 5 Quantizing gravity: path integral approach
- 6 Linking gravity, quantum theory, and thermodynamics
- 7 Creating space and time: the no-boundary proposal
- 8 Interpreting the wave function
- 9 Transitioning to different spacetimes
- 10 Going deeper yet: stringy cosmology
- Appendix A Constants of nature and cosmological quantities
- Appendix B Picard{Lefschetz theory and saddle-point approximation
- Appendix C Useful functions
- Appendix D Solutions to exercises
- Appendix E Guide to the bibliography
- Bibliography
- Index
5 - Quantizing gravity: path integral approach
Published online by Cambridge University Press: 02 February 2026
Book contents
- Frontmatter
- Dedication
- Contents
- Preface
- Acknowledgments
- Conventions and notation
- 1 Modeling the early universe
- 2 Blowing up the universe: inflation
- 3 Observing perturbative quantum gravity: fluctuations
- 4 Quantizing gravity: canonical approach
- 5 Quantizing gravity: path integral approach
- 6 Linking gravity, quantum theory, and thermodynamics
- 7 Creating space and time: the no-boundary proposal
- 8 Interpreting the wave function
- 9 Transitioning to different spacetimes
- 10 Going deeper yet: stringy cosmology
- Appendix A Constants of nature and cosmological quantities
- Appendix B Picard{Lefschetz theory and saddle-point approximation
- Appendix C Useful functions
- Appendix D Solutions to exercises
- Appendix E Guide to the bibliography
- Bibliography
- Index
Summary
The path integral quantization of gravity is developed, with an emphasis on physical intuition. It is shown how to deal with gauge transformations, and how this results in an ordinary integration over the lapse function. This formalism is applied to minisuperspace models, and transitions in a setting with a cosmological constant are explored for both Dirichlet and Neumann boundary conditions. The relation between the path integral and the Wheeler–DeWitt equation is derived, as well as the rules for composing transition amplitudes.
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- Quantum CosmologyAn Introduction, pp. 119 - 153Publisher: Cambridge University PressPrint publication year: 2026
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