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
8 - Interpreting the wave function
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
This chapter discusses how a classical universe arises out of the quantum wave function of the universe. The process of decoherence is described, first in general and then applied to cosmology. The classicalization of the background spacetime (and the associated reduction in interference between saddle points) as well as the classicalization of long-wavelength perturbation modes is discussed, by studying an example of interactions between background and fluctuations, as well as interaction between perturbation modes of different wavelengths. Comments on the interpretation of the wave function are included.
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- Quantum CosmologyAn Introduction, pp. 254 - 268Publisher: Cambridge University PressPrint publication year: 2026
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