Abstract
Quantum theory and general relativity contain different concepts of time. This is considered as one of the major obstacles to constructing a quantum theory of gravity. In my essay, I investigate those consequences for the concept of time in quantum gravity that may be drawn without a detailed knowledge of the final theory. The only assumptions are the experimentally supported universality of the linear structure of quantum theory and the recovery of general relativity in the classical limit. Among the consequences are the fundamental timelessness of quantum gravity, the approximate nature of a semiclassical time and the correlation of entropy with the size of the Universe.
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Notes
- 1.
There also exist the so-called diffeomorphism constraints, which state that \(\Psi \) is independent of the choice of spatial coordinates, see e.g. [4] for details.
- 2.
More precisely, some of the gravitational degrees of freedom can also remain quantum, while some of the non-gravitational variables can be macroscopic and enter the definition of time.
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Acknowledgements
I am grateful to Dennis Lehmkuhl for inviting me to an exciting conference. This contribution is a slightly revised version of my essay with the same title, which in 2009 received a second prize in the The Nature of Time essay context organized by the Foundational Questions Institute (www.fqxi.org). I thank Marcel Reginatto and H.-Dieter Zeh for their comments on an earlier version of this essay.
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Kiefer, C. (2017). Does Time Exist in Quantum Gravity?. In: Lehmkuhl, D., Schiemann, G., Scholz, E. (eds) Towards a Theory of Spacetime Theories. Einstein Studies, vol 13. Birkhäuser, New York, NY. https://doi.org/10.1007/978-1-4939-3210-8_10
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