Does time exist in quantum gravity?

Main Article Content

Claus Kiefer


Time is absolute in standard quantum theory and dynamical in general relativity. The combination of both theories into a theory of quantum gravity leads therefore to a “problem of time”. In my essay, I investigate those consequences for the concept of time that may be drawn without a detailed knowledge of quantum gravity. 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.

Article Details

How to Cite
Kiefer, C. (2015). Does time exist in quantum gravity?. Philosophical Problems in Science (Zagadnienia Filozoficzne W Nauce), (59), 7–24. Retrieved from


Albers, M., Kiefer, C., Reginatto, M., 2008. Measurement analysis and quantum gravity. Physical Review D, 78, p. 064051.

Anderson, E., 2012. Problem of time in quantum gravity. Annalen der Physik, 524, pp. 757–786.

Barbour, J.B. ,1986. Leibnizian time, Machian dynamics, and quantum gravity. In: R. Penrose and C.J. Isham, eds., Quantum concepts in space and time. Oxford: Oxford University Press, pp. 236–246.

Barbour, J.B., 1993. Time and complex numbers in canonical quantum gravity. Physical Review D, 47, pp. 5422–5429.

Damour, T., Nicolai, H., 2008. Symmetries, singularities and the deemergence of space. International Journal of Modern Physics

D, 17, pp. 525–531. DeWitt, B.S., 1967. Quantum theory of gravity. I. The canonical theory. Physical Review, 160, pp. 1113–1148.

Einstein, A., 1982. How I created the theory of relativity. Translated by Y.A. Ono. Physics Today, August, pp. 45–47.

Isham, C.J., 1993. Canonical quantum gravity and the problem of time. In: L.A. Ibort and M.A. Rodríguez, eds., Integrable systems, quantum groups, and quantum field theory, Dordrecht: Kluwer, pp. 157–287.

Joos, E., Zeh, H.D., Kiefer, C., Giulini, D., Kupsch, J., and Stamatescu, I.-O., 2003. Decoherence and the appearance of a classical world in quantum theory. 2nd ed. Berlin: Springer.

Kamenshchik, A.Y., Kiefer, C., Sandhöfer, B., 2007. Quantum cosmology with a big-brake singularity. Physical Review D, 76, p. 064032.

Kiefer, C., 1992. Decoherence in quantum electrodynamics and quantum gravity. Physical Review D, 46, pp. 1658–1670.

Kiefer, C., 1993. Topology, decoherence, and semiclassical gravity. Physical Review D, 47, pp. 5414–5421.

Kiefer, C. 2012. Quantum gravity. 3rd ed. Oxford: Oxford University Press.

Kiefer C., Krämer, M., 2012. Can effects of quantum gravity be observed in the cosmic microwave background? International Journal of Modern Physics D, 21, p. 1241001.

Kiefer, C., Singh, T.P., 1991. Quantum gravitational correction terms to the functional Schrödinger equation. Physical Review D, 44, pp. 1067–1076.

Kiefer, C., Zeh, H.D., 1995. Arrow of time in a recollapsing quantum universe. Physical Review D, 51, pp. 4145–4153.

Kuchař, K.V., 1993. Time and interpretations of quantum gravity. In: G. Kunstatter, D. Vincent, and J. Williams, eds., Proceedings of the 4th Canadian Conference on General Relativity and Relativistic Astrophysics. Singapore: World Scientific, pp. 211–314.

Maldacena, J., 2005, The illusion of gravity. Scientific American, November, pp. 56–63.

Mott, N.F., 1931. On the theory of excitation by collision with heavy particles. Proceedings of the Cambridge Philosophical Society, 27, pp. 553–560.

Peres, A., 1962. On Cauchy’s problem in general relativity–II. Nuovo Cimento, XXVI, pp. 53–62.

Schlosshauer, M., 2007. Decoherence and the quantum-to-classical transition. Berlin: Springer.

Schrödinger, E., 1926. Quantisierung als Eigenwertproblem II. Annalen der Physik, 384, pp. 489–527.

Wheeler, J.A., 1968. Superspace and the nature of quantum geometrodynamics. In: C.M. DeWitt and Wheeler, eds. Battelle rencontres, New York: Benjamin, pp. 242–307.

Zeh, H.D., 2007. The physical basis of the direction of time. 5th ed. Berlin: Springer.