PIRSA:26030080 Scientific Series Quantum Gravity

DOI10.48660/26030080

Series: Quantum Gravity

Carlip, S. (2026). Spacetime foam and the cosmological constant. Perimeter Institute. https://pirsa.org/26030080

Carlip, Steve. Spacetime foam and the cosmological constant. Perimeter Institute, Mar. 26, 2026, https://pirsa.org/26030080 

@misc{ pirsa_PIRSA:26030080,
  doi = {10.48660/26030080},
  url = {https://pirsa.org/26030080},
  author = {Carlip, Steve},
  keywords = {Quantum Gravity},
  language = {en},
  title = {Spacetime foam and the cosmological constant},
  publisher = {Perimeter Institute},
  year = {2026},
  month = {mar},
  note = {PIRSA:26030080 see, \url{https://pirsa.org}}
}

Abstract

Suppose our universe really had a huge cosmological constant.  What would this mean observationally?  For a homogeneous universe the answer is clear, but if the universe is inhomogeneous at the Planck scale the question becomes more subtle.  At the level of initial data, $\Lambda$ can be "hidden" in spacetime foam, rapidly expanding and contracting regions that coexist and give an average expansion near zero.  Classically, such data develop singularities, and we need a quantum description of their evolution.  I describe results from a spherically symmetric midisuperspace model in which the wave function can become "trapped" for long periods in regions in which the average expansion remains small, effectively hiding a large cosmological constant.

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