PIRSA:26040117 Conference Cosmology

DOI10.48660/26040117

Conference/School: Cosmological Frontiers in Fundamental Physics 2026

Tzanavaris, K. (2026). On the action principle in space-times with boundary. Perimeter Institute. https://pirsa.org/26040117

Tzanavaris, Kostas. On the action principle in space-times with boundary. Perimeter Institute, Apr. 28, 2026, https://pirsa.org/26040117 

@misc{ pirsa_PIRSA:26040117,
  doi = {10.48660/26040117},
  url = {https://pirsa.org/26040117},
  author = {Tzanavaris, Kostas},
  keywords = {Cosmology},
  language = {en},
  title = {On the action principle in space-times with boundary},
  publisher = {Perimeter Institute},
  year = {2026},
  month = {apr},
  note = {PIRSA:26040117 see, \url{https://pirsa.org}}
}

Abstract

In this talk, I will present a general methodology for assigning boundary conditions to boundaries of a space-time, which may or may not be singular, using the action principle alone. It is shown that Kasner-like solutions cannot satisfy this action principle, when the initial singularity is included, thereby excluding generic initial data, assuming the validity of the BKL conjecture. We further show that conformally regular geometries do satisfy this action principle. This argument, coupled with my co-authors’ previous work on the statistics of conformally regular geometries, provides an explanation for the horizon problem without the need of new physics beyond the standard model.

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