PIRSA:15100085

The Hawking-Hartle No Boundary Proposal in Causal Set Quantum Gravity

Surya, S. (2015). The Hawking-Hartle No Boundary Proposal in Causal Set Quantum Gravity. Perimeter Institute. https://pirsa.org/15100085

Surya, Sumati. The Hawking-Hartle No Boundary Proposal in Causal Set Quantum Gravity. Perimeter Institute, Oct. 15, 2015, https://pirsa.org/15100085 

          @misc{ pirsa_PIRSA:15100085,
            doi = {10.48660/15100085},
            url = {https://pirsa.org/15100085},
            author = {Surya, Sumati},
            keywords = {Quantum Gravity},
            language = {en},
            title = {The Hawking-Hartle No Boundary Proposal in Causal Set Quantum Gravity},
            publisher = {Perimeter Institute},
            year = {2015},
            month = {oct},
            note = {PIRSA:15100085 see, \url{https://pirsa.org}}
          }

Sumati Surya

Raman Research Institute

Talk number
PIRSA:15100085
Collection
Talk Type
Subject
Abstract

The Hartle-Hawking (HH) no-boundary proposal provides a Euclidean path integral prescription for a measure on the space of all possible initial conditions. Apart from  saddle point  and  minisuper-space calculations, it is hard to obtain results using the unregulated path integral. A promising choice of spacetime  regularisation comes from the causal set (CST) approach to quantum gravity.  Using analytic results as well as Markov Chain Monte Carlo and numerical integration methods we obtain  the HH wave function in a theory of non-perturbative 2d CST. We find that the  wave function is sharply peaked with the peak geometry changing discretely with "temperature". In the low temperature regime the peak corresponds to causal sets which have no continuum counterpart but exhibit physically interesting behaviour. They show a rapid spatial expansion with respect to the discrete proper time as well as  a high degree of spatial homogeneity due to extensive overlap of the causal past. While our results are limited to 2 dimensions they provide a concrete example of how quantum gravity could explain the initial conditions for our observable universe.