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University of Cambridge > Talks.cam > Isaac Newton Institute Seminar Series > de Sitter space is sometimes not empty

## de Sitter space is sometimes not emptyAdd to your list(s) Download to your calendar using vCal - Vijay Balasubramanian (University of Pennsylvania)
- Monday 27 November 2023, 10:00-11:00
- Seminar Room 1, Newton Institute.
If you have a question about this talk, please contact nobody. BLHW03 - Bridges between holographic quantum information and quantum gravity Multiple lines of evidence suggest that the Hilbert space of an isolated de Sitter (dS) universe is one dimensional, but can appear larger when probed by a gravitating observer. To test this idea, we compute the von Neumann entropy of a field theory in a two-dimensional dS universe which is entangled in a thermal-like state with the same field theory on a disjoint, asymptotically anti-de Sitter (AdS) black hole. We show that the entanglement entropy vanishes if the dS cosmological horizon is smaller than the AdS black hole horizon, but that non-perturbative contributions of wormholes in the gravitational path integral imply that the entanglement entropy is finite when the dS horizon is larger than the AdS horizon. Thus, the dS Hilbert space is effectively nontrivial only when the cosmological horizon is larger than the horizon of the entangled AdS black hole, which we can regard as a gravitating ``observer’’. In this sense, our result is a non-perturbative generalization of the recent perturbative argument that the algebra of observables on the de Sitter static patch becomes nontrivial in the presence of an observer. This talk is part of the Isaac Newton Institute Seminar Series series. ## This talk is included in these lists:- All CMS events
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