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SUMMARY:de Sitter space is sometimes not empty - Vijay Balasubramanian (Un
 iversity of Pennsylvania)
DTSTART:20231127T100000Z
DTEND:20231127T110000Z
UID:TALK203677@talks.cam.ac.uk
DESCRIPTION:Multiple lines of evidence suggest that the Hilbert space of a
 n isolated de Sitter (dS) universe is one dimensional\, but can appear lar
 ger 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. &nbsp\; We sh
 ow that the entanglement entropy vanishes if the dS cosmological horizon i
 s smaller than the AdS black hole horizon\, but that non-perturbative cont
 ributions of wormholes in the gravitational path integral imply that the e
 ntanglement entropy is finite when the dS horizon is larger than the AdS h
 orizon. Thus\, the dS Hilbert space is effectively nontrivial only when th
 e cosmological horizon is larger than the horizon of the entangled AdS bla
 ck hole\, which we can regard as a gravitating ``observer''. In this sense
 \, our result is a non-perturbative generalization &nbsp\;of the recent pe
 rturbative argument that the algebra of observables on the de Sitter stati
 c patch becomes nontrivial in the presence of an observer.&nbsp\;
LOCATION:Seminar Room 1\, Newton Institute
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