Comments on wormholes, ensembles, and cosmology

Abstract

Certain closed-universe big-bang/big-crunch cosmological spacetimes may be obtained by analytic continuation from asymptotically AdS Euclidean wormholes, as emphasized by Maldacena and Maoz. We investigate how these Euclidean wormhole spacetimes and their associated cosmological physics might be described within the context of AdS/CFT. We point out that a holographic model for cosmology proposed recently in arXiv:1810.10601 can be understood as a specific example of this picture. Based on this example, we suggest key features that should be present in more general examples of this approach to cosmology. The basic picture is that we start with two non-interacting copies of a Euclidean holographic CFT associated with the asymptotic regions of the Euclidean wormhole and couple these to auxiliary degrees of freedom such that the original theories interact strongly in the IR but softly in the UV. The partition function for the full theory with the auxiliary degrees of freedom can be viewed as a product of partition functions for the original theories averaged over an ensemble of possible sources. The Lorentzian cosmological spacetime is encoded in a wavefunction of the universe that lives in the Hilbert space of the auxiliary degrees of freedom.

23 pages, 6 figures, v2: references added

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• Euclidean wormhole in the SYK model
• Defect Extremal Surface for Reflected Entropy
• Islands in Kaluza-Klein black holes
• Cosmology from confinement?
• Wormholes & Holography: An Introduction
• Holographic spacetime, black holes and quantum error correcting codes: A review
• Brane Dynamics of Holographic BCFTs
• Islands for Entanglement Negativity
• Entanglement Islands in Generalized Two-dimensional Dilaton Black Holes
• Interacting systems and wormholes
• The Spectrum of Boundary States in Symmetric Orbifolds
• Accelerating cosmology from a holographic wormhole
• Finding $Ad{S}^5\times S^5$ in 2+1 dimensional SCFT physics
• Bounds on gravitational brane couplings and tomography in AdS3 black hole microstates
• The Dictionary for Double Holography and Graviton Masses in d Dimensions
• Holographic boundary states and dimensionally-reduced braneworld spacetimes
• Cosmologies, singularities and quantum extremal surfaces
• Bottom-up holographic models for cosmology
• The refined quantum extremal surface prescription from the asymptotic equipartition property
• Vacuum Transitions in Two-Dimensions and their Holographic Interpretation
• Ensemble averages, Poisson processes and Microstates
• Page Curve from Defect Extremal Surface and Island in Higher Dimensions
• Cosmologies inside hyperbolic black holes
• A Tale of Two Saddles
• Random Circuits in the Black Hole Interior
• On SYK traversable wormhole with imperfectly correlated disorders
• Euclidean-to-Lorentzian wormhole transition and gravitational symmetry breaking in the Sachdev-Ye-Kitaev model