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.
Highlights
Partition functions for the individual theories, so this partition function apparently does not carry information about the wormhole geometry
We investigate how these Euclidean wormhole spacetimes and their associated cosmological physics might be described within the context of AdS/CFT
In the simplest possible topological theory of gravity in two dimensions, the gravitational path integral with n circular boundaries has been shown to correspond to an ensemble average of partition functions as in (1.2) where the Hamiltonians are trivial H = 0 and the average is over the dimension of the Hilbert space [12]
Summary
We review the Black Hole Microstate Cosmology (BHMC) proposal of [19] for how to realize certain big bang/big crunch cosmologies within the context of AdS/CFT. We point out that this can be understood as a variant of the Maldacena-Maoz picture where a cosmological spacetime arises from the analytic continuation of a Euclidean wormhole. We explain how the field theory construction can be thought of as arising from coupling a pair of Euclidean holographic CFTs to some auxiliary degrees of freedom or alternatively as a type of ensemble average for the original theories
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