Comments on wormholes, ensembles, and cosmology

TL;DR

This paper explores how certain closed-universe cosmological models derived from Euclidean wormholes can be described within the AdS/CFT framework, proposing a holographic model that couples dual CFTs with auxiliary degrees of freedom to encode cosmology.

Contribution

It demonstrates a specific holographic model for cosmology based on Euclidean wormholes and suggests features for more general models within the AdS/CFT correspondence.

Findings

Euclidean wormholes relate to closed-universe cosmologies via analytic continuation.

A holographic model couples two CFTs with auxiliary degrees of freedom to encode cosmology.

The Lorentzian spacetime is represented by a wavefunction in the auxiliary Hilbert space.

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.