On tests for baby universes in AdS/CFT

TL;DR

This paper develops a new holographic map for bulk states with baby universes in AdS/CFT, demonstrating that the swap test cannot distinguish between different bulk duals and supporting the semiclassical validity of baby universes.

Contribution

It introduces a novel holographic map that accommodates baby universes, resolving previous ambiguities in tests for their existence in AdS/CFT.

Findings

The swap test cannot differentiate between the two candidate bulk duals.

A new holographic map supports the semiclassical description of baby universes.

The approach enables inclusion of observers in holographic mappings.

Abstract

To address a puzzle by Antonini and Rath -- where a single CFT state has two bulk duals, one with a baby universe and one without -- Engelhardt and Gesteau recently devised a test for baby universes in AdS/CFT. Using the extrapolate dictionary, they showed that the boundary dual of a bulk swap test favored bulk spacetimes without a baby universe, providing evidence against their semiclassical validity. However, recent work suggests that holographic maps should post-select on such closed universes, and we argue that this is consistent with the extrapolate dictionary. We therefore construct a new holographic map for bulk states with baby universes and use this to show that the swap test cannot distinguish between Antonini and Rath's two candidate bulk duals. This not only allows for a valid semiclassical description of the baby universe, but also enables the application of recent techniques for including observers in holographic maps.