Helping observers in closed universes reach their full potential

Abstract: Recent work by Engelhardt, Gesteau, and Harlow applies proposals for incorporating observers into holographic maps to study the Antonini-Rath puzzle for closed universes. In a new form of ``observer complementarity,'' they find that an AdS bulk observer measures a SWAP test to determine that there is no closed universe in the bulk, contrary to the (limited) description given by an observer inside the closed universe. In this work, we improve the predictions of both observers by using the holographic maps to define new operators to perform this same SWAP test. With these, we show that the AdS observer cannot rule out a baby universe in the bulk, and the closed universe observer can improve the accuracy of their description.