Baby Universes and Black Hole Information

In the 1980’s, work by Coleman and by Giddings and Strominger linked the physics of space- time wormholes to ’baby universes’ and an ensemble of theories. We revisit such ideas, using features associated with a negative cosmological constant and asymptotically AdS boundaries to strengthen the results, introduce a change in perspective, and connect with recent replica wormhole discussions of the Page curve. A key new feature is an emphasis on the role of null states. We explore this structure in detail in simple topological models of the bulk that allow us to compute the full spectrum of associated boundary theories. We also argue that similar properties must hold in any consistent gravitational path integral.