  We reformulate recent insights into black hole information in a manner
emphasizing operationally-defined notions of entropy, Lorentz-signature
descriptions, and asymptotically flat spacetimes. With the help of replica
wormholes, we find that experiments of asymptotic observers are consistent with
black holes as unitary quantum systems, with density of states given by the
Bekenstein-Hawking formula. However, this comes at the cost of superselection
sectors associated with the state of baby universes. Spacetimes studied by
Polchinski and Strominger in 1994 provide a simple illustration of the
associated concepts and techniques, and we argue them to be a natural late-time
extrapolation of replica wormholes. The work aims to be self-contained and, in
particular, to be accessible to readers who have not yet mastered earlier
formulations of the ideas above.
