Top Down Approach to Ensemble Averaging

<!--HTML--><p>Ensemble averaging in quantum field theory is a well-defined procedure which is also of much recent interest in the context of the AdS/CFT correspondence. In this talk we present a stringy realization of quantum field theory ensembles in D ≤ 4 spacetime dimensions. This provides a UV completion of a recent proposal of Marolf and Maxfield that there is a high-dimensional Hilbert space for baby universes, but one that is compatible with the proposed Swampland constraints of McNamara and Vafa. We identify two ways in which our construction breaks down, one of which is sensitive to short distance effects, and one which is an entropic effect for objects with a large number of microstates. The construction thus provides an explicit set of counterexamples to the claim that holography can be fully decoupled from top down considerations.</p>