Toward a mathematically consistent theory of semiclassical gravity or, How to have your wormholes and factorize, too

Abstract: We review three well known inconsistencies in the standard mathematical formulation of semiclassical gravity: the factorization problem, the information problem, and the closed universe problem. Building upon recent work, we explore how modifying the holographic dictionary may provide the necessary freedom to resolve these three problems in a unified manner while maintaining more well established aspects of the standard correspondence. Using the modified holographic dictionary as a scaffolding, we propose a program for constructing an `extended' semiclassical gravitational path integral which (i) is manifestly factorizing, (ii) computes a von Neumann entropy which satisfies the Page curve, and (iii) incorporates new operators that create closed baby universe states. Our construction may be interpreted as imposing a semiclassical version of background independence/a no global symmetry condition, defining a modified large N limit, preparing an ensemble of dual theories, or enforcing observer rules using gravitational degrees of freedom.