Ordinary wormholes

Abstract

Euclidean wormholes have played a key role in the recent ``disorder averaged" approaches to quantum gravity and holography, but are typically only considered in somewhat special theories of gravity, such as theories in low dimensions or theories with exotic matter content (such as axions). These exotic theories have advantage that both the matter and gravitational sectors can be treated completely classically. However, once this constraint is relaxed we find that Euclidean wormholes arise generically, with no special constraints on the matter content. The key point is that there is a self-consistent approximation where the metric is treated classically but matter is treated quantum mechanically. The resulting wormholes are {\it ordinary} in the sense that they rely on the usual approximations used in, for example, the construction of star or FRW solutions in general relativity. Indeed, these are the Euclidean continuations of ordinary FRW solutions with big bang/crunch singularities. We describe several examples of these ordinary wormholes and discuss the relation to existing constructions and the holographic interpretation in terms of a dual CFT.