Baby Universes in String Theory

TL;DR

This paper explores the holographic description of four-dimensional BPS black holes in string theory, demonstrating that multi-center solutions and baby universes can be coherently incorporated without losing quantum coherence.

Contribution

It introduces a string theory model where multi-center black holes and baby universes are described holographically, showing their effects on quantum coherence.

Findings

Multi-center solutions are naturally included in the holographic description.

Non-perturbative effects entangle Fermi surfaces in the dual theory.

Baby universes do not cause loss of quantum coherence.

Abstract

We argue that the holographic description of four-dimensional BPS black holes naturally includes multi-center solutions. This suggests that the holographic dual to the gauge theory is not a single AdS_2 times S^2 but a coherent ensemble of them. We verify this in a particular class of examples, where the two-dimensional Yang-Mills theory gives a holographic description of the black holes obtained by branes wrapping Calabi-Yau cycles. Using the free fermionic formulation, we show that O(e^{-N}) non-perturbative effects entangle the two Fermi surfaces. In an Euclidean description, the wave-function of the multi-center black holes gets mapped to the Hartle-Hawking wave-function of baby universes. This provides a concrete realization, within string theory, of effects that can be interpreted as the creation of baby universes. We find that, at least in the case we study, the baby universes do not lead to a loss of quantum coherence, in accord with general arguments.