Baby universe as logical qubits: information recovery in random encoding

TL;DR

This paper explores how baby universes in AdS/CFT can carry large entropy and act as logical qubits, with information encoded in a way that prevents individual observers from accessing the full state, revealing an emergent complementarity.

Contribution

It proposes that baby universes function as logical degrees of freedom with large entropy, arising from pseudorandom dynamics, and explains how this leads to emergent complementarity and observer-dependent microstates.

Findings

Baby universes can carry large entropy as logical qubits.

No single boundary observer can access the entire baby-universe state.

Emergent complementarity prevents cloning and information paradoxes.

Abstract

We revisit whether a semiclassical closed baby universe in AdS/CFT necessarily possess a trivial one-dimensional Hilbert space or may instead carry a large entropy. Recent results on Haar random encoding suggest a breakdown of complementary recovery, in which no logical operators can be reconstructed from individual bipartite subsystems. Motivated by this, we propose an interpretation where a baby universe emerges as logical degrees of freedom that cannot be accessed from either boundary alone, assuming pseudorandom dynamics in holographic CFT correlators. We then analyze two conceptual puzzles: an apparent cloning of baby-universe microstates and its eventual fate at the singularity. Both puzzles are avoided because no single boundary observer can access the baby-universe degrees of freedom, be it classical or quantum, reflecting an emergent form of complementarity due to the structure of random encoding. In this interpretation, observers arise naturally: the same heavy operator that prepares the baby-universe geometry also serves as observer-like degrees of freedom that define an observer-dependent baby-universe microstate.