According to one physical hypothesis, our voluminous world might be a projection from a flat surface. From such a Universe, tiny closed bubbles — baby universes — sometimes pinch off. For a long time, they were thought to be empty, devoid of internal diversity.
It turned out that the information inside them is scattered, like shards of a broken mirror. Each external observer sees only the reflection in their own shard — which means the degree of disorder is high, and the full picture is inaccessible to anyone. This explains why no one can peer into a black hole or grasp what's going on in curved spacetime during collapse.
This approach resolves old paradoxes like the disappearance of information. Hawking was the first to ponder these baby universes, while Maldacena and Susskind built a holographic model.
as written by the authors arXiv:2511.20747
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.
The idea of tiny universes first emerged in Stephen Hawking's work, but was long considered mathematical exotica.
In science fiction, similar ideas play out in the movie 'Interstellar,' where other dimensions opened up behind a bookshelf.