Every black hole has a singularity. But the singularity is covered by a thing called 'Event horizon'or ' Schwarzchild Radius'. Our universe is originated from a naked singularity. By naked singularity, I mean that the singularity wasn't covered by the event horizon. Is it possible that a black hole has a universe in itself?
I, and I’m sure many many others, have thought about this ever since knowing about black holes.
Both in popular media and in more scientific articles, there’s plenty of viewpoints/interpretations along these lines
Personally, I think if black holes can somehow be married with the ideas of quantum gravity/information one day, then recursive black holes (since the ‘universes’ inside them might also contain them) might prove to be impossible and that would somewhat contradict the recursive universe theories.
I also dread the day someone had to define exactly what a universe “U” would mean, from a definition point of view..