Universal String Theory

Background: Our universe exists entirely within a black hole in some "parent" universe, expanding infinitely within a finite space in that universe.

Implications:
- Objects (planets, megastructures, spaceships, people, etc) from the "parent" universe could fall into the black hole and appear in our own universe from out of nowhere.
- These trapped people/things could bring with them new technologies that could rapidly advance our own technologies and understanding of the universe (plot ships and the transition from "normal" to "scifi").
- Black holes in our universe could potentially also house other universes we could fall into... maybe.
- Escaping to the parent universe could also house other black holes with entire universes within them similar to our own... maybe.

Potential threats/plots:
- A ship from our parent universe falls into the black hole and needs our help to escape the black hole back to their own universe.
- Since our universe is infinitely expanding within a finite space (black hole), it will eventually become so massive it will implode... so to save the human race we need to escape the black hole (not just colonize other planets) as soon as we can.