A black hole universe possibilities?

There are various theories about our universe being inside a black hole which originated in a parent universe, which itself might be a black hole inside another universe. Some of the theories suggest that we're a 3+1 dimensional universe originated out of a black hole inside a 4+1 dimensional universe. While... show more There are various theories about our universe being inside a black hole which originated in a parent universe, which itself might be a black hole inside another universe. Some of the theories suggest that we're a 3+1 dimensional universe originated out of a black hole inside a 4+1 dimensional universe. While others suggest that the parent itself is also a 3+1 dimensional universe. What are the reasons for each theory?
Update: An example of a black hole universe theory from Loop Quantum Gravity:
https://physics.aps.org/articles/v11/127
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