The idea that the universe is "inside" a black hole in another universe is a pretty old idea, but there have been several papers on it in recent years, such as

The idea that the universe is "inside" a black hole in another universe is a pretty old idea, but there have been several papers on it in recent years, such as this one [1], explained here [2], which offers a holographic origin. [1] https://arxiv.org/abs/1309.1487 https://arxiv.org/abs/1309.1487 [2] https://www.perimeterinstitute.ca/news/black-hole-birth-universe https://www.perimeterinstitute.ca/news/black-hole-birth-univ...