Many other massive black holes might contain their own complete universe too.
We might be silly to think that the bottom of a black hole is an actual point of infinite density.
In fact, we could immediately see that our universe is just one of many inside massive black holes if we were not already inside our own black hole!
There’s an angle in the spin or momentum of all elementary particles. This angular spin of matter is a torsion in the geometry of space-time. Inside a black hole, this spinning torsion prevents matter from compressing to infinite density.
Because of spin, the bottom of a black hole is not straight-to-a-pinpoint compression, not the ‘time-arrow’ that shrinks to what we call singularity. Instead, space-time inside a black hole must instantly start rebounding, expanding into another universe. Ours is one of those.
To explain why particles in our universe show up with a ‘preferred direction’ in their spin. a spinning black hole would have imparted some spin to the space-time inside it. That immense ‘torsion’ will propel an expanding new universe inside the black hole.