Our Universe was born and lives in a black hole
One question is whether there is a singularity at the "bottom" of a black hole.
It seems to me that the gravitational collapse at the singularity of a black hole would match the "trigger event" of the creation of our Universe.
Within the (our) black hole there would be a singularity event which appears to us as the "creation of our Universe". Within such a black hole several effects likely occur.
One is the "hologram" idea (https://www.scientificamerican.com/article/is-our-universe-a-hologram-physicists-debate-famous-idea-on-its-25th-anniversary1/) which posits that our universe’s 4D spacetime could be a holographic projection of a lower-dimensional reality. This would fit nicely if the "surface" of the hologram was the "surface" of the inside of our black hole.
Another question arises as to whether the Universe is "infinite" and "what is it expanding into". Time and space would be extended toward the boundary of our black hole and would appear "infinite" but give something to "expand into" as both space and time would be changed when approaching the interior boundary of the hole. The boundary would appear to be "infinitely far away".
There could likely be other "universes" within other black holes both within our current black hole and/or within black holes "outside of our universe".
The "curvature of space-time" and the phenomena of "gravity" can be due to the "shape of the hole" from the inside.
The "cosmic background radiation" could be due to Hawking radiation at the boundary where we see the particles that did not escape yet never able to see the corresponding particle that "boils off outside" our black hole.
I refer to the idea of the Universe existing in "our black hole" as the Calcutta theory.
Tim Daly