This piece in New Scientist is about how every black hole may hold a hidden universe. General relativity equations plus Roger Penrose's idea of twistors (that warp space time under certain conditions) will get you there. The point being—we may be inside a black hole. This would be like the possibility that we are objects in a dream. (See my previous.)
The thing is, you can't peer inside them. “As you approach a black hole, the increasing gravitational field makes time tick slower and slower. So, for an external observer, any new universe inside would form only after an infinite amount of time had elapsed...” The black hole, in other words, is operationally closed.
Graham describes objects as black holes: so dense that no information can escape from them...
(Which by the way, is how I like to think of poems by Keats, who inaugurates what I and others call the objectivist mode of avant garde poetics...Keats's whole strategy is to create poetic black holes that are just so intensely pleasurable that they stick to you and you melt off them.