As long as we’ve known black holes existed, there has been speculation (some of which reads like science fiction) about where you’d end up if you were able to get out of the other side of a black hole alive. Proxmia Centauri? The other side of the universe? Tatooine? Narnia?
Ending up in another realm that actually exists—sorry, Tatooine—might not be so far-fetched if black holes are actually wormholes to places humans could never hope to reach by spaceship, unless we could figure out a way to stay alive while traveling at the speed of light. They may be dead ends. They may lead to white holes, a cosmic blast from the past. They might even be portals to another universe (Narnia?).
Assuming you wouldn’t be shredded by the unimaginable gravity of a black hole and somehow make it to the other side, you might end up in a Farscape type of situation where you’re suddenly dropped into another galaxy or even universe. How could that be possible? Even Einstein had ideas about them swirling in his brain when he started to theorize bridges to other worlds with physicist Nathan Rosen. The problem is actually getting evidence for this. Not even light can escape a black hole’s gravity, so there can be no photographic evidence that someone actually made it to the other side.
If you do end up on a living ship with a menagerie of aliens you’ve never seen in your life, please find a way to beam a message to Earth and let us know.
White holes are another possibility. This was a theory first proposed by Russian cosmologist Igor Novikov, who believed that a black hole might be a gateway to a white hole that exists in the past and allows matter and light to leave, but not enter. So it’s essentially the opposite of a black hole. More recently, scientists have been, at least theoretically, chasing white holes. Instead of a black hole collapsing, information would come out the other way because of a quantum bounce. Even Stephen Hawking believed particles and radiation get away from black holes, though that means they eventually vaporize.
Maybe black holes are just dead ends in space. For all we know, and we don’t know much, they may lead to nowhere at all. The newer AMPS firewall theory is a hypothesis that uses quantum mechanics to turn the event horizon into a gargantuan firewall that instantly burns anything that dares to enter. Unfortunately, this twists Einstein’s theory of general relativity because anyone crossing over supposedly wouldn’t feel the intense gravity. Also, a firewall burning things up and leaving no trace means information, which can never be lost according to Einstein, now can be lost.
Where do you think you’d end up if you managed to see the other side of a black hole in one piece? After the possibilities of being torn apart by gravitational forces or just burning up in seconds, Narnia doesn't sound that bad.