Can a black hole be a portal to another dimension?
Depends what you mean by "another dimension". The question does not mean anything as you have answered it.
The TLDR answer is "no".
Perhaps you are thinking of a wormhole?
TLDR: wormholes, if they can exist, would have a black-hole on one side, but not all black holes are entrances to a wormhole.
... for what's likely "inside" a regular black hole.
I've seen some stuff in cartoons and other sci-fi films where there are possibilities of the existence of somebody just like me in another part of the universe. Like, if I'm X, then somewhere else another person called X' exists. Can a black hole act as a portal to this 'another world' where a 'similar yet separate entity' exists?
Excuse me if it seems a little far-fetched but I'm young, and new to this. So I'm inquisitive :-D
We discuss mainstream science here at the PF, not cartoon fantasies.
Sorry. I'll keep that in mind.
No worries. Simon's links are a good place to start learning about black holes and wormholes.
Short answer is "no".
I'll concentrate on the science part.
The proposal has two parts.
1. you have a doppelganger someplace else in this Universe
2. you can meet you doppelganger via a black-hole
For 1. there are very famous calculations concerning the uniqueness of life on Earth and the individual human being. There may well be an Earth-like planet someplace else, and parallel evolution may well produce erect bipedal life forms capable of exploring the Universe in a manner recognizable to us. But the vast possibilities of morphology mean that you won't get a duplicate right down to the circumstances that go to make a particular individual.
For 2. See the links I gave you as to why this is a "no".
Since both parts are, separately, so unlikely as to call for zero odds over the entire lifetime of the Universe - the combination pretty much defines "impossible" - no way no how nosirree never.... etc.
I wanted to show you that to illustrate scientific thinking.
Artistic thinking OTOH is what cartoons are made of.
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