It seems like most sci-fi hasn't really touched much upon dark matter. Instead of making up all sorts of fantastical new dimensions or universes, why not focus on dark matter, something we legitimately don't understand and really exists? There's far more dark matter than baryonic matter. Is it possible that dark matter interacts with dark matter, and can form complex structures, maybe even worlds of dark matter? And maybe even creatures on those worlds, who live in a completely alien environment, which we can't see but they can. And they likewise cannot see us, except through gravity. They would experience almost totally different laws of physics, but, actually be part of our same universe.