@Diamond_Tiara
I always liked write-ups of what they used to call the Kerr Metric space warp in old sci-fi magazines. It was mind-blowing to imagine it. Leaving aside the obvious difficulties of creating it, and leaving aside that this is an extreme oversimplification, it's a toroidal black hole rotating at relativistic speeds and therefore stable or at least metastable insofar as centrifugal force more or less suffices to keep gravity from forcing it to vanish up its own butthole and disappear while you watch. And at least some models suggest that the area in the center could be a stable wormhole, or a pathway to places even more exotic, like the past, or the future, or even alternate timelines.

How practical any of this is, I don't know. It is only speculative, for us, here and now. But when I was a kid it tickled my imagination. It still does. There are similar concepts. Go look up Van Stockum Dust and the Gödel metric.

Even weirder is the Tipler Machine. Consider an infinite amount of mass—not just all the mass in the universe, but an infinite amount of mass. Consider it compressed into a black hole that has electrical charge. Consider the charged black hole stretched out into what could be thought of as an infinitely long cylinder. Consider it rotating about its own long axis at relativistic speeds. This is the Tipler Machine, and according to Frank Tipler's equations, it might exhibit similar properties to the Kerr Metric Space Warp: approach it and it sends you to the future, or the past, or a different history altogether. I don't know how to build one, of course, but the concept fascinates me. They figure fairly prominently in a number of science fiction novels, as you probably already suspected.

If we take Penrose's theories in a Kerr's blackhole, we can eventually surf on its event horizon into alternate universe, it don't have really an inside, since it's a hole, there's nothing in the middle of a hole, it's a 3-D hole going to another place, a mirror universe. You better have enough horses in your spoaceship to kick yourself out of the event horizon.

Anything divided by zero is a number that tends to an infinity. zero is a concept, not a reality, that's how I prefer to say a number ( let's not write it ) that tends to an infinity. Division is not the inverse of a multiplication, it's about concepts.

I have no idea.

Mordehai Milgrom's theory for Modified Newtonian Dynamics will explain clearly why we don't need dark matter and why it's an absurdity in physics ti invent a thing we cannot find and can't fit in the standard model. I think the rest can be explained by space-time fluctuations.