Lets assume that the Multiverse Theory is true.
Now lets talk about a Kardashev Type III Civilization living in one of these parallel universes. For the sake of the argument, lets assume that this parallel universe is identical to ours in very nearly every way.
This civilization is incredibly advanced and determines through science far beyond our understanding that their universe is approaching its heat death. They determine their universe will end in a finite, but still far away, period of time; let's call it fifty thousand years.
This civilization, having existed for many millions of years, wants to save itself from dying with their universe. With nowhere in their time-space continuum to escape to, they decide to look out to the multiverse to find a new, younger, universe to populate. Obviously they can't take their entire civilization with them, so they decide to build an ark. For the sake of the question, lets say the ark is planetoid-sized (whether natural or artificial is unimportant) and is designed to carry a living biodiverse ecosystem with a sentient population of around one hundred million.
This is where something goes wrong. A catastrophe of some kind happens and the ark is forced to launch ahead of schedule. The physical resources are all loaded, the "passengers" are on board, and the ark is physically finished, but a destination universe has not been identified yet. So rather than moving to a new universe, the ark is shifted to the space between universes in a self-contained pocket universe. It is now up to the "crew" of the ark to identify, from within the interdimensional space, a suitable universe to move the ark into.
Now to the actual question:
How different can different parallel universes be? Or, to phrase it another way, what parts of the universe are inherent to it (as we understand it of course)? I'm looking for horrifying universes for the ark to discover; universes that might drive the observer insane or universes that might cause the ark to be violently destroyed if it were shifted into it.
- Could there be a universe where the basic laws of motion don't apply?
- Could a universe have an inversed ratio (from ours) of matter to dark matter?
- Could a universe exist where gravity repels instead of attracts?
Assuming that all universes have time, and all universes have space, and all universes started with a Big Bang, how horrifying can I make them while still holding to a semi-realistic physics system?
I know our understanding of Multiverse Theory is limited at best (and it is just a theory), so this is asked within the context of our current understanding of the universe, and a very large expectation of creative license.