Perhaps "Navier-Stokes" and "complexity" and such are (ironically) overcomplicating things. Let's try to simplify:

I just walked out of a room with blue walls.

Is there a mathematically consistent universe in which, when I walk back in, the walls will have spontaneously turned red? Yellow? Plaid? (hint: for a universe with a set of physical rules S, is there anything mathematically inconsistent about the set "S union that-room-spontaneously-turns-red-in-2-minutes"?)

If all mathematically consistent universes exist and there is no special probability distribution preferring some over others, what subjective probability should I assign to the expectation that I will see the same shade of blue walls?

In the real world, what subjective probability should I assign?

If the previous two answers are different (for example, if the first probability is epsilon and the second is one minus epsilon...), why is that so?