You could imagine a situation where some parts of the universe had low
entropy at one end, and other parts had low entropy at the other end.
Then for this to lead to a consistent solution, the existence of what
we would perceive as causality paradoxes must be prevented somehow; only
universes in which such paradoxes never happen to occur would be legal
solutions to the equations with those boundary conditions.
These kinds of considerations are often invoked to explain what would happen
in other causality-challenging situations, like the closed timelike lines
which appear in some exotic systems of GR. You simply postulate that only
the universes in which the local laws of physics are observed can exist.
However this ends up looking like the Hand of God reaching down to stop you
from doing things which would produce a paradox.
I remember a comic book I read once where Superboy tried to go back
into time and prevent the assassination of Abraham Lincoln. Oops, he
ran into some red Kryptonite which paralyzed him for just long enough
to prevent him from changing history. This kind of thing would be
happening constantly if time travel were possible or if you had the
kind of bi-directional entropy gradients described above. The harder
you try to outwit the universe, the harder it would fight back. It seems
like a pretty implausible way for things to be.
Hal