Re: Countertime beings

Hal Finney (
Wed, 12 Mar 1997 22:01:09 -0800

I think the generally accepted explanation for time asymmetry goes to
boundary conditions at the beginning and end of the universe. For some
reason the early universe had very low entropy, so if you look at it as
a four dimensional object you see a gradient of increasing entropy in the
time direction away from the origin. This is what we perceive as the
arrow of time. (I don't know if there is a good theory for why this
asymmetry in the buondary conditions exists.)

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.