"Life in the Universe: Is Life Digital or Analog?"
About twenty years ago I published
in the Reviews of Modern Physics a
paper with the title ``Time Without End'', containing
a lot of unbridled
speculation about the remote future. I argued
that it might be possible
for life to survive for ever, adapting itself to changing
circumstances,
in a cold expanding universe. This year Lawrence
Krauss and Glenn
Starkman at Case Western Reserve University have written
a paper with the
title ``Life, the Universe, and Nothing'', sharply contradicting
my
conclusions. I was delighted when they sent
me their paper. It is much
better to be contradicted than to be ignored.
For the last six months
we have been engaged in a friendly battle, trying to
prove each other
wrong. So far, neither side is willing to
concede. I believe that the
disagreement arises from the fact that we have different
concepts of the
nature of life. We both define life as a
material system that can
acquire, store, process, and use information to organize
its activities.
We differ in our view of the information that life must
process. I
consider life to be analog; Krauss and Starkman consider
life to be
digital. It is remarkable that this difference
causes a big difference
in the possibility of survival. Analog computers
are in principle more
powerful than digital computers, and analog life can
survive conditions
that would be lethal to digital life.