>Now more to the point, I think Carl Sagan, Jill Tartar and the other ET
> hunters probably believe that they would recognize an 'intelligent' signal
>when they saw it, because they themselves have devised such signals with the
>intention of communicating to others. They make them simple, but not
>repetitive, with patterns that might correspond to something universal, such
>as the hydrogen atom Balmer series, etc. Others have suggested using
>sequences of prime numbers.
>There is a long history of literature on this question, which arose long
> before there was any technical means like SETI. Similar problems arise in
> cryptography theory, I imagine.
>
Actually, as I have thought about this problem today, what we may have in the
case of SETI is an example of Goedel's theorem. If we detect a signal from
Betelgeuse which has exactly the format to play on my TV, and I can see little
green men on the screen, then I know there is a signal. But within the
mathematical realm, I can not prove that there is a signal. This is what
Goedel's theorem is all about. There are true statements which can not be
proven true.
But in the case of DNA, information theory has shown that we can never decide
whether it was random chance or a Designer who created the DNA in living
systems. To me that is a significant point.
glenn