Re: [asa] Contact with Alien Civilizations

I recall reading about an even simpler test, a narrow signal not
associated with an atomic or molecular source. This excludes H II with
Doppler shift, for example. The reasoning was that most other
nonintelligent sources were gaussian. This took out the "little green
men" signal of pulsars, precisely timed but with a frequency spread.
Dave

On Mon, 18 Jun 2007 22:49:17 +0100 "Iain Strachan"
<igd.strachan@gmail.com> writes:

On 6/18/07, David Campbell <pleuronaia@gmail.com> wrote:
> The Carl Sagan (first contact) idea (often cited by Dembski) is a
sequence
> of prime numbers. That's not THAT intelligent, of course, but it would
be
> world headline news if such a signal were received from outer space.

This also illustrates a major difficulty of SETI. Most of our signals
are too complex for easy detection of pattern.

I don't think that's necessarily true. Non-noise exhibits a complex
probability distribution, where as true noise exhibits a simple
probability distribution. There is a well-known statistical technique
called Independent Components Analysis that can separate out
statistically independent components from a mixture of signals, by
looking at deviations from Gaussian noise (non-Gaussianity). This
technique is very good at "Blind source separation", for example
separating out the individual speakers from the mixture of voices at a
coctail party (aka "The Cocktail Party Problem"). One might envisage
techniques such as this to separate out independent channels from, for
example a mixture of radio signals.
 

Unless they are
deliberately sending a simple message so as to be readily detected,
it's unlikely to be detectable as non-noise.

This is the general idea - a deliberate "hello" to anyone out there.

I think the Sagan thesis goes along the following lines. Any alien
civilisation advanced enough to make radios must have discovered
mathematics. And they would reason that any civilisation advanced enough
to receive radio signals must also have discovered mathematics. So if
you want to communicate your presence, you would use the "universal
language" of mathematics.

Human scientists adopted this line of thought in the "Arecebo signal"
sent towards the globular cluster M13 in 1974.
http://en.wikipedia.org/wiki/Arecibo_message . The "image" consisted of
1679 pulses. This was chosen because 1679 is the product of two primes
(23x73) and so there would be only two ways of arranging the pulse
sequence into a 2-D image. The image depicted the first ten numbers, the
atomic numbers of the elements that make up DNA, a depiction of a
stick-like person, and various other astronomical images (all in a 23x73
pixel image!)

 Iain

(Of course, probably the
vast majority of electronic signaling on earth shows little sign of
intelligence even when processed with knowledge of the transmission
method). It's far from evident that an intelligent designer of the
sort envisioned by ID should be expected to encode something
analytically similar to a sequence of primes in DNA.

--
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.
-- 
-----------
After the game, the King and the pawn go back in the same box. 
- Italian Proverb
----------- 
To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.