X-Message-Number: 14560
From: "Cam Christie" <>
Subject: SETI
Date: Thu, 28 Sep 2000 21:25:45 +1200

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this appears to be a rehash on the extropian list from some yrs ago. However it 
may warrant some review:Posted to North West extropians list

"Is it possible that SETI are pursuing their research in the wrong direction

<<I believe that is would be useful to look for modulation in light wavelengths,
but that that too will be unproductive for some decades yet.

The problem is that an efficient (=advanced tech) transmission would use most of
the available bandwidth, and there would be little discernable

pattern to the signal even if you could decode such incredible bandwidth, again 
assuming an efficient modulation scheme.  This also assumes that

ET doesn't care about being found or would rather that we didn't snoop in on 
their conversation.  I'm speaking of the modulation bandwidth, not

the carrier frequency.  For visible light, the modulation bandwidth would be on 
the order of 1*10^15 symbols/second, or a petabit per second

using only one bit per symbol time (equivalent to 4800 baud on an analog phone 

(300,000,000M/S / 500nM = 600,000,000,000,000 Hz, *2 symbols per cycle).   To 
deal with signal propagation problems, I (a primitive

human bean) would use a direct sequence spread-spectrum modulation, and the 
useful bit rate in such a transmission would be perhaps a mere

terabit per second.  And the signal would look like noise unless you knew the 
spreading code.  Detecting such a signal is about five orders of

magnitude beyond our fastest digital receivers from a modulation bandwidth point
of view.  Looking backwards, our receivers have improved that
much in about 40 years, so I guess we have another 40 years to go.

Looks like we can't join the galactic club yet, if it exists.  Gotta grow up 
first.  I wrote about this subject on the EXI list several years ago.  It annoys
many SETI fans.

-PW(Phillip Whitman)

Cam Christie
New Zealand
" RISK  IT !! "


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