X-Message-Number: 14560 From: "Cam Christie" <> Subject: SETI Date: Thu, 28 Sep 2000 21:25:45 +1200 This is a multi-part message in MIME format. ------=_NextPart_000_005C_01C02992.A9DD71C0 Content-Type: text/plain; charset="iso-8859-1" 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 line). (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 http://www.clickit.com/cgi-bin/corrsrch.pl?terms=christie http://home.clear.net.nz/pages/import/ " RISK IT !! " ------=_NextPart_000_005C_01C02992.A9DD71C0 Content-Type: text/html; [ AUTOMATICALLY SKIPPING HTML ENCODING! ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=14560