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Misleading Statements about Optical SETIRadobs 01The literature on SETI is generally misleading in its rare references to the optical approach. Here are a few examples which will help to explain the difficulty I face when confronting the establishment view. In Isaac Asimov's 1979 book on "Extra-Terrestrial Intelligence - The First Encounter" (page 263) he says: "WITH LASER LIGHT WE COME CLOSER TO A PRACTICAL SIGNALLING DEVICE THAN ANYTHING YET MENTIONED, BUT EVEN A LASER SIGNAL ORIGINATING FROM A SOME PLANET WOULD, AT GREAT DISTANCE, BE DROWNED OUT BY THE GENERAL LIGHT OF THE STAR THE PLANET CIRCLES". He goes on to say "ONE POSSIBILITY THAT HAS BEEN SUGGESTED IS THIS--. THE SPECTRA OF SUNTYPE STARS HAVE NUMEROUS DARK LINES REPRESENTING MISSING PHOTONS--PHOTONS THAT HAVE BEEN PREFERENTIALLY ABSORBED BY SPECIFIC ATOMS IN THE STARS' ATMOSPHERES. SUPPOSE A PLANETARY CIVILIZATION SENDS OUT A STRONG LASER BEAM AT THE PRECISE ENERGY LEVEL OF ONE OF THE PROMINENT DARK LINES OF THE STAR'S SPECTRUM. THAT WOULD BRIGHTEN THAT DARK LINE . . .". Asimov also went on to imply that a laser system was complicated and that no civilization would be expected to use the harder method if a simpler (microwave) method is available. I have shown that not only can large space-based telescopes and probably ground based adaptive telescopes separate the laser light from the light of nearby stars, i.e., those nearer than a few hundred light years, but that working inside a so-called Fraunhofer dark line only produces a modest, about 10 dB, increase in signal-to-noise ratio. For a advanced technical civilization (ATC), a laser transmitting telescope is only SLIGHTLY more difficult to construct than a microwave transmitting dish, though Asimov appears to think otherwise. A book by Edward Ashpole on "The Search For Extra-terrestrial Intelligence", published in the U.K. in 1989, and which contains a forward by our own Bob Dixon: On page 79 and 80 are several paragraphs devoted to "Signalling By Lasers". At the top of page 80 is the following paragraph which I quote in full: "THE IDEA THAT ETIs MAY HAVE BEEN TRYING TO CONTACT US WITH POWERFUL LASERS HAS BEEN CRITICIZED BY SOME SCIENTISTS WHO POINT OUT THAT LASER BEAMS, UNLIKE RADIO BEAMS, ARE VISIBLE. WE MIGHT THEREFORE HAVE EXPECTED OUR ANCESTORS IN HISTORICAL TIMES (WHO WERE A GOOD DEAL MORE AWARE OF THE NIGHT SKY THAN WE ARE) TO HAVE NOTICED BEAMS IN THE SKY. YET THERE ARE APPARENTLY NO RECORDS OF ANY SUCH OBSERVATIONS." This statement, like so many others I have seen is rubbish! Didn't anyone sit down to do some calculations to determine relative intensities in sensible bandwidths? As I have shown, a hugely powerful 1 GW alien transmitter that could send "real-time" NTSC/PAL video of 10 light years, is only about 0.6% as bright as the aliens' star. The mistake in the above statement is, as always, to assume signal detection with bandwidths equivalent to that of the human eye. From the beginning of my analysis I have made it clear that we shouldn't expect to see extremely powerful flashes of light - for what is very dim to our eyes represents a very strong signal in conventional electronic communication bandwidths. A recent paper by Dr. Jill Tarter: Five lines from the top of page 192 she mentions the optical approach and dismisses it in two sentences. It is not true for a beamed signal that "ANY OPTICAL COMMUNICATION SIGNAL COMING FROM A PLANET CIRCLING A DISTANT STAR WOULD HAVE TO OUTSHINE THE STAR ITSELF IN ORDER FOR US TO DETECT IT". I suppose the problem is that some scientists have ventured an opinion without having checked the numbers, and these statements have been taken up by non-technical authors who don't have the wherewithal to check the reasoning. I have never come across a branch of science (SETI) before which has been so burdened by so many "mistaken" conceptions. I would hope that in future if you see such statements in books (papers or proposals) that you flag such statements as gross errors. I would like to hear about other citations with similar mistaken statements. Composition Date: December 11, 1990 Revision Date: June 1, 1992 File: RADOBS.01 BBOARD No. 261 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Dr. Stuart A. Kingsley, CEng, * * Consultant, * * MIEE, SMIEEE, * * The Planetary Society, * * Space Studies Institute, * * Columbus Astronomical Society, * * Volunteer, SETI Group, Ohio State. * * * * "Where No Photon Has Gone Before & * * The Impossible Takes A Little Longer" * * __________ * * FIBERDYNE OPTOELECTRONICS / \ * * 545 Northview Drive --- hf >> kT --- * * Columbus, Ohio 43209 \__________/ * * United States * * Tel/Fax: (614) 258-7402 .. .. .. .. .. * * Manual Fax Tone Access Code: 33 . . . . . . . . . . * * Bulletin Board System (BBS): .. .. .. .. * * Modem: (614) 258-1710, * * 300/1200/2400/4800/9600 Baud, MNP, 8N1. * * Email: skingsle@magnus.acs.ohio-state.edu * * CompuServe: 72376,3545 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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