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EJASA - Part 9


                                                                     Page 56

                                  DISCUSSION

        The thirty-year-old rationale which would have us believe that the
    low frequency end of the microwave regime is the place to search for
    ETI signals is seriously suspect.  If the underlying assumption of
    present-day SETI lore that the best ETIs could do would be to send us
    very weak low bandwidth signals is swept away, then almost all the
    so-called problems that are usually advanced to dismiss the optical
    approach become insignificant.  This is even more so if the use of
    optical heterodyne reception is assumed.  The increased immunity of
    such systems to background noise means that the signal detectability
    constraints set by Planckian starlight are essentially removed.  In
    addition, with dechirping of the local-oscillator to remove local
    Doppler drift along the line-of-sight, problems from local Doppler
    drift are eliminated.

        Because of the very narrow field-of-view of a photodetector array,
    Doppler drift compensation can be made simultaneously to all pixels in
    the array to a very high degree.  The larger bandwidths mean that the
    effects of finite laser linewidths, Doppler shift and residual drift
    are minimized, and the number of frequencies to search in the entire
    optical spectrum is in reality no more than in the microwave spectrum.

        Up to now, the SETI community has taken some comfort in the fact
    that the obvious explanation as to why we have not detected ETI signals
    is simply that they are too weak and that we need sophisticated
    hardware and signal processing algorithms to extract this information.
    An even simpler explanation for the lack of success so far is that
    there are strong signals but they are elsewhere in the electromagnetic
    spectrum.  Of course, Tipler [39] has an even more simpler explanation.

        It is the author's prediction that in years to come, it will be
    hard to understand how anyone in the late Twentieth Century, e.g.,
    people like Frank Tipler, could think it possible that humanity was all
    alone - that Earth is atypical in that we are the "first civilization".
    If anything, it is far more likely that the answer to "Where are they?"
    is that we live in a "Cosmic Zoo".  Tipler believes that ETI tech-
    nologies only slightly superior to our own, if they exist, would have
    produced self-replicating von Neumann machines (probes) that would have
    rapidly populated the galaxy.  Therefore, since we have not detected
    these machines or they have not contacted us, ETIs do not exist.

        The "Cosmic Zoo" rationale is probably the only viable alternative
    explanation as to why ETIs do not appear to have colonized the entire
    galaxy.  We could just as easily be a typical or atypical civilization,
    developing in a sector of the galaxy that is off limits for physical
    contact, i.e, the Prime Directive so much loved by STAR TREK fans.  As
    was stated in the Preface, if the author has any doubts about the
    efficacy of the Optical SETI, it surely has to do with the Kingsley
    Paradox of "why communicate when one can just as easily travel?".
    Nevertheless, the author is sufficiently convinced about the
    plausibility of this Optical SETI rationale to believe it worthwhile to
    construct his own Optical SETI Observatory and mount his own search.
    He intends to start this project as soon as possible.


                                                                     Page 57

        The author has taken some pains to try and understand why he
    believes Tipler is wrong.  The author finds it very difficult to accept
    that only once in the ten billion year history of our galaxy has
    intelligent life arisen.  Secondly, since the dawn of the Space Age,
    i.e., since about 1957, he has thought that life was common throughout
    the galaxy, and as a STAR TREK and science fiction fan, he has believed
    that the future for mankind was in space.  Thus, the idea that there
    would be no one to meet out there is an anathema.

        It is the author's intuitive feeling, that soon we will learn that
    life appears relatively rapidly, given the right environmental
    conditions.  Life, rather than being the exception to the rule, is
    the inevitable consequence of the mixture of certain elements,
    temperatures, cosmic catastrophes, and time.  In the roughly fifteen
    billion year existence of the Universe, there will have been no
    shortage of the latter.  At the moment, we still have a very sketchy
    picture of how life arose on this planet - that possibly, lines of
    evolution were erased and new lines initiated several times during
    Earth's history, due to bombardment by meteors, planetoids and comets.

        If ETIs are operating in the visible spectrum we should not expect
    to see flashing lights in the sky, for the power required to do this
    and outshine their stars is much greater than required to establish a
    decent communications channel.  Free space optical communications will
    be a mature technology for any spacefaring civilization.  It seems
    reasonable to assume that they will spinoff this technology for SETI
    transmitters should they wish to contact emerging technical
    civilizations.  The fact that optical magic frequencies are hard to
    identify at this time, save for 10,600 nm, is not an argument that such
    frequencies do not exist.
 
        Perhaps the only reasons for ETIs to build very large microwave
    arrays would be to eavesdrop on radio frequency leakage from primitive
    technical civilizations (like us), to beam microwave power, for astro-
    physical research, or to communicate with other galaxies.  Even this
    author has some problems in believing that the civilizations of
    extraterrestrials would be so altruistic and long-lived to attempt
    electromagnetic communications across the intergalactic voids.  The
    interstellar eavesdropping scenario is also problematic, as it is
    likely that a developing technical civilization only produces
    substantial radio frequency leakage for a short period in its history.
    In time, other technologies like fiber optics will replace high-power
    radio and TV transmitters, and military radar systems will be
    decommissioned.  For this reason, if we attempt eavesdropping with large
    radio frequency antennas ourselves, failure to detect such signals may
    not imply very much about the existence or lack thereof of ETIs.  Thus,
    if the MOP does not detect ETI in the next decade, we should not jump
    to the conclusion that we are alone in the Milky Way galaxy.

        On the other hand, some civilizations may be continually threatened
    by cosmic catastrophes in the form of bombardment by planetoids.  These
    races may have instigated powerful radar early warning systems for
    planetary defense purposes.  These comments are good examples of how
    difficult it is to predict the future.  Even Arthur C. Clarke and


                                                                     Page 58

    Stanley Kubrick appear to have been caught out by Pan Am going bankrupt
    before it had a chance to ply the heavens between Earth and the Moon
    (2001: A SPACE ODYSSEY, to the strains of the "Blue Danube"), or that
    there would be no Soviet Union in 1992, let alone in 2001 or 2010!  We
    can only hope (and pray) that there will be a dynamic American Space
    Program in 2001.  We should not be too hard on Arthur Clarke, for
    without his idea concerning "Extra-Terrestrial Relays" (Page 41), when
    the word "Extraterrestrial" meant something completely different, the
    Soviet Union might still be in existence.  One notes in passing, that
    the spaceship DISCOVERY, which was central to Arthur Clarke's 2001 and
    its sequel 2010, used microwave dishes for its communication's link with
    Earth. [94-96]  Surely, the main (high-gain) link should have been a
    laser-based system, notwithstanding the bright Earth background, and the
    high solar background that might on occasion be viewed by the DISCOVERY
    looking back towards Earth!  A heterodyning telescope of several meters
    diameter on the DISCOVERY, and a similar system on or near Earth, could
    easily sustain a 1-10 Gbit/s data rate out to Jupiter and beyond.

        We cannot even be sure that ETIs would want their signals to be
    detected within an atmosphere or otherwise too easily.  These are
    prevalent assumptions among most SETI proponents.  There might be
    logical reasons for ETIs to think that only when a technical
    civilization begins to "emerge" from its planet would it be truly
    mature enough, and in a culturally receptive frame of mind, to receive
    signals from ETIs.  Thus, the recipients' atmosphere itself might be
    used as an automatic protective blanket to avoid cultural shock.  In a
    way, the electromagnetic search for ETI is one of the greatest hunts
    and detective stories ever.  Unfortunately, there are still so few
    clues.


                                  CONCLUSIONS

        The author feels that it is still an open question as to what are
    the optimum electromagnetic frequencies for interstellar communi-
    cations.  As he concluded in his talk last year to the SETI Institute:
    "The jury is still out as to whether ETIs are signalling with low-
    energy microwave photons, or with high-energy optical photons".  What
    the author will say is that he feels a strong case has been made in
    this paper for the SETI community and NASA to review their present
    attitude towards the optical approach.  This does not mean that the
    Microwave Observing Project (MOP) should be abandoned or severely
    modified, since clearly we need to do a exhaustive search in the
    microwave spectrum.  Some of the signal processing techniques developed
    for MOP will also be applicable to the optical search.

        In many ways the Cyclops Report may have become the cornerstone
    upon which much of present-day SETI lore rests.  While the report
    itself was a very comprehensive study of Microwave SETI, and of high
    technical quality, certain very conservative assumptions in that study
    lead this author to consider the report flawed.  Just like for NASA's
    studies of the efficacy and cost of Microwave PowerSat technology back
    in the 1970's, if we ask the wrong questions we are likely to get
    incorrect answers.  Attempting to lift all the material for PowerSats


                                                                     Page 59

    from the deep gravitational well of Earth is sure to make the
    technology uneconomic and damaging to the environment.  Sweep away the
    inherent anthropocentric Assumption of Ineptitude of present SETI lore
    and the problems associated with the optical approach disappear.

        There appear to be some indications of group-think within the SETI
    community, where it is easier to agree with the consensus than disagree.
    The U.S. Space Shuttle CHALLENGER tragedy of 1986 is a classic example
    of how group-think and the desire to conform can have immense ramifi-
    cations.  The issues may not be so acute here: Nevertheless, they
    represent an impediment to the acceptance of new (or revisited) ideas.

        Planning for an extensive optical search should be started now, so
    that if by the year 2000 the results of the MOP are negative, we can
    immediately initiate Professional Optical SETI activities.  This would
    be a natural extension to MOP so that the program could eventually be
    renamed MOOP, the Microwave and Optical Observing Project.  In the
    meantime, amateur astronomers could be conducting a low-level
    (low-sensitivity) optical search, helping to establish some ground
    rules for a later high-sensitivity professional optical search.

        It is believed that Professional Optical SETI with large hetero-
    dyning telescopes is compatible with Professional Optical Astronomy in
    that they can share most of the hardware, yet be undertaken at
    different times so as not to interfere with each other's observations.
    There is theoretical and experimental evidence to suggest that the new
    adaptive telescope technology using Rayleigh or Sodium Resonance
    Fluorescence laser guide stars [69] can be made to work during daylight
    hours.  This clearly has important ramifications for the concept of
    Symbiotic (Serendip) Optical SETI.  The idea of modifying Earth's Great
    Optical Telescopes for Symbiotic (Serendip) Professional Optical SETI
    has many attractions; where the scientific endeavors of conventional
    and SETI astronomy could be of mutual benefit to each other.

        There is probably a case here for an automated retrospective
    historical study of stellar spectrographic plates to see if ETI signals
    actually exist and are on record.  It is quite possible that anomalous
    spectral lines will be found in the record, signifying laser trans-
    missions, but which had previously been overlooked, fogged the film,
    saturated the recording media, been mistaken for natural bright
    emission lines, or put down to "technical problems with the spectro-
    graphic equipment".  It would not be the first time that a major
    scientific discovery had been missed for lack of attention and
    curiosity.  There does appear to be some doubt as to whether C.W.
    ETI signals, if present, would have been accidently detected during
    conventional optical astronomy and recognized for what they were.  This
    is the crux of the matter as far as the efficacy of Amateur Optical
    SETI is concerned.

        It is left as an exercise for others to determine the probability
    of missing an ETI signal at any particular flux level.  It is the very
    concept that ETIs are supposed to be rare which makes it plausible to
    suggest that the historic accidental discovery of ETI by optical
    astronomers would be unlikely.


                                                                     Page 60

        Initially, to reduce the optical search time, we would concentrate
    on efficient laser transition frequencies presently known to humanity,
    and Fraunhofer dark lines.  It is suggested that we must keep an open
    mind here.  For thirty years we have been digging relatively deep
    trenches in a very small corner of our electromagnetic backyard.  Was
    it prudent to do this without at least turning over the topsoil in the
    rest of the electromagnetic garden, particularly in that part of the
    spectrum where solar output peaks, and which tells us and ETIs most
    about our Universe?

        The study also seems to indicate that the amateur SETI enthusiast
    could make a useful contribution to the search using medium-size
    amateur optical telescopes with photon-counting receivers.  It is
    certainly more debatable whether Optical ETI signals are present at
    sufficient flux intensities to be detectable by small incoherent
    telescopes.  However, although the theoretical SNRs described for small
    photon-counting (direct-detection) receiving telescopes are not
    particularly impressive, even if very high mean EIRPs are assumed, it
    must be remembered that ETI signals are likely to be pulsed and far
    more detectable than the C.W. signals assumed here for the simplified
    analyses.  This would be particularly true for detection systems with
    optical bandwidths greater than 100 GHz.

        Today, the technology is available to construct efficient,
    highly-sensitive photon-counting receivers for the visible and near-
    infrared regimes.  For several thousand dollars, top-of-the-line
    amateur optical telescopes could be equipped with the instrumentation
    to make unattended frequency searches of selected targeted stars.  If
    this new scientific endeavor really takes off, market growth will lead
    to considerable reductions in hardware and software costs, making this
    activity more affordable.

        Not only would it be possible to slave many amateur telescopes
    together at one site, to produce the equivalent of a larger telescope,
    but it may also be possible to slave telescopes at different sites and
    average the data.  This would, of course, require accurate time
    synchronization between the telescopes, though this should not be much
    of a problem.  However, the requirement to match the wavelength
    accuracy of the optical filter or monochromator to within 100 GHz is
    probably a more severe obstacle.  In the case of co-site slaving, where
    pre-detection combining of photons would occur, the SNR would increase
    at a rate proportional to the number of identical telescopes.  For
    remote site slaving, where only post-detection electrical signal
    combining could be employed, the SNR would increase at a rate
    proportional to the square root of the number of identical telescopes.

        While it is the author's view that Professional Optical SETI ought
    not to required the use of more sophisticated signal processing
    algorithms like KLTs [73,86] for extracting very weak pulsed signals
    from noise, Amateur Optical SETI may well benefit from its use.

        Perhaps one of the interesting aspects of the Amateur Optical SETI
    concept using incoherent detection is that not only may there be a
    useful contribution made by the enthusiast, but that such activities


                                                                     Page 61

    may occur before Professional (Visible) Optical SETI and its coherent
    detection systems get established.  A low-level search by amateurs
    might help set some of the criteria for later professional searches,
    even if the results are negative.  Amateur optical SETI has the
    potential to bring SETI to the masses, something that has not really
    been possible at microwave frequencies, except in a limited way for a
    few enthusiastic radio hams with modified satellite receivers
    (AMSETI). [26]  It also has the power to cause a renaissance in public
    interest for astronomy and the night sky.  It is an activity in which
    amateur optical astronomers who live in big cities can participate,
    unincumbered by light pollution, the bane of conventional amateur
    astronomers.  This could be the opportunity to dust off those old
    telescopes and put them to use again.

        It is clear, [27-29] that today there is an enormous interest in
    SETI amongst the population.  Professional SETI scientists could tap
    into that interest to receive increased SETI funding and the cooperation
    of enthusiastic amateurs.

        It does not appear that Amateur Optical SETI at the infrared Carbon
    Dioxide (CO2) wavelength of 10,600 nm would be very sensible because of
    the limitations set by the essentially 24-hour day, 300 K temperature
    background of the atmosphere, particularly for small apertures.  As we
    have seen, Professional Optical SETI in the visible and near-infrared
    can use coherent or incoherent optical receivers.  The coherent
    approach is generally more sensitive but far more complex and
    expensive.  However, based on performance considerations, both ground-
    based Professional and Amateur Optical SETI in the infrared would have
    to be restricted to coherent receivers.  This represents a complexity
    and cost problem for the amateur.  Of course, there could be very
    powerful CO2 ETI transmitters present, as powerful as conjectured for
    Visible SETI that have so far escaped detection, for we may not been
    looking in the right direction at the right moment, with suitable
    detection equipment.  The CO2 observational work now being undertaken by
    Dr. Albert Betz and Professor Charles Townes [57] is addressing this
    issue.

        Presently, Dr. Jill Tarter and Deborah Schwartz-Koyler of the SETI
    Institute are involved with a NASA project (NASA NCC 2-407) titled:
    "Supporting Research and Technology Activities in the Preparation of a
    Three-Dimensional Map of the Infrared Sky".  The goal of this project
    is to construct a detailed three dimensional model of the infrared sky,
    which will enable us to reconsider the question of the "best" frequency
    at which to conduct a search for electromagnetic radiation, which is
    indicative of the existence of an extraterrestrial technological
    civilization.  Thus, despite the general consensus that Microwave SETI
    has the greatest likelihood for success, others are even now beginning
    to probe deeper into the infrared part of the optical spectrum.

        Since the start of modern-day SETI thirty two years ago, a strong
    Microwave SETI constituency has developed.  It will be understandable
    if this author's views are attacked by that community, for many SETI
    researchers have much at stake - decades of work invested in the
    microwave regime and professional reputations.  I would council the


                                                                     Page 62

    following thought: The public, and by that I mean the taxpayer, and
    Members of Congress, should clearly be informed that it is quite
    possible that the search for ETI in the microwave spectrum will be
    unsuccessful - not because such signals are not present, but because we
    are presently tuned to the wrong frequencies.  It may well be necessary
    to extend the search into the optical regime before we can be sure
    whether electromagnetic ETI signals do or do not exist.  It will not
    look good for the SETI community if, in ten years time, they have to go
    back to Congress, cap in hand, and ask for more funding to extend the
    search into the optical regime after decades of maintaining that the
    optical approach was useless.  Note that these sentiments have
    previously been expressed privately to both the SETI Institute and
    NASA.  It is the author's contention that SETI has been "hijacked" by
    radio astronomers.  It should now be clear to the reader that for
    humanity to have devoted less than 5 percent of its SETI observation
    programs to the optical regime, and an even smaller percentage to basic
    Optical SETI research, was probably unwise.  The author hopes that
    readers will urge the SETI Institute, NASA, and Congress to rectify
    this omission.

        NASA should be able to put an end to recent problems in deploying
    large high-gain microwave antennas in space, e.g., on the Galileo
    probe, by moving to fixed high-gain optical antennas as soon as
    possible.  During the next few decades, other lights (visible and near-
    infrared) will appear in the sky of terrene origin: they will be the
    advanced laser communication systems of GEO and LEO satellites, along
    with signals coming back to Earth from NASA's next generation of deep
    space probes. [63-66]  Sometime next century, humans will be seen
    walking on the planet Mars.  These HDTV television signals are likely
    to traverse most of the distance between Mars and Earth via laser, be
    relayed around the globe via laser-based geosynchronous satellites, and
    arrive in people's home via optical fiber.  When humanity sends out
    (non-relativistic) interstellar probes to investigate nearby star
    systems, the data and pictures of those encounters (hopefully with
    other planetary systems) will come back to Earth via laser.  The
    computer technology of the day will also be substantially dependent on
    photonics.  See the January 13, 1992 issue of NEWSWEEK (pp. 56-57) for
    the article on "The Highway to the Future", describing a fiber-optic
    multi-gigabit data highway system being proposed for the United States.
    Also see the January 9, 1992 issue of ELECTRONIC DESIGN (pp. 73-80) for
    the article on "The World of Communications is Moving to Fiber Optics".
    The author has seen the future, and it is photonic.

        Truly, the superior communications and computing technology of the
    future will be photonic, a technology that is likely to be around for a
    while.  Indeed, in the future, one of the main uses for low-gain
    microwave space communications might well be the "acquisition" of the
    party at the other end of the link, so that the high-gain laser
    communications system can be locked on!  The amateur SETI enthusiast,
    with the right photonic receiving equipment, will be able to tune in on
    these Earth-bound optical transmissions.  How ironic, that next century
    the complaint will surely arise, that terrene optical transmissions are
    interfering with our ability to carry out Optical SETI free of false
    alarms!  Now where have we heard that before?


                                                                     Page 63

        We end as we began.  If we look at the basic beliefs that
    differentiate the proponents of the Microwave and Optical SETI
    rationales, or the belief in Unidentified Flying Objects (UFOs), an
    area that has been even more controversial than SETI, we find that the
    respective convictions hinge on our assumptions about the technical
    abilities of ETIs.  In the case of Microwave SETI, the proponents
    believe that while intelligent life within in galaxy is not rare, that
    ETIs do not have the technical wherewithal to get the full benefits of
    the superior optical technology for interstellar communications.  If
    the reader subscribes to the Optical SETI rationale, they will
    additionally believe that ETIs have the technical prowess to use the
    superior laser technology in an effective manner.  Advocates of UFOs
    essentially accept that ETI technology is so superior to our own that
    rapid interstellar travel is easy for them, and if these ETIs actually
    wanted to make contact, they would make physical contact.  In the end,
    the reader's belief will be limited only by their own vision.

        The theoretical results quoted in this paper are based on standard
    text book relationships, familiar to students of electrical
    engineering, physics, and astronomy.  Please refer to Appendix A for a
    list of most of these formulas and specimen calculations.  Perhaps the
    main reason for the difference between the conclusions of this analysis
    and many previous comparative SETI analyses, is that the author has
    shown a bit more imagination.

        A few additional closing statements.  It may appear from the
    author's comments throughout this document that he does not hold high
    regards for the efforts over the past thirty two years of many noted
    (microwave) SETI scientists.  This would be far from the truth.  It is
    the nature of science that for every two steps forward, it may often
    take a step back in the light of new discoveries or new ideas.  It is
    very easy with hindsight to criticize those who have gone before, but
    without their predecessors' work and developments in other scientific
    fields and technologies, it is unlikely that the new discovery or idea
    would ever have seen the light of day.  Each generation of scientists
    and engineers builds on the foundations laid by earlier generations.

        Readers are reminded that there is little which is innovative about
    the contents of this document which have not previously been described
    by Charles Townes [46-47,80] and others - the author has just been a
    bit more forceful.  Innovative ideas, like good wines, take time to
    mature.  The author hopes that the effort he has expended in this
    revisiting of the optical approach to the search for extraterrestrial
    intelligence will at last cause Optical SETI to be seriously considered
    by the scientific community as warranting closer study.

        This paper could be the start of an exciting new chapter in both
    SETI and professional/amateur optical astronomy.  One thing which can
    be said for certain is that should a professional or amateur
    astronomer discover electromagnetic (radio or optical) signals from
    ETIs, neither they nor humanity will ever be the same.  There is no
    doubt that a Nobel Prize will await the discoverer.  Perhaps now is the
    time to get familiar with those Post-Detection SETI Protocols! [25]
    See Appendix B for a description of these protocols.


Continued


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