Publications Department
Copyright © 1998 by H. Paul Shuch, Ph.D.Abstract
Executive Director, The SETI League, Inc.
PO Box 555, Little Ferry NJ 07643
email n6tx @ setileague.orgrunner-up in the National Institute for Discovery Science Essay Competition.
The author proposes a radically new approach to microwave SETI. Instead of a small number of extremely large, sensitive radio telescopes, we contemplate a global network of thousands of very small, inexpensive and relatively insensitive amateur instruments, coordinated through the Internet, making up in strength of numbers what they lack in individual sophistication. Network design, instrument design, and the results of a pilot study are discussed, and standards of proof of ETI contact analyzed. One advantage of the proposed network is that, when fully operational and properly coordinated, it will see in all directions at once, so that no direction in the sky shall evade our gaze. Another is that it will control both Type I and Type II experimental error, by affording us with simultaneous spatial coverage from widely separated terrestrial locations. This will minimize the incidence of false positives experienced by single-instrument searches, while eliminating the false negatives generated by the current temporally-displaced follow-up detection strategy.
Where Will We Meet Them? How Will We Know?
For nearly forty years, radio has been the dominant medium for seeking evidence of the existence of our cosmic companions. Since its inception at the National Radio Astronomy Observatory (NRAO) in 1960, the Search for Extra-Terrestrial Intelligence (SETI) continues to employ ever larger and more sensitive radio telescopes. Advances in microwave technology and digital signal processing are such that attempted microwave interception of intelligently generated extraterrestrial signals is still a favored strategy. However, accepting the dominant paradigm that instruments capable of interstellar communication must be large, complex and costly has led to the cancellation of most of the world's government-sponsored SETI programs.
A resource often overlooked by past SETI efforts is the global community of amateur radio astronomers. It is, after all, the world's amateur optical astronomers whose strength of numbers and unconstrained access to their modest instruments has enabled them to detect numerous comets, supernovae, and other highly intermittent astronomical phenomena. Similarly, the world's microwave radio amateurs and radio astronomy experimenters are in a position to observe at times and in directions unlikely to be covered using the world's great radio telescopes.
Standards of proof for SETI searches are appropriately set quite high. However, current signal verification and follow-up detection protocols are conservative to the extent of potentially introducing an unacceptable incidence of false negatives. A properly coordinated amateur search has the advantage of permitting real-time, widely separated follow-up detection to eliminate from consideration those hits related to local phenomena. In addition, a grass-roots international effort can do much to dispel public skepticism toward any results, either positive or negative, which might be announced by individual governments.
It is the opinion of the author that detection of artificially generated electromagnetic waves remains the most likely mechanism of contact between humans and ETI, at least at our present state of technological development, and excluding from consideration any laws of nature not presently in evidence. The photon is, after all, the fastest spaceship known to man. It travels relatively unimpeded through the interstellar medium, at the fastest speed which our understanding of physics would allow. Based upon the primitive state of Earth's communications technology, such contact is most likely to occur in the microwave spectrum, although optical SETI is becoming more viable. We would have a high confidence level that such contact had taken place upon simultaneous detection (at widely separated terrestrial coordinates) of signals of sufficient duration or periodicity to allow multiple independent observations. In addition, such signals must exhibit some reasonable combination of the following hallmarks of artificiality:
Review of SETI Prior Art
Drs. Giuseppe Cocconi and Philip Morrison (1) articulated the dominant model for detection of extra-terrestrial microwave emissions in 1959. Unbeknownst to them, while they were writing their paper for Nature, Dr. Frank Drake (2) was preparing equipment at the National Radio Astronomy Observatory (NRAO) in Green Bank WV, to perform the very experiment which they were describing. Drake's Project Ozma was a targeted search, concentrating the collecting area of a modest (26 meter diameter) radio telescope for hours on end upon two nearby Sun-like stars. In fact Drake's targets, Tau Ceti and Epsilon Eridani, both appeared high on Cocconi's and Morrison's candidate list, and are still frequently targeted by contemporary researchers.
Modern SETI consists of two distinct but complementary research elements: a targeted search of nearby sun-like stars, and an all-sky survey for interesting signals of unknown origin. Like dozens of microwave SETI projects in the intervening years, Project Ozma fell in the former category.
The best known and most advanced contemporary targeted search is Project Phoenix, being conducted by the prestigious SETI Institute, heirs apparent to the amply funded NASA SETI effort canceled by Congress in 1993. Working from a catalog of 1,000 Sun-like stars within 200 LY of Earth, Project Phoenix has observed from the 64 meter Parkes radio telescope in Australia, a 43 meter dish at NRAO Green Bank, and will soon go on-line at the 305 meter Arecibo radio observatory in Puerto Rico.
SETI Institute engineers, under the leadership of the late Dr. Bernard M. Oliver, developed an innovative Follow-Up Detection Device (FUDD) capability (3), pairing each of their telescopes with a smaller, distant instrument. Within five minutes of detecting a candidate signal, the FUDD observes the same celestial coordinates at the same frequency. Of thousands of candidate signals analyzed by Project Phoenix, none yet has been confirmed by a FUDD. Although it has been suggested that the intelligent extra-terrestrial origin of all such signals was thus disproved, an alternative hypothesis is that true ETI signals are highly intermittent, and were simply no longer present when scrutinized by the FUDD.
Targeted searches such as Project Phoenix involve aiming at likely candidate stars for long periods of time, a strategy well suited to large, steerable dishes, with their narrow beamwidths and high sensitivities. If we guess right as to which stars constitute likely candidates, the targeted search will provide us with the greatest likelihood of immediate success. But since only a limited number of relatively nearby candidate stars is known to us, concentrating our search in their direction may cause us to miss an equally good star of which we happen to be unaware.
An all-sky survey, on the other hand, makes no a priori assumptions as to the most likely direction to explore. The sky survey attempts to sweep out the entire sky which can be seen from a given location. No antenna tracking is required, since it is the entire sky, rather than individual stars, which we seek to scan. While target searching antennas must be constantly moved, sky survey radio telescopes are operated in what's called meridian transit mode, in which it is the Earth's rotation which turns them.
The best known of the several all-sky surveys conducted in the past four decades was performed at the Ohio State University "Big Ear" radio telescope from 1974 to 1997. OSU SETI was the longest continuously running experiment in SETI history, and was the search which detected one of the most intriguing unverified candidate signals to date. The so-called "Wow!" signal of 15 August 1977 (4) was named for a marginal note in a computer printout, penned by researcher Dr. Jerry Ehman when first he noticed an anomaly which seemed to fit all his expectations for an artifact of intelligent extra-terrestrial origin. Over twenty years later the "Wow!" serves as a benchmark for many of our SETI efforts.
Two decades of analysis of the "Wow!" data set have allowed researchers to consider and reject a number of alternative hypotheses as to its origin. Terrestrial interference, probabilistic noise, equipment malfunction, satellite interference, reflection of terrestrial signals off the Moon or space debris, and the possibility of a deliberate hoax have all been considered, analyzed and assigned a low probability. Two remaining hypotheses are a radiation artifact from a distant civilization, and a previously undiscovered astrophysical phenomenon. Unfortunately, we will probably never know which is the correct interpretation. Thus the "Wow!" observation is inconclusive, because the intermittency of the event precluded follow-on detection. Over 100 follow-up studies over a twenty year period have failed to reveal a repetition of this enigmatic signal.
The various all-sky surveys and targeted searches conducted to date share several important characteristics. They are generally conducted in the so-called Microwave Window, that region of the electromagnetic spectrum least plagued by noise, in which signals pass relatively unimpeded through the interstellar medium. They all employ high gain, narrow beamwidth microwave antennas; thus, they are restricted to observations with narrow angular dispersion. Energies are expended in the development of multi-channel spectrum analyzers, enabling monitoring of ever increasing spectral bandwidth. And despite years of our very best efforts, none of these searches has yet yielded conclusive proof of the existence of other radio-using civilizations in the cosmos.
Global Sky Survey Research Design
The late NASA High Resolution Microwave Survey (HRMS) was a two-pronged SETI project incorporating a targeted search and an all-sky survey component. The two complementary elements anticipated two distinct detection scenarios: the possibility that other civilizations might be radiating intentional beacons in our direction, and the hope of intercepting another civilization's domestic radio traffic. All-sky surveys are generally best suited to detection of radiation of the former variety, while targeted searches would be the most likely means of detecting the latter.
Initially budgeted at $12.5 Million US per year, the NASA HRMS was terminated by Congress just one year into its planned ten-year run. During its brief tenure the NASA targeted search had only begun to scan the very nearest sun-like stars, and the all-sky survey component had accumulated a scant 1000 hours of observing time. The SETI Institute's well-conceived Project Phoenix is a worthy successor to the HRMS targeted search component. However, to date no complementary all-sky survey has emerged as heir apparent to that element of HRMS. The nonprofit, membership-supported SETI League has been designing an experiment to fill the void.
Consider an all-sky survey performed at a facility akin to the recently demolished "Big Ear" radio telescope. Such instruments are extremely sensitive, and have exceptional resolving power, both desirable features achieved by using a high gain, narrow beamwidth parabolic reflector antenna. These giant dishes see perhaps one part in 106 of the sky, so that even if you have one turned on, and tuned to precisely the right frequency, at the very instant The Call comes in, there's still a 99.9999% probability that you'll be pointed the wrong way.
We note that a signal emanating from a high-gain, narrow-beamwidth antenna on a rotating planet will sweep across Earth for only a few seconds to minutes. Thus one can improve one's signal detection odds by looking in all directions at once. This is desirable because we can expect valid ETI signals to be brief in duration, and highly intermittent in nature. For example, the duration of the famous Ohio State University "Wow!" signal was insufficient for verification by reception in both of the "Big Ear" antenna's displaced feedhorns, and has never been seen by more than 100 follow-on studies over a 20-year period. A million "Big Ear" radio telescopes, properly positioned around the world and carefully coordinated, can be configured to cover all four pi steradians of sky in real time. But at a cost of perhaps $100 Million US apiece, we have very quickly exceeded the Gross Planetary Product.
Fortunately, there is another way. The SETI League, Inc. contemplates a radical departure from past all-sky survey strategies. While we certainly can't imagine funding a million research-grade instruments, we can achieve full sky coverage with a much smaller number of physically small, wider-beamwidth antennas. This approach has an intriguing financial benefit. The solid angle subtended by a parabolic antenna varies inversely with the square of its diameter, while the cost of such antennas varies roughly with the third power of antenna diameter. Thus, compared to a single dish, a large number of small antennas can give us an order of magnitude reduction in cost for equivalent sky coverage. This is the same inverse economy of size noted by Oliver in the landmark Cyclops study (5), the 1972 paper design of the greatest radio telescope never built.
For our source of low-cost antennas of modest size, we turn to the Domestic Communications Satellite (DOMSAT) industry. The typical C-band satellite TV dish is on the order of three to five meters in diameter, and is designed to afford around a one degree half-power beamwidth in the 4 GHz range. Such antennas will have about three times that beamwidth in the spectral region between the 21 cm hydrogen line and the 18 cm hydroxyl line, frequencies still considered prime real estate for the SETI enterprise. One such antenna covers perhaps one five-thousandth of the sky, so it stands to reason that a coordinated network of five thousand such small installations can achieve real-time full sky coverage. Our goal of enlisting that very number of microwave experimenters into a coordinated global search is by no means arbitrary.
The SETI League has dubbed its all-sky survey Project Argus, after the mythic Greek guard-beast who had 100 eyes, and could see in all directions at once. When fully operational, Project Argus will provide the first ever continuous monitoring of the entire sky, in all directions in real time. Mythology tells us that when Argus died, the gods put his eyes on the tail of the peacock. The SETI League prefers to think that Argus lives on in the plethora of small radio telescopes sprouting up even now, in the back gardens of dedicated amateur radio astronomers all around the world.
The down side of the proposed Project Argus sky survey is that antenna gain and beamwidth are inversely proportional. So all else being equal, an antenna which sees 200 times more sky than a giant radio telescope is going to be on the order of 23 dB less sensitive. From a practical standpoint, the reduced gain of amateur SETI antennas translates to reduced range. As far as this author knows, Congress has not yet repealed the inverse square law. This suggests that an extra- terrestrial signal which a major radio telescope can detect at, say, 200 light years (the upper range of targets selected for the HRMS and Phoenix targeted searches) would still be visible to our small dishes, but at a range of just under 20 LY (a distance encompassing our nearest 300 stellar neighbors). So initially, small-dish SETI will of necessity be concentrating on detecting those very strong (meaning probably nearby) yet highly intermittent signals of which the famed Ohio State "Wow!" signal is the best known example.
The conventional wisdom holds that in maximizing telecommunications range, there is no substitute for capture area. In fact, digital signal processing (DSP) techniques can indeed significantly increase the range of a small-aperture receiving station. The stations which this study proposes will incorporate DSP software the power of which is limited by the speed of the computers on which it is run. This is a good limitation to have, as the power and speed of computers has tended to double every year for the past two decades. Although it is always dangerous to extrapolate technological growth, we have every reason to expect the range and sensitivity of our small-terminal SETI stations to improve in the years ahead, as computer power continues to improve. However, the following section will demonstrate that even at today's level of technology, amateur built and operated SETI stations can achieve performance which is up to the task of detecting and evaluating likely signals over interstellar distances.
Argus Station Equipment Design
Any radio telescope which we might propose for any SETI survey must, of course, be capable of detecting signals of likely power levels. Let us assume for this analysis that the "Wow!" signal is a valid SETI candidate, of just such a likely level. (It is the most promising candidate signal which we have received to date, and was considered at the time of reception, as now, to be typical of the kind of signal levels we could expect from interstellar beacons). We know the Signal-to-Noise Ratio (SNR) of this candidate signal as received in 1977, and can easily compute the sensitivity of the Ohio State Radio Observatory at that point in time. Thus we can readily determine the flux density of the "Wow!", which establishes for us a practical sensitivity requirement for future SETI instruments.
It is reported that when the "Wow!" signal was intercepted, the gain of the Big Ear radio telescope was roughly equivalent to that of a circular parabolic reflector 52.5 meters in diameter (6). "Wow!" discoverer Dr. Jerry Ehman has indicated that the equivalent capture area of the antenna was roughly 1,000 square meters (7). At the 21 cm operating wavelength, the two figures correlate well if we assume a dish illuminated at roughly 50% efficiency, which is consistent with a feedhorn system designed to minimize sidelobes and antenna noise temperature (see Table I). The bin bandwidth, noise temperature, and integration time used during reception of the "Wow!" artifact are widely reported in the literature, and are also reflected in Table I. It can be seen that the resulting sensitivity of the Ohio State Radio Observatory on 15 August 1977 was on the order of 4 x 10-23 W/m^2. The amplitude of the "Wow!" signal is reported as 30 sigma above receiver background noise, for a SNR of +14.9 dB. The peak of the signal was concentrated in a single channel 10 kHz wide. This suggests that the signal's flux density in a 10 kHz bandwidth was 30 times (4 x 10-23 W/m^2), or 1.2 x 10-21 W/m^2. Thus any SETI instrument with a sensitivity exceeding 1.2 x 10-21 W/m^2 will, in theory, be capable of detecting a repeat of the "Wow!", or any similar signal which it should happen to intercept.
We now consider whether the proposed Project Argus instruments would be capable of detecting a repeat of the "Wow!" event. A photograph of the prototype Project Argus station, constructed in New Jersey in 1996, is seen as Figure 1. A block diagram is show as Figure 2. This station consists of a 12-foot diameter Paraclipse satellite TV dish, a cylindrical waveguide feedhorn, a low noise Gallium Arsenide preamplifier, an Icom microwave scanning receiver, and a personal computer equipped with a sound card and DSP software. The total cost of the prototype system was over $7000 US, although it has been subsequently duplicated by several experimenters for under $2000. Costs of the required hardware continue to decrease with increased public SETI awareness and demand. We can begin to contemplate the $1000 amateur SETI station, which should be readily available by late 1999.
A central question in the present analysis is whether the station just described is indeed capable of receiving signals of amplitudes on a par with the "Wow!" event. Our first Project Argus stations were prototypes in the fullest sense, in that they left much room for improvement. The first generation low noise amplifier (LNA) utilized a Gallium-Arsenide monolithic microwave integrated circuit (GaAs MMIC) with 23 dB gain and a noise temperature on the order of 150 K. Later stations reduced their preamp noise temperature to less than 50 Kelvins by using Pseudomorphic High Electron Mobility Transistors (PHEMTs). We conservatively estimate the overall system noise temperature for our first station at 200 K. Using 10 Hz DSP bin widths and 10 seconds of integration, the sensitivity of the prototype system is about 5 x 10-22 W/m^2. This result, reflected in Table II, is wholly adequate for reception of the "Wow!" signal, though it is about an order of magnitude short of the sensitivity achieved by Big Ear, circa 1977. More recent amateur systems are falling midway in performance between the prototype and Big Ear.
It is highly unlikely that these small stations will ever have the sensitivity of the world's great radio telescopes, given equivalent technology. However, by using the "Wow!" as a benchmark, we have shown that even these small stations have sensitivity more than adequate for SETI success.
Participant Coordination Requirements
Chief among the weaknesses of past microwave SETI projects has been the researchers' inability to provide independent, real-time signal verification. Although the FUDD technology employed in Project Phoenix is a welcome first step in correcting this limitation, it is possible that the five- minute lag between initial and follow-up detection may exclude from consideration valid ETI signals of brief duration. The grass-roots, cooperative nature of the Project Argus sky survey can do much to improve follow-up detection, but requires a high level of communication and coordination between participants.
Many of The SETI League's current 900 members are licensed amateur radio operators, and have exploited ham radio as a communications medium. However, if our search is to achieve full strength, we can expect participation from a large number of non-hams. The communications medium of choice for such a global research project is today the Internet. The SETI League is exploiting this medium by providing our members with an extensive website, currently upwards of 1300 pages, totaling more than 42 MBytes (!) of technical data. Our members now enjoy the use of four near-realtime email reflector lists, each dedicated to a specific coordination purpose. And we are developing software to allow automatic dissemination of critical time, frequency and celestial coordinate information to all participating stations, should one member station detect a promising candidate signal.
Effective search coordination, however, also requires that participants all share a common and precise time and frequency reference. Interferometry experiments such as the VLBI fulfill this need through the use of atomic clocks at each participating station. However, in the present application the cost of hydrogen masers and cesium beam standards is prohibitive. Fortunately, our members have free access to a constellation of 24 orbiting atomic clocks, to which their station can readily calibrate. Work is currently underway on developing low cost, very stable reference oscillators, locked in frequency and phase to precision timing signals available worldwide from the constellation of Global Positioning System (GPS) satellites. Long-term frequency stability on the order of a part in 10^11 has been demonstrated. This precision rivals the performance of atomic clocks, at a small fraction of their cost.
Signal Detection and Verification Protocols
Project Argus represents a radical departure from past SETI experiments, in that it is to be conducted by non-scientists. Laymen have the time, energy and enthusiasm to search in ways which the professional scientific community can not. However, there is valid concern as to whether those not schooled in the scientific method can do credible science. Premature announcement of an unverified ETI contact especially could undermine the credibility and respectability not just of Project Argus, but of all SETI experiments. Thus one of The SETI League's duties is to educate its members in scientific restraint.
In 1997 the Trustees of The SETI League, Inc. officially adopted the following twelve-step Signal Detection Protocols, which we ask all Project Argus participants to embrace.
"I, the undersigned, am an official Project Argus participant, and subscribe to the following Signal Detection Protocols:
The SETI League supplies its members with forms, templates, and software, to aid Project Argus participants in complying with the above protocols. But of the policies adopted by the Trustees of The SETI League to ensure scientific rigor, none has proved more controversial than the twelfth point, stating no Project Argus participant should publicly disclose any signal detections until they have been independently verified by another participant.
The reasoning behind the policy is simple: in statistical analysis, sample size is critical. When n=1, all bets are off. We learned from the Ohio State "Wow!" signal that an event which does not repeat and cannot be verified is no existence proof whatever. Science demands peer review, and in our case the panel of peers is comprised of our hundreds of observers around the world, all coordinating their observations and correlating their findings via the Internet.
One need only remember Cold Fusion. About ten years ago, two chemists in Utah thought they had sustained a fusion reaction at room temperature. After an exuberant press conference, a flurry of scientific papers and presentations, and the concerted efforts of physicists and chemists around the world, it appeared that their results could not be duplicated. To be sure, they had discovered something. Just what, we still can't say (it may have even been cold fusion), but if a discovery cannot be independently verified, it has little scientific merit. It's clear that Drs. Pons and Fleishman tarnished their reputations by premature disclosure of their work. And these were trained professional scientists!
So what could be wrong with waiting for confirmation before making an announcement? Many of our members feel the Detection Protocols adopted last year somehow impinge upon their personal liberties. Especially in the US, but elsewhere to be sure, a strong tradition of freedom of expression suggests that nobody tell anyone else what he or she can or cannot say, or to whom. The conspiracy theorists, many of whom are sure that NASA SETI discovered positive signs of life prompting Congress to shut them down, are concerned that The SETI League may become party to some grand cover-up scheme. Then, there is the fear that someone's proprietary findings might somehow be usurped, that those making great discoveries may somehow be denied their due. At the extreme of this line of reasoning is the fear of one's rightfully earned Nobel Prize, or other significant recognition, going to someone else.
We fully realize that my simply telling our members that these concerns are groundless may do little to dispel them. But in fact they are. Ours is a grand, grass-roots effort, perhaps unparalleled in the annals of science. The SETI League makes no proprietary claims to anyone's efforts. There are no SETI Police to arrest members if they violate the Protocols. Nobody's membership is going to be revoked for excessive exuberance. We are not here to restrict anyone's freedoms. What we are trying to do is urge restraint, and reasonable scientific rigor. Without it, we risk becoming a laughingstock, and any real discoveries made by our members being rejected by the scientific mainstream and the general public alike.
Pilot Study Results
As mentioned previously, five Project Argus prototype instruments went on the air in a pilot study on 21 April 1996. Just twenty days later Trevor Unsworth, one of our British volunteer Regional Coordinators in England, detected an anomalous signal at 1471.5 MHz , using a reconditioned surplus 3.5 meter dish. This signal, the first of dozens of candidates detected by Project Argus stations to date, is depicted in Figure 3.
Unsworth's candidate signal exhibited some sort of digital modulation, with a 270 Hz bandwidth, and its Doppler shift of -25 Hz/min suggested that it might possibly be radio frequency interference (RFI) from a Low Earth Orbit (LEO) satellite. This interpretation, however, was confounded by the fact that the signal was received on a frequency not allocated to, nor normally used by, satellite communications. At a subsequent meeting of radio astronomers at NRAO Green Bank, WV, the author showed a slide of Figure 3, and asked for help identifying the source of the signal. Several others had seen signals of this type in that same spectral region. One radio astronomer volunteered that the US Navy apparently has LEO satellites using that particular frequency region, but no further information was available. The military doesn't publicize its classified satellites to our satisfaction!
Actually, we are greatly encouraged by Unsworth's "hit" for several reasons. The signal is from a relatively weak source, which indicates that his system has reasonable sensitivity. Our member contacted SETI League headquarters first, not the BBC or the London Times, which suggests that our verification protocols are being respected. And the Doppler shift (indicated by the slope of the line in the spectral display) was clearly inconsistent with Earth rotation rates, which told us that the signal was not moving with sidereal time, hence must be considered RFI.
This first test of our ability to weed out RFI by its Doppler signature was entirely successful. Through Internet collaboration and the use of powerful signal analysis software, dozens of recent candidate signals have been analyzed by our members, and attributed to RFI as well. But the situation will only get worse. Despite its excellent FUDD methodology, there have been wide gaps in Project Phoenix's frequency coverage, regions where satellite RFI made monitoring for ETI sources impossible. New communications and navigation satellites, operating smack in the middle of SETI's prime water-hole spectrum, are being launched every month. SETI pioneer Barney Oliver once expressed fear that politics and paranoia might cause us some day to draw a curtain across the sky (8). That curtain is forming, but it's being caused by our own technology. Having determined analytically that we are capable of detecting "Wow!" type events, and empirically that we have the sensitivity to detect (but the computational power to differentiate from a valid hit) radio frequency interference, our pilot stations next set about cataloguing a variety of common RFI sources. Figure 4 depicts interference from one of the constellation of 24 orbiting Global Positioning Satellites which continue to plague professional and amateur SETI experiments alike. Figure 5 is a class of signal which Project Phoenix scientist Dr. Jill Tarter has dubbed "wigglers." (9) Project Argus participants have tracked down the source of several of these signals to the very computers which they were using to perform their signal analysis!
Not all Project Argus signal detections to date have been anomalous. In November of 1996, in a collaborative experiment with the world's radio amateurs, NASA activated the 1.3 Watt omnidirectional beacon aboard the Mars Global Explorer, while the spacecraft was enroute to Mars at some 5 Million km from Earth. The beacon's CW signal (Figure 6) was clearly detectable against the background noise, and its Doppler shift, determined from the slope in the spectral display, proved consistent with the spacecraft's relative velocity.
Network Implementation Schedule
The first five Project Argus prototype stations, all basically implemented in accordance with Figure 2, went on the air amid great fanfare in a public launch ceremony on Earth Day, 21 April 1996. Based upon our experience with those first stations, the system hardware and software designs have been refined, and technical details published on The SETI League's extensive website <http://www.setileague.org>. Almost exactly two years after the first prototypes were unveiled, The SETI League had 50 registered stations on the air, with hundreds more under construction, and began the feasibility study which continues to the present.
It is optimistic in the extreme to project a logarithmic growth curve from only two data points. Still, we in the SETI community are acknowledged optimists, else we would pursue a more immediately fruitful quest. If the present rate of growth continues, with order-of-magnitude increases in participation every two years, we can expect five hundred stations on-line in just two more years, and 5,000 participants two years thereafter. Thus our goal is now to achieve full sky coverage by mid-2002. (I hasten to point out that Sir Arthur C. Clarke, a member of The SETI League's advisory board, has suggested that we ought to aim for total sky coverage fully a year earlier than that. We would like to accommodate him, but make no promises.)
The author is frequently asked when, given the above implementation schedule, positive results can be anticipated. Answering such a question requires the gift of prophecy, which is not permitted to The SETI League, we being a non-profit organization. Nevertheless if we do the search, and we do it right, a generation from now we will either have achieved unambiguous evidence of other radio-using civilizations in the cosmos, or we will be forced reluctantly to reexamine our basic assumptions.
Either possibility boggles the imagination.
Standards of Proof
We now come to the issue of what constitutes incontrovertible proof of ETI contact. The question is complicated by the fact that the general public (from whom the Project Argus constituency is largely drawn) may make only a vague distinction between proof and faith. The spectrum of human skepticism vs. gullibility encompasses a wide range of extremes, characterized by diverse viewpoints ranging from "of course they exist -- we couldn't possibly be alone!" to "I'll believe in the existence of intelligent extra-terrestrials only when one walks up and shakes my hand." We must take pains to prevent such declarations of faith from clouding the judgment of our SETIzens.
We start by acknowledging that one can never conclusively prove the negative, but that it takes only one counter-example to disprove it. Conservative experimental design demands that we frame our research hypothesis in the null form: "resolved that there are no civilizations in the cosmos which could be recognized by their radio emissions." Now a single, unambiguous signal is all it takes to disprove the null hypothesis, and negate the notion of humankind's uniqueness.
But what constitutes an unambiguous signal? A popular definition holds it to be one which could not have been produced by any naturally occurring mechanism which we know and understand. But this is an insufficient condition. The first pulsars, after all, fitted that definition. They were first labeled "LGM" for Little Green Man, and their intelligent extra-terrestrial origin seriously considered for several months, until our knowledge of the mechanics of rapidly rotating, dense neutron stars became more complete. There is the risk that any signal which cannot be produced by any known natural mechanism could well have been generated by an astrophysical phenomenon which we have yet to discover. So we need an additional metric.
We listed at the outset several of the hallmarks of artificiality which we can expect from an electromagnetic emission of intelligent origin. The common denominator of all these characteristics, in fact of all human (and we anticipate, alien) existence, is that they are anentropic. Any emission which appears (at least at the outset) to defy entropy is a likely candidate for an intelligently generated artifact. In that regard, periodicity is a necessary, though not a sufficient, condition for artificiality (remembering once again the pulsar).
Unless we are blessed with communication rich in information content, signals which convey otherwise unknown information about the culture which generated them, we are unlikely to ever achieve absolute certainty that what we have received is indeed the existence proof we seek. Multiple independent observations, however, can do much to dispel the obvious alternative hypotheses of equipment malfunction, statistical anomaly, human made interference, and deliberate hoax. In that respect the development of well coordinated signal verification protocols can do much to narrow our search space. Once again, in signal verification activities, it is the null hypothesis we should be attempting to verify. We thus expect that we will ultimately rule out most candidate signals. There may eventually come a signal, however, which simply cannot be explained away.
"When you have ruled out the impossible," Arthur Conan Doyle wrote in the voice of Sherlock Holmes, "whatever remains, no matter how unlikely, must be the truth." Above all else, this truth must pass the inter-ocular trauma test: when the proof we seek is so powerful as to hit us between the eyes, we can no longer deny it. No Government pronouncement is likely to pass this demanding test, as far as a skeptical public is concerned. But if a diverse, international group of laymen, working independently, can produce multiple, internally consistent observations, the world is most likely to accept that group's interpretation as reasonable. SETI continues to seek clear, unambiguous evidence, without even knowing for certain what form that evidence will take. We hope to stumble across the inescapable. Until then, we will continue to test the null hypothesis.
Conclusions
During the last half-century, SETI has emerged out of the realm of science fiction, and into the scientific mainstream. Every few months we read about the discovery of yet another planetary system in space. We are beginning to learn about how life might have developed on other worlds. And we have completed the Copernican Revolution, finally realizing that we are not the center of all creation. Yet SETI programs continue to yield negative results. We are not discouraged. Not only have we not yet scratched the surface, we haven't even felt the itch.
The nonprofit, membership-supported SETI League has launched its search on Earth Day, and flies the Flag of Earth, because SETI is an enterprise which belongs not just to one country, government or organization, but to all humankind. Like Argus, the guard-beast of Greek mythology who had a hundred eyes, we seek to see in all directions at once, that we might capture those photons from distant worlds, which may well be falling on our heads even now.
Project Argus started in 1996 with a mere five prototype stations. This small step for humanity represents a humble beginning for what will ultimately be a global effort. At this writing we have 59 stations on-line in a proof-of-concept study. We can foresee 500 participants within another two years, and perhaps five thousand by the year 2002. When we reach that level, there will be no direction in the sky which evades our gaze. Then we can hope to find the answer to a fundamental question which has haunted humankind since first we realized that the points of light in the night sky are other suns: Are We Alone?
And when Project Argus grows
To full strength, we will show
That the suns shall never set on SETI. (10)
Appendix: SETI League Vision and Mission Statements
Recognizing that receiving signals of intelligent origin from beyond our planet will change forever our view of humanity's place in the cosmos, The SETI League envisions a worldwide network of thousands of experimenters, working together to hasten our entry into the galactic community.
To encourage and support the Search for Extra-Terrestrial Intelligence by:
References
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