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Standards of Proof for the Detection of Extra-Terrestrial Intelligence

Copyright © 1999 by H. Paul Shuch, Ph.D.
Executive Director, The SETI League, Inc.
PO Box 555, Little Ferry NJ 07643
email n6tx @

The following is an Invited Paper which Dr. Shuch presented at the Sixth International BioAstronomy Conference, Kohala Coast, Hawaii, on 6 August 1999.


The privatization of SETI has resulted in global participation in signal detection and analysis activities by a wide range of non-professionals. The SETI community welcomes this grass-roots support, every bit as much as the optical observing community honors the significant scientific contributions of the world's amateur astronomers. However, as SETI observatories spring up on college campuses and in home gardens worldwide, a need emerges for establishing rigorous signal verification protocols and stringent standards of proof.

SETI progress can be significantly hampered by both Type I and Type II experimental error. We recognize the possibility that overly rigorous verification standards can result in an unacceptably high incidence of false negatives. This risk must be balanced against the negative impact on SETI activities everywhere, should lax verification procedures result in the reporting of false positives. This paper proposes verification and reporting protocols that seek a middle ground.

A related problem is that non-professional involvement in SETI science increases the opportunity for the perpetration of hoaxes. The SETI League, Inc. has already been peripherally involved in three separate false claims of ETI contact. Such claims call for a prompt but measured response, so as not to subject the SETI community to charges of complicity in conspiracy or cover-up activities. We explore here the dilemma of encouraging grass-roots participation while avoiding association with fraudulent and pseudo-scientific claims.

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 radio amateurs and 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, on frequencies, 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:

Signal Detection and Verification Protocols

Project Argus, The SETI League's global all-sky survey initiated in 1996, 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 contact especially could undermine the credibility and respectability not just of The SETI League's preset Project Argus search, 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:

  1. I will assemble, operate and maintain my Project Argus receiving station in accordance with sound engineering practice.
  2. I will apply the utmost objectivity to the analysis of all candidate signals received.
  3. I will accurately determine my exact station location (latitude and longitude) and antenna aiming coordinates (azimuth and elevation).
  4. I will periodically verify my station's proper operation with a signal generator, the Sun, or other celestial radio source.
  5. I will promptly report to SETI League headquarters any substantive changes to my station configuration.
  6. I will maintain accurately calibrated time and frequency standards.
  7. I will calculate the signal duration and rate of change of Doppler shift which, for my station, are consistent with sidereal motion.
  8. I will employ the above information in determining whether any candidate signal received is of terrestrial origin.
  9. For all potentially relevant signals, I will accurately record time, frequency, and amplitude information.
  10. I will promptly report all pertinent observations by email to the closed SETI League signal verification email list.
  11. I will attempt to verify any candidate signals reported by other Project Argus participants.
  12. In order to avoid undermining the credibility of Project Argus by making premature disclosure of unverified signals, I will await instructions from The SETI League regarding any public announcements of my findings."

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. This states that no Project Argus participant should publicly disclose any signal detection until it has been verified independently 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 failing to repeat, and which 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. Nearly a dozen 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 verified independently, it has little scientific merit.

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.

The EQ Pegasi Hoax

A related problem is that non-professional involvement in SETI science increases the opportunity for the perpetration of hoaxes. The SETI League, Inc. has already been peripherally involved in three separate false claims of ETI contact. Two were simple cases of mistaken identity, easily rectified. But the third was an elaborate hoax perpetrated by an internet hacker who broke into our closed signal verification list.

It is small consolation to us that this hoaxter was not a member of The SETI League at all. In fact, in analyzing and refuting this claim, our members comported themselves admirably.

Responsible science demands that we attempt to prove the null hypothesis -- that is, to try our level best to disprove any claimed contact. Only if we fail in our very best efforts to discredit a signal can we begin to contemplate its validity. The claimed detection from EQ Pegasi was easy to discredit. The screen dumps which were posted to the internet were cut-and-paste masterpieces. They proved the power of our software -- not of our signal processing software, but of a graphics program called Paint Shop Pro.

Even though the fraudulent nature of the claims signed "anon1420" was instantly evident to knowledgable SETIzens, the press chose to imply that the SETI community was covering up some great discovery. Such claims call for a prompt but measured response, so as not to subject the SETI community to charges of complicity in conspiracy or cover-up activities. Thus we have a dilemma: how to encourage grass-roots participation while avoiding association with fraudulent and pseudo-scientific claims?

Standards of Proof

Which brings us 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 to be exhibited 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 anti-entropic. 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).

Ideally, we would hope to receive communication rich in information content, signals which convey otherwise unknown information about the culture which generated them. Unless we are blessed with such a message, 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.


The majority of SETI professionals consider amateur SETI success to be unlikely, but not impossible.

"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 backed by the corroboration of their professional counterparts, then 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.

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