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The Cosmic Haystack Is Large

JILL TARTER

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The Cosmic Haystack is large, unimaginably large, and at least nine-dimensional. [1] And that's only the haystack we can describe today with what we know about physics and technology in the twenty-first century, and from our terrestrial and inescapably anthropocentric vantage point. The fact that we've so far pulled a few straws from that haystack, examined them, and declared that no "needle" has yet been found doesn't make the haystack any smaller, nor invalidate the reasons we set out to try to explore it in the first place. If the history of the Search for Extraterrestrial Intelligence (SETI) argues for anything, it argues for better search tools, and fortunately that's what is happening. Skepticism is one of the most important tools in SETI efforts; it is disappointing to see it linked erroneously with human impatience and unfulfilled longing in Peter Schenkel's article.

Pogo said it best (and Calvin and Hobbs later echoed)-"Either way, it's a mighty soberin' thought." We search because we want to know the answer to the question, not because we demand cosmic company.

In the mid seventies, Stu Bowyer (an X-ray astronomer with an exceedingly clever idea about how to conduct a piggyback SETI program) gave me a copy of the Cyclops Report, a NASA Ames/Stanford/ASEE engineering design study edited by Bernard Oliver and John Billingham. Bowyer wanted to entice me to join his team because I knew how to program an obsolete PDP8/S computer that he'd been given as surplus equipment to use in his search. I read the Cyclops Report and drew two conclusions that remain valid to this day. First, I was lucky enough to live in the first generation of humans capable of attempting to do a scientific experiment to answer the question that thousands of previous generations had been able to address only to their priests and philosophers. Second, this was, and is, the most important scientific exploration humanity can undertake. The first conclusion is self-evident, the second one was later poetically phrased by Philip Morrison, who said, "SETI is the archaeology of the future."

The successful detection of a signal from an extraterrestrial technology requires that technologies (theirs and ours) survive for a long time-long, that is, in a cosmic sense, not in human terms. Detection of a signal therefore tells us that we (or at least our technology) can have a future. No other human endeavor today is capable of providing us with that information. This doesn't imply "extraterrestrial salvation"; how we get to that future will more than likely be up to us. But it does imply a proof of concept. Detection of a signal requires that we search. That is what I have been doing and will continue to do, and I am hopeful that my successors will do so as well. Quoting Morrison again (writing with Guiseppe Cocconi in Nature, vol. 184, p. 844 [1959]), "The probability of success is difficult to estimate, but if we never search, the chance of success is zero."

Schenkel spends a lot of time on the Drake Equation and suggests that it has some predictive power; it doesn't. The Drake Equation is simply a way to organize our ignorance in order to permit rational discussion. R* is the only factor in this so-called equation that has any current observational bounds. Within the next decade or so, we may have an idea of the range of values for fp and ne. L is unknown and unknowable, in the absence of a successful SETI program. Today, we can say only that approximately 6 percent of stars like the sun host "hot Jupiters" in short-period orbits. While this is vastly more than we could say prior to 1995, when such objects were unknown and unexpected, it says little about the prevalence of terrestrial planets, or other bodies suitable for life. Schenkel has misinterpreted what is now known from the rigorous searches for extrasolar planets, and has confused observational bias (inherent to the current generation of instrumentation and techniques) with results to conclude that habitable planets are rare. So too, he has confused the interesting and important speculations of the Rare Earth volume with results. Given our sample of one, it is difficult to distinguish between the contingent and the truly necessary in the saga of evolution to a technological civilization on planet Earth today. The data are precisely consistent with life (indeed intelligent life) being rare or extremely abundant in the Milky Way Galaxy; as yet we have no data. Which brings us back to the size of the Cosmic Haystack.

Conclusions based on the examination of a small number of stars on our galactic door step, at a few frequencies within the radio and optical portions of the electromagnetic spectrum, during a few minutes of time, with detectors optimized for a limited class of signal types, cannot be very robust. Forty-six years may seem to Schenkel to be a long time to search without positive results. Indeed it's longer than my professional career, during which I've worked very hard to conduct and improve those searches. However, it must be examined in a cosmic context-in light of the ten-billion-year history of our galaxy. For signals to be detectable, they must be co- temporal and that requires that technologies overlap (at least within the 100,000-year crossing time of our galaxy). We ourselves have just emerged as a technological civilization. Should we really be surprised that we haven't achieved instant success? Are we so confident that our current technology is the correct technology for the job? Are we still at the mercy of priests and philosophers, or will we use the power of our exponentiating technology to help us survive into old age, and perhaps along the way discover other long-lived technologies? Pogo was right, but we are a long way from having the data to draw the sobering negative conclusion.

The Allen Telescope Array (www.seti.org/ata) is just beginning an exploration of the astrophysical universe and a search for signals from technological civilizations. As the first telescope to be designed for continuous SETI observations, it will immediately speed up current search strategies by orders of magnitude. Exploitation of Moore's Law will make it faster yet throughout its lifetime. A new OSETI sky survey instrument at Harvard (http://seti.harvard.edu/oseti) is about to be dedicated. All readers of the Skeptical Inquirer are encouraged to follow the developments of these projects and other ongoing SETI search programs (see www.seti.org/searcharchive) and to contribute suggestions for their improvement or of alternative search strategies. However, if you are lonely and impatient, perhaps you need to consider an on-line dating service.

Success may be difficult to predict, but it's too soon to rule it out.

Note

1. The nine dimensions are: three of space, time, two of polarization (or perhaps photon rotation/twist), frequency, modulation, and sensitivity (a combination of transmitter power and distance).