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Today, it seems, the electromagnetic Search for Extra-Terrestrial Intelligence (SETI) is being conducted with the technological equivalent of a crystal radio. But it was not always thus. I can recall a time, not too many years ago, when governments vied to throw dollars (not to mention rubles, yen, pounds francs, Deutsch marks, and many an untested vehicle) into space. That was an era known as the Space Race, before the planetary epidemic of deficit reduction which may yet prove fatal to science. Sadly, that epidemic was triggered by science herself, in the form of a Superconducting Supercollider. The results have been disastrous for SETI.
The notion of humankind's uniqueness in the universe had been challenged by philosophers since before Copernican times. Nevertheless, it was only within the twentieth century that the existence of other technologically advanced civilizations in space became a possibility accepted within the scientific establishment, and far more recently still that the feasibility of detecting such other civilizations has entered mainstream thinking.
The first scientific paper seriously contemplating surveying nearby stars for intelligently directed microwave signals was written by Cornell physics professors Giuseppi Cocconi and Philip Morrison, and published in the British journal Nature in 1959. Unbeknownst to Morrison and Cocconi, as they were writing their pivotal paper, a young radio astronomer was preparing to perform the very experiment which they were describing. That scientist, Dr. Frank Drake, launched his Project Ozma search from the National Radio Astronomy Observatory (NRAO) facility at Green Bank, WV in 1960, ushering in the era of modern SETI.
Why do we suppose other civilizations might be detectable by their microwave radiation, and how will we know where to look for them? Consider that our Earth is currently surrounded by a sphere of microwave radiation roughly fifty light years in radius, which is readily detectable over interstellar distances utilizing technology such as is today available to amateur radio astronomers. This radiation, emanating primarily from our planet's UHF TV transmitters and long-range search radars, would mark our planet as inhabited to any similarly capable society within fifty light years. Within that range are found hundreds of stars, tens of which are sufficiently sun-like to probably host one or more habitable planets.
The distance over which we are detectable is limited only by the time since we first began transmitting sufficiently strong signals in the appropriate frequency range. Fifty years from now, we will be detectable out to 100 light years distance. At that point our signals will have engulfed thousands of stars, including hundreds of potential life sites. With every successive doubling of elapsed time (out to 1,000 years or so), the number of civilizations which our radiation signature can potentially reach goes up by a factor of eight. Sooner or later, our signals may well reach a distant radio telescope.
SETI hypothesizes that other technological civilizations are similarly surrounded by a detectable sphere of microwave radiation, the radius of which will be limited only by the length of time such civilizations have possessed sufficiently advanced radio technology. We depend upon our ability to intercept and recognize (though not necessarily decode) such a radiation signature to achieve the existence proof of other intelligent civilizations which SETI seeks.
The problem with seeking incidental radiation is that the unknown factors exceed the known. We can only guess as to where physically to point our antennas, when to listen, and on what frequency. The time dimension is resolved by starting to look now, and continuing until we detect something noteworthy. A large enough number of coordinated stations, effectively looking in all directions at once, resolves the pointing uncertainty. And we can narrow the search space in the frequency dimension by recognizing the range of frequencies which are least attenuated by planetary atmospheres and the interstellar medium. This, however, leaves us with most of the microwave spectrum, and much of the optical, as likely frequencies.
Since there are no "wrong" frequencies to search, SETI has attempted to scan them all. One person's guess is as good as another's, so any frequency for which you can assemble a sufficiently sensitive radio telescope is fair game. Radio astronomers have long explored protected portions of the 406 MHz, 610 MHz, 1.42 GHz and 10.6 GHz bands, and I can think of no good reason why not to pursue the SETI dream in those spectral regions as well.
The foregoing, however, applies only to the problem of scanning for incidental radiation from the distant civilization. What if another intelligent race were making a deliberate, concerted attempt to signal its presence to its interstellar neighbors? Is there a particular frequency, or range of frequencies, which would be self-evident to the receiving civilization? Can we narrow the search space?
Cocconi and Morrison thought so when they published their 1959 Nature article. They reasoned that 1420.405 MHz, a natural emission frequency of neutral hydrogen atoms, was a good place to start looking for deliberately beamed interstellar beacons. This frequency, which falls in the quietest part of the radio spectrum, is marked for all to see, by Nature herself. Everywhere you point a radio telescope, from anywhere in the Universe, you can hear this radiation, emanating from the one hydrogen atom found per cubic centimeter or so of interstellar space. There is nothing geocentric about hydrogen radiation; perhaps, it can be reasoned, selecting it for interstellar communication is a mark of intelligence, in and of itself.
Drake had arrived at this same conclusion independently of Morrison and Cocconi, and indeed set out to monitor a narrow band of frequencies encompassing the hydrogen line (also known as H1) during his Project Ozma search. Today, nearly four decades later, the hydrogen line region still looks like a good bet to many SETI professionals.
Fortunately for SETI, much classical radio astronomy research already goes on at the hydrogen line. Equipment for this frequency region is abundantly available, and much of it can be readily adapted to SETI use. There are indeed other likely "magic frequencies" which are being scanned for signals of possible intelligent extra-terrestrial origin, and once again, one person's guess is as valid as another's. Nevertheless, since many of the world's radio telescopes are already scanning the hydrogen line for natural astrophysical phenomena, and it's a small step to adapt their receivers to search for artificial signals as well. This is precisely what Project Ozma attempted to do in 1960.
Project Ozma must be considered the very first SETI study. It surveyed two nearby sun-like stars, for just a few weeks, at just one frequency, and detected no extra-terrestrial intelligent signals. Nevertheless, Ozma served as a model for dozens of later SETI projects.
The world's first SETI meeting was convened at Green Bank by Drake in 1961. As the agenda for that conference, Drake drafted an equation for estimating the number of possible communicative technologies in the cosmos. The Drake Equation is today the primary probabilistic tool whereby SETI scientists assess their prospects of success. Drake himself considers it a way of quantifying our ignorance. Its seven factors encompass cosmology, planetology, atmospheric science, evolutionary biology, psychology, technology, and sociology. Thus SETI is possibly the most interdisciplinary of the sciences.
In the four decades intervening, on the order of fifty different SETI projects have been conducted around the world, with frequency coverage extending throughout the microwave, millimeter-wave, and optical spectra. These searches have been attempted by Government agencies, educational institutions, non-profit scientific organizations, and, more recently, by amateurs.
Although no definitive proof of extra-terrestrial intelligence has yet been received, SETI has achieved scores of tantalizing hints that such signals might indeed exist. Many candidate signals have been attributed to terrestrial, aircraft, and satellite interference, others to equipment malfunction and natural astrophysical phenomena, but a few defy explanation. Since these signals have failed to repeat or otherwise eluded our attempts at verification, we can draw no conclusion save that there is much to be learned about the universe we inhabit.
Now what has all this to do with supercolliders? Well, SETI was emerging at a time when in the U.S., nationalism ruled science. Our government had set out in the late 1980s to become the world leader in subatomic particle research, and to do so, Congress had authorized funding for a multi-Billion dollar Superconducting Supercollider. Construction was actually begun near Waxahatchee, TX, and some hundreds of millions of dollars expended, before more mundane projects (such as feeding and clothing the populace) began to vie for attention.
At about this time, NASA had a modestly funded but technologically ambitions SETI project under way from headquarters at the Ames Research Center, Mountain View, CA. Budgeted at $12.6 Million annually (about 5 cents per American per year), NASA SETI kicked off on October 12, 1992, the 500th anniversary of Columbus' first voyage of discovery. The plan was to conduct a ten-year search.
Just one year later, in October of 1993, Congress pulled the plug on the Supercollider. Particle physics was deemed wasteful of our limited resources. And if particle physics was wasteful, the reasoning went, SETI was all the more so. In the same sweep of the hand, our elected leaders opted to cancel NASA SETI as well -- reducing the federal deficit in the process, by all of 0.0006 percent.
Now enter Richard Factor, a New Jersey radio amateur (WA2IKL), science buff, and industrialist of more than modest means. Factor's company, Eventide Inc., was a leader in broadcast and studio electronics, aircraft navigation equipment, and a number of other high-tech products. For years Factor had toyed with the notion of building up his own amateur SETI station, and scanning the stars for signs of life. With the termination of NASA SETI, his resolve intensified.
|"I got really mad when Congress killed SETI and the Superconducting Supercollider in the same year," says Factor. The Supercollider, with a price tag of $10 billion, was beyond his help. But SETI, he decided, could be salvaged. So he founded a non-profit, membership-supported educational and scientific corporation to privatize SETI. And he hired me, then an electronics professor in the Pennsylvania State University system, to run it. The SETI League was not my first taste of non-profit science, but it quickly became apparent that it would be the most challenging. For starters, it fell to me to decide exactly what role a citizen's group could play in resurrecting some component of the late NASA effort.||
NASA SETI had been comprised 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. The former, which involves aiming powerful radio telescopes at likely candidate stars for long periods of time, is 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 thinking goes, 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 targeted search antennas must be constantly moved, sky survey radio telescopes are operated in meridian transit, or drift-scan mode, in which the experimenter never needs to aim the antennas. Rather, it is the Earth's rotation which turns them.
Shortly after its demise, NASA's late targeted search was resurrected by the non-profit California-based SETI Institute. This scientific organization had been the institutional home of many key players in NASA SETI, and they set about securing private sponsorship. Their aim was to utilize the same receivers and computer analysis tools they had designed for NASA, in a private search of the thousand nearest sun-like stars. They called their search Project Phoenix, having risen from the ashes of NASA SETI's demise.
Their success in continuing the targeted search has been an inspiration to all who advocate the privatization of science. Project Phoenix employs some of the world's finest radio telescopes, aiming them sequentially at promising targets from a catalog of nearby sun-like stars. But since large antennas have quite narrow beamwidth, they see only a small portion of the sky at a given time. To sweep out the whole sky with such large antennas would consume inordinate amounts of time. A sky survey effort, by contrast to a targeted search, would be better performed with antennas of moderate size.
Smaller antennas can see more sky within their beam patterns, but have correspondingly less gain, thus more limited range. We achieve reasonable sensitivities through digital signal processing, the application of powerful computers to sift through the cosmic static for patterns which Nature cannot produce. But the antennas need to remain fixed on their targets for a relatively long time period, as the computers average out the background noise. With large antennas, this would require active tracking as the area of interest appears to drift east to west across the sky. Fortunately, when used in meridian transit mode, small antennas, with their relatively wide beamwidths, provide us with far greater signal acquisition time than do the larger antennas typically used for targeted searches.
The SETI League was actively attracting radio amateurs and microwave experimenters around the world, with the promise of some undefined great SETI project. And the sky survey approach seemed ideally suited to the community of amateur radio astronomers desiring to pursue SETI. So that is the aspect of SETI which Factor and his fledgling organization chose to pursue. A grass-roots effort which will ultimately grow to thousands of amateur radio telescopes worldwide, the SETI League's Project Argus sky survey was initiated in April of 1996. When fully deployed, it will provide (for the first time ever) real-time full-sky coverage, its thousands of antennas collectively looking in all directions at once, across all four pi steradians of space and time.
Full sky coverage will not occur overnight, but with a clear goal now articulated, it does stand a reasonable chance of becoming a reality. If signals are out there to be heard, I expect we will be able to detect and verify them, maybe even within my own lifetime. It takes only one verified signal to answer definitively 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?
Here's an optimistic song about SETI success.
If, on the other hand, after a generation or so of careful searching, we have still detected no evidence of other life, then we may be forced reluctantly to conclude that we are very much alone, the sole communicative species in our corner of the cosmos.
Either possibility, I am continually reminded, boggles the imagination.
Copyright © H. Paul Shuch, Ph.D.; Maintained by Microcomm
this page last updated 14 June 2007