It’s undoubtedly the best-known evidence that someone might be out there. Thirty-five years ago, on 15 August 1977, the “Big Ear” antenna at the Ohio State University Radio Observatory picked up a signal that had all the trademarks of a deliberately produced transmission from deep space. It was so impressive that Jerry Ehman, the astronomer on duty, wrote “Wow!” on the computer printout generated by the telescope. That bit of creative labeling ensured that the blip would become the most famous signal event in the history of the search for extraterrestrial intelligence, or SETI.
No one knows what the “Wow!” signal was. Several experiments have tried to find it again, including an automatic reobservation by the Ohio State antenna at the time of the detection. But it remains a permanent no-show. Maybe it was E.T. pinging our solar system. Then again, perhaps it was merely an instrumental glitch or terrestrial interference. The latter explanation is likely, according to the Ohio State scientists I’ve talked to. But in any case, without a confirming detection, no one can rightly claim that aliens were responsible for the “Wow!”
The idea of searching for radio signals that would betray extraterrestrial intelligence dates back more than a half-century, to 1960, when astronomer Frank Drake spent two months aiming an 85-foot antenna in the directions of two nearby stars. Tuning a 100-hertz swath of the microwave band, Drake heard only silence.
The search remains fruitless, despite the intrigue of signals like the “Wow!” While astronomers continue trying to eavesdrop on E.T.’s radio signals or, more recently, laser pulses, we still don’t know if we’re alone or not.
Some read this failure as possibly significant, suggesting that technologically competent life is exceedingly rare. Sure, there might be a lot of biology out there, but even if millions of worlds are carpeted with life, how often will intelligent beings evolve? Many biologists point to the contingency and accident that litter the evolutionary road to Homo sapiens and suggest that we shouldn’t expect sentient species elsewhere.
Others maintain that our searches are inadequate or hopelessly naive. Is electromagnetic radiation really the best method for communicating across interstellar space? Or could there be far more effective methods of sending information around the galaxy, making radio and light the contemporary equivalent of smoke signals?
Adding to SETI’s uncertainties is the lack of funding. Precious little money is available for doing the experiments. In the United States, which has the longest history of such effort, all searches are privately financed—they run on donations. This has been true since Congress canceled NASA’s SETI program in 1993.
Yet despite the minimal funding and unpromising history, the search continues to garner both adherents and interest. Much of that is due to the potential payoff. Finding the aliens may be a long shot, but knowing that we share the galaxy with other sentience would change humanity’s outlook forever. We would know that what’s transpired on this planet—the emergence of life and intelligence—is something that happens often. The philosophical import of this could be compared to the Copernican revolution.
But there’s another reason why SETI adherents persist in seeking new monies and swinging their instruments skyward: The perceived likelihood of finding a signal is growing. This is due to advances in two areas: astrobiology research and the technology of SETI itself.
The first category includes the relentless discovery of worlds around other stars—the so-called exoplanets. When SETI began, there were no known planets outside our solar system. In the last 17 years, many hundreds have been discovered and confirmed. NASA’s Kepler telescope, whose task is to find planets that could be habitable, has already identified several thousand exoplanet candidates. The majority will prove to be true planetary worlds. Indeed, astronomers now contend that the vast majority of stars are accompanied by planets, implying that upwards of a trillion such worlds orbit stars in the Milky Way.
Within a few years, Kepler will tell us what fraction of these worlds is habitable. No one knows what that number will be, but even if the fraction is as small as one in a million (surely a conservative guess), that would imply there are a million worlds in our galaxy upon which life could blossom. It appears that there is plentiful real estate for life in the cosmos, a fact that increases the lure of doing SETI experiments.
In addition, the discovery of terrestrial organisms in extreme environments—the scalding waters at deep-sea vents, for instance—has demonstrated that biology is tougher than we thought and able to survive in habitats that would once have been ruled out for life.
The greatest incentive to continue the search is the increasing speed at which our SETI instruments can examine the skies and sift through the radio spectrum. Drake’s experiment, and most of the efforts that followed, could observe one star system at a time, a slow procedure. In addition, they could parse the dial only in small chunks—each chunk a few tens of megahertz wide, with a spectral resolution of between 0.1 and 1 Hz. (SETI traditionally looks for narrowband signal components, as those are the signature of transmitters, rather than natural noise emitters.)
Today, thanks mostly to ever-cheaper digital processing, both of these bottlenecks are being widened. With more computational clout, instantaneous bandwidths of hundreds of megahertz are now feasible, speeding up the search by a factor of two or more. Of possibly greater import, the use of antenna arrays in synthetic-aperture imaging mode could allow radio SETI experiments to investigate large tracts of sky quickly, rather than settling for the tunnel vision of past efforts.
I have mentioned only radio SETI searches, but so-called optical SETI, which hunts for very short laser pulses, is also poised to make a major leap in speed. Today, most optical searches use photomultiplier tubes to sense incoming photons. Although an old technology, photomultiplier tubes are both extremely sensitive and able to respond to nanosecond photon bursts. But photomultiplier-based instruments can look at only one star system at a time. New two-dimensional, solid-state detectors will eventually widen the field of these experiments and achieve an increase in search speed analogous to what’s currently being experienced by radio SETI.
The bottom line is that the bottom line could change. No, we haven’t found any signals so far, but there’s a growing incentive provided by new findings in astronomy and biology, and the instruments are getting better. Thirty-five years from now, we may really find a signal that will make us say “Wow!”
About the Author
Seth Shostak is senior astronomer at the SETI Institute in Mountain View, Calif. With degrees in physics and astronomy from Princeton University and Caltech, he has a long history of research in radio astronomy and, since 1991, in SETI. He is a frequent guest and commentator on radio and television and is the chair of the International Academy of Astronautics’ SETI Permanent Committee. In addition to his research, Shostak hosts the SETI Institute’s weekly science radio show “ Big Picture Science” and is the author, most recently, of Confessions of an Alien Hunter: A Scientist’s Search for Extraterrestrial Intelligence.