An Alien Signal: Being Sure

Apr. 06, 2001

by Seth Shostak - Senior Astronomer

If extraterrestrials are out there, signals that would prove their existence are cascading over your body right now. Needless to say, you dont notice. The challenge for SETI researchers is to build an instrument that will. Rising to the challenge, the SETI Institute and others are developing new search strategies and telescopes, encouraging some scientists to speculate that a signal detection will occur in the next decade or two.

If that happens, then the "Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence" analyzed by Doug Vakoch, SETI scientist, will give general guidance regarding what the discoverers should do.

Its important to understand that we could easily trip over ETs signals without immediately knowing we have done so.

Radio SETI observers look for narrow-band emissions, similar to the carrier signals used for radio and television. These are the pure-tone squeals which your receiver uses to capture the attention-grabbing aspects of the broadcast, namely the sound or picture (the accompanying figure shows that a TV signal actually has two of these carriers, one for video and another less powerful for audio.)

Carriers are commonplace, but theyre not the only way to transmit. Your cell phone uses another technology, known as spread-spectrum, which is carrier-free. Spread-spectrum techniques, while useful for minimizing interference when lots of transmitters are present, is a wasteful way to make your presence known. It takes more power, and requires that both transmitters and receivers agree in advance on the method of encoding information.

If extraterrestrials wish to get in touch with distant, unknown beings that wont have access to alien technical manuals, then narrow-band signals make a lot more sense. They put all the transmitter power into a tiny spot on the radio dial, easing the task of discovery.

Unfortunately for SETI researchers, narrow-band signals on Earth are as ubiquitous as bathroom hair. When Project Phoenix is operating at the Arecibo Telescope, we pick up signals every few seconds. Checking them out involves reference to a large database of known terrestrial interference, observations by a second telescope and simple (but time-consuming) procedures that include nodding the telescope back and forth across the sky. SETI data are subject to more tests than a high school senior.

But suppose a signal survives this grueling gauntlet? Will the SETI scientists order a few thousand doughnuts and invite the media over? No. Reality is not entirely unlike the movies. In a 1996 film The Arrival, Charlie Sheen sees a blip on his oscilloscope, figures its ET on the line, and excitedly pulls a copy of his detection protocols off the shelf; total elapsed time: maybe three minutes.

In truth, any SETI researcher, who felt they had found a signal from light-years away, would let the protocols temporarily remain on the shelf. Instead, they would call up astronomers at another telescope and ask them to stop whatever theyre doing and verify the signal. Independent verification eliminates the possibility that the suspected detection is an unknown hardware bug -- or even an elaborate student prank (which would have to be very elaborate!).

The process would take a few days, and the number of people involved would be roughly double that of the original discovery team. In fact, it is possible that several observatories spaced around the globe would be asked to help with the confirmation, since the star system under scrutiny could be lost to view for 12 hours or more. The research horde actively looking for the signal would number in the dozens. The chance that their efforts could somehow be kept under wraps is nil. As Poor Richards Almanac so succinctly put it, "Three people may keep a secret, if two of them are dead." These folks arent dead.

Indeed, by this stage, theres every reason to expect that the news would be out. The less reputable media would be screaming the story in a font big enough to read from the next county. The SETI scientists would downplay this premature buzz, as they methodically proceed with verification. After perhaps a week of effort if the signal persisted they would order the doughnuts and hold a press conference to announce the discovery of the millennium.

Of course, they will be behind the curve. As with so many recent science discoveries, the probable nature, consequences and implication of the story would already have been spread far and wide. Other scientists people not directly connected with the SETI search would have been cajoled by the media into an orgy of speculation and debate. The world will know even before the initial detection has been fully verified that we are but one speck of foam on a vast, cosmic sea.