Waiting for a sign

BY MICHAEL D. LEMONICK

WHEN THE SUBJECT OF extraterrestrials comes up in polite conversation, any scientist whose lonely life’s work is listening for distant radio signals often has to deal with what Seth Shostak of the SETI Institute calls the “giggle factor.” And to be fair, amid a backdrop of The X-Files and The Twilight Zone and conspiracy nuts convinced the Air Force has aliens on ice in Area 51—not to mention those who figure visitors from space must have built the pyramids—even learned men can begin to sound ridiculous. Besides, no one has heard or seen anything so far, have they?

Yet whether life exists on planets other than ours is a scientific and philosophical issue of real import, its pedigree far older than many realize. As early as the sixth century B.C., the Pythagoreans—mathematically inclined philosophers (in other words, serious Greeks)—thought the moon hosted lush plant and animal life. In the 15th century A.D., German astronomer Nicholas of Cusa suggested that many “stars and parts of the heavens” are inhabited. In 1600 the Italian Giordano Bruno was burned at the stake for, among other things, saying, “The countless worlds in the universe are no worse and no less inhabited than our Earth.” And astronomer William Herschel (1738– 1822), discoverer of Uranus and inventor of many modern astronomy techniques, believed that the moon, Mars and even the sun were home to sentient beings.

Sure, even smart people can be very wrong. Still, by the late 1800s, the notion that other planets in our solar system were home to life of one sort or another was more or less mainstream, egged on by Giovanni Schiaparelli, an Italian astronomer who uncovered what seemed to be visual confirmation. Peering through his telescope at Mars, he made out ruts that crisscrossed the planet. “Canali,” he called them—channels—which he incautiously interpreted to be waterways dug by Martians to support their agriculture.

Soon after, Boston aristocrat Percival Lowell sank much of his wealth into building a private observatory in Arizona. He saw the canals too, and because of his man-of-letters reputation—not only did he go to Harvard, his brother was its president—his findings were trumpeted as fact.

They weren’t, of course. The canals were an optical illusion, the result of too much squinting through a too-weak telescope. And in the aftermath of Lowell’s public humiliation, all talk of alien life was avoided by the scientific community for decades, consigned to fiction writers such as H.G. Wells and Edgar Rice Burroughs.

The rationally curious couldn’t stay gun-shy forever, though. For many, the idea that life is unique to a single location in a universe billions of light-years wide seemed just too far-fetched. And in 1959, in a paper published in Nature, the Cornell University physicists Philip Morrison and Giuseppe Cocconi argued that “near some star rather like the sun there are civilizations with scientific interests and with technical possibilities much greater than those now available to us.” It would be foolish not to search for the inevitable signals of these civilizations. “The probability of success is difficult to estimate,” they wrote, “but if we never search, the chance of success is zero.”

Search parties were quick to convene. From the start, scientists were resigned to the fact that advanced alien civilizations, if they existed, would be the rarest form of life in the cosmos. Evolution, the thinking went, doesn’t necessarily progress in a particular direction. Single-celled organisms are almost certainly the first step, but what happens after could vary wildly, depending on local conditions. On Earth, it took some 2 billion years for single cells to evolve into multicellular organisms. On another world, it might take much longer, or it might not happen at all. On Earth, mammals began to flourish only after the dinosaurs were wiped out by an asteroid. But had that asteroid scooted by our planet instead of smashing into it, giant lizards might still be dominating the land.

So astrobiologists are thinking small, figuring the first extraterrestrial life they find will be simple, bacteria-like organisms, just because they’re likely to be the most common specimens. Maybe they’ll be in the soil of Mars or the subsurface oceans of the moons Europa (Jupiter), Enceladus (Saturn) or Ganymede (Jupiter). Maybe we’ll know them only by their waste gases circulating in the atmosphere of a distant exoplanet.

Then again, maybe an ET radio signal or laser beam is even now racing toward us at light speed. So don’t be surprised if the millennia-old question of whether we’re alone is resolved in the next decade or two by a new army of telescopes, probes and rovers. Unless, of course, it is answered with an electromagnetic ping the day after tomorrow.