The Great Silence: Why Can't We Find Alien Life?

News and commentary about environmental issues.
Nov. 28 2011 12:05 PM

The Great Silence

E.T. is out there. Why can’t we find him?

The Earth from space.
Researchers have been scanning the stars in hopes of picking up a signal from another civilization for over 50 years

Photograph by Digital Vision.

This is the first half of a two-part article on Earth's legacy and the search for extraterrestrial life. Read Part 2 here.

In 2002, a professor at the University of Hertfordshire set out to determine the world’s funniest joke. With help from the British Science Association—that bastion of comic authority—he set up a website where people could submit and vote on the entries.

The first runner-up, which only narrowly missed the laurels, was a joke about Sherlock Holmes and Watson on a camping trip. There are a few variations, but it basically goes like this:

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Sherlock Holmes and Dr. Watson are going camping. They pitch their tent under the stars and go to sleep. Sometime in the middle of the night, Holmes wakes Watson up and says: “Watson, look up and tell me what you see.”

Watson replies, “I see millions and millions of stars.” 

“And what do you deduce from that?” Holmes asks. 

Watson replies: “Well, if there are millions of stars, and if even a few of those have planets, it’s quite likely there are some planets like earth out there. And if there are a few planets like earth out there, there might also be life.” 

To which Holmes responds: “Watson, you idiot, somebody stole our tent!”

Watson, ever Holmes’ warm-blooded foil, has touched on the elementary reason why a handful of researchers have, for more than 50 years, been scanning the stars in hopes of picking up a signal from another civilization. More formally, you might say there are three arguments for the abundance of life in our galaxy and beyond. First, as Watson said, among the 200-some billion stars in the Milky Way alone, there must be a large number of hospitable planets. (In fact, we’ve already found a few dozen.) Second, nothing about our own existence suggests we are unique. And third, life forms can survive in the most treacherous of environments. If it could happen here, in other words, it could happen anywhere.

It takes a Watson to believe so much in the possibility of extraterrestrial life that he'd be willing to devote both time and money to searching it out. It’s the Sherlocks who have to sign the checks, though. Earlier this year, the SETI Institute—that’s “Search for Extraterrestrial Intelligence”—went dark after California slashed funding to the Allen Telescope Array that SETI uses to scan the skies for signals from other civilizations. (The SETI Institute, already in large part privately funded, was able to raise enough money to reopen in August.) It’s a familiar setback. NASA spent four years preparing the equipment for a major 10-year search that began in 1992. Congress cancelled the program in 1993, prompting many of the scientists working on that project to join the SETI Institute.

With its telescopes back online, 2011 is looking like the beginning of a golden age in alien hunting. In previous decades, SETI efforts were horribly inefficient, and consisted of pointing telescopes at nearby stars and briefly listening in for any signals that might suggest the presence of an advanced species. Now that NASA’s Kepler spacecraft has begun to identify planets elsewhere in the galaxy—so far it has found 1,200 of them, of which 54 look like they might have friendly conditions to support life—SETI will home in on these Earth-like bodies in a much more targeted approach. Though the White House has lately denied having any evidence of extraterrestrial intelligence, the odds of finding an alien civilization out there are about to increase immensely.

How immensely, though, is anyone’s guess, because there is one troubling problem with the search for radio emissions from other civilizations that no number of spacecraft or radio telescopes can resolve. Say, for example, that Kepler were to discover a very Earth-like planet 450 light years away—one capable of holding liquid water and all the other things that, by our present definition, are essential for life. So we tune our (privately-funded) radio telescopes at this star system. At this point, we’re listening for an activity that might have been going on there in the Earth year 1561. In order to detect anything, then, the civilization that exists on this planet has to be at least 400 years ahead of ours. (Likewise, if they were to turn their telescopes on us, they wouldn’t hear a thing, since no man-made signals were escaping out of the Earth's atmosphere in the 16th century.)

It’s perfectly possible that our fantasy civilization would be 500 years ahead of us—but no more likely than its being 500 years behind us, or 1 billion years behind, or awaiting us 1 billion years in the future. The universe is about 13 billion years old, and Earth’s arrival on the scene 4.5 billion years ago did not occur at some divine moment of planet formation. It’s possible that this other, Earth-like planet was at one point dotted with thriving alien cities, that it sustained an intelligent species for millions of years, but that life there winked out at around the same time we humans were working out the kinks in having opposable thumbs. If so, our neighbor’s dying signals would have passed us by millennia before we could invent the radio dishes to capture them.