Looking for aliens in all the wrong places

So why hasn't SETI, the Search for Extraterrestrial Intelligence, heard any alien radio signals yet, ask the report authors? The question is best known as "Fermi's Paradox," first posed by physicist Enrico Fermi in 1950, when he asked, "Where are they?" Even a modestly sophisticated alien species could likely colonize every star in the galaxy within 10 million years, Fermi reasoned, based on technologies understood more than half-a-century ago. Ever since, Fermi and his successors have been asking why we haven't heard from any aliens yet.

An artist?s impression of a unique type of exoplanet discovered with the Hubble Space Telescope. A study suggests that such sun-centered planets are the wrong place to look for alien life.

SETI has long searched for signals from aliens in radio transmissions. The focus has been on nearby sun-like stars, which may have life like our own, says astronomer Seth Shostak of the SETI Institute in Mountain View, Calif. The effort has been privately funded since 1994. So far, no alien signals, which some argue calls for a change in direction.

"The need for such reassessment is fueled not only by the failure of SETI thus far, but also by great advances recently made in astrophysics, astrobiology, computer science and future studies," say the New Astronomy report authors. One reason for the failure, they contend, may be that we are looking for the wrong aliens in the wrong part of the galaxy. Just like humanity today, any reasonably intelligent aliens will quickly develop and become dependent on computers, or "machine intelligence," they argue, following a suggestion made by science historian Steven Dick in 2003.

That matters, because, "as almost anyone having practical experience with computers will have experienced, heat is an enemy of computation," they note. So, they argue, since the stars where these computer-dependent aliens arose will slowly be burning up (our sun will turn into a red giant in 5 billion years, for example), the places where extraterrestrials will slowly migrate to, and perhaps build space colonies, is the place where computers are most comfortable. That would be in the cold depths of space at the edge of galaxies, far from the fiery stars.

SETI, Cirkovic and Bradbury charge, is "fundamentally flawed" because it looks for signals from aliens from nearby sun-like stars. "Outward migration of advanced technological species should be taken into account in future practical SETI projects," they write. "The true test here would be to detect signs of astro-engineering efforts at the outskirts of nearby spiral galaxies."

Shostak, of the SETI Institute, agrees that intelligent aliens likely are dependent on computers, or are computers themselves. But the assumption that computational efficiency will drive aliens ever outward, overriding any other goal, is a big one, he says. "It's a clever idea, but more than likely to be wrong."

After all, finding some place cold in space to do computations isn't the biggest problem that aliens will likely face, he says, compared to the energy lost in migrating outside the galaxy. Besides, "who knows what will motivate alien machines?" he asks. "Our knowledge of alien sociology is pretty sparse."

On a more practical level, the challenge for SETI astronomers is the simple fact that radio signals get weaker as they get farther away, limiting how many places we can actually listen to. Our galaxy's edge is loosely at least 25,000 light years away (one light year equals about 5.9 trillion miles), making radio signals from there quite faint.

The real problem is that the Milky Way galaxy contains several hundred billion stars, Shostak adds, so even looking at a million stars constitutes a search of only a tiny fraction of possible homes for aliens. And actually only about 800 nearby stars have been carefully listened to in recent SETI searches, making it a needle-in-the-haystack deal. "It all depends on your guess of the number of broadcast locations in the galaxy," Shostak says. Astronomer Frank Drake, one of SETI's founders, estimated that perhaps 10,000 alien species live in the Milky Way. "That means you have to look at a few million stars to have a reasonable chance," Shostak says.

Still, Shostak says that SETI would be happy to try looking. One thing they likely won't try is broadcasting messages, he says, because the speed of light puts a limit on how fast you can converse. Given that the nearest aliens might be 1,000 light years away, even if we are lucky, "that's long time to wait to hear back 'huh? could you repeat that?'," he says.