Image: Arecibo telescope
The receiver at the Arecibo radio telescope in Puerto Rico looks down through the 1,000-foot-wide dish. The reflecting aluminum mesh is riddled with small holes, making it semitransparent.
By Alan Boyle Science editor
msnbc.com

The debate over extraterrestrial intelligence is a strange one: Even a searcher concedes that aliens may be astronomically rare. But even a skeptic concedes that the search has to be undertaken. Why? Because the payoff could be astronomically great.

The search for extraterrestrial intelligence took center stage on the last day of this week’s “Cosmic Questions” conference, presented in Washington by the American Association for the Advancement of Science.

Friday afternoon’s big debate pitted Seth Shostak, public programs scientist for the SETI Institute (and a sometime MSNBC contributor), against Irven DeVore, curator of primatology at Harvard’s Peabody Museum of Anthropology. The topic: Could there be intelligent life beyond Earth? Even before DeVore articulated his doubts, he conceded that the search for alien signals had to go on.

“We must listen,” he said. “However unlikely I think the chances are that there will be anything responding to us, we obviously must try — because contact with extraterrestrial intelligence would be such a momentous thing in the history of this planet, it’s hard to even imagine. Everything else would pale into insignificance,” he said.

The 40-year-old concept behind the search for extraterrestrial intelligence, known as SETI, should be familiar to anyone who’s seen the movie “Contact” or read the book. In a nutshell, observing instruments scan the skies for electromagnetic signals that stick out from the random noise of space. Congressional critics blasted the idea as a search for “little green men” and succeeded in cutting off federal funding for SETI in 1993. But several groups, including the SETI Institute, use private funding to continue the search in the radio spectrum, and more recently in the optical spectrum as well.

The case against
DeVore began his argument with an unusual concession: Instead of questioning whether extraterrestrial life of any form was possible, he said “there’s been enough evidence of amino acids or nucleic acids in cosmic dust that probably life can get started on any ameliorative planet, depending on how you define that.”

However, he was more skeptical that intelligent life, or life forms amenable to SETI contact, could develop on other planets. In setting forth his case, he traced the multibillion-year series of evolutionary contingencies that allowed humans to inherit the earth, including mass extinctions that over time wiped out 99.9 percent of Earth’s species. A slightly different outcome at any point along the way could have left dinosaurs or rats, monkeys or other species in charge today — with no need for radio telescopes or computers.

“There is absolutely nothing inevitable about the evolution of intelligence,” he said. To his mind, it was almost inconceivable that another species on a distant planet could follow an evolutionary course similar enough to build radio transmitters. Thus, he said, “our chances for communication with other creatures in the universe are vanishingly small.”

The case for 
Shostak conceded that the rise of intelligent life was not inevitable, but insisted that “brain power does have survival value.”

“If intelligence gets started anywhere, then the kinds of catastrophes that several of the speakers today have talked about are less likely to wipe out the intelligent beings than some of the others, because they can defend against them,” he said.

He also noted scientific commonalities that were being discovered in widely separated regions of the universe, including the apparent plenitude of planets. “We’re tending toward the point of view that there may be such a thing as universal biology, in the same way that we have universal physics, or universal chemistry,” Shostak said.

Shostak said he was willing to at least momentarily grant DeVore’s premise that intelligent civilizations arose relatively rarely. “I maintain that we could still find the universe rife with intelligence, with sentient entities,” he said.

Even if intelligent beings developed on just a tiny fraction of the planets orbiting other stars, the fact that there were more than 100 billion stars in our Milky Way Galaxy alone tended to even the odds, he said.

But can intelligent life survive long enough to achieve contact? Shostak admitted that the prospects sometimes look grim, due to environmental degradation, international strife and the nuclear threat.

“We’re going through a bottleneck that will last 100 or 200 years,” he said.

If earthlings can survive that much longer, he said, they should be able to establish settlements on asteroids, the moon and other worlds. Once that happens, humanity could outlast even a planetwide catastrophe.

The big finish
Even further in the future, Shostak said humans just might be able to engineer “silicon life”: long-lived, artificially intelligent probes that would spread out through the galaxy. Indeed, the first contact could come from similar alien-made machines rather than biological life forms, Shostak said.

In closing, Shostak employed a bit of intellectual jiu-jitsu worthy of a “Star Trek” plot:

“Not finding the aliens doesn’t settle this debate,” he said. “In fact, the only way to settle this debate is to find something. In other words, this debate is asymmetric, and my position alone can be proven right. I mean, I may not win, but my opponent cannot win.”

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