Alone in the universe? There may be no advanced life but us.(extraterrestrial life)

As a long-time devotee of science fiction, I have always been excited by the possibility that mankind might encounter extraterrestrial life. But I have always tried to apply the rules of logic and reason to those prospects. And it is becoming increasingly clear to me, and others, that merely wanting to believe is not enough.

As our observation methods have improved, we've learned that somewhere on the order of 20-50 percent of all stars have planets orbiting them. We have no idea whether life-friendly planets are common, or what the chances are that life, much less intelligent life, exists on such planets, but if we assume that there is nothing special about our own solar system, we come up with some pretty optimistic numbers. Astronomers Frank Drake and Carl Sagan suggested that there could be 10 million civilizations as advanced as or more advanced than us in the galaxy today.

Such a theory, however, begs an important question, one raised by Italian physicist Enrico Fermi way back in 1950. He turned to his lunch partners at Los Alamos, who included Edward Teller, and asked simply, "Where is everybody?" If intelligent, communicating life is common, why haven't we seen evidence of it? After all, if the formation of civilizations has been fairly constant through the long life of the universe, then there should have been billions of them by now.

While the galaxy is a big place, it's also been around for a very long time, more than long enough for intelligent life to have placed signs throughout the galaxy. Los Alamos physicist John von Neumann calculated that self-replicating probes traveling at one fortieth the speed of light could spread through the entire galaxy in just 4 million years. That may sound like a long time, but the universe is more than three thousand times older than that, so there has been ample time for intelligent life to show itself if it exists outside our miraculous planet.

Even if every single other civilization that has existed over the vast life of our galaxy had chosen not to send out probes, we should still be able to pick up their traces. Most physicists who have studied the issue agree that if civilizations want to be heard, then we have the capacity to detect their most likely means of sending out signals.

But in 40 years of searching, we have detected no such signal. In 1967, we thought we had one, but that turned out to be the entirely natural signal of a pulsar. Ten years later, the Ohio State University Big Ear observatory detected a 37-second burst of activity that prompted astronomer Jerry Ehman to write, "Wow!" in the signal's margin. Yet attempts to find the Wow signal again have been unsuccessful; it seems likely now that it came from the mundane source of a manmade earth satellite. Yet the skies are vast, and there's a lot of material out there. So radio observatories are using the dispersed computer power of millions of interested PC owners who have agreed to let software run on their computers during down times to search for artificial signals. In six years, all those millions of computers have come up with just one candidate, a signal named SHGb02+ 14a, with a frequency of 1420 megahertz, which has important ties to the element hydrogen. This makes it a good candidate for being artificial, because signals tied to the laws of physics or mathematics are much more likely to be understood by an alien civilization than anything else. Even so, the SETI astronomers are not optimistic. It comes from a point in space with no star system within 1,000 light years. "We're not jumping up and down, but we are continuing to observe it," says Dan Werthimer, a University of California radio astronomer.

We are therefore led to the uncomfortable conclusion that there may be something wrong with the assumption that life can exist in numerous other places. Perhaps our solar system is not average at all. Perhaps life-friendly planets are rare. That is the conclusion of University of Washington scientists Peter Ward ...