Our "local" galaxy contains about a hundred billion stars. We see only a few thousand of the closest as actual points of light, though millions of others merge into a broad and diffuse glow that we notice on clear nights and call the Milky Way.

A hundred billion is such a big number that it's hard to have a real feel for it, so let's put it this way: there are enough stars in our galaxy for every human on earth to own sixteen apiece. Not only that, our galaxy is just one of the hundred billion galaxies that make up the known universe. If humans owned the whole cosmos, each of us could lay claim to more than a trillion stars. That's the astronomical equivalent of everyone being owed the National Debt, with each star and its planets priced at about a dollar.

Of course, there's a big "if" in there. We can only claim the universe if no others are out there to stake counterclaims and assert property rights. Which leads to the big question: Are there other living beings in the universe, at least as intelligent as we are; or are we the only smart, self-aware objects in creation? As the late Walt Kelly remarked, long ago, either way it's a mighty sobering thought.

Some people insist that intelligent aliens in the universe have appeared right here on Planet Earth, occasionally taking selected individuals for a space ride but otherwise keeping a low profile. I am not in that group of believers. I can't see why anyone would bother to travel such gigantic distances and then remain in hiding. The idea that aliens have actually crash-landed in remote parts of the country, and had their presence covered up by the government, has even less appeal. If anywhere, Washington, DC, is the place to look for aliens.

Let's take another approach. We have a rough idea of the total number of stars in all the galaxies. How many of those stars have planets? Ten years ago we had no direct evidence of any, but today some new planet around another star is discovered at least once a month. Suppose, then, that only one star in a thousand has a planet around it - a very low estimate. That still gives us a hundred million planets as candidates right here in our own galaxy. If just one percent of those can support life, a million other worlds have living things on them.

The next step is the hardest one. If a world has life, what are the chances that one of those living creatures will develop intelligence and technology, enough to build a starship, or at least to send out a signal to us?

We don't know. Let me state that more strongly: we have not the slightest idea. But we can listen, and we do, for evidence of alien existence. We listen not with sound waves, but with radio waves. For the past forty years, a search for extraterrestrial intelligence (SETI) program has been carried on in this country and around the world. Using radio telescopes capable of picking up the tiniest trickle of energy, we eavesdrop on the sky and hope to discover the organized series of pulses that would announce the presence of other thinking beings.

So far we have found nothing. This is sometimes called the Great Silence, sometimes the Fermi Paradox (the physicist, Enrico Fermi, asked the simple question, "Where are they?"). On the other hand, forty years of listening is no time at all in a universe at least ten billion years old, particularly since the SETI program is run on a shoestring. It has no government funding. It is paid for and operated by people who believe that a positive result to the search would change the way we think about everything.

Speaking for myself, I would just love to change the way we think. For instance, if we were willing to spend as much money listening to the stars as we do on, say, land mines, we might detect and decipher that world-altering message from the sky.

Are we alone in this galaxy, as an intelligent life form? It is hard to imagine a more profound question. I'd gladly give up any claim to the trillion-plus stars that represent my share of the universe, to know the answer.

And while I'm at it, I'll gladly give up my share of land mines.

Note: If you own a personal computer and a modem, you can become directly involved in analyzing radio data that may contain evidence of alien signals. Contact me if you would like to know how. (or you can hit the "Setiathome" link on our homepage. - Fenrir)

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