Researchers at SETI (the Search for Extraterrestrial Intelligence) might be looking for the wrong thing, says one of SETI's astronomers in The Guardian. They're looking for aliens that are like us. Seth Shostak explains that although scientists hunting for alien radio transmissions "don't really insist that the guys behind the microphone be either gray or glabrous" like Hollywood's anthropomorphized E.T., "they do--implicitly--assume that they've evolved on a world that, like Earth, is wrapped in oceans and an atmosphere. In other words, that the aliens are biological."

Why would we be looking for non-biological aliens? Well, argues Shostak, since we're already drawing on the experiences of life on our own planet to look for life elsewhere, we might as well take the full lesson from planet earth:

We are now building digital devices that can process information at blistering speeds. Our computers double in capability on timescales of only a few years. It's hardly outrageous to believe that we will successfully develop thinking machines within a handful of decades, or at most a century or two.

In other words, our self-improving machines might become the new space travelers. That leads to the following extrapolation:

If any species reaches the point of inventing radio, it is only a handful of centuries from inventing its intellectual successors. Biological intelligence is merely a short stepping stone on the path to the prodigious talents of machines. Consequently, the majority of the intelligence in the universe could well be artificial intelligence.

The conclusion? We should be looking for machines.