To date, SETI (Search for ExtraTerrestrial Intelligence) has focused on ETs who 'phone home' using the radio part of the electromagnetic spectrum, and even a very small region within that.

But what if ET's phone doesn't use radio waves? Sure the xkcd comic, is funny, but maybe it points to a deep flaw in our attempts to contact, or hear from, an ETI?

When Giuseppe Cocconi and Philip Morrison suggested the possibility of interstellar communication via electromagnetic waves in a 1959 paper in Nature, only radio was feasible, as we then had the ability to detect only artificial radio signals, if produced by ETIs with 1959 human technology. Since then we've developed the ability to detect a laser signal, brighter than the Sun (if only for a nanosecond) if it came from a source several light-years away … but lasers weren't invented then.

What might ET's equivalent of ants' pheromones be?

Back in 1959 if you'd said that the Earth would, within a mere half century, started to go 'radio quiet', not many people would have taken you seriously. Yet that's exactly what's happened! Free to air (FTA) broadcasting, especially for TV, is being replaced by TV delivered over coaxial cable, optical fibers, or even the phone company's twisted copper pairs. And where it's continuing, as in satellite TV broadcasting, its power has dropped (today's digital formats are more efficient than the old analog ones). Military radars, the brightest source of artificial radio waves by far, no longer broadcast in a single channel, but hop, rapidly, from frequency to frequency, to avoid jamming.

"Our improving technology is causing the Earth to become less visible," says astronomer Frank Drake, SETI’s paterfamilias. "If we are the model for the universe, that is bad news."

full article - http://www.universetoday.com/2010....g-phone