The SETI Institute has been around a while now, pointing radio dishes at stars and listening for signals of non-natural origin. If you've seen the movie Contact (at least, the first half hour or so), you get the idea of what they do—and also how funding, or scarcity thereof, figures into their work.
Trying to detect and discriminate the radio transmissions from a civilization in another star system is a bit like trying to hear a whisper from across a noisy room, hence the need for a sensitive listening device like the ATA. The ATA is an array of radio telescopes at the Hat Creek Radio Observatory in Northern California built to conduct high-resolution radio astronomy observations of cosmic events and objects, as well as to listen for the radio broadcasts of any alien civilizations that might be within hearing distance of Earth.
A couple of things make the ATA the most powerful tool in the search for extraterrestrial intelligence yet constructed. One is the collective size of radio dishes. Each dish isn't particularly large as radio telescopes go, but the plan is for as many as 350 linked dishes to make one giant radio "ear". Also, advancements in electronic and computing technologies give the ATA increased sensitivity and data processing speed .
While the question as to whether other civilizations (or life) even exist has not been answered, the ATA is capable of making the detection, particularly if such a civilization were in our stellar neighborhood…and frankly, this would be one of the greatest discoveries in all of history…
…but that's all on hold until a few million dollars of operating cash can be found.
ATA's hibernation came at a particularly unfortunate moment. As compelling as SETI's search was before, the recent discovery of over 1,200 candidate extrasolar planets (exoplanets) by NASA's Kepler mission has produced a list of highly desirable targets for the ATA. A number of the candidate worlds are of Earth-like stature, and a number of those dwell within their stars' habitable zones—potentially prime spots for life to have formed…and who knows, intelligence?
Should we actually hear the weak radio (or television!) signal of an extraterrestrial world—either inadvertent signal leakage, like ET's version of I Love Lucy, or a direct broadcast aimed at the cosmos with a message like "Hello out there!"—that would be a transformational day for the human race, the day we learn that there's not only life out there, but other intelligence, other thinkers. That would be a far bigger deal than discovering microbes on Mars….
So what would we hear? What would ET say? Would we be able to understand the language spoken? Would the discovery be any less monumental if we couldn't?
What we would hear from ET might be similar to what we'd say to her. Beyond the accidental leakage of our radio and television broadcasts, what would our message be? Hello, here we are. Anyone out there? Eh? Bueller? Bueller? But the nature of interstellar distances means we'd have to wait tens, or hundreds, or even thousands of years to hear any response to the query. It makes more practical sense just to listen….
As for ET hearing our own broadcasts, in the time since we started making them the "bubble" of transmissions has swept out through our stellar neighborhood, out to a distance of about 70 light years at this point, which encompasses hundreds of stars and, as we now know, hundreds of exoplanets….
Hopefully the hibernation of the ATA is only a temporary pause, and SETI will soon get back to the job of putting Earth's big ear to the candidate Kepler worlds and listen intently for that world-changing whisper….
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The Allen Telescope Array (ATA) at Hat Creek Radio