Hollywood may have had extensive communication with aliens in the movie Contact, but University of California, Berkeley researchers report that the most sensitive search for extraterrestrial radio signals ever conducted has turned up no evidence of anybody trying to call Earth.
The Berkeley survey, called the Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations, analyzed more than 500 trillion signals over the last six years, but found no pattern suggesting the signals came from an intelligent outer space source.
Airieau said the survey focused in part on nine stellar objects thought to be extrasolar system planets, but there were no recognizable, intelligent signals.
Dan Werthimer, co-director of the project, said that doesn't mean there aren't civilizations somewhere out there. He said the ET radio searches are covering only a small part of the total radio spectrum.
The Berkeley effort uses a detector mounted on the world's largest radio telescope, the dish at Arecibo, Puerto Rico. The searchers have no control over where the telescope is pointed, but wherever it looks they listen for signals.
Listening for intelligent radio signals is a growing activity, despite a congressional decision a few years back not to spend federal money on the project. Other ET searches are being conducted by the Search for Extraterrestrial Intelligence Institute, which was once funded by NASA, and by teams at Harvard University and Ohio State University.
The searches are also increasing in sophistication. A new Berkeley system will sample 168 million radio frequencies every 1.7 seconds. The signals are analyzed by computer immediately and certain signals are separated out for later analysis.
About a third of the sky is scanned every six months.
They are looking for repeating signals, such as those from a radio beacon.
Experts hypothesize that if a signal were detected, it would most likely come from an advanced civilization that was sending the signal intentionally, and not from an extraterrestrial version of the random "leakage" from ordinary radio and television communications on Earth.
The space radio survey equipment cannot pick up such random signals, Airieau said.
"The first civilization Earthlings detect is likely to be more advanced than ours -- perhaps 10,000 to billions of years old," Werthimer said.
Listening for a signal that may never come takes great patience, said Airiea.
"Sometimes it is really exhilarating," she said. "But it can be really disappointing."
She's not giving up.
"This is very worthwhile," said Airieau, noting that listening for ET addresses one of the basic cosmic questions: Are humans alone in the universe?
Written by Paul Recer
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