Such radio signals operate in a narrow band in a way that differs from natural radiation coming from molecules. Also, if the radio waves were coming from a planet that was revolving around a sun, the signals would appear to shift lightly.
Loeb and Zaldarriaga calculated that a facility such as the Low Frequency Demonstrator could detect Earth-like radio waves from 30 light-years away, a distance that encompasses about 1,000 of the nearest stars. A larger facility could theoretically detect signals from 1,500 light-years away, a distance that includes 100 million stars.
But just because the software picks up something suspicious doesn't mean it will have found another civilization.
It's possible that the observatory will record radio signals that appear to be coming from deep space, but in fact are Earth-generated waves that have bounced off the moon or have come from an unknown satellite.
"They could see a lot of false positives that are actually due to terrestrial sources," said Turner. "They will have to do a significant amount of work to reject those."
Another challenge will be in sifting through the huge of amounts of data in search of the artificial signal. "How much is it going to cost to adequately process the data coming out of these telescopes?" said Turner.
And what if, in the end, the signal is coming from deep space? According to Loeb, the brightest signals on Earth are generated by military radars.
"There is a cautionary remark," said Loeb. "The brightest civilizations out there could be militant." In that case, "we don't want to signal ourselves."
