Where are all the aliens? For decades, humans have searched for artificial signals, yet the skies above remain silent. But new research suggests that researchers’ investigations have so far not been particularly exhaustive; if the total possible search space were equivalent to the all the water in Earth’s oceans, we have examined only a hot tub’s worth of volume.
In many movies, the galaxy teems with intelligent life-forms who zip around on spaceships and produce other obvious signs of their existence. In reality, programs like the Search for Extraterrestrial Intelligence (SETI) have encountered no noticeable transmissions from another species. That lack of contact was first dubbed “the Great Silence” by sci-fi author and physicist David Brin in a classic 1983 paper in the Quarterly Journal of the Royal Astronomical Society.
“It is often said that we have been looking for 40 years or so, but we still haven’t found any signs of extraterrestrial civilization,” said Shubham Kanodia, an astronomy graduate student at Penn State University and co-author of the new paper in the preprint journal arXiv, which has been submitted to The Astronomical Journal. “We wanted to see how much have we looked and how much more do we need to look.”
Researchers see radio telescopes as an obvious instrument to use for such investigations, because radio waves travel easily through interstellar dust and, in certain parts of the radio spectrum, background interference is minimized. “It is the ‘cosmic quiet zone’ where we can best listen for a faint whisper across the interstellar expanse,” as an article on the SETI Institute’s website puts it.