Just how realistic is it to believe that humans will someday find evidence of extraterrestrial life?
NASA's chief scientist recently predicted that we'd find signs of life beyond Earth within a decade or so, but a new study by researchers at Penn State -- one of the most exhaustive of its type -- isn't very encouraging.
After surveying tens of thousands of galaxies surrounding our own Milky Way galaxy, the scientists turned up no sign of advanced alien civilizations.
"These galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist," Dr. Jason T. Wright, an assistant professor of astronomy and astrophysics at the university's Center for Exoplanets and Habitable Worlds and one of the researchers, said in a written statement. "Either they don't exist, or they don't yet use enough energy for us to recognize them."
Turning up the heat. For the research, Wright and his colleagues analyzed a vast catalog of observations made in 2010 by NASA's Wide-field Infrared Survey Explorer (WISE) space telescope. The team looked at the heat emitted by the 100,000 "most promising" candidates of the all-sky catalog's nearly 100 million entries.
"The idea behind our research is that, if an entire galaxy had been colonized by an advanced spacefaring civilization, the energy produced by that civilization's technologies would be detectable in mid-infrared wavelengths -- exactly the radiation that the WISE satellite was designed to detect for other astronomical purposes," Wright said in the statement.
The hypothesis that advanced civilizations could be recognized by their waste heat was first put forth by renowned theoretical physicist Freeman Dyson in 1960, according to Space.com.
Time to give it up? Despite his negative findings, Wright said his study, published April 15 in the Astrophysical Journal Supplement Series, was "just the beginning," and that further research may yet turn up evidence of alien technology.
And other experts involved in the search for extraterrestrial intelligence (SETI) told The Huffington Post that they're far from discouraged.
Dr. Avi Loeb, a theoretical physicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., told HuffPost Science in an email that it's possible alien civilizations are hard to detect because they use much less energy than Dyson proposed.
"The limits reported in this study rule out the most extreme environmental impact possible for an extraterrestrial civilization that harvests a significant fraction of the starlight in its host galaxy," he said. "For comparison, our civilization processes only a thousandth of a trillionth of the energy output of the sun. Less visible civilizations are much more likely to exist, both in terms of the technological feasibility of energy harvesting as well as in terms of their energy needs."
Legendary astronomer Dr. Jill Tarter, the former director of the Center for SETI Research in Mountain View, Calif. and the astronomer on whom Jodie Foster's character in the 1997 film "Contact" was loosely based, agreed that efforts to find extraterrestrial life should continine.
"It's absolutely not time to stop," she told The Huffington Post in an email. "It's time to improve the sensitivity and specificity of these searches to be able to discriminate between signals produced by Mother Nature and those produced by engineers."