In the thrilling search for extraterrestrial life, most scientists are going small, looking for things like complex organic molecules or maybe even microbes, but some are thinking big and are trying to find evidence for other highly advanced civilizations throughout the universe. Unfortunately for us, it seems that endeavors by scientists going for the latter have proved fruitless so far, as a team of astronomers have come out empty handed after scouring a whopping 100,000 galaxies.

But let’s not get down in the dumps: NASA reckons we will find signs of alien life within a decade, and the Curiosity rover just found evidence of liquid water on Mars. And rather than giving up at the first hurdle, scientists are using this as motivation to focus on improving our instruments so that we have a better chance of finding something, should it be out there.

For the current investigation, astronomers used data collected over time by NASA’s WISE orbiting observatory, which is designed to detect mid-infrared wavelengths. This stems from a hypothesis proposed back in the ‘60s by theoretical physicist Freeman Dyson that suggested that advanced extraterrestrial civilizations could be picked up by their waste heat, which would be detectable as infrared radiation.

“Whether an advanced spacefaring civilization uses the large amounts of energy from its galaxy’s stars to power computers, space flight, communication, or something we can’t yet imagine, fundamental thermodynamics tells us that this energy must be radiated away as heat in the mid-infrared wavelengths,” explains research leader Jason Wright. “This same basic physics causes your computer to radiate heat while it is turned on.”

After ploughing through a database of close to 100 million entries, lead study author Roger Griffith from Penn State identified 100,000 promising galaxies. Scientists then had the agonizing job of scrutinizing each of these to look for the best candidates, which narrowed the list down to 50 that seemed to be emitting abnormally high levels of mid-infrared radiation. Unfortunately, further investigation failed to find any convincing evidence that any of these galaxies were inhabited by advanced alien civilizations.

But this doesn’t mean that alien civilizations aren’t out there, or that we should stop looking. As theoretical physicist Avi Loeb points out to The Huffington Post, it’s possible that some use significantly less energy than suggested by Dyson, which would make them hard to detect.

“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 explains. “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.”

[Via Penn State and Huffington Post]