Scientists have searched 100,000 galaxies for signs of advanced extraterrestrial life, and come back empty-handed. Using NASA's WISE satellite, the researchers were looking for energy signatures that would suggest the use of advanced alien technology elsewhere in the Universe.

"The idea behind our research is that, if an entire galaxy had been colonised by an advanced spacefaring civilisation, the energy produced by that civilisation's technologies would be detectable in mid-infrared wavelengths - exactly the radiation that the WISE satellite was designed to detect," lead researcher Jason T. Wright, an astrophysicist at Penn State University in the US, said in a press release.

It sounds a little whacky, but the physics is solid - if a clever alien society has worked out how to harness the energy from its galaxy's stars and is using it to power technology, such as space flight, communication, or something beyond what we can imagine, then we should be able to detect it.

"Fundamental thermodynamics tells us that this energy must be radiated away as heat in the mid-infrared wavelengths," explained Wright in the release. "This same basic physics causes your computer to radiate heat while it is turned on."

The hypothesis that we can detect advanced civilisations by their energy emissions was first proposed in the 1960s by theoretical physicist Freeman Dyson, but it's only recently that we've had technology to help us do this. To search for these heat signatures, Wright and his team scoured nearly the entire catalogue of the WISE (which stands for Wide-field Infrared Survey Explorer, by the way) satellite's detections - almost 100 million entries - for any sign of galaxies emitting more mid-infrared radiation than expected.

The most promising 100,000 candidates were then individually studied. While 50 of these galaxies did emit high levels of mid-infrared radiation, the numbers didn't suggest any kind of alien civilisation. But the researchers will follow up with further observations.

"They are almost certainly natural astronomical phenomena, but we need to study them more carefully before we can say for sure exactly what's going on," said Steinn Sigurdsson, one of the researchers, in the release. The results have been published in The Astrophysical Journal Supplement Series.

This is the first time that such an extensive search of galaxies' heat emissions has been conducted, and it provides new insight into the galaxies in our Universe, and also suggests that alien civilisations may not be out there - or may not look and act the way we expect them to.

"Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilisation using most of the starlight in its galaxy for its own purposes," said Wright. "That's interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilisations, if they exist. Either they don't exist, or they don't yet use enough energy for us to recognise them."

This is the dilemma at the heart of the Fermi Paradox. Logically, there have been plenty of opportunities for life to occur around the Universe, so where are all the aliens? The short video below has some interesting ideas, but Wright hopes that his work will help provide some solid answers.

"As we look more carefully at the light from these galaxies," he said. "We should be able to push our sensitivity to alien technology down to much lower levels, and to better distinguish heat resulting from natural astronomical sources from heat produced by advanced technologies. This pilot study is just the beginning."