NASA's Wide-field Infrared Survey Explorer, which collected the information used for the survey - (Image via NASA/JPL-Caltech)

A team pouring through data from NASA’s Wide-field Infrared Survey Explorer (WISE) has completed their 100,000-galaxy search for signs of intelligent alien life… and have reportedly drawn a blank.

The Glimpsing Heat from Alien Technologies Survey (G-HAT) has been combing through WISE data since 2012 with a novel approach to the Search for Extra-Terrestrial Intelligence (SETI): rather than looking for radio or optical evidence, as have most other surveys have, they attempted to detect evidence of life from waste heat in the form of mid-infrared radiation emissions.

Although unusual, the team had good reason to suspect the method might have better results than the tradition manner of simply listening to the stars. Monitoring the cosmos for radio transmissions embodied the assumption that someone out there would be actively sending them out. Although humans have been blasting electromagnetic energy off Earth ever since we discovered radio, the strength of those signals is minuscule.

The amount of energy required to produce a detectable signal at the distance of, say, even the nearest star with planets capable of supporting life, is immense. An alien civilization seeking to communicate by such means would either be doing so intentionally and with enormous effort, or have technology advanced enough to harvest the tremendous energy required with minimal effort.

The thought behind the G-HAT approach is this: even with the ability to produce such transmissions, an alien civilization might not do so. They would, however, still betray their position simply by harnessing large amounts of energy. The inevitable production of waste heat could signify their presence even if they chose not to put that energy out in the form of radio transmissions.

This fundamental reality of thermodynamics was thought to provide a better basis for detection than radio scans. Unfortunately, as the team’s first paper reveals, it hasn’t generated any more positive results than radio-based surveys. Around 50 galaxies were detected with unusually high levels of mid-infrared radiation. None of it, however, was obviously artificial.

The team will continue to investigate the causes of those anomalous signals. As they do so, hopefully their work will yield the first positive evidence of life beyond planet Earth. Such a discovery—combined with the continuing failure of projects like G-HAT to reveal more distant proof of life—would provide fuel to the Fermi Paradox: the question of why, if the fundamental building blocks of life are abundant through the universe, and if life is found to start in a wide range of conditions, where is the evidence?

This, in turn, is sure to ignite further debate about the so-called “Great Filter.” The Great Filter is a conceptual answer to the Fermi Paradox; it tries to resolve the paradox by reasoning with the obstacles between the formation of life itself and the evolution and continued survival of intelligent species. With billions of years to evolve elsewhere, intelligent alien civilizations should have had plenty of time to grow to such scale as to be detectible by G-HAT’s methods.

Although the answers are not easy, the information being discovered at both ends of this spectrum of investigation will continue to fuel future investigations into the mysteries of life off Earth.

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