We May Have Already Detected Heat from Alien Civilizations
Have we already detected heat emitted from alien civilizations? Researchers from Pennsylvania State University are implementing a novel approach to finding extraterrestrial intelligence that involves scanning the universe for thermal radiation.
While most recent efforts to detect extraterrestrial life have focused on indicators of technological advancement, such as the emission of radio signals, this method (called G-HAT, or Glimpsing Heat from Alien Technologies) makes fewer assumptions about potential similarities between alien and human civilizations. Since machines and living things necessarily emit heat, the researchers reasoned that aliens can be found by searching for infrared radiation.
"This approach is very different," said Franck Marchis of the SETI Institute, who was not involved in this study. "I like it because it doesn't put any constraints on the origin of the civilization or their willingness to communicate."
"This effort is important because it tries to resolve the question of extraterrestrial life scientifically, using the laws of chemistry and physics that govern the universe," said astronomer Geoff Marcy of the University of California, Berkeley.
In order to gauge which galaxies may have a surplus of infrared radiation, the researchers analyzed images taken by the Wide-field Infrared Survey Explorer, or WISE, during the comprehensive infrared mapping of the local universe in 2012. In a galaxy without any life present, approximately 10% of its light should fall within the mid-infrared range. A higher concentration of infrared radiation may indicate that the galaxy is artificially warmed by technology or by biological processes. Their initial survey yielded "several dozen galaxies giving out a superlative amount of mid-infrared light," says Wright, and approximately 50 galaxies that are emitting more than 50% of their light in the mid-infrared range, far more than the predicted value of 10% for a lifeless galaxy.
This does not necessarily mean that these 50 galaxies contain alien civilizations, as there are several potential explanations for a false positive. A galaxy can release more thermal radiation than expected as a result of star formation or black hole feeding processes, for example. And when asked if we had "found" alien civilizations, Wright claimed that we may have technically "found" them in terms of initial detection, but the results will not be meaningful until we definitively identify them: "If by 'found them' you mean that WISE detected the waste heat from them, then yes, that's right – if these sorts of energy-hungry civilisations exist, WISE should have detected them. Distinguishing that waste heat from ordinary astrophysical dust will be very difficult in many cases, and proving it's of alien origin will be even harder."