Scientists propose there are three “magic wavelengths” of visible light that extraterrestrial civilizations could use to contact Earth: deep purple, deep red and yellow.
When the Search for ExtraTerrestrial Life (SETI) began in 1960, it focused on eking out radio frequencies that alien civilizations could be sending as beacons of their existence. More recently, scientists have taken a new approach in the search for extraterrestrial life: scanning the sky for laser light.
This process, known as OSETI (the Optical Search for Extraterrestrial Life) looks for light within the visible spectrum, whereas Radio SETI looks on the part of the electromagnetic spectrum that contains radio waves and microwaves, which are invisible to the human eye.
In a paper in New Astronomy, Shinya Narusawa and his colleagues at the University of Hyogo lay out three likely visible wavelengths through which alien civilizations might contact Earth. While they acknowledge that “higher evolved civilizations” might have greater technological capabilities, for "the strength of argument," Narusawa and his team focused on the hypothetical situation of a planet as advanced as Earth trying to make contact.
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