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From Spektrum.de: The search for aliens used to be easier. For decades, researchers have been on the lookout for signs of extraterrestrial civilizations as part of SETI (Search for Extraterrestrial Intelligence). And because they don’t know what to look for, they prefer to look in the radio part of the electromagnetic spectrum. That’s because radio waves travel fairly freely through space, and radio range is great for wirelessly transmitting information. Potential aliens could come to the same conclusion.

But that’s exactly the problem: The world’s large radio telescopes, which point their dishes and antennas at the sky are passive receivers, are picking up more and more man-made radio signals that we ourselves with our cell phones, our WiFi, our radar systems and our satellites all send kind. You can think of it a little like light pollution - only with radio signals.

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