Six Tricks That Alien Trackers Could Use

Earth's cities are visible at night from space because of their artificial lights, so populated exoplanets might give off light pollution of their own. But finding it might not be easy. Even if all the world's electricity were used to produce light, it would still be thousands of times fainter than a glint of sunlight reflected off the Earth's surface. (Image: NASA/GSFC)

From New Scientist:

So far, the search for extraterrestrial intelligence has focused on listening for radio signals deliberately sent our way. But even if alien civilisations are not trying to get our attention, their activities could produce detectable signs. Here are a few things we might detect, most of which are discussed in a recent paper by Richard Carrigan of the Fermi National Accelerator Laboratory in Batavia, Illinois.

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