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"Will We Really Find Alien Life Within 20 Years?"
Natalie Wolchover, Life's Little Mysteries Staff Writer

For Finkelstein's striking prediction to come true, certain conditions must be met: There must be a planet with an alien civilization that is capable of transmitting high-power radio or optical signals our way. That civilization needs to exist within 20 light-years of Earth and have been broadcasting those signals starting today, or earlier, in order to reach Earth within 20 light-years of today.

Actually, that's not true: we can find out if there's life by detecting certain elements in the atmosphere. Oxygen is one of them - it binds so easily with other elements that to find it alone in an atmosphere means that something else is releasing it (like plants, as on earth).