Radical Mundanity and the Zoo Hypothesis: Competing Views on Extraterrestrial Life

To the point

There is no proven life beyond Earth yet, and experts like Robin Corbet, John A. Ball, Michael Garrett, and Carl Sagan offer different ideas—aliens may be only slightly more advanced and hard to contact, contact would require enormous power and time, civilizations might deliberately avoid interference, or they could be hard to detect after evolving beyond biology—about why we have not found or heard from others.