How Could Non-Radio Technosignatures Reveal Extraterrestrial Intelligence?

Frank Drake’s Project Ozma began in 1960 with a radio telescope at Green Bank, West Virginia, and set the public image of the Search for Extraterrestrial Intelligence (SETI) as a listening exercise. Radio made scientific sense. It could cross interstellar distances, pass through much of the interstellar medium, carry narrowband artificial-looking patterns, and use technology already available to…