For more than sixty years, the search for extraterrestrial intelligence has often been imagined as an act of listening: a radio pulse, a laser flash, a message meant to cross the dark. But technology changes environments whether or not it speaks. Industry alters an atmosphere. Machines release waste heat. Satellites and debris can arrange themselves into patterns nature rarely makes. The first credible sign of another civilisation may therefore arrive not as a greeting, but as a residue.
Artificial intelligence could help find such traces by ranking anomalies across data sets too large for people to inspect one object at a time. It would not prove that aliens exist. It would do something more modest and useful: identify the few observations that deserve a closer human look, while every natural explanation is tested first.
A search built only for deliberate messages may miss the longer-lived evidence that technologies leave behind. Looking for traces expands the question from “Is anyone calling us?” to “Has intelligence changed a world in a way we can measure?”
This is the identical fact set, re-told at a different altitude. Switch any time — the reader keeps your place in the idea, not the prose.