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If there's a giant void in the universe it could also be evidence of a Type 3 Civilization, but probably not!
We'd still be able to see such civilizations from their infrared emissions. There was actually a search done a while back looking for Type III civilizations, the Ĝ survey, but it came up empty.
@ShaunaTheDead You never know with what we are finding today, but it is possible we wouldn't even understand it if it was:
kurzgesagt did a nice little overview of this: https://youtu.be/rhFK5_Nx9xY?si=5cr0miFH0iUKhtFb&t=412