I first read this theory in the book Calculating God, but it has also appeared in the Hyperion book series. I recently saw it in Black Mirror season 3 (for humanity).

Not exactly a new theory. Still has the problem of the exponential population expansion (in any form like probe or seeding or terraforming or colonization) leaving physical traces everywhere...if they were even marginally successful beyond an origin galaxy. The universe has been around a loooooooooooooooo...ng time.