Another interesting way to speculate is the "under our nose" concept, which is the concept that the existing distribution of stars and galaxies, as well as the recorded background noise, might be the byproduct of alien intervention. Binary star systems are a popular speculative example of "starivore" civilizations that consume entire stars that have been moved into the alien civilization's own star system, and perhaps some combination of multiple stars in a single system are not "naturally" occurring in the absence of alien influence. To an unsuspecting observer, some forms of distant astronomical-scale engineering could be mistakenly interpreted as natural astrophysics that the observers then incorporate into their standard models when refactoring to account for all of the observed data... Usually the simple explanations are correct, but when your models require really insane updates to handle the observed data, perhaps there are other explanations? At the same time though, what recourse would we have if 99% of the visible universe was already astro-engineered?