Comment by api

If we are being visited we would never see them unless they decided to show themselves, and if they did it would be absolutely unambiguous.

Someone with the tech to travel the stars (or something weirder like between dimensions) could make probes the size of bugs, sand, or dust. They could also image us at incredible resolution from afar, receive all our signals, and so on. They might be able to do even weirder and crazier forms of surveillance we don’t even understand yet, like high resolution imaging with neutrinos or gravity waves.

They could study us all they wanted and we’d never know.

Look into how advanced some of our spy tech is, and we have barely left our planet.