One of the arguments for lack of intelligent life is that we're not detecting any radio signals. But is it possible something is being overlooked? For arguments sake lets say there is at least one world with intelligence within a hundred light years of us. Is it a given we could know they're there? We certainly wouldn't if they weren't broadcasting anything or not using radio we could detect. Conversely is it possible they couldn't notice us either? Of course not if they didn't have sufficient technology, but if they did is it at all possible either of us might not notice the other for some reason or other? Thoughts anyone?