Well, we don't know what they look like, how to find them, or how to communicate with them when we do, but (1) we can make categorical statements about whether they exist or not, and (2) we can put a timeline of 25 years out there for finding them.
A whole lotta smoke gettin' blown here...
Patience, Commander Zebronk. We must lull the Earthlings into a sense of security before the invasion fleet arrives.
I firmly believe that I can't immediately identify everything that might be flying.