Usually lack of evidence is evidence of lacking. But given their existence AND lack of evidence, I think probability of purposefully hiding (or at least being cautious about not showing off too much) is bigger than they just doing their thing and we just don't see it even though we are looking really hard.
Usually lack of evidence is evidence of lacking.
Big difference between there being a lack of evidence, and a lack of an ability to detect and identify evidence which exists.
I think people are rather cheeky to assume that we necessarily have the ability to detect a SI.
For a moment lets assume there is some alien intelligent life on our galaxy which is older than us and that it have succeeded in creating super-intelligent self-modifying AI.
Then what set of values and/or goals it is plausible for it to have, given our current observations (I.e. that there is no evidence of it`s existence)?
Some examples:
It values non-interference with nature (some kind of hippie AI)
It values camouflage/stealth for it own defense/security purposes.
It just cares about exterminating their creators and nothing else.
Other thoughts?