[AndrewC]

An intelligence that we will never find (nor evidence that this intelligence ever did exist) would be, in practice, the same as an intelligence that didn't exist in fact

I think there's this cat that a lot of people argue over that would fall into your definition.

[js1138]

I think there's this cat that a lot of people argue over that would fall into your definition.

Not quite.

The longer and more thorough our search -- if the results remain negative -- the more certainty we have of the rarity of intelligent life. Rarity would be an important finding.

If faster than light travel is possible, then it stands to reason that other civilizations would have achieved it, given a billion or so year's head start.

So where are they, other than in the imagination of X-File writers? If they are indeed observing us, then with their advanced technology they have complete control over whether we see them (disregarding Douglas Adams' theory that aliens are really just teenage ETs out joyriding).

If faster than light travel is not a practical possibility, and civilizations are more than a hundred light-years apart, then commerce is unlikely. I mean would you give up a couple hundred years of medical progress to sell hundred year old products door-to-door?

[jennyp]

An intelligence that we will never find (nor evidence that this intelligence ever did exist) would be, in practice, the same as an intelligence that didn't exist in fact

I think there's this cat that a lot of people argue over that would fall into your definition.

But I don't think I could ever have a relationship with Schrodinger's Cat. You could never depend on it being there when dinner's ready.