We say that something is strange when it defies reason, when we can’t find an explanation satisfying enough to stop wondering what it is. There are at least two ways in which this can happen. A thing can be strange in effect or strange in fact. In philosophical terms, the first kind of strangeness might be called epistemological, meaning that it has to do with how we perceive things; the second kind of strangeness might be called ontological, meaning that it has to do with the way things actually are at their inmost.
Imagine being Joe Schmo on main street in 1964… Sitting outside a drug store (not a Starbucks) but the fake wooden streetscape of our earlier mental conjuration still remains the same. It’s a time before ‘real’ commercial airline travel — the first flight of a 747 is still 5 years away. The closest thing Joe has to the idea of air travel is a 1st generation airliner like a De Havilland Comet and only then because he heard about it on the radio (My Grandpa worked by the way on the De Havilland Comet decompression investigation), and Black and White TVs are still sold more than colour.
Meanwhile, you tell him this: there exists a separate world of classified technology and just one of those things is a Mach 3 Stealth Plane that can fly to the edge of space.
Do you think you could tell Ol’ Joe this without his hackles being raised? Do you think he’d believe you? There would be much shaking of heads and remonstration. I’m not sure Mr Schmo would accept it at all. It would just bounce off the carefully constructed bubble of Red Reality that he’s unknowingly internalised. At the time it would be indistinguishable to him from UFO reports.