Personally, I’m tending toward Vallee’s hypothesis that the stealthiness has more to do with extra dimensionality of the phenomenon. That is, the way UAP blink in and out of sight and the often reported combining of multiple objects into one, or vis versa, is better explained if UAP are multidimensional in nature. They might still be extraterrestrial probes, but they could be something far weirder.

I think this hypothesis makes sense based on the alleged observations. I’m getting ready to start Dimensions by Jacques Vallee. I’ve heard it’s a good read.