- Multiple expert witnesses, usually pilots or radar operators, getting visual and sensor confirmation from multiple vantage points
- Air and ground tracking
- High cohesion and consistency (in terms of object size, cardinality, dynamics, and timing) between the witness reports
Taken together, these reports form a closure over the set of plausible explanations that should approximately explain all or none of them. My 2c is that any plausible explanations are by and large "big" and non-trivial ones like shared delusions.
But of course alien civilizations—or (non-human?) co-terrestrial civilizations—are such an extraordinary hypothesis that I do not see why they should be treated as more plausible than (as you note) something like shared delusions.
Let me expand upon that a bit. My (tongue in cheek) explanation is this:
Humans have an undiscovered facility for shared perceptual delusions and (seemingly deliberate) confabulation. That is to say, individuals with shared cultural contexts may respond to the same environmental triggers (weird reflections, social stressors, I don't know!) by hallucinating the same things. Moreover, upon experiencing such a hallucination, some subjects will confabulate corroboratory evidence, perhaps even (unconsciously) going so far as to tamper with radar recordings or (unconsciously) colluding with other "witnesses"—and individuals who engage in this confabulation have no memory or recollection of it later.
This is a totally wild explanation, and I don't actually believe it. But is it as plausible as alien civilizations? I sorta think so!
Given the amount of evidence released so far, which seems more likely?
- Alien civilization
- Some other form of hyper-advanced technology
- The U.S. Military and/or various U.S. intelligence agencies are perpetrating a hoax in order to further some kind of strategic goal
I know which one I'm picking, barring much more widely acknowledged and damning evidence.
To be clear, I'm fairly conspiracy-friendly. I am just very skeptical of this new tech angle.
More reports from states that have obviously opposed the US would definitely make me think more about the veracity of the leaked "evidence".
Why?
This whole thing reminds me a bit of the "Havana Syndrome", in that:
- It's an extraordinary claim, presented with limited evidence.
- It defies obvious logical explanation (i.e., a motive).
- The phenomenon lacks a clear definition, leaving the door open for multiple disparate phenomena with different causes to be lumped together.
I believe the third aspect is really underemphasized as a causal factor in "hard to explain" phenomena: because this may in fact be multiple different phenomena, with different causes, it's likely that any single mundane explanation does not explain all observations, and thus appears to be a weaker explanation than it is.
This is sort of a "defender's dilemma" of strange phenomena: if you can't explain all of them, you appear to be unable to explain them. But because of the aforementioned definitional problem, that's not necessarily a surprising or meaningful thing.
To your specific point: the idea of a co-terrestrial civilization is extraordinary. I struggle to imagine the only evidence would be a few spurious radar signatures and odd videos.