If aliens are on earth their behavior is indistinguishable from no aliens being on earth. If I flip the switch in my head from believing that aliens are on earth to aliens not being on earth, what will I do differently?
Historically, humans from one group have succeeded in infiltrating humans of other groups,and all without superior intelligence or technology beyond what we all know about (or could if we read the internet).
I think what we already know is that if there are aliens, they are either relatively smart with relatively good tech, or they are biologically similar enough to us to pass the relative cursory inspections that most of us give most of the rest of us while going about our normal lives. Or both.
Recently I've been struck with a belief in Aliens being present on this Earth. It happened after I watched this documenary (and subsequently several others). My feeling of belief is not particular interesting in itself - I could be lunatic or otherwise psychological dysfunctional. What I'm interested in knowing is to what extend other people, who consider themselves rationalists, feel belief in the existence of aliens on this earth, after watching this documentary. Is anyone willing to try and watch it and then report back?
Another question arising in this matter is how to treat evidence of extraordinary things. Should one require 'extraordinary evidence for extraordinary claims'? I somehow feel that this notion is misguided - it discriminates evidence prior to observation. That is not the right time to start discriminating. At most we should ascribe a prior probability of zero and then do some Bayesian updating to get a posterior. Hmm, if no one has seen a black swan and some bayesian thinking person then sees a black swan a) in the distance or b) up front, what will his a posterior probability of the existence of black swans then be?