Another question arising in this matter is how to treat evidence of extraordinary things.
Dealing with extraordinary claims has not gotten the attention it deserves, IMO.
It gets to the distinction between an explanation, and a predictive model. Explanations assuage mental anxiety over the unknown. Predictive models, in general, allow you to do something. If, in some particular case, the predictive model associated with an explanation doesn't allow me to do something, it is not a useful model.
Let's assume some advanced alien intelligence is patrolling the globe. What then? What can I do with this knowledge? As far as I can tell, nothing. The aliens have chosen to hide from us. They seem very good at it. Shouldn't a space faring civilization be beyond our ability to force an interaction with? So, if there is nothing I can do with this knowledge, I'm going to ignore the possibility until they seem more interested in getting together. A predictive model whose predictions tell you that the model is useless, is useless.
At most we should ascribe a prior probability of zero and then do some Bayesian updating to get a posterior.
I believe if you start with a zero prior, you end up with a zero probability.
What can I do with this knowledge? As far as I can tell, nothing.
This MIGHT argue against putting much resources into refining your estimate of what is really going on with these aliens. It hardly argues for the validity of the hypothesis.
I think the continuing novelty of the world, the fact that the world continues to unfold in a way consistent with their being just gobs and gobs more you don't know than that you do know, argues for assuming that there is very much knowledge that you, or perhaps your children or your children's children, won't be a...
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?