A better term would just be “mystery.” If you assume life is at least somewhat likely and do some simple math we should see evidence of aliens. We don’t so some

A better term would just be “mystery.” If you assume life is at least somewhat likely and do some simple math we should see evidence of aliens. We don’t so something is either wrong in the assumed probabilities or there are unknown unknowns. My favorite hypothesis is that we are early. Due to low metallicity in the early universe it’s possible that advanced life only became likely “recently” (as in the last few billion years) and we are part of the first crop. We may be an early example in the first crop because our planet is particularly friendly to advanced stable life, so maybe a bit of rare Earth mixed in. Most other biospheres might be more hostile and take longer to produce anything capable of space flight. We don’t see star travelers all over the place because for the most part it’s too soon. There might be a few early birds out there but few intelligences are that advanced yet.