Also this from abstract: "we find a substantial ex ante probability of there being no other intelligent life in our observable universe" The keyword is "observ

Also this from abstract: "we find a substantial ex ante probability of there being no other intelligent life in our observable universe" The keyword is "observable" universe what about probability of life in unobservable universe. When we discovered microscope and telescope only then you could say that we started "observing" something. Modern science is only 100 years old and we can not even imagine what would be invented and discovered for 50 or 100 years.