We’re not licensed to ignore it, and in fact such an update should be done. Ignoring that update represents an implicit assumption that our prior over “how habitable are long-lived planets?” is so weak that the update wouldn’t have a big effect on our posterior. In other words, if the beliefs “long-lived planets are habitable” and “Z is much bigger than Y” are contradictory, we should decrease our confidence in both; but if we’re much more confident in the latter than the former, we mostly decrease the probability mass we place on the former.
Of course, maybe this could flip around if we get overwhelmingly strong evidence that long-lived planets are habitable. And that’s the Popperian point of making the prediction: if it’s wrong, the theory making the prediction (ie “Z is much bigger than Y”) is (to some extent) falsified.
We’re not licensed to ignore it, and in fact such an update should be done. Ignoring that update represents an implicit assumption that our prior over “how habitable are long-lived planets?” is so weak that the update wouldn’t have a big effect on our posterior. In other words, if the beliefs “long-lived planets are habitable” and “Z is much bigger than Y” are contradictory, we should decrease our confidence in both; but if we’re much more confident in the latter than the former, we mostly decrease the probability mass we place on the former.
Of course, maybe this could flip around if we get overwhelmingly strong evidence that long-lived planets are habitable. And that’s the Popperian point of making the prediction: if it’s wrong, the theory making the prediction (ie “Z is much bigger than Y”) is (to some extent) falsified.