That it is not due to chance or necessity?
Chance?
So what about the second alternative, that the fine-tuning is due to chance? The problem with this alternative is that the odds against the universe’s being life-permitting are so incomprehensibly great that they cannot be reasonably faced. In order to rescue the alternative of chance, its proponents have therefore been forced to adopt the hypothesis that there exists a sort of World Ensemble or multiverse of randomly ordered universes of which our universe is but a part. Now comes the key move: since observers can exist only in finely tuned worlds,
of course we observe our universe to be fine-tuned!
So this explanation of fine-tuning relies on (i) the existence of a specific type of World Ensemble and (ii) an observer self-selection effect. Now this explanation, wholly apart from objections to (i), faces a very formidable objection to (ii), namely, the Boltzmann Brain problem. In order to be observable the entire universe need
not be fine-tuned for our existence. Indeed, it is vastly more probable that a random fluctuation of mass-energy would yield a universe dominated by Boltzmann Brain observers than one dominated by ordinary observers like ourselves. In other words, the observer self-selection effect is explanatorily vacuous. As Robin Collins has noted, what needs to be explained is not just intelligent life, but embodied, interactive, intelligent agents like ourselves.Appeal to an observer self-selection effect accomplishes nothing because there’s no reason whatever to think that most observable worlds or the most probable observable worlds are worlds in which that kind of observer exists. Indeed, the opposite appears to be true: most observable worlds will be Boltzmann Brain worlds.
Since we presumably are not Boltzmann Brains, that fact strongly disconfirms a naturalistic World Ensemble or multiverse hypothesis.
