Anthropic Constraints on Fermion Masses *

It is conceivable that some of the properties of the physical world might not be uniquely determined by an underlying dynamical principle, but might instead reflect the requirement that those properties be compatible with the existence of intelligent observers like us, capable of studying them. In modern theoretical physics, this controversial idea is called the “anthropic principle” [1]. Broadly speaking, two camps are inclined to take the anthropic principle seriously, which we may call the “best-of-worlds” camp and the “worst-ofworlds” camp. The former, notably represented by the authors of [2], holds that since the parameters of physical laws seem finely tuned to allow life, the universe is somehow geared —perhaps by a superior intelligence— towards being hospitable to us. The second camp, represented by [3], holds that our universe is only barely capable of accommodating intelligent observers, which is what one might expect if the fundamental physical laws are not designed with us in mind, but allow for the existence of many universes with different properties, only a very few of which happen to be compatible with the evolution of intelligent life. The German philosopher Arthur Schopenhauer captured this distinction almost two centuries ago: