If we restrict ourselves to proposals which are falsifiable, what kind of explanations are available to us? In the history of science there have been two kinds of explanation which generally succeeded: explanations in terms of general principles; and explanations in terms of history. We are used to believing that the former are more fundamental than the latter. If we discover a fact that seems to hold universally, such as that all electrons have the same mass, we believe immediately that the reason for it must rest on principle and not on history. We usually expect a phenomenon to be contingent only if we see that it changes from instance to instance. If asked to justify this, we would say that something that is universally true cannot rest on contingent circumstances, which can vary from case to case. This makes sense, but it is an example of the kind of argument that works well only as long as it is not applied at the scale of the universe as a whole. When we are dealing with properties of the observable universe we no longer have any reason to insist that if something is true in every observable case, it cannot at the same time be contingent. One reason is that we have no justification to assert that the universe we see around us represents a good sample of all that exists, or that has existed, or that might in principle exist. There is in fact no logical reason to exclude the possibility that some of the facts about the elementary particles, which appear to hold throughout our observable universe, might at the same time be contingent.
The argument that Lee Smolin makes is pretty interesting. He suggests that “a process of self-organization like that of biological evolution shapes the universe, as it develops and eventually reproduces through black holes, each of which may result in a new big bang and a new universe. Natural selection may guide the appearance of the laws of physics, favoring those universes which best reproduce.” This is kind of terrifying, but much more interesting than the physics classes I’ve had so far.