In my past post, I suggested that theists could use a multiverse response to the problem of evil, much the way atheists do in response to the fine tuning argument. I also suggested that one objection to the theistic strategy might be that it’s ad hoc. However, it’s not obviously more ad hoc than the atheistic strategy. It then occurred to me that one could argue that the atheist’s multiverse (roughly the Everett interpretation of quantum mechanics) is not invoked simply to account for the evidence of fine tuning, but to explain other phenomena (e.g. why gravity is the weakest of the four fundamental forces). Also, given a certain interpretation of the way the laws of physics work, the laws entail a multiverse.
The question of ad hoc-ness is also related to simplicity. Theists sometimes allege that a multiverse is less simple than invoking God as an explanation. As we’ve seen, however, there is a response available to the atheist: the atheist isn’t invoking a multiverse per se, but the laws of physics (which happen to have a multiverse as an entailment) and the laws of physics are quite simple. Of course, theists who embrace the multiverse don’t object to the multiverse on grounds of simplicity. So how are we to assess the simplicity of an atheistic multiverse versus a theistic multiverse?
Well, atheistic multiverses arise from a certain interpretation of the laws of physics, which are quite simple. Some other physical multiverse theories have universes arising from a ‘parent’ universe. There is thus a single entity from which multiple universes are created. On the theistic multiverse model, universes are also created by a single entity, God, who is said to be simple (I’ll leave aside for now debates over divine simplicity). So the theories seem to be on a par.
What of the question of ad hoc-ness, then? I think the atheist could still press the point that s/he invokes the multiverse to explain a range of data, whereas the theist only invokes the multiverse to counter the argument from evil. But the theist also has a response available: multiverse theory explains a range of theological data. For example, the multiverse might supply an answer to the problem of ‘no best world.’ Perhaps the reason that God didn’t create the best of all possible worlds is that there is no such thing. Perhaps the concept of the ‘best world’ is like the concept of ‘the highest number.’ Perhaps, then, God, in his freedom and goodness, simply creates the full range of creation-worthy worlds, some of which contain evil, even lots of it. So there is a problem, that of no best world, that the multiverse hypothesis best explains. It’s still not obvious to me that this move is any more ad hoc than the atheist’s appeal to multiverse.