The scientific multiverse accounts presented are generally concerned not with the content of the universes; rather, they are concerned purely with the physical constants and ways by which these universes can come into existence given quantum mechanics and laws of nature. The concern of physicists and mathematicians is not with the moral content of these universes—whether they are good or bad in relation to some arbitrary scale of worthiness; rather, they are merely concerned with the sheer existence of the universes. The theist, on the other hand, may place considerable importance on the content of the universe, concerned with things such as ethical considerations, overall goodness, inherent value, and the like. Because of this, the scientific approach to the multiverse in most, if not all, cases entails the existence of far more universes than does the theistic one. The theist who aims to adopt a multiverse view and to incorporate the scientific case for that multiverse will then be forced to reconcile this difference, which may be seen as a drawback for theists in accepting multiverse theories. Essentially, a concession concerning the scope of universe inclusion within the multiverse will need to be made, either on the theological side or on the scientific side. Proponents of the theistic multiverse may try to reconcile this difference by inserting a threshold, such that any universe that falls below this threshold given whatever value and method of measurement is being used is not even a possible universe and thus would not be actualized at any point within the multiverse. This approach, however, demands that the theist justify his threshold, both in where he chooses to place the threshold and in what it purports to value. He must also provide reasoning as to why this particular threshold is more suitable than other potential thresholds that are placed at other locations and value other variables. This will not entirely solve the problem for the theist though, since the scientific models would call for very different thresholds and would set out very different definitions of possible, so still the issue remains for the theist that scientific multiverse models entail the existence of far more universes than they would generally like to acknowledge as possible. So many universes that the theist may not want to accept as possible that it may even prove to be damaging to the theist’s particular conception of God and how He operates.
The second potential drawback for the theist is that the multiverse theory undermines the design argument. Design arguments typically argue, in one way or another, that the universe appears to have been intelligently designed, which entails an intelligent designer, and that this intelligent designer is God (Ratzsch, 2010). The arguments generally “involve reasoning from seemingly purposeful features of the observable world to the existence of at least one supernatural designer” (Manson, 2003, p. 1). One particular example of such an observation and inference may be that the physical constants required to produce and sustain life are very narrow, and based on the fact that we see life in this universe, one can argue that it could not possibly be the case that all of these things simply came together by chance, but that the creation of something as complex as our universe would have required significant design and intent.6 It is important to note that many design arguments do not explicitly posit the existence of God, rather they point to the existence of just some supernatural designer, and that a further step is needed to identify that supernatural creator as God (Manson, 2003, p. 1).7 Design arguments, however, are typically used, and generally work better with, single-universe models rather than multiverse models. This is because such arguments appeal to the uniqueness of our particular universe, arguing that the chance of such a universe coming to exist as it has is virtually impossible without some sort of intent and creator behind it. Many multiverse theories, however, claim that since all possible universes have or will be actualized at some particular place or time, then the existence of a universe such as ours is not only highly likely but inevitable. For example, for proponents of cyclical multiverse models, it would merely be a matter of time before, at some point in the infinite sequence of universes coming into and going out of existence, our particular universe with all of these life-supporting features should come to exist.8 So, while the multiverse is not a direct challenge to the theistic view, it does undermine one of the stronger arguments that theists often appeal to in making a case for the existence of God. On most multiverse accounts there is no need to posit the existence of God to account for the apparent design of our universe since the existence of a universe just like ours is inevitable and is simply one of the wide variety of possible universes that has been actualized or that will, at some point, be actualized.
Finally, in the case of the ethical problem that the theistic proponent of multiverse models that entail the actualization of all possible states of affairs it faces, the theist will have to explain just how a traditional conception of morality can be maintained or if it needs to be maintained at all, in such a multiverse model. The issue is that, for an agent, his motivation for doing morally good acts may become diminished, trivialized, or altogether lost since, whether he does the morally good act or not, it will be actualized in some universe within the multiverse by either himself or one of his counterparts. Robert Adams captures the sentiment of this problem in writing that any particular agent in any particular universe could reasonably ask himself “[w]hat is wrong with actualizing evils, since they will occur in some other possible [universe] anyways if they don’t occur in this one” (1979, p. 195). Likewise, an agent’s refusal to commit some morally evil act will only make it so that that evil does not occur in his particular universe, which will further entail that that same evil that he refused to actualize will be actualized by one of his counterparts in some other part of the multiverse. The possible conclusion that stems from this is that it appears to trivialize all of our ethical considerations since whatever we do, or don’t do, will entail the opposite outcome in some other universe. On this, the motivation to perform morally good actions is seemingly lost since the agent could adopt an “if I don’t do it another version of me will” sort of attitude, as is discussed by Adams (1979). David Lewis, however, replies to such a worry as directed at modal realism, but what he says about modal realism can be applied to our case of the multiverse as well. He argues that
For those of us who think of morality in terms of virtue and honour, desert and respect and esteem, loyalties and affections and solidarity, the other-worldly evils should not seem even momentarily relevant to morality. Of course, our moral aims are egocentric. And likewise, all the more for those who think of morality in terms of rules, rights and duties; or as obedience to the will of God. (Lewis, 1986, p. 127)
Of course, such a reply is not readily accepted by everyone, and Yujin Nagasawa argues that the kind of reply provided by Lewis does not adequately solve the problem. Of such a reply, Nagasawa writes
However, if the multiverse model in question is correct, it is difficult not to extend our concerns to other possible universes in our context because even if people in other possible universes are morally irrelevant