Impossible possible worlds

In their debate on the problem of evil, Alvin Plantinga and Richard Gale were stalemated on the status of certain possible worlds. Although philosophical discussions regarding possible worlds can be very abstruse, humans of normal intelligence readily operate with a pretheoretical grasp of possible worlds. We deliberate about alternate courses of action. We have regrets about what might have been if only we had said or done differently. The Bible often describes many hypothetical situations. By the same token, this is the stock and trade of countless science fiction stories about time travel and alternate worlds. So the basic concept is very accessible to people who are not philosophers or metaphysicians. Our capacity for imagination is part of what makes us human. 

Many Christian philosophers rightly define God as a necessary being. According to modal logic, a necessary being exists in every possible world. 

In challenging Plantinga, Gale humorously postulated a possible world in which everyone spends his life with his head just above water, always on the verge of drowning, and chanting “nobody make waves”. Unfortunately, there's some devilish chap in a motorboat who does just that. He then posed the question, Does God exist in that possible world? 

From what I can tell, Plantinga's response was ambiguous. It wasn't clear to me if he denied that such a scenario is even possible, or if he merely denied that such a scenario is a live possibility. At least in on respect, it seems to be undeniable that there is such a world. After all, it's conceivable. Gale didn't propose an unintelligible scenario. Indeed, it's because Gale's scenario was conceivable that Plantinga rejected it. Had it been opaque, there wouldn't be a comprehensible proposition to assess.

However, that might be too facile. Conceivability isn't equivalent to possibility. When humans imagine possible worlds, we imagine possible-world segments. We lack the intelligence to imagine fully-furnished possible worlds. That's too complex for our finite minds. So a hypothetical scenario might be conceivable, but incoherent.

Indeed, Gale's scenario is hardly realistic. It's naturally impossible for humanoids to survive in that environment. We couldn't eat, sleep, reproduce, raise children, &c., if we spent all our time up to our necks in water. 

Nevertheless, the underlying question is whether some possible worlds are too pointless for God to exist in them. What about an evil world with no redeeming values? That doesn't appear to be inherently unrealistic. Yet that seems to generate a dilemma. For unless God exists in every possible world, then he's not a necessary being. 

Here's another prima facie difficulty: How can a possible world be merely possible if God exists in that world? How can something actual exist in a possible world? Doesn't that teeter on modal collapse?

But it depends on how you explicate a possible world. Suppose we view a possible world as God's concept of a possible world history, or God's concept of an alternate timeline. In that event, it's not so much a case of God existing in every possible world, but every possible world existing in God. That is to say, every possible world existing in the mind of God. We talk about God existing in possible worlds because that's a handy way to express the idea, but that may not be accurate. It's not that something real (God) exists in a possible world, but a possible world exists in something real (God). Every possible world exists in God's imagination. Indeed, God's imagination is what constitutes all these hypothetical scenarios in the first place. 

If possible worlds are divine ideas, then that preserves the distinction between possible and actual worlds. An actual world is a divine idea of a possible world that God instantiates in time and/or space. God's idea, like God himself, is timeless and spaceless. So an actual world exists distinct from God. 

On that view, there can be a possible evil world with no redeeming values because God is able to imagine that scenario. Indeed, God is unable not to imagine that scenario. God is omniscient. His omniscience extends to possibilities as well as actualities.

Mind you this works better for Reformed theism than freewill theism, since the latter requires ultimate autonomy on the part of creatures or even would-be creatures.