David Lewis’ theory of modal realism features a collection of concrete worlds, which are spatio-temporally connected societies in themselves but wholly isolated from one other. We live in one of these, which we call the actual world; the others we call possible worlds. But there is nothing special about being “actual”; it just refers to where we reside: actual is an indexical term.
In sketching my own ideas, I’ve rejected Lewis’ theory, but I’m now considering that his sense of actual may be the right one for my model as well. What follows is some “work-in-progress” thinking on this. (My modal realism posts are here).
Lewis’ worlds are completely separate, and they are static entities; his treatment of causation is Humean in spirit. On the other hand, in my preferred view, causation is a process of actualizing possibilities. The actual (concrete) world consists of the events we are already in causal contact with. At any given moment we are surrounded by adjacent (abstract) possible events which are available for our actualizing. More distant possibilities (and possible “worlds”) are rational constructions based on our experience with possibility (they are also accurate in their representations, if we embrace modal rationalism).
To those modal realists who disagreed with his account, and preferred to think of possible worlds as abstract objects, Lewis demanded an account of what magic accounted for the instantiation of one of the worlds as actual. But in my idea, it is not an entire world that is instantiated as actual all at once, rather a series of events are actualized through an active causal process. So it wasn’t clear that Lewis’ objections would apply in the same way.
We are on a journey through a space of possible events, actualizing certain ones as we go. At first, I thought this meant we are something magic or special in that we are blazing a causal path of actualization against a backdrop of a space of unactualized possibilities, and so I was feeling the bite of Lewis’s critique of his opponents: how can I account for our actualized “world” being thus special vs. the rest of the possibilia?
Then I realized that the mistake was to picture the space of possibilities as static. This was a hangover from Lewis’ model. In my model, a “possible” event is one we have not been in causal contact with from our particular perspective. But, from a different point of view this event could be actualized. Possibilities and actualities exist relative to a particular perspective. We just label the events unfolding in our local causal nexus “actual”, and the rest “possible”. All the events of modal space can be thought of as in an active process of becoming actual. The multiverse is alive, not static. And we are not special, after all.