I will be giving a talk at the GAP8 next week in Konstanz, Germany, entitled “When the actual world is not even possible”.
Here is an abstract:
Contemporary fundamental physics offers compelling reasons for the need of a quantum theory of gravity, i.e. a theory unifying classical general relativity with the quantum physics of the standard model of particle physics. Approaches to quantum gravity often involve the disappearance of space and time at the fundamental level. The metaphysical consequences of this disappearance are profound, as is illustrated with David Lewis’s analysis of modality. As Lewis’s possible worlds are unified by the spatiotemporal relations among their parts, the non-fundamentality of spacetime—if borne out—suggests a serious problem for his analysis: his pluriverse, for all its ontological abundance, does not contain our world.
If a Lewisian accepts, in a naturalistic vein, that physics may eliminate space and time from the fundamental furniture of the world, she can resist the argument by insisting that an empirical theory cannot coherently deny the existence of space and time, for all experience is experience of something being located somewhere at some time. I will argue that theories denying the fundamental existence of space and time are not incoherent in this sense, but only if they entail the non-fundamental, i.e., emergent existence of space and time. Unfortunately, this does not suffice to salvage the Lewisian account of modality. First, it is insufficient on principled grounds: a metaphysician will hardly be satisfied with being offered what is at best an approximately true account of modality which ignores the fundamental reality in favour of a description of emergent phenomena. Second, a Lewisian theory of modality trading in emergent spatiotemporal relations must remain inpotent in binding the basic constituents of actuality into one and the same possible world. The reason for this impotence is straightforward: there are no spatiotemporal (not even analogically spatiotemporal) relations exemplified in the fundamental structure, and the basal elements of this structure cannot be the relata of the emergent spacetime relations. Thus, non-spatiotemporal fundamental physics, naturalism, and Lewis’s analysis of modality are incompatible.