Modal Realism

Time within each world is substantival, infinite, one-dimensional, continuous, linear, and uni-directional, just as the physics of an ordinary world describes. Across the plurality, however, the totality of histories branches: every world realises a different complete history, and counterpart theory permits a branching reading of what could have been done. Lewis's analysis of counterfactuals via comparative similarity among worlds yields a structure in which freedom is rated as Both, since within a world events may unfold deterministically while across worlds there are always alternative possibilities for any agent's counterparts. Traversability is correspondingly branching at the level of the modal multiplicity.

Each world has its own substantival, infinite, three-dimensional, locally Euclidean space, and worlds are spatiotemporally as well as causally isolated from one another. There is no overarching super-space in which the plurality is laid out: the worlds simply are, each complete in itself. Curvature is flat in the standard idealisation, with relativistic variation absorbed within each world's physics. Locality holds within a world because Lewis builds his account of causation and counterfactual dependence on local intrinsic features and their similarity profiles across worlds.

Matter is substantival, infinite in aggregate across the plurality, three-dimensional, locally arranged, and conserved within each world. Each world contains its own concrete material inventory, every bit as real as the inventory of ours, and there is no privileged actuality: actuality, on Lewis's indexical analysis, just means this world from the speaker's standpoint. The doctrine of plenitude — that for every consistent description there is a world that realises it — entails that matter is variously arranged in maximally many ways. Material interactions remain local within each world.

Within each world the modal realist observer is an ordinary embodied subject located at a single point in space and time, with mediated, partial knowledge of its surroundings and no causal access whatsoever to any other world. Observers are plural within a world and, taken across the totality of worlds, the multiplicity is unimaginably greater, but each observer's perspective is local. Knowledge is mediated through the usual cognitive channels and is corrigible in just the way ordinary empirical knowledge is. The observer is active in framing modal claims that quantify over other worlds via the apparatus of counterpart theory, even though such theoretical commerce with other worlds is purely logical rather than causal. The framework counts spatial and temporal instances per observer, so each registers as Single even where the plurality of worlds is vast.

Energy is substantival and, summed across the pluriverse, infinite — Lewis's plenitude of possible worlds means that every consistent distribution of energy is somewhere actual. Within any single world, conservation holds in whatever form the physics of that world imposes; the modal realist does not legislate physics but assumes worlds are closed under their own laws. Dispersibility is irreversible within worlds whose physics has a thermodynamic arrow, but the pluriverse as a whole contains worlds with every possible thermodynamic profile. The interest of energy for the modal realist is less first-order physics than the modal status of the conservation laws themselves: they are contingent regularities of how things go in our world, not features that hold across the space of possibility.

Information is substantival, discrete, and conserved within each world: facts about a world are real features of that world, and Lewis's ontology of properties as sets of possibilia treats informational structures with mathematical precision. Across the plurality of worlds, the totality of facts is enormous but well-defined. The framework distinguishes scales: cosmic information is conserved within each world by ordinary physical law and across the modal multiplicity by the eternal existence of all worlds in their concreteness, while personal-identity information is non-conserved because individuals are world-bound and perish with their bodies, leaving only counterparts elsewhere who are similar but numerically distinct.