What is Extended modal realism?

Extended modal realism is a philosophical view regarding the nature of possible worlds and modal properties. It builds upon the traditional concept of modal realism, which was notably articulated by philosopher David Lewis. Modal realism claims that possible worlds are as real as the actual world; they are concrete entities that exist in a way similar to our own world, differing in terms of the ways they realize different possibilities. Extended modal realism takes this idea further by suggesting that not only do these possible worlds exist, but they may also vary in significant ways that go beyond mere different arrangements of existing entities. This can include the idea that possible worlds might have their own unique laws of nature, concepts of identity, and even entirely different kinds of entities or structures that do not exist in the actual world. In essence, while traditional modal realism often focuses on different ways the actual world could have been, extended modal realism emphasizes a broader and more diverse understanding of what possible worlds could entail, arguing for a richer ontology of possibilities. This view can lead to discussions about the implications for identity, causality, and the nature of existence itself across different worlds. Overall, extended modal realism invites deeper exploration of how possibilities are structured and how we think about reality beyond the confines of our actual, observable universe.