Are there other worlds that are other ways? I say there are. I advocate a thesis of plurality of worlds, or modal realism, which holds that our world is but one world among many. There are countless other worlds, other very inclusive things. Our world consists of us and all our surroundings, however remote in time and space; just as it is one big thing having lesser things as parts, so likewise do other worlds have lesser otherworldly things as parts. The worlds are something like remote planets; except that most of them are much bigger than mere planets, and they are not remote. Neither are they nearby. They are not at any spatial distance whatever from here. They are not far in the past or future, nor for that matter near; they are not at any temporal distance whatever from now. They are isolated: there are no spatiotemporal relations at all between things that belong to different worlds. Nor does anything that happens at one world cause anything to happen at another. Nor do they overlap; they have no parts in common, with the exception, perhaps, of immanent universals exercising their characteristic privilege of repeated occurrence.
>The worlds are many and varied. There are enough of them to afford worlds where (roughly speaking) I finish on schedule, or I write on behalf of impossibilia, or I do not exist, or there are no people at all, or the physical constants do not permit life, or totally different laws govern the doings of alien particles with alien properties. There are so many other worlds, in fact, that absolutely every way that a world could possibly be is a way that some world is. And as with worlds, so it is with parts of worlds. There are ever so many ways that a part of a world could be; and so many and so varied are the other worlds that absolutely every way that a part of a world could possibly be is a way that some part of some world is.
>The other worlds are of a kind with this world of ours. To be sure, there are differences of kind between things that are parts of different worlds, one world has electrons, and another has none. One has spirits, and another has none. But these differences of kind are no more than sometimes arise between things that are parts of one single world, for instance, in a world where electrons coexist with spirits. The difference between this and the other worlds is not a categorial difference.
The worlds are not of our own making; it may happen that one part of a world makes other parts, as we do, and as otherworldly gods and demiurgs on a grander scale. But if worlds are causally isolated, nothing outside a world ever makes a world, and nothing inside makes the whole of the world, for that would be an impossible kind of self-causation. We make languages and concepts and descriptions and imaginary representations that apply to worlds. We make stipulations that select some worlds rather than others for our attention. Some of us even make assertions to the effect none of the worlds exist. But none of these things we make are the worlds themselves.