 The typical explication of determinism fastens on the state of the (whole) world at a particular time (or instant), for a variety of reasons. We will briefly explain some of them. Why take the state of the whole world, rather than some (perhaps very large) region, as our starting point? One might, intuitively, think that it would be enough to give the complete state of things on Earth, say, or perhaps in the whole solar system, at t, to fix what happens thereafter (for a time at least). But notice that all sorts of influences from outside the solar system come in at the speed of light, and they may have important effects. Suppose Mary looks up at the sky on a clear night, and a particularly bright blue star catches her eye; she thinks “What a lovely star; I think I’ll stay outside a bit longer and enjoy the view.” The state of the solar system one month ago did not fix that that blue light from Sirius would arrive and strike Mary’s retina; it arrived into the solar system only a day ago, let’s say. So evidently, for Mary’s actions (and hence, all physical events generally) to be fixed by the state of things a month ago, that state will have to be fixed over a much larger spatial region than just the solar system. (If no physical influences can go faster than light, then the state of things must be given over a spherical volume of space 1 light-month in radius.)