The Order of Time

by Carlo Rovelli

The difference between Aristotle and Newton is glaring. For Newton, between two things there may also be “empty space.” For Aristotle, it is absurd to speak of “empty” space, because space is only the spatial order of things. If there are no things—their extension, their contacts—there is no space. Newton imagines that things are situated in a “space” that continues to exist, empty, even when divested of things. For Aristotle, this “empty space” is nonsensical, because if two things do not touch it means that there is something else between them, and if there is something, then this something is a thing, and therefore a thing that is there. It cannot be that there is “nothing.” For my part, I find it curious that both these ways of thinking about space originate from our everyday experience. The difference between them exists due to a quirky accident of the world in which we live: the lightness of air, the presence of which we only barely perceive. We can say: I see a table, a chair, a pen, the ceiling—and that between myself and the table there is nothing. Or we can say that between one and another of these things there is air. Sometimes we speak of air as if it were something, sometimes as if it were nothing. Sometimes as if it were there, sometimes as if it were not there. We are used to saying “This glass is empty” in order to say that it is full of air. We can consequently think of the world around us as “almost empty,” with just a few objects here and there, or alter...