ABSTRACT
The direction of time is the difference between being earlier than something and being later than it. Everyone agrees that time, whether linear or looped, is directed in a way that space is not. If so, earlier and later must differ in some substantive, non-formal way if the parallels noted in the first section, “Formalities,” are not to give time’s direction spatial counterparts. The difference between earlier and later must also be intrinsic, to distinguish it from substantive spatial differences, like that between clockwise and anticlockwise, which are merely extrinsic. B-theories of time’s direction use an “arrow of time,” a “process or phenomenon that has a definite direction in time”, such as the expansion of the universe. Time’s causal arrow also shows how the positrons of the sixth section, “Irreversibility,” differ from time-travelling electrons, by making a locally reversed time order entail a locally reversed causal order that positrons and electrons never exhibit.
