Abstract

During the last hundred years the notion of time flow has been held in low esteem by philosophers of science. Since the metaphor depends heavily on the analogy with motion, criticisms of time flow have either attacked the analogy as poorly founded, or else argued by analogy from a “static” conception of motion. Thus (1) Bertrand Russell argued that just as motion can be conceived as existence at successive places at successive times without commitment to a state of motion at an instant, so duration can be conceived as existence at each of the times at which a thing exists without any commitment to a becoming or flow from one instant to another. I call this the “at-at” objection to time flow. A second objection (2) is that the sufficiency of the “B-theoretic” conception of time for physics makes the concept of time flow otiose. On this rendering the existence of a thing through time is just the “tenseless existence” of the thing at each instant of the duration (or at each spacetime point), without any flow from one instant or point to another. A third objection (3) is that in relativity theory, owing to the relativity of simultaneity, there is no unique invariant ‘now’, or hyperplane of simultaneously occurring events. If time flow is conceived in terms of the flow of such a ‘now’, then the non-existence of a worldwide instant of occurrence appears to be refuted. Lastly, (4) a capstone to these criticisms is the objection famously raised by Jack Smart: if rate of flow of any quantity can only be reckoned with respect to time, then with respect to what does time flow? If it does not even make sense to ask how fast time flows, then surely the metaphor should be abandoned as confused.