  This paper investigates the mathematical representation of time in physics.
In existing theories time is represented by the real numbers, hence their
formal properties represent properties of time: these are surveyed. The central
question of the paper is whether the existing representation of time is
adequate, or whether it can or should be supplemented: especially, do we need a
physics incorporating some kind of `dynamical passage' of time? The paper
argues that the existing mathematical framework is resistant to such changes,
and might have to be rejected by anyone seeking a physics of passage. Then it
rebuts two common arguments for incorporating passage into physics, especially
the claim that it is an element of experience. Finally the paper investigates
whether, as has been claimed, `causal set theory' provides a physics of
passage.
