Each instant is irrevocable.

It can never recur by the very character of time.

But if on the relative theory an instant of time is simply the state of nature at that time, and the time-ordering relation is simply the relation between such states, then the irrevocableness of time would seem to mean that an actual state of all nature can never return.

I admit it seems unlikely that there should ever be such a recurrence down to the smallest particular.

But extreme unlikeliness is not the point.