Time travel and the open future

I argue that the thesis that time travel is logically possible, is inconsistent with the necessary truth of any of the usual ‘open future-objective present’ models of the universe. It has been relatively uncontroversial until recently to hold that presentism is inconsistent with the possibility of time travel. I argue that recent arguments to the contrary do not show that presentism is consistent with time travel. Moreover, the necessary truth of other open future-objective present models which we might, prima facie, have supposed to be more amenable to the possibility of time travel, turn out also to be inconsistent with this possibility. Let us say that a particular model of the universe is an ‘open futureobjective present’ model just if (i) according to the model there exist intrinsic properties of pastness, presentness and futurity such that for any given time t, there is a single moment that is the objective present, and, for any ontologically real moment that is other than the objective present, that moment is either in the objective past or the objective future and (ii) given that time t is the objective present, it is genuinely indeterminate what events will occur at temporal locations that are in the objective future. There are basically three different models that are consistent with the open future-objective present view of the universe. Two of these models are consistent with, but do not entail the truth of the open future-objective present model, while one is not only consistent with that model, but also entails it. Perhaps the most obvious of these models is presentism. According to presentists, only the present moment is ontologically real, and past and future locations are ontologically unreal. So presentism entails that there exists an objective present — the only ontologically real temporal location. It need not entail, however, that there exists an open future. After all, presentists do not hold that there exists an open past, despite the fact that past temporal locations are not, by their lights, ontologically real. The ‘higher-order property’ apparatus that presentists appeal to when