A central tenet of truthmaker theory is that necessitation is necessary for truthmaking (NEC). This paper defends NEC in a novel, piecemeal way, namely by responding to a potential counterexample involving a changing past. If Carter won a race at t1 but is later disqualified at t2, then Carter no longer won at t1. A wholly past event seems to have changed in the future. The event makes ‘Carter won the race at t1’ (RACE) true between t1‐2 but fails to (...) make it true at t2. So, we have a potential counterexample to necessitation: a truthmaker of RACE fails in another context to make the same truthbearer RACE true. I argue that the best solution to this challenge is not that there are different truthbearers at t1‐2 and t2 (the semantic response), or that RACE was never true because of the future disqualification or will always be true despite the future disqualification. The best solution is to accept that the past can change: past events can change based on what happens in the future (e.g., via their effects). This paper's novel defence of necessitation will illustrate the importance of utilising explicitly ontological and commonsensical tools in accounting for truth. (shrink)

There has been in recent years a huge surge of interest in the so-called extended Wigner’s friend scenario (EWFS). In short, a series of theorems (with some variation in detail) puts pressure on the ability of different agents in the scenario to account for each of the others’ measured outcomes: the outcomes cannot be assigned single well-defined values while also satisfying other reasonable physical assumptions. These theorems have been interpreted as showing that there can be no absolute, third-person, ‘God’s eye’ (...) description of our reality. The focus of this paper is the strongest of these no-go theorems, the ‘local friendliness’ theorem of Bong et al. (2020, _Nature Physics_, _16_, 1199–1205), which gives earnest consideration to the possibility of a measurement that unitarily reverses an entire lab system, including a conscious agent, thereby erasing the agent’s memory. The purpose of this paper is to begin the philosophical conversation regarding key questions concerning this process: Are the events in the lab merely ‘erased’, or do they in some sense not exist at all? What would it be like to be unitarily reversed? Should an agent care about any experiences they have inside the lab before they are reversed? This analysis employs a parallel case of memory erasure, to which this case can be contrasted, arising in the context of drug-induced amnesia as a result of administering anaesthesia during medical procedures (Carbonell, 2014, _Bioethics_, _28_(5), 245–254). I argue that the consequences of unitarily reversing an agent are much more dramatic than simply memory erasure—the set of events themselves, and the personal timeline of the agent, leave no record at all inside or outside the lab. I consider the ramifications of this for the picture of reality that arises from the EWFS. (shrink)

In some stories, time travellers cannot change the past. It is widely accepted that this is metaphysically possible. In some stories, time travellers can change the past. Many philosophers have explained how that, too, is metaphysically possible. This paper considers narratives where sometimes the past can change and sometimes it cannot, arguing that this is also something that is possible. Further, I argue that we can make sense of stories where some events appear to be ‘fixed points in time’.

This paper investigates ‘exterminous hypertime’, a model of time travel in which time travellers can change the past in virtue of there being two dimensions of time. This paper has three parts. Part one discusses the laws which might govern the connection between different ‘hypertimes’, showing that there are no problems with overdetermination. Part two examines a set of laws that mean changes to history take a period of hypertime to propagate through to the present. Those laws are of interest (...) because: (i) at such worlds, a particular problem for non-Ludovician time travel (‘the multiple time travellers’ problem) is avoided; and (ii) they allow us to make sense of certain fictional narratives. Part three discusses how to understand expectations and rational decision making in a world with two dimensions of time. I end with an appendix discussing how the different theories in the metaphysics of time (e.g., tensed/tenseless theories and presentism/eternalism/growing block theory) marry up with exterminous hypertime. (shrink)

This article discusses the possibility of some outlandish tropes from time travel fiction, such as people reversing in age as they time travel or the universe being destroyed because a time traveler kills their ancestor. First, I discuss what type of possibility we might have in mind, detailing ‘close possibility’ as one such candidate. Secondly, I argue that—with only little exception—these more outlandish tropes fail to be closely possible. Thirdly, I discuss whether these outlandish tropes may nevertheless be more broadly (...) possible (e.g., metaphysically or logically possible), arguing that whether they are or not depends upon your favored metaphysics of the laws of nature. (shrink)

Many defenders of the possibility of time travel into the past also hold that such time travel places no restrictions on what said time travelers can do. Some hold that it places at least a few restrictions on what time travelers can do. In attempting to resolve this dispute, I reached a contrary conclusion. Time travelers to the past cannot do other than what they in fact do. Using a very weak notion of can, I shall argue that the correspondingly (...) strong cannot do otherwise applies in the case of backwards time travel. I defend this result from objections. (shrink)

Despite a growing number of models argument for the logical possibility of changing the past there continues to be resistance to and confusion surrounding the possibility of changing the past. In this paper I shall attempt to mitigate the resistance and alleviate at least some of the confusion by distinguishing changing the past from what Richard Hanley calls ‘annulling’ the past and distinguishing both from what I shall call ‘otherwising’ the past.