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)

{June 2018 UPDATE: This work has been greatly surpassed by "Utilizing Future-Viewing Instruments" which will appear in the July 2018 issue of Progress in Physics. It can now be downloaded in PDF form from their website.} This is the full text of the paper that was published as a Kindle book on April 6th, 2014. In most respects, it has since been surpassed by "Potentials of Future-Viewing Machines," which is available here in this repository. Nevertheless, this earlier work addresses minutia (...) and interesting considerations that do not appear elsewhere, and it has a large bibliography, so it remains very useful for research purposes. (shrink)

{June 2018 UPDATE: This work has been greatly surpassed by "Utilizing Future-Viewing Instruments" which will appear in the July 2018 issue of Progress in Physics. It can now be downloaded in PDF form from their website.} -/- The introduction of new scientific instruments has always played a vital role in the advancement of science and society. All scientific instruments to date have only been able to gain information pertaining to events of our immediate and distant past. Concerning our attempts to (...) gain information about future events, thus far our sciences have been limited to prediction. However, what if we could develop instruments that would enable us, in a wide range of circumstances, to achieve direct empirical access to future states of our world? It is clear that any kind of future-viewing machine would have enormous impacts upon science and society, but what kinds of impacts? Questions as to whether such machines are physically possible and might ever be feasible from an engineering perspective will not be addressed; this work is devoted to exploring the logic of such machines and deducing some of the possibilities of their utilization. (shrink)

The philosophy of time travel is a sub-field of metaphysics – the study of what there is and what things are like – that considers questions about the possibility of time travel and what a world in which time travel is possible looks like. These questions range from whether time travel is actually possible, to how time travellers can act in the past or future. This thesis delves into a particularly interesting, yet historically undertreated theme: the abilities of time travellers (...) and relatedly their freedom as well. The abilities and freedom of time travellers has been the source of a lot of recent discussion with some polarising views. The minority (which includes Lewis (1976), but also Ted Sider (2002)) argue for the affirmative – that time travellers are free and have the same (or perhaps more) abilities as non-time travellers. The majority (which includes Kadri Vihvelin (1996), Michael Rea (2005), Stephanie Rennick (2015), Alison Fernandes (2020), amongst others) argue for the negative, that time travellers do not have exactly the same freedoms and abilities as non-time travellers. I think that it is a mistake to be so pessimistic about the abilities and freedom of time travellers. I treat concerns about the freedom of time travellers and concerns about the abilities of time travellers as two sides of the same coin. Therefore, in what follows, I argue for two related conclusions. First, I argue that time travellers have all sorts of abilities. Second, I argue that time travellers are just as free as non-time travellers. In arguing for these conclusions, I first produce a novel analysis of ability which reveals important details about how abilities track inputs rather than outputs. Second, I use this new analysis of ability to present a new compatibilist account of free will. If I am right in arguing positively for the abilities and freedoms of time travellers, then this has large implications for both the current time travel discourse and the general debate surrounding freedom. Significantly, I am arguing against some prominent views about time travel and in suggesting that these views are mistaken, I am presenting new ideas about ability and freedom: specifically, that time travellers have the ability and are free to do impossible things. (shrink)

This paper argues that the most famous objection to backward time travel can carry no weight. In its classic form, the objection is that backward time travel entails the occurrence of impossible things, such as auto-infanticide—and hence is itself impossible. David Lewis has rebutted the classic version of the objection: auto-infanticide is prevented by coincidences, such as time travellers slipping on banana peels as they attempt to murder their younger selves. I focus on Paul Horwich‘s more recent version of the (...) objection, according to which backward time travel entails not impossible things, but improbable ones—such as the string of slips on banana peels that would be required to stop a determined auto-infanticidal maniac from murdering her younger self—and hence is itself highly improbable. I argue that backward time travel does not entail unusual numbers of coincidences; and that, even if it did, that would not render its occurrence unlikely. (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.

In this paper I wish to examine the claim that it would be possible for us now to do something which would be the posterior efficient cause of some past event. I am not prepared to discuss the physics of elementary particles, and I will not consider what is sometimes called time reversal. Rather my analysis will be limited to cases in which it is alleged that we, in a world of middle-sized physical objects where most causes precede or are (...) simultaneous with their effects, could conceivably do something so that something else should have happened. I will argue that some of the cases which meet this description are indeed backwards causation if one is prepared to make certain assumptions about time. I will not evaluate these assumptions; rather I will try to clarify them and to make plain their implications for causality. For the argument about backwards causation is most fundamentally, or so I will try to show, an argument about the nature of time. (shrink)

The subject of time travel has been receiving increasing attention in the recent philosophical literature. Most of the articles that deal with it have been concerned to defend the logical consistency of time travel against those who claim that it entails one or more contradictions. Two sorts of defences have been offered. The first sort of defence involves showing that time travel does not entail those consequences which other philosophers allege it does entail. The second sort of defence involves an (...) admission that time travel does indeed involve that which its opponents allege it does involve, e.g., being in more than one place at a time, but arguing that such consequences in no way vitiate the logical consistency of this notion.My first aim in this paper is to provide a defence of time travel of the second sort. More specifically, I want to cut the ground from under an argument which might run thus:Time travel entails that certain effects can precede their causes.It is logically impossible for an effect to precede its cause. (shrink)

The idea that some of God's past beliefs depend on our future actions has a long history, going back to Origen in the third century CE. However, it is not always clear what this idea amounts to, since it is not always clear what kind of dependence is at issue. This paper surveys five different interpretations of dependence and, in each case, considers the implications for the debate over theological fatalism. Along the way, we discuss a number of related issues, (...) including the nature of explanation, the scope of metaphysical grounding, and the possibility of backward causation. (shrink)

The present paper advances an analogy between cases of extra-mathematical explanation and cases of what might be termed ‘extra-logical explanation’: the explanation of a physical fact by a logical fact. A particular case of extra-logical explanation is identified that arises in the philosophical literature on time travel. This instance of extra-logical explanation is subsequently shown to be of a piece with cases of extra-mathematical explanation. Using this analogy, we argue extra-mathematical explanation is part of a broader class of non-causal explanation. (...) This has important implications for extra-mathematical explanation, for time travel and for theories of explanation more generally. (shrink)

The aim of this paper is to help authors construct coherent time-travel narratives by establishing five features of multiverse time travel. To this end, multiverse time travel will be contrasted to fixed-universe time travel, and both versions related to various cases - where each case is designed to illustrate a key feature of multiverse time travel.