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- Theodore Sider (2005). Traveling in A- and B- Time. The Monist 88:329-335.Some say that presentism precludes time travel into the past since it implies that the past does not exist, but this is a bad argument. Presentism says that only currently existing entities exist, and that the only properties and relations those entities instantiate are those that they currently instantiate. This does in a sense imply that the past does not exist. But if that precluded time travel into the past, it would also preclude the one-second-per-second “time travel” into the future that is ordinary persistence, for presentism accords the future the same ontological status as the past. Instead of quantifying over past and future objects and events, presentists speak a tensed language, regimented with primitive sentential tense operators. For a presentist, a persisting person is one who did exist, and who will exist. Regimented, these claims become: it was the case that she exists, and it will be the case that she exists. The presentist may then apply the same strategy to time travel proper. Suppose Katy travels back to the time of the dinosaurs. The presentist can say that it was the case two hundred million years ago that Katy exists. This claim, which consists of a present-tense statement “Katy exists” embedded within the past tense operator it was the case two hundred million years ago that, is exactly the sort of statement about time that a presentist is free to accept. This has all been made clear by Simon Keller and Michael Nelson ( ). In addition to rebutting the bad argument against the consistency of presentism and time travel, Keller and Nelson argue positively in favor of consistency by showing how to translate David Lewis’s ( ) account of time travel into the presentist’s tensed language. The appearance of con ict between presentism and time travel, they argue, is due only to the fact that most defenders of time travel (for example Lewis) have tended to phrase their defenses in nonpresentist terms. As much as I applaud their rebuttal of the bad argument, I wish to sound a note of caution..Reading list | Discuss | Edit | Categorize |My bibliography
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Dynamic events such as a rolling ball moving from one place to another involve change and time intervals and thus presumably successions of static events occurring one after the other, e.g., the ball’s being at a certain place and then at another place during the interval in question. When dynamic events are experienced they should count as present and thus as existent from a presentist point of view. But this seems to imply the existence of the static events involved in them. This in turn seems to imply that there exist past and perhaps even future static events. Therefore, there is a problem for presentism. A possible way out for the presentist is proposed, based on allowing for time-indexed past-oriented and future-oriented properties. One may raise objections regarding the ontological status of these properties and the commitment to past and future objects and times that they seem to bring with them, but these objections can be put to rest.
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| | Other links: dx.doi.org | Scholar | At my library | More options ... There is a tension between the “growing block” account of time (closed past, open future) and the possibility of backwards time travel. If Tim the time traveler can someday travel backwards through time, then he has (in a certain sense) already been. He might discover this fact before (in another sense) he goes. Hence a dilemma: it seems that either Tim’s future is determined in an odd way or cases of (temporary) ontic indeterminate identity are possible. Either Tim cannot avoid heading for the past or he is only indeterminately that guy who appeared in the past with many of Tim’s memories. Determinacy in the past implies a degree of determinism in the future; indeterminism about the future seeps back to the past.
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| | Scholar | At my library | More options ... Talk about time travel is puzzling even if it isn't obviously contradictory. Philosophers however are divided about whether time travel involves empirical paradox or some deeper metaphysical incoherence. It is suggested that time travel requires a Parmenidean four-dimensionalist metaphysical conception of the world in time. The possibility of time travel is addressed (mainly) from within a Parmenidean metaphysical framework, which is accepted by David Lewis in his defence of the coherence of time travel. It is argued that time travel raises formidable difficulties which are not satisfactorily resolved by Lewis's ingenious defence of time travel. Objections to time travel considered include: (1) travel to other times is impossible because there is nowhere (or “nowhen”) to go to; (2) the problem that upon setting out on a journey to the past a time machine will collide with itself; (3) time travel generates a mysterious temporal dualism between experiential time and physical time; (4) travel to the past permits reverse causation, raising the possibility of causal loops and attendant problems arising, for example, from the prospect of empirical contradiction and the possibility of someone being one of their ancestors.
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| | Other links: journals.cambridge.org jstor.org dx.doi.org | Scholar | At my library | More options ... In this course we will examine several philosophical puzzles concerning time. We all seem to experience time in a very fundamental and direct way. Yet once we begin to reflect on what time really is, it is easy to feel as puzzled as St Augustine was, who wrote: “If no one asks me, I know what [time] is. If I wish to explain it to him who asks me, I do not know.” The first set of issues we will discuss concern the question whether time is ‘real.’ Time appears to consist of past, present and future. But do the past and the future exist in the same way as the present or is only the present real? Does time ‘flow’? In what ways is time different from space? What would it be to ‘spatialize’ time? Next we will ask whether certain views of time imply that there can be no freedom of the will. One might worry that if facts about the future (including facts about what I will do tomorrow) already existed in the same way as facts about the present exist, then I could not be free to choose what I will do. After all, how can I be free to decide to skip class tomorrow, if it is ‘already’ a fact today that I will attend class? What, if anything, is the connection between various views of time and ‘fatalism’? The third topic we will discuss is time travel. First we will ask whether time travel is a conceptual possibility. As we will see, there are certain conceptual puzzles associated with the possibility of time travel. For example, one might think that if time travel is possible, then I should be able to travel back in time and kill my father before the date of my conception. But this scenario seems to lead to a contradiction. Some have taken considerations such as these to argue that the very idea of time travel is incoherent. Is this right? If not, why not? Then we will look at what the theory of relativity says about the nature of time in general and about the physical possibility of time travel more specifically. Finally we will examine several issues concerning the asymmetry of time..
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| | Scholar | More options ... There is a debate in the philosophy of time over the status of non-present entities. Do these things exist, and if so, what sorts of things are they? Recently, the debate has split into two groups, presentists and eternalists. Presentists hold that no past or future things exist now. Socrates does not now exist, though he did in the past; my future daughter does not now exist, though she may in the future. Ontologically, the present is distinct, serving to demarcate all that currently has existence. As far as the eternalist is concerned, all entities - whether past, present, or future - are equally real. If it was, is, or will be, it can be found in the eternalist picture of time. As such, there is no distinct present at which some entities exist while others do not; rather, everything enjoys the same ontological status. I will be concerned to offer an assessment of the presentist view. Common objections against presentism will be examined, amplified, and answered where appropriate. I will not examine the arguments in favor of the presentist view. Rather, I wish to describe why it is that the eternalist feels compelled to deny presentism. Ultimately, my goal will be to show that although presentism survives some of the current objections raised against it, it does not survive them all. Presentism is an interesting, but ultimately unsatisfactory view. There is a modified form of presentism (call it presentism*) that can meet the objections raised against the original position, and after noting some of the objections raised against presentism, I will sketch the outlines of presentism* in some detail. I intend to show that presentism* is able to retain what is most valuable about presentism, while also withstanding certain objections that the latter view could not.
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| | Scholar | More options ... Thinking about time travel is an entertaining way to explore how to understand time and its location in the broad conceptual landscape that includes causation, fate, action, possibility, experience, and reality. It is uncontroversial that time travel towards the future exists, and time travel to the past is generally recognized as permitted by Einstein’s general theory of relativity, though no one knows yet whether nature truly allows it. Coherent time travel stories have added flair to traditional debates over the metaphysical status of the past, the reality of temporal passage, and the existence of free will. Moreover, plausible models of time travel and time machines can be used to investigate the subtle relation between space-time structure and causality.
It surveys some philosophical issues concerning time travel and should serves as a quick introduction. It includes a new and improved way to define a time machine.
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| | Scholar | At my library | More options ... How can we talk meaningfully about the past if it does not exist to be talked about? What gives time its direction? Is time travel possible? This defence of presentism - the view that only the present exists - makes an original contribution to a fast growing and exciting debate.
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| | Scholar | At my library | More options ... Presentists believe that only presently existing things exist. In a Newtonian framework of three spatial dimensions, for example, presentists would say that all that exists is a three-dimensional spatial manifold, and the events in that manifold change with time. Eternalists, by contrast, believe that past, present, and future things all exist. In the Newtonian framework, eternalists believe in a four-dimensional space-time manifold, where events are scattered throughout this four-dimensional ‘block universe’. It is often thought that presentism is incompatible with time travel. William Godfrey-Smith (1980: 72), for example, says that ‘the metaphysical picture which underlies time travel talk is that of the block universe.’ In an informal survey of philosophers, the predominant answer to my question ‘Is presentism compatible with time travel?’ was ‘No’. Simon Keller and Michael Nelson (2001: 334) also report that this is the common view. I will argue that this common view is incorrect. Specifically, I will argue that presentism is compatible with some stories that involve closed timelike curves, and that some of these stories are time-travel stories.1 A closed timelike curve is a special case of a causal loop. A causal loop exists when there is a causal chain such that event A causes event B, event B causes event … , where the chain eventually links back to event A. Prima facie, at least, causal loops are compatible with presentism: just have all the events in the loop occur at the same time. A timelike causal connection..
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| | Other links: blackwell-synergy.com spot.colorado.edu jstor.org analysis.oxfordjournals.org dx.doi.org | Scholar | At my library | More options ... Steven Hales constructs a novel argument against the possibility of presentist time travel called the suicide machine argument. Hales argues that if presentism were true, then time travel would result in the annihilation of the time traveler. But such a consequence is not time travel, therefore presentism cannot allow for the possibility of
time travel. This paper argues that in order for the suicide machine argument to succeed, it must make (at least) one of two assumptions, each of which beg the question. The argument must either assume that the sequence of moments is invariant, or that time travel requires distinct, co-instantiated moments. Because the former disjunct assumes that presentist time travel is impossible and the latter assumes that presentism is impossible, the suicide machine argument fails.
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| | Scholar | At my library | More options ... In the present paper, I offer a new argument to show that presentism about time is incompatible with time travel. Time travel requires leaving the present, which, under presentism, contains all of reality. Therefore to leave the present moment is to leave reality entirely; i.e. to go out of existence. Presentist “time travel” is therefore best seen as a form of suicide, not as a mode of transportation. Eternalists about time do not face the same difficulty, and time travel is compossible with eternalism.
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| | Other links: logos-and-episteme.proiectsbc.ro | Scholar | At my library | More options ... Discussion of Theodore Sider, Traveling in A- and B- time
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