Abstract
This chapter argues for a notion of time that allows time travel. In order to time traveling to happen, in contrast to Presentism, the chapter demonstrates that we can change the past and we have some place where to travel. It shows the advantages of a non-presentist ontology that advocates for indeterminacy of future facts based not on its absence of truth-value, but on the overdetermination of future facts. The conclusion is that to break the causal chain is impossible in we are placed in the same causal line. But if we rethink the time traveling as a trans-world traveling, it is possible to open a new causal line anytime that someone travel in time, to the past as well as to the future.
This work has been granted by Spanish Government, “Ministerio de Economía y Competividad”, Research Projects FFI2008-01205 (Points of View. A Philosophical Investigation), FFI2011-24549, (Points of View and Temporal Structures), and FFI2014-57409-R (Points of View, Dispositions, and Time. Perspectives in a World of Dispositions).
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Notes
- 1.
This ordinary conception has the following features, among others: (i) time flows, and it does it in one direction: What is future will be present and will be past; what is present was future and will be past; and what is past was present and was future; (ii) time-asymmetry of causation: causes are different from effects, and past events cannot be caused by future events: (a) the causal relation is asymmetric—if A is a cause of B, then B is not a cause of A—; and (b) effects never (or almost never) occur before their causes [12]; (iii) the causal continuity and change through time (the time traveller that departs has to be the same person that arrives to the moment in the past).
- 2.
The reader can find an immensity of books and movies about time travel. Perhaps the most well known is H.G. Wells’ The Time Machine. Lewis [6] talks about some classical works of R.A. Heinlen. The John Carter series written by E.R. Borroughs combines time travel and space long-distance travel. Among movies, Back to the Future saga is a classic, but also other films as La Jetée, Time Bandits, The Boy, 12 Monkeys, Donnie Darko, Timecrimes, or Loopers, to name just a few, include time traveling. Generally, we can distinguish two different kinds of time travel. The first one supposes just a physical lineal transportation of the time traveler from the original time to the new time (through the intentional or accidental use of some time traveling device). The second one, as Lewis [6: 148] points out, presupposes some causal loop that transports the time traveler from some concrete spot of time to a different one. We will focus on the first kind, but our conclusions here could be easily applied to the other kind.
- 3.
We shall accept in this paper the thesis of D. Lewis about the possibility of time travel. As him, we think that time traveling stories are, in some cases, perfectly consistent with the causal laws of our world (or some other possible world) and that “the paradoxes of time travel are just oddities, not impossibilities” [6: 145].
- 4.
We will avoid here the question about its empirical impossibility or whether time travel is even permitted by the stipulated scientific laws of nature because these are matters to be treated by empirical sciences. According to actual relativistic physical theories, nevertheless, time travel is theoretically possible.
- 5.
Notice that the impossibility of changing the past is not per se a reason against time travel. It has to be added to the principle of autonomy: on arriving in the past, a time traveller can locally engage in acts other that those ones that history records without being inconsistent with the way reality is, as long as this other acts are compatible with the laws of physics. Therefore, according to the autonomy principle, if time travel is possible, time travellers have the possibility of causally affecting past events. Consequently, we will have every right to ask how things could have been.
- 6.
This example is basically the same that can be found in Lewis [6: 149].
- 7.
This story is popularly known as the “Grandfather Paradox”.
- 8.
The problem of temporary intrinsics says that sometimes we can find objects with apparently contradictory or conflicting properties. This is to say, one object can seem, for instance, to be bent at one time and not bent at another. This is, obviously, a contradiction because supposedly the object needs to have the same properties to be the same object, to have some continuity. Lewis addresses this problem in Lewis [8]. See Footnote 10 for other examples of time paradoxes.
- 9.
Our use of the terms “Endurantism” and “Perdurantism” is very straightforward and is meant to be that way.
- 10.
We are supposing here that the time of the travel is always less than the period of time between the departure and the arrival. This means that a cryogenized traveler does not count as a time traveler. We are neither having into consideration the possibility that the duration of travel would be more than the time traveled, as in cases where the relativity of time can be involved. If curiosity is biting you, just think, for instance, in a cosmonaut that was traveling in the space with a velocity close to the light-speed for two years and when she goes back to the Earth discovers that here have passed more than fifty years and her grandsons are older than her.
- 11.
Defenses of this view can be found in Markosian [10] and Zimmerman [20], and in a number of books and papers.See also [3–5]. Rasmussen [16], nevertheless, thinks that Presentism is compatible with a tenseless theory of time by contradicting one of the principles of A-theory and reducing the A-properties (or determinations) to facts about B-relations. This is something that McTaggart himself rejects in his paper. Unfortunately, since this debate is not important for our argumentation here, we will say nothing about that.
- 12.
In contrast to what McTaggart calls the B-series: a tenseless ordination of slots of time characterized by two-place relations as ‘two days later than’, ‘one day later than’, ‘simultaneous with’, ‘one day earlier than’, and ‘two days earlier than’. The important thing in McTaggart’s argument is that the B-series does not constitute a proper time series by itself. Because B-series does not involve genuine change without the A-series, and change is essential to time. Then, he concludes, the A-series is essential to time. But the A-series is, according to him, contradictory because the different A-properties that a very same slot of time can have (past, present, and future) are incompatible with one another. Then, he concludes, time is unreal. According to our own point of view, denying both the A-series and Presentism does not necessarily imply that time is unreal.
- 13.
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Colomina, J.J., Chico, D.P. (2015). Presentism, Non-presentism and the Possibility of Time Travel. In: Vázquez Campos, M., Liz Gutiérrez, A. (eds) Temporal Points of View. Studies in Applied Philosophy, Epistemology and Rational Ethics, vol 23. Springer, Cham. https://doi.org/10.1007/978-3-319-19815-6_10
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