Abstract
Do time travellers retain their normal freedom and abilities when they travel back in time? Lewis, Horwich and Sider argue that they do. Time-travelling Tim can kill his young grandfather, his younger self, or whomever else he pleases—and so, it seems can reasonably deliberate about whether to do these things. He might not succeed. But he is still just as free as a non-time traveller. I’ll disagree. The freedom of time travellers is limited by a rational constraint. Tim can’t reasonably deliberate on killing his grandfather, certain that he’ll fail. If Tim follows his evidence, and appropriately self-predicts, he will be certain he won’t kill his grandfather. So if Tim is both evidentially and deliberatively rational, he can’t deliberate on killing his grandfather. This result has consequences. Firstly, it shows how evidential limits in the actual world contribute to our conception of the future as open. Secondly, it undercuts arguments against the possibility of time travel. Thirdly, it affects how we evaluate counterfactuals in time travel worlds, as well as our own. I’ll use the constraint to motivate an evidential and temporally neutral method of evaluating counterfactuals that holds fixed what a relevant deliberating agent has evidence of, independently of her decision. Using this method, an agent’s local abilities may be affected by what happens globally at other times, including the future.
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Notes
While Lewis (1976, p. 150) takes the evaluation of abilities to depend on context, he implies that the only contexts in which Tim’s failure are held fixed are fatalist ones, and don’t concern what Tim can do in any reasonable sense.
Even if spacetimes involving closed timelike curves allow for no global time ordering, so that we can only define temporal direction locally, and backwards time travel doesn’t involve local backwards causation, we still face problems evaluating counterfactuals that aren’t local—see Sect. 6.
I won’t distinguish sharply between actions and their intended results. For some purposes, a more general formulation is preferable, one that uses de-tensed propositions or states of affairs, so as not to presume agents deliberate only on the future. But, for grammatical ease, I’ll use the future-tensed action formulation.
Admittedly, it’s difficult to make sense of Tim’s motivation for travelling back without taking him to be irrational, or to have adopted a non-standard metaphysics of time. See Objections 5 and 6 below.
What if Tim allows for the possibility of young-gramps’ regeneration? Plausibly Tim intends to kill young-gramps in a permanent manner. For simplicity, I’ll take killing to imply permanently-killing. In any case, Tim aims to do something that will make the future different from what he believes it was.
I take causal relata to be states of affairs, although, for this paper, nothing significant hangs on this choice; I’ll also talk loosely of other relata.
There are other senses of trying which Tim would be unreasonable to engage in (see Objection 8).
Such agents might continue to take themselves to act, even when they no longer deliberate, or might take themselves to become mere ‘instruments of the world’. Smith (2005) explores other attitudes the time traveller might adopt.
A similar result can be reached by requiring deliberation to be between incompatible alternatives: certainty of intended result rules out other incompatible options as available.
If the causal relata are fine-grained, time travel without causal loops may not be possible. Even so, the time traveller’s freedom would not be affected in virtue of the potentially self-defeating nature of the casual loop, but in virtue of its evidential features.
For responses to objections involving curiosity, see Smith (1997, pp. 383–385).
More carefully, B can’t be known in a way that would leave the correlation between A and B intact.
One might still argue that an agent can bilk the correlation, even if she doesn’t. But then one would need to hear more about why this sense of ‘can’ is relevant to the correlation being causal, rather than one more closely tied to what an agent can reasonably deliberate on.
If counterfactuals are context-sensitive, we may need to specify that these are the kinds of counterfactuals relevant for decision-making and abilities.
Arguably, this is a necessary but not sufficient condition, since a causal condition may be required as well. My arguments won’t depend on this detail, or others concerning the condition’s content.
Perhaps ignoring a ‘transition period’ just prior to the antecedent (Lewis 1979).
For a related argument, see Kiourti (2008, pp. 349–350). Kiourti argues that future events are relevant to the time traveller’s ability to kill her younger-self because they’re in her ‘personal’ past. The argument I give here is more general: it does not rely on demarcating the time-traveller’s personal past, or on facts concerning the identity of the time traveller.
References
Albert, D. (2000). Time and chance. Cambridge, MA: Harvard University Press.
Arntzenius, F., & Maudlin, T. (2013). Time travel and modern physics. In Edward N. Zalta (Ed.) The stanford encyclopedia of philosophy (Winter 2013 Edition), http://plato.stanford.edu/archives/win2013/entries/time-travel-phys/.
Black, M. (1956). Why cannot an effect precede its cause? Analysis,16, 49–58.
Blanchard, T. (2014). Causation in a Physical World. PhD Thesis. Rutgers University.
Bratman, M. (1984). Two faces of intention. The Philosophical Review,93(3), 375–405.
Davidson, D. (1980). Essays on actions and events. Oxford: Clarendon Press.
Dennett, D. (1984). Elbow room. Cambridge, MA: MIT Press.
Dummett, M. (1964). Bringing about the past. Philosophical Review,73, 338–359.
Fernandes, A. (2016a). Varieties of epistemic freedom. Australasian Journal of Philosophy,94(4), 736–751.
Fernandes, A. (2016b). A deliberative account of causation: How the evidence of deliberating agents accounts for causation and its temporal direction. PhD Thesis. Columbia University.
Fernandes, A. (2017). A deliberative approach to causation. Philosophy and Phenomenological Research,95(3), 686–708.
Fernandes, A. (2018). Time travel and counterfactual asymmetry. (unpublished manuscript).
Fernandes, A. (2019). Time, flies, and why we can’t control the past. In B. Loewer, E. Winsberg, B. Weslake (Eds.), Time’s arrows and the probability structure of the world. Cambridge, MA: Harvard University Press (in press).
Ginet, C. (1962). Can the will be caused? The Philosophical Review,71(1), 49–55.
Grice, H. P. (1971). Intention and uncertainty. Proceedings of the British Academy,57, 263–279.
Hampshire, S., & Hart, H. L. A. (1958). Decision, intention and certainty. Mind,67(265), 1–12.
Harman, G. (1976). Practical reasoning. The Review of Metaphysics,29(3), 431–463.
Holton, R. (2006). The act of choice. Philosophers’ Imprint,6(3), 1–15.
Horwich, P. (1987). Asymmetries in time. Cambridge MA: MIT Press.
Ismael, J. (2003). Closed causal loops and the bilking argument. Synthese,136, 305–320.
Ismael, J. (2007). Freedom, compulsion and causation. Psyche,13(1), 1–11.
Ismael, J. (2011). Temporal experience. In C. Callender (Ed.), The Oxford handbook of philosophy of time. Oxford: Oxford University Press.
Kapitan, T. (1986). Deliberation and the presumption of open alternatives. The Philosophical Quarterly,36(143), 230–251.
Kiourti, I. (2008). Killing baby suzy. Philosophical Studies,139(3), 343–352.
Levi, I. (1980). The enterprise of knowledge. Cambridge, MA: MIT Press.
Levi, I. (1986). Hard choices. Cambridge: Cambridge University Press.
Lewis, D. (1976). The paradoxes of time travel. American Philosophical Quarterly,13, 145–152.
Lewis, D. (1979). Counterfactual dependence and time’s arrow. Noûs,13(4), 455–476.
Loewer, B. (2007). Counterfactuals and the second law. In H. Price & R. Corry (Eds.), Causation, physics, and the constitution of reality. New York: Oxford University Press.
Mellor, D. Hugh. (1998). Real time II. London: Routledge.
Owens, D. (2008). Deliberation and the first person. In A. E. Hatzimoysis (Ed.), Self-knowledge. Oxford: Oxford University Press.
Pearl, J. (2000). Causality: Models, reasoning and inference. Cambridge: Cambridge University Press.
Price, H. (1991). Agency and probabilistic causality. British Journal for the Philosophy of Science,42, 157–176.
Price, H. (1996). Time’s arrow & archimedes’ point. New York: Oxford University Press.
Prosser, S. (2016). Experiencing time. New York: Oxford University Press.
Rennick, S. (2015). Things mere mortals can do, but philosophers can’t. Analysis,75(1), 22–26.
Sider, T. (2002). Time travel, coincidences and counterfactuals. Philosophical Studies,110, 115–138.
Smith, N. J. J. (1997). Bananas enough for time travel? British Journal for the Philosophy of Science,48, 363–389.
Smith, N. J. J. (2005). Why would time travellers try to kill their younger selves? Monist,88(3), 388–395.
Vihvelin, K. (1996). What time travelers cannot do. Philosophical Studies,81, 315–330.
Wheeler, J., & Feynman, R. (1949). Classical electrodynamics in terms of direct interparticle action. Reviews of Modern Physics,21, 425–434.
Woodward, J. (2003). Making things happen. New York: Oxford University Press.
Acknowledgements
I would like to thank the following people for helpful comments, discussions and suggestions: David Albert, Achille Varzi, Nina Emery, Daniel Nolan, David Braddon-Mitchell, Mike Hicks, Zee Perry, Helen Beebbee, Robbie Williams, Tom Dougherty, Tim Button, Lukas Skiba, Nick Gorman, and audiences at the Joint Session, the Pacific APA, and the International Association for the Philosophy of Time Conference. This work was supported by a Postdoctoral Fellowship at the Center for Philosophy of Science, University of Pittsburgh and a Research Fellowship at the University of Warwick on an Arts and Humanities Research Council project ‘Time: Between Metaphysics and Psychology’ (AH/P00217X/1).
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Fernandes, A. Freedom, self-prediction, and the possibility of time travel. Philos Stud 177, 89–108 (2020). https://doi.org/10.1007/s11098-018-1181-9
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DOI: https://doi.org/10.1007/s11098-018-1181-9