Freedom, Self-Prediction, and the Possibility of Time Travel
Forthcoming. Philosophical Studies.
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.
Time Travel and Counterfactual Asymmetry
Forthcoming. Synthese.
Preprint Online Article
How should we evaluate counterfactuals and abilities in cases of backwards time travel? We ordinarily evaluate counterfactuals and abilities by holding the past fixed and keeping the future open. Your decision to eat the cake may be counterfactually correlated with the cake’s being eaten, but not its being there in the first place. You might be unable to eat the cake given you had a dental operation yesterday, but not given that you don’t. Lewis, Sider and others argue that these temporal asymmetries persists even in cases of backwards time travel. Holding the future fixed amounts to fatalism, and is no different from doing so in ordinary cases. I’ll argue that these asymmetries should be given up in cases of backwards time travel. The past shouldn’t be held past fixed, because backwards time travel implies backwards counterfactual dependence. Parts of the future should be held fixed, because they’re in the causal and evidential history of the past. We need temporally neutral methods for evaluating counterfactuals and abilities to ultimately explain causal asymmetry in the actual world.
Preprint Online Article
How should we evaluate counterfactuals and abilities in cases of backwards time travel? We ordinarily evaluate counterfactuals and abilities by holding the past fixed and keeping the future open. Your decision to eat the cake may be counterfactually correlated with the cake’s being eaten, but not its being there in the first place. You might be unable to eat the cake given you had a dental operation yesterday, but not given that you don’t. Lewis, Sider and others argue that these temporal asymmetries persists even in cases of backwards time travel. Holding the future fixed amounts to fatalism, and is no different from doing so in ordinary cases. I’ll argue that these asymmetries should be given up in cases of backwards time travel. The past shouldn’t be held past fixed, because backwards time travel implies backwards counterfactual dependence. Parts of the future should be held fixed, because they’re in the causal and evidential history of the past. We need temporally neutral methods for evaluating counterfactuals and abilities to ultimately explain causal asymmetry in the actual world.
A Deliberative Approach to Causation
2017 . Philosophy and Phenomenological Research. 95(3): 686–708.
Fundamental physics makes no clear use of causal notions; it uses laws that operate in relevant respects in both temporal directions and that relate whole systems across times. But by relating causation to evidence, we can explain how causation fits in to a physical picture of the world and explain its temporal asymmetry. This paper takes up a deliberative approach to causation, according to which causal relations correspond to the evidential relations we need when we decide on one thing in order to achieve another. Tamsin’s taking her umbrella is a cause of her staying dry, for example, if and only if her deciding to take her umbrella for the sake of staying dry is adequate grounds for believing she’ll stay dry. This correspondence explains why causation matters: knowledge of causal structure helps us make decisions that are evidence of outcomes we seek. The account also explains why we can control the future and not the past, and why causes come before their effects. When agents properly deliberate, their decisions can never count as evidence for any outcomes they may seek in the past. From this it follows that causal relations don’t run backwards. This deliberative asymmetry is itself traced back to asymmetries of evidence and entropy, providing a new way of deriving causal asymmetry from temporally symmetric laws.
Varieties of Epistemic Freedom
2016, Australasian Journal of Philosophy. 94(4): 736-751.
When we deliberate about what to do, we appear free to decide on different options. Three accounts use ordinary beliefs to explain this apparent freedom—appealing to different types of ‘epistemic freedom’. When an agent has epistemic freedom, her evidence while deliberating does not determine what decision she makes. This ‘epistemic gap’ between her evidence and decision explains why her decision appears free. The varieties of epistemic freedom appealed to might look similar. But there is an important difference. Two rely on an agent’s ability to justifiably form beliefs unconstrained by evidence, and identify decisions as beliefs—either beliefs about acts (Velleman) or decisions (Joyce and Ismael). But when used to explain apparent freedom, these accounts face serious problems: they imply agents have epistemic freedom over evidence-based beliefs, and rely on a faulty notion of justification. Underlying these troubles, it turns out these accounts presuppose an unexplained apparent ability to form different beliefs. A third variety of epistemic freedom uses ignorance conditions instead (Levi and Kapitan). We appear free partly because we’re ignorant of what we’ll decide. Ignorance-based accounts avoid the above problems, and remain a promising alternative.
Time, Flies, and Why We Can't Control the Past
Forthcoming, in Barry Loewer, Eric Winsberg and Brad Weslake (eds.) Time's Arrows and the Probability Structure of the World, Cambridge, Mass.: Harvard University Press.
David Albert explains why we can typically influence the future but not the past by appealing to an initial low-entropy state of the universe. And he argues that in the rare cases where we can influence the past, we cannot use this influence to knowingly gain future rewards: so it does not constitute control. I introduce an important new case in which Albert's account implies we can not only influence the past but control it: a case where our actions in the present are reliably correlated with several events in the present and past. To deal with such cases, we need to appeal to epistemic conditions on deliberation: being agents requires our decisions being epistemically undetermined at the time we make them. In a world with the past-hypothesis, this implies that deliberation will typically come prior to decision. Once deliberation in this direction is established, correlations towards the past cannot then be exploited for control. To explain why we cannot effectively control the past, we need to appeal to deliberation, whether as part of a defence of Albert's account, or used independently to explain the asymmetry of control.