- Although philosophers typically agree that we cannot change the past, most think it possible to causally affect the past. What’s the difference? Changing is altering a time from being one way, the first time around, to being some other way, the second time around (hence “the second time around fallacy”). Causally affecting a time is making a time the way that, in fact, it is. If anyone travels to the past they will causally affect the time to which they travel: they will breathe air, tread on bugs, talk to people, and so on. But nothing the time traveller does changes the past: instead, her actions are part of what makes that time the way that it is (and was).
- Conclusion: It doesn't really matter whether you’re travelling into the past, or the future; what matters is how much you know about the time to which you travel. If you know a lot about what you did, or will do, or if you know a lot about what did, or will, happen, then your capacity to deliberate about what to do is severely undermined. But if you don’t know what you did, or will do, and if you don’t know what did, or will, happen, then your capacity to deliberate remains intact. And if you think you know what did, or will, happen, and you’d prefer that it didn’t, or won’t, happen, then it might even be rational to produce misleading evidence as of that thing happening, in order to make it rational to travel in time to try and prevent that thing from happening. That all goes to show that time travel, and decisions of time travellers, are plenty interesting enough without needing to think that changing the past is possible.
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