‘ok so’
determinism is (not) the idea that you can perfectly predict the future by knowing the position and momentum of every particle (but it’s something like that).
…and it makes sense because obviously you can calculate where a particle is going to go and what it will do and how it will interact with every other particle, etc; psychohistoric!
…this also means there’s no free will because your brain is also ‘particles and stuff’[sic]
…but functionally there is free will because your personality and your decisions and so on all follow from those facts so whatever.
Some things, like quantum randomness, are ‘truly’ random, meaning that things can in theory happen which cannot be calculated by knowing the position and momentum of every particle. So now you can’t predict anything and determinism is invalidated, free will notwithstanding. In fact, this still means there’s no free will, since there isn’t any conscious effort going in to, say, the random appearance or disappearance of a quantum particle.
Let’s assume time is self-consistent, meaning time loops both can exist and don’t result in paradoxes (paradoxical time loops can’t exist). Under this assumption, free will does exist. Here’s how.
In Macbeth (1623), some witches make a prophecy claiming that Macbeth will become king of Scotland. A prophecy at its core is information from the future, or information sent back in time; the fact that Macbeth will become king is brought to the present by the witches from a point in time where he is king. Lady Macbeth, hearing about this, orchestrates events that cause Macbeth to become king of Scotland. This is a stable time loop.
This stable time loop hinges on Lady Macbeth’s actions in the situation where information comes from the future. Her actions there aren’t exclusively determined by the previous state of her brain and her world, because something that violates causality occurred, meaning her next actions are based on the position and momentum of all particles and an outside influence. Basically, Lady Macbeth’s personality decides what she does in a ‘new’ situation… which is exactly what the common understanding of ‘free will’ is.
Likewise, in Homestuck (2009), the character Vriska Homestuck decides to bring about the existence of the series’ antagonist because she already knows that the antagonist will be brought into existence. She decides that, since his existence is inevitable (due to being in the future, from which she has received information), she should have a hand in it, for clout. This is a stable time loop: Vriska created the antagonist, and because she did, her past self learns that the antagonist will be created, and chooses to create him.
Lady Macbeth orchestrating the murders that lead to her husband’s becoming king and Vriska orchestrating the creation of the antagonist of her series are functionally the same thing: someone’s personality directly affects the creation of a stable time loop, independent of standard determinism. They actively make a choices which are not determined by the past state of the world.
In Ted Chiang’s 2007 novelette The Merchant and the Alchemist’s Gate, the main character, a fabric merchant, meets an alchemist with a portal to the future (the titular ‘alchemist’s Gate’). The merchant says: ‘Suppose you learn that you are alive twenty years from now. Then nothing could kill you in the next twenty years. You could then fight in battles without a care, because your survival is assured?’
The alchemist responds, ‘…a man who would make use of such a guarantee would not find his older self alive when he first used the Gate.’
And, yeah, that wouldn’t be a stable time loop. This is a clear example where a stable time loop either does or does not exist based on someone’s personality, not their actions. Your personality determining your actions is what free will is: therefore, in a universe where there can be stable time loops, there is free will.
When my friend and I first published this anecdote it ended there (only, it had more typos). Now that I have a master’s degree, though, I feel I should be a bit more rigorous in my argument. Let’s have a look at the position of compatibilism, which claims to resolve the evident incompat—which aims to reconcile the notion of ‘free will’ with determinism. To reiterate and expand, causal determinism is the well-respected[citation needed] position that everything follows from everything else; that the current state of the world directly and inevitably leads to the next one, and the past states of the world led to the present one. The natural conclusion is that, since you probably didn’t exist as you are now (or indeed at all) in several past world-states, you follow inevitably from the facts of a world where you had no decision-making power. You still don’t have decision-making power, since everything you want now is just a necessary consequence of some whizzing brain-particles which used to be steak-particles or whatever you ate to grow that thing. Tough luck, but good on you for making it this far regardless! Or maybe you don’t deserve the congratulations, since you’re just a predictable lump of food and weather.
Moving on to a definition of ‘free will’, which my past self has helpfully excluded from the previous section. We can say that free will entails having the ability to do ‘otherwise’; that is, having control over what one does. You demonstrate free will when you act the way you want to. This is what past-Lucy meant when she said there ‘functionally is free will’: what you want is deterministic, and you act according to that. But that doesn’t ‘feel’ like free will; not as ‘free’ as if I said that what you want isn’t deterministic.
The compatibilist position is that, in certain real-life cases, a person can be demonstrated to have had free will, in some sense. One might say ‘if I were dancing on the French Riviera right now, I’d be a whole lot richer’ and mean not that, if they made it to the Riviera very, very quickly, they’d become fabulously wealthy, but only that if they were there now they know they’d have acquired sufficient wealth to make such an event possible (this example from Michael McKenna and Justin D. Coates’ Compatibilism). The compatibilists can speculate all they like on the real world, though—I’m here to talk about time-travel. All myself and my friend are arguing is that compatibility between free will and determinism follows from the existence of time-travel (even if the only thing travelling is information). Therefore the arguments used by real-world compatibilists are largely irrelevant, except where they serve as a nice point of comparison. What might be more interesting are the arguments of incompatibilists, who have a nice piece of reasoning they call the Consequence Argument:
It falls to compatibilists to defeat one or more of these points, or the ways they connect. It falls to if-prophecy-then-agency-ists to do the same, sort of. The fabric merchant’s future self demonstrates aliveness in full view of the alchemist’s Gate. In doing so, he does not change the facts of the past; if the facts were different, he wouldn’t be there to perform his demonstration. And nobody involved has stopped the facts of the past (such as the fact I’ve seen through the Gate that I’m alive in the future) from affecting the facts of the future. Nevertheless, the future-fact I’m alive right now is the case because the fabric merchant is a man who does not live his life dangerously upon learning that same future-fact. So the fabric merchant has free will, but none of the Waters of Mars clauses of the Argument are invalidated.
Is the preclusion of time-travel one of the ‘laws of nature’ mentioned by the Consequence Argument? Not really. It seems like what incompatibilists mean is that facts follow from other facts (which one had no power to alter) by immutable processes, like collisions between particles, and so the consequent facts are likewise inalterable. The fabric merchant’s life decisions are not magically altered by seeing the future. He continues to behave as he does. But the fact that he is alive in the future was decided by him. We seem to have some kind of hyper-compatibility, where free will and determinism and every part of the Consequence Argument get to work together, and all it takes is magic powers to make it happen.
Maybe compatibilists and incompatibilists alike will disagree that this sort of thing qualifies as ‘free will’, but that’s lame so I don’t care.