Chatting with your younger self

The psychology of a time traveler (part II)

Posted Apr 06, 2011

In a previous post I considered some questions about the nature of agency and decision in the context of considering someone who travels back in time. The thought was that if such a person comes to know everything about what happens in the past, including all the facts about what she herself will do in the past, then it no longer makes sense for her to try to decide what she will do when she finds herself in the past. She knows what she will do.

Many philosophers think that there is no significant difference between the time traveller and you and I, because there is no significant difference between locations that are in the past, the present or the future. What makes the time traveller's situation a bit different from ours, is that she (potentially, at least), can know everything that she will do in the past, by coming to know all of the facts about what did happen in the past.

The reason she can come to know what she will do, before she does it, is because she can have access to information about what did happen in the past. You might think that that makes the time traveller radically different from you or I. But in fact, many philosophers think that this difference is not a deep or fundamental one. It is true that in general we have better access to information about what did happen in the past, then we have information about what will happen in the future. The past leaves causal traces on the present: fossils, historical records, memories, and so forth. The future probably leaves few if any such traces (though it will leave some traces if there is backwards causation). But we can come to know things about the future, even if it is more difficult than coming to know things about the past.

 We can use thought experiments to try and get a handle on why you might think that the time traveller's predicament in knowing what she will do before she does it, is not a predicament that is peculiar to someone who travels backwards in time. For suppose that oracles exist: oracles are people who can predict the future with 100% accuracy. Now suppose that today, an oracle appears before you and tells you that tomorrow, you will decide to drive to the local pool and take a swim in the morning. It looks as though you are in a similar position to that of the time traveller: you know what you are going to do before you do it. And just as the time traveller could, in principle, know everything about what she will do when she travels back in time, before she does it, in principle the oracle could give you a complete account of what you will do tomorrow (or indeed for the rest of your life). Then just as we might worry that the time traveller is no longer in the position to deliberate about what to do, the same seems to be true of you once you meet the oracle.

What this tells us is that what raises difficulties for agency and deliberation is not travelling in time per se, but rather, coming to know what you do before you do it (and before you've decided to do it). And being a time traveller is just one way that could happen. One might be tempted to conclude therefore, that in a state of perfect knowledge (having knowledge of everything that you will do), there are no agents: there are beings that do certain things, but not beings that reason, deliberate and decide.

Still, it is all very well to conclude that in a state of perfect knowledge there are no agents, but that doesn't tell us anything about what it would be like to be in such a position. What would it be like to lack agency with respect to some choice? That seems like a valuable question to ponder, irrespective of what you think about whether there could ever be people who travel in time.

There are two cases to consider. One is a case in which there is an agent - someone who has a history of deliberating and making decisions - and that agent comes to know what they will do with respect to some future action. What would it be like, you might wonder, to be an agent that finds herself in that position? The second case to consider is one in which a being of some kind (I use that term because it is not clear whether such an entity would count as being a person or not) knows every action that he or she will perform. Thus she has perfect knowledge. If such a being is possible, then it is a being that is never an agent. Some philosophers think that if there were an all knowing being (as some people suppose a deity to be) then that being would be just like this. If a being knows everything, then she knows everything about what will happen in the future, and as such knows what she will do in the future. So an all-knowing being, whatever else it is, is not an agent. Let us call the first of these cases an impaired agency case, and the second a failure of agency case. In this blog I just want to focus on the first of these. The second of these will be the subject of a future entry.

So what would it be like to find one's agency impaired? Well we're all familiar with perfectly ordinary cases in which our agency is impaired. There are lots of things that we cannot choose to do. I cannot choose to fly, since I cannot fly. In general where I am physically prevented from doing some action, or physically forced to do some action, my agency is impaired and I will feel unfree with respect to the action. Thus I do not feel free to choose to fly. Likewise, if someone picks me up and carries me, I am not choosing to move from one location to another. I am being moved, I am not choosing to move.

Cases in which I am physically restrained in some way, however, seem appreciably different to a case in which I know what I will do before I do it. If I am tied up and cannot move, then it makes no sense for me to deliberate about whether or not to roll over. I know I will not roll over, since I cannot roll over. But here the reason I know what I will do is because I am unable to do anything other than what I know I will do. Yet that does not seem to be true in the case in which my knowing what I will do before I do it is the result of my being a time traveller or being told what I will do by an oracle.

After all, while I might know that I will drive to the local pool and go swimming tomorrow morning, clearly nothing compels me to do this, the way I am physically compelled to remain where I am given that I am tied up. It seems that it was perfectly open to me to decide to do something different with my day.  So how is it that even though I could have ended up doing something other than swimming, in fact I will go swimming, and what's more, once I know that I will go swimming I am no longer in a position to decide to go swimming, or indeed to decide to not go swimming. Once I know that I go swimming I do not seem to be free to do anything other than go swimming.

Let us consider an example. Suppose that when I was a teenager someone in their twenties came to visit me, and told me all about Zeno's paradoxes of motion. It turns out that the person who told me all of these things was an older time travelling me. The time travelling me remembers the encounter, since the time travelling me has the memories of what happened to teenage me. So time travelling me remembers being told about the Zeno paradoxes, though those memories are, of course all from the perspective of my teenage self. But the teenage self remembers quite clearly what was said in the exchange, since the experience was memorable. Now I am in my twenties and have access to a time machine. I consider travelling back in time to tell my younger self about the wonders of Zeno's paradoxes. But I remember what I did, in fact, say, and I remember that some of the explanations were not all that great and confused by teenage self. So it would be nice to offer better explanations. But since I know what I did say to my teenage self, I know that that is what I will end up saying to my teenage self.

So despite having good intentions of expressing the paradoxes more clearly, perhaps I ought to feel unfree just as if I were tied up. For I should feel destined to explain the paradoxes in the exactly the way I remember them being explained, even though I know that that is not the optimal way of explaining them. Whatever I try to do, I know that I will end up uttering the words that I remember hearing.

So what would it feel like to both want to explain the paradoxes differently, and yet to know that I will end up saying exactly what I remember my older-self saying? My colleague Dr. Nicholas Smith has given this some consideration. He thinks there are a number of ways of making sense of my psychology in the scenario just described.

First, suppose I (mistakenly) decide to try and say something different to what I remember myself saying. Since the past is one way and will not change from being that way, if I succeed in saying something other than what I remember saying, this means that my memory of what I said must have been faulty. Memories can be faulty. So here is one way that my time travelling self might have full agency and deliberate powers: she deliberates about how best to explain Zeno's paradoxes, and decides to say something different to what she remembers hearing as a teenager. What she decides to say is then what she does say to her teenage self. But the teenage self is somewhat confused, and memories change over time, and what the teenage self remembers hearing is different from what the time travelling self actually said. 

If this is what happens, then my time travelling self feels completely free to deliberate about what to say. Indeed, so long as my travelling self thinks that her memory of the encounter could be faulty, she has good reason to deliberate about what to say.  For she does not know for certain what she will say, she merely has good evidence of what she will say. So the agency of my time travelling self is not impaired as long as she can doubt her memory.

What about if she is certain that her memory is correct? Then she does know what she will say. But my time travelling self might have false metaphysical views. She might falsely believe that even though she remembers what she did say, that she will somehow be able to say something different to that when she travels back to that moment. So she will deliberate about what to say in that moment. So she will experience full agency. It is just that in the moment, she will end up saying just what she remembers saying. But she might not feel unfree as a result of this. Despite having deliberated and decided to say something else, perhaps when it comes down to the moment for some reason she changes her mind - perhaps in the heat of the moment, confused after the journey through time, she blurts out what she remembers having said despite her earlier decision not to do so. Or perhaps at the last moment she decides it is the better explanation. In either case, my time travelling self does indeed first deliberate about what to say despite knowing what she did say, and although she ultimately says something other than she intends to say, she need not on that account feel unfree as a result.  

Finally though, there is a case in which the time traveller might feel unfree. Suppose I remember what I did say, I know that the memory is reliable, and I know that I cannot change the past. Knowing all of this would seem to put me in a position of having impaired agency, and therefore, one might think, in a position of feeling unfree to say anything other than what I do say.

Well certainly I might feel unfree in the sense that I know what I will say, and know I will not say anything other than that. But that does not mean that in the moment in which I explain Zeno's paradox to my teenage self, that I feel somehow constrained or forced to utter the words I do. Perhaps my time travelling self wishes she could explain the paradox differently to the way she remembers it having been explained. When I find myself back in the past, talking to my teenage self, I am still "in charge" of what I say. In some good sense I say what I do because, in that moment, that is what I choose to say. Now maybe I choose to say it because I decide it is, in fact, the clearest explanation contrary to what I previously believed. Or perhaps I get flummoxed at meeting my younger self, and my previously prepared explanation of the paradox disappears from my mind, leaving me with only this version of the explanation. But these are very familiar sorts of phenomena that we often meet. These are not cases in which we feel unfree. They are not cases in which we open our mouths and try to utter worlds only to find ourselves uttering very different worlds.

So we need not suppose that there is anything mysterious happening here: we need not suppose that there is any constraining force on my freedom, nor that I must feel unfree given that I know what I will do. Perfectly ordinary choices that I make at the time determine which words I utter. The most likely explanation for why they are uttered, and not some other words, is that I choose to utter them despite earlier wanting not to utter them.

So while in a case of impaired agency of this kind I do not always need to deliberate about what I will do, because I know what I will do, that does not mean that when I am doing what I will do I will somehow feel unfree to do something else. Being tied up and unable to roll over need not involve anything like the same psychology as knowing that I will not roll over despite the fact that I could. I think this crucial difference explains the fact that although we would not hold someone responsible for an event that occurred while they were physically incapacitated, we would hold my time travelling self responsible for explaining Zeno's paradox in the way that she did.