The trouble with time travel

MARAUDERS BEWARE: I’m continuing my streak of Harry Potter posts with some serious plot spoilers for Harry Potter and the Cursed Child. You have been warned. Scroll past the pretty picture for the spoilers.


Much of the plot of the Cursed Child revolves around a timeturner. The timeturner allows the characters to dial back a few hours, days or even years, at which point they disappear from the present and reappear as avatars in the past, perhaps alongside their past selves. So far it seems to make sense: we can picture how it happens and work through some initial problems (what does your past self think when he encounters your future self, not knowing that timeturners exist: he goes mad; this is why when travelling in time, your avatar should make sure to conceal himself). But further examination reveals quite a lot of seemingly irresolvable problems. Here they are:

Moral responsibility

Imagine Harry decides to steal from Weasleys’ Wizarding Wheezes (obviously he wouldn’t, but bear with). He makes away with a Pygmy Puff and I think it’s fair to say he is culpable or blameworthy for this crime. Ten years later Harry is overcome with remorse and decides to right his wrong. We might think that sending George the requisite Galleons, adjusted for inflation, would be sufficient for this, but Harry feels a more complete show of regret would involve reversing the original decision so that George never suffered to begin with. He takes his contraband timeturner and goes back to that fateful day. He accosts his previous self and forcibly wrests the creature out of his hands and back onto the shelf. So while past Harry might have been culpable for a crime, present-day Harry prevents a crime, which it’s fair to say is praiseworthy. But then it seems like he is both praiseworthy and blameworthy at the same time, and for the same action. That can’t be possible. Alternatively, we could describe what happened as Harry having intended to commit a crime but having stopped himself from doing so. The crime wasn’t actually committed, so there is nothing to be blamed or praised for – unless you think overcoming temptation is praiseworthy.

So, is he guilty or not?!

Possible worlds

In the Cursed Child, there are two occasions when Albus and Scorpius change the past. When their first intervention results in an undesirable present in which some of their best friends ended up not being born, they go back again to perform another intervention designed to bring back the present they know and love. But their second intervention results in an even worse state of affairs. In this second altered present, it is Albus who is not born!

Typically we think of time like this: there are the things that happen, and there are the things that could have happened such that the present would be different. The world in which things actually happen is the actual world. The different present we would be inhabiting had different things happened could be called the other possible worlds. They are just that: possible. The people who use the timeturner are, of course, based in the actual world, in the actual present. Otherwise, they couldn’t be using the timeturner. Only the actual world is real. But we don’t seem to know which world is the actual world. Is the actual world the world in which Voldemort loses – the world from which Scorpius and Albus originally travel back in time – or is the actual world the world in which Voldemort won and Harry died – the world to which Scorpius returns after his second excursion? It seems like one is actual, and then another one is actual. But the actual world has to be just one of the possible worlds from the beginning of time till the next: it’s not a badge that can be passed between possible worlds at different points in time.

If there is a single actual world, then it’s quite easy to say what happened in it. In this scenario, did Voldemort kill Harry or not? Did Harry steal the Pygmy Puff or not? You see the problem!

Incidentally, this bears on the moral responsibility question. If time travel is possible, any of our present actions can be undone in the future. So what’s the point of moral reasoning? If it turns out we’ve made a bad choice, we can just go back in time and undo it. Perhaps moral reasoning is irrelevant for present you, but matters for future you, since it’s future you that does the overruling of present you, making present you unimportant. But future you can also be overruled an infinite number of times. Doesn’t an action have to decisively take place for it to be morally evaluable?

The Cursed Child

Personal identity

Now consider that Harry scenario again. How could there possibly be two Harry’s at once? Well, magic, right? No. Harry travelling back in time and encountering past Harry is not on the same level as Harry manipulating the physical environment via means not (currently!) available to us Muggles, such as to move a feather through the air. Think of it like this. We might think that one condition of being ourselves is that we are unique: there could never be more than one me at any one time. So you can have one me last year, and you can have another me today, but you can’t have me-last-year and me-today in the world at the same time. So even though we can envisage Harry fighting with Harry, this couldn’t ever happen. You can either have time travel, or it can be the case that there is only ever one you at one time, but you can’t have both.

The Prisoner of Azkaban

So what?

Time travel as formulated by JK and other writers throws spanners into our usual conceptions of moral responsibility, moral assessments and personal identity. Something has to give. The holes in JK’s account of time travel can’t be plugged with better imagination, however. In my opinion they are holes that could never be plugged by even the most inventive storyteller, because they are not problems of imagination but logical problems. Time travel, at least in anything like the form JK envisages, is as impossible as a round square.

Until you throw quantum into the mix, of course…

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