With the movies taking place in the Kelvin timeline, and Picard taking place in the original timeline, commencing after Nero has travelled back in time, it is established that both of these timelines exist. All well and good, right?

Wrong. This leads to some horrible implications over the whole of Star Trek. Let me explain.

The Timelines

Nero accidentally travels back in time from 2387, arriving in 2258. As Zachary Quinto’s Spock explains,

Nero’s very presence has altered the flow of history, beginning with the attack on the USS Kelvin, culminating in the events of today, thereby creating an entire new chain of incidents that cannot be anticipated by either party.^[1]

This lets the audience know that the universe won’t – or need not – turn out as they remembered from classic Star Trek. This is nice, because we can’t sit back happily knowing what’s going to happen.

But here Spock talks of Nero altering the flow of history. This suggests that the timeline was one way, and Nero’s travelling back in time has changed it. For one thing, Nero destroys Vulcan because he blames the Federation and Spock for the destruction of his own homeworld and wants revenge.

The storyline of Picard takes place after Nero has gone back in time, in 2399. So, we know that the timeline continued after Nero’s travelling back in time. And it continues with the same history it always had. In Picard’s history books, there is no mention of Nero encountering Starfleet in the 23^rd century. Vulcan is still intact. Everything has simply continued as normal, it seems, but without Nero and Spock (who presumably everyone thinks have mysteriously disappeared).

So, we have two timelines. “What’s the problem?” I hear you ask. Well, I’ll tell you!

What a Mess

For one, this is incongruous with lots of other instances of time travel in Star Trek. In First Contact, for instance, the Enterprise-E Borg sphere goes back in time. While somehow protected in a “temporal wake”, they see the effects of the Borg sphere travelling back; they see an Earth assimilated. As Data says, Earth then has a “population of nine billion, all Borg”.^[2] Presumably the Enterprise didn’t magically jump from one timeline to another here, so what would explain this? The obvious thought is that there is one timeline, and the Borg sphere altered it by preventing Zefram Cochrane’s launch and advancing humanity’s first encounter with the Borg by hundreds of years.

However, if it is the case that when you go back in time, rather than altering the timeline, you create another, this doesn’t make sense. What the Enterprise-E crew should have seen was everything continuing as normal – at least in their timeline. The Borg assimilation of Earth would have taken place in an entirely different timeline, as with Nero’s destruction of Vulcan.

Perhaps there is some way that we could explain this. Maybe sometimes – in special cases perhaps – going back in time creates a new timeline, but not always. As an explanation goes, however, that seems to raise more questions than answers!

Alternatively, we might think that this was a mistake, and we should ignore it like we do lots of other gaffes from writers. Sticking with First Contact, for instance, the Borg would be pretty stupid if they decided to invade 24^th century Earth then go back in time, rather than going back to the 21^st century and attacking the then-relatively-defenceless Earth. We tend to forgive things like this because we care about the general story. So a mystery of how the Enterprise-E could see what should have been in another timeline is maybe just something we should sweep under the rug.

Picard seems to commit us to the idea that when you change something in the past, a new timeline is formed, branching away from the old one. But both timelines exist.

However, the entire show of Picard is based on the premise that the destruction of Romulus happened, Nero went back in time, but things are still going on in the timeline as if everything was normal. So, it looks like we might have to accept this notion of time travel (with possible exceptions for looping cases, like in Time’s Arrow, where a person’s going back in time doesn’t change anything, because they were there already). [Editor's note: for more on time travel where you don't change the past, see the discussion here]

So, to clarify, it looked like Star Trek was endorsing a model where you could overwrite what happens in the past, replacing it with new events. But Picard seems to commit us to the idea that when you change something in the past, a new timeline is formed, branching away from the old one. But both timelines exist (hence the events of Picard happening).

Moral Motivation

However, I really don’t like this model, largely because of what it means for moral motivation in loads of classic Star Trek. There have been a lot of episodes over the various series that have made use of time travel. In fact, there have been so many that you could rank a top 15. In most of these, something bad happens, and our heroes try to prevent it from happening. Or so we thought.

For example, consider Endgame, the finale of Star Trek Voyager. We discover that Janeway did get Voyager home in 2394, but lost many of the crew along the way, including Seven of Nine. In 2404, Admiral Janeway gets her hands on some time travel technology and uses it to meet with Voyager back in 2378. With the help of 25^th century technology, she is able to get the crew home earlier, motivated principally by her desire to save Seven of Nine.

The branching model – in which a new timeline is created, via time travel, in addition to the original - changes the situation. The timeline where Seven of Nine died presumably continues. Janeway no longer saves Seven, but creates a whole new one, and a whole new universe along with her! In the First Contact case, things look even weirder. Rather than Picard restoring the timeline, if both timelines exist regardless, what he’s actually doing is deciding what timeline he wants to live in. This is hardly the noble goal that it looked like before.

Another example features in The New Generation’s Firstborn. In that episode, a mysterious Klingon, K’mtar, comes aboard the Enterprise to help Worf and Alexander. We discover through the episode that K’mtar is actually a future version of Alexander, who, wracked with guilt for events that led to his father dying, tries to fix this. But, if the timeline he comes from will exist no matter what, he doesn’t really fix anything. His father did still die. Nothing is altered there.

This seems to get something wrong about the characters’ motives. Janeway wants to save Seven. And in First Contact, Picard wants to stop the Borg from having assimilated Earth. Yet under the new model, that’s not really what’s happened at all.

And it gets weirder

Maybe all of this doesn’t bother you. Perhaps this seems fine. And bringing a new timeline into existence that has certain features isn’t so bad.

But when we think about how this affects how we should live, things can start to look weirder. Lots of philosophers (just like normal people!) are interested in how we should live our lives. What makes it good to act one way, or another? What makes a certain way of living right or wrong? What is the good life (if there is such a thing)? A popular response to this is the consequentialist solution. For the consequentialist, what you should do is make the world better. In fact, consequentialists usually think that what we have to do, morally speaking, is make the world as good as we can. So, if you’ve got two options before you, and one of them makes the world better than the other, that’s the one you should pick. Usually, consequences happen after you act, but when we think about backwards time travel, this need not be the case.

And when we think about the consequences of Nero going back in time, if he creates a whole new timeline, in addition to the one that already existed, we’ve got a whole universe of extra things in our ontology (the things that exist). So, we might think that he made the world (or more accurately, the complete set of things that exist) better, even though he destroyed Vulcan!

The consequentialist is likely to think even weirder things than that, if we have this model of time travel. Because they think you should cause everything to be as good as possible, if we think two universes are better than one, it looks like they have to say you’re morally required to make more universes. So long as, in total, the extra universe you create by going back in time is on the whole a good thing, it seems like that’s what you have to do!

Maybe we don’t actually think the world is that great, but most people seem to think it’s at least a good thing that it exists rather than nothing. Gottfried Leibniz actually thought that the world we’re in is the best of all possible worlds.^[3] If he’s right that we live in the best of all possible worlds, then even worlds close to ours would be pretty good, so we should make more of them!

Janeway no longer saves Seven, but creates a whole new one, and a whole new universe along with her!

And if I happen to have a time machine, and I think the universe is a good thing, it looks like I have an interesting choice ahead of me. I could try to continue in my current timeline, making it as happy as possible. Alternatively, I could go back in time and make a very tiny change. Perhaps one so insignificant that all the people in the new timeline will be pretty much exactly the same (maybe quantum events would take place differently?). This would in effect make the amount of happiness in this timeline since the branching point (and for the entire future ahead) happen twice. And I could keep doing this, sending grains of sand to very distant points in the universe fifty years ago, creating a new universe every time.

This strikes me as super weird. That in itself doesn’t give us any reason to believe it’s a bad model of time travel. But it does mean that whenever one of our heroes ‘goes back in time to fix things’, they’ve not fixed things at all. Instead, they’ve seen a timeline they don’t like and decided to leave and join a new one. This is hardly the exemplary behaviour I’ve come to expect from my protagonists!

Further Reading

If you’re interested in learning more about what philosophers say about time travel, a great place to start is David Lewis, The Paradoxes of Time Travel, American Philosophical Quarterly Vol. 13 No. 2 (1976), pp. 145-152.

For more on consequentialism (outside of time travel questions), and why people find it plausible, it’s worth checking out the Internet Encylopedia of Philosophy entry. For more in-depth information on moral motivation, see the SEP entry.

The grandfather paradox has been discussed in countless places. but usually proceeds as follows:

If I could travel back in time, I could kill my grandfather before my father was conceived, thereby preventing my own existence. But if I was not born, how could I travel back in time to kill my grandfather?

Here are just a couple of examples. First, from Doctor Who:

In the Futurama episode Roswell That Ends Well, Farnsworth warns Fry not to interact with the latter’s grandfather, lest he kill him and prevent his existence (but that’s not quite what happens...).

A common variant of this paradox is the ‘auto-infanticide paradox’, except instead of killing my grandfather, I try to kill my younger self. (Of course, our time traveller doesn’t have to be murderous to erase their existence: take Marty McFly in Back to the Future. All the time travellers who try to kill Hitler – a trope for another day – may, if they really could change the world, bring about a future they were no longer a part of. And so on.)

In all of these cases, it is argued, a contradiction ensues: I both could and could not kill my grandfather (or my earlier self). I could, because it’s tragically easy to kill people; provided I had the time machine, knowledge of where my grandfather was, sufficient training, a weapon, and so forth, I could carry out the murder. But I couldn’t, given that my existence – and thus my being there to perform the killing attempt – depends on my grandfather’s surviving to produce my father (or my younger self growing up to be me). This apparent contradiction has regularly (and I mean regularly) been employed as ‘evidence’ for the impossibility of time travel. As Lewis so pithily puts it,

If a time traveller visiting the past both could and couldn’t do something that would change it, then there could not possibly be such a time traveller.^[1]

But Harry seems to be such a time traveller.

(“What?!”, you exclaim. “I don’t remember Harry trying to kill his grandfather! He briefly tried to kill his godfather, but that was a mistake, and…”

“Sshh”, I say, calmly, and then make you a cup of tea.)

Harry doesn’t kill his grandfather, it’s true. Instead, he saves a life. The ‘first’ time around – or from Harry’s perspective, prior to his travelling in time – Buckbeak seems to have been killed by the executioner Macnair. Harry hears the swish and thud of the axe, and Hagrid’s sobs. But the ‘second’ time around, with the time turner on their side, Buckbeak is saved. If that’s true, then at the very same moment in time Buckbeak is both killed and not killed. Schrödinger aside, that can’t be right.

In the philosophical literature, attempts like these to change the past and thereby generate a contradiction are called bilking attempts.^[2] In order to avoid contradictions, either time travel must not occur, or bilking attempts must fail. Contradictions – especially the kind that allow people to be both existing and not existing at the very same time – are bad. Not ‘aaargh the universe will explode bad!’, despite what some fiction would tell you. Instead they’re impossible, and so if time travel led to contradictions, time travel would be impossible. And that would be a tragedy.

So, Harry’s bilking attempt (i.e. his attempt to save Buckbeak) must fail, if it’s a genuine bilking attempt…

So we know that he must fail, given the logic. But why does he fail? In other words, how do we explain his failure? What causes it? (And likewise, what causes me to fail every time I try to kill my baby self? What saves Hitler from the onslaught of time travellers?)

The short answer is that Harry doesn’t fail. It’s not a genuine bilking attempt. Harry might think he’s changing the past, but given all the other clues from the film (which is more explicit than the novel) – Hermione’s howls, the rock thrown through the window – the most charitable interpretation is that Buckbeak was never killed. The axe hit the pumpkin all along, and Hagrid’s tears were always joyous. This is the only possible version of the event that avoids contradictions and keeps the timeline consistent. Harry is filling a role he always played; he hasn’t changed the past, just precipitated the future he remembers.

But you mightn’t find that very satisfying. Generally, it’s easier to answer this in fiction than in life. It’s all very well in a story to wave a magic wand (literally, in Harry’s case), but what about if you had a time machine right now and tried to change the past? What would stop you? Do we need to posit some temporal guardian or unlikely consequences to prevent the impossible from occurring? And is it really logically impossible to change the past – would it always result in a contradiction? Are there theories of time which allow it? And if you can’t change it, how does that affect your free will?

These are all sensible questions. Well done, you. We’ll tackle them (cough, cough) in time.

If you have any time travel texts you’d like me to talk about in future instalments, or burning questions/comments, do let me know below.

References

• Max Black, Why cannot an effect precede its cause? Analysis,  Vol. 16 No. 3, 1956: 49-58.
• David Lewis, The Paradoxes of Time Travel, American Philosophical Quarterly, Vol. 13 No. 2, 1976: 145-152.

Mysterious thing, Time. Powerful, and when meddled with, dangerous.

Albus Dumbledore, Harry Potter and the Prisoner of Azkaban

More years ago than I’d like to admit, as an undergrad (or an ‘ickle secondie’, as Peeves might have called it), I had a paper about Harry Potter and time travel published in a small Sydney journal.^[1] My philosophical ability has (I hope) improved since then, but the usefulness and interest of the text in question hasn’t diminished: Harry Potter and the Prisoner of Azkaban is one of only a handful of internally consistent, philosophically plausible, time travel texts – and is an exemplar of three of the main ‘paradoxes’ that arise in the time travel literature. I use it in teaching, in giving talks, and now – dear readers – I bequeath it to you.

In this series, I’ll be looking at each of the three ‘paradoxes’ in turn, and how they can be overcome (or, as Heinlein put it – in a wonderful, if underutilised, portmanteau – ‘paradoctored’).^[2] But first: why all the scare quotes around ‘paradox’? Well, because it isn’t clear that all 3 of the puzzles we’re interested are strictly paradoxes, in the logical purist’s sense – they don’t involve an explicit contradiction, but rather a conclusion that strikes us as unacceptable. (I’ll avoid the punctuation from now on, unless I’m making a deliberate point.)

Paradoxes are a prime target for philosophical consideration: they’re the equivalent of an alarm or flashing red light, indicating something wrong with one’s reasoning or starting assumptions. If a given scenario or argument is paradoxical, that counts against it. Many of the arguments against the possibility of time travel employ the idea that time travel and its consequences are paradoxical.

For example, if I could travel back in time, it seems I could prevent my birth (think Back to the Future, or Futurama’s Roswell that Ends Well). But if I wasn’t born, how could I go back in time? (Never fear - as we’ll see, there’s good reason to think that time travel isn’t paradoxical in this way).

So paradoxes = bad, but interesting.

Now, where are the paradoxes in Harry Potter? (And, for those of you with insufficient dedication to re-reading/re-watching the series at every opportunity – where is the time travel?) Cast your mind back to the latter chapters of Prisoner of Azkaban…^[3]

Harry Potter, famous teen-wizard, is having a rather bad day. Hagrid’s hippogriff, Buckbeak, has apparently been executed…

‘Wait, wait, wait!’ I hear you exclaim. ‘APPARENTLY been executed? That’s not right, he WAS executed. And then Harry saved him. He changed the past!’ We’ll get to that. Promise. All that matters at this point is that it appears - rightly or wrongly – that Buckbeak has been executed. Let us resume.

Hagrid’s hippogriff, Buckbeak, has apparently been executed, and our hero is attacked by Dementors and possibly about to die. On the verge of unconsciousness, he sees what he believes to be his dead father, who casts a Patronus Charm to save him. He wakes up in hospital after his miraculous rescue, only to find out that his newly-discovered godfather is about to be killed.

On the advice of the ever-so-wise Albus Dumbledore, Harry travels three hours back in time with his friend Hermione (who, let’s be honest, is the real hero of this story, and, interestingly, one of the very few female time travellers actually in control of the time travel device).

Our daring duo save the ill-fated hippogriff. In the hopes of seeing his dead father, Harry watches the Dementors attacking, only to realise that it was himself that he saw, and proceeds to cast the life-saving Patronus (thanks to an odd bit of logic).

(‘Is that the bit where he…?’ Yes, yes, it is. We’ll get there.)

With Buckbeak’s help, Harry and Hermione free Sirius, and return to the hospital just as their earlier selves are using the Time Turner to depart. Thus ill-fortune is averted, several lives are saved, and the novel (and accompanying film) has a dramatic climax. Voila!

And now, with memories refreshed, the paradoxes:

1. Buckbeak the hippogriff appears to have been both killed and not killed.
2. Harry survives to save himself because he is saved by himself.
3. Harry knew he could cast the Patronus because he had “already done it.”

Paradoxes = bad, but interesting.

The first time we see the events in question, pre-time travel, Buckbeak seems to have been killed by the executioner Macnair: the golden trio hear the swish and thud of the axe, and Hagrid’s tears at the event. Post-time travel, we see Harry and Hermione save Buckbeak. Thus the following are both true – ‘Buckbeak was killed’ and ‘Buckbeak was not killed’ – and we have a (paradoxical) contradiction.

As for (2), Harry must survive the Dementor attack in order to be able to travel back in time to save himself, which leads to his survival and subsequent time travel… to save himself. The time travel seems to be ‘predestined’ by the circumstances of his survival, which leads to all sorts of questions: could he have chosen not to use the Time Turner? How can his future decisions affect whether he survives in the past?

And finally, how did Harry go about casting that Patronus? Such a charm requires a great deal of skill, far beyond the average third year, and a focus that Harry has struggled to muster in previous confrontations with the Dementors (and their Boggart mimics). This time, however, when it counts, Harry knows he can do it. Why? Because he’s already done it. But has he? Where does this confidence come from?

Parts 2, 3 and 4 of this series will cover each of these in turn. For now, give yourself permission to watch or read the novel ‘for academic purposes’ (i.e. guilt-free), and let us know in the comments what you think the solutions might be, and if you can find similar cases elsewhere.

References

• Heinlein, Robert A., – All You Zombies – , first published in The Magazine of Fantasy and Science Fiction, March 1959.

• Rennick, S., Harry Potter and the Time Travel Paradox, Cogito, Vol. 4 No. 3, 2009: 38-52.

• Rowling, J. K., Harry Potter and the Prisoner of Azkaban, London: Bloomsbury, 1999.

Further Reading

If you’re interested in the philosophy of time travel, the best place to start is always David Lewis, The Paradoxes of Time Travel, American Philosophical Quarterly, Vol. 13 No. 2, 1976: 145-152.

A Time Travel Website is a great blog focussing specifically on the philosophy of time travel, and well worth a visit.

And for a vast array of timey-wimey tropes, see http://tvtropes.org/pmwiki/pmwiki.php/Main/TimeTravelTropes.