The random witterings of Jonathan Morris, writer.

Tuesday, 13 October 2015

Rolling Back The Rivers In Time

Back to the heady days of 2010, and another article I wrote for Doctor Who Magazine...

A Brief History Of Time Paradoxes

“I’m not exactly breaking the laws of time, but I am bending them a little...”

It’s one of the greatest cliff-hangers in the show’s history. The Doctor is trapped inside the Pandorica, a prison constructed by an alliance of his greatest enemies specifically to hold him. He has been scanned, assessed, and understood, his limits and capacities have been extrapolated. There is no way he can get out, and no-one is coming to help him. His best friends are either dead, stuck inside an exploding TARDIS, or a Nestene Duplicate. And the rest of the creation has just ceased to ever have existed.

How does the Doctor escape? A Doctor from the future travels back in time to rescue him. Or rather, he gets Rory to do it, releasing the Doctor from the Pandorica using the future Doctor’s sonic screwdriver. Then all the Doctor has to do is to remember to travel back in time and give Rory his sonic screwdriver, so his former self can escape, so that he can travel back in time and give Rory his sonic screwdriver...

“What? What? What?” exclaims Doctor Who fandom in close-harmony indignation. “But that’s cheating! That’s breaking the rules!”

But what are the rules? Do they allow for exceptions? How does time-travel work within the Doctor Who universe? Is it a place where the future is predetermined? Why can the Doctor interfere in stories set in the future but not in stories set in the past? What does it mean if a point in history is ‘fixed’, ‘in flux’ or ‘Time Locked’? If somebody is ‘un-written’ from time, what precisely does that mean? What is the Blinovitch Limitation Effect? Which came first, the chicken or the Jagaroth?

And was the Doctor really cheating when he released himself from the Pandorica?

Of course, if there’s one consistent rule about how time works in Doctor Who, it’s that it always works in whatever way is most convenient for the show’s writers at the time. So I’ll also be touching on how time travel functions within storytelling; when does it serve the drama, and when does it undermine it?

Back when the show began, the show’s first Script Editor, David Whitaker, kept it simple. When the TARDIS lands in the present, the future, or on an alien world, our heroes can do what they like, but when it lands in the past, the Doctor is adamant that ‘You can’t rewrite history! Not one line!’. Presumably, if you are unaware what is supposed to happen, you can do what you like, but if you do know what is meant to happen, you have no choice but to allow events to take their course. Whitaker lays out the rules in his novelisation, Doctor Who And The Crusaders, where the Doctor is asked if you could assassinate Adolf Hitler in 1930:

“But Hitler wasn’t assassinated in 1930, was he? No, it would be impossible. Once we are on Earth, we become a part of the history that is being created and we are as subject to its laws as the people who are living in that period.”

Though even within this rule there is room for wriggle. When the Doctor says ‘You can’t rewrite history!’ does he mean ‘can’t’ in the sense of physically-impossible or shouldn’t? In the same way that someone might say, ‘You can’t drive through a red light’ – you could if you wanted, because it’s only a highway law, rather than a physical law, that is there to stop you. This is the case in The Massacre Of St Bartholomew’s Eve, in which the Doctor justifies abandoning Anne Chaplet to almost-entirely-certain death, it’s not the basis on that he can’t change history, but that he ‘dare not’.

Even in The Aztecs Barbara does end up making a difference to history, albeit only to the life of the priest, Autloc. So a principle is established that will eventually become the basis for stories like The Fires Of Pompeii and The Waters Of Mars: You can’t – or at least, shouldn’t - change the significant, history-book things, but you can save the ‘little people’. Though in The Waters Of Mars the Doctor admits that this is ‘only a theory’ and says ‘I think certain moments in time are fixed’, implying that this is something even the Doctor, even the Time Lords, aren’t sure about. Could it be that ‘fixed points’ in history are, in fact, not fixed at all?

The Doctor states in The Fires Of Pompeii that the destruction of Gallifrey in the Time War is, like the destruction of Pompeii, a ‘fixed point’. But we later learn in The Stolen Earth that the War was ‘Time Locked’ which seems to be a different thing altogether; rather than there being a theoretical or moral obstacle to the Doctor attempting to return to the war to save his people, it seems to be a physical barrier, from which “nothing can get in or out” – except for Dalek Caan, a Whitepoint Star, and the enigmatic Woman from The End Of Time.

The idea that all time travellers are free to make small alterations to time helps explain why the Butterfly Effect, of concern to Martha in The Shakespeare Code, doesn’t come into play; so long as a time traveller doesn’t change anything of great and lasting significance, they are free to accidentally stamp on as many hymenoptera as they wish. As the Doctor says in Turn Left, “the universe just compensates around tiny little changes” (contradicting Rose’s line in the same episode that “The wrong word in the wrong place can change the entire causal nexus” – but after the apocalyptic events of Father’s Day, Rose has reason to be cautious). The Doctor muses on this point in Remembrance Of The Daleks...

 “Every great decision creates ripples, like a huge boulder dropped in a lake. The ripples merge, rebound off the banks in unforeseeable ways. The heavier the decision, the more uncertain the consequences.”

...suggesting that small decisions, like tiny pebbles dropped in a lake, don’t make a vast deal of difference. So, for instance, the rescue of the Caecilius family in The Fires Of Pompeii appears to have had no repercussions, just as the universe accommodates the un-writing of the clerics in Flesh & Stone. Although they ceased to have ever existed, nothing else changes as a result. It’s like a version of It’s A Wonderful Life in which Jimmy Stewart visits a world in which he was never born and discovers that things would have turned out exactly the same.

But what about if you’re visiting the future or another planet? Surely, from the point of view of someone in the year 2165, the events of the year 2164 are history? In The Dalek Invasion Of Earth the Doctor tells Ian ‘I think we should pit our wits against [the Daleks] and defeat them!’ which, whilst being something of a no-sh**-Sherlock moment, is significant because it’s the first time the Doctor decides to interfere in Earth’s destiny. Which means either he’s altering history, or he knows the Daleks were defeated in 2164 and is making history happen, or that the Dalek occupation of Earth is an aberration from what should have happened and he is setting history back on its proper course.

The idea the future can be changed is challenged in The Tenth Planet, in which the Doctor knows that the planet of Mondas will be destroyed in 1986 and so resolves not to interfere. Certainly by Attack of the Cybermen he considers the destruction of Mondas in 1986 to be part of the ‘web of time’. So it seems that it’s not so much a question of whether you’re in the past or future, but whether or not you’re trying to change a ‘fixed point’; this is the dilemma the Doctor faces in The Waters Of Mars, effectively an ‘historical’ adventure set in the future. On the other hand, we learn in Cold Blood that whether humanity makes peace with the Silurians is not a ‘fixed point’; which is odd, given that handing over half the planet to prehistoric homo reptilia would be quite a big change to life in the twenty-first century, but then, if it were not an option the Doctor wouldn’t have been able to pursue that course in Doctor Who And The Silurians either.

The idea that history has a proper course suggests a version of history before time travel was discovered, though not ‘before’ in a strict chronological sense. Rather, it’s as if someone at the end of time – Professor Yana, say - wrote a history of the entire universe but then, because time travel was discovered, and time travellers began to influence events, history began to diverge from the written account. This implies that history is predetermined, it was ‘written’ in some sense, but that the discovery of time travel was not part of that predetermined history, so it wasn’t written in the book, but now that time travel exists it means that nothing is predetermined any longer, in the future or in the past... Hello there, This is Jonny from the end of the article. I’ve just travelled back in time to let you know that I’ll be picking up on the idea of ‘predetermined history’ later on. See you then. Bye.

When Dennis Spooner took over as show-runner, or ‘Story Editor’ as it was then called, the time travel rules changed. Most notably, you have The Space Museum, in which our heroes glimpse a potential future – like Scrooge, they see ‘shadows of things that May be’ rather than ‘shadows of things that Will be’ – and The Time Meddler, in which the Meddling Monk attempts to change the final score of the Battle of Hastings. So history can be re-written – indeed, The Time Meddler tells us that time has already been re-written, as the Monk has been giving tips to Leonardo and helped construct Stonehenge using anti-gravity lifts. So presumably the Meddling Monk was also in on the Pandorica Planning Committee.

But the story which really lifts the lid on the can of worms is, surprisingly, The Myth Makers. In this story, the Doctor is captured by Agamemnon and ordered to come up with a means for the Greeks to enter Troy. The Doctor knows his classics and so reluctantly – on pain of death – suggests they build a wooden horse. So it turns out that the wooden horse of Troy – which the Doctor had dismissed as a dramatic device invented by Homer – was actually the Doctor’s idea. Except it wasn’t, because he got the idea from Homer...

This is the earliest example what’s called an ‘ontological paradox’ or more simply, a ‘free-lunch paradox’. Because if the Doctor got the idea of the wooden horse from an account written about the time when the Doctor came up with the idea for the wooden horse... who came up with the idea of the wooden horse?

This is different from examples of the Doctor making history follows its correct course – either by preventing others disrupting it, such as in The Time Warrior, The King’s Demons, The Fires Of Pompeii or The Next Doctor, or inadvertently, by starting the fire of Rome in The Romans or the fire of London in The Visitation or burning down the old priory in Pyramids Of Mars (note: the Doctor is a well-known historical fire-hazard) or even telling Gareth which exam questions to answer in his mid-term paper in The TV Movie. Rather, this is the Doctor making something happen which wouldn’t otherwise have occurred using information from the future – having his ‘free-lunch’ and eating it.

Now, in the case of the wooden horse, it might be argued that Homer came up with the idea first, that he was the ‘first cause’, part of the ‘original’ history written at the end of time. So even if the Doctor’s interference has resulted in a ‘free lunch’ paradox, there is a starting point. Even though that starting point now did not happen. Which is another concept which has existed throughout the show’s run  – that you can retain information, memories, even memorabilia, from versions of history which have since been ‘un-written’.

This has been a frequent feature in recent years, but for clarity, here’s two examples from the old days. Firstly, in The War Games the Time Lords decide to ‘dematerialise’ the evil War Lord. He fades from view and we are told it will be ‘as though [he] had never existed.’ And yet had he never existed, he would not have been able to conduct the War Games in the first place. This would appear to be the first example of somebody being ‘un-written’; they are physically removed, all memories of them are lost and all trace of their existence is gone - but the effects of their actions remain. The universe comes up with a new version of events which makes sense (in the same way it compensates for disappearances into the Crack in the Time Field). So The War Games still happened, but somehow without the War Lord. In which the War Chief and the Security Chief spent even more time arguing.

A slightly less baffling example is Day Of The Daleks, in which the Doctor uncovers a ‘free-lunch’ paradox in which an explosion at the Peace Conference at Auderly House leads to World War III, allowing the Daleks to invade, which in turn inspires a group of guerrillas to travel back in time to prevent the explosion – only for one of the guerrillas, Shura, to be the one who causes it. However, the Doctor evacuates the Peace Conference, meaning that the ‘false’ future with the Dalek invasion is ‘un-written’. But its effect – a large, smoking hole where Auderly House used to be and several UNIT soldiers’ spouses now claiming widow’s pensions – remains. The Doctor and Jo Grant continue to remember their visit to the future Earth, even though it’s a future that can now no longer happen.

What this illustrates is that it’s possible to remember events – or even to take objects, such as Shura’s bomb – from pasts or futures which then cease to be part of history. In the same way that events that have been ‘un-written’ can still be remembered - the ravaged future Earths seen in Pyramids Of Mars and The Last Of The Time Lords, for instance.

However, the way people (and Leadworth ducks*) are ‘un-written’ by the Crack in the Time Field appears to be slightly different; although Rory has been removed from history, Amy still remembers him, subconsciously, and eventually recognises him in The Pandorica Opens. And even though Rory has been un-written, there’s still a Polaroid of him, in Roman regalia, in Amy’s bedroom. It would appear that when the Crack in the Time Field wipes people from time, it still leaves traces behind, but traces which cannot be consciously recognised. We learn in The Big Bang that the effects of this Crack are based upon Amy’s memories, as she has grown up next to it with ‘the universe pouring through her dreams every night’ – its influence is selective and dependent upon her, so if she remembers someone who has been un-written then they will be un-un-written, as becomes the case with Rory and the Doctor.

So how easy is it to change history? Not that easy, given that the universe compensates for ‘little changes’. No, you have to either be a time traveller or an extremely powerful being. As the Doctor says in Pyramids Of Mars, one man may change history ‘to a small extent’ but:

“It takes a being of Sutekh’s almost limitless power to destroy the future.”

Which holds true throughout the series. Attempting to change history is the preserve of the most powerful races; the Daleks in Evil Of The Daleks and The Stolen Earth, Cybermen in Attack Of The Cybermen, Sontarans in The Time Warrior, Scaroth in City Of Death, Fenric in The Curse Of Fenric and Time Lords like the Meddling Monk, the Master, Rassilon, even the Doctor himself.

Because you may not have noticed but the first person to change history in Doctor Who was the Doctor. In Carnival Of Monsters the Doctor has heard the mystery of the SS Bernice, a ship which disappeared in the Indian Ocean. Except that at the end of this story, the Doctor returns the SS Bernice to the Indian Ocean on the night of its disappearance so there never was any mystery. It may only be a small alteration, but nevertheless, this is the Doctor changing what, for him, is established history. He still remembers the disappearance of the SS Bernice even though it now no longer took place. Which might explain why Jo has never heard of it (but that could simply be due to ignorance, Jo Grant never having heard of most things.)

This isn’t the only time the Doctor alters history. In City Of Death he prevents Scaroth from attempting to re-write history – yet he re-writes history himself, in felt tip, on six canvases that will later be painted over with Mona Lisas. In The Unquiet Dead he considers giving the gaseous Gelth access to Victorian corpses. And from The Christmas Invasion onwards the tenth Doctor slides down a slippery slope, starting his tenure by un-writing the ‘Golden Age’ under Prime Minister Harriet Jones – a ‘Golden Age’ predicted in World War Three – before crossing into established events for ‘cheap tricks’ in Smith And Jones and becoming a Time Lord Victorious in The Waters Of Mars, with his disastrous attempt to save Adelaide Brooke.

But with the Time Lords destroyed in the Time War, who’s to stop him? It’s not as if the Time Lords weren’t above changing history themselves. The Three Doctors makes it clear that the Laws of Time are not physical laws, but laws enforced by the Time Lords – the ‘galactic ticket inspectors’ of The Time Warrior, who, according to Attack Of The Cybermen, have those who ‘transgress the laws of time’ destroyed. As the Doctor says in Father’s Day:

“[There] used to be laws that stopped this kind of thing from happening. My people would have stopped this. But now they’re gone.”

But these are laws more honoured in the breach than the observance. Forget the War Lord – it’s as if he never existed – and cast your mind back to Genesis Of The Daleks where a Time Lord appoints the Doctor to avert the Daleks’ creation. And although the Doctor doesn’t succeed, he does set their progress back a thousand years – meaning that all his previous adventures with the Daleks no longer occurred as he remembers them; The Dalek Invasion Of Earth of 2164 is now postponed to 3164. This isn’t a ‘tiny little change’ that could be ‘compensated’, this is the most powerful race in the universe engineering a new course of history, and would help explain why all the Dalek stories after Genesis Of The Daleks seem to take place in a different Dalek chronology.

(This isn’t the only time Dalek history has changed; in Dalek Van Statten doesn’t recognise a Dalek, yet after The Stolen Earth everyone on Earth knows what Daleks look like. However Victory Of The Daleks implies that everyone on Earth has forgotten – or that their presence was un-written – meaning that Van Statten’s ignorance makes sense after all. More-or-less.)

It’s one of the ironies of the Laws of Time that we see them being broken more often than being upheld; Time Lords taking Doctors out of time in The Three Doctors, The Five Doctors and The Trial Of A Time Lord, and in The End Of Time it seems that in the Time War both sides were breaking the laws of time, creating ‘The Could-Have-Been-King and his army of Mean-Whiles and Never-Weres.’ As Adric observes when reading the Doctor’s ‘Time-logs’ in The Keeper Of Traken, changes in history are quite commonplace:

"I read about something that's just happened - the next page says it didn't happen at all - and over the page it says it did happen, but many years ago!"

But surely if the Doctor – or anybody – were to change his own history, that would create all sorts of paradoxes? Well, not if you’re powerful enough and know what you’re doing. In The Last Of The Time Lords the Master converts the Doctor’s TARDIS into a ‘Paradox Machine’ in order to facilitate the Toclafane decimating their own ancestors, and the malevolent future Doctor in The Trial Of A Time Lord, the Valeyard, presumably had a similar approach in mind when he attempting to obtain his former self’s regenerations.

The clearest explanation of what happens if you change your past is in The Two Doctors, in which the sixth Doctor is briefly convinced that somebody has killed his second incarnation. We’ve already seen that later Doctors can be threatened by previous incarnations being displaced from their time-streams – the fifth Doctor experiencing ‘pangs of cosmic angst’ and being pulled into the time vortex in The Five Doctors – but in The Two Doctors the sixth believes he is a ‘temporal tautology’, caught in an embolism outside the time flow, waiting for his past ‘death’ to catch up with him, along with the collapse of the entire universe. Unfortunately this extremely dramatic idea is ignored for the rest of the story; instead when Doctor’s second incarnation is given Androgum inheritance, the sixth Doctor experiences the effects, suggesting an alternative history of Doctor Who in which the third, fourth and fifth Doctors went around with orange eyebrows savagely consuming everything in sight.

(However, this idea does form the basis of part of The Big Bang, as Amy only exists as a ‘temporal tautology’ – as her younger self ceases to exist before her eyes. This idea, an unravelling of ‘the causal nexus’, as feared by Rose in Turn Left, also occurs in Logopolis, where the Master is ‘interfering with cause and effect!’)

But what happens if you change history, and you don’t know what you’re doing, and the Time Lords aren’t around to tidy up? You get Father’s Day. The universe still seems to be attempting to ‘compensate’ but by using the Reapers to ‘sterilize the wound by consuming everything inside it’ with the TARDIS being ‘thrown out of the wound’. Presumably this is a case of the ‘holistic fabric of time’ being punctured as the Doctor had feared in The Two Doctors. What’s interesting, though, is that the crisis only results from the fact that Rose changed her own and the Doctor’s personal histories – causing their past selves to literally pop out of existence. It’s this which created the ‘vulnerable point’, implying that if Rose had rushed to save her father the first time round, he might have been one of the ‘little people’ who could be saved (like the Caecilius family in The Fires Of Pompeii), and it’s only the fact that she tried it the second time that caused the problem. Then again, the Doctor says that ‘the whole world is different’ because Pete is alive – suggesting that his death, like Adelaide Brooke’s, is a ‘fixed point’ and not open to revision, even though the precise location of his death – and whether he was comforted in his dying moments – are details which can be changed (“Different details, but the story’s the same”). Just like Day Of The Daleks and The Last Of The Time Lords, the events of this story end up being un-written as the status quo is restored, with only Rose and the Doctor remembering what took place.

Why should that be? In Flesh & Stone the Doctor says it’s because they are time-travellers and have a different perspective on the universe; they can still remember events and people that have been un-written. Cold Blood muddies this explanation by adding the proviso that this doesn’t apply to your own personal history, so Amy can remember un-written clerics but can’t remember Rory - at least, not consciously (she can remember enough of him for the Nestenes to take a memory print). And this doesn’t apply to the Doctor. But this ties in with City Of Death, in which the Doctor reminds Romana they exist in a ‘special relationship to time’ because they cross the time-fields so often, and thus are able to sense disturbances in time to which everyone else is oblivious. The Doctor exists outside of normal time, and is able to perceive the time loop in The Lodger without being caught in it, and can still move in slow motion while everyone else has been frozen in time in The Time Monster and Invasion of The Dinosaurs (or is being affected by the Time Destructor in The Daleks’ Master Plan).

So if you’re a time-traveller, you’re in “the eye of the storm” – immune to changes to history in general, only in danger from changes to your own personal history, or ‘time line’. Which brings us to the Blinovitch Limitation Effect, a concept introduced in Day Of The Daleks as a reason why the guerrillas couldn’t make multiple attempts at travelling back in time – the idea being that whilst they are free to change history, if they were to make a second attempt, they would be attempting to change their own personal histories, just like Rose does at the beginning of Father’s Day.

The Blinovitch Limitation Effect is related to the idea that if you come into contact with your former (or future) self you’ll cause an explosion, as in Father’s Day, and Mawdryn Undead, and yet it doesn’t apply to the Doctor nor to Amy in The Big Bang (although in Amy’s case, it’s not quite the same Amy).

However, the greatest danger seems to lie in creating a paradox which negates itself, such as killing one’s own grandfather, as mentioned by Martha in The Shakespeare Code. The Doctor prevents a self-negating paradox in City Of Death, as had Scaroth succeeded in preventing his former self from engaging the warp drive, there would be no Scaroth to prevent his former self from engaging the warp drive. And yet, in terms of paradoxes, what Scaroth is attempting is not really different from the Doctor preventing the disappearance of the SS Bernice.

With time travel, cause and effect can become very confused (as indeed can the viewers). In recent years, we’ve seen effect predating cause many times – the words Bad Wolf turning up before Rose has sent out the Bad Wolf message; the Torchwood Institute shooting down the Sycorax ship before the Doctor has had the adventure with Queen Victoria in which she establishes Torchwood; Mr Saxon making his presence felt before the Master’s restoration in Utopia, and most notably, River Song encountering the Doctor in Silence In The Library, which is for him their first encounter, and for her their last, with her diary of future adventures and frequent mentions of ‘Spoilers’. Plus there’s the Doctor’s escape from the Pandorica, in which effect – Rory rescuing the Doctor using the sonic screwdriver - precedes cause - the Doctor giving Rory the sonic screwdriver.

These are all a form of ‘free-lunch paradox’ called a predestination paradox. The idea being that an effect can be its own cause. This is tautological but not necessarily impossible, so long as the resulting time loop is consistent. They are quite common in literature – a good example is Macbeth, where Macbeth hears a prophecy that one day he will become king, and so decides to try to become king. Or you have the end of Bill & Ted’s Excellent Adventure, in which our heroes acquire the keys to a prison cell by deciding that later on they will travel back in time and leave themselves the keys to the prison cell.

Which is all great fun - except for what it implies about how time travel works, as it implies that everything within the time loop has been predetermined. Which takes us back to the idea that without time travel, all history would be predetermined. Excuse me for a moment, I’ll just pop to a point earlier in this article and mention that I’m going to return to this idea... Back now. For example; in New Earth Cassandra chooses a pattern for Chip based on the appearance of the last person to say she was beautiful – who was, we later learn, Chip. So Cassandra never had any choice in the matter; if she had chosen any other pattern, it would have created a self-negating paradox. She always must, and always will, have chosen the same pattern. Similarly, in Blink, could the Doctor have said anything on the Easter Egg other than the words transcribed by Lawrence? In Inferno the Doctor claims that free will is not an illusion, but if you have predestination paradoxes, then there is no such thing as free will. Life becomes like the lyrics of Doris Day’s Que Sera Sera – ‘Whatever will be, will be.’

Predestination paradoxes mean that even with time travel, history is still predetermined. That the Master always was going to be restored in Utopia, because he’s already on Earth, posing as Mr Saxon, in The Runaway Bride. Why worry whether River Song will be killed in The Pandorica Opens, because we’ve already seen her alive and well in The Time Of Angels? Cold Blood might have shown us that history can be un-written – with the bizarre notion that Amy would want to wave at herself across a hilltop two days in succession - but on the whole, if you’ve seen the effect, you know the cause will inevitably follow.

That is the danger with these paradoxes. Throughout the show’s run, pretty much every Script Editor has, in his notes for writers, made it clear that the Doctor should not use time-travel to solve his problems, it being the number one thing that new writers got wrong. Admittedly Douglas Adams broke that rule in City Of Death, but even there, the Doctor isn’t using time travel to change events, but to make sure they remain unchanged.

But if the Doctor can use predestination paradoxes as a way of getting out of tight corners – or tight Pandoricas – the risk is that it can get in the way of storytelling. Firstly, it’s very, very hard to think of a situation in which the Doctor is in jeopardy where he couldn’t be saved by his future self popping back in time to rescue him. Once he’s done it once, what’s to stop him doing it again? And why didn’t he do it all the times before when he had the chance? Yes - why didn’t he save Adric?

Secondly, there’s the fact that any predestination paradox invites the question ‘But how did this loop start?’ Sometimes it’s possible to imagine a ‘first cause’ that might have iterated to a self-generating loop, but sometimes – as with the problem of how Rory could have got the sonic screwdriver if the Doctor hadn’t been released – there is no plausible first cause. Of course, with predestination paradoxes you don’t need a first cause, as an effect can be its own cause, but nevertheless, it’s something that’s going to niggle viewers who are paying close attention to the story logic – and telling time-travel stories is inviting viewers to pay close attention. And even to draw their own diagrams.

But thirdly, and most importantly, it feels like a cheat. It’s not a cheat in the sense that it’s doing something impossible, or something that’s not been done in the show before, but in the sense that it’s too easy. The Big Bang gets away with it, but you need only watch other sci-fi shows to see how it can lead to predictable ‘cop-out’ endings. Because predestination paradoxes can be an anathema to suspenseful drama.

For example, take Blink. It’s a thrilling, suspenseful, twisty-turny narrative. But imagine it if had been told from the Doctor’s perspective. He’s running down a street and a good-looking girl rushes up to him with a folder giving him detailed instructions on what to do when he bumps into the Weeping Angels. It lists everything he must do, everything he must say. So all the Doctor has to do is to do as he’s told! How dull would that be to watch?

Good drama, I would suggest, is about characters making difficult decisions. And although fictional characters can’t have ‘free will’, if they exist in a predetermined universe, you can end up telling stories not about characters making difficult decisions, but about characters following instructions. Doing what they have to do because ‘that’s what they did last time’.

Next time you watch The Big Bang, ask yourself, at what point does the Doctor come up with a plan? When he escapes from the Pandorica, Rory tells him everything he must do in order to have facilitated his escape from the Pandorica. When he meets young Amelia at the museum, young Amelia shows the Doctor the notes he left to guide her to the museum. And when the Doctor encounters his future self, it’s his future self who tells him to distract the Dalek so he can slip inside the Pandorica. At each point, the Doctor is doing what he’s been told by somebody else, even if that somebody else is his future self. The Doctor doesn’t actually decide anything to shape his own destiny until he sets the Pandorica for take-off.

But Doctor Who should take place in a universe where anything can happen, where the Doctor is the master of his own destiny. That’s the point of the Crack in the Time Field, and that scene in Cold Blood, to show that everything is up for grabs, that even things that we-think-have-to-happen might not have to happen after all. That time is not a series of fixed-points in a history book that’s already been written, but something that’s always in flux.

So there you go. A brief history of Time Travel in Doctor Who. Now, if you’ll excuse me, I have to go and lie down in a darkened room until my head stops spinning.

* Having disappeared through a ‘quack in time’, I was hoping the ducks would come to the Doctor’s rescue in The Big Bang. But I suppose that would have been a ducks ex machina ending.


(A simplification of Han’s Moravec’s Time Travel And Computing, 1991.)

Suppose you have a basic form of time machine – a time telephone, which allows you to receive messages from your future self. You’re trying to crack the code to open a safe, and you only have one attempt – get it wrong and the alarm will sound.  You decide to operate the following plan:

* If you hear from your future self, you will follow their instructions.

* If you don’t hear from your future self, you will try the combination ‘000000’.

* If the combination you have tried works, you will use your time telephone to tell your former self the correct combination.

* If you the combination you have tried doesn’t work then, just before the police arrive, you will use your time telephone to tell your former self to try the combination the-number-you-tried-plus-one.

This is, of course, an iterative loop with a clear start point (‘000000’) and end point (the correct combination). But the only outcome which doesn’t give rise to a paradox is the following:

You hear from your future self, you try the combination they suggest, it works, so you use your time telephone to tell your former self the correct combination.

So that is the only outcome that can possibly happen!

(The two paradoxical outcomes are: You try a number, it doesn’t work, so you tell your former self a different number; and: You don’t hear from your future self, so you try ‘000000’, and whether or not it works, you then do get in contact with your former self.)