Time travel in Doctor Who

This essay is not going to be as long as you think.

In broad terms there are two ways to approach the topic of time travel in Doctor Who. In the top-down approach, I'm going to start from a strictly external, real-world point of view, looking at how the needs of the television production shape the time science inside it. In the bottom-up approach I'll look at the "in-universe" evidence and see if it's possible to assemble that evidence into anything meaningful and/or internally consistent.


Doctor Who is a television show which has existed in one form or another - with one significant gap - for more than half a century. The show has been running for so long, through the televisual equivalent of several geological epochs, that it's impossible for the show's purpose and driving forces not to have changed dramatically over time.

I'm not a scholar of the early days of Doctor Who but there must have been an early period of uncertainty when nobody really knew how much potential the show had, or whether anybody was going to watch it; a time when none of the show's mythology had been really explored and the rules hadn't been laid down. Some time after this, a time must have come when it was realised that Doctor Who was a television programme with serious staying power. As to whether the show was carefully designed from first principles to be this way, I couldn't say, but it cannot be denied that, whether accidentally or not, the entire show is built for longevity.

Two central story elements support this. The TARDIS, which is able to travel anywhere in time and space, is a "story spinner" of unlimited power, right out of the textbook. And the Doctor, the lead actor and main character of the show, is able to "regenerate" and change his face while remaining the same person, providing the show with a continuous thread of continuity across decades of stories, regardless of casting concerns. These are the two narrative powerhouses which more or less render the show unkillable by conventional means. It's a really smart design, and everything else - Time Lords, companions, intergalactic peril, monsters of the week - is built around this core. Doctor Who is a show which can theoretically last forever and - Batman take note - never even need a reboot.

Once this was realised it must also have become clear that this timelessness and (long, long) continuity was valuable. Extended and convoluted continuity isn't an unambiguously positive thing for a franchise to have, because the franchise can very easily become murky and inaccessible. But it certainly has merits and, because such continuity is time-consuming to build up, these merits are relatively rare and worth hanging on to. Because Doctor Who is a show which has run so long, and because it has the potential to run for so much longer after the present day, it becomes desirable to keep things that way.

Under these circumstances, the decisions you make in your storytelling - including your portrayal of time travel - change. It doesn't matter which particular episode of Doctor Who you are writing today, and it doesn't matter what year it is-- you can be sure that this isn't the last episode of Doctor Who which will ever be written, or the last series, or the last Doctor, or the last generation of viewers. The show may die and the show may come back again and the Doctor will still be the same character. Fifty more years from now, there's a genuine chance that people will be coming back and watching your fifty-year-old episode and comparing it with recent ones.

More to the point, there's a good chance that this time next year you will need to write another episode. Maybe a whole series of them!

Under these circumstances, what you obviously want to do, above all else, is avoid closing the door to future stories. This is a completely different proposition from writing a single book or a film. Those are fixed, capped stories, where you would have relatively unilateral control. You could kill everybody off by the final page, and as long as the story itself is compelling nobody will hold that against you. But writing for Doctor Who is different. This is franchise fiction, a renewable resource, a golden egg-laying goose. You must not kill it!

You also want to avoid loudly contradicting previously-established history. But luckily for you, nearly all prior writers were in exactly the same position as you are now. Hopefully, they won't have done anything for you which makes your job impossible, and hopefully you can be relied upon to pay this favour forward and not make future writers' jobs impossible either.

So the way this works out in practice is that you reveal the bare minimum of necessary hard facts to support the story currently being told. You keep information back, you wave your hands. You do acknowledge the important questions, but you nearly always dodge them, by ignoring them, or lying, or giving ambiguous answers. Locking down any specific fact not only constrains all possible future stories which could be told in that area, it also instantly rules out an unlimited number of other possible facts which could have been selected instead. Even seemingly harmless little factoids can turn out to be massively inconvenient years down the line. (Smarter writers are able to work in the opposite direction, using hints to bury groundwork which later stories can, if they choose, pick up and expand on.)

This can be seen in nearly every episode of the show. You only have to look at the glacially slow pace at which new information about the Doctor's species, homeworld, people, backstory and name have been revealed. What is the Doctor's name? What were his parents like? Is he married, does he have children? How many regenerations does he have? Is he always male, is he always white? If not, then why is he? Whose TARDIS did he steal and do they want it back? How long does a TARDIS live, how do you make one, where do they come from?

And obviously, as a natural result of this requirement to be cautious with the truth, the Doctor must be a private, secretive man, not liable to blab about his personal details. This remains a constant regardless of his external personality, which is frequently brash and noisy. Companions do often ask him the important questions directly, because it would be bizarrely inhuman of them not to, but he always sidesteps them somehow.

"Rule One: The Doctor lies." Do you see how unbelievably smart this line is? It means even on the rare occasions when the Doctor apparently talks candidly, we can still roll all his claims back later on!

That's not even the real Rule One!

With this in mind some things become naturally obvious about how time travel must work in Doctor Who. The keyword here is possibilities.

  • Time travel must be possible.

  • Time travel must be possible in both directions, forwards and backward.

  • Time travel must be relatively straightforward most of the time. (Contrast with e.g. Back To The Future where it is extremely difficult to travel through time, and this difficulty forms the principal conflict of the (finite) story.)

    That's not to say that we can't build stories where time travel is roadblocked in some way. But we want the flexibility to tell stories which aren't specifically about time travel, where we arrive in 1941 at the beginning of the story and leave 1941 at the end without any particular issues. If, every week, we need to find some outstandingly rare MacGuffin to power the time machine, then that's going to get quite tiresome quite quickly. As well as quickly straining credulity.

    This gives us the TARDIS's personality. It's reliable to a fault when the plot demands it. It's finicky and broken when the plot demands it. Making the TARDIS work is sometimes a critical problem and sometimes a non-issue.

    Note that this kind of fuzzy "Uh, it depends" behaviour is extremely honest. It works for us. Because this is how real people and animals and machines behave in reality! If something worked the same way every single time for a hundred years, that would be freakily suspicious.

  • History cannot be fixed.

    If every single time travel story boiled down to a collection of closed causal loops, that would get dull and predictable and repetitive. Furthermore, characters would be able to abuse this knowledge to solve problems too easily. That's not to say that causal loops should be outlawed entirely, because they're powerful and fun in the right hands. But other formations must also be possible. We need to be able to have it either way when we need it.

    Plus, there must be a credible danger of altering history, otherwise there is almost no tension in historical stories. "The Daleks are making a bid to conquer Earth in the eleventh century? Well, that obviously isn't going to work out for them. So... Bye!"

  • If history changes, then somebody should notice. The Doctor (and possibly his companions) should be able to perceive these changes, probably by virtue of their privileged perspective as time travellers.

  • "Let's just hop in the time machine, go back in time and fix everything" must not be a viable catch-all resolution to every episode's conflict. Time machines are insanely powerful devices for breaking stories and we have to limit that power one way or another!

  • The rules of time travel must be totally internally consistent within the confines a single episode. This is because fiction needs to make sense. (No, "It's science fiction!" is not justification to spew out complete narrative gibberish. A story must have rules, and it must obey those rules.) Ideally the rules should be consistent across the whole series, but this is nowhere near as critical, or practical.

And other than that... pretty much anything goes.

These rules give rise, on different days, to stories where time travel is nothing to do with the story, stories where time travel is involved and critically important and super difficult, and stories where we bounce backwards and forwards in time for comic effect. It means most things which make sense and drive a story are possible, and most things which make too much sense and would kill a story are impossible.

It also gives rise to some fairly obvious... I don't want to say contradictions (or paradoxes - a paradox is a scenario which apparently involves a contradiction but does not)... but at least I have to call them pain points.

For example, the characters can't fix everything using simple time travel because once they arrive in a situation they are "part of events". What does that mean? How long do they have to be part of events before they can leave? Is it like parking, no return within thirty minutes? Can they come back a hundred subjective years later? Can a different Doctor come back and fix this? How far back in time can you go before you're no longer part of the same events? What about in space? If 1930s New York is "blocked out" in some way, what's wrong with going to 1920s New Jersey and hanging around for a while, then getting on a bus?

There are fixed points in time. What if someone destroys the universe? What happens to all the fixed points after that time? Does the universe cobble something together somehow?

It doesn't matter. Well, it kind of matters, because it's never terribly satisfying for one character in the story to effectively turn to camera and say "We just can't fix this situation by doing the obvious thing, and I can't explain why! You just have to believe me that there's a genuine conflict going on here!" but as a show Doctor Who does tend to survive.

It does this principally through the means of excellent casting. A good Doctor can sell it. And regardless of the strength or weakness of the material, every Doctor (in the revival, anyway, can't speak about the classic series) has been able to sell it. And so we buy it, at least for that one episode, and that's as long as the illusion needs to last.

Still... Play this card too many times, leave too many obvious questions unanswered, and the wheels start churning and dissatisfaction does start to set in. "Don't think about it" just doesn't work as a defence mechanism. You cannot watch the same show for decades and decades without, at some point, starting to think about it.

And so it becomes somewhat desirable for the creators to try to maintain some kind of consistency, and for the viewers to try to construct some kind of framework.


This is where I get all fan fictiony.

Doctor Who is a show involving more time travel than any other show I can think of. It is contradictory and inexplicable and different every day. But it also provides us with some natural ways to understand all of this. Because Doctor Who is a show which is very often actually about time travel, and often about time, and the nature and structure of time. It even features characters called Time Lords who are - if I understand this right - actually responsible for the maintenance and upkeep of time itself.

This implies that time in Doctor Who is, if not a living thing, then at least a dynamic thing. It implies that the laws of time are subject to deliberate modification. Some or all of the laws may have been installed deliberately. And the laws may also change naturally, over the course of... well, some other form of time.

And that's basically it! It would be insane to take every single episode and try to line up all of the evidence. And it would be nearly impossible, and it isn't necessary. Genuinely malleable laws are all you need to justify most of the phenomena seen in the show. Time travel in Doctor Who is just different every time. The laws vary with real time, with subjective time, from place to place and from person to person. The laws will differ for two Doctors visiting the same era on the same planet. There are legions of edge cases and exceptions. There are freakish phenomena and monsters crawling out of the walls.

In-universe, although there may be an overall theory which explains everything, it must be insanely complicated, and to try to explain it to a doddering human viewer would be futile. And understanding time in terms of those laws is about as useful as understanding water - placid lakes, whitewater rapids, oceans, icebergs - exclusively by studying fluid dynamics equations. Eventually you might get somewhere, but you can't learn to surf that way.

Fortunately for us, the Doctor has an instinctive understanding of all of this. He has a perspective which lets him intuitively understand the fabric of local time, and what is or is not allowable. (This drives him a bit crazy sometimes.) He can explain what's going on to the companion (read: viewer surrogate), in simple terms, and always does. So we don't need the full and gory details. Which is fortunate, because honestly they simply do not exist.

And, as I say, it's probably for the best that they don't.

Discussion (22)

2015-07-17 22:01:40 by qntm:

One, the Doctor needs to be louder, angrier, and have access to a time machine. Two, whenever the Doctor's not on screen, all the other characters should be asking "Where's the Doctor"? Three--

2015-07-18 01:36:37 by Doctor Doctor:

-- The do everything device (screwdriver) must never, ever do wood. Four--

2015-07-18 01:50:30 by qntm:

One day, the Doctor will meet and defeat that villainous race of sentient continuity errors which has dogged his footsteps since time began.

2015-07-18 02:30:21 by T:

My favorite interpretation of the Time Lords is that once they invented time travel, and started noticing changes to the timeline caused by time travelers (both themselves, and others), they simply made up a preferred meta-history, and began enforcing it, as the self proclaimed Time Lords. And the new series has played with the idea that, in the absence of the Time Lords, everyone still kind of follows The Rules, because it turns out they were mostly for the sake of the universes' inhabitants, rather than being selfish.

2015-07-18 03:02:17 by Emma:

You know, with how much you talk about time travel, I'm surprised I've never thought to suggest that you might enjoy Homestuck!

2015-07-18 10:38:34 by Feep:

My favorite one-sentence explanation of (parts of) the physics of Doctor Who: "The Whoverse is physically granular at the scale of narrative." Evidence: The Wedding of River Song, the way the Rift in Cardiff works, every time the Daleks got scattered in time, and what happened? "One Dalek atom in Greece, one in New York?" No: one Dalek here, one Dalek ship there. Granularity at narrative scale.

2015-07-19 05:33:37 by Badwasabi:

Don't even joke, Emma. I'm pretty sure it'd break him. Incidentally, we do get to see what happens when a "fixed point" is violated. SPOILERS Time itself goes all wibbly potato. The spacetime continuum goes "no, screw this, I'm out".

2015-07-19 11:56:40 by Lumen:

There's homestuck stuff in his Ra playlist. Hasn't he already read it?

2015-07-19 21:49:15 by David:

The different uses of "fixed" to mean something "immovable" and then "repaired" confused me a little bit, but now I see what you mean. A "fixed timeline" could relate to two very different interpretations of time travel mechanics.

2015-07-20 19:23:39 by koboldskeep:

He's probably waiting for Homestuck to finish before he comments on it.

2015-07-20 19:36:52 by qntm:

I probably won't be able to comment on the time travel in Homestuck until I've finished reading it, which seems unlikely to happen in the near future because I've started two or three times and given up every time. I enjoy some of the music, and the Flash animations are neat, but there's so much text that I just can't get through it. The thing is longer than War And Peace.

2015-07-22 03:47:21 by john:

Don't even try to read Homestuck straight through in one go, it's too fragmentary and multi-threaded. Start with the fan wiki.

2015-07-23 11:40:49 by NotAGoodIdea:

Why settle for second-best, Sam? You'd probably enjoy https://parahumans.wordpress.com/ as well, and that's only about 1.5-to-2 times as long as Homestuck text-wise. It doesn't have its own interesting time-travel style per se, but maybe some types of precognition count?

2015-07-23 20:17:48 by John F.:

The way that T is putting it in his comment above, the Time Lords sound suspiciously similar to the Wheel Group.

2015-07-23 22:48:15 by Voidhawk:

Are you sure you haven't watched/read any old-who? You've managed to almost exactly hit the nail on the head, missing only exactly how much of the universe's laws are actually Time Lord "guidelines". Short history of the universe and the creation of time travel: 1) The Dark Time Everything runs on magic, and it's awful. The universe is fought over by evil aliens/demons/wizards, who deal in blood and souls. Precognition and seers exist, and nothing really makes much sense. Galifrey has conquered a galaxy with an empire based around slave trading, headed by a matriarchal dynasty of evil seers called the Pythia. They build/steal the first time machine, though don't seem to do much with it. 2) The Time of Chaos The Pythia's power wanes, along with much of the power of magic in the universe. Rassilon founds a group called the Neo-Technologists and rises to power. The last Pythia loses the power of precognition, curses all Galifreyens to sterility, and kills herself. 3) The Time of Rassilon Rassilon creates Genetic Looms to allow Time Lords to continue to reproduce. Then with Omega and "The Other" he begins experimenting with stars and black holes. This leads (after releasing an elder evil and fighting it for 1000 years, and accidentally stranding Omega in a parallel universe made of anti-matter) to the creation of the Eye of Harmony, the source of power for the Time Lords and the first Tardises. He then the Eye of Harmony to enforce the principles of causality and logic on the universe. The Other then declares he doesn't like what Rassilon is doing, and walks into a Genetic Loom. (This is why blowing up the Doctor's tardis is spectacually bad: it is currrently carrying the Eye of Harmony and holding the laws of the universe together. This also might explain why the laws of time travel are quite so wibbly-wobbly: because the only thing holding them together is plugged into a very unreliable Tardis. Oh yes, and basically every fan is certain The Doctor is a reincarnation of The Other.) 4) The "First" Great Time War Rassilon travels far into the future to discover the future of the Time Lord civilisation: instead he finds a time travelling race of insects, whose works have eclipsed the Time Lords. Enraged, he attempts to locate thier home world to destroy it in the past, but can only pin it to a vague area of multiple galaxies. He settles for spraying the entire area with a self-replicating bio-weapon molecule that will wipe out other life and ensure that all evolving forms are roughly Time-Lord shaped: DNA. Hence rubber-forehead aliens, including Humans. I could go on, but it just gets even more complicated. Instead, have the link to the most joyfully nerdy site I have ever seen: The Complete History of the Time Lords (as well as most of the rest of the universe) http://meshyfish.com/~roo/index.html As an example, here's an interpretation of the Big Bang from it: 13,500,017,903 BC (at least 3 or 4 cycles after the Shub-Niggurath appears) Event 0 - A massive Timestation journeys back to the beginning of Time. Due to instabilities it ejects the fuel from one of its engines. This ejected fuel is a condensed monoblock of matter that detonates when another timeship, named the Vipod Mor, materializes at its center creating the Big Bang. Grandfather Paradox eat your heart out.

2015-07-29 23:36:54 by Jesse M.:

Whenever there are science fictional universes that seem to involve both closed-loop stories and changing-the-past stories, like Doctor Who and Star Trek and Terminator, I like to imagine a variant of the type of time travel mentioned in the "two histories create each other" section of Sam's article at http://qntm.org/models , except with a lot more than just two histories mutually influencing one another. Basically, I imagine a complicated structure of many timelines where traveling back in time takes you to a different timeline, but where there can be loops involving multiple nearly-identical timelines. To use a familiar example from a different franchise, you could have a situation where in the 2029 of timeline #1, John Connor sends Kyle Reese back in time, and that version of Kyle Reese appears in the 1984 of timeline #2 and fathers the John Connor of timeline #2; then in the 2029 of timeline #2, John Connor sends the Kyle Reese who was born in timeline #2 back in time, and that version of Reese appears in the 1984 of timeline #1 and fathers the John Connor of timeline #1. So in both timelines it *appears* as if there was a single closed loop, even though the two timelines might differ slightly. In Doctor Who I also imagine that similar timelines tend to cluster together into "bundles" as if there was some sort of attraction between them, and time travelers departing one timeline tend to end up in a "nearby" timeline in the same bundle, so a trip to a given date will tend to take you to a timeline whose version of that date is very similar to that of the timeline you departed from. Further, this "attraction" between timelines implies that if you make a small change, history will tend to get pulled back on course to match the other timelines in the same bundle, and attempts to significantly change the course of history will be met with some kind of "resistance" (if we imagine Time as a quasi-sentient entity as suggested in the article, Time itself is trying to thwart your attempts to change history). This could explain why it's dangerous to try to change events whose outcomes you have already learned in some way, like in "The Girl in the Fireplace" (spoilers) where the Doctor can't go back to visit Madame Pompadour after learning that she died awaiting his return--not changing what you already know to have happened could be what the Doctor means when he says he can't use time travel to solve certain problems because he's "part of events". In my model it takes expertise and/or power to overcome this resistance in order to make major changes. This is suggested in the episode "Pyramids of Mars" (spoilers) where a powerful being named Sutekh is threatening to destroy the world in 1911, so Sarah Jane suggests they just return to her native period of 1980 to verify he didn't succeed, but when they do travel to 1980 they find that Earth has been reduced to a desolate lava-filled landscape. The Doctor explains "Every point in time has its alternative, Sarah. You've looked into alternative time." Then another person riding on the TARDIS asks "So a man can change the course of history?" and the Doctor replies " To a small extent. It takes a being of Sutekh's almost limitless power to destroy the future." In terms of the multiverse model, perhaps in all the timelines that stay within our "bundle" the Doctor thwarts Sutekh as seen in that episode, but there are a certain fraction of timelines that were part of our bundle up until 1911, but afterwards skewed in a different direction due to Sutekh being successful, perhaps branching off into a new bundle of "Sutekh victorious" timelines. And all the versions of the Doctor/Sarah/Laurence who travel forward to 1980 at that point will be briefly taken to a "Sutekh victorious" future, which might again be explained in terms of Time being quasi-sentient and "knowing" that they must witness the danger in order to have the motivation to play their proper role in stopping Sutekh in all the histories within our local bundle. This type of model doesn't make it totally futile to try to stop evil beings that want to change history like Sutekh, since we can imagine that different bundles can be "thicker" or "thinner" (each one containing different numbers of near-identical timelines), and time travelers are battling to ensure that their favored bundle is thicker (so that if you randomly select a being from the entire multiverse, they're more *likely* to be native to one of the thicker bundles). I'd also speculate that when less powerful/knowledgeable time travelers use their knowledge of future events to try to intentionally change something, one result can be that some timelines *begin* to skew in a different direction from others in the local bundle, but these skewed timelines are destroyed somehow before they can diverge very far. Something like this could explain what was seen in the episode "Father's Day" (spoilers), where Rose saves her father from dying and bat-like creatures appear to "sterilize" the "wound in time" by destroying everything in the area. By the way, there have been a number of episodes of Doctor Who involving parallel universes (like "Rise of the Cybermen" and "Inferno"), and there is some support for the idea that at least some parallel universes are created due to previously-identical timelines branching in different directions--the article at http://tardis.wikia.com/wiki/Parallel_universe quotes the Tenth Doctor in the episode "Doomsday" saying "every single decision we make creates a parallel existence" (I suspect the writers got the idea for this from a real-life speculation called the "many-worlds interpretation" of quantum physics). So this at least supports the idea that we should use some kind of multiverse model to explain how time travel works in Doctor Who, rather than a single rewritable timeline.

2015-07-30 01:12:15 by Jesse M.:

@Voidhawk - When you say Rassilon defeated the insect species by "spraying the entire area with a self-replicating bio-weapon molecule that will wipe out other life and ensure that all evolving forms are roughly Time-Lord shaped", is that something you got from the site you linked to? If so can you quote the lines that talk about it? Looking over the site, I noticed that on the sub-page at http://meshyfish.com/~roo/docwho2.html a different explanation for the ubiquity of humanoids is given, stating that Gallifreyans "are the first sentient humanoids to appear in the Universe. As such their morphic fields increase the chances of humanoids evolving on other planets. As these early Gallifreyans observed the Universe they set down laws to predict its actions. In doing so, their Observations physically began to create the rules by which the Universe operated. Morphic fields are created by the crystallization of history through observation by a conscious mind. Morphic fields don't follow the normal rules of the universe and are so complex that that a living minde is required to compute their mathamatics. The shape and nature of every lifeform in the universe is influenced by the morphic field of that species. The Artron Energy created by a living being creates the morphic field as a sort of collective psionic aura which acts as a species equivalent to an individual’s biodata. The longer a particular species has been around the stronger its morphic field. These fields build up over several generations (probably as a sideffect of the crystallization of history caused by observation). This is why there are so many species that look like Gallifreyans throughout the Universe. These early Gallifreyans are however only partly responsible for the number of humanoid species in the cosmos."

2015-09-04 18:01:27 by Anti:

Hey Sam, speaking of Homestuck, how far did you ever get into it? I would love to hear your thoughts on it at some point, because there's a lot of interesting mechanics at play: causal loops, changing the past, interaction between non-parallel timelines ("synchronicity"), and a huge theme of predestination v. personal choice (which distinction is a hell of a lot more salient when Paradox Space itself is pointedly teleological). The most impressive thing for me about Homestuck, though, is how much *sense* it ends up making. All the different types of time travel/universe hopping/&c. seem to fit together surprisingly well, and less of the temporal mechanics are completely ad-hoc than I thought when I was first going through the story. So, I think if you do happen to wind up continuing, you'd probably have a lot to say. However I get that none of that makes Homestuck any shorter; it's, what, something like two Bibles at this point, just counting the text? But you're saying that you'd like to finish it before writing down thoughts about it? Also, it's almost over (nominally "99%" by page count), so now you can finish reading it by attrition. Just read one page a day and you'll be fine. It'll only take about 22 years :::;)

2016-04-27 15:25:35 by Nonagon:

Now that Homestuck has ended I will try to write an essay akin to Sam's here on qntm.org/time. I've read a book called The Labyrinth of Time by Michael Lockwood, which I would recommend to anyone who wants to know about the theoretical physics and philosophy underpinning theories of time travel. Sam is definitely right that Homestuck is longer than War and Peace. By one count, the story is 817,612 words in length, compared to War and Peace's 516,093 words. In addition, Homestuck has just over four hours of animations and interactive, 'walkaround'-style games to explore that have additional conversations between characters (I believe these are included in the total word count). I'll definitely post a link to my essay when it is completed. By way of preview, the gist of Homestuck's conception of time travel is one of branching timelines, where time travelers in so called 'doomed timelines' can travel back to the 'alpha timeline' to correct mistakes that lead to the bad, 'offshoot timeline.' These time travelers can stay in the alpha timeline as an additional version of the same character. This concept is first demonstrated clearly by Dave in the doomed timeline created by the event where John gets killed by his denizen. By going back in time to prevent John from getting tricked into seeing his denizen too soon, the newly arrived future Dave has 'saved' the timeline from becoming doomed. (People like this version of Dave's Rose are scheduled to cease to exist when doomed timelines are cosmically 'pruned' because they do not contribute to Paradox Space's self-propagation.) We now have the Dave who is part of the alpha timeline and another Dave who just jumped back several months to save John (and their game session, by extension). The future Dave gives alpha Dave all of the sick gear he has acquired by playing the game for months, which includes the very device that future Dave uses to time travel! He then jumps into the sprite and becomes Davesprite. Even though people from doomed timelines are slated for death, Davesprite persists until the end of the story (with a twist at the end) because sprites are often attracted to dead or dying people for their second prototyping. A bit later in the story we start to see "the dead Daves piling up" as alpha Dave learns the rules of time travel: make an offshoot timeline because you made a mistake and you die soon after you travel back to fix the mistake, or you create stable time loops in the alpha timeline. That's all I will say for now. Of course, things get more complicated when we talk about Scratching sessions and the consequences of rebooting the universe by changing where the players' paradox clones get sent 'back in time' to Earth before SBURB was started. The metanarrative and retcon-powers John acquires near the end of the story introduce more complications that I will not get into right here.

2019-12-01 04:10:11 by The Apocalyptic:

I see fixed points in time as events which determine which of the future possible fixed points in time become fixed at a probability of either Certain or Impossible. The first such, therefore, is the Big Bang. @Jesse M.: There is also one recorded in-canon instance each of a parasite universe and a perpendicular universe.

2019-12-20 21:35:47 by The Architect:

My favorite description of Time Travel in Doctor Who doesn't actually come from Doctor Who itself, but instead the legally-distinct Faction Paradox spin-of from it. Specifically the one in the Book of War, it's really expensive to get a physical copy of it now, but there are pdfs acquirable by less... scrupulous means. Anyway, to give you a very basic gist of it: time does not have rules. Not time travel, but the actual structure of time itself is not, well, structured. The universe before the timelords is complete chaos, where magic and irrationality reign supreme, and causality itself does not exist. And the timelords don't like it, it gives them headaches. So they use the Caldera (the faction paradox name for the untempered schism) for an event known as the 'anchoring of the thread', where they create and enforce the laws of causality and time on the universe. This is not out of character, as even within normal continuity the time lords are responsible for rewriting the universal laws of physics on multiple occasions (for instance, removing Magic, and creating Black Holes) and time IS their domain. Anyway, this 'makes the universe rational', creating the causality that humans have always assumed is fundamental to reality, and it also places Gallifrey at the 'center' of the web of time (in FP, the Spiral Politic) which they also just created, with the Eye of Harmony acting as a focal point. The 'fixed points in time' and in fact, history as a concept, are a direct result of this event. They are events that the Time Lords MADE fixed for the purpose of stabilizing the universe. And which they would, pre-timelord, be directly maintaining, (Ep: Fathers Day), thus the doctor has a bit more leeway after they are gone. (though the web is self-correcting, so he still can't push it too far). Because the time-lords are the 'anchor' of universal history, they crystallize time wherever they go. - Say that someone dies, but no timelord is there to witness it, they become a temporal shrodingers cat, dead or alive depending on how the timeline is altered. - But then the Doctor shows up, and as an 'anchor' he acts as an objective temporal observer, so if he sees them dead the wavefunction collapses, they are dead and they now always have to die that way. (bar really high-effort timefuckery). This means that there can never be a paradox in Doctor Who, unless it involves a personal timeline of Time Lords or Time Lord technology. Otherwise the wavefunction just collapses into whatever one avoids paradox, where as if time lords cross the timeline of themselves (or potentially each other) the wavefunction has already collapsed in a contradictory way, and the web of time becomes a snarl, which will need to be addressed directly be a temporal engineer. (none of which existed post time-war, so the Doctor had to do his best at a patch job until they came back). The reason I appreciate this explanation so much, is that it nicely handwaves a lot of the problems with Doctor Who time travel, by making the rules of time not an absolute natural law, but instead an invention of the time lords, and an extension of Time Lord Law. - Time is Linear not because that's naturally how it is, but because Rassilon decreed it. Certain points can't be changed, because those are the anchoring points the Time Lords nailed history too to keep it from sliding too much. And most points CAN be changed, because the Timelords want to shape the universe to their whims. My explanation butchers the great work they did in that series, so if you're interested I highly recommend it. They definitely do some really cool things with their exploration of time travel. (even if I'm not really a fan of the Faction themselves)

2022-02-23 18:00:36 by Qwandri_XCI:

I think that 'Becoming part of events' means that the doctor has observed things to happen a particular way, and therefore cannot go back and change it as it would contradict the earlier observation (I recall this being violated on the episode 'Father's Day', but it was followed by time eating bats destroying everything, so this principle probably holds in the general case) Of course, this has a solution: travel back in time and drug the doctor such that the observation is actually a hallucination, and then you're free to do whatever. This does invalidate all the information gathered, so it does have a limit of usefulness. However, there is a solution to this too: After the event in question, go back in time to shortly after the event. The doctor, having anticipated this, will have written down useful facts about the event, that do not spoil the event's outcome. You, without looking at the doctor's memory, change it to the original observation, which of course must be consistent with the facts documented. Then you can go back and do whatever you want. ('You', of course, refers to a future version of the doctor). That was horrifically convoluted, so here's a simpler example: The Death Star is travelling towards your home plane, and you have concluded that there is no way to destroy it. Before anything conclusive happens, you hop in your time machine and introduce a critical but almost unnoticeable weakness into its design plans, then hop back to the present and tell a courageous young pilot. Ta-da! The Death Star is destroyed. The common thread is that you change the past in such a way that actual events are favourable to you, but your past self's observation of them remains the same.

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