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I have a problem with the Doctor Who timeline in several episodes. For example, in the 10th Doctor episode, "Blink", the Doctor and Martha Jones were trapped in 1969 and are able to leave a message for Sally in 2007 to assist them getting back the TARDIS, which was stuck in 2007. After the problem was solved,

Sally encountered the Doctor in 2008, but at that time the Doctor didn't even know Sally, and Sally passed the Doctor the clues to escape from 1969 - in particular, the DVD Easter Egg script that Larry wrote in 2007.

In my point of view, Sally wouldn't be able to solve the problem if the Doctor didn't know about Sally before the Weeping Angel sent them back to 1969, and the Doctor can't leave a message to Sally in 1969, because the Doctor couldn't know the exact events that would happen in 2007.

Sally needed to know about all this before the Doctor was trapped, and her source of information is the Doctor, and at that time the Doctor don't know about the trouble he was going to encounter.

This complex timeline of Doctor Who is a "chicken and egg" paradox, isn't it? There are other examples of this in Doctor Who, such as:

  • The 11th Doctor episode "The Big Bang" - how did the Doctor get out of the Pandorica?
  • The 10th and 11th Doctor "River Song" story arc.
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Time is like a big ball of wibbly wobbly timey wimey... stuff. –  Loïc Wolff Aug 9 '11 at 8:33
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Can we have a wiki explaining "Time"? –  lamwaiman1988 Aug 9 '11 at 15:31
    
And what exactly does "wibbly wobbly timey wimey" mean? –  lamwaiman1988 Aug 10 '11 at 1:27
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I think this is also called the Bootstrap Paradox. Information/item created from nothing. An example being a man going back in time to give himself a time machine which he then uses himself to give to himself. Where did the time machine come from in the first place? –  riv_rec Aug 10 '11 at 14:09
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"wibbly wobbly timey wimey" is a quote from the Doctor. c.f. the TV Tropes page about this: tvtropes.org/pmwiki/pmwiki.php/Main/TimeyWimeyBall –  Tony Meyer Aug 12 '11 at 10:58

6 Answers 6

up vote 37 down vote accepted

That's more or less what's explained in the episode.

Remember the video of The Doctor explaining what time is?

Time is like a big ball of wibbly wobbly timey wimey... stuff.

There's a "Children in Need" mini-episode on that theme, too. The Doctor (10th) find himself stuck with The Doctor (5th) on the TARDIS. The only way to save himself is to press a series of buttons on the TARDIS console.

Which he knows because he (the 5th) saw himself do it (the 10th). And the 10th knows, because 5th knows and they have the same memory.

It's a paradox, but it's not, because it's Doctor Who.

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I think that "wibbly wobbly timey wimey" pretty much explains any paradox in Doctor Who. –  Tango Aug 9 '11 at 21:24
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@TangoOversway: Not quite; it's the signal that the writer is declining to explain. (Quite rightly; sometimes it's better writing to give no explanation than invent a bad one.) –  Tynam Dec 18 '11 at 18:01
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There's also the Time/Space pair of mini-eps that play with "we got out because we told ourselves how to get out". –  Allen Gould Apr 24 '12 at 19:09
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"THE WIBBLY LEVER!" –  Loïc Wolff Apr 25 '12 at 7:33

Basically, the point of that episode and others like it (Such as Big Bang 2 when the only reason the Dr got out of the box is that after he got out he went back and told Rory to get him out.) is that time isn't "linear" in respect to itself - a person always moves forward along his own timeline, but the universe's timeline may have "loops". In the Doctor Who universe, time may be circular (and as noted by others, Paradoxical).

Look at it this way in Blink - once the Doctor was able to help Sally save the Tardis from the Angels, it was inevitable that Sally would, in her future, share the story with the doctor. Once the doctor received the information from Sally, it was inevitable that he would help her, in his future. It's a perfect, unbreakable circle - once entered at any point it cannot be left.

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But how can the circle be started? –  lamwaiman1988 Aug 9 '11 at 15:30
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it depends on who you are looking at. From the Dr.'s perspective, the circle starts when he receives the information from Sally. In his timeline, that is the start and the end is when he saves the Tardis. From Sally's perspective, the circle starts when she first receives contact with the Doctor and ends when she gives him the information. The struggle to understand is that you are looking at it as if there is a single, linear, timestream. Really, there is a timestream for each person, and those streams can intersect - you just can't loop back on yourself. (Think Madame De Pompedour.) –  user158017 Aug 9 '11 at 15:58
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@gunbuster363 Circles don't have a start, or an end either. That's the whole point. –  Blazemonger Feb 1 '12 at 18:50

Believe it or not, these sort of "closed timelike loops" aren't a paradox at all. They've been debated by better brains than yours or mine, and the mathematics holds out.

Quoting from Wikipedia's article on the "Novikov self-consistency principle":

Joseph Polchinski ... argued that one could avoid questions of free will by considering a potentially paradoxical situation involving a billiard ball sent through a wormhole which sends it back in time. In this scenario, the ball is fired into a wormhole at an angle such that, if it continues along that path, it will exit the wormhole in the past at just the right angle to collide with its earlier self, thereby knocking it off course and preventing it from entering the wormhole in the first place. Thorne deemed this problem "Polchinski's paradox".

After considering the problem, two students ... were able to find a solution beginning with the original billiard ball trajectory proposed by Polchinski which managed to avoid any inconsistencies. In this situation, the billiard ball emerges from the future at a different angle than the one used to generate the paradox, and delivers its younger self a glancing blow instead of knocking it completely away from the wormhole, a blow which changes its trajectory in just the right way so that it will travel back in time with the angle required to deliver its younger self this glancing blow.

This is the model that current "Doctor Who" writers follow whenever "wibbly wobbly timey wimey" is invoked.

In summary: time travel (whether using closed timelike loops or TARDISes) cannot be used to create a contradiction, which is a paradox -- but it can be used to create self-consistent loops.

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would that not be perpetual-motion-like though? –  FallingBullets Sep 3 '12 at 5:54
    
@FallingBullets: Yes, but if you have a time machine, perpetual motion is no problem. Certainly not compared to the Bootstrap paradox. (Having said that... the Doctor generates information paradoxes all the time, but he's careful to avoid physical object paradoxes. The note in "The Big Bang" is a perfect example of both - after he receives the note he knows information which is generated out of nowhere by paradox, but he's careful to throw it away and write the same note so as not to have a paradoxical object around.) –  Tynam Sep 3 '12 at 8:27
    
Setting aside quantum limitations, it would be possible for each iteration through the time loop to end up with the billiard ball's path being closer to an equilibrium path where it would knock itself into the exact same path repeatedly. Even if there would have been no reason for the ball to get onto the equilibrium path perfectly, its path could get so close as to be practically indistinguishable. Add in quantum limitations and the path could be indistinguishable. –  supercat Oct 16 at 22:43
    
@supercat -- no, that's not it. The ball never "gets closer" to the equilibrium path because it's always on the equilibrium path. –  Blazemonger Oct 17 at 13:58
    
@Blazemonger: Setting aside quantum effects, a ball could never "enter" the equilibrium path; the only way it could ever be on the equilibrium path would be if it had always been. On the other hand, if the equilibrium path served as an attractor, it would be possible for a ball to get arbitrarily close to the equilibrium path even if it started out on some other path. –  supercat Oct 17 at 20:32

i believe that the doctor may have sent out a different message "earlier" (in a previous continuity of time) to sally sparrow after meeting billy in 1969, either through a video or through billy (a simple message such as "send the TARDIS back" may have enough) later in 2008 she meets the doctor outside the dvd store and gives him some sort of account of what happened, so that when the doctor "later" (for the doctor this happens later on) gets stuck in 1969, he checks that information, and this may happen many times until it stabilizes into a healthy loop. the truth is, that once she tells the doctor even a little, "before" (from the doctors perspective) he travels to 1969, a time loop is created that will loop over until the same exact events happen in 1969 twice (think about it) so without a time loop there would be a problem.

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I think time uses all possibilities. The possibility Doctor does all to free past doctor, to be still alive, if not there again, and again stays created new possibility Doctor to use new possibility. Time Ping-Pong Paradox.

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Is this canon?? –  DVK Nov 14 '13 at 17:57
    
Canon? In Dr. Who? Always a slippery notion. Didn't really exist until several decades into the franchise at least, and was basically optional for the writers until the reboot. –  Jon Kiparsky Feb 6 at 16:16

Blink was a paradox/bad science or badly explained, but I am banking on the former since RTD is not as good as Steven Moffat. Yes, time-streams do not run linearly, but what happened in Blink could not conceivably have happened unless Sally, figured out on her own the first time, which I doubt that she did.

Regarding the Pandorica, easy explanation is that it was not an impenetrable prison after all, and that the Doctor escaped somehow and acquired a vortex manipulator since he no longer had access to the TARDIS.

The River Song arc is not paradoxical at all.

Let's say that Doctor A (which is the very first instance of the Doctor) reached the Field of Trenzalore and River A (First instance of River was not stolen from The Doctor's timeline). The Silence then go back to steal River B (Younger instance of River) in order to prevent The Doctor from reaching that point. River B grows up to attempt to kill Doctor B and uses up all her regeneration energy to save him, and the Doctor does not find out about his death since it has not happened yet. Eventually, River B ages some more, and is caught by Kovarian and sent to kill Doctor B (An instance of the Doctor after Doctor A), who is the first Doctor and ONLY instance of the Doctor dying at Lake Silencio. River B goes back in time to the Donna era with Doctor C and dies (First time that the Doctor is called to the Library since River is the one who beckons for him to come). The second instance of The Silence intervening results in a River C that uses up all of her regeneration energy to save Doctor C (older instance of the doctor), who finds out that he dies at Lake Silencio. The Teselecta dies in Doctor C's place for all of future instances of this scenario when River C kills it after finding out that the Doctor has no intention of dying, and River D and Doctor D (delayed invite for The Doctor) are invited to this event. River C does not suggest to Amy that she already knew that it would happen, just that she knew that the Doctor did not die. Eventually River C calls Doctor E to the library and is saved this time because Doctor D gave her his screwdriver in anticipation of her death. After it happens once again with River E and Doctor E being invited to the event, River D tells Amy that she already knew that the Doctor D wouldn't die as she had been invited to the event when she had been younger. I believe that the Pandorica occurred as a result of The Silence eventually finding out about Doctor D (and future instances) surviving to reach Trenzalore, resulting in the second Big Bang first occurring in Doctor E's timeline. Yes, I do believe that many extra points in time were created for future instances of The Doctor as they could not have feasibly occurred in previous scenarios where the timeline was being fixed so that The Doctor could reach Trenzalore.

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-1 for "RTD is not as good as Steven Moffat" –  deworde Oct 13 '11 at 14:56
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-1 for an offhanded "Blink sucks because the writer isn't my favorite" followed by a mass text unrelated to the original question. –  Allen Gould Apr 24 '12 at 19:09
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Super bonus -1 for "RTD is not as good as Steven Moffat" since Steven Moffat wrote that episode.. –  Michael Edenfield May 24 '12 at 20:24

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