In the Doctor Who episode "Blink", the Doctor has a one-way conversation with a video camera, reading off of a script. The script would have been written some years later by someone watching the video that the Doctor recorded. The person, Sally, watching the video years later wonders how the Doctor knew what to say, and the Doctor advised her to look to her left, viz at the transcriptionist. How did the Doctor know the transcriptionist was to Sally's left? Well, obviously, because the transcription said as much:it had the Doctor saying "look to your left", and he was reading it while recording the video.

I don't see any logical problem with this: at the time of the videography, the Doctor was reading a preexisting script, and at the time of the transcription, the transcriptionist was transcribing a preexisting video.

The problem arises if one posits that every bit of information one has must have a source. In that case, a source seems to be lacking for the Doctor's knowledge of the transcriptionist's being to Sally's left: he got it from the transcription, which got it from him, so there's no root source at all.

(I seem to recall the same problem arising in the book The Time Traveler's Wife, by Audrey Niffenegger. However, I read it some years ago and am not sure — and certainly don't remember the details.)

So my questions are several:

  • Do any sources from the sci-fi/fantasy world discuss seriously the issue of how the Doctor knew something only known from his own transcription, or the corresponding problem in other sci-fi/fantasy works?
  • Do any philosophers (or information-science people perhaps) propose a rule along the lines of "every bit of information must have an original source" (or its negation)? (This would have nothing to do with time travel, and is of independent interest.)
    • If so, do any sources connect that to the issue that I raised, which arises in sci-fi/fantasy works?
  • I may need to split this, with my first bullet point being asked here and my last two on Philosophy. If you think so, please comment (or edit).
    – msh210
    Jul 16, 2012 at 8:17
  • I'm not exactly sure what you're asking for. Are you asking for references to works that deal academically/intellectually with time travel and the Grandfather Paradox? Or to other scifi works that deal with similar issues? If it's the latter, you'll find quite a few in the Related questions section to the right ------> Jul 16, 2012 at 9:36
  • 3
    Wikipedia has some info on the Bootstrap paradox, including a list of it's use in fiction.
    – Oliver_C
    Jul 16, 2012 at 10:41
  • @AvnerShahar-Kashtan, in my first question I'm seeking just "how did the Doctor know", and Oliver_C's comment answers that. In my second I'm asking in part, as it turns out, for information on the bootstrap paradox, although I didn't know it was called that, and [continued]
    – msh210
    Jul 16, 2012 at 16:49
  • 1
    @msh210 There have been many different treatments of time travel and its paradoxes (or not) in SF. You will find some with a rule like the one you propose, and some without. Please note that lists of SF works and recommendations are explicitly not welcome on this site. You may want to chat about this.
    – user56
    Jul 16, 2012 at 19:10

2 Answers 2


I would say that the answer, with regards to Doctor Who specifically, comes in the very same conversation you are asking about.

"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint - it's more like a big ball of wibbly wobbly... time-y wimey... stuff." (from Blink (2007))

We view time as a line, with cause leading to effect. The Doctor contradicts that by saying that time is a "big ball." This would seem to indicate that the cause and the effect are somehow intertwined. The Doctor says the transcriptionist is to the left because he is to the left. The conversation between Sally and the Doctor happened because the Doctor had the transcript, and the transcript exists because the conversation happened. It doesn't make a whole lot of sense, with regards to how we think of time, but I think that's the point. The Doctor sees time much differently than we do. I don't think there's a solid "answer" beyond this.

  • +1, many thanks, although even my first question was more general.
    – msh210
    Jul 16, 2012 at 23:33
  • Fair enough, I just felt the need to answer, given that your first question does ask about the Doctor and his situation is...unique. However, I see now that you may be looking more towards other similar situations than the explanation of the original.
    – Zoneman
    Jul 17, 2012 at 13:51

This question isn't just science fiction, physicists and metaphysicists both talk about it quite a bit. No, the consensus is that it doesn't need an "original source". It's difficult to understand, but the logic of the universe isn't intuitive. There is no canon explanation for this, and I suspect that if there were, they'd just revisit it and say something contradictory anyway (the show is about a time-traveling alien after all).

If you need help visualizing it, imagine that "loop" running through a few billion times, and every 1000th time, the Doctor doesn't read the script perfectly. He adds something out of his own knowledge. And the transcriptionist does something similar every 5000th time. If this happens, then after billions of times through the loop, the "information" grows, even though it's coming from somewhere. Presumably all of it could have come into being in the same fashion. Of course, this is just an intellectual exercise... in actuality (can you say that for something that doesn't really happen?) this is arrived at instantly without the infinite iteration.

  • 1
    It is rather strong to say that the physicist have a "consensus " that there is no need for an original source. The question of cosmic censorship of closed time-like curves remains open. Jul 16, 2012 at 13:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.