So many years since I saw you last, but not a day of it on your face. He goes back through the fireplace to get her, when this happens (The Doctor calls back through the fireplace.)ĭOCTOR: Madame de Pompadour! Still want to see those stars? (The fireplace turns, taking the Doctor away.) Some examples of this in the newer revival include in The Big Band (S5E13) where the Doctor brings two sonic screwdrivers into close contact and sparks are emitted which appeared to confirm they were the same sonic screwdriver at different points in time.Īt first, the Doctor thought he wouldn't need the TARDIS in order to bring Madame de Pompadour along, he planned for her to come through the fireplace. The first aspect is similar to a real-world physics conjecture, the Novikov self-consistency principle.
It is usually understood as having two aspects: firstly, that a time traveller cannot "redo" an act that he has previously committed, and secondly, that a dangerous energy discharge will result if two temporal versions of the same person come into contact. In-universe, this is known sometimes as the Blinovitch Limitation Effect A variation of this explanation is the notion of time locks, which are placed on several important events including the Time War. Anyone who's hurt/dies/etc can be saved very easily. Out of universe, this is important because without it the show would be without consequence. Apparently, this can result in paradoxes, the butterfly effect, and generally bad things. Whilst Doctor Who officially doesn't have canon, this (or a similar) explanation is often employed to justify why he can't simply travel back in time and undo lots of regrettable events. It's certainly a poor explanation, but it's one that's used occasionally throughout Doctor Who. ROSE: (asks why they can't use the TARDIS instead of the time windows)ĭOCTOR: We can't use the TARDIS. At one point in the episode, there's the following exchange: