As a rough general rule, Stable Time Loops work, but doing something that will prevent you from going back in the first place has varying degrees of bad consequences. The specifics, however, are a bit more complicated... At least the show is honest about the fact that it's not consistent.
- It's actually mentioned in the classic series that the Time Lords deliberately took Gallifrey out of its own time to prevent any potential rogue Time Lord from ever altering Gallifrey's history. Then again, it's also stated time and time again in the old series that Gallifrey can't be destroyed, and look what they did in the NA and the new series. note
- To add to the weirdness that is time-travel in Doctor Who, look at its opinion on the Blinovitch Limitation Effect. In some cases it seems to suggest that Never the Selves Shall Meet, lest they cause reality to shatter. Or maybe that's only if there's another paradox nearby. Sometimes it causes memory loss if the two touch, like what happened to The Brigadier. Maybe the same object touching will just cause sparks. Or maybe nothing will happen at all except flirting. It's just whatever happens to work for the plot.
- The Doctor has also stated in the past that his knowledge of history is "perfect"; this may mean that he knows exactly what he may or may not change.
- And if there's any discrepancy, it's obviously history that got it wrong!
- Perhaps the show's earliest use of this is "The Space Museum". The First Doctor and his companions arrive at a planet with a space museum in it, but due to the TARDIS "jumping a time track", they arrive Just One Second Out of Sync, rendering them invisible and inaudible to anyone else. While there, they see themselves trapped in museum display cases. When their Invisible Main Character status wears off, the cases go away, they're still inside the museum, and they have to escape or otherwise find a way to avoid the fate they saw for themselves. The Doctor claims that time has alternatives.
- "Day of the Daleks" may have been the Trope Codifier for the Timey-Wimey Ball in Doctor Who. Guerrillas from an alternate 22nd century try to assassinate Sir Reginald Styles to prevent him from disrupting a peace conference, which caused wars enabling the Daleks to invade Earth. In the process, they disrupt the conference themselves. However, the Doctor is able to travel back from this alternate future and stop the guerrillas.
- The Doctor recognizes the Sontarans in "The Time Warrior", complete with asking about their interminable war against the Rutan Host, despite them never appearing in the series before. It's shown 12 years later that the Second Doctor had encountered them before, along with the Sixth Doctor. It's also possible, given that he's already been travelling for a few centuries, that he's heard of them or met them in a Noodle Incident.
- "Pyramids of Mars" has the Doctor show Sarah Jane how time has its alternatives. Even though Sarah Jane is from 1980 and knows that the world wasn't destroyed in 1911 by Sutekh, the Doctor takes her to 1980 and shows that Earth has been destroyed as they didn't stop Sutekh escaping. This is partly accounted for, as the Doctor says that individuals can shape the future but only powerful beings like Sutekh can destroy it.
- In "The Five Doctors", the Doctors remember their previous encounters with each other. Two also remembers Omega just fine. He also knows that Jamie and Zoe had their minds wiped, even though that happened just before he turned into Three, so there's no way for him to be aware of that when he's just travelling about freely. This was eventually explained away by the "Season 6B" fan-theory-turned-official-explanation, which has the Time Lords' Celestial Intervention Agency scooping up the Doctor after his trial and forcing him to run missions for them, culminating in his regeneration and the beginning of Season 7.
- "Father's Day" sums it up pretty well. Pete Tyler being alive created a paradox, and anything else would make it worse. So yeah, interacting with one's past self makes sparks, and a paradox fills the air with gas fumes. Sort of. Not really at all, but if that helps just think of it like that.
- "The Parting of the Ways": The Doctor says that the TARDIS protects itself from paradox. Whenever and wherever the TARDIS lands, the events that led it to go there, and led to the world it's in once it's there, become unalterable.
- The Girl in the Fireplace": The time portals that include the titular fireplace are so unusual that the Doctor has to make up new terms to describe them, and once the characters use them, the TARDIS can't enter the same region.
- The Trope Naming episode, "Blink", actually involves a mostly-internally-consistent Stable Time Loop. It's the show as a whole that fulfills the trope by being inconsistent.
- When the Tenth and Fifth Doctors meet up during Children in Need Special "Time Crash", Ten is in shocked disbelief to be seeing his former self, then goes on to use memories he picked up as Five meeting his future self to defuse the situation. When the illogic of this is brought up (not to mention the violation of multi-Doctor meet-up Canon established from the other three times this has happened), both Doctors mumble something about "Timey Wimey" and move on.
- "The Fires of Pompeii": Donna asks why the Doctor will thwart aliens but not stop a particular historical catastrophe, and the Doctor replies that some points in time are fixed, while others are in flux. Him being a Time Lord allows him to perceive which is which and act accordingly, even against his nobler instincts. It's revealed in the climax that the reason he can't change the catastrophe is because he's the one responsible for making it happen.
- More about fixed points in time in The Sarah Jane Adventures. Sarah Jane's parents dying is a fixed point in time because she has seen it, remembers it, and knows it happened. Changing that would be bad.
- River Song. Her encounters with the Doctor are not synchronized at all. The journal checking seen in "Silence in the Library" and "The Impossible Astronaut", as well as the "spotter's guide" from "The Time of Angels", seem to indicate that she meets the Doctor in a random order, but when River's past/future with the Doctor is brought up in Series 6, it's implied that they're traveling in practically reverse order the kiss at the end of "Day of the Moon" is implied to be River's last because it is the Doctor's first. This is despite the fact that they clearly aren't meeting in reverse order, since the Doctor meets her months after she is born four times after he "first" meets her. She also doesn't recognize Rory in "The Big Bang", despite seeming to know him already in "The Impossible Astronaut", which is earlier in her timeline (though that was most likely due to him having been erased from history at that point). In short, their meetings are mostly random, and any given time the two meet up may be synchronized, but overall they're moving in opposite directions.River: Rule 1.
Amy: The Doctor lies.
River: So do I. All the time. Have to. Spoilers.
- The Doctor tries to mess with a fixed point in "The Waters of Mars". It doesn't end well. He explicitly states that there are fixed points in history which cannot be changed. Those points in history greatly affect the future and allow for time to follow a more or less consistent path. Anything he does to try and change history will simply cause the event to occur regardless. Even the Daleks are shown to respect this. The Doctor, feeling frisky, tries to alter one. Events remind him that even a Time Lord has limits.
- In "The End of Time", the Doctor attempts to explain a Time Lock to Wilfred.The Doctor: They're sealed inside of a bubble. It's not a bubble, but just think of a bubble.
- The cracks in time running rampant in Series 5 did so much damage that it's implied they broke time itself. They are capable of retgoning anything they consume, as shown in "Flesh and Stone". However, in the same story, River tells the Doctor she'll see him again when the Pandorica opens. In those events, shown in "The Pandorica Opens"/"Flesh and Stone", the cracks are sealed, even though River, in her own future, was able to see and interact with one, therefore being in the cracked universe, even though she had already witnessed the events that lead to the cracks being repaired. Basically, they outright broke time travel logic.
- A "turnpoint moment" is mentioned in "Cold Blood"; the Doctor describes it as an "opportunity" here, stating that the rocky peace negotiations going on in this episode could really change the future to an outcome where humans and Silurians live in peace ever after. The eventual results are... mixed.
- The whole of "The Big Bang" is built on this trope: The Doctor saving the day and escaping from the Pandorica is built on an ontological paradox he shows up already escaped to enlist Auton!Rory in effecting his escape. The Doctor even explains that this would normally cause drastic side effects for the universe, but luckily the universe had already been destroyed. The affair was referred to in a later episode:River: He's interacting with his own past. It could rip a hole in the Universe.
Amy: Yes, but he's done it before!
Rory: And in fairness the Universe did blow up.
- "A Christmas Carol" also features this heavily. It starts with the Doctor showing a video Kazran made as a boy to the older him and travelling back in time to when he made it, leaving Kazran watching a video of the Doctor interfering in his past as his own memories change to reflect that this had happened. Kazran then has memories of not growing up while being visited by the Doctor, and memories of being visited by the Doctor. He then ponders how he's never met the Doctor before tonight, but seems to have known him all his life. It ends with the Doctor showing the younger Kazran the man he turns into, leading to the older one having a change of heart partly brought on by realizing that he's turned into his father, and partly by him being retroactively altered by the experience of being horrified at seeing his older self as a boy. Oof. It's implied that this method is far from perfect, as Kazran's own mind-reading controls no longer recognize him, despite the fact that they should logically have been programmed for the Kazran that existed in the current timeline. Who knows? It is a Timey-Wimey Ball, after all.
- This is explained in the episode. The controls don't recognize him because they were programmed by his father, and after all the changes the Doctor made, his father never gave him control.
- Just because the DW section for this trope needs to be larger, it's used extensively in "The Girl Who Waited". The TARDIS crew happens upon the Two Streams health centre. They take people who have contracted a fatal disease and place them in the "fast" stream, symbolised by a red waterfall. They can live their whole life and age normally in only a day. Meanwhile, their loved ones are in the slow stream, symbolised by a green anchor, and can watch their lover/family/friend have a fruitful life. Unfortunately, it all goes wrong when Amy gets trapped in the fast stream. Eventually Rory manages to break in to save her, but 39 years have passed, leaving his wife old and bitter. He can jump back in time to save younger Amy, but can only do so with older!Amy's help. However, she doesn't want to be re-written and stop existing. Eventually they decide to save both of them by breaking the laws of causality; at the last minute the Doctor reveals that this is actually a paradox and leaves Old!Amy behind to die. Though she won't really, because in a few minutes she'll never have existed.
- "The Wedding of River Song" finally shows what happens if you alter a fixed point too much. All of time collapses, happening at once. You'll have Holy Roman Emperor Winston Churchill riding around on his personal mammoth while they discuss the political pressures caused by the War of the Roses, greet a Roman Centurion, and see a Silurian doctor for a check-up. Meanwhile, pterodactyls are considered pests and Charles Dickens appears on the news to talk about his new Christmas special. Only some people will be able to hang on to their memories of "correct" time. The date and the time will never ever change. They are the date and the time of when the fixed point was supposed to happen. If allowed to continue, time itself will break, causing THE DESTRUCTION! OF REALITY! ITSELF!
- "The Day of the Doctor":
- The Eleventh Doctor is brought by the Moment to meet the Tenth Doctor and the War Doctor (an incarnation between the Eighth and the Ninth Doctors, whom the others don't recognize as a Doctor due to... questionable actions). The War Doctor gets annoyed at the childish things his future selves say, including "timey-wimey" (as stated by the Eleventh Doctor). The embarrassed Tenth Doctor (who invented the phrase) says he has no idea where the Eleventh Doctor picked this up.
- This episode also features time travel that dives into The Multiverse theory when the Doctor changes an event in his own timeline (namely, the end of the Time War). There's a hint that this was how it always was afterwards due to the lack of negative consequences, and the fact that the universe perceived that time was unchanged. The other super-timey-wimey moment is that it took 13 different Doctors to make it work, including one that could only exist thanks to the events of the NEXT episode.
- "Kill the Moon" gives us an inversion on fixed points. Where a fixed point is a historical event that must happen, what we get in "Kill the Moon" is a crossroads, in which a single decision by humanity could change its history for eons to come. Even the Doctor claims to be unable to see the ultimate outcome and, because he feels this is humanity's choice, refuses to help, leaving Clara to solve the crisis.
- "Orphan 55": The Doctor's speech at the end about how Orphan 55 is only one potential future for the Earth out of many relies on the Multiverse theory of time travel (every action creates a new timeline). Apart from the Tenth Doctor's explanation about the existence of parallel universes in "Army of Ghosts", the show has never explicitly used this in all of its great timey-wimey history. It is possible, however, that the Doctor was just saying that in order to cheer up her companions... (In addition, the Doctor has encountered various conflicting and incompatible futures of humanity and the Earth, so this wouldn't exactly be the first time the show's done something like this.)
- The novels have an equally insane version, in which the 8th Doctor (infected by Faction Paradox biodata) ends up interfering slightly in the life of the 3rd Doctor, leading to him regenerating on the wrong planet and being infected by Faction Paradox biodata. Of course, Faction Paradox live and breathe this trope (as well as Temporal Paradox) at the best of times. It's their hat.
- The Doctor Who New Adventures had the concept that Time itself was a sentient entity who consciously fixed various timeline hiccups resulting from time travel with the Doctor as her champion.
- Big Finish Doctor Who has used this trope from early on.
- The 8th Doctor saving Charlotte Pollard from her death on the R101 causes a paradox, meaning anti-time starts infecting the Universe, causing odd things with history to happen during the 8th Doctor audio stories leading up to "Zagreus". For example, Shakespeare has disappeared from history (which is explained in "The Time of the Daleks") and Benjamin Franklin was President. Finally, in "Neverland", Charley helps save the Web of Time, meaning that the paradox and anti-time infection become part of the Web of Time. To complicate matters further, she later travels with the 6th Doctor, even though she shouldn't be alive at his point in the Doctor's timestream.
- "Seasons of Fear" has a very complicated Timey-Wimey Ball. The Doctor goes back in time to stop Sebastian Grayle, because Grayle prompted him in an artificial alternate timeline in which the Doctor hadn't even met him yet. Grayle then develops a hatred for him, eventually leading to him creating an artificial alternate timeline. To make this more complicated, it isn't clear how the Doctor met this Sebastian Grayle, as in 1806, Grayle goes back in time and is killed by his past self.
- "The Foe from the Future" features the Doctor giving various speeches about how the human brain just isn't physically capable of understanding the necessary complex temporal equations to explain why Jalnik's original plan of mass evacuation into the past is a bad idea, or how Shibac can exist in the past even after his future has been erased.
- "Flip-Flop" features a very odd version of this trope, with an apparently Stable Time Loop between two alternate timelines, meaning there are two Seventh Doctor and Mel(s) who create one history by erasing another.
- "Jubilee" involves the Doctor going into a parallel universe, but about a hundred years after it has diverged, with the Sixth Doctor experiencing Flash Sideways and remembering being in a Dalek war a hundred years ago. Then the Doctor ends up accidentally causing the war a hundred years ago in the past that created that divergent timeline, only it's actually happening then as well, because the Doctor's presence caused the timelines to merge, somehow. Then the Dalek survivor of the war a century ago talks the invasion fleet into suicide, which unmakes the alternate universe and resets the timeline. It makes a lot more emotional sense than it makes logical sense (a sentence which just summarizes the whole darn show).
- Past Doctor Adventures
- Asylum starts off with Nyssa being picked up by a young Fourth Doctor, long after she had departed from the Fifth Doctor. Both she and he seem embarrassed about the situation and the Doctor specifically asks her not to tell him any details that could lead to a paradox, euphemistically describing it as "saving it for a nice surprise". She then discovers that the research she was doing on Roger Bacon has inexplicably changed into research on Isambard Kingdom-Brunel, forcing them to head back in time to Bacon's time to discover what caused the future to change.
- Festival of Death starts with the Fourth Doctor, Romana and K9 arriving on the G-Lock, a space station existing on a breach into hyperspace, where they find that everyone present already recognises them, to the extent that they are arrested and accused of the recent attack by the station supervisor and find that they have already arranged for someone to come and let them out. Over the course of the novel, they have to go back in time three more times to ensure that they have met everyone they have to meet; at one point there are two different versions of the Doctor and Romana on the station at once, the second versions taking care to avoid meeting their younger selves.
- Warmonger is a sequel and prequel to "The Brain of Morbius"; the Fifth Doctor is forced to go to Karn to get medical help for Peri after a serious injury and ends up becoming caught up in Morbius's original military campaign, to the extent that the Doctor must form a military alliance of various old enemies, such as the Sontarans, Cybermen and Ogrons, to oppose Morbius's forces.