Alternate timeline
An alternate timeline was a reality that diverged from the "true" or "natural timeline" due to the actions of time travellers or other temporal phenomena. They were different from parallel universes in that they did not separate cleanly at the point of creation, resulting in the new timeline destroying the old one. (PROSE: Imperial Moon) The phenomenon may also have been described as an "interstitial spillage of time." (AUDIO: Project: Lazarus)
Physics
Alternate timelines could be visited accidentally by jumping a time track (TV: The Space Museum, AUDIO: The Mutant Phase) or contacting other anomalies (AUDIO: Colditz) in the Time Vortex. Deliberate travel to these timelines was possible if the traveller possessed something, such as the sigil ring, that allowed them to change time streams. (PROSE: Goth Opera)
They may have diverged from points in history when there was temporal fluctuation. The power required to adjust the timeflow and overcome temporal inertia on such a scale couldn't fit on a single planet, but beings with enough power were capable of doing so, such as Sutekh, the Guardians of Time, Rassilon, and the Chronovores. Even the Doctor or the Master could have the know-how or inclination to create them. Because the universe only had a finite amount of mass and energy to exist as one universe, the creation of an alternate timeline or sub-universe adversely affected the real timeline, causing chaos throughout the universe; releasing enough energy could destroy the timeline and set history back on its correct course. The energy released when a TARDIS time rammed another could produce this energy. (PROSE: Blood Heat)
Though a timeline could be negated, memories of it could still be retained. (TV: The Big Bang, The Impossible Astronaut) Sometimes these memories were subconscious and only surfaced in dreams. (AUDIO: The Time of the Daleks, Jubilee) Multiple timelines could co-exist in one continuum; because of this, an individual with multiple futures could come in contact without any Blinovitch Limitation Effects. (AUDIO: Peri and the Piscon Paradox)
Occasionally, time was actually changed so that what was originally the future became an alternate timeline. These were not meant to replace the true timeline but were the result of changes to the real timeline including, apparently, WOTAN conquering Earth (PROSE: The Time Travellers) and the Doctor dying on Grace Alone (AUDIO: The First Wave) and later Trenzalore. (TV: The Name of the Doctor, The Time of the Doctor) This may have related to causality, with knowledge coming before an event rather than an event becoming knowledge. The Doctor encountered WOTAN after it'd conquered Earth in 1966, changing history when he later arrived in 1966; the opposite would be the Doctor arriving in an 1804 where the French Revolution was still happening, as he already knew this was incorrect. (PROSE: The Man in the Velvet Mask)
Two Earth Reptile temporal scientists theorised that after changes were made to history, it took twenty minutes for the new timeline to become established. (PROSE: The Crystal Bucephalus)
Metaphysics
From a metaphysical viewpoint, alternate timelines constantly winked in and out of existence with every decision made, (AUDIO: The Wrong Doctors) always being extinguished as fewer and fewer choices became open. This was particularly affected by time travellers who changed the future whenever they arrived in a new time. This was the cosmic pain of the universe and in this manner Gabriel and Tanith were personifications of the timelines that never existed. (PROSE: Falls the Shadow)
The existence/creation of alternate timelines and parallel universes was held in check by the existence of the Time Vortex, which was sustained by the existence of the Time Lords who created it. (PROSE: The Domino Effect)
Terminology
The phrase "alternate/alternative timeline/universe/reality" was sometimes used interchangeably with "parallel universe"; however, alternate timelines usually changed after a single moment in time, whereas parallel universes usually had more than one difference from the "normal" universe.
Timelines
Timelines encountered by the Doctor
Timelines encountered by others
Timeline | Negated By | Featured in |
Peri Brown was not assassinated and lived with King Yrcanos as a Warrior Queen | Not negated but existing due to a Time Lord faction | AUDIO: Peri and the Piscon Paradox |
Peri Brown did not live with Yrcanos and was returned to Earth with her memories of the Doctor erased save for her first adventure with him | Not negated but existing due to a Time Lord faction | AUDIO: Peri and the Piscon Paradox |
Peri Brown's future was altered another three times | Not negated but existing due to a Time Lord faction | AUDIO: Peri and the Piscon Paradox |
The Seventh Doctor defeated the Vardan invasion of Earth by leaving clues for his past self | The Monk | PROSE: No Future |
Insects of the Mind evolved as the dominant life on Earth | The existence of time travel | PROSE: Falls the Shadow |
Britain was a conformist republic | The existence of time travel | PROSE: Falls the Shadow |
Antonin's timeline | Not negated but existing within the Axis | AUDIO: Reborn |
Burner Doctor's timeline | Not negated but existing within the Axis | AUDIO: Disassembled |
True Lords' timeline | Not negated but existing within the Axis | AUDIO: Annihilation |
Regenerators' timeline | Not negated but existing within the Axis | AUDIO: Forever, Emancipation, Evolution, Arbitration, Extermination |
Romana's second incarnation regenerated on the Moros and Omega escaped the anti-matter universe during the ensuing presidency of her third incarnation | Irving Braxiatel | AUDIO: Intervention Earth, Enemy Lines |
The Watchmaker killed Narvin and Ace | Romana, Leela and the Watchmaker | AUDIO: Enemy Lines |
Torchwood and Divine Intervention failed to prevent a devastating war beginning in Hull involving humanoid wolves and androids | Mr Bird | AUDIO: Get Andy |
The War Master used the Anti-Genesis codes to replace Davros as the Daleks’ creator, creating his own race of Daleks who conquered the universe | The Master, another version of the Master from a parallel universe and the Dalek Time Strategist | AUDIO: Anti-Genesis |
Leela was killed in an alien attack on Gallifrey, prompting President Romana to order the destruction of the Cannavar system in retaliation | Not negated but existing within the Beyond | AUDIO: Beyond |
The Dark took over members of Torchwood | Torchwood and Bilis Manger | PROSE: The Twilight Streets |
Andrea Yates' World | alternate Andrea Yates | TV: Whatever Happened to Sarah Jane? |
The Trickster's World | Eddie and Barbara Smith | TV: The Temptation of Sarah Jane Smith |
Donna's World | alternate Donna Noble | TV: Turn Left |
The stars go out in Pete's World as the walls of reality broke down | DoctorDonna | TV: Journey's End |
Ship erased Sarah Jane Smith, Luke Smith and Clyde Langer | Adam Lloyd and Rani Chandra | TV: The Mad Woman in the Attic |
Taphony rapidly ages Alistair Gryffen while draining Jorjie Turner of her energy. | Taphony, by departing through the vortex of the Space-Time Manipulator, reversing time by a day and resulting in everyone forgeting her bar K9 Mark 2. | TV: Taphony and the Time Loop |
Ben and Katy die in a fire | Sarah Jane Smith and Emily Morris | TV: Lost in Time |
Deindum from the future conquered the galaxy | Bernice Summerfield | PROSE: Present Danger, AUDIO: Escaping the Future |
Use of GENIEs cause devastation to the Earth | A GENIE and those who commanded it | PROSE: The Stone Rose |
Simon Brown's public release of information regarding the atomic bomb causing Joseph Stalin to use his atomic bombs on the Earth to maintain control. | Honoré Lechasseur and Emily Blandish travelling back to 1949 to stop events from occurring. | PROSE: The Winning Side |
John Hart meets Queen Victoria in 1887, marries her and ultimately becomes King of the British Empire. | Jack Harkness, by dying despite being a fixed point in time, causing John Hart's version of reality to collapse. | AUDIO: The Death of Captain Jack |
The universe is consumed and left dead by the Master's ultimate form which exists as pure hunger | Missy being consumed by her future self, resulting in a paradox. | AUDIO: Masterful |
Species from alternate timelines
Some species existed entirely as a result of diverges in time, including the Haemovores, a result of Fenric poisoning humanity; (TV: The Curse of Fenric) the Mind, before being destroyed by Gabriel and Tanith; (PROSE: Falls the Shadow) the Daleks affected by the Mutant Phase - an evolution of Daleks; (AUDIO: The Mutant Phase) and the Skaro Degradations, Dalek permutations from other timelines. (PROSE: Engines of War)
Behind the scenes
Terminology
The phrase "alternate timeline" is used in The Ancestor Cell, Beige Planet Mars, The Eye of the Giant, Just War, Legacy, Mad Dogs and Englishmen and The Shadow of Weng-Chiang. The phrase "alternative timeline" is used in Blood Heat, The Blue Angel, Cold Fusion, The Eight Doctors, The Eyeless, Imperial Moon, The Ripple Effect, Spiral Scratch and The Temptation of Sarah Jane Smith.