Spock: You are assuming that Nero knows how events are predicted to unfold. The contrary - Nero's very presence - has altered the flow of history...thereby creating an entire new chain of incidents that cannot be anticipated by either party.
A specific type of Alternate Continuity in which the two continuities diverged off from a previous installment in the franchise. The two continuities are mutually exclusive, but both Canon. They share identical backstory, but the outcomes of the story in either continuity may turn out very differently. Often caused by Time Travel. Unlike plain vanilla Alternate Continuity, these kinds of timelines do not necessarily happen due to Adaptation Decay or Adaptation Distillation in moving from medium to medium, but were often chosen deliberately by creators to take a franchise in a new direction while preserving the original material. This can oftentimes prevent a Dork Age. Didn't like that last installment? It was in an Alternate Timeline and really has no effect on your main franchise. Sometimes, these forked timelines can run simultaneously, each providing a different take on the franchise, its characters, and its events. The Alternate Timeline can also be employed as a kind of "soft" Continuity Reboot, creating a new universe while keeping the original in-Canon. Some of these alternate timelines may be "What-If?" stories where one event went differently than in the main timeline, or the entire universe may be changed For Want of a Nail.
The most obvious difference between an Alternate Timeline and vanilla Alternate Continuity is that Alternate Timelines share Backstory, and were formed at a point of divergence. If what it diverged from is Real Life, then it's Alternate History. If this doesn't happen, particularly in Video Games with Multiple Endings, it's called "Cutting Off the Branches". In some stories involving alternate timelines, you can Flash Sideways or meet your Alternate Self.
- The finales of Neon Genesis Evangelion and The End of Evangelion (arguably) diverge at Episode 25. ("Arguably", because in the opinions of some fans, they merely present the same events from different points of views.)
- Dragon Ball Z has at least three of these, where the divergences were Future Trunks and Cell time traveling. As a result, Trunks can't actually Set Right What Once Went Wrong - but he can stop it from happening elsewhere, then take the skills he's gained back to his own timeline and curb-stomp the enemies he used to be powerless against. Both fans and official guidebooks have also speculated on the existence of a fourth timeline. According to Cell, he killed Trunks and stole his time machine because Trunks destroyed the androids Cell was supposed to absorb. Since the Future Trunks that the series focuses on knew when Cell would appear to kill him, the Trunks who was permanently killed and had this time machine stolen must have visited a timeline where Goku didn't die of a heart disease, but Cell never surfaced and the androids were presumably defeated somehow. The most accepted theory was laid out in one of the guidebooks, that Bulma built a remote control that was used to defeat the androids there and that Trunks took it back to his world to use there, too—since he never would have become strong enough to defeat them on his own without training for the Cell Games.
- Pokémon Special, when Celebi sends Ruby and Sapphire to another timeline where Norman, Courtney, and Steven are still alive. This creates one timeline where everyone is alive, and another where Ruby, Sapphire, Norman, Steven, and Courtney are dead and nothing is left that can stop the end of the world.
- Mirai Nikki: Paradox. It actually turns out the be very important to the main timeline in the last chapter, however.
- The Magical Girl Lyrical Nanoha A's Portable game series splits off from the main Lyrical Nanoha continuity at the end of Magical Girl Lyrical Nanoha A's. Here, Reinforce Eins does not perform a Heroic Sacrifice, causing Humanoid Abomination Evil Twins of Nanoha, Fate, and Hayate to be born from the remnants of the Darkness of the Book of Darkness.
- Fullmetal Alchemist did this. The first Anime took its own storyline when it Overtook the Manga.
- Puella Magi Madoka Magica shows that there is at least five (and it is implied that MANY more occured offscreen) of these as a result of Homura Akemi trying to Set Right What Once Went Wrong.
- Puella Magi Oriko Magica confirms that there is a sixth canon timeline.
- Steins;Gate is actually mostly about getting out of the so called Alpha timeline(s) and back into the original but so called Beta timeline(s). In the end they will get the possibility of the third timeline "behind the steins-gate.
- The Marvel Universe has tons of divergent "What If?" stories, but the Spider Girl series takes place in the MC2 universe, which diverged from the main continuity after the Clone Saga. in this continuity, Spider-Man's daughter survives and becomes Spider Girl in the future.
- Or the point of divergence may be even further back, as later on it's revealed that Simon Williams (aka Wonder Man) died in issue 9 and was never resurrected.
- One alternate Earth in the DC Multiverse was formed soon after Jason Todd died. Batman, stricken with grief, abandoned his Thou Shalt Not Kill policies and virtually eliminated crime worldwide.
- Transformers has done this multiple times.
- Notably, the Classics continuity follows on from the end of Marvel's G1 comic, but ignores the events of G2 and some(maybe all) of the UK comics. Don't ask where Earthforce fits in.
- Titan Magazines had a comic based off the 2007 film which diverges from the main timeline when the Decepticons win the Battle of Mission City.
- Even Archie Comics has ventured into this, with their controversial Archie Marries Veronica / Archie Marries Betty combined mini-series which became a combined regular series.
- Explained in-story in Star Trek. The two Star Trek timelines diverge at Kirk's birth. In the Prime timeline, Kirk is born on Earth and the timeline proceeds how you remember it. In the new timeline, Kirk is born in space, his father is killed by Nero, and Vulcan is eventually destroyed so there is no point asking Spock-Prime on what's going to happen next since he has no idea either now.
- The Godzilla series has done this several times to the point where each of the movies from Godzilla 2000 and onward (with the exception of the two with Mechagodzilla) are their own continuity branching off from the original.
- In Triangle Jess gets stuck in a Groundhog Day Loop of her co-passengers getting killed by a masked killer. The first Jess tries to break the chain by meeting the Jess from the next loop. This creates a new timeline where the other passengers died differently by getting killed by a different masked killer. Subverted in that the two timelines play off at the same time and each influence each other. For example the new timeline eventually causes the second Jess to have her own story, which we don't see, where she eventually killed some of the passengers as the second masked killer which eventually made the first Jess turn into the first masked killer
- In Sliding Doors, the movie shows two alternate timelines. The story starts off with the Main Character getting fired, while her boyfriend is cheating on her. The Main Character goes home, and either just catches the subway in time, finding her boyfriend in bed with another woman, or misses the subway, causing some other events to happen which means she arrives home after the other woman has left. The movie then alternates between the two story lines.
- It's almost certain that there are two continuities in the original Planet of the Apes franchise. The first is the continuity that led to the society of the original film, possibly as described by Cornelius to the committe in Escape. The second is the altered continuity that the birth of their son, Caesar, sparked. It appears that the ape revolution was greatly sped up with his arrival. However, fans are split as to whether the continuities ultimately re-merge when history reaches the point where the original film was set, and humans will again end up mute wild animals and the world destroyed by the Alpha-Omega bomb or whether history was changed for good by the end of 'Battle' and Caesar forged a new future. The editing of 'Battle' didn't help things, the theatrical release had a hopeful tone, but the unedited version on most DVD releases clearly sets up the beginnings of the mutant society of 'Beneath'. The TV series likely exists in one of these continuities somewhere, while the animated series, Planet 2001 don't, and and Rise may or may not. 'Rise' is a Continuity Reboot, but there have been statements by the PT Bs contradicting that and painting it as a prequel as well.
- The alternate timeline (and preventing it) make up about half of the plot of Back to the Future Part II.
Doc: Obviously, the time continuum has been disrupted creating this new temporal event sequence, resulting in this alternate reality.
- The Gary Paulsen book Hatchet ends with Brian being rescued. However, in the third book, Brian's Winter, it takes place in an alternate series of events where Brian has to survive through the winter. Of course, those spoiler tags are almost useless since they spoiled this on the back of the book.
- The Black Trillium novel was co-written by three authors, who each went on to write a Sequel (or two), effectively spawning three mostly incompatible timelines from a single root.
- The book, The Dark Tower of Stephen King's The Dark Tower series involves alternate timelines created in the previous book, The Dark Tower when Roland creates a paradox by saving the life of Jake in his own world, preventing him from travelling to Roland's world, and them ever meeting. The alternate timelines created, one where he travelled with Jake, and one where he was alone, slowly drive both Jake and Roland insane as their minds simultaneously believe both series' of events to be true.
- Terminator: The Sarah Connor Chronicles branches off from the movie continuity after T2: Judgement Day - Sarah and John Connor leap through time from 1999 to 2007, skipping Sarah's death from cancer in 2002 and the date at which Judgement Day would have happened if Rise of the Machines were Canon. Terminator Salvation, on the other hand, carries on from the Rise of the Machines continuity.
- Lampshaded in Eureka, where Henry explains to Sheriff Carter exactly why they can't accurately predict the future after hitting the Reset Button on the past five years to undo Henry meddling to keep his wife from dying in the past, since the differing actions alone will cause a Ripple Effect to make the timelines gradually diverge. And then something different happens.
- It should be noted that Eureka has now gotten two Alternate Timeline treatments. The first one (mentioned above) only lasted an episode before being reverted; the second one, however, seems to be the new permanent timeline for the show.
- The Malcolm in the Middle episode Bowling played with this, the divergence being which parent took the kids bowling instead of staying at home. The conclusion?
Lois / Hal: "Next time, you take 'em."
- Frasier did an episode that was in fact inspired by the movie Sliding Doors.
- The fourth season of Fringe takes place in an Alternate Timeline, one in which Peter Bishop was never saved by the Observer as a boy. The first four episodes explore all the changes to the continuity, big and small, that resulted from Peter not being around. And then the Peter from the original timeline returns. This is all in a series that spent three years knee-deep in the complexities of an Alternate Universe.
- It's also worth noting that, according to the time-sensitive Observers, the first three seasons already took place in an Alternate Timeline that was thrown off-course from what was supposed to happen by the actions of an Observer. The Alternate Timeline of season 4 is probably a lot closer to how the original timeline was supposed to run.
- The Community episode "Remedial Chaos Theory" explores 6 alternate timelines, each different depending on which number Jeff rolls on the Yatzee die. We then see the main timeline, which is where Abed catches the die instead of letting it roll.
- The Scrubs episode My Butterfly, where the cast explored what different events resulted from a butterfly landing on an attractive woman's chest or alternatively, an unattractive man's chest.
- A few later episodes of Farscape see John Crichton exploring a few of these, particularly as interdimensional wormholes and the associated wibblie-wobblies become more important to the plot.
- When Dallas retconned a whole season that had been unpopular with fans as All Just a Dream, the producers of the Spin-Off Knots Landing didn't want to retcon plots that had been influenced by events in that season, causing the show to split off as an Alternate Timeline.
- Bionicle had at least four different parallel timelines. For instance, in Dark Mirror, Takua was killed by a Toa of Iron, and in The Kingdom universe, as well as the universe briefly seen at the end of Brothers in Arms, he never became a Toa at all. He is a Toa in the main universe.
- The Legend of Zelda. According to Hyrule Historia, Ocarina of Time's history diverges at three points. In one timeline, Link defeats Ganon and goes back in time. Then, Ganon rises again, causing Hyrule to be flooded. The Wind Waker, Phantom Hourglass and Spirit Tracks follow this timeline. In another timeline, Ganon never takes over Hyrule in the first place, and is banished to the Twilight Realm because Link warned the king about his treachery after going back in time from the previously mentioned timeline.. Majora's Mask, Twilight Princess and Four Swords Adventures take place in this timeline. In the third timeline, Link is killed in battle by Ganon, causing the Imprisoning War. A Link to the Past, the Oracle games, Link's Awakening, the original Zelda and Zelda II the Adventure of Link take place in this timeline.
- Much of the temporal nastiness in Chrono Cross is the result of two alternate futures clashing in the world's distant past. It's complicated.
- The main premise of the Half-Life mod series "Timeline." Rogue Black Mesa scientists have discovered how to use the dimensional portals to permit time travel, and have been messing with and creating new timelines. Eventually this technology falls into the hands of Those Wacky Nazis...
- The Mega Man metaseries has one, expanded on in Mega Man Battle Network. Both Doctors Light and Wily presented their research to the government: network and robotics, respectively. In the world where Light's network research won out, the Battle Network and Mega Man Star Force games take place. However, when Wily's robotics were chosen instead, it led to the other series.
- Ghost Trick has an in-game instance: the first timeline is a Bad Future where everybody dies, Missile is unable to save them due to lacking the needed ghost tricks, and Sissel refuses to help Missile due to only being concerned about his own quest for identity. At the end, Missile uses Yomiel's no-longer-immortal body to travel back in time 10 years to the Tesmik Park incident and wait out those ten years until that night returns. Then starts the second timeline, which is the Bad Future again, but diverging when Sissel awakens and Missile from the first timeline guides him under the guise of Ray, making Sissel think he's a blond-haired man in red instead, so that he'll naturally save Lynne and everyone else that could be a lead in his quest for identity due to said man's interactions with them. The third timeline begins after Sissel, Missile from the second timeline, Yomiel, and Detective Jowd go back 10 years again like the original Missile did and Set Right What Once Went Wrong by saving Yomiel's life and thus preventing his Start of Darkness, undoing the first two timelines and the first Missile's existence in the process.
- The Babylon Project campaign "The Earth-Brakiri War" is set in an alternate 2260 where Babylon 5 had been destroyed and Earth had alienated itself from the other races due to a failure of diplomacy.
- The existence of one of these and the desire of certain odd factions to bring it back fuels the plot of Persona 2.
- Surprisingly this is present in the Metal Gear series: Ghost Babel takes place in an alternate timeline where neither the events of the second game nor the events of the solid series have taken place.
- In Super Robot Wars R, the Original Generation characters come from a Bad Future where the events of Mobile Suit Gundam Chars Counterattack and Martian Successor Nadesico: The Prince of Darkness play out. After accidentally traveling back in time, they unintentionally Set Right What Once Went Wrong by keeping the events of Mobile Suit Gundam Wing Endless Waltz from going bad, which makes everything better for everyone invovled.