An alternate timeline is a tangential space-time continuum, typically created upon the alteration of one or more events in the "past". Alternate timelines are frequently the result of unintentional temporal interference. There are many types of alternate timelines, but most of those observed fit into two main categories, "closed" and "open".
Alternate timeline models
Closed timelines occur when an alternate timeline is created then eliminated through actions of "external" agents. Typically, the participants within these timelines are unaware of any change, either upon the creation of the alternate timeline or once the timeline reverts to its "true" form unless shielded from those changes by temporally sensitive materials (see chronitons, temporal shields). Since this is the case, most incidents of closed timelines go unreported, except by the Department of Temporal Investigations. Such timelines usually involve a cyclic aspect (action in the original timeline altering the past/future, creating an alternate timeline, an object/person unaffected by the temporal change traveling to/already present in the past/future to ensure the original timeline is re-established).
These alternate timelines differ from closed timelines as the events continue to influence the timeline they altered, without "external" interference. The mirror universe is an example of such an alternate timeline, which has become a primary focus for Federation scientists.
- Some fans believe Star Trek: Enterprise takes place in such a timeline, effected either by the Temporal Cold War or events of Star Trek: First Contact. This seems unlikely, as Archer is heard referencing the trading post of Rigel X in a 24th century holoprogram in "These Are the Voyages..." (This involves the series premiere "Broken Bow", which introduced the Temporal Cold War). Some consider "These Are the Voyages..." to also be set in this alternate timeline, which would explain inconsistencies compared to the events of TNG: "The Pegasus".
In 2411, Commander Reshek Taryn, a Starfleet temporal agent from the mid-2450s, described the nature of time using the metaphor of a rope. Each strand of the rope was a string of probabilities that events were likely to occur. While most time travel was deterministic -- "go back, you've already been back, within that particular strand" -- major temporal incursions could cause alternate timelines to branch off entirely in a manner likened to fraying, a process that damaged time itself. Starfleet Intelligence Special Operations Section Eight had the mission of preventing such frays where feasible. She also spoke of a timeline branch where a multi-faction time war broke out, resulting in so many conflicting temporal incursions that the sequence of events ultimately erased itself. (Bait and Switch: "Brother on Brother, Daughter on Mother")
Fan works featuring alternate timelines
Fan film episodes involving alternate timelines:
- Star Trek: Hidden Frontier
- Star Trek: New Voyages
- Star Trek: Of Gods and Men
- Star Trek: Eagle
Fan fiction series set in alternate timelines are depicted in the following:
- Star Trek: Arcadia
- Star Trek: Pendragon - Pendragon universe
- Star Trek: Prometheus - Prometheus universe
- Star Trek: Remington - Remington universe
- RIS Bouteina
- Star Trek: Phoenix-X
- Bait and Switch
|existence of the expanded universe|
|dimension - history - multiverse - space - space-time continuum - time - universe|
|alternate dimension - alternate timeline - parallel universe - pocket universe - subspace and hyperspace|