Alternate timeline

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 timeline, but most of those observed fit into two main categories - the Closed, and the Open.

Closed Timelines
Closed Timelines occur when an alternate timeline is created, then eliminated through the 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 travelling to/already present in the past/future to ensure the original timeline is re-established).

Open Timelines
An Open Timeline is better described as a parallel universe. As a result of quantum determinism, every event that can occur, will occur in alternate universes. (TNG: "Parallels") These alternate timelines differ from the 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.


 * Many fans believe that Star Trek: Enterprise takes place in such a timeline, affected either by the Temporal Cold War, or the events of Star Trek: First Contact. However, this may seem 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). Of course, there are some who consider that the events of "These Are the Voyages..." could also be in this alternate timeline, which would explain some apparent inconsistancies between it and the events of TNG: "The Pegasus".

Episodes
Alternate timelines are depicted in the following episodes:

Star Trek

 * The City on the Edge of Forever
 * Mirror, Mirror

Star Trek: The Animated Series

 * Yesteryear

Star Trek: The Next Generation

 * Yesterday's Enterprise
 * Tapestry
 * Parallels
 * All Good Things...

Star Trek: Deep Space Nine

 * Crossover
 * Past Tense, Part I
 * Past Tense, Part II
 * Visionary
 * Through the Looking Glass
 * The Visitor
 * Shattered Mirror
 * Trials and Tribble-ations
 * Children of Time
 * Resurrection
 * The Emperor's New Cloak

Star Trek: Voyager

 * Time and Again
 * Non Sequitur
 * Before and After
 * Future's End, Part I
 * Future's End, Part II
 * Year of Hell, Part I
 * Year of Hell, Part II
 * Timeless
 * Relativity
 * Fury
 * Shattered
 * Endgame

Star Trek: Enterprise

 * Shockwave, Part I
 * Shockwave, Part II
 * Twilight
 * E²
 * Storm Front
 * Storm Front, Part II
 * In a Mirror, Darkly
 * In a Mirror, Darkly, Part II

Star Trek Movies

 * Star Trek IV: The Voyage Home
 * Star Trek: Generations
 * Star Trek: First Contact

Related topics

 * Temporal anomaly
 * Temporal mechanics
 * Time