Alternate timeline

An alternate timeline is a divergent space-time continuum, typically created upon the alteration of one or more events in the 'past'.

Unlike parallel universes, alternate timelines contained or stemmed from events that rewrote history, to the point of wiping out the original timeline.

Alternate timelines are frequently the result of unintentional temporal interference.

Every Starfleet officer is ordered to uphold the Temporal Prime Directive, which states that any attempt to alter the existing timeline is strictly forbidden,
and one must strive to uphold and maintain the existing timeline that the officer is in.

Classifications

Closed timeline

Occur when an alternate timeline is created, then eliminated through the actions of "external" agents.

• Typically, the participants within these types of 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 (for example, chronitons and temporal shields). As such, most incidents of closed timelines go unreported.
• Closed timelines usually involve, or revolve, around one pivotal moment: an action from the "original" timeline, which alters the past/future, creating an alternate timeline.

Pocket timeline

It is possible to artificially create "pockets" of time, where a previous timeline continued, while the timeline of the rest of the universe was changed.

Such technology as a subspace bubble, a subspace isolation field, temporal shields, or the wake of a temporal vortex kept any enveloped object in a pocket with its own timeline.

• For example, when the Borg attempted to assimilate all of Earth, the Enterprise-E followed closely behind, and were caught in the wake of a temporal vortex.

• From inside the vortex, the Enterprise could see the altered Earth, though they themselves were unchanged.

Time Loops

Temporal causality loops create independent fragments of time, inside which the time of the universe repeats itself.

From outside the loop, it appears as if anything inside it simply vanished from the space-time continuum.

• For people inside the loop, the memories from previous loops begin to assert themselves as a sense of déjá vu and eventually as clearer memories.

Time continuums

Within our universe, there are also several documented "parallel time continuums," which occupy the same space, but in different times.

• For example, the Devidians lived in a different time continuum, but a fraction of a second away.

Creation Methods

Time Travel

Time travel to the future of a timeline could create an alternate future, where the time traveler had never returned back to the past from the future.

• For example, this occurred when the USS Enterprise-C was thrown through a temporal rift (see similar: subspace rift) to the year 2366.

Temporal Incursion

A temporal incursion into the past could cause an alternate chain of events to unfold. However, in the cases where the time travel event was part of a predestination paradox, an alternate timeline would be created if the paradox wasn't completed.

• For example, when the crew of Deep Space 9 were thrown into the past, Captain Sisko was forced to assume the role of Gabriel Bell.
  As a result, it is Sisko's face pictured in archives, and not the true face of Gabriel Bell.

• See article: Bell Riots