Alternate timeline Alternate timelines were altered versions of the timeline . Unlike parallel universes , alternate timelines did not seem to diverge from the universe , but instead rewrote history to the point of wiping out the original timeline . ( ; ; ; ; ) There were several methods of temporal manipulation that could create an altered version of the timeline . As a rule , Starfleet officers were forbidden to cause changes in the timeline or to share their knowledge of future events by the Temporal Prime Directive . ( ) The Department of Temporal Investigations was tasked to ensure that time travel events did not contaminate the timeline . ( ) By the 28th century , changing the timeline had become more universally illegal after the Temporal Accord was established . ( ) By the 29th century , Starfleet had taken it on as a mission to use time travel as a means of upholding the integrity of the timeline by fixing changes in the past . It was also Starfleet policy by then to integrate different versions of people into one , when several coexisting ones appeared due to paradoxes and time travel . ( ) While the prime timeline was usually restored by operatives from the 29th to the 31st centuries , in some cases , the influence of alternate timelines remained as a part of the chain of events in the prime timeline . The crew of the , for instance , would not have learned that they had to travel to the past to convince Zefram Cochrane to make the test warp flight , had they not accidentally witnessed an alternate timeline , where the Borg prevented Human ity ' s First Contact with the Vulcan s and assimilate d Earth . ( , ) Warnings , temporal incursions and information of the original future were also an integral part of the prime timeline . Such was the case , when Captain Jean - Luc Picard shared his experiences of the future shown to him by Q , to his crew in 2370 , causing them to make different life choices that created a new and entirely different timeline of the future . ( ) was rescued and aided by its crew members from the future . In 2375 , a transmission from Harry Kim from 2390 averted the crash landing of the " Voyager " . In 2378 , technology and assistance from Admiral Janeway from 2404 saved the ship from a longer disastrous journey through the Delta and Beta Quadrant s . ( ) Alternate realities . Different versions of a timeline also sometimes coexist as parallel universe s . Most active temporal anomalies allow interaction between two different alternate timelines for a moment , making them parallel realities in relation to one another . Time continuums . Within the universe there were also several parallel time continuum s occupying the same space but in a different time . ( ) Appendices . Appearances . Alternate timelines are depicted in the following episodes or films : Apocrypha . According to the " " story " Places of Exile " by Christopher L . Bennett in the novel of the series , " Infinity ' s Prism " , the concept of quantum realities is synonymous with all types of alternate timelines . According to the 2008 novel " Fearful Symmetry " by Olivia Woods , the mirror universe is also a parallel quantum universe , further suggesting that even trans - dimensional realms are alternate timelines . The " " novel " Watching the Clock " , goes into detail about how and why some forms of time travel create parallel alternate realities and others lead to the overwriting of the same timeline . According to the novel , the only way one timeline could replace another is if they coexisted side by side from the moment of their divergence and were merged together again at a later point . Timelines diverge when they shift sufficiently out of phase to become non - interacting , but it is not impossible for them to interfere again at a later point in time . If they did become entangled as a single system , quantum information theory demands that only one of the two conflicting sets of information survive , as quantum history has to be self - consistent . After the merge , it would be as if one timeline suddenly transformed into another . The previous events would still have occurred , but they would no longer be remembered , as the information would have been destroyed . Two different timelines coming back into phase would violate entropy , so there needs to be some kind of force acting to merge them back together . The game " " features the a starship that came from an alternate future where the Borg controlled most of the Alpha Quadrant . Captain Thaddius Deming of the " Premonition " hoped to warn the Federation of a coming Borg invasion in time to prevent the Borg victory . With the help of Captain Jean - Luc Picard of the , and after making two further temporal incursions , the " Premonition " s mission was a success and she returned back to the future .