Alternate timeline

Multiple realities
(covers information from several alternate timelines)

A Zahl colony fired upon by the Krenim weapon ship...

...and the alternate timeline where the colony never existed

For the alternate timeline created by the destruction of the USS Kelvin, please see alternate reality.

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. (ENT: "Storm Front"; TOS: "The City on the Edge of Forever"; TNG: "Yesterday's Enterprise"; DS9: "Past Tense, Part I", "Past Tense, Part II"; VOY: "Non Sequitur", "Year of Hell", "Year of Hell, Part II", "Timeless") There were several methods of temporal manipulation that could create an altered version of the timeline.

Alternate timeline creation

• 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 was not completed. (DS9: "Trials and Tribble-ations") In at least one case, when accidental time travel from 2371 led to the premature death of Gabriel Bell in 2024, an altered future existed for the same amount of time it took for Benjamin Sisko to replace and complete Bell's vital role in the "Bell Riots" of 2024. (DS9: "Past Tense, Part I", "Past Tense, Part II")

• 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. Such was the case, for example, when the USS Enterprise-C traveled from 2344 to 2366 through a temporal rift. (TNG: "Yesterday's Enterprise"; DS9: "The Visitor"; ENT: "Shockwave", "Shockwave, Part II") This however did not always occur, such as in the case when Samuel Clemens visited the 24th century through a temporal distortion created by the Devidians. (TNG: "Time's Arrow, Part II")

• Sometimes objects and people who had traveled through time from the future into the past would vanish when the timeline is altered enough, such as an alternate Captain Jean-Luc Picard who came to the past through an energy vortex in 2365. (TNG: "Time Squared") When objects were pushed completely out of the space-time continuum, they were also erased from history, creating an altered timeline, where the object never came into being. Such was the case with the effect of the main energy beam weapon of the Krenim weapon ship and destroying the interspatial parasites that had infected Captain Jonathan Archer in the 22nd century. (VOY: "Year of Hell"; ENT: "Twilight") According to the Borg Queen, a similar fate would have awaited the alternate future Vice Admiral Kathryn Janeway, if the Queen had managed to kill her counterpart Captain Janeway in 2378. (VOY: "Endgame") More commonly though, changes to the past of a timeline did not cause the objects and people from an alternate future to vanish. Multiple versions would then coexist. These alternate versions could be reintegrated into a single person using 29th century technology. (VOY: "Relativity")
• Sometimes, the original version of the future would come to be regarded as an alternate timeline after changes to history were made. For example, Kes of 2376 in the original timeline damaged USS Voyager, murdered B'Elanna Torres, and vanished by traveling 5 years into the past. Her presence in the past altered the future, creating a new timeline where, at the time of Kes's return, Captain Janeway prevented harm from coming to her crew, and Kes returned to Ocampa instead of time traveling. (VOY: "Fury")

A display featuring several alternate timelines created by the Krenim

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. (VOY: "Shattered") The Department of Temporal Investigations was tasked to ensure that time travel events did not contaminate the timeline. (DS9: "Trials and Tribble-ations") By the 28th century, changing the timeline had become more universally illegal after the Temporal Accord was established. (ENT: "Cold Front") 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. (VOY: "Relativity")

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 USS Enterprise-E, 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 Humanity's First Contact with the Vulcans and assimilated Earth. (Star Trek: First Contact, VOY: "Relativity") 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. (TNG: "All Good Things...") USS Voyager 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 Quadrants. (VOY: "Timeless", "Endgame")

Alternate realities

"A parallel universe? The Science Directorate has examined all of these theories. They've found no evidence of alternate realities."
"The Tholians are a little more open-minded than your people. They detonated a tricobalt warhead here, inside the gravity well of a dead star. The explosion created an interphasic rift. A doorway into another universe."

– T'Pol and Archer, 2155 ("In a Mirror, Darkly")

Different versions of a timeline also sometimes coexist as parallel universes. Most active temporal anomalies allow interaction between two different alternate timelines for a moment, making them parallel realities in relation to one another.

This coexistence phenomenon has not, however, been referenced for alternate timelines which were created through disruptions in the past, which would cause one's destiny to be overwritten. (ENT: "Shockwave"; TOS: "The City on the Edge of Forever"; TNG: "Yesterday's Enterprise"; Star Trek)

In at least one example, the same quantum universe had been validated as unchanged, via analyzing the local quantum signature. This confirmation of an unchanged universe was made in spite of time travel resulting in USS Discovery's added absence from the timeline for nine months, having the consequence of the Federation's unstable footing being lost in the Federation-Klingon War. (DIS: "What's Past Is Prologue")

It should be noted that unlike with two similar prior and subsequent occurrences (ENT: "Shockwave", "Shockwave, Part II", TNG: "Yesterday's Enterprise"), this timeline was not later negated because the crew of Discovery managed to salvage the situation without additional time travel (DIS: "Will You Take My Hand?"); how the quantum signature would be affected in a true alternate reality is uncertain.

• The term "alternate reality" was briefly referenced by T'Pol and Archer when the two debated whether such a phenomenon even exists. (ENT: "In a Mirror, Darkly")

The Narada appearing out of a black hole, creating an alternate reality

• Time travel to the past by the Romulan mining vessel Narada through a black hole created with red matter resulted in the creation of an alternate reality. (Star Trek)

The writers of Star Trek, Alex Kurtzman and Roberto Orci, were asked about the implications of the new alternate reality that was introduced in the film in an interview. They explained the new reality runs parallel to the prime reality as a new quantum reality, as the concept was explained by Data in the episode TNG: "Parallels". [1]

• In 2370, Q allowed Picard to shift his consciousness between three different timeframes, one in the past, one in the present and one in the future from Picard's point of view, in order for him to create an anti-time eruption. The eruption was linking these timelines together, and when it collapsed the timelines ceased to exist. (TNG: "All Good Things...")

• In 2371, radiation poisoning and the temporal energy emissions of an artificial quantum singularity of a Romulan Warbird allowed Miles O'Brien to jump between the prime timeline and several alternate timelines, in some of which Deep Space 9 was destroyed. At least during some of the jumps two of the timelines coexisted. O'Brien was eventually replaced by one of his future selves. (DS9: "Visionary")

• Harry Kim considered an alternate reality as one possible cause for his sense of déjà vu and familiarity to a region of space in the Delta Quadrant, until the Taresian retrovirus was discovered to be the actual cause. (VOY: "Favorite Son")

Several statements in Star Trek suggest that all alternate timelines co-exist. It was stated in ENT: "Azati Prime" that the Sphere-Builders have technology that allows them to examine alternate timelines. In the episode, Daniels even had the technology to take Archer to the future of an alternate timeline. The time vortex was called a focal point of "all timelines" in TAS: "Yesteryear".

Pockets, folds, and fragments

An alternate Earth, assimilated by the Borg after their temporal incursion, seen from the wake of a temporal vortex

• It was possible to artificially create pockets 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, and the wake of a temporal vortex kept any enveloped object in a pocket with its own timeline. The Guardian of Forever was also capable of maintaining the time planet in its original timeline. (TOS: "The City on the Edge of Forever";TNG: "Timescape"; DS9: "Past Tense, Part I"; VOY: "Year of Hell", "Year of Hell, Part II"; Star Trek: First Contact)

• The race of the alien who took the shape of Cosimo existed in temporal inversion folds of the space-time matrix. The folds were parallel time streams visible as temporal anomalies intersecting the prime reality. Inside the folds, reality remained unaffected by changes in the timeline. It was possible to utilize a fold to exchange one's consciousness with an alternate timeline version of oneself. (VOY: "Non Sequitur")

• 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. (TNG: "Cause and Effect")

Time continuums

The Devidian time continuum

Within the universe there were also several parallel time continuums occupying the same space but in a different time. (TNG: "Time's Arrow")

• The Devidian lived in a different time continuum, only a fraction of a second away, with a positive phase variance of 0.004 percent from the normal timeline. (TNG: "Time's Arrow", "Time's Arrow, Part II")

• The quantum singularity lifeforms were native to a parallel time continuum. They utilized temporal apertures to travel between continuums and delivered their embryos to mature in nests inside the gravity wells of quantum singularities in our universe. The adult beings of the species were capable of taking humanoid form and were unaffected by temporal fractures. (TNG: "Timescape")

• Elysia was a small parallel time continuum that periodically touched the prime universe in the Delta Triangle region. Elysia was described by Devna as a pocket in the garment of time. The collisions between the two alternate universes produced time warp vortexes in the time barrier between the universes, that allowed passage from one side to the other at high warp speed. (TAS: "The Time Trap")

List of alternate timelines

Timeline	Timescale	Created by	Status	Appearance
Captain Archer disappears and the United Federation of Planets never forms	2152-31st century	Daniels transporting Archer to 31st century Earth	Negated when Archer returned to his own time	ENT: "Shockwave", "Shockwave, Part II"
The Xindi destroy Earth and all other Human colonies	2153-2165	Interspatial parasites	Negated when the parasites were erased from history	ENT: "Twilight"
The USS Defiant is used by Jonathan Archer and Hoshi Sato to overthrow the Terran emperor.	2268-2155	Interphasic rift created by the Tholians of the mirror universe transporting the Defiant into the past of the mirror universe	Presumed permanent alteration of the mirror universe's timeline	TOS: "The Tholian Web"; ENT: "In a Mirror, Darkly"
The USS Enterprise-J participates in the battle of Procyon V	2554	Unknown	Unknown, possibly negated by the destruction of the Delphic Expanse spheres in 2154	ENT: "Azati Prime"
Enterprise remains in the Delphic Expanse for 117 years	2037-2154	Temporal displacement of Enterprise by a subspace corridor	Presumed negated when Enterprise avoided time traveling	ENT: "E²"
Temporal War	1916-31st century	Unknown, caused by a predestination paradox	Negated when Enterprise prevented Vosk from returning to the 29th century	ENT: "Storm Front", "Storm Front, Part II"
The USS Discovery is transported nine months into their relative future while escaping the mirror universe to return to their own universe, during the Federation-Klingon War	2256-2257	Spore drive jump during the mycelial network's rapid regeneration, immediately following the destruction of the ISS Charon's mycelial core.	Presumed permanent alteration to timeline.	DIS: "What's Past Is Prologue"
John Christopher, a staff sergeant and the Omaha instillation personal encounter the Enterprise crew	July, 1969	Actions of the temporally-displaced Enterprise crew	Negated when John Christoper and the staff sergeant were returned to Earth at a point before they encountered the Enterprise	TOS: "Tomorrow is Yesterday"
Nazi Germany conquers Earth and the United Federation of Planets and Starfleet never form	1930-2267	Leonard McCoy preventing Edith Keeler's death	Negated when James T. Kirk stopped McCoy from saving Keeler	TOS: "The City on the Edge of Forever"
Spock dies at seven	2237-2269	Captain Kirk and Commander Spock	Negated by Spock's future self	TAS: "Yesteryear"
The USS Enterprise-D is destroyed by an energy vortex	2365	Unknown, possibly the original timeline	Negated when Jean-Luc Picard prevented the Enterprise's destruction	TNG: "Time Squared"
Mid-24th century Federation-Klingon War	2344-2366	Temporal displacement of the Enterprise-C	Negated when the Enterprise returned to the Battle of Narendra III	TNG: "Yesterday's Enterprise"
Thomas Halloway becomes Captain of the Enterprise-D instead of Jean-Luc Picard	2327-2369	Q causing Picard to prevent a fight against a group of Nausicaans	Negated when Picard returned to 2327 and started the fight	TNG: "Tapestry"
The Enterprise-D is destroyed by a warp core breach	2369	Quantum singularity lifeforms	Negated when Picard, Data, Deanna Troi, and Geordi La Forge reversed time to a point just before the breach occured	TNG: "Timescape"
Alexander Rozhenko never becomes a warrior and his father is murdered on the floor of the Klingon High Council	2370-2410	Original timeline	Negated when Alexander's future self convinced his past self to become a warrior	TNG: "Firstborn"
An anti-time eruption forms in the Devron system and prevents the formation of life on Earth	3.5 billion years ago, 2363-2364, 2370-2371, and 2395	Repeated temporal displacement of Picard by Q	Negated when Picard sealed the eruption with a static warp shell	TNG: "All Good Things..."
The Veridian system is destroyed by Tolian Soran	2371	Original timeline	Negated when Picard prevented the system's destruction	Star Trek: Generations
Gabriel Bell dies and the United Federation of Planets and Starfleet never form	2024-2371	Benjamin Sisko and Julian Bashir causing Bell's death	Negated when Sisko replaced Bell's role in history	DS9: "Past Tense, Part I", "Past Tense, Part II"
Kathryn Janeway dies on Makull's homeworld in a polaric ion explosion	2371	Unknown, caused by a predestination paradox	Negated when Janeway prevented the explosion	VOY: "Time and Again"
Miles O'Brien dies from a high-energy laser	2371	Unknown, possibly the original timeline	Negated by O'Brien learning of his death prematurely	DS9: "Visionary"
Miles O'Brien dies from radiation poisoning	2371	Unknown, possibly the original timeline	Negated by O'Brien warning the past Bashir of his death	DS9: "Visionary"
Deep Space 9 and the Bajoran wormhole are destroyed by a Romulan Warbird	2371	Unknown, possibly the original timeline	Negated by O'Brien warning Sisko of the attack 3.5 hours before it occured	DS9: "Visionary"
Daniel Byrd joins Voyager instead of Harry Kim	2371	Temporal inversion fold	Negated when Kim returned through the time stream	VOY: "Non Sequitur"
Second Federation-Klingon hostility	2372-2450	Energy discharge from the Defiant's warp core	Negated when Benjamin Sisko returned to the past and dodged the discharge	DS9: "The Visitor"
The Call of the Prophets is not finished	22nd century-2372	Temporal displacement of Akorem Laan by the Bajoran wormhole	Negated when the Prophets returned Akorem Laan to his proper time period	DS9: "Accession"
Henry Starling founds Chronowerx Industries and destroys the Sol system in a temporal explosion	1967-29th century	Unknown, caused by a predestination paradox	Negated when Voyager destroyed the Aeon before it arrived in the future	VOY: "Future's End", "Future's End, Part II"
The Borg Collective assimilates Earth	2063-2373	Borg Queen's sphere	Negated when the Enterprise-E defeated the Borg in the past	Star Trek: First Contact
First Year of Hell	2373-2379	Original timeline	Presumed negated by Tuvok due to Kes's actions in 2373	VOY: "Before and After"
The Defiant crashes on Gaia and colonizes the planet	22nd century-2373	Temporal displacement of the Defiant	Negated when Odo's older self altered the Defiant's flight plan	DS9: "Children of Time"
Second Year of Hell	2174-2374	Multiple temporal incursions by Annorax's weapon ship	Negated when Janeway caused the weapon ship to erase itself from history	VOY: "Year of Hell", "Year of Hell, Part II"
Molly O'Brien is stranded on Golana for 10 years	21st century	Time portal	Negated when Molly's younger self went back to 2374	DS9: "Time's Orphan"
Voyager crashes on an L-class icy planet upon emerging from a quantum slipstream	2375-2390	Original timeline	Negated when Harry Kim caused Voyager emerged from the slipstream 50,000 light-years from Earth	VOY: "Timeless"
Voyager is destroyed by a temporal disruptor	2371-2375	Captain Braxton planting the disruptor aboard Voyager	Negated when Janeway prevented Braxton from planting the device on Voyager	VOY: "Relativity"
Kes murders B'Elanna Torres and time travels to 2371	2376	Original timeline	Negated when Janeway and Tuvok took precautions to prevent history from repeating	VOY: "Fury"
Voyager is fractured into multiple different time periods in 2377	2371, 2372, 2373, 2374, 2375, 2377, and 2394	Chronokinetic surge	Negated when Chakotay reintegrated Voyager into one time period and prevented the surge from fracturing Voyager	VOY: "Shattered"
Voyager returns to Earth in 2394	2378-2404	Original timeline	Negated when Admiral Janeway returned Voyager home in 2378	VOY: "Endgame"
Alternate reality	2233 and beyond	Nero's appearance in 2233	Unclear with all evidence presented; Likely either presently overwriting the Prime timeline, or Coexisting as a parallel universe.	Star Trek, Star Trek Into Darkness, and Star Trek Beyond

Appendices

Appearances

Alternate timelines are depicted in the following episodes or films:

• TOS:
  • "Tomorrow is Yesterday" (Season 1)
  • "The City on the Edge of Forever"
• TAS:
  • "Yesteryear" (Season 1)
• TNG:
  • "Time Squared" (Season 2)
  • "Yesterday's Enterprise" (Season 3)
  • "Tapestry" (Season 6)
  • "Timescape"
  • "All Good Things..." (Season 7)
• DS9:
  • "Past Tense, Part I" (Season 3)
  • "Past Tense, Part II"
  • "Visionary"
  • "The Visitor" (Season 4)
  • "Children of Time" (Season 5)
  • "Time's Orphan" (Season 6)
• VOY:
  • "Time and Again" (Season 1)
  • "Non Sequitur" (Season 2)
  • "Future's End" (Season 3)
  • "Future's End, Part II"
  • "Before and After"
  • "Year of Hell" (Season 4)
  • "Year of Hell, Part II"
  • "Timeless" (Season 5)
  • "Relativity"
  • "Fury" (Season 6)
  • "Shattered" (Season 7)
  • "Endgame"
• ENT:
  • "Shockwave" (Season 1)
  • "Shockwave, Part II" (Season 2)
  • "Twilight" (Season 3)
  • "E²"
  • "Storm Front" (Season 4)
  • "Storm Front, Part II"
• Star Trek films
  • Star Trek Generations
  • Star Trek: First Contact
  • Star Trek
  • Star Trek Into Darkness
  • Star Trek Beyond

Related topics

• Temporal anomaly
• Temporal mechanics
• Time
• Alternate reality
• Parallel universe

Background information

A list of episodes involving an alternate timeline.

Episode	Time Periods	Cause	Effects
"The City on the Edge of Forever"	1930-2267	Edith Keeler's death averted by McCoy	Nazi Germany lasts beyond 1945, United Federation of Planets does not exist
"Yesteryear"	2269, 2237	Death of Spock as a child	Amanda Grayson has died, Thelin became USS Enterprise's first officer
"Yesterday's Enterprise"	2366	USS Enterprise-C went through a temporal rift in 2344	Federation embroiled in a long war with the Klingons By 2366, 22 years of war have raged between Klingons and the Federation, with the death toll in the billions. At that point, the war was going badly for the Federation, and a surrender seemed the most likely outcome. The USS Enterprise, while retaining her exterior, has been fitted as a battleship, with less luxury than the prime timeline USS Enterprise. The Enterprise has been fighting the Klingons for the past four years, and many, if not all, of the missions the "prime" Enterprise undertook have not been undertaken by this Enterprise. The Enterprise had no children on board as a result of the war. Wesley Crusher was a full ensign in 2366, which implies either an earlier acceptance into Starfleet Academy or, as seems more likely in this timeline, that he was drafted into the military.
"Past Tense, Part I", "Past Tense, Part II"	2024, 2048, 2371	Gabriel Bell dies	Federation does not exist, Romulans encroach on Alpha Centauri
"Accession"	9174 (Bajoran year) in the 22nd century (Earth calendar)	Akorem Laan disappears from history, entering the Bajoran wormhole	Akorem doesn't complete his poem The Call of the Prophets
"Non Sequitur"	2372	Timestream	Harry Kim did not join USS Voyager, Daniel Byrd joined instead
"Year of Hell", "Year of Hell, Part II"	2374	Krenim weapon ship	Numerous incursions
"Twilight"	2153-2165	Interspatial parasites	Archer removed as captain of Enterprise NX-01, Xindi destruction of Earth and Human colonies
"Storm Front", "Storm Front, Part II"	1916-1944	Multiple spatial incursions; Na'kuhl violate Temporal Accord; Temporal Cold War goes hot	Vladimir Lenin assassinated by unknown temporal agent and not replaced; Union of Soviet Socialist Republics never founded; Nazi Germany able to focus on West, resulting in an alternate World War II where, with the help of the Na'kuhl, Germany successfully invades the United States of America
Star Trek Generations	2371	Tolian Soran destroys the Veridian system	Civilization on Veridian IV wiped out; USS Enterprise crew killed; Soran enters the Nexus
Star Trek: First Contact	2063	Borg assimilate Earth	Humans never achieve warp drive; Federation never founded; Borg space in the Alpha Quadrant
Star Trek, Star Trek Into Darkness, Star Trek Beyond	2233 onwards	Accidental temporal incursion by the Narada, whose captain proceeds to enact a revenge plot that irrevocably changes the timeline	Among other changes: USS Kelvin destroyed, causing James T. Kirk to be born early and left without a father; Kirk joins Starfleet at a later date; Vulcan destroyed in 2258, leaving the Vulcans critically endangered; Earth nearly destroyed; Kirk given command of the USS Enterprise several years early; Christopher Pike promoted to admiral Militarization conspiracy; Khan Noonien Singh and his followers awakened early; Christopher Pike killed in 2259; Enterprise embarks on her five-year mission several years early Enterprise destroyed in 2263 rather than 2285; USS Franklin mystery solved; Enterprise-A launched in 2263 rather than 2286

Apocrypha

According to the Star Trek: Myriad Universes story "Places of Exile" by Christopher L. Bennett in the 2008 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 Star Trek: Department of Temporal Investigations 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 Star Trek: Armada features the USS Premonition (β) 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 USS Enterprise-E, and after making two further temporal incursions, the Premonition's mission was a success and she returned back to the future.

External link

• Alternate timeline at Memory Beta, the wiki for licensed Star Trek works