Time travel is having the ability to or the act of traveling forward or backward in time, thus breaking the seemingly irreversible flow of time. The study of this phenomenon is one of the focuses of temporal mechanics. Alterations to historical events can cause, among other things, alternate timelines and realities.
The United Federation of Planets had some form of time travel ability since at least 2268. It is possible that at least some of the regulations regarding time travel trace their origins back to this date. However, capability at this point was most likely inaccurate, making any attempt at time travel experimental and dangerous.
In addition to the Federation, the Borg Collective, Bajorans, and Klingon Empire were known to have some form of time travel capabilities. (Star Trek: First Contact; DS9: "Wrongs Darker Than Death or Night"; VOY: "Endgame")
As of 2378, at least forty different instances of some form of time travel had been noted in Federation records. Technologically speaking, the Federation's capabilities concerning time travel, for the most part, remained unclear.
In the 29th century, the Federation has the ability to scan time as well as space, and travel back (and presumably forward) in time to attempt to fix issues and anomalies. (VOY: "Future's End, Part II")
Crewman Daniels, an alleged time traveler from the 31st century, showed Jonathan Archer a group of time-traveling anthropologists from 2769 observing the building of the pyramids of Giza. (ENT: "Cold Front")
The USS Discovery, after being transported to another universe in late 2256 or early 2257 as a result of difficulties navigating the mycelial network, returned to her original universe nine months later. Her crew ended the Federation-Klingon War shortly thereafter. (DIS: "What's Past Is Prologue", "The War Without, The War Within", "Will You Take My Hand?")
In 2267, after an encounter with a black star, the Enterprise was hurled three hundred years into the past. Eventually, the Enterprise's science officer Spock devised a method for returning the Enterprise back to its original period. (TOS: "Tomorrow is Yesterday") Though other instances of time travel had been noted, this appears to be the first instance of controlled time travel by the Federation.
In 2286, Admiral James T. Kirk and his senior staff took a stolen Klingon Bird-of-Prey back in time to the year 1986 to retrieve a pair of then (2286)-extinct humpback whales to save Earth from destruction by an alien probe. (Star Trek IV: The Voyage Home)
In 2371, Captains Jean-Luc Picard and James T. Kirk used the Nexus as a means of controlled time travel, going to just before the destruction of the Veridian star, which Picard intended to save. (Picard arrived at the Nexus from just after the destruction of said star, whereas Kirk arrived from some 78 years before). (Star Trek Generations)
Data, unknowingly at first, traveled back in time to Earth circa. 1900 while investigating an alien species that was later found to be ingesting the neural energy from humans of that time period. The aliens acquired their sustenance by travelling through a portal back to that time and place from Devidia II, and were able to shield their presence from outsiders by being slightly out of temporal sync with everyone else, disguising their presence further by taking advantage of a local cholera outbreak. Picard, Riker, Crusher, La Forge, and Troi soon followed to retrieve Data and assess the situation. As the Enterprise crewmembers covertly endeavored to stop the aliens and return to their own time, Samuel Clemens was suspicious of them, and was accidentally sent to the 24th century with the Enterprise crewmembers (except Picard) when they used the alien portal to return to their own time. Luckily, Clemmens was able to go back through the portal and retrieve Picard, returning each man to his own time period before the Enterprise destroyed the aliens and their portal. (TNG: "Time's Arrow", "Time's Arrow, Part II")
Twice, Q took Picard back in time; once when Picard lay dying in a Starbase Medical facility during a replacement of a defective artificial heart that he received as a result of a a Nausicaan knife being stabbed through his heart immediately after Picard had graduated from Starfleet Academy on Starbase Earhart (TNG: "Tapestry") and another time to the beginning of life on Earth and also back and forth in Picard's lifetime. (TNG: "All Good Things...")
During a transporter accident above Earth in the USS Defiant caused by chroniton particles being accidentally fused to the ship's hull, Benjamin Sisko, Julian Bashir, and Jadzia Dax were sent back in time to early-21st century, just before the Bell Riots. This caused the Federation and Starfleet to vanish in the present, after the time travelers' interference leads to the death of Gabriel Bell before his crucial role in history. Only the Defiant was left protected by the chroniton particles. Sisko took on the identity of Gabriel Bell to ensure that he was remembered for saving hostages during the events, and ultimately allowing the Federation to come into being over a century later. (DS9: "Past Tense, Part I")
While on a trip to Earth to take Nog to Starfleet Acadamy, Quark, Rom, Nog, and Odo were accidentally propelled back to circa. 1950, crashing near Roswell, New Mexico, due to a sabotaged warp core on the ship that had been given to them by Quark's Cousin Gaila. They were able to return to their own time using the reaction between kemocite and the radiation of a nuclear explosion on Earth. These events - which included Quark attempting to alter the timeline by selling goods to the United States of America during the Cold War, and the Ferengi subsequently being interrogated on the suspicion that they were secretly planning an invasion - were kept secret from the public on Earth at the time. (DS9: "Little Green Men")
Akorem Laan, a poet and seer from Bajor's past (which history had recorded had mysteriously disappeared) was sent to the future by the Prophets, believing he was the Emissary of the Prophets. Ultimately, Sisko convinced the Prophets to send Laan back into his own period. Laan later went on to finish one of his prophetic poems, which Kira remembered as unfinished, after Laan had disappeared. Sisko points out that the ending of the poem had appeared in databases, along with new history of his life after his return to Bajor. Kira wonders why she could remember the previous timeline, if said previous timeline had been wiped out. Sisko commented that time works in mysterious ways whenever the Prophets are involved. (DS9: "Accession")
In 2373, the USS Defiant, commanded by Captain Sisko, traveled back in time to 2268 via the Bajoran Orb of Time, in an attempt by Arne Darvin to kill James T. Kirk and change the timeline. The crew of the Defiant stopped Darvin without any notable damage. Major Kira found a way to use the Orb to get the Defiant and its crew back to its own time. (DS9: "Trials and Tribble-ations")
Around Stardate 50814.2 in 2373, the Defiant became stuck behind a barrier on a planet in the Gamma Quadrant, where they met the inhabitants who told them they were the descendants of the crew of that crashed on the planet two hundred years in the past. With foreknowledge of the crash, the crew surmised that if they escaped that fate, the timeline would collapse and everything on the planet cease to exist. The descendant of Jadzia Dax, Yedrin, surmised that it would be possible to save their colony, due to an energy discharge that had hit Major Kira, which had created a subspace doubling effect, and for an instant created corresponding quantum duplicates of every molecule in her body. By amplifying the doubling effect through modifications to the Defiant, they could make a quantum duplicate of the entire ship, and this second ship would then be the one that would crash on the planet preserving the original timeline. However, the other Defiant would be able to escape as well. However, Yedrin had falsified information in his plan, with the intent of making sure that the original (un-duplicated) single Defiant would crash on the planet, thus ensuring that the colony would continue to exist. The Defiant crew ultimately made the decision to sacrifice the ship by flying into the temporal anomaly, in order to save the eight thousand colony members. However, the ship's flight plan was changed by the Odo who lived on the colony so that it would clear the barrier, the future Odo wanting to save Kira's life. This erased the settlement and all of its' inhabitants from the planet. (DS9: "Children of Time")
Kira used the Orb of Time to learn about her mother's life on Terok Nor. Before she began her orb experience, she was warned not to interfere with the timeline by Sisko. Kira nearly assassinated her own mother and Dukat, but changed her mind at the last moment. The orb then returned her to the present. (DS9: "Wrongs Darker Than Death or Night")
During a visit to the planet Golana with her family, Molly O'Brien was accidentally sent three hundred years into the past via a time portal created by the planet's long-lost civilization. She was retrieved by her parents, but was now a teenager reduced to a feral mindset, forcing them to use the portal to send her back. However, their subsequent use of the portal sent the teenage Molly back to shortly after her past self arrived in the past in the first place, allowing her to send her past self back to the present. Shortly after saving the younger Molly, the older Molly ceased to exist, vanishing from existence as the timeline corrected itself. (DS9: "Time's Orphan")
Also in 2373, an encounter with the 29th century timeship Aeon threw Voyager back to 1996, while the Aeon crash-landed in 1967 and was discovered by Henry Starling, who used its future technology to make himself rich. History was corrected when Captain Janeway destroyed the timeship before it could travel to the future and accidentally cause a temporal explosion. Voyager was returned to the correct time by an alternate version of the Aeon from the correct timeline. (VOY: "Future's End", "Future's End, Part II")
An alternate future version of Janeway (from 2404) traveled back to 2378 through the use of a chrono deflector to bring Voyager home from the Delta Quadrant sixteen years earlier than it had arrived in that alternate future. This future Janeway was killed in the attempt but succeeded in returning Voyager home and even delivered a crippling if not fatal blow to the Borg. (VOY: "Endgame")
In 2387, Nero and Spock were sent back in time through a Red matter black hole which had prevented a supernova from destroying the galaxy (but not before it had destroyed Romulus in the process). Nero was sent back to the past to 2233, inadvertently creating a new spacetime continuum where he destroyed the USS Kelvin. He and his crew then went into hiding for twenty-five years awaiting Spock's arrival. Spock arrived in Nero's new timeline in 2258. Nero destroyed Vulcan, while Spock watched from Delta Vega. The crew of the USS Enterprise with the help of James T. Kirk, stopped Nero from destroying Earth. (Star Trek)
Temporal Cold WarEdit
The events of the Temporal Cold War further complicated the understanding of Federation time travel capabilities.
As of the 28th century, a time traveling faction represented by a mysterious individual, could only communicate and exchange information and technologies through time, appearing as non-corporeal entities. By the 29th century, this technology was perfected to allow physical travel.
According to a Temporal Enforcement Agent from the 31st century named Daniels, all time travelers were bound by the observance of strict procedures set forth in the Temporal Accords. Daniels stated that the Temporal Accords were enacted after time travel was developed by all time travel-capable species to prevent catastrophic tampering with the timeline.
In 2153, the Sphere-Builders, a group previously thought to possess the ability only to examine alternate timelines, sent Xindi-Reptilians back to 21st century Detroit to develop a bio-weapon to destroy the Human race. (ENT: "Carpenter Street")
Ultimately the war ended when the Na'kuhl returned from an alternate 1944 (created by their very actions) and caused the Cold War to become a war with time-travelers changing time as they liked. Daniels brought Enterprise and Archer back to 1944 to stop Vosk, leader of the Nak'uhl, from returning to the future. With the help of Silik, a member of another faction of the Temporal Cold War, Archer shut off Vosk's compound's shields, allowing Enterprise to destroy it and thus destroying the temporal conduit and killing Vosk just as he was about to travel back to the future. Daniels pulled Archer to a place where they watched the time stream as all of the events that occurred when the Temporal War were undone and time reset itself to normal. Archer refused to have anything to do anymore with Daniels' "damn Temporal Cold War" and Daniels agreed, claiming it was finally coming to an end thanks to Archer's actions. (ENT: "Storm Front", "Storm Front, Part II")
- Black hole created by red matter
- Chrono deflector
- Light-speed breakaway factor (Slingshot effect)
- Orb of Time
- Q powers
- Temporal causality loop
- Temporal conduit
- Temporal transporter
- Temporal vortex
- Time portal
- Department of Temporal Investigations
- Janeway Factor
- Temporal anomaly
- Temporal Integrity Commission
- Temporal Prime Directive
In the novel Ishmael, Captain Spock embarked incognito aboard a Klingon ore transport, refitted with time travel capacity. The ore transport managed to go back to 1867 Earth after an acceleration close to a white dwarf near Starbase 12. The USS Enterprise was modified to follow the ship to 1867, becoming the first instance that a Federation ship utilized intentional and controlled time travel.
In the video game Star Trek: The Next Generation - Future's Past for the Super Nintendo, the computer mentions several temporal near-catastrophes in the 23rd century: the New York incident, the above-mentioned "Ishmael incident," and the "Eyeglass Loop Paradox" referring to what Kirk did in Voyage Home with his glasses.
The Department of Temporal Investigations novels Watching the Clock and Forgotten History go into detail about the principles of time travel, as well as the hows and whys of the various time travel incidents in Star Trek's history. The most significant of these demonstrates how Starfleet became aware that history could change- previously they had assumed that changing history just created an alternate timeline that those who changed history happened to get 'stuck' in-; when the DTI created Timeship One with the intention of deliberately travelling three days into the future, a future version of the ship appeared in their time thirty-two hours before it was due to launch, the crew all dead or dying from an accident that had occurred when they overshot. With this discovery postponing the planned launch, the future Timeship One and its crew disappeared once the time of the original launch had passed, confirming that history could be changed.