Time travel

"You only traveled back in time one day. What if you traveled back decades? Centuries? Imagine the havoc you could wreak."

- Harrison Wells to Barry Allen

Time travel is a concept in the multiverse that involves physical and temporal teleportation within an Earth's history without directly affecting other universes. Time travel is not without consequences, resulting in multiple possible, or at least altered, timelines. The mechanics of time travel differ greatly between that of meta-human speedsters and technological timeships, as used by Time Masters and time pirates. A specific timeline is considered the "main" or "true" timeline, and is protected by the Legends, the Time Bureau, and formerly the Time Masters, from possible alterations, the results of which are described as aberrations.

General concepts
"You've all seen how the timeline is malleable... in flux until it is set."

- Rip Hunter

Methods of travel
Time can be ventured through with the use of futuristic transport, such as a Time Sphere or a timeship, like the Waverider. Rip Hunter designed the first Time Sphere, and its designs were obtained by the Reverse-Flash, who would eventually need to use them to have Cisco Ramon build the 21st century version. The reason for that was the Reverse-Flash's loss of Speed Force control required for his speedster ability to time travel after killing Nora Allen. According to Vandal Savage, he also figured out another, unexplained form of travel of his own; and in a similar way Abra Kadabra was able to venture into the past without a timeship, but not back to the future. At some point Rip Hunter's Time Bureau created the time courier, a portable device allowing to create portals to different places in time and space. If an individual use a timeship to time travel, it will be through the temporal zone, in which the person can access different periods in the timeline. However, this is not the only method of time travel, in which also has the wormholes (in which the timeships can travel through it too ), other methods for example using the Time stone and through the Speed Force, in which the speedsters use to time travel across the different periods of the timeline.

Real and "mirage" timelines
For the reasons not entirely explained there exists a distinction between which timelines are considered "true", and thus protected by the Legends and formerly the Time Masters, and which are disregarded as "possible", "fluctuating" or "mirage" timelines. The so-called "Flashpoint" timeline, created as the result of The Flash of 2016's actions in the year 2000, followed by traveling back to the future of 2016, was described by Eobard Thawne as "a mirage", which, however, started to cement in reality, removing Barry's memories and powers every time he used the Speed Force. It is also possible that every possible timeline from every Earth exist alongside each other and when someone changes the timeline and then travels back to their own time, they cross timelines from their own to the new one. Barry and Eobard crossed from the real timeline to "Flashpoint" after Barry changed time and ran with Eobard back to 2016.

A variant of 2046's Star City encountered by Rip Hunter's team during their timeship's emergency landing after being shot down by Chronos was described by Rip Hunter as a future that is "not set", a result of time being malleable and in flux. As said by that timeline's version of Oliver Queen, however, the destroyed Star City as seen in 2046 was the result of Sara Lance and Ray Palmer never returning from their time travel quest. It is possible that this future would not come to pass should the two return and assist Oliver in stopping the new Deathstroke's army. Another possibility is Oculus shaping the time this way. It is unknown how the "truth" of a timeline is being figured out after the destruction of Oculus by Rip Hunter's team. For most members of Time Masters, the device was described as a way of seeing the true timeline that must be protected. However, in reality, the senior Time Masters, such as Druce, used it to manipulate the timeline, changing the effects of time travel when needed, with only the Vanishing Point, where the Time Masters HQ were located, being the sole place outside of the device's influence. It is possible that it was through the use of Oculus that the Time Masters prevented Rip Hunter's every time travel attempt to save his family from Vandal Savage and his shocktroopers, considering it of great importance to the timeline.

Array of timelines
When Barry Allen and Eobard Thawne changed the timeline in 2016, a notable change was the erasure of Sara Diggle from existence, and the addition of John Diggle, Jr. to the timeline. Very likely the future "Connor Hawke"/Green Arrow whom the Legends encountered in a "potential future", his older self's existence can be explained by an array of timelines - with each timeline within the array being the past and future of the succeeding and preceding ones, respectively. Thus, if someone were to travel to a future set in a timeline that seemingly contradicts the events and occurrences of the relative past they know of, it could be simply explained by changes from time travel, which created the future timeline, of the past timeline. This goes for all timelines created through time ruptues - each an "item", iterated through. As a result, the Legends not only went to a potential future, but a post-Flashpoint one. This itself is an example of temporal mutability - timelines simultaneously existing with other, or branching off the previous ones, whether they're coexisting with or "overwriting" them.

Multiverse and timelines
Different universes have different timelines, even if the "timeline" of one an into "contact" with that of another - for example, in the case of inhabitants of Earths One and Two crossing dimensions - the changes to the timeline of one Earth won't be reflected in that of another. When Barry Allen changed the timeline in 2016, creating a "Flashpoint", and then when Eobard Thawne subsequently created another timeline, closer to the pre-Flashpoint one - Harrison Wells and Jesse Quick weren't affected by the changes upon returning to Earth-1, being their pre-Flashpoint selves. This can be explained by Barry travelling through time after they returned to Earth-2 (and its timeline).

That said characters' post-Flashpoint selves have ceased to exist and been replaced by their pre-Flashpoint selves when the event of their return to Earth-2's timeline as if it occurred in the post-Flashpoint reality. The existence of multiple timelines coexisting together, across the multiverse, is yet another example of temporal mutability.

In the case of speedsters, it's possible to break the time and dimensional barriers altogether, shown when Barry Allen traveled to Earth-38 and stayed there for almost a day, but when he returned to his, only a few seconds had passed by. Alternatively, it's possible that time flows differently in different universes (and by extension, Earths) as a whole - and the differences may depend on how many dimensions away the Earths are, as with Earths One and Two, time flows roughly, if not exactly, the same, despite multiple other differences, like the changes in vibrations. It's also possible that when Barry accidentally traveled to Earth-38 and then returned to Earth-1, (seemingly seconds later) that he may have travelled through space and time simultaneously, and therefore it would appear that he was only away from Earth-1 for a brief moment.

Predestination and loops
Since, as said by Rip Hunter, "time wants to happen", a number of time travel attempts into the past to change effects of a future end up causing said future to happen in the first place. For example, finding his wife and son slain by Vandal Savage prompted Rip Hunter to travel back in time and attempt to kill Savage at the early period of his life, as Hath-Set. He failed, and was captured, making Hath-Set swear to hunt him down, and centuries later, after finding Rip's locket, to kill his family. The predestined time travel effects included Martin Stein's healing of Herbert G. Wells in the 19th century, or Mick Rory being hunted down by Chronos, his future self. A possible reason for such loops and predestined events is the Time Masters' control of Oculus, as time loops ensured that the current timeline would remain stable and free of major changes, even if altered, thus the free will of time travelers was ultimately seen and manipulated by the Time Masters. Without such a device, however, the time was now uncertain, forcing Time Masters to stop their support of Vandal Savage. It may have also resulted in the increase of aberrations.

Erased from time
One of the most dangerous effects of time travel, noted by both the Time Masters and speedsters, was the possibility of people being erased from the timeline due to actions deviating from the original timeline. After losing his Speed Force connection and becoming stranded in the year 2000, Eobard Thawne killed Tess Morgan and Harrison Wells, the original creators of S.T.A.R. Labs in the timeline Eobard hailed from, bringing major changes to the "main" timeline. Fifteen years later, Eobard was erased from existence when his ancestor Eddie Thawne killed himself to stop Eobard from killing Team Flash.

As Barry Allen and Eobard Thawne reversed the new timeline created by the former when he saved his mother from her death, a number of lives were also altered while the two traveled shielded in the Speed Force, such as Dante Ramon dying, and Sara Diggle getting erased from existence, with John Diggle, Jr. ending up as Lyla Michaels's child instead.

The Pilgrim, an agent of the Time Masters, preferred to kill her targets in their childhood, erasing them from further existence in the timeline and preventing them from doing the very thing that got them hunted in the first place. However, the time wouldn't cement instantaneously, which allowed the Legends to kidnap their younger selves and protect them from harm aboard the Waverider ' s temporal zone until Pilgrim was destroyed. Eobard Thawne, who would abuse time travel to achieve the best outcome in a conflict, after living through a timeline in which Rex Tyler figured out his plan and time-traveled himself to warn the Legends, went back to before his first meeting with Tyler and killed the vigilante, erasing him from that point in time. However, instead of preventing Tyler's meeting with the Legends altogether, it altered their conversation, before ending it in an abrupt way, with Rex disappearing before the Legends' eyes.

As Eobard continued to live when he wasn't supposed to exist, he found himself pursued by a Speed Force enforcer, Black Flash, in order to erase Eobard from the timeline. Despite Eobard's initial successes in throwing off Black Flash and even capturing the enforcer in an altered reality, he was unable to escape his fate and was eventually slain before he was erased from time.

The existence of Barry's evil time remnant Savitar stemmed from a causal loop; in order to ensure his survival, Savitar had to murder Iris West in 2017, prompting his younger self to create several time remnants in a later fight, one of whom would go on to become Savitar himself, continuing the endless cycle. However, since Harrison "H.R." Wells sacrificed his life instead to save Iris, Savitar was never created. Despite this, Savitar wasn't erased instantly as he continued to exist as an aberration for several days until the timeline eventually caught up to him.

In 2049, the daughter of Barry and Iris West-Allen, Nora West-Allen, traveled back in time to late 2017 to meet Team Flash, secretly with the help of a revived Eobard Thawne. In order to escape captivity, Eobard manipulated Nora into helping Team Flash stop Cicada and Cicada II in 2018-2019, which led to the destruction of Cicada's dagger, upon which Eobard was able to go free and a new timeline set in which Nora was never born. As a result, Nora became another victim of time itself as she disappeared out of existence in her parents' hands.

Despite the erasure of individuals from the timeline, any memories of those individuals don't seem to fade with them, as noted when the Legends could remember Rex Tyler and Eobard Thawne and Team Flash could vividly remember Eobard, Savitar, and Nora. It seems that some objects belonging to those individuals don't fade either; for example, Barry and Iris could view a message from Nora despite the fact that she would never be born to record it.

Time Vaults
Time Vaults are specific structures that allow their users to monitor the array of timelines and see how changes in the present can lead to the result, either different or same, as that of the other timeline. For example, the Time Vault used by Eobard Thawne was used to compare his current timeline's future to that of the future that he hailed from: the changing structure of a newspaper indicated that both timelines would see the Flash disappearing during a crisis with red skies above in 2024.

However, if the timeline changed to the effect of Barry losing those powers, that part of the timeline would disappear. For example, when Farooq Gibran used his powers on Barry in 2014, causing the latter to lose his speed, Eobard Thawne noticed that any mention of the Crisis in 2024 vanished, as well as any mention of "The Flash" or "Barry Allen" in the 2024 newspaper article. This was later resolved when Barry regained his speed, restoring the timeline and the events of the Crisis as it was before.

Interestingly, Harrison "Harry" Wells of Earth-2 also used a Time Vault of his own that he called by the same name. Although it's unknown how Harry came to know how to use the Time Vault, as he wasn't a known time traveler, it's likely that the Time Vault in Earth-2's S.T.A.R. Labs didn't possess the same capabilities as its Earth-1 version and couldn't see through the timeline, as it was only intended to be used as a hideout for Harry in the case of an attack by Zoom. Acting as a secret bunker rather than a timeline monitoring hideout.

Time fragmentations
Time fragmentations are specific points in space and time that are invisible to the Time Masters, even with the power of the Oculus. One such fragmentation is the town of Salvation in 1871, which the Legends used while on the run from the Time Masters. This allows people to hide out within these fragmentations, which forces the Time Masters or their hired mercenaries to individually check each one. These fragmentations don't have any effect on speedster-based time travel.

Time travel via timeship
"A Time Master's sacred charge is to do no harm to the timeline. Can you imagine what a timeship would look like in, say, Victorian England?"

- Rip Hunter

Features of timeships
Time Masters and time pirates would use timeships for time travel. These vessels appeared to operate like maneuverable spaceships with weaponry and capacity to use a Time Drive to enter the time stream, a space between time periods, from which a timeship could travel to one or the other point in time. The timeships would rely on the "Temporal Zone", protecting their users from aberrations, and having an emergency option of "scattering" its crew throughout timeline. Timeships could pursue each other in the time stream, allowing Chronos to attack the Waverider.

The Legion of Super Heroes had their own version of a timeship, but it time traveled using wormholes instead of going into the temporal zone.

"Rules of time travel"
According to Rip Hunter, the Time Masters have created a number of rules to keep the timeline stable. The prime of these rules is that time travelers can't go back and change events in which they participated. According to the Time Masters' rules, in this case time would fold in on itself, creating a temporal vortex. To punish those who would ignore the rules, the Time Masters employed bounty hunters and assassins. However, only by ignoring the rules did the Legends manage to stop Vandal Savage's final plot to revert the timeline back to Ancient Egypt, and then remain in one piece.

Co-existing with one's other self
Meta-human speedsters use the Speed Force to travel through time in two different ways. One way is similar to that of timeship time travel, allowing a past or future version of the speedster to exist in the same time and even interact with their other self. This way, time travel would not result in a new timeline, but bring alterations to the existing one. In Barry Allen's case, one of his time travel attempts led to Hartley Rathaway's reformation and the creation of weaponry that could be used against Time Wraiths. Barry used a similar form of time travel when traveling to the year 2000, as multiple other versions were seen at his house.

Superseding one's other self
The other version of speedster time travel involves superseding their selves from another time period, "becoming" them, instead of coexisting alongside their other selves. Barry Allen used this variation of time travel when saving Central City from a tidal wave sent by the Weather Wizard, and later after Vandal Savage sent a destructive wave of energy using the Staff of Horus. In both cases, Barry became himself from a day ago, allowing him to change the course of events. After stopping Eobard Thawne from killing his mother, Barry traveled the same way to a changed version of 2016, dubbed "Flashpoint", and was later bought back to the "main" timeline by Eobard in a similar manner.

Dangers of speedster time travel
The speedsters' time travel is especially dangerous, due to its tendency to fundamentally change and substitute the main timeline, as what happened when a version of Eobard Thawne lost his Speed Force connection after killing Nora Allen and traumatizing Barry. The time traveler was now stranded in 2000 and shaped history, including the creation of the Flash, according to his plans. The resulting timeline, while further altered multiple times, was now considered the main one, with the others being merely "possible" or "mirage" timelines. As a result of Eobard's actions, Tess Morgan and Harrison Wells were dead, Wells's reputation tarnished.

However, while Thawne's timeline changes were part of a plan, some changes could arise as unforeseen consequences of time travel, all the while not affecting the speedsters, protected by the Speed Force as a bunker, keeping them safe from the effects of time paradoxes, as well as memories they were supposed to have in this new timeline. After Eobard Thawne, at Barry's request, prevented Flashpoint from happening, he traveled together with Barry to 2016 using a superseding form of time travel, resulting in multiple changes. For the starters, protected by the Speed Force, Eobard was not erased from existence like a version of him from this timeline, disguised as Dr. Wells, had due to Eddie Thawne's suicide. Furthermore, while Eobard retained memories of his own original timeline (before the changes he brought as "Wells"), and Barry had the memories of his life as shaped by "Wells", the superseding resulted in Barry not knowing what memories he is supposed to have in the new, post-Flashpoint timeline, resulting in a conflict with Cisco Ramon, whose brother the Flash refused to save from death, and a feud in the West family, which Barry had to take time to unravel; as well as seeing people whom he's never seen before, yet has been supposed to, like Julian Albert. When Barry tried to go back in time again to correct these issues, he was stopped by Jay Garrick, who told the younger speedster that the altered timeline is akin to a broken cup: you can try to glue it together, but it will never be the same.

According to Savitar, the more a speedster uses time travel, the less the rules will apply which will lead to different causes and effects. Eddie Thawne killed himself so that his descendant Eobard Thawne would never be born, yet he still lived as a Time remnant before Hunter Zolomon erased him from existence.

Time remnants
"In the year 2020, you and your wife, Tess Morgan, successfully launched a Particle Accelerator that changed the course of history. I need it to happen a bit sooner if I'm going to get back. Much sooner."

- Eobard Thawne describes his original timeline to Harrison Wells

A time remnant is a side-effect of a speedster's time travel that appears out of the Speed Force to prevent further time paradoxes. Although Eobard Thawne originally fought the supposed Flash created in 2020 and thus couldn't have a first encounter with him in 2016, after "changing" the main timeline by killing Tess Morgan and creating the Flash in 2013, before being erased from existence, Thawne inadvertently forced a younger self of himself to appear in 2016 of this new timeline and "recreate" Eobard's first encounter with the Flash.

As time remnants come from erased and aborted timelines, some speedsters, like Hunter Zolomon and Barry Allen, found out how to abuse time travel in order to force the creation of a time remnant, via not superseding their past selves, aborting their timeline. Zolomon's time travel abuse, in particular, had him hunted down and caught by Time Wraiths, who trapped him inside the Speed Force.

Another idea is that time remnants are parts of a stable loop, with memories of timelines that they themselves doomed to non-existence, but having to continue their existence in the new timeline (created by their future actions - including those that occur in the relative past - being triggered to take effect at once) up until the point where they cease to exist, due to past instances of themselves having travelled through (and thus, been protected by) the Speed Force, in order to cause those changes in the first place.

Possible other methods
After being captured and interrogated by Rip Hunter, Vandal Savage claimed that after witnessing a time travel attempt by Rip in 1975, he studied for 200 years to devise his own time travel ability, eventually figuring it out on his own, allowing him to move in and out of the timestream, letting him proceed undetected. However, Savage may have been lying, as he was seen provided with a timeship by the Time Masters, although the two methods may not be exclusive. Additionally, The Pilgrim had a device or an ability to control time around her, stopping her enemies from attacking her. Abra Kadabra also used an unknown way of time travel to get to the 21st century, but could not return to the 64th without a timeship. Superfriends also figured out a way to use The Legion's special rings for time travel

In 1991 on Earth-90, after getting hit by a missile, Barry Allen accidentally travelled 10 years into the future. The nature of the missile and how it can allow time travel is unknown.

Mar Novu can open breaches to any point in time, as he warped Mia, William and Connor to 2019 from 2040.

History
At an unknown point in time, the Time Masters organization was created to control and oversee the "correct" timeline from the Vanishing Point. Using the Oculus device to manipulate certain events in time, as well as a Time Fleet and bounty hunters to combat the occasional time pirate, the Time Masters held their hold over the main timeline before their device was destroyed by Rip Hunter's team, along with the Oculus Wellspring. It can be noted that the Time Masters' efforts to maintain a "true" timeline were opposed beforehand, with the timeline greatly changing in the year 2000.

The rogue time traveler that brought these "changes" was Eobard Thawne, the Reverse Flash. After failing to kill a young Barry Allen and killing Nora Allen instead to traumatize the boy and stop him from becoming the Flash, Eobard unexpectedly lost his connection to the Speed Force, presumably since if his plan worked and the Flash never existed, so wouldn't the Reverse-Flash, who based his appearance, name and source of powers on the Flash. To restore his powers and return to his time as soon as possible, Eobard killed Tess Morgan and Harrison Wells, the original creators of the Flash from the timeline that Eobard hailed from, stealing Dr. Wells's appearance and identity, and deciding on a goal to create the S.T.A.R. Labs particle accelerator, and so, the Flash, as soon as possible, succeeding by the year 2013. He also supervised Barry Allen's movements, making sure that he'd be hit by lightning along with the Dark Matter energy from the particle accelerator and receive a connection to the Speed Force. After that, Eobard, in the guise of Wells, overlooked Barry's recovery in S.T.A.R. Labs.

These activities of Eobard were presumably intended by the Time Masters, because Eobard's personal timeline is a bootstrap paradox in which the Time Masters cannot interfere, in order to preserve the timeline itself. After this loop was broked when Eddie Thawne killed himself, the Time Masters considered a major alteration point in the "main" timeline being the fate of Vandal Savage's world conquest plan in the new future. Time Master Druce intended for Savage to conquer the world and then protect it from a Thanagarian invasion, but after the Oculus's destruction, this plan was aborted by the other Time Masters, who ceased their support of Savage's actions.

This "main" timeline was altered by Barry Allen multiple times. Twice in 2015, Barry traveled back in time one day and superseded his earlier self, allowing him to prevent the destruction of Central City in both instances and avert a number of deaths that would have occurred in the "main" timeline, including that of Cisco Ramon. The timeline was altered once again when Barry traveled back from 2016 to 2015 to receive the help of Eobard Thawne on the speed formula, causing a Time Wraith to pursue him and indirectly change the fate of Hartley Rathaway, with Rathaway becoming an ally of Team Flash in the wake of a Wraith attack rather the enemy he would become in the "main" timeline. Shortly after defeating Zoom, Barry traveled back in time once more to 2000 in order to save his mother, creating a completely new timeline where she and Henry Allen were alive and well and Barry never became the Flash, nicknamed "Flashpoint" by Eobard Thawne. After realizing the dangers that the new timeline brought, Barry requested Eobard to return to 2000 and undo his changes by killing Nora again, to which Eobard complied, although even after the timeline was supposedly "reset," Barry's initial action had brought upon several unforeseen alterations, including the death of Dante Ramon and the future birth of Savitar. In order to reverse the Post-Flashpoint alterations to the timeline, Barry attempted to travel back in time once more but was stopped by Jay Garrick, who pulled Barry to 1998 and urged the youth to refrain from unnecessary time travel in the future, to which Barry complied and returned to 2016 without making any changes.

Currently, the earliest known point in time visited by time travelers is South Dakota 70 million years ago, when a time-scattered Ray Palmer was saved by Mick Rory and Nate Heywood from an angry dinosaur.

Side Effects
As the human body is used to time unfolding linearly, time jumps cause sever side-effects that normally last a few minutes at a time, however, it should be noted that so far it has been shown that only jumps backwards cause side effects, as when jumping forwards, the Legends usually do not suffer side effects. Also, the more someone travels through time, the less severe side effects are, as Rip Hunter had been a Time Master for over a decade before recruiting the Legends, and thus did not suffer side effects until heading to 1871, a much longer jaunt then any previous mission his team has went on. After some time on the Waverider other Legends have also gradually stopped being affected by time jumps.

Finally, some people are not affected at all by time travel. Cisco Ramon and Felicity Smoak went with Mick, Amaya and Nate to 1951 to catch a Dominator. Despite never time travelling before, Cisco was unaffected while Felicity experienced side effects although, it is possible Cisco's connection to the space-time energy of the multiverse means he remains unaffected by time travel. Speedsters using the Speed Force to time jump also remain unaffected, but it is unknown whether they'd experience side effects when using a timeship, although Wally West has not been shown to suffer side effects, so it is possible that speedsters do not suffer side effects at all, or that because of their hyper-metabolism, side effects pass really quickly.

Possible side effects experienced during time travel include but are not limited to:
 * Nausea
 * Vertigo
 * Linguistic disorientation
 * Eye disorders
 * Temporary blindness
 * Bleeding from eyes (rare)
 * Triple vision
 * Blurriness in one eye
 * Time Drift: After spending too long in an alien time period, a person begins to lose their memories and become acclimatized to the alien period. Rip suffered from the drift when he visited 1868. Sara, Kendra and Ray all experienced the drift when stuck in 1958 when Chronos attacked the Waverider.
 * Personality Rewrite: Should someone make contact with a Time Drive, the temporal electrocution will scatter that person in time but also rewrite their personalities and memories for the new period, suppressing old memories that resurface as dreams. At one point Rip Hunter touched the drives and experienced the rewrite, until the Legion of Doom found a way to partially restore his personality, albeit as a servant of their will. The Legends eventually completely restored him to normal.

Temporal Physics
This temporal physics only works with timeship' based time travel and don't work with time travel through the Speed Force, due to the speedsters being protected by it.

Time Quakes
Time Quakes are temporal shockwaves created by huge changes to the timeline. They are felt in the Temporal Zone and can be detected by timeship A.I.s such as Gideon or by a temporal seismograph, invented by Nate Heywood. These quakes have epicentres to find what point in time has been changed. The Legends track the epicentres to try and prevent the "abberations" before they occur and damage history beyond repair.

Time Storm
Time Storms are incredibly cataclysmic space-time events caused by crossing your own timeline, however, time storms do not always occur when someone crosses their timeline. Martin Stein interacted with his past self as well as Sara and Mick interacting with themselves when trying to save their past selves from the Pilgrim. This means to cause one, several people need to cross their timelines and attempt to time jump together such as when the Legends visited 1916 twice to stop the Legion of Doom as the five Legends that survived Doomworld interacted with their younger selves causing a storm to begin.

Temporal Vortex
Temporal Vortexes were first mentioned by Rip Hunter to the Legends when they suggested returning to a time they already visited. Rip said doing this would "make time fold in on itself, creating a temporal vortex". After stopping the Legion of Doom, the resultant Time Storm the Legends created in their actions to stop the Legion created a vortex that caused hundreds of anachronisms throughout time and space by picking up seemingly random things, including animals and people, and flinging them to a new point in time. Rip and his new Time Bureau dedicated themselves to fixing the anachronisms with help from the Legends.

Time Wave
If an aberration is severe enough, an explosion of light will expand outward from the site of the aberration and hit the entire timeline, as well as the Temporal Zone. There will then be an immediate warping of reality according to the new timeline. This occurred once when John Constantine broke up with Desmond to save the latter's life and again when John undid this event.

The Flash (The CW)
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DC's Legends of Tomorrow
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Trivia

 * If a time traveler attempts to travel together with another version of themselves from a different point in their time via a timeship, it will damage time and cause it spit out buildings and people in the wrong time periods.

Behind the scenes

 * In the DC comics, time travel is a long-running concept, with many speedsters and other time travelers changing and creating timelines throughout the comics' runs.