In Star Trek IV: The Voyage Home, we see Kirk and his crew can perform fairly accurate time travel via the light-speed breakaway factor. Is there any reason they don't use this technique more frequently?

  • For example, if I were Worf, I would have used it to save Jadzia Dax by going back and keep on trying that until I get things sorted. Since we know the maneuver can be completed with a Klingon Bird of Prey, I would secure a ship and do what was necessary until I got it right.

  • Even if the maneuver is complicated and should therefore used only under extreme circumstances, why doesn't the Federation use it to fix every major problem they encounter?

From Worf's perspective it would certainly be worth the risk.

  • @JasonBaker: How is it that none of the answers discuss ST2009?? Any volunteers? Commented Apr 8, 2015 at 17:39

4 Answers 4


Why don't they use time travel more?

I'm going to leave aside the Temporal Prime Directive, because the answer to this question is really about the motivations behind that regulation:

The consequences are incredibly hard to predict1

Enterprise probably explores the consequences of time travel more than any other Star Trek series, and we get a wonderful example of this in the season 1 finale/season 2 premiere Shockwave. At one point in this episode, Captain Archer gets transported through time from the 22nd century to the 31st. As a result of him not being in a specific place at a specific time, the 31st century looks like this:

San Francisco, 31st Century

Needless to say, it's not meant to look like that2. This is a bit of an extreme situation, given that there were a lot of people futzing with time while this is going on, but ultimately all of the tight regulation of time travel boils down to this reason.

Voyager actually has a whole two-parter that reeks of this problem: Year of Hell. The main antagonist is a scientist who's devised a way of mapping changes to the timeline, and calculating the effect that interventions will have. Using this, he's spent two hundred years trying to restore his civilization to glory and prevent the death of his wife by performing surgical strikes against planets at different points in time.

At no point does he succeed; every single attempt to restore his desired timeline causes another problem that he needs to solve. It's implied by the end of the episode that his problem isn't solvable, although it actually sort of is: fixing time so that the ship never existed.

The point of all this is that time travel should only be considered a viable solution to a problem if that problem is of significant importance to the Federation, or if the problem was caused by time travel in the first place. Unfortunately for Worf, the death of his wife doesn't qualify.

Why wouldn't someone try anyway?

There's not a lot Starfleet could do to stop an individual using time travel without authorization. This is a fair point, although there are some counterpoints.

For one thing, we've seen evidence of Federation-aligned organizations working to preserve the timeline. The DS9 episode Trials and Tribble-ations introduces us to the Department of Temporal Investigations, a branch of the Federation government tasked with following up on time travel incidents.

Two separate Voyager episodes introduce us to the idea of Starfleet policing the timeline in the 29th century: Future's End, which shows a 29th-century timeship ready to destroy Voyager to prevent a temporal incursion in the future; and Relativity, which has a similar timeship recruit Seven of Nine to prevent disruptions to the timeline; finally, a major plot of the Enterprise series involved Daniels, a Starfleet Temporal Agent from the 31st century, trying to correct various attempted corruptions to the timeline.

Although these are the only occasions we see these organizations on-screen, we have to suspend our disbelief somewhat and assume that they kept working even when we don't see them. So any individual attempting time travel for their own ends (Especially one within Starfleet) would presumably have to answer to these organizations eventually.

My other counterpoint is more wishy-washy, but no less valid. Everyone in Starfleet knows the dangers of time travel by the time of DS9. In fact, every time there's a time travel episode we get at least a half-dozen lines of dialogue reminding everyone that our heroes can't do anything that may affect the timeline. So they know that there are regulations against it, they know the logic behind the regulation, and they agree that the regulations are sensible.

In the 21st century, you'd expect someone to give it a shot anyway. But in the world of Star Trek, that's usually been enough. TNG actually gives us that message as a minor plot point: The Neutral Zone gives us three humans from the 20th century who have been cryogenically frozen, and a subplot of the episode is them trying to adjust to the culture of the 24th century. In particular we have this (Paraphrased) exchange after one of them uses the comm to summon Picard:

Picard: You're not authorized to use that.

20th century investment banker: Then why isn't it guarded?

Picard: Because most people have enough sense that it's not necessary.

Needless to say this utopian vision of Star Trek softened somewhat after Gene Roddenberry's death, but the fact remains that most citizens of the Federation, and Starfleet personnel in particular, are sensible enough to know that the consequences outweigh the benefits of trying to use time travel this way. And for the ones who aren't, that's what the trigger-happy 29th century timeships are for.

1 There's some real-world basis to this, called the butterfly effect (good name for a movie). Essentially, dynamic systems, like the weather, are extremely sensitive to initial conditions. That's why you sometimes hear the adage "a butterfly flapping its wings in Brazil causes a tornado in Texas"; small changes in initial conditions (the atmospheric disturbances caused by the butterfly) are amplified by the interactions of the dynamic system, causing disproportionally huge results (tornado). Now imagine time as a dynamic system...

2 As Eric Smith points out in comments, the use of the word "meant" is somewhat troubling; it implies a measure of predestination which is difficult to justify philosophically. When I say "this wasn't meant to happen" I mean "to the best of our knowledge2, the only way this could have happened is by the direct intervention of time travellers". We can say this in the Star Trek universe, because it's been established that there is only one timeline, which can be changed from right under your feet. The City on the Edge of Forever, Yesterday's Enterprise, and Year of Hell are just three episodes that spring to mind that reinforce this4.

2 The stipulation "To the best of our knowledge" is important because, as Eric Smith also points out in comments, it's possible that history as we know it was caused by time travellers, and the timeline-detecting technology employed by Daniels and crew aren't sophisticated enough to detect this. We definitionally have to exclude this from consideration, because we have no way to prove this interference. If we've decided that meddling with the past is Bad (And the existence of Daniels indicates that we have), all we can do is police the incursions we can detect.

4 As Eric reminds me again, we have to rectify this "single timeline" against the existence of things like the Mirror Universe. This is a hard thing to do; every episode about time travel we've seen indicates that there's only a single timeline, and yet it's also a many-worlds situation where Zefram Cochrane blows away a Vulcan landing crew and founds the Space Nazis5. I'll leave the mechanics of reconciling this to the philosophers, and just note that Our Time Travel is Different

5 Not to be confused with Nazis....IN SPACE!

  • Nice try, but not fully convincing. As we have seen with the "Pegasus gate", once an Organisation can use a technology, there is nothing that can actually stop any member/sub-unit of it from using it, regardless of the nasty consequences it may cause. Let's assume Worf has got an extraordinary sense of compliance towards Federation's regulations. Dr. Bashir could arrange a team of Dax friends, steal a bird of prey and to hell with the timeline. I think that the authors 'gave' Federation the ability to time travel without thinking of all the plot holes this would have caused.
    – gd1
    Commented Nov 2, 2014 at 9:21
  • @gd1 The only "Pegasus Gate" I know is in relation to "Stargate"; I assume you meant The Pegasus, the episode of TNG with the illegal cloaking device? In any case you make a fair point, and I've updated my answer to reflect as best I can. Commented Nov 2, 2014 at 17:45
  • The "Pegasus Gate" was a sloppy joke (Water_gate_ scandal). I'll read your edit, thanks.
    – gd1
    Commented Nov 2, 2014 at 17:47
  • "it's not meant to look like that" - meant by whom? I think what you mean is "most humans don't want it to look like that"
    – Eric Smith
    Commented Nov 2, 2014 at 19:15
  • 1
    @Zibbobz Yeah, played by Max Headroom. The episode was A Matter of Time Commented Nov 5, 2014 at 16:47

Yes. The Federation has demonstrated the ability, with an alarming degree of accuracy, to effectively time travel and potentially alter the past. But just because you CAN do a thing, does not mean that you SHOULD.

  • The availability of time travel does not mean one should be using it. Since it had been conclusively proven altering the past affects the future, the Federation would one day create regulations governing the use of time travel to include the idea of "observation only" interactions with the past. (See: Temporal Prime Directive)

The Temporal Prime Directive was a fundamental Starfleet principle: All Starfleet personnel are strictly forbidden from directly interfering with historical events and are required to maintain the timeline and prevent history from being altered. It also restricts people from telling too much about the future, so as not to cause paradoxes or alter the timeline.

  • This lesson was driven home by the episode in TOS: "The City on the Edge of Forever", when Captain Kirk, experimenting with the Guardian of Time, travels to the past, inadvertently saves Edith Keeler and completely erases the timeline of the Federation.

enter image description here

  • And yes, they travel to the past several times in The Original Series Star Trek, but supposedly these jaunts to the past were considered necessary and vital to Federation security (or were completely accidental in the case of TOS "Tomorrow is Yesterday").

  • The episode with Gary Seven implied (but does not confirm) the Federation was actually time traveling on purpose to view the past. (TOS: All Our Yesterdays)

"Captain's log. Using the light-speed breakaway factor, the Enterprise has moved back through time to the 20th century. We are now in extended orbit around Earth, using our ship's deflector shields to remain unobserved. Our mission – historical research. We are monitoring Earth communications to find out how our planet survived desperate problems in the year 1968."

The Temporal Accord

In the 27th century, the Federation would establish the Temporal Accords, rules to prevent traveling into the past for the express intent of altering the past.

The Temporal Accord was an interstellar treaty signed after the development of time travel, prohibiting the use of the technology for changing history. It was in force by 2769. The Accord permitted time travel only for the purpose of scientific research, and set forth rules and procedures as to how to do so without contaminating the timeline. Certain groups who held time travel technology, however, chose to ignore those procedures, and actively attempted to alter history to suit their own ends. These factions were opposed by temporal agents in the 31st century, in a conflict known as the Temporal Cold War. (ENT: "Cold Front", "Shockwave", "Storm Front", "Storm Front, Part II")

Temporal Monitoring

Time travel is fraught with peril and potentially could destroy the Federation or even the entire Alpha Quadrant. This is so perilous that time travelers from the future of the Federation patrol space-time to prevent changes to the past.

enter image description here

The Aeon was a 29th century Federation timeship operated by Starfleet. Classified as an Aeon-type timeship, it was capable of traveling through time via generation of temporal rifts. Captain Braxton was the commanding officer of the ship.

  • Despite the Federations rules to the contrary, it was often shown throughout the series franchise, time travel did happen, accidentally, on purpose and on many occasions with malice and forethought (particularly through the Star Trek: Enterprise series). So much so, travelers from the future considered Captain Kirk a particular menace to the Federation timeline.

  • As the franchise aged, greater thought was given to the dangers of time travel which eventually led to the idea of the complexities of time. The Voyager episodes: Year of Hell demonstrate this well; a member of the Krenim Imperium attempts to control versions of the past in order to restore a particular element. While they were able to perform the 'temporal incursions' they were unable to completely restore the past they were specifically seeking.

  • Despite the ban on temporal travel, the Federation has many trips through time, with the majority of them able to restore the timeline to some semblance of order. This does not always mean they were successful in altering the past. REF: Episodes of Time Travel in Star Trek

  • Yet another example - the TAS episode "Yesteryear". Somehow, Spock's timeline is changed while he and Kirk travel through the Guardian to explore Orion's past, and Spock must travel back to his childhood to repair it. However, the repair isn't 100% seamless; minor events are changed. Poor I-Chaya.
    – John Bode
    Commented Dec 11, 2014 at 22:58
  • 1
    It's a little confusing that you have a picture of Relativity directly above a quote regarding Aeon. Commented Jan 22, 2015 at 13:58

This is a well-known flaw in the series. It was fixed slightly by DS9 with the introduction of the Temporal Prime Directive against time travel and Enterprise established the Temporal Cold War as methods of limiting time travel. The bigger plot hole is not why they don't use time travel more often, but why the combatants in the Temporal Cold War don't keep the instances of time travel that do occur in the various films and series from happening. We see time travel using the slingshot manoeuvre in TOS, including Assignment: Earth, and Tomorrow is Yesterday, but in both instances the timeline is not altered in any way that actually matters.

One must therefore conclude that the Temporal Prime Directive is only violated if time travel actually changes anything, whereas in all these cases bar one - the aforementioned Voyage Home - the time travel event resulted in no appreciable change to the timeline. Other time travel instances, such as that in The City on the Edge of Forever (god that episode is good) take place without using the slingshot manoeuvre, so presumably aren't included. Though, to be fair, Kirk and Spock fixed that timeline anyway.

In Star Trek IV, the Federation was probably willing to cut Kirk some slack since he saved Earth from destruction, and he was always shown to never care much for the rules anyway. The combatants of the Temporal Cold War included the Federation, so they likely covered their own backsides there as well. Worf saving Dax doesn't really qualify.

Then there's the simple reason that the effects of time travel are incredibly hard to predict. When McCoy saved a woman's life in the 1930s, that woman, a positive role model and all around great person, led the US into a pacifist philosophy that resulted in a Nazi victory in WWII. One crazy Suliban killing Lenin in 1916 was enough to let Nazi Germany invade the Continental United States. If you're going to travel through time, you want to make damn sure that the situation warrants such an extreme act.


There are a few points to be made with the Enterprise Crew's mission during Star Trek IV: The Voyage Home

-The use of time travel was not authorized by Starfleet or the UFP, it was essentially a "rogue" mission

-The objectives of the mission did not alter history or change the timeline in any significant way. The crew simply had to retrieve a whale (but ended up with two) since whales are extinct in the 23rd Century. There are very few major Federation-wide problems that involve needing something that no longer exists.

-It can be further argued that the Enterprise crew was "lucky" in that none of their seemingly innocuous actions damaged the timeline in any way. There was no way they could have known that removing Dr. Gillian Taylor from her home era wouldn't have any harmful impact on the timeline.

I bring up these points to show the difference between this use of time travel versus using time travel to save Jadzia Dax

  • Actually my point is: why aren't there more "rogue" missions like that one? There are quite a number of Star Trek characters (including Starfleet officers) that are unwilling to follow any rule. Dr. Bashir breaks and bends the rules when he pleases, and even Sisko pays Garak to forge a fake Cardassian memory bank. It's pretty clear that if time travel technology is at hand, somebody would just say "to hell with Starfleet orders" and use it. I believe they should have made time travel harder for the ST IV crew. I'm not convinced by the "regulations" thing: available = used by someone.
    – gd1
    Commented Dec 12, 2014 at 8:03
  • 2
    Moreover, that mission DID alter the timeline a hell of a lot. Earth is the head of Federation and Starfleet. I believe that having it destroyed by a giant "screaming" rod would help a few other races in the quadrant. Moreover, Earth deserved to be destroyed as we had killed the whales centuries before: Kirk messed with the timeline to save Federation's arse.
    – gd1
    Commented Dec 12, 2014 at 8:09

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