When McCoy altered the past, the entire Federation vanished. Meaning that this was a very critical event.

Temporal Agents were supposed to keep eyes on timeline. Whenever timeline was altered and Temporal Agents failed to prevent it, it was due to advanced tech of other factions in Temporal Cold War. 31st century tech could escape detection of Temporal Agents, but not 23rd century tech. In fact, McCoy didn't even try to escape detection.

Why didn't Temporal Agents stop McCoy?

When Temporal Agents failed to prevent timeline change, they at least tried to undo it. But, in McCoy's case, they never even appeared to undo changes. Why?

  • Temporal agents also appeared in Voyager.
    – Xantec
    Commented May 31, 2012 at 16:43
  • My mistake, memory-alpha says that Braxton was a Starfleet captain, not a temporal agent. Not sure if they can be one and the same, so it may or may not apply to Voyager as well.
    – Xantec
    Commented May 31, 2012 at 17:00
  • @Xantec: I did not follow ENT, but if I remember correctly, Braxton was also tasked to fix the timeline and to pursue and arrest anyone who tries to mess with it. If I recall correctly, his first officer stated that they were dedicated to keep the timeline in place.
    – Bobby
    Commented Jun 7, 2012 at 20:50
  • I think we have asked similar questions like this before and we can ask this question about EVERY major event in Star Trek. Honestly, I think we shouldn't encourage the creation of questions of this nature because they are completely speculative. We can't truly know why or why NOT, temporal policing works or doesn't. Commented Nov 6, 2014 at 19:48
  • @Xantec: "My mistake, memory-alpha says that Braxton was a Starfleet captain, not a temporal agent" That's funny, I thought he was a Boston homicide detective. (ducks and runs) Maybe he's on a protracted assignment, or it's an ancestor... ;-) Commented Aug 22, 2015 at 14:19

7 Answers 7


If it was possible to prevent temporal incursions (mistakes, errors, etc) before they happened then the temporal cold war in Enterprise wouldn't have happened. Since the cold war did happen (and other temporal mishaps occurred in TOS, TNG, DSN without any agents appearing) we can infer that it isn't possible to fix issues before the take place.

As such, we can only assume that McCoy was not stopped by any Temporal Agents (in the 20th or 23rd centuries) because once he changed the timeline they didn't exist any more, and when they were restored the timeline was already fixed so they did not need to interfere.

  • Temporal Incursions happened because other factions of Temporal Cold War had same level of tech with which they could escape detection on time (I've mentioned that in question)...
    – user931
    Commented May 31, 2012 at 20:06
  • I don't know how they kept eye on timeline, but if Spock (having 23rd century knowledge) was able to calculate possible outcomes, why couldn't Temporal Agents? Temporal Agents could calculate possible outcomes more efficiently (After McCoy entered 20th century)..
    – user931
    Commented May 31, 2012 at 20:13
  • @SachinShekhar It is (relatively) easy to calculate possible outcomes, but knowing which one will happen is less precise. That was a major premise in the Year of Hell.
    – Xantec
    Commented May 31, 2012 at 20:17
  • @SachinShekhar The agents could not do anything after McCoy entered the 20th century because they likely no longer existed (Starfleet no longer existed). And once McCoy was recovered and the timeline restored there was no reason to go back and stop McCoy from entering the portal as everything was already fixed (my second paragraph).
    – Xantec
    Commented May 31, 2012 at 20:20
  • In case of Year of Hell, I'd say he wasn't in this business for long. You can't apply same logic on Temporal Agents.. They were a dedicated team on this and also a faction of Temporal Cold War. They would have prevented incursions more than thousands times. Don't forget, they saved Suliban race after incursions. They only fails when advanced tech is involved from other factions..
    – user931
    Commented Jun 1, 2012 at 0:16

I didn't watch Enterprise very much, so I don't know too much about the Temporal Cold War.

Given its power and personality, it seems likely that the Guardian of Forever could and would prevent any tampering in its own timeline changes by any other machine or person.

The Guardian of Forever is very powerful, not only in terms of MegaWatts (the waves of temporal distortion it creates toss the Enterprise around like it's nothing), but also in that it is aware of multiple (infinite?) alternate timelines and apparently knows how to access them. There's a novel that states - or at least strongly implies - that the Guardian is aware of alternate timelines created by other time machines, not just its "own."

In addition to being powerful, the Guardian is also intelligent, it represents technology far beyond anything the Federation possesses, and it has a big, big ego (e.g. when it tells Spock how much more advanced it is than their technology).

  • What do you mean by powerful?? All time machines are powerful.
    – user931
    Commented May 31, 2012 at 17:42
  • Temporal Agents could stop McCoy before he entered Guardian of Forever.. It renders your answer meaningless..
    – user931
    Commented May 31, 2012 at 17:44
  • 1
    IF we take novels into account, en.wikipedia.org/wiki/Star_Trek:_The_Q_Continuum shows that the Guardian is capable of doing things even Q could not do on his own, although Q had to force the Guardian to let 0 through. So I guess it is save to say that it is a bit more powerful than your average time machine, it is more or less sentient (bit of a TARDIS, really, just stationary - maybe a TARDIS and an Iconian portal had a fling...:P)
    – BMWurm
    Commented Jul 28, 2014 at 10:51

The simplest answer would be that the crew of the Enterprise and the Guardian of Forever had matters well enough in hand that intervention was unnecessary. The timeline interference was accidental, and, sad to say, easy to fix. Temporal agents might have shown up if Kirk and Spock didn't figure out that Edith Keeler had to die. But they figured it out, so no need for temporal agents.

  • Temporal agents might have shown up if Kirk and Spock didn't figure out that Edith Keeler had to die. ~> Temporal Agents weren't in existence at that point of time. Future of Federation already went out of existence.
    – user931
    Commented Jun 23, 2013 at 3:32
  • That works, too
    – Amanda
    Commented Jul 1, 2013 at 1:34

Powerful is a relative term. A destroyer class Navy vessel is powerful compared to lighter craft, but a cruiser & battleship are even more so. Like each classification of navy vessel has its strength & weaknesses, along with individual applications; so too do time travel devices/machines in Sci-Fi. This can be seen in Star Trek, as some devices are small & worn on one's person, while others transport small or even large vessels. Some time travel devices also move their operators through space as well as time. Lets also not forget, the slingshot time travel method used in the movies & TV series. The Guardian of Forever, is much more than a time traveling device, it is sentient. I would not be surprised to find that, if the Gurdian of Forever is comprised of organic & inorganic materials. The episode of STOS, where where Gary 7 travels to alter the NASA rocket launch, I believe he said he also said, he was telaported from another galaxy, or something to that effect. So, it is vary possible that, the Guardian of Forever is more powerful than other time travel devices.


My guess is, most other means of altering the timeline are a bit crude, and always leave traces - 'time ripples', scattered variations of the 'quantum signature', or some such - that the Temporal Protection Agency can detect and use to track back to the source of the alteration. By contrast, the Guardian of Forever, being far more advanced, is able to alter history on a much more fundamental level which leaves none of the expected traces.


Temporal Prime Directive would require that the agents would work very hard not to interfere with events, and to not leave any confusing evidence of their interference behind. It would be probable that at least one agent observed and logged the time travel. Similar to how things like cloaked research labs are used to observe species without violating the Prime Directive, it is easy to presume that temporal Starfleet agents would have multiple precautions against detection and/or accidental interference. That Kirk's logs of these specific events make no log of temporal agent activities seems to indicate that any such activity was successful.

  • But, we've seen Temporal Agents violating Temporal Prime Directive. Plus, who would care if your existence itself is threatened?
    – user931
    Commented Nov 6, 2014 at 23:46
  • Sure, but we're also given many reasons to suspect that the Temporal Agents that violated the Temporal Prime Directive were not exactly the best that Starfleet has to offer and that violations of the Temporal Prime Directive were simply expedient means to an end. I still posit that successful Temporal Agents would work very hard to be invisible to history.
    – WorldMaker
    Commented Nov 7, 2014 at 15:41

Once McCoy had entered the portal, the present was instantly changed. The Enterprise was gone. Presumably, so was the Federation. As the Temporal Protection Agency was part of the Federation, the temporal agents would not exist to fix the timeline. And even if they did, they would be temporal agents from the new timeline, and would want to leave things as they are, lest they jeopardize their own existence. Only Kirk's away team was shielded from the changes to the timeline, probably due to their proximity to the Guardian.

Once Kirk and Spock had adjusted the timeline back to its original course, there was no need for the agents to get involved, except to maybe clean up the mess with the wino and the phaser, but the Enterprise crew would have no knowledge of that.

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