With the slingshot theory around the sun, any spaceship with warp speed 8 can travel backward or foward in time.

So, ok, it's broken and it's what happens when writers have no clue to end an episode, but it's canon now... so why has it never been used after?

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    Are you asking why it was never used in-universe, or why the writers never used the idea again?
    – DavidW
    Sep 22, 2020 at 20:05
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    @DavidW - that is a good clarification question on the original question, but, since it was used in-universe, and the writers did use it again, it becomes less important to answer...
    – Basya
    Sep 22, 2020 at 20:14
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    “why has it never been used after” — er... Sep 22, 2020 at 20:32
  • Sorry, my bad. I began Star Trek with TNG, DS9, VOY, ENT, DIS, PIC, Lower Decks and I'm finishing with TOS. So I've yet 60 TOS' episodes to look, their 6' movies and the 22 from the Animated Series :\ With 669 episodes and 4 TNG movies already seen, I wrongly assumed it was never used again.
    – GBMan
    Sep 22, 2020 at 21:08
  • voting to re-open. It's not opinion-based, merely based on a lack of information (which is what the site is for :). At worst, it merits possible downvotes, but not closing (imo)
    – NKCampbell
    Sep 23, 2020 at 18:23

1 Answer 1


Star Trek TOS "Assignment Earth":

Captain's log. Using the lightspeed breakaway factor, the Enterprise has moved back through time to the twentieth 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.


Star trek IV: The Voyage Home:

SPOCK: There is one possibility, but I cannot guarantee its success. We could attempt to find some humpback whales.

McCOY: You just said there aren't any, except on Earth of the past.

SPOCK: Yes Doctor, that's exactly what I said.

McCOY: Well, in that case... Now wait just a damn minute!

KIRK: Spock, start your computations for time warp. ...Bones, you come with me.


McCOY: Are you really going to try this time travel in this rust bucket?

KIRK: We've done it before.

McCOY: Sure, slingshot around the sun. If you pick up enough speed you're in time warp. If you don't, you fry.

KIRK: Would you prefer to do nothing?

McCOY: I'd prefer a dose of common sense. You are proposing to head backwards in time, find humpback whales, then bring them forward in time, drop them off, and hope to hell they tell this Probe what to do with itself!

KIRK: That's the general idea.

McCOY: That's crazy!

KIRK: You have a better idea, now's the time.


And a different time travel process was accidentially discovered at the end of "The Naked Time":

KIRK: Checked elapsed time, Mister Sulu.

SULU: My chronometer's running backwards, sir.

KIRK: Time warp. We're going backward in time. Helm, begin reversing power. Slowly.

SULU: Helm answering, sir. Power reversing.

SPOCK: We're back to normal time, Captain.


KIRK: The time warp. What did it do to us?

SPOCK: We've regressed in time seventy one hours. It is now three days ago, Captain. We have three days to live over again.

KIRK: Not those last three days.

SPOCK: This does open some intriguing prospects, Captain. Since the formula worked, we can go back in time, to any planet, any era.

KIRK: We may risk it someday, Mister Spock. Resume course to our next destination, Mister Sulu.


"Assignment Earth" is unclear whether they use the method from "The Naked Time" or the method from "Tomorrow is Yesterday", but Star trek IV: The Voyage Home clearly used the method from "Tomorrow is Yesterday".

  • Additional time travel method #1: the Guardian in "City on the Edge of Forever" (reused in TAS episode "Yesteryear"). Additional time travel method #2: the library in "All Our Yesterdays". Sep 23, 2020 at 20:09
  • Assignment Earth definitely uses the method discovered in the Naked time. However as a lifelong fan of star trek i never considered the effect in Tomorrow is Yesterday to be different. Time travel happens at warp speed in a strong gravitational field. A black star (likely black hole) will presumably work better than a sun or collapsing planet. Only potential difference is Tomorrow is Yesterday implies some distance jump as well since we never see the Enterprise at Earth in its own time so it's unlikely that's where the black star was passing when the accident happened. Sep 24, 2020 at 1:11
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    @Ross Presser The question asks about using the Enterprise as a time machine, not about individual persons stepping though a portal to the past. And the library in "All Our Yesterdays" was destroyed along with the entire planet minutes after they returned to the ship. The only way to use the Atavachron as a time machine would be to use the Enterprise as a time machine to return to when the Atavachron was in use. Sep 24, 2020 at 16:25

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