I've been belatedly watching "Star Trek: Lower Decks," and in the episode "I, Excretus," the crew participates in personalized, individual drills. Beckett Mariner enters a holopod and sees that the title of her drill is "Mirror Universe Encounter." She responds: "Mirror Universe? This is easy. Yeah, I can pretend to be evil. Ha ha ha ha!"

Now, the canonicity of Lower Decks is debatable (although it's firmly part of my own headcanon), but it got me wondering how well-known the details of the Mirror Universe are within Starfleet, or more broadly, to the Federation (or other starfaring organizations, I guess) at large. Discounting Lower Decks itself of course, where the answer for Starfleet at least is obviously "Quite well known."

Around eight years ago, I rewatched Deep Space Nine, which featured the largest number of Mirror Universe episodes when it originally aired, and the impression I recall from then is that it was known to Starfleet higher-ups like Sisko, as a serious but low-probability threat to be aware of (perhaps like Q), but not to the rank-and-file. Is that accurate? Is there any more definitive evidence from any other media?

  • Related scifi.stackexchange.com/questions/254055/… Commented Jan 6, 2022 at 0:20
  • youtu.be/dJf2ovQtI6w Star Trek Continues fan film that shows the aftermath of the TOS episode on the mirror side Commented Jan 6, 2022 at 0:41
  • No doubts Section 31 knows all about it and may or may not have visited it frequently to gather information on the Empire…….but they don’t exist so….. Commented Jan 6, 2022 at 4:13
  • It was known about by the crew of the USS Discovery, Sarek, and Admiral Cornwell but they decided to suppress all knowledge of the existance of the mirror universe Commented Jan 6, 2022 at 11:28
  • ST:LD is a parody. Why waste your time with it? Watch good Star Trek. Commented Jan 10, 2022 at 15:21

1 Answer 1


In the TNG era it's taught at the academy. (Edit: Taught may be too strong a word - but I'd assume read it at the Academy means the Academy wanted it read for education. Riker said something similar in the Naked Now to explain how he knew about the alcohol water bonding disease. And that only took an 8 hour Google search to track down :-) )

DS9 "Crossover" transcript http://www.chakoteya.net/DS9/443.htm

BASHIR: Learning a new trade. Do you have any idea what happened?

KIRA: Have you ever hear of a Starfleet Captain named James Kirk?

BASHIR: Kirk? Of course. The transporter accident. Read about it at the Academy. So that's where we are.

KIRA: That's where we are.

BASHIR: Is there another me here?

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    Good enough! I'd hoped also for a source on whether those who know of the universe's existence are aware of its "evil opposite" nature, but I suppose that Kirk's story would make that as obvious to in-universe readers as it is to us, the viewers.
    – Sean
    Commented Jan 6, 2022 at 17:06
  • I could've sworn I remembered Sisko saying something about knowledge of the MU being suppressed to prevent people crossing over to contact dead loved ones. Maybe I'm thinking of a different anomaly. Commented Jan 6, 2022 at 18:18
  • @BrianOrtiz I couldn't find anything speed reading though I agree it seems familiar. Maybe it's mostly this: INTENDANT: Well, you see, that's part of the problem. I don't know how to send you back. But, more than that, there is a certain protocol I'm supposed to follow. KIRA: I'm not sure what you mean. INTENDANT: After the first crossover, we were afraid that others might come to interfere in our affairs. It was decided then that if it ever happened again, we would promptly dispose of anyone who appeared from your side. KIRA: I see. Commented Jan 6, 2022 at 20:33

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