This has been driving me nuts. For most of Star Trek’s history, the Prime timeline holds together no matter what happens to it. Kirk jumps around, Picard gets stuck in time loops, Janeway rewrites entire centuries, and the universe just snaps back like it never happened. Time feels elastic but stable.
Then Nero falls through a black hole, and everything falls apart. The Kelvin event doesn’t just make a new branch going forward. The ripple hits both directions. It rewrites history that should already be set. Starfleet looks different. Vulcan feels different. Even the technology and design philosophy seem changed long before Nero was ever born. That sounds less like a branch and more like time itself got rewritten.
Once that happens, the Temporal Prime Directive starts to fall apart. It only works if time moves in one direction. You can “fix” something when there’s a clear before and after. But if the ripple goes both ways, there is no original timeline to go back to. The moment the Kelvin universe forms, the concept of Prime reality stops being a single point.
And that’s before you even touch the Mirror Universe, which is not a branch at all. It has been running beside the Prime since the beginning. So now we have at least three full continuums: Prime, Mirror, and Kelvin. But that’s not the end of it. The Star Trek Online timeline exists as an extension of Prime, playing out events after Nemesis and even connecting to the Temporal Cold War. The licensed novels follow yet another line, continuing after Destiny and Coda, where the multiverse literally starts to collapse under the weight of too many versions.
So what is the Federation even supposed to do with the Temporal Prime Directive at this point? Which universe counts as the real one? Do you merge them? Do you pick one and call it Prime? Or do you admit that every version is its own living reality with its own moral weight?
Maybe the point isn’t fixing anything anymore. Maybe the Temporal Prime Directive is just damage control. Once time starts rewriting itself both ways and spawning whole new continuums like STO or the book universe, there’s no putting it back together. The best you can do is keep the pieces from smashing into each other and hope reality doesn’t collapse under the strain.
To be fair, the Kelvin timeline had about 25 years to diverge technologically and aesthetically, considering the USS Kelvin was destroyed in 2233. 25 years is more than enough for the Starfleet design philosophy to completely change - look at the Enterprise C vs the Enterprise D.
The USS Kelvin looks pretty prime - a little fancier because of modern VFX, but not more advanced than the SNW Enterprise. I would chalk down discrepancies to just evolution in production effects; I mean, doesn’t even the NX-01 look more advanced in many ways than the TOS Enterprise? Effects getting anachronistically better in Star Trek is not new, and I don’t think it signifies a “back propagation” of timeline alteration.
Also, I don’t think Kelvin Vulcans are that weird; I think it’s mostly consistent with canon. Spock’s childhood in the film is practically a recap of TAS: Yesteryear, while the Vulcan education system seems consistent with the testing Spock did on himself at the beginning of Star Trek IV. The government and culture feel consistent with most depictions.
Additionally, the idea of infinite multiverses has been canon in Star Trek for a while, heavily suggested with TNG:”Parallels” and outright confirmed in Prodigy and Lower Decks - Wesley even explicitly names the Kelvin timeline as its own parallel universe called “the Narada Incursion” in PRO.
I think the variance in temporal mechanics in the franchise can be chalked up to the different methods in which time travel happens - each method is its own “User Interface” where your actions can affect reality differently. Some of them are more traditional time travel narratives, some are loops, some are parallel universes you can return from, etcetera.
Ultimately, I think the Temporal Prime Directive comes down to what you said; each timeline is its own “world” and it’s just best to leave them alone.
I think the plot of PRO is a perfect example of why the Temporal Prime Directive matters even in less-than-linear mechanics; going to the future can cause the future to alter the past, which causes the past to alter the future again and thus the past in a different way, and so on. Basically, messing with time and realities in any way is a dumpster fire in the making.