To assume that anything different from your preconceptions is automatically ridiculous is to close your mind to learning new things.
There are several time travel events in Trek that obviously change the future, such as the Temporal Cold War, First Contact, Assignment: Earth, Star Trek IV, etc. That "official stance" is just a bone to fans obsessed with creating a single, consistent timeline where such a feat is impossible.
Ahh, but "Assignment: Earth" and ST IV both explicitly stated that their events were part of the history of the Trek universe all along, that nothing was changed. Sometimes time travel involves a causal loop -- the intervention of time travellers is what created their own history in the first place. It's not a "change" from what came before; it's what always happened, but the characters just weren't aware of it until they went back in time and lived through it firsthand.
Indeed, according to real physics, that's the only kind of time travel that
could happen. The physical equations only add up if events are self-consistent, if time travellers cause their own past rather than preventing it. Also, quantum mechanics says that since you're already correlated with the events of your own future, then by going back and interacting with the past, you're correlating that past with your own future and guaranteeing that it's the future that will occur (or at least the only future you'll be able to perceive). The default position should be that time travel doesn't change anything. Time travel that does change things requires more exotic physics, a nonlinear form of quantum mechanics that's strictly hypothetical.
The problem is that most people who talk about time travel "changing" things aren't really asking the deeper question: What is change? Change is the transition from an earlier state to a later state. Change itself requires the passage of time. So how do you define an "earlier" or "later" state for time itself? How can, say, one version of 2063 come later than another version of 2063? They're the same year! In actuality, the two alternate versions of a given time exist simultaneously, by definition. It's only from the time traveler's perspective that one version appears to happen prior to the other, and for them, that creates the illusion that one version of history has been "replaced" by the other. But as far as the universe as a whole is concerned, they're simultaneous. As far as the universe as a whole is concerned, what Captain Kirk did in 1968 happened before what he did in 2267, even if from his subjective point of view it came afterward. So those events were already part of his timeline's past even if it seemed subjectively to him as though they hadn't happened yet.
Eh Assignment: Earth is a cluster fuck of an episode as SFDebris elegantly pointed out in a recent review. If the entire incident was recorded in the Enterprise's computers why didn't they cross reference them at the beginning of the episode when they were interrogating Gary Seven. Like Gary said to them. He belonged in that time, the Enterprise are her crew were what was out of place.
With TVH it's more like the Enterprise crew was taking the piss with their pollution of the timestream and saying F U to the temporal prime directive. Giving away the transparent alluminium equation to somebody they didn't know, taking Gillian back to the future, leaving a klingon disruptor in the hands of the US Navy, McCoy giving that pill to that woman, and removing 2 whales from their timeline. While the whales would eventually go extinct would have little effect in the grand scheme of things. The events the ENT crew changed would alter the course of history. But TVH isn't supposed to be taken seriously. It's supposed to be a fun ride. I don't recall them ever saying it was a predestination paradox.
Paramount's official position that there is only one timeline is just a way to skirt the issue and not get in to the knitty gritty of ALL the temporal alterations caused in Trek. If you tried to keep them all straight you'd go mad. What most people (Including Paramount) judge as one timeline because from the POV of the characters we follow. Things occurred for them had a beginning and an end, with a different episode continuing on next week that follows the precedent of the show when it started.
Unlike comic companies like DC or Marvel which embrace the multiverse theory and run with it. Most notably would be DC's multiverse and the 52.
A short summary of each:
Earth 1: Silver Age comics of the 50's-70's. Pre-Crisis Earth
Earth 2: Golden Age comics from 30's-40's
Earth 3: Where the heroes (Superman, Batman etc) are the villains.
Earth 5: Captain Marvel's universe
Earth 22: Kingdom Come verse. A spin-off of sorts of Earth 2
Earth 31: Frank Miller comics. The Dark Knight Returns, The
Dark Knight Strikes Again, Batman Year One, All Star Batman and Robin.
Antimatter universe: Similar to Earth 3
Earth Prime: Where the DC heroes exist only as comic books expect Superboy
Post-Crisis Earth: Blending of several different comicverses in to one continuity back in 1986
Post-Infinite Crisis Earth: The 2006 restoration of the multiverse.
Flashpoint Earth: The Flash changed the past and altered the destiny of Earth's heroes. Emperor Aquaman and Queen Wonder Woman are in a brutal war against one another. There is no superman and Batman is not Bruce but his father Thomas.
New 52: Current DC universe. Restored after the Flash from Flashpoint merged with his past self to prevent him from time traveling.
I'm less savvy on the Marvel multiverse but they do have the traditional universe and the Ultimate universe running side by side for 13 years now.
If you look at Trek and all the time travel episodes where there was no clever restoration of the status quo like in TOS "Tomorrow is YesterdaY" , and not idiotic like TOS "Assignment: Earth. You have to conclude there is more than one timeline and the existence of a multiverse.
TOS TVH: Travel back in time to bring whales to the future because the species is extinct in the 23rd century. Pollution of the 1986 timestream by the ENT crew.
TNG Yesterday's Enterprise: Omission of a ship contribution results in a 20 year war with the Klingons. Restoration of event cancels out the war time from the main character's POV but lingering remnants (Tasha Yar) are folded in to this new reality.
TNG Cause and Effect and Time Arrow: Casualty loops.
TNG Tapestry: "What if" future for Picard
TNG AGT: Alternate timelines converge together to same creation. Cause by Q.
TNG FC Film: Borg time travel to conquer the Federation in the past. They succeed, but the ENT-E follows shortly after and can't fully prevent pollution of the timestream. Restoration of 24th Earth restored.
DS9 Past Tense: Sisko impersonates a historical figure to maintain historical events because self righteous Julian got Gabrielle Bell killed in a knife fight.
DS9 The Visitor: Alternate future. Undone by Jake saving his dad in the past.
DS9 Trials and Tribble-ations: Similar to First Contact. Person uses time travel to rewrite history in their favor. Scheme fails thanks to the Defiant crew, but pollution of the timestream occurred. Not to mention Julian trying to bang his own grandma and make excuses for it. Ick
DS9 Children of Time: Alternate Future for the Defiant crew. Undone by Future Odo out of love for Kira. I always wondered how the Dominion War would've progressed without Sisko and company?
VOY Time and Again: Casualty Loop with Tom and Janeway
VOY Future's End: Massive Pollution of the timestream by a 29th century Temporal Starfleet idiot. Events undone by the destruction of the Aeon ship. While the future VOY episode Relativity would take the piss with the conclusion of this episode.
VOY Before and After: Alternate Future of Kes. Something's like the Krenim and the Year of Hell do happen, but Kes/Tom, Janeway and B'Elanna dying and the addition of 7 of 9 never happening. Yeah...
Year of Hell: Many alternate timelines coming in and out of phase thanks to the Krenim ship and Voyager's temporal shielding. Time meddling undone when the cause of the distrotions was destroyed by Janeway McClane.
VOY Timeless: Similar to TVH, FC, Trials and Tribble-ations. Guy uses time travel to supplant what exists because it offends him and rewrites history in his favor. Why did Chakotay go along with this plan again? He had a hot woman and was getting laid. Why did his woman HELP him break them up? grrrr
VOY Relativity: Taking the piss every which way imaginable. Insertion of a person in places they didn't exist before (7 on VOY at Drydock), retconning reasons Janeway wanted Tom Paris on her mission, retconning the Doctor's statement of when he was first and visiably shown activated, retconning what Capt Braxton's memories of Future's End, and a whole list of other things I can't think of at the moment.
VOY Fury: Similar to TVH, FC, Trials and Tribble-ations, and Timeless, Kes kills B'Elanna and uses the warpcore to travel back in time to destroy VOY in season 1. Crisis averted but Janeway and Tuvok have limited secret knowledge of future events. So when Kes shows up again to destroy VOY there is a plan to stop her. What happened to the timeline where B'Elanna died? Did it keep going or just disappear?
VOY Endgame: Similar to TVH, FC, Trials and Tribble-ations, Timeless, and Fury. Admrial Janeway uses time travel to rewrite the past in her favor. Gives technology and secret knowledge of the future to the VOY crew of season 7. Does the timeline Adm Janeway left still exist or did it become rewritten by her actions in the past?
ENT Shockwave: Similar to TVH, FC, Trials and Tribble-ations, Timeless, Fury, and Endgame.The Suliban and Future Guy succeed in conquering the future by preventing NX-01 mission in the past. Timeline restored to normal thanks to Daniels and Archer.
ENT The Expanse: The Xindi attack Earth out of fear of their own extermination. Knowledge and technology given to them by the Sphere Builders who have secret knowledge that in the 26th century the Federation and the Xindi will be allies in a war the Sphere Builders will be losing. Future Guy and the Suliban give Archer secret knowledge that the Xindi are being supported by another TCW faction who like himself is trying to rewrite history in their of favor. Opens the door that that like to TVH, FC, Trials and Tribble-ations, Timeless, Fury, Endgame and Shockwave. The Temporal Cold War is a bunch of people from the future all trying to rewrite history in their own image to benefit them in their respective timelines. Future Guy in the 28th century, Temporal Starfleet and Daniels in the 31st Century, the Sphere Builders from the 26th century and the Na'kuhl of the 29th century.
ENT Storm Front: Na'kuhl uses time travel to escape to 1944 Earth. Use a temporal conduit to destroy Daniels 31st century TCW faction. NX-01 arrive in the same span of time of 1944 that the Na'kuhl arrived to thanks to assitance from Daniels, and prevent the Na'kuhl from turning the TCW in to a hot war and ends the temporal conflicts.
Star Trek 2009: Red matter blackhole transports Nero to 2233 where he pollutes the timestream with his actios and exposure of 2387 technology to the past Federation. Further pollution caused by destroying Vulcan and fleets of Klingon and Federation ships. In a sense this is similar to Yesterday's Enterprise, where one event in history radically changes the entire course and destiny of our characters. What we don't see is any attempt to restore the status quo of the timeline before Nero's incursion. Also does it not bother anyone else that Chekov was born in 2245 in the prime universe by in 2241 in the JJverse? Is NuChekov possibly Piotr in the JJverse? Idk anyway things are different in the JJverse.
After analyzing all that the only conclusion is that there is a multiverse in the Trek universe. Like I said Paramount has not investment in saying there are many multiple timeline out there. As you can see things can get very confusing. My final point is the compound effect. Seen most clear in the TNG Episode Parallels.
Here the existence of a multiverse is shown to be canon. Briefly look at the 3 Riker's in the episode. We have the Riker we follow on the show every week serving under Picard. We have a Capt Riker who took over after saving Earth but failing to save Picard in BOBW. Lastly we have the grizzly and beared Capt Riker who failed to both save Earth and Picard. This compounds the notion of a multiverse not just based on happenstance but by decision. Somewhere along the lines with those other 2 Riker's things happened differently. Maybe someone made a mistake, said yes instead of no or turned right instead of left. It's compounded worse when you think that you can have a potentially infinite number of parallel Earths this way.
Quote from Owlman from DC's Crisis on Two Earth's
"Welcome to Earth Prime. Before there was thought, there was this place. One Earth. With a single history. But with the coming of man, came the illusion of free will. And with that illusion, came chaos. With every choice we make, we literally create a world. History branches in two, creating one Earth where we made the choice, and a second where we didn't. That's the secret of the universe, you know. Billions of people, making billions of choices, creating infinite Earths. Some so similar to each other that you could spend a lifetime searching for any distinction. Others so radically different, they defy comprehension."
Also with how frequent and random time anomalies happen (see VOY) you have to wonder, How many other Romulan, Klingon, Borg, Kazon, Dominion or just random aliens are falling through the cracks of reality and changing history because time anomalies happen on a whim in Trek?
OH God it's enough to give an asprin a headache.
