There was time travel involved because the Enterprise C passed through the rift. How else would it get to the future.
Well, going to the future is not really time travel. We are traveling into the future right now. Only by going to the past and changing events that already happened do you cause a paradox.
When Khan was frozen in the 20th century and woke up in the 23rd century, that wasn't time travel, even though from his point of view, he instantly traveled 200 years into the future.
Yes, the rift caused the Enterprise-C to instantly appear 20 years in the future (i.e., travel through time), but that did not change history, because the creation of the rift, and the disappearance of the Enterprise-C into it, was the natural and inevitable result of the photon torpedo explosions during the fight with the Romulans.
If it had not then events would have remained the same. How can a ship that is outside of it's own time be in any way the original timeline?
Well, the ship and the people on it are always within their own internal timeline (in the "Donnie Darko" sense of personal timelines). Like if you get on a train in Paris and travel to Rome, you are in a different country when you get off the train, but you were always on the same train, and Rome did not
replace Paris; you just traveled from one to the other. Paris still exists, even though you left it and may never go back. There are other people in Paris, and to them, you got on a train and never returned. But to them, Paris is still there.
A timeline is a physical place, a region of space-time, just like Paris and Rome are places. Time travel is like getting on a train and going from one place to another. If both places are in the same time period, then instantaneous travel between them is teleportation. If one place is in another time period, then instantaneous travel between them is time travel.
But even with time travel, unless you change something in the past, you have not left your own timeline (just like traveling from Paris to Rome, you have not left Europe). Going into the future, like we do every second of the day, or even jumping 20 years into the future, does not change historical events, so travel into the future is always into the same timeline.
(Again, I am defining "timeline" as a point of divergence in historical events. Maybe you would call it an "alternate reality" or a "parallel universe," but I am using the terms interchangeably -- like the timeline diagram Doc Brown drew on the black board in "Back to the Future II").
But back to "Yesterday's Enterprise." In all timelines (including the original timeline, i.e., the normal course of events without intervention from the future), The Enterprise-C fought the Romulans at the Klingon outpost. A spread of photon torpedoes created a rift. The Enterprise-C disappeared into the rift. That is an unbroken chain of causality, and happened the same way in all timelines. None of those events was caused by a paradox.
Following the disappearance of the Enterprise-C into the rift, the only logical line of causality is that the Klingons went to war with the Federation 20 years later, at which time the Enterprise-C emerged from the rift. Picard and Yar were faced with a choice. They could keep the Enterprise-C in the future to help fight the Klingon war, thus creating a predestination paradox like in "Time's Arrow." The Enterprise-C would not go back in time, thus keeping the timeline unchanged. (Like getting on a train in Paris, following a circular track, and you're still in Paris when you get off.) Then there would be only one timeline. (It would be like going to the Guardian of Forever, but not stepping through it. To change the past, someone must first decide to change the past, then act on that decision.)
So, Picard and Yar made the decision to change the past, and they acted on that decision. Yar went back in time on the Enterprise-C, and changed the past. If she had simply changed her own timeline (i.e., her own past) then in that new timeline, she would have been killed by a tar monster two years earlier, and she would cease to exist. No one on the Enterprise-C would have any recollection of the "Lt. Yar" timeline or the war with the Klingons, if, as you say, they REPLACED the timeline. (Like if you get on the train in Paris, the train doesn't move, and when you get off the train, Paris has been REPLACED by Rome, and Paris never existed.)
You could very well make this argument for one timeline "erasing" another timeline from existence, if "Yesterday's Enterprise" was the only TNG episode you ever watched. (It would be the same as the "Back to the Future" movies, where characters "erase" themselves by changing their own past.) However, since we know that Yar did not cease to exist (and in fact lived in the new timeline to have a daughter) then obviously the molecules of her body, and those forming memories of her life in her brain, must have come from another universe, or timeline or reality.
A basic tenet of physics is that matter cannot be created or destroyed. The amount of matter/energy in the universe is constant. When Yar popped out of the future on the Enterprise-C, she added about 130 pounds of mass to the universe. The atoms in her body, and the memory molecules in her brain, came from all the food and air she had consumed in her lifetime. And those food and air atoms came from her original timeline, or universe (which lost about 130 pounds of mass at the same time "our" timeline gained them, so conservation of matter is preserved across the "multiverse" of all timelines).
We saw at the very beginning of the episode the Enterprise C pass through the rift, when it did then we actually see the timeline change from what it was to an altered future. Which is a direct result of the Ship been displaced in time.
But the people in the "Lt. Worf" timeline never saw the Enterprise-C. They never had to decide whether to send it back in time or not. Nothing they did (or didn't do) changed their own (or anyone else's) past.
It was their own past that was altered by Lt. Yar from the original timeline, as we saw in future episodes when Sela appeared. Half of Sela's DNA was formed by molecules from her mother's body, which came from a real timeline that really existed, since matter and people and memories of that timeline still persist in the "Lt. Worf" timeline. The original timeline was not "replaced," people just traveled from it to another timeline. To the people in each, their own timeline is the "real" one.
The TNG timeline is not alternate because it was only changed in one episode when the Enterprise C passed through the rift.
If this was an alternate timeline then it would have stayed with the Warship Enterprise. You could just switch to an alternate timeline in any episode then. What is actually shown is the timeline changing not switching to a new different one.
That's exactly the point I was trying to make. The timeline you see in any TNG episode is the one being filmed by the cameras. It is the writers and directors who decide which timeline you are seeing, because it is the timeline they choose to write stories about that week. The "real" timeline, as you think of it, is what you watch every week on your television screen.
But, think about the "Enterprise" two-part episode, "In a Mirror, Darkly," which took place entirely in the Mirror Universe, including the "Terran Empire" opening credits. That is an example of the producers deciding which "real" universe you are seeing on your screen, because for two episodes, the cameras stayed in the Mirror Universe and never left. For the characters in that episode, the universe that the U.S.S.
Defiant came from was an "alternate reality." It all depends on the point of view of the characters that the cameras are following.
We know from the stardates in "In a Mirror, Darkly" and "Demons" that at the same time Mirror-Archer was trying to crush the alien uprising in the Mirror Universe, using the U.S.S. Defiant from the "alternate" reality, that on that same date, Captain Archer of that "alternate" reality was on his way to a peace conference to unite aliens from around the quadrant.
They both happened, in two alternate realities, at the same time. And they were both "real" at the time you were watching them, because cameras were recording the events in both realities.
It's the same thing with "Yesterday's Enterprise." Obviously, there is only one camera showing one timeline on your screen at any given time.
(Imagine if there had been a split-screen showing all the events in the "Lt. Yar" timeline alongside the first 60 "TNG" episodes before "Yesterday's Enterprise," or even during the entire "Yesterday's Enterprise" episode itself. You would have seen two unrelated universes that both happened to have an Enterprise-D, but the characters would have been doing completely different things, just like if every episode had a split-screen showing what's happening right now in the Mirror Universe.)
Everything you saw in "Yesterday's Enterprise," or "Endgame," or "Star Trek Generations" was the point-of-view of the camera crew following one character from one timeline to another. That camera's point-of-view manipulates you, the viewer, into believing that the last timeline the camera shows is the "real" or "only" timeline, because the cameras will continue to film in that same timeline the next week.
In "Yesterday's Enterprise," you saw an editing cut from the camera in the "Lt. Worf" timeline to the camera in the "Lt. Yar" timeline at the same moment. (Like between the end of "In a Mirror, Darkly, Part II" and "Demons," the cameras switched from showing the Mirror Universe to what was happening in "our" universe at the same moment. But that change in camera points-of-view does not mean that "our" universe "replaced" the Mirror Universe, just because one scene was filmed after the other.
In fact again there is nothing to prove this. Admiral Janeway changed the timeline and Voyager never stayed in the Delta Quadrant another 20 years. One timeline, changed.
No, in the first half of "Endgame," we saw the Voyager get to Earth 20 years later. That was not a paradox or a dream; that was the actual continuation of the "Voyager" TV series. Janeway really did use a Klingon time machine to go into the past, and alter past events. She really did give the past Voyager new shields and weapons, and she shared her memories of the next 20 years with the crew. She was really there, alive, in the new timeline. The atoms of her body were not "replaced" (like the "Back to the Future" characters fading away after changing their own past).
Admiral Janeway was a physically real person, from a physically real universe. The only reason that you're arguing that Admiral Janeway's timeline is not "real" is that the cameras followed her to the other timeline. (Again, it's like a camera crew following Janeway on a train ride from Paris to Rome. Would you argue that Paris no longer exists, solely because there are no cameras there to record it?)
What if the camera point-of-view remained in the future timeline at the beginning of "Endgame"? After the Voyager spent 20 years in the Delta Quadrant, Admiral Janeway would steal a shuttle and vanish into some other timeline, and never be heard from again. But everyone else would continue to go about their lives. Since the cameras don't follow Janeway into the past, you have no bias that the past timeline she went to is any more "real" than the future where the cameras stayed.
And if the cameras in "Star Trek Generations" had followed the point-of-view of the Enterprise-D (instead of following Picard into the Nexus), you would have seen the sun explode, everyone on the Enterprise-D would be dead, the planet would explode, and you'd be watching 30 minutes of radioactive debris floating around in space where a star system used to be. (Obviously, the point of view of Picard was far more interesting, which is why the writers and producers and director sent the camera crew into the new timeline along with him. What you think of as the "real" or "only" timeline, is just the more interesting timeline that the filmmakers choose to show you.)
No, you're just basing this on a theory that every time travel event creates a new timeline. It's been established a number of times that it's the same timeline that gets changed. Not an alternate one.
No, almost every "Star Trek" episode involving time travel is written by someone different, from Harlan Ellison to Brannon Braga to Roberto Orci and Alex Kurtzman, and every writer has his own idea of what time travel means (as you and I do).
We can both cite counter-examples all day to prove our points, because there are a dozen different time travel theories depicted in a dozen different episodes. In that sense, "Star Trek" is more like "The Twilight Zone" than "Star Wars" or "Babylon 5," in that it is an anthology of hundreds of writers inventing their own science fiction stories, which just happen to have the same characters every week.
Yes, some episodes show a single timeline, such as a causality loop, where they go back in time and nothing changes (as in "Time's Arrow). That is one theory of time travel, which is depicted in such sci-fi films as "Primer" and the recent Spanish film "Timecrimes" ("Los Cronocrimines").
Then there are episodes where the characters intentionally go to the past to change something, creating an entirely new timeline that is different from the one they remember, including "Yesterday's Enterprise," "Timeless," "Endgame," "The Visitor," "Star Trek Generations," and "Time Squared."
Then there are episodes where someone goes back to change the past, but then someone else follows them to "fix" the past, such as "Star Trek: First Contact," "Future's End," "The City on the Edge of Forever," and "Star Trek XI."
And then there are episodes depicting alternate realities (or parallel universes, or divergent timelines) where no time travel or paradoxes are involved, such as all the "Mirror Universe" episodes, or TNG's "Parallels," where multiple realities physically exist side-by-side, and all are equally real.
We see Janeway and crew return Home. That means that Admiral Janeway that we saw in this episode will never have existed because she changed the timeline. We don't see either of them together again after Janeway and the crew get back home. If we did then I'd agree with you that she is from an alternate timeline but that Admiral Janeway will never be.
Well here you're just factually wrong. Admiral Janeway was physically real. She really talked and interacted with the crew. She gave them real information and technology from her timeline. She died fighting the Borg, which is the only reason Admiral Janeway was not seen at the end of the episode. The atoms of her body still exist in this timeline, and the Voyager crew still remembers seeing and hearing her. (It's just that the producers chose for the camera to follow the living crew members rather than continuing to film Admiral Janeway's dead body for the last five minutes.)
You're trying to make it sound like Admiral Janeway (and her entire timeline) just faded away like the photograph of Marty in "Back to the Future," but that's not at all how time travel works in most "Star Trek" episodes. Just like Lt. Yar and Sela after "Yesterday's Enterprise," Admiral Janeway continued to exist after changing the past, because she did not "erase" her own past, she was physically in a new timeline, where there was physically a second version of herself at the atomic level, both living at the same time. Lt. Yar and Admiral Janeway and Captain Kirk all died because they were physically killed, not because they were erased from history.
Time travelers do not "merge," or "fade away," or "erase themselves" in most "Star Trek" episodes. There are examples, though, such as "Time Squared" and "We'll Always Have Paris," where we do see time travelers fade away, or merge with their past or future selves, rather than continuing to exist in new timelines. So in those specific episodes, you are absolutely right: they depict one timeline absorbing changes and erasing the time travelers from alternate timelines.
But again, there are dozens of different time travel episodes, and very few of them follow the "logic" of those two episodes. You can't use specific time travel theories shown in specific episodes as evidence that there is some grand unified time travel theory in all 750 episodes of "Star Trek." Like most other things in "Star Trek," the producers just make it up as they go along.
Look at the episode "Twilight" in Star Trek Enterprise. When the parasites is Archer's brain are destroyed they are removed from all scans of his brain taken in that timeline. Therefore it can't be an alternate timeline because in the very same timeline we see that the scan of years before has changed due to the parasites been eliminated. Can you explain how that is not the same timeline? An alternate timeline would not show this.
It's been a while since I saw "Twilight," but I think it's an example of a fourth type of paradox: "Anti-time," which was also the basis of the paradox in "All Good Things ..."
Anti-time paradoxes somehow use reverse causality, where future events cause past events in the same timeline, yet the characters still remember the past events that were changed.
How can characters logically remember something that is going backwards in time? If computer records of an event are erased from the past (like Marty's photo in "Back to the Future") how could people have memories of those events? (The events either happened or they didn't. Logically, you wouldn't have people remembering what never existed.)
I think anti-time paradox episodes like "Twilight" and "All Good Things ..." are evidence that the writers just like making up paradoxes with no logical or scientific basis. (You can just imagine Stephen Hawking sighing and rolling his eyes as he watches those episodes.)
