But if that's the case, then what happened to the already existing Enterprise E of that timeline? Did they too also end up going back in time but failed in their mission, thus only one Enterprise E existing when they come back?
Praxius:
Yes. The other Enterprise E failed in their mission and didn't make it back to their own time line. So another Enterprise E had filled the gap by returning. This means that the time stream has some type of built in self correcting function (that tries to minimize any type of damage to a particular time line (if possible)). Think of the time line as one giant collection of streams or rivers that are all interconnected. Some are so far apart from one another that they seem almost separate. And other time lines are within it's own river or stream. So, seeing the time stream is all interconnected, it is a possiblility that it might have some self correcting (or healing) functions to it (like a normal body has).
Furthermore, I believe that the time line also protects itself by creating time loops, too (like in Cause and Effect). As an example: in Back to Future or any other time travel movie that seemingly proposes to alter events within their own time line. If I travel back in time and change my own past and start to erase my own existence (like in Back to the Future), then how come the original time line up until the point of the actual time travel incident still exists (which is usually the events we see at the beginning of the film)? Well, my theory on fictional time travel is that whenever you time travel within your own time line, you create a feedback loop or a repeat of time. That is why we are allowed to see the original time line unfold before it is changed (by the time travel incident). I mean, you kind of have to look at time as if it has already happened. We are just looking back at all the alternate possibilities and changes that were made to that time line. And the infinite loop theory helps to suggest that we are allowed to see those changes.
Unless of course your a firm believer in the multi-verse time theory only. In which all time lines simply duplicate and diverge into separate time lines that are different or separate from the original or local time line.
The problem I find with them returning to their current time but a different reality, is that there's a chance that the reality they are entering has an Enterprise that never went back in time, thus two ships, two crews.... as the other Enterprise could have stopped the sphere before it went back in time, or the Borg may never have attacked in the first place.... then suddenly zoop.... hey where'd this ship come from? we got two Enterprises now.
As mentioned before: perhaps under the right circumstances the time line makes the necessary adjustments to guide a traveler to where they need to be.
However, that doesn't mean that things can't go wrong and duplicate Enterprises can't all encounter one another at some point (like in the TNG episode "Parallels").
As I personally see it, in order for it all to make sense, those who go back in time and return to their present with no noticeable changes did exactly what they were supposed to do all along..... otherwise, they came back to the present, altered the past, even so-slightly, and their futures would be different in some noticeable manner..... such as Sisko going back to pose as Gabriel Bell and then his photo being used throughout history..... his future, as proven through the continuing episodes afterwards, that he was always meant to do what he did and that there were no other noticeable changes.
The time loop (Which is a defense mechanism of the time stream) allows the original or previous time line to happen before it is altered. In other words, the time stream loops once as a normal reaction whenever a change is made. So two incidents to the same event can have two different ways of happening (if a change is made).
The real brain kicker is if while Picard and Crew were always meant to go back in time and set this complicated ball in motion.... based on NX-01 Enterprise suddenly being mentioned in the Star Trek Universe..... we're we seeing the very first loop of this timeline that was supposed to always exist and thus, was the timeline we were always viewing through all the other shows an incomplete ghost timeline going through it's first pass?
In other words, if this whole situation was the result of a predestination paradox which is an ever continuing loop over an extended period of time that binds both eras together.... then we saw the very first creation of this timeline through First Contact.
Well, there is a theory in time travel that proposes that there had to be an original time line that had not been altered by time yet.
But to answer your question... yes. Picard and crew were meant to change things in First Contact from the very beginning. However, because the time stream creates one time loop (of the unaltered time line) as a defense mechanism before the change can happen, we see the original or previous time line unaltered before the actual time travel incident takes place.
So...
When we watch...
1. The Original Series & It's Movies
2. Next Generation & Generations
3. Deep Space Nine (Before First Contact)
4. Voyager (Before First Contact)
We are witnessing the first loop (an echo if you will) of the Original Unaltered time line before it is changed in the time travel incident in First Contact.
So...
After First Contact....
We are seeing a re-creation of a different past when we watch...
1. Star Trek Enterprise
And when we watch...
1. Insurrection & Nemesis
2. Deep Space Nine (episodes after First Contact)
3. Voyager (episodes after First Contact)
We are seeing things from the perspective that it may be...
1. A Fixed or Repaired Time Line (Probably from the Future Temporal Agency)
2. A Similar But Separate Diverging Time Line
It is not the NX-01 Enterprise that's part of an alternate timeline..... everything we have seen up to first contact was part of an incomplete, 1st stage timeline
Enterprise's 22nd Century was too advanced to the way the 22nd Century was described to us in the other series. So, seeing the show started out with the Temporal Cold War mumbo jumbo it is pretty clear that we are looking at an altered time line. However, you would be correct that everything up until the point of First Contact (TOS - TNG - Generations - DS9 (Pre First Contact) - VOY (Pre First Contact)) is an incomplete 1st stage (original) time line, though.
which would also explain why the TOS era no longer matches anything close to the 2009 movie era.... where Spock and Nero going back in time was the final nail in the coffin from that previous timeline solidifying the current timeline the ST Universe is now following.
Some fans have thought this new timeline in the new 2009 Star Trek film as writing over or erasing the original (or ‘prime’) timeline. However in interviews with TrekMovie (and others), as well as in multiple online discussions, writer Roberto Orci has made it clear that in their Star Trek universe, the incursions of Nero and Spock created an alternate timeline, which will coexist (separately) with the ‘prime’ timeline (not unlike the ‘Mirror Universe’).
*Put's pieces of head back together and gets Borg nanites to repair the damage*
