It's not that the timeline instantly becomes written; events proceed at a normal pace *without* that version of the terminator in it. When our hypothetical terminator arrives in the future of its original timeline, everything that happened in the interim played out in normal time for everyone else while it would go by in a flash for the terminator. And every single thing that happens during that time becomes an unchangeable part of that timeline's past.
If you jump forward in time, you won't have any memories of the period you skipped. So, in your timeline that you're locked into, you essentially *did not exist* during that period.
Agreed.
The rest is so hard to explain.
But I think I can do it better if I personalize it. You'll have to let me know if the following makes enough sense and does the trick.
First off, there's no such thing as "changing your past." If you go back in time, and every event is playing out as you originally remember it, that's not what's actually happening. This is because you didn't exist in the original history that you remember, so you're already in an alternate version of your original past. In a case where you *did* remember your older self co-existing in your younger past, then you'd merely be going back in time to fulfill a causal loop.
Some version of you may have, but only some branched version of you. The same is true of our hypothetical terminator. It would have no "memories" of the interim that was skipped in the jump to the future. Any version of itself existing in that interim is now only existing there from having returned back in time and created a branched timeline.
I was initially confused by what you're saying in these parts - I even had appropriate youtube reaction clips lined up but I think I've come around to an understanding after I've been mulling over this response the past couple of days.
Again, if you visit yourself in the past, there had to exist a timeline when you didn't. Otherwise, you'd never have memories of the time period in question where you weren't visited by a future you. That'd be a closed loop. That's fate. That's not the "no fate" structure of Terminator that we (presumably) see evidence of by virtue of the T2 ending.
Agreed.
[EDIT] I went on a general BTTF tangent below without even addressing the Einstein scene itself.
Yes a-dev, the Delorean arriving with Einstein a minute after it left is indeed a simpler way to prove that the time travel equipment actually works (at least in a forward direction). I think you're right that Skynet would've done something similar to do a simpler test first.
Yeah, it would want a quick, verifiable proof that it can be done and it works before carrying out a much more longform mission.
BTTF is wrong. You don't go back to the past and get to "re-enter" the same timeline unless it's a closed loop. Since the rest of my answer here is about BTTF, and not Terminator, I'll use spoiler tags.
Remember when Marty arrives back in 1985 at the end? He sees himself leave and head to 1955, and he sees Doc get shot (but not die). Well, the Marty who left would've been the Marty from the 1985 where his parents aren't losers. That Marty had a new truck. That Marty would likely be wearing different clothes because his family was wealthier. That Marty wouldn't have needed to get to the mall on a skateboard and take it with him to 1955.
More importantly, that Marty would go back to 1955 with different memories. When he tells 1955 Doc about the "Enchantment Under the Sea Dance," he will tell him about how George punched out Biff. Marty would have to try to arrange *that* scenario in 1955 this time. He would've told Doc Brown a different story. He might not have even had the clock tower flyer.
It's all wrong. The logic of that kind of "changing the past" of your own timeline doesn't work. It's either causal closed loop, or it's branched-off alternate timelines by traveling back in time.
OK so this is you fixing how BTTF would play out according to our branched timeline rules. This had me stumped for days but I think I've got it. Marty is inadvertently sent back to 1955 and accidentally disrupts the original manner in which his parents got together. The new manner in which they do, as arranged in the movie would remain the way they got together in this branched timeline going forward so when this same Marty goes 'back' to the future - he'll actually be moving forward within this same timeline and not returning to his timeline of origin. Within the new timeline branch he'll skip the years between 1955 and 1985 - a version of him will have been born in the meantime that will not live the same life that our Marty did. Therefore that is the Marty that our Marty would witness going back in time near the end of the film (creating another branched timeline of his own) - assuming so much else played out as similarly as the original timeline such that this would even take place again - and that's a big assumption because technically there's a high likelihood neither the Marty from this timeline nor his siblings would even exist as they do or necessarily be born exactly when they originally were. With the changed circumstances in 1955, odds are, different sperm would meet different eggs creating entirely different people. And heck, if the new Marty didn't go back in time there would now permanently be 2 Marty's in this timeline. Jeez, what would 'our' Marty even do in that scenario?....would George and Lorraine take him in? Would they just pretend to other people they had had identical twins all along? Would our Marty be forced to admit that he had been the person they knew as 'Calvin Klein'? Interesting stuff. And grim implications for Marty's original timeline. Not only will his family's circumstances remain completely unchanged but now they'd have to deal with Marty having simply disappeared, never to return
Going back to our hypothetical Terminator scenario of a Terminator being sent into the future and then returning - although I do kinda question said hypothetical plan by Skynet- per this post
https://www.sideshowcollectors.com/forums/showthread.php?t=172427&p=10446432&viewfull=1#post10446432 - what say you to that?
but as a matter of interest lets continue to entertain it and see if I've got this right......
In a hypothetical timeline A Skynet sends its most top of the line Terminator - let's just say it's a T-800 - 30 years into the future to collect information, new discoveries and advancements. It does so knowing that it will not get the benefit of this mission's ultimate objective in this timeline and will simply have to proceed on its own natural course through time. Further to sending the T-800 into the future, this Skynet will have the role of being the very same Skynet who must take delivery of this old Terminator and send it back in time after giving it what it came for.
First question - does Skynet send the T-800 back to a point in time
after - possibly immediately after - it sent the T-800 to the future in the first place? Alternatively does Skynet send it back to a point
before it originally dispatched the Terminator into the future? I feel like the latter scenario makes things easier to process and here's why -
the T-800 arriving back in the past immediately creates the branched timeline B. As this timeline was the same as timeline A up until this branching point it means Skynet was planning to imminently undertake this mission of sending a Terminator into the future but now it doesn't need to because - here he is, he arrived before they even got around to sending him in the first place. Skynet will understand that an alternate version of itself must have done the honours. It can now reap the rewards.
However, in a scenario where the timeline branching occurs only
after Skynet sends the Terminator into the future does this not open the possibility of numerous - possibly even endless - alternate timelines? Because despite that a Terminator has arrived bearing gifts from the future to Skynet in timeline B, don't you still have to account for the T-800 that was
just sent per the part of the timeline that is in common with timeline A? So, when
that T-800 makes the return journey, you end up with repeating scenarios where A feeds into B, B will feed into a C, C into D, D into E and on and on and on. Now maybe that's fine, maybe Skynet would anticipate and not have any problem with that. It just messes with
my head, it's not as neat and tied off as I would like.
On the other hand if, for some reason, we
don't have to account for this Terminator* - or if I'm wrong about what future he will be travelling to - then everything I'm about to go into is moot and/or incorrect.
*It would surely also mean we don't have to account for the other Marty going back in time at the end of BTTF (while 'our' Marty arrived before other Marty goes back to the past he doesn't stop him from doing so and as such that Marty is ''in play'' like the timeline A T-800 I'm talking about above)
So..when the Terminator arrives from the future of Timeline A to create Timeline B Skynet from that point in the 'past' can now benefit from the knowledge and advancements of Timeline A's
future Skynet. It however had still sent a Terminator into the future just prior to the arrival of the other one from Timeline A, so that future-destined Terminator is still in play. Because travel into the future does not cross timelines or create a new branch he will go into the future of timeline B in which Skynet - as planned - will have now gained from the experience and knowledge of Skynet A and presumably become much more advanced. So now that heavily outdated T-800 will be collecting data from an even more advanced Skynet which will then return it to the point in time after it originally sent that Terminator.
Here's the thing - when that Terminator goes back to the past it will now create timeline C. Again, assuming it is returned to a point
after it was originally sent then per the commonality with timeline A, a Terminator still gets sent to the future...but there will potentially be an additional commonality now with timeline B - this Terminator bringing the intel from the future of timeline B now joins the prior time travelling Terminator, the one who previously carried the intel from Timeline
A's future into timeline B. That T-800 arriving from timeline A into timeline B had become part of that timeline - his arrival had become 'a thing that happens' in the very recent past when another Terminator now enters to commence the new branch Timeline C. As a result, we now have a C timeline which has 2 Terminators from 2 other futures occupying it (the future of A and the future of B) - this is assuming they didn't appear on the TDE pad at literally the exact same time and catastrophically phase into eachother or something (perhaps a reason Skynet would know to time the arrivals gradually later and later so as to avoid this clash). You see why I wanted to avoid all this? Jesus H Christ
This timeline (C) now proceeds with the combined awareness of and the knowledge gleaned from the 2 prior timelines....I guess. Its advancements are theoretically massive. Aaaaaannnd there was still a time travelling Terminator in play that this Skynet had sent off just before it won the 2 jackpots in one day. He's going to arrive in the future to find a ridiculously advanced Skynet that will be like ''LOL, a T-800! Remember those''. Aaaaannnd Skynet will send
him back to maybe a few minutes after the others had arrived to be on the safe side. Timeline D will have taken delivery of not one, not two but three T-800s and will make wild advancements off the back of future Skynets from timelines A, B and C. My brain is a bit frazzled by all this - I'm unclear if the information from the first two T-800s will even be necessary, could be that it's all gathered in entirety in the most recently arrived T-800 making the first two kind of moot.
Anyway, this could go on and on but I guess it doesn't necessarily have to -
I'm certainly not going to - what I mean is it doesn't have to follow that future Skynet will keep sending the T-800 back to the past after receiving it. It might decide to break the chain. Or circumstances could play out such that the chain is otherwise broken.
I'll leave it there, bejaysus.
Spoiler: 
And yes I do realize that BTTF II completely ignored my "you can't change *that* much" theory but the logic in that film was an irreconcilable mess so I'm not gonna worry about it, lol.
