There are two separate veins of time-travel/causality theories.

  1. A new timeline branches off when one goes back in time (not "going back in time" as much as simply going to a different alternate universe/timeline where conditions are identical to how things were at the target point. See: Dragon Ball Z).

  2. Causality is absolute, and there is a single timeline. any changes made to the past have already occurred, and thus are not "changes". They're simply events on the (immutable) timeline. Once something has been experienced, it is frozen and will always happen.

*Directly copied from acolyte's answer in Was Kyle Reese always John Connor's father?

So how does time travel really work in The Terminator Universe? (I'm talking about the movies, but If someone has information about how it works in SCC it's ok).

For example, in T1, we could say that they follow the second one, but in T2, we learn that the events in T1 did changed the future (first theory) because of the arm and chip of the first Terminator SkyNet technology was improved, BUT then in the same movie, Sarah, John and Uncle Bob destroyed Cyberdyne facility, and nothing happened, the liquid terminator is still there in the timeline, but ultimately they did push back judgement day. So they did changed the future.

Also in T4 John is surprised that SkyNet developed better terminators faster than in the original timeline.


This is also relevant: Why did future John Connor bother to send the T-101 Terminator back?

The most upvoted answer states:

The point is that time travel movies, by their very nature, have plot holes like this related to time-travel paradoxes. We, as the audience, just need to go with the flow, and take such things as a grain of salt.

So is time travel in Terminator inherently inconsistent and we just have to accept that it is the way it is? (My jerk brain is bothering me with this, but he is totally ok with the fact that Cyclops eyes are doors to another dimension)


I was having a conversation about this today, how cool is that?

I believe that, in the T1 movie they of course change the future, not enough to prevent war, but to change how machines are built (technology from the future trapped in past used to build better machines) so that's why we see how in T2 movie the Terminator is way better and evolved than T-400.

So, now we have 2 future time lines. The first one is rewrited to a second one, with more "evolved technology " but with the same "conclution", war, because IA machines get build anyways.

I wouldn't pay much attention to T3 and T4 movies...there are too many gaps in the temporal time lines, and in my opinion it makes all confusing.

P.S = sorry about my grammatical english, I'm kind of rusty :S

I'll edit my question, because here are explaning how this "time travel" works. :D

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First, there is clearly at least a third "vein" of time-travel/causality theories other than the two mentioned, which seems to be the usual vein of time-travel sci-fi:

3) There is one time-line, but time travelers can change the timeline by going back and changing events from what had occurred before they travel back. Doing so makes the previously-established timeline exist only in the memories and stories of the time travelers.

This is not the same as vein 1 mentioned in your question, because if that were the case, then time travel would just be a way to vacation and/or escape to new possibilities for yourself, without causing any change in the timeline you left except for your own absence from it. Well, I suppose it also creates a timeline where the future would be different, but it doesn't say that the timeline you left will be affected, unless you can return to that timeline, and bring with you some knowledge or artifact that would be helpful. In other words, if Skynet thought cause and effect worked like vein 1, it wouldn't expect anything it sends back to affect its own state. It might instead send itself back and happily conquer that new timeline from that point on.

But it doesn't do that. Skynet, and the humans, act as if it is the usual vein 3 I describe above, where a computer in 2500 can send a robot back to 1985 and change its own situation in 2500... as if there is one thread of cause and effect, and backwards time travel causes all history to be re-written from the point the traveler arrives in the past, forward.

This creates two types of timeline. One is the "current state of the timeline" but it and its shape are different at each point along the larger cause-and-effect timeline. I.e., you have a timeline that goes from 0 till the first reverse time traveler, then it hops back to whenever he went back to, then it falls forward in time until the next time traveler in that timeline, then the cause and effect falls forward from that point, etc.

That would be easy enough to track, except what we also have in Terminator and many other time travel stories, is multiple travelers from the future coming back to struggle with each other about what will happen next, which means that apparently the effect of sending something back doesn't have immediate and exclusive effects on the future somehow.

Further muddying everything in Terminator, of course, is the seeming paradox of post-apocalypse John Conner sending his adult friend back to pre-apocalypse times save his mother and ending up fathering himself. It seems to me that's not necessarily a paradox, if the John Conner on the first timeline was fathered by someone else, leading to a father upgrade to future war veteran in T1, which led to that John Conner to send back a Terminator to protect and raise him in T2 (father upgrade #2)... But that would be undermined by the photograph shown in a memory of John's Father in the original timeline future war, supposedly given to him but taken at the end of T1.

So there is what the characters think about how cause and effect works, and how it might actually be working, which is left as a kind of teasing uncertain question... unless/until the point that audiences start to suspect that the people making the films don't actually think these things through with a focus on having them make actual sense, and are much more focused on dramatic effect.

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