Steve's past was always his future. Simply going back and staying there isn't altering the past, especially because that was what he was always supposed to do, he just didn't know that he did, just like 2012 Cap didn't know what 2023 Cap does. Quantum theory says that the same object can exist in the same space if time travel was possible through quantum physics, and while that would create a parallel reality in theory, the film rule is that as long as the infinity stone don't leave their realities, there are no branches. If simply by time travelling an alternate reality is created, Cap's mission would never be successful: he simply going back would mean an alternate reality than the one they got the stones before.
The more I think about it, more the Russos explanation doesn't make sense and the screenwriters does.
No, again, you're getting it wrong.
The Infinity Stones missing dooms the already alternate timeline becasue it messes with the balance of that universe and leaves them vulnerable, it's not the only way a branch is created. When jumping into the past, they create a branche. Then they use the GPS to find that already branched timeline so the balance is never lost. It doesnt create a "A.1" timeline when returning to it, because they have the "space-time location" thanks to the GPS thing.
I don't think it does. Since Cap was always supposed to go back in time, the main timeline we've been following is the one in which Cap did go back in time. It's possible that there is another timeline out there in which Cap never went back depending on the interpretation of the Ancient One, but that is not our main timeline.
It does, the film scientists that figured out a way of traveling through the quantum realm states that you can't alter your own past. It means that there is one timeline, the prime, where Steve either doesn't come back, or does it after giving Falcon the Shield in our MCU Timeline.
In any case, this is where I am now: This discussion is a way of keeping people talking about it, going to the cinema again, and getting the public used to this shit since they are going to double down on it going forward.
I saw a picture that outlined in Gamora's death scene, that there is a redish sillouette where Natasha died. It kind of is there... COULD IT BE !?!??!!?!?!?