We know thanks to the Ancient One's explanation in Avengers: Endgame that when an Infinity Stone is removed from its own timeline and goes to the past or future, that an alternate reality is created. However, Bruce says if they return the Stones to the same time, that specific reality won't be affected and it'll be as if nothing happened.
My question is: the survival of the universe and all realities seem to be hinging on if the Stones get returned, so how does time work in the other realities/universes?
As soon as, let's say the Time Stone, is taken, that reality which it was taken from splits off and becomes a new one instead of the current one. But Bruce (and the Avengers) spend a lot of time using the Stones. So what is happening in that alternate reality with the Stones taken?
The entire fate of time itself seems to rest on if they return the Stones, not when. But, to me, this doesn't seem plausible because if it does rely on if they return the Stones (not when), then that other reality can only be doing so many things.
- That alternate reality can be moving time as usual, but if this is true, then a lot of things will have happened in all three realities where the Stones were taken and them taking the stones doesn't eliminate any of the risks. If time keeps moving as usual then the alternate realities are still doomed without the Stones.
- That alternate reality could have been frozen in time. However this doesn't seem plausible as that invalidates all the risks.
- That alternate reality could be moving a lot slower or faster in time, however nothing seems to suggest this
So really that leaves only the first option but again, that doesn't make sense. If it takes them 10,000 years to return the Stones, supposedly that would mean the alternate reality is fine. But if time doesn't matter, why does the "if" matter? Why not just wait a million years to return the Stones? Why not just wait an eternity to return the Stones?