How The Flash's Time-Travel Lines Up With DC's Legends of Tomorrow

In The Flash, there are certain, pivotal events that will be true no matter what universe or timeline a story takes place in. Aside from that, though, almost anything can change -- and those changes can happen in pretty radical ways. Taking a cue from Flashpoint, the comic on which most of the movie is based, The Flash uses a version of time-travel that is less intuitive than, say, Back to the Future. In that franchise, there is no multiverse. There's one timeline, and you can change it by going back to a any given point, with your changes happening only after that point.

In other words, when Marty McFly travels back to 1955, he can change the timeline -- but those changes will only take place after 1955. But in The Flash, things are a little different. When Barry made a change in 2012, the impact on the timeline was more like ripples in a pool, radiating out from the point of the change but making alterations in all directions. It's why, even though the change happened in 2012, the origin stories of Batman and Superman, which took place years before, are radically altered.

On the other hand, the changes made do not appear to erase the Snyderverse, or the Burtonverse. Yes, there are aspects of those realities in the timeline created by Barry's changes, but according to the movie's logic, Barry has created a whole new timeline. The way Keaton's Batman describes it, using spaghetti and ending his lecture with a pile of spaghetti, haphazardly intersecting and overlapping in a way that isn't nearly as clean as the branching, parallel timelines you get in stories like Back to the Future (or even Avengers: Endgame).

The idea of shattering time, sending spiderwebs of butterfly effect-style repercussions backwards and forward, is different to how DC usually depicts time-travel. Still, there is one thing that holds true: in The Flash, there are certain, immutable truths that hold across realities. This is pretty similar to what they call "fixed time" in the comments. Spider-Man: Across the Spider-Verse did something similar with its "canon events," and even in the Arrowverse, they had "fixed points."

In a season seven episode of DC's Legends of Tomorrow, titled "The Fixed Point," the team decided to save the life of Archduke Franz Ferdinand, stopping World War I, as part of a larger plan to call out the season's big bad. What they learned is that certain events are "fixed points" in time, and cannot be changed because time itself will fight back, making it impossible to change, and sometimes even doing harm to those who are trying to make the change. It later turned out to be the actions of timeline protectors hanging just out of sight, preventing anything from happening, but in the comics (and seemingly in The Flash) it wasn't people with their own motivations and free will, but rather a natural, almost immune response, from the universe.

...That is, unless there's something we don't know yet. But even if that's the case, the failure of The Flash almost certainly means there will be no follow-up on this version of DC's universe, let alone this version of time-travel.