I’ve strung together my personal understanding of how Fringe’s multiverse and overall timeline works here for my own reference and that of anyone else who might be interested.
In chronological order:
*In the beginning, there is only one timeline/universe.
*Around 250 million BC, a version of Peter Bishop from 2026 and the parts of Walter Bishop’s doomsday machine appear through a wormhole. Peter scatters the parts, along with cryptic instructions as to their use throughout space and time. At this point, the universe splits in two, creating Universe 1A (Blueverse) and 2A (Redverse).
*Despite massive political and social differences between the two universes (“In spite of a nail”) Walter, Peter, Olivia, and the rest of the main cast are all born in both universes
*Peter 1A dies. Walter steals Peter 2A from the other universe. At this point, the universe splits again. In worlds 1A and 2A, Peter survives the trip between universes. In worlds 1B and 2B, he drowns.
*In all worlds, the machine is found and reconstructed. It is unknown how it’s operated in universe 1B when Peter doesn’t exist there. It’s possible all versions of the machine are quantum entangled and activated when it was activated in universe 1A.
*Universe 2A is destroyed. Universe 1A begins to degrade rapidly. Olivia is murdered by Walternate. Peter goes back in time and prevents himself from destroying universe 2A by showing him his future. Peter 2A is now aware of what happened in the 15 year aborted timeline.
*The machine moves Peter from the bridge between universes 1A and 2A to Reiden Lake in universe 1B. Universe 1A advances as normal, with Peter now absent.