okay! so if I'm getting everything right, Fringe was started because Dr. Walter Bishop upsetted the balance of nature. Him travelling through time to take a kid that wasn't his (technically his but from an alternate universe) was wrong but also right. Peter's existence was to warn both universes of something far worse than what was happening between the alternate universes which was in the future (that's what happened in the S3 finale). now Peter has been deleted from existence cos he served his purpose according to THE OBSERVERS. But the first episode of the 4th season, it looks like Peter is still hanging around which according to the OBSERVERS, is an upset to the balance of nature and one of them had the chance to correct that mistake but he didn't which means we'll see Peter again. so right now, Olivia, Astrid, Agent Broyles even Walter have no idea who Peter is cos he's been wiped from existence as it stands but there's traces of him which seems like Walter is the only one seeing him due to his emotional ties. yeah it's a lot to make sense of till you start watching Fringe yourself 😂😂😂😂😂😂