Peter may have bridged the two universes but as we saw in those closing moments of last season, they are still very much at odds in the new timeline.
John Noble believes that in order to solve the problems of their worlds, the two Walters must put egos aside and join forces. Season 4 spoilers follow.
Speaking about Walter and Walternate, Noble notes, “we do have arguments with ourselves.” He explains:
“Most people seem to have this conflict within themselves and it can be quite vicious when you tend to say, ‘That was stupid. What are you doing?’ [The Walters] will build it up until such time as they realize they’re being childish and they have to put this extraordinary brain into one piece to solve a problem larger than their own egos.”
However, it’s not just egos that need to be overcome. Earlier, Noble declared that Walter has been put back to square one in the absence of Peter (Joshua Jackson):
“Without Peter, he’s insane. He won’t leave the lab. He hears voices and has hallucinations…he’s crazy! He still can solve problems, but he has to get Astrid (Jasika Nicole) to go out with a special [camera] so he can see the crime scenes because he won’t go out himself.”
Which adds additional context to the final scenes from last season, where a somewhat fractured Walter confronts Walternate inside the BBM room.
Source: TV Guide