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The 2009 Star Trek movie and its pending sequels are based on the concept of parallel realities introduced in the season 7 Next Generation episode "Parallels," laying out that anything that could happen has happened in a parallel universe. The Enterprise and its crew from the most recent movie are part of a parallel reality that was created when Nero and Spock came back through the black hole created by red matter in an attempt to stem the destruction caused by a supernova. For clarification, this crew will be referred to as Chris Pine's and the older movies as Shatner's.

In the movie Star Trek IV: The Voyage Home, a probe shows up in 2286 at Earth looking for whales that had disappeared decades before. Shatner's crew is faced with travelling back in time to try and retrieve two humpback whales in order to stop the cylindrical probe from destroying Earth. They do this using a Klingon Bird-of-Prey that was stolen in the previous movie, going back to 1986 to find the whales.

I think it's safe to assume that in Pine's reality, the probe will probably make an appearance again, since the destruction of whales probably wouldn't change. So Pine's crew will also be faced with the dilemma of travelling back to find humpbacks (although probably without using a Klingon ship).

If Pine's crew also goes back to the same instant in 1986 as Shatner's crew to find whales (which seems highly improbable given that hitting the same time period as Shatner would be ridiculous), would they run into Shatner's crew or would it create another parallel reality stemming from 1986? If it created another reality, that seems like some kind of backwards causality since the event that would be causing the new stem wouldn't be the instant before the ships arrived but an event in the future. Would time travel trump the parallel universe and both Kirks would be there at the same time?
