How did the Enterprise return to their own timeline at the end of First Contact?
At the start of Star Trek: First Contact, the Enterprise follows a Borg sphere into the past to stop them from changing history - preventing first contact with the Vulcans and assimilating Earth. It is made clear that the Enterprise itself does not possess the technology to travel through time and with this in mind it is unlikely that the people of Earth from a time pre-dating the Federation had time travel capabilities either.
At the end of the movie, once first contact has been made, how did the Enterprise return to their own timeline?
Best Answer
The Borg sphere's approach to time travel is described in two lines of the movie:
DATA: Sensors show chronometric particles emanating from the sphere.
PICARD: They're creating a temporal vortex.
The troublesome question of how the Enterprise returns is dealt with just as abruptly at the end of the film:
LAFORGE: Captain. I've reconfigured our warp field to match the chronometric readings of the Borg sphere.
PICARD: Re-create the vortex, commander.
So the Federation may not have the knowledge to make their own custom time vortex, but they can at least copy what the Borg have done. A case of "monkey see, monkey do".
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How did enterprise get back after first contact?
Now, fast forward to the end of the film - the crew of the Enterprise have to get back to the future, so Picard instructs whoever it is on the bridge to emit a reproduction of the inverse tachion pulse that opened the temporal vortex that the Borg sphere & the Enterprise went through to get back to the past at the near ...How did the Borg go back in time?
Through the usage of those particles, the Borg Sphere is able to manipulate a window through time, allowing the probe to move several hundred years back in time.How The Star Trek Timeline Changed After Enterprise and First Contact - Treksplaining
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Answer 2
The Enterprise recreates the temporal vortex that the Borg created and get back to their own timeline. From Memory Alpha:
Scanning Earth, the Enterprise crew found that, in the new timeline, humanity had been assimilated, and realized that they had to follow the sphere through the rift in order to correct the damage done to history. Later, after having successfully restored the timeline, Commander Geordi La Forge was able to reconfigure the Enterprise's warp field to match the chronometric readings of the sphere, thereby recreating the vortex and allowing the ship to return to its own time.
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