Since time travel is well established in Trek lore, assuming various timestream scans can be implemented to ensure that an individual is not going to mess with the timeline in a catastrophic way just by being there, imagine if one of the members of a Trek crew is a time traveler who has been sent back or forward in time for the same reason an officer might serve alongside a different service's personnel, or a student may travel to a foreign country for a year of school. To experience the future and gather intel (if necessary), or visit the past and do research (historical, sociological, experiential). What do you think of this idea?
Seems to me it would be basically impossible to avoid breaking the Temporal Prime Directive in that case, so they’d avoid it.
Technically, if you were to travel back in time, you would immediately create a new alternate timeline. Now there is at least one timeline in which you were not present and another in which you are. Your family and friends in the original timeline will never see you again as you have entered a different timeline. You cannot fix the past. Only create a variant of it.
I feel like for all of the franchise’s efforts to make the physics as ‘real’ as possible, time travel was the pseudo-scientific concept Trek seems to play the most fast and loose with in terms of how it works. Usually it was pretty much just Back To The Future rules, where you can faff around in the past as much as you like, and if you screw something up there’s a magic way to ‘fix’ everything back to normal. Or not even back to normal, of course. There’s an entire movie where the resolution is “Well, I guess we have whales again.” “But Jim, how will reintroducing a species into Earth’s oceans after three hundred years impact the ecosystem? Is it right that we’ve decided this one creature deserves to become un-extinct just because it got humanity out of a hole? What about all the other extinct creatures from Earth’s history? They deserve to stay dead just because their friends from across the galaxy haven’t sent a great big probe to come annihilate us? What if the Romulans use this as a precedent to slingshot around the Sun and steal a load of T-Rexes for the lols? Shouldn’t there be rules about—?“ “Shut up, Bones. We have whales again.” So if it’s an idea you’re interested in writing, I’d say go for it. I’m playing around with a slightly time-bending idea for a future story right now, and I’m pretty comfortable with the science being a bit all over the place, because the story is really about something happening to the characters themselves. And the time-bending element is just for fun.
Maybe you were always in the past, destined, by causation, to travel back there. Perhaps each "parallel" universe has its own, distinct and immutable timeline. The real disruption is in traversing universes, where one universe cannot respond to the sudden and seemingly random presence of an object or entity from another universe. In my own story, there are plans to travel a few thousand years into the distant past of Vulcan that had/has/will have a profound influence on Vulcan history. However, such a vector was destined to happen and merely helps explain a history that was already known. Oh yeah, the crew of Vulcan fxxx-up Vulcan history big time. I also plan to send them into an alternative universe where they will be instrumental in ending a Galactic war. It is human, and other sentient species', nature to recreate the environments in which they are most familiar with so, from their point of view, ending a Galactic war and laying the foundation for a mirror version of the Federation, seems like the best choice for everyone. Without all the futures known, everyone has to make their best call with what information they have. -Will