Michael Wong wrote:Time Travel
Ah, time travel. As a good Trekkie might say, "our last, best hope." I'm sure you've heard this argument before:
"The Federation would use time travel to jump into the past, and wipe out the Empire before it was ever created."
I left this for last because it requires a lengthy explanation. This argument is quite persuasive upon first glance, but upon reflection, a few obvious problems appear:
Why so rare? If time travel can be used as a panacea for every mistake, battlefield defeat, and ill turn of fortune, then why is it used so rarely on the show? Why were crushing defeats like Wolf 359 or the Romulan/Cardassian massacre in TDIC not reversed by time travellers? Federation law? Let's not be silly; if any ship with warp drive can use the slingshot, this opens up time travel to every half-assed starship captain in the galaxy.
Can they pull it off? We know starships can use the slingshot effect to travel several centuries into the past. However, this act requires fuel. It puts strain on the ship (serious strain, as we saw in ST4). So who's to say it could survive a much longer trip, say, a thousand years instead of a few hundred? What about ten thousand years? What about a hundred thousand?
What's the point? In the universe of Star Trek, there are an infinite number of parallel timelines (as seen in "Parallels" and "Mirror, Mirror"). When a ship performs a time-jump, it must create a divergent timeline (more on this later). It can wreak havoc in this divergent timeline, but why would its departure have any effect on its original timeline?
It may be helpful to list known examples of Federation time travel, all of which fall into a small number of categories:
Accidents
Too many to list. They usually involve some natural phenomenon, such as black holes, wormholes, or "temporal anomalies".
Assistance by outside forces.
Guardian of Forever: Seen in "City on the Edge of Forever". Not large enough for a starship, with a lower range limit of at least a few millenia. It cycles through a list of "permissible" destinations, generated through some unknown algorithm. Doctor McCoy inadvertently used it to go back to the 20th century.
Borg Sphere: Seen in STFC. Capable of moving entire starships, with a lower range limit of roughly three centuries. It sent itself back to the early 21st century in an attempt to assimilate Earth's past, and the Enterprise rode its "temporal wake".
Bajoran Orb of Time: Seen in "Trials and Tribble-ations". Capable of moving entire starships, with a lower range limit of roughly one century. It was used to send the USS Defiant 105 years back in time, as part of a failed assassination attempt against Captain Kirk. The use of this device, as with all of the Bajoran orbs, is presumably contingent upon the forbearance of the so-called "Prophets".
Atoz's time portal: Seen in "All our Yesterdays". Not large enough for a starship, with a lower range limit of many millenia, perhaps even millions of years. It was used on Kirk, McCoy and Spock, who all suffered loss of reasoning faculties when moved to a prehistoric era.
Timeships: Specialized time travel vehicles from the future or from alien civilizations. Seen in "A Matter of Time", "Future's End", and "Year of Hell". The latter two examples are Voyager episodes in which the writers' abuse of time travel finally reached the "ludicrous" stage, making TNG seem downright reasonable by comparison.
Slingshot effect.
The slingshot effect uses some horribly unrealistic pseudoscience to explain how one might use the Sun to travel backwards in time. It was used to send the Enterprise forward from the 20th century to the 23rd century in "Tomorrow is Yesterday."
A slingshot effect was used to send the Enterprise back to the 20th century in "Assignment Earth".
A slingshot effect was used to send a Bird of Prey back to the 20th century in ST4.
Transporters.
First seen in "Mirror, Mirror." A transporter accident (how many of these have we seen in Trek?) threw Captain Kirk into an alternate timeline. This timeline was visited again in the DS9 episodes "Crossover", "Through the Looking Glass", and "Shattered Mirror", again using the transporter.
Transporters were also used for time travel in "Time's Arrow", "Past Tense", and probably several other episodes, always to travel just a few centuries back in time.
As we can see, most Trek time travel has been limited to a few centuries of "temporal displacement". The small handful of long-range time travel incidents have involved technologies which can only move a person, not an entire ship (thus suggesting that movement through time is similar to movement through space; the bigger the object, the more difficult the move).
When we look through the list, we find that once we eliminate small-scale techniques and outside intervention, the only viable method of Federation time travel is the slingshot effect. This creates serious constraints. The slingshot effect places great strain on a starship, and long-range use of this technique has never been observed (or even attempted). The process consumes fuel at an undetermined rate. It places an undetermined stress on the ship. Given these problems, how can the Trekkies insist that there are no limits to the duration of time travel using the slingshot? How long must we suffer Trekkies who insist on assuming that every process is limitless and free unless proven otherwise?
In any case, even if they can somehow resolve the "how" part of the question, we must still wrestle with the "why" part of the question. It is widely assumed that problems can be "solved" through time travel, ie- if something went wrong, you can go back and make it "right". But does this make sense? How does time travel affect the timeline? This question affects the potential usefulness of time travel as a solution for problems, and it leads directly to the infamous "grandfather paradox."
The Grandfather Paradox
We've all heard about the Grandfather Paradox. You step into your handy-dandy time machine. You jump back in time. You murder your grandfather. Now he's dead, and he won't ever sire your father, who in turn won't sire you. This means that you won't be born. But if you were never born, then how could you go back in time and kill your grandfather?
This is an old question, pondered by scientists, philosophers, and anybody who watched "Back to the Future" or "The Terminator". One obvious solution is that time travel might simply be impossible, thus eliminating the problem. However, general relativity predicts the existence of wormholes, and wormholes would theoretically permit time travel. Stephen Hawking has suggested a sort of "cosmic censor" who acts as a universal timecop and ensures that causality paradoxes never happen. This timecop might kill you before you can kill your grandfather, or make him duck to tie his showlaces just as you pull the trigger, etc. And of course, those who optimistically predict the eventual feasibility of time travel tend to resort to the "many worlds" interpretation of quantum mechanics.
Now, I must preface this with the very important caveat that the "many worlds" interpretation of quantum mechanics has been widely discredited. However, if we are using suspension of disbelief, then we must assume that it is valid anyway, because the parallel universes predicted by the "many worlds" theory have actually been observed in Star Trek. Parallel universes were seen first in "Mirror, Mirror" and then more spectacularly in "Parallels", where hundreds of thousands of Enterprise-D's from parallel universes could be seen.
Now, how does the "many worlds" theory explain the Grandfather Paradox? Well, if an infinite number of parallel timelines exist, then the Grandfather Paradox can be explained quite easily. You step into your handy-dandy time machine. You jump back in time, but in the process, you create (or enter) a divergent timeline. You murder your grandfather, but this happens in the new timeline. Back in your original timeline, your grandfather was never murdered, so you still exist. In effect, you are an alien visitor to this new timeline, having come from a different universe.
This solution is not without problems. If you move from one universe to another, then mass/energy conservation laws will be violated because both universes will experience a mass/energy change. However, this can be solved if an equal amount of mass/energy goes the other way, to take your place. Interestingly enough, this is precisely what happened in "Mirror, Mirror". Kirk and his mirror-universe alter ego changed places, thus preserving symmetry. This symmetry is not seen in the TNG and DS9 time travel incidents, but that's merely another example of how TOS is superior to its bastard stepchildren. One could always rationalize it by saying that the return mass/energy was dispersed widely across space etc., but the symmetry shown in "Mirror, Mirror" is a better solution.
"Many worlds" in Star Trek
Some serious problems with Star Trek time travel can be solved once you accept the "many worlds" theory:
"City on the Edge of Forever": When Doctor McCoy jumped through the time portal, the other crewmembers on the planet's surface perceived the sudden disappearance of the entire Federation. Supposedly, he changed the past so that the Federation was never created. But that is impossible because the other crewmen still existed. They still had memories of the Federation. They still had Federation uniforms and Federation weapons. The "many worlds" theory neatly explains this problem: McCoy and all of the people on the planet's surface were all transported into a timeline (or parallel universe, whichever you prefer) in which the Federation never existed. The original timeline is not destroyed, thus explaining why they still remember its history, but they can no longer perceive it or return to it. When Kirk and Spock jumped back to "fix the damage", they caused everyone to jump into another timeline, in which the Federation was founded again, but with slightly different events surrounding Edith Keeler's death. This is not the same as "going home", but as far as they're concerned, it's good enough.
"Star Trek First Contact": When the Borg jumped into the past, the crew of the Enterprise perceived the disappearance of the Federation's entire history. This is impossible because they still exist, and they still retain all of their memories, equipment, history files, etc. Data suggests that they were somehow "shielded from the changes in the timeline", but he doesn't even attempt an explanation of how this is possible. The "many worlds" theory provided a neater explanation: they were dragged into a new timeline by the Borg sphere's "temporal wake", and when they stayed in the wake long enough to perform a similar jump, they ended up in yet another timeline. In this new timeline, they tried to "fix" events so that they unfolded more or less as they remembered (albeit with an orbital bombardment of Cochrane's launch facility which didn't occur in their original history). Note that the "many worlds" theory also explains the biggest conundrum of STFC: why the Borg fought their way to Earth before performing the time-jump, instead of making the jump from the safety of their own territory. The answer is that a time-jump would move the travellers to a divergent timeline but it would have no effect on the original timeline. Therefore, it would do the Collective no good. You might ask why they performed the jump at all if this is the case, but the Queen's attack had failed and she was facing imminent destruction. A jump into a divergent timeline would not change history in her original timeline, but she may have found the prospect preferable to simply being destroyed by one of Picard's quantum torpedoes.
"Yesterday's Enterprise": History seems to change when the Enterprise-C appears two decades away from where it was supposed to be destroyed in battle. But the original timeline is not gone, and in the new timeline, Guinan can actually perceive that the Enterprise-C belongs to a timeline other than her own (she can even perceive some of the history of that timeline). This perception manifests itself as a disquieting sensation that something is "wrong", but that's an oversimplification. After all, how can a timeline be "wrong?" With countless timelines in existence as seen in "Parallels", why would one be more "right" or "wrong" than another? A better explanation is that Guinan perceived enough of the Enterprise-C's original timeline to know that she thought it was better than the one she was currently in. We jumped to a divergent timeline when the Enterprise-C arrived and we jumped to another divergent timeline when it departed.
Although the "many worlds" theory may have been discredited in real life, it seems to be the only way to explain Star Trek time travel as we've seen it on the show. It explains causality paradoxes in "City on the Edge of Forever" and STFC, and it also explains why time travel is not being used to solve problems, because it means that time travel doesn't really change anything. It only moves the traveller into an alternate universe where events unfold more to his liking. An interesting consequence of this explanation is that we've really been following a group of characters as they move from timeline to timeline, so we haven't stayed in a single universe throughout the series run of Star Trek.
Conclusion
We can now answer the original three questions posed at the top of this section:
Why so rare? This question can be answered by concluding that it probably is not so rare; it simply isn't perceived. There are probably countless time travellers, but each time a traveller leaves, he simply moves to a divergent timeline and disappears from his original timeline. Since we don't follow any timeline jumpers but the main characters, we don't perceive their activities. At best, we might perceive unexplained disappearances of starships, or mysterious "transporter accidents".
Can they pull it off? That's an open question. We know that the only viable method is the slingshot, and we have evidence that there may be range and durability issues. However, the evidence allows us to establish lower limits but not upper limits. This remains an open question.
What's the point? This is the real problem. The "many worlds" solution to the causality paradox leads us to conclude that a time traveller cannot change his original timeline. He can only move to a different timeline, in which events unfold more to his liking. For a soldier losing a war, it would be an act of cowardice since he would quite literally be running away from his defeat. That explains why they only use it when they've been moved to a different timeline against their will or by accident, since they can't get home but they can at least get to a timeline which they find preferable.
This appears to be a very long-winded answer to a simple argument. But the original argument is only simple because it deliberately overlooks numerous complexities affecting Trek time travel. When we take a more serious look at it, the time travel argument doesn't work.
tl/dr; Star Trek Time travel heavily references the 'Many Worlds' theory in order to make sense. A time-travelling assassination attempt on the Emperor would create an alternate timeline, where the Federation may or may not succeed. The original timeline continues, sans Starfleet time agents.
