Trek at 50: The quest for a unifying theory of time travel in Star Trek — Part-3 of 3

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It’s 2016, meaning we now have many examples of Trek’s time paradoxes to explore.


Temporal investigations

The cover for Bennett’s first “Department of Temporal Investigations” novel: “Watching the Clock”


Aforementioned Trek novelist Christopher L. Bennett has taken on these questions in a series of novels that follows the Federation’s Department of Temporal Investigations (DTI).

While novels like this aren’t considered canon, that hasn’t stopped writers from working some of the expanded universe’s ideas into canon episodes and movies. They haven’t yet done so with Bennett’s, but perhaps they should take notice. The author presents an interesting, unique theory of time travel in Trek. Certainly no discussion of Trek time travel should ignore it.

In Bennett’s books, agents attempt to avoid time travel adventures themselves and instead sort through the ramifications of time travel done by Starfleet and others to minimize any damage to the timeline.

Doing so consistently requires an in-depth understanding of time travel. As such, Bennett set out to create a unified theory of time travel in Trek. He researched every example of time travel in episodes and movies and even delved into the novels and comics for more data. He also mined actual (if often theoretical) physics for explanations of the seemingly contradictory instances of time travel seen in the franchise.

“All my research into quantum theory revealed that, surprisingly, a lot of the stuff in Trek time travel that seemed absurd could actually be explained with legitimate (if unproven) theoretical physics,” Bennett explained on his blog.

The gist of his idea, built largely upon the many-worlds interpretation of quantum mechanics, is that traveling into the past and changing history can generate a new, totally separate timeline. (The movie Star Trek also drew on this theory for its time travel physics.)

When seen from outside time, all events in this worldview exist somewhere in the structure of time. Events that a time traveler remembers happening in his original timeline still happened. They can’t be erased.

This feels intuitively correct. For one thing, it solves the “grandfather” paradox. Go back in time to kill your grandfather and you won’t cease to exist; you’re just living in a separate timeline in which the alternate version of you will never be born. You were still born in your own timeline.

But what about all those times the crew of the Enterprise saw the timeline changing around them? Shouldn’t the Borg, traveling to Earth’s past in First Contact, have created a separate, assimilated timeline, leaving “our” Earth unaffected rather than replacing it, as we saw in the movie?

According to Bennett’s model, these two ideas fit together elegantly. When the Borg went back in time and assimilated 21st century Earth, they did create an alternate timeline. That timeline did not erase the events that occurred in our timeline but rather proceeded on its own path—up until the point in the 24th century when the Borg entered their temporal vortex, traveling into the past.

As the two timelines progressed towards that point, they drew towards each other. That’s because the two timelines were quantum entangled (due to the exchange of information between them which resulted from the original time travel event).

“And if they did become entangled as a single system,” Bennett explains in the first DTI novel, “then quantum information theory would demand that only one of the two conflicting sets of information would survive because a given quantum history has to be self-consistent. It would be as if one timeline suddenly transformed into another. The previous events would still have occurred, but they would no longer be remembered. The information would have been destroyed.”

Essentially, one timeline overwrites another. First Contact’s assimilated Earth timeline merged with our own at the point where the Borg ship left. If you were to follow the events of our timeline, you’d see just what the Enterprise saw: an unassimilated Earth, then the Borg ship going through its vortex, then an assimilated Earth. Until that moment, assimilated and unassimilated Earth were separate. Afterwards, there was only one, assimilated, Earth.

The crucial distinction between the First Contact scenario and the Star Trek movie is the method of time travel. In First Contact, the Borg and the Enterprise travel through an open vortex to the past; ships and particles and whatever else can travel through it in either direction. A ship in the past might well come through to the future. In Star Trek, however, Nero and Spock reach the past via a black hole.

The defining characteristic of a black hole is that gravity is so intense at its “surface” (the event horizon) that not even light can escape. This also means that, effectively, information from the past can’t leak into the present through the black hole. This prevents the two timelines from being attracted to each other, so one doesn’t overwrite the other. (Fans of the “prime” timeline, be glad Nero used a black hole and not some two-way portal!)

This distinction explains many of the time travel stories we’ve discussed throughout Trek. McCoy was able to overwrite the timeline in “The City on the Edge of Forever” because he traveled through the Guardian of Forever, a two-way time portal. However, the anti-time anomaly from TNG’s “All Good Things…” propagated through an extra time dimension into the past. Thus, it didn’t allow a trade of information between the past and the present. It makes sense this could create a number of separate timelines that would never overwrite one another.

But what about the consistent universe, in which the time traveler’s meddling becomes part of what was supposed to happen? Can that be reconciled with the other approaches?

Author Christoper L. Bennett

“I’m always puzzled by the attitude that those need to be reconciled, that time travel is only allowed to have one outcome or the other,” Bennett told Ars. “Physics doesn’t define a single outcome that has to happen but rather a range of possible outcomes. Put different initial variables into an equation and it will produce a different answer. Just because you’re in a universe that allows some time travels to change history, that doesn’t rule out the possibility of a time travel reinforcing history. It just depends on how the scenario plays out.”

From a quantum mechanical perspective, according to Bennett, time traveling into the past only causes the timeline to split under certain scenarios. If the changes to the timeline are small enough, they might get reabsorbed into the foam of quantum possibilities. This would never stabilize enough to become a full new timeline; rather, it would be a brief fluctuation that quickly gets absorbed by the main timeline.

So a time traveler’s actions only cause a divergence of timelines if their actions change things enough to create a stable alternate timeline. Of course, it’s impossible to tell which actions will be significant enough to cause a divergence and which are part of what was “supposed” to happen. The “butterfly effect” holds that even a minor change would have major impacts as the timeline progresses. Stepping on a butterfly could lead to a chain of events that could severely affect human history decades or centuries later. Even just breathing the air disturbs its molecules, which could lead to a divergent history in enough time.

But many of these changes may not be stable enough to persist long enough to generate a significant divergence. And since the two timelines are so closely related now (at the point the time traveler is mucking things up), the new timeline will likely fold back into the original before it can get started.

However, does that explain how a time traveler’s actions in the past can be a part of what was supposed to happen? Perhaps. It seems everything that happens is part of what was “supposed to happen” in one sense or another. The only question is which timeline it was supposed to happen in.

Consider all the “hybrids” we discussed earlier. The consistent time loops that rely on a changing timeline in the middle, such as Spock’s journey to his own past in TAS episode “Yesteryear.” In cases like that one, a timeline shift was supposed to happen. Same with TNG’s “Yesterday’s Enterprise,” in which the Enterprise-C’s departure from the past leads to its encounter with the future which in turn leads to it being sent back to the past. Every part of that story is part of what was “supposed to happen” and is a consistent piece of the backstory necessary for the existence of the Trek timeline as we know it.

The only difference is that some time travel adventures become part of their own timeline’s backstory, while others start a new timeline and become part of what was supposed to happen there. Sometimes different timelines depend on each other for existence, while at other times they are totally separate. But if you take the structure of space and time as a whole—the full histories of all the universes branching off from the main Star Trek one—it makes one, big, consistent history. It’s a complex and fascinating structure, but one where all the pieces fit together and make sense.

Physics: Sorting the real from the Trek

While Bennett’s model is largely based on real (if theoretical) physics, it necessarily takes liberties.

“The problem with every type of time travel that I have ever heard of, and also with this one, is the second law of thermodynamics,” theoretical physicist Sabine Hossenfelder told Ars. “Information doesn’t flow two ways. Information degrades forwards in time. Or, to put it differently, entropy increases. (That’s why there is a ‘forward’ to begin with.) For this reason, for example, entanglement tends to go away (decohere) rather than be created.”

“It is possible, yes, but it is exceedingly unlikely,” she continued. “It is possible that tomorrow all our memories will reassemble and we all forget that Star Wars episode 1 ever happened, and so for all practical purposes the past has changed. It is possible, yes, but it’s so exceedingly unlikely that you might as well say it’s impossible.”

It seems Jar Jar’s here to stay, folks. But Bennett is aware of this issue and acknowledges he bent the rules a bit:

I had to cheat to make [the] idea at all plausible. In real physics terms, there are only two possibilities: The Deutsch model where you create a parallel timeline that exists alongside the unaltered original and the post-selection model […] where just by going back in time, you quantum-correlate the past with your present and thereby guarantee that your own original timeline will occur. Fiction has conditioned us to expect the erasure of the original history by default, but real physics says the original timeline would always survive.

Now, in theory, it’s remotely possible for two divergent timelines to merge together again, in which case quantum information theory would require one version to be erased. But it’s like expecting the shards of a shattered glass to reassemble into an intact glass, a vanishingly improbable event. You’d need some sort of force that could do the work to decrease entropy and achieve that recombination. In Watching the Clock, I used the ‘anti-time’ gibberish from TNG’s ‘All Good Things’ as that force, since time is basically defined by the increase of entropy, so anti-time would logically be anti-entropy.”

Theoretical physicist Sean Carroll of CalTech, who literally wrote the book on time, also weighed in on Bennett’s model. “I think that’s a perfectly reasonable scenario by science-fiction standards generally (and Star Trek standards in particular),” he told Ars. “It’s not real-world physics, but it’s at least inspired by real-world physics, and at a brief glance it seems to make logical sense. If we forced ourselves to stick to realistic science, we would say ‘there is no time travel, and you can’t go faster than the speed of light, and aliens would not look like human beings,’ and Star Trekwould be a very different place.”


A time traveler from the future shows Captain Archer a holographic map of the various timelines, in his Temporal Observatory.

I’ve watched (and read and played) Star Trek in all its forms, but it wasn’t until I began rewatching the time travel episodes and doing research for this story that I realized just how interesting time travel is in Trek.

Prior to this, I favored a model of time travel akin to the one in the movie Star Trek, where time travel always creates a separate timeline. That seemed the only way to reconcile time travel’s inherent paradoxes while still making intuitive sense. (I couldn’t believe the universe would prevent you from killing your own grandfather if you went back in time. What, would you just keep tripping over things? What law of physics would make that happen?)

The kind of time travel we see throughout the Star Trek franchise, however, incorporates that model while ultimately being richer, messier, and more, well, logical. To be clear, I am in no way claiming that any of this time travel is physically possible in real life; but it’s absolutely believable as good science fiction. Like the real universe, it’s complicated and messy and works different ways under different circumstances. Expect a headache or two. But ultimately, also like the real universe, everything ties together.

It remains to be seen if time travel is actually possible; the laws of physics don’t forbid it as far as we know (not yet, anyway). But as physicist Carroll told me in a radio interview, time travel is “probably not possible given the laws of physics as we understand them.” He added that while it can’t be ruled out, “the smart money says that all those scenarios are unrealistic… I would not buy stock in anyone’s company selling time machines.”

If nothing else, Star Trek time travel stories explore interesting possibilities. Whether one is erasing whole civilizations from history and watching the results, finding out that one’s existence is a time loop (as is Spock’s in “Yesteryear”), or digging up one’s long-buried head near San Francisco, the franchise offers plenty of ideas to explore.

Read More:

This Not The End — Star Trek:  always go For!



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