Temporal effects are a common gimmick used in science fiction and fantasy. Unsurprisingly, it is handled with varying degrees of competence in various circumstances. In fact, aside from magic and/or technology (depending on context), it is probably the most mishandled gimmick of all.
Like with the rest of the writing process, where most writers fail is at the planning stages. They don’t think through the implications of time travel for either their characters or the universe those characters exist within. Below I am going to discuss several important factors that need to be considered when developing a time travel (or other temporal effect) story.
The most important thing to consider is causality. Your audience lives in a universe where effects follow causes linearly and usually in a straight forward manner. So do you, for that matter. What this means is that your audience will expect a chain of events that is consistent, and which makes sense. That is not to say that you have to spoon feed them every little implication or detail; most will be willing, or even pleased, to spend a bit of effort figuring out how things work. They will, however, be extremely miffed if when they finish expending that effort, they discover that you have provided them with an inconsistent mess that completely defies any concept of causality. What this means is that you must make absolutely certain that there are no holes in your causality chain that are introduced due to time travelling. This includes temporal paradoxes. Of course, this is somewhat less than a strict rule depending on other factors.
You must also think carefully about the mechanism that causes the temporal effect, whether it is one character living in the reverse order to everyone else or a garden variety time travel story or some funky temporal anomaly noodling around causing weirdness. You need not explain the physics or metaphysics behind the effect, and often it is better if you do not, but you do need to be absolutely clear about how it works and you must think through the implications of it carefully. You have to know what the effect allows to happen and what it does not. For instance, a simple time dilation field will likely only affect the speed at which time passes within the field. But this might have implications at the edge of the field. Also think about what happens if the field collapses, and why that might happen based on how the field works. Make sure you understand why you have chosen a particular effect and avoid having some cool effect happen simply to make your plot more tense. It must make sense within the existing context of your story. If it doesn’t, your audience will be left with a vague sense of confusion at best.
You should most certainly avoid adding cool sounding explanations of your effect in the event you are writing science fiction, especially if you are not a physicist involved in the field you are borrowing. Quantum mechanics is often abused to handwave away random weirdness, for instance. While this may be plausible, the more detail you give, the less plausible it is going to be, especially if you happen to get some detail of quantum mechanics subtly wrong. It’s much less jarring for the gimmick that allows your effect to be named after some fictional scientist who discovered it in your universe and leaving it at that. Or naming the gimmick after the actual effect it has.
You should also carefully consider if it will be possible to change the timeline if you allow time travel. Not allowing changes may seem like it severely limits your options for tension in the story because your characters’ actions will already be part of their own history, or it means that the future is predetermined depending which perspective you attack it from (one implies the other if you look at it carefully). However, an understanding of how history is recorded and how many details are simply not recorded at all, and even the fact that we notice only a fraction of what goes on around us at any time, should provide you with a nearly unlimited set of stories anyway.
On the other hand, if you do allow the timeline to be changed, you need a mechanism by which that can happen. This is the part of time travel that is usually messed up substantially because it is the one that directly affects causality. There are a number of aspects of this which need to be considered. For instance, if time is changed, what happens to the original time stream? Does it still exist in a branch? Does each choice create a branch in the time stream and time really isn’t changing at all? Does anyone remember the original timeline, and if so, why? What is the effect on causality? What happens if the change leads to a paradox (“I killed baby me.”)? Who can change the timeline? Is there an objective frame of reference from outside the timeline being changed? You begin to see the picture. There are many variations, some of which work better than others. It is probably helpful if you have at least an implied explanation of what mechanisms are at play.
It is probably clear to most that it is easier to do temporal weirdness in a magical universe than a technological one since magic is generally not bound by any rules of physics. But even so, if you are going to allow time travel in your fantasy universe, you still must define exactly how it works in the context of the universe. Otherwise, you will still end up with something that rings false.
I’ll close with a few examples.
The movie Timeline gets things exactly right. While it is unclear during much of the movie, the timeline is not altered at all during the course of the adventure. It turns out that their trip to the past was always part of the past. There is no rewriting time just so everyone gets a happy ending.
L. E. Modesitt, Jr.’s Timegod’s World is another example where things are basically sound. While the exact mechanism of the causality preservation system of the universe is not clear, it is clear that it has specific rules. There must always be one person that remembers things the way they were before the change. And, it turns out that the entire story is about the consequences of tinkering with time.
A recent episode of Sanctuary (“Carentan”) gets a time dilation field almost right. It may even be completely right depending what comes out in future episodes. However, there is a direct causality violation that seems apparent. If the time dilation field was merely causing time within to run at a vastly accelerated rate (6 years per 24 hours in this case), then collapsing the field would not have caused anything to cease to have existed. That effect seems to have been added in after the fact to add extra unnecessary tension to the overall plot, and possibly to avoid having to deal with the consequences later. It is not adequately explained how collapsing the field causes people born within to cease to exist yet does not kill or wipe out the outsiders. The comment about time resetting actually muddies the situation more rather than helping because a time reset would imply that absolutely nothing within the field even happened yet the main characters can clearly remember it. (And if none of it actually happened, how did the field get collapsed in the first place since that was done by characters within the field!)
Any discussion of temporal weirdnesses cannot avoid Doctor Who which makes no obvious attempt at internal consistency. It even goes so far as to describe time as a “wibbly wobbly ball of timey wimey stuff”. But then, that is the general point of the time related stuff in Doctor Who: it just doesn’t make sense. But even so, there are some rules that are generally followed and they do deal with paradoxes on occasion. And messing with time often goes badly or has long reaching consequences. That said, Doctor Who is most certainly not a model to emulate for time travel or other temporal weirdness stories.
Other works which I will not analyze in detail are listed below. Some get things right, some get them wrong, most get them partly right or partly wrong. Some might actually be consistent but there is insufficient information to figure it out.
- Back to the Future
- Millennium
- The Girl from Tomorrow
- The Time Tunnel
- Vanishing Point
- The Callahan stories by Spider Robinson
- The Time Machine
- A Connecticut Yankee in King Arthur’s Court
- Terminator (and sequels)
- Star Trek
- The Hitch Hiker’s Guide to the Galaxy (and related)
- Time Storm
- The Time Traveler’s Wife
- Planet of the Apes
- Seven Days
There are, of course, many other examples. Being familiar with what works and what doesn’t in many different examples will help you avoid the same pitfalls others have fallen into.
Of course, nothing is stopping you from writing a story that makes absolutely no sense and specifically uses every possible error when dealing with time. But if you do, expect ridicule, or indifference.