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So You Want To / Write a Time-Travel Story

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Well, if you want to write a time-travel story, you’re in precisely the right place - and time - to learn just that. Now, a time-travel story is, before all else a Story, so General story-writing tips are useful on the outset of any writing endeavour, and if you’re still new to that, then I highly recommend the guide “So You Want to Write a Story” as a good starting point. But, once you’ve got the basics down pat and you are interested in exploring a time-travel story, well, there are several particular elements of the Time-Travel Story which make this both interesting to read, and interesting to write.

Necessary Tropes

Before you even put pen to paper (or, finger to keyboard; chisel to stone; thought to mental interface...), there are several necessary elements you should familiarize yourself with first.
  • So You Want To Write a Science Fiction Story - Time-Travel stories are often a Sub-Genre of Science Fiction (and for that reason, this guide, may also be useful to you), but if you are not inclined towards science or physics, and what draws you to this type of story is the kinds of strange adventures you can explore, perhaps you may want to look into some Fantasy, Science Fantasy or even Urban Fantasy concepts, after all, magic can cause users to time-travel in some stories. But, if you’re playing with Soft Sci-Fi, or Science Fantasy, a lot of what I have to say here is much more loosely applicable, as Soft Sci-Fi often plays hard and fast with scientific concepts and research. However, if you are more interested in something with a semblance of scientific fortitude, then it’s good to look at some of the fundamentals of writing Science-Fiction before specifically looking into the time-travel aspect of such stories.
  • Mohs Scale of Science Fiction Hardness - Writing always has some challenge, but I am not referring to hard/easy difficulty, so much as just how much science you want in your fiction. If you want to explore more scientific concepts, of causality, paradox & relativity, and you’re interested in the mechanics of divergent time-streams and other pseudo-scientific principles, then you’re likely hoping to explore Hard Sci-Fi. However, if you’re not as interested in the science and physics as much as the story and the adventure, the unusual time-periods - dinosaurs and robots - then you’re probably wanting to write something that is Soft Sci-Fi, which means you needn’t stress too hard about figuring out the science-fiction theory - heck, this may not be science-fiction at all! You can have a Fantasy or Science Fantasy story, using magic to travel through time.
But, no matter what story you are dealing with, you will need to work out four things - which I have structured into the easy to remember (and not at all over-engineered) acronym of T.I.M.E. - You will need to determine first Travel, then Ideas, also Mechanics & finally, Extras. So, let us begin with:

Travel

This is a simple question - how, exactly, shall your character travel from one time to another? What is your Time Machine? Of course, not all time-travel requires a machine, but whether by magic or science, there are many and varied possibilities, and each has its fair share of Pros and Cons. So let’s look at a few common ones:
  • Time Portal - This type of time-travel comes in the form of a door, or perhaps a two-dimensional plane of some sort, which the prospective time-traveller simply steps through - although this can occasionally come in the form of a platform that one stands upon, or some form of time-energy projector. This makes the process of time-travel itself relatively easy for the traveller (the time and effort it takes to accumulate whatever energy, alignment or resources the portal requires, notwithstanding), as they can simply step into or through time like you or I walk into a room. Of course, there may be added dangers or safety measures, depending on how you want your portal to work.
    • Pros: One of the benefits of this is that it often means that the person is displaced literally just in time - especially if the portal travels to “itself” - the person steps through the portal, and steps out of the same portal in the same place, but a different time period (although this is not necessary). This is useful not only for travellers to get their bearings, but it means that the Portal cannot be stolen (although, it is possible that it may be taken over). For dramatic purposes, having the portal stay still can add to the tension, because it means that in order to deal with any problems happening in any particular time-period, your traveller must physically remove themselves from the location of the portal in order to go anywhere, which can add tension if they ever want to use the portal to change the period they reside in, or even simply to get back home. Another benefit is that this type of time travel may be “naturally occurring”, which means it doesn’t require a device to work at all - fantastic if you don’t want your main character to be a scientist of some sort. It may be a wormhole, or even simply a “time slip” in a room, a crack in a rock, or an empowered patch of wheat in a field somewhere, removing any need for a time machine inventor, if you wish.
    • Cons: The detriments of these portals, is that they can often have limited control. For instance, with a naturally-occurring time portal, whilst, you may travel through the portal, or back, it means you can only visit two pre-determined time-periods - when you were, and when you end up. Even if the portal is in the control of some “portal device”, it may mean that a traveller is unable to travel to any time before such a portal was invented, as otherwise there will be no portal device on the other side to step through to, meaning it either will not work, or any attempts will cause... dysfunction. Which brings up another issue, can the time portal be opened or closed? Even if the portal doesn’t require a device to “contain” it, this can still mean that if a portal closes after a traveller steps through, they may be stuck in whatever time they just stepped into, with no way back - or, they may even be left at the mercy of those controlling the portal back home to re-open the doorway and allow them back, which may add a ticking-clock element to a time-travel story if they must locate the returning portal at a certain time; or even a certain place, creating a road trip plot where they must get to the new location of the return portal, in order to get back home.
  • The Time Vehicle - This is a moving machine, such as a car, motorcycle, train, boat, space-ship, or some other science-fiction vehicle of your own design. Whatever the vehicle is, it is capable of motion in three-dimensional space (although this may have limits), but also has the ability to move through the fourth-dimension of time, and take any and all occupants aboard with it to this new time-period.
    • Pros: The benefits of a time vehicle are that the vehicle itself is often a Cool Ride, and it can not only be very viscerally exciting for your audience, but it can also lead to many merchandising opportunities on your part (if you’re into that kind of thing). The design of a time vehicle can even be thematically, aesthetically or narratively relevant to your story, like the iconically British phonebox visage of the TARDIS from the BBC’s Doctor Who, or Emmett Brown’s cheap, modified DeLorean, from Back to the Future with its iconic gull-wing doors and many plot-relevant operating issues, or even the classic look of the time-travelling sled from H.G. Wells’ The Time Machine, which is “technically” a vehicle, but cannot be physically moved under its own power. As well, the fact that time vehicles move means that they have an advantage for the user, as they will have transport and perhaps even some protection within their vehicle. Of course, if the machine is a space-ship, then that opens up several more possibilities for potential stories, exploring Space Opera tropes and aliens; but this is true of many forms the vehicle may take, be it a time-travelling tank, a time-travelling racecar or even, dare I suggest, a time-travelling Giant Mecha? This often also includes the benefit that the time traveller usually has more control over their vehicle, and may be free to choose the place and time they wish to travel to, opening up a whole timeline of possibilities for their adventures (although, again, there’s no guarantee).
    • Cons: However, the time vehicle is not without flaws. Namely time vehicles are notoriously difficult to operate, as time travel is often a highly-precise; energy-intensive; resource-heavy or even violent operation, which can lead to dysfunction, malfunction or tragedy if the time traveller isn’t fully versed in the safe operation of the vehicle. This also means that a time vehicle is prone to breaking, meaning that a traveller may be forced to fix the vehicle before they can Get Back to the Future. Also, if your vehicle is too uniquely designed, it may be conspicuous and attract a lot of attention in certain time periods - even if it’s not unique, if a device is taken to a time before that vehicle was invented (such as, taking an aeroplane to medieval times), you may not only confuse and scare the locals but possibly even cause a temporal paradox on sight, and travelling to the future in a machine which is outdated may be ''just'' as conspicuous. Another issue is that if the time machine is a single device which travels with you, then the traveller is at the most risk in the event that their vehicle is commandeered by someone with ill intent, as they will have lost their only means of returning to their domestic time-period.
  • The Time Jumper -This is, simply put, a person who can travel through time without a vehicle or external machine. This may be because they have an internal machine, or a small/wearable device on or within their person, or, this may even be a natural ability that this person or their species has been granted, or was born with. This is often related to teleportation, either allowing the traveller to move through space and time simultaneously, or the traveller may simply be able to teleport, and the time-travel is another, related ability.
    • Pros: This obviously has the benefit that it requires less preparation on the part of the user, they not only do not need to drive a vehicle, but they don’t even have to take a single step, they simply need to activate the ability. It also means that their travel can be more inconspicuous, so long as they travel to a place and time where persons like them existed (although they may have to change their clothing so as to fit in), and don’t do so in the middle of a crowded street. This form of time-travel is also the least susceptible to theft, especially if the ability is natural/biological making theft highly improbable (but not impossible). Also, whilst time travel can be just as difficult no matter the device used, as the time jumper often requires either innate ability or a compact device, the time travel mechanics are usually much simpler or safer to operate, in order to allow for a single person to travel unprotected, and/or for the mechanism itself to be so compact. This also means that they often have a low energy cost and/or resource drain, requiring low - or no - maintenance.
    • Cons: There are, of course, some downsides. Firstly, the fact that the traveller is so exposed means that there are some places which will be much harder, if not impossible to journey to, such as into a warzone, or anywhere with radiation or extreme heat, cold or weather, any place without an immediate ground to stand upon & anywhere lacking atmosphere; and the very instant that the traveller materializes/appears in their chosen time, they are vulnerable to any present dangers. Also, if this is a natural/innate ability, then precision is generally much harder to achieve, meaning that a person may only be able to jump forward or backward several dozen, hundred or thousand years at a time (or, in some cases, they may only be able to make small jumps forward or back a few minutes or hours, depending on the scope of the story). But, even if precision is possible, there’s still the issue that this kind of travel often limits the travelling capacity to ‘one’, meaning that if the traveller makes any friends (or lovers) along the way, or they wish to save someone from their fate/destiny, they probably won’t be able to simply stow them away on their return journey, and thus all problems faced in any time-period must be solved in the present moment (relatively speaking). Also, on the rare but nonetheless possible occasion that such a device does break, it may take some incredibly precise skills and technical efforts to repair, if it’s not entirely impossible to repair at all - especially if this is some innate or biological ability, as depending on its mechanism it may require surgical expertise, physiotherapy, biochemistry or, in some cases, mental or psychiatric care in order to be “repaired”. Also, this form moreso than the others is the most prone to giving the time-traveller no control at all as to when a time jump is initiated, or in which time period they will arrive.
Of course, those are the most common ways. There are some others which occasionally pop up, such as:
  • Mental Time Travel: This is when a person cannot travel physically, and can only take their memories/thoughts with them, and often requires them to possess the body of someone who does physically exist in that time. This may mean that a traveller is confined to their own lifetime, only able to possess the mind of their past or future self; but this sometimes allows the traveller to invade the mind and body of a contemporary of the time they travel to, à la Quantum Leap.
  • The Slow Path: when someone either simply waits for the future to come, or occasionally is placed/imprisoned in stasis or in a time-dilation field for a long period of time, getting to the future that way. This is often the most scientifically accurate form of time-travel, but it limits travel to a one-way trip.
  • Love Transcends Spacetime: This is more common in Soft Sci-Fi, and may result in The Power of Love allowing a time-displaced couple to reunite. It takes many forms, as it is more a magical concept, so I won’t go into explicit detail, except to say that unless you’re writing a Romance, this is a weird choice...
Note: Please do keep in mind, not only are these possibilities not the only possible means of time-travel, but some works combine these together! Consider Doctor Who, the Tardis is technically a time vehicle, but it operates by opening a portal to a Time Vortex. There are also some time portals which exist within a moving vehicle, essentially making the vehicle akin to a time vehicle, even though the vehicle itself doesn’t travel through time. There are also some time-jumpers which can take others with them, meaning that by giving someone a piggy-back, they are effectively turning a single time-jumper into a living time vehicle. The possibilities are literally endless, you simply need to pick a form of travel that suits your story best.

Ideas

So, what can you do when you go back in time? Well, just like the options for the forms of travel itself, the ideas you can explore are also literally endless. But, the concept of time travel has also been around for millennia. One of the earliest time travel stories can even be found in the Mahabharata, an ancient Hindu text first written in 400 BCE, which includes the tale of legendary King Kakudmi who visits Heaven to speak to Brahma, the creator, and returns home to see that “27 chatur-yuga” (roughly 100 million years) have passed, because time moves differently in Heaven. There are also similar stories in Jewish myth and Japanese fairytales, which deal with people traveling into the future after meeting gods or monsters. The point is, we have been exploring time-travel stories for literal ages, so there are quite a few different tropes for, and types of, time-travel stories that already exist. Whilst some people may find it disheartening to learn that there’s nothing new under the sun, this actually can help to inspire stories, by looking at the ways that certain ideas and tropes have been tackled in the past, to see if you want to explore similar concepts, or even attempt to improve on ideas done before. So, let’s have a look at a few common time-travel story ideas, for some potential inspiration...
  • Adventures in the Bible: Someone travels to the past, to experience or re-enact a well-known story from history (often a biblical one, hence the trope name, but not necessarily).
  • Back to the Early Installment: The characters in an established story use time-travel to return to a previous point in that story, such as an earlier chapter, episode, instalment or series.
  • Christmas Every Day: A story where Christmas (or another holiday/special occasion) repeats every day - often used to teach some kind of moral about that day’s importance, but not necessarily.
  • Conqueror from the Future: A conqueror from the future goes back in time to start his conquest in the past.
  • Future Self Reveal: Someone is revealed to be the future version of someone else.
  • Get Back to the Future: Someone gets stuck in the past and has to find their way back.
  • Godwin's Law of Time Travel: Someone tries to change the past, and ends up creating an alternate history where the Nazis won - this is worryingly easy to do in fiction.
  • "Groundhog Day" Loop: Someone - or a group of people - gets stuck repeating the same day.
  • Ominous Message from the Future: Someone from the future send a message back in time, warning that something bad is going to happen.
  • Precrime Arrest: Someone is arrested for a crime they haven't even committed yet.
  • Set Right What Once Went Wrong: Using time travel to undo bad events/consequences from history.
  • Terminator Twosome: Two people go back in time, one to change history and one to stop them.
  • Time Police: People who either outlaw time travel or enforce laws related to time travel.
  • Time-Travel Romance: Falling in love with someone from another time.
  • Trapped in the Past: Someone ends up in the past without knowing how to come back.
  • You Will Be Beethoven: Someone travels to a significant historical event, whereby the historical figure at the centre of that event dies (or never existed) and realizes that in order for the timeline to remain intact, they will have to "be" that person.
In writing your own time-travel stories, you can take inspiration from one of these, several of these, or even none of them, if that’s what you prefer. These are just some tropes, with a few different examples of time-travel related story concepts to give you an idea of the different ways that people have tackled them in the past, and will tackle them in the future. But, if in this present moment these don’t exactly appeal to you, well there are dozens more Time Travel Tropes where that came from, not to mention there are pages listing different ways stories have presented the past, and alternate histories, as well as ways stories have shown the future, and potential destinies, all of which is well worth checking out. The most important thing to remember when exploring these ideas for your story is, once again, you are writing a STORY. Whilst I personally think the idea of travelling to the future and playing the latest videogames using VR future-tech sounds incredibly cool, the vast majority of fiction tends to revolve around some kind of Conflict or Tension, so don’t simply focus on the aspects of time travel which sound really cool, you should also be asking what can go wrong… which brings me neatly to.

Mechanics

By currently known science, with only the exception of travelling forward, slowly (relatively speaking), through time, time-travel is impossible. For this reason, when exploring the concept of time-travel, writers are given a lot of freedom to determine how exactly travelling through time will affect the past, present and future - if at all. Essentially, a Time Machine is the Practice of Time Travel, it’s the act itself; whereas Temporal Mechanics is the Theory of Time Travel, it’s the science/principle behind how it works, and why the Time Machine ended up when it did. So, what are the principles of Temporal Mechanics that must be considered? Well...

Levels of Time-Line Mutability

Can you change time? If so, how? What happens when you do? To answer these questions, there is already a page discussing Temporal Mutability with several examples, but in this guide, I will list them (in order of mutability) with some pros and cons to consider while choosing which suits your story:
  • The Fixed Timeline - In this case, there is one time-line and you cannot change the past, because whatever you did already happened. There is one time-line, and it cannot be changed. You cannot attempt to change the past, as any attempt will either fail outright; appear to succeed, but actually fail to change the timeline in any significant way; or it will succeed... only because it was predestined that someone would (and technically, already has) come back and fixed what you tried to change.
    • Pros: This is light on temporal mechanics, since it requires a perfectly stable time-loop, and deviation from the set path is inherently impossible. It also appears to be the most scientifically consistent form of time-travel, as (in part due to the Anthropic Principle), we’ve only ever experienced time happening one way, so it makes sense that there is only one timeline. It can also be satisfying for the viewer to see, out of order, how exactly you tie up every loose thread of your story to stabilize the timeloop (assuming you DO tie up all the loose threads).
    • Cons: Writing a story that sidesteps paradoxes doesn’t always satisfy reader curiosity. Sure, you avoided the Grandfather Paradox when the grandson’s assassination attempt failed, but that doesn’t actually address the paradox, so it can leave some readers wondering about what might have happened, instead of paying attention to the plot. Similarly, the fact that time is unchangeable brings up issues of why the main characters bothered to travel through time in the first place... you can’t exactly Set Right What Once Went Wrong if the timeline is fixed and unchanging. This often results in plots where ignorance or naivete is the driving force behind most time-travel, which can turn your story into an Idiot Plot. Also, the fixed timeline may evoke the creeping realization that we have no willpower, freedom of choice or hope of escaping our inevitable destiny, which can really bum some viewers out.
  • The Rubber Timeline - In this case, there is one time-line and you cannot change the past, because if you try, the timeline will adjust to correct itself. The name says it all, as much as you try to push against it, it just pushes back. This can take two forms, the rubber ball and the rubber band. To explain them, let’s look at the example of the Grandfather Paradox.
Rubber Ball Timeline
If you go back and kill your grandfather, then time will correct itself by bringing him back to life, so it will bounce back against your change.
Rubber Band Timeline
If you go back and kill your grandfather, then time will heal itself by making someone else be your grandfather, so it will reshape around your change.
Either way, time deals with all changes by either bouncing back towards the original path, or stretching to redirect the timeline back to the original path, no harm done.
  • Pros: This resolves the issue of the Butterfly of Doom, whereby any action taken in the past could have catastrophic consequences, since any minor missteps in the past will be resolved by the time you get back home. Also, this kind of change appears to be giving Time itself a will and perhaps even a personality (perhaps playful, perhaps vindictive), as time itself is acting against your changes to fix it, which can help with the tone of your story. It’s also suitable for Soft Sci-Fi or Fantasy stories, especially if you don’t want to deal with Alternate History.
  • Cons: Just as with the Fixed Timeline, this may bring up daunting questions regarding free will, meaning & hope in a universe with an unchanging future. Also, depending on how characters act in the past, you may need to explain why killing George Washington didn’t change history as we know it, or why we don’t see time bounce back against changes happening in the present. For these reasons, many writers are forced to combine a Rubber Timeline with some other form of timeline, implying that time can change, but only if you do something significant, which is not a point in favour of this kind of timeline, you have to alter its mutability just to make it work.
  • The Brittle Timeline - In this case, there is one time-line and you cannot change the past, because if you try, you might break it. This can follow a lot of the same rules as the fixed timeline, except that if you attempt to change the timeline and create some kind of alternate history or paradoxes, this results in some catastrophe. Perhaps life, the universe & everything will be annihilated; perhaps it leads to an apocalyptic unravelling of space-time; perhaps it will reset the timeline; perhaps you will cease to exist, become Unstuck in Time or die horribly; perhaps it will cause this timeline to change its mutability; or perhaps... well, perhaps it hasn’t happened so far, and we don’t want to risk finding out.
    • Pros: This has all the pros of the fixed timeline that you have stable time loops and avoid paradoxes without the con of predestination paradoxes or loss of free will and choice, since the characters still have agency to choose. But if they make the wrong choice, it might destroy time/life/reality as we know it. Another advantage is that the way the timeline breaks may be interesting to explore. There have even been stories/chapters/episodes which start with time being broken, so as to explore what a world is like with broken time, and challenge the heroes to fix it (or endure its inevitable destruction). This can also set a tense atmosphere for your story, since it means characters won’t travel back in time unless it is worth the extreme risk.
    • Cons: If the destruction of time is too catastrophic, or you reuse the threat of its destruction too many times, then it can lend your characters some Plot Armour, as the audience realizes there’s still so many pages, or so much run-time, left, so obviously the universe has to continue for at least that much longer (although you could be all avant-garde, and end your story by leaving the last half blank after a time-wipe). And if you want your characters to break the fragile timeline during the course of your story, you’ll need to find some way of breaking time that suits your story and doesn’t feel like something you’re making up just so you can get to the next chapter already.
  • The Branching Timeline - In this case, there is one time-line, and you can change the past, but doing so creates a second timeline. This resolves paradoxes by simply saying that any paradoxical events happened in the other timeline. This resolves some issues, but there’s two main ways to have a branching timeline perform, either with the original branches are pruned and left crooked, or the branches split.
Crooked Timeline
any change diverts history in a new direction from the original, effectively leaving it “crooked”, and the only way to return to the original is to go back before the redirect and stop the timeline from changing.
Split Timeline
: any change splits history in half, and the original timeline continues concurrently alongside the new one. In this version, it may be possible to switch between universes (via your Time Machine, or some form of dimension-hopping machine), but even if that is impossible, some writers may simply switch narrative perspective to show how the separate universes unfold.
  • Pros: This kind of timeline resolves the paradoxes by giving you more timeline to work with, and it can create the classic Set Right What Once Went Wrong scenario, as well as give you the chance to explore alternate histories without having to rewrite your story’s canon (unless you want to). Also, if you use the split timeline version, it can create some fascinating stories as well as narrative structures, switching between, especially if you have the two timelines interact somehow - it’s even been used in non-science fiction stories. And if you create several split time-lines, you might even create a Multiverse!
  • Cons: If you create several split time-lines, you might even create a Multiverse. Alternate History can be confusing at the best of times, but Alternate Continuity is almost impossible to wrangle, even with several writers at the helm, and some readers find it overwhelming. But even without a multiverse, the split timeline creates the issue that you still can’t actually change the timeline, since any attempt leaves the timeline as it was, and creates a new, different timeline. Which reality is actually real? And you might need to consider, if a villain changes history, and you go back and stop them, are you actually “repairing history” or simply “creating a third timeline branch in which you won”, effectively leaving behind two branches of reality where you failed.
These are some of the most common in Time-Travel Stories, but there are some forms of time-line which show up, that you might consider, but I include these for the interests of completeness:
  • The Floating Timeline - In this case, there is one time-line, but the past slowly drifts forward to close the gap between the present and the time of publication, often deliberately avoiding using exact dates, even for critical events like Births, Deaths, Marriages, Wars or Catastrophes. This is commonly known as a Sliding Timescale, or Comic Book Time, as it exists due to comicbooks trying to stay “modern” without throwing out the continuity of the past. It’s inevitable in longer-running series that attempt to stay modern, as it takes [Webcomic Time longer to write, create and publish a work of fiction]] than it does to... well, exist.
    • Pros: It means the audience can more easily relate to the characters as they feel contemporary, no matter when you start reading. It also helps to set the tone for a less-realistic story or cartoon, especially for a Long Running Series
    • Cons: It makes literally no sense if you try to understand how the timeline works, and it punishes long-time fans for bothering to remember older publications of your story. Unless you want to attempt to make sense of it all... Also, some attempts to appeal to modern audiences can fall flat.
  • The Wibbly-Wobbly, Timey-Wimey Ball - In this case, there isn’t a timeline, so much as a convoluted ball of spacetime, wherein the mutability of time varies, changing due to factors like inter-temporal traffic, space-time stability or the whims of the writer. This concept was both named by - and exists because of - Doctor Who, a British time-travel show for children which has existed since the 60s, so inevitably the rules of time-travel haven’t been able to stay consistent during all of those writers over all of those years. This concept means that you can utilize the advantages of any and all of the timelines mentioned above, but if you’re not careful, it also means you may fall into the pitfalls of any and all of the disadvantages as well.
    • Pros: This allows for a much more fun, free and adventurous story, as you don’t need to worry too much about timeline consistency - you can use the rules which suit the chapter or episode of your story as you see fit, to make it work. It can fit well into a Soft Sci-Fi or Fantasy story very well, and it can be used for comedy. It also means that if two of the timeline concepts appeal to you, but you can’t decide, you can easily use them both. A timeline may be fixed, until some catastrophic cosmic event causes it to branch apart. Perhaps a timeline is rubbery and self-healing, but if you stretch it too far it branches off into several timelines. Or perhaps the timeline is brittle, but when you accidentally break it, you realize it’s actually been fixed all along and completely unchanging. Or, a timeline could be a branching timeline, but as you split it too far, it weakens reality and becomes brittle. There’s much more freedom to play with concepts, if you don’t want to follow strict rules.
    • Cons: Some readers like Rules. It doesn’t matter if your science device can cause you to create matter out of thin air, or uses perpetual motion machines, oe even magic, some readers are willing to suspend suspension of disbelief so long as the unrealistic effects remain consistent. Similarly, this does work best with a more light-hearted tone. That’s not to say you can’t have darker or more serious stories with a Wibbly-Wobbly Timeball, but if there’s more freedom to affect the flow of time, it might be harder to explain why you can’t go back and stop your mother’s death, whilst you can go back and punch Hitler in the face. But, if you do start trying to explain how this stuff “works”, it can easily degrade into Continuity Porn if you go too far, turning a concept designed to sidestep all this overthinking, and turn it into an exercise in excessive over-rethinking.

Paradox Events

Some of these forms of temporal mutability are designed to avoid paradoxes, since a paradox is, by definition, impossible. But, not all do, and if your timeline is mutable, you may have to consider what exactly happens when paradoxes happen.
WARNING
Paradoxes are by definition impossible, and trying to “understand” how they can “be possible” in certain situations can lead to overthinking, stress, and, in some cases, Writer's Block. Keep in mind the genre, tone & target audience of your work, as it is highly recommended that unless your work needs to figure out paradoxes for the sake of the plot, then breaking your brain trying to explain the inexplicable is a waste of your time and brain-power. If in doubt, remember: this is a story, it’s meant to be enjoyable. So, if you struggle to wrap your head around any of these, maybe consider a timeline or storyline that avoids paradoxes entirely.
There are a few categories of paradox, so for the sake of simplicity, I will focus on the major causal paradoxes.

What is a Causal Paradox?

This category of paradox is simply when causality is interrupted, broken or unbalanced. In reality as we understand it effect follows cause. Things can’t happen, unless we make them happen

To clap your hands: The Cause is swiftly colliding your hands together, the Effect is a loud “smack” sound.

To kick a ball: The Cause is your foot colliding with the ball at speed, the Effect is the ball moving.

This is not only necessary for understanding consequence, but also physics. Newton’s Third Law of Motion states that “For every Action there is an Equal and Opposite Reaction”. Clapping your hands with force results in a soundwave (W) with force equivalent to the clapping force’s kinetic energy (Wk) through the potential energy (Wp) of the medium, in this case air (W = Wp + Wk); Kicking a ball with force 𝑦 results in the ball moving at a speed of (mass x acceleration) equivalent to that force (F=ma). So, Cause not only leads to Effect, it should also equal Effect, at least in the context of “work”. I’m not a physicist (and don’t worry, I’m going to stop with the sciencey/mathsy jargon now), but what matters is that you can’t get something for nothing, as it has to balance out somehow. And more importantly, perhaps just as importantly, an Effect can itself be the Cause of another Effect in a Causal Chain. Line up dominoes and tip the first. This causes the first to collide with the next, with the effect of it tipping over; which causes it to collide with the next, with the effect of tipping that one over; causing it to collide with another, again and again until the last piece falls over in the line. These are the fundamentals of causality. Causal Paradoxes break this rule, by having Effect precede Cause; Effects without Causes or, in some cases, disruption of these fundamental Causal Chains. So, what kind of Paradoxes can result?

Consistency Paradox (or, “Grandfather Paradox”)

This one is the most well-known, but it’s also the most common (and easiest to understand). The example given is always the grandfather. If you go back in time and kill your grandfather before either of your parents are born, then due to the disruption of your ancestry, you can’t be born, and therefore don’t exist. Which begs the question, if you don’t exist... how can you kill your grandfather (what caused that effect)? Now, with apologies to all the nice grandfathers out there, the purpose of this avocide isn’t out of malice, but a thought experiment. But any equivalent action that prevents the Cause after the Effect would be a “grandfather paradox”. If you went back in time, and killed your grandmother, same paradox; if you went back in time and stole the phlebotinum needed to build the time machine, same paradox; if you went back in time and (somehow) sterilized your grandfather, same paradox; if you went back in time and tripped yourself before you stepped into the time machine, same paradox, & even if you went back in time and caused World War III, resulting in the destruction of your native country, meaning that nobody could have been born there, including you… also same paradox. This is the most common paradox as it’s the easiest to fall into by mistake, since if you go back in time “for a reason”, then by resolving the problem you are also removing the need to go back in time in the first place, creating this paradox once again. Consider a common one - Kill Hitler - Adolf Hitler is one of History’s most infamous tyrants and genocidal maniacs, and that has inspired a lot of people to say, if they had a time machine, they would go and kill Hitler. But, if you go back in time and Kill Hitler as a baby… then Hitler doesn’t exist, doesn’t create that history, meaning that by travelling in time, you remove the desire to travel back in time in the first place.

Ontological Paradox (or, “Bootstrap Paradox”)

This one is less well-known, but it does show up in a lot of fictional works (often as a joke). Ontology is a branch of metaphysics that studies the nature of existence and being, and this paradox is effectively caused when something’s existence is illogical. The paradox can be explained like this...

  1. You go to your garage, and discover a time machine there
  2. You go back in time (Adventure Ensues…).
  3. You arrive back at your house, five minutes before you left.
  4. Since you had so much fun, you park the time machine in your garage for you to find.

In this case... where did the time machine come from? A physical object, composed of matter, atoms, mass, and presumably complex circuitry, now exists in this reality, but where did all that matter come from, and why does it exist (hence, ontological). The time machine in Step 1 came from Step 4, but the machine in Step 4 came from Step 1 (following a Causal Chain from Steps 2 and 3). But this gets more complicated, because existence isn’t limited to physical objects, what about energy, or information? What if instead of “discovering a time machine there”, you get a notebook in the mail that says “Time Machine blueprints”. So…

  1. You go to your garage, and discover Time Machine blueprints there
  2. You build the time machine from metal, wiring and Phlebotinum from the local store
  3. You go back in time (Adventure Ensues…)
  4. You arrive back at your house, five minutes before you left.
  5. Since you had so much fun, you copy the instructions to build a time machine in a notebook that says “Time Machine blueprints” in your garage for you to find.

It’s a perfect time loop... but that’s the problem. Who invented the time machine? Sure, all the matter is accounted for, but where did the idea come from? Remember, you can’t get something for nothing, so how can you learn something (especially something as complex as time-machine construction), without it ever being discovered? This kind of paradox is also known as a Causal Loop, since it has no definitive starting cause in the loop of recurrent events, implying that “the loop caused itself”. Causal Loops apply to any effect without a definitive cause, not just ideas for inventing time machines. A lot of works of fiction use this as a joke, where some famous quote, lesson, song, joke or concept gets explained to the “creator” by the time traveller. But, if the time traveller learnt it because it was passed down through culture over time by the creator, and the creator learned it because the time-traveller told them… who learnt it first?

Predestination Paradox Is this even a thing?

Extras

So, as I’ve explained here, there’s a lot that can be done with time-travel stories, based on how it works. But, you might still want a bit more information about Time-Travel. So, I have a few more resources, as well as a glossary of common and useful terms, in regards to time travel.

Glossary

  • Closed Timelike Curve: In theoretical physics, a closed timelike curve is a stable model of reality (which can be represented with Lorentzian manifolds and spacetime embedding diagrams), which would allow spacetime to curve back on itself, allowing travel backwards in time. Whilst it is entirely theoretical, it can be a good starting point for either research, or technobabble, for writers looking for plausible time-travel science.
  • Fermi Paradox: The discrepancy between the high potential for the existence of aliens, compared with the rarity of evidence for aliens. Often expressed simply as "if aliens exist, why haven't we found any yet?". Whilst Enrico Fermi initially used this to refer to the possibility of alien life, the same paradox holds true for time travel. Namely, "if time travel where possible, where are all the time travel tourists?"
  • Imaginary Time: This is a mathematical representation of time in special relativity, which posits the existence of a temporal dimension which runs perpendicular to time, as we experience it, effectively creating two-dimensional time (note: this goes deep down the quantum mechanics rabbithole, so it may be a bit advanced if you're not an advanced physics student).
  • Novikov Self-Consistency Principle: This is a principle which asserts that temporal paradoxes are impossible. It was proposed by Russian physicist Igor Dmitriyevich Novikov. In all honesty, whilst he wrote a book about the subject of "closed timelike curves", this principle was little more than his opinion, but it sounds good for technobabble.
  • Ontological: Regarding one's being, or existence. As existence is often referred to as temporal, time travel has the potential for bringing up ontological dilemmas.
  • Paradox: A statement, instance, or scenario, which either contradicts itself, or is inconsistent with the fundamental laws of logic.
  • Retrocausality: Relating to a cause which comes after its effect.
  • San Dimas Time: An arbitrary, or artificial, sense of urgency during a time travel story, despite the fact that the ability to time travel would render any deadline ineffective (may be justifiable, depending on the temporal mechanics of a story).
  • Trouble with Tenses: in a world whenin time is traversable, it may become necessary to develop new language to refer to one's position, origin and destination in spacetime. Some examples of potentially useful new words include… ** Elsewhen - At a time different from the one being experienced or referred to (the temporal equivalent of "elsewhere")
    • Everywhen - To exist throughout all time, (the temporal equivalent of "everywhere").
    • Nowhen - To not exist in time, at all (the temporal equivalent of "nowhere").
    • Precedent - An instance of something, or someone, from an earlier time; past version; antecedent; precursor.
    • Subsequent - An instance of something, or someone, from an earlier time; future version; consequent; resultant.
    • Somewhen - At some unknown or unspecific time (the temporal equivalent of "somewhere").
    • Whenabouts - The time someone, or something, is generally occupying (the temporal equivalent of "whereabouts").

Alternative Title(s): Time Travel Tales

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