I've got a general outline for a campaign that deals heavily with time travel. Using Gynosphinx as the mechanic. Any sci-fi fan knows time travel is a slippery slope at best so I'm wondering if anyone has experience with time travel in a campaign and what was good/bad about it. How you dealt with paradoxes in the time line, or if you went with the approach that the universe corrects itself within certain bounds?

What do you need it to be? 

There are different types of time travel you can choose from. The least complicated one is parallel time lines, in my opinion. The time travelers simply create a new one and if they return, come back to their own. 

A self correcting timeline is second safest. You can just handwave any paradoxes away. 

You can raise the stakes by persistent changes that alter the only timeline, possibly eliminating the player characters if they prevent their own births.

Looper had an interesting approach, but I'm not sure if you can recreate that in-game. 

The game also changes depending on how far the time jumps will be. It will be less complicated if you jump centuries, as the immediate impact lessens.

Short time jumps may interfere with events you just ran earlier in the same campaign, or even the same session. 

I've only ever seen time travel dealt with well twice in sci-fi. And no, I'm not kidding with that number... in like 40 years of reading sci-fi, watching sci-fi movies and TV shows, etc... I've only seen it dealt with well two times that I can remember (might be forgetting one or two, but I doubt it).

The first time was in the 1980 movie The Final Countdown, starring Kirk Douglass and Martin Sheen. The premise of that movie is that the 1980s aircraft carrier USS Nimitz went back to the day before Pearl Harbor and had a chance to stop that attack from happening. Time travel in that movie was a closed loop. That is, everything that had happened, still happened, and it led to the NImitz going back in time. i.e., in the end, nothing changed. I will not say any more since that's already too many spoilers and if you have not seen the movie, and like time travel, it is 100% worth a watch. Best time travel movie ever, IMO.

The second time was the 1985 book The Proteus Operation by James P. Hogan, who was a nuclear physicist. This is probably my favorite way to do time travel -- Final Countdown's way is much more mind-bendy, but harder to deal with narratively, especially in an RPG with other players. Hogan's premise was the now so-called "many-worlds" interpretation of quantum mechanics (it was relatively new back then). According to the rules of his book, you can time travel into the past, but not into your own past. The act of going back in time creates an alternative universe in which you appear from the future, but this happens in that universe not your own past. When you return to your present, your universe remains unchanged relative to its own past. In that book, Americans from an alternate world in which the Nazis won WW II because the US did not get involved until it was too late, came back to our past to try and stop it from happening here (knowing their own world was effed).

Now, I like the 2nd version better, but I'm not sure it works well for a fantasy setting. D&D settings usually have other planes, but "alternate nearly-identical earths" is not the kind of thing one usually sees in fantasy. I am aware that D&D kind of has this baked in (that the Prime Material Plane includes all these alternate worlds like Eberron, Toril, Oerth, and whatnot). But usually one moves among those worlds without traveling in time. And they are much more different from "alternate earths" as usually depicted in a book like The Proteus Operation.

Not sure if any of this helps... But when I've run time travel (never in D&D, always in Champions), I've always used what I call the "Hogan Hypothesis," that you can't go back in time to your own world.

The best examples of the two types of time travel can be found in JJ Abrams' Star Trek, and in Harry Potter.

Type 1: Allows for paradoxes through changes made to the time stream resulting in offshoot parallel timelines. Nero goes back in time and kills Kirk's dad, changing the trajectory of history and resulting in the timeline that all the new Star Trek movies takes place in.

Type 2: Does not allow for paradox. You cannot go back in time to change something, rather if you go back in time, the effects of your journey will have been felt the first time around (whether or not you realize it at the time). Harry Potter is often criticized for including Time Turners, which most people consider a plot hole, but the way they're depicted in the books are pretty solidly Type 2. In book 3, they don't go back in time and undo Buckbeak's death, rather they go back in time and enable his escape, which he'd done already and the thud of the axe they thought they'd heard was just the executioner hitting a fence post in frustration. Hermione uses the time turner all year not to go back in time to take classes she missed the first time, but rather to have more time to take both classes and be in two places at once. It implies that terrible things happen to people who try to meddle with established events, and that they're never successful because timelines cannot be changed (ignore Cursed Child).

I'm actually currently DMing a campaign where the main villain is from an alternate future and is trying to make himself a god by creating paradoxes between the Prime and alternate timelines and then feeding on all the "paradox energy" leftover from the Prime timeline. The campaign takes place in the alternate timeline, so I basically developed the plot based on the villain having foreknowledge of everything that's going to happen in the next 15 years, and using that knowledge to sew chaos and death. He maneuvered himself into a position of power where he could pull strings from behind the scenes, he used his power to extend a brief skirmish between two nations into a full-blown war, he uncovered some powerful artifacts and weapons that hadn't been discovered yet in the alt timeline, and he manipulated the player character's lives secretly so they wouldn't grow into the people he knew them as in his home timeline (when he was a fellow hero in their party). For the last part I had to be careful to pull that off without taking any backstory choices away from my players (big no-no), but instead I looked for points where a single change could've sent the character down a completely different path. So for example, in the game, our fighter's childhood sweetheart (who she'd been promised to, since both their families were prominent nobles) was murdered by his brother for control of the family business. The fighter was forced to marry the evil brother, but she escaped just after the ceremony and began her adventuring career. That's what happened in the alternate timeline that the game takes place in, so I figured the big difference there is what if in the old Prime timeline, her sweetheart never died and they became adventurers together and eventually settled down and raised a family? When that character found out that there was a version of her that had gotten that happily ever after and been cheated out of it by the main villain (who'd encouraged the evil brother to act by promising him a contract to supply the kingdom weapons for the war, a deal the good brother would never have taken), hoo boy was that character invested in taking the BBEG down. 

Basically, time travel can give you a lot of great opportunities to work in player backstory and give great roleplay opportunities. Characters can have one last conversation with dead loved ones, they can get closure on a regret for seeing how things might have been, or they can feel pain for what they'd lost and never even known.  You can get all kinds of twisty and is great for big dramatic reveals or cliffhangers. Like any element of fiction, yes, you can work it into your DND game. 

I always think that time travel is just inherently paradoxical. And generally when you are reading/watching something with a time travel component, if you think about it, you are overthinking it. 
For D&D, I’d say just pick a method, stick with it, and go for the ride. No matter which one you choose, there will be logical inconsistencies. Accept that fact, tell your players you understand that, but these are the time travel rules you are going with, and that they shouldn’t think about it too much. 

Awesome! Thank you for your input folks! Thanks for the book and movie recommendations as well. I never saw the movie, but I the book sounds very familiar. I think I may have read it years ago. I'll have to give it a re-read.

I'm am familiar with the theories you all put out there. I recently read a book by Douglas E Richards. It was the second in The Enigma Cube series where he deals with time travel a different way. First that there aren't any alternate timelines, no alternate universes created by paradox. There's one time line and that's it. Basically the universe doesn't care about paradoxes and will kind of self correct in the event of someone, or something trying to change something big. I won't give details from the book in case someone wants to read them (They're well written and a fun read!) But basically if you try to change something big, like an event that was witnessed by thousands the universe would basically get in your way, and even though you may think you're taking actions that will change it, that's not the case and the event will happen anyway. However you can nudge it a bit. You can make some changes and the universe will figure out a way to fit them in. 

I'm not sure I'm explaining it so well but it's kind of like a river that will always flow to the sea. The sea is a major event that can't be changed, however the river can be diverted along the way. The new path it takes spawns new event but ultimately it still makes it to the river.

I guess that's pretty close to Acount256's second option.

I think this would probably be the easiest to deal with. The set-up is that something devastating is ABOUT to happen. Seers have seen it, the gods have spoken, whatever, but it's accepted by all that it's coming. Yet it hasn't happened yet. So this way changing the timeline is only changing the perceived future. Like the case of the executioners ax on the log. It was only perceived that Buckbead was dead.

I'm also thinking that the adventurers will have to travel back over fairly long periods of time. Giving less of a chance of interring with short term history as it's known.

AT least that's how I'm thinking of it at the moment, but mapping out even the basics of the plot line are giving me headache :) LOL

The Final Countdown is basically type 2. Again, worth a watch if you haven't seen it.

Before the worldwide shutdown happened, I DMed a spelljammer game that on the last session we did got utterly destroyed by time travel. They met a time traveler, stole his time-manipulating devices, and broke them, ate them, and just got absolutely scattered across Realmspace. One of them got sent back in time 10,000 years, another into the future 30ish years, another got stranded on an asteroid during the Spellplague, so they couldn't use their spelljamming helm, because the magic stopped working.

We unfortunately can't fix it until after the lockdown ends, but they were going to be put back together. 

So, don't do it how I did. If you want to do time travel, either do a simplified version using Chronurgists, or give them complete control over time travel, letting them travel together as a group. This will help you avoid paradoxes and allow you to have control over the power the players have. 

Nothing destroys the campaign more than time travel or the Deck of Many Things. 

Hmm, good points. I wasn't going to give the players any direct control over time travel. They would be using a gynosphinx in it's lair as the mechanic. So I would be able to keep a leash on them, so to say, having to go through a NPC. 

I know  time travel certainly has the ability to break the campaign and, honestly, I don't know if I can even pull it off. I do find it intriguing and difficult as a challenge so it makes me want to try even more :)

Quote from BTI_Brian >>

 

I think this would probably be the easiest to deal with. The set-up is that something devastating is ABOUT to happen. Seers have seen it, the gods have spoken, whatever, but it's accepted by all that it's coming. Yet it hasn't happened yet. So this way changing the timeline is only changing the perceived future. Like the case of the executioners ax on the log. It was only perceived that Buckbead was dead.

I'm also thinking that the adventurers will have to travel back over fairly long periods of time. Giving less of a chance of interring with short term history as it's known.

AT least that's how I'm thinking of it at the moment, but mapping out even the basics of the plot line are giving me headache :) LOL

 In this instance, where players are going back in time to stop an impending crisis, that should actually be fairly straightforward. Say the players have to accomplish something in three different era's before returning to the present to see if it worked/defeat the villain, then despite the fact that you started in the present and are ending there, you can feel free to treat the story itself as fairly linear time, since most of the action is taking place in the past. Maybe at the beginning you can set up some signposts for things that can be changed while they're back; legends of lost treasure, historic defeats, etc that the players may have the option to change like a sidequest (and when they return to the present maybe the descendants of the ancient hero they saved are ready and waiting to help fight), but other than that being an optional thing if you want to include it, you don't need to bend over backwards with weird time stuff. 

In this instance, I'd treat it more of like an inter-planar campaign, where you focus on exotic locations and NPC's, treating the different eras you go to more as locations rather than time periods. Then, if you want, you can decide how the player's actions there might have impacted history and show it for flavor when the players get back to the present. 

It is certainly rewarding to do it correctly. It became a huge mess. I could explain the circumstances more if you would like more info, but there's nothing like splitting the party across different time lines. I had to separate the players, discuss what they were doing in their new setting one on one based on what time they were sent to. They're still not stitched back together, but I'm working on it. It's hard when your players fail a lot of intelligence (arcana) checks, don't cast identify, and then swallow a time crystal. It breaks games really quickly.

The best way to keep time travel from breaking the game is railroading, which I typically don't like doing, but if they get to time travel, they normally don't care if it's railroady. 

@Levirocks "It's hard when your players fail a lot of intelligence (arcana) checks, don't cast identify," Just this is enough to break a game, lol, never mind the time piece.

@CharlesThePlant I like the idea of thinking of it as inter-planar. Not that it really changes anything about the campaign but for some reason it's easier to think about. My brain can digest it easier :)

So now I need to fill in the plot about some specific things that need to be changed, what repercussions they will have and how it leads to the solution, and come up with several alternatives for each scenario for when the players do something totally different than what I have planned, haha!

There is actually an official rule for time travel, in a 2nd edition book <Netheril - Empire of Magic>.