Idea about introducing mostly paradox free time travel, how to treat it.

[MonkeySage]

I had the idea that I wanted to introduce time travel(fully prepared for the complications involved) to a campaign. The setting in question already has a deity capable of facilitating time travel both forwards and backwards, one given special dominion and responsibility by the setting's overgod.

So, I had the idea that it could be treated as a form of interplanar travel.

1. Whenever a new time portal is opened, a new plane is created, and exists simultaneously alongside the "present" plane.

2. If a time portal is created to the "past", small changes made there have small effects on the "present" plane.

3. Larger changes, such as the death of a character native to the "past" cause larger changes to the "present" plane.

4. With some exceptions, time travelers are immune to changes made to their home time, and can remember how it was before it was changed. Exception being if their past self/ancestor is killed, their present self will be manually removed by a "cleaner" under the employ of the time god. Fellow time travelers are not affected, and remember the person, unless the cleaner manually wipes those memories.

5. The reason that the present plane is changed is that it is replaced by a new one, through the same process that creates a "past" plane. Since time travelers are outside that plane at the time it's replaced, their memories are not affected, and they're usually unharmed.

6. All of the above rules apply to traveling into the future as well.

7. The time god is the final arbiter in everything dealing with time travel, and normally does not allow it to happen. All time portals are preordained, a time traveler can pick which portal to go into, but can't pick when exactly the portal leads. If they mess up in the past, they have to deal with the mistake; once it's made, it can't be undone.

From here, i'm open to suggestions. I figured time travel wouldn't be as much of a headache if I didn't have to deal with temporal paradoxes, and by treating time travel the same as planar travel, I hoped it might remove that issue entirely. For the most part, this kind of time travel seems paradox free.

Major influences here are Doctor Who, Chrono Trigger, and Dragon Ball Z.

[icefractal]

I think you've still got paradoxes, as long as the past planes affect the present one. If you go with a "many worlds" version (traveling to the past creates a whole new parallel timeline, having no effect on your own timeline) then you do avoid paradoxes, IIRC.

If time travel is limited to specific portals, that does limit the paradoxes - there may still be some however. You'd still have the issue of people being able to create instant armies if they had allies. For example:
1) Bob busts into the HQ of a demon cult. "Stop that ritual right now!"
2) Demon Cult: "You and what army?"
3) Bob teleports away, goes to a portal in the past.
4) In the past, Bob meets up with his allies and arranges for an army to be present at the time and place he'll be going to confront the cult in 50 years.
5) Bob travels back to the present, teleports back to the cult. "This one!"
6) Army that was arranged for 50 years ago steps out of concealment.

[MonkeySage]

Hmm...
How bout this?

Player goes into the past, about 100 years. They plant a seed in a place that in their own time line has no trees.
Player came from World 1, and traveled into the past of World 2.
Because of their actions in World 2, Rionis(Time god) simply deletes World 1 and everything within it. Once player returns to the present, it's actually world 2's future.
They find trees where they planted their seed.
Since World 1 was deleted and not simply overwritten, Player remembers having stood in that location in their own(now deleted) time line, and not seeing any trees.

[Red Fel]

Since World 1 was deleted and not simply overwritten, Player remembers having stood in that location in their own(now deleted) time line, and not seeing any trees.

Closed loop paradox. Why would they have gone back to plant the seed if there were always trees there?

Misunderstood. Yes, okay, these PCs remember the other time. Does anybody else, or do only the displaced PCs remember?

And if their world was deleted, does this new present have alternative versions of them who remember trees always being there?

[MonkeySage]

Only the displaced characters remember.



And if their world was deleted, does this new present have alternative versions of them who remember trees always being there?

Lol, yeah I just now thought about that. I suspect... maybe the cleaners clear this up? ^_^ Or perhaps, the time traveling characters fuse with their alts upon reentry.

Maybe the cleaners facilitate said fusion? :)

[Red Fel]

Lol, yeah I just now thought about that. I suspect... maybe the cleaners clear this up? ^_^ Or perhaps, the time traveling characters fuse with their alts upon reentry.

Maybe the cleaners facilitate said fusion? :)

The problem with the fusion concept depends upon how common time travel is, and also how the fusion accounts for discrepancies.

With regard to the first point: If time travel is common, then just about everybody who travels will remember the world being different, creating a multitude of alternate histories that nobody remembers but me, which will drive people pretty crazy.

With regard to the second point: If you fuse traveler!you with new!you, what survives and what vanishes? Suppose traveler!you was hit by a Helm of Reverse Alignment or similar effect - what happens to the fused result? Suppose traveler!you had his arm cut off while traveling; does the fused result have the arm back, because new!you never went back in time and thus never lost his arm?

And let's look at another paradox element. Suppose the change you made was enough to prevent you from being born. Traveler!you is wiped by cleaners, as you say. But if you never existed, then you never went back in time to create the new timeline without you in it. The event creating this new timeline never actually happened. How is that resolved?

[MonkeySage]

I'll go ahead and address these point by point, since this is actually helping a lot.

For point 1: Time travel is very tightly regulated by Rionis, as final arbiter. Rionis only allows time travel in very special circumstances, and as a result time travelers are exceptionally rare. Not even a wish or miracle can allow time travel to a degree this extreme, and only those with Rionis's blessing can even see the portals, let alone passing through them.


With regard to the second point: If you fuse traveler!you with new!you, what survives and what vanishes? Suppose traveler!you was hit by a Helm of Reverse Alignment or similar effect - what happens to the fused result? Suppose traveler!you had his arm cut off while traveling; does the fused result have the arm back, because new!you never went back in time and thus never lost his arm?

Fused!player is a combination of both new and traveler, but traveler is dominant regarding memory. Fused!player has the memories of both, but remembers the traveler's timeline more strongly, realizing that the world around them is a direct result of their actions. Physically speaking, the new!player's body is dominant.

For the most part, this could be handled on a "which ever makes the most sense at the time" basis, I hope.


And let's look at another paradox element. Suppose the change you made was enough to prevent you from being born. Traveler!you is wiped by cleaners, as you say. But if you never existed, then you never went back in time to create the new timeline without you in it. The event creating this new timeline never actually happened. How is that resolved?

The world created by the traveler would continue to exist, because the cleaners don't go back into the traveler's past, they're still bound by the rules that Rionis set for them. They would simply erase the most current version of the traveler(from the travelers perspective), and anyone who came into contact with them before they were erased would still remember them unless those memories are wiped manually.

The New Present doesn't exist until either it happens, or the travelers go though the present portal.


Lastly... Say, players went back to monday at 1pm. If they stay till Tuesday at noon, then the past portal will take them back to tuesday at noon whenever they decide to come back. They can never go back to monday at 1pm, unless Rionis himself creates a new portal. Hence the rule that whatever mistakes they make can't be undone.

[veti]

I've never liked the "alternate universes" model of time travel. To me it feels like cheating. And as you've noted, it doesn't really clear up all the paradoxes - you still need the intervention of "cleaners".

I have a simpler attitude to time travel: You Can't Change Recorded History.

Unrecorded history? Go nuts. If no-one in your own time really knows what happened to this NPC, you can do what you like with them, up to and including bringing them back to the future with you. (See "Clayton, Clara".) This applies even if the truth will leave plenty of evidence, such as a DeLorean parked in a mine in 1885 - so long as nobody contemporary has noticed that evidence between the time it was planted and when you left your own time. (Or maybe they have, but you don't know about it. Which means, by inference, that it hasn't had a major effect on anything, or if it has, then the causes of that effect were unclear to you. Until you put them there. And possibly even afterwards.)

That means, by definition, you can't change anything that you knew about before you travelled back. Those things are going to happen, and nothing you can do will stop that. (You can facilitate, or even initiate, those things. But any attempt by you to prevent them will be railroaded into impotence, by any means necessary.)

It's the Terminator loop, and I love it for its simple elegance. In an RPG it might involve railroading, but the railroading concerned would be completely justified.

[Sith_Happens]

5. The reason that the present plane is changed is that it is replaced by a new one, through the same process that creates a "past" plane. Since time travelers are outside that plane at the time it's replaced, their memories are not affected, and they're usually unharmed.

Congratulations, you've just taken all of the usual problems of time travel and added the transporter problem (http://skepticalphilosopher.blogspot.com/2009/07/consciousness-sci-fi-transportation.html). If your "present"/"home plane" has been overwritten in its entirety by a new version due to a change you made to the "past," does that mean you've just murdered all of existence?


If time travel is limited to specific portals, that does limit the paradoxes - there may still be some however. You'd still have the issue of people being able to create instant armies if they had allies. For example:
1) Bob busts into the HQ of a demon cult. "Stop that ritual right now!"
2) Demon Cult: "You and what army?"
3) Bob teleports away, goes to a portal in the past.
4) In the past, Bob meets up with his allies and arranges for an army to be present at the time and place he'll be going to confront the cult in 50 years.
5) Bob travels back to the present, teleports back to the cult. "This one!"
6) Army that was arranged for 50 years ago steps out of concealment.

That's not a paradox.


I have a simpler attitude to time travel: You Can't Change Recorded History.

Unrecorded history? Go nuts. If no-one in your own time really knows what happened to this NPC, you can do what you like with them, up to and including bringing them back to the future with you. (See "Clayton, Clara".) This applies even if the truth will leave plenty of evidence, such as a DeLorean parked in a mine in 1885 - so long as nobody contemporary has noticed that evidence between the time it was planted and when you left your own time. (Or maybe they have, but you don't know about it. Which means, by inference, that it hasn't had a major effect on anything, or if it has, then the causes of that effect were unclear to you. Until you put them there. And possibly even afterwards.)

That means, by definition, you can't change anything that you knew about before you travelled back. Those things are going to happen, and nothing you can do will stop that. (You can facilitate, or even initiate, those things. But any attempt by you to prevent them will be railroaded into impotence, by any means necessary.)

It's the Terminator loop, and I love it for its simple elegance. In an RPG it might involve railroading, but the railroading concerned would be completely justified.

This is the same stance that Doctor Who and many other works take, up until the point of what happens if you try to change something "recorded." Rather than making it impossible to do so in the first place, they have it so that some form of Bad Stuff starts happening to you and doesn't stop until you go back again and undo what you did.

...Actually, thinking about it I supposed the rule in question is in fact different. By your explanation it matters if anyone knows what "originally" happened, while in most fiction with similar time travel mechanics it only matters if the time traveler knows what "originally" happened. The short version is, as long as you don't change your subjective past everything's fine.

[MonkeySage]

Congratulations, you've just taken all of the usual problems of time travel and added the transporter problem. If your "present"/"home plane" has been overwritten in its entirety by a new version due to a change you made to the "past," does that mean you've just murdered all of existence?

Hehe, kind of makes it an ethical question, doesn't it?

Yes, if a player's actions save one future, they necessarily destroy another one. Let's say that John's parents are Jewish holocaust refugee and a British soldier. If you go back and prevent Hitler from coming to power, and in so doing prevent the holocaust, John will be erased, along with the world he was born into. You've erased a whole ton of people who could have been, but saved countless lives in the process.

This was actually something I thought about, and in some ways it's intentional. The time traveler is the only one aware of this, once they come to realize it.


Technically, Rionis(who is true neutral) is the Chronicler, his primary function(when there aren't time travelers running around) is to record history as it happens, and his entire religion has a policy regarding interference. Record history, don't make yourself a part of it. That's the rule that his clergy live by. This is also part of why he, more than any other being in the multiverse, hates time travelers. And this disposition is why there are so few of them; he almost never grants access to time travel, and when he does it is very limited.

[veti]

Hehe, kind of makes it an ethical question, doesn't it?

Yes, if a player's actions save one future, they necessarily destroy another one. Let's say that John's parents are Jewish holocaust refugee and a British soldier. If you go back and prevent Hitler from coming to power, and in so doing prevent the holocaust, John will be erased, along with the world he was born into. You've erased a whole ton of people who could have been, but saved countless lives in the process.

Except that you haven't. Both timelines still "exist", in so far as they ever "existed" in the first place. All those people who died in the original timeline still died. The only difference is that the time traveller, and the time traveller only, has moved to a different timeline.

That's what I mean by "cheating". You can pat yourself on the back for having achieved some mighty force for good, but in fact all you've done is stick your fingers in your ears and sing "lalalalala" as evil goes on, but without touching you.

[Thrudd]

You can simplify a bit, you don't need the cleaners or erasing timelines.
Whenever you change something in the past, you create a new timeline/dimension. The native present of the traveler is not affected. Therefore you can't change your own past. You can create a parallel dimension where your parallel self has a different future (or where you don't exist if you kill yourself in the past). But the original traveler still exists, and the original timeline still exists.

The time regulating deity would need to monitor the creation of and travel to these different timelines, maybe there's a limit on how many timelines there can be before the system becomes unstable.

[MonkeySage]

Thanks to your help, everyone, I believe I've come to something I'm happy with. I'm not totally scrapping the many worlds idea, because to an extent it is a useful way to handle time travel in a d&d game. I'm not using many worlds, but I will borrow ideas from it. Main things I want to accomplish are these: History can be rewritten, to a limited degree. The traveler is largely unaffected, except in special circumstances. Paradoxes sort of work themselves out if they aren't too big, for instance the time travelling arborist still remembers when there was no forest, even after returning to his own time and seeing that now there is a forest. If the arborist brought friends along with him, and takes an action that threatens his own existence, his friends will remember him, and might be able to fix his mistake from that point, saving him.

Once again, Rionis is the final arbiter, and still maintains the job of keeping things running smoothly.

So, now that I'm sort of happy with the result(and it will be improved upon later), I need to figure out how i'm going to introduce it in game. My player already knows that the game will involve time travel in some way. I'll probably make a new thread for that.