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I'm a bit stuck here and I could use a bit of help. First of all, I'm not sure how to correctly describe the problem, so pardon me if some part of it seems unclear.

Imagine such a scenario:

• A player discovers/creates a world that allows for a time travel.
• For the sake of clarity, the time in this world moves in exactly same pace as outside, in objective reality.
  
• A player steps in, thus leaving the objective reality and the rest of his group behind.
  
• He undergoes a time travel, moving, let's say, 10 years to the past.
• He spends a year or so in the past.
• He steps outside of his world, back to the objective reality. Important thing (and the major reason behind this post) is that he DOESN'T use time travel to come back to the starting of his voyage. He exists his world in its past.
  

The question is where, or rather WHEN in objective reality he arrives?

The possibilities:

1. In objective reality's past, more precisely 10 years "ago" + 1 year he spent in his world's past. This makes it 9 years earlier than he stepped into his world and did time travel.

The problem here is results cause & effect paradox - one player is now in the past, while the rest of the party in the future, so whatever he does, will have repercussions in their timestream.

2. The objective reality is partially impervious to player's actions: he arrives at the moment he stepped into his world +1 year he spent in its past.

Now we have a huge hole in continuity: what if someone entered player's world, while the player was "away"? His actions might erase that certain time branch with all beings "inside". Also, what happens with beings native to this world, that stepped outside of it the moment player was gone? Let's say he killed them in his past - do they disappear from the objective reality as well?

3. In exact same point he pressed DO THE TIME TRAVEL button (so to speak), only now his world changed accordingly to his actions in its past.

Aka the laziest but also the least troublesome solution (from the perspective of the GM). The only problem here is very unlikely scenario of other time-travelers, each producing his own, a bit different local timestream, but it's not gonna happen as far as I'm concerned.

4. Other time?

Thoughts, opinions, suggestions?

Time travel plays a significant role in my campaign; of my two groups, the cousin of the lead PC in one group is not only the world's greatest temporal mage, but plays "time cop" a fair bit.  

In the second, the group's just recently bipped ten months into the past, and are doing their level best to keep an extremely low profile, far from home, and live off their own resources in the meantime.  One wrinkle is that the city they've picked to work and study in is the home base of the aforementioned WGTM, and three of the principals are known to him; they're trying very hard to avoid his notice, out of (probably not misplaced) fear that he's just going to sequester them to prevent any paradoxes.

Anyway, a couple of thoughts:

How time works is entirely up to you.  You can always declare that:

(1)  Time is very difficult to change, and if the player decides to off the Future Great War Hero, someone takes her place and does pretty much the things she would have done;

(2) the "Observer Effect" is in place, and the player can't change anything that he's observed to be a fact in his normal time.  The Future Great War Hero is a known quantity; the player fought in her army, and was a spectator at her victory parade.  She exists and he can't erase her;

(3) Changing the past doesn't alter the player's baseline reality; it just breaks off a new probability and a new timeline.  If he lives his life forward in this timeline, the future won't be what he thinks it ought to be.

(4) There are entities out there, of vast power, whose appointed task (self- or not) is to prevent people from screwing with Time.  Their scrying powers have detected the player, and they are out to kill him, wring dry his secrets, erase his mind and send him back to his correct time, or imprison him so he can't harm the timestream.

I'm running a game now that may have some emergent time travel -- the missus is a Dr Who (I mean David Tennant) fan. I'll be watching this thread with interest.

Depends if you run a deterministic universe, in that:

Determinism is the philosophical position that for every event, including human interactions, there exist conditions that could cause no other event. "There are many determinisms, depending on what pre-conditions are considered to be determinative of an event or action."

https://en.wikipedia.org/wiki/Determinism

So that details might change, but overall events won't. Go back far enough, effect an enormous amount of actions/events, and the time stream might change, the consequences still might not be known, however.

Unless I'm running a game about time travel and messing up history, I use Ravenswing's system 3) above. That is, there are many (infinite) possible unfoldings of the universe, and time travel (when/if possible) is about visiting a different thread of cause & effect, which has no cause & effect on other threads, except if the person somehow returns to the thread he came from, and in that case the only effect is in terms of any interesting information (or possibly objects) he might have brought with him, but even future information is just a possibility, not anything you can count on. In fact, traveling in time may bring someone to a VERY different world situation, because it's not just "egocentric time travel".

Unless the point is to deal with paradoxes and history alteration, though, I tend to dislike time travel with one history thread, because of how much destruction that inflicts upon story, continuity, free will, self-determination, etc. In other words, if there is an interesting plot where people are struggling with cause & effect, but that can all be made to "never have happened" because some jerk does time travel to a point before then and changes everything, then I find that about as annoying as authors who drag me though a huge plot and then say "but it was all a dream and never happened". My reaction tends to be "so why the heck did I care or bother to read all that" or as a player "why the heck did I bother playing and trying to achieve anything, if the whole world can be transformed by random people doing time travel".

If the point IS to be about changing worlds and history, then ok, but it makes for ego trips, and still gets undercut if anyone else travels in time. It seems like paradoxical BS and/or playing as gods. Unless you can eradicate all possibility of anyone else on the whole universe's timeline also going and undoing whatever you do, it makes it seem to me equally pointless to try to accomplish much. It also begs the question of what the narrative timeline is in relation to the universe's timelines, and how many of those there are, and which ones affect which other ones.

GURPS Time Travel is a good source for organizing thoughts around such issues.

Scratching head... :hmm:

Guys, I appreciate the input, I really do. It's just that it seems that I made a poor job at explaining what I actually need - your answers, while certainlu useful and applicable, deal with the problem of timetravel itself, while I'm already past that stage. It's already done, timetravel exists, I'm simply struggling with the challenge of proper synchronization between "local" and "objective" time, and possible hardships it brings.

Sorry, the blame is on me. :duh:

Both would be objective, you just need to pick which would be dominant.

If you're familiar with Chrono Trigger and Chrono Cross, this (https://www.chronocompendium.com/Term/Principles_of_Time_and_Dimensional_Travel.html) may prove useful reading.

A) The assumption that one world (I'll call it T for the time travel planet) has a different time stream to everything else in existence is odd. And if one world does, why not two, or three, or a billion.

B) The term "objective time" doesn't make any sense since you have clearly stated time is not objective, it is relative to your location. Time is one thing on world T and something else somewhere (maybe everywhere) else.

C) It would be easy to have time move at a different rate on world T (that's more or less special relativity). But that doesn't allow time travel into the past, only time travel into the future at varying rates.

D) Which raises another question. Does time on world T flow at the same rate? Is a year on world T equal to a year anywhere else or is it like the realm of fairy where a day on world T might be a second in the rest of the universe or a thousand years.

E) Which raises another question, does time on world T flow in the same direction? Maybe time runs backwards.

F) Personally I wouldn't assume what you are wanting to assume. I don't see how it makes any sense to go back in time on world T and to think you aren't simultaneously back in time with respect to any other world.

G) If you insist on keeping your two different times assumption, then I see five choices. Let's assume they leave the universe at large for world T at time t0.

• When they step off world T, treat the two times like vectors and use vector arithmetic to find out what time it is when they get off world T. Their start point is when they left the universe at large modified by any time travel on T modified by any time passage after any time travel on T. So if they went back in time on world T 10 years and lived on world T for 1 year thereafter. They return to the universe at large at time t0 - 10 years + 1 year.


• When they step off world T they return the instant they left the universe at large, so at time t0.


• Create a random time table and roll to see when they return to the outside universe. Be sure to include cool return times like (i) before all life existed, (ii) when dinosaurs ruled the earth, (iii) when something disaterous has happened like the major foes of the PCs ruling the world/universe, (iv) as (iii) but this disaster is due to the PCs' absence from the universe outside world T or to their tampering with time, (v) when humans have evolved or ascended into body less energy beings, and (vi) long after the sun has shrunk to a burned out cinder, (viii) the instant of the big bang or some other universally cataclysmic event.


• Surprise! They can't ever leave world T.


• They are destroyed, time looped out of the game, or cease to ever have existed. Mother Nature gets cranky when you tamper with time.

Quote from: JesterRaiin;890603I'm a bit stuck here and I could use a bit of help. First of all, I'm not sure how to correctly describe the problem, so pardon me if some part of it seems unclear.

Imagine such a scenario:

• A player discovers/creates a world that allows for a time travel.
• For the sake of clarity, the time in this world moves in exactly same pace as outside, in objective reality.
  
• A player steps in, thus leaving the objective reality and the rest of his group behind.
  
• He undergoes a time travel, moving, let's say, 10 years to the past.
• He spends a year or so in the past.
• He steps outside of his world, back to the objective reality. Important thing (and the major reason behind this post) is that he DOESN'T use time travel to come back to the starting of his voyage. He exists his world in its past.
  

The question is where, or rather WHEN in objective reality he arrives?

The possibilities:

1. In objective reality's past, more precisely 10 years "ago" + 1 year he spent in his world's past. This makes it 9 years earlier than he stepped into his world and did time travel.

The problem here is results cause & effect paradox - one player is now in the past, while the rest of the party in the future, so whatever he does, will have repercussions in their timestream.

2. The objective reality is partially impervious to player's actions: he arrives at the moment he stepped into his world +1 year he spent in its past.

Now we have a huge hole in continuity: what if someone entered player's world, while the player was "away"? His actions might erase that certain time branch with all beings "inside". Also, what happens with beings native to this world, that stepped outside of it the moment player was gone? Let's say he killed them in his past - do they disappear from the objective reality as well?

3. In exact same point he pressed DO THE TIME TRAVEL button (so to speak), only now his world changed accordingly to his actions in its past.

Aka the laziest but also the least troublesome solution (from the perspective of the GM). The only problem here is very unlikely scenario of other time-travelers, each producing his own, a bit different local timestream, but it's not gonna happen as far as I'm concerned.

4. Other time?

Thoughts, opinions, suggestions?

CS Lewis has characters return from Narnia to the 'real world' at the moment they left - that's probably the simplest and most coherent answer.

Quote from: JesterRaiin;890603I'm a bit stuck here and I could use a bit of help. First of all, I'm not sure how to correctly describe the problem, so pardon me if some part of it seems unclear.

Imagine such a scenario:

• A player discovers/creates a world that allows for a time travel.
• For the sake of clarity, the time in this world moves in exactly same pace as outside, in objective reality.
  
• A player steps in, thus leaving the objective reality and the rest of his group behind.
  
• He undergoes a time travel, moving, let's say, 10 years to the past.
• He spends a year or so in the past.
• He steps outside of his world, back to the objective reality. Important thing (and the major reason behind this post) is that he DOESN'T use time travel to come back to the starting of his voyage. He exists his world in its past.
  

The question is where, or rather WHEN in objective reality he arrives?

The possibilities:

1. In objective reality's past, more precisely 10 years "ago" + 1 year he spent in his world's past. This makes it 9 years earlier than he stepped into his world and did time travel.

The problem here is results cause & effect paradox - one player is now in the past, while the rest of the party in the future, so whatever he does, will have repercussions in their timestream.

2. The objective reality is partially impervious to player's actions: he arrives at the moment he stepped into his world +1 year he spent in its past.

Now we have a huge hole in continuity: what if someone entered player's world, while the player was "away"? His actions might erase that certain time branch with all beings "inside". Also, what happens with beings native to this world, that stepped outside of it the moment player was gone? Let's say he killed them in his past - do they disappear from the objective reality as well?

3. In exact same point he pressed DO THE TIME TRAVEL button (so to speak), only now his world changed accordingly to his actions in its past.

Aka the laziest but also the least troublesome solution (from the perspective of the GM). The only problem here is very unlikely scenario of other time-travelers, each producing his own, a bit different local timestream, but it's not gonna happen as far as I'm concerned.

4. Other time?

Thoughts, opinions, suggestions?

I've heard mention of a rule called "Don't split the party." I ignore that rule though. The key here is to make sure that every situation has at least two paths to take before such situations happen.

Quote from: Bren;890712G) If you insist on keeping your two different times assumption, then I see five choices. Let's assume they leave the universe at large for world T at time t0.

I see no reason not to. In this setting all worlds are bubbles connected to mmmmmm, a web, a Highway, a plane inbetween. It's that objective reality, the place all bubble worlds are compared to.

There's no reason why players couldn't find a world where time flows in a slower/faster pace to the one in objective reality. Heck, nothing stands in the way of visiting a world, where time flows backwards. It would be a nightmare to deal with, but it's not forbidden.

QuoteList of suggestions.

1. Yeah, I thought about it, it's in OP already.
2. Ditto.
3. Interesting, interesting indeed. It's not applicable to the game we're playing, but it would make a good, useful random table. :hmm:
4. Naaaah, not fond of inescapable traps aka "rock falls you die". ;)
5. Ditto.

Quote from: S'mon;890735CS Lewis has characters return from Narnia to the 'real world' at the moment they left - that's probably the simplest and most coherent answer.

Ya, that's the least troublesome solution. I'm a bit worried about it. Since my player managed to outsmart me into allowing for his timetraveling device to exist, the f...er probably already assumes I'll use this solution. And then he will probably scream "Aha! As expected" and explain to us all how we played into his plan, or something.

Damn... ;)

Quote from: Shawn Driscoll;890753I've heard mention of a rule called "Don't split the party." I ignore that rule though.

It's very reasonable rule, however the game we're playing is one of those scarce exceptions where it's not as bothersome as elsewhere. In-party conflicts, players separated by multiple dimensions and universes, lack of dice... It's all there. And more. :cool:

Quote from: Shawn Driscoll;890753The key here is to make sure that every situation has at least two paths to take before such situations happen.

I think I understand intuitively what you mean by that, but for the sake of clarity, would you care to expand that a bit?

Quote from: S'mon;890735CS Lewis has characters return from Narnia to the 'real world' at the moment they left - that's probably the simplest and most coherent answer.

But they arrived back as if no time had passed, still as children.

Does the OP want to reflect the changes made to the PC or does he want the PC to come back as he was?

I'd say that he comes back at the same time, so flicks away and then flicks back, but a year older with new scars, different clothing or whatever.

Who's to say the future he returns to is exactly the same as the one he left? after all everything no matter how minor he does in the past could cause a ripple that changes a few things...so although it seems like he outsmarted you when you used the returned to the same point he left idea, later in the campaign throw a few ripples at him and have the rest of the party go along with you as if they aren't ripples(shouldn't take much effort if it'll help make things fun and shut up the know it all lol) and see him change his tune :)

Quote from: Tahmoh;891187so although it seems like he outsmarted you when you used the returned to the same point he left idea, later in the campaign throw a few ripples at him and have the rest of the party go along with you as if they aren't ripples

...

..........

F...!
It's awesome idea. Totally borrowing it.

...and why didn't I think about it in the first place? :hmm:

Come to think about it, time might adjust to the changes... slowly. Piece by piece, one NPC at the time. Delayed ripple-effect. :hmm:

If the main world where the rest of the party is does not allow any reverse time travel at all, then I would tend to do think that hopping to other planes of existence and returning would also not allow that, so choices I would consider for when the described world-hopping PC returns would be:

1) The hopping PC returns as if his time in the other worlds had not happened... i.e. the same time he left, plus the time taken in the "highway" plane between worlds. Since he spent a year presumably aging in the other world, he's now a year older in the world he came from, than he would have been if he'd stayed home. This can be annoying because the PC who left gets to spend years doing stuff, while the PCs left behind can't really game anything out until that PC returns.

2) The subjective time the PC experienced, affects the time of return linearly. So the PC spent a year in the other world falling forward in time. The fact he went backwards 10 years doesn't affect his return time. So he returns a bit more than one year later in his original world - he's still exactly as old as he would have been. This is nice because it means the PCs left behind still get to do things.

3) Taking a page from modern physics, relative time dilation occurs, of some sort. This means the PC can travel at what seems to him faster than the speed of light, but the rest of the universe progresses faster than he does. This might impart a delay in the original world simply for moving to the other world and back. As for the reverse time travel in the other world, I don't know what that involves, but it might also have a time dilation side effect that affects the time the traveler will arrive if/when he returns to his original world. That is, it might be even more than 1:1, and/or might be based on the time traveled backwards. So it's like 2, but with additional multipliers and/or charges for the world travel and time travel. So the return time might be +1 year for the time hanging out in the other world, and maybe +10 (or +100, or + 1000), for the time traveled in reverse. So hopping worlds and traveling in time might impose a long delay on the time you can return to your original world. This is great for the GM not having to worry about meddling exploits, but can be "oh crap I'm screwed" for the PCs that do it. Unless an entire party does it, in which case the GM needs to decide if they want to advance time in their campaign world, or find new PCs to play with until those ones return.

(I've played in some interesting games where the party did fall forward a lot in time without aging, resulting in a new campaign world state. It's of course a huge world reboot for the GM.)

Of course there are reverse-time options too, though I would only do these if I were wanting to run a full time-travel intervention game (pretty unlikely). If the PC goes back in time 10 years in the other world, spends a year falling forward and then steps back, then it could also make sense that he returns 9 years before he left.

As explained in my previous post, I'd tend to rather have that create a new timeline/reality/universe where the old world is as it ways 9 years ago, but suddenly it has a new PC arriving from 10 years in the future on that old timeline. That PC would never appear again in the original universe, unless he somehow managed to find a way to target that thread of the universe. He'd need to be brilliant or find some sort of mega-competent time lord who was interested in helping him out.

But if as I said, I were really running a time-travel intervention game, then ok, he arrives 9 years before he left. My first question would be - what to do with the version of the PC that was already in the world 9 years ago. Three options come to mind immediately:
a) The younger PC vanishes from existence at the moment the older PC arrives. (easiest/avoids some problems)
b) The younger PC exists and is an NPC who will do what the PC did 9 years ago, up until he meets some new circumstances caused by time travel or it's side-effects or butterfly effects. Similar for the rest of the world, and the other PCs. This means the traveling PC's actions for the next 9 years need to not change much, or else the other PCs and past gameplay are going to be invalidated.
c) The younger PC exists and is an NPC, but suddenly has new agency, choices, luck, etc. The whole world starts doing more and more different things than it did originally. I like this, but it invalidates all future play and world events that were resolved in past gameplay in the original world. The other PCs left behind are invalid, unless they also somehow time travel to the same or an earlier time. So the other players may as well just be given new character sheets for their characters 9 years in the past, and/or be given the option to start new characters at that point in time.
d) The continuity of the time-traveling PC's history needs to be maintained, or else they will vanish in a puff of logic. That is, if the time-traveling PC does something that means he will not be able to time travel as he "did" 9 years in the future, he won't have done that, and so the timeline won't include him as a time traveler any more. Less minor side effects will also be carried forward. Unfortunately, this also applies to the world, events, and the other PCs... however, too much disruption will just cause the timeline to "correct" the PC's time travel, snapping back to the old timeline. For example, if the PC somehow causes something that would have the original party not end up at the time portal in exactly the same conditions that caused this time traveler to travel in time to cause the change, then that violates the logic of the timeline, so clearly that did not happen. That can either be enforced by having whatever the change is resist happening, or just by reverting to a timeline that makes sense. I.e. you can't use time travel to invalidate your own time travel as it happened for you in your past experience. However, it seems to me that that logic also invalidates time travel itself, which is one of the reasons I prefer to think interventionist time travel is nonsense anyway.
e) Intervention without logical continuity enforcement. The time-traveler can mess with themselves and their friends and the world and not vanish themselves in a puff of logic, despite some idea of this making sense with only one universe. Generally this involves a conceit and not thinking too much about it, and really having reality created by the continuity timeline created by gameplay and PC perspectives. I.e. each PC (or NPC the GM cares to pay attention to) has a valid experience and point in time and history that they can play with. The question becomes which point in time do you choose to play out next, and what side-effects, if any, do you have affect the other situations other characters are in, or not. I think this tends to be the mode that a lot of time travel stories/films operate in. The actual reality is the character's experience being paid attention to at the time, and things do or don't have consequences depending on what seems fun or interesting or clever or thematic. Of course, it introduces the conflict that if reverse time travel is possible and has consequences that get reconciled, then unless events wipe out everyone or all competition, then the future will be full of a near-infinite source of meddlers who might decide to travel back and change things, changing or invalidating who knows what. This is even harder to actually track than a universe with an infinite number of threads. It also seems infinitely pointless because a practically infinite number of time-traveling scoundrels, villains, heroes, police, spies, whatever can be expected to be competing to change everything until someone sooner or later just gets annoyed and decides to destroy it all to end the madness. ;)

Oh, and I think time travel is one of the places where staying experiential is most valuable. I would definitely stick as much as possible to only answering questions about what each PC experiences directly, and zero questions about what is actually going on, or how time travel or the universe work. When players inevitably start speculating and trying to draw the GM into discussions such as the above, or even to seek out world experts on time travel and so on, I would suggest picking a random perspective and having a discussion, but having that have no relation to how the GM is actually managing time travel and universes and butterfly effects or whatever. Mag'myzak the Lord High Wizard of Time may grant them an audience and talk to them for hours or days about his understanding of time and causation, but Fildar the White Scholar and Steven Hawking and Einstein and the Pope and the GM on Thursday and the GM on Friday may also do so, and express completely different ideas.

Limiting the players' knowledge of how time travel and the game universe works, to actual experience and perceptions of their PCs, makes it more mysterious and immersive, and keeps the game being played rather than talked about, and gives the GM peace to figure out what to do and choose how to do it, etc.