Time travel in RPing

[Photon]

I haven't seen time travel explored much in RPs, especially not when the time travelling system is anything more complex than Back to the Future. Recently I've been thinking a lot about time travel (largely due to both watching a lot of Doctor Who, and more recently playing a real time strategy game called Achron, in which you can control your units at various points in time, making for one of the more complex RTSs of recent times) and I have come up with a few systems which could occur in RPs without too much hassle. Bear in mind that these are all just speculation and while I would love to run a time travel based RP, I just don't have the time to do so, and won't for quite a while.

I should also mention that by 'system' I mean the handling of paradoxes and crossing timelines.

Back to the Future (multiple timelines)

In the movies, travelling to the past and altering something results in a new timeline branching off the original. It is not possible to travel between timelines, only back and forwards on the one the Traveler is currently on. Going to the future and altering something means that if you then travel back and then live forwards at the normal rate, you will eventually encounter yourself. Apparently no paradox occurs if you change what your past self does (at any point in time) unless doing so has major effects, in which case the universe slowly corrects itself. The grandfather paradox (grandkid travels back in time and kills his grandfather before his mother/father is born) results in the disappearance of the grandchild, but only at the point when his life becomes impossible, it avoids a paradox by him still appearing in the past for a short amount of time, having traveled from what then becomes an alternate timeline.

One timeline

Full of paradoxes, this system allows only one timeline. Any paradox results in the disappearance of the entire universe. Going to the future means that you don't exist for the period of time you skip. Travelling back in time instantly results in a paradox as either the butterfly effect or the result of two of the same person existing at once results in a paradox. This, while more realistic than most systems, also is the least involved (and in my opinion the least fun).

Out of Universe Control

This is my favorite system, and one that I am currently exploring in a creative writing project. Instead of actually time travelling, the timelines of two universes are separated, allowing brief connections between the two at the will of those in the "control" universe, in which time continues normally. The "Primary" universe gets a seriously screwed up timeline at the will of the controllers in the control universe. Various limitations and safeguards imposed by the technology used prevents paradoxes.

Out of time right now, I will expand on this in a few hours. What are your thoughts on the systems in terms of how they would work in RPs?

[Cadvin]

I should note that the "one timeline" doesn't have to result in paradox if you go back in time, provided it's always been like that. You wouldn't be able to go back in time and meet yourself if you had never seen a future version of yourself, and if you had met future you it would be certain that you'd go back in time and do the exact thing you did. What you're talking about, I suppose, is a single, modifiable timeline, while a much (In my opinion) interesting system is a single, unmodifiable timeline. You wouldn't have to worry about paradoxes because if you created the paradox you wouldn't have ever done this in the first place. With this, you could do some very nice and clever things. Invest stocks without worry for a butterfly effect, send messages to the past, so forth. My personal favorite is being able to, unless the universe is very unkind or crafty, get any easily testable password/combination/anything else.

Say you're trying to open a safe. First, you receive a message from the future. If you do not receive this message, then you will send one back. Therefore you will receive a message. The message should have the correct combination on it. If it is correct, then you write the combination down on another piece of paper and send it back. If it is not correct, you send nothing back. Therefore, unless the universe or circumstance is actively working against you, you will receive the correct combination.

Pretty useful, I'd say.

[Photon]

Ah, so a timeline which the universe had already 'worked out' to ensure a series of events without paradoxes? Somehow I had completely missed that one. I also can't remember what else I was going to mention when I wrote the post a few days back. I think I decided not to write a followup because of a lack of interest. Ah well. Any thoughts on how plausible it would be to have a RP in which each character could travel through time independently in any of these systems? The out of universe control is easy enough provided everyone pays attention, particularly if everyone has their main character in the secondary universe, but I've been thinking about it and can't think of a good way to play the others without ridiculous amounts of confusion and/or a heavily controlled rule-set.

[Cadvin]

Hmm. Well, no matter which RP, I think people are going to have to pay close attention and be fully aware of the system, but I think all of the systems could be workable. The one, fixed timeline system is okay so long as people don't, say, go back in time to stop themselves from something they'd done. The one modifiable, paradox-heavy timeline is potentially workable, so long as everyone only goes into the future, and always further into the future than any other time traveler had gone. Back to the future style seems simple enough provided that everyone time travels together, but if everyone can travel independently it could quickly get messy as everyone ends up is separate timelines. Not sure how to do that one.