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[piecewise]

Now, toady has expressed reservations with time travel, mostly because of the difficulty it presents. However, as I think about it I don't see much difficulty, simply more loading. For instance, say we're playing as a god who wishes to go back in time and kill some unfortunate soul. Now, the game would basically just have to go back in it's history, erase everything after the point to which the god travels and then plonk him down in that time. It would basically be like if you stopped world gen there. Now, the god could muck about and when He's ready to go back into the future the game could simply restart worldgen with the new history and run everything as though it had never been stopped.

This way you don't have to really worry about dynamically adjusting the world or anything like that and it shouldn't take too long to do. As per future movement that should be easy, just get worldgen to continue till the point at which you wish to stop. It seems easy, theoretically, but I'm sure there are coding problems and shortcuts that most likely make this impossible. Regardless, discuss the ways time travel could exist and how awesome it would be to reenact the ending of "12 Monkeys" by traumatizing your past self.

[smjjames]

Enter the Grandfather Paradox and a bunch of other time travel related paradoxes.

[nenjin]

"Simply more loading" = a game file that is exponentially larger because it has to track the entire game state more than once, or generate a future states. In a world someone has played 10, 20 games on, the game file is big already. You're talking like a several gig game file for really advanced games. Or more.

And that's on top of all the redacting and revision...no. I can see why he has reservations about it. Screwing with written history that's already happened, or has yet to happen, is pretty much made mind-boggling complex by the way Toady has set things up. I imagine this might be something people could write as a third party app, a self contained world editor that would make the necessary changes and revisions to the save file. 

[Mel_Vixen]

Given that you can read out and interpret the save-files. Anyway there is another problem: you.
I mean you as player. Say do a timetravel to stop yourself from doing something andyou met yourself what happens?

Nothing! Just plainly Nothing. The game doesnt know your intentions, your normal behavior, your reactions to certain situations. Heck it doesnt even track what you did except the times where you did something significant.

Even Games like Prince of Persia only record the last 30 seconds so you can use the rewind button which in no way is real timetravel.

To put this straight: Currently its technicaly impossible to do realistic timetravel thought there are certain possibilitys like creating a new timeline to avert the grandfather problem by not killing your father therefor killing the father of your parralel-self.

But for such solutions you have to store for example every "decission" (Aka every rolled dice/possibilty which came true) ever made in the game which would quickly pile up to a unhandleable mass. Then you have interconnection problems of "decissions" so that you have to go through the entire timeline to find the decission which you have to roll anew and which stay the same.

 Say you change 1 "Gene" on Worldgen you will change Millions if not Milliards (the european kind) of Individuals (till 1050) theyr characters and everything based on that while a good part of the population stays the same. For example if one Dwarf has two children and every descendant has 2 too you have to check after 10 generations (Approximate 200 years -> 20 years = 1 generation) over 2046 Personalities, treaits etc. etc. After 52 (0 - 1050) Generations you have to check 4503599627370496 individuals only for the latest generation given that noone has died withou children or more then 2 etc.

[clc02]

I could see the size of the save file being close to the same, having the same seeds saved in it, then generate the world until the time you want to 'go back' to, then kill whoever, resume the world gen until you are back to where you want to be.

[Mel_Vixen]

Sure and how do you undo your first murder if the outcome is less likeable as the first?

[nenjin]

We're not just talking seeds here. We're talking people, names, civs, objects, towns....I suppose you could resave and repack the world, but a fleshed out world would still be larger than the initial seed. 

[MrWiggles]

This just sounds like, World Gen, the game. For which I say, boo.

[Dakk]

Implementing time travel to the game IS possible in a way. Travelling to the future could be done by getting worldgen to start again from the point you use the spell, making it so that you are the only one not affected by it. Traveling BACK in time is the real issue. Making worldgen go backwards is not an option, since to do so it'd need to keep track of every single thing done in-between the time you used the spell to go back in time, and the time you want to go back to, and thats really unreasonable.

You could technicaly do it by creating a sort of save point at whatever point in time, and then later use a spell to go back to that time, which is basicaly just a fancier way to savescum.

[Soadreqm]

If you ignore the countless philosophical problems with time travel, you still have to record every single event in history to know what the past was like. This isn't really feasible with current hardware, but quite possible to do if you have infinite resources. Maybe in a decade or three?

The even bigger problem, I think, is that if you wanted to do it PROPERLY, you'd have to let NPCs use time travel. Having more than one agent in the world doing time travel at the same time rises to a level of "complicated" not really achievable by mundane means, and to make matters even worse, most of those people would have to be controlled by the AI. For example, see these diagrams (1, 2, 3) relating to this MSPA intermission. So, unless the quantum supercomputer you are playing DF on can either send data to the past, or simulate infinite alternate interacting timelines and predict player actions in all of them, time powers would pretty much have to be restricted to the adventurer. Which is kind of stupid since we're going for world simulation.

[Dakk]

^My thoughts exactly, if there are going to be multiple wizard entities in future versions, they should also be able to do it. Getting them to do it properly, for a proper reason, and getting the game to keep track of all changes in between is a logistical nightmare.

[Soralin]

As a proof of concept for a really nice looking implementation of time travel, check out http://achrongame.com/  Not only does it do time travel, but does it in multiplayer.

[Jude]

Currently its technicaly impossible to do realistic timetravel

realistic timetravel

realistic timetravel

[Quantum Toast]

We'll need pitchblende and a way to make nobles fall at exactly 88mph.

[Mel_Vixen]

Achron has a interesting approach but i see one problem for us: The Player is a "observer" from another place in Achron but isnt represented himself in the game. They ,the makers of Achron, go around the most problems by saying that:

1. the player is in the world since the beginning of time.
2. the player Replaces his choices by Timetravel.
3. they use only a Time-window (approx 8 Minutes).
3.a: Paradoxes get "chance solved" as soon the time window hits the limit (8 Minutes) until then they oscillate -> this means that there is a 50/50 chance you exist in the past and your father is dead or you are stuck in the present and your Father lives.
4. They have time-waves which allow you to "foresee" in some sense a change in time and its outcome before it arrives at your point in time.


In Df like most rpgs its more desire-able that the player can go back to times where he wasnt around and we have still the "Meet yourself" problem. Not to mention that the evil arch-wizard can still delete you from time.

But lets pretend that we preserve the player existence and his knowledge in time by excluding him from time-effects (to subvert the Grandfather Problem and replacing time-waves for simplicism) as soon he gets in contact with time magic the first time no matter what happen-s/ed (insert good excuse for time-effect-immunity here.). Lets say Ai-Agents with time Magic have the same advantage. As the last let us say that if we go back or get hit by a time-change our past/parallel counterparts get replaced by our Character - as in our past/parallel self gets deleted from time instantly and not the BTTF way. If we do all this! We just have 2 problems left:

1: How do we and the Ai learn what has changed.
2: How do we find our destination in time and space?
2.a: More so how do we get the Ai ton set up clever Timetravel plans?



If i forgot something please say something.