time travel

[reorith]

are there rules for time travel in d&d?

[Fizban]

In a word: no. The only official time travel I've seen baisically says "okay, now that you can cast 9th level spells ask your DM about time travel, if he says yes then great if he says no then forget about it".

[Assassinfox]

Not for 3.5, no.

[clarkvalentine]

The Dragonlance 3.5 sourcebook Legends of the Twins deals extensively with time travel and time magic, but it is very heavily rooted in that setting. Still, you might find some useful things in there if you're willing to drop a few bucks.

[TheOOB]

The Epic level hand book has like one epic spell that deals with time travel, and it doesn't even acually let you travel in time, it pulls a duplicate of you from the future to fight in the present, though in the future you have to go back and fight in the battle you allready fought...time travel is confusing.

Generally speaking, time travel is too powerful and two confusing for use in D&D. If your DM wants to use time travel, more power to 'em, but you won't find much official material reguarding it.

[Aximili]

Personaly, I find time travel to be something to avoid. The number of paradoxes, problems and questions it raises is enough to ruin a story. You'd either have to cut stuff by the root --setting a few strict rules and directly asking your players not to do some things--, or be a very¹ good DM, predicting the players' actions and making it so every action they take only makes thing happen the way the actually did.

¹and when I say very, I mean extremely.

ps:Unless you travel forwards, that's cool. Just, you know... Don't come back =P

[Muz]

I recently had a LITTLE bit of time travel in my campaign. Essentially the party didn't know about it for a long time, as they stumbled (well, one guy stumbled, the others followed after him) through a gate that popped them onto another continent. They knew the gate was a little unstable in time and space (in fact they showed up in slightly different places and months/weeks apart--one NPC showed up 9 months previous) and spent the next while on various adventures that wound up getting them home.

But when they got home, they found out the gate had sent them back in time, and the journey home had them arriving about a week before they left. One of the PCs ran into herself on the way to the very gate. She decided not to mess with things just in case, even though she knew from personal experience that the past-party was about to be captured. (Future-party had actually returned to that place to steal a magic item from the creatures that captured them in the first place.)

I was prepared, had the two parties decided to join up, to constantly evaluate the consequences and have them (future-party) be only partially substantial if they started doing things that would keep them from going through the gate. (Mostly playing it by ear.) I honestly was flying by the seat of my pants, though. I wouldn't recommend using time travel in a way that the players can actually control. One instance proved challenging enough. :smallsmile:

(What was fun was when one of the PCs had to go on a little prophecy-vision quest, and then giving them a vision of seeing themselves talking to themselves. The presence of doppelgangers in the campaign made this doubly amusing. ...For me, at least.)

[TSGames]

are there rules for time travel in d&d?
Yes, RFED.

[broderickdruce]

As far as actual rules go, no there is nothing. What there IS is a brief mention in one book ( i forget which, I think Heroes of Horror, whichever is the Mind Flayer centric one) about how the Illithids do it, and I think it gives the stats on their Spaceships/Timeships! WEEE!

Love the content of that book, hate the fluff...

Edit: On second thought I believe it was Heroes of Madness.

[Nerd-o-rama]

I haven't tried time travel in a campaign I run yet. Fortunately, if I decide to, most of my players are Star Trek fans, so it'll be fine if it creates tremendous plot holes and never works the same way twice.

[Assassinfox]

As far as actual rules go, no there is nothing. What there IS is a brief mention in one book ( i forget which, I think Heroes of Horror, whichever is the Mind Flayer centric one) about how the Illithids do it, and I think it gives the stats on their Spaceships/Timeships! WEEE!

Love the content of that book, hate the fluff...

Edit: On second thought I believe it was Heroes of Madness.

Lords of Madness, actually. And it was some big psionic ritual, not a timeship. The stats for their spaceships aren't even in the book.

[TheOOB]

You could always follow the time travel ideas of the book Timeline where it is impossible to travel in time, but it is possible to travel to alternate universes that are identical to a different time period of your universe.

[Wehrkind]

Time travel can avoid a lot of the paradoxes if you have them also cover a huge amount of space at the same time. For instance, send them back in time to a continent that has little contact with theirs, or to another planet. (Really screw with them and point out that 200 years prior the planet wasn't in that location, so who knows where you are now.)
Essentially all this does is eliminate the possiblity of them affecting their own future, as well as the general status quo, but if they REALLY want to go back in time, it is a way.

[clarkvalentine]

As far as actual rules go, no there is nothing.


Except for the rules that there are. :smallwink: It's just that they're setting-specific.

[Wehrkind]

Wait, it just occured to me that it is sort of silly to go back in time in D&D other than to change things. What are you going to do, stab cave men?
Unless your campaign has some serious history written about it (Dragonlance style) there probably is not a lot of point outside of breaking continuity, with the paradoxes that follow.

[TheOOB]

Hmm, most campaigns have at least one or two major events that could be changed, for instance in Greyhawk killing Rary before he betrays the free city and the circle of eight would change a lot.

[Jade_Tarem]

There's one rule that I know of for general DnD. It's in the epic level handbook, for the spell time duplicate.


Using this spell to snatch a single future self stretches time and probability to its limit; more powerful versions of time duplicate are not possible.

As per the previous mentioning of the spell, what you do is grab yourself from one round in the future to act on the current round. This means that both of you (literally, of YOU) can cast spells/move/whatever (except that you're down one standard action or quickened spell in order to cast the spell) in the current round. When your next turn starts, both of you disappear, as you now have to go one round back in time to help out your past self, and your future self went 2 rounds into the future, which is where you will be in 1 round. I'm sure that cleared everything up. :P

[Assassinfox]

Hmm, most campaigns have at least one or two major events that could be changed, for instance in Greyhawk killing Rary before he betrays the free city and the circle of eight would change a lot.

Or stopping Karsus from destroying Netheril...

[Dervag]

I have a simple guideline for this kind of problem:

The Law of Conservation of History.

In short, you can't change the recorded past because it already happened. If you try to go into the past and prevent the burning of the Library of Alexandria with a submachine gun, the gun is guaranteed to jam, because the library was burned. If you try to go back and time and warn Abraham Lincoln not to go to the theater, he won't listen. Those things already happened. They are now part of your causal past, so you can't change them.

Many people object to the grandfather paradox. I would argue by modus tollens that you have not killed your grandfather by travelling back in time, as demonstrated by the fact that you're still alive. And even if you try, you will fail, as demonstrated by the fact that you're alive to make the attempt.

[The_Snark]

That's a good way of doing it in games, since the DM is peculiarly well placed to enforce such a law. Alternatively, talking to the players and making sure they know that creating paradoxes may get them erased from existence will help prevent this sort of thing.

This (http://www.wizards.com/default.asp?x=dnd/pg/20030402x) has some Faerun-specific time-travel stuff, but some of it, especially the spell in part 2, is easily adaptable.

[Wehrkind]

Or you will become your OWN grandfather, as in Futurama.

"Oh sure, we are getting a lecture on preserving the time continuum from the boy who is his own grandpappy!"

God that was a great episode.

[Jade_Tarem]

I have a simple guideline for this kind of problem:

The Law of Conservation of History.

In short, you can't change the recorded past because it already happened. If you try to go into the past and prevent the burning of the Library of Alexandria with a submachine gun, the gun is guaranteed to jam, because the library was burned. If you try to go back and time and warn Abraham Lincoln not to go to the theater, he won't listen. Those things already happened. They are now part of your causal past, so you can't change them.

Many people object to the grandfather paradox. I would argue by modus tollens that you have not killed your grandfather by travelling back in time, as demonstrated by the fact that you're still alive. And even if you try, you will fail, as demonstrated by the fact that you're alive to make the attempt.

Aaaaaaand the topic blossoms into a true time travel debate. Ok, here we go...


What about the multiple timelines version of history? This is the one where each situation in a time has an infinite variety of outcomes, with one outcome becoming increasingly more probable than all the others until that point in time is reached and a certain outcome is determined. Of course, that one Sci-Fi story (Sound of Thunder?) shows that the farther back you go, the more drastic even a minor change is (killing a butterfly in the Jurassic Period had world-wide effects in the present), and this change is shown by a new "thread" forming along the timeline - or timeweb, as you may think of it. Specifically, these alternate threads would be parallel universes. An alteration in such a timeline merely guides your history down an different thread - granted, you may not exist in that thread, but chances are that when you're toying with magic that can screw with time, you are also protected from the reality-altering consequences of your actions. The best example that I can think of of a universe running like this in fiction is Star Trek - specifically the episode where they eventually manage to somehow summon all the Enterprises to one timeline and have to figure out how to put them back, and one didn't want to go back because thier home reality sucked - ("The Borg are everywhere! There's just 3 ships left!"). The next best is certain Twilight Zone plotlines.

Of course, I'm just playing devil's advocate here. I personally like the conservation of history thing. For added effect, you can have the actions of the time-travelling dude actually facilitate certain events in known history. Think Red vs. Blue where Church goes back in time to prevent his own death and ends up causing it, or Terminator, for the ulitmate example of inbreeding - that guy was his own grandfather and grandson, his girlfriend was his grandmother, and his son was his father.

[Yuki Akuma]

The "multiple realities" thing can actually work with the "Law of Conservation of History". Simply, yes, in some reality maybe someone did kill your grandfather. But you can't possibly go back in time and do it yourself, because if you did you wouldn't exist in that reality anymore, so you wouldn't have been born to go back in the first place...

Just make it impossible for time travellers to create parralel universes and you're golden. :smalltongue:

[BlueWizard]

Clearly up to the DM, but he better be good. I allow it at Epic levels, and if too much is changed remember all about alternative universes.

[Bears With Lasers]

Teleport Through Time (http://www.wizards.com/default.asp?x=dnd/pg/20030409b).

[Khantalas]

Well, you can buy one rank in Time Travel for two skill points. If you're playing Mutants and Masterminds.

[anphorus]

I love time travel personally, though I think it works better when the entire focus of a story is time travel. In situations like that you could have tiny little things have huge consequences. Like by giving something to a hungry family, you could turn a rich descendant of theirs from a miser into the world’s most generous man, because in the changed timeline he has been taught to be generous. (Blatantly stolen from Chrono Trigger). Or you could knock over a tree and change the name of a place (blatantly stolen from Back to the Future.)

I personally like the idea that, while travelling in time, the characters exist partially outside time and are thus slightly protected from the effects of altering the future, so they wouldn't simply cease to be instantly if they killed their own ancestor. For example if they accidentally stop World War Two, they will still remember that WWII happened and their ancestors will still meet up. Even though Marty inadvertently changed his family's history when he helps his dad become more confident, he still remembered the previous timeline. Marty wouldn't have been who he was, and wouldn't have done all the stuff he did in the past if he had a different upbringing, so the timeline which was created was one in which the time travelling could be accommodated.

I like to think of the universe as an organism, in paradox situations. The organism wants to keep existing, so if you kill your grandfather (or grandmother), someone else will simply provide the DNA required. This is basically The Law of Conservation of History, but I like to be more flexible. You can't stop yourself from existing but you could, say, prevent a war or change a society.

You may want to combine this with an aspect of destiny, no matter what you do you can't prevent Skynet from causing Judgement Day, you can't stop WWII by killing Hitler, another would simply take his place etc. None of this is set in stone for though. You may want there to be some big events that are changeable by time travel; it's up to the needs of the story really.

[ssjKammak]

Gday,

You could develop an interesting Campaign by allowing the player to time travel, and using the butterfly effect principal have them repeatedly performing action to correct or undo there work form previous adventures and play.

Cheers
A friendly Aussie

[Black Hand]

I've used Time travel before in Campaings, but it's usually Diety driven, or (in the case of forgotten realms) rare 10th-12th level magic that generally isn't used by the PC's anyways... It's fun though, but they can really fack things up in the present if they muddle around too much with past events....but that just makes the campaign more interesting then.

[CASTLEMIKE]

Netheril Empire of Magic (@1996) covered Time traveling via the Time Conduit spell and time wells.

The Time Conduit Spell (level 9, alteration and chronomancy) had a few limitations. First off Mystryl the previous incarnation of Mystra created it and was the primary regulator although Amaunator interpreted a divine contract to also oversee time travel. Basically you could back in time for a year and when you returned to the present a year would have passed. You couldn't take items that didn't exist back then with you including "New Modern Spells" and magic items (They were in limbo awaiting your return) and time traveling used up all your daily spells. Instead of spell casting memorized spells you basically cast like a sorcerer with all the known ancient spells from your spell books mechanically. Normally you couldn't change history but you could learn knowledge needed for the future or stash something in the past with the DM deciding how well you stashed and preserved it to recover it again in the future.

The few individuals who know the spell are people like Elminster, the Blackstaff and Larloch the Lich who would usually require something from you (generally a task) or you could spend a few years researching the spell.

Chronomancer @1995 devoted a source book to time traveling along with temporal prime, time lines, time police, time raiders, different classes, time elementals, past, present, future, chronomancy (time magic) and how it works in the different settings so you might be interested in locating a pdf and saving yourself some time.

Hope that helps.

[Collin152]

Ah, teleport through time, you old dog, how is it that you can be so useless while looking so powerful? By it's very definition, the material component is unobtainable.

[BCOVertigo]

Ah, teleport through time, you old dog, how is it that you can be so useless while looking so powerful? By it's very definition, the material component is unobtainable.

Unless you assume that because the spell is written to be castable that the past hasn't been changed until you change it. Which lends credence to dnd working on the 'parrallel universes' system for time alterations.

I think of time like a cracked window spidering out from a central point. Each of the infinite possibilities is a new line, which in turn splinters into another infinity of possible futures.

Time travel would be like tracing the crack backwards to the last split and taking a different course. This allows for a semblence of causality between universes because anything you change is merely an alternate set of events instead of remaking a single universe and creating paradox.

Personally I think a time travel campaign could be very interesting for everyone involved, so long as the DM thinks up creative results for the players decisions.

[Collin152]

No, I mean that you going there constitutes disturbing it, so it can't work.

[Clementx]

I have a simple guideline for this kind of problem: The Law of Conservation of History.

Actually, that is not your guideline; that is Novikov's self-consistency principle, and he beat you to it by two decades. I can read Wikipedia, too.

[Dervag]

What about the multiple timelines version of history?That one works too. I never said there weren't other ways to reconcile time travel with causality, I only suggested one such way.


This is the one where each situation in a time has an infinite variety of outcomes, with one outcome becoming increasingly more probable than all the others until that point in time is reached and a certain outcome is determined.This isn't the standard 'multiple timeline' interpretation. The standard multiple timeline version comes from the Copenhagen Interpretation of quantum mechanics, and says that whenever any event happens that could have happened differently, a cluster of parallel universes is spawned, one for each possible outcome of the event. These parallels cannot interact.

According to the standard multiple timeline version, when you travel back in time, a new cluster of parallel universes is created by your arrival. Your timeline, the one you started from, is the one where you failed to arrive and had no effect on the past whatsoever, not even on the butterfly effect level.

And once you do arrive, you've automatically shunted yourself into a universe other than the one you were born in: the one where everything happened differently because of your arrival. So you can never return to the universe you were born in.

Of course, this interpretation makes it effectively impossible to travel into the future (even to return to your own time). Because the 'future' of the universe you are in now is actually a huge multibranched cluster of universes. So there's no way for you to steer into the future of your own universe.


or Terminator, for the ulitmate example of inbreeding - that guy was his own grandfather and grandson, his girlfriend was his grandmother, and his son was his father.Logically, you can't be your own grandfather without being your own grandson, and if you are your own grandfather than your son must be your father. There's no way around it.

Of course, inbreeding isn't really a meaningful description of the consequences here, because nobody is really interbreeding with someone that they share a common ancestor with.


Just make it impossible for time travellers to create parralel universes and you're golden. :smalltongue:No need. According to the physics that justify the idea of parallel universes in the first place, every event, no matter how trivial, creates parallel universes. There's nothing unique about the arrival of time travels that would stop it from spawning parallel universes.

The point is that the time travelers started from some universe. Call that one "the Home Timeline."

Now, the past of the Home Timeline either contains intervention by time travelers, or it doesn't.

If it doesn't, then clearly the time travelers did not arrive in the past of the Home Timeline. So the Home Timeline must be one of the parallel universes arising from the possibility that they did not arrive, that their time machine blew up or they changed their minds at the last minute or something like that.

In that case, the set of parallel universes in which time travellers do arrive are not the Home Timeline. So the time travellers cannot affect their own past because their own past is safely off in some other universe where they did not arrive. They can't touch it.

On the other hand, what if the Home Timeline's past (that is, before the time that the time travellers came from) does contain intervention by time travellers?

Now the time travellers can affect their own past. In that case, one of the parallel universes that results from the actions of the time travellers is the Home Timeline. The Home Timeline is the universe that results from one specific set of things that the time travellers might have done.

Meanwhile, there are bunches and bunches of other timelines (not the Home Timeline) where the time travellers did something else, or failed in their mission, or never showed up at all.

The nice thing about the parallel universes theory of time travel is that your time travellers can do whatever they want with no consequences whatsoever to their own past. If they do something that makes their own past impossible (like killing their own grandfather), that simply means that they are now in a parallel universe other than the one that they will grow up in in the future.

The downside is that once you end up in a parallel universe different from the one you grew up in, you can never go home again no matter what. There can be no interaction between parallel universes according to the physics that implies their existence.

So your heroes still have an incentive not to change their own past. If they do, they can never go home again and are trapped in whatever universe their own actions created.


I personally like the idea that, while travelling in time, the characters exist partially outside time and are thus slightly protected from the effects of altering the future, so they wouldn't simply cease to be instantly if they killed their own ancestor.Again, according to the existing theories of time travel that have a strong basis in physics and philosophy, they don't have to worry about vanishing if they kill their own ancestor. If there is only one timeline, they can never kill their own ancestor because that would imply a contradiction (someone getting murdered by a person who does not exist). If there are multiple timelines, then they can kill their own ancestor, or stop World War Two, or whatever, in perfect safety because all they will do is spawn a parallel timeline... in which case, of course, they can't go home again.


I like to think of the universe as an organism, in paradox situations. The organism wants to keep existing, so if you kill your grandfather (or grandmother), someone else will simply provide the DNA required. This is basically The Law of Conservation of History, but I like to be more flexible. You can't stop yourself from existing but you could, say, prevent a war or change a society.But if you change society or prevent a war, the Butterfly Effect would change you or stop you from existing... unless you apply either the Law of Conservation of History in its strict form or the theory of parallel universes.

IF time travellers have any chance of altering their own past, then they must be the result of any and all changes that have been made by time travellers during their own past. A good example would be the cartoon Time Squad, in which people travel through time to prevent history from 'going wrong' in ways that are ahistorical. Thus, Time Squad acts to preserve its own timeline by intervening in ways that result in the events that are written in their history books.


Ah, teleport through time, you old dog, how is it that you can be so useless while looking so powerful? By it's very definition, the material component is unobtainable.All right, this time I'm going to give the catgirl a blindfold and cigarette, because I know what's about to happen.

According to the laws of relativity...
(READY...)
...if you have a method of travelling faster than light such as the teleport spell...
(AIM...)
...it is a simple task to use that method to travel into your own past by teleporting
(FIRE!)


Actually, that is not your guideline; that is Novikov's self-consistency principle, and he beat you to it by two decades. I can read Wikipedia, too.Don't get snippy. I didn't claim to have invented it, and I didn't put my own name on it.

I call it the Law of Conservation of History because that's what it was called where I read about it in a book by Larry Niven that was published more than two decades ago. I did not find it on Wikipedia.

[All the Myriad Ways, "The Theory and Practice of Time Travel," Ballantine Books, 1971]

[SpiderBrigade]

The downside is that once you end up in a parallel universe different from the one you grew up in, you can never go home again no matter what. There can be no interaction between parallel universes according to the physics that implies their existence.

So your heroes still have an incentive not to change their own past. If they do, they can never go home again and are trapped in whatever universe their own actions created.Doesn't the line that I bolded also mean that they wouldn't be able to travel into the past in the first place?

[Clementx]

Doesn't the line that I bolded also mean that they wouldn't be able to travel into the past in the first place?

It means that no matter how precise their machine, they can never reach the past of their own universe. They can travel into the past as much as they like, they can just never interact with the space and matter that gave rise to their lives. You could give the universe more slack by saying you cannot change your direct past, but you can alter anything that exists independently of your past life (to a certain threshold- after all, every particle in the universe exerts a non-zero gravitation pull on every other). Of course, the physics doesn't support that, but the physics don't work anyway, so have fun!

[Collin152]

All right, this time I'm going to give the catgirl a blindfold and cigarette, because I know what's about to happen.

According to the laws of relativity...
(READY...)
...if you have a method of travelling faster than light such as the teleport spell...
(AIM...)
...it is a simple task to use that method to travel into your own past by teleporting
(FIRE!)

The spell exists, and has the material component of "A flower that is in a location that has not ben disturbed by intelligent creatures since at lesat the desired time, which is picked at casting". So by definition, you can't obtain this flower.
Oh, and teleport being a means of traveling faster then light? Nonsense! Teleport works by bending the 3d plane into a 4d plane, moving your destination directly adjacent to yourself and pushing you through, then unbending. Esentially, your conjuring your destination to yourself in a different dimension.
For those who can't comprehend it, imagine our world was a two dimensional plane, and you were to fold it over so that two points touched. It's kinda like that.
(Lost my train of thought, as I had to hit my keyboard to get my sister's crumbs out of the blody thing.)

[kamikasei]

Oh, and teleport being a means of traveling faster then light? Nonsense! Teleport works by bending the 3d plane into a 4d plane, moving your destination directly adjacent to yourself and pushing you through, then unbending. Esentially, your conjuring your destination to yourself in a different dimension.

No... you're still traveling faster than light. If you teleport somewhere so as to arrive there before a beam of light that left at the same time as you, you've traveled faster than light. You haven't accelerated up to and beyond the speed of light, but you have outpaced a photon.

[Collin152]

It all depends how you define speed. Can you really compare movement in one dimension to movement in another?

[kamikasei]

It all depends how you define speed. Can you really compare movement in one dimension to movement in another?

Yes.

More to the point, the idea of time travel by moving faster than light that Dervag mentions (or at least, the version I know of) doesn't require you to be moving super fast wow look at the wind rushing by! It just requires you to cover a lot of distance in a short time. From your own point of view you may not seem to be moving very fast at all, but you're still moving faster than light, because you got there before the light did.

I am curious as to specifically what Dervag had in mind, though. The closest I know of is the twins' paradox wormhole trick.

[Jade_Tarem]

Indeed, velocity is the change in position over the change in time. If you and a photon move the same distance, and the photon takes longer to get there, then you have moved faster than light.

Speed is simply the absolute value of velocity.

[Collin152]

Yes.

More to the point, the idea of time travel by moving faster than light that Dervag mentions (or at least, the version I know of) doesn't require you to be moving super fast wow look at the wind rushing by! It just requires you to cover a lot of distance in a short time. From your own point of view you may not seem to be moving very fast at all, but you're still moving faster than light, because you got there before the light did.

I am curious as to specifically what Dervag had in mind, though. The closest I know of is the twins' paradox wormhole trick.
I fail to see how being somewhere before the image of you from before you were there gets there lets you move back in time. That theory does not really cover nstantaneous relocation, but rather Acceleration.
Anyhow, just how long does it take to teleport? 0 time, right? Do some math. Whats speed, distance over time? lets say you teleported 20 miles. 20/0 = Undefined. The math wont equate, the speed can not be proved to be faster then the speed of light.

[Dervag]

Doesn't the line that I bolded also mean that they wouldn't be able to travel into the past in the first place?No.

If you have the right toolkit, you can slide back along the past of your own timeline. But you can't hop 'sideways in time' to another timeline.

Your timeline is a tree of branching possibilities. You can certainly backtrack along your twig to a branch and along that branch to the trunk, even though you aren't allowed to go sideways to another twig parallel to your own.

Whether you can slide forward along your own timeline (from the trunk to some particular branch) given that your own timeline is actually a massive cluster of related parallel universes and not a single line is a different question. Then the problem is:

What happens when a forward-time-traveller encounters a branch point between parallel universes? Do they end up going all ways, so that every possible future leading away from the place they started ends up getting a set of time travellers?


It means that no matter how precise their machine, they can never reach the past of their own universe. They can travel into the past as much as they like, they can just never interact with the space and matter that gave rise to their lives.Says who?

Maybe the results of their interactions with their own past are part of their past. Maybe they were only born because they travelled back in time to save their ancestors from a horrible fate.

The point is that the past is already defined, not that the characters can't interact with it. The characters' interactions are just another part of the past.

So the heroes can't stop World War Two, but there's no reason why they can't participate in a way that leads to the same recorded results that historically took place.


Oh, and teleport being a means of traveling faster then light? Nonsense! Teleport works by bending the 3d plane into a 4d plane, moving your destination directly adjacent to yourself and pushing you through, then unbending. Esentially, your conjuring your destination to yourself in a different dimension.
For those who can't comprehend it, imagine our world was a two dimensional plane, and you were to fold it over so that two points touched. It's kinda like that.
(Lost my train of thought, as I had to hit my keyboard to get my sister's crumbs out of the blody thing.)Nonono. You miss my point.

My point is that in the mathematics of relativity, faster than light travel and backwards-in-time travel are the same thing. What you see as FTL travel (in the form of teleportation between two points widely separated in rectilinear space) in your form of reference, I can see as time travel in my frame of reference, and we're both right.

It's one of the implications of the space-time continuum. The rate at which you move in space affects the rate at which you move in time. If you can move faster than the speed of light in space, you can move at negative speeds in time.


I am curious as to specifically what Dervag had in mind, though. The closest I know of is the twins' paradox wormhole trick.It's a quirk in the equations. The important thing to consider is that the speed of light isn't just the speed at which little wiggles of electromagnetic fields happen to travel through space. It's a fundamental feature of space-time, as demonstrated by the fact that light appears to move at the same speed no matter what motion you have relative to it.

Think about a soda bottle thrown out of a car window when the car is moving at, say, 40 miles an hour. If you're sitting in the car, the bottle looks like it falls straight to the ground. If you stand on the side of the road, the bottle looks like it's moving at 40 miles an hour (because relative to you, the car is moving, and the bottle picks up the car's speed).

And if you're in the opposite lane going at 40 miles an hour, then the bottle looks like it's going at 80 miles an hour, because you're closing in on the bottle very quickly.

However, if we try the same experiment with light, it doesn't work. If I run away from light very fast and try to measure the apparent speed of light that is 'catching up with me', I get a constant value called 'c'. If I measure the speed of light that I am running towards, I still get a constant value called 'c'.

So light isn't like anything else in the universe. For everything else, it makes at least some difference how fast you move relative to it. Things look to be moving faster when you're closing in on them and slower when you're running away from them. But not light.

So, working on the assumption that the speed of light was a universal constant that applied to every point of view in the universe, Einstein came up with a new set of equations to describe things like motion, force, speed, and time. Those equations look a lot like the ordinary ones that Sir Isaac Newton came up with in the 1600s when we talk about normal speeds. But at speeds approaching the speed of light, there are BIG differences. Differences that we have checked, and that are definitely really there.

One of the things about relativity is that if you plug speeds higher than that of light into the relativistic equations, you get weird results. Really, really weird. Your length and mass become imaginary numbers, and so on.

Arguably, this means that relativity doesn't even describe what happens to you at FTL speeds. Or if it does, then quantities we think we understand (like mass) must mean something completely different at faster than light speeds.

And one thing that is definitely true is that faster than light travel is mathematically equivalent to backwards in time travel. Causation in the physical universe cannot go faster than light. If you can outrun light, you can outrun causation. Which means that you can make effects that happen before their causes, at least in any meaningful sense of the word 'before'.


I fail to see how being somewhere before the image of you from before you were there gets there lets you move back in time. That theory does not really cover nstantaneous relocation, but rather Acceleration.No, actually, the general theory of relativity does describe instantaneous relocation. Specifically, it calls that a 'spacelike effect', one that cannot be used to carry causation.

If you can use spacelike effects to carry causation, then you have just invented backwards time travel. The math supports it and in fact proves it. There are some interesting popularizations that treat the problem; I suggest you start with Stephen Hawking's A Brief History of Time.


Anyhow, just how long does it take to teleport? 0 time, right? Do some math. Whats speed, distance over time? lets say you teleported 20 miles. 20/0 = Undefined. The math wont equate, the speed can not be proved to be faster then the speed of light.Actually, it can. It is very well established that you just outran a beam of light. If you just outran a beam of light, then you have moved at a speed faster than light. In fact, you have moved at an infinite speed.

To you, this may sound like a showstopper. But physicists have had a fair amount of practice including infinite quantities into their models and equations; techniques like the Dirac delta function and the step function make it very, very possible. The idea of a discontinuous position (meaning that you're here and then instantly there) has very precise implications in general relativity; again, one of them is that you can make an effect happen before its cause.

[Khantalas]

Anyhow, just how long does it take to teleport? 0 time, right? Do some math. Whats speed, distance over time? lets say you teleported 20 miles. 20/0 = Undefined. The math wont equate, the speed can not be proved to be faster then the speed of light.

20 / 0 is faster than light, because basically the resulting figure is greater than all real numbers, and the velocity of light can be defined as a real number. However, you can't prove that a completely still figure doesn't have a velocity faster than light, because 0 / 0 is indefinite.

Infinite is undefined, but it is not indefinite. It may easily be compared to all real numbers. Virtual numbers is the thing that gets confusing.

Anyway, you want Time Travel? Mutants and Masterminds has it.

[Caelestion]

If we go back in time to before this thread was started, can we revive all the newly deceased catgirls?

[Yuki Akuma]

If we go back in time to before this thread was started, can we revive all the newly deceased catgirls?

No. But you can travel to a parralel universe in which the catgirls never died in the first place.

[Clementx]

Says who?

You did in your second post.


Your timeline, the one you started from, is the one where you failed to arrive and had no effect on the past whatsoever, not even on the butterfly effect level.

And once you do arrive, you've automatically shunted yourself into a universe other than the one you were born in: the one where everything happened differently because of your arrival. So you can never return to the universe you were born in."

Once you are shunted into a new parallel timeline, you aren't affecting anything of your own past. Everything before your arrival is unchanged. Everything after your arrival only happens in another universe. If you want to call Bizarro Dervag's life that you are changing your own, you can, but you aren't precisely correct. You might be able to hop into Bizarro world and join a universe you had a longer influence on, but it won't be yours.

And as for being predestined to do something, the Self-Consistency principle prevents a future element from interacting with a past element. Your ancestors are slaughtered before you can be born to prevent it. If you want be able to do that, you have to discard both the Self Consistency principle and the quantum universe thingy. So you can't have it all.

[Attilargh]

are there rules for time travel in d&d?
Sure. They're called "Age Categories (http://www.d20srd.org/srd/description.htm#tableAgingEffects)".

[Collin152]

20 / 0 is faster than light, because basically the resulting figure is greater than all real numbers, and the velocity of light can be defined as a real number. However, you can't prove that a completely still figure doesn't have a velocity faster than light, because 0 / 0 is indefinite.

Infinite is undefined, but it is not indefinite. It may easily be compared to all real numbers. Virtual numbers is the thing that gets confusing.

Anyway, you want Time Travel? Mutants and Masterminds has it.

If it's larger then all real numbers, its not a real number, correct? If it's not a real number, then how can you compare it to anything?

[Khantalas]

But you can't multiply both sides of an equation with 0, because then you get:

20 x (0 / 0) which is indefinite because 0 / 0 is indefinite.

[Murongo]

The entire idea that FTL travel causes you to move back in time is a theory. That theory is based on ANOTHER theory (black hole time dilation). Which, by the way, is incredibly unsound because we don't even know if black holes exist or if they act in that way. (Its likely, but we don't know)

The entire theory is based on the fact that sound waves get longer as they near a black hole- which doesn't make sense because the faster the sound wave moves the shorter it should get. The easiest explanation so far is that the black hole basically slows down time.

Its all interesting, but its all speculation.

Even if you could move back in time- anyone who was going to do it has already done it. Every event that has transpired must have already taken into account those people coming back in time and doing whatever it is they did.

So in terms of D&D, you can have your characters go back in time (perhaps to fight a god which has gone back in time to destroy the world a la terminator) but it can't affect the time-stream. Essentially, they had to have already done it. Its a good excuse to have some really epic characters fight some things like Hecatoncheries (I know for a fact that thats spelled wrong, phonetics ftw).

By the way calling it a time- "stream" or "line" is betraying. Really its time-point or time-dot or time-0-dimensional-figure.

[Collin152]

The entire idea that FTL travel causes you to move back in time is a theory. That theory is based on ANOTHER theory (black hole time dilation). Which, by the way, is incredibly unsound because we don't even know if black holes exist or if they act in that way. (Its likely, but we don't know)

The entire theory is based on the fact that sound waves get longer as they near a black hole- which doesn't make sense because the faster the sound wave moves the shorter it should get. The easiest explanation so far is that the black hole basically slows down time.

Its all interesting, but its all speculation.

Even if you could move back in time- anyone who was going to do it has already done it. Every event that has transpired must have already taken into account those people coming back in time and doing whatever it is they did.

So in terms of D&D, you can have your characters go back in time (perhaps to fight a god which has gone back in time to destroy the world a la terminator) but it can't affect the time-stream. Essentially, they had to have already done it. Its a good excuse to have some really epic characters fight some things like Hecatoncheries (I know for a fact that thats spelled wrong, phonetics ftw).

By the way calling it a time- "stream" or "line" is betraying. Really its time-point or time-dot or time-0-dimensional-figure.
Presicely; If we were ever going to discover time travel, wouldn't they go into the past and give it to us?

[Aximili]

Presicely; If we were ever going to discover time travel, wouldn't they go into the past and give it to us?
If they brought it to us, they would change a lot of what happened before them. So those that brought (will bring?) it to us will never be (won't have been?) born, and so they can't have brought it to us.

This stuff is full of possible paradoxes. Maybe they are real. Maybe future civilization is just to scared to try them out.

[Collin152]

If they brought it to us, they would change a lot of what happened before them. So those that brought (will bring?) it to us will never be (won't have been?) born, and so they can't have brought it to us.

This stuff is full of possible paradoxes. Maybe they are real. Maybe future civilization is just to scared to try them out.
NOnsense; they exist because they brought it back, or they never would have.

[Aximili]

They were born in a timeline in which civilation didn't yet have time travel. And they go into the past (our time) and change that timeline to one in which there is time travel.
That is a great impact to peoples' lives. Enough of an impact so that they might not have been born.

But, as you said yourself, if they didn't exist they never would have brought the technology to us.

By changing the past, they might prevent their own birth, which means they can't have changed the past in the first place. Which means they didn't avoid their birth. Which means they can still go back and hange the past. But then they might avoid...

[Dervag]

Once you are shunted into a new parallel timeline, you aren't affecting anything of your own past.Nononono.

That is only true if your history doesn't already include intervention by time travellers. If you read in the history books that 1000 years ago, a world-conquering army was stopped by a band of heroes that appeared from nowhere and rode off into the sunset, nothing is stopping your party from travelling back in time and being those heroes.

Neither the law of conservation of history nor the parallel time tracks theory actually prohibits you from interacting with your own past. What they do prohibit is changing your own past.

Everything that happened in your past is already part of your history and therefore determined. You may go back in time and play some role in making those events come out the way they 'historically' did. But you can't go back and make them happen in some ahistorical way, because you can't change the fact that those things did happen in your timeline.

Let's take an example of a historical event with some mysterious factors: the assassination of US President John F. Kennedy.

The conventional wisdom states that Kennedy was killed by a lone marksman firing from a tall building. However, analysis of where the bullets ended up suggested that some of the shots were fired from a completely different angle, and that they probably started at a place called 'the grassy knoll'.

The identity of the "second gunman on the grassy knoll" is completely unknown. Nobody has any idea who it was, and there's actually some doubt about whether or not the second gunman even existed. However, it is not definitively known that he did NOT exist.

Now, let's say that I decide to go back into my own past and be the second gunman on the grassy knoll. There are two possibilities:

a)I will fail, because someone else, other than time-travelling Dervag, was the second gunman...
or
b)I will succeed, in which case I was the second gunman.

Either way, the past is not changed by my actions, because my actions are entirely compatible with the history books. Nothing I did changes the course of history; therefore there is no reason why my actions can't be part of my own past, despite the fact that I wasn't even born until well after the Kennedy assassination.

All the Law of Conservation of History says is that if I try to prevent the Kennedy assassination or otherwise change the historical series of events, then I cannot do so within the timeline of my own personal past.

One possibility is that I will fail, so that events proceed as they did in the history books I read back home before stepping into the time machine. The other is that I will succeed, and end up in a parallel universe where President John F. Kennedy was saved because Dervag crashed through a window in a leprechaun costume and startled Lee Harvey Oswald into missing the shot that killed Kennedy.


Everything before your arrival is unchanged. Everything after your arrival only happens in another universe. If you want to call Bizarro Dervag's life that you are changing your own, you can, but you aren't precisely correct. You might be able to hop into Bizarro world and join a universe you had a longer influence on, but it won't be yours.That is true only if the events of Bizarro World are not the events of my own past.

If I am in fact Bizarro Dervag, the Dervag who was born in Bizarro World, then I can surely go back in time and do the things that lead to the creation of Bizarro World with no inconsistencies involved.


And as for being predestined to do something, the Self-Consistency principle prevents a future element from interacting with a past element.Why? The entire premise of time travel is that future elements can end up in the past and therefore interact with past elements.


Your ancestors are slaughtered before you can be born to prevent it.Again, there are two possibilities.

One is that my ancestors are slaughtered and I am never born.

The other is that my ancestors are almost slaughtered, but then at the last minute this weird guy called Dervag barges in and saves their lives. Then, centuries later, a child is born to the descendants of those ancestors. The child (me) is named Dervag. Dervag goes on to invent a time machine and go back into the past, where he sees a bunch of people about to be slaughtered.

So he barges in and saves their lives.

This is entirely self-consistent and there is no implied paradox. The point is that if the massacre of my ancestors succeeds there is no time travel, but that if there is time travel then the massacre must fail.

In normal logic, when we find something that implies a logical contradiction (such as the Grandfather Paradox), we assume that things can't work that way, because that would imply a contradiction. Why should time travel be any different? If we accept the existence of time travel, then we should assume that time-travel loops and the actions of time travellers must operate in such a way that the history of any given timeline will be internally consistent.


If it's larger then all real numbers, its not a real number, correct? If it's not a real number, then how can you compare it to anything?By observing that it IS larger than all real numbers.

For example:
A Snickers bar weighs, say, one ounce.

Ten Snickers bars weigh ten ounces.

Would an infinite number of Snickers bars weigh more than ten Snickers bars?

The answer is yes. In fact, it is very obviously yes, because infinity is more than ten. It is more than a billion. It is more than any number you can possibly describe with digits. That is the definition of infinity.

So when you have an infinite amount of something (like speed or Snickers bars), then you CAN compare it to real numbers (like a speed of ten miles an hour or a pile of ten Snickers bars), because the relationship of infinity to the set of all real numbers is very very simple.


The entire idea that FTL travel causes you to move back in time is a theory. That theory is based on ANOTHER theory (black hole time dilation). Which, by the way, is incredibly unsound because we don't even know if black holes exist or if they act in that way. (Its likely, but we don't know)Actually, we do know that black holes exist because we can see things falling into them. And we can do the math to describe them very well, so we have a pretty good idea of what happens when we're around them.

Moreover, the idea that FTL travel causes you to move back in time is a straightforward consequence of the extremely well tested and proven theory of general relativity. If you allow for motion that is faster than light from the perspective of some observer, then that motion will produce causes that precede effects for other observers.


Even if you could move back in time- anyone who was going to do it has already done it. Every event that has transpired must have already taken into account those people coming back in time and doing whatever it is they did.Yes, this is more or less my point.


So in terms of D&D, you can have your characters go back in time (perhaps to fight a god which has gone back in time to destroy the world a la terminator) but it can't affect the time-stream. Essentially, they had to have already done it. Its a good excuse to have some really epic characters fight some things like Hecatoncheries (I know for a fact that thats spelled wrong, phonetics ftw).Well, they can affect the timeline, but only in the ways that the history books say that it was affected. So they can save the universe from an evil god in the past, but they can't destroy the universe themselves.


By the way calling it a time- "stream" or "line" is betraying. Really its time-point or time-dot or time-0-dimensional-figure.Not really. Remember that if you could somehow percieve time as just another dimension, then any object with a duration would look like a line stretching from one point to another in time.

You are a time-point; namely, you are the cross-section of your life that happens to exist at this instant in time. However, your life, and the life of the universe, are time-lines, because they stretch between two points in time.

[okpokalypse]

The entire idea that FTL travel causes you to move back in time is a theory. That theory is based on ANOTHER theory (black hole time dilation). Which, by the way, is incredibly unsound because we don't even know if black holes exist or if they act in that way. (Its likely, but we don't know)

Well, faster than light travel has already been discovered by CERN. I don't have a link to the article, but certain heavy-element isotopes leak radiation that moves in excess of C.

However, Time should be navigable by all means. It's just another dimension. Unfortunately, we're not capable of conceiving it as anything but a linear stream. Mathematically speaking, String & M-String theory lead one in the direction of a multitude of dimensions, all potentially traversable when we gain enough knowledge - but it sure as hell won't be in our lifetimes. :smallsmile:

[thehothead]

I think the best thing is to screw with the PCs so if they go back in time to change something, make so that they accidentally CAUSED the event in the first place.

[Dervag]

I think the best thing is to screw with the PCs so if they go back in time to change something, make so that they accidentally CAUSED the event in the first place.This is essentially the effect of implementing the Law of Conservation of History.

On the other hand, it's also really annoying to the players because it's nothing but Oedipus Rex with the names changed and the serial numbers filed off.

[Collin152]

They were born in a timeline in which civilation didn't yet have time travel. And they go into the past (our time) and change that timeline to one in which there is time travel.
That is a great impact to peoples' lives. Enough of an impact so that they might not have been born.

But, as you said yourself, if they didn't exist they never would have brought the technology to us.

By changing the past, they might prevent their own birth, which means they can't have changed the past in the first place. Which means they didn't avoid their birth. Which means they can still go back and hange the past. But then they might avoid...
No, see, if they diddn't go back in time, they would not exist, so there would be nobody to go back in time. But if they do go back in time, they can be born. So if they are born, it means they must go back in time to give us the technology, which obviously was not developed by them, but they were instructed to do so. Therefore, time travel technology formed itself from nothingness.

[Dervag]

Or, as a third possibility, they invented it themselves didn't go back in time and didn't give us the technology, and are instead hoarding it for themselves in the future, the jerks.

[Jade_Tarem]

This is essentially the effect of implementing the Law of Conservation of History.

On the other hand, it's also really annoying to the players because it's nothing but Oedipus Rex with the names changed and the serial numbers filed off.

Er, what?

Oedipus Rex was about duplicity and acting on incomplete information, and also, to a certain extent, about hubris. Time travel wasn't involved. He fulfilled the prophecy while taking actions to avoid it. The closest you get is to sort of pretend like the future depicted by the prophecy was the "present" and that the present is the past. Despite this, your point is actually a good one. It's just a bad example.

[Beleriphon]

Well, you can buy one rank in Time Travel for two skill points. If you're playing Mutants and Masterminds.

Yeah, but that just works like the Super-speed array, so its not really time travel. ;)

[Khantalas]

What? It says you can travel back or forward at time up to one year at rank 1.

You're reading Time Control.

[Clementx]

Then, centuries later, a child is born to the descendants of those ancestors. The child (me) is named Dervag. Dervag goes on to invent a time machine and go back into the past, where he sees a bunch of people about to be slaughtered.

So he barges in and saves their lives.

This is entirely self-consistent and there is no implied paradox.

It is the very definition of paradox for linear time. The slaughter-threatening happens before the existence of the time-traveling hero. Which means their death is can only prevented by the existence of a element that only comes into being if their death is already averted, which is isn't by time of their deaths. You say the effect can predate the cause. Your whole idea of necessitated time-travel requires simultaneous existence of all time-states, in which cause and effect occur in different regions of reality, but both exist at the same time. Which you never stated. Assuming the future to already exist in the past is a big deal, and not a condition you stated for your argument. Hence me calling you on it.

Now, going all BttF on time-travel can be fun. But that requires an entirely different, more-plot-convenient, less-scientifically-consistent method of time-travel.

[Aximili]

No, see, if they diddn't go back in time, they would not exist, so there would be nobody to go back in time. But if they do go back in time, they can be born. So if they are born, it means they must go back in time to give us the technology, which obviously was not developed by them, but they were instructed to do so. Therefore, time travel technology formed itself from nothingness.
hmm.. Now I got your point (I think).

But then (as you said), the time travel technology would have no point of origin. That could prove that such technology will never exist (since no one has brought it to us), but it may also just prove it will never exist in that way. So it could still be created in a way as to have a fixed point of origin, and as to make it impossible for them to bring it here to us.

I'm not saying it is the latter. I'm just giving another possibility.

Now, going all BttF on time-travel can be fun. But that requires an entirely different, more-plot-convenient, less-scientifically-consistent method of time-travel.
Much less cientific convenient.:smallbiggrin:

Unless they want to go to the future. It's much easier to run forwards than to walk backwards when it comes to time travelling.

(but walking backwards is much more fun.:smallcool: )

[Collin152]

Well, anyways, ignoring the blatant catgirl killing, there are in fact rules published by wizards (on their site, no less) for going back in time, but it's useless because you can't get the material componant without corrupting it.

[Dervag]

Time travel wasn't involved. He fulfilled the prophecy while taking actions to avoid it.That's the key.

Oedipus Rex was the first literary example of someone obtaining information about the future, trying to prevent it, and accidentally bringing about the very future they were trying to prevent.

This plot concept has been rehashed over and over for the past 2500 years until it's practically a cliche. The classic version is still, of course, trying to avert a prophecy and accidentally causing it (see Star Wars III for reference). But the advent of the idea of time travel allows for a slight riff on the concept, even though the riff is still within the bounds of the basic plot concept.


It is the very definition of paradox for linear time. The slaughter-threatening happens before the existence of the time-traveling hero.No, it doesn't. It only happens before the birth of the time-traveling hero. The whole point of time travel into the past is that you can exist during intervals of time that precede your own birth.

If you don't assume that, then you don't assume time travel into the past. That's fine, but you should say so, which is why I'm calling you on it. Tacitly assuming the impossibility of time travel in a thread about time travel is a big deal.


Which means their death is can only prevented by the existence of a element that only comes into being if their death is already averted, which is isn't by time of their deaths.Except that they don't die, because of the element that came into being because they didn't die.

The problem here is that there's a difference between a causal loop and a causal paradox. A paradox requires some internal contradiction, such as:

"The barber shaves every man in town who does not shave himself, and only men who do not shave themselves. So, does the barber shave himself (in which case he's shaving someone who shaves themself) or not (in which case he has to go to himself to be shaved)?"

This is a paradox, because there is a contradiction implicit in the conditions that create the situation. The barber cannot both shave and not shave himself, just as the hero cannot both save and not save his own ancestors.

However, there is no paradox in a consistent causal loop in which A implies B which in turn implies A. This may be a temporal tautology, but it is not a temporal paradox.


Your whole idea of necessitated time-travel requires simultaneous existence of all time-states, in which cause and effect occur in different regions of reality, but both exist at the same time.Not true, unless you're using a very exotic definition of 'time'.

The history of a universe can be represented as a 'time line' with the universe at any moment being like a single 'frame' hanging off the line. If you had a God's eye view of the entire time line, you would be able to see all causes and all effects, and the difference between past and future would be no more profound than the difference between left and right.

If, on the other hand, you're a normal person, then you only ever see one frame at a time and you are being swept inexorably in one direction along the frames ('forward' in time). But this is not necessarily a profound deal. It is, in fact, a lot like the situation of a fish that lives in a fast-flowing river and cannot swim upstream. Upstream isn't different from downstream in a philosophical sense, but normal processes within the stream can never allow the fish to see places upstream of itself, while it can see places downstream of itself by just riding the current and waiting.


Assuming the future to already exist in the past is a big deal, and not a condition you stated for your argument. Hence me calling you on it.I assume that the state of any moment in time is determined entirely by events that happened before that moment in time. Time travel would allow you to relocate in time so that you can end up 'upstream' of some particular historical event (like the Kennedy assassination), and therefore gain the ability to affect its outcome.

Again, the difference between past and future in a many-dimensional universe is no more profound than the difference between left and right, or between 'forwards' and 'backwards' on a moving vehicle.

So it could still be created in a way as to have a fixed point of origin, and as to make it impossible for them to bring it here to us.Or they could just, y'know, not give it to us.

[Collin152]

Blasphemy! If you have the ability to give the past a better shot at survival, what voter wouldn't foolishly insist we do?