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A well known physical problem with FTL travel or communications is that it violates causality and is thus fundamentally the same as a form of time travel. What if the Force is the thing that prevents this paradox in the Star Wars universe? That of acting as a physical force that keeps all reference frames on equal footing. The fact that high-STL maneuvers are also not really seen in Star Wars also avoids the issue of relatavistic time(with the possible exception of the Millennium Falcon's trip to Bespin).

This also obviously destroys my odd idea about making The Force an AI, which has no means of dealing with this problem. Though that idea didn't really fit for a dozen other reasons anyway.

Sow-HOW exactly does the Force do this? We know that FTL travel and communications are an everyday occurance in the Wars universe, so how exactly does the Force prevent that from violating causality?

Okay, pardon my ignorance, but what makes you sure Star Wars FTL is transluminal velocity normal spacetime travel (and thus subject to time dilation), and not something more like what we see: wormhole travel? When they go into and out of hyperspace, they seem to be moving "normal" STL velocities.

Why can't Star Wars communications be using the same wormhole tech, instead of tachyons (FTL, backwards-in-time particles)?
Does relativistic time dilation work the same with wormholes? Serious question: I don't get it. My rough understanding answer is "No, because you aren't crossing all the spacetime between points A and B, you're short-cutting between points A and B."

We know that FTL travel and communications are an everyday occurance in the Wars universe, so how exactly does the Force prevent that from violating causality?

The easy answer is "It doesn't have to: there is no FTL velocity in play." Or that other stand-by: "It's magic."

Hyperspace is, canonically (still, IIRC), an alternate dimension. I don't know if that means wormholes, I don't think it does.

FTL as depicted in most major SciFi is actually not FTL in the literal sense. Star Wars hyperdrive, Babylon 5 hyperspace, Stargate wormholes and hyperspace, Battlestar Galactica jump drive...none of them actually move FTL. They are all alternate states of the universe (alternate dimensions, for lack of a better phrase) where the laws of physics act differently (except for Star Trek where it simply warps existing space, but the ship itself still isn't actually really pushing itself FTL) Take Babylon 5 as an example of how hyperspace works. You open a jump point into hyperspace, where the ship uses normal STL engines. Only thing is that for every mile you travel in hyperspace, that corresponds to a hundred miles in realspace. So it SEEMS like you're going FTL but the ship really isn't. So time dilation doesn't really matter here since at no time is anything actually exceeding the speed of light.

^ That, pretty much. It doesn't have much of anything to do with the Force per se as far as I know. The Force doesn't give much of a shit about what goes on in the universe unless you want to start getting religious about it.

You don't have to locally exceed the speed of light to violate causality; you just have to get from point A to point B before a photon could. It doesn't matter how you got there; if you do, there is a reference frame in which you arrived before you left. Relativity, causality, FTL: you can only have two . . . and relativity is too firmly established to throw out.

Many people believe that this means that no form of FTL travel is possible. However, if there are arguments for the necessity of causality beyond "well, things would be really weird without it", I haven't encountered them.

Since in a lot of SciFi FTL travel without time travel is very clearly possible maybe Einstein was wrong?

And I don't think you understand the magnitude of the problem losing causality would be.

Zeropoint wrote:You don't have to locally exceed the speed of light to violate causality; you just have to get from point A to point B before a photon could. It doesn't matter how you got there; if you do, there is a reference frame in which you arrived before you left. Relativity, causality, FTL: you can only have two . . . and relativity is too firmly established to throw out.

Okay, I wasn't sure on the math with this point. Hmm.

Batman wrote:Since in a lot of SciFi FTL travel without time travel is very clearly possible maybe Einstein was wrong?

Or most SF writers just ignore the practical problems with whatever version of FTL travel they depict. Hardly unknown.

Err-I meant for in-universe physics.

Adam Reynolds wrote:A well known physical problem with FTL travel or communications is that it violates causality and is thus fundamentally the same as a form of time travel.

No, it's not. Time travel is a form of FTL travel, not the other way around.

Sorry, that's not correct. If you have one, you have the other--they're fundamentally equivalent. If you have time travel, you can get to a destination before light emitted from your starting point (rather trivial, really) and if you have FTL, you can find a path that will lead to your own past. I won't try to explain it here, when others others have explained it better than I can, but it has to do with the fact that whether two events are simultaneous or not depends on your reference frame. Your FTL drive has you disappear from one place and "simultaneously" appear somewhere else . . . well, simultaneously for who? For some observers, you've gone back in time, and there's no way to say their perspective is any less correct than anyone else's.

Guys. Zeropoint particularly, and also Adam Reynolds are correct on this. It's not simply about superluminal velocity.

Any FTL, even magic extra-dimensional things, allows for a temporal paradox in a relativistic universe. A course can be plotted between any three relativistic points with the right relative velocities, to allow a broadcast at c to travel back in time from the frame of reference of the originator.

Nyrath's website has a good explanation of this. Here.

Yes, it applies to travel through wormholes, through alternate dimensions, and through the daemon infested hell of the warp; so long as the ship can carry messages and operates in normal space, the ability to move to a destination faster than light can travel there through a vacuum, indicates that it is possible to break causality.

It's nothing to do with time dialation, or the lightspeed barrier. If you've not read Nyrath's website, please do that before responding.

Elheru Aran wrote:Hyperspace is, canonically (still, IIRC), an alternate dimension. I don't know if that means wormholes, I don't think it does.

In the EU, there were several explanations, the one favoured by West End Games (alternate dimension, like in Babylon 5) but also a tachyonic one, as Curtis got one published in the ICS, in the films and TV shows, there is no reference to alternate dimensions, and it is explicitly in normal space, as it would not be possible to collide with comets in an alternate dimension, which is shown in TCW A Sunny Day in the Void.

If it is possible to hit something physical, you're in the physical universe.

Furthermore in The Force Awakens (Ghetto Spoiler) It is shown that the falcon can pilot through a shield at FTL with the right refresh rate, implying that without that refresh rate it might smack into it and then in the novel of film it is explicit that the ship travels FTL in normal space, and simply passes through the shield very fast.

Curtis' website, referencing the films, describes the theory he advocated in the ICS here and demonstrates a tachynoic superluminal vessel concept from the original films and some EU sources.

Batman wrote:And I don't think you understand the magnitude of the problem losing causality would be.

Causality is not a physical law in the Star Wars universe. Prophets exist, they gain information on events before they happen. The fact that this is done by mystic means is irrelevant. Our undestanding of Causality is empirically disproven in Star Wars.

Borgholio wrote:FTL as depicted in most major SciFi is actually not FTL in the literal sense. Star Wars hyperdrive, Babylon 5 hyperspace, Stargate wormholes and hyperspace, Battlestar Galactica jump drive...none of them actually move FTL.

Just for fun:

Star Wars has prophets.
Babylon 5 has time travel.
Stargate has time travel and prophets.
Battlestar galactica has prophets.
Star Trek has prophets and time travel.

In none of these is causality a physical law of the universe. More a sort of... trend of the cosmos.

Zeropoint wrote:Your FTL drive has you disappear from one place and "simultaneously" appear somewhere else . . . well, simultaneously for who? For some observers, you've gone back in time, and there's no way to say their perspective is any less correct than anyone else's.

True. But can you pick a situation from any science fiction and then produce the math to show that FTL=time travel should have had effects that the audience noticed ?

Or is the effect too small to matter in typical scenarios ?

bilateralrope wrote:

Zeropoint wrote:Your FTL drive has you disappear from one place and "simultaneously" appear somewhere else . . . well, simultaneously for who? For some observers, you've gone back in time, and there's no way to say their perspective is any less correct than anyone else's.

True. But can you pick a situation from any science fiction and then produce the math to show that FTL=time travel should have had effects that the audience noticed ?

Or is the effect too small to matter in typical scenarios ?

While I can't think of any explicit examples of this being relevant, it is part of the conceit of the Star Date in the original Star Trek:

We invented "Stardate" to avoid continually mentioning Star Trek's century (actually, about two hundred years from now), and getting into arguments about whether this or that would have developed by then. Pick any combination of four numbers plus a percentage point, use it as your story's stardate. For example, 1313.5 is twelve o'clock noon of one day and 1314.5 would be noon of the next day. Each percentage point is roughly equivalent to one-tenth of one day. The progression of stardates in your script should remain constant but don't worry about whether or not there is a progression from other scripts. Stardates are a mathematical formula which varies depending on location in the galaxy, velocity of travel, and other factors, can vary widely from episode to episode.

Batman wrote:Since in a lot of SciFi FTL travel without time travel is very clearly possible maybe Einstein was wrong?

And I don't think you understand the magnitude of the problem losing causality would be.

I do. But the Force already seems to violate it with instantaneous galactic communications(ROTS especially features this, with Yoda's survival reliant upon it) as well as genuine precognition(which will always violate causality by definition, even if it only seems to work at certain times). Though the prophecies don't necessarily come true, which somewhat lessens this problem over longer time periods. It is better to violate one scientific principle rather than two. Even if the one is worse than the other.

In the general sense, sidestepping relativity is probably better. Acubierre did come up with something that at least works mathematically, though it is still highly unlikely to ever be built in any reasonable sense. The best bet is science fiction that only features STL propulsion, though that isn't generally seen as interesting. It also creates things that just plain feel odd to a modern audience. That is likely the primary reason for FTL, it allows stories that feel like modern Earth in that issues like communications and travel are equivalent to a modern setting. Taking weeks to travel across a solar system or decades to travel interstellar distances will always feel odd with the timescales we are used to on modern Earth.

NecronLord wrote:Guys. Zeropoint particularly, and also Adam Reynolds are correct on this. It's not simply about superluminal velocity.

Any FTL, even magic extra-dimensional things, allows for a temporal paradox in a relativistic universe. A course can be plotted between any three relativistic points with the right relative velocities, to allow a broadcast at c to travel back in time from the frame of reference of the originator.

Movement at the speed of light means that travelling a distance of x and back to the origin requires a time of 2x/c. Moving slower than the speed of light means that travelling a distance of x and back to the origin requires a time of more than 2x/c, and moving faster than the speed of light means that travelling a distance of x and back to the origin requires a time of less than 2x/c.

Time travel requires that travelling and returning to the origin requires a time of less than 0, and 2x/c is always greater than 0. It does not follow that t < 0 (time travel) is equivalent to t = 0 (instantaneous teleportation) or 0 < t < 2x/c (FTL travel without time travel).

Time travel requires that travelling and returning to the origin requires a time of less than 0, and 2x/c is always greater than 0. It does not follow that t < 0 (time travel) is equivalent to t = 0 (instantaneous teleportation) or 0 < t < 2x/c (FTL travel without time travel).

Sure it does. Travel from A to B at sublight speeds, then pop back to the time you left. Bam, you've arrived at your destination simultaneous (from a certain reference frame) with your departure, although it won't seem instant to you. Alternately, you could travel at high relativistic speeds from A to B, then use your time machine to hop back. For example, you travel such that five years pass outside and one passes inside, then jump back four years.

Zeropoint wrote:

Time travel requires that travelling and returning to the origin requires a time of less than 0, and 2x/c is always greater than 0. It does not follow that t < 0 (time travel) is equivalent to t = 0 (instantaneous teleportation) or 0 < t < 2x/c (FTL travel without time travel).

Sure it does. Travel from A to B at sublight speeds, then pop back to the time you left. Bam, you've arrived at your destination simultaneous (from a certain reference frame) with your departure, although it won't seem instant to you. Alternately, you could travel at high relativistic speeds from A to B, then use your time machine to hop back. For example, you travel such that five years pass outside and one passes inside, then jump back four years.

That is not a rebuttal. That is the exact same nonsense I was talking about in my first post:

Grumman wrote:No, it's not. Time travel is a form of FTL travel, not the other way around.

Just because it is possible to use time travel to produce the effects of FTL travel, that does not mean that you can use FTL travel to produce the effects of time travel.

Grumman wrote: That is not a rebuttal. That is the exact same nonsense I was talking about in my first post:

Grumman wrote:No, it's not. Time travel is a form of FTL travel, not the other way around.

Just because it is possible to use time travel to produce the effects of FTL travel, that does not mean that you can use FTL travel to produce the effects of time travel.

Do you know what Relativity is?

Have you looked at the link I provided and read the highlighted section of Nyrath's page?

From an intuitive understanding of time, yes, what you're saying is accurate; that is an intuitive understanding where there is a single 'correct' frame of reference. However, relative frames of reference mean that any ability to move information between one place and another faster than c allows for information to be delivered into the relative-past.

The main problem regarding causality in star wars is not the generic loss of it but the fact that you could get around it via technological wizardry or relatively easy force tricks. Prophecy in star wars is portrayed as difficult, unreliable and only possible with the force; and changing your past is portrayed as impossible. If causality were to work in the way implied by special relativity you'd have the Rebel Alliance using hyperspace drives to try to stop Palpatine taking over the Senate and Sidious trying to force choke Yoda and Obi-Wan in the past using the Republic video archive.

I may be wrong here, but the impression I get on arguments about FTL leading to time travel is that they go under the assumption that the ftl mechanism has no preferred frame. Whilst having a preferred frame rather goes against the spirit of special relativity, if the ftl mechanism has a preferred frame and everything else acts like there isn't one, that is functionally identical to special relativity working and it may restore causality. You could modify the principle of relativity to say "the laws of physics are identical in all inertial reference frames, apart from hyperspace mechanisms, which have a preferred frame".

But actually, is there really anything in the Star Wars universe to indicate that it is Lorentz Invariant at all? I can't remember any relativistic effects in the canon star wars material, maybe special relativity doesn't occur in the star wars universe at all.

Jedi prophecy works extremely reliably. Reliably enough that they go into regular battle against robot killing machines with guns, and block all the shots aimed at them, using their prophecy. It gets less reliable over a longer time period, but it's extremely reliable in the immediate term.

Indeed it does seem like there is a special frame of reference. That's what the OP is talking about, vaguely. Adam is proposing that the force applies a special frame of reference; which is of course, unproven like all of Adam's crackpot theories, but as you say, the Rebels aren't sending the death star plans back in time so... presumably something stops them doing this.

What seems to be relativistic time dialation is in the Clone Wars episode Jedi Crash, though it may not be intended by the creators. In that episode, a Jedi cruiser has been damaged by Seperatist action and it drops out of hyperspace without being able to come to a reasonable stopping speed, it flies past a star, which they narrowly avoid hitting, and then hits a inhabitable planet on the far side, the travel time is so low that relativistic time dialation is the most plausible explanation for how they manage to go from a star's corona to crash landing (they are ostensibly decelerating all the time) on an inhabitable planet in the same system in under a minute. The writers may not have intended time dialation there, but it's the only thing that makes sense of the scene, and it's a physical law in our universe.

The whole scene can be seen on Brian Young's website at www.scifights.net or possibly it's on his youtube, I will link the video when I am on a home computer.

Grumman, I don't blame you for having trouble wrapping your head around the implications of the Theory of Relativity--it's weird, counter-intuitive, and alien to our low-speed, low-energy lives.

However, it remains the case that Relativity DOES tell us that FTL leads directly to time travel. I don't expect you to take my word for it, but I do expect you to read up on Relativity until you understand it a little better. The universe is stranger than you imagine.