FTL travel means causality stops working properly, or in other words implies the existence of time travel...

>he doesn't move the universe around him

Those are my favorite.

Go read any modern physics textbook, OP.

ONCE MODELED ME

if some of the basic laws of our unniverse don't apply there shouldn't whole crews fuse to the hull Philadelphia experiment style or have their atoms scattered to the 13 winds or some other unknowable catastrophe that would result from our bodies/surroundings not working properly anymore

IRL about a year ago FTL was "solved"

As in a theoretical model where you could effectively travel at FLT speed in real space but without actually going faster than light.

Its called the Alcubierre drive. Basically, we have the math and just need the tech now.

>all these people who think OP's wrong

physicsguy.com/ftl/html/FTL_part4.html

If you can go from point a to point b faster than light, by any method at all, then you will arrive before you left according to some reference frames.
These reference frames are not "wrong" or "mistaken" -- there is no privileged reference frame, ie not "right" one.

What's more, if you were to then turn around and go back to point a faster than light, you can quite easily arrive before you left in ALL reference frames, including your own. Shake hands with yourself and everything.

Most SF avoids dwelling on this because it's a huge can of worms, so there's plenty of handwaving and temporal prime directives and stuff to try to sweep it under the rug.

Because the easier answer is that relativity stops working.

We need exotic matter, a theoretical type of material, to make it work. There's no strong indication such a material even exists.

This is a visual effect user, just because you see them leaving before they arrived doesn't mean they actually are.

Ah yes the warp drive an old classic

Only if you can freely choose the frame you jump to. Buy what if you can't? What if you for example get a certain speed depending on how you jumped?

Visual effects could still cause some causality issues, though. Deciding not to go on a space trip because you just saw yourself come back from said space trip in some kind of horribly injured state, for example.

I think the point he's making is that even if *you* don't choose a reference frame within which this causes you to travel back in time, as long as you ever relocate yourself spatially at a rate faster than the speed of light, there is *a* reference frame where it could be interpreted that you went back in time. Maybe you have to speed up a lot before you trigger FTL, maybe your *destination* needs to speed up a lot, whatever, the option is there for anyone who wants to seek it out. Even if your software would *sensibly* seek to prevent you from raping causality, there's no way to construct FTL hardware that couldn't at least theoretically be used for time travel. And while there are some cosmological theories that compatibilise time travel to an extent, there is no way for time travel to ever not severely shake the foundations of causality, and render a whole lot of stuff we rely on tremendously uncertain.

If you can see them you can use visual effects to convey information - say, pictures of your trip making the trip unnecessary to begin with. You get what you wanted to see without actually ever travelling there.

That gif is wrong and you should feel bad for posting it. You can't just transform your axi and leave your ship in place.

>visual effect

Nope. I would imagine you're confused by the term "light cone."
Read the article, user. That vertical line? That's you, mapped through time. If you can touch an earlier part of that line, you can interact with yourself. It's not a trick, or an illusion, or anything, it's YOU in the past.

Some SF will handwave it away by saying their FTL only works when both sides are in the same reference frame, but this is a dodge. For one thing, it's logistically impossible, since stars and planets and everything are moving relative to each other, often at great velocities; for another, it doesn't stop the drive from violating causality in other reference frames, and since there is no privileged ("correct") reference frame, then the folks who saw you time travel are just as correct. So you violated causality, just not where you are.

The only way to prevent this is to make everything in the universe stop moving, or to become God and rewrite reality to have a universal reference frame/luminiferous aether to keep everything in order.

You should feel bad for not reading the article. Sure, you'll spend time accelerating to a different reference frame, but all you have to do is extend the distance of your FTL jump to make up for it. Adding that in would clutter the gif unnecessarily, so it's depicted the acceleration time as trivial compared to the jump distance, for clarity.

The principles are unchanged.

>Adding that in would clutter the gif unnecessarily, so it's depicted the acceleration time as trivial compared to the jump distance, for clarity.
I'm not talking about acceleration. I'm talking about the part where the ship has FTL jumped. They shift the axi back to reference frame 1 to "show" that the ship has time travelled. That's not how it works.

Alcubierre drives maintain local time. The real question is, how does that universe age relative to you? Does it get older at the same rate no matter what speed you go at? I mean, otherwise you could risk the entire universe being gone by the time you each your destination, and how did you even travel then? No it simply doesn't make sense.

FTL travel always uses pocket dimensions and other sci-fi bollocks to skip around the issue.

That said, I'm pretty sure they accidentally Time travelled from FTL bullshit in the Halo storyline. It might have got retconned when Halo Reach came out.

/thread

Golly Geeze, how will we maintain a typical view of spacetime while including faster then light travel?

Wait, a bunch of ways.

Learn to science.

Travel by wormhole is STL in all reference frames. It only appears FTL if you don't understand the shape of local space-time.

Because most writers are bad at math and hate people who aren't (see almost every science trope). There is no loophole and don't listen to any fuck who tells your otherwise; any form of faster than light travel/communication can result in time travel. Now the good writers accept this and build around it. An example would be having your ftl drive explode anytime someone tries to use it as a time machine. However, most writers will either willfully ignore the problem if they are even aware of it (see every shitty scifi novel ever written).

Star Trek dealt with time travel all the fucking time across nearly every entry in the IP.

I believe Gunbuster did FTL travel correctly but I haven't seen it in quite some time.

Depends on the setting of whatever mcguffin negates this effect.

The two Eschaton books sort of take it into account, by having a godlike AI in the far future watching its own timeline for anyone trying to fuck around with time travel and because it needs to exist for its own reasons it makes sure things went wrong when you attempted to time travel in its past.

Because time travel makes for bad stories unless it's the core of the thing, and not every space opera wants to revolve around time travel.

Duh.

It's not a loophole. Time travel via FTL is only possible if you are already doing something our understanding of physics says is impossible.

This means that it's likely impossible, and if FTL is possible it's going to be in a way that involves never acutely traveling faster then light like wormholes, or in a way our current theories don't account for.

When your mathematical model of how something works says 'time travel' then it's broken.

In Futurama Farnsworth say they just increased the speed of light. That avoids all the problems.

A ship using space warping would be at rest. Clocks would show minimal drift compared to planetary clocks

can somebody explain that time travel paradox in a way that doesn't sound completely baffling and contrived?
like from what i can tell, it happens like this:
>O and Op pass by eachother, Op shoots A
>B sees A die, this is apparently something that happens in his future even though it's already happened?
>B sends message to O, who apparently sees this before the shot's been fired?
>O passes by Op even though he's already passed by Op, tells him he's a faggot, Op decides not to fire the shot, even though he's already passed by and fired the shot
if Op's already shot A, how does B or O find out before it's happened despite B finding out after it happens? how does B travel back in time to tell O?
if O and Op have already passed by eachother, how does O receive a message before they've passed by Op?
it feels like it hinges a lot on wanking about reference frames even though realistically they wouldn't matter.

AFTER THE BLUNTEST TOOL IN THE SHED

I don't think he knows what he is taking about to be honest

But there is. See below.

But jumping doesn't mean that you have to change frame. For example, take some star that is moving very fast relative to right now, imagine we jump to it - it'd still move as fast, because we'd still be in the same frame, just in another position. What it would look like on the ship we jumped with is that we suddenly sped up to a very fast speed.
No privileged frame, but there is always the frame that we came from.

user no, it wasn't solved, stop reading shitty pop-sci news site.

I think the fact that he cannot write it clearly shows he doesn't understand it. He barely uses any math, which immediately makes me suspicious

I think it works like this....

The murderer travels FTL from A to B. At B there is a victim and a paladin. Paladin observes the death of victim at B. Now the information that the murderer left from A has not reached the Paladin, because FTL is faster than light. So the Paladin can go FTL from B to A, find the murderer and kill him. Except this is only light, an image. So the author is mistaken?

No, it just means the speed of information isn't constant any more. Instead of causality always travelling at the speed of light, it can travel faster, which means that in a certain frame of reference you COULD make the effect arrive before the cause, but in absolute terms the cause still happened first, it's just a relativistic illusion.
Also, going faster than light won't make time go backwards. γ=√[1-(v^2/c^2)], so if v^2 < c^2 the gamma factor is between one and zero and time contracts, but if v^2 > c^2 the gamma factor is not below zero, as most people assume, it's imaginary, so you'd start travelling through imaginary time if you could go through realspace faster than light.

Well, in the original iirc, it was more that it was only ftl from the perspective of the traveller, outside time still went on at a regular pace.

A kind of "one hour inside, one year outside" situation.

Armchair scientist arguments aside, time travel can mean two things. The first is the usual, where you try to pull Legacy of Kain level of shenanigans. The other is like in Interstellar, where travelling through space has the side effect of jumping around in relative time.

In the context of storytelling, both provide so much to work woth that unless the story specifically revolves around them they come across as wonky and stupid (Warlords of Draenor). As a logical consequence, RPGs, especially PCRPGs, just handwave it away as an unnecessary element in the story they want to tell.

And finally there's the problem of making a game too cranially demanding, one of the great demons of modern marketing departments of gaming companies, which is rooted in the demographic tragedy of a lot more dumbasses being alive compared to smart people.

Yes, now we just need a whole bunch of matter with negative mass.

Interstellar's time travel was more as a result of fucking around near black holes, where time gets generally wonky. The FTL travel happened through a wormhole, which isn't actually FTL travel since you're not accelerating to faster than light speeds, you're traveling at a normal speed through a spacetime shortcut.

There's also mass effect's method of doing something technobabbly with Higgs bosons to keep vessel mass down throughout acceleration so it never quite gets to the point where they need infinite energy to keep going faster (though this was mostly elaborated on in the first game, where whatshisname the head writer still gave a shit about the appearance of harder science fiction).

BODY

Which is how time dilation actually works from all known observation of the phenomenon.

>If you can go from point a to point b faster than light, by any method at all, then you will arrive before you left according to some reference frames.
100% right, nothing to debate here.
>What's more, if you were to then turn around and go back to point a faster than light, you can quite easily arrive before you left in ALL reference frames, including your own. Shake hands with yourself and everything.
100% wrong. You still left. You're gone. The time cone isn't "you", as said, it's the information of you. It's the light projected from you and the ripple of causality you send through the universe. It's not you, you might overtake your light and see yourself further back in time, but it's not you, it's your light echo.
That gif you posted was confusing and wrong. The Y axis there is time, inertial frames don't change absolute time progression, they change how different objects interact with each other. So yes, if you assume you can travel through time, you can travel through time!

The big issue here is that objective time doesn't exist, but objective time intervals do exist.
To demonstrate. You leave your planet and fly towards alpha centauri faster than light (let's assume hyperspace style FTL so we can avoid in-ship time dilation and imaginary time fuckery). In doing so, X absolute time passes in every reference frame, as no frame is travelling backwards, but as you reach Alpha Centauri you overtake your own light cone, which is travelling at c, so when you get to alpha centauri it looks like you've arrived before you left as the light of you leaving arrives after you get there.
What you have to remember though, is that nowhere here has dilation occurred. This is not Einsteinean relativity, this is Galilean relativity taken to an extreme. You have not actually gone backwards in time objectively, there is just the illusion of it due to light's limited speed.
Refer to the maths in if you were thinking of v>c, no hyperspace

Not to rain on Mass Effect's technobabble parade, their version of FTL can't work, since the Lorentz term doesn't give a flying fuck whether the starship's mass is one gram or ten million tonnes, it's still going to be infinite when you would hit the speed of light, and it's really fucking hard to race with infinity.

>I'm an uneducated pleb that never read any other sci-fi than space opera
Thanks for informing us all

Only if you insist that a certain wild extrapolation of the currently known laws of physics is infallibly, invariably true.

Alternatively, you could assume that time dilation is not so absolute and that there are ways of preventing, avoiding, or mitigating the exponential increase in mass that seems to occur as one approaches light speed. For example, see every setting that features FTL travel.

Thays a really shitty Peebee render on the right, holy fuck

The guy who wrote that article was wrong right? It seemed so confused and contrived it couldn't work like that.

>X absolute time passes in every reference frame

wew fucking lad, stop right there, there's no such thing as absolute time, the passage of time is nonlinear in ways that we do not understand beyond the speed of light.

your mistake is in this sentence:

>let's assume hyperspace style FTL so we can avoid in-ship time dilation and imaginary time fuckery

This is handwaving the problem that OP and that other user are talking about and completely misses the point. You're kinda sorta half correct in terms of what you yourself are arguing about but you're arguing it with no-one because you've completely skipped over the 99% of the conversation the rest of us are talking about.

For the same reason, you don't stop and think about thermodynamics and energy output in these games. It either only adds very little to the game or adds very little AND breaks the fuck out of the setting.

Plus if there's an option to travel back in time any way you want, there's no urgency. It's not something you would like to have if your games should have anything resembling dramatic tension.

The idiot who said time is imaginary is dumb. That mathematical relation does not model anything when v>c. It's completely moronic.

The author made a fundamental mistake in his work with his spacetime diagrams, conflating the ideas of using inertial frames as points of reference to study how objects interact with each other at a single point in time, and with superpositioning motion onto these inertial frames without due consideration of the effect this motion would have on the inertial frames themselves (because, you know, its inertia has changed?)
Just read this section. physicsguy.com/ftl/html/FTL_part4.html#sec:ftleqvofc
No maths, no equations, no adjusting time-postion diagrams to reflect changes in velocity (which is kind of important at relativistic speeds), just "Look! I drew a line on a graph that makes no sense!"
He's just fucking around with a graph and getting wrong answers and calling them paradoxes. It's the sort of shit you'd expect off a fifth year who just learned how vectors work, not knowing where to put them on the page or how they interact.
And then at the end he, again, misunderstands that light cones aren't a fundamental force of spacetime, they're cones of light, which is emitted from objects that exist independently. Just because something looks like it's in your past or future doesn't mean it actually is.

You're talking specifically about exceeding the speed of light, not all FTL.

Why do you think jump drives, gates, and other handwaved teleportation is used? Or warp drives that compress space instead of outright exceeding lightspeed?

I would say to stay in school, but you just need to read more.
Ex-fucking-actly.

>light cones aren't a fundamental force of spacetime, they're cones of light

holy shit kill yourself

the term "light cone" originally referred to this concept of the path of a photon through spacetime, however since roughly around 100 fucking years ago it's commonly understood to refer to the GR extrapolation of said concept which implies that all of causality itself can be described in such a cone.

Shit what's the chick on the left from? Can't place it.

Then that is good, it was (relatively) realistic.

It's Pris from Bladerunner movie.

Fucking leave, you fucking pleb

Isn't it Pris?

Yep, thanks.
Sorry I didn't recognize your waifu from a movie I haven't seen in ten years, faggot.

>All of casuality itself
And what exactly would that be ? The entire universe is in a light cone? :)

I drew this up for you

In other words, things affect other things.

Any idiot knows that drawing. I am asking you if you really think this murderer is stopped.

>you just took a shortcut
We don't know if this is actually possible or if it even makes sense. This idea is built on our current ignorance of physics. I call it "warp of the gaps".

in other words your supposition that "light cones are cones of light" is retarded.

Once again this does nothing to prove that the guy stopping the murderer sees anything but light. It was never proved that he travelled back in time.

...

it's impossible to "prove" you retard, it's a theoretical extrapolation of a set of rules not designed to work in the circumstances we're subjecting them to.

I'm assuming that you just read up on the wikipedia page for this and think you're hot shit, I'd hate to imagine someone actually taught you this somewhere.

Wasn't there a problem with the alcubierre drive in that it collected some sort of energy going forward and wherever it stopped would annihilate the solar system in front of you?

Actually, no.
Whatever garbage this guy tries to justify the result is that you have to travel back in time. The past light cone as you put it, are events which already influenced the murderer to leave. The savior was not in this cone, so he never influenced the event. If he travelled back in time, the event he influences cannot be the event of the murder, unless he caused it.

It's a nonesensical extrapolation. When things affect other things, they leave evidence of their effects. When someone finds that evidence, they can interpret it and figure out what happened in the past. This is deductive reasoning. It's not time travel, and neither is FTL speed.

sounds fun

1. Person A murders Person B
2. Person C witnesses this and sends an FTL message to Person D who lives in another solar system.
3. Their message to D says "when you get this send me a message back telling me to warn B about A"
4. Since the message is FTL it arrives before C sent it.
5. Person D sends his own FTL message back to C, again, since the message is FTL it arrives before D sent it.
6. C has now received a message from himself in the future that says "warn B about A"
7. C warns B about A
8. The Murder does not happen.

this is why light cones are important you fucking moron

Wrong

kill yourself

Because it doesn't make any fucking sense, that's why. Most readers don't have a bachelors in physics.

And you won't need eyes to see.

The Federation even had an entire department dedicated to dealing with time travel.

>Whatever garbage this guy tries to justify the result
You mean MATHS
MATHS is garbage then is it?
Think of it this way. The past light cone are events travelling at equal to or less than the speed of light that influenced the murder. Light cones and causality cones are conflated because there's no known way of going FTL ATM, but that doesn't mean they are the same, it's fully possible for the causality cone to distort out of sync with the past light cone if FTl is involved and this doesn't break physics if you do the fucking maths instead of just looking at a single graph meant for something else.

If the destination is 1.1 light years away, and your average speed during that trip is 10% faster than light, won't you arrive at your destination in one year? And if so, won't you have to wait 0.1 years at your destination to observe yourself leaving your starting point?

>5. Person D sends his own FTL message back to C, again, since the message is FTL it arrives before D sent it.
That's circular reasoning. You're attempting to attack people who can tell the difference between "faster than light" and "literal time travel", but your explanation relies on the assertion that they are exactly the same. You are using light cones as a metaphor for the simple fundamental concept of causality, that concept isn't unclear to anyone else and doesn't disprove FTL travel; traveling faster than light would allow you to interact with the effects of an event that propagate at light speed, but that's not the same as interacting with the cause of an event.

Here is an alternative scenario.

1. Person A murders Person B.
2. Person C witnesses this and sends an FTL message to Person D who lives ten light years away.
3. Person D sends a response.
4. Sense the messages are FTL C receives D's response in less than twenty years.

Time travel would be necessary for the message to arrive at its destination faster than an instantaneous effect, which would propagate from point A to point B in literally zero time. However, light does not move instantaneously; it has a speed. Since the speed of light is finite, a hypothetical faster-than-light object would also move at a finite speed, and would arrive at its destination after it was sent but before any photons which were going in the same direction.

Here's another scenario

1. A person rolls a ball down a hill.
2. The person runs down the hill faster than the ball rolls.
3. The person catches the ball that he himself rolled.

This is essentially how FTL "time paradoxes" work. Cause an effect, outrun the effect, and the effect happens to you.

Aren't you leaving out relativity?

Lol you think I'm disproving math? I am saying his arguments are void. He made some simple elementary calculations using formulas which do not represent anything physical, then argued that the results can be put back into reality and shows lol it doesn't work if I interpret it like this. Big fucking whoop, he has shown nothing of value.

user, MATHS isn't almighty. 2+2=5 is maths, but garbage, so are these equations that lead to 1+1=3.

In what way?