FTL travel means causality stops working properly, or in other

Come on Anon, I know you've heard of handwaving before.

>>52581424
SOMEBODY

>>52581424
Because of the Damn, Dirty Apes!

>>52581424
No, no no. If it were physically possible to accelerate to the speed of light, which it isn't, it's a logical conclusion from the math that measures relativity that time would move backwards for the object moving faster than light but only from specific points of view, which is impossible. Despite real world relativistic effects nothing resembling time travel in any direction, let alone backwards, has ever been observed, time dilation has never equaled time travel and never will.

That aside, in most fiction the form of FTL proposed makes relativity go away, not causality. So retardedly blaring "FTL, RELATIVITY, CAUSALITY, PICK ANY TWO" at fictions that very clearly stated their choice is just obnoxious.

>>52581424
Because it would make for much more confusing stories.

>>52581424
Some settings use the hyperspace option, in that they never actually move faster than light but access a separate dimension where the rules don't quite apply the same way they do here. Amusingly, while these manage to have an excuse for not having time shenangans they are more likely to include them.

>>52581424
Because that's not actually how relativity works. It's not time travel.

>>52581424
The fact that current time travel has only been asigned to small packets of fucksmol particles? Or the idea that it would require so much energy that you'd need to find pockets where spess gets naturally so riled up just for a one way trip?

IDK, I'm piss basic at this, maybe you want to ask on /sci/ and if they think you're not trolling them you might get probed in the right way direction.

There was this roguelike vidya in which you manhandle a ship towards some meaningful corner of the galaxy in hopes to find answers as to what killed earth and why. I believe the name was Out there or something. There are some black holes that you can use to travel by coating your current crumbling medium of locomotion in the equivalent of unobtanium nightmare fuel (implied to be harvesteable only by killing stars capable of having living planets orbiting them, and yes destroying those is an option too), and it is only at the last jump that time travel is also included.

>>52581475

A whole lot just enter hyperspace, where they enter a dimension which allows them to travel at higher speeds or is simply "smaller" geometrically so moving at relativistic speeds gets you further.

Also portals. Open one at your end, open another around where you want to end up, and move through it, probably through an aforementioned hyperspace dimension. You've never actually travelled faster than light, you just took a shortcut.

File: futurama-professor-farnsworth-large_transqvzuuqpflyliwib6ntmjwfsvwez_ven7c6bhu2jjnt8.jpg (53KB, 620x387px) Image search: [Google]

53KB, 620x387px

>>52581424
>he doesn't move the universe around him

>>52581547
Those are my favorite.

Go read any modern physics textbook, OP.

>>52581436
ONCE MODELED ME

>>52581547
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

>>52581424
>>52581547
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.

File: ftl time travel.gif (114KB, 323x402px) Image search: [Google]

114KB, 323x402px

>all these people who think OP's wrong

http://www.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.

>>52581424
Because the easier answer is that relativity stops working.

>>52583229
We need exotic matter, a theoretical type of material, to make it work. There's no strong indication such a material even exists.

>>52583250
This is a visual effect anon, just because you see them leaving before they arrived doesn't mean they actually are.

File: warp_cone_by_thefirstfleet-dac2004.jpg (5MB, 4096x2304px) Image search: [Google]

5MB, 4096x2304px

>>52583229
Ah yes the warp drive an old classic

>>52583250
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?

>>52583334
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.

>>52583359
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.

>>52583334
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.

>>52583250
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.

>>52583334

>visual effect

Nope. I would imagine you're confused by the term "light cone."
Read the article, anon. 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.

>>52583359

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.

>>52583492

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.

>>52583541
>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.

>>52581424
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.

>>52581424
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.

>>52581431
/thread

>>52581424

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.

>>52583250
Travel by wormhole is STL in all reference frames. It only appears FTL if you don't understand the shape of local space-time.

>>52581424
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).

>>52581424
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.

>>52583193
Depends on the setting of whatever mcguffin negates this effect.

>>52581424
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.

>>52581424
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.

>>52583930
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.

>>52584003
In Futurama Farnsworth say they just increased the speed of light. That avoids all the problems.

>>52583701
A ship using space warping would be at rest. Clocks would show minimal drift compared to planetary clocks

File: what the arthur.png (337KB, 439x480px) Image search: [Google]

337KB, 439x480px

>>52583250
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.

>>52583022
AFTER THE BLUNTEST TOOL IN THE SHED

>>52584146
I don't think he knows what he is taking about to be honest

>>52583480
But there is. See below.

>>52583541
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.

>>52583229
>>52583324
Anon no, it wasn't solved, stop reading shitty pop-sci news site.

>>52584146
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

>>52584146
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?

>>52581424
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.

>>52583954
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.

>>52583229
Yes, now we just need a whole bunch of matter with negative mass.

>>52584411
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).

File: SOME.jpg (34KB, 500x308px) Image search: [Google]

34KB, 500x308px

BODY

>>52584385
Which is how time dilation actually works from all known observation of the phenomenon.

>>52583250
>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 >>52583541 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 >>52584372 if you were thinking of v>c, no hyperspace

>>52584450
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.

>>52581424
>I'm an uneducated pleb that never read any other sci-fi than space opera
Thanks for informing us all

>>52581424
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.

>>52581424
Thays a really shitty Peebee render on the right, holy fuck

>>52584498
The guy who wrote that article was wrong right? It seemed so confused and contrived it couldn't work like that.

>>52584498
>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 anon 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.

>>52581424
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.

>>52584643
The idiot who said time is imaginary is dumb. That mathematical relation does not model anything when v>c. It's completely moronic.

>>52584583
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. http://www.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.

>>52581424
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.
>>52581547
Ex-fucking-actly.

>>52584665
>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.

>>52581424
Shit what's the chick on the left from? Can't place it.

>>52584476
Then that is good, it was (relatively) realistic.

>>52584693

It's Pris from Bladerunner movie.

>>52584693
Fucking leave, you fucking pleb

>>52584693
Isn't it Pris?

>>52584700
>>52584714
Yep, thanks.
>>52584707
Sorry I didn't recognize your waifu from a movie I haven't seen in ten years, faggot.

>>52584681
>All of casuality itself
And what exactly would that be ? The entire universe is in a light cone? :)

File: causality.png (24KB, 1152x648px) Image search: [Google]

24KB, 1152x648px

>>52584728

I drew this up for you

>>52584749
In other words, things affect other things.

>>52584749
Any idiot knows that drawing. I am asking you if you really think this murderer is stopped.

>>52581547
>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".

>>52584759
in other words your supposition that "light cones are cones of light" is retarded.

>>52584773
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.

File: FTL in a nutshell no fun allowed.jpg (173KB, 922x617px) Image search: [Google]

173KB, 922x617px

>>52584661

>>52584792
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?

>>52584799
>>52584807
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.

>>52584807
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.

>>52584815
sounds fun

>>52584848

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

>>52584866
Wrong

>>52584871
kill yourself

>>52581424
Because it doesn't make any fucking sense, that's why. Most readers don't have a bachelors in physics.

File: event_horizon_ver1.jpg (62KB, 501x755px) Image search: [Google]

62KB, 501x755px

>>52583193
And you won't need eyes to see.

File: Dulmur_and_Lucsly.jpg (18KB, 524x411px) Image search: [Google]

18KB, 524x411px

>>52583945
The Federation even had an entire department dedicated to dealing with time travel.

>>52584841
>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?

>>52584866
>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.

>>52584953

Aren't you leaving out relativity?

>>52584912
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.

>>52584912
Anon, MATHS isn't almighty. 2+2=5 is maths, but garbage, so are these equations that lead to 1+1=3.

>>52584976
In what way?

File: miller-jpg.jpg (185KB, 1600x682px) Image search: [Google]

185KB, 1600x682px

>>52584886
Fuck that ship.

>>52584815
Yes. Also needing matter with a negative energy density.

>>52581475
It's not impossible, you just need infinite energy lol

>>52584953
This nigger knows his shit. If nowhere in the maths do you see "MESSAGE GOES BACK IN TIME HERE" or a negative rate of travel in time, time travel has not occurred, causality remains intact. Sure, there might be one possible frame of reference where it APPEARS like the effect has happened before the cause, due to a light-cone/causality-cone dissonance, but this will only happen to an outside observer. It looks weird and it looks like causality has been broken, but events have still happened in a linear order, regardless of whether you saw them that way or not.

>>52584694
Yeah, however their reason for making it realistic was central to the themes of the story. Still was neat.

>>52581424
Because time travel is one of the Guaranteed ways to fuck up a setting's plot

>>52584927
mail yourself a letter to an out of state address, then drive there faster than the post office delivers it, you will probably have to wait for it to arrive.

if you move faster than the delivery method of visual information (light), you still didn't travel backwards through time. you did not arrive before you left, you arrived before anyone at the destination saw you leave.

>>52583250
> faster than light travel by definition exceeds the limits of relativity
> people still pretending that relative points of reference matter in such a circumstance

This is the equivalent of ancient astronomers assuming that the space between planets had to be filled with some kind of gas, because there was air on Earth. Sometimes when you go beyond the bounded system you are in, the rules change.

The fact of the matter is we don't know what the effects of FTL will be, because we don't have any hard science yet (no, not even the A drive) that we can model for it. Pretending like you know the answer to it is as asinine as claiming you know the answer to how the universe would work if exactly 10 randomly selected numbers were now colors instead, and you had to represent that in the math.

>>52583409
>Visual effects could still cause some causality issues, though.
This was donein a movie once and there were no causality issues, in Paycheck.
They invented a telescope that viewed light bend around some spacywacy crap so they could view the future.
No causality problems though, you see your future, take action to change it, then view a different one.
All older views are just past viewed light patterns generated by a warping spatial body, no causality to screw up.

Ben Affleck's character trolls the GM by using it, then breaking it so nobody else can see what he's gonna do and change it after he's done, putting himself in a no-way-to-lose scenario.
The GM gets pissed, wipes his memories, erasing his love interest, and throws a bunch of crap at him, but the player just pulls out the I-would-have-seen-this-and-planned-for-it card, sporting the smuggest of smug mugs.

>>52585559
Wait, what? I'm pretty sure that's not how that works. The light hasn't bounced off the future objects to produce the image you're looking for, so the image isn't there for you to see. You could see past light, but not future light.

>>52585004
so it's impossible, because infinite energy is impossible
no matter how inconceivably large the universe is, no matter how inconceivably much energy is, it is still finite

>>52584886
This movie was so bad, holy fuck.
There are so many scary things about the unending emptiness of cosmos, but no, they had to go through literal hell.
It would be a fun Doctor Who story, but it sucks as a sci-fi horror.

>>52585675
True.
I guess the light was bent around so far upon itself that it had a negative speed value.
Spacy. Wacy.

>>52585818
Not a WH40K fan, I take it?

>>52581424
Valerian and The Chronicles of Cyann explicitly aknowledge that and work it into their stories.

You're welcome.

>>52584866
that understanding requires that the FTL technique actually be something other than simply being 'faster than light'
if light takes one year to travel somewhere, and your message arrives at that somewhere in one day, that doesn't mean it's time travelled 364 days, it means that it's ordinary travelled for 1 day.
th message has 'merely' travelled FTL and hasn't gone into the past or anything retarded like that. it's gone from point A to point B at a very fast speed.

like, if my mate travels across town at 20km/h in the shittiest car ever, and if i travel across town at 200km/h it doesn't mean i'm time travelling or arrive before i leave just because i'm going 10x faster than him, it just means i'd get fucking arrested.
it's like that but with light being the shitty banger that only goes at c

so what you get is actually
>person A murders person B
>C immediately sends an FTL message to D about it because he's a faggot who only tweets about witnessing murders
>message is received after arbitrary delay, let's say 1 minute because it is very far away, but not that far
>message is sent back to C, again takes 1 minute, maybe takes like 3 or 4 minutes to type up
>C has now received a response message from D, 5 minutes after the incident
>no time travel actually occurs
>but we do have a mail system that can deliver to distant systems in the time it takes to boil a cuppa

>>52584866
Ok, explain this to me like I'm an idiot.

Say I've got a FTL message device that sends messages at twice the speed of light, and my buddy standing on the surface of the sun also has a device like this. It takes light about 8 minutes to go from the sun to earth, so my twice-as-fast-as-light device would only take 4. I'm unclear how time travel has occurred here, it's still takes me 8 minutes to receive a reply from my buddy.

>>52585969
>Ok, explain this to me like I'm an idiot.
>my buddy standing on the surface of the sun
You *are* an idiot.

>I'm unclear how time travel has occurred here
But you're still smarter than that anon.

>>52586025
The sun is just a useful frame of reference because it's a commonly known light-distance, you fucking autist.

>>52585833
It's not that, I just felt betrayed by the hard sci-fi decorations, the ships were so great and the initial premise looked like it's gonna be a hardish sci-fi.
WH40k doesn't pretend to be something it is not.

>>52581424

You're thinking 4-dimensionally again OP

File: ae283c[1].gif (8KB, 300x236px) Image search: [Google]

8KB, 300x236px

When you get closer to the speed of light, your reference point of time will be different from everyone elses.

At the speed of light, no time passes.

Past the speed of light, you reach normal time frames again, but if you are even faster than that, your reference frame slows down even more. If you hit a certain speed several times the speed of light, your time frame reference will be negative and you will be experiencing time backwards.

Bear in mind exceeding the speed of light already breaks the laws of physics.

>>52584987

WE HAF MATH TOO, BUT WE CALL DEM MAFFS BONG CHEERIO

>>52586051
Hey, a guy claims the sun has a surface, I call the guy an idiot.

>>52585957
The situation you're describing indeed isn't time travel. The problem is it also isn't the issue.

The issue is that if you can travel FTL (and if Special Relativity holds), then potentially you can arrive before you've left. Not a signal, but physically you. Not before the image of you leaving reaches some point, but before you actually leave. And you can arrive not somewhere far away, but right to your starting point.

>>52586254
Explain how

>>52586025
From what I understand, FTL works like so:
>You are in [Your Position].
>Your friend is in [Their Position], precisely 1 light year away.
>Light takes 1 year to travel between the two locations.
>If something is slower than light, it will take more than one year to travel between the two.
>If something is faster than light, it will take less than 1 year to reach its destination
>(This is impossible under classic Relativistic physics, so it can be assumed we have subverted those)
>If you travel faster than light to a location, your relativistic causality cones intersect... Through arriving before your light does.
>(Note that your causality cones widen to encapsulate ANY possible effect, so this is an error caused by purposefully excluding FTL travel from your causality cones)
>If you immediately return at faster than light, your round trip will take less than 2 years.
>Again, you could watch yourself leave from [Their Position], but, no matter how fast you go, the light from leaving [Your Position] will have advanced some distance, making it impossible for outside observers to watch yourself touch yourself without optical illusions.

>>52586254
That makes no sense.

If it takes light an hour to travel from point A to point B, and you can go twice the speed of light, it'll still take you a half-hour to get to point B. If you immediately turn around and go back to point A, you've still spent an hour traveling.

At no point does time travel occur. At best you could get some funny-looking visual effects where you can wave at yourself by outrunning the light, but it's just that; a visual effect.

>>52586089
Right, any object that approaches the speed of light also gains an altered timeframe and increases in mass at an exponential rate.

So, to have practical faster-than-light travel, one need also find a way to counteract time dilation.

On another note, there's evidence that gravity also moves at the speed of light; whenever an object is moved, the resulting changes to its gravitational field propagate at light speed. So there's likely to be some sort of unifying principle going on there.

>>52586254
why don't you explain it then
hell, that challenge has already been issued:
>>52584146

>>52586323
>making it impossible for outside observers to watch yourself touch yourself
Well yeah, they need to pay for the premium package for that.

>>52584997
He had one of the best lines in history of horror movies
https://www.youtube.com/watch?v=4sFd8aWT7Io

>>52584724
>Waifu
>In Blade Runner
It's a husbando movie, you pleb

>>52586334
>That makes no sense.
As I understand >>52586254 , the idea would be something like "As you speed increases, the time until you reach your destination decreases, so if your speed is high enough, the time decreases into the negatives, hence you arrive before you left.
And if that destination is five feet away, you position remains moreorless the same.

But this is all Cult of Cheese and Worms style thinking that leads to ideas like "Cold is negative heat", which are fundamentally impossible.

Someone could probably show the math on why my explanation couldn't happen.
It's been too long for me.
I just agreed with Einstein back then anyway.

>>52581424

Well, let's think about it logically.

>a solar system is 4 light years away
>with FTL travel, we can get there in 1 year
>we have not travelled back in time 3 years because we beat light there
>we are simply really far away and time is no different

>>52586334
Except that's not correct. Let's say I'm in a spaceship orbiting Earth, and I decide I want to go and check out a distant star that, in Earth's frame of reference, is 8.66 light years away (number chosen for convenience).

To do this, I will travel towards the star at 0.866 c (c=the speed of light). Now, to a guy on Earth, it will take me ten years to get to the Star (which is simple, 8.66 light-years/0.866c = 10 years).

However, in the rocket, I will not have spent 10 years on my journey. In my frame of reference, traveling at 0.866c, the distance between me and the star is contracted to half the distance it is in Earth's inertial frame (thanks to the convenient number I chose), so to me, the trip takes only 5 years (4.33 light-years/0.866c=5 years).

So while on Earth the journey takes ten years, the people on the rocket have only spent five years traveling.

>>52586074
>the hard sci-fi decorations, the ships were so great and the initial premise looked like it's gonna be a hardish sci-fi.
And From Dusk Till Dawn seemed like a crime flick at the start.
I, for one, appreciate seeing genres take place in novel setting or within the trappings of another genre.
Signs was another example, and people felt betrayed then too.
I can see it, but I enjoy the ride, even if I wouldn't go again.

>>52586281
>>52586334
>>52586358

The link in >>52583250 explains it very well, but it's wordy as hell, and you have to also read part 1. I'll try to make it brief by omitting the derivations and math.

If the Special Relativity holds, there can exist a frame of reference in which two events can happen in the different order for you than for an observer in that frame. I'm not talking about signals from these events reaching you, but about when they actually happen. The Ladder Paradox (https://en.wikipedia.org/wiki/Ladder_paradox) illustrates this.

As long as nothing can travel faster than light though, this is irrelevant, because such events can only be situated outside your light cone. You can't influence them or be influenced by them.

Now imagine event 1 is the opening of a wormhole from frame A to frame B. Event 2 is is the opening of a wormhole from frame B to frame A. And frame B is moving fast enough relative to frame A that these two events happen in the reverse order in B relative to A. Let's say event 1 happens first in B and second in A. You can jump into the wormhole, arrive in B, wait until event 2 and jump back to A, where this event 2 occured before event 1. Now you can hang around the place and high-five yourself once event 1 occurs.

>>52586497
I still think it's just wasted potential. There was no explanation. No setup. Just a series of jump scares that ended with "lol hell".

>>52586522
why does the ladder paradox apply at all to time, though? what about this makes it so that you ever travel back in time?
also your example still requires time travel to exist before the time travel actually starts. you can't say 'this event happens here at exactly this time but also over here at this other time'

like you waffle on about frames of reference but ultimately those frames are just part of something bigger, you know - the universe, and your insistence on 'when it actually happens' is ironic because you keep trying to distort when an event happens
you literally have to say that an event happens in a completely different order to the way it actually happened in order for this to work.

>>52586495
yes, but teleporting onto the rocket at any point during that 10 year trip will put you at the equivalent point during the trip in 'their time', just as teleporting off would
so travel 2 years and teleport off, you'll be at the 4-year mark relative to earth. if you were to wait 4 years relative to earth instead and then teleport on, you'd be at the 2 year mark relative to them.

>>52586597
>There was no explanation. No setup. Just a series of jump scares
Typical of certain sub-genres of supernatural horror.
Some horrors are diminished by exposition.

>>52586597
>Horror
>Explaination
Pick one.

I mean it's not like I'm going to defend this movie, as it was so-so and is mostly remembered for being the only non-Alien horror flick set in space that doesn't outright blow, but come on!
Not to mention there is enough explaination provided in the story already, especially in director's cut

>>52586694
>you can't say 'this event happens here at exactly this time but also over here at this other time'
I totally can. It's called "relativity of simultaneity" (https://en.wikipedia.org/wiki/Relativity_of_simultaneity), and it stems directly from the axioms of special relativity - abscence of a preferred frame of reference and constant speed of light in all frames.

>you literally have to say that an event happens in a completely different order to the way it actually happened in order for this to work.
It _actually_ happened in one order in one frame, and also _actually_ happened in the reverse order in another frame. Because there's no preferred frame, you can't say one frame was "more actual".
It's hard to visualise, but so are most things about relativity.

File: 1479260603712.jpg (188KB, 1260x1600px) Image search: [Google]

188KB, 1260x1600px

>>52581424

>>52584886
>watch Passengers in cinema when it comes out
>it's about people stuck on a slower than light ship
>movie is pretty bad and gets worse as it goes on
>suddenly Laurence Fishburne pops up as ship officer
>spend the entire rest of the movie imagining how much better it would be if it just turned into a horror movie about hell on a spaceship
And now I want Event Horizon II: Relativistic Boogaloo, in which would be about people stuck on a century-long journey with demons from hell.

>>52584169
I WAS LOOKING HELLA DUMB

>>52587113
>SOMEBODY
>STOP ME

File: space-time.png (31KB, 800x800px) Image search: [Google]

31KB, 800x800px

The thing is that speed of light is essentially the speed at which reality propagates. If you think of "things that have happened" as a wave (in the loosest sense of the term) that emanate out from events it begins to make sense. Light doesn't so much travel from place to place (which is why you can't trap photons in a box) as it exists (as a probabilistic spectrum of possibilities as to when it is at any given point) along given paths and that existence propagates at a certain rate, the speed of light.

Think of it this way. Where an object is in space is a function of its past locations and translated by its velocity. When an object is in time (at what point of its existence it currently sits) is a function of its past events translated by its velocity. Pic related isn't anything mathematically sound, there's a curve to that line but I'm too lazy to draw it, but the point is that all of existence exists on that red line (up to where it would meet the axes). Going beyond the axes would be the equivalent of going faster than the speed of light or slower than "full-stop". Going faster than light would mean that time becomes negative, which we commonly understand as "going backwards in time" (though without a way to experiment with that it's difficult to say that's actually how it would work in practice) and going slower than stopped would cause space to become negative, which I don't even know how that would work and it makes my head hurt thinking about it.

Either way, from a realistic standpoint, this is why going faster than light or slower than stopped are equally nonsensical. Fiction handwaves this though because we like stories about people visiting faraway planets in their lifetimes and we're willing to simply alter our understanding of spacetime so that it's really more like the planets are all just really close together. Space is big. Really big. You won't believe just how vastly, hugely, mind-bogglingly big it is. So big, it's not fun.

>>52583623

Wow, this thread blew up while I was asleep.

>They shift the axi back to reference frame 1 to "show" that the ship has time travelled. That's not how it works.

>to "show" that the ship has time traveled
>That's not how it works

You're right that that's now how it works, because you don't understand what it's showing. Read the article already.

>>52583904

But if one end of the wormhole moves it will experience time slower than the other end, and then if you enter the first end, you'll come out the other end before you went in. Wormholes explicitly permit time travel.

>>52584174
>But jumping doesn't mean that you have to change frame.

No, it doesn't. That's exactly the handwave I mentioned in the post you're responding to. It hides the problem, but does not fix it -- you've jumped through a bunch of hoops to get both ends stopped relative to each other, but you still violated causality, just not where you happen to be.


>>52585301

This is the direct effect of the mathematical equations governing relativity. The closer you get to light speed, the slower you experience time. At light speed this reaches 0, and beyond that it must therefore enter negative numbers. This is all experimentally verified, and mathematically sound.
If you've got math that says different, or experiments that show time dilation doesn't work that way, go ahead, but otherwise, you're no better than the ancient astonomers you're citing, just taking a wild guess based on jack squat.

Provided nothing gets anywhere faster than light, causality is maintained despite the fact that there is no definable "now" any more than there's a definable "stopped." Every bit of observable data we've collected in the history of science agrees that causes precede effects and no information ever arrives anywhere faster than light.
Maybe it's all a sham, but I wouldn't get my hopes up.

>>52586462

You did go back 3 years. There's no cosmic clock that says what the "real" time is. It's weird.

>>52586522

Thank you, I'm glad somebody read the article.

>>52587358

Pretty good, anon.

>>52581424
I fucking hate asari

>>52586705
I would be fine with goddamn Cthulhu, some ancient, incomprehensible entity from beyond, I don't know, whatever. Fucking void staring back.
But it had to be hell.

>>52588978
It was 97. The lovecraft revival hadn't happened yet so hell was probably the easiest/safest-for-execs way to telegraph 'really bad place' to the audience.

I get what you mean though. Its lame. A lot of scifi in the 90s was scrambling for some sort of enemy that wasn't commies.

File: 7e724d8f-eb04-4ce2-89ef-5b7235e402ad.jpg (10KB, 515x273px) Image search: [Google]

10KB, 515x273px

>>52588503
>and beyond that it must therefore enter negative numbers

And here's where we discover that you don't have a fucking clue how the math involved works.

No matter how big a value for v you plug in here, t' will never be negative. Go on, try it!

File: time_dilation.gif (4KB, 403x284px) Image search: [Google]

4KB, 403x284px

>>52589165
And your fucking up is apparently contagious.

>>52587358
>So big, it's not fun

And get bigger all the time, and faster.

The universe is a bit of a shit show, really.

>make a wormhole with both ends near each other
>shoot one end of the wormhole off at some high % of c towards your intended destination that is say, 10 LY away
>wormhole takes just over 10 years to get to its destination where it is somehow stopped
>but because it was going so fast it experienced time dilation so the moving end experienced less than 10 years to get there

>have a person at each end of the wormhole before you send one end off
>they communicate through said wormhole with no appreciable delay, no matter the distance. they can also see through the wormhole as if it had no length.
>travelling person should take less than 10 years to reach destination (time dilation)
>stationary person should see more than 10 years to reach destination (wormhole end travels just under light speed)

>travelling person from stationary persons perspective goes in slight slow motion (to stretch the <10 years to >10 years)
>stationary person from travelling persons perspective speeds up (to squash the >10 years to <10 years)

>if this didn't happen then travelling person could send a message back saying he had arrived before the stationary person saw that it had happened
>and the stationary person could travel through the wormhole himself before he saw it arrive and somehow end up at the destination

Relativity is fun

>>52590015
If the perception of time didn't change, when the travelling wormhole and person stops at their destination, if the travelling person goes through the wormhole he would be able to look back through it and see himself (since from the stationary end it hasn't arrived yet). Then he would be able to go through the wormhole the other way and meet himself before he arrived, creating time travel.

>>52586406
It's good to see a character in a horror movie actually decide to do the smart thing.

It's even better when it's combined with the scene that immediately follows it:
http://www.dailymotion.com/video/x2nugs3

>>52588503
>If one end of the wormholes moves..

Wormholes don't have ends. It's a singular point of connection.

>>52586495
This is time travel in exactly the same way you are currently time traveling.

>>52590015
>>52590298

Let's say you are at Earth and standing 3 feet from a wormhole connected to Tau Ceti.

How far are you from Tau Ceti? 12 light years?

No, 3 feet. Most light might go the long way around, but you and tau ceti are 3 feet apart.

>>52591130
That's boring. Moving wormholes with high levels of time dilation is more interesting.

It's like when you have two spaceships moving directly towards each other that are each going at 0.99999c and the closing speed is just a little bit over that.

Thus only super-advanced AI, posthumans, and transhumans can rule an atemporal space empire.

>>52591592

>you struggle to deal with the logistics of FTL temporality.
> yfw when the only large scale alien empire you can find flawlessly deals with the problem becausevtheir perception of time is always atemporal anyway.
> even your best computers are worse at predicting what they can recognize naturally

HFYfags cant handle this post.

Although what OP says it's true you have plenty of ways to avoid "proper" FTL travel

>Open some kind of portal from point A to point B with lenght L
>Create some distorsion in the fabric of space itself that travels in the form of a wave and ride the shit out of it. Relativity doesn't forbid space from "traveling" at speeds past c
>Other dimensions bullshit
>Relativity was wrong all along!

>>52590015
>>if this didn't happen then travelling person could send a message back saying he had arrived before the stationary person saw that it had happened
>>and the stationary person could travel through the wormhole himself before he saw it arrive and somehow end up at the destination
Well, yeah, because the light from the 10 LY destination has much farther to travel than the light going through the wormhole; naturally it'll take longer to see it arrive through your telescope than when it does actually arrive.

>>52592148
>when it does actually arrive

>implying privileged reference frames again

>>52591592
>no superhumans either

>>52591663
>bringing HFY into this for no reason
It's like you want to derail the thread, anon.

>>52581424
That implies that time exists as something more than a function of changes in the Universe.

No time as separate dimension - no time travel.

>>52592148

This. This is like saying its time travel to mail someone a package and drive to their house and back before it gets delivered.

>>52592157
But the stationary person can objectively measure the time it takes the traveling wormhole to reach its destination, that being slightly above 10 years, because they can see through the wormhole. This entire situation you've set up is nothing more than some light taking an exceedingly short route through space (wormhole) and some taking an exceedingly long route through space (actual space between origin and destination)

>>52592157

If all frames of reference are equal, how come you dont cease to exist when I close me eyes? From my frame of reference, you are not there.

Stop violating physics, you fucker.

>>52592211
>>52592230

>If Einstein is so smart, how come he's dead?

>>52592280
Nigga this is an entirely different situation to a ship achieving FTL velocity in a continuous path through space-time, you can meme all you want about relativistic fuckery then.

In this situation, though, you included wormholes. You literally joined to bits of spacetime together through some kind of space magic. The path an object would take through the wormhole is NOT the distance it would take from its origin to its destination if it had avoided the wormhole.

You're basically arguing that a ball that rolled one meter in one second actually rolled a hundred meters per second since you can define a path from its origin to its destination that is a hundred meters long, rather than the actual path it took.

>>52592148
Which is exactly why the perception of time by looking through the wormhole changes, because if it doesn't you get fucky things happening when you try to look through it.

>>52592503
But it doesn't. When you look through the wormhole, the traveling guy looks totally normal, and you do for him as well.
Light only has to go some trivially small distance.
He's stationary relative to you, because the wormhole is effectively the same point in space, and you're both stationary relative to it, and so you're both stationary to each other.
No time fuckery when you look through it, because you're fucking with the topology of spacetime rather than just going really, really fast.

>>52581547
>Wormhole Gates
My favorite type of FTL ever.

Just these huge fucking structures that interconnect to one another you fly a ship into to instantly get hundreds or thousands or more lightyears away.

>>52588503

>You did go back 3 years. There's no cosmic clock that says what the "real" time is. It's weird.

No, you didn't. If you travel to a star system 4 light years away but do it in 1 year, you will be there at year+1, not year-3. Everyone on Earth would be at year+1 when you arrive, and the planet you are on would be year+1. You won't get there before you've even set off.

Arguing about whether wormholes violate relativity is a bit like arguing that a wizard's fireball spell violates the laws of thermodynamics. You've already started with some form of magic, why are you then using that as a jumping off point to discuss the scientific ramifications of that?

>>52581424
Describe how taking that into account would make for a better story.

>>52594359
Magic is just sufficiently advanced tecnology.

because no one gives a shit

>>52583324
Not to mention a new type of magic material that can withstand temperatures 2 or 3 magnitudes hotter than the Sun.

>>52593955
It would be year+1 for everyone on Earth as you say, but for some observer moving very quickly in the opposite direction (no matter where they were) you would arrive before you left. Since their perspective is just as valid as yours or those on Earth, causality is violated. It's worth noting that you would experience some undefined time dilation (imaginary value) which is literally impossible to conceive - this is why there are no reference frames that move at or faster than the speed of light.

>>52594800
While I'm positive I don't completely understand the subject, creating a diagram or moving image to explain this concept doesn't seem impossible at all. Do you know of any visual representations of this?

File: leaving now.gif (3MB, 300x200px) Image search: [Google]

3MB, 300x200px

>>52594466
>Technology and science have done things that were once thought impossible
>Ergo, all things that are impossible are definitely possible with sufficient technological and scientific advancement
Anon, I... can't argue with that. You know what? You win. Good job. You've convinced me. This is definitely the most compelling argument I have ever seen. Congrats.

it breaks relativity OR causality, you mean. Most scifi things ignore relativity anyways, by means of a special privileged reference frame, because at small scales (ie the ones that most earth writers live and think in) you don't really have to deal with time shifts between reference frames and all. They impose causality by creating a universal clock, which is disallowed in relativistic theory.

>>52594881
Can't prove that something is impossible, anon. Physical truth is unknowable through neither empiricism nor rationality.

>>52594862
I might have been wrong about the direction of the other observer, but the main point holds. The image posted with >>52583250
is an animation of a Minkowski diagram (Google it for full explanation) which is useful for figuring this stuff out, although as an illustration tool they're a bit confusing. The way to figure this stuff out without the Minkowski diagram is to consider the different observers seeing light signals from the space ship as it moves, but this almost always ends up being more cumbersome and still kinda confusing.

>>52581475
>it's a logical conclusion from the math that measures relativity that time would move backwards for the object moving faster than light
The maths actually gives that time would become imaginary, meaning time and space swap places and temporal relationships become arbitrary.

File: MlHm0Zg.gif (979KB, 331x255px) Image search: [Google]

979KB, 331x255px

>>52594800
>for some observer moving very quickly in the opposite direction (no matter where they were) you would arrive before you left.
I can imagine how they would see you arrive and then see you leave, much like you hear a plane crash in front of you, then hear the sonic boom from it flying.
But that is sequence of perception.

>Since their perspective is just as valid as yours or those on Earth
Granted

>causality is violated
I still don't think so.
But that might be my take on the word "violated".
Observation of events is not the same as those events.
If we observe a star explode, then fly ftl to see the light from that star before it exploded, we have not violated anything.
We have moved from one valid perspective to another valid perspective.

Rewinding the tape doesn't violate causality.
But it does look like it.
If that's what you mean.

>>52595709
>If we observe a star explode, then fly ftl to see the light from that star before it exploded, we have not violated anything.
This tbqh, it's just information propagation.
I'm fairly sure that relativity and time dilation is actually a massive prank played on both unscientific rubes and the physics community by Einstein.

>>52595709
>If we observe a star explode, then fly ftl to see the light from that star before it exploded, we have not violated anything.
Imagine that instead of a star exploding you receive a radio signal from someone light years away. You then fly FTL to get there, before the signal is transmitted, and tell him not to transmit the signal. Then you fly FTL back to where you were before you received the signal, shake hands with yourself. Do you receive the signal?

This is why FTL makes no sense and what is meant by violating causality.

>>52595780
Except time dilation is experimentally confirmed. You can go do it yourself to prove it to yourself if need be.

https://en.wikipedia.org/wiki/Ives%E2%80%93Stilwell_experiment

>>52595839
>You then fly FTL to get there, before the signal is transmitted, and tell him not to transmit the signal.
But you don't fly there before the signal was transmitted.
If you're 10 LY away from where it was transmitted, and you fly FTL to where it was transmitted once you get it, 10 years have already passed.
There's no time travel involved, it's just space.

>>52595884
>10 years have already passed.
From when the signal was transmitted*

This is why I prefer fantasy

>>52595346
So something like this?

Two people, A and B, are at NASA. B goes off in a spaceship to orbit the Earth at relativistic speeds. To the observer on Earth, this trip will take 30 years, but because of relativity, B will see this trip as only taking 30 minutes. After the trip, B will land on a launchpad outside A's command room.

>A's perspective
Monitor and guide B's spaceship for 30 years, then walk outside and greet B, still roughly the same age as he was when he launched. If he were to contact B via radio or some shit, B's voice would come out extremely slowed down, so his 30 minutes of radio contact stretched out to 30 years of travel.

>B's perspective
Chill in a spaceship for 30 minutes. Maybe watch 30 minutes of Airplane! or something. Land on the launchpad, and walk outside to greet old-ass-nigga A in >current year+30. If he were to call A via radio or some shit, A's voice would come out super fucking fast, in order to fit 30 years of speaking into 30 minutes.

>cont.

What if we punch a hole into hell, fight off shit-tons of demons while getting to where we need to go, and then punch another hole out of hell.

>>52595971
>>52595346

But if we do the same scenario with a wormhole, shit gets weird. Now let's say that A has a wormhole in his command center, and B has the other end of the wormhole in his spaceship, and brings it with him as he orbits the Earth. Everything else is still the same from the previous example, but now B will exit via the wormhole when he lands, instead of the spaceship door.

>A's perspective
He can view B's trip without any delay in time or response and is probably watching Airplane! with him through the wormhole. 30 minutes into the trip, B exits and they both walk out onto the launchpad, where they can still see B orbiting the Earth at whatever-the-fuck velocity. Theoretically, A could remotely guide B's spaceship back down to Earth, where then B could walk out the door and go meet himself.

>B's perspective
He's still chilling in the spaceship, and still watching Airplane!, though A is watching with him via the wormhole. 30 minutes in, he starts to land on the launchpad. Looking out the shuttle windows, he can see Earth of 30 years from now, complete with old-nigga A greeting him. Yet if he looks through the wormhole, it's only been 30 minutes, and A is complaining that B is blocking the damn screen. If B drags A through the wormhole, A can go outside into the future, and greet himself as an old man.

Furthermore, either party could return to their normal time-frames by going back through the wormhole.

>>52595999
You time travel, but for entirely different reasons.

>>52587211
WITH MY PAINT AND MY BRUSH

>>52586074
>WH40k doesn't pretend to be something it is not.
It didn't used to anyway.

File: 028wdewa.jpg (164KB, 499x500px) Image search: [Google]

164KB, 499x500px

>>52584886
https://www.youtube.com/watch?v=DSAcLRD1J7Y

Writers and their fans want an ocean fantasy by a different name; not what space actually is. ~FTL~ is the magic they need to solve the problem, and since the readers want the ocean fantasy, as long as there is a thin excuse to handwave they don't care about realism.

Ofc, in a "realistic" setting that did have FTL, travelling across a desert to mine dead rocks is the worst possible thing to do with it!

FTL powered acausality is a godlike power. It enables:
>P=NP
>infinite energy [by temporal clone]
>infinite mass [by temporal clone]
>zero time computing
>negative reaction times

IOW, anyone with an FTL device and a basic computer to run it is the next best thing to omnipotent, omniscient god. They can have wacky post-singularity simulations that aren't even a simulation, they're real matter. That's just the beginning. Universe engineering is the next step and it's not a big one.

>>52595882
Time dilation has been confirmed, yes. Therefore, a practical method of FTL travel would require a method of accelerating to faster-than-light speeds without dilating time. Once that factor is cancelled out, it's no longer impossible or paradoxical.

>>52596236
Ocean fantasy with WW1 dogfights.

>>52595162

...is it possible to write a story without a privileged reference frame? The POV of the narrative is, itself, a frame of reference. And what you say is happening.

Trying to accommodate multiple frames of reference would just come off as shitty writing.

>>52596307
>FTL travel would require a method of accelerating to faster-than-light speeds without dilating time
That doesn't even make sense. Time dilation is not a strange phenomena that happens to things that move fast. It's merely a description of how their perspective is altered AS A RESULT OF THEIR VELOCITY.

>>52596307
That's an oxymoron, but that doesn't matter. It doesn't matter ~how~ the exact trick works because relativity only cares about the outcome.

Lightspeed is how fast massless particles move because it's the speed of information. Going FTL is like taking an instruction out of a stack and randomly reinserting it somewhere else. It is inherently an editing of causality.

>>52596489
Speed isn't by the distance of two points and the time taken to move between them; it's the distance of the path taken between two points, and the time taken to move along that path.

Wormholes don't violate causality because nothing is moving faster than light.

>>52584509
What if you lower mass to 0?

>>52584003
Even wormholes can be used for time travel, i.e. time loops in wormhole networks. Every serious scifi author that uses wormhole networks has them not work when people try do this, i.e a chronology protection postulate. Let's be clear however, it's not traveling in time that's the problem. It's traveling backwards in time, i.e. arriving at your destination before you left. Using wormholes to travel into the future doesn't violate the laws of physics as we know them.

Technically, you don't even need spaceships if you can make wormholes. Just use the wormhole as a light rocket. But like >>52596236 said, most writers want to treat space like an ocean.

>>52581424
Why does your sci-fi setting need to operate on the exact same laws of physics as the real world? Just say that time dilation doesn't exist in this universe, that the speed at which an object travels has no bearing on how quickly time passes for it. You're probably already including force-fields, impossible power generators, and weird aliens so just declare how things work in your setting and move on. In fact, you can infer that a setting's physics don't operate traditionally if FTL exists and time dilation isn't a factor, so DESU I don't see what you're complaining about really. Just go with it.

>>52581424
Watch this:
https://www.youtube.com/watch?v=HUMGc8hEkpc

>>52581424
Most settings move a region of space around or jump the ship to the destination.

>>52581424
Because RPG writers actually need their players to actually be able to play in their setting. If you want to do time dilation fuckery, go write a novel instead. Alistair Reynolds, Orson Scott Card, Poul Anderson and countless others already have a head start on you.

>>52595839
>This is why FTL makes no sense and what is meant by violating causality.
No, that is why you, not understanding FTL, make no sense.

>Imagine you receive a radio signal from someone light years away.
>You then fly FTL to get there, before the signal is transmitted,
Stop right there.
To do that, you need to travel back in time. FTL doesn’t necessarily send you back in time.
(I say "necessarily" because the math gets weird and I haven’t gone that fast myself)
FTL sends you to a point faster than the light of you leaving.

Let's fix this mess:
>Imagine you receive a radio signal from someone light years away.
>You then fly FTL to get to the origin of the signal.
>From this perspective, you observe yourself before you received the signal.
>You tell the one who sent the signal not to transmit the signal.
>They explain that they already sent it and how FTL works, and ask how you managed to use FTL without knowing this.
>You can still observe yourself before you received the signal.
>Then you fly FTL back to where you were before, where you find the space unoccupied, a short time after you left, as your perspective has now changed again.
>You sadly try to shake hands with yourself, your hand limply grasping air. You settle for shaking your other hand.
>You observe yourself arriving and talking to someone who appears to have regrets about sending that signal.
>Do you receive the signal?
No.
Do you get my message?

>>52598518
In case you didn't read the entire thread, there is not one universal reference frame to which everything belongs. Time and location are both -relative- to speed, which ranges like a parabola from zero to the rate at which real events propagate, the speed of light. You can't go slower than stopped and you can't go faster than light for the same reason: the very concepts of motion and causality immediately go out of the window if you do.

>>52595884
>>52595900
Well, time travel is involved, except it's the boring 1D one direction time travel.

>>52599017
>In case you didn't read the entire thread, there is not one universal reference frame to which everything belongs.

But that's fucking stupid

File: UnrealizedReality.jpg (95KB, 1024x576px) Image search: [Google]

95KB, 1024x576px

>>52599017
>In case you didn't read the entire thread, there is not one universal reference frame to which everything belongs.
>>52599310
>But that's fucking stupid
It's true though.
And I haven't read the entire thread because, well, look at it:

>>52596489
>Lightspeed is how fast massless particles move because it's the speed of information.
I mean, what does this even mean? Is it a causal statement or an explanatory one?


>Time and location are both -relative- to speed, which ranges like a parabola from zero to the rate at which real events propagate, the speed of light. You can't go slower than stopped and you can't go faster than light for the same reason: the very concepts of motion and causality immediately go out of the window if you do.
This sounds fine and I'm not sure how it directly relates to my post, but "going slower than stopped" is one of those ideas I was talking about here >>52586457

>the very concept of motion immediately goes out of the window
So assuming you could go FTL, you would no longer be "going", as we understand it.
I'm not gonna check your math so I won't ask you to show your work.
It checks out.

>>52581424
>Why does virtually every setting ignore this?
Because if it's written well, it works around it, often though cheating by not actually exceeding light speed.
And if it's not written well, what did you really expect?

>>52599582
>So assuming you could go FTL, you would no longer be "going", as we understand it.

It isn't just time that starts shifting when speeds get high. Mass and distance also dilate, in the same way that time does.

Now if you plug in a value for v (the speed) greater than c into the math here, you won't get negative values for mass, time and length. You get imaginary values. Time isn't going backwards, it's going off at right angles to the timeline. Distances likewise turns right angles to reality, and mass phases out as well. You, or the universe (depending on the frame of view) will have ceased to exist.

Not that you'll ever get there. Remember the bit about mass dilation? As you speed up, you get heavier. As your speed approaches c, your mass approaches infinite, and that means the acceleration caused by any finite force will approach zero. This makes it impossible to accelerate to the speed of light.

And of course at the speed of light we get a whole host of division by zero errors. So that's most likely just flat out fucking impossible, even if getting to that point hadn't in itself been impossible. Which shouldn't be very surprising, take a physical theory and force it to give you an answer for somethign impossible, and it bloody well shouldn't give you a proper answer.

>>52594800

>It would be year+1 for everyone on Earth as you say, but for some observer moving very quickly in the opposite direction (no matter where they were) you would arrive before you left.

I see where you're getting confused now. All an observer passing the FTL object would see is the reflected light of the FTL object. But the FTL object wouldn't actually be there. If they were to pass through the FTL object's after-image, they wouldn't be harmed by it, or be able to touch it.

>Since their perspective is just as valid as yours or those on Earth, causality is violated.

Causality is still fine.

>It's worth noting that you would experience some undefined time dilation (imaginary value) which is literally impossible to conceive - this is why there are no reference frames that move at or faster than the speed of light.

The assumption here is that the speed of light = the speed of time. However, that's not likely at all, since time is a part of space, not a single type of particle's speed. The more likely thing the FTL object would see is an extremely flattened version of objects before it (because moving into light would mean you would see things more rapidly), and nothing behind it (since light wouldn't catch up with it). The Doppler effect. But time would remain the same for them.

File: main-qimg-f81f14f05e874e87b44c36a33170cd69-c.jpg (18KB, 480x360px) Image search: [Google]

18KB, 480x360px

>>52599929
>The more likely thing the FTL object would see is an extremely flattened version of objects before it

No, that's if your relative speed is high, but still below c.

If your relative speed is greater than c, well, just plug that into the equation and see what you get. (L is the seen length, Lp the length at rest.)

Though since you didn't pick up on the guy you're replying to saying "imaginary time dilation", you will probably have to learn some more math to do so:

https://en.wikipedia.org/wiki/Imaginary_number

>>52600042

Except that equation has nothing to do with what the moving person sees, only an attempt to explain what an outside observer sees. So completely irrelevant to what the FTL object would see.

It would seem you need to spend some more time learning about these things, instead of just blindly parroting it.

>>52599929
>The assumption here is that the speed of light = the speed of time. However, that's not likely at all, since time is a part of space, not a single type of particle's speed.

You've got it backwards. It's not that reality propagates at the speed of light, it's that lightpropagates as fast as reality allows. All the relativistic fuckery happens when you approach the speed of reality. That light also moves at this speed is coincidental. If you were underwater (where speed of light is about 3/4c), all the weird shit would still happen and still depend on c, not 3/4c

>>52599929
>I see where you're getting confused now. All an observer passing the FTL object would see is the reflected light of the FTL object.
Nope. You would arrive before you left even accounting for the signal delay. None of this has to do with when you see something happen, only with when it actually happens relative to your frame of reference.

>>52600074

Except we can also slow light down, and time doesn't get altered. The assumption that surpassing the speed of light will magically alter the speed of time is flawed.

>>52600089

>Nope. You would arrive before you left even accounting for the signal delay.

Nope. You would arrive 1 year later, which would be 1 year after you left. To an outside observer, you wouldn't even arrive before you left, either. You'd arrive before your journey was finished (in their eyes), but never before you started.

File: 1477848418553.png (167KB, 540x540px) Image search: [Google]

167KB, 540x540px

>it's a "theoretical physicists make something much more complicated than it has to be instead of doing real science" episode

>>52585004
Infinite energy just gets you to the speed of light where time stops. You can't go faster and therefore backwards in time.

>>52600091
You've got it backwards again.
We can slow light down, and this won't change the speed of time, because the speed of time doesn't depend on the speed of light. It depends on c.

Now c is called "light speed" and is equal to the speed of light in vacuum, but this is incidental. c is what relativity is working with, c is the maximum possible speed, approaching c will cause time dilation. It has nothing to do with the actual speed of photons in some medium.

>>52600146

Except the assumption still being made is that there is a limit to speed that affects time. And yet it's called spacetime, not speedtime. So it doesn't matter whether you use the speed of light or the speed of a bullet, surpassing a speed does not alter time. All it does is cause visual illusions, not physical anomalies.

>>52600105
https://en.wikipedia.org/wiki/Relativity_of_simultaneity
This had already been posted in the thread.
You would arrive 1 year later relatively to Earth, and you would arrive less than 1 year later relatively to you, and both times are valid and real. If you had a clock counting the time of your abscence on Earth, and another one with you, you could fly somewhere then back and see the two clocks show completely different readings.

>>52600183
>Except the assumption still being made is that there is a limit to speed that affects time
This assumption has been confirmed by numerous physical experiments. I thought we aren't trying to disprove the theory of relativity in this thread.

>>52600185

>You would arrive 1 year later relatively to Earth, and you would arrive less than 1 year later relatively to you

No, you wouldn't. If you were to set off on a 4 light year journey and complete it in 1 year, you will arrive 1 year later.

>If you had a clock counting the time of your abscence on Earth, and another one with you, you could fly somewhere then back and see the two clocks show completely different readings.

Except they wouldn't, unless you're manipulating gravity, too.

>>52600205

>This assumption has been confirmed by numerous physical experiments.

Except it hasn't, since no one has ever been able to get an object even close to the speed of light, let alone surpass it.

>I thought we aren't trying to disprove the theory of relativity in this thread.

STR was already disproved. We don't need to disprove it again, just for you to catch up.

>>52600238
>STR was already disproved
Have I missed something? Or are you referring to GTR? Then please tell me how GTR disproves the speed of light thing.

>Except it hasn't, since no one has ever been able to get an object even close to the speed of light, let alone surpass it.
Except it has, because the implication of this can and have been observed.

>>52600213
1 year later relative to what?
Time is relative anon, you can't just say "no it's not"

>>52600275

>Have I missed something? Or are you referring to GTR? Then please tell me how GTR disproves the speed of light thing.

You said "disprove the theory of relativity", which encompasses both STR and GTR. Since STR was disproved, the theory of relativity as a complete package has been disproved.

>Except it has, because the implication of this can and have been observed.

Except it hasn't. Nobody has made an object move FTL.

>>52600238
>STR was already disproved
Are we talking to a fucking aetherfag

>>52600292

>1 year later relative to what?

Everyone. If the FTL object gets to its destination and opens a wormhole back to Earth, the people on Earth would say "wow, you did that in 1 year" and the crew on the FTL object would say "yeah, it took us 1 year". But the people on Earth would ALSO say "well, we can still see you travelling up there, but that clearly doesn't mean that's where you actually are, because the speed of light was just slower than your ship".

See?

>Time is relative anon, you can't just say "no it's not"

Except I've never said that. Take in all of what's being said, or don't bother at all. Doing only half does nothing of use.

>>52600298
>Since STR was disproved, the theory of relativity as a complete package has been disproved.
And since STR devolves into Newtonian mechanics at low speeds, the three laws of Newton have been disproved as well!

Really, anon?

STR was not disproved. It was generalized.

>>52600315

*blackholefag

>>52600340

>And since STR devolves into Newtonian mechanics at low speeds, the three laws of Newton have been disproved as well!

Doesn't work like that, sorry.

If you have 2 pieces of paper and you called it "the complete truth", but you could prove one of those pieces of paper had lies on it, you have disproven that those 2 are the complete truth (as in the encompassing phrase for both of them). You now have "a page of truth" and "a page of lies", so anyone who continued to claim them as "the complete truth" would be wrong.

>>52600238
>Except it hasn't, since no one has ever been able to get an object even close to the speed of light

The LHS gets protons to about 0.99999999c.
That ain't close enough for you? The physicist sure as hell have to account for the full range of relativistic effects when matching experiential results to theoretical models there.

>let alone surpass it.

Well, yeah, since that's outright fucking impossible that much should be painfully obvious.

>>52600378
>LHS
LHC, anon.
I don't think Chrysler's full-size luxury four-door sedan can move at 0.99999999c.

>>52600378

>The LHS gets protons to about 0.99999999c

You mean the LHC?

>That ain't close enough for you?

Let me know when they can do it with an object.

>The physicist sure as hell have to account for the full range of relativistic effects when matching experiential results to theoretical models there.

None of which involve FTL travel.

>Well, yeah, since that's outright fucking impossible that much should be painfully obvious.

As of now. People used to think it was impossible to send people into space, but we did it.

>>52600331
I traced the conversation further back, and I admit I was going in a bit of a wrong direction here.

Let's start anew from this point:
>It would be year+1 for everyone on Earth as you say, but for some observer moving very quickly in the opposite direction (no matter where they were) you would arrive before you left.

>I see where you're getting confused now. All an observer passing the FTL object would see is the reflected light of the FTL object. But the FTL object wouldn't actually be there. If they were to pass through the FTL object's after-image, they wouldn't be harmed by it, or be able to touch it.

The second statement here speaks about the light signals of events, while the first speaks about the events themselves. This is the point of misunderstanding.

>You would arrive 1 year later relatively to Earth, and you would arrive less than 1 year later relatively to you, and both times are valid and real.

This statement of mine was in error, because I assumed we're talking about STL.
But the other anon's statement:
>"It would be year+1 for everyone on Earth as you say, but for some observer moving very quickly in the opposite direction (no matter where they were) you would arrive before you left."
is correct, because there's no absolute frame of reference you can base time on.
And this:
>You would arrive before you left even accounting for the signal delay. None of this has to do with when you see something happen, only with when it actually happens relative to your frame of reference.
Is also correct.

>>52600406
>As of now. People used to think it was impossible to send people into space, but we did it.
Nigga people thought it was an insurmountable challenge to send people to space, not that it was literally, fundamentally in violation of physical laws.

>>52600369
That relativity isn't the full, complete truth has been known from the start. Black holes and all that. But that doesn't mean its wrong, just like the anomaly of Mercury's orbit didn't really prove Newton wrong.

What these anomalies do is to show us that these theories have a limited scope. There's a range of things they cover, and for those things they are correct. Then there are phenomena that lie outside of them, and they do not explain those.

Newton explained some things. Einstein expanded upon that to explain more things. Some other people will now have to come in to expand upon that to explain even more, perhaps one day reaching the point where everything has been covered.

But don't expect Newton's mechanics or Einstein's relativity to ever go away. They are both experimentally proven to a ridiculously thorough degree.

File: stupid.jpg (81KB, 687x369px) Image search: [Google]

81KB, 687x369px

>>52600406
>Let me know when they can do it with an object.
>As of now. People used to think it was impossible to send people into space, but we did it.

>>52600423

>Nigga people thought it was an insurmountable challenge to send people to space, not that it was literally, fundamentally in violation of physical laws.

And before that, they thought it was literally, fundamentally in violation of physical laws.

>>52591663
But challenge for Humanity in HFY stories is what they need!

>>52600445

Absolutely nothing in either of those statements is incompatible, especially in context.

>>52600430

>Then there are phenomena that lie outside of them, and they do not explain those.

Exactly. FTL travel is one of those things. Too many make the assumption that his theories HAVE to work at all times.

>>52600448
You know, if Einstein was wrong about all of this, that doesn't mean FTL travel is possible. He could simply have been wrong about why it's impossible.

(Ignoring that we've experientially verified it all.)

But that never crossed your mind it seems. Because, let's face it, you don't give a fuck about these things, nor do you understand them. You just want FTL travel to be possible, so you decide that it is, and that's that.

>>52584799

Question: you mention warp drive (obviously, Alcubierre-style) but also mention "hyperspace portal".

When you say "hyperspace" here, are you referring to the idea of an alternate dimension where relativity doesn't apply, like the Warp in 40k or the Star Wars hyperspace? I imagine you probably are, since it's the common definition, but I want to make sure.

I certainly like the idea, especially since I've always been more of a Star Wars fan than a Star Trek fan, but it seems to me that the Alcubierre warp drive has the distinct advantage of being based on actual scientific principles, despite relying on as-of-yet non-existent technology, while hyperspace remains very firmly in the realm of science fiction.

Do you intend to imply that there's reason to believe hyperspace actually exists, or are you just mentioning it as an example of what would be needed to make FTL possible?

>>52600477

>You know, if Einstein was wrong about all of this, that doesn't mean FTL travel is possible. He could simply have been wrong about why it's impossible.

Or, he was wrong about why it is actually possible.

>(Ignoring that we've experientially verified it all.)

We haven't.

>But that never crossed your mind it seems. Because, let's face it, you don't give a fuck about these things, nor do you understand them. You just want FTL travel to be possible, so you decide that it is, and that's that.

No, I completely understand them. I just also understand why they're flawed, which is something sheeple like yourself struggle with. Blind acceptance of something because you don't understand it is a weak stance to take, and you should really try to get to grips with it first before trying to argue for it.

>You just want FTL travel to be possible, so you decide that it is, and that's that.

There's no want involved. It doesn't affect me at all, since I won't live long enough to see FTL ships. If anything, the better option is wormhole travel. But I can see what sort of mind-set you have now, where you think desire is what determines truth. When you're older, you'll realise that what you want isn't what drives what is true.

>>52600512
Hyperspace is discovered!

Turn our c is even slower there.

>despite relying on as-of-yet non-existent technology

Not to mention things that IIRC, as far as anyone can tell, simply don't exist. A bit of a bummer that bit.

>>52600518
>>52600477

People have already forgot that this thread wasn't about whether FTL is possible, but about what to do with causality breaking if it is.

>>52600539

I was actually arguing that FTL travel doesn't result in a break in causality. It was the super-autist that started trying to argue its impossibility.

>>52600518
Yeah, you really are that stupid. Take your meds, have some therapy, and try again when your cat has stopped helping you with your equations.

>>52600547
Could you please reiterate your arguments?

>>52600548

There's really no need to get so mad. But if the projection helps you out, more power to you, I guess.

>>52600554

Only that FTL travel does not result in a reverse in time, so that if an object makes a 4 light year journey in only 1 year, they will not be arriving 3 years prior to even setting off, they will simply arrive 1 year after they set off.

>>52600554
I know better than the entire scientific community, so you're just gonna have to take my word for it.

>>52600565
Ah. But then an anon replied that there would be a frame of reference in which you would indeed arrive before you set off.
And I will add that you don't even have to travel FTL for such a frame to exist.
This is not the place where causality breaks though. To travel in time you have to travel FTL to another, sufficiently fast frame then travel back.

>>52600583

>Ah. But then an anon replied that there would be a frame of reference in which you would indeed arrive before you set off.

Which I contend to be the case. They didn't make the journey in -1 light year, they made it in 1, so they cannot arrive before setting off. Even accounting for illusions of after-images by exceeding the speed of light, they cannot arrive before they've set off, even by an outside observer.

Like how you see a flash of lightning before you hear the thunder. The thunder isn't heard before it has even occurred, nor is it happening the moment you hear it. What is heard is the after-effects of the event.

File: 1491478455300.jpg (527KB, 2552x2043px) Image search: [Google]

527KB, 2552x2043px

If we're talking about FTL travel over any useful distance then there's no meaningful paradox at the macro scale. Even a quick jump to Mars will show up as a small spike in EM radiation fifteen minutes later, at best, and only if someone on the opposite end knew exactly what to look for. If we assume wormholes can't be artificially created and that no FTL communication exists other than courier ships, then a simple human desire to stay in the same time frame as their friends and family will prevent most temporal shenanigans. Crisis averted, physics majors can go back to bed.

Now if we ever get permanent quantum entanglement of macro scale object pairs worked out in this setting, then we have a preferred time frame again and the relativity fun police can be disbanded.

>>52600709
>Now if we ever get permanent quantum entanglement of macro scale object pairs worked out in this setting, then we have a preferred time frame again and the relativity fun police can be disbanded.
Sounds like a fun setting.

>the scientists said there was no absolute reference frame, and as such relativity and causality would prevent full usage of FTL
>so we built an absolute reference frame

>>52581424
That assumes our current understanding of physics won't go the way of newton's

>>52601016
>That assumes our current understanding of physics won't go the way of newton's
A locally consistent system becoming the basis and groundwork for later generations of expanded physics theories?

>>52600615
The theory of relativity states that time, and even the order of events, is relative to the observer. So you can indeed arrive before setting off, not relative to you, but relative to some fast observer. And it won't be an aftereffect, nor an illusion. The analogy with thunder and lightning is wrong. The faraway observer will see you departing and arriving, then deduct the signal travel times and still conclude that you've arrived before departing.

I'll illustrate this with the following mental excersise. Suppose we have a barn with two doors across from each other, and a pole equal in length to the barn. Suppose you can open the barn doors by pushing them with the ladder, and a spring will close them as soon as the pole leaves the doors.

Now let's posit that an object travelling relative to some frame experiences length contraction in the direction of travel relative to that frame, as the theory of relativity states. Imagine that observer B takes the pole and runs at the barn doors at a significant fraction of c. Imagine also an observer A, who is at the barn's frame.

Relative to frame A, the pole experiences length contraction, so it can fit inside the barn completely. In other words, the pole pushes the front door open, then clears the door, which is closed by the spring, then pushes open the back door.

Relative to frame B, the lpole is at rest and it's the barn that's moving and experiencing length contraction. Now the pole is longer than the barn. In other words, the pole pushes the front door open, then pushes open the back door, then clears the front door.

As you can see, the order of events "front door closes" and "back door opens" is dependent on who observes them. And the signal delay isn't involved at all. Both observers could stand right at the door and still experience events in different order. Both event sequences are equally true.

>>52600448
No, they didn't

>>52600615
I'm the anon who stated that causality would be obviously screwed for an observer moving relative to both Earth and the FTL ship. As much as i hate appeal to authority, i do have a physics degree in which i studied this stuff - not that it helps much in the current job market...

Anyway when i said 'arrive before you leave' it was really shorthand for a whole load of causality-breaking situations. As an example, suppose the FTL ship emits light signals all while it's traveling, our other observer (who is moving forward in time just like an observer on Earth or all other reference frames) would see the FTL ship to be literally traveling backwards in time and causality for any process seen on said ship would be reversed - so other physical laws like increasing entropy would be violated.

The problems for length contraction would be equally screwed up in such a situation, since the gamma factor for observers on the FTL ship would be imaginary and the spacial dimension parallel to their direction of travel would become somehow timelike and any objects they saw would be inconceivably screwed up.

>>52601290
Just because an observer in some frame sees you arriving before leaving, does this allow that observer to warn someone not to leave? Can they affect this at all? in the frame of the Traveller, is he experincing arriving before leaving?

>>52581424
Unless it works on wormholes, in which case relativity isn't getting involved.

>>52601418
The traveller won't experience arriving before leaving if he stays within his frame.
And just observing the events in reverse order doesn't cause causality to break.
The barn paradox doesn't illustrate breaking causality, it illustrates the relativity of simultaneity.
It's only in combination with FTL travel that relativity of simultaneity can cause breaking of causality.

>>52601431
But it does. The method of FTL travel is irrelevant. As long as you can arrive somewhere before the light from your point of departure does, you can break causality.

>>52601290
This is nicely explained - the phenomenon is the relativity of simultaneity and the apparent paradox is resolved when one realises that while the observer stationary relative to the barn sees both sets of doors close simultaneously, the observer moving with the pole sees the doors open and close at different times so that the pole still makes it through unharmed.

>>52601444
I read Einstein's original paper on GR yesterday (translated), and at no point did he state anything about this shit. He just argued that without gravity you have the identity matrix in the linear element of coordinate spaces, then proceeded to fuck with tensors for a while. I thought it weird he didn't talk about all the strange effects.

>>52601444
So the proposition is that once you go faster than light you can take advantage of the relativity of simultaneity to change effects as observed in one frame by changing the cause in another. What happens at exactly the speed of light? Can photons destroy casuality?

>>52601444
>>52601418
Actually, let me elaborate on how exactly causality can be broken.

Imagine the experiment in >>52601290 again.Now suppose you're standing at the barn's back door and observe it opening. You know that at this moment the front door has already closed, but you want it open.

If you have means of FTL travel, you can travel into the pole's frame - where the front door hasn't closed yet - and break the spring that closes the front door. Voila, the front door never closes, because you prevented it, which you did only because it has closed, which it never did. Causality BTFOd.

>>52601497
These effects are investigated in SR

>>52601558
Sorry anon, I can't answer that.

>>52601566
>These effects are investigated in SR
Note that Einstein defined simultaneity as simultaneous arrival of signals, while the barn paradox uses a more strict definition. Theory of relativity has been worked on after Einstein too.

>>52601497
That's because this is Special Relativity, not General Relativity - this stuff was already understood and accepted by the physics community by that time (although not verified to the degree that it is today). One thing that hasn't been addressed in this thread is that all of the SR maths is required to make electromagnetic theory work and has been verified through that as well.

>>52601566
Wasn't it showed by some researchers that all solutions seem to be casual loops? This billiard ball FTL travel example for instance

>>52581475
>nothing resembling time travel in any direction, let alone backwards, has ever been observed
I have personally observed time travelling in the forward direction.

>>52602104
Nah because in some reference frame you haven't been born yet and no frame is privileged fugg xdd

>>52601290
So not only is there no "objective sequence of events", there's not even an objective form of events? And objects can be both shortened and lengthened in relation to each other at the same time?

The best description for this interpretation is "impossibly convoluted". The more it's explained, the more it sounds like someone interpreting the data from experiments in an unnecessarily dramatic way, interpreting those conclusions as inviolable absolutes, and extrapolating from those absolutes to reach utterly nonsensical conclusions.

>>52603495
Yep, it would be much better if we could easily visualise how nature works. But no such luck!

>>52603517
Is there any actual proof of an object simultaneously being longer and shorter than another object?

>>52603563
https://en.wikipedia.org/wiki/Tests_of_special_relativity
http://spacetimecentre.org/vpetkov/courses/reid.html

>>52603563
https://en.wikipedia.org/wiki/Length_contraction#Experimental_verifications

>>52596012
Assuming, of course, that the wormhole view does not function with the same dilation effects as the radio signal does, simply because it arrives very slightly faster.

Again, you're saying "If you assume time travel exists, then logically it's possible to travel through time."

>>52603830
>Again
I never posted in this thread with any other explanation before that one. I'm just trying to see if I have a good idea of the concept, so feel free to correct me.

Why would the wormhole's view dilate as a result of relativistic travel? Information from inside the spacecraft that travels through the wormhole to the command center isn't going any faster than it should, it's simply taking a shorter distance through space. I'd think the error would lie in assuming that wormholes can move in the first place.

>>52603963
That is a good example of the idea of using wormholes to travel through time. It's simpler than the usual one, which is nice too.

The issue is that the information WOULD be dilated. as the radio signal shows. Inside the ship any signal from outside, even through a wormhole that transmits instantly, would be sped up because you are receiving it at a the rate it was sent, not the rate you are moving at, and vice versa.

Imagine each wave of light from the ship hitting the wormhole and going through to a slower frame of reference than it came from. From it's perspective, now that the wave is on the other side of the wormhole the wave behind it is moving much slower, making a big gap between their arrival times, thus producing a massively slowed down scene as viewed from the earth side.

The reverse applies to light traveling through the wormhole to the ship, as each wave hits the portal it maintains it's speed as far as that wave is concerned, but the wave behind follows much faster than it should because the timescale of its new reference frame is so different than the frame they originated from.

>>52603963
Though practically, yes, moving a wormhole is probably impossible, and furthermore the image the ship receives would be a burst of lethal, high frequency radiation due to the wavelength change.
And trying to walk through the wormhole to earth you would disintegrate as each layer of cells in your body passed through the portal, lost circulation, died and crumbled away because it would take years for your entire body to arrive on the other side.

But that's assuming the wormhole works in a simple, sensible way and doesn't have special features that make it possible to use it for time travel.

>>52604823
I don't think wormholes work that way.

>>52596012
>I'm assuming a wormhole is two objects: The Post

Wormholes are singular, not pairs. You can't move one end without moving the other.

>>52604733
Now I get it, thanks.

>>52604924
Stargate wormholes basically work that way but then use space magic to put you back together on the other side.

>>52600518
>Dude FTL has to be possible!
>Doesn't pause to consider it might not be
>Lmao why do you think about what you want rather than what is?
You are completely insane.

>>52605433
Not him, but

>ever thinking anything is impossible
>thinking the impossibility of something can even be proved logically or empirically
At the very best, it's impossible through the understanding and methods of contemporary physics.

>>52601290

>The theory of relativity states that time, and even the order of events, is relative to the observer.

Actually, no, the order of events is the same. Event A causes event B, so event B will never be before event A.


>>52601411

>As an example, suppose the FTL ship emits light signals all while it's traveling, our other observer (who is moving forward in time just like an observer on Earth or all other reference frames) would see the FTL ship to be literally traveling backwards in time and causality for any process seen on said ship would be reversed - so other physical laws like increasing entropy would be violated.

That's not quite how it works. Lets say you could see an object set off from one point to another that's 4 light years away, but they manage to complete the journey in only 1 year (we'll assume the entire journey is an equal distance from the observer). The observer would not witness them time travelling. And that's precisely because the FTL object hasn't time travelled. It has simply beat light to its destination. From behind, it would be invisible, from the front it would appear further behind than it actually was, with its after image always trying to catch up to it. If people on the FTL object were to turn around at the end point, they'd be able to see their own arrival, but there wouldn't physically be two of them. It would just be an after image. Like when you move your hand really fast, and you can see what looks like two hands.


>>52605433

>Dude FTL has to be possible!

Weak attempt at creating a strawman.

>Doesn't pause to consider it might not be

Already have done, but there is nothing to suggest it is impossible.

>Lmao why do you think about what you want rather than what is?

You're just talking nonsense now.

>You are completely insane.

And you're a dishonest simpleton.

>>52605511
>through the understanding and methods of contemporary physics.

Which is the most well-supported, by actual evidence and theoretical analysis, viewpoint that currently exists.

Whereas the idea that FTL is possible is supported by wishful thinking and the tooth fairy.

So if you want to weight the likelihoods of possible and impossible being correct, then possible is pretty much right up there with the flat earth and time cube theories.

But sure, if you want to get really anal about it in a way that will have any serious philosopher reach for the barf bag, then the impossibility of it hasn't been proven to mathematical standards. Doing so would most likely be outright impossible.

But that doesn't mean we should hold it as possible. Until we actually have FTL that hasn't been proven to anywhere near that level either, meaning that the best you can get out of this is "we don't know". Which is also what you get out of absolutely anything short of, perhaps, pure math if you apply these evidence standards to it. Thus the barf bag.

Compare with creationists trying to poke hole in evolution because if that's not correct, then that must mean creationism is correct, right?

>>52605606
>Actually, no, the order of events is the same. Event A causes event B, so event B will never be before event A.

You didn't read that post, did you? The two events described there aren't in causal relationship. Also, their order is demonstrably not the same.

>>52584427
So your penis is the secret to ftl travel?

>>52583250
i thought it was the exact opposite, once you come back after a year of ftl travel a much larger portion of time has passed in the normal world
because of time dilation
heck starship troopers even briefly mentions this

>>52606261
>according to some reference frames
This is the key phrase anon

Also time dilation is a property of STL, not FTL.

>>52606031

>You didn't read that post, did you? The two events described there aren't in causal relationship. Also, their order is demonstrably not the same.

No, I read it. Problem is you're not keeping up with the discussion yourself. We're talking specifically about breaking causality.

As for order of events, if a person hears a thunderclap from 10 miles away and tries to claim that the event happened at the moment he heard it, he would be a fool. Even worse would be if he tried to claim it occurred before the thunderclap even actually happened.

>>52607044
That post explained relativity of simultaneity. Relativity of simultaneity + FTL results in breaking causality, as demonstrated in >>52601566

And your analogy with a thunderclap doesn't describe the issue at hand at all

>>52605748
>Compare with creationists trying to poke hole in evolution because if that's not correct, then that must mean creationism is correct, right?

>this level of argument
No; X not being absolutely proven means that Y has some probability (perhaps an infinitesimally small one) of being correct.
Saying "Due to the fact that human physical knowledge is incomplete, FTL may yet still be possible through future discovery" is not the same as saying "Because we don't know everything, FTL IS possible"

I'm even more concerned and disgusted by this disregard of "wishful thinking and the tooth fairy", in your words.
What is wrong with being optimistic? What is wrong with thinking "well, it doesn't work through our current understanding, but maybe we'll figure something else out" compared to "it doesn't work through our current understanding, ergo it is impossible for all reasonable purpose and should not be pursued further".
On the off chance that FTL (or any other far fetched supertech/superscience, since I know you'll bring up >perpetual energy) is possible through some mechanic we have no knowledge of yet, is it really that helpful to say "well, our known stuff says it doesn't work, so it doesn't work."

>>52607115

>That post explained relativity of simultaneity. Relativity of simultaneity + FTL results in breaking causality, as demonstrated in

That post only demonstrated that the poster still thinks time-travel involves going really fast. If an event has happened, you cannot go back to a time before then, even at FTL travel. Causality isn't broken, and non-causal events are irrelevant.

>And your analogy with a thunderclap doesn't describe the issue at hand at all

Except it does. It shows how sound is not the defining factor of the event, just as light is not for events involving FTL travel.

For example, a plane flies above you. You can't hear it, but you see it. Then as it's further away, you can suddenly hear the plane as if it's right above you again. It isn't above you, and time hasn't been re-wound simply because you've now "observed" it again. It's just sound being slow.

Same applies to FTL travel. What you're seeing when a FTL object passes isn't the object itself. It's the after-image. Time-travel is not happening. They would not be travelling before they've even set off.

>>52607434
>If an event has happened, you cannot go back to a time before then
You can, anon. If FTL travel is possible and SR holds, you can.

>light is not the defining factor for events involving FTL travel.

This is correct, but you make wrong conclusions from it.
Relativity of simultaneity doesn't deal with receiving signals from events. It deals with events themselves. Images of FTL objects are irrelevant to discussion. And the paradox in >>52601290 was constructed in such a way that signals don't enter the discussion at all. You didn't read it after all.

I'll reiterate. Seeing images of FTL objects isn't relevant to discussion at all. The events which are reversed aren't the lightning strike and its thunder, but two different lightning strikes.

>>52581424
wasn't the original premise of Mass effect that all the usage of element zero for FTL ( and all the other batshit uses) was destabilising the universe, and the reapers purpose was to prune back civlisations to allow the universe to continue?

>>52601497
Einstein didn't know how to solve his own equations and even declared them unsolvable. It was Schwarzschild who first came up with a solution a bit later, and showed various funky aspects of GR like the existence of event horizons. Schwarzschild actually came up with his solution while fighting in World War 1, and died shortly afterwards.

>>52601558
Sort of. Photon's can't break causality but they don't have any form of proper time, so as far as a photon it's entire lifetime happens at the moment.

On a general note, one thing to remember is that Einstein explicitly included an assumption of causality in his working. There are solutions to various equations that don't perverse causality, but scientists disregard those solutions as unphysical. So far, the experimental evidence backs them up.