# Considering the faster than light twin problem, where people on fast ships age...

Fried_Sushi

Considering the faster than light twin problem, where people on fast ships age slower than people on planets, how would a space empire with ftl ships keep society balanced?
You never see it mentioned in sci-fi movies, people fly around space in ftl but everyone stays the same age no matter what.

Imagine a future family where dad leaves his wife and two kids to visit a couple of systems for a year, only to return and see everyone has gotten 30 years older.

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StrangeWizard

Um, news flash. If the society has "ftl" ships then there is no twin paradox cuz there's no relativistic effects from traveling.

Nojokur

um
kill yourself
If the society has "ftl" ships then there is no twin paradox cuz there's no relativistic effects from traveling.
300,000km/s is ftl
you would be right if they had warp

Supergrass

The only feasible way to go "ftl" in these scenarios is assumed to be a "trick" like bending space in front of oneself. In that case, their velocity never breaks the speed of light, even though they're covering more distance than should be possible at that speed.

Fried_Sushi

You need to think this thing through, kid. Sure you're on the right board?

Need_TLC

We had a thread about this last week, people said that warp would still BTFO causality, because you could do shit like make phone calls into the past.

Lunatick

If you leave Earth at a faster-than-light speeds and travel a number of light years and then turn around and travel back faster than light, won't you have traveled into the past?

Garbage Can Lid

not an argument

Booteefool

Because there's no such thing as ftl and never will be.

You can't throw out relativistic effects because then you throw out causality.

FTL is space opera trash, nothing more.

Boy_vs_Girl

people said that warp would still BTFO causality
Mirin. This board's intelligence has increased since I was last here I see.

Proud of you Veeky Forums.

Soft_member

Warp can make phone calls to the past possible
Am I just too much of a brainlet to see how this works or is it made up bullshit?

farquit

People who think that are wrong. The past is not something you can interact with. It is literally gone. It's over. It doesn't exist at all. Time moves one way and that's into the future. You can move "faster" or "slower" into the future depending on how fast you're going but time is still only moving in one direction.
People can call it that but if it is Saturday March 24th and I get in a spaceship going ftl all the way to proxima centauri and back, when I get back it will still be either March 24th or later and not one picosecond earlier. Yes, I get the argument where people conflagration time with the other 3 dimensions and talk themselves into thinking they are time traveling. Guess what, you are. But it only goes one way. Into the future. Just because you wink out of existence here and show up on the other side of the universe and back doesn't put you somewhere else in time. If that were the case, you could just shut your eyes and pretend and say you traveled in the past. Except you didn't.
I mostly agree. But it would be foolish to say we have answered this question for the rest of eternity. That would be like some dude on the African savannah 200,000 years ago thinking he had figured something out that would apply forever. I understand physical laws of the universe are pretty damn fundamental but I wouldn't rule anything out.

cum2soon

I wish I still had that thread open, one user went an extra mile and actually drew pictures to get the point across.
Long story short, if you had tech that would allow you to jump hundreds of light years in virtually no time, and two of these ships communicated between each other the reply would arrive before the first message left.

idontknow

That... makes absolutely no sense to me. Even with instantaneous travel, at no point is any message actually being sent backwards in time.

Playboyize

I mostly agree. But it would be foolish to say we have answered this question for the rest of eternity. That would be like some dude on the African savannah 200,000 years ago thinking he had figured something out that would apply forever. I understand physical laws of the universe are pretty damn fundamental but I wouldn't rule anything out.

You are right it's naive to think we know everything. But I would raise the point that, within the field of physics, it is non-nonsensical to consider FTL since causality is fundamental in physics and it's impossible for FTL to not violate causality.

So we would have to first through out physics. Which means we are no longer dealing with science.

In that sense FTL is a more appropriate discussion for a philosophy board than a science and math board.

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PackManBrainlure

Just because you wink out of existence here and show up on the other side of the universe and back doesn't put you somewhere else in time. If that were the case, you could just shut your eyes and pretend and say you traveled in the past. Except you didn't.
Light travels at speed c, right? We know that a beam of light from a distant star has traveled to Earth at that speed over time so what we see from Earth is not actually what's happening in absolute time at the aforementioned star. If you travel to the star faster than the speed of light, doesn't that mean you will reach it before the current time? It means that when you arrive at your destination, you will see approximately the same thing as you saw from Earth.

If I'm terribly wrong forgive me. I am trying to understand.

PurpleCharger

Not buying it for a second. You can diagram this shit until heat death and I guarantee you you're missing something if you think you will violate the fundamental causality of the universe with some kind of hyperdimensional travel. 115ers have that habit of arguing themselves into all kind of ridiculous shit and this is a perfect example.
Lol. The pilot's response becomes an entirely new trajectory that's a mini version of the diagram. If the diagram actually represented 4 dimensional space you would see the pilot's response heading toward earth as the earth's time frame would be moving ahead 1 second per second so the response would arrive after the ansible sent its message. This is a semantic game semi-smart people play when they try to reduce complex hyperdimensional interactions into a 2d diagram with a few lines and words.
Here's the way I see it. My life here on earth is happening "now". What's happening in China is happening "now" also despite light taking some fraction of a second to get here. If I could somehow look through the earth and see China, the photons hitting my eyes don't reflect what is going on now but at the instant those photons left China. Just because the photons are bound by relativity doesn't mean that when they hit my eye is the "now" of whence they came. I understand that this means there is technically no shared time frame between me and China. Hell, when I look across the room, I am looking into the past. But here's the thing. At this moment, I am experiencing this as now. Across the universe at this moment is some other creature's now. These two "now's" are the same instant whether we can communicate or not. If I had a telescope and could see across the universe, I would be looking at events 100,000 years ago. That was "then". I get that due to how time works the observer effect, etc. people like to argue that I am always looking at "now" when I see Andromeda with my naked eye. I just don't buy it.

Supergrass

people like to argue that I am always looking at "now" when I see Andromeda with my naked eye
who the fuck does that?

Booteefool

To sum up, despite what we observe which is always on a delay due to light speed, events happen at a certain time. Time is obviously relative as it moves at different speeds depending on how fast you are moving. But for my now, there is a concurrent now everywhere else in the universe. An hour from now may not be an hour from now everywhere else but even then and any other moment, there is another now. If I look into a telescope, I'm looking at the past cuz it's just reflected light. The events happening now are not what I see in my telescope. So if I use ftl to go to the star, I'm not traveling into that planets future since I was never in its past. The waters are muddied by relativity and I see where people are coming from I just think they're wrong.
People that think if I use ftl to go to Andromeda in an instant, somehow I am time traveling. They think because my lightcone reference changes, my time is changing. People make claims like this all the time. I can see why. That's what happens when something very complicated and mathematical is distilled to imprecise descriptions.

Harmless_Venom

You're a brainlet.

Suppose you have 3 planets, connected in relative space like this

O ----- O
~~\~~~|
~~~\~~|
~~~~\~|
~~~~~O

Now lets suppose we are on the bottom planet (Planet C). Now a fleet from the top right planet (Planet B) calls us and says it detected heretics on the top left planet (Planet A). A and C are 7 ly apart. B to C are 10 ly apart. B and C are also 10 ly apart:

O --10ly--- O
~~\~~~~~~|
~~~7ly~~10ly
~~~~\~~~~|
~~~~~~~~O

Message is sent from B to C

O ----- O
~~\~~~;
~~~\~~|
~~~~\~|
~~~~~O

O ----- O
~~\~~~|
~~~\~~;
~~~~\~|
~~~~~O

O ----- O
~~\~~~|
~~~\~~|
~~~~\~;
~~~~~O

We are now observing B from the day it sent the message 10 years ago when it detected heresy.. We reply, it will take 10 years to reach B:

O ----- O
~~\~~~|
~~~\~~|
~~~~\~;
~~~~~O

O ----- O
~~\~~~|
~~~\~~;
~~~~\~|
~~~~~O

O ----- O
~~\~~~;
~~~\~~|
~~~~\~|
~~~~~O

Order is confirmed, fleet at B travels to A in just under 10 years. The heretics were detected 20 years ago:

O ----oO
~~\~~~|
~~~\~~|
~~~~\~|
~~~~~O

O ---o-O
~~\~~~|
~~~\~~|
~~~~\~|
~~~~~O

O -o---O
~~\~~~|
~~~\~~|
~~~~\~|
~~~~~O

O o----O
~~\~~~|
~~~\~~|
~~~~\~|
~~~~~O

Pew pew:

X o----O
~~\~~~|
~~~\~~|
~~~~\~|
~~~~~O

The Emperor is proud. We are observing A through a telescope, but this light will take 7 years to reach us at C.

X x----O
~~x~~~|
~~~\~~|
~~~~\~|
~~~~~O

X xxx--O
~~x~~~|
~~~x~~|
~~~~\~|
~~~~~O

X xxxxxO
~~x~~~|
~~~x~~|
~~~~x~|
~~~~~O

We see Planet A destroyed 37 years after the heretics were first detected. Everything has a cause in this universe.

NOW RESTART IN A UNIVERSE WITH FTL:

B detects heresy. Decides to call us at C, but they use an Ansible which can send messages FTL.

Pew pew:

X o----O
~~\~~~|
~~~\~~|
~~~~\~|
~~~~~O

BUT NOW TRACK THE DAYS AS IT HAPPENS IN REAL SPACE:

X x----O
~~x~~~;
~~~\~~|
~~~~\~|
~~~~~O

X xxx--O
~~x~~~|
~~~x~~;
~~~~\~|
~~~~~O

X xxxxxO
~~x~~~|
~~~x~~;
~~~~x~|
~~~~~O

What happened? We were looking at planet A and blew 7 years before planet B ever detected heresy. From our perspective on C planet B would not detect for another 3 years on the day it sends the message, however A is already destroyed and the Emperor is not happy.

w8t4u

B tells C there are heretics on A via the ansible, C tells B to go get 'em. Then C looks at A through the telescope. The emporer knows A is going to bite it in 10 years and B will tell him about it when it happens via the ansible but he won't see the result for 17 years because it will take 10 years for B to get to A then 7 years for the photons of A's demise to get to C. This isn't hard.

massdebater

This just cements information transfer at c between reference frames.
No causality has been violated.
There is only confirmation lag.

how would a space empire with ftl ships keep society balanced?
Put your family in cryo a few months per year when you leave. Nobody has to see anyone else grow old

I mean we'll have cured ageing by then though

he's got it in his head that when he looks in a telescope at planet A, he's seeing what is happening at the precise moment on A when C is there asking for confirmation to blow A up which the way he's got it figured happened 7 years ago so he'll already have seen the explosion before he even talks to C. This is ludicrous but many people think this way.

PackManBrainlure

B. When B is going to blow A up. That's it. I'm jetpacking out of here. I will never understand why people struggle with something as simple as causality and independent light cones sharing the same absolute time reference. Peace.

Flameblow

The emporer knows A is going to bite it in 10 years
So the Emperor can see into the future? Causality being violated...

e won't see the result for 17 years because it will take 10 years for B to get to A then 7 years for the photons of A's demise to get to C.

No see, but it only take 7 years in this universe not 17 because of the communication and travel are instantaneous, B will get to A 3 after they've already blown it up. This is the fundamental problem.

takes2long

This is ludicrous but many people think this way.
By "many people" are you referring to everyone who understands the relativity postulates?

That example is literally an adaptation from Halliday, Walker, and Resnick's introductory physics textbook.

Idiot.

massdebater

independent light
The problem is you think "light" in a sense of trying to disconnect it with "information".

Skullbone

In the hyperion cantos.
Unless you were a roving barbarian on giant space rocks. The people that travelled ftl were usually very rich, very important, or on "military time"

And it was controlled by an AI that pretty much "melded" with the entire fabric of space time.

Flameblow

I will never understand why people struggle with something as simple as causality and independent light cones sharing the same absolute time reference
Because what you're describing is one of those pesky built-in human intuitions that, unfortunately, does not reflect reality at all. I don't know where you got the idea in your head that people are failing to account for the travel speed of light and think they're seeing images of "now." That has never been the case and nobody ever made that assumption. Relativity of simultaneity is simply a consequence of the Lorentz transformations, and any suggestion that FTL communication/travel does NOT violate causality is to suggest that the Lorentz transformations are invalid, which is a claim requiring massive substantiation considering how precisely it matches our empirical measurements.

This has nothing to do with assuming that you're seeing everything as it is right now. This is an effect you observe when you DO recognize that everything you see is an image of the past. When you accept that c is constant in all inertial reference frames (which is mind-blowing in and of itself so it can be forgiven if you have trouble wrapping your head around it -- even the smartest physicists in the world had trouble too -- but the data is inarguable) then this conclusion regarding causality is inescapable.

Spazyfool

So this is the power of being caged in reference frames.
I will put timestamps on the events instead of ASCII autism doodles.
I'm not actually counting in shit like leap years and such because it's irrelevant to the point

Mar. 24. 2018 - 16:00:00
Fleet orbiting planet B 10 light years away from planet A and planet C confirms heresy on planet A which is only 7 light years away from planet C.
Mar. 24. 2018 - 16:10:00
Fleet commander send Ansible message to planet C, requesting permission to exterminate planet A,
Mar. 24. 2018 - 16:20:00
Command on planet C authorizes exterminatus of planet A.
Mar. 24. 2018 - 16:30:00
Fleet orbiting planet B plots course for planet A and warps out.
Mar. 24. 2018 -16:30:01
Fleet exits warp in planet A's orbit
Mar. 30. 2018 - 00:00:00
All incantations and rituals have been completed. The fleet drops the hammer on the planet A, blowing it to smithereens.
Mar. 30. 2018 - 00:05:00
Fleet confirms mission completed with Planet C and Warps out.
Mar. 30. 2018 - 00:05:01
Fleet returns to planet B's orbit

Mar. 24. 2027 - 16:30:01
Observer on planet C sees a planet B's fleet warp IN near planet A, while also seeing same fleet just chilling above the planet B (because they did fuckall up to that point for decades)
Mar. 30. 2027 - 00:00:00
Observer on planet C sees planet A get BTFO
Mar. 30. 2027 - 00:05:00
Observer on planet C sees planet B's fleet warp out from former planet A's orbit
Mar. 24. 2030 - 16:30:00
Observer on planet C sees planet B's fleet warp out from planet B's orbit
Mar. 30. 2030 - 00:05:01
Observer on planet C sees planet B's fleet return to planet B's orbit.

Causality has NOT been violated in any way.
If you can't wrap your head around this, I sincerely pity you.

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TreeEater

Mar. 24. 2027 - 16:30:01
Observer on planet C sees a planet B's fleet warp IN near planet A, while also seeing same fleet just chilling above the planet B (because they did fuckall up to that point for decades)
And what CAUSED the fleet to warp in at A? When the fleet is still at B not having transmitted or received any messages from C yet?

Now replace the human fleet with something that might make it easier for you to understand. Such an explosion caused by a transmission with a blast wave that traveled to A. The blast wave arrived at A before you set off the explosion. Nothing set it off. Causality violated. Physics out the window.

Carnalpleasure

No, he just understands basic special relativity.
That's what happens when something very complicated and mathematical is distilled to imprecise descriptions.
The irony is that if you understood relativity on a mathematical level your confusion would melt away.
This is a semantic game semi-smart people play when they try to reduce complex hyperdimensional interactions into a 2d diagram with a few lines and words.
The ideas needed to understand this work just as well in 1+1 dimensions as in 3+1 dimensions -- again this is something you'd understand a lot better if you actually studied special relativity in full mathematical detail!

TurtleCat

This. It's not even that hard you literally only need trig.

Why don't you faggots just go read an introductory SR chapter instead of wasting time fantasizing about pop-science and pretending to be smart?

You confuse yourselves with your own arguments. Just study the math. It's simple.

Inmate

And what CAUSED the fleet to warp in at A?
the fucking ansible transmission which is not dependent on radio waves moving at 300,000km/s

Poker_Star

the fucking ansible transmission which is not dependent on radio waves moving at 300,000km/s
But you can clearly fucking see the ship at B just chilling in the docks. They haven't made the transmission yet, they haven't left you. They won't for another 3 years.

See Mar. 24. 2018 - 16:10:00
Fleet commander send Ansible message to planet C, requesting permission to exterminate planet A,
Mar. 24. 2018 - 16:20:00
Command on planet C authorizes exterminatus of planet A.
Mar. 24. 2018 - 16:30:00
Fleet orbiting planet B plots course for planet A and warps out.

They warped out in 20 minutes after the transmission.

So this is what the universe from C's perspective is:

Fleet bombs the fuck out of Planet A. 3 years later the fleet is ordered to bom planet A.

Clearly the causality is reversed.

TreeEater

Also consider this.

After bombing A the fleet now has to fly back to B.

They warped out and warped in B to find themselves there. They won't leave for another 3 years. Now there are two fleets.

Can you see why your universe is fucked?

This is why you have the speed limit.

Skullbone

But you can clearly fucking see the ship at B just chilling in the docks. They haven't made the transmission yet, they haven't left you. They won't for another 3 years.
Are you retarded?
Are you actually fucking retarded?
You just see their image. It's jut fucking photons.
Because the light that bounced off their ships took 10 years to get to you from planet B, but only 7 years, from planet A.
This is not fucking time travel.
This is literally just light catching up with superluminal object, like sound has to catch up with supersonic aircraft.

If you stood on a landing pad and an ftl ship just warped in you would see it pop in out of nowhere and then you would see its afterimage shoot off at 300,000km/s, because that's the light the ship reflected on its way here, that just began to arrive.

Firespawn

You just see their image. It's jut fucking photons.
Image

Who said I was reading UV-VIS photons you fucking retard? Maybe I'm using gravitic sensors?

See

I'm reporting your posts. This kind of child-like stupitidy should be banned from Veeky Forums.

SniperGod

if you could travel faster than light you would just become dark matter / dark energy. and most likely separate yourself from the visible universe for ethical reasons.

TurtleCat

gravity also propagates at speed of light
and nowhere in that scenario did anyone go into the fucking past
The events played out in the span of 7 days
You are just detecting them in wonky order, but cannot interfere with them, because they happened a fucking decade ago

Fuzzy_Logic

You are just detecting them in wonky order,
You just experience the universe in a nonsensical way, that doesn't mean the universe is nonsensical or that the laws of physics have changed.

Even you agree that photons are energy right? We see 2 fleets. Therefore twice the amount of energy as before. Repeat the warp travelling order an infinite amount of times for an infinite amount of energy.

Your arguments are le troll physics comic tier.

Redraw the same scenario in a small scale experiment with C being the physicist as an observer. You've changed the laws of physics by violating causality.

Now go to bed.

Soft_member

We see 2 fleets. Therefore twice the amount of energy as before. Repeat the warp travelling order an infinite amount of times for an infinite amount of energy.

What the fuck are you smoking?
The fleet was NEVER at two places at the same time.
The progression of event was LINEAR.
You see it at two places at the same time, because one reflection is three years older than the other.
They have nothing to do with each other. That cannot physically be TWICE the energy.
Calm the fuck down and reflect on what you just proposed here.

cum2soon

The fleet was NEVER at two places at the same time.

You said yourself we see it at A and B at the same time. We see it at A it has to travel back to B. It can't wait there for 3 years because in no scenario does it wait there. It has to travel back (thought warp) to B.

And again the fleet has to stay at B for another 3 years before it can leave to A (which we have already seen).

We can keep doing this and you'll run into more and more causality violations.

You're the only one thinking linearly here, and you think that way because you've never studied SR and realized your thinking is contradictory. Reality can't work the way you think it does, because if it did there would constantly be causality violations.

New_Cliche

You said yourself we see it at A and B at the same time
yea, we see reflections of events which took place second apart, but the light arrives 3 years apart
nothing is violated

Techpill

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Carnalpleasure

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Inmate

Yes. If you could travel faster than light, you could go (or at least send information) into the past.
It's not a paradox because the initially assumption ("if you could go faster than light") isn't possible.

Protip: Movies aren't real. "Interstellar" hired a genuine expert in Relativity (since then, he's become a Nobel Prize winner) as a consultant. He told them that the part about going backwards in time though a black hole was total bullshit. The director thanked him for his input and went ahead and did it anyway.

SomethingNew

You never see it mentioned in sci-fi movies, people fly around space in ftl but everyone stays the same age no matter what.

uhhh have you not seen Interstellar? Also see Forever War

ok not ftl but time dilation is acknowledged

Nude_Bikergirl

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Playboyize

You can't throw out relativistic effects because then you throw out causality.
This is wrong and stupid. I can barely even guess at how you misunderstand it this badly.

The predictions coming from relativity and the experimental confirmation of relativity don't *require* the lack of a preferred frame of reference, they only *allow* it. With relativity, you can pick an inertial reference frame and treat it as the only one from which you can make objectively correct observations, and you would never have any problems with the predictions matching reality. That's the whole point: you can do this, and you can do it for more than one frame, therefore we can't single one out from isolated measurements.

The most likely consequence of discovering a means of faster-than-light communication or travel is the discovery of a preferred frame of reference, most likely the one stationary relative to the cosmic background radiation. While the laws of physics on their own haven't provided us a clear choice for a universally-applicable best frame of reference, nature a whole certainly has, with this pervasive radiation seemingly coming from everynothing.

so for a blind civilization that discovers travel faster than the speed of sound, it proves that supersonic aircraft are going backwards in time because you hear their in-flight megaphone transmissions backwards

Snarelure

Time moves one way and that's into the future
This implies uniqueness to the present which is contrary to every observation of symmetry and non locality in the history of science. So no, it is overwhelmingly unlikely this is correct.
there's no such thing as ftl and never will be.
Meanwhile there are multiple galaxies moving away from us at super luminal speeds, thus proving it is in fact possible.

WebTool

it proves that supersonic aircraft are going backwards in time because you hear their in-flight megaphone transmissions backward
wait what?

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FastChef

This is some good shit, thanks man.

Skullbone

Can you make a phone call while treavling faster than light or does that violate some law about information going faster than light?

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RumChicken

YOU GOOFED! THE TWIN PARADOX OCCURS WITHOUT FASTER THAN LIGHT TRAVEL!! YOU JUST NEED TO BE GOING AT AN APPRECIABLE FRACTION OF THE SPEED OF LIGHT!

whereismyname

I understand the secrets of the universe guise!!1

girlDog

Unless your communication method is preferably much faster than your transport method, you won't be skyping your grandma from an FTL ship with EM waves.
Those you emit up front will fall behind, so that you arrive before your own signal, and nothing EM will catch up to you from behind.
A close enough driveby could work for a Hello! Hi! kind of greeting maybe.

massdebater

Sure why not.

You're moving at 2c towards Earth. You're currently one light-year away and so predict you will reach Earth in 6 months. You call Earth and say "I'll be there soon!"

In your frame of reference, you are stationary and Earth is moving towards you at 2c. The phone call leaves your ship and progresses towards Earth at c. Four months later, you calculate that your message (moving away at c) is 4 light-months ahead of you and Earth (moving towards you at 2c) is 8 light-months closer to you -- the call has finally arrived!

At this point you are 4 light-months away from Earth. You will arrive in 2 months. Pleased that you were patient and didn't hang up the phone, you wonder how long you'll have to wait for their response. You become a little disappointed after doing some quick calculations, realizing that you won't hear what they have to say until two months after you arrive! This is because Earth is moving towards you faster than their response, which will be 2 light-months behind them by the time you land.

After two months of silence, without hanging up the phone, you finally arrive at Earth. You turn off your magic FTL drive and join Earth's frame of reference. Everyone enjoys some steak and mashed potatoes and shares stories of impossible physics thought experiments.

Two months go by, and loud and clear you hear your friend exclaiming through your earpiece: "Great! We can't wait!" -- the response finally caught up to you! You hang up. Call complete.

Four months later, while you're all sitting together watching TV, your friend's phone rings. You're sitting close enough to hear your own voice announcing your impending arrival. Your friend is not confused at all by this; it's exactly what he expected would happen for the call you made a year ago from a light-year away. Your friend responds "I know! You're already here!" smiling at you as he hangs up.

You briefly share his amusement before it gives way to horror: but who was phone?

Emberburn

You're moving at 2c towards Earth
In your frame of reference, you are stationary and Earth is moving towards you at 2c. The phone call leaves your ship and progresses towards Earth at c
Four months later, you calculate that your message (moving away at c) is 4 light-months ahead of you
WHAT?

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VisualMaster

The speed of light is the same for all observers, user. That's kind of the whole underpinning of special relativity.

After all, let's say FTL travel exists. Something somewhere in this vast universe must be moving faster than light right now. That means you and I are moving faster than light relative to some distant observer at this very moment, but the fact that we're able to post like this and the internet still works is convincing evidence that we aren't having any trouble with waiting for light to catch up.

DeathDog

supersonic aircraft are going backwards in time
If the speed of sound was constant in all inertial reference frames then yeah, this would indeed be a true statement.

Fortunately reality isn't quite THAT weird. Unlike what we observe with electromagnetic waves, you will indeed measure the speed of a sound wave relative to you depends on your speed relative to the material in which the wave is propagating. Light on the other hand does NOT have this property. If you accelerate to 99% light speed you will NOT observe that photons are moving away from you any slower than before nor towards you any faster.

but who was phone?
implying the self-consistency principle won't come into play and your friend didn't jokingly respond that he can't wait even though you were already there
Paradox solved. Go tell grandpa. In all seriousness I'm sure some really weird shit happens during that whole 'accelerate to join earth's frame of reference' step that was glossed over. Though I guess that depends on the type of travel too, since something crazy like the Alcubierre drive wouldn't necessarily work by acceleration in the first place.

JunkTop

The speed of light is the same for all observers, user
this has literally nothing to do with proposing that 1c message is speeding ahead of a 2c spaceship, this is against fucking logic
YOU are moving at 2c towards earth
what you see has fuckall to do with what is happening

Supergrass

this has literally nothing to do with proposing that 1c message is speeding ahead of a 2c spaceship, this is against fucking logic
No shit, this is why FTL travel or communication is impossible in the first place, because allowing it defies all logic. No matter how fast Earth measures you to be moving, YOU are still stationary. The laws of physics don't suddenly change for you just because an observer in another reference frame decided that you're moving at some given speed. You don't even need weird physics to understand that, this is fucking Galilean relativity we're talking about now.

No shit, this is why FTL travel or communication is impossible in the first place, because allowing it defies all logic
It DOES work, we can see it happening right now.
It just doesn't include shooting particles out of your ass to propel yourself.
If there is a way to facilitate FTL, it will be through contracting space in front of you.
Under no circumstances will a photon that hits you while doing this just reflect and reach anything ahead of you.

Soft_member

stop replying to him hes retarded, im annoyed just reading his brainlet replies

cum2soon

c is c>c
wat?

c isn't 300,000km/s

Playboyize

Firespawn

It's 299,792,458 m/s
So sue us.

Alcubierre found a perfectly valid solution to the Einstein equation but even he acknowledges that it's likely not physically possible.

Ever consider the consequences of such a drive, even if it was SLOWER than light?

Spaceship passes Earth at a relative velocity of 0.5 cee. Pilot and ground synchronize clocks at that instant. Who's moving? Doesn't matter. BOTH sides see the other's clock running slow. No preferred inertial frame.
Ship travels out 1 lightyear, then reverses course and heads back towards Earth. Doesn't matter if the reversal is made using rockets (which the pilot feels) or by hairpinning around a neutron star (which the pilot doesn't feel.)
As the ship passes Earth (still at 0.5 cee, but in the opposite direction now) for the second time, we can compare clocks. The pilot has aged less. Correct?

<continued>

LuckyDusty

Now, lets call the ship's initial movement as going LEFT and then he goes RIGHT on the return to Earth.

Rerun the experiment but, instead of turning around (and changing inertial frames), the pilot turns on the near-hyperdrive which takes him RIGHT at 0.9 cee. 0.9 cee measured in which reference frame? Relative to the Earth? Why should Earth matter? Relative to his motion at the instant before he turned the near-hyperdrive on? Seems more likely.
Whichever, he'll be moving towards Earth again. We can argue about whether an Earth observer would see him going 0.9 or 0.4 cee, but he's definitely going RIGHT.
After passing Earth, he turns off the near-hyperdrive and resumes his "kinetic" velocity -- which takes his past Earth again at 0.5 cee LEFTwards. Clocks can be compared.
How much has the pilot aged? If he's younger that means he's changed inertial frames (twice!) and undergone time-dilation. And if you experience Relativistic effects while going slower-than-light, the FTL is certainly impossible.
If he's NOT younger then General Relativity didn't apply. Only Special Relativity. Which brings back the Twin Paradox, only this time we don't have the "out" of acceleration.

So I don't see the Alcubierre Drive (or hyperspace or subspace or whatever) enabling us to avoid causal paradoxes.

Soft_member

ITT: People who have studied SR vs. people who haven't

haveahappyday

Under no circumstances will a photon that hits you while doing this just reflect and reach anything ahead of you.
It would, actually, it just wouldn't get very far. More accurately, it'd wouldn't exit the front of the bubble of spacetime that's carrying you, but you wouldn't notice anything wrong with your flashlights inside the ship no matter which direction you point them.

Crazy_Nice

Yeah, anything ahead of you, as in, reaching earth months before you.
I'm actually interested if this would accumulate a glowing ball of light in the cavity or not.
and also how would photons in rapidly expanding space behind the ship behave.

Spamalot

Yeah, anything ahead of you, as in, reaching earth months before you.
Right, that example was one where a ship moves through space at 2c relative to Earth, which would indeed observe that to be the case among many other impossible and broken things because there is no sensible FTL reference frame.

PurpleCharger

Funny story.
L. Ron Hubbard (who was a middlin' SF writer before discovering he could make a lot more money conning people with his inane "religion") wrote a novel about interstellar commerce in ships which traveled at near light-speed. Centuries passed on Earth during voyages which took a few months ship-time. This was about 1950.
Hubbard claimed he was one of only half-a-dozen people in the world who understood Einstein. Hubbard lied about himself routinely (including his military service. By his own telling, he was a great leader. By the Navy's record, he was removed for incompetence.)

Anyway, in the book, EVERYTHING is wrong! The ship's "speedometer" is a light projector pointed forward. When too many photons come back and hit them in the face, they know they're getting "too close" to lightspeed. Then they have to use retro-rockets to slow or risk actually attaining lightspeed and getting stuck there for Eternity in Time Zero -- or passing lightspeed and exploding into pure energy.

likme

With warp tech that wouldn't happen. It's not like you're actually going faster and time is therefore slowing down, it's more like you jump from place to place without a delay.

Booteefool

But if that's possible, so is backwards time travel.

likme

You're the one who doesn't understand Relativity.

If there WAS a preferred frame, Maxwell's equations become garbage. They predict a constant speed of light regardless of the motion of the source or the observer.

A preferred reference frame would also louse up all the conservation laws.

You don't realize just how interdependent all of physics is. You're not the first (not even the first on Veeky Forums) to propose the CMB is the preferred frame.
It doesn't work. Every galaxy (except for minor motions. like the way we and Andromeda are drifting together) sees itself stationary with respect to the CMB.
Wouldn't it be awfully coincidental that, out of all the billions and billions of galaxies, WE happened to be the only one without a major Doppler shift as we look at the CMB in all directions? Galaxy 45743857097, five billion light years from here and receding at quite a clip, sees exactly what we see.

RavySnake

The Risen Empire books have an aristocratic caste that travels around in relativistic pilgrimages to prolong their already-long lives.

Nude_Bikergirl

Not all magic space drives are the same, you know. I don't remember people experiencing relativistic effects in the moving space bubble.

Ignoramus

Because they change physics. Because FTL is equivalent to a "go back in time machine" in general relativity, every fiction with FTL has to posit alternative physics where FTL is possible without obvious temporal paradoxes.

Need_TLC

AFAIK, there are ways to permit FTL, in a way consistent with known observations and GR, that also avoid causality violations.

For example, FTL jumps are permitted, but only short jumps, and only from the co-moving "frame", e.g. a frame that is at rest relative to the observer's current CMB observations, as the user above implied. It's not exactly a single preferred frame, but it does suggest that some frames are more special than others. It's quite easy to do this, mathematically.

Poker_Star

implying aging won't be cured long before space empires become a reality

sens.org/

Attached: 2b9d0cf8-edac-11e6-930f-061b01e23655.jpg (596 KB, 2048x1152)

Methshot

Holy shit this user knows just enough to say the biggest idiocies possible.
You're right up at the top of mount stupid.

Evil_kitten

If I understand you correctly, there's a preferred frame at any single location. It may change galaxy to galaxy, but only short jumps are permitted so that's irrelevant. All sounds very artificial, but lets go with it.

Ship maneuvers until it's "at rest" with respect to the CMB. Captain hits the Jump button and they're a light year away, with the exact same motion-vector.
What happens if they're not PRECISELY "at rest"? 1 km/hr "off"? The drive no longer works? Or it works, but it's no longer instantaneous? You start arriving at the destination earlier or later than ship B, which jumped at the same time from the same place but WAS at rest.

You have to think about such "limiting" cases. Do infinitesimal changes make a difference? To make an analogy, Aristotle thought heavy objects fall faster than light ones. What happens if you glue a pebble to a boulder? Does the combo fall faster or slower than the boulder alone? What if the masses are only tied together with rope? With a long thread?
At some point you run into a paradox -- a discontinuity in the "physics" -- UNLESS you assume all objects accelerate at the same rate.

I'm basically describing the standard fiction trope Star Trek Hyperspace. All FTL travel happens relative to the co-moving frame. Don't think about it in terms of instantaneous jumping, but in terms of moving through a special series of inertial frames, e.g. "hyperspace". It's really not that hard to imagine - and seemingly you're not trying very hard. Give it a chance.

Gigastrength

You are correct. The Alcubierre Drive is supposed to evade relativistic effects.

But that leaves us with the Twin Paradox described in . I've drawn a diagram in an attempt to make it clearer. Solid lines are paths taken at, say, half lightspeed.
Clocks can be compared whenever the ship passes Earth, at A C D and G. At each of those points all observers see the "other guy's" clock running slow. At C and G they can compare the elapsed time since the previous pass.
The dotted line from E to F is traversed in Alcubierre drive.

If anyone out there is a genuine authority on Relativistic physics, I'd appreciate them chiming in. I'd really like to know the solution.
Anyone invoking aether, denying Relativity, or claiming space and/or time don't exist -- please be quiet.

Snarelure

I'd love to cruise the galaxy. I don't lack imagination and I've probably read more SF than 99% of present company. But no one in a century of trying has found a consistent alternative. I'll give Alcubierre a "maybe" if someone can resolve the seeming paradox in

Firespawn

The so-called Twin paradox is the name for the difficulty that many people have understanding the predictions of relativity, and particularly the standard two twin rocket scenario. In short, the twin that goes on the rocket and returns to Earth will be younger than the twin that stayed on Earth.
Again, there's nothing inconsistent or contradictory here. It's just called a paradox because some people find it hard to understand.

Second, Alcubierre warp drive, warpholes, etc., don't solve the fundamental problem that any FTL machine is also a "go back in time" machine under relativity. This statement is simply true no matter how you achieve FTL, including schemes that pretend to not be FTL by bending / folding space.

So, assuming that "go back in time" machines are impossible, and if we can FTL, that means it must be according to some other physics.

For example, the simplest physics would be to imagine something like hyperspace - a series of frames relative-to-which FTL trips are made. Remember, in order for a FTL machine to be a "go back in time" machine, it must be possible to go between spatial points A and B at FTL in different frames. The hyperspace idea is the simplest alternative physics that simply says "no no, there's a series of special frames for FTL, and you cannot choose any other frame for FTL, and therefore no go-back-in-time nonsense".

So
What sort of problem do you see, exactly? Are you sure that you understand the twin "paradox" of standard relativity, and how it's not about anything self-contradictory? What sort of problem do you see for FTL in the simple hyperspace approach?

The Twin Paradox is only an APPARENT paradox in Special Relativity. General Relativity "solves" it because turning around to return to Earth for a 2nd clock comparison introduces an asymmetry.
Either the ship changes inertial-frames using its rockets, or it dives deep into a gravity-well to swing around.

The ship in the lower part of 's image does neither of those. It "circles back" though hyperspace (or whatever).
The "distortion" which occurs at the turnaround has vanished -- and with it, the reason that the TP is only apparent.

Either going into (or coming out of) hyperspace causes effects analogous to "changing direction" in normal space -- or the TP is real. The clocks ticked at different rates yet they still match when compared a second time.
That's real and measurable no matter how FTL works -- UNLESS there's Newtonian absolute space and time (your CMB "preferred" frame.) If such exists, FTL experiments could determine it.

Even if that doesn't bother you, it means that the laws of physics depend on motion relative to that Absolute frame. As I said earlier, all the conservation laws (momentum. energy, etc.) are valid only if there is no such dependence. Might as well re-introduce phlogiston while we're revising physics..

I mean, you apparently agree that FTL = backwards time travel "unless it's according to some other physics." I'm just re-iterating that no one has thought of "other physics" which doesn't conflict at some point with known experiments. If the universe is sane, if must be consistent.

Crazy_Nice

it means that the laws of physics depend on motion relative to that Absolute frame.
That is the model that I described, yes. Also, it does bother me. I just posited it as a model. I'm not endorsing the model as real. My belief is that FTL is impossible.

which doesn't conflict at some point with known experiments
I'm unaware of any specific observation which specifically contradicts the hyperspace model. At best, you can say that it's inelegant, and contrary to Occam's razor, but that's about it. What experiments do you have that explicitly contradict the (silly) hyperspace model?

Inmate

We seem to be on the same page now, mostly.
I am unaware of any experimental proof that hyperspace doesn't exist. Only pointing out that, if it does and permitted FTL, there'd be consequences SF usually ignores.

Leaving "normal space" (or our "brane" if string theory is right) is supposed to be impossible since open strings (protons, neutrons, etc.) have their ends stuck firmly in our reality.

From a Relativistic perspective, space and time can be "stretched" but "cutting" is specifically prohibited". The theory breaks down at an "edge" of infinite curvature.

We often analogize higher dimension by using Flatland. A paper sheet can be folded so a Flatlander can take an Einstein-Rosen shortcut between distant points. This is flawed, Flatlanders do not glide around on the "surface" of their world. They are IN the plane, like ink soaked into paper. We 3D beings cannot lift a Flatlander off the surface.
We can fold his world so different points on the paper come into contact, but he still can't Jump across. The surfaces may touch across a limited area, but they are still distinct. We'd need to "squeeze" the paper until the planes inter-penetrated. That changes the basic geometry and introduces topological discontinuities.

SniperWish

there'd be consequences SF usually ignores.
Agreed.

farquit

Good.
I was still hoping someone could resolve the apparent conflict in

Wikipedia says Alcubierre himself acknowledges his concept permits time travel
en.wikipedia.org/wiki/Alcubierre_drive
and references his paper
ccrg.rit.edu/files/FasterThanLight.pdf

Therefore, IF warpdrive is possible (and someone solves the engineering problems) we have to explain why no one from the future has visited with plans for the Drive (and the practical fusion reactor, the impenetrable force shield, the quantum computer, and copies of next year's Wall Street Journal.) Unlike Kip Thorne's "traveling wormhole", a warpship can go back to a point prior to its construction.

PS: I've read upsetting stories where no one visits from the Future because there IS no Future. Something or other annihilates the entire cosmos. Sometimes that "something" is the maiden flight of the first FTL craft.

Lord_Tryzalot

If a spaceship emits a photon, that photon recedes from the ship at c, no matter the speed of the ship.

Playboyize

Nah because if you were going true ftl you'd be moving back in time. Checkmate fag!

girlDog

the time dilation formula is

sqrt( (1- (v^2/c^2))), so at v=c, time passes at sqrt(0), or zero. This would be one of the problems to surpass, because to go FTL, you would have to spend zero time at v=c.
But also, when you plug in FTL velocities, your time isn't negative, it's square root of a negative - whatever that would be timewise.

BlogWobbles

In fiction, just say wormholes, or hyperspace / subspace, or something.