Page 137: Adieu SG-51

[Victor_D]

(I wonder, Arioch, if you had given some thought to possible causality violations brought about by the existence of FTL; in a large part, these violations become far less likely if no FTL communications and no "free" FTL travel exists)

The system is constructed so that causal violations are essentially impossible. The entry and exit points of the jump are light years apart, so even if you did end up going backwards in time a fraction of a second, no one would notice.

That's what I thought, thanks It's great when sci-fi authors don't just handwave this stuff but cleverly work around it.

In fact, it makes the scenario even more WW1-like; forces on the fronts of the Great War were also greatly hampered by the primitive communications infrastructure, which showed especially during major offensives. Albeit, it mosty favoured the defender, whereas here it actually helps the attacker.

I'd say even worse than that; you could still send a message from the front lines back to London within a couple of hours if the lines hadn't been broken by artillery, rain, or clumsy soldiers (not quickly enough during battle, however). Outsider combat seems more akin to 19th Century Naval combat when the best messaging you had was semaphore flags and light shutters. Captains and Commanders were essentially left up to their own devices on how to achieve the Empires goals once they left harbour.

Pretty much yes, although I prefer land-war analogies here due to the static nature of strategic combat in Outsider. They have the "pony express" network of couriers so they can ask for general orders, but the commanders in field must by necessity have the authority to respond as they see fit. I think their "communication speed" is about 10 systems per day, so waiting for the Emperor to issue an order to retreat or commit reserves is not an option.

Funnily, this is why later Roman emperors preferred to stay closer to the frontiers...

Eek. This is gonna get messy. This is what happens when the enemy has a massive numbers advantage and is attacking along a wide front.

Someone in an earlier post said it was like the Soviets going on the full offensive against the Germans in the east during WW2 in the final phases of the war - that seems a particularly apt metaphor. The war might not be over, but it's a good metaphor.

I think that was I. The Loroi seem to be totally surprised; it reminds me of operation Bagration where the Loroi are the poor Army Group Centre about to be wiped out.

[SVlad]

(I wonder, Arioch, if you had given some thought to possible causality violations brought about by the existence of FTL; in a large part, these violations become far less likely if no FTL communications and no "free" FTL travel exists)

I've read a Russian science fiction book where author thought about this aspect. According to his calculations jump shouldn't be instant for outsider, but must take some delay to not allow to travel back in time. This delay is mostly defined by relative speed of stars, so for nearby stars delay would be marginal and constant. It shouldn't make any difference for any practical application.
Reference to book's wiki page about jump drive (in Russian):
http://www.spacians.net/wiki?name=Скачковый+двигатель
Looks like local parser is confused by Cyrillic letters in URLs.

[Arioch]

(I wonder, Arioch, if you had given some thought to possible causality violations brought about by the existence of FTL; in a large part, these violations become far less likely if no FTL communications and no "free" FTL travel exists)

I've read a Russian science fiction book where author thought about this aspect. According to his calculations jump shouldn't be instant for outsider, but must take some delay to not allow to travel back in time. This delay is mostly defined by relative speed of stars, so for nearby stars delay would be marginal and constant. It shouldn't make any difference for any practical application.
Reference to book's wiki page about jump drive (in Russian):
http://www.spacians.net/wiki?name=Скачковый+двигатель
Looks like local parser is confused by Cyrillic letters in URLs.

Yes, the jump is not instantaneous.

[saint of m]

I love how Alex is panicing, Talon is swearing up a storm because she's doing everything she can not to panic, and the cruiser captains are treating this like a game of starcraft. Seriously, I am almost expecting one of the captains to yell out GG.

[Nathan_]

(I wonder, Arioch, if you had given some thought to possible causality violations brought about by the existence of FTL; in a large part, these violations become far less likely if no FTL communications and no "free" FTL travel exists)

The system is constructed so that causal violations are essentially impossible. The entry and exit points of the jump are light years apart, so even if you did end up going backwards in time a fraction of a second, no one would notice.

While it isn't time travel, it is still a causal violation since the ship arrives long before the light of the ship making the jump gets to where it is. Whether this can be exploited to cause any wierdness is another matter.

[Victor_D]

(I wonder, Arioch, if you had given some thought to possible causality violations brought about by the existence of FTL; in a large part, these violations become far less likely if no FTL communications and no "free" FTL travel exists)

The system is constructed so that causal violations are essentially impossible. The entry and exit points of the jump are light years apart, so even if you did end up going backwards in time a fraction of a second, no one would notice.

While it isn't time travel, it is still a causal violation since the ship arrives long before the light of the ship making the jump gets to where it is. Whether this can be exploited to cause any wierdness is another matter.

It breaks relativity as all FTL must; my question was aimed at whether or not the Outsider-verse FTL is exploitable as something that can cause serious paradoxes relevant for the characters. As far as I am aware, all these schemes showing FTL completely breaking sanity by producing unsolvable paradoxes are predicated on the existence of effective FTL communication (which Outsider doesn't have) and unlimited FTL (in the sense that you can travel arbitrarily, like, say, with warp drive in Star Trek). Even then, they usually need to involve a ship moving at relativistic velocities for time paradoxes to occur when this ship perceives effect preceding the cause and communicating this via FTL communication.

In Outsider, a ship moving at relativistic speeds in relation to local space (say, the Leido-Sala theatre) may perceive significant causality violations occurring all around, but it has no means of communicating anything it sees back to base in time to make a difference, hence why this cannot be used e.g. to warn the Loroi fleet of Umiak invasion before it happens and cause other kinds of weirdness.

[boldilocks]

*fffffffffff-

[Werra]

A good indicator usually is whether Arioch has posted a WiP.

Oh well, I'm looking forward to the double update next week.

[Askaris]

"Do not my friends, become addicted to weekly updates! They will take hold of you, and you will resent their absence!"

[Chekist_Felix]

"Do not my friends, become addicted to weekly updates! They will take hold of you, and you will resent their absence!"

Today were hauling Aqua cola! Immortan Jim!

[Random Person]

It breaks relativity as all FTL must; my question was aimed at whether or not the Outsider-verse FTL is exploitable as something that can cause serious paradoxes relevant for the characters. As far as I am aware, all these schemes showing FTL completely breaking sanity by producing unsolvable paradoxes are predicated on the existence of effective FTL communication (which Outsider doesn't have) and unlimited FTL (in the sense that you can travel arbitrarily, like, say, with warp drive in Star Trek). Even then, they usually need to involve a ship moving at relativistic velocities for time paradoxes to occur when this ship perceives effect preceding the cause and communicating this via FTL communication.

In Outsider, a ship moving at relativistic speeds in relation to local space (say, the Leido-Sala theatre) may perceive significant causality violations occurring all around, but it has no means of communicating anything it sees back to base in time to make a difference, hence why this cannot be used e.g. to warn the Loroi fleet of Umiak invasion before it happens and cause other kinds of weirdness.

The old saying is "FTL, Relativity, Causality, pick two." It's relativity that introduces the causality issues. The FTL scheme in Outsider isn't anything special in that regard. "Unlimited FTL" as you call it is not required to violate Causality if Relativity holds. A loop of fixed wormholes is enough.

FTL travel is FTL communication, unless the FTL travel does something like scramble everything into completely random stuff, in which case it's kind of useless as a method of travel.

*fffffffffff-

*waves cane* I still consider a year with a single update to be a good year. Having stuck around here for well over a decade, through the Great Hiatus, I have been Pavlovianly conditioned to always be pleasantly surprised when Outsider updates.

[Werra]

How does FTL as it works in Outsider break causality?

[entity2636]

I suppose you can see your past self or receive radio transmissions from your past self, but that's about it.

If you do a hyperspace jump into another star system, say, 5 LY away, and after 5 years look at your origin system with a powerful enough telescope, you will see your ship as it is about to jump. Same way you will be able to receive any radio transmission your past self sent out if it's strong enough and aimed correctly. Not sure if that counts as a causality violation, but it definitely is a form of weird FTL side effects.

[Werra]

That can't be it. Then going supersonic and allowing the sound to catch up would also violate causality.

[Arioch]

Seeing yourself through a telescope 5 years ago does not break causality in any meaningful way. Causality is broken when you can see events from the future or influence events in the past.

Technically, any faster than light travel through spacetime breaks causality because the speed of light is actually the speed of causality within spacetime. However, this doesn't mean it's impossible for two objects to move relative to each other faster than light; in fact, the current theory of of the Big Bang (specifically, Inflation theory) requires that spacetime itself expanded much faster than the speed of light in the early fractions of a second after the Big Bang. Faster than light travel within the confines of flat spacetime is impossible, but you can travel faster than light away from another object if the spacetime itself between you stretches faster than light (as in cosmic inflation), or if you locally warp spacetime (as in an Alcubierre warp drive or a wormhole), or if you leave spacetime altogether (as in hyperdrive or jump/fold drive).

The problems for causality happen when you pair relativistic velocities with some sort of instantaneous communication or teleportation. For example, if you have two locations connected by an ansible which can communicate instantaneously, and one location is aboard a ship that is traveling at a high fraction of the speed of light, then the two points experience different rates of time despite being in communication with each other, and potential causal hijinx ensue. However, the way jump drive in Outsider works avoids such problems. Travel through hyperspace is not instantaneous, and ships in hyperspace do not experience extreme time dilation, and ships in hyperspace are blind to events in real spacetime, and the endpoints of the jump are so far away that there can be no meaningful causal interactions between them on the time scales of the jump.

And no, there's nothing unique about this FTL scheme.

[icekatze]

hi hi

The issue with FTL travel and causality is in large part because of the phenomenon in relativity that is commonly described as, "Simultaneity is Observer Dependent."

The way FTL works in Outsider does a pretty good job of avoiding paradoxes. Even though it might still be possible in some extreme cases, as long as the time it takes to complete a jump increases as the relative velocity and/or distance between start point and end point increases, then it should at least be impossible to create a paradox at the tech level of the current civilizations. (Not counting telepathy, which does not follow the FTL rules.)

If you take for example, a jump between Sol and Barnard's Star, the jump would need to take about 2.11 seconds, to prevent the possibility of a ship jumping one way, sending a message to a ship on the other side, and having that ship immediately jump back prior to the first ship's departure.

SpoilerShow

The minimum distance that you could jump instantly to another object, send them a message via laser, have them jump instantly to your start point, and send a message via laser, without risking a paradox, in a two reference frame model, is = (y-1)*distance between the two. Where y = 1/Sqrt(1-(Velocity_difference^2/Speed_light^2))

Barnard's Star is 5.958 light years away, and traveling at 142.6 km/s relative to Sol, for example.

We can derive from this the amount of time it would take a laser to bridge the distance as the amount of time the jump would need to take in order to jump directly to the object without risking a paradox.

[Contraltissimo]

Hi. I don't know if there were forums the last time I dropped you a line....

The snooty dark-blue-haired one with the twisty-plaits.... she forgot to switch her suit to nightlight-mode at the bottom of the page.

[Arioch]

Hi. I don't know if there were forums the last time I dropped you a line....

The snooty dark-blue-haired one with the twisty-plaits.... she forgot to switch her suit to nightlight-mode at the bottom of the page.

So I did, thanks. Should be fixed.

[RedDwarfIV]

I'd argued with people over similar complaints, and never got a satisfactory answer.

According to the argument, all FTL travel breaks the universe.

My view: A paradox requires that you go backwards in time. If all frames of reference (start point, starship, and destination) are moving forwards in time, then there is no way for a warp drive starship to go to another star system, return to its point of origin, and have arrived before it left.

ProjectRho gives the example of a relativistic ship going between Earth and Proxima Centauri. Earth sends Proxima a message by FTL comms. The relativistic ship sees the message arrive at Proxima before it is sent from Earth. Fine, that looks kind of weird.

But then it says:

if the ship had a FTL phone set up in the right way, they could call Earth before Earth placed the call.

I don't get it. They see the call arrive. The FTL phone doesn't send messages backwards.

This is what I'm imagining:

SpoilerShow

This is what they're saying:

SpoilerShow

I can see how the second one might be right if the FTL communicator was near instantaneous, as the earth-proxima line suggests... but how does an FTL drive that goes at a certain speed relative to the universe fit into that?

Say the relativistic ship sees the message, powers up a warp drive and decides to go to Earth. Why does that result in it arriving before the message left, if its all going forwards?




2:30 AM is way too late at night for me to be thinking about time travel.

[icekatze]

hi hi

certain speed relative to the universe

This is sort of the point, there is no universal constant, no privileged reference frame, every reference point is relative to every other reference point. There is no universal "now." What is happening right now, from one person's perspective, could be happening a week ago, from someone else's perspective in a different reference frame.

Relativity of simultaneity is something that science has tested extensively, and has very solid evidence.

Say the relativistic ship sees the message, powers up a warp drive and decides to go to Earth. Why does that result in it arriving before the message left, if its all going forwards?

From the relativistic ship's point of view, it is going to Earth "now," for it's definition of "now," but the message it received hasn't been sent yet, in it's frame of reference.