Page 137: Adieu SG-51

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Victor_D
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Re: Page 137: Adieu SG-51

Post by Victor_D »

Nathan_ wrote:
Arioch wrote:
Victor_D wrote:(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.

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Re: Page 137: Adieu SG-51

Post by boldilocks »

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Werra
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Re: Page 137: Adieu SG-51

Post by Werra »

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

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

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Re: Page 137: Adieu SG-51

Post by Askaris »

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

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Re: Page 137: Adieu SG-51

Post by Chekist_Felix »

Askaris wrote:"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!
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Random Person
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Re: Page 137: Adieu SG-51

Post by Random Person »

Victor_D wrote: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.
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Werra
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Re: Page 137: Adieu SG-51

Post by Werra »

How does FTL as it works in Outsider break causality?

entity2636
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Re: Page 137: Adieu SG-51

Post by 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.

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Werra
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Re: Page 137: Adieu SG-51

Post by Werra »

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

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Arioch
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Re: Page 137: Adieu SG-51

Post by 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.

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icekatze
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Re: Page 137: Adieu SG-51

Post by 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.

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Re: Page 137: Adieu SG-51

Post by 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.

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Arioch
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Re: Page 137: Adieu SG-51

Post by Arioch »

Contraltissimo wrote: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.

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Re: Page 137: Adieu SG-51

Post by 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
Image
This is what they're saying:
SpoilerShow
Image
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.
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Re: Page 137: Adieu SG-51

Post by icekatze »

hi hi
RedDwarfIV wrote: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.
RedDwarfIV wrote: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.

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Re: Page 137: Adieu SG-51

Post by GeoModder »

But the moment it arrives at Earth, its frame of reference adjusts to Earth's frame of reference, where the message *has* been sent in its past. Kinda making the point mood if you ask me.
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Re: Page 137: Adieu SG-51

Post by Sweforce »

icekatze wrote:hi hi
RedDwarfIV wrote: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.
RedDwarfIV wrote: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.
It is perfectly normal for people to return home before the postcards they sent back home arrive, it is hardly a causality problem, just the mail being a bit slow. I see it the same way with a ship that make an near instantaneous jump ahead of the slow light speed radio message sent just prior to the jump.

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Re: Page 137: Adieu SG-51

Post by icekatze »

hi hi
GeoModder wrote:But the moment it arrives at Earth, its frame of reference adjusts to Earth's frame of reference, where the message *has* been sent in its past. Kinda making the point mood if you ask me.
In which situation are you saying that this happens? In the Outsider universe, there is a time delay for FTL travel that could avoid paradoxes, but in RedDwarfIV's question, that is not necessarily the case. (Also, it becomes even more complicated when more that two reference frames are brought in to the equation.)

In RedDwarfIV's hypothetical example of a transit between Earth and Proxima Centauri, it is also important to point out that there is no single "Earth's reference frame," but rather there are a series of reference frames over time, none of which is preferred over any other. Time is a series of events in space-time, the progression of which depends on the observer's frame of reference.
Sweforce wrote:It is perfectly normal for people to return home before the postcards they sent back home arrive, it is hardly a causality problem, just the mail being a bit slow. I see it the same way with a ship that make an near instantaneous jump ahead of the slow light speed radio message sent just prior to the jump.
This has nothing to do with the problem at hand. The matter is not people arriving home before their postcards arrive, but their postcards that they sent from their destination arriving back home before they leave in the first place.

Relativity of Simultaneity is not an optical illusion, it isn't merely an issue of people experiencing latency, it is a fundamental quality of how the universe operates with regards to the speed of light.

Here's an animated explanation that might make it more clear

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Re: Page 137: Adieu SG-51

Post by Witty_Username »

Time Travel makes my head hurt.

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Re: Page 137: Adieu SG-51

Post by Siber »

Personally, while I rarely have enough grasp on the relativity issues to explain it, I take it as a general rule that FTL will enable time travel if you try hard enough, though some schemes may make it very hard to create testable breakage. I suspect with Outsider's setup you'd need to drag stars up to dialation-inducing relative velocities and then jump between them to really get spectacular results, which puts the bar for time travel pretty high. I never rule out someone clever than I coming up with an easier exploit, though.
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