How would a Heim- theory drive actually behave?

[Ford Prefect]

So we're strictly limited to some miserable fraction of c. So much for galactic empires.

Don't be so sure of that. It might take you a hundred thousand years to cross your domain, but so what? It might take three million years to conquer all the stars in the sky, but again, big deal. There's no real reason why you couldn't construct a vast, galactic scale empire even limited to slower than light speeds; it would not look much like the generic sci-fi empires that pop up in pulpy novels, but that's no real loss.

[montypython]

In a sense it may be better to call an 'FTL' drive a post-relativity drive in function, if one considers light as a universal reference point, in that case synchronizing and compressing time of movement would be a key aspect of movement (e.g, calculating one month's time to travel to Arcturus from Earth instead of by multiples of c).

[tchizek]

I have another question. The rule in Hard SF if usually "relativity, causality, FTL: pick any two." If you are basing your FTL on Heim theory, which two do you get? Causality, or Relativity?

You get to (have to) pick. If you have FTL and Causality then you assume (for story purposes) Relativity was wrong or incomplete in some fundamental way. If you have FTL and Relativity was not wrong in some fundamental way then you have the possibility of non-Causal interactions (i.e., people reacting now to something that was done several years ago, and being able to change the outcome of that event)

[Formless]

I already know that, what I was asking should be obvious: which two does the theory say I choose? I could make up whatever the fuck FTL drive I want and the choice would be mine. But that isn't what I'm after, I want to know which two does this theory predict, and work from there. Now, if you know the answer to that question, please tell me, but don't just reiterate what I already confirmed I understand!

[GrandMasterTerwynn]

I already know that, what I was asking should be obvious: which two does the theory say I choose? I could make up whatever the fuck FTL drive I want and the choice would be mine. But that isn't what I'm after, I want to know which two does this theory predict, and work from there. Now, if you know the answer to that question, please tell me, but don't just reiterate what I already confirmed I understand!

A drive built using Heim-Droescher physics appears to conform with general relativity, since you're just sidestepping into a region of spacetime where you're locally subluminal. Which suggests that the odd-man-out would be causality . . . i.e. it'd be possible to use a Heim FTL drive as a time machine, replete with all the headaches that would imply.

[McC]

It's worth noting that current experimentation seems to imply that the Chronology Protection Conjecture/Novikov Self-Consistency Principle (i.e. no spatial phenomena can violate causality) is, in fact, true (New Scientist, 2005; Arxiv paper).

I've been kicking around the idea of using this to mean that you can have relativity, causality, and FTL, but the second it has the potential to violate causality, your FTL field/wormhole/whatever destabilizes and shuts down, shunting you back to "normal" space.

[GrandMasterTerwynn]

It's worth noting that current experimentation seems to imply that the Chronology Protection Conjecture/Novikov Self-Consistency Principle (i.e. no spatial phenomena can violate causality) is, in fact, true (New Scientist, 2005; Arxiv paper).

I've been kicking around the idea of using this to mean that you can have relativity, causality, and FTL, but the second it has the potential to violate causality, your FTL field/wormhole/whatever destabilizes and shuts down, shunting you back to "normal" space.

No. What it means is if no spatial phenomena can violate causality, then you don't have FTL, full-stop. Even general relativity agrees that if you have a method of conveying information FTL, you have a time machine. So if there is chronology protection inherent in the universe, any attempt to travel FTL ought to fail spectacularly as a result.

[McC]

No. What it means is if no spatial phenomena can violate causality, then you don't have FTL, full-stop. Even general relativity agrees that if you have a method of conveying information FTL, you have a time machine. So if there is chronology protection inherent in the universe, any attempt to travel FTL ought to fail spectacularly as a result.

Sorry, I omitted some personal assumptions there. I'm assuming that you're using wormholes for "FTL", and that attempting to use one for time-travel causes it to decay before it permits traversability. Everything I've thus far read on the topic has lead me to understand that wormholes are permissible and do not necessarily violate either relativity or causality, though they contain the potential to if either end is accelerated in a relativistic manner. Consequently, the previously cited sources lead me to conclude that one cannot accelerate a wormhole mouth, since doing so will cause it to decay.

[Ryan Thunder]

It's worth noting that current experimentation seems to imply that the Chronology Protection Conjecture/Novikov Self-Consistency Principle (i.e. no spatial phenomena can violate causality) is, in fact, true (New Scientist, 2005; Arxiv paper).

I've been kicking around the idea of using this to mean that you can have relativity, causality, and FTL, but the second it has the potential to violate causality, your FTL field/wormhole/whatever destabilizes and shuts down, shunting you back to "normal" space.

No. What it means is if no spatial phenomena can violate causality, then you don't have FTL, full-stop. Even general relativity agrees that if you have a method of conveying information FTL, you have a time machine. So if there is chronology protection inherent in the universe, any attempt to travel FTL ought to fail spectacularly as a result.

I still find that to be a very interesting definition of time travel. I'd like to hear more about it, because it doesn't seem to follow to me that if you 'see' something arrive before you 'see' it leave, then it must be time travel... From your perspective, it might look like time travel, but then again, you could achieve a similar situation with sound based detection and a supersonic vehicle, and it'd do nothing to change the fact that it did, in fact, leave before it arrived...

[NetKnight]

From your perspective, it might look like time travel, but then again, you could achieve a similar situation with sound based detection and a supersonic vehicle, and it'd do nothing to change the fact that it did, in fact, leave before it arrived...

...Which would be precisely the case if there were a luminiferous æther for light to propagate in, or some other universal frame of reference. There isn't; hence, Relativity.

[Eleventh Century Remnant]

Which other reference frame, or at least much closer to it, might be provided by the inflationary force that Heim theory suggests is generatable.

Using that force is how a Heim drive would move at greater than lightspeed anyway, so what I think the theory is suggesting is that the speed of light is only the cosmic maximum and causal yardstick within a frame of reference which does not include the possibility of inflation, that, in other words, there really is a luminiferous aether that light propagates through.

This is a hell of a way to try to get around chronology protection, but it's all I can think of at the moment (close on 2 AM here, so I may be incoherent) that preserves all three options, causality- although light cones have to be replaced with inflationary cones- relativity and FTL travel.

Of course, I could be wildly wrong here.

[Ariphaos]

Which other reference frame, or at least much closer to it, might be provided by the inflationary force that Heim theory suggests is generatable.

Using that force is how a Heim drive would move at greater than lightspeed anyway, so what I think the theory is suggesting is that the speed of light is only the cosmic maximum and causal yardstick within a frame of reference which does not include the possibility of inflation, that, in other words, there really is a luminiferous aether that light propagates through.

This is a hell of a way to try to get around chronology protection, but it's all I can think of at the moment (close on 2 AM here, so I may be incoherent) that preserves all three options, causality- although light cones have to be replaced with inflationary cones- relativity and FTL travel.

Of course, I could be wildly wrong here.

I have no idea how the Heim drive actually works so I can't really speak to it.

It's easy to pick out a way in which special relativity can be encapsulated within a system that permits FTL along with causality - if something's perception of time is dependent on how fast it moves, you can create the effect of relativity within a larger framework where that permits causal FTL. You have a fixed frame (breaking Relativity in the Grand Scheme Of Things), but if you only take into account the Universe as humans observe it, special relativity can work just fine.

There are three main problems that need to be addressed if you take the 'relativity within a fixed frame + causal FTL' route, at least as far as I can see.

The first (and easiest to address) is the structure of our Universe. Since portions of our Universe are receding from us at FTL speeds, any such 'fixed frame' cannot exist as a fixed point within our Universe - it needs to be outside of it or at the very least use some mechanism well beyond my current understanding of math. It's a lot easier to imagine the former - the fixed frame is the hypersphere itself and 'true time' is the fourth dimension. Whatever.

The second is the nature of actually producing an FTL effect. What we are talking about is the rough equivalent of having your World of Warcraft character step out from your monitor screen and greet you in person. Just because a fixed frame like this exists does not mean you automatically can make some use of it. If the only thing we have access to - no matter the effort - works within the context of Relativity, then we're stuck. Of course, this is where the inflationary force comes in. The existence of the inflationary period has rather good support, and it's a rather exotic event in our Universe's history to put it mildly. There's little chance of finding evidence of it below ZeV-scale energies, but this is actually a physically achievable accomplishment for a near type-II civilization. For Solar Storms I have an entire arc just -about- the effort put into creating the first, tiny FTL signals. It's a big fucking deal.

General relativity is the last one. At least for me it's the most difficult to just handwave, because I simply don't have the mathematical skill to try. This only becomes a serious issue when you decide to include black holes and how they affect, well, everything.

---

That probably makes it sound way too easy. Achieving zettaelectronvolt energies with physically attainable materials requires a particle accelerator the size of Mercury's orbit. And even then the best you can hope for is a cosmic radio powered by a significant fraction of your star's output. Actually using it to transport a physical object requires a lot more magic.

[McC]

I think part of the reason the FTL/relativity problem is so hard for (layman) people to wrap their heads around is that it's always explained with a lightcone graph, which by its very nature implies a fixed coordinate system that relativity explicitly forbids. The graph becomes a reference frame all on its own. "If H is your point in space-time" is a relative concept, but depicting it with a graph makes it an absolute one.

[Eleventh Century Remnant]

Xeriar, that makes much more sense than my sleep deprived ravings.

Although I don't play WoW.

[Ryan Thunder]

I think part of the reason the FTL/relativity problem is so hard for (layman) people to wrap their heads around is that it's always explained with a lightcone graph, which by its very nature implies a fixed coordinate system that relativity explicitly forbids. The graph becomes a reference frame all on its own. "If H is your point in space-time" is a relative concept, but depicting it with a graph makes it an absolute one.

I'd have to agree. It's the point at which physics ceases to be intuitive that I tend to have problems with it. Quantum physics is similarly difficult.

For example, Electrons going from A to B without ever existing anywhere in between. => What the shit?

[McC]

I'd have to agree. It's the point at which physics ceases to be intuitive that I tend to have problems with it. Quantum physics is similarly difficult.

For example, Electrons going from A to B without ever existing anywhere in between. => What the shit?

I find teleportation a lot easier to wrap my head around than the notion that points "A" and "B" are not even really "points" in any sense that I can understand.

[Ariphaos]

I think part of the reason the FTL/relativity problem is so hard for (layman) people to wrap their heads around is that it's always explained with a lightcone graph, which by its very nature implies a fixed coordinate system that relativity explicitly forbids. The graph becomes a reference frame all on its own. "If H is your point in space-time" is a relative concept, but depicting it with a graph makes it an absolute one.

I think you might be misunderstanding what a light cone is supposed to represent - all events that may causally affect an observer, and all events that an observer can causally affect are within the light cone. It represents that observer's fixed frame and the fact that observers can disagree.

If the light cones for events A, B, and C have spacelike separation (that is, Events B and C do not occur within A's light cone, and the same for C not occurring withing B's light cone, etc), then not all observers will agree as to what order they occurred in. Observer O will see order A-> B -> C, observer P will see C -> B -> A...

If you hold relativity to be perfectly true while allowing FTL shenanigans, then event C can influence event A before it begins and event A can likewise influence event C before it begins.

[McC]

I think you might be misunderstanding what a light cone is supposed to represent - all events that may causally affect an observer, and all events that an observer can causally affect are within the light cone. It represents that observer's fixed frame and the fact that observers can disagree.

To be honest, I don't think I have ever correctly understood any of the more nebulous aspects of relativity. None of them make any damn sense.

To add fuel to the fire, the term "observer" -- so often used in discussions of relativity -- is also a poor choice, isn't it? Observer implies one who can observe. But in the reality of the situation, a rock can be an "observer," can it not?

What's more, "observer" implies that the individual is not a participant, which further clouds the issue by invoking the notion of all of this being illusory due to "light speed lag," which isn't in fact the case (if understand correctly, which of course remains dubious).

The whole thing is a giant clusterfuck.

[Nyrath]

I'd have to agree. It's the point at which physics ceases to be intuitive that I tend to have problems with it. Quantum physics is similarly difficult.

For example, Electrons going from A to B without ever existing anywhere in between. => What the shit?

However, the important point is: intuitive or not, quantum physics can be used to build things that work.

Tired old example: the Tunnel Diode. This is an electronic device that makes no sense intuitively, but does make sense in quantum mechanics. And it is a common electronic component, there are probably quite a few in the computer you are using to read this post with.

Intuitively, it makes no sense that electrons enter on one side, exit on the other side, but do not exist in the middle. But it makes perfect sense in the context of quantum tunneling.

But the tunnel diode doesn't know or care that it makes no sense to intuition, neither do the engineers who use them to design electronics.

[Ryan Thunder]

I'd have to agree. It's the point at which physics ceases to be intuitive that I tend to have problems with it. Quantum physics is similarly difficult.

For example, Electrons going from A to B without ever existing anywhere in between. => What the shit?

However, the important point is: intuitive or not, quantum physics can be used to build things that work.

Well of course, nobody's arguing otherwise. I just have trouble wrapping my head around it is all.

[Ariphaos]

To be honest, I don't think I have ever correctly understood any of the more nebulous aspects of relativity. None of them make any damn sense.

To add fuel to the fire, the term "observer" -- so often used in discussions of relativity -- is also a poor choice, isn't it? Observer implies one who can observe. But in the reality of the situation, a rock can be an "observer," can it not?

Allow me to be facetious for a moment and ask you what is wrong with that? Are you rock-ist?

I'm being (slightly) more serious than I come across - if you have a rock flying through space, and you want to know what can effect it / what affects it at a given moment in its timeline, a lightcone diagram is appropriate. It is an observer for all past events and a potential actor for all future events, but when you look at a lightcone diagram you are only analyzing a specific point in spacetime.

[McC]

Allow me to be facetious for a moment and ask you what is wrong with that? Are you rock-ist?

Not at all. The point I was trying to make -- and which you reiterated with your follow-up paragraph -- is that the "observer" in question does not, in fact, have to "observe" anything in the context of human-sensory perception. It's not a matter of "seeing" the light of an object doing something after the object has already done it because it did it at FTL; it's a matter of the object actually not doing that thing yet, from the perspective of the "observer" (which need not actually observe).

I'm not sure if that's making sense. Then again, I'm not sure if anything about relativity ever makes any sense when put into words.

[Formless]

Allow me to be facetious for a moment and ask you what is wrong with that? Are you rock-ist?

Not at all. The point I was trying to make -- and which you reiterated with your follow-up paragraph -- is that the "observer" in question does not, in fact, have to "observe" anything in the context of human-sensory perception. It's not a matter of "seeing" the light of an object doing something after the object has already done it because it did it at FTL; it's a matter of the object actually not doing that thing yet, from the perspective of the "observer" (which need not actually observe).

I'm not sure if that's making sense. Then again, I'm not sure if anything about relativity ever makes any sense when put into words.

Perhaps it would help to think of it in purely physical terms. What does it mean to "observe" light? If you are a human, it means that light falls on the photoreceptors of your eye, which sends a signal to the brain, which causes you to react... all these are physical processes, right? It leads to a causal chain insofar as the human reacts, but there is nothing special about the fact that he is alive and intelligent. What does it mean for an inanimate object like a rock to "observe" something? It means that light reflects off its surface, starting a causal chain related to that light. If you replace the rock with another inanimate object, like a spacecraft powered by a solar sail, it becomes more obvious: the light causes the sail to thrust in whichever direction it reflects at. No intelligence is required.

[McC]

Perhaps it would help to think of it in purely physical terms. What does it mean to "observe" light? If you are a human, it means that light falls on the photoreceptors of your eye, which sends a signal to the brain, which causes you to react... all these are physical processes, right? It leads to a causal chain insofar as the human reacts, but there is nothing special about the fact that he is alive and intelligent. What does it mean for an inanimate object like a rock to "observe" something? It means that light reflects off its surface, starting a causal chain related to that light. If you replace the rock with another inanimate object, like a spacecraft powered by a solar sail, it becomes more obvious: the light causes the sail to thrust in whichever direction it reflects at. No intelligence is required.

I understand that much. The problem is the role light itself plays in this, which you illustrate. Light is the mechanism for conveying information and travels at light speed. This information conveyor travels between all reference frames in its unique fixed fashion, but it still only conveys information; it's not conveying the frames themselves. If you've got an observer in an FTL frame, they are the final arbiter on what happens in their frame, aren't they? If some other observer says something happens to them in a way that is non-causal, that's just an artifact of the different reference frames.

It has always seemed to me that the underlying assumption that FTL violates causality remains an illusion of information propagation due to "light speed lag." Every multi-observer lightcone diagram I've ever seen always leads me back to thinking that this is the case. I'm also pretty sure that I'm wrong. But I don't understand.

[Ariphaos]

I understand that much. The problem is the role light itself plays in this, which you illustrate. Light is the mechanism for conveying information and travels at light speed. This information conveyor travels between all reference frames in its unique fixed fashion, but it still only conveys information; it's not conveying the frames themselves. If you've got an observer in an FTL frame, they are the final arbiter on what happens in their frame, aren't they? If some other observer says something happens to them in a way that is non-causal, that's just an artifact of the different reference frames.

No...

If you have a Universe in which an FTL frame makes sense (not always a given), then they will not automatically determine a proper ordering - Relativity states that there is no such thing.

It has always seemed to me that the underlying assumption that FTL violates causality remains an illusion of information propagation due to "light speed lag." Every multi-observer lightcone diagram I've ever seen always leads me back to thinking that this is the case. I'm also pretty sure that I'm wrong. But I don't understand.

If something is moving at .86 of c away from you, you will see its clock tick two seconds for every four that yours ticks. Likewise, it will see your clock tick two seconds for every four that its clock ticks. Relativity declares that both your frame and the receding object's are both equally valid. You send a signal to the other at one second, the target receives it at .5 seconds, you receive the reply at .25 seconds to the message you send .75 seconds later.

If you don't want to use cosmic censorship, don't want to allow time travel, and want to permit FTL, you need to break Relativity in some form or another.

A fixed frame then says that there is a true ordering - the receding ship receives the signal at some value between one and two seconds and you receive the reply at 1 second. The closer to 2 seconds that the receding ship gets the signal, the closer you are to the fixed frame for that particular point in space, assuming both you and the receding ship are close together and the fixed frame does not vary wildly over short distances, etc.