How accurate is the KSP interstellar Alcubierre Drive?

[SpaceLaunchSystem]

I've done some research, but I was wondering about the KSP Interstellar alcubierre drive. How accurate to the real world is it? I don't know a whole lot about that type of theoretical physics, but maybe someone more knowledgeable on the subject could explain it in simple terms.

[Kerbart]

I think the KSP one has addressed some issues that are still lingering with the real life one, the biggest being “it exists in working form.â€Â

[NFUN]

Yeah, to our knowledge, no exotic particles exist that would allow the Alcubierre Drive to work. Since the makers of Interstellar seemed to have done their research on most other things (or are fantastic at BS), I see no reason why the in-game drives wouldn't mirror theoretical versions.

[NovaSilisko]

Unfortunately, given all FTL in the real world is impossible due to causality... it's not accurate, at all. http://www.projectrho.com/public_html/rocket/fasterlight.php#id--Causality

[K^2]

Unfortunately, given all FTL in the real world is impossible due to causality... it's not accurate, at all.

Causality is only locally relevant in General Relativity. FTL is not a violation by any measure. Otherwise, Universe wouldn't be expanding at FTL speeds.

The biggest inaccuracy of KSP's Alcubierre Drive is that it doesn't properly take into account curvature due to gravity. You drop out of warp traveling at the same speed that you went into the warp at, but the frame of reference is accelerated. To account for this properly, author should have carried out parallel transport of the velocity vector in a curved space-time. Naturally, since gravity in KSP is a patched-conics approximation, it would be entirely acceptable to use Schwarzschild Metric for parallel transport as well, patching at SOI boundaries as necessary.

There are a few minor issues as well. Energy consumption, visual effect of the warp, etc. But these could be chalked up to sacrifices in the name of gameplay and limitations of the rendering engine.

[astropapi1]

...(or are fantastic at BS)...

Technobabble is one hell of a drug life saver. Maybe they're not blatantly using it, but I'm sure they have at some point.

[SpaceLaunchSystem]

-- Stupid comment removed --

[-Velocity-]

Not realistic at all, considering that IRL they do not exist, and almost certainly cannot exist because they can be used to violate causality, are quite possibly instantly destroyed by Hawking radiation when they exceed c, and would require truly vast amounts of non-existent exotic matter compressed to extremely high negative densities to even construct in the first place.

Edited November 18, 2014 by |Velocity|

[Mazon Del]

Alright guys, you've made your point. You think its not real. Now perhaps instead of a knee-jerk reaction to the fact that the thread as to do with a method of FTL, how about the actual question now where he is asking for a comparison between how the mod handles the drive compared the THEORETICAL effects one should experience from it.

To that end, thanks K^2!

[GregA]

Alright guys, you've made your point. You think its not real. Now perhaps instead of a knee-jerk reaction to the fact that the thread as to do with a method of FTL, how about the actual question now where he is asking for a comparison between how the mod handles the drive compared the THEORETICAL effects one should experience from it.

To that end, thanks K^2!

Oh, well in that case... You turn it on, you immediately detach from our 5 dimensional space time, you pop into the bulk. Fly alongside our universe in 11 dimensional space time. Then slide back into 5 dimensional space time at your destination.

easy peazy.

Just make sure your quantum cable car invariant capacitor is fully charged before you go!

If you run into any problems, try reversing to polarity.

[lajoswinkler]

Almost not accurate at all. Faster than light travel is a fantasy and some people need a reality check because real life is not a Hollywood movie.

[Mazon Del]

Oh, well in that case... You turn it on, you immediately detach from our 5 dimensional space time, you pop into the bulk. Fly alongside our universe in 11 dimensional space time. Then slide back into 5 dimensional space time at your destination.

easy peazy.

Just make sure your quantum cable car invariant capacitor is fully charged before you go!

If you run into any problems, try reversing to polarity.

*slow clap* I smiled at this one.

[Soda Popinski]

... require truly vast amounts of non-existent exotic matter....

"Vast" is relative. The original calculations required mathematically possible, but so far undetected exotic matter in excess of the mass of the observable universe. After further study, that was taken down to merely the mass of Jupiter. Newer geometries has since taken that down to about 700kg.

700kg could be considered vast, based on the fact we have 0g of the stuff, but it's a lot better than the mass of the observable universe.

[K^2]

cannot exist because they can be used to violate causality

I don't know why I bother. "Causality" is stuck in everyone's head like it's a universal absolute of some sort. For the second time in this thread alone. It's a local feature. Global causality is completely optional.

[rtxoff]

Well, unfortunately it is something like an universal absolute so far. At least i do not know anyone observing anything breaking causality. The real question someone could speculate about is: "Does the Alcubierre drive really break causality?" I mean it's not something anyone had the chance to observe and most people say FTL travel will be time travel. However such an statement is only speculation at best. As long as we don't build such an drive that actually works and see what happens when we use it this discussion is pretty senseless and it was already discussed to death here.

[*Aqua*]

The real question someone could speculate about is: "Does the Alcubierre drive really break causality?"

Actually the Alcubierre drive doesn't move the spaceship, it moves the space around it with FTL speeds. So far scientists say it is allowed within the current known laws of nature.

If I understand the principle correctly there wouldn't be any backwards time travel. The time in and outside of the 'warp bubble' will still move forward. That also means there'll be no break of causality.

[N_las]

Actually the Alcubierre drive doesn't move the spaceship, it moves the space around it with FTL speeds. So far scientists say it is allowed within the current known laws of nature.

If I understand the principle correctly there wouldn't be any backwards time travel. The time in and outside of the 'warp bubble' will still move forward. That also means there'll be no break of causality.

In older threads, we explained how any FTL travel will allow time travel. It has nothing to do with the movement of the ship.

http://en.wikipedia.org/wiki/Time_travel#Via_faster-than-light_.28FTL.29_travel

Edited November 19, 2014 by N_las

[K^2]

You can't really use warp drive to time-travel directly. You essentially need two objects traveling at FTL times to actually close the loop, and they have to communicate under conditions under which two Alcubierre ships can't. So you need something else going on. Or you can use a region of space-time that's warped to begin with to complete a CTC. Bottom line is, FTL of any kind violates causality, but it doesn't automatically mean a practical time machine. Not that a real time machine would cause any serious problems to underlying physics.

[N_las]

You can't really use warp drive to time-travel directly. You essentially need two objects traveling at FTL times to actually close the loop, and they have to communicate under conditions under which two Alcubierre ships can't. So you need something else going on. Or you can use a region of space-time that's warped to begin with to complete a CTC. Bottom line is, FTL of any kind violates causality, but it doesn't automatically mean a practical time machine. Not that a real time machine would cause any serious problems to underlying physics.

It doesn't need to be directly or practical:

Imagine a Bomb travelling with 99.999% light speed towards earth. It was set up by a hostile civilization. A Countermeasure-bomb is started from Earth to explode in the vicinity of the hostile bomb in the hope to destroy it. To have this counteraction take place as far from earth as possible, the Counter-Bomb is fittet with an alcubierre drive. It travels with greater than lightspeed towards the hostile bomb.

Event A is the start of the counter-bomb from Earth, and event B is the meeting of the counter-bomb with the hostile bomb. You will agree, that it is possible for event B to happen before event A in the inertial reference frame of the hostile bomb.

As soon as the counter-bomb reaches the vicinity of the hostile bomb, it explodes. I am not sure what should happen with the warp bubble. I assume the bomb has to exit it before or during the explosion. Now imagine the hostile bomb is also fittet with an alcubierre drive. It withstands the explosion (maybe the counter bomb exploded to far away). As some kind of counter-countermeasure, after detecting the counter-bombs explosion in its vicinity, it starts its alcubierre drive immediately. From it's point of view, event A hasn't even happen yet. If it travels at greater than light speed towards earth, it could reach it before event A. So it will destroy earth earlier BECAUSE we sent a counter-measure but BEFORE we sent the counter-measure.

Clearly, the information that we sent the countermeasure travelled into the past. And cleary, global causality is violated (if earth is destroyed because we sent the counter-bomb but before we sent the counter-bomb, then we couldn't sent the counter-bomb in the first place.)

I am not suggesting that any FTL drive would just be like a DeLorean in "Back to the future". But some people here on these forums don't accept that FTL travel would violate causality or they think that the alcubierre drive has some kind of "Get out of jail"-card for "FTL-travel without causality violations" because "it doesn't actually move, it's just warping the space around".

But any FTL communication technology will allow for a setup that sends information back to the past of the sender. And the alcubierre drive is some kind of FTL communication technology.

Edited November 20, 2014 by N_las

[Hary R]

Well all of this is pretty interesting but the topic stat KSPI warp drive and if I remember correctly (can't play with KSPI right know because of not enough memory), KSPI warp drive is a slower than light one, as such no FTL magic involve.

I would like to know if as a STL warp drive the KSPI warp is accurate. (K^2 have already said that id does not take into account space curvature but what else is inacuratre)

Let's leave the FTL part out for know ok.

[cicatrix]

There, I may not be an expert in general relativity, but:

It doesn't need to be directly or practical:

Imagine a Bomb travelling with 99.999% light speed towards earth. It was set up by a hostile civilization.

We're screwed. How would we know about the bomb?

OK, we should have a scout with a warp drive near their home system that would notice the launch.

It spots it and hurries back on Earth to warn us.

A Countermeasure-bomb is started from Earth to explode in the vicinity of the hostile bomb in the hope to destroy it. To have this counteraction take place as far from earth as possible, the Counter-Bomb is fittet with an alcubierre drive.

Here, there is something related to the time dilation. If their bomb travels at 0.99c thousands of years will pass on the enemy planet before it reaches its destination (correct me, if I'm wr

It travels with greater than lightspeed towards the hostile bomb.

Nothing can travel at FTL speed, not even the warp-drive. You don't travel with it, you simply appear at the target spot. Within your warp-bubble you can even not be moving at all. Spacetime distortion is not, strictly speaking, travel.

Event A is the start of the counter-bomb from Earth, and event B is the meeting of the counter-bomb with the hostile bomb. You will agree, that it is possible for event B to happen before event A in the inertial reference frame of the hostile bomb.

Hmm, here I'm not 100% sure.

Here's the bomb world line:

1. Bomb launch

2. Scout spots the bomb

3. Scout warps home and warns Earth

4. Bombs meet

Interceptor bomb cannot arrive earlier than #1, because the information about the bomb will be received on Earth only at #3.

Information cannot travel faster than light unless it's passed onboard the warp-capable ship.

Now imagine the hostile bomb is also fittet with an alcubierre drive. As a counter-countermeasure, after detecting the counter-bomb in its vicinity, it starts its alcubierre drive immediately.

Ok, we'll leave the question about how it would detect anything before itself if it travels at 0.99c and how it would detect the interceptor bomb APPEARING on its nosecone instantly.

P.S. Alcubierre's Drive is NOT a FTL propulsion system. Not in the terms that anything there actually moves faster than light. Therefore, the drive from the mod is absolutely not correct. You don't just fly towards your target, you simply appear near it.

There, I may not be an expert in general relativity, but since nothing is actually moving faster than light there would be no causality paradoxes.

Allright, I may be completely wrong about it.

[Hary R]

There, I may not be an expert in general relativity, but:

Here, there is something related to the time dilation. If their bomb travels at 0.99c thousands of years will pass on the enemy planet before it reaches its destination (correct me, if I'm wr

You are wrong, time dilatation will not affect their home planet if the bomb travel à 99.9%C, time dilatation will only affect the bomb in itself. For the home planet (let's say it is at 4 Light Year from Earth) the bomb will take a little more than 4 years to reach earth but a clock on the bomb will display a date closer to it launch date than those 4 years.

(I'm not even a scientist )

You don't just fly towards your target, you simply appear near it.

Sorry, that's not how it is supposed to work. yeah you appear next to your target for an observer that is at the target (target frame of reference) and you will also appear to leave some time after you arrive for him (if he observe the point where you came from) but for you, no local move indeed but you do "fly" toward your destination from your point of view, it will come closer and closer, well at FTL may be you will not see it. But you don't just appear, that make no sens.

.

Edited November 20, 2014 by Hary R

[cicatrix]

You are wrong, time dilatation will not affect their home planet if the bomb travel à 99.9%C, time dilatation will only affect the bomb in itself. For the home planet (let's say it is at 4 Light Year from Earth) the bomb will take a little more than 4 years to reach earth but a clock on the bomb will display a date closer to it lunch date than those 4 years.

(I'm not even a scientist )

.

That's what I meant. Although it would be 4 years since the start on the bomb's clock, there will be much more at the clocks of its home planet.

Sorry, that's not how it is supposed to work. yeah you appear next to your target for an observer that is at the target (target frame of reference) and you will also appear to leave some time after you arrive for him (if he observe the point where you came from) but for you, no local move indeed but you do "fly" toward your destination from your point of view, it will come closer and closer, well at FTL may be you will not see it. But you don't just appear, that make no sens.

Yeah, theoretically, at destination I can watch my own departure from the start, but since I do not fly, I would hardly 'see' transition. I should see severely distorted (like in a curved mirror) and very blue-shifted target which then becomes normal as I finish the transition.

Edited November 20, 2014 by cicatrix

[N_las]

We're screwed. How would we know about the bomb?

OK, we should have a scout with a warp drive near their home system that would notice the launch.

It spots it and hurries back on Earth to warn us.

We don't have to spot the bomb ourselfs. It doesn't matter for this scenario. Maybe the hostile civilization has contactes us thousands of years ago, explaining that it will send this kind of bomb in the future.

Here, there is something related to the time dilation. If their bomb travels at 0.99c thousands of years will pass on the enemy planet before it reaches its destination (correct me, if I'm wr

If the enemy planet is thousands of light years from earth then yes: thousands of years will pass on the enemy planet before the bomb reaches earth. Doesn't have anything directly to do with time dilation. But it doesn't matter. Maybe they sent it thousands of years ago. We don't have to discuss the reason behind alien military strategies.

Nothing can travel at FTL speed, not even the warp-drive. You don't travel with it, you simply appear at the target spot. Within your warp-bubble you can even not be moving at all. Spacetime distortion is not, strictly speaking, travel.

It doesn't matter. By "travel", i don't meen that the ship acutally has this velocity. "travel" simply means that I start at a start position and end up at a destination. It doesn't matter if i am actually moving, i can still travel FTL. If I appear at the destination faster than a light beam would reach the destination (that would have been send out at the start position instead of me), then the phrase "I traveld FTL" is justified, even if I didn't move.

Hmm, here I'm not 100% sure.

Here's the bomb world line:

1. Bomb launch

2. Scout spots the bomb

3. Scout warps home and warns Earth

4. Bombs meet

Interceptor bomb cannot arrive earlier than #1, because the information about the bomb will be received on Earth only at #3.

Information cannot travel faster than light unless it's passed onboard the warp-capable ship.

We don't need a scout for this scenario. And why are you talking about the counter-bomb to "arrive earlier than #1"? What does the start of the hostile bomb has to do with anything?

If event A is the start of the counter bomb, and event B is the meeting of the bombs, from earths inertal reference frame, then event B happens after event A. But because the counter bomb reached event B earlier than a light beam from event A would reach it (a light beam could not travel from event A to event , event B happens outside of the light cone of event A. Because Event B is outside of event As light cone, from the hostile bombs inertial reference frame (it travels near light speed) event B can happen before event A.

If the hostile bomb would travel at lower than light speeds, it couldn't reach the earth before event A, but if it itself has a warp-drive, it can reach Earth before event A.

Ok, we'll leave the question about how it would detect anything before itself if it travels at 0.99c and how it would detect the interceptor bomb APPEARING on its nosecone instantly.

The counter-bomb would try to destroy the hostile bomb. It has to have some kind of influence on the hostile bomb for that. Maybe a giant explosion just infront of the hostile bomb? Doesn't really matter for this scenario. The hostile bomb only has to survive the countermeasure, and has to notice the countermeasure.

There, I may not be an expert in general relativity, but since nothing is actually moving faster than light there would be no causality paradoxes.

Allright, I may be completely wrong about it.

Yes, you are wrong about this. My whole bomb scenario is there to illustrate how the warp-drive can violate causality. It isn't dependent on "something actually moving faster than light". The only important movement is the hostile bombs near-light-velocity relative to earth.

Edited November 20, 2014 by N_las

[Hary R]

That's what I meant. Although it would be 4 years since the start on the bomb's clock, there will be much more at the clocks of its home planet.

you get the thing right but you get the frame of reference wrong. If the Home planet is at 4 light year of earth, for them, an object traveling at near speed of light will take 4 or so to get to earth, but for the object and any observers traveling inside the object, it will be less than 4 years (Lorenz factor to be taken into account but I'm no mathematician). If the clock on the object that travel à 0.999C indicate 4 years, that mean that it come from further way way further than 4 light years away.