[nessus42]

I understand it perfectly fine for the purposes of this discussion.

Edit: I can't believe people down-vote irrefutable facts, so let me state this ONE MORE TIME:

It is an irrefutable fact of Special Relativity that if you can transmit any information from point A to point B faster than light would travel from point A to point B in a vacuum, then there are inertial frames of reference in which the information arrived at point B BEFORE it left point A.

THAT'S JUST A FACT OF SPECIAL RELATIVITY.

People can bitch and moan about whatever they want to, and come up with all sorts of creative ways to try to work around this FACT, but YOU CANNOT.

c, it's not just a good idea--IT'S THE LAW!

[sentientbicycle]

I'm sorry, but I just can't find any sort of citation stating that the Alcubierre drive violates any of these principles. I also can't find any mention of paradoxes incurred by the drive and there is only one mention of where the meta-materials themselves would have to violate the light speed limit. Here is how I understand it (and correct me if I'm wrong), but it is not travelling in a vacuum, it is crunching that vacuum in front and expanding it in the back. This doesn't violate any laws because we know our universe is actually already doing this (expanding at a greater than light speed). If what you say is true then the galaxies that are currently moving away from us at those "super-luminal" (not actual super-luminal because we all know that's impossible) speeds shouldn't exist, but we know these do exist and we know why they appear to be doing so. Because of the expansion of the universe. http://curious.astro.cornell.edu/question.php?number=575 So since this is already done naturally is it not feasible to do so artificially?

But aside from all that it seems a little short-sighted to howl about how people can't do something. Time and time again nay-sayers have been proven wrong.

[nessus42]

Did you read the part above where I wrote this:

    It is an irrefutable fact of Special Relativity that if you can transmit any
    information from point A to point B faster than light would travel from point
    A to point B in a vacuum, then there are inertial frames of reference in which
    the information arrived at point B BEFORE it left point A.

Is there a reason why I can write this irrefutable fact a dozen times and people continue to ignore it like it was never stated?

Look, I understand that people want perpetual motion machines. And I understand that people want the Earth to be the center of the universe. And I understand the fact that people want one plus one to equal three. But these things aren't going to happen.

With FTL, you have to pick two out of these three: FTL, Relativity, causality.

It is not a fact of science that you have to pick two out of the three. It is a fact of LOGIC.

Unless you've found a way to transcend the laws of logic, then we have to live within this constraint. So, if you want to have FTL, you either have to give up causality or Special Relativity. Is it conceivable that Special Relativity is wrong? Sure it's conceivable. Is it likely? NOT ON YOUR LIFE. And if you're willing to give up on Special Relativity, when why are we designing space ships based on General Relativity??? When Special Relativity goes out the window, so does GR!

So, are we going to give up on causality instead? Well, who am I to say yes or no. But if we decide that it's okay to give up on causality, then we have to bite the bullet and decide that we're okay with us being in a universe that is really, really strange. E.g., one that will thwart you somehow one way or another in any attempt you might make to transmit certain kinds of information, etc. One that might be perfectly okay with letting you visit your past self, and yet will suddenly give you a case of laryngitis if you try to tell your past self which stocks to buy. Who knows how weird it could get!

Re your space ship being in a vacuum or not: (1) It's still in a vacuum, and (2) it doesn't matter. What matters is if you can use it to transmit information from say Earth to Mars at a speed faster than a laser beam or radio signal would make it from Earth to Mars.

Re galaxies moving away from us at FTL speeds: (1) Yes, galaxies that are very far from us do move away from us at FTL speeds. Can you use this fact to transmit information between two points (e.g. two planets) at FTL speeds? No you cannot! Special Relativity says nothing at all about space itself moving at FTL speeds. It only puts constraints on information traveling from one point to another point at FTL speeds.

Go read the irrefutable fact at the top of this post again. Read it over and over again until you understand it. I can't keep repeating it over and over again for it only to fall on willfully deaf ears.

[sentientbicycle]

OOoohhhh. I totally get it now. You are an unpublished internet stranger and the Alcubierre drive has been scrutinized by some of the top minds in physics. But your criticisms are more important for some reason I don't know. Mkay, going to bed now.

Edit: By the way. I did read the thing about point A and B and understand it completely. The thing is, it doesn't matter. This is why I'm absolutely sure now that you haven't got a clue as to what the drive actually does. Here let me explain it to you like you are 5. If you send a packet of information from point A to point B, and it goes faster than light, then yes that will screw with causality. But if instead you bring point A closer to point B, it will appear as though it is "traveling" (notice the quotes) faster than light. It is however not traveling. it isn't moving. No movement through space. Freefall. zero movement. Stillness. Think about that for a moment. Absolutely positively no movement. Complete stillness. There is a lack of motion with this drive relative to the speed of light. Mind you this isn't a wormhole because even wormholes can screw with causality. This is a space creator/destoyer. Destroys in the front, creates in the back. No movement is involved. I know it's really hard to wrap your head around but just think about it for a couple of days. think about bringing point A closer to point B instead of going through all the trouble of sending the information. Remember, doesn't move.

[nessus42]

Where do any of these top minds of physics say that this drive does not violate causality??? They DON'T! If they asserted such a nonsensical thing, they would be the laughing stock of the scientific world and would no longer be considered any kind of mind, other than a quack. The only reason that you don't see much talk about this violation of causality is that it's just a fact that all physicists know. One physicist doesn't have to tell another physicist that an FTL drive violates causality; it just goes without saying. It would be like one physicist telling another physicist that 1 + 1 = 2. It doesn't need to be said!

It doesn't matter ONE TINY BIT to Special Relativity how it appears to YOU that you got information from point A to point B. What matters is how it appears to an OUTSIDE OBSERVER. If Earth and Mars are still 8 light minutes apart from some point of view, and you managed to transmit information from Earth to Mars in only 4 minutes, then there are frames of reference in which your message arrived at Mars BEFORE it left Earth.

This is just freshman-level Special Relativity. I guarantee you, that no one has found a work-around for that, especially since it is a matter of LOGIC. It follows LOGICALLY from the assertions of Special Relativity. If you wish to deny this conclusion, then you would have to deny Special Relativity.

If on the other hand, you have used your drive to permanently shred up space and time, rapidly crashing Mars into Earth and destroying all life on both planets, leaving the mess like that, and then stating you have successfully transmitted a message at FTL speeds, then more power to ya!

[sentientbicycle]

Alcumbierre himself states that it does not violate causality. from: http://www.npl.washington.edu/av/altvw81.html > The possibilities for FTL travel or communication implicit in the Alcubierre drive raise the possibility of causality violations and "timelike loops", i.e., back-in-time communication and time travel. Alcubierre points out that his metric CONTAINS NO SUCH CLOSED CAUSAL LOOPS, and so is free of their paradoxes. However, he speculates that it would probably be possible to construct a metric similar to the one he presented which would contain such loops.

    So either he's a laughing stock and nobody is talking about that or (more likely) you are wrong.

[nessus42]

He has only stated that there are no closed causal loops for one particular use-case of his drive. He never stated either that causality was not violated from the point of view of a distant observer in a different frame of reference. Nor did he state that such a drive would not allow closed causal loops to be generated. In fact, he implied the opposite.

[lmm]

I'm sure the authors of the paper know that the warpdrive violates causality.

It doesn't matter that you're warping space to move points A and B closer from your perspective. If an outside observer can see you at point A at time t, and at point B at distance d away at time <t+d, you have violated causality, and an observer moving at a suitable velocity will see you arrive at B before you left A. That is a basic, irrefutable fact of special relativity.

[dhughes]

> Is there a reason why I can write this irrefutable fact a dozen times and people continue to ignore it like it was never stated?

Because the tone of your replies are condescending.