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Thank you for explaining the GR vs SR aspect of this. I was somewhat aware that the no-FTL rule was different in GR but I didn't really understand how. I'll h

Thank you for explaining the GR vs SR aspect of this. I was somewhat aware that the no-FTL rule was different in GR but I didn't really understand how. I'll have to look into this more and now I know where to start. I'm not sure I follow the second part, about Lorentz invariance, but my physics is decades old, so that's not surprising. Time to do more reading.

yk 13y ago
Sorry for the botched formatting (HN is for some reason not showing me a edit link :/ ) A quite interesting paper on the topic is McMonigal & al. [1], it is a bit technical but they discuss the Alcubierre warp drive quite nicely. To elaborate on the second paragraph about special relativity, one way to define Lorentz transformations is, that they are the transformations which preserve the causal structure of Minkowsky space. On the other hand, the speed limit is a direct consequence of the Lorentz transformations. So the causal structure and the speed limit are directly related. To look again at the argument that a velocity larger than the speed of light implies causality violation: The moment you argue that a speed faster than the speed of light is possible, you implicitly change the meaning of causality. Then you use the Lorentz transformations to conclude that in on frame of reference event A precedes B and that event B precedes A in another. So you first deny the special status of the Lorentz transformation, just to go on and use Lorentz transformations. And my take on this is a strong maybe, the moment you start talking about local Lorentz invariance violation, anything goes. Perhaps there is causality violation, perhaps not, but this depends on your specific meaning of 'causality' and 'faster than light' and not very much on special relativity. [1] http://arxiv.org/abs/1202.5708 http://arxiv.org/abs/1202.5708

yk 13y ago

Sorry for the botched formatting (HN is for some reason not showing me a edit link :/ ) A quite interesting paper on the topic is McMonigal & al. [1], it is a bit technical but they discuss the Alcubierre warp drive quite nicely. To elaborate on the second paragraph about special relativity, one way to define Lorentz transformations is, that they are the transformations which preserve the causal structure of Minkowsky space. On the other hand, the speed limit is a direct consequence of the Lorentz transformations. So the causal structure and the speed limit are directly related. To look again at the argument that a velocity larger than the speed of light implies causality violation: The moment you argue that a speed faster than the speed of light is possible, you implicitly change the meaning of causality. Then you use the Lorentz transformations to conclude that in on frame of reference event A precedes B and that event B precedes A in another. So you first deny the special status of the Lorentz transformation, just to go on and use Lorentz transformations. And my take on this is a strong maybe, the moment you start talking about local Lorentz invariance violation, anything goes. Perhaps there is causality violation, perhaps not, but this depends on your specific meaning of 'causality' and 'faster than light' and not very much on special relativity. [1] http://arxiv.org/abs/1202.5708 http://arxiv.org/abs/1202.5708