The idea of a warp drive is to "expand space behind the ship and contract it in front"- in this way reaching a target destination faster than one could conventionally. However, the actual propagation of that space contraction and expansion would be limited by how fast spacetime distortions propagate in general, which historically has been observed to be the speed of light. Does the theoretical mechanism for a Alcubierre drive rely on the contracted space region propagating its effects all the way to the target destination, and would that be limited to the speed of light, ie could spacetime distortions propagate faster than the speed of light?
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Elfeiin asked: "Could spacetime distortions propagate faster than the speed of light?"
No they can't, since the speed of gravity is the same as the speed of light. Therefore the Wikipedia article on the subject and the reference therein states that you would have to build a road or tunnel beforehand:
Wikipedia wrote: "For example, if one wanted to travel to Deneb (2,600 light-years away) and arrive less than 2,600 years in the future according to external clocks, it would be required that someone had already begun work on warping the space from Earth to Deneb at least 2,600 years ago:"
Everett & Roman wrote: "In our four dimensional extension of this metric, a “tube” is constructed along the path of an outbound spaceship, which connects the Earth and the star. Inside the tube spacetime is flat, but the light cones are opened out so as to allow superluminal travel in one direction."
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$\begingroup$ Nice answer (+1) Would you agree that the Alcubierre metric seems to be describing a jet stream current? Steep curvature between the back and front of the pocket means very high geodesic forward velocity. Flat space inside pocket means the plane is not moving relative to the jet stream. Cosmic mass requirements to create such extreme curvature, travel direction being completely uncontrollable, difficulty to stop the plane once destination is close, difficulty to send communication outside the pocket, all seems to be describing a plane in a jet stream? $\endgroup$– JamesCommented Oct 8 at 11:48