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The models/depictions I've seen of warp bubbles show space compressed ahead of the bubble and expanded behind, so that the space inside the bubble moves with respect to the space outside. If that is so, then what is happening at the sides? It would seem that there is some sort of shear taking place between the space inside and outside. Is that correct, or is that based on a misinterpretation of the model?

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I don't really know the answer, so this is just speculation. "In front" of the bubble could span side to side, and "behind" the bubble could be the remaining 180 degrees. There is no "side" in the sense you mean, though the sides require negative energy. –  markovchain Aug 6 '13 at 17:06
There aren't really sides, there are places where the spheres overlap, touch or don't meet based on their radius. –  user6972 Aug 7 '13 at 7:22

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From Wikipedia:

Alcubierre has shown that a ship using an Alcubierre drive travels on a free-fall geodesic even while the warp bubble is accelerating: its crew would be in free fall while accelerating without experiencing accelerational g-forces. Enormous tidal forces, however, would be present near the edges of the flat-space volume because of the large space curvature there, but suitable specification of the metric would keep them very small within the volume occupied by the ship.

See also: http://arxiv.org/abs/gr-qc/0009013

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I don't see how this answers the question. –  John Rennie Jan 3 at 11:57
He asked what would happen along the sides of the bubble, and according to that source, tidal forces would, indeed, be present, as he assumed. –  AdamHovorka Jan 3 at 21:27

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