Agreed. The pattern could range practically forever, with "B"s appearing for any "A": A: It's a static solution; the warp bubble is eternal. There is no recip

Agreed. The pattern could range practically forever, with "B"s appearing for any "A": A: It's a static solution; the warp bubble is eternal. There is no recipe for turning it on or off. A: It's a vacuum solution; there is no "ship" inside, and no matter outside. It is everywhere exactly flat except for the compact region of spacetime in the bubble wall. The only way to decide whether it is even meaningfully moving in the sort of way intended is to add something else to the spacetime. One could make a more complicated vacuum solution with a qualitatively similar compact region, or "stitch" Alcubierre's solution into some other solution in a region where the latter is sufficiently flat to use an Israel-Darmois[1] approach, or add matter. A: Adding matter is hard. Practically anything either breaks the metric or alternatively requires releases from well-tested constraints on the eigenvalues and eigenvectors of the stress-energy tensor. There is really no point in rehashing Lobo & Visser [2] here, although it would be a decent public service if a good science communicator explained its results. At least Alcubierre's original paper[3] is short and easily digestible. Everyone should read from the paragraph before eq. (18) to the paragraph following eq. (19). - -- Ultimately though "B"s are slogans, and matching them with pithier "A" slogans won't make "B"s go away (cf. young Earth creationists and anti-vaxxer). Perhaps it's more fruitful to make it easy for people caught in the middle to distinguish between a sloganeer with no idea of the content of the physical theories involved, and someone who at least knows the standard theory and how to use it before attempting to depart from it (thus excluding e.g. Sonny White). - -- [1] Misner, Thorne, & Wheeler, §21.13. [2] Lobo & Visser (!) https://doi.org/10.1088/0264-9381/21/24/011 https://doi.org/10.1088/0264-9381/21/24/011 https://arxiv.org/abs/gr-qc/0406083 https://arxiv.org/abs/gr-qc/0406083 [3] Alcubierre https://doi.org/10.1088/0264-9381/11/5/001 https://doi.org/10.1088/0264-9381/11/5/001 https://arxiv.org/abs/gr-qc/0009013 https://arxiv.org/abs/gr-qc/0009013