Editing Alcubierre drive (section)

===Placement of matter===
Krasnikov proposed that if [[tachyon]]ic matter cannot be found or used, then a solution might be to arrange for masses along the path of the vessel to be set in motion in such a way that the required field was produced. But in this case, the Alcubierre drive vessel can only travel routes that, like a railroad, have first been equipped with the necessary infrastructure. The pilot inside the bubble is causally disconnected from its walls and cannot carry out any action outside the bubble: the bubble cannot be used for the first trip to a distant star because the pilot cannot place infrastructure ahead of the bubble while "in transit". For example, traveling to [[Vega]] (which is 25 light-years from Earth) requires arranging everything so that the bubble moving toward Vega with a superluminal velocity would appear; such arrangements will always take more than 25 years.<ref name="Krasnikov1998" />

Coule has argued that schemes, such as the one proposed by Alcubierre, are infeasible because matter placed ''en route'' of the intended path of a craft must be placed at superluminal speed—that constructing an Alcubierre drive requires an Alcubierre drive even if the metric that allows it is physically meaningful. Coule further argues that an analogous objection will apply to ''any'' proposed method of constructing an Alcubierre drive.<ref name="Coule" />