Multiple realities
(covers information from several alternate timelines)
A static warp shell is a non-propulsive energy field which could be produced by a vessel's warp drive.
In an alternate timeline, the USS Enterprise-D initiated a static warp shell in three different time periods, to act as an artificial subspace barrier to separate time and anti-time, thereby collapsing an anti-time eruption which had occurred as a result of the convergence of three inverse tachyon pulses in each time period at the same spatial coordinates. The act of collapsing the phenomenon resulted in the creation of a new timeline in which the eruption never occurred. (TNG: "All Good Things...")