1975 A. 51 140/1 For Klein–Gordon tachyons.., despite singularities in the upper half-plane and superluminal group velocities, signals do not propagate superluminally.
1994 10 Feb. 509/1 If..the influence is communicated superluminally, then time machines must surely be just around the corner.
2005 (U.K. ed.) July 6/2 The early universe was expanding very quickly and the light was emitted in a region that was receding superluminally.