Sound barrier
The sound barrier was the point at which an object started moving faster then the speed of sound. It used to be thought that the sound barrier could not be broken, but Chuck Yeager proved this wrong. Sybok cited this as one example of the unknown which man often feared. ()

In 2368, prior to the first flight of the soliton wave rider, Geordi La Forge  equated seeing Yeager breaking the sound barrier and Zefram Cochrane engaging the first warp drive to the impending event. ()

See also
Hypersonic pulse

External link 
 
Physics