Sonic boom is sufficiently long. A new metric has emerged, known as "perceived" loudness, measured in PLdB. This takes into account the frequency content, rise time, etc. A well-known example is the snapping of one's fingers in which the "perceived" sound is nothing more than an annoyance. The energy range of sonic boom is concentrated in the 0.1–100 hertz frequency range that is considerably below that of subsonic aircraft, gunfire and most industrial noise. Duration of sonic boom is brief; less than a second, 100 milliseconds (0.1 second) for most fighter-sized aircraft and 500 milliseconds for the space shuttle or Concorde jetliner.
Faster-than-light oscillator ticking too fast. In special relativity, it is impossible to accelerate an object the speed of light, or for a massive object to move the speed of light. However, it might be possible for an object to exist which moves faster than light. The hypothetical elementary particles with this property are called tachyonic particles. Attempts to quantize them failed to produce faster-than-light particles, and instead illustrated that their presence leads to an instability. Various theorists have suggested that the neutrino might have a tachyonic nature, while others have disputed the possibility. Mechanical equations to describe hypothetical exotic matter which