What makes a sonic boom?  The conventional explanations usually say something like, “a shock wave is generated by the jet” which is accompanied by a figure looking something like this:



Figure 1 The Shock Wave


There is no explanation of what this shock wave does, or how it is generated.  And what about the boom?


The real cause lies in the sound the plane generates as it is flying.  The sound moves ahead of the plane at 770 mph, or Mach 1 (Figure 2).  As the plane speeds up (Figure 3), it catches up with its own sound waves, until it reaches Mach 1 (Figure 4).  Now, the sound waves being generated and the sound waves that were previously generated reside in the same point in space.  The sound energy cannot be dissipated and it builds up until you get a huge energy pulse, which makes a load boom.  As the jet goes faster than Mach 1 (Figure 5), it outruns its sound energy, and the sound energy is dissipated behind the plane.  This is why there is only one speed at which there is a sonic boom: Mach 1.



Figure 2 The Jet's Sound Wave At 0 Mph



Figure 3 The Jet Begins To Catch Up To Its Sound Waves



Figure 4 The Jet Catches Up To Its Sound Waves




Figure 5  The Jet Outruns Its Soundwaves