Does the sound barrier apply to a silent aircraft? For my summer duty, I was looking at the sound barrier effects with a glimmer of hope to understand them:


"A supersonic aircraft is one that can travel faster that the speed of sound. As the plane approaches the speed of sound, it catches up with the sound waves traveling in front of it and pushes them up against each other. The result is a barrier of squashed air in front of the aircraft." Source  

Is it theoretically possible to design an aircraft totally silent or at least quiet?

In that case would the problems associated with transonic/supersonic speeds disappear, or at least are reduced?


  As the plane approaches the speed of sound, it catches up with the sound waves traveling in front of it and pushes them up against each
  other.


Or is there a silence barrier too?
The sound barrier has nothing to do with the noise the aircraft makes. It has to do with the fact that if it is going fast enough the air can't get out of the way. This creates a shock wave where the aircraft is pushing the air aside. A shock wave is where the speed of the air transitions from faster than sound to slower than sound and involves the release of considerable energy. You can control the shockwave to some extent by careful shaping of the surfaces, but a plane going fast enough can't be silent. 

You can make very quiet sub-sonic aircraft, but they tend to go slowly so that the noise of the air flowing over the craft is minimized.