Subject: Sound waves in vacuum

Traditional experiments on sound waves in a vacuum have suggested
that sound waves do not travel. 
Howvever, since pressure waves cannot propagate from a low 
pressure area to a higher pressure area, would it not be possible 
that we are just unable to register anything, being on the 
outside the vacuum?
I would also like to know if any experiments have studied the  
ultrasonic waves in vacuum.

Etienne Szekely

Re: Sound waves in vacuum