First off, I guess a solid definition of a perfect vacuum is needed. I think it is a region of space in which no Hadrons, Baryons, or Fermions exist. Is this correct? Secondly, assuming a region of space like this exists, surely this region must be permeated by some form of EM radiation propogating through it, right? With these two questions in mind, my main question then becomes... Isn't it impossible to have a region of space that is devoid of both elementary particles and photons? OT - If one subscribes to idea of a quantum foam, does this foam necessarily permeate every cubic inch of space, or could there be regions of space where no foam exists? Forgive me for the loosely worded questions, I am not conversant enough in QM to articulate them properly. Any suggestions or answers are welcome, ty.