This is probably very wrong. (yes. declarative.)
The way I understood the quantum vacuum, was that it spontaneously produces particle and antiparticle pairs, that exist for a very tiny amount of time, recombine, and then disappear. The energy needed to create these particle pairs from "nothing" is not elaborated on well; it is a matter of some controversy as I understand. However, the existence of these particles has been experimentally verified, as they produce real, measurable effects.
Likewise, a high energy photon has a certain probability of degrading into a pair of antiparticles with low mass, (electron positron pair), which then also recombines back into a high energy photon. This happens in the presence of matter, according to wikipedia. http://en.wikipedia.org/wiki/P... Even the very best made EMDrive is going to have SOME gas inside the chamber, so "Check".
Since the virtual particles have charge, and the electron-positron pair have charge, a charge interaction is possible. Since the quantum vacuum is random, this means that light will suffer some small dispersion from the interaction even in deep space (which also has diffuse hydrogen atoms). The question that makes many scientists so angry, is that when this "real particle pair interacting with a not-real particle pair" happens, the vector of motion of the real particle pair can be altered slightly, as will the not-real pair. That seems to be the explanation for EMDrive. However, the not-real pair will vanish from existence, and the real particles will turn back into a photon.
Energy is exchanged via the interaction, but the energy vanishes on one side of the interaction as the non-particles vanish into the quantum soup again.
A device like the EMDrive tries to manipulate the probabilities of these interactions so that light, and electromagnetic fields in the device create additional interactions.
When both the light and the virtual particle pairs emerge into "Being", they exhibit some electrical charge characteristics. This means that an ambient magnetic field (which will be induced by the cavity resonating with high energy microwaves) will also interact with this exchange. Some of the "momentum" will be conferred to the field, which will then push on the field's source-- the cavity walls.
This means that the interactions going on inside the chamber, if you can cause a statistically relevant change in how the interactions proceed, can produce a net push against the cavity wall which will cause pushing against "light" trapped inside the cavity (the microwaves, as expressed as an antiparticle pair), and the virtual particle plasma that exists only for small moments of time before vanishing.
This appears to violate conservation of momentum, because the other half of the equation literally disappears with the disappearing virtual particles.
it is possible that the kinetic energy imparted to the vacuum particles does not actually vanish, but instead may manifest as a local increase in virtual particle density at the aft end of the device. This could be measured as an increase in the casimir force, if you wanted to check. That's a wildly unfounded idea mind, but I would be curious enough to look if I had the nanotech casimir force detection equipment to do it, and an EMdrive to test against.