MMMMM does 0 Kelvin make any sense to any of you? Van der waals won't work because it's still based on Newtonian physics. You'll need Wave functions to actually quantify the quantum vaccum space. Think of it like looking at a hole in the ground, you know it's a hole because you see the ground on the edges of the hole. You'll have to use Schdronger's Wave mech. to know the "quantum ground" to see the "quantum hole" which would be vaccum. And it can't be a "particle" since "photon, boson, or whatever else you want to call it" are based on "wave/particle" concept. I think it's a very good question but we need revised quantum theory to go further. Perhaps a blend of wave mech., probablity and something I'm not very fond of "Strings".