I think he is simply saying this: 1] Even at the smallest measurable point, there is always something going on - as opposed to absolutely nothing - because there are always photons passing through any point. 2] At that smallest measurable scale, in that smallest measurable volume, any photons that enter it would pretty much essentially have to collide, or at least intersect. I don't think he meant to invoke "vast" numbers of anything. Arthur: are you aware of bosons and fermions? Bosons (such as photons) do not obey the Pauli Exclusion Principle, which means, unlike fermions (such as atoms) they do not take up volume - you can have as many as you want in a volume. They generally don't interact, and the volume doesn't get "saturated" like can would with atoms.