Haisch, Rueda, and Puthoff have, in their 2005 offering, shown that inertia and gravity can be shown as a force upon quark sized matter, a force of resistance generated by the quantum vacuum/zero point field. This resistance arises from the 'every which way' arrangement of the 'partons' (as Feynman called them) which are below the Planck scale of matter. I have decided that the resistance is actually the grains of dimension time as locked to the points of dimension space from the inflationary period. Said another way, dimension time is not what we have assumed it to be. It has linear, planar, and volumetric expressions.
The zero point field being the source for inertial mass and gravitational mass dues to the temporal expression of these partons would explain nicely why a photon crosses the Universe always in the present of its emission/creation, and arrives at a receiver/sensor without imparting an inertial collision ... the time of the photon is planar, whereas the time of the partons is linear.