I’d like to describe this in terms of energy rather than mass, using the most ubiquitous “particle” we see, namely the photon. If we consider one wavelength of the archetypal sinusoidal electromagnetic waveform, the electric field amplitude denotes the degree of spatial twist or deformation. If we could freeze-frame a photon in a cubic lattice representing space, the positive peak denotes a maximum twist where a horizontal lattice line has rotated to this disposition: \ . Tracing the waveform with your finger, the midway zero point indicates a rotation back to horizontal: _ , whilst the negative peak denotes a reverse rotation like this: /.
The magnetic field amplitude indicates the rate of the rotation, or “rate of turn”. There is however only one true field involved, which is the electromagnetic field. I have a separate essay/chapter on this, which describes it as a geometrical spatial disposition, essentially a “twist/turn” field.
The sinusoidal electromagnetic waveform is giving us the upper slope of pulse of stress-energy, essentially a pressure pulse. There’s an electromagnetic field variation, but no charge is present. Instead there is a form of current, namely an alternating “displacement” current. The result is rather like a gravitational wave in that there’s a change in distance as it passes through. The displacement rises to 3.86 x 10[SUP]-13[/SUP]m then falls back to zero. This is a distance or extension, and relates to Planck’s constant h in E=hf because action has the dimensionality of momentum x distance. And since this is a pressure pulse in a volume rather than at a surface, we have to consider the pressure to be isotropic, and the slope to be symmetrical in the photon polarization plane. It thus takes the lemon-like outline of a wavepacket. See arxiv.org/abs/0803.2596 figure 2.
This pressure imparts a pressure gradient into the surrounding space. When a significant amount of energy is tied up as the matter of a planet, this pressure gradient measurably alters vacuum impedance or the “strength” of space via a form of compression. Hence permittivity (twistability) and permeability (reciprocal of turnability) are altered, hence c varies. The end product is inhomogeneous space, or a gravitational field.