Which gives us that (by integrating):

kx + C = E
there is a linear process so k is not 0

{Energy cannot be created or destroyed
{All objects energy is increasing

That gives us:
The objects with energy are fusioning together, undivideably and becoming one with eachother.

I call it quantum fusion, but that term is probably already taken.

There may also be a frequency variation caused by interactions with photons etc. That variations always pendle around the linear process (that is in the middle). Photons enter and leave so the mass would still be increasing.

It may have something to do with the Zero-Point Energy Field. It is always contributing a little effort to the inertial body of mass.

It has itself to do with itself, if nothing else.