John RC,
"difficult to keep...spacetime from coming apart at the particles." Impossible I'd say. 'Spacetime' means quite different things to different people. After all the nonsensical interpretations that many still cling to Einstein ended up precisely where Minkowski started;
"not 'space' but infinitely many 'spaces' in relative motion" This gives the discrete inertial system or 'field' model (DFM). The particle interactions then divide them.
I could't penetrate far through the haze into your sample jar, so best to offer some simplifications which I think are compatible with that and the above.
Inertia is simply gyroscopic. It's not then bizarre finding a ton weight accelerating under G at the same rate as a pea. Imagine a ton of spinning gyroscopes fixed to a framework. Then beside it one tiny peas shaped gyroscope. Which is easiest for you to accelerate by pushing? Correct, the tiny one. So why do we expect gravity to do the opposite and accelerate the big one faster?
That shown the fundamental error sin all our assumptions. Errors we've become so familiar with that most are unable to challenge them. I did and a very simple model emerged, but it seems most can't so confusion remains.
If you wish to see the model you only need to read the essays. The limit on propagation speed of EM waves is then simple and relates to minimum wavelength gamma, which is at optical breakdown mode plasma density. (I'll post the link to the paper on that if you wish).
Best wishes
Peter
PS. It will make perfect sense to you when you read it but if you don't then also 'rehearse' it the whole dynamic will evaporate as our neural networks don't have a pre-set default mode to 'hang it on'.