Georgina,
Believe it or not, I have been able somewhat to follow your argument of substantial versus emergent reality and your perspective of Relativity(s). And it bears reminding oneself that Einstein himself felt saddled with the term and reiterated that what was relative, was simultaneity. His argument was that the Newtonian concept in Descartes orthogonal co-ordinate system, of a shoebox filled with identical cubical child's alphabet blocks representing absolute space and time, did not necessarily follow from simultaneity. Rather it is the (any) observer whom with the mathematics of the SR measurement methodology, whom could pinpoint two events at separation, as being simultaneous regardless of whether the event in block A was at a point in A's inertial domain where the rate of time was the same as at the point of the event in the Z block.
Too much emphasis on the 'revolutionary idea', is given this single element of *Relativity* that all relativistic thought has become attributed to him. And the whole scope of intellectual movement of his era has become largely ignored. And that itself has hindered the advance of classical, continuous causality in the quest for a complete theoretical rationale to explain how individual particle field domains in aggregate, meld together into and expanded volume of an inertial, self-limiting gravitational domain within which magentic, electrical and ballistic response all behave identically independent of scale.
As Akinbo asked; What is a magnetic line of force.
It is an isobar of arbitrarily chosen, measured intensity of magnetism which can be plotted as a graphical line. At the scale of a background independent, theoretical free rest mass material particle, the plot would be expected to be spherically symmetrical and no physical boundary would exist between any such arbitrarily chosen line. That intensity can be easily argued to be a functional property of the rate at which time progresses as has been experimentally corroborated, and intensity variation thus being a difference in rate of time.
In that hypothetical context, is true reality, the Universe in Newton's shoebox?
Breaktime for this Bozo, jrc :-)