Tom and Georgina,
Firstly, no one has a clue why light velocity is 'that' measured velocity, which is why we should take the postulates of SR as the best 'first approximation' of reality. AE didn't pull them out of imagination so as to make a new, weird theory. They are firmly grounded in classical Newtonian progress.
Yes, we can step back and take the analytical view of 'spacetime' and the relative vectors of several observers and do a comparative study of motion in an ubiquitous scalar time co-ordinate frame. But then we abdicate our own perspective as being one of those observers we are observing, we assume a preferred position of observation from Mt. Olympus. Time really is local to the reference frame of the observer whom cannot know of motion as other than relative to another, and can only measure from a set of constant scalar increments common only to ones self. My foot. My pulse. My push, climbing stairs.
Secondly, no one has a clue why the quantity of energy in Planck's Constant is a value preferred by spacetime. But it solved the 'violet catastrophe'. That does not necessarily mean that the Quantum is physically an inviolate 'least allowable quantity of energy'. QM simply and in finality assumes it to be so, axiomatically. And with a specific, stated purpose to deliberately make a system of purely mathematical probabilities.
Of course QM needs 'entanglement'. That's the gravity of the current situation. But QM does not have a theory of gravity, and the classical electromagnetic spectrum model does not have a gravitational component. We lack the necessary 'unified field' rationale to combine electromagnetism with gravity in a manner that explains both (ideal) spherical rest mass, and linear propagation of energy.
So it goes to finding probable connectivity. Like a two gallon pickle jar filled with cats eye marbles, initially at rest on its side, then rolled 2pi or 4pi. What vector does each cats eye now display? What if the pickle jar were on the space station?
Personally, we do not live in all approximate universes because they don't exist in any reality but our best guestimates. I don't expect things to pop into existence without cause, I expect that somewhere, sometime, something won't happen for no reason at all, and that alters what will then happen. jrc