Ray
Really appreciate you reading my essay. Your hurdler was unfortunately an incorrect analogy. Don't worry, most struggle to grasp the 3D visualisation at first, but then it becomes simple, as you see from the posts with yours.
I posted a reply, but reproduce it with a thought experiment here;
"Thanks for your post, and having an initial go, but you're not quite there with your hurdler. That's not what I'm saying. Did you read the 'bus' analogy in Lawrence's string? (repeated by Edwin in mine above).
If one hurdler jumps on a passing bus he's IN a different inertial frame (via acceleration). He may well run along the bus at the same speed as the others, but unfortunately is DISQUALIFIED from being observed in the same terms as the others without a mathematical adjustment. i.e. The camera at the finish is perfectly allowed to see him at an APPARENT C plus V, but there is only one VALID inertial frame, that of the running track.
There may be dozens of hurdlers around, on bikes, in cars, planes on infinitely many vectors, but only those in the SAME INERTIAL FRAME of the observer comply with the rules that the maximum possible speed is 'c'.
This means light on the bus will do 'c' with respect to 'wrt' the bus. (Let's imaging a pulse going through a gas on the bus.). The gas molecules scatter light sequentially, at 'c'. It goes through the window (n=1.5) and air at c/n, and everyone else will recive it at 'c'. The fact that to all them it may APPEAR to be doing C plus V DOES NOT MATTER, because in reality it isn't!!
(This is precisely what Georgina is saying, also consistent with Edwins, Constantinos Regazas and many other good essays here, as the posts above).
Yes it IS different, Yes it IS reasonable huge, and yes it does meet and explain both the SR postulates, and identifies how Equivalence works.! The boundary (between the bus and the track) in space is the quantum mechanism of diffraction of plasma, ionised particles, which form all shocks and may well prove to be the core constituent of dark matter. (Eddington was wrong). GR then slots in neatly as the ions condensed with speed ARE mass, with inertia.
The emipirical evidence is unbelievably consistent once we look. I't the discrete field model,(DFM), and you heard it here first, can you see it too? Have fun exploring it!
Best wishes.
Peter