Nick,
Right you are , but you used the durtiest word in the SRT language, "absolute", which, as I understand SRT, is a physical impossibility. In another forum that has quietly terminated opertion,currently, I was making the point that two photons emitted in oposite directions to each other have a defined and invariant midpoint. This is so for the reason that light moves in a straight line (isotropically), at a constant veloicty and independently of the motion of the source of the light (so the postulates of light say, which I agree with, so far). Therefore, these photons define an effective absolute zero velocity coordinate point from which all local motion can be measured: that is, from the emission point , which as a "postulational defined point", does not move, period [note the photons need not share the same trajectory line: the trajectories may cross at any angle. Here though the midpoint between the photons become a line bisecting the angle between the trajectories of the photons. The coordinate frame if enhanced in utility in the off parallel case.

I received questions such as, "at zero velocity with respect to what?" "Nothing", I say, " the point simply isn't moving, read the postulates". There are of course the "but an observer on the moving frame sees it differently and she considers herself at rest wrt the stationary fraem". "Fine", I say "let her consider all she wants to, Does her mere "perspective", or consideration" define the physics of time dilation and frame contraction?"

The positulates say the light not only doesn't know the frame is in the neighborhood, it could care less it it did know the frames was nearby, and moving though assumed at rest. You can fool humans into believing SRT , but you can't fool a photon, especially a photon that has moved a distance ct, then reflected back to the actual emission point after travelling another distance ct (total distance the left photon moves now 2ct). The physical device that emitted the photons has moved away from the point of emission, which is invariant, not because I say so, but because the photons have defined the point as such. I can certainly understand the observer looking at the point there in front of her and with no evidence one way or the other she assumes she is at rest. And, lo and behold, the photons begin to adjust speed just to satisfy her 'justified' assumption that she isn't moving.

If she were to look at the condition from the perspective that she had witnessed many similar tests when the frame was actually at rest wrt the embankment, and even conducted tests identical to the one she is now enagaged in many hundreds of times, she might just make a guess that she might be moving; before any "perceptions" are uttered that will change the physical dynamics of the motions under consideration -- she waits until all the data arrives. Then her perceptions and judgments can be based on rational structures such as experimental results, personal experience and an enhanced and educated sense of multi-angled understanding.

Isn't it SRT that lauds the acceptance of conditions that are "counter intuitive", and so very proudly so (as if the speakers were "special")? And aren't these notions advertised with a background tone of condescention and near derision directed at anyone maintaining a mental state of rational thought, based on observation and analysis?
In the figure time is broken down into 4 slots, 0,1,2,3 The emission point is invariant through out which is shown by the vertical line extending through all the time slots. Instead of defing the distances withmeter sticks, I merely use the distance traveled by light in time t, which seems to work rather nicely. For a mere "Newtonian" model light is a failry smooth sailing entity, but then this is just my opinion.

A typical figure posted regarding "zero velocity coordinate frame".

The arrangement here is a linear Sagnac setup. SRT says the photons will arrive at the two reflectors simultaneously, when the frame is moving wrt the stationary frame. This means that the photon that is chasing a detector/mirror goes through a contracted space with time dilated, and, I supppose, for the other photon moving toward an oncoming detector, the space and time are expanded to accomodate that photon moving left. Just think about it: the dilations, contractions and expansions are exactly enough to place the photons at the detectors simultaneously.

Am I getting this straight?: In SRT there is loss of simultaneioty when there is simultaneity, but when there isn't simultaneity then there is simultaneity? Well at least I know now what the words, "counter intuitive" mean.

Geistkiesel