PeterDonis said:
The 2nd postulate is a postulate of SR, not aether theory. Unless you can give a reference to back up "your" interpretation of that postulate as a postulate of SR, your comments based on it are personal speculation and are off limits here.
Actually, it was Dale, not me, who first mentioned the aether in this thread.
And in fact, I can give a reference to back up my "interpretation". I hope that Einstein isn't regarded as completely obsolete today. He writes in his
1905 paper, section 3, where he is deriving the Lorentz transformation:
"With the help of this result we easily determine the quantities
,
,
by expressing in equations that light (as required by the principle of the constancy of the velocity of light, in combination with the principle of relativity) is also propagated with velocity
c when measured in the moving system."
So, he justifies the claim that the light speed is
c measured in the "moving system", by saying that it is "required by the principle of constancy of the velocity of light (2nd postulate),
in combination with the principle of relativity (1st postulate)".
He doesn't justify this by the 2nd postulate alone, he also invokes the 1st postulate. I cannot interprete this in any other way than that he in the 2nd postulate only claims that the light speed is measured to
c in the "stationary" frame, and that the 1st postulate is needed to conclude this for other intertial frames too.
Just as I have claimed all the time.
But, if Einstein is completely passé today, then the postulates might be reformulated in most standard texts. Not to the better, in my opinion.