Does the Second Postulate Have Experiment Support? (1)
If reasoning cannot settle the problem down, experiment may give us a helping hand.
In the famous Michelson-Morley experiment,
in order to remove all possible error sources from the environment,
the instruments were put on a platform floating in a pool of mercury.
Today, the recognized speed of light in vacuum is 299,792,458 m/s.
I do not know how this number is obtained,
but I can imagine the highly sensitive nature of the experiment.
A regular airliner normally operates at a speed slightly slower than that of sound,
which is about 340m/s at room temperature.
Using an airliner as a moving observer to test the speed of light,
the error has to be controlled within about half the speed of sound.
That error is about one half in one million.
Now the question is: How many experiments have been done to check the light speed using a moving observer?
What kind of accuracy did these experiments provide?
Taking the fact that Special Relativity has troubled millions of us since its birth a century ago,
any such effort must have achieved the same publicity as the Michelson-Morley experiment,
if its result has the required accuracy.
To my limited knowledge, such experiment does not exist.