That the speed of light is variable, not constant, is obvious. Consider the following setup:
A light source emits a series of pulses equally distanced from one another. A stationary observer (receiver) measures the speed of the pulses to be c and the frequency to be f=c/d, where d is the distance between the pulses:
The observer starts moving with constant speed v (v c) towards the light source - the frequency he measures shifts from f=c/d to f'=(c+v)/d:
The following formula is correct:
f' = c'/d
where c' is the speed of the pulses as measured by the moving observer. And now the most difficult question in Einstein's schizophrenic world - a question Einsteinians never think of:
c' = ?
George Orwell: "Crimestop means the faculty of stopping short, as though by instinct, at the threshold of any dangerous thought. It includes the power of not grasping analogies, of failing to perceive logical errors, of misunderstanding the simplest arguments if they are inimical to Ingsoc, and of being bored or repelled by any train of thought which is capable of leading in a heretical direction. Crimestop, in short, means protective stupidity."