http://www.einstein-online.info/elem...speed_of_light
"All the different relativistic effects combine, quite generally, so that the following postulate holds true: For any observer on one of the space stations (for any inertial observer, in short), any light signal moves through empty space with the same constant speed, c=299,792,458 kilometers per second, independent of the motion of the light source."

Here are observers for which light does not move through empty space with the same constant speed, even though relativistic effects combine so craftily:

http://rt.com/news/225879-light-speed-slow-photons/
"Physicists manage to slow down light inside vacuum (...) ...even now the light is no longer in the mask, it's just the propagating in free space - the speed is still slow. (...) "This finding shows unambiguously that the propagation of light can be slowed below the commonly accepted figure of 299,792,458 metres per second, even when travelling in air or vacuum," co-author Romero explains in the University of Glasgow press release."

http://www.upi.com/Science_News/2015.../1191422035480
"The speed of light is a limit, not a constant - that's what researchers in Glasgow, Scotland, say. A group of them just proved that light can be slowed down, permanently."

https://www.youtube.com/watch?v=rM-fGNxxmSE
Glasgow researchers slow the speed of light

Do other scientists think of this slow speed of light? No one does:

http://ebooks.adelaide.edu.au/o/orwe...hapter2.9.html
"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."

Pentcho Valev