I'll respond to jjw before I read the following replies, so I don't steal any possible theories which might bac kme up a bit.
What makes me think that the speed of light is not constant?
Firstly, it is the ONLY constant.
Secondly, it means that light motion is not relative. It means that photons are the ONLY thing which relativaty does not apply to.
It is almost as if there is an ether again, through which only light travels.
I suppose that the only thing which has brought this back to my mind was reading a thread about black holes.
It made me wonder if, like the energy which escapes black holes, light does travel at greater speeds, but, transforms to a "quantum" format which, just as energy penetrates gravitational fields to escape black holes, penetrates all matter, uncluding our eyes, and all measuring euipment.
I could never understand why light emmited from an object moving towards us at half the speed of light moves at only the speed of light, not 1.5 x c. I'll just have to accept it as a fact I think.
Sorry jjw, that was not even philosophical, far less scientific.
Maybe matter is moving towards us at speeds above c, such that we cannot see it coming
