dehammer, you go wrong because you are making the (hidden) assumption of an absolute time. In nonrelativistic physics if two observers are moving relative to each other you have a transformation rule like:
x' = x - v t
t' = t
Here x is the position of an event that happens at time according to one observer. According to an observer that moves with velocity v in the x direction the x coordinate of the event is x' = x - v t if at time t = 0 he was at x = 0. t' and t are the same.
Accordng to special relativity, however:
x' = gamma (x - v t)
t' = gamma (t - v x/c^2)
where gamma = 1/(1-v^2/c^2)^?
In special relativity you assume constant c, which then necessarily implies the above Lorentz transformation rules implying that time isn't absolute. If you did have an absolute time then the speed of light would be observer dependent.
The two possibilites are not mutually consistent, they lead to different predictions for various experiments.
