Hello all. This question is not specifically about the theory itself; but the way of explaining or interpreting it. I have found few explanations about theory of simultaneity which explain in the below mentioned fashion. My doubt is that - 1.1 Light speed is same in all the reference frames. 1.2 If that is the case, irrespective of the observer's place, the light would travel with the same speed. 1.3 Go to this http://en.wikipedia.org/wiki/Relativity_of_simultaneity#The_train-and-platform_thought_experiment". Now, consider the first figure - inside the train. Here, the light would travel with the same speed irrespective of the speed of the train with respect to the platform. If that is the case, and if the train is traveling at relativistic speed from left to right, then obviously the light would take longer time to touch the right end than the left end. [Below I have paraphrased the same experiment in the link in my own words ... ] If the speed of light is frame invariant, then the light has to be frame independent. And if it is so, I can consider the following two scenarios. I am on one end of a sufficiently long railway coach and there is a mirror at the other end. Since I am in the frame under consideration, i can measure its true length "L". 1. Now, if the coach is stationary [I know that I cannot say an object to be stationary on its own, but only with reference to some outside frame of reference - just assume this for the time being], and if I fire a light ray, the light ray would reach the mirror in expected time period [L/c]. 2. Now, if the coach is moving at relativistic speed [again the same disclaimer], the light beam would have to take more time to reach the mirror than the usual one [explained in 1]. Is my pt.2 wrong or correct? The pt.2 is contrary to the first case of the example mentioned in the link. It would be great if anyone of you guys clarify my point.