He everybody :) I guess I am not the only one who cannot comprehend the idea that the light has same speed for all observers, regardless of the velocity between the source and the observer. In an attempt to get a picture of the idea, I constructed a thought experiment which I think could be performed. [PLAIN]http://onegative.org/light1.jpg [Broken] (the image above) Lets imagine that a truck traveling with high speed has attached a light source in its front and a detector "A" on its back. As the truck is moving with constant speed the light source emits a light pulse or a single photon if you prefer so. Knowing the speed of the truck we can calculate after what traveled distance the light will reach detector "A" and on the same line we place detector "B". Now both detectors will detect the light at the same time (simultaneously) [PLAIN]http://onegative.org/light2.gif [Broken] The second image shows the position of the truck when the light hits both detectors. We can see the difference in the distance traveled by the light to the two detectors for the same amount of time. Initially I built this experiment with the truck moving in the right direction, but I found out that it is kind of deceiving to figure out the distance traveled for the light for both detectors. I can post the other images if you think that it would be easier to explain the problem. Respectfully looking forward for your explanation and help. P.S. I'd like to ask Janus to make an animation for the above, which will make it easier for us to imagine the full path of the light as traved to both detectors.