I know this has been beaten to death in this forum and other places -> The problem is that I have not come across an explanation which I can understand!! I understand the most basic things of time dilation. And it makes sense to me. However, I cannot grasp the concept of how light always travels at roughly the same speed in a vacuum. If a spaceship travelling at 99% of the speed of light is racing after a photon of light, how is it that the photon is moving away from the spaceship at 100% of the speed of light...? Shouldn't the spaceship be only a small distance from the photon which it is chasing? It seems though that this is wrong. And that the photon should be moving away from the spaceship at c... meaning the photon would be extremely far away from the spaceship?! I have read many explanations, but none do it for me >.< Can someone explain this in a very simple manner? excuse my stupidity on the matter..