A train is moving at a very high velocity and its headlight is on, an observer stands on the track while the train moves towards him, another observer stands at the side of the track while third one on the roof of the train. Now we know the first observer will see the light as blue shifted, but if there are few particles in the path of light that direct it towards other two observers, how will they see the light? What I understand in doppler effect is that, suppose I am holding a torch and its light is in front me in form of oscillating electric and magnetic fields. Now when I move forward with the torch the positions of those oscillations in space also changes, like they move forward in space that much too. So when the train is moving, the headlight constantly gives out new oscillations but as the speed of the wave is constant, the troughs and crests come closer leading to a blue shift in direction of movement of train. For the photons case, I assumed that photons would be coming closer in the same way and local energy concentrations will increase leading to higher frequency light. So basically, is the light actually changing or its just for the observer. This is the best way I can put it in. I request for review of my explanation and please correct me where I was wrong, by reffering to the initial question.