Imagine there is a train moving at .9c with a person on the train and an observer on a platform watching the train go by. The person on the train walks forward while shining a flashlight. To the observer on the platform, the person on the train is time dilated and walks forward in "slow motion," but the observer measures the light from the person's flashlight as c because c is constant and independent of an inertial frame of reference. So my question is, is light (and other massless objects) immune to time dilation? As always, thank you.