Imagine the following scenario: Persons A and B are situated like so: A <--------C B There is a gun at C which is firing one bullet per second (from the reference frame of A) directly between A and B. They each observe the bullets passing between them. Imagine person B is undergoing time dilation relative to person A. We immediately run into problems. One of the following two scenarios must result: 1) When A and B are asked how many bullets have passed them, they give the same number as an answer. That's not possible if time for person B is passing at a different rate. For example, if time is passing at half the rate for B, he should only observe half the number of bullets as A did. 2) A and B give different answers. How is that possible since the bullets are coming from the same gun? This situation is directly analogous to two people inside of a tall building, one on top, the other on the ground floor. If time for the person on the top is passing more quickly then everything is speeded up, including the motion of the sun through the sky. Eventually, the person on top will be a day, then a week, then a month ahead. He will therefore observe more sunsets and sunrises than the person on the bottom. But how is that possible if they are fixed at the same location on Earth?