Simple question, but I don't expect a simple answer. What are the causes of Time Dilation relative Velocity? I can swallow the fact that gravitational fields can change the speed of time locally. But velocity? What the process behind Time Dilation related to velocity? I can never seem to get this question answered no matter what site I search. I'm sorry this is my one and only post but this is a burning question of mine. Is it just some math or are there practical reasons for Time Dilation from Velocity? - Thanks in Advance.