Though I believe I have understood some basic ideas, theories and mathematic formulas of SR, I still have a pretty fundamental question: Many text books start SR with a light clock consisting of two mirrors and a light blip bouncing in between, claiming that when the light clock moves, the light blip travels longer distance per bouncing, resulting in time dilation. Then it claims that other physics phenomena will also slow down - even a person ages slower. But it does not explain why if the light clock ticks slower, other physics phenomena also slow down. Is it possible that lorentz transformation only applies to electromagnetism while galileo transfer still applies to mechanics, even at high speed? As a result, the light clock will slows down but a mechanic clock (for example, spring based clock) will not slow down?