# Why does the light clock thought experiment apply to all clocks?

Ok, assuming the logic of why a moving light clock appears to slow down relative to the stationary observer is because the distance the moving clock photon travels is greater for the stationary observer compared to the moving observer. Now as far as i can see this logic works because a photon moves independant to it the source (i.e. despite the light source moving at (e.g.)200,000km/s, the photon will only be 300,000km/s (not 200,000 + 300,000km/s). Therefore it cannot transverse the apparent greater distance any faster, so the 'tick' of the light clock slows down (relative to the stationary observer).

But why should this logic apply to a normal watch that isnt based on a photon. I mean, its only light that's independant of the speed of its source. Wouldn't the speed of the clock hand be dependant on the speed of its source so it could travel the apparent extend distance faster to equalise the result. Or what if one replaced the light bouncing between to mirrors with a ball bearing......?

I know it does, but any help as to why would be appriciated!
13:14 Tue 15th May 2012