Why time slows down as you approach the speed of light ? The light clock thing just doesn't work for me - I can see where its going and how using one its possible to argue that the time when observed from a stationary object appears to be running slower - but what about a normal every day clockwork mechanism on a watch ? How would that ever run slower ? If you were to measure time not by a light clock or by a watch but instead by the decay of radioactive material how would that be slowed down ? I can see how an observers perception of time, or the mechanisms we use to measure time could be slowed down (in the instance of the light clock) but I can't understand the Twins Paradox at all. Sorry I can't get my head round this at all... Can any clever person out there explain it ? And just so its bass orientated would I need to change the speed on my metronome (or drum machine?) if I ever get a gig on a near light speed interspace cruise ship ?