I have two identical clocks. They have batterys carrying exact amounts of energy units. They have identical powerful lasers. They have identical gutters. And a spherical peice of matter. All clocks are measurment tools. The laser shines on the sphere. The sphere moves down the gutter (but takes a very, very logn time) Energy expended equals the amount of displacement the sphere moves down the gutter. Just to Clearify: The spheres in each clock displace exactly the same amount of distance per energy from battery. I put one clock in a spaceship that will travel the speed of light for say thirty years. The clocks are only 'on' in inertia reference. The spaceship arrives after 30 Earth years, during which it was traveling at c. Did each clock expend the same amount of energy after the trip? Did the laws of physics behave the same in each inertial reference? If one clock is slower or faster, what dictated physics to operate at another rate in one clocks frame of reference?