Observers at rest in two inertial reference frames are located
within the propagation space of the same electromagnetic
wave. Raising receiving antennas in a suitable way, these
observers use the electromagnetic oscillations in the wave as
an electromagnetic clock. The invariance of the wave phase
ensures that the observers of the two frames detect the same
phase of the oscillation when they are located at the same
point in space and consequently theirs synchronization proceeds
automatically. Because the Doppler Effect is free of any
clock synchronization, we use the formula that accounts for
this effect for deriving the basic formulas of relativistic kinematics.
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