Radar Units

Fundamentally, physics, including the kinematics of moving bodies, is based on measurements. The class of measurements we shall focus on are those made by identically constructed ``radar units'', each in its state of acceleration, which may be zero, in which case it is in a state of ``free-float''. The meaning of ``radar units'' is that each one of them has

• a Doppler radar which emits a standard frequency wave train, controlled by an atomic clock of neglegible size (``atomic wrist watch''),
• a frequency analyzer capable of measuring and recording the Fourier spectrum of the reflected Doppler signal or of the pulse train emitted by another radar unit,
• a reflecting surface so as to make the radar unit visible to the radar of the other units,
• a coincidence pulse radar which consists of a transponder (receiver+transmitter), which upon receiving a pulse will emit without any delay a replica of this pulse, and
• a recording device which counts and is capable of storing the intensity of the received pulses.

The coincidence pulse capability implies that if there are two radar units, then a pulse striking one of them initiates a process of a pulse bouncing back and forth between the two radar units. This is depicted in Figures 2 and 3, where the two radar units are labelled A and B.