Dear Friends, Discussion of the Einstein's Special Relativity clock paradox is often complicated by the role of accelerations and objects following curved or polygonal paths. In the following example considers the clock paradox in a situation which only involves linear motion. Imagine a rod with a clock and observer at each end. Following the Einstein/Poincaré method of clock synchronisation by light flashes, the observer at clock A sends a light flash to clock B, observes the reflected return flash and establishes that clocks A and B are synchronised. He also establishes that the length of the rod is L = t/c, where t is the time taken for a light flash to go from A to B. Imagine that there is a second rod with clocks (and observers) C and D at its ends, which is moving at velocity v towards the first rod, travelling on a line parallel to rod A-B which passes immediately alongside A-B. The observer at clock C sends a light flash to D, observes the reflected return flash and establishes that (in his frame of reference) clocks C and D are synchronised. He establishes that the length of the rod is also L (i.e. the same as the length that observer A has measured between A and B). When the rods are positioned with clock C alongside clock B, the observer at B compares their readings and finds that both clocks show t=0. Questions: (i) when the rod moves on and clock C is alongside A, what times does observer A see on clocks A and C? (ii) when clock D is alongside B, what times does observer B see on clocks B and D? Also (iii) when clock C is alongside A, what times does observer C see on clocks A and C? (iv) when clock D is alongside B, what times does observer D see on clocks B and D?