or clock paradox has been a subject of lively discussion and occasional disagreement
among both relativists and the public for over 100 years, and continues to attract
physicists who write papers giving new analyses or defending old ones, even though
many physicists now consider the matter only of educational interest. This paper
investigates the number of papers, which is increasing, and trends in explanations,
some of which are now targeted at professional physicists and other of which are
targeted at optical or radar visualization rather than problem solving. Observations
of students indicate that the latest techniques help but only somewhat. An analysis
is made of 21 previous treatments appearing in the education related American Journal
of Physics, Einstein’s discussions and several other pedagogical papers. A new memory
aid for simultaneity transformation is given that puts it on a par with “time dilation”
and “length contraction” for quick and easy problem visualization. The point of
view of a trailing twin is introduced to show how simultaneity changes account for
missing time in the turnaround. Length contraction is treated on equal footing with
time dilation, and Swann’s insight into clocks is extended to lengths. Treatments
using the conventionality of simultaneity are seen as equivalent to choice of co-moving
frames. Responses to difficult questions are suggested which avoid being dismissive,
and engage students’ critical thinking.
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