Aspects of clock synchronization in relativistic kinematics -- a tutorial

Abstract

This tutorial, addressing physics teachers and undergraduate students, aims at clarifying some aspects of time in special relativity. In particular, time dilation is usually presented only as the well-known ratio of lab time over proper time, $R$. Above ratio is useful, e.g. for describing the decay length of an unstable particle in the lab. But essential characteristics of time dilation, missed out in many textbooks, are manifest in the differences (quadratic, absolute and relative) between lab time and proper time. After an introduction to the basics, we regard the movement of a clock over a fixed spatial distance $\Delta x$. Explicit formulae are given for $R$ and for the differences, and their behaviour as functions of the velocity is discussed and plotted. Approximate formulae are given for very slow movements. Time synchronization within an inertial system by "slowly" moving a clock over a finite distance $\Delta x$, mentioned vaguely in some textbooks, may quantitatively be comprehended by requiring the time difference to be less than the clock's time resolution. We derive explicit formulae for the maximal velocity obeying these constraints (to the best of our knowledge not presented elsewhere).