Seminarium Teorii Względności i Grawitacji

In the talk an analysis of how to measure the circumference of a rigidly rotating circular ring of point particles is presented. This analysis is based on three components which are1. Recent recommendations of the Bureau international des poids et mesures (BIMP) concerning the performance of measurements in accordance with both theories of relativity.2. The Einsteinian approach to the issue of measuring spatial lengths.3. The analytical formalism of the spacetime geometry. The outcome of such an approach seems to lead to rather fundamental conclusions that exceed by far the academic character of the exercise posed at the beginning. One of the consequences is an intrinsic feature which should be taken into account when one measures the proper length of an arc of a spacelike curve in both theories of relativity.