@ARTICLE {, title = {O paradoxu dvojčat}, author = {Křížek, Michal}, journal = {Obzory matematiky, fyziky a informatiky}, year = {2021}, volume = {50}, number = {2}, pages = {1--10}, issn = {1335-4981}, abstract = {First we present several illustrative examples of the classical twin paradox, since there are still many doubts and conjectures about it. Further, we show that time in a gravitational field on the surface of a spherically symmetric mass body flows as quickly as the proper time of a clock moving by the corresponding second cosmic speed.}, }