The Thomas rotation

We review why the Thomas rotation is a crucial facet of special relativity, that is just as fundamental, and just as "unintuitive" and "paradoxical," as such traditional effects as length contraction, time dilation, and the a mbiguity of simultaneity. We show how this phenomenon can be quite naturall y introduced and investigated in the context of a typical introductory cour se on special relativity, in a way that is appropriate for, and completely accessible to, undergraduate students. We also demonstrate, in a more advan ced section aimed at the graduate student studying the Dirac equation and r elativistic quantum field theory, that careful consideration of the Thomas rotation will become vital as modern experiments in particle physics contin ue to move from unpolarized to polarized cross sections. (C) 2001 American Association of Physics Teachers.