Sincronizziamo gli orologi

Synchronizing distant clocks at rest in the same reference frame is far from a trivial issue. A review is presented of the several problems involved and of the practical approaches adopted in the course of time. The conventionalist view is discussed, and an argument is given in favour of the standard (a.k.a. Einstein’s) synchronization being not merely conventional, but grounded on experimental facts. a result not so obvious as sometimes assumed. The Sagnac effect is examined, as a counterexample to the conventionality of Einstein’s synchronization: in a rotating frame it is impossible to accomplish it in a consistent, i.e. fully transitive way. A case is made for spending some more time than usual in secondary school about these issues: what do we mean when we say that a clock is better than another? How can we synchronize distant clocks? This should happen before relativity enters the stage; rather as a general – and ancient – problem of physics.