Einstein synchronisation is a convention in relativity how to synchronize clocks at different places. Jump to: navigation, search Wikisource has original text related to this article: Relativity: The Special and General Theory Albert Einsteins theory of relativity is a set of two scientific theories in physics: special relativity and general relativity. ...

A light signal is send at time τ₁ from clock 1 to clock 2 and immediately back, e.g. by the mean of a mirror. Its arrival time back at clock 1 is τ₂. The Einstein synchronisation convention sets clock 2 so, that the time of signal reflection is (τ₁ + τ₂) / 2. Whereas the constant two-way speed of light is included in the axioms of special relativity, the Einstein synchronisation convention also sets the one-way speed of light to c. Cherenkov effect in a swimming pool nuclear reactor. ... In epistemology, an axiom is a self-evident truth upon which other knowledge must rest, from which other knowledge is built up. ...

The same synchronisation is achieved by "slowly" transporting a third clock from clock 1 to clock 2, in the limit of vanishing transport velocity. The literature discusses a lot of other thought experiments for clock synchronisation giving the same result.

But it is only in inertial frames where Einstein synchronisation looks so natural, that is easy to forget that it is only a convention. In general frames, most importantly in rotating ones, the non-transitivity of Einstein synchronisation dimishes its usefullness. If clock 1 and clock 2 are not synchronised directly, but using a chain of intermediate clocks, the synchronisation depends on the path choosen. Synchronisation around the circumference of a rotating disk gives a non vanishing time difference whose depends on the direction used. This is important in the Sagnac effect and the Ehrenfest paradox. Today there is even an important practical issue in this, as the Global Positioning System has to account for this effect. In physics, an inertial frame of reference, or inertial frame for short (also descibed as absolute frame of reference), is a frame of reference in which the observers move without the influence of any accelerating or decelerating force. ... In grammar, a verb is transitive if it takes an object. ... The Sagnac effect manifests itself in an experimental setup called ring interferometry. ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...

Literature

• H. Reichenbach, Axiomatization of the theory of relativity, Berkeley University Press, 1969
• H. Reichenbach, The philosophy of space & time, Dover, New York, 1958

Weblinks

• Neil Ashby, Relativity in the Global Positioning System, Living Rev. Relativity 6, (2003), [1]