2 00 6 Absolute simultaneity : Special relativity without light signals or synchronised clocks

Using only the reciprocity postulate, it is demonstrated that the spatial separation of two objects, at rest in some inertial frame, is invariant. This result holds in both Galilean and special relativity. A corollary is that there are no 'length contraction' or associated 'relativity of simultaneity' effects in the latter theory. A thought experiment employing four unsynchronised clocks and a single measuring rod provides a demonstration of the time dilatation effect. This effect, which is universal for all synchronised clocks at rest in any inertial frame, is the unique space-time phenomenon discriminating Galilean and special relativity. PACS 03.30.+p In the conventional presentation of special relativity theory (SRT), following the approach of Einstein's seminal paper on the subject [1], light signals and clock synchro-nisation play a crucial role in the development of predictions of space-time geometrical effects on the basis of the Lorentz transformation (LT). However, as early as 1910 [2], it was realised that Einstein's methodology is not the only, and not the most economical, way (in terms both of the number of postulates and their simplicity) to formulate the foundations of SRT. In a previous paper by the present author [3], using a similar approach to Ref. [2], it was shown that only two weak, and, from a naive point-of-view, 'evident' postulates, unrelated to classical electrodynamics or any other dynamical theory, suffice to derive the LT. This is true for events lying along the common x, x ′ axis of two frames S and S' in which the latter frame moves with constant velocity along the x-axis in S. All kinematical and space-time geometrical predictions of SRT may be derived from this LT. The two postulates are that, the LT must be a single-valued function of its arguments, and a restricted form of the special relativity principle that may be called the 'Measurement Reciprocity Postulate' (MRP): Reciprocal space-time measurements of similar measuring rods and clocks in two different inertial frames by observers at rest in these frames give identical results In order to derive the LT for events not lying along the common x, x ′ axis, the further postulate of spatial isotropy is required. This is, to the present writer's best knowledge, the minimum number of postulates, to date, from which the LT has been derived [3] a a Einstein stated explicitly only two postulates in Ref. [1], but at least three other postulates: linearity of the equations, …