Abstract

The roles played by real and apparent effects in Special Relativity are clarified. It is found that the observed effects of slowing down of moving clocks and shortening of moving rods in general are composed of two parts; a real part due to the movement with respect to the privileged frame and an apparent part due to the chosen synchronization. The question about the measurability of the one-way velocity of light is discussed. It is found that this question has no meaning within the Einsteinian interpretation of Special Relativity, whereas it within the Lorentzian interpretation is meaningful. Its answer is probably 'no', however, since a positive answer would mean that Poincare's principle about the impossibility to measure absolute velocities would be falsified.