Many relativistic formulas can be derived without explicitly using Lorentz transformations but, instead, directly from Einstein’s postulate: ‘‘All physical laws are the same for all inertial observers.’’ These formulas include time dilation, addition of velocities, the Doppler effect, and optical aberration. From the visual picture seen by one observer, one can deduce the picture seen at the same space‐time point by any other observer, without knowing anything about the speed or the three‐dimensional shape of the observed object. In particular, the apparent visual shape of a moving object is not contracted, but rotated.

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