Light on light: A response to Grøn

Einstein's second postulate (light-speed constancy) is modified in the following manner:(1) as to motion of light emitters, no modification is made;(2) as to motion of light absorbers, if the absorber moves with velocityv with respect to the observer, that observer will attribute to light the velocity (c+v). It is shown, with reference to the original Einstein train example, that such a modification of the second postulate restores to kinematics a concept of distant simultaneity. Thus is indicated the complicated (acausal) behavior that must be attributed to light in order that the simple behavior earlier attributed ⁽¹⁾ to matter (nonoccurrence of the Lorentz contraction) may be consistent with all known facts. A reply is made to Grøn's critique ⁽²⁾ of the earlier paper on metric standards. It is concluded that further experimental data are needed to decide the simple-light-complicated-matter versus complicated-light-simple-matter issue.