Consider a situation in which a charged object which is colorless in a stationary (w.r.t observer) frame is accelerating in a circular path such that it radiates EM waves of specific frequency (corresponding to say green color). Now consider an observer orbiting with the same angular velocity. Now with respect to the orbiting observer the charge is stationary but according to the frame of reference of the body the observer and charge orbiting the body should appear green(because its accelerating). But the observer who does not see any radiated EM waves should view the object as colorless.

So what is the color of the object ?.

Does color also depend on observer's relative motion w.r.t source.

If it does is their someway I could do this practically and prove that such is possible?

  • $\begingroup$ Hint: the observer moving on a circular path is not stationary in an inertial reference frame. $\endgroup$
    – The Photon
    Commented Jan 23, 2017 at 13:20
  • $\begingroup$ Well you could ask the same question but put a "point like" observer in a frame rotating about the centre of the object's orbit $\endgroup$
    – JMLCarter
    Commented Jan 23, 2017 at 13:55
  • $\begingroup$ "Colorless" means it's grey to a human, which is a mixture of wavelengths. You don't seem to intend that meaning, and seem to mean it's not radiating at all when stationary so that would be "non-radiating". $\endgroup$ Commented Jan 23, 2017 at 14:00

1 Answer 1


It doesn't matter where your observer or observers are, the "decision" to radiate or not is made in the frame of reference of the charged object. If there is radiation, different observers can see it frequency shifted, or measure the emission times as different depending on their velocity and acceleration relative to the frame of reference of the object.


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