(Solution) - Some of the familiar hydrogen lines appear in the spectrum -(2025 Original AI-Free Solution)

Paper Details

Some of the familiar hydrogen lines appear in the spectrum of quasar 3C9, but they are shifted so far toward the red that their wavelengths are observed to be 3.0 times as long as those observed for hydrogen atoms at rest in the laboratory.
(a) Show that the classical Doppler equation gives a relative velocity of recession greater than c for this situation.
(b) Assuming that the relative motion of 3C9 and Earth is due entirely to the cosmological expansion of the universe, find the recession speed that is predicted by the relativistic Doppler equation.