If the recessional speed of a galaxy is a significant fraction of the speed of light, each of the following expressions will be valid EXCEPT ONE. Which one is ONLY valid when the velocity is much less than the speed of light?

Question

Quizplus · Accepted Answer

The expression z = v/c (where z is the redshift, v is the recessional velocity, and c is the speed of light) is only valid when the velocity is much less than the speed of light. This is because it derives from a non-relativistic approximation. For velocities approaching the speed of light, relativistic effects become significant, and more complex equations are required to accurately describe the relationship between velocity and redshift.

If the Recessional Speed of a Galaxy Is a Significant