The recessional velocity of a distant quasar is measured to be 60% of the speed of light. This speed is large enough that we must take relativity into account in computing its distance, which proves to be 3290 Mpc. Suppose we just use the Hubble law (without taking into account relativity); what is the result?
A)779 Mpc
B)2470 Mpc
C)3290 Mpc
D)10,700 Mpc

Question

Quizplus · Accepted Answer

The Hubble law states that recessional velocity is proportional to distance, without taking into account relativity. Therefore, we can use the equation v = H0*d, where H0 is the Hubble constant. Solving for d, we get d = v/H0. Using v = 0.6c (where c is the speed of light) and a Hubble constant of approximately 70 km/s/Mpc, we get d = (0.6c)/(70 km/s/Mpc) = 2471 Mpc. This is different from the distance we got when taking relativity into account, so the correct answer is B.

The Recessional Velocity of a Distant Quasar Is Measured to Be