Question 10 A quasar is observed to have
a redshift z=0.5. What recessional
velocity does this correspond to?
a.4% of the speed of
light. b.38% of the
speed of light. c.50% of the speed of light. d.77% of the speed of light.
e.99% of the speed of light.
Use the relativistic Doppler equation: v/c = [(z+1)2 -1]/[(z+1)2+1]
V = 0.38 c
Question 11 If the expansion rate is
constant (no acceleration or deceleration)
and H equals 100 km/sec/Mpc (not the real value) then what would be the age of the universe? (Hint: you can
either derive the answer directly
from the appropriate equations, or you can find the answer by comparing this value of H to the more realistic one
of 72 km/sec/Mpc which
implies 13.6 billion years.)
a.5 billion years b.10 billion years c.15 billion years d. 20 billion years
This is just the simple-minded solution, time =
1/H. Working it out on the slide gives the right answer, 10 billion years, which
is 72% of 13.6 billion years.
Also note that even for constant expansion the
Hubble constant would be
larger in the past.