Hubble’s Law and the age of the Universe
The American astronomer Edwin Hubble studied distant objects in the Universe the realised
that the further away from Earth they were, the faster they seemed to be moving. This
relationship became known as Hubble’s Law and can be stated as:
v=Hd
where v is the velocity of a distant galaxy
d is the distance of the galaxy from Earth
H is the Hubble constant
The Hubble constant is actually a measure of how fast the universe is expanding. Since
velocity is normally equal to distance  time, H in Hubble’s Law above must be 1/t and so if
it is assumed that the expansion of the Universe has been uniform, and that the value of H
hasn’t changed, then the age of the universe can easily be calculated by t = 1/H
The data below comes from the Hubble Space Telescope Key Project team. It shows very
precise measurements of distance d and velocity v.
DISTANCE, d (Mpc)
VELOCITY, v (kms–1)
15
1 100
97
6 700
32
2 400
145
10 700
50
3 100
122
9 900
58
4 300
91
5 300
120
9 000
93
7 500
158
8 900
64
5 300
145
9 600
61
3 300
103
5 100
46
3 600
34
1 800
185
9 500
20
1 200


On graph paper or in an excel spreadsheet, graph this data, with distance on the x-axis
and velocity on the y-axis.
Draw a line of best fit (it should pass through the origin) and evaluate the gradient. This
will be your estimate of the value of the Hubble constant, H.
Best fit value of H with unit = ____________________________
Questions:
1.
Calculate the age of the universe using your value for H. Note that you will need to
show your working for the conversion of the units into billion years (109).
2.
Hubble originally found a value for the constant of 530 in the same units as your
graph. What does this value give for the age of the universe? Show your working.
3.
In the 1950s, the famous astronomer Baade, more than halved Hubble’s original
constant. What affect did this have on Hubble's value of the age of the universe?
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