E 6.4 - E 6.7

E 6.4
State Hubble's law
V = Ho d


E 6.5
Discuss the limitations of Hubble's law:
Hubble's law predicts that the recessional velocity of the galaxy will be Hx. the assumption is that the universe is travelling at this constant speed since the beginning of the Universe. However, the gravitational attraction between galaxies means that the speed of recession decreases cosntantly. The fact that we assume that the recession velocity is constant, is a limitation of Hubble's law. Also, the data points in the graph below are scattered around the trend line thus showing that there are quite big random errors in the measurements.