
495Newtonian Gravity and Newtonian Cosmology
© 2010 Taylor & Francis Group, LLC
So, we can calculate the acceleration of one galaxy A with respect to another galaxy O. We
have associated O with the center of the sphere, and A is at a distance R from it. The acceleration
to be found is a result of the gravitational attraction of matter inside the sphere of radius R only.
According to Newton’s law, it is given by
a = −GM/R
2
. (14.21)
The negative sign in Equation 14.21 reects the fact that the acceleration corresponds to attraction
rather than to repulsion.
Thus, any two galaxies in a homogeneous universe separated by a distance R experience a rela ...