  Galaxies are huge physical systems having dimensions of many tens of
thousands of light years. Thus any change at the galactic center will be
noticed at the rim only tens of thousands of years later. Those retardation
effects seems to be neglected in present day galactic modelling used to
calculate rotational velocities of matter in the rims of the galaxy and
surrounding gas. The significant differences between the predictions of
Newtonian instantaneous action at a distance and observed velocities are
usually explained by either assuming dark matter or by modifying the laws of
gravity (MOND). In this paper we will show that taking general relativity
seriously without neglecting retardation effects one can explain the radial
velocities of galactic matter without postulating dark matter.
