Since I was typing up my question:
So general relativity strictly speaking is a theory where only fields are allowed. To make calculations in it we often use the fluid approximation and think the matter surrounding us instead of stars, planets, dust, vacuum, etc as a continuum. Since I have used an approximation on the side of (the stress energy tensor) Einstien's field Equations (which introduces an error) what error is introduced in the einstien tensor. Specifically what does error does this introduce to the geodesic equation