The Interpretation of Inertial Force and The Existence of Absolute   Background
  The formalism of classical particle dynamics is reinvestigated according to the basic requirement of causal consistency, and a new equation of particle dynamics, which is more general and more in line with classical mechanics experiments than Newton's second law, is obtained. More importantly, the inertial frame of reference is no longer required and the inertial force is no longer introduced by hand. The new dynamical equation can be straightforwardly applied in any reference frame as long as which is irrotational with respect to the absolute background of the universe. The nature of the inertial force is nothing but the real forces acting on the reference object. The essence of this reform of classical particle dynamics is just a drawback of traditional formalism in Newtonian mechanics being corrected. However, it may be more important that a logical derivation of this new particle dynamics equation strongly suggests the existence of an absolute background for the whole space of the universe. In physical concepts, the absolute background for space does not conflict with the relative length of the base unit of space in Einstein's Special Relativity and General Relativity. Furthermore, the size of the base unit of space should essentially be understood as the length of the line segment, which is cut from the absolute background of space by the intrinsic physical events. 
ChiYi Chen