  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.
