  Besides the two fundamental postulates, (i) the principle of relativity and
(ii) the constancy of the one-way velocity of light in all inertial frames of
reference, the special theory of relativity employs another assumption. This
assumption concerns the flat structures of gravity-free space and time in the
usual inertial coordinate system. We introduce the primed inertial coordinate
system, in addition to the usual inertial coordinate system, for each inertial
frame of reference, and assume the flat structures of gravity-free space and
time in the primed inertial coordinate system and their generalized Finslerian
structures in the usual inertial coordinate system. Combining this alternative
assumption with (i) and (ii), we modify the special theory of relativity. The
modified theory involves two versions of the light speed, infinite speed c' in
the primed inertial coordinate system and finite speed c in the usual inertial
coordinate system. It involves the c'-type Galilean transformation between two
primed inertial coordinate systems and the localized Lorentz transformation
between two corresponding usual inertial coordinate systems. It also involves a
new physical principle. This principle is applied to reform of mechanics, field
theory and quantum field theory. The validity of relativistic mechanics in the
usual inertial coordinate system remains, while field theory is freshened.
Based on the establishment of a transformation law for the quantized field
systems, we construct a convergent and invariant quantum field theory, in full
agreement with experimental facts, founded on the modified special relativity
theory and the quantum mechanics theory.
