A popular example of an internal quantum number is known as the electric charge. In contrast, a popular example of an external “continuous” number is known as the mass. However, the general distinction between internal and external numbers is the property of physical quantization, between compactness and continuity, between singularity and uniformity, between anisotropy and homogeneity, between unity and infinity. The decidability of this property is properly given by the results of certain physical measurements. Unfortunately, most often this decidability is being based on the beauty of certain physical theories, which further complicated the property that deepen the complexity to the level of fractionalization of the two electric charges (plus-minus) of QED and the new creation of the three color charges (red-green-blue) of QCD and the unsolved mystery of quark confinement at best made plausible by the ideas of asymptotic freedom and infrared slavery, that respectively explicate why the strong color force gets weaker as the distance between quarks gets shorter, and why it gets stronger as the distance between them gets longer.

Nevertheless, the beauty of a new QSD as the quantum theory of space-time dynamics is its ability to preserve both local and global gauge symmetry without compromising the distinction for internal and external quantum numbers. Although both electric and color charges are examples of true relativistic invariance that is to say their measured values are not changed by increases in velocities approaching the speed of light, the continuous variability of mass approaches infinity from a minimum value as the linear speed approaches lightspeed called the relativistic mass increase. On the other hand, the zero rest mass of light quantum begins its positive definiteness as its speed decreases from the maximum lightspeed such that wherever and whenever two light quanta stop each other on their opposite tracks, the outcome is the creation of one electron and one positron as frequently observed in pair productions of high energy particle physics, thus vindicated the simultaneous exchange of external and internal quantum numbers.