Physicists consider the Coulomb force and the strong force to be independent fundamental forces because of their distinct behaviors and the different ways in which they manifest in physical phenomena. The fact that they are linked by the fine structure constant does not diminish their independent nature but rather provides insights into the underlying connections between different fundamental forces.
The fine structure constant, denoted by α (alpha), is a dimensionless constant that characterizes the strength of the electromagnetic interaction between charged particles. It arises as a combination of various fundamental constants, such as the elementary charge (e), the speed of light (c), and Planck's constant (h), in the context of quantum electrodynamics (QED). The fine structure constant is approximately equal to 1/137 and is a measure of the relative strength of the electromagnetic force compared to other forces.
The fine structure constant also appears in the theory of quantum chromodynamics (QCD), which describes the strong nuclear force that binds quarks together within atomic nuclei. The strong force is responsible for holding protons and neutrons together, but it is significantly stronger than the electromagnetic force. However, it is important to note that the strong force and the electromagnetic force have different fundamental properties and act on different types of particles.
While the fine structure constant appears in both QED and QCD, it does not imply that the Coulomb force and the strong force are the same or directly linked in the same way that, for example, the electromagnetic and weak forces are unified in the electroweak theory. The fine structure constant provides a measure of the relative strengths of the electromagnetic and strong forces but does not imply that they are dependent on each other.
Fundamental forces in physics are often treated as independent based on their unique behaviors, properties, and range of interactions. While there may be underlying connections between different forces, as suggested by the unification theories pursued in modern physics, these connections are explored through more comprehensive frameworks, such as Grand Unified Theories (GUTs) or theories of everything (such as string theory or M-theory), which aim to unify multiple fundamental forces into a single framework.
In summary, the independent treatment of the Coulomb force and the strong force as fundamental forces in physics is based on their distinct behaviors and properties, despite the presence of the fine structure constant as a common factor in their respective theories. The fine structure constant serves as a dimensionless measure of the relative strengths of the forces, but it does not imply a direct dependence or unification between them.