The Stern-Gerlach experiment cannot be explained solely by considering the action of charges. The experiment provided compelling evidence for the existence of intrinsic angular momentum, or "spin," in particles such as electrons.
In the experiment, a beam of particles, typically silver atoms or electrons, is directed through a region with a non-uniform magnetic field. According to classical physics, one would expect the charged particles to experience a force proportional to their charge and velocity, causing the beam to spread out continuously into a broad smear on a detector screen.
However, the observed results were drastically different. The beam split into two distinct paths, with particles either deflecting up or down, rather than forming a continuous distribution. This discrete splitting indicated the existence of an intrinsic property beyond charge and velocity that affected the behavior of the particles.
To explain these observations, spin was introduced as a fundamental property of particles. Spin is not a physical spinning motion but rather an intrinsic form of angular momentum associated with elementary particles, such as electrons. Spin behaves differently from orbital angular momentum (associated with the motion of particles in an orbit around an atomic nucleus) and cannot be explained by classical physics.
In the Stern-Gerlach experiment, the non-uniform magnetic field interacts with the intrinsic spin of the particles, causing them to align either with or against the magnetic field. As a result, the beam splits into two distinct paths corresponding to the different spin orientations.
The concept of spin is essential in quantum mechanics and is necessary to accurately describe and predict the behavior of particles at the atomic and subatomic levels. It is an intrinsic property that cannot be explained solely by the action of charges and has no classical analog.