Stern-Gerlach Experiment

In the experiment setup pictured below, we have Silver (Ag) atoms coming out of a furnace (1). Silver atoms have 47 electrons, 46 of which form a spherically symmetric structure. This results in atoms with a magnetic moment equal to the electron spin of the 47th electron. As the atoms go through the magnetic field below, they would follow a path determined by their magnetic moment along the $z$ direction.

1. Classically, we would expect the atoms to be continuously distributed as their Spin is uniformly distributed on the Circle group ${\mathbb{S}}^1$. This is represented by (4) below
2. In practice, we observe only 2 dots where the atoms are observed. These match the electron having electron spin $S_z=\pm \frac{1}{2}\hslash$. This is known as the measurement problem, where the Wave function collapses upon Measurement. The necessary collapse of the Wave function is made more obvious in the Sequential Stern-Gerlach Experiment.