Even if the electron is acted upon by a torque $ \vec{\tau} = \vec{\mu} \times \vec{B} $, how does it deviate the path of the incoming electrons? To do such a task, you need a force. Where does that force come from? The force comes from this equation: $ \vec{F} = -\vec{ \nabla }U $ where $ U = - \vec{\mu} \cdot \vec{B } $. If the magnetic field $ \vec{B}$ is aligned along say some z-axis, i.e. if $ \vec{B}=B_{z} \space \vec{e_z}$, then this equation tells you that the force is always directed along the z-axis and is proportional to the magnitude of the component of the magnetic moment of the electron along the z-axis (substitute and check that $ \vec{F} = \mu_{z} \frac{\partial B_z}{\partial z} \vec{e_z}$). It does not matter whether there are components of the magnetic moment along other axes, the force is always proportional to the z-component and directed along that axis.
The <PERSON> experiment does not tell you that $ \vec{\mu} = \mu_z \vec{e_z}$, but that $\mu_z$ is quantized to two fixed values. From a classical perspective, we would expect a continuum of values. 418
That does not happen. So we get spin-up and spin-down electrons corresponding to the two fixed values for $\mu_z$. This is from the perspective of the z-axis mind you! We don't know what happens with the components of the moment along the other axes. If we make the spin-up electrons (which are deflected in a certain direction) go through another S-G setup which probes $\mu_x$ say, then we will see that half of them are spin-up along x, and half are spin-down along x. If we make one of these beams go through yet another S-R setup that probes $\mu_z$, classically we expect to get only spin-up electrons 100% of the times, because that is what we started with. But we get 50% spin-up and 50% spin-down.
Two things need explanation: (1) the quantization of space, that is the absence of a continuum of values for $\mu_z$, and (2) the loss of memory of a previous measurement when a new measurement is made. These things cannot be explained classically. 400