How did the Stern-Gerlach experiment change physics?
The Stern-Gerlach experiment, in 1922, provided direct experimental evidence for a concept that was then primarily theoretical: the quantization of angular momentum. By sending a beam of neutral silver atoms through an inhomogeneous magnetic field, we expected the beam to split into two, based on the orientation of the atom's magnetic moment. What we observed was precisely this splitting, confirming that angular momentum, and therefore magnetic moments, are not continuous but come in discrete, quantized values. This was a critical empirical support for the burgeoning quantum theory.
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