In the early 1920s, scientists Otto Stern and Walther Gerlach conducted an experiment involving silver atoms and a magnetic field. They were aiming to disprove quantum theory, but instead, they made a significant discovery. The silver atoms, when subjected to the magnetic field, split into two distinct paths. This finding confirmed the existence of quantum phenomena and shook the world of physics. However, the interpretation of the experiment was later found to be incorrect. The splitting of the atoms was not due to the orbit of their outermost electron but rather the quantization of the electron’s internal angular momentum, known as spin. This serendipitous discovery led to a deeper understanding of quantum mechanics. Despite attempts by theorists in the 1930s to explain the experiment with a simpler interpretation, it was ultimately determined that splitting and recombining the electron’s two identities was impossible in practice.
https://www.quantamagazine.org/the-often-overlooked-experiment-that-revealed-the-quantum-world-20231205/