1922 – Stern-Gerlach experiment

In 1922, the Stern-Gerlach (named after Otto Stern and Walther Gerlach) experiment sent a beam of silver atoms through a deflecting magnetic field and onto a collecting plate. Charged electrons orbiting the nucleus of an atom create a “magnetic moment” (a vector of twisting force) that makes the atom behave as though it were a tiny magnet. The scattering of the silver atoms by the deflecting field would demonstrate the nature of the magnetic moment. Classical mechanics predicted that the beam would be spread out randomly and smoothly because the magnetic vector of the electron was expected to be random. Instead, the beam was split cleanly into two distinct halves. This suggested that the magnetic vector had two possible states and eventually led to the concept of electron “spin”.

PRECURSOR:
1873 – electromagnetic waves
1896 – Zeeman effect
1913 – quantum theory

CONCURRENT:
1924 – spin (Pauli)

SUBSEQUENT:
1926 – wave mechanics – Schrodinger wavefunction equation
1928 – Dirac equation

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