What's the Pauli-exclusion Principle?
In 1925, Wolfgang Pauli gave physics his exclusion principle as a way to explain
the arrangement of electrons in an atom. His hypothesis was that only one electron
can occupy a give quantum state. That is, each electron in an atom has a unique
set of quantum numbers (the principle quantum number which gives its energy level,
the magnetic quantum number which gives the direction of orbital angular momentum,
and the spin quantum number which gives the direction of its spin). If this
principle did not hold, all of the electrons in an atom would pile up in the lowest
energy state (the K shell). In fact, we now know that that the Pauli exclusion
principle holds for not just electrons but for any fermions (half-integer spin
particles like electrons, protons, neutrons, muons, and many more.)
Joseph Kozminski, B.S., Physics Grad Student, MSU, East Lansing, MI
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'To myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.'