Remember this little rule from High School physics or chemistry class? Usually taught as: No two electrons can occupy the same quantum states at the same time. Or, more generally, for those of us who went to school beyond the High School level: No two identical Fermions may occupy the same quantum state simultaneously.

Have you ever asked WHY this is so? Do you have an intuitive way of explaining the underlying cause for the above rule to your 12 year old kid, say? Not to worry. At the time of this writing  no one has such an intuitive and fundamental explanation. I recall reading Feynman’s lectures on physics and the dude himself admitting that because he could not come up with a simple and intuitive explanation for the Pauli Exclusion Principle he probably does not really understand it very well. Without this rule that is taught to all students of chemistry and physics without further explanation (and don’t give me the “wave-function for fermions are anti-symmetric” stuff; that really is just re-stating the same assumptions using different words) it’s impossible to understand anything as far as atoms or nuclei are concerned. I personally always hated this rule, because it was introduced ad hoc, without any explanation. Now I know that there is none, so far.

Anyway, I was reminded of this long forgotten little fact while browsing the web yesterday and stumbling upon a post on Wolfgang Pauli that has him ranked as the #10 most important physicist of all times.

P.S.: Wolfgang Pauli himself writes on page 31 of his Noble Lecture dated December 13, 1946 that

Already in my original paper I stressed the circumstance that I was unable to
give a logical reason for the exclusion principle or to deduce it from more
general assumptions. I had always the feeling and I still have it today, that
this is a deficiency.