= Pauli exclusion principle
{c}
{wiki}
Initially a phenomenological guess to explain the periodic table. Later it was apparently proven properly with the <spin-statistics theorem>, https://physics.stackexchange.com/questions/360140/theoretical-proof-of-paulis-exclusion-principle[].
And it was understood more and more that basically this is what prevents solids from collapsing into a single nucleus, not electrical repulsion: <electron degeneracy pressure>!
Bibliography:
* https://www.youtube.com/watch?v=EK_6OzZAh5k How Electron Spin Makes Matter Possible by <PBS Space Time> (2021)
\Video[https://www.youtube.com/watch?v=dQWn9NzvX4s]
{title=The Biggest Ideas in the Universe | 17. Matter by <Sean Carroll> (2020)}