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)
- Spin | 229, 866, 19
- Dirac equation | 329, 2k, 38
- Relativistic quantum mechanics | 99, 10k, 149
- Quantum mechanics | 169, 20k, 270
- Particle physics | 137, 32k, 512
- Physics | 276, 46k, 825
- Natural science | 0, 61k, 2k
- Science | 0, 66k, 2k
- Ciro Santilli's Homepage | 262, 218k, 4k