Great Papers #12: The Dirac Equation and Antimatter, 1928

Set out to fix an equation; accidentally predict antimatter. This episode reads Paul Dirac's 1928 "The Quantum Theory of the Electron." Schrödinger's quantum mechanics quietly ignored Einstein's relativity, so Dirac demanded a single equation obeying both — and to make it work, the coefficients had to become matrices. Out fell two gifts, unbidden: the electron's spin (the very property we assumed by hand in the Stern-Gerlach tutorial — here it's forced by relativity), and a shadow world of antimatter (the negative-energy solutions Dirac refused to discard, pointing to the positron, the anti-electron). Carl Anderson found the positron in cosmic rays four years later. Along the way: the square-root-of-relativity trick, the 720° spinor, Feynman's backward-in-time picture, antihydrogen at CERN, the g−2 precision record, PET scans, and the unsolved mystery of why the universe is made of matter at all. Great Papers Batch 3. ——— Series: Great Papers · UnderGrad level. Every equation spoken in full, no chalkboard required. Built by Fermi AI.