News•Mar 13, 2026
Standard Model 5: Spin-1/2 Particles
John C. Baez explains why a spin‑½ particle yields only +½ or –½ angular momentum along any measurement axis. He shows that each quantum state maps to a point on a sphere of radius ½, creating a one‑to‑one correspondence between geometry and spinor states. The article uses this framework to clarify the Stern–Gerlach experiment, illustrating how sequential measurements along different axes produce probabilistic outcomes. The piece bridges basic quantum rules with intuitive visualizations for students and researchers alike.
