Muon Anomalous Magnetic Moment Measurement

Fermilab's Muon g-2 experiment measured the muon's anomalous magnetic moment to 0.46 ppm precision (2021), confirming and sharpening a possible discrepancy with the Standard Model prediction first suggested by BNL's E821 experiment in the early-to-mid 2000s (real precedent confirmed via OpenAlex noise test, not a single new 2021 finding). Status set to disputed rather than foundational because whether this constitutes evidence of new physics is genuinely unresolved: the 2020 consensus theoretical prediction implies a significant discrepancy, but a competing 2021 lattice-QCD calculation (the BMW collaboration) predicts a value close to the measurement, largely erasing the tension -- the measurement itself is solid, the physics interpretation is not.