Neutrinos were originally proposed as a “desperate remedy” to fix missing energy in nuclear decay, but turned out to be real—just incredibly hard to detect. Tens of quadrillions can pass through matter before one interacts. Los Alamos physicists (Reines and Cowan) confirmed their existence in 1956 using a nuclear reactor as a source. Since then, neutrino experiments have repeatedly exposed gaps in the Standard Model—like neutrino oscillations, which proved they have mass, and ongoing hints at possible “sterile” neutrinos. What’s interesting is how detection capability drove the science: better detectors led to unexpected anomalies which led to new physics. Today, neutrinos are used as probes of everything from stellar processes to matter–antimatter asymmetry, and experiments are still chasing open questions like whether neutrinos are their own antiparticles.