Alain Aspect, Philippe Grangier, and Gérard Roger conducted experiments to test realistic local theories using Bell's theorem. They measured the polarization correlation of photons emitted in a calcium cascade. Their results agreed with quantum mechanics and violated Bell's inequalities, ruling out realistic local theories. The experiments were performed with a high-efficiency source, achieving high statistical accuracy. No significant changes were observed with polarizer separations up to 6.5 m. The experiment used a calcium cascade emitting two correlated photons. The setup involved lasers to excite calcium atoms, leading to photon emission. The photons were polarized and measured using polarizers. The results were compared to quantum mechanical predictions, showing strong agreement. The experiment tested Bell's inequalities without assuming rotational invariance, confirming quantum mechanical predictions. The results demonstrated that realistic local theories are invalid, and no distance effect was observed on correlations. The work was supported by various collaborators and institutions. The experiments provided strong evidence against realistic local theories and confirmed quantum mechanics.Alain Aspect, Philippe Grangier, and Gérard Roger conducted experiments to test realistic local theories using Bell's theorem. They measured the polarization correlation of photons emitted in a calcium cascade. Their results agreed with quantum mechanics and violated Bell's inequalities, ruling out realistic local theories. The experiments were performed with a high-efficiency source, achieving high statistical accuracy. No significant changes were observed with polarizer separations up to 6.5 m. The experiment used a calcium cascade emitting two correlated photons. The setup involved lasers to excite calcium atoms, leading to photon emission. The photons were polarized and measured using polarizers. The results were compared to quantum mechanical predictions, showing strong agreement. The experiment tested Bell's inequalities without assuming rotational invariance, confirming quantum mechanical predictions. The results demonstrated that realistic local theories are invalid, and no distance effect was observed on correlations. The work was supported by various collaborators and institutions. The experiments provided strong evidence against realistic local theories and confirmed quantum mechanics.