Clauser-Horne-Shimony-Holt (CHSH) inequality

The Clauser-Horne-Shimony-Holt (CHSH) inequality is a test in quantum physics that helps determine whether particles are connected in a way that classical physics can't explain. It involves measuring two particles in different ways and comparing results. If the measurements violate the inequality, it implies the particles are entangled—linked in a way that challenges traditional notions of locality and realism. This violation confirms the bizarre, non-intuitive predictions of quantum mechanics, demonstrating that particles can be instantaneously correlated regardless of distance, what Einstein famously called “spooky action at a distance.”