Quantum nonlocality is a phenomenon that challenges the classical understanding of distance and separability in the physical world. In classical physics, objects are considered to have independent existences that interact through deterministic forces over time and space. However, quantum mechanics introduces concepts that fundamentally alter this perspective.
Nonlocality primarily emerges in the context of entangled particles. When particles become entangled, the state of one particle is directly linked to the state of another, regardless of the distance between them. A change in the state of one particle will instantaneously affect the state of its entangled partner, a prediction that is at odds with the principle of locality. Locality presumes that physical processes occurring at one location should have no immediate effect on elements at another location unless mediated by some force transmitting at a finite speed, typically the speed of light.
The quintessential test of quantum nonlocality was established through Bell's theorem and subsequent experiments testing Bell inequalities. These experiments, notably those involving pairs of entangled photons, consistently support the predictions of quantum mechanics over classical interpretations. The violation of Bell inequalities confirms the presence of correlations that defy any local hidden variable theories designed to retain the classical notion of inherent properties independent of measurement.
These findings imply that the quantum world does not adhere to classical intuitions of space-time separation. Entangled particles remain interconnected in a manner that does not respect the conventional limits of distance, forcing a reevaluation of the fundamental structure of reality and the nature of causality in the quantum realm. The implications of nonlocality extend into diverse areas of physics and raise profound questions about the completeness of classical explanations, suggesting that underlying quantum processes operate within a framework that is not bounded by the macro-world’s space-time concepts.