Violation of local realism with freedom of choice

Understand

Bell's theorem shows that local realistic theories place strong restrictions on observable correlations between different systems, giving rise to Bell's inequality which can be violated in experiments using entangled quantum states.

• Bell's theorem is based on the assumptions of realism, locality, and the freedom to choose between measurement settings.
• In experimental tests, "loopholes" arise which allow observed violations to still be explained by local realistic theories.
• Violating Bell's inequality while simultaneously closing all such loopholes is one of the most significant still open challenges in fundamental physics today.