Quantum Entanglement

Quantum entanglement occurs when two particles become correlated in such a way that the quantum state of each cannot be described independently — measuring one instantly determines the other's state, regardless of distance. Einstein called it 'spooky action at a distance' and believed it proved quantum mechanics was incomplete (EPR paradox, 1935). John Bell formulated an experimental test in 1964; multiple experiments since (most definitively by Alain Aspect, 1982, and others) have confirmed that entanglement is real — non-local correlations genuinely exist. The 2022 Nobel Prize in Physics was awarded for these experiments. Quantum entanglement doesn't allow faster-than-light communication (the correlation contains no usable information), but it enables quantum cryptography (unhackable communication) and quantum computing.