Albert Einstein: "spooky action at a distance"

Quantum entanglement is a phenomenon where two or more particles become linked such that the state of one particle is instantly connected to the state of the other, no matter how far apart they are. If you measure the property (such as spin or polarization) of one particle, the corresponding property of the other particle will be immediately determined, even if they are separated by vast distances—potentially light-years.

This defies classical physics and seems to imply that information between entangled particles travels faster than the speed of light, which conflicts with Einstein's theory of relativity. Albert Einstein famously referred to this puzzling phenomenon as "spooky action at a distance." Experiments, such as those involving Bell's theorem, have repeatedly confirmed quantum entanglement, making it one of the most fascinating and mysterious aspects of quantum mechanics.