Quantum entanglement shows that reality can’t be local. Quantum entanglement stands as one of the strangest and hardest concepts to understand in physics.
Two or more particles can interact in a specific ways that leave them entangled, such that a later measurement on one system identifies what the outcome of a similar measurement on the second system—no matter how far they are separated in space. Repeated experiments have verified that this works even when the measurements are performed more quickly than light could travel between the sites of measurement: there's no slower-than-light influence that can pass between the entangled particles. Imagining the Tenth Dimension part 1 of 2. Symphony of Science - the Quantum World!
Symphony of Science - 'We Are All Connected' (ft. Sagan, Feynman, deGrasse Tyson & Bill Nye)