"Spooky Action at a Distance"
Quantum Entanglement links particles so they share a state regardless of distance. Even if separated by light-years, measuring one instantly affects the other. If one spin is Up, the other is instantly Down.
Einstein, Podolsky, and Rosen (EPR) argued that this violated the speed of light limit, calling it "spooky action at a distance." They believed hidden variables must exist.
However, John Bell's inequality and subsequent experiments proved Einstein wrong. The universe is non-local. Particles do not have defined properties until measured.
This phenomenon powers Quantum Computing and unhackable Quantum Cryptography, revolutionizing information technology.