>[!abstract] >Quantum entanglement is the phenomenon where the quantum state of each particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical physics and quantum physics: entanglement is a primary feature of quantum mechanics not present in classical mechanics. > >Einstein and others considered such behavior impossible, as it violated the local realism view of causality (Einstein referring to it as "*spukhafte Fernwirkung*" or "spooky action at a distance") and argued that the accepted formulation of quantum mechanics must therefore be incomplete (Wikipedia, 2025). >[!related] >- **North** (upstream): — >- **West** (similar): — >- **East** (different): — >- **South** (downstream): [[Bell's theorem]]