In quantum mechanics, entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated, interact, or share spatial proximity in ways such that the quantum state of each particle cannot be described independently of the others, even when the particles are separated by a large distance. The topic of entanglement is at the heart of the debate over whether quantum mechanics can accurately describe reality.
Einstein famously referred to entanglement as “spooky action at a distance.” In his view, it was impossible for two particles to be entangled; if they were, then they would have to be in instantaneous communication with one another, faster than the speed of light. This violated his theory of relativity, which states that nothing can travel faster than light.
However, experiments have since shown that entanglement does occur. It is now an accepted part of quantum mechanics. Entanglement has been used to create secure communications channels and to perform teleportation experiments. It also forms the basis for many proposed technologies, such as quantum computing and quantum cryptography.
How does entanglement work? When two particles are entangled, their combined state cannot be described independently of each other. This means that measuring one particle will instantaneously affect the state of the other particle—even if those particles are on opposite sides of the universe from each other.
This effect happens because both particles are still connected by what is known as an “entangling force.” This force ensures that any change made to one particle will instantly show up in measurements made on its partner particle. Even though these changes happen instantaneously (faster than the speed of light), they do not violate Einstein’s theory of relativity because no information is actually being exchanged between them—just a change in their combined state.