EPRparadoks

The EPR paradox, named after its proponents Albert Einstein, Boris Podolsky, and Nathan Rosen, is a thought experiment published in 1935 that challenges the completeness of quantum mechanics. It describes a hypothetical scenario involving two entangled particles, meaning their quantum states are linked, regardless of the distance separating them. If a measurement is performed on one particle, instantaneously determining a property like its spin, the corresponding property of the other particle is immediately known, even if it is light-years away.

Einstein, Podolsky, and Rosen argued that this apparent instantaneous influence violated the principle of locality, which states that an object is directly influenced only by its immediate surroundings. They proposed that quantum mechanics, by not accounting for these "hidden variables" that predetermine the properties of the particles, was an incomplete description of reality. They believed that a more complete theory would explain these correlations without resorting to non-local interactions.

Later developments, particularly John Stewart Bell's theorem and subsequent experimental tests, have largely supported the predictions of quantum mechanics. Bell's theorem showed that any theory relying on local hidden variables would produce statistical correlations between measurements that differ from those predicted by quantum mechanics. Experiments have consistently shown results that violate Bell's inequalities, suggesting that either locality or the completeness of quantum mechanics (or both, in a way that preserves quantum mechanics' predictions) must be abandoned. The EPR paradox remains a cornerstone in understanding the counterintuitive nature of quantum entanglement and its implications for our understanding of reality.