EinsteinPodolskyRodolsky

EinsteinPodolskyRodolsky, often abbreviated as EPR, refers to a thought experiment proposed by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935. Their aim was to challenge the completeness of quantum mechanics as a description of physical reality. The EPR paradox highlights a counterintuitive feature of quantum entanglement.

In quantum mechanics, entanglement is a phenomenon where two or more particles become linked in such a way that they share the same fate, regardless of the distance separating them. If one particle is measured and its state is determined, the state of the other entangled particle is instantaneously known, even if it is light-years away. This apparent "spooky action at a distance," as Einstein famously called it, seemed to violate the principle of locality, which states that an object is influenced directly only by its immediate surroundings.

The EPR paper argued that if quantum mechanics were a complete theory, then the instantaneous correlation between entangled particles would imply either that information can travel faster than light or that the particles must possess pre-determined properties that are not accounted for by the quantum mechanical description. They concluded that quantum mechanics must be incomplete and that there exist "hidden variables" that determine the outcomes of measurements.

Decades later, experiments based on Bell's theorem have provided strong evidence against local hidden variable theories and in favor of the predictions of quantum mechanics, suggesting that the correlations observed in entangled systems are indeed a fundamental aspect of nature, even if they challenge our classical intuition about reality.