The EPR (Einstein-Podolsky-Rosen) experiment is a thought experiment proposed by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935 to challenge certain aspects of quantum mechanics. The experiment involves entangled particles and explores the concept of non-locality.
In the EPR thought experiment, consider a pair of entangled particles, such as two particles that have interacted in the past and share a quantum state. According to quantum mechanics, the properties of entangled particles are correlated, even when they are physically separated.
The EPR argument focuses on the concept of "spooky action at a distance." It suggests that if one of the entangled particles is measured, instantaneously determining its properties (such as position or momentum), the measurement outcome of the other particle, when measured, would also be known instantly, regardless of the distance between them.
This apparent instantaneous correlation seems to violate the principle of relativity, which states that information cannot be transmitted faster than the speed of light. According to relativity, information must propagate within causal light-cones, and events in one region of space cannot influence events in another region instantaneously.
However, it is important to note that the EPR thought experiment does not involve a direct violation of relativity. The experiment is a theoretical scenario that challenges our understanding of the relationship between quantum mechanics and classical concepts, such as locality and realism.
In subsequent years, experiments inspired by the EPR argument have been conducted, such as the Bell's theorem experiments. These experiments have demonstrated violations of certain types of local realistic theories, indicating that nature does not operate according to such theories. The phenomena observed in these experiments are consistent with the predictions of quantum mechanics.
While the EPR experiment raises philosophical and conceptual questions about the nature of reality and the relationship between quantum mechanics and relativity, it does not necessarily imply a direct violation of the principles of relativity as formulated in modern physics.