EPR paradox


This contradicted the view associated with Niels Bohr and Werner Heisenberg, according to which a quantum particle does not have a definite value of a property like momentum until the measurement takes place. == History == The work was done at the Institute for Advanced Study in 1934, which Einstein had joined the prior year after he had fled Nazi Germany.


In a 1935 paper titled "Can Quantum-Mechanical Description of Physical Reality be Considered Complete?", they argued for the existence of "elements of reality" that were not part of quantum theory, and speculated that it should be possible to construct a theory containing them.

We believe, however, that such a theory is possible. The 1935 EPR paper condensed the philosophical discussion into a physical argument.

The fact that quantum mechanics violates Bell inequalities indicates that any hidden-variable theory underlying quantum mechanics must be non-local; whether this should be taken to imply that quantum mechanics itself is non-local is a matter of debate. ==Steering== Inspired by Schrödinger's treatment of the EPR paradox back in 1935, Wiseman et al.


He argued that, because of locality, the real state of particle B couldn't depend on which kind of measurement was done in A, and therefore the quantum states cannot be in one-to-one correspondence with the real states. ==Later developments== === Bohm's variant === In 1951, David Bohm proposed a variant of the EPR thought experiment in which the measurements have discrete ranges of possible outcomes, unlike the position and momentum measurements considered by EPR.


It seems as if information has propagated (faster than light) from Alice's apparatus to make Bob's positron assume a definite spin in the appropriate axis. === Bell's theorem === In 1964, John Bell published a paper investigating the puzzling situation at that time: on one hand, the EPR paradox purportedly showed that quantum mechanics was nonlocal, and suggested that a hidden-variable theory could heal this nonlocality.


Fine, Do Correlations need to be explained?, in Philosophical Consequences of Quantum Theory: Reflections on Bell's Theorem, edited by Cushing & McMullin (University of Notre Dame Press, 1986). M.


formalised it in 2007 as the phenomenon of quantum steering.

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