cianfa72 said:
1. What is the precise EPR explict assumption that QM explicitly denies ?
Sorry, could you be more specific about this point [the future measurement settings are the *only* parameters to the formula] ? Thanks.
1. As quoted from EPR above:
The position of QM: "
...since either one or the other, but not both simultaneously, of the [non-commuting] quantities P and Q can be predicted, they are not simultaneously real...This makes the reality of P and Q depend upon the process of measurement carried out on the first system, which does, not disturb the second system in any way."
Translation to modern terms: Reality is contextual; sometimes referred to as "non-realistic", "subjective" (based on chose of measurement basis" or "no hidden variables". Note that they slip in the assumption of locality in their statement of the QM position, by saying a measurement on one system does not disturb the other system in any way. This assumption can and has been challenged.
The position of EPR: "
No reasonable definition of reality could be expected to permit this."
Comment: This is pure 100% assumption, and is not backed up in any way. Note that no one disputes the basic EPR idea that a measurement by Alice may be used to predict an outcome for Bob with certainty - as long as both measurement are made on the same basis.
2. The spin statistics for spin 1/2 particles is typically something like sin^2(Theta), and for spin 1 photons something like cos^2(Theta) - it varies a bit according to the precise setup. The common variable is then Theta. Theta is defined as the difference between the angle setting for Alice and the angle setting for Bob.
What is important about this is: a) the angle settings (and therefore Theta) are values in the future of the entangled pair, and can be set or changed midflight; and b) there are no other known variables or input parameters. If there were any such parameters to the predictive formula, then they all exactly cancel out - leaving us Theta alone.
So... this makes it difficult to point to hidden variables as being the source of the observed statistics if they all magically happen to cancel each other out. Hence: a future context (the measurement settings) is the only determinant of the observed statistics according to quantum theory, and no other factor has been discovered to date in experiments.
This is the very definition of contextuality. Quantum Mechanics is contextual. This is the opposite of what is usual for classical mechanics, in which one or more input variables at time T=0 participate in predicting the results at time T>0.