- #71

DrChinese

Science Advisor

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martinbn said:It is not an objection but something that bothers me because it is not clear to me. Changing it to what Bob would say is not really an improvement. Between Bob's measurement and the meeting with Alice there is nothing strange or unusual about the reality of the measurement outcome. So the question really is what will Bob measure.

What I don't understand is the following. If you can predict with 100% certainty the value of a dynamical variable, then the measurment only reviels a preexisting value, and the theory should account for that. That is how I understand EPR's what is reasanable to consider as an element of reality. And they argue that this applies to Bob's measurment. But for me to predict the outcome of Bob's measurement means that given all the data in the past light-cone of that event you can calculate the value Bob will get. And that is not possible. What they do is to look at Alice's outcome and inffer Bob's. But that is not a prediction. It is almost like looking at the answer before saying what the answer is. Of course it is not quite like that, so I am not objecting to anything, I am only stating what bothers me. The two possible outcome for Alice and Bob are the pairs {1,-1} and {-1,1} . So if you see the first half of the pair you can "predict" the other, so!

If someone (Alice) hands the correctly predicted answer to what Bob will observe, that is an EPR "element of reality" - and you already acknowledge that. They *assume* (explicitly) that whoever/however (Alice) came up with that answer, did NOT affect what Bob will observe (of course that is subject to challenge). Thus the answer MUST have been predetermined.

So it seems to me your (non-)objection - that QM does not supply a way to predict that answer from the initial conditions - is not relevant to their particular argument. After all, perhaps those mechanics will perpetually be obscured to us. The important item is whether you agree that Bob's outcome was predetermined (using their argument*).*Which also has the explicit assumptions of a) locality and b) realism (being the simultaneous existence of all identifiable "elements of reality"). This is of course what Bell hopped on.