billschnieder
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Nonseparability has been mentioned but I doubt that it's impact to this discussion has been fully understood. In the the Gordon Watson's linked thread he mentioned "triangle inequality", I have a variation of it which may throw some light in a simple and common sense manner why "nonseparability" is so important to the issue being raised by Joy Christian. DrC may be interested in this because it blows the lid off his "negative probabilities" article.
A simple analogy is the x^2 + y^2 = z^2 relationship for right angled triangles, of sides, x, y and z. Consider a process which generates right angled triangles defined within a unit circle, where z is always = 1, x = cos(angle), y = sin(angle), where the angle is randomly chosen each time. Our goal is to measure the lengths of the sides x and y. But, assume that in the first experiment, we can only make a single measurement. So we run our experiment a gazzillion number of times and obtain the averages <x> and <y> averages. Do you think <x>^2 + <y>^2 will obey the relationship of being equal to 1. If you do, think again <x>^2 + <y>^2 converges to 0.8105... not 1, a violation. This is simply because x and y are non-separable in our relationship.
However we can imagine that in our experiment we also had corresponding values for both x and y for each individual measurement. So we might think that using our new dataset with all corresponding values included will result in <x>^2 + <y>^2 = 1, right? Wrong. We get exactly the same violation as before. The reason is separability. But there is one thing we can calculate in our second scenario which we could not in the first. We can calculate <x^2 + y^2> since we now have both points, and indeed we obtain 1 as the result which obeys the relationship.
In our first experiment, x and y do not commute therefore it is a mathematical error to use x and y in the same expression, that is why the violation was observed. In probability theory, an expectation value such as E(a,c) is undefined if A(a,lambda) and A(c,lambda) do not commute. Expectation values are only defined for E(a,c) if there is an underlying probability distribution P(a,c). But it is not possible to measure at angles "a" and "c" on the same particle pair therefore there is no P(a,c) probability distribution. The same is the case in Bell-test experiments and QM, in which it is possible to measure "a" and "b" but not "c" simultaneously so, the pairs measured in different runs do not correspond to each other, so we are left with calculating three different expectation values from three different probability distributions to plug into an inequality in which the terms are defined on the same probability distribution. This is a mathematical error.
Concerning negative probabilities, Dr C says:
Note how he defines X, Y and Z as being non commuting since only two of such angles can be measured at the same time, and yet he writes down an impossible equation which includes terms which can never be simultaneously valid. No doubt he obtains his result.X is determined by the angle between A and B, a difference of 67.5 degrees X = COS^2(67.5 degrees) = .1464 This prediction of quantum mechanics can be measured experimentally.*
Y is determined by the angle between A and C, a difference 45 degrees Y = SIN^2(45 degrees) = .5000 This prediction of quantum mechanics can be measured experimentally.*
Z is determined by the angle between B and C, a difference 22.5 degrees Z = COS^2(22.5 degrees) = .8536 This prediction of quantum mechanics can be measured experimentally.*
...
(X + Y - Z) / 2
Substituting values from g. above:
= (.1464 + .5000 - .8536)/2
= (-.2072)/2
= -.1036