Much of this comment is reproduced on Brian Whitworth's page. He begins, as many do, by denying local realism. That is the current trend, perhaps because it's 'sexy'. But one of the world's foremost experts, Anton Zeilinger, has written, Dance of the Photons, spelling out his key arguments in appendix A, where he substitutes, for quantum "properties" human properties, such as eye color, hair color, and height. He then proceeds to derive Bell's inequality and to claim that actual measurement results imply that the properties "do not exist until measured".
This is the key statement denying that local properties are real.
But changing the 'name' of the properties has absolutely no effect upon the logic of Bell's inequality, so either his logic is correct or it is not.
And here is the catch. The entire logic is based upon the assumption that the properties do not change en route to being measured! If this assumption is wrong, then the logic of Bell's inequality is wrong, and the drastic step of denying local realism is simply not justified.
Zeilinger begins with a "known" set of properties, and derives, based upon this set, Bell's inequality, and finds that measurements violate this inequality, then concludes that the properties do not exist until the measurement is made.
In Zeilinger's "user friendly" example, all that is necessary to refute this logic is to assert that one or more of the properties changed en route to the measurement. For example, one 'particle' dyes his hair, en route, thereby changing the measurement and violating Bell's inequality.
Now true believers will object, no, no, no -- you cannot equate 'hair color' with quantum properties -- but they are wrong. Bell's inequality does not depend on specific properties. All that is necessary to refute the argument is that properties change en route between the source and the detection.
As long as *both* entangled particles are treated exactly the same en route, the inequality is not violated, and there is no reason to question local realism. And this is exactly what is found experimentally. Only when the pair are interfered with in different ways en route is the inequality violated.
Therefore, one has to ask whether properties can change en route subject to differing physical interactions. And the answer is not available, because there is no rigorous analysis of photons, say in polarizing beam splitters. There is not even agreement on the (basically undefined) 'cut' or 'schnitt' that divides the quantum system being measured from the classical measuring 'apparatus'.
So the answer does not exist -- at this point only 'user preference' is involved. Some physicists are willing to give up local realism based on flimsy assumptions. I find that rather drastic, to put it mildly.
I am pursuing this here because my essay depends upon local realism and I've determined over the last few months that many FQXi'ers no longer believe in local realism.
Edwin Eugene Klingman
