minkwe wrote:Heinera wrote:minkwe wrote: It is impossible to measure a particle more than once. In QM terms, the E(a,b) measurement does not commute with the E(a,c) measurement on the same set of particles.

Don't you find it extremely ironic that you use a QM postulate ("It is impossible to measure a particle more than once") to argue against QM formalism and in favor of LHV models?

I had no idea electrons can be detected more than once in classical physics.

Michel, in that case, why talk about doing the same measurement several times on the same particles? Whether it is actually possible or actually impossible is totally irrelevant!

When we derive a mathematical inequality starting from some model assumptions, we do not actually measure particles at all. We have a probability distribution rho over a set of values of hidden variables Lambda, and we have two functions A(a, lambda) and B(b, lambda) delivering what the measurement outcomes would be under various settings a, b, .... We are working in a mathematical world (functions, sets, probability theory, expectation values ...).

We can *imagine* a pair of particles with value of the hidden variable lambda, and now one can *write down* A(a, lambda), A(a', lambda), B(b, lambda), B(b', lambda). Calling these four numbers, for short, A, A', B, B' one can now observe that AB + A'B + AB' - A'B' equals minus 2 or plus 2. One can now imagine drawing lambda at random and averaging over all possible values. And so on ...

Einstein, Podolsky and Rosen used quantum mechanics and locality in order to prove realism. The pair of particles each both have a well defined position and a well defined momentum. They don't discuss impossible experiments where several particles are simultaneously measured in several mutually incompatible ways at the same time.

Now if you *do* want to talk about doing several different measurements on the same particle, take a look at Joy Christian's experimental paper, and tell us what you think about it!

http://arxiv.org/abs/0806.3078 http://www.sciphysicsforums.com/spfbb1/viewtopic.php?f=6&t=52#p1898