Originally posted by subtillioN
It is still an effect of a change in the state of knowledge of an event.
Not at all. If there was no entanglement, the measurements would be different.
For instance, in Fermilab we are also working towards the measurement of Sin2Beta. Due to the fact that we collide protons vs antiprotons (which, being a quark mess, have a very different physics than that of electron-positron collisions), the
B meson pairs are not quantum-entangled. As a result, the asymmetry behaves in a different way than those in BaBar and Belle.
There is a somewhat simple way to show that the observed properties of spin are incompatible with the idea of a well determined value, hidden from observation. It was published some three years ago by David Mermin (I think). I'll try to find the complete reference.
Another, somewhat older, proof that classical thinking is incompatible with the (experimentally) observed behavior of quantum systems is called the "Kocher-Specker paradox". I'm not sure about the spelling,... I'll check on the net later.
[Edit: I just checked: Kochen-Specker theorem]