Dear WillieB .... QM basically says that 'spin orientation and its momentum'
cannot be simultaneously known with absolute accuracy (Heisenberg's Uncertainty Principle). So how is it that by observing one of the entangled particles we can predict with
accuracy exactly the properties of the other (how the other is behaving) ?
Einstein said that this is because the entangled particles were 'imprinted' with their properties prior to the time of their separation and therefore their properties can be known. (Einstein offered no explanation on how this imprinting occurs) This would seem to prove that QM is wrong, because QM says there is a degree of uncertainity about
every particle and always will be.
The QM physicists dis-agreed with Einstein. This was the basis of the EPR paradox which was finally answered by an Irish Physicist named Bell and experimentally proved in the 60s.
It proved to everybodys satisfaction (or dis-satisfaction) that the Universe was not local. It subverts cause and effect. In other words QM was proved right (or as right). This means there are now 2 explanations for our Universe.
Which one do you favour ??
As Dave says, the two particles appear to be entangled ... that is, there is some commonality between them that exists faster than light could have transmitted any cause or effect between the two. This is a matter of interpretation as they do not break Einsteins rules regarding anything (such as information) exceeding the speed of light.
This is my own intrepretation, and Dave (DLeviwing) will correct me if I'm wrong. You would need to read up on Bell's Theorem, difficult if your just beginning.
Best of luck ... Greg
PS: I too, found Sanctus's explanation confusing ! I have a good book at home that explains this by analogy ... but at this moment I can't remember its name. if you post back here I will remember to look it up and put it in a reply post for you.