[kgwgk]

This message clarifies what you mean. But you said before "A measurement of one entangled particle does NOTHING to the other particle. Its state is exactly the same as it was before.".

By measuring (one of the particles in) the system you are collapsing its wave function. Doesn't that mean the state of the system (both particles) is affected?

[lisper]

No. Collapse doesn't actually happen. Collapse is an approximation to the truth. It's a very (very!) good approximation for systems with a large number of mutually entangled degrees of freedom, but it is an approximation nonetheless. See the links I pointed to earlier to understand why.

[kgwgk]

Doesn't "the truth" involve any change in state at all? I'll look at your answer to quantum mysteries when I have time. But I suspect your original comment could have been phrased "the standard interpretation of quantum mechanics has to die"...

[lisper]

My complaint is more about rhetoric and pedagogy than it is about facts. There is essentially no serious dispute about the facts. But yes, it is true that the Copenhagen interpretation (by which I mean the idea that measurement involves some mysterious non-unitary process called "collapse") is untenable except as an approximation. There is no serious dispute over this.